The cytosolic DNA sensor AIM2 promotes Helicobacter-induced gastric pathology via the inflammasome

Helicobacter pylori (H. pylori) infection can trigger chronic gastric inflammation perpetuated by overactivation of the innate immune system, leading to a cascade of precancerous lesions culminating in gastric cancer. However, key regulators of innate immunity that promote H. pylori-induced gastric pathology remain ill-defined. The innate immune cytosolic DNA sensor absent in melanoma 2 (AIM2) contributes to the pathogenesis of numerous autoimmune and chronic inflammatory diseases, as well as cancers including gastric cancer. We therefore investigated whether AIM2 contributed to the pathogenesis of Helicobacter-induced gastric disease. Here, we reveal that AIM2 messenger RNA and protein expression levels are elevated in H. pylori-positive versus H. pylori-negative human gastric biopsies. Similarly, chronic Helicobacter felis infection in wild-type mice augmented Aim2 gene expression levels compared with uninfected controls. Notably, gastric inflammation and hyperplasia were less severe in H. felis-infected Aim2-/- versus wild-type mice, evidenced by reductions in gastric immune cell infiltrates, mucosal thickness and proinflammatory cytokine and chemokine release. In addition, H. felis-driven proliferation and apoptosis in both gastric epithelial and immune cells were largely attenuated in Aim2-/- stomachs. These observations in Aim2-/- mouse stomachs correlated with decreased levels of inflammasome activity (caspase-1 cleavage) and the mature inflammasome effector cytokine, interleukin-1β. Taken together, this work uncovers a pathogenic role for the AIM2 inflammasome in Helicobacter-induced gastric disease, and furthers our understanding of the host immune response to a common pathogen and the complex and varying roles of AIM2 at different stages of cancerous and precancerous gastric disease.

STAT3-mediated upregulation of the AIM2 DNA sensor links innate immunity with cell migration to promote epithelial tumourigenesis

OBJECTIVE

The absent in melanoma 2 (AIM2) cytosolic pattern recognition receptor and DNA sensor promotes the pathogenesis of autoimmune and chronic inflammatory diseases via caspase-1-containing inflammasome complexes. However, the role of AIM2 in cancer is ill-defined.

DESIGN

The expression of AIM2 and its clinical significance was assessed in human gastric cancer (GC) patient cohorts. Genetic or therapeutic manipulation of AIM2 expression and activity was performed in the genetically engineered gp130 ^F/F spontaneous GC mouse model, as well as human GC cell line xenografts. The biological role and mechanism of action of AIM2 in gastric tumourigenesis, including its involvement in inflammasome activity and functional interaction with microtubule-associated end-binding protein 1 (EB1), was determined in vitro and in vivo.

RESULTS

AIM2 expression is upregulated by interleukin-11 cytokine-mediated activation of the oncogenic latent transcription factor STAT3 in the tumour epithelium of GC mouse models and patients with GC. Genetic and therapeutic targeting of AIM2 in gp130 ^F/F mice suppressed tumourigenesis. Conversely, AIM2 overexpression augmented the tumour load of human GC cell line xenografts. The protumourigenic function of AIM2 was independent of inflammasome activity and inflammation. Rather, in vivo and in vitro AIM2 physically interacted with EB1 to promote epithelial cell migration and tumourigenesis. Furthermore, upregulated expression of AIM2 and EB1 in the tumour epithelium of patients with GC was independently associated with poor patient survival.

CONCLUSION

AIM2 can play a driver role in epithelial carcinogenesis by linking cytokine-STAT3 signalling, innate immunity and epithelial cell migration, independent of inflammasome activation.

Toll-like Receptor 9 Promotes Initiation of Gastric Tumorigenesis by Augmenting Inflammation and Cellular Proliferation

BACKGROUND & AIMS

Gastric cancer (GC) is strongly linked with chronic gastritis after Helicobacter pylori infection. Toll-like receptors (TLRs) are key innate immune pathogenic sensors that mediate chronic inflammatory and oncogenic responses. Here, we investigated the role of TLR9 in the pathogenesis of GC, including Helicobacter infection.

METHODS

TLR9 gene expression was profiled in gastric tissues from GC and gastritis patients and from the spontaneous gp130^F/F GC mouse model and chronic H felis-infected wild-type (WT) mice. Gastric pathology was compared in gp130^F/F and H felis infection models with or without genetic ablation of Tlr9. The impact of Tlr9 targeting on signaling cascades implicated in inflammation and tumorigenesis (eg, nuclear factor kappa B, extracellular signal-related kinase, and mitogen-activated protein kinase) was assessed in vivo. A direct growth-potentiating effect of TLR9 ligand stimulation on human GC cell lines and gp130^F/F primary gastric epithelial cells was also evaluated.

RESULTS

TLR9 expression was up-regulated in Helicobacter-infected gastric tissues from GC and gastritis patients and gp130^F/F and H felis-infected WT mice. Tlr9 ablation suppressed initiation of tumorigenesis in gp130^F/F:Tlr9^-/- mice by abrogating gastric inflammation and cellular proliferation. Tlr9^-/- mice were also protected against H felis-induced gastric inflammation and hyperplasia. The suppressed gastric pathology upon Tlr9 ablation in both mouse models associated with attenuated nuclear factor kappa B and, to a lesser extent, extracellular signal-related kinase, mitogen-activated protein kinase signaling. TLR9 ligand stimulation of human GC cells and gp130^F/F GECs augmented their proliferation and viability.

CONCLUSIONS

Our data reveal that TLR9 promotes the initiating stages of GC and facilitates Helicobacter-induced gastric inflammation and hyperplasia, thus providing in vivo evidence for TLR9 as a candidate therapeutic target in GC.

Inflammasome-Associated Gastric Tumorigenesis Is Independent of the NLRP3 Pattern Recognition Receptor

Inflammasomes are important multiprotein regulatory complexes of innate immunity and have recently emerged as playing divergent roles in numerous inflammation-associated cancers. Among these include gastric cancer (GC), the third leading cause of cancer-associated death worldwide, and we have previously discovered a pro-tumorigenic role for the key inflammasome adaptor apoptosis-associated speck-like protein containing a CARD (ASC) in the spontaneous genetic gp130^F/F mouse model for GC. However, the identity of the specific pattern recognition receptors (PRRs) that activate tumor-promoting inflammasomes during GC is unknown. Here, we investigated the role of the best-characterized inflammasome-associated PRR, nucleotide-binding domain, and leucine-rich repeat containing receptor, pyrin domain-containing (NLRP) 3, in GC. In gastric tumors of gp130^F/F mice, although NLRP3 expression was elevated at the mRNA (qPCR) and protein (immunohistochemistry) levels, genetic ablation of NLRP3 in gp130^F/F:Nlrp3^-/- mice did not alleviate the development of gastric tumors. Similarly, cellular processes associated with tumorigenesis in the gastric mucosa, namely, proliferation, apoptosis, and inflammation, were comparable between gp130^F/F and gp130^F/F:Nlrp3^-/- mice. Furthermore, inflammasome activation levels, determined by immunoblotting and immunohistochemistry for cleaved Caspase-1, which along with ASC is another integral component of inflammasome complexes, were unchanged in gp130^F/F and gp130^F/F:Nlrp3^-/- gastric tumors. We also observed variable NLRP3 expression levels (mRNA and protein) among independent GC patient cohorts, and NLRP3 was not prognostic for survival outcomes. Taken together, these data suggest that NLRP3 does not play a major role in promoting inflammasome-driven gastric tumorigenesis, and thus pave the way for further investigations to uncover the key inflammasome-associated PRR implicated in GC.

TLR2 activation promotes tumour growth and associates with patient survival and chemotherapy response in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) has an extremely poor prognosis, and is plagued by a paucity of targeted treatment options and tumour resistance to chemotherapeutics. The causal link between chronic inflammation and PDAC suggests that molecular regulators of the immune system promote disease pathogenesis and/or therapeutic resistance, yet their identity is unclear. Here, we couple endoscopic ultrasound-guided fine-needle aspiration, which captures tumour biopsies from all stages, with whole transcriptome profiling of PDAC patient primary tumours to reveal enrichment of the innate immune Toll-like receptor 2 (TLR2) molecular pathway. Augmented TLR2 expression associated with a 4-gene "TLR2 activation" signature, and was prognostic for survival and predictive for gemcitabine-based chemoresistance. Furthermore, antibody-mediated anti-TLR2 therapy suppressed the growth of human PDAC tumour xenografts, independent of a functional immune system. Our results support TLR2-based therapeutic targeting for precision medicine in PDAC, with further clinical utility that TLR2 activation is prognostic and predictive for chemoresponsiveness.

ADAM17 selectively activates the IL-6 trans-signaling/ERK MAPK axis in KRAS-addicted lung cancer

Oncogenic KRAS mutations are major drivers of lung adenocarcinoma (LAC), yet the direct therapeutic targeting of KRAS has been problematic. Here, we reveal an obligate requirement by oncogenic KRAS for the ADAM17 protease in LAC In genetically engineered and xenograft (human cell line and patient-derived) Kras ^G12D-driven LAC models, the specific blockade of ADAM17, including with a non-toxic prodomain inhibitor, suppressed tumor burden by reducing cellular proliferation. The pro-tumorigenic activity of ADAM17 was dependent upon its threonine phosphorylation by p38 MAPK, along with the preferential shedding of the ADAM17 substrate, IL-6R, to release soluble IL-6R that drives IL-6 trans-signaling via the ERK1/2 MAPK pathway. The requirement for ADAM17 in Kras ^G12D-driven LAC was independent of bone marrow-derived immune cells. Furthermore, in KRAS mutant human LAC, there was a significant positive correlation between augmented phospho-ADAM17 levels, observed primarily in epithelial rather than immune cells, and activation of ERK and p38 MAPK pathways. Collectively, these findings identify ADAM17 as a druggable target for oncogenic KRAS-driven LAC and provide the rationale to employ ADAM17-based therapeutic strategies for targeting KRAS mutant cancers.

Constitutive STAT3 Serine Phosphorylation Promotes Helicobacter-Mediated Gastric Disease

Gastric cancer is associated with chronic inflammation (gastritis) triggered by persistent Helicobacter pylori (H. pylori) infection. Elevated tyrosine phosphorylation of the latent transcription factor STAT3 is a feature of gastric cancer, including H. pylori-infected tissues, and aligns with nuclear transcriptional activity. However, the transcriptional role of STAT3 serine phosphorylation, which promotes STAT3-driven mitochondrial activities, is unclear. Here, by coupling serine-phosphorylated (pS)-STAT3-deficient Stat3^SA/SA mice with chronic H. felis infection, which mimics human H. pylori infection in mice, we reveal a key role for pS-STAT3 in promoting Helicobacter-induced gastric pathology. Immunohistochemical staining for infiltrating immune cells and expression analyses of inflammatory genes revealed that gastritis was markedly suppressed in infected Stat3^SA/SA mice compared with wild-type mice. Stomach weight and gastric mucosal thickness were also reduced in infected Stat3^SA/SA mice, which was associated with reduced proliferative potential of infected Stat3^SA/SA gastric mucosa. The suppressed H. felis-induced gastric phenotype of Stat3^SA/SA mice was phenocopied upon genetic ablation of signaling by the cytokine IL-11, which promotes gastric tumorigenesis via STAT3. pS-STAT3 dependency by Helicobacter coincided with transcriptional activity on STAT3-regulated genes, rather than mitochondrial and metabolic genes. In the gastric mucosa of mice and patients with gastritis, pS-STAT3 was constitutively expressed irrespective of Helicobacter infection. Collectively, these findings suggest an obligate requirement for IL-11 signaling via constitutive pS-STAT3 in Helicobacter-induced gastric carcinogenesis.

Helicobacter pylori Type IV Secretion System and Its Adhesin Subunit, CagL, Mediate Potent Inflammatory Responses in Primary Human Endothelial Cells

The Gram-negative bacterium, Helicobacter pylori, causes chronic gastritis, peptic ulcers, and gastric cancer in humans. Although the gastric epithelium is the primary site of H. pylori colonization, H. pylori can gain access to deeper tissues. Concurring with this notion, H. pylori has been found in the vicinity of endothelial cells in gastric submucosa. Endothelial cells play crucial roles in innate immune response, wound healing and tumorigenesis. This study examines the molecular mechanisms by which H. pylori interacts with and triggers inflammatory responses in endothelial cells. We observed that H. pylori infection of primary human endothelial cells stimulated secretion of the key inflammatory cytokines, interleukin-6 (IL-6) and interleukin-8 (IL-8). In particular, IL-8, a potent chemokine and angiogenic factor, was secreted by H. pylori-infected endothelial cells to levels ~10- to 20-fold higher than that typically observed in H. pylori-infected gastric epithelial cells. These inflammatory responses were triggered by the H. pylori type IV secretion system (T4SS) and the T4SS-associated adhesin CagL, but not the translocation substrate CagA. Moreover, in contrast to integrin α5β1 playing an essential role in IL-8 induction by H. pylori upon infection of gastric epithelial cells, both integrin α5β1 and integrin αvβ3 were dispensable for IL-8 induction in H. pylori-infected endothelial cells. However, epidermal growth factor receptor (EGFR) is crucial for mediating the potent H. pylori-induced IL-8 response in endothelial cells. This study reveals a novel mechanism by which the H. pylori T4SS and its adhesin subunit, CagL, may contribute to H. pylori pathogenesis by stimulating the endothelial innate immune responses, while highlighting EGFR as a potential therapeutic target for controlling H. pylori-induced inflammation.

Inflammasome Adaptor ASC Suppresses Apoptosis of Gastric Cancer Cells by an IL18-Mediated Inflammation-Independent Mechanism

Inflammasomes are key regulators of innate immunity in chronic inflammatory disorders and autoimmune diseases, but their role in inflammation-associated tumorigenesis remains ill-defined. Here we reveal a protumorigenic role in gastric cancer for the key inflammasome adaptor apoptosis-related speck-like protein containing a CARD (ASC) and its effector cytokine IL18. Genetic ablation of ASC in the gp130^F/F spontaneous mouse model of intestinal-type gastric cancer suppressed tumorigenesis by augmenting caspase-8-like apoptosis in the gastric epithelium, independently from effects on myeloid cells and mucosal inflammation. This phenotype was characterized by reduced activation of caspase-1 and NF-κB activation and reduced expression of mature IL18, but not IL1β, in gastric tumors. Genetic ablation of IL18 in the same model also suppressed gastric tumorigenesis, whereas blockade of IL1β and IL1α activity upon genetic ablation of the IL1 receptor had no effect. The specific protumorigenic role for IL18 was associated with high IL18 gene expression in the gastric tumor epithelium compared with IL1β, which was preferentially expressed in immune cells. Supporting an epithelial-specific role for IL18, we found it to be highly secreted from human gastric cancer cell lines. Moreover, IL18 blockade either by a neutralizing anti-IL18 antibody or by CRISPR/Cas9-driven deletion of ASC augmented apoptosis in human gastric cancer cells. In clinical specimens of human gastric cancer tumors, we observed a significant positive correlation between elevated mature IL18 protein and ASC mRNA levels. Collectively, our findings reveal the ASC/IL18 signaling axis as a candidate therapeutic target in gastric cancer.Significance: Inflammasome activation that elevates IL18 helps drive gastric cancer by protecting cancer cells against apoptosis, with potential implications for new therapeutic strategies in this setting. Cancer Res; 78(5); 1293-307. ©2017 AACR.

Therapeutic Targeting of the IL-6 Trans-Signaling/Mechanistic Target of Rapamycin Complex 1 Axis in Pulmonary Emphysema

RATIONALE

The potent immunomodulatory cytokine IL-6 is consistently up-regulated in human lungs with emphysema and in mouse emphysema models; however, the mechanisms by which IL-6 promotes emphysema remain obscure. IL-6 signals using two distinct modes: classical signaling via its membrane-bound IL-6 receptor (IL-6R), and trans-signaling via a naturally occurring soluble IL-6R.

OBJECTIVES

To identify whether IL-6 trans-signaling and/or classical signaling contribute to the pathogenesis of emphysema.

METHODS

We used the gp130^F/F genetic mouse model for spontaneous emphysema and cigarette smoke-induced emphysema models. Emphysema in mice was quantified by various methods including in vivo lung function and stereology, and terminal deoxynucleotidyl transferase dUTP nick end labeling assay was used to assess alveolar cell apoptosis. In mouse and human lung tissues, the expression level and location of IL-6 signaling-related genes and proteins were measured, and the levels of IL-6 and related proteins in sera from emphysematous mice and patients were also assessed.

MEASUREMENTS AND MAIN RESULTS

Lung tissues from patients with emphysema, and from spontaneous and cigarette smoke-induced emphysema mouse models, were characterized by excessive production of soluble IL-6R. Genetic blockade of IL-6 trans-signaling in emphysema mouse models and therapy with the IL-6 trans-signaling antagonist sgp130Fc ameliorated emphysema by suppressing augmented alveolar type II cell apoptosis. Furthermore, IL-6 trans-signaling-driven emphysematous changes in the lung correlated with mechanistic target of rapamycin complex 1 hyperactivation, and treatment of emphysema mouse models with the mechanistic target of rapamycin complex 1 inhibitor rapamycin attenuated emphysematous changes.

CONCLUSIONS

Collectively, our data reveal that specific targeting of IL-6 trans-signaling may represent a novel treatment strategy for emphysema.

Transcriptional regulation of inflammasome-associated pattern recognition receptors, and the relevance to disease pathogenesis

Over the last decade it has emerged that inflammasome complexes provide a pivotal platform for the host innate immune system to respond to exogenous infectious microbes (viruses, bacteria, fungi) and non-infectious environmental agents (cigarette smoke, pollution), as well as endogenous "danger" signals. Upon the canonical activation of inflammasomes, a key effector function is to catalyze, via caspase-1, the maturation of the potent pro-inflammatory cytokines interleukin (IL)-1β and IL-18, which, in addition to chronic inflammatory responses have also been intimately linked to the inflammatory form of lytic cell death, pyroptosis. However, recent evidence suggests that inflammasomes exhibit marked pleiotropism beyond their canonical functions, whereby their activation can also influence a large number of cellular responses including proliferation, apoptosis, autophagy and metabolism. It is therefore not surprising that the dysregulated expression and/or activation of inflammasomes is increasingly implicated in numerous disease states, such as chronic auto-inflammatory and autoimmune disorders, metabolic syndrome, neurodegenerative and cardiovascular diseases, as well as cancer. In this review we will highlight recent advancements in our understanding of the transcriptional regulation of genes encoding inflammasome-associated innate immune receptors, and the impact on a variety of cellular responses during disease pathogenesis.

Abstract 1462: Non-inflammatory role of ASC-dependent inflammasomes in promoting gastric tumourigenesis via IL-18

Introduction

Gastric cancer is the third most lethal cancer worldwide and represents a growing number of cancers linked with inflammation. However, the identity of innate immune regulators with oncogenic potential in the host gastric mucosal epithelium remains obscure. We aim to identify the molecular basis by which specific pattern recognition receptors belonging to the inflammasome family promotes gastric tumorigenesis.

Experimental procedures

We have employed the gp130F/F gastric cancer mouse model coupled with mice lacking specific inflammasome-related genes. In addition, human gastric cancer tumor (and matched non-tumor) biopsies and cell lines were used. Immunohistochemistry on gastric tissue sections was used to assess the extent of cellular proliferation, apoptosis, inflammation and angiogenesis, and quantitative real-time PCR was used to measure the expression of genes of interest. Immunoblotting and ELISA were used to measure the activation and expression levels of inflammasome-related proteins.

Results

A causal role for ASC-dependent inflammasomes in gastric tumorigenesis was confirmed upon the genetic ablation of ASC in gp130F/F:Asc-/- mice, which resulted in a ∼50% reduction in tumor burden compared to parental gp130F/F mice. The suppressed gastric tumorigenesis in gp130F/F:Asc-/- mice was associated with increased gastric epithelial (tumor) cell apoptosis, as determined by elevated numbers of TUNEL and caspase-8 positive cells. Surprisingly however, no changes in the number and activation status of inflammatory cells were observed. The suppressed gastric tumorigenesis in gp130F/F:Asc-/- mice was also characterized by a gene signature comprising apoptotic-related genes. In gastric tumor tissue, IL-18, but not IL-1β, protein levels were augmented compared to matched non-tumour tissue, and genetic ablation of IL-18 in gp130F/F:IL-18-/- mice suppressed gastric tumorigenesis comparable to that observed upon ASC deficiency. The treatment of human gastric cancer cells with IL-18 also potentiated their growth compared to IL-1β.

Conclusions

Collectively, these data reveal that ASC-dependent inflammasomes and their downstream mediator IL-18 represent a novel oncogenic mechanism in gastric cancer.

Citation Format: Brendan Jenkins, Virginie Deswaerte, Alison West, Paul Nguyen, Tracy Putoczki. Non-inflammatory role of ASC-dependent inflammasomes in promoting gastric tumourigenesis via IL-18. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1462.

Low-Density Lipoprotein Receptor-Dependent and Low-Density Lipoprotein Receptor-Independent Mechanisms of Cyclosporin A-Induced Dyslipidemia

OBJECTIVE

Cyclosporin A (CsA) is an immunosuppressant commonly used to prevent organ rejection but is associated with hyperlipidemia and an increased risk of cardiovascular disease. Although studies suggest that CsA-induced hyperlipidemia is mediated by inhibition of low-density lipoprotein receptor (LDLr)-mediated lipoprotein clearance, the data supporting this are inconclusive. We therefore sought to investigate the role of the LDLr in CsA-induced hyperlipidemia by using Ldlr-knockout mice (Ldlr(-/-)).

APPROACH AND RESULTS

Ldlr(-/-) and wild-type (wt) C57Bl/6 mice were treated with 20 mg/kg per d CsA for 4 weeks. On a chow diet, CsA caused marked dyslipidemia in Ldlr(-/-) but not in wt mice. Hyperlipidemia was characterized by a prominent increase in plasma very low-density lipoprotein and intermediate-density lipoprotein/LDL with unchanged plasma high-density lipoprotein levels, thus mimicking the dyslipidemic profile observed in humans. Analysis of specific lipid species by liquid chromatography-tandem mass spectrometry suggested a predominant effect of CsA on increased very low-density lipoprotein-IDL/LDL lipoprotein number rather than composition. Mechanistic studies indicated that CsA did not alter hepatic lipoprotein production but did inhibit plasma clearance and hepatic uptake of [(14)C]cholesteryl oleate and glycerol tri[(3)H]oleate-double-labeled very low-density lipoprotein-like particles. Further studies showed that CsA inhibited plasma lipoprotein lipase activity and increased levels of apolipoprotein C-III and proprotein convertase subtilisin/kexin type 9.

CONCLUSIONS

We demonstrate that CsA does not cause hyperlipidemia via direct effects on the LDLr. Rather, LDLr deficiency plays an important permissive role for CsA-induced hyperlipidemia, which is associated with abnormal lipoprotein clearance, decreased lipoprotein lipase activity, and increased levels of apolipoprotein C-III and proprotein convertase subtilisin/kexin type 9. Enhancing LDLr and lipoprotein lipase activity and decreasing apolipoprotein C-III and proprotein convertase subtilisin/kexin type 9 levels may therefore provide attractive treatment targets for patients with hyperlipidemia receiving CsA.

Promoting macrophage survival delays progression of pre-existing atherosclerotic lesions through macrophage-derived apoE

AIMS

Macrophage apoptosis is a prominent feature of atherosclerosis, yet whether cell death-protected macrophages would favour the resolution of already established atherosclerotic lesions, and thus hold therapeutic potential, remains unknown.

METHODS AND RESULTS

We irradiated then transplanted into Apoe(-/-) or LDLr(-/-) recipient mice harbouring established atherosclerotic lesions, bone marrow cells from mice displaying enhanced macrophage survival through overexpression of the antiapoptotic gene hBcl-2 (Mø-hBcl2 Apoe(-/-) or Mø-hBcl2 Apoe(+/+) LDLr(-/-)). Both recipient mice exhibited decreased lesional apoptotic cell content and reduced necrotic areas when repopulated with Mø-hBcl2 mouse-derived bone marrow cells. In contrast, only LDLr(-/-) recipients showed a reduction in plasma cholesterol levels and in atherosclerotic lesions. The absence of significant reduction of plasma cholesterol levels in the context of apoE deficiency highlighted macrophage-derived apoE as key in both the regulation of plasma and tissue cholesterol levels and the progression of pre-existing lesion. Accordingly, hBcl2 expression in macrophages was associated with larger pools of Kupffer cells and Ly-6C(low) monocytes, both high producers of apoE. Additionally, increased Kupffer cells population was associated with improved clearance of apoptotic cells and modified lipoproteins.

CONCLUSION

Collectively, these data show that promoting macrophage survival provides a supplemental source of apoE, which hinders pre-existing plaque progression.

Abstract 359: CD4+ Natural Killer T Cells Promote Atherosclerosis via Cytotoxic Mechanism

CD4 + NKT cells are atherogenic lymphocytes, but the mechanisms by which they promote atherosclerosis are not known. Here we investigated the role of other lymphocytes and NKT cell-derived cytokines and cytotoxins in NKT cell’s atherogenicity. First, CD4 + NKT cells were adoptively transferred into ApoE -/- mice; deficient in T, B cell and NKT cells (ApoE -/- Rag2 -/- ) and in T, B, NKT and NK cells (ApoE -/- Rag2 -/- γc -/- ). At the end of 8 week high fat diet, CD4 + NKT cells augmented aortic root atherosclerosis assessed by total intimal lesion area, lipid content and macrophage accumulation in both ApoE -/- Rag2 -/- mice and ApoE -/- Rag2 -/- γC -/- mice. These data indicate that CD4 + NKT cells can exert atherogenic effects in the absence of other lymphocytes. As NKT cells secrete cytokines and cytotoxins, we next investigated the role of NKT cell-derived cytokines and cytotoxins in atherosclerosis development. CD4 + NKT cells from mice deficient of IFN-γ, IL-4 and IL-21 cytokines and perforin and granzyme B cytotoxins were transferred into NKT cell-deficient ApoE -/- Jα18 -/- mice; controls were ApoE -/- Jα18 -/- mice that received PBS or wildtype NKT cells. At completion of 8 week high fat diet, wildtype CD4 + NKT cells and those deficient in IL-4, IFN-γ or IL-21 increased total intimal lesion area by ~65%, ~95%, ~80% and ~70% compared to vehicle control mice respectively. In contrast CD4 + NKT cells deficient in perforin or granzyme B failed to augment lesion size, lipid content and macrophage accumulation. Apoptotic cells, necrotic cores and proinflammatory VCAM-1 and MCP-1 were reduced in mice receiving perforin-deficient NKT cells. Our data suggest that CD4 + NKT cells require perforin and granzyme-B for atherosclerosis development, thereby increasing apoptotic and necrotic cells in lesions that in turn augments inflammation. Targeting NKT cell apoptotic cell mediators may be useful in attenuating atherosclerosis.

Blocking IL-6 trans-signaling prevents high-fat diet-induced adipose tissue macrophage recruitment but does not improve insulin resistance

Interleukin-6 (IL-6) plays a paradoxical role in inflammation and metabolism. The pro-inflammatory effects of IL-6 are mediated via IL-6 "trans-signaling," a process where the soluble form of the IL-6 receptor (sIL-6R) binds IL-6 and activates signaling in inflammatory cells that express the gp130 but not the IL-6 receptor. Here we show that trans-signaling recruits macrophages into adipose tissue (ATM). Moreover, blocking trans-signaling with soluble gp130Fc protein prevents high-fat diet (HFD)-induced ATM accumulation, but does not improve insulin action. Importantly, however, blockade of IL-6 trans-signaling, unlike complete ablation of IL-6 signaling, does not exacerbate obesity-induced weight gain, liver steatosis, or insulin resistance. Our data identify the sIL-6R as a critical chemotactic signal for ATM recruitment and suggest that selectively blocking IL-6 trans-signaling may be a more favorable treatment option for inflammatory diseases, compared with current treatments that completely block the action of IL-6 and negatively impact upon metabolic homeostasis.

CD4+ natural killer T cells potently augment aortic root atherosclerosis by perforin- and granzyme B-dependent cytotoxicity

RATIONALE

CD4(+) natural killer T (NKT) cells augment atherosclerosis in apolipoprotein E-deficient (ApoE)(-/-) mice but their mechanisms of action are unknown.

OBJECTIVES

We investigated the roles of bystander T, B, and NK cells; NKT cell-derived interferon-γ, interleukin (IL)-4, and IL-21 cytokines; and NKT cell-derived perforin and granzyme B cytotoxins in promoting CD4(+) NKT cell atherogenicity.

METHODS AND RESULTS

Transfer of CD4(+) NKT cells into T- and B-cell-deficient ApoE(-/-)Rag2(-/-) mice augmented aortic root atherosclerosis by ≈75% that was ≈30% of lesions in ApoE(-/-) mice; macrophage accumulation similarly increased. Transferred NKT cells were identified in the liver and atherosclerotic lesions of recipient mice. Transfer of CD4(+) NKT cells into T-, B-cell-deficient, and NK cell-deficient ApoE(-/-)Rag2(-/-)γC(-/-) mice also augmented atherosclerosis. These data indicate that CD4(+) NKT cells can exert proatherogenic effects independent of other lymphocytes. To investigate the role of NKT cell-derived interferon-γ, IL-4, and IL-21 cytokines and perforin and granzyme B cytotoxins, CD4(+) NKT cells from mice deficient in these molecules were transferred into NKT cell-deficient ApoE(-/-)Jα18(-/-) mice. CD4(+) NKT cells deficient in IL-4, interferon-γ, or IL-21 augmented atherosclerosis in ApoE(-/-)Jα18(-/-) mice by ≈95%, ≈80%, and ≈70%, respectively. Transfer of CD4(+) NKT cells deficient in perforin or granzyme B failed to augment atherosclerosis. Apoptotic cells, necrotic cores, and proinflammatory VCAM-1 (vascular cell adhesion molecule) and MCP-1 (monocyte chemotactic protein) were reduced in mice receiving perforin-deficient NKT cells. CD4(+) NKT cells are twice as potent as CD4(+) T cells in promoting atherosclerosis.

CONCLUSIONS

CD4(+) NKT cells potently promote atherosclerosis by perforin and granzyme B-dependent apoptosis that increases postapoptotic necrosis and inflammation.

Abstract 445: Increasing Macrophage Survival Delays Progression of Advanced Atherosclerotic Lesions Through Macrophage-Derived ApoE

Introduction/Hypothesis: We previously demonstrated that increasing macrophage survival delayed atherosclerotic plaque progression towards advanced stages. However, whether cell death-protected macrophages would still be efficient to hinder the progression and favor the resolution of already advanced atherosclerotic lesions, and thus prove therapeutic potential, remains unknown.

Methods: We used a transgenic mouse model in which macrophage lifespan is enhanced through specific overexpression of the antiapoptotic gene hBcl-2 under the control of the macrophage specific CD68 promoter (Mø-hBcl2). Apoe -/- or Ldlr -/- recipient mice with advanced atherosclerotic lesions were irradiated and then transplanted with bone marrow cells isolated from Apo e -/- Mø-h Bcl2 or Apo e +/+ Mø-hBcl2 mice respectively and their appropriate controls.

Results: Both Apoe -/- Mø-h Bcl2 → Apoe -/- and Apoe +/+ Mø-h Bcl2 → Ldl r -/- mice presented a significant decrease in lesional apoptotic cells content (-30%, P<0.05) as compared to their respective controls. Additionally, hBcl2 expression in macrophages was associated with a larger pool of tissue macrophages in vivo, including Küppfer cells in the liver, in both Apoe -/- (+40% P<0.05) and Ldlr -/- (+36% P<0.05) recipients. By contrast, only Ldlr -/- recipient mice showed reduction of lesional necrotic areas (-37%, P<0.05), plasma cholesterol levels (-15%, P<0.05) and atherosclerotic lesions (-30%, P<0.05). As those reductions were not significant in the context of ApoE deficiency, these findings supported that Mø-derived ApoE was key in regulating plasma cholesterol levels, lesional necrosis and advanced plaque progression in the context of increased macrophage pool. Indeed, increased liver Küpffer cells content in the liver of Ldlr -/- recipient mice was associated with elevated ApoE mRNA levels (+30%, P<0.05), which is likely to promote reverse cholesterol transport.

Conclusions: Collectively, these data suggest that macrophage survival hindered advanced lesion progression. One potential mechanistic explanation lied to the increased Küpffer cells content, which could modulate directly or indirectly cholesterol homeostasis.

Abstract 307: Influence of Dendritic Cells on Cholesterol Absorption and Excretion: Implication in Atherogenesis

Atherosclerosis represents the chronic pathophysiological process implicated in the majority of cardiovascular (CV) diseases and constitutes one of the leading causes of death in the world. The development of atherosclerotic lesions is characterized by an accumulation of extracellular and intracellular lipids in the arterial wall. These phenomena are associated with a strong local immuno-inflammatory response characterized by the recruitment of various populations of leucocytes including monocytes, macrophages and dendritic cells (DCs).

DCs are central to the regulation of immunity and the polarization of the immune response. We recently demonstrated that the longevity/depletion of DCs directly impacts plasma cholesterol levels, which is the main risk factor for atherosclerosis.

To gain insight into the cellular and molecular mechanisms underlying the inverse relationship between DC numbers and cholesterolemia, we have evaluated the impact of DCs on cholesterol homeostasis, using CD11c-hBcl2/apoE KO mice, in which specific DC-expression of the anti-apoptotic transgene hBcl2 increase their longevity and numbers. Firstly, we quantified DC populations in the liver and in the intestine, which are the main organs involved in cholesterol metabolism. Secondly, we measured the rates of dietary cholesterol absorption, tissue cholesterol content and sterol and bile salt excretion. Thirdly, we analysed the expression of genes associated with cholesterol metabolism in the liver and the intestine.

We found an increase of DC numbers in the liver and in the intestine in the CD11c-hBcl2 apoE KO mice relative to control apoE KO mice. This increase of DC numbers was associated with reduced intestinal cholesterol absorption and fecal bile acid excretion, but also with greater fecal excretion of sterols. Finally, there were no differences in the cholesterol content of the intestine and the liver. Our results suggest that the decrease in plasma cholesterol level in CD11c-hBcl2 apoE KO mice relative to apoE KO mice could be due to both a decrease of intestinal cholesterol absorption and an increase in sterol excretion. The role of intestinal DCs in dietary cholesterol absorption and excretion is presently under investigation but the present study reveal that DCs are central to the atherosclerotic process, because they are implicated in cholesterol metabolism.

Abstract 344: Bcl-x Inactivation in Macrophages Accelerates Progression of Advanced Atherosclerotic Lesions in Apoe -/- Mice

Background: Bcl-x is the most abundantly expressed member of the Bcl-2 gene family in macrophages but its role in macrophage apoptosis during atherogenesis is unknown.

Methods and results: We previously reported dual pro- and anti-atherogenic effects of macrophage survival in early versus advanced atherosclerotic lesions respectively, potentially reflecting growing impairment of efferocytosis during plaque progression. Here, we specifically inactivated Bcl-x in macrophages and evaluated its impact on atherosclerotic lesion formation in Apoe -/- mice at various stages of the disease. Bcl-x deficiency in macrophages increased susceptibility to apoptosis, resulting in the depletion of tissue macrophages in vivo, including its major pool, Küppfer cells in the liver. We also observed increased cholesterol levels, that was however not associated with any acceleration of early atherosclerotic plaque progression. This observation, suggests that the atheroprotective effect of macrophage apoptosis at that stage of disease was counterbalanced by enhanced cholesterol levels. Bcl-x KOmac/Apoe -/- mice exhibited significantly larger advanced lesions than control mice. These lesions showed vulnerable traits. Such enhanced lesion size may occur as a result not only of apoptotic cell accumulation but also of elevated cholesterol levels.

Conclusions: Modulation of macrophage resistance to apoptosis through targeted deletion of Bcl-x has a major impact on the entire macrophage cell population in the body, including Küpffer cells. Macrophage survival may, therefore, not only influence atherosclerotic plaque development and vulnerability but also cholesterol metabolism.

Bcl-x inactivation in macrophages accelerates progression of advanced atherosclerotic lesions in Apoe(-/-) mice

OBJECTIVE

Bcl-x is the most abundantly expressed member of the Bcl-2 gene family in macrophages, but its role in macrophage apoptosis during atherogenesis is unknown.

METHODS AND RESULTS

We previously reported dual pro- and antiatherogenic effects of macrophage survival in early versus advanced atherosclerotic lesions, respectively, potentially reflecting growing impairment of efferocytosis during plaque progression. Here, we specifically inactivated Bcl-x in macrophages and evaluated its impact on atherosclerotic lesion formation in Apoe(-/-) mice at various stages of the disease. Bcl-x deficiency in macrophages increased their susceptibility to apoptosis, resulting in the depletion of tissue macrophages in vivo, including its major pool, Küppfer cells in the liver. We also observed increased cholesterol levels that were, however, not associated with any acceleration of early atherosclerotic plaque progression. This observation suggests that the atheroprotective effect of macrophage apoptosis at that stage of disease was counterbalanced by enhanced cholesterol levels. Bcl-x KO(mac)/Apoe(-/-) mice exhibited significantly larger advanced lesions than control mice. These lesions showed vulnerable traits. Such enhanced lesion size may occur as a result not only of apoptotic cell accumulation but also of elevated cholesterol levels.

CONCLUSIONS

Modulation of macrophage resistance to apoptosis through targeted deletion of Bcl-x has a major impact on the entire macrophage cell population in the body, including Küpffer cells. Macrophage survival may, therefore, not only influence atherosclerotic plaque development and vulnerability but also cholesterol metabolism.

Conventional Dendritic Cells at the Crossroads Between Immunity and Cholesterol Homeostasis in Atherosclerosis

Background— Immunoinflammatory mechanisms are implicated in the atherogenic process. The polarization of the immune response and the nature of the immune cells involved, however, are major determinants of the net effect, which may be either proatherogenic or antiatherogenic. Dendritic cells (DCs) are central to the regulation of immunity, the polarization of the immune response, and the induction of tolerance to antigens. The potential role of DCs in atherosclerosis, however, remains to be defined.

Methods and Results— We created a mouse model in which the lifespan and immunogenicity of conventional DCs are enhanced by specific overexpression of the antiapoptotic gene hBcl-2 under the control of the CD11c promoter. When studied in either low-density lipoprotein receptor–deficient or apolipoprotein E–deficient backgrounds, DC-hBcl2 mice exhibited an expanded DC population associated with enhanced T-cell activation, a T-helper 1 and T-helper 17 cytokine expression profile, and elevated production of T-helper 1–driven IgG2c autoantibodies directed against oxidation-specific epitopes. This proatherogenic signature, however, was not associated with acceleration of atherosclerotic plaque progression, because expansion of the DC population was unexpectedly associated with an atheroprotective decrease in plasma cholesterol levels. Conversely, depletion of DCs in hyperlipidemic CD11c–diphtheria toxin receptor/apolipoprotein E–deficient transgenic mice resulted in enhanced cholesterolemia, thereby arguing for a close relationship between the DC population and plasma cholesterol levels.

Conclusions— Considered together, the present data reveal that conventional DCs are central to the atherosclerotic process, because they are directly implicated in both cholesterol homeostasis and the immune response.