Accelerated replicative senescence of medial smooth muscle cells derived from abdominal aortic aneurysms compared to the adjacent inferior mesenteric artery

Microvesicle-Mediated Tissue Regeneration Mitigates the Effects of Cellular Ageing

Extracellular vesicles (EVs), comprising microvesicles (MVs) and exosomes (Exos), are membranous vesicles secreted by cells which mediate the repair of cellular and tissue damage via paracrine mechanisms. The action of EVs under normative and morbid conditions in the context of ageing remains largely unexplored. We demonstrate that MVs, but not Exos, from Pathfinder cells (PCs), a putative stem cell regulatory cell type, enhance the repair of human dermal fibroblast (HDF) and mesenchymal stem cell (MSC) co-cultures, following both mechanical and genotoxic stress. Critically, this effect was found to be both cellular age and stress specific. Notably, MV treatment was unable to repair mechanical injury in older co-cultures but remained therapeutic following genotoxic stress. These observations were further confirmed in human dermal fibroblast (HDF) and vascular smooth muscle cell (VSMC) co-cultures of increasing cellular age. In a model of comorbidity comprising co-cultures of HDFs and highly senescent abdominal aortic aneurysm (AAA) VSMCs, MV administration appeared to be senotherapeutic, following both mechanical and genotoxic stress. Our data provide insights into EVs and the specific roles they play during tissue repair and ageing. These data will potentiate the development of novel cell-free therapeutic interventions capable of attenuating age-associated morbidities and avoiding undesired effects.

A Unified Model of Age-Related Cardiovascular Disease

Despite progress in biomedical technologies, cardiovascular disease remains the main cause of mortality. This is at least in part because current clinical interventions do not adequately take into account aging as a driver and are hence aimed at suboptimal targets. To achieve progress, consideration needs to be given to the role of cell aging in disease pathogenesis. We propose a model unifying the fundamental processes underlying most age-associated cardiovascular pathologies. According to this model, cell aging, leading to cell senescence, is responsible for tissue changes leading to age-related cardiovascular disease. This process, occurring due to telomerase inactivation and telomere attrition, affects all components of the cardiovascular system, including cardiomyocytes, vascular endothelial cells, smooth muscle cells, cardiac fibroblasts, and immune cells. The unified model offers insights into the relationship between upstream risk factors and downstream clinical outcomes and explains why interventions aimed at either of these components have limited success. Potential therapeutic approaches are considered based on this model. Because telomerase activity can prevent and reverse cell senescence, telomerase gene therapy is discussed as a promising intervention. Telomerase gene therapy and similar systems interventions based on the unified model are expected to be transformational in cardiovascular medicine.

Cellular senescence and abdominal aortic aneurysm: From pathogenesis to therapeutics

As China’s population enters the aging stage, the threat of abdominal aortic aneurysm (AAA) mainly in elderly patients is becoming more and more serious. It is of great clinical significance to study the pathogenesis of AAA and explore potential therapeutic targets. The purpose of this paper is to analyze the pathogenesis of AAA from the perspective of cellular senescence: on the basis of clear evidence of cellular senescence in aneurysm wall, we actively elucidate specific molecular and regulatory pathways, and to explore the targeted drugs related to senescence and senescent cells eliminate measures, eventually improve the health of patients with AAA and prolong the life of human beings.

The role of vascular smooth muscle cells in the development of aortic aneurysms and dissections

BACKGROUND

Aortic aneurysms (AA) are pathological dilations of the aorta, associated with an overall mortality rate up to 90% in case of rupture. In addition to dilation, the aortic layers can separate by a tear within the layers, defined as aortic dissections (AD). Vascular smooth muscle cells (vSMC) are the predominant cell type within the aortic wall and dysregulation of vSMC functions contributes to AA and AD development and progression. However, since the exact underlying mechanism is poorly understood, finding potential therapeutic targets for AA and AD is challenging and surgery remains the only treatment option.

METHODS

In this review, we summarize current knowledge about vSMC functions within the aortic wall and give an overview of how vSMC functions are altered in AA and AD pathogenesis, organized per anatomical location (abdominal or thoracic aorta).

RESULTS

Important functions of vSMC in healthy or diseased conditions are apoptosis, phenotypic switch, extracellular matrix regeneration and degradation, proliferation and contractility. Stressors within the aortic wall, including inflammatory cell infiltration and (epi)genetic changes, modulate vSMC functions and cause disturbance of processes within vSMC, such as changes in TGF-β signalling and regulatory RNA expression.

CONCLUSION

This review underscores a central role of vSMC dysfunction in abdominal and thoracic AA and AD development and progression. Further research focused on vSMC dysfunction in the aortic wall is necessary to find potential targets for noninvasive AA and AD treatment options.

Preservation of Smooth Muscle Cell Integrity and Function: A Target for Limiting Abdominal Aortic Aneurysm Expansion?

(1) Abdominal aortic aneurysm (AAA) is a silent, progressive disease with significant mortality from rupture. Whilst screening programmes are now able to detect this pathology early in its development, no therapeutic intervention has yet been identified to halt or retard aortic expansion. The inability to obtain aortic tissue from humans at early stages has created a necessity for laboratory models, yet it is essential to create a timeline of events from EARLY to END stage AAA progression. (2) We used a previously validated ex vivo porcine bioreactor model pre-treated with protease enzyme to create “aneurysm” tissue. Mechanical properties, histological changes in the intact vessel wall, and phenotype/function of vascular smooth muscle cells (SMC) cultured from the same vessels were investigated. (3) The principal finding was significant hyperproliferation of SMC from EARLY stage vessels, but without obvious histological or SMC aberrancies. END stage tissue exhibited histological loss of α-smooth muscle actin and elastin; mechanical impairment; and, in SMC, multiple indications of senescence. (4) Aortic SMC may offer a therapeutic target for intervention, although detailed studies incorporating intervening time points between EARLY and END stage are required. Such investigations may reveal mechanisms of SMC dysfunction in AAA development and hence a therapeutic window during which SMC differentiation could be preserved or reinstated.

Cyclic nucleotide phosphodiesterase 1C contributes to abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is characterized by aorta dilation due to wall degeneration, which mostly occurs in elderly males. Vascular aging is implicated in degenerative vascular pathologies, including AAA. Cyclic nucleotide phosphodiesterases, by hydrolyzing cyclic nucleotides, play critical roles in regulating vascular structure remodeling and function. Cyclic nucleotide phosphodiesterase 1C (PDE1C) expression is induced in dedifferentiated and aging vascular smooth muscle cells (SMCs), while little is known about the role of PDE1C in aneurysm. We observed that PDE1C was not expressed in normal aorta but highly induced in SMC-like cells in human and murine AAA. In mouse AAA models induced by Angiotensin II or periaortic elastase, PDE1C deficiency significantly decreased AAA incidence, aortic dilation, and elastin degradation, which supported a causative role of PDE1C in AAA development in vivo. Pharmacological inhibition of PDE1C also significantly suppressed preestablished AAA. We showed that PDE1C depletion antagonized SMC senescence in vitro and/or in vivo, as assessed by multiple senescence biomarkers, including senescence-associated β-galactosidase activity, γ-H2AX foci number, and p21 protein level. Interestingly, the role of PDE1C in SMC senescence in vitro and in vivo was dependent on Sirtuin 1 (SIRT1). Mechanistic studies further showed that cAMP derived from PDE1C inhibition stimulated SIRT1 activation, likely through a direct interaction between cAMP and SIRT1, which leads to subsequent up-regulation of SIRT1 expression. Our findings provide evidence that PDE1C elevation links SMC senescence to AAA development in both experimental animal models and human AAA, suggesting therapeutical significance of PDE1C as a potential target against aortic aneurysms.

Targeting mitochondrial fission as a potential therapeutic for abdominal aortic aneurysm

AIMS

Angiotensin II (AngII) is a potential contributor to the development of abdominal aortic aneurysm (AAA). In aortic vascular smooth muscle cells (VSMCs), exposure to AngII induces mitochondrial fission via dynamin-related protein 1 (Drp1). However, pathophysiological relevance of mitochondrial morphology in AngII-associated AAA remains unexplored. Here, we tested the hypothesis that mitochondrial fission is involved in the development of AAA.

METHODS AND RESULTS

Immunohistochemistry was performed on human AAA samples and revealed enhanced expression of Drp1. In C57BL6 mice treated with AngII plus β-aminopropionitrile, AAA tissue also showed an increase in Drp1 expression. A mitochondrial fission inhibitor, mdivi1, attenuated AAA size, associated aortic pathology, Drp1 protein induction, and mitochondrial fission but not hypertension in these mice. Moreover, western-blot analysis showed that induction of matrix metalloproteinase-2, which precedes the development of AAA, was blocked by mdivi1. Mdivi1 also reduced the development of AAA in apolipoprotein E-deficient mice infused with AngII. As with mdivi1, Drp1+/- mice treated with AngII plus β-aminopropionitrile showed a decrease in AAA compared to control Drp1+/+ mice. In abdominal aortic VSMCs, AngII induced phosphorylation of Drp1 and mitochondrial fission, the latter of which was attenuated with Drp1 silencing as well as mdivi1. AngII also induced vascular cell adhesion molecule-1 expression and enhanced leucocyte adhesion and mitochondrial oxygen consumption in smooth muscle cells, which were attenuated with mdivi1.

CONCLUSION

These data indicate that Drp1 and mitochondrial fission play salient roles in AAA development, which likely involves mitochondrial dysfunction and inflammatory activation of VSMCs.

MKL1 cooperates with p38MAPK to promote vascular senescence, inflammation, and abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a catastrophic disease with little effective therapy. Myocardin related transcription factor A (MRTFA, MKL1) is a multifaceted transcription factor, regulating diverse biological processes. However, a detailed understanding of the mechanistic role of MKL1 in AAA has yet to be elucidated. In this study, we showed induced MKL1 expression in thoracic and abdominal aneurysmal tissues, respectively in both mice and humans. MKL1 global knockout mice displayed reduced AAA formation and aortic rupture compared with wild-type mice. Both gene deletion and pharmacological inhibition of MKL1 markedly protected mice from aortic dissection, an early event in Angiotensin II (Ang II)-induced AAA formation. Loss of MKL1 was accompanied by reduced senescence/proinflammation in the vessel wall and cultured vascular smooth muscle cells (VSMCs). Mechanistically, a deficiency in MKL1 abolished AAA-induced p38 mitogen activated protein kinase (p38MAPK) activity. Similar to MKL1, loss of MAPK14 (p38α), the dominant isoform of p38MAPK family in VSMCs suppressed Ang II-induced AAA formation, vascular inflammation, and senescence marker expression. These results reveal a molecular pathway of AAA formation involving MKL1/p38MAPK stimulation and a VSMC senescent/proinflammatory phenotype. These data support targeting MKL1/p38MAPK pathway as a potential effective treatment for AAA.

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MKL1 expression is induced in both thoracic and abdominal aneurysmal tissues.

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Genetic ablation and pharmacological inhibition of MKL1 protect mice from aortic dissection and AAA induced by Ang II.

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Depletion of MKL1 in mice suppresses Ang II-induced vascular inflammation and senescence.

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Depletion of MKL1 blunts the activation of p38MAPK and STAT3 pathways.

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Loss of MAPK14 in VSMCs suppresses Ang II-induced AAA formation, vascular inflammation, and senescence marker expression.

Nucleolar stress induces a senescence-like phenotype in smooth muscle cells and promotes development of vascular degeneration

Senescence of smooth muscle cells (SMCs) has a crucial role in the pathogenesis of abdominal aortic aneurysm (AAA), a disease of vascular degeneration. Perturbation of cellular ribosomal DNA (rDNA) transcription triggers nucleolar stress response. Previously we demonstrated that induction of nucleolar stress in SMCs elicited cell cycle arrest via the ataxia-telangiectasia mutated (ATM)/ATM- and Rad3-related (ATR)-p53 axis. However, the specific roles of nucleolar stress in vascular degeneration remain unexplored. In the present study, we demonstrated for the first time that in both human and animal AAA tissues, there were non-coordinated changes in the expression of RNA polymerase I machinery components, including a downregulation of transcription initiation factor-IA (TIF-IA). Genetic deletion of TIF-IA in SMCs in mice (smTIF-IA^-/-) caused spontaneous aneurysm-like lesions in the aorta. In vitro, induction of nucleolar stress triggered a non-canonical DNA damage response, leading to p53 phosphorylation and a senescence-like phenotype in SMCs. In human AAA tissues, there was increased nucleolar stress in medial cells, accompanied by localized DNA damage response within the nucleolar compartment. Our data suggest that perturbed rDNA transcription and induction of nucleolar stress contribute to the pathogenesis of AAA. Moreover, smTIF-IA^-/- mice may be a novel animal model for studying spontaneous AAA-like vascular degenerations.

The role of autophagy in abdominal aortic aneurysm: protective but dysfunctional

Autophagy, an evolutionarily conserved mechanism that promotes cell survival by recycling nutrients and degrading long-lived proteins and dysfunctional organelles, is an important defense mechanism, and its attenuation has been well documented in senescence and aging-related diseases. Abdominal aortic aneurysm (AAA), a well-known aging-related disease, has been defined as a chronic degenerative process in the abdominal aortic wall; however, the complete mechanism is unknown, and a clinical treatment is lacking. Accumulating evidence has recently revealed that numerous drugs that can induce autophagy are effective in the treatment of AAA. The purpose of this systematic review was to focus on the cross-talk between autophagy and high-risk factors and the potential pathogenesis of AAA to understand not only the host defense and pathogenesis but also potential treatments.

Up-regulated MCPIP1 in abdominal aortic aneurysm is associated with vascular smooth muscle cell apoptosis and MMPs production

Abdominal aortic aneurysm (AAA) is often clinically silent before rupture characterized by extensive vascular inflammation and degenerative elasticity of aortic wall. Monocyte chemotactic protein-induced protein-1 (MCPIP1) exhibits anti-infllammatory and pro-apoptotic effects involved in atherogenesis. However, little is known about the expression and the contribution of MCPIP1 in AAA. In the present study, we collected clinical AAA specimens and constructed AAA mice model through Ang-II infusion, and found apparently increased MCPIP1 expression and severe inflammatory infiltration in AAA aortic membrane as evidenced by elevated levels of monocyte chemotactic protein 1 (MCP-1), interleukin 1 β (IL-1β) and NF-κB, as well as HE staining. The elasticity of aortic tunica media was impaired along with multiple apoptosis of vascular smooth muscle cells (VSMCs) in Ang-II-induced aneurysmal mouse. In vitro Ang-II administration of VSMCs induced MCPIP1 expression, accompanied by up-regulation of matrix metalloproteinase (MMP) 2 (MMP-2) and MMP-9, as well as enhancement of VSMCs proliferation and apoptosis, which may cause damage of intima–media elasticity. Silencing MCPIP1 reversed above effects to further restore the balance of proliferation and apoptosis in VSMCs. Overall, our data indicated that up-regulation of MCPIP1 may become a promising candidate for the diagnosis of AAA, and specific knockdown of MCPIP1 in VSMCs could inhibit VSMCs apoptosis and down-regulate MMPs to maintain vascular wall elasticity. Therefore, knockdown of MCPIP1 may serve as a potential target for gene therapy of AAA.

Role of smooth muscle cells in Cardiovascular Disease

Normally, smooth muscle cells (SMCs) are localized in the tunica media of the vasculature, where they take responsibility for vascular contraction and extracellular matrix (ECM) generation. SMCs also play a significant role in obedience and elastic rebound of the artery in response to the haemodynamic condition. However, under pathological or stressed conditions, phenotype switching from contractile to synthetic state or other cell types will occur in SMCs to positively or negatively contribute to disease progression. Various studies demonstrated that functional changes of SMCs are implicated in several cardiovascular diseases. In this review, we present the function of vascular SMCs (VSMCs) and the involved molecular mechanisms about phenotype switching, and summarize the roles of SMCs in atherosclerosis, hypertension, arterial aneurysms and myocardial infarction, hoping to obtain potential therapeutic targets against cardiovascular disease in the clinical practices.

Targeting senescent cells to attenuate cardiovascular disease progression

Cardiovascular disease (CVD) is the most common disease to increase as life expectancy increases. Most high-profile pharmacological treatments for age-related CVD have led to inefficacious results, implying that novel approaches to treating these pathologies are needed. Emerging data have demonstrated that senescent cardiovascular cells, which are characterized by irreversible cell cycle arrest and a distinct senescence-associated secretory phenotype, accumulate in aged or diseased cardiovascular systems, suggesting that they may impair cardiovascular function. This review discusses the evidence implicating senescent cells in cardiovascular ageing, the onset and progression of CVD, and the molecular mechanisms underlying cardiovascular cell senescence. We also review eradication of senescent cardiovascular cells by small-molecule-drug-mediated apoptosis and immune cell-mediated efferocytosis and toxicity as promising and precisely targeted therapeutics for CVD prevention and treatment.

IgE Aggravates the Senescence of Smooth Muscle Cells in Abdominal Aortic Aneurysm by Upregulating LincRNA-p21

Immunoglobulin E (lgE) activates immunity by binding to mast cells and basophils. It is well-known that IgE and its receptor, FcɛR1, play a key role in the development of airway inflammation and remodeling in allergic asthma. Recent studies show that IgE also plays an important role in abdominal aortic aneurysm (AAA) pathogenesis. However, the mechanism by which IgE promotes AAA remains unclear. Here we report that in our mouse model, asthma-induced high level of IgE aggravated AAA, but IgE lost this effect on AAA in FcɛR1^-/- mice. Our in vitro study revealed that IgE induced smooth muscle cell senescence via upregulating lincRNA-p21 against p21 without altering expression of p53. By this mechanism, IgE accelerated AAA in ApoE^-/- mice, which was blocked by knockdown of lincRNA-p21 in both vitro and vivo. This study suggests that IgE actives the lincRNAp21-p21 pathway to induce SMC senescence, which contributes to the formation of AAA, and lincRNA-p21 is a potential therapeutic target for AAA aggravated by asthma.

Role of Vascular Smooth Muscle Cell Phenotypic Switching and Calcification in Aortic Aneurysm Formation

Aortic aneurysm is a vascular disease whereby the ECM (extracellular matrix) of a blood vessel degenerates, leading to dilation and eventually vessel wall rupture. Recently, it was shown that calcification of the vessel wall is involved in both the initiation and progression of aneurysms. Changes in aortic wall structure that lead to aneurysm formation and vascular calcification are actively mediated by vascular smooth muscle cells. Vascular smooth muscle cells in a healthy vessel wall are termed contractile as they maintain vascular tone and remain quiescent. However, in pathological conditions they can dedifferentiate into a synthetic phenotype, whereby they secrete extracellular vesicles, proliferate, and migrate to repair injury. This process is called phenotypic switching and is often the first step in vascular pathology. Additionally, healthy vascular smooth muscle cells synthesize VKDPs (vitamin K-dependent proteins), which are involved in inhibition of vascular calcification. The metabolism of these proteins is known to be disrupted in vascular pathologies. In this review, we summarize the current literature on vascular smooth muscle cell phenotypic switching and vascular calcification in relation to aneurysm. Moreover, we address the role of vitamin K and VKDPs that are involved in vascular calcification and aneurysm. Visual Overview- An online visual overview is available for this article.

An update on clonality: what smooth muscle cell type makes up the atherosclerotic plaque?

Almost 50 years ago, Earl Benditt and his son John described the clonality of the atherosclerotic plaque. This led Benditt to propose that the atherosclerotic lesion was a smooth muscle neoplasm, similar to the leiomyomata seen in the uterus of most women. Although the observation of clonality has been confirmed many times, interest in the idea that atherosclerosis might be a form of neoplasia waned because of the clinical success of treatments for hyperlipemia and because animal models have made great progress in understanding how lipid accumulates in the plaque and may lead to plaque rupture. Four advances have made it important to reconsider Benditt's observations. First, we now know that clonality is a property of normal tissue development. Second, this is even true in the vessel wall, where we now know that formation of clonal patches in that wall is part of the development of smooth muscle cells that make up the tunica media of arteries. Third, we know that the intima, the "soil" for development of the human atherosclerotic lesion, develops before the fatty lesions appear. Fourth, while the cells comprising this intima have been called "smooth muscle cells", we do not have a clear definition of cell type nor do we know if the initial accumulation is clonal. As a result, Benditt's hypothesis needs to be revisited in terms of changes in how we define smooth muscle cells and the quite distinct developmental origins of the cells that comprise the muscular coats of all arterial walls. Finally, since clonality of the lesions is real, the obvious questions are do these human tumors precede the development of atherosclerosis, how do the clones develop, what cell type gives rise to the clones, and in what ways do the clones provide the soil for development and natural history of atherosclerosis?

Loss of vascular smooth muscle cell autophagy exacerbates angiotensin II-associated aortic remodeling

OBJECTIVE

The pathophysiologic processes of abdominal aortic aneurysms (AAAs) and atherosclerosis often intersect. Given that anomalies in vascular smooth muscle cell (SMC) autophagy have been noted in models of atherosclerosis, we sought to evaluate the potential role that SMC autophagy may play in the initiation and progression of AAAs.

METHODS

Studies were conducted in ATG7^flx/flxSM22α-Cre^tg/+ (SMC ATG7 knockout [SMC-ATG7-KO]) and ATG7^WT/WT; SM22α-Cre^tg/+ (SMC ATG7 wild-type [SMC-ATG7-WT]) littermates that were continuously infused with angiotensin II (Ang II; 1.5 mg/kg/d) for up to 12 weeks. Mortality, morbidity, hemodynamics, and aortic remodeling were documented.

RESULTS

During the 12-week observation window, all of the Ang II-treated SMC-ATG-WT mice (n = 6) survived, whereas 10 of the 19 Ang II-treated SMC-ATG-KO mice had died by week 7 (log-rank test, P < .001). Mean arterial pressure (128.07 ± 3.4 mm Hg for Ang II-treated SMC-ATG-KO vs 138.5 ± 5.87 mm Hg for Ang II-treated SMC-ATG-WT mice) and diastolic arterial pressure (109.7 ± 2.55 mm Hg for Ang II-treated SMC-ATG7-KO vs 119.4 ± 2.12 mm Hg for Ang II-treated SMC-ATG7-WT mice) were significantly different between the two groups (P < .01). Cardiac rupture, myocardial infarct, end-organ damage, pleural effusion, and venous distention were noted in Ang II-treated SMC-ATG7-KO but not in Ang II-treated SMC-ATG7-WT mice. Although the suprarenal aortic diameters of the Ang II-treated SMC-ATG7-KO group demonstrated a trending increase (at week 4, 1.26 ± 0.06 mm [n = 14] for Ang II-treated SMC-ATG-KO mice vs 1.09 ± 0.02 mm [n = 5] for Ang II-treated SMC-ATG-WT mice; P < .05), only 2 of the 19 developed abdominal aortic dissections.

CONCLUSIONS

Mice with SMC ATG7 deficiency that are chronically infused with Ang II do not tend to develop dissecting AAA but do exhibit adverse aortic remodeling and appreciable cardiac failure-associated mortality.

Progressive Development of Aberrant Smooth Muscle Cell Phenotype in Abdominal Aortic Aneurysm Disease

Abdominal aortic aneurysm (AAA) is a silent, progressive disease with a high mortality and an increasing prevalence with aging. Smooth muscle cell (SMC) dysfunction contributes to gradual dilatation and eventual rupture of the aorta. Here we studied phenotypic characteristics in SMC cultured from end-stage human AAA (≥5 cm) and cells cultured from a porcine carotid artery (PCA) model of early and end-stage aneurysm. Human AAA-SMC presented a secretory phenotype and expressed elevated levels of the differentiation marker miR-145 (2.2-fold, p < 0.001) and the senescence marker SIRT-1 (1.3-fold, p < 0.05), features not recapitulated in aneurysmal PCA-SMC. Human and end-stage porcine aneurysmal cells were frequently multi-nucleated (3.9-fold, p < 0.001, and 1.8-fold, p < 0.01, respectively, vs. control cells) and displayed an aberrant nuclear morphology. Human AAA-SMC exhibited higher levels of the DNA damage marker γH2AX (3.9-fold, p < 0.01, vs. control SMC). These features did not correlate with patients' chronological age and are therefore potential markers for pathological premature vascular aging. Early-stage PCA-SMC (control and aneurysmal) were indistinguishable from one another across all parameters. The principal limitation of human studies is tissue availability only at the end stage of the disease. Refinement of a porcine bioreactor model would facilitate the study of temporal modulation of SMC behaviour during aneurysm development and potentially identify therapeutic targets to limit AAA progression.

Resveratrol Inhibits Growth of Experimental Abdominal Aortic Aneurysm Associated With Upregulation of Angiotensin-Converting Enzyme 2

Objective—

Recent evidence suggests an important role for angiotensin-converting enzyme 2 (ACE2) in limiting abdominal aortic aneurysm (AAA). This study examined the effect of ACE2 deficiency on AAA development and the efficacy of resveratrol to upregulate ACE2 in experimental AAA.

Approach and Results—

Ace2 deletion in apolipoprotein-deficient mice ( ApoE −/− Ace2 −/y ) resulted in increased aortic diameter and spontaneous aneurysm of the suprarenal aorta associated with increased expression of inflammation and proteolytic enzyme markers. In humans, serum ACE2 activity was negatively associated with AAA diagnosis. ACE2 expression was lower in infrarenal biopsies of patients with AAA than organ donors. AAA was more severe in ApoE −/− Ace2 −/y mice compared with controls in 2 experimental models. Resveratrol (0.05/100-g chow) inhibited growth of pre-established AAAs in ApoE −/− mice fed high-fat chow and infused with angiotensin II continuously for 56 days. Reduced suprarenal aorta dilatation in mice receiving resveratrol was associated with elevated serum ACE2 and increased suprarenal aorta tissue levels of ACE2 and sirtuin 1 activity. In addition, the relative phosphorylation of Akt and ERK (extracellular signal-regulated kinase) 1/2 within suprarenal aorta tissue and gene expression for nuclear factor of kappa light polypeptide gene enhancer in B cells 1, angiotensin type-1 receptor, and metallopeptidase 2 and 9 were significantly reduced. Upregulation of ACE2 in human aortic smooth muscle cells by resveratrol in vitro was sirtuin 1-dependent.

Conclusions—

This study provides experimental evidence of an important role for ACE2 in limiting AAA development and growth. Resveratrol upregulated ACE2 and inhibited AAA growth in a mouse model.

Abdominal Aortic Aneurysm-Associated MicroRNA-516a-5p Regulates Expressions of Methylenetetrahydrofolate Reductase, Matrix Metalloproteinase-2, and Tissue Inhibitor of Matrix Metalloproteinase-1 in Human Abdominal Aortic Vascular Smooth Muscle Cells

BACKGROUND

MicroRNAs (miRNAs or miRs) have been highlighted to be involved in abdominal aortic aneurysm (AAA) with the emergence of recent miRNA microarray profiling studies. miR-516a-5p has been shown to be significantly overexpressed in vascular smooth muscle cells (VSMCs) from human AAA tissues from our previous microarray study, suggesting its crucial association with AAA. In addition, further bioinformatics analysis predicted methylenetetrahydrofolate reductase (MTHFR), which regulates homocysteine (Hcy) metabolism and is proposed to be a risk gene for AAA formation and to be the downregulation target of miR-516a-5p. However, the pathogenic role of miR-516a-5p in VSMCs for AAA formation remains unresolved. This study aims to investigate the role of miR-516a-5p in human VSMCs for AAA pathogenesis.

METHODS

miR-516a-5p was stably overexpressed and knocked down in VSMCs explant cultured from human abdominal aortic tissues by means of lentiviral system. The MTHFR protein expression was first examined by Western blotting. In addition, the protein expressions of several key components involved in AAA pathogenic features are as follows: matrix metalloproteinase (MMP)-2, MMP-9, tissue inhibitor of matrix metalloproteinase (TIMP)-1 and TIMP-2 for elastin degradation; collagen type 1 alpha 1 for compensatory collagen synthesis; monocyte chemoattractant protein-1 for inflammation, were also evaluated. Apoptotic level of VSMCs was examined by terminal deoxynucleotidyl transferase dUTP nick end labeling assay.

RESULTS

Results showed that protein expression of MTHFR was significantly downregulated on miR-516a-5p overexpression (P < 0.05) in VSMCs, whereas it was significantly upregulated on miR-516a-5p knockdown (P < 0.05). Of all the AAA key components investigated, only MMP-2 and TIMP-1 protein expressions were found altered. A significant increase in MMP-2 (P < 0.05) and decrease in TIMP-1 (P < 0.05) expressions were observed on miR-516a-5p overexpression in VSMCs. Apoptosis was not promoted on miR-516a-5p overexpression or knockdown in VSMCs.

CONCLUSIONS

Our findings suggested that miR-516a-5p may regulate MTHFR, MMP-2, and TIMP-1 expressions in human VSMCs, possibly promoting the disruption of Hcy metabolism and proteolytic degradation of elastin for AAA formation.

The putative role of autophagy in the pathogenesis of abdominal aortic aneurysms

Abdominal aortic aneurysms (AAA) are a significant cause of worldwide mortality and morbidity. While the histopathological characteristics of AAA are well documented, the cellular and molecular mechanisms involved in the pathogenesis of AAA are not entirely understood. Autophagy is a highly conserved basal cellular process in eukaryotic cells that involves the turnover of organelles and proteins. It is also activated as an adaptive response to stressful conditions to promote cell survival. While autophagy typically promotes pro-survival processes, it can sometimes lead to cellular demise. Preclinical studies have revealed autophagy to be a protective mechanism in certain vascular diseases with several autophagy-related genes reported to be markedly upregulated in human aneurysmal tissue. The role autophagy plays in the pathogenesis of AAA, however, remains poorly defined. In this review, we discuss the putative role of autophagy in AAA by reviewing several in vitro and in vivo studies that address the functional significance of autophagy in cells that are involved in the pathophysiology of AAA, amongst which are macrophages, smooth muscle and endothelial cells.

Sustained activation of ADP/P2ry12 signaling induces SMC senescence contributing to thoracic aortic aneurysm/dissection

Thoracic aortic aneurysm/dissection (TAAD) is characterized by excessive smooth muscle cell (SMC) loss, extracellular matrix (ECM) degradation and inflammation. However, the mechanism whereby signaling leads to SMC loss is unclear. We used senescence-associated (SA)-β-gal staining and analysis of expression of senescence-related proteins (p53, p21, p19) to show that excessive mechanical stretch (20% elongation, 3600cycles/h, 48h) induced SMC senescence. SMC senescence was also detected in TAAD specimens from both mice and humans. High-performance liquid chromatography and luciferin-luciferase-based assay revealed that excessive mechanical stretch increased adenosine diphosphate (ADP) release from SMCs both in vivo and in vitro. Elevated ADP induced SMC senescence while genetic knockout of the ADP receptor, P2Y G protein-coupled receptor 12 (P2ry12), in mice protected against SMC senescence and inflammation. Both TAAD formation and rupture were significantly reduced in P2ry12^-/- mice. SMCs from P2ry12^-/- mice were resistant to senescence induced by excessive mechanical stretch or ADP treatment. Mechanistically, ADP treatment sustained Ras activation, whereas pharmacological inhibition of Ras protected against SMC senescence and reduced TAAD formation. Taken together, excessive mechanical stress may induce a sustained release of ADP and promote SMC senescence via P2ry12-dependent sustained Ras activation, thereby contributing to excessive inflammation and degeneration, which provides insights into TAAD formation and progression.

Evidence of deregulated cholesterol efflux in abdominal aortic aneurysm

Previous studies indicated that lipids may be associated with abdominal aortic aneurysm (AAA); however the molecular mechanism involved is unclear. Our study aimed to investigate the expression pattern of cholesterol efflux related proteins in AAA. Liver X receptors (LXRα and LXRβ), ATP-binding-cassette transporter A1 (ABCA1), Apolipoprotein AI (ApoAI), smooth muscle α-actin (α-SM) and vimentin expression levels were evaluated in human AAA, atherosclerotic (ATH) and normal abdominal aortic tissues. We found significant differences in LXRα, LXRβ and ABCA1 mRNA expression levels between AAA, ATH and normal whole aortic tissues and also within the AAA, ATH and normal "intima-media" layers. Specifically, LXRα, LXRβ and ABCA1 mRNA levels were decreased in AAA compared to ATH-whole tissues, as well as in AAA "intima-media" compared to ATH and normal "intima-media" layers. Moreover, immunohistochemical evaluation revealed that LXRα and ABCA1 immunoreactivities (IR) were reduced in the AAA media compared to the normal and ATH media layers and that they were also reduced in the intima layer of AAA and ATH tissues, whereas ApoAI-IR was increased in the AAA and ATH aortic walls compared to normal pointing to possible deregulation of the cholesterol efflux mechanism in AAA. Furthermore, double staining for vimentin and α-SM showed vimentin expression in the intima and inner media layer of AAA with sparse vimentin positive SMCs designating possible SMCs phenotype switch from contractile to synthetic form. In addition, histochemical analysis showed excessive lipid accumulation in the AAA wall, while co-staining using Oil Red O with α-SM or CD68 revealed lipid accumulation in SMCs and macrophages, respectively. Our study provides novel evidence for impaired cholesterol efflux in AAA associated with lipid accumulation in SMCs and macrophages, as well as switch of SMCs phenotype from contractile to synthetic form.

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.

Smooth muscle cells from abdominal aortic aneurysms are unique and can independently and synergistically degrade insoluble elastin

BACKGROUND

The purpose of this study was to further elucidate the role of the vascular smooth muscle cells (SMCs) in abdominal aortic aneurysm (AAA) disease. We hypothesized that that AAA SMCs are unique and actively participate in the process of degrading the aortic matrix.

METHODS

Whole-genome expression profiles of SMCs from AAAs, nondilated abdominal aorta (NAA), and carotid endarterectomy (CEA) were compared. We quantified elastolytic activity by culturing SMCs in [(3)H]elastin-coated plates and measuring solubilized tritium in the media after 7 days. Matrix metalloproteinase (MMP)-2 and MMP-9 production was assessed using real-time polymerase chain reaction, zymography, and Western blotting.

RESULTS

Each SMC type exhibited a unique gene expression pattern. AAA SMCs had greater elastolytic activity than NAA-SMCs (+68%; P < .001) and CEA-SMCs (+45%; P < .001). Zymography showed an increase of active MMP-2 (62 kD) in media from AAA SMCs. AAA SMCs demonstrated twofold greater expression of MMP-2 messenger (m)RNA (P < .05) and 7.3-fold greater MMP-9 expression (P < .01) than NAA-SMCs. Culture with U937 monocytes caused a synergistic increase of elastolysis by AAA SMCs (41%; P < .001) but not NAA-SMCs or CEA-SMCs (P = .99). Coculture with U937 caused a large increase in MMP-9 mRNA in AAA-SMCs and NAA-SMCs (P < .001). MMP-2 mRNA expression was not affected. Western blots of culture media showed a fourfold increase of MMP-9 (92 kD) protein only in AAA-SMCs/U937 but not in NAA-SMCs/U937 (P < .001) and a large increase in active-MMP2 (62 kD), which was less apparent in NAA-SMCs/U937 media (P < .01).

CONCLUSIONS

AAA-SMCs have a unique gene expression profile and a proelastolytic phenotype that is augmented by macrophages. This may occur by a failure of post-transcriptional control of MMP-9 synthesis.

Exploring smooth muscle phenotype and function in a bioreactor model of abdominal aortic aneurysm

Background

Vascular smooth muscle cells (SMC) are central to arterial structure and function yet their involvement in the progression of abdominal aortic aneurysm (AAA) disease is not well studied. The progressive and silent nature of AAA in man essentially restricts research to the use of “end-stage” tissue recovered during surgical repair. This study aimed to generate an ex vivo model of AAA using protease-treated porcine carotid arteries maintained in a novel bioreactor, and to compare the structural and functional changes in SMC cultured from the recovered vessels with those from human tissue acquired at elective surgical repair.

Methods

Freshly isolated porcine arteries were pretreated with collagenase and/or elastase before culturing under flow in a bioreactor for 12 days. Human end-stage aneurysmal tissue and saphenous veins from age-matched controls were collected from patients undergoing surgery. SMC were cultured and characterised (immunocytochemistry, measurement of spread cell area) and assessed functionally at the level of proliferation (cell-counting) and matrix-metalloproteinase (MMP) secretion (gelatin zymography). Cellular senescence was investigated using β-galactosidase staining and apoptosis was quantified using a fluorescence-based caspase 3 assay.

Results

Co-expression of alpha-smooth muscle actin and smooth muscle myosin heavy chain confirmed all cell populations as SMC. Porcine SMC harvested and cultivated after collagenase/elastase pretreatment displayed a prominent “rhomboid” morphology, increased spread area (32%, P < 0.01), impaired proliferation (47% reduction, P < 0.05), increased senescence (52%, P < 0.001), susceptibility to apoptosis and reduced MMP-2 secretion (60% decrease, P < 0.01) compared with SMC from vehicle, collagenase or elastase pre-treated vessels. Notably, these changes were comparable to those observed in human AAA SMC which were 2.4-fold larger than non-aneurysmal SMC (P < 0.001) and exhibited reduced proliferation (39% reduction, P < 0.001), greater apoptosis (4-fold increase, P < 0.001), and increased senescence (61%, P < 0.05).

Conclusions

Combined collagenase/elastase exposure of porcine artery maintained in a bioreactor under flow conditions induced a SMC phenotype characteristic of those cultured from end-stage AAA specimens. This model has potential and versatility to examine temporal changes in SMC biology and to identify the molecular mechanisms leading to early aberrancies in SMC function. In the longer term this may inform new targets to maintain aortic SMC content and drive cells to a “reparative” phenotype at early stages of the disease.

Understanding the effects of tobacco smoke on the pathogenesis of aortic aneurysm

Aneurysmal arterial disease is a vascular degenerative condition that is distinct from atherosclerotic and other occlusive arterial diseases. There is regionalization of the predisposition to aneurysm formation within the vascular tree, and the pathological process varies with location. Infrarenal abdominal aortic aneurysm (AAA) is the most common manifestation of aneurysmal disease, and smoking is the dominant risk factor. Smoking is a much greater risk factor for AAA than for atherosclerosis. In addition to playing a role in the pathogenesis of AAA, smoking also increases the rate of expansion and risk of rupture of established AAA. The mechanistic relationship between AAA and smoking is being established by the use of enhanced animal models that are dependent on smoke or smoke components. The mechanisms seem to involve durable alterations in vascular smooth muscle cell and inflammatory cell function. This review examines the clinical, epidemiological, and mechanistic evidence implicating smoking as a cause of aneurysms, focusing on AAA.

Characteristics of TAV- and BAV-associated thoracic aortic aneurysms--smooth muscle cell biology, expression profiling, and histological analyses

OBJECTIVE

Past studies on the pathogenesis of thoracic aortic aneurysms have, by concentrating on histological and total tissue analyses, revealed several disease-relevant processes. Despite these studies, there is still a significant lack in the understanding of aneurysmal cell biology today. Hence, it was the goal of this study to assess differences between aneurysmal and healthy aortic smooth muscle cells (SMCs) on a broad - screening-like - basis, allowing us to formulate new hypotheses on the role of SMCs in thoracic aneurysm formation.

METHODS AND RESULTS

After histological characterization of a total of 16 samples from healthy aortas and thoracic aortic aneurysms (TAA) of patients with bicuspid (BAV) and tricuspid (TAV) aortic valves, we isolated aortic SMCs and subjected them to cell biological and gene expression analyses. The data obtained indicate that aneurysmal SMCs exert reduced proliferation and migration rates compared to controls. BAV TAA SMCs have significantly shorter telomeres, whereas TAV TAA SMCs showed a reduced metabolic activity. In BAV TAA SMCs osteopontin (OPN) expression was significantly elevated, and TAV TAA SMCs showed decreased expression of tissue inhibitor of metalloproteinase 3 (TIMP3).

CONCLUSION

Our study provides evidence that TAA-associated aortic wall disintegration in BAV and TAV TAAs shows similarities, but also significant differences. BAV and TAV TAAs differ with regard to medial elastic fiber mass and the occurrence of fibroblasts, SMC telomere length, metabolism, and gene expression. This study may form the basis for future in-depth analyses on the relevance of these findings in the pathophysiology of BAV and TAV TAAs.

Relevance of urocortins to cardiovascular disease

Acquired cardiovascular diseases such as coronary heart disease, peripheral artery disease and related vascular problems contribute to more than one-third of worldwide morbidity and mortality. In many instances, particularly in the under developed world, cardiovascular diseases are diagnosed at a late stage limiting the scope for improving outcomes. A range of therapies already exist for established cardiovascular disease, although there is significant interest in further understanding disease pathogenesis in order to improve diagnosis and achieve primary and secondary therapeutic goals. The urocortins are a group of recently defined peptide members of the corticotrophin-releasing factor family. Previous pre-clinical work and human association studies suggest that urocortins have potential to exert some beneficial and other detrimental effects on the heart and major blood vessels. More current evidence however favours beneficial effects of urocortins, for example these peptides have been shown to inhibit production of reactive oxygen species and vascular cell apoptosis, and thus may have potential to antagonise the progression of cardiovascular disease. This review summarises published data on the potential role of urocortins in cardiovascular disease.

Novel aspects of the pathogenesis of aneurysms of the abdominal aorta in humans

Aneurysm of the abdominal aorta (AAA) is a particular, specifically localized form of atherothrombosis, providing a unique human model of this disease. The pathogenesis of AAA is characterized by a breakdown of the extracellular matrix due to an excessive proteolytic activity, leading to potential arterial wall rupture. The roles of matrix metalloproteinases and plasmin generation in progression of AAA have been demonstrated both in animal models and in clinical studies. In the present review, we highlight recent studies addressing the role of the haemoglobin-rich, intraluminal thrombus and the adventitial response in the development of human AAA. The intraluminal thrombus exerts its pathogenic effect through platelet activation, fibrin formation, binding of plasminogen and its activators, and trapping of erythrocytes and neutrophils, leading to oxidative and proteolytic injury of the arterial wall. These events occur mainly at the intraluminal thrombus-circulating blood interface, and pathological mediators are conveyed outwards, where they promote matrix degradation of the arterial wall. In response, neo-angiogenesis, phagocytosis by mononuclear cells, and a shift from innate to adaptive immunity in the adventitia are observed. Abdominal aortic aneurysm thus represents an accessible spatiotemporal model of human atherothrombotic progression towards clinical events, the study of which should allow further understanding of its pathogenesis and the translation of pathogenic biological activities into diagnostic and therapeutic applications.

p53 Levels positively correlate with carotid intima-media thickness in patients with subclinical atherosclerosis

BACKGROUND

The level of circulating p53 is related to inflammation in asymptomatic subjects with cardiovascular risk factors. Whether p53 is associated with the severity of atherosclerosis remains to be determined.

HYPOTHESIS

This study examines the relationship of systemic p53 levels with atherosclerotic risk factors and subclinical atherosclerosis.

METHODS

Circulating levels of p53 and markers of inflammation were measured in 356 subjects with cardiovascular risk factors but who were free from clinical cardiovascular disease. Subclinical atherosclerosis was evaluated by both the mean carotid intima-media thickness (IMT) and the presence of atherosclerotic plaques with the use of B-mode ultrasound in all subjects.

RESULTS

p53 levels were positively correlated with age (r = 0.382, P < 0.001), intercellular adhesion molecular-1 (ICAM-1; r = 0.510, P < 0.01), vascular cell adhesion molecular-1 (VCAM-1; r = 0.497, P < 0.01), E-selectin (r = 0.337, P < 0.01), and carotid IMT (r = 0.594, P < 0.01). The association between p53 and IMT remained significant in multiple regression analysis (P < 0.01) when controlling for traditional atherosclerotic risk factors and inflammatory markers.

CONCLUSION

Higher plasma p53 levels were associated with an increase in inflammatory markers, as well as increased carotid IMT. Circulating p53 may be useful in identifying subclinical atherosclerosis in subjects symptomatically free from cardiovascular disease.

Digging in the "soil" of the aorta to understand the growth of abdominal aortic aneurysms

Extensive studies into the etiology of aortic aneurysm disease have focused on the characteristic and unique inflammatory infiltration and elaboration of products of inflammatory cells which can result in matrix degradation. While these changes clearly have a significant impact on the development of aneurysm disease, little attention has been paid to the changes in the parenchymal cells of the aorta. Under normal conditions, the vascular smooth muscle cells which populate the aortic wall are responsible for the maintenance of the matrix components of the media, particularly the elastic fibers. As our understanding of the mechanisms of aneurysm formation and normal arterial anatomy become more sophisticated, it is clear that specific changes to these smooth muscle cells make them active participants in the medial matrix destruction characteristic of aneurysm disease. As others have described for intimal arterial disease, this is the "soil" from which aortic aneurysms grow.

Intrinsic pathway-mediated apoptosis in elastase-induced aneurysms in rabbits

BACKGROUND AND OBJECTIVES

The pathophysiology of saccular aneurysms is complex and multifactorial. The aim of the present study was to understand the mechanism of apoptosis in an elastase-induced aneurysm model in rabbits.

MATERIALS AND METHODS

Elastase-induced saccular aneurysms were created at the origin of the right common carotid artery in 20 rabbits. Aneurysm samples were harvested at 2 and 12 weeks after creation. Expression of apoptosis-associated proteins, including caspases and bcl-2 proteins, were assessed by Western blot analysis (n = 5 at both time points). Terminal deoxynucleotidyltransferase-mediated dUTP nick end-labeling (TUNEL) staining, which indicates the presence of apoptosis, was performed in tissue sections (n = 5 at both time points). The unoperated contralateral common carotid artery was used as a control.

RESULTS

Expression of active caspase-3, the final executioner of apoptosis, and caspase-9, the mediator of the intrinsic mitochondrial pathway, was observed in aneurysms at 2 weeks, whereas the expression of activated caspase-8, the mediator of the extrinsic death receptor pathway, was absent at both time points. Expression of antiapoptotic proteins, Bcl-2 and phospho-Bad, was down-regulated in aneurysms compared with controls at 2 weeks. None of these proteins were differentially expressed at 12 weeks. These results were confirmed by the presence of TUNEL-positive cells in some aneurysms at the early time point.

CONCLUSIONS

In this study of elastase-induced aneurysms in a rabbit model, activation of apoptosis is mediated predominantly by the Bcl-2-mediated intrinsic pathway through the activation of caspase-9.

Cellular senescence: molecular mechanisms, in vivo significance, and redox considerations

Cellular senescence is recognized as a critical cellular response to prolonged rounds of replication and environmental stresses. Its defining characteristics are arrested cell-cycle progression and the development of aberrant gene expression with proinflammatory behavior. Whereas the mechanistic events associated with senescence are generally well understood at the molecular level, the impact of senescence in vivo remains to be fully determined. In addition to the role of senescence as an antitumor mechanism, this review examines cellular senescence as a factor in organismal aging and age-related diseases, with particular emphasis on aberrant gene expression and abnormal paracrine signaling. Senescence as an emerging factor in tissue remodeling, wound repair, and infection is considered. In addition, the role of oxidative stress as a major mediator of senescence and the role of NAD(P)H oxidases and changes to intracellular GSH/GSSG status are reviewed. Recent findings indicate that senescence and the behavior of senescent cells are amenable to therapeutic intervention. As the in vivo significance of senescence becomes clearer, the challenge will be to modulate the adverse effects of senescence without increasing the risks of other diseases, such as cancer. The uncoupled relation between cell-cycle arrest and the senescent phenotype suggests that this is an achievable outcome.

Cellular senescence, cardiovascular risk, and CKD: a review of established and hypothetical interconnections

Cellular senescence is associated with shortened or damaged telomeres and is characterized by permanent exit from the cell cycle, morphological changes, and altered function. It develops after repeated cell divisions and also can be induced prematurely by stress conditions. The senescent phenotype, depending on cell type and atherosclerosis phase, seems to be a proatherosclerotic one: it promotes endothelial dysfunction and appears to be implicated in plaque destabilization, as well as in endothelial progenitor cell alteration. Many traditional and nontraditional cardiovascular disease risk factors induce senescence in a variety of vascular cells. Several of these factors, such as diabetes, hypertension, oxidative stress, and inflammation, are clustered in patients with chronic kidney disease. In a limited number of recent studies, stress-induced premature cellular senescence in this biologically aged population also was described. The hypothesis that premature cellular senescence might be considered an additional atherosclerosis-inducing factor in patients with chronic kidney disease is proposed.

Angiotensin II-mediated oxidative DNA damage accelerates cellular senescence in cultured human vascular smooth muscle cells via telomere-dependent and independent pathways

Angiotensin II (Ang II) induces reactive oxygen species (ROS) production by human vascular smooth muscle cells (hVSMCs). ROS have been implicated in the development of both acute stress-induced premature senescence (SIPS) and chronic replicative senescence. Global oxidative DNA damage triggers SIPS and telomere DNA damage accelerates replicative senescence, both mediated via p53. This study tests the hypothesis that DNA is an important target for Ang II-induced ROS leading to senescence via telomere-dependent and independent pathways. DNA damage was quantified using the Comet assay, telomere DNA length by Southern blotting and hVSMC senescence by senescence-associated beta-galactosidase staining. Exposure to Ang II increased DNA damage in hVSMCs within 4 hours. Inhibition by an AT1 receptor antagonist (losartan metabolite: E3174) or catalase, confirmed that Ang II-induced DNA damage was AT1 receptor-mediated, via the induction of ROS. Acute exposure to Ang II resulted in SIPS within 24 hours that was prevented by coincubation with E3174 or catalase. SIPS was associated with increased p53 expression but was not dependent on telomere attrition because overexpression of human telomerase did not prevent Ang II-induced SIPS. Exposure to Ang II over several population doublings accelerated the rate of telomere attrition (by >2-fold) and induced premature replicative senescence of hVSMCs--an effect that was also attenuated by E3174 or catalase. These data demonstrate that Ang II-induced ROS-mediated DNA damage results in accelerated biological aging of hVSMCs via 2 mechanisms: (1) Acute SIPS, which is telomere independent, and (2) accelerated replicative senescence which is associated with accelerated telomere attrition.

Effect of smoking on abdominal aortic aneurysms: novel insights through murine models

Abdominal aortic aneurysm is a poorly understood and fatal disease. The etiology of the disease is believed to be multifactorial. Of all the recognized clinical associations, none has a greater impact on the incidence and progression of the disease than exposure to tobacco smoke. Novel murine models developed over the past several years present the opportunity to investigate the mechanism of this critical clinical relationship.

Gene expression profile of abdominal aortic aneurysm rupture

To search for novel transcriptional pathways that are activated in abdominal aortic aneurysm rupture, cDNA microarrays were used to compare global mRNA expression at the aneurysm rupture edge to anterior sac, and selected results were confirmed using quantitative real-time-polymerase chain reaction (QRT-PCR). This study identified apoptosis, angiogenesis, and inflammation as potentially important participants during the process of aneurysm rupture.

Vascular cell senescence: contribution to atherosclerosis

Cardiologists and most physicians believe that aging is an independent risk factor for human atherosclerosis, whereas atherosclerosis is thought to be a characteristic feature of aging in humans by many gerontologists. Because atherosclerosis is among the age-associated changes that almost always escape the influence of natural selection in humans, it might be reasonable to regard atherosclerosis as a feature of aging. Accordingly, when we investigate the pathogenesis of human atherosclerosis, it may be more important to answer the question of how we age than what specifically promotes atherosclerosis. Recently, genetic analyses using various animal models have identified molecules that are crucial for aging. These include components of the DNA-repair system, the tumor suppressor pathway, the telomere maintenance system, the insulin/Akt pathway, and other metabolic pathways. Interestingly, most of the molecules that influence the phenotypic changes of aging also regulate cellular senescence, suggesting a causative link between cellular senescence and aging. For example, DNA-repair defects can cause phenotypic changes that resemble premature aging, and senescent cells that show DNA damage accumulate in the elderly. Excessive calorie intake can cause diabetes and hyperinsulinemia, whereas dysregulation of the insulin pathway has been shown to induce cellular senescence in vitro. Calorie restriction or a reduction of insulin signals extends the lifespan of various species and decreases biomarkers of cellular senescence in vivo. There is emerging evidence that cellular senescence contributes to the pathogenesis of human atherosclerosis. Senescent vascular cells accumulate in human atheroma tissues and exhibit various features of dysfunction. In this review, we examine the hypothesis that cellular senescence might contribute to atherosclerosis, which is a characteristic of aging in humans.

Aging-associated vascular phenotype in mutant mice with low levels of BubR1

BACKGROUND AND PURPOSE

Aging is a major risk for stroke and a highly complex biological process believed to involve multiple mechanisms. Mutant mice that express low levels of the spindle assembly checkpoint protein BubR1 are known to develop several aging-associated phenotypes at a very young age, including cataracts, lordokyphosis, loss of subcutaneous fat, and impaired wound healing. However, whether BubR1 acts to prevent vascular aging has not yet been established. The present study was designed to investigate the vascular phenotype of mutant mice with low levels of BubR1.

METHODS

Morphological, functional, and biochemical analyses were performed on aortas and carotid arteries of 3- to 5-month-old BubR1 mutant mice and wild-type littermates.

RESULTS

Arterial wall thickness and inner diameter were significantly reduced in BubR1 mutant mice. Arterial walls of BubR1 mutant mice had low numbers of medial smooth muscle cells. Masson trichrome staining showed profound fibrosis in arterial walls of BubR1 mutant. In agreement with these morphological changes, functional analysis of pressurized isolated carotid arteries of BubR1 mutant mice demonstrated reduced elastic properties. Endothelium-dependent relaxations to acetylcholine and endothelium-independent relaxations to the nitric oxide donor DEA-NONOate were significantly reduced in carotid arteries of BubR1 mutant mice. Furthermore, enzymatic activity of nitric oxide synthase and levels of cyclic GMP were significantly reduced in aortas of mutant mice, but production of superoxide anions was significantly increased.

CONCLUSIONS

These findings demonstrate that BubR1 insufficiency in mice results in phenotypic changes reminiscent of vascular aging in humans and suggest a role for BubR1 in suppressing the vascular aging process.

Degeneration of the pulmonary autograft: An explant study

OBJECTIVE

We sought to determine the histologic features of pulmonary autografts explanted after the Ross operation.

METHODS

Histologic sections of 30 explanted autografts and 8 normal heart valves were compared and semiquantitatively scored by a blinded cardiovascular pathologist.

RESULTS

Pulmonary autografts (n = 30) were explanted on average 6.1 +/- 0.6 years (median, 6.6 years; range, 0.1-11.7 years) after the Ross operation (n = 28) or removed at autopsy (n = 2). Twelve (43%) of the patients undergoing reoperation had no or negligible autograft insufficiency on early transthoracic echocardiography, 12 (43%) had grade 1 autograft insufficiency, and 4 (14%) had grade 1-2 autograft insufficiency. Valve regurgitation with root dilatation was the most common indication for reoperation after root replacement (n = 26 [93%]) and regurgitation after subcoronary implanted autografts (n = 2 [7%]). Microscopy of the autograft explants revealed normal laminar architecture and cellularity. Wall specimens were characterized by reduced and fragmented elastin and increased collagen levels (fibrosis). Medial elastin changes were associated with the presence of hypertrophic smooth muscle cells. Fibrosis was most severe in the adventitia. Intimal thickening was a common finding. Valve explants showed significant thickening caused by fibrocellular tissue on the ventricular surface and marked thickening of the free margin. An autopsy explant with normal function before death showed similar features.

CONCLUSIONS

Pulmonary autograft explants showed severe aneurysmal degeneration of the wall, which was characterized by intimal thickening, medial elastin fragmentation, and adventitial fibrosis. Valve leaflets were thickened. The presence of these features in a nonfailing explant suggests these changes represent a common mode of remodeling.

Stem cell-derived Sca-1+ progenitors differentiate into smooth muscle cells, which is mediated by collagen IV-integrin alpha1/beta1/alphav and PDGF receptor pathways

Embryonic stem (ES) cells can differentiate into smooth muscle cells (SMCs) that can be used for tissue engineering and repair of damaged organs. However, little is known about the molecular mechanisms of differentiation in these cells. In the present study, we found collagen IV can promote ES cells to differentiate into stem cell antigen-1-positive (Sca-1(+)) progenitor cells and SMCs. Pretreatment of ES cells with antibodies against collagen IV significantly inhibited SMC marker expression. To further elucidate the effect of collagen IV on the induction and maintenance of SMC differentiation, Sca-1(+) progenitor cells were isolated with magnetic beads, placed in collagen-IV-coated flasks, and cultured in differentiation medium with or without platelet-derived growth factor (PDGF)-BB for 6-90 days. Both immunostaining and fluorescence-activated cell sorter analyses revealed that the majority of these cells were positive for SMC-specific markers. Pretreatment of Sca-1(+) progenitors with antibodies against integrin alpha(1), alpha(v), and beta(1), but not beta(3), inhibited focal adhesion kinase (FAK) and paxillin phosphorylation and resulted in a marked inhibition of SMC differentiation. Various tyrosine kinase inhibitors, and specific siRNA for phosphatidylinositol 3-kinase (PI 3-kinase) and PDGF receptor-beta significantly inhibited SMC marker expression. Taken together, we demonstrate for the first time that collagen IV plays a crucial role in the early stage of SMC differentiation and that integrin (alpha(1), beta(1), and alpha(v))-FAK-PI 3-kinase-mitogen-activated protein kinase and PDGF receptor-beta signaling pathways are involved in SMC differentiation.

Biomechanical properties of ruptured versus electively repaired abdominal aortic aneurysm wall tissue

OBJECTIVE

The purpose of this study was to evaluate and compare the biomechanical properties of abdominal aortic aneurysm (AAA) wall tissue from patients who experienced AAA rupture with that of those who received elective repair.

METHODS

Rectangular, circumferentially oriented AAA wall specimens (approximately 2.5 cm x 7 mm) were obtained fresh from the operating room from patients undergoing surgical repair. The width and thickness were measured for each specimen by using a laser micrometer before testing to failure with a uniaxial tensile testing system. The force and deformation applied to each specimen were measured continuously during testing, and the data were converted to stress and stretch ratio. The tensile strength was taken as the peak stress obtained before specimen failure, and the distensibility was taken as the stretch ratio at failure. The maximum tangential modulus and average modulus were also computed according to the peak and average slope of the stress-stretch ratio curve.

RESULTS

Twenty-six specimens were obtained from 16 patients (aged 73 +/- 3 years [mean +/- SEM]) undergoing elective repair of their AAA (diameter, 7.0 +/- 0.5 cm). Thirteen specimens were resected from nine patients (aged 73 +/- 3 years; P = not significant in comparison to the electively repaired AAAs) during repair of their ruptured AAA (diameter, 7.8 +/- 0.6 cm; P = not significant). A significant difference was noted in wall thickness between ruptured and elective AAAs: 3.6 +/- 0.3 mm vs 2.5 +/- 0.1 mm, respectively (P < .001). The tensile strength of the ruptured tissue was found to be lower than that for the electively repaired tissue (54 +/- 6 N/cm2 vs 82 +/- 9.0 N/cm2; P = .04). Considering all specimens, no significant correlation was noted between tensile strength and diameter (R = -0.10; P = .55). Tensile strength, however, had a significant negative correlation with wall thickness (R = -0.42; P < .05) and a significant positive correlation with the tissue maximum tangential modulus (R = 0.76; P < .05).

CONCLUSIONS

Our data suggest that AAA rupture is associated with aortic wall weakening, but not with wall stiffening. A widely accepted indicator for risk of aneurysm rupture is the maximum transverse diameter. Our results suggest that AAA wall strength, in large aneurysms, is not related to the maximum transverse diameter. Rather, wall thickness or stiffness may be a better predictor of rupture for large AAAs.

A Review of Biological Factors Implicated in Abdominal Aortic Aneurysm Rupture

Abdominal aortic aneurysm (AAA) rupture is the 13th commonest cause of death in the Western World. Although considerable research has been applied to the aetiology and mechanism of aneurysm expansion, little is known about the mechanism of rupture. Aneurysm rupture was historically considered to be a simple physical process that occurred when the aortic wall could no longer contain the haemodynamic stress of the circulation. However, AAAs do not conform to the law of Laplace and there is growing evidence that aneurysm rupture involves a complex series of biological changes in the aortic wall. This paper reviews the available data on patient variables associated with aneurysm rupture and presents the evidence implicating biological factors in AAA rupture.

Treatment with simvastatin suppresses the development of experimental abdominal aortic aneurysms in normal and hypercholesterolemic mice

OBJECTIVE

To determine if treatment with hydroxymethylglutaryl-coenzyme A reductase inhibitors (statins) can influence the development of experimental abdominal aortic aneurysms (AAAs).

SUMMARY BACKGROUND DATA

AAAs are associated with atherosclerosis, chronic inflammation, and matrix metalloproteinase (MMP)-mediated connective tissue destruction. Because statins exert antiinflammatory activities independent of their lipid-lowering effects, these agents may help suppress aneurysmal degeneration.

METHODS

C57Bl/6 wild-type and hypercholesterolemic apoE-deficient mice underwent transient perfusion of the aorta with elastase followed by subcutaneous treatment with either 2 mg/kg simvastatin per day or vehicle. Aortic diameter (AD) was measured before and 14 days after elastase perfusion. The extent of aortic dilatation (DeltaAD) was determined with AAAs defined as DeltaAD >100%.

RESULTS

Wild-type mice treated with simvastatin exhibited a 21% reduction in DeltaAD and a 33% reduction in AAAs compared with vehicle-treated controls. Suppression of AAAs in simvastatin-treated mice was associated with preservation of medial elastin and vascular smooth muscle cells, as well as a relative reduction in aortic wall expression of MMP-9 and a relative increase in expression of TIMP-1. In hypercholesterolemic apoE-deficient mice, treatment with simvastatin was associated with a 26% reduction in DeltaAD and a 30% reduction in AAAs. Treatment with simvastatin had no effect on serum cholesterol levels in either normal or hypercholesterolemic mice.

CONCLUSIONS

Treatment with simvastatin suppresses the development of experimental AAAs in both normal and hypercholesterolemic mice. The mechanisms of this effect are independent of lipid-lowering and include preservation of medial elastin and smooth muscle cells, as well as altered aortic wall expression of MMPs and their inhibitors.

Adaptive cellular immunity in aortic aneurysms: cause, consequence, or context?

Abdominal aortic aneurysms are common and life threatening. Although CD4(+) T cells are abundant in aneurysm tissue, their role in disease progression remains unclear. A new study shows that mouse aortic allografts placed in animals lacking IFN-gamma receptors develop a Th2 inflammatory response with aortic aneurysms, whereas Th1 responses promote intimal hyperplasia. It is expected that these surprising findings will stimulate further efforts to clarify whether adaptive cellular immunity in aneurysm disease is detrimental or potentially beneficial.