Influence of Vitamin D Receptor Signalling and Vitamin D on Colonic Epithelial Cell Fate Decisions in Ulcerative Colitis

Background and Aims Epidemiological studies have shown that subnormal levels of vitamin D (25[OH]D) are associated with a more aggravated clinical course of ulcerative colitis [UC]. Despite an increased focus on the therapeutic importance of vitamin D and vitamin D receptor [VDR] signalling, the mechanisms underlying the effects of the vitamin D-VDR axis on UC remain elusive. Therefore, we aimed to investigate whether exposure to active vitamin D (1,25[OH]2D3/VDR) signalling in human organoids could influence the maintenance of the colonic epithelium.Methods Intestinal VDR expression was studied by immunohistochemistry, RNA expression arrays, and single-cell RNA sequencing of colonic biopsy specimens obtained from patients with UC and healthy individuals. To characterise the functional and transcriptional effects of 1,25[OH]2D3, we used patient-derived colonic organoids. The dependency of VDR was assessed by knocking out the receptor with CRISPR/Cas9.Results Our results suggest that 1,25[OH]2D3/VDR stimulation supports differentiation of the colonic epithelium and that impaired 1,25[OH]2D3/VDR signalling thereby may compromise the structure of the intestinal epithelial barrier, leading to flares of UC. Furthermore, a transcriptional response to VDR activity was observed primarily in fully differentiated cells at the top of the colonic crypt, and this response was reduced during flares of UC.Conclusions We identified an important role of vitamin D signalling in supporting differentiated cell states in the human colonic epithelium, and thereby maintenance of the intestinal barrier integrity. This makes the vitamin D-VDR signalling axis an interesting target for therapeutic efforts to achieve and maintain remission in patients with UC. Graphical Abstract