An obesogenic diet increases atherosclerosis through promoting microbiota dysbiosis-induced gut lymphocyte trafficking into the periphery

Although high-fat diet (HFD)-induced gut microbiota dysbiosis is known to affect atherosclerosis, the underlying mechanisms remain to be fully explored. Here, we show that the progression of atherosclerosis depends on a gut microbiota shaped by an HFD but not a high-cholesterol (HC) diet and, more particularly, on low fiber (LF) intake. Mechanistically, gut lymphoid cells impacted by HFD- or LF-induced microbiota dysbiosis highly proliferate in mesenteric lymph nodes (MLNs) and migrate from MLNs to the periphery, which fuels T cell accumulation within atherosclerotic plaques. This is associated with the induction of mucosal addressin cell adhesion molecule 1 (MAdCAM-1) within plaques and the presence of enterotropic lymphocytes expressing β7 integrin. MLN resection or lymphocyte deficiency abrogates the pro-atherogenic effects of a microbiota shaped by LF. Our study shows a pathological link between a diet-shaped microbiota, gut immune cells, and atherosclerosis, suggesting that a diet-modulated microbiome might be a suitable therapeutic target to prevent atherosclerosis.

Genetic inhibition of CARD9 accelerates the development of atherosclerosis in mice through CD36 dependent-defective autophagy

Caspase recruitment-domain containing protein 9 (CARD9) is a key signaling pathway in macrophages but its role in atherosclerosis is still poorly understood. Global deletion of Card9 in Apoe-/- mice as well as hematopoietic deletion in Ldlr-/- mice increases atherosclerosis. The acceleration of atherosclerosis is also observed in Apoe-/-Rag2-/-Card9-/- mice, ruling out a role for the adaptive immune system in the vascular phenotype of Card9 deficient mice. Card9 deficiency alters macrophage phenotype through CD36 overexpression with increased IL-1β production, increased lipid uptake, higher cell death susceptibility and defective autophagy. Rapamycin or metformin, two autophagy inducers, abolish intracellular lipid overload, restore macrophage survival and autophagy flux in vitro and finally abolish the pro-atherogenic effects of Card9 deficiency in vivo. Transcriptomic analysis of human CARD9-deficient monocytes confirms the pathogenic signature identified in murine models. In summary, CARD9 is a key protective pathway in atherosclerosis, modulating macrophage CD36-dependent inflammatory responses, lipid uptake and autophagy.

JAK2V617F mutation drives vascular resident macrophages toward a pathogenic phenotype and promotes dissecting aortic aneurysm

JAK2V617F mutation is associated with an increased risk for athero-thrombotic cardiovascular disease, but its role in aortic disease development and complications remains unknown. In a cohort of patients with myeloproliferative neoplasm, JAK2V617F mutation was identified as an independent risk factor for dilation of both the ascending and descending thoracic aorta. Using single-cell RNA-seq, complementary genetically-modified mouse models, as well as pharmacological approaches, we found that JAK2V617F mutation was associated with a pathogenic pro-inflammatory phenotype of perivascular tissue-resident macrophages, which promoted deleterious aortic wall remodeling at early stages, and dissecting aneurysm through the recruitment of circulating monocytes at later stages. Finally, genetic manipulation of tissue-resident macrophages, or treatment with a Jak2 inhibitor, ruxolitinib, mitigated aortic wall inflammation and reduced aortic dilation and rupture. Overall, JAK2V617F mutation drives vascular resident macrophages toward a pathogenic phenotype and promotes dissecting aortic aneurysm.

[Le LDL-cholestérol : une brique supplémentaire dans le mur de l'athérosclérose]

Atherosclerosis is one of the two major causes of mortality worldwide along with cancer and is responsible for myocardial infarction, stroke, and arteritis. Its pathophysiology is still partially understood which allows doubts referring to the preventive and curative treatments. Population screening for atherosclerosis remains marginal even though it should be the common practice. To encourage preventive screening and therapies, we propose a simple and easily understandable pathophysiology of atherosclerosis, explaining how the brick-wall of atheroma is build inside the intima of arteries using a metaphor: the LDL-cholesterol bricks, the oxidation cement, and the inflammatory mason.

Regulatory T-Cell Response to Low-Dose Interleukin-2 in Ischemic Heart Disease

Regulatory T-Cell Response to Low-Dose Interleukin-2 in Ischemic Heart Disease This phase 1b/2a, randomized, double-blind, placebo-controlled, dose-escalation trial tested low-dose subcutaneous aldesleukin (recombinant IL-2) in patients with ischemic heart disease. Low-dose IL-2 expanded Tregs, without adverse events of major concern. Single-cell RNA-sequencing of circulating immune cells was used to provide mechanistic assessment of the treatment's effects.

TREM-1 orchestrates angiotensin II-induced monocyte trafficking and promotes experimental abdominal aortic aneurysm

The triggering receptor expressed on myeloid cells 1 (TREM-1) drives inflammatory responses in several cardiovascular diseases but its role in abdominal aortic aneurysm (AAA) remains unknown. Our objective was to explore the role of TREM-1 in a mouse model of angiotensin II-induced (AngII-induced) AAA. TREM-1 expression was detected in mouse aortic aneurysm and colocalized with macrophages. Trem1 gene deletion (Apoe-/-Trem1-/-), as well as TREM-1 pharmacological blockade with LR-12 peptide, limited both AAA development and severity. Trem1 gene deletion attenuated the inflammatory response in the aorta, with a reduction of Il1b, Tnfa, Mmp2, and Mmp9 mRNA expression, and led to a decreased macrophage content due to a reduction of Ly6Chi classical monocyte trafficking. Conversely, antibody-mediated TREM-1 stimulation exacerbated Ly6Chi monocyte aorta infiltration after AngII infusion through CD62L upregulation and promoted proinflammatory signature in the aorta, resulting in worsening AAA severity. AngII infusion stimulated TREM-1 expression and activation on Ly6Chi monocytes through AngII receptor type I (AT1R). In human AAA, TREM-1 was detected and TREM1 mRNA expression correlated with SELL mRNA expression. Finally, circulating levels of sTREM-1 were increased in patients with AAA when compared with patients without AAA. In conclusion, TREM-1 is involved in AAA pathophysiology and may represent a promising therapeutic target in humans.

Correction to: Elevated plasma IL-6 and CRP levels are associated with adverse clinical outcomes and death in critically ill SARS-CoV-2 patients: infammatory response of SARS-CoV-2 patients

An amendment to this paper has been published and can be accessed via the original article.

Regulatory T Cell-Enhancing Therapies to Treat Atherosclerosis

Experimental studies have provided strong evidence that chronic inflammation triggered by the sub-endothelial accumulation of cholesterol-rich lipoproteins in arteries is essential in the initiation and progression of atherosclerosis. Recent clinical trials highlighting the efficacy of anti-inflammatory therapies in coronary patients have confirmed that this is also true in humans Monocytes/macrophages are central cells in the atherosclerotic process, but adaptive immunity, through B and T lymphocytes, as well as dendritic cells, also modulates the progression of the disease. Analysis of the role of different T cell subpopulations in murine models of atherosclerosis identified effector Th1 cells as proatherogenic, whereas regulatory T cells (Tregs) have been shown to protect against atherosclerosis. For these reasons, better understanding of how Tregs influence the atherosclerotic process is believed to provide novel Treg-targeted therapies to combat atherosclerosis. This review article summarizes current knowledge about the role of Tregs in atherosclerosis and discusses ways to enhance their function as novel immunomodulatory therapeutic approaches against cardiovascular disease.

Cytotoxic CD8+ T cells promote granzyme B-dependent adverse post-ischemic cardiac remodeling

Acute myocardial infarction is a common condition responsible for heart failure and sudden death. Here, we show that following acute myocardial infarction in mice, CD8⁺ T lymphocytes are recruited and activated in the ischemic heart tissue and release Granzyme B, leading to cardiomyocyte apoptosis, adverse ventricular remodeling and deterioration of myocardial function. Depletion of CD8⁺ T lymphocytes decreases apoptosis within the ischemic myocardium, hampers inflammatory response, limits myocardial injury and improves heart function. These effects are recapitulated in mice with Granzyme B-deficient CD8⁺ T cells. The protective effect of CD8 depletion on heart function is confirmed by using a model of ischemia/reperfusion in pigs. Finally, we reveal that elevated circulating levels of GRANZYME B in patients with acute myocardial infarction predict increased risk of death at 1-year follow-up. Our work unravels a deleterious role of CD8⁺ T lymphocytes following acute ischemia, and suggests potential therapeutic strategies targeting pathogenic CD8⁺ T lymphocytes in the setting of acute myocardial infarction.

Immune cells contribute to adverse remodeling following myocardial infarction. Here the authors show in mice and pigs that CD8⁺ lymphocytes release Granzyme B in the infarcted heart leading to cardiomyocyte death, enhanced inflammation and deterioration of cardiac function.

Elevated plasma IL-6 and CRP levels are associated with adverse clinical outcomes and death in critically ill SARS-CoV-2 patients: inflammatory response of SARS-CoV-2 patients

Background

SARS coronavirus 2 (SARS-CoV-2) is responsible for high morbidity and mortality worldwide, mostly due to the exacerbated inflammatory response observed in critically ill patients. However, little is known about the kinetics of the systemic immune response and its association with survival in SARS-CoV-2+ patients admitted in ICU. We aimed to compare the immuno-inflammatory features according to organ failure severity and in-ICU mortality.

Methods

Six-week multicentre study (N = 3) including SARS-CoV-2+ patients admitted in ICU. Analysis of plasma biomarkers at days 0 and 3–4 according to organ failure worsening (increase in SOFA score) and 60-day mortality.

Results

101 patients were included. Patients had severe respiratory diseases with PaO2/FiO2 of 155 [111–251] mmHg), SAPS II of 37 [31–45] and SOFA score of 4 [3–7]. Eighty-three patients (83%) required endotracheal intubation/mechanical ventilation and among them, 64% were treated with prone position. IL-1β was barely detectable. Baseline IL-6 levels positively correlated with organ failure severity. Baseline IL-6 and CRP levels were significantly higher in patients in the worsening group than in the non-worsening group (278 [70–622] vs. 71 [29–153] pg/mL, P < 0.01; and 178 [100–295] vs. 100 [37–213] mg/L, P < 0.05, respectively). Baseline IL-6 and CRP levels were significantly higher in non-survivors compared to survivors but fibrinogen levels and lymphocyte counts were not different between groups. After adjustment on SOFA score and time from symptom onset to first dosage, IL-6 and CRP remained significantly associated with mortality. IL-6 changes between Day 0 and Day 3–4 were not different according to the outcome. A contrario, kinetics of CRP and lymphocyte count were different between survivors and non-survivors.

Conclusions

In SARS-CoV-2+ patients admitted in ICU, a systemic pro-inflammatory signature was associated with clinical worsening and 60-day mortality.

Endothelial Cell Indoleamine 2, 3-Dioxygenase 1 Alters Cardiac Function After Myocardial Infarction Through Kynurenine

BACKGROUND

Ischemic cardiovascular diseases, particularly acute myocardial infarction (MI), is one of the leading causes of mortality worldwide. Indoleamine 2, 3-dioxygenase 1 (IDO) catalyzes 1 rate-limiting step of L-tryptophan metabolism, and emerges as an important regulator of many pathological conditions. We hypothesized that IDO could play a key role to locally regulate cardiac homeostasis after MI.

METHODS

Cardiac repair was analyzed in mice harboring specific endothelial or smooth muscle cells or cardiomyocyte or myeloid cell deficiency of IDO and challenged with acute myocardial infarction.

RESULTS

We show that kynurenine generation through IDO is markedly induced after MI in mice. Total genetic deletion or pharmacological inhibition of IDO limits cardiac injury and cardiac dysfunction after MI. Distinct loss of function of IDO in smooth muscle cells, inflammatory cells, or cardiomyocytes does not affect cardiac function and remodeling in infarcted mice. In sharp contrast, mice harboring endothelial cell-specific deletion of IDO show an improvement of cardiac function as well as cardiomyocyte contractility and reduction in adverse ventricular remodeling. In vivo kynurenine supplementation in IDO-deficient mice abrogates the protective effects of IDO deletion. Kynurenine precipitates cardiomyocyte apoptosis through reactive oxygen species production in an aryl hydrocarbon receptor-dependent mechanism.

CONCLUSIONS

These data suggest that IDO could constitute a new therapeutic target during acute MI.

Low dose interleukin-2 in patients with stable ischaemic heart disease and acute coronary syndrome (LILACS)

Background

Regulatory T lymphocytes (Tregs) are critical for immune homeostasis. Pre-clinical models have demonstrated that Tregs can modulate post-ischaemic immune responses and promote myocardial healing. Patients with ischaemic heart disease (IHD) display reduced anti-inflammatory Tregs and increased pro-inflammatory effector T cells (Teffs). Low-dose interleukin-2 (ld-IL2) has been shown to increase Tregs in patients with autoimmune diseases but is currently contraindicated in patients with IHD.

Purpose

To assess the safety and pharmacodynamic effect of ld-IL-2 in patients with IHD.

Methods

LILACS was a prospective, randomised, double-blind, placebo-controlled, dose-escalation, Phase I/II clinical trial, which tested ld-IL-2 (aldesleukin) given once daily subcutaneously, for five consecutive days. In Part A, 25 patients with stable IHD were randomised (drug:placebo ratio of 3:2) in 5 dose groups (0.3, 0.6, 1.2, 2.4 and 3x106 IU/day); whilst in Part B, 16 patients with non-ST elevation myocardial infarction (NSTEMI) were randomised (drug:placebo ratio of 6:2) in two dose groups (1.5 and 2.5x106 IU/day). Follow up was performed the day after dosing and again 7 days later. Doses were determined after blinded review. An independent committee reviewed unblinded data prior to commencing Part B. The primary endpoint was safety in parts A and B. Additionally in Part B, a co-primary endpoint was to calculate the dose required to increase Tregs by 75%. [NCT03113773]

Results

Ld-IL2 was well tolerated for all dose groups with the commonest adverse events being mild injection site reactions. Two serious adverse events, not considered to be drug related, occurred in Part B – one prior to dosing and resulting in withdrawal. The other was a recurrent NSTEMI after dosing ended in a patient with severe triple vessel coronary artery disease awaiting urgent bypass surgery. In Part A, Tregs increased with dose escalation whilst no Teff increases were noted (Figure 1A). In Part B, patients treated with 1.5 and 2.5x106 IU/day doses had a median increase in Tregs of 80.5% (CI 36.2–124.7%, p=0.003) and 108.3% (CI 55.3–161.3%, p=0.002) respectively (Figure 1B). A linear regression model estimated an increase of 43.3% (CI 23.6–63.0%, p=0.0003) per unit dose. The estimated dose to achieve a 75% increase in Tregs was 1.46x106 IU/day (CI 1.06–1.87). No increase in Teffs cells were seen however, a dose-dependent decrease was measured in B cells, whilst NK cells and eosinophils increased at the top 2.5 and 3x106 IU/day dose. A panel of 29 cytokines and chemokines showed a dose-dependent type 1 and 2 cytokine response. Single-cell RNA sequencing was performed on immune cells before and after dosing.

Conclusions

Ld-IL2 was safe and well-tolerated. An induction dose of 1.5x106 IU per day for 5 days provided an effective expansion of Tregs without increasing Teffs. This work provides important data for the future therapeutic use of ld-IL-2 which is ongoing.

Funding Acknowledgement

Type of funding source: Public Institution(s). Main funding source(s): Medical Research Council, British Heart Foundation Cambridge Centre of Excellence

Thymic stromal lymphopoietin is a key cytokine for the immunomodulation of atherogenesis with Freund's adjuvant

Adaptive immune responses regulate the development of atherosclerosis, with a detrimental effect of type 1 but a protective role of type 2 immune responses. Immunization of Apolipoprotein E‐deficient (ApoE^−/−) mice with Freund's adjuvant inhibits the development of atherosclerosis. However, the underlying mechanisms are not fully understood. Thymic stromal lymphopoietin (TSLP) is an IL7‐like cytokine with essential impact on type 2 immune responses (Th2). Thymic stromal lymphopoietin is strongly expressed in epithelial cells of the skin, but also in various immune cells following appropriate stimulation. In this study, we investigated whether TSLP may be crucial for the anti‐atherogenic effect of Freund's adjuvant. Subcutaneous injection of complete Freund's adjuvant (CFA) rapidly led to the expression of TSLP and IL1β at the site of injection. In male mice, CFA‐induced TSLP occurred in immigrated monocytes—and not epithelial cells—and was dependent on NLRP3 inflammasome activation and IL1β‐signalling. In females, CFA‐induced TSLP was independent of IL1β and upon ovariectomy. CFA/OVA led to a more pronounced imbalance of the T cell response in TSLPR^−/− mice, with increased INFγ/IL4 ratio compared with wild‐type controls. To test whether TSLP contributes to the anti‐atherogenic effects of Freund's adjuvant, we treated ApoE^−/− and ApoE^−/−/TSLPR^−/− mice with either CFA/IFA or PBS. ApoE^−/− mice showed less atherogenesis upon CFA/IFA compared with PBS injections. ApoE^−/−/TSLPR^−/− mice had no attenuation of atherogenesis upon CFA/IFA treatment. Freund's adjuvant executes significant immune‐modulating effects via TSLP induction. TSLP‐TSLPR signalling is critical for CFA/IFA‐mediated attenuation of atherosclerosis.

A defect in endothelial autophagy occurs in patients with non-alcoholic steatohepatitis and promotes inflammation and fibrosis

BACKGROUND & AIMS

Previous studies demonstrated that autophagy is protective in hepatocytes and macrophages, but detrimental in hepatic stellate cells in chronic liver diseases. The role of autophagy in liver sinusoidal endothelial cells (LSECs) in non-alcoholic steatohepatitis (NASH) is unknown. Our aim was to analyze the potential implication of autophagy in LSECs in NASH and liver fibrosis.

METHODS

We analyzed autophagy in LSECs from patients using transmission electron microscopy. We determined the consequences of a deficiency in autophagy: (a) on LSEC phenotype, using primary LSECs and an LSEC line; (b) on early stages of NASH and on advanced stages of liver fibrosis, using transgenic mice deficient in autophagy specifically in endothelial cells and fed a high-fat diet or chronically treated with carbon tetrachloride, respectively.

RESULTS

Patients with NASH had half as many LSECs containing autophagic vacuoles as patients without liver histological abnormalities, or with simple steatosis. LSECs from mice deficient in endothelial autophagy displayed an upregulation of genes implicated in inflammatory pathways. In the LSEC line, deficiency in autophagy enhanced inflammation (Ccl2, Ccl5, Il6 and VCAM-1 expression), features of endothelial-to-mesenchymal transition (α-Sma, Tgfb1, Col1a2 expression) and apoptosis (cleaved caspase-3). In mice fed a high-fat diet, deficiency in endothelial autophagy induced liver expression of inflammatory markers (Ccl2, Ccl5, Cd68, Vcam-1), liver cell apoptosis (cleaved caspase-3) and perisinusoidal fibrosis. Mice deficient in endothelial autophagy treated with carbon tetrachloride also developed more perisinusoidal fibrosis.

CONCLUSIONS

A defect in autophagy in LSECs occurs in patients with NASH. Deficiency in endothelial autophagy promotes the development of liver inflammation, features of endothelial-to-mesenchymal transition, apoptosis and liver fibrosis in the early stages of NASH, but also favors more advanced stages of liver fibrosis.

LAY SUMMARY

Autophagy is a physiological process controlling endothelial homeostasis in vascular beds outside the liver. This study demonstrates that autophagy is defective in the liver endothelial cells of patients with non-alcoholic steatohepatitis. This defect promotes liver inflammation and fibrosis at early stages of non-alcoholic steatohepatitis, but also at advanced stages of chronic liver disease.

Anticytokine Immune Therapy and Atherothrombotic Cardiovascular Risk

Accumulating observations in humans and animals indicate that inflammation plays a key role in atherosclerosis development and subsequent complications. Moreover, the use of loss- or gain-of-function genetically modified, atherosclerosis-prone mice has provided strong experimental evidence for a causal role of innate and adaptive immunity in atherosclerosis and has revealed the pathogenic activity of proinflammatory cytokines, including TNF (tumor necrosis factor)-α, IL (interleukin)-1β, IL-6, and IL-18, and the atheroprotective effect of anti-inflammatory cytokines, including IL-10 and TGF-β. For the past 15 years, treatments using monoclonal antibodies specifically targeting cytokines, commonly referred as biological therapies, have transformed the treatment of chronic inflammatory diseases, such as rheumatoid arthritis or psoriasis, both conditions associated with increased cardiovascular risk. Analyzing the impact of anticytokine therapies on the cardiovascular outcomes of patients with chronic inflammatory diseases provides insight into the clinical relevance of experimental data on the role of inflammation in atherothrombotic cardiovascular diseases. CANTOS (Canakinumab Antiinflammatory Thrombosis Outcome Study) provided the first evidence that targeting inflammation in humans with atherosclerosis could improve clinical outcomes. Treatment with the anti-IL-1β antibody canakinumab significantly reduced recurrent cardiovascular events in individuals with stable coronary artery disease well-treated with standard-of-care measures. Other clinical studies support the protective effects of treatment with anti-TNF-α and anti-IL-6 receptor monoclonal antibodies on cardiovascular risk. Blockade of the IL-23/IL-17 axis, however, warrants caution as a cardiovascular intervention. Targeting this pathway has improved psoriasis but may augment cardiovascular risk in certain patients. Thus, careful consideration of the cardiovascular risk profile may influence the choice of the most appropriate treatment for patients with chronic inflammatory diseases.Visual Overview: An online visual overview is available for this article.

MicroRNA-21 Deficiency Alters the Survival of Ly-6C lo Monocytes in ApoE −/− Mice and Reduces Early-Stage Atherosclerosis—Brief Report

Objective—

To determine the role of microRNA-21 (miR-21) on the homeostasis of monocyte subsets and on atherosclerosis development in ApoE −/− (apolipoprotein E) mice.

Approach and Results—

In ApoE −/− mice, miR-21 expression was increased in circulating Ly-6C lo nonclassical monocytes in comparison to Ly-6C hi monocytes. The absence of miR-21 significantly altered the survival and number of circulating Ly-6C lo nonclassical monocytes in ApoE −/− mice. In the early stages of atherosclerosis, the absence of miR-21 limited lesion development both in the aortic sinus (by almost 30%) and in the aorta (by almost 50%). This was associated with less monocyte availability in circulation and increased apoptosis of local macrophages in plaques. At later stages of atherosclerosis, lesion size in the aortic root was similar in ApoE −/− and ApoE −/− miR-21 −/− mice, but plaques showed a less stable phenotype (larger necrotic cores) in the latter. The loss of protection in advanced stages was most likely because of excessive inflammatory apoptosis related to an impairment of local efficient efferocytosis.

Conclusions—

Gene deletion of miR-21 in ApoE −/− mice alters Ly-6C lo nonclassical monocytes homeostasis and contribute to limit early-stage atherosclerosis.

Adaptive Immune Responses Contribute to Post-ischemic Cardiac Remodeling

Myocardial infarction (MI) is a common condition responsible for mortality and morbidity related to ischemic heart failure. Accumulating experimental and translational evidence support a crucial role for innate immunity in heart failure and adverse heart remodeling following MI. More recently, the role of adaptive immunity in myocardial ischemia has been identified, mainly in rodents models of both transient and permanent heart ischemia. The present review summarizes the experimental evidence regarding the role of lymphocytes and dendritic cells in myocardial remodeling following coronary artery occlusion. Th1 and potentially Th17 CD4⁺ T cell responses promote adverse heart remodeling, whereas regulatory T cells appear to be protective, modulating macrophage activity, cardiomyocyte survival, and fibroblast phenotype. The role of CD8⁺ T cells in this setting remains unknown. B cells contribute to adverse cardiac remodeling through the modulation of monocyte trafficking, and potentially the production of tissue-specific antibodies. Yet, further substantial efforts are still required to confirm experimental data in human MI before developing new therapeutic strategies targeting the adaptive immune system in ischemic cardiac diseases.

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.

Gingival fibroblasts protect against experimental abdominal aortic aneurysm development and rupture through tissue inhibitor of metalloproteinase-1 production

Aims

Abdominal aortic aneurysm (AAA), frequently diagnosed in old patients, is characterized by chronic inflammation, vascular cell apoptosis and metalloproteinase-mediated extracellular matrix destruction. Despite improvement in the understanding of the pathophysiology of aortic aneurysm, no pharmacological treatment is yet available to limit dilatation and/or rupture. We previously reported that human gingival fibroblasts (GFs) can reduce carotid artery dilatation in a rabbit model of elastase-induced aneurysm. Here, we sought to investigate the mechanisms of GF-mediated vascular protection in two different models of aortic aneurysm growth and rupture in mice.

Methods and results

In vitro, mouse GFs proliferated and produced large amounts of anti-inflammatory cytokines and tissue inhibitor of metalloproteinase-1 (Timp-1). GFs deposited on the adventitia of abdominal aorta survived, proliferated, and organized as a layer structure. Furthermore, GFs locally produced Il-10, TGF-β, and Timp-1. In a mouse elastase-induced AAA model, GFs prevented both macrophage and lymphocyte accumulations, matrix degradation, and aneurysm growth. In an Angiotensin II/anti-TGF-β model of aneurysm rupture, GF cell-based treatment limited the extent of aortic dissection, prevented abdominal aortic rupture, and increased survival. Specific deletion of Timp-1 in GFs abolished the beneficial effect of cell therapy in both AAA mouse models.

Conclusions

GF cell-based therapy is a promising approach to inhibit aneurysm progression and rupture through local production of Timp-1.

Abstract 585: Card9 Deficiency Accelerates Experimental Atherosclerosis

Introduction: There are accumulating evidences that innate and adaptive immunity play a major role in the development of atherosclerosis. Pattern-recognition receptors (PRRs) engagement including Toll-like receptors and Dectins are involved in the modulation of immune responses and atherosclerosis development but little is known about downstream signaling pathways. Card9 for Caspase recruitment domain-containing protein-9, is an adaptor protein expressed by antigen presenting cells required for PRRs-induced activation of myeloid cells. We hypothesized that Card9 pathway regulates systemic immune response and impacts on the development of atherosclerosis.

Method and results: To evaluate the effect of Card9 deficiency on experimental atherosclerosis, Ldlr -/- mice were lethally irradiated and reconstituted with Card9 -/- or Card9 +/+ bone marrow cells and put under a high fat diet during 8 weeks. Animal weight and cholesterolemia were not different between groups. We observed an increase of atherosclerosis plaque size in the aortic sinus in chimeric Ldlr -/- Card9 -/- mice compared to chimeric Ldlr -/- Card9 +/+ mice (+32%, P=0.04). A more inflammatory plaque phenotype was found in chimeric Ldlr -/- Card9 -/- mice compared to control mice with an increase in both macrophage accumulation (+86%, P=0.0005) and necrotic core size (+102%, P=0.006). Card9 deficiency induced a deviation of the systemic immune response toward a pro-inflammatory profile. Lps/Ifn-γ-stimulated Card9 -/- bone marrow-derived macrophages (BMDM) produced less IL-10 (-22%, P<0.05) than Card9 +/+ BMDM. Lps/Ifn-γ-stimulated splenocytes from chimeric LDLr -/- Card9 -/- mice produced more IL-12p70 (+151%, P<0.01) than splenocytes from control mice. Anti-CD3 stimulated CD4 + T cells from chimeric Ldlr -/- Card9 -/- mice produced less Ifn-γ (-92%, P<0.05) and IL-17A (-100%, P<0.05) than control CD4 + T cells. A second atherosclerosis mouse model ApoE -/- Card9 -/- confirmed the protective role of Card9 with an increase in both atherosclerosis plaque size and macrophage accumulation in ApoE -/- Card9 -/- mice compared to ApoE -/- Card9 +/+ mice.

Conclusion: Card9 deficiency accelerated atherosclerosis development in mice and induced a more inflammatory plaque phenotype.

Abstract 322: Exploring the Role of Triggering Receptor Expressed on Myeloid Cells-1 in Experimental Abdominal Aortic Aneurysm

Introduction: Non-syndromic Abdominal Aortic Aneurysm (AAA) is one of the leading causes of cardiovascular death in elderly men. AAA is characterized by extracellular matrix degradation, smooth muscle cell apoptosis and infiltration of inflammatory cells in the aortic wall. Monocyte recruitment particularly plays an important role in the pathophysiology of AAA. TREM (Triggering Receptor Expressed on Myeloid cells)-1, a receptor expressed by myeloid cells, is a key regulator of innate immune cell activity, and we hypothesized that it might be involved in AAA development.

Objective: We aim to decipher the role of TREM-1 in the immuno-inflammatory response associated with AAA development and rupture.

Method: To study the role of TREM-1 in AAA development, we used an experimental model of Angiotensin-II-induced AAA in ApoE -/- Trem-1 -/- and ApoE -/- Trem-1 +/+ mice. At day 0, 3, 7 and 28, we analyzed monocyte trafficking (flow cytometry), inflammatory cell infiltration within the aortic wall (immunostaining, qPCR), aortic wall remodeling (histology) and finally AAA development.

Results: Angiotensin II infusion induced a 2-fold increased of TREM-1 expression on classical monocytes at day 3. TREM-1 deficiency ( ApoE -/- Trem-1 -/- ) abolished Angiotensin II-induced monocytosis at day 3 and prevented macrophage infiltration within the aorta at day 7. TREM-1 genetic deletion also limited pro-inflammatory response ( Il-1beta and Tnf-alpha mRNA expression) and metalloprotease activity in the aortic wall and protected against elastin degradation at day 7. At day 28 (n=10/group), under angiotensin II infusion, ApoE -/- Trem-1 -/- mice are characterized by reduced mean aorta diameter (702+/-36 μm versus 1081+/-51 μm, p<0.01), less severe AAA disease (p<0.001, Chi-squared for a trend) when compared to ApoE -/- Trem-1 +/+ mice. In addition, TREM-1 deficiency protected against lethal AAA rupture (28-Day survival 100% versus 82% p=0.05).

Conclusion: We showed that TREM-1 deficiency reduced AAA development and rupture in an Angiotensin II-induced mouse model.

Endothelial autophagic flux hampers atherosclerotic lesion development

Blood flowing in arteries generates shear forces at the surface of the vascular endothelium that control its anti-atherogenic properties. However, due to the architecture of the vascular tree, these shear forces are heterogeneous and atherosclerotic plaques develop preferentially in areas where shear is low or disturbed. Here we review our recent study showing that elevated shear forces stimulate endothelial autophagic flux and that inactivating the endothelial macroautophagy/autophagy pathway promotes a proinflammatory, prosenescent and proapoptotic cell phenotype despite the presence of atheroprotective shear forces. Specific deficiency in endothelial autophagy in a murine model of atherosclerosis stimulates the development of atherosclerotic lesions exclusively in areas of the vasculature that are normally resistant to atherosclerosis. Our findings demonstrate that adequate endothelial autophagic flux limits atherosclerotic plaque formation by preventing endothelial apoptosis, senescence and inflammation.

Genetic Depletion or Hyperresponsiveness of Natural Killer Cells Do Not Affect Atherosclerosis Development

Rationale:

Chronic inflammation is central in the development of atherosclerosis. Both innate and adaptive immunities are involved. Although several studies have evaluated the functions of natural killer (NK) cells in experimental animal models of atherosclerosis, it is not yet clear whether NK cells behave as protective or proatherogenic effectors. One of the main caveats of previous studies was the lack of specificity in targeting loss or gain of function of NK cells.

Objectives:

We used 2 selective genetic approaches to investigate the role of NK cells in atherosclerosis: (1) Ncr1 iCre/+ R26 lsl− DTA/+ mice in which NK cells were depleted and (2) Noé mice in which NK cells are hyperresponsive.

Methods and Results:

No difference in atherosclerotic lesion size was found in Ldlr −/− (low-density lipoprotein receptor null) mice transplanted with bone marrow (BM) cells from Ncr1 iCre R26R lsl− DTA , Noé , or wild-type mice. Also, no difference was observed in plaque composition in terms of collagen content, macrophage infiltration, or the immune profile, although Noé chimera had more IFN (interferon)-γ–producing NK cells, compared with wild-type mice. Then, we investigated the NK-cell selectivity of anti–asialoganglioside M1 antiserum, which was previously used to conclude the proatherogenicity of NK cells. Anti–asialoganglioside M1 treatment decreased atherosclerosis in both Ldlr −/− mice transplanted with Ncr1 iCre R26R lsl− DTA or wild-type bone marrow, indicating that its antiatherogenic effects are unrelated to NK-cell depletion, but to CD8 + T and NKT cells. Finally, to determine whether NK cells could contribute to the disease in conditions of pathological NK-cell overactivation, we treated irradiated Ldlr −/− mice reconstituted with either wild-type or Ncr1 iCre R26R lsl− DTA bone marrow with the viral mimic polyinosinic:polycytidylic acid and found a significant reduction of plaque size in NK-cell–deficient chimeric mice.

Conclusions:

Our findings, using state-of-the-art mouse models, demonstrate that NK cells have no direct effect on the natural development of hypercholesterolemia-induced atherosclerosis, but may play a role when an additional systemic NK-cell overactivation occurs.

Apoptosis as a Determinant of Atherothrombosis

Clinical manifestations of atherosclerosis are the consequences of atherosclerotic plaque rupture that triggers thrombus formation. Tissue factor (TF) is a key element in the initiation of the coagulation cascade and is crucial in thrombus formation following plaque disruption. TF activity is highly dependent on the presence of phosphatidylserine (PS), an anionic phospholipid that is redistributed on the cell surface during apoptotic death conferring a potent procoagulant activity to the apoptotic cell. Apoptosis occurs in the human atherosclerotic plaque and shed membrane apoptotic microparticles rich in PS are produced in considerable amounts within the lipid core. These microparticles carry almost all TF activity and are responsible for the procoagulant activity of the plaque. Moreover, luminal endothelial cell apoptosis might be responsible for thrombus formation on eroded plaques without rupture. Apoptosis might also play a major role in blood thrombogenicity via circulating procoagulant microparticles that are found at high levels in patients with acute coronary syndromes.

Genetic and pharmacological inhibition of microRNA-92a maintains podocyte cell cycle quiescence and limits crescentic glomerulonephritis

Crescentic rapidly progressive glomerulonephritis (RPGN) represents the most aggressive form of acquired glomerular disease. While most therapeutic approaches involve potentially toxic immunosuppressive strategies, the pathophysiology remains incompletely understood. Podocytes are glomerular epithelial cells that are normally growth-arrested because of the expression of cyclin-dependent kinase (CDK) inhibitors. An exception is in RPGN where podocytes undergo a deregulation of their differentiated phenotype and proliferate. Here we demonstrate that microRNA-92a (miR-92a) is enriched in podocytes of patients and mice with RPGN. The CDK inhibitor p57^Kip2 is a major target of miR-92a that constitutively safeguards podocyte cell cycle quiescence. Podocyte-specific deletion of miR-92a in mice de-repressed the expression of p57^Kip2 and prevented glomerular injury in RPGN. Administration of an anti-miR-92a after disease initiation prevented albuminuria and kidney failure, indicating miR-92a inhibition as a potential therapeutic strategy for RPGN. We demonstrate that miRNA induction in epithelial cells can break glomerular tolerance to immune injury.

Crescentic rapidly progressive glomerulonephritis is a severe form of glomerula disease characterized by podocyte proliferation and migration. Here Henique et al. demonstrate that inhibition of miRNA-92a prevents kidney failure by promoting the expression of CDK inhibitor p57^Kip2 that regulates podocyte cell cycle.

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.

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.

Angiotensin II synergizes with BAFF to promote atheroprotective regulatory B cells

Angiotensin II (AngII) promotes hypertension, atherogenesis, vascular aneurysm and impairs post-ischemic cardiac remodeling through concerted roles on vascular cells, monocytes and T lymphocytes. However, the role of AngII in B lymphocyte responses is largely unexplored. Here, we show that chronic B cell depletion (Baffr deficiency) significantly reduces atherosclerosis in Apoe ^-/- mice infused with AngII. While adoptive transfer of B cells in Apoe ^-/- /Baffr ^-/- mice reversed atheroprotection in the absence of AngII, infusion of AngII in B cell replenished Apoe ^-/- /Baffr ^-/- mice unexpectedly prevented the progression of atherosclerosis. Atheroprotection observed in these mice was associated with a significant increase in regulatory CD1d^hiCD5⁺ B cells, which produced high levels of interleukin (IL)-10 (B10 cells). Replenishment of Apoe ^-/- /Baffr ^-/- mice with Il10 ^-/- B cells reversed AngII-induced B cell-dependent atheroprotection, thus highlighting a protective role of IL-10⁺ regulatory B cells in this setting. Transfer of AngII type 1A receptor deficient (Agtr1a ^-/-) B cells into Apoe ^-/- /Baffr ^-/- mice substantially reduced the production of IL-10 by B cells and prevented the AngII-dependent atheroprotective B cell phenotype. Consistent with the in vivo data, AngII synergized with BAFF to induce IL-10 production by B cells in vitro via AngII type 1A receptor. Our data demonstrate a previously unknown synergy between AngII and BAFF in inducing IL-10 production by B cells, resulting in atheroprotection.

Abstract 590: Autophagy is Required for Endothelial Atheroprotective Signaling Under Physiological Flow

Objective: Preferential development of atherosclerotic lesions in areas of low shear stress is associated with increased endothelial inflammation, apoptosis and senescence. On the contrary, high shear stress areas are protected from plaque development, but the mechanisms remain elusive. Autophagy is a protective mechanism allowing recycling of defective organelles and proteins to maintain cellular homeostasis. Our aim was to understand the role of autophagy in athero-protective effects of high shear stress.

Approach and Results: We used the parallel plate chamber system in vitro to generate different shear stress conditions on endothelial cell deficient or not in autophagy (shRNA Atg5 vs. control) and examined autophagic flux in cells transfected with RFP-GFP-LC3 plasmid. Endothelial autophagy was silenced in Atg5 flox/flox ; VE-cadherin-cre mice. We first demonstrated in human and murine arteries and in cultured endothelial cells that atheroprotective shear stress activates endothelial autophagic flux. On the opposite, endothelial cells exposed to atheroprone low shear stress displayed inefficient autophagy, associated with activation of mTOR, inhibition of AMPKα pathways and blockade of the autophagic flux. Interestingly, plaque burden augmented specifically in areas usually atheroresistant in ApoE -/- hypercholesterolemic mice deficiency in endothelial autophagy. Both in cultured endothelial cells and in transgenic mice, deficiency in endothelial autophagy was associated with a defect in endothelial alignment with flow direction, a hallmark of endothelial cell health. Deficiency in endothelial autophagy increased endothelial senescence and TNFα-induced inflammation under high shear stress conditions. These effects were associated with impaired KLF2 activation. In transgenic mice, endothelial senescence and apoptosis was augmented in high shear stress areas of the descending thoracic aorta when compared to control littermate mice.

Conclusions: Altogether, these results show that adequate endothelial autophagic flux under high shear stress limits atherosclerotic plaque formation by preventing inflammation, senescence and apoptosis.