Cellular expression of cathepsin proteases in symptomatic and asymptomatic AAA

Abstract

Background: Inflammatory and proteolytic processes are playing a pivotal role in formation and rupture of abdominal aortic aneurysm (AAA) [1]. Thus, load bearing collagenous and elastic fibres are potential substrates of the highly potent cathepsin proteases in aortic wall. While in general an over expression of several cathepsins parallel to severe inhibitor deficiency (Cystatin C) has already been described [2] the specific expression of cathepsin-subtypes of the various cells in the wall of symptomatic and asymptomatic AAA remains unknown. In this study we analysed therefore the co-expression of cathepsin-B, D, S,-K,-L, und Cystatin C with vascular smooth muscle cells (vSMC), inflammatory infiltrates (IF), macrophages (MC) and neovascularisations (NV) in the wall of symptomatic and asymptomatic AAA. Material und Methods: Aortic wall samples of 4 symptomatic, 17 asymptomatic AAA patients and 6 organ donors were operatively retrieved, histologically processed and consecutively analysed. The aortic tissues sections were then routinely stained with hematoxylin and eosin (HE) and Elastica van Gieson (EvG) to assess the tissue structure of all AAA samples, their cellular composition, degree of infiltration with inflammatory cells and the content of elastin and collagen fibres. For differentiation of cathepsin-B,-D,-S,-K,-L, cystatin C expression and the various aortic wall cells immunostaining was performed (NV: factor VIII; vSMCs; SM-actin; MC: CD68; IF: CD45, CD3). In addition, co-expressions of cathepsins with the corresponding aortic wall cell types were detected by antibody double staining and analysed semi-quantitatively. Results: In comparison to control AAA wall samples showed significantly higher expression of cathepsin-D and-S (p<0.05). Moreover, aortic wall specimen of symptomatic AAA showed significantly higher expression of cathepsin-D and in particular of cathepsin-S than asymptomatic patients. Thereby overexpression of cathepsin-D and cathepsin-S was associated strongly with the density of macrophages, less with inflammatory infiltrates and scarcely with vSMC and NV. Furthermore, collagenous and elastin fibre degradation was significantly correlated to cathepsin-D and-S overexpression, in particular in symptomatic AAA (R=0.6). In contrast, all aneurysm wall samples were only weak positive for cathepsin inhibitor cystatin C. With the exception of cathepsin-D in vSMC all cathepsins showed only minimal or none expression in non aneurysmatic aortic wall of control patients. Comparable low expression was found for cathepsin-B,-K,-L in AAA wall. Conclusion: Of all cathepsin-subtypes studied only Cathepsin-D and-S seem to be relevant for structure protein degradation in aortic aneurysm wall. Particularly in symptomatic patient main sources of cathepsin-D und-S expression are inflammatory cells as macrophages and mono-lymphocytic infiltrates witch may contribute therefore to proteolytic destabilisation of AAA wall. These findings confirm and complete previous reports about cathepsines in AAA [3]. However, further studies and quantitative analyses are needed to define the precise role of cathepsin-D and-S in AAA formation and rupture.