Integrated stress response control of granulosa cell translation and proliferation during normal ovarian follicle development.

Mechanisms that directly control mammalian ovarian primordial follicle (PF) growth activation and the selection of individual follicles for survival are largely unknown. Follicle cells produce factors that can act as potent inducers of cellular stress during normal function. Consistent with this, we show here that normal, untreated ovarian cells, including pre-granulosa cells of dormant PFs, express phenotype and protein markers of the activated integrated stress response (ISR), including stress-specific protein translation (phospho-Serine 51 eukaryotic initiation factor 2α; P-EIF2α), active DNA damage checkpoints, and cell-cycle arrest. We further demonstrate that mRNAs upregulated in primary (growing) follicles versus arrested PFs mostly include stress-responsive upstream open reading frames (uORFs). Treatment of a granulosa cell (GC) line with the PF growth trigger tumor necrosis factor alpha results in the upregulation of a 'stress-dependent' translation profile. This includes further elevated P-eIF2α and a shift of uORF-containing mRNAs to polysomes. Because the active ISR corresponds to slow follicle growth and PF arrest, we propose that repair and abrogation of ISR checkpoints (e.g. checkpoint recovery) drives the GC cell cycle and PF growth activation (PFGA). If cellular stress is elevated beyond a threshold(s) or, if damage occurs that cannot be repaired, cell and follicle death ensue, consistent with physiological atresia. These data suggest an intrinsic quality control mechanism for immature and growing follicles, where PFGA and subsequent follicle growth and survival depend causally upon ISR resolution, including DNA repair and thus the proof of genomic integrity.

High-fat diet induces an ovulatory defect associated with dysregulated endothelin-2 in mice.

High-fat diet (HFD) consumption in female rodents causes impaired estrous cyclicity, fewer pups per litter, and dysregulation of key ovulatory genes suggesting that HFD-induced subfertility may be due to ovulatory dysfunction. To test this hypothesis female mice were fed chow or HFD for 10 weeks at which point ovulation and ovarian gene expression of endothelin-2 (Edn2), a gene critical for ovulation, were assessed. After 10 weeks of HFD, both mice that remained lean and those that became obese had fewer ovulated oocytes than chow controls (P = 0.041, P = 0.0030, respectively). In chow controls, Edn2 was expressed as expected with basal levels during diestrus and proestrus, increased 11.6-fold during estrus, and decreased to basal levels during metestrus. In HFD mice, Edn2 was dysregulated across the entire estrous cycle as were other Edn2 system components (endothelin converting enzyme 1 (Ece-1), and the endothelin receptors (Ednra, Ednrb)). Interestingly, we found dysregulation of key ovarian steroidogenic genes after HFD. We also found that estradiol treatment in prepubertal mice increased Edn2 expression in the ovary (P = 0.030), suggesting that impaired steroidogenesis may be involved in the HFD-induced dysregulation of ovarian Edn2. In conclusion, HFD leads to ovulatory dysfunction regardless of the development of obesity, which appears to be mediated through dysregulation of ovarian Edn2 expression.