Common and divergent pathways in early stages of glutamate and tau-mediated toxicities in neurodegeneration

It has been shown that excitotoxicity and tau-mediated toxicities are major contributing factors to neuronal death in Alzheimer's disease (AD). The excitatory amino acid transporter 2 (EAAT2 or GLT-1), the major glutamate transporter in the brain that regulates glutamate levels synaptically and extrasynaptically, has been shown to be deficient in AD brains, leading to excitotoxicity and subsequent cell death. Similarly, buildup of neurofibrillary tangles, which consist of hyperphosphorylated tau protein, correlates with cognitive decline and neuronal atrophy in AD. However, common genes and pathways that are critical in the aforementioned toxicities have not been well elucidated. To investigate the impact of glutamate dyshomeostasis and tau accumulation on translational profiles of affected hippocampal neurons, we used mouse models of excitotoxicity and tau–mediated toxicities (GLT-1^−/− and P301S, respectively) in conjunction with BAC-TRAP technology. Our data show that GLT-1 deficiency in CA3 pyramidal neurons leads to translational signatures characterized by dysregulation of pathways associated with synaptic plasticity and neuronal survival, while the P301S mutation induces changes in endocytic pathways and mitochondrial dysfunction. Finally, the commonly dysregulated pathways include impaired ion homeostasis and metabolic pathways. These common pathways may shed light on potential therapeutic targets for ameliorating glutamate and tau-mediated toxicities in AD.