Background and Objective: Recent clinical studies demonstrated that abdominal adiposity is associated with increased risk of abdominal aortic aneurysm (AAA) development. Calpains are non-lysosomal calcium dependent cysteine proteases that are highly expressed in human and experimental AAAs. Using a pharmacological inhibitor and genetically deficient mice, we identified that calpain-2 (a major ubiquitous isoform) plays a critical role in Angiotensin II (AngII)-induced AAA formation in mice. In addition, calpain inhibition strongly suppressed adipose tissue inflammation in obese mice. The purpose of this study was to determine the functional contribution of calpain-2 in obesity-accelerated AAA.
Methods and Results: Calpain-2 floxed mice that were hemizygous for β-actin Cre-ERT2 were produced by breeding male Cre-ERT2 to female calpain-2 floxed mice. At 8 weeks of age, male non-Cre littermates (Cre-) and Calp-2 x Cre-ERT2 (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 and periaortic adipose tissue from Cre+ mice compared to non-Cre littermates. Mice were fed a high fat diet (60% Kcal) for 20 weeks. After 16 weeks of diet feeding, mice were infused with AngII (1,000 ng/kg/min) by osmotic minipumps for 4 weeks. Depletion of calpain-2 had no effect on high fat diet-induced body weight gain, fat mass, glucose and insulin tolerance. Interestingly, calpain-2 depletion significantly attenuated AngII-induced expansion of ex-vivo maximal diameter of abdominal aortas in obese mice (Cre-: 1.4 ± 0.14; Cre+: 0.9 ± 0.04 mm; P<0.001). In addition, calpain-2 depletion significantly reduced the incidence of AngII-induced AAAs in mice (Cre-: 75%, Cre+: 7%; P< 0.001).
Conclusion: These findings suggest that calpain-2 plays a critical role in AngII-induced AAA development in diet-induced obese mice.