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Differential Expression Analyses on Human Aortic Tissue Reveal Novel Genes and Pathways Associated With Abdominal Aortic Aneurysm Onset and Progression

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Abstract

Background Abdominal aortic aneurysms (AAAs) are focal dilatations of the abdominal aorta that expand progressively, increasing their risk of rupture. Rupture of an AAA is associated with high mortality rates, but the mechanisms underlying the initiation, expansion, and rupture of AAAs are not yet fully understood. We aimed to characterize the pathophysiology of AAAs and identify new genes associated with AAA initiation and progression. Methods and Results This study used RNA sequencing data on 140 samples, becoming the largest RNA sequencing data set for differential expression studies of AAAs. We performed differential expression analyses and analyses of differential splicing between dilated and nondilated aortic tissue samples, and between AAAs of different diameters. We identified 3002 differentially expressed genes between AAAs and controls that were independent of ischemic time, 1425 of which were new. Additionally, 8 genes ( EXTL3 , ZFR , DUSP8 , DISP1 , USP33 , VPS37C , ZNF784 , RFX1 ) were differentially expressed between AAAs of varying diameters and between AAAs and control samples. Finally, 7 genes ( SPP1 , FHL1 , GNAS , MORF4L2 , HMGN1 , ARL1 , RNASE4 ) with differential splicing patterns were also differentially expressed genes between AAAs and controls, suggesting that splicing differences in these genes may contribute to the observed expression changes and disease development. Conclusions This study identifies new genes and splicing patterns associated with AAAs and validates previous relevant pathways on AAAs. These findings contribute to the understanding of the complex mechanisms underlying AAAs and may provide potential targets to limit AAA progression and mortality risk.

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Background: Clinical decision making in abdominal aortic aneurysms (AAA) relies completely on diameter. At this point, improved decision tools remain an unmet medical need. Our goal was to identify changes at the molecular level specifically leading up to AAA rupture. Methods and results: Aortic wall tissue specimens were collected during open elective (eAAA; n=31) or emergency repair of ruptured AAA (rAAA; n=17), and gene expression was investigated using microarrays. Identified candidate genes were validated with quantitative real-time polymerase chain reaction in an independent sample set (eAAA: n=46; rAAA: n=18). Two gene sets were identified, 1 set containing 5 genes linked to terminal progression, that is, positively associated with progression of larger AAA, and with rupture (HILPDA, ANGPTL4, LOX, SRPX2, FCGBP), and a second set containing 5 genes exclusively upregulated in rAAA (ADAMTS9, STC1, GFPT2, GAL3ST4, CCL4L1). Genes in both sets essentially associated with processes related to impaired tissue remodeling, such as angiogenesis and adipogenesis. In gene expression experiments we were able to show that upregulated gene expression for identified candidate genes is unique for AAA. Functionally, the selected upregulated factors converge at processes coordinated by the canonical HIF-1α signaling pathway and are highly expressed in fibroblasts but not inflammatory cells of the aneurysmatic wall. Histological quantification of angiogenesis and exploration of the HIF-1α network in rAAA versus eAAA shows enhanced microvessel density but also clear activation of the HIF-1α network in rAAA. Conclusions: Our study shows a specific molecular fingerprint for terminal AAA disease. These changes appear to converge at activation of HIF-1α signaling in mesenchymal cells. Aspects of this cascade might represent targets for rupture risk assessment.
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RNA sequencing (RNA-seq) is a genomic approach for the detection and quantitative analysis of messenger RNA molecules in a biological sample and is useful for studying cellular responses. RNA-seq has fueled much discovery and innovation in medicine over recent years. For practical reasons, the technique is usually conducted on samples comprising thousands to millions of cells. However, this has hindered direct assessment of the fundamental unit of biology-the cell. Since the first single-cell RNA-sequencing (scRNA-seq) study was published in 2009, many more have been conducted, mostly by specialist laboratories with unique skills in wet-lab single-cell genomics, bioinformatics, and computation. However, with the increasing commercial availability of scRNA-seq platforms, and the rapid ongoing maturation of bioinformatics approaches, a point has been reached where any biomedical researcher or clinician can use scRNA-seq to make exciting discoveries. In this review, we present a practical guide to help researchers design their first scRNA-seq studies, including introductory information on experimental hardware, protocol choice, quality control, data analysis and biological interpretation.
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Transcriptomics technologies are the techniques used to study an organism’s transcriptome, the sum of all of its RNA transcripts. The information content of an organism is recorded in the DNA of its genome and expressed through transcription. Here, mRNA serves as a transient intermediary molecule in the information network, whilst noncoding RNAs perform additional diverse functions. A transcriptome captures a snapshot in time of the total transcripts present in a cell. The first attempts to study the whole transcriptome began in the early 1990s, and technological advances since the late 1990s have made transcriptomics a widespread discipline. Transcriptomics has been defined by repeated technological innovations that transform the field. There are two key contemporary techniques in the field: microarrays, which quantify a set of predetermined sequences, and RNA sequencing (RNA-Seq), which uses high-throughput sequencing to capture all sequences. Measuring the expression of an organism’s genes in different tissues, conditions, or time points gives information on how genes are regulated and reveals details of an organism’s biology. It can also help to infer the functions of previously unannotated genes. Transcriptomic analysis has enabled the study of how gene expression changes in different organisms and has been instrumental in the understanding of human disease. An analysis of gene expression in its entirety allows detection of broad coordinated trends which cannot be discerned by more targeted assays.
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Although cardiovascular complications are the most common cause of death in patients with autosomal-dominant polycystic kidney disease (ADPKD), the incidence and risk of aortic aneurysm and dissection (AAD) in ADPKD remains unclear due to limited data and insufficient cases. We utilized the data from Taiwan National Health Insurance Research Database (NHIRD) to do a population-based cohort study (1997-2008). After excluding those patients with age <18 years old and initially concomitant diagnoses of end-stage renal disease and AAD, a total of 2076 ADPKD patients were selected from 1,000,000 of general population. Additionally, the non-ADPKD group was set up as comparison group in 1:10 ratio after matching with age, gender, income and urbanization (n=20760). The result showed that ADPKD group had higher frequency of comorbidities than non-ADPKD group. The frequency of AAD in ADPKD was significantly higher than in general population (0.92% v.s. 0.11%, p<0.0001). Of them, 58% of AAD were acute aortic dissection. In addition, Kaplan-Meier analysis demonstrated that cumulative incidence of AAD was remarkably higher in the ADPKD than non-ADPKD group (p<0.001). The mean time period from ADPKD diagnosis to AAD occurrence was 4.02±3.16 years. After adjusting for age, gender and comorbidities, the ADPKD patients had up to 5.49-fold greater risk for AAD occurrence as compared to non-ADPKD counterparts (95% CI 2.86-10.52, p<0.0001). Particularly, those patients with co-existing ADPKD and hypertension had very high risk for future development of AAD. In conclusion, the risk of AAD significantly increases in patients with ADPKD as compared with those of general population.
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Haplotype phasing of genetic variants is important for clinical interpretation of the genome, population genetic analysis and functional genomic analysis of allelic activity. Here we present phASER, an accurate approach for phasing variants that are overlapped by sequencing reads, including those from RNA sequencing (RNA-seq), which often span multiple exons due to splicing. Using diverse RNA-seq data we demonstrate that this provides more accurate phasing of rare variants compared with population-based phasing and allows phasing of variants in the same gene up to hundreds of kilobases away that cannot be obtained from DNA sequencing (DNA-seq) reads. We show that in the context of medical genetic studies this improves the resolution of compound heterozygotes. Additionally, phASER provides measures of haplotypic expression that increase power and accuracy in studies of allelic expression. In summary, phasing using RNA-seq and phASER is accurate and improves studies where rare variant haplotypes or allelic expression is needed.
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Abdominal aortic aneurysm (AAA) and aortic occlusive disease (AOD) represent common causes of morbidity and mortality in elderly populations which were previously believed to have common aetiologies. The aim of this study was to assess the gene expression in human AAA and AOD. We performed microarrays using aortic specimen obtained from 20 patients with small AAAs (≤ 55mm), 29 patients with large AAAs (> 55mm), 9 AOD patients, and 10 control aortic specimens obtained from organ donors. Some differentially expressed genes were validated by quantitative-PCR (qRT-PCR)/immunohistochemistry. We identified 840 and 1,014 differentially expressed genes in small and large AAAs, respectively. Immune-related pathways including cytokine-cytokine receptor interaction and T-cell-receptor signalling were upregulated in both small and large AAAs. Examples of validated genes included CTLA4 (2.01-fold upregulated in small AAA, P = 0.002), NKTR (2.37-and 2.66-fold upregulated in small and large AAA with P = 0.041 and P = 0.015, respectively), and CD8A (2.57-fold upregulated in large AAA, P = 0.004). 1,765 differentially expressed genes were identified in AOD. Pathways upregulated in AOD included metabolic and oxidative phosphorylation categories. The UCP2 gene was downregulated in AOD (3.73-fold downregulated, validated P = 0.017). In conclusion, the AAA and AOD transcriptomes were very different suggesting that AAA and AOD have distinct pathogenic mechanisms.
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The concordance of RNA-sequencing (RNA-seq) with microarrays for genome-wide analysis of differential gene expression has not been rigorously assessed using a range of chemical treatment conditions. Here we use a comprehensive study design to generate Illumina RNA-seq and Affymetrix microarray data from the same liver samples of rats exposed in triplicate to varying degrees of perturbation by 27 chemicals representing multiple modes of action (MOAs). The cross-platform concordance in terms of differentially expressed genes (DEGs) or enriched pathways is linearly correlated with treatment effect size (R2≈0.8). Furthermore, the concordance is also affected by transcript abundance and biological complexity of the MOA. RNA-seq outperforms microarray (93% versus 75%) in DEG verification as assessed by quantitative PCR, with the gain mainly due to its improved accuracy for low-abundance transcripts. Nonetheless, classifiers to predict MOAs perform similarly when developed using data from either platform. Therefore, the endpoint studied and its biological complexity, transcript abundance and the genomic application are important factors in transcriptomic research and for clinical and regulatory decision making.
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Human ascending thoracic aortic aneurysms (ATAAs) are life threatening and constitute a leading cause of mortality in the United States. Previously, we demonstrated that collagens α2(V) and α1(XI) mRNA and protein expression levels are significantly increased in ATAAs. In this report, the authors extended these preliminary studies using high-throughput proteomic analysis to identify additional biomarkers for use in whole blood real-time RT-PCR analysis to allow for the identification of ATAAs before dissection or rupture. Human ATAA samples were obtained from male and female patients aged 65±14 years. Both bicuspid and tricuspid aortic valve patients were included and compared with nonaneurysmal aortas (mean diameter 2.3 cm). Five biomarkers were identified as being suitable for detection and identification of ATAAs using qRT-PCR analysis of whole blood. Analysis of 41 samples (19 small, 13 medium-sized, and 9 large ATAAs) demonstrated the overexpression of 3 of these transcript biomarkers correctly identified 79.4% of patients with ATAA of ≥4.0 cm (P<0.001, sensitivity 0.79, CI=0.62 to 0.91; specificity 1.00, 95% CI=0.42 to 1.00). A preliminary transcript biomarker panel for the identification of ATAAs using whole blood qRT-PCR analysis in men and women is presented.
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Recruitment of macrophage precursors to the adventitia plays a key role in the pathogenesis of abdominal aortic aneurysms (AAAs), but molecular mechanisms remain undefined. The innate immune signaling molecule CD14 was reported to be upregulated in adventitial macrophages in a murine model of AAA and in monocytes cocultured with aortic adventitial fibroblasts (AoAf) in vitro, concurrent with increased interleukin-6 (IL-6) expression. We hypothesized that CD14 plays a crucial role in adventitial macrophage precursor recruitment early during AAA formation. CD14(-/-) mice were resistant to AAA formation induced by 2 different AAA induction models: aortic elastase infusion and systemic angiotensin II (AngII) infusion. CD14 gene deletion led to reduced aortic macrophage infiltration and diminished elastin degradation. Adventitial monocyte binding to AngII-infused aorta in vitro was dependent on CD14, and incubation of human acute monocytic leukemia cell line-1 (THP-1) monocytes with IL-6 or conditioned medium from perivascular adipose tissue (PVAT) upregulated CD14 expression. Conditioned medium from AoAf and PVAT induced CD14-dependent monocyte chemotaxis, which was potentiated by IL-6. CD14 expression in aorta and plasma CD14 levels were increased in AAA patients compared with controls. These findings link CD14 innate immune signaling via a novel IL-6 amplification loop to adventitial macrophage precursor recruitment in the pathogenesis of AAA.
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Aims Unstable atherosclerotic plaque is the main pathological basis of acute coronary syndrome, which is the leading cause of death and disability worldwide. Therefore, we combined multiple bioinformatics tools to identify key genes related to unstable plaque. Main methods GSE94605 contained 7 plasma sample pools of 175 healthy and 6 sample pools of 150 unstable angina pectoris (UAP) patients, and detected with miRNA array while GSE60993 collected peripheral blood from 7 normal and 9 UAP, and detected with mRNA array. GSE120521 collected carotid plaques from 4 patients and dissected in stable and unstable regions, then detected with RNA-seq. Differentially expressed miRNAs (DEMs) and genes (DEGs) in UAP were re-analyzed. Gene Ontology (GO)/Kyoto Encyclopedia of Genes and Genomes (KEGG) and Protein-protein interaction (PPI) network were applied on top 10 up-regulated or down-regulated DEMs targets, and whole DEGs. MiRNAs-mRNAs network was constructed with these DEMs and DEGs, and the expression profile of genes within the network was finally validated in GSE120521. Key findings Totally, 263 up-regulated and 201 down-regulated DEMs were identified in GSE94605, and 78 up-regulated and 29 down-regulated DEGs were identified in GSE60993. Subsequently, a miRNAs-mRNAs network was constructed with 6 up-regulated miRNAs targeted to 12 down-regulated genes, and 4 down-regulated miRNAs targeted to 8 up-regulated genes. Finally, MORF4L2, RAB3IL1 and MMP9 within the network were considered as hub genes in unstable plaque progression after being validated in GSE120521. Significance These 3 genes may provide new targets for diagnosis and therapy of unstable atherosclerotic plaque.
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Objective: There is no medical treatment to prevent abdominal aortic aneurysm (AAA) growth and rupture, both of which are linked to smoking. Our objective was to map the tunica-specific pathophysiology of AAAs compared with control aorta, with consideration of the intraluminal thrombus, age, and sex, and to subsequently identify which mechanisms were linked to smoking and diameter growth rate. Approach and Results: Microarray analyses were performed on 246 samples from 76 AAA patients and 13 controls. In media and adventitia, there were 5889 and 2701 differentially expressed genes, respectively. Gene sets related to adaptive and innate immunity were upregulated in both tunicas. Media-specific gene sets included increased matrix disassembly and angiogenesis, as well as decreased muscle cell development, contraction, and differentiation. Genes implicated in previous genome-wide association studies were dysregulated in media. The intraluminal thrombus had a pro-proteolytic and proinflammatory effect on the underlying media. Active smoking resulted in increased inflammation, oxidative stress, and angiogenesis in all tissues, with lipid processes enriched in adventitia. Processes enriched with active smoking in control aortas overlapped to a high extent with those dysregulated in AAA. The AAA diameter growth rate (n=24) correlated with T- and B-cell expression in media, as well as lipid-related processes in the adventitia. Conclusions: This tunica-specific analysis of gene expression in a large study enabled the detection of features not previously described in AAA disease. Smoking was associated with increased expression of aneurysm processes, of which adaptive immunity and lipid-related processes correlated with growth rate.
Article
Objective: Remodeling of the extracellular matrix plays a vital role in cardiovascular diseases. Using a mouse model of postnatal ascending aortic aneurysms (termed Fbln4SMKO), we have reported that abnormal mechanosensing led to aneurysm formation in Fbln4SMKO with an upregulation of the mechanosensitive transcription factor, Egr1 (Early growth response 1). However, the role of Egr1 and its upstream regulator(s) in the initiation of aneurysm development and their relationship to an aneurysmal microenvironment are unknown. Approach and Results: To investigate the contribution of Egr1 in the aneurysm development, we deleted Egr1 in Fbln4SMKO mice and generated double knockout mice (DKO, Fbln4SMKO; Egr1-/-). Aneurysms were prevented in DKO mice (42.8%) and Fbln4SMKO; Egr1+/- mice (26%). Ingenuity Pathway Analysis identified PAR1 (protease-activated receptor 1) as a potential Egr1 upstream gene. Protein and transcript levels of PAR1 were highly increased in Fbln4SMKO aortas at postnatal day 1 before aneurysm formed, together with active thrombin and MMP (matrix metalloproteinase)-9, both of which serve as a PAR1 activator. Concordantly, protein levels of PAR1, Egr1, and thrombin were significantly increased in human thoracic aortic aneurysms. In vitro cyclic stretch assays (1.0 Hz, 20% strain, 8 hours) using mouse primary vascular smooth muscle cells induced marked expression of PAR1 and secretion of prothrombin in response to mechanical stretch. Thrombin was sufficient to induce Egr1 expression in a PAR1-dependent manner. Conclusions: We propose that thrombin, MMP-9, and mechanical stimuli in the Fbln4SMKO aorta activate PAR1, leading to the upregulation of Egr1 and initiation of ascending aortic aneurysms.
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The common approach to the multiplicity problem calls for controlling the familywise error rate (FWER). This approach, though, has faults, and we point out a few. A different approach to problems of multiple significance testing is presented. It calls for controlling the expected proportion of falsely rejected hypotheses — the false discovery rate. This error rate is equivalent to the FWER when all hypotheses are true but is smaller otherwise. Therefore, in problems where the control of the false discovery rate rather than that of the FWER is desired, there is potential for a gain in power. A simple sequential Bonferronitype procedure is proved to control the false discovery rate for independent test statistics, and a simulation study shows that the gain in power is substantial. The use of the new procedure and the appropriateness of the criterion are illustrated with examples.
Article
Objective: Previous in vitro and animal studies have suggested that osteopontin (OPN), an inflammatory extracellular matrix protein, is involved in the formation and growth of abdominal aortic aneurysms (AAAs). However, the mechanism by which this occurs continues to be nebulous. The relationship between OPN and inflammation-suppressing lymphocytes present in the human AAA condition was investigated and presented herein. Methods: Serum OPN concentrations were measured in healthy, risk factor-matched non-AAA and AAA patients by enzyme-linked immunosorbent assay (ELISA). Immunohistochemistry was used to determine the source of OPN secretion using aortic tissue collected from multiorgan donors and AAA patients undergoing open surgical repair. Vascular smooth muscle cells (VSMCs) were exposed to various inflammatory mediators, and OPN expression was evaluated by quantitative reverse transcriptase-polymerase chain reaction and ELISA. The inflammatory nature of OPN and the aortic wall was determined using a TR1 suppressor cell induction assay as a surrogate and characterized by ELISA and fluorescence-activated cell sorting. Results: OPN was found to be elevated in both the plasma and aortic homogenate of AAA patients compared with controls. On immunohistochemistry, OPN localized to the tunica media of the diseased aorta but was minimally expressed in healthy aorta. In vitro, cigarette smoke extract was the most potent stimulator of OPN secretion by VSMCs and increased both messenger RNA and supernatant concentrations. OPN demonstrated an ability to inhibit the induction of interleukin 10-secreting TR1 lymphocytes, a depleted population in the AAA patient, from naive precursors. Last, neutralizing receptor targets of OPN in the setting of AAA homogenate coincubation abrogated the inhibition of TR1 induction. Conclusions: OPN, secreted by the VSMCs of the tunica media, is elevated in the circulating plasma and aortic wall of patients with AAA. It can inhibit the induction of the TR1 suppressor cell, leading to an overall proinflammatory state contributing to progressive aortic wall breakdown and dilation.
Article
Background: Decision-making related to the care of patients with an abdominal aortic aneurysm (AAA) is complex. Aneurysms present with varying risks of rupture, and patient-specific factors influence anticipated life expectancy, operative risk, and need to intervene. Careful attention to the choice of operative strategy along with optimal treatment of medical comorbidities is critical to achieving excellent outcomes. Moreover, appropriate postoperative surveillance is necessary to minimize subsequent aneurysm-related death or morbidity. Methods: The committee made specific practice recommendations using the Grading of Recommendations Assessment, Development, and Evaluation system. Three systematic reviews were conducted to support this guideline. Two focused on evaluating the best modalities and optimal frequency for surveillance after endovascular aneurysm repair (EVAR). A third focused on identifying the best available evidence on the diagnosis and management of AAA. Specific areas of focus included (1) general approach to the patient, (2) treatment of the patient with an AAA, (3) anesthetic considerations and perioperative management, (4) postoperative and long-term management, and (5) cost and economic considerations. Results: Along with providing guidance regarding the management of patients throughout the continuum of care, we have revised a number of prior recommendations and addressed a number of new areas of significance. New guidelines are provided for the surveillance of patients with an AAA, including recommended surveillance imaging at 12-month intervals for patients with an AAA of 4.0 to 4.9 cm in diameter. We recommend endovascular repair as the preferred method of treatment for ruptured aneurysms. Incorporating knowledge gained through the Vascular Quality Initiative and other regional quality collaboratives, we suggest that the Vascular Quality Initiative mortality risk score be used for mutual decision-making with patients considering aneurysm repair. We also suggest that elective EVAR be limited to hospitals with a documented mortality and conversion rate to open surgical repair of 2% or less and that perform at least 10 EVAR cases each year. We also suggest that elective open aneurysm repair be limited to hospitals with a documented mortality of 5% or less and that perform at least 10 open aortic operations of any type each year. To encourage the development of effective systems of care that would lead to improved outcomes for those patients undergoing emergent repair, we suggest a door-to-intervention time of <90 minutes, based on a framework of 30-30-30 minutes, for the management of the patient with a ruptured aneurysm. We recommend treatment of type I and III endoleaks as well as of type II endoleaks with aneurysm expansion but recommend continued surveillance of type II endoleaks not associated with aneurysm expansion. Whereas antibiotic prophylaxis is recommended for patients with an aortic prosthesis before any dental procedure involving the manipulation of the gingival or periapical region of teeth or perforation of the oral mucosa, antibiotic prophylaxis is not recommended before respiratory tract procedures, gastrointestinal or genitourinary procedures, and dermatologic or musculoskeletal procedures unless the potential for infection exists or the patient is immunocompromised. Increased utilization of color duplex ultrasound is suggested for postoperative surveillance after EVAR in the absence of endoleak or aneurysm expansion. Conclusions: Important new recommendations are provided for the care of patients with an AAA, including suggestions to improve mutual decision-making between the treating physician and the patients and their families as well as a number of new strategies to enhance perioperative outcomes for patients undergoing elective and emergent repair. Areas of uncertainty are highlighted that would benefit from further investigation in addition to existing limitations in diagnostic tests, pharmacologic agents, intraoperative tools, and devices.
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Cardiovascular disease (CVD) is a leading cause of mortality worldwide. Proper mitochondrial function is necessary in tissues and organs that are of high energy demand, including the heart. Mitochondria are very sensitive to nutrient and oxygen supply and undergo metabolic adaptation to the changing environment. In CVD, such an adaptation is impaired, which, in turn, leads to a progressive decline of the mitochondrial function associated with abnormalities in the respiratory chain and ATP synthesis, increased oxidative stress, and loss of the structural integrity of mitochondria. Uncoupling of the electron transport chain in dysfunctional mitochondria results in enhanced production of reactive oxygen species, depletion of cell ATP pool, extensive cell damage, and apoptosis of cardiomyocytes. Mitophagy is a process, during which cells clear themselves from dysfunctional and damaged mitochondria using autophagic mechanism. Deregulation of this process in the failing heart, accumulation of dysfunctional mitochondria makes the situation even more adverse. In cardiac pathology, aberrations of the activity of the respiratory chain and ATP production may be considered as a core of mitochondrial dysfunction. Indeed, therapeutic restoration of these key functional properties can be considered as a primary goal for improvement of mitochondrial dysfunction in CVD. • Key messages • Mitochondrial dysfunction plays a crucial role in cardiovascular disease pathogenesis. • Cardiovascular disease is associated with altered mithochondrial biogenesis and clearance. • In cardiovascular disease, impaired mitochondrial function results in decreased ATP production and enhanced ROS formation.
Article
Allele-specific sequencing reads provide a powerful signal for identifying molecular quantitative trait loci (QTLs), but they are challenging to analyze and are prone to technical artifacts. Here we describe WASP, a suite of tools for unbiased allele-specific read mapping and discovery of molecular QTLs. Using simulated reads, RNA-seq reads and chromatin immunoprecipitation sequencing (ChIP-seq) reads, we demonstrate that WASP has a low error rate and is far more powerful than existing QTL-mapping approaches.
Article
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. Read More: http://informahealthcare.com/eprint/WNvTASmHEgKcFbHfkRhz/full
Article
Histological examination of abdominal aortic aneurysm (AAA) tissues demonstrates extracellular matrix (ECM) destruction and infiltration of inflammatory cells. Previous work with mouse models of AAA has shown that anti-inflammatory strategies can effectively attenuate aneurysm formation. Thrombospondin-1 (TSP1) is a matricellular protein involved in the maintenance of vascular structure and homeostasis through the regulation of biological functions such as cell proliferation, apoptosis, and adhesion. Expression levels of TSP1 correlate with vascular disease conditions. To use TSP1 deficient (Thbs1(-/-)) mice to test the hypothesis that TSP1 contributes to pathogenesis of AAAs. Mouse experimental AAA was induced either through perivascular treatment with calcium phosphate, intraluminal perfusion with porcine elastase, or systemic administration of Angiotensin II. Induction of AAA increased TSP1 expression in aortas of C57BL/6 or apoE-/- mice. Compared to Thbs1(+/+) mice, Thbs1(-/-) mice developed significantly smaller aortic expansion when subjected to AAA inductions, which was associated with diminished infiltration of macrophages. Thbs1(-/-) monocytic cells had reduced adhesion and migratory capacity in vitro compared to wildtype counterparts. Adoptive transfer of Thbs1(+/+) monocytic cells or bone marrow reconstitution rescued aneurysm development in Thbs1(-/-) mice. TSP1 expression plays a significant role in regulation of migration and adhesion of mononuclear cells, contributing to vascular inflammation during AAA development.
Article
Objective Abdominal aortic aneurysm (AAA) represents a common cause of morbidity and mortality in elderly populations but the mechanisms involved in AAA formation remain incompletely understood. Previous human studies have focused on biopsies obtained from the center of the AAA however it is likely that pathological changes also occur in relatively normal appearing aorta away from the site of main dilatation. The aim of this study was to assess the gene expression profile of biopsies obtained from the neck of human AAAs. Methods We performed a microarray study of aortic neck specimens obtained from 14 patients with AAA and 8 control aortic specimens obtained from organ donors. Two-fold differentially expressed genes were identified with correction for multiple testing. Mechanisms represented by differentially expressed genes were identified using Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Some of the differentially expressed genes were validated by quantitative real-time PCR (qPCR) and immunohistochemistry. Results We identified 1,047 differentially expressed genes in AAA necks. The KEGG analysis revealed marked upregulation of genes related to immunity. These pathways included cytokine-cytokine receptor interaction (P=8.67*10-12), chemokine signaling pathway (P=5.76*10-07), and antigen processing and presentation (P=4.00*10-04). Examples of differentially expressed genes validated by qPCR included the T-cells marker CD44 (2.16-fold upregulated, P=0.008) and the B-cells marker CD19 (3.14-fold upregulated, P=0.003). The presence of B-cells in AAA necks was confirmed by immunohistochemistry. Conclusions The role of immunity in AAA is controversial. This study suggests that immune pathways are also upregulated within the undilated aorta proximal to an AAA.
Article
Background We previously reported the prevalence and associations of abdominal aortic aneurysm (AAA) in 73,451 veterans aged 50 to 79 years who underwent ultrasound screening. Objective To understand the prevalence of and principal positive and negative risk factors for AAA, and to assess reproducibility of our previous findings. Methods In the new cohort of veterans undergoing screening, 52,745 subjects aged 50 to 79 without history of AAA underwent successful ultrasound screening for AAA, after completing a questionnaire on demographics and potential risk factors. Results We detected AAA of 4.0 cm or larger in 613 participants (1.2%; compared with 1.4% in the earlier cohort). The direction and magnitude of the important associations reported in the first cohort were confirmed. Respective odds ratios for the major associations with AAA for the second and for the combined cohorts were as follows: 1.81 and 1.71 for age (per 7 years), 0.12 and 0.18 for female sex, 0.59 and 0.53 for black race, 1.94 and 1.94 for family history of AAA, 4.45 and 5.07 for smoking, 0.50 and 0.52 for diabetes, and 1.60 and 1.66 for atherosclerotic diseases. The excess prevalence associated with smoking accounted for 75% of all AAAs of 4.0 cm or larger in the total population of 126,196. Associations for AAA of 3.0 to 3.9 cm were similar but tended to be somewhat weaker. Conclusions Our findings confirm our previous cohort findings. Age, smoking, family history of AAA, and atherosclerotic diseases remained the principal positive associations with AAA, and female sex, diabetes, and black race remained the principal negative associations.