Ontogeny of rdh9 (Crad3) expression: ablation causes changes in retinoid and steroid metabolizing enzymes, but RXR and androgen signaling seem normal

Crad3 (cis-retinol/androgen dehydrogenase 3), a short-chain dehydrogenase/reductase, converts 9-cis-retinol into 9-cis-retinal and 3alpha-androstanediol into dihydrotestosterone. Crad3 may serve in biosynthesis of 9-cis-retinoic acid, a putative RXR ligand, and/or regeneration of potent androgens. RT-PCR showed that expression of the gene that encodes Crad3, rdh9, begins in liver by e11.5, and in kidney, testis, brain and intestine during e15.5-e16.5. In situ hybridization showed rdh9 expression in embryonic liver, ganglia, small intestine, lung, skin and vertebral cartilage. In adult, in situ hybridization revealed rdh9 expression intensely in hepatocytes, weakly in kidney glomerulus, and intensely in collecting tubules. In intestine, undifferentiated epithelia had greater expression than differentiated epithelia at the distal villus end. Testes expressed rdh9 in spermatogonia, and weakly in Leydig cells. Adult brain expressed rdh9 in the dentate gyrus and CA regions of the hippocampus, the cerebellum Purkinje cells, and the glomerular and mitral cell layers of the olfactory bulb. Rdh9-null mice, backcrossed against C57BL/6J mice, were born in Mendelian frequency, were healthy and fertile, and had normal tissue retinoid and serum dihydrotestosterone levels. Expression of rdh1, a gene that encodes an efficient retinol dehydrogenase, decreased 3- to 8-fold in rdh9-null mice, depending on dietary vitamin A. Microarray analysis and quantitative PCR revealed 2- to 4-fold increases in mRNA of enzymes that catalyze xenobiotic and steroid metabolism, including Cyp2, Cyp3, 11beta-hydroxysteroid dehydrogenase type 2, and 17beta-hydroxsteroid dehydrogenases types 4 and 5. These data indicate widespread Crad3 function(s) in steroid and/or retinoid metabolism starting mid embryogenesis.     

Ontogeny of rdh9 (Crad3) expression: Ablation causes changes in retinoid and steroid metabolizing enzymes,but RXR and androgen signaling seem normal

Crad3 (cis-retinol/androgen dehydrogenase 3), a short-chain dehydrogenase/reductase, converts 9-cis-retinol into 9-cis-retinal and 3α-androstanediol into dihydrotestosterone. Crad3 may serve in biosynthesis of 9-cis-retinoic acid, a putative RXR ligand, and/or regeneration of potent androgens. RT-PCR showed that expression of the gene that encodes Crad3, rdh9, begins in liver by e11.5, and in kidney, testis, brain and intestine during e15.5–e16.5. In situ hybridization showed rdh9 expression in embryonic liver, ganglia, small intestine, lung, skin and vertebral cartilage. In adult, in situ hybridization revealed rdh9 expression intensely in hepatocytes, weakly in kidney glomerulus, and intensely in collecting tubules. In intestine, undifferentiated epithelia had greater expression than differentiated epithelia at the distal villus end. Testes expressed rdh9 in spermatogonia, and weakly in Leydig cells. Adult brain expressed rdh9 in the dentate gyrus and CA regions of the hippocampus, the cerebellum Purkinje cells, and the glomerular and mitral cell layers of the olfactory bulb. Rdh9-null mice, backcrossed against C57BL/6J mice, were born in Mendelian frequency, were healthy and fertile, and had normal tissue retinoid and serum dihydrotestosterone levels. Expression of rdh1, a gene that encodes an efficient retinol dehydrogenase, decreased 3- to 8-fold in rdh9-null mice, depending on dietary vitamin A. Microarray analysis and quantitative PCR revealed 2- to 4-fold increases in mRNA of enzymes that catalyze xenobiotic and steroid metabolism, including Cyp2, Cyp3, 11β-hydroxysteroid dehydrogenase type 2, and 17β-hydroxsteroid dehydrogenases types 4 and 5. These data indicate widespread Crad3 function(s) in steroid and/or retinoid metabolism starting mid embryogenesis.     

SDR-O: an orphan short-chain dehydrogenase/reductase localized at mouse chromosome 10/human chromosome 12

We report cloning a cDNA that encodes a novel short-chain dehydrogenase/reductase, SDR-O, conserved in mouse, human and rat. Human and mouse liver express SDR-O (short-chain dehydrogenase/reductase-orphan) mRNA intensely. The mouse embryo expresses SDR-O mRNA as early as day seven. Human SDR-O localizes on chromosome 12; mouse SDR-O localizes on chromosome 10 with CRAD1, CRAD2 and RDH4. SDR-O shares highest amino acid similarity with rat RoDH1 and mouse RDH1 (69-70%), but does not have the retinol and 3alpha-hydroxysteroid dehydrogenase activity of either, nor is it active as a 17beta- or 11beta-hydroxysteroid dehydrogenase. Short-chain dehydrogenase/reductases catalyse the metabolism of ligands that bind with nuclear receptors: the occurrence of 'orphan' nuclear receptors may imply existence of 'orphan' SDR, suggesting that SDR-O may catalyse the metabolism of another class of nuclear receptor ligand. Alternatively, SDR-O may not have a catalytic function, but may regulate metabolism by binding substrates/products and/or by serving as a regulatory factor.     

cis-Retinol/androgen dehydrogenase, isozyme 3 (CRAD3): a short-chain dehydrogenase active in a reconstituted path of 9-cis-retinoic acid biosynthesis in intact cells

9-cis-Retinoic acid activates retinoid X receptors, which serve as heterodimeric partners with other nuclear hormone receptors, yet the enzymology of its physiological generation remains unclear. Here, we report the identification and molecular/enzymatic characterization of a previously unknown member of the short-chain dehydrogenase/reductase family, CRAD3 (cis-retinoid/androgen dehydrogenase, type 3), which catalyzes the first step in 9-cis-retinoic acid biosynthesis, the conversion of 9-cis-retinol into 9-cis-retinal. CRAD3 shares amino acid similarity with other retinoid/steroid short-chain dehydrogenases/reductases: CRAD1, CRAD2, and RDH4. Relative to CRAD1, CRAD3 has greater 9-cis-retinol/all-trans-retinol discrimination and lower efficiency as an androgen dehydrogenase. CRAD3 has apparent efficiency (V/K(m)) for 9-cis-retinol about equivalent to that for CRAD1 and 3 orders of magnitude greater than that for RDH4. (CRAD2 does not recognize 9-cis-retinol as a substrate). CRAD3 contributes to 9-cis-retinoic acid production in intact cells, in conjunction with each of three retinal dehydrogenases that recognize 9-cis-retinal (RALDH1/AHD2, RALDH2, and ALDH12). Liver and kidney, two tissues reportedly with the highest concentrations of 9-cis-retinoids, show the most intense mRNA expression of CRAD3, but expression also occurs in testis, lung, small intestine, heart, and brain. These data are consistent with the participation of CRAD3 in the biogeneration of 9-cis-retinoic acid.