Angiotensin II type 1 receptor 1166C polymorphism is associated with abdominal aortic aneurysm in three independent cohorts

Proteome-Wide Mendelian Randomization Identifies Therapeutic Targets for Abdominal Aortic Aneurysm

BACKGROUND

The proteome is a key source of therapeutic targets. We conducted a comprehensive Mendelian randomization analysis across the proteome to identify potential protein markers and therapeutic targets for abdominal aortic aneurysm (AAA).

METHODS AND RESULTS

Our study used plasma proteomics data from the UK Biobank, comprising 2923 proteins from 54 219 individuals, and from deCODE Genetics, which measured 4907 proteins across 35 559 individuals. Significant proteomic quantitative trait loci were used as instruments for Mendelian randomization. Genetic associations with AAA were sourced from the AAAgen consortium, a large-scale genome-wide association study meta-analysis involving 37 214 cases and 1 086 107 controls, and the FinnGen study, which included 3869 cases and 381 977 controls. Sequential analyses of colocalization and summary-data-based Mendelian randomization were performed to verify the causal roles of candidate proteins. Additionally, single-cell expression analysis, protein-protein interaction network analysis, pathway enrichment analysis, and druggability assessments were conducted to identify cell types with enriched expression and prioritize potential therapeutic targets. The proteome-wide Mendelian randomization analysis identified 34 proteins associated with AAA risk. Among them, 2 proteins, COL6A3 and PRKD2, were highlighted by colocalization analysis, summary-data-based Mendelian randomization, and the heterogeneity in an independent instrument test, providing the most convincing evidence. These protein-coding genes are primarily expressed in macrophages, smooth muscle cells, and mast cells within abdominal aortic aneurysm tissue. Several causal proteins are involved in pathways regulating lipid metabolism, immune responses, and extracellular matrix organization. Nine proteins have already been targeted for drug development in diabetes and other cardiovascular diseases, presenting opportunities for repurposing as AAA therapeutic targets.

CONCLUSIONS

This study identifies causal proteins for AAA, enhancing our understanding of its molecular cause and advancing the development of therapeutics.

Inflammation in Abdominal Aortic Aneurysm: Cause or Comorbidity?

Aortic aneurysm is a potentially deadly disease. It is chronic degeneration of the aortic wall that involves an inflammatory response and the immune system, aberrant remodelling of the extracellular matrix, and maladaptive transformation of the aortic cells. This review article focuses on the role of the inflammatory cells in abdominal aortic aneurysm. Studies in human aneurysmal specimens and animal models have identified various inflammatory cell types that could contribute to formation or expansion of aneurysms. These include the commonly studied leukocytes (neutrophils and macrophages) as well as the less commonly explored natural killer cells, dendritic cells, T cells, and B cells. Despite the well-demonstrated contribution of inflammatory cells and the related signalling pathways to development and expansion of aneurysms, anti-inflammatory therapy approaches have demonstrated limitations and may require additional considerations such as a combinational approach in targeting multiple pathways for significant beneficial outcomes.

Medical treatments for abdominal aortic aneurysm: an overview of clinical trials

INTRODUCTION

Abdominal aortic aneurysm is a progressive, segmental, abdominal aortic dilation associated with a high mortality rate. Abdominal aortic aneurysms with diameters larger than 55 mm are associated with a high risk of rupture, and the most effective treatment options are surgical repair. Close observation and lifestyle adjustments are recommended for smaller abdominal aortic aneurysms with lower rupture risk. The development of medical therapies that limit or prevent the progression, expansion, and eventual rupture of abdominal aortic aneurysms remains an unmet clinical need.

AREAS COVERED

This review provides an overview of completed and ongoing clinical trials examining the efficacies of various drug classes, including antibiotics, antihypertensive drugs, hypolipidemic drugs, hypoglycemic drugs, and other potential therapies for abdominal aortic aneurysms. A search of PubMed, Web of Science, Clinical Trials, and another six clinical trial registries was conducted in January 2024.

EXPERT OPINION

None of the drugs have enough evidence to indicate that they can effectively inhibit the dilation of abdominal aortic aneurysm. More clinical trial data is required to support the efficacy of propranolol. Future research should also explore different drug delivery mechanisms, such as nanoparticles, to elevate drug concentration at the aneurysm wall.

Comparison of Genes Associated with Thoracic and Abdominal Aortic Aneurysms

Aneurysms impacting the ascending thoracic aorta and the abdominal aorta affect patient populations with distinct clinical characteristics. Through a literature review, this paper compares the genetic associations of ascending thoracic aortic aneurysm (ATAA) with abdominal aortic aneurysms (AAA). Genes related to atherosclerosis, lipid metabolism, and tumor development are associated specifically with sporadic AAA, while genes controlling extracellular matrix (ECM) structure, ECM remodeling, and tumor growth factor β function are associated with both AAA and ATAA. Contractile element genes uniquely predispose to ATAA. Aside from known syndromic connective tissue disease and poly-aneurysmal syndromes (Marfan disease, Loeys-Dietz syndrome, and Ehlers-Danlos syndrome), there is only limited genetic overlap between AAA and ATAA. The rapid advances in genotyping and bioinformatics will elucidate further the various pathways associated with the development of aneurysms affecting various parts of the aorta.

Cartilage oligomeric matrix protein is an endogenous β-arrestin-2-selective allosteric modulator of AT1 receptor counteracting vascular injury

Compelling evidence has revealed that biased activation of G protein-coupled receptor (GPCR) signaling, including angiotensin II (AngII) receptor type 1 (AT1) signaling, plays pivotal roles in vascular homeostasis and injury, but whether a clinically relevant endogenous biased antagonism of AT1 signaling exists under physiological and pathophysiological conditions has not been clearly elucidated. Here, we show that an extracellular matrix protein, cartilage oligomeric matrix protein (COMP), acts as an endogenous allosteric biased modulator of the AT1 receptor and its deficiency is clinically associated with abdominal aortic aneurysm (AAA) development. COMP directly interacts with the extracellular N-terminus of the AT1 via its EGF domain and inhibits AT1-β-arrestin-2 signaling, but not Gq or Gi signaling, in a selective manner through allosteric regulation of AT1 intracellular conformational states. COMP deficiency results in activation of AT1a-β-arrestin-2 signaling and subsequent exclusive AAA formation in response to AngII infusion. AAAs in COMP^-/- or ApoE^-/- mice are rescued by AT1a or β-arrestin-2 deficiency, or the application of a peptidomimetic mimicking the AT1-binding motif of COMP. Explorations of the endogenous biased antagonism of AT1 receptor or other GPCRs may reveal novel therapeutic strategies for cardiovascular diseases.

Pathophysiological Aspects of the Development of Abdominal Aortic Aneurysm with a Special Focus on Mitochondrial Dysfunction and Genetic Associations

Abdominal aortic aneurysm (AAA) is a complex degenerative vascular disease, with considerable morbidity and mortality rates among the elderly population. The mortality of AAA is related to aneurysm expansion (the enlargement of the aortic diameter up to 30 mm and above) and the subsequent rupture. The pathogenesis of AAA involves several biological processes, including aortic mural inflammation, oxidative stress, vascular smooth muscle cell apoptosis, elastin depletion, and degradation of the extracellular matrix. Mitochondrial dysfunction was also found to be associated with AAA formation. The evidence accumulated to date supports a close relationship between environmental and genetic factors in AAA initiation and progression. However, a comprehensive pathophysiological understanding of AAA formation remains incomplete. The open surgical repair of AAA is the only therapeutic option currently available, while a specific pharmacotherapy is still awaited. Therefore, there is a great need to clarify pathophysiological cellular and molecular mechanisms underlying AAA formation that would help to develop effective pharmacological therapies. In this review, pathophysiological aspects of AAA development with a special focus on mitochondrial dysfunction and genetic associations were discussed.

PPARγ agonist rosiglitazone alters the temporal and spatial distribution of inflammation during abdominal aortic aneurysm formation

Research into inflammation during abdominal aortic aneurysm (AAA) formation remains inconclusive. The present study aimed to demonstrate the temporal and spatial distribution of inflammatory cytokines, and to confirm the effect of peroxisome proliferator‑activated receptor γ (PPARγ) on the incidence of AAA formation and the distribution of inflammation in the disease process. Male apolipoprotein E‑/‑ mice were randomly divided into eight groups: Angiotensin II (Ang‑II)‑only 7, 14, 21, 28 and 42 days groups, Ang‑II with rosiglitazone (RGZ) 28 and 42 days groups, and the saline control 42 days group. The early stage was defined as between 7 and 21 days, and the late stage as between 28 and 42 days. Incidences of early rupture and late rupture, aneurysm formation and the maximum diameters of the aorta were recorded. Suprarenal abdominal aortic tissues were collected for histological analysis, and western blotting was performed to reveal the distribution of inflammation. Treatment with Ang‑II caused a significant dilation of the aorta in the late stage; however, this was not observed in the early stage. RGZ reduced the maximum diameters in the late stage. With the pathological process alterations, the inflammatory type shifted. Regarding temporal distribution, the tumor necrosis factor (TNF)‑α expression level was increased over time, and the interleukin (IL)‑10 expression level significantly decreased. When considering the spatial distribution, TNF‑α was expressed dominantly in the aneurysmal body and IL‑10 was dominant in the aneurysmal neck in the late stage. The PPARγ agonist RGZ may reduce the expression of TNF‑α in the late stage and increase the expression level of IL‑10, maintaining the TNF‑α or IL‑10 expression levels at the same levels as in the early stage. Aortic inflammation during AAA formation is dynamic. Protective anti‑inflammatory cytokines are upregulated in the early 'compensatory stage'; however, pro‑inflammatory cytokines are dominant in the late 'decompensatory stage'. PPARγ is likely to continue to upregulate the expression of anti‑inflammatory cytokines, extend the 'compensatory stage', and decelerate the process of AAA development and rupture.

Unravelling the Lesser Known Facets of Angiotensin II Type 1 Receptor

PURPOSE OF REVIEW

Hypertension is an important risk factor in various pathologies. Despite enormous advancements in health sciences, the number of hypertensive individuals is increasing worldwide. The complex interplay between genetic and epigenetic factors seems to be a promising pathway to exploring the pathophysiology of hypertension.

RECENT FINDINGS

Various single gene and genome wide association studies have generated huge but non-reproducible data that highlights the role of some additional but as yet unidentified factor(s) in disease outcome. Dietary pattern and epigenetic mechanism (mainly DNA methylation) have shown a profound effect on blood pressure regulation. Angiotensin II and its receptors are known to play an important role in maintaining blood pressure; hence, a larger section of antihypertensive drugs targets the renin-angiotensin system (RAS). Angiotensin II type 1 receptor (AT1R), besides maintaining blood pressure, also has a role in cancer progression. Besides other pathways, RAS still remains the main player in blood pressure regulation. Additionally, AT1R has recently emerged as a molecule with diverse roles ranging from physiologic to cancer progression.

Screening key genes for abdominal aortic aneurysm based on gene expression omnibus dataset

Background

Abdominal aortic aneurysm (AAA) is a common cardiovascular system disease with high mortality. The aim of this study was to identify potential genes for diagnosis and therapy in AAA.

Methods

We searched and downloaded mRNA expression data from the Gene Expression Omnibus (GEO) database to identify differentially expressed genes (DEGs) from AAA and normal individuals. Then, Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analysis, transcriptional factors (TFs) network and protein-protein interaction (PPI) network were used to explore the function of genes. Additionally, immunohistochemical (IHC) staining was used to validate the expression of identified genes. Finally, the diagnostic value of identified genes was accessed by receiver operating characteristic (ROC) analysis in GEO database.

Results

A total of 1199 DEGs (188 up-regulated and 1011 down-regulated) were identified between AAA and normal individual. KEGG pathway analysis displayed that vascular smooth muscle contraction and pathways in cancer were significantly enriched signal pathway. The top 10 up-regulated and top 10 down-regulated DEGs were used to construct TFs and PPI networks. Some genes with high degrees such as NELL2, CCR7, MGAM, HBB, CSNK2A2, ZBTB16 and FOXO1 were identified to be related to AAA. The consequences of IHC staining showed that CCR7 and PDGFA were up-regulated in tissue samples of AAA. ROC analysis showed that NELL2, CCR7, MGAM, HBB, CSNK2A2, ZBTB16, FOXO1 and PDGFA had the potential diagnostic value for AAA.

Conclusions

The identified genes including NELL2, CCR7, MGAM, HBB, CSNK2A2, ZBTB16, FOXO1 and PDGFA might be involved in the pathology of AAA.

Paracrine and Intracrine Angiotensin 1-7/Mas Receptor Axis in the Substantia Nigra of Rodents, Monkeys, and Humans

In addition to the classical hormonal (tissue-to-tissue) renin-angiotensin system (RAS), there are a paracrine (cell-to-cell) and an intracrine (intracellular/nuclear) RAS. A local paracrine brain RAS has been associated with several brain disorders, including Parkinson’s disease (PD). Classically, angiotensin II (Ang II) is the main RAS effector peptide and acts through two major receptors: Ang II type 1 and 2 (AT1 and AT2) receptors. It has been shown that enhanced activation of the Ang II/AT1 axis exacerbates dopaminergic cell death. Several new components of the RAS have more recently been discovered. However, the role of new Ang 1-7/Mas receptor RAS component was not investigated in the brain and particularly in the dopaminergic system. In the present study, we observed Mas receptor labeling in dopaminergic neurons and glial cells in rat mesencephalic primary cultures; substantia nigra of rats, monkeys, and humans; and human induced pluripotent stem (iPS) cells derived from healthy controls and sporadic PD patients. The present data support a neuroprotective role of the Ang 1-7/Mas receptor axis in the dopaminergic system. We observed that this axis is downregulated with aging, which may contribute to the aging-related vulnerability to neurodegeneration. We have also identified an intracellular Ang 1-7/Mas axis that modulates mitochondrial and nuclear levels of superoxide. The present data suggest that nuclear RAS receptors regulate the adequate balance between the detrimental and the protective arms of the cell RAS. The results further support that the brain RAS should be taken into account for the design of new therapeutic strategies for PD.

Angiotensin type 1 receptor A1166C polymorphism and systemic lupus erythematosus: correlation with cellular immunity and oxidative stress markers

Angiotensin II, one of the rennin–angiotensin system components, is important in the cardiovascular hemodynamic and plays an important role in the development of cardiovascular disease in systemic lupus erythematosus (SLE) patients. The angiotensin II, through interaction with angiotensin II type 1 receptor (AGTR1), promotes proliferation, inflammation and fibrosis. The single nucleotide polymorphism of the AGTR1 (dbSNP: rs5186) gene can be associated with development and progression of SLE disease. The aims of this study were to compare the frequency of AGTR1 rs5186 in SLE patients with healthy individuals and to evaluate possible association between AGTR1 A1166C gene polymorphism and serum level of lipids, neopterin and malondialdehyde in SLE patients from a population of West Iran. One hundred SLE patients and 98 healthy subjects were studied. The AGTR1 A1166C polymorphism was detected by polymerase chain reaction– restriction fragment length polymorphism method and the serum lipid profile was obtained by enzymatic method. Neopterin and malondialdehyde were detected using high-performance liquid chromatography. We did not detect significant association between AGTR1 A1166C polymorphism and the risk of SLE. The levels of triglyceride (225 ± 118 mg/dl), neopterin (30 ± 24 nmol/l) and malondialdehyde (25 ± 9.6 nmol/l) in SLE patients were significantly higher than those in control subjects (139 ± 56 mg/dl, p = 0.03, 6.4 ± 2, p = 0.03, 9.4 ± 2.5 nmol/l, p = 0.01, respectively). Individuals with AGTR1 AC + CC genotype had higher levels of total cholesterol and malondialdehyde compared with those with AGTR1 AA genotype. SLE patients with either AGTR1 AA or AGTR1AC + CC genotype had significantly higher malondialdehyde or neopterin levels compared with the corresponding control subjects. In conclusion, although the present study did not find any association between AGTR1 A1166C polymorphism and the risk of SLE, the presence of this polymorphism was associated with higher levels of malondialdehyde and higher concentration of neopterin in patients.

Genetic risk models: Influence of model size on risk estimates and precision

Disease risk estimation plays an important role in disease prevention. Many studies have found that the ability to predict risk improves as the number of risk single-nucleotide polymorphisms (SNPs) in the risk model increases. However, the width of the confidence interval of the risk estimate is often not considered in the evaluation of the risk model. Here, we explore how the risk and the confidence interval width change as more SNPs are added to the model in the order of decreasing effect size, using both simulated data and real data from studies of abdominal aortic aneurysms and age-related macular degeneration. Our results show that confidence interval width is positively correlated with model size and the majority of the bigger models have wider confidence interval widths than smaller models. Once the model size is bigger than a certain level, the risk does not shift markedly, as 100% of the risk estimates of the one-SNP-bigger models lie inside the confidence interval of the one-SNP-smaller models. We also created a confidence interval-augmented reclassification table. It shows that both more effective SNPs with larger odds ratios and less effective SNPs with smaller odds ratios contribute to the correct decision of whom to screen. The best screening strategy is selected and evaluated by the net benefit quantity and the reclassification rate. We suggest that individuals whose upper bound of their risk confidence interval is above the screening threshold, which corresponds to the population prevalence of the disease, should be screened.

Association of the KLK1 rs5516 G allele and the ACE D allele with aortic aneurysm and atherosclerotic stenosis

OBJECTIVE

Atherosclerosis underlies aortic aneurysm (AA) and atherosclerotic stenosis (AS). Kallikrein-1 (KLK1) and angiotensin-converting enzyme (ACE) are 2 key molecules in kallikrein-kinin systems and renin-angiotensin systems, respectively, which are responsible for maintaining vascular balance and stability, playing important roles in atherosclerosis. We aimed to assess the involvement of single nucleotide polymorphism rs5516 in KLK1 as well as the insertion/deletion rs4646994 polymorphism in ACE in the development of AA and AS.

METHODS

We enrolled Chinese Han patients with AA (N = 408) and AS (N = 432), as well as healthy controls (N = 408). Clinical and demographic characteristics were assessed. Genotypes were analyzed with recessive and dominant models.

RESULTS

The rs5516 G allele of KLK1 was significantly associated with AA (P < 0.001), and the D allele of ACE was significantly associated with both AA (P < 0.001) and AS (P < 0.001). The GG and DD genotypes were significantly associated with both AA (P = 0.013) and AS (P < 0.001) in a recessive model, and were synergistic with hypertension in AA patients, but not in AS. Patients with CC/DD, CG/ID, or GG/II genotypes, which were synergistic with hypertension, had a greater risk of developing AA, while CC/DD, CG/DD, GG/ID, or GG/DD genotypes, which were not synergistic with hypertension, contributed to the development of AS.

CONCLUSION

The KLK1 rs5516 G allele is closely associated with AA, and the ACE D allele is closely related to AA and AS.

Lipoprotein(a) Levels in Patients With Abdominal Aortic Aneurysm

Circulating markers relevant to the development of abdominal aortic aneurysm (AAA) are currently required. Lipoprotein(a), Lp(a), is considered a candidate marker associated with the presence of AAA. The present meta-analysis aimed to evaluate the association between circulating Lp(a) levels and the presence of AAA. The PubMed-based search was conducted up to April 30, 2015, to identify the studies focusing on Lp(a) levels in patients with AAA and controls. Quantitative data synthesis was performed using a random effects model, with standardized mean difference (SMD) and 95% confidence interval (CI) as summary statistics. Overall, 9 studies were identified. After a combined analysis, patients with AAA were found to have a significantly higher level of Lp(a) compared to the controls (SMD: 0.87, 95% CI: 0.41-1.33, P < .001). This result remained robust in the sensitivity analysis, and its significance was not influenced after omitting each of the included studies from the meta-analysis. The present meta-analysis confirmed a higher level of circulating Lp(a) in patients with AAA compared to controls. High Lp(a) levels can be associated with the presence of AAA, and Lp(a) may be a marker in screening for AAA. Further studies are needed to establish the clinical utility of measuring Lp(a) in the prevention and management of AAA.

Elevated Adiponectin Levels Suppress Perivascular and Aortic Inflammation and Prevent AngII-induced Advanced Abdominal Aortic Aneurysms

Abdominal aortic aneurysm (AAA) is a degenerative disease characterized by aortic dilation and rupture leading to sudden death. Currently, no non-surgical treatments are available and novel therapeutic targets are needed to prevent AAA. We investigated whether increasing plasma levels of adiponectin (APN), a pleiotropic adipokine, provides therapeutic benefit to prevent AngII-induced advanced AAA in a well-established preclinical model. In the AngII-infused hyperlipidemic low-density lipoprotein receptor-deficient mouse (LDLR^-/-) model, we induced plasma APN levels using a recombinant adenovirus expressing mouse APN (AdAPN) and as control, adenovirus expressing green florescent protein (AdGFP). APN expression produced sustained and significant elevation of total and high-molecular weight APN levels and enhanced APN localization in the artery wall. AngII infusion for 8 weeks induced advanced AAA development in AdGFP mice. Remarkably, APN inhibited the AAA development in AdAPN mice by suppressing aortic inflammatory cell infiltration, medial degeneration and elastin fragmentation. APN inhibited the angiotensin type-1 receptor (AT1R), inflammatory cytokine and mast cell protease expression, and induced lysyl oxidase (LOX) in the aortic wall, improved systemic cytokine profile and attenuated adipose inflammation. These studies strongly support APN therapeutic actions through multiple mechanisms inhibiting AngII-induced AAA and increasing plasma APN levels as a strategy to prevent advanced AAA.

Understanding the pathogenesis of abdominal aortic aneurysms

An aortic aneurysm is a dilatation in which the aortic diameter is ≥3.0 cm. If left untreated, the aortic wall continues to weaken and becomes unable to withstand the forces of the luminal blood pressure resulting in progressive dilatation and rupture, a catastrophic event associated with a mortality of 50-80%. Smoking and positive family history are important risk factors for the development of abdominal aortic aneurysms (AAA). Several genetic risk factors have also been identified. On the histological level, visible hallmarks of AAA pathogenesis include inflammation, smooth muscle cell apoptosis, extracellular matrix degradation and oxidative stress. We expect that large genetic, genomic, epigenetic, proteomic and metabolomic studies will be undertaken by international consortia to identify additional risk factors and biomarkers, and to enhance our understanding of the pathobiology of AAA. Collaboration between different research groups will be important in overcoming the challenges to develop pharmacological treatments for AAA.

Abdominal Aortic Aneurysm Genetic Associations: Mostly False? A Systematic Review and Meta-analysis

OBJECTIVE/BACKGROUND

Many associations between abdominal aortic aneurysm (AAA) and genetic polymorphisms have been reported. It is unclear which are genuine and which may be caused by type 1 errors, biases, and flexible study design. The objectives of the study were to identify associations supported by current evidence and to investigate the effect of study design on reporting associations.

METHODS

Data sources were MEDLINE, Embase, and Web of Science. Reports were dual-reviewed for relevance and inclusion against predefined criteria (studies of genetic polymorphisms and AAA risk). Study characteristics and data were extracted using an agreed tool and reports assessed for quality. Heterogeneity was assessed using I(2) and fixed- and random-effects meta-analyses were conducted for variants that were reported at least twice, if any had reported an association. Strength of evidence was assessed using a standard guideline.

RESULTS

Searches identified 467 unique articles, of which 97 were included. Of 97 studies, 63 reported at least one association. Of 92 studies that conducted multiple tests, only 27% corrected their analyses. In total, 263 genes were investigated, and associations were reported in polymorphisms in 87 genes. Associations in CDKN2BAS, SORT1, LRP1, IL6R, MMP3, AGTR1, ACE, and APOA1 were supported by meta-analyses.

CONCLUSION

Uncorrected multiple testing and flexible study design (particularly testing many inheritance models and subgroups, and failure to check for Hardy-Weinberg equilibrium) contributed to apparently false associations being reported. Heterogeneity, possibly due to the case mix, geographical, temporal, and environmental variation between different studies, was evident. Polymorphisms in nine genes had strong or moderate support on the basis of the literature at this time. Suggestions are made for improving AAA genetics study design and conduct.

An update on the etiology of abdominal aortic aneurysms: implications for future diagnostic testing

Abdominal aortic aneurysm (AAA) disease is multifactorial with both environmental and genetic risk factors. The current research in AAA revolves around genetic profiles and expression studies in both human and animal models. Variants in genes involved in extracellular matrix degradation, inflammation, the renin-angiotensin system, cell growth and proliferation and lipid metabolism have been associated with AAA using a variety of study designs. However, the results have been inconsistent and without a standard animal model for validation. Thus, despite the growing body of knowledge, the specific variants responsible for AAA development, progression and rupture have yet to be determined. This review explores some of the more significant genetic studies to provide an overview of past studies that have influenced the current understanding of AAA etiology. Expanding our understanding of disease pathogenesis will inform research into novel diagnostics and therapeutics and ultimately to improve outcomes for patients with AAA.

Potential Interactions Between Genetic Polymorphisms of the Transforming Growth Factor-β Pathway and Environmental Factors in Abdominal Aortic Aneurysms

OBJECTIVE/BACKGROUND

Evidence has accumulated that multiple polymorphisms in the transforming growth factor (TGF)-β pathway and renin-angiotensin system play important roles in determining susceptibility to abdominal aortic aneurysm (AAA). Few studies have considered interactions between these gene polymorphisms and environmental factors. The aim of this study was to evaluate the contribution of single nucleotide polymorphisms (SNPs) and complex gene-environment interactions in AAA.

METHODS

Six SNPs located in TGFB, TGFBR1, TGFBR2 and AGTR1 were selected. Genotyping of blood samples and collection of lifestyle factors were performed in 155 unrelated participants with AAAs and 310 non-AAA controls. Unconditional logistic regression was performed to assess the effects of SNPs on the risk of AAA. Generalized multifactor dimensionality reduction (GMDR) was used to evaluate gene-gene and gene-environment interactions.

RESULTS

Participants carrying TGFB1 rs1800469 TT (odds ratio [OR] 1.83, 95% confidence interval [CI] 1.18-2.85) or AGTR1 rs12695895 TT (OR 4.21, 95% CI 1.41-12.53) genotypes had a higher risk of AAA than those with the common CC genotype. The gene-gene interaction of AGTR1 rs5182, TGFBR1 rs1626340, and TGFB1 rs1800469 was found to be the best model according to the results of the GMDR analysis (cross validation consistency [CVC]) 10/10; p = .010). Smoking, dyslipidemia, and rs1800469 together contributed to the risk of AAA, which demonstrated a potential and complex gene-environment interaction among the three variants that might affect AAA risk (CVC 6/10; p = .001).

CONCLUSION

In this study of the Chinese population, homozygosity of TGFB1 rs1800469-T and AGTR1 rs12695895-T might be associated with increased risk of AAA. The complex gene-gene and gene-environment interactions might contribute to the risk of AAA. As a small study, the preliminary results need extensive validation and replication in larger populations.

Non coding RNAs in aortic aneurysmal disease

An aneurysm is a local dilatation of a vessel wall which is >50% its original diameter. Within the spectrum of cardiovascular diseases, aortic aneurysms are among the most challenging to treat. Most patients present acutely after aneurysm rupture or dissection from a previous asymptomatic condition and are managed by open surgical or endovascular repair. In addition, patients may harbor concurrent disease contraindicating surgical intervention. Collectively, these factors have driven the search for alternative methods of identifying, monitoring and treating aortic aneurisms using less invasive approaches. Non-coding RNA (ncRNAs) are emerging as new fundamental regulators of gene expression. The small microRNAs have opened the field of ncRNAs capturing the attention of basic and clinical scientists for their potential to become new therapeutic targets and clinical biomarkers for aortic aneurysm. More recently, long ncRNAs (lncRNAs) have started to be actively investigated, leading to first exciting reports, which further suggest their important and yet largely unexplored contribution to vascular physiology and disease. This review introduces the different ncRNA types and focus at ncRNA roles in aorta aneurysms. We discuss the potential of therapeutic interventions targeting ncRNAs and we describe the research models allowing for mechanistic studies and clinical translation attempts for controlling aneurysm progression. Furthermore, we discuss the potential role of microRNAs and lncRNAs as clinical biomarkers.

Expanding Horizons for Abdominal Aortic Aneurysms

Recent technological advances have allowed researchers to interrogate the genetic basis of abdominal aortic aneurysms in great detail. The results from these studies are expected to transform our understanding of this complex disease with both multiple genetic and environmental risk factors. Clinicians need to keep abreast of these genetic findings and understand the implications for their practice. Patients will become increasingly informed on genetic risk, and a new era of individualized risk assessment for AAA is just beginning. This brief update aims to provide the clinician with a succinct précis of the recent progress in this area.

The AGTR1 gene A1166C polymorphism as a risk factor and outcome predictor of primary intracerebral and aneurysmal subarachnoid hemorrhages

Associations between the angiotensin II type 1 receptor (AGTR1) gene A1166C polymorphism and hypertension, aortic abdominal aneurysms (as a risk factor) as well as cardiovascular disorders (as a risk factor and an outcome predictor) have been demonstrated. We aimed to investigate the role of this polymorphism as risk factors and outcome predictors in primary intracerebral hemorrhage (PICH) and aneurysmal subarachnoid hemorrhage (aSAH). We have prospectively recruited 1078 Polish participants to the study: 261 PICH patients, 392 aSAH patients, and 425 unrelated control subjects. The A1166C AGTR1 gene polymorphism was studied using the tetra-primer ARMS-PCR method. Allele and genotype frequencies were compared with other ethnically different populations. The A1166C polymorphism was not associated with the risk of PICH or aSAH. Among the aSAH patients the AA genotype was associated with a good outcome, defined by a Glasgow Outcome Scale of 4 or 5 (p<0.02). The distribution of A1166C genotypes in our cohort did not differ from other white or other populations of European descent. In conclusion, we found an association between the A1166C AGTR1 polymorphism and outcome of aSAH patients, but not with the risk of PICH or aSAH.

Association of insertion/deletion polymorphism of angiotensin-converting enzyme gene among Malay male hypertensive subjects in response to ACE inhibitors

INTRODUCTION

Several studies show that the insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) gene has been associated with hypertension in various populations. The present study sought to determine the association of the I/D gene polymorphism among Malay male essential hypertensive subjects in response to ACE inhibitors (enalapril and lisinopril).

MATERIALS AND METHODS

A total of 72 patients with newly diagnosed hypertension and 72 healthy subjects were recruited in this study. Blood pressure was recorded from 0 to 24 weeks of treatment with enalapril or lisinopril. Genotyping of the I/D polymorphism was carried out using a standard PCR method.

RESULTS

Statistically significant association of the D allele of the ACE gene was observed between the case and control subjects (p < 0.01). There was a decrease in blood pressure in the patients carrying the DD genotype (SBP=18.5±8.1 mmHg, DBP=15.29±7.1 mmHg) rather than the ID (SBP=4.1±3.3 mmHg, DBP=9.1±3.5 mmHg) and II genotypes (SBP= 3.0±0.2 mmHg, DBP 0.11±6.1 mmHg) of the ACE gene.

CONCLUSION

Patients carrying the DD genotype had higher blood pressure-lowering response when treated with ACE inhibitors enalapril or lisinopril than those carrying ID and II genotypes, suggesting that the D allele may be a possible genetic marker for essential hypertension among Malay male subjects.

Adiponectin attenuates abdominal aortic aneurysm formation in hyperlipidemic mice

OBJECTIVE

Abdominal aortic aneurysms (AAA) are age-associated, life-threatening inflammatory dilations of the abdominal aorta. Human population studies have shown an association between obesity and AAA formation, but the molecular mechanisms underlying this connection remain largely unexplored. Adiponectin is an anti-inflammatory adipokine that is downregulated in obesity. In this study we evaluated the role of adiponectin in a model of AAA using apolipoprotein E/adiponectin double-knockout (Apoe(-/-)Apn(-/-)) mice.

APPROACH AND RESULTS

Angiotensin II (Ang II)-infusion in male Apoe(-/-)Apn(-/-) mice led to a higher incidence of AAA and a significant increase of maximal aortic diameter compared with that of Apoe(-/-) mice (2.12 ± 0.07 mm vs. 1.67 ± 0.09 mm, respectively at 28 days). Adiponectin deficiency augmented the early infiltration of macrophages and increased the expression of pro-inflammatory factors in the dilated aortic wall. MMP-2 and MMP-9 activation was also augmented in the aorta of Apoe(-/-)Apn(-/-) mice compared to Apoe(-/-) mice. These data suggest that the downregulation of adiponectin could directly contribute to the elevated incidence of AAA observed in obese individuals.

CONCLUSIONS

Adiponectin attenuates Ang II-induced vascular inflammation and AAA formation in mice.

Analysis of multiple genetic polymorphisms in aggressive-growing and slow-growing abdominal aortic aneurysms

BACKGROUND

The natural history of abdominal aortic aneurysms (AAAs) suggests that some remain slow in growth rate whereas many develop a more accelerated growth rate and reach a threshold for intervention. We hypothesized that different mechanisms are responsible for AAAs that remain slow growing and never become actionable vs the aggressive AAAs that require intervention and may be reflected by distinct associations with genetic polymorphisms.

METHODS

AAA growth rate was determined from serial imaging data in 168 control and 141 AAA patients with ultrasound or computed tomography imaging studies covering ∼5 years. Genetic polymorphisms all previously reported as showing a significant correlation with AAA with functional effects on the expression or function were determined by analysis of the genomic DNA, including angiotensin 1 receptor (rs5186), interleukin-10 (IL-10; rs1800896), methyl-tetrahydrofolate reductase (rs1801133), low-density lipoprotein receptor-related protein 1 (LRP1; rs1466535), angiotensin-converting enzyme (rs1799752), and several matrix metalloproteinase 9 (MMP-9) single nucleotide polymorphisms.

RESULTS

Of the AAA patients, 81 were classified as slow AAA growth rate (<3.25 mm/y) vs 60 with aggressive AAA growth rate (>3.25 mm/y, those presenting with a rupture, or those with maximal aortic diameter >5.5 cm [male] or >5.0 cm [female]). Discriminating confounds between the groups were identified by logistic regression. Analyses identified MMP-9 p-2502 single nucleotide polymorphism (odds ratio [OR], 0.54; 95% confidence interval [CI], 0.31-0.94; P = .029) as a significant confound discriminating between control vs slow-growth AAA, MMP-9 D165N (OR, 0.49; 95% CI, 0.26-0.95; P = .035) and LRP1 (OR, 4.99; 95% CI, 1.13-22.1; P = .034) between control vs aggressive-growth AAAs, and methyltetrahydrofolate reductase (OR, 2.99; 95% CI, 1.01-8.86; P = .048), MMP-9 p-2502 (OR, 2.19; 95% CI, 1.05-4.58; P = .037), and LRP1 (OR, 4.96; 95% CI, 1.03-23.9; P = .046) as the statistically significant confounds distinguishing slow-growth AAAs vs aggressive-growth AAAs.

CONCLUSIONS

Logistic regression identified different genetic confounds for the slow-growth and aggressive-growth AAAs, indicating a potential for different genetic influences on AAAs of distinct aggressiveness. Future logistic regression studies investigating for potential genetic or clinical confounds for this disease should take into account the growth rate and size of the AAA to better identify confounds likely to be associated with aggressive AAAs likely to require intervention.

Update on abdominal aortic aneurysm research: from clinical to genetic studies

An abdominal aortic aneurysm (AAA) is a dilatation of the abdominal aorta with a diameter of at least 3.0 cm. AAAs are often asymptomatic and are discovered as incidental findings in imaging studies or when the AAA ruptures leading to a medical emergency. AAAs are more common in males than females, in individuals of European ancestry, and in those over 65 years of age. Smoking is the most important environmental risk factor. In addition, a positive family history of AAA increases the person's risk for AAA. Interestingly, diabetes has been shown to be a protective factor for AAA in many large studies. Hallmarks of AAA pathogenesis include inflammation, vascular smooth muscle cell apoptosis, extracellular matrix degradation, and oxidative stress. Autoimmunity may also play a role in AAA development and progression. In this Outlook paper, we summarize our recent studies on AAA including clinical studies related to surgical repair of AAA and genetic risk factor and large-scale gene expression studies. We conclude with a discussion on our research projects using large data sets available through electronic medical records and biobanks.

Prevalence of HLA-B27 in the New Zealand population: effect of age and ethnicity

INTRODUCTION

HLA-B27 genotyping is commonly used to support a diagnosis of ankylosing spondylitis (AS). A recent study has suggested that HLA-B27 may adversely affect longevity. The objectives of this study were to determine, for the first time, the prevalence of HLA-B27 in the New Zealand population, and to test whether HLA-B27 prevalence declines with age.

METHODS

117 Caucasian controls, 111 New Zealand Māori controls, and 176 AS patients were directly genotyped for HLA-B27 using PCR-SSP. These participants and a further 1103 Caucasian controls were genotyped for the HLA-B27 tagging single nucleotide polymorphisms (SNPs) rs4349859 and rs116488202. All AS patients testing positive for HLA-B27 of New Zealand Māori ancestry underwent high resolution typing to determine sub-allele status.

RESULTS

HLA-B27 prevalence was 9.2% in New Zealand Caucasian controls and 6.5% in Māori controls. No decline in HLA-B27 prevalence with age was detected in Caucasian controls (p = 0.92). Concordance between HLA-B27 and SNP genotypes was 98.7-99.3% in Caucasians and 76.9-86% in Māori. Of the 14 AS patients of Māori ancestry, 1 was negative for HLA-B27, 10 were positive for HLAB*2705, and 3 positive for HLAB*2704. All cases of genotype discordance were explained by the presence of HLAB*2704.

CONCLUSIONS

HLA-B27 prevalence in New Zealand Caucasians is consistent with that of Northern European populations and did not decline with increasing age. In Māori with AS who were HLA-B27 positive, 76.9% were positive for HLA-B*2705, suggesting that genetic susceptibility to AS in Māori is primarily due to admixture with Caucasians.

Associations between the insertion/deletion polymorphism of the angiotensin-converting enzyme and susceptibility to aortic aneurysms: A meta-analysis

INTRODUCTION

The purpose of this study is to examine whether the insertion (I) and deletion (D) polymorphism of the angiotensin-converting enzyme (ACE) confers susceptibility to aortic aneurysms (AAs).

MATERIALS AND METHODS

A meta-analysis was conducted on the associations between the ACE I/D polymorphism and all AAs and abdominal aortic aneurysms (AAAs).

RESULTS

Ten studies consisting of 2784 cases and 2682 controls were available for the meta-analysis. Meta-analysis showed a significant association between the D allele and all types of AA (OR 1.378, 95% CI 1.103-1.723, p = 0.005) and AAA (OR 1.274, 95% CI 1.004-1.617, p = 0.046). Meta-analysis of both the DD genotype and the DD vs. II genotype showed an association with AAAs. Stratification by ethnicity indicated an association between the D allele of the ACE I/D polymorphism and AAAs in Europeans (OR = 1.338, 95% CI = 1.026-1.745, p = 0.031), but not in Asians (OR = 0.927, 95% CI = 0.660-1.303, p = 0.663). Furthermore, analysis using the recessive model, dominant model, and homozygote contrast all showed the same pattern for the D allele.

CONCLUSIONS

Our meta-analysis demonstrates that the ACE I/D polymorphism is associated with susceptibility to AAAs in European populations.

Involvement of the renin-angiotensin system in abdominal and thoracic aortic aneurysms

Aortic aneurysms are relatively common maladies that may lead to the devastating consequence of aortic rupture. AAAs (abdominal aortic aneurysms) and TAAs (thoracic aortic aneurysms) are two common forms of aneurysmal diseases in humans that appear to have distinct pathologies and mechanisms. Despite this divergence, there are numerous and consistent demonstrations that overactivation of the RAS (renin-angiotensin system) promotes both AAAs and TAAs in animal models. For example, in mice, both AAAs and TAAs are formed during infusion of AngII (angiotensin II), the major bioactive peptide in the RAS. There are many proposed mechanisms by which the RAS initiates and perpetuates aortic aneurysms, including effects of AngII on a diverse array of cell types and mediators. These experimental findings are complemented in humans by genetic association studies and retrospective analyses of clinical data that generally support a role of the RAS in both AAAs and TAAs. Given the lack of a validated pharmacological therapy for any form of aortic aneurysm, there is a pressing need to determine whether the consistent findings on the role of the RAS in animal models are translatable to humans afflicted with these diseases. The present review compiles the recent literature that has shown the RAS as a critical component in the pathogenesis of aortic aneurysms.

Genomic research to identify novel pathways in the development of abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a common disease with a large heritable component. There is a need to improve our understanding of AAA pathogenesis in order to develop novel treatment paradigms. Genomewide association studies have revolutionized research into the genetic variants that underpin the development of many complex diseases including AAA. This article reviews the progress that has been made to date in this regard, including mechanisms by which loci identified by GWAS may contribute to the development of AAA. It also highlights potential post-GWAS analytical strategies to improve our understanding of the disease further.

Assessment of insertion/deletion polymorphism of the angiotensin-converting enzyme gene in abdominal aortic aneurysm and inguinal hernia

The aim of the paper is to determine whether the angiotensin-converting enzyme (ACE) gene insertion/deletion (I/D) polymorphism is associated with abdominal aortic aneurysm (AAA) and inguinal hernia. A case-control study was conducted in 264 subjects: 65 patients with AAA, 91 patients with inguinal hernia, 19 patients with both AAA and hernia, and 89 controls were investigated for the ACE I/D polymorphism. Genotype analysis was performed using a polymerase chain reaction technique. Significant differences in the genotype between the patient groups and controls were identified (aneurysm versus control, P = 0.011; aneurysm plus hernia versus control, P = 0.022; hernia versus control, P = 0.001), whereas no differences were found within patient groups. Patients with AAA and/ or hernia had an increased prevalence of I/D heterozygosity, which persisted even after adjusting for differences in confounding clinical variables (aneurysm versus control, OR 0.3, 95% CI 0.2–0.8, P = 0.005; aneurysm plus hernia versus control, OR 0.3, 95% CI 0.1-0.9, P = 0.040; hernia versus control, OR 0.4, 95% CI 0.2–0.7, P = 0.004). In conclusion, an association between the heterozygote ACE I/D state and the presence of AAA and/or hernia was identified. The role of the ACE I/D polymorphism in aneurysm and hernia needs further investigation.

Angiotensin-converting enzyme insertion/deletion polymorphism is a risk factor for thoracic aortic aneurysm in patients with bicuspid or tricuspid aortic valves

OBJECTIVE

The angiotensin-converting enzyme (ACE) is highly expressed in the aneurysmal vascular wall, in both animal models and human disease. Genetic variations in ACE could be crucial in determining the risk of thoracic aortic aneurysm (TAA). The aim of the present study was to examine the role of ACE insertion/deletion polymorphism on the risk of TAA in patients with bicuspid aortic valves or tricuspid aortic valves.

METHODS

We enrolled 216 patients (158 men; age, 58.9±14.9 years) with TAA, associated with bicuspid aortic valves (n=105) and tricuspid aortic valves (n=111) compared with 312 patients (252 men; age, 54.6±11.0 years) with angiographically proven coronary artery disease and 300 healthy controls (91 men; age, 40.4±10.5 years).

RESULTS

The genotype distribution of ACE insertion/deletion was significantly different between the patients with TAA compared with both the control group (P=.0005) and the coronary artery disease group (P=.03). The genotypes were not different between the control group and the coronary artery disease group (P=.3). Compared with the controls, both the bicuspid aortic valve patients (P=.0008) and tricuspid aortic valve patients (P<.0001) had a greater frequency of allele D. The aortic diameters were significantly different among the three genotypes (48.3±6.6, 45.3±8.9, 39.9±8.7 for the DD, DI, and II genotypes, respectively; P=.0002). A synergistic effect between the ACE D allele and hypertension was found for both an increased aortic diameter (P=.003) and the risk of TAA (P<.001). On multivariate logistic regression analysis, D allele (odds ratio, 3.0; 95% confidence interval, 1.1-8.1; P=.03) was a significant predictor of TAA.

CONCLUSIONS

ACE insertion/deletion polymorphism represents a genetic biomarker for TAA. These findings could have a significant effect on both the early detection and effective pharmacologic treatment of aortic disease.

Complex pathologies of angiotensin II-induced abdominal aortic aneurysms

Angiotensin II (AngII) is the primary bioactive peptide of the renin angiotensin system that plays a critical role in many cardiovascular diseases. Subcutaneous infusion of AngII into mice induces the development of abdominal aortic aneurysms (AAAs). Like human AAAs, AngII-induced AAA tissues exhibit progressive changes and considerable heterogeneity. This complex pathology provides an impediment to the quantification of aneurysmal tissue composition by biochemical and immunostaining techniques. Therefore, while the mouse model of AngII-induced AAAs provides a salutary approach to studying the mechanisms of the evolution of AAAs in humans, meaningful interpretation of mechanisms requires consideration of the heterogeneous nature of the diseased tissue.

Protective effects of angiotensin-converting enzyme I/I and matrix metalloproteinase-3 6A/6A polymorphisms on dilatative pathology within the ascending thoracic aorta

OBJECTIVE

Activation of matrix metalloproteinases and the renin/angiotensin signaling pathways is under investigation with regard to their potential pathogenesis in dilatative pathology of the aorta. The purpose of this study was to explore matrix metalloproteinase-3 5A/6A and angiotensin-converting enzyme I/D polymorphisms as predisposing factors to dilatative pathology of the aorta.

METHODS

We studied 107 patients who underwent aortic reconstruction surgery due to dilatative pathology of ascending thoracic aorta and a random sample of the population (n = 773), all from Lithuania. The insertion/deletion (-1171 5A/6A) polymorphism in the promoter region of matrix metalloproteinase-3 studied by real-time polymerase-chain-reaction amplification and the D and I alleles were identified on the basis of standard polymerase-chain-reaction amplification of the respective fragments from intron 16 of the angiotensin-converting enzyme gene.

RESULTS

The frequency of the angiotensin-converting enzyme D allele was significantly higher in dilatative pathology of ascending thoracic aorta patients than in the reference group subjects (0.55 vs 0.48, respectively). The latter group had a significantly higher frequency of the angiotensin-converting enzyme I/I genotype than in dilatative pathology of ascending thoracic aorta patients (27.4% vs 16.5%, respectively). In the reference group, the frequency of combined angiotensin-converting enzyme I/I and matrix metalloproteinase-3 6A/6A genotypes was 7.5%, while in the dilatative pathology of ascending thoracic aorta patient group, there was no one carrying that combined genotype (p = 0.001).

CONCLUSIONS

The present study showing a role of angiotensin-converting enzyme and matrix metalloproteinase-3 in the development of dilatative pathology of ascending thoracic aorta permits us to entertain a possible protective mechanism for the combined effects of the angiotensin-converting enzyme I/I and the matrix metalloproteinase-3 6A/6A genotypes.

Genome wide association studies of abdominal aortic aneurysms-biological insights and potential translation applications

Abdominal aortic aneurysm (AAA) is a complex disease with important environmental risk factors and a heritability of approximately 70%. Genome wide association studies have revolutionised the study of complex disorders and offer the potential for innovative insight into disease pathogenesis and development of individualised therapeutic options. This paper reviews the progress of genome wide association studies in AAA, highlighting novel disease pathways and potential translational applications of genomic discoveries.

Impaired abdominal aortic wall integrity in elderly men carrying the angiotensin-converting enzyme D allele

OBJECTIVE

A polymorphism in the angiotensin-converting-enzyme gene (ACE I/D) has been associated with abdominal aortic aneurysm and a link between aortic aneurysm and aortic stiffness has been suggested. This study aimed to explore the links between ACE I/D polymorphism, circulating ACE and abdominal aortic wall integrity as reflected by abdominal aortic wall stiffness.

MATERIAL

A total of 212 men and 194 women, aged 70-88 years, were studied.

METHODS

Mechanical properties of the abdominal aorta were determined using the Wall Track System, ACE genotype using the polymerase chain reaction (PCR) and circulating ACE level by enzyme-linked immunosorbent assay (ELISA).

RESULTS

In men, pulsatile diameter change differed between genotypes (II 0.70, ID 0.55 and DD 0.60 mm, P = 0.048), whereas a tendency was seen for distensibility coefficient (DC) (II 10.38, ID 7.68 and ID 8.79, P = 0.058). Using a dominant model (II vs. ID/DD), men carrying the ACE D allele had lower pulsatile diameter change (P = 0.014) and DC (P = 0.017) than II carriers. Multiple regression analyses showed additional associations between the D allele and increased stiffness β, and reduced compliance coefficient.

CONCLUSION

Men carrying the ACE D allele have stiffer abdominal aortas compared with II carriers. Deranged abdominal aortic stiffness indicates impaired vessel wall integrity, which, along with other local predisposing factors, may be important in aneurysmal disease.

The role of the renin-angiotensin system in thoracic aortic aneurysms: clinical implications

Thoracic aortic aneurysms (TAAs) are a potential life-threatening disease with limited pharmacological treatment options. Current treatment options are aimed at lowering aortic hemodynamic stress, predominantly with β-adrenoceptor blockers. Increasing evidence supports a role for the renin-angiotensin system (RAS) in aneurysm development. RAS blockade would not only lower blood pressure, but might also target the molecular pathways involved in aneurysm formation, in particular the transforming growth factor-β and extracellular signal-regulated kinase 1/2 pathways. Indeed, the angiotensin II type 1 (AT₁) receptor blocker losartan was effective in lowering aortic root growth in mice and patients with Marfan's syndrome. RAS inhibition (currently possible at 3 levels, i.e. renin, ACE and the AT₁ receptor) is always accompanied by a rise in renin due to interference with the negative feedback loop between renin and angiotensin II. Only during AT₁ receptor blockade will this result in stimulation of the non-blocked angiotensin II type 2 (AT₂) receptor. This review summarizes the clinical aspects of TAAs, provides an overview of the current mouse models for TAAs, and focuses on the RAS as a new target for TAA treatment, discussing in particular the possibility that AT₂ receptor stimulation might be crucial in this regard. If true, this would imply that AT₁ receptor blockers (and not ACE inhibitors or renin inhibitors) should be the preferred treatment option for TAAs.

Coding polymorphisms in the genes of the alternative complement pathway and abdominal aortic aneurysm

Variants in the genes of the alternative complement pathway are associated with risk of numerous inflammatory diseases. Abdominal aortic aneurysm is associated with inflammation and is a common cause of illness and death among European populations. This study tested 49 single nucleotide polymorphisms, including common putatively functional polymorphisms, in the genes of the alternative complement cascade (CFH, CFB, CFD, CFI, properdin, CR1, CR1L, CR2, CD46, vitronectin, C3, C5, C6, C7, C8A, C8B, C8G and C9). The study group were 434 cases with infra-renal aortic diameter ≥30 mm and 378 disease-free controls from two UK centres, all with self-reported European ancestry. There was no evidence for significant association with presence or size of aneurysm following correction for multiple testing. This study suggests that variation in the genes of the alternative pathway is not an important cause of abdominal aortic aneurysm development.

Analysis of positional candidate genes in the AAA1 susceptibility locus for abdominal aortic aneurysms on chromosome 19

BACKGROUND

Abdominal aortic aneurysm (AAA) is a complex disorder with multiple genetic risk factors. Using affected relative pair linkage analysis, we previously identified an AAA susceptibility locus on chromosome 19q13. This locus has been designated as the AAA1 susceptibility locus in the Online Mendelian Inheritance in Man (OMIM) database.

METHODS

Nine candidate genes were selected from the AAA1 locus based on their function, as well as mRNA expression levels in the aorta. A sample of 394 cases and 419 controls was genotyped for 41 SNPs located in or around the selected nine candidate genes using the Illumina GoldenGate platform. Single marker and haplotype analyses were performed. Three genes (CEBPG, PEPD and CD22) were selected for DNA sequencing based on the association study results, and exonic regions were analyzed. Immunohistochemical staining of aortic tissue sections from AAA and control individuals was carried out for the CD22 and PEPD proteins with specific antibodies.

RESULTS

Several SNPs were nominally associated with AAA (p < 0.05). The SNPs with most significant p-values were located near the CCAAT enhancer binding protein (CEBPG), peptidase D (PEPD), and CD22. Haplotype analysis found a nominally associated 5-SNP haplotype in the CEBPG/PEPD locus, as well as a nominally associated 2-SNP haplotype in the CD22 locus. DNA sequencing of the coding regions revealed no variation in CEBPG. Seven sequence variants were identified in PEPD, including three not present in the NCBI SNP (dbSNP) database. Sequencing of all 14 exons of CD22 identified 20 sequence variants, five of which were in the coding region and six were in the 3'-untranslated region. Five variants were not present in dbSNP. Immunohistochemical staining for CD22 revealed protein expression in lymphocytes present in the aneurysmal aortic wall only and no detectable expression in control aorta. PEPD protein was expressed in fibroblasts and myofibroblasts in the media-adventitia border in both aneurysmal and non-aneurysmal tissue samples.

CONCLUSIONS

Association testing of the functional positional candidate genes on the AAA1 locus on chromosome 19q13 demonstrated nominal association in three genes. PEPD and CD22 were considered the most promising candidate genes for altering AAA risk, based on gene function, association evidence, gene expression, and protein expression.

Genes and abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a multifactorial disease with a strong genetic component. Since the first candidate gene studies were published 20 years ago, approximately 100 genetic association studies using single nucleotide polymorphisms (SNPs) in biologically relevant genes have been reported on AAA. These studies investigated SNPs in genes of the extracellular matrix, the cardiovascular system, the immune system, and signaling pathways. Very few studies were large enough to draw firm conclusions and very few results could be replicated in another sample set. The more recent unbiased approaches are family-based DNA linkage studies and genome-wide genetic association studies, which have the potential of identifying the genetic basis for AAA, only when appropriately powered and well-characterized large AAA cohorts are used. SNPs associated with AAA have already been identified in these large multicenter studies. One significant association was of a variant in a gene called contactin-3, which is located on chromosome 3p12.3. However, two follow-up studies could not replicate this association. Two other SNPs, which are located on chromosome 9p21 and 9q33, were replicated in other samples. The two genes with the strongest supporting evidence of contribution to the genetic risk for AAA are the CDKN2BAS gene, also known as ANRIL, which encodes an antisense ribonucleic acid that regulates expression of the cyclin-dependent kinase inhibitors CDKN2A and CDKN2B, and DAB2IP, which encodes an inhibitor of cell growth and survival. Functional studies are now needed to establish the mechanisms by which these genes contribute toward AAA pathogenesis.

A population-based study of polymorphisms in genes related to sex hormones and abdominal aortic aneurysm

Male gender and family history are risk factors for abdominal aortic aneurysm (AAA). We hypothesized that genes involved in sex hormones might be important in AAA. We investigated the association of aortic diameter with single-nucleotide polymorphisms (SNPs) in genes determining circulating sex hormones and their action. We genotyped 74 tagging SNPs across four genes (steroid 5α reductase, subfamily A, polypeptide 1 (SRD5A1), cytochrome P450, family 19, subfamily A, polypeptide 1 (CYP19A1), androgen receptor (AR) and estrogen receptor 2 (ESR2)) related to sex hormone production and action in 1711 men, 640 of whom had an AAA. One genotype was also assessed in an independent cohort of 782 men, of whom 513 had large AAAs. Associations were assessed adjusting for other risk factors for AAA. One SNP in CYP19A1 was strongly associated with aortic diameter. Subjects who had the rare homozygote genotype (TT) for CYP19A1g.49412370C>T (SNP ID rs1961177), had an increased aortic diameter (coefficient 5.058, SE 1.394, P=0.0003, under a recessive model). This SNP was not associated with aortic diameter in an independent cohort, which included patients with larger AAAs. Our findings do not support an important role of genetic polymorphisms in genes determining sex hormones in aortic dilatation in men. The association of one SNP in CYPA9A1 with small but not large AAA may suggest differences between AAA formation and progression. This SNP warrants further investigation in another large population, including patients with small AAAs.

Group X secretory phospholipase A(2) augments angiotensin II-induced inflammatory responses and abdominal aortic aneurysm formation in apoE-deficient mice

OBJECTIVE

Abdominal aortic aneurysm (AAA) is a complex vascular disease characterized by matrix degradation and inflammation and is a major cause of mortality in older men. Specific interventions that prevent AAA progression remain to be identified. In this study, we tested the hypothesis that Group X secretory phospholipase A(2) (GX sPLA(2)), an enzyme implicated in inflammatory processes, mediates AAA.

METHODS AND RESULTS

GX sPLA(2) was detected by immunostaining in human aneurysmal tissue and in angiotensin II (Ang II)-induced AAAs in apolipoprotein E-deficient (apoE(-/-)) mice. GX sPLA(2) mRNA was increased significantly (11-fold) in abdominal aortas of apoE(-/-) mice in response to Ang II infusion. To define the role of GX sPLA(2) in experimental AAAs, apoE(-/-) and apoE(-/-) x GX sPLA(2)(-/-) (GX DKO) mice were infused with Ang II for either 10 (n=7) or 28 (n=24-26) days. Deficiency of GX sPLA(2) significantly reduced the incidence and severity of AAAs, as assessed by ultrasound measurements in vivo of aortic lumens and by computer-assisted morphometric analyses ex vivo of external diameter. Results from gene expression profiling indicated that the expression of specific matrix metalloproteinases and inflammatory mediators was blunted in aortas from GX DKO mice compared to apoE(-/-) mice after 10-day Ang II infusion. Ang II induction of cyclooxygenase-2, interleukin-6, matrix metalloproteinase (MMP)-2, MMP-13 and MMP-14 was reduced significantly in GX DKO mice compared to apoE(-/-) mice.

CONCLUSION

GX sPLA(2) promotes Ang II-induced pathological responses leading to AAA formation.

Cardiovascular Disease, Single Nucleotide Polymorphisms; and the Renin Angiotensin System: Is There a MicroRNA Connection?

Essential hypertension is a complex disorder, caused by the interplay between many genetic variants, gene-gene interactions, and environmental factors. Given that the renin-angiotensin system (RAS) plays an important role in blood pressure (BP) control, cardiovascular regulation, and cardiovascular remodeling, special attention has been devoted to the investigation of single-nucleotide polymorphisms (SNP) harbored in RAS genes that may be associated with hypertension and cardiovascular disease. MicroRNAs (miRNAs) are a family of small, ∼21-nucleotide long, and nonprotein-coding RNAs that recognize target mRNAs through partial complementary elements in the 3′-untranslated region (3′-UTR) of mRNAs and inhibit gene expression by targeting mRNAs for translational repression or destabilization. Since miRNA SNPs (miRSNPs) can create, destroy, or modify miRNA binding sites, this review focuses on the hypothesis that transcribed target SNPs harbored in RAS mRNAs, that alter miRNA gene regulation and consequently protein expression, may contribute to cardiovascular disease susceptibility.