Redefining the targets of the vitamin D receptor (VDR) utilizing a novel VDR reporter mouse

Abstract The vitamin D receptor (VDR) is a ligand-activated nuclear protein that regulates gene transcription. Vitamin D target cells are identified by the expression of VDR. Kidney and colon epithelial cells constitutively express high levels of the VDR. Immune cells also express the VDR; however, at significantly lower levels. Western blots show very low expression of the VDR in spleen, and lymph nodes. Gene expression studies in macrophage, B cells and T cells showed that activation for 24–48 hours increased the VDR mRNA levels. We have developed transgenic mice that express Cre recombinase within the VDR locus (VDRcre) and crossed these with a reporter line (Tdtomatofl/fl). Cre expression in the VDR locus results in a VDR +/− mice. The frequencies of immune cells were similar between VDR−/− and VDR +/− mice. The VDRcre expressing offspring had pink skin. Kidneys, small intestine and colon were also distinctly pink suggesting high expression of the Tdtomato-VDR reporter. Splenic T cells, activated with CD3e antibody showed upregulation of VDR mRNA and protein. Regardless of activation status, naive, effector or memory T cells had similar and high levels of the VDR reporter. VDR expression was detected at various stages of T cell thymic development with a 80% in the CD4-CD8- cells and 90% of CD4+CD8+ cells, 84% CD4+ and 88% CD8+ thymocytes. High expression of the VDR reporter in multiple T cell types and precursors suggests that the VDR is expressed throughout the life of a T cell. Future work will identify immune cells negative for the VDR reporter and the kinetics of VDR expression following activation in various cell types.