Inducible Depletion of Calpain-2 Mitigates Abdominal Aortic Aneurysm in Mice

BACKGROUND Cytoskeletal structural proteins maintain cell structural integrity by bridging extracellular matrix (ECM) with contractile filaments. During AAA development, (i) aortic medial degeneration is associated with loss of smooth muscle cell (SMC) integrity, and (ii) fibrogenic mesenchymal cells (FMSCs) mediates ECM remodeling. Calpains cleave cytoskeletal proteins that maintain cell structural integrity. Pharmacological inhibition of calpains exert beneficial effects on Angiotensin II (AngII)-induced AAAs in low density receptor deficient (LDLR-/-) mice. OBJECTIVES To evaluate the functional contribution of FMSCs-derived calpain-2 on (i) cytoskeletal structural protein and ECM alterations, and (ii) AAA progression. METHODS Calpain-2 protein, and cytoskeletal protein (e.g. filamin or talin) fragmentation in human and mice AAA tissues were assessed by immunohistochemical and western blot analyses. LDLR-/- mice that were either inducible-whole body or FMSC-specific calpain-2 deficient were fed a fat-enriched diet and infused with AngII for 4 weeks. The association of cytoskeletal protein to ECM was evaluated using aortic SMCs, in vitro. In addition, the effect of calpain-2 deficiency on the stability of established AAA was examined. RESULTS Calpain-2 protein, and filamin/talin fragmentation are significantly elevated in AAAs. Ubiquitous or FMSC-specific depletion of calpain-2 suppressed AngII-induced AAAs, filamin/talin fragmentation and promoted ECM protein, collagen. Calpain-2 silencing in SMCs reduced AngII-induced filamin/talin fragmentation. In addition, silencing of filamin or talin in SMCs significantly reduced collagen protein. Furthermore, calpain-2 deficiency suppressed established AAA rupture. CONCLUSION Calpain-2 activation promotes cytoskeletal structural protein fragmentation and ECM degradation of experimental AAA aortas. Treatment with calpain-2 specific inhibitor may facilitate the clinical management of AAA. ### Competing Interest Statement The authors have declared no competing interest. * AngII : angiotensin II AAA : abdominal aortic aneurysm LDL : low-density lipoprotein ECM : extracellular matrix SMC : smooth muscle cell