Expression and localization of macrophage elastase (matrix metalloproteinase-12) in abdominal aortic aneurysms

Gene polymorphisms of matrix metalloproteinase-2, -9 and -12 in periodontal health and severe chronic periodontitis

AIM

Matrix metalloproteinases (MMPs) are involved in periodontal tissue remodeling and degradation. MMP polymorphisms could alter transcription and function of these enzymes. The aim of this study was to investigate MMP-2, MMP-9 and MMP-12 gene polymorphisms in relation to susceptibility to severe chronic periodontitis (CP).

METHODS

Genomic DNA was obtained from peripheral blood of 87 severe CP patients and 107 periodontally healthy subjects. MMP-2 -735C/T, MMP-9 -1562C/T and MMP -12357Asn/Ser gene polymorphisms were genotyped by polymerase chain reaction and restriction fragment length polymorphism. Probing depth, clinical attachment loss, supragingival plaque accumulation and bleeding on probing were recorded. The data were analyzed by chi-square, logistic regression and Mann-Whitney-U-tests.

RESULTS

The genotype distributions and allele frequencies of MMP-2, MMP-9 and MMP-12 genes were similar in CP and healthy subjects (p>0.05). Differences between rare allele carriage rates of CP and healthy groups regarding MMP-2, MMP-9 and MMP-12 gene polymorphisms were not significant (p>0.05). However, T allele carriers of MMP-9 -1562 gene had less risk for CP (OR=0.36; 95% CI=0.16-0.81).

CONCLUSION

These data suggest that MMP-2 -735C/T, MMP-9 -1562C/T and MMP-12 357Asn/Ser polymorphisms are not associated with susceptibility to severe CP in Turkish population. However, T allele of MMP-9 -1562 gene might be associated with decreased susceptibility to severe CP.

Apolipoprotein C1 and apolipoprotein E are differentially expressed in atheroma of the carotid and femoral artery

BACKGROUND

A number of the genes and proteins as the causes of carotid atherosclerotic disease have been recently reported, but the major factors for atherosclerosis have still not been identified.

METHODS

The atherosclerotic atheromas were obtained during endarterectomy for each of 10 cases of diseased carotid and femoral arteries. As the nonatherosclerotic arteries, the iliac arteries were obtained during organ harvest from five cases of brain-dead donors, and the leg arteries were obtained during leg amputation from five cases of Buerger's disease. The total RNAs and proteins were isolated from the atheromas and arteries. The annealing control primer method was used to screen the differentially expressed mRNAs. To identify if the mRNA expression of screened gene was associated with the protein expression, we performed an immunohistochemical analysis.

RESULTS

We found that the apolipoprotein C1 (apo C1) gene was prominently expressed in the atheroma of the carotid and femoral arteries, as compared to the nonatherosclerotic arteries. Immunohistochemical analysis showed the high expression of apo C1 protein in the atheromas of the carotid and femoral arteries. Apo E protein was also highly expressed in atheromas compared with the nonatherosclerotic arteries, but there was no difference for apo C2 protein between those four groups of arteries.

DISCUSSION

The expression of apo C1 and apo E are closely associated with the susceptibility to the pathogenesis of atherosclerosis. This study suggests that these factors might play important roles in the future to screen for preventing atherosclerosis and for diagnostic testing of patients.

Solution structure of inhibitor-free human metalloelastase (MMP-12) indicates an internal conformational adjustment

Macrophage metalloelastase or matrix metalloproteinase-12 (MMP-12) appears to exacerbate atherosclerosis, emphysema, aortic aneurysm, rheumatoid arthritis, and inflammatory bowel disease. An inactivating E219A mutation, validated by crystallography and NMR spectra, prevents autolysis of MMP-12 and allows us to determine its NMR structure without an inhibitor. The structural ensemble of the catalytic domain without an inhibitor is based on 2813 nuclear Overhauser effects (NOEs) and has an average RMSD to the mean structure of 0.25 A for the backbone and 0.61 A for all heavy atoms for residues Trp109-Gly263. Compared to crystal structures of MMP-12, helix B (hB) at the active site is unexpectedly more deeply recessed under the beta-sheet. This opens a pocket between hB and beta-strand IV in the active-site cleft. Both hB and an internal cavity are shifted toward beta-strand I, beta-strand III, and helix A on the back side of the protease. About 25 internal NOE contacts distinguish the inhibitor-free solution structure and indicate hB's greater depth and proximity to the sheet and helix A. Line broadening and multiplicity of amide proton NMR peaks from hB are consistent with hB undergoing a slow conformational exchange among subtly different environments. Inhibitor-binding-induced perturbations of the NMR spectra of MMP-1 and MMP-3 map to similar locations across MMP-12 and encompass the internal conformational adjustments. Evolutionary trace analysis suggests a functionally important network of residues that encompasses most of the locations adjusting in conformation, including 18 residues with NOE contacts unique to inhibitor-free MMP-12. The conformational change, sequence analysis, and inhibitor perturbations of NMR spectra agree on the network they identify between structural scaffold and the active site of MMPs.

Ageing of the conduit arteries

Conduit arteries become stiffer with age due to alterations in their morphology and the composition of the their major structural proteins, elastin and collagen. The elastic lamellae undergo fragmentation and thinning, leading to ectasia and a gradual transfer of mechanical load to collagen, which is 100-1000 times stiffer than elastin. Possible causes of this fragmentation are mechanical (fatigue failure) or enzymatic (driven by matrix metallo proteinases (MMP) activity), both of which may have genetic or environmental origins (fetal programming). Furthermore, the remaining elastin itself becomes stiffer, owing to calcification and the formation of cross-links due to advanced glycation end-products (AGEs), a process that affects collagen even more strongly. These changes are accelerated in the presence of disease such as hypertension, diabetes and uraemia and may be exacerbated locally by atherosclerosis. Raised MMP activity, calcification and impaired endothelial function are also associated with a high level of plasma homocysteine, which itself increases with age. Impaired endothelial function leads to increased resting vascular smooth muscle tone and further increases in vascular stiffness and mean and/or pulse pressure. The effect of increased stiffness, whatever its underlying causes, is to reduce the reservoir/buffering function of the conduit arteries near the heart and to increase pulse wave velocity, both of which increase systolic and pulse pressure. These determine the peak load on the heart and the vascular system as a whole, the breakdown of which, like that of any machine, depends more on the maximum loads they must bear than on their average. Reversing or stabilising the increased arterial stiffness associated with age and disease by targeting any or all of its causes provides a number of promising new approaches to the treatment of systolic hypertension and its sequelae, the main causes of mortality and morbidity in the developed world.

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.

Role of matrix metalloproteinase inhibitors in preventing abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a significant health problem in the United States, with approximately 30,000 repair operations annually. Treatment of AAA is associated with more than 150,000 hospital admissions per year. The development of AAA is characterized by destruction of the elastic media of the aortic wall. A large body of evidence suggests that a group of enzymes called matrix metalloproteinases (MMPs) plays a significant role in the destruction of extracellular matrix in the aortic wall. MMP inhibition has, therefore, been viewed as an alternative pharmacotherapeutic approach to slow down the development and progression of small AAAs, thus reducing the need for surgical intervention.

Expansive remodeling in venous bypass grafts: novel implications for vein graft disease

OBJECTIVE

To date, intimal hyperplasia has been regarded as the principle mechanism responsible for subsequent vein graft disease. Lumen remodeling has not been previously considered as an additional mechanism. The objectives of this study were to determine changes in lumen remodeling in arterialized vein grafts, the accompanying cellular and extracellular matrix events contributing to remodeling, and the effects of a high cholesterol diet.

METHODS AND RESULTS

Reversed jugular vein-to-common carotid artery interposition grafts were constructed in 70 normocholesterolemic and 11 hypercholesterolemic male New Zealand white rabbits. The lumen area initially remained unchanged between 1 and 4 weeks but significantly increased by 40% at 12 weeks. This phase of expansive positive remodeling was accompanied by significantly increased cell apoptosis, collagen synthesis (1.7-fold), collagen content (3.7-fold), gelatinase (MMP-2 and MMP-9) levels and decreased tissue inhibitor of metalloproteinase (TIMP) levels. Expansive remodeling temporally corresponded to high macrophage infiltration and increased low density lipoprotein (LDL) retention (fourfold) in the vein grafts. A high cholesterol diet stimulated early macrophage infiltration and increased MMP-12 (metalloelastase) levels, which was associated with earlier onset of expansive remodeling.

CONCLUSION

Expansive lumenal remodeling is a novel mechanism of vein graft response to the arterial circulation, which is accelerated by a high cholesterol diet.

Synthesis and matrix metalloproteinase (MMP)-12 inhibitory activity of ageladine A and its analogs

Ageladine A (1) and its analogs 2-10 were expeditiously synthesized by featuring the biosynthetic route proposed for 1 (for 1-10) and by employing 2-(N-t-butoxycarbonylamino)imidazol-4-carbaldehyde as the starting material (for 1-8). From MMP-12 inhibitory activity assay, it appeared evident that the two bromine atoms and the three NH groups (1-NH, 14-NH, and 15-NH2) were indispensable for 1 to exhibit excellent activity.

Elastin expression and elastic fibre width in the anterior vaginal wall of postmenopausal women with and without prolapse

OBJECTIVES

To compare elastin expression and elastic fibre width in the anterior vaginal wall of postmenopausal women with and with no bladder prolapse.

PATIENTS AND METHODS

Full-thickness specimens were obtained from the upper lateral anterior vaginal wall of women having a large cystocele repaired (stage III or IV; prolapse group, 33) and the same location in patients with no prolapse having radical cystectomy (control group, 10). The percentage of elastin-positive tissue and elastic fibre width were measured by immunohistochemistry on 6 microm thick tissue sections from 10 random field readings per sample using image analysis software. The examiner was unaware of sample identity and the patients' clinical history.

RESULTS

The age was comparable between the control and prolapse groups (median 70.5 years), and the parity, vaginal deliveries, hormone replacement use, cigarette smokers and body mass index were no different between the groups. Immunohistochemical staining and morphometric analysis indicated that elastin expression in the prolapse group was 10.6%, vs 14.4% in the control group (P = 0.049). The median width of elastic fibres was 0.9 microm in the prolapse and 1.8 microm in the control groups (P < 0.001). Elastin expression and elastic fibre width appeared to be stable with increasing age in the prolapse group.

CONCLUSIONS

In this case-control study investigating elastin changes in postmenopausal women with prolapse, the elastin expression and fibre width were significantly lower in the vaginal wall of patients with a large cystocele than in controls of a similar age.

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.

Elevated tissue plasminogen activator in patients with screening-detected abdominal aortic aneurysm

OBJECTIVE

A population-based case-control study with historical and current data was conducted in a population with a high prevalence of disease to explore the hypothesis that the fibrinolytic system may be involved in the early pathogenesis of abdominal aortic aneurysm (AAA).

METHODS

Forty-two patients found to have AAA at population-based screening were compared with 100 controls matched for age and sex. Mass concentration of tissue plasminogen activator (tPA mass) and tissue plasminogen activator/plasminogen activator inhibitor-1 complex (tPA/PAI-1 complex mass) were analyzed in blood samples obtained at the screening (current), and in blood samples obtained from a study conducted 12 years previously on the same population (historical).

RESULTS

Current tPA mass levels were significantly higher in AAA patients compared with controls (13.6 vs 11.4 microg/L, P=.016). A similar trend was observed in historical tPA mass levels (9.8 vs 8.2 microg/L, P=.062). Current and historical mass concentrations of tPA/PAI complex in AAA patients were similar to those in controls. Current tPA mass levels retained the associations with AAA in a logistic regression model after adjustment for history of atherosclerosis (odds ratio [OR], 1.1 per microg/L, P=.039) and current smoking (OR 1.1 per microg/L, P=.039). When family history of AAA was added in a logistic regression model, the OR for current tPA mass was 1.1 per microg/L (P=.056) and 1.1 per microg/L (P=.070) when treated hypertension was added.

CONCLUSION

The finding of elevated tPA mass, in contrast to tPA/PAI-1 complex, in plasma among patients with screening-detected AAA supports the hypothesis that the fibrinolytic system may be important in the early pathogenesis of AAA.

Plasma metalloproteinase-12 and tissue inhibitor of metalloproteinase-1 levels and presence, severity, and outcome of coronary artery disease

Several matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) have been implicated in the development and outcome of coronary artery disease (CAD). We investigated whether MMP-12 and TIMP-1 levels were associated with risk, severity, and outcome of CAD. Plasma MMP-12 and TIMP-1 levels are measured in 50 and 44 patients with CAD, respectively, by enzyme-linked immunosorbent assay. Of all patients, 16 were taking statins. Patients who were not on statins were classified into 3 groups according to number of >50% stenotic vessels. Compared with 29 volunteers without CAD, patients without statins (n = 34) had higher MMP-12 concentrations (1.71 vs 1.08 ng/ml, p = 0.021). MMP-12 levels were significantly lower in patients with than in those without statin treatment (0.99 vs 1.71 ng/ml, p = 0.008). There was no association between MMP-12 levels and number of >50% stenotic vessels. MMP-12 concentrations were not associated with outcome of CAD. However, plasma TIMP-1 levels were associated with restenosis independently of number of stenotic vessels and age (p = 0.035) but not with risk or severity of CAD. In conclusion, plasma MMP-12 concentration was associated with the presence of CAD. Statin therapy decreases plasma MMP-12 levels in patients with CAD. Increased TIMP-1 levels may prevent restenosis after angioplasty.

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.

Cigarette smoking increases aortic dilatation without affecting matrix metalloproteinase-9 and -12 expression in a modified mouse model of aneurysm formation

OBJECTIVE

The development of abdominal aortic aneurysms (AAA) is presumed to result from multiple genetic and environmental factors, with exposure to tobacco smoke the single largest known factor predisposing to aneurysm growth. We have attempted to adapt the elastase-perfused animal model to determine whether tobacco exposure can lower the threshold of aortic injury necessary for AAA development.

METHODS

Adult C57BL/6 mice underwent transient perfusion of the infrarenal aorta with an active solution of elastase: high-dose (HDE, 0.19 U/mL, n=9), standard-dose (SDE, 0.16 U/mL, n=21) or low-dose (LDE, 0.07 U/mL, n=24). Control animals (n=24) were treated with heat inactivated elastase (HIE). Twenty LDE perfused mice were exposed to cigarette smoke (LDE-S) beginning 2 weeks before perfusion and continuing until aortic harvest. Aortic diameter (AD) was measured preperfusion, postperfusion, and at harvest on day 14. AAA was defined as %DeltaAD>or=100% between preperfusion and harvest. Aortas from each group (except HDE) were analyzed for matrix metalloproteinase-9 (MMP-9) and MMP-12 expression by real-time polymerase chain reaction normalized to glyceraldehyde-3-phosphate dehydrogenase.

RESULTS

All SDE mice developed large AAA by %DeltaAD (189.3%+/-16.9%, mean+/-standard error of the mean), but control mice had only a small dilatation (69.7%+/-3.7%, P<.01). Higher doses of elastase did not produce larger aneurysms in HDE mice. In contrast, only 63% of LDE mice showed aneurysmal dilatation, and these were significantly smaller (104.3%+/-4.2%, P<.01). When exposed to cigarette smoke, LDE animals developed significantly larger aneurysms (%DeltaAD, 134.5%+/-7.9%, P=.0021). There was no difference in normalized aortic MMP-9 and MMP-12 expression between elastase doses or between smoke-exposed and unexposed animals. Histologic analysis revealed that smoking increased the extent of aortic elastin degradation when compared with LDE-S animals.

CONCLUSION

Aneurysm development in the elastase model is dependent on the quantity of active elastase infused. Exposure of animals to tobacco smoke after a relatively minor aortic elastase injury produces increases in elastin degradation and aneurysm size without affecting MMP-9 or MMP-12 expression. To our knowledge, this is the first demonstration in an animal model that smoking can act as a synergistic factor in AAA development. Further understanding of the relationship between smoking and AAA in this model may help unveil the pathophysiologic pathways involved between cigarette smoke and AAAs.

Increase in the expression of matrix metalloproteinase-12 in the airways of rats with allergic bronchial asthma

Although an involvement of matrix metalloproteinase (MMP)-12 in the development of chronic obstructive pulmonary disease (COPD) and airway inflammation has been suggested, its detailed role in the airways is not well known now. In the present study, the changes in the expression and localization of MMP-12 in airways of repeatedly antigen-challenged rats were investigated to show an association of MMP-12 with allergic bronchial asthma. Rats sensitized by dinitrophenylated Ascaris antigen were 3 times repeatedly challenged with aerosolized antigen solution to induce an asthmatic reaction. Twenty-four hours after the last antigen challenge, marked airway inflammation and bronchial smooth muscle hyperresponsiveness were observed. In this animal model of allergic bronchial asthma, a significant increase in the expression/activity of MMP-12 was found: the peak was observed at 12 h after the last antigen challenge. Furthermore, mRNA expression of MMP-12 was also increased at the early phase (1-3 h) after the last antigen challenge. Immunohistochemical studies revealed that MMP-12 was mainly expressed in airway epithelia and alveolar macrophages. These findings suggest that MMP-12 is upregulated after the induction of asthmatic reaction. MMP-12 might be a new target for the therapy against allergic bronchial asthma.

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.

Versican, a major hyaluronan-binding component in the dermis, loses its hyaluronan-binding ability in solar elastosis

Versican interacts with hyaluronan (HA) at its N-terminus and with fibrillin-1 at its C terminus. As versican in the dermis connects microfibrils to the HA-rich matrix for viscoelasticity, dermal diseases may involve destruction of these complexes. A recombinant versican protein, rVN, covering the HA binding region (HABR) of human versican and a polyclonal antibody, 6084, against rVN were prepared and characterized. Blotting analyses of skin extracts with 6084 and biotin-conjugated HA revealed that versican was a major HA-binding component in the dermis. Matrix metalloprotease-12, which is expressed in areas of solar elastosis, degraded versican and abrogated its HA-binding ability. Immunohistochemical analyses revealed that the elastic materials in solar elastosis lesions were negative for 6084, but positive for 2B1, an antibody recognizing the C-terminus of versican, indicating loss of the HABR in the aggregated elastic fibers. This loss of the HA-binding ability of versican followed by HA exclusion may be responsible for the pathological and phenotypical changes observed in solar elastosis.

Role of Oxidative Stress in the Pathogenesis of Abdominal Aortic Aneurysms

The role of inflammation in the pathogenesis of abdominal aortic aneurysms (AAA) is well established. The inflammatory process leads to protease-mediated degradation of the extracellular matrix and apoptosis of smooth muscle cells (SMC), which are the predominant matrix synthesizing cells of the vascular wall. These processes act in concert to progressively weaken the aortic wall, resulting in dilatation and aneurysm formation. Oxidative stress is invariably increased in, and contributes importantly to, the pathophysiology of inflammation. Moreover, reactive oxygen species (ROS) play a key role in regulation of matrix metalloproteinases and induction of SMC apoptosis. ROS may also contribute to the pathogenesis of hypertension, a risk factor for AAA. Emerging evidence suggests that ROS and reactive nitrogen species (RNS) are associated with AAA formation in animal models and in humans. Although experimental data are limited, several studies suggest that modulation of ROS production or activity may suppress AAA formation and improve experimental outcome in rodent models. Although a number of enzymes can produce injurious ROS in the vasculature, increasing evidence points toward a role for NADPH oxidase as a source of oxidative stress in the pathogenesis of AAA.

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.

Spatiotemporal expression and localization of matrix metalloproteinas-9 in a murine model of thoracic aortic aneurysm

OBJECTIVE

Matrix metalloproteinase-9 (MMP-9) has been widely described to play a critical role in aneurysm development. The goal of this study was to determine the spatiotemporal changes in MMP-9 expression and abundance in the early stages of aortic dilatation during the course of thoracic aortic aneurysm (TAA) formation in a mouse model.

METHODS

In this study, TAAs were surgically induced in a transgenic reporter mouse strain expressing the beta-galactosidase (beta-gal) gene under control of the MMP-9 promoter. Terminal studies were performed during the early stages of TAA development at 1 week (n = 6), 2 weeks (n = 6), and 4 weeks (n = 6) post-TAA induction surgery. Changes in aortic outer diameter were determined in vivo by video micrometry. MMP-9 transcriptional activity (beta-gal staining) and protein content (immunohistochemistry) were quantified at each time point and expressed as a percentage of unoperated reference control mice (n = 6).

RESULTS

Aortic dilatation was evident at 1 week and reached maximal size at 2 weeks (21% +/- 6% increase from baseline, P < .05). MMP-9 transcriptional activity was detected at 1 week post-TAA induction (722% +/- 323%, P = .19), reached a maximum within the adventitia at 2 weeks (1770% +/- 505%, P < .05), and returned to baseline by 4 weeks (167% +/- 47%, P = .21). MMP-9 transcription at 2 weeks colocalized with fibroblasts and smooth muscle cells. MMP-9 protein content within the aortic adventitia was increased at 2 weeks post-TAA induction (413% +/- 124%, P < .05) and remained elevated at 4 weeks (222% +/- 41%, P < .05). MMP-9 staining was most intense at the adventitial-medial border and could be detected throughout the elastic media.

CONCLUSIONS

These findings demonstrate a unique spatiotemporal pattern of MMP-9 transcriptional activation and protein content in the developing TAA. Colocalization studies suggest that early dilatation may be driven in part by MMP-9 produced by endogenous cells residing within the aortic vascular wall.

Matrix biology of abdominal aortic aneurysms in diabetes: mechanisms underlying the negative association

Several case-control studies have shown a significant negative association between diabetes and abdominal aortic aneurysm (AAA). This interaction has the potential to further our understanding of these two diseases but has attracted little research. The changes seen in the walls of aneurysmal aortas include inflammation and the activation of proteolytic pathways resulting in loss of elastin and other structural proteins. In contrast, diabetes is associated with increased synthesis and reduced degradation of matrix. The deposition of advanced glycation end products also renders vascular matrix resistant to proteolysis in diabetic patients. The aim of our present minireview is to compare the changes in matrix biology seen in diabetes and AAA and to explore molecular mechanisms that may explain the negative association and identify possible therapeutic implications.

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.

Heterogeneity in the remodeling of aneurysms of the ascending aorta with tricuspid aortic valves

OBJECTIVES

The study addresses mechanisms driving the formation of ascending aortic aneurysms by comparing the maximal dilatation area with the transition area immediately adjacent to the normal aortic tissue left in place during surgical repair.

METHODS

Aortic wall specimens were taken from the maximal dilatation area and transition area in 10 patients undergoing surgery for ascending aortic aneurysms and fixed for histology and immunohistochemistry for vascular smooth muscle cells (alpha-actin), endothelial cells (CD31), and macrophages (CD68). Tissue concentrations of vascular endothelial growth factor, matrix metalloproteinase-2, and matrix metalloproteinase-9 were determined by enzyme-linked immunosorbent assay. The results are expressed as medians with their 25th and 75th centiles.

RESULTS

Vascular smooth muscle cells were significantly more abundant in the maximal dilatation area than in the transition area (20.3 [14.8-24.4]/10(-2) mm2 vs 8.0 [6.4-9.3]/10(-2) mm2, respectively, P = .002). In the maximal dilatation area, vascular smooth muscle cells had lost their typical lamellar organization, whereas it was preserved in the transition area. Microvessels were significantly more abundant in the media of transition area than in the maximal dilatation area (7.5 [2.9-10.1]/mm2 vs 1.75 [1.5-2.0]/mm2, respectively, P = .008) and were associated with an inflammatory cell infiltration that predominated in their immediate vicinity. There were no significant differences in vascular endothelial growth factor, matrix metalloproteinase-2, and matrix metalloproteinase-9 between both areas.

CONCLUSIONS

The transition area appears as a disease progression front characterized by microvessel formation and inflammatory cell infiltration. In contrast, increased vascular smooth muscle cell density in the maximal dilatation area suggests a healing process, although inefficient to prevent aortic dilatation.

Temporal disparity in the induction of matrix metalloproteinases and tissue inhibitors of metalloproteinases after thoracic aortic aneurysm formation

BACKGROUND

An important component of matrix remodeling during thoracic aortic aneurysm progression is the balance between matrix metalloproteinases and their endogenous inhibitors (tissue inhibitors of metalloproteinases). However, whether and to what degree matrix metalloproteinase/tissue inhibitor of metalloproteinases profiles change over time with an evolving thoracic aortic aneurysm remains unclear.

METHODS

Descending thoracic aortic aneurysms were induced in mice (FVB strain, 15 minutes of 0.5 mol/L CaCl2 exposure) and followed for 24 hours, 72 hours, 1 week, 2 weeks, 4 weeks, or 8 weeks (each group, n = 13). Thoracic aortic aneurysm size was determined by means of video micrometry, and immunoblotting was used to measure aortic matrix metalloproteinase 2, 8, 9, and 12 and tissue inhibitor of metalloproteinases 1 and 4 levels (expressed as a percentage of control values, n = 13).

RESULTS

Increased aortic diameter was detected by 72 hours and reached a maximal size at 4 weeks (135% +/- 4% increase from baseline, P < .05), which is consistent with thoracic aortic aneurysm progression. Active matrix metalloproteinase 8 (collagenase) levels increased at 72 hours (178% +/- 49%, P < .05 from control), and active matrix metalloproteinase 12 (elastase) levels increased by 24 hours (138% +/- 11%, P < .05), whereas active matrix metalloproteinase 2 levels increased at 72 hours and 1 week after thoracic aortic aneurysm induction (72 hours: 158% +/- 12%, 1 week: 162% +/- 19%; P < .05). At 1 week after thoracic aortic aneurysm induction, active matrix metalloproteinase 9 and 12 levels decrease (matrix metalloproteinase 9: 55% +/- 5%; matrix metalloproteinase 12: 63% +/- 5%; P < .05); however, matrix metalloproteinase 9 and 12 levels were increased from these values at 4 and 8 weeks (P < .05). Tissue inhibitor of metalloproteinases 1 levels were decreased at 1 week (52% +/- 15%, P < .05) and later returned to control values, whereas tissue inhibitor of metalloproteinases 4 levels increased at the late thoracic aortic aneurysm time points (4 weeks: 278% +/- 46%; 8 weeks: 213% +/- 40%; P < .05).

CONCLUSIONS

These findings show 2 phases of matrix metalloproteinase abundance during murine thoracic aortic aneurysm formation. The late tissue inhibitor of metalloproteinases 4 increase might explain prevention of further aortic dilation past 4 weeks. Unique matrix metalloproteinase/tissue inhibitor of metalloproteinases temporal relationships occurred during the natural history of thoracic aortic aneurysm progression that might hold both diagnostic and therapeutic relevance.

Induction of macrophage chemotaxis by aortic extracts of the mgR Marfan mouse model and a GxxPG-containing fibrillin-1 fragment

BACKGROUND

The primary cause of early death in untreated Marfan syndrome (MFS) patients is aortic dilatation and dissection.

METHODS AND RESULTS

We investigated whether ascending aortic samples from the fibrillin-1-underexpressing mgR mouse model for MFS or a recombinant fibrillin-1 fragment containing an elastin-binding protein (EBP) recognition sequence can act as chemotactic stimuli for macrophages. Both the aortic extracts from the mgR/mgR mice and the fibrillin-1 fragment significantly increased macrophage chemotaxis compared with extracts from wild-type mice or buffer controls. The chemotactic response was significantly diminished by pretreatment of macrophages with lactose or with the elastin-derived peptide VGVAPG and by pretreatment of samples with a monoclonal antibody directed against an EBP recognition sequence. Mutation of the EBP recognition sequence in the fibrillin-1 fragment also abolished the chemotactic response. These results indicate the involvement of EBP in mediating the effects. Additionally, investigation of macrophages in aortic specimens of MFS patients demonstrated macrophage infiltration in the tunica media.

CONCLUSIONS

Our findings demonstrate that aortic extracts from mgR/mgR mice can stimulate macrophage chemotaxis by interaction with EBP and show that a fibrillin-1 fragment possesses chemotactic stimulatory activity similar to that of elastin degradation peptides. They provide a plausible molecular mechanism for the inflammatory infiltrates observed in the mgR mouse model and suggest that inflammation may represent a component of the complex pathogenesis of MFS.

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.

Expression of matrix metalloproteinases and endogenous inhibitors within ascending aortic aneurysms of patients with Marfan syndrome

BACKGROUND

Marfan syndrome (MFS) is known to cause ascending thoracic aortic aneurysms (ATAAs). Transforming growth factor beta (TGF-beta) has recently been implicated in this process. Imbalances between the matrix metalloproteinases (MMPs) and their endogenous inhibitors (TIMPs) have also been shown to contribute to aneurysm formation. Whether and to what degree MMP, TIMP, and TGF-beta signaling profiles are altered in ATAAs in MFS compared with non-MFS patients remains unknown.

METHODS AND RESULTS

ATAA samples taken during aortic replacement from age-matched MFS (n=9) and non-MFS (n=18) patients were assessed for representative subtypes of all MMP classes, all 4 known TIMPs, and type 2 TGF-beta receptors (TGFBR2). Results were expressed as a percentage (mean+/-SEM) of reference control samples (100%; n=18) obtained from patients without ATAA. In MFS, decreased MMP-2 (76+/-7; P<0.05 versus control), increased MMP-12 (161+/-27% versus control; P<0.05), and increased MT1-MMP (248+/-64% versus 91+/-21 non-MFS and control; P<0.05) were observed. TIMP-3 (74+/-23%) was reduced compared with control values (P<0.05) and TIMP-2 was elevated (128+/-31%) compared with non-MFS (73+/-19%; P<0.05). In non-MFS samples, MMP-1 (70+/-16%), MMP-3 (77+/-18%), MMP-8 (75+/-11%), MMP-9 (69+/-14%), and MMP-12 (85+/-15%) were decreased compared with control (P<0.05). TIMPs 1 to 3 were reduced in non-MFS compared with control values (P<0.05). TGFBR2 were increased in MFS (193+/-32%) compared with non-MFS (95+/-16%) and controls (P<0.05).

CONCLUSIONS

A unique MMP and TIMP portfolio was observed in ATAAs from MFS compared with non-MFS patients. In addition, MFS samples showed evidence of increased TGF-beta signaling. These differences suggest disparate mechanisms of extracellular matrix remodeling between these 2 groups of patients.

Prevention of abdominal aortic aneurysms by simultaneous inhibition of NFkappaB and ets using chimeric decoy oligonucleotides in a rabbit model

Abdominal aortic aneurysm (AAA) is one of the major vascular diseases caused by atherosclerosis. Because treatment for AAA mainly consists of surgery to prevent deaths from AAA rupture and there is a conspicuous absence of alternative therapeutic strategies, the development of minimally invasive treatment is needed. To develop a novel therapeutic approach, we examined the simultaneous inhibition of the transcription factors NFkappaB and ets, which regulate inflammation and matrix degradation, in a rabbit AAA model. In this study, we employed chimeric decoy oligodeoxynucleotides (ODN), containing the consensus sequences of both the NFkappaB- and ets-binding sites, to inhibit both the transcription factors simultaneously. Using a delivery sheet, we examined the inhibitory effect of chimeric decoy ODN on aortic dilatation. Ultrasound and angiographic analysis demonstrated that treatment with chimeric decoy ODN significantly prevented the progression of elastase-induced aortic dilatation. The inhibitory effect of chimeric decoy ODN on aortic dilatation was also confirmed by histological studies. Treatment with chimeric decoy ODN reduced the activities of matrix metalloproteinase (MMP)-2 and MMP-9 and markedly inhibited the proteolysis of elastin as compared to scrambled decoy ODN. Interestingly, treatment with chimeric decoy ODN also suppressed VCAM-1 and MCP-1 gene expression, leading to inhibition of macrophage infiltration in the adventitia and media. The present study in a rabbit model provides a novel strategy to treat AAA by the simultaneous inhibition of both NFkappaB and ets using chimeric decoy ODN. Further modification of chimeric decoy ODN would be useful to treat AAA as a decoy-based therapy.

Macrophage Metalloelastase Accelerates the Progression of Atherosclerosis in Transgenic Rabbits

BACKGROUND

Macrophage metalloelastase (matrix metalloproteinase [MMP]-12) is upregulated in atherosclerotic lesions and aneurysm; thus, increased MMP-12 activity may play an important role in the pathogenesis of atherosclerosis. However, the pathological roles of MMP-12 in the initiation and progression of atherosclerosis have not been defined.

METHODS AND RESULTS

We compared the susceptibility of MMP-12 transgenic (Tg) rabbits to cholesterol-rich diet-induced atherosclerosis with that of non-Tg littermate rabbits. The rabbits were maintained at either relatively lower levels of hypercholesterolemia for shorter periods or higher levels of hypercholesterolemia for longer periods through a diet containing different amounts of cholesterol. We found no significant difference in the aortic atherosclerotic lesion size or quality between Tg and non-Tg rabbits at lower hypercholesterolemia. At higher hypercholesterolemia for longer periods, however, Tg rabbits developed more extensive atherosclerosis in the aortas and coronary arteries than did non-Tg rabbits. Histological examinations revealed that atherosclerotic lesions of Tg rabbits contained prominent macrophage infiltration associated with marked disruption of the elastic lamina in the tunica media with occasional formation of aneurysm-like lesions. Furthermore, increased expression of MMP-12 derived from macrophages was associated with elevated expression of MMP-3, suggesting that MMP-12 may play a pivotal role in the cascade activation of other MMPs, thereby exacerbating extracellular matrix degradation during the progression of atherosclerosis.

CONCLUSIONS

Overexpression of MMP-12 causes accelerated atherosclerosis in Tg rabbits. These results suggest that macrophage-derived MMP-12 participates in the progression of atherosclerosis.

Development of Selective Inhibitors and Substrate of Matrix Metalloproteinase-12

Four phosphinic peptide libraries with compounds having the general formula p-Br-Ph-(PO2-CH2)-Xaa'-Yaa'-Zaa'-NH2 have been prepared and screened against 10 matrix metalloproteinases (MMPs). We identified two phosphinic peptides with Ki values of 0.19 and 4.4 nM toward MMP-12 (macrophage elastase) that are more than 2-3 orders of magnitude less potent toward the other MMPs tested. These highly selective MMP-12 inhibitors contain a Glu-Glu motif in their Yaa'-Zaa' positions. Incorporation of this Glu-Glu motif into the sequence of a nonspecific fluorogenic peptide cleaved by MMPs provides a highly selective substrate for MMP-12. A model of one of these inhibitors interacting with MMP-12 suggests that the selectivity observed might be due, in part, to the presence of two unique polar residues in MMP-12, Thr239 and Lys177. These MMP-12-selective inhibitors may have important therapeutic applications to diseases in which MMP-12 has been suggested to play a key role, such as in emphysema, atherosclerosis, and aortic abdominal aneurysm.

Abdominal aortic aneurysm is associated with high serum levels of tenascin-X and decreased aneurysmal tissue tenascin-X

BACKGROUND

Tenascin-X is a large extracellular matrix protein that is abundantly expressed in several connective tissues. A 140-kDa C-terminal fragment of tenascin-X is present in human serum. Complete deficiency of tenascin-X is associated with Ehlers-Danlos syndrome, and these patients show major connective tissue alterations in their skin, as well as blood vessel fragility. In this study, we investigated whether tenascin-X is present in normal human aorta and abdominal aortic aneurysm (AAA) tissues and whether an association exists between serum tenascin-X levels and AAA.

METHODS AND RESULTS

Five normal aortas and 5 AAA tissues were immunostained for tenascin-X and elastin. Tenascin-X was present throughout the entire aorta and was especially abundant near the elastic lamellae, whereas tenascin-X expression was strongly decreased in AAA tissue. Measurement of tenascin-X serum concentration by enzyme-linked immunosorbent assay (ELISA) in 87 AAA patients and 86 controls demonstrated an increasing risk for AAA with increasing tenascin-X serum concentrations. After adjustment for established risk factors, tenascin-X serum concentrations in the highest quartile were associated with a 5-fold increase in risk of AAA (odds ratio, 5.3; 95% confidence interval, 2.0 to 13.8).

CONCLUSIONS

Tenascin-X expression is markedly decreased in AAA tissue, and AAA is associated with high serum concentrations of tenascin-X.

Selective cyclooxygenase-2 inhibition with celecoxib decreases angiotensin II-induced abdominal aortic aneurysm formation in mice

OBJECTIVE

Inflammation plays an integral role in the development of abdominal aortic aneurysms (AAAs), and the expression of cyclooxygenase (COX)-2 is increased in aneurysmal tissue compared with normal aorta. Nonsteroidal anti-inflammatory drugs, which inhibit the activity of COX-1 and COX-2, decrease AAA expansion in humans and animal models of the disease. In the current study, we investigated the effectiveness of selective inhibition of COX-1 or COX-2 in attenuating AAA formation.

METHODS AND RESULTS

Eight-week-old male apolipoprotein E-deficient mice were treated with selective inhibitors of COX-1 or COX-2, SC-560 (approximately 25 mg.kg(-1).day(-1)), or celecoxib (approximately 125 mg.kg(-1).day(-1)), respectively. COX inhibitors were administered 1 week before angiotensin II (Ang II; 1000 ng.kg(-1).min(-1)) or saline infusion and throughout the time course of the experiment. COX-1 inhibition had no effect on incidence (control: 90% [9:10] versus SC-560: 89% [8:9]) or severity of Ang II-induced AAA formation. In contrast, celecoxib decreased the incidence (control: 74% [22:30] versus celecoxib: 11% [2:19]; P<0.001) and severity (P=0.001) of AAA formation. Celecoxib also decreased the incidence and severity of AAAs in nonhyperlipidemic mice.

CONCLUSIONS

COX-2-derived prostanoids play a fundamental role in the development of Ang II-induced AAAs in both hyperlipidemic and nonhyperlipidemic mice.

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.

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.

Inflammation and cellular immune responses in abdominal aortic aneurysms

Expansion and rupture of abdominal aortic aneurysms (AAA) result in high morbidity and mortality rates. Like stenotic atherosclerotic lesions, AAA accumulate inflammatory cells, but usually exhibit much more extensive medial damage. Leukocyte recruitment and expression of pro-inflammatory Th1 cytokines typically characterize early atherogenesis of any kind, and modulation of inflammatory mediators mutes atheroma formation in mice. However, the mechanistic differences between stenotic and aneurysmal manifestations of atherosclerosis remain unexplained. We recently showed that aortic allografts deficient in interferon-gamma (IFN-gamma) signaling developed AAA correlating with skewed Th2 cytokine environments, suggesting important regulatory roles for Th1/Th2 cytokine balance in modulating matrix remodeling and important implications for the pathophysiology of aortic aneurysm and atherosclerosis. Further probing of their distinct aspects of immune and inflammatory responses in vascular diseases should continue to shed new light on the pathophysiologic mechanisms that give rise to aneurysmal versus occlusive manifestations and atherosclerosis.

Overexpression of transforming growth factor-beta1 stabilizes already-formed aortic aneurysms: a first approach to induction of functional healing by endovascular gene therapy

BACKGROUND

The cell response to transforming growth factor-beta1 (TGF-beta1), a multipotent cytokine with healing potential, varies according to tissue context. We have evaluated the ability of TGF-beta1 overexpression by endovascular gene therapy to stabilize abdominal aortic aneurysms (AAAs) already injured by inflammation and proteolysis.

METHODS AND RESULTS

Active TGF-beta1 overexpression was obtained in already-developed experimental AAAs in rats after endovascular delivery of an adenoviral construct encoding for a mutated form of active simian TGF-beta1 and in an explant model using human atherosclerotic AAA fragments incubated with recombinant active TGF-beta1. Transient exogenous TGF-beta1 overexpression by endovascular gene delivery was followed by induction of endogenous rat TGF-beta1. Overexpression of active TGF-beta1 in experimental AAAs was associated with diameter stabilization, preservation of medial elastin, decreased infiltration of monocyte-macrophages and T lymphocytes, and a decrease in matrix metalloproteinase-2 and -9, which was also observed in the explant model, in both thrombus and wall. In parallel with downregulation of the destructive process, active TGF-beta1 overexpression triggered endoluminal reconstruction, replacing the thrombus by a vascular smooth muscle cell-, collagen-, and elastin-rich intima.

CONCLUSIONS

Local TGF-beta1 self-induction after transient exogenous overexpression reprograms dilated aortas altered by inflammation and proteolysis and restores their ability to withstand arterial pressure without further dilation. This first demonstration of stabilization of expanding AAAs by delivery of a single multipotent self-promoting gene supports the view that endovascular gene therapy should be considered for treatment of aneurysms.

Matrix Metalloproteinase-8 and -9 Are Increased at the Site of Abdominal Aortic Aneurysm Rupture

Background— Abdominal aortic aneurysm (AAA) expansion is characterized by extracellular matrix degradation and widespread inflammation. In contrast, the processes that characterize AAA rupture are not well understood. The aim of this study was to investigate the proteolytic and cellular activity of ruptured AAA, focusing on matrix metalloproteinases (MMPs) and their inhibitors (TIMPs).

Methods and Results— Anterior aneurysm wall biopsies were taken from 55 nonruptured and 21 ruptured AAAs. A further biopsy from the site of rupture was taken from 12 of the ruptured AAAs. MMP-1, -2, -3, -8, -9, and -13, as well as TIMP-1 and -2, were quantified in each biopsy with ELISA. A comparison of anterior aneurysm biopsies showed no difference in MMP or TIMP concentrations between nonruptured and ruptured AAA. In a comparison of ruptured AAA biopsies, MMP-8 and -9 levels were significantly elevated in the 12 rupture site biopsies compared with their 12 paired anterior wall biopsies, whereas other MMPs and TIMPs showed no difference (MMP-8, P <0.001; MMP-9, P =0.01). MMP-8 and -9 expression was mediated by native mesenchymal cells and was independent of the inflammatory infiltrate.

Conclusions— A localized increase in MMP-8 and –9, mediated by native mesenchymal cells, presents a potential pathway for collagen breakdown and AAA rupture.

Genotypes and haplotypes of matrix metalloproteinase 1, 3 and 12 genes and the risk of lung cancer

The MMPs (matrix metalloproteinases) are a family of secreted zinc metalloproteases that degrade the collagens of the extracellular matrix important in tissue remodeling and repair during development and inflammation. We investigated the associations between polymorphisms of MMP-1 (-1607 1G/2G, rs1799750), MMP-3 (-1171 5A/6A, rs3025058), and MMP-12 (-82AG, rs2276109, and 1082A/G, rs652438) and the risk of lung cancer in 2014 Caucasian lung cancer patients and 1323 healthy controls. The results were analyzed using logistic regression models, adjusting for covariates. The four polymorphisms were in Hardy-Weinberg disequilibrium. Except for the 1G-1082A, the other linkage disequilibrium tests between the four MMP polymorphisms were statistically significant (P < 0.001). There was no overall association between individual MMP polymorphism and the risk of lung cancer. The MMP polymorphisms jointly were associated with a non-statistically significant higher risk of lung cancer, with the adjusted odds ratio (AOR) of subjects with 5+ variant alleles versus zero variant allele of 1.31 [95% confidence interval (CI), 0.92-1.88]. Stronger associations were observed in never-smokers and males, with the corresponding AORs of 2.44 (95%CI, 1.10-5.43, P(trend) = 0.04) in never smokers and 1.35 (95%CI, 0.79-2.30, P(trend) = 0.04) in men. In haplotype analysis, the 1G-6A-82A-1082G haplotype was associated with higher risk of lung cancer among never smokers, with the AOR of 3.65 (95%CI, 1.62-8.20) when compared with the most common 1G-5A-82A-1082A haplotype. In conclusion, the combined MMP genotypes and associated haplotypes may be associated with higher risk of lung cancer, particularly among never smokers and men.

Suppression of matrix metalloproteinase-9 by prostaglandin E(2) in peritoneal macrophage is associated with severity of endometriosis

Decreased phagocytotic ability of macrophages has been reported to be associated with the severity of endometriosis, although the underlying mechanism remains uncharacterized. Expression and secretion of matrix metalloproteinase (MMP)-9 by macrophages is a means to degrade the extracellular matrix of cells that are designated for phagocytosis. Here, we describe the regulation of MMP-9 expression and activity in peritoneal macrophages of women with endometriosis. Results demonstrated that peritoneal macrophages isolated from women with endometriosis have decreased levels of protein and enzyme activity of MMP-9. Treatment of macrophages with peritoneal fluid obtained from patients with severe endometriosis inhibited MMP-9 expression and gelatinase activity. Further investigation identified prostaglandin (PG) E(2) as the major factor in the peritoneal fluid that inhibited MMP-9 activity. The inhibitory effect of PGE(2) was mediated via the EP2/EP4-dependent PKA pathway. Furthermore, expression of tissue inhibitor of metalloproteinase-1, tissue inhibitor of metalloproteinase-2, and RECK in macrophages was not affected by treatment with PGE(2), indicating the effect of PGE(2) on suppressing MMP-9 activity was not mediated by up-regulation of its inhibitor. Our results suggest that decreased phagocytotic capability of peritoneal macrophage in patients with endometriosis may be caused by PGE(2)-mediated decreases in MMP-9 expression.

HMG-CoA reductase inhibitors (statins) decrease MMP-3 and MMP-9 concentrations in abdominal aortic aneurysms

BACKGROUND

An imbalance in matrix metalloproteinases (MMPs) and their inhibitors (TIMPs) are implicated in AAA formation. 3-Hydroxy-3-methylglutaryl coenzyme-A reductase inhibitors (statins) are known to reduce MMP levels. The aim of this study was to investigate the in vivo effect of statins on MMP levels in AAA.

METHODS

Infra-renal aortic biopsies were obtained from the anterior sac of 63 patients undergoing asymptomatic repair. Seventeen patients were taking a statin pre-operatively, while 46 were not. The concentrations of MMP-1, -2, -3, -8, -9, -13, TIMP-1 and TIMP-2 were quantified using ELISA.

RESULTS

There was no difference in the concentration of MMP-1, -2, -8, -13, TIMP-1 or -2 in patients taking versus not taking a statin pre-operatively. In contrast levels of MMP-9 and MMP-3 were significantly lower in patients taking a statin.

CONCLUSIONS

These data demonstrate that statins decrease MMP-9 and MMP-3 levels and represent a potential pharmacotherapy in established AAA.

Analysis of the inflammatory response induced by rhMMP-12 catalytic domain instilled in mouse airways

Macrophage elastase (MMP-12) is a metalloproteinase able to degrade extracellular matrix components such as elastin. As many MMPs, MMP-12 is involved in acute and chronic lung injury. However, its role in the inflammatory process of the lung parenchyma is not clearly understood. In this study, we have investigated the effects of airway instillation of rhMMP-12 on inflammatory cell recruitment, cytokine release and gelatinase expression in bronchoalveolar lavage fluid (BALF) or in lung homogenate supernatants in mice. Numbers of total and individual cell types were examined in BALF during the first 72 h following rhMMP-12 instillation. A marked recruitment of neutrophils was observed with a maximum increase at 18 h. This cellular recruitment was associated with a very transient increase in IL-6, TNF-alpha MIP-1alpha, MCP-1 and KC levels and gelatinase expression in BALF and in lung homogenate supernatants. From days 4 to 15, performing the same analyses, we observed an important and stable recruitment of macrophages in BALF in absence of the other studied inflammatory markers. These results demonstrate that rhMMP-12 itself is able to induce an early inflammatory response characterized by neutrophil infiltration, cytokine release and gelatinase activation followed by a later response composed mainly of macrophage recruitment.

Predominance of Th2 response in human abdominal aortic aneurysm: mistaken identity for IL-4-producing NK and NKT cells?

Abdominal aortic aneurysm (AAA) is a complex remodeling process that involves both synthesis and degradation of extracellular matrix proteins in the aortic wall, leading to decreased tensile strength, progressive dilation and eventual rupture. Chronic inflammation, increased local production of elastin-degrading proteases by inflammatory cells and destruction of medial elastic lamellae play important roles in aneurysm progression. Neovascularization in all layers of the arterial wall is prominent and angiogenesis can facilitate chronic inflammation. It is still unclear what initiates aneurysmal dilation and what determines its progression. The complex nature of the process has defied elucidation. Apart from macrophages, the predominant immune cell infiltrates reported so far are CD3(+)T cells that express CD4 and CD8. Infiltrates of type 2 Th cells and their production of IL-4 and IL-5 have been implicated in AAA development. However, NKT and NK cells have a Th0 cytokine profile and can also produce type 2 as well as type 1 (IL-2 and IFNgamma) cytokines. We have demonstrated the presence of NK and NKT cells in AAA tissue. With their growing importance in autoimmunity and transplantation, they may play a role in AAA development. Therefore, there is a need to use a combination of T and NK markers to fully characterize both innate and adaptive lymphoid cell subsets in local inflammatory infiltrates in order to elucidate their roles in AAA progression.

Up-regulation and coexpression of MIF and matrix metalloproteinases in human abdominal aortic aneurysms

Abdominal aortic aneurysm (AAA) is a localized dilatation of the arterial wall as a result of extensive breakdown of its structural proteins by matrix metalloproteinases (MMPs). AAA continuously expand and may eventually rupture, causing high mortality rates. The molecular processes underlying expansion and rupture of AAA are only poorly understood. In this study, evidence was sought for a direct involvement of macrophage migration inhibitory factor (MIF) in the pathogenesis of AAA through up-regulating MMPs, with particular reference to macrophages. To this end, expression and cellular localization of MIF were analyzed in human aortic wall samples of stable AAA and ruptured AAA, and compared with control aorta and atherosclerotic aorta (AS). MIF expression was up-regulated in stable AAA and further intensified in ruptured AAA. The increased aneurysmal MIF expression was paralleled by an enhanced expression of specific MMPs, viz. MMP-1, MMP-9, and MMP-12, and by a decrease of their inhibitors. Immunohistochemical analysis of AAA and AS showed MIF protein in endothelial cells, smooth muscle cells (SMCs), macrophages, and T cells. MMP-1 (in SMCs and macrophages) and MMP-9 (in macrophages) were colocalized with MIF at the cellular level in ruptured AAA. The up-regulation of aneurysmal MIF/MMP expression was associated with an increased content of cytotoxic T cells.

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.

Crystal structures of MMPs in complex with physiological and pharmacological inhibitors

Matrix Metalloproteinases (MMPs) are a family of multidomain zinc endopeptidases that function in the extracellular space or attached to the cell membrane. Their proteolytic activity is controlled by the presence of endogenous inhibitors, the tissue inhibitors of matrix metalloproteinases (TIMPs), alpha-macroglobulin and others. Disruption of the proteinase-inhibitor balance is observed in serious diseases such as arthritis, tumor growth and metastasis, rendering the MMPs attractive targets for drug intervention by pharmacological inhibitors. The determination of MMP structures is of critical importance in order to understand their substrate preferences, dimerization events, and their association with matrix components and inhibitors. Thus, MMP structures may contribute significantly to the development of specific MMP inhibitors, which should allow precise control of individual members of the MMP family without affecting all members or the closely related metalloproteinases such as ADAMs and ADAMTSs.