Person:

Sun, Jiusong

Abdominal aortic aneurysm (AAA), an inflammatory disease, involves leukocyte recruitment, immune responses, inflammatory cytokine production, vascular remodeling, neovascularization, and vascular cell apoptosis, all of which contribute to aortic dilatation. This study demonstrates that mast cells, key participants in human allergic immunity, participate in AAA pathogenesis in mice. Mast cells were found to accumulate in murine AAA lesions. Mast cell–deficient KitW-sh/KitW-sh mice failed to develop AAA elicited by elastase perfusion or periaortic chemical injury. KitW-sh/KitW-sh mice had reduced aortic expansion and internal elastic lamina degradation; decreased numbers of macrophages, CD3+ T lymphocytes, SMCs, apoptotic cells, and CD31+ microvessels; and decreased levels of aortic tissue IL-6 and IFN-γ. Activation of mast cells in WT mice via C48/80 injection resulted in enhanced AAA growth while mast cell stabilization with disodium cromoglycate diminished AAA formation. Mechanistic studies demonstrated that mast cells participated in angiogenesis, aortic SMC apoptosis, and matrix-degrading protease expression. Reconstitution of KitW-sh/KitW-sh mice with bone marrow–derived mast cells from WT or TNF-α–/– mice, but not from IL-6–/– or IFN-γ–/– mice, caused susceptibility to AAA formation to be regained. These results demonstrate that mast cells participate in AAA pathogenesis in mice by releasing proinflammatory cytokines IL-6 and IFN-γ, which may induce aortic SMC apoptosis, matrix-degrading protease expression, and vascular wall remodeling, important hallmarks of arterial aneurysms.

Objective: Cathepsin K (CatK) is one of the most potent mammalian elastases. We have previously shown increased expression of CatK in human abdominal aortic aneurysm (AAA) lesions. Whether this protease participates directly in AAA formation, however, remains unknown. Methods and Results: Mouse experimental AAA was induced with aortic perfusion of a porcine pancreatic elastase. Using this experimental model, we demonstrated that absence of CatK prevented AAA formation in mice 14 days postperfusion. CatK deficiency significantly reduced lesion CD4 T-cell content, total lesion and medial cell proliferation and apoptosis, medial smooth muscle cell (SMC) loss, elastinolytic CatL and CatS expression, and elastin fragmentation, but it did not affect AAA lesion Mac-3 macrophage accumulation or CD31 microvessel numbers. In vitro studies revealed that CatK contributed importantly to CD4 T-cell proliferation, SMC apoptosis, and other cysteinyl cathepsin and matrix metalloproteinase expression and activities in SMCs and endothelial cells but played negligible roles in microvessel growth and monocyte migration. AAA lesions from CatK-deficient mice showed reduced elastinolytic cathepsin activities compared with those from wild-type control mice. Conclusion: This study demonstrates that CatK plays an essential role in AAA formation by promoting T-cell proliferation, vascular SMC apoptosis, and elastin degradation and by affecting vascular cell protease expression and activities.

Objective—The development of abdominal aortic aneurysms (AAA) requires extensive aortic wall matrix degradation. Human AAA lesions express high levels of cathepsin L (CatL), one of the most potent mammalian elastases. Whether this protease participates directly in AAA pathogenesis, however, is unknown.

Methods and Results—We generated experimental AAA with aortic elastase perfusion in mice and established an essential role of CatL in AAA formation. After 14 days postperfusion, most wild-type (Ctsl+/+) mice developed AAA, but none of the CatL-deficient (Ctsl−/−) mice did. AAA lesion macrophage contents, CD4+ T cell numbers, CD31+ and laminin-5 angiogenic fragment γ2+ microvessel numbers, and elastin fragmentation were all significantly lower in Ctsl−/− mice than in Ctsl+/+ mice. While lesions from Ctsl−/− mice contained fewer Ki67+ proliferating cells than did Ctsl+/+ mice, the absence of CatL did not affect lesion apoptotic cell contents or medial smooth-muscle cell loss significantly. Mechanistic studies indicated that the absence of CatL reduced lesion chemokine monocyte chemotactic protein-1 content, macrophage and T-cell in vitro transmigration, and angiogenesis, and altered the expression and activities of matrix metalloproteinases and other cysteinyl cathepsins in inflammatory cells, vascular cells, and AAA lesions.

Conclusion—CatL contributes to AAA formation by promoting lesion inflammatory cell accumulation, angiogenesis, and protease expression.

The cysteine protease cathepsin L is one of the most potent mammalian elastases and collagenases, widely expressed at basal levels in most tested tissues and cell types, and regulated by pro-inflammatory stimuli. The inflammatory arterial diseases abdominal aortic aneurysm (AAA) and atherosclerosis involve extensive vascular remodeling that requires elastolysis and collagenolysis. This study examined the hypothesis that cathepsin L is over-expressed in human AAA and atherosclerotic lesions and its expression in vascular cell types found in these lesions is regulated by pro-inflammatory cytokines. Immunohistochemical and tissue extract immunoblot analysis demonstrated increased expression of cathepsin L in human AAA and atheromata and localized its expression to lesional smooth muscle cells (SMC), endothelial cells (EC), and macrophages. In primary cultured human SMC, EC, and monocyte-derived macrophages, pro-inflammatory cytokines or growth factors induced the expression of cathepsin L and its activity against extracellular collagen and elastin. Patients with coronary artery stenosis (n = 65) had higher serum cathepsin L levels than those without lesions detectable by quantitative coronary angiography (n = 30) (1.47 ± 0.33 ng/ml versus 0.60 ± 0.06 ng/ml, p < 0.02). A strong correlation between the percent of stenosis of left anterior descending coronary artery and serum cathepsin L levels in patients with stenosis (R = 0.542, p < 0.0001), also suggests involvement of cathepsin L in these vascular diseases.