Under normal physiological conditions, glutamate-mediated activation of excitatory receptors on neurons is transient. However, under pathological conditions, extracellular glutamate levels can become elevated, resulting in prolonged stimulation of the excitatory receptors, and leading to excitotoxic death of neurons. Five excitatory amino acid transporters (EAATs 1-5) play a key role in insuring that excitatory transmission is transient by rapidly clearing glutamate from synaptic clefts, and the extracellular environment. However, under certain pathological conditions, such as ischemia, reversal of these transporters may actually contribute to pathology and neuronal damage. Thus, glutamate transporters have the potential to promote either neuroprotection or neurodegeneration. Contradictions exist in the current literature in regards to the contribution that individual transporter isotypes provide towards neuroprotection or neurodegeneration in the context of excitotoxic injury. The model systems used to study glutamate transporters have been primarily limited to transporter inhibition. Pharmacological studies have successfully identified a number of glutamate analogs that globally inhibit glutamate transporters. Very few pharmacological agents have been identified which enhance glutamate transporter activity and none have the ability to discriminate between selected transporters in a cell type specific manner. In contrast, our preliminary data strongly suggests that the expression of individual transporter isotypes can be either inhibited or enhanced in a cell type specific manner by using recombinant Adeno-associated virus (AAV) vectors to deliver selected glutamate transporter genes in either the sense or antisense orientation, under the control of cell type specific promoters. However, we have observed that gene expression is limited to focal regions within the CNS following stereotactic delivery of AAV vectors. Our goal in this proposal is to rigorously test this tool and determine to what extent functional transporter expression can be modulated and further develop this method to provide global, cell type specific transporter gene distribution and expression in the CNS through intracerebral ventricular injection of P0 rat pups with novel AAV serotypes. Relevance The development of this viral based gene delivery method will provide a novel tool which will permit the examination of glutamate transporter function in a way that has not been previously possible. This approach will allow us to directly test critical hypotheses regarding how individual glutamate transporter isotypes contribute to neuroprotection or neuropathology in diseases and disorders such as stroke, epilepsy and ALS. The development of these tools will also provide a solid scientific basis for future translational research involving the cell type specific modulation of selected transporters as potential treatments for disorders involving an excitotoxic component. ? ?
| Weller, M L; Stone, I M; Goss, A et al. (2008) Selective overexpression of excitatory amino acid transporter 2 (EAAT2) in astrocytes enhances neuroprotection from moderate but not severe hypoxia-ischemia. Neuroscience 155:1204-11 |
