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This project was supported by the Region Basse-Normandie and the AXA postdoctoral fellowship program, the INSERM, and the university of Caen. We thank Mr Gilbert Pigree and Mr Maxime Lemarchand for their help with the production of radioactive tPA (IMOGERE platform, University of Caen, France). Thanks to Dr Mario Gonzalez-Gronow for the gift of recombinant Grp78; International audience; The unfolded protein response (UPR) is an endoplasmic reticulum (ER)-related stress conserved pathway that aims to protect cells from being overwhelmed. However, when prolonged, UPR activation converts to a death signal, which relies on its PERK-eIF2α branch. Overactivation of the UPR has been implicated in many neurological diseases, including cerebral ischaemia. Here, by using an in vivo thromboembolic model of stroke on transgenic ER stress-reporter mice and neuronal in vitro models of ischaemia, we demonstrate that ischaemic stress leads to the deleterious activation of the PERK branch of the UPR. Moreover, we show that the serine protease tissue-type plasminogen activator (tPA) can bind to cell surface Grp78 (78 kD glucose-regulated protein), leading to a decrease of the PERK pathway activation, thus a decrease of the deleterious factor CHOP, and finally promotes neuroprotection. Altogether, this work highlights a new role and a therapeutic potential of the chaperone protein Grp78 as a membrane receptor of tPA capable to prevent from ER stress overactivation.

Summary Although recent technical advances in thrombectomy have revolutionised acute stroke treatment, prevalence of disability and death related to stroke remain high. Therefore, plasminogen activators—eukaryotic, bacterial, or engineered forms that can promote fibrinolysis by converting plasminogen into active plasmin and facilitate clot breakdown—are still commonly used in the acute treatment of ischaemic stroke. Hence, plasminogen activators have become a crucial area for clinical investigation for their ability to recanalise occluded arteries in ischaemic stroke and to accelerate haematoma clearance in haemorrhagic stroke. However, inconsistent results, insufficient evidence of efficacy, or reports of side-effects in trial settings might reduce the use of plasminogen activators in clinical practice. Additionally, the mechanism of action for plasminogen activators could extend beyond the vessel lumen and involve plasminogen-independent processes, which would suggest that plasminogen activators have also non-fibrinolytic roles. Understanding the complex mechanisms of action of plasminogen activators can guide future directions for therapeutic interventions in patients with stroke.

Worldwide, ischaemic stroke is a major cause of death and the leading cause of acquired disability. To date, pharmacological thrombolysis with tissue-type plasminogen activator (alone or with mechanical thrombectomy) remains the gold standard acute treatment for ischaemic stroke. Many strategies of neuroprotection have been tested in the past, but none has ever succeeded in clinical trials. Accumulating evidence suggests that stroke activates the endoplasmic reticulum (ER) stress response, which likely deleteriously contribute to stroke damages. However, this remains to be clearly established. In the present chapter, we provide a snapshot on ER stress in ischaemic stroke, and intend to show that knowledge on ER stress in ischaemic context affecting other organs than the brain can provide interesting therapeutic avenues for neuroprotection.

Familial encephalopathy with neuroserpin inclusion bodies (FENIB) is a conformational proteinopathy characterised by neuronal inclusion bodies composed of the serine protease inhibitor (SERPIN), neuroserpin. Presenting clinically as a familial dementia-epilepsy syndrome, the molecular mechanism of the pathogenic abnormalities in neuroserpin has been characterised at atomic resolution. There is a remarkable genotype-phenotype correlation between the degree of molecular destabilisation of the several variants of the neuroserpin protein, their propensity to self-associate and the age of onset of the dementia-epilepsy complex. As with other serpinopathies there appears to be a mix of cell-autonomous toxicity, due to neuronal accumulation of neuroserpin, and non-cell autonomous toxicity, caused by loss of protease inhibition, in this case the dysregulated protease is likely to be tissue plasminogen activator (tPA). FENIB should be considered in cases of progressive myoclonic epilepsy and dementia particularly where there is family history of neuropsychiatric disease.

International audience; In humans, spatial cognition and navigation impairments are a frequent situation during physiological and pathological aging, leading to a dramatic deterioration in the quality of life. Despite the discovery of neurons with location-specific activity in rodents, that is, place cells in the hippocampus and later on grid cells in the entorhinal cortex (EC), the molecular mechanisms underlying spatial cognition are still poorly known. Our present data bring together in an unusual combination 2 molecules of primary biological importance: a major neuronal excitatory receptor, N-methyl-D-aspartate receptor (NMDAR), and an extracellular protease, tissue plasminogen activator (tPA), in the control of spatial navigation. By using tPA-deficient mice and a structure-selective pharmacological approach, we demonstrate that the tPA-dependent NMDAR signaling potentiation in the EC plays a key and selective role in the encoding and the subsequent use of distant landmarks during spatial learning. We also demonstrate that this novel function of tPA in the EC is reduced during aging. Overall, these results argue for the concept that encoding of proximal versus distal landmarks is mediated not only by different anatomical pathways but also by different molecular mechanisms, with the tPA-dependent potentiation of NMDAR signaling in the EC that plays an important role.

International audience; Reverse transcription quantitative-polymerase chain reaction (RT-qPCR) has become a routine method in many laboratories. Normalization of data from experimental conditions is critical for data processing and is usually achieved by the use of a single reference gene. Nevertheless, as pointed by the Minimum Information for Publication of Quantitative Real-Time PCR Experiments (MIQE) guidelines, several reference genes should be used for reliable normalization. Ageing is a physiological process that results in a decline of many expressed genes. Reliable normalization of RT-qPCR data becomes crucial when studying ageing. Here, we propose a RT-qPCR study from four mouse brain regions (cortex, hippocampus, striatum and cerebellum) at different ages (from 8 weeks to 22 months) in which we studied the expression of nine commonly used reference genes. With the use of two different algorithms, we found that all brain structures need at least two genes for a good normalization step. We propose specific pairs of gene for efficient data normalization in the four brain regions studied. These results underline the importance of reliable reference genes for specific brain regions in ageing.

Summary In conformational diseases, native protein conformers convert to pathological intermediates that polymerize. Structural characterization of these key intermediates is challenging. They are unstable and minimally populated in dynamic equilibria that may be perturbed by many analytical techniques. We have characterized a forme fruste deficiency variant of α1-antitrypsin (Lys154Asn) that forms polymers recapitulating the conformer-specific neo-epitope observed in polymers that form in vivo. Lys154Asn α1-antitrypsin populates an intermediate ensemble along the polymerization pathway at physiological temperatures. Nuclear magnetic resonance spectroscopy was used to report the structural and dynamic changes associated with this. Our data highlight an interaction network likely to regulate conformational change and do not support the recent contention that the disease-relevant intermediate is substantially unfolded. Conformational disease intermediates may best be defined using powerful but minimally perturbing techniques, mild disease mutants, and physiological conditions., Highlights ► An α1-antitrypsin deficiency mutant is a forme fruste model for the Z variant ► NMR spectroscopic and ion-mobility mass spectrometric characterization of the mutant ► Residue-specific discrimination of disease-relevant and denaturant-induced ensembles ► A “clasp” motif caps a network of stabilizing interactions in α1-antitrypsin

J. Neurochem. (2011) 119, 920–931. Abstract Pituitary adenylate cyclase-activating polypeptide (PACAP) and tissue plasminogen activator (tPA) play important roles in neuronal migration and survival. However, a direct link between the neurotrophic effects of PACAP and tPA has never been investigated. In this study, we show that, in PC12 cells, PACAP induced a 9.85-fold increase in tPA gene expression through activation of the protein kinase A- and protein kinase C-dependent signaling pathways. In immature cerebellar granule neurons (CGN), PACAP stimulated tPA mRNA expression and release of proteolytically active tPA. Immunocytochemical labeling revealed the presence of tPA in the cytoplasm and processes of cultured CGN. The inhibitory effect of PACAP on CGN motility was not affected by the tPA substrate plasminogen or the tPA inhibitor plasminogen activator inhibitor-1. In contrast, plasminogen activator inhibitor-1 significantly reduced the stimulatory effect of PACAP on CGN survival. Altogether, these data indicate that tPA gene expression is activated by PACAP in both tumoral and normal neuronal cells. The present study also demonstrates that PACAP stimulates the release of tPA which promotes CGN survival by a mechanism dependent of its proteolytic activity.

Background and Purpose— Tissue-type plasminogen activator (tPA) is the only drug approved for the acute treatment of ischemic stroke but with two faces in the disease: beneficial fibrinolysis in the vasculature and damaging effects on the neurovascular unit and brain parenchyma. To improve this profile, we developed a novel strategy, relying on antibodies targeting the proneurotoxic effects of tPA. Methods— After production and characterization of antibodies (αATD-NR1) that specifically prevent the interaction of tPA with the ATD-NR1 of N-methyl- d -aspartate receptors, we have evaluated their efficacy in a model of murine thromboembolic stroke with or without recombinant tPA-induced reperfusion, coupled to MRI, near-infrared fluorescence imaging, and behavior assessments. Results— In vitro, αATD-NR1 prevented the proexcitotoxic effect of tPA without altering N-methyl- d -aspartate-induced neurotransmission. In vivo, after a single administration alone or with late recombinant tPA-induced thrombolysis, antibodies dramatically reduced brain injuries and blood–brain barrier leakage, thus improving long-term neurological outcome. Conclusions— Our strategy limits ischemic damages and extends the therapeutic window of tPA-driven thrombolysis. Thus, the prospect of this immunotherapy is an extension of the range of treatable patients.

Members of the serine protease inhibitor (serpin) superfamily are found in all branches of life and play an important role in the regulation of enzymes involved in proteolytic cascades. Mutants of the serpins result in a delay in folding, with unstable intermediates being cleared by endoplasmic reticulum-associated degradation. The remaining protein is either fully folded and secreted or retained as ordered polymers within the endoplasmic reticulum of the cell of synthesis. This results in a group of diseases termed the serpinopathies, which are typified by mutations of a1-antitrypsin and neuroserpin in association with cirrhosis and the dementia familial encephalopathy with neuroserpin inclusion bodies, respectively. Current evidence strongly suggests that polymers of mutants of a1-antitrypsin and neuroserpin are linked by the sequential insertion of the reactive loop of one molecule into b-sheet A of another. The ordered structure of the polymers within the endoplasmic reticulum stimulates nuclear factor-kappa B by a pathway that is independent of the unfolded protein response. This chronic activation of nuclear factor-kappa B may contribute to the cell toxicity associated with mutations of the serpins. We review the pathobiology of the serpinopathies and the development of novel therapeutic strategies for treating the inclusions that cause disease. These include the use of small molecules to block polymerization, stimulation of autophagy to clear inclusions and stem cell technology to correct the underlying molecular defect.

Few data are available on the involvement of brain microvascular endothelial cells (BMECs) in excitotoxic neonatal brain lesions. Therefore, we developed an original approach for investigating mouse-derived BMECs in vitro. We hypothesized that newborn and adult BMEC cultures would show age-related differences in phenotype and sensitivity to glutamate. Expression of the monocarboxylate transporter, MCT1, was higher in neonatal than in adult BMECs, whereas expression of the glucose transporter, GLUT1, was higher in adult than in neonatal BMECs that overexpressed the N-methyl-D-aspartate receptor NR1 subunit (NMDAR1) compared with adult BMECs. The ability of neonatal and adult BMECs to be activated by glutamate was confirmed through intracellular calcium ([Ca2+]i) recording. The glutamate-induced [Ca2+]i increase was blocked by the selective NMDAR antagonist, MK-801. Significant glutamate-evoked concentration-dependent release of tissue-type plasminogen activator (t-PA) and matrix metalloproteinases (MMPs) activities was found in supernatants of neonatal, but not in adult BMECs. The glutamate-mediated release of t-PA, MMP-2, and MMP-9 proteolytic activities in neonatal BMECs was blocked by MK-801. Conceivably, this protease release from neonatal BMECs may participate in neonatal brain lesions.

Background and Purpose— Desmoteplase, a recombinant form of the plasminogen activator DSPAα1 from Desmodus rotundus , may offer improved clinical benefits for acute ischemic stroke treatment over the current therapy, recombinant tissue plasminogen activator (rtPA). Accumulating evidence suggests that clinical use of rtPA could be limited by unfavorable properties, including its ability to cross the blood–brain barrier (BBB), thus potentially adding to the pro-excitotoxic effect of endogenous tPA in cerebral parenchyma. Here, to investigate whether desmoteplase may display a safer profile than the structurally-related tPA, both agents were compared for their ability to cross the BBB and promote neurotoxicity. Methods— First, the passage of vascular DSPA and rtPA was investigated in vitro in a model of BBB, subjected or not to oxygen and glucose deprivation. Second, we studied DSPA- and rtPA-mediated effects in an in vivo paradigm of excitotoxic necrosis. Results— The rtPA and desmoteplase cross the intact BBB by LRP-mediated transcytosis. Under conditions of oxygen and glucose deprivation, translocation rates of both compounds increased; however, unlike rtPA, desmoteplase transport remained LRP-dependent. Additionally, neither intracerebral nor intravenous desmoteplase administration enhanced NMDA-induced excitotoxic striatal damage in vivo. Interestingly, intravenous but not intrastriatal coadministration of desmoteplase and rtPA reduced the pro-excitotoxic effect of rtPA. Conclusions— We show that desmoteplase crosses the BBB but does not promote neuronal death. Moreover, intravenous administration of desmoteplase antagonizes the neurotoxicity induced by vascular rtPA. This action may be caused by competition of desmoteplase with rtPA for LRP binding at the BBB, thus effectively blocking rtPA access to the brain parenchyma.

International audience; Fine-tuning of NMDA glutamatergic receptor signalling strategically controls crucial brain functions. This process depends on several ligands and modulators, one of which unexpectedly includes the serine protease tissue-type plasminogen activator (tPA). In vitro, tPA increases NMDA-receptor-mediated calcium influx by interacting with, and then cleaving, the NR1 subunit within its N-terminal domain. Owing to lack of in vivo evidence of the relevance and contribution of this mechanism in physiological and pathological brain processes, active immunisation was developed here in mice, to allow transient and specific prevention of the interaction of tPA with the NR1 subunit. Immunisation significantly reduced the severity of ischemic and excitotoxic insults in the mouse brain. Cognitive function was altered in some, but not all behavioural tasks affected in tPA-deficient mice. Our data demonstrate that in vivo, tPA controls neurotoxicity and the encoding of novel spatial experiences by binding to and cleaving the NMDA receptor NR1 subunit. Interesting therapeutic possibilities for several brain pathologies that involve excitotoxicity may now be envisaged.

Serpins are well-known inhibitors of plasminogen activators, key components of fibrinolysis. Within the last decades, tissue-type plasminogen activator (tPA) became more than a fibrinolytic agent and has been demonstrated to be a neuromodulator with physiological and pathological roles within the brain. Indeed, tPA is involved in brain plasticity, learning and memory and development. But in a stroke context, tPA contributes to the increase of intraneuronal calcium, by interacting with the GluN1 subunit of the NMDA receptor, leading to an increase in excitotoxicity. It also promotes blood-brain barrier leakage and inflammation, but in certain conditions tPA can also exert beneficial effects in stroke.

International audience; Endoplasmic reticulum (ER) dysfunction is important in the pathogenesis of many neurological diseases. In this review, we examine the evidence for ER dysfunction in a range of neurological conditions including cerebral ischaemia, sleep apnoea, Alzheimer's disease, multiple sclerosis, amyotrophic lateral sclerosis, the prion diseases and Familial Encephalopathy with Neuroserpin Inclusion Bodies (FENIB). Protein misfolding in the endoplasmic reticulum initiates a well-studied 'Unfolded Protein Response' in energy-starved neurones during stroke that is relevant to the toxicity of reperfusion. The toxic peptide Aβ induces 'ER stress' in Alzheimer's disease leading to activation of similar pathways, while the accumulation of polymeric neuroserpin in the neuronal ER triggers a poorly understood 'ER overload response'. In other neurological disorders such as Parkinson's and Huntington's diseases ER dysfunction is well recognised but the mechanisms for this are less clear. By targeting components of these signalling responses, it may prove possible to ameliorate their toxic effects and treat a range of neurodegenerative conditions.

Alpha-1 antitrypsin (α1-AT) is the most abundant circulating protease inhibitor. The common severe Z allele of α1-AT (Glu342Lys) causes the protein to form ordered polymers that are retained within the endoplasmic reticulum of hepatocytes. These polymers form the periodic acid-Schiff positive inclusions that are associated with cirrhosis. The lack of circulating α1-AT predisposes the Z α1-AT homozygote to early onset emphysema. We review here the molecular basis of α1-AT deficiency and show how understanding the liver disease provides new insights in the pathobiology of the associated emphysema. The mechanism of α1-AT deficiency provides a paradigm for a wider group of conditions that we have termed the serpinopathies. We also examine the strategies that are being pursued to develop novel therapies for α1-AT deficiency. This review considers our understanding of the pathobiology of α1-AT deficiency and then illustrate the therapeutic possibilities that can ensue once we understand basic mechanisms of disease.

The serpinopathies result from point mutations in members of the serine protease inhibitor or serpin superfamily. They are characterized by the formation of ordered polymers that are retained within the cell of synthesis. This causes disease by a "toxic gain of function" from the accumulated protein and a "loss of function" as a result of the deficiency of inhibitors that control important proteolytic cascades. The serpinopathies are exemplified by the Z (Glu342Lys) mutant of α₁-antitrypsin that results in the retention of ordered polymers within the endoplasmic reticulum of hepatocytes. These polymers form the intracellular inclusions that are associated with neonatal hepatitis, cirrhosis, and hepatocellular carcinoma. A second example results from mutations in the neurone-specific serpin-neuroserpin to form ordered polymers that are retained as inclusions within subcortical neurones as Collins' bodies. These inclusions underlie the autosomal dominant dementia familial encephalopathy with neuroserpin inclusion bodies or FENIB. There are different pathways to polymer formation in vitro but not all form polymers that are relevant in vivo. It is therefore essential that protein-based structural studies are interpreted in the context of human samples and cell and animal models of disease. We describe here the biochemical techniques, monoclonal antibodies, cell biology, animal models, and stem cell technology that are useful to characterize the serpin polymers that form in vivo.

Members of the serine protease inhibitor (serpin) superfamily are found in all branches of life and play an important role in the regulation of enzymes involved in proteolytic cascades. Mutants of the serpins result in a delay in folding, with unstable intermediates being cleared by endoplasmic reticulum-associated degradation. The remaining protein is either fully folded and secreted or retained as ordered polymers within the endoplasmic reticulum of the cell of synthesis. This results in a group of diseases termed the serpinopathies, which are typified by mutations of α(1)-antitrypsin and neuroserpin in association with cirrhosis and the dementia familial encephalopathy with neuroserpin inclusion bodies, respectively. Current evidence strongly suggests that polymers of mutants of α(1)-antitrypsin and neuroserpin are linked by the sequential insertion of the reactive loop of one molecule into β-sheet A of another. The ordered structure of the polymers within the endoplasmic reticulum stimulates nuclear factor-kappa B by a pathway that is independent of the unfolded protein response. This chronic activation of nuclear factor-kappa B may contribute to the cell toxicity associated with mutations of the serpins. We review the pathobiology of the serpinopathies and the development of novel therapeutic strategies for treating the inclusions that cause disease. These include the use of small molecules to block polymerization, stimulation of autophagy to clear inclusions and stem cell technology to correct the underlying molecular defect.

International audience; Cessation of chronic ethanol consumption can increase the sensitivity of the brain to excitotoxic damages. Cannabinoids have been proposed as neuroprotectants in different models of neuronal injury, but their effect have never been investigated in a context of excitotoxicity after alcohol cessation. Here we examined the effects of the pharmacological activation/inhibition of the endocannabinoid system in an in vitro model of chronic ethanol exposure and withdrawal followed by an excitotoxic challenge. Ethanol withdrawal increased N-methyl-D-aspartate (NMDA)-evoked neuronal death, probably by altering the ratio between GluN2A and GluN2B NMDA receptor subunits. The stimulation of the endocannabinoid system with the cannabinoid agonist HU-210 decreased NMDA-induced neuronal death exclusively in ethanol-withdrawn neurons. This neuroprotection could be explained by a decrease in NMDA-stimulated calcium influx after the administration of HU-210, found exclusively in ethanol-withdrawn neurons. By contrast, the inhibition of the cannabinoid system with the CB1 receptor antagonist rimonabant (SR141716) during ethanol withdrawal increased death of ethanol-withdrawn neurons without any modification of NMDA-stimulated calcium influx. Moreover, chronic administration of rimonabant increased NMDA-stimulated toxicity not only in withdrawn neurons, but also in control neurons. In summary, we show for the first time that the stimulation of the endocannabinoid system is protective against the hyperexcitability developed during alcohol withdrawal. By contrast, the blockade of the endocannabinoid system is highly counterproductive during alcohol withdrawal.

International audience; Owing to its ability to generate the clot-dissolving protease plasmin, tissue plasminogen activator (tPA) is the only approved drug for the acute treatment of ischemic stroke. However, tPA also promotes hemorrhagic transformation and excitotoxic events. High mobility group box-1 protein (HMGB-1) is a non-histone transcription factor and a pro-inflammatory cytokine, which has also been shown to bind to both tPA and plasminogen. We thus investigated the cellular and molecular effects through which HMGB-1 could influence the vascular and parenchymal effects of tPA during ischemia. We demonstrate that HMGB-1 not only increases clot lysis by tPA, but also reduces the passage of vascular tPA across the blood-brain barrier, as well as tPA-driven leakage of the blood-brain barrier. In addition, HMGB-1 prevents the pro-neurotoxic effect of tPA, by blocking its interaction with N-methyl-D-aspartate (NMDA) receptors and the attendant potentiation of NMDA-induced neuronal Ca²⁺ influx. In conclusion, we show in vitro that HMGB-1 can promote the beneficial effects of tPA while counteracting its deleterious properties. We suggest that derivatives of HMGB-1, devoid of pro-inflammatory properties, could be used as adjunctive therapies to improve the overall benefit of tPA-mediated thrombolysis following stroke.

Neuroserpin is a member of the serine protease inhibitor or serpin superfamily of proteins. It is secreted by neurones and plays an important role in the regulation of tissue plasminogen activator at the synapse. Point mutations in the neuroserpin gene cause the autosomal dominant dementia familial encephalopathy with neuroserpin inclusion bodies or FENIB. This is one of a group of disorders caused by mutations in the serpins that are collectively known as the serpinopathies. Others include α(1)-antitrypsin deficiency and deficiency of C1 inhibitor, antithrombin and α(1)-antichymotrypsin. The serpinopathies are characterised by delays in protein folding and the retention of ordered polymers of the mutant serpin within the cell of synthesis. The clinical phenotype results from either a toxic gain of function from the inclusions or a loss of function, as there is insufficient protease inhibitor to regulate important proteolytic cascades. We describe here the methods required to characterise the polymerisation of neuroserpin and draw parallels with the polymerisation of α(1)-antitrypsin. It is important to recognise that the conditions in which experiments are performed will have a major effect on the findings. For example, incubation of monomeric serpins with guanidine or urea will produce polymers that are not found in vivo. The characterisation of the pathological polymers requires heating of the folded protein or alternatively the assessment of ordered polymers from cell and animal models of disease or from the tissues of humans who carry the mutation.

PPACK-Desmodus rotundus salivary plasminogen activator (cDSPAα1) prevents the passage of tissuetype plasminogen activator (rt-PA) across the blood-brain barrier and neurotoxicity

International audience; Recombinant tissue-type plasminogen activator (tPA) is the fibrinolytic drug of choice to treat stroke patients. However, a growing body of evidence indicates that besides its beneficial thrombolytic role, tPA can also have a deleterious effect on the ischaemic brain. Although ageing influences stroke incidence, complications and outcome, age-dependent relationships between endogenous tPA and stroke injuries have not been investigated yet. Here, we report that ageing is associated with a selective lowering of brain tPA expression in the murine brain. Moreover, our results show that albumin D site-binding protein (DBP) as a key age-associated regulator of the neuronal transcription of tPA. Additionally, inhibition of DBP-mediated tPA expression confers in vitro neuroprotection. Accordingly, reduced levels of tPA in old mice are associated with smaller excitotoxic/ischaemic injuries and protection of the permeability of the neurovascular unit during cerebral ischaemia. Likewise, we provide neuroradiological evidence indicating the existence of an inverse relationship between age and the volume of the ischaemic lesion in patients with acute ischaemic stroke. Together, these results indicate that the relationship among DBP, tPA and ageing play an important role in the outcome of cerebral ischaemia.

The autosomal dominant dementia familial encephalopathy with neuroserpin inclusion bodies is characterized by the accumulation of ordered polymers of mutant neuroserpin within the endoplasmic reticulum of neurones. We show here that intracellular neuroserpin polymers activate NF-kappaB by a pathway that is independent of the IRE1, ATF6, and PERK limbs of the canonical unfolded protein response but is dependent on intracellular calcium. This pathway provides a mechanism for cells to sense and react to the accumulation of folded structures of mutant serpins within the endoplasmic reticulum. Our results provide strong support for the endoplasmic reticulum overload response being independent of the unfolded protein response.

International audience; NXY-059, a polar compound with limited transport across the blood-brain barrier, has demonstrated neuroprotection in several animal models of acute ischemic stroke but failed to confirm clinical benefit in the second phase III trial (SAINT-II). To improve the understanding of the mechanisms responsible for its neuroprotective action in preclinical models a series of experiments was carried out in an in vitro blood-brain barrier (BBB) model. A clinically attainable concentration of 250 μmol/L of NXY-059 administered at the onset or up to 4 h after oxygen glucose deprivation (OGD) produced a significant reduction in the increased BBB permeability caused by OGD. Furthermore, OGD produced a huge influx of tissue plasminogen activator across the BBB, which was substantially reduced by NXY-059. This study suggests that the neuroprotective effects of NXY-059 preclinically, may at least in part be attributed to its ability to restore functionality of the brain endothelium.

International audience; Thrombolysis with tissue-type plasminogen activator (tPA) is used for the treatment of patients with acute ischemic stroke. However, a growing body of evidence indicates that, besides the unquestionable benefit from its thrombolytic activity, tPA also has a deleterious effect on the ischemic brain including cytotoxicity and increased permeability of the neurovascular unit with the development of cerebral edema. Because an increasing number of acute stroke patients are treated with tPA, it is important to know the mechanisms of harmful effects of tPA on the ischemic brain. Here, the best studied pathways of tPA neurotoxicity are discussed along with future directions for a safer use of tPA as a thrombolytic agent in the setting of acute ischemic stroke. Overview The World Health Organization (WHO; www.who.int) defines stroke as 'rapidly developing clinical signs of focal (or global) disturbance of cerebral function, with symptoms lasting 24 h or longer or leading to death, with no apparent cause other than that of vascular origin'. Stroke might be classified as either ischemic or hemorrhagic. Ischemic stroke is a leading cause of disability and the third cause of mortality after heart disease and cancer (American Heart Association report, 2008, www.americanheart.org), accounting for 5.5 million deaths worldwide, two-thirds of which are in developing countries [1]. Additionally, each year millions of ischemic stroke survivors have to adapt to a life with restrictions in the activities of daily living, and many of them depend on other people's support to survive. Three approaches have been investigated for the treatment of patients with acute ischemic stroke: neuroprotec-tion, thrombolysis and mechanical removal of the clot. In contrast to neuroprotection, which has been largely unsuccessful , thrombolysis with tissue-type plasminogen activa-tor (tPA) [2] and mechanical removal of the clot [3,4] have been approved by the Food and Drug Administration (FDA; www.fda.gov) for the treatment of patients with acute ischemic stroke. In a study performed by the National Institute of Neurological Disorders and Stroke (NINDS; www.ninds.nih.gov), treatment with tPA within 3 h of the onset of symptoms of acute ischemic stroke resulted in an 11–13% absolute increase in the number of patients with good outcome and in a reduction in the proportion of patients severely disabled or dead at 3 months [2]. Based on these results, intravenous tPA is currently the standard of care for patients with acute ischemic stroke presenting within 3 h of onset of the ischemic event. By contrast, there is a growing body of evidence indicating that tPA also has a deleterious effect in the ischemic brain. Indeed, in the NINDS study the use of tPA was associated with a 10-fold increase in the incidence of intracerebral hemorrhage, which had a 60% mortality [2]. Likewise, animal studies have demonstrated that either genetic deficiency of tPA [5,6] or inhibition of tPA with neuroserpin [7] results in a decrease in the volume of the ischemic lesion after experimental occlusion of the middle cerebral artery. Taken together, these studies indicate a pleiotropic role for tPA in the ischemic brain that is highly dependent of the compartment whereupon tPA acts (intravascular versus extravascular). Here, we review both the beneficial and deleterious effects of tPA in the ischemic brain and discusses potential approaches to improve the treatment of patients with acute ischemic stroke.

Current thrombolytic therapy for acute ischemic stroke with tissue-type plasminogen activator (tPA) has clear global benefits. Nevertheless, evidences argue that in addition to its prohemorrhagic effect, tPA might enhance excitotoxic necrosis. In the brain parenchyma, tPA, by binding to and then cleaving the amino-terminal domain (ATD) of the NR1 subunit of N-methyl-D-aspartate (NMDA) glutamate receptors, increases calcium influx to toxic levels. We show here that tPA binds the ATD of the NR1 subunit by a two-sites system (KD=24 nmol/L). Although tenecteplase (TNK) and reteplase also display two-sites binding profiles, the catalytically inactive mutant TNKS478A displays a one-site binding profile and desmoteplase (DSPA), a kringle 2 (K2) domain-free plasminogen activator derived from vampire bat, does not interact with NR1. Moreover, we show that in contrast to tPA, DSPA does not promote excitotoxicity. These findings, together with three-dimensional (3D) modeling, show that a critical step for interaction of tPA with NR1 is the binding of its K2 domain, followed by the binding of its catalytic domain, which in turn cleaves the NR1 subunit at its ATD, leading to a subsequent potentiation of NMDA-induced calcium influx and neurotoxicity. This could help design safer new generation thrombolytic agents for stroke treatment. © 2008 ISCBFM All rights reserved., This work was supported by grants from INSERM, the French Ministry of Research and Technology, the Regional Council of Lower Normandy, the Regional Platform for Cell Imaging of Upper Normandy, the Medical Research Foundation, the University of Caen, Fonds Europeéns de Développement Régional, the Paul Hamel Foundation, the Diagnosis in Molecular Imaging Program (FP6-project DiMI-LSHB-CT-2005-512146-), and PAION Deutschland GmbH.

International audience; Although the mechanism of action of tissue-type plasmino-gen activator (tPA) in excitotoxic necrosis is well documented , whether this serine protease can influence the apoptotic cascade remains a subject of debate. Here, we report that tPA protects cultured cortical neurones against apoptotic cell death induced by serum deprivation, an effect associated with a reduction of caspase-3 activation. Interestingly , blocking tPA proteolytic activity by either tPA stop or neuroserpin did not prevent this neuroprotection. Similarly , prevention of the interaction between tPA and its receptor low-density lipoprotein receptor-related protein (LRP) could not alter tPA anti-apoptotic activity. Interestingly , the survival-promoting effect of tPA was blocked by the phosphatidylinositol-3 (PI-3) kinase inhibitor, LY294002, but not by the mitogen-activated protein (MAP) kinase inhibitor, U0126. In conclusion, the present demonstration of an anti-apoptotic effect of tPA, independent of its enzymatic activity, reveals an additional level of complexity in our understanding of this critical mediator of brain physiology and pathology. Keywords: apoptosis, serine protease, serum deprivation, tissue-type plasminogen activator.