The acidic amino acid, glutamate, is the predominant excitatory neurotransmitter in the mammalian CNS. Although there are millimolar concentrations of this excitatory amino acid (EAA) in brain, extracellular concentrations are maintained in the nanomolar range to facilitate crisp synaptic transmission and to prevent excessive activation of receptors that can result in the death of neurons (or other cell types that express glutamate receptors). A family of Na+dependent high-affinity glutamate transporters is responsible for the regulation and clearance of extracellular EAAs. Over the last few years, we and others have developed evidence that the expression and activity of these transporters is quite plastic. In this competitive renewal, we wish to focus on two mechanisms that have the potential to spatially and temporally regulate transporter levels. Based on our preliminary data, we wish to pursue the hypothesis protein kinase C (PKC) causes ubiquitination, internalization, and degradation of the predominant forebrain glial glutamate transporter (called GLT-1 or EAAT2) (Aim I). Also based on our preliminary data, we wish to pursue the hypothesis that RNA for the predominant forebrain neuronal glutamate transporter (called EAAC1 or EAAT3) is targeted to dendrites, that this targeting is dependent upon portions of the 3'untranslated region, and that there is a pool of EAAC1 mRNA that is available for regulated translation (Aim II). Finally, based on our preliminary studies, we would like to pursue the hypothesis that both of these regulatory mechanisms are increased in the hippocampus of an animal model of temporal lobe epilepsy (Aim III).
Glutamate transporters normally prevent excessive activation of its receptors and the consequent cell death that can occur;this process of excitotoxicity is associated with several different acute and chronic neurologic diseases, including epilepsy. We propose to characterize two novel mechanisms that regulate transporter levels and determine how these mechanisms are altered in an animal model of temporal lobe epilepsy.
