- Retinol dehydrogenases catalyze the rate-limiting step in the biosynthesis of retinoic acid, a bioactive lipid molecule that regulates the expression of hundreds of genes by binding to nuclear transcription factors, the retinoic acid receptors. Several enzymes exhibit retinol dehydrogenase activities in vitro; however, their physiological relevance for retinoic acid biosynthesis in vivo remains unclear. Here, we present evidence that two murine epidermal retinol dehydrogenases, short-chain dehydrogenase/reductase family 16C member 5 (SDR16C5) and SDR16C6, contribute to retinoic acid biosynthesis in living cells and are also essential for the oxidation of retinol to retinaldehyde in vivo.
- Retinol dehydrogenase 11 (RDH11) is a microsomal short-chain dehydrogenase/reductase that recognizes all-trans– and cis–retinoids as substrates and prefers NADPH as a cofactor. Previous work has suggested that RDH11 contributes to the oxidation of 11-cis–retinol to 11-cis–retinaldehyde during the visual cycle in the eye's retinal pigment epithelium. However, the role of RDH11 in metabolism of all-trans–retinoids remains obscure. Here, we report that microsomes isolated from the testes and livers of Rdh11−/− mice fed a regular diet exhibited a 3- and 1.7-fold lower rate of all-trans–retinaldehyde conversion to all-trans–retinol, respectively, than the microsomes of WT littermates.
- All-trans-retinoic acid (RA), a bioactive derivative of vitamin A, exhibits diverse effects on gene transcription and non-genomic regulatory pathways. The steady-state levels of RA are therefore tightly controlled, but the mechanisms responsible for RA homeostasis are not fully understood. We report a molecular mechanism that allows cells to maintain a stable rate of RA biosynthesis by utilizing a biological circuit generated by a bifunctional retinoid oxidoreductive complex (ROC). We show that ROC is composed of at least two subunits of NAD+-dependent retinol dehydrogenase 10 (RDH10), which catalyzes the oxidation of retinol to retinaldehyde, and two subunits of NADPH-dependent dehydrogenase reductase 3 (DHRS3), which catalyzes the reduction of retinaldehyde back to retinol.