Pathogenesis Of Abdominal Aortic Aneurysm Research Articles

Reduced Nhe1 (Na+-H+ Exchanger-1) Function Protects ApoE-Deficient Mice From Ang II (Angiotensin II)-Induced Abdominal Aortic Aneurysms.

IgE-mediated activation of Nhe1 (Na+-H+ exchanger-1) induces aortic cell extracellular acidification and promotes cell apoptosis. A pH-sensitive probe pHrodo identified acidic regions at positions of macrophage accumulation, IgE expression, and cell apoptosis in human and mouse abdominal aortic aneurysm (AAA) lesions. Ang II (angiotensin II)-induced AAA in Nhe1-insufficient Apoe-/-Nhe1+/- mice and Apoe-/-Nhe1+/+ littermates tested Nhe1 activity in experimental AAA, because Nhe1-/- mice develop ataxia and epileptic-like seizures and die early. Nhe1 insufficiency reduced AAA incidence and size, lesion macrophage and T-cell accumulation, collagen deposition, elastin fragmentation, cell apoptosis, smooth muscle cell loss, and MMP (matrix metalloproteinase) activity. Nhe1 insufficiency also reduced blood pressure and the plasma apoptosis marker TCTP (translationally controlled tumor protein) but did not affect plasma IgE. While pHrodo localized the acidic regions to macrophage clusters, IgE expression, and cell apoptosis in AAA lesions from Apoe-/-Nhe1+/+ mice, such acidic areas were much smaller in lesions from Apoe-/-Nhe1+/- mice. Nhe1-FcεR1 colocalization in macrophages from AAA lesions support a role of IgE-mediated Nhe1 activation. Gelatin zymography, immunoblot, and real-time polymerase chain reaction analyses demonstrated that Nhe1 insufficiency reduced the MMP activity, cysteinyl cathepsin expression, IgE-induced apoptosis, and NF-κB activation in macrophages and blocked IgE-induced adhesion molecule expression in endothelial cells. A near-infrared fluorescent probe (LS662) together with fluorescence reflectance imaging of intact aortas showed reduced acidity in AAA lesions from Nhe-1-insufficient mice. This study revealed extracellular acidity at regions rich in macrophages, IgE expression, and cell apoptosis in human and mouse AAA lesions and established a direct role of Nhe1 in AAA pathogenesis.

Detection of Macrophage Localization in the Abdominal Aortic Aneurysm Wall Using Ex Vivo Superparamagnetic Iron Oxide–Enhanced Magnetic Resonance Imaging

Macrophages in the aneurysmal wall play an important role in the pathogenesis of abdominal aortic aneurysms (AAAs). Superparamagnetic iron oxide (SPIO) is a macrophage-specific contrast agent that results in negative enhancement on magnetic resonance imaging (MRI). SPIO-enhanced MRI targeting the intraluminal thrombus of AAAs has been previously reported. However, macrophages in the media and adventitia of AAA wall have not been investigated in detail. This study aimed to evaluate macrophage localization using SPIO-enhanced MRI in the media and adventitia of AAA wall, as macrophages play a crucial role in AAA pathogenesis. Here, we included study and control patients planning to undergo open surgery for AAA. The study patients received SPIO injection 2days preoperatively (the SPIO group, n=7), whereas the control patients did not receive this injection (the control group). Exvivo MRI was performed on the harvested AAA wall in the SPIO group during the surgery. The concordance between the number of macrophages and berlin blue (BB)-stained areas was histologically evaluated in both groups. Moreover, the concordance between regions of interest in MR images and BB-stained areas was evaluated. The proportion of BB-stained macrophages was higher in the SPIO group (0.93; interquartile range [IQR], 0.83-0.95) than in the control group (0.03; IQR, 0.026-0.11) (P<0.05), indicating uptake of SPIO by macrophages in the AAA wall. A significant positive correlation was found between the number of BB-stained macrophages and BB-stained areas using Kendall rank correlation coefficient in the SPIO group (τ=0.58; P<0.05). Significant correlations were found in the distributions of the region of interest of SPIO-enhanced MRI and BB-stained areas in the media and adventitia in 5 of 7 patients. Macrophages present in the media and adventitia of the AAA wall showed an uptake of the SPIO contrast agent injected 2days prior, which were then detected by exvivo MRI. This suggests that SPIO-enhanced MR images help detect the localization of macrophages on the AAA wall, indicating its potential to serve as a novel index for AAA pathogenesis.

Microarray analysis of human abdominal aortic aneurysm (AAA) detected altered gene expression profiles including H19

Abstract AAA is often a life-threatening disease with poorly understood pathogenesis. We examined gene expression profiles between AAA and normal aorta specimens by cDNA microarray analysis. AAA wall specimens from 5 patients with AAA and grossly normal aortic walls from 3 transplant donors were employed in this study. Total RNA was extracted from each specimen, RT into cDNA, and labeled with phosphorus α-32P. cDNA probes were then hybridized onto human cardiovascular microarray and analyzed by densitometry. Quantitative differences of some genes were further explored by SYBR green-mediated qRT-PCR analysis. Pairwise comparisons of both microarray and qRT-PCR results were made by Student t-test. Most of the 588 genes studied had similar expression among AAA specimens and control aortas, however, 25 genes were upregulated and 26 downregulated. Expression of MMP-9, TIMP3, collagen 1A1 (COL1A1), COL6A3, COL15A1, decorin, MCP 1, Apo E, Apo D, H19 and others was increased. Expression of COL4A4, biglycan, caveolin 3, galectin 1, LDL receptor-related protein 1, extracellular SOD 3, ANP receptor A precursor and others was decreased. Most qRT-PCR results agreed well with those from microarray analysis, with few exceptions. A number of genes that have been previously postulated to participate in AAA pathogenesis, have been upregulated or their expression has been altered. We also revealed some genes that have not been yet studied in human AAA. Of note, H19, one of the most highly up-regulated transcripts in two mouse aneurysm models, was also significantly upregulated in human AAA. These results indicate that many genes involved in different cellular functions might contribute to the pathogenesis of AAA. Supported in part by grant RO1 HL64340 from NIH.

Kallistatin correlates with inflammation in abdominal aortic aneurysm and suppresses its formation in mice.

Kallistatin (KS), encoded by SERPINA4, was suggested to play a protective role in many cardiovascular diseases. However, its role in the pathogenesis of abdominal aortic aneurysm (AAA) remains unclear. The aim of this study was to examine the potential association of KS with AAA pathogenesis. We examined KS (SERPINA4) expression in human AAA by PCR, immunohistochemistry, western blotting, and enzyme-linked immunosorbent assay (ELISA) and analyzed correlations between kallistain and clinical data. We then analyzed the effect of recombinant KS on AAA formation and the Wingless (Wnt) signaling pathway in a mouse AAA model developed by angiotensin II (AngII) infusion to apolipoprotein E-deficient (ApoE-/-) mice. In AAA tissue samples, KS was significantly increased compared with samples from the control group (P<0.001, P<0.001, respectively). Clinically, decreased SERPINA4 expression in AAA tissue samples represented an increased rate of iliac artery aneurysm [odds ratio (OR): 0.017; P=0.040]. And decreased plasma KS level represented a high risk for rupture (OR: 0.837; P=0.034). KS inhibited AAA formation and blocked the Wnt signaling pathway in AngII-infused ApoE-/- mice. The present study demonstrates that aberrant changes in KS expression occur in AAA. KS plays an important anti-inflammatory role and showed important clinical correlations in AAA. Decreased KS (SERPINA4) level is a risk factor of AAA rupture. Our pre-clinical animal experiments indicate that treatment with recombination KS suppresses AngII-induced aortic aneurysm formation and might be a new target for the drug therapy of AAA.

Runx2 (Runt-Related Transcription Factor 2)-Mediated Microcalcification Is a Novel Pathological Characteristic and Potential Mediator of Abdominal Aortic Aneurysm

Abdominal aortic aneurysms (AAAs) are highly lethal diseases without effective clinical predictors and therapeutic targets. Vascular microcalcification, as detected by fluorine-18-sodium fluoride, has recently been recognized as a valuable indicator in predicting atherosclerotic plaque rupture and AAA expansion. However, whether vascular microcalcification involved in the pathogenesis of AAA remains elusive. Approach and Results: Microcalcification was analyzed in human aneurysmal aortas histologically and in AngII (angiotensin II)-infused ApoE-/- mouse aortas by fluorine-18-sodium fluoride positron emission tomography and X-ray computed tomography scanning in chronological order in live animals. AAA patients' aortic tissue showed markedly enhanced microcalcification in the aortic media within the area proximal to elastic fiber degradation, compared with non-AAA patients. Enhanced fluorine-18-sodium fluoride uptake preceded significant aortic expansion in mice. Microcalcification-positive mice on day 7 of AngII infusion showed dramatic aortic expansion on subsequent days 14 to 28, whereas microcalcification-negative AngII-infused mice and saline-induced mice did not develop AAA. The application of hydroxyapatite, the main component of microcalcification, aggravated AngII-induced AAA formation in vivo. RNA-sequencing analysis of the suprarenal aortas of 4-day-AngII-infused ApoE-/- mice and bioinformatics analysis with ChIP-Atlas database identified the potential involvement of the osteogenic transcriptional factor Runx2 (runt-related transcription factor 2) in AAA. Consistently, vascular smooth muscle cell-specific Runx2 deficiency markedly repressed AngII-induced AAA formation in the ApoE-/- mice compared with the control littermates. Our studies have revealed microcalcification as a novel pathological characteristic and potential mediator of AAA, and targeting microcalcification may represent a promising strategy for AAA prevention and treatment.

CDR1as/miR-7/CKAP4 axis contributes to the pathogenesis of abdominal aortic aneurysm by regulating the proliferation and apoptosis of primary vascular smooth muscle cells.

Abdominal aortic aneurysm (AAA) is characterized as dilation of the aortic wall. Dysregulation of vascular smooth muscle cells (VSMCs) can contribute to the development of this phenotype. Circular RNAs and microRNAs (miRNAs) can regulate the proliferation and apoptosis of VSMCs. This present study aimed to identify the mechanisms of action behind the regulation of cerebellar degeneration-related protein 1 antisense RNA (CDR1as)/miRNA (miR)-7 in VSMCs. The expression levels of miR-7 were upregulated, whereas the levels of CDR1as and cytoskeleton-associated protein 4 (CKAP4) were downregulated in aortic specimens obtained from 10 patients who underwent surgery for AAA compared with aortic specimens from 10 control patients who underwent coronary artery bypass surgery. The molecular mechanism of action of CDR1as/miR-7 was investigated in primary VSMCs. The results of Cell Counting kit-8 and cell growth curve assays revealed that overexpression of CDR1as and knockdown of miR-7, increased VSMC proliferation, whereas knockdown of CDR1as and overexpression of miR-7 suppressed VSMC proliferation. In addition, overexpression of CDR1as and knockdown of miR-7, suppressed apoptosis in VSMCs, indicated by the decreased levels of reactive oxygen species (ROS) and lactate dehydrogenase (LDH) activity, whereas knockdown of CDR1as and overexpression of miR-7 exhibited the opposite effects. The results of luciferase reporter and biotin pull-down assays confirmed that CDR1as directly bound to miR-7 and suppressed its expression. Additionally, the CDR1as-induced proliferation and suppressed apoptosis was reversed by the overexpression of miR-7. Furthermore, luciferase reporter, reverse transcription-quantitative PCR and western blot assays revealed that miR-7 directly targeted CKAP4 and suppressed its expression. Additionally, the miR-7-suppressed proliferation and increased ROS and LDH activity were reversed by the overexpression of CKAP4. CDR1as also decreased caspase 3/7 activity, which was reversed by miR-7 mimics. miR-7 increased the activity of caspase 3/7, which was again reversed by the overexpression of CKAP4. Therefore, CDR1as, miR-7 and CKAP4 may act in the same pathway to regulate VSMC proliferation and apoptosis.

Single-Photon Emission Computed Tomography Imaging Using Formyl Peptide Receptor 1 Ligand Can Diagnose Aortic Aneurysms in a Mouse Model

BackgroundOur previous studies showed that neutrophil infiltration and activation plays an important role in the pathogenesis of abdominal aortic aneurysms (AAA). However, there is a lack of noninvasive, inflammatory cell-specific molecular imaging methods to provide early diagnosis of AAA formation. Formyl peptide receptor 1 (FPR1) is rapidly upregulated on neutrophils during inflammation. Therefore, it is hypothesized that the use of cinnamoyl-F-(D)L-F-(D)L-F-K (cFLFLF), a PEGylated peptide ligand that binds FPR1 on activated neutrophils, would permit accurate and noninvasive diagnosis of AAA via single-photon emission computed tomography (SPECT) imaging. Materials and methodsMale C57BL/6 (wild-type) mice were treated with topical elastase (0.4 U/mL type 1 porcine pancreatic elastase) or heat-inactivated elastase (control), and aortic diameter was measured by video micrometry. Comparative histology was performed on Day 14 to assess neutrophil infiltration in aortic tissue. We performed near-infrared fluorescence imaging using c-FLFLF-Cy7 probe on Days 7 and 14 postelastase treatment and measured fluorescence intensity ex vivo in excised aortic tissue. A separate group of animals were injected with 99mTc-c-FLFLF 2 h before SPECT imaging on Day 14 using a SPECT/computed tomography/positron emission tomography trimodal scanner. Coexpression of neutrophils with c-FLFLF was also performed on aortic tissue by immunostaining on Day 14. ResultsAortic diameter was significantly increased in the elastase group compared with controls on Days 7 and 14. Simultaneously, a marked increase in neutrophil infiltration and elastin degradation as well as decrease in smooth muscle integrity were observed in aortic tissue after elastase treatment compared with controls. Moreover, a significant increase in fluorescence intensity of c-FLFLF-Cy7 imaging probe was also observed in elastase-treated mice on Day 7 (approximately twofold increase) and Day 14 (approximately 2.5-fold increase) compared with respective controls. SPECT imaging demonstrated a multifold increase in signal intensity for 99mTc-cFLFLF radiolabel probe in mice with AAA compared with controls on Day 14. Immunostaining of aortic tissue with c-FLFLF-Cy5 demonstrated a marked increase in coexpression with neutrophils in AAA compared with controls. ConclusionscFLFLF, a novel FPR1 ligand, enables quantifiable, noninvasive diagnosis and progression of AAAs. Clinical application of this inflammatory, cell-specific molecular probe using SPECT imaging may permit early diagnosis of AAA formation, enabling targeted therapeutic interventions and preventing impending aortic rupture.

Different Drugs Effect on Mesenchymal Stem Cells Isolated From Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is a progressive dilation of the aortic wall, determined by the unbalanced activity of matrix metalloproteinase (MMPs). Invitro and invivo studies support the pivotal role of MMP-9 to AAA pathogenesis. In our experience, we elucidated the expression of MMP-9 in an exvivo model of human mesenchymal stem cells isolated from AAA specimen (AAA-MSCs). Thus, MMP-9 inhibition could be an attractive therapeutic strategy for inhibiting AAA degeneration and rupture. Our study was aimed at testing the effect of 3 different drugs (pioglitazone, doxycycline, simvastatin) on MMP-9 and peroxisome proliferator-activated receptor (PPAR)-γ expression in AAA-MSCs. Aneurysmal aortic wall segments were taken from AAA patients after the open surgical treatment. MSCs were isolated from AAA (n=20) tissues through enzymatic digestion. AAA-MSCs were exposed to different doses of pioglitazone (5-10-25μM), doxycycline (10-25μM), and simvastatin (10μM) for 24h. The effect of each drug was evaluated in terms of cell survival, by crystal violet stain. MMP-9 and PPAR-γ mRNA were analyzed using real-time PCR. AAA-MSCs were not affected by the exposure to the selected drugs, as shown by the analysis of cell viability. Interestingly, MMP-9 mRNA resulted significantly decreased after each treatment, recording a downregulation of 50% in presence of pioglitazone, 90% with doxycycline, and 40% with exposed to simvastatin, in comparison to untreated cells. We further analyzed the expression of PPAR-γ, target of pioglitazone, observing an upregulation in exposed AAA-MSCs to controls. Our data support the potential therapeutic effect of pioglitazone, doxycycline, and simvastatin on AAA by reducing the MMP-9 expression in a patient-specific model (AAA-MSCs). In addition, pioglitazone drives the increase of PPAR-G, another promising target for AAA therapy. Further studies are necessary to elucidate the mechanism drivingthis inhibitory pathway, which can reduces the mortality risk associated with AAA rupture.

The way forward to understand aortic disease.

Content List ‐ Read more articles from the symposium: “Uppsala Aortic summit”.

Genetic and epigenetic regulation of abdominal aortic aneurysms.

Abdominal aortic aneurysms (AAAs) are focal dilations of the aorta that develop from degenerative changes in the media and adventitia of the vessel. Ruptured AAAs have a mortality of up to 85%, thus it is important to identify patients with AAA at increased risk for rupture who would benefit from increased surveillance and/or surgical repair. Although the exact genetic and epigenetic mechanisms regulating AAA formation are not completely understood, Mendelian cases of AAA, which result from pathologic variants in a single gene, have helped provide a basic understanding of AAA pathophysiology. More recently, genome wide associated studies (GWAS) have identified additional variants, termed single nucleotide polymorphisms, in humans that may be associated with AAAs. While some variants may be associated with AAAs and play causal roles in aneurysm pathogenesis, it should be emphasized that the majority of SNPs do not actually cause disease. In addition to GWAS, other studies have uncovered epigenetic causes of disease that regulate expression of genes known to be important in AAA pathogenesis. This review describes many of these genetic and epigenetic contributors of AAAs, which altogether provide a deeper insight into AAA pathogenesis.

Circular RNA expression profile and its potential regulative role in human abdominal aortic aneurysm

BackgroundThis study aimed to identify the differentially expressed circular RNAs (circRNAs) between human abdominal aortic aneurysm (AAA) and the control group.MethodsHigh-throughput sequencing was applied to determine the circRNA expression profiles of 4 paired aortic samples. Real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was carried out to testify 6 randomly selected dysregulated circRNAs. Kyoto Encyclopedia of Genes and Genomes and Gene ontology (GO) analysis were conducted for functional annotation of the parental genes. Additionally, interaction networks between circRNA and 5 putative microRNA (miRNA) partners were constructed.ResultsFinally, 411 differentially expressed circRNAs were discovered, including 266 downregulated and 145 upregulated circRNAs. Compared with the control group, the expression level of hsa (Homo sapiens) _circ_0005360 (LDLR) and hsa_circ_0002168 (TMEM189) were proved significantly lower in the AAA group by qRT-PCR. Regarding upregulated circRNAs, the most enriched GO molecular function, biological process and cellular component terms were poly(A) RNA binding, negative regulation of transcription from RNA polymerase II promoter and nucleoplasm, respectively. Moreover, circRNA/miRNA interaction networks showed that hsa_circ_0005360/miR-181b and hsa_circ_0002168/miR-15a axis might have a regulative role in human AAA.ConclusionsThis study revealed new circRNAs potentially related to the pathogenesis of AAA. Further experimental studies are warranted to clarify the potential molecular mechanisms.

Circular RNA CCDC66 facilitates abdominal aortic aneurysm through the overexpression of CCDC66.

Abdominal aortic aneurysm (AAA) is fatal meanwhile unpredictable asymptomatic cardiovascular disease. Available data suggests the potential participation of circular RNAs (circRNAs) in AAA pathogenesis. But direct evidence is limited. The present study is to functionally and mechanically characterize circRNA CCDC66 (circCCDC66) in AAA. Previous work indicated the differentially expressed circCCDC66 in AAA. At molecular level, circCCDC66, miR-342-3p and CCDC66 transcript were measured through real-time quantitative polymerase chain reaction assay. Functionally, we examined the cellular behaviours of circCCDC66-depleted or CCDC66-depleted vascular smooth muscle cells (VSMCs) including proliferation and apoptosis. It elucidated that depletion of circCCDC66 induced proliferation facilitation and apoptosis reduction. Mechanically, we addressed the interplay among circCCDC66, miR-342-3p and CCDC66 transcript using RNA immunoprecipitation, RNA pull-down and luciferase reporter experiments. Through mechanical validation, we discovered the positive regulation of circCCDC66 on its host gene CCDC66. Loss of CCDC66 mimicked the effects of circCCDC66 silencing on VSMC growth. Moreover, it uncovered that circCCDC66 regulated CCDC66-dependent VSMC growth through sponging miR-342-3p. Rescue experiments aimed to address the functional role of regulatory network formed by circCCDC66, miR-342-3p and CCDC66 in VSMC growth and apoptosis. Suppressing miR-342-3p or overexpressing CCDC66 could reverse VSMC growth caused by circCCDC66 deficiency. Our study further emphasized and first unveiled the function of circCCDC66 in VSMC proliferation. CircCCDC66 upregulated its host gene through its role of miR-342-3p sponge, and hinted a novel molecular mechanism in AAA. SIGNIFICANCE OF THE STUDY: It was firstly displayed in our study that depletion of circCCDC66 induced proliferation augmentation and apoptosis reduction of vascular smooth muscle cells (VSMCs). Meanwhile, circCCDC66/miR-342-3p/CCDC66 axis was proved can play the function of modulating the cell proliferation and apoptosis of VSMCs, which provided us a novel molecular mechanism in AAA.

STAT3-induced up-regulation of lncRNA NEAT1 as a ceRNA facilitates abdominal aortic aneurysm formation by elevating TULP3.

Long noncoding RNAs (lncRNAs) were viewed as crucial participants in the pathogenesis of abdominal aortic aneurysm (AAA). LncRNA NEAT1 was recognized as an oncogenic gene in various diseases. However, its function and mechanism in AAA were not precisely documented. Here, we explored the functional role and molecular mechanism of NEAT1 in AAA. Functionally, the effect of NEAT1 on the proliferation was assessed by CCK-8 and EdU assay, while its impact on the apoptosis was evaluated through caspase-3/9 activity and TUNEL assays. As a result, we found that NEAT1 knockdown enhanced the proliferation and impaired the apoptosis of vascular smooth muscle cells (VSMCs). Reversely, overexpressed NEAT1 exerted anti-proliferation and pro-apoptosis effects in VSMCs. Mechanically, we found that STAT3 acted as a transcription factor and contributed to NEAT1 transcription by ChIP and luciferase reporter assays. In addition, NEAT1 was confirmed as a sponge of miR-4688 and thereby increase the expression of TULP3 in VSMCs via RIP assay and RNA pull-down assay. Rescue experiments indicted that TULP3 overexpressing countervailed the impact of NEAT1 depletion on AAA biological processes. Conclusively, lncRNA NEAT1 induced by STAT3 was identified as a ceRNA and facilitated AAA formation by targeting miR-4688/TULP3 axis.

Depletion of CD11c+ cell attenuates progression of abdominal aortic aneurysm.

Chronic inflammation of the arterial wall has been implicated in the development of abdominal aortic aneurysm (AAA). However, the detailed molecular mechanism(s) by which inflammatory cells contributes to AAA pathogenesis remains largely unclear. In their article in Clinical Science, Krishna et al. have reported that depletion of CD11c+ dendritic cells inhibited experimental AAA formation in mice. The authors also demonstrated a decrease in CD4 and CD8 positive T cells in the circulation, lower plasma neutrophil elastase activity, and aortic matrix remodeling. These novel findings will help clarify the underlying mechanisms of AAA progression and may provide a new target for future therapeutic research in AAA formation.

Increased matrix metalloproteinase 9 activity correlates with flow-mediated intraluminal thrombus deposition and wall degeneration in human abdominal aortic aneurysm

ObjectiveWe have previously demonstrated that human abdominal aortic aneurysm (AAA) rupture occurs in zones of low wall shear stress where flow recirculation and intraluminal thrombus (ILT) deposition are increased. Matrix metalloproteinase-9 (MMP-9) is involved in the pathogenesis of AAA via its lytic effect on collagen and elastin. We hypothesize that flow-mediated ILT deposition promotes increased local inflammatory and MMP-9 activity that leads to AAA wall degeneration. The purpose of this study was to examine the correlation between predicted pulsatile flow dynamics and regional differences in MMP-9, elastin, collagen, and ILT deposition in human AAA. MethodsFull-thickness aortic tissue samples were collected from 24 patients undergoing open AAA repair. Control infrarenal aortic tissue was obtained from 6 patients undergoing aortobifemoral bypass. Full-thickness aortic tissue and ILT were assessed for MMP-9 levels using a cytokine array assay. Histologic and immunohistochemical assessment of inflammation, collagen and elastin content, and MMP-9 levels were also measured. Three-dimensional AAA geometry was generated from computed tomography angiogram (CTA) images using Mimics software and computational fluid dynamics was used to predict pulsatile aortic blood flow. ResultsThe majority of AAA showed eccentric ILT deposition which was correlated with predicted recirculation blood flow (R2 = –0.17; P < .05). The regions of high ILT were associated with significant increases in inflammation and loss of elastin and collagen compared with regions of low ILT, or with control tissue. MMP-9 was significantly higher in areas of high ILT deposition compared with areas devoid of ILT. Tissue MMP-9 was correlated with the thickness of ILT deposition (R2 = 0.46; P < .05), and was also present in high levels in thick compared with thin ILT. ConclusionsWe have shown a correlation between flow-mediated ILT deposition with increased tissue levels of MMP-9 activity, increased inflammatory infiltrate, and decreased elastin and collagen content in stereotactically sampled human AAA, suggesting that ILT deposition is associated with local increases in proteolytic activity that may preferentially weaken and promote rupture at selected regions.

GSK2593074A blocks progression of existing abdominal aortic dilation

ObjectiveReceptor interacting proteins kinase 1 and 3 (RIPK1 and RIPK3) have been shown to play essential roles in the pathogenesis of abdominal aortic aneurysms (AAAs) by mediating necroptosis and inflammation. We previously discovered a small molecular inhibitor GSK2593074A (GSK’074) that binds to both RIPK1 and RIPK3 with high affinity and prevents AAA formation in mice. In this study, we evaluated whether GSK’074 can attenuate progression of existing AAA in the calcium phosphate model. MethodsC57BL6/J mice were subjected to the calcium phosphate model of aortic aneurysm generation. Mice were treated with either GSK’074 (4.65 mg/kg/day) or dimethylsulfoxide (DMSO) controls starting 7 days after aneurysm induction. Aneurysm growth was monitored via ultrasound imaging every 7 days until harvest on day 28. Harvested aortas were examined via immunohistochemistry. The impact of GSK’074 on vascular smooth muscle cells and macrophages were evaluated via flow cytometry and transwell migration assay. ResultsAt the onset of treatment, mice in both the control (DMSO) and GSK’074 groups showed similar degree of aneurysmal expansion. The weekly ultrasound imaging showed a steady aneurysm growth in DMSO-treated mice. The aneurysm growth was attenuated by GSK’074 treatment. At humane killing, GSK’074-treated mice had significantly reduced progression in aortic diameter from baseline as compared with the DMSO-treated mice (83.2% ± 13.1% [standard error of the mean] vs 157.2% ± 32.0% [standard error of the mean]; P < .01). In addition, the GSK’074-treated group demonstrated reduced macrophages (F4/80, CD206, MHCII), less gelatinase activity, a higher level of smooth muscle cell-specific myosin heavy chain, and better organized elastin fibers within the aortic walls compared with DMSO controls. In vitro, GSK’074 inhibited necroptosis in mouse aortic smooth muscle cells; whereas, it was able to prevent macrophage migration without affecting Il1b and Tnf expression. ConclusionsGSK’074 is able to attenuate aneurysm progression in the calcium phosphate model. The ability to inhibit both vascular smooth muscle cell necroptosis and macrophage migration makes GSK’074 an attractive drug candidate for pharmaceutical treatment of aortic aneurysms.

Identification of key genes and pathways in abdominal aortic aneurysm by integrated bioinformatics analysis.

ObjectivesTo identify key genes associated with abdominal aortic aneurysm (AAA) by integrating a microarray profile and a single-cell RNA-seq dataset.MethodsThe microarray profile of GSE7084 and the single-cell RNA-seq dataset were obtained from the Gene Express Omnibus database. Differentially expressed genes (DEGs) were chosen using the R package and annotated by Gene Ontology and Kyoto Encyclopedia of Genes and Genomics analysis. The hub genes were identified based on their degrees of interaction in the protein-protein interaction (PPI) network. Expression of hub genes was determined using single-cell RNA-seq analysis.ResultsIn total, 507 upregulated and 842 downregulated DEGs were identified and associated with AAA. The upregulated DEGs were enriched into 9 biological processes and 10 biological pathways, which were closely involved in the pathogenesis and progression of AAA. Based on the PPI network, we focused on six hub genes, four of which were novel target genes compared with the known aneurysm gene database. Using single-cell RNA-seq analysis, we explored the four genes expressed in vascular cells of AAA: CANX, CD44, DAXX, and STAT1.ConclusionsWe identified key genes that may provide insight into the mechanism of AAA pathogenesis and progression and that have potential to be therapeutic targets.

Adipocytes promote interleukin-18 binding to its receptors during abdominal aortic aneurysm formation in mice.

Obesity is a risk factor of abdominal aortic aneurysm (AAA). Inflammatory cytokine interleukin-18 (IL18) has two receptors: IL18 receptor (IL18r) and Na-Cl co-transporter (NCC). In human and mouse AAA lesions, IL18 colocalizes to its receptors at regions rich in adipocytes, suggesting a role of adipocytes in promoting IL18 actions in AAA development. We localized both IL18r and NCC in human and mouse AAA lesions. Murine AAA development required both receptors. In mouse AAA lesions, IL18 binding to these receptors increased at regions enriched in adipocytes or adjacent to perivascular adipose tissue. 3T3-L1 adipocytes enhanced IL18 binding to macrophages, aortic smooth muscle cells (SMCs), and endothelial cells by inducing the expression of both IL18 receptors on these cells. Adipocytes also enhanced IL18r and IL18 expression from T cells and macrophages, AAA-pertinent protease expression from macrophages, and SMC apoptosis. Perivascular implantation of adipose tissue from either diet-induced obese mice or lean mice but not that from leptin-deficient ob/ob mice exacerbated AAA development in recipient mice. Further experiments established an essential role of adipocyte leptin and fatty acid-binding protein 4 (FABP4) in promoting IL18 binding to macrophages and possibly other inflammatory and vascular cells by inducing their expression of IL18, IL18r, and NCC. Interleukin-18 uses both IL18r and NCC to promote AAA formation. Lesion adipocyte and perivascular adipose tissue contribute to AAA pathogenesis by releasing leptin and FABP4 that induce IL18, IL18r, and NCC expression and promote IL18 actions.

Modeling Tissue Re-modeling During the Pathogenesis of Abdominal Aortic Aneurysms

Modeling Tissue Re-modeling During the Pathogenesis of Abdominal Aortic Aneurysms

Increased m6A methylation level is associated with the progression of human abdominal aortic aneurysm.

The role of N6-methyladenosine (m6A) modification in abdominal aortic aneurysm (AAA) has not been extensively studied. This study therefore aimed to investigate m6A RNA methylation and the expressions of the corresponding modulators in AAA. A comparative study between AAA tissue samples (n=32) and healthy aortas (n=12) was performed using m6A methylation quantification for messenger RNA (mRNA) m6A status, quantitative polymerase chain reaction (qPCR), and western blot for the expressions of m6A modulators and immunohistochemistry (IHC) to detect locations of the modulators in AAA tissues. The m6A level significantly increased in AAA as compared to healthy aorta tissues. Among AAA patients, the high m6A level represented an even greater risk of AAA rupture as compared to non-ruptured AAA [odds ratio (OR), 1.370; 95% confidence interval (CI), 1.007-1.870]. The major N6-adenosine modulators, including YTHDF1, YTHDF3, FTO, and METTL14, are the main factors involved in aberrant m6A modification and the expression of both was significantly correlated to the proportion of m6A in total mRNA. Clinically, YTHDF3 represented an even greater risk of rupture (OR, 1.036; 95% CI, 1.001-1.072). Regarding the cellular location, METTL14 seemed to be associated with inflammatory infiltrates and neovascularization. Furthermore, a strong correlation was seen between FTO and aneurysmal smooth muscle cells (SMCs), YTHDF3, and macrophage infiltrate. We were first to observe m6A modification in human AAA tissues. The results also reveal the important roles of m6A modulators, including YTHDF3, FTO, and METTL14, in the pathogenesis of human AAA and provide a new view on m6A modification in AAA. Our findings suggest a potential mechanism of epigenetic alterations in clinical AAA.