Estradiol Regulates Mrna Levels Of Estrogen Receptor Beta 4 And Beta 5 Isoforms And Modulates Human Granulosa Cell Apoptosis

Estrogen receptor beta (ER beta) plays a critical role in granulosa cell (GC) functions. The existence of four human ER beta splice isoforms in the ovary suggests their differential implication in 17 beta-estradiol (E2) actions on GC apoptosis causing follicular atresia. In this study, we investigated whether E2 can regulate ER beta isoforms expression to fine tune its apoptotic activities in human GC. For this purpose, we measured by RT-qPCR the expression of ER beta isoforms in primary culture of human granulosa cells (hGCs) collected from patients undergoing in vitro fertilization, before and after E2 exposure. Besides, we assessed the potential role of ER beta isoforms on cell growth and apoptosis after their overexpression in a human GC line (HGrC1 cells). We confirmed that ER beta 1, ER beta 2, ER beta 4, and ER beta 5 isoform mRNAs were predominant over that of ER alpha in hGCs, and found that E2 selectively regulates mRNA levels of ER beta 4 and ER beta 5 isoforms in these cells. In addition, we demonstrated that overexpression of ER beta 1 and ER beta 4 in HGrC1 cells increased cell apoptosis by 225% while ER beta 5 or ER beta 2 had no effect. Altogether, our study revealed that E2 may influence GC fate by specifically regulating the relative abundance of ER beta isoforms mRNA to modulate the balance between pro-apoptotic and non-apoptotic ER beta isoforms.