Journal Article

Degraded collagen induces calpain-mediated apoptosis and destruction of the X-chromosome-linked inhibitor of apoptosis (xIAP) in human vascular smooth muscle cells

Karin von Wnuck Lipinski, Petra Keul, Susann Lucke, Gerd Heusch, Jeremias Wohlschlaeger, Hideo A. Baba and Bodo Levkau

in Cardiovascular Research

Published on behalf of European Society of Cardiology

Volume 69, issue 3, pages 697-705
Published in print February 2006 | ISSN: 0008-6363
Published online February 2006 | e-ISSN: 1755-3245 | DOI: http://dx.doi.org/10.1016/j.cardiores.2005.08.005
Degraded collagen induces calpain-mediated apoptosis and destruction of the X-chromosome-linked inhibitor of apoptosis (xIAP) in human vascular smooth muscle cells

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Abstract

Objective: The extracellular matrix (ECM) of the atherosclerotic lesion is a crucial determinant of its stability, while its degradation by matrix metalloproteinases (MMPs) has been implied in plaque rupture. As accumulation of both MMP-derived collagen fragments and apoptotic smooth muscle cells (SMC) is observed at sites of plaque rupture, we tested the effect of polymerized and degraded type I collagen on the susceptibility of SMC to apoptosis.

Methods: Human SMC were cultured on monomeric or polymerized collagen, and collagen gels were degraded by collagenase. Apoptosis was evaluated using antibodies to active caspases and their substrates. Calpain and caspase activity were measured using fluorogenic substrates.

Results: Culture of SMC on polymerized collagen led to increased apoptosis compared to culture on monomeric collagen. In addition, we observed a distinct proteolytic degradation of the endogenous caspase inhibitor X-chromosome-linked inhibitor of apoptosis (xIAP). As MMP-1 was strongly activated in SMC on polymerized collagen, we examined the effect of degraded collagen fragments on xIAP cleavage and apoptosis. Degraded collagen induced rapid proteolytic processing of xIAP identical to that on polymerized collagen. We identified calpains as the proteolytic enzymes responsible for xIAP processing as: i) they were rapidly activated by degraded collagen; ii) recombinant calpain II processed xIAP in an identical manner, and iii) inhibition of calpains by BAPTA or calpeptin abrogated xIAP degradation in intact cells. The functional consequence of xIAP processing by calpains was a loss of its caspase-inhibitory potential. Calpain activation distinctly preceded caspase activation, and inhibition of calpains suppressed apoptosis.

Conclusions: Collagen fragments proteolytically released from the ECM by MMPs may propagate apoptosis of SMC by calpain-mediated inactivation of anti-apoptotic proteins such as xIAP. This may be a novel mechanism of SMC apoptosis in biological settings of enhanced collagen degradation such as vascular remodeling, neointima formation, and atherosclerotic plaque rupture.

Keywords: Apoptosis; Smooth muscle; Calpain; Extracellular matrix; Matrix metalloproteinases

Journal Article.  5677 words.  Illustrated.

Subjects: Cardiovascular Medicine

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