Retinoic acid enhances ovarian steroidogenesis by regulating granulosa cell proliferation and MESP2/STAR/CYP11A1 pathway

Abstract

IntroductionOvarian steroidogenesis not only affects the embryonic development and pregnancy outcome, but also associates with many diseases in mammals and women. Exploring the nutrients and mechanisms influencing ovarian steroidogenesis is critical to maintaining the optimal reproductive performance, as well as guaranteeing body health. ObjectivesThis research aimed to explore the effect of retinol metabolism on ovarian steroidogenesis and the underlying mechanisms. MethodsComparative transcriptomic analysis of ovaries from normal and low reproductive performance sows were performed to identify the main causes leading to low fertility. The metabolites regulating steroid hormones synthesis were investigated in ovarian granulosa cells. Gene interference, overexpression, dual-luciferase reporter assays, chromatin immunoprecipitation and transcriptome analysis were further conducted to explore the underlying mechanisms of Aldh1a1 mediating ovarian steroidogenesis. ResultsTranscriptome analysis of ovaries from normal and low reproductive performance sows showed the significant differences in both retinol metabolism and steroid hormones synthesis, indicating retinol metabolism probably influenced steroid hormones synthesis. The related metabolite retinoic acid was furtherly proven a highly active and potent substance strengthening estrogen and progesterone synthesis in ovarian granulosa cells. For the first time, we revealed that retinoic acid synthesis in porcine and human ovarian granulosa cells was dominated by Aldh1a1, and required the assistance of Aldh1a2. Importantly, we demonstrated that Aldh1a1 enhanced the proliferation of ovarian granulosa cells by activating PI3K-Akt-hedgehog signaling pathways. In addition, Aldh1a1 regulated the expression of transcription factor MESP2, which targeted the transcription of Star and Cyp11a1 through binding to corresponding promoter regions. ConclusionOur data identified Aldh1a1 modulates ovarian steroidogenesis through enhancing granulosa cell proliferation and MESP2/STAR/CYP11A1 pathway. These findings provide valuable clues for improving ovarian health in mammals.