Interaction of native and cell-modified low density lipoprotein with collagen gel

Early echocardiographic signs of cardiovascular affection in pediatric familial hypercholesterolemia

Familial hypercholesterolemia (FH) is a rare autosomal dominant genetic disorder caused by defective low-density lipoprotein (LDL) receptors or abnormal apolipoprotein B. FH raises the risk of premature atherosclerotic disease and cardiovascular death in young adults. However, cardiovascular affection in children needs to be more adequately studied. Our study aimed to evaluate the effect of hypercholesterolemia on the cardiovascular system of pediatric patients with homozygous FH using conventional and advanced echocardiographic parameters such as tissue Doppler imaging (TDI) and 2-dimensional speckle-tracking echocardiography (2D-STE). This case-control study matched 25 healthy children with 21 patients with homozygous FH. Both groups had conventional echocardiography, TDI, and 2D-STE. Myocardial velocities of the left and right ventricles, left ventricular strain, and aortic stiffness parameters were measured. The FH group had greater systolic blood pressure, dilated coronary arteries, and hypertrophied left ventricle (LV) compared to the control (P = 0.0001, P = 0.001, P = 0.01, respectively). The mitral E/E' ratio was higher in the patient group than in the control group (P = 0.007), indicating LV diastolic dysfunction in patients. At the same time, LV systolic function evaluated by 2D-STE was comparable to that in the control group. The abdominal aorta circumferential strain and ascending aorta M-mode-derived strain were significantly lower in patients compared to those in the control (P = 0.024, P = 0.0001, respectively), indicating increased aortic stiffness in the patients' group; moreover, 85.7% of patients had mild aortic insufficiency.  Conclusion: Mild aortic insufficiency, coronary artery dilatation, left ventricular (LV) diastolic dysfunction, and increased aortic stiffness are among early cardiovascular markers in pediatric patients with homozygous FH before impaired LV systolic function. What is Known: • Familial hypercholesterolemia (FH) in adults is associated with accelerated atherosclerosis, aortic valvopathy, dilated coronary arteries, ischemic heart disease, and premature cardiovascular death. • The cardiovascular effects of FH in children require additional research. What is New: • Pediatric patients with familial hypercholesterolemia tend to have an early affection for left ventricular diastolic function before the affection for the systolic function. • The diastolic dysfunction associated with pediatric FH is correlated to the aortic stiffness and low-density lipoprotein levels.

The interaction of plasma sialylated and desialylated lipoproteins with collagen from the intima and media of uninvolved and atherosclerotic human aorta

We have evaluated the binding of sialylated and desialylated lipoproteins to collagen isolated from the proteoglycan and musculoelastic layers of intima and media of uninvolved human aorta and atherosclerotic lesions. Comparing various collagen preparations from the uninvolved intima-media, the binding of sialylated apoB-containing lipoproteins was best to collagen from the intimal PG-rich layer. Binding of sialylated apoB-containing lipoproteins to collagen from this layer of fatty streak and fibroatheroma was 1.4- and 3.1-fold lower, respectively, in comparison with normal intima. Desialylated VLDL versus sialylated one exhibited a greater binding (1.4- to 3.0-fold) to all the collagen preparations examined. Desialylated IDL and LDL showed a higher binding than sialylated ones when collagen from the intimal layers of fibroatheroma was used. Binding of desialylated HDL to collagen from the intimal PG-rich layer of normal tissue, initial lesion, and fatty streak was 1.2- to 2.0-fold higher compared with sialylated HDL.

Collagen-bound LDL modifies endothelial cell adhesion to type V collagen: Implications for atherosclerosis

Low density lipoprotein (LDL) is retained in the extracellular matrix of the arterial wall where it is considered to be atherogenic, but little is known about how cell adhesion to the matrix is affected by collagen-bound LDL. We tested the effect of native, oxidized and acetylated LDL reacted with adsorbed monomeric type I, III and V collagen on endothelial cell adhesion to collagen using a colorimetric adhesion assay. We found that none of the LDL species affected adhesion to type I and III collagen, but that collagen-bound native and acetylated LDL enhanced attachment to type V collagen, whereas bound oxidized LDL inhibited adhesion to this collagen. We therefore suggest that oxidized LDL associated with type V collagen in the arterial wall would favor de-endothelialization and contribute to atherogenesis and thrombosis.

Absence of the protease inhibitor cystatin C in inflammatory cells results in larger plaque area in plaque regression of apoE-deficient mice

Matrix remodelling plays an important role in regulating plaque stability. Cystatin C, an inhibitor of the elastin-degrading cysteine proteases of the cathepsin family, is believed to be one of the key protease inhibitors in this process. The aim of the present study was to investigate the role of leukocyte-specific cystatin C expression under conditions that favour plaque regression. Apolipoprotein E-deficient mice (apoE-/-) were given a Western-type diet 15 weeks prior transplantation with bone marrow from mice lacking cystatin C (cysC-/-) or cystatin C positive (cysC+/+) mice, in both cases apoE+/+ to create conditions favouring plaque regression. Transplantations were verified with PCR and Western analyses. Transplanted mice showed a 70% decrease in lipid content and reduction in plaque area compared to baseline ApoE-/- mice, demonstrating plaque regression due to apoE expression in macrophages. apoE-/- mice transplanted with cysC-/- bone marrow were then compared to mice transplanted with cysC+/+ bone marrow. Mice receiving cysC-/- bone marrow had a 30% larger plaque area, despite absence of significant differences in plasma cholesterol and lipid contents in plaque. Unexpectedly, mice transplanted with cystatin C-deficient bone marrow cells had increased elastin and collagen content in lesions. These observations suggest that leukocyte-specific expression of cystatin C is actively involved in matrix remodelling associated with plaque regression.

Molecular interactions leading to lipoprotein retention and the initiation of atherosclerosis

Atherosclerosis is distinguished by the accumulation of lipoprotein lipid within the arterial wall. An ionic interaction of positively charged regions of apolipoprotein (apo) B with matrix proteins, including proteoglycans, collagen, and fibronectin, is thought to initiate this process. Proteoglycans are complex glycoproteins containing highly negatively charged carbohydrate chains. These proteins are abundant in atherosclerosis lesions, and they associate with apoB-containing lipoproteins. Several specific regions of apoB may mediate this process. Other lipoprotein-associated proteins, including apoE and lipases, might also participate in this process. In addition, retention may occur via lipoprotein association with other matrix molecules or as a consequence of intra-arterial lipoprotein aggregation.

Vascular collagens: spotlight on the role of type VIII collagen in atherogenesis

Collagens play a central role in maintaining the integrity and stability of the undiseased as well as of the atherosclerotic vessel wall. An imbalanced metabolism may lead to uncontrolled collagen accumulation reducing vessel wall velocity, frequently resulting in arterial occlusion or thrombosis. A reduced production of collagen and its uncontrolled degradation may affect the stability of the vessel wall and especially of the atherosclerotic plaques by making them prone to rupture and aneurysm. This review presents an overview on the four groups of vascular collagens and on their role in atherogenesis. The major focus was to highlight the extraordinary role and importance of the short chain network forming type VIII collagen in the extracellular matrix of undiseased arteries and of atherosclerotic plaques. The molecular structure of type VIII collagen, its cellular origin, its implication in atherogenesis, its temporal and spatial expression patterns in human and experimental models of atherogenesis, the factors modulating its expression, and--not at least--its potential function is discussed.

Oxidative modifications of LDL increase its binding to extracellular matrix from human aortic intima: influence of lesion development, lipoprotein lipase and calcium

Retention of atherogenic lipoproteins in the arterial intima by extracellular matrix (ECM) is assumed to occur during early atherogenesis and its further development. Low density lipoprotein (LDL) trapped in the intima may undergo oxidative modifications, which initiate a chain reaction in atherogenesis. Lipoprotein lipase (LPL) has been found to mediate the binding of native and oxidized LDL to ECM produced by cultured cells and to contribute to foam cell formation by mildly oxidized LDL. In this study ECM, isolated from human aortic intima with different atherosclerotic lesions, was used for the first time to measure the binding to it in vitro of native and differently oxidized 125I-LDL. Oxidation of 125I-LDL increased its binding to the ECM, which was most prominent with the material isolated from intima at the early stage of atherogenesis. With the progression of atherosclerosis, the ability of the isolated intimal ECM to bind native and oxidized 125I-LDL decreased, and strongly oxidized 125I-LDL decreased more than native and moderately oxidized 125I-LDL. LPL increased the binding of moderately oxidized 125I-LDL to the ECM more than native 125I-LDL, while it had only a small effect on strongly oxidized 125I-LDL. LPL-mediated binding of native and oxidized 125I-LDL decreased with the development of atherosclerotic lesions. Calcium ions also increased the binding of LDL to the ECM. This enhanced binding increased with the extent of LDL oxidation, especially at the early stage of atherogenesis, and decreased with lesion progression. These data suggest that the ability of ECM to retain LDL in arterial intima depends on LDL oxidation status and changes with the progression of atherogenesis. In addition, LPL and calcium ions may participate in the retention of LDL in vivo.

ApoE knockout mice expressing human matrix metalloproteinase-1 in macrophages have less advanced atherosclerosis

Matrix metalloproteinase-1 (MMP-1), or interstitial collagenase, has been hypothesized to contribute to the progression of the human atherosclerotic lesions by digesting the fibrillar collagens of the neointimal ECM. The apolipoprotein E knockout (apoE0) mouse model develops complex atherosclerotic lesions, but mice do not possess a homologue for MMP-1. To provide an in vivo evaluation of the role of MMP-1 in atherogenesis, we created a transgenic mouse model that expresses this enzyme specifically in the macrophage, under the control of the scavenger receptor A (SCAV) enhancer/promoter. The MMP-1 transgenic mice were crossed into the apoE0 background and fed an atherogenic diet for 16-25 weeks. Surprisingly, the transgenic mice demonstrated decreased lesion size compared with control littermates. The lesions of the transgenic animals were less extensive and immature, with fewer cellular layers and a diminished content of fibrillar collagen. There was no evidence of plaque rupture. Our data suggest that remodeling of the neointimal extracellular matrix by MMP-1 is beneficial in the progression of lesions.

Interaction of native and modified low-density lipoproteins with extracellular matrix

Lipoprotein-matrix interactions play an important role in arterial disease. Extracellular matrix proteoglycans bind and retain specific positively charged domains on apolipoproteins B- and E-containing lipoproteins during atherogenesis. Retained lipoproteins can undergo several modifications, which may alter their interaction with extracellular matrix molecules. Growth factors, cytokines and oxidized low density lipoproteins influence proteoglycan structure, rendering them more likely to bind and retain lipoproteins during atherogenesis. Lipoproteins, native and modified, also can modulate the expression of several of the matrix degrading enzymes present in vascular tissue, thereby influencing plaque stability. Thus, the interaction of atherogenic lipoproteins with arterial wall matrix molecules can influence the genesis and progression of atherosclerosis and its complications.

Oxidized low density lipoproteins regulate synthesis of monkey aortic smooth muscle cell proteoglycans that have enhanced native low density lipoprotein binding properties

Oxidized low density lipoproteins (Ox-LDL) affect several biological processes involved in atherogenesis. However, it is not known whether Ox-LDL can regulate proteoglycan expression and thus affect arterial wall lipoprotein retention. This study evaluated whether Ox-LDL, as compared with native LDL, regulates proteoglycan expression by monkey arterial smooth muscle cells in vitro and whether proteoglycans synthesized in the presence of Ox-LDL exhibit altered lipoprotein binding properties. Ox-LDL stimulated glycosaminoglycan synthesis, as measured by (35)SO(4) incorporation, by 30-50% over that of native LDL. The effect was maximal after 72 h of exposure to 5 microg/ml of Ox-LDL. The molecular sizes of versican, biglycan, and decorin increased in response to Ox-LDL, as indicated by size exclusion chromatography and SDS-polyacrylamide gel electrophoresis. These effects could be mimicked by the lipid extract of Ox-LDL. These size increases were largely due to chain elongation and not to alterations in the ratio of (35)SO(4) to [(3)H]glucosamine incorporation. Affinity chromatography indicated that Ox-LDL stimulated the synthesis of proteoglycans with high affinity for native LDL. Ox-LDL also specifically stimulated mRNA expression for biglycan (but not versican or decorin), which was correlated with increased expression of secreted biglycan. Thus, Ox-LDL may influence lipoprotein retention by regulating synthesis of biglycan and also by altering glycosaminoglycan synthesis of vascular proteoglycans so as to enhance lipoprotein binding properties.

Oxidized LDL, glomerular mesangial cells and collagen

Lipid deposits, foam cell collection and accumulation of mesangial matrix components are recognized as early events in the development of focal segmental glomerulosclerosis (FSGS). Studies have suggested that oxidative stress is increased in uremic patients. Oxidized low-density lipoprotein (Ox-LDL) has been identified in the lesions of FSGS. Dietary antioxidants reduced not only the staining intensity of Ox-LDL but also the severity of renal injury in rats with experimental FSGS possibly by making lipoproteins resistant to oxidation. In vitro studies showed that LDL during its incubation with human mesangial cells (HMC) was peroxidatively modified and stimulated alpha1(I), alpha1(III), and alpha1(IV) collagen mRNA expression. Vitamin E, an antioxidant, and antibody against Ox-LDL caused a marked reduction in collagen mRNA stimulated by LDL. These findings suggest that LDL deposited and oxidized in the glomeruli may be implicated in the development of glomerulosclerosis by facilitating excessive mesangial matrix generation.

Oxidized LDL-containing immune complexes induce Fc gamma receptor I-mediated mitogen-activated protein kinase activation in THP-1 macrophages

Our previous studies have shown that Fc gamma receptor (FcgammaR)-mediated uptake of LDL-containing immune complexes (oxLDL-ICs) by human monocyte-derived macrophages leads to not only transformation of macrophages into foam cells but also macrophage activation and release of cytokines. It has been shown that cross-linking of FcgammaR triggers activation of signal transduction pathways that alter gene expression in macrophages. In this study, we determined whether engagement of FcgammaR by oxLDL-ICs leads to activation of mitogen-activated protein (MAP) kinase pathway, a signaling cascade serving many important functions, including the regulation of gene expression, in THP-1 macrophage-like cells. Our results from immunoblotting, using specific anti-phosphorylated MAP kinase antibodies, showed that oxLDL-ICs induced extracellular signal regulated kinase 2 (ERK2) MAP kinase phosphorylation in THP-1 macrophage-like cells in time- and dose-dependent manners. Cholesterol loading before stimulation led to a longer phosphorylation of ERK2. Nuclear translocation of phosphorylated ERK was markedly increased after the stimulation. Moreover, our data showed that oxLDL-IC induction of MAP kinase was prevented by human monomeric IgG1, suggesting that the specific engagement of type I FcgammaR by oxLDL-IC is responsible for the MAP kinase activation. Finally, we showed that human anti-oxLDL autoantibody-containing immune complexes immobilized on type I collagen induced MAP kinase activation in THP-1 cells. These results strongly suggest that oxLDL-IC, which has been detected in atherosclerotic plaques, may play an important role in macrophage activation and atherogenesis.

Expression of type VIII collagen after cholesterol diet and injury in the rabbit model of atherosclerosis

This study presents an analysis of the expression of type VIII collagen mRNA in response to cholesterol diet and balloon injury in the rabbit iliac artery. The design of the animal experiments was as follows: 28 male New Zealand White rabbits were divided into the 3 different treatment groups. Group 1 received regular chow; group 2 was fed with a 1% cholesterol diet for 6 weeks and normal chow for 5 weeks; and group 3 underwent balloon injury, then 6 weeks of a 1% cholesterol diet, which was followed by 5 weeks of normal chow. The expression pattern of type VIII collagen mRNA was compared with that of the fibrillar collagen types I and III, transforming growth factor-beta1, a factor known to exert the most potent stimulatory effect on collagen synthesis in vitro, and matrix metalloproteinase 1, a collagen-degrading enzyme. The cholesterol diet resulted in an upregulation of type VIII collagen, fibrillar collagens, transforming growth factor-beta1, and matrix metalloproteinase I in the adventitia. Although the number of type VIII collagen mRNA-expressing cells in the media increased, no significant difference in overall expression levels was detectable by northern blot analysis. The ratio of medial smooth muscle cells expressing type VIII collagen mRNA to those expressing type I and type III collagen mRNA (CVIII:CI:CIII) changed from 1:1.88:0.03 in the normal media to 1:0.78:0.29. When cholesterol feeding was preceded by balloon injury, type VIII collagen mRNA expression concomitant with the fibrillar collagens was further upregulated over and above that level reported after cholesterol diet alone. In general, low levels of transforming growth factor-beta1 mRNA correlated with high expression of matrix metalloproteinase I. Our study indicates that a cholesterol diet resulted in a balanced reorganization of the collagen composition but did not result in marked collagen accumulation. This may provide an extracellular environment that favors migration and proliferation processes during early atherogenesis. It also demonstrates that type VIII collagen is highly expressed and deposited at later stages, and this may be linked to processes such as tissue reorganization during vascular repair and plaque stabilization.

Changes in cultured arterial smooth muscle cells isolated from chicks upon cholesterol feeding

We have developed cultures of smooth muscle cells (SMC) isolated from arterial hypercholesterolemic chicks (cholesterol-SMC). These cultures are suitable for the study at the molecular level of the changes in arterial SMC induced by a cholesterol diet. By using a strong dose of cholesterol (5%) for 10 d, we obtained very proliferative SMC which became foam cells after 30 d in culture. On the other hand, SMC cultures isolated from control-fed chicks had a lower growth rate than the SMC ones under the same culture conditions. DNA synthesis was fourfold greater in cholesterol-SMC than in control-SMC cultures. Intracellular cholesterol concentrations were the same in both cholesterol and control SMC during the first 14 d of culture but afterward increased in differing ways: after 20 d of culture the cholesterol-SMC increased their cholesterol content to double the control. We give here the results obtained from transmission electron microscopy, lipid analysis, proliferation studies, DNA, RNA and protein synthesis, and then discuss their implications.

Limits of lipid-lowering therapy: the potential benefits of amlodipine as an antiatherosclerotic agent

Treatment of atherosclerosis has focused mainly on decreasing low-density lipoprotein cholesterol (LDL-C). However, recent coronary angiography trials have revealed that aggressive lowering of LDL-C below 100 mg/dl arrests atherosclerosis progression in only 50% to 60% of patients. Furthermore, with quantitative coronary angiography, significant regression occurred only in advanced fibrous-fatty plaques (> or = 50% stenosis) and not in the younger, more cell-proliferative lesions (< 50% stenosis). It is clear that lipid-lowering therapy has limited efficacy; therefore, other drugs, especially antiproliferative agents, may be useful for secondary and primary prevention. To test this hypothesis a new calcium antagonist, amlodipine, which has in vitro antiproliferative, cell membrane stabilizing, and antioxidative properties, was studied to determine whether it has antiatherogenic effects in nonhuman primates. Amlodipine normalized elevated levels of oxidized arterial cholesterol without reducing elevated total plasma cholesterol levels and significantly suppressed atherosclerosis progression in monkeys who had been fed an atherogenic diet. These data suggest that amlodipine may be an excellent candidate, in combination with lipid-lowering drugs, for dual therapy of atherosclerotic vascular disease, and also may be effective monotherapy, even when LDL-C is not lowered satisfactorily.

In vitro interactions of oxidatively modified LDL with type I, II, III, IV, and V collagen, laminin, fibronectin, and poly-D-lysine

The accumulation of LDL in the arterial intima is considered a key event in atherogenesis. We investigated the binding of oxidized LDL (ox-LDL) to microtiter plates coated with type I or II collagen, laminin, fibronectin, or poly-D-lysine. Oxidation of LDL, 125I-LDL, or Eu(3+)-LDL was performed with CuCl2, varying the time of oxidation. Bound lipoprotein was assessed by counting radioactivity or fluorescence in the wells. Binding of highly ox-LDL in PBS followed the order: type I collagen > poly-D-lysine > type II collagen > laminin > fibronectin. Comparing various collagen types, the binding of ox-LDL followed the order: type I > type V and, type III > type IV > type II collagen. Binding of ox-LDL in PBS was dependent on an increase in negative charge of ox-LDL. Testing certain amino acids as competitors for binding of highly ox-LDL to type I collagen put lysine first, followed by arginine and histidine. On laminin, histidine competed most, followed by lysine and arginine. When studying the influence of Na+, K+, Ca2+, Mg2+ (equivalent to their concentrations in the interstitial fluid), native LDL, moderately ox-LDL, and highly ox-LDL showed the same affinity to type I collagen. However, a fivefold dilution of the buffer increased the affinity of moderately and highly ox-LDL 3.9- and 10-fold compared with native LDL. Application of the F(ab')2 from a monoclonal antibody to ox-LDL revealed a strong competition of the binding of highly ox-LDL to type II collagen (60%), laminin (35%), type I collagen (20%), and poly-D-lysine (15%), whereas the binding to fibronectin was not affected.

Dietary antioxidant inhibits lipoprotein oxidation and renal injury in experimental focal segmental glomerulosclerosis

Lipid peroxidation may be involved in the pathogenesis of focal segmental glomerulosclerosis (FSGS). In the present study we examined whether lipid-soluble antioxidants, probucol and vitamin E, could inhibit renal injury in rats with chronic puromycin aminonucleoside (PA) nephrosis and dietary hypercholesterolemia by protecting lipoproteins from oxidation. Male Sprague-Dawley rats received six intraperitoneal injections of PA over a 10 week period and were fed a high cholesterol (HC) diet (PA-HC) or the same diet supplemented with either 1% probucol or vitamin E (100 IU/kg) for 32 weeks. For comparison, a group of rats received PA injections and a normal diet (PA-normal) with or without probucol or vitamin E. Another group rats received saline injections instead of PA and were fed a HC diet (Sal-HC) with or without probucol or vitamin E. At the end of the experiment, proteinuria, FSGS and tubulointerstitial lesions were present in the untreated rats with PA-HC or PA-normal. The magnitude of these lesions was significantly greater in the PA-HC rats than the PA-normal. In contrast to the PA-HC group with hypercholesterolemia, the PA-normal group did not show hypercholesterolemia from week 16 onwards. The rats with PA-HC alone showed significantly higher renal cortical malondialdehyde (MDA) levels and greater susceptibility of plasma very low density lipoprotein (VLDL) + low density lipoprotein (LDL) to the copper-mediated oxidation than the rats with PA-normal or Sal-HC alone. The administration of probucol or vitamin E in the rats with PA-HC significantly reduced the susceptibility of plasma VLDL + LDL to in vitro oxidation, renal cortical MDA level, proteinuria, mesangial volume density and magnitude of FSGS and interstitial lesions. Immunohistochemical staining of renal tissue showed focal segmental distribution of oxidized LDL (Ox-LDL) in the glomeruli of rats with PA-HC. Administration of probucol or vitamin E reduced the intensity of Ox-LDL staining. The staining with ED1 demonstrated that infiltrating glomerular macrophages were significantly more prevalent in the untreated rats with PA-HC than PA-normal or Sal-HC. Treatment with probucol or vitamin E significantly reduced the number of glomerular macrophages in the rats with PA-HC. These results suggest that alimentary hypercholesterolemia aggravates the renal damage in association with increased renal lipid peroxides in chronic PA nephrosis, and that dietary probucol or vitamin E attenuates renal injury in rats with PA-HC possibly by making lipoproteins resistant to oxidation and by inhibiting intraglomerular macrophage infiltration.

The proteoglycan decorin links low density lipoproteins with collagen type I

Decorin is a small dermatan sulfate-rich proteoglycan which binds to collagen type I in vitro and in vivo. In atherosclerotic lesions the contents of low density lipoprotein (LDL), decorin, and collagen type I are increased, and ultrastructural studies have suggested an association between LDL and collagen in the lesions. To study interactions between LDL, decorin, and collagen type I, we used solid phase systems in which LDL was coupled to a Sepharose column, or in which LDL, decorin, or collagen type I was attached to microtiter wells. The interaction between LDL and decorin in the fluid phase was evaluated using a gel mobility shift assay. We found that LDL binds to decorin by ionic interactions. After treatment with chondroitinase ABC, decorin did not bind to LDL, showing that the glycosaminoglycan side chain of decorin is essential for LDL binding. Acetylated and cyclohexanedione-treated LDL did not bind to decorin, demonstrating that both lysine and arginine residues of apoB-100 are necessary for the interaction. When collagen type I was attached to the microtiter plates, only insignificant amounts of LDL bound to the collagen. However, if decorin was first allowed to bind to the collagen, binding of LDL to the decorin-collagen complexes was over 10-fold higher than to collagen alone. Thus, decorin can link LDL with collagen type I in vitro, which suggests a novel mechanism for retention of LDL in collagen-rich areas of atherosclerotic lesions.

Interactions between macrophages and oxidized low density lipoprotein in the presence of type I collagen

In order to investigate the influence of collagen on the interactions between macrophages and oxidatively modified low density lipoprotein (ox-LDL), type I collagen was isolated from rat tail tendon and prepared as a gel. The binding of 125I-ox-LDL, 125I-malondialdehyde (MDA)-LDL and 125I-acetyl-LDL to collagen was higher but the binding of 125I-4-hydroxynonenal (HNE)-LDL was lower than that of native 125I-LDL. When mouse peritoneal macrophages were cultivated on this collagen gel, most of the modified LDL was bound to the collagen gel rather than taken up by macrophages. The amount of modified 125I-LDL degraded by the macrophages decreased in the presence of the collagen gel. In the absence of gel a similar degree of reduction in degradation of modified 125I-LDL by macrophages was obtained when the cells were treated with cytochalasin D, an inhibitor of non-specific phagocytosis. However, the treatment of the macrophages cultivated on the collagen gel with cytochalasin D did not influence the degradation of 125I-ox-LDL and 125I-HNE-LDL. These results suggest that the uptake of ox-LDL by macrophages grown on collagen gel is primarily mediated via the scavenger receptors pathway, whereas in the absence of collagen also other mechanisms of uptake are operating.

Involvement of oxidation in LDL-induced collagen gene regulation in mesangial cells

Oxidized low-density lipoprotein (Ox-LDL) is present in the lesions of focal segmental glomerulosclerosis (FSGS), but the role of Ox-LDL in the disease process is not clear. Recent studies have shown that LDL stimulates the type IV collagen mRNA expression in cultured mesangial cells. Thus, we examined whether oxidative stress is responsible for the stimulation of LDL-induced collagen gene expression in cultured human mesangial cells (HMCs). When quiescent HMCs were exposed to serum-free media containing LDL for 48 hours, peroxidation of LDL was induced as shown by the increased production of thiobarbituric acid-reactive substances (TBARS). LDL stimulated the alpha 1 (I), alpha 1 (III), and alpha 1 (IV) mRNA expression in a dose-dependent manner. At a concentration of 200 micrograms/ml, LDL enhanced the levels of alpha 1 (I), alpha 1 (III), and alpha 1 (IV) mRNA by 3.7-, 3.8- and 3.2-fold, respectively, over the levels in the control cells. These transcripts were further increased 5.4-, 6.7-, and 5.9-fold, respectively, by the addition of 500 micrograms/ml of LDL. Cu(2+)-catalyzed Ox-LDL at a concentration of 200 micrograms/ml also stimulated the alpha 1 (I), alpha 1 (III), and alpha 1 (IV) mRNA expression 4.4-, 5.9-, and 2.8-fold, respectively, compared with the control cells. The addition of monoclonal antibody (mAb) OL-10, which recognizes the malondialdehyde (MDA)-modified peptide epitope, or vitamin E (50 microM) to cultured HMC exposed to LDL markedly inhibited the stimulation of collagen gene expression. When HMCs were incubated with MDA (200 microM), alpha 1 (I), alpha 1 (III), and alpha 1 (IV) mRNA levels increased by two- to threefold compared to control cells. Immunohistochemical staining utilizing mAb OL-10 demonstrated the presence of MDA-modified proteins in the cytoplasm of HMC exposed to either LDL or MDA. These results suggest that peroxidative products of LDL stimulate collagen gene expression possibly via modification of proteins, which are responsible for the expression of collagen genes in cultured HMCs. Given that, lipid peroxidation of LDL may be implicated in the development of glomerulosclerosis by facilitating excessive mesangial matrix generation.

Interstitial inflammation and fibrosis in rats with diet-induced hypercholesterolemia

Abnormalities in lipid metabolism appear to play a pathogenic role in progressive renal disease. To elucidate the cellular and molecular basis of renal interstitial fibrosis in uninephrectomized rats with diet-induced hypercholesterolemia, we fed experimental rats with standard rat chow supplemented with 4% cholesterol and 1% cholic acid. Control rats were fed an isocaloric diet. Groups of 7 control and 7 experimental rats were killed after 4, 8, and 12 weeks. Hypercholesterolemic rats developed albuminuria; serum creatinine was elevated at 12 weeks. By 12 weeks numerous oil red O-positive cells were present throughout the interstitium and to a lesser extent in tubules. Total renal lipid-peroxidation products were significantly increased (172 +/- 15, 198 +/- 28, and 197 +/- 13 mmol malondialdehyde/kidney at 4, 8, and 12 weeks vs. 123 +/- 17, 144 +/- 6, and 125 +/- 10 mmol in controls). Immunostaining revealed oxidatively modified lipoproteins within tubular and interstitial cells. The interstitial disease was characterized by an interstitial infiltrate of monocytes. Significant increases were detected in renal cortical mRNA levels for monocyte chemoattractant protein-1 (MCP-1), osteopontin, and vascular cell adhesion molecule-1 (VCAM-1), associated with changes in the pattern of immunostaining for each encoded proteins. Total kidney collagen was significantly increased at 12 weeks (9.8 +/- 0.9 mg/kidney vs. 7.8 +/- 0.9 mg in controls). At 12 weeks there was a significant increase in interstitial immunostaining for collagen I, collagen III, collagen IV, fibronectin and tenascin. A significant threefold increase in renal cortical mRNA levels for transforming growth factor beta-1 (TGF-beta 1) at 4 and 12 weeks was associated with the appearance of TGF-beta 1-positive interstitial cells. Renal matrix protein mRNA levels were measured at 4, 8, and 12 weeks. The only statistically significant elevations were procollagen alpha 1(I) and procollagen alpha 1(III) at weeks 8 and 12. In contrast, renal cortical mRNA levels for the tissue inhibitor of metalloproteinases-1 (TIMP-1) were significantly increased at 4, 8 and 12 weeks (1.4 +/- 0.5, 2.7 +/- 0.9 and 2.7 +/- 1.4 arbitrary densitometric units, respectively, vs. 1.0 +/- 0.4, 1.0 +/- 0.5 and 1.0 +/- 0.4 units for controls), and urokinase-type plasminogen activator (muPA) mRNA levels were significantly decreased at 4, 8, and 12 weeks (0.4 +/- 0.1 arbitrary densitometric units for all three experimental groups vs. 1.0 +/- 0.4, 1.0 +/- 0.3, and 1.0 +/- 0.4 units for the control groups). In summary, rats with diet-induced hypercholesterolemia develop renal interstitial fibrosis over several weeks. Following the accumulation of lipids within tubulointerstitial cells, interstitial nephritis develops. The fibrotic phase is characterized by modest changes in matrix protein mRNA levels, up-regulated TIMP-1, and down-regulated muPA levels, suggesting that altered matrix degradation plays a role in the interstitial fibrogenesis in this model.

Benzoporphyrin derivative decreases the binding of low density lipoprotein to the glycosaminoglycan chondroitin-6-sulfate in vitro

We have investigated the effect of the hydrophobic photosensitizer (PS), benzoporphyrin derivative (BPD), on low density lipoprotein (LDL) binding to the glycosaminoglycan (GAG), chondroitin-6-sulfate (C-6-S) in vitro. Agarose electrophoresis of the BPD-LDL complexes indicated that ratios of 50 ng BPD per microgram LDL protein and above displayed increased net negative charge. Ratios less than 10 ng BPD per microgram LDL protein slightly increased the association of the LDL with the C-6-S. Ratios of 10 ng BPD per microgram LDL protein and greater decreased the association between LDL and GAG in a BPD concentration dependent manner. Since the retention of LDL by the extracellular matrix (ECM) GAG in the artery wall is a key event in atherogenesis, the reported effects of BPD on LDL binding to C-6-S may be of interest.

Isolation of 115 human chromosome 8-specific expressed-sequence tags by exon amplification

Exon-amplification experiments were undertaken to isolate potentially transcribable sequences from cosmid clones that previously had been mapped to subchromosomal bands of human chromosome 8 by fluorescence in situ hybridization. From 253 cosmids subjected to this procedure so far, we isolated 169 fragments and confirmed that they had been derived from the original cosmid clones. Among them, 38 revealed homology to repetitive DNA sequences such as Alu and L1 elements. The other 131 were unique sequences, but of these only 115 contained discernible open reading frames. Among these 115 sequences, 15 were identical to parts of six known genes listed in the public database. On the basis of information derived from mapping the original cosmid clones, we were able to localize two of these known genes, zinc finger protein 7 and heat shock transcription factor 1, to 8q24.3. Furthermore, we have proven that some of these clones are parts of the transcribed products by an exon connection method or by isolation of a novel cDNA that is homologous to murine clathrin-associated protein. The expressed-sequence tags isolated here will be useful resources for a transcriptional map of chromosome 8 and for isolation of new genes.

Increased prevalence of coronary ectasia in heterozygous familial hypercholesterolemia

BACKGROUND

Although coronary atherosclerosis most commonly produces clinical effects as a result of stenosis, aneurysmal disease also occurs. We have found an increased prevalence of ectasia and aneurysmal disease in familial hypercholesterolemia (FH) suggesting a link between plasma lipoproteins and coronary aneurysms.

METHODS AND RESULTS

In 197 asymptomatic subjects with FH, we examined the prevalence of ectasia and its association with coronary risk factors. An ectatic segment was defined as one with a luminal diameter > 1.5 times that of the adjacent normal segment, excluding poststenotic dilation. Among subjects with FH, 15% had ectasia compared with 2.5% of an age- and sex-matched control group of 198 subjects without FH presenting for coronary angiography (P < .001). These control patients had significantly more severe coronary atherosclerosis than patients with FH. Ectasia was 3 times more common in men than women (P < .025). Neither age nor hypertension was predictive. Although in part reflecting the striking sex differential, ectasia was strongly associated with a lower HDL cholesterol level (P = .003), a higher LDL/HDL ratio (P = .003), and to a lesser extent, a higher LDL cholesterol level (P = .07). No association was found with plasma triglycerides or very low-density lipoprotein cholesterol levels. Among FH patients, ectasia was strongly associated with an overall index of occlusive atherosclerotic disease, based on quantitative angiography (P = .004). Intracoronary ultrasound interrogation of aneurysmal segments revealed circumferential intimal thickening.

CONCLUSIONS

Coronary ectasia is more prevalent in patients with FH than in other patients with coronary atherosclerosis and shows a strong inverse association with HDL cholesterol levels. This suggests that disordered lipoprotein metabolism in FH may predispose patients to aneurysmal coronary artery disease.

Low density lipoproteins bind more to type I and III collagens by negative charge-dependent mechanisms than to type IV and V collagens

The accumulation of low density lipoprotein (LDL) in the arterial intima is an important characteristic of atherosclerosis. We investigated the mechanisms by which LDL binds to different types of collagen. The binding activities of 125I-labeled human native LDL (nLDL) and copper-oxidized LDL (oxLDL) with different collagen gels prepared in type I collagen-based mixtures with types I, III, IV and V (I+I, I+III, I+IV and I+V, respectively) were examined. A concentration of 20 micrograms LDL protein/150 micrograms collagen/well was used. The diffusion of both nLDL and oxLDL into the collagen gels reached an equilibrium after 48 h. All of the collagen gels showed the same rates of diffusion with both LDLs. The binding activities of oxLDL were significantly greater than those of nLDL (P < 0.001%), while the binding activities for both LDLs followed the order I+I and I+III > I+V > I+IV. However, the increased binding rate of oxLDL compared to nLDL was 1.66 for I+IV, 1.50 for I+V, 1.33 for I+I and 1.19 for I+III. When a 10-fold higher dose of NaCl (1 M) was added to the oxLDL medium, the binding rate of oxLDL was reduced (rate of reduction: 52% (I+I), 48% (I+III), 35% (I+IV), 13% (I+V)). These results suggest that oxLDL binds more to type I and III collagens by negative charge-dependent mechanisms than to type IV and V collagens. Therefore, types I and III collagens may play an important role in trapping LDL, especially oxLDL. Therefore, oxidatively modified LDL may contribute to atherogenesis due to its longer retention in the arterial wall.

Proliferation versus atrophy--the ambivalent role of smooth muscle cells in human atherosclerosis

Most of the current concepts on morphogenesis of atherosclerosis attribute the development of atherosclerotic lesions to the combined effects of two main cellular events: 1) activation of macrophages leading to lipoprotein phagocytosis by scavenger cells, and 2) proliferation of smooth muscle cells (SMC). SMC-like cells producing collagenous fibers and extracellular matrix are particularly involved in the formation of the so-called fibrous caps surrounding the core of an atheroma composed of foam cells and fatty debris. The fiber-forming SMC, in general, are said to result from a proliferation of media SMC which once have moved into the intima. This view of origin of the fiber-forming SMC and the alleged proliferation of media SMC is mainly derived from experimental assays exposing the vessel wall to various kinds of physical or chemical injuries. It is the purpose of this paper to demonstrate that the results of those more or less ephemeral experiments differ from findings obtained from a combined histochemical and morphometric analysis of SMC in the aortic media in spontaneous human arteriosclerosis. Instead of any proliferation, a significant atrophy of SMC occurs in the media with advancing age and progress of atherosclerosis. To some extent, this decrease in numerical and volumetric density of SMC is accompanied with intra- and extracellular calcification. It seems likely that the loss of contractile capacity of the media resulting from wasting of SMC, does slow down the stream of the interstitial fluid in the arterial wall. This stagnation must increase the life span of LDL moving through the interstitial space. The chemical alteration ensuing from aging of LDL mediates its binding to the scavenger receptors and uptake by macrophages. So far, muscular atrophy of the media forms an atherogenic factor of its own, leading to final results similar to those as known from conditions of intravascular aging of LDL in hyperlipoproteinaemia. The augmentation of SMC-like cells in the intima is hardly to be derived from the atrophic media, but rather seems to be due to local proliferation of cells which, in the normal state, do occur in small numbers in the subendothelial space. These so-called myointimal or Langhans-cells share with SMC their content of alpha-actin, but they differ by their stellate configuration from the bipolar shape SMC of the media.

Non-enzymic glycation of collagen inhibits binding of oxidized low-density lipoprotein

We have examined the effect of non-enzymic glycation of native soluble collagen, in solution or in gels, on binding of oxidized low-density lipoprotein (LDL). We found the following. (1) Glycation markedly inhibited binding of LDL. This is contrary to results previously reported; the difference may be attributable to the use of detergent- and heat-denatured collagen, covalently bound to agarose beads, in the earlier study. (2) With increased duration of glycation, collagen solution would not gel, and preformed gels dissolved. (3) [14C]Glucose bound to collagen gels dissociated slowly, even at pH 5, suggesting that it was not present as a Schiff's base; in addition, ketoamines, pentosidine and fluorescent advanced glycation products were not detectable in glycated collagen gels, although they accumulated in tendon collagen glycated under the same conditions. It is hypothesized that the difference in glycation effects between gel and tendon may be due to the strength of cross-linking before glycation: the increase in intermolecular distance in collagen fibrils which results from glycation disrupts the fibrils in gels, preventing binding of LDL and formation of glycation-dependent cross-links, whereas the extensive cross-linking in tendon maintains the intermolecular distances within a range which permits formation of glycation cross-links.

Cellular mechanisms of lipid injury in the glomerulus

Hyperlipidemias may play a role in the progression of various renal diseases, including diabetes mellitus. We therefore examined the characteristics of low-density lipoprotein (LDL) binding and uptake in cultured rat mesangial cells. Mesangial cells bound and took up LDL in a manner consistent with specific receptor mediation. Furthermore, exposure of mesangial cells to LDL enhanced intracellular cholesteryl esterification and decreased de novo cholesterol synthesis. Mesangial cells expressed mRNA for LDL receptor and their expression was downregulated after preloading of cells with LDL. These results are consistent with regulation of cholesterol uptake and metabolism by a specific LDL receptor mechanism. During diabetes the apolipoprotein B of LDL undergoes nonenzymatic glycation, which may alter its affinity for the LDL receptor. Glycation of LDL reduced its affinity for binding to the receptor sites and decreased its uptake by mesangial cells. Thus, during diabetes less LDL may be taken up and more remain extracellularly, where it can be trapped in the matrix. Oxidation of LDL bound to extracellular matrix is believed to be a major factor in the pathobiology of hyperlipidemias. Specific scavenger receptors for oxidized LDL have been described and cloned. We therefore examined whether rat mesangial cells bound and took up oxidized LDL. We demonstrated low-affinity but high-capacity binding sites for oxidized LDL on mesangial cells. In contrast to LDL, which supported mesangial cell proliferation, oxidized LDL was cytotoxic for the cells and resulted in stimulation of mesangial cell prostaglandin E2 production. Trapping of LDL in the extracellular matrix is considered an initial event in LDL-induced vascular pathology. We therefore evaluated binding of LDL and modified LDL to extracellular matrix produced by cultured mesangial cells. Mesangial matrix had a high capacity to bind LDL and modified LDL (glycated or oxidized) in a nonsaturable manner. These results obtained with cultured mesangial cells and their matrix allow the formulation of a working hypothesis. Under normal eulipemic conditions mesangial cells handle LDL in a regulated manner. During hyperlipidemia or expansion of extracellular matrix LDL accumulates in the matrix. There LDL would be subject to oxidative modifications, especially under conditions of mesangial cell stress, such as inflammatory, mechanical, or ischemic injury. Part of the oxidized LDL could be taken up by scavenger receptors on mesangial cells and monocyte-macrophages, resulting in foam cell formation. Excess oxidized LDL, and specifically the lipid peroxides and lysolipids of oxidized LDL, would act as cytotoxic agents on mesangial, epithelial, and endothelial cells, thereby contributing to a vicious cycle of cell damage and sclerosis.

Inhibition by serum components of oxidation and collagen-binding of low-density lipoprotein

Low-density lipoprotein (LDL) is oxidized by cellular and noncellular mechanisms, both leading to an increased binding to collagen. We have investigated the effect of serum on lipid peroxidation, apoprotein oxidation and the binding of oxidized apoprotein to collagen. During noncellular oxidation, lipoprotein-deficient serum strongly inhibited all three processes. The serum fraction of M(r) > 100,000 was equally inhibitory; this effect was not due to alpha 1 or gamma globulins, alpha 2 macroglobulins, haptoglobins or ceruloplasmin. The serum fraction of M(r) 30,000-100,000 stimulated the binding of oxidized apoprotein but the albumin in this fraction inhibited lipid peroxidation and apoprotein oxidation. Serum ultrafiltrate (M(r) < 1000) inhibited lipid and protein oxidation, and binding; the inhibitory effect was abolished by deionization which removed histidine. The effects of lipoprotein-deficient serum and its fractions on cellular oxidation were similar but weaker than those on noncellular oxidation, HDL inhibited noncellular oxidation as well as binding of oxidized apoprotein. VLDL also inhibited oxidation; this could not be accounted for by its content of apo B. If present in vivo, these inhibitory effects would completely suppress both cellular and noncellular oxidation of LDL and its subsequent binding to collagen.

Interactions of LDL and modified LDL with mesangial cells and matrix

Hyperlipidemia may play a role in the progression of diabetic and other renal diseases. Low density lipoprotein (LDL) and other proteins including extracellular matrix components undergo nonenzymatic glycation in vivo. We examined the effects of glycation of LDL as occurs in diabetes (4 to 8%) on binding and uptake by mesangial cells and their proliferation. The glycation of LDL (g-LDL) significantly decreased its binding and uptake by mesangial cells by 15 to 20%, indicating that glycated LDL binds to the LDL receptor, but with lower affinity than LDL. Both LDL and g-LDL modestly stimulated [3H] thymidine incorporation into mesangial cells at 5 to 10 micrograms/ml. Native, oxidized (Ox-LDL) and glycated LDL all bound to the extracellular matrix generated by rat mesangial cells in culture. The binding of LDL, Ox-LDL and g-LDL to mesangial matrix was two to four times higher than to mesangial cells. Binding of LDL and g-LDL was significantly higher to glycolaldehyde modified matrix, which serves as an in vitro model for nonenzymatic glycation end-product cross-linking of matrix which occurs in long-standing diabetes. Based on these findings, we propose that glycation of LDL decreases its binding and uptake by the LDL receptor of mesangial cells and may slow its catabolism. Furthermore, LDL bound to extracellular mesangial matrix can undergo oxidation and generate cytotoxic LDL components. This process may be further enhanced by advanced glycation of the mesangial matrix in diabetes, contributing to glomerular pathology.

Effects of copper and histidine on oxidative modification of low density lipoprotein and its subsequent binding to collagen

It was previously shown that serum low density lipoprotein (LDL) binds to type I collagen gels and that the binding is increased after modification by cultured endothelial cells. It is now demonstrated that when LDL is incubated with cells cultured in Dulbecco's modified minimal essential medium (DMEM), the subsequent binding of LDL to collagen is considerably less than after incubation with endothelial cells cultured in Ham's F-12 medium (F12). To determine the reason for this difference, collagen gels were made with saline containing ingredients of DMEM individually or in groups, and binding of LDL to such gels was measured. Modification of LDL, manifested by a high level of binding to the collagen, by lipid peroxidation (production of thiobarbituric acid-reactive substances), and by increased electrophoretic mobility occurred on exposure to collagen gels made in saline; these changes were almost completely inhibited by the addition of histidine at a concentration equal to that in DMEM. They were also inhibited by butylated hydroxytoluene, desferrioxamine, and EDTA; penicillamine and hydroxyl-radical scavengers inhibited collagen binding but did not inhibit lipid peroxidation or the increase in electrophoretic mobility. Nominally, DMEM contains 270 microM histidine but no copper, whereas F12 contains 135 microM histidine and 10 nM copper; addition of copper (as much as 5 microM) to DMEM or of histidine (as much as 2.16 mM) to F12 did not overcome the differences between the media in supporting LDL oxidation by endothelial cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Display of low density lipoprotein receptors is clustered, not dispersed, in fibroblast and hepatocyte plasma membranes

Although the principal details of low density lipoprotein (LDL) uptake by receptor-mediated endocytosis and its subsequent intracellular fate have been thoroughly investigated, an aspect of this mechanism that continues to provoke controversy concerns the manner of display of LDL receptors upon their initial insertion at the cell surface. While our studies based on electron microscopy of platinum/carbon replicas of gold-labeled cells have previously suggested a clustered display pattern, others have concluded, before and since, that LDL receptors are inserted individually at random widely dispersed sites in the plasma membrane. In this article, we present a series of experiments designed to discriminate between these competing hypotheses. In addition to the use of LDL-colloidal gold complexes, visualized electron microscopically, on cells subjected to a variety of experimental procedures, these experiments include the application of anti-apolipoprotein B-100 antibodies, anti-LDL-receptor antibodies, and direct visualization of native (unlabeled) LDL molecules at the cell surface. All results point to a loose-cluster arrangement, not one involving widely dispersed individual units, as the initial display pattern of newly inserted LDL receptors. A comparison of LDL and beta-very low density lipoprotein receptor distribution in fibroblasts and hepatocytes suggests that this cluster pattern is a characteristic of the LDL (apolipoprotein B/E) receptor across cell types, but that the closely related apolipoprotein E receptor differs in that it is inserted individually in a highly dispersed state, in common with a variety of other receptor types.

Type I macrophage scavenger receptor contains alpha-helical and collagen-like coiled coils

The macrophage scavenger receptor is a trimeric membrane glycoprotein with unusual ligand-binding properties which has been implicated in the development of atherosclerosis. The trimeric structure of the bovine type I scavenger receptor, deduced by complementary DNA cloning, contains three extracellular C-terminal cysteine-rich domains connected to the transmembrane domain by a long fibrous stalk. This stalk structure, composed of an alpha-helical coiled coil and a collagen-like triple helix, has not previously been observed in an integral membrane protein.

Coiled-coil fibrous domains mediate ligand binding by macrophage scavenger receptor type II

The macrophage scavenger receptor, which has been implicated in the pathogenesis of atherosclerosis, has an unusually broad binding specificity. Ligands include modified low-density lipoprotein and some polyanions (for example, poly(I) but not poly(C]. The scavenger receptor type I (ref. 3) has three principal extracellular domains that could participate in ligand binding: two fibrous coiled-coil domains (alpha-helical coiled-coil domain IV and collagen-like domain V), and the 110-amino-acid cysteine-rich C-terminal domain VI. We have cloned complementary DNAs encoding a second scavenger receptor which we have termed type II. This receptor is identical to the type I receptor, except that the cysteine-rich domain is replaced by a six-residue C terminus. Despite this truncation, the type II receptor mediates endocytosis of chemically modified low-density lipoprotein with high affinity and specificity, similar to that of the type I receptor. Therefore one or both of the extracellular fibrous domains are responsible for the unusual ligand-binding specificity of the receptor.