Retinoids and their target genes in liver functions and diseases.

Retinoids have been reported to prevent several kinds of cancers, including hepatocellular carcinoma (HCC). Retinoic acid (RA) coupled with retinoic acid receptor/retinoid X receptor heterodimer exerts its functions by regulating its target genes. We previously reported that transgenic mice, in which RA signaling is suppressed in a hepatocyte-specific manner, developed liver cancer at a high rate, and that disruption of RA functions led to the increased oxidative stress via aberrant metabolisms of lipid and iron, indicating that retinoids play an important role in liver pathophysiology. These data suggest that exploring the metabolism of retinoids in liver diseases and their target genes provides us with useful information to understand the liver functions and diseases. Consequently, the altered metabolism of retinoids was observed in liver diseases, including non-alcoholic fatty liver disease. In this review, we summarize the metabolism of retinoids in the liver, highlight the functions of retinoids in HCC, non-alcoholic fatty liver disease, and alcoholic liver disease, and discuss the target genes of RA. Investigation of retinoids in the liver will likely help us identify novel therapies and diagnostic modalities for HCC.