Seasonal Change in Glucose Metabolism and Steroidogenesis in the Ovaries of Wild Ground Squirrels (Spermophilus dauricus)

Precise regulation of ovarian glucose metabolism and steroidogenesis is pivotal for the reproductive success of seasonal breeders. This study investigated seasonal variations in ovarian glucose metabolism and its association with follicular development and steroidogenesis in wild ground squirrels (Spermophilus dauricus). Results showed that ovarian weight and volume, and serum levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), 17β-estradiol, and progesterone were significantly higher in the breeding season (BS) than in the non-breeding season (NBS). Ovarian glycogen content was elevated in the BS, whereas circulating glucose levels decreased remarkably. Histologically, the BS ovaries contained follicles at all developmental stages (primary to Graafian) and corpora lutea, while corpora lutea were absent in the NBS. Integrated transcriptomic and metabolomic analyses revealed upregulated glycogen synthesis, glycolytic pathways, and altered steroidogenic metabolites in the BS. Quantitative real-time PCR (qRT-PCR) confirmed higher expression of glucose transporter 1 (GLUT1), glucose metabolism-related enzymes (G6PD, PFKFB3, PFKM), glycogen synthase (GYS), and steroidogenic factors (StAR, P450scc, P450c17, 3β-HSD, P450arom) in the BS, whereas glycogen synthase kinase-3β (Gsk-3β) was upregulated in the NBS. Immunohistochemistry demonstrated colocalization of steroidogenic and glucose-metabolizing enzymes in granulosa and theca cells, and correlation analyses confirmed positive associations between glucose metabolism, steroidogenesis, and ovarian weight. Collectively, these findings indicate that enhanced ovarian glucose metabolism in the BS is tightly coupled with elevated steroidogenesis, synergistically promoting seasonal follicular development and ovulatory competence in this species.