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Comment |
Human bone morphogenetic protein 8A promotes expansion and prevents apoptosis of cumulus cells in vitro. Wu FJ et al. (2020) Cumulus expansion is essential for ovulation and oocyte maturation in mammals. Previous studies suggest that this process requires certain cumulus expansion enabling factors, induced by LH surge, that activate SMAD signaling locally. However, their identities remain uncertain. Using a superovulated rat model, we showed that Bmp8 transcripts were abundant in cumulus cell-oocyte complexes (COCs) and their levels can be further induced during ovulation. By analyzing human COC-related transcriptomic datasets, BMP8 transcripts in cumulus cells were also found to be significantly elevated along with the maturation status and developmental competence of enclosed oocytes. In cultured rat COCs, treatment with recombinant BMP8A protein activated both SMAD1/5/8 and SMAD2/3 pathways; the resulting SMAD2/3 signaling induced COC expansion as well as the expression of COC expansion-related genes, whereas the resulting SMAD2/3 and SMAD1/5/8 activations were both required for protecting expanded cumulus cells from apoptosis. Taken together, our data demonstrated that addition of BMP8 protein in the in vitro rat COC cultures not only promotes cumulus expansion but also sustains survival of expanded cumulus cells via different SMAD downstreams. With these capabilities, BMP8 may have clinical applications to ameliorate the fertilizability and subsequent developmental competence of the enclosed oocytes when doing in vitro COC maturation.////////////////// Human BMP8A suppresses luteinization of rat granulosa cells via the SMAD1/5/8 pathway. Wu FJ et al. (2020) Bone morphogenetic proteins (BMPs) are known to play an indispensable role in preventing the precocious luteinization of granulosa cells within growing ovarian follicles. In this study, we found that the transcripts of BMP8 genes are enriched in the ovaries of humans and rodents. When analyzing transcriptomic datasets obtained from human mature granulosa cells, we further found that the BMP8 transcripts not only show the highest abundance among the searchable BMP-related ligands but also decrease significantly in women of advanced age or women with polycystic ovarian syndrome. The correlation between the BMP8 levels in granulosa cells and the decline in ovarian function in these subjects suggests that BMP8 protein may be involved in the regulation of granulosa cell function(s). Using a rat model, we demonstrated that human BMP8A protein activates the SMAD1/5/8 and the SMAD2/3 pathways simultaneously in both immature and mature granulosa cells. Furthermore, the expression of potential type I and type II receptors used by BMP8 in rat granulosa cells was characterized. We found that BMP8A treatment can significantly inhibit gonadotropin-induced progesterone production and steroidogenesis-related gene expression in granulosa cells. Pathway dissection using receptor inhibitors further revealed that such inhibitory effects occur specifically through the BMP8-activated SMAD1/5/8, but not SMAD2/3, pathway. Taken together, considering its abundance and possible functions in granulosa cells, we suggest that BMP8 may act as a novel luteinization inhibitor in growing follicles.//////////////////
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