Molecular 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. Sixteen 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. We 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. Women 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.

中文翻译：

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胚胎移植前月经周期子宫内膜中VDR和CYP27B1表达的特征：对子宫内膜容受性的影响

在典型的循环子宫内膜中维生素D的分子分析在生殖领域受到的研究很少。这项研究旨在评估子宫内膜维生素D受体（VDR）和CYP27B1（一种维生素D代谢酶）的表达在育龄妇女的月经周期中如何变化。此外，本研究探讨了在植入窗口期间维生素D-VDR系统的表达与子宫内膜容受性之间的关系。16例患者接受了标准化的体外受精（IVF）治疗和全冷冻技术。胚胎移植前，通过血样测定血清总25（OH）D水平，通过子宫内膜样测定VDR，CYP27B1，HOXA10和CYP19表达。还使用电子显微镜评估子宫内膜的接受度。我们发现，与增生期相比，整个子宫内膜分泌期的VDR蛋白表达均显着降低，而CYP27B1的表达在月经周期保持不变。在植入窗口期间，超微结构评估表明，较高的血清维生素D水平与更成熟的pinopode有关；与非孕妇相比，孕妇中的VDR和HOXA10蛋白表达显着升高。VDR蛋白水平与HOXA10水平呈正相关。此外，子宫内膜中血清维生素D水平与VDR和HOXA10蛋白水平呈正相关。子宫内膜VDR表达增加的女性，尤其是在月经周期的植入窗口期间，与表达下降的女性相比，怀孕的可能性要高得多。我们的研究结果支持了维生素D-VDR系统在子宫内膜容受性发展过程中发挥作用的假设。