The Dendritic Cell Receptor DNGR-1 Promotes the Development of Atherosclerosis in Mice.

RATIONALE: Necrotic core formation during the development of atherosclerosis is associated with a chronic inflammatory response and promotes accelerated plaque development and instability. However, the molecular links between necrosis and the development of atherosclerosis are not completely understood. Clec9a (C-type lectin receptor) or DNGR-1 (dendritic cell NK lectin group receptor-1) is preferentially expressed by the CD8α+ subset of dendritic cells (CD8α+ DCs) and is involved in sensing necrotic cells. We hypothesized that sensing of necrotic cells by DNGR-1 plays a determinant role in the inflammatory response of atherosclerosis. OBJECTIVE: We sought to address the impact of total, bone marrow-restricted, or CD8α+ DC-restricted deletion of DNGR-1 on atherosclerosis development. METHODS AND RESULTS: We show that total absence of DNGR-1 in Apoe (apolipoprotein e)-deficient mice (Apoe-/-) and bone marrow-restricted deletion of DNGR-1 in Ldlr (low-density lipoprotein receptor)-deficient mice (Ldlr-/-) significantly reduce inflammatory cell content within arterial plaques and limit atherosclerosis development in a context of moderate hypercholesterolemia. This is associated with a significant increase of the expression of interleukin-10 (IL-10). The atheroprotective effect of DNGR-1 deletion is completely abrogated in the absence of bone marrow-derived IL-10. Furthermore, a specific deletion of DNGR-1 in CD8α+ DCs significantly increases IL-10 expression, reduces macrophage and T-cell contents within the lesions, and limits the development of atherosclerosis. CONCLUSIONS: Our results unravel a new role of DNGR-1 in regulating vascular inflammation and atherosclerosis and potentially identify a new target for disease modulation

Selective EGF-Receptor Inhibition in CD4+ T Cells Induces Anergy and Limits Atherosclerosis.

BACKGROUND: Several epidermal growth factor receptor (EGFR) inhibitors have been successfully developed for the treatment of cancer, limiting tumor growth and metastasis. EGFR is also expressed by leukocytes, but little is known about its role in the modulation of the immune response. OBJECTIVES: The aim of this study was to determine whether EGFR expressed on CD4+ T cells is functional and to address the consequences of EGFR inhibition in atherosclerosis, a T cell-mediated vascular chronic inflammatory disease. METHODS: The authors used EGFR tyrosine kinase inhibitors (AG-1478, erlotinib) and chimeric Ldlr-/-Cd4-Cre/Egfrlox/lox mouse with a specific deletion of EGFR in CD4+ T cells. RESULTS: Mouse CD4+ T cells expressed EGFR, and the EGFR tyrosine kinase inhibitor AG-1478 blocked in vitro T cell proliferation and Th1/Th2 cytokine production. In vivo, treatment of Ldlr-/- mice with the EGFR inhibitor erlotinib induced T cell anergy, reduced T cell infiltration within atherosclerotic lesions, and protected against atherosclerosis development and progression. Selective deletion of EGFR in CD4+ T cells resulted in decreased T cell proliferation and activation both in vitro and in vivo, as well as reduced interferon-γ, interleukin-4, and interleukin-2 production. Atherosclerotic lesion size was reduced by 2-fold in irradiated Ldlr-/- mice reconstituted with bone marrow from Cd4-Cre/Egfrlox/lox mice, compared to Cd4-Cre/Egfr+/+ chimeric mice, after 4, 6, and 12 weeks of high-fat diet, associated with marked reduction in T cell infiltration in atherosclerotic plaques. Human blood T cells expressed EGFR and EGFR inhibition reduced T cell proliferation both in vitro and in vivo. CONCLUSIONS: EGFR blockade induced T cell anergy in vitro and in vivo and reduced atherosclerosis development. Targeting EGFR may be a novel strategy to combat atherosclerosis

Genetic and Pharmacological Inhibition of TREM-1 Limits the Development of Experimental Atherosclerosis.

BACKGROUND: Innate immune responses activated through myeloid cells contribute to the initiation, progression, and complications of atherosclerosis in experimental models. However, the critical upstream pathways that link innate immune activation to foam cell formation are still poorly identified. OBJECTIVES: This study sought to investigate the hypothesis that activation of the triggering receptor expressed on myeloid cells (TREM-1) plays a determinant role in macrophage atherogenic responses. METHODS: After genetically invalidating Trem-1 in chimeric Ldlr-/-Trem-1-/- mice and double knockout ApoE-/-Trem-1-/- mice, we pharmacologically inhibited Trem-1 using LR12 peptide. RESULTS: Ldlr-/- mice reconstituted with bone marrow deficient for Trem-1 (Trem-1-/-) showed a strong reduction of atherosclerotic plaque size in both the aortic sinus and the thoracoabdominal aorta, and were less inflammatory compared to plaques of Trem-1+/+ chimeric mice. Genetic invalidation of Trem-1 led to alteration of monocyte recruitment into atherosclerotic lesions and inhibited toll-like receptor 4 (TLR 4)-initiated proinflammatory macrophage responses. We identified a critical role for Trem-1 in the upregulation of cluster of differentiation 36 (CD36), thereby promoting the formation of inflammatory foam cells. Genetic invalidation of Trem-1 in ApoE-/-/Trem-1-/- mice or pharmacological blockade of Trem-1 in ApoE-/- mice using LR-12 peptide also significantly reduced the development of atherosclerosis throughout the vascular tree, and lessened plaque inflammation. TREM-1 was expressed in human atherosclerotic lesions, mainly in lipid-rich areas with significantly higher levels of expression in atheromatous than in fibrous plaques. CONCLUSIONS: We identified TREM-1 as a major upstream proatherogenic receptor. We propose that TREM-1 activation orchestrates monocyte/macrophage proinflammatory responses and foam cell formation through coordinated and combined activation of CD36 and TLR4. Blockade of TREM-1 signaling may constitute an attractive novel and double-hit approach for the treatment of atherosclerosis

Genetic deficiency of indoleamine 2,3-dioxygenase promotes gut microbiota-mediated metabolic health.

The association between altered gut microbiota, intestinal permeability, inflammation and cardiometabolic diseases is becoming increasingly clear but remains poorly understood1,2. Indoleamine 2,3-dioxygenase is an enzyme induced in many types of immune cells, including macrophages in response to inflammatory stimuli, and catalyzes the degradation of tryptophan along the kynurenine pathway. Indoleamine 2,3-dioxygenase activity is better known for its suppression of effector T cell immunity and its activation of regulatory T cells3,4. However, high indoleamine 2,3-dioxygenase activity predicts worse cardiovascular outcome5-9 and may promote atherosclerosis and vascular inflammation6, suggesting a more complex role in chronic inflammatory settings. Indoleamine 2,3-dioxygenase activity is also increased in obesity10-13, yet its role in metabolic disease is still unexplored. Here, we show that obesity is associated with an increase of intestinal indoleamine 2,3-dioxygenase activity, which shifts tryptophan metabolism from indole derivative and interleukin-22 production toward kynurenine production. Indoleamine 2,3-dioxygenase deletion or inhibition improves insulin sensitivity, preserves the gut mucosal barrier, decreases endotoxemia and chronic inflammation, and regulates lipid metabolism in liver and adipose tissues. These beneficial effects are due to rewiring of tryptophan metabolism toward a microbiota-dependent production of interleukin-22 and are abrogated after treatment with a neutralizing anti-interleukin-22 antibody. In summary, we identify an unexpected function of indoleamine 2,3-dioxygenase in the fine tuning of intestinal tryptophan metabolism with major consequences on microbiota-dependent control of metabolic disease, which suggests indoleamine 2,3-dioxygenase as a potential therapeutic target

B cell depletion reduces the development of atherosclerosis in mice

B cell depletion significantly reduces the burden of several immune-mediated diseases. However, B cell activation has been until now associated with a protection against atherosclerosis, suggesting that B cell–depleting therapies would enhance cardiovascular risk. We unexpectedly show that mature B cell depletion using a CD20-specific monoclonal antibody induces a significant reduction of atherosclerosis in various mouse models of the disease. This treatment preserves the production of natural and potentially protective anti–oxidized low-density lipoprotein (oxLDL) IgM autoantibodies over IgG type anti-oxLDL antibodies, and markedly reduces pathogenic T cell activation. B cell depletion diminished T cell–derived IFN-γ secretion and enhanced production of IL-17; neutralization of the latter abrogated CD20 antibody–mediated atheroprotection. These results challenge the current paradigm that B cell activation plays an overall protective role in atherogenesis and identify new antiatherogenic strategies based on B cell modulation

B lymphocytes trigger monocyte mobilization and impair heart function after acute myocardial infarction.

Acute myocardial infarction is a severe ischemic disease responsible for heart failure and sudden death. Here, we show that after acute myocardial infarction in mice, mature B lymphocytes selectively produce Ccl7 and induce Ly6C(hi) monocyte mobilization and recruitment to the heart, leading to enhanced tissue injury and deterioration of myocardial function. Genetic (Baff receptor deficiency) or antibody-mediated (CD20- or Baff-specific antibody) depletion of mature B lymphocytes impeded Ccl7 production and monocyte mobilization, limited myocardial injury and improved heart function. These effects were recapitulated in mice with B cell-selective Ccl7 deficiency. We also show that high circulating concentrations of CCL7 and BAFF in patients with acute myocardial infarction predict increased risk of death or recurrent myocardial infarction. This work identifies a crucial interaction between mature B lymphocytes and monocytes after acute myocardial ischemia and identifies new therapeutic targets for acute myocardial infarction.This work was supported by Inserm, British Heart Foundation (Z.M.), European Research Council (Z.M.), Fondation Coeur et Recherche (Z.M., T.S., N.D.), Fondation pour la Recherche Medicale (J.S.S.), European Union Seven Framework programme TOLERAGE (Z.M.), Fondation Leducq transatlantic network (C.J.B., D.T., A.T., J.S.S., Z.M.), National Institutes of Health grants AI56363 and AI057157, and a grant from The Lymphoma Research Foundation (T.F.T).This is the author accepted manuscript. The final version is available from Nature Publishing Group at http://dx.doi.org/10.1038/nm.3284

Liens entre l'obésité et l'athérosclérose : rôle du métabolisme du tryptophane

Obesity, a major component of the metabolic syndrome, contributes to a considerable increase in cardiovascular diseases, such as atherosclerosis. Therefore, understanding the pathogenesis and interaction of these co-morbidities is of paramount importance and will lead to the identification of new relevant therapeutic targets. More recently, the diet impacting the intestinal microbiota has been the subject of much research to determine the role of the microbiota in intestinal homeostasis and in various pathologies. Our hypothesis was that the high-fat diet known to induce obesity is responsible for the development of atherosclerosis via the intestinal microbiota. In particular, the enzyme involved in the catabolism of tryptophan, indoleamine 2,3-dioxygenase 1 (IDO), could represent a link between obesity and atherosclerosis via the intestinal microbiota. Indeed, tryptophan is a key amino acid for intestinal homeostasis. It is also responsible for the production, by the microbiota, of indoles responsible for the induction of a cytokine important for intestinal homeostasis, IL-22, via the activation of the AhR (aryl hydrocarbon receptor). In a first work, we have shown that the high fat diet induces intestinal dysbiosis which is responsible for the development of atherosclerosis. This was shown by fecal microbiota transplantation experiments from mice fed with a high-fat diet. This diet is also responsible for the increase in intestinal activity of IDO, which converts tryptophan into Kynurenine. We have shown that in the absence of IDO, protection against weight gain, insulin resistance, hepatic steatosis and intestinal dysbiosis is observed. Similarly, inhibition of IDO activity by 1-Methyl Tryptophan improves insulin sensitivity, preserves intestinal homeostasis, decreases endotoxemia and inflammation. We have shown that this protection in the absence of IDO is dependent on the microbiota. In particular, in the absence of IDO, we observe a switch in the metabolism of tryptophan towards the production of indole derivatives and IL-22 to the detriment of kynurenine. Moreover, the neutralization of IL-22 in this model abolished the beneficial effects observed in the absence of IDO, which shows the involvement of this cytokine. We have identified a novel function of IDO in the regulation of tryptophan metabolism at the intestinal level impacting the metabolic syndrome via the microbiota, making IDO an attractive new therapeutic target. In perspective, it would be interesting to study the effect of IDO invalidation at the intestinal level as well as its impact on the development of cardiometabolic diseases.L'obésité, constituant majeur du syndrome métabolique, contribue à une augmentation considérable des maladies cardiovasculaires, comme l'athérosclérose. Par conséquent, la compréhension de la pathogenèse et de l'interaction de ces comorbidités est d'une importance capitale et permettra d'identifier de nouvelles cibles thérapeutiques pertinentes. Plus récemment, l'alimentation impactant le microbiote intestinal a fait l'objet de nombreuses recherches pour déterminer le rôle du microbiote dans l'homéostasie intestinale et dans différentes pathologies. Notre hypothèse était que le régime riche en matière grasse, connu pour induire l'obésité est responsable du développement de l'athérosclérose via le microbiote intestinal. En particulier, l'enzyme impliquée dans le catabolisme du tryptophane, l'indoleamine 2,3-dioxygénase 1 (IDO), pourrait constituer un lien entre l'obésité et l'athérosclérose via le microbiote intestinal. En effet, le tryptophane est un acide aminé clé pour l'homéostasie intestinale. Il est également à l'origine de la production, par le microbiote, d'indoles responsables de l'induction d'une cytokine importante pour l'homéostasie intestinale, IL-22 via l'activation de l'AhR (aryl hydrocarbon receptor). Dans un premier travail, nous avons montré que le régime gras induit une dysbiose qui est responsable du développement de l'athérosclérose. Ceci a été démontré par des expériences de transfert de flore à partir de souris nourries avec un régime riche en matières grasses. Ce régime gras est également responsable de l'augmentation de l'activité intestinale d'IDO, qui convertit le tryptophane en kynurénine. Nous avons montré qu'en absence d'IDO, on observe une protection contre la prise de poids, l'insulino-résistance, la stéatose hépatique et la dysbiose intestinale. De manière similaire, l'inhibition de l'activité IDO par le 1-Méthyl-Tryptophane a amélioré la sensibilité à l'insuline, a préservé l'homéostasie intestinale, a diminué l'endotoxémie et l'inflammation. Nous avons montré que cette protection en absence d'IDO est dépendante du microbiote. En particulier, en absence d'IDO, on observe un switch du métabolisme du tryptophane vers la production de dérivés indoles et de l'IL-22 au détriment de la kynurénine. De plus, la neutralisation de l'IL-22 dans ce modèle a aboli les effets bénéfiques observés en absence d'IDO ce qui montre l'implication de cette cytokine. Nous avons ainsi identifié une nouvelle fonction d'IDO dans la régulation du métabolisme du tryptophane au niveau intestinal impactant le syndrome métabolique via le microbiote, faisant d'IDO une nouvelle cible thérapeutique attrayante. En perspective, il serait intéressant d'étudier l'effet de l'invalidation d'IDO au niveau intestinal ainsi que son impact sur le développement des maladies cardiométaboliques