Abstract 516: Calpain-2 Compensation Promotes Angiotensin II-induced Ascending and Abdominal Aortic Aneurysms in Calpain-1 Deficient Mice

Abstract

Background and Objective We demonstrated that angiotensin II (AngII)-infusion profoundly increased both aortic protein and activity of calpains, calcium-activated cysteine proteases, in mice. In addition, pharmacological inhibition of calpain attenuated AngII-induced abdominal aortic aneurysm (AA) in mice. Recent studies have shown that AngII infusion into mice leads to aneurysmal formation localized to the ascending aorta. However, the precise functional contribution of calpain isoforms (-1 or -2) in AngII-induced abdominal AA formation is not known. Similarly, a functional role of calpain in AngII-induced ascending AA remains to be defined. Using BDA-410, an inhibitor of calpains, and calpain-1 genetic deficient mice, we examined the relative contribution of calpain isoforms in AngII-induced ascending and abdominal AA development. Methods and Results Male LDLr-/- mice that were either calpain-1 +/+ or -/- were fed a saturated fat-enriched diet and infused with AngII (1,000 ng/kg/min) for 4 weeks. Calpain-1 deficiency had no effect on body weight or blood pressure during AngII infusion. Intimal areas of ascending aorta and maximum external width of the suprarenal abdominal aorta were measured by en face. Calpain-1 deficiency showed no discernible effects on AngII-induced ascending and abdominal AA development (P = NS). Interestingly, AngII infusion induced increased expression of calpain-2 protein, thus compensating for total calpain activity in aortas of calpain-1 deficient mice. Oral administration of BDA-410 along with AngII infusion significantly attenuated AngII-induced ascending (Vehicle - +/+: 15.0 ± 1.0, -/-: 14.9 ± 0.8; BDA: +/+: 11.5 ± 0.6, -/-: 12.1 ± 0.6 mm 2 ; P<0.05) and abdominal (Vehicle - +/+: 1.7 ± 0.1, -/-: 1.6 ± 0.1; BDA: +/+: 1.0 ± 0.1, -/-: 1.1 ± 0.1 mm; P<0.05) AA formation in both calpain-1 +/+ and -/- mice as compared to vehicle administered mice. Western blot and immunostaining analyses revealed BDA-410 administration attenuated AngII-induced C-terminal fragmentation of filamin A (P<0.05), an actin binding cytoskeletal protein, and medial macrophage accumulation in aorta. Conclusion Calpain-2 compensates for loss of calpain-1, and promotes AngII-induced ascending and abdominal AAs in calpain-1 deficient mice.