Vitamin A nutritional status and retinoic acid as regulators of gene expression in rat liver

Vitamin A (retinol) is an essential precursor for the production of retinoic acid (RA), which in turn is a major regulator of gene expression, affecting cell differentiation throughout the body. Understanding how vitamin A nutritional status, as well as therapeutic retinoid treatment, regulates the expression of retinoid homeostatic genes is important for improving dietary recommendations and therapeutic strategies using retinoids. This study investigated genes central to processes of retinoid uptake and storage, release to plasma, and oxidation in the liver of rats under steady-state conditions after different exposures to dietary vitamin A (deficient, marginal, adequate and supplemented), and acutely after administration of a therapeutic dose of all-trans-RA. Over a very wide range of dietary vitamin A, lecithin:retinol acyltransferase (LRAT) as well as multiple cytochrome P450s (CYP26A1, CYP26B1, and CYP2C22) differed by diet and were highly correlated with one another and with vitamin A status assessed by liver retinol concentration (all correlations, P<0.05). After acute treatment with RA, the same genes were rapidly and concomitantly induced, preceding RAR, a classical direct target of RA. CYP26A1 mRNA exhibited the greatest dynamic range (change of log26 in 3 h). Moreover, CYP26A1 increased more rapidly in the liver of RA-primed rats than nave rats. By in situ hybridization, CYP26A1 mRNA was strongly regulated within hepatocytes, closely resembling RBP4 in location. Overall, whether RA is produced endogenously from retinol or administered exogenously, changes in retinoid homeostatic gene expression simultaneously favor both retinol esterification and RA oxidation, with CYP26A1 exhibiting the greatest dynamic change.

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Ross AC, Cifelli CJ, Zolfaghari R, Li NQ