Early human atherosclerosis: accumulation of lipid and proteoglycans in intimal thickenings followed by macrophage infiltration

Loss of Biglycan Enhances Thrombin Generation in Apolipoprotein E -Deficient Mice

Objective—

Thrombin signaling promotes atherosclerosis by initiating inflammatory events indirectly through platelet activation and directly via protease-activated receptors. Therefore, endogenous thrombin inhibitors may be relevant modulators of atheroprogression and cardiovascular risk. In addition, endogenous thrombin inhibitors may affect the response to non–vitamin K-dependent oral anticoagulants. Here, the question was addressed whether the small leucine-rich proteoglycan biglycan acts as an endogenous thrombin inhibitor in atherosclerosis through activation of heparin cofactor II.

Approach and Results—

Biglycan concentrations were elevated in the plasma of patients with acute coronary syndrome and in male Apolipoprotein E -deficient ( ApoE −/− ) mice. Biglycan was detected in the glycocalyx of capillaries and the subendothelial matrix of arterioles of ApoE −/− mice and in atherosclerotic plaques. Thereby a vascular compartment is provided that may mediate the endothelial and subendothelial activation of heparin cofactor II through biglycan. ApoE and Bgn double-deficient ( ApoE −/− /Bgn −/0 ) mice showed higher activity of circulating thrombin, increased platelet activation and platelet adhesion in vivo, supporting a role of biglycan in balancing thrombin activity. Furthermore, concentrations of circulating cytokines and aortic macrophage content were elevated in ApoE −/− /Bgn −/0 mice, suggesting a proinflammatory phenotype. Elevated platelet activation and macrophage accumulation were reversed by treating ApoE −/− /Bgn −/0 mice with the thrombin inhibitor argatroban. Ultimately, ApoE −/− /Bgn −/0 mice developed aggravated atherosclerosis.

Conclusions—

The present results indicate that biglycan plays a previously unappreciated protective role during the progression of atherosclerosis by inhibiting thrombin activity, platelet activation, and finally macrophage-mediated plaque inflammation.

So Much Cholesterol: the unrecognized importance of smooth muscle cells in atherosclerotic foam cell formation

PURPOSE OF REVIEW

Smooth muscle cells (SMCs) form the thickened intimal layer in atherosclerosis-prone arteries in early life, and provide the initial site for retention and uptake of atherogenic lipoproteins. Here we review current knowledge regarding the importance of SMCs in the deposition of cholesterol in atherosclerotic plaque.

RECENT FINDINGS

SMCs were found to comprise at least 50% of total foam cells in human coronary artery atherosclerosis, and exhibit a selective loss of expression of the cholesterol efflux promoter ATP-binding cassette transporter A1. Cholesterol loading induced a loss of SMC gene expression and an increase in macrophage and proinflammatory marker expression by cultured mouse and human arterial SMCs, with reversal of these effects upon removal of the excess cholesterol. Mice engineered to track all cells of SMC lineage indicated that, at most, SMCs make up about one-third of total cells in atherosclerotic plaque in these animals.

SUMMARY

SMCs appear to be the origin of the majority of foam cells in human atherosclerotic plaque. Recent studies suggest a renaissance of research on the role of SMCs in atherosclerosis is needed to make the next leap forward in the prevention and treatment of this disease.

Histopathological Characteristics of Post-inflamed Coronary Arteries in Kawasaki Disease-like Vasculitis of Rabbits

Kawasaki disease (KD) is a systemic vasculitis in infants that develops predominantly in the coronary arteries. Despite the clinically transient nature of active inflammation in childhood albeit rare complications (e.g., coronary artery aneurysm), KD has recently been suggested to increase the incidence of ischemic heart diseases in young adulthood. However, little is known about the histopathology of the coronary artery long after development of the acute KD vasculitis. To address this, we conducted histological studies of rabbit coronary arteries in adolescent phase after induction of the KD-like vasculitis induced by horse serum administration. After a transmural infiltration of inflammatory cells in acute phase at day 7, the artery exhibited a gradual decrease in the number of inflammatory cells and thickening of the intima during the chronic phase up to day 90, where proteoglycans were distinctly accumulated in the intima with abundant involvement of α-smooth muscle actin (α-SMA)-positive cells, most of which accompanied expression of VCAM-1 and NF-κB. Distinct from classical atherosclerosis, inflammatory cells, e.g., macrophages, were barely detected during the chronic phase. These observations indicate that the KD-like coronary arteritis is followed by intimal thickening via accumulation of proteoglycans and proliferation of α-SMA-positive cells, reflecting aberrant coronary artery remodeling.

Evaluation of the potential synergism of imatinib-related poly kinase inhibitors using growth factor stimulated proteoglycan synthesis as a model response

INTRODUCTION

Tyrosine kinase inhibitors were the first class of smart drugs being specifically designed to inhibit a disease causing target. There is a very important but unresolved question as whether or not the overall therapeutic role of an individual tinib results from an action at its primary target, a single most likely, tyrosine kinase, or from the combined or aggregate action at the multiple targets which each tinib addresses.

METHODS

We selected a series of ten tinibs (gefitinib, sunitinib, lapatinib, erlotinib, imatinib, sorafenib, axitinib, vanitinib, bosutinib, dasatinib) with various known targets and investigated their activities in the inhibition of proteoglycan synthesis and GAG hyperelongation stimulated by a tyrosine kinase receptor agonist, platelet derived growth factor (PDGF) and for contrast, a serine/threonine kinase receptor agonist, TGF β and some downstream signalling pathways.

RESULTS

The inhibitory activity varied from little to total inhibition. The actions of the tinibs were directed more towards inhibition of the tyrosine kinase, PDGF receptor signalling pathway compared to the TGF β.

CONCLUSION

There was no suggestion of any synergistic effect arising from inhibition of multiple kinases as the most potent compound, dasatinib, is known to inhibit the broadest spectrum of kinases.

Atherogenesis: hyperhomocysteinemia interactions with LDL, macrophage function, paraoxonase 1, and exercise

Despite great strides in understanding the atherogenesis process, the mechanisms are not entirely known. In addition to diet, cigarette smoking, genetic predisposition, and hypertension, hyperhomocysteinemia (HHcy), an accumulation of the noncoding sulfur-containing amino acid homocysteine (Hcy), is a significant contributor to atherogenesis. Although exercise decreases HHcy and increases longevity, the complete mechanism is unclear. In light of recent evidence, in this review, we focus on the effects of HHcy on macrophage function, differentiation, and polarization. Though there is need for further evidence, it is most likely that HHcy-mediated alterations in macrophage function are important contributors to atherogenesis, and HHcy-countering strategies, such as nutrition and exercise, should be included in the combinatorial regimens for effective prevention and regression of atherosclerotic plaques. Therefore, we also included a discussion on the effects of exercise on the HHcy-mediated atherogenic process.

Potential contributions of intimal and plaque hypoxia to atherosclerosis

Injury of arterial endothelium by abnormal shear stress and other insults induces migration and proliferation of vascular smooth muscle cells (VSMCs), which in turn leads to intimal thickening, hypoxia, and vasa vasorum angiogenesis. The resultant new blood vessels extend from the tunica media into the outer intima, allowing blood-borne oxidized low-density lipoprotein (oxLDL) particles to accumulate in outer intimal tissues by extravasation through local capillaries. In response to oxLDL accumulation, monocytes infiltrate into arterial wall tissues, where they differentiate into macrophages and subsequently evolve into foam cells by uptaking large quantities of oxLDL particles, the latter process being stimulated by hypoxia. Increased oxygen demand due to expanding macrophage and foam cell populations contributes to persistent hypoxia in plaque lesions, whereas hypoxia further promotes plaque growth by stimulating angiogenesis, monocyte infiltration, and oxLDL uptake into macrophages. Molecularly, the accumulation of hypoxia-inducible factor (HIF)-1α and the expression of its target genes mediate many of the hypoxia-induced processes during plaque initiation and growth. It is hoped that further understanding of the underlying mechanisms may lead to novel therapies for effective intervention of atherosclerosis.

Peroxynitrous acid induces structural and functional modifications to basement membranes and its key component, laminin

Basement membranes (BM) are specialized extracellular matrices underlying endothelial cells in the artery wall. Laminin, the most abundant BM glycoprotein, is a structural and biologically active component. Peroxynitrous acid (ONOOH), a potent oxidizing and nitrating agent, is formed in vivo at sites of inflammation from superoxide and nitric oxide radicals. Considerable data supports ONOOH formation in human atherosclerotic lesions, and an involvement of this oxidant in atherosclerosis development and lesion rupture. These effects may be mediated, at least in part, via extracellular matrix damage. In this study we demonstrate co-localization of 3-nitrotyrosine (a product of tyrosine damage by ONOOH) and laminin in human atherosclerotic lesions. ONOOH-induced damage to BM was characterized for isolated murine BM, and purified murine laminin-111. Exposure of laminin-111 to ONOOH resulted in dose-dependent loss of protein tyrosine and tryptophan residues, and formation of 3-nitrotyrosine, 6-nitrotryptophan and the cross-linked material di-tyrosine, as detected by amino acid analysis and Western blotting. These changes were accompanied by protein aggregation and fragmentation as detected by SDS-PAGE. Endothelial cell adhesion to isolated laminin-111 exposed to 10 μM or higher levels of ONOOH was significantly decreased (~25%) compared to untreated controls. These data indicate that laminin is oxidized by equimolar or greater concentrations of ONOOH, with this resulting in structural and functional changes. These modifications, and resulting compromised cell-matrix interactions, may contribute to endothelial cell dysfunction, a weakening of the structure of atherosclerotic lesions, and an increased propensity to rupture.

The small leucine-rich repeat proteoglycans in tissue repair and atherosclerosis

Proteoglycans consist of a protein core with one or more covalently attached glycosaminoglycan (GAG) side chains and have multiple roles in the initiation and progression of atherosclerosis. Here we discuss the potential and known functions of a group of small leucine-rich repeat proteoglycans (SLRPs) in atherosclerosis. We focus on five SLRPs, decorin, biglycan, lumican, fibromodulin and PRELP, because these have been detected in atherosclerotic plaques or demonstrated to have a role in animal models of atherosclerosis. Decorin and biglycan are modified post-translationally by substitution with chondroitin/dermatan sulphate GAGs, whereas lumican, fibromodulin and PRELP have keratan sulphate side chains, and the core proteins have leucine-rich repeat (LRR) motifs that are characteristic of the LRR superfamily. The chondroitin/dermatan sulphate GAG side chains have been implicated in lipid retention in atherosclerosis. The core proteins are discussed here in the context of (i) interactions with collagens and their implications in tissue integrity, fibrosis and wound repair and (ii) interactions with growth factors, cytokines, pathogen-associated molecular patterns and cell surface receptors that impact normal physiology and disease processes such as inflammation, innate immune responses and wound healing (i.e. processes that are all important in plaque development and progression). Thus, studies of these SLRPs in the context of wound healing are providing clues about their functions in early stages of atherosclerosis to plaque vulnerability and cardiovascular disease at later stages. Understanding of signal transduction pathways regulated by the core protein interactions is leading to novel roles and therapeutic potential for these proteins in wound repair and atherosclerosis.

Pathophysiology of native coronary, vein graft, and in-stent atherosclerosis

Plaque rupture, usually of a precursor lesion known as a 'vulnerable plaque' or 'thin-cap fibroatheroma', is the leading cause of thrombosis. Less-frequent aetiologies of coronary thrombosis are erosion, observed with greatest incidence in women aged <50 years, and eruptive calcified nodules, which are occasionally identified in older individuals. Various treatments for patients with coronary artery disease, such as CABG surgery and interventional therapies, have led to accelerated atherosclerosis. These processes occur within months to years, compared with the decades that it generally takes for native disease to develop. Morphological identifiers of accelerated atherosclerosis include macrophage-derived foam cells, intraplaque haemorrhage, and thin fibrous cap. Foam-cell infiltration can be observed within 1 year of a saphenous vein graft implantation, with subsequent necrotic core formation and rupture ensuing after 7 years in over one-third of patients. Neoatherosclerosis occurs early and with greater prevalence in drug-eluting stents than in bare-metal stents and, although rare, complications of late stent thrombosis from rupture are associated with high mortality. Comparison of lesion progression in native atherosclerotic disease, atherosclerosis in saphenous vein grafts, and in-stent neoatherosclerosis provides insight into the pathogenesis of atheroma formation in natural and iatrogenic settings.

Disturbed Laminar Blood Flow Vastly Augments Lipoprotein Retention in the Artery Wall

Objective—

Atherosclerosis develops initially at branch points and in areas of high vessel curvature. Moreover, experiments in hypercholesterolemic mice have shown that the introduction of disturbed flow in straight, atherosclerosis-resistant arterial segments turns them highly atherosclerosis susceptible. Several biomechanical mechanisms have been proposed, but none has been demonstrated. In the present study, we examined whether a causal link exists between disturbed laminar flow and the ability of the arterial wall to retain lipoproteins.

Approach and Results—

Lipoprotein retention was detected at natural predilection sites of the murine thoracic aorta 18 hours after infusion of fluorescently labeled low-density lipoprotein. To test for causality between blood flow and the ability of these areas to retain lipoproteins, we manipulated blood flow in the straight segment of the common carotid artery using a constrictive collar. Disturbed laminar flow did not affect low-density lipoprotein influx, but increased the ability of the artery wall to bind low-density lipoprotein. Concordantly, disturbed laminar flow led to differential expression of genes associated with phenotypic modulation of vascular smooth muscle cells, increased expression of proteoglycan core proteins associated with lipoprotein retention, and of enzymes responsible for chondroitin sulfate glycosaminoglycan synthesis and sulfation.

Conclusions—

Blood flow regulates genes associated with vascular smooth muscle cell phenotypic modulation, as well as the expression and post-translational modification of lipoprotein-binding proteoglycan core proteins, and the introduction of disturbed laminar flow vastly augments the ability of a previously resistant, straight arterial segment to retain lipoproteins.

Site-Specific Secretome Map Evidences VSMC-Related Markers of Coronary Atherosclerosis Grade and Extent in the Hypercholesterolemic Swine

A major drawback in coronary atherosclerosis (ATS) research is the difficulty of investigating early phase of plaque growth and related features in the clinical context. In this study, secreted proteins from atherosclerotic coronary arteries in a hypercholesterolemic swine model were characterized by a proteomics approach and their expression was correlated to site-specific ATS stage and extent. A wide coronary artery map of secreted proteins has been obtained in high fat (HF) diet induced ATS swine model and a significantly different expression of many proteins related to vascular smooth muscle cell (VSMC) activation/migration has been identified. Significant associations with ATS stage of HF coronary lesions were found for several VSMC-derived proteins and validated for chitinase 3 like protein 1 (CHI3L1) by tissue immunoexpression. A direct correlation (R(2) = 0.85) was evidenced with intima to media thickness ratio values and ELISA confirmed the higher blood concentrations of CHI3L1 in HF cases. These findings confirmed the pivotal role of VSMCs in coronary plaque development and demonstrated a strong site-specific relation between VSMC-secreted CHI3L1 and lesion grade, suggesting that this protein could be proposed as a useful biomarker for diagnosing and staging of atherosclerotic lesions in coronary artery disease.

Natural progression of atherosclerosis from pathologic intimal thickening to late fibroatheroma in human coronary arteries: A pathology study

OBJECTIVE

Smooth muscle cells, macrophage infiltration and accumulation of lipids, proteoglycans, collagen matrix and calcification play a central role in atherosclerosis. The early histologic changes of plaque progression from pathologic intimal thickenings (PIT) to late fibroatheroma lesions have not been fully characterized.

METHODS

A total of 151 atherosclerotic coronary lesions were collected from 67 sudden death victims. Atherosclerotic plaques were classified as PIT without macrophage infiltration, PIT with macrophages, and early and late fibroatheromas. Presence of macrophages and proteoglycans (versican, decorin and biglycan) were recognized by specific antibodies while hyaluronan was detected by affinity histochemistry. Lipid deposition was identified by oil-red-O, and calcification was assessed following von Kossa and alizarin red staining.

RESULTS

Lesion progression from PIT to late fibroatheroma was associated with increase in macrophage accumulation (p < 0.001) and decreasing apoptotic body clearance by macrophages (ratio of engulfed-to-total apoptotic bodies) (p < 0.001). Lipid deposition in lipid pool of PIT had a microvesicular appearance whereas those in the necrotic core were globular in nature. Overall, the accumulation of hyaluronan (p < 0.001), and proteoglycan versican (p < 0.001) and biglycan (p = 0.013) declined along with lesion progression from PIT to fibroatheromas. Microcalcification was first observed only within areas of lipid pools and its presence and size increased in lesions with necrotic core.

CONCLUSIONS

PIT to fibroatheroma lesions are accompanied by early lipid accumulation, followed by macrophage infiltration with defective clearance of apoptotic bodies along with decrease in proteoglycan and hyaluronan in lipid pools that convert to necrotic cores. Calcification starts in PIT and increases with plaque progression.

Cell-composition effects in the analysis of DNA methylation array data: a mathematical perspective

Background

The impact of cell-composition effects in analysis of DNA methylation data is now widely appreciated. With the availability of a reference data set consisting of DNA methylation measurements on isolated cell types, it is possible to impute cell proportions and adjust for them, but there is increasing interest in methods that adjust for cell composition effects when reference sets are incomplete or unavailable.

Results

In this article we present a theoretical basis for one such method, showing that the total effect of a phenotype on DNA methylation can be decomposed into orthogonal components, one representing the effect of phenotype on proportions of major cell types, the other representing either subtle effects in composition or global effects at focused loci, and that it is possible to separate these two types of effects in a finite data set. We demonstrate this principle empirically on nine DNA methylation data sets, showing that the first few principal components generally contain a majority of the information on cell-type present in the data, but that later principal components nevertheless contain information about a small number of loci that may represent more focused associations. We also present a new method for determining the number of linear terms to interpret as cell-mixture effects and demonstrate robustness to the choice of this parameter.

Conclusions

Taken together, our work demonstrates that reference-free algorithms for cell-mixture adjustment can produce biologically valid results, separating cell-mediated epigenetic effects (i.e. apparent effects arising from differences in cell composition) from those that are not cell mediated, and that in general the interpretation of associations evident from DNA methylation should be carefully considered.

Electronic supplementary material

The online version of this article (doi:10.1186/s12859-015-0527-y) contains supplementary material, which is available to authorized users.

Deficiency in lymphotoxin β receptor protects from atherosclerosis in apoE-deficient mice

RATIONALE

Lymphotoxin β receptor (LTbR) regulates immune cell trafficking and communication in inflammatory diseases. However, the role of LTbR in atherosclerosis is still unclear.

OBJECTIVE

The aim of this study was to elucidate the role of LTbR in atherosclerosis.

METHODS AND RESULTS

After 15 weeks of feeding a Western-type diet, mice double-deficient in apolipoprotein E and LTbR (apoE(-/-)/LTbR(-/-)) exhibited lower aortic plaque burden than did apoE(-/-) littermates. Macrophage content at the aortic root and in the aorta was reduced, as determined by immunohistochemistry and flow cytometry. In line with a decrease in plaque inflammation, chemokine (C-C motif) ligand 5 (Ccl5) and other chemokines were transcriptionally downregulated in aortic tissue from apoE(-/-)/LTbR(-/-) mice. Moreover, bone marrow chimeras demonstrated that LTbR deficiency in hematopoietic cells mediated the atheroprotection. Furthermore, during atheroprogression, apoE(-/-) mice exhibited increased concentrations of cytokines, for example, Ccl5, whereas apoE(-/-)/LTbR(-/-) mice did not. Despite this decreased plaque macrophage content, flow cytometric analysis showed that the numbers of circulating lymphocyte antigen 6C (Ly6C)(low) monocytes were markedly elevated in apoE(-/-)/LTbR(-/-) mice. The influx of these cells into atherosclerotic lesions was significantly reduced, whereas apoptosis and macrophage proliferation in atherosclerotic lesions were unaffected. Gene array analysis pointed to chemokine (C-C motif) receptor 5 as the most regulated pathway in isolated CD115(+) cells in apoE(-/-)/LTbR(-/-) mice. Furthermore, stimulating monocytes from apoE(-/-) mice with agonistic anti-LTbR antibody or the natural ligand lymphotoxin-α1β2, increased Ccl5 mRNA expression.

CONCLUSIONS

These findings suggest that LTbR plays a role in macrophage-driven inflammation in atherosclerotic lesions, probably by augmenting the Ccl5-mediated recruitment of monocytes.

Identification of microRNAs 758 and 33b as potential modulators of ABCA1 expression in human atherosclerotic plaques

BACKGROUND AND AIM

Adenosine triphosphate (ATP)-binding cassette (ABC) transporters A1 and G1 are the main transporters involved in macrophage cholesterol efflux. The understanding of the molecular mechanism(s) of their regulation in atherosclerosis is crucial for potential therapeutic approaches. Preclinical studies support a role for microRNAs in the posttranscriptional regulation of these transporters; however, no evidence is still available on human atherosclerosis. Thus, the aim of this study was to investigate the modulation of the ABCA1 and ABCG1 pathway in human atherosclerotic plaques and microRNA involvement in its modulation.

METHODS AND RESULTS

Thirty-one human atherosclerotic plaques were obtained from patients undergoing carotid endarterectomy for high-grade (>70%) vessel stenosis, and divided into normocholesterolemic (n = 15) and hypercholesterolemic groups (n = 16) according to the presence/absence of hypercholesterolemia. Both ABCA1 and ABCG1 messenger RNAs (mRNAs) were significantly upregulated in carotid plaques from hypercholesterolemic patients as assessed by real-time polymerase chain reaction (RT-PCR). Despite this result, no difference was found at the protein levels analyzed by Western blot, thus suggesting a strong posttranscriptional modulation. MicroRNA microarray and subsequent validation by RT-PCR showed a significant upregulation of ABCA1-linked miR-758 and miR-33b in plaques from hypercholesterolemic patients.

CONCLUSION

We provide evidence of a strong posttranscriptional regulation of ABCA1 and ABCG1 expression in human atherosclerotic plaques from hypercholesterolemic patients. This effect is potentially due to the concomitant increase of miR-33b and miR-758, two well-established regulators of ABCA1 and ABCG1 expression. The identification of miR-33b and miR-758 as putative key regulators of ABCA1 protein expression within human atherosclerotic plaques provides further data for the realization of new anti-atherosclerotic drugs with specific targets based on anti-miRNA technologies.

The glycosylation-dependent interaction of perlecan core protein with LDL: implications for atherosclerosis

Perlecan is a major heparan sulfate (HS) proteoglycan in the arterial wall. Previous studies have linked it to atherosclerosis. Perlecan contains a core protein and three HS side chains. Its core protein has five domains (DI–DV) with disparate structures and DII is highly homologous to the ligand-binding portion of LDL receptor (LDLR). The functional significance of this domain has been unknown. Here, we show that perlecan DII interacts with LDL. Importantly, the interaction largely relies on O-linked glycans that are only present in the secreted DII. Among the five repeat units of DII, most of the glycosylation sites are from the second unit, which is highly divergent and rich in serine and threonine, but has no cysteine residues. Interestingly, most of the glycans are capped by the negatively charged sialic acids, which are critical for LDL binding. We further demonstrate an additive effect of HS and DII on LDL binding. Unlike LDLR, which directs LDL uptake through endocytosis, this study uncovers a novel feature of the perlecan LDLR-like DII in receptor-mediated lipoprotein retention, which depends on its glycosylation. Thus, perlecan glycosylation may play a role in the early LDL retention during the development of atherosclerosis.

Prevalence of nonatheromatous lesions in peripheral arterial disease

OBJECTIVE

The histopathology of peripheral arterial disease and the accompanying calcification are poorly defined, and it is not known whether this varies according to different risk factors.

APPROACH AND RESULTS

Sections from 176 upper and lower leg arteries were examined histologically in specimens from amputations of 60 patients with peripheral arterial disease, of whom 58% had diabetes mellitus, 35% had end-stage renal disease, and 48% had a history of smoking. The most common findings were calcification of the media (72% of arteries) and intimal thickening without lipid (68% of arteries), with the presence of atheromas in only 23% of arteries. Intimal calcification occurred in 43% and was generally much less extensive than medial calcification. Nonatheromatous intimal thickening was frequently severe, resulting in complete occlusion in some vessels. The absence of lipid and macrophages was confirmed by staining with oil red O and staining for CD68. Other than a greater prevalence and severity of medial calcification in end-stage renal disease, the findings did not differ between diabetics, patients with end-stage renal disease, or smokers.

CONCLUSIONS

The results indicate that the majority of arteries in patients with peripheral arterial disease have a vascular lesion that is distinct from atherosclerosis, suggesting a different pathogenesis. This pattern does not differ substantially between patients with different risk factors for peripheral arterial disease. The bulk of vascular calcification in the lower extremities is medial rather than intimal.

Clinical significance of macrophage phenotypes in cardiovascular disease

The emerging understanding of macrophage subsets and their functions in the atherosclerotic plaque has led to the consensus that M1 macrophages are pro-atherogenic while M2 macrophages may promote plaque stability, primarily though their tissue repair and anti-inflammatory properties. As such, modulating macrophage function to promote plaque stability is an exciting therapeutic prospect. This review will outline the involvement of the different macrophage subsets throughout atherosclerosis progression and in models of regression. It is evident that much of our understanding of macrophage function comes from in vitro or small animal models and, while such knowledge is valuable, we have much to learn about the roles of the macrophage subsets in the clinical setting in order to identify the key pathways to target to possibly promote plaque stability.

Targeting arterial wall sulfated glycosaminoglycans in rabbit atherosclerosis with a mouse/human chimeric antibody

The progression of atherosclerosis is favored by increasing amounts of chondroitin sulfate proteoglycans in the artery wall. We previously reported the reactivity of chP3R99 monoclonal antibody (mAb) with sulfated glycosaminoglycans and its association with the anti-atherogenic properties displayed. Now, we evaluated the accumulation of this mAb in atherosclerotic lesions and its potential use as a probe for specific in vivo detection of the disease. Atherosclerosis was induced in NZW rabbits (n = 14) by the administration of Lipofundin 20% using PBS-receiving animals as control (n = 8). Accumulation of chP3R99 mAb in atherosclerotic lesions was assessed either by immunofluorescence detection of human IgG in fresh-frozen sections of aorta, or by immunoscintigraphy followed by biodistribution of the radiotracer upon administration of (99m)Tc-chP3R99 mAb. Immunofluorescence studies revealed the presence of chP3R99 mAb in atherosclerotic lesions 24 h after intravenous administration, whereas planar images showed an evident accumulation of (99m)Tc-chP3R99 mAb in atherosclerotic rabbit carotids. Accordingly, (99m)Tc-chP3R99 mAb uptake by lesioned aortic arch and thoracic segment was increased 5.6-fold over controls and it was 3.9-folds higher in carotids, in agreement with immunoscintigrams. Moreover, the deposition of (99m)Tc-chP3R99 mAb in the artery wall was associated both with the presence and size of the lesions in the different portions of evaluated arteries and was greater than in non-targeted organs. In conclusion, chP3R99 mAb preferentially accumulates in arterial atherosclerotic lesions supporting the potential use of this anti-glycosaminoglycans antibody for diagnosis and treatment of atherosclerosis.

The pigeon (Columba livia) model of spontaneous atherosclerosis

Multiple animal models have been employed to study human atherosclerosis, the principal cause of mortality in the United States. Each model has individual advantages related to specific pathologies. Initiation, the earliest disease phase, is best modeled by the White Carneau (WC-As) pigeon. Atherosclerosis develops spontaneously in the WC-As without either external manipulation or known risk factors. Furthermore, susceptibility is caused by a single gene defect inherited in an autosomal recessive manner. The Show Racer (SR-Ar) pigeon is resistant to atherosclerosis. Breed differences in the biochemistry and metabolism of celiac foci cells have been described. For example, WC-As have lower oxidative metabolism but higher amounts of chondroitin-6-sulfate and nonesterified fatty acids compared with SR-Ar. Gene expression in aortic smooth muscle cells was compared between breeds using representational difference analysis and microarray analysis. Energy metabolism and cellular phenotype were the chief gene expression differences. Glycolysis and synthetic cell types were related to the WC-As but oxidative metabolism and contractile cell types were related to the SR-Ar. Rosiglitazone, a PPARγ agonist, blocked RNA binding motif (RBMS1) expression in WC-As cells. The drug may act through the c-myc oncogene as RBMS1 is a c-myc target. Proteomic tests of aortic smooth muscle cells supported greater glycosylation in the WC-As and a transforming growth factor β effect in SR-Ar. Unoxidized fatty acids build up in WC-As cells because of their metabolic deficiency, ultimately preventing the contractile phenotype in these cells. The single gene responsible for the disease is likely regulatory in nature.

Evidence that multiple defects in lipid regulation occur before hyperglycemia during the prodrome of type-2 diabetes

BACKGROUND

Blood-vessel dysfunction arises before overt hyperglycemia in type-2 diabetes (T2DM). We hypothesised that a metabolomic approach might identify metabolites/pathways perturbed in this pre-hyperglycemic phase. To test this hypothesis and for specific metabolite hypothesis generation, serum metabolic profiling was performed in young women at increased, intermediate and low risk of subsequent T2DM.

METHODS

Participants were stratified by glucose tolerance during a previous index pregnancy into three risk-groups: overt gestational diabetes (GDM; n = 18); those with glucose values in the upper quartile but below GDM levels (UQ group; n = 45); and controls (n = 43, below the median glucose values). Follow-up serum samples were collected at a mean 22 months postnatally. Samples were analysed in a random order using Ultra Performance Liquid Chromatography coupled to an electrospray hybrid LTQ-Orbitrap mass spectrometer. Statistical analysis included principal component (PCA) and multivariate methods.

FINDINGS

Significant between-group differences were observed at follow-up in waist circumference (86, 95%CI (79-91) vs 80 (76-84) cm for GDM vs controls, p<0.05), adiponectin (about 33% lower in GDM group, p = 0.004), fasting glucose, post-prandial glucose and HbA1c, but the latter 3 all remained within the 'normal' range. Substantial differences in metabolite profiles were apparent between the 2 'at-risk' groups and controls, particularly in concentrations of phospholipids (4 metabolites with p ≤ 0.01), acylcarnitines (3 with p ≤ 0.02), short- and long-chain fatty acids (3 with p<  = 0.03), and diglycerides (4 with p ≤ 0.05).

INTERPRETATION

Defects in adipocyte function from excess energy storage as relatively hypoxic visceral and hepatic fat, and impaired mitochondrial fatty acid oxidation may initiate the observed perturbations in lipid metabolism. Together with evidence from the failure of glucose-directed treatments to improve cardiovascular outcomes, these data and those of others indicate that a new, quite different definition of type-2 diabetes is required. This definition would incorporate disturbed lipid metabolism prior to hyperglycemia.

Imbalanced response of ATP-binding cassette transporter A1 and CD36 expression to increased oxidized low-density lipoprotein loading contributes to the development of THP-1 derived foam cells

ATP-binding cassette transporter A1 (ABCA1) and CD36, type B scavenger receptor, function as the key mediators of macrophages cholesterol efflux and intake, respectively. However, their contribution to development of foam cells still remains uncertain. We here examined the effects of increased oxidized low-density lipoprotein (oxLDL) loading on the ABCA1 and CD36 expression, and lipid accumulation in THP-1 macrophages. The cultured THP-1 macrophages were treated with different copper-oxLDL concentrations. The intracellular lipid contents and cholesterol efflux were measured, and the ABCA1 and CD36 expression were assessed. We found that expression of ABCA1 and CD36 were coordinately induced upon low to moderate doses of oxLDL loading. However, higher doses of oxLDL stimulation resulted in the imbalanced expression of ABCA1 and CD36 proteins with more preferentially suppressed ABCA1 protein, attenuated cholesterol efflux and development of THP-1 derived foam cells. The PPAR-γ expression was remarkably induced, and PPAR-γ agonist, pioglitazone, significantly promoted the ABCA1 and CD36 expression. Additionally, ABCA1 and CD36 proteins were strong colocalized in THP-1 macrophages membrane. In conclusion, the more preferentially suppressed ABCA1 expression as compared with CD36 at higher doses of oxLDL stimulation may be the initiator for the formation of macrophage-derived foam cells.

Biglycan deficiency: increased aortic aneurysm formation and lack of atheroprotection

Proteoglycans of the arterial wall play a critical role in vascular integrity and the development of atherosclerosis owing to their ability to organize extracellular matrix molecules and to bind and retain atherogenic apolipoprotein (apo)-B containing lipoproteins. Prior studies have suggested a role for biglycan in aneurysms and in atherosclerosis. Angiotensin II (angII) infusions into mice have been shown to induce abdominal aortic aneurysm development, increase vascular biglycan content, increase arterial retention of lipoproteins, and accelerate atherosclerosis. The goal of this study was to determine the role of biglycan in angII-induced vascular diseases. Biglycan-deficient or biglycan wildtype mice crossed to LDL receptor deficient (Ldlr-/-) mice (C57BL/6 background) were infused with angII (500 or 1000ng/kg/min) or saline for 28days while fed on normal chow, then pumps were removed, and mice were switched to an atherogenic Western diet for 6weeks. During angII infusions, biglycan-deficient mice developed abdominal aortic aneurysms, unusual descending thoracic aneurysms, and a striking mortality caused by aortic rupture (76% for males and 48% for females at angII 1000ng/kg/min). Histological analyses of non-aneurysmal aortic segments from biglycan-deficient mice revealed a deficiency of dense collagen fibers and the aneurysms demonstrated conspicuous elastin breaks. AngII infusion increased subsequent atherosclerotic lesion development in both biglycan-deficient and biglycan wildtype mice. However, the biglycan genotype did not affect the atherosclerotic lesion area induced by the Western diet after treatment with angII. Biglycan-deficient mice exhibited significantly increased vascular perlecan content compared to biglycan wildtype mice. Analyses of the atherosclerotic lesions demonstrated that vascular perlecan co-localized with apoB, suggesting that increased perlecan compensated for biglycan deficiency in terms of lipoprotein retention. Biglycan deficiency increases aortic aneurysm development and is not protective against the development of atherosclerosis. Biglycan deficiency leads to loosely packed aortic collagen fibers, increased susceptibility of aortic elastin fibers to angII-induced stress, and up-regulation of vascular perlecan content.

Evolution of the biochemical profile of children treated or undergoing treatment for moderate or severe stunting: consequences of metabolic programming?

OBJECTIVE

to evaluate changes in the biochemical profile of children treated or being treated for moderate or severe stunting in a nutrition recovery and education center.

METHODS

this was a retrospective longitudinal study of 263 children treated at this center between August of 2008 to August of 2011, aged 1 to 6 years, diagnosed with moderate (z-score of height-for-age [HAZ] < -2) or severe stunting (HAZ < -3). Data were collected on socioeconomic conditions, dietary habits, and biochemical changes, as well as height according to age.

RESULTS

the nutritional intervention showed an increase in HAZ of children with moderate (0.51 ± 0.4, p = 0.001) and severe (0.91 ± 0.7, p = 0.001) stunting during the monitoring. Increased levels of insulin-like growth factor 1 (IGF-1) (initial: 71.7 ng/dL; final: 90.4 ng/dL; p = 0.01) were also observed, as well as a reduction in triglycerides (TG) in both severely (initial: 91.8mg/dL; final: 79.1mg/dL; p = 0.01) and in moderately malnourished children (initial: 109.2mg/dL; final 88.7mg/dL; p = 0.01), and a significant increase in high-density lipoprotein cholesterol HDL-C only in the third year of intervention (initial: 31.4mg/dL; final: 42.2mg/dL). The values of total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) levels remained high throughout the treatment (initial: 165.1mg/dL; final: 163.5mg/dL and initial: 109.0mg/dL; final: 107.3mg/dL, respectively).

CONCLUSION

the nutritional treatment for children with short stature was effective in reducing stunting and improving TG and HDL-C after three years of intervention. However, the levels of LDL-C and TC remained high even in treated children. It is therefore speculated that these changes may result from metabolic programming due to malnutrition.

Evaluation of a porcine model of early aortic valve sclerosis

BACKGROUND

Calcific aortic valve disease (CAVD) is associated with significant cardiovascular morbidity. While late-stage CAVD is well-described, early pathobiological processes are poorly understood due to the lack of animal models that faithfully replicate early human disease. Here we evaluated a hypercholesterolemic porcine model of early diet-induced aortic valve sclerosis.

METHODS

Yorkshire swine were fed either a standard or high-fat/high-cholesterol diet for 2 or 5 months. Right coronary aortic valve leaflets were excised and analyzed (immuno)histochemically.

RESULTS

Early human-like proteoglycan-rich onlays formed between the endothelial layer and elastic lamina in the fibrosa layer of valve leaflets, with accelerated formation associated with hypercholesterolemia (P<.05). Lipid deposition was more abundant in hypercholesterolemic swine (P<.001), but was present in a minority (28%) of onlays. No myofibroblasts, MAC387-positive macrophages, or fascin-positive dendritic cells were detected in 2-month onlays, with only scarce myofibroblasts present at 5 months. Cells that expressed osteochondral markers Sox9 and Msx2 were preferentially found in dense proteoglycan-rich onlays (P<.05) and with hypercholesterolemia (P<.05). Features of more advanced human CAVD, including calcification, were not observed in this necessarily short study.

CONCLUSIONS

Early aortic valve sclerosis in hypercholesterolemic swine is characterized by the formation of proteoglycan-rich onlays in the fibrosa, which can occur prior to significant lipid accumulation, inflammatory cell infiltration, or myofibroblast activation. These characteristics mimic those of early human aortic valve disease, and thus the porcine model has utility for the study of early valve sclerosis.

Oxidation modifies the structure and function of the extracellular matrix generated by human coronary artery endothelial cells

ECM (extracellular matrix) materials, such as laminin, perlecan, type IV collagen and fibronectin, play a key role in determining the structure of the arterial wall and the properties of cells that interact with the ECM. The aim of the present study was to investigate the effect of peroxynitrous acid, an oxidant generated by activated macrophages, on the structure and function of the ECM laid down by HCAECs (human coronary artery endothelial cells) in vitro and in vivo. We show that exposure of HCAEC-derived native matrix components to peroxynitrous acid (but not decomposed oxidant) at concentrations >1 μM results in a loss of antibody recognition of perlecan, collagen IV, and cell-binding sites on laminin and fibronectin. Loss of recognition was accompanied by decreased HCAEC adhesion. Real-time PCR showed up-regulation of inflammation-associated genes, including MMP7 (matrix metalloproteinase 7) and MMP13, as well as down-regulation of the laminin α2 chain, in HCAECs cultured on peroxynitrous acid-treated matrix compared with native matrix. Immunohistochemical studies provided evidence of co-localization of laminin with 3-nitrotyrosine, a biomarker of peroxynitrous acid damage, in type II-III/IV human atherosclerotic lesions, consistent with matrix damage occurring during disease development in vivo. The results of the present study suggest a mechanism through which peroxynitrous acid modifies endothelial cell-derived native ECM proteins of the arterial basement membrane in atherosclerotic lesions. These changes to ECM and particularly perlecan and laminin may be important in inducing cellular dysfunction and contribute to atherogenesis.

Atherogenic, fibrotic and glucose utilising actions of glucokinase activators on vascular endothelium and smooth muscle

Background

Pharmaceutical interventions for diabetes aim to control glycaemia and to prevent the development of complications, such as cardiovascular diseases. Some anti-hyperglycaemic drugs have been found to have adverse cardiovascular effects in their own right, limiting their therapeutic role. Glucokinase activity in the pancreas is critical in enhancing insulin release in response to hyperglycaemia. Glucokinase activators (GKAs) are novel agents for diabetes which act by enhancing the formation of glucose-6-phosphate leading to increased insulin production and subsequent suppression of blood glucose. Little, however, is known about the direct effects of GKAs on cardiovascular cells.

Methods

The effect of the GKAs RO28-1675 and Compound A on glucose utilisation in bovine aortic endothelial cells (BAEC) and rat MIN6 was observed by culturing the cells at high and low glucose concentration in the presence and absence of the GKAs and measuring glucose consumption. The effect of RO28-1675 at various concentrations on glucose-dependent signalling in BAEC was observed by measuring Smad2 phosphorylation by Western blotting. The effect of RO28-1675 on TGF-β stimulated proteoglycan synthesis was measured by ³⁵S-SO₄ incorporation and assessment of proteoglycan size by SDS-PAGE. The effects of RO28-1675 on TGF-β mediated Smad2C phosphorylation in BAEC was observed by measurement of pSmad2C levels. The direct actions of RO28-1675 on vascular reactivity were observed by measuring arteriole tone and lumen diameter.

Results

GKAs were demonstrated to increase glucose utilisation in pancreatic but not endothelial cells. Glucose-activated Smad2 phosphorylation was decreased in a dose-dependent fashion in the presence of RO28-1675. No effect of RO28-1675 was observed on TGF-β stimulated proteoglycan production. RO28-1675 caused a modest dilation in arteriole but not contractile sensitivity.

Conclusions

GKA RO28-1675 did not increase glucose consumption in endothelial cells indicating the absence of glucokinase in those cells. No direct deleterious actions, in terms of atherogenic changes or excessive vasoactive effects were seen on cells or vessels of the cardiovascular system in response to GKAs. If reflected in vivo, these drugs are unlikely to have their use compromised by direct cardiovascular toxicity.

Increased atherosclerosis in mice with increased vascular biglycan content

OBJECTIVE

The response to retention hypothesis of atherogenesis proposes that atherosclerosis is initiated via the retention of atherogenic lipoproteins by vascular proteoglycans. Co-localization studies suggest that of all the vascular proteoglycans, biglycan is the one most closely co-localized with LDL. The goal of this study was to determine if over-expression of biglycan in hyperlipidemic mice would increase atherosclerosis development.

METHODS

Transgenic mice were developed by expressing biglycan under control of the smooth muscle actin promoter, and were crossed to the LDL receptor deficient (C57BL/6 background) atherosclerotic mouse model. Biglycan transgenic and non-transgenic control mice were fed an atherogenic Western diet for 4-12 weeks.

RESULTS

LDL receptor deficient mice overexpressing biglycan under control of the smooth muscle alpha actin promoter had increased atherosclerosis development that correlated with vascular biglycan content.

CONCLUSION

Increased vascular biglycan content predisposes to increased lipid retention and increased atherosclerosis development.

Atheroprotective remodelling of vascular dermatan sulphate proteoglycans in response to hypercholesterolaemia in a rat model

Proteoglycan accumulation within the arterial intima has been implicated in atherosclerosis progression in humans. Nevertheless, hypercholesterolaemia is unable to induce intimal thickening and atheroma plaque development in rats. The study was performed to analyse proteoglycans modifications in rats fed with a high-cholesterol diet to understand whether vascular wall remodelling protects against lesions. Sections obtained from rat aortas showed normal features, in intimal-to-media ratio and lipid accumulation. However, focal endothelial hyperplasia and neo-intima rearrangement were observed in high-cholesterol animals. Besides, hypercholesterolaemia induced an inflammatory microenviroment. We determined the expression of different proteoglycans from aortic cells by Western blot and observed a diminished production of decorin and biglycan in high-cholesterol animals compared with control (P < 0.01 and P < 0.05, respectively). Versican was increased in high-cholesterol animals (P < 0.05), whereas perlecan production showed no differences. No modification of the total content of glycosaminoglycans (GAGs) was found between the two experimental groups. In contrast, the chondroitin sulphate/dermatan sulphate ratio was increased in the high-cholesterol group as compared to the control (0.56 and 0.34, respectively). Structural alterations in the disaccharide composition of galactosaminoglycans were also detected by HPLC, as the ratio of 6-sulphate to 4-sulphate disaccharides was increased in high-cholesterol animals (P < 0.05). Our results suggest that attenuation of decorin and biglycan expression might be an effective strategy to inhibit the first step in atherogenesis, although specific GAG structural modification associated with the development of vascular disease took place. Results emphasize the potential application of therapies based on vascular matrix remodelling to treat atherosclerosis.

A review on the genetic, environmental, and lifestyle aspects of the early-life origins of cardiovascular disease

This article is a comprehensive review on developmental origins of health and disease regarding various factors related to the origins of cardiovascular diseases from early life. It presents a summary of the impacts of various factors such as epigenetics; gene-environment interaction; ethnic predisposition to cardiovascular diseases and their underlying risk factors; prenatal factors; fetal programming; maternal weight status and weight gain during pregnancy; type of feeding during infancy; growth pattern during childhood; obesity; stunting; socioeconomic status; dietary and physical activity habits; active, secondhand, and thirdhand smoking, as well as environmental factors including air pollution and global climate change on the development and progress of cardiovascular diseases and their risk factors. The importance of early identification of predisposing factors for cardiovascular diseases for primordial and primary prevention of cardiovascular diseases from early life is highlighted.

Contribution of intimal smooth muscle cells to cholesterol accumulation and macrophage-like cells in human atherosclerosis

BACKGROUND

Intimal smooth muscle cells (SMCs) contribute to the foam cell population in arterial plaque, and express lower levels of the cholesterol exporter ATP-binding cassette transporter A1 (ABCA1) in comparison with medial arterial SMCs. The relative contribution of SMCs to the total foam cell population and their expression of ABCA1 in comparison with intimal monocyte-derived macrophages, however, are unknown. Although the expression of macrophage markers by SMCs following lipid loading has been described, the relevance of this phenotypic switch by SMCs in human coronary atherosclerosis has not been determined.

METHODS AND RESULTS

Human coronary artery sections from hearts explanted at the time of transplantation were processed to clearly delineate intracellular and extracellular lipids and allow costaining for cell-specific markers. Costaining for oil red O and the SMC-specific marker SM α-actin of foam cell-rich lesions revealed that 50±7% (average±standard error of the mean, n=14 subjects) of total foam cells were SMC derived. ABCA1 expression by intimal SMCs was significantly reduced between early and advanced atherosclerotic lesions, with no loss in ABCA1 expression by myeloid lineage cells. Costaining with the macrophage marker CD68 and SM α-actin revealed that 40±6% (n=15) of CD68-positive cells originated as SMCs in advanced human coronary atherosclerosis.

CONCLUSIONS

These findings suggest SMCs contain a much larger burden of the excess cholesterol in human coronary atherosclerosis than previously known, in part, because of their relative inability to release excess cholesterol via ABCA1 in comparison with myeloid lineage cells. Our results also indicate that many cells identified as monocyte-derived macrophages in human atherosclerosis are in fact SMC derived.

Decorin and biglycan retain LDL in disease-prone valvular and aortic subendothelial intimal matrix

OBJECTIVE

Subendothelial LDL retention by intimal matrix proteoglycans is an initial step in atherosclerosis and calcific aortic valve disease. Herein, we identify decorin and biglycan as the proteoglycans that preferentially retain LDL in intimal matrix at disease-prone sites in normal valve and vessel wall.

METHODS

The porcine aortic valve and renal artery ostial diverter, initiation sites of calcific valve disease and renal atherosclerosis, respectively, from normal non-diseased animals were used as models in these studies.

RESULTS

Fluorescent human LDL was selectively retained on the lesion-prone collagen/proteoglycan-enriched aortic surface of the valve, where the elastic lamina is depleted, as previously observed in lesion-prone sites in the renal ostium. iTRAQ mass spectrometry of valve and diverter protein extracts identified decorin and biglycan as the major subendothelial intimal matrix proteoglycans electrostatically retained on human LDL affinity columns. Decorin levels correlated with LDL binding in lesion-prone sites in both tissues. Collagen binding to LDL was shown to be proteoglycan-mediated. All known basement membrane proteoglycans bound LDL suggesting they may modulate LDL uptake into the subendothelial matrix. The association of purified decorin with human LDL in an in vitro microassay was blocked by serum albumin and heparin suggesting anti-atherogenic roles for these proteins in vivo.

CONCLUSIONS

LDL electrostatic interactions with decorin and biglycan in the valve leaflets and vascular wall is a major source of LDL retention. The complementary electrostatic sites on LDL or these proteoglycans may provide a novel therapeutic target for preventing one of the earliest events in these cardiovascular diseases.

Lysophosphatidylcholine and carotid intima-media thickness in young smokers: a role for oxidized LDL-induced expression of PBMC lipoprotein-associated phospholipase A2?

Background

Although cigarette smoking has been associated with carotid intima-media thickness (CIMT) the mechanisms are yet not completely known. Lysophosphatidylcholine (lysoPC), a main product of lipoprotein-associated phospholipase A2 (Lp-PLA2) activity, appears to be a major determinant of the pro-atherogenic properties of oxidized LDL (oxLDL) and to induce proteoglycan synthesis, a main player in intimal thickening. In this study we assessed whether cigarette smoking-induced oxidative stress may influence plasma Lp-PLA2 and lysoPC and Lp-PLA2 expression in peripheral blood mononuclear cells (PBMC), as well as the relationship between lysoPC and CIMT.

Methods/Results

45 healthy smokers and 45 age and sex-matched subjects participated in this study. Smokers, compared to non-smokers, showed increased plasma concentrations of oxLDL, Lp-PLA2 and lysoPC together with up-regulation of Lp-PLA2 (mRNA and protein) expression in PBMC (P<0.001). Plasma Lp-PLA2 positively correlated with both lysoPC (r=0.639, P<0.001) and PBMC mRNA Lp-PLA2 (r=0.484, P<0.001) in all subjects. Moreover CIMT that was higher in smokers (P<0.001), positively correlated with lysoPC (r=0.55, P<0.001). Then in invitro study we demonstrated that both oxLDL (at concentrations similar to those found in smoker’s serum) and oxidized phospholipids contained in oxLDL, were able to up-regulate mRNA Lp-PLA2 in PBMC. This effect was likely due, at least in part, to the enrichment in oxidized phospholipids found in PBMC after exposure to oxLDL. Our results also showed that in human aortic smooth muscle cells lysoPC, at concentrations similar to those found in smokers, increased the expression of biglycan and versican, two main proteoglycans.

Conclusions

In smokers a further effect of raised oxidative stress is the up-regulation of Lp-PLA2 expression in PBMC with subsequent increase of plasma Lp-PLA2 and lysoPC. Moreover the correlation between lysoPC and CIMT together with the finding that lysoPC up-regulates proteoglycan synthesis suggests that lysoPC may be a link between smoking and intimal thickening.

A peripheral blood gene expression score is associated with plaque volume and phenotype by intravascular ultrasound with radiofrequency backscatter analysis: results from the ATLANTA study

BACKGROUND

A composite, peripheral gene expression score based on quantitative RNA-measurements has been validated for detecting stenosis against invasive coronary X-ray angiography. IVUS/VH has been validated for quantitative measurements of coronary plaque volume and composition and has been shown to be predictive of outcomes and treatment effects. The correlation between peripheral gene expression and coronary plaque composition by intravascular ultrasound with radiofrequency backscatter (IVUS/VH) is unknown.

METHODS

Peripheral blood gene expression score (GES) was prospectively measured in 18 patients undergoing IVUS/VH. Plaque volume and composition [fibrous tissue (FI), fibro-fatty tissue (FF), necrotic core (NC) and dense calcium (DC)] were quantified in 3 dimensions in all plaques within the entire pullback. The relationship to GES was assessed by Spearman rank correlation.

RESULTS

Mean age was 61.1±8.6 years; 67% were male. 1,158 mm of coronary anatomy was imaged by IVUS/VH. Using a validated scale of 1-40, mean GES was 21.6±9.4. GES was associated with plaque volume (R(2)=0.55; P=0.018), NC volume (R(2)=0.56; P=0.015), DC volume (R(2)=0.60; P=0.007), and non-calcified plaque volume (R(2)=0.50; P=0.036) by Spearman rank correlation.

CONCLUSIONS

In this preliminary report, increased GES was associated with higher plaque volume and a more vulnerable plaque phenotype as evidenced by NC and DC. This composite GES is not only associated with obstructive coronary disease, but also with higher plaque volume and vulnerable phenotype.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

LOX-1 deletion and macrophage trafficking in atherosclerosis

BACKGROUND

Atherosclerosis is associated with macrophage accumulation. LOX-1 has been shown to induce macrophage attachment, and its deletion (LOX-1 knockout, KO) reduces atherosclerosis in LDLr KO mice fed a high cholesterol diet. We examined differences in macrophage trafficking in age-matched wild type, LOX-1 KO, LDLr KO, and LDLr/LOX-1 double KO mice.

METHODS

Sections of aortas of mice fed high cholesterol diet were collected at weeks 0, 4, 8, 12 and 19 and analyzed by immunohistochemistry and flow cytometry.

RESULTS

In the LDLr KO mice aorta, CD68 positivity (macrophage accumulation) increased over time up to 12 weeks, and then the accumulation fell modestly but significantly. The periaortal fat and adventitia showed more CD68 positivity than the media and intima. This pattern was also evident in the non-atherosclerotic areas. Importantly, LOX-1 KO and LDLr-LOX-1 double KO mice showed diminished CD68 positivity in comparison to wild type and LDLR KO mice, respectively. Further, macrophages from LOX-1 KO mice revealed a marked reduction in migration (vs. macrophages from wild type mice) in in vitro migration assay.

CONCLUSIONS

LOX-1 deletion translates into reduction in macrophage trafficking in the aorta of LDLr KO mice. Most of the macrophage trafficking appears in the subadventitial regions.

Oxidized low density lipoprotein (LDL) affects hyaluronan synthesis in human aortic smooth muscle cells

Thickening of the vessel in response to high low density lipoprotein(s) (LDL) levels is a hallmark of atherosclerosis, characterized by increased hyaluronan (HA) deposition in the neointima. Human native LDL trapped within the arterial wall undergoes modifications such as oxidation (oxLDL). The aim of our study is to elucidate the link between internalization of oxLDL and HA production in vitro, using human aortic smooth muscle cells. LDL were used at an effective protein concentration of 20-50 μg/ml, which allowed 80% cell viability. HA content in the medium of untreated cells was 28.9 ± 3.7 nmol HA-disaccharide/cell and increased after oxLDL treatment to 53.9 ± 5.6. OxLDL treatments doubled the transcripts of HA synthase HAS2 and HAS3. Accumulated HA stimulated migration of aortic smooth muscle cells and monocyte adhesiveness to extracellular matrix. The effects induced by oxLDL were inhibited by blocking LOX-1 scavenger receptor with a specific antibody (10 μg/ml). The cholesterol moiety of LDL has an important role in HA accumulation because cholesterol-free oxLDL failed to induce HA synthesis. Nevertheless, cholesterol-free oxLDL and unmodified cholesterol (20 μg/ml) induce only HAS3 transcription, whereas 22,oxysterol affects both HAS2 and HAS3. Moreover, HA deposition was associated with higher expression of endoplasmic reticulum stress markers (CHOP and GRP78). Our data suggest that HA synthesis can be induced in response to specific oxidized sterol-related species delivered through oxLDL.

Prevention of TGFβ induction attenuates angII-stimulated vascular biglycan and atherosclerosis in Ldlr-/- mice

Angiotensin II (angII) accelerates atherosclerosis, but the mechanisms are not fully understood. The aim of this study was to determine whether TGFβ is required for angII-induced atherosclerosis. Ldlr-null mice fed a normal chow diet were infused with angII or saline for 28 days. A single injection of TGFβ neutralizing antibody 1D11 (2 mg/kg) prevented angII-induction of TGFβ1 levels, and strikingly attenuated angII-induced accumulation of aortic biglycan content. To study atherosclerosis, mice were infused with angII or saline for 4 weeks, and then fed Western diet for a further 6 weeks. 1D11 had no effect on systolic blood pressure or plasma cholesterol; however, angII-infused mice that received 1D11 had reduced atherosclerotic lesion area by 30% (P < 0.05). Immunohistochemical analyses demonstrated that angII induced both lipid retention and accumulation of biglycan and perlecan which colocalized with apoB. 1D11 strikingly reduced the effect of angII on biglycan but not perlecan. 1D11 decreased total collagen content (P < 0.05) in the lesion area without changing plaque inflammation markers (CD68 and CD45). Thus, this study demonstrates that neutralization of TGFβ attenuated angII stimulation of biglycan accumulation and atherogenesis in mice, suggesting that TGFβ-mediated biglycan induction is one of the mechanisms underlying angII-promoted atherosclerosis.