Person:

Chen, Han

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.