Intimal thickening, the accumulation of cells and extracellular matrix within the inner vessel wall, is a physiological response to mechanical injury, increased wall stress, or chemical insult (e.g., atherosclerosis). If excessive, it can lead to the obstruction of blood flow and tissue ischemia. Together with expansive or constrictive remodeling, the extent of intimal expansion determines final lumen size and vessel wall thickness. Plaque rupture represents a failure of intimal remodeling, where the fibrous cap overlying an atheromatous core of lipid undergoes catastrophic mechanical breakdown. Plaque rupture promotes coronary thrombosis and myocardial infarction, the most prevalent cause of premature death in advanced societies. The matrix metalloproteinases (MMPs) can act together to degrade the major components of the vascular extracellular matrix. All cells present in the normal and diseased blood vessel wall upregulate and activate MMPs in a multistep fashion driven in part by soluble cytokines and cell-cell interactions. Activation of MMP proforms requires other MMPs or other classes of protease. MMP activation contributes to intimal growth and vessel wall remodeling in response to injury, most notably by promoting migration of vascular smooth muscle cells. A broader spectrum and/or higher level of MMP activation, especially associated with inflammation, could contribute to pathological matrix destruction and plaque rupture. Inhibiting the activity of specific MMPs or preventing their upregulation could ameliorate intimal thickening and prevent myocardial infarction.

Intimal thickening occurs in blood vessels in response to injury or atherosclerosis. The balance of migration and proliferation of vascular smooth muscle cells (VSMC) over death by apoptosis has an important impact on the final size of intimal thickening and may also affect atherosclerotic plaque stability. All aspects of VSMC behaviour are under coordinated control by growth factors, cell-matrix and cell-cell interactions. We review the evidence that matrix-degrading metalloproteinases (MMPs) regulate migration, proliferation and survival of VSMC. Moreover, we discuss critically the underlying mechanisms, which include changing growth factor availability and remodelling cell-matrix and cell-cell contacts. We conclude that MMPs influence VSMC behaviour by cleaving both matrix and non-matrix substrates.

Matrix metalloproteinase (MMPs) enzymes are implicated in matrix remodelling during proliferative inflammatory processes including wound healing. We report here synergistic upregulation of MMP-9 protein and mRNA by platelet-derived growth factor (PDGF) or basic fibroblast growth factor (bFGF) in combination with interleukin-1K K (IL-1K K) or tumour necrosis factor-K K (TNF-K K) in primary rabbit and human dermal fibroblasts. The synergistic interaction between growth factors and cytokines implies that basement membrane remodelling is maximal physiologically when both are present together. The signalling pathways mediating this synergistic regulation are not understood, although analysis of the MMP-9 promoter has identified an essential proximal AP-1 element and an upstream nuclear factor kappa-B (NF-U UB) site. Using electromobility shift assays, binding to the AP-1 site was only slightly increased by growth factors and cytokines. NF-U UB binding was rapidly induced by IL-1K K or TNF-K K but was neither induced nor potentiated by bFGF or PDGF. Neither AP-1 nor NF-U UB was therefore sufficient on its own for synergistic regulation. Using a recently developed adenovirus that overexpresses the inhibitory subunit, IU UBK K, we demonstrated an absolute requirement for NF-U UB in upregulation of MMP-9. Activation of NF-U UB binding by inflammatory cytokines was therefore necessary but not sufficient for synergistic upregulation of MMP-9.z 1998 Federation of European Biochemical Societies.

Abstract-Matrix metalloproteinases (MMPs) can degrade strength-giving collagens and other structural proteins of the arterial extracellular matrix. Overproduction of MMPs by monocyte/macrophages could therefore promote atherosclerotic plaque rupture and myocardial infarction. Freshly-recruited monocyte macrophages appear to use a prostaglandin (PG)-dependent pathway to coordinately upregulate a broad and potentially highly-destructive spectrum of MMPs. is an important contributory cause of atherosclerotic plaque rupture, which underlies most cases of myocardial infarction. 1 Net loss of collagen, which normally provides the main tensile strength of the artery wall, closely colocalizes with areas of activated foam-cell macrophages especially at so-called "shoulder regions." 2 Advanced plaques show large lipid cores in which macrophages are often present and the ECM has been extensively degraded. Advanced lesions also have a hypo-cellular fibrous cap probably attributable to death of macrophages and vascular smooth muscle cells (VSMCs). Recent evidence has revealed considerable diversity in the monocyte and macrophage populations in plaques. Two monocytes subsets have been defined, and plaques shown to attract predominantly the more inflammatory phenotype. 3 A variety of macrophage phenotypes have also been defined, 4 and at least 2 of these (so-called M1 and M2) were recently shown to be present in atherosclerotic plaques. 5 Lipopolysaccharide (LPS) and inflammatory cytokines such as tumor necrosis factor (TNF)-␣, interleukin (IL)-1␤, and interferon (IFN)-␥ are all believed to induce the M1 macrophage phenotype. 4 The alternative, so-called M2, macrophage phenotype is generated in response to cytokines that include IL-4. 4 The roles of these different macrophage phenotypes in plaque progression and instability are just beginning to be investigated.Macrophages secrete several classes of neutral extracellular proteases, including serine proteases, cathepsins, and metalloproteinases (MMPs). 6 Although these proteases act in concert, for limitations of space, this review focuses on the MMPs. MMPs are a family of some 23 genetically related proteins that share a common Zn 2ϩ -based catalytic mechanism. 7 MMP activity is increased by transcription of MMP proform genes and activation of proenzymes by proteolytic cascades, often (but not always) mediated by induction of other MMPs. 7 Inactivation is largely by binding to endogenous tissue inhibitors of MMPs (TIMPs). 7 Collectively MMPs have the ability to completely degrade collagen and most other ECM components 7 ; they also modify other soluble and cell surface proteins, including cytokines and chemokines, leading to regulation of plaque cell behavior including migration proliferation and death. 8 The reasons for considering MMPs culprits in plaque rupture are discussed in several recent reviews. 6,9,10 Briefly summarized, studies consistently demonstrate colocalization of MMPs with areas of degraded ECM in human plaques. Several, although not all, MMP knockout a...

Matrix metalloproteinases (MMPs) are thought to be involved in the growth, destabilization, and eventual rupture of atherosclerotic lesions. Using the mouse brachiocephalic artery model of plaque instability, we compared apolipoprotein E (apoE)͞MMP-3, apoE͞MMP-7, apoE͞MMP-9, and apoE͞MMP-12 double knockouts with their age-, strain-, and sex-matched apoE single knockout controls. Brachiocephalic artery plaques were significantly larger in apoE͞MMP-3 and apoE͞MMP-9 double knockouts than in controls. The number of buried fibrous layers was also significantly higher in the double knockouts, and both knockouts exhibited cellular compositional changes indicative of an unstable plaque phenotype. Conversely, lesion size and buried fibrous layers were reduced in apoE͞MMP-12 double knockouts compared with controls, and double knockouts had increased smooth muscle cell and reduced macrophage content in the plaque, indicative of a stable plaque phenotype. ApoE͞MMP-7 double knockout plaques contained significantly more smooth muscle cells than controls, but neither lesion size nor features of stability were altered in these animals. Hence, MMP-3 and MMP-9 appear normally to play protective roles, limiting plaque growth and promoting a stable plaque phenotype. MMP-12 supports lesion expansion and destabilization. MMP-7 has no effect on plaque growth or stability, although it is associated with reduced smooth muscle cell content in plaques. These data demonstrate that MMPs are directly involved in atherosclerotic plaque destabilization and clearly show that members of the MMP family have widely differing effects on atherogenesis.animal models ͉ atherosclerosis M atrix metalloproteinases (MMPs) are a group of Ͼ20 zinccontaining endopeptidases that are either secreted or expressed at the cell surface of all of the main vascular cell types. MMPs have overlapping specificities, but each can process at least one extracellular matrix component, and many nonmatrix substrates have also been described. Given this complexity it is not surprising that multiple roles for MMPs have been proposed, including regulation of cell migration, proliferation, and death. As a result, roles for MMPs in atherosclerotic plaque growth and fibrous cap formation have been suggested (1). On the other hand, the presence of elevated mRNA, protein, and activity levels of MMPs within atherosclerotic lesions, particularly at the shoulder regions of the fibrous cap (2-5), has led to the suggestion that they degrade strength-giving extracellular matrix components, including fibrillar collagens. By this mechanism MMPs could promote atherosclerotic plaque destabilization, the main cause of myocardial infarction in humans.Intervention studies in animal models have been used to investigate the potential roles of MMPs in cardiovascular disease. For example, inhibition of MMP activity by adenovirusmediated delivery of the gene for human tissue inhibitor of metalloproteinases (TIMP)-1 reduced lesion size in the aortic root of apolipoprotein E (apoE) knockout mice (6). H...

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The existence of endothelium-derived vascular relaxant factor (EDRF) was postulated by Furchgott and colleagues when they observed that acetylcholine paradoxically relaxed preconstricted aortic strip preparations by an endothelium-dependent mechanism. This phenomenon has since been demonstrated in different blood vessels and mammalian species and it can be elicited by several other agents. EDRF has been thought to be a humoral agent, a lipoxygenase derivative and possibly a free radical. In the study reported here, by using aortic preparations from the rabbit, alone and in cascade experiments with isolated perfused coronary preparations, we demonstrate definitively that EDRF is a humoral agent. It is released from unstimulated aortic preparations containing endothelium, its release can be stimulated for prolonged periods by acetylcholine, and it is not a lipoxygenase derivative or free radical but an unstable compound with a carbonyl group at or near its active site.

Objective-Production of several metalloproteinases (MMPs) from smooth muscle cells (SMCs) and macrophages causes matrix destruction and atherosclerotic plaque instability. Statins, which inhibit HMG-CoA reductase and hence cholesterol and isoprenoid synthesis, stabilize plaques. We investigated whether statins inhibit MMP secretion from SMCs and macrophages. Methods and Results-We used human saphenous vein and rabbit aortic SMC and foamy macrophages from cholesterol-fed rabbits. Cerivastatin (50 nmol/L) inhibited inducible MMP-1, -3, and -9 secretion from human SMC by 52Ϯ19%, 71Ϯ18%, and 73Ϯ17%, respectively (PϽ0.01, nϭ3). Similar dose-related effects of cerivastatin (50 to 500 nmol/L), simvastatin (1 to 20 mol/L), and lovastatin (5 to 20 mol/L) were consistent with their relative potencies against HMG-CoA reductase. Statins also inhibited inducible MMP-1, -3, and -9 and constitutive MMP-2 secretion but not TIMP-1 or -2 secretion from rabbit SMC. Statins also dose-dependently inhibited MMP-1, -3, and -9 secretion from rabbit foam cells; cerivastatin (50 nmol/L) inhibited by 68Ϯ18%, 74Ϯ14%, and 74Ϯ14%, respectively (PϽ0.01, nϭ4 [3][4][5][6] Overexpression of MMPs, including MMP-1, MMP-3, and MMP-9, has been demonstrated in human and animal atherosclerotic plaques, [7][8][9][10][11][12][13][14][15][16] where it is colocalized with morphological and mechanical determinants of plaque rupture. MMPs together can catalyze the complete destruction of interstitial collagen, 17 which is the main component of fibrous caps responsible for their tensile strength. Loss of collagen leads to structural weakness and less resistance to the mechanical stresses imposed during systole. 18 This results ultimately in plaque rupture, the key event in triggering coronary thrombosis and hence acute coronary syndromes such as unstable angina and myocardial infarction. 19 Expression of MMPs-1, -3, and -9 is upregulated in cells present in atheromas, including endothelial cells, 20 VSMCs, 21-25 and macrophages. 26 -29 Inflammatory mediators, including interleukin-1 (IL-1), CD-40 ligand, and tumor necrosis factor-␣, upregulate MMP activity in vascular cells, especially in combination with platelet-derived growth factor (PDGF) or basic fibroblast growth factor. 23,25 Tissue inhibitors of metalloproteinases (TIMPs) are a family of naturally occurring specific inhibitors of MMPs whose activity in atherosclerotic plaques seems to correlate with decreased MMP activity 30,31 and hence reduced matrix remodelling.Statins are a structurally related group of hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase inhibitors that are widely used to treat hyperlipidemia. Their use is associated with significant reduction of adverse coronary events, including myocardial infarction, and a marginal regression of plaque size. 32,33 Furthermore, recent studies, both in vitro and in vivo, have suggested that the beneficial effects of statins may extend to mechanisms beyond cholesterol reduction. [33][34][35][36] These pleiotropic effects of statins are mediate...