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(Circulation. 2009;119:1785-1794.)
© 2009 American Heart Association, Inc.

Valvular Heart Disease

Arterial and Aortic Valve Calcification Abolished by Elastolytic Cathepsin S Deficiency in Chronic Renal Disease

Elena Aikawa, MD, PhD; Masanori Aikawa, MD, PhD; Peter Libby, MD; Jose-Luiz Figueiredo, MD; Gabriel Rusanescu, PhD; Yoshiko Iwamoto, BS; Daiju Fukuda, MD, PhD; Rainer H. Kohler, PhD; Guo-Ping Shi, DSc; Farouc A. Jaffer, MD, PhD; Ralph Weissleder, MD, PhD

From the Center for Molecular Imaging Research (E.A., J.-L.F., G.R., Y.I., R.H.K., R.W.), Massachusetts General Hospital, Harvard Medical School, Boston; Donald W. Reynolds Cardiovascular Clinical Research Center on Atherosclerosis at Harvard Medical School (E.A., M.A., P.L., F.A.J., R.W.), Boston, Mass; Center for Systems Biology (R.W.), Massachusetts General Hospital, Boston; and Cardiovascular Division (M.A., P.L., D.F., G.-P.S.), Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, Mass.

Correspondence to Elena Aikawa, MD, PhD, Center for Molecular Imaging Research, Massachusetts General Hospital, Harvard Medical School, 149 13th St, Room 5420, Charlestown, MA 02129. E-mail eaikawa{at}mgh.harvard.edu

Received October, 10, 2008; accepted January 28, 2009.

Background— Clinical studies have demonstrated that 50% of individuals with chronic renal disease (CRD) die of cardiovascular causes, including advanced calcific arterial and valvular disease; however, the mechanisms of accelerated calcification in CRD remain obscure, and no therapies can prevent disease progression. We recently demonstrated in vivo that inflammation triggers cardiovascular calcification. In vitro evidence also indicates that elastin degradation products may promote osteogenesis. Here, we used genetically modified mice and molecular imaging to test the hypothesis in vivo that cathepsin S (catS), a potent elastolytic proteinase, accelerates calcification in atherosclerotic mice with CRD induced by 5/6 nephrectomy.

Methods and Results— Apolipoprotein-deficient (apoE^–/–)/catS^+/+ (n=24) and apoE^–/–/catS^–/– (n=24) mice were assigned to CRD and control groups. CRD mice had significantly higher serum phosphate, creatinine, and cystatin C levels than those without CRD. To visualize catS activity and osteogenesis in vivo, we coadministered catS-activatable and calcification-targeted molecular imaging agents 10 weeks after nephrectomy. Imaging coregistered increased catS and osteogenic activities in the CRD apoE^–/–/catS^+/+ cohort, whereas CRD apoE^–/–/catS^–/– mice exhibited less calcification. Quantitative histology demonstrated greater catS-associated elastin fragmentation and calcification in CRD apoE^–/–/catS^+/+ than CRD apoE^–/–/catS^–/– aortas and aortic valves. Notably, catS deletion did not cause compensatory increases in RNA levels of other elastolytic cathepsins or matrix metalloproteinases. Elastin peptide and recombinant catS significantly increased calcification in smooth muscle cells in vitro, a process further amplified in phosphate-enriched culture medium.

Conclusions— The present study provides direct in vivo evidence that catS-induced elastolysis accelerates arterial and aortic valve calcification in CRD, providing new insight into the pathophysiology of cardiovascular calcification.

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CLINICAL PERSPECTIVE

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Clinical Summaries
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