CALCIUM SENSING RECEPTOR DELETION IN THE MOUSE ESOPHAGUS ALTERS BARRIER FUNCTION.

Abstract

Calcium sensing receptor (CaSR) is the molecular sensor by which cells respond to small changes in extracellular Ca+2 concentrations. CaSR has been reported to play a role in glandular and fluid secretion in the gastro-intestinal (GI) tract and to regulate differentiation and proliferation of skin keratinocytes. CaSR is present in the esophageal epithelium, but its role in this tissue has not been defined. We deleted CaSR in the mouse esophagus by generating KRT5-CreER; CaSRFlox+l+ compound mutants, where loxP sites flank exon 7 of CaSR gene. Recombination was initiated with multiple tamoxifen injections and we demonstrated exon 7 deletion by PCR analysis of genomic DNA. qRT-PCR & Western blot (WB) analyses showed a significant reduction in CaSR mRNA and protein expression in the knock-out mice (EsoCaSR-/-) as compared to control mice. Microscopic examination of EsoCaSR-/- esophageal tissues showed morphological changes including elongation of the rete pegs, abnormal keratinization and stratification, and bacterial build-up on the luminal epithelial surface. Western analysis revealed a significant reduction in levels of adherens junction proteins E-cadherin and β catenin and tight junction protein claudin-1, 4 & 5. Levels of small GTPase proteins Rac/Cdc42, involved in actin remodeling, were also reduced. Ussing chamber experiments showed a significantly lower transepithelial resistance (TEER) in KO tissues. In addition, luminal-to serosal-fluorescein dextran (4 kD) flux was higher in KO tissues. Our data indicate that CaSR plays a role in regulating keratinization and cell-cell junctional complexes and is therefore important for the maintenance of the barrier function of the esophagus.