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(Circulation Research. 2008;102:1529.)
© 2008 American Heart Association, Inc.

Molecular Medicine

Chronic Apoptosis of Vascular Smooth Muscle Cells Accelerates Atherosclerosis and Promotes Calcification and Medial Degeneration

Murray C.H. Clarke, Trevor D. Littlewood, Nichola Figg, Janet J. Maguire, Anthony P. Davenport, Martin Goddard, Martin R. Bennett

From the Division of Cardiovascular Medicine (M.C.H.C., T.D.L., N.F., M.R.B.) and Department of Clinical Pharmacology (J.J.M., A.P.D.), University of Cambridge, Addenbrooke’s Hospital; and Department of Histopathology (M.G.), Papworth Hospital, Cambridge, UK.

Correspondence to Martin R. Bennett, University of Cambridge, Division of Cardiovascular Medicine, Addenbrookes Centre for Clinical Investigation, Box 110, Addenbrookes Hospital, Hills Road, Cambridge CB2 2QQ, United Kingdom. E-mail mrb{at}mole.bio.cam.ac.uk

Vascular smooth muscle cell (VSMC) accumulation is implicated in plaque development. In contrast, VSMC apoptosis is implicated in plaque rupture, coagulation, vessel remodeling, medial atrophy, aneurysm formation, and calcification. Although VSMC apoptosis accompanies multiple pathologies, there is little proof of direct causality, particularly with the low levels of VSMC apoptosis seen in vivo. Using a mouse model of inducible VSMC–specific apoptosis, we demonstrate that low-level VSMC apoptosis during either atherogenesis or within established plaques of apolipoprotein (Apo)E^–/– mice accelerates plaque growth by two-fold, associated with features of plaque vulnerability including a thin fibrous cap and expanded necrotic core. Chronic VSMC apoptosis induced development of calcified plaques in younger animals and promoted calcification within established plaques. In addition, VSMC apoptosis induced medial expansion, associated with increased elastic lamina breaks, and abnormal matrix deposition reminiscent of cystic medial necrosis in humans. VSMC apoptosis prevented outward remodeling associated with atherosclerosis resulting in marked vessel stenosis. We conclude that VSMC apoptosis is sufficient to accelerate atherosclerosis, promote plaque calcification and medial degeneration, prevent expansive remodeling, and promote stenosis in atherosclerosis.

Key Words: VSMC • apoptosis • atherosclerosis • mouse models • calcification

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