Loss of function of retinoic acid in liver leads to steatohepatitis and liver tumor: A NASH animal model

To explore the role of retinoic acid (RA) in liver, we developed transgenic mice expressing retinoic acid receptor α dominant negative form (RARE) in hepatocytes using by albumin promoter and enhancer. At 4 months of age, the RARE transgenic mice developed microvesicular steatosis and spotty focal necrosis. Mitochondrial β-oxidation activity of fatty acids and expression of its related enzymes including VLCAD, LCAD and HCD were down-regulated. On the other hand, peroxisomal β-oxidation and its related enzymes including AOX and BFE were up-regulated. Expression of CYP4a10, CYP4a12 and CYP4a14 was increased, suggesting that ω-oxidation of fatty acids in microsome was accelerated. In addition, formation of H2O2 and 8-hydroxy-2′-deoxyguanosine was increased. After 12 months of age, these mice developed liver tumors which are hepatocellular carcinoma or adenoma. The incidence of tumor formation was increased with age. Expression of β-catenin and cyclin D1 was enhanced, and TCF-4/β-catenin complex was increased whereas RARα/β-catenin complex was decreased. Feeding on high RA diet reversed histological and biochemical abnormalities, and inhibited occurrence of liver tumor. Taken together, hepatic loss of RA function leads to development of steatohepatitis and liver tumor and RA plays an important role in preventing hepatocarcinogenesis in association with fatty acid metabolism and Wnt signaling.