Vitamin D status alters genes involved in ovarian steroidogenesis in muskrat granulosa cells

This study aims to explore the relationship between altered vitamin D (VitD₃) status and ovarian steroidogenesis in muskrats during the breeding and non-breeding seasons. During the breeding season, the ovaries of muskrats were observably enlarged and increased in weight, accompanied by elevated serum and ovarian VitD₃ status. Vitamin D receptor (VDR), VitD₃ metabolic molecules (CYP2R1, CYP27B1, and CYP24A1), and steroidogenic enzymes were immunolocalized in the ovarian cells of muskrats. The mRNA levels of VDR, CYP2R1, CYP27B1, and steroidogenic enzymes were considerably higher during the breeding season compared to the non-breeding season. RNA-seq analysis revealed a prominent enrichment of vitamin-related and ovarian steroidogenesis pathways. Furthermore, the addition of 1,25(OH)₂D₃ to the muskrat granulosa cells in vitro increased VDR and steroidogenic enzymes mRNA levels and enhanced the 17β-estradiol level. Overall, these findings supported that VitD₃ promotes the secretion of steroid hormones, thereby affecting seasonal changes in ovarian function in the muskrats.