Reproduction Abstracts

In recent years it has become apparent that vitamin D3 (VD) has a fundamental role in reproductive function, with deficiency of the hormone being implicated in several reproductive pathologies: endometriosis, pre-eclampsia and PCOS. VD is essential for oestrogen synthesis in both males and females; via indirect mechanisms of calcium homeostasis but also direct regulation of aromatase expression. Women with PCOS are more likely to suffer from VD deficiency, with an inverse correlation between serum VD concentrations and BMI/insulin resistance. VD supplementation has been shown to improve ovulation frequency and insulin sensitivity, indicating its significant role in ovarian steroidogenesis, ovulation and fertility. The aim of our study was to investigate VDR mRNA expression in human ovarian tissue (using qPCR), and the effect of VD on aromatase mRNA expression and promoter II (PII) activity (using a luciferase assay) in the human KGN cell-line. VDR mRNA was found in cortex and stroma of normal and PCO tissue, with higher levels in PCO cortex. VDR mRNA levels were significantly up-regulated in theca from follicles 7–12 mm compared to 5–6 mm; and was more pronounced in PCO compared normal ovaries. This expression pattern of VDR highlights the importance of VD in antral follicle progression. KGN cells were cultured with forskolin (to stimulate cAMP) ± VD at 0.02, 0.2, 2 and 20nM, with testosterone (5×10⁻⁷ M) as an aromatase substrate for 48 h. Cells were also transfected with PII-specific luciferase reporter construct. As expected, forskolin up-regulated aromatase mRNA expression 50-fold and interestingly VD reduced this stimulation by half but only at the two lowest doses of VD used. This was a direct effect on PII activity. VD serum levels <50 nM indicate deficiency, with severe deficiency at <12.5 nM. Hence our data showing substantial reduction of cAMP-driven aromatase expression at low VD doses, indicate that VD deficiency could contribute to the impaired folliculogenesis/ovulation identified in women with PCOS.