Overexpression of transforming growth factor beta1 in smooth muscle cells of human abdominal aortic aneurysm

The mechanism and therapy of aortic aneurysms

Aortic aneurysm is a chronic aortic disease affected by many factors. Although it is generally asymptomatic, it poses a significant threat to human life due to a high risk of rupture. Because of its strong concealment, it is difficult to diagnose the disease in the early stage. At present, there are no effective drugs for the treatment of aneurysms. Surgical intervention and endovascular treatment are the only therapies. Although current studies have discovered that inflammatory responses as well as the production and activation of various proteases promote aortic aneurysm, the specific mechanisms remain unclear. Researchers are further exploring the pathogenesis of aneurysms to find new targets for diagnosis and treatment. To better understand aortic aneurysm, this review elaborates on the discovery history of aortic aneurysm, main classification and clinical manifestations, related molecular mechanisms, clinical cohort studies and animal models, with the ultimate goal of providing insights into the treatment of this devastating disease. The underlying problem with aneurysm disease is weakening of the aortic wall, leading to progressive dilation. If not treated in time, the aortic aneurysm eventually ruptures. An aortic aneurysm is a local enlargement of an artery caused by a weakening of the aortic wall. The disease is usually asymptomatic but leads to high mortality due to the risk of artery rupture.

The Genetics and Typical Traits of Thoracic Aortic Aneurysm and Dissection

Genetic predisposition and risk factors such as hypertension and smoking can instigate the development of thoracic aortic aneurysm (TAA), which can lead to highly lethal aortic wall dissection and/or rupture. Monogenic defects in multiple genes involved in the elastin-contractile unit and the TGFβ signaling pathway have been associated with TAA in recent years, along with several genetic modifiers and risk-conferring polymorphisms. Advances in omics technology have also provided significant insights into the processes behind aortic wall degeneration: inflammation, epigenetics, vascular smooth muscle phenotype change and depletion, reactive oxygen species generation, mitochondrial dysfunction, and angiotensin signaling dysregulation. These recent advances and findings might pave the way for a therapy that is capable of stopping and perhaps even reversing aneurysm progression.

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.

Imaging Biological Pathways in Abdominal Aortic Aneurysms Using Positron Emission Tomography

[Figure: see text].

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.

Aortic α-smooth muscle actin expressions in aortic disorders and coronary artery disease: An immunohistochemical study

Objective:

The is to report immunohistochemical observations of aortic α-smooth muscle actin (SMA) expressions in patients with aortic aneurysm, acute aortic dissection, and coronary artery disease and to discuss phenotypic switching of smooth muscle cells (SMCs) of these lesions.

Methods:

Forty-nine consecutive patients scheduled for surgical treatment for acute type A aortic dissection (20 patients), aortic aneurysm (9 patients), and coronary artery disease (20 patients) were included. Surgical specimens of the aorta were obtained and prepared for hematoxylin and eosin and immunohistochemical stainings.

Results:

A comparison of aortic structural changes between the three groups showed that patients with coronary artery disease had the least severe aorta degeneration with the most intense α-SMA positivity. Aortic structural impairment was the most severe in patients with aortic dissection, whereas α-SMA positivity was more intense in patients with aortic dissection than in those with aortic aneurysm.

Conclusion:

Disparities in α-SMA expressions in the aortic tissues of the three groups represent the extent of SMC degenerations or a phenotypic switching between contractile and synthetic SMCs. The results imply severe SMC degenerations in patients with aortic aneurysm, which may be beneficial because of the production of extracellular matrix necessary for healing of the vascular wall, but severe disruptions in elastic fibers in patients with aortic dissection. Patients with coronary artery disease show slight SMC degeneration and phenotypic switching among the three groups. The possible apoptotic and genetic mechanisms of aortic structural impairments warrant further elaborations.

Endovascular repair of tortuous recurrent femoral-popliteal aneurysm in a patient with Loeys-Dietz syndrome

Loeys-Dietz syndrome is a rare connective tissue disorder with widespread arterial tortuosity and aneurysms. This syndrome is most notable for its aortic disease, including aortic root dilation and aortic dissection or rupture. Although not as well studied, peripheral artery aneurysms are a prevalent concurrent manifestation and have previously been repaired with both open and endovascular approaches. There are minimal data about the durability and technical considerations of endovascular repair in this disease. We report a case of a patient who developed an extremely tortuous recurrent femoral-popliteal artery aneurysm secondary to aneurysmal degeneration around previously placed stents that was treated with an endovascular approach.

Aetiology and management of hereditary aortopathy

Aortic aneurysms are a major health problem because they account for 1-2% of all deaths in the Western population. Although abdominal aortic aneurysms (AAAs) are more prevalent than thoracic aortic aneurysms (TAAs), TAAs have been more exhaustively studied over the past 2 decades because they have a higher heritability and affect younger individuals. Gene identification in both syndromic and nonsyndromic TAA is proceeding at a rapid pace and has already pinpointed >20 genes associated with familial TAA risk. Whereas these genes explain <30% of all cases of familial TAA, their functional characterization has substantially improved our knowledge of the underlying pathological mechanisms. As such, perturbed extracellular matrix homeostasis, transforming growth factor-β signalling, and vascular smooth muscle cell contractility have been proposed as important processes in TAA pathogenesis. These new insights enable novel treatment options that are currently being investigated in large clinical trials. Moreover, together with the advent of next-generation sequencing approaches, these genetic findings are promoting a shift in the management of patients with TAA by enabling gene-tailored interventions. In this Review, we comprehensively describe the molecular landscape of familial TAA, and we discuss whether familial TAA, from a biological point of view, can serve as a paradigm for the genetically more complex forms of the condition, such as sporadic TAA or AAA.

α-Smooth Muscle Actin and ACTA2 Gene Expressions in Vasculopathies

α-smooth muscle actin, encoded by ACTA2 gene, is an isoform of the vascular smooth muscle actins, typically expressed in the vascular smooth muscle cells contributing to vascular motility and contraction. ACTA2 gene mutations cause a diversity of diffuse vasculopathies such as thoracic aortic aneurysms and dissections as well as occlusive vascular diseases, including premature coronary artery disease and ischemic stroke. Dynamics of differentiation-specific α-smooth muscle actin in arterial smooth muscle cells and proliferation of the proteins have been well described. Although a variety of research works have been undertaken in terms of modifications of α-smooth muscle actin and mutations of ACTA2 gene and myosin, the underlying mechanisms towards the pathological processes by way of gene mutations are yet to be clarified. The purpose of the present article is to describe the phenotypes of α-smooth muscle actin and implications of ACTA2 mutations in vasculopathies in order to enhance the understanding of potential mechanisms of aortic and coronary disorders.

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.

Vascular smooth muscle cell phenotypic changes in patients with Marfan syndrome

OBJECTIVE

Marfan's syndrome is characterized by the formation of ascending aortic aneurysms resulting from altered assembly of extracellular matrix microfibrils and chronic tissue growth factor (TGF)-β signaling. TGF-β is a potent regulator of the vascular smooth muscle cell (VSMC) phenotype. We hypothesized that as a result of the chronic TGF-β signaling, VSMC would alter their basal differentiation phenotype, which could facilitate the formation of aneurysms. This study explores whether Marfan's syndrome entails phenotypic alterations of VSMC and possible mechanisms at the subcellular level.

APPROACH AND RESULTS

Immunohistochemical and Western blotting analyses of dilated aortas from Marfan patients showed overexpression of contractile protein markers (α-smooth muscle actin, smoothelin, smooth muscle protein 22 alpha, and calponin-1) and collagen I in comparison with healthy aortas. VSMC explanted from Marfan aortic aneurysms showed increased in vitro expression of these phenotypic markers and also of myocardin, a transcription factor essential for VSMC-specific differentiation. These alterations were generally reduced after pharmacological inhibition of the TGF-β pathway. Marfan VSMC in culture showed more robust actin stress fibers and enhanced RhoA-GTP levels, which was accompanied by increased focal adhesion components and higher nuclear localization of myosin-related transcription factor A. Marfan VSMC and extracellular matrix measured by atomic force microscopy were both stiffer than their respective controls.

CONCLUSIONS

In Marfan VSMC, both in tissue and in culture, there are variable TGF-β-dependent phenotypic changes affecting contractile proteins and collagen I, leading to greater cellular and extracellular matrix stiffness. Altogether, these alterations may contribute to the known aortic rigidity that precedes or accompanies Marfan's syndrome aneurysm formation.

Applications of nuclear reprogramming and directed differentiation in vascular regenerative medicine

As vertebrates proceed through embryonic development the growing organism cannot survive on diffusion of oxygen and nutrients alone and establishment of vascular system is fundamental for embryonic development to proceed. Dysfunction of the vascular system in adults is at the heart of many disease states such as hypertension and atherosclerosis. In this review we will focus on attempts to generate the key cells of the vascular system, the endothelial and smooth muscle cells, using human embryonic stem cells (hESCs) and human induced pluripotent stem cells (iPSCs). Regardless of their origin, be it embryonic or via somatic cell reprogramming, pluripotent stem cells provide limitlessly self-renewing populations of material suitable for the generation of multi-lineage isogenic vascular cells-types that can be used as tools to study normal cell and tissue biology, model disease states and also as tools for drug screening and future cell therapies.

Disruption of TGF-β signaling in smooth muscle cell prevents elastase-induced abdominal aortic aneurysm

Transforming growth factor-β (TGF-β) signaling has been significantly implicated in the pathogenesis of aneurysm, prominently the initiation and progression of abdominal aortic aneurysm (AAA). Vascular smooth muscle cell (SMC) is the principal resident cell in aortic wall and is essential for its structure and function. However, the role of TGF-β pathway in SMC for the formation of AAA remains unknown. Therefore, the goal of the present study was to investigate the effect of TGF-β pathway in SMC for AAA pathogenesis, by using a genetical smooth muscle-specific (SM-specific) TGF-β type II receptor (Tgfbr2) disruption animal model. Mice deficient in the expression of Tgfbr2 (MyhCre.Tgfbr2(f/f) and MyhCre.Tgfbr2(WT/f)) and their corresponding wild-type background mice (MyhCre.Tgfbr2(WT/WT)) underwent AAA induction by infrarenal peri-adventitial application of elastase. Fourteen days after elastase treatment, the aortas were analyzed and indicated that disruption of 1 or 2 alleles of Tgfbr2 in SMC provided markedly step-wise protection from AAA formation. And elastin degradation, medial SMC loss, macrophage infiltration, and matrix metalloproteinases (MMP) expression were all significantly reduced in Tgfbr2 deletion mice. Our study demonstrated, for the first time, that the TGF-β signaling pathway in SMC plays a critical role in AAA and disruption can prevent the aneurysm formation.

Regional changes in elastic fiber organization and transforming growth factor β signaling in aortas from a mouse model of marfan syndrome

In Marfan Syndrome (MFS), development of thoracic aortic aneurysms (TAAs) is characterized by degeneration of the medial layer of the aorta, including fragmentation and loss of elastic fibers, phenotypic changes in the smooth muscle cells, and an increase in the active form of transforming growth factor-β (TGFβ), which is thought to play a major role in development and progression of the aneurysm. We hypothesized that regional difference in elastic fiber fragmentation contributes to TGFβ activation and hence the localization of aneurysm formation. The fibrillin-1-deficient mgR/mgR mouse model of MFS was used to investigate regional changes in elastin fiber fragmentation, TGFβ activation and changes in gene expression as compared to wild-type littermates. Knockdown of Smad 2 and Smad 3 with shRNA was used to determine the role of the specific transcription factors in gene regulation in aortic smooth muscle cells. We show increased elastin fiber fragmentation in the regions associated with aneurysm formation and altered TGFβ signaling in these regions. Differential effects of Smad 2 and Smad 3 were observed in cultured smooth muscle cells by shRNA-mediated knockdown of expression of these transcription factors. Differential signaling through Smad 2 and Smad 3 in regions of active vascular remodeling likely contribute to aneurysm formation in the mgR/mgR model of MFS. Increased elastin fiber fragmentation in these regions is associated with these changes as compared to other regions of the thoracic aorta and may contribute to the changes in TGFβ signaling in these regions.

Proteins associated with the size and expansion rate of the abdominal aortic aneurysm wall as identified by proteomic analysis

OBJECTIVES

Identification of biomarkers for the natural history of abdominal aortic aneurysms (AAA) holds the key to non-surgical intervention and improved selection for AAA repair. We aimed to associate the basic proteomic composition of AAA wall tissue with the expansion rate and size in patients with AAA.

METHODS

A proteomic approach was used, consisting of two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and mass spectrometry (MS) to identify differentially expressed proteins in AAA tissue. Relevant protein spots were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS).

RESULTS

Spearman's correlation analysis revealed 16 protein spots were strongly correlated with AAA expansion rate (ρ>±0.75). Nine protein spots were identified. Six protein spots showed correlation with AAA size (ρ>±0.5). Three protein spots were identified: vitronectin with traces of calreticulin, albumin and a spot containing two proteins: collagen α-3(VI) chain and vitamin D binding protein. Interestingly, in our previous study vitronectin was shown to be down-regulated in a ruptured AAA group compared with non-ruptured AAA. Western blot analysis in the present study confirmed a correlation of vitronectin bands with AAA size in aortic aneurysm tissue.

CONCLUSION

A proteomic approach seems valuable, and identified several candidates not previously associated with AAA. Larger studies are required to confirm the potential and clinical role of the identified proteins.

Impaired fibrillin-1 function promotes features of plaque instability in apolipoprotein E-deficient mice

BACKGROUND

Arterial stiffness has been associated with an increased cardiovascular risk. The aim of this study was to investigate the interaction between arterial stiffness and atherosclerosis.

METHODS AND RESULTS

Mice with a mutation C1039G+/-) in the fibrillin-1 gene leading to fragmentation of the elastic fibers were crossbred with apolipoprotein E-deficient (ApoE-/-) mice. Subsequently, ApoE-/- and ApoE-/-C1039G+/- mice were fed a Western-type diet for 10 or 20 weeks. Our results show that the interaction between arterial stiffness and atherosclerosis is bidirectional. On the one hand, arterial stiffness in ApoE-/-C1039G+/- mice increased more rapidly in the presence of atherosclerotic plaques. On the other hand, arterial stiffness promoted the development of larger and more unstable plaques in ApoE-/-C1039G+/- mice. The plaque area at the aortic root was increased 1.5- and 2.1-fold in ApoE-/-C1039G+/- mice after 10 and 20 weeks of Western-type diet, respectively. After 10 weeks of Western-type diet, plaques of ApoE-/-C1039G+/- mice showed increased apoptosis of smooth muscle cells, which was associated with a decrease in collagen content, an enlargement of the necrotic core, and an increase in macrophages. After 20 weeks of Western-type diet, the number of buried fibrous caps was increased in atherosclerotic lesions of ApoE-/-C1039G+/- mice, not only at the level of the aortic valves but also in the brachiocephalic artery and in the upper, middle, and lower thoracic aorta. Furthermore, acute plaque rupture was observed.

CONCLUSIONS

These results indicate that fragmentation of the elastic fibers leads to increased vascular stiffness, which promotes features of multifocal plaque instability.

Atorvastatin Modulates Matrix Metalloproteinase Expression, Activity, and Signaling in Abdominal Aortic Aneurysms

Statins may reduce abdominal aortic aneurysm (AAA) progression. We sought to measure how atorvastatin (AT) treatment might modulate matrix metalloproteinase (MMP) expression and/or activity in human AAA. Tissue from human AAAs at surgical repair was obtained from patients who were either not on statins (NST, n = 19) or treated with AT (n = 19). Immunoblots measured expression and zymography measured activity. Expression of most proteins was greater in the central compared with distal AAA region. Matrix metalloproteinase 1, MMP2, MMP3, MMP9, Tissue Inhibitor of Metalloproteinase (TIMP2), TIMP3, TIMP4, or total Sma Mothers Against Decapentaplegia (SMAD2) expression did not differ with treatment. There was a trend toward reduced MMP8 and TIMP1 expression and MMP2 zymographic activity in the AT-treatment group. In contrast, AT-treated samples had significantly reduced MMP13 (P = .02), latent-transforming growth factor (TGF)-β (P = .02), and phospho-SMAD2 (P = .029) expression than NST-treated samples. We conclude that the AT-mediated decrease in MMP expression and activity reduces TGF-β signaling in the central region of human AAAs.

Smooth muscle phenotypic modulation is an early event in aortic aneurysms

OBJECTIVES

Vascular smooth muscle cells can undergo profound changes in phenotype, defined by coordinated repression of smooth muscle cell marker genes and production of matrix metalloproteinases in response to injury. However, little is known of the role of smooth muscle cells in aortic aneurysms. We hypothesized that smooth muscle cells undergo phenotypic modulation early in the development of aortic aneurysms.

METHODS

Abdominal aortas from C57B6 mice (n = 79) were perfused with elastase or saline (control) and harvested at 1, 3, 7, or 14 days. Aortas were analyzed by means of quantitative polymerase chain reaction and immunohistochemistry for smooth muscle cell marker genes, including SM22A, smooth muscle alpha-actin, and matrix metalloproteinases 2 and 9. In complimentary experiments human aneurysms (n = 10) and control aorta (n = 10) were harvested at the time of surgical intervention and analyzed.

RESULTS

By 14 days, aortic diameter was larger after elastase perfusion compared with control diameter (100% +/- 9.6% vs 59.5% +/- 18.9%, P = .0002). At 7 days, elastase-perfused mice had a 78% and 85% reduction in SM22 alpha and smooth muscle alpha-actin expression, respectively, compared with that seen in control animals well before aneurysms were present, and these values remained repressed at 14 days. Immunohistochemistry confirmed less SM22 alpha and smooth muscle alpha-actin in experimental aneurysms at 14 days in concert with increased matrix metalloproteinase 2 and 9 expression at 7 and 14 days. Similarly, human aneurysms had less SM22 alpha and smooth muscle alpha-actin and increased matrix metalloproteinase 2 and 9 staining, compared with control values, as determined by means of quantitative polymerase chain reaction.

CONCLUSIONS

Aneurysms demonstrate smooth muscle cell phenotypic modulation characterized by downregulation of smooth muscle cell marker genes and upregulation of matrix metalloproteinases. These events in experimental models occur before aneurysm formation. Targeting smooth muscle cells to a reparative phenotype might provide a novel therapy in the treatment of aortic aneurysms.

Assessment of the association between genetic polymorphisms in transforming growth factor beta, and its binding protein (LTBP), and the presence, and expansion, of Abdominal Aortic Aneurysm

OBJECTIVES

Abdominal Aortic Aneurysm (AAA) has a strong genetic predisposition. Transforming growth factor beta 1 (TGF-beta1) is a causal factor in ascending aortic dilatation; however, a role in AAA pathology is unclear. The aim of the study was to determine whether genes coding TGF-beta and its binding protein are associated with the presence and expansion of AAA.

METHODS

Four geographically distinct case control studies, totaling 1890 AAA cases and 3785 controls, were genotyped and compared to the presence, size and growth rate of AAA. 26 single nucleotide polymorphisms (SNPs) in 5 genes were genotyped in the UK cohort and the result was replicated in 3 independent cohorts.

RESULTS

No associations between genotypes or haplotypes and the presence of AAA disease were confirmed. Five SNPs in Latent TGF-beta Binding Protein (LTBP4) and an allelic variant of TGFB3 were associated with a significant decrease in AAA growth (p< or =0.02), in the UK cohort. Altered growth was demonstrated in carriers of two common haplotypes of LTBP4 (+0.38 mm/year, p=0.003; -0.41 mm/year, p=0.02, per haplotype copy) and a single haplotype of TGFB3 (-0.53 mm/year, p=0.05). This association with AAA growth could not be demonstrated in two other independent cohorts. Meta-analysis of AAA size and growth rates in larger AAA (> or =45 mm), in all four cohorts, demonstrated a significant association with the LTBP4 21011A>T genotype (a 2% decrease in AAA diameter, or a 0.53 mm/year reduction in AAA growth rate, per T allele [p=0.03, p=0.01]).

CONCLUSION

This study suggests that the LTBP4 gene may contribute to AAA progression.

Association of the TGF-beta receptor genes with abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a multifactorial condition. The transforming growth factor beta (TGF-beta) pathway regulates vascular remodeling and mutations in its receptor genes, TGFBR1 and TGFBR2, cause syndromes with thoracic aortic aneurysm (TAA). The TGF-beta pathway may be involved in aneurysm development in general. We performed an association study by analyzing all the common genetic variants in TGFBR1 and TGFBR2 using tag single nucleotide polymorphisms (SNPs) in a Dutch AAA case-control population in a two-stage genotyping approach. In stage 1, analyzing 376 cases and 648 controls, three of the four TGFBR1 SNPs and nine of the 28 TGFBR2 SNPs had a P<0.07. Genotyping of these SNPs in an independent cohort of 360 cases and 376 controls in stage 2 confirmed association (P<0.05) for the same allele of one SNP in TGFBR1 and two SNPs in TGFBR2. Joint analysis of the 736 cases and 1024 controls showed statistically significant associations of these SNPs, which sustained after proper correction for multiple testing (TGFBR1 rs1626340 OR 1.32 95% CI 1.11-1.56 P=0.001 and TGFBR2 rs1036095 OR 1.32 95% CI 1.12-1.54 P=0.001 and rs4522809 OR 1.28 95% CI 1.12-1.46 P=0.0004). We conclude that genetic variations in TGFBR1 and TGFBR2 associate with AAA in the Dutch population. This suggests that AAA may develop partly by similar defects as TAA, which in the future may provide novel therapeutic options.

Association Between the Coronary Artery Disease Risk Locus on Chromosome 9p21.3 and Abdominal Aortic Aneurysm

Background— Recent genome-wide studies have shown a significant association of a locus on chromosome 9p21.3 and coronary artery disease. We performed a case-control study to investigate the association between this locus and abdominal aortic aneurysm (AAA).

Methods and Results— A total of 1714 patients (899 patients with AAA and 815 controls) were genotyped for the lead single-nucleotide polymorphism, rs1333049, on chromosome 9p21. The frequency of the C (risk) allele of rs1333049 in the control group was 0.471. There was a significant association between the C allele and AAA (odds ratio, 1.22; 95% confidence interval, 1.06 to 1.39; P =0.004). The genotypic-specific odds ratios (compared with the GG genotype) were 1.17 (95% confidence interval, 0.93 to 1.47; P =0.191) for the GC genotype and 1.50 (95% confidence interval, 1.14 to 1.97; P =0.004) for the CC genotype. In logistic regression modeling, the association of the CC genotype with AAA was independent of the presence of clinical coronary artery disease (odds ratio, 1.46; 95% confidence interval, 1.11 to 1.94; P =0.008).

Conclusions— Our study shows that the recently identified chromosome 9 variant that increases risk of coronary artery disease is also associated with the presence of AAA. The findings suggest that the effect of this locus on risk of cardiovascular disease extends beyond the coronary circulation.

Transforming growth factor-beta signaling in thoracic aortic aneurysm development: a paradox in pathogenesis

Thoracic aortic aneurysms (TAAs) are potentially devastating, and due to their asymptomatic behavior, pose a serious health risk characterized by the lack of medical treatment options and high rates of surgical morbidity and mortality. Independent of the inciting stimuli (biochemical/mechanical), TAA development proceeds by a multifactorial process influenced by both cellular and extracellular mechanisms, resulting in alterations of the structure and composition of the vascular extracellular matrix (ECM). While the role of enhanced ECM proteolysis in TAA formation remains undisputed, little attention has been focused on the upstream signaling events that drive the remodeling process. Recent evidence highlighting the dysregulation of transforming growth factor-beta (TGF-beta) signaling in ascending TAAs from Marfan syndrome patients has stimulated an interest in this intracellular signaling pathway. However, paradoxical discoveries have implicated both enhanced TGF-beta signaling and loss of function TGF-beta receptor mutations, in aneurysm formation; obfuscating a clear functional role for TGF-beta in aneurysm development. In an effort to elucidate this subject, TGF-beta signaling and its role in vascular remodeling and pathology will be reviewed, with the aim of identifying potential mechanisms of how TGF-beta signaling may contribute to the formation and progression of TAA.

Pravastatin increases the expression of the tissue inhibitor of matrix metalloproteinase-1 and the oncogeneBaxin human aortic abdominal aneurysms

The effect of pravastatin on matrix metalloproteinase-9 (MMP-9) and the level of tissue inhibitor of metalloproteinase (TIMP)-1 and TIMP-2 was studied in explants of human abdominal aortic aneurysm (AAA) obtained from 13 patients. The effect of pravastatin on the apoptotic status of human AAA explants was also examined. Total MMP-9 content did not differ in human AAA explants incubated in vitro in the presence or absence of pravastatin (10−6mol/L) for 48 h. TIMP-1 levels were significantly increased in pravastatin-incubated AAA explants, but TIMP-2 production was not modified by pravastatin. Western blot experiments showed that, whereas Bax expression was increased in pravastatin-incubated AAA explants, the expression of Bcl-2 was not modified. On the other hand, the ratio of the expression of Bax to Bcl-2, an apoptotic index, was not modified by pravastatin. In the human AAA explants, the increase in Bax expression, but not the increase in TIMP-1 expression elicited by pravastatin, was reversed by l-mevalonate, a downstream HMG-CoA reductase metabolite, suggesting that the expression of Bax and TIMP-1 followed HMG-CoA reductase-dependent and -independent pathways, respectively. In conclusion, pravastatin increases both TIMP-1 and Bax expression in human AAA explants without changes in either MMP-9 activity or the apoptotic status.

Adventitial mast cells contribute to pathogenesis in the progression of abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is histologically characterized by medial degeneration and various degrees of chronic adventitial inflammation, although the mechanisms for progression of aneurysm are poorly understood. In the present study, we carried out histological study of AAA tissues of patients, and interventional animal and cell culture experiments to investigate a role of mast cells in the pathogenesis of AAA. The number of mast cells was found to increase in the outer media or adventitia of human AAA, showing a positive correlation between the cell number and the AAA diameter. Aneurysmal dilatation of the aorta was seen in the control (+/+) rats following periaortic application of calcium chloride (CaCl2) treatment but not in the mast cell-deficient mutant Ws/Ws rats. The AAA formation was accompanied by accumulation of mast cells, T lymphocytes and by activated matrix metalloproteinase 9, reduced elastin levels and augmented angiogenesis in the aortic tissue, but these changes were much less in the Ws/Ws rats than in the controls. Similarly, mast cells were accumulated and activated at the adventitia of aneurysmal aorta in the apolipoprotein E-deficient mice. The pharmacological intervention with the tranilast, an inhibitor of mast cell degranulation, attenuated AAA development in these rodent models. In the cell culture experiment, a mast cell directly augmented matrix metalloproteinase 9 activity produced by the monocyte/macrophage. Collectively, these data suggest that adventitial mast cells play a critical role in the progression of AAA.

Increased apoptosis and cysteinyl aspartate specific protease-3 gene expression in human intracranial aneurysm

OBJECTIVE

To investigate apoptosis in vascular smooth muscle cells (VSMCs) and caspase-3 expression in ruptured intracranial aneurysm.

METHODS

Tissue samples of 15 ruptured intracranial aneurysms, 6 abdominal aortic aneurysms (AAA) and 6 normal vessels were evaluated. Apoptosis in VSMCs was determined on transmission electron microscopy. Immunohistochemistry for alpha-SMC actin and direct cell counts (medial VSMCs per high-power field (HPF)) were employed to determine medial VSMC density. Additionally, gene expression of caspase-3 was determined using real-time RT-PCR.

RESULTS

We demonstrated medial VSMCs exhibiting morphological apoptotic changes in cerebral aneurysm and AAA. Medial VSMC density was significantly decreased in intracranial aneurysm (43.9+/-4.3 SMCs/HPF) and AAA (53.2+/-9.4 SMCs/HPF) compared with the normal arteries (222.8+/-12.1 SMCs/HPF; p<0.01). An 8.94-fold and 6.73-fold increase in expression of caspase-3mRNA in intracranial aneurysm and AAA, respectively, were obtained relative to the normal vessels.

CONCLUSIONS

These results suggest that real time RT-PCR provides a useful tool to test gene expression in small samples, and may contribute to a better understanding of the role of apoptosis in ruptured intracranial aneurysm.

The role of myoendothelial gap junctions in the formation of arterial aneurysms: the hypothesis of "connexin 43:40 stoichiometry"

Heterocellular myoendothelial gap junctions (MEGJs) are essential in coordinating and regulating vasomotion. Little is known about their potential role in disease states. We discuss how alteration in the Cx 43:40 expression ratio at the level of MEGJs may begin a chain of reactions in the arterial wall resulting in an aneurysm formation. In this model, we assumed that aneurysm is a chronic arterial disease associated with medial degeneration and intimal hyperplasia. It also was assumed that MEGJs are composed of Cx43 and Cx40 in different stoichiometry and that the characteristic of a given junction is in the favor of its most abundantly expressed constituent. The hypothesis of Cx 43:40 stoichiometry indicates that impaired MEGJs may play a role in the pathogenesis of arterial aneurysms. Cx43 upregulation and Cx40 downregulation (increased Cx 43:40 stoichiometry) may induce a cascade of inflammatory, electrical, metabolic and proliferative derangements in the arterial wall, which finally lead to the matrix degradation, intimal hyperplasia, endothelial-medial dissociation and loss of endothelium-dependent hyperpolarizing currents, irregular vasomotion, impaired growth factor activation, and arterial sympathetic deprivation. The final consequence of these alterations is aneurysm formation.

Matrix biology of abdominal aortic aneurysms in diabetes: mechanisms underlying the negative association

Several case-control studies have shown a significant negative association between diabetes and abdominal aortic aneurysm (AAA). This interaction has the potential to further our understanding of these two diseases but has attracted little research. The changes seen in the walls of aneurysmal aortas include inflammation and the activation of proteolytic pathways resulting in loss of elastin and other structural proteins. In contrast, diabetes is associated with increased synthesis and reduced degradation of matrix. The deposition of advanced glycation end products also renders vascular matrix resistant to proteolysis in diabetic patients. The aim of our present minireview is to compare the changes in matrix biology seen in diabetes and AAA and to explore molecular mechanisms that may explain the negative association and identify possible therapeutic implications.

Overexpression of transforming growth factor-beta1 stabilizes already-formed aortic aneurysms: a first approach to induction of functional healing by endovascular gene therapy

BACKGROUND

The cell response to transforming growth factor-beta1 (TGF-beta1), a multipotent cytokine with healing potential, varies according to tissue context. We have evaluated the ability of TGF-beta1 overexpression by endovascular gene therapy to stabilize abdominal aortic aneurysms (AAAs) already injured by inflammation and proteolysis.

METHODS AND RESULTS

Active TGF-beta1 overexpression was obtained in already-developed experimental AAAs in rats after endovascular delivery of an adenoviral construct encoding for a mutated form of active simian TGF-beta1 and in an explant model using human atherosclerotic AAA fragments incubated with recombinant active TGF-beta1. Transient exogenous TGF-beta1 overexpression by endovascular gene delivery was followed by induction of endogenous rat TGF-beta1. Overexpression of active TGF-beta1 in experimental AAAs was associated with diameter stabilization, preservation of medial elastin, decreased infiltration of monocyte-macrophages and T lymphocytes, and a decrease in matrix metalloproteinase-2 and -9, which was also observed in the explant model, in both thrombus and wall. In parallel with downregulation of the destructive process, active TGF-beta1 overexpression triggered endoluminal reconstruction, replacing the thrombus by a vascular smooth muscle cell-, collagen-, and elastin-rich intima.

CONCLUSIONS

Local TGF-beta1 self-induction after transient exogenous overexpression reprograms dilated aortas altered by inflammation and proteolysis and restores their ability to withstand arterial pressure without further dilation. This first demonstration of stabilization of expanding AAAs by delivery of a single multipotent self-promoting gene supports the view that endovascular gene therapy should be considered for treatment of aneurysms.

Cytokines and growth factors involved in apoptosis and proliferation of vascular smooth muscle cells

This review focuses on the role of cytokines and growth factors involved in the regulation of smooth muscle cells in an atherosclerotic plaque. As a plaque begins to develop, upon endothelial injury inflammatory cells within the lesion interact with the accumulating LDL, other inflammatory cells and smooth muscle cells and release cytokines and growth factors. The mediators released from the activated cells regulate the proliferation and/or survival of smooth muscle cells. This determines the stability and integrity of a plaque. New data emerging from various studies have provided novel insights into many of the cellular interactions and signaling mechanisms involving apoptosis of smooth muscle cells in the atherosclerotic plaques. A number of these studies, focusing on activation of inflammatory cells and the roles of chemokines, cytokines and growth factors, are addressed in this review.

Endoglin gene insertion polymorphism not associated with aneurysmal subarachnoid hemorrhage

Object. Data concerning an association between the ENG gene intronic insertion polymorphism and intracranial aneurysms (IAs) remain inconsistent. In this study the authors investigated whether this polymorphism is associated with a subarachnoid hemorrhage (SAH) caused by a ruptured IA in a Polish population.

Methods. One hundred nineteen patients with aneurysmal SAH and 119 sex-matched healthy volunteers were studied. The insertion ENG gene polymorphism in intron 7 was identified using polymerase chain reaction—single-strand chain polymorphism method.

The distribution of the insertion allele did not differ between the SAH (13%) and control (16%) cases (p = 0.36). The homozygous insertion/insertion genotype frequencies in these cases were 3.4 and 0.8%, respectively (p = 0.18).

Conclusions. The authors failed to find an association between the intronic insertion polymorphism of the ENG gene and aneurysmal SAH in a Polish population.

Relationship between iNOS expression and aortic cell proliferation and apoptosis in an elastase-induced model of aorta aneurysm and the effect of 1400 W administration

BACKGROUND

In the present study, we employed an elastase infusion-dependent abdominal aortic aneurysm (AAA) model to examine inducible nitric oxide synthase (iNOS) expression in relation to cellular proliferation and apoptosis in this pathologic condition. Furthermore, we employed N-(3-(aminomethyl)benzyl)acetamidine (1400 W), a previously shown selective iNOS inhibitor, to further explore this relationship.

METHODS

Adult male Wistar rats were randomized into separate groups. Group A served as a control and received an intra-aortic saline infusion, while groups B, C, and D received an intra-aortic elastase infusion according to standard protocols. The animals in group C were administered postoperatively the highly selective iNOS inhibitor, 1400 W, while rats in group D received regularly the same compound preoperatively and postoperatively. The animals were killed at postoperative days 7 and 14. Aorta diameter and nitric oxide (NO), nitrite/nitrate, and MDA levels were measured. iNOS expression was assessed by immunohistochemistry and Western blot analysis, while Ki-67 immunohistochemistry and TUNEL assay were used to evaluate cellular proliferation and apoptosis, respectively.

RESULTS

Increased iNOS and NO levels accompanied aneurysm development in groups B, C, and D, but these levels were significantly lower in groups C and D, compared with group B. Interestingly, very low but detectable levels of iNOS were found in the control group, indicating a basal constitutive level. Cell growth parameters were augmented in group B compared with group A. In contrast, groups C and D exhibited a significant decrease of the cellular growth parameters but did not attain normal values.

CONCLUSIONS

iNOS-derived NO is associated with the cellular growth parameters of the vessel cells, predominantly smooth muscle cells. Selective iNOS blockage ameliorates the cellular remodeling in AAAs.