Decline of the atherogenic theory of the etiology of the abdominal aortic aneurysm and rise of the autoimmune hypothesis

MicroRNA-disease Network Analysis Repurposes Methotrexate for the Treatment of Abdominal Aortic Aneurysm in Mice

Abdominal aortic aneurysm (AAA) is a permanent dilatation of the abdominal aorta and is highly lethal. The main purpose of the current study is to search for noninvasive medical therapies for AAA, for which there is currently no effective drug therapy. Network medicine represents a cutting-edge technology, as analysis and modeling of disease networks can provide critical clues regarding the etiology of specific diseases and therapeutics that may be effective. Here, we proposed a novel algorithm to quantify disease relations based on a large accumulated microRNA-disease association dataset and then built a disease network covering 15 disease classes and 304 diseases. Analysis revealed some patterns for these diseases. For instance, diseases tended to be clustered and coherent in the network. Surprisingly, we found that AAA showed the strongest similarity with rheumatoid arthritis and systemic lupus erythematosus, both of which are autoimmune diseases, suggesting that AAA could be one type of autoimmune diseases in etiology. Based on this observation, we further hypothesized that drugs for autoimmune diseases could be repurposed for the prevention and therapy of AAA. Finally, animal experiments confirmed that methotrexate, a drug for autoimmune diseases, was able to alleviate the formation and development of AAA.

Micro- and Macrovascular Effects of Inflammation in Peripheral Artery Disease-Pathophysiology and Translational Therapeutic Approaches

Inflammation has a critical role in the development and progression of atherosclerosis. On the molecular level, inflammatory pathways negatively impact endothelial barrier properties and thus, tissue homeostasis. Conformational changes and destruction of the glycocalyx further promote pro-inflammatory pathways also contributing to pro-coagulability and a prothrombotic state. In addition, changes in the extracellular matrix composition lead to (peri-)vascular remodelling and alterations of the vessel wall, e.g., aneurysm formation. Moreover, progressive fibrosis leads to reduced tissue perfusion due to loss of functional capillaries. The present review aims at discussing the molecular and clinical effects of inflammatory processes on the micro- and macrovasculature with a focus on peripheral artery disease.

The presence of activating IgG Fc receptors in macrophages aggravates the development of experimental abdominal aortic aneurysm

INTRODUCTION

Abdominal aortic aneurysm (AAA) is a multifactorial, degenerative disease characterized by progressive aortic dilation and chronic activation of inflammation, proteolytic activity, and oxidative stress in the aortic wall. The immune response triggered by antibodies against antigens present in the vascular wall participates in the formation and progression of AAA through mechanisms not completely understood. This work analyses the function of specific IgG receptors (FcγR), especially those expressed by monocytes/macrophages, in the development of experimental AAA.

METHODS

In the elastase-induced AAA model, the abdominal aortas from wildtype and FcγR deficient mice with/without macrophage adoptive transfer were analysed by histology and quantitative PCR. In vitro, mouse macrophages were transfected with RNA interference of FcγRIV/CD16.2 or treated with Syk kinase inhibitor before stimulation with IgG immune complexes.

RESULTS

Macrophage adoptive transfer in FcγR deficient mice increased the susceptibility to AAA development. Mice receiving macrophages with functional FcγR exhibited higher aortic diameter increase, higher content of macrophages and B lymphocytes, and upregulated expression of chemokine CCL2, cytokines (TNF-α and IL-17), metalloproteinase MMP2, prooxidant enzyme NADPH oxidase-2, and the isoforms FcγRIII/CD16 and FcγRIV/CD16.2. In vitro, both FcγRIV/CD16.2 gene silencing and Syk inhibition reduced cytokines and reactive oxygen species production induced by immune complexes in macrophages.

CONCLUSIONS

Activation of macrophage FcγR contributes to AAA development by inducing mediators of inflammation, proteolysis, and oxidative stress. Modulation of FcγR or effector molecules may represent a potential target for AAA treatment.

Blood immunological profile of abdominal aortic aneurysm based on autoimmune injury

Abdominal aortic aneurysm (AAA) occupies a large part of aorta aneurysm, and if there's no timely intervention or treatment, the risks of rupture and death would rise sharply. With the depth of research in AAA, more and more evidence showed correlations between AAA and autoimmune injury. Currently, a variety of bioactive peptides and cells have been confirmed to be related with AAA progression. Despite the tremendous progress, more than half researches were sampling from lesion tissues, which would be difficult to obtain. Given that the intrusiveness and convenience, serological test take advantages in initial diagnosis. Here we review blood biomarkers associated with autoimmune injury work in AAA evolution, aiming to make a profile on blood immune substances of AAA and provide a thought for potential clinical practice.

The AIM2 inflammasome: A novel biomarker and target in cardiovascular disease

Absent in melanoma 2 (AIM2) is a cytoplasmic sensor that recognises the double-strand DNA. AIM2 inflammasome is a protein platform in the cell that initiates innate immune responses by cleaving pro-caspase-1 and converting IL-1β and IL-18 to their mature forms. Additionally, AIM2 inflammasome promotes pyroptosis by converting Gasdermin-D (GSDMD) to GSDMD-N fragments. An increasing number of studies have indicated the important and decisive roles of the AIM2 inflammasome, IL-1β, and pyroptosis in cardiovascular diseases, such as coronary atherosclerosis, myocardial infarction, ischaemia/reperfusion injury, heart failure, aortic aneurysm and ischaemic stroke. Here, we review the molecular mechanism of the activation and effect of the AIM2 inflammasome in cardiovascular disease, revealing new insights into pathogenic factors that may be targeted to treat cardiovascular disease and related dysfunctions.

Changes in Serum IgG Glycosylation Patterns for Abdominal Aortic Aneurysm Patients

Background: B cells and autoantibodies play an important role in the pathogenesis of abdominal aortic aneurysm (AAA). IgG glycosylations are highly valued as potential disease biomarkers and therapeutic targets. Methods: Lectin microarray was applied to analyze the expression profile of serum IgG glycosylation in 75 patients with AAA, 68 autoimmune disease controls, and 100 healthy controls. Lectin blots were performed to validate the differences. The clinical relevance of lectins binding from the microarray results was explored in AAA patients. Results: Significantly lower binding level of SBA (preferred GalNAc) was observed for the AAA group compared with DCs (p < 0.001) and HCs (p = 0.049). A significantly lower binding level of ConA (preferred mannose) was observed in patients with aneurysm diameter >5 cm. Significantly higher binding of CSA (preferred GalNAc) was present for dyslipidemia patients, whereas a lower binding level of AAL (preferred fucose) was observed for hypertensive patients. Patients with diabetes had lower binding levels of IRA (preferred GalNAc) and HPA (preferred GalNAc) compared with those not with DM. PTL-L (R = 0.36, p = 0.0015, preferred GalNAc) was positively associated with aneurysm diameters, whereas DSL (R = 0.28, p = 0.014, preferred (GlcNAc)2-4) was positively associated with patients’ age. Symptomatic patients had a lower binding level of ConA (p = 0.032), and patients with coronary heart disease had higher binding levels of STL (p = 0.0029, preferred GlcNAc). Patients with ILT bound less with black bean crude (p = 0.04, preferred GalNAc). Conclusions: AAA was associated with a decreased IgG binding level of SBA (recognizing glycan GalNAc). Symptomatic patients with aneurysm <5 cm had a higher binding level of ConA (preferred mannose). Coronary heart disease and elder age were associated with increased IgG bisecting GlcNAc. IgG O-glycosylation (GalNAc) may play an important role in AAA pathogenesis and progression.

Human abdominal aortic aneurysm (AAA): Evidence for an autoimmune antigen-driven disease

Abdominal aortic aneurism (AAA) is a complex immunological disease with a strong genetic component, and one of the ten leading causes of death of individuals 55-74 years old worldwide. Strong evidence has been accumulated suggesting that AAA is an autoimmune specific antigen-driven disease. Mononuclear cells infiltrating AAA lesions comprised of T and B lymphocytes and other cells expressing early-, intermediate- and late-activation antigens, and the presence of antigen-presenting cells have been documented, demonstrating an ongoing immune response. The three components of the trimolecular complex, T-cell receptor (TCR)/peptide (antigen)/HLA have been identified in AAA, and specifically: (i) clonal expansions of T-cell clones in AAA lesions; (ii) the association of AAA with particular HLA Class I and Class II; and (iii) self or nonself putative AAA-associated antigens. IgG autoantibodies recognizing proteins present in normal aortic tissue have been reported in patients with AAA. Molecular mimicry, defined as the sharing of antigenic epitopes between microorganisms (bacteria, viruses) and self antigens, maybe is responsible for T-cell responses and antibody production in AAA. Also, the frequency and the suppressor activity of CD4 + CD25 + FOXP3+ Tregs and the expression of FOXP3 transcripts and protein have been reported to be significantly impaired in AAA patients vs normal donors.

Trained Immunity in Perivascular Adipose Tissue of Abdominal Aortic Aneurysm—A Novel Concept for a Still Elusive Disease

Abdominal aortic aneurysm (AAA) is a chronic, life-threatening vascular disease whose only therapeutic option is a surgical repair to prevent vessel rupture. The lack of medical therapy results from an inadequate understanding of the etiopathogenesis of AAA. Many studies in animal and human models indicate a ‘short-circuiting’ of the regulation of the inflammatory-immune response as a major player in the AAA chronic process. In this regard, perivascular adipose tissue (PVAT) has received increasing interest because its dysfunction affects large arteries primarily through immune cell infiltration. Consistently, we have recently produced evidence that innate and adaptive immune cells present in the PVAT of AAAs contribute to sustaining a damaging inflammatory loop. However, it is still unclear how the complex crosstalk between adaptive and innate immunity can be self-sustaining. From our perspective, trained immunity may play a role in this crosstalk. Trained immunity is defined as a form of innate immune memory resulting in enhanced responsiveness to repeated triggers. Specific innate stimuli and epigenetic and metabolic reprogramming events induce and shape trained immunity in myeloid progenitor cells improving host defense, but also contributing to the progression of immune-mediated and chronic inflammatory diseases. Here we present this hypothesis with data from the literature and our observations to support it.

Mechanisms of abdominal aortic aneurysm progression: A review

Abdominal aortic aneurysm (AAA) is a common disease associated with significant cardiovascular morbidity and mortality. Up to now, there is still controversy on the choice of treatment method of AAA. Even so, the mechanisms of AAA progression are poorly defined, making targeting new therapies problematic. Current evidence favors an interaction of the hemodynamic microenvironment with local and systemic immune responses. In this review, we aim to provide an update of mechanisms in AAA progression, involving hemodynamics, perivascular adipose tissue, adventitial fibroblasts, vasa vasorum remodeling, intraluminal thrombus, and distribution of macrophage subtypes.

Fcγ receptor activation mediates vascular inflammation and abdominal aortic aneurysm development

BACKGROUND

Abdominal aortic aneurysm (AAA), a degenerative vascular pathology characterized by permanent dilation of the aorta, is considered a chronic inflammatory disease involving innate/adaptive immunity. However, the functional role of antibody-dependent immune response against antigens present in the damaged vessel remains unresolved. We hypothesized that engagement of immunoglobulin G (IgG) Fc receptors (FcγR) by immune complexes (IC) in the aortic wall contributes to AAA development. We therefore evaluated FcγR expression in AAA lesions and analysed whether inhibition of FcγR signaling molecules (γ-chain and Syk kinase) influences AAA formation in mice.

METHODS

FcγR gene/protein expression was assessed in human and mouse AAA tissues. Experimental AAA was induced by aortic elastase perfusion in wild-type (WT) mice and γ-chain knockout (γKO) mice (devoid of activating FcγR) in combination with macrophage adoptive transfer or Syk inhibitor treatment. To verify the mechanisms of FcγR in vitro, vascular smooth muscle cells (VSMC) and macrophages were stimulated with IgG IC.

RESULTS

FcγR overexpression was detected in adventitia and media layers of human and mouse AAA. Elastase-perfused γKO mice exhibited a decrease in AAA incidence, aortic dilation, elastin degradation, and VSMC loss. This was associated with (1) reduced infiltrating leukocytes and immune deposits in AAA lesions, (2) inflammatory genes and metalloproteinases downregulation, (3) redox balance restoration, and (4) converse phenotype of anti-inflammatory macrophage M2 and contractile VSMC. Adoptive transfer of FcγR-expressing macrophages aggravated aneurysm in γKO mice. In vitro, FcγR deficiency attenuated inflammatory gene expression, oxidative stress, and phenotypic switch triggered by IC. Additionally, Syk inhibition prevented IC-mediated cell responses, reduced inflammation, and mitigated AAA formation.

CONCLUSION

Our findings provide insight into the role and mechanisms mediating IgG-FcγR-associated inflammation and aortic wall injury in AAA, which might represent therapeutic targets against AAA disease.

Abdominal Aortic Aneurysm: Roles of Inflammatory Cells

Abdominal aortic aneurysms (AAAs) are local dilations of infrarenal segment of aortas. Molecular mechanisms underlying the pathogenesis of AAA remain not fully clear. However, inflammation has been considered as a central player in the development of AAA. In the past few decades, studies demonstrated a host of inflammatory cells, including T cells, macrophages, dendritic cells, neutrophils, B cells, and mast cells, etc. infiltrating into aortic walls, which implicated their crucial roles. In addition to direct cell contacts and cytokine or protease secretions, special structures like inflammasomes and neutrophil extracellular traps have been investigated to explore their functions in aneurysm formation. The above-mentioned inflammatory cells and associated structures may initiate and promote AAA expansion. Understanding their impacts and interaction networks formation is meaningful to develop new strategies of screening and pharmacological interventions for AAA. In this review, we aim to discuss the roles and mechanisms of these inflammatory cells in AAA pathogenesis.

IgG Anti-High Density Lipoprotein Antibodies Are Elevated in Abdominal Aortic Aneurysm and Associated with Lipid Profile and Clinical Features

High-density lipoproteins cholesterol (HDLc) levels are decreased in abdominal aortic aneurysm (AAA), which is hallmarked by autoimmunity and lipid aortic deposits. To investigate whether IgG anti-HDL antibodies were present in AAA and their potential association with clinical features, IgG anti-HDL and total IgG along with HDLc plasma levels were measured in 488 AAA patients and 184 controls from the Viborg Vascular (VIVA) study, and in tissue-conditioned media from AAA intraluminal thrombus and media layer samples compared to control aortas. Higher IgG anti-HDL levels were found in AAA compared to controls, even after correcting for total IgG, and after adjusting for potential confounders. IgG anti-HDL levels were correlated with aortic diameter in univariate and adjusted multivariate analyses. IgG anti-HDL antibodies were negatively associated with HDLc levels before and after correcting for potential confounders. Increased anti-HDL antibodies were identified in tissue-conditioned media from AAA samples compared to healthy aortas, with higher levels being observed in the media layer. In conclusion, increased IgG anti-HDL levels (both in plasma and in tissue) are linked to AAA, associated with aortic diameter and HDLc levels. These data suggest a potential immune response against HDL in AAA and support an emerging role of anti-HDL antibodies in AAA.

Alterations in phenotype and gene expression of adult human aneurysmal smooth muscle cells by exogenous nitric oxide

Abdominal aortic aneurysms (AAA) are characterized by matrix remodeling, elastin degradation, absence of nitric oxide (NO) signaling, and inflammation, influencing smooth muscle cell (SMC) phenotype and gene expression. Little is known about the biomolecular release and intrinsic biomechanics of human AAA-SMCs. NO delivery could be an attractive therapeutic strategy to restore lost functionality of AAA-SMCs by inhibiting inflammation and cell stiffening. We aim to establish the differences in phenotype and gene expression of adult human AAA-SMCs from healthy SMCs. Based on our previous study which showed benefits of optimal NO dosage delivered via S-Nitrosoglutathione (GSNO) to healthy aortic SMCs, we tested whether such benefits would occur in AAA-SMCs. The mRNA expression of three genes involved in matrix degradation (ACE, ADAMTS5 and ADAMTS8) was significantly downregulated in AAA-SMCs. Total protein and glycosaminoglycans synthesis were higher in AAA-SMCs than healthy-SMCs (p < 0.05 for AAA-vs. healthy- SMC cultures) and was enhanced by GSNO and 3D cultures (p < 0.05 for 3D vs. 2D cultures; p < 0.05 for GSNO vs. non-GSNO cases). Elastin gene expression, synthesis and deposition, desmosine crosslinker levels, and lysyl oxidase (LOX) functional activity were lower, while cell proliferation, iNOS, LOX and fibrillin-1 gene expressions were higher in AAA-SMCs (p < 0.05 between respective cases), with differential benefits from GSNO exposure. GSNO and 3D cultures reduced MMPs -2, -9, and increased TIMP-1 release in AAA-SMC cultures (p < 0.05 for GSNO vs. non-GSNO cultures). AAA-SMCs were inherently stiffer and had smoother surface than healthy SMCs (p < 0.01 in both cases), but GSNO reduced stiffness (~25%; p < 0.01) and increased roughness (p < 0.05) of both cell types. In conclusion, exogenously-delivered NO offers an attractive strategy by providing therapeutic benefits to AAA-SMCs.

Inflammasome activity in leucocytes decreases with abdominal aortic aneurysm progression

Abdominal aortic aneurysms (AAAs) are characterized by chronic inflammatory cell infiltration. The present extended immunohistochemistry study aimed to characterize inflammation in AAA and aortic control samples. In specific, the composition of the infiltrating immune cells and the expression of five inflammasome components in these immune cells were evaluated, in order to characterize their role in AAA development. A total of 104 biopsies from 48 AAA patients and 40 healthy specimens from organ donors were evaluated for their grade of inflammation. Infiltrating leukocytes were characterized by specific markers (CD3, CD20 and CD68), intramural localization and inflammasome protein expression [NLR family pyrin domain containing 3 (NLRP3), absent in melanoma 2 (AIM2), apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), Caspase-1 and Caspase-5]. Macrophages, B and T lymphocytes were detected to a similar extent in grade 1, 2 and 3 AAA specimens, whereas in control samples, B and T lymphocytes were rarely observed in grade 1 lesions. Expression frequencies of NLRP3, AIM2 and Caspase-5 were significantly higher in grade 1 lesions of AAA samples compared with grade 1 lesions in control samples. Finally, AIM2, ASC, and Caspase-5 displayed significantly lower expression frequencies in grade 3 compared with grade 2 AAA specimens, and all inflammasome components were less frequently detected in grade 3 than in grade 1 lesions of AAA. This indicates that inflammasome activities decrease with AAA progression in infiltrating leukocytes. No statistically significant association was found for grade 2 and grade 3 lesions and total leukocyte count, C-reactive protein levels, maximal aortic diameter, plasma cholesterol level or biomechanical parameters (derived from finite element analysis) of the respective patients. Overall, the aortic wall of AAA contained lymphocytes and macrophages with different states of activity. The present data suggested that therapeutic inhibition of specific inflammasome components might counteract AAA development and progression.

Clonally expanded alpha-chain T-cell receptor (TCR) transcripts are present in aneurysmal lesions of patients with Abdominal Aortic Aneurysm (AAA)

Abdominal aortic aneurysm (AAA) is a life-threatening immunological disease responsible for 1 to 2% of all deaths in 65 year old or older individuals. Although mononuclear cell infiltrates have been demonstrated in AAA lesions and autoimmunity may be responsible for the initiation and account for the propagation of the disease, the information available about the pathogenesis of AAA is limited. To examine whether AAA lesions from patients with AAA contain clonally expanded α-chain TCR transcripts, we amplified by the non-palindromic adaptor-PCR (NPA-PCR)/Vα-specific PCR and/or the Vα-specific PCR these α-chain TCR transcripts. The amplified transcripts were cloned and sequenced. Substantial proportions of identical α-chain TCR transcripts were identified in AAA lesions of 4 of 5 patients, demonstrating that clonally expanded T cells are present in these AAA lesions. These results were statistically significant by the bimodal distribution. Three of 5 of these patients were typed by DNA-based HLA-typing and all three expressed DRB1 alleles containing the DRβGln70 amino acid residue that has been demonstrated to be associated with AAA. All three patients exhibited clonally expanded T cells in AAA lesions. Four of the 5 patients with AAA who exhibited clonal expansions of α-chain TCR transcripts, also exhibited clonal expansions of β-chain TCR transcripts in AAA lesions, as we have demonstrated previously (J Immunol 192:4897, 2014). αβ TCR-expressing T cells infiltrating AAA lesions contain T-cell clones which have undergone proliferation and clonal expansion in vivo in response to as yet unidentified specific antigens that may be self or nonself. These results provide additional evidence supporting the hypothesis that AAA is a specific antigen-driven T-cell autoimmune disease.

Autoimmunity in the Abdominal Aortic Aneurysm and its Association with Smoking

Smoking increases the risk of abdominal aortic aneurysm (AAA) in both humans and mice, although the underlying mechanisms are not completely understood. An adventitial aortic antigen, AAAP-40, has been partially sequenced. It has motifs with similarities to all three fibrinogen chains and appears to be connected in evolution to a large family of proteins called fibrinogen-related proteins. Fibrinogen may undergo non-enzymatic nitration, which may result from exposure to nitric oxide in cigarette smoke. Nitration of proteins renders them more immunogenic. It has recently been reported that anti-fibrinogen antibody promotes AAA development in mice. Also, anti-fibrinogen antibodies are present in patients with AAA. These matters are reviewed in the overall context of autoimmunity in AAA. The evidence suggests that smoking amplifies an auto-immune reaction that is critical to the pathogenesis of AAA.