Identification of intimal subendothelial cells from human aorta in primary culture

Cyclooxygenase-2 promotes early atherosclerotic lesion formation in LDL receptor-deficient mice

BACKGROUND

Atherosclerosis has features of an inflammatory disease. Because cyclooxygenase (COX)-2 is expressed in atherosclerotic lesions and promotes inflammation, we tested the hypotheses that selective COX-2 inhibition would reduce early lesion formation in LDL receptor-deficient (LDLR-/-) mice and that macrophage COX-2 expression contributes to atherogenesis in LDLR-/- mice.

METHODS AND RESULTS

Treatment of male LDLR-/- mice fed the Western diet with rofecoxib or indomethacin for 6 weeks resulted in significant reductions in atherosclerosis in the proximal aorta (25% and 37%) and in the aorta en face (58% and 57%), respectively. Rofecoxib treatment did not inhibit platelet thromboxane production, a COX-1-mediated process, but it significantly reduced the urinary prostacyclin metabolite 2,3-dinor-6-keto-PGF1alpha. Fetal liver cell transplantation was used to generate LDLR-/- mice null for expression of the COX-2 gene by macrophages. After 8 weeks on the Western diet, COX-2-/- --> LDLR-/- mice developed significantly less (33% to 39%) atherosclerosis than control COX-2+/+ --> LDLR-/- mice. In both the inhibitor studies and the transplant studies, serum lipids did not differ significantly between groups.

CONCLUSIONS

The present studies provide strong pharmacological and genetic evidence that COX-2 promotes early atherosclerotic lesion formation in LDLR-/- mice in vivo. These results support the potential of anti-inflammatory approaches to the prevention of atherosclerosis.

Increased atherosclerosis in LDL receptor-null mice lacking ACAT1 in macrophages

During atherogenesis, circulating macrophages migrate into the subendothelial space, internalize cholesterol-rich lipoproteins, and become foam cells by progressively accumulating cholesterol esters. The inhibition of macrophage acyl coenzyme A:cholesterol acyltransferase (ACAT), which catalyzes the formation of cholesterol esters, has been proposed as a strategy to reduce foam cell formation and to treat atherosclerosis. We show here, however, that hypercholesterolemic LDL receptor-deficient (LDLR(-/-)) mice reconstituted with ACAT1-deficient macrophages unexpectedly develop larger atherosclerotic lesions than control LDLR(-/-) mice. The ACAT1-deficient lesions have reduced macrophage immunostaining and more free cholesterol than control lesions. Our findings suggest that selective inhibition of ACAT1 in lesion macrophages in the setting of hyperlipidemia can lead to the accumulation of free cholesterol in the artery wall, and that this promotes, rather than inhibits, lesion development.

Aortic endothelial cells regulate proliferation of human monocytes in vitro via a mechanism synergistic with macrophage colony-stimulating factor. Convergence at the cyclin E/p27(Kip1) regulatory checkpoint

Monocyte-derived macrophages (Mphis) are pivotal participants in the pathogenesis of atherosclerosis. Evidence from both animal and human plaques indicates that local proliferation may contribute to accumulation of lesion Mphis, and the major Mphi growth factor, macrophage colony stimulating factor (MCSF), is present in atherosclerotic plaques. However, most in vitro studies have failed to demonstrate that human monocytes/Mphis possess significant proliferative capacity. We now report that, although human monocytes cultured in isolation showed only limited MCSF-induced proliferation, monocytes cocultured with aortic endothelial cells at identical MCSF concentrations underwent enhanced (up to 40-fold) and prolonged (21 d) proliferation. In contrast with monocytes in isolation, this was optimal at low seeding densities, required endothelial cell contact, and could not be reproduced by coculture with smooth muscle cells. Intimal Mphi isolated from human aortas likewise showed endothelial cell contact-dependent, MCSF-induced proliferation. Consistent with a two-signal mechanism governing Mphi proliferation, the cell cycle regulatory protein, cyclin E, was rapidly upregulated by endothelial cell contact in an MCSFindependent fashion, but MCSF was required for successful downregulation of the cell cycle inhibitory protein p27(Kip1) before cell cycling. Thus endothelial cells and MCSF differentially and synergistically regulate two Mphi genes critical for progression through the cell cycle.

Langhans cells of human arterial intima: uniform by stellate appearance but different by nature

The stellate cells in human arterial intima known as Langhans cells were investigated. Arterial specimens were obtained during carotid endarterectomy and aortic reconstruction and included atherosclerotic lesions as well as areas of the adjacent normal appearing arterial wall. Following immunohistochemical and electron microscopic analysis, most of the stellate cells were found to inhabit the elastic-hyperplastic layer of the intima in the normal arterial wall but in atherosclerotic lesions, stellate cells were distributed throughout all intimal layers. Immunohistochemical examination revealed that different types of intimal cells, including smooth muscle cells (HHF-35; smooth muscle alpha-actin +) and vascular dendritic cells (CD1a+, S-100+), exhibited a typical stellate appearance but the cell processes of macrophages (HAM56+, CD68+) were too short for macrophages to be considered as stellate. No other intimal cells formed processes which could be detected under immunohistochemical examination. In atherosclerotic lesions, some smooth muscle cells transforming to foam cells retained their stellate shape. Smooth muscle cells interacted with each other through gap junctions while other intimal cells including vascular dendritic cells contacted each other without forming any specialized structures. We conclude that Langhans cells comprise two histological types of intimal cells, namely, smooth muscle cells and vascular dendritic cells.

Immunohistochemical study of primary and recurrent basal cell and metatypical carcinomas of the skin

We investigated cell proliferation and expression of cytoskeletal proteins in 32 cases of primary basal cell carcinomas (BCC), 10 cases of recurrent BCC, and 10 cases of metatypical carcinomas (MTC). Paraffin-embedded biopsies were evaluated immunohistochemically with a battery of antibodies. Antibodies to proliferating cell nuclear antigen (PCNA) demonstrated comparatively low numbers of proliferating cells in 25 of 32 cases of primary BCC. In contrast, both recurrent BCC and MTC exhibited three to four times higher levels of proliferating cells than primary BCC. PCNA-positive cells were usually distributed uniformly throughout the lobules; at times, however, they were localized to the outer areas of those neoplasms, with a comparatively low level of proliferation index. Antibodies to keratin 17 strongly stained cells of all BCC cases, and antibodies to keratin 8 reacted with most of them. In contrast, the staining intensity of both types of keratin in MTC was decreased six to eight times as compared with all BCC. In addition, cells of eight BCC and three MTC reacted with antibodies to smooth muscle alpha-actin and myosin, neoplasms that did not differ by the number of PCNA-positive nuclei from carcinomas without contractile proteins. The differences in cell proliferation and keratin expression between BCC and MTC may be useful criteria for further distinguishing these carcinomas. The appearance of contractile proteins in some BCC and MTC may be the result of, or implies, myoepithelial differentiation.

Interaction of avidin-carrying red blood cells with nucleated cells

In vivo application of red blood cells (RBC) modified with avidin-biotin complex has been suggested recently for various purposes. However, avidin attachment to RBC alters their biocompatibility. Thus, it has been described that avidin-carrying biotinylated RBC were lysed by the complement. In the present work interaction between avidin-carrying RBC and nucleated cells has been examined. It was found that attachment of avidin, but not streptavidin, to RBC led to binding of avidin-carrying RBC to nucleated cells. Adhesiveness of nucleated cells for avidin-carrying RBC varied for different types of nucleated cells. The strongest adhesion was observed with human fibroblasts and rat Kupffer cells, while rat liver endothelial cells were practically non-adhesive for avidin-carrying RBC of corresponding species. In contrast with avidin (streptavidin)-induced lysis by the complement, avidin-induced adhesion was independent of temperature, the presence of divalent ions and mode of avidin attachment. Polyanions (dextran sulphate and heparin) efficiently inhibited the adhesion presumably due to interaction with the membrane-bound avidin. Polyanions to a much lesser extent inhibited lysis of avidin-carrying RBC, which might be a result of their interaction with the complement components. Polycations also blocked adhesion of avidin-carrying RBC to nucleated cells, presumably due to interaction with negatively charged cell-surface components. Therefore, attachment of avidin to RBC alters their biocompatibility, due to both high positive charge of avidin and the cross-linking of biotinylated membrane proteins.

Monocyte/macrophage accumulation and smooth muscle cell phenotypes in early atherosclerotic lesions of human aorta

In a search for early atherosclerotic lesions, we have investigated grossly normal areas of human thoracic aortas taken at autopsy from 40 trauma victims aged from 3 to 40 years. Two areas of aorta were compared: lesion predisposed to atherosclerosis (LP) area localized on the dorsal aspect of the vessel along the row of intercostal branching sites, and lesion resistant (LR) area located on the ventral aspect of the vessel. Accumulation of apolipoprotein B (apo B) was found in LP aortic area of each child older than 6 years. Similar retention of apo B in LR area appeared only in aortas of teenagers. The apo B staining increased with age in both areas tested but was usually of a greater extent in LP area than in LR area. Typical smooth muscle cells (SMCs) and a few monocytes/macrophages (Mn/Mph) were revealed in the intimal layer of all aortas examined. The number of Mn/Mph dramatically increased in LP areas of individuals over 17 years. Quantitative study of double stained sections has shown a 2- to 6-fold enhanced number of Mn/Mph in LP area compared with LR aortic area of 10 men over 21 years. Focal infiltration of Mn/Mph in aortas of young adults occurred without endothelial denudation. In addition, some intimal SMCs in LP area of 12 aortas out of 29 expressed desmin and contained well-developed endoplasmic reticulum, while such cells were seldom detected in LP area of the vessels. Thus, focal accumulation of apo B with subsequent Mn/Mph infiltration and SMC phenotypic modulation in LP aortic area of young adults may be causally involved in fatty streak and atherosclerotic plaque formation.

Nature of aortic smooth muscle cellular activity induced by cholesterol incorporation through an LDL-receptor-independent pathway: preventive role of trifluoperazine on such activity

The present study was addressed to understand two specific issues: (a) whether atherogenic activity of smooth muscle cells could be initiated by incorporating cholesterol within their membranes through a LDL-receptor-independent pathway; and (b) whether trifluoperazine, which we had recently shown to prevent the cholesterol-induced atherogenesis in an experimental animal model system, could prevent such activity of these cells induced by cholesterol in vitro. The results of such a study revealed that trifluoperazine could prevent the cholesterol-induced stimulation of (a) DNA synthesis, (b) cholesterol synthesis, (c) intracellular cGMP levels, (d) intracellular free and esterified cholesterol accumulation, and (e) collagen secretion. Furthermore, the drug caused stimulation of cholesterol-induced suppression of LDL-receptor synthesis. On this basis, we suggest that acquisition of cholesterol by smooth muscle cells through the LDL-receptor-independent pathway may be the fundamental process responsible for atherogenic activity of these cells and that the drug trifluoperazine has the inherent capacity to prevent the membrane-cholesterol-modulated atherogenic activity of smooth muscle cells in vitro.

Localization of apolipoprotein E in normal and atherosclerotic human aorta

To elucidate the role of apolipoprotein E (apo E) in atherogenesis, we have investigated the localization of apo E in normal and atherosclerotic aortas as well as in other tissues of 32 post-mortem individuals. Using double immunofluorescence it has been found that normal intima of individuals older than 20 years and some adolescents contained immunoreactive material that reacted with poly- and monoclonal antibodies to apo E. A staining pattern of apo E differed from that of apolipoprotein B, the latter being seen in normal intima of each child older than 7 years. Apo E was present extracellularly in lipid streaks and atheromatous plaques, where its staining was particularly intensive around the necrotic zone of plaques. Some macrophages in the plaques of 4 aortas exhibited apo E-positive staining, while aortic endothelial and smooth muscle cells never contained apo E. Apo E-positive staining was not found in the majority of vessel cells, it was always, however, observed in other types of cells including hepatocytes. Kupffer cells, spleen macrophages and cerebral astrocytes. Our findings indicate that only some macrophages in human aorta may be responsible for the production of apo E that can participate in reverse cholesterol transport. At the same time, apo E accumulation in the aortic wall may promote the development of atherosclerosis.

Effect of trifluoperazine on DNA and LDL-receptor synthesis in smooth muscle cells exposed to hypercholesterolemic medium in vitro

We recently demonstrated that calmodulin and/or protein kinase C may play a crucial role in cholesterol-induced atherogenesis in experimental animal model system. The present study, which was undertaken to elucidate the effect of trifluoperazine (known as a potent inhibitor of calmodulin and protein kinase C) on DNA and LDL-receptor synthesis of aortic smooth muscle cells exposed to hypercholesterolemic medium, revealed that (a) trifluoperazine at a concentration of 25 microM caused an approximately threefold increase in the [35S]methionine-incorporated LDL-receptor protein as compared with values found in control cells; (b) the drug at concentrations greater than or equal to 0.1 microM caused inhibition of DNA synthesis as compared with values found in control cells. These results demonstrate that the preventive effect of trifluoperazine on the atherogenic activity of smooth muscle cells may be due to its ability to increase LDL-receptors synthesis as well as concomitant inhibitory action on DNA synthesis of smooth muscle cells exposed to hypercholesterolemic medium.

Balloon catheter injury to rabbit carotid artery. II. Selective increase in reactivity to some vasoconstrictor drugs

The present study examined the changes in reactivity to a variety of vasoconstrictor drugs of the rabbit carotid artery during development of an intimal thickening induced by injury with an inflated balloon catheter. The injured and the unoperated contralateral carotid arteries were studied at 2 and 6 weeks after the operation. To differentiate areas of the injured artery lined by modified smooth muscle cells from areas lined by regenerated endothelial cells, each rabbit was injected with Evans blue dye before sacrifice. Ring segments (3 mm length) from the control and injured arteries were mounted in organ baths to record the circumferential isometric force with a technique that ensured that all rings were set to equivalent initial resting conditions of passive transmural stretch. Compared with the controls, the experimental arteries had a significantly decreased maximum contraction (Emax) in response to KCl at both 2 and 6 weeks. The experimental arteries were also significantly less sensitive to the alpha 1-adrenoceptor agonist, methoxamine, at both 2 weeks (approximately sevenfold) and 6 weeks (fourfold), with a marked decrease in Emax at 2 weeks, which returned to control values at 6 weeks. There was no change in Emax to either serotonin or the thromboxane A2-mimetic, U46619, in the experimental arteries at either time. There was, however, a small but significant increase in the sensitivity to both drugs. There was no difference in response to any of the constrictor agents between the white and blue regions of the experimental vessels.(ABSTRACT TRUNCATED AT 250 WORDS)