High-Fat Diet Induces Fibrosis in Mice Lacking CYP2A5 and PPARa: A New Model for Steatohepatitis-Associated Fibrosis

Obesity is linked to nonalcoholic steatohepatitis. Peroxisome proliferator-activated receptor-a (PPARa) 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 PPARa is elevated in cyp2a5 -/- mice. To examine why the upregulated PPARa failed to prevent the enhanced steatosis in cyp2a5 -/- mice, we abrogate the upregulated PPARa in cyp2a5 -/- mice by cross-breeding cyp2a5 -/- mice with PPARa knockout (ppara-/- ) mice to create ppara-/- /cyp2a5 -/- mice. The ppara-/- /cyp2a5 -/- mice, ppara-/- mice, and cyp2a5 -/- mice were fed HFD to induce steatosis. After HFD feeding, more severe steatosis was developed in ppara-/- /cyp2a5 -/- mice than in ppara-/- mice and cyp2a5 -/- mice. The ppara-/- /cyp2a5 -/- mice and ppara-/- 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 ppara-/- /cyp2a5 -/- mice but not in ppara-/- mice and cyp2a5 -/- mice. In ppara-/- /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 ppara-/- /cyp2a5 -/- mice is associated with steatosis, and CYP2A5 interacts with PPARa to participate in regulating steatohepatitis-associated fibrosis