Abstract
Background and Objective: Chronic infusion of angiotensin II (AngII) induces abdominal aortic aneurysms (AAAs) in normal and hypercholesterolemic mice. Recently, we demonstrated that pharmacological inhibition of calpain-1 and -2 (a class of calcium-activated, neutral cysteine proteases) attenuated AngII-induced AAAs in mice. In addition, calpain-2 compensates for the loss of calpain-1 and promoted AngII-induced AAA formation in calpain-1 deficient mice. The purpose of this study was to determine the relative contribution of calpain-2 to AngII-induced AAA development. To perform this study, calpain-2 floxed mice were bred to express an inducible form of Cre under the control of the ubiquitous promoter, chicken α-actin (Cre-ERT2). Methods and Results: Calpain-2 floxed mice that were hemizygous for Cre-ERT2 in an LDLr -/- background were produced by breeding male LDLr -/- x Cre-ERT2 to female LDLr -/- x 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 from Cre+ mice compared to non-Cre littermates. Male Cre- (N=23) and Cre+ (N=21) mice were fed a saturated fat-enriched diet (21% wt/wt fat; 0.15% wt/wt cholesterol) for 5 weeks. After 1 week of diet feeding, mice were infused with AngII (1,000 ng/kg/min) by osmotic minipumps for 4 weeks. AngII increases in systolic blood pressures were not influenced by calpain-2 depletion (post-infusion Cre-: 187 ± 5; Cre+-: 190 ± 3 mm Hg). Depletion of calpain-2 had no effect on plasma cholesterol concentrations (Cre-: 1597 ± 43; Cre+: 1541 ± 63 mg/dL) during AngII infusion. Interestingly, depletion of calpain-2 significantly attenuated AngII-induced aortic luminal dilation (Cre-: 1.70 ± 0.08; Cre+: 1.0 ± 0.03 mm; P<0.001), and expansion of ex-vivo maximal diameters of abdominal aortas in mice (Cre-: 1.90 ± 0.13; Cre+: 1.1 ± 0.07 mm; P<0.001). In addition, calpain-2 depletion significantly reduced the incidence of AngII-induced AAAs (Cre-: 91%, Cre+: 30%; P< 0.001). Conclusion: These findings suggest that calpain-2 plays a critical role in the development of AngII-induced AAA formation in mice.
Published Version
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