Novel Role of DRA/SLC26A3 Downregulation in Gut Dysbiosis, Inflammation and Infection

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Down regulated in adenoma (DRA) or SLC26A3 is the key intestinal chloride transporter involved in electrolyte and water absorption in the gut. Loss of function mutations in DRA result in “Congenital Chloride Diarrhea” or CLD disease. Extensive studies from our group have now established that downregulation of DRA is one of the key events in infectious and IBD-associated diarrhea. Emerging evidence from our group and others and GWAS studies have now also established DRA gene to be an IBD susceptibility locus. DRA knockout (KO) mice exhibit a CLD phenotype, thinner mucus layer and increased susceptibility to colitis. We recently showed that DRA KO mice exhibit some of the key features of IBD, including dysbiosis and compromised barrier integrity. Our preliminary studies further showed that DRA KO mice are more susceptible to pathogen infection and exhibit immune cell dysregulation. However, the detailed mechanisms underlying dysbiosis and its role in defective mucus-epithelial barrier observed in DRAKO mice and their increased susceptibility to gut inflammation and pathogen infection have not been fully investigated. Our exciting data further showed that the dysbiosis in DRA KO mice was associated with decreased short chain fatty acid (SCFA) producing taxa, fecal SCFA levels and enrichment in mucin-degrading bacteria. Cohousing studies of DRA KO with wildtype mice showed that part of the compromised barrier integrity was secondary to microbial dysbiosis. Further, in preliminary studies, DRA KO mice showed a marked reduction in Innate Lymphoid Cells-3 and IL-22, critical for combating pathogen infection. Preliminary data also showed that the expression of key mucins (MUC2 and 4) was significantly higher in goblet cells but appeared to be trapped in cells suggesting abnormal secretion. Based upon these findings, our overall hypothesis is that “Gut dysbiosis in response to the loss of DRA function contribute to compromised mucus and epithelial barrier integrity leading to increased susceptibility to gut inflammation and pathogen infection and strategies to upregulate DRA expression may alleviate these effects”. The key component of this hypothesis for this R56 proposal will be tested by the following Specific Aims: Aim 1a: Examine the age-dependent dynamic changes in the microbiome and mucus and epithelial barrier defects in DRA KO mice; Aim 1b: Investigate if cohousing with WT mice modulates the epithelium-associated factors including TJs, mucin synthesis and secretion; Aim 1c: Examine the role of altered bacterial species and metabolites by in-depth metabolomic and metagenomic analysis in DRA KO mice; Aim 1d: Evaluate the role of altered microbiome in affecting mucus layer and epithelial integrity via fecal microbial transplant approaches from WT and DRA KO mice to GF mice. The proposed studies will provide mechanistic insights into the role of DRA induced dysbiosis in defective mucus and epithelial barrier integrity and susceptibility to inflammation and infection and may aid in unraveling novel therapeutic targets.