Increased expression of elastolytic cathepsins S, K, and V and their inhibitor cystatin C in stenotic aortic valves

Objective-To investigate the possible role of elastolytic cathepsins S, K, and V and their endogenous inhibitor cystatin C in adverse extracellular matrix remodeling of stenotic aortic valves. Methods and Results-Stenotic aortic valves were collected at valve replacement surgery and control valves at cardiac transplantations. The expression of cathepsins S, K, and V and cystatin C was studied by conventional and real-time polymerase chain reaction and by immunohistochemistry. Total cathepsin activity in the aortic valves was quantified by a fluorometric microassay. When compared with control valves, stenotic valves showed increased mRNA expression of cathepsins S, K, and V (P < 0.05 for each) and a higher total cathepsin activity (P < 0.001). In stenotic valves, cystatin C mRNA was increased (P < 0.05), and cystatin C protein was found particularly in areas with infiltrates of inflammatory cells. Both cathepsin S and cystatin C were present in bony areas of the valves, whereas cathepsin V localized to endothelial cells in areas rich of neovascularization. Incubation of thin sections of aortic valves with cathepsins S, K, and V resulted in severe disruption of elastin fibers, and this cathepsin effect could be blocked by adding cystatin C to the incubation system.