Phosphorylation of tau at Y18, but not tau-fyn binding, is required for tau to modulate NMDA receptor-dependent excitotoxicity in primary neuronal culture

Abstract

BackgroundHyperexcitability of neuronal networks can lead to excessive release of the excitatory neurotransmitter glutamate, which in turn can cause neuronal damage by overactivating NMDA-type glutamate receptors and related signaling pathways. This process (excitotoxicity) has been implicated in the pathogenesis of many neurological conditions, ranging from childhood epilepsies to stroke and neurodegenerative disorders such as Alzheimer’s disease (AD). Reducing neuronal levels of the microtubule-associated protein tau counteracts network hyperexcitability of diverse causes, but whether this strategy can also diminish downstream excitotoxicity is less clear.MethodsWe established a cell-based assay to quantify excitotoxicity in primary cultures of mouse hippocampal neurons and investigated the role of tau in exicitotoxicity by modulating neuronal tau expression through genetic ablation or transduction with lentiviral vectors expressing anti-tau shRNA or constructs encoding wildtype versus mutant mouse tau.ResultsWe demonstrate that shRNA-mediated knockdown of tau reduces glutamate-induced, NMDA receptor-dependent Ca2+ influx and neurotoxicity in neurons from wildtype mice. Conversely, expression of wildtype mouse tau enhances Ca2+ influx and excitotoxicity in tau-deficient (Mapt −/−) neurons. Reconstituting tau expression in Mapt −/− neurons with mutant forms of tau reveals that the tau-related enhancement of Ca2+ influx and excitotoxicity depend on the phosphorylation of tau at tyrosine 18 (pY18), which is mediated by the tyrosine kinase Fyn. These effects are most evident at pathologically elevated concentrations of glutamate, do not involve GluN2B–containing NMDA receptors, and do not require binding of Fyn to tau’s major interacting PxxP motif or of tau to microtubules.ConclusionsAlthough tau has been implicated in diverse neurological diseases, its most pathogenic forms remain to be defined. Our study suggests that reducing the formation or level of pY18-tau can counteract excitotoxicity by diminishing NMDA receptor-dependent Ca2+ influx.Electronic supplementary materialThe online version of this article (doi:10.1186/s13024-017-0176-x) contains supplementary material, which is available to authorized users.

A peptide inhibitor of Tau-SH3 interactions ameliorates amyloid-β toxicity

“…Other Tau-SH3 interactions besides Tau-Fyn might also play a role. One recent report suggested that the Tau-Fyn interaction may not be critical for glutamate-induced excitotoxicity (32). This would not be inconsistent with the observations here, particularly because the mechanisms of Aβoand glutamateinduced toxicity are different.…”

Dendritic Tau in Alzheimer’s Disease

“…At the post-synapse, the tau/Fyn complex interacts with the PDZ (post-synaptic density, discs-large, zona occludens protein-1) domain protein PSD-95 (Ittner et al, 2010;Lopes et al, 2016; Mondragó n-Rodríguez et al, 2012), a key scaffolding protein for post-synaptic receptors (Kim and Sheng, 2004). While tau is essential for recruiting Fyn to the PSD-95 complex, it is the localized activity of Fyn that is critical for NMDAR-mediated excitotoxicity ( Figure 3A) (Ittner et al, 2010;Knox et al, 2014;Miyamoto et al, 2017). Several phosphorylation targets of Fyn may act in concert to regulate NMDAR-mediated excitotoxicity.…”

Activation of NMDA receptors mediated iron accumulation via modulating iron transporters in Parkinson's disease

“…NRs are glutamate receptors that mediate excitatory neurotransmission and participate in the regulation of many important physiologic functions in the brain (19). However, excessive activation of NRs has been implicated in the neuronal degeneration due to excitatory neurotoxicity (30,31). There are 3 subtypes of NRs: NR1, NR2, and NR3 (32).…”