Macrophage plasma membrane chondroitin sulfate proteoglycan binds oxidized low-density lipoprotein

Extraction, Physicochemical Properties, and In Vitro Antioxidant Activities of Chondroitin Sulfate from Bovine Nose Cartilage

Beef is an important high-nutrition livestock product, and several byproducts, such as bovine cartilage, are produced during slaughter. To effectively utilize these agricultural and pastoral byproducts, combined (trypsin-papain) enzymolysis and cetylpyridine chloride purification methods were used to obtain chondroitin sulfate (CS) from the nasal cartilage of Shaanxi Yellow cattle. The effects of pH, temperature, and time on the CS yield during enzymatic hydrolysis were investigated, and the CS extraction process was optimized using response surface methodology. The best yield of CS was 21.62% under the optimum conditions of pH 6.51, temperature of 64.53°C, and enzymolysis time of 19.86 h. The molecular weight of CS from Shaanxi cattle nasal cartilage was 89.21 kDa, glucuronic acid content was 31.76 ± 0.72%, protein content was 1.12 ± 0.03%, and sulfate group content was 23.34 ± 0.08%. The nasal cartilage CS of the Yellow cattle showed strong DPPH•, •OH, and ABTS+• radical scavenging abilities and ferrous reduction ability in the experimental concentration range. This study could contribute to "turn waste into treasure" and improve the comprehensive utilization of regional characteristic biological resources.

Role of angiotensin II in cellular entry and replication of dengue virus

Previous studies have demonstrated the relevance of several soluble molecules in the pathogenesis of dengue. In this regard, a possible role for angiotensin II (Ang II) in the pathophysiology of dengue has been suggested by the observation of a blockade of Ang II in patients with dengue, increased expression of molecules related to Ang II production in the plasma of dengue patients, increased expression of circulating cytokines and soluble molecules related to the action of Ang II, and an apparent relationship between DENV, Ang II effects, and miRNAs. In addition, in ex vivo experiments, the blockade of Ang II AT1 receptor and ACE-1 (angiotensin converting enzyme 1), both of which are involved in Ang II production and its function, inhibits infection of macrophages by DENV, suggesting a role of Ang II in viral entry or in intracellular viral replication of the virus. Here, we discuss the possible mechanisms of Ang II in the entry and replication of DENV. Ang II has the functions of increasing the expression of DENV entry receptors, creation of clathrin-coated vesicles, and increasing phagocytosis, all of which are involved in DENV entry. This hormone also modulates the expression of the Rab5 and Rab7 proteins, which are important in the endosomal processing of DENV during viral replication. This review summarizes the data related to the possible involvement of Ang II in the entry of DENV into cells and its replication.

High-Resolution Proteomic Profiling Shows Sexual Dimorphism in Zebrafish Heart-Associated Proteins

Understanding the molecular basis of sexual dimorphism in the cardiovascular system may contribute to the improvement of the outcome in biological, pharmacological, and toxicological studies as well as on the development of sex-based drugs and therapeutic approaches. Label-free protein quantification using high-resolution mass spectrometry was applied to detect sex-based proteome differences in the heart of zebrafish Danio rerio. Out of almost 3000 unique identified proteins in the heart, 79 showed significant abundance differences between male and female fish. The functional differences were mapped using enrichment analyses. Our results suggest that a large amount of materials needed for reproduction (e.g., sugars, lipids, proteins, etc.) may impose extra pressure on blood, vessels, and heart on their way toward the ovaries. In the present study, the female's heart shows a clear sexual dimorphism by changing abundance levels of numerous proteins, which could be a way to safely overcome material-induced elevated pressures. These proteins belong to the immune system, oxidative stress response, drug metabolization, detoxification, energy, metabolism, and so on. In conclusion, we showed that sex can induce dimorphism at the molecular level in nonsexual organs such as heart and must be considered as an important factor in cardiovascular research. Data are available via ProteomeXchange with identifier PXD023506.

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.

Mouse Cytomegalovirus Differentially Exploits Cell Surface Glycosaminoglycans in a Cell Type-Dependent and MCK-2-Independent Manner

Many viruses initiate interaction with target cells by binding to cell surface glycosaminoglycans (GAGs). Heparan sulfate (HS) appears to be particularly important in fibroblasts, epithelial cells and endothelial cells, where it represents the dominant GAG. How GAGs influence viral infectivity in HS-poor target cells such as macrophages has not been clearly defined. Here, we show that mouse cytomegalovirus (MCMV) targets HS in susceptible fibroblasts and cultured salivary gland acinar cells (SGACs), but not in macrophage cell lines and primary bone marrow-derived macrophages, where chondroitin sulfate was the dominant virus-binding GAG. MCK-2, an MCMV-encoded GAG-binding chemokine that promotes infection of macrophages as part of a gH/gL/MCK-2 entry complex, was dispensable for MCMV attachment to the cell surface and for direct infection of SGACs. Thus, MCMV tropism for target cells is markedly influenced by differential GAG expression, suggesting that the specificity of anti-GAG peptides now under development as HCMV therapeutics may need to be broadened for effective application as anti-viral agents.

Effect of Polarization and Chronic Inflammation on Macrophage Expression of Heparan Sulfate Proteoglycans and Biosynthesis Enzymes

Heparan sulfate (HS) proteoglycans on immune cells have the ability to bind to and regulate the bioactivity more than 400 bioactive protein ligands, including many chemokines, cytokines, and growth factors. This makes them important regulators of the phenotype and behavior of immune cells. Here we review how HS biosynthesis in macrophages is regulated during polarization and in chronic inflammatory diseases such as rheumatoid arthritis, atherosclerosis, asthma, chronic obstructive pulmonary disease and obesity, by analyzing published micro-array data and mechanistic studies in this area. We describe that macrophage expression of many HS biosynthesis and core proteins is strongly regulated by macrophage polarization, and that these expression patterns are recapitulated in chronic inflammation. Such changes in HS biosynthetic enzyme expression are likely to have a significant impact on the phenotype of macrophages in chronic inflammatory diseases by altering their interactions with chemokines, cytokines, and growth factors.

Clinical significance of macrophage phenotypes in cardiovascular disease

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

Glycosaminoglycan (GAG) biosynthesis and GAG-binding proteins

Two major types of glycosaminoglycan (GAG) polysaccharides, heparan sulfate and chondroitin sulfate, are polymerized and modified by enzymes that are encoded by more than 40 genes in animal cells. Because of the expression repertoire of the GAG assembly and modification enzymes, each heparan sulfate and chondroitin sulfate chain has a sulfation pattern, chain length, and fine structure that is potentially unique to each animal cell. GAGs interact with hundreds of proteins. Such interactions protect growth factors, chemokines, and cytokines against proteolysis. GAGs catalyze protease (such as thrombin) inhibition by serpins. GAGs regulate multiple signaling pathways including, but not limited to, fibroblast growth factor (FGF)/FGFR, hepatocyte growth factor (HGF)/c-Met, glial cell line-derived neurotrophic factor (GDNF)/c-Ret/GFRalpha1, vascular endothelial growth factor (VEGF)/VEGFR, platelet derived growth factor (PDGF)/PDGFR, BAFF/TACI, Indian hedgehog, Wnt, and BMP signaling pathways,where genetic studies have revealed an absolute requirement for GAGs in these pathways. Most importantly, protein/GAG aggregates induce thrombin generation and immune system upregulation by activating the contact system. Abnormal protein/GAG aggregates are associated with a variety of devastating human diseases including, but not limited to, Alzheimer's, diabetes, prion or transmissible spongiform encephalopathies, Lupus, heparin-induced thrombocytopenia/thrombosis, and different kinds of cancers. Therefore, GAGs are essential components of modern molecular biology and human physiology. Understanding GAG structure and function at molecular level with regard to development and health represents a unique opportunity in combating different kinds of human diseases.

Uptake of 99mTc-labeled chondroitin sulfate by chondrocytes and cartilage: a promising agent for imaging of cartilage degeneration?

Chondroitin sulfate (CS) is used in the treatment of human osteoarthritis as a slow-acting symptomatic drug. For this reason, we performed uptake studies with (99m)TcCS using different chondrocyte cultures, as well as cartilage tissue in vitro. For uptake studies, adherent monolayer cultures of human chondrocytes (2.7 x 10(4) cells/well) and (99m)TcCS (1 microCi) were used. In parallel, we also performed uptake studies with cell suspensions of human chondrocytes at 1 x 10(6) cells/well incubated with (99m)TcCS (5 microCi) under identical conditions. Uptake was studied also in cartilage tissue samples and frozen tissue sections for autoradiography. The uptake was monitored for 10-240 min, every 10-30 min for cell cultures and for cartilage tissue up to 72 h. As the commercially available drug Condrosulf (IBSA, Lugano, Switzerland) contains magnesium (Mg) stearate as additive, we investigated the uptake with and without this additive. The washout of the tracer was assessed after the uptake experiments with PBS buffer for different time intervals (10 min-3 h). Tracer uptake in monolayer+/-additives with low number of cells was low. With the use of chondrocytes in culture suspensions with higher number of cells, a higher uptake of 5.9+/-0.65% and 1.0+/-0.1% (n=6) was found, with and without additive, respectively. The saturation was achieved after 100 min. With the use of human rib cartilage, the uptake of (99m)TcCS was continuously increasing with time and was very high with additive amounting to 101.8+/-5.2% vs. 53.0+/-8.3% (n=6) without after 72 h and showing delayed saturation up to 30 h. Thus, not only the resorption of the drug is enhanced by Mg-stearate, but also the uptake. The washout of the tracer from cartilage after 3 h of uptake amounted to 3.75+/-1.5% with additive vs. 13.1+/-2.1% without. After 24 h, washout was lower amounting to 1.75+/-0.15% vs. 3.25+/-0.25%, respectively. The autoradiographic studies paralleled the results of in vitro cartilage tissue uptake. These data show that (99m)TcCS accumulates in cartilage tissue, either by acting as a substrate for proteoglycan synthesis or by adsorption to cartilage. (99m)TcCS could therefore be a possible agent to target and radioimage osteoarthritis.

Nanoscale anionic macromolecules for selective retention of low-density lipoproteins

Synthetically designed anionic nanocarriers that mimic the charge properties of glycosaminoglycans can potentially sequester low-density lipoproteins (LDL) during the treatment of atherosclerosis. In this study, we explore the LDL retentivity of 15-20 nm anionic micelles formed from amphiphilic scorpion-like macromolecules (AScMs) as building blocks. The macromolecules comprise four aliphatic chains attached to mucic acid and a linear polyethylene glycol (PEG) segment to form micellar nanocarriers with a hydrophobic core and hydrophilic corona. Dynamic light scattering and transmission electron microscopy studies indicate that the carboxylate-terminated nanocarriers (20 nm) sequester LDL (22 nm), resulting in complexes with a diameter of 60-90 nm, but neutral ethoxy-terminated nanocarriers do not retain LDL. Further, carboxylate-terminated nanocarriers consistently bound to unoxidized LDL (Relative Electrophoretic Mobility, REM=1.0) and mildly oxidized LDL (REM=1.5), but not highly oxidized LDL (REM=3.6), whereas the neutral nanocarriers displayed no preference/affinity at all, indicating that the nanocarrier-LDL binding is charge-dependent. The binding affinity of unoxidized LDL for differentially charged nanocarriers, formed from varying ratios of carboxylate- and ethoxy-terminated macromolecules, was quantified. The 100% carboxylated nanocarriers elicited the highest binding affinity (K(d)=567 nm), whereas mixed micelles elicited significantly lower levels of binding affinity. Our results highlight the promise of synthetically designed nanomaterials in lipoprotein retention, a key step in managing the escalation of atherosclerosis.

Molecular interactions leading to lipoprotein retention and the initiation of atherosclerosis

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

Human Single-Chain Antibodies Reactive with Native Chondroitin Sulfate Detect Chondroitin Sulfate Alterations in Melanoma and Psoriasis

Chondroitin sulfate (CS) belongs to the group of glycosaminoglycans (GAGs), which are linear polysaccharides, located in the extracellular matrix and on the cell surface. To study the structure and distribution of CS in human skin and skin disorders, we have selected antibodies using phage display technique against CS. Four unique human anti-CS single-chain antibodies were selected: IO3D9, IO3H10, IO3H12, and IO4C2. We determined their amino acid sequence and evaluated their CS reactivity using ELISA and immunohistochemistry. Antibodies were reactive with CS, but not with other GAGs except for IO4C2, which was also reactive with heparin. Antibody IO3D9 showed a strong reactivity with highly sulfated CS (CSE). All antibodies displayed a different staining pattern in rat kidney, indicating the recognition of unique CS epitopes. In normal skin, the papillary dermis but not the reticular dermis was strongly stained. Antibody IO3H12 also stained basal keratinocytes. We applied these antibodies to study CS expression and localization in melanoma and psoriasis. A strong immunoreactivity with the extracellular matrix of melanoma metastases could be observed for all four antibodies, while in atypical nevi a less extensive reactivity with only the papillary dermis was observed. In psoriatic lesions, CS could be observed in the papillary dermis and in the reticular dermis, whereas the specific location in the papillary dermis found in normal skin was completely lost. In conclusion, human phage-display-derived anti-CS antibodies have been selected, characterized, and applied to detect CS alterations in skin conditions. Altered CS composition was detected in melanoma and psoriasis.

Oxidized low-density lipoprotein-induced apoptosis

Cultured cells are able to oxidize low-density lipoproteins (LDL) and oxidized LDL (oxLDL), which are present in atherosclerosis areas, exhibit a variety of biological properties potentially involved in atherogenesis. This review is focused on the toxicity of oxLDL, more precisely on the toxic compounds generated during LDL oxidation, the features and the mechanisms of cell death (apoptosis or necrosis) induced by oxLDL. After internalization, toxic oxidized lipids, namely lipid peroxides, oxysterols and aldehydes, induce modifications of cell proteins, elicit oxidative stress, lipid peroxidation and alter various signaling pathways and gene expression. These events may participate in the toxic effect, and converge to trigger an intense, delayed and sustained calcium peak which elicits either apoptosis or necrosis processes. OxLDL-induced apoptosis involves both mitochondrial and death-receptor (Fas/FasL) apoptotic pathways, thereby activating the classical caspase cascade and subsequent biochemical and morphological apoptotic features. When apoptosis is blocked by overexpression of Bcl-2, oxLDL trigger necrosis through a calcium-dependent pathway. Apoptosis occurring in atherosclerotic areas is potentially involved in endothelial cell lining defects, necrotic core formation and plaque rupture or erosion which may trigger atherothrombotic events. However, the precise role of oxLDL in apoptosis/necrosis occurring in vivo in atherosclerotic plaques remains to be clarified.

Phospholipids in amelogenesis and dentinogenesis

Phospholipids have been identified in enamel and dentin. Before demineralization, a group of phospholipids extracted by lipid solvents was associated with cell membranes and is therefore closely related to cell growth and intracellular regulations. After demineralization, a second group of phospholipids, associated with the extracellular matrix, was extracted; this group is probably linked to the mineralized phase. Using imidazole-osmium tetroxide fixation of rat incisors, we stained cellular unsaturated fatty acids, so that we could visualize the membrane domains, coated pits, and endocytic inclusions. Filipin, a probe for cholesterol, varied in density along the plasma membrane of secretory ameloblasts, and allowed us to visualize membrane remnants inside the forming enamel. With respect to phospholipids located in the extracellular matrix, the malachite-green-glutaraldehyde (MGA) method or iodoplatinate (IP) reaction retains and visualizes enamel and dentin phospholipids. In predentin, aggregates appearing as granules and filaments, or liposome-like structures, were located in the spaces between collagen fibrils. In dentin, organic envelopes coating the crystals, also named "crystal-ghost" structures, outlined groups of collagen fibrils. Histochemical data provided evidence that phospholipids are co-distributed or interact with proteoglycans. Radioautography after IP reaction established that [3H] choline was detected in dentin as early as 30 min after the intravenous injection of the labeled precursor, before any labeling was seen in odontoblasts and predentin. This suggests that blood-serum-labeled phospholipids pass between odontoblasts, cross the distal permeable junctional complex, and diffuse in dentin prior to any cellular uptake and phospholipid synthesis. Pharmacologically and genetically induced pathology also supports the suggestion that phospholipids play an important role in the formation and mineralization of dental tissues.

Hypolipidemic effect of glycosaminoglycans from the sea cucumber Metriatyla scabra in rats fed a cholesterol-supplemented diet

The purpose of this study was to determine the hypolipidemic effects of the glycosaminoglycans (GAGs) extracted from a sea cucumber, Metriatyla scabra. Using DEAE column chromatography, two major peaks containing GAGs were obtained: peak 1 (P-1) contained mainly GAGs (as hexuronic acid and hexosamine), whereas P-2 contained mostly free glycan (as fucose) with little hexuronic acid or hexosamine. Therefore, we used only the P-1 fraction (with molecular weights in the range 200-500 kDa) for evaluation of hypolipidemic effects. The lyophilized GAGs were administered orally to male Wistar rats at 5, 10, 20, and 50 mg/kg body weight for six consecutive weeks, during which the rats were fed ad libitum a basal laboratory diet with or without 1% cholesterol. The results show that the 1% cholesterol diet significantly increased plasma total cholesterol, LDL-cholesterol, and atherogenic index. Cholesterol supplementation also significantly increased hepatic TG, cholesterol, phospholipid, and liver weight. When rats fed the 1% cholesterol diet were supplemented orally with the sea cucumber GAGs, plasma levels of total cholesterol, LDL-cholesterol, and atherogenic index were significantly decreased, while HDL-cholesterol was significantly increased, although these effects of the GAGs were only dose-dependent at doses lower than 20 mg/kg b.w. Similarly, the GAGs significantly prevented the increase (p < 0.05) in hepatic contents of triglyceride, cholesterol, and phospholipid. Thus, the present study demonstrates that the sea cucumber GAGs have the potential of being used for reducing the risk of atherosclerosis and hyperlipoproteinemia.

Binding of [99mTc]chondroitin sulfate to scavenger receptors on human chondrocytes as compared to binding of oxidized [125I]LDL on human macrophages

Chondroitin sulfate (CS) used for treatment of osteoarthritis exerts distinct effects on human articular chondrocytes in vitro. We performed a binding analysis with 99mTc-labeled CS (Condrosulf, a commercial CS preparation containing calcium stearate) and cultured human chondrocytes in order to evaluate the presence of specific receptors. Saturation binding at 37 degrees C for 2 h revealed the presence of high-affinity binding sites for CS with a Kd of 2.3 x 10(-9) mol/L and a Bmax of 5.0 x 10(8). Extensive dialysis of Chondrosulf led to a decrease of the binding affinity by 52.5 +/- 19.5% and of the number of CS binding sites/cell by 62.0 +/- 14.0%, demonstrating that the additive present in the Condrosulf preparation enhances CS binding. The nature of the binding site is not yet known but evidence exists in the literature that the scavenger receptor CD36, thoroughly investigated on macrophages, is also found on chondrocytes and might be involved in CS binding. Therefore, we undertook a comparative binding study with human monocytes and labelled LDL and oxidized LDL, the latter being a postulated atherogenic agent in atherosclerosis. For [125I]-LDL binding we found a Kd of 0.45 x 10(-8) mol/L and a Bmax of 0.14 x 10(6) on quiescent monocytes and for [125I]-(ox)LDL binding a Kd of 1.8 x 10(-8) mol/L and a Bmax of 1.3 x 10(6) using LPS-activated monocytes. These data are comparable to the binding affinity found for lipoprotein-proteoglycan-complexes and hence are an indication but not a proof that CD36 is involved in CS binding to human chondrocytes.

Interaction of classical swine fever virus with membrane-associated heparan sulfate: role for virus replication in vivo and virulence

Passage of native classical swine fever virus (CSFV) in cultured swine kidney cells (SK6 cells) selects virus variants that attach to the surface of cells by interaction with membrane-associated heparan sulfate (HS). A Ser-to-Arg change in the C terminus of envelope glycoprotein E(rns) (amino acid 476 in the open reading frame of CSFV) is responsible for selection of these HS-binding virus variants (M. M. Hulst, H. G. P. van Gennip, and R. J. M. Moormann, J. Virol. 74:9553-9561, 2000). In this investigation we studied the role of binding of CSFV to HS in vivo. Using reverse genetics, an HS-independent recombinant virus (S-ST virus) with Ser(476) and an HS-dependent recombinant virus (S-RT virus) with Arg(476) were constructed. Animal experiments indicated that this adaptive Ser-to-Arg mutation had no effect on the virulence of CSFV. Analysis of viruses reisolated from pigs infected with these recombinant viruses indicated that replication in vivo introduced no mutations in the genes of the envelope proteins E(rns), E1, and E2. However, the blood of one of the three pigs infected with the S-RT virus contained also a low level of virus particles that, when grown under a methylcellulose overlay, produced relative large plaques, characteristic of an HS-independent virus. Sequence analysis of such a large-plaque phenotype showed that Arg(476) was mutated back to Ser(476). Removal of HS from the cell surface and addition of heparin to the medium inhibited infection of cultured (SK6) and primary swine kidney cells with S-ST virus reisolated from pigs by about 70% whereas infection with the administered S-ST recombinant virus produced in SK6 cells was not affected. Furthermore, E(rns) S-ST protein, produced in insect cells, could bind to immobilized heparin and to HS chains on the surface of SK6 cells. These results indicated that S-ST virus generated in pigs is able to infect cells by an HS-dependent mechanism. Binding of concanavalin A (ConA) to virus particles stimulated the infection of SK6 cells with S-ST virus produced in these cells by 12-fold; in contrast, ConA stimulated infection with S-ST virus generated in pigs no more than 3-fold. This suggests that the surface properties of S-ST virus reisolated from pigs are distinct from those of S-ST virus produced in cell culture. We postulate that due to these surface properties, in vivo-generated CSFV is able to infect cells by an HS-dependent mechanism. Infection studies with the HS-dependent S-RT virus, however, indicated that interaction with HS did not mediate infection of lung macrophages, indicating that alternative receptors are also involved in the attachment of CSFV to cells.

Retention of oxidized LDL by extracellular matrix proteoglycans leads to its uptake by macrophages: an alternative approach to study lipoproteins cellular uptake

Interaction between arterial macrophages and oxidized LDL (Ox-LDL) leads to foam cell formation, a critical step during early atherogenesis. Until now, cellular uptake of lipoproteins was studied through incubation of the media-soluble lipoprotein with cultured macrophages. However, as lipoproteins in the arterial wall are bound to subendothelial matrix, we questioned whether the retention (binding) of Ox-LDL to a macrophage-derived extracellular matrix (ECM) could lead to enhanced uptake by macrophages. The uptake of ECM-bound Ox-LDL by activated macrophages (by phorbol myristate acetate) was lipoprotein dose dependent, time dependent and higher (by 1.5-fold) than the uptake of ECM-bound native LDL. Preincubation of the ECM with lipoprotein lipase before the addition of Ox-LDL was essential for the uptake of ECM-bound Ox-LDL by the macrophages. After radiolabeling of the ECM glycosaminoglycans (GAGs), we found that ECM-bound Ox-LDL is taken up by the macrophages together with the ECM-GAG. Finally, these results were further confirmed through the use of ECM obtained from mouse peritoneal macrophages (MPMs), derived from atherosclerotic, apoE-deficient mice. In 24-week-old mice with developed atherosclerosis, the GAG content of their MPM-derived ECM increased by 52%, the ability of their MPM-derived ECM to bind Ox-LDL increased by 57%, and macrophage uptake of Ox-LDL that was retained by the MPM-derived ECM increased by 86%. In conclusion, the present study demonstrated that ECM-bound Ox-LDL is taken up by activated macrophages. This may represent a physiopathological phenomenon that leads to cholesterol and oxysterol accumulation in arterial macrophages, the hallmark of early atherosclerosis.

The multiple actions of angiotensin II in atherosclerosis

Angiotensin II (Ang II), the effector peptide of the renin-angiotensin system, has been implied in the pathogenesis of atherosclerosis on various levels. There is abundant experimental evidence that pharmacological antagonism of Ang II formation by angiotensin converting enzyme inhibition or blockade of the cellular effects of Ang II by angiotensin type 1 receptor blockade inhibits formation and progression of atherosclerotic lesions. Angiotensin promotes generation of oxidative stress in the vasculature, which appears to be a key mediator of Ang II-induced endothelial dysfunction, endothelial cell apoptosis, and lipoprotein peroxidation. Ang II also induces cellular adhesion molecules, chemotactic and proinflammatory cytokines, all of which participate in the induction of an inflammatory response in the vessel wall. In addition, Ang II triggers responses in vascular smooth muscle cells that lead to proliferation, migration, and a phenotypic modulation resulting in production of growth factors and extracellular matrix. While all of these effects contribute to neointima formation and development of atherosclerotic lesions, Ang II may also be involved in acute complications of atherosclerosis by promoting plaque rupture and a hyperthrombotic state. Accordingly, Ang II appears to have a central role in the pathophysiology of atherosclerosis.