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ABSTRACT: Simultaneously to phospholipid flip-flop that supports the procoagulant activity of activated platelets, blebs, supported by actin reorganization, are formed at the plasma membrane and generate microvesicles. The molecular mechanism of microvesicle shedding from activated platelets implicates Ca influx and Ca-dependent protease, calpain. We previously demonstrated that the formation of lamellipodias and filopodias associated with platelet shape change involved the reorganization of actin filaments through a Cdc42/Rac1/p21-activated kinase (PAK)-dependent pathway. Here, we investigated whether platelet blebbing also depends on the Cdc42/Rac1/PAK pathway. Exposure of platelets in vitro to either a mixture of thrombin receptor-activating peptide (TRAP) and collagen or the Ca ionophore A23187 in the presence of Ca generates microvesicles that can be identified by flow cytometry. The calpain inhibitor, calpeptin, diminished microvesicle formation induced by the Ca ionophore A23187, confirming the role of calpain in this process. PAK1/2 is cleaved in a calpain-dependent manner, and calpeptin prevents this cleavage and allows a transient activation of the kinase. Inhibition of Cdc42 and Rac1 by toxin B from Clostridium difficile, that suppresses PAK1/2 activation induced by TRAP and collagen or by A23187 in the presence of calpeptin, decreases polymerization of actin, lamellipodia and filopodia formation and interferes with the shedding of microvesicles. We conclude that the Rac1/Cdc42/PAK pathway controls actin reorganization that is necessary for microvesicle shedding.
Blood coagulation & fibrinolysis: an international journal in haemostasis and thrombosis 01/2009; 20(1):63-70. · 1.25 Impact Factor
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Steve Simoneau,
Human Rezaei,
Nicole Salès,
Gunnar Kaiser-Schulz,
Maxime Lefebvre-Roque, Catherine Vidal,
Jean-Guy Fournier,
Julien Comte,
Franziska Wopfner,
Jeanne Grosclaude,
Hermann Schätzl,
Corinne Ida Lasmézas
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ABSTRACT: The mechanisms underlying prion-linked neurodegeneration remain to be elucidated, despite several recent advances in this field. Herein, we show that soluble, low molecular weight oligomers of the full-length prion protein (PrP), which possess characteristics of PrP to PrPsc conversion intermediates such as partial protease resistance, are neurotoxic in vitro on primary cultures of neurons and in vivo after subcortical stereotaxic injection. Monomeric PrP was not toxic. Insoluble, fibrillar forms of PrP exhibited no toxicity in vitro and were less toxic than their oligomeric counterparts in vivo. The toxicity was independent of PrP expression in the neurons both in vitro and in vivo for the PrP oligomers and in vivo for the PrP fibrils. Rescue experiments with antibodies showed that the exposure of the hydrophobic stretch of PrP at the oligomeric surface was necessary for toxicity. This study identifies toxic PrP species in vivo. It shows that PrP-induced neurodegeneration shares common mechanisms with other brain amyloidoses like Alzheimer disease and opens new avenues for neuroprotective intervention strategies of prion diseases targeting PrP oligomers.
PLoS Pathogens 09/2007; 3(8):e125. · 9.13 Impact Factor
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ABSTRACT: Magnetic resonance spectroscopy studies in animal models of prion disease are very few and concern terminal stages of infection. In order to study earlier stages of the disease, we used in-vivo magnetic resonance spectroscopy in a mouse model of scrapie and, for the first time, in mice infected with a bovine spongiform encephalopathy strain. In bovine spongiform encephalopathy-infected mice, we observed an increase in myo-inositol preceding clinical signs by 20 days, followed by a decrease in N-acetylaspartate at advanced stages. In scrapie-infected mice, changes in N-acetylaspartate and myo-inositol were detected at the beginning of the symptomatic phase. These results show that magnetic resonance spectroscopy is a valuable tool for detecting subtle metabolic changes associated to gliosis and neuronal dysfunction in prion diseases.
Neuroreport 02/2006; 17(1):89-93. · 1.66 Impact Factor
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Medecine sciences: M/S 01/2006; 21(12):1112-4. · 0.64 Impact Factor
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ABSTRACT: Complex mechanisms of human immunodeficiency virus type-1 (HIV-1) brain pathogenesis suggest the contribution of individual HIV-1 gene products. Among them, the Nef protein has been reported to harbor a major determinant of pathogenicity in AIDS-like disease. The goal of the present study was to determine whether Nef protein expressed in vivo by primary macrophages could induce a brain toxicity also affecting the behavior of the rat. To achieve this goal we grafted Nef-transduced macrophages into the rat hippocampus. Two months post-transplantation, we observed that Nef induces monocyte/macrophage recruitment, expression of TNF-alpha, and astrogliosis. No apoptotic event was detected. We further demonstrated that Nef neurotoxicity is associated with cognitive deficits.
The FASEB Journal 01/2005; 18(15):1851-61. · 5.71 Impact Factor
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ABSTRACT: Platelet activation by thrombin or thrombin receptor-activating peptide (TRAP) results in extensive actin reorganization that leads to filopodia emission and lamellae spreading concomitantly with activation of the Rho family small G proteins, Cdc42 and Rac1. Evidence has been provided that direct binding of Cdc42-guanosine triphosphate (GTP) and Rac1-GTP to the N-terminal regulatory domain of the p21-activated kinase (PAK) stimulates PAK activation and actin reorganization. In the present study, we have investigated the relationship between shape change and PAK activation. We show that thrombin, TRAP, or monoclonal antibody (MoAb) anti-Fc(gamma)RIIA IV.3 induces an activation of Cdc42 and Rac1. The GpVI ligand, convulxin (CVX), that forces platelets to lamellae spreading efficiently activates Rac1. Thrombin, TRAP, MoAb IV.3, and CVX stimulate autophosphorylation and kinase activity of PAK. Inhibition of Cdc42 and Rac1 with clostridial toxin B inhibits PAK activation and lamellae spreading. The cortical-actin binding protein, p80/85 cortactin, is constitutively associated with PAK in resting platelets and dissociates from PAK after thrombin stimulation. Inhibition of PAK autophosphorylation by toxin B prevents the dissociation of cortactin. These results suggest that Cdc42/Rac1-dependent activation of PAK may trigger early platelet shape change, at least in part through the regulation of cortactin binding to PAK.
Blood 01/2003; 100(13):4462-9. · 9.90 Impact Factor
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ABSTRACT: Examined the effects of lesions of the prelimbic area of the prefrontal cortex on acquisition and retention of nonmatching (NMTS) and matching-to-sample (MTS) tasks. 64 male rats participated. Both tasks involved a reference and a working memory component, but only working memory was impaired by the lesions. A comparison of the 2 tasks revealed quantitatively similar deficits in postoperatively trained rats. In preoperatively trained rats, however, the deficits were more important in the MTS task than in the NMTS task. In addition, an effect of interference between successive trials was observed in the NMTS task but not in the MTS task. Perseverative tendencies were observed in the MTS task only. Results suggest that prefrontal lesions induce working memory deficits as a result of poor temporal encoding and increased susceptibility to interference, and impair effortful processing, such as that engaged in response selection mechanisms. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Behavioral Neuroscience 09/1994; 108(5):883-891. · 2.62 Impact Factor
