Low-density lipoprotein receptor-related protein 5 gene polymorphisms and genetic susceptibility to abdominal aortic aneurysm

Lipoprotein (a) Levels and Abdominal Aortic Aneurysm. A Systematic Review and Meta-analysis

BACKGROUND

Several studies have linked high Lipoprotein (a) (Lp(a)) concentrations to cardiovascular events, including the formation of Abdominal Aortic Aneurysms (AAA). We review and meta-analyze existing evidence on the association of Lp(a) levels with AAA.

METHODS

Studies evaluating the link of Lp(a) with AAA, up to December 27th 2021, were identified by a systematic search of PubMed, SCOPUS, and Web of Science databases. The results were qualitatively and quantitatively synthesized according to PRISMA guidelines. Results are presented as standardized mean differences (SMD) with 95% confidence intervals (CI).

RESULTS

A total of 5,078 subjects (1,637 patients with AAA vs. 3,441 controls) from 11 studies were included in the meta-analysis, with a mean age of 69.9 years and a male sex prevalence of 85.8%. Based on the qualitative synthesis, high Lp(a) concentrations are linked to abdominal aortic wall degradation and extracellular matrix disarrangement. Moreover, despite the considerable variability among races, high Lp(a) levels are related to increased AAA risk, independently of race differences. Accordingly, patients with AAA displayed significantly higher Lp(a) levels compared to controls (SMD: 0.86, 95% CI: 0.55-1.17, p < 0.001). The outcome was not affected in a sensitivity analysis excluding three outlying studies (SMD: 0.40, 95% CI: 0.22-0.58, p < 0.001).

CONCLUSION

This meta-analysis indicates the association between high Lp(a) levels and the presence of AAA, although existing literature presents high heterogeneity. Further studies are needed to standardize Lp(a) measurements and to conclude whether Lp(a) can be used as a sensitive biomarker of early presymptomatic AAA diagnosis.

Effect of Cyclic Stretch on Vascular Endothelial Cells and Abdominal Aortic Aneurysm (AAA): Role in the Inflammatory Response

Abdominal aortic aneurysm (AAA) is a focal dilatation of the aorta, caused by both genetic and environmental factors. Although vascular endothelium plays a key role in AAA progression, the biological mechanisms underlying the mechanical stress involvement are only partially understood. In this study, we developed an in vitro model to characterize the role of mechanical stress as a potential trigger of endothelial deregulation in terms of inflammatory response bridging between endothelial cells (ECs), inflammatory cells, and matrix remodeling. In AAA patients, data revealed different degrees of calcification, inversely correlated with wall stretching and also with inflammation and extracellular matrix degradation. In order to study the role of mechanical stimulation, endothelial cell line (EA.hy926) has been cultured in healthy (10% strain) and pathological (5% strain) dynamic conditions using a bioreactor. In presence of tumor necrosis factor alpha (TNF-α), high levels of matrix metalloproteinase-9 (MMP-9) expression and inflammation are obtained, while mechanical stimulation significantly counteracts the TNF-α effects. Moreover, physiological deformation also plays a significant role in the control of the oxidative stress. Overall our findings indicate that, due to wall calcification, in AAA there is a significant change in terms of decreased wall stretching.

LRP1 (Low-Density Lipoprotein Receptor-Related Protein 1) Regulates Smooth Muscle Contractility by Modulating Ca2+ Signaling and Expression of Cytoskeleton-Related Proteins

Objective- Mutations affecting contractile-related proteins in the ECM (extracellular matrix), microfibrils, or vascular smooth muscle cells can predispose the aorta to aneurysms. We reported previously that the LRP1 (low-density lipoprotein receptor-related protein 1) maintains vessel wall integrity, and smLRP1-/- mice exhibited aortic dilatation. The current study focused on defining the mechanisms by which LRP1 regulates vessel wall function and integrity. Approach and Results- Isometric contraction assays demonstrated that vasoreactivity of LRP1-deficient aortic rings was significantly attenuated when stimulated with vasoconstrictors, including phenylephrine, thromboxane receptor agonist U-46619, increased potassium, and L-type Ca2+ channel ligand FPL-64176. Quantitative proteomics revealed proteins involved in actin polymerization and contraction were significantly downregulated in aortas of smLRP1-/- mice. However, studies with calyculin A indicated that although aortic muscle from smLRP1-/- mice can contract in response to calyculin A, a role for LRP1 in regulating the contractile machinery is not revealed. Furthermore, intracellular calcium imaging experiments identified defects in calcium release in response to a RyR (ryanodine receptor) agonist in smLRP1-/- aortic rings and cultured vascular smooth muscle cells. Conclusions- These results identify a critical role for LRP1 in modulating vascular smooth muscle cell contraction by regulating calcium signaling events that potentially protect against aneurysm development.

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.

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.

A Meta-Analysis of the Association of Chronic Obstructive Pulmonary Disease with Abdominal Aortic Aneurysm Presence

BACKGROUND

Several case-control and population-based abdominal aortic aneurysm (AAA) screening studies have reported inconclusive results of the association of chronic obstructive pulmonary disease (COPD) with AAA presence. To determine whether COPD is associated with AAA presence, we performed a meta-analysis of contemporary clinical studies.

METHODS

To identify all contemporary case-control and population-based AAA screening studies evaluating the association of COPD with AAA presence, databases including MEDLINE and EMBASE were searched from January 2000 to May 2015 using Web-based search engines (PubMed and OVID). An adjusted odds ratio (OR) and 95% confidence intervals (CI) for COPD or AAA presence (using multivariable logistic regression) were abstracted from each individual study. We took an OR for AAA presence to be representative of an OR for COPD presence.

RESULTS

Of 159 potentially relevant articles screened initially, there were 7 case-control and 4 population-based AAA screening studies that met eligibility requirements and were included. Pooled analysis of all the 11 studies (14 estimates, 155,731 participants), 7 case-control studies (4171 participants), and 4 population-based AAA screening studies (7 estimates, 151,560 participants) respectively demonstrated a statistically significant 1.78-fold (OR 1.78, 95% CI 1.38-2.30, P < 0.00001), 3.05-fold (OR 3.05, 95% CI 1.44-6.49, P = 0.004), and 1.24-fold (OR 1.24, 95% CI 1.04-1.48, P = 0.02) increased prevalence/incidence of COPD in patients with AAA relative to subjects without AAA (i.e., a statistically significant 1.78-, 3.05-, and 1.24-fold increased prevalence/incidence of AAA in patients with COPD relative to subjects without COPD) (P for subgroup differences = 0.02).

CONCLUSION

The present meta-analysis demonstrated 1.8-fold increased prevalence/incidence of COPD in patients with AAA relative to subjects without AAA (i.e., 1.8-fold increased prevalence/incidence of AAA in patients with COPD relative to subjects without COPD), which suggests that COPD is associated with AAA presence.

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.

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.

Novel biomarkers of abdominal aortic aneurysm disease: identifying gaps and dispelling misperceptions

Abdominal aortic aneurysm (AAA) is a prevalent and potentially life-threatening disease. Early detection by screening programs and subsequent surveillance has been shown to be effective at reducing the risk of mortality due to aneurysm rupture. The aim of this review is to summarize the developments in the literature concerning the latest biomarkers (from 2008 to date) and their potential screening and therapeutic values. Our search included human studies in English and found numerous novel biomarkers under research, which were categorized in 6 groups. Most of these studies are either experimental or hampered by their low numbers of patients. We concluded that currently no specific laboratory markers allow screeing for the disease and monitoring its progression or the results of treatment. Further studies and studies in larger patient groups are required in order to validate biomarkers as cost-effective tools in the AAA disease.

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.

Association of rs1466535 LRP1 but not rs3019885 SLC30A8 and rs6674171 TDRD10 gene polymorphisms with abdominal aortic aneurysm in Italian patients

OBJECTIVE

Recently, a large genome-wide association study in patients with abdominal aortic aneurysm (AAA) and control subjects identified nine loci associated with AAA. Besides the significant association of the rs1466535 single nucleotide polymorphism in the low-density lipoprotein receptor-related protein 1 gene (LRP1), two of eight remaining loci, rs6674171 in the tudor domain containing protein 10 (TDRD10) and rs3019885 in solute carrier family 30 zinc transporter member 8 (SLC30A8) gene, showed a weakly significant association with AAA requiring further attention. Therefore, the aim of our study was to evaluate the role of these three polymorphisms in conferring AAA genetic susceptibility.

METHODS

We studied these three polymorphisms in 423 patients and 423 sex- and age-comparable control subjects from Italy. All subjects were genotyped with the use of the real-time TaqMan approach. Multiple logistic regression analysis adjusted for traditional cardiovascular risk factor and chronic obstructive pulmonary disease was used to estimated odds ratios and 95% confidence intervals for AAA risk.

RESULTS

The prevalence of carriers of the rs3019885 SLC30A8 G allele was higher in control subjects (67.8%) than in patients (60.3%, P = .022), suggesting a protective effect for AAA. The prevalence of carriers of the rs1466535 LRP1 T allele was higher in patients (51.8%) than in control subjects (39.7%, P = .0004), suggesting a risk effect for AAA. rs6674171 polymorphism genotype distribution did not differ between AAA patients and control subjects. In the multiple logistic regression analysis adjusted for traditional AAA risk factors, only the rs1466535 polymorphism remained significantly associated with AAA (odds ratio, 1.85; 95% confidence interval, 1.2-2.84; P = .01).

CONCLUSIONS

Our findings confirm the role as significant and independent susceptibility factor for AAA of the rs1466535 LRP1 polymorphism (T allele) in an Italian population. Nevertheless, our findings consistently differed from previous published data because in the genome-wide association study, the risk allele was the most frequent rs1466535 C allele. Our findings are consistent with literature data of LRP1 knock-out mice developing atherosclerotic lesions and aortic dilatation and association of the T allele with reduced LRP1 gene expression in humans.

CLINICAL RELEVANCE

Our work supports the evidence that the T allele of the rs1466535 LRP1 polymorphism is an independent risk factor for abdominal aortic aneurysm. Our findings are consistent with literature data of Lrp1 knock-out mice developing atherosclerotic lesions and aortic dilatation, and association of the T allele with reduced LRP1 gene expression in humans. These data could have a crucial role for developing future diagnostic or prognostic scores based on biohumoral, clinical, genetic, proteomic, and imaging data to be applied in everyday clinical practice in order to improve the management of these high-risk patients in consideration of their characteristics and pathophysiological complexity.