High-fat diet induces fibrosis in mice lacking CYP2A5 and PPARα: a new model for steatohepatitis-associated fibrosis.

Obesity is linked to nonalcoholic steatohepatitis. Peroxisome proliferator-activated receptor-α (PPARα) regulates lipid metabolism. Cytochrome P-450 2A5 (CYP2A5) is a potential antioxidant and CYP2A5 induction by ethanol is CYP2E1 dependent. High-fat diet (HFD)-induced obesity and steatosis are more severe in CYP2A5 knockout (cyp2a5(-/-)) mice than in wild-type mice although PPARα is elevated in cyp2a5(-/-) mice. To examine why the upregulated PPARα failed to prevent the enhanced steatosis in cyp2a5(-/-) mice, we abrogate the upregulated PPARα in cyp2a5(-/-) mice by cross-breeding cyp2a5(-/-) mice with PPARα knockout (pparα(-/-)) mice to create pparα(-/-)/cyp2a5(-/-) mice. The pparα(-/-)/cyp2a5(-/-) mice, pparα(-/-) mice, and cyp2a5(-/-) mice were fed HFD to induce steatosis. After HFD feeding, more severe steatosis was developed in pparα(-/-)/cyp2a5(-/-) mice than in pparα(-/-) mice and cyp2a5(-/-) mice. The pparα(-/-)/cyp2a5(-/-) mice and pparα(-/-) mice exhibited comparable and impaired lipid metabolism. Elevated serum alanine transaminase and liver interleukin-1β, liver inflammatory cell infiltration, and foci of hepatocellular ballooning were observed in pparα(-/-)/cyp2a5(-/-) mice but not in pparα(-/-) mice and cyp2a5(-/-) mice. In pparα(-/-)/cyp2a5(-/-) mice, although redox-sensitive transcription factor nuclear factor erythroid 2-related factor 2 and its target antioxidant genes were upregulated as a compensation, thioredoxin was suppressed, and phosphorylation of JNK and formation of nitrotyrosine adduct were increased. Liver glutathione was decreased, and lipid peroxidation was increased. Interestingly, inflammation and fibrosis were all observed within the clusters of lipid droplets, and these lipid droplet clusters were all located inside the area with CYP2E1-positive staining. These results suggest that HFD-induced fibrosis in pparα(-/-)/cyp2a5(-/-) mice is associated with steatosis, and CYP2A5 interacts with PPARα to participate in regulating steatohepatitis-associated fibrosis.