Oocyte-Secreted Factors Strongly Stimulate sFRP4 Expression in Human Cumulus Cells
Abstract Secreted frizzled-related protein-4 (SFRP4) belongs to a family of soluble ovarian-expressed proteins that participate in female reproduction, particularly in rodents. In humans, SFRP4 is highly expressed in cumulus cells. However, the mechanisms that stimulate SFRP4 in cumulus cells have not been examined. We hypothesise that oocyte-secreted factors such as growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) are involved in the regulation of SFRP4. Human cumulus cells were collected from patients undergoing fertility treatments and treated with GDF9 or BMP15 or their combination in the presence of follicle-stimulating hormone (FSH) or vehicle. FSH treatment significantly decreased SFRP4 mRNA levels when compared with nontreated cells. However, SFRP4 mRNA levels were increased significantly by GDF9 plus BMP15 in a concentration-dependent manner in the presence or absence of FSH. The combination of GDF9 plus BMP15 also increased SFRP4 protein levels and decreased the activity of the β-catenin/TCF-responsive promoter significantly. GDF9 plus BMP15 inhibited steroidogenic acute regulatory protein and luteinising hormone/choriogonadotrophin (LH/hCG) receptor stimulation by FSH, while treatment with SFRP4 blocked the stimulatory effect of FSH on these genes. The evidence demonstrates that GDF9 and BMP15 act in coordination to stimulate SFRP4 expression and suggests that SFRP4 mediates the anti-luteinising effects of the oocyte in human cumulus cells.