Nfat5 positively controls glycolysis in intestinal cells

Background.Tight junction structures are essential in intestinal barrier integrity, inflammation, and cancer.The disruption of tight junctions is a common manifestation of various diseases including colon cancer.Claudin-5 is a tight junction protein expressed in epithelia and endothelia and form para-cellular barriers and pores that determine permeability.Claudin-5 is downregulated in human colon cancer.Vitamin D and Vitamin D receptor (VDR) play important roles in maintaining intestinal homeostasis and barrier functions.Both VDR and Claudin-5 are involved in tumorigenesis, however, it remains unclear whether they function collaboratively or independently.Methods In the current study, we investigate the novel role of VDR in regulating Claudin-5, using whole body VDR knockout (VDR -/-) and intestinal epithelial VDR knockout (VDR DIEC ) mice.In vitro, VDR -/- embryonic fibroblasts (MEF) cells, cultured human intestinal epithelial cells, organoids, and human colon cancer samples were used to determine the molecular mechanisms.Results In intestinal samples of patients with colon cancer, we found low VDR expression and decreased Claudin-5 expression.In an AOM/DSS induced cancer model, mice lacking VDR had higher numbers and bigger sizes of tumors compared to the VDR +/+ mice.In the colon of VDR -/- mice and VDR DIEC mice, deletion of VDR led to decreased Claudin-5 at the protein and mRNA levels.This observation was also confirmed by immunostaining of Claudin-5.In VDR -/- MEF cells, both Western blot and real time PCR revealed that VDR deletion led to lower protein and mRNA levels of Claudin-5 in cells without any treatment.Vitamin D3 is known to increase VDR expression and activate VDR signaling.With 1, 25 vitamin D3 treatment, the protein and mRNA levels of Claudin-5 were significantly elevated in mice, organoids, and human intestinal epithelial cells.As a transcriptional factor, VDR binds to the vitamin D response element (VDRE) in the promoter of target genes to regulate gene transcription.We further identified the VDRE in the Claudin-5 promoter using CHIP assay, suggesting that the Claudin-5 gene is a downstream target of the VDR signaling pathway.Deletion of VDR leads to increased intestinal permeability and enhanced risk of colon cancer.Conclusion Taken together, we showed that VDR is an important upstream regulator of tight junction protein Claudin-5.This study revealed a complex role for vitamin D/VDR in maintaining the physiological level and function of intestinal tight junctions and protecting again tumorigenesis.