Up-regulation of cell apoptosis, autophagy and mitochondrial dynamics in ovarian granulosa cells of Daurian ground squirrels during the pre-hibernation period

Abstract

Daurian ground squirrel (Spermophilus dauricus) exhibits both seasonal breeding and hibernation characteristics, but the adaptive changes in ovaries during the transition from seasonal reproduction to hibernation remain poorly understood. The aim of this study is to investigate the regulatory characteristics of granulosa cell apoptosis, autophagy and mitochondrial dynamics in the ovaries of wild Daurian ground squirrels across the April (breeding period), June (non-breeding period), and September (non-breeding and pre-hibernation period). The results proved that ovarian weight, as well as serum reproductive hormones, significantly decreased in June and September compared with April. Interestingly, unlike in June, many growing antral follicles emerged in the ovaries of wild Daurian ground squirrels during September. Furthermore, the molecular studies revealed a significant increase in ovarian gene expression related to cell apoptosis (Casp3, Bax/Bcl-2), autophagy (Becn1, Pink1, Parkin, Sqstm1) and mitochondrial dynamics (Mfn1, Mfn2, Drp1) during September compared to June. Additionally, immunohistochemical results indicated that the protein levels of the aforementioned genes and LC3A/B were concurrently upregulated, predominantly located in ovarian granulosa cells. Consistently, comparative analysis of ovarian transcriptomic data across different periods further confirmed that genes differentially expressed during the three periods were enriched in pathways related to apoptosis, autophagy, and mitochondrial dynamics. In summary, these results revealed a significant up-regulation of cell apoptosis, autophagy, and mitochondrial dynamism in ovarian granulosa cells of wild ground squirrels during the pre-hibernation period, may play a critical role in ovarian development for hibernation and subsequent stage.