Biomedical subjects

Karim Benchenane

Publications and source records attributed to Karim Benchenane.

9 recordsLinked to original sources

PubMed2006

Tissue-type plasminogen activator rescues neurones from serum deprivation-induced apoptosis through a mechanism independent of its proteolytic activity.

Although the mechanism of action of tissue-type plasminogen 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.

Analysis of Variance↗

PubMed2005

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

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.

Animals↗

PubMed2005

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

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.

Animals↗

PubMed2004

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.

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.

Alanine↗

PubMed2004

Is tissue-type plasminogen activator a neuromodulator?

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.

Action Potentials↗

PubMed2004

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

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.

Animals↗

PubMed2004

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

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.

Animals↗

PubMed2002

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

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.

Animals↗

PubMed2002

Selective blockade of endothelin-B receptors exacerbates ischemic brain damage in the rat.

BACKGROUND AND PURPOSE: Endothelins act through 2 receptors, namely, ET(A) and ET(B). In the cerebral circulation, ET(A) mediates marked and prolonged vasoconstriction, and its blockade increases cerebral blood flow (CBF) and reduces ischemic brain damage. However, the role of ET(B) receptors remains unclear. In this study we examined, in rats, the kinetics of expression of ET(B) and the effects of ET(B) blockade on changes in CBF and brain damage after focal cerebral ischemia and N-methyl-D-aspartate (NMDA)-induced excitotoxic injury. METHODS: Rats were subjected to transient (60 minutes) focal cerebral ischemia or cortical injection of NMDA. The selective ET(B) antagonist BQ-788 was injected intracerebroventricularly 30 minutes before and 30 minutes after the onset of ischemia. Cortical perfusion was monitored by laser-Doppler flowmetry. The volume of infarction or NMDA-induced cortical lesion was assessed at 24 hours after the insult. The reverse transcription-polymerase chain reaction technique was used to assess ET(B) expression. RESULTS: Cerebral ischemia failed to alter the expression of ET(B) mRNA in both acute and chronic stages. Administration of BQ-788 resulted in an increase in infarction volume (178%; P<0.05) accompanied by a decrease in residual CBF (-26.7% versus control; P<0.01). In these animals we found a positive correlation between the volume of infarction and the severity of the decrease in CBF. NMDA-induced cortical lesions were not affected by the administration of BQ-788. CONCLUSIONS: Our results suggest that the ET(B) antagonist BQ-788 induces deleterious effects that are mediated by the reduction of residual blood flow after ischemia and argue that the optimal therapeutic strategy in stroke would be to target the use of selective ET(A) antagonists and not mixed ET(A)/ET(B) antagonists.

Animals↗