Leveraging menstrual effluent (ME) to investigate vitamin D and human decidualization, a potential link with fertility.

Abstract

Low vitamin D levels have been associated with female infertility, but the underlying mechanisms are not understood. To examine vitamin D treatment, in vitro and in vivo, on human endometrial stromal cell (eSC) decidualization, including mediating pathways. To assess feasibility of vitamin D measurement in menstrual effluent (ME). ME, ME-eSCs, and peripheral plasma were collected from participants in the Research Outsmarts Endometriosis (ROSE) study (2017-2024) and the Investigation of Vitamin D and Menstrual Cycles trial (inVitD) (2022-2024; NCT05050916). ROSE study: North America; inVitD study: Detroit, MI and Durham, NC. Healthy females aged 19-40 years. The inVitD trial participants provided ME pre- and post-cholecalciferol supplementation. Oral cholecalciferol supplementation (50,000 IU/week or 4,200 IU/week x 3 months) was provided to vitamin D deficient inVitD trial participants. First, we examined the effect of active vitamin D (calcitriol) on ME-eSC decidualization in vitro. Second, we compared ME-eSC decidualization pre- and post-oral cholecalciferol supplementation. Mechanistic studies investigated target signaling proteins and mRNA expression. Third, we compared levels of vitamin D biomarkers in peripheral plasma versus ME. Calcitriol increased eSC decidualization measured by IGFBP1 (p<0.0001) and prolactin levels (p<0.0001). Calcitriol and decidualization alone induced VDR mRNA expression. Calcitriol reduced AKT and PRAS40 phosphorylation during decidualization. Decidualization capacity increased following in vivo cholecalciferol supplementation (p=0.07). Peripheral plasma 1,25(OH)2D levels were correlated with ME levels (r=0.66, p=0.01). Vitamin D enhances eSC decidualization, likely through reduced AKT signaling and downstream events, highlighting its potential role in fertility. Vitamin D biomarkers were measurable in ME.