MiR-4261 Regulates Granulosa Cell Proliferation Mediated by Progesterone via FZD5 in Human Ovarian Granulosa Cell Line

Background: The effect of different controlled ovarian hyperstimulation (COH) protocols on the microenvironment of follicular growth may be reflected by microRNA (miRNA) expression profiles. Downregulation of miR-4261 when progesterone is added in the follicular phase has been reported in our previous research. The purpose of this study is to observe how miR-4261 regulates the function of granulosa cells, so as to find the specific pathway and mechanism of progesterone acting on the follicular microenvironment. Results: The human ovarian granulosa cell line (KGN cells) is used to conduct cell experiments as granulosa cells. Compared with microRNA-negative control (miR-NC), KGN cells transfected with the miR-4261 mimic showed progressively reduced proliferation at 24, 48, and 72 h (p < 0.01). The levels of Frizzled 5 (FZD5) mRNA and protein were also significantly reduced (p < 0.01). In the dual-luciferase reporter gene experiment, the fluorescence value of KGN cells co-transfected with wild type-FZD5 (wt-FZD5) and the miR-4261 mimic/inhibitor decreased/increased (p < 0.01), and there was no significant difference in fluorescence value between mutant-FZD5 (mut-FZD5) and the miR-4261 mimic/inhibitor co-transfected KGN cells (p > 0.05). The proliferation activity of KGN cells transfected with small interfering FZD5 (siFZD5) decreased significantly at 48 h (p < 0.01) compared with the control. Compared with KGN cells co-transfected with siFZD5 and miR-NC, there was no significant difference in the proliferation activity of KGN cells co-transfected with siFZD5 and miR-4261 inhibitor (p > 0.05). Conclusions: The down-regulation of miR-4261 can promote the proliferation of granulosa cells. The knockdown of FZD5 can inhibit the proliferation of granulosa cells. FZD5 is the direct downstream target gene of miR-4261 in KGN cells. miR-4261 can regulate granulosa cell proliferation by targeting FZD5.