Vitamin D Receptor Expression and Potential Role of Vitamin D on Cell Proliferation and Steroidogenesis in Goat Ovarian Granulosa Cells

This study aimed to investigate the expression of the vitamin D receptor (VDR) in goat follicles and to determine the effects of Vit D supplementation on goat granulosa cells (GCs) function linked to follicular development. The results demonstrated that VDR was prominently localized in GCs, with expression increasing with follicle diameter. Addition of Vit D (1α,25-(OH)VD; 10 nM) to GCs caused an increase in VDR and in steroidogenic acute regulator (StAR) and 3β-hydroxysteroid dehydrogenase (3β-HSD) mRNA expression. Additionally, Vit D increased the cyclic adenosine monophosphate (cAMP), estradiol (E), and progesterone (P) levels, while it decreased anti-müllerian hormone receptor (AMHR) and follicle-stimulating hormone receptor (FSHR) mRNA expression (P < 0.05). Addition of FSH remarkably increased E P, and cAMP levels (P < 0.05), and Vit D further enhanced the E and cAMP levels in the presence of FSH (P < 0.05). Vit D significantly induced the mRNA expression of CDK4 and CyclinD1, and downregulated P21 gene expression (P < 0.05). In addition, Vit D significantly decreased reactive oxygen species (ROS) production and increased the mRNA and protein expression of superoxide dismutase 2 (SOD2) and catalase (CAT) (P < 0.05). In conclusion, VDR is expressed in GCs of the goat ovaries and Vit D might play an important role in GCs proliferation by regulating cellular oxidative stress and cell cycle-related genes. Meanwhile, Vit D enhances the E and P output of GCs by regulating the expression of 3β-HSD and StAR and the level of cAMP, which regulate steroidogenesis, supporting a potential role for Vit D in follicular development.