Elevated expression of monocyte chemoattractant protein 1 by vascular smooth muscle cells in hypercholesterolemic primates

MCP-1-stimulated monocyte attachment to laminin is mediated by beta 2-integrins

Migration of monocytes to sites of inflammation involves a series of attachments and detachments to extracellular matrix proteins. We examined the capacity of a chemokine, monocyte chemoattractant protein-1 (MCP-1), to regulate attachment of human monocytes to laminin, collagen I, collagen IV, or fibronectin. MCP-1 increased monocyte attachment to laminin in a dose- and time-dependent manner and stimulated a lesser increase to the other matrix proteins. Function-blocking monoclonal antibodies (MAbs) to the integrin beta 2-subunit (CD18), including Fab' fragments and alpha M (CD11b) blocked > 70% of attachment, whereas MAbs to the beta 1-integrin subunit reduced attachment by < 30%. This suggests that the CD11b/CD18 integrin is the predominant molecule involved in adhesion of MCP-1-stimulated monocytes to laminin. The association of CD11b with F-actin illustrated by confocal microscopy further supports this concept. In contrast, when monocytes were stimulated with the beta 1-stimulatory MAb TS2/16, monocyte adhesion to laminin occurred through beta 1-integrins. Thus MCP-1 can stimulate monocyte attachment to laminin, and this process is mediated through beta 2-integrins, principally CD11b/CD18.

Expression of monocyte chemoattractant protein 1 in human osteoblastic cells stimulated by proinflammatory mediators

Monocyte chemoattractant protein 1 (MCP-1) is a member of the chemokine superfamily of genes that induces chemotaxis of monocytes in inflammatory processes. The effects of interleukin-1 beta (IL-1 beta), tumor necrosis factor alpha (TNF-alpha), interleukin-6 (IL-6), transforming growth factor beta (TGF-beta), platelet-derived growth factor (PDGF-BB), parathyroid hormone (PTH), and 1,25(OH)2D3 on MCP-1 expression in human osteoblastic cells were compared. Inflammatory or proinflammatory cytokines stimulated the production of MCP-1 in normal human osteoblastic cells as determined by RIA. The osteotrophic mediators PTH and 1,25(OH)2D3 and PDGF-BB had no effect on MCP-1 expression. In further studies, the steady-state mRNA and MCP-1 protein levels in two human osteoblastic cell lines, MG-63 and SaOS-2, were examined. MCP-1 expression at both the protein and mRNA levels was greatly increased by IL-1 beta and TNF-alpha. At the mRNA level, IL-1 beta and TNF-alpha strongly induced MCP-1 expression; TGF-beta and IL-6 induced MCP-1 but to a lesser extent. No significant changes in MCP-1 mRNA or MCP-1 protein secretion were observed when cells were treated with PDGF-BB, PTH, and 1,25(OH)2D3. When tested on preosteoclasts, MCP-1 was shown to have no effect on the formation of multinucleated, tartrate-resistant acid phosphatase (TRAP)-positive osteoclastic cells.

Fluid shear stress induces a biphasic response of human monocyte chemotactic protein 1 gene expression in vascular endothelium

The focal distribution of atherosclerotic lesions in the arterial tree is related to the local shear stress generated by blood flow, but the molecular basis of the atherogenic response of endothelial cells in these lesion-prone areas is still unclear. We report that shear stress mediates a biphasic response of monocyte chemotactic protein 1 (MCP-1) gene expression in vascular endothelial cells (EC). Northern blot analysis indicated that the level of MCP-1 mRNA in human umbilical vein EC (HUVEC) subjected to a shear stress of 16 dynes/cm2 (1 dyne = 10 microN) for 1.5 hr increased by 2- to 3-fold when compared with static cells. The MCP-1 gene expression decreased to the basal level at 4 hr and then declined further to become completely quiescent at 5 hr after the onset of shear. Once the gene expression was fully suppressed, it remained quiescent even after static incubation for 1.5 hr and would not respond to reshearing after this static incubation. However, if the postshearing incubation extended from 1.5 to 24 hr, the MCP-1 mRNA returned to the basal level and was then able to increase after the reapplication of shear stress. Nuclear run-on experiments showed that the shear-induced increased MCP-1 mRNA in HUVEC was regulated at the transcriptional level. By using cycloheximide, it was shown that de novo protein synthesis was not necessary for the induction of MCP-1 by shear stress. The biphasic response of MCP-1 gene expression was found in experiments in which the applied shear stress was 6, 16, or 32 dynes/cm2, and it was observed not only in HUVEC but also in HeLa cells, glioma cell lines, and skin fibroblasts. This in vitro study demonstrates that the response of MCP-1 gene to shear stress represents an immediate early gene activation and suggests that this gene is probably suppressed in EC that have been exposed to a constant shear stress.

A novel biologic activity of thrombin: stimulation of monocyte chemotactic protein production

Thrombin is a serine protease that is released at sites of vascular injury and exerts a variety of biologic effects on different cell types. Thrombin is postulated to play a role in the pathogenesis of a number of diseases including atherosclerosis, since it activates vascular smooth muscle and endothelial cells. Thrombin mediates these effects through a specific receptor that is upregulated in vascular cells in atherosclerosis. Atherosclerosis and glomerulosclerosis are characterized by the presence of monocyte-macrophages in the lesions. Monocyte chemotactic protein (MCP-1) is believed to be an important mediator of monocyte recruitment to the tissue and can be induced in a broad variety of cells including mesangial cells. We studied the effect of thrombin on MCP-1 production and gene expression in well-characterized human mesangial cells, vascular pericytes that play a central role in fibrosis of the glomerular microvascular bed. alpha thrombin stimulates MCP-1 production and gene expression in mesangial cells in a dose- and time-dependent manner. Experiments with diisopropylfluorophosphate thrombin and gamma thrombin demonstrate that this thrombin effect requires both receptor binding as well as catalytic activity, features consistent with the known properties of the recently characterized and cloned thrombin receptor. Moreover, a human thrombin receptor activating peptide (TRAP1-7) also stimulates MCP-1 production. Northern blot analysis demonstrated that mesangial cells express an mRNA transcript that hybridizes with labeled human thrombin receptor cDNA. These data describe a novel biologic activity of thrombin and suggest an additional mechanism by which this coagulation factor may participate in the progression of glomerulosclerosis, and by analogy, atherosclerosis.

Expression of monocyte chemoattractant protein 1 in human inflamed gingival tissues

Gingival inflammation is initiated by bacterial colonization on the tooth surface. It is characterized by infiltration of mononuclear cells, a common feature of many forms of chronic inflammation. Monocyte chemoattractant protein 1 (MCP-1) is the predominant monocyte chemoattractant secreted by a variety of different cells in vitro. For this report, we examined MCP-1 expression in bacterially induced gingival inflammation by immunohistochemistry and in situ hybridization. The cell types expressing MCP-1 are identified as vascular endothelial cells and monocytes/macrophages. Correlation analysis shows that the number of cells expressing MCP-1 is related to the degree of inflammation. Our finding that MCP-1 is expressed in inflamed gingival tissue suggests that MCP-1 plays an important role in the recruitment of monocytes and amplification of inflammatory signals in bacterially induced inflammation.

Chronic rejection in experimental cardiac transplantation: studies in the Lewis-F344 model

Despite recognition of chronic vascular injection by numerous investigators since the beginning of experimental and solid organ transplantation, the pathogenesis of graft arteriosclerosis remains poorly understood. We have defined a reproducible model of this disease by transplanting heterotopic cardiac grafts across minor histocompatibility barriers using inbred strains of rat. We found that long-term surviving Lewis grafts in untreated F344 recipients are subjected to a chronic rejection process which results in the development of diffuse graft arteriosclerotic lesions, indistinguishable in appearance from those seen in human cardiac grafts. Immunohistochemical studies confirm that end-stage lesions are similar in composition to human lesions, made up predominantly of vascular smooth muscle cells with occasional monocytes and T cells. Analysis of serial rejecting allografts demonstrates that a distinct inflammatory stage precedes smooth muscle cell accumulation in areas of intimal thickening, suggesting that mononuclear cells play a role in the developing lesion. Endothelial expression of class II and ICAM-1 appears to lead to early mononuclear cell adherence to the endothelium. Analysis using quantitative RT-PCR confirms that MCP-1 is expressed by ED1-positive monocyte/macrophages in rejecting cardiac grafts, suggesting that this chemoattractant may help drive mononuclear cell accumulation in the expanding intima. Immunohistochemical labelling of PDGF, TNF, and IL-1 in vascular lesions suggests that these growth factors may trigger intimal vascular smooth muscle cell proliferation in chronically rejecting allografts. Hypercholesterolemia did not enhance the severity of lesion development in long-term surviving allografts, suggesting that lipid levels are not a major etiologic factor in graft arteriosclerotic lesion formation in the Lewis-F344 model. Finally, the dietary manipulation of EFAD reduced graft infiltration by mononuclear cells and markedly diminished arterial lesion development in chronically rejecting grafts. Heparin anologues have previously been shown to inhibit proliferative vascular smooth muscle cell lesions in rats following endothelial injury (Clowes & Karnovsky 1977), and we are currently assessing the role of heparin in the therapy of graft arteriosclerosis in the Lewis-F344 model. We are also investigating the role of CD4-positive mononuclear cells in the pathogenesis of lesion development, using the anti-CD4 monoclonal antibody BWH-4 to deplete recipients of CD4-positive cells (Sayegh et al. 1991). In summary, our studies in the Lewis-F344 model suggest that monocyte/macrophages play an important role in the pathogenesis of cardiac graft arteriosclerosis. Future studies utilizing this model should help further elucidate the mechanisms resulting in--and help define potential therapies for--chronic rejection in cardiac transplantation.

Early and persistent induction of monocyte chemoattractant protein 1 in rat cardiac allografts

The early response gene for monocyte chemoattractant protein 1 (MCP-1) encodes a potent chemotactic factor that is specific for monocytes. To determine whether MCP-1 is involved in macrophage recruitment in cardiac allografts, we studied time-dependent MCP-1 gene and protein expression patterns in the heterotopic, Lewis to F-344 rat transplantation model (by reverse transcription-PCR and immunohistochemistry). There was a significant increase (8- to 12-fold) in MCP-1 gene transcripts in cardiac allografts compared with host hearts at 7, 14, and 28 days after transplantation. This induction was not observed with syngeneic transplants or hosts exposed to the same circulating cells and blood products. The MCP-1 gene product was expressed predominantly by mononuclear cells that double-stained with antimacrophage antibody (ED1) and localized to the interstitial and vascular spaces of the allografts. Immunocytochemical cell counting revealed significant increases in both MCP-1- and ED1-immunopositive cells in 7-, 14-, and 28-day allografts (in comparison with day 0 hearts). The absolute number of MCP-1-positive cells (5-7%) was lower than that of ED1-positive cells (25-34%) at all time points, suggesting that MCP-1-positive cells represent a subpopulation of activated macrophages. The persistent expression of MCP-1 in association with increased macrophage localization suggests that this inducible mediator contributes to the chronic inflammatory response following cardiac transplantation and that it may play a role in the pathogenesis of transplant arteriosclerosis.