Calpains and Abdominal Aortic Aneurysms

Grants and Contracts Details


Abdominal aortic aneurysm (AAA) is a permanent dilation of the abdominal aorta with over 80% mortality after rupture. The current therapy is restricted to surgical repair, highlighting the need to explore mechanic insights into the development of effective, non-surgical therapeutics. In AAA patients, structural integrity of the aortic wall is disrupted due to dissociation of smooth muscle cell (SMC) contractile filaments from extracellular matrix by proteases. This association is mediated by cytoskeletal linker proteins. However, the mechanism underlying loss of vessel wall structural integrity in AAA formation is not completely understood. Recently, using Angiotensin II (AngII)-induced animal model of AAA, we demonstrated AngII infusion profoundly increased aortic protein and activity of calpain, a calcium dependent cysteine protease in mice. In addition, calpain inhibition significantly attenuated AngII-induced AAA formation in mice. Calpains are the only known proteolytic enzymes targeting an array of cytoskeletal proteins that maintain structural integrity of the aorta, including filamin. The two major isoforms, calpain-1 and -2, are ubiquitously expressed. Using calpain-1 and -2 specific deficient mice, we identified that inhibition of calpain-2 not calpain-1 completely blunted AngII-induced AAA formation. Calpain-2 deficiency attenuated AngII-induced fragmentation of cytoskeletal proteins – filamin A, and talin in the aorta. Immunostaining of AAA revealed expression of calpain-2 protein by infiltrated macrophages and aortic adventitial fibroblasts (AoAFs). Macrophage specific calpain-2 deficiency in mice had no influence on AngII-induced AAA formation, which suggest a critical role for vessel wall mainly AoAFs derived-calpain-2. In cultured AoAFs, AngII promotes ASK-1/NF-kB mediated inflammatory cytokine induction via activation of calpain-2. Further, calpain-2 silencing suppressed (myo)fibroblast differentiation and migration via TGF-â and Rho kinase signaling. Based on the described background, we will test the hypothesis that calpain-2 activation promotes AngII-induced AAAs by accelerating adventitial fibroblast-derived NF-kB/ASK-1 mediated adventitial inflammation, and (myo)fibroblasts migration to aortic media, which in turn causes medial destruction by upregulating cytoskeletal filament fragmentation in SMCs. To test this hypothesis, the following aims are proposed: Aim 1: Determine the contribution of fibroblasts derived-calpain-2 in AngII-induced AAA. A. Does calpain-2 deficiency in fibroblasts attenuate AngII-induced AAA formation? B. Does calpain-2 regulate TGF-â and Rho kinase via LTBP3 and RhoGDI1 in promoting AngII-induced (myo)fibroblasts differentiation ? C. Does calpain-2 depletion in AoAFs attenuate AngII-induced cytoskeletal protein- filamin A and talin fragmentation in aortic SMCs in vitro? Aim 2: Define the mechanism by which calpain-2 promotes AngII-induced adventitial inflammation? A. Does calpain-2 contribute to ASK-1 and NF-kB activation and correlate with adventitial inflammation during AAA development? B. Does calpain-2 regulate AngII-induced ASK-1 and NF-kB activation and inflammation via TRX and IkB in AoAFs? C. Does cytoskeletal protein fragmentation in human AAA tissue associate with calpain expression? Aim 3: Determine the effect of calpain-2 deficiency on progression of established AAAs. Does pharmacological or genetic inhibition of calpain-2 prevents the progression of established AngII-induced AAAs?
Effective start/end date8/10/177/31/22


  • National Heart Lung and Blood Institute: $1,912,500.00


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