Mechanisms of NaCl Absorption in the Human Colon

Jesse Brown Va Medical Center, Chicago IL

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Abstract

DESCRIPTION (provided by applicant): Diarrhea associated with inflammatory bowel diseases (IBD) or infections by food-borne pathogens remains a major health problem in our veteran patient population. Despite major medical advances, diarrheal diseases still result in very high morbidity and mortality worldwide. Therefore, a better understanding of the pathophysiology of diarrhea associated with these diseases is critical for designing novel and superior strategies for intervention. Diarrhea results from increased intestinal secretion and/or decreased absorption. A major route of electrolyte absorption in the human intestine involves coupled operation of Na+/H+ and Cl-/HCO3- exchangers. The gene Slc26a3, whose mutations are associated with congenital chloride diarrhea, encodes DRA (Down-Regulated in Adenoma), a protein known to play a critical role in mediating intestinal chloride absorption. Recently, significant reduction of DRA expression has been shown to be one of the major mechanisms responsible for diarrhea in IBD patients. To date, however, very little is known about the molecular mechanisms involved in decreasing DRA expression in diarrheal diseases. In order to elucidate the mechanisms underlying the downregulation of DRA expression in IBD, our studies focused on the role of hepatic nuclear factors (HNFs, transcription factors essential for the expression of many transport proteins) and miRNAs (known to be upregulated in IBD patients and animal models of IBD). Our extensive preliminary data provided strong evidence for the regulation of DRA expression by both HNFs and their activators dexamenthasone (DEX) and conjugated linoleic acids (CLAs), as well as miRNAs. Based on these data, we hypothesize that a down-regulation of HNFs and upregulation of certain miRNAs in inflamed gut may underlie the decrease in DRA expression via transcriptional and post-transcriptional mechanisms, respectively. The current application is, therefore, designed to investigate the regulation of DRA by HNFs and miRNAs utilizing both in vitro (Aims 1 & 2) and in vivo models (Aim 3) as follows: Aim 1. Elucidate detailed mechanisms underlying basal regulation of DRA promoter by HNFs, in decreased DRA expression in IBD and to establish the molecular basis for the upregulation of DRA by DEX and CLAs; Aim 2: Extensively analyze the mechanisms underlying post-transcriptional regulation of DRA by miRNAs; and Aim 3: Analyze the regulation of DRA by HNFs and miRs in wild type and IL-10 knock out mouse model for IBD. The outcome of these studies should define the role of HNFs in basal, inflammatory or CLA/DEX-mediated upregulation of DRA, and will also establish for the first time, the role of miRs in the modulation of intestinal NaCl absorption under normal and inflammatory conditions. These studies should also identify novel targets for intervention in IBD associated diarrhea.