Distinct functions of chemokine receptor axes in the atherogenic mobilization and recruitment of classical monocytes

Circadian Control of Inflammatory Processes in Atherosclerosis and Its Complications

Physiological cardiovascular functions show daily diurnal variations, which are synchronized by intrinsic molecular clocks and environment-driven cues. The clinical manifestation of cardiovascular disease also exhibits diurnal variation, with an increased incidence in the early morning. This coincides with circadian oscillations of circulating parameters, such as hormones and leukocyte counts. We are just at the beginning of understanding how circadian rhythms of immune functions are related to cardiovascular disease progression and outcome after an acute ischemic event. Here, we briefly summarize clinical data on oscillations of circulating inflammatory parameters, as well as experimental evidences for the role of circadian clocks in atherosclerosis, postmyocardial infarction inflammatory responses, and cardiac healing.

Isotrifoliol inhibits pro-inflammatory mediators by suppression of TLR/NF-κB and TLR/MAPK signaling in LPS-induced RAW264.7 cells

Soybeans, produced by Glycine max (L.) Merr., contain high levels of isoflavones, such as genistein and daidzein. However, soy leaves contain more diverse and abundant flavonol glycosides and coumestans, as compared to the soybean. This study investigated the anti-inflammatory effects of the major coumestans present in soy leaf (coumestrol, isotrifoliol, and phaseol) in lipopolysaccharide (LPS)-induced RAW264.7 cells. Coumestans significantly reduced LPS-induced nitric oxide (NO), prostaglandin E2 (PGE2), and reactive oxygen species (ROS) production; isotrifoliol had the most potent anti-inflammatory activity. Isotrifoliol reduced LPS-mediated induction of mRNA expression of inducible nitric-oxide synthase (iNOS), cyclooxygenase-2 (COX-2), interleukin (IL)-1β, IL-6, tumor necrosis factor alpha (TNFα), and chemokines, such as chemokine (C-C motif) ligand (CCL) 2, CCL3, and CCL4. Isotrifoliol prevented NF-κB p65 subunit activation by reducing the phosphorylation and degradation of the inhibitor of NF-κB. And isotrifoliol significantly suppressed phosphorylation of the extracellular signal-regulated protein kinase 1/2 (ERK1/2) and p38 mitogen-activated protein kinase (MAPK). Furthermore, isotrifoliol suppressed LPS-induced Toll-like Receptor (TLR) signaling pathway, including mRNA expression of TNF receptor associated factor 6, transforming growth factor beta-activated kinase 1 (TAK1), TAK1 binding protein 2 (TAB2), and TAB3. These results demonstrate that isotrifoliol exerts an anti-inflammatory effect by suppressing the expression of inflammatory mediators via inhibition of TLR/NF-κB and TLR/MAPK signaling in LPS-induced RAW264.7 macrophages. Therefore, isotrifoliol can be used as an anti-inflammatory agent, and coumestan-rich soy leaf extracts may provide a useful dietary supplement.

Endothelial Protective Monocyte Patrolling in Large Arteries Intensified by Western Diet and Atherosclerosis

Supplemental Digital Content is available in the text.

Rationale:

Nonclassical mouse monocyte (CX3CR1^high, Ly-6C^low) patrolling along the vessels of the microcirculation is critical for endothelial homeostasis and inflammation. Because of technical challenges, it is currently not established how patrolling occurs in large arteries.

Objective:

This study was undertaken to elucidate the molecular, migratory, and functional phenotypes of patrolling monocytes in the high shear and pulsatile environment of large arteries in healthy, hyperlipidemic, and atherosclerotic conditions.

Methods and Results:

Applying a new method for stable, long-term 2-photon intravital microscopy of unrestrained large arteries in live CX3CR1-GFP (green fluorescent protein) mice, we show that nonclassical monocytes patrol inside healthy carotid arteries at a velocity of 36 μm/min, 3× faster than in microvessels. The tracks are less straight but lead preferentially downstream. The number of patrolling monocytes is increased 9-fold by feeding wild-type mice a Western diet or by applying topical TLR7/8 (Toll-like receptor) agonists. A similar increase is seen in CX3CR1^+/GFP/apoE^−/− mice on chow diet, with a further 2- to 3-fold increase on Western diet (22-fold over healthy). In plaque conditions, monocytes are readily captured onto the endothelium from free flow. Stable patrolling is unaffected in CX3CR1-deficient mice and involves the contribution of LFA-1 (lymphocyte-associated antigen 1) and α₄ integrins. The endothelial damage in atherosclerotic carotid arteries was assessed by electron microscopy and correlates with the number of intraluminal patrollers. Abolishing patrolling monocytes in Nr4a1^−/− apoE^−/− mice leads to pronounced endothelial apoptosis.

Conclusions:

Arterial patrolling is a prominent new feature of nonclassical monocytes with unique molecular and kinetic properties. It is highly upregulated in hyperlipidemia and atherosclerosis in a CX3CR1-independent fashion and plays a potential role in endothelial protection.

Identification of Motile Sperm Domain-Containing Protein 2 as Regulator of Human Monocyte Migration

Binding of chemokines to their cognate receptors on monocytes instigates a cascade of events that directs these cells to migrate to sites of inflammation and cancerous tissues. Although targeting of selected chemokine receptors on monocytes exhibited preclinical efficacy, attempts to translate these studies to the clinic have failed thus far, possibly due to redundancy of the target receptor. We reveal that motile sperm domain-containing protein 2 (MOSPD2), a protein with a previously unknown function, regulates monocyte migration in vitro. This protein was found to be expressed on the cytoplasmic membrane of human monocytes. Silencing or neutralizing MOSPD2 in monocytes restricted their migration when induced by different chemokines. Mechanistically, silencing MOSPD2 inhibited signaling events following chemokine receptor ligation. When tested for expression in other immune cell subsets, MOSPD2 was apparent also, though less abundantly, in neutrophils, but not in lymphocytes. Thus, in the presence of neutralizing Abs, neutrophil migration was inhibited to some extent whereas lymphocyte migration remained intact. In view of these results, we suggest MOSPD2 as a potential target protein for treating diseases in which monocyte and neutrophil accumulation is correlated with pathogenesis.

Treatment with Cestode Parasite Antigens Results in Recruitment of CCR2+ Myeloid Cells, the Adoptive Transfer of Which Ameliorates Colitis

Awareness of the immunological underpinnings of host-parasite interactions may reveal immune signaling pathways that could be used to treat inflammatory disease in humans. Previously we showed that infection with the rat tapeworm, Hymenolepis diminuta, used as a model helminth, or systemic delivery of worm antigen (HdAg) significantly reduced the severity of dinitrobenzene sulfonic acid (DNBS)-induced colitis in mice. Extending these analyses, intraperitoneal injection of HdAg dose-dependently suppressed dextran sodium sulfate (DSS)-induced colitis, and this was paralleled by reduced gamma interferon (IFN-γ), interleukin-17 (IL-17), and tumor necrosis factor alpha (TNF-α) production and increased IL-10 production from mitogen-activated splenocytes. Treatment with HdAg resulted in a CCR2-dependent recruitment of CDllb⁺ F4/80⁺ Ly6C^hi Gr-1^lo monocyte-like cells into the peritoneum 24 h later that were predominantly programmed death ligand 1 (PD-L1) positive and CXCR2 negative. In vitro assays indicated that these cells were unable to suppress T cell proliferation but enhanced IL-10 and IL-4 production from activated T cells. Adoptive transfer of the HdAg-recruited monocytic cells into naive mice blocked DSS-induced colitis. These findings add to the variety of means by which treatment with parasitic helminth-derived antigens can ameliorate concomitant disease. A precise understanding of the mechanism(s) of action of HdAg and other helminth-derived antigens (and a parallel consideration of putative side effects) may lead to the development of novel therapies for human idiopathic disorders such as inflammatory bowel disease.

Targeting of CCL2-CCR2-Glycosaminoglycan Axis Using a CCL2 Decoy Protein Attenuates Metastasis through Inhibition of Tumor Cell Seeding

The CCL2-CCR2 chemokine axis has an important role in cancer progression where it contributes to metastatic dissemination of several cancer types (e.g., colon, breast, prostate). Tumor cell–derived CCL2 was shown to promote the recruitment of CCR2⁺/Ly6C^hi monocytes and to induce vascular permeability of CCR2⁺ endothelial cells in the lungs. Here we describe a novel decoy protein consisting of a CCL2 mutant protein fused to human serum albumin (dnCCL2-HSA chimera) with enhanced binding affinity to glycosaminoglycans that was tested in vivo. The monocyte-mediated tumor cell transendothelial migration was strongly reduced upon unfused dnCCL2 mutant treatment in vitro. dnCCL2-HSA chimera had an extended serum half-life and thus a prolonged exposure in vivo compared with the dnCCL2 mutant. dnCCL2-HSA chimera bound to the lung vasculature but caused minimal alterations in the leukocyte recruitment to the lungs. However, dnCCL2-HSA chimera treatment strongly reduced both lung vascular permeability and tumor cell seeding. Metastasis of MC-38GFP, 3LL, and LLC1 cells was significantly attenuated upon dnCCL2-HSA chimera treatment. Tumor cell seeding to the lungs resulted in enhanced expression of a proteoglycan syndecan-4 by endothelial cells that correlated with accumulation of the dnCCL2-HSA chimera in the vicinity of tumor cells. These findings demonstrate that the CCL2-based decoy protein effectively binds to the activated endothelium in lungs and blocks tumor cell extravasation through inhibition of vascular permeability.

TREM-1 links dyslipidemia to inflammation and lipid deposition in atherosclerosis

Triggering receptor expressed on myeloid cells-1 (TREM-1) is a potent amplifier of pro-inflammatory innate immune responses, but its significance in non-infectious diseases remains unclear. Here, we demonstrate that TREM-1 promotes cardiovascular disease by exacerbating atherosclerosis. TREM-1 is expressed in advanced human atheromas and is highly upregulated under dyslipidemic conditions on circulating and on lesion-infiltrating myeloid cells in the Apoe^−/− mouse model. TREM-1 strongly contributes to high-fat, high-cholesterol diet (HFCD)-induced monocytosis and synergizes with HFCD serum-derived factors to promote pro-inflammatory cytokine responses and foam cell formation of human monocyte/macrophages. Trem1^−/−Apoe^−/− mice exhibit substantially attenuated diet-induced atherogenesis. In particular, our results identify skewed monocyte differentiation and enhanced lipid accumulation as novel mechanisms through which TREM-1 can promote atherosclerosis. Collectively, our findings illustrate that dyslipidemia induces TREM-1 surface expression on myeloid cells and subsequently synergizes with TREM-1 to enhance monopoiesis, pro-atherogenic cytokine production and foam cell formation.

TREM-1 is a receptor that amplifies acute pro-inflammatory responses in infection. Here the authors show that TREM-1 plays an important role in atherosclerosis, a chronic and non-infectious disease, by critically skewing myelopoiesis towards preferential monocyte differentiation and by contributing to CD36-driven cellular lipid accumulation.

Cathepsin G Controls Arterial But Not Venular Myeloid Cell Recruitment

BACKGROUND

Therapeutic targeting of arterial leukocyte recruitment in the context of atherosclerosis has been disappointing in clinical studies. Reasons for such failures include the lack of knowledge of arterial-specific recruitment patterns. Here we establish the importance of the cathepsin G (CatG) in the context of arterial myeloid cell recruitment.

METHODS

Intravital microscopy of the carotid artery, the jugular vein, and cremasteric arterioles and venules in Apoe^-/-and CatG-deficient mice (Apoe^-/-Ctsg^-/-) was used to study site-specific myeloid cell behavior after high-fat diet feeding or tumor necrosis factor stimulation. Atherosclerosis development was assessed in aortic root sections after 4 weeks of high-fat diet, whereas lung inflammation was assessed after inhalation of lipopolysaccharide. Endothelial deposition of CatG and CCL5 was quantified in whole-mount preparations using 2-photon and confocal microscopy.

RESULTS

Our observations elucidated a crucial role for CatG during arterial leukocyte adhesion, an effect not found during venular adhesion. Consequently, CatG deficiency attenuates atherosclerosis but not acute lung inflammation. Mechanistically, CatG is immobilized on arterial endothelium where it activates leukocytes to firmly adhere engaging integrin clustering, a process of crucial importance to achieve effective adherence under high-shear flow. Therapeutic neutralization of CatG specifically abrogated arterial leukocyte adhesion without affecting myeloid cell adhesion in the microcirculation. Repetitive application of CatG-neutralizing antibodies permitted inhibition of atherogenesis in mice.

CONCLUSIONS

Taken together, these findings present evidence of an arterial-specific recruitment pattern centered on CatG-instructed adhesion strengthening. The inhibition of this process could provide a novel strategy for treatment of arterial inflammation with limited side effects.

Recruitment of classical monocytes can be inhibited by disturbing heteromers of neutrophil HNP1 and platelet CCL5

In acute and chronic inflammation, neutrophils and platelets, both of which promote monocyte recruitment, are often activated simultaneously. We investigated how secretory products of neutrophils and platelets synergize to enhance the recruitment of monocytes. We found that neutrophil-borne human neutrophil peptide 1 (HNP1, α-defensin) and platelet-derived CCL5 form heteromers. These heteromers stimulate monocyte adhesion through CCR5 ligation. We further determined structural features of HNP1-CCL5 heteromers and designed a stable peptide that could disturb proinflammatory HNP1-CCL5 interactions. This peptide attenuated monocyte and macrophage recruitment in a mouse model of myocardial infarction. These results establish the in vivo relevance of heteromers formed between proteins released from neutrophils and platelets and show the potential of targeting heteromer formation to resolve acute or chronic inflammation.

Nestin(+) cells direct inflammatory cell migration in atherosclerosis

Atherosclerosis is a leading death cause. Endothelial and smooth muscle cells participate in atherogenesis, but it is unclear whether other mesenchymal cells contribute to this process. Bone marrow (BM) nestin⁺ cells cooperate with endothelial cells in directing monocyte egress to bloodstream in response to infections. However, it remains unknown whether nestin⁺ cells regulate inflammatory cells in chronic inflammatory diseases, such as atherosclerosis. Here, we show that nestin⁺ cells direct inflammatory cell migration during chronic inflammation. In Apolipoprotein E (ApoE) knockout mice fed with high-fat diet, BM nestin⁺ cells regulate the egress of inflammatory monocytes and neutrophils. In the aorta, nestin⁺ stromal cells increase ∼30 times and contribute to the atheroma plaque. Mcp1 deletion in nestin⁺ cells—but not in endothelial cells only— increases circulating inflammatory cells, but decreases their aortic infiltration, delaying atheroma plaque formation and aortic valve calcification. Therefore, nestin expression marks cells that regulate inflammatory cell migration during atherosclerosis.

Bone marrow cells producing the intermediate filament nestin guide monocyte egress to the bloodstream in response to infection. Here, the authors show that nestin-producing stromal cells direct inflammatory cell migration in atherosclerosis, and that stromal Mcp1 is crucial in this process.

Monocyte Adhesion and Plaque Recruitment During Atherosclerosis Development Is Regulated by the Adapter Protein Chat-H/SHEP1

OBJECTIVE

The chronic inflammation associated with atherosclerosis is caused by lipid deposition followed by leukocyte recruitment to the arterial wall. We previously showed that the hematopoietic cell-specific adaptor protein Cas- and Hef1-associated signal transducer hematopoietic isoform (Chat-H)/SHEP1 regulated lymphocyte adhesion and migration. In this study, we analyzed the role of Chat-H in atherosclerosis development.

APPROACH AND RESULTS

Using Chat-H-deficient bone marrow transplantation in low-density lipoprotein receptor-deficient mice, we found that Chat-H regulated atherosclerotic plaque formation. Chat-H deficiency in hematopoietic cells associated with lower plaque complexity and fewer leukocytes in the lesions, whereas myeloid-specific deletion of Chat-H was sufficient for conferring atheroprotection. Chat-H deficiency resulted in reduced recruitment of classical Ly6c(high) and nonclassical Ly6c(low) monocytes to the plaques, which was accompanied by increased numbers of both monocyte subsets in the blood. This associated with defective adhesion of Chat-H-deficient Ly6c(high) and Ly6c(low) monocytes to vascular cell adhesion molecule-1 in vitro and impaired infiltration of fluorescent bead-loaded monocytes to atherosclerotic plaques. In contrast, Chat-H was dispensable for CX3CL1 and CCR1/CCR5-dependent migration of monocytes.

CONCLUSIONS

Our findings highlight Chat-H as a key protein that regulates atherosclerosis development by controlling monocyte adhesion and recruitment to the plaques and identify a novel target that may be exploited for treating atherosclerosis.

Tissue resident macrophages: Key players in the pathogenesis of type 2 diabetes and its complications

There is increasing evidence showing that chronic inflammation is an important pathogenic mediator of the development of type 2 diabetes (T2D). It is now generally accepted that tissue-resident macrophages play a major role in regulation of tissue inflammation. T2D-associated inflammation is characterized by an increased abundance of macrophages in different tissues along with production of inflammatory cytokines. The complexity of macrophage phenotypes has been reported from different human tissues. Macrophages exhibit a phenotypic range that is intermediate between two extremes, M1 (pro-inflammatory) and M2 (anti-inflammatory). Cytokines and chemokines produced by macrophages generate local and systemic inflammation and this condition leads to pancreatic β-cell dysfunction and insulin resistance in liver, adipose and skeletal muscle tissues. Data from human and animal studies also suggest that macrophages contribute to T2D complications such as nephropathy, neuropathy, retinopathy and cardiovascular diseases through cell-cell interactions and the release of pro-inflammatory cytokines, chemokines, and proteases to induce inflammatory cell recruitment, cell apoptosis, angiogenesis, and matrix protein remodeling. In this review we focus on the functions of macrophages and the importance of these cells in the pathogenesis of T2D. In addition, the contribution of macrophages to diabetes complications such as nephropathy, neuropathy, retinopathy and cardiovascular diseases is discussed.

Resolving Lipid Mediators Maresin 1 and Resolvin D2 Prevent Atheroprogression in Mice

RATIONALE

Atheroprogression is a consequence of nonresolved inflammation, and currently a comprehensive overview of the mechanisms preventing resolution is missing. However, in acute inflammation, resolution is known to be orchestrated by a switch from inflammatory to resolving lipid mediators. Therefore, we hypothesized that lesional lipid mediator imbalance favors atheroprogression.

OBJECTIVE

To understand the lipid mediator balance during atheroprogression and to establish an interventional strategy based on the delivery of resolving lipid mediators.

METHODS AND RESULTS

Aortic lipid mediator profiling of aortas from Apoe^-/- mice fed a high-fat diet for 4 weeks, 8 weeks, or 4 months revealed an expansion of inflammatory lipid mediators, Leukotriene B4 and Prostaglandin E2, and a concomitant decrease of resolving lipid mediators, Resolvin D2 (RvD2) and Maresin 1 (MaR1), during advanced atherosclerosis. Functionally, aortic Leukotriene B4 and Prostaglandin E2 levels correlated with traits of plaque instability, whereas RvD2 and MaR1 levels correlated with the signs of plaque stability. In a therapeutic context, repetitive RvD2 and MaR1 delivery prevented atheroprogression as characterized by halted expansion of the necrotic core and accumulation of macrophages along with increased fibrous cap thickness and smooth muscle cell numbers. Mechanistically, RvD2 and MaR1 induced a shift in macrophage profile toward a reparative phenotype, which secondarily stimulated collagen synthesis in smooth muscle cells.

CONCLUSIONS

We present evidence for the imbalance between inflammatory and resolving lipid mediators during atheroprogression. Delivery of RvD2 and MaR1 successfully prevented atheroprogression, suggesting that resolving lipid mediators potentially represent an innovative strategy to resolve arterial inflammation.

Cytokines: roles in atherosclerosis disease progression and potential therapeutic targets

Atherosclerosis, the primary cause of cardiovascular disease (CVD), is a chronic inflammatory disorder in the walls of medium and large arteries. CVD is currently responsible for about one in three global deaths and this is expected to rise in the future due to an increase in the prevalence of obesity and diabetes. Current therapies for atherosclerosis mainly modulate lipid homeostasis and while successful at reducing the risk of a CVD-related death, they are associated with considerable residual risk and various side effects. There is, therefore, a need for alternative therapies aimed at regulating inflammation in order to reduce atherogenesis. This review will highlight the key role cytokines play during disease progression as well as potential therapeutic strategies to target them.

Macrophage Phenotype and Function in Different Stages of Atherosclerosis

The remarkable plasticity and plethora of biological functions performed by macrophages have enticed scientists to study these cells in relation to atherosclerosis for >50 years, and major discoveries continue to be made today. It is now understood that macrophages play important roles in all stages of atherosclerosis, from initiation of lesions and lesion expansion, to necrosis leading to rupture and the clinical manifestations of atherosclerosis, to resolution and regression of atherosclerotic lesions. Lesional macrophages are derived primarily from blood monocytes, although recent research has shown that lesional macrophage-like cells can also be derived from smooth muscle cells. Lesional macrophages take on different phenotypes depending on their environment and which intracellular signaling pathways are activated. Rather than a few distinct populations of macrophages, the phenotype of the lesional macrophage is more complex and likely changes during the different phases of atherosclerosis and with the extent of lipid and cholesterol loading, activation by a plethora of receptors, and metabolic state of the cells. These different phenotypes allow the macrophage to engulf lipids, dead cells, and other substances perceived as danger signals; efflux cholesterol to high-density lipoprotein; proliferate and migrate; undergo apoptosis and death; and secrete a large number of inflammatory and proresolving molecules. This review article, part of the Compendium on Atherosclerosis, discusses recent advances in our understanding of lesional macrophage phenotype and function in different stages of atherosclerosis. With the increasing understanding of the roles of lesional macrophages, new research areas and treatment strategies are beginning to emerge.

CCR5+T-bet+FoxP3+ Effector CD4 T Cells Drive Atherosclerosis

RATIONALE

CD4 T cells are involved in the pathogenesis of atherosclerosis, but atherosclerosis-specific CD4 T cells have not been described. Moreover, the chemokine(s) that regulates T-cell trafficking to the atherosclerotic lesions is also unknown.

OBJECTIVE

In Apoe(-/-) mice with mature atherosclerotic lesions (5 months of high fat diet), we find that most aortic T cells express CCR5 and interferon-γ with a unique combination of cell surface markers (CD4(+)CD25(-)CD44(hi)CD62L(lo)) and transcription factors (FoxP3(+)T-bet(+)). We call these cells CCR5Teff. We investigated the role of CCR5 in regulating T-cell homing to the atherosclerotic aorta and the functionality of the CCR5Teff cells.

METHODS AND RESULTS

CCR5Teff cells are exclusively found in the aorta and para-aortic lymph nodes of Apoe(-/-) mice. They do not suppress T-cell proliferation in vitro and are less potent than regulatory T cells at inhibiting cytokine secretion. Blocking or knocking out CCR5 or its ligand CCL5 significantly blocks T-cell homing to atherosclerotic aortas. Transcriptomic analysis shows that CCR5Teff cells are more similar to effector T cells than to regulatory T cells. They secrete interferon-γ, interleukin-2, interleukin-10, and tumor necrosis factor. Adoptive transfer of these CCR5Teff cells significantly increases atherosclerosis.

CONCLUSIONS

CCR5 is specifically needed for CD4 T-cell homing to the atherosclerotic plaques. CCR5(+)CD4 T cells express an unusual combination of transcription factors, FoxP3 and T-bet. Although CCR5Teff express FoxP3, we showed that they are not regulatory and adoptive transfer of these cells exacerbates atherosclerosis.

Structure-Based Design of Peptidic Inhibitors of the Interaction between CC Chemokine Ligand 5 (CCL5) and Human Neutrophil Peptides 1 (HNP1)

Protein-protein interactions (PPIs) are receiving increasing interest, much sparked by the realization that they represent druggable targets. Recently, we successfully developed a peptidic inhibitor, RRYGTSKYQ ("SKY" peptide), that shows high potential in vitro and in vivo to interrupt a PPI between the platelet-borne chemokine CCL5 and the neutrophil-derived granule protein HNP1. This PPI plays a vital role in monocyte adhesion, representing a key mechanism in acute and chronic inflammatory diseases. Here, we present extensive and detailed computational methods applied to develop the SKY peptide. We combined experimentally determined binding affinities (KD) of several orthologs of CCL5 with HNP1 with in silico studies to identify the most likely heterodimeric CCL5-HNP1 complex which was subsequently used as a starting structure to rationally design peptidic inhibitors. Our method represents a fast and simple approach that can be widely applied to determine other protein-protein complexes and moreover to design inhibitors or stabilizers of protein-protein interaction.

Niacin Suppresses Progression of Atherosclerosis by Inhibiting Vascular Inflammation and Apoptosis of Vascular Smooth Muscle Cells

Background

Niacin is a broad-spectrum lipid-regulating drug used for the clinical therapy of atherosclerosis; however, the mechanisms by which niacin ameliorates atherosclerosis are not clear.

Material/Methods

The effect of niacin on atherosclerosis was assessed by detection of atherosclerotic lesion area. Adhesion molecules in arterial endothelial cells were determined by using qRT-PCR and Western blot analysis. The levels of serum inflammatory cytokines in ApoE^−/− mice were detected by using ELISA. We detected the expression levels of phosphorylated nuclear factors-κB (NF-κB) p65 in aortic endothelial cells of mice using Western blot analysis. Furthermore, we investigated the anti-inflammation effect and endothelium-protecting function of niacin and their regulatory mechanisms in vitro.

Results

Niacin inhibited the progress of atherosclerosis and decreased the levels of serum inflammatory cytokines and adhesion molecules in ApoE^−/− mice. Niacin suppressed the activity of NF-κB and apoptosis of vascular smooth muscle cells (VSMCs). Furthermore, niacin induced phosphorylated focal adhesion kinase (FAK) and FAK inhibitor PF-573228 reduced the level of Bcl-2 and elevated the level of cleaved caspase-3 in VSMCs.

Conclusions

Niacin inhibits vascular inflammation and apoptosis of VSMCs via inhibiting the NF-κB signaling and the FAK signaling pathway, respectively, thus protecting ApoE^−/− mice against atherosclerosis.

Regulation of atherosclerotic plaque inflammation

The immune reactions that regulate atherosclerotic plaque inflammation involve chemokines, lipid mediators and costimulatory molecules. Chemokines are a family of chemotactic cytokines that mediate immune cell recruitment and control cell homeostasis and activation of different immune cell types and subsets. Chemokine production and activation of chemokine receptors form a positive feedback mechanism to recruit monocytes, neutrophils and lymphocytes into the atherosclerotic plaque. In addition, chemokine signalling affects immune cell mobilization from the bone marrow. Targeting several of the chemokines and/or chemokine receptors reduces experimental atherosclerosis, whereas specific chemokine pathways appear to be involved in plaque regression. Leukotrienes are lipid mediators that are formed locally in atherosclerotic lesions from arachidonic acid. Leukotrienes mediate immune cell recruitment and activation within the plaque as well as smooth muscle cell proliferation and endothelial dysfunction. Antileukotrienes decrease experimental atherosclerosis, and recent observational data suggest beneficial clinical effects of leukotriene receptor antagonism in cardiovascular disease prevention. By contrast, other lipid mediators, such as lipoxins and metabolites of omega-3 fatty acids, have been associated with the resolution of inflammation. Costimulatory molecules play a central role in fine-tuning immunological reactions and mediate crosstalk between innate and adaptive immunity in atherosclerosis. Targeting these interactions is a promising approach for the treatment of atherosclerosis, but immunological side effects are still a concern. In summary, targeting chemokines, leukotriene receptors and costimulatory molecules could represent potential therapeutic strategies to control atherosclerotic plaque inflammation.

Atherogenic lipids and macrophage subsets

PURPOSE OF REVIEW

Macrophage foam cells are important cells in the vascular wall that contribute to the inflammation associated with atherosclerotic lesions. Recent studies have demonstrated the heterogeneity of macrophages in lesions. In this review, advances in our understanding of the formation of foam cells by macrophage subsets in atherosclerotic plaques will be discussed.

RECENT FINDINGS

Macrophage subsets develop in response to the microenvironment in the arterial wall. The uptake of lipoproteins, particularly oxidized LDL, has been considered the major mechanism of foam cell formation. However, native and aggregated LDL can also be taken up by macrophages and M2 macrophages have been shown to be efficient in the uptake of apoptotic cells that can contribute lipids to the cells. The ability of the macrophage subsets to respond to bioactive lipids in the artery wall to either promote macrophage subset polarization and/or to promote foam cell formation is only beginning to be understood.

SUMMARY

Although we are beginning to appreciate the heterogeneity of macrophages present in atherosclerotic plaques, further work is required to fully understand the molecular basis for the differential ability of macrophage subsets to form foam cells and to respond to bioactive lipids.

CXCR2 inhibition suppresses acute and chronic pancreatic inflammation

Pancreatitis is a significant clinical problem and the lack of effective therapeutic options means that treatment is often palliative rather than curative. A deeper understanding of the pathogenesis of both acute and chronic pancreatitis is necessary to develop new therapies. Pathological changes in pancreatitis are dependent on innate immune cell recruitment to the site of initial tissue damage, and on the coordination of downstream inflammatory pathways. The chemokine receptor CXCR2 drives neutrophil recruitment during inflammation, and to investigate its role in pancreatic inflammation, we induced acute and chronic pancreatitis in wild-type and Cxcr2(-/-) mice. Strikingly, Cxcr2(-/-) mice were strongly protected from tissue damage in models of acute pancreatitis, and this could be recapitulated by neutrophil depletion or by the specific deletion of Cxcr2 from myeloid cells. The pancreata of Cxcr2(-/-) mice were also substantially protected from damage during chronic pancreatitis. Neutrophil depletion was less effective in this model, suggesting that CXCR2 on non-neutrophils contributes to the development of chronic pancreatitis. Importantly, pharmacological inhibition of CXCR2 in wild-type mice replicated the protection seen in Cxcr2(-/-) mice in acute and chronic models of pancreatitis. Moreover, acute pancreatic inflammation was reversible by inhibition of CXCR2. Thus, CXCR2 is critically involved in the development of acute and chronic pancreatitis in mice, and its inhibition or loss protects against pancreatic damage. CXCR2 may therefore be a viable therapeutic target in the treatment of pancreatitis.

Chemokines and their receptors in Atherosclerosis

Atherosclerosis, a chronic inflammatory disease of the medium- and large-sized arteries, is the main underlying cause of cardiovascular diseases (CVDs) most often leading to a myocardial infarction or stroke. However, atherosclerosis can also develop without this clinical manifestation. The pathophysiology of atherosclerosis is very complex and consists of many cells and molecules interacting with each other. Over the last years, chemokines (small 8-12 kDa cytokines with chemotactic properties) have been identified as key players in atherogenesis. However, this remains a very active and dynamic field of research. Here, we will give an overview of the current knowledge about the involvement of chemokines in all phases of atherosclerotic lesion development. Furthermore, we will focus on two chemokines that recently have been associated with atherogenesis, CXCL12, and macrophage migration inhibitory factor (MIF). Both chemokines play a crucial role in leukocyte recruitment and arrest, a critical step in atherosclerosis development. MIF has shown to be a more pro-inflammatory and thus pro-atherogenic chemokine, instead CXCL12 seems to have a more protective function. However, results about this protective role are still quite debatable. Future research will further elucidate the precise role of these chemokines in atherosclerosis and determine the potential of chemokine-based therapies.

MIF and CXCL12 in Cardiovascular Diseases: Functional Differences and Similarities

Coronary artery disease (CAD) as part of the cardiovascular diseases is a pathology caused by atherosclerosis, a chronic inflammatory disease of the vessel wall characterized by a massive invasion of lipids and inflammatory cells into the inner vessel layer (intima) leading to the formation of atherosclerotic lesions; their constant growth may cause complications such as flow-limiting stenosis and plaque rupture, the latter triggering vessel occlusion through thrombus formation. Pathophysiology of CAD is complex and over the last years many players have entered the picture. One of the latter being chemokines (small 8-12 kDa cytokines) and their receptors, known to orchestrate cell chemotaxis and arrest. Here, we will focus on the chemokine CXCL12, also known as stromal cell-derived factor 1 (SDF-1) and the chemokine-like function chemokine, macrophage migration-inhibitory factor (MIF). Both are ubiquitously expressed and highly conserved proteins and play an important role in cell homeostasis, recruitment, and arrest through binding to their corresponding chemokine receptors CXCR4 (CXCL12 and MIF), ACKR3 (CXCL12), and CXCR2 (MIF). In addition, MIF also binds to the receptor CD44 and the co-receptor CD74. CXCL12 has mostly been studied for its crucial role in the homing of (hematopoietic) progenitor cells in the bone marrow and their mobilization into the periphery. In contrast to CXCL12, MIF is secreted in response to diverse inflammatory stimuli, and has been associated with a clear pro-inflammatory and pro-atherogenic role in multiple studies of patients and animal models. Ongoing research on CXCL12 points at a protective function of this chemokine in atherosclerotic lesion development. This review will focus on the role of CXCL12 and MIF and their differences and similarities in CAD of high risk patients.

Chemokines and microRNAs in atherosclerosis

The crucial role of chemokines in the initiation and progression of atherosclerosis has been widely recognized. Through essential functions in leukocyte recruitment, chemokines govern the infiltration with mononuclear cells and macrophage accumulation in atherosclerotic lesions. Beyond recruitment, chemokines also provide homeostatic functions supporting cell survival and mediating the mobilization and homing of progenitor cells. As a new regulatory layer, several microRNAs (miRNAs) have been found to modulate the function of endothelial cells (ECs), smooth muscle cells and macrophages by controlling the expression levels of chemokines and thereby affecting different stages in the progression of atherosclerosis. For instance, the expression of CXCL1 can be down-regulated by miR-181b, which inhibits nuclear factor-κB activation in atherosclerotic endothelium, thus attenuating the adhesive properties of ECs and exerting early atheroprotective effects. Conversely, CXCL12 expression can be induced by miR-126 in ECs through an auto-amplifying feedback loop to facilitate endothelial regeneration, thus limiting atherosclerosis and mediating plaque stabilization. In contrast, miR-155 plays a pro-atherogenic role by promoting the expression of CCL2 in M1-type macrophages, thereby enhancing vascular inflammation. Herein, we will review novel aspects of chemokines and their regulation by miRNAs during atherogenesis. Understanding the complex cross-talk of miRNAs controlling chemokine expression may open novel therapeutic options to treat atherosclerosis.

CD8+ T Cells Regulate Monopoiesis and Circulating Ly6C-high Monocyte Levels in Atherosclerosis in Mice

RATIONALE

Proinflammatory adaptive immune responses are recognized as major drivers of atherosclerotic lesion formation. Although CD8(+) T cells have recently been proposed as a proatherogenic cell subset, their full scope of actions remains to be elucidated.

OBJECTIVE

We here addressed the contribution of CD8(+) T cells to monocyte trafficking in atherosclerosis.

METHOD AND RESULTS

We observed that CD8(+) T cells express proinflammatory cytokines (interferon-γ, tumor necrosis factor-α, and interleukin-12) within atherosclerotic lesions and spleens of high-fat diet-fed low-density lipoprotein receptor-deficient (Ldlr(-/-)) mice. Antibody-mediated CD8(+) T-cell depletion in high-fat diet-fed Ldlr(-/-) mice decreased atherosclerotic plaque formation, associated with decreased macrophage accumulation within lesions. Despite a reduction in vascular chemokine (CC-motif) ligand 2 and chemokine (CXC-motif) ligand 1 expression, CD8(+) T-cell depletion did not directly affect monocyte recruitment to inflamed vessels. However, CD8(+) T-cell depletion decreased chemokine (CC-motif) ligand serum concentrations and circulating Ly6C(high) monocyte counts. We further evidenced that CD8(+) T-cell depletion decreased levels of mature monocytes and myeloid granulocyte-monocyte progenitors in the bone marrow and spleen of hypercholesterolemic mice, effects that were partially reproduced by interferon-γ neutralization, showing a role for interferon-γ.

CONCLUSIONS

These data suggest that CD8(+) T cells promote atherosclerosis by controlling monopoiesis and circulating monocyte levels, which ultimately contributes to plaque macrophage burden without affecting direct monocyte recruitment, identifying this cell subset as a critical regulator of proatherogenic innate immune cell responses in atherosclerosis.

Cytokines in atherosclerosis: Key players in all stages of disease and promising therapeutic targets

Atherosclerosis, a chronic inflammatory disorder of the arteries, is responsible for most deaths in westernized societies with numbers increasing at a marked rate in developing countries. The disease is initiated by the activation of the endothelium by various risk factors leading to chemokine-mediated recruitment of immune cells. The uptake of modified lipoproteins by macrophages along with defective cholesterol efflux gives rise to foam cells associated with the fatty streak in the early phase of the disease. As the disease progresses, complex fibrotic plaques are produced as a result of lysis of foam cells, migration and proliferation of vascular smooth muscle cells and continued inflammatory response. Such plaques are stabilized by the extracellular matrix produced by smooth muscle cells and destabilized by matrix metalloproteinase from macrophages. Rupture of unstable plaques and subsequent thrombosis leads to clinical complications such as myocardial infarction. Cytokines are involved in all stages of atherosclerosis and have a profound influence on the pathogenesis of this disease. This review will describe our current understanding of the roles of different cytokines in atherosclerosis together with therapeutic approaches aimed at manipulating their actions.

Macrophages and immune cells in atherosclerosis: recent advances and novel concepts

Atherosclerotic lesion-related thrombosis is the major cause of myocardial infarction and stroke, which together constitute the leading cause of mortality worldwide. The inflammatory response is considered as a predominant driving force in atherosclerotic plaque formation, growth and progression towards instability and rupture. Notably, accumulation of macrophages in the intima and emergence of a pro-inflammatory milieu are a characteristic feature of plaque progression, and these processes can be modulated by adaptive immune responses. Recently, novel evidences of onsite proliferation of macrophages in lesions and transdifferentiation of smooth muscle cells to macrophages have challenged the prevalent paradigm that macrophage accumulation mostly relies on recruitment of circulating monocytes to plaques. Furthermore, previously unrecognized roles of inflammatory cell subsets such as plasmacytoid dendritic cells, innate response activator B cells or CD8(+) T cells in atherosclerosis have emerged, as well as novel mechanisms by which regulatory T cells or natural killer T cells contribute to lesion formation. Here, we review and discuss these recent advances in our understanding of inflammatory processes in atherosclerosis.

Chemokines Control Mobilization, Recruitment, and Fate of Monocytes in Atherosclerosis

Atherosclerosis is a chronic inflammatory disease of large arteries and, among others, characterized by continuous influx of monocytes into the subendothelial space, subsequent macrophage accumulation, and foam cell formation. Chemokines and their receptors tightly orchestrate monocyte trafficking and fate from birth to death. This brief review summarizes our current understanding of the interplay between monocytes and chemokines entertaining crucial processes in atherosclerosis development, progression, and regression.

Atherosclerosis - A matter of unresolved inflammation

Atherosclerosis is commonly looked upon as a chronic inflammatory disease of the arterial wall arising from an unbalanced lipid metabolism and a maladaptive inflammatory response. However, atherosclerosis is not merely an inflammation of the vessel wall. In fact, the cardinal signs of unstable atherosclerotic lesions are primarily characteristics of failed resolution of a chronic inflammation. In contrast to acute inflammatory events which are typically self-limiting, atherosclerosis is an unresolved inflammatory condition, lacking the switch from the pro-inflammatory to the pro-resolving phase, the latter characterized by termination of inflammatory cell recruitment, removal of inflammatory cells from the site of inflammation by apoptosis and dead cell clearance, reprogramming of macrophages toward an anti-inflammatory, regenerative phenotype, and finally egress of effector cells and tissue regeneration. Here we present an overview on mechanisms of failed resolution contributing to atheroprogression and deliver a summary of novel therapeutic strategies to restore resolution in inflamed arteries.

Regulation of leucocyte homeostasis in the circulation

The functions of blood cells extend well beyond the immune functions of leucocytes or the respiratory and hemostatic functions of erythrocytes and platelets. Seen as a whole, the bloodstream is in charge of nurturing and protecting all organs by carrying a mixture of cell populations in transit from one organ to another. To optimize these functions, evolution has provided blood and the vascular system that carries it with various mechanisms that ensure the appropriate influx and egress of cells into and from the circulation where and when needed. How this homeostatic control of blood is achieved has been the object of study for over a century, and although the major mechanisms that govern it are now fairly well understood, several new concepts and mediators have recently emerged that emphasize the dynamism of this liquid tissue. Here we review old and new concepts that relate to the maintenance and regulation of leucocyte homeostasis in blood and briefly discuss the mechanisms for platelets and red blood cells.

Macrophages shine bright

In this issue of Blood, Iqbal et al created a novel mouse model with a strong expression of green fluorescence protein (GFP) in monocytes, tissue resident macrophages, and inflammatory macrophages, and may provide an important tool for future studies focusing on macrophage biology. Several transgenic mice with expression of fluorescent proteins in myeloid cells exist, among them the CCR2-RFP and the CX3CR1GFP mouse. However, both of these mice have several limitations: they are knock-in constructs under control of chemokine receptors with potential effects on monocyte mobilization from the bone marrow, recruitment to sites of inflammation, or survival. Alteration of chemokine receptor expression during macrophage differentiation may affect expression of fluorescent proteins and thus render macrophages nonfluorescent.

Chemokine-mediated inflammation in the degenerating retina is coordinated by Müller cells, activated microglia, and retinal pigment epithelium

BACKGROUND

Monocyte infiltration is involved in the pathogenesis of many retinal degenerative conditions. This process traditionally depends on local expression of chemokines, though the roles of many of these in the degenerating retina are unclear. Here, we investigate expression and in situ localization of the broad chemokine response in a light-induced model of retinal degeneration.

METHODS

Sprague-Dawley (SD) rats were exposed to 1,000 lux light damage (LD) for up to 24 hrs. At time points during (1 to 24 hrs) and following (3 and 7 days) exposure, animals were euthanized and retinas processed. Microarray analysis assessed differential expression of chemokines. Some genes were further investigated using polymerase chain reaction (PCR) and in situ hybridization and contrasted with photoreceptor apoptosis using terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL). Recruitment of retinal CD45 (+) leukocytes was determined via fluorescence activated cell sorting (FACS), and expression of chemokine receptors determined using PCR.

RESULTS

Exposure to 24 hrs of LD resulted in differential expression of chemokines including Ccl3, Ccl4, Ccl7, Cxcl1, and Cxcl10. Their upregulation correlated strongly with peak photoreceptor death, at 24 hrs exposure. In situ hybridization revealed that the modulated chemokines were expressed by a combination of Müller cells, activated microglia, and retinal pigment epithelium (RPE). This preceded large increases in the number of CD45(+) cells at 3- and 7-days post exposure, which expressed a corresponding repertoire of chemokine receptors.

CONCLUSIONS

Our data indicate that retinal degeneration induces upregulation of a broad chemokine response whose expression is coordinated by Müller cells, microglia, and RPE. The findings inform our understanding of the processes govern the trafficking of leukocytes, which are contributors in the pathology of retinal degenerations.

Inflammation in arterial diseases

The pathophysiology of some inflammatory arterial diseases (such as vasculitis, atherogenesis and aneurysms) has been widely investigated in the last decades. Among different soluble molecules, proinflammatory cytokines (such as TNF-α, IL-1 and IL-6) were shown to trigger critical pathways regulating these arterial diseases. Together with these cytokines, chemokines were also associated with endothelial dysfunction and intima injury in arterial diseases. Recently, autoantibodies have been also described to pathophysiologically influence not only autoimmune vasculitis but also atherogenesis and more in general vascular inflammation. These soluble mediators actively trigger inflammatory functions of leukocytes and vascular cells. For instance, B and T lymphocytes, macrophages and neutrophils were shown to actively participate in inflammatory processes within the arterial wall in vasculitis, atherogenesis and aneurysms. The aim of this narrative review is to provide an overview of pathophysiology and treatments targeting arterial inflammation in these diseases.

Intravital Microscopy for Atherosclerosis Research

Recruitment of leukocytes into arteries is a hallmark event throughout all stages of atherosclerosis and hence stands out as a primary therapeutic target. To understand the molecular mechanisms of arterial leukocyte subset infiltration, real-time visualization of recruitment processes of leukocyte subsets at high resolution is a prerequisite. In this review we provide a balanced overview of optical imaging modalities in the more commonly used experimental models for atherosclerosis (e.g., mouse models) allowing for in vivo display of recruitment processes in large arteries and further detail strategies to overcome hurdles inherent to arterial imaging. We further provide a synopsis of techniques allowing for non-toxic, photostable labeling of target structures. Finally, we deliver a short summary of ongoing developments including the emergence of novel labeling approaches, the use of superresolution microscopy, and the potentials of opto-acoustic microscopy and intravascular 2-dimensional near-infrared fluorescence microscopy.

Monocyte fate in atherosclerosis

Monocytes and their descendant macrophages are essential to the development and exacerbation of atherosclerosis, a lipid-driven inflammatory disease. Lipid-laden macrophages, known as foam cells, reside in early lesions and advanced atheromata. Our understanding of how monocytes accumulate in the growing lesion, differentiate, ingest lipids, and contribute to disease has advanced substantially over the last several years. These cells' remarkable phenotypic and functional complexity is a therapeutic opportunity: in the future, treatment and prevention of cardiovascular disease and its complications may involve specific targeting of atherogenic monocytes/macrophages and their products.

Angiotensin II mobilizes spleen monocytes to promote the development of abdominal aortic aneurysm in Apoe-/- mice

OBJECTIVE

Abdominal aortic aneurysm (AAA) is widespread among elderly people and results in progressive expansion and rupture of the aorta with high mortality. Macrophages, which are the main population observed within the site of aneurysm, are thought to derive from circulating monocytes although no direct evidence has been provided to date. In this study, we were particularly interested in understanding the trafficking behavior of monocyte subsets in AAA and their role in disease pathogenesis.

APPROACH AND RESULTS

Using bone marrow transplantation in Apoe(-/-) mice, we showed that circulating monocytes give rise to abdominal aortic macrophages in hypercholesterolemic mice submitted to angiotensin II (AngII). Detailed monitoring of monocyte compartmentalization revealed that lymphocyte antigen 6C(high) and lymphocyte antigen 6C(low) monocytes transiently increase in blood early after AngII infusion and differentially infiltrate the abdominal aorta. The splenic reservoir accounted for the mobilization of the 2 monocyte subsets after 3 days of AngII infusion. Spleen removal or lymphocyte deficiency in Apoe(-/-) Rag2(-/-) mice similarly impaired early monocyte increase in blood in response to AngII and protected against AAA development, independently of blood pressure. Reconstitution of Apoe(-/-) Rag2(-/-) mice with total splenocytes but not with B-cell-depleted splenocytes restored monocyte mobilization in response to AngII and enhanced susceptibility to AAA.

CONCLUSIONS

Taken together, the data show that lymphocyte antigen 6C(high) and lymphocyte antigen 6C(low) monocytes are mobilized from the spleen in response to AngII. Intriguingly, the process is dependent on the presence of B cells and significantly contributes to the development of AAA and the occurrence of aortic rupture.

Annexin A1 counteracts chemokine-induced arterial myeloid cell recruitment

RATIONALE

Chemokine-controlled arterial leukocyte recruitment is a crucial process in atherosclerosis. Formyl peptide receptor 2 (FPR2) is a chemoattractant receptor that recognizes proinflammatory and proresolving ligands. The contribution of FPR2 and its proresolving ligand annexin A1 to atherosclerotic lesion formation is largely undefined.

OBJECTIVE

Because of the ambivalence of FPR2 ligands, we here investigate the role of FPR2 and its resolving ligand annexin A1 in atherogenesis.

METHODS AND RESULTS

Deletion of FPR2 or its ligand annexin A1 enhances atherosclerotic lesion formation, arterial myeloid cell adhesion, and recruitment. Mechanistically, we identify annexin A1 as an endogenous inhibitor of integrin activation evoked by the chemokines CCL5, CCL2, and CXCL1. Specifically, the annexin A1 fragment Ac2-26 counteracts conformational activation and clustering of integrins on myeloid cells evoked by CCL5, CCL2, and CXCL1 through inhibiting activation of the small GTPase Rap1. In vivo administration of Ac2-26 largely diminishes arterial recruitment of myeloid cells in a FPR2-dependent fashion. This effect is also observed in the presence of selective antagonists to CCR5, CCR2, or CXCR2, whereas Ac2-26 was without effect when all 3 chemokine receptors were antagonized simultaneously. Finally, repeated treatment with Ac2-26 reduces atherosclerotic lesion sizes and lesional macrophage accumulation.

CONCLUSIONS

Instructing the annexin A1-FPR2 axis harbors a novel approach to target arterial leukocyte recruitment. With the ability of Ac2-26 to counteract integrin activation exerted by various chemokines, delivery of Ac2-26 may be superior in inhibition of arterial leukocyte recruitment when compared with blocking individual chemokine receptors.

Hyperreactivity of junctional adhesion molecule A-deficient platelets accelerates atherosclerosis in hyperlipidemic mice

RATIONALE

Besides their essential role in hemostasis, platelets also have functions in inflammation. In platelets, junctional adhesion molecule (JAM)-A was previously identified as an inhibitor of integrin αIIbβ3-mediated outside-in signaling and its genetic knockdown resulted in hyperreactivity.

OBJECTIVE

This gain-of-function was specifically exploited to investigate the role of platelet hyperreactivity in plaque development.

METHODS AND RESULTS

JAM-A-deficient platelets showed increased aggregation and cellular and sarcoma tyrosine-protein kinase activation. On αIIbβ3 ligation, JAM-A was shown to be dephosphorylated, which could be prevented by protein tyrosine phosphatase nonreceptor type 1 inhibition. Mice with or without platelet-specific (tr)JAM-A-deficiency in an apolipoprotein e (apoe(-/-)) background were fed a high-fat diet. After ≤12 weeks of diet, trJAM-A(-/-)apoe-/- mice showed increased aortic plaque formation when compared with trJAM-A(+/+) apoe(-/-) controls, and these differences were most evident at early time points. At 2 weeks, the plaques of the trJAM-A(-/-) apoe(-/-) animals revealed increased macrophage, T cell, and smooth muscle cell content. Interestingly, plasma levels of chemokines CC chemokine ligand 5 and CXC-chemokine ligand 4 were increased in the trJAM-A(-/-) apoe(-/-)mice, and JAM-A-deficient platelets showed increased binding to monocytes and neutrophils. Whole-blood perfusion experiments and intravital microscopy revealed increased recruitment of platelets and monocytes to the inflamed endothelium in blood of trJAM-A(-/-) apoe(-/-)mice. Notably, these proinflammatory effects of JAM-A-deficient platelets could be abolished by the inhibition of αIIbβ3 signaling in vitro.

CONCLUSIONS

Deletion of JAM-A causes a gain-of-function in platelets, with lower activation thresholds and increased inflammatory activities. This leads to an increase of plaque formation, particularly in early stages of the disease.

Monocyte subsets in atherosclerosis

Endothelial dysfunction and chronic inflammation of the arterial wall continuously drive the development of atherosclerotic lesions. Monocytes, as cells of the innate immunity, are particularly involved in this process. In the last decade, heterogeneity of circulating monocytes has widely been acknowledged, and a recent consensus nomenclature subdivides classical, intermediate and nonclassical monocytes. Accumulating experimental and clinical data suggest a differential, subset-specific contribution of monocytes to the pathology of atherosclerosis. This review summarizes recent key findings on human and mouse monocyte subpopulations, specifically highlighting their phenotype, functional characteristics and mechanisms of recruitment at homeostatic conditions, in atherosclerotic vascular disease, and after acute myocardial infarction.

Characterization of the CD14++CD16+ monocyte population in human bone marrow

Numerous studies have divided blood monocytes according to their expression of the surface markers CD14 and CD16 into following subsets: classical CD14⁺⁺CD16⁻, intermediate CD14⁺⁺CD16⁺ and nonclassical CD14⁺CD16⁺⁺ monocytes. These subsets differ in phenotype and function and are further correlated to cardiovascular disease, inflammation and cancer. However, the CD14/CD16 nature of resident monocytes in human bone marrow remains largely unknown. In the present study, we identified a major population of CD14⁺⁺CD16⁺ monocytes by using cryopreserved bone marrow mononuclear cells from healthy donors. These cells express essential monocyte-related antigens and chemokine receptors such as CD11a, CD18, CD44, HLA-DR, Ccr2, Ccr5, Cx3cr1, Cxcr2 and Cxcr4. Notably, the expression of Ccr2 was inducible during culture. Furthermore, sorted CD14⁺⁺CD16⁺ bone marrow cells show typical macrophage morphology, phagocytic activity, angiogenic features and generation of intracellular oxygen species. Side-by-side comparison of the chemokine receptor profile with unpaired blood samples also demonstrated that these rather premature medullar monocytes mainly match the phenotype of intermediate and partially of (non)classical monocytes. Together, human monocytes obviously acquire their definitive CD14/CD16 signature in the bloodstream and the medullar monocytes probably transform into CD14⁺⁺CD16⁻ and CD14⁺CD16⁺⁺ subsets which appear enriched in the periphery.

Treatment with Evasin-3 abrogates neutrophil-mediated inflammation in mouse acute pancreatitis

BACKGROUND

Acute pancreatitis is characterized by inflammatory processes affecting not only the pancreas, but also the lung. Here, we investigated timing of leucocyte infiltration and chemokine expression within lung and pancreas during pancreatitis and whether treatments selectively inhibiting chemokines (using Evasins) could improve organ injury.

MATERIAL AND METHODS

C57Bl/6 mice were submitted in vivo to 10-h intraperitoneal injections of cerulein and followed for up to 168 h. Five minutes after the first cerulein injection, a single intraperitoneal injection of 10 μg Evasin-3, 1 μg Evasin-4 or an equal volume of vehicle (PBS) was performed. Leucocytes, reactive oxygen species (ROS), necrosis and chemokine/cytokine mRNA expression were assessed in different organs by immunohistology and real-time RT-PCR, respectively.

RESULTS

In the lung, neutrophil infiltration and macrophage infiltration peaked at 12 h and were accompanied by increased CXCL2 mRNA expression. CCL2, CXCL1 and TNF-alpha significantly increased after 24 h as compared to baseline. No increase in CCL3 and CCL5 was observed. In the pancreas, neutrophil infiltration peaked at 6 h, while macrophages increased only after 72 h. Treatment with Evasin-3 decreased neutrophil infiltration, ROS production and apoptosis in the lung and reduced neutrophils, macrophages apoptosis and necrosis in the pancreas. Evasin-4 only reduced macrophage content in the lung and did not provide any benefit at the pancreas level.

CONCLUSION

Chemokine production and leucocyte infiltration are timely regulated in lung and pancreas during pancreatitis. CXC chemokine inhibition with Evasin-3 improved neutrophil inflammation and injury, potentially interfering with damages in acute pancreatitis and related pulmonary complications.

Inflammatory role and prognostic value of platelet chemokines in acute coronary syndrome

Activated platelets and neutrophils exacerbate atherosclerosis. Platelets release the chemokines CXCL4, CXCL4L1 and CCL5, whereas myeloperoxidase (MPO) and azurocidin are neutrophil-derived. We investigated whether plasma levels of these platelet and neutrophil mediators are affected by the acute coronary syndrome (ACS), its medical treatment, concomitant clinical or laboratory parameters, and predictive for the progression of coronary artery disease (CAD). In an observational study, the association of various factors with plasma concentrations of platelet chemokines and neutrophil mediators in 204 patients, either upon admission with ACS and 6 hours later or without ACS or CAD, was determined by multiple linear regression. Mediator release was further analysed after activation of blood with ACS-associated triggers such as plaque material. CXCL4, CXCL4L1, CCL5, MPO and azurocidin levels were elevated in ACS. CXCL4 and CCL5 but not CXCL4L1 or MPO were associated with platelet counts and CRP. CXCL4 (in association with heparin treatment) and MPO declined over 6 hours during ACS. Elevated CCL5 was associated with a progression of CAD. Incubating blood with plaque material, PAR1 and PAR4 activation induced a marked release of CXCL4 and CCL5, whereas CXCL4L1 and MPO were hardly or not altered. Platelet chemokines and neutrophil products are concomitantly elevated in ACS and differentially modulated by heparin treatment. CCL5 levels during ACS predict a progression of preexisting CAD. Platelet-derived products appear to dominate the inflammatory response during ACS, adding to the emerging evidence that ACS per se may promote vascular inflammation.

Lower Apo A-I and lower HDL-C levels are associated with higher intermediate CD14++CD16+ monocyte counts that predict cardiovascular events in chronic kidney disease

OBJECTIVE

Patients with chronic kidney disease (CKD) display impaired cholesterol efflux capacity and elevated CD14(++)CD16(+) monocyte counts. In mice, dysfunctional cholesterol efflux causes monocytosis. It is unknown whether cholesterol efflux capacity and monocyte subsets are associated in CKD.

APPROACH AND RESULTS

In 438 patients with CKD, mediators of cholesterol efflux capacity (high-density lipoprotein cholesterol/apolipoprotein A-I) and monocyte subsets were analyzed as predictors of cardiovascular events. Monocyte subset-specific intracellular lipid content, CD36, CD68, and ABCA1 were measured in a subgroup. Experimentally, we analyzed subset-specific cholesterol efflux capacity and response to oxidized low-density lipoprotein cholesterol stimulation in CKD. Epidemiologically, both low Apo-I and low high-density lipoprotein cholesterol were associated with high CD14(++)CD16(+) monocyte counts in linear regression analyses (apolipoprotein A-I: β=-0.171; P<0.001; high-density lipoprotein cholesterol: β=-0.138; P=0.005), but not with counts of other monocyte subsets. In contrast to apolipoprotein A-I or high-density lipoprotein cholesterol, higher CD14(++)CD16(+) monocyte counts independently predicted cardiovascular events (hazard ratio per increase of 1 cell/μL: 1.011 [1.003-1.020]; P=0.007). Experimentally, CD14(++)CD16(+) monocytes demonstrated preferential lipid accumulation, high CD36, CD68, and low ABCA1 expression and, consequently, displayed low cholesterol efflux capacity, avid oxidized low-density lipoprotein cholesterol uptake, and potent intracellular interleukin-6, interleukin-1β, and tumor necrosis factor-α production.

CONCLUSIONS

Taken together, mediators of cholesterol efflux are associated with CD14(++)CD16(+) monocyte counts, which independently predict adverse outcome in CKD.

Molecular characterization of a CXCL8-like protein from ayu and its effect on chemotaxis of neutrophils and monocytes/macrophages

CXCL8, a CXC-type chemokine, plays a crucial role in acute inflammation by recruiting and mediating neutrophils and other cells. In this study, the cDNA and genomic DNA sequence of a CXCL8-like protein (PaCXCL8l) from ayu (Plecoglossus altivelis) was determined. Sequence analysis showed that PaCXCL8l represented the typical structure of animal CXCL8s. Phylogenetic tree analysis indicated that PaCXCL8l was closest to CXCL8 of Atlantic cod (Gadus morhua). Constitutive expression of PaCXCL8l was detected in all tested tissues and monocytes/macrophages, and its expression dramatically increased upon Listonella anguillarum infection. In vitro, recombinant PaCXCL8l exhibited a significant chemotactic effect on neutrophils at 0.1 μg/ml and on monocytes/macrophages at 1.0 μg/ml. In vivo, the numbers of peritoneal neutrophils and monocytes/macrophages were both up-regulated following intraperitoneal administration of recombinant PaCXCL8l. These results suggest that PaCXCL8l is crucially involved in the immune response of ayu by mediating chemotaxis of neutrophils and monocytes/macrophages.

Monocyte homeostasis and the plasticity of inflammatory monocytes

Monocytes are mononuclear myeloid cells that develop in the bone marrow and circulate within the bloodstream. Although they have long been argued to play a role in the repopulation of tissue-resident macrophages, this has been questioned by numerous recent studies, which has forced a reappraisal of their biology. Here we discuss monocyte development, as well as the homeostatic control of monocyte subpopulations within the blood. We also outline the known functions of monocyte subsets. Finally, we highlight the plastic nature of monocytes, which are capable of a remarkable range of phenotypic and functional changes that depend on signals from local microenvironments.

Inflammation and its resolution as determinants of acute coronary syndromes

Inflammation contributes to many of the characteristics of plaques implicated in the pathogenesis of acute coronary syndromes. Moreover, inflammatory pathways not only regulate the properties of plaques that precipitate acute coronary syndromes but also modulate the clinical consequences of the thrombotic complications of atherosclerosis. This synthesis will provide an update on the fundamental mechanisms of inflammatory responses that govern acute coronary syndromes and also highlight the ongoing balance between proinflammatory mechanisms and endogenous pathways that can promote the resolution of inflammation. An appreciation of the countervailing mechanisms that modulate inflammation in relation to acute coronary syndromes enriches our fundamental understanding of the pathophysiology of this important manifestation of atherosclerosis. In addition, these insights provide glimpses into potential novel therapeutic interventions to forestall this ultimate complication of the disease.