Functional and transcriptomic dose-response analysis of follicle-stimulating hormone in ex vivo mouse folliculogenesis and oogenesis
The gonadotropin-dependent phase of ovarian folliculogenesis primarily requires follicle-stimulating hormone (FSH) to support one or multiple early antral follicles, dependent on the species, to mature fully and support steroidogenesis, oogenesis, and ovulation, which critically sustain female reproductive cycles and fertility. At molecular levels, FSH binds to its membrane receptor, FSHR, in granulosa cells to activate a suite of genes and signal transduction pathways. Both insufficient FSH caused by genetic or non-genetic reasons and excessive FSH used for ovarian stimulation in assisted reproductive technology (ART) can cause poor female reproductive outcomes, but the underlying mechanisms remain elusive. Here, we used an ex vivo folliculogenesis and oogenesis system along with single-follicle and -oocyte RNA sequencing analysis and other approaches to investigate the effects of different concentrations of FSH on key follicular events. The results revealed that a minimum FSH threshold is required for follicle maturation, and such threshold is moderately variable among individual follicles. FSH at the subthreshold, threshold, and suprathreshold levels induced distinct expression patterns of follicle maturation-related genes and the entire follicular transcriptomics. The RNA-seq analysis identified several new genes and signaling pathways that may critically regulate follicle maturation. The treatment of excessive FSH resulted in multiple ovarian disorders including premature luteinization, high production of androgen and proinflammatory factors, and reduced expression of energy metabolism-related genes in oocytes.  Together, our study enables a better understanding of the gonadotropin-dependent folliculogenesis, and the novel findings shed crucial insights into how ovarian stimulation with high doses of FSH used in ART impact follicular health, oocyte quality, pregnancy success, and systemic health. Overall design: Follicles in  eIVFG on day 4 and 6 treated with follicle-stimulating hormone (FSH) of 5, 10, 20 and 30 mIU/mL were collected for single-follicle RNA sequencing; At 16-hours post human chorionic gonadotropin (hCG) treatment, oocytes from follicles treated with FSH of 10 and 30 mIU/mL were collected for single-oocyte SMART-seq RNA sequencing.