ACTIVATION OF THE PPAR NUCLEAR RECEPTORS BY OXYLIPINS AND THEIR POTENTIAL EFFECTS ON DIFFERENTIATION AND GENE EXPRESSION IN MYOCYTES

Obesity and non-alcoholic fatty liver diseases are a growing issue worldwide. Decreased expression of CYP2B6 is associated with obesity in humans and Cyp2b-null mice are diet-induced obese; however fatty liver disease is worse in humanized CYP2B6 transgenic mice than WT or Cyp2b-null mice despite lower obesity. CYP2B6 produces several oxylipins with preference for metabolism at the 9- and 13-positions with 9-HODE and 13-HODE (from linoleic acid; n-6), and 9-HOTrE and 13-HOTrE (from a-linolenic acid; n-3) preferentially produced. Oxylipins serve as signaling molecules for many processes, such as inflammatory pathways, lipid distribution, and lipid metabolism. Due to their diversity, oxylipins can act as ligands for a variety of receptors, including the peroxisome proliferator-activated receptors (PPARa/d/g) that play a role in regulation of lipid metabolism, inflammation, and dyslipidemia. Transactivation assays for each PPAR revealed the oxylipins 9-HODE and 9-HOTrE are agonists of PPARa, 13-HOTrE is an antagonist of PPARd, and 13-oxoODE is an agonist of PPARg. All PPARs play a role in lipid metabolism, but their expression in tissues varies. Less research has focused on PPARd, especially as it relates to obesity. PPARd is primarily expressed in skeletal muscle tissue; therefore, negatively perturbing PPARd activity in skeletal muscle may reduce fat use in muscle and increase accumulation in other tissues by increasing availability, which can impact obesity and fatty liver. To determine the effects of 13-HOTrE on skeletal muscle, C2C12 myocytes were exposed to 0.6 to 6 mM 13-HOTrE during differentiation and RNA was extracted to evaluate gene expression by qPCR. Significant changes in several genes related to metabolism, including the sterol regulatory-element binding proteins (SREBPs) that are required for cholesterol and fatty acid biosynthesis were observed. In addition, C2C12 myocytes were exposed to 0.6 to 6 mM 13-HOTrE and a Mito-Stress test was performed (SeaHorse, Agilent). 13-HOTrE increased ATP-coupled mitochondrial metabolism in a concentration-dependent manner. These results suggests that 13-HOTrE plays a role in inducing pathways related to fatty acid metabolism and mitochondrial respiration