1,25(OH)₂D₃ Regulates Androgen Synthesis via Transcriptional Control of Steroidogenic Enzymes and LHR in the Scented Glands of Muskrats (Ondatra zibethicus).

Photoperiodic changes induce seasonal variations in vitamin D₃ levels, which can affect reproductive function. The muskrat, a seasonal breeder, possesses a pair of scented glands that secrete musky substances to attract mates. The scented glands can also synthesize androgens, which regulate their function through autocrine or paracrine signaling. This study aimed to investigate whether active vitamin D₃ was synthesized locally and to explore how seasonal changes affected the specific mechanisms of androgen synthesis in the scented glands. The scented glands showed significant seasonal changes in morphology and histology. Transcriptomic analysis revealed that differentially expressed genes were enriched in pathways related to sex steroid hormone synthesis and calcium signaling. Quantitative analyses using qPCR and Western blotting demonstrated significant seasonal variations in the expressions of vitamin D₃ receptors (VDR) and key synthetic and metabolic enzymes. Seasonal fluctuations in 1,25(OH)₂D₃ levels were positively correlated with the expressions of steroidogenic enzymes and androgen concentrations in the scented glands. Additionally, 1,25(OH)₂D₃ enhanced the expressions of steroidogenic enzymes in cultured primary cells. ChIP-seq analysis revealed that VD/VDR directly regulated the transcription of Cyp11a1, Cyp17a1, and Lhr by binding to their promoter regions. Furthermore, elevated androgen levels were observed when hCG was combined with 1 nM 1,25(OH)₂D₃. This study suggests that the scented glands can produce 1,25(OH)₂D₃ in autocrine or paracrine forms, with levels varying seasonally. VD/VDR enhanced androgen synthesis through a dual mechanism: (1) directly up-regulating the transcription of Cyp11a1 and Cyp17a1 to increase steroidogenic enzyme levels, and (2) indirectly promoting the expressions of steroidogenic enzymes by modulating Lhr transcription.