Furin and membrane type-1 metalloproteinase mRNA levels and activation of metalloproteinase-2 are associated with arterial remodeling

High-Resolution Intracranial Vessel Wall MRI Findings Among Different Middle Cerebral Artery Territory Infarction Types

Objective

Intracranial atherosclerotic stroke occurs through various mechanisms, mainly by artery-to-artery embolism (AA) or branch occlusive disease (BOD). This study evaluated the spatial relationship between middle cerebral artery (MCA) plaques and perforating arteries among different MCA territory infarction types using vessel wall magnetic resonance imaging (VW-MRI).

Materials and Methods

We retrospectively enrolled patients with acute MCA infarction who underwent VW-MRI. Thirty-four patients were divided into three groups according to infarction pattern: 1) BOD, 2) both BOD and AA (BOD-AA), and 3) AA. To determine the factors related to BOD, the BOD and BOD-AA groups were combined into one group (with striatocapsular infarction [BOD+]) and compared with the AA group. To determine the factors related to AA, the BOD-AA and AA groups were combined into another group (with cortical infarction [AA+]) and compared with the BOD group. Plaque morphology and the spatial relationship between the perforating artery orifice and plaque were evaluated both quantitatively and qualitatively.

Results

The plaque margin in the BOD+ group was closer to the perforating artery orifice than that in the AA group (p = 0.011), with less enhancing plaque (p = 0.030). In the BOD group, plaques were mainly located on the dorsal (41.2%) and superior (41.2%) sides where the perforating arteries mainly arose. No patient in the AA group had overlapping plaques with perforating arteries at the cross-section where the perforator arose. Perforating arteries associated with culprit plaques were most frequently located in the middle two-thirds of the M1 segment (41.4%). The AA+ group had more stenosis (%) than the BOD group (39.73 ± 24.52 vs. 14.42 ± 20.96; p = 0.003).

Conclusion

The spatial relationship between the perforating artery orifice and plaque varied among different types of MCA territory infarctions. In patients with BOD, the plaque margin was closer and blocked the perforating artery orifice, and stenosis degree and enhancement were less than those in patients with AA.

Establishment of proprotein convertase, furinA knocked-out lines in medaka, Oryzias latipes, and unique form of medaka furin-like prorprotein convertase (mflPC)

Furin is a member of the subtilisin-like proprotein convertase family. Medaka furin-like proprotein convertase (mflPC), a unique form of medaka FurinA (mFurinA) (GenBank accession no. AB092685.1) was cloned from the ovary cDNA library. Compared to human furin (GenBank accession no. NM_002569.3) and mFurinA in the structural motif of mflPC, only the catalytic domain and the N-terminal region of the P domain are highly conserved, but more C-terminal domains are truncated. Based on our research, there three forms of furin, mFurinA, mflPC and mFurinB that exist in medaka. These three genes are expressed in the developing embryos and ubiquitously in adult tissues. To investigate the function of mFurinA and mflPC, as a first step, mFurinA KO lines were established. The mFurinA KO larvae with abnormal phenotypes exhibit edema, abnormal body fluid accumulation in the pericardial and yolk sacs, enlarged hearts, clogged blood vessels, structurally weak eyes, and a very short life. The data suggests that abnormal processing of TGF-β may be one of the causes of these disorders. FurinA KO medaka is a good model for the study of human diseases such as Fraser Syndrome and Marfan syndrome. The creation of human genomic disorder models using recently advanced genome editing procedures informs us of the function of key molecules and their role in causing equivalent human disorders and will be useful as a tool to identify the mechanisms involved.

Morphologic Features of Carotid Plaque Rupture Assessed by Optical Coherence Tomography

BACKGROUND AND PURPOSE

Rupture of the plaque fibrous cap and subsequent thrombosis are the major causes of stroke. This study evaluated morphologic features of plaque rupture in the carotid artery by using optical coherence tomography in vivo.

MATERIALS AND METHODS

Thirty-six carotid plaques with high-grade stenosis were prospectively imaged by optical coherence tomography. "Plaque rupture" was defined as a plaque containing a cavity that had overlying residual fibrous caps. The fibrous cap thickness was measured at its thinnest part for both ruptured and nonruptured plaques. The distance between the minimum fibrous cap thickness site and the bifurcation point was also measured. Optical coherence tomography identified 24 ruptured and 12 nonruptured plaques.

RESULTS

Multiple ruptures were observed in 9 (38%) patients: Six patients had 2 ruptures in the same plaque, 2 patients had 3 ruptures in the same plaque, and 1 patient had 5 ruptures in the same plaque. Most (84%) of the fibrous cap disruptions were identified at the plaque shoulder and near the bifurcation point (within a 4.2-mm distance). The median thinnest cap thickness was 80 μm (interquartile range, 70-100 μm), and 95% of ruptured plaques had fibrous caps of <130 μm. Receiver operating characteristic analysis revealed that a fibrous cap thickness of <130 μm was the critical threshold value for plaque rupture in the carotid artery.

CONCLUSIONS

Plaque rupture was common in high-grade stenosis and was located at the shoulder of the carotid plaque close to the bifurcation. A cap thickness of <130 μm was the threshold for plaque rupture in the carotid artery.

Fluid shear stress promotes proprotein convertase-dependent activation of MT1-MMP

During angiogenesis, endothelial cells (ECs(1)) initiate new blood vessel growth and invade into the extracellular matrix (ECM). Membrane type-1 matrix metalloproteinase (MT1-MMP) facilitates this process and translocates to the plasma membrane following activation to promote ECM cleavage. The N-terminal pro-domain within MT1-MMP must be processed for complete activity of the proteinase. This study investigated whether MT1-MMP activation was altered by sphingosine 1-phosphate (S1P) and wall shear stress (WSS), which combine to stimulate EC invasion in three dimensional (3D) collagen matrices. MT1-MMP was activated rapidly and completely by WSS but not S1P. Proprotein convertases (PCs) promoted MT1-MMP processing, prompting us to test whether WSS or S1P treatments increased PC activity. Like MT1-MMP, PC activity increased with WSS, while S1P had no effect. A pharmacological PC inhibitor completely blocked S1P- and WSS-induced EC invasion and MT1-MMP translocation to the plasma membrane. Further, a recombinant PC inhibitor reduced MT1-MMP activation and decreased lumen formation in invading ECs, a process known to be controlled by MT1-MMP. Thus, we conclude that PC and MT1-MMP activation are mechanosensitive events that are required for EC invasion into 3D collagen matrices.

Bone marrow alterations and lower endothelial progenitor cell numbers in critical limb ischemia patients

BACKGROUND

Critical limb ischemia (CLI) is characterized by lower extremity artery obstruction and a largely unexplained impaired ischemic neovascularization response. Bone marrow (BM) derived endothelial progenitor cells (EPC) contribute to neovascularization. We hypothesize that reduced levels and function of circulating progenitor cells and alterations in the BM contribute to impaired neovascularization in CLI.

METHODS

Levels of primitive (CD34(+) and CD133(+)) progenitors and CD34(+)KDR(+) EPC were analyzed using flow cytometry in blood and BM from 101 CLI patients in the JUVENTAS-trial (NCT00371371) and healthy controls. Blood levels of markers for endothelial injury (sE-selectin, sICAM-1, sVCAM-1, and thrombomodulin), and progenitor cell mobilizing and inflammatory factors were assessed by conventional and multiplex ELISA. BM levels and activity of the EPC mobilizing protease MMP-9 were assessed by ELISA and zymography. Circulating angiogenic cells (CAC) were cultured and their paracrine function was assessed.

RESULTS

Endothelial injury markers were higher in CLI (P<0.01). CLI patients had higher levels of VEGF, SDF-1α, SCF, G-CSF (P<0.05) and of IL-6, IL-8 and IP-10 (P<0.05). Circulating EPC and BM CD34(+) cells (P<0.05), lymphocytic expression of CXCR4 and CD26 in BM (P<0.05), and BM levels and activity of MMP-9 (P<0.01) were lower in CLI. Multivariate regression analysis showed an inverse association between IL-6 and BM CD34(+) cell levels (P = 0.007). CAC from CLI patients had reduced paracrine function (P<0.0001).

CONCLUSION

CLI patients have reduced levels of circulating EPC, despite profound endothelial injury and an EPC mobilizing response. Moreover, CLI patients have lower BM CD34(+)-cell levels, which were inversely associated with the inflammatory marker IL-6, and lower BM MMP-9 levels and activity. The results of this study suggest that inflammation-induced BM exhaustion and a disturbed progenitor cell mobilization response due to reduced levels and activity of MMP-9 in the BM and alterations in the SDF-1α/CXCR4 interaction contribute to the attenuated neovascularization in CLI patients.

Matrix production and remodeling capacity of cardiomyocyte progenitor cells during in vitro differentiation

Cell-based therapy has emerged as a treatment modality for myocardial repair. Especially cardiac resident stem cells are considered a potential cell source since they are able to differentiate into cardiomyocytes and have improved heart function after injury in a preclinical model for myocardial infarction. To avoid or repair myocardial damage it is important not only to replace the lost cardiomyocytes, but also to remodel and replace the scar tissue by "healthy" extracellular matrix (ECM). Interestingly, the role of cardiac stem cells in this facet of cardiac repair is largely unknown. Therefore, we investigated the expression and production of ECM proteins, matrix metalloproteinases (MMPs) and their inhibitors (TIMPs) in human cardiomyocyte progenitor cells (CMPCs) undergoing differentiation towards the cardiomyogenic lineage. Our data suggest that CMPCs have the capacity to synthesize and modulate their own matrix environment, especially during differentiation towards the cardiomyogenic lineage. While undifferentiated CMPCs expressed collagen I, III, IV and fibronectin, but no elastin, during the process of differentiation the expression of collagen I, III, IV and fibronectin increased and interestingly also elastin expression was induced. Furthermore, undifferentiated CMPCs express MMP-1 -2 and -9 and upon differentiation the expression of MMP-1 decreased, while the expression of MMP-2 and MMP-9, although the latter only in the early stage of differentiation, increased. Additionally, the expression of TIMP-1, -2 and -4 was induced during differentiation. This study provides new insights into the matrix production and remodeling capacity of human CMPCs, with potential beneficial effects for the treatment of cardiac injury.

Rare, nonsynonymous variant in the smooth muscle-specific isoform of myosin heavy chain, MYH11, R247C, alters force generation in the aorta and phenotype of smooth muscle cells

RATIONALE

Mutations in myosin heavy chain (MYH11) cause autosomal dominant inheritance of thoracic aortic aneurysms and dissections. At the same time, rare, nonsynonymous variants in MYH11 that are predicted to disrupt protein function but do not cause inherited aortic disease are common in the general population and the vascular disease risk associated with these variants is unknown.

OBJECTIVE

To determine the consequences of the recurrent MYH11 rare variant, R247C, through functional studies in vitro and analysis of a knock-in mouse model with this specific variant, including assessment of aortic contraction, response to vascular injury, and phenotype of primary aortic smooth muscle cells (SMCs).

METHODS AND RESULTS

The steady state ATPase activity (actin-activated) and the rates of phosphate and ADP release were lower for the R247C mutant myosin than for the wild-type, as was the rate of actin filament sliding in an in vitro motility assay. Myh11(R247C/R247C) mice exhibited normal growth, reproduction, and aortic histology but decreased aortic contraction. In response to vascular injury, Myh11(R247C/R247C) mice showed significantly increased neointimal formation due to increased SMC proliferation when compared with the wild-type mice. Primary aortic SMCs explanted from the Myh11(R247C/R247C) mice were dedifferentiated compared with wild-type SMCs based on increased proliferation and reduced expression of SMC contractile proteins. The mutant SMCs also displayed altered focal adhesions and decreased Rho activation, associated with decreased nuclear localization of myocardin-related transcription factor-A. Exposure of the Myh11(R247C/R247C) SMCs to a Rho activator rescued the dedifferentiated phenotype of the SMCs.

CONCLUSIONS

These results indicate that a rare variant in MYH11, R247C, alters myosin contractile function and SMC phenotype, leading to increased proliferation in vitro and in response to vascular injury.

Chronic hyperhomocysteinemia causes vascular remodelling by instigating vein phenotype in artery

In the present study we tested the hypothesis whether hyperhomocysteinemia, an elevated homocysteine level, induces venous phenotype in artery. To test our hypothesis, we employed wild type (WT) and cystathionine β-synthase heterozygous (+/-) (CBS+/-) mice treatment with or without folic acid (FA). Aortic blood flow and velocity were significantly lower in CBS+/-mice compared to WT. Aortic lumen diameter was significantly decreased in CBS+/-mice, whereas FA treatment normalized it. Medial thickness and collagen were significantly increased in CBS+/-aorta, whereas elastin/collagen ratio was significantly decreased. Superoxide and gelatinase activity was significantly high in CBS+/-aorta vs WT. Western blot showed significant increase in MMP-2, -9,-12, TIMP-2 and decrease in TIMP-4 in aorta. RT-PCR revealed significant increase of vena cava marker EphB4, MMP-13 and TIMP-3 in aorta. We summarize that chronic HHcy causes vascular remodelling that transduces changes in vascular wall in a way that artery expresses vein phenotype.

The proprotein convertase furin in human trophoblast: Possible role in promoting trophoblast cell migration and invasion

Furin, a proprotein convertase (PC), is ubiquitously expressed and implicated in many physiological and pathological processes. This study is aimed to identify the role of furin in human trophoblast invasion and migration. Furin was found to be highly expressed in placental villi of both rhesus monkeys and human beings during early pregnancy. Specifically, furin was found in trophoblast column and trophoblast shell, regions where highly invasive cytotrophoblast cells invade the maternal decidua during human placentation. To determine whether furin plays any role in trophoblast invasion and migration, we employed human extravillous HTR8/SVneo cells in Matrigel invasion and transwell migration assays. Knocking-down furin expression by siRNA significantly inhibited invasion and migration of HTR8/SVneo cells (P<0.01), with corresponding decrease of matrix metalloproteinase-9 (MMP-9) activities. In contrast, over-expression of furin markedly increased cell invasion and migration (P<0.01), accompanied by significant increase of MMP-9 activities. Furthermore, furin siRNA significantly increased the levels of both tissue inhibitors of MMPs (TIMP)-1 and -2. Our results suggest that furin may play an important role in the invasion and migration of human trophoblast cells during early pregnancy.

Caveolin-1 influences vascular protease activity and is a potential stabilizing factor in human atherosclerotic disease

Caveolin-1 (Cav-1) is a regulatory protein of the arterial wall, but its role in human atherosclerosis remains unknown. We have studied the relationships between Cav-1 abundance, atherosclerotic plaque characteristics and clinical manisfestations of atherosclerotic disease.We determined Cav-1 expression by western blotting in atherosclerotic plaques harvested from 378 subjects that underwent carotid endarterectomy. Cav-1 levels were significantly lower in carotid plaques than non-atherosclerotic vascular specimens. Low Cav-1 expression was associated with features of plaque instability such as large lipid core, thrombus formation, macrophage infiltration, high IL-6, IL-8 levels and elevated MMP-9 activity. Clinically, a down-regulation of Cav-1 was observed in plaques obtained from men, patients with a history of myocardial infarction and restenotic lesions. Cav-1 levels above the median were associated with absence of new vascular events within 30 days after surgery [0% vs. 4%] and a trend towards lower incidence of new cardiovascular events during longer follow-up. Consistent with these clinical data, Cav-1 null mice revealed elevated intimal hyperplasia response following arterial injury that was significantly attenuated after MMP inhibition. Recombinant peptides mimicking Cav-1 scaffolding domain (Cavtratin) reduced gelatinase activity in cultured porcine arteries and impaired MMP-9 activity and COX-2 in LPS-challenged macrophages. Administration of Cavtratin strongly impaired flow-induced expansive remodeling in mice.This is the first study that identifies Cav-1 as a novel potential stabilizing factor in human atherosclerosis. Our findings support the hypothesis that local down-regulation of Cav-1 in atherosclerotic lesions contributes to plaque formation and/or instability accelerating the occurrence of adverse clinical outcomes. Therefore, given the large number of patients studied, we believe that Cav-1 may be considered as a novel target in the prevention of human atherosclerotic disease and the loss of Cav-1 may be a novel biomarker of vulnerable plaque with prognostic value.

Arterial adaptations to chronic changes in haemodynamic function: coupling vasomotor tone to structural remodelling

Healthy mature arteries are usually extremely quiescent tissues with cell proliferation rates much below 1%/day and with extracellular matrix constituents exhibiting half-lives of years to decades. However, chronic physiological or pathological changes in haemodynamic function elicit arterial remodelling processes that may involve substantial tissue synthesis, degradation or turnover. Although these remodelling processes accommodate changing demands placed upon the cardiovascular system by physiological adaptations, they can compromise further perfusion in the context of arterial occlusive disease and they entrench hypertension and may exacerbate its progression. Recent findings indicate that some of the most important such remodelling responses involve the integrated effects of persistently altered vascular tone that feed into restructuring responses, with common signalling pathways frequently interacting in the control of both phases of the response. Current efforts to define these signals and their targets may provide new directions for therapeutic interventions to treat important vascular disorders.

Morphological and biochemical characterization of remodeling in aorta and vena cava of DOCA-salt hypertensive rats

Arterial remodeling occurs in response to mechanical and neurohumoral stimuli. We hypothesized that veins, which are not exposed to higher pressures in hypertension, would demonstrate less active remodeling than arteries. We assessed remodeling with two standard measures of arterial remodeling: vessel morphometry and the expression/function of matrix metalloproteinases (MMPs). Thoracic aorta and vena cava from sham normotensive and DOCA-salt hypertensive rats (110 ± 4 and 188 ± 8 mmHg systolic blood pressure, respectively) were used. Wall thickness was increased in DOCA-salt vs. sham aorta (301 ± 23 vs. 218 ± 14 μm, P < 0.05), as was medial area, but neither measure was altered in the vena cava. The aorta and vena cava expressed the gelatinases MMP-2, MMP-9, transmembrane proteinase MT1-MMP, and tissue inhibitor of metalloproteinase-2 (TIMP-2). Immunohistochemically, MMP-2 localized to smooth muscle in the aorta and densely in endothelium/smooth muscle of the vena cava. Western and zymographic analyses verified that MMP-2 was active in all vessels and less active in the vena cava than aorta. In hypertension, MMP-2 expression and activity in the aorta were increased (59.1 ± 3.7 and 74.5 ± 6.1 units in sham and DOCA, respectively, P < 0.05); similar elevations were not observed in the vena cava. MMP-9 was weakly expressed in all vessels. MT1-MMP was expressed by the aorta and vena cava and elevated in the vena cava from DOCA-salt rats. TIMP-2 expression was significantly increased in the aorta of DOCA rats compared with sham but was barely detectable in the vena cava of sham or DOCA-salt hypertensive rats. These findings suggest that large veins may not undergo vascular remodeling in DOCA-salt hypertension.

Why don't fistulas mature?

Fistula maturation requires a compliant and responsive vasculature capable of dilating in response to the increased velocity of blood flowing into the newly created low-resistance circuit. Successful maturation to a high volume flow circuit capable of sustaining hemodialysis typically occurs within the first few weeks after creation. Failure to achieve maturation within 4-8 weeks should prompt a search for reversible etiologies; however, an accepted definition of maturation, particularly for patients not yet on dialysis remains elusive. The most commonly identified etiology is neointimal hyperplasia typically occurring in the juxta-anastomotic vein. However, failed maturation has also been reported secondary to impaired arterial and venous dilation and accessory veins. The exact frequency of each of these etiologies is unclear. Understanding the etiologies of impaired fistula maturation will focus future studies of targeted interventions to improve the rate of fistula maturation and increase the number of dialysis patients with a functioning autogenous fistula.

Proprotein convertases furin and PC5: targeting atherosclerosis and restenosis at multiple levels

Several growth factors, chemokines, adhesion molecules, and proteolytic enzymes important for cell-cell/cell-matrix interactions in atherosclerosis and restenosis are initially synthesized as inactive precursor proteins. Activation of proproteins to biologically active molecules is regulated by limited endoproteolytic cleavage at dibasic amino acid residues. This type of activation typically requires the presence of suitable proprotein convertases (PCs). The PC-isozymes furin and PC5 are expressed in human atherosclerotic lesions and have been found to be up-regulated, following vascular injury in animal models in vivo. In vitro, these PCs can regulate vascular smooth muscle cell and macrophage functions and signaling events, through activation of pro-alpha-integrins and/or pro-membrane-type matrix metalloproteinases. Integrins link the cytoskeleton with the extracellular matrix and mediate bidirectional signaling and mechanotransduction, whereas matrix metalloproteinases are the major matrix-degrading enzymes. Both activities are required for cell recruitment to the intima. Furthermore, cleavage of extracellular matrix molecules by matrix metalloproteinases potentially contributes to weakening of the fibrous cap, promoting plaque rupture. Based on these recent in vitro and in vivo data, furin and PC5 are potential contributors to the initiation, progression, and complications of atherosclerosis and restenosis. Targeting these PCs may provide future anti-atherosclerotic therapies.

Increase in Collagen Turnover But Not in Collagen Fiber Content Is Associated with Flow-Induced Arterial Remodeling

BACKGROUND

Degradation and synthesis of collagen are common features in arterial geometrical remodeling. Previous studies described an association between arterial remodeling and an increase in collagen fiber content after balloon injury. However, this does not exclude that the association between collagen content and remodeling depends on arterial injury since the association of collagen fiber content and arterial remodeling, without arterial injury, has not been investigated. The aim of the present study was to study the relation between flow-induced arterial geometrical remodeling, without arterial injury, and collagen synthesis and degradation, collagen fiber content and cell-migration-associated moesin levels.

METHODS AND RESULTS

In 23 New Zealand White rabbits an arteriovenous shunt (AV shunt) was created in the carotid and femoral artery to induce a structural diameter increase or a partial ligation (n = 27 rabbits) to induce a diameter decrease. In both models, arterial remodeling was accompanied by increased procollagen synthesis, reflected by increased procollagen mRNA or Hsp47 protein levels. In both models, however, no changes were detected in collagen fiber content. Active MMP-2 and moesin levels were increased after AV shunting.

CONCLUSIONS

Collagen synthesis and MMP-2 activation were associated with arterial remodeling. However, a change in collagen fiber content was not observed. These results suggest that, during flow-induced geometrical arterial remodeling, increases in collagen synthesis are used for matrix collagen turnover and cell migration but not to augment collagen fiber content.

Clinicopathologic significance of plasma matrix metalloproteinase-2 and -9 levels in patients with undifferentiated nasopharyngeal carcinoma

Increased in plasma pro-MMP2 and pro-MMP9 levels in patients with advanced stage NPC were observed. Plasma pro-MMP2 is a significant independent prognostic marker for undifferentiated NPC.

AIM

Upregulation of matrix metalloproteinase-2 and -9 (MMP-2 and MMP-9) expression is observed in many cancers and high level of these proteins are found in peripheral blood of many cancer patients. In this study, we aimed at evaluating the plasma pro-MMP2 and pro-MMP9 pro-enzymes (pro-MMP2 and pro-MMP9) levels and their clinical significances in patients with undifferentiated nasopharyngeal carcinoma (NPC).

METHODS

The plasma pro-MMP2 and pro-MMP9 levels were measured in 40 NPC patients and 40 normal individuals by enzyme linked immunosorbant assay.

RESULTS

By using the Cox-regression model, a high pro-MMP2 level was found to be significantly correlated with poorer survival. Patients with plasma pro-MMP2 below 650 ng/ml had higher 5-year survival rate of 89%, compared with 50% for patients with plasma pro-MMP2 above 650 ng/ml.

CONCLUSIONS

A high level of plasma pro-MMP2 was associated with poor survival of NPC patients independent of sex, age and stage.

Activation of MMP-2 in response to vascular injury is mediated by phosphatidylinositol 3-kinase-dependent expression of MT1-MMP

Phosphatidylinositol 3-kinase (PI3K) is required for smooth muscle cell (SMC) proliferation. This study reports that inhibitors of PI3K also prevent SMC migration and block neointimal hyperplasia in an organ culture model of restenosis. Inhibition of neointimal formation by LY-294002 was concentration and time dependent, with 10 muM yielding the maximal effect. Continuous exposure for at least the first 4-7 days of culture was essential for significant inhibition. To assess the role of matrix metalloproteinases (MMPs) in this process, we monitored MMP secretion by injured vessels in culture. Treatment with LY-294002 selectively reduced active MMP-2 in media samples according to zymography and Western blot analysis without concomitant changes in latent MMP-2. Parallel results with wortmannin indicate that MMP-2 activation is PI3K dependent. Previous research has shown a role for both furin and membrane-type 1 (MT1)-MMP (MMP-14) in the activation of MMP-2. The furin inhibitor decanoyl-Arg-Val-Lys-Arg-chloromethylketone did not prevent MMP-2 activation after balloon angioplasty. In contrast, balloon angioplasty induced a significant increase in the levels of MT1-MMP, which was suppressed by LY-294002. No change in MT1-MMP mRNA was observed with LY-294002, because equivalent amounts of this mRNA were present in both injured and noninjured vessels. These results implicate PI3K-dependent regulation of MT1-MMP protein synthesis and subsequent activation of latent MMP-2 as critical events in neointimal hyperplasia after vascular injury.

Mutations in two matrix metalloproteinase genes, MMP-2 and MT1-MMP, are synthetic lethal in mice

The matrix metalloproteinase (MMP) family (approximately 25 members in mammals) has been implicated in extracellular matrix remodeling associated with embryonic development, cancer formation and progression, and various other physiological and pathological events. Inactivating mutations in individual matrix metalloproteinase genes in mice described so far, however, are nonlethal at least up to the first few weeks after birth, suggesting functional redundancy among MMP family members. Here, we report that mice lacking two MMPs, MMP-2 (nonmembrane type) and MT1-MMP (membrane type), die immediately after birth with respiratory failure, abnormal blood vessels, and immature muscle fibers reminiscent of central core disease. In the absence of MMP-2 and MT1-MMP, myoblast fusion in vitro is also significantly retarded. These findings suggest functional overlap in mice between the two MMPs with distinct molecular natures.

Matrix metalloproteinase inhibition reduces intimal hyperplasia in a porcine arteriovenous-graft model

BACKGROUND

The patency of arteriovenous (AV) polytetrafluoroethylene grafts for hemodialysis is impaired by intimal hyperplasia (IH) at the venous outflow tract. IH mainly consists of vascular smooth muscle cells, fibroblasts, and extracellular matrix proteins. Because matrix metalloproteinases (MMPs) are enzymes able to degrade extracellular matrix proteins such as elastin and collagen and also stimulate migration of vascular smooth muscle cells, we hypothesized that BB2983 (a broad-spectrum MMP inhibitor) could reduce IH in AV grafts.

METHODS

In 12 pigs, AV grafts were created bilaterally between the carotid artery and the jugular vein. Six pigs received the oral MMP inhibitor (MMPi), and six pigs served as a control. Four weeks after AV shunting, the grafts and adjacent vessels were excised and underwent histologic analysis. Quantification of elastin content was performed on Elastin von Gieson-stained sections.

RESULTS

At the venous outflow tract, IH was strongly inhibited after MMPi when compared with the control group (1.02 +/- 0.26 mm(2) vs 2.14 +/- 0.38 mm(2); P =.027). The medial area did not differ significantly. In the control group elastin density decreased compared with nonoperated veins. This decrease was not observed in the MMPi group (nonoperated, 6.3% +/- 0.4%; MMPi, 7.2% +/- 0.7% vs untreated, 3.6% +/- 0.5%; P =.0004). Outward remodeling of the vein was not influenced by MMP inhibition.

CONCLUSION

MMPi reduces IH formation at the venous outflow tract of AV grafts in pigs, probably by inhibiting elastin degradation. These data suggest that MMP inhibitors might be useful for minimizing IH in AV grafts, thus prolonging patency rates of AV grafts in patients on hemodialysis.

Expansive arterial remodeling: location, location, location

The artery is a dynamic organ capable of changing its geometry in response to atherosclerotic plaque formation. Expansion of the vessel diameter retards luminal narrowing and is considered a compensatory response. However, the expansive remodeling response is a "wolf in sheep's clothes," because expansion is associated with the presence of inflammatory cells, proteolysis, and a thrombotic plaque phenotype. The prevalence and clinical presentation of expansively remodeled lesions may differ among vascular beds. However, it is evident that all types of atherosclerotic arterial expansive lesions share the presence of inflammatory cells and subsequent protease activities. The potential role of inflammation and protease activity in the development of the different remodeling modes is discussed.

Toll-like receptor 4 is involved in outward arterial remodeling

BACKGROUND

Toll-like receptor 4 (Tlr4) is the receptor for exogenous lipopolysaccharides (LPS). Expression of endogenous Tlr4 ligands, heat shock protein 60 (Hsp60) and extra domain A of fibronectin, has been observed in arthritic and oncological specimens in which matrix turnover is an important feature. In atherosclerosis, outward remodeling is characterized by matrix turnover and a structural change in arterial circumference and is associated with a vulnerable plaque phenotype. Since Tlr4 ligands are expressed during matrix turnover, we hypothesized that Tlr4 is involved in arterial remodeling.

METHODS AND RESULTS

In a femoral artery cuff model in the atherosclerotic ApoE3 (Leiden) transgenic mouse, Tlr4 activation by LPS stimulated plaque formation and subsequent outward arterial remodeling. With the use of the same model in wild-type mice, neointima formation and outward remodeling occurred. In Tlr4-deficient mice, however, no outward arterial remodeling was observed independent of neointima formation. Carotid artery ligation in wild-type mice resulted in outward remodeling without neointima formation in the contralateral artery. This was associated with an increase in Tlr4 expression and EDA and Hsp60 mRNA levels. In contrast, outward remodeling was not observed after carotid ligation in Tlr4-deficient mice.

CONCLUSIONS

These findings provide genetic evidence that Tlr4 is involved in outward arterial remodeling, probably through upregulation of Tlr4 and Tlr4 ligands.

Furin interacts with proMT1-MMP and integrin alphaV at specialized domains of renal cell plasma membrane

Matrix metalloproteinases (MMPs) and integrins are essential for cell and extracellular matrix homeostasis. Both membrane type-1 MMP (MT1-MMP) and the integrin alphaV subunit are fully activated upon cleavage at a furin recognition site. Furin is shuttled to the cell surface through the trans-Golgi network and endosomal system, and its only known role on plasma membrane consists in activation of opportunistic pathogenic entities. Here, we report findings about the interaction of furin with MT1-MMP and the integrin alphaV at the cell surface. By using in vivo gene delivery, western blotting and immunogold electron microscopy, we provide evidence of significant pools of furin and proMT1-MMP along the surface of cells lining basement membranes. Moreover, furin and integrin alphaV are frequently found associated with the slit diaphragm of renal podocytes and around endothelial fenestrations. ProMT1-MMP, by contrast, is concentrated at the slit diaphragm. Coimmunoprecipitations and double immunogold labelings indicate that furin interacts with proMT1-MMP and alphaV at points of insertion of the slit diaphragm. Our results suggest that these focalized complexes could trigger basement membrane proteolysis either directly by activation of proMT1-MMP or indirectly by promoting activation of proMMP2.

The acute phase protein haptoglobin is locally expressed in arthritic and oncological tissues

Haptoglobin is an acute phase protein known to be highly expressed in the liver. Recently, we showed increased local arterial haptoglobin expression after flow-induced arterial remodelling and found that haptoglobin is involved in cell migration and arterial restructuring probably through accumulation of a temporary gelatin matrix. Since cell migration and matrix turnover are important features in the pathology of arthritis and cancer, we hypothesized that haptoglobin is also locally expressed in arthritic and oncological tissues. In this study, we investigated local haptoglobin expression in arthritic rats (n = 12) using semi-quantitative PCR and Western blotting, and we studied haptoglobin mRNA localization in human kidney tumours (n = 3) using in situ hybridization. The arthritic rats demonstrated an increase of haptoglobin mRNA (2.5-fold, P < 0.001) and protein (2.6-fold, P < 0.001) in the arthritic Achilles tendon. Haptoglobin protein was also increased in the arthritic ankle (2.6-fold, P < 0.001) but not in the non-arthritic knee. In human kidney tumours, tumour and stromal cells produced haptoglobin mRNA. This study shows that the liver protein haptoglobin is, in addition to the artery, also expressed in arthritic and oncological tissues that are recognized for enhanced cell migration and matrix turnover.

Atherosclerotic expansive remodeled plaques: a wolf in sheep's clothing

Geometric arterial remodeling is an important determinant of luminal narrowing in atherosclerotic disease. Expansive remodeling retards while constrictive remodeling accelerates luminal narrowing by plaque formation. Cross-sectional as well as follow-up studies revealed that expansive remodeling is associated with adverse cardiovascular events and a vulnerable plaque phenotype. Although the relation between expansive remodeling and plaque vulnerability is associative rather than causal, expansively remodeled plaques should be considered as a wolf in sheep's clothes. Further understanding of the processes that regulate arterial remodeling and plaque rupture may lead to new strategies to responsibly manipulate these processes for the benefit of patient outcomes.

Morphologic and angiographic features of coronary plaque rupture detected by intravascular ultrasound

OBJECTIVES

This study was designed to report the clinical and angiographic correlates of plaque rupture detected by intravascular ultrasound (IVUS).

BACKGROUND

Acute coronary syndromes result from spontaneous plaque rupture and thrombosis.

METHODS

We report 300 plaque ruptures in 257 arteries in 254 patients. Plaque ruptures were detected during pre-intervention IVUS. Standard clinical, angiographic, and IVUS parameters were collected and/or measured. One lesion per patient was analyzed.

RESULTS

Multiple ruptures were observed in 39 of 254 patients (15%), 36 in the same artery. Plaque rupture occurred not only in patients with unstable angina (46%) or myocardial infarction (MI, 33%), but also stable angina (11%) or no symptoms (11%). The tear in the fibrous cap could be identified in 157 of 254 patients; 63% occurred at the shoulder of the plaque and 37% in the center of the plaque. Thrombi were more common in patients with unstable angina or MI (p = 0.02) and in multiple ruptures (p = 0.04). The plaque rupture site contained the minimum lumen area (MLA) site in only 28% of patients; rupture sites had larger arterial and lumen areas and more positive remodeling than MLA sites. Intravascular ultrasound plaque rupture strongly correlated with complex angiographic lesion morphology: ulceration in 81%, intimal flap in 40%, thrombus in 7%, and aneurysm in 7%.

CONCLUSIONS

Plaque ruptures occur with varying clinical presentations, strongly correlate with angiographic complex lesion morphology, may be multiple, and usually do not cause lumen compromise.

Acute-phase protein haptoglobin is a cell migration factor involved in arterial restructuring

Collagen turnover and cell migration are fundamental aspects of arterial restructuring. To identify mRNAs involved in blood flow-induced arterial restructuring, we performed subtraction polymerase chain reaction and found expression of haptoglobin mRNA in adventitial fibroblasts of rabbit arteries. Haptoglobin is highly expressed in liver, but its arterial expression and function are unknown. In vitro studies revealed that stimulation of haptoglobin expression by lipopolysaccharides in mice fibroblasts stimulated migration of wild-type fibroblasts but had no effect on migration of haptoglobin knockout fibroblasts. In vivo studies showed that flow-induced arterial restructuring was delayed in haptoglobin knockout mice. This new function of haptoglobin might be explained by facilitating cell migration through accumulation of a temporary gelatin matrix because cell culture showed that haptoglobin is involved in the breakdown of gelatin. We conclude that haptoglobin is highly expressed in arterial tissue and is involved in arterial restructuring. This new haptoglobin function may also apply to other functional and pathological restructuring processes such as angiogenesis, tissue repair, and tumor cell invasion.

Inhibitory potency and specificity of subtilase-like pro-protein convertase (SPC) prodomains

The SPCs (subtilisin-like pro-protein convertases) are a family of enzymes responsible for the proteolytic processing of numerous precursor proteins of the constitutive and regulated secretory pathways. SPCs are themselves synthesized as inactive zymogens. Activation of SPCs occurs via the intramolecular autocatalytic removal of the prodomain. SPC prodomains have been proposed as templates in the development of potent and specific SPC inhibitors. In this study, we investigated the specificity and potency of complete prodomains and short C-terminal prodomain peptides of each SPC on highly purified, soluble enzyme preparations of human SPC1, SPC6, and SPC7. Progress curve kinetic analysis of prodomain peptides and complete prodomains showed competitive inhibitory profiles in the low nanomolar range. Complete prodomains were 5-100 times more potent than C-terminal prodomain peptides, suggesting that N-terminal determinants are involved in the recognition process. However, complete prodomains and prodomain peptides exhibit only a partial specificity toward their cognate enzyme. Ala-scan structure activity studies indicated the importance of basic residues in the P(4), P(5), and P(6) positions for inhibition of SPC1. In contrast, hydrophobic residues in P(6) and P(7), as well as basic residues in P(4) and P(5), were critical for inhibition of SPC7. Our data demonstrated that the use of prodomains as specific inhibitors acting in trans would be of limited usefulness, unless modified into more specific compounds.