Cysteine protease cathepsins in cardiovascular disease: from basic research to clinical trials

Cysteine protease cathepsins have traditionally been considered as lysosome-restricted proteases that mediate proteolysis of unwanted proteins. However, studies from the past decade demonstrate that these proteases are localized not only in acidic compartments (endosomes and lysosomes), where they participate in intracellular protein degradation, but also in the extracellular milieu, plasma membrane, cytosol, nucleus, and nuclear membrane, where they mediate extracellular matrix protein degradation, cell signalling, and protein processing and trafficking through the plasma and nuclear membranes and between intracellular organelles. Studies in experimental disease models and on cathepsin-selective inhibitors, as well as plasma and tissue biomarker data from animal models and humans, have verified the participation of cysteinyl cathepsins in the pathogenesis of many cardiovascular diseases, including atherosclerosis, myocardial infarction, cardiac hypertrophy, cardiomyopathy, abdominal aortic aneurysms, and hypertension. Clinical trials of cathepsin inhibitors in chronic inflammatory diseases suggest the utility of these inhibitors for the treatment of cardiovascular diseases and associated complications. Moreover, development of cell transfer technologies that enable ex vivo cell treatment with cathepsin inhibitors might limit the unwanted systemic effects of cathepsin inhibition and provide new avenues for targeting cysteinyl cathepsins. In this Review, we summarize the available evidence implicating cysteinyl cathepsins in the pathogenesis of cardiovascular diseases, discuss their potential as biomarkers of disease progression, and explore the potential of cathepsin inhibitors for the treatment of cardiovascular diseases.