title: Mitochondrial dysfunction in insulin resistance: differential contributions of chronic insulin and saturated fatty acid exposure in muscle cells.
abstract: Mitochondrial dysfunction has been associated with insulin resistance, obesity and diabetes. Hyperinsulinaemia and hyperlipidaemia are hallmarks of the insulin-resistant state. We sought to determine the contributions of high insulin and saturated fatty acid exposure to mitochondrial function and biogenesis in cultured myocytes. Differentiated C2C12 myotubes were left untreated or exposed to chronic high insulin or high palmitate. Mitochondrial function was determined assessing: oxygen consumption, mitochondrial membrane potential, ATP content and ROS (reactive oxygen species) production. We also determined the expression of several mitochondrial genes. Chronic insulin treatment of myotubes caused insulin resistance with reduced PI3K (phosphoinositide 3-kinase) and ERK (extracellular-signal-regulated kinase) signalling. Insulin treatment increased oxygen consumption but reduced mitochondrial membrane potential and ROS production. ATP cellular levels were maintained through an increased glycolytic rate. The expression of mitochondrial OXPHOS (oxidative phosphorylation) subunits or Mfn-2 (mitofusin 2) were not significantly altered in comparison with untreated cells, whereas expression of PGC-1α (peroxisome-proliferator-activated receptor γ co-activator-1α) and UCPs (uncoupling proteins) were reduced. In contrast, saturated fatty acid exposure caused insulin resistance, reducing PI3K (phosphoinositide 3-kinase) and ERK (extracellular-signal-regulated kinase) activation while increasing activation of stress kinases JNK (c-Jun N-terminal kinase) and p38. Fatty acids reduced oxygen consumption and mitochondrial membrane potential while up-regulating the expression of mitochondrial ETC (electron chain complex) protein subunits and UCP proteins. Mfn-2 expression was not modified by palmitate. Palmitate-treated cells also showed a reduced glycolytic rate. Taken together, our findings indicate that chronic insulin and fatty acid-induced insulin resistance differentially affect mitochondrial function. In both conditions, cells were able to maintain ATP levels despite the loss of membrane potential; however, different protein expression suggests different adaptation mechanisms.
authors: Department of Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Liverpool, U.K.
authors: Chenjing
authors: C
authors: Yang
authors: Cho Cho
authors: CC
authors: Aye
authors: Xiaoxin
authors: X
authors: Li
authors: Angels
authors: A
authors: Diaz Ramos
authors: Antonio
authors: A
authors: Zorzano
authors: Silvia
authors: S
authors: Mora
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D005227:Fatty Acids / Q000494:pharmacology*; D020558:GTP Phosphohydrolases / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D007328:Insulin / Q000494:pharmacology*; D007333:Insulin Resistance / Q000502:physiology*; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D051379:Mice; D008928:Mitochondria / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000187:drug effects; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism*; D019308:Palmitic Acid / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D015398:Signal Transduction; D014475:Uncoupling Agents / Q000494:pharmacology; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D005227:Fatty Acids; D007328:Insulin; D024101:Mitochondrial Proteins; D014475:Uncoupling Agents; D019308:Palmitic Acid; D000255:Adenosine Triphosphate; D019869:Phosphatidylinositol 3-Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D020558:GTP Phosphohydrolases; C488751:Mfn2 protein, mouse