How Vitamin D Receptor Influences Intestinal Barriers

Salmonella enterica serotypes are invasive enteric pathogens spread through fecal contamination of food and water sources. It represents a constant public health threat in the U.S. and around the world. Impaired intestinal barriers are associated with bacterial infection. Vitamin D and its receptor (VDR) levels are inversely related to chronic inflammation in infectious diseases. The objective of this application is to study VDR regulation of intestinal tight junctions (TJs) in response to Salmonella infection. Our publications and preliminary data have shown that: (1) lack of VDR makes the host susceptible to Salmonella invasion; (2) Salmonella targets TJ proteins (e.g., ZO-1, Claudin) and facilitates pathogenic enteric bacterial invasion. (3) We have identified the sequence of functional vitamin D response element in Claudin- 5 and 15, two novel target genes of VDR; (4) impaired VDR leads to reduced expression of TJ proteins Claudin- 5 and 15, increased “leaky” protein Claudin 2, and increased permeability in infection; and (5) probiotics and their products enhance VDR function and inhibit Salmonella infection. Thus, we hypothesize that: “intestinal epithelial VDR regulation of barrier function is aberrant or lost in infectious states and restoring VDR function will attenuate severe infection and chronic inflammation.” We have now developed state-of-the-art transgenic models and cutting-edge methods, e.g., integrated three-dimensional microscopy for a spatial junction protein atlas and single-cell spatial proteomics for geographic profiling of the TJ protein expressions. Our research team includes experts in the following areas: epithelial biology, animal models, bioengineering, and microbiology. Two Specific Aims have been designed: Aim 1. Determine the cellular and molecular mechanisms by which intestinal VDR regulates barrier function that is essential for mucosal homeostasis. We will: A. Elucidate the mechanism for abnormal epithelial TJs coregulated by Claudins and their interactions in the VDR-/- organoids in vitro. B. Study regional and spatial Claudins, their interactions, and integrations with other barrier layers: microbiome and mucin. And C. Determine the mechanism for abnormal epithelial TJs, including spatial and omics studies of TJs, in the intestine of the VDRΔIEC and VDR overexpressed mice with or without infection. Aim 2. Investigate microbial metabolites and TJs vs. VDR for therapeutic strategies in inflammation and infection. We will A. Evaluate the roles and mechanisms of enhanced intestinal TJs vs. VDR expression by probiotic lactic acid bacterial proteins and metabolites in infected mice. B. Engineer probiotic bacteria strains for better outcomes in treatment of inflammation and infection. Our studies are innovative because they are focused on 1) understanding novel regulatory roles of VDR in Claudins and their interactions in infection; 2) developing cutting edge technologies and tools (organoids, transgenic mice, and spatial imaging) for studying intestinal biology; and 3) enhancing intestinal VDR expression by probiotics and microbial metabolites. This knowledge can then be exploited for strategies to prevent and treat digestive diseases by restoring VDR and enhancing barrier functions.