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

•Dysfunction of steroid hormone synthesis mediated by retinol metabolism was the main cause of low fertility of sows.•Retinoic acid synthesis was dominated by ALDH1A1, and required the assistance of ALDH1A2 in ovarian granulosa cells.•ALDH1A1 enhanced the proliferation of ovarian granulosa cells by activating PI3K-Akt-hedgehog signaling pathways.•ALDH1A1 regulated the expression of transcription factor MESP2, which targeted the transcription of STAR and CYP11A1 through directly binding to their promoter regions.