Expression of recombinant NMDA receptors in hippocampal neurons by adenoviral-mediated gene transfer

N-methyl-d-aspartate (NMDA) receptors have attracted a great deal of attention because they are intimately involved in brain development, synaptic plasticity and a variety of neurological disorders. The ability to artificially alter the properties of NMDA receptors in central nervous system (CNS) neurons would be useful for elucidating the physiological roles of these receptors. It would also raise the possibility of gene therapy of neurological diseases caused by malfunction of NMDA receptors. In this study, we constructed three recombinant adenoviruses encoding rat NMDA receptor subunit cDNAs, NMDAR1 (NR1), NMDAR2B (NR2B) and mutant NR1(N598R) in which the asparagine (N) site of the wild-type NR1 was replaced with arginine (R) by site-directed mutagenesis. PC12 cells co-infected with recombinant adenoviruses bearing NR1 and NR2B cDNAs expressed conventional NMDA receptors that were permeable to Ca2+ and sensitive to Mg2+, whereas those with viruses bearing NR1(N598R) and NR2B cDNAs expressed Ca2+-impermeable and Mg2+-insensitive receptors. When rat hippocampal neurons in culture were infected with NR1(N598R) and NR2B viruses, both Ca2+ permeability and Mg2+ sensitivity of NMDA receptors were markedly reduced in the infected neurons. Excitatory postsynaptic currents (EPSCs) mediated by NMDA receptors also became much less sensitive to Mg2+. Thus, the NR1(N598R)/NR2B receptors were more dominant than the native NMDA receptors in the infected neurons, and the former receptors introduced by the adenoviral vectors functioned as postsynaptic receptors. These results indicate that the functional properties of postsynaptic NMDA receptors can be manipulated by gene transfer technology using adenoviral vectors.