Cellular and molecular mechanisms that regulate EAAT4 - a neuronal glutamate transporter. (360G-Wellcome-077946_Z_05_Z)

Extracellular glutamate levels must be tightly regulated in order to prevent neurotoxicity but maintain normal neurotransmission and neurodevelopment. EAAT4 is the glutamate transporter that is predominantly expressed in the Purkinje cell neurons of the cerebellum. There are two aspects of its expression pattern that are critical for modulating glutamate levels. First, EAAT4 is concentrated at extrasynaptic sites enabling the amount of glutamate that escapes synapses to be tightly regulated. This is important for maintaining synapse specificity and accurate information processing within densely packed terminals. Secondly, a large number of functional transporter molecules are required at the cell surface for rapid clearance. The turnover time of transport is too slow for multiple cycles to account for the efficientuptake process.We have identified the first proteins (GTRAPs) that interact with the intracellular COOH-terminus of EAAT4 and positively modulate its cellsurface expression and uptake activity. We propose to study genetically modified mice lacking the GTRAP-b-spectrin gene in order to investigate the role of this protein in EAAT4 localisation/activity, glutamatergic neurotransmission, and Purkinje cell development and survival. We also proposeto elucidate what cellular mechanisms are involved in the membrane traffickingof EAAT4 by examining the role of endocytosis, protein phosphorylation and GTRAP binding in the regulation of cell surface expression. These studies may offer new insights into therapeutic avenues for neurological diseases initiated by or propagated by glutamate-mediated excitotoxicity