Transforming growth factor-β and abdominal aortic aneurysms

Epigenetic modifications in abdominal aortic aneurysms: from basic to clinical

Abdominal Aortic Aneurysm (AAA) is a disease characterized by localized dilation of the abdominal aorta, involving multiple factors in its occurrence and development, ultimately leading to vessel rupture and severe bleeding. AAA has a high mortality rate, and there is a lack of targeted therapeutic drugs. Epigenetic regulation plays a crucial role in AAA, and the treatment of AAA in the epigenetic field may involve a series of related genes and pathways. Abnormal expression of these genes may be a key factor in the occurrence of the disease and could potentially serve as promising therapeutic targets. Understanding the epigenetic regulation of AAA is of significant importance in revealing the mechanisms underlying the disease and identifying new therapeutic targets. This knowledge can contribute to offering AAA patients better clinical treatment options beyond surgery. This review systematically explores various aspects of epigenetic regulation in AAA, including DNA methylation, histone modification, non-coding RNA, and RNA modification. The analysis of the roles of these regulatory mechanisms, along with the identification of relevant genes and pathways associated with AAA, is discussed comprehensively. Additionally, a comprehensive discussion is provided on existing treatment strategies and prospects for epigenetics-based treatments, offering insights for future clinical interventions.

Advances and challenges in regenerative therapies for abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a significant source of mortality worldwide and carries a mortality of greater than 80% after rupture. Despite extensive efforts to develop pharmacological treatments, there is currently no effective agent to prevent aneurysm growth and rupture. Current treatment paradigms only rely on the identification and surveillance of small aneurysms, prior to ultimate open surgical or endovascular repair. Recently, regenerative therapies have emerged as promising avenues to address the degenerative changes observed in AAA. This review briefly outlines current clinical management principles, characteristics, and pharmaceutical targets of AAA. Subsequently, a thorough discussion of regenerative approaches is provided. These include cellular approaches (vascular smooth muscle cells, endothelial cells, and mesenchymal stem cells) as well as the delivery of therapeutic molecules, gene therapies, and regenerative biomaterials. Lastly, additional barriers and considerations for clinical translation are provided. In conclusion, regenerative approaches hold significant promise for in situ reversal of tissue damages in AAA, necessitating sustained research and innovation to achieve successful and translatable therapies in a new era in AAA management.

Animal Models, Pathogenesis, and Potential Treatment of Thoracic Aortic Aneurysm

Thoracic aortic aneurysm (TAA) has a prevalence of 0.16-0.34% and an incidence of 7.6 per 100,000 person-years, accounting for 1-2% of all deaths in Western countries. Currently, no effective pharmacological therapies have been identified to slow TAA development and prevent TAA rupture. Large TAAs are treated with open surgical repair and less invasive thoracic endovascular aortic repair, both of which have high perioperative mortality risk. Therefore, there is an urgent medical need to identify the cellular and molecular mechanisms underlying TAA development and rupture to develop new therapies. In this review, we summarize animal TAA models including recent developments in porcine and zebrafish models: porcine models can assess new therapeutic devices or intervention strategies in a large mammal and zebrafish models can employ large-scale small-molecule suppressor screening in microwells. The second part of the review covers current views of TAA pathogenesis, derived from recent studies using these animal models, with a focus on the roles of the transforming growth factor-beta (TGFβ) pathway and the vascular smooth muscle cell (VSMC)-elastin-contractile unit. The last part discusses TAA treatment options as they emerge from recent preclinical studies.

Clonal Expansion in Cardiovascular Pathology

Clonal expansion refers to the proliferation and selection of advantageous "clones" that are better suited for survival in a Darwinian manner. In recent years, we have greatly enhanced our understanding of cell clonality in the cardiovascular context. However, our knowledge of the underlying mechanisms behind this clonal selection is still severely limited. There is a transpiring pattern of clonal expansion of smooth muscle cells and endothelial cells-and, in some cases, macrophages-in numerous cardiovascular diseases irrespective of their differing microenvironments. These findings indirectly suggest the possible existence of stem-like vascular cells which are primed to respond during disease. Subsequent clones may undergo further phenotypic changes to adopt either protective or detrimental roles. By investigating these clone-forming vascular cells, we may be able to harness this inherent clonal nature for future therapeutic intervention. This review comprehensively discusses what is currently known about clonal expansion across the cardiovascular field. Comparisons of the clonal nature of vascular cells in atherosclerosis (including clonal hematopoiesis of indeterminate potential), pulmonary hypertension, aneurysm, blood vessel injury, ischemia- and tumor-induced angiogenesis, and cerebral cavernous malformations are evaluated. Finally, we discuss the potential clinical implications of these findings and propose that proper understanding and specific targeting of these clonal cells may provide unique therapeutic options for the treatment of these cardiovascular conditions.

Dysregulations of Key Regulators of Angiogenesis and Inflammation in Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is a chronic vascular disease caused by localized weakening and broadening of the abdominal aorta. AAA is a clearly underdiagnosed disease and is burdened with a high mortality rate (65-85%) from AAA rupture. Studies indicate that abnormal regulation of angiogenesis and inflammation contributes to progression and onset of this disease; however, dysregulations in the molecular pathways associated with this disease are not yet fully explained. Therefore, in our study, we aimed to identify dysregulations in the key regulators of angiogenesis and inflammation in patients with AAA in peripheral blood mononuclear cells (using qPCR) and plasma samples (using ELISA). Expression levels of ANGPT1, CXCL8, PDGFA, TGFB1, VEGFB, and VEGFC and plasma levels of TGF-alpha, TGF-beta 1, VEGF-A, and VEGF-C were found to be significantly altered in the AAA group compared to the control subjects without AAA. Associations between analyzed factors and risk factors or biochemical parameters were also explored. Any of the analyzed factors was associated with the size of the aneurysm. The presented study identified dysregulations in key angiogenesis- and inflammation-related factors potentially involved in AAA formation, giving new insight into the molecular pathways involved in the development of this disease and providing candidates for biomarkers that could serve as diagnostic or therapeutic targets.

Genetic and clinical determinants of abdominal aortic diameter: genome-wide association studies, exome array data and Mendelian randomization study

Progressive dilation of the infrarenal aortic diameter is a consequence of the ageing process and is considered the main determinant of abdominal aortic aneurysm (AAA). We aimed to investigate the genetic and clinical determinants of abdominal aortic diameter (AAD). We conducted a meta-analysis of genome-wide association studies in 10 cohorts (n = 13 542) imputed to the 1000 Genome Project reference panel including 12 815 subjects in the discovery phase and 727 subjects [Partners Biobank cohort 1 (PBIO)] as replication. Maximum anterior-posterior diameter of the infrarenal aorta was used as AAD. We also included exome array data (n = 14 480) from seven epidemiologic studies. Single-variant and gene-based associations were done using SeqMeta package. A Mendelian randomization analysis was applied to investigate the causal effect of a number of clinical risk factors on AAD. In genome-wide association study (GWAS) on AAD, rs74448815 in the intronic region of LDLRAD4 reached genome-wide significance (beta = -0.02, SE = 0.004, P-value = 2.10 × 10-8). The association replicated in the PBIO1 cohort (P-value = 8.19 × 10-4). In exome-array single-variant analysis (P-value threshold = 9 × 10-7), the lowest P-value was found for rs239259 located in SLC22A20 (beta = 0.007, P-value = 1.2 × 10-5). In the gene-based analysis (P-value threshold = 1.85 × 10-6), PCSK5 showed an association with AAD (P-value = 8.03 × 10-7). Furthermore, in Mendelian randomization analyses, we found evidence for genetic association of pulse pressure (beta = -0.003, P-value = 0.02), triglycerides (beta = -0.16, P-value = 0.008) and height (beta = 0.03, P-value < 0.0001), known risk factors for AAA, consistent with a causal association with AAD. Our findings point to new biology as well as highlighting gene regions in mechanisms that have previously been implicated in the genetics of other vascular diseases.

Role of Extracellular Matrix and Inflammation in Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is one of the most dangerous cardiovascular diseases, occurring mainly in men over the age of 55 years. As it is asymptomatic, patients are diagnosed very late, usually when they suffer pain in the abdominal cavity. The late detection of AAA contributes to the high mortality rate. Many environmental, genetic, and molecular factors contribute to the development and subsequent rupture of AAA. Inflammation, apoptosis of smooth muscle cells, and degradation of the extracellular matrix in the AAA wall are believed to be the major molecular processes underlying AAA formation. Until now, no pharmacological treatment has been implemented to prevent the formation of AAA or to cure the disease. Therefore, it is important that patients are diagnosed at a very early stage of the disease. Biomarkers contribute to the assessment of the concentration level, which will help to determine the level and rate of AAA development. The potential biomarkers today include homocysteine, cathepsins, osteopontin, and osteoprotegerin. In this review, we describe the major aspects of molecular processes that take place in the aortic wall during AAA formation. In addition, biomarkers, the monitoring of which will contribute to the prompt diagnosis of AAA patients over the age of 55 years, are described.

Peptide-siRNA nanoparticles targeting NF-κB p50 mitigate experimental abdominal aortic aneurysm progression and rupture

Abdominal aortic aneurysm (AAA) is a progressive vascular condition associated with high risk of mortality if left untreated. AAA is an inflammatory process with excessive local production of extracellular matrix degrading enzymes, leading to dilatation and rupture of the abdominal aorta. We posit that targeting NF-κB, a signaling pathway that controls inflammation, will halt AAA progression and prevent rupture. In an elastase-induced AAA model we observed that NF-κB activation increased progressively post-elastase perfusion. Unexpectedly, we found that AAA progression was marked by predominant nuclear accumulation of the NF-κB p50 subunit at the exclusion of p65. Using the amphipathic peptide p5RHH to form nanocomplexes with siRNA, we sought to mitigate AAA progression by knocking down the expression of different NF-κB subunits. We found that the administration of NF-κB p65 siRNA was only beneficial when given early (day 3 post-elastase perfusion) while p50 siRNA was still effective in mitigating elastase-induced AAA even when delivery was delayed until day 5. Additionally, systemic delivery of p50 siRNA, but not p65 siRNA decreased the risk of aortic rupture and sudden death in the transforming growth factor-beta blockade model of AAA. In both murine models, knockdown of NF-κB was accompanied by a significant decrease in leukocyte infiltrates, inflammatory cytokine release, inducible nitric oxide synthase expression, and cell apoptosis. These results suggest that the NF-κB p50 and p65 subunits contribute differentially at different stages of disease and the timing of in vivo siRNA delivery was of critical importance. The results also provide a rationale for selective targeting of p50 for more specific therapeutic intervention in the medical treatment of small AAA.

Cytokines in Abdominal Aortic Aneurysm: Master Regulators With Clinical Application

Abdominal aortic aneurysm (AAA) is a potentially life-threatening disorder with a mostly asymptomatic course where the abdominal aorta is weakened and bulged. Cytokines play especially important roles (both positive and negative) among the molecular actors of AAA development. All the inflammatory cascades, extracellular matrix degradation and vascular smooth muscle cell apoptosis are driven by cytokines. Previous studies emphasize an altered expression and a changed epigenetic regulation of key cytokines in AAA tissue samples. Such cytokines as IL-6, IL-10, IL-12, IL-17, IL-33, IL-1β, TGF-β, TNF-α, IFN-γ, and CXCL10 seem to be crucial in AAA pathogenesis. Some data obtained in animal studies show a protective function of IL-10, IL-33, and canonical TGF-β signaling, as well as a dual role of IL-4, IFN-γ and CXCL10, while TNF-α, IL-1β, IL-6, IL-12/IL-23, IL-17, CCR2, CXCR2, CXCR4 and the TGF-β noncanonical pathway are believed to aggravate the disease. Altogether data highlight significance of cytokines as informative markers and predictors of AAA. Pathologic serum/plasma concentrations of IL-1β, IL-2, IL-6, TNF-α, IL-10, IL-8, IL-17, IFN-γ, and PDGF have been already found in AAA patients. Some of the changes correlate with the size of aneurysms. Moreover, the risk of AAA is associated with polymorphic variants of genes encoding cytokines and their receptors: CCR2 (rs1799864), CCR5 (Delta-32), IL6 (rs1800796 and rs1800795), IL6R (rs12133641), IL10 (rs1800896), TGFB1 (rs1800469), TGFBR1 (rs1626340), TGFBR2 (rs1036095, rs4522809, rs1078985), and TNFA (rs1800629). Finally, 5 single-nucleotide polymorphisms in gene coding latent TGF-β-binding protein (LTBP4) and an allelic variant of TGFB3 are related to a significantly slower AAA annual growth rate.

Adventitial Fibroblasts in Aortic Aneurysm: Unraveling Pathogenic Contributions to Vascular Disease

Aortic aneurysm (AA) is a degenerative vascular disease that involves aortic dilatation, and, if untreated, it can lead to rupture. Despite its significant impact on the healthcare system, its multifactorial nature and elusive pathophysiology contribute to limited therapeutic interventions that prevent the progression of AA. Thus, further research into the mechanisms underlying AA is paramount. Adventitial fibroblasts are one of the key constituents of the aortic wall, and they play an essential role in maintaining vessel structure and function. However, adventitial fibroblasts remain understudied when compared with endothelial cells and smooth muscle cells. Adventitial fibroblasts facilitate the production of extracellular matrix (ECM), providing structural integrity. However, during biomechanical stress and/or injury, adventitial fibroblasts can be activated into myofibroblasts, which move to the site of injury and secrete collagen and cytokines, thereby enhancing the inflammatory response. The overactivation or persistence of myofibroblasts has been shown to initiate pathological vascular remodeling. Therefore, understanding the underlying mechanisms involved in the activation of fibroblasts and in regulating myofibroblast activation may provide a potential therapeutic target to prevent or delay the progression of AA. This review discusses mechanistic insights into myofibroblast activation and associated vascular remodeling, thus illustrating the contribution of fibroblasts to the pathogenesis of AA.

Mesenchymal Stem Cells Alter MicroRNA Expression and Attenuate Thoracic Aortic Aneurysm Formation

BACKGROUND

Thoracic aortic aneurysms (TAA) are a progressive disease characterized by inflammation, smooth muscle cell activation and matrix degradation. We hypothesized that mesenchymal stem cells (MSCs) can immunomodulate vascular inflammation and remodeling via altered microRNA (miRNAs) expression profile to attenuate TAA formation.

MATERIALS AND METHODS

C57BL/6 mice underwent topical elastase application to form descending TAAs. Mice were also treated with MSCs on days 1 and 5 and aortas were analyzed on day 14 for aortic diameter. Cytokine array was performed in aortic tissue and total RNA was tagged and hybridized for miRNAs microarray analysis. Immunohistochemistry was performed for elastin degradation and leukocyte infiltration.

RESULTS

Treatment with MSCs significantly attenuated aortic diameter and TAA formation compared to untreated mice. MSC administration also attenuated T-cell, neutrophil and macrophage infiltration and prevented elastic degradation to mitigate vascular remodeling. MSC treatment also attenuated aortic inflammation by decreasing proinflammatory cytokines (CXCL13, IL-27, CXCL12 and RANTES) and upregulating anti-inflammatory interleukin-10 expression in aortic tissue of elastase-treated mice. TAA formation demonstrated activation of specific miRNAs that are associated with aortic inflammation and vascular remodeling. Our results also demonstrated that MSCs modulate a different set of miRNAs that are associated with decrease leukocyte infiltration and vascular inflammation to attenuate the aortic diameter and TAA formation.

CONCLUSIONS

These results indicate that MSCs immunomodulate specific miRNAs that are associated with modulating hallmarks of aortic inflammation and vascular remodeling of aortic aneurysms. Targeted therapies designed using MSCs and miRNAs have the potential to regulate the growth and development of TAAs.

TGF-β signaling and microRNA cross-talk regulates abdominal aortic aneurysm progression

Abdominal aortic aneurysms (AAA) are permanent and irreversible local dilatations of the abdominal aortic wall. Recent data indicate that the transforming growth factor-beta (TGF-β) signaling pathway exerts a protective effect on the development of AAA. Some dysregulated microRNAs (miRNA) also appear involved in the expansion of AAA and miRNA-based therapeutics have been shown to effectively inhibit this process. New evidence has revealed that TGF-β signaling and miRNA interaction may of physiologic and pathophysiologic significance including the progression of AAA. As such, miRNA that regulate TGF-β signaling may hold promise as potential therapeutic targets. This review explores potential crosstalk between TGF-β signaling and miRNA in AAA in order improve our understanding of this pathology and explore development of potential therapeutic targets.

Mouse models for abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) rupture is estimated to cause 200,000 deaths each year. Currently, the only treatment for AAA is surgical repair; however, this is only indicated for large asymptomatic, symptomatic or ruptured aneurysms, is not always durable, and is associated with a risk of serious perioperative complications. As a result, patients with small asymptomatic aneurysms or who are otherwise unfit for surgery are treated conservatively, but up to 70% of small aneurysms continue to grow, increasing the risk of rupture. There is thus an urgent need to develop drug therapies effective at slowing AAA growth. This review describes the commonly used mouse models for AAA. Recent research in these models highlights key roles for pathways involved in inflammation and cell turnover in AAA pathogenesis. There is also evidence for long non-coding RNAs and thrombosis in aneurysm pathology. Further well-designed research in clinically relevant models is expected to be translated into effective AAA drugs.

Stem cell derived extracellular vesicles for vascular elastic matrix regenerative repair

Abdominal aortic aneurysms (AAA) are localized expansions of the abdominal aorta that develop due to chronic proteolytic disruption of the structural extracellular matrix (ECM) components (elastin and collagen) within the aorta wall. Major limitations in arresting or reversing AAAs lie in naturally poor and aberrant regeneration and repair of elastic matrix structures in the aorta wall. Bone marrow derived mesenchymal stem cells (BM-MSCs) have emerged as a promising regenerative tool and their therapeutic effects are also known to be effected through their paracrine secretions. Extracellular vesicles (EVs) present in these secretions have emerged as critical cellular component in facilitating many therapeutic benefits of MSCs. EV treatment is thus potentially appealing as a stem cell-inspired cell-free approach to avoid possible phenotypic plasticity of MSCs in vivo. In this study, we investigated the thus far unknown effects of BM-MSC derived EVs on vascular elastic matrix repair in the context of AAA treatment. EVs isolated from BM-MSC source were characterized and their pro-regenerative and their anti-proteolytic effects were evaluated on our established in vitro experimental conditions derived from AAA rat model. Our studies revealed the efficacy of BM-MSC derived EVs in attenuating the proteolytic activity and also in imparting elastic matrix regenerative benefits under aneurysmal environment. Interestingly, compared to cell culture conditioned media (CCM), EVs demonstrated superior regenerative and anti-proteolytic benefits in a proteolytic injury culture model of AAA. From these studies, it appears that EVs derived from BM-MSCs could be beneficial in undertaking a reparative effort in AAA induced degeneration of vascular tissue. Statement of Significance Abdominal aortic aneurysms (AAAs) are localized, rupture-prone expansions of the aorta which result from loss of wall flexibility due to enzymatic breakdown of elastic fibers. There are no established alternatives to surgery, which possess high risk for the mostly elderly patients. Our previous studies have established the elastic regenerative and reparative effect of cell culture secretions derived from adult stem cell source. In this study, we propose to isolate extracellular vesicles (exosomes) from these secretions and evaluate their regenerative benefits in AAA smooth muscle cell culture model. This simple and innovative treatment approach has the potential to arrest or reverse AAA growth to rupture, not possible so far.

Lung-derived HMGB1 is detrimental for vascular remodeling of metabolically imbalanced arterial macrophages

Pulmonary disease increases the risk of developing abdominal aortic aneurysms (AAA). However, the mechanism underlying the pathological dialogue between the lungs and aorta is undefined. Here, we find that inflicting acute lung injury (ALI) to mice doubles their incidence of AAA and accelerates macrophage-driven proteolytic damage of the aortic wall. ALI-induced HMGB1 leaks and is captured by arterial macrophages thereby altering their mitochondrial metabolism through RIPK3. RIPK3 promotes mitochondrial fission leading to elevated oxidative stress via DRP1. This triggers MMP12 to lyse arterial matrix, thereby stimulating AAA. Administration of recombinant HMGB1 to WT, but not Ripk3^-/- mice, recapitulates ALI-induced proteolytic collapse of arterial architecture. Deletion of RIPK3 in myeloid cells, DRP1 or MMP12 suppression in ALI-inflicted mice repress arterial stress and brake MMP12 release by transmural macrophages thereby maintaining a strengthened arterial framework refractory to AAA. Our results establish an inter-organ circuitry that alerts arterial macrophages to regulate vascular remodeling.

The TGF-β pathway plays a key role in aortic aneurysms

Aortic dissection and aortic aneurysms are currently among the most high-risk cardiovascular diseases due to their rapid onset and high mortality. Although aneurysm research has been extensive, the pathogenesis remains unknown. Studies have found that the TGF-β/Smad pathway and aneurysm formation appear linked. For example, the TGF-β signaling pathway was significantly activated in aneurysm development and aortic dissection. Aneurysms are not, however, mitigated following knockdown of TGF-β signaling pathway-related genes. Incidence and mortality rate of ruptured thoracic aneurysms increase with the down-regulation of the classical TGF-β signaling pathway. In this review, we summarize recent findings and evaluate the differential role of classical and non-classical TGF-β pathways on aortic aneurysm. It is postulated that the TGF-β signaling pathway is necessary to maintain vascular function, but over-activation will promote aneurysms whereas over-inhibition will lead to bypass pathway over-activation and promote aneurysm occurrence.

Inflammation and TGF-β Signaling Differ between Abdominal Aneurysms and Occlusive Disease

Abdominal aortic aneurysms (AAA), are usually asymptomatic until rupture causes fatal bleeding, posing a major vascular health problem. AAAs are associated with advanced age, male gender, and cardiovascular risk factors (e.g. hypertension and smoking). Strikingly, AAA and AOD (arterial occlusive disease) patients have a similar atherosclerotic burden, yet develop either arterial dilatation or occlusion, respectively. The molecular mechanisms underlying this diversion are yet unknown. As this knowledge could improve AAA treatment strategies, we aimed to identify genes and signaling pathways involved. We compared RNA expression profiles of abdominal aortic AAA and AOD patient samples. Based on differential gene expression profiles, we selected a gene set that could serve as blood biomarker or as pharmacological intervention target for AAA. In this AAA gene list we identified previously AAA-associated genes COL11A1, ADIPOQ, and LPL, thus validating our approach as well as novel genes; CXCL13, SLC7A5, FDC-SP not previously linked to aneurysmal disease. Pathway analysis revealed overrepresentation of significantly altered immune-related pathways between AAA and AOD. Additionally, we found bone morphogenetic protein (BMP) signaling inhibition simultaneous with activation of transforming growth factor β (TGF-β) signaling associated with AAA. Concluding our gene expression profiling approach identifies novel genes and an interplay between BMP and TGF-β signaling regulation specifically for AAA.

Matrix Metalloproteinase in Abdominal Aortic Aneurysm and Aortic Dissection

Abdominal Aortic Aneurysm (AAA) affects 4–5% of men over 65, and Aortic Dissection (AD) is a life-threatening aortic pathology associated with high morbidity and mortality. Initiators of AAA and AD include smoking and arterial hypertension, whilst key pathophysiological features of AAA and AD include chronic inflammation, hypoxia, and large modifications to the extra cellular matrix (ECM). As it stands, only surgical methods are available for preventing aortic rupture in patients, which often presents difficulties for recovery. No pharmacological treatment is available, as such researchers are attempting to understand the cellular and molecular pathophysiology of AAA and AD. Upregulation of matrix metalloproteinase (MMPs), particularly MMP-2 and MMP-9, has been identified as a key event occurring during aneurysmal growth. As such, several animal models of AAA and AD have been used to investigate the therapeutic potential of suppressing MMP-2 and MMP-9 activity as well as modulating the activity of other MMPs, and TIMPs involved in the pathology. Whilst several studies have offered promising results, targeted delivery of MMP inhibition still needs to be developed in order to avoid surgery in high risk patients.

The potential of cardiac rehabilitation as a method of suppressing abdominal aortic aneurysm expansion: a pilot study

This study is a prospective evaluation of the effectiveness of cardiac rehabilitation (CR) in terms of clinical outcomes for small abdominal aortic aneurysms (AAA) that were previously reported in a retrospective cohort study. We conducted a prospective non-randomized trial on patients with small AAA (N = 40; mean age 75.0 ± 6.6 years). Patients were enrolled into one of two groups, rehabilitation (CR) or non-rehabilitation (non-CR) group. Only CR group participated in a supervised-CR program including bicycle ergometer for 150 days. The AAA expansion rate and the risk of AAA repair were compared between two groups. We also researched the relationship between AAA expansion rate and body composition, blood IL-6 and TGFβ1 levels. The CR (N = 15) and non-CR groups (N = 25) were comparable in terms their baseline data. The CR group had a significantly smaller change in the maximal AAA size (- 1.3 ± 2.4 mm/years) compared to the non-CR group (2.0 ± 3.6 mm/years) (p < 0.01). The IL-6, and TGFβ1 levels were unrelated to the changes in AAA size. There was mild positive correlation between the change in systolic blood pressure from rest to exercise and the AAA expansion rate (p = 0.06). The risk of AAA repair after 12 months was lower in the CR group compared to the non-CR group (0% vs. 28%, respectively). CR in patients with small AAA significantly suppressed AAA expansion and resulted in a lowered risk of AAA repair.Clinical trial Trial name: The study of the profitability and protective effect of cardiac rehabilitation on abdominal aortic aneurysm. Number: UMIN000028237. UTL: https://upload.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R0000323.

TGFβ (Transforming Growth Factor-β) Blockade Induces a Human-Like Disease in a Nondissecting Mouse Model of Abdominal Aortic Aneurysm

OBJECTIVE

Current experimental models of abdominal aortic aneurysm (AAA) do not accurately reproduce the major features of human AAA. We hypothesized that blockade of TGFβ (transforming growth factor-β) activity-a guardian of vascular integrity and immune homeostasis-would impair vascular healing in models of nondissecting AAA and would lead to sustained aneurysmal growth until rupture.

APPROACH AND RESULTS

Here, we test this hypothesis in the elastase-induced AAA model in mice. We analyze AAA development and progression using ultrasound in vivo, synchrotron-based ultrahigh resolution imaging ex vivo, and a combination of biological, histological, and flow cytometry-based cellular and molecular approaches in vitro. Systemic blockade of TGFβ using a monoclonal antibody induces a transition from a self-contained aortic dilatation to a model of sustained aneurysmal growth, associated with the formation of an intraluminal thrombus. AAA growth is associated with wall disruption but no medial dissection and culminates in fatal transmural aortic wall rupture. TGFβ blockade enhances leukocyte infiltration both in the aortic wall and the intraluminal thrombus and aggravates extracellular matrix degradation. Early blockade of IL-1β or monocyte-dependent responses substantially limits AAA severity. However, blockade of IL-1β after disease initiation has no effect on AAA progression to rupture.

CONCLUSIONS

Endogenous TGFβ activity is required for the healing of AAA. TGFβ blockade may be harnessed to generate new models of AAA with better relevance to the human disease. We expect that the new models will improve our understanding of the pathophysiology of AAA and will be useful in the identification of new therapeutic targets.

Non-coding RNA Contribution to Thoracic and Abdominal Aortic Aneurysm Disease Development and Progression

Multiple research groups have started to uncover the complex genetic and epigenetic machinery necessary to maintain cardiovascular homeostasis. In particular, the key contribution of non-coding RNAs (ncRNAs) in regulating gene expression has recently received great attention. Aneurysms in varying locations of the aorta are defined as permanent dilations, predisposing to the fatal consequence of rupture. The characteristic pathology of an aneurysm is characterized by progressive vessel wall dilation, promoted by dying vascular smooth muscle cells and limited proliferation, as well as impaired synthesis and degradation of extracellular matrix components, which at least partially is the result of transmural inflammation and its disruptive effect on vessel wall homeostasis. Currently no conservative pharmacological approach exists that could slow down aneurysm progression and protect from the risk of acute rupture. In the recent past, several non-coding RNAs (mainly microRNAs) have been discovered as being involved in aneurysm progression throughout varying locations of the aorta. Exploring ncRNAs as key regulators and potential therapeutic targets by using antisense oligonucleotide strategies could open up promising opportunities for patients in the near future. Purpose of this current review is to summarize current findings and novel concepts of perspectivly utilizing ncRNAs for future therapeutic and biomarker applications.

Genetic and Epigenetic Regulation of Aortic Aneurysms

Aneurysms are characterized by structural deterioration of the vascular wall leading to progressive dilatation and, potentially, rupture of the aorta. While aortic aneurysms often remain clinically silent, the morbidity and mortality associated with aneurysm expansion and rupture are considerable. Over 13,000 deaths annually in the United States are attributable to aortic aneurysm rupture with less than 1 in 3 persons with aortic aneurysm rupture surviving to surgical intervention. Environmental and epidemiologic risk factors including smoking, male gender, hypertension, older age, dyslipidemia, atherosclerosis, and family history are highly associated with abdominal aortic aneurysms, while heritable genetic mutations are commonly associated with aneurysms of the thoracic aorta. Similar to other forms of cardiovascular disease, family history, genetic variation, and heritable mutations modify the risk of aortic aneurysm formation and provide mechanistic insight into the pathogenesis of human aortic aneurysms. This review will examine the relationship between heritable genetic and epigenetic influences on thoracic and abdominal aortic aneurysm formation and rupture.

Wnt Signaling Pathway Inhibitor Sclerostin Inhibits Angiotensin II-Induced Aortic Aneurysm and Atherosclerosis

OBJECTIVE

Sclerostin (SOST) has been identified as an important regulator of bone formation; however, it has not been previously implicated in arterial disease. The aim of this study was to assess the role of SOST in aortic aneurysm (AA) and atherosclerosis using human samples, a mouse model, and in vitro investigations.

APPROACH AND RESULTS

SOST protein was downregulated in human and mouse AA samples compared with controls. Transgenic introduction of human SOST in apolipoprotein E-deficient (ApoE^-/-) mice (SOST^Tg .ApoE^-/-) and administration of recombinant mouse Sost inhibited angiotensin II-induced AA and atherosclerosis. Serum concentrations of several proinflammatory cytokines were significantly reduced in SOST^Tg .ApoE^-/- mice. Compared with controls, the aortas of mice receiving recombinant mouse Sost and SOST^Tg .ApoE^-/- mice showed reduced matrix degradation, reduced elastin breaks, and preserved collagen. Decreased inflammatory cell infiltration and a reduction in the expression of wingless-type mouse mammary virus integration site/β-catenin responsive genes, including matrix metalloproteinase-9, osteoprotegerin, and osteopontin, were observed in the aortas of SOST^Tg .ApoE^-/- mice. SOST expression was downregulated and the wingless-type mouse mammary virus integration site/β-catenin pathway was activated in human AA samples. The cytosine-phosphate-guanine islands in the SOST gene promoter showed significantly higher methylation in human AA samples compared with controls. Incubation of vascular smooth muscle cells with the demethylating agent 5-azacytidine resulted in upregulation of SOST, suggesting that SOST is epigenetically regulated.

CONCLUSIONS

This study identifies that SOST is expressed in the aorta and downregulated in human AA possibly because of epigenetic silencing. Upregulating SOST inhibits AA and atherosclerosis development, with potential important implications for treating these vascular diseases.

Periodontitis May Deteriorate Sinus of Valsalva Dilatation in Marfan Syndrome Patients

Marfan syndrome (MFS) is a systemic connective tissue disorder that is caused by mutations of fibrillin-1. While MFS patients are at a high risk of periodontitis and aortic diseases, little causal information has been provided to date. To clarify the relationship, their oral condition and sinus of Valsalva (SoV) were evaluated.The subjects were patients with MFS (n = 33) who attended the University of Tokyo Hospital. We divided them into two groups; MFS patients with highly dilated (the diameters were equal to or more than 39 mm) SoV (high group, n = 18) and MFS patients with mildly dilated (less than 39 mm) SoV (mild group, n = 15). Blood examinations, echocardiograms, and full-mouth clinical measurements, including number of teeth, probing pocket depth (PPD), bleeding on probing (BOP), and community periodontal index (CPI) were performed.We found that the high group patients had greater rates of BOP compared to that of the mild group. Furthermore, the high group tended to have higher serum levels of C-reactive protein, matrix metalloproteinase-9, and transforming growth factor-β compared to the mild group.Periodontitis may deteriorate SoV dilatation in MFS patients.

Matricellular protein CCN3 mitigates abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a major cause of morbidity and mortality; however, the mechanisms that are involved in disease initiation and progression are incompletely understood. Extracellular matrix proteins play an integral role in modulating vascular homeostasis in health and disease. Here, we determined that the expression of the matricellular protein CCN3 is strongly reduced in rodent AAA models, including angiotensin II-induced AAA and elastase perfusion-stimulated AAA. CCN3 levels were also reduced in human AAA biopsies compared with those in controls. In murine models of induced AAA, germline deletion of Ccn3 resulted in severe phenotypes characterized by elastin fragmentation, vessel dilation, vascular inflammation, dissection, heightened ROS generation, and smooth muscle cell loss. Conversely, overexpression of CCN3 mitigated both elastase- and angiotensin II-induced AAA formation in mice. BM transplantation experiments suggested that the AAA phenotype of CCN3-deficient mice is intrinsic to the vasculature, as AAA was not exacerbated in WT animals that received CCN3-deficient BM and WT BM did not reduce AAA severity in CCN3-deficient mice. Genetic and pharmacological approaches implicated the ERK1/2 pathway as a critical regulator of CCN3-dependent AAA development. Together, these results demonstrate that CCN3 is a nodal regulator in AAA biology and identify CCN3 as a potential therapeutic target for vascular disease.

Aneurysm miRNA Signature Differs, Depending on Disease Localization and Morphology

Limited comprehension of aneurysm pathology has led to inconclusive results from clinical trials. miRNAs are key regulators of post-translational gene modification and are useful tools in elucidating key features of aneurysm pathogenesis in distinct entities of abdominal and popliteal aneurysms. Here, surgically harvested specimens from 19 abdominal aortic aneurysm (AAA) and 8 popliteal artery aneurysm (PAA) patients were analyzed for miRNA expression and histologically classified regarding extracellular matrix (ECM) remodeling and inflammation. DIANA-based computational target prediction and pathway enrichment analysis verified our results, as well as previous ones. miRNA-362, -19b-1, -194, -769, -21 and -550 were significantly down-regulated in AAA samples depending on degree of inflammation. Similar or inverse regulation was found for miR-769, 19b-1 and miR-550, -21, whereas miR-194 and -362 were unaltered in PAA. In situ hybridization verified higher expression of miR-550 and -21 in PAA compared to AAA and computational analysis for target genes and pathway enrichment affirmed signal transduction, cell-cell-interaction and cell degradation pathways, in line with previous results. Despite the vague role of miRNAs for potential diagnostic and treatment purposes, the number of candidates from tissue signature studies is increasing. Tissue morphology influences subsequent research, yet comparison of distinct entities of aneurysm disease can unravel core pathways.

The pathophysiologic basis of abdominal aortic aneurysm progression: a critical appraisal

An aneurysm of the abdominal aorta is a common pathology and a major cause of sudden death in the elderly. Currently, abdominal aortic aneurysms (AAAs) can only be treated by surgery and an effective medical therapy is urgently missing. The pathophysiology of AAAs is complex and is believed to be best described as a comprehensive inflammatory response with an accompanying proteolytic imbalance; the latter being held responsible for the progressive weakening of the aortic wall. Remarkably, while interference in inflammatory and/or proteolytic cascades proves highly effective in preclinical studies, emerging clinical studies consistently fail to show a benefit. In fact, some anti-inflammatory interventions appear to adversely influence the disease process. Altogether, recent clinical observations not only challenge the prevailing concepts of AAA progression, but also raise doubt on the translatability of findings from rodent models for growing AAA.

SMAD3 deficiency promotes vessel wall remodeling, collagen fiber reorganization and leukocyte infiltration in an inflammatory abdominal aortic aneurysm mouse model

TGF-β signaling plays critical roles in the pathogenesis of aneurysms; however, it is still unclear whether its role is protective or destructive. In this study, we investigate the role of SMAD3 in the pathogenesis of calcium chloride (CaCl₂)-induced abdominal aortic aneurysms (AAA) in Smad3^−/−, Smad3^+/− and Smad3^+/+ mice. We find that loss of SMAD3 drastically increases wall thickening of the abdominal aorta. Histological analyses show significant vessel wall remodeling with elastic fiber fragmentation. Remarkably, under polarized light, collagen fibers in the hyperplastic adventitia of Smad3^−/− mice show extensive reorganization accompanied by loosely packed thin and radial collagen fibers. The expressions of matrix metalloproteinases including MMP2, MMP9, and MMP12 and infiltration of macrophage/T cells are drastically enhanced in the vascular wall of Smad3^−/− mice. We also observe marked increase of NF-κB and ERK1/2 signaling as well as the expression of nuclear Smad2, Smad4 and TGF-β1 in the vessel wall of Smad3^−/− mice. In addition, we find that SMAD3 expression is reduced in the dedifferentiated medial smooth muscle-like cells of human AAA patients. These findings provide direct in vivo evidence to support the essential roles of SMAD3 in protecting vessel wall integrity and suppressing inflammation in the pathogenesis of AAAs.

Possible dual role of decorin in abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is characterized by chronic inflammation, which leads to pathological remodeling of the extracellular matrix. Decorin, a small leucine-rich repeat proteoglycan, has been suggested to regulate inflammation and stabilize the extracellular matrix. Therefore, the present study investigated the role of decorin in the pathogenesis of AAA. Decorin was localized in the aortic adventitia under normal conditions in both mice and humans. AAA was induced in mice using CaCl2 treatment. Initially, decorin protein levels decreased, but as AAA progressed decorin levels increased in all layers. Local administration of exogenous decorin prevented the development of CaCl2-induced AAA. However, decorin was highly expressed in the degenerative lesions of human AAA walls, and this expression positively correlated with matrix metalloproteinase (MMP)-9 expression. In cell culture experiments, the addition of decorin inhibited secretion of MMP-9 in vascular smooth muscle cells, but had the opposite effect in macrophages. The results suggest that decorin plays a dual role in AAA. Adventitial decorin in normal aorta may protect against the development of AAA, but macrophages expressing decorin in AAA walls may facilitate the progression of AAA by up-regulating MMP-9 secretion.

Differential expression of Hedgehog/Notch and transforming growth factor-β in human abdominal aortic aneurysms

OBJECTIVE

The molecular mechanisms leading to the development of abdominal aortic aneurysms (AAAs) remain poorly understood. The aim of this study was to determine the expression of Sonic Hedgehog (SHh), transforming growth factor β (TGF-β), and Notch signaling components in human aneurysmal and nonaneurysmal aorta in vivo.

METHODS

Paired tissue samples were obtained from aneurysmal and nonaneurysmal (control) segments of the aortic wall of eight patients with suitable anatomy undergoing open repair of infrarenal AAAs. Protein and messenger RNA (mRNA) expression levels were determined by Western blot and quantitative real-time polymerase chain reaction analysis.

RESULTS

Aneurysm development resulted in a significant reduction in vascular smooth muscle (vSMC) differentiation genes α-actin and SMC22α at both mRNA and protein levels. In parallel experiments, an 80.0% ± 15% reduction in SHh protein expression was observed in aneurysmal tissue compared with control. SHh and Ptc-1 mRNA levels were also significantly decreased, by 82.0% ± 10% and 75.0% ± 5%, respectively, in aneurysmal tissue compared with nonaneurysmal control tissue. Similarly, there was a 50.0% ± 9% and 60.0% ± 4% reduction in Notch receptor 1 intracellular domain and Hrt-2 protein expression, respectively, in addition to significant reductions in Notch 1, Notch ligand Delta like 4, and Hrt-2 mRNA expression in aneurysmal tissue compared with nonaneurysmal tissue. There was no change in Hrt-1 expression observed in aneurysmal tissue compared with control. In parallel experiments, we found a 2.2 ± 0.2-fold and a 5.6 ± 2.2-fold increase in TGF-β mRNA and protein expression, respectively, in aneurysmal tissue compared with nonaneurysmal tissue. In vitro, Hedgehog signaling inhibition with cyclopamine in human aortic SMCs resulted in decreased Hedgehog/Notch signaling component and vSMC differentiation gene expression. Moreover, cyclopamine significantly increased TGF-β1 mRNA expression by 2.6 ± 0.9-fold.

CONCLUSIONS

These results suggest that SHh/Notch and TGF-β signaling are differentially regulated in aneurysmal tissue compared with nonaneurysmal tissue. Changes in these signaling pathways and the resulting changes in vSMC content may play a causative role in the development of AAAs.

Role of TGF-β pathway polymorphisms in sporadic thoracic aortic aneurysm: rs900 TGF-β2 is a marker of differential gender susceptibility

Thoracic aortic aneurysm (TAA) is a progressive disorder involving gradual dilation of ascending and/or descending thoracic aorta with dissection or rupture as complications. It occurs as sporadic or defined syndromes/familial forms.Genetic, molecular and cellular mechanims of sporadic TAA forms are poorly characterized and known. Thus, our interest has been focused on investigating the role of genetic variants of transforming growth factor-β (TGF-β) pathways in TAA risk. On the other hand, no data on the role of genetic variants of TGF-β pathway in sporadic TAA exist until now. In addition, other cytokines, including IL-10, orchestrate TAA pathophysiology. Their balance determines the ultimate fate of the aortic wall as healing atherosclerosis or aneurysm formation. Thus, in this paper it was analyzed the role of ten polymorphisms of genes encoding TGF-β isoforms and receptors, and IL-10 in sporadic TAA. Our study included cases affected by sporadic TAA and two control groups. The most relevant finding obtained allows us to propose that rs900 TGF-β2 SNP is associated with sporadic TAA in women. This might open new perspectives for the analysis of sporadic TAA susceptibility factors and prevention.