- Liver is the central metabolic hub that coordinates carbohydrate and lipid metabolism. The bioactive derivative of vitamin A, retinoic acid (RA), was shown to regulate major metabolic genes including phosphoenolpyruvate carboxykinase, fatty acid synthase, carnitine palmitoyltransferase 1, and glucokinase among others. Expression levels of these genes undergo profound changes during adaptation to fasting or in metabolic diseases such as type 1 diabetes (T1D). However, it is unknown whether the levels of hepatic RA change during metabolic remodeling.
- 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.