Editing for an AMPA receptor subunit RNA in prefrontal cortex and striatum in Alzheimer's disease, Huntington's disease and schizophrenia

Abstract

Animal studies and cell culture experiments demonstrated that posttranscriptional editing of the transcript of the GluR-2 gene, resulting in substitution of an arginine for glutamine in the second transmembrane region (TM II) of the expressed protein, is associated with a reduction in Ca 2+ permeability of the receptor channel. Thus, disturbances in GluR-2 RNA editing with alteration of intracellular Ca 2+ homeostasis could lead to neuronal dysfunction and even neuronal degeneration. The present study determined the proportions of edited and unedited GluR-2 RNA in the prefrontal cortex of brains from patients with Alzheimer's disease, in the striatum of brains from patients with Huntington's disease, and in the same areas of brains from age-matched schizophrenics and controls, by using reverse transcriptase-polymerase chain reaction, restriction endonuclease digestion, gel electrophoresis and scintillation radiometry. In the prefrontal cortex of controls, < 0.1% of all GluR-2 RNA molecules were unedited and *> 99.9% were edited; in the prefrontal cortex both of schizophrenics and of Alzheimer's patients ∼ 1.0% of all GluR-2 RNA molecules were unedited and 99% were edited. In the striatum of controls and of schizophrenics, ∼ 0.5% of GluR-2 RNA molecules were unedited and 99.5% were edited; in the striatum of Huntington's patients nearly 5.0% of GluR-2 RNA was unedited. In the prefrontal white matter of controls, ∼ 7.0% of GluR-2 RNA was unedited. In the normal human prefrontal cortex and striatum, the large majority of GluR-2 RNA molecules contains a CGG codon for arginine in the TMII coding region; this implies that the corresponding AMPA receptors have a low Ca 2+ permeability, as previously demonstrated for the rat brain. The process of GluR-2 RNA editing is compromised in a region-specific manner in schizophrenia, in Alzheimer's disease and Huntington's Chorea although in each of these disorders there is still a large excess of edited GluR-2 RNA molecules. Disturbances of GluR-2 RNA editing leading to excessive Ca 2+ permeability, may contribute to neuronal dysfunction in schizophrenia and to neuronal death in Alzheimer's disease and Huntington's disease.