Abdominal Aortic Aneurysm Model Research Articles

The contribution of matrix metalloproteinases and their inhibitors to the development, progression, and rupture of abdominal aortic aneurysms.

Abdominal aortic aneurysms (AAAs) account for up to 8% of deaths in men aged 65 years and over and 2.2% of women. Patients with AAAs often have atherosclerosis, and intimal atherosclerosis is generally present in AAAs. Accordingly, AAAs are considered a form of atherosclerosis and are frequently referred to as atherosclerotic aneurysms. Pathological observations advocate inflammatory cell infiltration alongside adverse extracellular matrix degradation as key contributing factors to the formation of human atherosclerotic AAAs. Therefore, macrophage production of proteolytic enzymes is deemed responsible for the damaging loss of ECM proteins, especially elastin and fibrillar collagens, which characterise AAA progression and rupture. Matrix metalloproteinases (MMPs) and their regulation by tissue inhibitors metalloproteinases (TIMPs) can orchestrate not only ECM remodelling, but also moderate the proliferation, migration, and apoptosis of resident aortic cells, alongside the recruitment and subsequent behaviour of inflammatory cells. Accordingly, MMPs are thought to play a central regulatory role in the development, progression, and eventual rupture of abdominal aortic aneurysms (AAAs). Together, clinical and animal studies have shed light on the complex and often diverse effects MMPs and TIMPs impart during the development of AAAs. This dichotomy is underlined from evidence utilising broad-spectrum MMP inhibition in animal models and clinical trials which have failed to provide consistent protection from AAA progression, although more encouraging results have been observed through deployment of selective inhibitors. This review provides a summary of the supporting evidence connecting the contribution of individual MMPs to AAA development, progression, and eventual rupture. Topics discussed include structural, functional, and cell-specific diversity of MMP members; evidence from animal models of AAA and comparisons with findings in humans; the dual role of MMPs and the requirement to selectively target individual MMPs; and the advances in identifying aberrant MMP activity. As evidenced, our developing understanding of the multifaceted roles individual MMPs perform during the progression and rupture of AAAs, should motivate clinical trials assessing the therapeutic potential of selective MMP inhibitors, which could restrict AAA-related morbidity and mortality worldwide.

Fabrication of deformable patient-specific AAA models by material casting techniques.

Abdominal Aortic Aneurysm (AAA) is a balloon-like dilatation that can be life-threatening if not treated. Fabricating patient-specific AAA models can be beneficial for in-vitro investigations of hemodynamics, as well as for pre-surgical planning and training, testing the effectiveness of different interventions, or developing new surgical procedures. The current direct additive manufacturing techniques cannot simultaneously ensure the flexibility and transparency of models required by some applications. Therefore, casting techniques are presented to overcome these limitations and make the manufactured models suitable for in-vitro hemodynamic investigations, such as particle image velocimetry (PIV) measurements or medical imaging. Two complex patient-specific AAA geometries were considered, and the related 3D models were fabricated through material casting. In particular, two casting approaches, i.e. lost molds and lost core casting, were investigated and tested to manufacture the deformable AAA models. The manufactured models were acquired by magnetic resonance, computed tomography (CT), ultrasound imaging, and PIV. In particular, CT scans were segmented to generate a volumetric reconstruction for each manufactured model that was compared to a reference model to assess the accuracy of the manufacturing process. Both lost molds and lost core casting techniques were successful in the manufacturing of the models. The lost molds casting allowed a high-level surface finish in the final 3D model. In this first case, the average signed distance between the manufactured model and the reference was () mm. However, this approach was more expensive and time-consuming. On the other hand, the lost core casting was more affordable and allowed the reuse of the external molds to fabricate multiple copies of the same AAA model. In this second case, the average signed distance between the manufactured model and the reference was () mm. However, the final model's surface finish quality was poorer compared to the model obtained by lost molds casting as the sealing of the outer molds was not as firm as the other casting technique. Both lost molds and lost core casting techniques can be used for manufacturing patient-specific deformable AAA models suitable for hemodynamic investigations, including medical imaging and PIV.

The protective effects of pirfenidone in preventing abdominal aortic aneurysm formation.

Vascular endothelial growth factor (VEGF)-mediated angiogenesis participates in the initiation and progression of abdominal aortic aneurysm (AAA). Pirfenidone is a compound that has anti-inflammatory and antioxidant properties and suppresses angiogenesis. Pirfenidone targets the extracellular matrix (ECM) and has therapeutic effects on fibrotic diseases. Therefore, we speculated that pirfenidone might have meaningful therapeutic effects in AAA, and the current study was designed to investigate this capacity. An AAA model was constructed in mice using a long-term injection of angiotensin II (Ang II), followed by a 28-day administration of 200 mg/kg/day pirfenidone. Increased maximal external diameter of the abdominal artery, promoted levels of VEGF-A and its receptor VEGF-R2, upregulated matrix metallopeptidases (MMP)-2 and MMP-9, and elevated release of pro-inflammatory cytokines were observed in AAA mice, which were extremely repressed by 200 mg/kg pirfenidone. Human aortic endothelial cells (HAECs) were stimulated with Ang II for 1 day, in the presence or absence of pirfenidone (100 nM). Elevated expression of VEGF-A and VEGF-R2, facilitated proliferation, increased tube formation ability, and upregulated MMP-2 and MMP-9 were observed in Ang II-stimulated HAECs, all of which were significantly rescued by 100 nM pirfenidone. Finally, the elevated levels of myeloid differentiation primary response 88 and phosphorylated nuclear factor-kappa-B subunit p65 observed in Ang II-stimulated HAECs were repressed by pirfenidone. Collectively, pirfenidone alleviated AAA by inhibiting ECM degradation and ameliorating endothelial dysfunction.

An evidence update to explore molecular targets and protective mechanisms of apigenin against abdominal aortic aneurysms based on network pharmacology and experimental validation.

Abdominal aortic aneurysms (AAA) is a life-threatening disease and the incidence of AAA is still on the rise in recent years. Numerous studies suggest that dietary moderate consumption of polyphenol exerts beneficial effects on cardiovascular disease. Apigenin (API) is a promising dietary polyphenol and possesses potent beneficial effects on our body. Although our previous study revealed protective effects of API on experimental AAA formation, up till now few studies were carried out to further investigate its involved molecular mechanisms. In the present study, network pharmacology combined molecular docking and experimental validation was used to explore API-related therapeutic targets and mechanisms in the treatment of AAA. Firstly, we collected 202 API-related therapeutic targets and 2475 AAA-related pathogenetic targets. After removing duplicates, a total of 68 potential therapeutic targets were obtained. Moreover, 5 targets with high degree including TNF, ACTB, INS, JUN, and MMP9 were identified as core targets of API for treating AAA. In addition, functional enrichment analysis indicated that API exerted pharmacological effects in AAA by affecting versatile mechanisms, including apoptosis, inflammation, blood fluid dynamics, and immune modulation. Molecular docking results further supported that API had strong affinity with the above core targets. Furthermore, protein level of core targets and related pathways were evaluated in a Cacl2-induced AAA model by using western blot and immunohistochemistry. The experimental validation results demonstrated that API significantly attenuated phosphorylation of JUN and protein level of predicted core targets. Taken together, based on network pharmacological and experimental validation, our study systematically explored associated core targets and potential therapeutic pathways of API for AAA treatment, which could supply valuable insights and theoretical basis for AAA treatment.

Long noncoding RNA TUG1 regulates smooth muscle cell differentiation via KLF4-myocardin axis.

Abdominal aortic aneurysms (AAAs) are asymptomatic vascular diseases that have life-threatening outcomes. Smooth muscle cell (SMC) dysfunction plays an important role in AAA development. The contribution of non-coding genome, specifically the role of long non-coding RNAs (lncRNAs) in SMC dysfunction, is relatively unexplored. We investigated the role of lncRNA TUG1 in SMC dysfunction. To identify potential lncRNAs relevant to SMC functionality, lncRNA profiling was performed in angiotensin-II-treated SMCs. AAA was induced by angiotensin-II treatment in mice. Transcriptional regulation of TUG1 was studied using promoter luciferase and chromatin-immuno-precipitation experiments. Gain-or-loss-of-function experiments were performed in vitro to investigate TUG1-mediated regulation of SMC function. Immunoprecipitation experiments were conducted to elucidate the mechanism underlying TUG1-mediated SMC dysfunction. TUG1 was upregulated in SMCs following angiotensin-II treatment. Similarly, TUG1 levels were elevated in abdominal aorta in a mouse model of angiotensin-II-induced AAA. Further investigations showed that angiotensin-II-induced TUG1 expression could be suppressed by inhibiting Notch-signaling pathway, both in vitro and in mouse AAA model and that TUG1 is a direct transcriptional target of the Notch pathway. In aneurysmal tissues, TUG1 expression was inversely correlated with the expression of SMC contractile genes. Overexpression of TUG1 repressed SMC differentiation in vitro, whereas siRNA/shRNA-mediated TUG1 knockdown showed an opposite effect. Mechanistically, TUG1 interacts with transcriptional repressor KLF4 and facilitates its recruitment to myocardin promoter ultimately leading to the repression of SMC differentiation. In summary, our study uncovers a novel role for the lncRNA TUG1 wherein it modulates SMC differentiation via the KLF4-myocardin axis, which may have potential implications in AAA development.NEW & NOTEWORTHY TUG1 is an angiotensin-II-induced long noncoding RNA that mediates smooth muscle cell (SMC) dysfunction through interaction with transcriptional repressor KLF4.

Targeted PERK inhibition with biomimetic nanoclusters confers preventative and interventional benefits to elastase-induced abdominal aortic aneurysms.

Abdominal aortic aneurysm (AAA) is a progressive aortic dilatation, causing ∼80% mortality upon rupture. Currently, there is no approved drug therapy for AAA. Surgical repairs are invasive and risky and thus not recommended to patients with small AAAs which, however, account for ∼90% of the newly diagnosed cases. It is therefore a compelling unmet clinical need to discover effective non-invasive strategies to prevent or slow down AAA progression. We contend that the first AAA drug therapy will only arise through discoveries of both effective drug targets and innovative delivery methods. There is substantial evidence that degenerative smooth muscle cells (SMCs) orchestrate AAA pathogenesis and progression. In this study, we made an exciting finding that PERK, the endoplasmic reticulum (ER) stress Protein Kinase R-like ER Kinase, is a potent driver of SMC degeneration and hence a potential therapeutic target. Indeed, local knockdown of PERK in elastase-challenged aorta significantly attenuated AAA lesions in vivo. In parallel, we also conceived a biomimetic nanocluster (NC) design uniquely tailored to AAA-targeting drug delivery. This NC demonstrated excellent AAA homing via a platelet-derived biomembrane coating; and when loaded with a selective PERK inhibitor (PERKi, GSK2656157), the NC therapy conferred remarkable benefits in both preventing aneurysm development and halting the progression of pre-existing aneurysmal lesions in two distinct rodent models of AAA. In summary, our current study not only establishes a new intervention target for mitigating SMC degeneration and aneurysmal pathogenesis, but also provides a powerful tool to facilitate the development of effective drug therapy of AAA.

In Vivo Validation of Modulated Acoustic Radiation Force-Based Imaging in Murine Model of Abdominal Aortic Aneurysm Using VEGFR-2-Targeted Microbubbles.

The objective of this study is to validate the modulated acoustic radiation force (mARF)-based imaging method in the detection of abdominal aortic aneurysm (AAA) in murine models using vascular endothelial growth factor receptor 2 (VEGFR-2)-targeted microbubbles (MBs). The mouse AAA model was prepared using the subcutaneous angiotensin II (Ang II) infusion combined with the β-aminopropionitrile monofumarate solution dissolved in drinking water. The ultrasound imaging session was performed at 7 days, 14 days, 21 days, and 28 days after the osmotic pump implantation. For each imaging session, 10 C57BL/6 mice were implanted with Ang II-filled osmotic pumps, and 5 C57BL/6 mice received saline infusion only as the control group. Biotinylated lipid MBs conjugated to either anti-mouse VEGFR-2 antibody (targeted MBs) or isotype control antibody (control MBs) were prepared before each imaging session and were injected into mice via tail vein catheter. Two separate transducers were colocalized to image the AAA and apply ARF to translate MBs simultaneously. After each imaging session, tissue was harvested and the aortas were used for VEGFR-2 immunostaining analysis. From the collected ultrasound image data, the signal magnitude response of the adherent targeted MBs was analyzed, and a parameter, residual-to-saturation ratio ( Rres - sat ), was defined to measure the enhancement in the adherent targeted MBs signal after the cessation of ARF compared with the initial signal intensity. Statistical analysis was performed with the Welch t test and analysis of variance test. The Rres - sat of abdominal aortic segments from Ang II-challenged mice was significantly higher compared with that in the saline-infused control group ( P < 0.001) at all 4 time points after osmotic pump implantation (1 week to 4 weeks). In control mice, the Rres - sat values were 2.13%, 1.85%, 3.26%, and 4.85% at 1, 2, 3, and 4 weeks postimplantation, respectively. In stark contrast, the Rres - sat values for the mice with Ang II-induced AAA lesions were 9.20%, 20.6%, 22.7%, and 31.8%, respectively. It is worth noting that there was a significant difference between the Rres - sat for Ang II-infused mice at all 4 time points ( P < 0.005), a finding not present in the saline-infused mice. Immunostaining results revealed the VEGFR-2 expression was increased in the abdominal aortic segments of Ang II-infused mice compared with the control group. The mARF-based imaging technique was validated in vivo using a murine model of AAA and VEGFR-2-targeted MBs. Results in this study indicated that the mARF-based imaging technique has the ability to detect and assess AAA growth at early stages based on the signal intensity of adherent targeted MBs, which is correlated with the expression level of the desired molecular biomarker. The results may suggest, in very long term, a pathway toward eventual clinical implementation for an ultrasound molecular imaging-based approach to AAA risk assessment in asymptomatic patients.

Radiomic-based Textural Analysis of Intraluminal Thrombus in Aortic Abdominal Aneurysms: A Demonstration of Automated Workflow.

Our main objective is to investigate how the structural information of intraluminal thrombus (ILT) can be used to predict abdominal aortic aneurysms (AAA) growth status through an automated workflow. Fifty-four human subjects with ILT in their AAAs were identified from our database; those AAAs were categorized as slowly- (< 5mm/year) or fast-growing (≥ 5mm/year) AAAs. In-house deep-learning image segmentation models were used to generate 3D geometrical AAA models, followed by automated analysis. All features were fed into a support vector machine classifier to predict AAA's growth status.The most accurate prediction model was achieved through four geometrical parameters measuring the extent of ILT, two parameters quantifying the constitution of ILT, antihypertensive medication, and the presence of co-existing coronary artery disease. The predictive model achieved an AUROC of 0.89 and a total accuracy of 83%. When ILT was not considered, our prediction's AUROC decreased to 0.75 (P-value < 0.001).

Dexmedetomidine Alleviates Abdominal Aortic Aneurysm by Activating Autophagy Via AMPK/mTOR Pathway.

Abdominal aortic aneurysms (AAA) are a critical global health issue with increasing prevalence. Dexmedetomidine (DEX) is a highly selective α2-adrenoceptor agonist that has previously been shown to play a protective role in AAA. Nevertheless, the mechanisms underlying its protection effect remain not fully understood. A rat AAA model was established via intra-aortic porcine pancreatic elastase perfusion with or without DEX administration. The abdominal aortic diameters of rats were measured. Hematoxylin-eosin and Elastica van Gieson staining were conducted for histopathological observation. TUNEL and immunofluorescence staining were utilized to detect cell apoptosis and α-SMA/LC3 expression in the abdominal aortas. Protein levels were determined using western blotting. DEX administration repressed the dilation of aortas, alleviated pathological damage and cell apoptosis, and suppressed phenotype switching of vascular smooth muscle cells (VSMCs). Moreover, DEX activated autophagy and regulated the AMP-activated protein kinase/mammalian target of the rapamycin (AMPK/mTOR) signaling pathway in AAA rats. Administration of the AMPK inhibitor attenuated the DEX-mediated ameliorative effects on AAA in rats. DEX ameliorates AAA in rat models by activating autophagy via the AMPK/mTOR pathway.

The Histone Methyltransferase SETDB2 Modulates Tissue Inhibitors of Metalloproteinase-Matrix Metalloproteinase Activity During Abdominal Aortic Aneurysm Development.

To determine macrophage-specific alterations in epigenetic enzyme function contributing to the development of abdominal aortic aneurysms (AAAs). AAA is a life-threatening disease, characterized by pathologic vascular remodeling driven by an imbalance of matrix metalloproteinases and tissue inhibitors of metalloproteinases (TIMPs). Identifying mechanisms regulating macrophage-mediated extracellular matrix degradation is of critical importance to developing novel therapies. The role of SET Domain Bifurcated Histone Lysine Methyltransferase 2 (SETDB2) in AAA formation was examined in human aortic tissue samples by single-cell RNA sequencing and in a myeloid-specific SETDB2 deficient murine model induced by challenging mice with a combination of a high-fat diet and angiotensin II. Single-cell RNA sequencing of human AAA tissues identified SETDB2 was upregulated in aortic monocyte/macrophages and murine AAA models compared with controls. Mechanistically, interferon-β regulates SETDB2 expression through Janus kinase/signal transducer and activator of transcription signaling, which trimethylates histone 3 lysine 9 on the TIMP1-3 gene promoters thereby suppressing TIMP1-3 transcription and leading to unregulated matrix metalloproteinase activity. Macrophage-specific knockout of SETDB2 ( Setdb2f/fLyz2Cre+ ) protected mice from AAA formation with suppression of vascular inflammation, macrophage infiltration, and elastin fragmentation. Genetic depletion of SETDB2 prevented AAA development due to the removal of the repressive histone 3 lysine 9 trimethylation mark on the TIMP1-3 gene promoter resulting in increased TIMP expression, decreased protease activity, and preserved aortic architecture. Lastly, inhibition of the Janus kinase/signal transducer and activator of the transcription pathway with an FDA-approved inhibitor, Tofacitinib, limited SETDB2 expression in aortic macrophages. These findings identify SETDB2 as a critical regulator of macrophage-mediated protease activity in AAAs and identify SETDB2 as a mechanistic target for the management of AAAs.

A novel rabbit model of abdominal aortic aneurysm: Construction and evaluation

Prior research has indicated that animal models of abdominal aortic aneurysm (AAA) utilizing porcine pancreatic elastase (PPE) exhibit a perfusion duration of 30 min, and extended perfusion durations are associated with elevated mortality rates. Similarly, the AAA model, which relies solely on balloon dilation (BD), is limited by the occurrence of self-healing aneurysms. Consequently, we constructed a novel AAA model by PPE combined with balloon expansion to shorten the modeling time and improve the modeling success rate. The findings indicated that 5 min was the optimal BD time for rabbits, 3 min BD was ineffective for aneurysm formation, and 10 min BD had a high mortality rate. The model, constructed in combination with PPE and 5 min BD, exhibited a 100% model formation rate and a 244.7% ± 9.83% dilation rate. HE staining exhibited that severe disruption of the inner, middle, and outer membranes of the abdominal aorta, with a marked decrease in smooth muscle cells and elastase, and a marked increase in fibroblasts of the middle membrane, and many infiltrating inflammatory cells were seen in all three layers, especially in the middle membrane. EVG staining displayed that the elastic fibers of the abdominal aortic wall were fractured and degraded, and lost their normal wavy appearance. The protein expression of inflammatory factor (IL-1β, IL-6 and TNF-α) as well as extracellular matrix components (MMP-2 and MMP-9) were significantly increased compared to PPE and 5 min BD alone. In conclusion, PPE combined with BD allows the establishment of a novel AAA model that closely mimics human AAA in terms of histomorphology, inflammatory cell infiltration, and vascular stromal destruction. This model provides an ideal animal model for understanding the pathogenesis of AAA.

LncRNA FGD5-AS1 Promotes Abdominal Aortic Aneurysm Growth Through the Activation of MMP3 in Vascular Smooth Muscle Cells.

Long noncoding RNAs (lncRNAs) can serve as treatment targets for abdominal aortic aneurysms (AAAs). Nonetheless, the exact role of FGD5 antisense RNA 1 (FGD5-AS1) in AAAs is unclear. Therefore, this study investigated the contribution of FGD5-AS1 to AAA growth regulated by vascular smooth muscle cells (VSMCs) and its potential mechanisms. ApoE-/- mice were used to establish the angiotensin II (Ang II)-elicited AAA model. RNA pull-down assay and dual luciferase reporter assay (DLRA) in human VSMCs were used in examining the interactions between FGD5-AS1 and its downstream proteins or miRNA targets. FGD5-AS1 expression in the mouse Ang II perfusion group was dramatically increased relative to the PBS-infused group. In the mouse AAA model, FGD5-AS1 overexpression induced SMC apoptosis, thereby promoting AAA growth. miR-195-5p acts as a potential FGD5-AS1 downstream target, whereas FGD5-AS1 promotes MMP3 expression by inhibiting miR-195-5p expression, thereby inhibiting proliferation and promoting apoptosis of smooth muscle cells. LncRNA FGD5-AS1 is detrimental to the proliferation and survival of SMCs during AAA growth. Therefore, FGD5-AS1 could be a novel treatment target for AAA.

Effect of Intraluminal Thrombus Burden on the Risk of Abdominal Aortic Aneurysm Rupture.

Abdominal aortic aneurysm (AAA) is a critical health disorder, where the abdominal aorta dilates more than 50% of its normal diameter. Enlargement in abdominal aorta alters the hemodynamics and flow-induced forces on the AAA wall. Depending on the flow conditions, the hemodynamic forces on the wall may result in excessive mechanical stresses that lead to AAA rupture. The risk of rupture can be predicted using advanced computational techniques such as computational fluid dynamics (CFD) and fluid-structure interaction (FSI). For a reliable rupture risk assessment, formation of intraluminal thrombus (ILT) and uncertainty in arterial material properties should be taken into account, mainly due to the patient-specific differences and unknowns in AAAs. In this study, AAA models are computationally investigated by performing CFD simulations combined with FSI analysis. Various levels of ILT burdens are artificially generated in a realistic AAA geometry, and the peak effective stresses are evaluated to elucidate the effect of material models and ILT formation. The results indicate that increasing the ILT burden leads to lowered effective stresses on the AAA wall. The material properties of the artery and ILT are also effective on the stresses; however, these effects are limited compared to the effect of ILT volume in the AAA sac.

Augmented Reality Improves Learning Curve of Endovascular Navigation

Intra-Operative Positioning System (IOPS) (Centerline Biomedical, Cleveland, OH) is a 3D electromagnetic (EM) endovascular navigation system approved by the US Food and Drug Administration and developed as an adjunct to fluoroscopy. It provides real-time 3D display of sensorized material on an anatomical map on a flat screen. An investigational prototype based on IOPS incorporates the ability to map implanted stent grafts and visualize the stents and anatomy using augmented reality headset. The aim of this study was to compare the completion of bifurcated stent graft gate cannulation performed by participants of varying experience using fluoroscopy or different variations of IOPS. The task was cannulation of the gate of a bifurcated aortic endograft deployed into a 3D printed abdominal aortic aneurysm model connected to flow pump reproducing physiological conditions, performed in a hybrid operating room (GE Allia IGS 7). Each participant performed the tasks with fluoroscopy, EM guidance with flat screen display (EM-FS), and EM guidance with augmented reality headset (EM-AR) (Fig 1), in randomized order. All participants used the same sensorized guidewire and steerable sensorized 6F catheter for the three runs. Participants were classified in three groups of experience. Primary end points included cannulation time and technical success, defined as the advancement of the catheter over the guidewire within the graft main body. Fifteen minutes was the cutoff time for each trial. There were 26 participants including 13 endovascular naïve trainees (group 1), 12 in training surgeons (group 2) and one advanced level vascular surgeon. In group 1, mean cannulation time was lower using EM-AR versus fluoroscopy (4.3 ± 4.4 vs 7.1 ± 4.9 minutes; P = .04), with no difference between EM-FS and fluoroscopy (6.3 ± 4.5 vs 7.1 ± 4.9 minutes; P = .63). In group 1, technical success was 77% with fluoroscopy and 92% with both EM modalities (P = .59). In group 2, there was a trend toward shorter times with EM-FS or EM-AR as compared to fluoroscopy (mean of 2.5 ± 0.9, 4.4 ± 4.0 and 5.2 ± 4.5 minutes, respectively). In group 2, technical success was 92% with fluoroscopy and 100% with IOPS (P > .99). The advanced level vascular surgeon repeated the cannulation task four times for each endovascular approach, with 100% technical success and no difference in mean time (P = .89) (Fig 2). Augmented reality allows for reducing the gate cannulation time as compared to fluoroscopy in participants with no previous experience in endovascular navigation. This auspicious finding suggests that augmented reality can be beneficial for individuals early in their career and can mitigate the learning curve.Fig 2Mean cannulation times of bifurcated stent graft gate cannulation using electromagnetic (EM) guidance with flat screen display or augmented reality compared to fluoroscopy, performed by operators of varying experience.View Large Image Figure ViewerDownload Hi-res image Download (PPT)

Nicotine Administration Augments Abdominal Aortic Aneurysm Progression in Rats.

Inflammation and elastin degradation are key hallmarks in the pathogenesis of abdominal aortic aneurysms (AAAs). It has been acknowledged that activation of alpha7 nicotinic acetylcholine receptors (α7nAChRs) attenuates inflammation, termed the cholinergic anti-inflammatory pathway (CAP). Thus, we hypothesize that low-dose nicotine impairs the progression of elastase-induced AAAs in rats by exerting anti-inflammatory and anti-oxidative stress properties. Male Sprague-Dawley rats underwent surgical AAA induction with intraluminal elastase infusion. We compared vehicle rats with rats treated with nicotine (1.25 mg/kg/day), and aneurysm progression was monitored by weekly ultrasound images for 28 days. Nicotine treatment significantly promoted AAA progression (p = 0.031). Additionally, gelatin zymography demonstrated that nicotine significantly reduced pro-matrix metalloproteinase (pro-MMP) 2 (p = 0.029) and MMP9 (p = 0.030) activity in aneurysmal tissue. No significant difference was found in the elastin content or the score of elastin degradation between the groups. Neither infiltrating neutrophils nor macrophages, nor aneurysmal messenger RNA (mRNA) levels of pro- or anti-inflammatory cytokines, differed between the vehicle and nicotine groups. Finally, no difference in mRNA levels of markers for anti-oxidative stress or the vascular smooth muscle cells' contractile phenotype was observed. However, proteomics analyses of non-aneurysmal abdominal aortas revealed that nicotine decreased myristoylated alanine-rich C-kinase substrate and proteins, in ontology terms, inflammatory response and reactive oxygen species, and in contradiction to augmented AAAs. In conclusion, nicotine at a dose of 1.25 mg/kg/day augments AAA expansion in this elastase AAA model. These results do not support the use of low-dose nicotine administration for the prevention of AAA progression.

Abstract 155: Platelet-derived Transforming Growth Factor-β1 Ameliorates AAA in a Murine Model

Background: Platelets are rapidly recruited to the forming intraluminal thrombus in abdominal aortic aneurysm (AAA), stabilizing the aortic wall and preventing rupture. Adhesion and activation of platelets releases a mix of inflammatory mediators such as transforming growth factor β (TGFβ), which mediates cellular proliferation, inflammatory signaling, and fibrosis. Importantly, while TGFβ neutralization results in increased rupture and disease progression in mouse models of AAA, the source of protective TGFβ signaling remains controversial. We hypothesized that platelet-derived TGFβ1 attenuates aortic growth in the elastase AAA model. Methods and Results: Ldlr -/- mice with platelet-specific deletion of Tgfβ1 were produced by breeding hemizygous male mice expressing Cre under the control of the Pf4 promoter to female Tgfβ1 floxed mice (Jackson Labs). Mice were subjected to laparotomy and topical elastase application to the abdominal aorta (10 mg/mL porcine pancreatic elastase for 5 minutes) and sacrificed at day 28 to determine AAA progression via aortic diameter. Male TGFβ1-Pf4 Cre+ mice (n=8) had significantly increased abdominal aortic diameters compared to Male TGFβ1-Pf4 Cre- mice (n=7) ( Cre- : 1.70 ± 0.12 mm; Cre+ : 2.66 ± 0.25 mm; P &lt; 0.004). Additionally, 25% of male TGFβ1-Pf4 Cre+ mice died of AAA rupture compared to 0% in the TGFβ1-Pf4 Cre- cohort. To determine if these actions were occurring via TGFβ1 activation of the TGFβ receptor 2 (βr 2 ), Ldlr -/- /βr2 Flox /PF4 Cre+ and Cre- mice were created, similarly to the previously described Tgfβ1 mice. Male βr2-Pf4 Cre+ (n=7) had increased aortic diameter compared to βr2-Pf4 Cre- (n=6) ( Cre- : 1.70± 0.20 mm; Cre+ : 2.45 ± 0.38 mm; P &lt; 0.138). Additionally, female βr2-Pf4 Cre+ (n=9) also had significantly larger aortic diameters compared to βr2-Pf4 Cre- (n = 5) ( Cre- : 1.27± 0.04 mm; Cre+ : 1.90 ± 0.23 mm; P &lt; 0.01). Conclusions: Our results further support TGFβ signaling playing a protective role in AAA. More specifically, platelet-derived TGFβ1 ligand and signaling via platelet TGFβr2 mitigates aortic diameter expansion. Further research into the pertinent TGFβ isoforms and the mechanism of TGFβr2 activation will ideally yield insights into therapeutic targets for an, as yet, intractable disease.

Abstract 273: Smooth Muscle Cell Specific Beclin-1 Deficiency Accelerates Aortic Aneurysms In Male And Female Normolipidemic And Hypercholesterolemic Mice

Background and Objective: Ascending and abdominal aortic aneurysms (AAs) are permanent dilations of the aorta with 80% mortality after rupture. Vascular smooth muscle cell (SMC)-rich aortic media is disrupted in AAs. Autophagy is a process by which cell recycles their cytoplasmic materials for energy purposes under stress. Recent clinical studies highlighted that Beclin-1, an autophagy induction gene, is upregulated in AA tissues from patients. Using Angiotensin II (AngII) infusion model of AAs, we examined the functional role of SMC-derived Beclin-1 during AA development in normolipidemic and hypercholesterolemic mice. Methods and Results: Mice with inducible deletion of Beclin-1 in SMCs were produced by breeding male Acta2-Cre ERT2 hemizygous mice female Beclin-1 floxed mice in normolipidemic and hypercholesterolemic (LDLR-/-) background. At 8 weeks of age, Beclin-1 x Acta2-Cre ERT2 (Cre+) and non-Cre littermates (Cre-) mice were injected with tamoxifen (75 mg/kg, i.p.) for 5 days. After 2 weeks, Western blot analyses showed depletion of Beclin-1 protein in the aortic media from Cre+ mice compared to Cre- littermates. To study the role of SMC-Beclin-1, normolipidemic or hypercholesterolemic male Cre+ and Cre- (N=7 per group) mice were fed either chow or fat-enriched diet (21% fat; 0.15% cholesterol) for 5 weeks. After 1 week of diet feeding, mice were infused with saline or low dose of AngII (500 ng/kg/min) by osmotic mini-pumps for 4 weeks. SMC-Beclin-1 deficiency in either normolipidemic or hypercholesterolemic mice spontaneously but significantly accelerated ascending (Cre-: 1.2 ± 0.07 vs Cre+: 1.8 ± 0.04 mm; P &lt;0.001), arch (Cre-: 1.1 ± 0.04 vs Cre+: 1.8 ± 0.03 mm; P &lt;0.001), descending (Cre-: 1.1 ± 0.04 vs Cre+: 1.5 ± 0.04 mm; P &lt;0.001), and abdominal (Cre-: 1.0 ± 0.02 vs Cre+: 1.5 ± 0.14 mm; P &lt;0.001) aortic expansion. AngII-infusion had no additional influence on SMC-Beclin-1 deficiency accelerated aortic expansion. In addition, SMC-Beclin-1 deficiency significantly increased aortic medial hypertrophy and elastin breaks (P&lt;0.001 Cre- vs Cre+) associated with complete loss of medial alpha-SMC actin positive area. Conclusion: These findings demonstrate that SMC-Beclin-1 plays a critical role in suppressing aortic aneurysmal formation in mice.

Abstract 584: Myeloid Kruppel-like Factor 14 Mediates Sexual Dimorphism Of Abdominal Aortic Aneurysm Via Estrogen Receptor β

Rationale: Abdominal aortic aneurysm (AAA) is an irreversible degenerative disease of the abdominal aorta. Monocytes/macrophages are important mediators of inflammation and proteolysis during AAA development. In both human and rodent models, AAA has strong sexual dimorphism with a 4-6-fold higher prevalence in males than females, largely attributed to the estrogen/estrogen receptor signaling pathway. Krüppel-Like Factor 14 (KLF14) mediates anti-inflammatory response during disease pathogenesis and shows sexual heterogeneity in human genetic studies. However, whether and how KLF14 regulates sexual dimorphism during AAA progression has largely been unknown. Objective: Herein, we generated a novel insight into the anti-inflammatory effect and sexual dimorphic regulation of KLF14 during AAA pathogenesis. Methods and Results: We induced AAA model in myeloid cell-specific Klf14 knockout mice in ApoE -deficient background ( Klf14 LysM ApoE -/- ) and their littermate control mice ( Klf14 fl/fl ApoE -/- ). Klf14 deficiency in macrophages completely abrogated the sexual dimorphism observed in control mice by showing higher AAA incidence with more macrophage infiltration and more severe elastin degradation in female mice. Mechanistically, KLF14 upregulates the transcription of estrogen receptors, especially ESR2 , in macrophages. Perhexiline, a KLF14 inducer, induces Esr2 expression dependent on Klf14 and exerts an anti-inflammatory effect partially dependent on Esr2 in macrophages. Furthermore, Klf14 or Esr2 deficiency in macrophages abolished the protective effect of exogenous estradiol (E 2 ) treatment in male control mice. Conclusions: These studies provide evidence that Klf14 deficiency within myeloid lineage cells accelerated AAA development in female mice, resulting in the loss of sexual dimorphism in AAA pathogenesis. KLF14 showed protective effects, likely via transcriptionally regulating ESR2 expression and suppressing inflammation.

Abstract 112: Pcsk6 Ablation In Vascular Smooth Muscle Cells Promotes Abdominal Aortic Aneurysm Development And Rupture

Background and Aim: We have previously shown that Proprotein Convertase Subtilisin/Kexin type 6 (Pcsk6) is strongly enriched in atherosclerotic plaques and plays a key role in lesion vulnerability and vessel wall healing by regulating vascular smooth muscle cell (VSMC) migration, proliferation, and extracellular matrix remodeling. Considering the broad importance of these processes in vascular pathologies, this study aimed to investigate the expression and function of Pcsk6 in the abdominal aortic aneurysm (AAA). Methods and Results: Bioinformatic analysis of human transcriptome microarray and RNA-sequencing data from human AAA biobanks of the Karolinska Institute and the Technical University of Munich have demonstrated a significantly increased level of Pcsk6 transcript in AAA tissues compared to controls, and even higher levels in ruptured AAAs. Single-cell RNA sequencing data demonstrated a significantly increased level of Pcsk6 transcript in fibroblasts and T cells but decreased in VSMCs. To further clarify if Pcsk6 dysregulation in VSMCs is a pathological reaction or if it has a causal role in AAA development and aortic dissection, we performed pilot animal studies: 1) peri-adventitial porcine pancreatic elastase (PPE) induced AAA model on male VSMC conditional Tagln-Pcsk6 deficient and control mice; 2) AngII infusion model on male Tagln-Pcsk6 deficient and control mice with ApoE-/- background. Interestingly, although no difference in baseline blood pressure, aortic dilatation, and constriction was found between Tagln-Pcsk6 deficient and control mice, ultrasound imaging and histology analyses showed that mice with Pcsk6 deficiency in VSMCs manifested remarkably larger AAA, as well as significantly increased rupture and dissection rate. Mechanistically, RNA sequencing analysis indicated significant inhibition of extracellular matrix components and biosynthesis signaling in aortas from Tagln-Pcsk6 deficient mice. Conclusion: PCSK6 expressed by VSMCs plays a substantial role in AAA progression and aortic dissection, opening new avenues for the therapy of aortic disease. Further mechanistic studies are necessary before this translational aspect can be evaluated.

Intraluminal Thrombus Characteristics in AAA Patients: Non-Invasive Diagnosis Using CFD.

Abdominal aortic aneurysms (AAA) continue to pose a high mortality risk despite advances in medical imaging and surgery. Intraluminal thrombus (ILT) is detected in most AAAs and may critically impact their development. Therefore, understanding ILT deposition and growth is of practical importance. To assist in managing these patients, the scientific community has been researching the relationship between intraluminal thrombus (ILT) and hemodynamic parameters wall shear stress (WSS) derivatives. This study analyzed three patient-specific AAA models reconstructed from CT scans using computational fluid dynamics (CFD) simulations and a pulsatile non-Newtonian blood flow model. The co-localization and relationship between WSS-based hemodynamic parameters and ILT deposition were examined. The results show that ILT tends to occur in regions of low velocity and time-averaged WSS (TAWSS) and high oscillation shear index (OSI), endothelial cell activation potential (ECAP), and relative residence time (RRT) values. ILT deposition areas were found in regions of low TAWSS and high OSI independently of the nature of flow near the wall characterized by transversal WSS (TransWSS). A new approach is suggested which is based on the estimation of CFD-based WSS indices specifically in the thinnest and thickest ILT areas of AAA patients; this approach is promising and supports the effectiveness of CFD as a decision-making tool for clinicians. Further research with a larger patient cohort and follow-up data are needed to confirm these findings.