Enhanced expression of vascular matrix metalloproteinases induced in vitro by cytokines and in regions of human atherosclerotic lesions.

Dysregulated extracellular matrix (ECM) metabolism may contribute to vascular remodeling during atherogenesis. The ability of vascular cells to synthesize the components of ECM is well characterized, but less is known about their capacity to degrade ECM and the factors that may regulate this process. We therefore studied the expression of matrix metalloproteinases (MMPs), enzymes that degrade various components of ECM, and of tissue inhibitors of MMPs (TIMPs) by untreated or cytokine-stimulated human smooth muscle cells (SMC). Messenger RNA was studied by Northern blotting, and proteins secreted in culture by SMC were identified by immunoprecipitation. Gelatinolytic and caseinolytic activity of MMPs was detected zymographically. SMC constitutively produced a 72 kDa type IV gelatinase (GL), TIMP-1, and TIMP-2. Upon stimulation with IL1 or TNF alpha, SMC synthesized in addition 92 kDa GL, stromelysin, and interstitial collagenase, MMPs that together can degrade all of the ECM components. IL1 or TNF alpha did not alter the level of TIMP mRNA and protein, suggesting that a net excess of MMP production under these conditions may promote breakdown of the vascular ECM. To test the in vivo relevance of these in vitro findings, we analyzed immunohistochemically normal human arteries and carotid atheromas. Normal tissue and the medial layer underlying lesions stained uniformly for 72 kDa GL and TIMPs 1 and 2. Lesions showed regionally increased MMP expression: the shoulders of atherosclerotic plaques contained stromelysin and 92 kDa GL associated with SMC, and clusters of macrophage-derived foam cells associated with the lipid core stained intensely for all MMPs studied. Endothelial cells covering atheroma or of the plaque microvasculature contained interstitial collagenase. In pathological conditions associated with local release of cytokines in the vessel wall, enhanced regional expression of vascular MMPs may contribute to SMC migration and weakening of matrix that would favor plaque rupture, events associated with the development or complication of the atherosclerotic lesions.

Cytokine-stimulated human vascular smooth muscle cells synthesize a complement of enzymes required for extracellular matrix digestion.

Vascular matrix remodeling occurs during development, growth, and several pathological conditions that affect blood vessels. We investigated the capacity of human smooth muscle cells (SMCs) to express matrix metalloproteinases (MMPs), enzymes that selectively digest components of the extracellular matrix (ECM), in the basal state or after stimulation with certain cytokines implicated in vascular homeostasis and pathology. Enzymatic activity associated with various proteins secreted in the culture media was detected by gelatin or casein sodium dodecyl sulfate-polyacrylamide gel electrophoresis zymography. Proteins were identified by immunoprecipitation and mRNA by Northern blotting. SMCs constitutively secreted a 72-kD gelatinase and the tissue inhibitors of MMPs (TIMPs) types 1 and 2. SMCs stimulated with interleukin-1 or tumor necrosis factor-alpha synthesized de novo 92-kD gelatinase, interstitial collagenase, and stromelysin. Several lines of evidence suggest that when stimulated by cytokines, SMCs produce activated forms of MMPs. Together, the constitutive and the cytokine-induced enzymes can digest all the major components of the vascular ECM. Moreover, since these mediators augment the production of MMPs without appreciably affecting the synthesis of TIMPs, locally secreted cytokines may tip the regional balance of MMP activity in favor of vascular matrix degradation.