High-Fat Diet Induces Fibrosis In Mice Lacking Cyp2a5 And Ppar Alpha: A New Model For Steatohepatitis-Associated Fibrosis

Obesity is linked to nonalcoholic steatohepatitis. Peroxisome proliferator-activated receptor -a (PPAR alpha) 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 PPAR alpha failed to prevent the enhanced steatosis in cyp2a5(-/-) mice, we abrogate the upregulated PPAR alpha in cyp2a5(-/-) mice by cross-breeding cyp2a5(-/-) mice with PPAR alpha knockout (ppara-/-) mice to create ppar alpha(-/-)/cyp2a5(-/-)mice. The ppar alpha(-/-)/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 ppar alpha(-/-)/cyp2a5-/- mice and ppara(-/-) mice exhibited comparable and impaired lipid metabolism. Elevated serum alanine transaminase and liver interleukin-1 beta, liver inflammatory cell infiltration, and foci of hepatocellular ballooning were observed in ppara(-/-)/cyp2a5(-/-) mice but not in ppar alpha-/- 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 per oxidation 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.NEW & NOTEWORTHY PPAR alpha is upregulated in cyp2a5(-/-) mice, but HFD-induced steatosis is still deteriorated. PPAR alpha abrogation makes cyp2a5(-/-) mice more sensitive to HFD-induced steatosis, liver inflammation, and fibrosis, suggesting that PPAR alpha upregulation in cyp2a5(-/-) mice is a compensation response. HFD induced liver inflammation, fibrosis, and nitrotyrosine formation in ppara(-/-)/cyp2a5(-/-) mice are all within clusters of lipid droplets, and lipid droplets are all within CYP2E1-positive area.