The most important regulator of angiogenesis is vascular endothelial growth factor (VEGF), which acts mostly through two receptors: VEGF receptor 1 (VEGF-R1) and 2 (VEGF-R2). The role of VEGF and its receptors for ovarian folliculogenesis is not known. Preliminary results obtained in a mouse and non-human primate model demonstrate that neutralizing antibodies to VEGF and VEGF-R2 affect follicular angicgenesis and follicle development. The overall objective of this proposal is to expand on these findings and to further define the role of VEGF and its receptors VEGF-R1 and VEGF-R2 in cyclic folliculogenesis using specific blocking antibodies and ad-vectors expressing angiogenic substances. As the role of VEGF-R1 for ovarian function is unknown, in aim 1 we will evaluate the importance of the VEGF-R1 for follicular angiogenesis and follicle development with a blocking antibody using a hypophysectomised (HX) mouse model in which gonadotropin administration reliably induces follicular angiogenesis and maturation. Direct tissue analysis will be performed to study the effect of the antibody on vascular density, endothelial and granulosa cell proliferation, follicular growth stages, and levels of atresia. It is not known whether VEGF has gonadotropin-like action and can stimulate ovarian function. We will test such a possibility in aim 2 by creating supraphysiologic VEGF levels using a replication-defective adenovirus expressing mouse VEGF164 and studying their effect on follicular angiogenesis and follicle development in the absence of gonadotropins. We will also test whether VEGF added to PMSG can enhance the biological effects on the ovary beyond the level seen with PMSG alone.
In aim 3 we will focus on a second model, the rhesus monkey, whose menstrual cycle better reflects that of the human. We will complete our study of the physiologic role of VEGF and its 2 receptors in the follicular phase of the monkey by testing: 1) the effects of anti-VEGF-R1 and anti-VEGF antibody in the early follicular phase when follicle recruitment/selection happens; and 2) the effects of anti-VEGF-R1 and anti-VEGF-R2 in the late follicular phase when the dominant follicle matures into a preovulatory follicle. Understanding the physiological role of VEGF and its receptors for folliculogenesis both in the rodent and rhesus monkey will lay the foundation to better understand pathophysiologic states in the ovary with abnormal angiogenesis. ? ?
