The Effect of the Treatment with Various Lipid Species on Mitochondrial and Cellular Functions of Hepatocytes

Abstract

Non-alcoholic fatty liver disease (NAFLD) is a growing epidemic characterized by increased intrahepatic lipid accumulation. In some individuals, NAFLD progresses to non-alcoholic steatohepatitis (NASH), with complications including hepatocellular carcinoma and cirrhosis. As a rise in NAFLD cases has been associated with an increase in the consumption of high levels of fats and carbohydrates, also known as a high-caloric diet, and in obesity, understanding how dietary fatty acids contribute to the development of NAFLD through their effects on mitochondrial biogenesis and fatty acid oxidation may expand an array of potential therapeutics for the treatment of NAFLD. In this study, hepatocytes were treated with two concentrations (800uM and 250uM) of dietary fatty acids (oleic, palmitic, and butyric). These treatments resulted in changes in lipid accumulation, the ratio of mitochondrial to nuclear DNA, and the levels of expression of mRNAs involved in mitochondrial homeostasis and lipid processing. Interestingly, oleic and palmitic acids, although both classified as long-chain fatty acids, did not have the same effect on those cellular characteristics. Specifically, treatment with either 800uM or 250uM of oleic acid resulted in a decrease in CPT-1a expression, suggesting a decrease in mitochondrial fatty acid import. In comparison, treatment with 800uM palmitic acid resulted in a significant increase in CPT-1a expression, suggesting an increase in mitochondrial fatty acid import. Palmitic acid also induced increased expression of ACOX1 and MFn2 suggesting increased peroxisomal beta-oxidation and reorganization of the mitochondrial architecture. Exposure to a short chain fatty acid, butyrate, resulted in lipid accumulation, changes in expression pattern of genes involved in beta-oxidation, and no change in the ratio of mitochondrial to nuclear DNA. Overall, this study profiled the dynamic and complex responses of hepatocytes to exogenous free fatty acids. Differences in expression levels of genes involved in beta-oxidation brings some insight into a dynamic interplay of fatty acids, their breakdown by beta-oxidation, and transcriptional regulation in human hepatocytes in response to fatty acids.