NMDA receptor subunit composition determines beta-amyloid-induced neurodegeneration and synaptic loss

Aggregates of amyloid-beta (A beta) and tau are hallmarks of Alzheimer's disease (AD) leading to neurodegeneration and synaptic loss. While increasing evidence suggests that inhibition of N-methyl-D-aspartate receptors (NMDARs) may mitigate certain aspects of AD neuropathology, the precise role of different NMDAR subtypes for A beta- and tau-mediated toxicity remains to be elucidated. Using mouse organotypic hippocampal slice cultures from arcA beta transgenic mice combined with Sindbis virus-mediated expression of human wild-type tau protein (hTau), we show that A beta caused dendritic spine loss independently of tau. However, the presence of hTau was required for A beta-induced cell death accompanied by increased hTau phosphorylation. Inhibition of NR2B-containing NMDARs abolished A beta-induced hTau phosphorylation and toxicity by preventing GSK-3 beta activation but did not affect dendritic spine loss. Inversely, NR2A-containing NMDAR inhibition as well as NR2A-subunit knockout diminished dendritic spine loss but not the A beta effect on hTau. Activation of extrasynaptic NMDARs in primary neurons caused degeneration of hTau-expressing neurons, which could be prevented by NR2B-NMDAR inhibition but not by NR2A knockout. Furthermore, caspase-3 activity was increased in arcA beta transgenic cultures. Activity was reduced by NR2A knockout but not by NR2B inhibition. Accordingly, caspase-3 inhibition abolished spine loss but not hTau-dependent toxicity in arcA beta transgenic slice cultures. Our data show that A beta induces dendritic spine loss via a pathway involving NR2A-containing NMDARs and active caspase-3 whereas activation of eSyn NR2B-containing NMDARs is required for hTau-dependent neurodegeneration, independent of caspase-3. Cell Death and Disease (2013) 4, e608; doi:10.1038/cddis.2013.129; published online 25 April 2013