Simultaneous analysis of 1176 gene products in normal human aorta and abdominal aortic aneurysms using a membrane-based complementary DNA expression array

Evidence Accumulates: Patients with Ascending Aneurysms Are Strongly Protected from Atherosclerotic Disease

Ascending thoracic aortic aneurysms may be fatal upon rupture or dissection and remain a leading cause of death in the developed world. Understanding the pathophysiology of the development of ascending thoracic aortic aneurysms may help reduce the morbidity and mortality of this disease. In this review, we will discuss our current understanding of the protective relationship between ascending thoracic aortic aneurysms and the development of atherosclerosis, including decreased carotid intima-media thickness, low-density lipoprotein levels, coronary and aortic calcification, and incidence of myocardial infarction. We also propose several possible mechanisms driving this relationship, including matrix metalloproteinase proteins and transforming growth factor-β.

Dysregulations of Key Regulators of Angiogenesis and Inflammation in Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is a chronic vascular disease caused by localized weakening and broadening of the abdominal aorta. AAA is a clearly underdiagnosed disease and is burdened with a high mortality rate (65-85%) from AAA rupture. Studies indicate that abnormal regulation of angiogenesis and inflammation contributes to progression and onset of this disease; however, dysregulations in the molecular pathways associated with this disease are not yet fully explained. Therefore, in our study, we aimed to identify dysregulations in the key regulators of angiogenesis and inflammation in patients with AAA in peripheral blood mononuclear cells (using qPCR) and plasma samples (using ELISA). Expression levels of ANGPT1, CXCL8, PDGFA, TGFB1, VEGFB, and VEGFC and plasma levels of TGF-alpha, TGF-beta 1, VEGF-A, and VEGF-C were found to be significantly altered in the AAA group compared to the control subjects without AAA. Associations between analyzed factors and risk factors or biochemical parameters were also explored. Any of the analyzed factors was associated with the size of the aneurysm. The presented study identified dysregulations in key angiogenesis- and inflammation-related factors potentially involved in AAA formation, giving new insight into the molecular pathways involved in the development of this disease and providing candidates for biomarkers that could serve as diagnostic or therapeutic targets.

Cathepsin H: molecular characteristics and clues to function and mechanism

Cathepsin H (CatH) is a lysosomal cysteine protease with a unique aminopeptidase activity that is extensively expressed in the lung, pancreas, thymus, kidney, liver, skin, and brain. Owing to its specific enzymatic activity, CatH has critical effects on the regulation of biological behaviours of cancer cells and pathological processes in brain diseases. Moreover, a neutral pH level is optimal for CatH activity, so it is expected to be active in the extra-lysosomal and extracellular space. In the present review, we describe the expression, maturation, and enzymatic properties of CatH, and summarize the available experimental evidence that mechanistically links CatH to various physiological and pathological processes. Finally, we discuss the challenges and potentials of CatH inhibitors in CatH-induced disease therapy.

Thymosin β4 preserves vascular smooth muscle phenotype in atherosclerosis via regulation of low density lipoprotein related protein 1 (LRP1)

Atherosclerosis is a progressive, degenerative vascular disease and a leading cause of morbidity and mortality. In response to endothelial damage, platelet derived growth factor (PDGF)-BB induced phenotypic modulation of medial smooth muscle cells (VSMCs) promotes atherosclerotic lesion formation and destabilisation of the vessel wall. VSMC sensitivity to PDGF-BB is determined by endocytosis of Low density lipoprotein receptor related protein 1 (LRP1)-PDGFR β complexes to balance receptor recycling with lysosomal degradation. Consequently, LRP1 is implicated in various arterial diseases. Having identified Tβ4 as a regulator of LRP1-mediated endocytosis to protect against aortic aneurysm, we sought to determine whether Tβ4 may additionally function to protect against atherosclerosis, by regulating LRP1-mediated growth factor signalling. By single cell transcriptomic analysis, Tmsb4x, encoding Tβ4, strongly correlated with contractile gene expression and was significantly down-regulated in cells that adopted a modulated phenotype in atherosclerosis. We assessed susceptibility to atherosclerosis of global Tβ4 knockout mice using the ApoE-/- hypercholesterolaemia model. Inflammation, elastin integrity, VSMC phenotype and signalling were analysed in the aortic root and descending aorta. Tβ4KO; ApoE-/- mice develop larger atherosclerotic plaques than control mice, with medial layer degeneration characterised by accelerated VSMC phenotypic modulation. Defects in Tβ4KO; ApoE-/- mice phenocopied those in VSMC-specific LRP1 nulls and, moreover, were underpinned by hyperactivated LRP1-PDGFRβ signalling. We identify an atheroprotective role for endogenous Tβ4 in maintaining differentiated VSMC phenotype via LRP1-mediated PDGFRβ signalling.

Cytokines in Abdominal Aortic Aneurysm: Master Regulators With Clinical Application

Abdominal aortic aneurysm (AAA) is a potentially life-threatening disorder with a mostly asymptomatic course where the abdominal aorta is weakened and bulged. Cytokines play especially important roles (both positive and negative) among the molecular actors of AAA development. All the inflammatory cascades, extracellular matrix degradation and vascular smooth muscle cell apoptosis are driven by cytokines. Previous studies emphasize an altered expression and a changed epigenetic regulation of key cytokines in AAA tissue samples. Such cytokines as IL-6, IL-10, IL-12, IL-17, IL-33, IL-1β, TGF-β, TNF-α, IFN-γ, and CXCL10 seem to be crucial in AAA pathogenesis. Some data obtained in animal studies show a protective function of IL-10, IL-33, and canonical TGF-β signaling, as well as a dual role of IL-4, IFN-γ and CXCL10, while TNF-α, IL-1β, IL-6, IL-12/IL-23, IL-17, CCR2, CXCR2, CXCR4 and the TGF-β noncanonical pathway are believed to aggravate the disease. Altogether data highlight significance of cytokines as informative markers and predictors of AAA. Pathologic serum/plasma concentrations of IL-1β, IL-2, IL-6, TNF-α, IL-10, IL-8, IL-17, IFN-γ, and PDGF have been already found in AAA patients. Some of the changes correlate with the size of aneurysms. Moreover, the risk of AAA is associated with polymorphic variants of genes encoding cytokines and their receptors: CCR2 (rs1799864), CCR5 (Delta-32), IL6 (rs1800796 and rs1800795), IL6R (rs12133641), IL10 (rs1800896), TGFB1 (rs1800469), TGFBR1 (rs1626340), TGFBR2 (rs1036095, rs4522809, rs1078985), and TNFA (rs1800629). Finally, 5 single-nucleotide polymorphisms in gene coding latent TGF-β-binding protein (LTBP4) and an allelic variant of TGFB3 are related to a significantly slower AAA annual growth rate.

Targeting Platelet Activation in Abdominal Aortic Aneurysm: Current Knowledge and Perspectives

Abdominal aortic aneurysm (AAA) is a potentially fatal vascular disease that involves complex multifactorial hemodynamic, thrombotic, inflammatory, and aortic wall remodeling processes. However, its mechanisms are incompletely understood. It has become increasingly clear that platelets are involved in pathological processes of vascular diseases beyond their role in hemostasis and thrombosis. Platelet activation with membrane receptors and secreted mediators promotes thrombus formation and the accumulation of inflammatory cells, which may play an important role in the development of AAA by destroying the structural integrity and stability of the vessel wall. Turbulent blood flow in aortic aneurysms promotes platelet activation and aggregation. Platelet count and heterogeneity are important predictive, diagnostic, and prognostic indicators of AAA. We summarize the relationship between platelet activation and AAA development and propose future research directions and possible clinical applications.

Galectin-3 as a Biomarker for Stratifying Abdominal Aortic Aneurysm Size in a Taiwanese Population

Abdominal aortic aneurysm (AAA) ruptures are unpredictable and lethal. A biomarker predicting AAA rupture risk could help identify patients with small, screen-detected AAAs. Galectin-3 (Gal-3), a β-galactosidase–binding lectin, is involved in inflammatory processes and may be associated with AAA incidence. We investigated whether Gal-3 can be used as a biomarker of AAA size. Plasma Gal-3 protein concentrations were examined in patients with AAA (n = 151) and control patients (n = 195) using Human ProcartaPlex multiplex and simplex kits. Circulating Gal-3 levels were significantly higher in patients with AAA than in control patients. The area under the receiver operating characteristic curve for Gal-3 was 0.91. Multivariate logistic regression analysis revealed a significant association between Gal-3 level and the presence of AAA. Circulating Gal-3 levels were significantly correlated with aortic diameter in a concentration-dependent manner. In conclusion, higher plasma Gal-3 concentrations may be a useful biomarker of AAA progression.

Thymosin β4 protects against aortic aneurysm via endocytic regulation of growth factor signaling

Vascular stability and tone are maintained by contractile smooth muscle cells (VSMCs). However, injury-induced growth factors stimulate a contractile-synthetic phenotypic modulation which increases susceptibility to abdominal aortic aneurysm (AAA). As a regulator of embryonic VSMC differentiation, we hypothesized that Thymosin β4 (Tβ4) may function to maintain healthy vasculature throughout postnatal life. This was supported by the identification of an interaction with low density lipoprotein receptor related protein 1 (LRP1), an endocytic regulator of platelet-derived growth factor BB (PDGF-BB) signaling and VSMC proliferation. LRP1 variants have been implicated by genome-wide association studies with risk of AAA and other arterial diseases. Tβ4-null mice displayed aortic VSMC and elastin defects that phenocopy those of LRP1 mutants, and their compromised vascular integrity predisposed them to Angiotensin II-induced aneurysm formation. Aneurysmal vessels were characterized by enhanced VSMC phenotypic modulation and augmented PDGFR-β signaling. In vitro, enhanced sensitivity to PDGF-BB upon loss of Tβ4 was associated with dysregulated endocytosis, with increased recycling and reduced lysosomal targeting of LRP1-PDGFR-β. Accordingly, the exacerbated aneurysmal phenotype in Tβ4-null mice was rescued upon treatment with the PDGFR-β antagonist Imatinib. Our study identifies Tβ4 as a key regulator of LRP1 for maintaining vascular health, and provides insights into the mechanisms of growth factor-controlled VSMC phenotypic modulation underlying aortic disease progression.

Angiotensin II and leukocyte trafficking: New insights for an old vascular mediator. Role of redox-signaling pathways

Inflammation and activation of the immune system are key molecular and cellular events in the pathogenesis of cardiovascular diseases, including atherosclerosis, hypertension-induced target-organ damage, and abdominal aortic aneurysm. Angiotensin II (Ang-II) is the main effector peptide hormone of the renin-angiotensin system. Beyond its role as a potent vasoconstrictor and regulator of blood pressure and fluid homeostasis, Ang-II is intimately involved in the development of vascular lesions in cardiovascular diseases through the activation of different immune cells. The migration of leukocytes from circulation to the arterial subendothelial space is a crucial immune response in lesion development that is mediated through a sequential and coordinated cascade of leukocyte-endothelial cell adhesive interactions involving an array of cell adhesion molecules present on target leukocytes and endothelial cells and the generation and release of chemoattractants that activate and guide leukocytes to sites of emigration. In this review, we outline the key events of Ang-II participation in the leukocyte recruitment cascade, the underlying mechanisms implicated, and the corresponding redox-signaling pathways. We also address the use of inhibitor drugs targeting the effects of Ang-II in the context of leukocyte infiltration in these cardiovascular pathologies, and examine the clinical data supporting the relevance of blocking Ang-II-induced vascular inflammation.

Cysteinyl cathepsins in cardiovascular diseases

Cysteinyl cathepsins are lysosomal/endosomal proteases that mediate bulk protein degradation in these intracellular acidic compartments. Yet, studies indicate that these proteases also appear in the nucleus, nuclear membrane, cytosol, plasma membrane, and extracellular space. Patients with cardiovascular diseases (CVD) show increased levels of cathepsins in the heart, aorta, and plasma. Plasma cathepsins often serve as biomarkers or risk factors of CVD. In aortic diseases, such as atherosclerosis and abdominal aneurysms, cathepsins play pathogenic roles, but many of the same cathepsins are cardioprotective in hypertensive, hypertrophic, and infarcted hearts. During the development of CVD, cathepsins are regulated by inflammatory cytokines, growth factors, hypertensive stimuli, oxidative stress, and many others. Cathepsin activities in inflammatory molecule activation, immunity, cell migration, cholesterol metabolism, neovascularization, cell death, cell signaling, and tissue fibrosis all contribute to CVD and are reviewed in this article in memory of Dr. Nobuhiko Katunuma for his contribution to the field.

A Pilot Study of Protein Microarray for Simultaneous Analysis of 274 Cytokines Between Abdominal Aortic Aneurysm and Normal Aorta

Cytokines play an important role in the pathogenesis of abdominal aortic aneurysm (AAA). We evaluated the cytokine expression profile of large AAA walls using a 274-cytokine protein array. We hypothesized that AAAs are characterized by an inflammatory, chemotactic cytokine profile. We investigated the cytokine expression profile of 12 patients with AAA and 6 nonaneurysmal controls using an antibody-based protein array. The array generated antibodies against homogenized human aortic tissues to validate the cytokines differentially expressed in AAAs and normal aortas. Data were quantified using fluorescent signal intensities and statistically analyzed by the t test. Fifty-nine cytokines were differentially expressed between the AAA and control samples. Of the 35 selected cytokines that had relative expression >1000, 29 were significantly higher and 6 were lower in AAA samples than in controls. They respectively belonged to CC chemokines, CXC chemokines, pro-inflammatory cytokines, growth factors, proteolytic proteins and inhibitors, and cell adhesion cytokines. Our results show that distinct cytokines are involved in AAAs and suggest that the pathways involving these cytokines may be associated with the pathogenesis and development of AAAs. These findings, if confirmed by larger studies, may suggest treatment targets.

Role of Noncoding RNAs in the Pathogenesis of Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is a local dilatation of the abdominal aortic vessel wall and is among the most challenging cardiovascular diseases as without urgent surgical intervention, ruptured AAA has a mortality rate of >80%. Most patients present acutely after aneurysm rupture or dissection from a previously asymptomatic condition and are managed by either surgery or endovascular repair. Patients usually are old and have other concurrent diseases and conditions, such as diabetes mellitus, obesity, and hypercholesterolemia making surgical intervention more difficult. Collectively, these issues have driven the search for alternative methods of diagnosing, monitoring, and treating AAA using therapeutics and less invasive approaches. Noncoding RNAs-short noncoding RNAs (microRNAs) and long-noncoding RNAs-are emerging as new fundamental regulators of gene expression. Researchers and clinicians are aiming at targeting these microRNAs and long noncoding RNAs and exploit their potential as clinical biomarkers and new therapeutic targets for AAAs. While the role of miRNAs in AAA is established, studies on long-noncoding RNAs are only beginning to emerge, suggesting their important yet unexplored role in vascular physiology and disease. Here, we review the role of noncoding RNAs and their target genes focusing on their role in AAA. We also discuss the animal models used for mechanistic understanding of AAA. Furthermore, we discuss the potential role of microRNAs and long noncoding RNAs as clinical biomarkers and therapeutics.

Metabolomic profiling of ascending thoracic aortic aneurysms and dissections - Implications for pathophysiology and biomarker discovery

Objective

Our basic understanding of ascending thoracic aortic aneurysm (ATAA) pathogenesis is still very limited, hampering early diagnosis, risk prediction, and development of treatment options. “Omics”-technologies, ideal to reveal tissue alterations from the normal physiological state due to disease have hardly been applied in the field. Using a metabolomic approach, with this study the authors seek to define tissue differences between controls and various forms of ATAAs.

Methods

Using a targeted FIA-MS/MS metabolomics approach, we analysed and compared the metabolic profiles of ascending thoracic aortic wall tissue of age-matched controls (n = 8), bicuspid aortic valve-associated aneurysms (BAV-A; n = 9), tricuspid aortic valve-associated aneurysms (TAV-A; n = 14), and tricuspid aortic valve-associated aortic dissections (TAV-Diss; n = 6).

Results

With sphingomyelin (SM) (OH) C22:2, SM C18:1, SM C22:1, and SM C24:1 only 4 out of 92 detectable metabolites differed significantly between controls and BAV-A samples. Between controls and TAV-Diss samples only phosphatidylcholine (PC) ae C32:1 differed. Importantly, our analyses revealed a general increase in the amount of total sphingomyelin levels in BAV-A and TAV-Diss samples compared to controls.

Conclusions

Significantly increased levels of sphingomyelins in BAV-A and TAV-Diss samples compared to controls may argue for a repression of sphingomyelinase activity and the sphingomyelinase-ceramide pathway, which may result in an inhibition of tissue regeneration; a potential basis for disease initiation and progression.

The Role Matrix Metalloproteinases in the Production of Aortic Aneurysm

Matrix metalloproteinases (MMPs) have been implicated in the pathogenesis of aortic aneurysm because the histology of thoracic aortic aneurysm (TAA) and abdominal aortic aneurysm (AAA) is characterized by the loss of smooth muscle cells in the aortic media and the destruction of extracellular matrix (ECM). Furthermore, AAA have evidence of inflammation and the cellular elements involved in inflammation such as macrophages can produce and/or activate MMPs This chapter focuses on human aortic aneurysm that are not due to specific known genetic causes because this type of aneurysm is the more common type. This chapter will also focus on MMP protein expression rather than on genetic data which may not necessarily translate to increased MMP protein expression. There are supporting data that certain MMPs are increased in the aortic wall. For TAA, it is most notably MMP-1, -9, -12, and -14 and MMP-2 when a bicuspid aortic valve is present. For AAA, it is MMP-1, -2, -3, -9, -12, and -13. The data are weaker or insufficient for the other MMPs. Several studies of gene polymorphisms support MMP-9 for TAA and MMP-3 for AAA as potentially important factors. The signaling pathways in the aorta that can lead to MMP activation include JNK, JAK/stat, osteopontin, and AMP-activated protein kinase alpha2. Substrates in the human vasculature for MMP-3, MMP-9, or MMP-14 include collagen, elastin, ECM glycoprotein, and proteoglycans. Confirmed and potential substrates for MMPs, maintain aortic size and function so that a reduction in their content relative to other components of the aortic wall may produce a failure to maintain aortic size leading to dilatation and aneurysm formation.

Matrix Metalloproteinases in the Aneurysm Wall of Patients Treated with Low-Dose Doxycycline

The purpose of this study was to determine the effect of low-dose doxycycline on matrix metalloproteinase (MMP) and tissue inhibitor of metalloproteinase (TIMP)-1 expression in the wall of abdominal aortic aneurysms.

A double-blind, randomized study was conducted of patients treated with doxycycline (100 mg/d orally) or placebo for 1 month prior to surgery. MMP-2, -3, and -9 (zymogen and activity); MMP-1, -2, -3, -7, -9, -11, -12, and -14; and TIMP-1 (messenger ribonucleic acid [mRNA]) were measured in the aneurysm wall.

No differences were found between the treatment and placebo groups in zymogen levels of MMP-2, -3, or -9 or in the free or total activities of MMP-2 and -9. Treatment with doxycycline also had no effect on the concentration of any mRNA measured. No relationship was found between the number of tablets taken and MMP or TIMP protein, mRNA, or activity levels in the aneurysm wall.

Low-dose doxycycline treatment does not alter the expression or activity of metalloproteinases or their inhibitor, TIMP-1, in the aneurysm wall.

Cytochrome P450 1B1 Contributes to the Development of Angiotensin II-Induced Aortic Aneurysm in Male Apoe(-/-) Mice

Cytochrome P450 (CYP) 1B1 is implicated in vascular smooth muscle cell migration, proliferation, and hypertension. We assessed the contribution of CYP1B1 to angiotensin (Ang) II-induced abdominal aortic aneurysm (AAA). Male Apoe(-/-)/Cyp1b1(+/+) and Apoe(-/-)/Cyp1b1(-/-) mice were infused with Ang II or its vehicle for 4 weeks; another group of Apoe(-/-)/Cyp1b1(+/+) mice was coadministered the CYP1B1 inhibitor 2,3',4,5'-tetramethoxystilbene (TMS) every third day for 4 weeks. On day 28 of Ang II infusion, AAAs were analyzed by ultrasound and ex vivo by Vernier calipers, mice were euthanized, and tissues were harvested. Ang II produced AAAs in Apoe(-/-)/Cyp1b1(+/+) mice; mice treated with TMS or Apoe(-/-)/Cyp1b1(-/-) mice had reduced AAAs. Ang II enhanced infiltration of macrophages, T cells, and platelets and increased platelet-derived growth factor D, Pdgfrb, Itga2, and matrix metalloproteinases 2 and 9 expression in aortic lesions; these changes were inhibited in mice treated with TMS and in Apoe(-/-)/Cyp1b1(-/-) mice. Oxidative stress resulted in cyclooxygenase-2 expression in aortic lesions. These effects were minimized in Apoe(-/-)/Cyp1b1(+/+) mice treated with TMS and in Apoe(-/-)/Cyp1b1(-/-) mice and by concurrent treatment with the superoxide scavenger 4-hydroxyl-2,2,6,6-tetramethylpiperidine-1-oxyl. CYP1B1 contributed to the development of Ang II-induced AAA and associated pathogenic events in mice, likely by enhancing oxidative stress and associated signaling events. Thus, CYP1B1 may serve as a target for therapeutic agents for AAA in males.

Increased Expression of Lamin A/C Correlate with Regions of High Wall Stress in Abdominal Aortic Aneurysms

BACKGROUND

Since aortic diameter is the most -significant risk factor for rupture, we sought to identify stress-dependent changes in gene expression to illuminate novel molecular processes in aneurysm rupture.

MATERIALS AND METHODS

We constructed finite element maps of abdominal computerized tomography scans (CTs) of seven abdominal aortic aneurysm (AAA) patients to map wall stress. Paired biopsies from high- and low-stress areas were collected at surgery using vascular landmarks as coordinates. Differential gene expression was evaluated by Illumina Array analysis, using the whole genome DNA-mediated, annealing, selection, extension, and ligation (DASL) gene chip (n = 3 paired samples).

RESULTS

The sole significant candidate from this analysis, Lamin A/C, was validated at the protein level, using western blotting. Lamin A/C expression in the inferior mesenteric vein (IMV) of AAA patients was compared to a control group and in aortic smooth muscle cells in culture in response to physiological pulsatile stretch. -Areas of high wall stress (n = 7) correlate to those -regions which have the thinnest walls [778 µm (585-1120 µm)] in comparison to areas of lowest wall stress [1620 µm (962-2919 µm)]. Induced expression of Lamin A/C -correlated with areas of high wall stress from AAAs but was not significantly induced in the IMV from AAA patients compared to controls (n = 16). Stress-induced expression of Lamin A/C was mimicked by exposing aortic smooth muscle cells to prolonged pulsatile stretch.

CONCLUSION

Lamin A/C protein is specifically increased in areas of high wall stress in AAA from patients, but is not increased on other vascular beds of aneurysm patients, suggesting that its elevation may be a compensatory response to the pathobiology leading to aneurysms.

Microarray-based Gene Expression Profiling of Abdominal Aortic Aneurysm

OBJECTIVE/BACKGROUND

Microarray-based gene expression profiling studies may detect transcriptional signatures carrying prognostic value in abdominal aortic aneurysms (AAA). A gene expression profiling study was conducted to compare individuals with AAA with screened controls.

METHODS

The peripheral blood transcriptome was compared between 12 individuals with AAA and 12 age- and sex-matched controls using microarray. Validation by Taqman real-time quantitative (qPCR) was performed in an independent group as described. Peripheral blood RNA was hybridized to Illumina microarrays, each representing 37,846 genes, allowing comparison of gene expression between cases and controls. Eleven differentially expressed genes were re-quantified by qPCR in the independent group with AAA (n = 95), controls (n = 92), pre- and postendovascular AAA repair (EVAR, n = 31); or open AAA repair (n = 13), AAA wall biopsies (n = 11), and in matched smooth muscle cultures (n = 7).

RESULTS

Microarray detected 47 significantly differentially expressed genes in AAA after correction for multiple testing (p < .05). These genes conferred roles in regulation of apoptosis, proteolysis, the electron transport chain, leukocyte migration, and the humoral immune response. Gene quantification in the independent group demonstrated three genes to be downregulated in AAA compared with controls: MSN, PSMB10, and STIM1; however, their expression remained unchanged post-AAA repair. PSMB10 was the only gene conferring a consistent direction of effect in both the discovery and validation analyses (downregulated). EIF3G, SIVA, PUF60, CYC1, FIBP, and CARD8 were downregulated post-EVAR. Expression of all 11 genes of interest was detected in aortic biopsies and matched smooth muscle cultures.

CONCLUSION

This study demonstrates differential expression of transcripts in peripheral blood of individuals with AAA, with functional roles in proteolysis, inflammation, and apoptotic processes. These were modulated by aneurysm exclusion from the circulation and expressed in matched aortic biopsies and smooth muscle cultures. These observations further support the key roles for these pathways in the pathogenesis of AAA.

Two C-C Family Chemokines, Eotaxin and RANTES, Are Novel Independent Plasma Biomarkers for Abdominal Aortic Aneurysm

BACKGROUND

Inflammation of the aortic wall is recognised as a key pathogenesis of abdominal aortic aneurysm (AAA). This study was undertaken to determine whether inflammatory cytokines could be used as biomarkers for the presence of AAA.

METHODS AND RESULTS

Tissue profiles of 27 inflammatory cytokine were examined in AAA (n=14) and nonaneurysmal (n=14) aortic tissues. Three cytokines, regulated upon activation normally T-cell expressed and secreted (RANTES), eotaxin, and macrophage inflammatory protein 1 beta (MIP-1b), had increased expression in AAA, particularly within the adventitial layer of the aortic wall. Basic fibroblast growth factor (bFGF) had reduced expression in all layers of the AAA wall. Examination of the circulating plasma profiles of AAA (n=442) and AAA-free controls (n=970) suggested a (risk factor adjusted) AAA-association with eotaxin, RANTES, and high sensitivity C-reactive protein (hsCRP). A plasma inflammatory cytokine score, calculated using these three markers, suggested a strong risk association with AAA (odds ratio, 4.8; 95% CI, 3.5-6.7; P<0.0001), independent of age, sex, history of ischemic heart disease, and smoking.

CONCLUSIONS

Contrary to reports suggesting a distinct T helper 2-associated inflammatory profile in AAA, this current study suggests a more-generalized pattern of inflammation, albeit with some potentially distinct features, including elevated plasma eotaxin and decreased plasma RANTES. In combination with hsCRP, these markers may have potential utility as AAA biomarkers.

Identification of key genes associated with the human abdominal aortic aneurysm based on the gene expression profile

The present study was aimed at screening the key genes associated with abdominal aortic aneurysm (AAA) in the neck, and to investigate the molecular mechanism underlying the development of AAA. The gene expression profile, GSE47472, including 14 AAA neck samples and eight donor controls, was downloaded from the Gene Expression Omnibus database. The total AAA samples were grouped into two types to avoid bias. Differentially expressed genes (DEGs) were screened in patients with AAA and subsequently compared with donor controls using linear models for microarray data, or the Limma package in R, followed by gene ontology enrichment analysis. Furthermore, a protein-protein interaction (PPI) network based on the DEGs was constructed to detect highly connected regions using a Cytoscape plugin. In total, 388 DEGs in the AAA samples were identified. These DEGs were predominantly associated with limb development, including embryonic limb development and appendage development. Nuclear receptor co-repressor 1 (NCOR1), histone 4 (H4), E2F transcription factor 4 (E2F4) and hepatocyte nuclear factor 4α (HNF4A) were the four transcription factors associated with AAA. Furthermore, HNF4A indirectly interacted with the other three transcription factors. Additionally, six clusters were selected from the PPI network. The DEG screening process and the construction of an interaction network enabled an understanding of the mechanism of AAA to be gleaned. HNF4A may exert an important role in AAA development through its interactions with the three other transcription factors (E2F4, NCOR1 and H4), and the mechanism of this coordinated regulation of the transcription factors in AAA may provide a suitable target for the development of therapeutic intervention strategies.

Rule out of acute aortic dissection with plasma matrix metalloproteinase 8 in the emergency department

Introduction

Matrix metalloproteinases (MMPs) are involved in aortic pathophysiology. Preliminary studies have detected increased plasma levels of MMP8 and MMP9 in patients with acute aortic dissection (AAD). However, the performance of plasma MMP8 and MMP9 for the diagnosis of AAD in the emergency department is at present unknown.

Methods

The levels of MMP8 and MMP9 were measured by ELISA on plasma samples obtained from 126 consecutive patients evaluated in the emergency department for suspected AAD. All patients were subjected to urgent computed tomography (CT) scan for final diagnosis.

Results

In the study cohort (N = 126), AAD was diagnosed in 52 patients and ruled out in 74 patients. Median plasma MMP8 levels were 36.4 (interquartile range 24.8 to 69.3) ng/ml in patients with AAD and 13.2 (8.1 to 31.8) ng/ml in patients receiving an alternative final diagnosis (P <0.0001). Median plasma MMP9 levels were 169.2 (93.0 to 261.8) ng/ml in patients with AAD and 80.5 (41.8 to 140.6) ng/ml in patients receiving an alternative final diagnosis (P = 0.001). The area under the curve (AUC) on receiver-operating characteristic (ROC) analysis of MMP8 and MMP9 for the diagnosis of AAD was respectively 0.75 and 0.70, as compared to 0.87 of D-dimer. At the cutoff of 3.6 ng/ml, plasma MMP8 had a sensitivity of 100.0% (95% CI, 93.2% to 100.0%) and a specificity of 9.5% (95% CI, 3.9% to 18.5%) and ruled out AAD in 5.6% of patients. Combination of plasma MMP8 with D-dimer increased the AUC on ROC analysis to 0.89. Presence of MMP8 <11.0 ng/ml and D-dimer <1.0 or <2.0 µg/ml provided a negative predictive value of 100% and ruled out AAD in 13.6% and 21.4% of patients respectively.

Conclusions

Low levels of plasma MMP8 can rule out AAD in a minority of patients. Combination of plasma MMP8 and D-dimer at individually suboptimal cutoffs could safely rule out AAD in a substantial proportion of patients evaluated in the emergency department.

Profile of macrophages in human abdominal aortic aneurysms: a transcriptomic, proteomic, and antibody protein array study

Abdominal aortic aneurysms (AAA) are defined by an increased aortic diameter and characterized by impairment of the extracellular matrix, macrophages infiltration and decreased density of smooth muscle cells. Our aim is to identify the key molecules involved in the pathogenesis of AAAs. This study investigated transcriptomic and proteomic profiles of macrophages from AAA patients (>50 mm aortic diameter) (n = 24) and peripheral arterial occlusion (PAO) patients without AAA detected (n = 18), who both needed a surgery. An antibody protein microarray, generated by printing antibodies onto membranes against proteins selected from the transcriptomic and proteomic analysis, was performed to validate the proteins differentially expressed specifically in macrophages and plasma from the same patients. We found a restricted number of proteins differentially expressed between AAA and PAO patients: TIMP-3, ADAMTS5, and ADAMTS8 that differ significantly in plasma of AAA patients compared to PAO patients, as found in the macrophages. In contrast to plasma MMP-9, soluble glycoprotein V (sGPV) and plasmin-antiplasmin complex levels, plasma TIMP-3 levels were not correlated to AAA size but interestingly correlated to sGPV, a platelet activation marker. Combining transcriptomic and proteomic is a valid approach to identify diseases causing proteins and potential biomarkers.

Spontaneous arterial dissection: phenotype and molecular pathogenesis

Arterial dissection (AD) is defined as the longitudinal splitting up of the arterial wall caused by intramural bleeding. It can occur as a spontaneous event in all large and medium sized arteries. The histological hallmark of AD is medial degeneration. Histological investigations, gene expression profiling and proteome studies of affected arteries reveal disturbances in many different biological processes including inflammation, proteolytic activity, cell proliferation, apoptosis and smooth muscle cell (SMC) contractile function. Medial degeneration can be caused by various rare dominant Mendelian disorders. Genetic linkage analysis lead to the identification of mutations in different disease-causing genes involved in the biosynthesis of the extracellular matrix (FBN1, COL3A1), in transforming growth factor (TGF) beta signaling (FBN1, TGFBR1, TGFBR2) and in the SMC contractile system (ACTA2, MYH11). Genome wide association studies suggest that the CDKN2A/CDKN2B locus plays a role in the etiology AD and other arterial diseases.

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

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

Whole genome expression analysis within the angiotensin II-apolipoprotein E deficient mouse model of abdominal aortic aneurysm

BACKGROUND

An animal model commonly used to investigate pathways and potential therapeutic interventions relevant to abdominal aortic aneurysm (AAA) involves subcutaneous infusion of angiotensin II within the apolipoprotein E deficient mouse. The aim of this study was to investigate genes differentially expressed in aneurysms forming within this mouse model in order to assess the relevance of this model to human AAA.

RESULTS

Using microarrays we identified genes relevant to aneurysm formation within apolipoprotein E deficient mice. Firstly we investigated genes differentially expressed in the aneurysm prone segment of the suprarenal aorta in these mice. Secondly we investigated genes that were differentially expressed in the aortas of mice developing aneurysms relative to those that did not develop aneurysms in response to angiotensin II infusion. Our findings suggest that a host of inflammation and extracellular matrix remodelling pathways are upregulated within the aorta in mice developing aneurysms. Kyoto Encyclopedia of Genes and Genome categories enriched in the aortas of mice with aneurysms included cytokine-cytokine receptor interaction, leukocyte transendothelial migration, natural killer cell mediated cytotoxicity and hematopoietic cell lineage. Genes associated with extracellular matrix remodelling, such as a range of matrix metalloproteinases were also differentially expressed in relation to aneurysm formation.

CONCLUSION

This study is the first report describing whole genome expression arrays in the apolipoprotein E deficient mice in relation to aneurysm formation. The findings suggest that the pathways believed to be critical in human AAA are also relevant to aneurysm formation in this mouse model. The findings therefore support the value of this model to investigate interventions and mechanisms of human AAA.

Whole genome-expression profiling reveals a role for immune and inflammatory response in abdominal aortic aneurysm rupture

OBJECTIVES

This study used the whole transcriptome approach to investigate the role of genes involved in immune and inflammatory response at the site of aneurysm rupture.

MATERIALS AND METHODS

Rupture site and paired anterior sac biopsies (internal control) of ruptured abdominal aortic aneurysms (AAAs) (n=10) were analysed with Affymetrix Human Genome U133A plus 2.0 microarray. Twenty-one differentially expressed genes were selected for validation using quantitative reverse transcriptase polymerase chain reaction (QRT-PCR).

RESULTS

A total of 139 genes (123 upregulated, 16 downregulated) at the aneurysm rupture site were differentially expressed (>2.5-fold, P<0.005). Immune and inflammatory responses (Gene Ontology Classification) were frequently associated with the differentially expressed genes. Genes with immune and inflammatory functions that were confirmed, by QRT-PCR, to be overexpressed at the aneurysm rupture site were interleukins-6 and -8 (IL-6 and -8), Selectin E (SELE), prostaglandin-endoperoxidase synthase 2 (COX2) and prokineticin 2 (PROK2). IL-6 (pro-immune) and IL-8 (pro-immune and pro-inflammatory) have previously been linked to aneurysm rupture; and SELE and COX2 (pro-inflammatory) have previous associations with aneurysm development but not rupture.

CONCLUSIONS

The differential expression of genes involved in immune and inflammatory responses was confirmed at AAA rupture site. These genes may represent novel targets for treatment of aneurysms.

Gene expression analysis of a porcine native abdominal aortic aneurysm model

INTRODUCTION

We sought to characterize the gene expression patterns occurring during the development of aneurysms in the native porcine aorta.

METHODS

In Yorkshire swine, the infrarenal aorta was balloon dilated and infused with a solution of type I collagenase/pancreatic porcine elastase (16,000 U/1,000 U). Aneurysmal and control aortic samples were obtained at 1 (n = 3), 2 (n = 6), and 4 (n = 5) weeks following aneurysm induction. RNA was isolated, converted to biotin-modified antisense RNA and hybridized to porcine genome arrays. Aneurysmal and control gene intensities were compared using the 2-sample-for-means z-test. P < .01 was considered statistically significant.

RESULTS

Extracellular matrix remodeling genes that were upregulated in aneurysmal compared with control tissue included matrix metalloproteinase-1, -2, -3, and -9; MT-MMP; cathepsin-D, -H, -K, and -S; tissue inhibitor of metalloproteinase-1; and collagen I-alpha1 chain (P < .01). Elastin exhibited temporally downregulated gene expression (P < .01). Inflammatory genes that were upregulated included intercellular adhesion molecule-2, tumor necrosis factor-alpha, interleukin (IL)-1 beta, IL-10, chemokine receptor-4, and tissue plasminogen activator (P < .01). Atherosclerosis and cancer genes that were upregulated included apolipoprotein E, acyl-CoA binding protein, friend leukemia virus integration-1, and E26 transformation-specific sequence (P < .01).

CONCLUSION

The porcine model replicates the gene expression patterns that are observed during the development of aneurysms in human studies as well as in rodent models. The porcine model thereby represents a novel method to study the impact of endovascular, cell-based, and other therapeutic interventions on AAA pathophysiology.

Cysteine protease activity in the wall of abdominal aortic aneurysms

BACKGROUND

Cysteine proteases are potent elastolytic enzymes and together with their inhibitor, cystatin C, have been linked with the growth of abdominal aortic aneurysms (AAAs). These enzymes and their inhibitors have previously been studied in AAAs, but comparisons have always been made with wall from normal aorta. Atherosclerosis is a feature of aneurysmal disease and may therefore confound comparisons with normal wall. This study compared the expression and activity of cysteine proteases and their inhibitors in aneurysm wall with their expression in the aortic wall of patients with aortic occlusive disease (AOD).

METHODS

Aortic wall was obtained from 82 patients with AAA and 13 with AOD. Protein expression and activity of cathepsin B, H, K, L and S, and cystatins A, B, and C were measured by enzyme-linked immunosorbent assay and specific fluorogenic substrate assays. Matrix metalloproteinase 9 (MMP-9) activity was measured by quantitative bioimmunoassay in the same extracts.

RESULTS

AAA wall had 330% more cathepsin H protein (P = .007) and >30% less cystatin C (P = .03) than the aortic wall from patients with AOD. The activity of cathepsins B, H, L, and S was significantly greater in AAA than AOD (376%, [P < .0001], 191%, [P = 0.019], 223%, P = 0.002, and approximately 20% [P = 0.045] respectively). MMP-9 activity was also increased in AAA compared with AOD (P<0.0001) and levels in the wall of AAA correlated positively with cathepsin L activity (r = 0.42, P<.0001) and negatively with cystatin C (r = -0.75, P<.0001).

CONCLUSIONS

The activity of four cathepsins B, H, L, and S was higher in the aneurysm wall than in aortic wall of patients with occlusive disease. This was associated with a reduced level of cystatin C in the aneurysmal wall. Cathepsin H was the only protein in which there was a correlation between protein level and activity, which suggests that post-translational modifications were responsible for activation of the other cathepsins. Increased cathepsin activity may influence the activity of MMP-9, which is thought to have an important role in aneurysm development.

Preservation of Rabbit Aorta Elastin From Degradation by Gingival Fibroblasts in an Ex Vivo Model

Objective— Embryo-like gingival healing properties are attributed to the gingival fibroblast (GF) and could be used as a model for other types of healing dysfunctions. Abdominal aortic aneurysm (AAA) formation is associated with elastin degradation and increase in matrix metalloproteinase (MMP)-9 activity. We aimed to validate the concept of using GF healing properties in arteries.

Methods and Results— We evaluated MMP-9 and its tissue inhibitor (TIMP-1) in rabbit aortic rings cultured in collagen gels with or without GFs and observed throughout 21 days. We also performed cocultures of human smooth muscle cells (hSMCs) with either gingival, dermal, or adventitial fibroblasts, and alone (control). In control arteries, elastic fibers became spontaneously sparse. In presence of GFs, elastic fibers were preserved. There was a dramatically reduced protein level of MMP-9 in coculture of aorta and GFs, in contrast with control aorta. MMP-9 expression was unaffected by GFs. MMP-9 inhibition was related to increased TIMP-1 secretion, TIMP-1 forming a complex with MMP-9. Cell cocultures of hSMC with GFs showed similar results. Dermal and adventitial fibroblasts did not affect MMP-9.

Conclusions— Elastic fiber degradation was specifically preserved by GFs via reduction of MMP-9 protein level by increasing TIMP-1 synthesis. Vascular transfer of gingival fibroblasts could be a promising approach to treat AAA.

Whole genome expression profiling reveals a significant role for immune function in human abdominal aortic aneurysms

BACKGROUND

Abdominal aortic aneurysms are a common disorder with an incompletely understood etiology. We used Illumina and Affymetrix microarray platforms to generate global gene expression profiles for both aneurysmal (AAA) and non-aneurysmal abdominal aorta, and identified genes that were significantly differentially expressed between cases and controls.

RESULTS

Affymetrix and Illumina arrays included 18,057 genes in common; 11,542 (64%) of these genes were considered to be expressed in either aneurysmal or normal abdominal aorta. There were 3,274 differentially expressed genes with a false discovery rate (FDR) </= 0.05. Many of these genes were not previously known to be involved in AAA, including SOST and RUNX3, which were confirmed using Q-RT-PCR (Pearson correlation coefficient for microarray and Q-RT-PCR data = 0.89; p-values for differences in expression between AAA and controls for SOST: 4.87 x 10-4 and for RUNX3: 4.33 x 10-5). Analysis of biological pathways, including Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG), indicated extreme overrepresentation of immune related categories. The enriched categories included the GO category Immune Response (GO:0006955; FDR = 2.1 x 10-14), and the KEGG pathways natural killer cell mediated cytotoxicity (hsa04650; FDR = 5.9 x 10-6) and leukocyte transendothelial migration (hsa04670; FDR = 1.1 x 10-5).

CONCLUSION

Previous studies have provided evidence for the involvement of the immune system in AAA. The current expression analysis extends these findings by demonstrating broad coordinate gene expression in immunological pathways. A large number of genes involved in immune function were differentially expressed in AAA, and the pathway analysis gave these results a biological context. The data provide valuable insight for future studies to dissect the pathogenesis of human AAA. These pathways might also be used as targets for the development of therapeutic agents for AAA.

MF-tricyclic inhibits growth of experimental abdominal aortic aneurysms

BACKGROUND

Experimental abdominal aortic aneurysm (AAA) development can be pharmacologically suppressed by inhibiting matrix metalloproteinase-9 (MMP-9). Cyclooxygenase-2 (COX-2) inhibitors are potent anti-inflammatory agents that have been demonstrated to inhibit experimental aneurysm development. We hypothesized that treatment with MF-tricyclic, a selective COX-2 inhibitor, incorporated into rodent chow would inhibit aneurysm development in a rat AAA model.

METHODS

Twelve male Sprague Dawley rats underwent induction of experimental AAA using intra-aortic porcine elastase infusion. Six rats received control feed, and six received MF-tricyclic rodent chow for a period of 14 days. Aortic diameters were measured pre- and postinfusion as well as at harvest. Aortic tissue samples were evaluated by real-time polymerase chain reaction (RT-PCR) for MMP-9, by immunohistochemistry for elastin.

RESULTS

Elastase infusion produced AAA in all untreated rats. At 14 days MF-tricyclic-treated rats had significantly reduced aortic diameter (1.9 +/- 0.1 mm versus 2.4 +/- 0.0 mm, P = 0.00001). Percent increase in aortic diameter was also significantly less in animals receiving MF-tricyclic (65.7 +/- 8.5% versus 132.3 +/- 7.3%, P = 0.0001). RT-PCR demonstrated a decrease in the mean expression of MMP-9 in the treated animals (0.414 ng of RNA versus 1.114 ng of RNA) (P = 0.07). Sections stained for elastin demonstrated preserved elastin integrity in MF-tricyclic treated aortas.

CONCLUSIONS

COX-2 inhibition helps to retard the growth of experimental AAAs possibly through inhibition of MMP-9. Experimentally treated animals demonstrated smaller aortic diameters and lower levels of tissue MMP-9 when compared to untreated animals. Selective COX-2 inhibition may offer an additional method to pharmacologically inhibit AAAs.

Turning back the clock: regression of abdominal aortic aneurysms via pharmacotherapy

Abdominal aortic aneurysm (AAA) is a common disease that causes progressive expansion and rupture of the aorta with high mortality. There is a large and unmet need for nonsurgical treatment for AAA. Research has shown that an intricate network of inflammatory cells and interstitial cells contributes to the formation of AAA by producing pro-inflammatory mediators that activate enzymes to degrade the extracellular matrix (ECM) and impair ECM biosynthesis. Pharmacological agents such as statins and angiotensin-converting enzyme inhibitors may promote tissue stabilization in AAA by diminishing pro-inflammatory signaling and normalizing metabolism of the ECM. Our recent experiments in animal models demonstrate that inhibition of c-Jun N terminal kinase (JNK) inhibits multiple pathological processes and causes regression of established AAA. Thus, emerging evidence indicates that pharmacological intervention targeting pro-inflammatory signaling and abnormal ECM metabolism is a promising strategy for treatment of AAA.

Cathepsin cysteine proteases in cardiovascular disease

Extracellular matrix (ECM) remodeling is one of the underlying mechanisms in cardiovascular diseases. Cathepsin cysteine proteases have a central role in ECM remodeling and have been implicated in the development and progression of cardiovascular diseases. Cathepsins also show differential expression in various stages of atherosclerosis, and in vivo knockout studies revealed that deficiency of cathepsin K or S reduces atherosclerosis. Furthermore, cathepsins are involved in lipid metabolism. Cathepsins have the capability to degrade low-density lipoprotein and reduce cholesterol efflux from macrophages, aggravating foam cell formation. Although expression studies also demonstrated differential expression of cathepsins in cardiovascular diseases like aneurysm formation, neointima formation, and neovascularization, in vivo studies to define the exact role of cathepsins in these processes are lacking. Evaluation of the feasibility of cathepsins as a diagnostic tool revealed that serum levels of cathepsins L and S seem to be promising as biomarkers in the diagnosis of atherosclerosis, whereas cathepsin B shows potential as an imaging tool. Furthermore, cathepsin K and S inhibitors showed effectiveness in (pre) clinical evaluation for the treatment of osteoporosis and osteoarthritis, suggesting that cathepsin inhibitors may also have therapeutic effects for the treatment of atherosclerosis.

The pro-inflammatory and chemotactic cytokine microenvironment of the abdominal aortic aneurysm wall: A protein array study

OBJECTIVE

Cytokines are inflammatory mediators implicated in abdominal aortic aneurysm (AAA) pathogenesis. The cytokine expression profile of the AAA is poorly defined and has focused on the expression of pro-inflammatory cytokines, at the expense of chemokines and growth factors. This study aims to investigate the cytokine expression profile of the established AAA wall.

METHODS

Cytokine protein expression was measured in homogenized human aortic tissue (10 AAAs and 9 nonaneurysmal controls) using a 42-cytokine antibody-based protein array. Data were quantified using densitometric analysis and statistically analyzed using a Mann-Whitney U test.

RESULTS

A significant difference in cytokine expression between AAA and control samples was found in 15 of 42 cytokines. Several pro-inflammatory cytokines were upregulated within the AAA compared with the control: interleukin (IL)-6 (P = .001), IL-1alpha (P = .001), IL-1beta (P < .001), tumor necrosis factor (TNF)-alpha (P = .002), TNF-beta (P = .002), and oncostatin M (P = .007). The anti-inflammatory cytokine IL-10 was also upregulated (P = .002). Members of the chemokine family were also highly expressed within AAA samples: IL-8 (P = .001), epithelial neutrophil-activating peptide-78 (ENA-78; P = .006), growth related oncogene (GRO; P < .001), monocyte chemoattractant protein (MCP)-1 (P = .003), MCP-2 (P < .001), and regulated upon activation, normal T-cell expressed and secreted (RANTES; P = .001). Of the growth factors examined, granulocyte colony-stimulating factor (GCSF; P = .003) and macrophage colony-stimulating factor (MCSF; P = .004) were significantly higher in the AAA.

CONCLUSIONS

The established AAA is characterized by a distinct cytokine profile consisting of pro-inflammatory cytokines, chemokines, and specific growth factors. This suggests that these cytokines may contribute to pathologic changes within the established, preruptured aneurysm.

Abdominal aortic aneurysm: pathogenesis and implications for management

Abdominal aortic aneurysm (AAA) affects approximately 5% of elderly men and is responsible for a significant number of deaths in Western Countries. At present surgery by open or endovascular means is the only widely used therapy for this condition. In this review we examine the risk factors, serum, and genetic associations of AAA. Epidemiology studies suggest that smoking cessation and control of cholesterol and blood pressure should reduce the number of patients developing AAA. Natural history studies suggest that smoking cessation should reduce the rate of progression of AAA. Clear level 1 evidence for drug treatments of AAA are presently lacking; however, animal and human in vitro studies suggest that medication targeted at reducing inflammation and proteolysis are most likely to be beneficial, with limited data to support the use of statins, Angiotensin II inhibitors, and macrolides. Work has commenced in understanding which patients, identified by clinical, serum, and genotype, are more at risk of AAA progression and thus should be selected out for aggressive treatment. Well designed large multicenter randomized controlled trials are required to examine the medical treatment of AAA.

Temporal changes in mouse aortic wall gene expression during the development of elastase-induced abdominal aortic aneurysms

OBJECTIVE

To characterize temporal changes in mouse aortic wall gene expression associated with the development of experimental abdominal aortic aneurysms.

METHODS

C57BL/6 mice underwent transient perfusion of the abdominal aorta with either elastase (n = 61) or heat-inactivated elastase as a control (n = 68). Triplicate samples of radiolabeled aortic wall complementary DNA were prepared at intervals of 0, 3, 7, 10, and 14 days, followed by hybridization to nylon microarrays (1181 genes). Autoradiographic intensity data were normalized by conversion to z scores, and differences in gene expression were defined by two-tailed z tests at a significance threshold of P < .01.

RESULTS

Elastase perfusion caused a progressive increase in aortic diameter up to 14 days accompanied by transmural inflammation and destructive remodeling of the elastic media. No aneurysms occurred in the control group. Compared with healthy aorta, 336 genes exhibited significant alterations during at least 1 interval after elastase perfusion (135 at more than 1 interval and 14 at all intervals), with pronounced increases for interleukin 6, cyclin E2, interleukin 1beta, osteopontin, CD14/lipopolysaccharide receptor, P-selectin glycoprotein ligand 1, and gelatinase B/matrix metalloproteinase 9 (all >20-fold on day 3). Sixty-two genes exhibited synchronous alterations in the elastase and control groups, thus suggesting a nonspecific response. By direct comparisons between the elastase and control groups, there were 384 genes with significant differences in expression for at least 1 interval after aortic perfusion, including 234 with differential upregulation (eg, p44MAPK/ERK1, osteopontin, heat shock protein 84, hypoxia-inducible factor 1alpha, apolipoprotein E, monocyte chemotactic protein 3, MIG (monokine induced by gamma interferon), and interleukin 2 receptor gamma) and 163 with differential downregulation (eg, prothrombin, granzyme B, ataxia telangiectasia mutated, and interleukin-converting enzyme).

CONCLUSIONS

Development of elastase-induced abdominal aortic aneurysms in mice is accompanied by altered aortic wall expression of genes associated with acute and chronic inflammation, matrix degradation, and vascular tissue remodeling. Knowledge of these alterations will facilitate further studies on the functional molecular mechanisms that underlie aneurysmal degeneration.

An overview of matrix metalloproteinases in the pathogenesis and treatment of abdominal aortic aneurysms

Recent basic and clinical research has established a link between the pathogenesis of abdominal aortic aneurysms (AAA) and matrix metalloproteinases (MMP). The discovery of the influence of MMPs on in vitro and in vivo aneurysm development has yielded promising information that may eventually decode the pathogenetic factors affecting the initiation and growth rate of AAAs. In this review, an analysis of MMPs involved in AAA disease is presented, including the data from recent research studies and planned clinical drug trails designed to retard the AAA growth by inhibiting MMP activity.

Disruption of the cathepsin K gene reduces atherosclerosis progression and induces plaque fibrosis but accelerates macrophage foam cell formation

BACKGROUND

Cathepsin K (catK), a lysosomal cysteine protease, was identified in a gene-profiling experiment that compared human early plaques, advanced stable plaques, and advanced atherosclerotic plaques containing a thrombus, where it was highly upregulated in advanced stable plaques.

METHODS AND RESULTS

To assess the function of catK in atherosclerosis, catK(-/-)/apolipoprotein (apo) E(-/-) mice were generated. At 26 weeks of age, plaque area in the catK(-/-)/apoE(-/-) mice was reduced (41.8%) owing to a decrease in the number of advanced lesions as well as a decrease in individual advanced plaque area. This suggests an important role for catK in atherosclerosis progression. Advanced plaques of catK(-/-)/apoE(-/-) mice showed an increase in collagen content. Medial elastin fibers were less prone to rupture than those of apoE(-/-) mice. Although the relative macrophage content did not differ, individual macrophage size increased. In vitro studies of bone marrow derived-macrophages confirmed this observation. Scavenger receptor-mediated uptake (particularly by CD36) of modified LDL increased in the absence of catK, resulting in an increased macrophage size because of increased cellular storage of cholesterol esters, thereby enlarging the lysosomes.

CONCLUSIONS

A deficiency of catK reduces plaque progression and induces plaque fibrosis but aggravates macrophage foam cell formation in atherosclerosis.

Factors Associated with Development of Large Abdominal Aortic Aneurysm in Middle-aged Men

OBJECTIVES

To investigate whether any variables in a health-screened population study were associated with later development of large abdominal aortic aneurysms (AAA).

SETTING

Malmö, Southern Sweden.

MATERIAL AND METHODS

Within the Malmö Preventive Study 22,444 men and 10,982 women were investigated between 1974 and 1991. The mean age at the health screening was 43.7 years.

RESULTS

After a median follow-up of 21 years, 126 men and six women (p<0.001) had large AAA that were symptomatic or evaluated for operation (5 cm diameter or more) or had autopsy-verified ruptured AAA. The male group (mean age 47 years) was, because of difference in age (p<0.001) also compared with an age-matched control group. The male patients with AAA showed increased diastolic blood pressure (p<0.007) at the health screening. Smoking predicted the development of AAA (p<0.0001). No difference in forced vital capacity or BMI was seen. Those who were physically inactive (e.g. not walking or cycling to work) had an increased risk of developing AAA (p<0.001). Among the laboratory markers measured, the erythrocyte sedimentation rate did not differ (7.1+/-5.9 vs. 6.4+/-5.7), but cholesterol (6.3+/-1.12 vs. 5.8+/-1.0) (p<0.0001) and triglycerides (1.9+/-0.12 vs. 1.5+/-0.07) (p<0.001) were significantly elevated in these individuals who subsequently developing AAA. The inflammatory proteins alfa-1-antitrypsin, ceruloplasmin, orosmucoid, fibrinogen, and haptoglobulin were increased (p<0.001).

CONCLUSION

Male gender, smoking, physical inactivity and cholesterol are significant factors associated with the development of AAA.

A Review of Biological Factors Implicated in Abdominal Aortic Aneurysm Rupture

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

Altered patterns of gene expression specific to thoracic aortic aneurysms: microarray analysis of surgically resected specimens

Changes in the expression levels of several genes have been described in aortic aneurysm specimens, however, the spectrum of diverse molecular alterations remains to be elucidated. We attempted to identify key molecules that modulate the pathogenesis of aortic aneurysm, using a complimentary DNA microarray carrying approximately 13,000 human genes. Segments of thoracic aortic aneurysms (TAA) and adjacent normal thoracic aortic tissues without aneurysmal changes (NTA) were obtained from 20 patients undergoing graft surgery. RNA obtained from five pairs of TAA and NTA samples was compared to determine aneurysm-specific alterations using microarray. Further, the expression levels of several genes of interest were verified in the remaining specimens by real-time reverse transcription-polymerase chain reaction (RT-PCR). In microarray assays, several types of the matrix metalloproteinases were upregulated as reported previously. Also, 220 genes suggested to be involved in protein degradation, inflammation, apoptosis, stress response, intracellular signaling, and other processes were significantly upregulated. Many of these genes have not been previously implicated in cardiovascular disease. The real time RT-PCR independently confirmed that the expression levels of MMP-2, MMP-9, ADAMTS-1, and caspase 4 were consistently increased in TAA. The results indicate that many genes are involved in a complicated manner in the pathogenesis of TAA. Investigation of these genes will help clarify the pathogenesis of this disease, and may lead to the discovery of novel therapeutic targets.

Application of real-time RT-PCR to quantifying gene expression of matrix metalloproteinases and tissue inhibitors of metalloproteinases in human abdominal aortic aneurysm

BACKGROUND

The relative expression levels of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs), key regulators in remodeling of extracellular matrix, are considered to play a pivotal role in the development of abdominal aortic aneurysm (AAA). However, few data exist regarding quantitative assessment of their expression in clinical settings.

METHODS

In 22 patients with AAA who underwent graft replacement, tissue samples of the AAA and non-dilated aorta were obtained. Using a real-time RT-PCR method that enabled quantitative measurement of mRNA levels in small tissue samples, we determined gene expression levels of MMPs and TIMPs relative to that of glutaraldehyde 3-phosphate dehydrogenase in each sample.

RESULTS

The expression levels of the MMP-1 and -3 genes were significantly augmented in AAA compared with non-dilated regions (4.48 +/- 2.01 versus 0.26 +/- 0.12, P < 0.01 and 1.89 +/- 1.00 versus 5.01 +/- 0.97, P < 0.05, respectively). Although genes for TIMP-1, -2 and -3 tended to be upregulated in AAA, relative expression levels of MMP-1 to TIMP-1, MMP-1 to TIMP-2, MMP-1 to TIMP-3, and MMP-3 to TIMP-2 were still higher in AAA than in non-dilated regions (1.12 +/- 0.63 versus 0.10 +/- 0.03, 4.13 +/- 1.12 versus 0.43 +/- 0.11, 1.61 +/- 0.59 versus 0.14 +/- 0.03, and 7.81 +/- 1.60 versus 2.56 +/- 0.76, respectively, P < 0.05).

CONCLUSION

These results demonstrate that the present real-time RT-PCR method is reliable for the determination of mRNA levels in small samples of vascular tissue and that disproportional expression of both MMP-1 and MMP-3 relative to TIMPs relates pathologically to the evolution of AAA.

Differential expression of immunoglobulin kappa chain constant region in human abdominal aortic aneurysm

BACKGROUND

A number of the research into the pathogenesis of the abdominal aortic aneurysm (AAA) have focused on the alteration of gene expression. The current technique for elucidating alterations of gene expression has a setback in that many artifact complementary DNA (cDNA) products present abnormal polymerase chain reaction (PCR) amplification. Our study was designed to identify differentially expressed genes in AAA using the annealing control primer (ACP) system, which was recently developed to identify only authentic genes.

MATERIALS AND METHODS

The tissues of the human abdominal aorta were obtained from the patients of AAA and aortic occlusive disease (AOD), and normal abdominal aorta (NA) from brain death donors. Total RNAs were isolated from three groups of human abdominal aorta (10 AAA, five NA, three AOD) and then reverse transcribed into complementary DNA (cDNA). The ACP method was done to screen the difference in the expression pattern of the mRNA (mRNA).

RESULTS

One differentially expressed cDNA band was detected in AAA but not in NA and AOD. This cDNA was sequenced and computer searching against the GenBank revealed that the cDNA had more than 90% identity with the immunoglobulin kappa chain constant region (Ig kappa-C).

DISCUSSION

Our finding suggests that differentially expressed Ig kappa-C gene only in AAA is a candidate gene that may play a pivotal role in the pathogenesis of AAA formation. The correlation of mRNA level and protein level is, however, not clear. Thus, to directly identify the role of Ig light chains in the pathogenic event of AAA, the further study comparing the level and kinds of expressed protein with the corresponding Ig kappa-C gene will be required.