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P Libby

Publications and source records attributed to P Libby.

At least 145 records · Page 8Linked to original sources
PubMed1997

Fas is expressed in human atherosclerotic intima and promotes apoptosis of cytokine-primed human vascular smooth muscle cells.

The membrane protein Fas/Apo-1/CD95 signals programmed cell death or apoptosis in activated T lymphocytes. Vascular smooth muscle cells (SMCs) bear markers of programmed cell death or apoptosis in advanced atherosclerotic plaques that contain immune cells e.g., macrophages and T lymphocytes. This study tested the hypothesis that the Fas death-signaling pathway contributes to apoptosis of SMCs exposed to proinflammatory cytokines produced by these immune cells during atherogenesis. All atherosclerotic plaques examined (n = 14) contained immunoreactive Fas. The majority of the Fas+ SMCs localized in the intima of the plaques, whereas the medial SMCs expressed Fas antigen less prominently. Double staining for DNA fragments (TUNEL) and Fas or cell identification markers colocalized Fas with TUNEL+ SMCs in the areas that contained CD3+ T cells and CD68+ macrophages, suggesting a role for Fas in the induction of SMC apoptosis by activated T cells during atherogenesis. In culture, stimulation with interferon-gamma, tumor necrosis factor-alpha, and interleukin-1 beta increased expression of Fas in SMCs. Incubation with an activating anti-Fas antibody triggered apoptosis of the cytokine-primed but not the untreated SMCs, as demonstrated by TUNEL and electrophoresis of oligonucleosomal DNA fragments. These data suggest that activation of the Fas death-signaling pathway contributes to the induction of SMC apoptosis during atherogenesis and furnish a mechanism whereby immune cells and their cytokines promote this cell death process related to vascular remodeling and plaque rupture.

Apoptosis↗
PubMed1997

Thrombin promotes activation of matrix metalloproteinase-2 produced by cultured vascular smooth muscle cells.

Thrombin generated at sites of vascular injury not only participates in the coagulation cascade but can signal other events related to development and complication of atherosclerotic plaques. We investigated here a novel non-thrombotic action of thrombin: the possibility that this protease influences the expression or activation of matrix metalloproteinases (MMPs) produced by vascular smooth muscle cells (SMCs). Matrix-degrading proteinases likely contribute to several aspects of vascular lesion development. Vascular SMCs constitutively elaborate the zymogen form of gelatinase A (MMP-2), found in cell supernatants complexed with its inhibitor, the tissue inhibitor of metalloproteinases (TIMP)-2. When activated, MMP-2 digests collagens and elastin and may thus promote cell migration and vascular remodeling. Analysis of culture supernatants harvested from either human or rabbit vascular SMCs by gelatin zymography revealed that compared with supernatants of unstimulated SMCs, media conditioned by thrombin-stimulated cells contained increased amounts of proteolytically processed MMP-2, suggesting activation of this MMP. Further experiments tested whether thrombin directly activates MMP-2. In cell-free experiments, when added to medium harvested from unstimulated SMCs, alpha-thrombin increased in a dose- and time-dependent manner the amount of proteolytically processed MMP-2, as shown by zymography and by Western blotting with specific antibodies. Thrombin cleaved pro-MMP-2 within 4 hours, even when the gelatinase was bound with its inhibitor, TIMP-2. Thrombin treatment rendered culture media of unstimulated SMCs able to degrade collagen type IV, consistent with generation of active MMP-2. Addition of inhibitors of either thrombin or MMPs decreased this type IV collagenolytic activity, but thrombin in the absence of SMC-conditioned medium containing pro-MMP-2 exhibited only minimal collagenolysis. Our results suggest that at sites of vascular injury, thrombin may activate locally produced MMP-2 and thereby facilitate cell migration and proliferation. In the case of complicated atherosclerotic plaques, episodes of intraplaque hemorrhage or plaque disruption with thrombosis may promote plaque instability by increasing local matrix-degrading activity.

Animals↗
PubMed1997

Mechanical strain tightly controls fibroblast growth factor-2 release from cultured human vascular smooth muscle cells.

Although fibroblast growth factor-2 (FGF-2) participates in the response to vascular injury, the role of cellular deformation in FGF-2 release is incompletely understood. To test the hypothesis that mechanical strain tightly controls FGF-2 release, a novel device was used to impose homogeneous and uniform biaxial strain to human vascular smooth muscle cells. Release of FGF-2 increased with the number of cycles of strain (14%, 1 Hz); 1, 9, and 90 cycles of strain, respectively, released 0.55 +/- 0.06%, 2.9 +/- 0.3%, and 5.5 +/- 1.3% of the total cellular FGF-2 (versus 0.00 +/- 0.40% for control, P < .05), but release was not further increased for strain of 90 to 90,000 cycles. Mechanical release of FGF-2 depended on both the frequency and amplitude of deformation. For example, strain (90 cycles, 1 Hz) at 4% amplitude released only 0.1 +/- 0.1% of the total FGF-2, but strain at 14% and 33% amplitudes, respectively, released 5.7 +/- 0.5% and 19.0 +/- 3.0% of the FGF-2 cellular pool (P < .05), suggesting a strain amplitude threshold for FGF-2 release. Injury to a subpopulation of cells increased with the frequency and amplitude of strain, but cells were not injured by strains below 10% amplitude. Strain following pretreatment with heparin released 12.6 +/- 1.6% of the total FGF-2 (versus 15.8 +/- 0.9% for strain alone, P < .05), indicating that most FGF-2 was liberated from the nuclear or cytoplasmic pools and not from low-affinity extracellular receptors. Conversely, strain in the presence of heparin released 25.2 +/- 3.5% of the total FGF-2 (versus 15.6 +/- 2.6% for strain alone, P < .05). Thus, cellular strain closely modulates the release of intracellular FGF-2 from human vascular smooth muscle cells, but FGF-2 release is negligible in response to the smaller strains that occur in the normal artery. In addition, larger mechanical strains lead to transfer of intracellular FGF-2 to the extracellular low-affinity receptors, where FGF-2 may be displaced by heparin. These observations provide insight into the mechanisms by which deforming vascular injury, such as that produced by arterial interventions, may elicit a proliferative response.

Cells, Cultured↗
PubMed1997

Regulation of matrix metalloproteinase expression in human vascular smooth muscle cells by T lymphocytes: a role for CD40 signaling in plaque rupture?

Physical disruption of an atheromatous lesion often underlies acute coronary syndromes. Matrix-degrading enzymes, eg, matrix metalloproteinases (MMPs), may cause loss in mechanical integrity of plaque tissue that favors rupture. T lymphocytes accumulate at sites where atheromata rupture, but the mechanisms by which these immune cells may contribute to plaque destabilization are unknown. This study tested the hypothesis that the T-lymphocyte surface molecule CD40 ligand (CD40L), recently localized in atherosclerotic plaques, regulates the expression of MMPs in human vascular smooth muscle cells (SMCs), the most numerous cell type in arteries. We report here that stimulated human T lymphocytes induced the expression of the matrix-degrading enzymes, ie, interstitial collagenase (MMP-1), stromelysin (MMP-3), gelatinase B (MMP-9), and activated gelatinase A (MMP-2), in human vascular SMCs by cell contact via CD40 ligation, as demonstrated by Western blot analysis, zymography, and antibody neutralization. Recombinant human CD40L (rCD40L) induced de novo synthesis of MMP-1, MMP-3, and MMP-9 on vascular SMCs and stimulated the expression of these enzymes to a greater extent than did maximally effective concentrations of tumor necrosis factor-alpha or interleukin-1beta, established agonists of MMP expression. Interferon gamma, another T-lymphocyte- derived cytokine, inhibited the induction of MMPs by rCD40L. Immunohistochemical analysis of human coronary atheromata colocalized MMP-1 and MMP-3 with CD40-positive SMCs. These results demonstrated that CD40 ligand, expressed on T lymphocytes, promoted the expression of matrix-degrading enzymes in vascular SMCs and thus established a new pathway of immune-modulated destabilization in human atheromata.

Arteriosclerosis↗
PubMed1997

Role of macrophage colony-stimulating factor in atherosclerosis: studies of osteopetrotic mice.

Previous in vitro and in vivo studies have suggested that macrophage colony-stimulating factor (M-CSF) plays a role in atherogenesis. To examine this hypothesis, we have studied atherogenesis in osteopetrotic (op/op) mice, which lack M-CSF due to a structural gene mutation. Atherogenesis was induced either by feeding the mice a high fat, high cholesterol diet or by crossing op mice with apolipoprotein E (apo E) knockout mice to generate mice lacking both M-CSF and apo E. In both the dietary and apo E knockout models, M-CSF deficiency resulted in significantly reduced atherogenesis. For example, in the apo E knockout model, homozygosity for the op mutation totally abolished aortic atherogenesis in male mice and reduced the size of the lesions approximately 97% in female mice. Mice heterozygous for the op mutation also exhibited a significant decrease in lesion size. Among apo E knockout mice, the frequency of atherosclerosis in aortic arch was 0/6 (op/op), 1/15 (op/+), and 12/16 (+/+). The effect of the M-CSF on atherosclerosis did not appear to be mediated by changes in plasma lipoproteins, as the op mice exhibited higher levels of atherogenic lipoprotein particles. The effects of the op mutation on atherogenesis may have resulted from decreased circulating monocytes, reduced tissue macrophages, or diminished arterial M-CSF.

Animals↗
PubMed1996

Pathogenic mechanisms of atherosclerosis: effect of lipid lowering on the biology of atherosclerosis.

Numerous trials have demonstrated that cholesterol-lowering therapy leads to marked reductions in cardiovascular and overall mortality and in the need for coronary revascularization. Angiographic regression trials have shown that cholesterol lowering can reduce progression and, in some instances, achieve regression of coronary atherosclerotic lesions. However, recent studies have contradicted the traditional view that the clinical course of coronary artery disease is closely linked to the severity of coronary artery stenosis. It is now apparent that stenoses responsible for myocardial infarction or unstable angina are typically mild rather than severe. These observations suggest that regression may not be the principal mechanism by which cholesterol lowering affects cardiovascular risk. Two mechanisms---plaque stabilization and improved endothelial function-have been examined in this regard. Basic studies suggest that cholesterol lowering favorably alters those features of atherosclerosis that promote plaque stability. Recent clinical studies have clearly established that aggressive lipid-lowering therapy improves endothelial function and reduces myocardial ischemia in patients with hypercholesterolemia.

Acetylcholine↗
PubMed1996

Nitric oxide attenuates vascular smooth muscle cell activation by interferon-gamma. The role of constitutive NF-kappa B activity.

Atherogenesis involves cellular immune responses and altered vascular smooth muscle cell (SMC) function. Cytokines such as interleukin (IL)-1 alpha and interferon-gamma (IFN-gamma) may contribute to this process by activating SMC. To determine whether the anti-atherogenic mediator, nitric oxide (.NO), can modulate cytokine-induced SMC activation, we investigated the effects of various .NO-generating compounds on the expression of intercellular and vascular cell adhesion molecules (ICAM-1 and VCAM-1). Induction of ICAM-1 expression by IL-1 alpha and VCAM-1 expression by IFN-gamma was attenuated by .NO donors but not by cGMP analogues. Nuclear run-on assays and transfection studies using various VCAM-1 promoter constructs linked to the chloramphenicol acetyl-transferase reporter gene showed that .NO repressed IFN-gamma-induced VCAM-1 gene transcription, in part, through inhibition of nuclear factor-kappa B (NF-kappa B). Electrophoretic mobility shift assay revealed that SMC possess basal constitutive NF-kappa B activity, which was augmented by treatment with IL-1 alpha. In contrast, IFN-gamma induced and activated interferon regulatory factor (IRF)-1 but had little effect on basal constitutive NF-kappa B activity. .NO donors had no inhibitory effect on IRF-1 activation but did inhibit basal and IL-1 alpha-stimulated NF-kappa B activation. These findings suggest that the induction of ICAM-1 and VCAM-1 expression requires NF-kappa B activation and that .NO attenuates IFN-gamma-induced VCAM-1 expression primarily by inhibiting basal constitutive NF-kappa B activity in SMC.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1996

Induction of DNA synthesis by a single transient mechanical stimulus of human vascular smooth muscle cells. Role of fibroblast growth factor-2.

BACKGROUND: Although mechanical vascular injury leads to smooth muscle cell proliferation that contributes to restenosis after balloon angioplasty, the role of the single transient mechanical stimulation of smooth muscle cells in this process is unknown. METHODS AND RESULTS: To test the hypothesis that a single transient mechanical stimulus can increase DNA synthesis, human vascular smooth muscle cells cultured in a three-dimensional collagen gel system were subjected to transient compression. Transient compression (5-minute duration) of smooth muscle cell-collagen gel cultures in defined serum-free conditions led to delayed increases in [3H]thymidine incorporation. At 12 to 24 hours after compression, there was a 3.3 +/- 0.5-fold (P<.001 versus control) and 3.0 +/- 0.6-fold (P<.002 versus control) increase for 60% and 80% strain, respectively; at 24 to 36 hours after compression, there was a 1.8 +/- 0.5-fold (P<.05 versus control) and 4.3 +/- 0.8-fold (P<.001 versus control) increase. Also, serum-free media conditioned by transiently compressed gel cultures induced DNA synthesis in control, unstimulated smooth muscle cell cultures, suggesting the release of growth factors by transient compression. Although neutralizing antibodies against platelet-derived growth factor did not affect the mechanical induction of DNA synthesis, a neutralizing monoclonal antibody against fibroblast growth factor-2 (FGF-2) decreased this induction by 89% and completely blocked the increase in DNA synthesis caused by media conditioned by transiently compressed gels. Media conditioned by transient compression contained elevated levels of FGF-2 (17 +/- 5 versus 2 +/- 2 pg/mL for control, P<.005) with no increase in lactate dehydrogenase activity, suggesting release of FGF-2 with sublethal cellular injury. CONCLUSIONS: A single transient mechanical stimulus increases DNA synthesis in human vascular smooth muscle cells, in part by autocrine or paracrine FGF-2 release.

Cells, Cultured↗
PubMed1996

Control of endothelial leukocyte adhesion molecules by fatty acids.

Dietary balance of long-chain fatty acids (FA) may influence human susceptibility to pathological processes which involve the interaction of leukocytes with vascular endothelium, such as atherogenesis and inflammation. Such interaction is largely mediated by the de novo or increased expression of endothelial leukocyte adhesion molecules on vascular endothelial cells, able to tether and stably bind leukocytes onto the vessel wall, and by the production of leukocyte chemoattractants. Endothelial cells do not normally support high levels of leukocyte adhesion. They do so, however, when exposed to a number of stimuli, such as oxidized low density lipoprotein bacterial lipopolysaccharides, and inflammatory cytokines, which induce phenotypic changes generally referred to as "endothelial activation." We compared various FA in their ability to modulate endothelial activation by cytokines. FA included linoleic, arachidonic, oleic, eicosapentaenoic and, docosa-hexaenoic acid (DHA) as representatives of the n-6, n-3 polyunsaturated FA and of the monounsaturated FA. The n-3 FA DHA, and, to a lesser extent, oleate, at nutritionally compatible concentrations, were able to reduce endothelial expression of Vascular Cell and Adhesion Molecule-1 (VCAM-1). In further studies, DHA dose- and time-dependently reduced also the expression of E-selectin, Intercellular Adhesion Molecule-1, interleukin (IL)-6 and IL-8, in response to IL-1, IL-4, tumor-necrosis factor, or bacterial endotoxin. The magnitude of this effect paralleled its incorporation into cellular phospholipids. Also, coordinate with reduced surface adhesion molecule expression, DHA reduced the adhesion of human monocytes and of monocytic U937 cells to cytokine-stimulated endothelial cells. These effects were accompanied by a quantitatively consistent reduction in VCAM-1 mRNA, indicating a pretranslational control of adhesion molecule gene expression. These novel properties of FA as modulators of endothelial activation may help to explain the influence of dietary FA intake on atherogenesis and inflammation.

Cells, Cultured↗
PubMed1996

Macrophages and atherosclerotic plaque stability.

Physical disruption of atheroma frequently causes coronary thrombosis. Ruptured plaques usually have thin fibrous caps overlying a large thrombogenic lipid core rich in lipid-laden macrophages. The biology of plaque monocyte-derived macrophages thus assumes critical importance in understanding plaque instability. Monocyte recruitment involves binding to leukocyte adhesion receptors on the endothelial surface such as intercellular adhesion molecule-1 and vascular cell adhesion molecule-1. Once adherent to the endothelial surface, monocytes enter the intima at sites of lesion predilection. This process probably requires directed migration of the mononuclear cells. A number of chemoattractant molecules, such as the monocyte chemoattractant molecule-1, may participate in signaling this entry of adherent monocytes into the artery wall. Once resident in the arterial intima, monocytes accumulate lipid, via increasingly well characterized receptor-mediated uptake, and transform into macrophage foam cells. These lesional macrophages also acquire other functional properties including production of the potent procoagulant, tissue factor, apolipoprotein E, and an increasing list of cytokines (protein mediators of information and immunity) that may participate importantly in autocrine and paracrine signaling among leukocytes and vascular endothelial and smooth muscle cells. Fatty streaks seldom cause clinical events but may evolve into complicated atheromatous plaques characterized by an accumulation of smooth muscle cells and extracellular matrix and formation of a central core containing extracellular lipid. Death of macrophages, including programmed cell death or apoptosis, probably promotes formation of this thrombogenic lipid pool whose size correlates with plaque instability. Lesion complication often culminates in rupture of the fibrous cap overlying this lipid core. The integrity of the fibrous cap, and thus its resistance to rupture, depends critically on the collagenous extracellular matrix of the plaque's fibrous cap. This aspect of plaque structure in turn depends upon the balance between synthesis and degradation of the macromolecules that comprise the extracellular matrix of the cap, principally interstitial forms of collagen derived from arterial smooth muscle cells. Collagen breakdown, however, appears to depend critically on macrophages. Plaque macrophages express a variety of matrix-degrading enzymes that can contribute to the weakening of the fibrous cap. In this way, macrophages can critically influence aspects of the biology of human atheroma related to lesion stability. We hypothesize that lipid-lowering reduces clinical events, as shown in recent trials, by stabilizing lesions in part by reversing some of the maladaptive functions of macrophages described above.

Arteriosclerosis↗
PubMed1996

Biological mechanisms for the clinical success of lipid-lowering in coronary artery disease and the use of surrogate end-points.

The small changes in luminal narrowing observed with lowering total cholesterol are unlikely to be the principal mechanism by which lipid-lowering achieves a reduction in clinical events and revascularization rates. Endothelium dependent vasomotor function, and the cellular characteristics of plaques that seem to be intimately related to rupture and thrombosis, are factors that may explain the clinical success from correcting the dyslipidemias. Dyslipidemias cause endothelial dysfunction that predisposes to vasoconstriction of the epicardial coronary arteries and the resistance vessels relative to metabolic demand. Dysfunctional endothelium also promotes the recruitment of inflammatory cells into the vessel wall which contributes to the activation of vascular smooth muscle cells and sets up an environment within the plaque that predisposes to rupture and a prothrombotic state. Aggressive lowering of total cholesterol, and especially LDL and oxidized LDL, improves coronary endothelial function both of the epicardial and resistance vessels, and leads to a reduction in myocardial ischemia. Lipid-lowering may promote plaque stability in part by reducing the recruitment of inflammatory cells, and possibly by changing the size or consistency of the lipid-rich core of plaques. A thicker fibrous cap and stiffer plaque that is less likely to rupture may result, and in the event that rupture does occur, cholesterol lowering may reduce the formation of overlying thrombus. Testing coronary or peripheral artery endothelial vasomotor dysfunction may be a surrogate measure for assessing the effectiveness of interventions to prevent coronary heart disease. These tests are likely to be used increasingly to identify interventions that deserve greater attention in larger clinical trials, as well as providing mechanisms for any observed clinical benefits.

Animals↗
PubMed1996

Proliferating arterial smooth muscle cells after balloon injury express TNF-alpha but not interleukin-1 or basic fibroblast growth factor.

We have recently reported that balloon withdrawal injury to rabbit abdominal aortas induces sustained activation indicated by the expression of certain adhesion molecules such as vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 in regenerating endothelial cells and/or proliferating smooth muscle cells (SMCs). Local cytokine signaling may contribute to ongoing modulation of cellular functions and proliferation of intimal SMCs after acute vascular injury. We therefore studied the expression of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta), proinflammatory and SMC growth-promoting cytokines, and basic fibroblast growth factor (bFGF) in SMCs of rabbit aorta at 2 (n = 4), 5 (n = 4), and 10 days (n = 6) after balloon injury. All animals were given bromodeoxyuridine (BrdU, 10 mg/kg per day) continuously to label proliferating SMCs. Frozen cross sections of injured vessels at each time point after balloon injury were examined by immunoperoxidase staining with monoclonal antibodies. As early as 2 days after injury, before intimal thickening begins, foci of medial SMCs expressed TNF-alpha, but not all TNF-alpha-positive medial SMCs had incorporated BrdU, suggesting that TNF-alpha expression by medial SMCs may precede their proliferation. At 5 days, TNF-alpha-bearing and BrdU-labeled medial SMCs increased in number. At 10 days after injury, when uniform intimal thickening occurred, almost all neointimal SMCs and foci of medial SMCs labeled with BrdU. Most of the BrdU-positive (proliferating) SMCs expressed immunoreactive TNF-alpha. Reverse transcription polymerase chain reaction showed increased TNF-alpha mRNA at 10 days after ballooning in the injured portion of the aorta. In contrast, regions of SMC proliferation showed inconsistent IL-1 beta expression, and bFGF, abundant in normal rabbit arteries, was not detected in areas of SMC replication. These data indicate that replication of arterial SMCs after balloon injury occurs in regions of TNF-alpha but not IL-1 beta expression and correlates inversely with the presence of bFGF. These results indicate that SMC-derived TNF-alpha serves as a marker of modulated SMC phenotype after acute vascular injury and may contribute to local cellular activation and proliferation of SMCs at sites of arterial injury.

Animals↗
PubMed1996

Apoptosis of vascular smooth muscle cells induced by in vitro stimulation with interferon-gamma, tumor necrosis factor-alpha, and interleukin-1 beta.

Recent studies have documented evidence for the death of smooth muscle cells (SMCs) within advanced human atheroma. These lesions contain macrophages and T lymphocytes in addition to SMCs. We therefore investigated whether interferon-gamma (IFN-gamma), a cytokine secreted by T lymphocytes, or interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha), two cytokines characteristically produced by activated macrophages, can trigger apoptosis of vascular SMCs. Simultaneous treatment with IFN-gamma and TNF-alpha and/or IL-1 beta but not with each cytokine alone promoted death of human and rat SMCs. Exposure for 48 hours to a combination of IFN-gamma (400 U/mL), TNF-alpha (400 U/mL), and IL-1 beta (100 U/mL) significantly (P < .001) increased the accumulation of oligonucleosomes comprising DNA fragments and histones in human SMCs. Electrophoresis of genomic DNA showed internucleosomal fragments of genomic DNA isolated from the cytokine-cotreated SMCs of both humans and rats. These cells exhibited morphological changes typical of apoptosis, including cell shrinkage, membrane blebbing, chromatin condensation, and nuclear fragmentation. In situ 3' end labeling of DNA fragments with terminal transferase confirmed the fragmentation of genomic DNA in these cells. Simultaneous treatment with IFN-gamma and TNF-alpha or IL-1 beta induced elaboration of nitrite, an end product of nitric oxide, in rat but not human SMCs. NG-monomethyl-L-arginine inhibited nitrite accumulation and also partly blocked cytokine-induced apoptosis of rat SMCs but had little effect on human SMCs, suggesting operation of both nitric oxide-dependent and -independent mechanisms for cytokine-induced apoptosis in vascular SMCs. Production of immune cytokines by vascular cells and/or infiltrating leukocytes may regulate apoptotic death of SMCs during atherogenesis.

Acridine Orange↗
PubMed1996

Circumferential stress and matrix metalloproteinase 1 in human coronary atherosclerosis. Implications for plaque rupture.

Atherosclerotic plaque rupture may occur when regions of weakened extracellular matrix are subjected to increased mechanical stresses. Since collagen is a major determinant of extracellular matrix strength, enzymes that degrade collagen may play an important role in destabilizing the atherosclerotic lesion. To test the hypothesis that matrix metalloproteinase 1 (interstitial collagenase, or MMP-1), which initiates degradation of fibrillar collagens, colocalizes with increased stress in the fibrous cap of the atherosclerotic lesion, 12 unruptured human coronary lesions were studied. Finite-element analysis was used to determine the distribution of stress in the lesion, with estimates of material properties from previous measurements of human tissues. A computerized image analysis system was used to determine the distribution of immunoreactive MMP-1 within the fibrous tissue of the lesion. There was a significant correlation between immunoreactive MMP-1 and circumferential tensile stress in the fibrous cap within a given lesion (median Spearman rank correlation coefficient, .36; interquartile range, -.02 to .81; P < .02). Within a given lesion, the highest-stress region had twofold greater MMP-1 expression than the lowest-stress regions. In unruptured human atherosclerotic coronary lesions, overexpression of MMP-1 is associated with increased circumferential stress in the fibrous plaque. Degradation and weakening of the collagenous extracellular matrix at these critical high-stress regions may play a role in the pathogenesis of plaque rupture and acute ischemic syndromes.

Collagenases↗
PubMed1996

Regulation of matrix metalloproteinases and plasminogen activator inhibitor-1 synthesis by plasminogen in cultured human vascular smooth muscle cells.

Plasmin and matrix metalloproteinases (MMPs) both participate in extracellular matrix remodeling. This study examined the effects of tumor necrosis factor-alpha (TNF-alpha) and plasminogen on collagenase, stromelysin, and plasminogen activator inhibitor-1 (PAI-1) synthesis of collagenase and stromelysin, which remained predominantly in proenzyme forms, as determined by Western analysis of culture media. In contrast, plasminogen and plasmin not only increased secretion of MMPs but also induced cleavage to their active forms. The serine protease inhibitor aprotinin inhibited this activation of MMPs by plasminogen and plasmin. TNF-alpha reduced plasminogen-induced activation of MMPs, suggesting induction of an inhibitor or plasmin generation, such as PAI-1. Enzyme-linked immunosorbent assay of culture media showed that TNF-alpha (10 ng/mL) increased PAI-1 secretion by 4.2 fold compared with control (105.5 +/- 9.6) versus 24.9 +/- 1.7 ng/mL, n = 3). Surprisingly plasminogen also increased PAI-1 secretion by vascular SMCs (3.6-fold over control). These results demonstrate coordination of cytokines and serine proteases in regulating MMP secretion and activation. In addition, the induction of PAI-1 by TNF-alpha and plasminogen suggests a negative feedback mechanisms limit both plasmin-mediated and MMP-mediated matrix degradation.

Cells, Cultured↗