Pathogenesis Of Aneurysms Research Articles

Geometric Features Associated with Middle Cerebral Artery Bifurcation Aneurysm Formation: A Matched Case-Control Study

ObjectivesThe pathogenesis of intracranial aneurysms is multifactorial and includes genetic, environmental, and anatomic influences. We aimed to identify image-based morphological parameters that were associated with middle cerebral artery (MCA) bifurcation aneurysms. Materials and methodsWe evaluated three-dimensional morphological parameters obtained from CT angiography (CTA) or digital subtraction angiography (DSA) from 317 patients with unilateral MCA bifurcation aneurysms diagnosed at the Brigham and Women's Hospital and Massachusetts General Hospital between 1990 and 2016. We chose the contralateral unaffected MCA bifurcation as the control group, in order to control for genetic and environmental risk factors. Diameters and angles of surrounding parent and daughter vessels of 634 MCAs were examined. ResultsUnivariable and multivariable statistical analyses were performed to determine statistical significance. Sensitivity analyses with smaller (≤ 3 mm) aneurysms only and with angles excluded, were also performed. In a multivariable conditional logistic regression model we showed that smaller diameter size ratio (OR 0.0004, 95% CI 0.0001–0.15), larger daughter-daughter angles (OR 1.08, 95% CI 1.06–1.11) and larger parent-daughter angle ratios (OR 4.24, 95% CI 1.77–10.16) were significantly associated with MCA aneurysm presence after correcting for other variables. In order to account for possible changes to the vasculature by the aneurysm, a subgroup analysis of small aneurysms (≤ 3 mm) was performed and showed that the results were similar. ConclusionsEasily measurable morphological parameters of the surrounding vasculature of the MCA may provide objective metrics to assess MCA aneurysm formation risk in high-risk patients.

Long non-coding RNA PVT1/microRNA miR-3127-5p/NCK-associated protein 1-like axis participates in the pathogenesis of abdominal aortic aneurysm by regulating vascular smooth muscle cells

ABSTRACT The long non-coding RNA plasmacytoma variant translocation 1 (lncRNA PVT1) has been implicated in the progression of abdominal aortic aneurysms (AAA). However, the detailed mechanism requires further analysis. Our study was aimed at interrogating the mechanism of PVT1 in an H2O2-induced AAA model in vitro. The expression of lncRNA PVT1, microRNA miR-3127-5p, and NCK-associated protein 1-like (NCKAP1L) was examined in AAA tissues and H2O2-treated vascular smooth muscle cells (VSMCs). Cell proliferation was assayed using Cell Counting Kit-8 (CCK8) and 5-Bromodeoxyuridine (BrdU) assays. Meanwhile, 5-Ethynyl-2′-deoxyuridine (EdU) staining was performed to assess cell apoptosis and caspase-3 activity. IL-1β and caspase-1 expression was also assessed using Western blotting to determine inflammasome activation in H2O2-treated VSMCs. Luciferase reporter assays addressed the possible interaction between miR-3127-5p and PVT1 or NCKAP1L, which was predicted by starBase analysis. PVT1 and NCKAP1L expression was elevated in AAA tissues and induced the AAA model in vitro, whereas miR-3127-5p showed the opposite trend. Functionally, PVT1 silencing promoted cell proliferation and reduced the apoptotic rate and inflammasome activation in H2O2-treated VSMCs. Mechanical investigation demonstrated that PVT1 acted as a sponge of miR-3127-5p to modulate NCKAP1L expression, resulting in suppression of VSMC proliferation, induction of apoptosis, and activation of inflammation. In conclusion, PVT1 participates in AAA progression through the miR-3127-5p/NCKAP1L axis and may be a promising biosignature and therapeutic target for AAA.

Analysis of the associations of the T-786C and Glu298Asp polymorphisms of the eNOS gene as risk factors in the rupture of intracranial aneurysms

SummaryThe mechanisms involved in aneurysmal etiology are complex and only partially understood. Genetic risk factors have already been related to the process of aneurysm rupture. Among the genetic factors, the T-786C and Glu298Asp polymorphisms of the eNOS gene have great clinical relevance, as they can affect the bioavailability of nitric oxide for the cerebrovascular system. ObjectiveTo evaluate the relationship between eNOS T-786C and Glu298Asp polymorphisms and the aneurysm pathogenesis of patients seen in the Neurosurgery Department of Santa Casa de Belo Horizonte, as well as to compare them with sociodemographic characteristics and risk factors. MethodsA total of 211 whole blood samples were collected from patients with cerebral aneurysms, 160 with ruptured aneurysms, 51 with unruptured aneurysms and 215 controls. After DNA extraction, genotyping was performed using the PCR-RFLP technique. Allele and genotype frequencies were obtained using the GENEPOP 4.2 software, and statistical analysis was performed using the GraphPad Prism 5.0 program and RStudio version 1.4. ResultsAge, female sex, smoking and small diameter of the aneurysms were associated with aneurysm development and rupture in the study population. The CC genotype of the T-786C polymorphism was associated with unruptured aneurysms with a diameter >12 mm. ConclusionAge, female sex and smoking were associated with rupture. This study revealed that the CC mutant genotype of the eNOS gene T-786C polymorphism was associated with unruptured intracranial aneurysms larger than 12 mm in our study population, revealing a new association.

A Review of the Impact of Neutrophils and Neutrophil Extracellular Traps (NETs) on the Development of Aortic Aneurysms in Animal and Human Studies.

The pathogenesis of the aortic aneurysm (AA) includes several mechanisms, such as chronic sterile inflammation and homeostasis imbalance, with arteriosclerosis, hemodynamic forces, and genetic factors. In addition to the roles of these processes in the development of AA, neutrophilic activity may play a pivotal role (mostly in inflammation and thrombus formation). Neutrophils, which play a crucial role in innate immunity, can release neutrophil extracellular traps (NETs), one of the mechanisms against fighting pathogens, beside phagocytosis and degranulation. NETs are structures composed of nuclear elements (eg, chromatin and modified histones) and granular and cytoplasmic components, which can lead to inflammation and coagulation changes. In addition, the exacerbation of NETosis (the process of NET formation) can be noticed in vascular diseases, including in the development of AA and myocardial infarction and in diabetes, hypertension, and COPD, which are the risk factors of the presence of AA. The discharge of NETs, which are extracellular materials formed by citrullinated histones (Cit-H), cell-free DNA fibers (cf-DNA), and granular and cytoplasmic molecules, is a newly identified method of neutrophil activation that can be activated by endogenous inflammatory stimuli, which contribute to AA development. Cit-H and cf-DNA can be used as biomarkers of AA growth. By understanding the neutrophilic influence of NET release, a new pathway of screening AA growth (by measurement of biomarkers of NETosis) and pharmacological assessment (by repression of NET formation) can be developed. This review summarizes the current knowledge about the influence of NETs on AA growth in human and animal studies.

Comparative analysis of aneurysm subtypes associated genes based on protein\u2013protein interaction network

The arterial aneurysm refers to localized dilation of blood vessel wall and is common in general population. The majority of aneurysm cases remains asymptomatic until a sudden rupture which is usually fatal and of extremely high mortality (~ 50–60%). Therefore, early diagnosis, prevention and management of aneurysm are in urgent need. Unfortunately, current understanding of disease driver genes of various aneurysm subtypes is still limited, and without appropriate biomarkers and drug targets no specialized drug has been developed for aneurysm treatment. In this research, aneurysm subtypes were analyzed based on protein–protein interaction network to better understand aneurysm pathogenesis. By measuring network-based proximity of aneurysm subtypes, we identified a relevant closest relationship between aortic aneurysm and aortic dissection. An improved random walk method was performed to prioritize candidate driver genes of each aneurysm subtype. Thereafter, transcriptomes of 6 human aneurysm subtypes were collected and differential expression genes were identified to further filter potential driver genes. Functional enrichment of above driver genes indicated a general role of ubiquitination and programmed cell death in aneurysm pathogenesis. Especially, we further observed participation of BCL-2-mediated apoptosis pathway and caspase-1 related pyroptosis in the development of cerebral aneurysm and aneurysmal subarachnoid hemorrhage in corresponding transcriptomes.

Epistatic Interaction and Causal Genetic Mediation in Abdominal Aortic Aneurysm Pathogenesis: Abdominal Aortic Aneurysms

Introduction: Whereas previous studies have shown associations between candidate genes polymorphisms and abdominal aortic aneurysms (AAAs), it is notable that genetic information cascades through multiple complex signalling molecular pathways. There is further evidence to suggest that some of these pathways are shared by many genetic and non-genetic risk factors leading to emergent pathological processes that underlie AAA pathogenesis. The aim of this study was to identify a causal interaction between the ACE insertion/deletion (I/D) and MTHFR C677T genetic polymorphisms in AAA pathogenesis.

Vascular Smooth Muscle Cells in Aortic Aneurysm: From Genetics to Mechanisms.

Aortic aneurysm, including thoracic aortic aneurysm and abdominal aortic aneurysm, is the second most prevalent aortic disease following atherosclerosis, representing the ninth‐leading cause of death globally. Open surgery and endovascular procedures are the major treatments for aortic aneurysm. Typically, thoracic aortic aneurysm has a more robust genetic background than abdominal aortic aneurysm. Abdominal aortic aneurysm shares many features with thoracic aortic aneurysm, including loss of vascular smooth muscle cells (VSMCs), extracellular matrix degradation and inflammation. Although there are limitations to perfectly recapitulating all features of human aortic aneurysm, experimental models provide valuable tools to understand the molecular mechanisms and test novel therapies before human clinical trials. Among the cell types involved in aortic aneurysm development, VSMC dysfunction correlates with loss of aortic wall structural integrity. Here, we discuss the role of VSMCs in aortic aneurysm development. The loss of VSMCs, VSMC phenotypic switching, secretion of inflammatory cytokines, increased matrix metalloproteinase activity, elevated reactive oxygen species, defective autophagy, and increased senescence contribute to aortic aneurysm development. Further studies on aortic aneurysm pathogenesis and elucidation of the underlying signaling pathways are necessary to identify more novel targets for treating this prevalent and clinical impactful disease.

Abstract 9487: Sildenafil (Viagra) Aggravates the Development of Experimental Abdominal Aortic Aneurysm

Introduction: PDE5 plays a critical role in vascular smooth muscle cell (SMC) contraction by hydrolyzing 3’,5’ cyclic monophosphate (cGMP) and antagonizing cGMP-dependent protein kinase I (PKGI)-mediated vascular relaxation. SMC contractile dysfunction is implicated in the pathogenesis of aortic aneurysm (AA). PDE5 inhibitors, such as Sildenafil, have been used clinically for treating erectile dysfunction (Viagra) and pulmonary hypertension (Revatio), through promoting SMC relaxation via elevating cGMP. However, it has been reported that PDE5 expression is reduced in human thoracic aneurysms and Viagra usage is associated with human aneurysm rupture or aortic dissection in several case reports. Objective: We aim to investigate the effect of sildenafil in the development of experimental abdominal aortic aneurysm (AAA), the most common form of AA that mainly occurs in elderly male. Methods and Results: AAA was induced in C57BL/6J mouse by periaortic elastase in combination with 3-aminopropionitrile fumarate salt (BAPN) treatment to block elastin/collagen formation. Immunofluorescent staining showed decreased PDE5 expression in mouse AAA. The effect of Sildenafil was examined on pre-existing moderate AAA by providing in drinking water for 28 days. We found that Sildenafil significantly aggravated aneurysmal wall dilation and elastin degradation. Mechanistically, the effect of Sildenafil on the signaling of SMC contraction and PKGI activation were examined in the medial lesion area of AAA. Immunofluorescent staining revealed that Sildenafil significantly decreased the phosphorylation of myosin light chain 2 (MLC2) at Ser19 in AAA, a biochemical marker of SMC contraction. Proximity ligation assay (PLA) revealed an increase of cGMP-PKGI interaction by Sildenafil, an indication of PKGI activation. Conclusions: Chronic Sildenafil treatment aggravated experimental AAA development and elastin degradation by dysregulating contractile signaling in SMCs. Our findings may raise caution of clinical usage of Viagra in aneurysmal patients.

Abstract 9860: P38MAPK Deficiency in VSMCs Mitigates Abdominal Aortic Aneurysm and Atherosclerosis Progression via Promoting MKL1 Ubiquitin Proteasome Degradation

Cardiovascular diseases (CVD) are the leading cause of death in developed countries. Two major manifestations of CVD are aortic aneurysm and atherosclerosis, which are devastating and lack effective pharmacological therapy. The stress responsive pathway, p38 mitogen-activated protein kinase (MAPK), has been reported as a pivotal regulator in diverse processes, including cell proliferation, migration, inflammation, and apoptosis, contributing to cardiovascular development and pathology. However, a detailed understanding of the mechanistic role of p38MAPK in vascular smooth muscle cells (VSMCs) in the pathogenesis of aortic aneurysm and atherosclerosis has yet to be elucidated. Using a VSMC-specific lineage tracing reporter system, we showed that the phosphorylated form of p38MAPK (p-p38MAPK) was markedly elevated in VSMCs of aneurysmal vessels. VSMC-specific p38α ( Mapk14 ) knockout mice displayed attenuated abdominal aortic aneurysm (AAA) and atherosclerotic lesion formation compared to wild-type control mice. Further, loss of MAPK14 in VSMCs abolished the protein expression of multiple ER stress markers, including BIP, Protein Disulfide Isomerase (PDI), and ATF4, which was accompanied by the downregulation of the cleaved Caspase-3 and upregulation of BCL2 protein. This indicates a crucial role of p38MAPK in potentiating ER stress and apoptosis. Interestingly, aortas from VSMC-MAPK14 null mice displayed dramatically reduced protein levels of MKL1, a vital transcription factor with a well-recognized role in promoting AAA and atherosclerosis progression via regulating vascular apoptosis. In vitro, deficiency of p38MAPK in VSMCs via siRNA or SB203580, a selective inhibitor of p38MAPK pathway, downregulated whereas forced expression of MKK6 (activates p38MAPK) increased MKL1 protein expression. Finally, activation of p38MAPK inhibited MKL1 ubiquitination, which was partially rescued by SB203580. Collectively, our data demonstrated a critical role of VSMC-p38MAPK in promoting AAA and atherosclerosis progression, likely through stabilization of MKL1 via p38MAPK-dependent inhibition of MKL1 ubiquitin proteasome degradation.

Abstract 14026: Systemic Delivery of SOD2 mRNA to Experimental Abdominal Aortic Aneurysm Mitigates Expansion

Rationale: Oxidative stress and the overproduction of reactive oxygen species are implicated in the pathogenesis of abdominal aortic aneurysm (AAA). Antioxidant delivery as a therapeutic for AAA is of substantial interest. Yet, despite promising experimental studies, clinical translation of antioxidant therapy has met with significant challenges due to limitations in achieving sufficient levels locally at the site of AAA. Herein, we explore a nanoparticle (NP)-based approach for the systemic delivery of antioxidants. Methods and Results: We employ a peptide-based NP that allows efficient in vivo delivery of mRNA to overexpress a key modulator of oxidative stress, superoxide dismutase 2 (SOD2). The SOD2 mRNA sequence containing the appropriate endcaps, poly-A tail, and base modifications (~1,000 nt) to enhance translation was mixed with p5RHH (an amphipathic peptide capable of efficiently delivering nucleic acids in vivo ) at a ratio of 3,200:1 (peptide:mRNA) to form a self-assembled NP of ~50-55 nm in diameter. The NP was further stabilized by a coating of hyaluronic acid (HA), which binds to CD44 expressed on a wide range of cells, enhancing targeting and uptake. Delivery of SOD2 mRNA suppresses expansion of small AAA. Mitigation of AAA following SOD2 mRNA delivery was accompanied by enhanced SOD2 protein expression in aortic wall tissue, decreased inducible nitric oxide synthase expression, lower nitric oxide production and cell death. Conclusions: The results will serve as proof-of-concept that the delivery of mRNA using the p5RHH-based NP holds promise to overcome challenges associated with systemic delivery of antioxidants in AAA medical management. Figure 1. Mice were perfused with elastase and administered NP iv (1 μg mRNA) on days 5, 8, 11. (A) Increase in (AD), measured on day 14 as increase in mm or %. Day 14 aortic sections (n = 5-6 aortas) were stained for SOD2 (red) and nitrotyrosine (green, NO) and expressed as relative ratios. * P <0.05, ** P <0.01, *** P <0.01.

Abstract 11068: Smad3-Deficiency in Murine Smooth Muscle Cells Causes Global Defects in Expression of Focal Adhesion Components, but Drives Subset-Specific Compensatory Mechanisms Promoting Matrix Degradation and Oxidative Stress

The pathogenesis of aortic aneurysms caused by mutations that impair TGF-β/Smad signaling without completely ablating it remains unclear. To investigate TGF-β’s role independently of its developmental functions, we used mouse models to inactivate Smad3 specifically in smooth muscle cells (SMCs) at 6 weeks of age, when postnatal matrix deposition is largely completed. This intervention was sufficient to induce dilation in the aortic root, but not the ascending aorta. To identify factors underlying this regional vulnerability, we analyzed aortas from control and Smad3-deficient mice by single-cell transcriptomics 10 weeks and 18 weeks after deletion, when dilation is undetectable and moderate, respectively. Three major SMC clusters were identified regardless of genotype or time-point. In situ hybridization showed that the aortic root and proximal ascending aorta were enriched in SMCs expressing cluster-defining transcripts for Cluster 3 and 2, while distal ascending and aortic arch were for Cluster 1. At the early time-point, all SMC clusters showed defective expression of genes coding for components ( Fblim1 , Svil , Tes and Tln1 ) and regulators ( Abra and Rock1) of focal adhesions in response to Smad3 inactivation. These defects associated with Cluster 3-specific upregulation of positive effectors of the TGF-β pathway, such as Tgfb2, and down-regulation of negative regulators of Angiotensin II signaling, such as Rgs2 and Rgs4 . At the later time point, whereas Smad3-deficient SMCs in Cluster 3 retained a similar profile, those in Cluster 2 showed transcriptional alterations consistent with increased TGF-β/Smad2 activation, accompanied by upregulation of Neat1 , a lnc-RNA critical for SMC phenotypic switching. These included potentially adaptive changes, such as upregulation of genes coding for collagen and its processing enzymes ( Col1a2 , Col3a1, Lox and Loxl1), and maladaptive ones such as upregulation of proteases ( Fap and Mmp9) , and upregulation of enzymes promoting oxidative stress ( Nox4 ). These data suggest that Smad3-deficiency causes defective expression of focal adhesion machinery in SMCs, initiating secondary subset-specific compensatory mechanisms driving localized pathogenic increases in proteolysis and oxidative stress.

Involvement of FAK in aortic dissection: potential role in aortic interstitial cells

Abstract Background Aortic dissection (AD) is a fatal disease where the intimomedial layer of the aorta suddenly fail. Although it is widely accepted that hemodynamic stress on the aortic wall triggers its destruction that is further promoted by inflammatory response as exemplified by the infiltration of neutrophils and macrophages, molecular mechanism is unknown for the link of aortic wall stress, inflammation and tissue destruction. In general, mechanical stress to the tissue is converted to the cellular response through the cell adhesion molecules and the activation of focal adhesion kinase (Fak). Although it has been reported that Fak is involved in pathogenesis of aortic aneurysm by promoting migration and activation of macrophages, its role in AD is unknown. We hypothesized that Fak may be involved in AD pathogenesis. Purpose We investigated the involvement of Fak in AD pathogenesis, focusing on its role in inflammatory cells. Methods and results We created a mouse model of AD by continuous infusion of beta-aminopropionitrile, a collagen crosslink inhibitor, and angiotensin II (BAPN + Ang II). Immunostaining for activated Fak revealed that Fak was not activated in normal aorta, but was activated in the infiltrating inflammatory cells and in interstitial cells of the aortic wall after AD development. We examined the role of Fak by oral administration of PND-1186, a specific Fak inhibitor, in mouse AD model. Vehicle-treated group showed 63.6% mortality, whereas PND-1186-treated group showed 20% mortality (P<0.01, n=20 for each group) in 14 days of the observational period. The aortic arch lesion, the most critical part in AD, was improved from 1.96±0.41 mm in vehicle group to 0.66±0.29 mm in PND group (P<0.05). We next examined the cell type-specific role of Fak in AD by creating macrophage and granulocyte-specific deletion of Fak driven by LysM-Cre and floxed Fak system. Unexpectedly, the genetic deletion of Fak in macrophages and granulocytes had no impact on the mortality nor the severity of AD. Conclusions These findings proved that Fak plays a critical role in AD progression and death. Because Fak is dispensable for macrophages and granulocytes, other cell types, possibly aortic wall interstitial cells, may be regulated by Fak in AD pathogenesis. Deciphering the role of Fak would provide the fundamental understanding of AD pathogenesis. Funding Acknowledgement Type of funding sources: None.

Involvement of Angiogenesis in the Pathogenesis of Coronary Aneurysms.

The present study aimed to evaluate the plasma concentration of pro and antiangiogenic factors and their role in the pathogenesis of coronary artery abnormal dilation (CAAD). We measured the plasma concentration of matrix metalloproteinase-8 (MMP-8), transforming growth factor beta 1 (TGF-β1), Angiopoietin-2, vascular endothelial growth factor (VEGF), and fibroblast growth factor (FGF) using a sandwich ELISA technique in the plasma of patients with coronary artery abnormal dilation (CAAD, Group 1), coronary artery disease (CAD, Group 2), and normal coronary arteries (NCA, Group 3). Patients suffering from CAAD showed significantly higher plasma concentrations of VEGF (p = 0.002) than those from the control group. Both pathological angiogenesis and inflammation appear to be crucial in the pathogenesis of aneurysmal dilatation of the coronary arteries.

Neutrophils as Regulators and Biomarkers of Cardiovascular Inflammation in the Context of Abdominal Aortic Aneurysms.

Neutrophils represent up to 70% of circulating leukocytes in healthy humans and combat infection mostly by phagocytosis, degranulation and NETosis. It has been reported that neutrophils are centrally involved in abdominal aortic aneurysm (AAA) pathogenesis. The natural course of AAA is growth and rupture, if left undiagnosed or untreated. The rupture of AAA has a very high mortality and is currently among the leading causes of death worldwide. The use of noninvasive cardiovascular imaging techniques for patient screening, surveillance and postoperative follow-up is well established and recommended by the current guidelines. Neutrophil-derived biomarkers may offer clinical value to the monitoring and prognosis of AAA patients, allowing for potential early therapeutic intervention. Numerous promising biomarkers have been studied. In this review, we discuss neutrophils and neutrophil-derived molecules as regulators and biomarkers of AAA, and our aim was to specifically highlight diagnostic and prognostic markers. Neutrophil-derived biomarkers may potentially, in the future, assist in determining AAA presence, predict size, expansion rate, rupture risk, and postoperative outcome once validated in highly warranted future prospective clinical studies.

MLKL and CaMKII Are Involved in RIPK3-Mediated Smooth Muscle Cell Necroptosis.

Receptor interacting protein kinase 3 (RIPK3)-mediated smooth muscle cell (SMC) necroptosis has been shown to contribute to the pathogenesis of abdominal aortic aneurysms (AAAs). However, the signaling steps downstream from RIPK3 during SMC necroptosis remain unknown. In this study, the roles of mixed lineage kinase domain-like pseudokinase (MLKL) and calcium/calmodulin-dependent protein kinase II (CaMKII) in SMC necroptosis were investigated. We found that both MLKL and CaMKII were phosphorylated in SMCs in a murine CaCl2-driven model of AAA and that Ripk3 deficiency reduced the phosphorylation of MLKL and CaMKII. In vitro, mouse aortic SMCs were treated with tumor necrosis factor α (TNFα) plus Z-VAD-FMK (zVAD) to induce necroptosis. Our data showed that both MLKL and CaMKII were phosphorylated after TNFα plus zVAD treatment in a time-dependent manner. SiRNA silencing of Mlkl-diminished cell death and administration of the CaMKII inhibitor myristoylated autocamtide-2-related inhibitory peptide (Myr-AIP) or siRNAs against Camk2d partially inhibited necroptosis. Moreover, knocking down Mlkl decreased CaMKII phosphorylation, but silencing Camk2d did not affect phosphorylation, oligomerization, or trafficking of MLKL. Together, our results indicate that both MLKL and CaMKII are involved in RIPK3-mediated SMC necroptosis, and that MLKL is likely upstream of CaMKII in this process.

Is the middle cerebral artery bifurcation aneurysm affected by morphological parameters of bifurcation?

Aneurysm formation is a multifactorial process involving genetic, anatomical and environmental risk factors. A research focusing on the relationship between the presence of aneurysm and the morphology of the arteries will help in the pathogenesis and prediction of intracranial aneurysms. In this study, the relationship between the presence of aneurysm and various morphological parameters of aneurysm-related arteries was evaluated in patients with saccular middle cerebral artery (MCA) bifurcation aneurysm. The archival images of 74 patients (62.2% women) were evaluated retrospectively. In this study, the angle between the ipsilateral MCA M1 segment and the dominant truncus (Φ1), the angle between the M1 segment and the recessive truncus (Φ2), and the bifurcation angle (Φ1 + Φ2) were compared. Bilateral internal carotid artery (ICA), MCA M1 segment, dominant and recessive truncus diameters and these diameters ratios were compared with the aneurysmal side and the contralateral side without aneurysm. When the dominant truncus, recessive truncus angles and bifurcation angle were compared, a significant difference was found on the aneurysmal side (p < 0.0001). In the receiver operating characteristic analysis, when the bifurcation angle of 147.5° was accepted as the limit value, 78.4% sensitivity, 79.7% specificity, 79.5% positive predictive value and 78.7% negative predictive value were determined (area under the curve: 0.85). Our study of the morphological features of arteries associated with MCA bifurcation aneurysms showed that the presence of MCA aneurysms was significantly associated with large bifurcation angles.

Abstract 131: Gata4 Ablation In Smooth Muscle Cells Reduces Aortic Root Dilation In A Murine Model Of Loeys-Dietz Syndrome

Loeys-Dietz syndrome (LDS) is a connective tissue disorder characterized by predisposition to aneurysm. Although dilation can develop in all segments of the arterial tree, the aortic root is especially prone to disease. This aortic region is primarily composed of vascular smooth muscle cells (VSMCs) derived from secondary heart field (SHF) progenitors, while VSMCs derived from the cardiac neural crest (CNC) predominate in the more distal ascending aorta. Although intrinsic differences have been found between these two types of VSMCs, it remains unclear how these may contribute to localized risk. To identify transcripts associated with the vulnerability of the aortic root in LDS, we performed single cell transcriptomic analysis on proximal aortas from 16-week-old control and Tgfbr1 M318R/+ LDS mice, which carry a kinase-inactivating mutation in TGF-β Receptor 1. We identified four major VSMC clusters regardless of genotype, with two clusters being defined by CNC-enriched transcripts and two clusters by SHF-enriched transcripts. The latter were defined by expression of Gata4 , which codes for a transcription factor required for development of SHF-derived vascular structures, as well as by higher expression of transcripts previously involved in aneurysm pathogenesis such as Thbs1 , Tgfb1, and Tgfb3. In situ RNA hybridization confirmed that Gata4 -expressing VSMCs were enriched in the aortic root and proximal ascending aorta, with almost no expression in the more distal ascending aorta, suggesting that this transcript defined the aortic region most susceptible to the effects of the Tgfbr1 M318R/+ mutation. GATA4 protein levels were also upregulated in the aortic root of LDS mice. To test if excessive GATA4 expression or activity in VSMCs contributed to aortic root dilation in LDS, we generated LDS mice in which Gata4 was specifically deleted in VSMCs by tamoxifen administration at 6 weeks of age. We found that this intervention significantly reduced aortic root growth from 8 to 20 weeks of age. Although the mechanisms remain under investigation, these data suggest that expression of Gata4 might sensitize specific subsets of aortic VSMCs to the effects of an LDS mutation, rendering the aortic root more susceptible to disease.

Defective autophagy in vascular smooth muscle cells enhances the healing of abdominal aortic aneurysm.

Autophagy is an evolutionarily conserved cellular catabolic process essential for cell homeostasis, and thus its failure is associated with several diseases. While autophagy has been reported to play a role in vascular smooth muscle cells (SMCs) in vascular disorders, its precise role in the pathogenesis of abdominal aortic aneurysm (AAA) has not yet been elucidated. In this study, we investigated the role of SMC autophagy in AAA formation. As a mouse model of AAA, we used control apolipoprotein E‐deficient (apoeKO) mice and Atg7cKO (SMC‐specific Atg7‐deficient mice):apoeKO mice administered angiotensin II for 4 weeks. Intriguingly, Kaplan‐Meier curves showed that the survival rates of Atg7cKO:apoeKO mice were significantly higher than those of apoeKO mice. The hematoma area in AAA of Atg7cKO:apoeKO mice was smaller than in apoeKO mice despite the lack of a significant difference in AAA incidence between the two groups. Furthermore, the amount of granulomatous tissues was significantly larger and the collagen‐positive area within AAA was significantly larger in Atg7cKO:apoeKO mice than in apoeKO mice. In accordance with these findings, SMCs cultured from Atg7cKO mice showed increased expression of collagens, independent of angiotensin II action. Taken together, our data suggest that defective autophagy in SMCs elicits AAA healing that may underlie the better survival rate under dyslipidemia and angiotensin II infusion.

Kallistatin limits abdominal aortic aneurysm by attenuating generation of reactive oxygen species and apoptosis

Inflammation, vascular smooth muscle cell apoptosis and oxidative stress are believed to play important roles in abdominal aortic aneurysm (AAA) pathogenesis. Human kallistatin (KAL; gene SERPINA4) is a serine proteinase inhibitor previously shown to inhibit inflammation, apoptosis and oxidative stress. The aim of this study was to investigate the role of KAL in AAA through studies in experimental mouse models and patients. Serum KAL concentration was negatively associated with the diagnosis and growth of human AAA. Transgenic overexpression of the human KAL gene (KS-Tg) or administration of recombinant human KAL (rhKAL) inhibited AAA in the calcium phosphate (CaPO4) and subcutaneous angiotensin II (AngII) infusion mouse models. Upregulation of KAL in both models resulted in reduction in the severity of aortic elastin degradation, reduced markers of oxidative stress and less vascular smooth muscle apoptosis within the aorta. Administration of rhKAL to vascular smooth muscle cells incubated in the presence of AngII or in human AAA thrombus-conditioned media reduced apoptosis and downregulated markers of oxidative stress. These effects of KAL were associated with upregulation of Sirtuin 1 activity within the aortas of both KS-Tg mice and rodents receiving rhKAL. These results suggest KAL-Sirtuin 1 signalling limits aortic wall remodelling and aneurysm development through reductions in oxidative stress and vascular smooth muscle cell apoptosis. Upregulating KAL may be a novel therapeutic strategy for AAA.

Recombinant Interleukin-19 Suppresses the Formation and Progression of Experimental Abdominal Aortic Aneurysms.

BackgroundInterleukin‐19 is an immunosuppressive cytokine produced by immune and nonimmune cells, but its role in abdominal aortic aneurysm (AAA) pathogenesis is not known. This study aimed to investigate interleukin‐19 expression in, and influences on, the formation and progression of experimental AAAs.Methods and ResultsHuman specimens were obtained at aneurysm repair surgery or from transplant donors. Experimental AAAs were created in 10‐ to 12‐week‐old male mice via intra‐aortic elastase infusion. Influence and potential mechanisms of interleukin‐19 treatment on AAAs were assessed via ultrasonography, histopathology, flow cytometry, and gene expression profiling. Immunohistochemistry revealed augmented interleukin‐19 expression in both human and experimental AAAs. In mice, interleukin‐19 treatment before AAA initiation via elastase infusion suppressed aneurysm formation and progression, with attenuation of medial elastin degradation, smooth‐muscle depletion, leukocyte infiltration, neoangiogenesis, and matrix metalloproteinase 2 and 9 expression. Initiation of interleukin‐19 treatment after AAA creation limited further aneurysmal degeneration. In additional experiments, interleukin‐19 treatment inhibited murine macrophage recruitment following intraperitoneal thioglycolate injection. In classically or alternatively activated macrophages in vitro, interleukin‐19 downregulated mRNA expression of inducible nitric oxide synthase, chemokine C‐C motif ligand 2, and metalloproteinases 2 and 9 without apparent effect on cytokine‐expressing helper or cytotoxic T‐cell differentiation, nor regulatory T cellularity, in the aneurysmal aorta or spleen of interleukin‐19–treated mice. Interleukin‐19 also suppressed AAAs created via angiotensin II infusion in hyperlipidemic mice.ConclusionsBased on human evidence and experimental modeling observations, interleukin‐19 may influence the development and progression of AAAs.