RESUMO
Human umbilical vein endothelial cells (ECs) adhere in vitro to proteins of the extracellular matrix including fibronectin (fn) and vitronectin (vn). Specific receptors for fn and vn have been previously characterized. These receptors belong to a family of membrane glycoproteins characterized (a) by being a transmembrane complex of two noncovalently linked subunits and (b) by recognizing the tripeptide Arg-Gly-Asp on their respective ligands. In this paper we investigated how vn and fn control the organization of their respective receptors over the surface of ECs. It was found that the clustering of individual receptors and the organization thereafter of focal contacts occurred only when ECs were exposed to the specific ligand and did not occur on the opposite ligand. The shape of receptor clusters was slightly different and a colocalization of the two receptors was found when ECs were cultured on a mixed matrix of fn plus vn. Adhesion was selectively inhibited by vn or fn receptor antibodies on their respective substrates. The clustering of both receptors preceded the association of vinculin with focal contacts and stress fiber formation. Also, the vn receptor, in the absence of associated fn receptor, was capable of inducing the organization of the membrane-microfilament interaction complex. Overall, these results indicate that individual matrix ligands induce only the clustering of their respective membrane receptors. The clustering of only one receptor is capable of supporting the subsequent formation of focal contacts and the local assembly of related cytoskeletal proteins.
Assuntos
Proteínas Sanguíneas/fisiologia , Endotélio Vascular/metabolismo , Fibronectinas/fisiologia , Glicoproteínas/fisiologia , Receptores Imunológicos/metabolismo , Receptores de Peptídeos , Adesão Celular , Células Cultivadas , Imunofluorescência , Humanos , Imunoensaio , Ligantes , Proteínas Musculares/análise , Proteínas Musculares/metabolismo , Testes de Precipitina , Receptores de Fibronectina , Receptores Imunológicos/análise , Receptores de Vitronectina , Vinculina , VitronectinaRESUMO
Low molecular weight (LMW) heparin prevents venous thrombosis by potentiating the inhibition of coagulation factor Xa. Heparin, however, has other biological properties whose role in the prevention of thrombosis is still unknown. The aim of our study was to compare the antithrombotic activity of a LMW heparin and its parent molecule in an attempt to understand better the mechanism and structural requirements for heparin's antithrombotic effect. We studied a preparation of an unfractionated pig mucosal heparin pure by any accepted criteria (electrophoresis in various systems, conductimetric titration and NMR spectra) and a LMW heparin fraction obtained from the former by fractional precipitation with ethanol. Both heparins completely prevented thrombus formation in an experimental model of stasis-induced venous thrombosis in rats. When administered intravenously to rats, the unfractionated heparin had an ex vivo anti-Xa/APTT ratio of 1.67, versus 6.60 of the LMW heparin fraction. Unexpectedly, both heparins induced a significant prolongation of tail bleeding time, performed by two different techniques, the "transection" (mostly exploring blood clotting) and the "template" (exploring the platelet/vessel wall interactions). This study suggests that, beside anticoagulation, other effects may play a role in both the antithrombotic and haemorrhagic effects of some heparins and LMW heparin fractions.
Assuntos
Coagulação Sanguínea/efeitos dos fármacos , Heparina/farmacologia , Trombose/prevenção & controle , Animais , Heparina/isolamento & purificação , Masculino , Peso Molecular , Tempo de Tromboplastina Parcial , Contagem de Plaquetas , Ratos , Ratos Endogâmicos , SuínosRESUMO
A new type of low-molecular-weight heparin (ss-LMW-H) was prepared (by controlled depolymerization and concurrent sulfation of heparin with a mixture of sulfuric and chlorosulfonic acid), to test the influence of extra-sulfate groups on biological properties of heparin fragments. The fragments had an average molecular weight ranging from 5000 to 10,000, a sulfate-to-carboxyl molar ratio of 2.8-3.1, and electrophoretic mobilities and NMR spectra distinctly different from those of the parent heparins. Depolymerization with oversulfation reduced the anticoagulant activity of heparin (ex vivo, in rats) much more than depolymerization alone, to about 10% of the original APTT and 25-30% of the original a.Xa units. By contrast, the antithrombotic activity (venous stasis model, in rats) was still comparable to that of heparin, and bleeding times were not significantly increased. The lipasemic (lipoprotein-lipase-releasing) activity of ss-LMW-H fragments was more than twice that of heparin. Results are discussed in terms of contribution of charge-density effects to different activities and to different mechanisms for the same activity of heparin.
Assuntos
Heparina/análise , Fragmentos de Peptídeos/análise , Animais , Fenômenos Químicos , Físico-Química , Cromatografia em Gel , Heparina/farmacologia , Lipase Lipoproteica/metabolismo , Espectroscopia de Ressonância Magnética , Peso Molecular , Fragmentos de Peptídeos/farmacologia , SuínosRESUMO
Heparin or heparin-like substances have been described to induce the release of plasminogen activator (PA) activity in different animal perfusion models. In this paper we report that Dermatan Sulphate (DS) is able to induce PA activity release in the perfused rat hindquarters. Perfusion of different doses of DS (0.1 to 0.8 mg/mL) stimulates a release of PA activity that is maximum after the initial two minutes of perfusion. The amount of PA activity released rises progressively within a certain concentration range of DS (0.1 to 0.4 mg/mL) and declines thereafter (0.6 to 0.8 mg/mL). The type of PA activity increased during DS perfusion was characterized by SDS-PAGE and fibrin autography as tissue-type PA (t-PA) on the basis of its mol wt (67,000 d) and inhibition by a specific anti t-PA antiserum. This effect might be considered as potentially contributing to the antithrombotic activity of DS, at least at the local level.
Assuntos
Condroitina/análogos & derivados , Dermatan Sulfato/farmacologia , Fibrinolíticos , Ativadores de Plasminogênio/metabolismo , Animais , Endotélio Vascular/fisiologia , Fibrinólise , Heparina/farmacologia , Membro Posterior , RatosRESUMO
It has been suggested that glycosaminoglycans (GAG) such as heparan sulphate (HS), dermatan sulphate (DS), chondroitin-4-sulphate and chondroitin-6-sulphate contribute to the nonthrombogenic properties of the vascular wall. We have investigated the potential role of DS and HS as antithrombotic agents in an experimental model of stasis-induced venous thrombosis in rats. We utilized a range of doses of both DS and HS (0.25-4 mg/kg BW) to test both their antithrombotic activity and potential bleeding effects. The results were evaluated with reference to an unfractionated heparin (0.5-2 mg/kg BW). We report that the antithrombotic activity of DS is not related to its anticoagulant activity as measured by the activated partial thromboplastin time (APTT), thrombin time (TT) and anti-Xa tests. The dose of DS which was able to inhibit thrombus formation by 70% did not prolong the bleeding time measured using two techniques (template and tail transection); in contrast, with HS a prolongation of both times could clearly be seen. On the other hand, standard unfractionated heparin, at a dose which is equipotent to that of DS in preventing thrombus formation, significantly prolonged the bleeding time. These results suggest that DS may be a useful antithrombotic agent with a lower haemorrhagic effect than heparin, unlike HS which expresses a haemorrhagic risk similar to heparin.
Assuntos
Condroitina/análogos & derivados , Dermatan Sulfato/uso terapêutico , Tromboflebite/tratamento farmacológico , Animais , Tempo de Sangramento , Heparitina Sulfato/uso terapêutico , Masculino , Ratos , Ratos Endogâmicos , Veia Cava Inferior/patologiaRESUMO
We have studied the mechanism of release of plasminogen activator (PA) activity induced by epinephrine in the perfused rat hindleg model. Epinephrine perfusion at the dose of 12.5 microM caused a slighter effect on PA activity but an immediate increase in the perfusion pressure. At 25 microM, epinephrine induced a marked increase in PA activity that reached the maximum level at the end of the drug perfusion. The same response was induced by repeated stimulations with epinephrine (25 microM) only if the second stimulus was given 20-25 min apart from the first one. PA release could be blocked by propranolol (300 microM), a nonspecific beta-blocker, and not by phentolamine, a nonspecific alpha-blocker, unless used at very high concentrations (1,250 microM). Perfusion with dibutyryl adenosine 3',5'-cyclic monophosphate (DbcAMP) alone induces an immediate and transient increase in PA activity, but no potentiation could be demonstrated if theophylline was perfused together with epinephrine. The released PA has been characterized on the basis of molecular weight and immunological criteria as t-PA- and u-PA-like molecules in basal conditions. Epinephrine perfusion induced an increase only in the t-PA-like protein. These data indicate that the release of t-PA-like activity observed after epinephrine perfusion is mainly mediated by beta-receptors and is independent from its vasoactive action.
Assuntos
Epinefrina/farmacologia , Músculos/fisiologia , Ativadores de Plasminogênio/metabolismo , Animais , Bucladesina/farmacologia , Relação Dose-Resposta a Droga , Fibrinólise/efeitos dos fármacos , Membro Posterior , Masculino , Músculos/efeitos dos fármacos , Perfusão , Fentolamina/farmacologia , Propranolol/farmacologia , Ratos , Ratos Endogâmicos , Valores de Referência , Ativador de Plasminogênio Tecidual/metabolismo , Ativador de Plasminogênio Tipo Uroquinase/metabolismoRESUMO
Human osteoclasts (OCLs) obtained from cell suspensions of surgically excised giant cell bone tumors (osteoclastomas) were attached to glass coverslips and analyzed by immunofluorescence with antibodies to integrins and cytoskeletal proteins. It was found that in OCLs (i) podosomes, identified by their F-actin core and by interference reflection microscopy, were predominantly found in a peripheral belt as described in avian OCLs; (ii) each F-actin core was surrounded by a ring of vinculin and talin; (iii) beta 1 integrin was diffuse in the ventral membrane; (iv) beta 3 integrin was distributed in intensely fluorescent rings surrounding F-actin cores; (v) beta 2 integrin was absent; (vi) beta 4 integrin was absent. The macrophages detected in the same coverslips displayed podosomes containing beta 2 but not beta 3, fibroblasts showed adhesion plaques positive for beta 1 and beta 3 but not for beta 2, and platelets were intensely positive for beta 3. These results indicate that OCLs produce an integrin complex that is absent in the monocyte-macrophage lineage.
Assuntos
Neoplasias Ósseas/patologia , Proteínas do Citoesqueleto/análise , Matriz Extracelular/ultraestrutura , Tumores de Células Gigantes/patologia , Proteínas de Membrana/análise , Proteínas Musculares/análise , Osteoclastos/patologia , Receptores de Superfície Celular/análise , Actinas/análise , Imunofluorescência , Humanos , Integrina beta3 , Osteoclastos/ultraestrutura , Talina , Células Tumorais Cultivadas/citologia , VinculinaRESUMO
Rat pheochromocytoma PC12 cells exposed to nerve growth factor differentiate as sympathetic neurons and extend neurites on laminin and to a much lesser extent on fibronectin. Analysis of laminin fragments indicated that neurite outgrowth occurs mainly on fragment P1, corresponding to the center of the cross, and only poorly on fragment E8, a long arm structure that is active with other neuronal cells. Integrin antibodies prevented adhesion and neurite sprouting of these cells on laminin, fragment P1, and fibronectin. By affinity chromatography we isolated an integrin-type receptor for laminin consisting of two subunits with molecular massess of 180 and 135 kDa. The latter is recognized by an antiserum to integrin beta 1 subunit. The bound laminin receptor could be displaced by EDTA, but not by Arg-Gly-Asp or Tyr-Ile-Gly-Ser-Arg peptides. Affinity chromatography on laminin fragments showed that the 180/135 kDa receptor binds to P1. The expression of the 180-kDa alpha subunit of the laminin receptor at the cell surface was increased 10-fold after NGF treatment. The effect of NGF is specific since the amount of a 150-kDa fibronectin-binding integrin alpha subunit remained unchanged. Moreover, the increased expression of the 180/135 kDa receptor at the cell surface corresponded to a selective increase in cell adhesion to laminin and to fragment P1. The 180/135-kDa complex is thus an integrin-type receptor for laminin whose expression and binding specificity correlates with the capacity of NGF-induced PC12 cells to extend neurites on laminin.
Assuntos
Integrinas/metabolismo , Laminina/metabolismo , Fatores de Crescimento Neural/farmacologia , Neurônios/citologia , Receptores Imunológicos/metabolismo , Neoplasias das Glândulas Suprarrenais , Sequência de Aminoácidos , Animais , Axônios/ultraestrutura , Adesão Celular/efeitos dos fármacos , Diferenciação Celular , Ácido Edético/farmacologia , Eletroforese em Gel de Poliacrilamida , Fibronectinas/metabolismo , Dados de Sequência Molecular , Peso Molecular , Neurônios/metabolismo , Neurônios/ultraestrutura , Oligopeptídeos/farmacologia , Feocromocitoma , Ratos , Receptores Imunológicos/isolamento & purificação , Receptores de Laminina , Sistema Nervoso Simpático/citologia , Células Tumorais CultivadasRESUMO
In this study we provide a characterization of the fibronectin (FN) binding to endothelial cells (EC), and we identify the FN binding site on these cells. 125I-FN binding to EC in suspension was time dependent and reached a plateau at 4 h. Cold FN inhibited this interaction in a concentration-dependent way, but vitronectin, fibrinogen, and IgG were poorly effective. About 80% of the total FN associated to EC at the equilibrium was specifically bound; of this, 60% was reversibly bound, while 20% appeared to be internalized. The FN binding was saturable and an apparent dissociation constant of about 0.23 x 10(-6) mol/L and a maximal number of binding sites of about 9.8 x 10(5) was estimated from binding isotherms. Autoradiography data showed that EC-associated 125I-FN was all in high mol wt form that did not enter the gel. We then characterize the FN receptor (FNR) in EC. An antiserum to the FNR isolated from human placenta inhibited FN binding to EC by 89%, and using the immunoblotting technique, it recognized two bands in the EC detergent extract of mol wt 125/160 Kd. This antiserum also recognized the EC membrane protein complex eluted from the FN affinity column by an arg-gly-asp (RGD) peptide. When this complex was included into liposomes, it poorly bound to FN. However, the binding was strikingly increased by addition of Mn in the buffer and was specific for FN in respect to other substrata. These data define the FN binding site in EC and indicate that it is functionally and structurally related to that isolated from human placenta.