Society: AGA

This session will provide the latest progress in genetics-related developmental GI research.

Mutations in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) chloride (Cl^-) and bicarbonate (HCO₃^-) channel lead to Cystic Fibrosis (CF) and multiple intestinal defects including increased acidity linked to inspissated mucus, malabsorption, obstruction, infection, inflammation, and cancer that increases morbidity and reduces quality of life for CF patients. CFTR High Expresser Cells (CHEs), a subpopulation of small intestinal enterocytes, express unusually high levels of CFTR compared to neighboring villus enterocytes. How CHEs contribute to intestinal disease in CF is unknown. CHEs are present in human and rat duodenum and jejunum. Recently, fluorescence in situ hybridization (FISH) identified CHEs as the major source of uroguanylin (UGN) in the human duodenum. UGN, a peptide hormone that is secreted into the intestinal lumen, regulates HCO₃^- secretion through CFTR in response to an acidic milieu. To characterize UGN protein expression in CHEs and understand the role of CHEs and UGN in intestinal CF pathophysiology, intestinal tissue from rats harboring the common dF508 mutation and control littermates were employed. Double-labeling immunofluorescence (IF) of CFTR and UGN or CFTR and guanylate cyclase C (GC-C), the UGN receptor, were performed along the rostrocaudal axis of rat intestine. CFTR subcellular distribution in CHEs was examined after low luminal pH and CHE abundance was quantified. Single-labeling FISH of guanylate cyclase activator 2B (GUCAB) or IF double-labeling of GC-C and MEIS1, a transcription factor specific to CHEs, were performed in dF508 jejunum samples and respective control. Consistent with published findings by ISH, UGN protein was highest in the duodenum and decreased along the rostrocaudal axis of the small intestine. All CHEs in rat duodenum were UGN+, but not all UGN+ cells were CHEs. In rat jejunum, CHEs displayed varying levels of UGN expression and some CHEs displayed minimal or no UGN label. CHEs in duodenum and jejunum expressed high levels of the GC-C receptor. Apical GC-C label was identified in Brunner’s gland of rat proximal duodenum. Luminal exposure to pH 2.0 for 30 min robustly increased apical CFTR in duodenal villus CHEs compared to PBS (pH 7.4), and increased CHE abundance 3-fold. dF508 rat jejunum displayed villus atrophy and intraepithelial lymphocytes compatible with human CF. dF508 jejunum displayed increased number of GUCA2B+ cells and GC-C/MEIS1+ CHEs compared to control jejunum. CHEs in dF508 jejunum displayed higher levels of GC-C compared to neighboring enterocytes. Conclusions: Our findings suggest an important role for CHEs in sensing and regulating pH and fluid secretion in the small intestine. Ongoing studies will characterize the role of UGN/GC-C and CHEs in the pathophysiology of CF intestinal disease.

Martin Donnelley

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