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    Regulation et functions of the transcription factor ChREBP in the gut

    Wafa Charifi

    Mai 20th 2021 2 pm

    Rosalind Franklin room

    Institut Cochin, 22 rue Méchain, Paris 75014

    (Videoconference for the public)

     


    Supervisor: Sandra Guilmeau

    Team: Insulin signaling, glucose sensing and glucotoxicity

    Department: Endocrinology, Metabolism and Diabetes

    Abstract:

    The transcription factor ChREBP has been reported as a key player of glucose intracellular signaling in the liver and the adipose tissue. ChREBP is indeed activated in those tissues by glucose metabolites and regulate the expression of genes involved in glycolysis and de novo lipogenesis. Interestingly, ChREBP knockout mice, although intolerant to a peripheral glucose injection, are more tolerant to an oral glucose administration, suggesting an alteration of the incretin response. Therefore, the objectives of my thesis were: (1) to characterize the regulation of ChREBP expression and activity by dietary sugars in the gut, and (2) to identify intestinal functions contributing to glycemic control that ChREBP regulates. We first demonstrated that ChREBP is abundantly expressed in the proximal gut epithelium. Exposure to high sugar challenge stimulates ChREBP expression in the upper small intestine as compared to normal diet. Intestinal invalidation of the glucose transporter GLUT2 increase epithelial expression of ChREBP and its target genes in response to glucose suggesting that the absence of basolateral GLUT2 in enterocytes leads to an intracellular accumulation of metabolized glucose while glucose absorption at the apical pole is compensated by other glucose transporters. The deficiency for the fructose transporter GLUT5, completely abolishes the expression of ChREBP and its target genes induced by fructose in intestinal epithelial cells. Interestingly, the pharmacological inhibition of sugar receptors (TasR), potentiates the activation of ChREBP pathway in response to glucose and fructose, suggesting a negative regulation of TasR on ChREBP activity. The use of non-metabolizable glucose and fructose analogues, or pharmacological and genetic inhibition of glycolytic or fructolytic metabolism led to a drastic reduction of ChREBP mRNA levels and its target genes. Altogether, these data therefore highlight that absorption and intracellular metabolism of glucose and fructose are required for the activation of ChREBP in the intestinal epithelium. In mice, total (ChREBP-/-) or intestinal (ChREBPΔGUT) ChREBP deficiency is associated with decreased GLP-1 portal concentrations and intestinal content in response to oral glucose challenge and reduced gut Gcg gene (encoding GLP-1 precursor) expression levels without concomitant alteration of insulinemia. Interestingly, ChREBP expression is enriched in GLP-1 producing L cells and its pharmacological inhibition (SBI-477) in the GLUTag entero-endocrine cell line or its genetic invalidation in isolated L cells leads to the downregulation of Gcg gene expression, underlying the role of ChREBP in GLP-1 production. Taken together, these data demonstrate that improved oral glucose tolerance in ChREBP-/- mice is independent of an increased incretin response. Therefore, we next evaluated the contribution of ChREBP to intestinal glucose absorption, another gut function contributing to glycemic control. By using radioactive tracers (glucose 14C, 18F-FDG), we show that the glucose transepithelial intestinal transport is significantly decreased in ChREBP-/- or ChREBPΔGUT mice and triggers gut glucose malabsorption. This is associated with a decrease in the expression of monosaccharide transporters and disaccharide hydrolytic enzymes, suggesting that intestinal sugar digestion is also affected upon local ChREBP deficiency. Furthermore, ultrastructural analyses of intestinal mucosa from ChREBP-/- and ChREBPΔGUT mice demonstrate a significant reduction in microvilli length, as commonly observed during caloric restriction. Consistent with these results, intestinal ChREBP deficiency is accompanied by sugar intolerance due to impaired gut capacities to properly absorb fructose and galactose. In conclusion, our results show that ChREBP loss in the intestinal epithelium alters glucose uptake and delayed glucose distribution to peripheral tissues, contributing to a better tolerance to an oral glucose challenge.