Abstract 271: Mechanisms for the Generation of Potently Proteolytic Microvesicles from Human Macrophages After Tobacco Smoke Exposure: A Potential Role in Plaque Destabilization
BACKGROUND— Cigarette smoking greatly increases the risk of atherosclerotic plaque rupture and subsequent intravascular thrombosis, but the underlying mechanisms remain poorly understood. We recently reported that tobacco smoke induces human monocytes and macrophages to generate tissue factor-positive, procoagulant microvesicles (MVs, also known as microparticles).
AIMS— We now sought to determine whether exposure of human macrophages to tobacco smoke induces the release of MVs with proteolytic activity, what the nature of the major proteases on smoke-induced MVs might be, and what cellular mechanisms might be responsible for their production and release.
METHODS/RESULTS— We found that MVs released from human macrophages after exposure to tobacco smoke extract (TSE) carry substantial gelatinolytic and collagenolytic activities that, surprisingly, can be attributed to a single, dominant, transmembrane protease of the matrix metalloproteinase (MMP) superfamily - namely, MMP14 (also known as membrane type 1-MMP). Flow cytometric counts revealed that exposure of human macrophages to TSE for 20h more than quadrupled their production of MMP14-positive MVs (control: 1112±231, TSE-induced: 5823±2192 MMP14-positive MVs per μl of conditioned medium, mean±SEM, n=6, P<0.01). Based on our biochemical and confocal studies, the production of these MVs relies on a series of dynamic, regulated steps that include activation of the JNK and p38 MAP kinases, MAPK-dependent induction of cellular MMP14, cleavage of pro-MMP14 into its active mature form, a remarkable trafficking of MMP14 into nascent plasma membrane blebs, and finally caspase- and MAPK-dependent apoptosis and apoptotic blebbing.
CONCLUSION— The ability of tobacco smoke to induce expression of MMP14 by human macrophages, and then the activation and export of these molecules on MVs, may be novel contributors to increased risk of atherosclerotic plaque destabilization. Proteolytically active MVs induced by tobacco smoke may be novel mediators of matrix destruction in a variety of locations, including the fibrous cap of atheromata.
- © 2012 by American Heart Association, Inc.