ABSTRACT
PURPOSE: To investigate the mechanisms of impairments in oxidative metabolism in obese and diabetic (T2DM) skeletal muscle, this study analysed the adaptive expression of genes involved in fatty acid (FA) oxidation and mitochondrial biogenesis in primary myotubes treated with elevated FAs. METHODS: Muscle samples from obese or obese T2DM donors were stored or processed into human primary skeletal muscle myotubes, which were treated for 6 h with a saturated (palmitic acid) or a monounsaturated (oleic acid) FA with or without a polyunsaturated FA (eicosapentaenoic acid: EPA). Real-time PCR analysis was used to determine mRNA expression. RESULTS: Basal pyruvate dehydrogenase kinase 4 (PDK4) mRNA expression in whole muscle samples from obese and T2DM subjects was increased compared to lean (P < 0.05; n = 13-20/group). In obese- and T2DM-derived myotubes, oleic acid treatment alone and in combination with EPA increased PDK4 mRNA expression compared to control (P < 0.05; n = 7/group), whereas palmitic acid alone and in combination with EPA only increased PDK4 mRNA in T2DM-derived myotubes compared to control (P < 0.05; n = 7/group). EPA alone did not alter mRNA expression of PDK4. CONCLUSIONS: These findings show that FAs induce the expression of PDK4 mRNA, which was increased in myotubes cultured from obese and T2DM donors. This persistent difference in PDK4 expression, present after culturing, suggests a fundamental alteration in the FA-mediated gene expression. This may in turn translate to differences in the regulation of oxidative substrate flux to impact on insulin sensitivity.
Subject(s)
Diabetes Mellitus, Type 2/enzymology , Gene Expression Regulation , Muscle Fibers, Skeletal/enzymology , Obesity/enzymology , Protein Serine-Threonine Kinases/metabolism , Adult , Blood Glucose/metabolism , Body Mass Index , Body Weight , Cells, Cultured , Cholesterol/blood , Eicosapentaenoic Acid/pharmacology , Female , Humans , Insulin/blood , Male , Middle Aged , Muscle Fibers, Skeletal/cytology , Oleic Acid/pharmacology , Palmitic Acid/pharmacology , Protein Serine-Threonine Kinases/genetics , Pyruvate Dehydrogenase Acetyl-Transferring Kinase , RNA, Messenger/genetics , RNA, Messenger/metabolism , Triglycerides/bloodABSTRACT
Gene knockout and agonist studies indicate that activation of the G protein-coupled receptor, GPR119, protects against diet-induced obesity and insulin resistance. It is not known if GPR119 activation in skeletal muscle mediates these effects. To address this uncertainty, we measured GPR119 expression in skeletal muscle and determined the effects of PSN632408, a GPR119 agonist, on the expression of genes and proteins required for fatty acid and glucose oxidation in cultured myotubes. GPR119 expression was readily detected in rat skeletal muscle and mRNAs were induced by 12 weeks of high-fat feeding. Treatment of cultured mouse C2C12 myotubes with 5 µM PSN632408 or 0.5 mM palmitate reduced expression of mRNAs encoding fatty acid oxidation genes to similar extents. More so, treatment with PSN632408 decreased AMPKα (Thr172 phosphorylation) activity in the absence of palmitate and ACC (Ser79 phosphorylation) activity in the presence of palmitate. In human primary myotubes PSN632408 decreased expression of PDK4 and AMPKα2 mRNA in myotubes derived from obese donors. These data suggest GPR119 activation in skeletal muscle may impair fatty acid and glucose oxidation.
