Expression of Enzymes Synthesizing (Aldehyde Dehydrogenase 1 and Retinaldehyde Dehydrogenase 2) and Metabolizing (Cyp26) Retinoic Acid in the Mouse Female Reproductive System*

Abstract Vitamin A is required for female reproduction. Rodent uterine cells are able to synthesize retinoic acid (RA), the active vitamin A derivative, and express RA receptors. Here, we report that two RA-synthesizing enzymes [aldehyde dehydrogenase 1 (Aldh1) and retinaldehyde dehydrogenase 2 (Raldh2)] and a cytochrome P450 (Cyp26) that metabolizes vitamin A and RA into more polar metabolites exhibit dynamic expression patterns in the mouse uterus, both during the ovarian cycle and during early pregnancy. Aldh1 expression is up-regulated during diestrus and proestrus in the uterine glands, whereas Raldh2 is highly induced in the endometrial stroma in metestrus. Cyp26 expression, which is not detectable during the normal ovarian cycle, is strongly induced in the uterine luminal epithelium, 24 h after human CG hormonal administration. Raldh2 stromal expression also strongly responds to gonadotropin (PMSG and human CG) induction. Furthermore, Raldh2 expression can be hormonally induced in stromal cells of the vagina and cervix. All three enzymes exhibit differential expression profiles during early pregnancy. Aldh1 glandular expression is sharply induced at 2.5 gestational days, whereas Raldh2 stromal expression increases more steadily until the implantation phase. Cyp26 epithelial expression is strongly induced between 3.5–4.5 gestational days, i.e. when the developing blastocysts colonize the uterine lumen. These data suggest a need for precise regulation of RA synthesis and/or metabolism, in both cycling and pregnant uterus.