Inhibition of integrated stress response by ISRIB promotes mouse and human primordial follicle activation via the mTOR pathway.

Abstract

Purpose: The aim of this study is to investigate the effect of integrated stress response (ISR) inhibitor (ISRIB) on primordial follicle activation.

Methods: We identified drugs promoting primordial follicle activation and investigated their mechanisms through culturing newborn mouse ovaries in vitro. Validation was performed in vivo through intraperitoneal injection in newborn mice. Additionally, we analyzed its potential mechanisms through transcriptome sequencing. Finally, the function and mechanisms of ISRIB were further validated through culturing human ovarian tissues in vitro.

Results: ISR activity was present in neonatal mouse ovaries. ISRIB in vitro culture and in vivo intraperitoneal injection significantly decreased the protein levels of phosphorylated eukaryotic translation initiation factor 2 subunit alpha (p-eIF2α) and activating transcription factor 4 (ATF4). ISRIB also significantly increased the growing follicle number and the protein levels of phosphorylated mammalian target of rapamycin (p-mTOR), KIT ligand (KITL), phosphorylated protein kinase B (p-Akt), and phosphorylated forkhead Box O3a (p-FOXO3a) in neonatal mouse ovaries and/or cultured human ovarian fragments. ISRIB significantly increased the relative fluorescence intensities of p-mTOR in the pre-granulosa cells of primordial follicles, and ISRIB-induced increase of p-Akt and p-FOXO3a was completely reversed by KIT inhibitor ISCK03. In the excessive ISR mouse model induced by corticosterone, ISRIB could partially reverse the apoptosis of primordial and growing follicles.

Conclusion: ISRIB promoted mouse and human primordial follicle activation via the mTOR pathway and partly reversed corticosterone-induced decrease of growing follicles. These results suggest that ISRIB may be a potential drug for rescuing infertility in POI patients.