oxLDL Uptake Research Articles

A high cholesterol diet causes fat uptake by synovial lining macrophages and enhances joint inflammation and cartilage destruction during experimental arthritis

Backgroundand objectivesEarlier studies have shown that synovial lining macrophages are crucial in mediating joint inflammation and cartilage destruction during experimental arthritis.1 Oxidised low-density lipoprotein (ox-LDL) has been shown to activate...

Current Concepts of the Role of Oxidized LDL Receptors in Atherosclerosis.

Atherosclerosis is characterized by accumulation of lipids and inflammatory cells in the arterial wall. Oxidized low-density lipoprotein (ox-LDL) plays important role in the genesis and progression of atheromatous plaque. Various scavenger receptors have been recognized in the past two decades that mediate uptake of ox-LDL leading to formation of foam cells. Inhibition of scavenger receptor A and CD36 has been shown to affect progression of atherosclerosis by decreasing foam cell formation. Lectin-type oxidized LDL receptor 1 (LOX-1) participates at various steps involved in the pathogenesis of atherosclerosis, and in experimental studies its blockade has been shown to affect the progression of atherosclerosis at multiple levels. In this review, we summarize the role of ox-LDL and scavenger receptors in the formation of atheroma with emphasis on effects of LOX-1 blockade.

LDL Receptor Knock-Out Mice Are a Physiological Model Particularly Vulnerable to Study the Onset of Inflammation in Non-Alcoholic Fatty Liver Disease

Background & AimsNon-alcoholic steatohepatitis (NASH) involves steatosis combined with inflammation, which can progress into fibrosis and cirrhosis. Exploring the molecular mechanisms of NASH is highly dependent on the availability of animal models. Currently, the most commonly used animal models for NASH imitate particularly late stages of human disease. Thus, there is a need for an animal model that can be used for investigating the factors that potentiate the inflammatory response within NASH. We have previously shown that 7-day high-fat-high-cholesterol (HFC) feeding induces steatosis and inflammation in both APOE2ki and Ldlr−/− mice. However, it is not known whether the early inflammatory response observed in these mice will sustain over time and lead to liver damage. We hypothesized that the inflammatory response in both models is sufficient to induce liver damage over time.Methods APOE2ki and Ldlr−/− mice were fed a chow or HFC diet for 3 months. C57Bl6/J mice were used as control.ResultsSurprisingly, hepatic inflammation was abolished in APOE2ki mice, while it was sustained in Ldlr−/− mice. In addition, increased apoptosis and hepatic fibrosis was only demonstrated in Ldlr−/− mice. Finally, bone-marrow-derived-macrophages of Ldlr−/− mice showed an increased inflammatory response after oxidized LDL (oxLDL) loading compared to APOE2ki mice.Conclusion Ldlr−/− mice, but not APOE2ki mice, developed sustained hepatic inflammation and liver damage upon long term HFC feeding due to increased sensitivity for oxLDL uptake. Therefore, the Ldlr−/− mice are a promising physiological model particularly vulnerable for investigating the onset of hepatic inflammation in non-alcoholic steatohepatitis.

Kinetically assembled nanoparticles of bioactive macromolecules exhibit enhanced stability and cell-targeted biological efficacy.

Kinetically assembled nanoparticles are fabricated from an advanced class of bioactive macromolecules that have potential utility in counteracting atherosclerotic plaque development via receptor-level blockage of inflammatory cells. In contrast to micellar analogs that exhibit poor potency and structural integrity under physiologic conditions, these kinetic nanoparticle assemblies maintain structural stability and demonstrate superior bioactivity in mediating oxidized low-density lipoprotein (oxLDL) uptake in inflammatory cells.

Rubus coreanusInhibits Oxidized-LDL Uptake by Macrophages Through Regulation of JNK Activation

Oxidized low-density lipoprotein (oxLDL) contributes to atherosclerosis in part by being taken up into macrophages via scavenger receptors and leading to foam cell formation. Herbal compounds that have been used to treat blood stasis (a counterpart of atherosclerosis) for centuries include extracts of medicinal plants in the Rosaceae and Leguminosae families. In this study, we investigated the effect of the unripe Rubus coreanus (Korean black raspberry) fruit extract on oxLDL uptake by murine macrophage cells. In the presence of Rubus coreanus extract (RCE), Dil-labeled oxLDL uptake was inhibited in a dose-dependent manner. SP600125, a specific JNK inhibitor, inhibited the uptake of Dil-oxLDL into macrophages. RCE also inhibited JNK phosphorylation in a time- and dose-dependent manner in macrophages treated with oxLDL. These results indicate that among the mitogen-activated protein kinases, JNK phosphorylation is inhibited by RCE, which is likely the mechanism underlying the RCE-induced inhibition of oxLDL uptake by macrophages.

CD9 Tetraspanin Interacts with CD36 on the Surface of Macrophages: A Possible Regulatory Influence on Uptake of Oxidized Low Density Lipoprotein

CD36 is a type 2 scavenger receptor with multiple functions. CD36 binding to oxidized LDL triggers signaling cascades that are required for macrophage foam cell formation, but the mechanisms by which CD36 signals remain incompletely understood. Mass spectrometry analysis of anti-CD36 immuno-precipitates from macrophages identified the tetraspanin CD9 as a CD36 interacting protein. Western blot showed that CD9 was precipitated from mouse macrophages by anti-CD36 monoclonal antibody and CD36 was likewise precipitated by anti-CD9, confirming the mass spectrometry results. Macrophages from cd36 null mice were used to demonstrate specificity. Membrane associations of the two proteins on intact cells was analyzed by confocal immunofluorescence microscopy and by a novel cross linking assay that detects proteins in close proximity (<40 nm). Functional significance was determined by assessing lipid accumulation, foam cell formation and JNK activation in wt, cd9 null and cd36 null macrophages exposed to oxLDL. OxLDL uptake, lipid accumulation, foam cell formation, and JNK phosphorylation were partially impaired in cd9 null macrophages. The present study demonstrates that CD9 associates with CD36 on the macrophage surface and may participate in macrophage signaling in response to oxidized LDL.

Effect of oxidized low-density lipoprotein concentration polarization on human smooth muscle cells' proliferation, cycle, apoptosis and oxidized low-density lipoprotein uptake

To clarify the effect of concentration polarization of oxidative modification of low-density lipoproteins (ox-LDLs) on human smooth muscle cells (SMCs), the proliferation, ox-LDL uptake and apoptosis with SMCs cultured on permeable (the permeable group) or non-permeable membranes (the non-permeable group) were analysed by 3-(4, 5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide (MTT) assay, spectrofluorometry and flow cytometry using a parallel-plate flow chamber technique. The concentration polarization of ox-LDLs at the surface of the cultured cell monolayer was assessed by confocal laser microscopy. The results showed that concentration polarization of ox-LDLs could indeed occur at the cultured cell monolayer surface of the permeable group, leading to an enhanced wall concentration of ox-LDLs that was over 15 per cent higher than the bulk concentration of the perfusion solution at a pressure of 100 mmHg. When concentration of ox-LDLs in the perfusion solution was less than or equal to 100 µg ml(-1), SMCs' proliferation was induced, while cell apoptosis was induced when its concentration was above 150 µg ml(-1). The uptake of ox-LDLs by the cultured cells was significantly higher for the permeable group than for the non-permeable group. In addition, the ox-LDL-induced cell death and apoptosis were much more severe in the permeable group than that in the non-permeable group. Therefore, the experimental study suggests that concentration polarization of ox-LDLs plays an adverse role in the vascular system owing to its toxicity to vascular cells, in turn enhance ox-LDL infiltration into the arterial wall and accelerate SMC apoptosis.

Vav Protein Guanine Nucleotide Exchange Factor Regulates CD36 Protein-mediated Macrophage Foam Cell Formation via Calcium and Dynamin-dependent Processes

Atherosclerosis, a chronic inflammatory disease, results in part from the accumulation of modified lipoproteins in the arterial wall and formation of lipid-laden macrophages, known as "foam cells." Recently, we reported that CD36, a scavenger receptor, contributes to activation of Vav-family guanine nucleotide exchange factors by oxidatively modified LDL in macrophages. We also discovered that CD36-dependent uptake of oxidized LDL (oxLDL) in vitro and foam cell formation in vitro and in vivo was significantly reduced in macrophages deficient of Vav proteins. The goal of the present study was to identify the mechanisms by which Vav proteins regulate CD36-dependent foam cell formation. We now show that a Vav-dynamin signaling axis plays a critical role in generating calcium signals in mouse macrophages exposed to CD36-specific oxidized phospholipid ligands. Chelation of intracellular Ca(2+) or inhibition of phospholipase C-γ (PLC-γ) inhibited Vav activation (85 and 70%, respectively, compared with vehicle control) and reduced foam cell formation (approximately 75%). Knockdown of expression by siRNA or inhibition of GTPase activity of dynamin 2, a Vav-interacting protein involved in endocytic vesicle fission, significantly blocked oxLDL uptake and inhibited foam cell formation. Immunofluorescence microscopy studies showed that Vav1 and dynamin 2 colocalized with internalized oxLDL in macrophages and that activation and mobilization of dynamin 2 by oxLDL was impaired in vav null cells. These studies identified previously unknown components of the CD36 signaling pathway, demonstrating that Vav proteins regulate oxLDL uptake and foam cell formation via calcium- and dynamin 2-dependent processes and thus represent novel therapeutic targets for atherosclerosis.

Increased atherosclerosis and vascular smooth muscle cell activation in AIF-1 transgenic mice fed a high-fat diet

Allograft inflammatory factor-1 (AIF-1) is a cytoplasmic, scaffold signal transduction protein constitutively expressed in inflammatory cells, but inducible in vascular smooth muscle cells (VSMCs) in response to injury or inflammatory stimuli. Although several basic science and population studies have reported increased AIF-1 expression in human and experimental atherosclerosis, a direct causal effect of AIF-1 expression on development of atherosclerosis has not been reported. The purpose of this study is to establish a direct relationship between AIF-1 expression and development of atherosclerosis. AIF-1 expression is detected VSMC in atherosclerotic lesions from ApoE−/− mice, but not normal arteries from wild-type mice. AIF-1 expression can be induced in cultured VSMC by stimulation with oxidized LDL (ox-LDL). Transgenic mice in which AIF-1 expression is driven by the G/C modified SM22 alpha promoter to restrict AIF-1 expression to VSMC develop significantly increased atherosclerosis compared with wild-type control mice when fed a high-fat diet (P=0.022). Cultured VSMC isolated from Tg mice demonstrated significantly increased migration in response to ox-LDL compared with matched controls (P<0.001). VSMC isolated from Tg mice and cultured human VSMC which over express AIF-1 demonstrated increased expression of MMP-2 and MMP-9 mRNA and protein and increased NF-κB activation in response to ox-LDL as compared with wild-type control mice. VSMC which over express AIF-1 have significantly increased uptake of ox-LDL, and increased CD36 expression. Together, these data suggest a strong association between AIF-1 expression, NF-κB activation, and development of experimental atherosclerosis.

Oxidized Low-Density Lipoprotein Activates p66 Shc via Lectin-Like Oxidized Low-Density Lipoprotein Receptor-1, Protein Kinase C-β, and c-Jun N-Terminal Kinase Kinase in Human Endothelial Cells

Deletion of the mitochondrial gene p66(Shc) protects from endothelial dysfunction and atherosclerotic plaque formation in mice fed a high-fat diet. However, the molecular mechanisms underlying this beneficial effect have not yet been delineated. The present study was designed to elucidate the proatherogenic mechanisms by which p66(Shc) mediates oxidized low-density lipoprotein (oxLDL) uptake by the endothelium, a critical step in plaque formation. Incubation of human aortic endothelial cells with oxLDL led to phosphorylation of p66(Shc) at Ser36. Inhibition of lectin-like oxLDL receptor-1 prevented p66(Shc) phosphorylation, confirming that this effect is mediated by lectin-like oxLDL receptor-1. OxLDL also increased phosphorylation of protein kinase C β(2) (PKCβ(2)) at both Thr641 and Ser660, as well as c-Jun N-terminal kinase (JNK). Furthermore, inhibition of PKCβ(2) prevented the activation of JNK, suggesting that PKCβ2 is upstream of JNK. Finally, p66(Shc) silencing blunted oxLDL-induced O(2)(-·) production, underscoring the critical role of p66(Shc) in oxLDL-induced oxidative stress in endothelial cells. In this study we provide the molecular mechanisms mediating the previously observed atherogenic properties of p66(Shc). Taken together, our data set the stage for the design of novel therapeutic tools to retard atherogenesis through the inhibition of p66(Shc).

Dual use of amphiphilic macromolecules as cholesterol efflux triggers and inhibitors of macrophage athero-inflammation

Activated vascular wall macrophages can rapidly internalize modified lipoproteins and escalate the growth of atherosclerotic plaques. This article proposes a biomaterials-based therapeutic intervention for depletion of non-regulated cholesterol accumulation and inhibition of inflammation of macrophages. Macromolecules with high scavenger receptor (SR)-binding activity were investigated for SR-mediated delivery of agonists to cholesterol-trafficking nuclear liver-X receptors. From a diverse feature space of a family of amphiphilic macromolecules of linear and aromatic mucic acid backbones modified with varied aliphatic chains and conjugated with differentially branched poly(ethylene glycol), a key molecule (carboxyl-terminated, C12-derivatized, linear mucic acid backbone) was selected for its ability to preferentially bind scavenger receptor A (SR-A) as the key target. At a basal level, this macromolecule suppressed the pro-inflammatory signaling of activated THP-1 macrophages while competitively lowering oxLDL uptake in vitro through scavenger receptor SRA-1 targeting. To further deplete intracellular cholesterol, the core macromolecule structure was exploited to solubilize a hydrophobic small molecule agonist for nuclear Liver-X Receptors, which regulate the efflux of intracellular cholesterol. The macromolecule-encapsulated agonist system was found to reduce oxLDL accumulation by 88% in vitro in comparison to controls. in vivo studies were designed to release the macromolecules (with or without encapsulated agonist) to injured carotid arteries within Sprague Dawley rats fed a high fat diet, conditions that yield enhanced cholesterol accumulation and macrophage recruitment. The macromolecules lowered intimal levels of accumulated cholesterol (50% for macromolecule alone; 70% for macromolecule-encapsulated agonist) and inhibited macrophage retention (92% for macromolecule; 96% for macromolecule-encapsulated agonist; 4 days) relative to non-treated controls. Thus, this study highlights the promise of designing bioactive macromolecule therapeutics based on scavenger receptor targeting, for potential management of vascular arterial disease.

OxLDL-mediated survival of macrophages does not require LDL internalization or signalling by major pattern recognition receptors

Macrophages play a key role in the pathogenesis of atherosclerosis, in part by destabilizing plaques. We and others have shown that low concentrations of oxidized LDL (oxLDL) inhibit macrophage apoptosis. As oxLDL is present in lesions, this may be a mechanism by which macrophage populations in the intima are expanded. We have previously shown that oxLDL activates prosurvival signalling pathways such as the phosphoinositide 3-kinase (PI3K) pathway in bone marrow derived macrophages (BMDMs). However, little is known about more upstream signalling events especially at the receptor level. The endocytic pattern recognition receptors (PRRs), scavenger receptor A (SR-A) and CD36, are the main receptors on macrophages for uptake of oxLDL and are therefore important in foam cell formation. The signalling PRRs such as toll-like receptor (TLR) 2 and 4 also bind some types of oxLDL. This study was done to determine if any of the known PRRs are required for the anti-apoptotic effects of oxLDL in BMDMs. To do this, we tested the effect of oxLDL on viability of BMDMs lacking both SR-A and CD36 or lacking TLR2, TLR4, CD14, FcγRIIb, or RAGE. Our results indicate that none of these receptors are essential for activating the oxLDL prosurvival pathway. Furthermore, we show that the anti-apoptotic effect is not dependent on the uptake of oxLDL.

Correlation between hsCRP and Anti-beta2GPI Antibody in Metabolic Syndrome

BACKGROUND: Several researches reported that inflammatory and immunological mechanism such as autoantibody to β2-glycoprotein I (anti β2GPI) appear as related factors in initiation and progress of atherosclerosis lesion in patient with autoimmune disease. Antibody to β2GPI titers are correlated with atherosclerosis and in vitro studies showed that they enhance oxidized low density lipoprotein (ox-LDL) uptake by macrophages. Immunization with auto-antigen β2GPI elicits an immune response to influence lesion progression that mostly happens in autoimmune subjects. The metabolic syndrome (MetS) is combination of several metabolic disorders such as obesity, dyslipidemia, Diabetes Mellitus (DM) and conditions due to inflammation and stress oxidative. The Correlation between inflammatory markers such as High sensitivity C-Reactive Protein (hsCRP) and anti-β2GPI antibody in MetS needs to be further investigated.METHODS: This was an observational study with cross sectional design on subject with MetS as determined by the International Diabetes Federation (IDF) 2005’s criteria.RESULTS:There was a positive and significant correlation between hsCRP and anti-β2GPI antibody in MetS group (r=0.406; p≤0.05) as compared to non-MetS group. We found that there was elevated level of anti-β2GPI antibody in hsCRP of 3-10 mg/L.CONCLUSIONS: Anti-β2GPI antibody may be elevated in subjects with MetS who have low grade of inflammation as shown by hsCRP.KEYWORDS: metabolic syndrome, inflammation, autoantigen, atherosclerosis, obesity

Effect of overexpression of human SR-AI on oxLDL uptake and apoptosis in 293T cells

Type I class A macrophage scavenger receptor (SR)-AI plays an important role in foam cell formation and in apoptosis in atherosclerosis, however the mechanism remains unclear. Therefore, we generated a pEGFP-C1-SR-AI plasmid construct for transient transfection of 293T human embryonic kidney cells and observed if SR-AI expression led: (i) to foam cell formation or apoptosis; and (ii) to expression of apoptosis-related genes Bcl-2 and Bak-1 in cells treated with oxidized low-density lipoprotein (oxLDL). The pEGFP-C1 (empty vector) transfected cell line was used as a control. Transfection efficiency of each group was >90% and transfected cells expressed functional SR-AI protein. Binding and uptake of 3,3′-dioctadecylindocarbocyanine-labeled oxLDL (DiI-oxLDL) were verified by flow cytometry; increases in the rate of oxLDL binding and uptake were observed in pEGFP-C1-SR-AI transfected 293T cells and incubation with oxLDL also led to increased apoptosis (≈50%) compared with controls. A decrease in Bcl-2 and an increase in Bak-1 mRNA and protein expression were observed in pEGFP-C1-SR-AI transfected cells compared with controls. We conclude that transient over-expression of SR-AI leads to an increase in oxLDL uptake and binding in a non-macrophage cell line. In addition, over-expression of SR-AI induced non-macrophage cell apoptosis via downregulation of Bcl-2 and upregulation of Bak-1 expression. We conclude that the 293T cell expression described here is a model for foam cell formation. These results may form the basis of further research into SR-AI structure and function (including lipoprotein uptake, apoptosis modulation and adhesion), which may give an insight into the progression of atherosclerosis in vivo.

Loxin polymorphism is associated with increased resistin levels and with oxidative status

Objectives We hypothesized that LOX-1 polymorphism may impact on inflammation and cardiovascular risk by modulating systemic resistin expression. Design and methods 276 men were randomly selected from a population-based cohort. Metabolic and inflammatory markers were evaluated at baseline and after 6-years follow-up, OLR1 (loxin) IVS4-14 A>G polymorphism was assessed. Results Mean plasma resistin and nitrotyrosine values were significantly higher, and TAS was significantly lowered in homozygous for the G allele. The G allele was significantly and directly associated with resistin and nitrotyrosine values. Conclusion Enhanced oxidized-LDL uptake by LOX-1 G-allele carriers is associated with increased pro-oxidant status and resistin levels, suggesting a major uptake of ox-LDL by macrophages, smooth muscle cells, and monocytes.

Dendritic Cells, Antibodies Reactive with oxLDL, and Inflammation

Periodontitis appears to promote chronic inflammatory diseases, including atherosclerosis, but relevant mechanisms need clarification. Oral bacteria induce antibodies that bind not only bacteria, but also oxLDL. Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans induce remarkable IgG responses that are dominated by IgG2, and IgG2 is IFN-γ-dependent and is promoted by dendritic cells (DCs). LDL-reactive antibodies induced by P. gingivalis and A. actinomycetemcomitans include anti-phosphorylcholine (α-PC) and β2-glycoprotein-1-dependent anticardiolipin (α-CL), and these antibodies may link chronic inflammatory diseases at a mechanistic level. Antibody-mediated uptake of oxLDL or bacteria dramatically enhances DC-IL-12, and DC-IL-12 induces NK-cell-IFN-γ responses that promote Th-1 responses and sustained inflammation. DCs may be derived from monocytes, and this is striking in cultures of aggressive periodontitis (AgP) monocytes, where DC numbers are about double control levels. Moreover, serum α-CL levels in individuals with AgP are frequently elevated, and these antibodies promote atherosclerosis in persons with antiphospholipid syndrome. Elevated serum levels of soluble-intercellular adhesion molecule, soluble-vascular cell adhesion molecule, and soluble-E-selectin are atherosclerosis-associated indicators of vascular inflammation, and these markers are elevated in the subset of AgP patients with high α-CL. We reason that periodontitis patients with elevated antibodies reactive with oxLDL could be a subgroup at high risk for cardiovascular sequelae.

Function modification of SR-PSOX by point mutations of basic amino acids

BackgroundAtherosclerosis (AS) is a common cardiovascular disease. Transformation of macrophages to form foam cells by internalizing modified low density-lipoprotein (LDL) via scavenger receptor (SR) is a key pathogenic process in the onset of AS. It has been demonstrated that SR-PSOX functions as either a scavenger receptor for uptake of atherogenic lipoproteins and bacteria or a membrane-anchored chemokine for adhesion of macrophages and T-cells to the endothelium. Therefore, SR-PSOX plays an important role in the development of AS. In this study the key basic amino acids in the chemokine domain of SR-PSOX have been identified for its functions.ResultsA cell model to study the functions of SR-PSOX was successfully established. Based on the cell model, a series of mutants of human SR-PSOX were constructed by replacing the single basic amino acid residue in the non-conservative region of the chemokine domain (arginine 62, arginine 78, histidine 80, arginine 82, histidine 85, lysine 105, lysine 119, histidine 123) with alanine (designated as R62A, R78A, H80A, R82A, H85A, K105A, K119A and H123A, respectively). Functional studies showed that the mutants with H80A, H85A, and K105A significantly increased the activities of oxLDL uptake and bacterial phagocytosis compared with the wild-type SR-PSOX. In addition, we have also found that mutagenesis of either of those amino acids strongly reduced the adhesive activity of SR-PSOX by using a highly non-overlapping set of basic amino acid residues.ConclusionOur study demonstrates that basic amino acid residues in the non-conservative region of the chemokine domain of SR-PSOX are critical for its functions. Mutation of H80, H85, and K105 is responsible for increasing SR-PSOX binding with oxLDL and bacteria. All the basic amino acids in this region are important in the cells adhesion via SR-PSOX. These findings suggest that mutagenesis of the basic amino acids in the chemokine domain of SR-PSOX may contribute to atherogenesis.

Oxidized Low Density Lipoprotein Induces Bone Morphogenetic Protein-2 in Coronary Artery Endothelial Cells via Toll-like Receptors 2 and 4

Vascular calcification is a common complication in atherosclerosis. Bone morphogenetic protein-2 (BMP-2) plays an important role in atherosclerotic vascular calcification. The aim of this study was to determine the effect of oxidized low density lipoprotein (oxLDL) on BMP-2 protein expression in human coronary artery endothelial cells (CAECs), the roles of Toll-like receptor (TLR) 2 and TLR4 in oxLDL-induced BMP-2 expression, and the signaling pathways involved. Human CAECs were stimulated with oxLDL. The roles of TLR2 and TLR4 in oxLDL-induced BMP-2 expression were determined by pretreatment with neutralizing antibody, siRNA, and overexpression. Stimulation with oxLDL increased cellular BMP-2 protein levels in a dose-dependent manner (40-160 μg/ml). Pretreatment with neutralizing antibodies against TLR2 and TLR4 or silencing of these two receptors reduced oxLDL-induced BMP-2 expression. Overexpression of TLR2 and TLR4 enhanced the cellular BMP-2 response to oxLDL. Furthermore, oxLDL was co-localized with TLR2 and TLR4. BMP-2 expression was associated with activation of nuclear factor-κB (NF-κB), p38 mitogen-activated protein kinase (MAPK), and extracellular signal-regulated kinase (ERK)1/2. Inhibition of NF-κB and ERK1/2 reduced BMP-2 expression whereas inhibition of p38 MAPK had no effect. In conclusion, oxLDL induces BMP-2 expression through TLR2 and TLR4 in human CAECs. The NF-κB and ERK1/2 pathways are involved in the signaling mechanism. These findings underscore an important role for TLR2 and TLR4 in mediating the BMP-2 response to oxLDL in human CAECs and indicate that these two immunoreceptors contribute to the mechanisms underlying atherosclerotic vascular calcification.

Antigen presentation by dendritic cells in the aortic wall triggers T helper immune responses in atherosclerosis (54.16)

Abstract Atherosclerosis is an immune-mediated disease associated with lipid accumulation and formation of atherosclerotic plaques in the major arteries of the body. Vascular dendritic cells (DC) are present throughout the adventitia of the normal mouse aorta and expand under atherosclerotic conditions, but their function remains incompletely understood. To test whether DC can mediate productive antigen presentation directly in the aortic wall, we used two-photon microscopy. CD11cYFP tagged DC were motile in mouse aortas and interacted with T cells in an antigen dependent manner. In atherosclerotic Apoe-/- CD11cYFP mice, DC interacted with transferred T cells from Apoe-/-, but not C57BL/6 mice. Interaction with DC decreased T cell migration velocity and induced secretion of IFN-γ, TNF-α and IL-17, which enhanced oxLDL uptake by primary macrophages. Using flow cytometry of digested whole aorta from C57BL/6 and Apoe-/- mice fed either Western diet or regular chow diet, we found CD11b+CD11c+ and CD11b-CD11c+ DC in the aortic wall of C57BL/6 mice, and this population expanded in Apoe-/- mice on western diet. Under these conditions, CD8a+ and CD103 DC appear among the CD11c+ DC population. Taken together, our data show the emergence of distinct subsets of DC in the mouse aorta during the progression of atherosclerosis and demonstrate that the aortic wall can be a site of active antigen presentation leading to the induction of a pro-atherogenic immune response.

C‐reactive protein upregulates lectin‐like oxidized LDL receptor‐1 expression in THP‐1‐derived macrophages through NF‐κB

Lectin-like oxidized LDL receptor-1 (LOX-1), a newly identified scavenger receptor, has been increasingly linked to atherosclerosis. C-reactive protein (CRP), a prototypic inflammatory marker, has been proven to promote atherogenesis. In this study, we evaluated the in vitro effects of CRP on LOX-1 expression and the associated signal transduction pathway in THP-1-derived macrophages. Our study showed that incubation of macrophages with CRP significantly enhanced expression of LOX-1 protein and mRNA levels in macrophages in a dose-dependent manner; this expression could be suppressed by the nuclear factor kappa B (NF-κB) pathway inhibitor BAY11-7085. However, LOX-1 was not inhibited by the inhibitor of mitogen-activated protein kinase (MAPK) proteins (SP600125-JNK/SAPK, SB203580-p38, and U0126-ERK1/2) in macrophages. In conclusion, human native CRP up-regulated LOX-1 expression in THP-1-derived macrophages primarily through the NF-κB signaling pathway. Practical applications: Identification of LOX-1 and definition of its biological role in pathophysiological states provided a new clue for understanding the nature of oxLDL uptake into macrophages. Internalization of modified lipoprotein by macrophages and foam cell formation are critical events in hypertension, diabetes mellitus, and dyslipidemia, which are the most important risk factors for atherosclerosis. As a characteristic inflammatory marker, CRP has been proven to play a pivotal role in promoting atherogenesis. However, crosstalk between CRP and LOX-1 on macrophages has not been elucidated. Therefore, determining the regulatory process for LOX-1 and the underlying signal transduction pathways may provide a new insight into the mechanism of atherosclerosis.