Sarah J. George

Divergent effects of tissue inhibitor of metalloproteinase-1, -2, or -3 overexpression on rat vascular smooth muscle cell invasion, proliferation, and death in vitro. TIMP-3 promotes apoptosis.

Tissue inhibitors of metalloproteinases (TIMPs) are a family of closely related secreted proteins that limit matrix metalloproteinase (MMP) activity and also have direct effects on cell growth. We used the highly efficient adenoviral delivery system to overexpress individual TIMPs from the cytomegalovirus immediate early promoter in rat aortic smooth muscle cells. Overexpression of TIMP-1, -2, or -3, or a synthetic MMP inhibitor similarly inhibited SMC chemotaxis and invasion through reconstituted basement membrane. TIMP-1 overexpression did not effect cell proliferation. By contrast, TIMP-2 caused a dose-dependent reduction in proliferation, an effect not mimicked by a synthetic MMP inhibitor. TIMP-3 overexpression induced DNA synthesis, and promoted SMC death by apoptosis, a phenotype reproduced by adding TIMP-3 to uninfected cells, but not by a synthetic MMP inhibitor. Our study is the first to compare systematically the effect of overexpression of three TIMPs in any cell. We found similar effects on invasion mediated by inhibition of MMP activity, but widely divergent effects on proliferation and death through actions of TIMP-2 and -3 independent of MMP inhibition. These findings have important implications for the physiological roles of TIMPs and their use in gene therapy.

Divergent effects of matrix metalloproteinases 3, 7, 9, and 12 on atherosclerotic plaque stability in mouse brachiocephalic arteries

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, apoE/MMP-7, apoE/MMP-9, and apoE/MMP-12 double knockouts with their age-, strain-, and sex-matched apoE single knockout controls. Brachiocephalic artery plaques were significantly larger in apoE/MMP-3 and apoE/MMP-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 apoE/MMP-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. ApoE/MMP-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.

Inhibition of Late Vein Graft Neointima Formation in Human and Porcine Models by Adenovirus-Mediated Overexpression of Tissue Inhibitor of Metalloproteinase-3

BACKGROUND Autologous saphenous vein coronary artery bypass graft surgery is complicated by late graft failure due to neointima formation and subsequent atherosclerosis. Growth factors and metalloproteinases (MMPs) act in concert to promote neointima formation. Tissue inhibitor of metalloproteinase-3 (TIMP-3), an extracellular matrix-associated MMP inhibitor, uniquely promotes apoptosis of isolated vascular smooth muscle cells. Here, we overexpressed TIMP-3 at the luminal surface of human saphenous veins before organ culture and in pig saphenous veins before interposition grafting into carotid arteries in vivo to assess neointima formation. METHODS AND RESULTS In both models, high TIMP-3 immunoreactivity occurred in the luminal and upper medial extracellular matrix after adenovirus delivery. MMP activity measured by in situ zymography was reduced throughout the veins, confirming a bystander effect. By use of 3 independent techniques, apoptosis levels in the neointima and medial layer were significantly elevated by TIMP-3 overexpression. Neointima formation was reduced by 84% in 14-day human organ cultures and by 58% in 28-day pig vein grafts (both P<0.05). In contrast, TIMP-2 overexpression had no effect on neointima formation in vivo. CONCLUSIONS Our results highlight the potential therapeutic benefit for TIMP-3 overexpression to reduce neointima formation associated with late vein graft failure.

Gene transfer of tissue inhibitor of metalloproteinase-2 inhibits metalloproteinase activity and neointima formation in human saphenous veins

Metalloproteinases (MMPs) are implicated in neointima formation and hence vein graft failure. Gene transfer to elevate local levels of tissue inhibitor of metalloproteinases (TIMPs) is therefore a potential treatment. In this study, we have used lumenal application of a replication-defective recombinant adenovirus to overexpress TIMP-2 and observe the effects on neointimal thickening in a well characterised human saphenous vein organ culture model. Increased TIMP-2 expression was localised to lumenal surface cells but nevertheless increased total functional TIMP-2 secretion after 14 days culture from 4.0 ± 2.0 to 21.8 ± 2.9 ng/mg wet weight/day (P < 0.05, n = 3). in situ zymography revealed a marked inhibition of gelatinolytic activity by timp-2 gene transfer throughout the vein segments. neointima formation and neointimal cell numbers were reduced 79% and 71%, respectively (p < 0.05; n = 8). timp-2 overexpression had no effect on smooth muscle cell proliferation, secretion of pro-mmp-2 or -9 and did not inhibit the processing of pro-mmp-2 to its active form. our data indicate that timp-2 overexpression reduces neointimal thickening, primarily by inhibiting mmp activity and hence smooth muscle cell migration.

Surgical preparative injury and neointima formation increase MMP-9 expression and MMP-2 activation in human saphenous vein

OBJECTIVES Injury stimulates smooth muscle cell (SMC) migration and proliferation by mechanisms that are incompletely understood. Surgical preparative injury is an important determinant of neointimal thickening in human saphenous vein bypass grafts. We investigate here whether basement-membrane-degrading metalloproteinases (MMPs) are stimulated by surgical preparation and culturing of human saphenous veins in organ culture. METHODS Secretion of MMP-2 and MMP-9 was measured by zymography and Western blotting. Sites of MMP secretion were localised by immunocytochemistry and in situ hybridisation. RESULTS Freshly isolated veins secreted pro-MMP-2 and much lower amounts of active MMP-2 and pro-MMP-9. MMP-2 was expressed in all cells whereas MMP-9 expression was confined to endothelial cells and at low levels to 55 +/- 10% (mean +/- s.e.m., n = 6) of medial SMC. Surgical preparative injury increased pro-MMP-2, active MMP-2 and pro-MMP-9 secretion. MMP-9 expression 3 h after surgical preparation occurred at high levels in 59 +/- 5% of medial SMC (P < 0.05 vs. freshly isolated, n = 6). Culturing in serum for 12 days increased pro-MMP-2, active MMP-2 and pro-MMP-9 secretion to equal levels in freshly isolated and surgically prepared veins. MMP-9 expression was greatest in the highly proliferative neointimal SMC and was more widespread in medial SMC of surgically prepared than freshly isolated veins (89 +/- 3 vs. 67 +/- 11%, n = 6, P < 0.05), paralleling the differences in proliferative index (18 +/- 3 vs. 8 +/- 4 cell/mm2, P < 0.05). CONCLUSIONS The data provide new insights into the mechanisms underlying human SMC proliferation. Activation of MMP-2 and increased MMP-9 expression are shown to be important components of the response to injury in this model. Furthermore, MMP-9 expression is closely associated with medial and neointimal SMC proliferation.

Suppression of Atherosclerotic Plaque Progression and Instability by Tissue Inhibitor of Metalloproteinase-2. Involvement of Macrophage Migration and Apoptosis

Background— Matrix metalloproteinase (MMP)–associated extracellular matrix degradation is thought to contribute to the progression and rupture of atherosclerotic plaques. However, direct evidence of this concept remains elusive. We hypothesized that overexpression of tissue inhibitor of metalloproteinase (TIMP)-1 or TIMP-2 would attenuate atherosclerotic plaque development and instability in high fat–fed apolipoprotein E–knockout (apoE−/−) mice. Methods and Results— Seventy male apoE−/− mice (n=10/group) fed a high-fat diet for 7 weeks were injected intravenously with first-generation adenoviruses expressing the gene for human TIMP-1 (RAdTIMP-1) or TIMP-2 (RAdTIMP-2) or a control adenovirus (RAd66) and were fed a high-fat diet for a further 4 weeks. Analysis of brachiocephalic artery plaques revealed that RAdTIMP-2 but not RAdTIMP-1 infection resulted in a marked reduction (48±13%, P<0.05) in lesion area compared with that in control animals. Markers associated with plaque instability, assessed by smooth muscle cell and macrophage content and the presence of buried fibrous caps, were significantly reduced by RAdTIMP-2. Effects on lesion size were not sustained with first-generation adenoviruses, but murine TIMP-2 overexpression mediated by helper-dependent adenoviral vectors exerted significant effects on plaques assessed 11 weeks after infection. In an attempt to determine the mechanism of action, we treated macrophages and macrophage-derived foam cells with exogenous TIMP-2 in vitro. TIMP-2 significantly inhibited migration and apoptosis of macrophages and foam cells, whereas TIMP-1 failed to exert similar effects. Conclusions— Overexpression of TIMP-2 but not TIMP-1 inhibits atherosclerotic plaque development and destabilisation, possibly through modulation of macrophage and foam cell behavior. Helper-dependent adenovirus technology is required for these effects to be maintained long term.

Dismantling of Cadherin-Mediated Cell-Cell Contacts Modulates Smooth Muscle Cell Proliferation

Abstract— Proliferation of vascular smooth muscle cells (VSMCs) contributes to intimal thickening during atherosclerosis and restenosis. The cadherins are transmembrane proteins, which form cell-cell contacts and may regulate VSMC proliferation. In this study, N-cadherin protein concentration was significantly reduced by stimulation of proliferation with fetal calf serum (FCS) and platelet-derived growth factor-BB (PDGF-BB) in human saphenous vein VSMCs. Furthermore, overexpression of a truncated N-cadherin, which acts as a dominant-negative increased VSMC proliferation. The amount of an extracellular fragment of N-cadherin (≈90 kDa) in the media after 24 hours was increased by 12-fold by FCS and 11-fold by PDGF-BB, suggesting that N-cadherin levels are regulated by proteolytic shedding. Incubation with a synthetic metalloproteinase inhibitor or adenoviral overexpression of the endogenous tissue inhibitors of metalloproteinases (TIMPs) demonstrated that metalloproteinase activity was responsible in part for this proteolysis. Although total levels of &bgr;-catenin protein were not affected, &bgr;-catenin was translocated to the nucleus after stimulation with FCS and PDGF-BB. Our data indicates cadherin-mediated cell-cell contacts modulate proliferation in VSMCs. Furthermore, disruption of N-cadherin cell-cell contacts mediated in part by metalloproteinase activity occurs during VSMC proliferation, releasing &bgr;-catenin and possibly inducing &bgr;-catenin-mediated intracellular signaling.

Regulation of Smooth Muscle Cell Proliferation by β-Catenin/T-Cell Factor Signaling Involves Modulation of Cyclin D1 and p21 Expression

We previously observed that stimulation of vascular smooth muscle cell (VSMC) proliferation with growth factors is associated with dismantling of cadherin junctions and nuclear translocation of &bgr;-catenin. In this study we demonstrate directly that growth factors stimulate &bgr;-catenin/T-cell factor (TCF) signaling in primary VSMCs. To determine whether &bgr;-catenin/TCF signaling regulates VSMC proliferation via modulation of the &bgr;-catenin/TCF responsive cell cycle genes, cyclin D1 and p21, we inhibited &bgr;-catenin/TCF signaling by adenoviral-mediated over-expression of N-Cadherin, ICAT (an endogenous inhibitor of &bgr;-catenin/TCF signaling), or a dominant negative (dn) mutant of TCF-4. N-cadherin, ICAT or dnTCF-4 over-expression significantly reduced proliferation of isolated human VSMCs by approximately 55%, 80%, and 45% respectively. Similar effects were observed in human saphenous vein medial segments where proliferation was reduced by approximately 55%. Transfection of dnTCF-4 in the ISS10 human VSMC line significantly lowered TCF and cyclin D1 reporter activity but significantly elevated p21 reporter activity, indicating regulation of these genes by &bgr;-catenin/TCF signaling. In support of this, over-expression of N-cadherin, ICAT or dnTCF-4 in isolated human VSMCs significantly lowered levels of cyclin D1 mRNA and protein levels. In contrast, over-expression of N-Cadherin, ICAT or dnTCF4 significantly elevated p21 mRNA and protein levels. In summary, we have demonstrated that increasing N-cadherin and inhibiting &bgr;-catenin/TCF signaling reduces VSMC proliferation, decreases the expression of cyclin D1 and increases levels of the cell cycle inhibitor, p21. We therefore suggest that the N-cadherin and &bgr;-catenin/TCF signaling pathway is a key modulator of VSMC proliferation via regulation of these 2 &bgr;-catenin/TCF responsive genes.

Proliferation, migration, matrix turnover, and death of smooth muscle cells in native coronary and vein graft atherosclerosis.

Smooth muscle cells migrate into the vascular intima, proliferate, and lay down extracellular matrix, thereby forming an important component of the occlusive mass of atherosclerotic plaques in native arteries and in saphenous vein grafts. The viability of smooth muscle cells and the integrity of their surrounding extracellular matrix also determine the liability of plaques to rupture and hence precipitate myocardial infarction and vein graft occlusion. This update reviews recent developments in the molecular understanding of relevant aspects of smooth muscle cell biology. It highlights the increasing importance attached to interactions between growth factors and components of the extracellular matrix in regulating migration and proliferation and the new roles assigned to apoptosis in these cells. It illustrates, furthermore, how the application of the techniques of molecular biology is identifying new targets for conventional and gene therapy.

Vulnerable atherosclerotic plaque metalloproteinases and foam cell phenotypes

Plaque rupture underlies most myocardial infarctions. Plaques vulnerable to rupture have thin fibrous caps, an excess of macrophages over vascular smooth muscle cells, large lipid cores, and depletion of collagen and other matrix proteins form the cap and lipid core. Production of matrix metalloproteinases from macrophages is prominent in human plaques, and studies in genetically modified mice imply a causative role for metalloproteinases in plaque vulnerability. Recent in-vitro studies on human monocyte-derived macrophages and on foam-cell macrophages generated in vivo suggest the existence of several macrophage phenotypes with distinct patterns of metalloproteinase expression. These phenotypes could play differing roles in cap, core and aneurysm formation.