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

Platelet biology and function: plaque erosion vs. rupture

The leading cause of heart disease in developed countries is coronary atherosclerosis, which is not simply a result of ageing but a chronic inflammatory process that can lead to acute clinical events upon atherosclerotic plaque rupture or erosion and arterial thrombus formation. The composition and location of atherosclerotic plaques determine the phenotype of the lesion and whether it is more likely to rupture or to erode. Although plaque rupture and erosion both initiate platelet activation on the exposed vascular surface, the contribution of platelets to thrombus formation differs between the two phenotypes. In this review, plaque phenotype is discussed in relation to thrombus composition, and an overview of important mediators (haemodynamics, matrix components, and soluble factors) in plaque-induced platelet activation is given. As thrombus formation on disrupted plaques does not necessarily result in complete vessel occlusion, plaque healing can occur. Therefore, the latest findings on plaque healing and the potential role of platelets in this process are summarized. Finally, the clinical need for more effective antithrombotic agents is highlighted.

The Contribution of Vascular Proteoglycans to Atherothrombosis: Clinical Implications

The vascular extracellular matrix (ECM) produced by endothelial and smooth muscle cells is composed of collagens and glycoproteins and plays an integral role in regulating the structure and function of the vascular wall. Alteration in the expression of these proteins is associated with endothelial dysfunction and has been implicated in the development and progression of atherosclerosis. The ECM composition of atherosclerotic plaques varies depending on plaque phenotype and vulnerability, with distinct differences observed between ruptured and erodes plaques. Moreover, the thrombi on the exposed ECM are diverse in structure and composition, suggesting that the best antithrombotic approach may differ depending on plaque phenotype. This review provides a comprehensive overview of the role of proteoglycans in atherogenesis and thrombosis. It discusses the differential expression of the proteoglycans in different plaque phenotypes and the potential impact on platelet function and thrombosis. Finally, the review highlights the importance of this concept in developing a targeted approach to antithrombotic treatments to improve clinical outcomes in cardiovascular disease.

Integrating Mechanisms in Thrombotic Peripheral Arterial Disease

Peripheral arterial disease (PAD), a manifestation of systemic atherosclerosis, is underdiagnosed in the general population. Despite the extensive research performed to unravel its pathophysiology, inadequate knowledge exists, thus preventing the development of new treatments. This review aims to highlight the essential elements of atherosclerosis contributing to the pathophysiology of PAD. Furthermore, emphasis will be placed on the role of thrombo-inflammation, with particular focus on platelet and coagulation activation as well as cell-cell interactions. Additional insight will be then discussed to reveal the contribution of hypercoagulability to the development of vascular diseases such as PAD. Lastly, the current antithrombotic treatments will be discussed, and light will be shed on promising new targets aiming to aid the development of new treatments.

Glycocalyx components affect platelet function, whole blood coagulation, and fibrinolysis: an in vitro study suggesting a link to trauma-induced coagulopathy

BACKGROUND

The mechanisms of trauma induced coagulopathy (TIC) are considered multifactorial. Amongst others, however, shedding of the endothelial glycocalyx resulting in increased concentrations of glycocalyx fragments in plasma might also play a role. Thus, we hypothesized that shedded glycocalyx components affect coagulation and may act as humoral mediators of TIC.

METHODS

To investigate effects of heparan sulfate, chondroitin sulfate, syndecan-1, versican, and thrombomodulin we added these fragments to in vitro assays of whole blood from healthy volunteers to yield concentrations observed in trauma patients. Platelet function, whole blood coagulation, and fibrinolysis were measured by standard coagulation tests, impedance aggregometry (IA), and viscoelastic tests (VET). To assess dose-response relationships, we performed IA with increasing concentrations of versican and VET with increasing concentrations of thrombomodulin.

RESULTS

Intrinsically activated clotting times (i.e., activated partial thromboplastin time and intrinsically activated VET with and without heparinase) were unaffected by any glycocalyx fragment. Thrombomodulin, however, significantly and dose-dependently diminished fibrinolysis as assessed by VET with exogenously added rt-PA, and increased rt-PA-induced lysis Indices after 30 (up to 108% of control, p <  0,0001), 45 (up to 368% of control, p <  0,0001), and 60 min (up to 950% of control, p <  0,0001) in VET. Versican impaired platelet aggregation in response to arachidonic acid (up to - 37,6%, p <  0,0001), ADP (up to - 14,5%, p <  0,0001), and collagen (up to - 31,8%, p <  0,0001) in a dose-dependent manner, but did not affect TRAP-6 induced platelet aggregation. Clotting time in extrinsically activated VET was shortened by heparan sulfate (- 7,2%, p = 0,024), chondroitin sulfate (- 11,6%, p = 0,016), versican (- 13%, p = 0,012%), and when combined (- 7,2%, p = 0,007).

CONCLUSIONS

Glycocalyx components exert distinct inhibitory effects on platelet function, coagulation, and fibrinolysis. These data do not support a 'heparin-like auto-anticoagulation' by shed glycosaminoglycans but suggest a possible role of versican in trauma-induced thrombocytopathy and of thrombomodulin in trauma-associated impairment of endogenous fibrinolysis.

High Levels of Circulating MicroRNA-3667-3p Are Associated with Coronary Plaque Erosion in Patients with ST-Segment Elevation Myocardial Infarction

Plaque erosion (PE) is a significant substrate of acute coronary thrombosis. An improved ability to distinguish plaque phenotype in vivo among patients with ST-segment elevation myocardial infarction (STEMI) is of considerable interest because of the potential to formulate tailored treatment. This study assessed the plaque features and screened the circulating microRNAs (miRNAs) characteristically expressed in patients with PE compared with those with plaque rupture (PR). An miRNA microarray profile was generated in an initial cohort of eight STEMI patients with PE and eight clinically matched subjects with PR to select the circulating miRNAs with significant differences. miRNAs of interest were validated in a prospective cohort, and the plaque characteristics of enrolled patients were assessed by optical coherence tomography (OCT). Thirty culprit lesions were classified as PE (32.6%) and 46 as PR (50%). The main component of PE was fibrotic tissue, whereas the chief component of PR was lipids (P < 0.001). Thirty-four miRNAs were differentially expressed between the two groups; we validated five candidates and found that only the level of circulating miR-3667-3p exhibited significant discriminatory power in predicting the presence of PE (AUC = 0.767; P < 0.001). Our results show that high levels of circulating miR-3667-3p are closely related to PE in STEMI patients, which provides further evidence for PE pathophysiology and potential tailor treatment strategies.

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.

Versican localizes to the nucleus in proliferating mesenchymal cells

OBJECTIVE

Versican is a versatile and highly interactive chondroitin sulfate proteoglycan that is found in the extracellular matrix (ECM) of many tissues and is a major component of developing and developed lesions in atherosclerotic vascular disease. In this paper, we present data to indicate that versican may have important intracellular functions in addition to its better known roles in the ECM.

METHODS AND RESULTS

Rat aortic smooth muscle cells were fixed and immunostained for versican and images of fluorescently labeled cells were obtained by confocal microscopy. Intracellular versican was detected in the nucleus and cytosol of vascular smooth muscle cells. The use of a synthetic neutralizing peptide eliminated versican immunostaining, demonstrating the specificity of the antibody used in this study. Western blot of pure nuclear extracts confirmed the presence of versican in the nucleus, and multifluorescent immunostaining showed strong colocalization of versican and nucleolin, suggesting a nucleolar localization of versican in nondividing cells. In dividing valve interstitial cells, a strong signal for versican was observed in and around the condensed chromosomes during the various stages of mitosis. Multifluorescent immunostaining for versican and tubulin revealed versican aggregated at opposing poles of the mitotic spindle during metaphase. Knockdown of versican expression using siRNA disrupted the organization of the mitotic spindle and led to the formation of multipolar spindles during metaphase.

CONCLUSIONS

Collectively, these data suggest an intracellular function for versican in vascular cells where it appears to play a role in mitotic spindle organization during cell division. These observations open a new avenue for studies of versican, suggesting even more diverse roles in vascular health and disease.

Effect of Rotary Blood Pump Pulsatility on Potential Parameters of Blood Compatibility and Thrombosis in Inflow Cannula Tips

Purpose

Rotary Blood Pump (RBP) pulsatile strategies relative to the native cardiac cycle have been widely studied because of their benefits to hemodynamics. However, the effects that inducing pulses has on the blood compatibility of ventricular assist device (VAD) support have not yet been understood. Inflow cannulae have been found to be associated with thrombosis under conventional constant speed support of RBPs. To prevent further risks to blood compatibility, it is necessary to understand the relationship between cannula tip design and the induced pulsatility. The purpose of this study was to evaluate the flow field of 5 different tip geometries under RBP pulsatile support using stereo-particle image velocimetry (PIV).

Methods

Inflow cannulae with conventional tip geometries (blunt, blunt with 4 side ports, beveled with 3 side ports, and cage) and a custom designed crown tip were studied. All cannulae were interposed between a mixed-flow RBP and a silicone left ventricle. The contractile function and hemodynamics were reproduced in a mock circulation loop (MCL). The RBP was configured to induce synchronous and counter-synchronous pulses relative to cardiac cycles while supporting the failing ventricle.

Results

Between both pulsing strategies, low shear volume ([Formula: see text], potential parameter of thrombus formation) showed no significant difference. However, counter-synchronous pulsatile mode induced less increase of both high shear volume ([Formula: see text], potential parameter of platelet activation) and recirculation volume (Vz>0, potential parameter of thrombus formation).

Conclusions

Although the clinical relationship cannot be inferred from this measurement, when considering the inflow tips only, a necessary trade-off should be made between adverse effects on blood compatibility and benefits for hemodynamics during RBP pulsatile mode.

Ovarian cancer stem cells and inflammation

Epithelial ovarian cancer (EOC) is the fourth leading cause of cancer-related deaths in women in the United States and the leading cause of gynecologic cancer deaths. The major limiting factor in the treatment of ovarian cancer is recurrence and chemoresistance. Individuals who succumb to advanced-stage ovarian cancer inevitably become refractory to chemotherapy, resulting in disease progression and death. The source of recurrence and lack of response to chemotherapy is unknown. The focus of this review is to evaluate the question of recurrence and chemoresistance based on the concept of the cancer stem cells and inflammation.

ADAMTS proteases: key roles in atherosclerosis?

The ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) proteases are secreted enzymes that regulate extracellular matrix turnover by degrading specific matrix components. Roles for the proteases in inflammation and atherosclerosis have been suggested by a number of recent studies, and the role of ADAMTS-4 and -5 in the breakdown of aggrecan and subsequent degradation of cartilage during osteoarthritis has also been established. The ability of the ADAMTS proteases to degrade versican, the primary proteoglycan in the vasculature, is thought to be central to any hypothesized role for the proteases in atherosclerosis. In this review, we introduce the structure and function of the ADAMTS family of proteases and review the literature that links them with inflammation and atherosclerosis.

Topographical variation in the distributions of versican, aggrecan and perlecan in the foetal human spine reflects their diverse functional roles in spinal development

We evaluated the immunohistochemical distribution of three major proteoglycans of cartilage, i.e., aggrecan, versican and perlecan vis-a-vis collagens I and II in the developing human spine of first-trimester foetuses. Aggrecan and perlecan were prominently immunolocalised in the cartilaginous vertebral body rudiments and to a lesser extent within the foetal intervertebral disc. In contrast, versican was only expressed in the developing intervertebral disc interspace. Using domain-specific monoclonal antibodies against the various modules of versican, we discovered the V0 isoform as the predominant form present. Versican immunolocalisations conducted with antibodies directed to epitopes in its N and C termini and GAG-alpha and GAG-beta core protein domains provided evidence that versican in the nucleus pulposus was either synthesised devoid of a G3 domain or this domain was proteolytically removed in situ. The V0 versican isoform was localised with prominent fibrillar components in the annular lamellae of the outer annulus fibrosus. Perlecan was a notable pericellular proteoglycan in the annulus fibrosus and nucleus pulposus but poorly immunolocalised in the marginal tissues of the developing intervertebral disc, apparently delineating the intervertebral disc-vertebral body interface region destined to become the cartilaginous endplate in the mature intervertebral disc. The distribution of collagens I and II in the foetal spine was mutually exclusive with type I present in the outer annulus fibrosus, marginal tissues around the vertebral body rudiment and throughout the developing intervertebral disc, and type II prominent in the vertebral rudiment, absent in the outer annulus fibrosus and diffusely distributed in the inner annulus fibrosus and nucleus pulposus. Collectively, our findings suggest the existence of an intricate and finely balanced interplay between various proteoglycans and collagens and the spinal cell populations which synthesise and assemble these components during spinal development.

Cell-bound IL-8 increases in bronchial epithelial cells after arylsulfatase B silencing due to sequestration with chondroitin-4-sulfate

The chemokine IL-8 is critically important in inflammatory processes in human tissues, and IL-8 interactions with sulfated glycosaminoglycans have been implicated in modification of inflammatory responses in bronchial epithelium. To determine the role of chondroitin-4-sulfate (C4S) in mediating effects of IL-8, we silenced the enzyme N-acetylgalactosamine-4-sulfatase (arylsulfatase B [ASB]) that removes the 4-sulfate group from C4S, in the IB3-1 and C38 bronchial epithelial cell lines and in normal primary bronchial epithelial cells. When ASB was silenced and IL-8 production stimulated by exposure to TNF-alpha, ASB activity declined by roughly 75%, cellular C4S content increased by over 7.5 microg/mg protein, cell-bound IL-8 increased by over 530 pg/mg protein, and secreted IL-8 declined by over 520 pg/mg protein in all cell lines (P < 0.001). When cell lysates were immunoprecipitated with C4S antibody after ASB silencing and TNF-alpha, the IL-8 content of the immunoprecipitate was approximately 500 pg/mg protein, indicating that most of the cell-bound IL-8 was associated with C4S. Cell fractionation demonstrated that the IL-8 content associated with the cell membranes was about twice that of the cytosolic fraction. Also, ASB appeared to localize in the cell membrane, as well as in lysosomes. Neutrophil attraction to the cell lysates increased after ASB silencing, consistent with increased attraction to the cell-bound IL-8. These findings provide evidence for the influential role of ASB and C4S in the regulation of IL-8 secretion, and suggest that changes in ASB activity and C4S content may have a significant impact on IL-8-mediated inflammatory responses.

Differential distribution of aggrecan isoforms in perineuronal nets of the human cerebral cortex

Aggrecan is a component of the CNS extracellular matrix (ECM) and we show here that the three primary alternative spliced transcripts of the aggrecan gene found in cartilage are also present in the adult CNS. Using a unique panel of core protein-directed antibodies against human aggrecan we further show that different aggrecan isoforms are deposited in perineuronal nets (PNNs) and neuropil ECM of Brodmann’s area 6 of the human adult cerebral cortex. According to their distribution pattern, the identified cortical aggrecan isoforms were subdivided into five clusters spanning from cluster 1, comprised isoforms that appeared widespread throughout the cortex, to cluster 5, which was an aggrecan-free subset. Comparison of brain and cartilage tissues showed a different relative abundance of aggrecan isoforms, with cartilage-specific isoforms characterizing cluster 5, and PNN-associated isoforms lacking keratan sulphate chains. In the brain, isoforms of cluster 1 were disclosed in PNNs surrounding small-medium interneurons of layers II–V, small-medium pyramidal neurons of layers III and V and large interneurons of layer VI. Aggrecan PNNs enveloped both neuron bodies and neuronal processes, encompassing pre-terminal nerve fibres, synaptic boutons and terminal processes of glial cells and aggrecan was also observed in continuous ‘coats’ associated with satellite, neuron-associated cells of a putative glial nature. Immunolabelling for calcium-binding proteins and glutamate demonstrated that aggrecan PNNs were linked to defined subsets of cortical interneurons and pyramidal cells. We suggest that in the human cerebral cortex, discrete, layer-specific PNNs are assembled through the participation of selected aggrecan isoforms that characterize defined subsets of cortical neurons.

Versican/PG-M Assembles Hyaluronan into Extracellular Matrix and Inhibits CD44-mediated Signaling toward Premature Senescence in Embryonic Fibroblasts

Versican/PG-M is a large chondroitin sulfate proteoglycan of the extracellular matrix which interacts with hyaluronan at the N-terminal G1 domain, composed of A, B, and B' subdomains. Recently, we generated knock-in mice Cspg2(Delta3/Delta3), whose versican, without the A subdomain, has decreased hyaluronan (HA) binding affinity, thereby exhibiting reduced deposition of versican in the extracellular matrix. Here, we show that the Cspg2(Delta3/Delta3) fibroblasts within 20 passages proliferate more slowly and acquire senescence. Whereas the extracellular matrix of the wild type fibroblasts exhibited a network structure of hyaluronan and versican, that of the Cspg2(Delta3/Delta3) fibroblasts exhibited approximately 35 and approximately 85% deposition of versican and HA, without such a structure. The Cspg2(Delta3/Delta3) fibroblasts showed a substantial increase of ERK1/2 phosphorylation and expression of senescence markers p53, p21, and p16. Treatment of wild type fibroblasts with hyaluronidase and exogenous hyaluronan enhanced ERK1/2 phosphorylation, and treatment with an anti-CD44 antibody that blocks HA-CD44 interaction inhibited the phosphorylation. These results demonstrate that versican is essential for matrix assembly involving hyaluronan and that diminished versican deposition increases free hyaluronan fragments that interact with CD44 and increase phosphorylation of ERK1/2, leading to cellular senescence.

Alteration of chondroitin sulfate composition on proteoglycan produced by knock-in mouse embryonic fibroblasts whose versican lacks the A subdomain

Versican/proteoglycan-mesenchymal (PG-M) is a large chondroitin sulfate (CS) proteoglycan of the extracellular matrix (ECM) that is constitutively expressed in adult tissues such as dermis and blood vessels. It serves as a structural macromolecule of the ECM, while in embryonic tissue it is transiently expressed at high levels and regulates cell adhesion, migration, proliferation, and differentiation. Knock-in mouse embryonic (Cspg2(Delta3/Delta3)) fibroblasts whose versican lack the A subdomain of the G1 domain exhibit low proliferation rates and acquire senescence. It was suspected that chondroitin sulfate on versican core protein would be altered when the A subdomain was disrupted, so fibroblasts were made from homozygous Cspg2(Delta3/Delta3) mouse embryos to investigate the hypothesis. Analysis of the resulting versican deposition demonstrated that the total versican deposited in the Cspg2(Delta3/Delta3) fibroblasts culture was approximately 50% of that of the wild type (WT), while the versican deposited in the ECM of Cspg2(Delta3/Delta3) fibroblasts culture was 35% of that of the WT, demonstrating the lower capacity of mutant (Cspg2(Delta3/Delta3)) versican deposited in the ECM. The analysis of CS expression in the Cspg2(Delta3/Delta3) fibroblasts culture compared with wild-type fibroblasts showed that the composition of the non-sulfate chondroitin sulfate isomer on the versican core protein increased in the cell layer but decreased in the culture medium. Interestingly, chondroitin sulfate E isomer was found in the culture medium. The amount of CS in the Cspg2(Delta3/Delta3) cell layer of fibroblasts with mutant versican was dramatically decreased, contrasted to the amount in the culture medium, which increased. It was concluded that the disruption of the A subdomain of the versican molecule leads to lowering of the amount of versican deposited in the ECM and the alteration of the composition and content of CS on the versican molecule.

Aggrecan, versican and type VI collagen are components of annular translamellar crossbridges in the intervertebral disc

The aim of this study was to undertake a detailed analysis of the structure of the inter and intra-lamellar regions of the annulus fibrosus. A total of 30 newborn to 6 year-old lumbar ovine intervertebral discs (IVDs) were fixed and decalcified en-bloc to avoid differential swelling artifacts during processing and vertical mid-sagittal, and horizontal 4 mum sections were cut. These were stained with toluidine blue to visualise anionic proteoglycan (PG) species, H & E for cellular morphology and picro-sirius red (viewed under polarized light) to examine collagenous organization. Immunolocalisations were also undertaken using anti-PG core-protein and glycosaminoglycan (GAG) side chain antibodies to native chondroitin sulphate (CS), Delta C-4-S and C-6-S unsaturated stubs generated by chondroitinase ABC digestion of CS, keratan sulphate (KS), and with antibodies to type I, II, VI, IX and X collagens. Trans-lamellar cross bridges (TLCBs), discontinuities in annular lamellae's which provide transverse interconnections, stained prominently with toluidine blue in the adult IVDs but less so in the newborn IVDs. In adult discs TLCBs were evident in both the posterior and anterior AF where they extended from the outermost annular lamellae almost to the transitional zone extending across as many as eight lamellar layers displaying a characteristic circuitous, meandering, serpentine type course. There were significantly fewer TLCBs in 2 week-old compared with skeletally mature sheep and there was a further increase from 2 to 6 years. Immunolocalisation of perlecan delineated blood vessels in the TLBs of the newborn but not adult IVDs extending into the mid AF. In contrast adult but not 2 week-old TLCBs were immunopositive for C-4-S, C-6-S, KS, aggrecan, versican and type VI collagen. The change in number and matrix components of the trans-lamellar cross bridges with skeletal maturity and ageing suggest that they represent an adaptation to the complex biomechanical forces occurring in the annulus fibrosus.

Instrument and technique for the in vitro screening of platelet activation from whole blood samples

The measurement of platelet activation is very difficult to accomplish clinically as platelets are readily activated by in vitro manipulations. Although techniques such as platelet aggregation and flow cytometry exist to estimate platelet function, important limitations prevent these techniques to be widely accepted. In this study, low-fouling surfaces used to limit ex vivo platelet activation were locally bioactivated to rapidly detect platelet activation from whole blood through the selective local adhesion and aggregation of artificially activated platelets. To achieve this result, a fabrication method was developed to create arrays of anti-CD62 and anti-CD61 proteins covalently immobilized on substrates covered by low-fouling graft layers. Moreover, to further limit ex vivo platelet activation and to obtain reproducible results, a custom-made flow chamber was designed and fabricated with the help of computer-assisted mathematical modeling to create defined shear environments. This diagnostic instrument has the potential to allow the rapid estimation of platelet activation levels in whole blood.

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.

Distinct antithrombotic consequences of platelet glycoprotein Ibalpha and VI deficiency in a mouse model of arterial thrombosis

BACKGROUND

Collagen and von Willebrand factor (VWF) are considered essential to initiate platelet deposition at sites of vascular injury, but their respective roles remain to be elucidated.

METHODS

We used a model of carotid artery thrombosis induced by a ferric chloride injury to compare the time to first occlusion and occlusion rate at 25 min postinjury in mice lacking the collagen receptor, glycoprotein (GP) VI, or the ligand-binding domain of the VWF receptor, GP Ibalpha.

RESULTS

In normal mice used as controls (n = 12), a complete obstruction of blood flow developed within 8.05 +/- 0.47 min (mean +/- SEM), and the occlusion rate was 100%. The results were variable in 26 GP VI(-/-) mice. The artery never occluded in eight mice, but the time to first occlusion in the remaining 18 (8.36 +/- 0.27 min) was not different from normal (P = 0.556). Nonetheless, the occlusion rate was 42%, because in seven mice the occluded artery reopened and stayed patent at 25 min. In contrast, the artery never occluded in 12 mice lacking GP Ibalpha. In ex vivo perfusion experiments, GP VI(-/-) platelets failed to form thrombi onto collagen type I fibrils, but formed thrombi of normal size when exposed to endothelial or fibroblast extracellular matrix.

CONCLUSIONS

Absence of GP Ibalpha function has a more profound antithrombotic effect in vivo than absence of the GP VI-dependent pathway of collagen-induced adhesion/activation. Components of the extracellular matrix may elicit a thrombogenic response in the absence of GP VI but not GP Ibalpha.

Approaching theProteoglycome: Molecular Interactions of Proteoglycans and Their Functional Output

[Image: see text] Through their diverse core protein modules and glycan/glycosaminoglycan moieties, proteoglycans may engage in numerous cellular and molecular interactions which are dispensable during embryogenesis, are essential for the maintenance of a healthy state and are prone to modulation in pathological conditions. Proteoglycan interactions may involve binding to other structural components of the ECM, to cell surface receptors, to membrane-associated components, and to soluble signaling molecules, which through this interaction may become entrapped in the ECM or sequestered at the cell surface. Understanding of these multiple interplays is therefore of paramount importance and requires a detailed mapping through what we define as the proteoglycome.

The accumulation of specific types of proteoglycans in eroded plaques: a role in coronary thrombosis in the absence of rupture

PURPOSE OF REVIEW

Although fibrous cap rupture is the primary cause of coronary thrombosis, plaque erosion is responsible for 30%-40% of acute thrombotic events. The interface of the eroded surface involves a denuded endothelium allowing direct contact of the platelet/fibrin thrombus with the underlying lesion. This review discusses the putative role of extracellular matrix molecules, in particular proteoglycans/hyaluronan, in the development of acute coronary thrombosis associated with erosion.

RECENT FINDINGS

The plaque/thrombus interface in erosion presents a unique surface since it consists of predominantly SMCs and proteoglycans with minimal or no inflammation. The lack of significant inflammation raises the possibility that erosion represents chronic wounding rather than true atherogenesis. The abundance of proteoglycan and hyaluronan matrix suggests their potential role in the development of thrombosis. Matrix changes may contribute to endothelial loss, the magnitude of the thrombotic event, or both. Versican facilitates platelet adhesion at low shear and cooperates with collagen to promote platelet aggregation. Further, versican may, in part, regulate water content and in turn support coagulation because water-dependent functionality of anticoagulation molecules. Finally, experimental models of plaque erosion are currently being developed guided by the premise that the loss of surface endothelium together with other procoagulant factors may underlie the development of platelet-rich thrombi.

SUMMARY

The loss of endothelium and exposure of a potentially procoagulant versican-hyaluronan matrix may be largely responsible for plaque erosion. The development of relevant animal models should allow further insight into the pathophysiology of coronary thrombosis in the absence of rupture.

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.

The globular domains of PG-M/versican modulate the proliferation-apoptosis equilibrium and invasive capabilities of tumor cells

To dissect the role of the globular domains of PGM/versican--a large hyaluronan binding proteoglycan (PG) enriched in tumor lesions--we have stably transduced a human leiomyosarcoma cell line with either the G1 or G3 domain of the PG and subsequently assayed the effect of this manipulation on several cellular processes in vitro and in vivo. G1- and G3-overexpressing cells were found to exhibit an enhanced growth that was more accentuated in the absence of serum components and was seen both when cells were cultured on ECM substrates and in the absence of ECM anchorage. Accordingly, if inoculated subcutaneously into nude mice, G1 transfectants formed larger tumor masses than control cells at the site of implantation, albeit after a certain latency period. Upon binding to cell surface CD44, proliferation of G1-, but not G3-, overexpressing cells were dose dependently inhibited by exogenous hyaluronan (HA) or HA fragments. G1- and G3-transduced cells did not differ in their intrinsic ability to adhere and migrate on various purified ECM components, whereas G1-overproducing sarcoma cells were more invasive than the corresponding G3 mutants, and their locomotion was perturbed by exogenous HA. The augmented anchorage-independent growth exhibited solely by G1-transduced was largely ascribable to a reduced apoptotic rate, thereby indicating a shift in the proliferation--apoptosis equilibrium of the cells toward the former. In fact, G1-overexpressing cells appeared resistant to both cytotoxic drug-induced and Fas-dependent programmed cell death, and this resistance implicated mitochondrial apoptotic genes. The results indicate that the terminal domains of versican may differentially control propagation of tumor cells and diversely modulate their responses to environmental HA.

Chondroitin sulfate anticoagulant activity is linked to water transfer: relevance to proteoglycan structure in atherosclerosis

OBJECTIVE

Changes in chondroitin sulfate (CS) proteoglycan (PG) during atherosclerosis are associated with chronic inflammatory changes and increased incidence of thrombosis. To explore how glycosaminoglycan changes could influence the thrombogenicity of atherosclerotic lesions, water-transfer reactions were examined during activation of antithrombin by CS.

METHODS AND RESULTS

Advanced type IV atherosclerotic lesions prone to thrombosis contained CSPG (versican) with undersulfated CS relative to CS of the adjacent healthy aorta. Approximately 11% of the CS disaccharide in versican from healthy arteries was oversulfated, but this proportion decreased markedly to 3% in atherosclerotic lesions. Oversulfated CS functionally bound antithrombin with a dissociation constant of 3.3+/-1.9 micromol/L. Measured by osmotic stress (OS) techniques with an approximately 26-A probe, the reaction was linked to transfer of approximately 2500 mol water per mole of coagulation factor Xa inhibited. Under OS, the anticoagulant efficiency of CS was 1.3 (micromol/L)(-1) x s(-1), approximately 5- and 15-fold higher than heparan sulfate efficiency measured under OS and standard conditions, respectively.

CONCLUSIONS

Decreased sulfation of high molecular weight CSPG in the advancing atherosclerotic lesions may predispose the lesions to thrombosis by disrupting osmotic regulation, limiting avidity for antithrombin and decreasing activation efficiency.

Von Willebrand factor, platelets and endothelial cell interactions

The adhesive protein von Willebrand factor (VWF) contributes to platelet function by mediating the initiation and progression of thrombus formation at sites of vascular injury. In recent years there has been considerable progress in explaining the biological properties of VWF, including the structural and functional characteristics of specific domains. The mechanism of interaction between the VWF A1 domain and glycoprotein Ibalpha has been elucidated in detail, bringing us closer to understanding how this adhesive bond can oppose the fluid dynamic effects of rapidly flowing blood contributing to platelet adhesion and activation. Moreover, novel findings have been obtained on the link between regulation of VWF multimer size and microvascular thrombosis. This progress in basic research has provided critical information to define with greater precision the role of VWF in vascular biology and pathology, including its possible involvement in the onset of atherosclerosis and its acute thrombotic complications.