1. Mitochondrial dysfunction in insulin resistance: differential contributions of chronic insulin and saturated fatty acid exposure in muscle cells
- Author
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A. Ramos, Antonio Zorzano, Silvia Mora, Xiaoxin Li, Cho Cho Aye, and Chenjing Yang
- Subjects
medicine.medical_treatment ,Muscle Fibers, Skeletal ,peroxisome-proliferator-activated receptor γ co-activator-1α ,OXPHOS, oxidative phosphorylation ,Palmitic Acid ,lcsh:Life ,lcsh:QR1-502 ,ANT, ATP/ADP translocator ,Mitochondrion ,Biochemistry ,p38 Mitogen-Activated Protein Kinases ,lcsh:Microbiology ,GTP Phosphohydrolases ,Mice ,Phosphatidylinositol 3-Kinases ,0302 clinical medicine ,Adenosine Triphosphate ,FOXO, forkhead box O ,insulin resistance ,DCF-DA, 2′,7′-dichlorofluorescein diacetate ,mitochondrion ,Glycolysis ,OCR, oxygen consumption rate ,Cells, Cultured ,myocyte ,Membrane Potential, Mitochondrial ,0303 health sciences ,DMEM, Dulbecco's modified Eagle's medium ,Kinase ,Fatty Acids ,Prdx III, peroxiredoxin ,Mitochondria ,FCCP, carbonyl cyanide p-trifluoromethoxyphenylhydrazone ,ERRα, oestrogen-related receptor α ,Saturated fatty acid ,JNK, c-Jun N-terminal kinase ,GptxI, glutathione peroxidase ,NRF1, nuclear respiratory factor-1 ,PPAR, peroxisome-proliferator-activated receptor ,UCP, uncoupling protein ,PI3K, phosphoinositide 3-kinase ,Signal Transduction ,medicine.medical_specialty ,insulin ,Biophysics ,Tfam, mitochondrial transcripton factor A ,Oxidative phosphorylation ,Biology ,ERK, extracellular-signal-regulated kinase ,TCA, trichloroacetic acid ,S4 ,Mitochondrial Proteins ,03 medical and health sciences ,Insulin resistance ,ROS, reactive oxygen species ,Internal medicine ,SOD, superoxide dismutase ,medicine ,Animals ,CR, calorie restriction ,Muscle, Skeletal ,Molecular Biology ,030304 developmental biology ,Original Paper ,ECAR, extracellular acidification rate ,Uncoupling Agents ,Insulin ,JNK Mitogen-Activated Protein Kinases ,Cell Biology ,medicine.disease ,ETC, electron chain complex ,mtDNA, mitochondrial DNA ,Insulin receptor ,PGC-1, PPARγ co-activator-1 ,lcsh:QH501-531 ,Endocrinology ,Gene Expression Regulation ,biology.protein ,fatty acid ,membrane potential ,030217 neurology & neurosurgery ,MAPK, mitogen-activated protein kinase ,Mfn-2, mitofusin 2 ,Cox2 etc., cytochrome c oxidase subunit 2 etc - 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.
- Published
- 2012