SIRT5 regulates granulosa cell proliferation and apoptosis in polycystic ovarian syndrome via desuccinylation of GLI1

Polycystic ovarian syndrome (PCOS) is a major cause of infertility. Succinylation is involved in disease processes; however, its role in PCOS remains unknown. This study aimed to analyze the effect of desuccinylase SIRT5 on granulosa cell phenotype and the molecular mechanism. The levels of succinylation-related enzymes were measured using reverse transcription-quantitative polymerase chain reaction and immunoblotting. Cell proliferation was evaluated using MTT and colony formation assays, and apoptosis was assessed using flow cytometry. The succinylation was analyzed using immunoprecipitation, cycloheximide chase assay, and immunoblotting. The results showed that SIRT5 was highly expressed in PCOS, and knockdown of SIRT5 promoted granulosa cell proliferation and inhibited apoptosis, as well as activated the SHH pathway. Moreover, silencing of SIRT5 promoted GLI1 succinylation at lysine (K)232 site and thereby suppressed its degradation. GLI1 knockdown reversed the promotion of proliferation and the inhibition of apoptosis caused by SIRT5 knockdown. Besides, SIRT5 knockdown attenuated ovarian dysfunction and inhibited apoptosis in PCOS rats by increasing GLI expression. In conclusion, silencing of SIRT5 facilitates granulosa cell proliferation and impedes apoptosis by succinylation of GLI1 at K232 site, and thus attenuates PCOS. The findings suggest that SIRT5 may be a promising target for PCOS therapy.