Differential regulation of 5′ splice variants of the glutamate transporter EAAT2 in an in vivo model of chemical hypoxia induced by 3‐nitropropionic acid

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Abstract
Defective glutamate uptake has been implicated as a pathogenic event of neuronal damage related to cerebral ischemia and hypoxia. In several models of ischemia‐hypoxia, a reduced immunoreactivity and altered RNA expression of excitatory amino acid transporter 2 (EAAT2), the major excitatory amino acid transporter, have been reported. However, the gene regulation of EAAT2 under these conditions is incompletely understood. In this study, we investigated alternative splicing of EAAT2 in an in vivo mouse model of chemical hypoxia as induced by 3‐nitropropionic acid (3‐NP). The neurotoxin 3‐NP is an inhibitor of mitochondrial energy production. Furthermore, it is known to inhibit glutamate reuptake directly, representing at least one of the mechanisms responsible for 3‐NP‐induced neurodegeneration. Here we report an expression analysis of five known (mEAAT2/5UT1–5) and two novel (mEAAT2/5UT6, ‐7) 5′ splice variants of EAAT2 using semiquantitative PCR. The RNA expression was studied at 2, 12, 24, 48, and 72 hr and 7 days after 3‐NP administration. mEAAT2/5UT4 and mEAAT2/5UT5 were up‐regulated in the frontal cortex and down‐regulated in the hippocampus 12–72 hr after chemical hypoxia. In the cerebellum, there was an increased expression of mEAAT2/5UT4 and a down‐regulation of mEAAT2/5UT5. mEAAT2/5UT3 show a different regional expression pattern, being regulated in the cerebellum only. mEAAT2/5UT1–7 encoded distinct 5′ regulatory sequences, including conserved elements of translational control. It is easily conceivable that expression alterations of 5′ splice variants of EAAT2 are related to glutamate transporter malfunction after chemical hypoxia. Our findings contribute to the hypothesis that RNA splicing events can serve as a molecular mechanism of posthypoxic gene regulation.