Mast Cell Mediated Regulation of Small Intestinal Chloride Malabsorption in SAMP1/YitFc Mouse Model of Spontaneous Chronic Ileitis.

M Motiur Rahman,Subha Arthur,Uma Sundaram,Sheuli Afroz

doi:10.3390/cells10030697

Abstract

In Inflammatory Bowel Disease (IBD), malabsorption of electrolytes (NaCl) results in diarrhea. Inhibition of coupled NaCl absorption, mediated by the dual operation of Na:H and Cl:HCO3 exchangers on the brush border membrane (BBM) of the intestinal villus cells has been reported in IBD. In the SAMP1/YitFcs (SAMP1) mice model of spontaneous ileitis, representing Crohn’s disease, DRA (Downregulated in Adenoma) mediated Cl:HCO3 exchange was shown to be inhibited secondary to diminished affinity of the exchanger for Cl. However, NHE3 mediated Na:H exchange remained unaffected. Mast cells and their secreted mediators are known to be increased in the IBD mucosa and can affect intestinal electrolyte absorption. However, how mast cell mediators may regulate Cl:HCO3 exchange in SAMP1 mice is unknown. Therefore, the aim of this study was to determine the effect of mast cell mediators on the downregulation of DRA in SAMP1 mice. Mast cell numbers and their degranulation marker enzyme (β-hexosaminidase) levels were significantly increased in SAMP1 mice compared to control AKR mice. However, treatment of SAMP1 mice with a mast cell stabilizer, ketotifen, restored the β-hexosaminidase enzyme levels to normal in the intestine, demonstrating stabilization of mast cells by ketotifen. Moreover, downregulation of Cl:HCO3 exchange activity was restored in ketotifen treated SAMP1 mice. Kinetic studies showed that ketotifen restored the altered affinity of Cl:HCO3 exchange in SAMP1 mice villus cells thus reinstating its activity to normal. Further, RT-qPCR, Western blot and immunofluorescence studies showed that the expression levels of DRA mRNA and BBM protein, respectively remained unaltered in all experimental conditions, supporting the kinetic data. Thus, inhibition of Cl:HCO3 exchange resulting in chloride malabsorption leading to diarrhea in IBD is likely mediated by mast cell mediators.

Highlights

Introduction iationsCrohn’s disease (CD), part of a group of gastrointestinal disorders named as inflammatory bowel diseases (IBD), is characterized by transmural inflammation and skip lesions that might occur throughout the length of the gastrointestinal tract [1]
We have previously demonstrated that Cl:HCO3 exchange was downregulated in ileal villus cell brush border membrane (BBM)
In vivo treatment of SAMP1 mice with ketotifen reduced the degranulation of mast cells, which appeared round or oval with uniform color and intact cell membranes (Figure 1E)

Summary

Introduction

Introduction iationsCrohn’s disease (CD), part of a group of gastrointestinal disorders named as inflammatory bowel diseases (IBD), is characterized by transmural inflammation and skip lesions that might occur throughout the length of the gastrointestinal tract [1]. The incidence of CD, variable in different geographical regions, has been steadily increasing over the years in North America, Western Europe, Asia, and South America [2,3], in the United States The etiopathogenesis of this incurable disease is said to be complex and is known to involve interacting elements including genetic susceptibility of the host, intestinal microbiota, environmental factors, and immunological abnormalities of the host [4]. The chronic inflammation of CD is due to dysregulated host immune inflammatory response leading to its pathogenesis [5]. Many of the immune inflammatory mediators released in the chronically inflamed mucosa of IBD profoundly affect the absorptive.

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