Cystatin C Deficiency Promotes Inflammation in Angiotensin II-Induced Abdominal Aortic Aneurisms in Atherosclerotic Mice

An imbalance between cysteinyl cathepsins and their principal endogenous inhibitor cystatin C (CystC) may favor proteolysis in the pathogenesis of human abdominal aortic aneurysms (AAA), yet a direct role of CystC in AAA remains unproven. This study used CystC and apolipoprotein E (ApoE) compound mutant (CystC−/−ApoE−/−) mice to examine directly the role of cysteine protease/protease inhibitor imbalance in AAA formation in angiotensin II-induced AAA. CystC-deficiency increased lumenal diameter and lesion size compared with control mice. CystC−/− ApoE−/− lesions also demonstrated enhanced inflammatory cell accumulation, more severe elastin fragmentation, and fewer smooth muscle cells in the tunica media. Macrophage content, measured as percent positive area (23.2 ± 1.4% versus 11.2 ± 1.4%; P = 0.0003) and number of the CD4+ T cells (ninefold; P = 0.048), increased significantly in CystC−/−ApoE−/− lesions. CystC deficiency increased cathepsin activity (5.5 fold; P = 0.001) in AAA, yielding greater elastin degradation and proangiogenic laminin-5 γ2 peptide production, which may account for increased microvascularization in CystC−/−ApoE−/− compared with ApoE−/− lesions. Increased leukocyte adhesion molecule VCAM-1 expression and leukocyte proliferation might also promote inflammation in CystC-deficient AAA. These data indicate that CystC contributes to experimental AAA pathogenesis and that enhanced cysteine protease activity, due to the lack of CystC, favors inflammation in AAA lesions induced in atherosclerotic mice by promoting microvascularization and smooth muscle cell apoptosis as well as leukocytes adhesion and proliferation.