Abstract
A growing body of evidence indicates that angiogenesis in folliculogenesis contributes to oocyte developmental competence in natural and in-vitro fertilization (IVF) cycle of animals. Among the known angiogenic factors, vascular endothelial growth factor (VEGF) has an important role involved in angiogenesis. However, its expression level and regulatory mechanism in ovarian follicular fluid (FF) in patients undergoing IVF with controlled ovarian stimulation (COS) remains to be explored. In this study, the primary cultured human ovarian follicular granulosa cells (GCs) were prepared from FF and their identity was characterized by the presence of the GC specific markers. The transforming growth factor β1 (TGFβ1) was found to induce a significant increase in VEGF mRNA level and protein expression/secretion in GCs. In line with these observations, TGFβ1 could be detected in the ovarian FF, ranging from about 400 to 2000 pg/mL among three IVF patient groups with different patient's serum Anti-Müllerian hormone level. The cellular signaling analysis revealed that TGFβ1 induced VEGF production through TGFβ receptor (TGFβR), Smad2/3, PI3 K/AKT, and JNK1/2-related signaling pathways. Finally, in a functional study, the TGFβ1-primed GC VEGF secretion promoted in-vitro angiogenesis in vascular endothelial cells and ex-vivo vessel sprouting in aortic ring. Taken together, we demonstrated here that TGFβ1 expressed in ovarian FF is an inducer for promoting VEGF production in follicular GCs through TGFβR-mediated signaling pathways and the released VEGF subsequently leads to angiogenesis. This possibly contributes to oocyte developmental competence in folliculogenesis of IVF patients with a COS protocol.