Increased chromatin accessibility following 1α,25-dihydroxyvitamin D₃ treatment in human endometrial stromal cells

Vitamin D signaling has recognized roles in female reproductive physiology, but its effects at the chromatin level in endometrial stromal cells are still unclear. Here, we investigated how the active form of vitamin D, 1α,25-dihydroxyvitamin D₃, or calcitriol, influences the accessible chromatin landscape of human endometrial stromal cells. Assay for transposase-accessible chromatin using sequencing (ATAC-seq) was performed on human telomerase reverse transcriptase (hTERT)-immortalized human endometrial stromal cell line (T-HESC) treated with either a vehicle or 1,25(OH)₂D₃. Ligand treatment increased overall chromatin accessibility, shown by higher ATAC-seq signal intensity, while causing only minor changes in the total number of called peaks. Peak annotation revealed that accessible regions were spread across both promoter-proximal and distal genomic areas. Integrating this data with Cleavage Under Targets and Release Using Nuclease (CUT&RUN) and RNA sequencing showed that most vitamin D-responsive cistromic modifications and transcripts were linked to nearby open chromatin, though fewer were associated with regions that were significantly differentially accessible. These results suggest that 1,25(OH)₂D₃-dependent transcription mainly occurs within a permissive, pre-accessible chromatin environment. This study offers new evidence that active vitamin D influences the epigenomic landscape of human endometrial stromal cells, establishing the chromatin-based molecular response to a chemically-defined vitamin D receptor (VDR) ligand, 1,25(OH)₂D₃, relevant to stromal differentiation and preparation for decidualization.