Inhibition of vascular endothelial growth factor in the primate ovary up-regulates hypoxia-inducible factor-1α in the follicle and corpus luteum

Vascular endothelial growth factor (VEGF)-dependent angiogenesis is crucial for follicular growth, and corpus luteum formation and function, in the primate ovary. In the ovary VEGF can be hormonally regulated, but in other systems, the main regulator of VEGF expression is hypoxia. We hypothesized that hypoxia was involved in the regulation of angiogenesis in the cycling ovary. We therefore used immunohistochemistry to localize hypoxia-inducible factor (HIF)-1 alpha in the marmoset ovary across the ovarian cycle. We also investigated the effect of VEGF inhibition, using VEGF Trap (aflibercept), on HIF-1 alpha localization during the follicular and luteal phases of the cycle. Finally, we studied the effect of chorionic gonadotropin stimulation of the corpus luteum during early pregnancy. Nuclear HIF-1 alpha staining was largely absent from normally growing preantral and antral follicles. However, there was marked up-regulation of nuclear HIF-1 alpha in the granulosa cells at ovulation that persisted into the early corpus luteum. Mature corpora lutea and those collected during early pregnancy had minimal nuclear HIF-1 alpha staining. The inhibition of VEGF in the mid-luteal stage resulted in a time-dependent up-regulation of luteal nuclear HIF-1 alpha staining (P < 0.05). There was never any nuclear HIF-1 alpha in the theca cells of the follicle, but VEGF Trap treatment during the follicular (P < 0.001) or luteal (P < 0.001) phase increased the proportion of antral follicles with nuclear HIF-1 alpha staining in the granulosa cells. These results indicate that HIF-1 alpha is up-regulated after vascular inhibition, using VEGF Trap, in the follicle and corpus luteum. However, it is also acutely up-regulated during ovulation. This suggests a role for HIF-1 alpha in both hypoxic and hormonal regulation of ovarian VEGF expression in vivo.