Human coronary smooth muscle cells internalize versican-modified LDL through LDL receptor-related protein and LDL receptors

Mechanisms modulating foam cell formation in the arterial intima: exploring new therapeutic opportunities in atherosclerosis

In recent years, the role of macrophages as the primary cell type contributing to foam cell formation and atheroma plaque development has been widely acknowledged. However, it has been long recognized that diffuse intimal thickening (DIM), which precedes the formation of early fatty streaks in humans, primarily consists of lipid-loaded smooth muscle cells (SMCs) and their secreted proteoglycans. Recent studies have further supported the notion that SMCs constitute the majority of foam cells in advanced atherosclerotic plaques. Given that SMCs are a major component of the vascular wall, they serve as a significant source of microvesicles and exosomes, which have the potential to regulate the physiology of other vascular cells. Notably, more than half of the foam cells present in atherosclerotic lesions are of SMC origin. In this review, we describe several mechanisms underlying the formation of intimal foam-like cells in atherosclerotic plaques. Based on these mechanisms, we discuss novel therapeutic approaches that have been developed to regulate the generation of intimal foam-like cells. These innovative strategies hold promise for improving the management of atherosclerosis in the near future.

Soluble low-density lipoprotein receptor-related protein 1 as a surrogate marker of carotid plaque inflammation assessed by 18F-FDG PET in patients with a recent ischemic stroke

BACKGROUND

18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET) identifies carotid plaque inflammation and predicts stroke recurrence.

AIM

Our aim was to evaluate the performance of soluble low-density lipoprotein receptor-related protein 1 (sLRP1) as an indicator of carotid plaque inflammation.

METHODS

A prospective study was conducted among adult patients with recent (< 7 days) anterior circulation ischemic stroke and at least one atherosclerotic plaque in the ipsilateral internal carotid artery. Patients underwent an early (< 15 days from inclusion) 18F-FDG PET, and the maximum standardized uptake value (SUVmax) within the plaque was measured. sLRP1 levels were measured in plasma samples by ELISA. The association of sLRP1 with SUVmax was assessed using bivariate and multivariable linear regression analyses. Hazard ratios (HR) were estimated with Cox regression to evaluate the association between circulating sLRP1 and stroke recurrence.

RESULTS

The study was conducted with 64 participants, of which 57.8% had ≥ 50% carotid stenosis. The multivariable linear and logistic regression analyses showed that sLRP1 was independently associated with (i) SUVmax within the plaque (β = 0.159, 95% CI 0.062-0.257, p = 0.002) and (ii) a probability of presenting SUVmax ≥ 2.85 g/mL (OR = 1.31, 95% CI 1.00-1.01, p = 0.046), respectively. Participants with stroke recurrence showed higher sLRP1 levels at baseline [6447 ng/mL (4897-11163) vs. 3713 ng/mL (2793-4730); p = 0.018].

CONCLUSIONS

sLRP1 was independently associated with carotid plaque inflammation as measured by 18F-FDG PET in patients with recent ischemic stroke and carotid atherosclerosis.

Targeting cholesteryl ester accumulation in the heart improves cardiac insulin response

BACKGROUND

Antibodies against the P3 sequence (Gly1127-Cys1140) of LRP1 (anti-P3 Abs) specifically block cholesteryl ester (CE) accumulation in vascular cells. LRP1 is a key regulator of insulin receptor (InsR) trafficking in different cell types. The link between CE accumulation and the insulin response are largely unknown. Here, the effects of P3 peptide immunization on the alterations induced by a high-fat diet (HFD) in cardiac insulin response were evaluated.

METHODS

Irrelevant (IrP)- or P3 peptide-immunized rabbits were randomized into groups fed either HFD or normal chow. Cardiac lipid content was characterized by thin-layer chromatography, confocal microscopy, and electron microscopy. LRP1, InsR and glucose transporter type 4 (GLUT4) levels were determined in membranes and total lysates from rabbit heart. The interaction between InsR and LRP1 was analyzed by immunoprecipitation and confocal microscopy. Insulin signaling activity and glucose uptake were evaluated in HL-1 cells exposed to rabbit serum from the different groups.

FINDINGS

HFD reduces cardiac InsR and GLUT4 membrane levels and the interactions between LRP1/InsR. Targeting the P3 sequence on LRP1 through anti-P3 Abs specifically reduces CE accumulation in the heart independently of changes in the circulating lipid profile. This restores InsR and GLUT4 levels in cardiac membranes as well as the LRP1/InsR interactions of HFD-fed rabbits. In addition, anti-P3 Abs restores the insulin signaling cascade and glucose uptake in HL-1 cells exposed to hypercholesterolemic rabbit serum.

INTERPRETATION

LRP1-immunotargeting can block CE accumulation within the heart with specificity, selectivity, and efficacy, thereby improving the cardiac insulin response; this has important therapeutic implications for a wide range of cardiac diseases.

FUNDING

Fundació MARATÓ TV3: grant 101521-10, Instiuto de Salud Carlos III (ISCIII) and ERDFPI18/01584, Fundación BBVA Ayudas a Equipos de Investigación 2019. SECyT-UNC grants PROYECTOS CONSOLIDAR 2018-2021; FONCyT, Préstamo BID PICT grant 2015-0807 and grant 2017-4497.

Smooth Muscle Cell—Macrophage Interactions Leading to Foam Cell Formation in Atherosclerosis: Location, Location, Location

Cholesterol-overloaded cells or “foam cells” in the artery wall are the biochemical hallmark of atherosclerosis, and are responsible for much of the growth, inflammation and susceptibility to rupture of atherosclerotic lesions. While it has previously been thought that macrophages are the main contributor to the foam cell population, recent evidence indicates arterial smooth muscle cells (SMCs) are the source of the majority of foam cells in both human and murine atherosclerosis. This review outlines the timeline, site of appearance and proximity of SMCs and macrophages with lipids in human and mouse atherosclerosis, and likely interactions between SMCs and macrophages that promote foam cell formation and removal by both cell types. An understanding of these SMC-macrophage interactions in foam cell formation and regression is expected to provide new therapeutic targets to reduce the burden of atherosclerosis for the prevention of coronary heart disease, stroke and peripheral vascular disease.

The Dual Role of Low-Density Lipoprotein Receptor-Related Protein 1 in Atherosclerosis

Low-density lipoprotein receptor–related protein-1 (LRP1) is a large endocytic and signaling receptor belonging to the LDL receptor (LDLR) gene family and that is widely expressed in several tissues. LRP1 comprises a large extracellular domain (ECD; 515 kDa, α chain) and a small intracellular domain (ICD; 85 kDa, β chain). The deletion of LRP1 leads to embryonic lethality in mice, revealing a crucial but yet undefined role in embryogenesis and development. LRP1 has been postulated to participate in numerous diverse physiological and pathological processes ranging from plasma lipoprotein homeostasis, atherosclerosis, tumor evolution, and fibrinolysis to neuronal regeneration and survival. Many studies using cultured cells and in vivo animal models have revealed the important roles of LRP1 in vascular remodeling, foam cell biology, inflammation and atherosclerosis. However, its role in atherosclerosis remains controversial. LRP1 not only participates in the removal of atherogenic lipoproteins and proatherogenic ligands in the liver but also mediates the uptake of aggregated LDL to promote the formation of macrophage- and vascular smooth muscle cell (VSMC)-derived foam cells, which causes a prothrombotic transformation of the vascular wall. The dual and opposing roles of LRP1 may also represent an interesting target for atherosclerosis therapeutics. This review highlights the influence of LRP1 during atherosclerosis development, focusing on its dual role in vascular cells and immune cells.

Adipocyte-Derived Versican and Macrophage-Derived Biglycan Control Adipose Tissue Inflammation in Obesity

Obesity is characterized by adipose tissue inflammation. Because proteoglycans regulate inflammation, here we investigate their role in adipose tissue inflammation in obesity. We find that adipose tissue versican and biglycan increase in obesity. Versican is produced mainly by adipocytes and biglycan by adipose tissue macrophages. Both proteoglycans are also present in adipose tissue from obese human subjects undergoing gastric bypass surgery. Deletion of adipocyte-specific versican or macrophage-specific biglycan in mice reduces macrophage accumulation and chemokine and cytokine expression, although only adipocyte-specific versican deletion leads to sustained improvement in glucose tolerance. Macrophage-derived biglycan activates inflammatory genes in adipocytes. Versican expression increases in cultured adipocytes exposed to excess glucose, and adipocyte-conditioned medium stimulates inflammation in resident peritoneal macrophages, in part because of a versican breakdown product, versikine. These findings provide insights into the role of adipocyte- and macrophage-derived proteoglycans in adipose tissue inflammation in obesity.

Aggregated LDL turn human macrophages into foam cells and induce mitochondrial dysfunction without triggering oxidative or endoplasmic reticulum stress

Uptake of modified lipoproteins by macrophages turns them into foam cells, the hallmark of the atherosclerotic plaque. The initiation and progression of atherosclerosis have been associated with mitochondrial dysfunction. It is known that aggregated low-density lipoproteins (agLDL) induce massive cholesterol accumulation in macrophages in contrast with native LDL (nLDL) and oxidized LDL (oxLDL). In the present study we aimed to assess the effect of agLDL on the mitochondria and ER function in macrophage-derived foam cells, in an attempt to estimate the potential of these cells, known constituents of early fatty streaks, to generate atheroma in the absence of oxidative stress. Results show that agLDL induce excessive accumulation of free (FC) and esterified cholesterol in THP-1 macrophages and determine mitochondrial dysfunction expressed as decreased mitochondrial membrane potential and diminished intracellular ATP levels, without generating mitochondrial reactive oxygen species (ROS) production. AgLDL did not stimulate intracellular ROS (superoxide anion or hydrogen peroxide) production, and did not trigger endoplasmic reticulum stress (ERS) or apoptosis. In contrast to agLDL, oxLDL did not modify FC levels, but stimulated the accumulation of 7-ketocholesterol in the cells, generating oxidative stress which is associated with an increased mitochondrial dysfunction, ERS and apoptosis. Taken together, our results reveal that agLDL induce foam cells formation and mild mitochondrial dysfunction in human macrophages without triggering oxidative or ERS. These data could partially explain the early formation of fatty streaks in the intima of human arteries by interaction of monocyte-derived macrophages with non-oxidatively aggregated LDL generating foam cells, which cannot evolve into atherosclerotic plaques in the absence of the oxidative stress.

ADAMTS proteases in cardiovascular physiology and disease

The a disintegrin-like and metalloproteinase with thrombospondin motif (ADAMTS) family comprises 19 proteases that regulate the structure and function of extracellular proteins in the extracellular matrix and blood. The best characterized cardiovascular role is that of ADAMTS-13 in blood. Moderately low ADAMTS-13 levels increase the risk of ischeamic stroke and very low levels (less than 10%) can cause thrombotic thrombocytopenic purpura (TTP). Recombinant ADAMTS-13 is currently in clinical trials for treatment of TTP. Recently, new cardiovascular roles for ADAMTS proteases have been discovered. Several ADAMTS family members are important in the development of blood vessels and the heart, especially the valves. A number of studies have also investigated the potential role of ADAMTS-1, -4 and -5 in cardiovascular disease. They cleave proteoglycans such as versican, which represent major structural components of the arteries. ADAMTS-7 and -8 are attracting considerable interest owing to their implication in atherosclerosis and pulmonary arterial hypertension, respectively. Mutations in the ADAMTS19 gene cause progressive heart valve disease and missense variants in ADAMTS6 are associated with cardiac conduction. In this review, we discuss in detail the evidence for these and other cardiovascular roles of ADAMTS family members, their proteolytic substrates and the potential molecular mechanisms involved.

Role of the Scavenger Receptor CD36 in Accelerated Diabetic Atherosclerosis

Diabetes mellitus entails increased atherosclerotic burden and medial arterial calcification, but the precise mechanisms are not fully elucidated. We aimed to investigate the implication of CD36 in inflammation and calcification processes orchestrated by vascular smooth muscle cells (VSMCs) under hyperglycemic and atherogenic conditions. We examined the expression of CD36, pro-inflammatory cytokines, endoplasmic reticulum (ER) stress markers, and mineralization-regulating enzymes by RT-PCR in human VSMCs, cultured in a medium containing normal (5 mM) or high glucose (22 mM) for 72 h with or without oxidized low-density lipoprotein (oxLDL) (24 h). The uptake of 1,1′-dioctadecyl-3,3,3′,3-tetramethylindocarbocyanine perchlorate-fluorescently (DiI) labeled oxLDL was quantified by flow cytometry and fluorimetry and calcification assays were performed in VSMC cultured in osteogenic medium and stained by alizarin red. We observed induction in the expression of CD36, cytokines, calcification markers, and ER stress markers under high glucose that was exacerbated by oxLDL. These results were confirmed in carotid plaques from subjects with diabetes versus non-diabetic subjects. Accordingly, the uptake of DiI-labeled oxLDL was increased after exposure to high glucose. The silencing of CD36 reduced the induction of CD36 and the expression of calcification enzymes and mineralization of VSMC. Our results indicate that CD36 signaling is partially involved in hyperglycemia and oxLDL-induced vascular calcification in diabetes.

Lipid efflux mechanisms, relation to disease and potential therapeutic aspects

Lipids are hydrophobic and amphiphilic molecules involved in diverse functions such as membrane structure, energy metabolism, immunity, and signaling. However, altered intra-cellular lipid levels or composition can lead to metabolic and inflammatory dysfunction, as well as lipotoxicity. Thus, intra-cellular lipid homeostasis is tightly regulated by multiple mechanisms. Since most peripheral cells do not catabolize cholesterol, efflux (extra-cellular transport) of cholesterol is vital for lipid homeostasis. Defective efflux contributes to atherosclerotic plaque development, impaired β-cell insulin secretion, and neuropathology. Of these, defective lipid efflux in macrophages in the arterial walls leading to foam cell and atherosclerotic plaque formation has been the most well studied, likely because a leading global cause of death is cardiovascular disease. Circulating high density lipoprotein particles play critical roles as acceptors of effluxed cellular lipids, suggesting their importance in disease etiology. We review here mechanisms and pathways that modulate lipid efflux, the role of lipid efflux in disease etiology, and therapeutic options aimed at modulating this critical process.

ADAMTS-5: A difficult teenager turning 20

A Disintegrin And Metalloproteinase with ThromboSpondin motif (ADAMTS)-5 was identified in 1999 as one of the enzymes responsible for cleaving aggrecan, the major proteoglycan in articular cartilage. Studies in vitro, ex vivo and in vivo have validated ADAMTS-5 as a target in osteoarthritis (OA), a disease characterized by extensive degradation of aggrecan. For this reason, it attracted the interest of many research groups aiming to develop a therapeutic treatment for OA patients. However, ADAMTS-5 proteoglycanase activity is not only involved in the dysregulated aggrecan proteolysis, which occurs in OA, but also in the physiological turnover of other related proteoglycans. In particular, versican, a major ADAMTS-5 substrate, plays an important structural role in heart and blood vessels and its proteolytic processing by ADAMTS-5 must be tightly regulated. On the occasion of the 20th anniversary of the discovery of ADAMTS-5, this review looks at the evidence for its detrimental role in OA, as well as its physiological turnover of cardiovascular proteoglycans. Moreover, the other potential functions of this enzyme are highlighted. Finally, challenges and emerging trends in ADAMTS-5 research are discussed.

Molecular basis for the protective effects of low-density lipoprotein receptor-related protein 1 (LRP1)-derived peptides against LDL aggregation

Aggregated LDL is the first ligand reported to interact with the cluster II CR9 domain of low-density lipoprotein receptor-related protein 1 (LRP1). In particular, the C-terminal half of domain CR9, comprising the region Gly¹¹²⁷-Cys¹¹⁴⁰ exclusively recognizes aggregated LDL and it is crucial for aggregated LDL binding. Our aim was to study the effect of the sequence Gly¹¹²⁷-Cys¹¹⁴⁰ (named peptide LP3 and its retro-enantio version, named peptide DP3) on the structural characteristics of sphingomyelinase- (SMase) and phospholipase 2 (PLA₂)-modified LDL particles. Turbidimetry, gel filtration chromatography (GFC) and transmission electronic microscopy (TEM) analysis showed that LP3 and DP3 peptides strongly inhibited SMase- and PLA₂-induced LDL aggregation. Nondenaturing polyacrylamide gradient gel electrophoresis (GGE), agarose gel electrophoresis and high-performance thin-layer chromatography (HPTLC) indicated that LP3 and DP3 prevented SMase-induced alterations in LDL particle size, electric charge and phospholipid content, respectively, but not those induced by PLA₂. Western blot analysis showed that LP3 and DP3 counteracted changes in ApoB-100 conformation induced by the two enzymes. LDL proteomics (LDL trypsin digestion followed by mass spectroscopy) and computational modeling methods evidenced that peptides preserve ApoB-100 conformation due to their electrostatic interactions with a basic region of ApoB-100. These results demonstrate that LRP1-derived peptides are protective against LDL aggregation, even in conditions of extreme lipolysis, through their capacity to bind to ApoB-100 regions critical for ApoB-100 conformational preservation. These results suggests that these LRP1(CR9) derived peptides could be promising tools to prevent LDL aggregation induced by the main proteolytic enzymes acting in the arterial intima.

miR-505-3p controls chemokine receptor up-regulation in macrophages: role in familial hypercholesterolemia

Familial hypercholesterolemia (FH) conveys a high risk of premature atherosclerosis as a result of lifelong exposure to high LDL cholesterol levels that are not fully reduced by standard-of-care lipid-lowering treatment. Inflammatory mediators have played a role in the progression of atherosclerotic lesions. Here, we investigated whether innate immunity cells in patients with FH have a specific proinflammatory phenotype that is distinct from that of cells in normal participants. To this end, miR-505-3p-a microRNA related to chronic inflammation-and its target genes were investigated in monocyte-derived macrophages (MACs) of patients with FH (FH-MACs) and non-FH controls (co-MACs). On the basis of the profiler PCR array analysis of agomiR-505-3p-transfected MACs, we identified the chemokine receptors, CCR3, CCR4, and CXCR1, as genes that are regulated by miR-505-3p via the transcription factor, RUNX1. miR-505-3p was significantly down-regulated, whereas CCR3, CCR4, CXCR, and RUNX1 were increased in FH-MAC compared with co-MAC, with the increase being more evident in the proinflammatory M1-like FH-MAC. Chemokine receptor levels were unrelated to LDL plasma levels at entry, but correlated with age in patients with FH, not in controls. In summary, we demonstrate for first time to our knowledge that MACs from FH-MACs have an inflammatory phenotype that is characterized by the up-regulation of CCR3, CCR4, and CXCR1 under the control of miR-505-3p. These results suggest a chronic inflammatory condition in FH innate immunity cells that is not reverted by standard lipid-lowering treatment.-Escate, R., Mata, P., Cepeda, J. M., Padró, T., Badimon, L. miR-505-3p controls chemokine receptor up-regulation in macrophages: role in familial hypercholesterolemia.

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.

Protein disulphide-isomerase A2 regulated intracellular tissue factor mobilisation in migrating human vascular smooth muscle cells

Protein-disulphide isomerase family (PDI) are an ER-stress protein that controls TF-procoagulant activity but its role in HVSMC migration and coronary artery disease remains to be elucidated. We aimed to investigate whether in human coronary smooth muscle cells (HVSMC) the ER-stress protein-disulphide isomerase family A member 2 (PDIA2) regulates tissue factor (TF) polarisation during migration and atherosclerotic remodeling. PDIA2 and TF were analysed by confocal microscopy, silenced by small interfering RNAs (siRNA) and their function analysed by transwell and migration assays in vitro and in vivo. PDIA2and TF co-localise in the front edge of motile HVSMC. Silencing PDIA2, as well as silencing TF, reduces migration. PDIA2 silenced cells show increased TF-rich microparticle shedding. In vivo cell-loaded plug implants in nude mice of PDIA2 silenced HVSMC together with microvascular endothelial cells showed a significant impairment in mature microvessel formation. PDIA2 and TF are found in remodelled atherosclerotic plaques but not in healthy coronaries. In conclusion, we demonstrate that TF is chaperoned by PDIA2 to the HVSMC membrane and to the cell migratory front. Absence of PDIA2 impairs TF intracellular trafficking to its membrane docking favoring its uncontrolled release in microparticles. TF-regulated HVSMC migration and microvessel formation is under the control of the ER-protein PDIA2.

miR-505-3p controls chemokine receptor up-regulation in macrophages: role in familial hypercholesterolemia

Familial hypercholesterolemia (FH) conveys a high risk of premature atherosclerosis as a result of lifelong exposure to high LDL cholesterol levels that are not fully reduced by standard-of-care lipid-lowering treatment. Inflammatory mediators have played a role in the progression of atherosclerotic lesions. Here, we investigated whether innate immunity cells in patients with FH have a specific proinflammatory phenotype that is distinct from that of cells in normal participants. To this end, miR-505-3p-a microRNA related to chronic inflammation-and its target genes were investigated in monocyte-derived macrophages (MACs) of patients with FH (FH-MACs) and non-FH controls (co-MACs). On the basis of the profiler PCR array analysis of agomiR-505-3p-transfected MACs, we identified the chemokine receptors, CCR3, CCR4, and CXCR1, as genes that are regulated by miR-505-3p via the transcription factor, RUNX1. miR-505-3p was significantly down-regulated, whereas CCR3, CCR4, CXCR, and RUNX1 were increased in FH-MAC compared with co-MAC, with the increase being more evident in the proinflammatory M1-like FH-MAC. Chemokine receptor levels were unrelated to LDL plasma levels at entry, but correlated with age in patients with FH, not in controls. In summary, we demonstrate for first time to our knowledge that MACs from FH-MACs have an inflammatory phenotype that is characterized by the up-regulation of CCR3, CCR4, and CXCR1 under the control of miR-505-3p. These results suggest a chronic inflammatory condition in FH innate immunity cells that is not reverted by standard lipid-lowering treatment.-Escate, R., Mata, P., Cepeda, J.M., Padró, T., Badimon, L. miR-505-3p controls chemokine receptor up-regulation in macrophages: role in familial hypercholesterolemia. FASEB J. 32, 601-612 (2018). www.fasebj.org.

Macrophages of genetically characterized familial hypercholesterolaemia patients show up-regulation of LDL-receptor-related proteins

Familial hypercholesterolaemia (FH) is a major risk for premature coronary heart disease due to severe long‐life exposure to high LDL levels. Accumulation of LDL in the vascular wall triggers atherosclerosis with activation of the innate immunity system. Here, we have investigated (i) gene expression of LDLR and LRPs in peripheral blood cells (PBLs) and in differentiated macrophages of young FH‐patients; and (ii) whether macrophage from FH patients have a differential response when exposed to high levels of atherogenic LDL. PBLs in young heterozygous genetically characterized FH patients have higher expression of LRP5 and LRP6 than age‐matched healthy controls or patients with secondary hypercholesterolaemia. LRP1 levels were similar among groups. In monocyte‐derived macrophages (MACs), LRP5 and LRP1 transcript levels did not differ between FHs and controls in resting conditions, but when exposed to agLDL, FH‐MAC showed a highly significant up‐regulation of LRP5, while LRP1 was unaffected. PBL and MAC cells from FH patients had significantly lower LDLR expression than control cells, independently of the lipid‐lowering therapy. Furthermore, exposure of FH‐MAC to agLDL resulted in a reduced expression of CD163, scavenger receptor with anti‐inflammatory and atheroprotective properties. In summary, our results show for first time that LRPs, active lipid‐internalizing receptors, are up‐regulated in innate immunity cells of young FH patients that have functional LDLR mutations. Additionally, their reduced CD163 expression indicates less atheroprotection. Both mechanisms may play a synergic effect on the onset of premature atherosclerosis in FH patients.

Versican localizes to the nucleus in proliferating mesenchymal cells

OBJECTIVE

Versican is a versatile and highly interactive chondroitin sulfate proteoglycan that is found in the extracellular matrix (ECM) of many tissues and is a major component of developing and developed lesions in atherosclerotic vascular disease. In this paper, we present data to indicate that versican may have important intracellular functions in addition to its better known roles in the ECM.

METHODS AND RESULTS

Rat aortic smooth muscle cells were fixed and immunostained for versican and images of fluorescently labeled cells were obtained by confocal microscopy. Intracellular versican was detected in the nucleus and cytosol of vascular smooth muscle cells. The use of a synthetic neutralizing peptide eliminated versican immunostaining, demonstrating the specificity of the antibody used in this study. Western blot of pure nuclear extracts confirmed the presence of versican in the nucleus, and multifluorescent immunostaining showed strong colocalization of versican and nucleolin, suggesting a nucleolar localization of versican in nondividing cells. In dividing valve interstitial cells, a strong signal for versican was observed in and around the condensed chromosomes during the various stages of mitosis. Multifluorescent immunostaining for versican and tubulin revealed versican aggregated at opposing poles of the mitotic spindle during metaphase. Knockdown of versican expression using siRNA disrupted the organization of the mitotic spindle and led to the formation of multipolar spindles during metaphase.

CONCLUSIONS

Collectively, these data suggest an intracellular function for versican in vascular cells where it appears to play a role in mitotic spindle organization during cell division. These observations open a new avenue for studies of versican, suggesting even more diverse roles in vascular health and disease.

A novel truncated form of apolipoprotein A-I transported by dense LDL is increased in diabetic patients

Diabetic (DM) patients have exacerbated atherosclerosis and high CVD burden. Changes in lipid metabolism, lipoprotein structure, and dysfunctional HDL are characteristics of diabetes. Our aim was to investigate whether serum ApoA-I, the main protein in HDL, was biochemically modified in DM patients. By using proteomic technologies, we have identified a 26 kDa ApoA-I form in serum. MS analysis revealed this 26 kDa form as a novel truncated variant lacking amino acids 1-38, ApoA-IΔ(1-38). DM patients show a 2-fold increase in ApoA-IΔ(1-38) over nondiabetic individuals. ApoA-IΔ(1-38) is found in LDL, but not in VLDL or HDL, with an increase in LDL3 and LDL4 subfractions. To identify candidate mechanisms of ApoA-I truncation, we investigated potentially involved enzymes by in silico data mining, and tested the most probable molecule in an established animal model of diabetes. We have found increased hepatic cathepsin D activity as one of the potential proteases involved in ApoA-I truncation. Cathepsin D-cleaved ApoA-I exhibited increased LDL binding affinity and decreased antioxidant activity against LDL oxidation. In conclusion, we show for the first time: a) presence of a novel truncated ApoA-I form, ApoA-IΔ(1-38), in human serum; b) ApoA-IΔ(1-38) is transported by LDL; c) ApoA-IΔ(1-38) is increased in dense LDL fractions of DM patients; and d) cathepsin D-ApoA-I truncation may lead to ApoA-IΔ(1-38) binding to LDLs, increasing their susceptibility to oxidation and contributing to the high cardiovascular risk of DM patients.

K Domain CR9 of Low Density Lipoprotein (LDL) Receptor-related Protein 1 (LRP1) Is Critical for Aggregated LDL-induced Foam Cell Formation from Human Vascular Smooth Muscle Cells

Low density lipoprotein receptor-related protein (LRP1) mediates the internalization of aggregated LDL (AgLDL), which in turn increases the expression of LRP1 in human vascular smooth muscle cells (hVSMCs). This positive feedback mechanism is thus highly efficient to promote the formation of hVSMC foam cells, a crucial vascular component determining the susceptibility of atherosclerotic plaque to rupture. Here we have determined the LRP1 domains involved in AgLDL recognition with the aim of specifically blocking AgLDL internalization in hVSMCs. The capacity of fluorescently labeled AgLDL to bind to functional LRP1 clusters was tested in a receptor-ligand fluorometric assay made by immobilizing soluble LRP1 "minireceptors" (sLRP1-II, sLRP1-III, and sLRP1-IV) recombinantly expressed in CHO cells. This assay showed that AgLDL binds to cluster II. We predicted three well exposed and potentially immunogenic peptides in the CR7-CR9 domains of this cluster (termed P1 (Cys(1051)-Glu(1066)), P2 (Asp(1090)-Cys(1104)), and P3 (Gly(1127)-Cys(1140))). AgLDL, but not native LDL, bound specifically and tightly to P3-coated wells. Rabbit polyclonal antibodies raised against P3 prevented AgLDL uptake by hVSMCs and were almost twice as effective as anti-P1 and anti-P2 Abs in reducing intracellular cholesteryl ester accumulation. Moreover, anti-P3 Abs efficiently prevented AgLDL-induced LRP1 up-regulation and counteracted the down-regulatory effect of AgLDL on hVSMC migration. In conclusion, domain CR9 appears to be critical for LRP1-mediated AgLDL binding and internalization in hVSMCs. Our results open new avenues for an innovative anti-VSMC foam cell-based strategy for the treatment of vascular lipid deposition in atherosclerosis.

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.

Whole-exome sequencing reveals TopBP1 as a novel gene in idiopathic pulmonary arterial hypertension

RATIONALE

Idiopathic pulmonary arterial hypertension (IPAH) is a life-threatening disorder characterized by progressive loss of pulmonary microvessels. Although mutations in the bone morphogenetic receptor 2 (BMPR2) are found in 80% of heritable and ∼15% of patients with IPAH, their low penetrance (∼20%) suggests that other unidentified genetic modifiers are required for manifestation of the disease phenotype. Use of whole-exome sequencing (WES) has recently led to the discovery of novel susceptibility genes in heritable PAH, but whether WES can also accelerate gene discovery in IPAH remains unknown.

OBJECTIVES

To determine whether WES can help identify novel gene modifiers in patients with IPAH.

METHODS

Exome capture and sequencing was performed on genomic DNA isolated from 12 unrelated patients with IPAH lacking BMPR2 mutations. Observed genetic variants were prioritized according to their pathogenic potential using ANNOVAR.

MEASUREMENTS AND MAIN RESULTS

A total of nine genes were identified as high-priority candidates. Our top hit was topoisomerase DNA binding II binding protein 1 (TopBP1), a gene involved in the response to DNA damage and replication stress. We found that TopBP1 expression was reduced in vascular lesions and pulmonary endothelial cells isolated from patients with IPAH. Although TopBP1 deficiency made endothelial cells susceptible to DNA damage and apoptosis in response to hydroxyurea, its restoration resulted in less DNA damage and improved cell survival.

CONCLUSIONS

WES led to the discovery of TopBP1, a gene whose deficiency may increase susceptibility to small vessel loss in IPAH. We predict that use of WES will help identify gene modifiers that influence an individual's risk of developing IPAH.

Molecular and functional characterization of LRP1 promoter polymorphism c.1-25 C>G (rs138854007)

The transcription of the Low-density lipoprotein receptor-related protein (LRP1) is upregulated by aggregated LDL (agLDL) and angiotensin II (AngII) in human vascular smooth muscle cells (hVSMC). The polymorphism c.1-25C>G creates a new GC-box in the LRP1 promoter recognized by Sp1/Sp3 transcription factors. The aims of this study were 1) to evaluate the impact of c.1-25C>G polymorphism on LRP1 transcriptional activity and expression, and 2) to examine the response of c.1-25C>G LRP1 promoter to LDL and AngII. EMSA and Luciferase assays in HeLa cells showed that -25G promoter has enhanced basal transcriptional activity and specific Sp1/Sp3 binding. hVSMC with GG genotype (GG-hVSMC) had higher LRP1 mRNA and protein levels, respectively than CC genotype (CC-hVSMC). EMSA assays showed that the polymorphism determines scarce amount of SRE-B/SREBP-2 complex formation and the failure of agLDL to further reduce these SRE-B/SREBP-2 complexes. Taken together, these results suggest that c.1-25C>G, by difficulting SREBP-2 binding, prevents SREBP-2 displacement required for LRP1 promoter response to LDL. In contrast, c.1-25C>G strongly favours Sp1/Sp3 binding and AngII-induced activity in Sp1/Sp3 dependent manner in GG-hVSMC. This increase is functionally translated into a higher capacity of GG-hVSMC to become foam cells from agLDL in presence of AngII. These results suggest that c.1-25C>G determines a lack of response to agLDL and an exacerbated response to AngII. It is thus conceivable that the presence of the polymorphism would be easily translated to vascular alterations in the presence of the pro-hypertensive autacoid, AngII.

Tissue factor induces human coronary artery smooth muscle cell motility through Wnt-signalling

BACKGROUND

Tissue factor (TF) is the most relevant physiological trigger of thrombosis contributing to the presentation of clinical ischemic events after plaque rupture. However, the role of human vascular smooth muscle cell (HVSMC) TF in vascular remodeling, restenosis and atherosclerosis is less known. We have hypothesized that TF contributes to atherosclerotic lesion formation, triggering smooth muscle cell migration through a specific yet unknown signaling pathway.

OBJECTIVES

The aim of this study has been to investigate the signal transduction mechanism by which TF may contribute to the transition of resident static contractile HVSMC into a migrating cell that promotes atherosclerotic plaque progression.

METHODS

We have used a system biology discovery approach with gene-engineered HVSMCs to identify genes/proteins involved in the TF-triggered effects in HVSMC obtained from the coronary arteries of human adult hearts.

RESULTS

Analysis of wild-type HVSMC (TF(+) ) and TF(-) silenced HVSMC (TF(-) ) showed that TF is involved in the regulation of Wnt signaling and in the expression of downstream proteins that affect the atherosclerotic process.

CONCLUSIONS

The 'in silico' analysis pointed to specific Wnt-pathway proteins that have been validated in cell culture and also have been found expressed in human advanced atherosclerotic plaques but not in early lesions. TF signals through Wnt to regulate coronary smooth muscle cell migration and vascular remodeling.

Lipid loading of human vascular smooth muscle cells induces changes in tropoelastin protein levels and physical structure

Aggregated low-density lipoprotein (agLDL), one of the main LDL modifications in the arterial intima, contributes to massive intracellular cholesteryl ester (CE) accumulation in human vascular smooth muscle cells (VSMC), which are major producers of elastin in the vascular wall. Our aim was to analyze the levels, physical structure, and molecular mobility of tropoelastin produced by agLDL-loaded human VSMC (agLDL-VSMC) versus that produced by control VSMC. Western blot analysis demonstrated that agLDL reduced VSMC-tropoelastin protein levels by increasing its degradation rate. Moreover, our results demonstrated increased levels of precursor and mature forms of cathepsin S in agLDL-VSMC. Fourier transform infrared analysis revealed modifications in the secondary structures of tropoelastin produced by lipid-loaded VSMCs. Thermal and dielectric analyses showed that agLDL-VSMC tropoelastin has decreased glass transition temperatures and distinct chain dynamics that, in addition to a loss of thermal stability, lead to strong changes in its mechanical properties. In conclusion, agLDL lipid loading of human vascular cells leads to an increase in cathepsin S production concomitantly with a decrease in cellular tropoelastin protein levels and dramatic changes in secreted tropoelastin physical structure. Therefore, VSMC-lipid loading likely determines alterations in the mechanical properties of the vascular wall and plays a crucial role in elastin loss during atherosclerosis.

Low density lipoprotein receptor-related protein 1 expression correlates with cholesteryl ester accumulation in the myocardium of ischemic cardiomyopathy patients

Our hypothesis was that overexpression of certain lipoprotein receptors might be related to lipid accumulation in the human ischemic myocardium. Intramyocardial lipid overload contributes to contractile dysfunction and arrhythmias in cardiomyopathy. Thus, the purpose of this study was to assess the effect of hypercholesterolemic LDL and hypertrigliceridemic VLDL dose on LRP1 expression in cardiomyocytes, as well as the potential correlation between LRP1 expression and neutral lipid accumulation in the left ventricle tissue from ischemic cardiomyopathy patients. Cell culture experiments include control and LRP1-deficient cardiomyocytes exposed to lipoproteins under normoxic and hypoxic conditions. Explanted hearts from 18 ICM patients and eight non-diseased hearts (CNT) were included. Low density lipoprotein receptor-related protein 1 (LRP1), very low density lipoprotein receptor (VLDLR) and low density lipoprotein receptor (LDLR) expression was analyzed by real time PCR and Western blotting. Cholesteryl ester (CE), triglyceride (TG) and free cholesterol (FC) content was assess by thin layer chromatography following lipid extraction. Western blotting experiments showed that protein levels of LRP1, VLDLR and HIF-1α were significantly upregulated in ischemic hearts. Immunohistochemistry and confocal microscopy analysis showed that LRP1 and HIF-1α were upregulated in cardiomyocytes of ICM patients. In vitro studies showed that VLDL, LDL and hypoxia exerted an upregulatory effect on LRP1 expression and that LRP1 played a major role in cholesteryl ester accumulation from lipoproteins in cardiomyocytes. Myocardial CE accumulation strongly correlated with LRP1 levels in ischemic hearts. Taken together, our results suggest that LRP1 upregulation is key for myocardial cholesterol ester accumulation in ischemic human hearts and that LRP1 may be a target to prevent the deleterious effects of myocardial cholesterol accumulation in ischemic cardiomyopathy.

LDL-induced impairment of human vascular smooth muscle cells repair function is reversed by HMG-CoA reductase inhibition

Growing human atherosclerotic plaques show a progressive loss of vascular smooth muscle cells (VSMC) becoming soft and vulnerable. Lipid loaded-VSMC show impaired vascular repair function and motility due to changes in cytoskeleton proteins involved in cell-migration. Clinical benefits of statins reducing coronary events have been related to repopulation of vulnerable plaques with VSMC. Here, we investigated whether HMG-CoA reductase inhibition with rosuvastatin can reverse the effects induced by atherogenic concentrations of LDL either in the native (nLDL) form or modified by aggregation (agLDL) on human VSMC motility. Using a model of wound repair, we showed that treatment of human coronary VSMC with rosuvastatin significantly prevented (and reversed) the inhibitory effect of nLDL and agLDL in the repair of the cell depleted areas. In addition, rosuvastatin significantly abolished the agLDL-induced dephosphorylation of myosin regulatory light chain as demonstrated by 2DE-electrophoresis and mass spectrometry. Besides, confocal microscopy showed that rosuvastatin enhances actin-cytoskeleton reorganization during lipid-loaded-VSMC attachment and spreading. The effects of rosuvastatin on actin-cytoskeleton dynamics and cell migration were dependent on ROCK-signalling. Furthermore, rosuvastatin caused a significant increase in RhoA-GTP in the cytosol of VSMC. Taken together, our study demonstrated that inhibition of HMG-CoA reductase restores the migratory capacity and repair function of VSMC that is impaired by native and aggregated LDL. This mechanism may contribute to the stabilization of lipid-rich atherosclerotic plaques afforded by statins.

Cholesterol-lowering strategies reduce vascular LRP1 overexpression induced by hypercholesterolaemia

BACKGROUND

Low density lipoprotein receptor-related protein (LRP1) plays a key role on vascular functionality and is upregulated by hypercholesterolemia and hypertension. To investigate the effect of cholesterol-lowering interventions on vascular LRP1 over expression and whether simvastatin influences LRP1 expression.

MATERIAL AND METHODS

Male New Zealand rabbits were recruited into various groups, one group was fed a normal chow diet for 28 days (control group, n = 6), other group (n = 24) was fed a hypercholesterolemic diet (HC), six rabbits were euthanized at day 28 to test the capacity of HC diet to induce early atherosclerosis and the rest at day 60 (n = 18) after receiving either HC diet (HC group, n = 6), HC diet with simvastatin (2·5 mg/kg.day) (HC+simv group, n = 6), or a normal chow diet (NC group, n = 6) for the last 32 days.

RESULTS

High-cholesterol diet raised vascular LRP1 concomitantly with increased lipid, VSMC and macrophage content in the arterial intima. Simvastatin and return to normocholesterolemic diet significantly reduced systemic cholesterol levels and vascular lipid content. Interestingly, these interventions also downregulate LRP1 overexpression in the vascular wall although to a different extent (HC+simv: 75 ± 3·6%vs NC: 50 ± 3·5% versus, P = 0·002). Immunohistochemistry studies showed that LRP1 diminushion was associated to a reduction in the number of intimal VSMC in HC+simv.group. Simvastatin per se did not exert any significant effect on LRP1 expression in rabbit aortic smooth muscle cells (rSMC).

CONCLUSIONS

Our results demonstrate that cholesterol-lowering interventions exerted down regulatory effects on vascular LRP1 over expression induced by hypercholesterolemia and that simvastatin did not influence LRP1 expression beyond its cholesterol-lowering effects.

ADAMTS proteases: key roles in atherosclerosis?

The ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) proteases are secreted enzymes that regulate extracellular matrix turnover by degrading specific matrix components. Roles for the proteases in inflammation and atherosclerosis have been suggested by a number of recent studies, and the role of ADAMTS-4 and -5 in the breakdown of aggrecan and subsequent degradation of cartilage during osteoarthritis has also been established. The ability of the ADAMTS proteases to degrade versican, the primary proteoglycan in the vasculature, is thought to be central to any hypothesized role for the proteases in atherosclerosis. In this review, we introduce the structure and function of the ADAMTS family of proteases and review the literature that links them with inflammation and atherosclerosis.

Aggregated low density lipoprotein induces tissue factor by inhibiting sphingomyelinase activity in human vascular smooth muscle cells

BACKGROUND

Our previous results demonstrated that aggregated low density lipoprotein (agLDL) induces tissue factor (TF) expression and activation through Rho A translocation in human vascular smooth muscle cells (VSMC). We also previously demonstrated that membrane sphingomyelin (SM) content is higher in agLDL-exposed VSMC than in control cells. The main enzymes regulating cellular SM content are the family of sphingomyelinases (Smases) that hydrolize SM to phosphorylcholine and ceramide (CER).

OBJECTIVES

We wished to investigate whether agLDL has the ability to modulate acidic- (A-) and neutral (N-) Smase activity and whether or not this effect is related to the upregulatory effect of agLDL on Rho A translocation and TF activation in human VSMC.

METHODS AND RESULTS

By measuring generated [(14)C]-phosphorylcholine, we found that agLDL significantly decreased A-Smase and specially N-Smase activity. Pharmacological Smase inhibitors increased Rho A and TF. Specific loss-of-function of A-Smase or N-Smase 1 (N1-Smase) by siRNA treatment (500 nmol L(-1), 12 hours) dramatically increased membrane Rho A protein levels (5- and 3-fold, respectively). Concomitantly, TF protein expression and TF procoagulant activity were also increased. Inhibition of A-Smase or N-Smase activity by agLDL, siRNA-anti A- or N1-Smase or pharmacological treatment significantly increased the SM content of vascular cells. The inhibition of SM synthesis by fumonisin B(1) (FB(1)) prevented the upregulatory effect of agLDL on TF.

CONCLUSIONS

These results demonstrate that inhibition of both A- and N1-Smase might explain the upregulatory effect of agLDL on TF activation, and suggest that this effect is related, at least in part, to membrane SM enrichment.

Low‐density lipoprotein receptor‐related protein 5 variant Q89R is associated with hypertension in Japanese females

We examined the influence of the Q89R variant in low-density lipoprotein receptor-related protein 5 on hypertension in a large Japanese cohort. We used multivariate logistic regression analysis to adjust for the effects of other factors known to influence hypertension such as age, body mass index, blood chemistry and lifestyle. Our cohort consisted of 1444 males and 1161 females selected from 3834 male and 2591 female workers in a single company. Hypertension was defined as systolic blood pressure 140 mmHg and/or diastolic blood pressure 90 mmHg or the use of antihypertensive medication. Because the RR genotype was so rare (three normotensive males and three normotensive females), they were excluded from analyses. Genotype distributions for Q89R in hypertensive females (QR = 14, QQ = 60) were significantly different (p = 0.033) from normotensive females (QR = 113, QQ = 971). In contrast, those in hypertensive males (QR = 26, QQ = 230) and in normotensive males (QR = 145, QQ = 1040) were similar. Allele distributions were not significantly different in either gender. In females, multivariate logistic regression showed that the QR genotype was associated with hypertension with odds ratio of 2.1 compared to the QQ genotype. This study indicates that the Q89R polymorphism is an independent factor for hypertension in Japanese females.

Athsq1 is an atherosclerosis modifier locus with dramatic effects on lesion area and prominent accumulation of versican

OBJECTIVE

Susceptibility to atherosclerosis is genetically complex, and modifier genes that do not operate via traditional risk factors are largely unknown. A mouse genetics approach can simplify the genetic analysis and provide tools for mechanistic studies.

METHODS AND RESULTS

We previously identified atherosclerosis susceptibility QTL (Athsq1) on chromosome 4 acting independently of systemic risk factors. We now report confirmation of this locus in congenic strains carrying the MOLF-derived susceptibility allele in the C57BL/6J-Ldlr(-/-) genetic background. Homozygous congenic mice exhibited up to 4.5-fold greater lesion area compared to noncongenic littermates (P<0.0001). Analysis of extracellular matrix composition revealed prominent accumulation of versican, a presumed proatherogenic matrix component abundant in human lesions but almost absent in the widely-used C57BL/6 murine atherosclerosis model. The results of a bone marrow transplantation experiment suggested that both accelerated lesion development and versican accumulation are mediated, at least in part, by macrophages. Interestingly, comparative mapping revealed that the Athsq1 congenic interval contains the mouse region homologous to a widely-replicated CHD locus on human chromosome 9p21.

CONCLUSIONS

These studies confirm the proatherogenic activity of a novel gene(s) in the MOLF-derived Athsq1 locus and provide in vivo evidence for a causative role of versican in lesion development.

Aggregated low density lipoproteins decrease metalloproteinase-9 expression and activity in human coronary smooth muscle cells

Plaque stability largely depends on vascular smooth muscle cell (VSMC) function. VSMC secrete metalloproteinases (MMPs), matrix degrading endopeptidases, that regulate VSMC migration and function. Among them, gelatinase B or MMP-9 seems to have a protective effect by promoting a stable plaque phenotype. In macrophage foam cells oxidized LDL (oxLDL) uptake regulates MMP-9 expression. However, it is unknown whether VSMC-lipid loading by aggregated LDL (agLDL) internalization produces any effect on MMP-9 production by human resident vascular cells. In the present study, we analyzed the effect of lipid-internalization in MMP-9 and MMP-2 expression and activity and its consequences in VSMC migration. Our results show that agLDL-internalization down-regulates MMP-9 activity in a time-dependent manner up to 42% at 48h and in a dose-dependent manner up to 87% at 300 microg/mL. nLDL induced similar but not sustained decrease on MMP-9 activity. However, neither agLDL nor nLDL exerted any significant effect on MMP-2 and TIMP-1. VSMC regrowth after a scratch injury was significantly reduced by exposure to agLDL. We conclude that agLDL-lipid loading reduces MMP-9 activity and this effect is associated to inhibition of VSMC migration. Thus, agLDL internalization may have consequences on vascular remodeling after injury, and the stability of lipid-rich atherosclerotic plaques.

Adipocyte differentiation-related protein is induced by LRP1-mediated aggregated LDL internalization in human vascular smooth muscle cells and macrophages

Aggregated LDL (agLDL) is internalized by LDL receptor-related protein (LRP1) in vascular smooth muscle cells (VSMCs) and human monocyte-derived macrophages (HMDMs). AgLDL is, therefore, a potent inducer of massive intracellular cholesteryl ester accumulation in lipid droplets. The adipocyte differentiation-related protein (ADRP) has been found on the surface of lipid droplets. The objectives of this work were to analyze whether agLDL uptake modulates ADRP expression levels and whether the effect of agLDL internalization on ADRP expression depends on LRP1 in human VSMCs and HMDMs. AgLDL strongly upregulates ADRP mRNA (real-time PCR) and protein expression (Western blot) in human VSMCs (mRNA: by 3.06-fold; protein: 8.58-fold) and HMDMs (mRNA: by 3.5-fold; protein: by 3.71-fold). Treatment of VSMCs and HMDMs with small anti-LRP1-interfering RNA (siRNA-LRP1) leads to specific inhibition of LRP1 expression. siRNA-LRP1 treatment significantly reduced agLDL-induced ADRP overexpression in HMDMs (by 69%) and in VSMCs (by 53%). Immunohystochemical studies evidence a colocolocalization between ADRP/macrophages and ADRP/VSMCs in advanced lipid-enriched atherosclerotic plaques. These results demonstrate that agLDL-LRP1 engagement induces ADRP overexpression in both HMDMs and human VSMCs and that ADRP is highly expressed in advanced lipid-enriched human atherosclerotic plaques. Therefore, LRP1-mediated agLDL uptake might play a pivotal role in vascular foam cell formation.

Sterol regulatory element-binding protein-2 negatively regulates low density lipoprotein receptor-related protein transcription

Low density lipoprotein receptor-related protein (LRP1) binds aggregated LDL (agLDL) leading to a high intracellular cholesteryl ester (CE) accumulation. AgLDL up-regulates LRP1 expression concomitantly with an LDL receptor (LDLR) and sterol regulatory element binding protein (SREBP-2) down-regulation. The objectives were to investigate whether SREBP-2 regulates LRP1 transcription and determine the molecular mechanisms involved in the process. Down-regulation of active SREBP-2 by nLDL and agLDL led to LDLR down-regulation and LRP1 up-regulation. Enforced expression of an active form of SREBP-2 (SREBP-2-NT, amino acid residues 1-468) decreased LRP1 expression and LRP1 promoter (WT-LRP1) luciferase activity in a dose-dependent manner. LDL did not exert any significant effect on LRP1 promoter activity when a putative sterol regulatory element (SRE) (5-GTGGGGTGA-3'; +225 to +233) was mutated (SRE-MT-LRP1). SREBP-2 overexpression exerted stronger down-regulatory effects on WT-LRP1 than on SRE-MT-LRP1 promoter activity both in control, nLDL- and agLDL-exposed HeLa cells. Gel mobility shift assays showed that recombinant SREBP-2-NT protein (1-468) binds to a double-stranded LRP1 DNA fragment (215 to 245) containing a wild-type (wt) SRE sequence but not to a mutated SRE (mt) sequence (5-GAATTCGA-3'). Our results demonstrate that LDL stimulates LRP1 transcription and decreases SREBP-2 active form which negatively regulates LRP1 transcription. SRE sequence (+225 to +233) plays a pivotal role for the down-regulatory effect of SREBP-2 on LRP1 promoter activity.

Intracellular lipid accumulation, low-density lipoprotein receptor-related protein expression, and cell survival in vascular smooth muscle cells derived from normal and atherosclerotic human coronaries

BACKGROUND

Vascular smooth muscle cell (VSMC) regulation during atherosclerotic plaque progression is determinant for plaque stability.

AIMS

To study lipid accumulation, low-density lipoprotein receptor-related protein (LRP) expression, and cell survival in VSMCs isolated from nonatherosclerotic areas (normal VSMCs) and advanced atherosclerotic plaques (plaque-VSMCs) of human coronaries.

DESIGN

Normal or plaque-VSMCs were obtained from the intima by modification of the explant technique.

RESULTS

Aggregated low-density lipoprotein (agLDL) (100 micro g mL(-1)) internalization induced higher intracellular cholesteryl ester (CE) accumulation in plaque-VSMC compared with normal VSMCs (89.28 +/- 6.1 vs. 60.34 +/- 4.1 micro g CE mg(-1) of protein; P < 0.05). This internalization was associated with LRP expression, as plaque-VSMCs show higher levels of LRP mRNA (6.06 +/- 0.55 vs. 3.87 +/- 0.28; P < 0.05) and LRP protein expression than normal VSMCs. However, plaque-VSMCs showed a lower proliferative response than normal VSMCs (6536 +/- 636 vs. 11151 +/- 815 c.p.m. [(3)H]thymidine; P < 0.05) and did not respond to platelet-derived growth factor BB (PDGF-BB) stimulus. In agreement, the Bcl(2)/BAX ratio was significantly lower in plaque-VSMCs compared with normal VSMCs (0.14 +/- 0.05 vs. 0.51 +/- 0.07; P < 0.05) and it was independent of lipid loading.

CONCLUSIONS

These results indicate that higher intracellular lipid deposition in plaque-VSMCs is related to higher LRP expression levels. However, LRP-mediated agLDL internalization is not directly related to the reduced survival of plaque-VSMCs.

Versican in epithelial ovarian cancer: relation to hyaluronan, clinicopathologic factors and prognosis

Versican, a proteoglycan previously reported to increase in other malignant tumours, was studied immunohistochemically in 299 primary epithelial ovarian cancers, their 43 metastases and 6 normal ovaries to evaluate its prognostic value and relation to hyaluronan, another extracellular matrix molecule increased in cancer and a binding partner of versican. The stainings were scored according to the area percentage of strong versican signal of total peri- and intratumoural stroma as low (<15%) or high (>or=15%). Epithelial staining of the tumours was scored as positive or negative. Low and high area percentage of strong stromal versican staining were observed in 133 and 166 carcinomas, respectively. A low area percentage of strong stromal versican staining correlated with mucinous histology (p = 0.019) and early International Federation of Gynecologists and Obstetritians (FIGO) stage (p < 0.0005), whereas a high percentage was associated with reduced 5-year survival rate of the patients (44% vs. 32%; p = 0.032). Versican was associated with the cancer cells in 151 tumours and correlated with clear cell histology (p < 0.0005), early FIGO stage (p = 0.049) and increased recurrence-free survival (63% vs. 47%; p = 0.032). However, in Cox's multivariate analyses with the conventional prognostic factors included, neither stromal nor cancer cell-associated versican reached a significant prognostic value. Versican is thus enriched in the malignant stroma surrounding and promoting the growth of ovarian cancer, probably acting with hyaluronan, and associates with unfavourable prognosis but does not constitute an independent indicator of patient survival.