In situ localization and quantification of seventy-two-kilodalton type IV collagenase in aneurysmal, occlusive, and normal aorta

The role of vascular smooth muscle cells in the development of aortic aneurysms and dissections

BACKGROUND

Aortic aneurysms (AA) are pathological dilations of the aorta, associated with an overall mortality rate up to 90% in case of rupture. In addition to dilation, the aortic layers can separate by a tear within the layers, defined as aortic dissections (AD). Vascular smooth muscle cells (vSMC) are the predominant cell type within the aortic wall and dysregulation of vSMC functions contributes to AA and AD development and progression. However, since the exact underlying mechanism is poorly understood, finding potential therapeutic targets for AA and AD is challenging and surgery remains the only treatment option.

METHODS

In this review, we summarize current knowledge about vSMC functions within the aortic wall and give an overview of how vSMC functions are altered in AA and AD pathogenesis, organized per anatomical location (abdominal or thoracic aorta).

RESULTS

Important functions of vSMC in healthy or diseased conditions are apoptosis, phenotypic switch, extracellular matrix regeneration and degradation, proliferation and contractility. Stressors within the aortic wall, including inflammatory cell infiltration and (epi)genetic changes, modulate vSMC functions and cause disturbance of processes within vSMC, such as changes in TGF-β signalling and regulatory RNA expression.

CONCLUSION

This review underscores a central role of vSMC dysfunction in abdominal and thoracic AA and AD development and progression. Further research focused on vSMC dysfunction in the aortic wall is necessary to find potential targets for noninvasive AA and AD treatment options.

TRPV1 inhibits smooth muscle cell phenotype switching in a mouse model of abdominal aortic aneurysm

The natural outcome of abdominal aortic aneurysm (AAA) is that of slow progression and ultimate rupture, then a life-threatening hemorrhage consequently. Ruptured AAA is a dramatic catastrophe and constitutes one of the leading causes of acute death in elderly men. However, the mechanism of AAA is still unclear. Transient receptor potential vanilloid (TRPV) family has protective effects in cardiovascular diseases. In this study, we revealed the expression and the pathogenesis of TRPV1 in a mouse AAA model. The results presented here identify TRPV1 could be a potential therapeutic target for AAA treatment.

TRPV5 attenuates abdominal aortic aneurysm in mice by regulating KLF4-dependent phenotype switch of aortic vascular smooth muscle cells

Abdominal aortic aneurysm (AAA) is a fatal vascular disease with insidious symptoms. However, the mechanism behind its development remains unclear. The transient receptor potential vanilloid (TRPV) family has crucial protective effects against cardiovascular diseases, but the role of TRPV5 in AAA has yet to be reported. In this study, ApoE^-/- mice were intraperitoneally injected with AAV-GFP or AAV-TRPV5. After 30 days, mice were further administered with angiotensin II (Ang II, 1.44 mg/kg/day) by using osmotic pumps to induce the AAA model or Saline for 28 days, (i.e., Saline + AAV-GFP, Saline + AAV-TRPV5, Ang II + AAV-GFP and Ang II + AAV-TRPV5 groups were established). Compared with the control group, the incidence of AAA and the maximal diameter of the abdominal aorta markedly decreased in Ang II + AAV-TRPV5, which was detected by vascular ultrasound at 28 day. Meanwhile, less collagen and elastin degradation were observed in the Ang II + AAV-TRPV5 group by using Masson and Elastin stains. Moreover, more α-SMA and less MMP2 was observed in the abdominal aortas collected at 28 day by immunohistochemistry. In vitro, primary mouse vascular smooth muscle cells (VSMCs) were treated with Ang II (1 μM) to induce phenotype switch. Sh-TRPV5 and AdTRPV5 were used to transfect VSMCs. PCR and Western blotting were used to access the expression of contractile marker, including α-SMA and SM-22α. The results showed that the mRNA and protein level of α-SMA and SM-22α were decreased under the stimulation of Ang II, but could be attenuated by TRPV5 overexpression. The cell scratch assay demonstrated that the migration ability of VSMCs was increased in Ang II treated group and could be ameliorated by TRPV5 overexpression. Above all, VSMCs transformed from the contractile into secretory phenotype under Ang II stimuli, but could be rescued by TRPV5 overexpression. Furthermore, TRPV5 overexpression suppressed the increased expression of KLF4 induced by Ang II treatment in VSMCs. The data demonstrated that TRPV5 could inhibit AAA formation and play a critical role in the VSMC phenotype switch by downregulating KLF4, suggesting TRPV5 as a new strategy for treating AAA.

Abdominal Aortic Aneurysm-Associated MicroRNA-516a-5p Regulates Expressions of Methylenetetrahydrofolate Reductase, Matrix Metalloproteinase-2, and Tissue Inhibitor of Matrix Metalloproteinase-1 in Human Abdominal Aortic Vascular Smooth Muscle Cells

BACKGROUND

MicroRNAs (miRNAs or miRs) have been highlighted to be involved in abdominal aortic aneurysm (AAA) with the emergence of recent miRNA microarray profiling studies. miR-516a-5p has been shown to be significantly overexpressed in vascular smooth muscle cells (VSMCs) from human AAA tissues from our previous microarray study, suggesting its crucial association with AAA. In addition, further bioinformatics analysis predicted methylenetetrahydrofolate reductase (MTHFR), which regulates homocysteine (Hcy) metabolism and is proposed to be a risk gene for AAA formation and to be the downregulation target of miR-516a-5p. However, the pathogenic role of miR-516a-5p in VSMCs for AAA formation remains unresolved. This study aims to investigate the role of miR-516a-5p in human VSMCs for AAA pathogenesis.

METHODS

miR-516a-5p was stably overexpressed and knocked down in VSMCs explant cultured from human abdominal aortic tissues by means of lentiviral system. The MTHFR protein expression was first examined by Western blotting. In addition, the protein expressions of several key components involved in AAA pathogenic features are as follows: matrix metalloproteinase (MMP)-2, MMP-9, tissue inhibitor of matrix metalloproteinase (TIMP)-1 and TIMP-2 for elastin degradation; collagen type 1 alpha 1 for compensatory collagen synthesis; monocyte chemoattractant protein-1 for inflammation, were also evaluated. Apoptotic level of VSMCs was examined by terminal deoxynucleotidyl transferase dUTP nick end labeling assay.

RESULTS

Results showed that protein expression of MTHFR was significantly downregulated on miR-516a-5p overexpression (P < 0.05) in VSMCs, whereas it was significantly upregulated on miR-516a-5p knockdown (P < 0.05). Of all the AAA key components investigated, only MMP-2 and TIMP-1 protein expressions were found altered. A significant increase in MMP-2 (P < 0.05) and decrease in TIMP-1 (P < 0.05) expressions were observed on miR-516a-5p overexpression in VSMCs. Apoptosis was not promoted on miR-516a-5p overexpression or knockdown in VSMCs.

CONCLUSIONS

Our findings suggested that miR-516a-5p may regulate MTHFR, MMP-2, and TIMP-1 expressions in human VSMCs, possibly promoting the disruption of Hcy metabolism and proteolytic degradation of elastin for AAA formation.

Nanoparticles Effectively Target Rapamycin Delivery to Sites of Experimental Aortic Aneurysm in Rats

Several drugs targeting the pathogenesis of aortic aneurysm have shown efficacy in model systems but not in clinical trials, potentially owing to the lack of targeted drug delivery. Here, we designed a novel drug delivery system using nanoparticles to target the disrupted aortic aneurysm micro-structure. We generated poly(ethylene glycol)-shelled nanoparticles incorporating rapamycin that exhibited uniform diameter and long-term stability. When injected intravenously into a rat model in which abdominal aortic aneurysm (AAA) had been induced by infusing elastase, labeled rapamycin nanoparticles specifically accumulated in the AAA. Microscopic analysis revealed that rapamycin nanoparticles were mainly distributed in the media and adventitia where the wall structures were damaged. Co-localization of rapamycin nanoparticles with macrophages was also noted. Rapamycin nanoparticles injected during the process of AAA formation evinced significant suppression of AAA formation and mural inflammation at 7 days after elastase infusion, as compared with rapamycin treatment alone. Correspondingly, the activities of matrix metalloproteinases and the expression of inflammatory cytokines were significantly suppressed by rapamycin nanoparticle treatment. Our findings suggest that the nanoparticle-based delivery system achieves specific delivery of rapamycin to the rat AAA and might contribute to establishing a drug therapy approach targeting aortic aneurysm.

Hyperglycemia Suppresses Calcium Phosphate-Induced Aneurysm Formation Through Inhibition of Macrophage Activation

Background

The aim of this study was to elucidate aspects of diabetes mellitus–induced suppression of aneurysm. We hypothesized that high glucose suppresses aneurysm by inhibiting macrophage activation via activation of Nr1h2 (also known as liver X receptor β), recently characterized as a glucose‐sensing nuclear receptor.

Methods and Results

Calcium phosphate (CaPO₄)–induced aneurysm formation was significantly suppressed in the arterial wall in type 1 and 2 diabetic mice. A murine macrophage cell line, RAW264.7, was treated with tumor necrosis factor α (TNF‐α) plus CaPO₄ and showed a significant increase in matrix metalloproteinase 9 (Mmp9) mRNA and secreted protein expression compared with TNF‐α alone. Elevated Mmp9 expression was significantly suppressed by hyperglycemic conditions (15.5 mmol/L glucose) compared with normoglycemic conditions (5.5 mmol/L glucose) or normoglycemic conditions with high osmotic pressure (5.5 mmol/L glucose +10.0 mmol/L mannitol). Nr1h2 mRNA and protein expression were suppressed by treatment with TNF‐α plus CaPO₄ but were restored by hyperglycemic conditions. Activation of Nr1h2 by the antagonist GW3965 during stimulation with TNF‐α plus CaPO₄ mimicked hyperglycemic conditions and inhibited Mmp9 upregulation, whereas the deactivation of Nr1h2 by small interfering RNA (siRNA) under hyperglycemic conditions canceled the suppressive effect and restored Mmp9 expression induced by TNF‐α plus CaPO₄. Moreover, Nr1h2 activation with GW3965 significantly suppressed CaPO₄‐induced aneurysm in mice compared with vehicle‐injected control mice.

Conclusions

Our results show that hyperglycemia suppresses macrophage activation and aneurysmal degeneration through the activation of Nr1h2. Although further validation of the underlying pathway is necessary, targeting Nr1h2 is a potential therapeutic approach to treating aneurysm.

Local Quantification of Wall Thickness and Intraluminal Thrombus Offer Insight into the Mechanical Properties of the Aneurysmal Aorta

Wall stress is a powerful tool to assist clinical decisions in rupture risk assessment of abdominal aortic aneurysms. Key modeling assumptions that influence wall stress magnitude and distribution are the inclusion or exclusion of the intraluminal thrombus in the model and the assumption of a uniform wall thickness. We employed a combined numerical-experimental approach to test the hypothesis that abdominal aortic aneurysm (AAA) wall tissues with different thickness as well as wall tissues covered by different thrombus thickness, exhibit differences in the mechanical behavior. Ultimate tissue strength was measured from in vitro tensile testing of AAA specimens and material properties of the wall were estimated by fitting the results of the tensile tests to a histo-mechanical constitutive model. Results showed a decrease in tissue strength and collagen stiffness with increasing wall thickness, supporting the hypothesis of wall thickening being mediated by accumulation of non load-bearing components. Additionally, an increase in thrombus deposition resulted in a reduction of elastin content, collagen stiffness and tissue strength. Local wall thickness and thrombus coverage may be used as surrogate measures of local mechanical properties of the tissue, and therefore, are possible candidates to improve the specificity of AAA wall stress and rupture risk evaluations.

Asymmetric expansion of aortic aneurysms on computed tomography imaging

OBJECTIVE

To investigate whether wall growth during aneurysm development spares the aortic wall between the intercostal or lumbar arteries or, alternatively, is uniform around the circumference.

METHODS

Computed tomography scans of 155 patients with aortic aneurysms (40 thoracic, 50 thoracoabdominal, and 65 abdominal) in a single hospital of a large academic institution were retrospectively inspected. Computed tomography studies of 100 control subjects (40 thoracic and 60 abdominal) were also reviewed. In all 255 patients, the ratio of the arc length between the origins of the intercostal or lumbar arteries (interbranch arc length) to the remainder of the aortic residual circumference was calculated. These ratios were compared between all subjects with aneurysms and the controls at each vertebral body level and between those with thoracic or thoracoabdominal or abdominal aneurysms and controls at each vertebral body level.

RESULTS

Interbranch arc lengths and residual aortic circumferences were larger in aneurysm patients than in control subjects, but the differences were statistically significant only at T4 and from T8 to L4 (P = .009 to P < .001) and from T4 to L4 (P < .001), respectively. The ratio of interbranch arc length to residual circumference in aneurysmal aortas was significantly smaller than that in controls at 12 out of 13 levels from T4 to L4 (P = .004 to P < .001). There was a statistically significant smaller ratio at 8 out of 9 levels for thoracic aneurysms (P = .006 to P < .001), 12 out of 13 levels for thoracoabdominal aneurysms (P = .008 to P < .001), and 3 out of 4 levels for abdominal aneurysms compared with controls (P = .006 to P < .001).

CONCLUSIONS

Wall growth in aortic aneurysms is asymmetric, with greater aneurysmal growth in the anterior aorta wall and relative sparing of the portion of aortic wall between the intercostal or lumbar arteries. The mechanisms effecting this asymmetric growth have not been fully characterized.

Pathogenesis of abdominal aortic aneurysms: role of nicotine and nicotinic acetylcholine receptors

Inflammation, proteolysis, smooth muscle cell apoptosis, and angiogenesis have been implicated in the pathogenesis of abdominal aortic aneurysms (AAAs), although the well-defined initiating mechanism is not fully understood. Matrix metalloproteinases (MMPs) such as MMP-2 and -9 and other proteinases degrading elastin and extracellular matrix are the critical pathogenesis of AAAs. Among the risk factors of AAAs, cigarette smoking is an irrefutable one. Cigarette smoke is practically involved in various aspects of the AAA pathogenesis. Nicotine, a major alkaloid in tobacco leaves and a primary component in cigarette smoke, can stimulate the MMPs expression by vascular SMCs, endothelial cells, and inflammatory cells in vascular wall and induce angiogenesis in the aneurysmal tissues. However, for the inflammatory and apoptotic processes in the pathogenesis of AAAs, nicotine seems to be moving in just the opposite direction. Additionally, the effects of nicotine are probably dose dependent or associated with the exposure duration and may be partly exerted by its receptors—nicotinic acetylcholine receptors (nAChRs). In this paper, we will mainly discuss the pathogenesis of AAAs involving inflammation, proteolysis, smooth muscle cell apoptosis and angiogenesis, and the roles of nicotine and nAChRs.

Selective microRNA suppression in human thoracic aneurysms: relationship of miR-29a to aortic size and proteolytic induction

BACKGROUND

Increasing evidence points to a direct role for altered microRNA (miRNA or miR) expression levels in cardiovascular remodeling and disease progression. Although alterations in miR expression levels have been directly linked to cardiac hypertrophy, fibrosis, and remodeling, their role in regulating gene expression during thoracic aortic aneurysm (TAA) development has yet to be explored.

METHODS AND RESULTS

The present study examined miR expression levels in aortic tissue specimens collected from patients with ascending TAAs by quantitative real-time PCR, and observed decreased miR expression (miRs -1, -21, -29a, -133a, and -486) as compared with normal aortic specimens. A significant relationship between miR expression levels (miRs -1, -21, -29a, and -133a) and aortic diameter was identified; as aortic diameter increased, miR expression decreased. Through the use of a bioinformatics approach, members of the matrix metalloproteinase (MMP) family, proteins involved in TAA development, were examined for putative miR binding sites. MMP-2 and MMP-9 were identified as potential targets for miR-29a and miR-133a, respectively, and MMP-2 was subsequently verified as a miR-29a target in vitro. A significant inverse relationship between miR-29a and total MMP-2 was then identified in the clinical TAA specimens.

CONCLUSIONS

These findings demonstrate altered miR expression patterns in clinical TAA specimens, suggesting that the loss of specific miR expression may allow for the elaboration of specific MMPs capable of driving aortic remodeling during TAA development. Importantly, these data suggest that these miRs have biological and clinical relevance to the behavior of TAAs and may provide significant targets for therapeutic and diagnostic applications.

Matrix metalloproteinases and descending aortic aneurysms: parity, disparity, and switch

Central to the pathologic changes in developing aortic aneurysms are alterations in the abundance and activity of proteases, of which the most important for aneurysm production comprise the matrix metalloproteinase (MMP) family. In this review, literature demonstrating the role of MMPs in the development of aortic aneurysms is presented, with emphasis on the parity and disparity between the thoracic and abdominal aorta. Furthermore, the role of embryologic cellular origins and evidence of phenotypic switch will be addressed in terms of how this process alters MMP production during aneurysm development.

Imaging of Abdominal Aortic Aneurysm: the present and the future

Abdominal Aortic Aneurysm (AAA) is a common, progressive, and potentially lethal vascular disease. A major obstacle in AAA research, as well as patient care, is the lack of technology that enables non-invasive acquisition of molecular/cellular information in the developing AAA. In this review we will briefly summarize the current techniques (e.g. ultrasound, computed tomography, and magnetic resonance imaging) for anatomical imaging of AAA. We also discuss the various functional imaging techniques that have been explored for AAA imaging. In many cases, these anatomical and functional imaging techniques are not sufficient for providing surgeons/clinicians enough information about each individual AAA (e.g. rupture risk) to optimize patient management. Recently, molecular imaging techniques (e.g. optical and radionuclide-based) have been employed to visualize the molecular alterations associated with AAA, which are discussed in this review. Lastly, we try to provide a glance into the future and point out the challenges for AAA imaging. We believe that the future of AAA imaging lies in the combination of anatomical and molecular imaging techniques, which are largely complementary rather than competitive. Ultimately, with the right molecular imaging probe, clinicians will be able to monitor AAA growth and evaluate the risk of rupture accurately, so that the life-saving surgery can be provided to the right patients at the right time. Equally important, the right imaging probe will also allow scientists/clinicians to acquire critical data during AAA development and to more accurately evaluate the efficacy of potential treatments.

Genes and abdominal aortic aneurysm

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

Matrix metalloproteinases, a disintegrin and metalloproteinases, and a disintegrin and metalloproteinases with thrombospondin motifs in non-neoplastic diseases

Cellular functions within tissues are strictly regulated by the tissue microenvironment which comprises extracellular matrix and extracellular matrix-deposited factors such as growth factors, cytokines and chemokines. These molecules are metabolized by matrix metalloproteinases (MMP), a disintegrin and metalloproteinases (ADAM) and ADAM with thrombospondin motifs (ADAMTS), which are members of the metzincin superfamily. They function in various pathological conditions of both neoplastic and non-neoplastic diseases by digesting different substrates under the control of tissue inhibitors of metalloproteinases (TIMP) and reversion-inducing, cysteine-rich protein with Kazal motifs (RECK). In neoplastic diseases MMP play a central role in cancer cell invasion and metastases, and ADAM are also important to cancer cell proliferation and progression through the metabolism of growth factors and their receptors. Numerous papers have described the involvement of these metalloproteinases in non-neoplastic diseases in nearly every organ. In contrast to the numerous review articles on their roles in cancer cell proliferation and progression, there are very few articles discussing non-neoplastic diseases. This review therefore will focus on the properties of MMP, ADAM and ADAMTS and their implications for non-neoplastic diseases of the cardiovascular system, respiratory system, central nervous system, digestive system, renal system, wound healing and infection, and joints and muscular system.

Quantitative characterization of developing collagen gels using optical coherence tomography

Nondestructive optical imaging methods such as optical coherence tomography (OCT) have been proposed for characterizing engineered tissues such as collagen gels. In our study, OCT was used to image collagen gels with different seeding densities of smooth muscle cells (SMCs), including acellular gels, over a five-day period during which the gels contracted and became turbid with increased optical scattering. The gels were characterized quantitatively by their optical properties, specified by analysis of OCT data using a theoretical model. At 6 h, seeded cell density and scattering coefficient (mu(s)) were correlated, with mu(s) equal to 10.8 cm(-1)(10(6) cells mL). Seeded cell density and the scattering anisotropy (g) were uncorrelated. Over five days, the reflectivity in SMC gels gradually doubled with little change in optical attenuation, which indicated a decrease in g that increased backscatter, but only a small drop in mu(s). At five days, a subpopulation of sites on the gel showed substantially higher reflectivity (approximately a tenfold increase from the first 24 h). In summary, the increased turbidity of SMC gels that develops over time is due to a change in the structure of collagen, which affects g, and not simply due to a change in number density of collagen fibers due to contraction.

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.

Cleaved high molecular weight kininogen, a novel factor in the regulation of matrix metalloproteinases in vascular smooth muscle cells

We previously reported that Brown Norway Katholiek rats, which feature a deficiency of plasma kininogens, develop severe abdominal aortic aneurysm. Increased activity of matrix metalloproteinases (MMPs) in the aortic wall, leading to degradation of extracellular matrix components, is considered to play a crucial role in aneurysm formation. Using an in vitro model of vascular smooth muscle cells (VSMCs), cultured from the rat aorta, we investigated whether the cleaved form of high molecular weight kininogen, designated HKa, affects the expression of MMP-9 and MMP-2 and their tissue inhibitors (TIMPs). Treatment of VSMCs with HKa reduced in a concentration-dependent manner IL-1alpha-induced release of MMP-9 and MMP-2, associated with decreased MMP enzymatic activity levels in conditioned media, as demonstrated by gelatin zymography and fluorescein-labeled gelatin substrate assay, respectively. Real-time PCR revealed that HKa reduced corresponding MMP-9 mRNA levels. Further investigations showed that this effect did not result from a modified rate of MMP-9 mRNA degradation. TIMP-1 mRNA levels, already increased as a result of cytokine-stimulation, were significantly enhanced by HKa. Furthermore, we found elevated basal mRNA expression levels of MMP-2 and TIMP-2 in VSMCs derived from kininogen-deficient Brown Norway Katholiek rats. These results demonstrate for the first time that HKa affects the regulation of MMPs in VSMCs.

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.

A theoretical model for fibroblast-controlled growth of saccular cerebral aneurysms

A new theoretical model for the growth of saccular cerebral aneurysms is proposed by extending the recent constitutive framework of Kroon and Holzapfel [2007a. A model for saccular cerebral aneurysm growth by collagen fibre remodelling. J. Theor. Biol. 247, 775-787]. The continuous turnover of collagen is taken to be the driving mechanism in aneurysmal growth. The collagen production rate depends on the magnitude of the cyclic deformation of fibroblasts, caused by the pulsating blood pressure during the cardiac cycle. The volume density of fibroblasts in the aneurysmal tissue is taken to be constant throughout the growth process. The growth model is assessed by considering the inflation of an axisymmetric membranous piece of aneurysmal tissue, with material characteristics representative of a cerebral aneurysm. The diastolic and systolic states of the aneurysm are computed, together with its load-free state. It turns out that the value of collagen pre-stretch, that determines growth speed and stability of the aneurysm, is of pivotal importance. The model is able to predict aneurysms with typical berry-like shapes observed clinically, and the predicted wall stresses correlate well with the experimentally obtained ultimate stresses of this type of tissue. The model predicts that aneurysms should fail when reaching a size of about 1.2-3.6mm, which is smaller than what has been clinically observed. With some refinements, the model may, however, be used to predict future growth of diagnosed aneurysms.

Tissue inhibitor of metalloproteinase-1 (TIMP-1) polymorphisms in a Caucasian population with abdominal aortic aneurysm

BACKGROUND

The formation of a sporadic abdominal aortic aneurysm (AAA) is explained by the remodeling of the extracellular matrix (ECM) and breakdown of structural components of the vascular wall. Matrix metalloproteinases are the principal matrix-degrading proteases and are known to play a major role in the remodeling of the extracellular matrix in arterial vessels. Their activity is controlled by tissue inhibitors of metalloproteinases (TIMPs). Decreased TIMP-1 and TIMP-2 expression in the extracellular matrix of the walls of AAAs has been shown in several studies. This case control study was designed to investigate the possible impact of genetic variants of the TIMP-1 gene in the etiology of AAA.

METHODS

TIMP-1 single nucleotide polymorphisms (SNPs) were analyzed in a primary study sample of 50 patients with AAA and 44 controls. Differences in genotype and allele frequencies of identified polymorphisms were determined after sequencing the entire coding region and selected parts of the promoter using the automated laser fluorescence technique. A second sample (96 patients vs. 89 controls) was investigated by single-base sequencing to confirm significant results.

RESULTS

Three polymorphisms were identified, one of which, described for the first time in this article, is located in intron 4 (TIMP-1: 328 + 16C > T). A statistically significant difference in allele frequencies for SNP TIMP-1 372T>C was detected in the primary study group. The C allele was more frequent in male patients with AAA than in the control group [23 vs. 4, p = 0.029, OR (95% CI) 4.38 (1.13-20.47)]. However, this result could not be confirmed in a second sample of males [52 vs. 45, p = 0.624, OR (95% CI) 1.16 (0.65-2.06)]. There were no statistically significant differences in genotype or allele frequencies of the other detected SNPs between the two groups.

CONCLUSIONS

Our analysis of the entire coding region and selected parts of the promoter of the TIMP-1 gene failed to show an association between genetic polymorphisms and AAA, suggesting that variations in the TIMP-1 gene do not contribute to the development of AAA.

A biologic basis for asymmetric growth in descending thoracic aortic aneurysms: a role for matrix metalloproteinase 9 and 2

OBJECTIVE

This study was undertaken to define matrix metalloproteinase (MMP) expression in the anterior and posterior wall of descending thoracic aortic aneurysms (TAAs) and correlate it with specific computed tomography (CT) image sites within the descending thoracic aorta.

METHODS

Serial CT images of patients with TAAs were compared with age- and gender-matched normal descending thoracic aortas at levels T4-T12. The mean circumference of the TAAs was 153 mm (n = 12) and 148 mm (n = 11) at T8 and T10, respectively, compared with 75 mm (n = 12) and 75 mm (n = 10) in controls (P < .001). Aortic tissue was collected from a separate set of eight patients undergoing descending TAA resection (processed < or =12 hours of excision) and six cadavers (processed < or =24 hours of death). Tissue collected between the intercostals arteries was defined as posterior wall, and directly opposite was the anterior wall. MMP-9 and MMP-2 messenger RNA (mRNA) extracted from aortic tissue was analyzed by quantitative real time polymerase chain reaction (PCR) and normalized to beta-actin. Immunohistochemistry was performed for MMP-9 and MMP-2. CT aortic measurements and MMP expression were compared by t tests and analysis of variance, respectively.

RESULTS

The ratio of arc distance between the intercostals on the posterior wall to total aortic circumference was 0.14 in healthy controls compared with 0.08 in TAAs at vertebral level T8 (P = .001). At T10, the ratio was 0.15 in healthy controls compared with 0.11 in TAAs (P = .001). MMP-9 expression in TAAs was 4.3-fold higher in the anterior wall compared with the posterior wall (P = .03). Conversely, MMP-2 expression in TAAs was 3.2-fold higher in the posterior wall compared with the anterior wall (P = .008). MMP expression was not detected in control cadaver aortas.

CONCLUSION

Anterior walls of expanding TAAs grow at a greater rate than the posterior wall, as determined from the lower ratio of intercostal arc distance to total circumference in TAAs. Differential MMP expression appears to be a biologic marker for asymmetric growth in the TAA wall.

CLINICAL RELEVANCE

The pathogenesis of thoracic aortic aneurysms (TAAs) is poorly understood. Multiple lines of evidence suggest that matrix metalloproteinases (MMPs), a family of enzymes, are important in aneurysm development. Earlier experiments documented a regional variation of MMP-9 in stimulated rodent aortas, with production greater in the abdominal aorta compared with the thoracic aorta. The present study extends that observation and documents asymmetric aneurysm development in the TAA wall, with increased anterior wall growth in correlation to increased MMP-9 production. An improved understanding of the mechanisms by which MMP production is regulated is critical.

Effect of smoking on abdominal aortic aneurysms: novel insights through murine models

Abdominal aortic aneurysm is a poorly understood and fatal disease. The etiology of the disease is believed to be multifactorial. Of all the recognized clinical associations, none has a greater impact on the incidence and progression of the disease than exposure to tobacco smoke. Novel murine models developed over the past several years present the opportunity to investigate the mechanism of this critical clinical relationship.

Differential regulation of the superoxide dismutase family in experimental aortic aneurysms and rat aortic explants

OBJECTIVE

Oxidative stress has been implicated in abdominal aortic aneurysm pathogenesis. This study sought to characterize the relevance of superoxide dismutases (SOD), a family of reactive oxygen catalyzing metalloenzymes, including manganese SOD (MnSOD), copper-zinc SOD (CuZnSOD), and extracellular SOD (EcSOD), in a rodent aortic aneurysm model.

METHODS

Male rat infrarenal abdominal aortas were perfused with either saline (control) or porcine pancreatic elastase (6 U/mL). Aortic diameter was measured and aortas harvested on post-operation days 1, 2, and 7 (N=5-6 per treatment group per day). MnSOD, CuZnSOD, EcSOD, catalase, MMP-2, MMP-9, and beta-actin expression in aortic tissue was determined by quantitative real-time PCR. MnSOD protein levels were measured using western immunoblotting and immunohistochemistry. In subsequent experiments, aimed at understanding the mechanism by which SOD is involved in AAA pathogenesis, rat aortic explants (RAEs) were incubated in media for 24 h in the presence of interleukin-1beta (IL-1beta, 2 ng/mL) and TEMPOL (SOD mimetic), catalase, or a combined SOD and catalase mimetic. Media MMP-2 and MMP-9 activity was determined by zymography. Data were analyzed by Student's t-tests and ANOVA.

RESULTS

Elastase-perfused aortic diameters were significantly increased compared to control aortas by post-perfusion day 7 (P=0.016). MnSOD mRNA levels in elastase perfused aortas were 6.0 (P=0.05) and 7.5 times (P<0.01) greater than control aortas at post-perfusion days 1 and 2, respectively. EcSOD, CuZnSOD, catalase, and MMP-2 mRNA expression did not statistically vary between the two groups. MMP-9 expression was 3.5-fold higher in the elastase group on post-perfusion day 2 (P=0.04). Western immunoblotting confirmed MnSOD protein was up-regulated on day 4 in the elastase-perfused group compared to controls (P=0.02). Immunohistrochemistry demonstrated increased MnSOD staining in the elastase group on day 4. In RAE experiments, TEMPOL increased both MMP-9 and MMP-2 activity 2 (P=0.09) and 3-fold (P=0.05), respectively, whereas catalase and the combined SOD/catalase mimetic failed to increase MMP-2 or MMP-9 activity.

CONCLUSION

Experimental abdominal aortic aneurysm formation is associated with early increases in MnSOD expression and an increase in MMP-9 activity. Strategies aimed at inhibiting oxidative stress during AAA formation should focus on MnSOD.

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.

Matrix metalloproteinase-2: the forgotten enzyme in aneurysm pathogenesis

The pathogenesis of abdominal aortic aneurysm (AAAs) involves progressive cycles of proteolysis and inflammation, the product of proteolysis driving subsequent inflammation. Little is yet known about the initiating events. We review the specific literature examining the possibility that MMP-2 may be the initial catalyst. Histologically, elastolysis is one of the earliest observable events in aneurysm genesis. Matrix metalloproteinase-2 (MMP-2), as the dominant gelatinase differentially expressed in aneurysmal tissue and cells derived from aneurysms, would be a good candidate. We report the results of in vivo and in vitro experiments, which lend support to the importance of MMP-2 as an aneurysmal initiator.

Proteinase systems and thoracic aortic aneurysm progression

Thoracic aortic aneurysms (TAAs) are a rare but potentially devastating condition. Current surgical treatment of TAAs usually involves a major operation, which conveys many risks to the patient. Better knowledge of the cellular events that lead to aneurysm formation may elucidate less morbid treatment options for this condition. A number of recent studies have identified that the relative abundance and activity of extracellular matrix (ECM) proteolytic systems are increased with TAAs. Specifically, the matrix metalloproteinases (MMPs) have been linked through numerous studies to TAA formation. MMPs comprise a family of ECM-degrading proteinases. Endogenous tissue inhibitors (TIMPs) normally regulate MMP activity, and the activation of MMPs is complex and tightly controlled. Aneurysm formation may be related to relative changes in the balance between MMP/TIMP abundance favoring proteolysis. Through ECM degradation, the medial layer will undergo structural remodeling and a loss of structural integrity, leading to TAA formation. The goals of this review are to examine the structure of the normal and aneurysmal thoracic aorta and to place the new findings regarding ECM proteolysis in perspective with regard to TAA formation and progression. Through an integration of basic and clinical studies regarding the underlying molecular basis for proteolysis of the thoracic aorta, improved diagnostic, prognostic, and therapeutic strategies for this disease process are likely to be realized.

Effects of tissue inhibitor of metalloproteinase 2 deficiency on aneurysm formation

OBJECTIVE

Matrix metalloproteinase (MMP)-2 has been shown to play a pivotal role in aortic aneurysm formation. Its activation requires formation of a trimolecular complex of MMP-2, tissue inhibitor of metalloproteinase-2 (TIMP-2), and membrane type 1 (MT1)-MMP, which is attached to the cell surface. At higher concentrations, TIMP-2 becomes an inhibitor of MMP-2. Thus, TIMP-2 could both augment and inhibit matrix degradation. This study was undertaken to define the net effect of TIMP-2 on matrix destruction and aneurysm formation.

METHODS

The abdominal aortas of wild-type and TIMP-2-deficient (TIMP-2 -/-) mice were exposed to 0.25 mol/L CaCl2 or 0.9% NaCl for 15 minutes after laparotomy. Aortic diameters were measured before treatment and 6 weeks after aneurysm induction. In addition, aortic tissues were studied for MMP-2 activation by zymography, and matrix structure was studied by connective tissue staining.

RESULTS

The aortic diameter increased in both wild-type and TIMP-2-/- mice. The increase in the TIMP-2 -/- mice was significantly smaller after CaCl2 treatment (51% +/- 3%) compared with the diameter of wild-type mice (67% +/- 4%). Connective staining of aortic sections from the CaCl2-treated mice revealed disruption and fragmentation of the medial elastic lamellae in both wild-type and TIMP-2 -/- mice. Zymographic analysis showed that active MMP-2 levels were decreased in TIMP-2 -/- aortas compared with wild-type mice.

CONCLUSIONS

Targeted deletion of TIMP-2 results in attenuation of aneurysm development. Despite its name as an inhibitor of MMPs, TIMP-2 promotes aortic enlargement in vivo, presumably through its role as a cofactor in the activation of MMP-2.

CLINICAL RELEVANCE

Abdominal aortic aneurysmal (AAA) disease is a potentially fatal disorder that screening studies have detected in 2% to 9% of the general population. Medical therapy designed to inhibit the progression of small aneurysms includes control of hypertension and smoking cessation; neither of these measures is of proven benefit. Effective and directed medical treatments for small AAAs await elucidation of key etiologic factors. Understanding precisely which molecules mediate AAA development, and blocking the activity of these molecules, could lead to important new therapies. Through our research, we have found that tissue inhibitor of metalloproteinase (TIMP)-2 has a role in this process in an experimental model of aortic aneurysms. We believe that TIMP-2 promotes aortic enlargement in vivo by activating matrix metalloproteinase 2.

The nitric oxide donor DETA-NONOate decreases matrix metalloproteinase-9 expression and activity in rat aortic smooth muscle and abdominal aortic explants

Our objective was to examine the role of an exogenous nitric oxide (NO) donor, DETA-NONOate (DETA), on matrix metalloproteinase (MMP)-9, MMP-2, and tissue inhibitor of matrix metalloproteinases (TIMP)-1 expression and activity in interleukin (IL)-1beta-induced rat aortic smooth muscle cells (RA-SMCs) and rat aortic explants (RAEs). RA-SMCs were incubated with IL-1beta (2 ng/ml), an inflammatory cytokine known to induce MMP-9 expression, and increasing concentrations of DETA (0, 1.0, 10, 100 microM; n = 3/group) for 48 hr. RAEs were incubated with IL-1beta (2 ng/mL) and increasing concentrations of DETA (0, 5.0, 50, 100, and 500 microM; n = 3/group) for 48 hr. Media were collected and assayed for NO(x) by the Griess reaction and MMP-9 activity by zymography. Messenger RNA (mRNA) was extracted from cells and analyzed for MMP-9, MMP-2, and TIMP-1 expression levels by quantitative real-time reverse-transcriptase polymerase chain reaction. All statistical analyses were performed by analysis of variance. In RA-SMCs and RAEs, DETA administration resulted in a dose-dependent increase in media NOx concentration (RA-SCM p < 0.01, RAE p < 0.01) and a concurrent decrease in both MMP-9 expression (RASMC p = 0.01, RAE p = 0.01) and activity (RASMC p = 0.04, RAE p = 0.006). There were no significant differences seen in MMP-2 and TIMP-1 expression or activity in response to DETA exposure. DETA decreased IL-1beta-induced MMP-9 expression and activity in both RA-SMCs and RAEs in a dose-dependent fashion. In addition, DETA administration had no effect on MMP-2 or TIMP-1 expression or activity in vitro. These data suggest that NO donors may be beneficial in decreasing MMP-9 levels and might serve to inhibit MMP-9-dependent vessel wall remodeling seen during abdominal aortic aneurysm formation.

Early increased MT1-MMP expression and late MMP-2 and MMP-9 activity during Angiotensin II induced aneurysm formation

BACKGROUND

Angiotensin II (Ang II) is associated with a variety of cardiovascular diseases including aneurysm formation. The aim of this study was to evaluate the temporal changes in MT1-matrix metalloproteinase (MMP) and MMP-2 and -9 expression and activity during the course of Ang II induced experimental aneurysm formation.

METHODS

Apolipoprotein E knockout mice (ApoE null) were infused with either 1000 ng/kg/min of Ang II (n = 20) or saline (n = 20) and then sacrificed at 7, 14, 21, and 28 days of infusion (n = 5/group/strain). Aortic diameters were measured by digital microscopy. Systolic blood pressure (SBP) was measured in the rodent tail. Suprarenal abdominal aortas had MT1-MMP mRNA levels and MMP-2 and MMP-9 mRNA levels and activity quantitated using reverse transcriptase-polymerase chain reaction (rt-PCR) and gelatin zymography, respectively. Statistical analyses included nonpaired t-test, Fisher's exact test, and analysis of variance (ANOVA).

RESULTS

Aneurysms occurred in 40, 40, 20, and 80% of ApoE null-Ang II mice at 7, 14, 21, and 28 days, respectively. An early and significant rise in MT1-MMP mRNA occurred in ApoE null mice infused with Ang II mice, while there was no significant change in MMP-2 or MMP-9 mRNA levels. Total MMP-2 and MMP-9 activity increased over time in ApoE null mice infused with Ang II, peaking at 28 days (ANOVA, P < 0.01). SBP was significantly elevated by 7 days in ApoE null mice infused with Ang II compared to ApoE null mice infused with saline (123 +/- 16 versus 102 +/- 6 mm Hg, P < 0.05).

CONCLUSIONS

Angiotensin II induces an early increase in aortic MT1-MMP expression with a subsequent increase in MMP-2 and MMP-9 activity. The process by which these changes cause aneurysm formation warrants further investigation.

The elevated level of circulating matrix metalloproteinase-9 in patients with abdominal aortic aneurysms decreased to levels equal to those of healthy controls after an aortic repair

Matrix metalloproteinase-9 (MMP-9) is abundantly expressed in abdominal aortic aneurysms (AAAs), and it is considered to play a pivotal role in aneurysmal formation. Elevated circulating concentrations of MMP-9 have been reported in patients with AAA, but the influence of an operation on circulating MMP-9 is unclear. Therefore, to clarify the influence of an operation on circulating MMP-9 levels and to determine the role of MMP-9 in the progression of AAA, we measured serum MMP-9 levels in patients before and after AAA repair. Blood samples were obtained from 53 patients with AAA; 22 patients underwent AAA operations, including 17 patients with arterial occlusive disease (AOD), and nine normal control subjects. Serum MMP-9 levels were determined by an enzyme-linked immunosorbent assay. The serum MMP-9 concentration was significantly higher in AAA patients (622.0 +/- 400.2 ng/mL) than in either AOD patients (284.3 +/- 151.4 ng/mL) or healthy controls (280.8 +/- 165.5 ng/mL) (p < 0.001). The mean serum MMP-9 levels in patients undergoing surgery for AAA (268.1 +/- 215.9 ng/mL) was significantly lower than that in AAA patients (p < 0.01). Among the 10 patients whose sera were obtained preoperatively and postoperatively, the serum MMP-9 concentration fell significantly after the patients underwent the operation (p = 0.004). No significant difference was identified in serum MMP-9 concentrations among AOD patients, controls, and postoperative patients. These studies suggest that MMP-9 plays a pivotal role in aneurysm formation, and the circulating MMP-9 level is thus considered to reflect the biological behavior of the aneurysm.

Biomechanical properties of ruptured versus electively repaired abdominal aortic aneurysm wall tissue

OBJECTIVE

The purpose of this study was to evaluate and compare the biomechanical properties of abdominal aortic aneurysm (AAA) wall tissue from patients who experienced AAA rupture with that of those who received elective repair.

METHODS

Rectangular, circumferentially oriented AAA wall specimens (approximately 2.5 cm x 7 mm) were obtained fresh from the operating room from patients undergoing surgical repair. The width and thickness were measured for each specimen by using a laser micrometer before testing to failure with a uniaxial tensile testing system. The force and deformation applied to each specimen were measured continuously during testing, and the data were converted to stress and stretch ratio. The tensile strength was taken as the peak stress obtained before specimen failure, and the distensibility was taken as the stretch ratio at failure. The maximum tangential modulus and average modulus were also computed according to the peak and average slope of the stress-stretch ratio curve.

RESULTS

Twenty-six specimens were obtained from 16 patients (aged 73 +/- 3 years [mean +/- SEM]) undergoing elective repair of their AAA (diameter, 7.0 +/- 0.5 cm). Thirteen specimens were resected from nine patients (aged 73 +/- 3 years; P = not significant in comparison to the electively repaired AAAs) during repair of their ruptured AAA (diameter, 7.8 +/- 0.6 cm; P = not significant). A significant difference was noted in wall thickness between ruptured and elective AAAs: 3.6 +/- 0.3 mm vs 2.5 +/- 0.1 mm, respectively (P < .001). The tensile strength of the ruptured tissue was found to be lower than that for the electively repaired tissue (54 +/- 6 N/cm2 vs 82 +/- 9.0 N/cm2; P = .04). Considering all specimens, no significant correlation was noted between tensile strength and diameter (R = -0.10; P = .55). Tensile strength, however, had a significant negative correlation with wall thickness (R = -0.42; P < .05) and a significant positive correlation with the tissue maximum tangential modulus (R = 0.76; P < .05).

CONCLUSIONS

Our data suggest that AAA rupture is associated with aortic wall weakening, but not with wall stiffening. A widely accepted indicator for risk of aneurysm rupture is the maximum transverse diameter. Our results suggest that AAA wall strength, in large aneurysms, is not related to the maximum transverse diameter. Rather, wall thickness or stiffness may be a better predictor of rupture for large AAAs.

Matrix metalloproteinase 2 polymorphisms in a caucasian population with abdominal aortic aneurysm

BACKGROUND

The formation of sporadic abdominal aortic aneurysm (AAA) is explained by remodeling of the extracellular matrix (ECM) and breakdown of structural components of the vascular wall. Matrix metalloproteinase 2 (MMP2) is one of the principal matrix-degrading proteases and is known to play a major role in the remodeling of the extracellular matrix in arterial vessels. Increased MMP2 expression in the extracellular matrix of the walls of AAAs has been shown in several studies. To investigate the possible impact of genetic variants of the MMP2 gene in the etiology of AAA, we conducted this case-control study.

PATIENTS AND METHODS

We analyzed MMP2 single-nucleotide polymorphisms (SNPs) in 51 patients with AAA and 48 controls. Differences in genotype and allele frequencies of identified polymorphisms were determined after sequencing the entire coding region and three selected parts of the promoter.

RESULTS

Eighteen polymorphisms were identified, 6 of which are newly described, with 3 located in the introns (c.IVS1+31C>G, c.IVS7-18G>A, c.IVS10+26C>T) and 3 located in the coding region (c.124G>A, c.1368C>T, c.1860C>T). There were no statistically significant differences in genotype or allele frequencies between the two groups.

CONCLUSIONS

Our analysis of the entire coding region and three parts of the promoter of the MMP2 gene failed to show an association between genetic polymorphisms and AAA, suggesting that variations in the MMP2 gene do not contribute to the development of AAA.

A failure of matrix metalloproteinase inhibition in the prevention of rat intracranial aneurysm formation

We tested the hypothesis that nonspecific matrix metalloproteinase (MMP) inhibition with doxycycline would decrease the incidence of intracranial aneurysm formation in a rat aneurysm model. We performed common carotid artery ligation on 96 Long-Evans rats. A treatment group of 48 animals was chosen at random to receive oral doxycycline (3 mg/kg) in addition to standard rat chow, and the control group of 48 animals received standard rat chow only. The major circle of Willis arteries was dissected at 1 year following carotid ligation, and the proportions of animals with aneurysms were compared between groups using Fisher's exact test. Four animals given oral doxycycline and ten control animals expired before 1 year. Of the examined animals, eight saccular intracranial aneurysms were found in 8 of 45 animals which had received doxycycline (17.8%) and seven saccular intracranial aneurysms were found in 7 of 37 control animals (18.9%). There was no significant difference in aneurysm formation between the doxycycline-treated and control groups (P=0.894). Nonspecific MMP inhibition with doxycycline is not effective in preventing intracranial aneurysm formation in a rat model.

Deficiencies in estrogen-mediated regulation of cerebrovascular homeostasis may contribute to an increased risk of cerebral aneurysm pathogenesis and rupture in menopausal and postmenopausal women

Despite the catastrophic consequence of ruptured intracranial aneurysms, very little is understood regarding their pathogenesis, and there are no reliable predictive markers for identifying at-risk individuals. Few studies have addressed the molecular pathological basis and mechanisms of intracranial aneurysm formation, growth, and rupture. The pathogenesis and rupture of cerebral aneurysms have been associated with inflammatory processes, and these have been implicated in the digestion and breakdown of vascular wall matrix. Epidemiological data indicate that the risk of cerebral aneurysm pathogenesis and rupture in women rises during and after menopause as compared to premenopausal women, and has been attributed to hormonal factors. Moreover, experimental evidence supports a role for estrogen in the modulation of each phase of the inflammatory response implicated in cerebral aneurysm pathogenesis and rupture. While the risk of aneurysm rupture in men also increases with age, this increased risk has been attributed to other recognized risk factors including cigarette smoking, use of alcohol, and history of hypertension, all of which are more common in men than women. We hypothesize, therefore, that decreases in both circulating estrogen levels and cerebrovascular estrogen receptor density may contribute to an increased risk of cerebral aneurysm pathogenesis and rupture in women during and after menopause. To test our hypothesis, experiments are needed to identify genes regulated by estrogen and to evaluate gene expression and intracellular mechanisms in cells/tissues exposed to varying concentrations and duration of treatment with estrogen, metabolites of estrogen, and selective estrogen receptor modulators (SERMs). Furthermore, it is not likely that the regulation of cerebrovascular homeostasis is due to the actions of estrogen alone, but rather the interplay of estrogen and other hormones and their associated receptor expression. The potential interactions of these hormones in the maintenance of normal cerebrovascular tone need to be elucidated. Additional studies are needed to define the role that estrogen and other sex hormones may play in the cerebrovascular circulation and the pathogenesis and rupture of cerebral aneurysms. Efforts directed at understanding the basic pathophysiological mechanisms of aneurysm pathogenesis and rupture promise to yield dividends that may have important therapeutic and clinical implications. The development of non-invasive tools such as molecular MRI for the detection of specific cells, molecular markers, and tissues may facilitate early diagnosis of initial pathophysiological changes that are undetectable by clinical examination or other diagnostic tools, and can also be used to evaluate the state of activity of cerebral aneurysm pathogenesis before, during, and after treatment.

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.

Hyperplastic Cellular Remodeling of the Media in Ascending Thoracic Aortic Aneurysms

Background— Progressive medial degeneration and atrophy is thought to be a cause of ascending thoracic aortic aneurysms in the elderly. Extensive apoptosis of vascular smooth muscle cells (VSMCs) has been demonstrated in the media of abdominal aortic aneurysms. We investigated whether medial atrophy from loss of VSMCs occurs in primary ascending thoracic aortic aneurysms.

Methods and Results— Morphometric analysis of 28 nonaneurysmal ascending thoracic aortas and 29 ascending thoracic aortic aneurysms was performed by directly measuring the thickness of their vascular layers and by indirectly calculating the area of their vascular compartments. The cellular and matrix composition of the media was assessed at the structural, protein, and transcript levels. Despite thinning of the media secondary to vascular dilatation, there was an overall increase in the medial area of aneurysms. VSMC density was preserved, implying cellular hyperplasia as a result of the increased medial mass. There was decreased expression of matrix proteins, despite sustained synthesis of these molecules, which was associated with evidence of increased matrix degradation. The remodeling and expansion of the media was most evident in comparisons between nonaneurysmal aortas versus smaller aneurysms and did not evolve further in larger aneurysms.

Conclusions— The mechanisms for luminal enlargement in thoracic and abdominal aortic aneurysms differ significantly with regard to the survival of VSMCs and atrophy of the media but share common pathophysiology involving degeneration of the matrix. Hyperplastic cellular remodeling of the media in ascending thoracic aortic aneurysms may be an initial adaptive response to minimize increased wall stress resulting from vascular dilatation.

Systemic dilation diathesis in patients with abdominal aortic aneurysms: a role for matrix metalloproteinase-9?

INTRODUCTION

Accumulating evidence suggests that patients with abdominal aortic aneurysm (AAA) suffer from a systemic dilating condition affecting all arteries. Matrix metalloproteinases (MMPs) and their natural inhibitors, the tissue inhibitors of metalloproteinases (TIMPs), appear to be involved in aneurysm formation, as evidenced by increased aortic tissue MMP activity and plasma MMP levels in patients with AAA. Hypothesizing that an imbalance in plasma MMP/TIMP level might be associated with a systemic dilation diathesis, we studied mechanical vessel wall properties of non-affected arteries of patients with either AAA or aorto-iliac obstructive lesions in association with plasma MMP-9 and TIMP-1 levels.

METHODS

Twenty-two patients with AAA and 12 with aorto-iliac occlusive disease (AOD) were included. Diastolic diameter (d) and distension (Deltad) were measured at the level of the common carotid artery (CCA) and suprarenal aorta (SA) using ultrasonography. Distensibility (DC) and compliance (CC) were calculated from d, Deltad and brachial pulse pressure. Plasma MMP-9 and TIMP-1 were determined with specific immunoassays.

RESULTS

The average (+/-SD) age was 72.3+/-5.6 and 65.0+/-8.2 years for the AAA and AOD patients, respectively, (P=0.005). CCA diameter was 9.1+/-1.3mm in AAA patients and AOD 7.8+/-1.4mm in AOD patients, P=0.009. This difference persisted after correction for age. Plasma MMP-9 and TIMP-1 did not differ significantly between AAA and AOD patients. In the total 34 patients, the MMP-9/TIMP-1 ratio was correlated inversely with distensibility (r=-0.74, P=0.002) and to compliance (r=-0.58, P=0.024) of the suprarenal aorta.

CONCLUSIONS

The CCA diameter was larger in AAA patients compared to AOD patients. MMP-9/TIMP-1 ratio was associated with decreased distensibility and compliance of the suprarenal aorta. These data support the idea that AAA patients exhibit a systemic dilation diathesis, which might be attributable to MMP/TIMP imbalances.

Elastin-derived peptides induce a T-helper type 1 polarization of human blood lymphocytes

OBJECTIVE

Increased level of elastin-derived peptides (EDPs) is observed in the serum of patients with manifestations of arterial diseases. We here investigated whether EDPs might exert, at systemic level, a regulatory role for the T-helper type 1 (Th-1)/Th-2 cellular immune response by human peripheral blood lymphocytes (PBLs) expressing the spliced-galactosidase (S-gal)-elastin receptor.

METHODS AND RESULTS

Using flow cytometry and Western blot analysis, we demonstrated that EDPs led to an activation of the S-gal-elastin receptor associated with cytokine production on PBLs and CD4+ T cell subpopulations. The constitutive expression of the S-gal-elastin receptor at the surface of human PBLs was upregulated at the mRNA (RT-PCR) and protein (ELISA) levels on cell activation. In nonactivated and phytohemagglutinin-activated conditions, expressions of the predominant Th-2 cytokine interleukin-5 (IL-5) and IL-10 were reduced, whereas those of the major Th-1 cytokines interferon-gamma and IL-2 were enhanced by EDPs. Furthermore, we evidenced that EDPs could not only potentiate the IL-12-induced Th-1 profile but also could reverse the Th-2 (over Th-1) profile induced by IL-4. Finally, Th-1 cytokine upregulation was associated to an increased activator protein-1 DNA binding and enhanced pro-matrix metalloproteinase-9 secretion.

CONCLUSIONS

This study highlights the importance of EDPs as stimuli for Th-1 differentiation, whether T cells are in an inactivated state or already orientated toward a Th-1 (IL-12) or Th-2 (IL-4) response.

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.

ONO-4817, a novel matrix metalloproteinase inhibitor, attenuates allograft vasculopathy in a rat cardiac transplant

BACKGROUND

Cardiac allograft vasculopathy (CAV), a disorder characterized by rapid development and progression of obliterative vasculopathy in the transplanted heart, continues to be a major cause of graft failure in long-surviving human transplants. The mechanisms and histopathologic processes of CAV remain unknown. Previous animal studies have shown that inhibition of matrix metalloproteinase (MMP) prevents migration and proliferation of smooth muscle cells in CAV. In this study, we hypothesized that MMPs may be expressed in and may play an important role in CAV.

METHODS

An F344-to-WKAH rat heterotopic heart transplantation model was used. Tacrolimus was administered intramuscularly 14 days after transplantation to prevent acute rejection and to allow the development of CAV. We divided the animals into 2 groups according to post-operative treatment: an ONO group received an MMP inhibitor (ONO-4817) daily by oral gavage for 14 days after transplantation (n = 6), and a control (n = 6) group received no treatment. Grafts were harvested 60 days after treatment.

RESULTS

Immunohistochemical staining revealed that MMP-2 and tissue inhibitors of metalloproteinase-2 (TIMP-2) were expressed more strongly in the neointima and media of the control CAV animals than in the ONO-CAV animals. The animals given ONO-4817 exhibited a significant decrease in the percentage of affected vessels, in the percentage of intimal proliferation, in the intima-to-media ratio, and in the expression of MMP-2 and TIMP-2.

CONCLUSION

These results suggest that MMP-2 and TIMP-2 play an important role in the development of CAV and that the use of an MMP inhibitor (ONO-4817) may prevent neointimal proliferation in patients with CAV.

Early MT-1 MMP expression following elastase exposure is associated with increased cleaved MMP-2 activity in experimental rodent aortic aneurysms

OBJECTIVE

The objective of this study was to determine the significance of membrane type 1 matrix metalloproteinase (MT1-MMP) activation of MMP-2 in experimental abdominal aortic aneurysms.

METHODS

Rat aortas were perfused with either saline as a control or elastase, and harvested on 2, 4, or 7 days after perfusion (n = 5 per treatment group/day). Aortic MT1-MMP and MMP-2 expression and protein were determined by real time polymerase chain reaction and Western blotting, respectively. Aortic explants were used to measure MMP-2 activity by zymography. Rat aortic smooth muscle cells in vitro were exposed to increasing doses of elastase and analyzed for MT-1 MMP expression.

RESULTS

Aneurysms formed in 80% of the elastase-perfused aortas at 7 days, whereas none formed in the saline-perfused aortas. Significantly increased MT1-MMP expression was observed only on day 4, when levels were 6.5-fold higher in elastase-perfused aortas compared with saline-perfused aortas (P < .01). By day 7, MT1-MMP protein was present only in the elastase-perfused aortas (P = .02). By immunohistochemistry, MT1-MMP was detectable only in the elastase-perfused group at day 7. Cleaved MMP-2 activity (P = .045) was increased in elastase-perfused aortas compared with saline perfused aortas at day 7. In rat aortic smooth muscle cells, MT-1 MMP expression increased in response to elastase (P = .02).

CONCLUSION

The rodent aortic aneurysm model exhibits upregulation of MT1-MMP expression and protein with subsequent increased conversion of MMP-2 from the latent to the cleaved form.

Key roles of CD4+ T cells and IFN-gamma in the development of abdominal aortic aneurysms in a murine model

Abdominal aortic aneurysm (AAA) is one of a number of diseases associated with a prominent inflammatory cell infiltrate and local destruction of structural matrix macromolecules. This inflammatory infiltrate is predominately composed of T lymphocytes and macrophages. Delineating specific contribution of these inflammatory cells and their cytokines in AAA formation is the key to understanding AAA and other chronic inflammatory disease processes. Our previous studies have demonstrated that macrophages are the major source of matrix metalloproteinase-9, which is required for aneurysmal degeneration in the murine AAA model. However, the role of CD4(+) T cells, the most abundant infiltrates in aneurysmal aortic tissue, is uncertain. In the present study, we found that in the absence of CD4(+) T cells, mice are resistant to aneurysm induction. Previous studies have shown that IFN-gamma levels are increased in AAA. IFN-gamma is a main product of T cells. Intraperitoneal IFN-gamma was able to partially reconstitute aneurysms in CD4(-/-) mice. Furthermore, mice with a targeted deletion of IFN-gamma have attenuation of MMP expression and inhibition of aneurysm development. Aneurysms in IFN-gamma(-/-) mice can be reconstituted by reinfusion of competent splenocytes from the corresponding wild-type mice. This study demonstrates the pivotal role that T cells and the T cell cytokine, IFN-gamma, play in orchestrating matrix remodeling in AAA. This study has important implications for other degenerative diseases associated with matrix destruction.

Matrix metalloproteinases: contribution to pathogenesis, diagnosis, surveillance and treatment of abdominal aortic aneurysms

BACKGROUND

Aortic abdominal aneurysm (AAA) represents a common chronic degenerative disease of the aortic wall. Chronic inflammation and enzymatic degradation of elastic lamellae and extracellular matrix (ECM) proteins constitute the most prominent characteristics of AAAs. There is mounting evidence that matrix metalloproteinases (MMPs) are the predominant proteinases in the AAA wall. These enzymes represent a potential target for therapeutic intervention to modify vascular pathology. This paper is an overview of matrix metalloproteinases and their role in the pathophysiology, diagnosis and treatment of AAA.

LITERATURE SEARCH

Comprehensive search of the MEDLINE, EMBASE and HEAL-Link databases from 1980 to 2003.

FINDINGS

Increased levels of MMPs expression and activity have been demonstrated within the aortic wall of AAA, associating with histological alterations. An imbalance between MMPs and their inhibitors (Tissue Inhibitors of Matrix Metalloproteinases - TIMPs), may tip the equilibrium towards matrix degradation. MMPs as systemic biochemical markers of AAAs may contribute to diagnosis of unsuspected AAAs or to the surveillance of patients with small AAAs. Evidence of variations in MMPs, TIMPs and their mediator genes promoting the increased inheritance susceptibility of AAAs is less well documented. However,a broad spectrum of pharmaceutical agents (e.g. doxycycline, statins etc.) is known to inhibit MMP activity and attenuate medial destruction.

CONCLUSION

Randomized clinical studies in patients in the early stages of AAA or in healthy individuals with great propensity to AAA development are required to demonstrate the causative relationship between MMPs and AAA. It still remains obscure whether long-term administration of MMP inhibitors can decelerate or even prevent the need for surgical repair.

Increased MMP-9 expression and activity by aortic smooth muscle cells after nitric oxide synthase inhibition is associated with increased nuclear factor-kappaB and activator protein-1 activity

OBJECTIVE

To determine the mechanism underlying increased expression and activity of matrix metalloproteinase 9 (MMP-9) by rat aortic smooth muscle cells (RA-SMC) after inhibition of inducible nitric oxide synthase (iNOS).

METHODS AND RESULTS

Treatment of interleukin-1beta-stimulated RA-SMC with aminoguanidine led to an increase of 96% in MMP-9 activity (P = 0.003) by gelatin zymography, a 40% increase in pro-MMP-9 protein (P = 0.018) by Western blot, and a 155% increase in MMP-9 mRNA (P = 0.06) by reverse transcription polymerase chain reaction. Aminoguanidine also caused a 26% decrease in cytosolic IkappaB levels (P = 0.014) by Western blot, as well as a 97% increase in nuclear factor-kappaB binding and a 216% increase in activator protein-1 binding as measured by electrophoretic mobility shift assay. No significant changes were noted in MMP-2 or TIMP-1 expression, protein levels, or activity after aminoguanidine administration.

CONCLUSIONS

MMP-9 expression and activity is increased in cytokine stimulated RA-SMCs after iNOS inhibition, coincident with activation of the nuclear factor-kappaB and activator protein-1 pathways. We speculate that local derangements in iNOS may favor MMP-9-dependent vessel wall damage in vivo via an inflammatory cascade mechanism.

Mechanism of inhibition of matrix metalloproteinase-2 expression by doxycycline in human aortic smooth muscle cells

Degradation of the extracellular matrix components elastin and collagen has been implicated in vascular diseases, including abdominal aortic aneurysm (AAA) and atherosclerotic plaque rupture. Increased expression of matrix metalloproteinases (MMPs) is involved in these disease processes. Our previous studies have demonstrated that MMP-2 derived from mesenchymal cells is required for aneurysm development in a murine model. Doxycycline is a nonspecific inhibitor of MMPs. In the present study, the mechanisms of the inhibitory effects of doxycycline on MMP-2 expression from cultured human aortic smooth muscle cells (SMCs) and human aortic aneurysm tissue explants were studied. Doxycycline inhibited MMP-2 expression from cultured SMCs in a concentration-dependent manner (5-40 microg/mL; inhibitory concentration of 50%, 6.5 microg/mL). At normal therapeutic serum concentration (5 microg/mL) doxycycline significantly reduced MMP-2 production from SMCs (37%; P <.05), which were stimulated with conditioned media from macrophage or lymphocyte co-culture simulating the inflammatory milieu of AAA tissue. This correlated with a decrease in MMP-2 mRNA half-life, from 49 hours to 28 hours, which suggests that doxycycline inhibits SMC MMP-2 production in part by reducing MMP-2 mRNA stability. When AAA tissue was cultured for 10 days with doxycycline at concentrations of 2.5 to 40 microg/mL, the media exhibited a concentration-dependent decrease in both active and latent forms of MMP-2 and MMP-9. Doxycycline at a concentration of 5 microg/mL reduced active and latent MMP-2 secreted from cultured AAA tissue by 50% and 30%, respectively (P <.05). These study findings demonstrate that doxycycline at standard therapeutic serum concentrations inhibits MMP-2 expression from cultured human aortic SMCs and AAA tissue explants. Inasmuch as MMP activity contributes to extracellular matrix degradation in AAAs and atherosclerotic plaque, doxycycline may have potential value in treating these diseases.

A nonintrinsic regional basis for increased infrarenal aortic MMP-9 expression and activity

OBJECTIVE

This investigation was undertaken to determine whether intrinsic or regional factors at different anatomic sites of the aorta affect expression and activity of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs).

METHODS

Aortas from Sprague-Dawley rats (n = 22) were divided into arch, descending thoracic, and infrarenal abdominal segments. Specimens were stimulated with interleukin-1beta (IL-1beta) (2 ng/mL) for 72 hours. In separate experiments, syngeneic aortic segments were transplanted from the thoracic or abdominal aortas of donor rats into the infrarenal aortic position of recipient rats (n = 12 each). At 4 weeks, aortas from rats who had received transplants were harvested, sectioned into arch, thoracic, and transplanted thoracic or transplanted abdominal segments, and stimulated with IL-1beta. Reverse transcriptase polymerase chain reaction, zymography, and reverse zymography were performed to assess MMP-9, MMP-2, and TIMP-1 in all aortic segments. Differences were assessed with analysis of variance (ANOVA) and post-hoc Tukey test.

RESULTS

In control rats, abdominal segments had significantly higher MMP-9 expression compared with arch and thoracic segments (P <.002). Total MMP-9 activity was also higher in abdominal segments (P <.02). In rats who received transplants, transplanted thoracic (P <.004) and transplanted abdominal (P <.05) segments demonstrated upregulation of MMP-9 expression, compared with control arch and thoracic segments. Zymography documented increased total MMP-9 activity in transplanted thoracic (P <.03) and transplanted abdominal (P <.04) segments versus arch and thoracic segments. No significant difference in MMP-9 expression was found between control abdominal, transplanted thoracic, or transplanted abdominal segments. No significant differences in MMP-2 or TIMP-1 expression or activity were demonstrated in either control or transplanted segments.

CONCLUSIONS

These data demonstrate that variations in aortic MMP-9 expression and activity result from regional factors affecting the aorta rather than intrinsic aortic wall differences. Increases in abdominal aortic MMP-9 may contribute to the predilection for aneurysm to develop in the infrarenal aorta.

Enhanced invasive properties exhibited by smooth muscle cells are associated with elevated production of MMP-2 in patients with aortic aneurysms

BACKGROUND

abdominal aortic aneurysms (AAA) are associated with excessive vascular matrix remodelling. Recent findings suggest a systemic overproduction of matrix metalloproteinases-2 (MMP-2) by vascular smooth muscle cells (SMC) may be pivotal aetiologically. SMC migration is facilitated by MMP mediated proteolysis of the basement membrane and extracellular matrix. Our aim was to see if enhanced MMP-2 production by these SMC exhibit increased invasion, in an in vitro model of migration.

METHOD

SMC were derived from inferior mesenteric vein (IMV) harvested from patients undergoing aneurysm repair (n=6) or colectomy for diverticulosis (n=6, control). Using a modified Boyden chamber chemotaxis was measured towards platelet derived growth factor (PDGF) and foetal calf serum (FCS) and invasion through a Matrigel layer. MMP-2 production was quantified by ELISA and gelatin zymography.

RESULTS

chemoattractant studies demonstrated no difference in the effect of PDGF or FCS between the two populations of SMC. However, invasive studies demonstrated a significant increase in the number of migrating SMC isolated from IMV of AAA patients. Analysis of culture media extracts revealed that this difference was associated with a significant increase in production of MMP-2.

CONCLUSION

SMC derived from patients with AAA demonstrate increased invasive properties when compared to a control group. Increased migration appears to be due to overproduction of MMP-2. The enhanced migratory potential of these SMC may lead to extracellular matrix remodelling and subsequent medial disruption demonstrated in the aneurysmal aorta. These data further support evidence of the proteolytic role of MMP-2 in cell migration.