4. Discussion
In this study, the chorionic villous and decidual tissues from first trimester pregnancies co-expressed VDR mRNA and protein. The results of real-time RT-qPCR analysis were consistent with those of the Western blot analysis; specifically, the expression levels of VDR were reduced in the chorionic villi and decidua in the RPL group compared with the controls. Based on the immunohistochemistry and CLSM results, in the first trimester of human pregnancy, VDR is expressed in villous cells, including trophoblasts, villous stromal cells, and vascular endothelial cells, as well as in decidual cells, including stromal, glandular epithelial, and vascular endothelial cells. Furthermore, VDR expression was mostly decreased in cytotrophoblasts, decidual glandular epithelial cells, and villous and decidual stromal cells. These results provide evidence for disrupted VDR metabolic homeostasis in early pregnancy loss. Several recent studies have reported that trophoblast cells are the principal cells expressing VDR in human term placentas [12,14]. VDR protein expression has also been previously demonstrated in isolated cultured human extravillous trophoblasts (EVT) from first trimester placentas [15]. In all of the studies, VDR expression has been mainly addressed in the term placenta or cultured human trophoblasts. However, to our knowledge, this is the first study reporting the expression and distribution of VDR in human chorionic villi and decidua during the first trimester of pregnancy in vivo. Furthermore, this is the first report of a correlation between VDR expression and RPL. The presence of VDR in both villi and decidua indicates that vitamin D metabolism and localized autocrine or paracrine regulatory signaling occurs in the fetal-maternal interface in early human pregnancy.
