Ascending Aortic Aneurysm in Angiotensin II-Infused Mice: Formation, Progression, and the Role of Focal Dissections

Ubiquitin-like modifier-activating enzyme 1 as a potential therapeutic target for aortic dissection

Aortic dissection (AD) is a life-threatening aortopathy with no specific pharmacological therapy. Ubiquitination, a highly orchestrated enzymatic cascade involving sequential E1-E2-E3 interactions, is suggested to contribute to the disease pathogenesis. However, the specific role of E1 enzymes in AD progression remains unknown. In this study, we analyzed the aortic transcriptional profiles of a human ascending dissection dataset (GSE52093) and identified ubiquitin-like modifier-activating enzyme 1 (UBA1) as a significantly up-regulated E1 enzyme in human AD. This finding was further corroborated by immunohistochemistry and RT-qPCR in a mouse model of AD induced by β-aminopropionitrile (BAPN). Treatment of TAK-243, a specific UBA1 inhibitor, prevented BAPN-induced AD formation in mice and attenuated aortic medial degeneration, as evidenced by decreased elastin fragmentation (evaluated by EVG scoring), reduced vascular smooth muscle cell loss (visualized by α-SMA immunohistochemistry), and less extracellular matrix degradation (indicated by diminished MMP2 and MMP9 expression in immunohistochemistry and RT-qPCR). Furthermore, TAK-243 treatment attenuated lesional macrophage accumulation and activation, as demonstrated by CD68 immunohistochemistry and RT-qPCR analysis of aortic pro-inflammatory cytokine expression. In vitro, UBA1 activation was observed in macrophages (RAW264.7 cells) treated with angiotensin II (AngII), and TAK-243 significantly reduced AngII-induced macrophage activation, at least partially through the inhibition of IκBα and NF-κB p65 phosphorylation. In conclusion, we demonstrate that UBA1 may facilitate AD progression by promoting macrophage activation via the NF-κB signaling pathway. These findings reveal a pathogenic role for the E1 enzyme UBA1 in AD and show a pharmacological potential of UBA1-targeted therapy against this disease.

ANK Deficiency-Mediated Cytosolic Citrate Accumulation Promotes Aortic Aneurysm

BACKGROUND

Disturbed metabolism and transport of citrate play significant roles in various pathologies. However, vascular citrate regulation and its potential role in aortic aneurysm (AA) development remain poorly understood.

METHODS

Untargeted metabolomics by mass spectrometry was applied to identify upregulated metabolites of the tricarboxylic acid cycle in AA tissues of mice. To investigate the role of citrate and its transporter ANK (progressive ankylosis protein) in AA development, vascular smooth muscle cell (VSMC)-specific Ank-knockout mice were used in both Ang II (angiotensin II)- and CaPO4-induced AA models.

RESULTS

Citrate was abnormally increased in both human and murine aneurysmal tissues, which was associated with downregulation of ANK, a citrate membrane transporter, in VSMCs. The knockout of Ank in VSMCs promoted AA formation in both Ang II- and CaPO4-induced AA models, while its overexpression inhibited the development of aneurysms. Mechanistically, ANK deficiency in VSMCs caused abnormal cytosolic accumulation of citrate, which was cleaved into acetyl coenzyme A and thus intensified histone acetylation at H3K23, H3K27, and H4K5. Cleavage under target and tagmentation analysis further identified that ANK deficiency-induced histone acetylation activated the transcription of inflammatory genes in VSMCs and thus promoted a citrate-related proinflammatory VSMC phenotype during aneurysm diseases. Accordingly, suppressing citrate cleavage to acetyl coenzyme A downregulated inflammatory gene expression in VSMCs and restricted ANK deficiency-aggravated AA formation.

CONCLUSIONS

Our studies define the pathogenic role of ANK deficiency-induced cytosolic citrate accumulation in AA pathogenesis and an undescribed citrate-related proinflammatory VSMC phenotype. Targeting ANK-mediated citrate transport may emerge as a novel diagnostic and therapeutic strategy in AA.

Establishment of Mouse Models of Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is a chronic vascular disease that commonly affects elderly individuals but has recently increased in younger populations. As the aneurysm grows, it can cause compression symptoms such as abdominal pain, rupture, and bleeding, which are absent in the early stages. Once an AAA ruptures and causes bleeding, the mortality rate is alarmingly high. Currently, the pathogenesis for AAA is unknown, and therapeutic options are limited, necessitating improvement in treatment efficacy. An essential research method for studying the processes and potential treatment of AAA is establishing animal models using mice. The present study provides a detailed overview of the widely used AAA mouse animal models and their construction strategies, advantages, disadvantages, scope of applications, and prospects.

Gasdermin D deficiency attenuates development of ascending aortic dissections in a novel mouse model

Background

Thoracic aortic dissection (TAD) is a silent killer. Approximately two-thirds of the cases occur in the ascending aorta (i.e. type A dissection) and majority of them are unrelated to genetic mutations. However, animal models of spontaneous type A dissection are not widely available. In the present study, a novel mouse TAD model was created. Further, the role of gasdermin D (GSDMD) in TAD development was evaluated.

Methods

TADs were created by treating ascending aorta of adult mice (C57BL/6J) with active elastase (40.0 U/ml) and β-aminopropionitrile (Act E+BAPN). The temporal progress of the TAD pathology was rigorously characterized by histological evaluation and scanning electron microscopy, while potential mechanisms explored with bulk RNA sequencing of specimens collected at multiple timepoints. With this novel TAD model, further experiments were performed with Gsdmd -/- mice to evaluate its impact on TAD formation.

Results

The ascending aorta challenged with Act E+BAPN developed pathology characterized by an early onset of intimomedial tears (complete penetration) and intramural hematoma, followed by progressive medial loss and aortic dilation. Ingenuity Pathway Analysis and functional annotation of differentially expressed genes suggested that a unique inflammatory micro-environment, rather than general inflammation, promoted the onset of TADs by specifically recruiting neutrophils to the aortic wall, while the pathology at the advanced stage was driven by T-cell mediated immune injury. Gsdmd -/- attenuated medial loss, adventitial fibrosis, and dilation of TADs. This protective effect was associated with a reduced number of TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling) positive cells and T-cells in TADs.

Conclusions

A novel mouse TAD model was created in the ascending aorta. It produces a unique microenvironment to activate different immune cell subsets, promoting onset and subsequent remodeling of TADs. Consistently, Gsdmd -/- attenuates TAD development, with modulation of cell death and T-cell response likely acting as the underlying mechanism.

The role of oxidative stress in aortic dissection: a potential therapeutic target

The incidence of aortic dissection (AD) is steadily increasing, driven by the rising prevalence of chronic conditions such as hypertension and the global aging of the population. Oxidative stress emerges as a pivotal pathophysiological mechanism contributing to the progression of AD. Oxidative stress triggers apoptosis in vascular smooth muscle cells, reshapes the extracellular matrix (ECM), and governs ECM degradation and remodeling, subsequently impacting aortic compliance. Furthermore, oxidative stress not only facilitates the infiltration of macrophages and mononuclear lymphocytes but also disrupts the integral structure and functionality of endothelial cells, thereby inducing endothelial cell dysfunction and furthering the degeneration of the middle layer of the aortic wall. Investigating antioxidants holds promise as a therapeutic avenue for addressing AD.

Therapeutic potential of natural products and underlying targets for the treatment of aortic aneurysm

Aortic aneurysm is a vascular disease characterized by irreversible vasodilatation that can lead to dissection and rupture of the aortic aneurysm, a life-threatening condition. Thoracic aortic aneurysm (TAA) and abdominal aortic aneurysm (AAA) are two main types. The typical treatments for aortic aneurysms are open surgery and endovascular aortic repair, which are only indicated for more severe patients. Most patients with aneurysms have an insidious onset and slow progression, and there are no effective drugs to treat this stage. The inability of current animal models to perfectly simulate all the pathophysiological states of human aneurysms may be the key to this issue. Therefore, elucidating the molecular mechanisms of this disease, finding new therapeutic targets, and developing effective drugs to inhibit the development of aneurysms are the main issues of current research. Natural products have been applied for thousands of years to treat cardiovascular disease (CVD) in China and other Asian countries. In recent years, natural products have combined multi-omics, computational biology, and integrated pharmacology to accurately analyze drug components and targets. Therefore, the multi-component and multi-target complexity of natural products have made them a potentially ideal treatment for multifactorial diseases such as aortic aneurysms. Natural products have regained popularity worldwide. This review provides an overview of the known natural products for the treatment of TAA and AAA and searches for potential cardiovascular-targeted natural products that may treat TAA and AAA based on various cellular molecular mechanisms associated with aneurysm development.

Pharmacological Inhibition of MMP-12 Exerts Protective Effects on Angiotensin II-Induced Abdominal Aortic Aneurysms in Apolipoprotein E-Deficient Mice

Human abdominal aortic aneurysms (AAAs) are characterized by increased activity of matrix metalloproteinases (MMP), including MMP-12, alongside macrophage accumulation and elastin degradation, in conjunction with superimposed atherosclerosis. Previous genetic ablation studies have proposed contradictory roles for MMP-12 in AAA development. In this study, we aimed to elucidate if pharmacological inhibition of MMP-12 activity with a phosphinic peptide inhibitor protects from AAA formation and progression in angiotensin (Ang) II-infused Apoe-/- mice. Complimentary studies were conducted in a human ex vivo model of early aneurysm development. Administration of an MMP-12 inhibitor (RXP470.1) protected hypercholesterolemia Apoe-/- mice from Ang II-induced AAA formation and rupture-related death, associated with diminished medial thinning and elastin fragmentation alongside increased collagen deposition. Proteomic analyses confirmed a beneficial effect of MMP-12 inhibition on extracellular matrix remodeling proteins combined with inflammatory pathways. Furthermore, RXP470.1 treatment of mice with pre-existing AAAs exerted beneficial effects as observed through suppressed aortic dilation and rupture, medial thinning, and elastin destruction. Our findings indicate that pharmacological inhibition of MMP-12 activity retards AAA progression and improves survival in mice providing proof-of-concept evidence to motivate translational work for MMP-12 inhibitor therapy in humans.

Cardiac and perivascular myofibroblasts, matrifibrocytes, and immune fibrocytes in hypertension; commonalities and differences with other cardiovascular diseases

Hypertension is a major cause of cardiovascular diseases such as myocardial infarction and stroke. Cardiovascular fibrosis occurs with hypertension and contributes to vascular resistance, aortic stiffness, and cardiac hypertrophy. However, the molecular mechanisms leading to fibroblast activation in hypertension remain largely unknown. There are two types of fibrosis: replacement fibrosis and reactive fibrosis. Replacement fibrosis occurs in response to the loss of viable tissue to form a scar. Reactive fibrosis occurs in response to an increase in mechanical and neurohormonal stress. Although both types of fibrosis are considered adaptive processes, they become maladaptive when the tissue loss is too large, or the stress persists. Myofibroblasts represent a subpopulation of activated fibroblasts that have gained contractile function to promote wound healing. Therefore, myofibroblasts are a critical cell type that promotes replacement fibrosis. Although myofibroblasts were recognized as the fibroblasts participating in reactive fibrosis, recent experimental evidence indicated there are distinct fibroblast populations in cardiovascular reactive fibrosis. Accordingly, we will discuss the updated definition of fibroblast subpopulations, the regulatory mechanisms, and their potential roles in cardiovascular pathophysiology utilizing new knowledge from various lineage tracing and single-cell RNA sequencing studies. Among the fibroblast subpopulations, we will highlight the novel roles of matrifibrocytes and immune fibrocytes in cardiovascular fibrosis including experimental models of hypertension, pressure overload, myocardial infarction, atherosclerosis, aortic aneurysm, and nephrosclerosis. Exploration into the molecular mechanisms involved in the differentiation and activation of those fibroblast subpopulations may lead to novel treatments for end-organ damage associated with hypertension and other cardiovascular diseases.

Angiotensin II constricts mouse iliac arteries: possible mechanism for aortic aneurysms

Abdominal aortic aneurysms (AAA) result from maladaptive remodeling of the vascular wall and reduces structural integrity. Angiotensin II (AngII) infusion has become a standard laboratory model for studying AAA initiation and progression. We determined the different vasoactive responses of various mouse arteries to Ang II. Ex vivo isometric tension analysis was conducted on 18-week-old male C57BL/6 mice (n = 4) brachiocephalic arteries (BC), iliac arteries (IL), and abdominal (AA) and thoracic aorta (TA). Arterial rings were mounted between organ hooks, gently stretched and an AngII dose response was performed. Rings were placed in 4% paraformaldehyde for immunohistochemistry analysis to quantify peptide expression of angiotensin type 1 (AT1R) and 2 receptors (AT2R) in the endothelium, media, and adventitia. Results from this study demonstrated vasoconstriction responses in IL were significantly higher at all AngII doses when compared to BC, and TA and AA responses (maximum constriction-IL: 68.64 ± 5.47% vs. BC: 1.96 ± 1.00%; TA: 3.13 ± 0.16% and AA: 2.75 ± 1.77%, p < 0.0001). Expression of AT1R was highest in the endothelium of IL (p < 0.05) and in the media and (p < 0.05) adventitia (p < 0.05) of AA. In contrast, AT2R expression was highest in endothelium (p < 0.05), media (p < 0.01, p < 0.05) and adventitia of TA. These results suggest that mouse arteries display different vasoactive responses to AngII, and the exaggerated response in IL arteries may play a role during AAA development.

The future for the therapeutics of abdominal aortic aneurysm: engineered nanoparticles drug delivery for abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a severe cardiovascular disease with a high mortality rate. Several screening and diagnostic methods have been developed for AAA early diagnosis. Open surgery and endovascular aortic repair (EVAR) are clinically available for patients who meet the indications for surgery. However, for non-surgical patients, limited drugs exist to inhibit or reverse the progression of aneurysms due to the complex pathogenesis and biological structure of AAA, failing to accumulate precisely on the lesion to achieve sufficient concentrations. The recently developed nanotechnology offers a new strategy to address this problem by developing drug-carrying nanoparticles with enhanced water solubility and targeting capacity, prolonged duration, and reduced side effects. Despite the rising popularity, limited literature is available to highlight the progression of the field. Herein, in this review, we first discuss the pathogenesis of AAA, the methods of diagnosis and treatment that have been applied clinically, followed by the review of research progressions of constructing different drug-loaded nanoparticles for AAA treatment using engineered nanoparticles. In addition, the feasibility of extracellular vesicles (EVs) and EVs-based nanotechnology for AAA treatment in recent years are highlighted, together with the future perspective. We hope this review will provide a clear picture for the scientists and clinicians to find a new solution for AAA clinical management.

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

OBJECTIVES

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).

MATERIALS AND METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Inhibition of smooth muscle cell death by Angiotensin 1-7 protects against abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) represents a debilitating vascular disease characterized by aortic dilatation and wall rupture if it remains untreated. We aimed to determine the effects of Ang 1-7 in a murine model of AAA and to investigate the molecular mechanisms involved. Eight- to 10-week-old apolipoprotein E-deficient mice (ApoEKO) were infused with Ang II (1.44 mg/kg/day, s.c.) and treated with Ang 1-7 (0.576 mg/kg/day, i.p.). Echocardiographic and histological analyses showed abdominal aortic dilatation and extracellular matrix remodeling in Ang II-infused mice. Treatment with Ang 1-7 led to suppression of Ang II-induced aortic dilatation in the abdominal aorta. The immunofluorescence imaging exhibited reduced smooth muscle cell (SMC) density in the abdominal aorta. The abdominal aortic SMCs from ApoEKO mice exhibited markedly increased apoptosis in response to Ang II. Ang 1-7 attenuated cell death, as evident by increased SMC density in the aorta and reduced annexin V/propidium iodide-positive cells in flow cytometric analysis. Gene expression analysis for contractile and synthetic phenotypes of abdominal SMCs showed preservation of contractile phenotype by Ang 1-7 treatment. Molecular analyses identified increased mitochondrial fission, elevated cellular and mitochondrial reactive oxygen species (ROS) levels, and apoptosis-associated proteins, including cytochrome c, in Ang II-treated aortic SMCs. Ang 1-7 mitigated Ang II-induced mitochondrial fission, ROS generation, and levels of pro-apoptotic proteins, resulting in decreased cell death of aortic SMCs. These results highlight a critical vasculo-protective role of Ang 1-7 in a degenerative aortic disease; increased Ang 1-7 activity may provide a promising therapeutic strategy against the progression of AAA.

ER stress mediates Angiotensin II-augmented innate immunity memory and facilitates distinct susceptibilities of thoracic from abdominal aorta to aneurysm development

To determine the roles of endoplasmic reticulum (ER) stress and trained immunity, we performed transcriptome analyses on the thoracic aorta (TA) and abdominal aorta (AA) from the angiotensin II (Ang II)-HFD-ApoE-KO aneurysm model and made significant findings: 1) Ang II bypassed HFD-induced metabolic reprogramming and induced stronger inflammation in AA than in TA; 2) Ang II and HFD upregulated 890 genes in AA versus TA and induced cytokine signaling; 3) Ang II AA and TA upregulated 73 and 68 cytokines, scRNA-Seq identified markers of macrophages and immune cells, cell death regulators, respectively; transdifferentiation markers of neuron, glial, and squamous epithelial cells were upregulated by Ang II-AA and TA; and pyroptosis signaling with IL-1β and caspase-4 were more upregulated in Ang II-AA than in TA; 4) Six upregulated transcriptomes in patients with AAA, Ang II AA, Ang II TA, additional aneurysm models, PPE-AAA and BAPN-Ang II-AAA, were partially overlapped with 10 lists of new ER stress gene sets including 3 interaction protein lists of ER stress regulators ATF6, PERK, and IRE1, HPA ER localization genes, KEGG signal genes, XBP1 transcription targets, ATF4 (PERK) targets, ATF6 targets, thapsigargin ER stress genes, tunicamycin-ER stress genes, respectively; 5) Ang II-AA and TA upregulated ROS regulators, MitoCarta genes, trained immunity genes, and glycolysis genes; and 6) Gene KO transcriptomes indicated that ATF6 and PERK played more significant roles than IRE1 in promoting AAA and trained immunity whereas antioxidant NRF2 inhibited them. Our unprecedented ER-focused transcriptomic analyses have provided novel insights on the roles of ER as an immune organelle in sensing various DAMPs and initiating ER stress that triggers Ang II-accelerated trained immunity and differs susceptibilities of thoracic and abdominal aortas to diseases.

Murine model of elastase-induced proximal thoracic aortic aneurysm through a midline incision in the anterior neck

Objective

This study was performed to develop a murine model of elastase-induced proximal thoracic aortic aneurysms (PTAAs).

Methods

The ascending thoracic aorta and aortic arch of adult C57BL/6J male mice were exposed through a midline incision in the anterior neck, followed by peri-adventitial elastase or saline application. The maximal ascending thoracic aorta diameter was measured with high-resolution micro-ultrasound. Twenty-eight days after the operation, the aortas were harvested and analyzed by histopathological examination and qualitative polymerase chain reaction to determine the basic characteristics of the aneurysmal lesions.

Results

Fourteen days after the operation, the dilation rate (mean ± standard error) in the 10-min elastase application group (n = 10, 71.44 ± 10.45%) or 5-min application group (n = 9, 42.67 ± 3.72%) were significantly higher than that in the saline application group (n = 9, 7.37 ± 0.94%, P < 0.001 for both). Histopathological examination revealed aortic wall thickening, degradation of elastin fibers, loss of smooth muscle cells, more vasa vasorum, enhanced extracellular matrix degradation, augmented collagen synthesis, upregulated apoptosis and proliferation capacity of smooth muscle cells, and increased macrophages and CD4⁺ T cells infiltration in the PTAA lesions. Qualitative analyses indicated higher expression of the proinflammatory markers, matrix metalloproteinase-2 and -9 as well as Collagen III, Collagen I in the PTAAs than in the controls.

Conclusion

We established a novel in vivo mouse model of PTAAs through a midline incision in the anterior neck by peri-adventitial application of elastase. This model may facilitate research into the pathogenesis of PTAA formation and the treatment strategy for this devastating disease.

Attenuation of Smooth Muscle Cell Phenotypic Switching by Angiotensin 1-7 Protects against Thoracic Aortic Aneurysm

Thoracic aortic aneurysm (TAA) involves extracellular matrix (ECM) remodeling of the aortic wall, leading to reduced biomechanical support with risk of aortic dissection and rupture. Activation of the renin-angiotensin system, and resultant angiotensin (Ang) II synthesis, is critically involved in the onset and progression of TAA. The current study investigated the effects of angiotensin (Ang) 1-7 on a murine model of TAA. Male 8-10-week-old ApoEKO mice were infused with Ang II (1.44 mg/kg/day) and treated with Ang 1-7 (0.576 mg/kg/day). ApoEKO mice developed advanced TAA in response to four weeks of Ang II infusion. Echocardiographic and histological analyses demonstrated increased aortic dilatation, excessive structural remodelling, perivascular fibrosis, and inflammation in the thoracic aorta. Ang 1-7 infusion led to attenuation of pathological phenotypic alterations associated with Ang II-induced TAA. Smooth muscle cells (SMCs) isolated from adult murine thoracic aorta exhibited excessive mitochondrial fission, oxidative stress, and hyperproliferation in response to Ang II. Treatment with Ang 1-7 resulted in inhibition of mitochondrial fragmentation, ROS generation, and hyperproliferation. Gene expression profiling used for characterization of the contractile and synthetic phenotypes of thoracic aortic SMCs revealed preservation of the contractile phenotype with Ang 1-7 treatment. In conclusion, Ang 1-7 prevented Ang II-induced vascular remodeling and the development of TAA. Enhancing Ang 1-7 actions may provide a novel therapeutic strategy to prevent or delay the progression of TAA.

Targeted Inhibition of Matrix Metalloproteinase-8 Prevents Aortic Dissection in a Murine Model

Aortic dissection (AD) is a lethal aortic pathology without effective medical treatments since the underlying pathological mechanisms responsible for AD remain elusive. Matrix metalloproteinase-8 (MMP8) has been previously identified as a key player in atherosclerosis and arterial remodeling. However, the functional role of MMP8 in AD remains largely unknown. Here, we report that an increased level of MMP8 was observed in 3-aminopropionitrile fumarate (BAPN)-induced murine AD. AD incidence and aortic elastin fragmentation were markedly reduced in MMP8-knockout mice. Importantly, pharmacologic inhibition of MMP8 significantly reduced the AD incidence and aortic elastin fragmentation. We observed less inflammatory cell accumulation, a lower level of aortic inflammation, and decreased smooth muscle cell (SMC) apoptosis in MMP8-knockout mice. In line with our previous observation that MMP8 cleaves Ang I to generate Ang II, BAPN-treated MMP8-knockout mice had increased levels of Ang I, but decreased levels of Ang II and lower blood pressure. Additionally, we observed a decreased expression level of vascular cell adhesion molecule-1 (VCAM1) and a reduced level of reactive oxygen species (ROS) in MMP8-knockout aortas. Mechanistically, our data show that the Ang II/VCAM1 signal axis is responsible for MMP8-mediated inflammatory cell invasion and transendothelial migration, while MMP8-mediated SMC inflammation and apoptosis are attributed to Ang II/ROS signaling. Finally, we observed higher levels of aortic and serum MMP8 in patients with AD. We therefore provide new insights into the molecular mechanisms underlying AD and identify MMP8 as a potential therapeutic target for this life-threatening aortic disease.

Embryonic Heterogeneity of Smooth Muscle Cells in the Complex Mechanisms of Thoracic Aortic Aneurysms

Smooth muscle cells (SMCs) are the major cell type of the aortic wall and play a pivotal role in the pathophysiology of thoracic aortic aneurysms (TAAs). TAAs occur in a region-specific manner with the proximal region being a common location. In this region, SMCs are derived embryonically from either the cardiac neural crest or the second heart field. These cells of distinct origins reside in specific locations and exhibit different biological behaviors in the complex mechanism of TAAs. The purpose of this review is to enhance understanding of the embryonic heterogeneity of SMCs in the proximal thoracic aorta and their functions in TAAs.

Evolving Mural Defects, Dilatation, and Biomechanical Dysfunction in Angiotensin II-Induced Thoracic Aortopathies

BACKGROUND

Thoracic aortopathy associates with extracellular matrix remodeling and altered biomechanical properties. We sought to quantify the natural history of thoracic aortopathy in a common mouse model and to correlate measures of wall remodeling such as aortic dilatation or localized mural defects with evolving microstructural composition and biomechanical properties of the wall.

METHODS

We combined a high-resolution multimodality imaging approach (panoramic digital image correlation and optical coherence tomography) with histopathologic examinations and biaxial mechanical testing to correlate spatially, for the first time, macroscopic mural defects and medial degeneration within the ascending aorta with local changes in aortic wall composition and mechanical properties.

RESULTS

Findings revealed strong correlations between local decreases in elastic energy storage and increases in circumferential material stiffness with increasing proximal aortic diameter and especially mural defect size. Mural defects tended to exhibit a pronounced biomechanical dysfunction that is driven by an altered organization of collagen and elastic fibers.

CONCLUSIONS

While aneurysmal dilatation is often observed within particular segments of the aorta, dissection and rupture initiate as highly localized mechanical failures. We show that wall composition and material properties are compromised in regions of local mural defects, which further increases the dilatation and overall structural vulnerability of the wall. Identification of therapies focused on promoting robust collagen accumulation may protect the wall from these vulnerabilities and limit the incidence of dissection and rupture.

Angiotensin II Induces Aortic Rupture and Dissection in Osteoprotegerin-Deficient Mice

Background

The biological mechanism of action for osteoprotegerin, a soluble decoy receptor for the receptor activator of nuclear factor‐kappa B ligand in the vascular structure, has not been elucidated. The study aim was to determine if osteoprotegerin affects aortic structural integrity in angiotensin II (Ang II)‐induced hypertension.

Methods and Results

Mortality was higher (P<0.0001 by log‐rank test) in 8‐week‐old male homozygotes of osteoprotegerin gene‐knockout mice given subcutaneous administration of Ang II for 28 days, with an incidence of 21% fatal aortic rupture and 23% aortic dissection, than in age‐matched wild‐type mice. Ang II‐infused aorta of wild‐type mice showed that osteoprotegerin immunoreactivity was present with proteoglycan. The absence of osteoprotegerin was associated with decreased medial and adventitial thickness and increased numbers of elastin breaks as well as with increased periostin expression and soluble receptor activator of nuclear factor‐kappa B ligand concentrations. PEGylated human recombinant osteoprotegerin administration decreased all‐cause mortality (P<0.001 by log‐rank test), the incidence of fatal aortic rupture (P=0.08), and aortic dissection (P<0.001) with decreasing numbers of elastin breaks, periostin expressions, and soluble receptor activator of nuclear factor‐kappa B ligand concentrations in Ang II‐infused osteoprotegerin gene‐knockout mice.

Conclusions

These data suggest that osteoprotegerin protects against aortic rupture and dissection in Ang II‐induced hypertension by inhibiting receptor activator of nuclear factor‐kappa B ligand activity and periostin expression.

Imaging Techniques for Aortic Aneurysms and Dissections in Mice: Comparisons of Ex Vivo, In Situ, and Ultrasound Approaches

Aortic aneurysms and dissections are life-threatening conditions that have a high risk for lethal bleeding and organ malperfusion. Many studies have investigated the molecular basis of these diseases using mouse models. In mice, ex vivo, in situ, and ultrasound imaging are major approaches to evaluate aortic diameters, a common parameter to determine the severity of aortic aneurysms. However, accurate evaluations of aortic dimensions by these imaging approaches could be challenging due to pathological features of aortic aneurysms. Currently, there is no standardized mode to assess aortic dissections in mice. It is important to understand the characteristics of each approach for reliable evaluation of aortic dilatations. In this review, we summarize imaging techniques used for aortic visualization in recent mouse studies and discuss their pros and cons. We also provide suggestions to facilitate the visualization of mouse aortas.

Second Heart Field-derived Cells Contribute to Angiotensin II-mediated Ascending Aortopathies

Background: The ascending aorta is a common location for aneurysm and dissection. This aortic region is populated by a mosaic of medial and adventitial cells that are embryonically derived from either the second heart field (SHF) or the cardiac neural crest. SHF-derived cells populate areas that coincide with the spatial specificity of thoracic aortopathies. The purpose of this study was to determine whether and how SHF-derived cells contribute to ascending aortopathies. Methods: Ascending aortic pathologies were examined in patients with sporadic thoracic aortopathies and angiotensin II (AngII)-infused mice. Ascending aortas without overt pathology from AngII-infused mice were subjected to mass spectrometry assisted proteomics, and molecular features of SHF-derived cells were determined by single cell transcriptomic analyses. Genetic deletion of either low-density lipoprotein receptor-related protein 1 (Lrp1) or transforming growth factor-β receptor 2 (Tgfbr2) in SHF-derived cells was conducted to examine the impact of SHF-derived cells on vascular integrity. Results: Pathologies in human ascending aortic aneurysmal tissues were predominant in outer medial layers and adventitia. This gradient was mimicked in mouse aortas following AngII infusion that was coincident with the distribution of SHF-derived cells. Proteomics indicated that brief AngII infusion, prior to overt pathology, evoked downregulation of SMC proteins and differential expression of extracellular matrix proteins, including several LRP1 ligands. LRP1 deletion in SHF-derived cells augmented AngII-induced ascending aortic aneurysm and rupture. Single cell transcriptomic analysis revealed that brief AngII infusion decreased Lrp1 and Tgfbr2 mRNA abundance in SHF-derived cells and induced a unique fibroblast population with low abundance of Tgfbr2 mRNA. SHF-specific Tgfbr2 deletion led to embryonic lethality at E12.5 with dilatation of the outflow tract and retroperitoneal hemorrhage. Integration of proteomic and single cell transcriptomics results identified plasminogen activator inhibitor 1 (PAI1) as the most increased protein in SHF-derived SMCs and fibroblasts during AngII infusion. Immunostaining revealed a transmural gradient of PAI1 in both ascending aortas of AngII-infused mice and human ascending aneurysmal aortas that mimicked the gradient of medial and adventitial pathologies. Conclusions: SHF-derived cells exert a critical role in maintaining vascular integrity through LRP1 and TGF-β signaling associated with increases of aortic PAI1.

mTOR inhibition prevents angiotensin II-induced aortic rupture and pseudoaneurysm but promotes dissection in Apoe-deficient mice

Aortic dissection and rupture are triggered by decreased vascular wall strength and/or increased mechanical loads. We investigated the role of mTOR signaling in aortopathy using a well-described model of angiotensin II–induced dissection, aneurysm, or rupture of the suprarenal abdominal aorta in Apoe-deficient mice. Although not widely appreciated, nonlethal hemorrhagic lesions present as pseudoaneurysms without significant dissection in this model. Angiotensin II–induced aortic tears result in free rupture, contained rupture with subadventitial hematoma (forming pseudoaneurysms), dilatation, or healing, while the media invariably thickens regardless of mural tears. Medial thickening results from smooth muscle cell hypertrophy and extracellular matrix accumulation, including matricellular proteins. Angiotensin II activates mTOR signaling in vascular wall cells, and inhibition of mTOR signaling by rapamycin prevents aortic rupture but promotes dissection. Decreased aortic rupture correlates with decreased inflammation and metalloproteinase expression, whereas extensive dissection correlates with induction of matricellular proteins that modulate adhesion of vascular cells. Thus, mTOR activation in vascular wall cells determines whether aortic tears progress to dissection or rupture. Previous mechanistic studies of aortic aneurysm and dissection by angiotensin II in Apoe-deficient mice should be reinterpreted as clinically relevant to pseudoaneurysms, and mTOR inhibition for aortic disease should be explored with caution.

Injection of Matrix Metalloproteinase-9 Leads to Ventricular Remodeling

OBJECTIVE

Previous studies have found that some ventricular remodeling is accompanied by increased matrix metalloproteinase-9 (MMP-9) in vivo, and MMP-9 inhibitors can reduce ventricular remodeling. However, there is still no direct evidence that MMP-9 causes ventricular remodeling. In this study, MMP-9 was injected into rats to observe whether MMP-9 caused ventricular remodeling, thereby providing direct evidence of MMP-9-induced ventricular remodeling.

METHODS

Forty-eight eight-week-old male Wistar rats were randomly divided, by weight, into control, low-, medium-, and high-dose MMP-9 groups and were administered normal saline or recombinant rat MMP-9 0.7, 1.4, or 2.1 ng/g, respectively, via intraperitoneal injection, twice per week. On the 28th day, six rats were randomly selected from each group (Stage I). The remaining rats continued receiving injections until the 56th day (Stage II). Echocardiography was performed to observe cardiac structure and function, and the left ventricular mass index (LVWI) was calculated. Myocardial pathological changes and the collagen volume fraction (CVF) were observed by HE and VG staining in myocardial tissue. MMP-9 levels in serum were tested using ELISA. Myocardial MMP-9 levels were measured using Western blots, and the myocardial expression levels of MMP-9 mRNA were assessed using RT-PCR.

RESULTS

During Stage I, serum MMP-9 and myocardial MMP-9 mRNA levels are increased; hypertrophic cardiomyocytes, disorderly arrangement of fibers, and endochylema dissolution are observed in the medium- and high-dose groups. The left ventricular weight index (LVWI) and myocardial MMP-9 increased, and the collagen volume fraction (CVF) reduced in the high-dose group. In Stage II, the left ventricular end-diastolic volume (LVEDV) and diameter (LVIDd) are higher, and CVF decreased in the medium- and high-dose groups. Myocardial pathological lesions intensified. Serum MMP-9 in the model groups and myocardial MMP-9 in the medium- and high-dose groups are increased.

CONCLUSIONS

Injection of MMP-9 can lead to ventricular remodeling.

Exosomes in Cardiovascular Diseases: Pathological Potential of Nano-Messenger

Cardiovascular diseases (CVDs) represent a major global health problem, due to their continued high incidences and mortality. The last few decades have witnessed new advances in clinical research which led to increased survival and recovery in CVD patients. Nevertheless, elusive and multifactorial pathophysiological mechanisms of CVD development perplexed researchers in identifying efficacious therapeutic interventions. Search for novel and effective strategies for diagnosis, prevention, and intervention for CVD has shifted research focus on extracellular vesicles (EVs) in recent years. By transporting molecular cargo from donor to recipient cells, EVs modulate gene expression and influence the phenotype of recipient cells, thus EVs prove to be an imperative component of intercellular signaling. Elucidation of the role of EVs in intercellular communications under physiological conditions implied the enormous potential of EVs in monitoring and treatment of CVD. The EVs secreted from the myriad of cells in the cardiovascular system such as cardiomyocytes, cardiac fibroblasts, cardiac progenitor cells, endothelial cells, inflammatory cells may facilitate the communication in physiological and pathological conditions. Understanding EVs-mediated cellular communication may delineate the mechanism of origin and progression of cardiovascular diseases. The current review summarizes exosome-mediated paracrine signaling leading to cardiovascular disease. The mechanistic role of exosomes in cardiovascular disease will provide novel avenues in designing diagnosis and therapeutic interventions.

Uncertainty quantification in subject-specific estimation of local vessel mechanical properties

Quantitative estimation of local mechanical properties remains critically important in the ongoing effort to elucidate how blood vessels establish, maintain, or lose mechanical homeostasis. Recent advances based on panoramic digital image correlation (pDIC) have made high-fidelity 3D reconstructions of small-animal (e.g., murine) vessels possible when imaged in a variety of quasi-statically loaded configurations. While we have previously developed and validated inverse modeling approaches to translate pDIC-measured surface deformations into biomechanical metrics of interest, our workflow did not heretofore include a methodology to quantify uncertainties associated with local point estimates of mechanical properties. This limitation has compromised our ability to infer biomechanical properties on a subject-specific basis, such as whether stiffness differs significantly between multiple material locations on the same vessel or whether stiffness differs significantly between multiple vessels at a corresponding material location. In the present study, we have integrated a novel uncertainty quantification and propagation pipeline within our inverse modeling approach, relying on empirical and analytic Bayesian techniques. To demonstrate the approach, we present illustrative results for the ascending thoracic aorta from three mouse models, quantifying uncertainties in constitutive model parameters as well as circumferential and axial tangent stiffness. Our extended workflow not only allows parameter uncertainties to be systematically reported, but also facilitates both subject-specific and group-level statistical analyses of the mechanics of the vessel wall.

Apelin expression deficiency in mice contributes to vascular stiffening by extracellular matrix remodeling of the aortic wall

Numerous recent studies have shown that in the continuum of cardiovascular diseases, the measurement of arterial stiffness has powerful predictive value in cardiovascular risk and mortality and that this value is independent of other conventional risk factors, such as age, cholesterol levels, diabetes, smoking, or average blood pressure. Vascular stiffening is often the main cause of arterial hypertension (AHT), which is common in the presence of obesity. However, the mechanisms leading to vascular stiffening, as well as preventive factors, remain unclear. The aim of the present study was to investigate the consequences of apelin deficiency on the vascular stiffening and wall remodeling of aorta in mice. This factor freed by visceral adipose tissue, is known for its homeostasic role in lipid and vascular metabolisms, or again in inflammation. We compared the level of metabolic markers, inflammation of white adipose tissue (WAT), and aortic wall remodeling from functional and structural approaches in apelin-deficient and wild-type (WT) mice. Apelin-deficient mice were generated by knockout of the apelin gene (APL-KO). From 8 mice by groups, aortic stiffness was analyzed by pulse wave velocity measurements and by characterizations of collagen and elastic fibers. Mann-Whitney statistical test determined the significant data (p < 5%) between groups. The APL-KO mice developed inflammation, which was associated with significant remodeling of visceral WAT, such as neutrophil elastase and cathepsin S expressions. In vitro, cathepsin S activity was detected in conditioned medium prepared from adipose tissue of the APL-KO mice, and cathepsin S activity induced high fragmentations of elastic fiber of wild-type aorta, suggesting that the WAT secretome could play a major role in vascular stiffening. In vivo, remodeling of the extracellular matrix (ECM), such as collagen accumulation and elastolysis, was observed in the aortic walls of the APL-KO mice, with the latter associated with high cathepsin S activity. In addition, pulse wave velocity (PWV) and AHT were increased in the APL-KO mice. The latter could explain aortic wall remodeling in the APL-KO mice. The absence of apelin expression, particularly in WAT, modified the adipocyte secretome and facilitated remodeling of the ECM of the aortic wall. Thus, elastolysis of elastic fibers and collagen accumulation contributed to vascular stiffening and AHT. Therefore, apelin expression could be a major element to preserve vascular homeostasis.

Significance of Hemodynamics Biomarkers, Tissue Biomechanics and Numerical Simulations in the Pathogenesis of Ascending Thoracic Aortic Aneurysms

Guidelines for the treatment of aortic wall diseases are based on measurements of maximum aortic diameter. However, aortic rupture or dissections do occur for small aortic diameters. Growing scientific evidence underlines the importance of biomechanics and hemodynamics in aortic disease development and progression. Wall shear stress (WWS) is an important hemodynamics marker that depends on aortic wall morphology and on the aortic valve function. WSS could be helpful to interpret aortic wall remodeling and define personalized risk criteria. The complementarity of Computational Fluid Dynamics and 4D Magnetic Resonance Imaging as tools for WSS assessment is a promising reality. The potentiality of these innovative technologies will provide maps or atlases of hemodynamics biomarkers to predict aortic tissue dysfunction. Ongoing efforts should focus on the correlation between these non-invasive imaging biomarkers and clinico-pathologic situations for the implementation of personalized medicine in current clinical practice.

Anti-Atherogenic Effect of 10% Supplementation of Anchovy (Engraulis encrasicolus) Waste Protein Hydrolysates in ApoE-Deficient Mice

Fish protein consumption exerts beneficial metabolic effects on human health, also correlating with a decreased risk for cardiovascular disease. Fish waste contains high amount of proteins and utilization may offer the opportunity for generating compounds advantageous for human health. Especially, fish waste protein hydrolysates beneficially influence pathways involved in body composition, exerting anti-inflammatory and antioxidant activities, making their potential supplementation in human disorders of increased interest. This study assessed the effect of a 10% (w/w) anchovy waste protein hydrolysate (APH) diet for 12 weeks in reducing atherosclerosis in ApoE^-/- mice, through histological and immunohistochemical methods. In addition, monitoring of plaque development was performed, using high-frequency ultrasound and magnetic resonance imaging. Overall, the APH diet attenuated atherosclerotic plaque development, producing a regression of arterial lesions over time (p < 0.05). Twelve weeks on an APH diet had an anti-obesity effect, improving lipid metabolism and reducing hepatic enzyme activity. A significant reduction in plaque size and lipid content was observed in the aortic sinus of APH-fed mice, compared to the control (p < 0.001), whereas no differences in the extracellular matrix and macrophage recruitment were observed. Supplementation of APH significantly attenuates atherosclerosis in ApoE^-/- mice, exerting a lipid-lowering activity. The opportunity to use fish waste protein hydrolysates as a nutraceutical in atherosclerosis is worthy of future investigations, representing a low cost, sustainable, and nutritional strategy with minimal environmental impact.

Weighted Gene Co-Expression Network Analysis Reveals Key Genes and Potential Drugs in Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is a prevalent aortic disease that causes high mortality due to asymptomatic gradual expansion and sudden rupture. The underlying molecular mechanisms and effective pharmaceutical therapy for preventing AAA progression have not been fully identified. In this study, we identified the key modules and hub genes involved in AAA growth from the GSE17901 dataset in the Gene Expression Omnibus (GEO) database through the weighted gene co-expression network analysis (WGCNA). Key genes were further selected and validated in the mouse dataset (GSE12591) and human datasets (GSE7084, GSE47472, and GSE57691). Finally, we predicted drug candidates targeting key genes using the Drug-Gene Interaction database. Overall, we identified key modules enriched in the mitotic cell cycle, GTPase activity, and several metabolic processes. Seven key genes (CCR5, ADCY5, ADCY3, ACACB, LPIN1, ACSL1, UCP3) related to AAA progression were identified. A total of 35 drugs/compounds targeting the key genes were predicted, which may have the potential to prevent AAA progression.

Systemic delivery of targeted nanotherapeutic reverses angiotensin II-induced abdominal aortic aneurysms in mice

Abdominal aortic aneurysm (AAA) disease causes dilation of the aorta, leading to aortic rupture and death if not treated early. It is the 14th leading cause of death in the U.S. and 10th leading cause of death in men over age 55, affecting thousands of patients. Despite the prevalence of AAA, no safe and efficient pharmacotherapies exist for patients. The deterioration of the elastic lamina in the aneurysmal wall is a consistent feature of AAAs, making it an ideal target for delivering drugs to the AAA site. In this research, we conjugated nanoparticles with an elastin antibody that only targets degraded elastin while sparing healthy elastin. After induction of aneurysm by 4-week infusion of angiotensin II (Ang II), two biweekly intravenous injections of pentagalloyl glucose (PGG)-loaded nanoparticles conjugated with elastin antibody delivered the drug to the aneurysm site. We show that targeted delivery of PGG could reverse the aortic dilation, ameliorate the inflammation, restore the elastic lamina, and improve the mechanical properties of the aorta at the AAA site. Therefore, simple iv therapy of PGG loaded nanoparticles can be an effective treatment option for early to middle stage aneurysms to reverse disease progression and return the aorta to normal homeostasis.

Early Detection of Aortic Degeneration in a Mouse Model of Sporadic Aortic Aneurysm and Dissection Using Nanoparticle Contrast-Enhanced Computed Tomography

[Figure: see text].

Review of Current Advances in the Mechanical Description and Quantification of Aortic Dissection Mechanisms

Aortic dissection is a life-threatening event associated with a very poor outcome. A number of complex phenomena are involved in the initiation and propagation of the disease. Advances in the comprehension of the mechanisms leading to dissection have been made these last decades, thanks to improvements in imaging and experimental techniques. However, the micro-mechanics involved in triggering such rupture events remains poorly described and understood. It constitutes the primary focus of the present review. Towards the goal of detailing the dissection phenomenon, different experimental and modeling methods were used to investigate aortic dissection, and to understand the underlying phenomena involved. In the last ten years, research has tended to focus on the influence of microstructure on initiation and propagation of the dissection, leading to a number of multiscale models being developed. This review brings together all these materials in an attempt to identify main advances and remaining questions.

A validated mouse model capable of recapitulating the protective effects of female sex hormones on ascending aortic aneurysms and dissections (AADs)

Fewer females develop AADs (ascending aortic aneurysms and dissections) and the reasons for this protection remain poorly understood. The present study seeks to develop a mouse model that may be utilized to address this sexual dimorphism. Adult normolipidemic mice were challenged with BAPN (β-aminopropionitrile), AngII (angiotensin II), or BAPN + AngII. An initial protocol optimization found that 0.2% BAPN in drinking water plus AngII-infusion at 1,000 ng kg-1  min-1 produced favorable rates of AAD rupture (~50%) and dilation (~40%) in 28 days. Using these dosages, further experiments revealed that BAPN is toxic to naïve mature aortas and it acted synergistically with AngII to promote aortic tears and dissections. BAPN + AngII provoked early infiltration of myeloid cells and subsequent recruitment of lymphoid cells to the aortic wall. AADs established with BAPN + AngII, but not AngII alone, continued to expand after the cessation of AngII-infusion. This indefinite growth precipitated a 61% increase in the AAD diameter in 56 days. More importantly, with the optimized protocol, significant differences in AAD dilation (p = .012) and medial degeneration (p = .036) were detected between male and female mice. Treatment of ovariectomized mice with estradiol protected AAD formation (p = .014). In summary, this study developed a powerful mouse AAD model that can be used to study the sexual dimorphism in AAD formation.

Early Morphofunctional Changes in AngII-Infused Mice Contribute to Regional Onset of Aortic Aneurysm and Dissection

Aortic aneurysms and dissections are silent and lethal conditions, whose pathogenesis remains incompletely understood. Although angiotensin II (AngII)-infused ApoE-/- mice have been widely used to study aortic aneurysm and dissection, early morphofunctional alterations preceding the onset of these conditions remain unknown. The goal of this study was to unveil early morphofunctional changes underlying the onset of aneurysm and dissection. At 3 days post-AngII infusion, suprarenal abdominal aorta presented significant volumetric dilatation and microstructural damage. Ex vivo assessment of vascular reactivity of the suprarenal dissection-prone aorta and its side branches, showed an endothelial and contractile dysfunctions that were severe in the suprarenal aorta, moderate distally, and absent in the side branches, mirroring the susceptibility to dissection of these different vascular segments. Early and specific morphofunctional changes of the suprarenal aorta may contribute to the regional onset of aortic aneurysm and dissection by exacerbating the biomechanical burden arising from its side branches.

Recent Advances in Biomechanical Characterization of Thoracic Aortic Aneurysms

Thoracic aortic aneurysm (TAA) is a focal enlargement of the thoracic aorta, but the etiology of this disease is not fully understood. Previous work suggests that various genetic syndromes, congenital defects such as bicuspid aortic valve, hypertension, and age are associated with TAA formation. Though occurrence of TAAs is rare, they can be life-threatening when dissection or rupture occurs. Prevention of these adverse events often requires surgical intervention through full aortic root replacement or implantation of endovascular stent grafts. Currently, aneurysm diameters and expansion rates are used to determine if intervention is warranted. Unfortunately, this approach oversimplifies the complex aortopathy. Improving treatment of TAAs will likely require an increased understanding of the biological and biomechanical factors contributing to the disease. Past studies have substantially contributed to our knowledge of TAAs using various ex vivo, in vivo, and computational methods to biomechanically characterize the thoracic aorta. However, any singular approach typically focuses on only material properties of the aortic wall, intra-aneurysmal hemodynamics, or in vivo vessel dynamics, neglecting combinatorial factors that influence aneurysm development and progression. In this review, we briefly summarize the current understanding of TAA causes, treatment, and progression, before discussing recent advances in biomechanical studies of TAAs and possible future directions. We identify the need for comprehensive approaches that combine multiple characterization methods to study the mechanisms contributing to focal weakening and rupture. We hope this summary and analysis will inspire future studies leading to improved prediction of thoracic aneurysm progression and rupture, improving patient diagnoses and outcomes.

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

OBJECTIVE

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.

CONCLUSIONS

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.

Cellular signaling in Abdominal Aortic Aneurysm

Abdominal aortic aneurysms (AAAs) are highly lethal cardiovascular diseases without effective medications. However, the molecular and signaling mechanisms remain unclear. A series of pathological cellular processes have been shown to contribute to AAA formation, including vascular extracellular matrix remodeling, inflammatory and immune responses, oxidative stress, and dysfunction of vascular smooth muscle cells. Each cellular process involves complex cellular signaling, such as NF-κB, MAPK, TGFβ, Notch and inflammasome signaling. In this review, we discuss how cellular signaling networks function in various cellular processes during the pathogenesis and progression of AAA. Understanding the interaction of cellular signaling networks with AAA pathogenesis as well as the crosstalk of different signaling pathways is essential for the development of novel therapeutic approaches to and personalized treatments of AAA diseases.

Identification of crucial genes in abdominal aortic aneurysm by WGCNA

Background

Abdominal aortic aneurysm (AAA) is the full thickness dilation of the abdominal aorta. However, few effective medical therapies are available. Thus, elucidating the molecular mechanism of AAA pathogenesis and exploring the potential molecular target of medical therapies for AAA is of vital importance.

Methods

Three expression datasets (GSE7084, GSE47472 and GSE57691) were downloaded from the Gene Expression Omnibus (GEO). These datasets were merged and then normalized using the “sva” R package. Differential expressed gene (DEG) analysis and weighted gene co-expression network analysis (WGCNA) were conducted. We compared the co-expression patterns between AAA and normal conditions, and hub genes of each functional module were identified. DEGs were mapped to co-expression network under AAA condition and a DEG co-expression network was generated. Crucial genes were identified using molecular complex detection (MCODE) (a plugin in Cytoscape).

Results

In our study, 6 and 10 gene modules were detected for the AAA and normal conditions, respectively, while 143 DEGs were screened. Compared to the normal condition, genes associated with immune response, inflammation and muscle contraction were clustered in three gene modules respectively under the AAA condition; the hub genes of the three modules were MAP4K1, NFIB and HPK1, respectively. A DEG co-expression network with 102 nodes and 303 edges was identified, and a hub gene cluster with 10 genes from the DEG co-expression network was detected. YIPF6, RABGAP1, ANKRD6, GPD1L, PGRMC2, HIGD1A, GMDS, MGP, SLC25A4 and FAM129A were in the cluster. The expression levels of these 10 genes showed potential diagnostic value.

Conclusion

Based on WGCNA, we detected 6 modules under the AAA condition and 10 modules in the normal condition. Hub genes of each module and hub gene clusters of the DEG co-expression network were identified. These genes may act as potential targets for medical therapy and diagnostic biomarkers. Further studies are needed to elucidate the detailed biological function of these genes in the pathogenesis of AAA.

Synchrotron-based visualization and segmentation of elastic lamellae in the mouse carotid artery during quasi-static pressure inflation

In computational aortic biomechanics, aortic and arterial tissue are typically modelled as a homogeneous layer, making abstraction not only of the layered structure of intima, media and adventitia but also of the microstructure that exists within these layers. Here, we present a novel method to visualize the microstructure of the tunica media along the entire circumference of the vessel. To that end, we developed a pressure-inflation device that is compatible with synchrotron-based phase-contrast imaging. Using freshly excised left common carotid arteries from n = 12 mice, we visualized how the lamellae and interlamellar layers inflate as the luminal pressure is increased from 0 to 120 mm Hg in quasi-static steps. A graph-based segmentation algorithm subsequently allowed us to automatically segment each of the three lamellae, resulting in a three-dimensional geometry that represents lamellae, interlamellar layers and adventitia at nine different pressure levels. Our results demonstrate that the three elastic lamellae unfold and stretch simultaneously as luminal pressure is increased. In the long term, we believe that the results presented in this work can be a first step towards a better understanding of the mechanics of the arterial microstructure.

Intracellular retention of mutant lysyl oxidase leads to aortic dilation in response to increased hemodynamic stress

Heterozygous missense mutations in lysyl oxidase (LOX) are associated with thoracic aortic aneurysms and dissections. To assess how LOX mutations modify protein function and lead to aortic disease, we studied the factors that influence the onset and progression of vascular aneurysms in mice bearing a Lox mutation (p.M292R) linked to aortic dilation in humans. We show that mice heterozygous for the M292R mutation did not develop aneurysmal disease unless challenged with increased hemodynamic stress. Vessel dilation was confined to the ascending aorta although both the ascending and descending aortae showed changes in vessel wall structure, smooth muscle cell number and inflammatory cell recruitment that differed between wild-type and mutant animals. Studies with isolated cells found that M292R-mutant Lox is retained in the endoplasmic reticulum and ultimately cleared through an autophagy/proteasome pathway. Because the mutant protein does not transit to the Golgi where copper incorporation occurs, the protein is never catalytically active. These studies show that the M292R mutation results in LOX loss-of-function due to a secretion defect that predisposes the ascending aorta in mice (and by extension humans with similar mutations) to arterial dilation when exposed to risk factors that impart stress to the arterial wall.

Aortic Strain Correlates with Elastin Fragmentation in Fibrillin-1 Hypomorphic Mice

Background

High frequency ultrasound has facilitated in vivo measurements of murine ascending aortas, allowing aortic strains to be gleaned from two-dimensional images. Thoracic aortic aneurysms associated with mutations in fibrillin-1 (FBN1) display elastin fragmentation, which may impact aortic strain. In this study, we determined the relationship between elastin fragmentation and aortic circumferential strain in wild type and fibrillin-1 hypomorphic (FBN1 ^mgR/mgR) mice.

Methods and Results

Luminal diameters of the ascending aorta from wild type and FBN1 hypomorphic (FBN1 ^mgR/mgR) mice were measured in systole and diastole. Expansion of the ascending aorta during systole in male and female wild type mice was 0.21±0.02 mm (16.3%) and 0.21±0.01 mm (17.0%) respectively, while expansion in male and female FBN1 ^mgR/mgR mice was 0.11±0.04 mm (4.9%) and 0.07±0.02 mm (4.5%) respectively. Reduced circumferential strain was observed in FBN1 ^mgR/mgR mice compared to wild type littermates. Elastin fragmentation was inversely correlated to circumferential strain (R^2 = 0.628 p = 0.004) and significantly correlated with aortic diameter. (R^2 = 0.397, p = 0.038 in systole and R^2 = 0.515, p =0.013 in diastole).

Conclusions

FBN1 ^mgR/mgR mice had increased aortic diameters, reduced circumferential strain, and increased elastin fragmentation. Elastin fragmentation in FBN1 ^mgR/mgR and their wild type littermates was correlated with reduced circumferential strain.

Exogenous Vasohibin-2 Exacerbates Angiotensin II-Induced Ascending Aortic Dilation in Mice

Background: Chronic angiotensin II (AngII) infusion promotes ascending aortic dilation in C57BL/6J mice. Meanwhile, vasohibin-2 (VASH2) is an angiogenesis promoter in neovascularization under various pathologic conditions. The aim of this study was to investigate whether exogenous VASH2 influences chronic AngII-induced ascending aortic dilation.

Methods and Results: Eight–ten-week-old male C57BL/6J mice were injected with adenovirus (Ad) expressing either VASH2 or LacZ. One week after the injection, mice were infused with either AngII or saline s.c. for 3 weeks. Mice were divided into 4 groups: AngII+VASH2, AngII+LacZ, saline+VASH2, and saline+LacZ. Overexpression of VASH2 significantly increased AngII-induced intimal areas as well as the external diameter of the ascending aorta. In addition, VASH2 overexpression promoted ascending aortic medial elastin fragmentation in AngII-infused mice, which was associated with increased matrix metalloproteinase activity and medial smooth muscle cell (SMC) apoptosis. On western blot analysis, accumulation of apoptotic signaling proteins, p21 and p53 was increased in the AngII+VASH2 group. Furthermore, transfection of human aortic SMC with Ad VASH2 increased p21 and p53 protein abundance upon AngII stimulation. Positive TUNEL staining was also detected in the same group of the human aortic SMC.

Conclusions: Exogenous VASH2 exacerbates AngII-induced ascending aortic dilation in vivo, which is associated with increased medial apoptosis and elastin fragmentation.

Involvement of B cells in the pathophysiology of β-aminopropionitrile-induced thoracic aortic dissection in mice

Thoracic aortic dissection (TAD) is a life-threatening disease that is characterized by an inflammatory response. Innate and cellular immunity has long been known to be involved in TAD, but the role of humoral immunity in the pathophysiology of TAD remains unknown. We administered the lysyl oxidase inhibitor β-aminopropionitrile (BAPN; 1 g/kg/day) in 3-week-old male C57BL/6J mice for 4 weeks to establish an animal model of TAD. Animals that died were immediately dissected. Animals that survived were sacrificed on days 7, 14, and 28 after BAPN challenge. The incidence and rupture rates of BAPN-induced TAD were 90% (9/10) and 70% (7/10), respectively, at 28 days. Victoria blue-nuclear fast red staining of aortic tissue revealed elastic lamellae destruction and the formation of a false lumen in the BAPN group. Hematoxylin-eosin staining revealed the infiltration of both plasmacytoid mononuclear cells and polymorphonuclear inflammatory cells in TAD tissues. Enzyme-linked immunosorbent assay and immunohistochemistry indicated that plasma immunoglobin M (IgM) and IgG were elevated at 7, 14, and 28 days, and CD19-positive B cells infiltrated into the adventitia of aortic tissue in BAPN-treated mice. The transcriptional analysis showed an increase in the expression of B cell receptor signaling-associated genes. These results indicate that B cells and immunoglobulins might participate in the pathogenesis of TAD, suggesting that humoral immunity may be a possible therapeutic target for TAD.

Ultrasound Imaging of the Thoracic and Abdominal Aorta in Mice to Determine Aneurysm Dimensions

Contemporary high-resolution ultrasound instruments have sufficient resolution to facilitate the measurement of mouse aortas. These instruments have been widely used to measure aortic dimensions in mouse models of aortic aneurysms. Aortic aneurysms are defined as permanent dilations of the aorta, which occur most frequently in the ascending and abdominal regions. Sequential measurements of aortic dimensions by ultrasound are the principal approach for assessing the development and progression of aortic aneurysms in vivo. Although many reported studies used ultrasound imaging to measure aortic diameters as a primary endpoint, there are confounding factors, such as probe position and cardiac cycle, that may impact the accuracy of data acquisition, analysis, and interpretation. The purpose of this protocol is to provide a practical guide on the use of ultrasound to measure the aortic diameter in a reliable and reproducible manner. This protocol introduces the preparation of mice and instruments, the acquisition of appropriate ultrasound images, and data analysis.

Local variations in material and structural properties characterize murine thoracic aortic aneurysm mechanics

We recently developed an approach to characterize local nonlinear, anisotropic mechanical properties of murine arteries by combining biaxial extension-distension testing, panoramic digital image correlation, and an inverse method based on the principle of virtual power. This experimental-computational approach was illustrated for the normal murine abdominal aorta assuming uniform wall thickness. Here, however, we extend our prior approach by adding an optical coherence tomography (OCT) imaging system that permits local reconstructions of wall thickness. This multimodality approach is then used to characterize spatial variations of material and structural properties in ascending thoracic aortic aneurysms (aTAA) from two genetically modified mouse models (fibrillin-1 and fibulin-4 deficient) and to compare them with those from angiotensin II-infused apolipoprotein E-deficient and wild-type control ascending aortas. Local values of stored elastic energy and biaxial material stiffness, computed from spatial distributions of the best fit material parameters, varied significantly with circumferential position (inner vs. outer curvature, ventral vs. dorsal sides) across genotypes and treatments. Importantly, these data reveal an inverse relationship between material stiffness and wall thickness that underlies a general linear relationship between stiffness and wall stress across aTAAs. OCT images also revealed sites of advanced medial degeneration, which were captured by the inverse material characterization. Quantification of histological data further provided high-resolution local correlations among multiple mechanical metrics and wall microstructure. This is the first time that such structural defects and local properties have been characterized mechanically, which can better inform computational models of aortopathy that seek to predict where dissection or rupture may initiate.