Role of calpain in AngII-induced Ascending Aortic Aneurysm

Ascending aortic aneurysm (AA) is an asymptomatic life threatening disorder which causes death by aortic rupture in Marfan’s syndrome (MFS) patients. The current available therapy is restricted to surgical repair, highlighting the need to explore mechanic insights into the development of effective, non-surgical therapeutics. In ascending AA patients, the structural integrity of aortic wall is disrupted due to dissociation of smooth muscle cell contractile filaments from extracellular matrix (ECM) by proteases. This association is mediated by cytoskeletal proteins. However, the mechanism underlying ECM degradation in ascending AA formation is not completely understood. Angiotensin II (AngII) infusion into mice leads to ascending AA development as similar to fibrillin-1 mutant mice, an animal model of MFS. Recently, we demonstrated AngII infusion profoundly increased aortic protein and activity of calpain, a calcium dependent cysteine protease in mice. The two major isoforms, calpain-1 and -2, are ubiquitously expressed along with their endogenous inhibitor, calpastatin. In our preliminary studies, using a specific inhibitor of calpains, and calpain-1 deficient mice, we identified that calpain inhibition significantly attenuated AngII-induced ascending AAs, whereas calpain-1 deficiency itself had no effect on ascending AA. Calpains are the only known proteolytic enzymes targeting an array of cytoskeletal and membrane proteins that maintain structural integrity of the aorta, including filamin A. The beneficial effect of calpain inhibition was associated with blunted Ang II-induced filamin A fragmentation. Based on the described background, we will test the hypothesis that AngII promotes ascending AAs by upregulating filamin A fragmentation in the aortic media via stimulation and activation of calpain-2 by vessel wall resident cell types. To test this hypothesis, the following aims are proposed: Aim 1. Determine whether whole body deficiency of calpain-2 attenuates the development of AngII-induced ascending AAs. Aim 2. Determine the cellular source of calpain-2 in the development of AngII-induced ascending AAs.