Abstract 14649: Chloride Channel Calcium-activated-1 Reduces Mouse Abdominal Aortic Aneurysm by Blocking Macrophage Migration Inhibitory Factor Activity in Macrophage Activation

Introduction: Human chloride channel calcium-activated-1 (CLCA1) protein is a secretory protein that goblet cells from trachea epithelium express abundantly where it participates in hypersecretory lung diseases by mucus overproduction. Studies from CLCA1-deficient mice or CLCA1 blocking agents have however yielded inconsistent conclusions. CLCA1 not only regulates mucin expression, but also participates in innate immune responses by binding to yet unidentified molecules on the inflammatory cells and regulating cytokine and chemokine production. Seeking CLCA1 binding proteins identified CLCA1 expression by endothelial cells (EC), smooth muscle cells (SMC), and macrophages in human and mouse abdominal aortic aneurysms (AAA). Ligation of CLCA1 mediated the actions of macrophage migration inhibitory factor (MIF). Hypothesis: CLCA1 controls AAA growth by regulating MIF activity. Methods and Results: Immunoblots revealed high levels of the 110 and 75-kDa CLCA1 fragments in human abdominal aneurysm lesions, but normal human aortas contained predominantly the 35-kDa carboxyl-terminal fragments. Cultured human EC and SMC contained only the 35-kDa fragment, but human monocyte-derived macrophages contained both the 75 and 35-kDa fragments. Confocal microscopy colocalized CLCA1 and MIF in macrophages from human AAA lesions. CLCA1 immunoprecipitation followed by MIF immunoblot showed that the 35-kDa CLCA1 fragment complexes with MIF in cultured macrophages. Adventitial CaPO 4 -induced AAA in male Clca1 -/- mice demonstrated significantly greater aneurysm diameter, and increased lesion neutrophil and eosinophil content, as well as neutrophil- and eosinophil-associated chemokine (CXCL1, 2, 5, CCR3, and eotaxin-2 and 3) expression than those in wild-type or sham-operated mice. Macrophages cultured from Clca1 -/- bone-marrow showed enhanced MIF activity compared to those from wild-type mice. Conclusions: The 35-kDa CLCA1 fragment reduces formation of experimental AAA by acting as a decoy receptor, sequestering MIF and thus limiting MIF-mediated macrophage activation.