Epas1 expression is controlled by the progesterone receptor and regulates hCG-induced gene expression in Granulosa Cells during ovulation in mice.

Ovulation is induced via a surge in gonadotrophin hormones, which increases the expression of the essential ovulatory transcription factor progesterone receptor (PGR) and its target genes. The importance of PGR in ovulation is well defined; however, the role of its many downstream genes largely remains unknown. Using mouse models of ovulation, we show that the Epas1 gene, which encodes the hypoxia inducible transcription factor 2α (HIF-2α), is expressed in a PGR-dependent manner during ovulation. Numerous HIF target genes increase in expression upon gonadotrophin stimulation in mouse granulosa cells, with expression of Epas1, but not its related isoform, Hif1a, increasing in a PGR-dependent manner. PGR directly binds introns of the Epas1 locus to enhance chromatin accessibility in ovarian granulosa cells in vivo, yet no evidence of PGR-dependent Epas1 expression was observed in PGR-expressing breast cancer cell lines, suggesting ovary-specific mechanisms of PGR-dependent Epas1 regulation. PGR activation in response to hormonal stimulation induced expression of a HIF reporter system in primary human granulosa cells, with HIF-2 inhibition with the small molecule PT-2385 confirming a HIF-2 contribution to this response. Upon HIF-2 inhibition with PT-2385 in mice, no change in ovulation counts were observed. However, gonadotrophin-induced ovary gene expression was significantly disrupted, supporting a model where HIF-2α contributes to the control of periovulatory gene expression downstream of PGR. In particular, inflammatory gene expression was dysregulated and a cohort of gonadotrophin-dependent genes, including Pgr, were elevated, suggesting impaired downregulation post-ovulation. These findings provide an important insight into regulation of the hypoxia inducible transcription factors during ovulation and how targeting HIF-2α may be of benefit in future fertility treatments.