Abstract
BackgroundMolecular analyses of vitamin D in a typical cycling endometrium has received minimal research attention in the reproductive field. This study was designed to assess how expression of the endometrial vitamin D receptor (VDR) and CYP27B1, a vitamin D metabolizing enzyme, change during the menstrual cycle in women of reproductive age. In addition, this study explores the association between expression of vitamin D-VDR system and endometrial receptivity during the implantation window.MethodsSixteen patients underwent standardized in vitro fertilization (IVF) treatment and freeze-all techniques. Before embryo transfer, total serum 25(OH) D levels were determined through blood samples and VDR, CYP27B1, HOXA10, and CYP19 expression were determined through endometrial samples. Endometrial receptivity was also assessed using an electron microscope.ResultsWe found that VDR protein expression was significantly lower throughout the endometrial secretory phase compared to the proliferative phase, while CYP27B1 expression remained constant during the menstrual cycle. During the implantation window, ultrastructural evaluation showed that higher serum vitamin D levels were associated with more mature pinopodes; VDR and HOXA10 protein expression were substantially elevated in pregnant women compared to non-pregnant women; and VDR protein levels were positively correlated with HOXA10 levels. In addition, serum vitamin D levels were positively correlated with VDR and HOXA10 protein levels in the endometrium.ConclusionsWomen with increased VDR expression in the endometrium, especially during the implantation window of the menstrual cycle, were significantly more likely to be pregnant than women with decreased expression. Our results support the hypothesis that the Vitamin D-VDR system performs a role during the development of endometrial receptivity.
Highlights
Vitamin D is well-known for, maintaining phosphorus and calcium homeostasis and promoting bone formation, and for its role in cell proliferation, differentiation, and apoptosis; and the regulation of the immune system, hormones; and other biological processes [1]
Our findings suggest that the vitamin D-vitamin D receptor (VDR) system is extensively linked to the regulation of endometrial receptivity thereby further affecting pregnancy outcomes
Similar to Zelenko’s study, we found that the protein expression of VDR in the secretory phase was significantly reduced compared to the proliferative phase in these women
Summary
Vitamin D is well-known for, maintaining phosphorus and calcium homeostasis and promoting bone formation, and for its role in cell proliferation, differentiation, and apoptosis; and the regulation of the immune system, hormones; and other biological processes [1]. Vitamin D acts as a steroid hormone, in some cases, as it helps regulate the manifestation of numerous genes in reproductive tissues. Vitamin D is associated with modulation of the human reproductive process [2, 3]. Extrarenal CYP27B1 mRNA, as well as its protein expression, have been detected in the human endometrium, implying local vitamin D metabolism and influence on endometrial function [4]. This study was designed to assess how expression of the endometrial vitamin D receptor (VDR) and CYP27B1, a vitamin D metabolizing enzyme, change during the menstrual cycle in women of reproductive age. This study explores the association between expression of vitamin D-VDR system and endometrial receptivity during the implantation window
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