The FSH–HIF-1α–VEGF Pathway Is Critical for Ovulation and Oocyte Health but Not Necessary for Follicular Growth in Mice

Abstract

Follicle-stimulating hormone (FSH)-induced growth of ovarian follicles is independent of follicular vascularization. Recent evidence has indicated that follicular vascularization is critical to ovarian follicle development and survival. FSH, a gonadotropin that induces follicular growth and development, also acts as the major survival factor for antral follicles. FSH has been reported to stimulate angiogenesis in the theca layers mediated in part by the vascular endothelial growth factor A (VEGFA) and the transcription factor hypoxia inducible factor 1α (HIF-1α). However, it remains largely undetermined whether FSH-dependent growth and survival of antral follicles relies on FSH-induced vascularization. Here, we first demonstrated that induction of angiogenesis through the FSH–HIF–1α-VEGFA axis is not required for FSH-stimulated follicular growth in mouse ovary. FSH increased the total number of blood vessels in mouse ovarian follicles, which was correlated with elevated expression of VEGFA and HIF-1α in granulosa cells. In contrast, blocking of follicular angiogenesis using inhibitors against the HIF-1α-VEGFA pathway repressed vasculature formation in follicles despite FSH administration. Interestingly, by measuring follicular size and ovarian weight, we found that the suppression of angiogenesis via HIF-1α–VEGFA pathway did not influence FSH-mediated follicular growth. However, inhibition of FSH-induced follicular vascularization by PX-478, a small-molecule inhibitor that suppresses HIF-1α activity, blocked ovulation and triggered atresia in large follicles. On the other hand, PX-478 injection reduced oocyte quality via impairing the meiotic apparatus, showing a prominently defective spindle assembly and actin dynamics. Collectively, our findings unveiled a vascularization-independent effect of FSH on follicular growth, whereas follicular survival, ovulation, and oocyte development relies on FSH-mediated angiogenesis in the follicles.

Hypoxia‐inducible factor‐1alpha and nitric oxide synthases in bovine follicles close to ovulation and early luteal angiogenesis

“…A steady increase of HIF1A immunostaining in the GC was observed towards the lumen of the follicle (Berisha et al, 2017). The interaction signalling pathways regulating the most important angiogenic factor VEGFA via HIF1A is suggested to be the key mechanisms during ovulation and CL formation (Li et al, 2020;Zhang, Yin, & Wang, 2011). The critical role of HIF1A…”

“…and NOS isoforms seem to be highly important regulatory mediators for the regulation of final follicle development, ovulation and CL formation (Anteby et al, 1996;Berisha et al, 2017;Faes et al, 2009;Guo et al, 2019;Jablonka-Shariff & Olson, 1997;Li et al, 2020).…”

“…It is well known that the leading regulators of angiogenesis in ovarian follicles and CL include molecules like VEGF, ANPT, FGF and IGF family members (Berisha & Schams, 2005; Berisha, Schams, Rodler, & Pfaffl, 2016; Ribatti, Vacca, & Presta, 2000; Woad & Robinson, 2016). Some recent studies, however, suggested that the pro‐angiogenic molecules HIF1A and NOS isoforms seem to be highly important regulatory mediators for the regulation of final follicle development, ovulation and CL formation (Anteby et al., 1996; Berisha et al., 2017; Faes et al., 2009; Guo et al., 2019; Jablonka‐Shariff & Olson, 1997; Li et al., 2020).…”

“…In the context of the locally produced pro‐angiogenic molecules, HIF1A seems to be a highly crucial regulatory mediator for the follicle growth, development and ovulation in mice (Li et al., 2020). The present study demonstrates a specific pattern of HIF1A expression, which depends on the developmental stage of the follicles before and after the LH surge and after ovulation (early CL).…”

“…A steady increase of HIF1A immunostaining in the GC was observed towards the lumen of the follicle (Berisha et al., 2017). The interaction signalling pathways regulating the most important angiogenic factor VEGFA via HIF1A is suggested to be the key mechanisms during ovulation and CL formation (Li et al., 2020; Zhang, Yin, & Wang, 2011). The critical role of HIF1A for angiogenesis has been reported in different mammalian species and cattle (Boonyaprakob, Gadsby, Hedgpeth, Routh, & Almond, 2005; Duncan et al., 2008; Meidan et al., 2013; Nishimura & Okuda, 2010).…”