Oxidized Lipid-Driven Chemokine Receptor Switch, CCR2 to CX3CR1, Mediates Adhesion of Human Macrophages to Coronary Artery Smooth Muscle Cells Through a Peroxisome Proliferator-Activated Receptor γ–Dependent Pathway

Mechanistic insights into the anti-restenotic effects of HSP27 and HO1 modulated by reconstituted HDL on neointimal hyperplasia

High-density lipoprotein (HDL) therapy has demonstrated beneficial effects in acute stroke and acute myocardial infarction models by reducing infarct size. In this study, we investigated the inhibitory effects of reconstituted HDL (rHDL) on neointimal hyperplasia and elucidated its underlying mechanism using a balloon injury rat model. Our finding revealed a significant 37% reduction in the intima to media ratio in the arteries treated with 80 mg/kg rHDL compared to those subjected to injury alone (p < 0.05), indicating a specific inhibition of neointimal hyperplasia. In vivo analysis further supported the positive effects of rHDL by demonstrating a reduction in smooth muscle cell (SMC) proliferation and an increase in endothelial cell (EC) proliferation. Additionally, rHDL treatment led to decreased infiltration of leukocytes and downregulated the expression of matrix metallopeptidase 9 (MMP9) in the neointimal area. Notably, rHDL administration resulted in decreased expression of VCAM1 and HIF1α, alongside increased expression of heme oxygenase 1 (HO1) and heat shock protein 27 (HSP27). Overexpression of HSP27 and HO1 effectively inhibited SMC proliferation. Moreover, rHDL-mediated suppression of injury-induced HIF1α coincided with upregulation of HSP27. Interestingly, HSP27 and HO1 had varying effects on the expression of chemokine receptors and rHDL did not exert significant effect on chemokine receptor expression in THP1 cells. These findings underscore the distinct roles of HSP27 and HO1 as potential regulatory factors in the progression of restenosis. Collectively, our study demonstrates that rHDL exerts a potent anti-neointimal hyperplasia effect by reducing leukocytes infiltration and SMC proliferation while promoting EC proliferation.

The Problem of Wound Healing in Diabetes—From Molecular Pathways to the Design of an Animal Model

Chronic wounds are becoming an increasingly common clinical problem due to an aging population and an increased incidence of diabetes, atherosclerosis, and venous insufficiency, which are the conditions that impair and delay the healing process. Patients with diabetes constitute a group of subjects in whom the healing process is particularly prolonged regardless of its initial etiology. Circulatory dysfunction, both at the microvascular and macrovascular levels, is a leading factor in delaying or precluding wound healing in diabetes. The prolonged period of wound healing increases the risk of complications such as the development of infection, including sepsis and even amputation. Currently, many substances applied topically or systemically are supposed to accelerate the process of wound regeneration and finally wound closure. The role of clinical trials and preclinical studies, including research based on animal models, is to create safe medicinal products and ensure the fastest possible healing. To achieve this goal and minimize the wide-ranging burdens associated with conducting clinical trials, a correct animal model is needed to replicate the wound conditions in patients with diabetes as closely as possible. The aim of the paper is to summarize the most important molecular pathways which are impaired in the hyperglycemic state in the context of designing an animal model of diabetic chronic wounds. The authors focus on research optimization, including economic aspects and model reproducibility, as well as the ethical dimension of minimizing the suffering of research subjects according to the 3 Rs principle (Replacement, Reduction, Refinement).

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

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

ApoA-I mimetics reduce systemic and gut inflammation in chronic treated HIV

Novel therapeutic strategies are needed to attenuate increased systemic and gut inflammation that contribute to morbidity and mortality in chronic HIV infection despite potent antiretroviral therapy (ART). The goal of this study is to use preclinical models of chronic treated HIV to determine whether the antioxidant and anti-inflammatory apoA-I mimetic peptides 6F and 4F attenuate systemic and gut inflammation in chronic HIV. We used two humanized murine models of HIV infection and gut explants from 10 uninfected and 10 HIV infected persons on potent ART, to determine the in vivo and ex vivo impact of apoA-I mimetics on systemic and intestinal inflammation in HIV. When compared to HIV infected humanized mice treated with ART alone, mice on oral apoA-I mimetic peptide 6F with ART had consistently reduced plasma and gut tissue cytokines (TNF-α, IL-6) and chemokines (CX3CL1) that are products of ADAM17 sheddase activity. Oral 6F attenuated gut protein levels of ADAM17 that were increased in HIV-1 infected mice on potent ART compared to uninfected mice. Adding oxidized lipoproteins and endotoxin (LPS) ex vivo to gut explants from HIV infected persons increased levels of ADAM17 in myeloid and intestinal cells, which increased TNF-α and CX3CL1. Both 4F and 6F attenuated these changes. Our preclinical data suggest that apoA-I mimetic peptides provide a novel therapeutic strategy that can target increased protein levels of ADAM17 and its sheddase activity that contribute to intestinal and systemic inflammation in treated HIV. The large repertoire of inflammatory mediators involved in ADAM17 sheddase activity places it as a pivotal orchestrator of several inflammatory pathways associated with morbidity in chronic treated HIV that make it an attractive therapeutic target.

Macrophage-Mediated Immune Responses: From Fatty Acids to Oxylipins

Macrophages have diverse functions in the pathogenesis, resolution, and repair of inflammatory processes. Elegant studies have elucidated the metabolomic and transcriptomic profiles of activated macrophages. However, the versatility of macrophage responses in inflammation is likely due, at least in part, to their ability to rearrange their repertoire of bioactive lipids, including fatty acids and oxylipins. This review will describe the fatty acids and oxylipins generated by macrophages and their role in type 1 and type 2 immune responses. We will highlight lipidomic studies that have shaped the current understanding of the role of lipids in macrophage polarization.

Electronic and Tobacco Cigarettes Alter Polyunsaturated Fatty Acids and Oxidative Biomarkers

[Figure: see text].

Non-alcoholic fatty liver disease: a metabolic burden promoting atherosclerosis

Non-alcoholic fatty liver disease (NAFLD) has become the fastest growing chronic liver disease, with a prevalence of up to 25% worldwide. Individuals with NAFLD have a high risk of disease progression to cirrhosis, hepatocellular carcinoma (HCC), and liver failure. With the exception of intrahepatic burden, cardiovascular disease (CVD) and especially atherosclerosis (AS) are common complications of NAFLD. Furthermore, CVD is a major cause of death in NAFLD patients. Additionally, AS is a metabolic disorder highly associated with NAFLD, and individual NAFLD pathologies can greatly increase the risk of AS. It is increasingly clear that AS-associated endothelial cell damage, inflammatory cell activation, and smooth muscle cell proliferation are extensively impacted by NAFLD-induced systematic dyslipidemia, inflammation, oxidative stress, the production of hepatokines, and coagulations. In clinical trials, drug candidates for NAFLD management have displayed promising effects for the treatment of AS. In this review, we summarize the key molecular events and cellular factors contributing to the metabolic burden induced by NAFLD on AS, and discuss therapeutic strategies for the improvement of AS in individuals with NAFLD.

The surrounding tissue contributes to smooth muscle cells’ regeneration and vascularization of small diameter vascular grafts

The surrounding tissue contributes to smooth muscle cells’ regeneration and vascularization in the vascular regeneration process.

Circulating low density lipoprotein (LDL)

Low-density lipoprotein (LDL) particles are known as atherogenic agents in coronary artery diseases. They modify to other electronegative forms and may be the subject for improvement of inflammatory events in vessel subendothelial spaces. The circulating LDL value is associated with the plasma PCSK-9 level. They internalize into macrophages using the lysosomal receptor-mediated pathways. LDL uptake is related to the membrane scavenger receptors, modifications of lipid and protein components of LDL particles, vesicular maturation and lipid stores of cells. Furthermore, LDL vesicular trafficking is involved with the function of some proteins such as Rab and Lamp families. These proteins also help in the transportation of free cholesterol from lysosome into the cytosol. The aggregation of lipids in the cytosol is a starting point for the formation of foam cells so that they may participate in the primary core of atherosclerosis plaques. The effects of macrophage subclasses are different in the formation and remodeling of plaques. This review is focused on the cellular and molecular events involved in cholesterol homeostasis.

Human Gingiva-Derived Mesenchymal Stem Cells Modulate Monocytes/Macrophages and Alleviate Atherosclerosis

Atherosclerosis is the major cause of cardiovascular diseases. Current evidences indicate that inflammation is involved in the pathogenesis of atherosclerosis. Human gingiva-derived mesenchymal stem cells (GMSC) have shown anti-inflammatory and immunomodulatory effects on autoimmune and inflammatory diseases. However, the function of GMSC in controlling atherosclerosis is far from clear. The present study is aimed to elucidate the role of GMSC in atherosclerosis, examining the inhibition of GMSC on macrophage foam cell formation, and further determining whether GMSC could affect the polarization and activation of macrophages under different conditions. The results show that infusion of GMSC to AopE^−/− mice significantly reduced the frequency of inflammatory monocytes/macrophages and decreased the plaque size and lipid deposition. Additionally, GMSC treatment markedly inhibited macrophage foam cell formation and reduced inflammatory macrophage activation, converting inflammatory macrophages to anti-inflammatory macrophages in vitro. Thus, our study has revealed a significant role of GMSC on modulating inflammatory monocytes/macrophages and alleviating atherosclerosis.

The homozygous CX3CR1-M280 mutation impairs human monocyte survival

Several reports have demonstrated that mouse Cx3cr1 signaling promotes monocyte/macrophage survival. In agreement, we previously found that, in a mouse model of systemic candidiasis, genetic deficiency of Cx3cr1 resulted in increased mortality and impaired tissue fungal clearance associated with decreased macrophage survival. We translated this finding by showing that the dysfunctional CX3CR1 variant CX3CR1-M280 was associated with increased risk and worse outcome of human systemic candidiasis. However, the impact of this mutation on human monocyte/macrophage survival is poorly understood. Herein, we hypothesized that CX3CR1-M280 impairs human monocyte survival. We identified WT (CX3CR1-WT/WT), CX3CR1-WT/M280 heterozygous, and CX3CR1-M280/M280 homozygous healthy donors of European descent, and we show that CX3CL1 rescues serum starvation-induced cell death in CX3CR1-WT/WT and CX3CR1-WT/M280 but not in CX3CR1-M280/M280 monocytes. CX3CL1-induced survival of CX3CR1-WT/WT monocytes is mediated via AKT and ERK activation, which are both impaired in CX3CR1-M280/M280 monocytes, associated with decreased blood monocyte counts in CX3CR1-M280/M280 donors at steady state. Instead, CX3CR1-M280/M280 does not affect monocyte CX3CR1 surface expression or innate immune effector functions. Together, we show that homozygocity of the M280 polymorphism in CX3CR1 is a potentially novel population-based genetic factor that influences human monocyte signaling.

Transcriptional control of microglia phenotypes in health and disease

Microglia are the main resident macrophage population of the CNS and perform numerous functions required for CNS development, homeostasis, immunity, and repair. Many lines of evidence also indicate that dysregulation of microglia contributes to the pathogenesis of neurodegenerative and behavioral diseases. These observations provide a compelling argument to more clearly define the mechanisms that control microglia identity and function in health and disease. In this Review, we present a conceptual framework for how different classes of transcription factors interact to select and activate regulatory elements that control microglia development and their responses to internal and external signals. We then describe functions of specific transcription factors in normal and pathological contexts and conclude with a consideration of open questions to be addressed in the future.

Cooperation of Gastric Mononuclear Phagocytes with Helicobacter pylori during Colonization

Helicobacter pylori, the dominant member of the human gastric microbiota, elicits immunoregulatory responses implicated in protective versus pathological outcomes. To evaluate the role of macrophages during infection, we employed a system with a shifted proinflammatory macrophage phenotype by deleting PPARγ in myeloid cells and found a 5- to 10-fold decrease in gastric bacterial loads. Higher levels of colonization in wild-type mice were associated with increased presence of mononuclear phagocytes and in particular with the accumulation of CD11b+F4/80hiCD64+CX3CR1+ macrophages in the gastric lamina propria. Depletion of phagocytic cells by clodronate liposomes in wild-type mice resulted in a reduction of gastric H. pylori colonization compared with nontreated mice. PPARγ-deficient and macrophage-depleted mice presented decreased IL-10-mediated myeloid and T cell regulatory responses soon after infection. IL-10 neutralization during H. pylori infection led to increased IL-17-mediated responses and increased neutrophil accumulation at the gastric mucosa. In conclusion, we report the induction of IL-10-driven regulatory responses mediated by CD11b+F4/80hiCD64+CX3CR1+ mononuclear phagocytes that contribute to maintaining high levels of H. pylori loads in the stomach by modulating effector T cell responses at the gastric mucosa.

Leukocyte Trafficking in Cardiovascular Disease: Insights from Experimental Models

Chemokine-induced leukocyte migration into the vessel wall is an early pathological event in the progression of atherosclerosis, the underlying cause of myocardial infarction. The immune-inflammatory response, mediated by both the innate and adaptive immune cells, is involved in the initiation, recruitment, and resolution phases of cardiovascular disease progression. Activation of leukocytes via inflammatory mediators such as chemokines, cytokines, and adhesion molecules is instrumental in these processes. In this review, we highlight leukocyte activation with the main focus being on the mechanisms of chemokine-mediated recruitment in atherosclerosis and the response postmyocardial infarction with key examples from experimental models of cardiovascular inflammation.

Effects of dyslipidaemia on monocyte production and function in cardiovascular disease

Monocytes are heterogeneous effector cells involved in the maintenance and restoration of tissue integrity. Monocytes and macrophages are involved in cardiovascular disease progression, and are associated with the development of unstable atherosclerotic plaques. Hyperlipidaemia can accelerate cardiovascular disease progression. However, monocyte responses to hyperlipidaemia are poorly understood. In the past decade, accumulating data describe the relationship between the dynamic blood lipid environment and the heterogeneous circulating monocyte pool, which might have profound consequences for cardiovascular disease. In this Review, we explore the updated view of monocytes in cardiovascular disease and their relationship with macrophages in promoting the homeostatic and inflammatory responses related to atherosclerosis. We describe the different definitions of dyslipidaemia, highlight current theories on the ontogeny of monocyte heterogeneity, discuss how dyslipidaemia might alter monocyte production, and explore the mechanistic interface linking dyslipidaemia with monocyte effector functions, such as migration and the inflammatory response. Finally, we discuss the role of dietary and endogenous lipid species in mediating dyslipidaemic responses, and the role of these lipids in promoting the risk of cardiovascular disease through modulation of monocyte behaviour.

Macrophages and RhoA Pathway in Transplanted Organs

RhoA is a small GTPase that, via its downstream effectors, regulates a variety of cell functions such as cytokinesis, cell migration, vesicular trafficking, and phagocytosis. As such the RhoA pathway is also pivotal for proper functioning of immune cells including macrophages. By controlling actin cytoskeleton organization, RhoA pathway modulates macrophage's polarity and basic functions: phagocytosis, migration, and extracellular matrix degradation. Numerous studies indicate that macrophages are very important effectors contributing to acute and chronic rejection of transplanted organs. In this review we discuss the role of RhoA pathway in governance of macrophage's functions in terms of transplanted organs.

Macrophage PPARγ inhibits Gpr132 to mediate the anti-tumor effects of rosiglitazone

Tumor-associated macrophage (TAM) significantly contributes to cancer progression. Human cancer is enhanced by PPARγ loss-of-function mutations, but inhibited by PPARγ agonists such as TZD diabetes drugs including rosiglitazone. However, it remains enigmatic whether and how macrophage contributes to PPARγ tumor-suppressive functions. Here we report that macrophage PPARγ deletion in mice not only exacerbates mammary tumor development but also impairs the anti-tumor effects of rosiglitazone. Mechanistically, we identify Gpr132 as a novel direct PPARγ target in macrophage whose expression is enhanced by PPARγ loss but repressed by PPARγ activation. Functionally, macrophage Gpr132 is pro-inflammatory and pro-tumor. Genetic Gpr132 deletion not only retards inflammation and cancer growth but also abrogates the anti-tumor effects of PPARγ and rosiglitazone. Pharmacological Gpr132 inhibition significantly impedes mammary tumor malignancy. These findings uncover macrophage PPARγ and Gpr132 as critical TAM modulators, new cancer therapeutic targets, and essential mediators of TZD anti-cancer effects.

DOI:http://dx.doi.org/10.7554/eLife.18501.001

The immune system can both contribute to cancer progression and restrain the growth of tumors. Some immune cells – called macrophages – create an inflammatory environment around a tumor, which can support the spread of the cancer cells.

Independent observations and experiments have shown that a protein called PPARγ can suppress the development and growth of tumors. Drugs called thiazolidinediones (or TZDs for short), which are normally used to treat type 2 diabetes, activate PPARγ and therefore have anti-tumor effects. However, it is not fully understood how PPARγ and TZDs suppress tumor development.

Cheng et al. hypothesized that the PPARγ protein and TZDs can inhibit the activity of the inflammatory macrophages that help tumors to develop. To test this, mice were genetically engineered so that their macrophages could not produce the PPARγ protein. These engineered mice were more likely to develop breast cancer than normal. Furthermore, the breast tumors in the modified mice did not shrink when they were treated with TZDs, whereas the tumors of normal mice did.

Cheng et al. also found that PPARγ inhibits the ability of macrophages to produce a protein called Gpr132, which itself contributes to inflammation and allows breast cancer cells to grow. Mice that were unable to produce Grp132 displayed less inflammation, and cancer growth was blocked. Drugs that inhibited the activity of Grp132 in normal mice also reduced the ability of breast tumors to spread.

Future experiments will need to examine exactly how the Gpr132 proteins produced by macrophages communicate with the cancer cells. Furthermore, developing new drugs that can inhibit Gpr132 could ultimately lead to more effective treatments for cancer.

DOI:http://dx.doi.org/10.7554/eLife.18501.002

Macrophage/monocyte-specific deletion of Ras homolog gene family member A (RhoA) downregulates fractalkine receptor and inhibits chronic rejection of mouse cardiac allografts

BACKGROUND

The cellular and molecular mechanisms of chronic rejection of transplanted organs remain obscure; however, macrophages are known to play a critical role in the injury and repair of allografts. Among multiple factors influencing macrophage infiltration to allografts, the fractalkine chemokine (C-X3-C motif) ligand 1(CX3CL1)/chemokine (C-X3-C motif) receptor 1 (CX3CR1) signaling pathway and actin cytoskeleton, which is regulated by a small guanosine-5׳-triphosphatase Ras homolog gene family member A (RhoA), are of the utmost importance. To define the role of macrophage/RhoA pathway involvement in chronic rejection, we generated mice with monocyte/macrophage-specific deletion of RhoA.

METHODS

Hearts from BALB/c (H-2d) donors were transplanted into RhoA^flox/flox (no Cre) and heterozygous Lyz2^Cre+/-RhoA^flox/flox recipients treated with cytotoxic T-lymphocyte-associated protein 4 immunoglobulin to inhibit early T-cell response. Allografts were assessed for chronic rejection and monocyte/macrophage functions.

RESULTS

The deletion of RhoA inhibited macrophage infiltration, neointimal hyperplasia of vasculature, and abrogated chronic rejection of the allografts. The RhoA deletion downregulated G protein-coupled fractalkine receptor CX3CR1, which activates the RhoA pathway and controls monocyte/macrophage trafficking into the vascular endothelium. This in turn promotes, through overproliferation and differentiation of smooth muscle cells in the arterial walls, neointimal hyperplasia.

CONCLUSIONS

Our finding of codependence of chronic rejection on monocyte/macrophage CX3CR1/CX3CL1 and RhoA signaling pathways may lead to the development of novel anti-chronic rejection therapies.

PER1 prevents excessive innate immune response during endotoxin-induced liver injury through regulation of macrophage recruitment in mice

The severity of acute liver failure (ALF) induced by bacterial lipopolysaccharide (LPS) is associated with the hepatic innate immune response. The core circadian molecular clock modulates the innate immune response by controlling rhythmic pathogen recognition by the innate immune system and daily variations in cytokine gene expression. However, the molecular link between circadian genes and the innate immune system has remained unclear. Here, we showed that mice lacking the clock gene Per1 (Period1) are more susceptible to LPS/d-galactosamine (LPS/GalN)-induced macrophage-dependent ALF compared with wild-type (WT) mice. Per1 deletion caused a remarkable increase in the number of Kupffer cells (KCs) in the liver, resulting in an elevation of the levels of pro-inflammatory cytokines after LPS treatment. Loss of Per1 had no effect on the proliferation or apoptosis of macrophages; however, it enhanced the recruitment of macrophages, which was associated with an increase in CC chemokine receptor 2 (Ccr2) expression levels in monocytes/macrophages. Deletion of Ccr2 rescued d-GalN/LPS-induced liver injury in Per1^−/− mice. We demonstrated that the upregulation of Ccr2 expression by Per1 deletion could be reversed by the synthetic peroxisome proliferator-activated receptor gamma (PPAR-γ) antagonist GW9662. Further analysis indicated that PER1 binds to PPAR-γ on the Ccr2 promoter and enhanced the inhibitory effect of PPAR-γ on Ccr2 expression. These results reveal that Per1 reduces hepatic macrophage recruitment through interaction with PPAR-γ and prevents an excessive innate immune response in endotoxin-induced liver injury.

Genomewide effects of peroxisome proliferator-activated receptor gamma in macrophages and dendritic cells--revealing complexity through systems biology

BACKGROUND

Systems biology approaches have become indispensable tools in biomedical and basic research. These data integrating bioinformatic methods gained prominence after high-throughput technologies became available to investigate complex cellular processes, such as transcriptional regulation and protein-protein interactions, on a scale that had not been studied before. Immunology is one of the medical fields that systems biology impacted profoundly due to the plasticity of cell types involved and the accessibility of a wide range of experimental models.

MATERIALS AND METHODS

In this review, we summarize the most important recent genomewide studies exploring the function of peroxisome proliferator-activated receptor γ in macrophages and dendritic cells. PPARγ ChIP-seq experiments were performed in adipocytes derived from embryonic stem cells to complement the existing data sets and to provide comparators to macrophage data. Finally, lists of regulated genes generated from such experiments were analysed with bioinformatics and system biology approaches.

RESULTS

We show that genomewide studies utilizing high-throughput data acquisition methods made it possible to gain deeper insights into the role of PPARγ in these immune cell types. We also demonstrate that analysis and visualization of data using network-based approaches can be used to identify novel genes and functions regulated by the receptor.

CONCLUSIONS

The example of PPARγ in macrophages and dendritic cells highlights the crucial importance of systems biology approaches in establishing novel cellular functions for long-known signaling pathways.

CX3CL1-CX3CR1 Interaction Increases the Population of Ly6C(-)CX3CR1(hi) Macrophages Contributing to Unilateral Ureteral Obstruction-Induced Fibrosis

Chemokines modulate inflammatory responses that are prerequisites for kidney injury. The specific role of monocyte-associated CX3CR1 and its cognate ligand CX3CL1 in unilateral ureteral obstruction (UUO)-induced kidney injury remains unclear. In this study, we found that UUO caused a CCR2-dependent increase in numbers of Ly6C(hi) monocytes both in the blood and kidneys and of Ly6C(-)CX3CR1(+) macrophages in the obstructed kidneys of mice. Using CX3CR1(gfp/+) knockin mice, we observed a rapid conversion of infiltrating proinflammatory Ly6C(+)CX3CR1(1o) monocytes/macrophages to anti-inflammatory Ly6C(-)CX3CR1(hi) macrophages. CX3CR1 deficiency affected neither monocyte trafficking nor macrophage differentiation in vivo upon renal obstruction, but CX3CR1 expression in monocytes and macrophages was required for increases in fibrosis in the obstructed kidneys. Mechanistically, CX3CL1-CX3CR1 interaction increases Ly6C(-)CX3CR1(hi) macrophage survival within the obstructed kidneys. Therefore, CX3CL1 and CX3CR1 may represent attractive therapeutic targets in obstructive nephropathy.

CX3CR1-expressing inflammatory dendritic cells contribute to the progression of steatohepatitis

Liver monocytes play a major role in the development of NASH (non-alcoholic steatohepatitis). In inflamed tissues, monocytes can differentiate in both macrophages and dendritic cells. In the present study, we investigated the role of moDCs (monocyte-derived inflammatory dendritic cells) in experimental steatohepatitis induced in C57BL/6 mice by feeding on a MCD (methionine/choline-deficient) diet. The evolution of steatohepatitis was characterized by an increase in hepatic CD45+ / CD11b+ myeloid cells displaying the monocyte/macrophage marker F4-80(+). In the early phases (4 weeks of treatment), Ly6C(high)/CD11b(+)/F4-80(+) inflammatory macrophages predominated. However, their frequency did not grow further with the disease progression (8 weeks of treatment), when a 4-fold expansion of CD11b(+)/F4-80(+) cells featuring the fractalkine receptor (CX3CR1) was evident. These CX3CR1+ cells were also characterized by the combined expression of inflammatory monocyte (Ly6C, CD11b) and dendritic cell (CD11c, MHCII) markers as well as by a sustained TNFα (tumour necrosis factor α) production, suggesting monocyte differentiation into inflammatory moDCs. The expansion of TNFα-producing CX3CR1+ moDCs was associated with an elevation in hepatic and circulating TNFα level and with the worsening of parenchymal injury. Hydrogen sulfide (H2S) has been shown to interfere with CX3CR1 up-regulation in monocyte-derived cells exposed to pro-inflammatory stimuli. Treating 4-week-MCD-fed mice with the H2S donor NaHS while continuing on the same diet prevented the accumulation of TNFα-producing CX3CR1+ moDCs without interfering with hepatic macrophage functions. Furthermore, NaHS reduced hepatic and circulating TNFα levels and ameliorated transaminase release and parenchymal injury. Altogether, these results show that inflammatory CX3CR1+ moDCs contributed in sustaining inflammation and liver injury during steatohepatitis progression.

Elevated atherosclerosis-related gene expression, monocyte activation and microparticle-release are related to increased lipoprotein-associated oxidative stress in familial hypercholesterolemia

Objective

Animal and in vitro studies have suggested that hypercholesterolemia and increased oxidative stress predisposes to monocyte activation and enhanced accumulation of oxidized LDL cholesterol (oxLDL-C) through a CD36-dependent mechanism. The aim of this study was to investigate the hypothesis that elevated oxLDL-C induce proinflammatory monocytes and increased release of monocyte-derived microparticles (MMPs), as well as up-regulation of CD36, chemokine receptors and proinflammatory factors through CD36-dependent pathways and that this is associated with accelerated atherosclerosis in subjects with heterozygous familial hypercholesterolemia (FH), in particular in the presence of Achilles tendon xanthomas (ATX).

Approach and Results

We studied thirty FH subjects with and without ATX and twenty-three healthy control subjects. Intima-media thickness (IMT) and Achilles tendon (AT) thickness were measured by ultrasonography. Monocyte classification and MMP analysis were performed by flow cytometry. Monocyte expression of genes involved in atherosclerosis was determined by quantitative PCR. IMT and oxLDL-C were increased in FH subjects, especially in the presence of ATX. In addition, FH subjects had elevated proportions of intermediate CD14++CD16+ monocytes and higher circulating MMP levels. Stepwise linear regression identified oxLDL-C, gender and intermediate monocytes as predictors of MMPs. Monocyte expression of pro-atherogenic and pro-inflammatory genes regulated by oxLDL-C-CD36 interaction was increased in FH, especially in ATX+ subjects. Monocyte chemokine receptor CX₃CR1 was identified as an independent contributor to IMT.

Conclusions

Our data support that lipoprotein-associated oxidative stress is involved in accelerated atherosclerosis in FH, particularly in the presence of ATX, by inducing pro-inflammatory monocytes and increased release of MMPs along with elevated monocyte expression of oxLDL-C-induced atherosclerosis-related genes.

Chemokine receptors CXCR2 and CX3CR1 differentially regulate functional responses of bone-marrow endothelial progenitors during atherosclerotic plaque regression

AIMS

Atherosclerosis manifests itself as arterial plaques, which lead to heart attacks or stroke. Treatments supporting plaque regression are therefore aggressively pursued. Studies conducted in models in which hypercholesterolaemia is reversible, such as the Reversa mouse model we have employed in the current studies, will be instrumental for the development of such interventions. Using this model, we have shown that advanced atherosclerosis regression occurs when lipid lowering is used in combination with bone-marrow endothelial progenitor cell (EPC) treatment. However, it remains unclear how EPCs home to regressing plaques and how they augment atherosclerosis reversal. Here we identify molecules that support functional responses of EPCs during plaque resolution.

METHODS AND RESULTS

Chemokines CXCL1 and CX3CL1 were detected in the vascular wall of atheroregressing Reversa mice, and their cognate receptors CXCR2 and CX3CR1 were observed on adoptively transferred EPCs in circulation. We tested whether CXCL1-CXCR2 and CX3CL1-CX3CR1 axes regulate functional responses of EPCs during plaque reversal. We show that pharmacological inhibition of CXCR2 or CX3CR1, or genetic inactivation of these two chemokine receptors interfered with EPC-mediated advanced atherosclerosis regression. We also demonstrate that CXCR2 directs EPCs to regressing plaques while CX3CR1 controls a paracrine function(s) of these cells.

CONCLUSION

CXCR2 and CX3CR1 differentially regulate EPC functional responses during atheroregression. Our study improves understanding of how chemokines and chemokine receptors regulate plaque resolution, which could determine the effectiveness of interventions reducing complications of atherosclerosis.

Critical Role of IP-10 on Reducing Experimental Corneal Neovascularization

AIM AND SCOPE

To address the role of interferon-induced protein of 10 kDa (IP-10) in the course of corneal neovascularization (CrNV) in a mouse model of experimental corneal neovascularization.

MATERIAL AND METHOD

BALB/c mice that were 7- to 8-week-old male were included in the study. Corneal injury was induced by NaOH. Mice were randomly divided into 2 groups of IP-10 and vehicle. The alkali-treated eyes received 5 μl of 5 μg/ml IP-10 dissolved in 0.2% sodium hyaluronate for IP-10-treated group, or 5 μl of 0.2% sodium hyaluronate for vehicle-treated group twice a day for 7 days immediately after the alkali injury. 2 weeks after alkali injury, corneas were removed and used for whole mount CD31 staining. The percentages of neovascularization on corneal photographs were examined with digital image analysis. In other experiments, at indicated time intervals, the corneas were removed. Angiogenic factor expression in the early phase after injury was quantified by real-time PCR and western blot. The VEGF expression in macrophages infiltrating into burned corneas was examined by Flow cytometry (FCM) and immunofluorescence. Tube formation and cell proliferation of human retinal endothelial cells (HRECs) were detected after being stimulated with IP-10 in vitro.

RESULTS

The mRNA and protein expression of IP-10 and C-X-C motif chemokine receptor 3 (CXCR3) was augmented after the alkali injury (p < 0.05). Compared with vehicle-treated mice, IP-10-treated mice exhibited reduced CrNV 2 weeks after injury, as evidenced by diminished CD31-positive areas (p < 0.05). Concomitantly, the intracorneal mRNA and protein expression enhancement of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) was lower in IP-10-treated mice than in vehicle-treated mice after injury (p < 0.05). Moreover, IP-10 inhibited HREC tube formation and proliferation in vitro.

CONCLUSION

IP-10-treated mice exhibited reduced alkali-induced CrNV through decreasing intracorneal VEGF and bFGF expression, and inhibiting endothelial cell proliferation and tube formation.

Oxidized lipids and lysophosphatidylcholine induce the chemotaxis, up-regulate the expression of CCR9 and CXCR4 and abrogate the release of IL-6 in human monocytes

Lipids through regulation of chronic inflammation play key roles in the development of various diseases. Here, we report that a mixed population of human primary monocytes migrated towards LPC, as well as oxidized linoleic acid isoforms 9-S-HODE, 9-R-HODE and 13-R-HODE. Incubation with 9-R-HODE, 13-R-HODE and LPC resulted in increased expression of CXCR4, the receptor for SDF-1α/CXCL12, correlated with increased monocyte migration towards SDF-1α/CXCL12. Further, we report increased expression of CCR9, the receptor for TECK/CCL25, after stimulation with these lipids. Upon examining the migratory response towards TECK/CCL25, it was observed that an increase in CCR9 expression upon pre-treatment with 9-S-HODE, 9-R-HODE, 13-R-HODE and LPC resulted in increased migration of monocytes expressing CCR9. Only LPC but not any other lipid examined increased the influx of intracellular Ca²⁺ in monocytes. Finally, 9-S-HODE, 9-R-HODE, 13-R-HODE, or LPC inhibited the release of IL-6 from monocytes suggesting that these lipids may play important role in controlling inflammatory responses.

Roles of the chemokine system in development of obesity, insulin resistance, and cardiovascular disease

The escalating epidemic of obesity has increased the incidence of obesity-induced complications to historically high levels. Adipose tissue is a dynamic energy depot, which stores energy and mobilizes it during nutrient deficiency. Excess nutrient intake resulting in adipose tissue expansion triggers lipid release and aberrant adipokine, cytokine and chemokine production, and signaling that ultimately lead to adipose tissue inflammation, a hallmark of obesity. This low-grade chronic inflammation is thought to link obesity to insulin resistance and the associated comorbidities of metabolic syndrome such as dyslipidemia and hypertension, which increase risk of type 2 diabetes and cardiovascular disease. In this review, we focus on and discuss members of the chemokine system for which there is clear evidence of participation in the development of obesity and obesity-induced pathologies.

Oxidative Low Density Lipoprotien Prohibited Plasmodium Falciparum Clearance in type 2 Diabetes Mellitus Via Cluster Differentiation 36

Background:

Cluster of differentiation 36 (CD36) is reported to function as a receptor of erythrocytes infected with Plasmodium falciparum (PF) and as an oxidized low-density lipoprotein (oxLDL).

Aim:

The aim of this study was to investigate the impact of CD36 in PF parasitized red blood cells in high concentration of oxLDL of T2 diabetes mellitus patients.

Material and Methods:

This cross-sectional study was conducted among diabetic patients. A total of 45 samples were collected from diabetic patients with more than 8% of HbA1c and more than 170 mg/dL of oxLDL.

Results:

The mean difference between CD36 negative and positive controls was found to be statistically significant (P ≤ 0.001). The mean difference between CD36 positive control and CD36 in diabetic patients with oxLDL ≥ 170 mg/dL also was statistically significant.

Conclusion:

High concentration of oxidative low density of lipoprotein more than 170 mg/dL leads to block CD36 receptor on infected red blood. This process believed to contribute in parasite survival by avoiding phagocytic clearance in the spleen.

PBMCs reflect the immune component of the WAT transcriptome--implications as biomarkers of metabolic health in the postprandial state

SCOPE

Food and nutrition studies often require accessing metabolically active tissues, including adipose tissue. This can involve invasive biopsy procedures that can be a limiting factor in study design. In contrast, peripheral blood mononuclear cells (PBMCs) are a population of circulating immune cells that are easily accessible through venipuncture. As transcriptomics is of growing importance in food and metabolism research, understanding the transcriptomic relationship between these tissue types can provide insight into the utility of PBMCs in this field.

METHODS AND RESULTS

We examine this relationship within eight subjects, in two postprandial states (following oral lipid tolerance test and oral glucose tolerance test). Multivariate analysis techniques were used to examine variation between tissues, samples, and subjects in order to define which genes havecommon/disparate expression profiles associated with highly defined metabolic phenotypes. We demonstrate global similarities in gene expression between PBMCs and white adipose tissue, irrespective of the metabolic challenge type. Closer examination of individual genes revealed this similarity to be strongest in pathways related to immune response/inflammation. Notably, the expression of metabolism-related nuclear receptors, including PPARs, LXR, etc. was discordant between tissues

CONCLUSION

The PBMC transcriptome may therefore provide a unique insight into the inflammatory component of metabolic health, as opposed to directly reflecting the metabolic component of the adipose tissue transcriptome.

The role of lipid-activated nuclear receptors in shaping macrophage and dendritic cell function: From physiology to pathology

Nuclear receptors are ligand-activated transcription factors linking lipid signaling to the expression of the genome. There is increasing appreciation of the involvement of this receptor network in the metabolic programming of macrophages and dendritic cells (DCs), essential members of the innate immune system. In this review we focus on the role of retinoid X receptor, retinoic acid receptor, peroxisome proliferator-associated receptor γ, liver X receptor, and vitamin D receptor in shaping the immune and metabolic functions of macrophages and DCs. We also provide an overview of the contribution of macrophage- and DC-expressed nuclear receptors to various immunopathologic conditions, such as rheumatoid arthritis, inflammatory bowel disease, systemic lupus erythematosus, asthma, and some others. We suggest that systematic analyses of the roles of these receptors and their activating lipid ligands in immunopathologies combined with complementary and focused translational and clinical research will be crucial for the development of new therapies using the many molecules available to target nuclear receptors.

The downstream regulation of chemokine receptor signalling: implications for atherosclerosis

Heterotrimeric G-protein-coupled receptors (GPCRs) are key mediators of intracellular signalling, control numerous physiological processes, and are one of the largest class of proteins to be pharmacologically targeted. Chemokine-induced macrophage recruitment into the vascular wall is an early pathological event in the progression of atherosclerosis. Leukocyte activation and chemotaxis during cell recruitment are mediated by chemokine ligation of multiple GPCRs. Regulation of GPCR signalling is critical in limiting vascular inflammation and involves interaction with downstream proteins such as GPCR kinases (GRKs), arrestin proteins and regulator of G-protein signalling (RGS) proteins. These have emerged as new mediators of atherogenesis by functioning in internalisation, desensitisation, and signal termination of chemokine receptors. Targeting chemokine signalling through these proteins may provide new strategies to alter atherosclerotic plaque formation and plaque biology.

Effect of S-aspirin, a novel hydrogen-sulfide-releasing aspirin (ACS14), on atherosclerosis in apoE-deficient mice

Hydrogen sulfide (H(2)S) is a novel gaseous mediator that plays important roles in atherosclerosis. The present study investigated the effect of a novel H(2)S-releasing aspirin, ACS14 (2-acetyloxybenzoic acid 4-(3-thioxo-3H-1,2-dithiol-5-yl)phenyl ester), on atherosclerotic plaques in fat-fed apoE(-/-) mice and the underlying mechanism with respect to CX3C chemokine receptor 1 (CX3CR1) in macrophages. Mouse macrophage cell line RAW264.7 or mouse peritoneal macrophages were preincubated with aspirin (50, 100 or 200μM), ACS14 (50, 100 or 200μM) or vehicle for 6h, and then stimulated with interferon (IFN)-γ (500U/ml) or lipopolysaccharide (LPS; 10μg/ml) for 12h. ACS14, but not aspirin, dose-dependently inhibited IFN-γ or LPS-induced CX3CR1 expression and CX3CR1-mediated chemotaxis in macrophages. The inhibitory effect of ACS14 on CX3CR1 expression was abolished by pretreatment with GW9662, a selective peroxisome proliferator-activated receptor (PPAR)-γ antagonist, suggesting that suppression of macrophage CX3CR1 expression by ACS14 is PPAR-γ dependent. Eight-week-old male apoE(-/-) mice received intraperitoneal ACS14 (15 or 30μmol/kg/day) or aspirin (15 or 30μmol/kg/day) 4 weeks after fat feeding. Twelve weeks after ACS14 or aspirin treatment, mice were sacrificed to evaluate the extent of atherosclerosis and CX3CR1 expression in brachiocephalic artery (BCA). We found that ACS14, but not aspirin, significantly downregulated CX3CR1 expression in atherosclerotic plaques. ACS14 considerably impeded the formation and development of atherosclerosis as compared to a molar equivalent dose of aspirin. These data indicate that ACS14 may prevent the progression of atherosclerosis by downregulating macrophage CX3CR1 expression via a PPAR-γ-dependent mechanism.

Hydrogen sulfide inhibits the development of atherosclerosis with suppressing CX3CR1 and CX3CL1 expression

Hydrogen sulfide, as a novel gaseous mediator, has been suggested to play a key role in atherogenesis. However, the precise mechanisms by which H(2)S affects atherosclerosis remain unclear. Therefore, the present study aimed to investigate the potential role of H(2)S in atherosclerosis and the underlying mechanism with respect to chemokines (CCL2, CCL5 and CX3CL1) and chemokine receptors (CCR2, CCR5, and CX3CR1) in macrophages. Mouse macrophage cell line RAW 264.7 or mouse peritoneal macrophages were pre-incubated with saline or NaHS (50 µM, 100 µM, 200 µM), an H(2)S donor, and then stimulated with interferon-γ (IFN-γ) or lipopolysaccharide (LPS). It was found that NaHS dose-dependently inhibited IFN-γ or LPS-induced CX3CR1 and CX3CL1 expression, as well as CX3CR1-mediated chemotaxis in macrophages. Overexpression of cystathionine γ-lyase (CSE), an enzyme that catalyzes H(2)S biosynthesis resulted in a significant reduction in CX3CR1 and CX3CL1 expression as well as CX3CR1-mediated chemotaxis in stimulated macrophages. The inhibitory effect of H(2)S on CX3CR1 and CX3CL1 expression was mediated by modulation of proliferators-activated receptor-γ (PPAR-γ) and NF-κB pathway. Furthermore, male apoE(-/-) mice were fed a high-fat diet and then randomly given NaHS (1 mg/kg, i.p., daily) or DL-propargylglycine (PAG, 10 mg/kg, i.p., daily). NaHS significantly inhibited aortic CX3CR1 and CX3CL1 expression and impeded aortic plaque development. NaHS had a better anti-atherogenic benefit when it was applied at the early stage of atherosclerosis. However, inhibition of H(2)S formation by PAG increased aortic CX3CR1 and CX3CL1 expression and exacerbated the extent of atherosclerosis. In addition, H(2)S had minimal effect on the expression of CCL2, CCL5, CCR2 and CCR5 in vitro and in vivo. In conclusion, these data indicate that H(2)S hampers the progression of atherosclerosis in fat-fed apoE(-/-) mice and downregulates CX3CR1 and CX3CL1 expression on macrophages and in lesion plaques.

Nuclear hormone receptors enable macrophages and dendritic cells to sense their lipid environment and shape their immune response

A key issue in the immune system is to generate specific cell types, often with opposing activities. The mechanisms of differentiation and subtype specification of immune cells such as macrophages and dendritic cells are critical to understand the regulatory principles and logic of the immune system. In addition to cytokines and pathogens, it is increasingly appreciated that lipid signaling also has a key role in differentiation and subtype specification. In this review we explore how intracellular lipid signaling via a set of transcription factors regulates cellular differentiation, subtype specification, and immune as well as metabolic homeostasis. We introduce macrophages and dendritic cells and then we focus on a group of transcription factors, nuclear receptors, which regulate gene expression upon receiving lipid signals. The receptors we cover are the ones with a recognized physiological function in these cell types and ones which heterodimerize with the retinoid X receptor. These are as follows: the receptor for a metabolite of vitamin A, retinoic acid: retinoic acid receptor (RAR), the vitamin D receptor (VDR), the fatty acid receptor: peroxisome proliferator-activated receptor γ (PPARγ), the oxysterol receptor liver X receptor (LXR), and their obligate heterodimeric partner, the retinoid X receptor (RXR). We discuss how they can get activated and how ligand is generated and eliminated in these cell types. We also explore how activation of a particular target gene contributes to biological functions and how the regulation of individual target genes adds up to the coordination of gene networks. It appears that RXR heterodimeric nuclear receptors provide these cells with a coordinated and interrelated network of transcriptional regulators for interpreting the lipid milieu and the metabolic changes to bring about gene expression changes leading to subtype and functional specification. We also show that these networks are implicated in various immune diseases and are amenable to therapeutic exploitation.

Elevated fractalkine in patients with obstructive sleep apnea hypopnea syndrome

BACKGROUND

Obstructive sleep apnea hypopnea syndrome (OSAHS) has been increasingly linked to cardiovascular disease. Inflammatory processes associated with OSAHS may contribute to atherosclerosis in these patients. Fractalkine is a unique chemokine which has both adhesive and chemoattractant functions. We tested the hypothesis that OSAHS patients have increased fractalkine.

METHODS AND RESULTS

We studied 20 patients (18 males and 2 females) with newly diagnosed OSAHS, who were free of other diseases, had never been treated for OSAHS, and were taking no medications. We compared fractalkine measurements in these patients to measurements obtained in 15 control subjects (14 males and 1 female) who were matched for age and body mass index, and in whom occult OSAHS was excluded. Plasma fractalkine levels were significantly higher in patients with OSAHS than in controls (463.15 ± 110.78 versus 364.67 ± 64.81 pg/mL, F = 2.58, P = 0.004). Fractalkine were associated with AHI (r = 0.756, P < 0.0001), lowest oxygen saturation (r = -0.466, P = 0.005), and mean oxygen saturation (r = -0.344, P = 0.043). Plasma fractalkine levels were significantly decreased in patients with OSAHS after four nights nCPAP (463.15 ± 110.78 versus 416.75 ± 97.67 pg/mL, P = 0.001).

CONCLUSIONS

OSAHS is associated with elevated levels of fractalkine, a marker of inflammation related to atherosclerosis. The severity of OSAHS is proportional to the fractalkine level.

Physiological effects of oxidized phospholipids and their cellular signaling mechanisms in inflammation

Oxidized phospholipids, such as the products of the oxidation of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine by nonenzymatic radical attack, are known to be formed in a number of inflammatory diseases. Interest in the bioactivity and signaling functions of these compounds has increased enormously, with many studies using cultured immortalized and primary cells, tissues, and animals to understand their roles in disease pathology. Initially, oxidized phospholipids were viewed largely as culprits, in line with observations that they have proinflammatory effects, enhancing inflammatory cytokine production, cell adhesion and migration, proliferation, apoptosis, and necrosis, especially in vascular endothelial cells, macrophages, and smooth muscle cells. However, evidence has emerged that these compounds also have protective effects in some situations and cell types; a notable example is their ability to interfere with signaling by certain Toll-like receptors (TLRs) induced by microbial products that normally leads to inflammation. They also have protective effects via the stimulation of small GTPases and induce up-regulation of antioxidant enzymes and cytoskeletal rearrangements that improve endothelial barrier function. Oxidized phospholipids interact with several cellular receptors, including scavenger receptors, platelet-activating factor receptors, peroxisome proliferator-activated receptors, and TLRs. The various and sometimes contradictory effects that have been observed for oxidized phospholipids depend on their concentration, their specific structure, and the cell type investigated. Nevertheless, the underlying molecular mechanisms by which oxidized phospholipids exert their effects in various pathologies are similar. Although our understanding of the actions and mechanisms of these mediators has advanced substantially, many questions do remain about their precise interactions with components of cell signaling pathways.

Cross talk between smooth muscle cells and monocytes/activated monocytes via CX3CL1/CX3CR1 axis augments expression of pro-atherogenic molecules

OBJECTIVE

In atherosclerotic lesions, fractalkine (CX3CL1) and its receptor (CX3CR1) expressed by smooth muscle cells (SMC) and monocytes/macrophages, mediate the heterotypic anchorage and chemotaxis of these cells. We questioned whether, during the close interaction of monocytes with SMC, the CX3CL1/CX3CR1 pair modulates the expression of pro-atherogenic molecules in these cells.

METHODS AND RESULTS

SMC were co-cultured with monocytes or LPS-activated monocytes (18h) and then the cells were separated and individually investigated for the gene and protein expression of TNFα, IL-1β, IL-6, CX3CR1 and metalloproteinases (MMP-2, MMP-9). We found that SMC-monocyte interaction induced, in each cell type, an increased mRNA and protein expression of TNFα, IL-1β, IL-6, CX3CR1, MMP-2 and MMP-9. Blocking the binding of fractalkine to CX3CR1 (by pre-incubation of monocytes with anti-CX3CR1 or by CX3CR1 siRNA transfection) before cell co-culture decreased the production of TNFα, CX3CR1 and MMP-9. Monocyte-SMC interaction induced the phosphorylation of p38MAPK and activation of AP-1 transcription factor. Silencing the p65 (NF-kB subunit) inhibited the IL-1β and IL-6 and silencing c-jun inhibited the TNFα, CX3CR1 and MMP-9 induced by SMC-monocyte interaction.

CONCLUSIONS

The cross-talk between SMC and monocytes augments the inflammatory response in both cell types as revealed by the increased expression of TNFα, IL-1β, IL-6, CX3CR1 and MMPs. Up-regulation of TNFα, CX3CR1 and MMP-9 is further increased upon interaction of SMC with activated monocytes and is dependent on fractalkine/CXRCR1 pair. These data imply that the fractalkine/CX3RCR1 axis may represent a therapeutic target to impede the inflammatory process associated with atherosclerosis.

Anti-inflammatory therapeutics for the treatment of atherosclerosis

Atherosclerosis is the primary cause of heart disease and stroke and is thus the underlying pathology of the leading causes of death in the western world. Although risk can be reduced by lowering lipid levels, the equally important contribution of inflammation to the development of cardiovascular disease is not adequately addressed by existing therapies. Here, we summarize the evidence supporting a role for inflammation in the pathogenesis of atherosclerosis, discuss agents that are currently in the clinic and provide a perspective on the challenges faced in the development of drugs that target vascular inflammation.

Fractalkine/CX3CR1 and atherosclerosis

Fractalkine is a unique chemokine which has both adhesive and chemoattractant functions. With the increasing emphasis on the importance of inflammation in atherosclerosis, more attention has been focused on the role of chemokines in atherosclerosis. It has been shown that fractalkine/CX3CR1 participates in the atherosclerotic pathological process through mediating the recruitment of leukocytes and the interaction of vascular cells and leukocytes. Some signal pathways are simultaneously activated through fractalkine/CX3CR1 coupling to promote the inflammatory response in atherosclerotic vessels. Additionally, fractalkine has cytotoxic effects on endothelium as well as anti-apoptosis and proliferative effects on vascular cells which consequently changes plaque components and stability in plaque. Several studies have showed that fractalkine or CX3CR1 deficiency in atherosclerotic mice would ameliorate the severity of plaque. Population studies on CX3CR1 polymorphism have confirmed that 280M-containing haplotype is associated with reduced risk of atherosclerotic disease. Despite the apparent association with atherosclerosis, further studies on fractalkine/CX3CR1 chemokine pair are clearly warranted to more fully elucidate this relationship.

Dual targeting of CCR2 and CX3CR1 in an arterial injury model of vascular inflammation

OBJECTIVES

The chemokine receptors CCR2 and CX3CR1 are important in the development of coronary artery disease. The purpose of this study is to analyze the effect of a novel CCR2 inhibitor in conjunction with CX3CR1 deletion on vascular inflammation.

METHODS

The novel CCR2 antagonist MRL-677 was characterized using an in vivo model of monocyte migration. To determine the relative roles of CCR2 and CX3CR1 in vascular remodeling, normal or CX3CR1 deficient mice were treated with MRL-677. After 14 days, the level of intimal hyperplasia in the artery was visualized by paraffin sectioning and histology of the hind limbs.

RESULTS

MRL-677 is a CCR2 antagonist that is effective in blocking macrophage trafficking in a peritoneal thioglycollate model. Intimal hyperplasia resulting from vascular injury was also assessed in mice. Based on the whole-blood potency of MRL-677, sufficient drug levels were maintained for the entire 14 day experimental period to afford good coverage of mCCR2 with MRL-677. Blocking CCR2 with MRL-677 resulted in a 56% decrease in the vascular injury response (n = 9, p < 0.05) in normal animals. Mice in which both CCR2 and CX3CR1 pathways were targeted (CX3CR1 KO mice given MRL-677) had an 88% decrease in the injury response (n = 6, p = 0.009).

CONCLUSION

In this study we have shown that blocking CCR2 with a low molecular weight antagonist ameliorates the inflammatory response to vascular injury. The protective effect of CCR2 blockade is increased in the presence of CX3CR1 deficiency suggesting that CX3CR1 and CCR2 have non-redundant functions in the progression of vascular inflammation.

High-density lipoproteins suppress chemokines and chemokine receptors in vitro and in vivo

OBJECTIVE

To investigate whether high-density lipoproteins (HDLs) suppress chemokine (CCL2, CCL5, and CX(3)CL1) and chemokine receptor (CCR2 and CX(3)CR1) expression, a mechanism for the atheroprotective properties of HDLs.

METHODS AND RESULTS

Apolipoprotein (apo) E(-/-) mice were fed a high-fat diet for 12 weeks. Before being euthanized, the mice received 5 consecutive daily injections of lipid-free apoA-I, 40 mg/kg, or saline (control). The injection of apoA-I reduced CCR2 and CX(3)CR1 expression in plaques compared with controls (P<0.05). ApoA-I-injected mice had lower plasma CCL2 and CCL5 levels. Hepatic CCL2, CCL5, and CX(3)CL1 levels were also reduced (P<0.05). In vitro studies found that reconstituted HDL (rHDL) reduced monocyte CCR2 and CX(3)CR1 expression and inhibited their migration toward CCL2 and CX(3)CL1 (P<0.05). Preincubation with rHDL reduced CCL2, CCL5, and CX(3)CL1 expression in monocytes and human coronary artery endothelial cells. The stimulation of CX(3)CR1 with peroxisome proliferator-activated receptor gamma agonist CAY10410 was suppressed by preincubation with rHDL but did not affect the peroxisome proliferator-activated receptor gamma antagonist (GW9664)-mediated increase in CCR2. In monocytes and human coronary artery endothelial cells, rHDL reduced the expression of the nuclear p65 subunit, IkappaB kinase activity, and the phosphorylation of IkappaBalpha (P<0.05).

CONCLUSIONS

Lipid-free apoA-I and rHDL reduce the expression of chemokines and chemokine receptors in vivo and in vitro via modulation of nuclear factor kappaB and peroxisome proliferator-activated receptor gamma.

Hydroxyoctadecadienoic acids: novel regulators of macrophage differentiation and atherogenesis

Hydroxyoctadecadienoic acids (HODEs) are stable oxidation products of linoleic acid, the generation of which is increased where oxidative stress is increased, such as in diabetes. In early atherosclerosis, 13-HODE is generated in macrophages by 15-lipoxygenase-1. This enhances protective mechanisms through peroxisome proliferator-activated receptor (PPAR)-g activation leading to increased clearance of lipid and lipid-laden cells from the arterial wall. In later atherosclerosis, both 9-HODE and 13-HODE are generated nonenzymatically. At this stage, early protective mechanisms are overwhelmed and pro-inflammatory effects of 9-HODE, acting through the receptor GPR132, and increased apoptosis predominate leading to a fragile, acellular plaque. Increased HODE levels thus contribute to atherosclerosis progression and the risk of clinical events such as myocardial infarction or stroke. Better understanding of the role of HODEs may lead to new pharmacologic approaches to modulate their production or action, and therefore lessen the burden of atherosclerotic disease in high-risk patients.

Functional alterations of myeloid cell subsets in hyperlipidaemia: relevance for atherosclerosis

Atherosclerosis is a chronic inflammatory disease wherein the infiltration of myeloid cells of the vessel wall is a hallmark event. Lymphocytes, platelets and endothelial cells stand out as prominent suspects being involved in atherosclerosis. However, recent advances suggest a crucial role for myeloid leucocytes, specifically monocyte subsets, neutrophils, dendritic cells and endothelial progenitor cells. These cell types are not just rapidly recruited or already reside in the vascular wall, but also initiate and perpetuate core mechanisms in plaque formation and destabilization. Hyperlipidaemia is an independent risk factor for atherosclerosis. Herein, hyperlipidaemia skews myeloid cell haemostasis, phenotype and transcriptional regulation of pro-inflammatory factors ultimately promoting myeloid cell extravasation and atherosclerosis. We here review the role of myeloid cells in atherosclerosis as well as the effects of hyperlipidaemia on these cells.

Regulation of the migration and survival of monocyte subsets by chemokine receptors and its relevance to atherosclerosis

Monocytes are central mediators in the advance of atherosclerotic plaque, making them a natural therapeutic target for reducing disease burden. Here, we highlight recent advances in our current understanding of monocyte heterogeneity and its relevance to regulation of monocyte accumulation and function within atherosclerotic plaques. Differences that distinguish monocyte subsets include differential expression of chemokine receptors, especially CCR2 and CX3CR1. Ablation of expression of these 2 receptors (or their ligands) in mice has an additive inhibition on monocyte recruitment to atherosclerotic plaques. Moreover, simultaneously interfering with 3 key pathways--CCR2, CX3CR1, and CCR5--essentially abolishes atherosclerosis in mice. Here, we discuss how these chemokine receptors act at multiple points on at least 1 monocyte subset, regulating their mobilization from bone marrow, survival, or recruitment to plaques. Finally, we discuss how this knowledge may be useful clinically, emphasizing that CX3CR1 may in particular be a viable target for therapeutic manipulation of monocyte-derived cell fate in cardiovascular disease.

Atherogenic lipids induce high-density lipoprotein uptake and cholesterol efflux in human macrophages by up-regulating transmembrane chemokine CXCL16 without engaging CXCL16-dependent cell adhesion

Atherosclerosis is a complex pathologic process in which chemokine-mediated leukocyte accumulation in arterial walls is thought to be an important mechanism of pathogenesis. An interesting exception to this paradigm is the chemokine CXCL16, also known as the scavenger receptor for phosphatidylserine and oxidized low density lipoprotein, which is highly expressed in mouse and human atherosclerotic lesions, yet appears to be atheroprotective. In this study, we address potential mechanisms responsible for this activity. Consistent with its presence in atherosclerotic plaque, we found that atherogenic lipids up-regulated CXCL16 in primary human monocyte-derived macrophages. However, the same lipids down-regulated the CXCL16-targeted protease ADAM10, resulting in preferential expression of CXCL16 as the transmembrane form, not the shed form. Although transmembrane CXCL16 is known to mediate cell-cell adhesion by binding its receptor CXCR6, and atherogenic lipids are known to stimulate macrophage adhesion to coronary artery smooth muscle cells, we found that heterotypic adhesion of these cell types occurred in a CXCL16-independent manner. Instead we found that in macrophages, CXCL16 promoted internalization of both oxidized low density lipoprotein and high density lipoprotein, as well as release of cholesterol. Moreover, CXCL16 deficiency in macrophages interfered with oxidized low density lipoprotein-induced up-regulation of atheroprotective genes: adenosine triphosphate-binding cassette transporter A1 and G1 as well as apolipoprotein E. Thus, our findings support the hypothesis that CXCL16 mediates atheroprotection through its scavenger role in macrophages and not by cell-cell adhesion.