Retinoic Acid Regulation of Aromatase Expression in the Ovary

Retinoic acid is the active derivative of vitamin-A in the body. Retinoic acid is essential in normal embryonic development, and studies from the Kipp laboratory have also demonstrated its importance in the developing ovary. Aromatase, encoded by the gene Cyp19a1, is an enzyme that converts androgens to estrogens, and is primarily expressed in the granulosa cells of the ovary. Previous studies have suggested that retinoic acid influences aromatase expression in a few different tissue types; however, how retinoic acid may regulate aromatase expression in the ovary is not known. Therefore, the purpose of this study was to examine the role of retinoic acid in regulating aromatase expression in granulosa cells from the mouse ovary. Granulosa cells were isolated and treated with retinoic acid, a retinoic acid metabolism blocking agent R115866, a pan-retinoic acid receptor inhibitor AGN193109, and combinations of these treatments. Cells were treated for 24- and 72- hours, after which mRNA and proteins were collected for RT-PCR and western blot analyses, respectively. The results showed that retinoic acid or R115866 treatment increased Cyp19a1 mRNA levels at 24-hours. The stimulatory effects were specific as they were abolished by AGN193109. AGN193109 continued to suppress Cyp19a1 mRNA levels after 72-hours, but no stimulatory effect by retinoic acid was observed, possibly due to the short half-life of the mRNA. Retinoic acid and R115866 also increased aromatase protein expression at 24- and 72- hours. It was observed that 19-day MT-α transgenic mice had increased levels of Cyp26b1 mRNA, which encodes an enzyme that metabolizes retinoic acid, and decreased levels of Cyp19a1 mRNA, suggesting retinoic acid signaling is important in aromatase expression in vivo. Overall, this study provides strong evidence that further supports an important role of retinoic acid in ovarian development, as it demonstrates that retinoic acid regulates ovarian aromatase expression