Endotoxinemia Accelerates Atherosclerosis Through Electrostatic Charge-Mediated Monocyte Adhesion.

BACKGROUND: Acute infection is a well-established risk factor of cardiovascular inflammation increasing the risk for a cardiovascular complication within the first weeks after infection. However, the nature of the processes underlying such aggravation remains unclear. Lipopolysaccharide derived from Gram-negative bacteria is a potent activator of circulating immune cells including neutrophils, which foster inflammation through discharge of neutrophil extracellular traps (NETs). Here, we use a model of endotoxinemia to link acute infection and subsequent neutrophil activation with acceleration of vascular inflammation Methods: Acute infection was mimicked by injection of a single dose of lipopolysaccharide into hypercholesterolemic mice. Atherosclerosis burden was studied by histomorphometric analysis of the aortic root. Arterial myeloid cell adhesion was quantified by intravital microscopy. RESULTS: Lipopolysaccharide treatment rapidly enhanced atherosclerotic lesion size by expansion of the lesional myeloid cell accumulation. Lipopolysaccharide treatment led to the deposition of NETs along the arterial lumen, and inhibition of NET release annulled lesion expansion during endotoxinemia, thus suggesting that NETs regulate myeloid cell recruitment. To study the mechanism of monocyte adhesion to NETs, we used in vitro adhesion assays and biophysical approaches. In these experiments, NET-resident histone H2a attracted monocytes in a receptor-independent, surface charge-dependent fashion. Therapeutic neutralization of histone H2a by antibodies or by in silico designed cyclic peptides enables us to reduce luminal monocyte adhesion and lesion expansion during endotoxinemia. CONCLUSIONS: Our study shows that NET-associated histone H2a mediates charge-dependent monocyte adhesion to NETs and accelerates atherosclerosis during endotoxinemia.

Roles of PAD4 and NETosis in Experimental Atherosclerosis and Arterial Injury: Implications for Superficial Erosion.

RATIONALE: Neutrophils likely contribute to the thrombotic complications of human atheromata. In particular, neutrophil extracellular traps (NETs) could exacerbate local inflammation and amplify and propagate arterial intimal injury and thrombosis. PAD4 (peptidyl arginine deiminase 4) participates in NET formation, but an understanding of this enzyme's role in atherothrombosis remains scant. OBJECTIVE: This study tested the hypothesis that PAD4 and NETs influence experimental atherogenesis and in processes implicated in superficial erosion, a form of plaque complication we previously associated with NETs. METHODS AND RESULTS: Bone marrow chimeric Ldlr deficient mice reconstituted with either wild-type or PAD4-deficient cells underwent studies that assessed atheroma formation or procedures designed to probe mechanisms related to superficial erosion. PAD4 deficiency neither retarded fatty streak formation nor reduced plaque size or inflammation in bone marrow chimeric mice that consumed an atherogenic diet. In contrast, either a PAD4 deficiency in bone marrow-derived cells or administration of DNaseI to disrupt NETs decreased the extent of arterial intimal injury in mice with arterial lesions tailored to recapitulate characteristics of human atheroma complicated by erosion. CONCLUSIONS: These results indicate that PAD4 from bone marrow-derived cells and NETs do not influence chronic experimental atherogenesis, but participate causally in acute thrombotic complications of intimal lesions that recapitulate features of superficial erosion.

Stage-dependent differential effects of interleukin-1 isoforms on experimental atherosclerosis.

AIMS: Targeting interleukin-1 (IL-1) represents a novel therapeutic approach to atherosclerosis. CANTOS demonstrated the benefits of IL-1ß neutralization in patients post-myocardial infarction with residual inflammatory risk. Yet, some mouse data have shown a prominent role of IL-1α rather than IL-1ß in atherosclerosis, or even a deleterious effect of IL-1 on outward arterial remodelling in atherosclerosis-susceptible mice. To shed light on these disparate results, this study investigated the effect of neutralizing IL-1α or/and IL-1ß isoforms starting either early in atherogenesis or later in ApoE-/- mice with established atheroma. METHODS AND RESULTS: The neutralization of IL-1α or of both IL-1 isoforms impaired outward remodelling during early atherogenesis as assessed by micro-computed tomographic and histologic assessment. In contrast, the neutralization of IL-1ß did not impair outward remodelling either during early atherogenesis or in mice with established lesions. Interleukin-1ß inhibition promoted a slant of blood monocytes towards a less inflammatory state during atherogenesis, reduced the size of established atheromata, and increased plasma levels of IL-10 without limiting outward remodelling of brachiocephalic arteries. CONCLUSION: This study established a pivotal role for IL-1α in the remodelling of arteries during early experimental atherogenesis, whereas IL-1ß drives inflammation during atherogenesis and the evolution of advanced atheroma in mice.

Neutrophil Extracellular Traps Induce Endothelial Cell Activation and Tissue Factor Production Through Interleukin-1α and Cathepsin G.

Objective- Coronary artery thrombosis can occur in the absence of plaque rupture because of superficial erosion. Erosion-prone atheromata associate with more neutrophil extracellular traps (NETs) than lesions with stable or rupture-prone characteristics. The effects of NETs on endothelial cell (EC) inflammatory and thrombogenic properties remain unknown. We hypothesized that NETs alter EC functions related to erosion-associated thrombosis. Approach and Results- Exposure of human ECs to NETs increased VCAM-1 (vascular cell adhesion molecule 1) and ICAM-1 (intercellular adhesion molecule 1) mRNA and protein expression in a time- and concentration-dependent manner. THP-1 monocytoid cells and primary human monocytes bound more avidly to NET-treated human umbilical vein ECs than to unstimulated cells under flow. Treatment of human ECs with NETs augmented the expression of TF (tissue factor) mRNA, increased EC TF activity, and hastened clotting of recalcified plasma. Anti-TF-neutralizing antibody blocked NET-induced acceleration of clotting by ECs. NETs alone did not exhibit TF activity or acceleration of clotting in cell-free assays. Pretreatment of NETs with anti-interleukin (IL)-1α-neutralizing antibody or IL-1Ra (IL-1 receptor antagonist)-but not with anti-IL-1ß-neutralizing antibody or control IgG-blocked NET-induced VCAM-1, ICAM-1, and TF expression. Inhibition of cathepsin G, a serine protease abundant in NETs, also limited the effect of NETs on EC activation. Cathepsin G potentiated the effect of IL-1α on ECs by cleaving the pro-IL-1α precursor and releasing the more potent mature IL-1α form. Conclusions- NETs promote EC activation and increased thrombogenicity through concerted action of IL-1α and cathepsin G. Thus, NETs may amplify and propagate EC dysfunction related to thrombosis because of superficial erosion.

Mechanisms of erosion of atherosclerotic plaques.

PURPOSE OF REVIEW: The present review explores the mechanisms of superficial intimal erosion, a common cause of thrombotic complications of atherosclerosis. RECENT FINDINGS: Human coronary artery atheroma that give rise to thrombosis because of erosion differ diametrically from those associated with fibrous cap rupture. Eroded lesions characteristically contain few inflammatory cells, abundant extracellular matrix, and neutrophil extracellular traps (NETs). Innate immune mechanisms such as engagement of Toll-like receptor 2 (TLR2) on cultured endothelial cells can impair their viability, attachment, and ability to recover a wound. Hyaluronan fragments may serve as endogenous TLR2 ligands. Mouse experiments demonstrate that flow disturbance in arteries with neointimas tailored to resemble features of human eroded plaques disturbs endothelial cell barrier function, impairs endothelial cell viability, recruits neutrophils, and provokes endothelial cells desquamation, NET formation, and thrombosis in a TLR2-dependent manner. SUMMARY: Mechanisms of erosion have received much less attention than those that provoke plaque rupture. Intensive statin treatment changes the characteristic of plaques that render them less susceptible to rupture. Thus, erosion may contribute importantly to the current residual burden of risk. Understanding the mechanisms of erosion may inform the development and deployment of novel therapies to combat the remaining atherothrombotic risk in the statin era.

Moderate hypoxia potentiates interleukin-1ß production in activated human macrophages.

RATIONALE: Inflammation drives atherogenesis. Animal and human studies have implicated interleukin-1ß (IL-1ß) in this disease. Moderate hypoxia, a condition that prevails in the atherosclerotic plaque, may conspire with inflammation and contribute to the evolution and complications of atherosclerosis through mechanisms that remain incompletely understood. OBJECTIVE: This study investigated the links between hypoxia and inflammation by testing the hypothesis that moderate hypoxia modulates IL-1ß production in activated human macrophages. METHODS AND RESULTS: Our results demonstrated that hypoxia enhances pro-IL-1ß protein, but not mRNA, expression in lipopolysaccharide-stimulated human macrophages. We show that hypoxia limits the selective targeting of pro-IL-1ß to autophagic degradation, thus prolonging its half-life and promoting its intracellular accumulation. Furthermore, hypoxia increased the expression of NLRP3, a limiting factor in NLRP3 inflammasome function, and augmented caspase-1 activation in lipopolysaccharide-primed macrophages. Consequently, hypoxic human macrophages secreted higher amounts of mature IL-1ß than did normoxic macrophages after treatment with crystalline cholesterol, an endogenous danger signal that contributes to atherogenesis. In human atherosclerotic plaques, IL-1ß localizes predominantly to macrophage-rich regions that express activated caspase-1 and the hypoxia markers hypoxia-inducible factor 1α and hexokinase-2, as assessed by immunohistochemical staining of carotid endarterectomy specimens. CONCLUSIONS: These results indicate that hypoxia potentiates IL-1ß expression in cultured human macrophages and in the context of atheromata, therefore unveiling a novel proinflammatory mechanism that may participate in atherogenesis.

CXCR3 controls T-cell accumulation in fat inflammation.

OBJECTIVE: Obesity associates with increased numbers of inflammatory cells in adipose tissue (AT), including T cells, but the mechanism of T-cell recruitment remains unknown. This study tested the hypothesis that the chemokine (C-X-C motif) receptor 3 (CXCR3) participates in T-cell accumulation in AT of obese mice and thus in the regulation of local inflammation and systemic metabolism. APPROACH AND RESULTS: Obese wild-type mice exhibited higher mRNA expression of CXCR3 in periepididymal AT-derived stromal vascular cells compared with lean mice. We evaluated the function of CXCR3 in AT inflammation in vivo using CXCR3-deficient and wild-type control mice that consumed a high-fat diet. Periepididymal AT from obese CXCR3-deficient mice contained fewer T cells than obese controls after 8 and 16 weeks on high-fat diet, as assessed by flow cytometry. Obese CXCR3-deficient mice had greater glucose tolerance than obese controls after 8 weeks, but not after 16 weeks. CXCR3-deficient mice fed high-fat diet had reduced mRNA expression of proinflammatory mediators, such as monocyte chemoattractant protein-1 and regulated on activation, normal T cell expressed and secreted, and anti-inflammatory genes, such as Foxp3, IL-10, and arginase-1 in periepididymal AT, compared with obese controls. CONCLUSIONS: These results demonstrate that CXCR3 contributes to T-cell accumulation in periepididymal AT of obese mice. Our results also suggest that CXCR3 regulates the accumulation of distinct subsets of T cells and that the ratio between these functional subsets across time likely modulates local inflammation and systemic metabolism.

The clonal hematopoiesis mutation Jak2V617F aggravates endothelial injury and thrombosis in arteries with erosion-like intimas.

BACKGROUND: Superficial plaque erosion causes many acute coronary syndromes. However, mechanisms of plaque erosion remain poorly understood, and we lack directed therapeutics for thrombotic complication. Human eroded plaques can harbor neutrophil extracellular traps (NETs) that propagate endothelial damage at experimental arterial lesions that recapitulate superficial erosion. Clonal Hematopoiesis of Indeterminate Potential (CHIP) denotes age-related clonal expansion of bone marrow-derived cells harboring somatic mutations in the absence of overt hematological disease. CHIP heightens the risk of cardiovascular disease, with the greatest increase seen in individuals with JAK2V617F. Neutrophils from mice and humans with JAK2V617F undergo NETosis more readily than Jak2WT (wild-type) cells. We hypothesized that JAK2V617F, by increasing propensity to NETosis, exacerbates aspects of superficial erosion. METHODS AND RESULTS: We generated Jak2V617F and Jak2WT mice with heterozygous Jak2V617F in myeloid cells. We induced areas of denuded endothelium that recapitulate features of superficial erosion and assessed endothelial integrity, cellular composition of the erosion, thrombosis rates, and response to ruxolitinib, a clinically available JAK1/2 inhibitor, in relation to genotype. Following experimental erosion, Jak2V617F mice have greater impairment of endothelial barrier function and increased rates of arterial thrombosis. Neointimas in Jak2V617F mice exhibit increased apoptosis, NETosis, and platelet recruitment. Jak2V617F mice treated with ruxolitinib show increased endothelial continuity and reduced apoptosis in the neointima comparable to levels in Jak2WT. CONCLUSIONS: These observations provide new mechanistic insight into the pathophysiology of superficial erosion, the heightened risk for myocardial infarction in JAK2V617F CHIP, and point the way to personalized therapeutics based on CHIP status.

Adiponectin induces pro-inflammatory programs in human macrophages and CD4+ T cells.

Abundant experimental and clinical data support a modulatory role for adiponectin in inflammation, dysmetabolism, and disease. Because the activation of cells involved in innate and adaptive immunity contributes to the pathogenesis of diseases such as atherosclerosis and obesity, this study investigated the role of adiponectin in human macrophage polarization and T cell differentiation. Examination of the adiponectin-induced transcriptome in primary human macrophages revealed that adiponectin promotes neither classical (M1) nor alternative (M2) macrophage activation but elicits a pro-inflammatory response that resembles M1 more closely than M2. Addition of adiponectin to polyclonally activated CD4(+) T lymphocytes did not affect cell proliferation but induced mRNA expression and protein secretion of interferon (IFN)-γ and interleukin (IL)-6. Adiponectin treatment of CD4(+) T cells increased phosphorylation of p38 mitogen-activated protein kinase (MAPK) and signal transducer and activation of transcription (STAT) 4 and augmented T-bet expression. Inhibition of p38 with SB203580 abrogated adiponectin-induced IFN-γ production, indicating that adiponectin enhances T(H)1 differentiation through the activation of the p38-STAT4-T-bet axis. Collectively, our results demonstrate that adiponectin can induce pro-inflammatory functions in isolated macrophages and T cells, concurring with previous observations that adiponectin induces a limited program of inflammatory activation that likely desensitizes these cells to further pro-inflammatory stimuli.

Loss of myeloid related protein-8/14 exacerbates cardiac allograft rejection.

BACKGROUND: The calcium-binding proteins myeloid-related protein (MRP)-8 (S100A8) and MRP-14 (S100A9) form MRP-8/14 heterodimers (S100A8/A9, calprotectin) that regulate myeloid cell function and inflammatory responses and serve as early serum markers for monitoring acute allograft rejection. Despite functioning as a proinflammatory mediator, the pathophysiological role of MRP-8/14 complexes in cardiovascular disease is incompletely defined. This study investigated the role of MRP-8/14 in cardiac allograft rejection using MRP-14(-/-) mice that lack MRP-8/14 complexes. METHODS AND RESULTS: We examined parenchymal rejection after major histocompatibility complex class II allomismatched cardiac transplantation (bm12 donor heart and B6 recipients) in wild-type (WT) and MRP-14(-/-) recipients. Allograft survival averaged 5.9±2.9 weeks (n=10) in MRP-14(-/-) recipients compared with >12 weeks (n=15; P<0.0001) in WT recipients. Two weeks after transplantation, allografts in MRP-14(-/-) recipients had significantly higher parenchymal rejection scores (2.8±0.8; n=8) than did WT recipients (0.8±0.8; n=12; P<0.0001). Compared with WT recipients, allografts in MRP-14(-/-) recipients had significantly increased T-cell and macrophage infiltration and increased mRNA levels of interferon-γ and interferon-γ-associated chemokines (CXCL9, CXCL10, and CXCL11), interleukin-6, and interleukin-17 with significantly higher levels of Th17 cells. MRP-14(-/-) recipients also had significantly more lymphocytes in the adjacent para-aortic lymph nodes than did WT recipients (cells per lymph node: 23.7±0.7×10(5) for MRP-14(-/-) versus 6.0±0.2×10(5) for WT; P<0.0001). The dendritic cells (DCs) of the MRP-14(-/-) recipients of bm12 hearts expressed significantly higher levels of the costimulatory molecules CD80 and CD86 than did those of WT recipients 2 weeks after transplantation. Mixed leukocyte reactions with allo-endothelial cell-primed MRP-14(-/-) DCs resulted in significantly higher antigen-presenting function than reactions using WT DCs. Ovalbumin-primed MRP-14(-/-) DCs augmented proliferation of OT-II (ovalbumin-specific T cell receptor transgenic) CD4(+) T cells with increased interleukin-2 and interferon-γ production. Cardiac allografts of B6 major histocompatibility complex class II(-/-) hosts and of B6 WT hosts receiving MRP-14(-/-) DCs had significantly augmented inflammatory cell infiltration and accelerated allograft rejection compared with WT DCs from transferred recipient allografts. Bone marrow-derived MRP-14(-/-) DCs infected with MRP-8 and MRP-14 retroviral vectors showed significantly decreased CD80 and CD86 expression compared with controls, indicating that MRP-8/14 regulates B7-costimulatory molecule expression. CONCLUSIONS: Our results indicate that MRP-14 regulates B7 molecule expression and reduces antigen presentation by DCs and subsequent T-cell priming. The absence of MRP-14 markedly increased T-cell activation and exacerbated allograft rejection, indicating a previously unrecognized role for MRP-14 in immune cell biology.

Mechanisms of cardiac arrhythmias and sudden death in transgenic rabbits with long QT syndrome.

Long QT syndrome (LQTS) is a heritable disease associated with ECG QT interval prolongation, ventricular tachycardia, and sudden cardiac death in young patients. Among genotyped individuals, mutations in genes encoding repolarizing K+ channels (LQT1:KCNQ1; LQT2:KCNH2) are present in approximately 90% of affected individuals. Expression of pore mutants of the human genes KCNQ1 (KvLQT1-Y315S) and KCNH2 (HERG-G628S) in the rabbit heart produced transgenic rabbits with a long QT phenotype. Prolongations of QT intervals and action potential durations were due to the elimination of IKs and IKr currents in cardiomyocytes. LQT2 rabbits showed a high incidence of spontaneous sudden cardiac death (>50% at 1 year) due to polymorphic ventricular tachycardia. Optical mapping revealed increased spatial dispersion of repolarization underlying the arrhythmias. Both transgenes caused downregulation of the remaining complementary IKr and IKs without affecting the steady state levels of the native polypeptides. Thus, the elimination of 1 repolarizing current was associated with downregulation of the reciprocal repolarizing current rather than with the compensatory upregulation observed previously in LQTS mouse models. This suggests that mutant KvLQT1 and HERG interacted with the reciprocal wild-type alpha subunits of rabbit ERG and KvLQT1, respectively. These results have implications for understanding the nature and heterogeneity of cardiac arrhythmias and sudden cardiac death.

Targeted delivery of protein arginine deiminase-4 inhibitors to limit arterial intimal NETosis and preserve endothelial integrity.

AIMS: Recent evidence suggests that 'vulnerable plaques', which have received intense attention as underlying mechanism of acute coronary syndromes over the decades, actually rarely rupture and cause clinical events. Superficial plaque erosion has emerged as a growing cause of residual thrombotic complications of atherosclerosis in an era of increased preventive measures including lipid lowering, antihypertensive therapy, and smoking cessation. The mechanisms of plaque erosion remain poorly understood, and we currently lack validated effective diagnostics or therapeutics for superficial erosion. Eroded plaques have a rich extracellular matrix, an intact fibrous cap, sparse lipid, and few mononuclear cells, but do harbour neutrophil extracellular traps (NETs). We recently reported that NETs amplify and propagate the endothelial damage at the site of arterial lesions that recapitulate superficial erosion in mice. We showed that genetic loss of protein arginine deiminase (PAD)-4 function inhibited NETosis and preserved endothelial integrity. The current study used systemic administration of targeted nanoparticles to deliver an agent that limits NETs formation to probe mechanisms of and demonstrate a novel therapeutic approach to plaque erosion that limits endothelial damage. METHODS AND RESULTS: We developed Collagen IV-targeted nanoparticles (Col IV NP) to deliver PAD4 inhibitors selectively to regions of endothelial cell sloughing and collagen IV-rich basement membrane exposure. We assessed the binding capability of the targeting ligand in vitro and evaluated Col IV NP targeting to areas of denuded endothelium in vivo in a mouse preparation that recapitulates features of superficial erosion. Delivery of the PAD4 inhibitor GSK484 reduced NET accumulation at sites of intimal injury and preserved endothelial continuity. CONCLUSIONS: NPs directed to Col IV show selective uptake and delivery of their payload to experimentally eroded regions, illustrating their translational potential. Our results further support the role of PAD4 and NETs in superficial erosion.

Adiponectin inhibits pro-inflammatory signaling in human macrophages independent of interleukin-10.

Macrophages participate pivotally in the pathogenesis of many chronic inflammatory diseases including atherosclerosis. Adiponectin, a vasculoprotective molecule with insulin-sensitizing and anti-atherogenic properties, suppresses pro-inflammatory gene expression in macrophages by mechanisms that remain incompletely understood. This study investigated the effects of adiponectin on major pro-inflammatory signaling pathways in human macrophages. We demonstrate that pretreatment of these cells with adiponectin inhibits phosphorylation of nuclear factor kappaB inhibitor (IkappaB), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK), induced by either lipopolysaccharide (LPS) or tumor necrosis factor (TNF) alpha, as well as STAT3 phosphorylation induced by interleukin-6 (IL6). Antagonism of IL10 by either neutralizing antibodies or siRNA-mediated silencing did not abrogate the anti-inflammatory actions of adiponectin, indicating that the ability of adiponectin to render human macrophages tolerant to various pro-inflammatory stimuli does not require this cytokine. A systematic search for adiponectin-inducible genes with established anti-inflammatory properties revealed that adiponectin augmented the expression of A20, suppressor of cytokine signaling (SOCS) 3, B-cell CLL/lymphoma (BCL) 3, TNF receptor-associated factor (TRAF) 1, and TNFAIP3-interacting protein (TNIP) 3. These results suggest that adiponectin triggers a multifaceted response in human macrophages by inducing the expression of various anti-inflammatory proteins that act at different levels in concert to suppress macrophage activation.

T-cell activation leads to reduced collagen maturation in atherosclerotic plaques of Apoe(-/-) mice.

Rupture of the collagenous, fibrous cap of an atherosclerotic plaque commonly causes thrombosis. Activated immune cells can secrete mediators that jeopardize the integrity of the fibrous cap. This study aimed to determine the relationship between T-cell-mediated inflammation and collagen turnover in a mouse model of experimental atherosclerosis. Both Apoe(-/-) x CD4dnTbetaRII mice with defective transforming growth factor-beta receptors in T cells (and hence released from tonic suppression of T-cell activation) and lesion size-matched Apoe(-/-) mice were used. Picrosirius red staining showed a lower content of thick mature collagen fibers in lesions of Apoe(-/-) x CD4dnTbetaRII mice, although both groups had similar levels of procollagen type I or III mRNA and total collagen content in lesions. Analysis of both gene expression and protein content showed a significant decrease of lysyl oxidase, the extracellular enzyme needed for collagen cross-linking, in aortas of Apoe(-/-)--CD4dnTbetaRII mice. T-cell-driven inflammation provoked a selective and limited increase in the expression of proteinases that catabolize the extracellular matrix. Atheromata of Apoe(-/-)--CD4dnTbetaRII mice had increased levels of matrix metalloproteinase-13 and cathepsin S mRNAs and of the active form of cathepsin S protein but no increase was detected in collagen fragmentation. Our results suggest that exaggerated T-cell-driven inflammation limits collagen maturation in the atherosclerotic plaque while having little effect on collagen degradation.

Interferon-gamma, a Th1 cytokine, regulates fat inflammation: a role for adaptive immunity in obesity.

Adipose tissue (AT) can accumulate macrophages and secrete several inflammatory mediators. Despite its pivotal role in the progression of chronic inflammatory processes such as atherosclerosis, the adaptive role of immunity in obesity remains poorly explored. Visceral AT of diet-induced obese C57BL/6 mice had higher numbers of both CD4(+) and CD8(+) T cells than lean controls, monitored by flow cytometry. When stimulated in vitro, T cells from obese AT produced more interferon (IFN)gamma than those from controls. AT from obese animals also had more cells expressing I-A(b), a mouse class II histocompatibility marker implicated in antigen presentation, as determined by immunostaining. Differentiated 3T3-L1 cells stimulated with recombinant IFNgamma or T-helper 1-derived supernatant produced several chemokines and their mRNAs. Obese IFNgamma-deficient animals had significantly reduced AT expression of mRNA-encoding inflammatory genes such as tumor necrosis factor-alpha and monocyte chemoattractant protein-1, decreased AT inflammatory cell accumulation, and better glucose tolerance than control animals consuming the same diet. Obese mice doubly deficient for IFNgamma receptor and apolipoprotein (Apo)E on a mixed 129SvEv/C57BL/6 (129/B6) genetic background, despite exhibiting similar AT mRNA levels of tumor necrosis factor-alpha and monocyte chemoattractant protein-1 as 129/B6-ApoE(-/-) controls, had decreased expression of important T cell-related genes, such as IFNgamma-inducible protein-10 and I-A(b), and lower plasma triglycerides and glucose. These results indicate a role for T cells and IFNgamma, a prototypical T-helper 1 cytokine, in regulation of the inflammatory response that accompanies obesity.

Adiponectin inhibits the production of CXC receptor 3 chemokine ligands in macrophages and reduces T-lymphocyte recruitment in atherogenesis.

Obese individuals often have low plasma adiponectin and concomitant chronic inflammation with a predisposition to metabolic and cardiovascular diseases. The present study reports a novel antiinflammatory action of adiponectin in human monocyte-derived macrophages (MPhi) suppressing T-lymphocyte accumulation in atherogenesis. RNA profiling of lipopolysaccharide-stimulated human MPhi identified CXC chemokine ligands (CXCLs), such as IP-10 (interferon [IFN]-inducible protein 10) (CXCL10), I-TAC (IFN-inducible T-cell alpha chemoattractant) (CXCL11), and Mig (monokine induced by IFN-gamma) (CXCL9), T-lymphocyte chemoattractants associated with atherogenesis, among the top 14 transcripts suppressed by adiponectin. Real-time quantitative RT-PCR and ELISA verified that adiponectin inhibited expression of these chemokines at both the mRNA and protein levels in a concentration-dependent manner. Adiponectin reduced the release by lipopolysaccharide-stimulated MPhi of chemoattractant activity for CXC chemokine receptor 3-transfected (receptor for IP-10, Mig, and I-TAC) lymphocytes. Adiponectin decreased lipopolysaccharide-inducible IP-10 promoter activity in promoter-transfected THP-1 MPhi but did not change IP-10 mRNA stability. In lipopolysaccharide-stimulated MPhi, reduction of IFN-beta by adiponectin preceded inhibition of IP-10 mRNA expression. Immunoblot and chromatin immunoprecipitation analyses demonstrated that adiponectin attenuated activation of the transcription factor IFN regulatory factor 3, involved in the MyD88-independent pathway of Toll-like receptor 4 signaling, and subsequent IFN regulatory factor 3 binding to IFN-beta promoter. In vivo studies further demonstrated that apolipoprotein E/adiponectin double-deficient (apoE-/-APN-/-) mice had increased plasma IP-10 levels, accelerated T-lymphocyte accumulation in atheromata, and augmented atherogenesis compared with apoE single-deficient (apoE-/-APN+/+) mice. This study establishes that low levels of adiponectin associated with obesity, the metabolic syndrome, and diabetes favor T-lymphocyte recruitment and contribute to adaptive immune response during atherogenesis.

Inflammation in atherosclerosis: transition from theory to practice.

Inflammation drives the formation, progression, and rupture of atherosclerotic plaques. Experimental studies have demonstrated that an inflammatory subset of monocytes/macrophages preferentially accumulate in atherosclerotic plaque and produce proinflammatory cytokines. T lymphocytes can contribute to inflammatory processes that promote thrombosis by stimulating production of collagen-degrading proteinases and the potent procoagulant tissue factor. Recent data link obesity, inflammation, and modifiers of atherosclerotic events, a nexus of growing clinical concern given the worldwide increase in the prevalence of obesity. Modulators of inflammation derived from visceral adipose tissue evoke production of acute phase reactants in the liver, implicated in thrombogenesis and clot stability. Additionally, C-reactive protein levels rise with increasing levels of visceral adipose tissue. Adipose tissue in obese mice contains increased numbers of macrophages and T lymphocytes, increased T lymphocyte activation, and increased interferon-gamma (IFN-gamma) expression. IFN-gamma deficiency in mice reduces production of inflammatory cytokines and inflammatory cell accumulation in adipose tissue. Another series of in vitro and in vivo mouse experiments affirmed that adiponectin, an adipocytokine, the plasma levels of which drop with obesity, acts as an endogenous antiinflammatory modulator of both innate and adaptive immunity in atherogenesis. Thus, accumulating experimental evidence supports a key role for inflammation as a link between risk factors for atherosclerosis and the biology that underlies the complications of this disease. The recent JUPITER trial supports the clinical utility of an assessment of inflammatory status in guiding intervention to limit cardiovascular events. Inflammation is thus moving from a theoretical concept to a tool that provides practical clinical utility in risk assessment and targeting of therapy.

Oxidized Low-Density Lipoprotein Induces Macrophage Production of Prothrombotic Microparticles.

Background Activated vascular cells produce submicron prothrombotic and proinflammatory microparticle vesicles. Atherosclerotic plaques contain high levels of microparticles. Plasma microparticle levels increase during acute coronary syndromes and the thrombotic consequences of plaque rupture likely involve macrophage-derived microparticles (MΦMPs). The activation pathways that promote MΦMP production remain poorly defined. This study tested the hypothesis that signals implicated in atherogenesis also stimulate MΦMP production. Methods and Results We stimulated human primary MΦs with proinflammatory cytokines and atherogenic lipids, and measured MΦMP production by flow cytometry. Oxidized low-density lipoprotein (oxLDL; 25 µg/mL) induced MΦMP production in a concentration-dependent manner (293% increase; P<0.001), and these oxLDL MΦMP stimulatory effects were mediated by CD36. OxLDL stimulation increased MΦMP tissue factor content by 78% (P<0.05), and oxLDL-induced MΦMP production correlated with activation of caspase 3/7 signaling pathways. Salvionolic acid B, a CD36 inhibitor and a CD36 inhibitor antibody reduced oxLDL-induced MΦMP by 67% and 60%, respectively. Caspase 3/7 inhibition reduced MΦMP release by 52% (P<0.01) and caspase 3/7 activation increased MΦMP production by 208% (P<0.01). Mevastatin pretreatment (10 µM) decreased oxLDL-induced caspase 3/7 activation and attenuated oxLDL-stimulated MΦMP production and tissue factor content by 60% (P<0.01) and 43% (P<0.05), respectively. Conclusions OxLDL induces the production of prothrombotic microparticles in macrophages. This process depends on caspases 3 and 7 and CD36 and is inhibited by mevastatin pretreatment. These findings link atherogenic signaling pathways, inflammation, and plaque thrombogenicity and identify a novel potential mechanism for antithrombotic effects of statins independent of LDL lowering.

AGE-BSA decreases ABCG1 expression and reduces macrophage cholesterol efflux to HDL.

BACKGROUND: Previous reports have suggested that advanced glycation end products (AGE) participate in the pathogenesis of diabetic macroangiopathy. However, current understanding of the mechanisms by which AGE may accelerate atherogenesis remains incomplete. METHODS AND RESULTS: Microarray and reverse transcription real-time PCR analyses revealed that exposure to AGE-BSA (BSA, bovine serum albumin) reduced mRNA levels (60%) in the ATP-binding cassette transporter G1 (ABCG1) but not ABCA1 in human macrophages. AGE-BSA also reduced ABCG1 protein levels. These effects occurred mainly through the receptor for AGE (RAGE), as an anti-RAGE antibody significantly limited ABCG1 mRNA reduction. Functional studies demonstrated that exposure to AGE-BSA decreased cholesterol efflux to high-density lipoprotein (HDL) (P<0.05) but not to apolipoprotein AI, compared to BSA treatment. Although liver X receptors (LXR) augment ABCG1 expression, macrophages treated with AGE-BSA showed no reduction in LXR mRNA levels or in the binding of nuclear proteins to the LXR response element, compared with BSA. CONCLUSIONS: Our data show that AGE-BSA can decrease cholesterol efflux from macrophages to HDL via an LXR-independent pathway. This novel mechanism may contribute to accelerated foam cell production and atherogenesis in diabetic patients.