No abstract

Tissue factor (TF) is a major activator of the coagulation cascade and may play a role in initiating thrombosis after intravascular injury. To investigate whether medial vascular smooth muscle provides a source of TF following arterial injury, the induction of TF mRNA and protein was studied in balloon-injured rat aorta. After full length aortic injury, aortas were harvested at various times and the media and adventitia separated using collagenase digestion and microscopic dissection. In uninjured aortic media, TF mRNA was undetectable by RNA blot hybridization. 2 h after balloon injury TF mRNA levels increased markedly. Return to near baseline levels occurred at 24 h. In situ hybridization with a 35S-labeled antisense rat TF cRNA probe detected TF mRNA in the adventitia but not in the media or endothelium of uninjured aorta. 2 h after balloon dilatation, a marked induction of TF mRNA was observed in the adventitia and media. Using a functional clotting assay, TF procoagulant activity was detected at low levels in uninjured rat aortic media and rose by 10-fold 2 h after balloon dilatation.Return to baseline occurred within 4 d. These data demonstrate that vascular injury rapidly induces active TF in arterial smooth muscle, providing a procoagulant that may result in thrombus initiation or propagation. (J. Clin. Invest. 1993.

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.

No abstract

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-1␤ (MIP-1␤), were detected in smooth muscle cells and macrophages of the atherosclerotic plaque. In smooth muscle cell culture, MIP-1␤ induced a significant increase in intracellular calcium concentrations, which was blocked by an antibody to CCR5. In addition, MIP-1␤ 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-1␤ is an agonist for these cells.