Regulation of hepatic mitochondrial metabolism in response to a high fat diet: a longitudinal study in rats

Mitochondrial dysfunctions have been detected in non-alcoholic steatohepatitis, but less information exists regarding adaptation of mitochondrial function during the initiation of hepatic steatosis. This study aimed to determine in rat liver the sequence of mitochondrial and metabolic adaptations occurring during the first 8 weeks of a moderate high fat diet (HFD). Sprague-Dawley rats were fed a HFD during 2, 4, and 8 weeks. Mitochondrial oxygen consumption, respiratory chain complexes activity, and oxidative phosphorylation efficiency were assessed in isolated liver mitochondria. Gene expression related to fat metabolism and mitochondrial biogenesis were determined. Results were compared to data collected in a group of rats sacrificed before starting the HFD feeding. After 2 and 4 weeks of HFD, there was a development of fatty liver and a concomitant increase the expression of mitochondrial glycerol-3-phosphate acyltransferase (mtGPAT) and peroxisome proliferator-activated receptor gamma. Higher serum beta-hydroxybutyrate levels and enhanced hepatic pyruvate dehydrogenase kinase 4 expression suggested increased fatty acid oxidation. However, mitochondrial respiration and respiratory chain activity were normal. After 8 weeks of HFD, lower accumulation of liver triglycerides was associated with reduced expression of mtGPAT. At this time, oxygen consumption with palmitoyl-l-carnitine was decreased whereas oxidative phosphorylation efficiency (ATP/O) with succinate was enhanced. Hepatic levels of mtDNA were unchanged whatever the time points. This longitudinal study in rats fed a HFD showed that hepatic lipid homeostasis and mitochondrial function can adapt to face the increase in fatty acid availability.