HIV envelope gp120 activates human arterial smooth muscle cells.

There have been increasing reports of acute coronary thrombotic events in patients with HIV. Although these clinical events have been attributed primarily to dyslipidemia associated with protease inhibitor therapy, autopsy studies in children with HIV suggest the presence of an underlying arteriopathy. This study demonstrates that the HIV envelope protein, gp120, activates human arterial smooth muscle cells to express tissue factor, the initiator of the coagulation cascade. The induction of tissue factor by gp120 is mediated by two biologically relevant coreceptors for HIV infection, CXCR4 and CCR5, and is also dependent on the presence of functional CD4. Induction of tissue factor by gp120 requires activation of mitogen-activating protein kinases, activation of protein kinase C, and generation of reactive oxygen species, signaling pathways that have protean effects on smooth muscle cell physiology. The activation of smooth muscle cells by gp120 may play an important role in the vascular, thrombotic, and inflammatory responses to HIV infection.

Release of active tissue factor by human arterial smooth muscle cells.

Tissue factor (TF), the initiator of coagulation, is thought to function predominantly at the cell surface. Recent data have suggested that active TF is present extracellularly in atherosclerotic plaques, the arterial wall, and the blood. This study was conducted to determine whether smooth muscle cells (SMCs), a major source of arterial TF, could generate extracellular TF. Active TF accumulated in the medium of cultured human SMCs, representing approximately 10% of that measured in the underlying cells at 24 hours. Platelet-derived growth factor, phorbol ester, and tumor necrosis factor-alpha caused approximately 3-fold increases in TF activity in the medium. Release of TF into the medium was dependent on the presence of the TF transmembrane domain but not the cytoplasmic domain. Antibodies to TF precipitated most of the activity from the culture medium, whereas antibodies to the beta(1)-integrin subunit precipitated approximately 33% of the activity. Treatment with detergent or phosphatidylserine:phosphatidylcholine did not increase activity, suggesting that all TF released by SMCs was in the appropriate lipid milieu and not encrypted. Western blotting showed that the medium contained full-length TF protein. Fluorescent cytometry showed that extracellular TF was present largely in particles < or =200 nm, which had a density of 1.10 g/mL. We hypothesize that active extracellular TF found in the injured arterial wall and atherosclerotic plaques derives, in part, from SMC microparticles.

Human vascular smooth muscle cells possess functional CCR5.

CC chemokine receptors are important modulators of inflammation. Although CC chemokine receptors have been found predominantly on leukocytes, recent studies have suggested that vascular smooth muscle cells respond to CC chemokines. We now report that human smooth muscle cells express CCR5, a co-receptor for human immunodeficiency virus. CCR5 mRNA was detectable by RNA blot hybridization in human aortic and coronary artery smooth muscle cells. The cDNA generated by reverse transcription-polymerase chain reaction from aortic smooth muscle cells had 100% identity throughout the entire coding region with the CCR5 cloned from THP-1 cells. By immunohistochemistry, CCR5 and the CCR5 ligand, macrophage inflammatory protein-1beta (MIP-1beta), were detected in smooth muscle cells and macrophages of the atherosclerotic plaque. In smooth muscle cell culture, MIP-1beta induced a significant increase in intracellular calcium concentrations, which was blocked by an antibody to CCR5. In addition, MIP-1beta caused a calcium-dependent increase in tissue factor activity. Tissue factor is the initiator of coagulation and is thought to play a key role in arterial thrombosis. These data suggest that human arterial smooth muscle cells express functional CCR5 receptors and MIP-1beta is an agonist for these cells.

Regulation of the procoagulant response to arterial injury.

The last few years have provided increasing evidence to support a major role for TF in the initiation and propagation of thrombosis after acute arterial injury. Although thrombotic occlusion occurs in a small minority of patients undergoing acute coronary interventions or bypass surgery, mural thrombi are likely to be present in almost all cases. These thrombi may stimulate SMC and promote the development of intimal hyperplasia and luminal narrowing. The use of inhibitors of TF and factor VIIa, therefore, may not only be valuable for inhibiting thrombus formation associated with acute arterial interventions, but may also have benefit in attenuating intimal hyperplasia. Although this paper focuses on the role of TF in establishing a procoagulant state after arterial injury, the fibrinolytic system undoubtedly plays a role in balancing the effects of increased TF production in the arterial wall. This is underscored by the success of activators of fibrinolysis (tissue plasminogen activator, streptokinase, urokinase) in revascularization in the setting of acute myocardial infarction and is reviewed elsewhere. Likewise, local regulation of TFPI in the atherosclerotic plaque and injured vessel wall may be important in attenuating the effects of increased TF synthesis and accumulation. It has been assumed that the primary source of active TF after arterial injury is either SMC or invading macrophages and that active TF is anchored to the surface of these cells. Recent data have suggested that the majority of cell-associated TF is either encrypted on the cell surface or present in an intracellular pool. Arterial injury may, therefore, involve the de-encryption of surface TF or the release of intracellular TF. In addition, active vascular TF may be present in microparticles that are not anchored to the arterial wall and may be washed into the circulation. The procoagulant state may be further accentuated by the accumulation of bloodborne TF at sites of arterial injury and in developing thrombi. This TF is likely to arise from circulating leukocytes, including neutrophils and monocytes. These studies suggest that the cellular processing of TF may be an important target for inhibiting thrombotic complications associated with arterial injury and acute coronary events.

Tissue factor expression in human arterial smooth muscle cells. TF is present in three cellular pools after growth factor stimulation.

Tissue factor (TF) is a transmembrane glycoprotein that initiates the coagulation cascade. Because of the potential role of TF in mediating arterial thrombosis, we have examined its expression in human aortic and coronary artery smooth muscle cells (SMC). TF mRNA and protein were induced in SMC by a variety of growth agonists. Exposure to PDGF AA or BB for 30 min provided all of the necessary signals for induction of TF mRNA and protein. This result was consistent with nuclear runoff analyses, demonstrating that PDGF-induced TF transcription occurred within 30 min. A newly developed assay involving binding of digoxigenin-labeled FVIIa (DigVIIa) and digoxigenin-labeled Factor X (DigX) was used to localize cellular TF. By light and confocal microscopy, prominent TF staining was seen in the perinuclear cytoplasm beginning 2 h after agonist treatment and persisting for 10-12 h. Surface TF activity, measured on SMC monolayers under flow conditions, increased transiently, peaking 4-6 h after agonist stimulation and returning to baseline within 16 h. Peak surface TF activity was only approximately 20% of total TF activity measured in cell lysates. Surface TF-blocking experiments demonstrated that the remaining TF was found as encrypted surface TF, and also in an intracellular pool. The relatively short-lived surface expression of TF may be critical for limiting the thrombotic potential of intact SMC exposed to growth factor stimulation. In contrast, the encrypted surface and intracellular pools may provide a rich source of TF under conditions associated with SMC damage, such as during atherosclerotic plaque rupture or balloon arterial injury.

Tissue factor is induced by monocyte chemoattractant protein-1 in human aortic smooth muscle and THP-1 cells.

Monocyte chemoattractant protein-1 (MCP-1) is a C-C chemokine thought to play a major role in recruiting monocytes to the atherosclerotic plaque. Tissue factor (TF), the initiator of coagulation, is found in the atherosclerotic plaque, macrophages, and human aortic smooth muscle cells (SMC). The exposure of TF during plaque rupture likely induces acute thrombosis, leading to myocardial infarction and stroke. This report demonstrates that MCP-1 induces the accumulation of TF mRNA and protein in SMC and in THP-1 myelomonocytic leukemia cells. MCP-1 also induces TF activity on the surface of human SMC. The induction of TF by MCP-1 in SMC is inhibited by pertussis toxin, suggesting that the SMC MCP-1 receptor is coupled to a Gi-protein. Chelation of intracellular calcium and inhibition of protein kinase C block the induction of TF by MCP-1, suggesting that in SMC it is mediated by activation of phospholipase C. SMC bind MCP-1 with a Kd similar to that previously reported for macrophages. However, mRNA encoding the macrophage MCP-1 receptors, CCR2A and B, is not present in SMC, indicating that they possess a distinct MCP-1 receptor. These data suggest that in addition to being a chemoattractant, MCP-1 may have a procoagulant function and raise the possibility of an autocrine pathway in which MCP-1, secreted by SMC and macrophages, induces TF activity in these same cells.

Tissue factor in the pathogenesis of atherosclerosis.

TF antigen and activity are found in abundance in human atherosclerotic plaques, particularly in the lipid-rich core. TF is also readily induced in the arterial wall by balloon injury and accumulates in the resulting neointima. In chronic atherosclerosis, the macrophage is likely to be the major source of TF within the plaque. TF accumulates as an early event associated with the migration of monocytes to the vessel wall in response to chemoattractants, such as MCP-1, and their differentiation into macrophages. As SMC become activated in the developing plaque, they provide a second source of TF. Macrophages and SMC accumulate lipid and become foam cells, ultimately degenerating into a necrotic core rich in TF. Spontaneous plaque rupture or acute interventions expose active TF in the core to circulating blood, triggering thrombosis. In acute arterial injury, SMC appear to be the chief source of TF. In normal vessels, the induction of TF in the medial SMC is not sufficient to generate fibrin, presumably because the TF is not readily accessible on the luminal surface. In contrast, endothelial denudation of previously injured arteries may expose intimal TF to circulating blood, resulting in rapid fibrin deposition. In advanced human atherosclerosis, it is likely that even in areas that do not contain "unstable" or "stable" plaques, the vessel wall is not normal and more closely resembles that of a previously injured artery possessing an active intima. Interventions, such as balloon angioplasty, coronary atherectomy, or stent placement may expose intimal TF, leading to fibrin deposition. As the initiator of coagulation, TF is a potential target for inhibiting the thrombotic complications of atherosclerosis. TFPI (reviewed in 52) is currently under clinical investigation as an anticoagulant and its effects on intimal hyperplasia in animal models are being studied. Direct factor Xa inhibitors, such as tick anticoagulant peptide (TAP) and leech anticoagulant peptide (ATS), are also under investigation (53-54). Finally, the recent crystallization of TF (55) and the TF:VIIa (56) should provide important new insights into the design of molecules for directly inhibiting TF.

Influence of gender, race, and education on patient preferences and receipt of cardiac catheterizations among coronary care unit patients.

The extent to which a preference for less aggressive care explains the lower rate of invasive cardiac services for women and African-Americans is unknown. A prospective observational study of 272 patients admitted to the coronary care unit was conducted at a tertiary referral teaching hospital and a community teaching hospital. In stepwise multivariate analysis, having less than a college education, poor cardiac function, not having undergone a previous cardiac catheterization, being a patient in a nonreferral community hospital, and current smoking were positively associated with a patient's stating that he or she would disagree with a physician's recommendation for a cardiac catheterization. The step-wise multivariate model with cardiac catheterization as the dependent variable indicated that being a patient in a referral medical center, patient willingness to accept a physician's recommendation for a cardiac catheterization, severe heart disease, and having attended high school were predictive. Women did not differ from men in their preference for or receipt of cardiac catheterization. Patients in the coronary care unit with lower levels of education were less likely to undergo cardiac catheterization. This association was only partly explained by less educated patients' being less willing to accept a physician's recommendation to undergo cardiac catheterization.

Current controversies in gastric lymphoma: case report and commentary.

Controversy regarding the optimal approaches for diagnosis and management of primary gastric lymphoma (PGL) continues. Currently, it is possible to diagnose and stage PGL in many cases without resorting to surgical exploration. These factors are highlighted in the case presented.