Regulation By FSH Of Retinol Uptake And Metabolism In The Mouse Ovary

Retinol(vitamin A)and its derivatives,collectively known as retinoids,play crucial roles in female reproduction.In follicular cells,retinol can be oxidized to retinoic acid(RA),which can regulate follicular development,ovarian steroidogenesis and oocyte maturation through the transcriptional regulatory activity.Besides,ovarian retinoid levels vary with the estrous cycle,and the concentrations of retinol are higher in the fluids of dominant follicles than that of small follicles.To date,however,the regulatory mechanism of ovarian retinol uptake and metabolism has not yet been fully understood.Retinol-binding protein 4(RBP4),which acts as the mediator for the systemic and intercellular transport of retinol,plays an important role in cellular retinol influx,efflux,and exchange.The levels of RBP4 in the fluids of large follicles were higher than that of medium or small follicles.The present study first investigated the expression pattern of RBP4 during different stages of development and the estrous cycle and the effects of ovary-related reproductive hormones on its expression.The results showed that RBP4 mRNA levels in mouse ovaries remained constant at 1 to 3 weeks postnatal and then notably increased at 4 weeks.In adult mice ovaries,RBP4 expression levels peaked at estrus and were lowest at diestrus.Besides,the strong immunostaining of RBP4 protein was observed in the granulosa cell layers of the large antral follicles.This study then found that the mouse ovarian RBP4 expression was mainly regulated by FSH through the cAMP-PKA signaling pathway and involved transcriptional factors HMGA1,SF-1,and LRH-1.To further investigate the effects of FSH on retinol uptake and metabolism in the mouse ovary,this study examined the levels of retinol and its derivatives through liquid chromatography coupled with mass spectrometry,as well as the expression levels of genes involved in the pathway of retinol uptake and metabolism through real-time PCR.The results showed that FSH increased the levels of total retinoids and RA and decreased retinyl ester levels in the mouse ovaries.The expression of dehydrogenases ADH1 and ALDH1A1 increased in the ovaries of mice treated with FSH,while retinol-esterifying enzyme LRAT expression decreased.In the granulosa cells cultured in vitro,FSH increased the levels of total retinoids,retinal and retinyl esters and enhanced the expression of STRA6,CRBP1,ADH1,ADH7 and ALDH1A1,however,inhibited LRAT expression.In summary,during the follicular development,the expression of RBP4 is primarily regulated by FSH through the cAMP-PKA pathway,involving transcriptional factors HMGA1,SF-1,and LRH-1,which may help the accumulation of retinol in antral follicles;meanwhile,FSH promotes retinol uptake in follicular cells through stimulating STRA6 and CRBP1 expression,and promotes its conversion to RA through stimulating ADH1,ADH7 and ALDH1A1 expression,in the mouse ovary.Thus,FSH can promote retinol uptake and its conversion to RA through affecting the pathways of retinol uptake and metabolism in the ovary.The innovations of this study embody in employing LC-MS technology to examine the levels of retinol and its derivatives in the FSH-stimulated mouse ovaries and investigate the regulatory mechanism of vitamin A level in the ovary.