The role of excitatory amino acid transporters in neuroprotection and neuropathology

Glutamate is the most abundant excitatory neurotransmitter found within the CNS. Glutamate has been shown to play a prominent role in development, plasticity, learning and memory. Sodium dependent glutamate transporters (EAAT1-5) facilitate termination of glutamate signaling. Altered expression profiles and function of these transporters have been shown to promote neurodegradation and have been implicated in multiple disease states, including amyotrophic lateral sclerosis (ALS), Alzheimer's disease, stroke, and epilepsy. The two studies detailed in this dissertation investigate the role of EAAT2 and EAAC1 (EAAT3) in neuroprotection and neuropathology.; Excitatory amino acid transporter 2 (EAAT2) is responsible for up to 90% of all glutamate uptake and is primarily localized on astrocytes. Many studies have attempted to elevate EAAT2 expression to compensate for loss of function and expression in disease. The aim of this study was to isolate and characterize the contribution of increased astrocytic EAAT2 expression towards neuroprotection. A novel recombinant adeno-associated virus, rAAV1-GFAP-EAAT2, was designed and used to selectively increase astrocytic EAAT2 expression. Under conditions of oxygen glucose deprivation, elevated astrocytic EAAT2 expression was shown to offer neuroprotection. This approach offers the first evidence supporting sole regulation of EAAT2 expression in astrocytes and the specific role of this transporter in neuroprotection.; Excitatory amino acid carrier 1 (EAAC1) is present throughout the CNS with a small percentage being uniquely expressed on inhibitory presynaptic terminals and provides a primary source of glutamate for GABA synthesis. Alterations to this or other pathways leading to GABA synthesis, may result in abnormal inhibitory synaptic transmission, neuronal hyperexcitability and epileptiform activity. Prior studies have shown GABA synthesis and signaling were reduced and seizure-like behaviors were heightened under global pharmacological inhibition or antisense knockdown of EAAC1. We hypothesized that increased GABAergic EAAC1 expression would enhance GABA synthesis, shift seizure susceptibility, and promote neuroprotection. Using recombinant adeno-associated virus vectors, we were able to specifically target transgene delivery to GABAergic neurons and direct over-expression and knockdown of EAAC1 in vivo. Modulation of GABAergic EAAC1 expression resulted in alterations in GABA synthesis, seizure susceptibility and neuroprotection.