Diacylglycerol O-acyltransferase (DGAT) isoforms play a role in peridroplet mitochondrial fatty acid metabolism in bovine liver
ABSTRACT Hepatocellular lipid accumulation characterizes fatty liver in dairy cows. Lipid droplets (LD), specialized organelles that store lipids and maintain cellular lipid homeostasis, are responsible for the ectopic storage of lipids associated with several metabolic disorders. In recent years, non-ruminant studies have reported that LD-mitochondria interactions play an important role in lipid metabolism. Due to the role of diacylglycerol acyltransferase isoforms (DGAT1 and DGAT2) in LD synthesis, we explored mechanisms of mitochondrial fatty acid transport in ketotic cows using liver biopsies and isolated primary hepatocytes. Compared with healthy cows, cows with fatty liver had massive accumulation of LD and high protein expression of the triglyceride (TAG) synthesis-related enzymes DGAT1 and DGAT2, LD synthesis-related proteins perilipin 2 (PLIN2) and perilipin 5 (PLIN5), and the mitochondrial fragmentation-related proteins dynamin-related protein 1 (DRP1) and fission 1 (FIS1). In contrast, factors associated with fatty acid oxidation, mitochondrial fusion and mitochondrial electron transport chain complex were lower compared with those in the healthy cows. In addition, transmission electron microscopy revealed significant contacts between LD-mitochondria in liver tissue from cows with fatty liver. Compared with isolated cytoplasmic mitochondria, expression of carnitine palmitoyl transferase 1A (CPT1A) and DRP1 was lower, but mitofusin 2 (MFN2) and mitochondrial electron transport chain complex was greater in isolated peridroplet mitochondria from hepatic tissue of cows with fatty liver. In vitro data indicated that exogenous free fatty acids (FFA) induced hepatocyte LD synthesis and mitochondrial dynamics consistent with in vivo results. Furthermore, DGAT2 inhibitor treatment attenuated the FFA-induced upregulation of PLIN2 and PLIN5 and rescued the impairment of mitochondrial dynamics. Inhibition of DGAT2 also restored mitochondrial membrane potential and reduced hepatocyte reactive oxygen species production. The present in vivo and in vitro results indicated there are functional differences among different types of mitochondria in the liver tissue of dairy cows with ketosis. Activity of DGAT2 may play a key role in maintaining liver mitochondrial function and lipid homeostasis in dairy cows during the transition period.
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