BMP2 increases the production of BDNF through the upregulation of proBDNF and furin expression in human granulosa-lutein cells.

Abstract

Locally produced in human granulosa cells of the developing follicle, bone morphogenetic protein 2 (BMP2) plays a crucial role in the regulation of ovarian folliculogenesis and luteal formation. Brain-derived neurotrophic factor (BDNF) is an intraovarian neurotrophic factor that has been shown to promote oocyte maturation and subsequent fertilization competency. At present, little is known regarding the intracellular regulation, assembly and secretion of endogenous BDNF in human granulosa cells. The aim of this study was to explore the effect of BMP2 on the expression and production of BDNF in human granulosa cells and the molecular mechanisms underlying this effect. An immortalized human granulosa cell line (SVOG) and primary human granulosa-lutein (hGL) cells were utilized as in vitro study models. Our results showed that BMP2 significantly increased the mRNA and secreted levels of BDNF. Additionally, BMP2 upregulated the expression of furin at the transcriptional and translational levels. Knockdown of endogenous furin partially attenuated the BMP2-induced increase in BDNF production, indicating that furin is involved in the maturation process of BDNF. Using pharmacological (kinase receptor inhibitors) and siRNA-mediated inhibition approaches, we demonstrated that BMP2-induced upregulation of BDNF and furin expression is most likely mediated by the activin receptor-like kinase (ALK)2/ALK3-SMAD4 signaling pathway. Notably, analysis using clinical samples revealed that there was a positive correlation between follicular fluid concentrations of BMP2 and those of BDNF. These results indicate that BMP2 increases the production of mature BDNF by upregulating the precursor BDNF and promoting the proteolytic processing of mature BDNF. Finally, we also investigated the effects of BMP2 on ovarian steroidogenesis and the results showed that BMP2 treatment significantly increased the accumulated level of estradiol (by upregulating the expression of FSH receptor and cytochrome P450 aromatase), whereas it decreased the accumulated level of progesterone (by downregulating the expression of LH receptors and steroidogenic acute regulatory protein) in primary hGL cells. Our findings provide a novel paracrine mechanism underlying the regulation of an intraovarian growth factor in human granulosa cells.