A novel monoclonal antibody against the extracellular domain of GPIbbeta modulates vWF mediated platelet adhesion

GPIbbeta is disulfide-linked to GPIbalpha to form GPIb, a platelet receptor for von Willebrand factor (vWF). GPIb is in turn non covalently linked to GPIX and GPV to form the GPIb/V/IX complex. Apart from its contribution to controlling surface expression of the complex, the exact function of GPIbbeta is not well established due to a lack of suitable ligands or antibodies. The present report describes a monoclonal antibody (RAM.1) that labeled the 26 kDa GPIbbeta subunit on western blots and coprecipitated the three subunits of the GPIb/IX complex from lysates of platelets and transfected CHO and K562 cells. RAM.1 bound to GPIbbeta deleted of its intracellular domain whereas Gi27, directed against intracellular GPIbbeta, did not. Using synthetic peptides, the RAM.1 epitope was mapped to a putative cysteine loop within the COOH-terminal leucine-rich flanking region. In functional assays, RAM.1 had no effect on platelet aggregation induced by ADP, collagen or thrombin, but inhibited ristocetin induced platelet agglutination and botrocetin induced vWF binding. RAM.1 inhibited adhesion of GPIb/V/IX transfected K562 cells to a vWF matrix under flow, increased their rolling velocity and decreased the resistance of cells to detachment at high shear. This study suggests a role of GPIbbeta in modulating the adhesive properties of GPIb/V/IX and describes a useful tool to analyze the exact functions of GPIbbeta.

Proteolysis of the exodomain of recombinant protease-activated receptors: prediction of receptor activation or inactivation by MALDI mass spectrometry

Protease-activated receptors (PARs) mediate cell activation after proteolytic cleavage of their extracellular amino terminus. Thrombin selectively cleaves PAR1, PAR3, and PAR4 to induce activation of platelets and vascular cells, while PAR2 is preferentially cleaved by trypsin. In pathological situations, other proteolytic enzymes may be generated in the circulation and could modify the responses of PARs by cleaving their extracellular domains. To assess the ability of such proteases to activate or inactivate PARs, we designed a strategy for locating cleavage sites on the exofacial NH(2)-terminal fragments of the receptors. The first extracellular segments of PAR1 (PAR1E) and PAR2 (PAR2E) expressed as recombinant proteins in Escherichia coli were incubated with a series of proteases likely to be encountered in the circulation during thrombosis or inflammation. Kinetic and dose-response studies were performed, and the cleavage products were analyzed by MALDI-TOF mass spectrometry. Thrombin cleaved PAR1E at the Arg41-Ser42 activation site at concentrations known to induce cellular activation, supporting a native conformation of the recombinant polypeptide. Plasmin, calpain and leukocyte elastase, cathepsin G, and proteinase 3 cleaved at multiple sites and would be expected to disable PAR1 by cleaving COOH-terminal to the activation site. Cleavage specificities were further confirmed using activation site defective PAR1E S42P mutant polypeptides. Surface plasmon resonance studies on immobilized PAR1E or PAR1E S42P were consistent with cleavage results obtained in solution and allowed us to determine affinities of PAR1E-thrombin binding. FACS analyses of intact platelets confirmed the cleavage of PAR1 downstream of the Arg41-Ser42 site. Mass spectrometry studies of PAR2E predicted activation of PAR2 by trypsin through cleavage at the Arg36-Ser37 site, no effect of thrombin, and inactivation of the receptor by plasmin, calpain and leukocyte elastase, cathepsin G, and proteinase 3. The inhibitory effect of elastase was confirmed on native PAR1 and PAR2 on the basis of Ca(2+) signaling studies in endothelial cells. It was concluded that none of the main proteases generated during fibrinolysis or inflammation appears to be able to signal through PAR1 or PAR2. This strategy provides results which can be extended to the native receptor to predict its activation or inactivation, and it could likewise be used to study other PARs or protease-dependent processes.

Modulation by heparin of the interaction of the A1 domain of Von Willebrand factor with glycoprotein Ib

The conformation of the A1 domain of von Willebrand factor (vWF) is a critical determinant of its interaction with the glycoprotein (GP) Ib/V/IX complex. To better define the regulatory mechanisms of vWF A1 domain binding to the GPIb/V/IX complex, we studied vWF-dependent aggregation properties of a cell line overexpressing the GPIbalpha, GPIbbeta, and GPIX subunits (CHO-GPIbalphabeta/IX cells). We found that CHO-GPIbalphabeta/IX cell aggregation required the presence of both soluble vWF and ristocetin. Ristocetin-induced CHO-GPIbalphabeta/IX cell aggregation was completely inhibited by the recombinant VCL fragment of vWF that contains the A1 domain. Surprisingly, the substitution of heparin for ristocetin resulted in the formation of CHO-GPIbalphabeta/IX cell aggregates. Using monoclonal antibodies blocking vWF interaction with GPIb/V/IX or mocarhagin, a venom metalloproteinase that removes the amino-terminal fragment of GPIbalpha extending from aa 1 to 282, we demonstrated that both ristocetin- and heparin-induced aggregations involved an interaction between the A1 domain of vWF and the GPIbalpha subunit of the GPIb/V/IX complex. The involvement of heparin in cell aggregation was also demonstrated after treatment of heparin with heparinase that abolished CHO-GPIbalphabeta/IX cell aggregation. These results indicated that heparin was able to induce vWF-dependent CHO-GPIbalphabeta/IX cell aggregation. In conclusion, we demonstrated that heparin is capable of positively modulating the vWF interaction with the GPIb/V/IX complex.

Ser752 mutation to Pro or Ala in the beta3 integrin subunit differentially affects the kinetics of cell spreading to von Willebrand factor and fibrinogen

The beta3 cytoplasmic domain of the alpha v beta3 integrin is essential for intracellular signals required for cytoskeletal rearrangements. Expression of beta3Ser752Pro mutation in heterologous cells profoundly affects cell spreading and beta3 localization into focal contacts. However, the beta3Ser752Ala substitution mostly restores normal integrin functions, suggesting that the presence of Pro is responsible for the receptor's loss of function. To further assess the role of the Ser752 of the beta3 cytoplasmic domain in the cytoskeletal organization of adherent cells, we developed a computer-assisted method of image analysis allowing the automatic classification of spread cells according to the quantitative analysis of their cell morphology. We compared adhesion and spreading to von Willebrand factor (vWF) or fibrinogen (Fg) of cells expressing beta3 wild type, beta3Ser752Pro or beta3Ser752Ala mutated integrin subunit as a chimeric alpha v beta3 receptor. The beta3Ser752Ala substitution did not impair the general ability of cells to spread, but resulted in a delayed and reduced spreading on both vWF and Fg. Moreover, the beta3Ser752Ala mutation produced modifications of the morphology of spread cells, suggesting a disorganization of their cytoskeleton. Attachment studies showed that the beta3Ser752Ala mutation did not modify the capacity of cells to attach to the substrate, indicating no change in the ligand binding affinity of the alpha v beta3 integrin. Furthermore, we identified a slight defect of beta3Ser752Pro cell attachment to vWF and Fg, beside their impairment of spreading. Taken together, these results suggest a role of Ser752 of the beta3 cytoplasmic domain in the optimal cytoskeletal organization of adherent cells.

Relative importance of the glycoprotein Ib-binding domain and the RGD sequence of von Willebrand factor for its interaction with endothelial cells

Endothelial cell adhesion to von Willebrand Factor is mainly mediated through an interaction between the alpha vbeta3 integrin and the RGD sequence of von Willebrand factor (vWF). To define the potential involvement of glycoprotein Ib alpha (GPIb alpha) as an endothelial vWF receptor, we compared cell adhesion to three recombinant vWF, the wild-type (WT-rvWF) and two mutants, RGGS-rvWF (D1746G), defective for binding to platelet alphaIIb beta3, and deltaA1-rvWF with a deletion between amino-acids 478 and 716, which does not bind to platelet GPIb alpha. Adhesion of human umbilical vein endothelial cells to purified vWF recombinants was measured by automatized cell counting using an image analyzer. Whereas cell adhesion to delta A1-rvWF was unchanged compared with WT-rvWF, reaching a plateau of 40% total cells at a concentration of 2.5 microg/mL rvWF, adhesion to RGGS-rvWF was only 10% of total cells. Cell stimulation by tumor necrosis factor-alpha (TNF alpha), reported to upregulate the expression of the putative endothelial GPIb alpha, did not modify adhesion to these rvWF. Monoclonal antibodies to vWF or GPIb alpha, blocking vWF interaction with platelet GPIb alpha, were unable to inhibit endothelial cell adhesion to rvWF. In contrast, antibody 9 to vWF, blocking the alpha vbeta3-dependent endothelial cell adhesion to plasma vWF, inhibited adhesion to WT-rvWF as efficiently as to deltaA1-rvWF (50% inhibition at a concentration of 11 and 15 microg/mL, respectively). In agreement with the fact that endothelial cell adhesion to vWF appeared independent of the GPIb alpha-binding domain, we were unable to detect endothelial surface expression of GPIb alpha by flow cytometry or in cell lysates by immunoprecipitation followed by immunoblotting. Moreover, expression of GPIb alpha mRNA was undetectable in endothelial cells, even after stimulation by TNF alpha. These studies indicate that GPIb alpha is not expressed in human cultured endothelial cells and is not involved in adhesion to vWF-containing surfaces. Thus, in static conditions, cultured endothelial cells adhere to vWF through an alpha vbeta3-dependent, GPIb alpha-independent mechanism.

[And if we speak about men?]

This article raises questions about some of the perverse effects of the reasoning behind correlations between sex and health in our socio-cultural context. Such a reasoning strongly denounces the psychosocial problems of women, but tends to forget the vulnerability of men which is nonetheless clearly evident in official statistics on suicide, dependence on alcohol and other drugs, violence and itinerancy.

[The Santé-Québec survey and mental health of Québecers : conceptual framework and methodology.]

The Santé Québec study is the most important inquiry into health yet undertaken in Quebec on life habits and the physical and psychological state of health of almost 20,000 persons aged 15 years and over living in private homes. The mental-health section of the study is situated within the tradition of socio-epidemiological inquiries. The article describes the reasoning behind the choice of mental-health indicators (psychological well-being, psychological distress, suicide thoughts and attempts, several severe psychological problems) and the measuring instruments. The study's usefulness and limits are discussed.

Family support system in newborn medicine: does it work? Follow-up study of infants at risk

Acute illness in early childhood generates chronic anxiety in parents, which may manifest itself in part by inappropriate use of health care. To minimize this and the development of other psychosocial sequelae associated with neonatal illness, a family support system (FSS) was developed and implemented in a neonatal intensive care unit. The effectiveness of the FSS was assessed by the evaluation of emergency room and inpatient hospital service utilization in 80 patients born before, and 90 patients born after the institution of the program. At the outset, the groups had similar medical and social characteristics. There was no difference between the two groups in the utilization of emergency services in the first year after discharge. However, during the second year the control group used the emergency room twice as often as the study group did (P less than 0.025). During the first 2 years, half of the control group was readmitted, compared with less than a third of the study group (P less than 0.005). Overall, after discharge from the neonatal intensive care unit the control group spent an average of 9 days per patient in hospital, compared with a mean of 3 days per patient in the study group (P less than 0.025). It appears, therefore, that the FSS may be an effective way to reduce some of the psychosocial sequelae of illness in newborn infants requiring intensive care.

[Evaluation of information programs on sexual assault in six elementary schools in east Montréal.]

Within the sex education program given to four hundred and sixty five (465) students approximately eleven years in age, a new information project on exhibitionism, sexual harassment, rape and incest was introduced in the eighteen (18) sixth grade classes of ten (10) elementary schools in the east end of Montréal. The evaluation of the project implementation gives us good indications of the concerted action that is necessary, the process needed to elaborate teaching material and also shows the immediate reaction of educators, parents and, of course, the students concerned. Very little resistance to this new teaching was noted within the school system. All parents had been informed of the project, no negative comments were received after-wards at schools. Incest was perceived by children as a problem "you do not speak of ' because it is susceptible to bring about worse things than the abuse itself, normaly the separation of the parents or the emprisonment of the abusive parent.

Upper gastrointestinal hemorrhage: aggressive management decreases mortality

In a retrospective study of 630 patients with upper gastrointestinal hemorrhage admitted to the Royal Victoria Hospital between 1963 and 1971, the overall mortality was 12.54%. Mortality increased in patients receiving more than 10 units of blood and in patients over 60 years of age. Mortality decreased in patients in whom the site of hemorrhage was known prior to operation. Early surgery for gastric ulcers and conservative therapy for acute gastric erosions reduced mortality. Therefore in 334 patients admitted to the Royal Victoria Hospital between 1973 and 1976 with upper gastrointestinal hemorrhage, an aggressive approach to diagnosis and management was emphasized. There was a significant decrease in patients with duodenal ulcers, acute gastric erosions, and gastric ulcers who received more than 10 units of blood. There was a significant increase in the use of endoscopy to establish the source of hemorrhage and a significant increase in the use of endoscopy to establish the source of hemorrhage and a significant decrease in the number of patients who did not have a diagnosis prior to operation. There was also a significant increase in early surgery for gastric ulcers. This regimen led to a significant decrease in mortality (6.69% vs. 12.54%). This report demonstrates that early diagnosis and management based on the lesion found reduces mortality from upper gastrointestinal hemorrhage.

L'INDEXAGE DES TUBERCULES DE POMMES DE TERRE EN VUE DE DÉCELER LA FLÉTRISSURE BACTÉRIENNE (CORYNEBACTERIUM SEPEDONICUM) (SPIECK 8 : KOTT.) SKAPTASON & BURKHOLDER

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ACTION DE LA THIAMINE SUR LE PHYTOPHTHORA INFESTANS (MONT.) DE BARY

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