Intestine is a major target of vitamin D and several studies indicate an association between vitamin D deficiency and inflammatory bowel diseases (IBD), but also increased colorectal cancer (CRC) risk and mortality. However, the putative effects of 1α,25-dihydroxyvitamin D3 (calcitriol), the active vitamin D metabolite, on human colonic stem cells are unknown. Here we show by immunohistochemistry and RNAscope in situ hybridization that vitamin D receptor (VDR) is unexpectedly expressed in LGR5+ colon stem cells in human tissue and in normal and tumor organoid cultures generated from patient biopsies. Interestingly, normal and tumor organoids respond differentially to calcitriol with profound and contrasting changes in their transcriptomic profiles. In normal organoids, calcitriol upregulates stemness-related genes, such as LGR5, SMOC2, LRIG1, MSI1, PTK7, and MEX3A, and inhibits cell proliferation. In contrast, in tumor organoids calcitriol has little effect on stemness-related genes while it induces a differentiated phenotype, and variably reduces cell proliferation. Concordantly, electron microscopy showed that calcitriol does not affect the blastic undifferentiated cell phenotype in normal organoids but it induces a series of differentiated features in tumor organoids. Our results constitute the first demonstration of a regulatory role of vitamin D on human colon stem cells, indicating a homeostatic effect on colon epithelium with relevant implications in IBD and CRC.

The studies were funded by Networks of Excellence from Spanish Ministry of Science, Innovation and Universities (MICINN) SAF2016‐76377‐R, ‘Nuclear Receptors in Cancer, Metabolism and Inflammation’ (NuRCaMeIn) SAF2017‐90604‐REDT to A.M., ISCIII‐Biomedical Research Networking Centres‐Oncology (CIBERONC) CB16/12/00273 to A.M. and A.B.; CB16/12/00453 to F.X.R.; CB16/12/00342 to E.B. and CB16/12/00241 to F.R. ISCIII‐Biomedical Research Networking Centres‐Respiratory Diseases (CIBERES) CB15/00037 to L.dP, and ISCIII‐FEDER PI15/00934 to F.R.