Abstract 587: Leukocyte Calpain Deficiency Reduces Angiotensin II-induced Inflammation and Atherosclerosis in Hypercholesterolemic Mice

Abstract

Background and Objective: Chronic angiotensin II (AngII) infusion promotes atherosclerosis and abdominal aortic aneurysms (AAAs) in mice. Recently, we demonstrated that pharmacological inhibition of calpain-1 and -2 (a class of calcium-activated, neutral cysteine proteases) attenuated AngII-induced atherosclerosis, AAAs, and medial macrophage accumulation in mice. Using mice that overexpress calpastatin (CAST), the endogenous inhibitor of ubiquitous calpain-1 and -2 or mice with specific deficiency of calpain-1 or -2, the purpose of this study was to determine whether calpains in bone marrow (BM)-derived cells contribute to AngII-induced atherosclerosis and AAAs in hypercholesterolemic mice. Methods and Results: Irradiated male LDL receptor -/- mice were repopulated with BM-derived cells that were harvested from either wild type (WT) or CAST overexpression transgenic (Tg) mice. Four weeks after BM repopulation, recipient mice were fed a saturated fat-enriched diet and infused with either saline or AngII (1,000 ng/kg/min) for 4 weeks. AngII infusion increased systolic blood pressure equivalently in both genotypes. Ex vivo measurement of maximal diameter of abdominal aorta showed a comparable dilation in WT and Tg mice (1.28 ± 0.11 versus 1.32 ± 0.08 mm, P = NS). Interestingly, overexpression of CAST in BM-derived cells significantly attenuated AngII-induced atherosclerotic lesion formation in aortic arches by en face measurement (Intimal lesions: WT = 19.9 ± 1.8 % vs Tg = 9.9 ± 1.0 %; n=14, P<0.05). Using either BM cells-derived from calpain-1 deficient mice or mice with leukocyte-specific calpain-2 deficiency (Calpain-2f/f LysM Cre), further studies demonstrated that deficiency of either calpain-1 or -2 in leukocytes resulted in a modest, but significant, (P<0.05) decrease in AngII-induced atherosclerosis (Calpain-1: WT- 15 ± 1.2 % vs KO- 10 ± 0.96 %; Calpain-2f/f: LysM Cre WT-16 ± 1.4 % vs KO-11 ± 1.2 %). CAST overexpression significantly attenuated AngII-induced inflammatory responses in macrophages in vivo, and suppressed macrophage migration towards MCP-1 and adhesion to endothelial cells in vitro. Conclusion: Calpain inhibition in BM-derived cells attenuated AngII-induced atherosclerosis by influencing macrophage function.