EPAS1 expression contributes to maintenance of the primordial follicle pool in the mouse ovary.

Oxygen availability can have profound effects on cell fate decisions and survival, in part by regulating expression of hypoxia-inducible factors (HIFs). In the ovary, HIF expression has been characterised in granulosa cells, however, any requirement in oocytes remains relatively undefined. Here we developed a Hif2a/Epas1 germline-specific knockout mouse line in which females were fertile, however produced 40% fewer pups than controls. No defects in follicle development were detected, and quality of MII oocytes was normal, as per assessments of viability, intracellular reactive oxygen species, and spindle parameters. However, a significant diminishment of the primordial follicle pool was evident in cKO females that was attributed to accelerated follicle loss from postnatal day 6 onwards, potentially via disruption of the autophagy pathway. These data demonstrate the importance of HIF signalling in oocytes, particularly at the primordial follicle stage, and lend to the importance of controlling oxygen tension in the development of in vitro growth and maturation approaches for assisted reproduction.

The hypoxia-inducible factor EPAS1 is required for spermatogonial stem cell function in regenerative conditions.

In this study we explored the role of hypoxia and the hypoxia-inducible transcription factor EPAS1 in regulating spermatogonial stem cell (SSC) function in the mouse testis. We have demonstrated that SSCs reside in hypoxic microenvironments in the testis through utilization of the oxygen-sensing probe pimonidazole, and by confirming the stable presence of EPAS1, which is degraded at >5% O2. Through the generation of a germline-specific Epas1 knockout mouse line, and through modulation of EPAS1 levels in primary cultures of spermatogonia with the small drug molecule Daprodustat, we have demonstrated that EPAS1 is required for robust SSC function in regenerative conditions (post-transplantation and post-chemotherapy), via the regulation of key cellular processes such as metabolism. These findings shed light on the relationship between hypoxia and male fertility and will potentially facilitate optimization of in vitro culture conditions for infertility treatment pipelines using SSCs, such as those directed at pediatric cancer survivors.