Andreas Zirlik

Ly-6Chigh Monocytes Depend on Nr4a1 to Balance both Inflammatory and Reparative Phases in the Infarcted Myocardium

Rationale: Healing after myocardial infarction involves the biphasic accumulation of inflammatory lymphocyte antigen 6C (Ly-6C)high and reparative Ly-6Clow monocytes/macrophages (Mo/M&PHgr;). According to 1 model, Mo/M&PHgr; heterogeneity in the heart originates in the blood and involves the sequential recruitment of distinct monocyte subsets that differentiate to distinct macrophages. Alternatively, heterogeneity may arise in tissue from 1 circulating subset via local macrophage differentiation and polarization. The orphan nuclear hormone receptor, nuclear receptor subfamily 4, group a, member 1 (Nr4a1), is essential to Ly-6Clow monocyte production but dispensable to Ly-6Clow macrophage differentiation; dependence on Nr4a1 can thus discriminate between systemic and local origins of macrophage heterogeneity. Objective: This study tested the role of Nr4a1 in myocardial infarction in the context of the 2 Mo/M&PHgr; accumulation scenarios. Methods and Results: We show that Ly-6Chigh monocytes infiltrate the infarcted myocardium and, unlike Ly-6Clow monocytes, differentiate to cardiac macrophages. In the early, inflammatory phase of acute myocardial ischemic injury, Ly-6Chigh monocytes accrue in response to a brief C–C chemokine ligand 2 burst. In the second, reparative phase, accumulated Ly-6Chigh monocytes give rise to reparative Ly-6Clow F4/80high macrophages that proliferate locally. In the absence of Nr4a1, Ly-6Chigh monocytes express heightened levels of C–C chemokine receptor 2 on their surface, avidly infiltrate the myocardium, and differentiate to abnormally inflammatory macrophages, which results in defective healing and compromised heart function. Conclusions: Ly-6Chigh monocytes orchestrate both inflammatory and reparative phases during myocardial infarction and depend on Nr4a1 to limit their influx and inflammatory cytokine expression.

CD40 Ligand Mediates Inflammation Independently of CD40 by Interaction With Mac-1

Background— Strong evidence supports a role for CD40 ligand (CD40L) as marker and mediator of inflammatory diseases such as atherosclerosis. Despite extensive characterization of CD40, the classic receptor of CD40L, its role in immune defense against inflammatory diseases remains uncertain. The present study aimed to characterize the contribution of CD40 signaling to atherogenesis. Methods and Results— Surprisingly, mice deficient in both CD40 and the low-density lipoprotein receptor did not develop smaller lesions in the aortic arch, root, and thoracoabdominal aorta compared with mice deficient only in the low-density lipoprotein receptor that consumed an atherogenic diet for 8 and 16 weeks. By flow cytometry, radioactive binding assays, and immunoprecipitation, we demonstrate that CD40L interacts with the integrin Mac-1, which results in Mac-1–dependent adhesion and migration of inflammatory cells as well as myeloperoxidase release in vitro. Furthermore, mice deficient in CD40L show significantly reduced thioglycolate-elicited invasion of inflammatory cells into the peritoneal cavity compared with mice deficient in CD40 and wild-type controls. Inhibition of Mac-1 in low-density lipoprotein receptor–deficient mice attenuates lesion development and reduces lesional macrophage accumulation. Conclusions— These observations identify the interaction of CD40L and Mac-1 as an alternative pathway for CD40L-mediated inflammation. This novel mechanism expands understanding of inflammatory signaling during atherogenesis.

Interleukin-18, the Metabolic Syndrome, and Subclinical Atherosclerosis Results From the Dallas Heart Study

Objective—Although IL-18 promotes atherogenesis in animal studies and predicts cardiovascular risk in humans, it is unknown whether elevated IL-18 levels are associated with coronary atherosclerosis in the general population. Methods and Results—IL-18 plasma levels were determined by ELISA in 2231 subjects from the Dallas Heart Study. In univariable analysis, IL-18 levels associated with traditional cardiovascular risk factors and particularly with components of the metabolic syndrome (MS, P<0.01 for trend across the number of MS components); IL-18 also associated with coronary artery calcium (CAC) scores measured by electron beam computed tomography and aortic plaque measured by MRI (P<0.01 for each). In multivariable analyses, IL-18 remained associated with multiple components of the MS but not with CAC or aortic plaque. Conclusions—In a large population-based sample, elevated IL-18 plasma levels associated with risk factors for atherosclerosis and with the metabolic syndrome. The association between IL-18 and atherosclerosis diminished after accounting for traditional cardiovascular risk factors. These data suggest that IL-18 does not add independently to detection of atherosclerotic burden in asymptomatic individuals.

Associations between soluble CD40 ligand, atherosclerosis risk factors, and subclinical atherosclerosis: results from the Dallas Heart Study.

Objectives—The purpose of this study was to evaluate the associations between plasma levels of soluble CD40 ligand (sCD40L), atherosclerosis risk factors, and evidence of subclinical atherosclerosis. Methods and Results—Plasma levels of sCD40L were measured in 2811 subjects from the Dallas Heart Study, a multiethnic population-based cross-sectional study. Electron Beam Computed Tomography measurements of coronary artery calcium (CAC) and MRI measurements of aortic plaque were performed in 2198 and 1965 subjects, respectively. No association was observed between quartiles of sCD40L and age, sex, race, body mass index, diabetes, smoking, creatinine clearance, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, or C-reactive protein. In contrast, weak but statistically significant associations were observed between sCD40L and total cholesterol and triglycerides. The prevalence of detectable CAC (CAC score ≥10) and aortic plaque did not differ across sCD40L quartiles, and individuals with CAC scores <10, ≥10 to 100, >100 to 400, and >400 had similar sCD40L levels. Conclusions—In a large and representative multiethnic population-based sample, sCD40L was not associated with most atherosclerotic risk factors or with subclinical atherosclerosis. These findings suggest that sCD40L will not be useful as a tool to screen for the presence of subclinical atherosclerosis in the population. Further evaluation of this biomarker should focus on settings in which platelet activation is common, such as following acute coronary syndromes or coronary revascularization procedures.

TRAF-1, -2, -3, -5, and -6 Are Induced in Atherosclerotic Plaques and Differentially Mediate Proinflammatory Functions of CD40L in Endothelial Cells

Objective—Several lines of evidence implicate CD40 ligand (CD40L, CD154) as a mediator and marker of atherosclerosis. This study investigated the involvement of tumor necrosis factor receptor-associated factors (TRAFs) in CD40 signaling in endothelial cells (ECs) and their expression in atheromata and cells involved in atherogenesis. Methods and Results—CD40L enhanced the basal expression of TRAF-1, -2, -3, and 6, but not TRAF-5 in ECs. TRAFs associated with CD40 on ligation by CD40L. Study of ECs from TRAF-1, -2, and -5-deficient mice demonstrated functional involvement of TRAFs in proinflammatory CD40 signaling. Whereas TRAF-1 deficiency enhanced CD40L-induced IL-6 and MCP-1 expression, TRAF-2 and TRAF-5 deficiency inhibited CD40L-inducible IL-6 but not MCP-1 expression. Gene silencing in human ECs further delineated functions of TRAFs in CD40 signaling. TRAF-3 silencing in ECs showed increased CD40L-induced IL-6, MCP-1, and IL-8 expression, whereas TRAF-6 silencing increased selectively CD40L-induced MCP-1 expression. Enhanced TRAF levels in atherosclerotic lesions further supports involvement of members of this family of signaling molecules in arterial disease. Conclusions—These results implicate endothelial TRAF-1, -2, -3, -5, and -6 in CD40 signaling in atherogenesis, identifying these molecules as potential targets for selective therapeutic intervention.

Urine Proteome Analysis Reflects Atherosclerotic Disease in an ApoE−/− Mouse Model and Allows the Discovery of New Candidate Biomarkers in Mouse and Human Atherosclerosis

Noninvasive diagnosis of atherosclerosis via single biomarkers has been attempted but remains elusive. However, a previous polymarker or pattern approach of urine polypeptides in humans reflected coronary artery disease with high accuracy. The aim of the current study is to use urine proteomics in ApoE−/− mice to discover proteins with pathophysiological roles in atherogenesis and to identify urinary polypeptide patterns reflecting early stages of atherosclerosis. Urine of ApoE−/− mice either on high fat diet (HFD) or chow diet was collected over 12 weeks; urine of wild type mice on HFD was used to exclude diet-related proteome changes. Capillary electrophoresis coupled to mass spectrometry (CE-MS) of samples identified 16 polypeptides specific for ApoE−/− mice on HFD. In a blinded test set, these polypeptides allowed identification of atherosclerosis at a sensitivity of 90% and specificity of 100%, as well as monitoring of disease progression. Sequencing of the discovered polypeptides identified fragments of α1-antitrypsin, epidermal growth factor (EGF), kidney androgen-regulated protein, and collagen. Using immunohistochemistry, α1-antitrypsin, EGF, and collagen type I were shown to be highly expressed in atherosclerotic plaques of ApoE−/− mice on HFD. Urinary excretion levels of collagen and α1-antitrypsin fragments also significantly correlated with intraplaque collagen and α1-antitrypsin content, mirroring plaque protein expression in the urine proteome. To provide further confirmation that the newly identified proteins are relevant in humans, the presence of collagen type I, α1-antitrypsin, and EGF was also confirmed in human atherosclerotic disease. Urine proteome analysis in mice exemplifies the potential of a novel multimarker approach for the noninvasive detection of atherosclerosis and monitoring of disease progression. Furthermore, this approach represents a novel discovery tool for the identification of proteins relevant in murine and human atherosclerosis and thus also defines potential novel therapeutic targets.

Direct attenuation of plasminogen activator inhibitor type-1 expression in human adipose tissue by thiazolidinediones.

Adipose tissue produces substantial amounts of plasminogen activator inhibitor type-1 (PAI-1), an established cardiovascular risk factor. This study evaluated PAI-1 expression in human adipose tissue in response to thiazolidinediones, insulin sensitising drugs activating peroxisome proliferator-activated receptor-gamma (PPAR-gamma). Troglitazone, rosiglitazone, and ciglitazone significantly reduced PAI-1 protein expression in human preadipocytes under basal conditions and after stimulation of the cells with TGF-beta. Pioglitazone had no effect. In human adipocytes all four thiazolidinediones significantly attenuated PAI-1 expression. Signalling appeared to be mediated via PPAR-gamma and effects reflected, at least in part, changes in transcription. Accordingly, patients with insulin resistance may benefit from treatment with thiazolidinediones with respect to diminution of PAI-1 expression in adipose tissue and consequent potential reduction of cardiovascular risk.

Innate Response Activator B Cells Aggravate Atherosclerosis by Stimulating T Helper-1 Adaptive Immunity

Background— Atherosclerotic lesions grow via the accumulation of leukocytes and oxidized lipoproteins in the vessel wall. Leukocytes can attenuate or augment atherosclerosis through the release of cytokines, chemokines, and other mediators. Deciphering how leukocytes develop, oppose, and complement each other’s function and shape the course of disease can illuminate our understanding of atherosclerosis. Innate response activator (IRA) B cells are a recently described population of granulocyte macrophage colony-stimulating factor–secreting cells of hitherto unknown function in atherosclerosis. Methods and Results— Here, we show that IRA B cells arise during atherosclerosis in mice and humans. In response to a high-cholesterol diet, IRA B cell numbers increase preferentially in secondary lymphoid organs via Myd88-dependent signaling. Mixed chimeric mice lacking B cell–derived granulocyte macrophage colony-stimulating factor develop smaller lesions with fewer macrophages and effector T cells. Mechanistically, IRA B cells promote the expansion of classic dendritic cells, which then generate interferon &ggr;–producing T helper-1 cells. This IRA B cell–dependent T helper-1 skewing manifests in an IgG1-to-IgG2c isotype switch in the immunoglobulin response against oxidized lipoproteins. Conclusions— Granulocyte macrophage colony-stimulating factor–producing IRA B cells alter adaptive immune processes and shift the leukocyte response toward a T helper-1–associated milieu that aggravates atherosclerosis.

Atherogenesis in Mice Does Not Require CD40 Ligand From Bone Marrow–Derived Cells

Objective—Recent research suggests a central role for CD40 ligand (CD40L) in atherogenesis. However, the relevant cellular source of this proinflammatory cytokine remains unknown. To test the hypothesis that CD40L expressed on hematopoietic cell types (eg, macrophages, lymphocytes, platelets) is crucial to atherogenesis, we performed bone marrow reconstitution experiments using low-density receptor-deficient (ldlr−/−) and ldlr−/−/cd40l−/− compound-mutant mice. Methods and Results—As expected, systemic lack of CD40L in hypercholesterolemic ldlr−/− mice significantly reduced the development of atherosclerotic lesions in the aortic arch, aortic root, and abdominal aorta compared with ldlr−/− mice. Furthermore, atheromata in ldlr−/−/cd40l−/− mice showed reduced accumulation of macrophages and lipids and increased content in smooth muscle cells and collagen compared with ldlr−/− mice. Surprisingly, reconstitution of irradiated ldlr−/− mice with ldlr−/−/cd40l−/− bone marrow did not affect the size or composition of atherosclerotic lesions in the root or arch of hypercholesterolemic ldlr−/− mice. Moreover, lipid deposition in the abdominal aorta diminished only marginally compared with mouse aortas reconstituted with ldlr−/− bone marrow. Conclusions—These experiments demonstrate that CD40L modulates atherogenesis, at least in mice, primarily by its expression on nonhematopoietic cell types rather than monocytes, T lymphocytes, or platelets, a surprising finding with important pathophysiologic and therapeutic implications.

CD40L induces inflammation and adipogenesis in adipose cells - a potential link between metabolic and cardiovascular disease

CD40L figures prominently in atherogenesis. Recent data demonstrate elevated levels of sCD40L in the serum of patients with the metabolic syndrome (MS). This study investigated the role of CD40L in pro-inflammatory gene expression and cellular differentiation in adipose tissue to obtain insight into mechanisms linking the MS with atherosclerosis. Human adipocytes and preadipocytes expressed CD40 but not CD40L. Stimulation with recombinant CD40L or membranes over-expressing CD40L induced a time- and dose-dependent expression of IL-6, MCP-1, IL-8, and PAI-1. Supernatants of CD40L-stimulated adipose cells activated endothelial cells, suggesting a systemic functional relevance of our findings. Neutralising antibodies against CD40L attenuated these effects substantially. Signalling studies revealed the involvement of mitogen-activated protein kinases and NFkB. Furthermore, stimulation with CD40L resulted in enhanced activation of C/EBPa and PPARg and promoted adipogenesis of preadipose cells in the presence and absence of standard adipogenic conditions. Finally, patients suffering from the metabolic syndrome with high levels of sCD40L also displayed high levels of IL-6, in line with the concept that CD40L may induce the expression of inflammatory cytokines in vivo in this population. Our data reveal potent metabolic functions of CD40L aside from its known pivotal pro-inflammatory role within plaques. Our data suggest that CD40L may mediate risk at the interface of metabolic and atherothrombotic disease.