Prevention of radiotherapy-induced arterial inflammation by interleukin-1 blockade

Aims

Radiotherapy-induced cardiovascular disease is an emerging problem in a growing population of cancer survivors where traditional treatments, such as anti-platelet and lipid-lowering drugs, have limited benefits. The aim of the study was to investigate vascular inflammatory patterns in human cancer survivors, replicate the findings in an animal model, and evaluate whether interleukin-1 (IL-1) inhibition could be a potential treatment.

Methods and results

Irradiated human arterial biopsies were collected during microvascular autologous free tissue transfer for cancer reconstruction and compared with non-irradiated arteries from the same patient. A mouse model was used to study the effects of the IL-1 receptor antagonist, anakinra, on localized radiation-induced vascular inflammation. We observed significant induction of genes associated with inflammasome biology in whole transcriptome analysis of irradiated arteries, a finding supported by elevated protein levels in irradiated arteries of both, pro-caspase and caspase-1. mRNA levels of inflammasome associated chemokines CCL2, CCL5 together with the adhesion molecule VCAM1, were elevated in human irradiated arteries as was the number of infiltrating macrophages. A similar pattern was reproduced in Apoe−/− mouse 10 weeks after localized chest irradiation with 14 Gy. Treatment with anakinra in irradiated mice significantly reduced Ccl2 and Ccl5 mRNA levels and expression of I-A^b.

Conclusion

Anakinra, administered directly after radiation exposure for 2 weeks, ameliorated radiation induced sustained expression of inflammatory mediators in mice. Further studies are needed to evaluate IL-1 blockade as a treatment of radiotherapy-induced vascular disease in a clinical setting.

Lipoxin and Resolvin Receptors Transducing the Resolution of Inflammation in Cardiovascular Disease

A non-resolving inflammation results in a chronic inflammatory response, characteristic of atherosclerosis, abdominal aortic aneurysms and several other cardiovascular diseases. Restoring the levels of specialized proresolving mediators to drive the chronic cardiovascular inflammation toward resolution is emerging as a novel therapeutic principle. The lipid mediators lipoxins and resolvins exert their proresolving actions through specific G-protein coupled receptors (GPCR). So far, four GPCR have been identified as the receptors for lipoxin A4 and the D- and E-series of resolvins, namely ALX/FPR2, DRV1/GPR32, DRV2/GPR18, and ERV1/ChemR23. At the same time, other pro-inflammatory ligands also activate some of these receptors. Recent studies of genetic targeting of these receptors in atherosclerotic mouse strains have revealed a major role for proresolving receptors in atherosclerosis. The present review addresses the complex pharmacology of these four proresolving GPCRs with focus on their therapeutic implications and opportunities for inducing the resolution of inflammation in cardiovascular disease.

Abstract 652: MicroRNA-29b Mediates the Chronic Inflammatory Response in Radiotherapy-induced Vascular Disease

Radiotherapy is an established therapeutic method in many different cancer types. Its success raises a new problem, namely radiotherapy-induced vascular disease (vRTx), which typically manifests as coronary disease, heart failure or carotid stenosis. A chronic inflammatory response likely underlies vRTx, involving complex processes, such as vascular smooth muscle cell de-differentiation, oxidative stress, and ECM remodeling. These processes are tightly regulated and thus far difficult to influence therapeutically. In other diseases, a set of microRNAs (miRs) is known to orchestrate these processes. We hypothesized that they similarly could play a role in vRTx and be targets for treatment or prevention of the disease.

We performed qRT-PCR screening of 11 pre-selected miRs, which identified miR-29b as significantly decreased in irradiated arteries collected from patients undergoing free tissue transfer reconstruction, compared with non-irradiated arteries from the same patient (n=15). In a vascular biology context, miR-29b is known as inhibitor of collagen- and ECM associated mRNA targets, and has been shown to play a detrimental role in aneurysm disease and advanced atherosclerotic lesions.

Consistent with human tissue data, vascular smooth muscle and endothelial cells in vitro receiving two radiation doses of 2 Gy, showed decreased miR-29b upon 24 hours after exposure. In these irradiated SMCs, miR-29b induction reduced soluble collagen levels, while inhibition further increased them.

Array-based tissue gene expression analysis showed that Pentraxin-3 (PTX) and dipeptidyl-peptidase 4 (DPP4), both targets of miR-29b and pivotal in inflammation and adverse wound healing, were downregulated in the same patient cohort. Carotid arteries of Apoe -/- mice treated with miR-29b mimic, 24h before and 24h after irradiation (14 Gy to the upper chest and neck), displayed a downward trend (non-significant) in Ptx3 and Dpp4 gene expression.

Our results suggest that miR-29b overexpression therapy could have a place in the prevention of vRTx. To further strengthen this conclusion, additional Apoe -/- mice irradiation experiments are currently ongoing, to further establish PTX3 and DPP4 as mediators of anti-inflammatory and anti-fibrotic strategies.

Abstract 149: Analysis of Radiotherapy Induced Vascular Lesions Reveals Potential Therapies Against Innate Inflammation in an ApoE Knockout Mouse Model

Clinical studies show an increase risk for cardiovascular disease (CVD) at the site of irradiation years after exposure. Radiotherapy together with other cancer therapies contributes to a growing population of cancer survivors in risk of developing radiotherapy induced vascular disease. However, traditional treatments for CVD such as thrombolytic inhibitors and lipid lowering drugs (statins) seem to have no effect on radiation induced vascular disease in mouse models. We have previously demonstrated a sustained chronic inflammation by NF-kB activation in irradiated human arteries. To further investigate radiation induced vascular disease and potential therapies against innate inflammation, we established a mouse model of local irradiation in an atherosclerotic prone ApoE-/- background. ApoE-/- mice fed chow diet were exposed to a single dose of 0 Gy (sham/controls) or 14 Gy at the upper chest and neck area and harvested 10 weeks later. Plasma, thoracic aorta, aortic arch, heart were retrieved and taken for plasma, blood count, en face, mRNA, immunohistochemistry and immunofluorescence analysis. Irradiated mice presented higher total plasma cholesterol levels than controls. En face analysis of aortic arches showed a decreased percentage of lesion size in irradiated arteries compared to controls. However, an increase of MHC class II (IA-b) staining in irradiated aortic roots suggested an induction of inflammation in the context of radiotherapy. These data were supported by the quantification of monocyte chemotactic protein 1 mRNA expression in the thoracic aorta showing a significant increase in irradiated animals compared to unirradiated (p≤0,001).

The current data demonstrated that radiotherapy induces a macrophage-rich and inflamed plaque that may explain the increased risk of developing severe clinical events i.e. myocardial infarction or stroke. Further analyses of this partial irradiation mouse model are on-going to assess the potential therapeutic targets involved in innate immunity and NF-kB activation. Results of currently performed therapeutic experiments will be further presented.

Abstract 151: miR-29b and miR-146b Mediate the Chronic Inflammatory Response in Radiotherapy-induced Vascular Disease

Radiotherapy is an established therapeutic method in many different cancer types. The success of modern cancer treatment raises a new problem, namely radiotherapy-induced vascular disease (vRTx) or vasculopathy, which typically emerges in irradiated areas of the heart, neck and brain and manifests as coronary disease, heart failure or carotid stenosis. A chronic inflammatory response likely underlies vRTx. Like in atherosclerosis, complex biological processes such as vascular cell proliferation, remodeling, oxidative stress, DNA repair, and tumor growth factor β (TGF-β)-regulated nuclear factor kappa B (NF-κB) activation are involved. These processes are tightly regulated by a multitude of factors, which on their own are difficult to influence therapeutically.

In other diseases, a set of miRNAs is known to orchestrate these processes. It is likely that they also play a role in vRTx, and might be modifiable in order to treat or prevent this disease. We selected miR-29b, miR-125a, miR-126, miR-143, miR-145, miR-146, miR-155, miR-221 and miR-222, and determined their potential contribution to vRTx. Using qRT-PCR screening of human material from microvascular free tissue transfer reconstructions, where irradiated (R) vascular tissue (branches from external carotid arteries and internal jugular veins) can be compared with non-irradiated control tissue (NR) within the same patient ( n =15), we found miR-29b and miR-146b to be deregulated after irradiation. These miRNAs target genes involved in the innate immune response, which we could confirm with Affymetrix-based tissue gene expression analysis in the same human cohort. In vascular smooth muscle and endothelial cells in vitro receiving two radiation doses of 2 Gy, miR-29b and miR-146b, respectively, were deregulated 24 hours after exposure. Using local irradiation in Apoe -/- mice as a model for vRTx, we are currently analyzing the expression and localization of miR-29b and miR-146b in R vs NR vascular tissue at various time points after a single, 14 Gy irradiation dose. In this model, we aim to modulate miRNA expression in order to dampen radiation-induced inflammatory responses at an early stage, thereby exploring miRNA modulation as a therapeutic option to prevent vRTx in cancer survivors.

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 368: Inhibition of Ido-mediated Tryptophan Metabolism Aggravates Atherosclerosis in Hypercholesterolemic Mice

Introduction: Indoleamine 2,3-dioxygenase (IDO), an enzyme catalyzing the first step of tryptophan (Trp) degradation along the kynurenine pathway, has been shown to control autoimmunity and inflammation. Pharmacological inhibition of IDO by 1-methyl-tryptophan (1-MT), a competitive inhibitor of IDO, aggravates disease in several chronic inflammation models. Yet, the role of IDO-mediated Trp metabolism in the pathogenesis of atherosclerosis is unknown.

Hypothesis: We assessed the hypothesis that inhibition of tryptophan metabolism affects the development of atherosclerosis in hypercholesterolemic Apoe-/- mice.

Methods/Results: Twelve-week old Apoe-/- mice were treated with 1-MT in the drinking water for 8 weeks. Systemic IDO inhibition led to significantly larger atherosclerotic lesions in the aortic root (0.211± 0.024 vs 0.118± 0.025 mm2; mean ± SEM for 1-MT and controls, respectively; n=9-10). IDO inhibition resulted in increased aortic mRNA levels of TNF, MCP-1, and VCAM-1. Immunohistochemical staining of plaques showed increased CD68+ macrophage infiltration and VCAM-1 expression in 1-MT-treated mice. Additionally, IDO inhibition increased VCAM-1 expression in the smooth muscle cells (SMCs) of the tunica media. Moreover, we found that IDO-dependent Trp metabolism by SMCs regulates VCAM-1 expression, and that 1-MT-induced acceleration of atherosclerosis can be reversed by exogenous administration of the downstream Trp metabolite 3-hydroxyanthranilic acid (3-HAA). Importantly, 3-HAA supplementation reversed the 1-MT-induced VCAM-1 expression in the medial compartment.

Conclusion: IDO-mediated Trp metabolism plays a major role in vascular inflammation and atherosclerosis in Apoe-/- mice.

Abstract 556: Targeted Screening Reveals microRNAs of Therapeutic Interest in Radiotherapy-Induced Vascular Disease

Radiotherapy is an established therapeutic method in many different cancer types. The success of modern cancer treatment raises a new problem, namely radiotherapy-induced vascular disease (vRTx) or vasculopathy, which typically emerges in irradiated areas of the heart, neck and brain and manifests itself as coronary disease, heart failure or carotid stenosis. A chronic inflammatory response likely underlies vRTx. Like in atherosclerosis, complex biological processes such as vascular cell proliferation, remodeling, oxidative stress, and tumor growth factor β (TGF-β)-regulated nuclear factor kappa B (NF-κB) activation are involved. These processes are tightly regulated by a multitude of factors, which separately are difficult to influence.

A set of miRNAs known to orchestrate these processes in other disease contexts likely also play a role in vRTx, and might be modifiable in order to treat or prevent RTx-induced vascular disease. We selected miR-29b, miR-125a, miR-126, miR-143, miR-145, miR-146a, miR-155, miR-221, miR-222, and miR-503 and determined their potential contribution to vRTx. Utilizing unique biobank material from microvascular free tissue transfer reconstructions, where irradiated (R) vascular tissue (branches from external carotid arteries and internal jugular veins) can be compared with non-irradiated control tissue (NR) within the same patient (n=10), we could precisely determine which miRNAs become deregulated after irradiation. Currently we are using a mouse model of local irradiation for further analysis and assessment of miRNA modulation effects. Apoe -/- mice are irradiated in the mediastinal area; control littermates were sham irradiated. We checked the expression of the 10 pre-selected miRNAs in R vs. NR vascular tissue (ascending and thoracic aorta).

Of the 10 miRNAs, three (miR-29b up-; miR-143, miR-145 downregulated) were significantly differentially regulated between R and NR human arteries. miR-146a trended upward, but not significantly. Ongoing studies are aimed at histological analysis of mouse R vs. NR tissue, functional modulation of deregulated miRNAs in vivo to assess vRTx outcome, and in vitro assessment of miRNA expression differences in different human vascular cell lines exposed to radiation.

Abstract 121: Pro-inflammatory Cytokine Ifng Modulates Hepatic Sortilin Expression and Lipid Metabolism

Rationale: Hypercholesterolemia and immunity are two major risk factors for cardiovascular diseases (CVDs). Yet, we reported increased atherosclerosis upon depletion of regulatory T lymphocytes (Tregs). The effect was associated with increased hepatic inflammation and reduction of Sortilin expression and lipid uptake in the liver.

Objective: To define how inflammatory milieu in the liver can modulate Sortilin and lipid metabolism.

Methods: To reproduce the inflammatory milieu, hepatocytes (AML-12) were treated in vitro with IFNg. Expression of genes and proteins of interest were followed by qPCR and western blot. In silico method was used to find binding sites of signal transducer and activator of transcription (STAT1) on Sortilin, confirmed later by chromatin immune precipitation assays (Chip). Lipid uptake by hepatocytes was assessed via incubation of cells with radioactive lipoproteins.

Results: Culture of AML-12 cells with IFNg induced the phosphorylation of STAT1 showing an active signaling pathway. In the same inflammatory conditions, Sort1 mRNA is decreased meanwhile its inhibitor (Atf3) expression is increased. Kinetic experiments revealed the reduction of Sortilin after 12 hours of culture, suggesting a post-transcriptional regulation of Sort1 by STAT1.

In silico analysis revealed putative binding sites for STAT1 on Sortilin gene which was confirmed by chromatin immunoprecipitation assay (Chip).

IFNg treated hepatocytes that were incubated with radioactive lipoproteins demonstrated a reduced uptake capacity of VLDL and LDL particles compared to control cultures.

Conclusion: All together, these results suggest that inflammation through production of IFNg is able to directly modulate the lipid metabolism in hepatocytes by acting on Sortilin expression.

Inhibition of indoleamine 2,3-dioxygenase promotes vascular inflammation and increases atherosclerosis in Apoe-/- mice

AIMS

Atherosclerosis is a chronic inflammatory disease that is initiated by the retention and accumulation of low-density lipoprotein in the artery, leading to maladaptive response of cells from the immune system and vessel wall. Strong evidence implicates indoleamine 2,3-dioxygenase (IDO), the first and rate-limiting enzyme of the kynurenine pathway of tryptophan (Trp) degradation, with immune regulation and anti-inflammatory mechanisms in different diseases. However, the role of IDO and the endogenous degradation of Trp have never been directly examined in atherosclerosis development. We used the IDO inhibitor 1-methyl-Trp (1-MT) to determine the role of IDO-mediated Trp metabolism in vascular inflammation and atherosclerosis.

METHODS AND RESULTS

Apoe(-/-) mice were treated with 1-MT in drinking water for 8 weeks. Systemic IDO inhibition led to a significant increase in atherosclerotic lesions that were ∼58 and 54% larger in the aortic arch and root, respectively. 1-MT treatment enhanced vascular inflammation, up-regulated VCAM-1 and CCL2, and increased CD68 macrophage accumulation into the plaque. Notably, the rise in VCAM-1 expression was not limited to the plaque but also found in smooth muscle cells (SMCs) of the tunica media. Furthermore, we found that IDO-dependent Trp metabolism by SMCs regulates VCAM-1 expression, and that 1-MT-induced acceleration of atherosclerosis and vascular inflammation can be reversed by exogenous administration of the Trp metabolite 3-hydroxyanthranilic acid (3-HAA).

CONCLUSION

IDO-mediated Trp metabolism regulates vascular inflammation and plaque formation in hypercholesterolaemic Apoe(-/-) mice. Our data establish that this pathway plays a major role in the pathological process of atherogenesis.

Physiopathology of necrobiotic xanthogranuloma with monoclonal gammopathy

RATIONALE

Xanthomatosis associated with monoclonal gammopathy includes hyperlipidaemic xanthoma (HX), normolipidaemic xanthoma (NX) and necrobiotic xanthogranuloma (NXG). All three pathologies are characterized by skin or visceral lesions related to cholesterol accumulation, monoclonal immunoglobulin (MIg) and hypocomplementemia. The pathophysiology underlying NXG remains unknown although the involvement of MIg is suspected.

OBJECTIVE

To provide further insights into the pathophysiology of NXG, we evaluated the plasma lipid phenotype, mechanisms involved in cellular cholesterol accumulation and role of MIg in an analysis of blood and plasma markers of inflammation in 16 patients with xanthomatosis [NXG (n = 8) and NX (n = 8)] associated with monoclonal IgG relative to the relevant controls.

RESULTS

The lipid profile of patients with NXG was characterized by a low HDL-C phenotype and an abnormal distribution of HDL particles. Sera from patients with NXG induced cholesterol accumulation in human macrophages. This accumulation was due in part to a significant reduction in the HDL capacity to promote cholesterol efflux from macrophages, which was not found in the case of NX. The MIg of NXG and NX patients was tested positively by ELISA to recognize a large spectrum of lipoproteins. High plasma levels of pro-inflammatory cytokines (TNFα and IL-6), soluble cytokine receptors (sIL-6R, sTNFRI and sTNFRII), adhesion molecules (VCAM-1 and ICAM-1) and chemokines (MCP-1, IL-8 and MIP-1α) were observed in both patients with NXG and NX, revealing a specific xanthoma inflammatory signature which was inversely correlated with plasma levels of anti-inflammatory HDL. However, patients with NXG were distinguished by elevated levels of IL-15 and a marked increase in the rate of intermediate CD14++CD16+ monocytes.

CONCLUSION

This study revealed that NXG is characterized by impaired macrophage lipid homeostasis associated with a systemic inflammatory profile that may result from the interaction of MIg and lipoproteins.

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.