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

The Influence of Simvastatin on NGAL, Matrix Metalloproteinases and Their Tissue Inhibitors in Human Intraluminal Thrombus and Abdominal Aortic Aneurysm Tissue

OBJECTIVE/BACKGROUND

Matrix metalloproteinases (MMPs) play a pivotal role in the development and progression of abdominal aortic aneurysms (AAAs). The action of MMPs depends on a balance between tissue inhibitors of MMPs (TIMPs) and compounds that may prolong protease activity, such as neutrophil gelatinase-associated lipocalin (NGAL).

METHODS

The study was designed to analyse gene expression and protein concentration of MMPs, TIMPs, and NGAL in AAA walls and intraluminal thrombi (ILTs) of patients on simvastatin (n = 10) and not on statins (n = 10). The patients were matched by age, sex, and AAA diameter. Expression of MMP2, MMP9, TIMP1, TIMP2, and NGAL was investigated by real time polymerase chain reaction, and MMP2, MMP9, MMP9/TIMP1, MMP9/TIMP2, and MMP9/NGAL protein levels by enzyme-linked immunosorbent assay.

RESULTS

MMP2 and MMP9 protein and mRNA levels were comparable in the simvastatin and non-statin groups (p > .05); however, there was a significant decrease in TIMP1 mRNA in AAA tissue (p = .04). Moreover, a significant increase in MMP9/TIMP2 complex concentration in ILTs of patients on simvastatin was noted (median 94.71 ng/mL in the simvastatin group vs. 36.80 ng/mL in the non-statin group; p = .01). No significant difference was observed for NGAL mRNA or protein content in AAA and ILT.

CONCLUSION

Simvastatin treatment in patients with AAAs may influence the concentration of proteases and their inhibitors (TIMPs) in aneurysmal wall tissue and ILTs. Thus, further studies should be undertaken to understand the different influence of statin therapy on the components of the MMP/TIMP system in AAAs and ILTs.

Matrix metalloproteinase interactions with collagen and elastin

Most abundant in the extracellular matrix are collagens, joined by elastin that confers elastic recoil to the lung, aorta, and skin. These fibrils are highly resistant to proteolysis but can succumb to a minority of the matrix metalloproteinases (MMPs). Considerable inroads to understanding how such MMPs move to the susceptible sites in collagen and then unwind the triple helix of collagen monomers have been gained. The essential role in unwinding of the hemopexin-like domain of interstitial collagenases or the collagen binding domain of gelatinases is highlighted. Elastolysis is also facilitated by the collagen binding domain in the cases of MMP-2 and MMP-9, and remote exosites of the catalytic domain in the case of MMP-12.

Stanford-A acute aortic dissection, inflammation, and metalloproteinases: a review

Acute aortic dissection (AAD) is a life-threatening disease with an incidence of about 2.6-3.6 cases per 100,000/year. Depending on the site of rupture, AAD is classified as Stanford-A when the ascending aortic thoracic tract and/or the arch are involved, and Stanford-B when the descending thoracic aorta and/or aortic abdominal tract are targeted. It was recently shown that inflammatory pathways underlie aortic rupture in both type A and type B Stanford AAD. An immune infiltrate has been found within the middle and outer tunics of dissected aortic specimens. It has also been observed that the recall and activation of macrophages inside the middle tunic are key events in the early phases of AAD. Macrophages are able to release metalloproteinases (MMPs) and pro-inflammatory cytokines which, in turn, give rise to matrix degradation and neoangiogenesis. An imbalance between the production of MMPs and MMP tissue inhibitors is pivotal in the extracellular matrix degradation underlying aortic wall remodelling in dissections occurring both in inherited conditions and in atherosclerosis. Among MMPs, MMP-12 is considered a specific marker of aortic wall disease, whatever the genetic predisposition may be. The aim of this review is, therefore, to take a close look at the immune-inflammatory mechanisms underlying Stanford-A AAD.

Inactivation of PI3Kδ induces vascular injury and promotes aneurysm development by upregulating the AP-1/MMP-12 pathway in macrophages

OBJECTIVE

An aneurysm is an inflammatory vascular condition. Phosphatidylinositol 3-kinases δ is highly expressed in leukocytes, and play a key role in innate immunity. However, the link between phosphatidylinositol 3-kinases δ and aneurysm development has not yet been elucidated.

APPROACH AND RESULTS

Carotid ligation unexpectedly induced characteristic aneurysm formation beneath the ligation point in p110δ(D910A/D910A) mice (n=25; P<0.001 versus wild-type). Besides, p110δ inactivation exacerbated CaCl2-induced abdominal aortic aneurysms development. A reverse transcription polymerase chain reaction microarray revealed significant extracellular matrix components degradation and matrix metalloproteinases (MMPs) upregulation in the abdominal aorta of p110δ(D910A/D910A) mice. Similarly, the expression of both collagen I and IV was significantly decreased (n=10; P<0.05 versus wild-type) in carotid artery. Western blot assay confirmed that MMP-12 was significantly upregulated in arteries of p110δ(D910A/D910A) mice (n=10; P<0.01 versus wild-type). In vitro, p110δ inactivation marked increase peritoneal macrophages recruitment and synergistically enhance tumor necrosis factor-α-induced recruitment. A specific phosphatidylinositol 3-kinases δ inhibitor (IC87114) or genetic p110δ inactivation upregulated MMP-12 expression and c-Jun phosphorylation (n=6; P<0.05 versus wild-type macrophages). IC87114 also increased activator protein-1 DNA-binding activity (n=6; P<0.001 versus control) and enhanced the effect of tumor necrosis factor-α on activator protein-1-binding activity (n=5; P<0.01 versus tumor necrosis factor-α treatment groups). Knockdown of c-Jun suppressed the effect of the IC87114 and tumor necrosis factor-α on MMP-12 mRNA expression (n=5 in each group; P<0.01 versus scrRNA treatment groups).

CONCLUSIONS

Our findings demonstrate that p110δ inactivation leads to extracellular matrix degradation in vessels and promotes aneurysm development by inducing macrophages migration and upregulating the activator protein-1/MMP-12 pathway in macrophages.

Ambidextrous binding of cell and membrane bilayers by soluble matrix metalloproteinase-12

Matrix metalloproteinases (MMPs) regulate tissue remodelling, inflammation and disease progression. Some soluble MMPs are inexplicably active near cell surfaces. Here we demonstrate the binding of MMP-12 directly to bilayers and cellular membranes using paramagnetic NMR and fluorescence. Opposing sides of the catalytic domain engage spin-labelled membrane mimics. Loops project from the β-sheet interface to contact the phospholipid bilayer with basic and hydrophobic residues. The distal membrane interface comprises loops on the other side of the catalytic cleft. Both interfaces mediate MMP-12 association with vesicles and cell membranes. MMP-12 binds plasma membranes and is internalized to hydrophobic perinuclear features, the nuclear membrane and inside the nucleus within minutes. While binding of TIMP-2 to MMP-12 hinders membrane interactions beside the active site, TIMP-2-inhibited MMP-12 binds vesicles and cells, suggesting compensatory rotation of its membrane approaches. MMP-12 association with diverse cell membranes may target its activities to modulate innate immune responses and inflammation.

Meta-analysis and meta-regression analysis of biomarkers for abdominal aortic aneurysm

Background

Many studies have investigated the systemic and local expression of biomarkers in patients with abdominal aortic aneurysm (AAA). The natural history of AAA varies between patients, and predictors of the presence and diameter of AAA have not been determined consistently. The aim of this study was to perform a systematic review, meta-analysis and meta-regression of studies comparing biomarkers in patients with and without AAA, with the aim of summarizing the association of identified markers with both AAA presence and size.

Methods and results

Literature review identified 106 studies suitable for inclusion. Meta-analysis demonstrated a significant difference between matrix metalloproteinase (MMP) 9, tissue inhibitor of matrix metalloproteinase 1, interleukin (IL) 6, C-reactive protein (CRP), α1-antitrypsin, triglycerides, lipoprotein(a), apolipoprotein A and high-density lipoprotein in patients with and without AAA. Although meta-analysis was not possible for MMP-2 in aortic tissue, tumour necrosis factor α, osteoprotegerin, osteopontin, interferon γ, intercellular cell adhesion molecule 1 and vascular cell adhesion molecule 1, systematic review suggested an increase in these biomarkers in patients with AAA. Meta-regression analysis identified a significant positive linear correlation between aortic diameter and CRP level.

Conclusion

A wide variety of biomarkers are dysregulated in patients with AAA, but their clinical value is yet to be established. Future research should focus on the most relevant biomarkers of AAA, and how they could be used clinically.

Prevention of abdominal aortic aneurysm by anti-microRNA-712 or anti-microRNA-205 in angiotensin II-infused mice

OBJECTIVE

Abdominal aortic aneurysm (AAA) is characterized as a progressive dilation and degradation of the aortic wall, associated with activation of matrix metalloproteinases (MMPs) and inflammation. Emerging evidence indicates a role for microRNAs (miRNAs) in AAA pathogenesis, but it is unclear whether abdominal aortic endothelial miRNAs play a role in the disease process. We aimed to identify miRNAs in the abdominal aortic endothelium that play a critical role in AAA development.

APPROACH AND RESULTS

The mouse model of AAA induced by angiotensin II infusion was used in this study. Through a miRNA array and validation study, we initially identified the murine-specific miR-712 and subsequently its human/murine homolog miR-205 as angiotensin II-induced miRNAs in the abdominal aortic endothelium in vivo and in vitro. Mechanistically, miR-712 stimulated MMP activity in the aortic wall by directly targeting 2 MMP inhibitors: tissue inhibitor of metalloproteinase 3 (TIMP3) and reversion-inducing cysteine-rich protein with kazal motifs (RECK). Silencing of miR-712 and miR-205 by using anti-miR-712 and anti-miR-205, respectively, significantly decreased the aortic MMP activity and inflammation, preventing AAA development in angiotensin II-infused ApoE(-/-) mice. Further, upregulation of 4 angiotensin II-sensitive miRNAs, miR-205, -21, -133b, and -378, identified in this murine study were confirmed in human AAA samples compared with nondiseased control.

CONCLUSIONS

Our results demonstrate that angiotensin II-sensitive miR-712 and its human homolog miR-205 downregulate TIMP3 and RECK, which in turn stimulate aortic MMP activity and inflammation, leading to AAA development. Targeting these miRNAs may be a novel therapeutic strategy to prevent AAA.

MMP-12 as a new marker of Stanford-A acute aortic dissection

BACKGROUND

The study evaluated macrophage cytokines and macrophage metalloprotease (MMP)-12 levels in patients with Stanford-A acute aortic dissection (AAD) and in patients with critical carotid artery stenosis (CAS) compared with patients matched for age, sex, and traditional cardiovascular risk factors (RF). The aim was to identify possible early serum markers of risk for atherosclerotic complications.

MATERIALS AND METHODS

We selected 65 patients: 23 AAD patients, 21 CAS patients, 21 RF, and 10 healthy subjects (HS). In each patient and control serum, levels of interleukin (IL)-6, IL-8, tumour necrosis factor (TNF)-α, monocyte chemoattractant protein (MCP)-1, vascular endothelial growth factor (VEGF), and MMP-12 were assessed by ELISA.

RESULTS

A significant increase of MMP-12, IL-6, and IL-8 levels in AAD versus CAS was found. Moreover, MMP-12 was shown to be significantly higher in AAD versus RF, but not in CAS versus RF. A significant increase of IL-6, IL-8, MCP-1, TNF-α, and VEGF levels was observed both in AAD and CAS versus RF.

CONCLUSIONS

The results suggest that MMP-12 may be considered to be a specific marker of Stanford-A AAD. Furthermore, the study confirmed that in AAD and CAS macrophage cytokines play a key role in the progression of the atherosclerotic disease towards complications.

Elasto-regenerative properties of polyphenols

Abdominal aortic aneurysms (AAA) are progressive dilatations of infra-renal aorta causing structural weakening rendering the aorta prone to rupture. AAA can be potentially stabilized by inhibiting inflammatory enzymes such as matrix metalloproteinases (MMP); however, active regression of AAA is not possible without new elastic fiber regeneration. Here we report the elastogenic benefit of direct delivery of polyphenols such as pentagalloyl glucose (PGG), epigallocatechin gallate (EGCG), and catechin, to smooth muscle cells obtained either from healthy or from aneurysmal rat aorta. Addition of 10 μg/ml PGG and ECGC induce elastin synthesis, organization, and crosslinking while catechin does not. Our results indicate that polyphenols bind to monomeric tropoelastin and enhance coacervation, aid in crosslinking of elastin by increasing lysyl oxidase (LOX) synthesis, and by blocking MMP-2 activity. Thus, polyphenol treatments leads to increased mature elastin fibers synthesis without increasing the production of intracellular tropoelastin.

The multitasking role of macrophages in Stanford type A acute aortic dissection

OBJECTIVES

The aim of the study was to determine whether the release by macrophages of matrix metalloproteinase (MMP)-12 and vascular endothelial growth factor (VEGF) - leading to inflammation, matrix degradation and neoangiogenesis - represents an effective pathway that underlies aortic wall remodeling in Stanford type A acute aortic dissection (AAD).

METHODS

Twenty-one consecutive patients with no genetic predisposition, with Stanford type A AAD were selected. In each patient, the levels of serum VEGF, MMP-12, serum interleukin (IL)-6, IL-8 and monocyte chemoattractant protein (MCP)-1 were evaluated using enzyme-linked immunosorbent assay. Ascending aortic specimens were collected for immunohistochemical identification of any presence of inflammatory infiltrate, VEGF and CD31 expression.

RESULTS

A significant increase in serum VEGF (p = 0.044), MMP-12 (p = 0.007), IL-6 (p = 0.0001), IL-8 (p = 0.0001) and MCP-1 (p = 0.0001) levels was observed in the AAD group compared to the control group. Furthermore, all AAD samples were positive for VEGF in the tunica media and showed vessel growth and immune-inflammatory infiltrate. A large number of cases (62.79%) showed inflammation at the edge of the dissection and approximately half (51.42%) showed neovessels growing at the edge of the dissection.

CONCLUSIONS

The results suggest that VEGF-mediated angiogenesis and matrix degradation play a role in AAD. Finally, we believe that MMP-12 should be considered a marker of AAD.

Current status of medical treatment for abdominal aortic aneurysm

Although cardiovascular disease is widely recognized as the leading cause of death, a lesser known fact is that aortic aneurysm is the 15th leading cause of death over the age of 65 years in the USA. The golden standard of the treatments are invasive interventions either with open surgical repair (OS) or endovascular aneurysm repair (EVAR). The concept of medical treatment is to prevent abdominal aortic aneurysm (AAA) from rupture and avoid surgical treatment by preventing aneurysm enlargement or even reducing aneurysm size. Matrix metalloproteinases (MMP) are structurally related metalloendopeptidases that can degrade the extracellular matrix and is thought to play important roles in AAA. There are many proposed pharmacological treatments including: β-blockers, angiotensin-converting enzyme inhibitor (ACE inhibitors), angiotensin-receptor blocker (ARB), statins, macrolides and, doxycycline, an inhibitor of the MMP. The latter is a potential promising drug as medical treatment for AAA and the Non-invasive Treatment of Abdominal Aortic Aneurysm Clinical Trial (N-TA(3)CT) is currently ongoing in the USA. Here, the pathophysiology and potential medical therapy for AAA will be reviewed.

Smooth muscle cells from abdominal aortic aneurysms are unique and can independently and synergistically degrade insoluble elastin

BACKGROUND

The purpose of this study was to further elucidate the role of the vascular smooth muscle cells (SMCs) in abdominal aortic aneurysm (AAA) disease. We hypothesized that that AAA SMCs are unique and actively participate in the process of degrading the aortic matrix.

METHODS

Whole-genome expression profiles of SMCs from AAAs, nondilated abdominal aorta (NAA), and carotid endarterectomy (CEA) were compared. We quantified elastolytic activity by culturing SMCs in [(3)H]elastin-coated plates and measuring solubilized tritium in the media after 7 days. Matrix metalloproteinase (MMP)-2 and MMP-9 production was assessed using real-time polymerase chain reaction, zymography, and Western blotting.

RESULTS

Each SMC type exhibited a unique gene expression pattern. AAA SMCs had greater elastolytic activity than NAA-SMCs (+68%; P < .001) and CEA-SMCs (+45%; P < .001). Zymography showed an increase of active MMP-2 (62 kD) in media from AAA SMCs. AAA SMCs demonstrated twofold greater expression of MMP-2 messenger (m)RNA (P < .05) and 7.3-fold greater MMP-9 expression (P < .01) than NAA-SMCs. Culture with U937 monocytes caused a synergistic increase of elastolysis by AAA SMCs (41%; P < .001) but not NAA-SMCs or CEA-SMCs (P = .99). Coculture with U937 caused a large increase in MMP-9 mRNA in AAA-SMCs and NAA-SMCs (P < .001). MMP-2 mRNA expression was not affected. Western blots of culture media showed a fourfold increase of MMP-9 (92 kD) protein only in AAA-SMCs/U937 but not in NAA-SMCs/U937 (P < .001) and a large increase in active-MMP2 (62 kD), which was less apparent in NAA-SMCs/U937 media (P < .01).

CONCLUSIONS

AAA-SMCs have a unique gene expression profile and a proelastolytic phenotype that is augmented by macrophages. This may occur by a failure of post-transcriptional control of MMP-9 synthesis.

Structural and vibrational properties of imidazo[4,5-c]pyridine, a structural unit in natural products

The molecular structures and vibrational properties of 1H-imidazo[4,5-c]pyridine in its monomeric and dimeric forms are analyzed and related to the experimental results derived from the XRD, IR, and Raman studies. The theoretical data are discussed on the basis of DFT quantum chemical calculations using the B3LYP correlation functional and 6-311G(2d,2p) basis set. This compound crystallizes in the non-centrosymmetric orthorhombic space group Fdd2. The asymmetric unit contains one molecule of 1H-imidazo[4,5-c]pyridine and disordered molecules of solvents. The molecules are organized in hydrogen-bonded chains propagating along the [1 0 -3] direction. The stability of the dimeric form arising from charge delocalization and the existence of an N-H···N intermolecular hydrogen bond has been analyzed using the natural bond orbital approach. The normal modes, which are unique for the imidazopyridine skeleton, have been identified. The spectra of other compounds containing the imidazopyridine unit have been analyzed.

Exploring smooth muscle phenotype and function in a bioreactor model of abdominal aortic aneurysm

Background

Vascular smooth muscle cells (SMC) are central to arterial structure and function yet their involvement in the progression of abdominal aortic aneurysm (AAA) disease is not well studied. The progressive and silent nature of AAA in man essentially restricts research to the use of “end-stage” tissue recovered during surgical repair. This study aimed to generate an ex vivo model of AAA using protease-treated porcine carotid arteries maintained in a novel bioreactor, and to compare the structural and functional changes in SMC cultured from the recovered vessels with those from human tissue acquired at elective surgical repair.

Methods

Freshly isolated porcine arteries were pretreated with collagenase and/or elastase before culturing under flow in a bioreactor for 12 days. Human end-stage aneurysmal tissue and saphenous veins from age-matched controls were collected from patients undergoing surgery. SMC were cultured and characterised (immunocytochemistry, measurement of spread cell area) and assessed functionally at the level of proliferation (cell-counting) and matrix-metalloproteinase (MMP) secretion (gelatin zymography). Cellular senescence was investigated using β-galactosidase staining and apoptosis was quantified using a fluorescence-based caspase 3 assay.

Results

Co-expression of alpha-smooth muscle actin and smooth muscle myosin heavy chain confirmed all cell populations as SMC. Porcine SMC harvested and cultivated after collagenase/elastase pretreatment displayed a prominent “rhomboid” morphology, increased spread area (32%, P < 0.01), impaired proliferation (47% reduction, P < 0.05), increased senescence (52%, P < 0.001), susceptibility to apoptosis and reduced MMP-2 secretion (60% decrease, P < 0.01) compared with SMC from vehicle, collagenase or elastase pre-treated vessels. Notably, these changes were comparable to those observed in human AAA SMC which were 2.4-fold larger than non-aneurysmal SMC (P < 0.001) and exhibited reduced proliferation (39% reduction, P < 0.001), greater apoptosis (4-fold increase, P < 0.001), and increased senescence (61%, P < 0.05).

Conclusions

Combined collagenase/elastase exposure of porcine artery maintained in a bioreactor under flow conditions induced a SMC phenotype characteristic of those cultured from end-stage AAA specimens. This model has potential and versatility to examine temporal changes in SMC biology and to identify the molecular mechanisms leading to early aberrancies in SMC function. In the longer term this may inform new targets to maintain aortic SMC content and drive cells to a “reparative” phenotype at early stages of the disease.

Biochemomechanics of intraluminal thrombus in abdominal aortic aneurysms

Most computational models of abdominal aortic aneurysms address either the hemodynamics within the lesion or the mechanics of the wall. More recently, however, some models have appropriately begun to account for the evolving mechanics of the wall in response to the changing hemodynamic loads. Collectively, this large body of work has provided tremendous insight into this life-threatening condition and has provided important guidance for current research. Nevertheless, there has yet to be a comprehensive model that addresses the mechanobiology, biochemistry, and biomechanics of thrombus-laden abdominal aortic aneurysms. That is, there is a pressing need to include effects of the hemodynamics on both the development of the nearly ubiquitous intraluminal thrombus and the evolving mechanics of the wall, which depends in part on biochemical effects of the adjacent thrombus. Indeed, there is increasing evidence that intraluminal thrombus in abdominal aortic aneurysms is biologically active and should not be treated as homogeneous inert material. In this review paper, we bring together diverse findings from the literature to encourage next generation models that account for the biochemomechanics of growth and remodeling in patient-specific, thrombus-laden abdominal aortic aneurysms.

Cysteine protease cathepsins and matrix metalloproteinases in the development of abdominal aortic aneurysms

Both cysteine protease cathepsins and matrix metalloproteinases are implicated in the pathogenesis of abdominal aortic aneurysms (AAAs) in humans and animals. Blood and aortic tissues from humans or animals with AAAs contain much higher levels of these proteases, and often lower levels of their endogenous inhibitors, than do blood and aortic tissues from healthy subjects. Protease- and protease inhibitor-deficient mice and synthetic protease inhibitors have affirmed that cysteinyl cathepsins and matrix metalloproteinases both participate directly in AAA development in several experimental model systems. Here, we summarize our current understanding of how proteases contribute to the pathogenesis of AAA, and discuss whether proteases or their inhibitors may serve as diagnostic biomarkers or potential therapeutic targets for this common human arterial disease.

Potential mechanisms linking atherosclerosis and increased cardiovascular risk in COPD: focus on Sirtuins

The development of atherosclerosis is a multi-step process, at least in part controlled by the vascular endothelium function. Observations in humans and experimental models of atherosclerosis have identified monocyte recruitment as an early event in atherogenesis. Chronic inflammation is associated with ageing and its related diseases (e.g., atherosclerosis and chronic obstructive pulmonary disease). Recently it has been discovered that Sirtuins (NAD⁺-dependent deacetylases) represent a pivotal regulator of longevity and health. They appear to have a prominent role in vascular biology and regulate aspects of age-dependent atherosclerosis. Many studies demonstrate that SIRT1 exhibits anti-inflammatory properties in vitro (e.g., fatty acid-induced inflammation), in vivo (e.g., atherosclerosis, sustainment of normal immune function in knock-out mice) and in clinical studies (e.g., patients with chronic obstructive pulmonary disease). Because of a significant reduction of SIRT1 in rodent lungs exposed to cigarette smoke and in lungs of patients with chronic obstructive pulmonary disease (COPD), activation of SIRT1 may be a potential target for chronic obstructive pulmonary disease therapy. We review the inflammatory mechanisms involved in COPD-CVD coexistence and the potential role of SIRT1 in the regulation of these systems.

Reestablishment of the Endothelial Lining by Endothelial Cell Therapy Stabilizes Experimental Abdominal Aortic Aneurysms

Background—

Loss of the endothelium and its replacement by a thick thrombus are structural features of human abdominal aortic aneurysms (AAAs). In AAAs, the relationship between aortic diameter expansion, the presence of thrombus, and the lack of endothelial cells (ECs) remains unexplored. We hypothesized that reendothelialization by cell therapy would modulate aortic wall destruction and ultimately stabilize AAAs. We evaluated the impact of local seeding of rat aortic ECs or peripheral blood–derived outgrowth ECs on AAA evolution.

Methods and Results—

Rat aortic ECs (n=30) or serum-free medium (controls; n=29) were seeded endovascularly immediately (day 0) or 14 days after surgery in the rat xenograft model. Rat aortic EC seeding prevented AAA formation and stabilized formed AAAs at 28 days (diameter increase at day 0+28, 51±6% versus 83±6%; day 14+28, −1±4% versus 22±6% in rat aortic ECs and controls, respectively; P <0.01). This stabilizing effect was associated with the reestablishment of the endothelial lining, the suspension of proteolysis, and the reconstitution of new aortic wall rich in smooth muscle cells and extracellular matrix. Transplanted rat aortic ECs did not participate directly in aortic wall repair but exerted their healing properties through paracrine mechanisms involving the upregulation of endothelium-derived stabilizing factors and the recruitment of resident vascular cells. In rats, the transplantation of outgrowth ECs (n=7) significantly reduced by 30% the progression of AAAs and restored the abluminal endothelium at 28 days compared with controls (n=9).

Conclusion—

Our study demonstrates the potential of restoring the endothelial lining to control AAA dynamics and designates ECs as an efficient therapy to stop AAA expansion.

Expression of matrix metalloproteinase-12 in aortic dissection

BACKGROUND

Aortic dissection(AD) is an acute process of large blood vessels characterized by dangerous pathogenic conditions and high disability and high mortality. The pathogenesis of AD remains debated. Matrix metalloproteinase-12 (MMP-12) participates in many pathological processes such as abdominal aortic aneurysm, atherosclerosis, emphysema and cancer. However, this elastase has rarely been assessed in the presence of AD. The aim of the present study was to investigate the expression of MMP-12 in aortic tissue so as to offer a better understanding of the possible mechanisms of AD.

METHODS

The protein expression levels of MMP-12 were analyzed and compared in aorta tissue and the blood serum samples by reverse transcription polymerase chain reaction(RT-PCR), Western blotting, immuno-histochemistry, fluorescence resonance energy transfer ( FRET ) activity assay and enzyme-linked immuno sorbent assay ( ELISA ), respectively. Ascending aorta tissue specimens were obtained from 12 patients with an acute Stanford A-dissection at the time of aortic replacement, and from 4 patients with coronary artery disease (CAD) undergoing coronary artery bypass surgery. Meanwhile, serum samples were harvested from 15 patients with an acute Stanford A-dissection and 10 healthy individuals who served as the control group.

RESULTS

MMP-12 activity could be detected in both AD and CAD groups, but the level in the AD group was higher than those in the CAD group (P < 0.05). MMP-12 proteolysis existed in both serum samples of the AD and healthy groups, and the activity level in the AD group was clearly higher than in the healthy group (P < 0.05). For AD patients, MMP-12 activity in serum was higher than in the aorta wall (P < 0.05). MMP-12 activity in the aortic wall tissue can be inhibited by MMP inhibitor v (P < 0.05).

CONCLUSION

The present study directly demonstrates that MMP-12 proteolytic activity exists within the aorta specimens and blood samples from aortic dissection patients. MMP-12 might be of potential relevance as a clinically diagnostic tool and therapeutic target in vascular injury and repair.

ADAMTS1, ADAMTS5, ADAMTS9 and aggrecanase-generated proteoglycan fragments are induced following spinal cord injury in mouse

ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) proteinases are involved in a variety of biological processes such as angiogenesis, cancer and arthritis. ADAMTSs appears to be responsible for the cleavage of proteoglycans in several tissues including brain and cartilage. Chondroitin sulfate proteoglycans (CSPGs) maintains the integrity of the brain extracellular matrix and major inhibitory contributors for glial scar and neural plasticity. The activity of aggrecanases in the central nervous system (CNS) has been reported. ADAMTSs are an enzyme degrading CSPGs in the brain. However, there is a little knowledge regarding ADAMTSs in the CNS. We investigated the expression levels of ADAMTSs mRNAs by RT-PCR after spinal cord injury in mouse. Transcripts encoding 4 of the 19 known ADAMTSs were evaluated in the mouse spinal cord following injury. ADAMTS1, -5 and -9 expression levels were found to be upregulated. No change was observed in ADAMTS4 expression. By means of immunohistochemistry, ADAMTSs were detected in the astrocytes implying its cellular source in SCI. Western blot analyses indicated that aggrecanase-generated proteoglycan fragments are produced after SCI.

Clopidogrel, a platelet P2Y12 receptor inhibitor, reduces vascular inflammation and angiotensin II induced-abdominal aortic aneurysm progression

Medial degeneration and inflammation are features of abdominal aortic aneurysms (AAAs). However, the early inflammatory event initiating aneurysm formation remains to be identified. Activated platelets release abundant proinflammatory cytokines and are involved in initial inflammation in various vascular diseases. We investigated the role of platelets in progression of AAA in vivo and in vitro. Histological studies of tissues of patients with AAA revealed that the number of platelets was increased in aneurysm sites along with the increased infiltration of T lymphocytes and augmented angiogenesis. In a murine model of AAA, apolipoprotein E-knockout mice infused with 1,000 ng/kg/min angiotensin II, treatment with clopidogrel, an inhibitor of platelets, significantly suppressed aneurysm formation (47% decrease, P<0.05). The clopidogrel also suppressed changes in aortic expansion, elastic lamina degradation and inflammatory cytokine expression. Moreover, the infiltration of macrophages and production of matrix metalloproteinases (MMPs) were also significantly reduced by clopidogrel treatment. In vitro incubation of macrophages with isolated platelets stimulated MMP activity by 45%. These results demonstrate a critical role for platelets in vascular inflammation and AAA progression.

Dysfunction in elastic fiber formation in fibulin-5 null mice abrogates the evolution in mechanical response of carotid arteries during maturation

Elastin fragmentation is a common characteristic of vascular diseases, such as abdominal aortic aneurysms, peripheral arterial disease, and aortic dissection. Examining growth and remodeling in the presence of dysfunctional elastic fibers provides insight into the adaptive or maladaptive changes that tissues undergo in compensating for structural deficiencies. This study used the maturation of fibulin-5 knockout (KO) and wild-type mice to study the effects of fragmented elastic fibers on the growth and remodeling of carotid arteries. The microstructural content and organization and the biaxial mechanical behavior of common carotid arteries were measured, and parameter estimation performed from KO and WT mice aged 3, 4, 8, and 13 wk. Gross measurements and biaxial tests revealed significant differences in pressure-diameter behavior, in vivo axial stretch, opening angle, compliance, and wall stresses during maturation of wild-type arteries, but little change in these values in KO mice. Multiphoton microscopy used to image collagen fibers across the vessel wall in pressurized and stretched arteries suggests that there is little variation in fiber angles between different ages. Parameter estimation revealed significant differences in material parameters between genotypes and age groups. This study suggests that neonatal formation and cross-linking of functional elastic fibers, followed by increases in artery size due to growth with little remodeling of the elastic fibers, endow arteries with large distensibility and contribute to the evolution of mechanical behavior of arteries during maturation. Dysfunction in neonatal formation of elastic fibers abrogates many of the changes in mechanical response that take place during the maturation.

Locally applied leptin induces regional aortic wall degeneration preceding aneurysm formation in apolipoprotein E-deficient mice

OBJECTIVE

Leptin promotes atherosclerosis and vessel wall remodeling. As abdominal aortic aneurysm (AAA) formation involves tissue remodeling, we hypothesized that local leptin synthesis initiates and promotes this process.

METHODS AND RESULTS

Human surgical AAA walls were analyzed for antigen and mRNA levels of leptin and leptin receptor, as well as mRNA for matrix metalloproteinases (MMP)-9 and MMP-12. Leptin and leptin receptor antigen were evident in all AAAs, and leptin, MMP-9, and MMP-12 mRNA was increased relative to age-matched nondilated controls. To simulate in vivo local leptin synthesis, ApoE(-/-) mice were subjected to a paravisceral periaortic application of low-dose leptin. Leptin-treated aortas exhibited decreased transforming growth factor-β and increased MMP-9 mRNA levels 5 days after surgery, and leptin receptor mRNA was upregulated by day 28. Serial ultrasonography demonstrated accelerated regional aortic diameter growth after 28 days, correlating with local medial degeneration, increased MMP-9, MMP-12, and periadventitial macrophage clustering. Furthermore, the combination of local periaortic leptin and systemic angiotensin II administration augmented medial MMP-9 synthesis and aortic aneurysm size.

CONCLUSIONS

Leptin is locally synthesized in human AAA wall. Paravisceral aortic leptin in ApoE(-/-) mice induces local medial degeneration and augments angiotensin II-induced AAA, thus suggesting novel mechanistic links between leptin and AAA formation.

Novel mechanism of aortic aneurysm development in mice associated with smoking and leukocytes

OBJECTIVE

The purpose of this study was to evaluate potential mechanisms promoting abdominal aortic aneurysm development with tobacco smoke (TS) exposure.

METHODS AND RESULTS

Experiments used the elastase perfusion model of abdominal aortic aneurysms with smoke-free controls. The effect of TS exposure was evaluated in C57/Bl6 mice, after broad-spectrum matrix metalloproteinase inhibition with doxycycline and in mice deficient in matrix metalloproteinase-9, matrix metalloproteinase-12, Cathepsin-S, and Neutrophil Elastase. Preparations of washed marrow, spleen, and peripheral blood leukocytes were transferred to smoke-free mice from 6-week TS-exposed mice or smoke-free mice. All mice were euthanized 14 days after elastase perfusion, and the percentage of change in aortic diameter (%Δ aortic diameter) was calculated. Electron microscopy of aortic tissue from animals exposed to TS without elastase exposure did not demonstrate any ultrastructural changes. Neither doxycycline nor any specific elastase deficiency was effective at preventing an increase in %Δ aortic diameter in TS-exposed animals. Smoke exposure for 6 weeks increased the %Δ aortic diameter after a smoke-free interval of up to 6 weeks before elastase perfusion. Leukocyte preparations from TS-exposed mice localized to abdominal aortic aneurysms and increased the %Δ aortic diameter in smoke-free mice.

CONCLUSIONS

The effect of TS on the development of abdominal aortic aneurysms is not dependent on the activity of elastolytic enzymes and persists for long periods despite cessation of TS. Alterations in leukocyte response to aortic injury appear to mediate this effect.

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.

Doxycycline does not influence established abdominal aortic aneurysms in angiotensin II-infused mice

Background

There is no proven medical approach to attenuating expansion and rupture of abdominal aortic aneurysms (AAAs). One approach that is currently being investigated is the use of doxycycline. Despite being primarily used as an antimicrobial drug, doxycycline has been proposed to function in reducing AAA expansion. Doxycycline is effective in reducing the formation in the most commonly used mouse models of AAAs when administered prior to the initiation of the disease. The purpose of the current study was to determine the effects of doxycycline on established AAAs when it was administered at a dose that produces therapeutic serum concentrations.

Methods and Results

LDL receptor −/− male mice fed a saturated-fat supplemented diet were infused with AngII (1,000 ng/kg/min) via mini-osmotic pumps for 28 days. Upon verification of AAA formation by noninvasive high frequency ultrasonography, mice were stratified based on aortic lumen diameters, and continuously infused with AngII while also administered either vehicle or doxycycline (100 mg/kg/day) in drinking water for 56 days. Administration of doxycycline led to serum drug concentrations of 2.3±0.6 µg/ml. Doxycycline administration had no effect on serum cholesterol concentrations and systolic blood pressures. Doxycycline administration did not prevent progressive aortic dilation as determined by temporal measurements of lumen dimensions using high frequency ultrasound. This lack of effect on AAA regression and progression was confirmed at the termination of the study by ex vivo measurements of maximal width of suprarenal aortas and AAA volumes. Also, doxycycline did not reduce AAA rupture. Medial and adventitial remodeling was not overtly changed by doxycycline as determined by immunostaining and histological staining.

Conclusions

Doxycycline administration did not influence AngII-induced AAA progression and aortic rupture when administered to mice with established AAAs.

Recent advances in pharmacotherapy development for abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a common disease causing segmental expansion and rupture of the aorta with a high mortality rate. The lack of nonsurgical treatment represents a large and unmet need in terms of pharmacotherapy. Advances in AAA research revealed that activation of inflammatory signaling pathways through proinflammatory mediators shifts the balance of extracellular matrix (ECM) metabolism toward tissue degradation. This idea is supported by experimental evidence in animal models that pharmacologic intervention at each pathological step can prevent AAA development. Previously, we identified c-Jun N-terminal kinase (JNK), a pro-inflammatory signaling molecule, as a therapeutic target for AAA. Abnormal activation of JNK in AAA tissue regulates multiple pathological processes in a coordinated manner. Pharmacologic inhibition of JNK tips the ECM balance back towards repair rather than degradation. Interventions targeting signaling molecules such as JNK in order to manipulate multiple pathological processes may be an ideal therapeutic strategy for AAA. Furthermore, the development of biomarkers as well as appropriate drug delivery systems is essential to produce clinically practical pharmacotherapy for AAA.

Clinical evaluation of a matrix metalloproteinase-12 cleaved fragment of titin as a cardiovascular serological biomarker

BACKGROUND

Titin is a muscle-specific protein found in cardiac and skeletal muscles which is responsible for restoring passive tension. Levels and functioning of titin have been shown to be affected by cardiac damage. Due to the inherent difficulty of measuring titin levels in vivo in a clinical setting, we aimed to develop an assay that could reliably measure fragments of degraded titin in serum and potentially be used in the assessment of cardiac muscle damage.

METHODS

A competitive ELISA was developed to specifically measure levels of the titin sequence 12670' NVTVEARLIK 12679', derived by the degradation of titin by matrix metalloproteinase (MMP)-12. Serum samples from 90 individuals were divided into 3 equally sized groups. One group had been diagnosed with acute myocardial infarction (AMI) while the remaining two were asymptomatic individuals either with CT-scan signs of coronary calcium (CT-plusCa) or without coronary calcium (CT-noCa).

RESULTS

Mean geometric levels of the titin fragment in the CT-noCa group were 506.5 ng/ml (± 43.88). The CT-plusCa group showed 50.6% higher levels of the marker [763 ng/ml (± 90.14)] (P < 0.05). AMI patients showed 56.3% higher levels [792 ng/ml (± 149)] (P < 0.05).

CONCLUSIONS

The titin-12670 fragment is present in both individuals with undiagnosed and diagnosed CVD. The statistically significant increase in level of the marker in the AMI group is indicative that this neoepitope biomarker may be a useful serological marker in AMI.

Quercetin, a flavonoid with anti-inflammatory activity, suppresses the development of abdominal aortic aneurysms in mice

Inflammation has been implicated as a contributing factor in the development of abdominal aortic aneurysms (AAA). Quercetin, a natural flavonoid with anti-inflammatory properties, is known for its beneficial effects on vascular disease. In this study, we examined the effects of quercetin to inflammatory cell infiltration, subsequent expression of cytokines and activation of proteases on the expansion of experimental AAA. Aneurysms were induced by abluminal application of calcium chloride in C57/BL6 mice. Quercetin (60 mg/kg) was administered once daily by gavage beginning 2 weeks before AAA induction and continuing for 8 weeks. Mice treated with quercetin exhibited a 32.7% reduction in aortic size compared with vehicle-treated controls. Prevention of AAA was associated with preservation of medial structure, as well as a relative reduction in macrophage and CD3(+) T cell infiltration in aortic tissue, inflammatory cytokines release and nuclear factor κB activation. Quercetin also reduced the expression of matrix metalloproteinase (MMP)-2, MMP-9, cathepsin B, and cathepsin K in aortic tissue. In addition, quercetin treatment increased tissue inhibitors of metalloproteinases (TIMP)-1 gene expression. These data indicate that quercetin may be useful for the prevention and treatment of AAA via blocking the inflammatory response and inhibiting the proteases involved in the pathogenesis of this disease.

MicroRNA expression signature in human abdominal aortic aneurysms

BACKGROUND

Abdominal aortic aneurysm (AAA) is a dilatation of the aorta affecting most frequently elderly men. Histologically AAAs are characterized by inflammation, vascular smooth muscle cell apoptosis, and extracellular matrix degradation. The mechanisms of AAA formation, progression, and rupture are currently poorly understood. A previous mRNA expression study revealed a large number of differentially expressed genes between AAA and non-aneurysmal control aortas. MicroRNAs (miRNAs), small non-coding RNAs that are post-transcriptional regulators of gene expression, could provide a mechanism for the differential expression of genes in AAA.

METHODS

To determine differences in miRNA levels between AAA (n = 5) and control (n = 5) infrarenal aortic tissues, a microarray study was carried out. Results were adjusted using Benjamini-Hochberg correction (adjusted p < 0.05). Real-time quantitative RT-PCR (qRT-PCR) assays with an independent set of 36 AAA and seven control tissues were used for validation. Potential gene targets were retrieved from miRNA target prediction databases Pictar, TargetScan, and MiRTarget2. Networks from the target gene set were generated and examined using the network analysis programs, CytoScape® and Ingenuity Pathway Core Analysis®.

RESULTS

A microarray study identified eight miRNAs with significantly different expression levels between AAA and controls (adjusted p < 0.05). Real-time qRT-PCR assays validated the findings for five of the eight miRNAs. A total of 222 predicted miRNA target genes known to be differentially expressed in AAA based on a prior mRNA microarray study were identified. Bioinformatic analyses revealed that several target genes are involved in apoptosis and activation of T cells.

CONCLUSIONS

Our genome-wide approach revealed several differentially expressed miRNAs in human AAA tissue suggesting that miRNAs play a role in AAA pathogenesis.

Emerging role of mast cells and macrophages in cardiovascular and metabolic diseases

Mast cells are essential in allergic immune responses. Recent discoveries have revealed their direct participation in cardiovascular diseases and metabolic disorders. Although more sophisticated mechanisms are still unknown, data from animal studies suggest that mast cells act similarly to macrophages and other inflammatory cells and contribute to human diseases through cell-cell interactions and the release of proinflammatory cytokines, chemokines, and proteases to induce inflammatory cell recruitment, cell apoptosis, angiogenesis, and matrix protein remodeling. Reduced cardiovascular complications and improved metabolic symptoms in animals receiving over-the-counter antiallergy medications that stabilize mast cells open another era of mast cell biology and bring new hope to human patients suffering from these conditions.

Matrix metalloproteinase inhibition therapy for vascular diseases

The matrix metalloproteinases (MMPs) are 23 secreted or cell surface proteases that act together and with other protease classes to turn over the extracellular matrix, cleave cell surface proteins and alter the function of many secreted bioactive molecules. In the vasculature MMPs influence the migration proliferation and apoptosis of vascular smooth muscle, endothelial cells and inflammatory cells, thereby affecting intima formation, atherosclerosis and aneurysms, as substantiated in clinical and mouse knockout and transgenic studies. Prominent counterbalancing roles for MMPs in tissue destruction and repair emerge from these experiments. Naturally occurring tissue inhibitors of MMPs (TIMPs), pleiotropic mediators such as tetracyclines, chemically-synthesised small molecular weight MMP inhibitors (MMPis) and inhibitory antibodies have all shown effects in animal models of vascular disease but only doxycycline has been evaluated extensively in patients. A limitation of broad specificity MMPis is that they prevent both matrix degradation and tissue repair functions of different MMPs. Hence MMPis with more restricted specificity have been developed and recent studies in models of atherosclerosis accurately replicate the phenotypes of the corresponding gene knockouts. This review documents the established actions of MMPs and their inhibitors in vascular pathologies and considers the prospects for translating these findings into new treatments.

Aortic dilatation with bicuspid aortic valves: cusp fusion correlates to matrix metalloproteinases and inhibitors

BACKGROUND

Congenital bicuspid aortic valves (BAVs) result from fusion of 2 valve cusps, resulting in left-noncoronary (L-N), right-left (R-L), and right-noncoronary (R-N) morphologic presentations. BAVs predispose to ascending thoracic aortic aneurysms (ATAAs). This study hypothesized that ATAAs with each BAV morphologic group possess unique signatures of matrix metalloproteinases (MMPs) and endogenous tissue inhibitors of metalloproteinases (TIMPs).

METHODS

Ascending thoracic aortic aneurysm tissue from 46 patients with BAVs was examined for MMP/TIMP abundance, and global MMP activity was compared with normal aortic specimens (n=15). Proteolytic balance was calculated as the ratio of MMP abundance to a composite TIMP score. Results were stratified by valve morphologic group (L-N [n=6], R-L [n=31], and R-N [n=9]).

RESULTS

The BAV specimens (p<0.05 versus normal aorta, 100%) displayed elevated global MMP activity (273%±63%), MMP-9 (263%±47%), and decreased MMP-7 (56%±10%), MMP-8 (58%±11%), TIMP-1 (63%±7%), and TIMP-4 (38%±3%). The R-L group showed increased global MMP activity (286%±89%) and MMP-9 (267%±55%) with reduced MMP-7 (45%±7%), MMP-8 (68%±15%), TIMP-1 (58%±7%), and TIMP-4 (35%±3%). The L-N group showed elevated global MMP activity (284%±71%) and decreased MMP-8 (37%±17%) and TIMP-4 (48%±14) activity. In the R-N group, MMP-7 (46%±13%) and MMP-8 (36%±17%) and TIMP-1 (59%±10%) and TIMP-4 (42%±5%) were decreased. The R-L group demonstrated an increased proteolytic balance for MMP-1, MMP-9, and MMP-12 relative to L-N and R-N.

CONCLUSIONS

Each BAV morphologic group possesses a unique signature of MMPs and TIMPs. MMP/TIMP score ratios suggest that the R-L group may be more aggressive, justifying earlier surgical intervention.

Human matrix metalloproteinases: an ubiquitarian class of enzymes involved in several pathological processes

Human matrix metalloproteinases (MMPs) belong to the M10 family of the MA clan of endopeptidases. They are ubiquitarian enzymes, structurally characterized by an active site where a Zn(2+) atom, coordinated by three histidines, plays the catalytic role, assisted by a glutamic acid as a general base. Various MMPs display different domain composition, which is very important for macromolecular substrates recognition. Substrate specificity is very different among MMPs, being often associated to their cellular compartmentalization and/or cellular type where they are expressed. An extensive review of the different MMPs structural and functional features is integrated with their pathological role in several types of diseases, spanning from cancer to cardiovascular diseases and to neurodegeneration. It emerges a very complex and crucial role played by these enzymes in many physiological and pathological processes.

Elevated concentrations of matrix metalloproteinase-12 and elastin degradation products in the sera of pregnant women infected with Toxoplasma gondii

Although the expression of matrix metalloproteinase-12 (MMP-12) appears to be increased in most inflammatory diseases, the role of this enzyme in the pathogenesis of toxoplasmosis in pregnant women, if any, is unknown. In a recent study in Taiwan, the serum concentrations of MMP-12 and its substrate elastin were evaluated in pregnant women with Toxoplasma gondii infection. Compared with the healthy pregnant and non-pregnant women used as controls, the pregnant women with toxoplasmosis had significantly higher serum concentrations of MMP-12 and significantly higher levels of elastin synthesis and degradation. Interaction between MMP-12 and elastin in the serum samples was confirmed by co-immunoprecipitation. It seems possible that MMP-12 may contribute to elastin degradation occurring during the pathogenesis of toxoplasmosis in pregnant women.

Remote exosites of the catalytic domain of matrix metalloproteinase-12 enhance elastin degradation

How does matrix metalloproteinase-12 (MMP-12 or metalloelastase) degrade elastin with high specific activity? Nuclear magnetic resonance suggested soluble elastin covers surfaces of MMP-12 far from its active site. Two of these surfaces have been found, by mutagenesis guided by the BINDSIght approach, to affect degradation and affinity for elastin substrates but not a small peptide substrate. Main exosite 1 has been extended to Asp124 that binds calcium. Novel exosite 2 comprises residues from the II-III loop and β-strand I near the back of the catalytic domain. The high degree of exposure of these distal exosites may make them accessible to elastin made more flexible by partial hydrolysis. Importantly, the combination of one lesion each at exosites 1 and 2 and the active site decreased the catalytic competence toward soluble elastin by 13-18-fold to the level of MMP-3, homologue and poor elastase. Double-mutant cycle analysis of conservative mutations of Met156 (exosite 2) and either Asp124 (exosite 1) or Ile180 (active site) showed they had additive effects. Compared to polar substitutions observed in other MMPs, Met156 enhanced affinity and Ile180 the k(cat) for soluble elastin. Both residues detracted from the higher folding stability with polar mutations. This resembles the trend in enzymes of an inverse relationship between folding stability and activity. Restoring Asp124 from combination mutants enhanced the k(cat) for soluble elastin. In elastin degradation, exosites 1 and 2 contributed in a manner independent of each other and Ile180 at the active site, but with partial coupling to Ala182 near the active site. The concept of weak, separated interactions coalescing somewhat independently can be extended to this proteolytic digestion of a protein from fibrils.

Retinoblastoma protein modulates the inverse relationship between cellular proliferation and elastogenesis

The mechanism that leads to the inverse relationship between heightened cellular proliferation and the cessation of elastic fibers production, observed during formation of the arterial occlusions and dermal scars, is not fully understood. Because the retinoblastoma protein (Rb), responsible for cell cycle initiation, has also been implicated in insulin-like growth factor-I-mediated signaling stimulating elastin gene activation, we explored whether differential phosphorylation of Rb by various cyclin·cyclin-dependent kinase complexes would be responsible for promoting either elastogenic or pro-proliferative signals. We first tested cultures of dermal fibroblasts derived from Costello syndrome patients, in which heightened proliferation driven by mutated oncogenic H-Ras coincides with inhibition of elastogenesis. We found that Costello syndrome fibroblasts display elevated level of Rb phosphorylation on serine 780 (Ser(P)-780-Rb) and that pharmacological inhibition of Ras with radicicol, Mek/Erk with PD98059, or cyclin-dependent kinase 4 with PD0332991 not only leads to down-regulation of Ser(P)-780-Rb levels but also enhances Rb phosphorylation on threonine-821 (Thr(P)-821-Rb), which coincides with the recovery of elastin production. Then we demonstrated that treatment of normal skin fibroblasts with the pro-proliferative PDGF BB also up-regulates Ser(P)-780-Rb levels, but treatment with the pro-elastogenic insulin-like growth factor-I activates cyclinE-cdk2 complex to phosphorylate Rb on Thr-821. Importantly, we have established that elevation of Thr(P)-821-Rb promotes Rb binding to the Sp1 transcription factor and that successive binding of the Rb-Sp1 complex to the retinoblastoma control element within the elastin gene promoter stimulates tropoelastin transcription. In summary, we provide novel insight into the role of Rb in mediating the inverse relationship between elastogenesis and cellular proliferation.

Synthesis and matrix metalloproteinase-12 inhibitory activity of ageladine A analogs

Synthesis of the 37 ageladine A analogs was accomplished by employing the total synthetic route of natural ageladine A previously explored by us. From the matrix metalloproteinase-12 (MMP-12) inhibitory activity assay carried out using the novel analogs, it appeared evident that the halogen atom at the 2-position of pyrrole ring was essential for the inhibitory activity and that the introduction of a bromine atom into the 4-position of pyrrole ring is very effective for producing potent activity. In addition, exchange of the pyrrole ring to an imidazole ring was extremely effective in increasing activity, and the analog 29 thus obtained was found to show approximately 4 times more potent activity than natural ageladine A.

Matrix metalloproteinase-12 leads to elastin degradation in BALB/c mice with eosinophilic meningitis caused by Angiostrongylus cantonensis

The rat lugworm Angiostrongylus cantonensis can cause eosinophilic meningitis. The purpose of this study was to determine whether matrix metalloproteinase (MMP)-12 and its substrate elastin participate in this inflammatory response. We showed that the MMP-12/tissue inhibitor of metalloproteinase-1 ratio was significantly increased in the CSF of A. cantonensis-infected mice from day 10 p.i., and reached high levels on days 20 and 25 p.i. MMP-12 production was correlated with elastin degradation, eosinophil count, blood-CSF barrier permeability and pathological changes in the subarachnoid space. Also, MMP-12 might contribute to elastin degradation in the meningeal vessel of the subarachnoid space. Simultaneous administration of albendazole and doxycycline significantly reduced the levels of MMP-12, elastin and Evans blue in mice with meningitis. These results imply that MMP-12 contributes to the elastin degradation that occurs in angiostrongyliasis meningitis, and doxycycline can reverse related inflammatory events by inhibition of MMP-12.

Differential roles of endothelin-1 in angiotensin II-induced atherosclerosis and aortic aneurysms in apolipoprotein E-null mice

Because both endothelin-1 (ET-1) and angiotensin II (AngII) are independent mediators of arterial remodeling, we sought to determine the role of ET receptor inhibition in AngII-accelerated atherosclerosis and aortic aneurysm formation. We administered saline or AngII and/or bosentan, an endothelin receptor antagonist (ERA) for 7, 14, or 28 days to 6-week- and 6-month-old apolipoprotein E-knockout mice. AngII treatment increased aortic atherosclerosis, which was reduced by ERA. ET-1 immunostaining was localized to macrophage-rich regions in aneurysmal vessels. ERA did not prevent AngII-induced aneurysm formation but instead may have increased aneurysm incidence. In AngII-treated animals with aneurysms, ERA had a profound effect on the non-aneurysmal thoracic aorta via increasing wall thickness, collagen/elastin ratio, wall stiffness, and viscous responses. These observations were confirmed in acute in vitro collagen sheet production models in which ERA inhibited AngII's dose-dependent effect on collagen type 1 α 1 (COL1A1) gene transcription. However, chronic treatment reduced matrix metalloproteinase 2 mRNA expression but enhanced COL3A1, tissue inhibitor of metalloproteinase 1 (TIMP-1), and TIMP-2 mRNA expressions. These data confirm a role for the ET system in AngII-accelerated atherosclerosis but suggest that ERA therapy is not protective against the formation of AngII-induced aneurysms and can paradoxically stimulate a chronic arterial matrix remodeling response.

Liberation of desmosine and isodesmosine as amino acids from insoluble elastin by elastolytic proteases

The development of atherosclerotic lesions and abdominal aortic aneurysms involves degradation and loss of extracellular matrix components, such as collagen and elastin. Releases of the elastin cross-links desmosine (DES) and isodesmosine (IDE) may reflect elastin degradation in cardiovascular diseases. This study investigated the production of soluble elastin cross-linking structures by proteinases implicated in arterial diseases. Recombinant MMP-12 and neutrophil elastase liberated DES and IDE as amino acids from insoluble elastin. DES and IDE were also released from insoluble elastin exposed to monocyte/macrophage cell lines or human primary macrophages derived from peripheral blood monocytes. Elastin oxidized by reactive oxygen species (ROS) liberated more unconjugated DES and IDE than did non-oxidized elastin when incubated with MMP-12 or neutrophil elastase. These results support the exploration of free DES and IDE as biomarkers of elastin degradation.

Overexpression of matrix metalloproteinase-12 (MMP-12) correlates with poor prognosis of hepatocellular carcinoma

Tumour recurrence and metastasis are pressing issues of hepatocellular carcinoma (HCC) patients who receive surgical treatments. Matrix metalloproteinase-12 (MMP-12), previously identified from our animal model, is involved in tumour invasiveness of rat hepatoma. We aimed to investigate the significance and prognostic value of MMP-12 expression in human HCC. MMP-12 mRNA level of 139 pairs of tumour and non-tumour liver tissues of HCC patients after hepatectomy were investigated by quantitative real-time RT-PCR. MMP-12 mRNA was significantly elevated in tumour liver tissues of HCC patients compared to non-tumour and normal liver tissues. By comparing paired tumour and non-tumour liver tissues, MMP-12 mRNA was overexpressed in 58% of tumour tissue of HCC patients. Overexpression of MMP-12 mRNA was significantly correlated with presence of venous infiltration (p=0.004), high serum AFP level (p=0.012), early tumour recurrence (p=0.018) and poor overall survival (p=0.02) of HCC patients. Moreover, MMP-12 mRNA was an independent factor in predicting the 1- and 3-year overall survival of HCC patients after hepatectomy. Our data demonstrated that MMP-12 mRNA may be a valuable prognostic marker for both overall survival and tumour recurrence of HCC patients after liver resection.