Epithelial calcium-sensing receptor activation by eosinophil granule protein analog stimulates collagen matrix contraction

BACKGROUND: Eosinophils reside in normal gastrointestinal tracts and increase in disease. Receptors for eosinophil derived granule proteins (EDGPs) have not been identified but highly cationic molecules, similar to eosinophil proteins, bind extracellular calcium-sensing receptors (CaSR). We hypothesized that stimulation of CaSR by eosinophil proteins activates epithelial cells. METHODS: Caco2 intestinal epithelial cells, AML14.3D10 eosinophils, wild type human embryonic kidney 293 (HEK293) cells not expressing CaSR (HEK-WT) or CaSR transfected HEK293 cells (HEK-CaSR) were stimulated with an eosinophil protein analog poly-L-arginine (PA) and phosphorylated extracellular signal-regulated kinases 1/2 (pERK) was measured. Functional activation was measured with collagen lattice contraction assays. RESULTS: Co-culture of Caco2 cells with AML14.3D10 eosinophils augmented lattice contraction compared to lattices containing Caco2 cells alone. PA stimulation of Caco2 lattices augmented contraction. HEK-CaSR stimulation with PA or Ca(2+) resulted in greater pERK activation than stimulated HEK-WT cells. PA stimulated greater HEK-CaSR lattice contraction than unstimulated lattices. Contraction of PA stimulated and unstimulated HEK-WT lattices did not differ. CONCLUSION: Exposure of intestinal epithelia to the EDGP analog, PA, stimulates CaSR dependent ERK phosphorylation and epithelial mediated collagen lattice contraction. We speculate that EDGP release within the epithelial layers activates the CaSR receptor leading to matrix contraction and tissue fibrosis.