Seasonal changes of vitamin D3 and ovarian steroidogenesis in the wild ground squirrels (Citellus dauricus Brandt)

Abstract

There is mounting evidence that vitamin D₃ regulates female reproductive function critically, while little is known about the function of seasonally variable vitamin D₃ in regulating ovarian steroidogenesis. This study examined the seasonal expressions of vitamin D receptor (VDR), vitamin D metabolic molecules (CYP2R1, CYP27B1, and CYP24A1), and steroidogenic enzymes (P450scc, 3β-HSD, P450c17, and P450arom) in the ovaries of the wild ground squirrels (Citellus dauricus Brandt) during the different breeding seasons. VDR, CYP2R1, CYP27B1, and CYP24A1 were shown to be localized in different types of ovarian cells in the wild ground squirrels during the breeding and non-breeding seasons. Meanwhile, the mRNA levels of VDR, CYP2R1, CYP27B1, CYP11A1, HSD3B1, CYP17A1, and CYP19A1 in the ovaries were remarkably higher in the breeding season. Furthermore, RNA-seq data of ovaries revealed that 6036 genes were differentially expressed genes (DEGs); further analysis revealed that several DEGs known to be involved in ovarian steroidogenesis pathway and cellular response to vitamin D pathway were identified. In addition, during the breeding season, the concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), progesterone, and 17β-estradiol were greater in the serum of the wild female ground squirrels. This observation was positively correlated with seasonal changes in the concentration of 25(OH)D₃, supporting the fact that the 25(OH)D₃ content in the ovaries was significantly higher in the breeding season. These findings suggested that seasonal changes in vitamin D₃ might regulate the ovarian steroidogenesis of the wild female ground squirrels.

Keywords: Ovary; Steroidogenic enzymes; Vitamin D receptor; Vitamin D(3); Wild ground squirrels.