Myeloid vitamin D receptor influences cell proliferation in small intestine

Abstract

The vitamin D receptor (VDR) is a ubiquitous nuclear receptor that acts as a transcription factor when vitamin D binds with VDR. Intestinal epithelial VDR has various physiological and anatomical benefits to intestine. Interactions between intestinal epithelial cells (IEC) and immune cells are critical for gut health. Cellular proliferation through Wnt/β‐catenin signaling is a result of immune and IEC crosstalk. Wnt proteins from macrophages bind to intestinal epithelial cells and activate the Wnt/β‐catenin pathway. This pathway is critical for cell proliferation which enables food and water absorption in the small intestine. However, the importance of myeloid VDR in regulating the Wnt/β‐catenin pathway in epithelial cells is not fully understood. The objective of this study is to assess how the presence of myeloid VDR in the intestinal epithelial cells influences cellular proliferation through the Wnt/β‐catenin pathway. We hypothesize that the low level of myeloid VDR will reduce expression of Wnt/β‐catenin signaling downstream and alleviate cell proliferation in the small intestine. This experiment utilized selective deletion of myeloid VDR in an ex‐vivo and in‐vivo set‐up. For the ex‐vivo, control mice (VDRLoxP) were crossed with lysozyme (M) ‐cre mice to create specific knockout of myeloid VDR (VDRrLyz) mice. Twelve mice (6 VDRLoxP mice and 6 VDRrLyz) were sacrificed and mucosal scrapings from the ileum (small intestine) were collected for westerns. For cell culture, small intestine organoids derived from the intestinal stem cells were cultured alone or co‐cultured with macrophages (VDR+/+ or VDR−/−). After 3 days, the organoids and organoid‐macrophage co‐cultures were collected for western blots. Western blots were used to measure and compare expression of Wnt/β‐catenin signaling proteins. The VDR−/− organoid macrophage co‐culture showed significantly decreased expression of β‐catenin and PCNA (a cell proliferation marker), compared to the VDR+/+ organoid macrophage co‐culture. Our results suggest that myeloid VDR influences the Wnt/β‐catenin signaling pathway. We present a novel role of myeloid VDR signaling in mediating immune/epithelial cell cross talk in intestine.