Arild Christian Rustan

• Lair, Benjamin; Cazorla, Clément; Lobeto, Alicia; Labour, Axel; Couloutchy, Lorenzo & Laurens, Claire [Show all 11 contributors for this article] (2026). MyoFuse is a fully AI-based workflow for automated quantification of skeletal muscle cell fusion in vitro. Scientific Reports. 16(1). doi: 10.1038/s41598-026-40047-y. Full text in Research Archive Show summary

  The fusion index (FI) is widely used to assess myoblast differentiation into myotubes, but manual quantification is tedious and biased. Existing automated methods face limitations in nucleus segmentation and classification and often misidentify myoblast nuclei located above or below myotubes, leading to FI overestimation. To address these issues, we developed MyoFuse, an AI-based workflow enabling fully automated and unbiased FI quantification. MyoFuse combines nucleus segmentation using Cellpose with a classification network trained with Svetlana on fluorescence images of mouse C2C12 and human primary myotubes. Performance was evaluated by comparing MyoFuse-derived FI values with expert annotations and by assessing classification accuracy at the single-nucleus level. MyoFuse achieved strong accuracy scores in mouse C2C12 and human primary myotubes (0.954 and 0.911 respectively), and showed strong correlations with expert-derived FI values (r = 0.991 and r = 0.937 respectively; p < 0.0001). Unlike current approaches that overestimate FI, MyoFuse reliably segments nuclei even within dense clusters and distinguishes myotube from myoblast nuclei based solely on cytoplasmic staining. By processing large images, it further reduces selection bias and accounts for heterogeneity in myotube density. MyoFuse thus provides a robust, high-throughput, and accurate method for FI quantification in skeletal muscle cell culture.

• Dalmao-Fernandez, Andrea; Katare, Parmeshwar Bajirao; Bakke, Hege Gilbø; Hamarsland, Håvard; Ellefsen, Stian & Singh, Sachin [Show all 10 contributors for this article] (2025). The use of three-dimensional primary human myospheres to explore skeletal muscle effects of in vivo krill oil supplementation. In vitro models. ISSN 2731-3433. 4(2), p. 145–155. doi: 10.1007/s44164-025-00087-6. Full text in Research Archive Show summary

  Supplementation with krill oil has shown effects on whole-body lipid and glucose metabolism, as well as on skeletal muscle strength and function. We previously showed that krill oil intervention in vivo promoted fatty acid metabolism and protein synthesis in cultured human myotubes in a two-dimensional (2D) model. The aim of this study was to explore the effects of krill oil supplementation in vivo in a 3D myosphere model, and to compare a the human skeletal muscle 3D cell model to a 2D model. Myospheres were formed from myoblasts obtained before and after 7&nbsp;weeks of in vivo krill oil intervention. Glucose and oleic acid metabolism were assessed, and transcriptomic and proteomic analyses were performed. In vivo intervention with krill oil increased glucose metabolism in myospheres, while no effect was observed on fatty acid metabolism. Transcriptomic analyses of myospheres after krill oil intervention showed increased expression of genes involved in pathways like motor proteins and hypertrophy, as well as in calcium signaling, of which motor proteins and hypertrophy pathways have not been described in 2D myotube cultures. Proteomic analyses after krill oil intervention showed increased expression of proteins in glycolysis/gluconeogenesis and fatty acid degradation. Comparison of proteins expressed in the 3D myosphere model and the 2D myotube model at the basal level showed that in myospheres, mitochondrial gene expression and translation dominated, while in 2D cultures, mitochondrial organization and response to oxidative stress were more important. These findings suggest that in vivo krill oil intervention induces different metabolic effects when comparing 3D and 2D cultures. In contrast to the 2D model, data obtained with the 3D model showed gene expression changes that are more compatible with previously observed results in vivo concerning skeletal muscle motoric function. Hence, the 3D cell model might better reflect krill oil-induced modifications in skeletal muscle performance in vivo than the 2D model.

• Nundal, Camilla Hatlevoll; Lunde, Siri; Bakke, Hege Gilbø; Bohov, Pavol; Aloysius, Thomas Aquinas & Rustan, Arild Christian [Show all 15 contributors for this article] (2025). Herring oil rich in long-chain monounsaturated fatty acid (C22: 1n-11) lowers plasma lipids and modulates fatty acid composition, oxidation, and inflammation in rats. Frontiers in Nutrition. 12, p. 1–11. doi: 10.3389/fnut.2025.1611166. Full text in Research Archive Show summary

  Introduction: Marine oils and fatty fish rich in long-chain n-3 polyunsaturated fatty acids (PUFAs), such as eicosapentaenoic acid (C20:5n-3, EPA) and docosahexaenoic acid (C22:6n-3, DHA), have been reported to enhance fatty acid (FA) oxidation and reduce plasma triacylglycerol and cholesterol levels. In addition to n-3 PUFAs, herring oil contains long-chain monounsaturated fatty acids (MUFAs), including cetoleic acid (C22:1n-11). This study aimed to investigate the effect of consuming CETO3® oil—derived from herring and naturally rich in n-3 PUFAs and cetoleic acid—on plasma lipid levels, FA composition, mitochondrial oxidation, and inflammation in rats. Methods: Rats were fed low-fat diets supplemented with 5% CETO3® oil (experimental) or soy oil (control) for 10 weeks. Plasma lipid profile (triglycerides (TG), total cholesterol, low-density lipoprotein (LDL) and high-density lipoprotein (HDL)) and FA composition in both liver and plasma were analyzed. In vitro substrate oxidation was assessed using ¹⁴CO₂-trapping in human liver and human myotubes. Safety parameters, including blood hematology, glucose tolerance, and organ weights, were also measured. Results: CETO3® supplementation decreased plasma levels of total fat (−58%), TG (−55%), total cholesterol (−41%), and LDL cholesterol (−45%), while increasing the ratio of HDL to LDL cholesterol (46%). Supplementation also increased hepatic and plasma levels of long-chain n-3, n-9, and n-11 MUFAs, including C22:1n-11, and decreased n-6 FA accumulation. The reduction in saturated long-chain FAs in both the liver and plasma indicated increased hepatic peroxisomal and mitochondrial activity. Furthermore, increased oleic acid oxidation was observed in human myotubes in the presence of C20:1n-11 and C20:1n-9. Discussion: These findings suggest that intake of CETO3® oil lowers plasma lipids, potentially through enhanced peroxisomal and mitochondrial FA oxidation. The shift in FA composition, with reduced n-6 FAs and increased n-3 and n-11 MUFAs, indicates an anti-inflammatory effect. CETO3® oil also appears safe, as hematological parameters, glucose tolerance, and organ weights remained unaffected.

• Katare, Parmeshwar Bajirao; Tingstad, Ragna Husby; Beajani, Siver; Indseth, Jørgen Pasjkurov; Telle-Hansen, Vibeke & Myhrstad, Mari Charlotte Wik [Show all 10 contributors for this article] (2025). Divergent effects of monomethyl branched-chain fatty acids on energy metabolism and insulin signaling in human myotubes. Journal of Lipid Research. ISSN 0022-2275. 66(3), p. 1–12. doi: 10.1016/j.jlr.2025.100764. Full text in Research Archive Show summary

  Branched-chain fatty acids (BCFAs) are predominantly saturated fatty acids with one or more methyl branches on the carbon chain, typically found in dairy products and measured in micromolar concentrations in human plasma. The biological function of BCFAs in humans remains ill-defined, but a relationship between circulating BCFAs and cardiometabolic health has been suggested. The objective of this study was to evaluate the impact of BCFAs on energy metabolism in human myotubes. The results revealed distinct effects of BCFAs. 12-Methyltetradecanoic acid (12-MTD) increased glucose uptake and glycogen synthesis, while 13-methyltetradecanoic acid (13-MTD), 14-methylhexadecanoic acid (14-MHD), and 15-methylhexadecanoic acid (15-MHD) increased oleic acid uptake and 13-MTD and 15-MHD oleic acid oxidation, indicating a more general stimulatory effect on fatty acid than glucose metabolism. Interestingly, the same BCFAs, 13-MTD, 14-MHD, and 15-MHD, appeared to reduce insulin-stimulated glycogen synthesis. Insulin-stimulated phosphorylation of IRS1 was not apparent after exposure to 12-MTD, 13-MTD, and 15-MHD, whereas insulin-stimulated phosphorylation of Akt was unchanged by BCFAs. Incorporation of [14C]leucine into lipids was affected, as 13-MTD increased the total lipid content, and 12-MTD altered the distribution of lipid classes. Metabolic flux analysis indicated that 14-MHD stimulated extracellular acidification. The effects of BCFAs might involve increased mRNA expression of pyruvate dehydrogenase kinase 4. In conclusion, the study demonstrates that different BCFAs have distinct effects on energy metabolism in myotubes, 12-MTD mainly affect glucose metabolism, while 13-MTD, 14-MHD, and 15-MHD modulated oleic acid metabolism. These data suggest that some BCFAs might have therapeutic applications by improving energy metabolism

• Skagen, Christine; Stevanovic, Stanislava; Bakke, Hege Gilbø; Nyman, Tuula Anneli; Stensland, Maria & Kase, Eili Tranheim [Show all 9 contributors for this article] (2025). Reduced lipid and glucose oxidation and reduced lipid synthesis in AMPKα2/ myotubes. Archives of Physiology and Biochemistry. ISSN 1381-3455. 131(3), p. 483–492. doi: 10.1080/13813455.2024.2449409. Full text in Research Archive Show summary

  Adenosine 5’-monophosphate (AMP)-activated protein kinase (AMPK) plays a crucial role in regulation ofmetabolic homeostasis. To understand the role of the catalytic α2 subunit of AMPK in skeletal muscleenergy metabolism, myotube cultures were established from AMPKα2+/+ and AMPKα2-/- mice. Myotubesfrom AMPKα2-/- mice had lower basal oleic acid and glucose oxidation compared to myotubes fromAMPKα2+/+ mice. However, the relative response to mitochondrial uncoupling was increased for oleicacid oxidation. Incorporation of acetate into lipids was also lower in myotubes from AMPKα2-/- mice.Proteomics analysis revealed that AMPKα2-/- myotubes had upregulated pathways related to mitochondrialfunction and fatty acid oxidation, and decreased pathways related to fatty acid biosynthesis. Inconclusion, ablation of AMPKα2 catalytic subunit in skeletal muscle cells resulted in reduced basaloxidation of glucose and fatty acids, however upregulated pathways related to mitochondrial functionand fatty acid oxidation and reduced lipid formation

• Tingstad, Ragna Husby; Witczak, Oliwia; Beajani, Siver; Seo, Seaung Hee; Løvsletten, Nils Gunnar & Skagen, Christine [Show all 11 contributors for this article] (2025). Impact of Short-Chain Fatty Acids on Glucose, Fatty Acid and Leucine Metabolism in Primary Human Myotubes. Endocrinology, Diabetes & Metabolism. 8(2). doi: 10.1002/edm2.70042. Full text in Research Archive Show summary

  Introduction Short-chain fatty acids (SCFAs) are small molecule metabolites mainly produced during microbial fermentation of dietary fibre in the gut and have been shown to have a beneficial impact on human health. The aim of this study was to evaluate the effect of SCFAs on human skeletal muscle energy metabolism. Methods Primary human myotubes were analysed for glucose and fatty acid (oleic acid) metabolism, as well as insulin sensitivity and protein synthesis in the presence or absence of SCFAs. Results The most pronounced effects of SCFAs were observed on 14C-oleic acid uptake and oxidation, as well as 14C-leucine uptake and protein synthesis, following butyrate treatment. Butyrate increased 14C-leucine accumulation twofold, potentially due to protein incorporation. On the other hand, the conversion of 14C-leucine into free fatty acids was reduced by more than 50% by butyrate. Both 14C-acetate and 14C-butyrate were shown to be taken up and utilised by primary human myotubes. None of the SCFAs were found to influence glucose metabolism or insulin effects. Conclusion The results from the current study thus suggest that among the SCFAs, butyrate emerges as the most powerful SCFA in regulating primary human myotube metabolism.

• Lund, Jenny; Lähteenmäki, Emilia; Eklund, Tiia; Bakke, Hege Gilbø; Thoresen, G. Hege & Pirinen, Eija [Show all 9 contributors for this article] (2024). Human HDL subclasses modulate energy metabolism in skeletal muscle cells. Journal of Lipid Research. ISSN 0022-2275. 65:100481(1), p. 1–16. doi: 10.1016/j.jlr.2023.100481. Full text in Research Archive Show summary

  In addition to its antiatherogenic role, HDL reportedly modulates energy metabolism at the whole-body level. HDL functionality is associated with its structure and composition, and functional activities can differ between HDL subclasses. Therefore, we studied if HDL2 and HDL3, the two major HDL subclasses, are able to modulate energy metabolism of skeletal muscle cells. Differentiated mouse and primary human skeletal muscle myotubes were used to investigate the influences of human HDL2 and HDL3 on glucose and fatty uptake and oxidation. HDL-induced changes in lipid distribution and mRNA expression of genes related to energy substrate metabolism, mitochondrial function, and HDL receptors were studied with human myotubes. Additionally, we examined the effects of apoA-I and discoidal, reconstituted HDL particles on substrate metabolism. In mouse myotubes, HDL subclasses strongly enhanced glycolysis upon high and low glucose concentrations. HDL3 caused a minor increase in ATP-linked respiration upon glucose conditioning but HDL2 improved complex I–mediated mitochondrial respiration upon fatty acid treatment. In human myotubes, glucose metabolism was attenuated but fatty acid uptake and oxidation were markedly increased by both HDL subclasses, which also increased mRNA expression of genes related to fatty acid metabolism and HDL receptors. Finally, both HDL subclasses induced incorporation of oleic acid into different lipid classes. These results, demonstrating that HDL subclasses enhance fatty acid oxidation in human myotubes but improve anaerobic metabolism in mouse myotubes, support the role of HDL as a circulating modulator of energy metabolism. Exact mechanisms and components of HDL causing the change, require further investigation.

• Osoble, Nimo Mukhtar Mohamud; Lunde, Ngoc Nguyen; Jafari, Abbas; Thoresen, G. Hege; Solberg, Rigmor & Rustan, Arild Christian (2024). The cysteine protease legumain decreases glucose metabolism and enhances fatty acid uptake in human myotubes. Biochimie. ISSN 0300-9084. 231, p. 127–136. doi: 10.1016/j.biochi.2024.12.012. Full text in Research Archive Show summary

  Skeletal muscle has an important role in whole body energy metabolism and various proteases are involved in skeletal muscle functions. We have previously identified the cysteine protease legumain in cultured human skeletal muscle cells. However, the potential role of legumain in regulation of energy metabolism remains unexplored. This study aimed to investigate cellular uptake, processing, and activation of prolegumain in human myotubes. Additionally, we sought to determine the effects of prolegumain on energy substrate metabolism in these cells. During differentiation of human myoblast to myotubes, legumain mRNA expression and activity were upregulated. Interestingly, legumain activity in myotubes was inversely correlated with the body mass index (BMI) of the obese cell donors. Myotubes exposed to conditioned medium enriched in prolegumain during the last two days of differentiation demonstrated the capacity to internalize and process prolegumain into its active form. Pre-treatment with prolegumain induced a metabolic shift towards increased fatty acid uptake in myotubes, as evidenced by elevated oleic acid uptake whereas glucose uptake and oxidation were reduced. The metabolic changes were not reversed by a legumain inhibitor, indicating a different mechanism for this effect. The metabolic alterations were accompanied by increased mRNA expression of the fatty acid transporter CD36, whereas the glucose transporter GLUT1 mRNA level remained unchanged. These findings suggest that legumain may play a regulatory role in skeletal muscle energy metabolism, highlighting its potential as a novel therapeutic target of metabolic disorders.

• Katare, Parmeshwar Bajirao; Dalmao-Fernandez, Andrea; Mengeste, Abel Mulu; Navabakbar, Farnaz; Hamarsland, Håvard & Ellefsen, Stian [Show all 12 contributors for this article] (2024). Krill oil supplementation in vivo promotes increased fuel metabolism and protein synthesis in cultured human skeletal muscle cells. Frontiers in Nutrition. 11:1452768, p. 1–14. doi: 10.3389/fnut.2024.1452768. Full text in Research Archive Show summary

  Introduction: Krill oil is a dietary supplement derived from Antarctic krill; a small crustacean found in the ocean. Krill oil is a rich source of omega-3 fatty acids, specifically eicosapentaenoic acid and docosahexaenoic acid, as well as the antioxidant astaxanthin. The aim of this study was to investigate the effects of krill oil supplementation, compared to placebo oil (high oleic sunflower oil added astaxanthin), in vivo on energy metabolism and substrate turnover in human skeletal muscle cells. Methods: Skeletal muscle cells (myotubes) were obtained before and after a 7-week krill oil or placebo oil intervention, and glucose and oleic acid metabolism and leucine accumulation, as well as effects of different stimuli in vitro, were studied in the myotubes. The functional data were combined with proteomic and transcriptomic analyses. Results: In vivo intervention with krill oil increased oleic acid oxidation and leucine accumulation in skeletal muscle cells, however no effects were observed on glucose metabolism. The krill oil-intervention-induced increase in oleic acid oxidation correlated negatively with changes in serum low-density lipoprotein (LDL) concentration. In addition, myotubes were also exposed to krill oil in vitro. The in vitro study revealed that 24 h of krill oil treatment increased both glucose and oleic acid metabolism in myotubes, enhancing energy substrate utilization. Transcriptomic analysis comparing myotubes obtained before and after krill oil supplementation identified differentially expressed genes associated with e.g., glycolysis/gluconeogenesis, metabolic pathways and calcium signaling pathway, while proteomic analysis demonstrated upregulation of e.g., LDL-receptor in myotubes obtained after the krill oil intervention. Conclusion: These findings suggest that krill oil intervention promotes increased fuel metabolism and protein synthesis in human skeletal muscle cells, with potential implications for metabolic health.

• Stevanovic, Stanislava; Dalmao-Fernandez, Andrea; Mohamed, Derya; Nyman, Tuula Anneli; Kostovski, Emil & Iversen, Per Ole [Show all 11 contributors for this article] (2024). Time-dependent reduction in oxidative capacity among cultured myotubes from spinal cord injured individuals. Acta Physiologica. ISSN 1748-1708. 240:e14156(7), p. 1–15. doi: 10.1111/apha.14156. Full text in Research Archive Show summary

  Background Skeletal muscle adapts in reaction to contractile activity to efficiently utilize energy substrates, primarily glucose and free fatty acids (FA). Inactivity leads to atrophy and a change in energy utilization in individuals with spinal cord injury (SCI). The present study aimed to characterize possible inactivity-related differences in the energy metabolism between skeletal muscle cells cultured from satellite cells isolated 1- and 12-months post-SCI. Methods To characterize inactivity-related disturbances in spinal cord injury, we studied skeletal muscle cells isolated from SCI subjects. Cell cultures were established from biopsy samples from musculus vastus lateralis from subjects with SCI 1 and 12 months after the injury. The myoblasts were proliferated and differentiated into myotubes before fatty acid and glucose metabolism were assessed and gene and protein expressions were measured. Results The results showed that glucose uptake was increased, while oleic acid oxidation was reduced at 12 months compared to 1 month. mRNA expressions of PPARGC1α, the master regulator of mitochondrial biogenesis, and MYH2, a determinant of muscle fiber type, were significantly reduced at 12 months. Proteomic analysis showed reduced expression of several mitochondrial proteins. Conclusion In conclusion, skeletal muscle cells isolated from immobilized subjects 12 months compared to 1 month after SCI showed reduced fatty acid metabolism and reduced expression of mitochondrial proteins, indicating an increased loss of oxidative capacity with time after injury.

• Irshad, Zehra; Lund, Jenny; Sillars, Anne; Løvsletten, Nils Gunnar; Gharanei, Seley & Salt, Ian P. [Show all 11 contributors for this article] (2023). The roles of DGAT1 and DGAT2 in human myotubes are dependent on donor patho-physiological background. The FASEB Journal. ISSN 0892-6638. 37(11), p. 1–20. doi: 10.1096/fj.202300960RR. Full text in Research Archive Show summary

  Abstract The roles of DGAT1 and DGAT2 in lipid metabolism and insulin responsiveness of human skeletal muscle were studied using cryosections and myotubes prepared from muscle biopsies from control, athlete, and impaired glucose regulation (IGR) cohorts of men. The previously observed increases in intramuscular triacylglycerol (IMTG) in athletes and IGR were shown to be related to an increase in lipid droplet (LD) area in type I fibers in athletes but, conversely, in type II fibers in IGR subjects. Specific inhibition of both diacylglycerol acyltransferase (DGAT) 1 and 2 decreased fatty acid (FA) uptake by myotubes, whereas only DGAT2 inhibition also decreased fatty acid oxidation. Fatty acid uptake in myotubes was negatively correlated with the lactate thresholds of the respective donors. DGAT2 inhibition lowered acetate uptake and oxidation in myotubes from all cohorts whereas DGAT1 inhibition had no effect. A positive correlation between acetate oxidation in myotubes and resting metabolic rate (RMR) from fatty acid oxidation in vivo was observed. Myotubes from athletes and IGR had higher rates of de novo lipogenesis from acetate that were normalized by DGAT2 inhibition. Moreover, DGAT2 inhibition in myotubes also resulted in increased insulin‐induced Akt phosphorylation. The differential effects of DGAT1 and DGAT2 inhibition suggest that the specialized role of DGAT2 in esterifying nascent diacylglycerols and de novo synthesized FA is associated with synthesis of a pool of triacylglycerol, which upon hydrolysis results in effectors that promote mitochondrial fatty acid oxidation but decrease insulin signaling in skeletal muscle cells.

• Krapf, Solveig; Lund, Jenny; Bakke, Hege Gilbø; Nyman, Tuula Anneli; Bartesaghi, Stefano & Peng, Xiao-Rong [Show all 9 contributors for this article] (2023). SENP2 knockdown in human adipocytes reduces glucose metabolism and lipid accumulation, while increases lipid oxidation. Metabolism Open. 18. doi: 10.1016/j.metop.2023.100234. Full text in Research Archive Show summary

  Adipose tissue is one of the main regulative sites for energy metabolism. Excess lipid storage and expansion of white adipose tissue (WAT) is the primary contributor to obesity, a strong predisposing factor for development of insulin resistance. Sentrin-specific protease (SENP) 2 has been shown to play a role in metabolism in murine fat and skeletal muscle cells, and we have previously demonstrated its role in energy metabolism of human skeletal muscle cells. In the present work, we have investigated the impact of SENP2 on fatty acid and glucose metabolism in primary human fat cells by using cultured primary human adipocytes to knock down the SENP2 gene. Glucose uptake and oxidation, as well as accumulation and distribution of oleic acid into complex lipids were decreased, while oleic acid oxidation was increased in SENP2-knockdown cells compared to control adipocytes. Furthermore, lipogenesis was reduced by SENP2-knockdown in adipocytes. Although TAG accumulation relative to total uptake was unchanged, there was increased mRNA expression of metabolically relevant genes such as UCP1 and PPARGC1A and mRNA and proteomic data revealed increased levels of mRNA and proteins related to mitochondrial function by SENP2-knockdown. In conclusion, SENP2 is an important regulator of energy metabolism in primary human adipocytes and its knockdown reduce glucose metabolism and lipid accumulation, while increasing lipid oxidation in human adipocytes.

• Lunde, Ngoc Nguyen; Osoble, Nimo Mukhtar Mohamud; Dalmao-Fernandez, Andrea; Lukacs, Alfreda Serwah; Jafari, Abbas & Singh, Sachin [Show all 10 contributors for this article] (2023). Interplay between Cultured Human Osteoblastic and Skeletal Muscle Cells: Effects of Conditioned Media on Glucose and Fatty Acid Metabolism. Biomedicines. 11:2908(11), p. 1–20. doi: 10.3390/biomedicines11112908. Full text in Research Archive Show summary

  The interplay between skeletal muscle and bone is primarily mechanical; however, biochemical crosstalk by secreted mediators has recently gained increased attention. The aim of this study was to investigate metabolic effects of conditioned medium from osteoblasts (OB-CM) on myotubes and vice versa. Human skeletal muscle cells incubated with OB-CM showed increased glucose uptake and oxidation, and mRNA expression of the glucose transporter (GLUT) 1, while fatty acid uptake and oxidation, and mRNA expression of the fatty acid transporter CD36 were decreased. This was supported by proteomic analysis, where expression of proteins involved in glucose uptake, glycolytic pathways, and the TCA cycle were enhanced, and expression of several proteins involved in fatty acid metabolism were reduced. Similar effects on energy metabolism were observed in human bone marrow stromal cells differentiated to osteoblastic cells incubated with conditioned medium from myotubes (SKM-CM), with increased glucose uptake and reduced oleic acid uptake. Proteomic analyses of the two conditioned media revealed many common proteins. Thus, our data may indicate a shift in fuel preference from fatty acid to glucose metabolism in both cell types, induced by conditioned media from the opposite cell type, possibly indicating a more general pattern in communication between these tissues.

• Cho, Bennet S.; Fligor, Scott C.; Fell, Gillian L.; Secor, Jordan D.; Tsikis, Savas T. & Pan, Amy [Show all 16 contributors for this article] (2023). A medium-chain fatty acid analogue prevents hepatosteatosis and decreases inflammatory lipid metabolites in a murine model of parenteral nutrition-induced hepatosteatosis. PLOS ONE. 18(12). doi: 10.1371/journal.pone.0295244. Full text in Research Archive Show summary

  Background Parenteral (intravenous) nutrition is lifesaving for patients with intestinal failure, but long-term use of parenteral nutrition often leads to liver disease. SEFA-6179 is a synthetic medium-chain fatty acid analogue designed to target multiple fatty acid receptors regulating metabolic and inflammatory pathways. We hypothesized that SEFA-6179 would prevent hepatosteatosis and lipotoxicity in a murine model of parenteral nutrition-induced hepatosteatosis. Methods Two in vivo experiments were conducted. In the first experiment, six-week-old male mice were provided an ad lib fat-free high carbohydrate diet (HCD) for 19 days with orogastric gavage of either fish oil, medium-chain triglycerides, or SEFA-6179 at a low (0.3mmol/kg) or high dose (0.6mmol/kg). In the second experiment, six-week-old mice were provided an ad lib fat-free high carbohydrate diet for 19 days with every other day tail vein injection of saline, soybean oil lipid emulsion, or fish oil lipid emulsion. Mice then received every other day orogastric gavage of medium-chain triglyceride vehicle or SEFA-6179 (0.6mmol/kg). Hepatosteatosis was assessed by a blinded pathologist using an established rodent steatosis score. Hepatic lipid metabolites were assessed using ultra-high-performance liquid chromatography-mass spectrometry. Effects of SEFA-6179 on fatty acid oxidation, lipogenesis, and fatty acid uptake in human liver cells were assessed in vitro. Results In the first experiment, mice receiving the HCD with either saline or medium-chain triglyceride treatment developed macrovesicular steatosis, while mice receiving fish oil or SEFA-6179 retained normal liver histology. In the second experiment, mice receiving a high carbohydrate diet with intravenous saline or soybean oil lipid emulsion, along with medium chain triglyceride vehicle treatment, developed macrovescular steatosis. Treatment with SEFA-6179 prevented steatosis. In each experiment, SEFA-6179 treatment decreased arachidonic acid metabolites as well as key molecules (diacylglycerol, ceramides) involved in lipotoxicity. SEFA-6179 increased both β- and complete fatty oxidation in human liver cells, while having no impact on lipogenesis or fatty acid uptake. Conclusions SEFA-6179 treatment prevented hepatosteatosis and decreased toxic lipid metabolites in a murine model of parenteral nutrition-induced hepatosteatosis. An increase in both β- and complete hepatic fatty acid oxidation may underlie the reduction in steatosis.

• Dalmao-Fernandez, Andrea; Aizenshtadt, Aleksandra; Bakke, Hege Gilbø; Krauss, Stefan Johannes Karl; Rustan, Arild Christian & Thoresen, G. Hege [Show all 7 contributors for this article] (2023). Development of three-dimensional primary human myospheres as culture model of skeletal muscle cells for metabolic studies. Frontiers in Bioengineering and Biotechnology. 11, p. 1–13. doi: 10.3389/fbioe.2023.1130693. Full text in Research Archive Show summary

  Introduction: Skeletal muscle is a major contributor to whole-body energy homeostasis and the utilization of fatty acids and glucose. At present, 2D cell models have been the most used cellular models to study skeletal muscle energy metabolism. However, the transferability of the results to in vivo might be limited. This project aimed to develop and characterize a skeletal muscle 3D cell model (myospheres) as an easy and low-cost tool to study molecular mechanisms of energy metabolism. Methods and results: We demonstrated that human primary myoblasts form myospheres without external matrix support and carry structural and molecular characteristics of mature skeletal muscle after 10 days of differentiation. We found significant metabolic differences between the 2D myotubes model and myospheres. In particular, myospheres showed increased lipid oxidative metabolism than the 2D myotubes model, which oxidized relatively more glucose and accumulated more oleic acid. Discussion and conclusion: These analyses demonstrate model differences that can have an impact and should be taken into consideration for studying energy metabolism and metabolic disorders in skeletal muscle.

• Janovska, Petra; Zouhar, Petr; Bardova, Kristina; Otahal, Jakub; Vrbacky, Marek & Mracek, Tomas [Show all 17 contributors for this article] (2023). Impairment of adrenergically-regulated thermogenesis in brown fat of obesity-resistant mice is compensated by non-shivering thermogenesis in skeletal muscle. Molecular Metabolism. 69. doi: 10.1016/j.molmet.2023.101683. Full text in Research Archive Show summary

  Objective Non-shivering thermogenesis (NST) mediated by uncoupling protein 1 (UCP1) in brown adipose tissue (BAT) can be activated via the adrenergic system in response to cold or diet, contributing to both thermal and energy homeostasis. Other mechanisms, including metabolism of skeletal muscle, may also be involved in NST. However, relative contribution of these energy dissipating pathways and their adaptability remain a matter of long-standing controversy. Methods We used warm-acclimated (30 °C) mice to characterize the effect of an up to 7-day cold acclimation (6 °C; CA) on thermoregulatory thermogenesis, comparing inbred mice with a genetic background conferring resistance (A/J) or susceptibility (C57BL/6 J) to obesity. Results Both warm-acclimated C57BL/6 J and A/J mice exhibited similar cold endurance, assessed as a capability to maintain core body temperature during acute exposure to cold, which improved in response to CA, resulting in comparable cold endurance and similar induction of UCP1 protein in BAT of mice of both genotypes. Despite this, adrenergic NST in BAT was induced only in C57BL/6 J, not in A/J mice subjected to CA. Cold tolerance phenotype of A/J mice subjected to CA was not based on increased shivering, improved insulation, or changes in physical activity. On the contrary, lipidomic, proteomic and gene expression analyses along with palmitoyl carnitine oxidation and cytochrome c oxidase activity revealed induction of lipid oxidation exclusively in skeletal muscle of A/J mice subjected to CA. These changes appear to be related to skeletal muscle NST, mediated by sarcolipin-induced uncoupling of sarco(endo)plasmic reticulum calcium ATPase pump activity and accentuated by changes in mitochondrial respiratory chain supercomplexes assembly. Conclusions Our results suggest that NST in skeletal muscle could be adaptively augmented in the face of insufficient adrenergic NST in BAT, depending on the genetic background of the mice. It may provide both protection from cold and resistance to obesity, more effectively than BAT.

• Skagen, Christine; Løvsletten, Nils Gunnar; Asoawe, Lucia; Al-Karbawi, Zeineb; Rustan, Arild Christian & Thoresen, G. Hege [Show all 7 contributors for this article] (2023). Functional expression of the thermally activated transient receptor potential channels TRPA1 and TRPM8 in human myotubes. Journal of Thermal Biology. ISSN 0306-4565. 116. doi: 10.1016/j.jtherbio.2023.103623. Full text in Research Archive Show summary

  Transient potential (TRP) ion channels expressed in primary sensory neurons act as the initial detectors of environmental cold and heat, information which controls muscle energy expenditure. We hypothesize that non-neuronal TRPs have direct cellular responses to thermal exposure, also affecting cellular metabolism. In the present study we show expression of TRPA1, TRPM8 and TRPV1 in rat skeletal muscle and human primary myotubes by qPCR. Effects of TRP activity on metabolism in human myotubes were studied using radiolabeled glucose. FURA-2 was used for Ca2+ imaging. TRPA1, TRPM8 and TRPV1 were expressed at low levels in primary human myotubes and in m. gastrocnemius, m. soleus, and m. trapezius from rat. Activation of TRPA1 by ligustilide resulted in an increased glucose uptake and oxidation in human myotubes, whereas activation of TRPM8 by menthol and icilin significantly decreased glucose uptake and oxidation. Activation of heat sensing TRPV1 by capsaicin had no effect on glucose metabolism. Agonist-induced increases in intracellular Ca2+ levels by ligustilide and icilin in human myotubes confirmed a direct activation of TRPA1 and TRPM8, respectively. The mRNA expression of some genes involved in thermogenesis, i.e. peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), uncoupling protein (UCP) 1 and UCP3, were downregulated in human myotubes following TRPA1 activation, while the mRNA expression of TRPM8 and TRPA1 were downregulated following TRPM8 activation by menthol and icilin, respectively. Cold exposure (18 °C) of cultured myotubes followed by a short recovery period had no effect on glucose uptake and oxidation in the basal situation, however when TRPA1 and TRPM8 channels were chemically inhibited a temperature-induced difference in glucose metabolism was found. In conclusion, mRNA of TRPA1, TRPM8 and TRPV1 are expressed in rat skeletal muscle and human skeletal muscle cells. Modulation of TRPA1 and TRPM8 by chemical agents induced changes in Ca2+ levels and glucose metabolism in human skeletal muscle cells, indicating functional receptors.

• Fraser, David A.; Wang, Xiaoyu; Lund, Jenny; Nikolic, Natasa; Iruarrizaga-Lejarreta, Marta & Skjaeret, Tore [Show all 11 contributors for this article] (2022). A structurally engineered fatty acid, icosabutate, suppresses liver inflammation and fibrosis in NASH. Journal of Hepatology. ISSN 0168-8278. 76(4), p. 800–811. doi: 10.1016/j.jhep.2021.12.004. Full text in Research Archive
• Krapf, Solveig; Lund, Jenny; Saqib, Awais Ur Rehman; Bakke, Hege Gilbø; Rustan, Arild Christian & Thoresen, G. Hege [Show all 7 contributors for this article] (2022). Pancreatic Cancer Cell-Conditioned, Human-Derived Primary Myotubes Display Increased Leucine Turnover, Increased Lipid Accumulation, and Reduced Glucose Uptake. Metabolites. 12(11). doi: 10.3390/metabo12111095. Full text in Research Archive Show summary

  Metabolic alterations occurring in cancer cells have been seen to also occur in other tissues than cancerous tissue. For instance, cachexia, peripheral insulin resistance, or both are commonly seen in patients with cancer. We explored differences in substrate use in myotubes conditioned with the medium from a pancreatic cancer cell line, PANC-1, or primary human pancreatic cells, hPECs. Protein turnover was assessed using scintillation proximity assay, glucose and oleic acid handling were analyzed by substrate oxidation assay. We performed qPCR to study gene expression and immunoblotting and proteomic analyses to study protein expression. PANC-1-conditioned myotubes had an imbalance in protein turnover with decreased accumulation, increased decay, and decreased MYH2 gene expression. Glucose uptake decreased despite increased insulin-stimulated Akt phosphorylation. Fatty acid uptake increased, whereas fatty acid oxidation was unchanged, leading to accumulation of intracellular lipids (TAG) in PANC-1-conditioned myotubes. Secretome analyses revealed increased release of growth factors and growth factor receptor from PANC-1 cells, potentially affecting muscle cell metabolism. Myotubes exposed to pancreatic cancer cell medium displayed altered energy metabolism with increased protein/leucine turnover and lipid accumulation, while glucose uptake and oxidation reduced. This indicates production and release of substances from pancreatic cancer cells affecting skeletal muscle.

• Mengeste, Abel Mulu; Nikolic, Natasa; Fernandez, Andrea Dalmao; Feng, Yuan Zeng; Nyman, Tuula Anneli & Kersten, Sander [Show all 11 contributors for this article] (2022). Insight Into the Metabolic Adaptations of Electrically Pulse-Stimulated Human Myotubes Using Global Analysis of the Transcriptome and Proteome. Frontiers in Physiology. 13. doi: 10.3389/fphys.2022.928195. Full text in Research Archive Show summary

  Electrical pulse stimulation (EPS) has proven to be a useful tool to interrogate cell-specific responses to muscle contraction. In the present study, we aimed to uncover networks of signaling pathways and regulatory molecules responsible for the metabolic effects of exercise in human skeletal muscle cells exposed to chronic EPS. Differentiated myotubes from young male subjects were exposed to EPS protocol 1 (i.e. 2 ms, 10 V, and 0.1 Hz for 24 h), whereas myotubes from middle-aged women and men were exposed to protocol 2 (i.e. 2 ms, 30 V, and 1 Hz for 48 h). Fuel handling as well as the transcriptome, cellular proteome, and secreted proteins of EPS-treated myotubes from young male subjects were analyzed using a combination of high-throughput RNA sequencing, high-resolution liquid chromatography-tandem mass spectrometry, oxidation assay, and immunoblotting. The data showed that oxidative metabolism was enhanced in EPS-exposed myotubes from young male subjects. Moreover, a total of 81 differentially regulated proteins and 952 differentially expressed genes (DEGs) were observed in these cells after EPS protocol 1. We also found 61 overlapping genes while comparing the DEGs to mRNA expression in myotubes from the middle-aged group exposed to protocol 2, assessed by microarray. Gene ontology (GO) analysis indicated that significantly regulated proteins and genes were enriched in biological processes related to glycolytic pathways, positive regulation of fatty acid oxidation, and oxidative phosphorylation, as well as muscle contraction, autophagy/mitophagy, and oxidative stress. Additionally, proteomic identification of secreted proteins revealed extracellular levels of 137 proteins were changed in myotubes from young male subjects exposed to EPS protocol 1. Selected putative myokines were measured using ELISA or multiplex assay to validate the results. Collectively, our data provides new insight into the transcriptome, proteome and secreted proteins alterations following in vitro exercise and is a valuable resource for understanding the molecular mechanisms and regulatory molecules mediating the beneficial metabolic effects of exercise.

• Katare, Parmeshwar Bajirao; Fernandez, Andrea Dalmao; Mengeste, Abel Mulu; Hamarsland, Håvard; Ellefsen, Stian & Bakke, Hege Gilbø [Show all 9 contributors for this article] (2022). Energy metabolism in skeletal muscle cells from donors with different body mass index. Frontiers in Physiology. 13. doi: 10.3389/fphys.2022.982842. Full text in Research Archive
• Mengeste, Abel Mulu; Katare, Parmeshwar Bajirao; Fernandez, Andrea Dalmao; Lund, Jenny; Bakke, Hege Gilbø & Baker, David [Show all 11 contributors for this article] (2022). Knockdown of sarcolipin (SLN) impairs substrate utilization in human skeletal muscle cells. Molecular Biology Reports. ISSN 0301-4851. p. 6005–6017. doi: 10.1007/s11033-022-07387-0. Full text in Research Archive Show summary

  Abstract Background Recent studies have highlighted that uncoupling of sarco-/endoplasmic reticulum Ca 2+ -ATPase (SERCA) by sarcolipin (SLN) increases ATP consumption and contributes to heat liberation. Exploiting this thermogenic mechanism in skeletal muscle may provide an attractive strategy to counteract obesity and associated metabolic disorders. In the present study, we have investigated the role of SLN on substrate metabolism in human skeletal muscle cells. Methods and results After generation of skeletal muscle cells with stable SLN knockdown (SLN-KD), cell viability, glucose and oleic acid (OA) metabolism, mitochondrial function, as well as gene expressions were determined. Depletion of SLN did not influence cell viability. However, glucose and OA oxidation were diminished in SLN-KD cells compared to control myotubes. Basal respiration measured by respirometry was also observed to be reduced in cells with SLN-KD. The metabolic perturbation in SLN-KD cells was reflected by reduced gene expression levels of peroxisome proliferator-activated receptor γ coactivator 1α ( PGC1α ) and forkhead box O1 ( FOXO1 ). Furthermore, accumulation of OA was increased in cells with SLN-KD compared to control cells. These effects were accompanied by increased lipid formation and incorporation of OA into complex lipids. Additionally, formation of complex lipids and free fatty acid from de novo lipogenesis with acetate as substrate was enhanced in SLN-KD cells. Detection of lipid droplets using Oil red O staining also showed increased lipid accumulation in SLN-KD cells. Conclusions Overall, our study sheds light on the importance of SLN in maintaining metabolic homeostasis in human skeletal muscle. Findings from the current study suggest that therapeutic strategies involving SLN-mediated futile cycling of SERCA might have significant implications in the treatment of obesity and associated metabolic disorders. Graphical abstract

• Krajčová, Adéla; Skagen, Christine; Džupa, Valér; Urban, Tomáš; Rustan, Arild Christian & Jiroutková, Kateřina [Show all 9 contributors for this article] (2022). Effect of noradrenaline on propofol-induced mitochondrial dysfunction in human skeletal muscle cells. Intensive Care Medicine Experimental. 10:47(1), p. 1–14. doi: 10.1186/s40635-022-00474-3. Full text in Research Archive Show summary

  Background Mitochondrial dysfunction is a hallmark of both critical illness and propofol infusion syndrome and its severity seems to be proportional to the doses of noradrenaline, which patients are receiving. We comprehensively studied the effects of noradrenaline on cellular bioenergetics and mitochondrial biology in human skeletal muscle cells with and without propofol-induced mitochondrial dysfunction. Methods Human skeletal muscle cells were isolated from vastus lateralis biopsies from patients undergoing elective hip replacement surgery (n = 14) or healthy volunteers (n = 4). After long-term (96 h) exposure to propofol (10 µg/mL), noradrenaline (100 µM), or both, energy metabolism was assessed by extracellular flux analysis and substrate oxidation assays using [14C] palmitic and [14C(U)] lactic acid. Mitochondrial membrane potential, morphology and reactive oxygen species production were analysed by confocal laser scanning microscopy. Mitochondrial mass was assessed both spectrophotometrically and by confocal laser scanning microscopy. Results Propofol moderately reduced mitochondrial mass and induced bioenergetic dysfunction, such as a reduction of maximum electron transfer chain capacity, ATP synthesis and profound inhibition of exogenous fatty acid oxidation. Noradrenaline exposure increased mitochondrial network size and turnover in both propofol treated and untreated cells as apparent from increased co-localization with lysosomes. After adjustment to mitochondrial mass, noradrenaline did not affect mitochondrial functional parameters in naïve cells, but it significantly reduced the degree of mitochondrial dysfunction induced by propofol co-exposure. The fatty acid oxidation capacity was restored almost completely by noradrenaline co-exposure, most likely due to restoration of the capacity to transfer long-chain fatty acid to mitochondria. Both propofol and noradrenaline reduced mitochondrial membrane potential and increased reactive oxygen species production, but their effects were not additive. Conclusions Noradrenaline prevents rather than aggravates propofol-induced impairment of mitochondrial functions in human skeletal muscle cells. Its effects on bioenergetic dysfunctions of other origins, such as sepsis, remain to be demonstrated.

• Schjølberg, Tiril; Asoawe, Lucia; Krapf, Solveig Astrid; Rustan, Arild Christian; Thoresen, G. Hege & Haugen, Fred (2022). Experimental Models for Cold Exposure of Muscle in vitro and in vivo. Bio-protocol. 12(13). doi: 10.21769/BioProtoc.4461. Full text in Research Archive Show summary

  Work in cold environments may have a significant impact on occupational health. In these and similar situations, cold exposure localized to the extremities may reduce the temperature of underlying tissues. To investigate the molecular effects of cold exposure in muscle, and since adequate methods were missing, we established two experimental cold exposure models: 1) In vitroexposure to cold (18degreeC) or control temperature (37degreeC) of cultured human skeletal muscle cells (myotubes); and 2) unilateral cold exposure of hind limb skeletal muscle in anesthetized rats (intramuscular temperature 18degreeC), with contralateral control (37degreeC). This methodology enables studies of muscle responses to local cold exposures at the level of gene expression, but also other molecular outcomes.

• Tingstad, Ragna Husby; Norheim, Frode Amador; Haugen, Fred; Feng, Yuan Zeng; Tunsjø, Hege & Thoresen, G. Hege [Show all 9 contributors for this article] (2021). The effect of toll-like receptor ligands on energy metabolism and myokine expression and secretion in cultured human skeletal muscle cells. Scientific Reports. 11(1). doi: 10.1038/s41598-021-03730-w. Full text in Research Archive Show summary

  Skeletal muscle plays an important role in glycaemic control and metabolic homeostasis, making it a tissue of interest with respect to type 2 diabetes mellitus. The aim of the present study was to determine if ligands of Toll-like receptors (TLRs) could have an impact on energy metabolism and myokine expression and secretion in cultured human skeletal muscle cells. The myotubes expressed mRNA for TLRs 1–6. TLR3, TLR4, TLR5 and TLR6 ligands (TLRLs) increased glucose metabolism. Furthermore, TLR4L and TLR5L increased oleic acid metabolism. The metabolic effects of TLRLs were not evident until after at least 24 h pre-incubation of the cells and here the metabolic effects were more evident for the metabolism of glucose than oleic acid, with a shift towards effects on oleic acid metabolism after chronic exposure (168 h). However, the stimulatory effect of TLRLs on myokine expression and secretion was detected after only 6 h, where TLR3-6L stimulated secretion of interleukin-6 (IL-6). TLR5L also increased secretion of interleukin-8 (IL-8), while TLR6L also increased secretion of granulocyte–macrophage colony stimulating factor (GM-CSF). Pre-incubation of the myotubes with IL-6 for 24 h increased oleic acid oxidation but had no effect on glucose metabolism. Thus IL-6 did not mimic all the metabolic effects of the TLRLs, implying metabolic effects beyond the actions of this myokine.

• Skagen, Christine; Nyman, Tuula Anneli; Xiao-Rong, Peng; O'Mahony, Sven; Kase, Eili Tranheim & Rustan, Arild Christian [Show all 7 contributors for this article] (2021). Chronic treatment with terbutaline increases glucose and oleic acid oxidation and protein synthesis in cultured human myotubes. Current Research in Pharmacology and Drug Discovery (CRPHAR). 2, p. 1–11. doi: 10.1016/j.crphar.2021.100039. Full text in Research Archive
• Mengeste, Abel Mulu; Lund, Jenny; Katare, Parmeshwar Bajirao; Ghobadi, Roya; Bakke, Hege Gilbø & Lunde, Per Kristian [Show all 13 contributors for this article] (2021). The small molecule SERCA activator CDN1163 increases energy metabolism in human skeletal muscle cells. Current Research in Pharmacology and Drug Discovery (CRPHAR). 2, p. 1–12. doi: 10.1016/j.crphar.2021.100060. Full text in Research Archive
• Vid, Jan; Mis, Katarina; Nikolic, Natasa; Dolinar, Klemen; Petric, Metka & Bone, Andraz [Show all 11 contributors for this article] (2021). Effect of differentiation, de novo innervation, and electrical pulse stimulation on mRNA and protein expression of Na+,K+-ATPase, FXYD1, and FXYD5 in cultured human skeletal muscle cells. PLOS ONE. doi: 10.1371/journal.pone.0247377. Full text in Research Archive Show summary

  Denervation reduces the abundance of Na + ,K + -ATPase (NKA) in skeletal muscle, while reinnervation increases it. Primary human skeletal muscle cells, the most widely used model to study human skeletal muscle in vitro , are usually cultured as myoblasts or myotubes without neurons and typically do not contract spontaneously, which might affect their ability to express and regulate NKA. We determined how differentiation, de novo innervation, and electrical pulse stimulation affect expression of NKA (α and β) subunits and NKA regulators FXYD1 (phospholemman) and FXYD5 (dysadherin). Differentiation of myoblasts into myotubes under low serum conditions increased expression of myogenic markers CD56 (NCAM1), desmin, myosin heavy chains, dihydropyridine receptor subunit α 1S , and SERCA2 as well as NKAα2 and FXYD1, while it decreased expression of FXYD5 mRNA. Myotubes, which were innervated de novo by motor neurons in co-culture with the embryonic rat spinal cord explants, started to contract spontaneously within 7–10 days. A short-term co-culture (10–11 days) promoted mRNA expression of myokines, such as IL-6, IL-7, IL-8, and IL-15, but did not affect mRNA expression of NKA, FXYDs, or myokines, such as musclin, cathepsin B, meteorin-like protein, or SPARC. A long-term co-culture (21 days) increased the protein abundance of NKAα1, NKAα2, FXYD1, and phospho-FXYD1 Ser68 without attendant changes in mRNA levels. Suppression of neuromuscular transmission with α-bungarotoxin or tubocurarine for 24 h did not alter NKA or FXYD mRNA expression. Electrical pulse stimulation (48 h) of non-innervated myotubes promoted mRNA expression of NKAβ2, NKAβ3, FXYD1, and FXYD5. In conclusion, low serum concentration promotes NKAα2 and FXYD1 expression, while de novo innervation is not essential for upregulation of NKAα2 and FXYD1 mRNA in cultured myotubes. Finally, although innervation and EPS both stimulate contractions of myotubes, they exert distinct effects on the expression of NKA and FXYDs.

• Lund, Jenny; Krapf, Solveig Astrid; Sistek, Medina; Bakke, Hege Gilbø; Bartesagi, Stefano & Xiao-Rong, Peng [Show all 9 contributors for this article] (2021). SENP2 is vital for optimal insulin signaling and insulin-stimulated glycogen synthesis in human skeletal muscle cells. Current Research in Pharmacology and Drug Discovery (CRPHAR). 2, p. 1–10. doi: 10.1016/j.crphar.2021.100061. Full text in Research Archive
• Mengeste, Abel Mulu; Rustan, Arild Christian & Lund, Jenny (2021). Skeletal muscle energy metabolism in obesity. Obesity. ISSN 1930-7381. 29(10), p. 1582–1595. doi: 10.1002/oby.23227. Full text in Research Archive
• Mars, Tomaz; Mis, Katarina; Meznaric, Marija; Mihevc, Sonja Prpar; Vid, Jan & Haugen, Fred [Show all 11 contributors for this article] (2020). Innervation and electrical pulse stimulation – in vitro effects on human skeletal muscle cells. Applied Physiology, Nutrition and Metabolism. ISSN 1715-5312. doi: 10.1139/apnm-2019-0575. Full text in Research Archive Show summary

  Contraction-induced adaptations in skeletal muscles are well characterized in vivo, but the underlying cellular mechanisms are still not completely understood. Cultured human myotubes represent an essential model system for human skeletal muscle which can be modulated ex vivo, but they are quiescent and do not contract unless being stimulated. Stimulation can be achieved by innervation of human myotubes in vitro by co-culturing with embryonic rat spinal cord, or by replacing motor neuron activation by electrical pulse stimulation (EPS). Effects of these two in vitro approaches, innervation and EPS, were characterized with respects to the expression of myosin heavy chains (MyHCs) and metabolism of glucose and oleic acid in cultured human myotubes. Adherent human myotubes were either innervated with rat spinal-cord segments or exposed to EPS. The expression pattern of MyHCs was assessed by qPCR, immunoblotting, and immunofluorescence, while the metabolism of glucose and oleic acid were studied using radiolabeled substrates. Innervation and EPS promoted differentiation towards different fiber types in human myotubes. Expression of the slow MyHC-1 isoform was reduced in innervated myotubes, whereas it remained unaltered in EPS-treated cells. Expression of both fast isoforms (MyHC-2A and MyHC-2X) tended to decrease in EPS-treated cells. Both approaches induced a more oxidative phenotype, reflected in increased CO2 production from both glucose and oleic acid. Novelty: • Innervation and EPS favour differentiation into different fiber types in human myotubes. • Both innervation and EPS promote a metabolically more oxidative phenotype in human myotubes.

• Løvsletten, Nils Gunnar; Vu, Helene Loang Ngo; Skagen, Christine; Lund, Jenny; Kase, Eili Tranheim & Thoresen, G. Hege [Show all 8 contributors for this article] (2020). Treatment of human skeletal muscle cells with inhibitors of diacylglycerol acyltransferases 1 and 2 to explore isozyme-specific roles on lipid metabolism. Scientific Reports. 10:238, p. 1–13. doi: 10.1038/s41598-019-57157-5. Full text in Research Archive Show summary

  Diacylglycerol acyltransferases (DGAT) 1 and 2 catalyse the final step in triacylglycerol (TAG) synthesis, the esterification of fatty acyl-CoA to diacylglycerol. Despite catalysing the same reaction and being present in the same cell types, they exhibit different functions on lipid metabolism in various tissues. Yet, their roles in skeletal muscle remain poorly defined. In this study, we investigated how selective inhibitors of DGAT1 and DGAT2 affected lipid metabolism in human primary skeletal muscle cells. The results showed that DGAT1 was dominant in human skeletal muscle cells utilizing fatty acids (FAs) derived from various sources, both exogenously supplied FA, de novo synthesised FA, or FA derived from lipolysis, to generate TAG, as well as being involved in de novo synthesis of TAG. On the other hand, DGAT2 seemed to be specialised for de novo synthesis of TAG from glycerol-3-posphate only. Interestingly, DGAT activities were also important for regulating FA oxidation, indicating a key role in balancing FAs between storage in TAG and efficient utilization through oxidation. Finally, we observed that inhibition of DGAT enzymes could potentially alter glucose–FA interactions in skeletal muscle. In summary, treatment with DGAT1 or DGAT2 specific inhibitors resulted in different responses on lipid metabolism in human myotubes, indicating that the two enzymes play distinct roles in TAG metabolism in skeletal muscle.

• Lund, Jenny & Rustan, Arild (2020). Fatty Acids: Structures and Properties. Encyclopedia of Life Sciences. doi: 10.1002/9780470015902.a0029198. Full text in Research Archive
• Aas, Vigdis; Thoresen, G. Hege; Rustan, Arild & Lund, Jenny (2020). Substrate oxidation in primary human skeletal muscle cells is influenced by donor age. Cell and Tissue Research. ISSN 0302-766X. 382, p. 599–608. doi: 10.1007/s00441-020-03275-w. Full text in Research Archive Show summary

  Primary human myotubes represent an alternative system to intact skeletal muscle for the study of human diseases related to changes in muscle energy metabolism. This work aimed to study if fatty acid and glucose metabolism in human myotubes in vitro were related to muscle of origin, donor gender, age, or body mass index (BMI). Myotubes from a total of 82 donors were established from three different skeletal muscles, i.e., musculus vastus lateralis, musculus obliquus internus abdominis, and musculi interspinales, and cellular energy metabolism was evaluated. Multiple linear regression analyses showed that donor age had a significant effect on glucose and oleic acid oxidation after correcting for gender, BMI, and muscle of origin. Donor BMI was the only significant contributor to cellular oleic acid uptake, whereas cellular glucose uptake did not rely on any of the variables examined. Despite the effect of age on substrate oxidation, cellular mRNA expression of pyruvate dehydrogenase kinase 4 (PDK4) and peroxisome proliferator–activated receptor gamma coactivator 1 alpha (PPARGC1A) did not correlate with donor age. In conclusion, donor age significantly impacts substrate oxidation in cultured human myotubes, whereas donor BMI affects cellular oleic acid uptake.

• Lindquist, Carine; Bjørndal, Bodil; Bakke, Hege Gilbø; Slettom, Grete; Clason, Marie Karoliussen & Rustan, Arild [Show all 10 contributors for this article] (2019). A mitochondria-targeted fatty acid analogue influences hepatic glucose metabolism and reduces the plasma insulin/glucose ratio in male Wistar rats. PLOS ONE. 14:e0222558(9), p. 1–17. doi: 10.1371/journal.pone.0222558. Full text in Research Archive Show summary

  A fatty acid analogue, 2-(tridec-12-yn-1-ylthio)acetic acid (1-triple TTA), was previously shown to have hypolipidemic effects in rats by targeting mitochondrial activity predominantly in liver. This study aimed to determine if 1-triple TTA could influence carbohydrate metabolism. Male Wistar rats were treated for three weeks with oral supplementation of 100 mg/kg body weight 1-triple TTA. Blood glucose and insulin levels, and liver carbohydrate metabolism gene expression and enzyme activities were determined. In addition, human myotubes and Huh7 liver cells were treated with 1-triple TTA, and glucose and fatty acid oxidation were determined. The level of plasma insulin was significantly reduced in 1-triple TTA-treated rats, resulting in a 32% reduction in the insulin/glucose ratio. The hepatic glucose and glycogen levels were lowered by 22% and 49%, respectively, compared to control. This was accompanied by lower hepatic gene expression of phosphenolpyruvate carboxykinase, the rate-limiting enzyme in gluconeogenesis, and Hnf4A, a regulator of gluconeogenesis. Gene expression of pyruvate kinase, catalysing the final step of glycolysis, was also reduced by 1-triple TTA. In addition, pyruvate dehydrogenase activity was reduced, accompanied by 10-15-fold increased gene expression of its regulator pyruvate dehydrogenase kinase 4 compared to control, suggesting reduced entry of pyruvate into the TCA cycle. Indeed, the NADPH-generating enzyme malic enzyme 1 (ME1) catalysing production of pyruvate from malate, was increased 13-fold at the gene expression level. Despite the decreased glycogen level, genes involved in glycogen synthesis were not affected in livers of 1-triple TTA treated rats. In contrast, the pentose phosphate pathway seemed to be increased as the hepatic gene expression of glucose-6-phosphate dehydrogenase (G6PD) was higher in 1-triple TTA treated rats compared to controls. In human Huh7 liver cells, but not in myotubes, 1-triple-TTA reduced glucose oxidation and induced fatty acid oxidation, in line with previous observations of increased hepatic mitochondrial palmitoyl-CoA oxidation in rats. Importantly, this work recognizes the liver as an important organ in glucose homeostasis. The mitochondrially targeted fatty acid analogue 1-triple TTA seemed to lower hepatic glucose and glycogen levels by inhibition of gluconeogenesis. This was also linked to a reduction in glucose oxidation accompanied by reduced PHD activity and stimulation of ME1 and G6PD, favouring a shift from glucose- to fatty acid oxidation. The reduced plasma insulin/glucose ratio indicate that 1-triple TTA may improve glucose tolerance in rats.

• Løvsletten, Nils Gunnar; Rustan, Arild; Laurens, Claire; Thoresen, G. Hege; Moro, Cedric & Nikolic, Natasa (2019). Primary defects in lipid handling and resistance to exercise in myotubes from obese donors with and without type 2 diabetes. Applied Physiology, Nutrition and Metabolism. ISSN 1715-5312. doi: 10.1139/apnm-2019-0265. Full text in Research Archive
• Pettersen, Ina Katrine Nitschke; Tusubira, Deusdedit; Ashrafi, Hanan; Dyrstad, Sissel Elisabeth; Hansen, Lena & Liu, Xiaozheng [Show all 18 contributors for this article] (2019). Upregulated PDK4 expression is a sensitive marker of increased fatty acid oxidation. Mitochondrion (Amsterdam. Print). ISSN 1567-7249. 49, p. 97–110. doi: 10.1016/j.mito.2019.07.009. Full text in Research Archive Show summary

  Fatty acid oxidation is a central fueling pathway for mitochondrial ATP production. Regulation occurs through multiple nutrient- and energy-sensitive molecular mechanisms. We explored if upregulated mRNA expression of the mitochondrial enzyme pyruvate dehydrogenase kinase 4 (PDK4) may be used as a surrogate marker of increased mitochondrial fatty acid oxidation, by indicating an overall shift from glucose to fatty acids as the preferred oxidation fuel. The association between fatty acid oxidation and PDK4 expression was studied in different contexts of metabolic adaption. In rats treated with the modified fatty acid tetradecylthioacetic acid (TTA), Pdk4 was upregulated simultaneously with fatty acid oxidation genes in liver and heart, whereas muscle and white adipose tissue remained unaffected. In MDA-MB-231 cells, fatty acid oxidation increased nearly threefold upon peroxisome proliferator-activated receptor α (PPARα, PPARA) overexpression, and four-fold upon TTA-treatment. PDK4 expression was highly increased under these conditions. Further, overexpression of PDK4 caused increased fatty acid oxidation in these cells. Pharmacological activators of PPARα and AMPK had minor effects, while the mTOR inhibitor rapamycin potentiated the effect of TTA. There were minor changes in mitochondrial respiration, glycolytic function, and mitochondrial biogenesis under conditions of increased fatty acid oxidation. TTA was found to act as a mild uncoupler, which is likely to contribute to the metabolic effects. Repeated experiments with HeLa cells supported these findings. In summary, PDK4 upregulation implies an overarching metabolic shift towards increased utilization of fatty acids as energy fuel, and thus constitutes a sensitive marker of enhanced fatty acid oxidation.

• Løvsletten, Nils Gunnar; Bakke, Siril Skaret; Kase, Eili Tranheim; Ouwens, D. Margriet; Thoresen, G. Hege & Rustan, Arild (2018). Increased triacylglycerol - Fatty acid substrate cycling in human skeletal muscle cells exposed to eicosapentaenoic acid. PLOS ONE. 13:e0208048(11), p. 1–15. doi: 10.1371/journal.pone.0208048. Full text in Research Archive Show summary

  It has previously been shown that pretreatment of differentiated human skeletal muscle cells (myotubes) with eicosapentaenoic acid (EPA) promoted increased uptake of fatty acids and increased triacylglycerol accumulation, compared to pretreatment with oleic acid (OA) and palmitic acid (PA). The aim of the present study was to examine whether EPA could affect substrate cycling in human skeletal muscle cells by altering lipolysis rate of intracellular TAG and re-esterification of fatty acids. Fatty acid metabolism was studied in human myotubes using a mixture of fatty acids, consisting of radiolabelled oleic acid as tracer (14C-OA) together with EPA or PA. Co-incubation of myotubes with EPA increased cell-accumulation and incomplete fatty acid oxidation of 14C-OA compared to co-incubation with PA. Lipid distribution showed higher incorporation of 14C-OA into all cellular lipids after co-incubation with EPA relative to PA, with most markedly increases (3 to 4-fold) for diacylglycerol and triacylglycerol. Further, the increases in cellular lipids after co-incubation with EPA were accompanied by higher lipolysis and fatty acid re-esterification rate. Correspondingly, basal respiration, proton leak and maximal respiration were significantly increased in cells exposed to EPA compared to PA. Microarray and Gene Ontology (GO) enrichment analysis showed that EPA, related to PA, significantly changed i.e. the GO terms “Neutral lipid metabolic process” and “Regulation of lipid storage”. Finally, an inhibitor of diacylglycerol acyltransferase 1 decreased the effect of EPA to promote fatty acid accumulation. In conclusion, incubation of human myotubes with EPA, compared to PA, increased processes of fatty acid turnover and oxidation suggesting that EPA may activate futile substrate cycling of fatty acids in human myotubes. Increased TAG—FA cycling may be involved in the potentially favourable effects of long-chain polyunsaturated n-3 fatty acids on skeletal muscle and whole-body energy metabolism.

• Lund, Jenny; Helle, Siw A; Li, Yuchuan; Løvsletten, Nils Gunnar; Stadheim, Hans Kristian & Jensen, Jørgen [Show all 9 contributors for this article] (2018). Higher lipid turnover and oxidation in cultured human myotubes from athletic versus sedentary young male subjects. Scientific Reports. 8(1). doi: 10.1038/s41598-018-35715-7. Full text in Research Archive Show summary

  In this study we compared fatty acid (FA) metabolism in myotubes established from athletic and sedentary young subjects. Six healthy sedentary (maximal oxygen uptake (VO2max)≤ 46 ml/kg/min) and six healthy athletic (VO2max> 60 ml/kg/min) young men were included. Myoblasts were cultured and diferentiated to myotubes from satellite cells isolated from biopsy of musculus vastus lateralis. FA metabolism was studied in myotubes using [14C]oleic acid. Lipid distribution was assessed by thin layer chromatography, and FA accumulation, lipolysis and re-esterifcation were measured by scintillation proximity assay.Gene and protein expressions were studied. Myotubes from athletic subjects showed lower FA accumulation, lower incorporation of FA into total lipids, triacylglycerol (TAG), diacylglycerol and cholesteryl ester, higherTAG-related lipolysis and re-esterifcation, and higher complete oxidation and incomplete β-oxidation of FA compared to myotubes from sedentary subjects. mRNA expression of the mitochondrial electron transport chain complex III gene UQCRB was higher in cells from athletic compared to sedentary. Myotubes established from athletic subjects have higher lipid turnover and oxidation compared to myotubes from sedentary subjects.Our fndings suggestthat cultured myotubes retain some of the phenotypic traits of their donors.

• Malecki, Jedrzej Mieczyslaw; Jakobsson, Magnus; Ho, Angela Yeuan Yen; Moen, Anders; Rustan, Arild & Falnes, Pål (2017). Uncovering human METTL12 as a mitochondrial methyltransferase that modulates citrate synthase activity through metabolite-sensitive lysine methylation. Journal of Biological Chemistry. ISSN 0021-9258. 292(43), p. 17950–17962. doi: 10.1074/jbc.M117.808451. Full text in Research Archive Show summary

  Lysine methylation is an important and much-studied posttranslational modification of nuclear and cytosolic proteins but is present also in mitochondria. However, the responsible mitochondrial lysine-specific methyltransferases (KMTs) remain largely elusive. Here, we investigated METTL12, a mitochondrial human S-adenosylmethionine (AdoMet)-dependent methyltransferase and found it to methylate a single protein in mitochondrial extracts, identified as citrate synthase (CS). Using several in vitro and in vivo approaches, we demonstrated that METTL12 methylates CS on Lys-395, which is localized in the CS active site. Interestingly, the METTL12-mediated methylation inhibited CS activity and was blocked by the CS substrate oxaloacetate. Moreover, METTL12 was strongly inhibited by the reaction product S-adenosylhomocysteine (AdoHcy). In summary, we have uncovered a novel human mitochondrial KMT that introduces a methyl modification into a metabolic enzyme and whose activity can be modulated by metabolic cues. Based on the established naming nomenclature for similar enzymes, we suggest that METTL12 be renamed CS-KMT (gene name CSKMT). This research was originally published in the Journal of Biological Chemistry. © 2017 American Society for Biochemistry and Molecular Biology

• Lund, Jenny; Rustan, Arild; Løvsletten, Nils Gunnar; Mudry, Jonathan M.; Langleite, Torgrim Mikal & Feng, Yuan Zeng [Show all 19 contributors for this article] (2017). Exercise in vivo marks human myotubes in vitro: Training-induced increase in lipid metabolism. PLOS ONE. 12:e0175441(4), p. 1–24. doi: 10.1371/journal.pone.0175441. Full text in Research Archive Show summary

  Background and aims: Physical activity has preventive as well as therapeutic benefits for overweight subjects. In this study we aimed to examine effects of in vivo exercise on in vitro metabolic adaptations by studying energy metabolism in cultured myotubes isolated from biopsies taken before and after 12 weeks of extensive endurance and strength training, from healthy sedentary normal weight and overweight men. Methods: Healthy sedentary men, aged 40–62 years, with normal weight (body mass index (BMI) < 25 kg/m2) or overweight (BMI ≥ 25 kg/m2) were included. Fatty acid and glucose metabolism were studied in myotubes using [14C]oleic acid and [14C]glucose, respectively. Gene and protein expressions, as well as DNA methylation were measured for selected genes. Results: The 12-week training intervention improved endurance, strength and insulin sensitivity in vivo, and reduced the participants’ body weight. Biopsy-derived cultured human myotubes after exercise showed increased total cellular oleic acid uptake (30%), oxidation (46%) and lipid accumulation (34%), as well as increased fractional glucose oxidation (14%) compared to cultures established prior to exercise. Most of these exercise-induced increases were significant in the overweight group, whereas the normal weight group showed no change in oleic acid or glucose metabolism. Conclusions: 12 weeks of combined endurance and strength training promoted increased lipid and glucose metabolism in biopsy-derived cultured human myotubes, showing that training in vivo are able to induce changes in human myotubes that are discernible in vitro.

• Åstrand, Ove Alexander Høgmoen; Viktorsson, Elvar Örn; Kristensen, Aleksander Lim; Ekeberg, Dag; Røberg-Larsen, Hanne & Wilson, Steven Ray Haakon [Show all 12 contributors for this article] (2017). Synthesis, in vitro and in vivo biological evaluation of new oxysterols as modulators of the liver X receptors. Journal of Steroid Biochemistry and Molecular Biology. ISSN 0960-0760. 165, p. 323–330. doi: 10.1016/j.jsbmb.2016.07.010. Full text in Research Archive Show summary

  Liver X Receptor (LXR) modulators have shown potential as drugs since they target genes affecting metabolism and fatty acid synthesis. LXR antagonists are of particular interest since they are able to reduce the synthesis of complex fatty acids and glucose uptake. Based on molecular modeling, five new cholesterol mimics were synthesized, where four contained a hydroxyl group in the 22-S-position. The new compounds were screened in vitro against several genes affecting lipid metabolism. The compound that performed best in vitro was a dimethylamide derivative of 22(S)-hydroxycholesterol and it was chosen for in vivo testing. However, the blood plasma analysis from the in vivo tests revealed a concentration lower than needed to give any response, indicating either rapid metabolism or low bioavailability.

• Lund, Jenny; Tangen, Daniel S.; Wiig, Håvard; Stadheim, Hans Kristian; Siw, Anette Helle & Birk, Jesper B. [Show all 12 contributors for this article] (2017). Glucose metabolism and metabolic flexibility in cultured skeletal muscle cells is related to exercise status in young male subjects. Archives of Physiology and Biochemistry. ISSN 1381-3455. 124(2), p. 119–130. doi: 10.1080/13813455.2017.1369547. Full text in Research Archive Show summary

  We hypothesised that skeletal muscles of healthy young people have a large variation in oxidative capacity and fibre-type composition, and aimed therefore to investigate glucose metabolism in biopsies and myotubes isolated from musculus vastus lateralis from healthy males with varying degrees of maximal oxygen uptake. Trained and intermediary trained subjects showed higher carbohydrate oxidation in vivo. Fibre-type distribution in biopsies and myotubes did not differ between groups. There was no correlation between fibre-type I expression in biopsies and myotubes. Myotubes from trained had higher deoxyglucose accumulation and fractional glucose oxidation (glucose oxidation relative to glucose uptake), and were also more sensitive to the suppressive action of acutely added oleic acid to the cells. Despite lack of correlation of fibre types between skeletal muscle biopsies and cultured cells, myotubes from trained subjects retained some of their phenotypes in vitro with respect to enhanced glucose metabolism and metabolic flexibility.

• Feng, Yuan Zeng; Lund, Jenny; Li, Yuchuan; Knabenes, Irlin; Bakke, Siril Skaret & Kase, Eili Tranheim [Show all 11 contributors for this article] (2017). Loss of perilipin 2 in cultured myotubes enhances lipolysis and redirects the metabolic energy balance from glucose oxidation towards fatty acid oxidation. Journal of Lipid Research. ISSN 0022-2275. 58(11), p. 2147–2161. doi: 10.1194/jlr.M079764. Full text in Research Archive Show summary

  Lipid droplet (LD) coating proteins are essential for the formation and stability of intracellular LDs. Plin2 is an abundant LD coating protein in skeletal muscle, but its importance for muscle function is unclear. We show that myotubes established from Plin2−/− mice contain reduced content of LDs and accumulate less oleic acid (OA) in triacylglycerol (TAG) due to elevated LD hydrolysis in comparison with Plin2+/+ myotubes. The reduced ability to store TAG in LDs in Plin2−/− myotubes is accompanied by a shift in energy metabolism. Plin2−/− myotubes are characterized by increased oxidation of OA, lower glycogen synthesis, and reduced glucose oxidation in comparison with Plin2+/+ myotubes, perhaps reflecting competition between FAs and glucose as part of the Randle cycle. In accord with these metabolic changes, Plin2−/− myotubes have elevated expression of Ppara and Ppargc1a, transcription factors that stimulate expression of genes important for FA oxidation, whereas genes involved in glucose uptake and oxidation are suppressed. Loss of Plin2 had no impact on insulin-stimulated Akt phosphorylation. Our results suggest that Plin2 is essential for protecting the pool of skeletal muscle LDs to avoid an uncontrolled hydrolysis of stored TAG and to balance skeletal muscle energy metabolism. This article was originally published in the Journal of Lipid Research. © 2017 American Society for Biochemistry and Molecular Biology

• Kong, Xiang Yi; Feng, Yuan Zeng; Eftestøl, Einar; Kase, Eili Tranheim; Haugum, Hanne & Eskild, Winnie [Show all 8 contributors for this article] (2016). Increased glucose utilization and decreased fatty acid metabolism in myotubes from Glmpgt/gt mice. Archives of Physiology and Biochemistry. ISSN 1381-3455. 122(1), p. 36–45. doi: 10.3109/13813455.2015.1120752. Full text in Research Archive
• Lund, Jenny; Stensrud, Camilla; Rajender, Melanie Müller; Bohov, Pavol; Thoresen, G. Hege & Berge, Rolf Kristian [Show all 11 contributors for this article] (2016). The molecular structure of thio-ether fatty acids influences PPAR-dependent regulation of lipid metabolism. Bioorganic & Medicinal Chemistry. ISSN 0968-0896. 24(6), p. 1191–1203. doi: 10.1016/j.bmc.2016.01.045. Full text in Research Archive
• Kase, Eili Tranheim; Feng, Yuan Zeng; Badin, Pierre-Marie; Bakke, Siril Skaret; Laurens, C & Coue, M [Show all 11 contributors for this article] (2015). Primary defects in lipolysis and insulin action in skeletal muscle cells from type 2 diabetic individuals. Biochimica et Biophysica Acta - Molecular and Cell Biology of Lipids. ISSN 1388-1981. 1851(9), p. 1194–1201. doi: 10.1016/j.bbalip.2015.03.005. Full text in Research Archive
• Feng, Yuan Zeng; Nikolic, Natasa; Bakke, Siril Skaret; Kase, Eili Tranheim; Guderud, Kari & Hjelmesæth, Jøran [Show all 9 contributors for this article] (2015). Myotubes from lean and severely obese subjects with and without type 2 diabetes respond differently to an in vitro model of exercise. American Journal of Physiology - Cell Physiology. 308(7), p. C548–C556. doi: 10.1152/ajpcell.00314.2014. Full text in Research Archive
• Aas, Vigdis; Lund, Jenny; Kase, Eili Tranheim; Feng, Yuan Zeng; Rustan, Arild & Thoresen, G. Hege (2015). Blodglukosesenkende legemidler ved type 2-diabetes. Norsk Farmaceutisk Tidsskrift (NFT). ISSN 0029-1935. 123(5), p. 20–24. Full text in Research Archive
• Covington, Jeffrey D.; Noland, Robert C.; Hebert, R. Caitlin; Masinter, Blaine S.; Smith, Steven R. & Rustan, Arild [Show all 8 contributors for this article] (2015). Perilipin 3 differentially regulates skeletal muscle lipid oxidation in active, sedentary, and type 2 diabetic males. Journal of Clinical Endocrinology and Metabolism (JCEM). ISSN 0021-972X. 100(10), p. 3683–3692. doi: 10.1210/JC.2014-4125. Full text in Research Archive
• Kong, Xiang Yi; Kase, Eili Tranheim; Herskedal, Anette; Schjalm, Camilla; Damme, Markus & Nesset, Cecilie Kåsi [Show all 9 contributors for this article] (2015). Lack of the lysosomal membrane protein, GLMP, in mice results in metabolic dysregulation in liver. PLOS ONE. 10(6). doi: 10.1371/journal.pone.0129402. Full text in Research Archive Show summary

  Ablation of glycosylated lysosomal membrane protein (GLMP, formerly known as NCU-G1) has been shown to cause chronic liver injury which progresses into liver fibrosis in mice. Both lysosomal dysfunction and chronic liver injury can cause metabolic dysregulation. Glmpgt/gt mice (formerly known as Ncu-g1gt/gtmice) were studied between 3 weeks and 9 months of age. Body weight gain and feed efficiency of Glmpgt/gt mice were comparable to wild type siblings, only at the age of 9 months the Glmpgt/gt siblings had significantly reduced body weight. Reduced size of epididymal fat pads was accompanied by hepatosplenomegaly in Glmpgt/gt mice. Blood analysis revealed reduced levels of blood glucose, circulating triacylglycerol and non-esterified fatty acids in Glmpgt/gt mice. Increased flux of glucose, increased de novo lipogenesis and lipid accumulation were detected in Glmpgt/gt primary hepatocytes, as well as elevated triacylglycerol levels in Glmpgt/gt liver homogenates, compared to hepatocytes and liver from wild type mice. Gene expression analysis showed an increased expression of genes involved in fatty acid uptake and lipogenesis in Glmpgt/gt liver compared to wild type. Our findings are in agreement with the metabolic alterations observed in other mouse models lacking lysosomal proteins, and with alterations characteristic for advanced chronic liver injury.

• Coué, Marine; Badin, Pierre-Marie; Vila, Isabelle K.; Laurens, Claire; Louche, Katie & Marquès, Marie-Adeline [Show all 15 contributors for this article] (2015). Defective natriuretic peptide receptor signaling in skeletal muscle links obesity to type 2 diabetes. Diabetes. ISSN 0012-1797. 64(12), p. 4033–4045. doi: 10.2337/db15-0305. Full text in Research Archive
• Bakke, Siril Skaret; Feng, Yuan Zeng; Nikolic, Natasa; Kase, Eili Tranheim; Moro, Cedric & Stensrud, Camilla [Show all 14 contributors for this article] (2015). Myotubes from Severely Obese Type 2 Diabetic Subjects Accumulate Less Lipids and Show Higher Lipolytic Rate than Myotubes from Severely Obese Non-Diabetic Subjects. PLOS ONE. 10(3). doi: 10.1371/journal.pone.0119556. Full text in Research Archive Show summary

  About 80% of patients with type 2 diabetes are classified as overweight. However, only about 1/3 of severely obese subjects have type 2 diabetes. This indicates that several se- verely obese individuals may possess certain characteristics that protect them against type 2 diabetes. We therefore hypothesized that this apparent paradox could be related to funda- mental differences in skeletal muscle lipid handling. Energy metabolism and metabolic flexi- bility were examined in human myotubes derived from severely obese subjects without (BMI 44 ± 7 kg/m 2 ) and with type 2 diabetes (BMI 43 ± 6 kg/m 2 ). Lower insulin sensitivity was observed in myotubes from severely obese subjects with type 2 diabetes. Lipolysis rate was higher, and oleic acid accumulation, triacylglycerol content, and fatty acid adaptability were lower in myotubes from severely obese subjects with type 2 diabetes compared to se- verely obese non-diabetic subjects. There were no differences in lipid distribution and mRNA and protein expression of the lipases HSL and ATGL, the lipase cofactor CGI-58, or the lipid droplet proteins PLIN2 and PLIN3. Glucose and oleic acid oxidation were also simi- lar in cells from the two groups. In conclusion, myotubes established from severely obese donors with established type 2 diabetes had lower ability for lipid accumulation and higher li- polysis rate than myotubes from severely obese donors without diabetes. This indicates that a difference in intramyocellular lipid turnover might be fundamental in evolving type 2 diabetes.

• Covington, Jeffrey D.; Myland, Cassandra K.; Rustan, Arild; Ravussin, Eric; Smith, Steven R. & Bajpeyi, Sudip (2015). Effect of serial cell passaging in the retention of fiber type and mitochondrial content in primary human myotubes. Obesity. ISSN 1930-7381. 23(12), p. 2414–2420. doi: 10.1002/oby.21192. Full text in Research Archive
• Covington, Jeffrey D.; Galgani, Jose E.; Moro, Cedric; LaGrange, Jamie M; Zhang, Zhengyu & Rustan, Arild [Show all 8 contributors for this article] (2014). Skeletal muscle perilipin 3 and coatomer proteins are increased following exercise and are associated with fat oxidation. PLOS ONE. 9(3). doi: 10.1371/journal.pone.0091675. Full text in Research Archive
• Feng, Yuan Zeng; Nikolic, Natasa; Bakke, Siril Skaret; Boekschoten, Mark V.; Kersten, Sander & Kase, Eili Tranheim [Show all 8 contributors for this article] (2014). PPARδ activation in human myotubes increases mitochondrial fatty acid oxidative capacity and reduces glucose utilization by a switch in substrate preference. Archives of Physiology and Biochemistry. ISSN 1381-3455. 120(1), p. 12–21. doi: 10.3109/13813455.2013.829105. Full text in Research Archive
• Åstrand, Ove Alexander Høgmoen; Gikling, Ingveig; Sylte, Ingebrigt; Rustan, Arild; Thoresen, G. Hege & Rongved, Pål [Show all 7 contributors for this article] (2014). Development of new LXR modulators that regulate LXR target genes and reduce lipogenesis in human cell models. European Journal of Medicinal Chemistry. ISSN 0223-5234. 74, p. 258–263. doi: 10.1016/j.ejmech.2014.01.003. Full text in Research Archive
• Kong, Xiang Yi; Nesset, Cecilie Kåsi; Damme, Markus; Løberg, Else Marit; Lübke, Torben & Mæhlen, Jan [Show all 13 contributors for this article] (2014). Loss of lysosomal membrane protein NCU-G1 in mice results in spontaneous liver fibrosis with accumulation of lipofuscin and iron in Kupffer cells. Disease Models and Mechanisms. ISSN 1754-8403. 7(3), p. 351–362. doi: 10.1242/dmm.014050. Full text in Research Archive Show summary

  Human kidney predominant protein, NCU-G1, is a highly conserved protein with an unknown biological function. Initially described as a nuclear protein, it was later shown to be a bona fide lysosomal integral membrane protein. To gain insight into the physiological function of NCU-G1, mice with no detectable expression of this gene were created using a gene-trap strategy, and Ncu-g1gt/gt mice were successfully characterized. Lysosomal disorders are mainly caused by lack of or malfunctioning of proteins in the endosomal-lysosomal pathway. The clinical symptoms vary, but often include liver dysfunction. Persistent liver damage activates fibrogenesis and, if unremedied, eventually leads to liver fibrosis/cirrhosis and death. We demonstrate that the disruption of Ncu-g1 results in spontaneous liver fibrosis in mice as the predominant phenotype. Evidence for an increased rate of hepatic cell death, oxidative stress and active fibrogenesis were detected in Ncu-g1gt/gt liver. In addition to collagen deposition, microscopic examination of liver sections revealed accumulation of autofluorescent lipofuscin and iron in Ncu-g1gt/gt Kupffer cells. Because only a few transgenic mouse models have been identified with chronic liver injury and spontaneous liver fibrosis development, we propose that the Ncu-g1gt/gt mouse could be a valuable new tool in the development of novel treatments for the attenuation of fibrosis due to chronic liver damage.

• Bajpeyi, Sudip; Myrland, Cassandra Kim; Covington, Jeffrey D.; Obanda, Diana; Cefalu, W.T. & Smith, Steven R. [Show all 8 contributors for this article] (2014). Lipid in skeletal muscle myotubes is associated to the donors' insulin sensitivity and physical activity phenotypes. Obesity. ISSN 1930-7381. 22(2), p. 426–434. doi: 10.1002/oby.20556. Full text in Research Archive
• Smith, Robert; Solberg, Rigmor; Jacobsen, Linn Løkken; Voreland, Anette Larsen; Rustan, Arild & Thoresen, G. Hege [Show all 7 contributors for this article] (2014). Simvastatin inhibits glucose metabolism and legumain activity in human myotubes. PLOS ONE. 9(1:85721). doi: 10.1371/journal.pone.0085721. Full text in Research Archive
• Aas, Vigdis; Bakke, Siril Skaret; Feng, Yuan Zeng; Kase, Eili Tranheim; Jensen, Jørgen & Bajpeyi, Sudip [Show all 8 contributors for this article] (2013). Are cultured human myotubes far from home? Cell and Tissue Research. ISSN 0302-766X. 354(3), p. 671–682. doi: 10.1007/s00441-013-1655-1. Full text in Research Archive Show summary

  Satellite cells can be isolated from skeletal muscle biopsies, activated to proliferating myoblasts and differentiated into multinuclear myotubes in culture. These cell cultures represent a model system for intact human skeletal muscle and can be modulated ex vivo. The advantages of this system are that the most relevant genetic background is available for the investigation of human disease (as opposed to rodent cell cultures), the extracellular environment can be precisely controlled and the cells are not immortalized, thereby offering the possibility of studying innate characteristics of the donor. Limitations in differentiation status (fiber type) of the cells and energy metabolism can be improved by proper treatment, such as electrical pulse stimulation to mimic exercise. This review focuses on the way that human myotubes can be employed as a tool for studying metabolism in skeletal muscles, with special attention to changes in muscle energy metabolism in obesity and type 2 diabetes.

• Kase, Eili Tranheim; Nikolic, Natasa; Bakke, Siril Skaret; Bogen, Kaja Kamilla; Aas, Vigdis & Thoresen, G. Hege [Show all 7 contributors for this article] (2013). Remodelling of oxidative energy metabolism by galactose improves glucose handling and metabolic switching in human skeletal muscle cells. PLOS ONE. 8(4). doi: 10.1371/journal.pone.0059972. Full text in Research Archive Show summary

  Cultured human myotubes have a low mitochondrial oxidative potential. This study aims to remodel energy metabolism in myotubes by replacing glucose with galactose during growth and differentiation to ultimately examine the consequences for fatty acid and glucose metabolism. Exposure to galactose showed an increased [14C]oleic acid oxidation, whereas cellular uptake of oleic acid uptake was unchanged. On the other hand, both cellular uptake and oxidation of [14C]glucose increased in myotubes exposed to galactose. In the presence of the mitochondrial uncoupler carbonylcyanide p-trifluormethoxy-phenylhydrazone (FCCP) the reserve capacity for glucose oxidation was increased in cells grown with galactose. Staining and live imaging of the cells showed that myotubes exposed to galactose had a significant increase in mitochondrial and neutral lipid content. Suppressibility of fatty acid oxidation by acute addition of glucose was increased compared to cells grown in presence of glucose. In summary, we show that cells grown in galactose were more oxidative, had increased oxidative capacity and higher mitochondrial content, and showed an increased glucose handling. Interestingly, cells exposed to galactose showed an increased suppressibility of fatty acid metabolism. Thus, galactose improved glucose metabolism and metabolic switching of myotubes, representing a cell model that may be valuable for metabolic studies related to insulin resistance and disorders involving mitochondrial impairments.

• Hessvik, Nina Pettersen; Bakke, Siril Skaret; Smith, Robert; Ravna, aina westrheim; Sylte, Ingebrigt & Rustan, Arild [Show all 8 contributors for this article] (2012). The liver X receptor modulator 22(S)-hydroxycholesterol exerts cell-type specific effects on lipid and glucose metabolism. Journal of Steroid Biochemistry and Molecular Biology. ISSN 0960-0760. 128, p. 154–164. doi: 10.1016/j.jsbmb.2011.10.006. Full text in Research Archive
• Kase, Eili Tranheim; Nikolic, Natasa; Hessvik, Nina Pettersen; Fjeldheim, Åse-Karine; Jensen, Jørgen & Thoresen, G. Hege [Show all 7 contributors for this article] (2012). Dietary supplementation with 22-S-hydroxycholesterol to rats reduces body weight gain and the accumulation of liver triacylglycerol. Lipids. ISSN 0024-4201. 47(5), p. 483–493. doi: 10.1007/s11745-012-3663-4. Full text in Research Archive Show summary

  This study explores the pharmacokinetics of 22-S-hydroxycholesterol (22SHC) in vivo in rats. We also carried out a metabolic study to explore whether the beneficial effects observed of 22SHC on glucose and lipid metabolism in vitro could be seen in vivo in rats. In the pharmacokinetic study, rats were given 50 mg/kg of [3H]22-S-hydroxycholesterol before absorption, distribution and excretion were monitored. In the metabolic study, the effect of 22SHC (30 mg/kg/day for 3 weeks) in rats on body weight gain [chow and high-fat diet (HFD)], serum lipids triacylglycerol (TAG) content and gene expression in liver and skeletal muscle were examined. Results showed that 22SHC was well absorbed after oral administration and distributed to most organs and mainly excreted in feces. Rats receiving 22SHC gained less body weight than their controls regardless whether the animals received chow diet or HFD. Moreover, we observed that animals receiving HFD had elevated levels of serum TAG while this was not observed for animals on HFD supplemented with 22SHC. The amount of TAG in liver was reduced after 22SHC treatment in animals receiving either chow diet or HFD. Gene expression analysis revealed that two genes (carnitine palmitoyltransferase 2 and uncoupling protein 3) involved in fatty acid oxidation and energy dissipation were increased in liver. Ucp3 expression (both protein and mRNA level) was increased in skeletal muscle, but insulin-stimulated glucose uptake and TAG content were unchanged. In conclusion, 22SHC seems to be an interesting model substance in the search of treatments for disorders involving aberrations in lipid metabolism.

• Nikolic, Natasa; Bakke, Siril Skaret; Kase, Eili Tranheim; Rudberg, Ida; Halle, Ingeborg Flo & Rustan, Arild [Show all 8 contributors for this article] (2012). Electrical Pulse Stimulation of Cultured Human Skeletal Muscle Cells as an In Vitro Model of Exercise. PLOS ONE. 7(3). doi: 10.1371/journal.pone.0033203. Full text in Research Archive Show summary

  Background and Aims Physical exercise leads to substantial adaptive responses in skeletal muscles and plays a central role in a healthy life style. Since exercise induces major systemic responses, underlying cellular mechanisms are difficult to study in vivo. It was therefore desirable to develop an in vitro model that would resemble training in cultured human myotubes. Methods Electrical pulse stimulation (EPS) was applied to adherent human myotubes. Cellular contents of ATP, phosphocreatine (PCr) and lactate were determined. Glucose and oleic acid metabolism were studied using radio-labeled substrates, and gene expression was analyzed using real-time RT-PCR. Mitochondrial content and function were measured by live imaging and determination of citrate synthase activity, respectively. Protein expression was assessed by electrophoresis and immunoblotting. Results High-frequency, acute EPS increased deoxyglucose uptake and lactate production, while cell contents of both ATP and PCr decreased. Chronic, low-frequency EPS increased oxidative capacity of cultured myotubes by increasing glucose metabolism (uptake and oxidation) and complete fatty acid oxidation. mRNA expression level of pyruvate dehydrogenase complex 4 (PDK4) was significantly increased in EPS-treated cells, while mRNA expressions of interleukin 6 (IL-6), cytochrome C and carnitin palmitoyl transferase b (CPT1b) also tended to increase. Intensity of MitoTracker®Red FM was doubled after 48 h of chronic, low-frequency EPS. Protein expression of a slow fiber type marker (MHCI) was increased in EPS-treated cells. Conclusions Our results imply that in vitro EPS (acute, high-frequent as well as chronic, low-frequent) of human myotubes may be used to study effects of exercise.

• Norheim, Frode; Gjelstad, Ingrid Merethe Fange; Hjorth, Marit; Vinknes, Kathrine; Langleite, Torgrim Mikal & Holen, Torgeir [Show all 12 contributors for this article] (2012). Molecular nutrition research - the modern way of performing nutritional science. Nutrients. 4(12), p. 1898–1944. doi: 10.3390/nu4121898. Full text in Research Archive Show summary

  In spite of amazing progress in food supply and nutritional science, and a striking increase in life expectancy of approximately 2.5 months per year in many countries during the previous 150 years, modern nutritional research has a great potential of still contributing to improved health for future generations, granted that the revolutions in molecular and systems technologies are applied to nutritional questions. Descriptive and mechanistic studies using state of the art epidemiology, food intake registration, genomics with single nucleotide polymorphisms (SNPs) and epigenomics, transcriptomics, proteomics, metabolomics, advanced biostatistics, imaging, calorimetry, cell biology, challenge tests (meals, exercise, etc.), and integration of all data by systems biology, will provide insight on a much higher level than today in a field we may name molecular nutrition research. To take advantage of all the new technologies scientists should develop international collaboration and gather data in large open access databases like the suggested Nutritional Phenotype database (dbNP). This collaboration will promote standardization of procedures (SOP), and provide a possibility to use collected data in future research projects. The ultimate goals of future nutritional research are to understand the detailed mechanisms of action for how nutrients/foods interact with the body and thereby enhance health and treat diet-related diseases.

• Bakke, Siril Skaret; Moro, Cedric; Nikolic, Natasa; Hessvik, Nina Pettersen; Badin, Pierre-Marie & Lauvhaug, Line [Show all 13 contributors for this article] (2012). Palmitic acid follows a different metabolic pathway than oleic acid in human skeletal muscle cells; lower lipolysis rate despite an increased level of adipose triglyceride lipase. Biochimica et Biophysica Acta - Molecular and Cell Biology of Lipids. ISSN 1388-1981. 1821(10), p. 1323–1333. doi: 10.1016/j.bbalip.2012.07.001. Full text in Research Archive
• Nikolic, Natasa; Rhedin, M; Rustan, Arild; Storlien, Len H.; Thoresen, G. Hege & Strømstedt, Maria (2012). Overexpression of PGC-1α Increases Fatty Acid Oxidative Capacity of Human Skeletal Muscle Cells. Biochemistry Research International. ISSN 2090-2247. 2012. doi: 10.1155/2012/714074. Full text in Research Archive
• Badin, Pierre-Marie; Loubière, Camille; Coonen, Maarten; Louche, Katie; Tavernier, Geneviève & Bourlier, Virginie [Show all 11 contributors for this article] (2012). Regulation of skeletal muscle lipolysis and oxidative metabolism by the co-lipase CGI-58. Journal of Lipid Research. ISSN 0022-2275. 53(5), p. 839–848. doi: 10.1194/jlr.M019182. Full text in Research Archive
• Norheim, Frode; Raastad, Truls; Thiede, Bernd; Rustan, Arild; Drevon, Christian A & Haugen, Fred (2011). Proteomic identification of secreted proteins from human skeletal muscle cells and expression in response to strength training. American Journal of Physiology. Endocrinology and Metabolism. ISSN 0193-1849. 301(5), p. E1013–E1021. doi: 10.1152/ajpendo.00326.2011. Full text in Research Archive
• Badin, Pierre-Marie; Louche, Katie; Mairal, Aline; Liebisch, Gerhard; Schmitz, Gerd & Rustan, Arild [Show all 9 contributors for this article] (2011). Altered Skeletal Muscle Lipase Expression and Activity Contribute to Insulin Resistance in Humans. Diabetes. ISSN 0012-1797. 60(6), p. 1734–1742. doi: 10.2337/db10-1364. Full text in Research Archive
• Fraser, David; Hessvik, Nina Pettersen; Nikolic, Natasa; Aas, Vigdis; Hanssen, Kristian Folkvord & Bøhn, Siv Kjølsrud [Show all 8 contributors for this article] (2011). Benfotiamine increases glucose oxidation and downregulates NADPH oxidase 4 expression in cultured human myotubes exposed to both normal and high glucose concentrations. Genes & Nutrition. ISSN 1555-8932. doi: 10.1007/s12263-011-0252-8. Full text in Research Archive Show summary

  The aim of the present work was to study the effects of benfotiamine (S-benzoylthiamine O-monophosphate) on glucose and lipid metabolism and gene expression in differentiated human skeletal muscle cells (myotubes) incubated for 4 days under normal (5.5 mM glucose) and hyperglycemic (20 mM glucose) conditions. Myotubes established from lean, healthy volunteers were treated with benfotiamine for 4 days. Glucose and lipid metabolism were studied with labeled precursors. Gene expression was measured using real-time polymerase chain reaction (qPCR) and microarray technology. Benfotiamine significantly increased glucose oxidation under normoglycemic (35 and 49% increase at 100 and 200 μM benfotiamine, respectively) as well as hyperglycemic conditions (70% increase at 200 μM benfotiamine). Benfotiamine also increased glucose uptake. In comparison, thiamine (200 μM) increased overall glucose metabolism but did not change glucose oxidation. In contrast to glucose, mitochondrial lipid oxidation and overall lipid metabolism were unchanged by benfotiamine. The expression of NADPH oxidase 4 (NOX4) was significantly downregulated by benfotiamine treatment under both normo- and hyperglycemic conditions. Gene set enrichment analysis (GSEA) showed that befotiamine increased peroxisomal lipid oxidation and organelle (mitochondrial) membrane function. In conclusion, benfotiamine increases mitochondrial glucose oxidation in myotubes and downregulates NOX4 expression. These findings may be of relevance to type 2 diabetes where reversal of reduced glucose oxidation and mitochondrial capacity is a desirable goal.

• Aas, Vigdis; Hessvik, Nina Pettersen; Wettergreen, Marianne; Hvammen, Anders Wensaas; Hallen, Stefan & Thoresen, G. Hege [Show all 7 contributors for this article] (2011). Chronic hyperglycemia reduces substrate oxidation and impairs metabolic switching of human myotubes. Biochimica et Biophysica Acta - Molecular Basis of Disease. ISSN 0925-4439. 1812(1), p. 94–105. doi: 10.1016/j.bbadis.2010.09.014. Full text in Research Archive Show summary

  Skeletal muscle of insulin resistant individuals is characterized by lower fasting lipid oxidation and reduced ability to switch between lipid and glucose oxidation. The purpose of the present study was to examine if chronic hyperglycemia would impair metabolic switching of myotubes. Human myotubes were treated with or without chronic hyperglycemia (20 mmol/l glucose for 4 days), and metabolism of [14C]oleic acid (OA) and [14C]glucose was studied. Myotubes exposed to chronic hyperglycemia showed a significantly reduced OA uptake and oxidation to CO2, whereas acid-soluble metabolites were increased compared to normoglycemic cells (5.5 mmol/l glucose). Glucose suppressibility, the ability of acute glucose (5 mmol/l) to suppress lipid oxidation, was 50% in normoglycemic cells and reduced to 21% by hyperglycemia. Adaptability, the capacity to increase lipid oxidation with increasing fatty acid availability, was not affected by hyperglycemia. Glucose uptake and oxidation were reduced by about 40% after hyperglycemia, and oxidation of glucose in presence of mitochondrial uncouplers showed that net and maximal oxidative capacities were significantly reduced. Hyperglycemia also abolished insulin-stimulated glucose uptake. Moreover, ATP concentration was reduced by 25% after hyperglycemia. However, none of the measured mitochondrial genes were downregulated nor was mitochondrial DNA content. Microarray and real-time RT-PCR showed that no genes were significantly regulated by chronic hyperglycemia. Addition of chronic lactate reduced both glucose and OA oxidation to the same extent as hyperglycemia. In conclusion, chronic hyperglycemia reduced substrate oxidation in skeletal muscle cells and impaired metabolic switching. The effect is most likely due to an induced mitochondrial dysfunction.

• Nehlin, Jan O.; Just, Marlene; Rustan, Arild & Gaster, Michael (2011). Human myotubes from myoblast cultures undergoing senescence exhibit defects in glucose and lipid metabolism. Biogerontology (Dordrecht). ISSN 1389-5729. 12(4), p. 349–365. doi: 10.1007/s10522-011-9336-5. Full text in Research Archive
• Ciocoiu, Calin C.; Ravna, aina westrheim; Sylte, Ingebrigt; Rustan, Arild & Hansen, Trond Vidar (2011). Synthesis, molecular modeling studies and biological evaluation of fluorine substituted analogs of GW 501516. Bioorganic & Medicinal Chemistry. ISSN 0968-0896. 19, p. 6982–6988. doi: 10.1016/j.bmc.2011.10.020. Full text in Research Archive
• Thoresen, G. Hege; Hessvik, Nina Pettersen; Bakke, Siril Skaret; Aas, Vigdis & Rustan, Arild (2011). Metabolic switching of human skeletal muscle cells in vitro. Prostaglandins, Leukotrienes and Essential Fatty Acids. ISSN 0952-3278. 85(5), p. 227–234. doi: 10.1016/j.plefa.2011.04.017. Full text in Research Archive Show summary

  In this review we will focus on external factors that may modify energy metabolism in human skeletal muscle cells (myotubes) and the ability of the myotubes to switch between lipid and glucose oxidation. We describe the metabolic parameters suppressibility, adaptability and substrate-regulated flexibility, and show the influence of nutrients such as fatty acids and glucose (chronic hyperglycemia), and some pharmacological agents modifying nuclear receptors (PPAR and LXR), on these parameters in human myotubes. Possible cellular mechanisms for changes in these parameters will also be highlighted.

• Sparks, LM; Moro, C; Ukropcova, B; Bajpeyi, S; Civitarese, AE & Hulver, MW [Show all 9 contributors for this article] (2011). Remodeling Lipid Metabolism and Improving Insulin Responsiveness in Human Primary Myotubes. PLOS ONE. 6(7). doi: 10.1371/journal.pone.0021068. Full text in Research Archive

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• Thoresen, G. Hege; Simonsen, terje; Christensen, Hege; Johansen, Harald Thidemann; Kase, Eili Tranheim & Robertsen, Ida [Show all 9 contributors for this article] (2021). Basal farmakologi. Fagbokforlaget. ISBN 9788245033557. 405 p. Full text in Research Archive
• Thoresen, G. Hege; Solberg, Rigmor; Johansen, Harald Thidemann; Kase, Eili Tranheim; Rustan, Arild Christian & Christensen, Hege [Show all 7 contributors for this article] (2020). Illustrert farmakologi. Fagbokforlaget. ISBN 9788245033564. 392 p. Full text in Research Archive

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• Pirkmajer, Sergej; Garcia-Roves, Pablo M.; Rustan, Arild Christian & Chibalin, Alexander V. (2022). Editorial: Untangling energy metabolism in skeletal muscle: From physiology to pharmacology. Frontiers in Physiology. 13. doi: 10.3389/fphys.2022.1113860. Full text in Research Archive
• Feng, Yuan Zeng; knabenes, Irlin Knivsland; Bakke, Siril S.; Lund, Jenny; Lee, Y.K. & kimmel, Alan [Show all 9 contributors for this article] (2015). Increased lipid oxidation and decreased lipid storage in myotubes lacking the lipid droplet binding protein perilipin2. Full text in Research Archive
• Viktorsson, Elvar Örn; Åstrand, Ove Alexander Høgmoen; Rustan, Arild; Thoresen, G. Hege; Kase, Eili Tranheim & Rongved, Pål (2015). Analogs of 22-S-hydroxycholesterol as potential Liver X Receptor-modulators: Synthesis and biological evaluation. Full text in Research Archive
• Feng, Yuan Zeng; knabenes, Irlin Knivsland; Lund, Jenny; Lee, Y.K.; kimmel, Alan & Thoresen, G. Hege [Show all 8 contributors for this article] (2014). Increased lipid oxidation and decreased lipid storage in myotubes lacking perilipin2. Full text in Research Archive
• Kong, Xiang Yi; Nesset, Cecilie Kåsi; Schjalm, Camilla; Løberg, Else Marit; Rustan, Arild & Thoresen, G. Hege [Show all 8 contributors for this article] (2014). NCU-G1GT/GT MICE: A LONG-LIVED MODEL FOR LIVER FIBROSIS. Full text in Research Archive
• Smith, Robert; Johansen, Harald Thidemann; Jacobsen, Linn Løkken; Voreland, Anette Larsen; Rustan, Arild & Thoresen, G. Hege [Show all 7 contributors for this article] (2013). Simvastatin inhibits legumain activity and processing in human myotubes. Full text in Research Archive
• Covington, Jeffrey D.; Galgani, Jose E.; Rustan, Arild; Zhang, Zhengyu; Moro, Cedric & Smith, Steven R. [Show all 8 contributors for this article] (2013). Muscle perilipin 3 is reduced using in vitro and in vivo exercise models and negatively associated with exercise lipid oxidation. The FASEB Journal. ISSN 0892-6638. 27. Full text in Research Archive
• Kase, Eili Tranheim; Lund, Jenny; Feng, Yuan Zeng; Langleite, Torgrim Mikal; Aas, Vigdis & Jensen, Jan S. [Show all 11 contributors for this article] (2013). Effect of exercise on fatty acid and glucose metabolism in cultured human myotubes. Diabetologia. ISSN 0012-186X. 56, p. S250–S250. Full text in Research Archive
• Bakke, Siril Skaret; Feng, Yuan Zeng; Rustan, Arild; Hjelmesæth, Jøran; Thoresen, G. Hege & Aas, Vigdis (2012). Lower lipolysis to counteract the development of type 2 diabetes mellitus - evidence from myotubes established from extremely obese subjects. Full text in Research Archive
• Bakke, Siril Skaret; Nikolic, Natasa; Rustan, Arild; Hjelmesæth, Jøran; Thoresen, G. Hege & Aas, Vigdis (2012). ALTERED ENERGY METABOLISM IN SKELETAL MUSCLE CELLS DERIVED FROM MORBIDLY OBESE INDIVIDUALS. Full text in Research Archive Show summary

  Introduction: Obesity is strongly associated with insulin resistance and type 2 diabetes (T2D). It has been revealed that less than 1 out of 3 morbidly obese subjects have T2D (Obes Surg 2010; 20:302-7), indicating that many morbidly obese subjects possess certain characteristics that protect them against developing T2D. Skeletal muscle is an important organ involved in fatty acid and glucose metabolism and therefore one of the organs where insulin resistance is most prominent. Metabolic flexibility is defined as the muscle’s ability to change energy metabolism between fed and fasted conditions, and this ability is reduced in insulin resistance and T2D. Methods: We examined fatty acid and glucose metabolism as well as metabolic flexibility in human skeletal muscle cells using radiolabeled precursors. The cells were derived from lean healthy subjects (BMI 23±0.9 kg/m2), morbidly obese with normal glucose tolerance (BMI 44±2.0 kg/m2) and morbidly obese subjects with T2D (BMI 43±1.5 kg/m2). Results: A 2-fold increase in fatty acid metabolism was observed in cells established from morbidly obese subjects (measured as accumulation and oxidation of oleic acid) and a approximately 40% lower metabolic flexibility (measured as the ability to switch from fatty acid to glucose oxidation) compared to cells from lean subjects. Triacylglycerol lipolysis was 30% higher for obese T2D subjects compared to the other groups. Conclusion: Muscle cells derived from morbidly obese showed increased lipid metabolism, but had a lower metabolic flexibility than cells from lean. Obese subjects with T2D had increased lipolysis, which may be important for development of T2D. Conflict of Interest None disclosed Funding Norwegian Research Council, Norwegian Diabetes Foundation, Freia Chocolade Fabriks Medical Foundation and Anders Jahre’s Foundation.

• Aas, Vigdis; Bakke, Siril Skaret; Nikolic, Natasa; Hjelmesæth, Jøran; Thoresen, G. Hege & Rustan, Arild (2012). Altered energy metabolism in skeletal muscle cells derived from morbidly obese subjects. Full text in Research Archive
• Bakke, Siril Skaret; Nikolic, Natasa; Rustan, Arild; Hjelmesæth, Jøran; Thoresen, G. Hege & Aas, Vigdis (2012). Altered energy metabolism in skeletal muscle cells derived from morbidly obese donors. Full text in Research Archive
• Halle, Ingeborg F.; Nikolic, Natasa; Bakke, Siril Skaret; Thoresen, G. Hege; Rustan, Arild & Aas, Vigdis (2011). Electrical pulse stimulation of cultured human skeletal muscle cells as a model of exercise in vitro. Full text in Research Archive
• Lauvhaug, Line; Bakke, Siril Skaret; Thoresen, G. Hege & Rustan, Arild (2011). Different handling of oleic, palmitic, linoleic and eicosapentaenoic acids in cultured human skeletal muscle cells. Full text in Research Archive
• Bakke, Siril Skaret; Nikolic, Natasa; Moro, Cedric; Lauvhaug, Line; Hessvik, Nina Pettersen & Thoresen, G. Hege [Show all 7 contributors for this article] (2011). Different handling of palmitic acid and oleic acid in human skeletal muscle cells. Full text in Research Archive
• Bakke, Siril Skaret; Nikolic, Natasa; Moro, Cedric; Lauvhaug, Line; Hessvik, Nina Pettersen & Thoresen, G. Hege [Show all 7 contributors for this article] (2011). DIFFERENT HANDLING OF PALMITIC ACID AND OLEIC ACID IN HUMAN SKELETAL MUSCLE CELLS. Full text in Research Archive
• Nikolic, Natasa; Bakke, Siril Skaret; Thoresen, G. Hege; Rustan, Arild & Aas, Vigdis (2010). Chronic electrical pulse stimulation of cultured human skeletal muscle cells as an in vitro model of exercise. Full text in Research Archive
• Nikolic, Natasa; Bakke, Siril Skaret; Thoresen, G. Hege; Rustan, Arild & Aas, Vigdis (2010). Energimetabolismen i humane skjelettmuskelceller - Utvikling av in vitro treningsmodell. Full text in Research Archive
• Nikolic, Natasa; Bakke, Siril Skaret; Thoresen, G. Hege; Rustan, Arild & Aas, Vigdis (2010). Chronic electrical pulse stimulation of cultured human skeletal muscle cells as an in vitro model of exercise. Full text in Research Archive
• Aas, Vigdis; Hessvik, Nina Pettersen; Thoresen, G. Hege & Rustan, Arild (2010). Chronic hyperglycemia impairs mitochondrial function in human myotubes. Full text in Research Archive
• Rustan, Arild (2010). The impact of eicosapentaenoic acid (EPA) on regulation of fatty acid metabolism, metabolic flexibility and gene expression in human skeletal muscle cells. Full text in Research Archive Show summary

  Our recent studies with differentiated human skeletal muscle cells (myotubes) suggests a positive role for eicosapentaenoic acid (EPA) compared to the other fatty acids (FAs) in improving overall energy metabolism and metabolic switching in skeletal muscle, which may contribute to the beneficial effects of dietary intake of very long-chain n-3 fatty acids. In a study using myotubes established from lean donors we showed that EPA increased suppressibility, the ability of acute glucose to suppress FA oxidation. Substrate-regulated flexibility, the ability to increase FA oxidation when changing from a high glucose, low fatty acid condition (“fed”) to a high fatty acid, low glucose (“fasted”) condition, was increased by EPA. Adaptability, the capacity to increase FA oxidation with increasing FA availability, was enhanced after pretreatment with EPA, linoleic acid (LA) and palmitic acid (PA). EPA per se accumulated less in the cells, however, EPA, LA and oleic acid (OA) treatment increased the number of lipid droplets (LDs) in myotubes. LD volume and intensity, as well as mitochondrial mass were independent of FA pretreatment. Microarray and PCR analysis showed that EPA regulated more genes than the other FAs and specific pathways involved in carbohydrate metabolism were induced only by EPA. The present study suggest a favorable effect of EPA on skeletal muscle metabolic switching and glucose utilization. Additional experiments with ALA and DHA indicated that the metabolic effects could be due to a general quality of n-3 FAs. Based on finding from this study we also suggest the use of three parameters called suppressibility, adaptability and substrate-regulated flexibility in functional studies of fuel selection and energy metabolism in cell cultures. In another study we wanted to identify the potential effects of EPA and a synthetic fatty acid derivative (TTA) on energy metabolism, insulin resistance and gene expression (PCR). Here we compared the effects of EPA, TTA, and OA in myotubes established from obese individuals with type 2 diabetes and obese healthy control subjects. Our results suggest that 1) mitochondrial dysfunction in diabetic myotubes was caused by disturbances downstream of fatty acid β-oxidation; 2) EPA promoted accumulation of triacylglycerol (TAG), enhanced β-oxidation, and increased glucose oxidation; and 3) TTA improved complete palmitic acid oxidation in diabetic myotubes, opposed increased lipid accumulation, and increased glucose oxidation.

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