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.

Increased atherosclerotic plaque in AOC3 knock-out in ApoE−/− mice and characterization of AOC3 in atherosclerotic human coronary arteries

Introduction

Amine oxidase copper containing 3 (AOC3) displays adhesion between leukocytes and endothelial cells and enzymatic functions. Given its controversial role in atherogenesis, we proposed to investigate the involvement of AOC3 in the formation of atherosclerotic plaques in ApoE^−/−AOC3^−/− mice and human coronary arteries.

Methods

Lesions, contractile markers, and AOC3 were studied in aortic tissues from 15- and 25-week-old mice and different stages of human coronary atherosclerotic arteries by immunohistochemistry (IHC) and/or western blot. Human VSMCs, treated or not with LJP1586, an AOC3 inhibitor, were used to measure differentiation markers by qPCR. AOC3 co-localization with specific cell markers was studied by using confocal microscopy in mice and human samples.

Results

At 15 weeks old, the absence of AOC3 was associated with increased lesion size, α-SMA, and CD3 staining in the plaque independently of a cholesterol modification. At 25 weeks old, advanced plaques were larger with equivalent staining for α-SMA while CD3 increased in the media from ApoE^−/−AOC3^−/− mice. At both ages, the macrophage content of the lesion was not modified. Contractile markers decreased whereas MCP-1 appeared augmented only in the 15-week-old ApoE^−/−AOC3. AOC3 is mainly expressed by mice and human VSMC is slightly expressed by endothelium but not by macrophages.

Conclusion

AOC3 knock-out increased atherosclerotic plaques at an early stage related to a VSMC dedifferentiation associated with a higher T cells recruitment in plaques explained by the MCP-1 augmentation. This suggests that AOC3 may have an important role in atherosclerosis independent of its canonical inflammatory effect. The dual role of AOC3 impacts therapeutic strategies using pharmacological regulators of SSAO activity.

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.

The impact of carcinoma in situ in ureteral margins during radical cystectomy: A case-controlled study

BACKGROUND AND OBJECTIVE

The presence of carcinoma in situ (Cis) in association with bladder cancer is associated with a poor prognosis. However, the prognosis associated with the presence of Cis in ureteral margins (CUM) during radical cystectomy has been poorly defined. To assess the prognosis associated with the presence of Cis in ureteral margins in patients with pM0 bladder cancer who have not undergone neoadjuvant chemotherapy.

MATERIALS AND METHODS

A retrospective case-control study was conducted between 2001 and 2016 using data from one academic center in France. From 1,450 radical cystectomies, 122 patients (case) who had CUM were matched according to age, sex, pTNM stage and urinary diversion method with a population sample of 122 patients (controls) who did not have Cis in ureteral margins during radical cystectomy. The survival analysis was performed by Kaplan-Meier using a (95%) CI. Multivariate Cox regression analysis was used to test the effect of CUM on cancer-specific survival. Recurrence-free survival was defined as a recurrence of urothelial carcinoma in the upper urinary tract.

RESULTS AND LIMITATIONS

The mean follow-up period was 55.43 ± 39.6 months. The rate of Cis in the bladder in the CUM cases group was evaluated at 11.47%. The median overall and specific survival was inferior in the CUM cases group estimated at 43.3 [35.33-56.93] months, 52.43 [42.16-68.93] months respectively compared to the control group with a significant difference (P= 0.001, P= 0.0039). The cumulative probability of urothelial recurrence-free survival was decreased in the case group compared with the control group (63.9% vs. 92.6%, P = 0.0001). Multivariate analysis shown that urothelial recurrence was associated with CUM [(P <0.001), (HR adjusted =11.31), (95% CI): (3.38-37.77)] and the macroscopic appearance of the ureter (thickened, dilated) [(P= 0.003), (HR adjusted =4.62), (95% CI): (3.31-8.84)].

CONCLUSION

CUM is a poor prognostic factor that impacts cancer-specific survival and Recurrence-free survival. The presence of CUM has been independently associated with a significant increase in the risk of urothelial recurrence, and a decrease in both overall and specific survival. This supports the use of frozen section analysis to complete radical cystectomy without CUM.

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.

[Estimated impact of the current colorectal screening program in France]

BACKGROUND

Colorectal cancer is the third most common cancer and the second most deadly in France. A Cochrane meta-analysis has confirmed the benefits of colorectal cancer screening. A nationwide colorectal screening program was set up in France in 2009 for medium-risk, asymptomatic people aged 50 to 74 years. It has been based, since 2015, on the Fecal Immunochemical Test. The participation rate for 2016-2017 was 34%, which is lower than the European objectives. The objective of this study was to evaluate the impact of the program at the current participation rate and at rates of 45% and 65%.

METHODS

The epidemiological impact of the program was estimated from the results of an individual simulation model adapted from the Microsimulation Screening Analysis Colon model, calibrated and transposed to the French context. An initial analysis was conducted to estimate the individual impact of screening and a second for the entire eligible population, at various participation rates.

RESULTS

The test is associated with a lifetime reduction in the risk of colorectal cancer of 24% for men and 21% for women, and a reduction in the risk of death from colorectal cancer of 51% and 43% respectively. At the current level of participation, the program reduces incidence by 5% and mortality by 14% compared to no organized screening. The impact would be reduced by an additional 3% and 8% for participation rates of 45% and 65% respectively. Similarly, mortality would decrease by an additional 8% and 22%.

CONCLUSION

These results confirm that in a population at medium risk for colorectal cancer, the organised programme is an effective strategy for reducing its incidence. They also confirm that the achievement of European objectives remains a key issue for improving the effectiveness of organized screening. An evolution of immunological test delivery modalities could help to achieve these participation objectives.

Estimation of the epidemiological impact of the organized screening program for colorectal cancer

Introduction

Colorectal cancer (CRC) is the third most common cancer and the second most deadly in France. A CRC national organized screening (OS) program was set up in France in 2009. It targets asymptomatic people aged 50 to 74 year with medium risk of CRC. OS program is based on fecal immunochemical test (FIT) followed by colonoscopy. Participation rate over the last period showed a participation rate of 34%, far from the European standards and the 45% target objective of the French cancer plan.

Methods

The epidemiological impact of the DO-CCR was estimated from the results of an individual simulation model adapted from the MISCAN-Colon model, calibrated and transposed to the French context. The model simulates the natural history of CRC in a cohort of 5,000,000 individuals from birth to death. The simulated population reproduced the age and sex structure of the French population. Current screening strategy was simulated for the entire population. A first analysis was conducted to estimate the individual impact of screening by sex and by age of screening initiation and cessation. A second analysis was carried out to estimate the global impact of the based on various participation rates.

Results

FIT every 2 years, from the age of 50, is associated with a reduction in the CRC incidence of 21% for women and 24% for men and a reduction in CRC mortality of 43% for women and 51% for men. At the current level of participation, the OS reduces incidence by 5% and mortality by 14% (2,200 CCR and 2,600 deaths per year) compared to no OS. The impact would be reduced by an additional 3% and 8% for participation rates of 45% and 65% respectively, a decrease of 1,300 and 3,500 cases per additional year. Similarly, mortality would decrease by an additional 8% and 22% for participation rates of 45% and 65%, respectively additional decreases of 1,400 and 4,000 deaths per year.

Key messages

These results confirm that in a population at medium risk for CRC, the OS is an effective strategy for reducing incidence of CRC. Increasing participation rate to reach the Cancer Plan’s objectives remains a key issue in France.

Tryptophan Dietary Impacts Gut Barrier and Metabolic Diseases

The intestine has a major role in the digestion and absorption of nutrients, and gut barrier is the first defense line against harmful pathogens. Alteration of the intestinal barrier is associated with enhanced intestinal permeability and development of numerous pathological diseases including gastrointestinal and cardiometabolic diseases. Among the metabolites that play an important role within intestinal health, L Tryptophan (Trp) is one of the nine essential amino acids supplied by diet, whose metabolism appears as a key modulator of gut microbiota, with major impacts on physiological, and pathological pathways. Recently, emerging evidence showed that the Trp catabolism through one major enzyme indoleamine 2,3-dioxygenase 1 (IDO1) expressed by the host affects Trp metabolism by gut microbiota to generate indole metabolites, thereby altering gut function and health in mice and humans. In this mini review, I summarize the most recent advances concerning the role of Trp metabolism in host–microbiota cross-talk in health, and metabolic diseases. This novel aspect of IDO1 function in intestine will better explain its complex roles in a broad range of disease states where the gut function affects local as well as systemic health, and will open new therapeutic strategies.

Vascular Smooth Muscle Cell Plasticity and Autophagy in Dissecting Aortic Aneurysms

Objective- Recent studies suggested the occurrence of phenotypic switching of vascular smooth muscle cells (VSMCs) during the development of aortic aneurysm (AA). However, lineage-tracing studies are still lacking, and the behavior of VSMCs during the formation of dissecting AA is poorly understood. Approach and Results- We used multicolor lineage tracing of VSMCs to track their fate after injury in murine models of Ang II (angiotensin II)-induced dissecting AA. We also addressed the direct impact of autophagy on the response of VSMCs to AA dissection. Finally, we studied the relevance of these processes to human AAs. Here, we show that a subset of medial VSMCs undergoes clonal expansion and that VSMC outgrowths are observed in the adventitia and borders of the false channel during Ang II-induced development of dissecting AA. The clonally expanded VSMCs undergo phenotypic switching with downregulation of VSMC differentiation markers and upregulation of phagocytic markers, indicative of functional changes. In particular, autophagy and endoplasmic reticulum stress responses are activated in the injured VSMCs. Loss of autophagy in VSMCs through deletion of autophagy protein 5 gene ( Atg5) increases the susceptibility of VSMCs to death, enhances endoplasmic reticulum stress activation, and promotes IRE (inositol-requiring enzyme) 1α-dependent VSMC inflammation. These alterations culminate in increased severity of aortic disease and higher incidence of fatal AA dissection in mice with VSMC-restricted deletion of Atg5. We also report increased expression of autophagy and endoplasmic reticulum stress markers in VSMCs of human dissecting AAs. Conclusions- VSMCs undergo clonal expansion and phenotypic switching in Ang II-induced dissecting AAs in mice. We also identify a critical role for autophagy in regulating VSMC death and endoplasmic reticulum stress-dependent inflammation with important consequences for aortic wall homeostasis and repair.

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.

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.

Deletion of IRF8 (Interferon Regulatory Factor 8)-Dependent Dendritic Cells Abrogates Proatherogenic Adaptive Immunity

Rationale:

Despite an established role for adaptive immune responses in atherosclerosis, the contribution of dendritic cells (DCs) and their various subsets is still poorly understood.

Objective:

Here, we address the role of IRF8 (interferon regulatory factor 8)-dependent DCs (lymphoid CD8α + and their developmentally related nonlymphoid CD103 + DCs) in the induction of proatherogenic immune responses during high fat feeding.

Methods and Results:

Using a fate-mapping technique to track DCs originating from a DNGR1 + (dendritic cell natural killer lectin group receptor 1) precursor ( Clec9a +/cre Rosa +/EYFP mice), we first show that YFP hi CD11c hi MHCII hi (major histocompatibility complex class II) DCs are present in the atherosclerotic aorta of low-density lipoprotein receptor–deficient ( Ldlr −/− ) mice and are CD11b – CD103 + IRF8 hi . Restricted deletion of IRF8 in DCs ( Irf8 flox/flox Cd11c Cre ) reduces the accumulation of CD11c hi MHCII hi DCs in the aorta without affecting CD11b + CD103 – DCs or macrophages but completely abolishes the accumulation of aortic CD11b – CD103 + DCs. Lymphoid CD8α + DCs are also deleted. This is associated with a significant reduction of aortic T-cell accumulation and a marked reduction of high-fat diet–induced systemic T-cell priming, activation, and differentiation toward T helper type 1 cells, T follicular helper cells, and regulatory T cells. As a consequence, B-cell activation and germinal center responses to high-fat diet are also markedly reduced. IRF8 deletion in DCs significantly reduces the development of atherosclerosis, predominantly in the aortic sinus, despite a modest increase in total plasma cholesterol levels.

Conclusions:

IRF8 expression in DCs plays a nonredundant role in the development of proatherogenic adaptive immunity.

TGFβ (Transforming Growth Factor-β) Blockade Induces a Human-Like Disease in a Nondissecting Mouse Model of Abdominal Aortic Aneurysm

OBJECTIVE

Current experimental models of abdominal aortic aneurysm (AAA) do not accurately reproduce the major features of human AAA. We hypothesized that blockade of TGFβ (transforming growth factor-β) activity-a guardian of vascular integrity and immune homeostasis-would impair vascular healing in models of nondissecting AAA and would lead to sustained aneurysmal growth until rupture.

APPROACH AND RESULTS

Here, we test this hypothesis in the elastase-induced AAA model in mice. We analyze AAA development and progression using ultrasound in vivo, synchrotron-based ultrahigh resolution imaging ex vivo, and a combination of biological, histological, and flow cytometry-based cellular and molecular approaches in vitro. Systemic blockade of TGFβ using a monoclonal antibody induces a transition from a self-contained aortic dilatation to a model of sustained aneurysmal growth, associated with the formation of an intraluminal thrombus. AAA growth is associated with wall disruption but no medial dissection and culminates in fatal transmural aortic wall rupture. TGFβ blockade enhances leukocyte infiltration both in the aortic wall and the intraluminal thrombus and aggravates extracellular matrix degradation. Early blockade of IL-1β or monocyte-dependent responses substantially limits AAA severity. However, blockade of IL-1β after disease initiation has no effect on AAA progression to rupture.

CONCLUSIONS

Endogenous TGFβ activity is required for the healing of AAA. TGFβ blockade may be harnessed to generate new models of AAA with better relevance to the human disease. We expect that the new models will improve our understanding of the pathophysiology of AAA and will be useful in the identification of new therapeutic targets.

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.

Type-2 innate lymphoid cells control the development of atherosclerosis in mice

Type-2 innate lymphoid cells (ILC2) are a prominent source of type II cytokines and are found constitutively at mucosal surfaces and in visceral adipose tissue. Despite their role in limiting obesity, how ILC2s respond to high fat feeding is poorly understood, and their direct influence on the development of atherosclerosis has not been explored. Here, we show that ILC2 are present in para-aortic adipose tissue and lymph nodes and display an inflammatory-like phenotype atypical of adipose resident ILC2. High fat feeding alters both the number of ILC2 and their type II cytokine production. Selective genetic ablation of ILC2 in Ldlr^−/− mice accelerates the development of atherosclerosis, which is prevented by reconstitution with wild type but not Il5^−/− or Il13^−/− ILC2. We conclude that ILC2 represent a major innate cell source of IL-5 and IL-13 required for mounting atheroprotective immunity, which can be altered by high fat diet.

Type-2 innate lymphoid cells (ILC2) affect adipose tissue metabolism and function. Here the authors show that the ILC2 are present in para-aortic adipose tissue and represent a major source of IL-5 and IL-13 required for mounting atheroprotective immunity, which can be altered by high fat diet.

Abstract 226: C-type Lectin Receptor Clec9a on Cd8a+ Dendritic Cells Promotes the Development of Atherosclerosis in Mice

Necrotic core formation during the development of atherosclerosis is associated with a chronic inflammatory response and promotes accelerated plaque development and instability. We hypothesized that sensing of necrotic cells by CLEC9A, a C-type lectin receptors selectively expressed by the CD8α + subset of dendritic cells (CD8α + DCs), plays a determinant role in the inflammatory response of atherosclerosis.

Reconstitution of lethally-irradiated Ldlr-/- with bone marrow from CLEC9A-/- mice significantly reduced atherosclerotic lesion size in aortic root after 5 weeks of high fat diet (HFD) (-45%, p=0,0059) and after 7 weeks of HFD (-40%, p=0,0017), as compared to mice transplanted with wild-type bone marrow-derived cells. However, no effect of CLEC9A was observed after 13 weeks of HFD (p=0,4996), suggesting early effect of CLEC9A on atherosclerosis development.

The same phenotype was observed in 20-week-old Apoe-/-CLEC9A-/- compared to Apoe-/- mice put on chow diet (-50%, p=0,0022).

Interestingly, an increase of IL-10 expression (+60%, p=0,0093) was observed in spleens of mice deficient for CLEC9A. Furthermore, the beneficial effect observed in CLEC9A-/- was abolished in CLEC9A-/-IL-10-/- compared to IL-10-/- (p=0,4452). Moreover, a specific deletion of Clec9a in CD8α + DC cells significantly increases Il10 expression, reduces macrophage and T cell contents within the lesions, and significantly limits the development of atherosclerosis. In conclusion, our results identify a new role of Clec9a in regulating vascular inflammation and atherosclerosis development and potentially identify a new target for disease modulation.

Abstract 309: Blockade of Transforming Growth Factor Beta Activity in Elastase-Induced Aortic Injury in Mice Induces a Human-Like Abdominal Aneurysm

Background: Abdominal aortic aneurysm (AAA) carries important morbidity and mortality and is resistant to medical therapy. Current experimental models do not accurately reproduce the major features of the human disease. There are 2 major categories of mouse models of AAA: those that induce medial dissection, which is not a major characteristic of human AAA, and those that induce aortic dilatation but are self-contained and do not progress to rupture.

Methods: We hypothesized that blockade of TGFβ activity, a guardian of vascular integrity and immune homeostasis, and a major causal factor in genetically triggered thoracic aortic aneurysms in humans, would impair vascular healing in models of ‘non-dissecting’ abdominal aortic dilatation, and would lead to continuous aneurysmal growth until rupture. We tested this hypothesis in the elastase-induced abdominal aortic dilatation model in mice. We analyzed AAA development and progression using ultrasound in vivo, advanced synchrotron-based ultrahigh resolution imaging ex-vivo, and a combination of biological, histological and flow cytometry-based cellular and molecular approaches in vitro.

Results: We show that systemic blockade of TGFβ activity using a neutralizing mouse monoclonal anti-TGFβ antibody induces a transition from a model of self-contained aortic dilatation to a model of sustained aneurysmal growth culminating in rupture. TGFβ blockade enhances leukocyte infiltration and extracellular matrix degradation, and leads to sustained aneurysmal aortic dilatation, associated with the formation of an intra-luminal thrombus infiltrated with neutrophils, as seen in the human disease. Persistent AAA growth throughout the duration of the experiment is associated with wall disruption without medial dissection, and culminates in fatal aortic wall rupture. Monocyte/macrophage depletion substantially limits AAA severity.

Conclusions: Endogenous TGFβ activity is required for the resolution of elastase-induced aortic injury. We expect that this new model will improve our understanding of the pathophysiology of AAA, and will be useful to identify new therapeutic targets.

Acute Ischemic Stroke Infarct Topology: Association with Lesion Volume and Severity of Symptoms at Admission and Discharge

BACKGROUND AND PURPOSE

Acute stroke presentation and outcome depend on both ischemic infarct volume and location. We aimed to determine the association between acute ischemic infarct topology and lesion volume and stroke severity at presentation and discharge.

MATERIALS AND METHODS

Patients with acute ischemic stroke who underwent MR imaging within 24 hours of symptom onset or last seen well were included. Infarcts were segmented and coregistered on the Montreal Neurological Institute-152 brain map. Voxel-based analyses were performed to determine the distribution of infarct lesions associated with larger volumes, higher NIHSS scores at admission and discharge, and greater NIHSS/volume ratios.

RESULTS

A total of 238 patients were included. Ischemic infarcts involving the bilateral lentiform nuclei, insular ribbons, middle corona radiata, and right precentral gyrus were associated with larger infarct volumes (average, 76.7 ± 125.6 mL versus 16.4 ± 24.0 mL, P < .001) and higher admission NIHSS scores. Meanwhile, brain stem and thalami infarctions were associated with higher admission NIHSS/volume ratios. The discharge NIHSS scores were available in 218 patients, in whom voxel-based analysis demonstrated that ischemic infarcts of the bilateral posterior insular ribbons, middle corona radiata, and right precentral gyrus were associated with more severe symptoms at discharge, whereas ischemic lesions of the brain stem, bilateral thalami, and, to a lesser extent, the middle corona radiata were associated with higher ratios of discharge NIHSS score/infarct volume.

CONCLUSIONS

Acute ischemic infarcts of the insulae, lentiform nuclei, and middle corona radiata tend to have larger volumes, more severe presentations, and worse outcomes, whereas brain stem and thalamic infarcts have greater symptom severity relative to smaller lesion volumes.

CARD9 impacts colitis by altering gut microbiota metabolism of tryptophan into aryl hydrocarbon receptor ligands

Complex interactions between the host and the gut microbiota govern intestinal homeostasis but remain poorly understood. Here we reveal a relationship between gut microbiota and caspase recruitment domain family member 9 (CARD9), a susceptibility gene for inflammatory bowel disease (IBD) that functions in the immune response against microorganisms. CARD9 promotes recovery from colitis by promoting interleukin (IL)-22 production, and Card9(-/-) mice are more susceptible to colitis. The microbiota is altered in Card9(-/-) mice, and transfer of the microbiota from Card9(-/-) to wild-type, germ-free recipients increases their susceptibility to colitis. The microbiota from Card9(-/-) mice fails to metabolize tryptophan into metabolites that act as aryl hydrocarbon receptor (AHR) ligands. Intestinal inflammation is attenuated after inoculation of mice with three Lactobacillus strains capable of metabolizing tryptophan or by treatment with an AHR agonist. Reduced production of AHR ligands is also observed in the microbiota from individuals with IBD, particularly in those with CARD9 risk alleles associated with IBD. Our findings reveal that host genes affect the composition and function of the gut microbiota, altering the production of microbial metabolites and intestinal inflammation.

Indoleamine 2,3-Dioxygenase Fine-Tunes Immune Homeostasis in Atherosclerosis and Colitis through Repression of Interleukin-10 Production

Indoleamine 2,3-dioxygenase 1 (Ido1) is a rate-limiting enzyme that catalizes the degradation of tryptophan along the kynurenine pathway. Here, we show that Ido1 activity sustains an immunostimulatory potential through inhibition of interleukin (Il)10. In atherosclerosis, Ido1-dependent inhibition of Il10 translates into disease exacerbation. The resistance of Ido1-deficient mice to enhanced immune activation is broken in Ido1/Il10 double-deficient mice, which show exaggerated immune responses and develop severe spontaneous colitis. We demonstrate that Ido1 activity is required for the regulation of Il10 and that kynurenic acid (Kna), an Ido1-derived metabolite, is responsible for reduced Il10 production through activation of a cAMP-dependent pathway and inhibition of Erk1/2 phosphorylation. Resupplementation of Ido1-deficient mice with Kna limits Il10 expression and promotes atherosclerosis. In human atherosclerotic lesions, increased levels of Kna are associated with an unstable plaque phenotype, and its blood levels predict death and recurrent myocardial infarction in patients with coronary artery disease.