Impact of vitamin D deficiency on defective endometrial decidualization and the repressive role of vitamin D receptor (VDR) in the epigenomic network.

Identifying the factors that regulate female reproduction is crucial to understanding how the environment affects female reproductive health. The vitamin D receptor (VDR) and its ligands (primarily 1,25(OH)2D3) have a recognized role in calcium homeostasis; however, their broader impact on female reproduction remains underexplored. We demonstrate that the VDR and its ligands are involved in the hormonal induction of uterine decidualization. Mice fed a vitamin D-deficient diet displayed an impaired hormonally induced decidual response. In a human telomerase reverse transcriptase-immortalized human endometrial stromal cell line (T-HESC), VDR decreased during in vitro decidualization. Small interfering RNA (siRNA) knockdown of VDR in T-HESC enhanced in vitro decidualization, while overexpression of VDR inhibited it. Chromatin accessibility and histone modification analyses revealed that VDR functions as a chromatin regulator, restricting accessibility and repressing transcription in specific genomic regions. Transcriptomic analyses confirmed that VDR broadly modulates gene expression, with most ligand-mediated effects occurring through the VDR. These findings identify VDR as a key regulator of transcriptional and chromatin landscapes in human endometrial stromal cells, offering novel insights into vitamin D signaling in reproduction. This study highlights the potential of targeting vitamin D pathways to treat uterine disorders associated with impaired decidualization and reduced fertility.