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McKenna CF, Stierwalt HD, Zemski Berry KA, Ehrlicher SE, Robinson MM, Zarini S, Kahn DE, Snell-Bergeon JK, Perreault L, Bergman BC, Newsom SA. Intramuscular diacylglycerol accumulates with acute hyperinsulinemia in insulin-resistant phenotypes. Am J Physiol Endocrinol Metab 2024; 327:E183-E193. [PMID: 38895980 DOI: 10.1152/ajpendo.00368.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/06/2023] [Revised: 05/30/2024] [Accepted: 06/02/2024] [Indexed: 06/21/2024]
Abstract
Elevated skeletal muscle diacylglycerols (DAGs) and ceramides can impair insulin signaling, and acylcarnitines (acylCNs) reflect impaired mitochondrial fatty acid oxidation, thus, the intramuscular lipid profile is indicative of insulin resistance. Acute (i.e., postprandial) hyperinsulinemia has been shown to elevate lipid concentrations in healthy muscle and is an independent risk factor for type 2 diabetes (T2D). However, it is unclear how the relationship between acute hyperinsulinemia and the muscle lipidome interacts across metabolic phenotypes, thus contributing to or exacerbating insulin resistance. We therefore investigated the impact of acute hyperinsulinemia on the skeletal muscle lipid profile to help characterize the physiological basis in which hyperinsulinemia elevates T2D risk. In a cross-sectional comparison, endurance athletes (n = 12), sedentary lean adults (n = 12), and individuals with obesity (n = 13) and T2D (n = 7) underwent a hyperinsulinemic-euglycemic clamp with muscle biopsies. Although there were no significant differences in total 1,2-DAG fluctuations, there was a 2% decrease in athletes versus a 53% increase in T2D during acute hyperinsulinemia (P = 0.087). Moreover, C18 1,2-DAG species increased during the clamp with T2D only, which negatively correlated with insulin sensitivity (P < 0.050). Basal muscle C18:0 total ceramides were elevated with T2D (P = 0.029), but not altered by clamp. Acylcarnitines were universally lowered during hyperinsulinemia, with more robust reductions of 80% in athletes compared with only 46% with T2D (albeit not statistically significant, main effect of group, P = 0.624). Similar fluctuations with acute hyperinsulinemia increasing 1,2 DAGs in insulin-resistant phenotypes and universally lowering acylcarnitines were observed in male mice. In conclusion, acute hyperinsulinemia elevates muscle 1,2-DAG levels with insulin-resistant phenotypes. This suggests a possible dysregulation of intramuscular lipid metabolism in the fed state in individuals with low insulin sensitivity, which may exacerbate insulin resistance.NEW & NOTEWORTHY Postprandial hyperinsulinemia is a risk factor for type 2 diabetes and may increase muscle lipids. However, it is unclear how the relationship between acute hyperinsulinemia and the muscle lipidome interacts across metabolic phenotypes, thus contributing to insulin resistance. We observed that acute hyperinsulinemia elevates muscle 1,2-DAGs in insulin-resistant phenotypes, whereas ceramides were unaltered. Insulin-mediated acylcarnitine reductions are also hindered with high-fat feeding. The postprandial period may exacerbate insulin resistance in metabolically unhealthy phenotypes.
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Affiliation(s)
- Colleen F McKenna
- Division of Endocrinology, Metabolism and Diabetes, School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado, United States
| | - Harrison D Stierwalt
- School of Exercise, Sport, and Health Sciences, College of Health, Oregon State University, Corvallis, Oregon, United States
| | - Karin A Zemski Berry
- Division of Endocrinology, Metabolism and Diabetes, School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado, United States
| | - Sarah E Ehrlicher
- School of Exercise, Sport, and Health Sciences, College of Health, Oregon State University, Corvallis, Oregon, United States
| | - Matthew M Robinson
- School of Exercise, Sport, and Health Sciences, College of Health, Oregon State University, Corvallis, Oregon, United States
| | - Simona Zarini
- Division of Endocrinology, Metabolism and Diabetes, School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado, United States
| | - Darcy E Kahn
- Division of Endocrinology, Metabolism and Diabetes, School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado, United States
| | - Janet K Snell-Bergeon
- Division of Endocrinology, Metabolism and Diabetes, School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado, United States
| | - Leigh Perreault
- Division of Endocrinology, Metabolism and Diabetes, School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado, United States
| | - Bryan C Bergman
- Division of Endocrinology, Metabolism and Diabetes, School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado, United States
| | - Sean A Newsom
- School of Exercise, Sport, and Health Sciences, College of Health, Oregon State University, Corvallis, Oregon, United States
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Abstract
As the principal tissue for insulin-stimulated glucose disposal, skeletal muscle is a primary driver of whole-body glycemic control. Skeletal muscle also uniquely responds to muscle contraction or exercise with increased sensitivity to subsequent insulin stimulation. Insulin's dominating control of glucose metabolism is orchestrated by complex and highly regulated signaling cascades that elicit diverse and unique effects on skeletal muscle. We discuss the discoveries that have led to our current understanding of how insulin promotes glucose uptake in muscle. We also touch upon insulin access to muscle, and insulin signaling toward glycogen, lipid, and protein metabolism. We draw from human and rodent studies in vivo, isolated muscle preparations, and muscle cell cultures to home in on the molecular, biophysical, and structural elements mediating these responses. Finally, we offer some perspective on molecular defects that potentially underlie the failure of muscle to take up glucose efficiently during obesity and type 2 diabetes.
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Ramos PA, Lytle KA, Delivanis D, Nielsen S, LeBrasseur NK, Jensen MD. Insulin-Stimulated Muscle Glucose Uptake and Insulin Signaling in Lean and Obese Humans. J Clin Endocrinol Metab 2021; 106:e1631-e1646. [PMID: 33382888 PMCID: PMC7993573 DOI: 10.1210/clinem/dgaa919] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/11/2020] [Indexed: 12/29/2022]
Abstract
PURPOSE Skeletal muscle is the primary site for insulin-stimulated glucose disposal, and muscle insulin resistance is central to abnormal glucose metabolism in obesity. Whether muscle insulin signaling to the level of Akt/AS160 is intact in insulin-resistant obese humans is controversial. METHODS We defined a linear range of insulin-stimulated systemic and leg glucose uptake in 14 obese and 14 nonobese volunteers using a 2-step insulin clamp (Protocol 1) and then examined the obesity-related defects in muscle insulin action in 16 nonobese and 25 obese male and female volunteers matched for fitness using a 1-step, hyperinsulinemic, euglycemic clamp coupled with muscle biopsies (Protocol 2). RESULTS Insulin-stimulated glucose disposal (Si) was reduced by > 60% (P < 0.0001) in the obese group in Protocol 2; however, the phosphorylation of Akt and its downstream effector AS160 were not different between nonobese and obese groups. The increase in phosphorylation of Akt2 in response to insulin was positively correlated with Si for both the nonobese (r = 0.53, P = 0.03) and the obese (r = 0.55, P = 0.01) groups. Total muscle GLUT4 protein was 17% less (P < 0.05) in obese subjects. CONCLUSIONS We suggest that reduced muscle glucose uptake in obesity is not due to defects in the insulin signaling pathway at the level of Akt/AS160, which suggests there remain significant gaps in our knowledge of muscle insulin resistance in obesity. Our data imply that models of acute lipotoxicity do not replicate the pathophysiology of obesity.
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Affiliation(s)
- Paola A Ramos
- Endocrine Research Unit, Mayo Clinic, Rochester, MN, USA
| | - Kelli A Lytle
- Endocrine Research Unit, Mayo Clinic, Rochester, MN, USA
| | | | - Søren Nielsen
- Steno Diabetes Center Aarhus, Aarhus University Hospital, Aarhus C, Denmark
| | | | - Michael D Jensen
- Endocrine Research Unit, Mayo Clinic, Rochester, MN, USA
- Correspondence: Michael D. Jensen, MD, Division of Endocrinology, Mayo Clinic, 200 First St SW, Joseph Rm 5–194, Rochester MN 55905, USA.
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Stierwalt HD, Ehrlicher SE, Robinson MM, Newsom SA. Skeletal Muscle ACSL Isoforms Relate to Measures of Fat Metabolism in Humans. Med Sci Sports Exerc 2021; 53:624-632. [PMID: 32796254 PMCID: PMC8117722 DOI: 10.1249/mss.0000000000002487] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
INTRODUCTION Evidence from model systems implicates long-chain acyl-coenzyme A synthetase (ACSL) as key regulators of skeletal muscle fat oxidation and fat storage; however, such roles remain underexplored in humans. PURPOSE We sought to determine the protein expression of ACSL isoforms in skeletal muscle at rest and in response to acute exercise and identify relationships between skeletal muscle ACSL and measures of fat metabolism in humans. METHODS Sedentary adults (n = 14 [4 males and 10 females], body mass index = 22.2 ± 2.1 kg·m-2, V˙O2max = 32.2 ± 4.5 mL·kg-1⋅min-1) completed two study visits. Trials were identical other than completing 1 h of cycling exercise (65% V˙O2max) or remaining sedentary. Vastus lateralis biopsies were obtained 15-min postexercise (or rest) and 2-h postexercise to determine ACSL protein abundance. Whole-body fat oxidation was assessed at rest and during exercise using indirect calorimetry. Skeletal muscle triacylglycerol (TAG) was measured via lipidomic analysis. RESULTS We detected protein expression for four of the five known ACSL isoforms in human skeletal muscle. ACSL protein abundances were largely unaltered in the hours after exercise aside from a transient increase in ACSL5 15-min postexercise (P = 0.01 vs rest). Skeletal muscle ACSL1 protein abundance tended to be positively related with whole-body fat oxidation during exercise (P = 0.07, r = 0.53), when skeletal muscle accounts for the majority of energy expenditure. No such relationship between ACSL1 and fat oxidation was observed at rest. Skeletal muscle ACSL6 protein abundance was positively associated with muscle TAG content at rest (P = 0.05, r = 0.57). CONCLUSION Most ACSL protein isoforms can be detected in human skeletal muscle, with minimal changes in abundance after acute exercise. Our findings agree with those from model systems implicating ACSL1 and ACSL6 as possible determinants of fat oxidation and fat storage within skeletal muscle.
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Affiliation(s)
- Harrison D. Stierwalt
- School of Biological and Population Health Sciences, College of Public Health and Human Sciences, Oregon State University, Corvallis, OR
| | - Sarah E. Ehrlicher
- School of Biological and Population Health Sciences, College of Public Health and Human Sciences, Oregon State University, Corvallis, OR
| | - Matthew M. Robinson
- School of Biological and Population Health Sciences, College of Public Health and Human Sciences, Oregon State University, Corvallis, OR
| | - Sean A. Newsom
- School of Biological and Population Health Sciences, College of Public Health and Human Sciences, Oregon State University, Corvallis, OR
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Pyrroloquinoline Quinone Modifies Lipid Profile, but Not Insulin Sensitivity, of Palmitic Acid-Treated L6 Myotubes. Int J Mol Sci 2020; 21:ijms21218382. [PMID: 33171690 PMCID: PMC7664924 DOI: 10.3390/ijms21218382] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Revised: 11/03/2020] [Accepted: 11/06/2020] [Indexed: 12/28/2022] Open
Abstract
Pyrroloquinoline quinone (PQQ) is a novel stimulator of mitochondrial biogenesis and cellular energy metabolism. This is the first study investigating regulatory mechanisms and metabolic responses underlying PQQ’s action in palmitate-exposed L6 myotubes. Particularly, we assessed alterations in lipid content and composition, expression of metabolic enzymes, and changes in glucose transport. The experiments were conducted using muscle cells subjected to short (2 h) and prolonged (24 h) incubation with PQQ in a sequence of pre- and post-palmitic acid (PA) exposure. We demonstrated the opposite effects of 2 and 24 h treatments with PQQ on lipid content, i.e., a decline in the level of free fatty acids and triacylglycerols in response to short-time PQQ incubation as compared to increases in diacylglycerol and triacylglycerol levels observed after 24 h. We did not demonstrate a significant impact of PQQ on fatty acid transport. The analysis of metabolic enzyme expression showed that the vast majority of PQQ-dependent alterations cumulated in the PA/PQQ 24 h group, including elevated protein amount of peroxisome proliferator activated receptor γ co-activator 1α (PGC-1α), sirtuin-1 (SIRT1), phosphorylated 5′AMP-activated protein kinase (pAMPK), carnitine palmitoyltransferase I (CPT1), citrate synthase (CS), fatty acid synthase (FAS), and serine palmitoyltransferase, long chain base subunit 1 (SPT1). In conclusion, the results mentioned above indicate PQQ-dependent activation of both fatty acid oxidation and lipid synthesis in order to adapt cells to palmitic acid-rich medium, although PQQ did not attenuate insulin resistance in muscle cells.
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Møller LLV, Jaurji M, Kjøbsted R, Joseph GA, Madsen AB, Knudsen JR, Lundsgaard AM, Andersen NR, Schjerling P, Jensen TE, Krauss RS, Richter EA, Sylow L. Insulin-stimulated glucose uptake partly relies on p21-activated kinase (PAK)2, but not PAK1, in mouse skeletal muscle. J Physiol 2020; 598:5351-5377. [PMID: 32844438 DOI: 10.1113/jp280294] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2020] [Accepted: 08/24/2020] [Indexed: 12/28/2022] Open
Abstract
KEY POINTS Muscle-specific genetic ablation of p21-activated kinase (PAK)2, but not whole-body PAK1 knockout, impairs glucose tolerance in mice. Insulin-stimulated glucose uptake partly relies on PAK2 in glycolytic extensor digitorum longus muscle By contrast to previous reports, PAK1 is dispensable for insulin-stimulated glucose uptake in mouse muscle. ABSTRACT The group I p21-activated kinase (PAK) isoforms PAK1 and PAK2 are activated in response to insulin in skeletal muscle and PAK1/2 signalling is impaired in insulin-resistant mouse and human skeletal muscle. Interestingly, PAK1 has been suggested to be required for insulin-stimulated glucose transporter 4 translocation in mouse skeletal muscle. Therefore, the present study aimed to examine the role of PAK1 in insulin-stimulated muscle glucose uptake. The pharmacological inhibitor of group I PAKs, IPA-3 partially reduced (-20%) insulin-stimulated glucose uptake in isolated mouse soleus muscle (P < 0.001). However, because there was no phenotype with genetic ablation of PAK1 alone, consequently, the relative requirement for PAK1 and PAK2 in whole-body glucose homeostasis and insulin-stimulated muscle glucose uptake was investigated. Whole-body respiratory exchange ratio was largely unaffected in whole-body PAK1 knockout (KO), muscle-specific PAK2 KO and in mice with combined whole-body PAK1 KO and muscle-specific PAK2 KO. By contrast, glucose tolerance was mildly impaired in mice lacking PAK2 specifically in muscle, but not PAK1 KO mice. Moreover, while PAK1 KO muscles displayed normal insulin-stimulated glucose uptake in vivo and in isolated muscle, insulin-stimulated glucose uptake was slightly reduced in isolated glycolytic extensor digitorum longus muscle lacking PAK2 alone (-18%) or in combination with PAK1 KO (-12%) (P < 0.05). In conclusion, glucose tolerance and insulin-stimulated glucose uptake partly rely on PAK2 in glycolytic mouse muscle, whereas PAK1 is dispensable for whole-body glucose homeostasis and insulin-stimulated muscle glucose uptake.
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Affiliation(s)
- Lisbeth L V Møller
- Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, Faculty of Science, University of Copenhagen, Copenhagen, Denmark
| | - Merna Jaurji
- Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, Faculty of Science, University of Copenhagen, Copenhagen, Denmark
| | - Rasmus Kjøbsted
- Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, Faculty of Science, University of Copenhagen, Copenhagen, Denmark
| | - Giselle A Joseph
- Department of Cell, Developmental, and Regenerative Biology, Icahn School of Medicine at Mount Sinai, NY, USA
| | - Agnete B Madsen
- Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, Faculty of Science, University of Copenhagen, Copenhagen, Denmark
| | - Jonas R Knudsen
- Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, Faculty of Science, University of Copenhagen, Copenhagen, Denmark.,Microsystems Laboratory 2, Institute of Microengineering, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
| | - Anne-Marie Lundsgaard
- Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, Faculty of Science, University of Copenhagen, Copenhagen, Denmark
| | - Nicoline R Andersen
- Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, Faculty of Science, University of Copenhagen, Copenhagen, Denmark
| | - Peter Schjerling
- Institute of Sports Medicine, Department of Orthopaedic Surgery M, Bispebjerg Hospital, Copenhagen, Denmark.,Center for Healthy Aging, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Thomas E Jensen
- Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, Faculty of Science, University of Copenhagen, Copenhagen, Denmark
| | - Robert S Krauss
- Department of Cell, Developmental, and Regenerative Biology, Icahn School of Medicine at Mount Sinai, NY, USA
| | - Erik A Richter
- Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, Faculty of Science, University of Copenhagen, Copenhagen, Denmark
| | - Lykke Sylow
- Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, Faculty of Science, University of Copenhagen, Copenhagen, Denmark
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Hosawi SB, Humphries JD, Coward RJ, Knight D, Humphries MJ, Lennon R. Global proteomic analysis of insulin receptor interactors in glomerular podocytes. Wellcome Open Res 2020; 5:202. [PMID: 33458251 PMCID: PMC7788524 DOI: 10.12688/wellcomeopenres.16072.1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/13/2020] [Indexed: 12/16/2022] Open
Abstract
Background: Insulin signalling contributes to diverse cellular activities including protein synthesis, proliferation and cell survival. Insulin resistance describes the inability of cells to activate the insulin signalling pathway effectively; leading to pathological effects in multiple organ systems including the kidney. In diabetic kidney disease, there is progressive glomerular dysfunction and recent studies have demonstrated that the kidney podocyte is a direct target for insulin action. In this study we defined the literature-based insulin receptor (INSR) interactome and utilised an unbiased proteomic approach to examine INSR interactors in podocytes. Methods: Human podocytes expressing the INSR were characterised under basal and insulin resistant conditions. The INSR was isolated by whole cell immunoprecipitation following a time course stimulation of 2, 7, and 15 minutes with of 100nM insulin. The resulting INSR complexes were analysed by label-free mass spectrometry (MS) to detect protein interactors. Results: We identified 27 known, direct INSR interactors in addition to novel interactors including doublecortin domain-containing protein 2 (DCDC2). The interaction of DCDC2 with the INSR was confirmed by immunoprecipitation and immunofluorescence, and under insulin resistant conditions, DCDC2 had increased association with the INSR. siRNA knockdown of DCDC2 in podocytes resulted in cell morphological change and altered INSR localisation. Conclusion: This study provides insight into the complexity of INSR interactors in podocytes and highlights DCDC2 as a novel INSR binding protein. Involvement of this novel interactor in insulin signalling and podocyte biology may explain how insulin resistance alters morphology and integrity of the glomerular filtration barrier.
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Affiliation(s)
- Salman B. Hosawi
- Wellcome Centre for Cell-Matrix Research, University of Manchester, Manchester, M13 9PT, UK
- Department of Biochemistry, King AbdulAziz University, Jeddah, Saudi Arabia
| | - Jonathan D. Humphries
- Wellcome Centre for Cell-Matrix Research, University of Manchester, Manchester, M13 9PT, UK
| | | | - David Knight
- Biomolecular Analysis Core Facility, University of Manchester, Manchester, M13 9PT, UK
| | - Martin J. Humphries
- Wellcome Centre for Cell-Matrix Research, University of Manchester, Manchester, M13 9PT, UK
| | - Rachel Lennon
- Wellcome Centre for Cell-Matrix Research, University of Manchester, Manchester, M13 9PT, UK
- Department of Paediatric Nephrology, Royal Manchester Children’s Hospital, Manchester, UK
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Attenuation of Free Fatty Acid (FFA)-Induced Skeletal Muscle Cell Insulin Resistance by Resveratrol is Linked to Activation of AMPK and Inhibition of mTOR and p70 S6K. Int J Mol Sci 2020; 21:ijms21144900. [PMID: 32664532 PMCID: PMC7404286 DOI: 10.3390/ijms21144900] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2020] [Revised: 07/03/2020] [Accepted: 07/09/2020] [Indexed: 12/13/2022] Open
Abstract
Insulin resistance, a main characteristic of type 2 diabetes mellitus (T2DM), is linked to obesity and excessive levels of plasma free fatty acids (FFA). Studies indicated that significantly elevated levels of FFAs lead to skeletal muscle insulin resistance, by dysregulating the steps in the insulin signaling cascade. The polyphenol resveratrol (RSV) was shown to have antidiabetic properties but the exact mechanism(s) involved are not clearly understood. In the present study, we examined the effect of RSV on FFA-induced insulin resistance in skeletal muscle cells in vitro and investigated the mechanisms involved. Parental and GLUT4myc-overexpressing L6 rat skeletal myotubes were used. [3H]2-deoxyglucose (2DG) uptake was measured, and total and phosphorylated levels of specific proteins were examined by immunoblotting. Exposure of L6 cells to FFA palmitate decreased the insulin-stimulated glucose uptake, indicating insulin resistance. Palmitate increased ser307 (131% ± 1.84% of control, p < 0.001) and ser636/639 (148% ± 10.1% of control, p < 0.01) phosphorylation of IRS-1, and increased the phosphorylation levels of mTOR (174% ± 15.4% of control, p < 0.01) and p70 S6K (162% ± 20.2% of control, p < 0.05). Treatment with RSV completely abolished these palmitate-induced responses. In addition, RSV increased the activation of AMPK and restored the insulin-mediated increase in (a) plasma membrane GLUT4 glucose transporter levels and (b) glucose uptake. These data suggest that RSV has the potential to counteract the FFA-induced muscle insulin resistance.
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Nisr RB, Shah DS, Ganley IG, Hundal HS. Proinflammatory NFkB signalling promotes mitochondrial dysfunction in skeletal muscle in response to cellular fuel overloading. Cell Mol Life Sci 2019; 76:4887-4904. [PMID: 31101940 PMCID: PMC6881256 DOI: 10.1007/s00018-019-03148-8] [Citation(s) in RCA: 79] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2019] [Revised: 05/08/2019] [Accepted: 05/13/2019] [Indexed: 11/29/2022]
Abstract
Sustained nutrient (fuel) excess, as occurs during obesity and diabetes, has been linked to increased inflammation, impaired mitochondrial homeostasis, lipotoxicity, and insulin resistance in skeletal muscle. Precisely how mitochondrial dysfunction is initiated and whether it contributes to insulin resistance in this tissue remains a poorly resolved issue. Herein, we examine the contribution that an increase in proinflammatory NFkB signalling makes towards regulation of mitochondrial bioenergetics, morphology, and dynamics and its impact upon insulin action in skeletal muscle cells subject to chronic fuel (glucose and palmitate) overloading. We show sustained nutrient excess of L6 myotubes promotes activation of the IKKβ-NFkB pathway (as judged by a six-fold increase in IL-6 mRNA expression; an NFkB target gene) and that this was associated with a marked reduction in mitochondrial respiratory capacity (>50%), a three-fold increase in mitochondrial fragmentation and 2.5-fold increase in mitophagy. Under these circumstances, we also noted a reduction in the mRNA and protein abundance of PGC1α and that of key mitochondrial components (SDHA, ANT-1, UCP3, and MFN2) as well as an increase in cellular ROS and impaired insulin action in myotubes. Strikingly, pharmacological or genetic repression of NFkB activity ameliorated disturbances in mitochondrial respiratory function/morphology, attenuated loss of SDHA, ANT-1, UCP3, and MFN2 and mitigated the increase in ROS and the associated reduction in myotube insulin sensitivity. Our findings indicate that sustained oversupply of metabolic fuel to skeletal muscle cells induces heightened NFkB signalling and that this serves as a critical driver for disturbances in mitochondrial function and morphology, redox status, and insulin signalling.
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Affiliation(s)
- Raid B Nisr
- Division of Cell Signalling and Immunology, Sir James Black Centre, School of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
| | - Dinesh S Shah
- Division of Cell Signalling and Immunology, Sir James Black Centre, School of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
| | - Ian G Ganley
- MRC Protein Phosphorylation and Ubiquitylation Unit, Sir James Black Centre, School of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
| | - Harinder S Hundal
- Division of Cell Signalling and Immunology, Sir James Black Centre, School of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK.
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Robinson MM, Sather BK, Burney ER, Ehrlicher SE, Stierwalt HD, Franco MC, Newsom SA. Robust intrinsic differences in mitochondrial respiration and H 2O 2 emission between L6 and C2C12 cells. Am J Physiol Cell Physiol 2019; 317:C339-C347. [PMID: 31091142 DOI: 10.1152/ajpcell.00343.2018] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Rat L6 and mouse C2C12 cell lines are commonly used to investigate myocellular metabolism. Mitochondrial characteristics of these cell lines remain poorly understood despite mitochondria being implicated in the development of various metabolic diseases. To address this need, we performed high-resolution respirometry to determine rates of oxygen consumption and H2O2 emission in suspended myoblasts during multiple substrate-uncoupler-inhibitor titration protocols. The capacity for oxidative phosphorylation supported by glutamate and malate, with and without succinate, or supported by palmitoyl-l-carnitine was lower in L6 compared with C2C12 myoblasts (all P < 0.01 for L6 vs. C2C12). Conversely, H2O2 emission during oxidative phosphorylation was greater in L6 than C2C12 myoblasts (P < 0.01 for L6 vs. C2C12). Induction of noncoupled respiration revealed a significantly greater electron transfer capacity in C2C12 compared with L6 myoblasts, regardless of the substrate(s) provided. Mitochondrial metabolism was also investigated in differentiated L6 and C2C12 myotubes. Basal rates of oxygen consumption were not different between intact, adherent L6, and C2C12 myotubes; however, noncoupled respiration was significantly lower in L6 compared with C2C12 myotubes (P = 0.01). In summary, L6 myoblasts had lower respiration rates than C2C12 myoblasts, including lesser capacity for fatty acid oxidation and greater electron leak toward H2O2. L6 cells also retain a lower capacity for electron transfer compared with C2C12 following differentiation to form fused myotubes. Intrinsic differences in mitochondrial metabolism between these cell lines should be considered when modeling and investigating myocellular metabolism.
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Affiliation(s)
- Matthew M Robinson
- School of Biological and Population Health Sciences, College of Public Health and Human Sciences, Oregon State University, Corvallis, Oregon
| | - Bergen K Sather
- School of Biological and Population Health Sciences, College of Public Health and Human Sciences, Oregon State University, Corvallis, Oregon
| | - Emily R Burney
- School of Biological and Population Health Sciences, College of Public Health and Human Sciences, Oregon State University, Corvallis, Oregon
| | - Sarah E Ehrlicher
- School of Biological and Population Health Sciences, College of Public Health and Human Sciences, Oregon State University, Corvallis, Oregon
| | - Harrison D Stierwalt
- School of Biological and Population Health Sciences, College of Public Health and Human Sciences, Oregon State University, Corvallis, Oregon
| | - Maria Clara Franco
- Department of Biochemistry and Biophysics, College of Science, Oregon State University, Corvallis, Oregon
| | - Sean A Newsom
- School of Biological and Population Health Sciences, College of Public Health and Human Sciences, Oregon State University, Corvallis, Oregon
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Møller LLV, Klip A, Sylow L. Rho GTPases-Emerging Regulators of Glucose Homeostasis and Metabolic Health. Cells 2019; 8:E434. [PMID: 31075957 PMCID: PMC6562660 DOI: 10.3390/cells8050434] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Revised: 05/02/2019] [Accepted: 05/06/2019] [Indexed: 12/11/2022] Open
Abstract
Rho guanosine triphosphatases (GTPases) are key regulators in a number of cellular functions, including actin cytoskeleton remodeling and vesicle traffic. Traditionally, Rho GTPases are studied because of their function in cell migration and cancer, while their roles in metabolism are less documented. However, emerging evidence implicates Rho GTPases as regulators of processes of crucial importance for maintaining metabolic homeostasis. Thus, the time is now ripe for reviewing Rho GTPases in the context of metabolic health. Rho GTPase-mediated key processes include the release of insulin from pancreatic β cells, glucose uptake into skeletal muscle and adipose tissue, and muscle mass regulation. Through the current review, we cast light on the important roles of Rho GTPases in skeletal muscle, adipose tissue, and the pancreas and discuss the proposed mechanisms by which Rho GTPases act to regulate glucose metabolism in health and disease. We also describe challenges and goals for future research.
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Affiliation(s)
- Lisbeth Liliendal Valbjørn Møller
- Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, Faculty of Science, University of Copenhagen, 2100 Copenhagen Oe, Denmark.
| | - Amira Klip
- Cell Biology Program, The Hospital for Sick Children, Toronto, Ontario M5G 0A4, Canada.
| | - Lykke Sylow
- Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, Faculty of Science, University of Copenhagen, 2100 Copenhagen Oe, Denmark.
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