The proteolytic activity of tissue-plasminogen activator enhances NMDA receptor-mediated signaling

Abstract

Tissue-plasminogen activator (t-PA) is now available for the treatment of thrombo-embolic stroke but adverse effects have been reported in some patients, particularly hemorrhaging. In contrast, the results of animal studies have indicated that t-PA could increase neuronal damage after focal cerebral ischemia. Here we report for the first time that t-PA potentiates signaling mediated by glutamatergic receptors by modifying the properties of the N-methyl-D-aspartate (NMDA) receptor. When depolarized, cortical neurons release bio-active t-PA that interacts with and cleaves the NR1 subunit of the NMDA receptor. Moreover, the treatment with recombinant t-PA leads to a 37% increase in NMDA-stimulated fura-2 fluorescence, which may reflect an increased NMDA-receptor function. These results were confirmed in vivo by the intrastriatal injection of recombinant-PA, which potentiated the excitotoxic lesions induced by NMDA. These data provide insight into the regulation of NMDA-receptor-mediated signaling and could initiate therapeutic strategies to improve the efficacy of t-PA treatment in man.

Nitric oxide mediates neurodegeneration and breakdown of the blood-brain barrier in tPA-dependent excitotoxic injury in mice

“…We explored two possibilities as mechanisms through which tPA might promote nNOS activation. The first was based on reports that tPA can cleave the NR1 subunit of the NMDA receptor (NMDAR), leading to potentiated signaling (Nicole et al, 2001), and that NMDAR signaling Journal of Cell Science 119 (2) activates nNOS (Garthwaite et al, 1989). To examine this potential pathway, we injected 1 mg/kg of the NMDAR antagonist MK-801 30 minutes prior to KA injection and found that inhibition of NMDAR signaling blocked NOS activation (Fig.…”

“…tPA functions through both proteolytic and non-proteolytic pathways (Tsirka et al, 1997;Rogove et al, 1999;Nicole et al, 2001;Melchor et al, 2003). To determine whether tPA activity is crucial for the increase in NOS activity, we pharmacologically inhibited tPA in wild-type mice prior to the injection of KA using the synthetic tPA inhibitor tPA Stop, which successfully prevented the increase in NOS activity (Fig.…”

“…These receptors generate excitatory signals following glutamate stimulation. It has been reported that tPA can directly interact with the NMDAR and cleave the NR1 subunit, thus allowing for an increase in the influx of Ca 2+ (Nicole et al, 2001). Since nNOS activation leads to the production of NO (Bredt and Snyder, 1990), and nNOS is closely linked to the NMDAR, it is possible that the interaction of tPA with the NMDAR can result in the production of NO.…”

Induction of the Wnt Antagonist, Dickkopf-1, Contributes to the Development of Neuronal Death in Models of Brain Focal Ischemia

“…However, the narrow time window (3-6 h after stroke) and the risk of hemorrhagic complications limit the use of tissue plasminogen activator to a minority of patients with stroke (Heuschmann et al, 2004). In addition, animal studies suggest that tissue plasminogen activator paradoxically enhances neuronal death by cleaving and activating N-methyl-D-aspartic acid receptors and matrix metalloproteinases (Nicole et al, 2001). The use of neuroprotective agents may help to overcome these limitations, thus improving the neurologic outcome in ischemic patients.…”

Comment optimiser l’utilisation du tPA ?

“…En effet, le tPA est exprimé non seulement par les cellules endothéliales vasculaires [2], mais également par des cellules du cerveau, dont les neurones qui peuvent le libérer par un processus d'exocytose [3]. Cet effet délétère du tPA endogène dans le parenchyme cérébral a été confirmé par plusieurs auteurs [4,5], suscitant le doute dans la communauté scientifique, les effets bénéfiques de la thrombolyse pouvant être limités ou masqués par les conséquen-ces délétères. Si la plupart des études basées sur un modèle thrombotique ont confirmé que l'injection intraveineuse du tPA a un effet de protection du cerveau parce qu'il facilite la reperfusion [6], d'autres études, utilisant les modèles mécaniques d'occlusion de l'artère céré-brale moyenne et ne prenant pas en compte la composante vasculaire du tPA, ont clairement montré un renforcement des dommages isché-miques.…”