Immune effector mechanisms implicated in atherosclerosis: from mice to humans

Targeted Delivery of Shear Stress-Inducible Micrornas by Nanoparticles to Prevent Vulnerable Atherosclerotic Lesions

Atherosclerosis is a chronic inflammatory vascular wall disease, and endothelial cell dysfunction plays an important role in its development and progression. Under the influence of laminar shear stress, however, the endothelium releases homeostatic factors such as nitric oxide and expresses of vasoprotective microRNAs that are resistant to atherosclerosis. Adhesion molecules such as E-selectin, exhibited on the endothelial surface, recruit monocytes that enter the vessel wall to form foam cells. Accumulation of these foam cells form fatty streaks that may progress to atherosclerotic plaques in the blood vessel wall. Interestingly, E-selectin may also serve as an affinity moiety for targeted drug delivery against atherosclerosis. We have recently developed an E-selectin-targeted platform that enriches therapeutic microRNAs in the inflamed endothelium to inhibit formation of vulnerable atherosclerotic plaques.

Use of a proximity extension assay proteomics chip to discover new biomarkers associated with albuminuria

Background The underlying mechanisms for the development of albuminuria and the increased cardiovascular risk in patients with elevated albuminuria levels are incompletely understood. We therefore investigated the associations between 80 cardiovascular proteins and the urinary albumin to creatinine ratio (ACR). Methods We used a discovery/replication approach in two independent community-based cohorts of elderly patients: the Uppsala Longitudinal Study of Adult Men ( n = 662; mean age 78 years) and the Prospective Investigation of the Vasculature in Uppsala Seniors ( n = 757; mean age 75 years; 51% women). A proteomic chip with a panel of 80 plasma proteins associated with different aspects of cardiovascular disease was analysed. In the discovery cohort, we used a false discovery rate of 5% to take into account the multiple statistical testing. Nominal p values were used in the replication. Results Higher levels of T-cell immunoglobulin mucin-1, placenta growth factor, growth/differentiation factor-15, urokinase plasminogen activator surface receptor and kallikrein-11 were robustly associated with a higher ACR in both cohorts in multivariable linear regression models adjusted for sex, established cardiovascular risk factors, antihypertensive treatment, prevalent cardiovascular disease and glomerular filtration rate ( p < 0.02 for all). All associations were also significant in separate analyses of patients without diabetes. Conclusions We discovered and replicated associations between ACR and five cardiovascular proteins involved in tubular injury, atherosclerosis, endothelial function, heart failure, inflammation, glomerulosclerosis and podocyte injury. Our findings put forward multiplex proteomics as a promising approach to explore novel aspects of the complex detrimental interplay between kidney function and the cardiovascular system.

KERIS: kaleidoscope of gene responses to inflammation between species

A cornerstone of modern biomedical research is the use of animal models to study disease mechanisms and to develop new therapeutic approaches. In order to help the research community to better explore the similarities and differences of genomic response between human inflammatory diseases and murine models, we developed KERIS: kaleidoscope of gene responses to inflammation between species (available at http://www.igenomed.org/keris/). As of June 2016, KERIS includes comparisons of the genomic response of six human inflammatory diseases (burns, trauma, infection, sepsis, endotoxin and acute respiratory distress syndrome) and matched mouse models, using 2257 curated samples from the Inflammation and the Host Response to Injury Glue Grant studies and other representative studies in Gene Expression Omnibus. A researcher can browse, query, visualize and compare the response patterns of genes, pathways and functional modules across different diseases and corresponding murine models. The database is expected to help biologists choosing models when studying the mechanisms of particular genes and pathways in a disease and prioritizing the translation of findings from disease models into clinical studies.

TREM-1 links dyslipidemia to inflammation and lipid deposition in atherosclerosis

Triggering receptor expressed on myeloid cells-1 (TREM-1) is a potent amplifier of pro-inflammatory innate immune responses, but its significance in non-infectious diseases remains unclear. Here, we demonstrate that TREM-1 promotes cardiovascular disease by exacerbating atherosclerosis. TREM-1 is expressed in advanced human atheromas and is highly upregulated under dyslipidemic conditions on circulating and on lesion-infiltrating myeloid cells in the Apoe^−/− mouse model. TREM-1 strongly contributes to high-fat, high-cholesterol diet (HFCD)-induced monocytosis and synergizes with HFCD serum-derived factors to promote pro-inflammatory cytokine responses and foam cell formation of human monocyte/macrophages. Trem1^−/−Apoe^−/− mice exhibit substantially attenuated diet-induced atherogenesis. In particular, our results identify skewed monocyte differentiation and enhanced lipid accumulation as novel mechanisms through which TREM-1 can promote atherosclerosis. Collectively, our findings illustrate that dyslipidemia induces TREM-1 surface expression on myeloid cells and subsequently synergizes with TREM-1 to enhance monopoiesis, pro-atherogenic cytokine production and foam cell formation.

TREM-1 is a receptor that amplifies acute pro-inflammatory responses in infection. Here the authors show that TREM-1 plays an important role in atherosclerosis, a chronic and non-infectious disease, by critically skewing myelopoiesis towards preferential monocyte differentiation and by contributing to CD36-driven cellular lipid accumulation.

Study of oxidative and inflammatory parameters in LDLr-KO mice treated with a hypercholesterolemic diet: Comparison between the use of Campomanesia xanthocarpa and acetylsalicylic acid

BACKGROUND

Atherosclerosis is an inflammatory disease that affects the arterial wall leading to myocardial, cerebral, and peripheral ischemic syndromes. The use of low doses of aspirin inhibits platelet aggregation and inflammation and prevents cardiovascular mortality. However, ASA may produce hemorrhagic events. Thus, several studies have sought new natural compounds to suppress platelet aggregation without causing serious adverse effects.

PURPOSE

In this sense, this study aims to compare the effects of Campomanesia xanthocarpa plant extract with those of acetylsalicylic acid (ASA) on inflammatory parameters observed in homozygous mice knockout for the low-density lipoprotein receptor (LDLr-KO) treated with a hypercholesterolemic diet.

MATERIAL AND METHODS

In this study, 28 male LDLr-KO mice were divided into three groups and fed a hypercholesterolemic diet for 4 weeks. Thereafter, the animals that received the hypercholesterolemic diet were treated for 5 days with (1) distilled water, (2) C. xanthocarpa extract, or (3) acetylsalicylic acid. The levels of inflammatory markers were assessed in the blood samples. The gastric tolerability of the animals after oral administration of the treatments was assessed through quantification of the lesions in the gastric mucosa.

RESULTS

The levels of proinflammatory cytokines IL-1, IL-6, TNF-α, and INF-γ were reduced to 19.2 ± 3%, 20.4 + 1.3%, 24.7 ± 1.2%, and 20.8 ± 1.7%, respectively, in the group treated with C. xanthocarpa, when compared to control group. Furthermore, treatment with plant extract significantly increased the levels of the anti-inflammatory cytokine IL-10 by 27.3 ± 5.9%, but ASA showed no significant effect on the same cytokines when compared to the control group, with the exception of IL-10, which presented an increase of 8.6 ± 3.5%. Treatments with C. xanthocarpa and ASA also caused significant reductions of 26.4 ± 3% and 38.4± 6% in the serum levels of oxLDL, respectively. However, only treatment with C. xanthocarpa reduced the levels of anti-oxLDL antibodies when compared with the control (25.8 ± 6%). In addition, the analyzed extract did not induce ulcerogenic activity, while ASA induced the formation of lesions.

CONCLUSION

In conclusion, treatment with C. xanthocarpa causes anti-inflammatory activity in hypercholesterolemic animals, with results superior to those obtained with the use of ASA.

Artery Tertiary Lymphoid Organs: Powerhouses of Atherosclerosis Immunity

Artery tertiary lymphoid organs (ATLOs) are atherosclerosis-associated lymphoid aggregates with varying degrees of complexity ranging from small T/B-cell clusters to well-structured lymph node-like though unencapsulated lymphoid tissues. ATLOs arise in the connective tissue that surrounds diseased arteries, i.e., the adventitia. ATLOs have been identified in aged atherosclerosis-prone hyperlipidemic apolipoprotein E-deficient (ApoE-/-) mice: they are organized into distinct immune cell compartments, including separate T-cell areas, activated B-cell follicles, and plasma cell niches. Analyses of ATLO immune cell subsets indicate antigen-specific T- and B-cell immune reactions within the atherosclerotic arterial wall adventitia. Moreover, ATLOs harbor innate immune cells, including a large component of inflammatory macrophages, B-1 cells, and an aberrant set of antigen-presenting cells. There is marked neoangiogenesis, irregular lymphangiogenesis, neoformation of high endothelial venules, and de novo synthesis of lymph node-like conduits. Molecular mechanisms of ATLO formation remain to be identified though media vascular smooth muscle cells may adopt features of lymphoid tissue organizer-like cells by expressing lymphorganogenic chemokines, i.e., CXCL13 and CCL21. Although these data are consistent with the view that ATLOs participate in primary T- and B-cell responses against elusive atherosclerosis-specific autoantigens, their specific protective or disease-promoting roles remain to be identified. In this review, we discuss what is currently known about ATLOs and their potential impact on atherosclerosis and make attempts to define challenges ahead.

BubR1 Insufficiency Results in Decreased Macrophage Proliferation and Attenuated Atherogenesis in Apolipoprotein E-Deficient Mice

Background

Budding uninhibited by benzimidazole‐related 1 (BubR1), a cell cycle–related protein, is an essential component of the spindle checkpoint that regulates cell division. BubR1 insufficiency causes early aging‐associated vascular phenotypes. We generated low‐BubR1‐expressing mutant (BubR1^L/L) and apolipoprotein E‐deficient (ApoE^−/−) mice (BubR1^L/L‐ApoE^−/− mice) to investigate the effects of BubR1 on atherosclerosis.

Methods and Results

Eight‐week‐old male BubR1^L/L‐ApoE^−/− mice and age‐matched ApoE^−/− mice were used in this study. Atherosclerotic lesion development after being fed a high‐cholesterol diet for 12 weeks was inhibited in BubR1^L/L‐ApoE^−/− mice compared with ApoE^−/− mice, and was accompanied by decreased accumulation of macrophages. To address the relative contribution of BubR1 on bone marrow–derived cells compared with non‐bone marrow–derived cells, we performed bone marrow transplantation in ApoE^−/− and BubR1^L/L‐ApoE^−/− mice. Decreased BubR1 in bone marrow cells and non‐bone marrow–derived cells decreased the atherosclerotic burden. In vitro assays indicated that decreased BubR1 expression impaired proliferation, but not migration, of bone marrow–derived macrophages.

Conclusions

BubR1 may represent a promising new target for regulating atherosclerosis.

Atherosclerosis-Driven Treg Plasticity Results in Formation of a Dysfunctional Subset of Plastic IFNγ+ Th1/Tregs

RATIONALE

Forkhead box P3⁺ T regulatory cells (Tregs) are key players in maintaining immune homeostasis. Evidence suggests that Tregs respond to environmental cues to permit or suppress inflammation. In atherosclerosis, Th1-driven inflammation affects Treg homeostasis, but the mechanisms governing this phenomenon are unclear.

OBJECTIVE

Here, we address whether atherosclerosis impacts Treg plasticity and functionality in Apoe^-/- mice, and what effect Treg plasticity might have on the pathology of atherosclerosis.

METHODS AND RESULTS

We demonstrate that atherosclerosis promotes Treg plasticity, resulting in the reduction of CXCR3⁺ Tregs and the accumulation of an intermediate Th1-like interferon (IFN)-γ⁺CCR5⁺ Treg subset (Th1/Tregs) within the aorta. Importantly, Th1/Tregs arise in atherosclerosis from bona fide Tregs, rather than from T-effector cells. We show that Th1/Tregs recovered from atherosclerotic mice are dysfunctional in suppression assays. Using an adoptive transfer system and plasticity-prone Mir146a^-/- Tregs, we demonstrate that elevated IFNγ⁺ Mir146a^-/- Th1/Tregs are unable to adequately reduce atherosclerosis, arterial Th1, or macrophage content within Apoe^-/- mice, in comparison to Mir146a^+/+ Tregs. Finally, via single-cell RNA-sequencing and real-time -polymerase chain reaction, we show that Th1/Tregs possess a unique transcriptional phenotype characterized by coexpression of Treg and Th1 lineage genes and a downregulation of Treg-related genes, including Ikzf2, Ikzf4, Tigit, Lilrb4, and Il10. In addition, an ingenuity pathway analysis further implicates IFNγ, IFNα, interleukin-2, interleukin-7, CTLA-4 (cytotoxic T-lymphocyte-associated protein 4), T-cell receptor, and Csnk2b-related pathways in regulating Treg plasticity.

CONCLUSIONS

Atherosclerosis drives Treg plasticity, resulting in the accumulation of dysfunctional IFNγ⁺ Th1/Tregs that may permit further arterial inflammation and atherogenesis.

Potential Role of Lipometabolism-Related MicroRNAs in Peripheral Blood Mononuclear Cells as Biomarkers for Coronary Artery Disease

Aim: To explore the relationship between lipometabolism-related microRNAs (miRNAs) in peripheral blood mononuclear cells (PBMCs) and the presence of coronary artery disease (CAD).

Methods: In the present study, 161 stable CAD patients and 149 health controls were enrolled. The expression levels of seven miRNAs (miR-21, miR-24, miR-29a, miR-33a, miR-34a, miR-103a, and miR-122) in PBMCs were qualified by quantitative real-time polymerase chain reaction (qRT-PCR). The miRNA markers that showed significant difference between the two groups were used for further analysis. The risk of miRNA contributing to the presence of CAD was estimated by univariate and multivariate logistic regression models. The area under the receiver operating characteristic curve (AUC) was used to evaluate diagnostic accuracy.

Results: The expression levels of miR-24, miR-33a, miR-103a, and miR-122 in PBMCs were significantly increased in CAD patients compared with controls and were significantly correlated with blood lipids in both CAD patients and controls. The increased levels of miR-24 (adjusted OR = 1.32, 95% CI 1.07–1.62, P = 0.009), miR-33a (adjusted OR = 1.57, 95% CI 1.35–1.81, P < 0.001), miR-103a (adjusted OR = 1.01, 95% CI 1.01–1.02, P < 0.001), and miR-122 (adjusted OR = 1.03, 95% CI 1.01–1.04, P < 0.001) were associated with risk of CAD. We identified a miRNA panel (miR-24, miR-33, miR-103a, and miR-122) that provided a high diagnostic accuracy of CAD (AUC= 0.911, 95% CI 0.880–0.942).

Conclusion: The increased expression levels of miR-24, miR-33a, miR-103a, and miR-122 in PBMCs are associated with risk of CAD. A panel of the four miRNAs has considerable clinical value in diagnosing stable CAD.

Discovery of new biomarkers for atrial fibrillation using a custom-made proteomics chip

BACKGROUND

Apart from several established clinical risk factors for atrial fibrillation (AF), a number of biomarkers have also been identified as potential risk factors for AF. None of these have so far been adopted in clinical practice.

OBJECTIVE

To use a novel custom-made proteomics chip to discover new prognostic biomarkers for AF risk.

METHODS

In two independent community-based cohorts (Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study (978 participants without AF, mean age 70.1 years, 50% women, median follow-up 10.0 years) and Uppsala Longitudinal Study of Adult Men (ULSAM) (n=725, mean age 77.5 years, median follow-up 7.9 years)), ninety-two plasma proteins were assessed at baseline by a proximity extension assay (PEA) chip. Of those, 85 proteins showed a call rate >70% in both cohorts.

RESULTS

Thirteen proteins were related to incident AF in PIVUS (148 events) using a false discovery rate of 5%. Of those, five were replicated in ULSAM at nominal multivariable p value (123 events, N-terminal pro-B-type natriuretic peptide (NT-pro-BNP), fibroblast growth factor 23 (FGF-23), fatty acid-binding protein 4 (FABP4), growth differentiation factor 15 (GDF-15) and interleukin-6 (IL-6)). Of those, NT-pro-BNP and FGF-23 were also associated with AF after adjusting for established AF risk factors. In a prespecified secondary analysis pooling the two data sets, T-cell immunoglobulin and mucin domain 1 (TIM-1) and adrenomedullin (AM) were also significantly related to incident AF in addition to the aforementioned five proteins (Bonferroni-adjustment). The addition of NT-pro-BNP to a model with established risk factors increased the C-statistic from 0.605 to 0.676 (p<0.0001).

CONCLUSIONS

Using a novel proteomics approach, we confirmed the previously reported association between NT-pro-BNP, FGF-23, GDF-15 and incident AF, and also discovered four proteins (FABP4, IL-6, TIM-1 and AM) that could be of importance in the development of AF.

Ferric Chloride-induced Murine Thrombosis Models

Arterial thrombosis (blood clot) is a common complication of many systemic diseases associated with chronic inflammation, including atherosclerosis, diabetes, obesity, cancer and chronic autoimmune rheumatologic disorders. Thrombi are the cause of most heart attacks, strokes and extremity loss, making thrombosis an extremely important public health problem. Since these thrombi stem from inappropriate platelet activation and subsequent coagulation, targeting these systems therapeutically has important clinical significance for developing safer treatments. Due to the complexities of the hemostatic system, in vitro experiments cannot replicate the blood-to-vessel wall interactions; therefore, in vivo studies are critical to understand pathological mechanisms of thrombus formation. To this end, various thrombosis models have been developed in mice. Among them, ferric chloride (FeCl3) induced vascular injury is a widely used model of occlusive thrombosis that reports platelet activation and aggregation in the context of an aseptic closed vascular system. This model is based on redox-induced endothelial cell injury, which is simple and sensitive to both anticoagulant and anti-platelets drugs. The time required for the development of a thrombus that occludes blood flow gives a quantitative measure of vascular injury, platelet activation and aggregation that is relevant to thrombotic diseases. We have significantly refined this FeCl3-induced vascular thrombosis model, which makes the data highly reproducible with minimal variation. Here we describe the model and present representative data from several experimental set-ups that demonstrate the utility of this model in thrombosis research.

Hypoxia in Atherogenesis

The anoxemia theory proposes that an imbalance between the demand for and supply of oxygen in the arterial wall is a key factor in the development of atherosclerosis. There is now substantial evidence that there are regions within the atherosclerotic plaque in which profound hypoxia exists; this may fundamentally change the function, metabolism, and responses of many of the cell types found within the developing plaque and whether the plaque will evolve into a stable or unstable phenotype. Hypoxia is characterized in molecular terms by the stabilization of hypoxia-inducible factor (HIF) 1α, a subunit of the heterodimeric nuclear transcriptional factor HIF-1 and a master regulator of oxygen homeostasis. The expression of HIF-1 is localized to perivascular tissues, inflammatory macrophages, and smooth muscle cells adjacent to the necrotic core of atherosclerotic lesions and regulates several genes that are important to vascular function including vascular endothelial growth factor, nitric oxide synthase, endothelin-1, and erythropoietin. This review summarizes the effects of hypoxia on the functions of cells involved in atherogenesis and the evidence for its potential importance from experimental models and clinical studies.

Combined B, T and NK Cell Deficiency Accelerates Atherosclerosis in BALB/c Mice

This study focused on the unique properties of both the Ldlr knockout defect (closely mimicking the human situation) and the BALB/c (C) inbred mouse strain (Th-2 slanted immune response). We generated two immunodeficient strains with severe combined B- and T-cell immunodeficiency with or without a complete lack of natural killer cells to revisit the role of adaptive immune responses on atherogenesis. C-Ldlr^-/-Rag1^-/- mice, which show severe combined B- and T-cell immunodeficiency and C-Ldlr^-/-Rag1^-/-Il2rg^-/- mice, which combine the T- and B-cell defect with a complete lack of natural killer cells and inactivation of multiple cytokine signalling pathways were fed an atherogenic Western type diet (WTD). Both B6-Ldlr^-/- and C-Ldlr^-/- immunocompetent mice were used as controls. Body weights and serum cholesterol levels of both immunodeficient strains were significantly increased compared to C-Ldlr^-/- controls, except for cholesterol levels of C-Ldlr^-/-Rag1^-/- double mutants after 12 weeks on the WTD. Quantification of the aortic sinus plaque area revealed that both strains of immunodeficient mice developed significantly more atherosclerosis compared to C-Ldlr^-/- controls after 24 weeks on the WTD. Increased atherosclerotic lesion development in C-Ldlr^-/-Rag1^-/-Il2rg^-/- triple mutants was associated with significantly increased numbers of macrophages and significantly decreased numbers of smooth muscle cells compared to both C-Ldlr^-/- wild type and C-Ldlr^-/-Rag1^-/- double mutants pointing to a plaque destabilizing effect of NK cell loss. Collectively, the present study reveals a previously unappreciated complexity with regard to the impact of lymphocytes on lipoprotein metabolism and the role of lymphocyte subsets in plaque composition.

Plasma IL-6 levels are independently associated with atherosclerosis and mortality in HIV-infected individuals on suppressive antiretroviral therapy

OBJECTIVE

To determine the associations of markers of immune activation with atherosclerosis and mortality, in participants with treated and suppressed HIV infection.

DESIGN

Observational study of 149 HIV-infected participants with virologic suppression on antiretroviral therapy.

METHODS

Cryopreserved mononuclear cells and plasma were used to evaluate markers of T cell and monocyte activation, inflammation and coagulopathy. Carotid artery intima-media thickness (CIMT) was measured by high-resolution ultrasound at the common, bifurcation and internal carotid regions. Associations of immunologic markers with CIMT and all-cause mortality were assessed using multivariable linear regression and Cox proportional hazards regression.

RESULTS

The majority of participants were men (93%) and white (67%), median age of 48.5 years and median CD4 T-cell count of 522 cells/μl. The median baseline IMT was 1.0 mm. Over a median of 8.3-year follow-up, 12 deaths occurred. In multivariate analysis, adjusted for traditional cardiovascular risk factors, higher monocyte C-C motif chemokine receptor 5 (CCR5) expression [5.4%, P = 0.001] was associated with greater common CIMT. Higher plasma IL-6 was associated with greater bifurcation [8.0%, P = 0.007] and overall mean IMT [5.2%, P = 0.026]. Finally, higher plasma IL-6 [hazard ratio 1.9, P = 0.030], internal carotid [hazard ratio 4.1, P = 0.022] and mean IMT [hazard ratio 5.2, P = 0.026] were individually associated with all-cause mortality.

CONCLUSION

Higher monocyte CCR5 expression and plasma IL-6 were associated with atherosclerosis, independent of traditional cardiovascular risk factors. IL-6 and CIMT were individually associated with all-cause mortality. The impact of therapies targeting immune activation in cardiovascular disease in treated HIV infection merits additional investigation.

Recent Advances of Radionuclide-Based Molecular Imaging of Atherosclerosis

Atherosclerosis is a systemic disease characterized by the development of multifocal plaque lesions within vessel walls and extending into the vascular lumen. The disease takes decades to develop symptomatic lesions, affording opportunities for accurate detection of plaque progression, analysis of risk factors responsible for clinical events, and planning personalized treatment. Of the available molecular imaging modalities, radionuclidebased imaging strategies have been favored due to their sensitivity, quantitative detection and pathways for translational research. This review summarizes recent advances of radiolabeled small molecules, peptides, antibodies and nanoparticles for atherosclerotic plaque imaging during disease progression.

A nanoformulation containing a scFv reactive to electronegative LDL inhibits atherosclerosis in LDL receptor knockout mice

Atherosclerosis is a chronic inflammatory disease responsible for the majority of cases of myocardial infarction and ischemic stroke. The electronegative low-density lipoprotein, a modified subfraction of native LDL, is pro-inflammatory and plays an important role in atherogenesis. To investigate the effects of a nanoformulation (scFv anti-LDL(-)-MCMN-Zn) containing a scFv reactive to LDL(-) on the inhibition of atherosclerosis, its toxicity was evaluated in vitro and in vivo and further it was also administered weekly to LDL receptor knockout mice. The scFv anti-LDL(-)-MCMN-Zn nanoformulation did not induce cell death in RAW 264.7 macrophages and HUVECs. The 5mg/kg dose of scFv anti-LDL(-)-MCMN-Zn did not cause any typical signs of toxicity and it was chosen for the evaluation of its atheroprotective effect in Ldlr(-/-) mice. This nanoformulation significantly decreased the atherosclerotic lesion area at the aortic sinus, compared with that in untreated mice. In addition, the Il1b mRNA expression and CD14 protein expression were downregulated in the atherosclerotic lesions at the aortic arch of Ldlr(-/-) mice treated with scFv anti-LDL(-)-MCMN-Zn. Thus, the scFv anti-LDL(-)-MCMN-Zn nanoformulation inhibited the progression of atherosclerotic lesions, indicating its potential use in a future therapeutic strategy for atherosclerosis.

Smooth Muscle Cell-Derived Interleukin-17C Plays an Atherogenic Role via the Recruitment of Proinflammatory Interleukin-17A+ T Cells to the Aorta

OBJECTIVE

Atherosclerosis is characterized by frequent communication between infiltrating leukocytes and vascular cells, through chemokine and cytokine networks. Interleukin-17C (IL-17C) is detectable within atherosclerotic lesions; however, the potential involvement of this cytokine has not been examined. Thus, we sought to investigate the role of IL-17C in atherosclerosis.

APPROACH AND RESULTS

The expression of IL-17 cytokines was profiled within aortas of apolipoprotein E double knockout (Apoe(-/-)) mice, and Il17c expression was elevated. Flow cytometry experiments revealed a major population of aortic IL-17C-producing smooth muscle cells. Next, we generated Il17c(-/-)Apoe(-/-) mice and demonstrated that atherosclerotic lesion and collagen content was diminished within Western diet-fed Il17c(-/-)Apoe(-/-) aortas and aortic roots in comparison to Apoe(-/-) controls. Smooth muscle cells and fibroblasts were mainly responsible for the reduced Col1A1 expression in the aorta of Il17c(-/-)Apoe(-/-) mice. Importantly, IL-17C-treated Apoe(-/-) aortas showed upregulated Col1A1 expression ex vivo. Il17c(-/-)Apoe(-/-) mice displayed a proportional reduction in aortic macrophages, neutrophils, T cells, T helper 1 cells, and T regulatory cells, without corresponding changes in the peripheral immune composition. Examination of aortic IL-17A(+) T-cell receptor γδ T cells and Th17 cells demonstrated a stark reduction in the percentage and number of these subsets within Il17c(-/-)Apoe(-/-) versus Apoe(-/-) mice. Explanted 12-week Western diet-fed Apoe(-/-) aortas treated with IL-17C resulted in the induction of multiple vascular chemokines and cytokines. Th17 cells demonstrated attenuated migration toward supernatants from cultures of Il17c(-/-)Apoe(-/-) smooth muscle cells, and short-term homing experiments revealed diminished recruitment of Th17 cells to the aorta of Il17c(-/-)Apoe(-/-) recipients.

CONCLUSIONS

Smooth muscle cell-derived IL-17C plays a proatherogenic role by supporting the recruitment of Th17 cells to atherosclerotic lesions.

Th17/Treg Imbalance Induced by Dietary Salt Variation Indicates Inflammation of Target Organs in Humans

The functions of T helper 17 (Th17) and regulatory T (Treg) cells are tightly orchestrated through independent differentiation pathways that are involved in the secretion of pro- and anti-inflammatory cytokines induced by high-salt dietary. However, the role of imbalanced Th17/Treg ratio implicated in inflammation and target organ damage remains elusive. Here, by flow cytometry analysis, we demonstrated that switching to a high-salt diet resulted in decreased Th17 cells and reciprocally increased Treg cells, leading to a decreased Th17/Treg ratio. Meanwhile, Th17-related pathway was down-regulated after one day of high salt loading, with the increase in high salt loading as shown by microarray and RT-PCR. Subsequently, blood oxygen level-dependent magnetic resonance imaging (BOLD-MRI) observed hypoxia in the renal medulla (increased R2^* signal) during high-salt loading, which was regressed to its baseline level in a step-down fashion during low-salt feeding. The flow-mediated vasodilatation (FMD) of the branchial artery was significantly higher on the first day of high salt loading. Collectively, these observations indicate that a short-term increase in dietary salt intake could induce reciprocal switches in Th17/Treg ratio and related cytokines, which might be the underlying cellular mechanism of high-salt dietary induced end organ inflammation and potential atherosclerotic risk.

Innate sensing of oxidation-specific epitopes in health and disease

Ageing, infections and inflammation result in oxidative stress that can irreversibly damage cellular structures. The oxidative damage of lipids in membranes or lipoproteins is one of these deleterious consequences that not only alters lipid function but also leads to the formation of neo-self epitopes - oxidation-specific epitopes (OSEs) - which are present on dying cells and damaged proteins. OSEs represent endogenous damage-associated molecular patterns that are recognized by pattern recognition receptors and the proteins of the innate immune system, and thereby enable the host to sense and remove dangerous biological waste and to maintain homeostasis. If this system is dysfunctional or overwhelmed, the accumulation of OSEs can trigger chronic inflammation and the development of diseases, such as atherosclerosis and age-related macular degeneration. Understanding the molecular components and mechanisms that are involved in this process will help to identify individuals with an increased risk of developing chronic inflammation, and will also help to indicate novel modes of therapeutic intervention.

Lipid signaling and lipotoxicity in metaflammation: indications for metabolic disease pathogenesis and treatment

Lipids encompass a wide variety of molecules such as fatty acids, sterols, phospholipids, and triglycerides. These molecules represent a highly efficient energy resource and can act as structural elements of membranes or as signaling molecules that regulate metabolic homeostasis through many mechanisms. Cells possess an integrated set of response systems to adapt to stresses such as those imposed by nutrient fluctuations during feeding-fasting cycles. While lipids are pivotal for these homeostatic processes, they can also contribute to detrimental metabolic outcomes. When metabolic stress becomes chronic and adaptive mechanisms are overwhelmed, as occurs during prolonged nutrient excess or obesity, lipid influx can exceed the adipose tissue storage capacity and result in accumulation of harmful lipid species at ectopic sites such as liver and muscle. As lipid metabolism and immune responses are highly integrated, accumulation of harmful lipids or generation of signaling intermediates can interfere with immune regulation in multiple tissues, causing a vicious cycle of immune-metabolic dysregulation. In this review, we summarize the role of lipotoxicity in metaflammation at the molecular and tissue level, describe the significance of anti-inflammatory lipids in metabolic homeostasis, and discuss the potential of therapeutic approaches targeting pathways at the intersection of lipid metabolism and immune function.

Systematic Evaluation of the Cellular Innate Immune Response During the Process of Human Atherosclerosis

Background

The concept of innate immunity is well recognized within the spectrum of atherosclerosis, which is primarily dictated by macrophages. Although current insights to this process are largely based on murine models, there are fundamental differences in the atherosclerotic microenvironment and associated inflammatory response relative to humans. In this light, we characterized the cellular aspects of innate immune response in normal, nonprogressive, and progressive human atherosclerotic plaques.

Methods and Results

A systematic analysis of innate immune response was performed on 110 well‐characterized human perirenal aortic plaques with immunostaining for specific macrophage subtypes (M1 and M2 lineage) and their activation markers, neopterin and human leukocyte antigen–antigen D related (HLA‐DR), together with dendritic cells (DCs), natural killer (NK) cells, mast cells, neutrophils, and eosinophils. Normal aortae were devoid of low‐density lipoprotein, macrophages, DCs, NK cells, mast cells, eosinophils, and neutrophils. Early, atherosclerotic lesions exhibited heterogeneous populations of (CD68⁺) macrophages, whereby 25% were double positive “M1” (CD68⁺/ inducible nitric oxide synthase [iNOS]⁺/CD163⁻), 13% “M2” double positive (CD68⁺/iNOS⁻/CD163⁺), and 17% triple positive for (M1) iNOS (M2)/CD163 and CD68, with the remaining (≈40%) only stained for CD68. Progressive fibroatheromatous lesions, including vulnerable plaques, showed increasing numbers of NK cells and fascin‐positive cells mainly localized to the media and adventitia whereas the M1/M2 ratio and level of macrophage activation (HLA‐DR and neopterin) remained unchanged. On the contrary, stabilized (fibrotic) plaques showed a marked reduction in macrophages and cell activation with a concomitant decrease in NK cells, DCs, and neutrophils.

Conclusions

Macrophage “M1” and “M2” subsets, together with fascin‐positive DCs, are strongly associated with progressive and vulnerable atherosclerotic disease of human aorta. The observations here support a more complex theory of macrophage heterogeneity than the existing paradigm predicated on murine data and further indicate the involvement of (poorly defined) macrophage subtypes or greater dynamic range of macrophage plasticity than previously considered.

Smooth Muscle Cell Foam Cell Formation, Apolipoproteins, and ABCA1 in Intracranial Aneurysms: Implications for Lipid Accumulation as a Promoter of Aneurysm Wall Rupture

Saccular intracranial aneurysm (sIA) aneurysm causes intracranial hemorrhages that are associated with high mortality. Lipid accumulation and chronic inflammation occur in the sIA wall. A major mechanism for lipid clearance from arteries is adenosine triphosphate-binding cassette A1 (ABCA1)-mediated lipid efflux from foam cells to apolipoprotein A-I (apoA-I). We investigated the association of wall degeneration, inflammation, and lipid-related parameters in tissue samples of 16 unruptured and 20 ruptured sIAs using histology and immunohistochemistry. Intracellular lipid accumulation was associated with wall remodeling (p = 0.005) and rupture (p = 0.020). Foam cell formation was observed in smooth muscle cells, in addition to CD68- and CD163-positive macrophages. Macrophage infiltration correlated with intracellular lipid accumulation and apolipoproteins, including apoA-I. ApoA-I correlated with markers of lipid accumulation and wall degeneration (p = 0.01). ApoA-I-positive staining colocalized with ABCA1-positive cells particularly in sIAs with high number of smooth muscle cells (p = 0.003); absence of such colocalization was associated with wall degeneration (p = 0.017). Known clinical risk factors for sIA rupture correlated inversely with apoA-I. We conclude that lipid accumulation associates with sIA wall degeneration and risk of rupture, possibly via formation of foam cells and subsequent loss of mural cells. Reduced removal of lipids from the sIA wall via ABCA1-apoA-I pathway may contribute to this process.

Atherosclerosis: the interplay between lipids and immune cells

PURPOSE OF REVIEW

Cardiovascular disease is the leading cause of mortality worldwide. The underlying cause of the majority of cardiovascular disease is atherosclerosis. In the past, atherosclerosis was considered to be the result of passive lipid accumulation in the vessel wall. However, today's picture of the pathogenesis of atherosclerosis is much more complex, with a key role for immune cells and inflammation in conjunction with hyperlipidemia, especially elevated (modified) LDL levels. Knowledge on immune cells and immune responses in atherosclerosis has progressed tremendously over the past decades, and the same is true for the role of lipid metabolism and the different lipid components. However, it is largely unknown how lipids and the immune system interact. In this review, we will describe the effect of lipids on immune cell development and function, and the effects of immune cells on lipid metabolism.

RECENT FINDINGS

Recently, novel data have emerged that show that immune cells are affected, and behave differently in a hyperlipidemic environment. Moreover, immune cells have reported to be able to affect lipid metabolism.

SUMMARY

In this review, we will summarize the latest findings on the interactions between lipids and the immune system, and we will discuss the potential consequences of these novel insights for future therapies for atherosclerosis.

T Cell CX3CR1 Mediates Excess Atherosclerotic Inflammation in Renal Impairment

Reduced kidney function increases the risk for atherosclerosis and cardiovascular death. Leukocytes in the arterial wall contribute to atherosclerotic plaque formation. We investigated the role of fractalkine receptor CX3CR1 in atherosclerotic inflammation in renal impairment. Apoe(-/-) (apolipoprotein E) CX3CR1(-/-) mice with renal impairment were protected from increased aortic atherosclerotic lesion size and macrophage accumulation. Deficiency of CX3CR1 in bone marrow, only, attenuated atherosclerosis in renal impairment in an independent atherosclerosis model of LDL receptor-deficient (LDLr(-/-)) mice as well. Analysis of inflammatory leukocytes in atherosclerotic mixed bone-marrow chimeric mice (50% wild-type/50% CX3CR1(-/-) bone marrow into LDLr(-/-) mice) showed that CX3CR1 cell intrinsically promoted aortic T cell accumulation much more than CD11b(+)CD11c(+) myeloid cell accumulation and increased IL-17-producing T cell counts. In vitro, fewer TH17 cells were obtained from CX3CR1(-/-) splenocytes than from wild-type splenocytes after polarization with IL-6, IL-23, and TGFβ Polarization of TH17 or TREG cells, or stimulation of splenocytes with TGFβ alone, increased T cell CX3CR1 reporter gene expression. Furthermore, TGFβ induced CX3CR1 mRNA expression in wild-type cells in a dose- and time-dependent manner. In atherosclerotic LDLr(-/-) mice, CX3CR1(+/-) T cells upregulated CX3CR1 and IL-17A production in renal impairment, whereas CX3CR1(-/-) T cells did not. Transfer of CX3CR1(+/-) but not Il17a(-/-) T cells into LDLr(-/-)CX3CR1(-/-) mice increased aortic lesion size and aortic CD11b(+)CD11c(+) myeloid cell accumulation in renal impairment. In summary, T cell CX3CR1 expression can be induced by TGFβ and is instrumental in enhanced atherosclerosis in renal impairment.

BCG lowers plasma cholesterol levels and delays atherosclerotic lesion progression in mice

BACKGROUND AND AIMS

Bacille-Calmette-Guérin (BCG), prepared from attenuated live Mycobacterium bovis, modulates atherosclerosis development as currently explained by immunomodulatory mechanisms. However, whether BCG is pro- or anti-atherogenic remains inconclusive as the effect of BCG on cholesterol metabolism, the main driver of atherosclerosis development, has remained underexposed in previous studies. Therefore, we aimed to elucidate the effect of BCG on cholesterol metabolism in addition to inflammation and atherosclerosis development in APOE*3-Leiden.CETP mice, a well-established model of human-like lipoprotein metabolism.

METHODS

Hyperlipidemic APOE*3-Leiden.CETP mice were fed a Western-type diet containing 0.1% cholesterol and were terminated 6 weeks after a single intravenous injection with BCG (0.75 mg; 5 × 10(6) CFU).

RESULTS

BCG-treated mice exhibited hepatic mycobacterial infection and hepatomegaly. The enlarged liver (+53%, p = 0.001) coincided with severe immune cell infiltration and a higher cholesterol content (+31%, p = 0.03). Moreover, BCG reduced plasma total cholesterol levels (-34%, p = 0.003), which was confined to reduced nonHDL-cholesterol levels (-36%, p = 0.002). This was due to accelerated plasma clearance of cholesterol from intravenously injected [(14)C]cholesteryl oleate-labelled VLDL-like particles (t½ -41%, p = 0.002) as a result of elevated hepatic uptake (+25%, p = 0.05) as well as reduced intestinal cholestanol and plant sterol absorption (up to -37%, p = 0.003). Ultimately, BCG decreased foam cell formation of peritoneal macrophages (-18%, p = 0.02) and delayed atherosclerotic lesion progression in the aortic root of the heart. BCG tended to decrease atherosclerotic lesion area (-59%, p = 0.08) and reduced lesion severity.

CONCLUSIONS

BCG reduces plasma nonHDL-cholesterol levels and delays atherosclerotic lesion formation in hyperlipidemic mice.

CCR5+T-bet+FoxP3+ Effector CD4 T Cells Drive Atherosclerosis

RATIONALE

CD4 T cells are involved in the pathogenesis of atherosclerosis, but atherosclerosis-specific CD4 T cells have not been described. Moreover, the chemokine(s) that regulates T-cell trafficking to the atherosclerotic lesions is also unknown.

OBJECTIVE

In Apoe(-/-) mice with mature atherosclerotic lesions (5 months of high fat diet), we find that most aortic T cells express CCR5 and interferon-γ with a unique combination of cell surface markers (CD4(+)CD25(-)CD44(hi)CD62L(lo)) and transcription factors (FoxP3(+)T-bet(+)). We call these cells CCR5Teff. We investigated the role of CCR5 in regulating T-cell homing to the atherosclerotic aorta and the functionality of the CCR5Teff cells.

METHODS AND RESULTS

CCR5Teff cells are exclusively found in the aorta and para-aortic lymph nodes of Apoe(-/-) mice. They do not suppress T-cell proliferation in vitro and are less potent than regulatory T cells at inhibiting cytokine secretion. Blocking or knocking out CCR5 or its ligand CCL5 significantly blocks T-cell homing to atherosclerotic aortas. Transcriptomic analysis shows that CCR5Teff cells are more similar to effector T cells than to regulatory T cells. They secrete interferon-γ, interleukin-2, interleukin-10, and tumor necrosis factor. Adoptive transfer of these CCR5Teff cells significantly increases atherosclerosis.

CONCLUSIONS

CCR5 is specifically needed for CD4 T-cell homing to the atherosclerotic plaques. CCR5(+)CD4 T cells express an unusual combination of transcription factors, FoxP3 and T-bet. Although CCR5Teff express FoxP3, we showed that they are not regulatory and adoptive transfer of these cells exacerbates atherosclerosis.

The Effect of a High-Fat Diet on Brain Plasticity, Inflammation and Cognition in Female ApoE4-Knockin and ApoE-Knockout Mice

Apolipoprotein E4 (ApoE4), one of three common isoforms of ApoE, is a major risk factor for late-onset Alzheimer disease (AD). ApoE-deficient mice, as well as mice expressing human ApoE4, display impaired learning and memory functions and signs of neurodegeneration. Moreover, ApoE protects against high-fat (HF) diet induced neurodegeneration by its role in the maintenance of the integrity of the blood-brain barrier. The influence of a HF diet on the progression of AD-like cognitive and neuropathological changes was assessed in wild-type (WT), human ApoE4 and ApoE-knockout (ApoE^-/-) mice to evaluate the modulatory role of ApoE in this process. From 12 months of age, female WT, ApoE4, and ApoE^-/- mice were fed either a standard or a HF diet (19% butter, 0.5% cholate, 1.25% cholesterol) throughout life. At 15 months of age mice performed the Morris water maze, evaluating spatial learning and memory. ApoE^-/- showed increased spatial learning compared to WT mice (p = 0.009). HF diet improved spatial learning in WT mice (p = 0.045), but did not affect ApoE4 and ApoE^-/- mice. Immunohistochemical analyses of the hippocampus demonstrated increased neuroinflammation (CD68) in the cornu ammonis 1 (CA1) region in ApoE4 (p = 0.001) and in ApoE^-/- (p = 0.032) mice on standard diet. HF diet tended to increase CD68 in the CA1 in WT mice (p = 0.052), while it decreased in ApoE4 (p = 0.009), but ApoE^-/- remained unaffected. A trend towards increased neurogenesis (DCX) was found in both ApoE4 (p = 0.052) and ApoE^-/- mice (p = 0.068). In conclusion, these data suggest that HF intake induces different effects in WT mice compared to ApoE4 and ApoE^-/- with respect to markers for cognition and neurodegeneration. We propose that HF intake inhibits the compensatory mechanisms of neuroinflammation and neurogenesis in aged female ApoE4 and ApoE^-/- mice.

Expansion of CD8(+) T cells lacking the IL-6 receptor α chain in patients with coronary artery diseases (CAD)

BACKGROUND AND AIMS

The pathogenesis of coronary artery disease (CAD) is closely associated with chronic inflammatory processes. CD8(+) T cells are a key participant in the pathogenesis of atherosclerosis, the major cause of CAD; however, it remains unclear which CD8(+) T-cell subset is responsible. We investigated the immunological features of CD8(+) T cells expressing low and high levels of the IL-6 receptor α chain (IL-6Rα), a cytokine known to play a key role in cardiovascular diseases.

METHODS

The expression of IL-6Rα on CD8(+) T cells and its association with plasma levels of soluble components of the IL-6/IL-6Rs as well as with clinical parameters were analyzed using FACS analysis and ELISA of CAD patients and age-matched healthy controls (HCs). Immunological characteristics of CD8(+) T cells expressing low and high levels of IL-6Rα (CD8(+)IL-6Rα(low or high)) were examined by in vitro culture and intracellular FACS analysis.

RESULTS

CAD patients had higher frequencies of circulating CD8(+)IL-6Rα(low) effector memory (EM) T cells compared with HCs (median frequency; 74.59% vs. 60.09%, p = 0.0158). Expanded CD8(+)IL-6Rα(low) T cells positively correlated with the frequency of senescent, cytotoxic CD8(+)CD57(+) T cells (r = 0.6655, p < 0.0001) and plasma IL-6 level (r = 0.3995, p = 0.0432) in CAD patients. Loss of IL-6Rα expression on CD8(+) T cells was induced by the combination of IL-6 and IL-15 with accompanying TCR-independent proliferation (p = 0.0101). Moreover, these CD8(+)IL-6Rα(low) T cells had features of type 1 cytotoxic CD8(+) T cells.

CONCLUSIONS

Our findings suggest the possible involvement of expanded CD8(+)IL-6Rα(low) EM T cells in CAD through their pro-inflammatory and highly cytotoxic capacities.

Atherosclerosis--do we know enough already to prevent it?

In this review, we have briefly summarized the characteristics of lipids and lipoproteins and the atherosclerotic process. The development of atherosclerosis is a continuous process that involves numerous cellular and acellular processes that influence the behavior of each other. These include oxidative stress, lipoprotein modifications, macrophage polarization, macrophage lipid accumulation, generation of pro- and anti-inflammatory components, calcification, cellular growth and proliferation, and plaque rupture. The precise role(s) of many of these are unknown. Understanding the events at each particular stage might shed more light onto the process as a whole and could potentially reveal targets for intervention. Therapeutic modalities that work at one stage may have little to no influence on other stages of the disease.

Therapeutic potential of the dual peroxisome proliferator activated receptor (PPAR)α/γ agonist aleglitazar in attenuating TNF-α-mediated inflammation and insulin resistance in human adipocytes

Adipose tissue inflammation is a mechanistic link between obesity and its related sequelae, including insulin resistance and type 2 diabetes. Dual ligands of peroxisome proliferator activated receptor (PPAR)α and γ, combining in a single molecule the metabolic and inflammatory-regulatory properties of α and γ agonists, have been proposed as a promising therapeutic strategy to antagonize adipose tissue inflammation. Here we investigated the effects of the dual PPARα/γ agonist aleglitazar on human adipocytes challenged with inflammatory stimuli. Human Simpson-Golabi-Behmel syndrome (SGBS) adipocytes were treated with aleglitazar or - for comparison - the selective agonists for PPARα or γ fenofibrate or rosiglitazone, respectively, for 24h before stimulation with TNF-α. Aleglitazar, at concentrations as low as 10nmol/L, providing the half-maximal transcriptional activation of both PPARα and PPARγ, reduced the stimulated expression of several pro-inflammatory mediators including interleukin (IL)-6, the chemokine CXC-L10, and monocyte chemoattractant protein (MCP)-1. Correspondingly, media from adipocytes treated with aleglitazar reduced monocyte migration, consistent with suppression of MCP-1 secretion. Under the same conditions, aleglitazar also reversed the TNF-α-mediated suppression of insulin-stimulated ser473 Akt phosphorylation and decreased the TNF-α-induced ser312 IRS1 phosphorylation, two major switches in insulin-mediated metabolic activities, restoring glucose uptake in insulin-resistant adipocytes. Such effects were similar to those obtainable with a combination of single PPARα and γ agonists. In conclusion, aleglitazar reduces inflammatory activation and dysfunction in insulin signaling in activated adipocytes, properties that may benefit diabetic and obese patients. The effect of aleglitazar was consistent with dual PPARα and γ agonism, but with no evidence of synergism.

Apolipoprotein B-100 Antibody Interaction With Atherosclerotic Plaque Inflammation and Repair Processes

BACKGROUND AND PURPOSE

Treatment with IgG against the malondialdehyde (MDA)-modified apolipoprotein B-100 epitope p45 reduces atherosclerosis in experimental models. This study investigated the association between p45 IgG autoantibodies and plaque inflammation in subjects with advanced cardiovascular disease.

METHODS

Native and MDA-p45 IgG levels were analyzed by ELISA in 349 carotid endarterectomy patients. In a subcohort of 195 subjects, endarterectomy samples were analyzed by immunohistochemistry and ELISA to determine plaque constituents and inflammation. Peripheral blood mononuclear cells were isolated from healthy donors.

RESULTS

Patients with preoperative events of neurological ischemia had lower levels of native p45 IgG. Low levels of MDA-p45 IgG were associated with increased risk of postoperative cardiovascular death during a mean follow-up of 54 months. High plasma levels of native p45 IgG were associated with increased plaque content of collagen and smooth muscle cell growth factors, as well as with lower levels of proinflammatory cytokines. Exposure of peripheral blood mononuclear cells from healthy donors to recombinant MDA-p45 IgG in presence of oxidized low-density lipoprotein reduced the expression of tumor necrosis factor-α and stimulated release of smooth muscle cell growth factors.

CONCLUSIONS

This study confirms previous experimental findings of anti-inflammatory properties of apolipoprotein B-100 p45 antibodies and provides the first clinical evidence of associations between p45 IgG autoantibody levels and atherosclerotic plaque inflammation, plaque repair as well as prevalent and incident cardiovascular events in carotid endarterectomy patients. These findings suggest the possibility that treatment with anti-p45 antibodies may have beneficial effects in advanced cardiovascular disease.

Serum monokine induced by gamma interferon as a novel biomarker for coronary artery calcification in humans

BACKGROUND

T-cell-mediated immune responses play important roles in the progression of atherosclerotic disease. Studies have linked various inflammatory biomarkers with the burden of coronary artery calcification, but the significance of T-cell-specific chemokines in coronary artery calcification has not been confirmed. We aimed to examine the association between serum levels of the monokine induced by gamma interferon (MIG) and the coronary artery calcium score (CACS).

METHODS

We enrolled 456 individuals (285 men, 66.5±5.8 years) who were registered in the Mapo-gu public health center cohort. We selected 228 individuals with a CACS of more than 100 and 228 age-matched and sex-matched individuals with a CACS of less than 100. All participants underwent coronary computed tomography for CACS measuring. Clinical and laboratory variables including serum MIG levels were analyzed at the time of enrollment.

RESULTS

The serum level of MIG was significantly higher in participants with a CACS of more than 100 (152.1±119.1 vs. 130.3±112.9, P=0.046). Serum MIG levels correlated significantly with CACS (r=0.113, P=0.016), and higher levels of MIG were associated with severe plaque burden (CACS>400, P=0.025). Multiple linear regression analysis showed that serum MIG levels were associated independently with CACS after controlling for confounding factors and medications (β=0.114, P=0.026).

CONCLUSION

Serum MIG levels were associated independently with CACS after adjusting for traditional cardiovascular risk factors. These findings suggest that MIG may be used as a novel biomarker for T-cell inflammation and atherosclerotic plaque burden in humans.

Extracellular vesicles as mediators of vascular inflammation in kidney disease

Vascular inflammation is a common cause of renal impairment and a major cause of morbidity and mortality of patients with kidney disease. Current studies consistently show an increase of extracellular vesicles (EVs) in acute vasculitis and in patients with atherosclerosis. Recent research has elucidated mechanisms that mediate vascular wall leukocyte accumulation and differentiation. This review addresses the role of EVs in this process. Part one of this review addresses functional roles of EVs in renal vasculitis. Most published data address anti-neutrophil cytoplasmic antibody (ANCA) associated vasculitis and indicate that the number of EVs, mostly of platelet origin, is increased in active disease. EVs generated from neutrophils by activation by ANCA can contribute to vessel damage. While EVs are also elevated in other types of autoimmune vasculitis with renal involvement such as systemic lupus erythematodes, functional consequences beyond intravascular thrombosis remain to be established. In typical hemolytic uremic syndrome secondary to infection with shiga toxin producing Escherichia coli, EV numbers are elevated and contribute to toxin distribution into the vascular wall. Part two addresses mechanisms how EVs modulate vascular inflammation in atherosclerosis, a process that is aggravated in uremia. Elevated numbers of circulating endothelial EVs were associated with atherosclerotic complications in a number of studies in patients with and without kidney disease. Uremic endothelial EVs are defective in induction of vascular relaxation. Neutrophil adhesion and transmigration and intravascular thrombus formation are critically modulated by EVs, a process that is amenable to therapeutic interventions. EVs can enhance monocyte adhesion to the endothelium and modulate macrophage differentiation and cytokine production with major influence on the local inflammatory milieu in the plaque. They significantly influence lipid phagocytosis and antigen presentation by mononuclear phagocytes. Finally, platelet, erythrocyte and monocyte EVs cooperate in shaping adaptive T cell immunity. Future research is needed to define changes in uremic EVs and their differential effects on inflammatory leukocytes in the vessel wall.

Role of neutrophils in atherogenesis: an update

BACKGROUND

The role of neutrophils in the beginning and the progression of the atherosclerotic process did not receive much attention until the last years. On the contrary, recent data, in both the experimental animals and humans, suggest important effects of these cells with possible clinical consequences.

MATERIALS AND METHODS

This narrative review was based on the papers found on PubMed and MEDLINE up to July 2015. The search terms used were 'neutrophil, atherosclerosis' in combination with 'recruitment, chemokine, plaque destabilization and pathophysiology'.

RESULTS

Different models demonstrate the presence and the actions of neutrophils in the early steps of the atherogenesis confirming the fundamental role of these cells in the response of the innate immune system to different pathogens (in this context the modified lipoproteins). However, also the late phases of the atherosclerotic process, in particular the destabilization of a mature plaque, seem to be modulated by the neutrophils, possibly through the interaction with recently discovered biological systems such as the endocannabinoids.

CONCLUSIONS

The understanding of the mechanisms involved in the modulation exerted by neutrophils in atherosclerosis is pivotal in terms of the complete definition of the overall picture. This approach will certainly give us new targets and new pharmacological opportunities for the anti-inflammatory strategy of the cardiovascular prevention.

Inhibition of Orai1 Store-Operated Calcium Channel Prevents Foam Cell Formation and Atherosclerosis

OBJECTIVE

To determine the role of orai1 store-operated Ca(2+) entry in foam cell formation and atherogenesis.

APPROACH AND RESULTS

Acute administration of oxidized low-density lipoprotein (oxLDL) activates an orai1-dependent Ca(2+) entry in macrophages. Chelation of intracellular Ca(2+), inhibition of orai1 store-operated Ca(2+) entry, or knockdown of orai1 dramatically inhibited oxLDL-induced upregulation of scavenger receptor A, uptake of modified LDL, and foam cell formation. Orai1-dependent Ca(2+) entry induces scavenger receptor A expression and foam cell formation through activation of calcineurin but not calmodulin kinase II. Activation of nuclear factor of activated T cells is not involved in calcineurin signaling to foam cell formation. However, oxLDL dephosohorylates and activates apoptosis signal-regulating kinase 1 in macrophages. Orai1 knockdown prevents oxLDL-induced apoptosis signal-regulating kinase 1 activation. Knockdown of apoptosis signal-regulating kinase 1, or inhibition of its downstream effectors, JNK and p38 mitogen-activated protein kinase, reduces scavenger receptor A expression and foam cell formation. Notably, orai1 expression is increased in atherosclerotic plaques of apolipoprotein E(-/-) mice fed with high-cholesterol diet. Knockdown of orai1 with adenovirus harboring orai1 siRNA or inhibition of orai1 Ca(2+) entry with SKF96365 for 4 weeks dramatically inhibits atherosclerotic plaque development in high-cholesterol diet feeding apolipoprotein E(-/-) mice. In addition, inhibition of orai1 Ca(2+) entry prevents macrophage apoptosis in atherosclerotic plaque. Moreover, the expression of inflammatory genes in atherosclerotic lesions and the infiltration of myeloid cells into the aortic sinus plaques are decreased after blocking orai1 signaling.

CONCLUSIONS

Orai1-dependent Ca(2+) entry promotes atherogenesis possibly by promoting foam cell formation and vascular inflammation, rendering orai1 Ca(2+) channel a potential therapeutic target against atherosclerosis.

Differences in Hypercholesterolemia and Atherogenesis Induced by Common Androgen Deprivation Therapies in Male Mice

BACKGROUND

Treatment of prostate cancer often involves androgen deprivation therapy (ADT) by gonadotropin-releasing hormone (GnRH) receptor agonists, GnRH receptor antagonists, or orchiectomy. ADT may increase the rate of cardiovascular disease events, but recent clinical studies suggested that not all means of ADT carry the same risk, raising the possibility of non-testosterone-mediated effects of different forms of ADT on atherosclerosis. Here we compared effects of ADT on atherosclerosis in intact and orchiectomized Apoe-deficient mice.

METHODS AND RESULTS

Chow-fed Apoe-deficient mice were allocated to orchiectomy and/or monthly injections with the GnRH receptor agonist leuprolide or the GnRH receptor antagonist degarelix. Atherosclerosis was quantified at 26 weeks of age in the aortic arch by en face examination and in the aortic root by histology. In intact Apoe-deficient mice, all types of ADT reduced testosterone production to castration levels. Although hypercholesterolemia was accentuated in leuprolide-treated mice, the amount and composition of atherosclerosis was not different between the different types of ADT. In orchiectomized Apoe-deficient mice, leuprolide, but not degarelix, augmented hypercholesterolemia, changed body, thymus, and spleen weights, and increased atherosclerosis in the aortic root. No direct effects of the drugs were detectable on cytokine secretion from murine bone marrow-derived macrophages or on splenocyte proliferation.

CONCLUSIONS

No differences in the development of atherosclerosis were detected among groups of intact Apoe-deficient mice treated with different types of ADT. A pro-atherogenic, possibly cholesterol-mediated, effect of leuprolide was seen in orchiectomized mice that might be relevant for understanding the potential cardiovascular risk associated with GnRH agonist-based ADT.

Critical role of the C5a-activated neutrophils in high-fat diet-induced vascular inflammation

Exceed and chronic high-fat diet (HFD) contributes to the diagnosis and development of atherosclerosis, obesity, and metabolic syndrome. However, the key molecular component(s) triggered by HFD responsible for initiating vascular inflammation remain unknown. We observed that feeding HFD for 4 weeks is sufficient to induce leukocyte recruitment in the femoral artery of wild-type mice. Neutrophil- and monocyte-depletion analyses confirmed the preferential recruitment of neutrophils in these mice. Protein analysis of sera from HFD-fed mice revealed a marked elevation of complement component C5a levels. Exogenous C5a alone induced leukocyte recruitment, which was abolished by a C5a-receptor antagonist. We also examined the role of neutrophil-derived MCP-1 in accumulation of leukocytes in the artery. These results demonstrated a previously unrecognized role for C5a and neutrophils in the early onset of HFD-induced vascular inflammation. Further study may help in elucidating a novel regulatory pathway to control diet-induced inflammation such as that in case of atherosclerosis.

Plaque Size Is Decreased but M1 Macrophage Polarization and Rupture Related Metalloproteinase Expression Are Maintained after Deleting T-Bet in ApoE Null Mice

Background

Thelper1 (Th1) lymphocytes have been previously implicated in atherosclerotic plaque growth but their role in plaque vulnerability to rupture is less clear. We investigated whether T-bet knockout that prevents Th1 lymphocyte differentiation modulates classical (M1) macrophage activation or production of matrix degrading metalloproteinases (MMPs) and their tissue inhibitors, TIMPs.

Methods & Results

We studied the effect of T-bet deletion in apolipoproteinE (ApoE) knockout mice fed a high fat diet (HFD) or normal chow diet (ND). Transcript levels of M1/M2 macrophage polarization markers, selected MMPs and TIMPs were measured by RT-qPCR in macrophages isolated from subcutaneous granulomas or in whole aortae. Immunohistochemistry of aortic sinus (AS) and brachiocephalic artery (BCA) plaques was conducted to quantify protein expression of the same factors.

Deletion of T-bet decreased mRNA for the M1 marker NOS-2 in granuloma macrophages but levels of M2 markers (CD206, arginase-1 and Ym-1), MMPs-2, -9, -12, -13, -14 and -19 or TIMPs-1 to -3 were unchanged. No mRNA differences were observed in aortic extracts from mice fed a HFD for 12 weeks. Moreover, AS and BCA plaques were similarly sized between genotypes, and had similar areas stained for NOS-2, COX-2, MMP-12 and MMP-14 proteins. T-bet deletion increased MMP-13, MMP-14 and arginase-1 in AS plaques. After 35 weeks of ND, T-bet deletion reduced the size of AS and BCA plaques but there were no differences in the percentage areas stained for M1 or M2 markers, MMPs-12, -13, -14, or TIMP-3.

Conclusions

Absence of Th1 lymphocytes is associated with reduced plaque size in ApoE knockout mice fed a normal but not high fat diet. In either case, M1 macrophage polarization and expression of several MMPs related to plaque instability are either maintained or increased.

A Translational Model for Diet-related Atherosclerosis: Effect of Statins on Hypercholesterolemia and Atherosclerosis in a Minipig

Models of atherosclerosis are used in preclinical studies but often fail to translate to humans. A model that better reflects human atherosclerosis is necessary. We recently engineered the ExeGen™ low-density lipoprotein receptor (LDLR) miniswine, in which the LDL receptor gene is modified to drive hypercholesterolemia and atherosclerosis, and showed diet-related exacerbation of these phenotypes. Five groups of animals, either wild type (+/+) or heterozygous (+/-), were fed either a normal or high-fat diet for 6 months. One group of heterozygous pigs fed a high-fat diet was also administered atorvastatin at 3 mg/kg/day. Clinical chemistry and anatomic pathology parameters were measured biweekly and at termination. The high-fat diet resulted in increased adiposity and interspersion of adipocytes within the salivary glands. The heterozygous pigs on the high-fat diet gained more weight and had significant increases in total cholesterol, high-density lipoprotein, and LDL compared to wild-type animals or heterozygous animals fed a normal diet. Atorvastatin attenuated these parameters, indicating the statin had a beneficial effect, even in a high-fat diet scenario. Atorvastatin treatment also reduced the intensity of Oil Red O staining in pigs on high-fat diet. Atorvastatin-related amelioration of several indices of cardiovascular pathophysiology in this model underscores its utility for drug discovery.

Two-Point Stretchable Electrode Array for Endoluminal Electrochemical Impedance Spectroscopy Measurements of Lipid-Laden Atherosclerotic Plaques

Four-point electrode systems are commonly used for electric impedance measurements of biomaterials and tissues. We introduce a 2-point system to reduce electrode polarization for heterogeneous measurements of vascular wall. Presence of endoluminal oxidized low density lipoprotein (oxLDL) and lipids alters the electrochemical impedance that can be measured by electrochemical impedance spectroscopy (EIS). We developed a catheter-based 2-point micro-electrode configuration for intravascular deployment in New Zealand White rabbits. An array of 2 flexible round electrodes, 240 µm in diameter and separated by 400 µm was microfabricated and mounted on an inflatable balloon catheter for EIS measurement of the oxLDL-rich lesions developed as a result of high-fat diet-induced hyperlipidemia. Upon balloon inflation, the 2-point electrode array conformed to the arterial wall to allow deep intraplaque penetration via alternating current (AC). The frequency sweep from 10 to 300 kHz generated an increase in capacitance, providing distinct changes in both impedance (Ω) and phase (ϕ) in relation to varying degrees of intraplaque lipid burden in the aorta. Aortic endoluminal EIS measurements were compared with epicardial fat tissue and validated by intravascular ultrasound and immunohistochemistry for plaque lipids and foam cells. Thus, we demonstrate a new approach to quantify endoluminal EIS via a 2-point stretchable electrode strategy.

PKR is not obligatory for high-fat diet-induced obesity and its associated metabolic and inflammatory complications

Protein kinase R (PKR) has previously been suggested to mediate many of the deleterious consequences of a high-fat diet (HFD). However, previous studies have observed substantial phenotypic variability when examining the metabolic consequences of PKR deletion. Accordingly, herein, we have re-examined the role of PKR in the development of obesity and its associated metabolic complications in vivo as well as its putative lipid-sensing role in vitro. Here we show that the deletion of PKR does not affect HFD-induced obesity, hepatic steatosis or glucose metabolism, and only modestly affects adipose tissue inflammation. Treatment with the saturated fatty acid palmitate in vitro induced comparable levels of inflammation in WT and PKR KO macrophages, demonstrating that PKR is not necessary for the sensing of pro-inflammatory lipids. These results challenge the proposed role for PKR in obesity, its associated metabolic complications and its role in lipid-induced inflammation.

Protein kinase R (PKR) has been suggested to act as a mediator of ER stress and inflammation in obesity. Here, Lancaster et al. find that genetic loss of PKR does not alter the development of obesity, and suggest that the use of littermate controls may explain differences in mouse knockout phenotypes.

NSun2 Deficiency Protects Endothelium From Inflammation via mRNA Methylation of ICAM-1

RATIONALE

Vascular endothelial inflammation, including the expression of intercellular adhesion molecule 1 (ICAM-1), is a key event in vascular diseases. However, the mechanisms underlying the regulation of ICAM-1 are largely unknown.

OBJECTIVE

To investigate the mechanisms on the regulation of ICAM-1 by NOP2/Sun domain family, member 2 (NSun2)-mediated mRNA methylation and the impact of NSun2-ICAM-1 regulatory process in vascular inflammation and allograft arteriosclerosis.

METHODS AND RESULTS

By using in vitro, in cells, and in vivo methylation assays, we showed that the tRNA methyltransferase NSun2 methylated the ICAM-1 mRNA. Methylation by NSun2 promoted the translation of ICAM-1, thereby increasing the adhesion of leukocytes to endothelial cells. Tumor necrosis factor-α or homocysteine activated the methyltransferase activity of NSun2 by repressing the phosphorylation of NSun2 by Aurora-B. The levels of ICAM-1 induction and of leukocyte adhesion to vascular endothelium observed with homocysteine treatment in wild-type rats were markedly decreased in NSun2(-/-) rats. In a rat model of aortic allograft, the lack of donor NSun2 impaired the formation of allograft arteriosclerosis.

CONCLUSIONS

NSun2 upregulates the expression of ICAM-1 by methylating ICAM-1 mRNA. This regulatory process impacts on vascular inflammation and allograft arteriosclerosis.

Targeting T cells to treat atherosclerosis: odyssey from bench to bedside

More than 150 years from the initial description of inflammation in atherosclerotic plaques, randomized clinical trials to test anti-inflammatory therapies in atherosclerosis have recently been initiated. Lymphocytes and macrophages are main participants in the inflammatory response in atherosclerosis. T lymphocytes operate mainly by exerting strong influences on the function of many cells in the immune system and beyond, and co-ordinating their interactions. Importantly, T lymphocytes are not a homogenous population, but include several subsets with specialized functions that can either promote or suppress inflammation. The interactions between these T-lymphocyte subsets have critical consequences on the course and outcome of inflammation. The complexity of the inflammatory response in atherosclerosis poses significant challenges on translating experimental findings into clinical therapies and makes the journey from bench to bedside an arduous one. Here, we summarize recent advances on the role of CD4⁺ T cells in the inflammatory process in atherosclerosis and discuss potential therapies to modulate these lymphocytes that may provide future breakthroughs in the treatment of atherosclerosis.

Influence of pre-existing inflammation on the outcome of acute coronary syndrome: a cross-sectional study

OBJECTIVES

Inflammation is a well-established risk factor for the development of coronary artery disease (CAD) and acute coronary syndrome (ACS). However, less is known about its influence on the outcome of ACS. The aim of this study was to determine if blood biomarkers of inflammation were associated specifically with acute myocardial infarction (MI) or unstable angina (UA) in patients with ACS.

DESIGN

Cross-sectional study.

SETTING

Patients admitted to the coronary care unit, via the emergency room, at a central county hospital over a 4-year period (1992-1996).

PARTICIPANTS

In a substudy of Carlscrona Heart Attack Prognosis Study (CHAPS) of 5292 patients admitted to the coronary care unit, we identified 908 patients aged 30-74 years, who at discharge had received the diagnosis of either MI (527) or UA (381).

MAIN OUTCOME MEASURES

MI or UA, based on the diagnosis set at discharge from hospital.

RESULTS

When adjusted for smoking, age, sex and duration of chest pain, concentrations of plasma biomarkers of inflammation (high-sensitivity C reactive protein>2 mg/L (OR=1.40 (1.00 to 1.96) and fibrinogen (p for trend=0.035)) analysed at admission were found to be associated with MI over UA, in an event of ACS. A strong significant association with MI over UA was found for blood cell markers of inflammation, that is, counts of neutrophils (p for trend<0.001), monocytes (p for trend<0.001) and thrombocytes (p for trend=0.021), while lymphocyte count showed no association. Interestingly, eosinophil count (p for trend=0.003) was found to be significantly lower in patients with MI compared to those with UA.

CONCLUSIONS

Our results show that, in patients with ACS, the blood cell profile and degree of inflammation at admission was associated with the outcome. Furthermore, our data suggest that a pre-existing low-grade inflammation may dispose towards MI over UA.

Cellular Model of Atherogenesis Based on Pluripotent Vascular Wall Pericytes

Pericytes are pluripotent cells that can be found in the vascular wall of both microvessels and large arteries and veins. They have distinct morphology with long branching processes and form numerous contacts with each other and with endothelial cells, organizing the vascular wall cells into a three-dimensional network. Accumulating evidence demonstrates that pericytes may play a key role in the pathogenesis of vascular disorders, including atherosclerosis. Macrovascular pericytes are able to accumulate lipids and contribute to growth and vascularization of the atherosclerotic plaque. Moreover, they participate in the local inflammatory process and thrombosis, which can lead to fatal consequences. At the same time, pericytes can represent a useful model for studying the atherosclerotic process and for the development of novel therapeutic approaches. In particular, they are suitable for testing various substances' potential for decreasing lipid accumulation induced by the incubation of cells with atherogenic low-density lipoprotein. In this review we will discuss the application of cellular models for studying atherosclerosis and provide several examples of successful application of these models to drug research.

CD4+ CD56+ natural killer T-like cells secreting interferon-γ are associated with incident coronary events

BACKGROUND

CD3(+) CD56(+) natural killer T (NKT)-like cells are a subset of T cells characterized by expression of NK receptors and potent antitumour activity. It has also been suggested that they have a role in autoimmune disease, and levels of NKT-like cells are elevated in patients with coronary disease.

OBJECTIVES

To investigate whether high levels of CD3(+) CD56(+) NKT-like cells are associated with an increased incidence of cardiovascular disease and a lower incidence of cancer.

METHODS

This was a prospective study including 700 subjects participating in the baseline investigation of the Malmö Diet and Cancer study between 1991 and 1994. Leucocytes obtained at the baseline investigation and stored at -140 °C were thawed and CD3(+) CD56(+) cells analysed by flow cytometry. The incidence rates of cancer and coronary events during a mean follow-up of 15 years were determined through national registers.

RESULTS

Subjects in the lowest tertile of interferon (IFN)-γ-expressing CD4(+) CD56(+) cells were found to have an increased risk of incidence of coronary events (log-rank test: P < 0.05). This association remained significant after controlling for age, sex, smoking, body mass index, hypertension, diabetes and the Th1/Th2 and Th1/Treg cell ratios in a Cox proportional hazards regression model (hazard ratio 1.98, 95% confidence interval 1.24-3.16), but not when the LDL/HDL ratio was included in the model. There were no associations between CD3(+) CD56(+) NKT-like cells and incident cancer.

CONCLUSIONS

The present results could not confirm the hypothesis that low levels of CD3(+) CD56(+) NKT-like cells are associated with a higher incidence of cancer and a lower incidence of cardiovascular disease. However, we found that low levels of IFN-γ-expressing CD3(+) CD4(+) CD56(+) NKT-like cells were associated with an increased incidence of coronary events and that this association may be dependent on lipoproteins.