Deposition of PG-M/versican is a major cause of human coronary restenosis after percutaneous transluminal coronary angioplasty

A role for proteoglycans in vascular disease

The content of proteoglycans (PGs) is low in the extracellular matrix (ECM) of vascular tissue, but increases dramatically in all phases of vascular disease. Early studies demonstrated that glycosaminoglycans (GAGs) including chondroitin sulfate (CS), dermatan sulfate (DS), keratan sulfate (KS) and heparan sulfate (HS) accumulate in vascular lesions in both humans and in animal models in areas of the vasculature that are susceptible to disease initiation (such as at branch points) and are frequently coincident with lipid deposits. Later studies showed the GAGs were covalently attached to specific types of core proteins that accumulate in vascular lesions. These molecules include versican (CSPG), biglycan and decorin (DS/CSPGs), lumican and fibromodulin (KSPGs) and perlecan (HSPG), although other types of PGs are present, but in lesser quantities. While the overall molecular design of these macromolecules is similar, there is tremendous structural diversity among the different PG families creating multiple forms that have selective roles in critical events that form the basis of vascular disease. PGs interact with a variety of different molecules involved in disease pathogenesis. For example, PGs bind and trap serum components that accumulate in vascular lesions such as lipoproteins, amyloid, calcium, and clotting factors. PGs interact with other ECM components and regulate, in part, ECM assembly and turnover. PGs interact with cells within the lesion and alter the phenotypes of both resident cells and cells that invade the lesion from the circulation. A number of therapeutic strategies have been developed to target specific PGs involved in key pathways that promote vascular disease. This review will provide a historical perspective of this field of research and then highlight some of the evidence that defines the involvement of PGs and their roles in the pathogenesis of vascular disease.

Provisional matrix: A role for versican and hyaluronan

Hyaluronan and versican are extracellular matrix (ECM) components that are enriched in the provisional matrices that form during the early stages of development and disease. These two molecules interact to create pericellular "coats" and "open space" that facilitate cell sorting, proliferation, migration, and survival. Such complexes also impact the recruitment of leukocytes during development and in the early stages of disease. Once thought to be inert components of the ECM that help hold cells together, it is now quite clear that they play important roles in controlling cell phenotype, shaping tissue response to injury and maintaining tissue homeostasis. Conversion of hyaluronan-/versican-enriched provisional matrix to collagen-rich matrix is a "hallmark" of tissue fibrosis. Targeting the hyaluronan and versican content of provisional matrices in a variety of diseases including, cardiovascular disease and cancer, is becoming an attractive strategy for intervention.

Heparan sulfate side chains have a critical role in the inhibitory effects of perlecan on vascular smooth muscle cell response to arterial injury

Perlecan is a proteoglycan composed of a 470-kDa core protein linked to three heparan sulfate (HS) glycosaminoglycan chains. The intact proteoglycan inhibits the smooth muscle cell (SMC) response to vascular injury. Hspg2(Δ3/Δ3) (MΔ3/Δ3) mice produce a mutant perlecan lacking the HS side chains. The objective of this study was to determine differences between these two types of perlecan in modifying SMC activities to the arterial injury response, in order to define the specific role of the HS side chains. In vitro proliferative and migratory activities were compared in SMC isolated from MΔ3/Δ3 and wild-type mice. Proliferation of MΔ3/Δ3 SMC was 1.5× greater than in wild type (P < 0.001), increased by addition of growth factors, and showed a 42% greater migratory response than wild-type cells to PDGF-BB (P < 0.001). In MΔ3/Δ3 SMC adhesion to fibronectin, and collagen types I and IV was significantly greater than wild type. Addition of DRL-12582, an inducer of perlecan expression, decreased proliferation and migratory response to PDGF-BB stimulation in wild-type SMC compared with MΔ3/Δ3. In an in vivo carotid artery wire injury model, the medial thickness, medial area/lumen ratio, and macrophage infiltration were significantly increased in the MΔ3/Δ3 mice, indicating a prominent role of the HS side chain in limiting vascular injury response. Mutant perlecan that lacks HS side chains had a marked reduction in the inhibition of in vitro SMC function and the in vivo arterial response to injury, indicating the critical role of HS side chains in perlecan function in the vessel wall.

Proteoglycan degradation by the ADAMTS family of proteinases

Proteoglycans are key components of extracellular matrices, providing structural support as well as influencing cellular behaviour in physiological and pathological processes. The diversity of proteoglycan function reported in the literature is equally matched by diversity in proteoglycan structure. Members of the ADAMTS (A Disintegrin And Metalloproteinase with ThromboSpondin motifs) family of enzymes degrade proteoglycans and thereby have the potential to alter tissue architecture and regulate cellular function. In this review, we focus on ADAMTS enzymes that degrade the lectican and small leucine-rich repeat families of proteoglycans. We discuss the known ADAMTS cleavage sites and the consequences of cleavage at these sites. We illustrate our discussion with examples from the literature in which ADAMTS proteolysis of proteoglycans makes profound changes to tissue function.

Cholesterol in human atherosclerotic plaque is a marker for underlying disease state and plaque vulnerability

Background

Cholesterol deposition in arterial wall drives atherosclerosis. The key goal of this study was to examine the relationship between plaque cholesterol content and patient characteristics that typically associate with disease state and lesion vulnerability. Quantitative assays for free cholesterol, cholesteryl ester, triglyceride, and protein markers in atherosclerotic plaque were established and applied to plaque samples from multiple patients and arterial beds (Carotid and peripheral arteries; 98 lesions in total).

Results

We observed a lower cholesterol level in restenotic than primary peripheral plaque. We observed a trend toward a higher level in symptomatic than asymptomatic carotid plaque. Peripheral plaque from a group of well-managed diabetic patients displayed a weak trend of more free cholesterol deposition than plaque from non-diabetic patients. Plaque triglyceride content exhibited less difference in the same comparisons. We also measured cholesterol in multiple segments within one carotid plaque sample, and found that cholesterol content positively correlated with markers of plaque vulnerability, and negatively correlated with stability markers.

Conclusions

Our results offer important biological validation of cholesterol as a key lipid marker for plaque severity. Results also suggest cholesterol is a more sensitive plaque marker than routine histological staining for neutral lipids.

Cell death-associated ADAMTS4 and versican degradation in vascular tissue

High blood flow through baboon polytetrafluorethylene aorto-iliac grafts increases neointimal vascular smooth muscle cell (SMC) death, neointimal atrophy, and cleavage of versican to generate the DPEAAE neoepitope, a marker of ADAMTS-mediated proteolysis. In this study, we have determined the effect of high blood flow on transcript abundance in the neointima for ADAMTS1, -4, -5, -8, -9, -15, and -20. We found that after 24 hr of flow, the mRNA for ADAMTS4 was significantly increased, whereas that for the other family members was unchanged. Because vascular SMC death is markedly increased in the graft after 24 hr of high flow, we next examined the possibility that the ADAMTS4 induction and the cell death are causally related. The addition of Fas ligand to SMC cultures increased both ADAMTS4 mRNA and cell death approximately 5-fold, consistent with the idea that ADAMTS4-dependent cleavage of versican may be partly responsible for cell death and tissue atrophy under these conditions.

Characterization of carotid atherosclerosis and detection of soft plaque with use of black-blood MR imaging

BACKGROUND AND PURPOSE

In the treatment of carotid atherosclerosis, the rate of stenosis and characteristics of plaque should be assessed to diagnose vulnerable plaques that increase the risk for cerebral infarction. We performed carotid black-blood (BB) MR imaging to diagnose plaque components and assess plaque hardness based on MR signals.

MATERIALS AND METHODS

Three images of BB-MR imaging per plaque were obtained from 70 consecutive patients who underwent carotid endarterectomy (CEA) to generate T1- and T2-weighted images. To evaluate the relative signal intensity (rSI) of plaque components and the relationship between histologic findings and symptoms, we prepared sections at 2-mm intervals from 34 intact plaques. We then calculated the relative overall signal intensity (roSI) of 70 plaques to assess the relationship between MR signal intensity and plaque hardness and symptoms.

RESULTS

The characteristics of rSI values on T1- and T2-weighted images of fibrous cap (FC), fibrosis, calcification, myxomatous tissue, lipid core (LC) with intraplaque hemorrhage (IPH), and LC without IPH differed. Symptomatic plaques were associated with FC disruption (P < .001) and LC with IPH (P < .05). The roSI on T1-weighted images was significantly higher for soft than nonsoft plaques. When the roSI cutoff value was set at 1.25 (mean of the roSI), soft plaques were diagnosed with 79.4% sensitivity and 84.4% specificity. The roSI was also significantly higher for symptomatic than for asymptomatic plaques. Soft and nonsoft plaques as well as symptomatic and asymptomatic plaques did not significantly differ on T2-weighted images.

CONCLUSION

BB-MR imaging can diagnose plaque components and predict plaque hardness. This procedure provides useful information for planning therapeutic strategies of carotid atherosclerosis.

ADAMTS-4 and -8 are inflammatory regulated enzymes expressed in macrophage-rich areas of human atherosclerotic plaques

OBJECTIVES

Remodeling of extracellular matrix (ECM) plays an important role in inflammatory disorders such as atherosclerosis. ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) is a recently described family of proteinases that is able to degrade the ECM proteins aggrecan and versican expressed in blood vessels. The purpose of the present study was to analyze the expression and regulation of several ADAMTSs before and after macrophage differentiation and after stimulation with IFN-gamma, IL-1beta and TNF-alpha. ADAMTS expression was also examined during atherosclerosis development in mice and in human atherosclerotic plaques.

METHODS AND RESULTS

Real time RTPCR showed that, of the nine different ADAMTS members examined, only ADAMTS-4 and -8 were induced during monocyte to macrophage differentiation, which was also seen at protein level. Macrophage expression of ADAMTS-4, -7, -8 and -9 mRNA were enhanced upon stimulation with IFN-gamma or TNF-alpha. Furthermore, immunohistochemical analyses revealed that ADAMTS-4 and -8 were expressed in macrophage rich areas of human atherosclerotic carotid plaques and coronary unstable plaques. In addition, ADAMTS-4 expression was upregulated during the development of atherosclerosis in LDLR(-/-)ApoB(100/100) mice. Whereas ADAMTS-4 expression was low in non-atherosclerotic aortas, it was significantly higher in aortas from 30-40-week old atherosclerotic animals.

CONCLUSION

The present study suggests that ADAMTS-4 and -8 are inflammatory regulated enzymes expressed in macrophage-rich areas of atherosclerotic plaques. This is the first study associating ADAMTS-4 and -8 expression with atherosclerosis. However, further experiments are required to understand the physiological and pathological functions of ADAMTS in the vascular wall, and tools to measure ADAMTS activity need to be developed.

Interleukin-1β selectively decreases the synthesis of versican by arterial smooth muscle cells

Proteoglycans accumulate in lesions of atherosclerosis but little is known as to which factors regulate the synthesis of these molecules. Interleukin-1beta (IL-1beta) is a cytokine involved in vascular lesion development but it is not clear whether it has specific effects on proteoglycan synthesis by arterial smooth muscle cells (ASMC). Monkey ASMC were treated with IL-1beta and proteoglycan synthesis assessed using [(35)S]-sulfate and [(35)S]-Trans amino acid labeling. Four prominent size populations of proteoglycans, as determined by SDS-PAGE gradient gel electrophoresis, were observed in the culture medium and identified as versican, biglycan, decorin, and an unknown population that migrated to the gel interface. IL-1beta treatment decreased significantly the synthesis of versican, while increasing the synthesis of decorin, but having no effect on biglycan synthesis. Northern blot analyses confirmed this selective effect on versican and decorin mRNA transcripts. Nuclear run-on and RNA inhibition studies showed that decreased mRNA for versican was due to increased mRNA degradation and not to changes in transcription. In addition, IL-1beta increased the synthesis of the population of proteoglycans that separated at the SDS-PAGE gel interface. Chondroitinase ABC lyase digestion of this population revealed a complex of proteins composed of versican (350 kDa), an unidentified protein (215 kDa), and a 23 kDa protein identified by sequence analyses as serglycin. These data demonstrate that IL-1beta selectively downregulates versican synthesis by ASMC, while positively regulating the synthesis of other proteoglycans.

Versican degradation and vascular disease

Versican is an abundant proteoglycan in the blood vessel wall that is increased after vascular injury and accumulates in advanced atherosclerotic plaques. Versican is a large molecule with domains that mediate binding to cytokines, enzymes, lipoproteins, other extracellular matrix molecules, and signaling receptors. There is evidence that versican exists in the normal, as well as the diseased, vessel wall as discrete fragments, which represent these functional domains. We review the literature on versican degradation in vascular tissue and the function of versican domains, all of which suggest that proteolytic modification of versican may have physiologic as well as pathologic implications for the vascular system.

Sirolimus blocks the accumulation of hyaluronan (HA) by arterial smooth muscle cells and reduces monocyte adhesion to the ECM

Sirolimus (SRL), an inhibitor of human arterial smooth muscle cell (ASMC) proliferation and migration, prevents in-stent restenosis (ISR). Little is known about the effect of SRL on the extracellular matrix (ECM) component, hyaluronan, a key macromolecule in neointimal hyperplasia and inflammation. In this study, we investigated SRL regulation of the synthesis of hyaluronan by cultured human ASMC and the effect of SRL on hyaluronan mediated monocyte adhesion to the ECM. Hyaluronan production on a per cell basis was significantly inhibited by SRL at 4 days and remained so through 10 days. This reduction was correlated with reduced levels of hyaluronan synthase mRNAs while hyaluronan degradation rates were unchanged. Poly I:C, a viral mimetic, caused increased hyaluronan accumulation by ASMC cell layers and this increase was inhibited by SRL. The inhibition was paralleled by a reduction in hyaluronan-dependent monocyte adhesion to the ECM. This study demonstrates that SRL not only regulates the proliferation of ASMC but reduces the production of hyaluronan by these cells. This alteration in ECM composition results in reduced monocyte adhesion to the ECM in cultures of ASMC. Alterations in hyaluronan accumulation may contribute to the inhibition of ISR that is achieved by SRL.

Versican G3 domain promotes blood coagulation through suppressing the activity of tissue factor pathway inhibitor-1

We have detected versican, a member of the large chondroitin sulfate proteoglycans, and its degraded C-terminal G3 fragments in human plasma and observed that the versican G3 domain promoted blood coagulation. Silencing G3 expression with small interfering RNA reduced the effect of G3 on coagulation. Plasma coagulation assays suggest that G3 enhances coagulation irrespective of its actions on platelets and white blood cells. To examine how versican affected blood coagulation, we used normal human plasma and different types of coagulation factor-deficient plasmas. The experiments indicated that versican enhanced coagulation through the extrinsic pathway, and that Factor VII was the target molecule. FVII activity assays showed that G3 activated FVII in the presence of plasma but not with purified FVII directly. Yeast two-hybrid, immunoprecipitation, and gel co-migration assays showed that G3 interacted with the tissue factor pathway inhibitor-1 (TFPI-1). TFPI-1 activity assays suggested that G3 inhibited TFPI-1 activity, allowing FVIIa and FXa to facilitate the coagulation process. G3-induced blood coagulation was further confirmed with a mouse model in a real-time manner. Taken together, these results indicate that versican may represent a new target for the development of therapies against atherosclerosis.

Tenascin-C—coated platinum coils for acceleration of organization of cavities and reduction of lumen size in a rat aneurysm model

Object. Detachable platinum coils are widely used in the endovascular treatment of intracranial aneurysms. The use of coil placement produces a higher incidence of aneurysm recurrence compared with surgical clipping. To reduce the incidence of recurrence by promoting clot organization, the authors designed a platinum coil coated with tenascin-C (TNC), an extracellular matrix glycoprotein, and then histologically examined tissue responses.

Methods. Platinum coils were prepared by successive coatings with cationic polyethyleneimine and anionic heparin and then TNC or basic fibroblast growth factor (bFGF) was immobilized by affinity binding to the heparin. Six unmodified, six heparin-coated, six bFGF-coated, or eight TNC-coated platinum coils were inserted into ligated common carotid arteries (CCAs) of adult male rats, and CCA segments were harvested after 14 or 28 days.

The percentages of organized areas occupying the luminal cavity in unmodified, heparin-coated, bFGF-coated, and TNC-coated groups were 4.8 ± 4.6, 1.6 ± 1.1, 17.9 ± 10.7, and 93.4 ± 6.9%, respectively. In addition, the mean lumen size in the TNC-coated group (0.35 ± 0.23 mm2) was reduced to less than half that of the unmodified group (0.72 ± 0.21 mm2). Immunohistochemical analysis revealed that α—smooth muscle actin—positive cells were a major cellular component of the organized tissue within the TNC-coated coils but not in the bFGF group. Collagen fibrils in the organized areas were also much thicker and denser with TNC-coated coils than with bFGF-coated coils.

Conclusions. Placement of TNC-coated coils can remarkably accelerate organization of luminal cavities and reduce their volume, providing improved efficacy of these coils for endovascular embolization.

PG-M/versican binds to P-selectin glycoprotein ligand-1 and mediates leukocyte aggregation

P-selectin glycoprotein ligand-1 (PSGL-1), a glycoprotein expressed on the cell surface of leukocytes, binds to selectins and mediates leukocyte rolling on the vascular endothelium. Here we report that PSGL-1 binds to the C-terminal (G3 domain) of the extracellular proteoglycan PG-M/versican. Cells transfected with PSGL-1 or a shorter form containing the binding site, or cells expressing endogenous PSGL-1 aggregate in the presence of versican or G3 product. The aggregation appears to be induced by G3 multimers that bind to PSGL-1 and form a network. Endogenous versican and/or G3-containing fragments also bind to PSGL-1 in human plasma. Removal of the endogenous G3-containing fragments reduces the effect of plasma on leukocyte aggregation. Finally, the roles of G3-containing fragments in leukocyte aggregation were confirmed in a mouse model. Taken together, our results strongly support a physiologically relevant role for PSGL-1/versican binding and may have implications in the immunoresponse.

Proteoglycans in Atherosclerosis and Restenosis

The proteoglycan versican is one of several extracellular matrix (ECM) molecules that accumulate in lesions of atherosclerosis and restenosis. Its unique structural features create a highly interactive molecule that binds growth factors, enzymes, lipoproteins, and a variety of other ECM components to influence fundamental events involved in vascular disease. Versican is one of the principal genes that is upregulated after vascular injury and is a prominent component in stented and nonstented restenotic lesions. The synthesis of versican is highly regulated by specific growth factors and cytokines and the principal source of versican is the smooth muscle cell. Versican interacts with hyaluronan, a long chain glycosaminoglycan, to create expanded viscoelastic pericellular matrices that are required for arterial smooth muscle cell (ASMC) proliferation and migration. Versican is also prominent in advanced lesions of atherosclerosis, at the borders of lipid-filled necrotic cores as well as at the plaque-thrombus interface, suggesting roles in lipid accumulation, inflammation, and thrombosis. Versican influences the assembly of ECM and controls elastic fiber fibrillogenesis, which is of fundamental importance in ECM remodeling during vascular disease. Collectively, these studies highlight the critical importance of this specific ECM component in atherosclerosis and restenosis.

Distribution of PG-M/versican variants in human tissues and de novo expression of isoform V3 upon endothelial cell activation, migration, and neoangiogenesis in vitro

We have carried out a comprehensive molecular mapping of PG-M/versican isoforms V0-V3 in adult human tissues and have specifically investigated how the expression of these isoforms is regulated in endothelial cells in vitro. A survey of 21 representative tissues highlighted a prevalence of V1 mRNA; demonstrated that the relative frequency of expression was V1 > V2 > V3 >or= V2; and showed that <15% of the tissues transcribed significant levels of all four isoforms. By employing novel and previously described anti-versican antibodies we verified a ubiquitous versican deposition in normal and tumor-associated vascular structures and disclosed differences in the glycanation profiles of versicans produced in different vascular beds. Resting endothelial cells isolated from different tissue sources transcribed several of the versican isoforms but consistently failed to translate these mRNAs into detectable proteoglycans. However, if stimulated with tumor necrosis factor-alpha or vascular endothelial growth factor, they altered their versican expression by de novo transcribing the V3 isoform and by exhibiting a moderate V1/V2 production. Induced versican synthesis and de novo V3 expression was also observed in endothelial cells elicited to migrate in a wound-healing model in vitro and in angiogenic endothelial cells forming tubule-like structures in Matrigel or fibrin clots. The results suggest that, independent of the degree of vascularization, human adult tissues show a limited expression of versican isoforms V0, V2, and V3 and that endothelial cells may contribute to the deposition of versican in vascular structures, but only following proper stimulation.

Expression profiling identifies 147 genes contributing to a unique primate neointimal smooth muscle cell phenotype

OBJECTIVE

This study represents the first in an effort to systematically characterize different intimas by using expression array analysis.

METHODS AND RESULTS

We compared smooth muscle cells (SMCs) of the neointima formed 4 weeks after aortic grafting with those from normal aorta and vena cava from cynomolgus monkeys. Hybridization to cDNA arrays identified subsets of 147 and 45 genes differentially expressed in the neointima versus the aorta and vena cava, respectively. The expression pattern differentiating neointima from aortic SMCs was characterized largely by suppression. Only 13 genes were induced in the neointima: 7 encoded matrix proteins (6 collagens and 1 versican) and 2 encoded inducers of matrix synthesis (osteoblast-specific factor-2/Cbfa1 and connective tissue growth factor). The genes suppressed most in the neointima included the regulator of G-protein signaling-5, SPARClike-1/hevin, and nonmuscle myosin heavy chain-B. A smaller gene set differentiated the neointima from the vena cava. Most were induced (39 of 45 genes), and overlap with the neointima-aorta set was significant (10 of 13 genes). Array results were validated with Northern analysis, in situ hybridization, or immunohistochemistry.

CONCLUSIONS

These data underscore the importance of matrix synthesis in neointimal maturation, and novel genes, newly associated with neointimal SMCs (regulator of G-protein signaling-5 and osteoblast-specific factor-2/Cbfa1), have raised new hypotheses regarding the pathogenesis of intimal hyperplasia.

Vascular PG-M/versican variants promote platelet adhesion at low shear rates and cooperate with collagens to induce aggregation

We have identified a novel von Willebrand factor/fibrinogen/selectin-independent, platelet adhesion-promoting function of vascular PG-M/versicans that may be relevant in normal venous thrombosis and critical in atherosclerotic conditions. A purification scheme was devised to obtain vascular versicans, which by biochemical, immunochemical, and ultrastructural means were asserted to be 1) composed primarily of isoforms V1 and V2; 2) free of contaminants; 3) prevalently substituted with chondroitin-4-sulfate and dermatan sulfate (DS) chains; and 4) capable of binding hyaluronan to form link protein-stabilized ternary complexes. Real-time analysis of human platelet perfused under diverse shear forces showed that they largely failed to bind to several vascular and nonvascular proteoglycans (PGs). In contrast, they bound in a dose- and shear rate-dependent manner to vascular versicans, exhibiting a unique attachment-detachment kinetics and establishing a firm substrate tethering characterized with no significant aggregation. Digestion of these PGs with lyases and competition experiments with purified glycosaminoglycans revealed that platelet adhesion to vascular versicans was primarily mediated by their DS chains. Incorporation of the versicans into fibrillar collagen substrates augmented their adhesive activity and strongly promoted platelet aggregation at low and high shear rates. Affinity chromatography of platelet surfaces on DS columns identified a 120-140 kDa polypeptide complex that behaved as a specific vascular versican binding membrane ligand in solid-phase binding assays. These findings indicate that selective versican variants of the subendothelium may serve as ancillary GPIbalpha/integrin/selectin-independent platelet ligands in healthy and diseased vascular beds and may be directly responsible for the platelet accruing after rupture of atherosclerotic plaques.

Differential gene expression in vascular smooth muscle cells in primary atherosclerosis and in stent stenosis in humans

OBJECTIVE

We sought to identify differentially expressed genes in human in stent stenosis (ISS) to provide insights into the mechanism of disease.

METHODS AND RESULTS

Using representation difference analysis, we examined differential gene expression between cultured normal human medial vascular smooth muscle cells (VSMCs) and cells from primary atherosclerotic plaques or ISS sites. Specific groups of genes were overexpressed in ISS and plaque VSMCs, including cell cycle regulatory proteins and cell matrix and contractile proteins. Differential expression was validated by virtual Northern analysis, reverse transcriptase-polymerase chain reaction, in situ hybridization, and immunohistochemistry. All ISS genes were expressed by normal intima and had even higher expression in primary plaque VSMCs.

CONCLUSIONS

ISS VSMCs have a stable gene expression profile reflecting an intimal pattern, intermediate between normal medial and primary plaque VSMCs. Differential expression profiling may identify markers of disease that are overexpressed in ISS and also help elucidate the origin of the ISS lesion.

Versican interacts with fibrillin-1 and links extracellular microfibrils to other connective tissue networks

Fibrillin-containing microfibrils are polymeric structures that are difficult to extract from connective tissues. Proteolytic digestion of tissues has been utilized to release microfibrils for study. Few of the molecules that connect microfibrils to other elements in the matrix have been identified. In this study, electron microscopic immunolocalization of anti-versican antibodies in tissues and in extracted microfibrils demonstrated that the C-terminal region of versican is found associated with fibrillin microfibrils. Extraction of microfibrils followed by treatment of microfibrils under dissociating conditions suggested that the versican C terminus is covalently bound to microfibrils. Binding assays using recombinant fibrillin-1 polypeptides and recombinant lectican lectin domains indicated that the versican lectin domain binds to specific fibrillin-1 polypeptides. The versican lectin domain also bound to molecules comigrating with authentic fibrillin-1 monomers in an assay using cell culture medium. In assays using microfibrils, the versican lectin domain demonstrated preferential binding compared with other lecticans. Binding was calcium-dependent. The binding site for versican in microfibrils is most likely within a region of fibrillin-1 between calcium-binding epidermal growth factor-like domains 11 and 21. Human mutations in this region can result in severe forms of the Marfan syndrome ("neonatal" Marfan syndrome). The connection between versican and fibrillin microfibrils may be functionally significant, particularly in cardiovascular tissues.

Mechanisms of angioplasty and stent restenosis: implications for design of rational therapy

Restenosis after angioplasty or stenting remains the major limitation of both procedures. A vast array of drug therapies has been used to prevent restenosis, but they have proven to be predominantly unsuccessful. Recent trends in drug therapy have attempted to refine the molecular and biological targets of therapy, based on the assumption that a single biological process or molecule is critical to restenosis. In contrast, both stenting and brachytherapy, which are highly nonspecific, can successfully reduce restenosis after angioplasty or stenting, respectively. This review examines the biology of both angioplasty and stent stenosis, focussing on human studies. We also review the landmark human trials that have definitively proven successful therapies, such as stenting and brachytherapy. We suggest that the successful trials of stenting and brachytherapy and the failure of other treatments have highlighted the shortcomings of conventional animal models of arterial intervention, and gaps in our knowledge of human disease. In contrast to arguments advocating gene therapy, these studies suggest that the most likely successful drug therapy will have a wide therapeutic range, targeting as many of the components or biological processes contributing to restenosis as possible.

Transcriptome analysis reveals a role of interferon-gamma in human neointima formation

The most effective immediate cure for coronary stenosis is stent-supported angioplasty. Restenosis due to neointima proliferation represents a major limitation. We investigated the expression of 2435 genes in atherectomy specimens and blood cells of patients with restenosis, normal coronary artery specimens, and cultured human smooth muscle cells (SMCs). Of the 223 differentially expressed genes, 37 genes indicated activation of interferon-gamma (IFN-gamma) signaling in neointimal SMCs. In cultured SMCs, IFN-gamma inhibited apoptosis. Genetic disruption of IFN-gamma signaling in a mouse model of restenosis significantly reduced the vascular proliferative response. Our data suggest an important role of IFN-gamma in the control of neointima proliferation.

Local photodynamic action of methylene blue favorably modulates the postinterventional vascular wound healing response

PURPOSE

Photodynamic therapy (PDT), the light activation of photosensitizers to produce free radicals, is known to inhibit experimental intimal hyperplasia (IH). However, its clinical application has been limited by the lack of a suitable approach and a clinically appropriate photosensitizer. The aim of this study was to determine the effectiveness of a clinical approach for PDT, while testing its ability to favorably modulate the vascular wound healing response.

METHODS

Rat carotid arteries were balloon-injured (BI), and for PDT, the arteries were irradiated with thermoneutral laser light (lambda = 660 nm, 100 J/cm(2)) after the photosensitizer methylene blue (MB) was delivered locally. Control rats included BI alone and MB after BI alone. Arteries were analyzed after 2 weeks with morphometric evaluation (n = 6) and in situ hybridization for versican and procollagen type I gene expression (digitized image pixel analyses, n = 3).

RESULTS

No IH developed in PDT-treated arteries (0 +/- 0 mm(2); compared with BI, 0.192 +/- 0.006 mm(2); P <.0001). The diameters remained unchanged (PDT, 0.95 +/- 0.04 mm; BI, 0.94 +/- 0.05 mm; uninjured artery, 0.91 +/- 0.06 mm). Arterial injury resulted in an increase of versican and procollagen type I messenger RNA (mRNA) in the adventitia and neointima. In the repopulating cells of the adventitia after PDT, there was a significant decrease in versican mRNA (% of positive pixels per high-power field: PDT, 1.13% +/- 0.39%; BI, 2.93% +/- 0.61%; P <.02), but not in procollagen type I mRNA.

CONCLUSION

The decrease of versican mRNA expression of repopulating cells after PDT reflects favorable healing on a molecular level. Site-specific delivery of MB, a clinically appropriate photosensitizer, followed by PDT represents a suitable method to promote favorable healing after balloon intervention and further supports its role for inhibiting postinterventional restenosis.

Fibulin-1 is a ligand for the C-type lectin domains of aggrecan and versican

The aggregating proteoglycans (aggrecan, versican, neurocan, and brevican) are important components of many extracellular matrices. Their N-terminal globular domain binds to hyaluronan, but the function of their C-terminal region containing a C-type lectin domain is less clear. We now report that a 90-kDa protein copurifies with recombinant lectin domains from aggrecan and versican, but not from the brain-specific neurocan and brevican. Amino acid sequencing of tryptic peptides from this protein identified it as fibulin-1. This extracellular matrix glycoprotein is strongly expressed in tissues where versican is expressed (blood vessels, skin, and developing heart), and also expressed in developing cartilage and bone. It is thus likely to interact with these proteoglycans in vivo. Surface plasmon resonance measurements confirmed that aggrecan and versican lectin domains bind fibulin-1, whereas brevican and neurocan do not. As expected for a C-type lectin, the interactions with fibulin-1 are Ca2+-dependent, with KD values in the low nanomolar range. Using various deletion mutants, the binding site for aggrecan and versican lectin domains was mapped to the epidermal growth factor-like repeats in domain II of fibulin-1. No difference in affinity was found for deglycosylated fibulin-1, indicating that the proteoglycan C-type lectin domains bind to the protein part of fibulin-1.

Effects of diabetes and insulin treatment of diabetic rats on hyaluronan and hyaluronectin production in injured aorta

The present study was conducted to determine the effect of diabetes with and without insulin treatment on the production of hyaluronen (HA) and distribution of hyaluronectin (HN) in the rat aorta 14 days after injury with a catheter balloon. Injury increased intima-media wet weight (+11%) and DNA content (+37.5%). This increase was slightly enhanced in untreated diabetic rats (+14.7% for wet weight and +48.9% for DNA content) and was significantly greater in diabetic rats treated with insulin (+28.9% for wet weight and +54% for DNA content). HA content increase in the injured aorta of nondiabetic rats (+43.6%) was similar in untreated diabetic (+44.7%) and more pronounced in diabetic rats treated with insulin (+91.3%). HA was markedly expressed in the neointima of nondiabetic rats, particularly near the lumen of the aorta. In untreated diabetic rats, HA was present throughout the neointima and not mainly close to the lumen. HA staining in the neointima of diabetic rats treated with insulin was similar to that in nondiabetic rats. HN was strongly expressed throughout the neointima of all groups. Injury enhanced the production of a high molecular mass HN (>400 kDa); this was not observed either in untreated or in insulin-treated diabetic rats. In conclusion, insulin treatment promoted the proliferative response of aorta to injury and this was associated mainly with increased HA production. This finding suggests that HA, which has been shown to play a crucial role in smooth muscle cell proliferation and migration, may be involved in the promoting effect of insulin treatment on arterial wall reaction to injury.

The extracellular matrix in balloon arterial injury: a novel target for restenosis prevention

The role of the extracellular matrix (ECM) in the pathobiology of restenosis has not been fully appreciated. Recent discoveries have shown the ECM to be a complex, heterogeneous structure whose components are dynamically altered in response to vascular injury. This report reviews the structure and function of vascular ECM and the importance of the matrix in modulating the vascular response to arterial injury such as balloon angioplasty and atherosclerosis.

Effect of aging on neointima formation and hyaluronan, hyaluronidase and hyaluronectin production in injured rat aorta

Few studies have examined the effect of aging on arterial wall response to injury, and the results are discordant. Moreover, the effect of aging on hyaluronan synthesis in injured vessels is unknown. The aim of this present study was to determine the effect of aging on neointima formation and hyaluronan (HA), hyaluronidase and hyaluronectin production in injured rat aorta. Aorta was analysed in sham-operated rats (group D0) and 14 (D14) and 28 (D28) days after injury using biochemical and immunohistochemical techniques. Uninjured aorta of old rats was more thickened than that of young rats; it showed a decreased number of arterial smooth muscle cells (ASMC) and was characterized by HA accumulation in the intima and increased hyaluronidase activity. Intima-media wet weight was significantly increased in young rats at D14 and D28 but remained unchanged in old rats. DNA content was significantly enhanced at D14 in both young and old rats. DNA decreased slightly in young rats at D28 but significantly in old rats to return to control level. HA content and hyaluronidase activity in the intima-media were markedly increased in young rats at D14 (+148% and +116% respectively) but slightly in old rats (+23% and +15% respectively). Both HA and hyaluronidase activity continued to increase at D28, but remained more produced in young rats. The immunohistochemical analysis showed the formation of a thickened neointima in young rats, which was associated with strong expression of HA and HN. Neointima of old rats was reduced; it also showed strong expression of HA and HN but their distributions were different from those observed in neointima of young rats. In conclusion, aorta of old rats showed an increased amount of HA in the intima and elevated activity of hyaluronidase. Injury induced formation of a significant neointima in young rats but not in old rats. This was correlated with more HA and hyaluronidase production in injured aorta of young rats. As HA is considered to increase extracellular matrix space and to promote ASMC proliferation and migration, our findings suggest that HA may be implicated in intima thickening with age and after injury.