Atypical chemokine receptor 1 on nucleated erythroid cells regulates hematopoiesis.

Healthy individuals of African ancestry have neutropenia that has been linked with the variant rs2814778(G) of the gene encoding atypical chemokine receptor 1 (ACKR1). This polymorphism selectively abolishes the expression of ACKR1 in erythroid cells, causing a Duffy-negative phenotype. Here we describe an unexpected fundamental role for ACKR1 in hematopoiesis and provide the mechanism that links its absence with neutropenia. Nucleated erythroid cells had high expression of ACKR1, which facilitated their direct contact with hematopoietic stem cells. The absence of erythroid ACKR1 altered mouse hematopoiesis including stem and progenitor cells, which ultimately gave rise to phenotypically distinct neutrophils that readily left the circulation, causing neutropenia. Individuals with a Duffy-negative phenotype developed a distinct profile of neutrophil effector molecules that closely reflected the one observed in the ACKR1-deficient mice. Thus, alternative physiological patterns of hematopoiesis and bone marrow cell outputs depend on the expression of ACKR1 in the erythroid lineage, findings with major implications for the selection advantages that have resulted in the paramount fixation of the ACKR1 rs2814778(G) polymorphism in Africa.

Neuroimmune cardiovascular interfaces control atherosclerosis.

Atherosclerotic plaques develop in the inner intimal layer of arteries and can cause heart attacks and strokes1. As plaques lack innervation, the effects of neuronal control on atherosclerosis remain unclear. However, the immune system responds to plaques by forming leukocyte infiltrates in the outer connective tissue coat of arteries (the adventitia)2-6. Here, because the peripheral nervous system uses the adventitia as its principal conduit to reach distant targets7-9, we postulated that the peripheral nervous system may directly interact with diseased arteries. Unexpectedly, widespread neuroimmune cardiovascular interfaces (NICIs) arose in mouse and human atherosclerosis-diseased adventitia segments showed expanded axon networks, including growth cones at axon endings near immune cells and media smooth muscle cells. Mouse NICIs established a structural artery-brain circuit (ABC): abdominal adventitia nociceptive afferents10-14 entered the central nervous system through spinal cord T6-T13 dorsal root ganglia and were traced to higher brain regions, including the parabrachial and central amygdala neurons; and sympathetic efferent neurons projected from medullary and hypothalamic neurons to the adventitia through spinal intermediolateral neurons and both coeliac and sympathetic chain ganglia. Moreover, ABC peripheral nervous system components were activated: splenic sympathetic and coeliac vagus nerve activities increased in parallel to disease progression, whereas coeliac ganglionectomy led to the disintegration of adventitial NICIs, reduced disease progression and enhanced plaque stability. Thus, the peripheral nervous system uses NICIs to assemble a structural ABC, and therapeutic intervention in the ABC attenuates atherosclerosis.

Generation of complex bone marrow organoids from human induced pluripotent stem cells.

The human bone marrow (BM) niche sustains hematopoiesis throughout life. We present a method for generating complex BM-like organoids (BMOs) from human induced pluripotent stem cells (iPSCs). BMOs consist of key cell types that self-organize into spatially defined three-dimensional structures mimicking cellular, structural and molecular characteristics of the hematopoietic microenvironment. Functional properties of BMOs include the presence of an in vivo-like vascular network, the presence of multipotent mesenchymal stem/progenitor cells, the support of neutrophil differentiation and responsiveness to inflammatory stimuli. Single-cell RNA sequencing revealed a heterocellular composition including the presence of a hematopoietic stem/progenitor (HSPC) cluster expressing genes of fetal HSCs. BMO-derived HSPCs also exhibited lymphoid potential and a subset demonstrated transient engraftment potential upon xenotransplantation in mice. We show that the BMOs could enable the modeling of hematopoietic developmental aspects and inborn errors of hematopoiesis, as shown for human VPS45 deficiency. Thus, iPSC-derived BMOs serve as a physiologically relevant in vitro model of the human BM microenvironment to study hematopoietic development and BM diseases.

Externalized histone H4 orchestrates chronic inflammation by inducing lytic cell death.

The perpetuation of inflammation is an important pathophysiological contributor to the global medical burden. Chronic inflammation is promoted by non-programmed cell death1,2; however, how inflammation is instigated, its cellular and molecular mediators, and its therapeutic value are poorly defined. Here we use mouse models of atherosclerosis-a major underlying cause of mortality worldwide-to demonstrate that extracellular histone H4-mediated membrane lysis of smooth muscle cells (SMCs) triggers arterial tissue damage and inflammation. We show that activated lesional SMCs attract neutrophils, triggering the ejection of neutrophil extracellular traps that contain nuclear proteins. Among them, histone H4 binds to and lyses SMCs, leading to the destabilization of plaques; conversely, the neutralization of histone H4 prevents cell death of SMCs and stabilizes atherosclerotic lesions. Our data identify a form of cell death found at the core of chronic vascular disease that is instigated by leukocytes and can be targeted therapeutically.

Targeting platelet-derived CXCL12 impedes arterial thrombosis.

The prevention and treatment of arterial thrombosis continue to be clinically challenging, and understanding the relevant molecular mechanisms in detail may facilitate the quest to identify novel targets and therapeutic approaches that improve protection from ischemic and bleeding events. The chemokine CXCL12 augments collagen-induced platelet aggregation by activating its receptor CXCR4. Here we show that inhibition of CXCR4 attenuates platelet aggregation induced by collagen or human plaque homogenate under static and arterial flow conditions by antagonizing the action of platelet-secreted CXCL12. We further show that platelet-specific CXCL12 deficiency in mice limits arterial thrombosis by affecting thrombus growth and stability without increasing tail bleeding time. Accordingly, neointimal lesion formation after carotid artery injury was attenuated in these mice. Mechanistically, CXCL12 activated via CXCR4 a signaling cascade involving Bruton's tyrosine kinase (Btk) that led to integrin αIIbß3 activation, platelet aggregation, and granule release. The heterodimeric interaction between CXCL12 and CCL5 can inhibit CXCL12-mediated effects as mimicked by CCL5-derived peptides such as [VREY]4. An improved variant of this peptide, i[VREY]4, binds to CXCL12 in a complex with CXCR4 on the surface of activated platelets, thereby inhibiting Btk activation and preventing platelet CXCL12-dependent arterial thrombosis. In contrast to standard antiplatelet therapies such as aspirin or P2Y12 inhibition, i[VREY]4 reduced CXCL12-induced platelet aggregation and yet did not prolong in vitro bleeding time. We provide evidence that platelet-derived CXCL12 is involved in arterial thrombosis and can be specifically targeted by peptides that harbor potential therapeutic value against atherothrombosis.

The Amino Acid Homoarginine Inhibits Atherogenesis by Modulating T-Cell Function.

BACKGROUND: Amino acid metabolism is crucial for inflammatory processes during atherogenesis. The endogenous amino acid homoarginine is a robust biomarker for cardiovascular outcome and mortality with high levels being protective. However, the underlying mechanisms remain elusive. We investigated the effect of homoarginine supplementation on atherosclerotic plaque development with a particular focus on inflammation. METHODS: Female ApoE-deficient mice were supplemented with homoarginine (14 mg/L) in drinking water starting 2 weeks before and continuing throughout a 6-week period of Western-type diet feeding. Control mice received normal drinking water. Immunohistochemistry and flow cytometry were used for plaque- and immunological phenotyping. T cells were characterized using mass spectrometry-based proteomics, by functional in vitro approaches, for example, proliferation and migration/chemotaxis assays as well as by super-resolution microscopy. RESULTS: Homoarginine supplementation led to a 2-fold increase in circulating homoarginine concentrations. Homoarginine-treated mice exhibited reduced atherosclerosis in the aortic root and brachiocephalic trunk. A substantial decrease in CD3+ T cells in the atherosclerotic lesions suggested a T-cell-related effect of homoarginine supplementation, which was mainly attributed to CD4+ T cells. Macrophages, dendritic cells, and B cells were not affected. CD4+ T-cell proteomics and subsequent pathway analysis together with in vitro studies demonstrated that homoarginine profoundly modulated the spatial organization of the T-cell actin cytoskeleton and increased filopodia formation via inhibition of Myh9 (myosin heavy chain 9). Further mechanistic studies revealed an inhibition of T-cell proliferation as well as a striking impairment of the migratory capacities of T cells in response to relevant chemokines by homoarginine, all of which likely contribute to its atheroprotective effects. CONCLUSIONS: Our study unravels a novel mechanism by which the amino acid homoarginine reduces atherosclerosis, establishing that homoarginine modulates the T-cell cytoskeleton and thereby mitigates T-cell functions important during atherogenesis. These findings provide a molecular explanation for the beneficial effects of homoarginine in atherosclerotic cardiovascular disease.

Endothelial ENPP2 (Ectonucleotide Pyrophosphatase/Phosphodiesterase 2) Increases Atherosclerosis in Female and Male Mice.

BACKGROUND: Maladapted endothelial cells (ECs) secrete ENPP2 (ectonucleotide pyrophosphatase/phosphodiesterase 2; autotaxin)-a lysophospholipase D that generates lysophosphatidic acids (LPAs). ENPP2 derived from the arterial wall promotes atherogenic monocyte adhesion induced by generating LPAs, such as arachidonoyl-LPA (LPA20:4), from oxidized lipoproteins. Here, we aimed to determine the role of endothelial ENPP2 in the production of LPAs and atherosclerosis. METHODS: We quantified atherosclerosis in mice harboring loxP-flanked Enpp2 alleles crossed with Apoe-/- mice expressing tamoxifen-inducible Cre recombinase under the control of the EC-specific bone marrow X kinase promoter after 12 weeks of high-fat diet feeding. RESULTS: A tamoxifen-induced EC-specific Enpp2 knockout decreased atherosclerosis, accumulation of lesional macrophages, monocyte adhesion, and expression of endothelial CXCL (C-X-C motif chemokine ligand) 1 in male and female Apoe-/- mice. In vitro, ENPP2 mediated the mildly oxidized LDL (low-density lipoprotein)-induced expression of CXCL1 in aortic ECs by generating LPA20:4, palmitoyl-LPA (LPA16:0), and oleoyl-LPA (LPA18:1). ENPP2 and its activity were detected on the endothelial surface by confocal imaging. The expression of endothelial Enpp2 established a strong correlation between the plasma levels of LPA16:0, stearoyl-LPA (LPA18:0), and LPA18:1 and plaque size and a strong negative correlation between the LPA levels and ENPP2 activity in the plasma. Moreover, endothelial Enpp2 knockout increased the weight of high-fat diet-fed male Apoe-/- mice. CONCLUSIONS: We demonstrated that the expression of ENPP2 in ECs promotes atherosclerosis and endothelial inflammation in a sex-independent manner. This might be due to the generation of LPA20:4, LPA16:0, and LPA18:1 from mildly oxidized lipoproteins on the endothelial surface.

Heterocomplexes between the atypical chemokine MIF and the CXC-motif chemokine CXCL4L1 regulate inflammation and thrombus formation.

To fulfil its orchestration of immune cell trafficking, a network of chemokines and receptors developed that capitalizes on specificity, redundancy, and functional selectivity. The discovery of heteromeric interactions in the chemokine interactome has expanded the complexity within this network. Moreover, some inflammatory mediators, not structurally linked to classical chemokines, bind to chemokine receptors and behave as atypical chemokines (ACKs). We identified macrophage migration inhibitory factor (MIF) as an ACK that binds to chemokine receptors CXCR2 and CXCR4 to promote atherogenic leukocyte recruitment. Here, we hypothesized that chemokine-chemokine interactions extend to ACKs and that MIF forms heterocomplexes with classical chemokines. We tested this hypothesis by using an unbiased chemokine protein array. Platelet chemokine CXCL4L1 (but not its variant CXCL4 or the CXCR2/CXCR4 ligands CXCL8 or CXCL12) was identified as a candidate interactor. MIF/CXCL4L1 complexation was verified by co-immunoprecipitation, surface plasmon-resonance analysis, and microscale thermophoresis, also establishing high-affinity binding. We next determined whether heterocomplex formation modulates inflammatory/atherogenic activities of MIF. Complex formation was observed to inhibit MIF-elicited T-cell chemotaxis as assessed by transwell migration assay and in a 3D-matrix-based live cell-imaging set-up. Heterocomplexation also blocked MIF-triggered migration of microglia in cortical cultures in situ, as well as MIF-mediated monocyte adhesion on aortic endothelial cell monolayers under flow stress conditions. Of note, CXCL4L1 blocked binding of Alexa-MIF to a soluble surrogate of CXCR4 and co-incubation with CXCL4L1 attenuated MIF responses in HEK293-CXCR4 transfectants, indicating that complex formation interferes with MIF/CXCR4 pathways. Because MIF and CXCL4L1 are platelet-derived products, we finally tested their role in platelet activation. Multi-photon microscopy, FLIM-FRET, and proximity-ligation assay visualized heterocomplexes in platelet aggregates and in clinical human thrombus sections obtained from peripheral artery disease (PAD) in patients undergoing thrombectomy. Moreover, heterocomplexes inhibited MIF-stimulated thrombus formation under flow and skewed the lamellipodia phenotype of adhering platelets. Our study establishes a novel molecular interaction that adds to the complexity of the chemokine interactome and chemokine/receptor-network. MIF/CXCL4L1, or more generally, ACK/CXC-motif chemokine heterocomplexes may be target structures that can be exploited to modulate inflammation and thrombosis.

MicroRNA-21 Controls Circadian Regulation of Apoptosis in Atherosclerotic Lesions.

BACKGROUND: The necrotic core partly formed by ineffective efferocytosis increases the risk of an atherosclerotic plaque rupture. Microribonucleic acids contribute to necrotic core formation by regulating efferocytosis and macrophage apoptosis. Atherosclerotic plaque rupture occurs at increased frequency in the early morning, indicating diurnal changes in plaque vulnerability. Although circadian rhythms play a role in atherosclerosis, the molecular clock output pathways that control plaque composition and rupture susceptibility are unclear. METHODS: Circadian gene expression, necrotic core size, apoptosis, and efferocytosis in aortic lesions were investigated at different times of the day in Apoe-/-Mir21+/+ mice and Apoe-/-Mir21-/- mice after consumption of a high-fat diet for 12 weeks. Genome-wide gene expression and lesion formation were analyzed in bone marrow-transplanted mice. Diurnal changes in apoptosis and clock gene expression were determined in human atherosclerotic lesions. RESULTS: The expression of molecular clock genes, lesional apoptosis, and necrotic core size were diurnally regulated in Apoe-/- mice. Efferocytosis did not match the diurnal increase in apoptosis at the beginning of the active phase. However, in parallel with apoptosis, expression levels of oscillating Mir21 strands decreased in the mouse atherosclerotic aorta. Mir21 knockout abolished circadian regulation of apoptosis and reduced necrotic core size but did not affect core clock gene expression. Further, Mir21 knockout upregulated expression of proapoptotic Xaf1 (XIAP-associated factor 1) in the atherosclerotic aorta, which abolished circadian expression of Xaf1. The antiapoptotic effect of Mir21 was mediated by noncanonical targeting of Xaf1 through both Mir21 strands. Mir21 knockout in bone marrow cells also reduced atherosclerosis and necrotic core size. Circadian regulation of clock gene expression was confirmed in human atherosclerotic lesions. Apoptosis oscillated diurnally in phase with XAF1 expression, demonstrating an early morning peak antiphase to that of the Mir21 strands. CONCLUSIONS: Our findings suggest that the molecular clock in atherosclerotic lesions induces a diurnal rhythm of apoptosis regulated by circadian Mir21 expression in macrophages that is not matched by efferocytosis, thus increasing the size of the necrotic core.

Endothelial ACKR3 drives atherosclerosis by promoting immune cell adhesion to vascular endothelium.

Atherosclerosis is the foundation of potentially fatal cardiovascular diseases and it is characterized by plaque formation in large arteries. Current treatments aimed at reducing atherosclerotic risk factors still allow room for a large residual risk; therefore, novel therapeutic candidates targeting inflammation are needed. The endothelium is the starting point of vascular inflammation underlying atherosclerosis and we could previously demonstrate that the chemokine axis CXCL12-CXCR4 plays an important role in disease development. However, the role of ACKR3, the alternative and higher affinity receptor for CXCL12 remained to be elucidated. We studied the role of arterial ACKR3 in atherosclerosis using western diet-fed Apoe-/- mice lacking Ackr3 in arterial endothelial as well as smooth muscle cells. We show for the first time that arterial endothelial deficiency of ACKR3 attenuates atherosclerosis as a result of diminished arterial adhesion as well as invasion of immune cells. ACKR3 silencing in inflamed human coronary artery endothelial cells decreased adhesion molecule expression, establishing an initial human validation of ACKR3's role in endothelial adhesion. Concomitantly, ACKR3 silencing downregulated key mediators in the MAPK pathway, such as ERK1/2, as well as the phosphorylation of the NF-kB p65 subunit. Endothelial cells in atherosclerotic lesions also revealed decreased phospho-NF-kB p65 expression in ACKR3-deficient mice. Lack of smooth muscle cell-specific as well as hematopoietic ACKR3 did not impact atherosclerosis in mice. Collectively, our findings indicate that arterial endothelial ACKR3 fuels atherosclerosis by mediating endothelium-immune cell adhesion, most likely through inflammatory MAPK and NF-kB pathways.

Histone Deacetylase 9 Activates IKK to Regulate Atherosclerotic Plaque Vulnerability.

RATIONALE: Arterial inflammation manifested as atherosclerosis is the leading cause of mortality worldwide. Genome-wide association studies have identified a prominent role of HDAC (histone deacetylase)-9 in atherosclerosis and its clinical complications including stroke and myocardial infarction. OBJECTIVE: To determine the mechanisms linking HDAC9 to these vascular pathologies and explore its therapeutic potential for atheroprotection. METHODS AND RESULTS: We studied the effects of Hdac9 on features of plaque vulnerability using bone marrow reconstitution experiments and pharmacological targeting with a small molecule inhibitor in hyperlipidemic mice. We further used 2-photon and intravital microscopy to study endothelial activation and leukocyte-endothelial interactions. We show that hematopoietic Hdac9 deficiency reduces lesional macrophage content while increasing fibrous cap thickness thus conferring plaque stability. We demonstrate that HDAC9 binds to IKK (inhibitory kappa B kinase)-α and ß, resulting in their deacetylation and subsequent activation, which drives inflammatory responses in both macrophages and endothelial cells. Pharmacological inhibition of HDAC9 with the class IIa HDAC inhibitor TMP195 attenuates lesion formation by reducing endothelial activation and leukocyte recruitment along with limiting proinflammatory responses in macrophages. Transcriptional profiling using RNA sequencing revealed that TMP195 downregulates key inflammatory pathways consistent with inhibitory effects on IKKß. TMP195 mitigates the progression of established lesions and inhibits the infiltration of inflammatory cells. Moreover, TMP195 diminishes features of plaque vulnerability and thereby enhances plaque stability in advanced lesions. Ex vivo treatment of monocytes from patients with established atherosclerosis reduced the production of inflammatory cytokines including IL (interleukin)-1ß and IL-6. CONCLUSIONS: Our findings identify HDAC9 as a regulator of atherosclerotic plaque stability and IKK activation thus providing a mechanistic explanation for the prominence of HDAC9 as a vascular risk locus in genome-wide association studies. Its therapeutic inhibition may provide a potent lever to alleviate vascular inflammation. Graphical Abstract: A graphical abstract is available for this article.

A MIF-Derived Cyclopeptide that Inhibits MIF Binding and Atherogenic Signaling via the Chemokine Receptor CXCR2.

Macrophage migration inhibitory factor (MIF) is an inflammatory cytokine and atypical chemokine with a key role in inflammatory diseases including atherosclerosis. Key atherogenic functions of MIF are mediated by noncognate interaction with the chemokine receptor CXCR2. The MIF N-like loop comprising the sequence 47-56 is an important structural determinant of the MIF/CXCR2 interface and MIF(47-56) blocks atherogenic MIF activities. However, the mechanism and critical structure-activity information within this sequence have remained elusive. Here, we show that MIF(47-56) directly binds to CXCR2 to compete with MIF receptor activation. By using alanine scanning, essential and dispensable residues were identified. Moreover, MIF(cyclo10), a designed cyclized variant of MIF(47-56), inhibited key inflammatory and atherogenic MIF activities in vitro and in vivo/ex vivo, and exhibited strongly improved resistance to proteolytic degradation in human plasma in vitro, thus suggesting that it could serve as a promising basis for MIF-derived anti-atherosclerotic peptides.

Tick Saliva Protein Evasin-3 Allows for Visualization of Inflammation in Arteries through Interactions with CXC-Type Chemokines Deposited on Activated Endothelium.

Atherosclerosis is one of the leading causes of mortality in developed and developing countries. The onset of atherosclerosis development is accompanied by overexpression of several inflammatory chemokines. Neutralization of these chemokines by chemokine-binding agents attenuates atherosclerosis progression. Here, we studied structural binding features of the tick protein Evasin-3 to chemokine (C-X-C motif) ligand 1 (CXCL1). We showed that Evasin-3-bound CXCL1 is unable to activate the CXCR2 receptor, but retains affinity to glycosaminoglycans. This observation was exploited to detect inflammation by visualizing a group of closely related CXC-type chemokines deposited on cell walls in human endothelial cells and murine carotid arteries by a fluorescent Evasin-3 conjugate. This work highlights the applicability of tick-derived chemokine-binding conjugates as a platform for the development of new agents for inflammation imaging.

CD36-triggered cell invasion and persistent tissue colonization by tumor microvesicles during metastasis.

Tumor microvesicles are a peculiar type of extracellular vesicles that circulate in the blood of patients with metastatic cancer. The itineraries and immune cell interactions of tumor microvesicles during the intravascular and extravascular stages of metastasis are largely unknown. We found that the lipid receptor CD36 is a major mediator of the engulfment of pancreatic tumor microvesicles by myeloid immune cells in vitro and critically samples circulating tumor microvesicles by resident liver macrophages in mice in vivo. Direct nanoscopic imaging of individual tumor microvesicles shows that the microvesicles rapidly decay during engulfment whereby their cargo is targeted concomitantly to the plasma membrane and the cytoplasm excluding lysosomal compartments. CD36 also promotes internalization of blood cell (nontumor) microvesicles, which involves endolysosomal pathways. A portion of tumor microvesicles circulating in the liver microcirculation traverses the vessel wall in a CD36-dependent way. Extravasated microvesicles colonize distinct perivascular Ly6C- macrophages for at least 2 wk. Thus, the microvesicles are increasingly integrated into CD36-induced premetastatic cell clusters and enhance development of liver metastasis. Hence, promotion of metastasis by pancreatic tumor microvesicles is associated with CD36-regulated immune cell invasion and extravasation of microvesicles and persistent infiltration of specific tissue macrophages by microvesicle cargo.-Pfeiler, S., Thakur, M., Grünauer, P., Megens, R. T. A., Joshi, U., Coletti, R., Samara, V., Müller-Stoy, G., Ishikawa-Ankerhold, H., Stark, K., Klingl, A., Fröhlich, T., Arnold, G. J., Wörmann, S., Bruns, C. J., Algül, H., Weber, C., Massberg, S., Engelmann, B. CD36-triggered cell invasion and persistent tissue colonization by tumor microvesicles during metastasis.

Pericardial Adipose Tissue Regulates Granulopoiesis, Fibrosis, and Cardiac Function After Myocardial Infarction.

BACKGROUND: The pericardial adipose tissue (AT) contains a high density of lymphoid clusters. It is unknown whether these clusters play a role in post-myocardial infarction (MI) inflammatory responses and cardiac outcome. METHODS: Lymphoid clusters were examined in epicardial AT of humans with or without coronary artery disease. Murine pericardial lymphoid clusters were visualized in mice subjected to coronary artery ligation. To study the relevance of pericardial clusters during inflammatory responses after MI, we surgically removed the pericardial AT and performed B-cell depletion and granulocyte-macrophage colony-stimulating factor blockade. Leukocytes in murine hearts, pericardial AT, spleen, mediastinal lymph nodes, and bone marrow were quantified by flow cytometry. Cannabinoid receptor CB2 (CB2-/-) mice were used as a model for enhanced B-cell responses. The effect of impaired dendritic cell (DC) trafficking on pericardial AT inflammatory responses was tested in CCR7-/- mice subjected to MI. Cardiac fibrosis and ventricular function were assessed by histology and echocardiography. RESULTS: We identified larger B-cell clusters in epicardial AT of human patients with coronary artery disease in comparison with controls without coronary artery disease. Infarcted mice also had larger pericardial clusters and 3-fold upregulated numbers of granulocyte-macrophage colony-stimulating factor-producing B cells within pericardial AT, but not spleen or lymph nodes. This was associated with higher DC and T-cell counts in pericardial AT, which outnumbered DCs and T cells in lymph nodes. Analysis of DC maturation markers, tracking experiments with fluorescently labeled cells, and use of CCR7-deficient mice suggested that activated DCs migrate from infarcts into pericardial AT via CCR7. B-cell depletion or granulocyte-macrophage colony-stimulating factor neutralization inhibited DC and T-cell expansion within pericardial AT, and translated into reduced bone marrow granulopoiesis and cardiac neutrophil infiltration 3 days after MI. The relevance of the pericardial AT in mediating all these effects was confirmed by removal of pericardial AT and ex vivo coculture with pericardial AT and granulocyte progenitors. Finally, enhanced fibrosis and worsened ejection fraction in CB2-/- mice were limited by pericardial AT removal. CONCLUSIONS: Our findings unveil a new mechanism by which the pericardial AT coordinates immune cell activation, granulopoiesis, and outcome after MI.

Mif-deficiency favors an atheroprotective autoantibody phenotype in atherosclerosis.

The inflammatory cytokine macrophage migration-inhibitory factor (MIF) promotes atherosclerosis via lesional monocyte and T-cell recruitment. B cells have emerged as important components in atherogenesis, but the interaction between MIF and B cells in atherogenesis is unknown. Here, we investigated the atherosclerotic phenotype of Mif-gene deletion in Apoe-/- mice. Apoe-/- Mif-/- mice fed a Western diet exhibited strongly reduced atherosclerotic lesions in brachiocephalic artery (BC) and abdominal aorta compared with controls. This phenotype was accompanied by reduced circulating B cells. Flow cytometry revealed a B-cell developmental defect with increased premature and immature B-cell counts in bone marrow (BM) of Apoe-/- Mif-/- mice and diminished B-cell numbers in spleen. This finding was linked with a decreased expression of Baff-R and differentiation-driving transcription factors at the immature B-cell stage, whereas peritoneal B cells exhibited unchanged CD80 and CD86 expression but vastly decreased CD9 and elevated CD23 levels, indicating that the developmental block favors the generation of immature, egressing, and reactive B cells. Mif deficiency did not affect absolute B-cell numbers in the vessel wall but favored a relative increase of B cells in the atheroprone BC region and the appearance of periadventitial B-cell-rich clusters. Of note, Mif-/- mice exhibited a significant increase in oxidized low-density lipoprotein (oxLDL)-specific antibodies after the injection of oxLDL, indicating that Mif deficiency is associated with higher sensitivity of B cells against natural-occurring antigens such as oxLDL. Importantly, Apoe-/- mice adoptively transplanted with Apoe-/-Mif-/- BM showed reduced peripheral B cells compared with Apoe-/- BM transplantation but no atheroprotection in the BC; also, whereas there was a selective increase in atheroprotective IgM-anti-oxLDL-antibodies in global Mif deficiency, BM-specific Mif deficiency also led to elevated proatherogenic anti-oxLDL-IgG. Together, these findings reveal a novel link between MIF and B cells in atherogenesis. Protection from atherosclerosis by Mif deficiency is associated with enhanced B-cell hypersensitivity, which in global but not BM-restricted Mif deficiency favors an atheroprotective autoantibody profile in atherosclerotic mice. Targeting MIF may induce protective B-cell responses in atherosclerosis.-Schmitz, C., Noels, H., El Bounkari, O., Straussfeld, E., Megens, R. T. A., Sternkopf, M., Alampour-Rajabi, S., Krammer, C., Tilstam, P. V., Gerdes, N., Bürger, C., Kapurniotu, A., Bucala, R., Jankowski, J., Weber, C., Bernhagen, J. Mif-deficiency favors an atheroprotective autoantibody phenotype in atherosclerosis.

Chronic Intake of the Selective Serotonin Reuptake Inhibitor Fluoxetine Enhances Atherosclerosis.

OBJECTIVE: Cardiovascular diseases and depression are the leading causes of disability in Western countries. Clinical data on potential cardiovascular effects of serotonin reuptake inhibitors (SSRIs), the most commonly used antidepressant drugs, are controversial. In addition to blocking serotonin reuptake transporter in the brain, SSRIs deplete the major peripheral serotonin (5-hydroxytryptamine [5-HT]) storage by inhibiting serotonin reuptake transporter-mediated uptake in platelets. In this study, we aimed to investigate the effect of chronic SSRI intake on the development of atherosclerosis. APPROACH AND RESULTS: Treatment of apolipoprotein E-deficient mice with the SSRI fluoxetine for 2, 4, or 16 weeks increased atherosclerotic lesion formation, with most pronounced effect during early plaque development. Intravital microscopy of carotid arteries revealed enhanced myeloid cell adhesion on fluoxetine treatment. Mechanistically, we found that fluoxetine augmented vascular permeability and increased chemokine-induced integrin-binding activity of circulating leukocytes. In vitro stimulation of murine blood demonstrated that fluoxetine, but not 5-HT, could directly promote ß1 and ß2 integrin activation provided C-C motif chemokine ligand 5 was also present. Similar effects were observed with the SSRI escitalopram. Enhanced C-C motif chemokine ligand 5-induced integrin activation by fluoxetine was also confirmed in a human neutrophil-like cell line. In contrast to the proatherogenic properties of fluoxetine, pharmacological inhibition of the peripheral 5-HT synthesizing enzyme tryptophan hydroxylase 1 did not promote atherosclerosis, suggesting that the proatherogenic effect of fluoxetine occurs independent of peripheral 5-HT depletion. CONCLUSIONS: SSRI intake may promote atherosclerosis and therefore potentially increase the risk for acute cardiovascular events by a mechanism that is independent of 5-HT depletion.

Vascular CXCR4 Limits Atherosclerosis by Maintaining Arterial Integrity: Evidence From Mouse and Human Studies.

BACKGROUND: The CXCL12/CXCR4 chemokine ligand/receptor axis controls (progenitor) cell homeostasis and trafficking. So far, an atheroprotective role of CXCL12/CXCR4 has only been implied through pharmacological intervention, in particular, because the somatic deletion of the CXCR4 gene in mice is embryonically lethal. Moreover, cell-specific effects of CXCR4 in the arterial wall and underlying mechanisms remain elusive, prompting us to investigate the relevance of CXCR4 in vascular cell types for atheroprotection. METHODS: We examined the role of vascular CXCR4 in atherosclerosis and plaque composition by inducing an endothelial cell (BmxCreERT2-driven)-specific or smooth muscle cell (SMC, SmmhcCreERT2- or TaglnCre-driven)-specific deficiency of CXCR4 in an apolipoprotein E-deficient mouse model. To identify underlying mechanisms for effects of CXCR4, we studied endothelial permeability, intravital leukocyte adhesion, involvement of the Akt/WNT/ß-catenin signaling pathway and relevant phosphatases in VE-cadherin expression and function, vascular tone in aortic rings, cholesterol efflux from macrophages, and expression of SMC phenotypic markers. Finally, we analyzed associations of common genetic variants at the CXCR4 locus with the risk for coronary heart disease, along with CXCR4 transcript expression in human atherosclerotic plaques. RESULTS: The cell-specific deletion of CXCR4 in arterial endothelial cells (n=12-15) or SMCs (n=13-24) markedly increased atherosclerotic lesion formation in hyperlipidemic mice. Endothelial barrier function was promoted by CXCL12/CXCR4, which triggered Akt/WNT/ß-catenin signaling to drive VE-cadherin expression and stabilized junctional VE-cadherin complexes through associated phosphatases. Conversely, endothelial CXCR4 deficiency caused arterial leakage and inflammatory leukocyte recruitment during atherogenesis. In arterial SMCs, CXCR4 sustained normal vascular reactivity and contractile responses, whereas CXCR4 deficiency favored a synthetic phenotype, the occurrence of macrophage-like SMCs in the lesions, and impaired cholesterol efflux. Regression analyses in humans (n=259 796) identified the C-allele at rs2322864 within the CXCR4 locus to be associated with increased risk for coronary heart disease. In line, C/C risk genotype carriers showed reduced CXCR4 expression in carotid artery plaques (n=188), which was furthermore associated with symptomatic disease. CONCLUSIONS: Our data clearly establish that vascular CXCR4 limits atherosclerosis by maintaining arterial integrity, preserving endothelial barrier function, and a normal contractile SMC phenotype. Enhancing these beneficial functions of arterial CXCR4 by selective modulators might open novel therapeutic options in atherosclerosis.

Multi-photon microscopy in cardiovascular research.

Multiphoton laser scanning microscopy has proven profound value for ex vivo 3D histology and in vivo imaging of motionless tissue. The development of triggering systems and fast imaging methods, combined with advanced preparation procedures solved the challenging task of intravital imaging of the fast pulsating heart and major arteries in animals and further increased the popularity of intravital multiphoton imaging in cardiovascular research. This review article will highlight the potential of multiphoton microscopy for the visualization and characterization of dynamical and structural processes involved in cardiac and vascular diseases, both in an ex vivo and an intravital animal setting. Examples will be given how multiphoton microscopy can be applied to imaging of atherosclerotic plaque development and progression at subcellular level as well as to intravital imaging of inflammatory processes in the heart. In addition to highlighting the potential of multiphoton microscopy in preclinical cardiovascular research, we will discuss how this tool and its applications may be clinically translated to support disease diagnosis and therapy in patients.