The proteoglycan skeleton of the Kurloff body as evidenced by Cuprolinic Blue staining

Summary This study deals with the ultrastructure of the chondroitin sulphate proteoglycans of the Kurloff body, a large lysosome organelle, metachromatic towards Toluidine Blue, of a blood cell unique to the guinea pig and called the Kurloff cell. Splenic Kurloff cell from oestrogen-treated guinea pig cells were examined after staining with Cuprolinic Blue, a cationic phthalocyanine-like dye, in the presence of MgCl₂ in a critical electrolyte concentration method. Better results were obtained when the fixation-staining by the glutaraldehyde Cuprinolinic Blue MgCl₂ mixture was preceded by a glutaraldehyde pre-fixation. On light microscopy, Kurloff bodies generally exhibited an overall pink and glassy metachromasia, sometimes with additional darker metachromatic small dots at their peripheries. At the ultrastructural level, the metachromatic central matrix of the Kurloff body usually exhibited, as a major feature, a typical network pattern of ribbon-like or stellate electron-dense precipitates suggesting the presence of a skeleton of Cuprolinic Blue-reactive filamentous structures. Taking into account their high anionicity (as shown by the stability of the dye binding in the presence of 0.3 m MgCl₂) and their susceptibility to chondroitinase ABC, these anionic structures were assumed to be related to the proteochondroitin-4-sulphate previously characterized as the only major sulphated glycoconjugate of the Kurloff cell.     

Ultrastructure of Kurloff body proteoglycans after high pressure freezing, cryosubstitution and postembedding staining with cuprolinic blue

Very high pressure freezing and cryosubstitutlon of Kurloffcells preserves the ultrastructural morphology of Kurloff bodies,particularly the myelin figures, as shown by embedding in epoxyresin and conventional postembedding staining. It also preservesthe Kurloff body proteoglycans as more expanded spindle-likeshapes than does fixation with formaldehyde at atmospheric pressure.But., proteoglycans were not discernible in the Kurloff bodymatrix on either unstained or conventionally stained thin sections.The Kurloff body skeleton of proteoglycans in their native expandedshape was stained with the electron-dense cationic ministaincuprolinic blue, using thin sections embedded in LR white. Themean equatorial diameter of the spindles was 20–30 nm,while the collapsed filaments produced by aldehyde fixationwere about 10–15 nm wide. The spindles were often about200–300 nm long but could be much longer, depending onthe plane of the section. Thus, high pressure freezing, freezesubstitution, embedding in LR white, and staining with cationicdyes such as phthalocyanins seems to be a convenient way ofvisualizing intracellular proteoglycans that are well preservedand in very much like their native expanded state. cuprolinic blue high pressure freezing Kurloff cell proteoglycans ultrastructure     

Interaction of fibrinogen and its derivatives with fibrin

The binding between complementary polymerization sites of fibrin monomers plays an essential role in the formation of the fibrin clot. One set of polymerization sites involved in the interaction of fibrin monomers is believed to pre-exist in fibrinogen, while the complementary set of binding sites is exposed after the cleavage of fibrinopeptides from fibrinogen. The polymerization sites present in fibrinogen and its derivatives mediate their binding to fibrin. Although the binding of fibrinogen and its derivatives to fibrin have been qualitatively studied, there has been no systematic, quantitative investigation of their interaction with forming or preformed clots. In the present study, the binding of fibrinogen and fragments DD, D1, and E1 was measured using a sonicated suspension of plasminogen- and thrombin-free human cross-linked fibrin as a model of a preformed clot. Dissociation constants of 0.056, 0.19, and 2.44 microM, and the number of binding sites corresponding to 0.10, 0.21, and 0.13/fibrin monomer unit of fibrin polymer were found for fibrinogen, fragment DD, and fragment D1, respectively. Fragment E1 did not bind to sonicated noncross-linked or cross-linked fibrin suspensions. However, it was bound to forming fibrin clots as well as to fibrin-Celite, suggesting that the binding sites on fibrin involved in the interaction with fragment E1 may have been altered upon sonication. Affinity chromatography of various fibrinogen derivatives on a fibrin-Celite column showed that only part of the bound fragment DD was displaced by arginine, whereas fragments D1 and E1 were completely eluted under the same conditions. The results indicate that interaction of fibrinogen with the preformed fibrin clots is characterized by affinity in the nanomolar range and that binding between fibrin monomers, in the process of clot formation, could be characterized by even a higher affinity.     

Isolation of Kurloff cells by Percoll density gradient centrifugation. Protein labeling with 35S-methionine of these cells

Large populations of splenic Kurloff (150 - 200 X 10(6) Kurloff cells) were obtained from estrogenized guinea pigs by isopycnic centrifugation in a Percoll solution of 1.085 g/ml starting density. The Kurloff cells settled at a buoyant density of about 1.100 g/ml. The purity of these cell suspensions reached 95%, as assessed by phase contrast microscopy and by specific staining. The viability assessed by Trypan blue exclusion test was also about 95%. Moreover, the good transmission electron microscopic appearance of these Kurloff cells and their ability to take up 35S-methionine in culture confirmed their physiological integrity. By autohistoradiography, this protein labeling was localized between the nucleus and the Kurloff body, and also on the Kurloff body itself. This data reinforces the hypothesis of de novo synthesis of the Kurloff body.     

Lateral packing of protofibrils in fibrin fibers and fibrinogen polymers

The distinctive transverse banding pattern of fibrin fibers clearly indicates ordering of molecules in the longitudinal direction. In this study we examined the fibers of fibrin clots, as well as two types of fibrinogen polymers, by thin-section electron microscopy. The fibrinogen polymers have a transverse banding pattern identical to that of fibrin fibers—clearly indicating a regular longitudinal repeat—but they are larger in diameter, and show little or no branching. We therefore expected their overall ordering to be better than that of fibrin fibers. Several different fixation protocols were used. We readily observed the typical transverse banding seen previously by negative stain and metal replication techniques. However, only very rarely was any regular lateral lattice seen in any of the samples. X-ray diffraction was used to examine unfixed specimens of the two fibrinogen polymers and, once again, although a longitudinal repeat was evident, only rarely was evidence for lateral crystallinity seen. The electron-microscope and x-ray results showed that the needles and pellet fibers of fibrinogen have essentially the same internal architecture as thick fibrin fibers, and that all three types of polymer, although clearly transversely banded, have almost no crystallinity in their lateral protofibril packing.     

纤维蛋白单体D区与E区聚合后E区结构的变化

应用纤维蛋白单克隆抗体IF 5 3,观察当纤维蛋白的“A”位点与另一纤维蛋白D区域的“a”位点结合后纤维蛋白E区的变化 .纤维蛋白原Aα链经赖氨酰肽链内切酶消化后 ,应用反相HPLC分离纯化 ;通过ELISA法检测单克隆抗体IF 5 3与纤维蛋白原及其衍生物的反应情况 ;应用放射免疫法检测RGD合成肽抑制纤维蛋白单体与IF 5 3反应的情况 .发现IF 5 3能与纤维蛋白原Aα链的一个片段反应 ,该片段经氨基酸序列分析显示为纤维蛋白原Aα链氨基末端 (1～ 2 9) .该抗体能与酸溶解的纤维蛋白单体和可溶性纤维蛋白及XDP反应 ,但不能与酸化纤维蛋白原或GPRP反应 ,因此IF 5 3的抗原决定簇在Aα 2 0～ 2 9,与凝血酶作用于纤维蛋白肽A ,暴露出的聚合位点“A”(Aα17～19)紧邻 .当GPRP存在于纤维蛋白原溶液时 ,经凝血酶作用产生这种纤维蛋白单体不能与IF 5 3反应 .Aα(93～ 99) (ILRGDFS)合成肽部分抑制纤维蛋白单体与IF 5 3的反应 .实验结果提示 ,当纤维蛋白单体相互聚合 ,或纤维蛋白单体与纤维蛋白原聚合时 ,纤维蛋白单体结构会发生变化 ,其中Aα2 0～ 2 9片段成为新抗原暴露于E区表面 ,并且Aα2 0～ 2 9与纤维蛋白原细胞粘附区域RGD1片段邻近     

Gly-Pro-Arg-Pro modifies the glutamine residues in the alpha- and gamma-chains of fibrinogen: inhibition of transglutaminase cross-linking

During blood clotting Factor XIIIa, a transglutaminase, catalyzes the formation of covalent bonds between the epsilon-amino group of lysine and the gamma-carboxamide group of peptide-bound glutamine residues between fibrin molecules. We report that glycyl-L-prolyl-L-arginyl-L-proline (GPRP), a tetrapeptide that binds to the fibrin polymerization sites (D-domain) in fibrin(ogen), inhibits transglutaminase cross-linking by modifying the glutamine residues in the alpha- and gamma-chains of fibrinogen. Purified platelet Factor XIIIa, and tissue transglutaminase from adult bovine aortic endothelial cells were used for the cross-linking studies. Gly-Pro (GP) and Gly-Pro-Gly-Gly (GPGG), peptides which do not bind to fibrinogen, had no effect on transglutaminase cross-linking. GPRP inhibited platelet Factor XIIIa-catalyzed cross-linking between the gamma-chains of the following fibrin(ogen) derivatives: fibrin monomers, fibrinogen and polymerized fibrin fibers. GPRP functioned as a reversible, noncompetitive inhibitor of Factor XIIIa-catalyzed incorporation of [3H]putrescine and [14C]methylamine into fibrinogen and Fragment D1. GPRP did not inhibit 125I-Factor XIIIa binding to polymerized fibrin, demonstrating that the Factor XIIIa binding sites on fibrin were not modified. GPRP also had no effect on Factor XIIIa cross-linking of [3H]putrescine to casein. This demonstrates that GPRP specifically modified the glutamine cross-linking sites in fibrinogen, and had no effect on either Factor XIIIa or the lysine residues in fibrinogen. GPRP also inhibited [14C]putrescine incorporation into the alpha- and gamma-chains of fibrinogen without inhibiting beta-chain incorporation, suggesting that the intermolecular cross-linking sites were selectively affected. Furthermore, GPRP inhibited tissue transglutaminase-catalyzed incorporation of [3H]putrescine into both fibrinogen and Fragment D1, without modifying [3H]putrescine incorporation into casein. GPRP also inhibited intermolecular alpha-alpha-chain cross-linking catalyzed by tissue transglutaminase. This demonstrates that the glutamine residues in the alpha-chains involved in intermolecular cross-linking are modified by GPRP. This is the first demonstration that a molecule binding to the fibrin polymerization sites on the D-domain of fibrinogen modifies the glutamine cross-linking sites on the alpha- and gamma-chains of fibrinogen.     

Cytochemical localization of acid phosphatase and trimetaphosphatase activities in Kurloff cells

After stimulation of guinea pigs with estradiol to increase their Kurloff cell number, spleen imprints were prepared in order to detect non-specific acid phosphatase (AcPase) activity by light microscopic cytochemistry using naphthol AS-BI phosphate as substrate and pararosanilin or fast garnet GBC as coupler. For ultracytochemistry, Kurloff cells were prepared from spleens by filtration through a homogeneizer screen followed by repeated centrifugation. AcPase and trimetaphosphatase activities were tested using beta-glycerophosphate, cytidine-5'-monophosphate and inorganic trimetaphosphate as substrates. Significant enzymatic activities were demonstrated with all the substrates used in the cytoplasmic inclusion body of the Kurloff cells.     

Conebulization of surfactant and urokinase restores gas exchange in perfused lungs with alveolar fibrin formation

Alveolar fibrin generation has been suggested to possess strong surfactant-inhibitory potency. In perfused rabbit lungs, fibrin formation in the alveolar space was induced by sequential ultrasonic aerosolization of fibrinogen and thrombin, and the efficacy of rescue administration of surfactant and urokinase was investigated. Ventilation-perfusion (VA/Q) distribution was assessed by the multiple inert gas elimination technique. Aerosolization of fibrinogen (approximately 20 mg/kg body wt) increased shunt flow to approximately 7%. Sequential nebulization of fibrinogen and thrombin (1.3 U/kg body wt) caused alveolar fibrin deposition, documented immunohistologically, and provoked marked shunt flow, progressing to approximately 22% at the end of the experiments. The hemodynamics were virtually unchanged. Rescue aerosolization of natural bovine surfactant (15 mg/kg body wt) or urokinase-type plasminogen activator (4,500 U/kg body wt), undertaken after fibrin formation, improved gas exchange but progressive shunt flow still occurred (efficacy, surfactant > urokinase). In contrast, conebulization of surfactant and urokinase reversed shunt flow to approximately 7%, with an increased appearance of normal VA/Q matching. We conclude that alveolar fibrin formation is a potent surfactant-inhibitory mechanism in intact lungs, provoking severe VA/Q mismatch with a predominance of shunt flow, and that rescue aerosolization of surfactant plus urokinase may offer restoration of gas exchange under these conditions.     

Interaction of plasminogen and fibrin in plasminogen activation

Glu1-, Lys77-, miniplasminogens, kringle 1-3, kringle 1-5A, and kringle 1-5R were able to bind with fibrin, while microplasminogen and kringle 4 did not bind significantly. Kringle 1-5A, but not kringle 1-3, effectively inhibited the binding of Glu1-, Lys77-, and miniplasminogens with fibrin. Miniplasminogen also inhibited the binding of Glu1-plasminogen with fibrin. The binding of kringle 1-3 with fibrin was blocked by mini- or Glu1-plasminogen. It is therefore evident that there are two fibrin-binding domains in plasminogen and that the one in kringle 5 is of higher affinity than that in kringle 1-3. CNBr cleavage products of fibrinogen effectively enhanced the activation of Glu1-, Lys77-, or miniplasminogens, but not microplasminogen, by tissue-type plasminogen activator. Kringle 1-5, but not kringle 1-3, dose-dependently inhibited the enhancement by fibrinogen degradation products of Glu1-plasminogen activation by the activator. Lysine and epsilon-aminocaproic acid could inhibit the binding of plasminogens and plasminogen derivatives with fibrin and block the enhancement effect of fibrinogen degradation products on plasminogen activation. The data clearly illustrate that the binding of plasminogen with fibrin, mainly determined by kringle 5, is essential for effective activation by tissue-type plasminogen activator. However, the presence of kringle 1-4 in the plasminogen molecule is required for the full enhancing effect since the kcat/Km of miniplasminogen activation in the presence of fibrinogen degradation products was 8.2 microM-1 min-1 which is significantly less than 52.0 microM-1 min-1 of Glu1-plasminogen.     

Fibrin specific peptides derived by phage display: characterization of peptides and conjugates for imaging

Peptides that bind to fibrin but not to fibrinogen or serum albumin were selected from phage display libraries as targeting moieties for thrombus molecular imaging probes. Three classes of cyclic peptides (cyclized via disulfide bond between two Cys) were identified with consensus sequences XArXCPY(G/D)LCArIX (Ar = aromatic, Tn6), X(2)CXYYGTCLX (Tn7), and NHGCYNSYGVPYCDYS (Tn10). These peptides bound to fibrin at ～2 sites with K(d) = 4.1 μM, 4.0 μM, and 8.7 μM, respectively, whereas binding to fibrinogen was at least 100-fold weaker. The peptides also bind to the fibrin degradation product DD(E) with similar affinity to that measured for fibrin. The Tn7 and Tn10 peptides bind to the same site on fibrin, while the Tn6 peptides bind to a unique site. Alanine scanning identified the N- and C-terminal ends of the Tn6 and Tn7 peptides as most tolerant to modification. Peptide conjugates with either fluorescein or diethylenetriaminepentaaceto gadolinium(III) (GdDTPA) at the N-terminus were prepared for potential imaging applications, and these retained fibrin binding affinity and specificity in plasma. Relaxivity and binding studies on the GdDTPA derivatives revealed that an N-terminal glycyl linker had a modest effect on fibrin affinity but resulted in lower fibrin-bound relaxivity.     

Kurloff cell ultrastructure after combined formaldehyde-cetylpyridinium chloride fixation and high-iron diamine staining

Summary This study deals with the ultrastructure of the chondroitin sulphate proteoglycans of the Kurloff body, a large lysosomal organelle that stains metachromatically with Toluidine Blue and which is present in Kurloff cells (a blood cell unique to the guinea pig). Splenic tissues were fixed with 1% cetylpyridinium chloride (CPC) added to 4% paraformaldehyde and examined either after Spicer's high-iron diamine staining for sulphated anionic sites followed by post-fixation with ferrocyanide-osmium tetroxide or after a simple post-fixation with ferrocyanide-osmium tetroxide. CPC-precipitated sulphated sites were preferentially located at the periphery of the Kurloff body but, unexpectedly, were absent in the central matrix. Although their electron opacity was lower, these anionic sites were readily observable in the absence of HID-staining after sole post-fixation by ferrocyanide-reduced osmium. CPC-precipitated sulphated anionic sites were either associated with the myelin figures or constituted unexpected structures. They contained (i) tightly-stacked lamellae, with a very regular 4 nm periodicity, and (ii) groups of 2, 3, 4 short dense lines with a 3–5 nm periodicity. By taking into account the susceptibility of these HID-reactive structures towards chondroitinase ABC, these different sulphated components were assumed to be related to the proteochondroitin-4-sulphate previously characterized as the only major sulphated glycoconjugate of the Kurloff cell. Their colocalization with phospholipidic structures was suggested following, observation of sections treated by a chloroform-methanol mixture.     

Urinary Fibrinogen Derivative Excretion and Intraglomerular Fibrin Deposition in Glomerulonephritis

The relations between glomerular fibrin deposition, urinary excretion of fibrinogen derivatives (F.D.), and proteinuria were explored in 81 patients with glomerulonephritis. A positive correlation existed between proteinuria and F.D. excretion even when no fibrin could be detected in the glomerulus. In two patients with tubular proteinuria F.D. excretion was also raised, suggesting that tubular reabsorption or catabolism of F.D. or both normally occur.Disproportionately high titres of F.D. were observed when fibrin was deposited in an extracapillary site, but mesangial fibrin deposition was not accompanied by a higher excretion of F.D. than that observed in patients in whom intraglomerular fibrin was not detected. These observations suggest that the immunofluorescent findings on renal biopsies should be the major criteria on which a trial of anticoagulants in proliferative glomerulonephritis might be instituted and that measurement of urinary F.D. is likely to be of value in monitoring therapy in patients with extracapillary fibrin deposition.     

Expression of soluble and functional snake venom fibrinolytic enzyme fibrolase via the co-expression of DsbC in Escherichia coli

Fibrolase is a non-hemorrhagic zinc metalloproteinase found in southern copperhead snake venom (Agkistrodon contortrix contortrix). It is capable of degrading fibrin clots that result from purified fibrinogen or blood plasma. The DNA of fibrolase was amplified by recursive PCR, and cloned into the pET25b(+) expression vector. The effect of co-expression of signalless versions of catalysts or molecular chaperones FkpA, Skp and DsbC in cytoplasm was examined. When co-expressed with DsbC, compared to the totally insoluble inclusion bodies of fibrolase expressed separately, more than 90 % of recombinant fibrolase was soluble, according to denaturing polyacrylamide gel electrophoresis analysis. We also determined that FkpA and Skp had no effects on the solubility of target protein when co-expressed with fibrolase in Escherichia coli. Fibrolase was successfully purified using metal ion affinity chromatography and hydrophobic chromatography, and a maximum yield of 20 mg/L fibrolase was obtained. Fibrinolytic activity of recombinant fibrolase was demonstrated using fibrin plate assays and fibrinogen hydrolysis.     

Antifibrinolytic effect of single apo(a) kringle domains: relationship to fibrinogen binding

Elevated plasma concentrations of lipoprotein(a) [Lp(a)] are associated with an increased risk for the development of atherosclerotic disease which may be attributable to the ability of Lp(a) to attenuate fibrinolysis. A generally accepted mechanism for this effect involves direct competition of Lp(a) with plasminogen for fibrin(ogen) binding sites thus reducing the efficiency of plasminogen activation. Efforts to determine the domains of apolipoprotein(a) [apo(a)] which mediate fibrin(ogen) interactions have yielded conflicting results. Thus, the purpose of the present study was to determine the ability of single KIV domains of apo(a) to bind plasmin-treated fibrinogen surfaces as well to determine their effect on fibrinolysis using an in vitro clot lysis assay. A bacterial expression system was utilized to express and purify apo(a) KIV (2), KIV (7), KIV (9) DeltaCys (which lacks the seventh unpaired cysteine) and KIV (10) which contains a strong lysine binding site. We also expressed and examined three mutant derivatives of KIV (10) to determine the effect of changing critical residues in the lysine binding site of this kringle on both fibrin(ogen) binding and fibrin clot lysis. Our results demonstrate that the strong lysine binding site in apo(a) KIV (10) is capable of mediating interactions with plasmin-modified fibrinogen in a lysine-dependent manner, and that this kringle can increase in vitro fibrin clot lysis time by approximately 43% at a concentration of 10 microM KIV (10). The ability of the KIV (10) mutant derivatives to bind plasmin-modified fibrinogen correlated with their lysine binding capacity. Mutation of Trp (70) to Arg abolished binding to both lysine-Sepharose and plasmin-modified fibrinogen, while the Trp (70) -->Phe and Arg (35) -->Lys substitutions each resulted in decreased binding to these substrates. None of the KIV (10) mutant derivatives appeared to affect fibrinolysis. Apo(a) KIV (7) contains a lysine- and proline-sensitive site capable of mediating binding to plasmin-modified fibrinogen, albeit with a lower apparent affinity than apo(a) KIV (10). However, apo(a) KIV (7) had no effect on fibrinolysis in vitro. Apo(a) KIV (2) and KIV (9) DeltaCys did not bind measurably to plasmin-modified fibrinogen surfaces and did not affect fibrinolysis in vitro.     

Analysis of soluble fibrin complexes by agarose gel chromatography and protamine sulfate gelation.

The molecular makeup of soluble fibrin complexes was studied by gel exclusion chromatography using radio-labelling to characterize individual components in protein mixtures. Products of limited plasmin degradation of fibrinogen and mixtures of fibrinogen and "early" fibrinogen digests formed high molecular weight soluble fibrin complexes upon incubation with thrombin. Purified, nonclottable fragment Y did not incorporate into soluble fibrin complexes, nor could we demonstrate incorporation of fragments D and E as previously described from our laboratory. Thus, under the conditions of these experiments, soluble fibrin complexes have two identifiable components, fibrin monomer and clottable fragment X monomer, although incorporation of native fibrinogen or fragment X unreacted by thrombin into soluble fibrin complexes cannot be excluded. Individual fractions of thrombin-treated early fibrinogen digests isolated by agarose gel chromatography were treated with protamine sulfate at 37 degrees C resulting in precipitation-gelation of greater than 90 per cent of high molecular weight soluble fibrin complexes; whereas, less than 10 per cent of lower molecular weight fibrinogen degradation products precipitated by protamine sulfate. These findings do not support the widely held concept that soluble fibrin complexes incorporate nonclottable degradation products of fibrinogen proteolysis, nor do they support the notion that the so-called paracoagulation reaction induced by protamine sulfate results from the splitting of complexes between fibrin monomer and nonclottable fibrinogen degradation products.     

A 130-kDa protein on endothelial cells binds to amino acids 15-42 of the B beta chain of fibrinogen.

Factors which stimulate the release of von Willebrand factor (vWf) from endothelial cell Weibel-Palade bodies and which induce the expression of the leukocyte-binding adhesion molecule P-selectin (PADGEM, GMP-140, CD62) on the endothelial cell surface remain incompletely characterized. Fibrin but not fibrinogen is a potent stimulus for the release of stored von Willebrand factor from endothelial cells. Removal of fibrinopeptides A and B from fibrinogen occurs during the formation of fibrin, and the removal of fibrinopeptide B is a requirement for fibrin to induce vWf secretion. The cleavage of fibrinopeptide A by reptilase enzyme forms a fibrin gel yet it is incapable of stimulating Weibel-Palade body degranulation. As a consequence of removing fibrinopeptide B, B beta 15-42 becomes the new NH2 terminus of the beta chain of fibrin. We have shown that the peptide B beta 15-42 in solution inhibits the release of vWf stimulated by fibrin. In addition, B beta 15-42 coupled to ovalbumin supports the binding and spreading of endothelial cells, while a scrambled form of this peptide coupled to the same carrier does not. We investigated whether these determinants near the amino terminus of the beta chain of fibrin bind to a specific protein on the surface of endothelial cells. A 130-kDa protein was isolated from surface-labeled human umbilical vein endothelial cells by specific binding to B beta 15-42 immobilized on Sepharose. This glycoprotein was eluted with the B beta 15-42 peptide in solution but not with the scrambled form of this peptide. The fibrin-derived peptides B beta 19-26 and B beta 37-56-cysteine were also incapable of eluting the 130-kDa protein bound to immobilized B beta 15-42 as were the arginine-glycine-aspartic acid-serine RGDS tetrapeptide and EDTA. The 130-kDa protein is recognized neither by antibodies to the known integrins found on endothelial cells nor by antibodies to CD31 (endoCAM, PECAM-1), a member of the immunoglobulin family of receptors found on endothelial cells. The beta chain of fibrin thus contains a sequence near its amino terminus which specifically binds to what is likely a novel endothelial cell surface protein. This glycoprotein may promote endothelial cell adhesion to fibrin during the wound healing process and is a candidate for a receptor involved in fibrin-mediated release of Weibel-Palade bodies from endothelial cells.     

Potentiation of endothelial cell proliferation by fibrin(ogen)-bound fibroblast growth factor-2.

Endothelial cell growth is stimulated by fibroblast growth factor-2 (FGF-2), and both adhesion and proliferation are modulated by interactions with fibrinogen and fibrin. Previous evidence indicates that FGF-2 binds specifically and with high affinity to fibrinogen and fibrin, suggesting that their effects on endothelial cells may be coordinated. In this study, we have, therefore, investigated the ability of FGF-2 bound to fibrinogen and fibrin to stimulate proliferation of endothelial cells. Human umbilical vein endothelial cells were cultured in the presence of FGF-2 with or without fibrinogen, and proliferation was assessed by microscopic examination of cultures, incorporation of [3H]thymidine and by cell counting. Cells cultured in the presence of both FGF-2 and fibrinogen proliferated more rapidly than those with FGF-2 alone and exhibited a decreased population doubling time. At concentrations of FGF-2 up to 150 ng/ml, there was greater endothelial cell proliferation in the presence of fibrinogen than in its absence with the most pronounced effect below 1 ng/ml. The maximum effect of fibrinogen was observed at a molar ratio of fibrinogen to FGF-2 of 2:1, corresponding to the maximum molar binding ratio. Endothelial cells proliferated when plated on fibrin or surface-immobilized fibrinogen with FGF-2, indicating that FGF-2 bound to surface-associated fibrin(ogen) retained activity. We conclude that fibrinogen- or fibrin-bound FGF-2 is able to support endothelial cell proliferation and that fibrinogen potentiates the proliferative capacity of FGF-2.     

Fibrinogen and plantar edema induced by lambda carrageenan

1. Batroxobine which induces fibrinogen consumption, accelerates the development of 48/80 and lambda carrageenan oedema: in the rat the various products released from fibrinogen and fibrin increase these inflammatory reactions. 2. Heparin and epsilon-aminocaproic acid have no influence on carrageenan oedema: the derivatives of fibrinogen do not take part in the constitution of the inflammatory reaction induced by carrageenan. 3. The anti-inflammatory action of this sulfated polygalactose does not depend on its anti-coagulant activity.     

Ultrastructure of clots during isometric contraction

We explored the retraction or contraction of platelet-fibrin clots under isometric conditions. In the presence of micromolar calcium clots of normal platelet-rich plasma developed tension at an initial rate of 0.1 to 0.2 g/min per cm2 (initial cross-sectional area). Electron microscopy of clots fixed after attaining a force of 1.6 g/cm2 revealed platelets with elongated bodies and pseudopods in close apposition to fibrin strands which were oriented in cablelike fashion in the direction of tension. The development of tension could not be explained simply on the basis of platelet-platelet association and interaction alone. First, factor XIII-dependent cross-linking of fibrin fibers was critical to normal isometric contraction. Second, tension decreased linearly, rather than exponentially, when the platelet count in the platelet-fibrin clot was decreased, suggesting that platelets must be interacting with another component (i.e. fibrin). Thrombasthenic platelets, deficient in fibrinogen receptors, failed to develop tension or to align fibrin strands or pseudopods in the clot. Platelet-fibrin clots treated with vincristine to disassemble microtubules or cytochalasin B to disrupt microfilaments failed to develop tension and relaxed if these agents were added after tension had developed. Relaxation under these conditions, however, was not associated with loss of orientation of fibrin strands. Our findings suggest that platelet-fibrin interaction in clots under isometric conditions leads to orientation of fibrin strands and platelets in the direction of force generation. Tension develops as platelets simultaneously attach to and spread along fibrin strands, and contract. The contraction draws some fibrin into platelet-fibrin clumps and aligns other strands in the long axis of tension. The achievement and maintenance of maximum tension appears to depend on the development of platelet-fibrin attachments and extension of platelet bodies and long pseudopods containing bundles of microfilaments and microtubules along the oriented fibrin fibers.