Scavenger receptors in atherosclerosis: beyond lipid uptake

Nicotine potentiates proatherogenic effects of oxLDL by stimulating and upregulating macrophage CD36 signaling

Cigarette smoking is a major risk factor for atherosclerosis and cardiovascular disease. CD36 mediates oxidized LDL (oxLDL) uptake and contributes to macrophage foam cell formation. We investigated a role for the CD36 pathway in nicotine-induced activation of macrophages and foam cell formation in vitro and in vivo. Nicotine in the same plasma concentration range found in smokers increased the CD36(+)/CD14(+) cell population in human peripheral blood mononuclear cells, increased CD36 expression of human THP1 macrophages, and increased macrophage production of reactive oxygen species, PKCδ phosphorylation, and peroxisome proliferator-activated receptor-γ (PPARγ) expression. Nicotine-induced CD36 expression was suppressed by antioxidants and by specific PKCδ and PPARγ inhibitors, implicating mechanistic roles for these intermediates. Nicotine synergized with oxLDL to increase macrophage expression of CD36 and cytokines TNF-α, monocyte chemoattractant protein-1, IL-6, and CXCL9, all of which were prevented by CD36 small interfering (si)RNA. Incubation with oxLDL (50 μg/ml) for 72 h resulted in lipid deposition in macrophages and foam cell formation. Preincubation with nicotine further increased oxLDL-induced lipid accumulation and foam cell formation, which was also prevented by CD36 siRNA. Treatment of apoE-/- mice with nicotine markedly exacerbated inflammatory monocyte levels and atherosclerotic plaque accumulation, effects that were not seen in CD36-/- apoE-/- mice. Our results show that physiological levels of nicotine increase CD36 expression in macrophages, a pathway that may account at least in part for the known proinflammatory and proatherogenic properties of nicotine. These results identify such enhanced CD36 expression as a novel nicotine-mediated pathway that may constitute an independent risk factor for atherosclerosis in smokers. The results also suggest that exacerbated atherogenesis by this pathway may be an adverse side effect of extended use of high concentrations of nicotine independent of their mode of administration.

Lipid regulators during atherogenesis: expression of LXR, PPAR, and SREBP mRNA in the human aorta

Transcription factors LXRs, PPARs, and SREBPs have been implicated in a multitude of physiological and pathological processes including atherogenesis. However, little is known about the regulation of these transcription factors at different stages of atherosclerosis progression. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to compare the contents of mRNAs in pairs intact-injured aorta fragments taken from the same donors. Only minor changes in LXRα, LXRβ, PPARα, PPARγ, SREBP1, and SREBP2 mRNA levels were found in initial lesions as compared with intact non-diseased tissue. The contents of all mRNAs but SREBP2 mRNA were found to be progressively up-regulated in fatty streaks and fibrous lipoid plaques. These changes were only partially reproduced in cultured macrophages upon lipid loading. Wave-shaped changes in abundance of correlations between given group of mRNAs and 28 atherosclerosis-related mRNA species in the course of atherogenesis were observed. The impact of specific mRNA correlations on the total correlations also significantly varied between different lesion types. The study suggests that the extent and forms of LXR/PPAR/SREBP participation in intima functions vary nonlinear in individual fashion in atherogenesis. We speculate that the observed changes in mRNAs expression and coupling reflect shifts in lipid ligands availability and cellular composition in the course of atherosclerosis progression.

Major vault protein regulates class A scavenger receptor-mediated tumor necrosis factor-α synthesis and apoptosis in macrophages

Atherosclerosis is considered a disease of chronic inflammation largely initiated and perpetuated by macrophage-dependent synthesis and release of pro-inflammatory mediators. Class A scavenger receptor (SR-A) expressed on macrophages plays a key role in this process. However, how SR-A-mediated pro-inflammatory response is modulated in macrophages remains ill defined. Here through immunoprecipitation coupled with mass spectrometry, we reported major vault protein (MVP) as a novel binding partner for SR-A. The interaction between SR-A and MVP was confirmed by immunofluorescence staining and chemical cross-linking assay. Treatment of macrophages with fucoidan, a SR-A ligand, led to a marked increase in TNF-α production, which was attenuated by MVP depletion. Further analysis revealed that SR-A stimulated TNF-α synthesis in macrophages via the caveolin- instead of clathrin-mediated endocytic pathway linked to p38 and JNK, but not ERK, signaling pathways. Importantly, fucoidan invoked an enrichment of MVP in lipid raft, a caveolin-reliant membrane structure, and enhanced the interaction among SR-A, caveolin, and MVP. Finally, we demonstrated that MVP elimination ameliorated SR-A-mediated apoptosis in macrophages. As such, MVP may fine-tune SR-A activity in macrophages which contributes to the development of atherosclerosis.

Transcriptome analysis of genes regulated by cholesterol loading in two strains of mouse macrophages associates lysosome pathway and ER stress response with atherosclerosis susceptibility

Cholesterol loaded macrophages in the arterial intima are the earliest histological evidence of atherosclerosis. Studies of mouse models of atherosclerosis have shown that the strain background can have a significant effect on lesion development. We have previously shown that DBA/2 ApoE(-/-) mice have aortic root lesions 10-fold larger than AKR ApoE(-/-) mice. The current study analyzes the response to cholesterol loading of macrophages from these two strains. Macrophages from the atherosclerosis susceptible DBA/2 strain had significantly higher levels of total and esterified cholesterol compared to atherosclerosis resistant AKR macrophages, while free cholesterol levels were higher in AKR cells. Gene expression profiles were obtained and data were analyzed for strain, cholesterol loading, and strain-cholesterol loading interaction effects by a fitted linear model. Pathway and transcriptional motif enrichment were identified by gene set enrichment analysis. In addition to observed strain differences in basal gene expression, we identified many transcripts whose expression was significantly altered in response to cholesterol loading, including P2ry13 and P2ry14, Trib3, Hyal1, Vegfa, Ccr5, Ly6a, and Ifit3. Eight pathways were significantly enriched in transcripts regulated by cholesterol loading, among which the lysosome and cytokine-cytokine receptor interaction pathways had the highest number of significantly regulated transcripts. Of the differentially regulated transcripts with a strain-cholesterol loading interaction effect, we identified three genes known to participate in the endoplasmic reticulum (ER) stress response, Ddit3, Trib3 and Atf4. These three transcripts were highly up-regulated by cholesterol in AKR and either down-regulated or unchanged in loaded DBA/2 macrophages, thus associating a robust ER stress response with atherosclerosis resistance. We identified significant transcripts with strain, loading, or strain-loading interaction effect that reside within previously described quantitative trait loci as atherosclerosis modifier candidate genes. In conclusion, we characterized several strain and cholesterol induced differences that may lead to new insights into cellular cholesterol metabolism and atherosclerosis.

Oxidized low density lipoprotein induced caspase-1 mediated pyroptotic cell death in macrophages: implication in lesion instability?

BACKGROUND

Macrophage death in advanced lesion has been confirmed to play an important role in plaque instability. However, the mechanism underlying lesion macrophage death still remains largely unknown.

METHODS AND RESULTS

Immunohistochemistry showed that caspase-1 activated in advanced lesion and co-located with macrophages and TUNEL positive reaction. In in-vitro experiments showed that ox-LDL induced caspase-1 activation and this activation was required for ox-LDL induced macrophages lysis, IL-1β and IL-18 production as well as DNA fragmentation. Mechanism experiments showed that CD36 and NLRP3/caspase-1/pathway involved in ox-LDL induced macrophage pyroptosis.

CONCLUSION

Our study here identified a novel cell death, pyroptosis in ox-LDL induced human macrophage, which may be implicated in lesion macrophages death and play an important role in lesion instability.

Fetuin-A-containing calciprotein particles reduce mineral stress in the macrophage

The formation of fetuin-A-containing calciprotein particles (CPP) may facilitate the clearance of calcium phosphate nanocrystals from the extracellular fluid. These crystals may otherwise seed extra-osseous mineralization. Fetuin-A is a partially phosphorylated glycoprotein that plays a critical role in stabilizing these particles, inhibiting crystal growth and aggregation. CPP removal is thought to be predominantly mediated by cells of the reticuloendothelial system via type I and type II class A scavenger receptor (SR-AI/II). Naked calcium phosphate crystals are known to stimulate macrophages and other cell types in vitro, but little is known of the effect of CPP on these cells. We report here, for the first time, that CPP induce expression and secretion of tumour necrosis factor (TNF)-α, interleukin (IL)-1β in murine RAW 264.7 macrophages. Importantly, however, CPP induced significantly lower cytokine secretion than hydroxyapatite (HAP) crystals of equivalent size and calcium content. Furthermore, CPP only had a modest effect on macrophage viability and apoptosis, even at very high levels, compared to HAP crystals, which were strongly pro-apoptotic at much lower levels. Fetuin-A phosphorylation was found to modulate the effect of CPP on cytokine secretion and apoptosis, but not uptake via SR-AI/II. Prolonged exposure of macrophages to CPP was found to result in up-regulated expression of SR-AI/II. CPP formation may help protect against some of the pro-inflammatory and harmful effects of calcium phosphate nanocrystals, perhaps representing a natural defense system for calcium mineral stress. However, in pathological states where production exceeds clearance capacity, these particles may still stimulate pro-inflammatory and pro-apoptotic cascades in macrophages, which may be important in the pathogenesis of vascular calcification.

Scavenger receptor class A member 3 (SCARA3) in disease progression and therapy resistance in multiple myeloma

This study evaluates the role of scavenger receptor class A member 3 (SCARA3) in multiple myeloma (MM). SCARA3 expression was induced upon treatment with oxidative stressors (ionizing radiation and chemotherapeutic drugs). An epigenetic inactivation of SCARA3 was noted in MM.1S myeloma cells. Myeloma cell killing by dexamethasone and bortezomib was inhibited by up-regulation of SCARA3 while SCARA3 knockdown sensitized myeloma cells to the drugs. Clinical samples showed an inverse correlation between SCARA3 gene expression, myeloma progression, and favorable clinical prognosis. In MM, SCARA3 protects against oxidative stress-induced cell killing and can serve as predictor of MM progression and therapeutic response.

Immunometabolism of AMPK in insulin resistance and atherosclerosis

Obesity leads to insulin resistance and atherosclerosis, which precede Type 2 diabetes and cardiovascular disease. Immunometabolism addresses how metabolic and inflammatory pathways converge to maintain health and a contemporary problem is determining how obesity-induced inflammation precipitates chronic diseases such as insulin resistance and atherosclerosis. AMP-activated protein kinase (AMPK) is an important serine/threonine kinase well known for regulating metabolic processes and maintaining energy homeostasis. However, both metabolic and immunological AMPK-mediated effects play a role in disease. Pro-inflammatory mediators suppress AMPK activity and hinder lipid oxidation. In addition, AMPK activation curbs inflammation by directly inhibiting pro-inflammatory signaling pathways and limiting the build-up of specific lipid intermediates that elicit immune responses. In the context of obesity and chronic disease, these reciprocal responses involve both immune and metabolic cells. Therefore, the immunometabolism of AMPK-mediated processes and therapeutics should be considered in atherosclerosis and insulin resistance.

Role of MyD88-dependent and MyD88-independent signaling in Porphyromonas gingivalis-elicited macrophage foam cell formation

Clinical studies and experimental modeling identify a potential link between periodontal disease and periodontal pathogens such as Porphyromonas gingivalis and atherosclerosis and formation of macrophage foam cells. Toll-like receptors and molecules governing their intracellular signaling pathways such as MyD88 play roles in atherosclerosis, as well as host response to P. gingivalis. The aim of this study was to define roles of MyD88 and TRIF during macrophage foam cell formation in response to P. gingivalis. In the presence of human low-density lipoprotein (LDL) mouse bone-marrow-derived macrophages (BMφ) cultured with P. gingivalis responded with significant reduction in tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6). The BMφ stained strongly with oil red O, regardless of whether bacterial challenge occurred concurrent with or before LDL treatment. Heat-killed P. gingivalis stimulated foam cell formation in a similar way to live bacteria. The BMφ from MyD88-knockout and Lps2 mice revealed a significant role for MyD88, and a minor role for TRIF in P. gingivalis-elicited foam cell formation. Porphyromonas gingivalis-elicited TNF-α and IL-6 were affected by MyD88 ablation and to a lesser extent by TRIF status. These data indicate that LDL affects the TNF-α and IL-6 response of macrophages to P. gingivalis challenge and that MyD88 and TRIF play important roles in P. gingivalis-elicited foam cell formation.

Associations of CXCL16/CXCR6 with carotid atherosclerosis in patients with metabolic syndrome

BACKGROUND & AIMS

Chemokine CXC ligand 16 (CXCL16) has chemokine, adhesion molecule and scavenger receptor functions involving the immune function. Atherosclerosis is an inflammatory disease. We aimed to study the association of chemokine CXCL16/CXCR6 and carotid atherosclerosis in patients with metabolic syndrome.

METHODS

Carotid ultrasonography was determined in 30 patients with metabolic syndrome and 30 controls. The mRNA levels of CXCL6/CXCR6 were detected by real-time RT-PCR. The activation of T cells and expression of CXCR6 in T lymphocyte cells and natural killer T (NKT) cells was detected by flow cytometry. The serum level of sol-CXCL6 was determined by ELISA.

RESULTS

Compared with controls, patients with metabolic syndrome showed significantly increased waist circumference and levels of total cholesterol, triglycerides and low-density lipoprotein cholesterol (all P < 0.001), with increased abnormalities of the structure and function of the carotid artery (P < 0.05). In metabolic syndrome, the levels of sol-CXCL16 and CXCL16mRNA were increased and associated with max IMT and plaque index. Patients with metabolic syndrome showed increased number of CXCR6+ T cells and CXCR6+ NKT cells, which was associated with max IMT and plaque index.

CONCLUSIONS

CXCL16 and CXCR6 may be associated the formation of carotid atherosclerotic plaque in metabolic syndrome, and T cells may be the important effector cells in the pathogenesis of the atherosclerosis.

Low levels of IgM antibodies to oxidized cardiolipin increase and high levels decrease risk of cardiovascular disease among 60-year olds: a prospective study

Background

Antibodies against cardiolipin (aCL) are associated with increased risk of cardiovascular disease (CVD). We here determine the role of antibodies against oxidized CL (aOxCL).

Methods

One third of sixty-year olds from the Stockholm County were screened (2039 men, 2193 women), where 211 incident CVD-cases and 633 age- and sex-matched controls were identified (5–7 year follow-up). Antibodies were determined by ELISA and uptake of oxLDL in macrophages by FACScan.

Results

IgM aOxCL was lower among CVD cases than controls (p=0.024). aOxCL-levels were divided in quartiles with the highest quartile set as the reference group. After adjustment for smoking, BMI, type II diabetes, hypercholesterolaemia and hypertension, an increased risk was determined in the lowest quartile of IgM aOxCL (OR: 1.80, CI: 1.12–2.91, p=0.0159); OR for men in the lowest quartile was 2.46 (CI 1.34–4.53, p=0.0037) for CVD and for stroke: 12.28 (CI: 1.48-101.77, p=0.02). IgG aOxCL levels did not differ between quartiles in CVD-risk. High levels of IgM aOxCL (reaching significance above 86th) and IgG aOxCL (above 95th percentile) were associated with decreased risk of CVD (OR: 0.485, CI: 0.283-0.829; p=0.0082 and OR: 0.23, CI: 0.07-0.69; p=0.0091). aCL were not associated with CVD. oxCL but not CL competed out uptake of OxLDL in macrophages, and aOxLDL recognized oxCL but not CL. In contrast to aCL, aOxCL was not dependent on co-factor Beta2-glycoprotein-I.

Conclusions

aOxCL is a novel risk/protection marker for CVD, with therapeutic implications. OxCL competes with oxLDL for uptake in macrophages and the possibility that aOxCL inhibits such uptake by interfering with same or similar epitopes in oxCL and oxLDL should be further studied.

Neutrophil-derived myeloperoxidase aggravates non-alcoholic steatohepatitis in low-density lipoprotein receptor-deficient mice

Background

Chronic inflammation and oxidative stress play fundamental roles in the pathogenesis of non-alcoholic steatohepatitis (NASH). Previously, we reported that myeloperoxidase (MPO), an aggressive oxidant-generating neutrophil enzyme, is associated with NASH severity in man. We now investigated the hypothesis that MPO contributes to the development and progression of NASH.

Methodology

Low-density lipoprotein receptor-deficient mice with an MPO-deficient hematopoietic system (LDLR^−/−/MPO^−/−tp mice) were generated and compared with LDLR^−/−/MPO^+/+tp mice after induction of NASH by high-fat feeding.

Results

High-fat feeding caused a ∼4-fold induction of liver MPO in LDLR^−/−/MPO^+/+ mice which was associated with hepatic sequestration of MPO-positive neutrophils and high levels of nitrotyrosine, a marker of MPO activity. Importantly, LDLR^−/−/MPO^−/−tp mice displayed markedly reduced hepatic neutrophil and T-lymphocyte infiltration (p<0.05), and strong down regulation of pro-inflammatory genes such as TNF-α and IL-6 (p<0.05, p<0.01) in comparison with LDLR^−/−/MPO^+/+tp mice. Next to the generalized reduction of inflammation, liver cholesterol accumulation was significantly diminished in LDLR^−/−/MPO^−/−tp mice (p = 0.01). Moreover, MPO deficiency appeared to attenuate the development of hepatic fibrosis as evident from reduced hydroxyproline levels (p<0.01). Interestingly, visceral adipose tissue inflammation was markedly reduced in LDLR^−/−/MPO^−/−tp mice, with a complete lack of macrophage crown-like structures. In conclusion, MPO deficiency attenuates the development of NASH and diminishes adipose tissue inflammation in response to a high fat diet, supporting an important role for neutrophils in the pathogenesis of metabolic disease.

Induction of oxidative stress by oxidized LDL via meprinα-activated epidermal growth factor receptor in macrophages

AIMS

The aim of this study was to explore meprinα-mediated transactivation of the epidermal growth factor receptor (EGFR) and reactive oxygen species (ROS) production in macrophages.

METHODS AND RESULTS

Accelerated atherosclerotic lesions were established by administration of a high-fat diet in apolipoprotein E-deficient (apoE(-/-)) mice. Lentiviral overexpression of meprinα in the thoracic aortic artery during plaque formation enhanced intra-plaque macrophage induction of ROS as well as formation of atherosclerotic plaques, whereas AG1478 (specific inhibitor of the EGFR) treatment exerted the opposite effect. A meprinα inhibitor abrogated EGFR activation in mice. In cultured J774a.1 macrophages, oxidized low-density lipoprotein (OxLDL) increased ROS formation and EGFR activation through a ligand [heparin-binding epidermal growth factor-like growth factor (HB-EGF)]-dependent pathway. However, a meprinα inhibitor or specific siRNA inhibited ROS production and EGFR activation. Recombinant mouse meprinα enhanced OxLDL-stimulated production of ROS and induced HB-EGF. Inhibition of p38 mitogen-activated protein kinase by SB203580 decreased OxLDL-stimulated production of ROS. Conversely, inhibition of meprinα or PI3K-Rac1 inhibitors also decreased p38 activity in OxLDL-stimulated macrophages. In addition, inhibition of meprinα reversed OxLDL-stimulated activation of PI3K.

CONCLUSION

Meprinα promotes OxLDL-induced plaque formation and ROS release by transactivation of the EGFR, followed by activation of the PI3K/Rac1/p38 pathway.

Synergistic effect of scavenger receptor A and low-density lipoprotein receptor on macrophage foam cell formation under inflammatory stress

To provide experimental evidence for the effect of inflammation on cholesterol accumulation in macrophages, we investigated the expression of low-density lipoprotein receptor (LDL-R) and scavenger receptor A (SR-A) genes and proteins in the lipopolysaccharide (LPS)-stimulated macrophage-like RAW264.7 cell line. RAW264.7 cells were incubated in serum-free medium in the absence or presence of LDL alone, LDL+LPS and LPS alone. Intracellular cholesterol content, tumor necrosis factor α levels in the supernatants, mRNA and protein expression of LDL-R and SR-A in the treated cells were assessed by Oil Red O staining cholesterol enzymatic assay, enzyme-linked immunosorbent assay, semi-quantitative polymerase chain reaction and western blot analysis, respectively. Our results demonstrated that LPS was able to upregulate SR-A mRNA and protein expression, override LDL-R suppression induced by a high dose of LDL and increase LDL uptake by enhancing receptor expression, leading to foam cell formation in RAW264.7 cells. These findings suggest that the synergy of the upregulation of SR-A and dysregulation of LDL-R under inflammatory stress may contribute to macrophage-derived foam cell formation.

Ultrasound imaging in an animal model of vascular inflammation following balloon injury

Cardiovascular disease is a major cause of morbidity and mortality in the world and better prevention and treatment strategies are needed. Studies from this laboratory have shown that perfluorocarbon exposed sonicated dextrose albumin (PESDA) microbubbles bind to inflamed vasculature through interactions with scavenger receptors (SR). This current study details the use of PESDA as a tool for accessing and quantifying the extent of vascular inflammation. Angioplastied rat aortas were evaluated with low mechanical index microbubble imaging techniques contrast pulse sequencing (CPS); Siemens Acuson Sequoia 15L8, 7-15 MHz ultrasound probe with a mechanical index of 0.09 to detect microbubble binding. Real-time polymerase chain reaction (RT-PCR) analysis of angioplastied aortas demonstrated a significantly (p < 0.01) increased expression of both SRs and Interleukin 6 (IL-6). Vessel wall enhancement was quantified using densitometry of CPS ultrasound images and correlated with the upregulated expression of scavenger receptors, Toll-like receptors and IL-6. This study demonstrates that PESDA, in conjunction with CPS ultrasound, is an effective imaging technique to better detect early vascular inflammation and potential cardiovascular disease.

Conditional targeting of tumor necrosis factor receptor-associated factor 6 reveals opposing functions of Toll-like receptor signaling in endothelial and myeloid cells in a mouse model of atherosclerosis

BACKGROUND

Previous studies implicated Toll-like receptor signaling as a critical pathogenic pathway in atherosclerosis, but the cell-specific mechanisms by which Toll-like receptors act to control atherosclerotic plaque development remain poorly understood.

METHODS AND RESULTS

To study the cell-specific role of tumor necrosis factor receptor-associated factor 6 (TRAF6) in atherosclerosis, we generated ApoE(-/-) mice with endothelial cell- or myeloid cell-specific TRAF6 deficiency using Cre/LoxP-mediated gene targeting. Endothelial TRAF6 deficiency reduced atherosclerosis in female ApoE(-/-) mice by inhibiting nuclear factor-κB-dependent proinflammatory gene expression and monocyte adhesion to endothelial cells. In contrast, myeloid cell-specific TRAF6 deficiency caused exacerbated atherosclerosis, with larger plaques containing more necrotic areas in both male and female ApoE(-/-) mice. TRAF6-deficient macrophages showed impaired expression of the antiinflammatory and atheroprotective cytokine interleukin-10, elevated endoplasmic reticulum stress, increased sensitivity to oxidized low-density lipoprotein-induced apoptosis, and reduced capacity to clear apoptotic cells. Thus, the reduced antiinflammatory properties, coupled with increased sensitivity to apoptosis and impaired efferocytosis capacity of TRAF6-deficient macrophages, result in exacerbated atherosclerosis development in TRAF6(MYKO)/ApoE(-/-) mice.

CONCLUSION

Toll-like receptor-mediated TRAF6 signaling acts in endothelial cells to promote atherosclerosis but displays atheroprotective, antiinflammatory and prosurvival functions in myeloid 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.

Regulation of gene expression in atherosclerosis: insights from microarray studies in monocytes/macrophages

Atherosclerosis is a pathological phenomenon in which the walls of large arteries thicken and lose elasticity as a result of the growth of atheromatous lesions. It is a complex, multifactorial disease that involves several cell types and various pathobiological processes. Its genetic basis has not yet been deciphered, but it is related to complex multigene patterns influenced by environmental interactions. In this review, we focus specifically on the application of microarrays to atherosclerosis research using monocytes and monocyte-derived macrophages, as these are key cells in all phases of atherosclerosis, from the formation of foam cells to the destabilization and rupture of the atherosclerotic plaque. These studies have provided relevant information on genes involved in atherosclerosis development, contributing to our understanding of the molecular mechanisms that underlie this complex disease.

Carbohydrate clearance receptors in transfusion medicine

BACKGROUND

Complex carbohydrates play important functions for circulation of proteins and cells. They provide protective shields and refraction from non-specific interactions with negative charges from sialic acids to enhance circulatory half-life. For recombinant protein therapeutics carbohydrates are especially important to enhance size and reduce glomerular filtration loss. Carbohydrates are, however, also ligands for a large number of carbohydrate-binding lectins exposed to the circulatory system that serve as scavenger receptors for the innate immune system, or have more specific roles in targeting of glycoproteins and cells.

SCOPE OF REVIEW

Here we provide an overview of the common lectin receptors that play roles for circulating glycoproteins and cells, and present a discussion of ways to engineer glycosylation of recombinant biologics and cells to improve therapeutic effects.

MAJOR CONCLUSIONS

While the pharmaceutical industry has learned how to exploit carbohydrates to improve pharmacokinetic properties of recombinant therapeutics, our understanding of how to improve cell-based therapies by manipulation of complex carbohydrates is still at its infancy. Progress with the latter has recently been achieved with cold-stored platelets, where exposure of uncapped glycans lead to rapid clearance from circulation by several lectin-mediated pathways.

GENERAL SIGNIFICANCE

Understanding lectin-mediated clearance pathways is essential for progress in development of biological pharmaceuticals.

Increased stability of phosphatase and tensin homolog by intermedin leading to scavenger receptor A inhibition of macrophages reduces atherosclerosis in apolipoprotein E-deficient mice

Intermedin, a novel member of calcitonin gene-related peptide family, is an endogenous cardiovascular-protective peptide. Because intermedin exists in human atherosclerotic plaque, we studied the role of intermedin in macrophage scavenger receptor A (SR-A)-mediated foam-cell formation and atherogenesis. In an in vitro foam-cell formation model (induced by acetylated low-density lipoprotein [AcLDL]) with mouse (C57BL/6J) macrophages, intermedin reduced AcLDL uptake and binding, decreased intracellular cholesterol content, and suppressed both mRNA and protein levels of SR-A. Simultaneously, intermedin increased phosphatase and tensin homolog (PTEN) protein levels by increasing PTEN phosphorylation and inhibiting ubiquitin-mediated PTEN degradation. These effects were blocked by the intermedin receptor antagonist or cAMP-protein kinase A inhibitors. PTEN overexpression mimicked the inhibitory effects of intermedin on SR-A expression and AcLDL uptake. However, knockdown of PTEN by short-hairpin RNA completely blocked all inhibitory effects of intermedin. Furthermore, in apolipoprotein E-deficient (apoE(-/-)) mice, 6-week intermedin infusion reduced AcLDL uptake and SR-A mRNA and protein levels and increased PTEN protein level in peritoneal macrophages. PTEN level was increased and SR-A expression decreased in parallel in macrophages in atherosclerotic lesions. Thus, intermedin inhibited atherosclerosis in apoE(-/-) mice. Increased stability of PTEN by intermedin leads to SR-A inhibition in macrophages, which ameliorates foam-cell formation and atherosclerosis in apoE(-/-) mice.

TGF-β inhibits the uptake of modified low density lipoprotein by human macrophages through a Smad-dependent pathway: a dominant role for Smad-2

The anti-atherogenic cytokine, TGF-β, plays a key role during macrophage foam cell formation by modulating the expression of key genes involved in the control of cholesterol homeostasis. Unfortunately, the molecular mechanisms underlying these actions of TGF-β remain poorly understood. In this study we examine the effect of TGF-β on macrophage cholesterol homeostasis and delineate the role of Smads-2 and ‐3 during this process. Western blot analysis showed that TGF-β induces a rapid phosphorylation-dependent activation of Smad-2 and ‐3 in THP-1 and primary human monocyte-derived macrophages. Small interfering RNA-mediated knockdown of Smad-2/3 expression showed that the TGF-β-mediated regulation of key genes implicated in the uptake of modified low density lipoproteins and the efflux of cholesterol from foam cells was Smad-dependent. Additionally, through the use of virally delivered Smad-2 and/or Smad-3 short hairpin RNA, we demonstrate that TGF-β inhibits the uptake of modified LDL by macrophages through a Smad-dependent mechanism and that the TGF-β-mediated regulation of CD36, lipoprotein lipase and scavenger receptor-A gene expression was dependent on Smad-2. These studies reveal a crucial role for Smad signaling, particularly Smad-2, in the inhibition of foam cell formation by TGF-β through the regulation of expression of key genes involved in the control of macrophage cholesterol homeostasis.

An essential function for MKP5 in the formation of oxidized low density lipid-induced foam cells

The uptake of oxidized low density lipoprotein (ox-LDL) by macrophages usually leads to the formation of lipid-laden macrophages known as "foam cells," and this process plays an important role in the development of atherosclerosis. Ox-LDL activates mitogen-activated protein kinase (MAP) kinases and nuclear factor (NF)-κB, and activations of p38 and NF-κB are important for the formation of foam cells. MAP kinase phosphatase (MKP) 5 is a member of the dual specificity phosphatases (DUSPs) family that can selectively dephosphorylate activated MAPKs to regulate innate and adaptive immune responses. However, the role of MKP5 in the formation of foam cells remains unknown. Here, we found that stimulation of ox-LDL induces the expression of MKP5 in macrophages. MKP5 deficiency blocked the uptake of ox-LDL and the formation of foam cells. Further analysis revealed that deletion of MKP5 reduced the ox-LDL-induced activation of NF-κB. Also, MKP5 deficiency markedly inhibited the production of TNF-α, but enhanced the levels of TGF-β1 in ox-LDL-stimulated macrophages. Moreover, inhibition of NF-κB by p65 RNAi significantly reduced foam cell formation in macrophages from WT mice relative to MKP5-deficient mice. Thus, MKP5 has an essential role in the formation of foam cells through activation of NF-κB, and MKP5 represents a novel target for the therapeutic intervention of atherosclerosis.

Native LDL-induced oxidative stress in human proximal tubular cells: multiple players involved

Dyslipidemia is a well-established condition proved to accelerate the progression of chronic kidney disease leading to tubulo-interstitial injury. However, the molecular aspects of the dyslipidemia-induced renal damage have not been fully clarified and in particular the role played by low-density lipoproteins (LDLs). This study aimed to examine the effects of native non-oxidized LDL on cellular oxidative metabolism in cultured human proximal tubular cells. By means of confocal microscopy imaging combined to respirometric and enzymatic assays it is shown that purified native LDL caused a marked increase of cellular reactive oxygen species (ROS) production, which was mediated by activation of NADPH oxidase(s) and by mitochondrial dysfunction by means of a ROS-induced ROS release mechanism. The LDL-dependent mitochondrial alterations comprised inhibition of the respiratory chain activity, enhanced ROS production, uncoupling of the oxidative phosphorylation efficiency, collapse of the mtΔΨ, increased Ca²⁺ uptake and loss of cytochrome c. All the above LDL-induced effects were completely abrogated by chelating extracellular Ca²⁺ as well as by inhibition of the Ca²⁺-activated cytoplas-mic phospholipase A2, NADPH oxidase and mitochondrial permeability transition. We propose a mechanicistic model whereby the LDL-induced intracellular redox unbalance is triggered by a Ca²⁺ inward flux-dependent commencement of cPLA2 followed by activation of a lipid- and ROS-based cross-talking signalling pathway. This involves first oxidants production via the plasmamembrane NADPH oxidase and then propagates downstream to mitochondria eliciting redox- and Ca²⁺-dependent dysfunctions leading to cell-harming conditions. These findings may help to clarify the mechanism of dyslipidemia-induced renal damage and suggest new potential targets for specific therapeutic strategies to prevent oxidative stress implicated in kidney diseases.

Diverse roles of macrophages in atherosclerosis: from inflammatory biology to biomarker discovery

Cardiovascular disease, a leading cause of mortality in developed countries, is mainly caused by atherosclerosis, a chronic inflammatory disease. Macrophages, which differentiate from monocytes that are recruited from the blood, account for the majority of leukocytes in atherosclerotic plaques. Apoptosis and the suppressed clearance of apoptotic macrophages (efferocytosis) are associated with vulnerable plaques that are prone to rupture, leading to thrombosis. Based on the central functions of macrophages in atherogenesis, cytokines, chemokines, enzymes, or microRNAs related to or produced by macrophages have become important clinical prognostic or diagnostic biomarkers. This paper discusses the impact of monocyte-derived macrophages in early atherogenesis and advanced disease. The role and possible future development of macrophage inflammatory biomarkers are also described.

TARGETING OF MACROPHAGE FOAM CELLS IN ATHEROSCLEROTIC PLAQUE USING OLIGONUCLEOTIDE-FUNCTIONALIZED NANOPARTICLES

Macrophage foam cells are key components of atherosclerotic plaque and play an important role in the progression of atherosclerosis leading to plaque rupture and thrombosis. Foam cells are emerging as attractive targets for therapeutic intervention and for imaging the progression of disease. Therefore, designing nanoparticles (NPs) targeted to macrophage foam cells in plaque is of considerable therapeutic significance. Here we report the construction of an oligonucleotide functionalized NP system with high affinity for foam cells. Nanoparticles functionalized with a 23-mer poly-Guanine (polyG) oligonucleotide are specifically recognized by the scavenger receptors on lipid-laden foam cells in vitro and ex vivo. The enhanced uptake of polyG-functionalized NPs by foam cells is inhibited in the presence of acetylated-LDL, a known ligand of scavenger receptors. Since polyG oligonucleotides are stable in serum and are unlikely to induce an immune response, their use for scavenger receptor-mediated targeting of macrophage foam cells provides a strategy for targeting atherosclerotic lesions.

Role of macrophage scavenger receptors in atherosclerosis

Accumulating evidence indicates that atherosclerosis is a chronic inflammatory disease. The key innate immune cells that are involved in the pathogenesis of atherosclerosis are circulating monocytes and plaque macrophages. Complex interplay between immune and metabolic processes results in pathological activity of these cells. The best understood pathological process mediated by macrophages is their inability to process modified lipoproteins properly resulting in the formation of foamy cells, which are a dangerous component of atherosclerotic plaques. Key molecules involved in the recognition and processing of modified lipoproteins are scavenger receptors (SR). This is a large family of surface expressed structurally heterogeneous receptors with a broad spectrum of endogenous and exogenous ligands. The common functional feature of SR is internalisation of extracellular components and targeting them for lysosomal degradation. However, these relatively simple functions can have complex consequences, since they are linked to diverse specific signalling pathways and to other membrane transport pathways. Moreover, scavenger receptors can co-operate with other types of receptors increasing the variability of the macrophage response to multiple extracellular ligands. At least some SRs respond to modified lipoproteins by amplification of inflammation and accumulation of macrophages in the plaque, while some SRs may support tolerogenic reactions. Outcome of different SR activities will be the decision of monocytes and macrophage to guard homeostatic balance, support atherosclerosis progression and plaque instability by inflammatory reactions, or support rapid fibrotic processes in the plaque that stabilise it. Despite the accumulating knowledge about the molecular mechanisms of scavenger receptor action, their role in the progression of atherosclerosis remains controversial. The activities of scavenger receptors that can contribute to each of these processes are a subject of current review.

Interleukin-17 deficiency reduced vascular inflammation and development of atherosclerosis in Western diet-induced apoE-deficient mice

OBJECTIVE

Several reports describe the role of interleukin (IL)-17 in the development of atherosclerosis; however, its precise role remains controversial. We generated double-deficient mice for apolipoprotein E (apoE) and IL-17 (apoE(-/-)IL-17(-/-) mice) and investigated the effect of IL-17 deficiency on vascular inflammation and atherosclerosis.

METHODS AND RESULTS

Atherosclerotic plaque areas in apoE(-/-)IL-17(-/-) mice fed a Western diet (WD) were significantly reduced compared with those in apoE(-/-) mice. No significant differences in plasma lipid profiles were observed between apoE(-/-) and apoE(-/-)IL-17(-/-) mice. The number of infiltrated macrophages in the plaques was significantly decreased in WD-fed apoE(-/-)IL-17(-/-) mice compared with WD-fed apoE(-/-) mice, whereas vascular smooth muscle cell content was not altered by IL-17 deficiency. Expression of inflammatory cytokines (MCP-1, IL-1β, IL-6, IFN-γ, and IL-12 p40) and scavenger receptors (Msr-1, Scarb1, and Olr1) in the plaques was inhibited in WD-fed apoE(-/-)IL-17(-/-) mice. Furthermore, expression of inducible nitric oxide (M1 marker) and arginase-1 (M2 marker) was inhibited in WD-fed apoE(-/-)IL-17(-/-) mice.

CONCLUSION

Our results indicate that IL-17 deficiency reduces vascular inflammation and atherosclerosis and that modulation of IL-17 could be a potential target for prevention and treatment of atherosclerosis.

The LOX-1 Scavenger Receptor and Its Implications in the Treatment of Vascular Disease

Cardiovascular disease is the leading cause of death. The disease is due to atherosclerosis which is characterized by lipid and fat accumulation in arterial blood vessel walls. A key causative event is the accumulation of oxidised low density lipoprotein particles within vascular cells, and this is mediated by scavenger receptors. One such molecule is the LOX-1 scavenger receptor that is expressed on endothelial, vascular smooth muscle, and lymphoid cells including macrophages. LOX-1 interaction with OxLDL particles stimulates atherosclerosis. LOX-1 mediates OxLDL endocytosis via a clathrin-independent internalization pathway. Transgenic animal model studies show that LOX-1 plays a significant role in atherosclerotic plaque initiation and progression. Administration of LOX-1 antibodies in cellular and animal models suggest that such intervention inhibits atherosclerosis. Antiatherogenic strategies that target LOX-1 function using gene therapy or small molecule inhibitors would be new ways to address the increasing incidence of vascular disease in many countries.

Contribution of monocyte-derived macrophages and smooth muscle cells to arterial foam cell formation

Smooth muscle cells (SMCs) are the main cell type in intimal thickenings and some stages of human atherosclerosis. Like monocyte-derived macrophages, SMCs accumulate excess lipids and contribute to the total intimal foam cell population. In contrast, apolipoprotein (Apo)E-deficient and LDL receptor-deficient mice develop atherosclerotic lesions that are macrophage- as opposed to SMC-rich. The lesser contribution of SMCs to lesion development in these mouse models has distracted attention away from the importance of SMC cholesterol homeostasis in the artery wall. Intimal SMCs accumulate excess amounts of cholesteryl esters when compared with medial layer SMCs, possibly explained by reduced ATP-binding cassette transporter A1 expression and ApoA-I binding to intimal-type SMCs. The aim of this review is to compare the relative contribution of monocyte-derived macrophages and SMCs to human vs. mouse atherosclerosis, and describe what is known about lipid uptake and removal mechanisms contributing to arterial macrophage and SMC foam cell formation. An increased understanding of the contribution of these cell types to lesion development will help to delineate their relative importance in atherogenesis and as potential therapeutic targets.

Lipopolysaccharide represses the expression of ATP-binding cassette transporter G1 and scavenger receptor class B, type I in murine macrophages

OBJECTIVE AND DESIGN

To investigate the regulation of cholesterol transporters, including ATP-binding cassette transporter A1 (ABCA1), ABCG1 and scavenger receptor class B, type I (SR-BI), by inflammatory stimuli in macrophages. MATERIALS AND TREATMENTS: RAW 264.7 macrophages and mouse peritoneal macrophages were treated with inflammatory stimuli with or without rosiglitazone, a peroxisome proliferator activated receptor γ (PPARγ) agonist, or T0901317, a liver X receptor (LXR) agonist.

METHODS

Real-time PCR and Western blotting for cholesterol transporters as well as cellular cholesterol efflux to high-density lipoprotein 2 (HDL(2)) were determined.

RESULTS

In RAW 264.7 macrophages, lipopolysaccharide (LPS) significantly reduced ABCG1 and PPARγ as well as cholesterol efflux to HDL(2). Rosiglitazone and T0901317 induced ABCA1 and ABCG1 several-fold, but LPS reduced only ABCG1. ABCG1 and SR-BI proteins, but not ABCA1, were decreased by LPS. In mouse peritoneal macrophages, LPS, tumor necrosis factor α and interleukin-1β decreased ABCG1, SR-BI, LXRα and PPARγ mRNA. The agonists increased ABC transporter expression but LPS reduced mRNA of T0901317-induced ABCA1 as well as basal and agonists-induced ABCG1. SR-BI protein was increased by rosiglitazone but LPS decreased the levels.

CONCLUSION

The data suggest that inflammatory insults repress ABCG1 and SR-BI expression partly dependent on PPARγ with a minimal effect on ABCA1 expression.

Peroxisome Proliferator-Activator Receptor γ: A Link between Macrophage CD36 and Inflammation in Malaria Infection

Severe malaria infection caused by Plasmodium falciparum is a global life-threatening disease and a leading cause of death worldwide. Intensive investigations have demonstrated that macrophages play crucial roles in control of inflammatory and immune responses and clearance of Plasmodium-falciparum-parasitized erythrocytes (PE). This paper focuses on how macrophage CD36 recognizes and internalizes PE and participates the inflammatory signaling in response to Plasmodium falciparum. In addition, recent advances in our current understanding of the biological actions of PPARγ on CD36 and malaria clearance from the hosts are highlighted.

Modified low density lipoproteins decrease the activity and expression of lysosomal acid lipase in human endothelial and smooth muscle cells

Lysosomal acid lipase (LAL), the only lysosomal enzyme involved in the hydrolysis of LDL-cholesteryl esters, is a key regulator of cellular cholesterol and fatty acid homeostasis and its deficiency contributes to the pathophysiology of various diseases. In this study, we questioned whether oxidized or glycated LDL, a common occurrence in atherosclerosis and diabetes, affect the activity and expression of LAL in vascular endothelial cells (EC) and smooth muscle cells (SMC). LAL activity and expression were assayed in cultured human EC and SMC exposed to oxidized LDL (oxLDL), (±)9-hydroxyoctadecadienoic acid-cholesteryl ester (HODE), glycated LDL (gLDL), or native LDL (nLDL) as control, in the presence or absence of LXR or PPAR-gamma agonists. We found that LAL activity and expression were significantly down regulated by oxLDL and HODE in EC, and by gLDL in SMC. The LXR agonist T0901317 reversed the decreased LAL expression in modified LDL- or HODE-exposed EC (P < 0.001) and in gLDL-exposed SMC, whereas PPAR-gamma agonist rosiglitazone induced a low effect only in EC. In conclusion, modified LDL down regulates LAL expression in human EC and SMC by a process involving the LXR signaling pathway. This is the first demonstration that modified LDL modulate LAL expression, in a cell specific manner.

Parahydrogen-induced polarization (PHIP) hyperpolarized MR receptor imaging in vivo: a pilot study of 13C imaging of atheroma in mice

MR techniques using hyperpolarized (13)C have successfully produced examples of angiography and intermediary metabolic imaging, but, to date, no receptor imaging has been attempted. The goal of this study was to synthesize and evaluate a novel hyperpolarizable molecule, 2,2,3,3-tetrafluoropropyl 1-(13)C-propionate-d(2,3,3) (TFPP), for the detection of atheromatous plaques in vivo. TFPP binds to lipid bilayers and its use in hyperpolarized MR could prove to be a major step towards receptor imaging. The precursor, 2,2,3,3-tetrafluoropropyl 1-(13)C-acrylate-d(2,3,3) (TFPA), binds to 1,2-dimyristoylphosphatidylcholine lipid bilayers with a 1.6-ppm chemical shift in the (19)F MR spectrum. This molecule was designed to be hyperpolarized through the addition of parahydrogen to the (13)C-acrylate moiety by parahydrogen-induced polarization. TFPA was hyperpolarized to TFPP to an extent similar to that of the hydroxyethylacrylate to hydroxyethylpropionate transition: 17 ± 4% for TFPP versus 20% for hydroxyethylpropionate; T(1) relaxation times (45 ± 2 s versus 55 ± 2 s) were comparable and the hyperpolarized properties of TFPP were characterized. Hydroxyethylacrylate, like TFPA, has a chemical structure with an acrylate moiety, but does not contain the lipid-binding tetrafluoropropyl functional group. Hyperpolarized TFPP binds to the lipid bilayer, appearing as a second, chemically shifted (13)C hyperpolarized MR signal with a further reduction in the longitudinal relaxation time (T(1) = 21 ± 1 s). In aortas harvested from low-density lipoprotein receptor knock-out mice fed with a high-fat diet for 9 months, and in which atheroma is deposited in the aorta and heart, TFPP showed greater binding to lipid on the intimal surface than in control mice fed a normal diet. When TFPP was hyperpolarized and administered in vivo to atheromatous mice in a pilot study, increased binding was observed on the endocardial surface of the intact heart compared with normally fed controls. Hyperpolarized TFPP has bio-sensing specificity for lipid, coupled with a 42,000-fold sensitivity gain in the MR signal at 4.7 T. Binding of TFPP with lipids results in the formation of a characteristic second peak in MRS. TFPP therefore has the potential to act as an in vivo molecular probe for atheromatous plaque imaging and may serve as a model of receptor-targeted bio-imaging with enhanced MR sensitivity.

Inflammation and the development of atherosclerosis

Atherosclerosis is a progressive disease causally associated with multiple cardiovascular risk factors, including dyslipidemia. Without effective intervention, atherosclerosis becomes evidenced clinically as coronary artery and cerebrovascular disease, both of which remain the leading causes of death worldwide. Multiple lines of investigation indicate a central role for inflammation in atherosclerotic plaque progression, vulnerability and thrombogenicity. Randomized clinical trials have documented the benefit of lipid-lowering therapy for both primary and secondary prevention of cardiovascular events. Statins, a class of drugs that lower cholesterol levels by inhibiting 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, have been shown to slow the progression of the atheroma and the frequency of associated clinical events to an extent that cannot be attributed solely to LDL reduction. The non-LDL or pleiotropic effects of statins are attributed to anti-inflammatory activity, enhanced endothelial function, and inhibition of oxidative stress. In this review, we discuss the role of inflammation in atherogenesis along with the effects of statins in slowing this process through LDL-dependent and -independent mechanisms.

Lowbush blueberries inhibit scavenger receptors CD36 and SR-A expression and attenuate foam cell formation in ApoE-deficient mice

Blueberries have recently been reported to reduce atherosclerotic lesion progression in apoE deficient (apoE(-/-)) mice. However, the underlying mechanisms are not fully understood. The objective of this study was to determine whether lowbush blueberries altered scavenger receptor expression and foam cell formation in apoE(-/-) mice. ApoE(-/-) mice were fed AIN-93 diet (CD) or CD formulated to contain 1% freeze-dried lowbush blueberries (BB) for 20 weeks. Gene expression and protein levels of scavenger receptor CD36 and SR-A in aorta and thioglycollate-elicited peritoneal macrophages (PM) were lower in mice fed BB (P < 0.05). In the second experiment, apoE(-/-) mice were fed CD or BB for 5 weeks. PM were collected and cultured. Gene expression and protein levels of CD36 and SR-A were found to be lower in PM of BB fed mice (P < 0.05). In PM from BB fed mice, fewer oxLDL-induced foam cells were formed compared to those from mice fed CD. Gene expression and protein levels of PPARγ were lower in the PM of BB fed mice (P < 0.05). Detectable isomers of hydroxyoctadecadienoic acids (HODEs) and hydroxyeicosatetraenoic acid (HETEs) were also lower in the PM of BB fed mice (P < 0.05 or P < 0.01). In conclusion, BB inhibited expression of the two major scavenger receptors CD36 and SR-A in PM of apoE(-/-) mice, at least in part through down-regulating PPARγ and reducing its endogenous ligands HODEs and HETEs. We proposed that BB mediated reduction of scavenger receptor expression and attenuation of oxLDL-induced foam cell formation in PM of apoE(-/-) mice are important mechanisms of the athero-protective effects of BB.

Effect of exposure of human monocyte-derived macrophages to high, versus normal, glucose on subsequent lipid accumulation from glycated and acetylated low-density lipoproteins

During atherosclerosis monocyte-derived macrophages accumulate cholesteryl esters from low-density lipoproteins (LDLs) via lectin-like oxidised LDL receptor-1 (LOX-1) and class AI and AII (SR-AI, SR-AII) and class B (SR-BI, CD36) scavenger receptors. Here we examined the hypothesis that hyperglycaemia may modulate receptor expression and hence lipid accumulation in macrophages. Human monocytes were matured into macrophages in 30 versus 5 mM glucose and receptor expression and lipid accumulation quantified. High glucose elevated LOX1 mRNA, but decreased SR-AI, SR-BI, LDLR, and CD36 mRNA. SR-BI and CD36 protein levels were decreased. Normo- and hyperglycaemic cells accumulated cholesteryl esters from modified LDL to a greater extent than control LDL, but total and individual cholesteryl ester accumulation was not affected by glucose levels. It is concluded that, whilst macrophage scavenger receptor mRNA and protein levels can be modulated by high glucose, these are not key factors in lipid accumulation by human macrophages under the conditions examined.

Ultrastructural features of human atherosclerosis

Healthy human arteries are composed of three layers: the intima, the media, and the adventitia. Endothelial cells, which form the tunica intima, provide the physical interface between blood and surrounding tissue, regulate nutrient and blood component traffic, and participate in many physiologic events, such as hemostasis, inflammation, and angiogenesis. Within the tunica media, smooth muscle cells and extracellular matrix proteins, such as elastin, collagen, and proteoglycans, are quantitatively the largest components of the aortic vascular wall. The structural changes with atherosclerosis are currently considered degenerative phenomena, which primarily involve a sequence of reactions within the intima and include monocyte recruitment and macrophage formation, lipid deposition, smooth muscle cell migration, proliferation, and extracellular matrix synthesis. The molecular and cellular mechanisms underlying the disease cascade have been thoroughly investigated in experimental animals and cell culture, but the question of how these models can correctly mimic the human course of the disease remains open to debate. In the present review the basic structure of healthy human arteries and the pathological events occurring during the atherosclerotic process have been examined by both transmission and scanning electron microscopy. Human atherosclerotic lesions are presented and described in the following order: initial lesions, fatty dots and streaks, intermediate lesions, atheroma and fibrofatty plaques, and complicated lesions.

Increased plasma CXCL16 levels in patients with chronic kidney diseases

BACKGROUND

C-X-C chemokine ligand 16 (CXCL16) is a scavenger receptor for oxidized low-density lipoprotein that has been shown to promote atherogenic effects in vivo and to predict the long-term mortality in acute coronary syndrome. We conducted a cross-sectional study to test the hypothesis that elevated CXCL16 concentrations are associated with the change in renal function in patients with chronic kidney disease (CKD) at different stages of disease.

MATERIALS AND METHODS

Two hundred and forty subjects including 200 patients with CKD (146 CKD from outpatients and 54 CKD with long-term haemodialysis) and 40 normal control subjects were recruited into this study. All CKD subjects underwent echocardiograms to assess left ventricular mass index. Plasma levels of CXCL16 and other relevant clinical and biochemical parameters in all subjects were obtained upon standard clinical examinations.

RESULTS

Plasma CXCL16 levels were significantly increased with the development of CKD from early- and end-stage (P < 0·001 for trend) and significantly higher in CKD subjects than those of normal subjects (P<0·001). Furthermore, plasma CXCL16 levels in CKD patients with type 2 diabetes mellitus (DM) were higher than those of CKD patients without DM. Multiple stepwise regression analyses indicated that plasma CXCL16 levels were independently associated with estimated glomerular filtration rate, C-reactive protein and adiponectin (all P<0·05).

CONCLUSIONS

Plasma CXCL16 levels are significantly increased with the development of early- to end-stage CKD and are independently associated with the change in renal function. Elucidating the role of CXCL16 as a biomarker or disease modifier in CKD progression requires further study.

Hexarelin Signaling to PPARgamma in Metabolic Diseases

Investigating the metabolic functions of the nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ) has been extremely rewarding over the past years. Uncovering the biologic roles of PPARγ and its mechanism of action has greatly advanced our understanding of the transcriptional control of lipid and glucose metabolism, and compounds such as thiazolidinediones which directly regulate PPARγ have proven to exhibit potent insulin-sensitizer effects in the treatment of diabetes. We review here recent advances on the emerging role of growth hormone releasing peptides in regulating PPARγ through interaction with scavenger receptor CD36 and ghrelin GHS-R1a receptor. With the impact that these peptides exert on the metabolic pathways involved in lipid metabolism and energy homeostasis, it is hoped that the development of novel approaches in the regulation of PPAR functions will bring additional therapeutic possibilities to face problems related to metabolic diseases.

A novel function of apolipoprotein E: upregulation of ATP-binding cassette transporter A1 expression

Despite the well known importance of apolipoprotein (Apo) E in cholesterol efflux, the effect of ApoE on the expression of ATP-binding cassette transporter A1 (ABCA1) has never been investigated. The objective of this study was to determine the effect of ApoE on ApoB-carrying lipoprotein-induced expression of ABCA1, a protein that mediates cholesterol efflux. Our data demonstrate that ApoB-carrying lipoproteins obtained from both wild-type and ApoE knockout mice induced ApoAI-mediated cholesterol efflux in mouse macrophages, which was associated with an enhanced ABCA1 promoter activity, and an increased ABCA1 mRNA and protein expression. In addition, these lipoproteins increased the level of phosphorylated specificity protein 1 (Sp1) and the amount of Sp1 bound to the ABCA1 promoter. However, all these inductions were significantly diminished in cells treated with ApoE-free lipoproteins, when compared to those treated with wild-type lipoproteins. Enrichment with human ApoE3 reversed the reduced inducibility of ApoE-free lipoproteins. Moreover, we observed that inhibition of Sp1 DNA-binding by mithramycin A diminished ABCA1 expression and ApoAI-mediated cholesterol efflux induced by ApoB-carrying lipoproteins, and that mutation of the Sp1-binding motif in the ABCA1 promoter region diminished ApoB-carrying lipoprotein-induced ABCA1 promoter activity. Collectively, these data suggest that ApoE associated with ApoB-carrying lipoproteins has an upregulatory role on ABCA1 expression, and that induction of Sp1 phosphorylation is a mechanism by which ApoE upregulates ABCA1 expression.