Atherosclerosis in perlecan heterozygous mice

Molecular Interactions Between Vascular Smooth Muscle Cells and Macrophages in Atherosclerosis

Atherosclerosis is the largest contributor toward life-threatening cardiovascular events. Cellular activity and cholesterol accumulation lead to vascular remodeling and the formation of fatty plaques. Complications arise from blood clots, forming at sites of plaque development, which may detach and result in thrombotic occlusions. Vascular smooth muscle cells and macrophages play dominant roles in atherosclerosis. A firm understanding of how these cells influence and modulate each other is pivotal for a better understanding of the disease and the development of novel therapeutics. Recent studies have investigated molecular interactions between both cell types and their impact on disease progression. Here we aim to review the current knowledge. Intercellular communications through soluble factors, physical contact, and extracellular vesicles are discussed. We also present relevant background on scientific methods used to study the disease, the general pathophysiology and intracellular factors involved in phenotypic modulation of vascular smooth muscle cells. We conclude this review with a discussion of the current state, shortcomings and potential future directions of the field.

Methods to Analyze the Effect of Diet-Derived Metabolites on Endothelial Inflammation and Cell Surface Glycosaminoglycans

The glycocalyx is a biologically active barrier that covers the luminal side of the vascular endothelium and it is comprised of proteoglycans [core proteins with glycosaminoglycans (GAG) side chains], glycoproteins, and plasma proteins. Evidence shows that the disruption in the structure and function of the endothelial glycocalyx exacerbates vascular inflammation and atherosclerosis. The GAG components of the glycocalyx undergo remodeling in the setting of diabetes and these alterations in endothelial GAGs negatively impact the vascular function. Hence, the preservation and restoration of GAGs in altered vasculature may be a novel strategy to ameliorate vascular complications in diabetes and metabolic syndrome. Human studies support the beneficial vascular effects of flavonoids which are widely found in fruits and vegetables. Flavonoids are extensively metabolized by the intestinal microbiota and digestive enzymes in humans, suggesting that their biological activities may be mediated by their circulating metabolites. Studies indicate that counteracting the damage to GAGs using dietary compounds improve vascular complications. In this article, we describe the methods to analyze the effect of diet-derived metabolites such as metabolites of flavonoids on endothelial inflammation and cell surface glycosaminoglycans.

Macrophages bind LDL using heparan sulfate and the perlecan protein core

The retention of low-density lipoprotein (LDL) is a key process in the pathogenesis of atherosclerosis and largely mediated via smooth-muscle cell-derived extracellular proteoglycans including the glycosaminoglycan chains. Macrophages can also internalize lipids via complexes with proteoglycans. However, the role of polarized macrophage-derived proteoglycans in binding LDL is unknown and important to advance our understanding of the pathogenesis of atherosclerosis. We therefore examined the identity of proteoglycans, including the pendent glycosaminoglycans, produced by polarized macrophages to gain insight into the molecular basis for LDL binding. Using the quartz crystal microbalance with dissipation monitoring technique, we established that classically activated macrophage (M1)- and alternatively activated macrophage (M2)-derived proteoglycans bind LDL via both the protein core and heparan sulfate (HS) in vitro. Among the proteoglycans secreted by macrophages, we found perlecan was the major protein core that bound LDL. In addition, we identified perlecan in the necrotic core as well as the fibrous cap of advanced human atherosclerotic lesions in the same regions as HS and colocalized with M2 macrophages, suggesting a functional role in lipid retention in vivo. These findings suggest that macrophages may contribute to LDL retention in the plaque by the production of proteoglycans; however, their contribution likely depends on both their phenotype within the plaque and the presence of enzymes, such as heparanase, that alter the secreted protein structure.

Lipoprotein receptor signalling in atherosclerosis

The founding member of the lipoprotein receptor family, low-density lipoprotein receptor (LDLR) plays a major role in the atherogenesis through the receptor-mediated endocytosis of LDL particles and regulation of cholesterol homeostasis. Since the discovery of the LDLR, many other structurally and functionally related receptors have been identified, which include low-density lipoprotein receptor-related protein (LRP)1, LRP5, LRP6, very low-density lipoprotein receptor, and apolipoprotein E receptor 2. The scavenger receptor family members, on the other hand, constitute a family of pattern recognition proteins that are structurally diverse and recognize a wide array of ligands, including oxidized LDL. Among these are cluster of differentiation 36, scavenger receptor class B type I and lectin-like oxidized low-density lipoprotein receptor-1. In addition to the initially assigned role as a mediator of the uptake of macromolecules into the cell, a large number of studies in cultured cells and in in vivo animal models have revealed that these lipoprotein receptors participate in signal transduction to modulate cellular functions. This review highlights the signalling pathways by which these receptors influence the process of atherosclerosis development, focusing on their roles in the vascular cells, such as macrophages, endothelial cells, smooth muscle cells, and platelets. Human genetics of the receptors is also discussed to further provide the relevance to cardiovascular disease risks in humans. Further knowledge of the vascular biology of the lipoprotein receptors and their ligands will potentially enhance our ability to harness the mechanism to develop novel prophylactic and therapeutic strategies against cardiovascular diseases.

Review of Alterations in Perlecan-Associated Vascular Risk Factors in Dementia

Perlecan is a heparan sulfate proteoglycan protein in the extracellular matrix that structurally and biochemically supports the cerebrovasculature by dynamically responding to changes in cerebral blood flow. These changes in perlecan expression seem to be contradictory, ranging from neuroprotective and angiogenic to thrombotic and linked to lipid retention. This review investigates perlecan's influence on risk factors such as diabetes, hypertension, and amyloid that effect Vascular contributions to Cognitive Impairment and Dementia (VCID). VCID, a comorbidity with diverse etiology in sporadic Alzheimer's disease (AD), is thought to be a major factor that drives the overall clinical burden of dementia. Accordingly, changes in perlecan expression and distribution in response to VCID appears to be injury, risk factor, location, sex, age, and perlecan domain dependent. While great effort has been made to understand the role of perlecan in VCID, additional studies are needed to increase our understanding of perlecan's role in health and in cerebrovascular disease.

Smooth Muscle Cell-Proteoglycan-Lipoprotein Interactions as Drivers of Atherosclerosis

In humans, smooth muscle cells (SMCs) are the main cell type in the artery medial layer, in pre-atherosclerotic diffuse thickening of the intima, and in all stages of atherosclerotic lesion development. SMCs secrete the proteoglycans responsible for the initial binding and retention of atherogenic lipoproteins in the artery intima, with this retention driving foam cell formation and subsequent stages of atherosclerosis. In this chapter we review current knowledge of the extracellular matrix generated by SMCs in medial and intimal arterial layers, their relationship to atherosclerotic lesion development and stabilization, how these findings correlate with mouse models of atherosclerosis, and potential therapies aimed at targeting the SMC matrix-lipoprotein interaction for atherosclerosis prevention.

Serum Heparanase Level Is Decreased in Stable Coronary Artery Disease

OBJECTIVE

Heparanase (HPA), mammalian endo-β-D-glu-cu-ronidase, separates heparan sulfate chains of proteoglycans and changes the structure of the extracellular matrix. We investigated whether serum levels of HPA differ in patients with stable coronary artery disease (SCAD) and subjects with normal coronary arteries.

METHODS

This study enrolled 92 patients with SCAD and 34 controls with normal coronary arteries. Levels of HPA were measured by a commercially available human HPA enzyme-linked immunosorbent assay kit.

RESULTS

Serum HPA levels were significantly lower in the SCAD group (137.5 [104.1-178.9] vs. 198.8 [178.2-244.9] pg/mL; p < 0.001). Serum HPA levels were significantly higher in subjects with diabetes mellitus (DM) compared to those without DM (p = 0.008). Levels of HPA were lower in the SCAD group, both in the diabetic and nondiabetic subgroups, as compared to controls (p < 0.001 for both subgroups). Levels of HPA positively correlated with fasting blood glucose (FBG) (r: 0.42; p < 0.001). In multiple logistic regression analysis, serum HPA level (odds ratio [OR]: 0.975; 95% confidence interval [CI]: 0.966, 0.985; p < 0.001) and FBG (OR: 1.028; 95% CI: 1.010, 1.047; p = 0.002) were independently associated with SCAD. The receiver operating characteristic curve showed that HPA levels less than 160.6 pg/mL predicted SCAD with 65% sensitivity and 97% specificity (AUC: 0.80; 95% CI: 0.728, 0.878; p < 0.001).

CONCLUSION

Diabetes and FBG levels were closely associated with serum levels of HPA. Low serum levels of HPA may predict SCAD in both diabetic and nondiabetic populations.

A role for proteoglycans in vascular disease

The content of proteoglycans (PGs) is low in the extracellular matrix (ECM) of vascular tissue, but increases dramatically in all phases of vascular disease. Early studies demonstrated that glycosaminoglycans (GAGs) including chondroitin sulfate (CS), dermatan sulfate (DS), keratan sulfate (KS) and heparan sulfate (HS) accumulate in vascular lesions in both humans and in animal models in areas of the vasculature that are susceptible to disease initiation (such as at branch points) and are frequently coincident with lipid deposits. Later studies showed the GAGs were covalently attached to specific types of core proteins that accumulate in vascular lesions. These molecules include versican (CSPG), biglycan and decorin (DS/CSPGs), lumican and fibromodulin (KSPGs) and perlecan (HSPG), although other types of PGs are present, but in lesser quantities. While the overall molecular design of these macromolecules is similar, there is tremendous structural diversity among the different PG families creating multiple forms that have selective roles in critical events that form the basis of vascular disease. PGs interact with a variety of different molecules involved in disease pathogenesis. For example, PGs bind and trap serum components that accumulate in vascular lesions such as lipoproteins, amyloid, calcium, and clotting factors. PGs interact with other ECM components and regulate, in part, ECM assembly and turnover. PGs interact with cells within the lesion and alter the phenotypes of both resident cells and cells that invade the lesion from the circulation. A number of therapeutic strategies have been developed to target specific PGs involved in key pathways that promote vascular disease. This review will provide a historical perspective of this field of research and then highlight some of the evidence that defines the involvement of PGs and their roles in the pathogenesis of vascular disease.

Heparanase inhibition attenuates atherosclerosis progression and liver steatosis in E0 mice

BACKGROUND AND AIMS

Increased oxidative stress is associated with accelerated atherosclerosis. Emerging evidence highlights the role of heparanase in atherogenesis, where heparanase inhibitor PG545 reduces oxidative stress in apolipoprotein E deficient mice (E₀ mice). Herein, we studied the effects of PG545 on atherosclerosis progression in E₀ mice.

METHODS

Male E₀ mice fed a high-fat diet (n = 20) were divided into 3 groups treated with weekly intraperitoneal injections of either low (0.2 mg/mouse) or high dose (0.4 mg/mouse)PG545 or normal saline (controls) for twelve weeks. Body weight and food intake were measured weekly. At the end of the treatment period, blood pressure was measured, animals were sacrificed and serum samples were collected and assessed for biochemical parameters and oxidative stress. Aortic vessels and livers were collected for atherosclerotic plaques and histopathological analysis, respectively.

RESULTS

Blood pressure decreased in mice treated with low, but not high dose of PG545. In addition, heparanase inhibition caused a dose-dependent reduction in serum oxidative stress, total cholesterol, low-density lipoproteins, triglycerides, high-density lipoproteins, and aryl esterase activity. Although food intake was not reduced by PG545, body weight gain was significantly attenuated in PG545 treated groups. Both doses of PG545 caused a marked reduction in aortic wall thickness and atherosclerosis development, and liver steatosis. Liver enzymes and serum creatinine were not affected by PG545.

CONCLUSIONS

Heparanase inhibition by PG545 caused a significant reduction in lipid profile and serum oxidative stress along with attenuation of atherosclerosis, aortic wall thickness, and liver steatosis. Moreover, PG545 attenuated weight gain without reducing food intake. Collectively, these findings suggest that heparanase blockade is highly effective in slowing atherosclerosis formation and progression, and decreasing liver steatosis.

The heparan sulfate proteoglycan grip on hyperlipidemia and atherosclerosis

Heparan sulfate proteoglycans are found at the cell surface and in the extracellular matrix, where they interact with a plethora of proteins involved in lipid homeostasis and inflammation. Over the last decade, new insights have emerged regarding the mechanism and biological significance of these interactions in the context of cardiovascular disease. The majority of cardiovascular disease-related deaths are caused by complications of atherosclerosis, a disease that results in narrowing of the arterial lumen, thereby reducing blood flow to critical levels in vital organs, such as the heart and brain. Here, we discuss novel insights into how heparan sulfate proteoglycans modulate risk factors such as hyperlipidemia and inflammation that drive the initiation and progression of atherosclerotic plaques to their clinical critical endpoint.

Heparanase Inhibition Reduces Glucose Levels, Blood Pressure, and Oxidative Stress in Apolipoprotein E Knockout Mice

Background

Atherosclerosis is a multifactorial process. Emerging evidence highlights a role of the enzyme heparanase in various disease states, including atherosclerosis formation and progression.

Objective

The aim of the study was to investigate the effect of heparanase inhibition on blood pressure, blood glucose levels, and oxidative stress in apoE−/− mice.

Methods

Male apoE−/− mice were divided into two groups: one treated by the heparanase inhibitor PG545, administered intraperitoneally weekly for seven weeks, and the other serving as control group (injected with saline). Blood pressure was measured a day before sacrificing the animals. Serum glucose levels and lipid profile were measured. Assessment of oxidative stress was performed as well.

Results

PG545 significantly lowered blood pressure and serum glucose levels in treated mice. It also caused significant reduction of the serum oxidative stress. For safety concerns, liver enzymes were assessed, and PG545 caused significant elevation only of alanine aminotransferase, but not of the other hepatic enzymes.

Conclusion

Heparanase inhibition by PG545 caused marked reduction of blood pressure, serum glucose levels, and oxidative stress in apolipoprotein E deficient mice, possibly via direct favorable metabolic and hemodynamic changes caused by the inhibitor. Possible hepatotoxic and weight wasting effects are subject for future investigation.

The central role of arterial retention of cholesterol-rich apolipoprotein-B-containing lipoproteins in the pathogenesis of atherosclerosis: a triumph of simplicity

PURPOSE OF REVIEW

Today, it is no longer a hypothesis, but an established fact, that increased plasma concentrations of cholesterol-rich apolipoprotein-B (apoB)-containing lipoproteins are causatively linked to atherosclerotic cardiovascular disease (ASCVD) and that lowering plasma LDL concentrations reduces cardiovascular events in humans. Here, we review evidence behind this assertion, with an emphasis on recent studies supporting the 'response-to-retention' model - namely, that the key initiating event in atherogenesis is the retention, or trapping, of cholesterol-rich apoB-containing lipoproteins within the arterial wall.

RECENT FINDINGS

New clinical trials have shown that ezetimibe and anti-PCSK9 antibodies - both nonstatins - lower ASCVD events, and they do so to the same extent as would be expected from comparable plasma LDL lowering by a statin. These studies demonstrate beyond any doubt the causal role of apoB-containing lipoproteins in atherogenesis. In addition, recent laboratory experimentation and human Mendelian randomization studies have revealed novel information about the critical role of apoB-containing lipoproteins in atherogenesis. New information has also emerged on mechanisms for the accumulation in plasma of harmful cholesterol-rich and triglyceride-rich apoB-containing remnant lipoproteins in states of overnutrition. Like LDL, these harmful cholesterol-rich and triglyceride-rich apoB-containing remnant lipoprotein remnants become retained and modified within the arterial wall, causing atherosclerosis.

SUMMARY

LDL and other cholesterol-rich, apoB-containing lipoproteins, once they become retained and modified within the arterial wall, cause atherosclerosis. This simple, robust pathophysiologic understanding may finally allow us to eradicate ASCVD, the leading killer in the world.

A current view of perlecan in physiology and pathology: A mosaic of functions

Perlecan, a large basement membrane heparan sulfate proteoglycan, is expressed in a wide array of tissues where it regulates diverse cellular processes including bone formation, inflammation, cardiac development, and angiogenesis. Here we provide a contemporary review germane to the biology of perlecan encompassing its genetic regulation as well as an analysis of its modular protein structure as it pertains to function. As perlecan signaling from the extracellular matrix converges on master regulators of autophagy, including AMPK and mTOR, via a specific interaction with vascular endothelial growth factor receptor 2, we specifically focus on the mechanism of action of perlecan in autophagy and angiogenesis and contrast the role of endorepellin, the C-terminal fragment of perlecan, in these cellular and morphogenic events.

Perlecan deficiency causes endothelial dysfunction by reducing the expression of endothelial nitric oxide synthase

Perlecan is a major heparan sulfate proteoglycan found in the subendothelial extracellular matrix of the vascular wall. The aim of this study was to investigate the role of perlecan in the regulation of vascular tone. A previously developed conditional perlecan‐deficient mouse model was used to measure changes in the isometric force of isolated aortic rings. The vessels were first precontracted with phenylephrine, and then treated with increasing concentrations of vasorelaxants. Endothelium‐dependent relaxation, elicited by acetylcholine, was significantly reduced in the perlecan‐deficient aortas, whereas endothelium‐independent relaxation caused by the exogenous nitric oxide donor sodium nitroprusside remained well preserved. The expression of the endothelial nitric oxide synthase (eNOS) gene, detected by real‐time polymerase chain reaction, was significantly decreased in the perlecan‐deficient aortas. The expression of eNOS protein detected using Western blotting was also significantly decreased in the perlecan‐deficient aortas. We examined the role of perlecan in eNOS gene expression by creating perlecan knockdown human aortic endothelial cells using small interfering RNA (siRNA) for perlecan. Perlecan gene expression was significantly reduced in the perlecan siRNA‐treated cells, resulting in a significant decrease in eNOS gene expression. Perlecan deficiency induced endothelial dysfunction, as indicated by a reduction in endothelium‐dependent relaxation due, at least partly, to a reduction in eNOS expression. These findings suggest that perlecan plays a role in the activation of eNOS gene expression during normal growth processes.

Perlecan deficiency induced endothelial dysfunction at least partly, to a reduction in eNOS expression. These findings suggest that perlecan plays a role in the activation of the eNOS expression during normal growth processes.

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.

A brief elevation of serum amyloid A is sufficient to increase atherosclerosis

Serum amyloid A (SAA) has a number of proatherogenic effects including induction of vascular proteoglycans. Chronically elevated SAA was recently shown to increase atherosclerosis in mice. The purpose of this study was to determine whether a brief increase in SAA similarly increased atherosclerosis in a murine model. The recombination activating gene 1-deficient (rag1(-/-)) × apolipoprotein E-deficient (apoe(-/-)) and apoe(-/-) male mice were injected, multiple times or just once respectively, with an adenoviral vector encoding human SAA1 (ad-SAA); the injected mice and controls were maintained on chow for 12-16 weeks. Mice receiving multiple injections of ad-SAA, in which SAA elevation was sustained, had increased atherosclerosis compared with controls. Strikingly, mice receiving only a single injection of ad-SAA, in which SAA was only briefly elevated, also had increased atherosclerosis compared with controls. Using in vitro studies, we demonstrate that SAA treatment leads to increased LDL retention, and that prevention of transforming growth factor beta (TGF-β) signaling prevents SAA-induced increases in LDL retention and SAA-induced increases in vascular biglycan content. We propose that SAA increases atherosclerosis development via induction of TGF-β, increased vascular biglycan content, and increased LDL retention. These data suggest that even short-term inflammation with concomitant increase in SAA may increase the risk of developing CVD.

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.

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.

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.

Involvement of heparanase in atherosclerosis and other vessel wall pathologies

Heparanase, the sole mammalian endoglycosidase degrading heparan sulfate, is causally involved in cancer metastasis, angiogenesis, inflammation and kidney dysfunction. Despite the wide occurrence and impact of heparan sulfate proteoglycans in vascular biology, the significance of heparanase in vessel wall disorders is underestimated. Blood vessels are highly active structures whose morphology rapidly adapts to maintain vascular function under altered systemic and local conditions. In some pathologies (restenosis, thrombosis, atherosclerosis) this normally beneficial adaptation may be detrimental to overall function. Enzymatic dependent and independent effects of heparanase on arterial structure mechanics and repair closely regulate arterial compliance and neointimal proliferation following endovascular stenting. Additionally, heparanase promotes thrombosis after vascular injury and contributes to a pro-coagulant state in human carotid atherosclerosis. Importantly, heparanase is closely associated with development and progression of atherosclerotic plaques, including stable to unstable plaque transition. Consequently, heparanase levels are markedly increased in the plasma of patients with acute myocardial infarction. Noteworthy, heparanase activates macrophages, resulting in marked induction of cytokine expression associated with plaque progression towards vulnerability. Together, heparanase emerges as a regulator of vulnerable lesion development and potential target for therapeutic intervention in atherosclerosis and related vessel wall complications.

Arterial retention of remnant lipoproteins ex vivo is increased in insulin resistance because of increased arterial biglycan and production of cholesterol-rich atherogenic particles that can be improved by ezetimibe in the JCR:LA-cp rat

BACKGROUND

Literature supports the "response-to-retention" hypothesis-that during insulin resistance, impaired metabolism of remnant lipoproteins can contribute to accelerated cardiovascular disease progression. We used the JCR:LA-cp rat model of metabolic syndrome (MetS) to determine the extent of arterial accumulation of intestinal-derived remnants ex vivo and potential mechanisms that contribute to exacerbated cholesterol deposition in insulin resistance.

METHODS AND RESULTS

Arteries from control and MetS (insulin-resistant) JCR:LA-cp rats were perfused ex vivo with Cy5-labeled remnant lipoproteins, and their arterial retention was quantified by confocal microscopy. Arterial proteoglycans were isolated from control and MetS rats at 6, 12, and 32 weeks of age. There was a significant increase in the arterial retention of remnants and in associated cholesterol accumulation in MetS rats as compared to control rats. Mechanistic studies reveal that increased cholesterol deposition is a result of greater arterial biglycan content; longer glycosaminoglycans and increased production of cholesterol-rich intestinal-derived remnants, as compared to controls. Additionally, perfusion of vessels treated with ezetimibe, alone or in combination with simvastatin, with remnants isolated from the respective treatment group reduced ex vivo arterial retention of remnant-derived cholesterol ex vivo as compared to untreated controls.

CONCLUSIONS

Increased progression of atherosclerotic cardiovascular disease in MetS and type 2 diabetes mellitus might be explained in part by an increase in the arterial retention of cholesterol-rich remnants. Furthermore, ezetimibe alone or in combination treatment with simvastatin could be beneficial in ameliorating atherosclerotic cardiovascular disease in insulin resistance and MetS.

Extracellular matrix molecules facilitating vascular biointegration

All vascular implants, including stents, heart valves and graft materials exhibit suboptimal biocompatibility that significantly reduces their clinical efficacy. A range of biomolecules in the subendothelial space have been shown to play critical roles in local regulation of thrombosis, endothelial growth and smooth muscle cell proliferation, making these attractive candidates for modulation of vascular device biointegration. However, classically used biomaterial coatings, such as fibronectin and laminin, modulate only one of these components; enhancing endothelial cell attachment, but also activating platelets and triggering thrombosis. This review examines a subset of extracellular matrix molecules that have demonstrated multi-faceted vascular compatibility and accordingly are promising candidates to improve the biointegration of vascular biomaterials.

Changes in expression of proteoglycan core proteins and heparan sulfate enzymes in the developing and adult murine aorta

Proteoglycan core proteins are linked to four different classes of linear sugar chains referred to as glycosaminoglycans. Heparan sulfate constitutes one of these classes of glycosaminoglycans, and has been shown to be important in developmental processes as well as disease. We designed a low-density gene expression array to identify expression levels of heparan sulfate biosynthetic enzymes and proteoglycan core proteins in the aorta of late stage embryos (E18.5) and adult mice (12 weeks). Significant changes were found in mRNA expression of proteoglycan core proteins syndecan, glypican, decorin, perlecan, and versican from development to adulthood (n = 8, p < 0.05). Immunohistochemistry revealed a striking localization of both decorin and perlecan staining to the subendothelium in adult vessels, which differed from consistent staining of the endothelium, smooth muscle, and adventitia in development. Significant differences were also identified in the expression of the heparan sulfate modifying enzymes, glururonyl C5 epimerase, 2-O and 6-O sulfotransferases, and N-deacetylase/N sulfotransferases 1-3 (n = 8, p < 0.05). In conclusion, proteoglycan core proteins and heparan sulfate biosynthetic enzymes in the aorta undergo significant changes in their expression from development to adulthood. These findings may have important biological significance in the specific cell-defined roles of proteoglycan and heparan sulfate related targets in vascular development, maintenance, and response to various perturbations.

Regulation of heparanase expression in coronary artery disease in diabetic, hyperlipidemic swine

OBJECTIVE

Enzymatic degradation of the extracellular matrix is known to be powerful regulator of atherosclerosis. However, little is known about the enzymatic regulation of heparan sulfate proteoglycans (HSPGs) during the formation and progression of atherosclerotic plaques.

METHODS AND RESULTS

Swine were rendered diabetic through streptozotocin injection and hyperlipidemic through a high fat diet. Arterial remodeling and local endothelial shear stress (ESS) were assessed using intravascular ultrasound, coronary angiography and computational fluid dynamics at weeks 23 and 30. Coronary arteries were harvested and 142 arterial subsegments were analyzed using histomorphologic staining, immunostaining and real time PCR. Heparanase staining and activity was increased in arterial segments with low ESS, in lesions with thin cap fibroatheroma (TCFA) morphology and in lesions with severely degraded internal elastic laminae. In addition, heparanase staining co-localized with staining for CD45 and MMP-2 within atherosclerotic plaques. Dual staining with gelatinase zymography and heparanase immunohistochemical staining demonstrated co-localization of matrix metalloprotease activity with heparanase staining. A heparanase enzymatic activity assay demonstrated increased activity in TCFA lesions, subsegments with low ESS and in macrophages treated with oxidized LDL or angiotensin II.

CONCLUSIONS

Taken together, our results support a critical role for heparanase in the development of vulnerable plaques and suggest a novel therapeutic target for the treatment of atherosclerosis.

Proteoglycan mediated lipoprotein retention: a mechanism of diabetic atherosclerosis

The response to retention hypothesis outlines the initial stages of atherosclerotic lesion formation. The central theme of the hypothesis is that proteoglycan mediated lipoprotein retention plays a critical step in the initiation of atherosclerosis development. Recent research using human arterial specimens, transgenic mouse models and molecular biology techniques have added to our understanding of atherosclerosis development, and provided experimental data in support of the response to retention hypothesis. In this review we summarize the recent data, in particular that which addresses mechanisms by which diabetes can accelerate atherosclerosis formation, with a focus on proteoglycan-mediated LDL retention.

Serum amyloid A, but not C-reactive protein, stimulates vascular proteoglycan synthesis in a pro-atherogenic manner

Inflammatory markers serum amyloid A (SAA) and C-reactive protein (CRP) are predictive of cardiac disease and are proposed to play causal roles in the development of atherosclerosis, in which the retention of lipoproteins by vascular wall proteoglycans is critical. The purpose of this study was to determine whether SAA and/or CRP alters vascular proteoglycan synthesis and lipoprotein retention in a pro-atherogenic manner. Vascular smooth muscle cells were stimulated with either SAA or CRP (1 to 100 mg/L) and proteoglycans were then isolated and characterized. SAA, but not CRP, increased proteoglycan sulfate incorporation by 50 to 100% in a dose-dependent manner (P < 0.0001), increased glycosaminoglycan chain length, and increased low-density lipoprotein (LDL) binding affinity (K(d), 29 microg/ml LDL versus 90 microg/ml LDL for SAA versus control proteoglycans; P < 0.005). Furthermore, SAA up-regulated biglycan via the induction of endogenous transforming growth factor (TGF)-beta. To determine whether SAA stimulated proteoglycan synthesis in vivo, ApoE(-/-) mice were injected with an adenovirus expressing human SAA-1, a null virus, or saline. Mice that received adenovirus expressing SAA had increased TGF-beta concentrations in plasma and increased aortic biglycan content compared with mice that received either null virus or saline. Thus, SAA alters vascular proteoglycans in a pro-atherogenic manner via the stimulation of TGF-beta and may play a causal role in the development of atherosclerosis.

Heparan sulfate in perlecan promotes mouse atherosclerosis: roles in lipid permeability, lipid retention, and smooth muscle cell proliferation

Heparan sulfate (HS) has been proposed to be antiatherogenic through inhibition of lipoprotein retention, inflammation, and smooth muscle cell proliferation. Perlecan is the predominant HS proteoglycan in the artery wall. Here, we investigated the role of perlecan HS chains using apoE null (ApoE0) mice that were cross-bred with mice expressing HS-deficient perlecan (Hspg2(Delta3/Delta3)). Morphometry of cross-sections from aortic roots and en face preparations of whole aortas revealed a significant decrease in lesion formation in ApoE0/Hspg2(Delta3/Delta3) mice at both 15 and 33 weeks. In vitro, binding of labeled mouse triglyceride-rich lipoproteins and human LDL to total extracellular matrix, as well as to purified proteoglycans, prepared from ApoE0/Hspg2(Delta3/Delta3) smooth muscle cells was reduced. In vivo, at 20 minutes influx of human (125)I-LDL or mouse triglyceride-rich lipoproteins into the aortic wall was increased in ApoE0/Hspg2(Delta3/Delta3) mice compared to ApoE0 mice. However, at 72 hours accumulation of (125)I-LDL was similar in ApoE0/Hspg2(Delta3/Delta3) and ApoE0 mice. Immunohistochemistry of lesions from ApoE0/Hspg2(Delta3/Delta3) mice showed decreased staining for apoB and increased smooth muscle alpha-actin content, whereas accumulation of CD68-positive inflammatory cells was unchanged. We conclude that the perlecan HS chains are proatherogenic in mice, possibly through increased lipoprotein retention, altered vascular permeability, or other mechanisms. The ability of HS to inhibit smooth muscle cell growth may also influence development as well as instability of lesions.

Heparan Sulfate in Perlecan Promotes Mouse Atherosclerosis

Heparan sulfate (HS) has been proposed to be antiatherogenic through inhibition of lipoprotein retention, inflammation, and smooth muscle cell proliferation. Perlecan is the predominant HS proteoglycan in the artery wall. Here, we investigated the role of perlecan HS chains using apoE null (ApoE0) mice that were cross-bred with mice expressing HS-deficient perlecan ( Hspg2 Δ3/Δ3 ). Morphometry of cross-sections from aortic roots and en face preparations of whole aortas revealed a significant decrease in lesion formation in ApoE0/ Hspg2 Δ3/Δ3 mice at both 15 and 33 weeks. In vitro, binding of labeled mouse triglyceride-rich lipoproteins and human LDL to total extracellular matrix, as well as to purified proteoglycans, prepared from ApoE0/ Hspg2 Δ3/Δ3 smooth muscle cells was reduced. In vivo, at 20 minutes influx of human 125 I-LDL or mouse triglyceride-rich lipoproteins into the aortic wall was increased in ApoE0/ Hspg2 Δ3/Δ3 mice compared to ApoE0 mice. However, at 72 hours accumulation of 125 I-LDL was similar in ApoE0/ Hspg2 Δ3/Δ3 and ApoE0 mice. Immunohistochemistry of lesions from ApoE0/ Hspg2 Δ3/Δ3 mice showed decreased staining for apoB and increased smooth muscle α-actin content, whereas accumulation of CD68-positive inflammatory cells was unchanged. We conclude that the perlecan HS chains are proatherogenic in mice, possibly through increased lipoprotein retention, altered vascular permeability, or other mechanisms. The ability of HS to inhibit smooth muscle cell growth may also influence development as well as instability of lesions.

Subendothelial lipoprotein retention as the initiating process in atherosclerosis: update and therapeutic implications

The key initiating process in atherogenesis is the subendothelial retention of apolipoprotein B-containing lipoproteins. Local biological responses to these retained lipoproteins, including a chronic and maladaptive macrophage- and T-cell-dominated inflammatory response, promote subsequent lesion development. The most effective therapy against atherothrombotic cardiovascular disease to date--low density lipoprotein-lowering drugs--is based on the principle that decreasing circulating apolipoprotein B lipoproteins decreases the probability that they will enter and be retained in the subendothelium. Ongoing improvements in this area include more aggressive lowering of low-density lipoprotein and other atherogenic lipoproteins in the plasma and initiation of low-density lipoprotein-lowering therapy at an earlier age in at-risk individuals. Potential future therapeutic approaches include attempts to block the interaction of apolipoprotein B lipoproteins with the specific subendothelial matrix molecules that mediate retention and to interfere with accessory molecules within the arterial wall that promote retention such as lipoprotein lipase, secretory sphingomyelinase, and secretory phospholipase A2. Although not the primary focus of this review, therapeutic strategies that target the proatherogenic responses to retained lipoproteins and that promote the removal of atherogenic components of retained lipoproteins also hold promise. The finding that certain human populations of individuals who maintain lifelong low plasma levels of apolipoprotein B lipoproteins have an approximately 90% decreased risk of coronary artery disease gives hope that our further understanding of the pathogenesis of this leading killer could lead to its eradication.

Allograft vasculopathy versus atherosclerosis

Over the last 4 decades, heart transplantation (HTx) has evolved as a mainstream therapy for heart failure. Approximately half of patients needing HTx have organ failure consequent to atherosclerosis. Despite advances in immunosuppressive drugs, long-term success of HTx is limited by the development of a particular type of coronary atherosclerosis, referred to as cardiac allograft vasculopathy (CAV). Although the exact pathogenesis of CAV remains to be established, there is strong evidence that CAV involves immunologic mechanisms operating in a milieu of nonimmunologic risk factors. The immunologic events constitute the principal initiating stimuli, resulting in endothelial injury and dysfunction, altered endothelial permeability, with consequent myointimal hyperplasia and extracellular matrix synthesis. Lipid accumulation in allograft arteries is prominent, with lipoprotein entrapment in the subendothelial tissue, through interactions with proteoglycans. The apparent endothelial "intactness" in human coronary arteries of the transplanted heart suggest that permeability and function of the endothelial barrier altered. Various insults to the vascular bed result in vascular smooth muscle cell (SMC) activation. Activated SMCs migrate from the media into the intima, proliferate, and elaborate cytokines and extracellular matrix proteins, resulting in luminal narrowing and impaired vascular function. Arteriosclerosis is a broad term that is used to encompass all diseases that lead to arterial hardening, including native atherosclerosis, postangioplasty restenosis, vein bypass graft occlusion, and CAV. These diseases exhibit many similarities; however, they are distinct from one another in numerous ways as well. The present review summarizes the current understanding of the risk factors and the pathophysiological similarities and differences between CAV and atherosclerosis.

Approaching theProteoglycome: Molecular Interactions of Proteoglycans and Their Functional Output

[Image: see text] Through their diverse core protein modules and glycan/glycosaminoglycan moieties, proteoglycans may engage in numerous cellular and molecular interactions which are dispensable during embryogenesis, are essential for the maintenance of a healthy state and are prone to modulation in pathological conditions. Proteoglycan interactions may involve binding to other structural components of the ECM, to cell surface receptors, to membrane-associated components, and to soluble signaling molecules, which through this interaction may become entrapped in the ECM or sequestered at the cell surface. Understanding of these multiple interplays is therefore of paramount importance and requires a detailed mapping through what we define as the proteoglycome.

Reduced perlecan expression and accumulation in human carotid atherosclerotic lesions

Heparan sulfate in the extracellular matrix of the artery wall has been proposed to possess anti-atherogenic properties by interfering with lipoprotein retention, suppression of inflammation, and inhibition of smooth muscle cell growth. Previously, the amount of heparan sulfate in atherosclerotic lesions from humans and animals has been shown to be reduced but the identity or identities of the heparan sulfate molecules being down regulated in this disease are not known. In this study, atherosclerotic lesions were retrieved from 44 patients undergoing surgery for symptomatic carotid stenosis. Normal iliac arteries from organ donors were used as controls. Analysis of the specimens by gene microarray showed a selective reduction in perlecan gene expression, whereas, expression of the other heparan sulfate proteoglycans in the artery wall, agrin and collagen XVIII, remained unchanged. Expression of the large chondroitin sulfate proteoglycan, versican, also remained unchanged. Real-time PCR confirmed the decrease in perlecan gene expression and the unchanged expression of versican. The findings were supported by immunohistochemical analysis demonstrating a reduced accumulation of both perlecan core protein and heparan sulfate in carotid lesions. The study demonstrates a reduction of perlecan mRNA-expression and protein deposition in human atherosclerosis, which in part explains the low levels of heparan sulfate in this disease.

Lipoprotein Retention—and Clues for Atheroma Regression

Subendothelial retention of apoB-lipoproteins is the key initiating event in atherosclerosis, provoking a cascade of pathogenic responses. Dissection of the molecular participants provides fresh insight into how this major killer might be reversed. Efflux of harmful lipids derived from retained lipoproteins may be crucial in promoting beneficial remodeling of lesions.

Oxidation, lipoproteins, and atherosclerosis: which is wrong, the antioxidants or the theory?

PURPOSE OF REVIEW

Paradoxically, many well-established components of the heart-healthy lifestyle are pro-oxidant, including polyunsaturated fat and moderate alcohol consumption. Moreover, antioxidant supplements have failed to decrease cardiovascular risk in extensive human clinical trials to date. Recent progress in understanding the roles of oxidants in regulating VLDL secretion and as essential signaling molecules supports the concept that oxidation may be beneficial in certain circumstances but damaging in others. We summarize recent data on the roles played by oxidative metabolism in different tissues and pathways, and address whether it is currently advisable to use antioxidant supplements to reduce cardiovascular risk.

RECENT FINDINGS

Our recent study reported that in liver cells, polyunsaturated fatty acids increased reactive oxygen species, which in turn lowered the secretion of the atherogenic lipoprotein, VLDL, in vitro and in vivo. Antioxidant treatments prevented VLDL-lowering effects of polyunsaturated fatty acids in vitro, suggesting that supplemental antioxidants could either raise apolipoprotein-B-lipoprotein plasma levels in vivo, or impair the response to lipid-lowering therapies. The failure of antioxidants to decrease cardiovascular disease risk in many trials is also discussed in the context of current models for atherosclerosis progression and regression.

SUMMARY

Oxidation includes distinct biochemical reactions, and it is overly simplistic to lump them into a unitary process that affects all cell types and metabolic pathways adversely. Guidelines for diet should adhere closely to what has been clinically proved, and by this standard there is no basis to recommend antioxidant use, beyond what is inherent to the 'heart healthy' diet in order to benefit cardiovascular health.