[Death of motor neurons and molecular change of glutamate receptors in ALS].

AMPA receptor-mediated neuronal death is initiated by exaggerated Ca2+ influx through AMPA receptor channels, and the Ca2+ permeability of the AMPA receptor ion channel depends strongly upon the presence or absence in its composition of an edited GluR2 subunit whose glutamine (Q) residue is substituted by arginine (R) at the Q/R site due to RNA editing. The pivotal role of the RNA editing at the GluR2 Q/R site in neuronal death has been clearly demonstrated in animal experiments and its deficiency is a direct cause of neuronal death. We demonstrated that the editing efficiency at the GluR2 mRNA Q/R site varied greatly, from 0% to 100%, among the single motoneurons of each individual with ALS, whereas it remained 100% among those of normal controls. In addition, the editing efficiency was more than 99% in the cerebellar Purkinje cells of ALS, spinocerebellar degeneration and normal control groups. By contrast, there was no significant difference as to both the amount and the proportion to total GluRs mRNA of GluR2 mRNA between normal and ALS motoneurons. Thus, marked GluR2 underediting in ALS motoneurons occurs in a disease specific and region selective manner, and may be closely relevant to ALS etiology.