Abstract 25: Inducible Depletion of Calpain-2 Attenuates Angiotensin II-induced Cytoskeletal Structural Protein Destruction During Abdominal Aortic Aneurysm Development in Mice

Abstract

Background and Objective: In abdominal aortic aneurysm (AAA) patients, structural integrity of the aortic wall is disrupted due to the dissociation of cytoskeletal structural proteins that bridge SMC contractile filaments with extracellular matrix by proteases. However, identity of functional proteases which target cytoskeletal structural linker proteins remain unknown. Recently, using the angiotensin II (AngII)-induced AAA model, we demonstrated that AngII significantly increased fragmentation of cytoskeletal structural protein, Filamin A, in AAAs. Further, using a pharmacological inhibitor and genetic deficient mice, we identified that calpain-2 (a class of calcium-activated, intracellular cysteine proteases) plays a critical role in AngII-induced AAA formation in mice. The purpose of this study was to determine the functional contribution of calpain-2 in AngII-induced cytoskeletal structural protein destruction during AAA development. Methods and Results: Calpain-2 floxed mice that were hemizygous for Cre-ERT2 in an LDLr -/- background were produced by breeding male Cre-ERT2 to female calpain-2 floxed mice. At 8 weeks of age, male Calp-2 x Cre-ERT2 (Cre+) and non-Cre littermates (Cre-) mice were injected with tamoxifen (25 mg/kg, i.p.) daily for 5 consecutive days. After 2 weeks, Western blot analyses showed a complete depletion of calpain-2 protein in the aorta from Cre+ mice compared to Cre- littermates. Male Cre+ and Cre- (N=12 each) mice were fed a Western diet and infused with saline or AngII (1,000 ng/kg/min) by osmotic minipumps for 2 weeks. AngII infusion significantly (P<0.05 vs saline) increased c-terminal fragmentation of cytoskeletal structural protein, talin and kinases such as integrin linked kinase-1 (ILK-1), and focal adhesion kinase in addition to filamin A. Inducible depletion of calpain-2 significantly (P<0.05; Cre+ vs Cre-) blunted AngII-induced fragmentation of talin, filamin A and ILK-1. Further siRNA mediated silencing of calpain-2 in aortic SMCs and fibroblasts significantly reduced AngII-induced fragmentation of filamin A and talin. Conclusion: These findings suggest that calpain-2 plays a critical role in AngII-induced cytoskeletal structural protein fragmentation during AAA development in mice.