Abstract
This study aimed to investigate the expression of the vitamin D receptor (VDR) in goat follicles and to determine the effects of Vit D3 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 D3 (1α,25-(OH)2VD3; 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 D3 increased the cyclic adenosine monophosphate (cAMP), estradiol (E2), and progesterone (P4) 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 E2, P4, and cAMP levels (P < 0.05), and Vit D3 further enhanced the E2 and cAMP levels in the presence of FSH (P < 0.05). Vit D3 significantly induced the mRNA expression of CDK4 and CyclinD1, and downregulated P21 gene expression (P < 0.05). In addition, Vit D3 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 D3 might play an important role in GCs proliferation by regulating cellular oxidative stress and cell cycle-related genes. Meanwhile, Vit D3 enhances the E2 and P4 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 D3 in follicular development.