Anti-NR1 N-terminal-domain vaccination unmasks the crucial action of tPA on NMDA-receptor-mediated toxicity and spatial memory

Abstract

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.

NR2D-containing NMDA receptors mediate tissue plasminogen activator-promoted neuronal excitotoxicity

“…7 The interaction between tPA and the NR1 subunit was shown in vivo to be involved in both excitotoxic and memory paradigms in mice. 12 The intimate link between tPA and NMDAR is reinforced by other observations, such as the modulation of the phosphorylation state of the NR2B subunit of the NMDAR in conditions of chronic alcohol consumption and contextual fear conditioning 13,14 or the promotion of NMDAR-dependent extracellular signal-regulated kinase (Erk( 1 2 )) signalling in hippocampal neurons. 6,15 Thus, there is now accumulating evidence that tPA must be considered as a positive neuromodulator of NMDAR-mediated glutamatergic transmission.…”

“…[1][2][3] However, tPA not only activates plasminogen, but rather acts through several modalities 4 by interacting with the low-density lipoproteinrelated receptor protein (LRP), [5][6][7][8] annexin-II 9 or N-methyl-Daspartate receptors (NMDAR). 1,[10][11][12] These interactions mediate several potentially damaging effects of tPA, including potentiation of NMDAR-mediated signalling and excitotoxicity. 6,7,10 During excitotoxic conditions, tPA has been shown to promote NMDA-induced calcium influx in cortical neurons and subsequent neuronal death through the binding to and cleavage of the NR1 subunit of the NMDAR, either directly 10,11 or through the recruitment of LRP.…”

GluN2D Subunit-Containing NMDA Receptors Control Tissue Plasminogen Activator-Mediated Spatial Memory

“…For instance, tPA influences some brain functions and dysfunctions by activating plasminogen into plasmin and subsequent degradation of the extracellular matrix (Plow et al, 1995;Chen and Strickland 1997;Wu et al, 2000;Hu et al, 2006) or conversion of the precursor form of brain-derived neurotrophic factor (BDNF) to its mature form (Pang et al, 2004). tPA was also reported to mediate some of its effects through a direct interaction with the NMDA receptor (NMDAR) (Nicole et al, 2001;Benchenane et al, 2007).…”

Comment optimiser l’utilisation du tPA ?

“…En accord avec ces données, une stratégie d'immunothérapie in vivo avec des anticorps anti-NR1 cherchant à inhiber l'interaction du tPA avec NR1 réduit les dommages ischémiques chez la souris [11]. Conceptuellement, l'agent thrombolytique idéal devrait être un agent fibrinolytique efficace et « pur », exempt d'effets nocifs sur des cellules gliales ou neuronales et sur la barrière hémato-encéphalique.…”