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Accueil > Agenda > Les séminaires Jean Roche > L’activateur tissulaire du plasminogène (tPA) : un nouveau neuromodulateur (...)

L’activateur tissulaire du plasminogène (tPA) : un (...)

Lundi 12 juin 2006,11h, salle Lissitzky.


1 : Cytokine Growth Factor Rev. 2006 Feb-Apr ;17(1-2):121-8. Epub 2005 Nov 3.

Transforming growth factor-beta signalling in brain disorders.

Vivien D, Ali C.

INSERM-Avenir tPA in the working brain, Centre CYCERON, Universite de Caen, Bd H.Becquerel, BP 5229, 14074 Caen Cedex, France. vivien

Transforming growth factor-beta (TGF-beta) has been characterized as an injury-related factor, based on the observation that it is strongly up-regulated in many acute or chronic central nervous system disorders. TGF-beta is generally thought to be neuroprotective and several mechanisms have been proposed to explain this beneficial action. For instance, TGF-beta protects neurons against the potentiating effect of tissue-type plasminogen activator on NMDA receptor-mediated excitotoxicity, by up-regulating type-1 plasminogen activator inhibitor expression in astrocytes. TGF-beta has also anti-apoptotic properties, through a recruitment of a mitogen-activated protein kinase pathway and a concomitant activation of anti-apoptotic members of the Bcl-2 family. These multiple mechanisms might reflect the pleiotropic nature of TGF-beta, reinforcing the potential therapeutic value of this cytokine in several central nervous system disorders.

2 : Mol Cell Neurosci. 2005 Dec ;30(4):552-8. Epub 2005 Oct 4.

The brain-specific tissue-type plasminogen activator inhibitor, neuroserpin, protects neurons against excitotoxicity both in vitro and in vivo.

Lebeurrier N, Liot G, Lopez-Atalaya JP, Orset C, Fernandez-Monreal M, Sonderegger P, Ali C, Vivien D.

INSERM-Avenir, tPA in the working brain, GIP CYCERON, Universite de Caen, GIP Cyceron-Bd Henri Becquerel, 14074 Caen Cedex, France.

Considering its brain-specific expression, neuroserpin (NS), a potent inhibitor of tissue-type plasminogen activator (tPA), might be a good therapeutic target to limit the pro-excitotoxic effects of tPA within the cerebral parenchyma, without affecting the benefit from thrombolysis in stroke patients. Here, we aimed at determining the mechanisms of action responsible for the previously reported neuroprotective activity of NS in rodent experimental cerebral ischemia. First, we show in vivo that exogenous NS protects the cortex and the striatum against NMDA-induced injury. Then, the cellular mechanisms of this neuroprotection were investigated in primary cultures of cortical neurons. We show that NS fails to prevent serum deprivation-induced apoptotic neuronal death, while it selectively prevents NMDA- but not AMPA-induced excitotoxicity. This beneficial effect is associated to a decrease in NMDA receptor-mediated intracellular calcium influx. Altogether, these data suggest that an overexpression of neuroserpin in the brain parenchyma might limit the deleterious effect of tPA on NMDA receptor-mediated neuronal death, which occurs following experimental ischemia.

3 : Circulation. 2005 May 3 ;111(17):2241-9. Epub 2005 Apr 25.

Tissue-type plasminogen activator crosses the intact blood-brain barrier by low-density lipoprotein receptor-related protein-mediated transcytosis.

Benchenane K, Berezowski V, Ali C, Fernandez-Monreal M, Lopez-Atalaya JP, Brillault J, Chuquet J, Nouvelot A, MacKenzie ET, Bu G, Cecchelli R, Touzani O, Vivien D.

INSERM-Avenir tPA in the working brain, Universite de Caen, GIP Cyceron, Caen, France.

BACKGROUND : Accumulating evidence demonstrates a critical involvement of tissue-type plasminogen activator (tPA) in pathological and physiological brain conditions. Determining whether and how vascular tPA can cross the blood-brain barrier (BBB) to enter the brain is thus important, not only during stroke but also in physiological conditions. METHODS AND RESULTS : In the present work, we provide evidence in vivo that intravenous injection of tPA increases NMDA-induced striatal lesion in the absence of BBB leakage. Accordingly, we show that tPA crosses the BBB both after excitotoxic lesion and in control conditions. Indeed, vascular injected tPA can be detected within the brain parenchyma and in the cerebrospinal fluid. By using an in vitro model of BBB, we have confirmed that tPA can cross the intact BBB. Its passage was blocked at 4 degrees C, was saturable, and was independent of its proteolytic activity. We have shown that tPA crosses the BBB by transcytosis, mediated by a member of the LDL receptor-related protein family. CONCLUSIONS : We demonstrate that blood-derived tPA can reach the brain parenchyma without alteration of the BBB. The molecular mechanism of the passage of tPA from blood to brain described here could represent an interesting target to improve thrombolysis in stroke.

4 : Stroke. 2005 May ;36(5):1065-70. Epub 2005 Apr 7.

Oxygen glucose deprivation switches the transport of tPA across the blood-brain barrier from an LRP-dependent to an increased LRP-independent process.

Benchenane K, Berezowski V, Fernandez-Monreal M, Brillault J, Valable S, Dehouck MP, Cecchelli R, Vivien D, Touzani O, Ali C.

INSERM-Avenir, Centre Cyceron, Universite de Caen, France.

BACKGROUND AND PURPOSE : Despite uncontroversial benefit from its thrombolytic activity, the documented neurotoxic effect of tissue plasminogen activator (tPA) raises an important issue : the current emergency stroke treatment might not be optimum if exogenous tPA can enter the brain and thus add to the deleterious effects of endogenous tPA within the cerebral parenchyma. Here, we aimed at determining whether vascular tPA crosses the blood-brain barrier (BBB) during cerebral ischemia, and if so, by which mechanism. METHODS : First, BBB permeability was assessed in vivo by measuring Evans Blue extravasation following intravenous injection at 0 or 3 hours after middle cerebral artery electrocoagulation in mice. Second, the passage of vascular tPA was investigated in an in vitro model of BBB, subjected or not to oxygen and glucose deprivation (OGD). RESULTS : We first demonstrated that after focal permanent ischemia in mice, the BBB remains impermeable to Evans Blue in the early phase (relative to the therapeutic window of tPA), whereas at later time points massive Evans Blue extravasation occurs. Then, the passage of tPA during these 2 phases, was investigated in vitro and we show that in control conditions, tPA crosses the intact BBB by a low-density lipoprotein (LDL) receptor-related protein (LRP)-dependent transcytosis, whereas OGD leads to an exacerbation of tPA passage, which switches to a LRP-independent process. CONCLUSIONS : We evidence 2 different mechanisms through which vascular tPA can reach the brain parenchyma, depending on the state of the BBB. As discussed, these data show the importance of taking the side effects of blood-derived tPA into account and offer a basis to improve the current thrombolytic strategy.

5 : J Biol Chem. 2005 Jul 1 ;280(26):24941-7. Epub 2005 Mar 29.

Akt-dependent expression of NAIP-1 protects neurons against amyloid-beta toxicity.

Lesne S, Gabriel C, Nelson DA, White E, Mackenzie ET, Vivien D, Buisson A.

UMR CNRS 6185, Universite de Caen, Bd. H. Becquerel BP5229, 14074 Caen, France and Howard Hughes Medical Institute, Rutgers University, Piscataway, New Jersey 08854, USA.

Neurotrophins are a family of growth factors that attenuate several forms of pathological neuronal cell death and may represent a putative therapeutic approach to neurodegenerative diseases. In Alzheimer disease, amyloid-beta (Abeta) is thought to play a central role in the neuronal death occurring in brains of patients. In the present study, we evaluate the ability of neurotrophin-3 (NT-3) to protect neurons against the toxicity induced by aggregated Abeta. We showed that in primary cultures of cortical neurons, NT-3 reduces Abeta-induced apoptosis by limiting caspase-8, caspase-9, and caspase-3 cleavage. This neuroprotective effect of NT-3 was concomitant to an increased level of Akt phosphorylation and was abolished by an inhibitor of the phosphatidylinositol-3 kinase (PI-3K), LY294002. In parallel, NT-3 treatment reduced Abeta induced caspase-3 processing to control levels. In an attempt to link PI-3K/Akt to caspase inhibition, we evaluated the influence of the PI-3K/Akt axis on the expression of a member of the inhibitors of apoptosis proteins (IAPs), the neuronal apoptosis inhibitory protein-1. We demonstrated that NT-3 induces an up-regulation of neuronal apoptosis inhibitory protein-1 expression in neurons that promotes the inhibition of Abeta-induced neuronal apoptosis. Together, these findings demonstrate that NT-3 signaling counters Abeta-dependent neuronal cell death and may represent an innovative therapeutic intervention to limit neuronal death in Alzheimer disease.

6 : J Cereb Blood Flow Metab. 2004 Oct ;24(10):1153-9.

2,7-Bis-(4-amidinobenzylidene)-cycloheptan-1-one dihydrochloride, tPA stop, prevents tPA-enhanced excitotoxicity both in vitro and in vivo.

Liot G, Benchenane K, Leveille F, Lopez-Atalaya JP, Fernandez-Monreal M, Ruocco A, Mackenzie ET, Buisson A, Ali C, Vivien D.

Universite de Caen, Center Cyceron, Caen Cedex, France.

Tissue-type plasminogen activator (tPA) is available for the treatment of thromboembolic stroke in humans. However, adverse effects of tPA have been observed in animal models of ischemic brain injuries. In the present study, we have used a synthetic tPA inhibitor, named 2,7-bis-(4-amidino-benzylidene)-cycloheptan-1-one dihydrochloride (tPA stop), to investigate the role of endogenous tPA in the cerebral parenchyma. In mouse cortical cell cultures, we observed that although tPA stop reduced N-methyl-D-aspartic acid (NMDA)-mediated excitotoxic neuronal death, it failed to modulate alpha-amino-2,3-dihydro-5-methyl-3-oxo-4-isoxazole propanoic acid or kainate-mediated necrosis. In addition, we found that tPA stop could prevent the deleterious effects of both endogenous and exogenous tPA during NMDA exposure. At the functional level, tPA stop was found to prevent tPA-dependent potentiation of NMDA receptor-evoked calcium influx. The relevance of those findings was strengthened by the observation of a massive reduction of NMDA-induced excitotoxic lesion in rats when tPA stop was co-injected. Altogether, these data demonstrate that the blockade of the endogenous proteolytic activity of tPA in the cerebral parenchyma could be a powerful neuroprotective strategy raised against brain pathologies associated with excitotoxicity.

7 : J Biol Chem. 2004 Dec 3 ;279(49):50850-6. Epub 2004 Sep 23.

Arginine 260 of the amino-terminal domain of NR1 subunit is critical for tissue-type plasminogen activator-mediated enhancement of N-methyl-D-aspartate receptor signaling.

Fernandez-Monreal M, Lopez-Atalaya JP, Benchenane K, Cacquevel M, Dulin F, Le Caer JP, Rossier J, Jarrige AC, Mackenzie ET, Colloc’h N, Ali C, Vivien D.

CNRS UMR 6185, University of Caen, Centre Cyceron, Bd. Henri Becquerel, BP 5229, 14074, Caen, France.

Tissue-type plasminogen activator (tPA) has been involved in both physiological and pathological glutamatergic-dependent processes, such as synaptic plasticity, seizure, trauma, and stroke. In a previous study, we have shown that the proteolytic activity of tPA enhances the N-methyl-D-aspartate (NMDA) receptor-mediated signaling in neurons (Nicole, O., Docagne, F., Ali, C., Margaill, I., Carmeliet, P., MacKenzie, E. T., Vivien, D., and Buisson, A. (2001) Nat. Med. 7, 59-64). Here, we show that tPA forms a direct complex with the amino-terminal domain (ATD) of the NR1 subunit of the NMDA receptor and cleaves this subunit at the arginine 260. Furthermore, point mutation analyses show that arginine 260 is necessary for both tPA-induced cleavage of the ATD of NR1 and tPA-induced potentiation of NMDA receptor signaling. Thus, tPA is the first binding protein described so far to interact with the ATD of NR1 and to modulate the NMDA receptor function.

PMID : 15448144 [PubMed - indexed for MEDLINE]

8 : Curr Drug Targets. 2004 Aug ;5(6):529-34.

Cytokines in neuroinflammation and Alzheimer’s disease.

Cacquevel M, Lebeurrier N, Cheenne S, Vivien D.

University, of CAEN, UMR CNRS 6185, Centre Cyceron, Bd. Henri Becquerel, BP 5229, 14047, Caen, France.

Inflammation has been reported in numerous neurodegenerative disorders such as Parkinson’s disease, stroke and Alzheimer’s disease (AD). In AD, the inflammatory response is mainly located to the vicinity of amyloid plaques. Cytokines, such as Interleukin-1 (IL-1), Interleukin-6 (IL-6), Tumor Necrosis Factor alpha (TNF-alpha) and Transforminng Growth Factor beta (TGF-beta) have been clearly involved in this inflammatory process. Although their expression is induced by the presence of amyloid-beta peptide, these cytokines are also able to promote the accumulation of amyloid-beta peptide. Altogether, IL-1, IL-6, TNF-alpha and TGF-beta should be considered as key players of a vicious circle leading to the progression of the disease.

9 : Expert Opin Ther Targets. 2004 Aug ;8(4):309-20.

The complexity of tissue-type plasminogen activator : can serine protease inhibitors help in stroke management ?

Lebeurrier N, Vivien D, Ali C.

Universite de Caen, UMR-CNRS 6185, Caen, France.

Stroke, the third leading cause of death in industrialised countries, represents a major burden on healthcare authorities. The elucidation of molecular events sustaining infarct evolution in experimental models has allowed the development of putative therapeutic agents. However, despite marked benefits in animals, most of them have failed in clinical trials. At present, the only approved therapy for stroke is early reperfusion by intravenous injection of the thrombolytic agent, tissue-type plasminogen activator (tPA). tPA-dependent thrombolysis sometimes promotes haemorrhage, but improves neurological outcome in a great proportion of patients, provided it is performed within the recommended therapeutic window. In addition to the benefit of tPA injection in the vascular compartment, this endogenously produced serine protease could also promote excitotoxic processes within the cerebral parenchyma. This article reviews the various aspects of tPA during stroke, and discusses potential improvements to current clinical management, with a particular emphasis on targeting the deleterious actions of tPA through endogenous serine protease inhibitors (serpins).

10 : Biochem J. 2004 Oct 15 ;383(Pt 2):393-9.

Sp1 and Smad transcription factors co-operate to mediate TGF-beta-dependent activation of amyloid-beta precursor protein gene transcription.

Docagne F, Gabriel C, Lebeurrier N, Lesne S, Hommet Y, Plawinski L, Mackenzie ET, Vivien D.

UMR CNRS 6185, Bd H. Becquerel, BP 5229, 14074 Caen Cedex, France. docagne

Abnormal deposition of Abeta (amyloid-beta peptide) is one of the hallmarks of AD (Alzheimer’s disease). This peptide results from the processing and cleavage of its precursor protein, APP (amyloid-beta precursor protein). We have demonstrated previously that TGF-beta (transforming growth factor-beta), which is overexpressed in AD patients, is capable of enhancing the synthesis of APP by astrocytes by a transcriptional mechanism leading to the accumulation of Abeta. In the present study, we aimed at further characterization of the molecular mechanisms sustaining this TGF-beta-dependent transcriptional activity. We report the following findings : first, TGF-beta is capable of inducing the transcriptional activity of a reporter gene construct corresponding to the +54/+74 region of the APP promoter, named APP(TRE) (APP TGF-beta-responsive element) ; secondly, although this effect is mediated by a transduction pathway involving Smad3 (signalling mother against decapentaplegic peptide 3) and Smad4, Smad2 or other Smads failed to induce the activity of APP(TRE). We also observed that the APP(TRE) sequence not only responds to the Smad3 transcription factor, but also the Sp1 (signal protein 1) transcription factor co-operates with Smads to potentiate the TGF-beta-dependent activation of APP. TGF-beta signalling induces the formation of nuclear complexes composed of Sp1, Smad3 and Smad4. Overall, the present study gives new insights for a better understanding of the fine molecular mechanisms occurring at the transcriptional level and regulating TGF-beta-dependent transcription. In the context of AD, our results provide additional evidence for a key role for TGF-beta in the regulation of Abeta production.

11 : Exp Neurol. 2004 May ;187(1):38-46.

Neurotrophin-3-induced PI-3 kinase/Akt signaling rescues cortical neurons from apoptosis.

Liot G, Gabriel C, Cacquevel M, Ali C, MacKenzie ET, Buisson A, Vivien D.

Universite de Caen, CNRS UMR 6551, Centre CYCERON, IFR 47, 14074 Caen Cedex, France.

A number of cytokines including neurotrophins have been tested for their neuroprotective activity against different paradigms of neuronal death. However, as for neurotrophin-3 (NT-3), their mechanisms of action have not been fully identified. By using cultures of mouse cortical neurons, we have investigated the molecular mechanisms by which neurotrophin-3 could protect cortical neurons against apoptosis. In a model of caspase-dependent apoptosis leading to the recruitment of active initiators caspase-8 and -9 and of executioner caspase-3, we have evidenced that NT-3 displayed an anti-apoptotic effect in a dose-dependent manner. First, we showed that, in cultured cortical neurons, NT-3 could promote extracellular signal-regulated protein kinase/mitogen-activated protein kinase (ERK/MAPK) and phosphatidylinositol-3’ (PI-3) kinase/Akt phosphorylation. Second, we showed that although the blockade of the Akt pathway prevented the anti-apoptotic effect of NT-3, blockade of the ERK pathway did not. Altogether, our data demonstrate that NT-3 displayed an anti-apoptotic effect on cultured cortical neurons through a mechanism involving the recruitment of the PI-3 kinase/Akt signaling pathway.

12 : Mol Cell Neurosci. 2004 Apr ;25(4):594-601.

Is tissue-type plasminogen activator a neuromodulator ?

Fernandez-Monreal M, Lopez-Atalaya JP, Benchenane K, Leveille F, Cacquevel M, Plawinski L, MacKenzie ET, Bu G, Buisson A, Vivien D.

University of Caen, CNRS, 14047, Caen, France.

In the last few years, it has been evidenced that serine proteases play key roles in the mammalian brain, both in physiological and pathological conditions. It has been well established that among these serine proteases, the tissue-type plasminogen activator (t-PA) is critically involved in development, plasticity, and pathology of the nervous system. However, its mechanism of action remains to be further investigated. By using pharmacological and immunological approaches, we have evidenced in the present work that t-PA should be considered as a neuromodulator. Indeed, we have observed that : (i). neuronal depolarization induces a release of t-PA ; (ii). this release of t-PA is sensitive to exocytosis inhibition and calcium chelation ; (iii). released t-PA modulates NMDA receptor signaling and (iv). astrocytes are able to recapture extracellular t-PA through a low-density lipoprotein (LDL) receptor-related protein (LRP)-dependent mechanism.

13 : Trends Neurosci. 2004 Mar ;27(3):155-60.

Equivocal roles of tissue-type plasminogen activator in stroke-induced injury.

Benchenane K, Lopez-Atalaya JP, Fernandez-Monreal M, Touzani O, Vivien D.

Universite de Caen, CNRS UMR 6551, Centre Cyceron, IFR 47, Boulevard H. Becquerel, BP 5229, 14074 CAEN Cedex, France.

Stroke represents a major health problem in the ever-ageing population of industrialized nations. Each year, over three million people in the USA alone suffer from this affliction. Stroke, which results from the obstruction of an intra- or extra-cerebral artery, induces irreversible neuronal damage. The clot-busting drug tissue-type plasminogen activator (tPA) is the only FDA-approved therapy for acute stroke. Although tPA has been successfully used to treat myocardial infarction due to clot formation, its use in the treatment of occlusive cerebrovascular diseases remains controversial. Indeed, tPA is clearly beneficial as a thrombolytic agent. However, increasing evidence suggests that tPA could have direct and deleterious effects on neurons and glial cells.

14 : Cell Mol Neurobiol. 2003 Oct ;23(4-5):539-50.

Transforming growth factor-beta and ischemic brain injury.

Buisson A, Lesne S, Docagne F, Ali C, Nicole O, MacKenzie ET, Vivien D.

Universite de CAEN, UMR CNRS 6551, IFR 47, Feder, Centre CYCERON, bd H. Becquerel, Caen, France.

1. Necrosis and apoptosis are the two fundamental hallmarks of neuronal death in stroke. Nevertheless, thrombolysis, by using the recombinant serine protease t-PA, remains until now the only approved treatment of stroke in man. 2. Over the last years, the cytokine termed Transforming Growth Factor-beta1 (TGF-beta1) has been found to be strongly up-regulated in the central nervous system following ischemia-induced brain damage. 3. Recent studies have shown a neuroprotective activity of TGF-beta1 against ischemia-induced neuronal death. In vitro, TGF-beta1 protects neurons against excitotoxicity by inhibiting the t-PA-potentiated NMDA-induced neuronal death through a mechanism involving the up-regulation of the type-1 plasminogen activator inhibitor (PAI-1) in astrocytes 4. In addition, TGF-beta1 has been recently characterized as an antiapoptotic factor in a model of staurosporine-induced neuronal death through a mechanism involving activation of the extracellular signal-regulated kinase 1/2 (Erk1/2) and a concomitant increase phosphorylation of the antiapoptotic protein Bad. 5. Altogether, these observations suggest that either TGF-beta signaling or TGF-beta1-modulated genes could be good targets for the development of new therapeutic strategies for stroke in man.

15 : J Soc Biol. 2003 ;197(2):145-50. [Does transforming growth factor-beta (TGF-beta) act as a neuroprotective agent in cerebral ischemia ?]

[Article in French]

Docagne F, Ali C, Lesne S, Nicole O, MacKenzie ET, Buisson A, Vivien D.

Universite de CAEN, CNRS UMR 6551, IFR 47, Centre CYCERON, bd H. Becquerel, BP 5229, 14074 CAEN, France.

Necrosis and apoptosis are the two fundamental hallmarks of neuronal death in stroke. Nevertheless, thrombolysis, by means of the recombinant serine protease t-PA, remains until now the only approved treatment of stroke in man. Over the last years, the cytokine termed Transforming Growth Factor-beta 1 (TGF-beta 1) has been found to be strongly up regulated in the central nervous system following ischemia-induced brain damage. Recent studies have shown a neuroprotective activity of TGF-beta 1 against ischemia-induced neuronal death. In vitro, TGF-beta 1 protects neurons against excitotoxicity by inhibiting the t-PA-potentiated NMDA-induced neuronal death through a mechanism involving the up-regulation of the type-1 plasminogen activator inhibitor (PAI-1) in astrocytes. Altogether, these observations suggest that either TGF-beta signaling or TGF-beta 1-modulated genes could be good targets for the development of new therapeutic strategies for stroke in man.

16 : J Biol Chem. 2003 May 16 ;278(20):18408-18. Epub 2003 Mar 7.

Transforming growth factor-beta 1 potentiates amyloid-beta generation in astrocytes and in transgenic mice.

Lesne S, Docagne F, Gabriel C, Liot G, Lahiri DK, Buee L, Plawinski L, Delacourte A, MacKenzie ET, Buisson A, Vivien D.

Unite Mixte de Recherche (UMR) CNRS 6551, IFR47, Universite de Caen, Cyceron, Caen Cedex 14074, France.

Accumulation of the amyloid-beta peptide (Abeta) in the brain is crucial for development of Alzheimer’s disease. Expression of transforming growth factor-beta1 (TGF-beta1), an immunosuppressive cytokine, has been correlated in vivo with Abeta accumulation in transgenic mice and recently with Abeta clearance by activated microglia. Here, we demonstrate that TGF-beta1 drives the production of Abeta40/42 by astrocytes leading to Abeta production in TGF-beta1 transgenic mice. First, TGF-beta1 induces the overexpression of the amyloid precursor protein (APP) in astrocytes but not in neurons, involving a highly conserved TGF-beta1-responsive element in the 5’-untranslated region (+54/+74) of the APP promoter. Second, we demonstrated an increased release of soluble APP-beta which led to TGF-beta1-induced Abeta generation in both murine and human astrocytes. These results demonstrate that TGF-beta1 potentiates Abeta production in human astrocytes and may enhance the formation of plaques burden in the brain of Alzheimer’s disease patients.

17 : FASEB J. 2003 Mar ;17(3):443-5. Epub 2003 Jan 2.

Angiopoietin-1-induced PI3-kinase activation prevents neuronal apoptosis.

Valable S, Bellail A, Lesne S, Liot G, Mackenzie ET, Vivien D, Bernaudin M, Petit E.

Universite de Caen, UMR 6551-CNRS, IFR 47, Centre Cyceron, Bd H. Becquerel, BP 5229, 14074 Caen cedex, France.

Although angiopoietin-1 (Ang-1) is recognized as an endothelial growth factor, its presence in brain following an ischemic event suggests a role in the evolution of neuronal damage. Using primary neuronal cultures, we showed that neurons express Ang-1 and possess the functional angiopoietin-receptor Tie-2, which is phosphorylated in the presence of Ang-1. We further investigated in vitro whether Ang-1 could protect neurons against either excitotoxic necrosis or apoptosis induced by serum deprivation (SD). A neuroprotective effect for Ang-1 was detected exclusively in the apoptotic paradigm. Treatment of cells with the phosphatidyl-inositol 3-kinase (PI3-K) inhibitor, LY294002, inhibited Ang-1-induced phosphorylation of Akt, restored the cleavage of the effector caspase-3, and reduced the protective effect of Ang-1 against SD-induced toxicity. These findings suggest that Ang-1 has a neuroprotective effect against apoptotic stress and that this effect is dependent on the PI3-K/Akt pathway and inhibition of caspase-3 cleavage. This study provides evidence that Ang-1 is not just angiogenic but also neuroprotective. The understanding of neuroprotective mechanisms induced by Ang-1 may promote strategies based on the pleiotropic effects of angiogenic factors. Such approaches could be useful for the treatment of brain diseases in which both neuronal death and angiogenesis are involved.

18 : Mol Cell Neurosci. 2002 Dec ;21(4):634-44.

Smad3-dependent induction of plasminogen activator inhibitor-1 in astrocytes mediates neuroprotective activity of transforming growth factor-beta 1 against NMDA-induced necrosis.

Docagne F, Nicole O, Gabriel C, Fernandez-Monreal M, Lesne S, Ali C, Plawinski L, Carmeliet P, MacKenzie ET, Buisson A, Vivien D.

Universite de Caen, CNRS UMR 6551, Bd H. Becquerel, B.P. 5229, 14074 Caen Cedex, France.

The intravenous injection of the serine protease, tissue-type plasminogen activator (t-PA), has shown to benefit stroke patients by promoting early reperfusion. However, it has recently been suggested that t-PA activity, in the cerebral parenchyma, may also potentiate excitotoxic neuronal death. The present study has dealt with the role of the t-PA inhibitor, PAI-1, in the neuroprotective activity of the cytokine TGF-beta1 and focused on the transduction pathway involved in this effect. We demonstrated that PAI-1, produced by astrocytes, mediates the neuroprotective activity of TGF-beta 1 against N-methyl-D-aspartate (NMDA) receptor-mediated excitotoxicity. This t-PA inhibitor, PAI-1, protected neurons against NMDA-induced neuronal death by modulating the NMDA-evoked calcium influx. Finally, we showed that the activation of the Smad3-dependent transduction pathway mediates the TGF-beta-induced up-regulation of PAI-1 and subsequent neuroprotection. Overall, this study underlines the critical role of the t-PA/PAI-1 axis in the regulation of glutamatergic neurotransmission.

19 : FASEB J. 2003 Feb ;17(2):277-9. Epub 2002 Dec 17.

Transforming growth factor alpha-induced expression of type 1 plasminogen activator inhibitor in astrocytes rescues neurons from excitotoxicity.

Gabriel C, Ali C, Lesne S, Fernandez-Monreal M, Docagne F, Plawinski L, MacKenzie ET, Buisson A, Vivien D.

Universite de CAEN, UMR CNRS 6551, IFR 47, Centre CYCERON, Bd H. Becquerel, BP 5229, 14074 CAEN Cedex, France.

Although transforming growth factor (TGF)-alpha, a member of the epidermal growth factor (EGF) family, has been shown to protect neurons against excitotoxic and ischemic brain injuries, its mechanism of action remains unknown. In the present study, we used in vitro models of apoptotic or necrotic paradigms demonstrating that TGF-alpha rescues neurons from N-methyl-D-aspartate (NMDA)-induced excitotoxic death, with the obligatory presence of astrocytes. Because neuronal tissue-type plasminogen activator (t-PA) release was shown to potentiate NMDA-induced excitotoxicity, we observed that TGF-alpha treatment reduced NMDA-induced increase of t-PA activity in mixed cultures of neurons and astrocytes. In addition, we showed that although TGF-alpha induces activation of the extracellular signal-regulated kinases (ERKs) in astrocytes, it failed to activate p42/p44 in neurons. Finally, we showed that TGF-alpha, by an ERK-dependent mechanism, stimulates the astrocytic expression of PAI-1, a t-PA inhibitor, which mediates the neuroprotective activity of TGF-alpha against NMDA-mediated excitotoxic neuronal death. Taken together, we indicate that TGF-alpha rescues neurons from NMDA-induced excitotoxicity in mixed cultures through inhibition of t-PA activity, involving PAI-1 overexpression by an ERK-dependent pathway in astrocytes.

20 : J Cereb Blood Flow Metab. 2002 Oct ;22(10):1165-9.

Matching gene expression with hypometabolism after cerebral ischemia in the nonhuman primate.

Chuquet J, Benchenane K, Liot G, Fernandez-Monreal M, Toutain J, Blanchet S, Eveno E, Auffray C, Pietu G, Buisson A, Touzani O, MacKenzie ET, Vivien D.

UMR CNRS 6551, University of Caen, IFR-47, Center Cyceron, Caen, France.

To correlate brain metabolic status with the molecular events during cerebral ischemia, a cDNA array was performed after positron emission tomography scanning in a model of focal cerebral ischemia in baboons. Cluster analysis for the expression of 74 genes allowed the identification of 4 groups of genes. In each of the distinct groups, the authors observed a marked inflection in the pattern of gene expression when the CMRo was reduced by 48% to 66%. These patterns of coordinated modifications in gene expression could define molecular checkpoints for the development of an ischemic infarct and a molecular definition of the penumbra.

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