The long-term objective of this research is to characterize the developmental and regional expression of glutamate transport in the human central nervous system, leading to a better understanding of the role of glutamate transport in disorders of the developing brain. Glutamate transport is the major mechanism responsible for clearance of excitatory amino acids, and protects central neurons against excitotoxicity. Paradoxically, glutamate transporters also appear to be the source of toxic concentrations of extracellular glutamate that accumulate in hypoxia/ischemia. The glutamate transporter GLT1 (EAAT2 in the human) appears to be the most important in the forebrain. Although GLT1 has been thought to be primarily localized in astrocytes, we have recently found a splice variant (GLT1b) that is expressed in neurons. In addition, studies using embryonic rat neurons in culture suggest that GLT1 transport activity and protein expression are both regulated by neuronal activity. In this project, the goal is to characterize the developmental and regional expression of EAAT2 in the human brain, and to understand how this transporter is modulated. This information will be important because the locations in which glutamate transporters are heavily expressed are likely to be sites in which glutamatergic mechanisms are operating under normal circumstances, and potentially, excitotoxic mechanisms are operating during hypoxia/ischemia. The hypothesis motivating this project is that EAAT2 variant forms will show independent developmental and regional variation in the human brain and that their activity and expression will be regulated by different mechanisms.
The specific aims of this project are to: 1. Characterize the developmental and regional expression of EAAT2 mRNA in the human brain. 2. Characterize the developmental and regional expression of EAAT2 protein in the human brain. 3. Characterize the effect of neuronal activity on glutamate uptake by GLT1 and expression of GLT1a and GLT1b in rat embryonic neurons in culture. These studies will have important consequences for our understanding of the pathogenesis of periventricular leukomalacia, bilirubin encephalopathy, hypoxia/ischemia, epilepsy, and schizophrenia, as well as for our understanding of the effects in children of drugs that are used to treat these conditions.
