Targeting NMDA Receptor Pathways in Alzheimer's Disease, From Cellular Mechanisms to Treatment Strategies.
The Alzheimer's Disease (AD) lacks effective disease-modifying therapy, even though amyloid-targeting immunotherapies have recently been applied clinically. N-methyl-D-Aspartate Receptors (NMDARs) play a central yet mechanistically complicated role in the pathophysiology of AD, where they are convergence points of amyloid-beta (Aβ) oligomer toxicity, tau-dependent excitotoxicity, and progressive synaptic failure. This critical review examines NMDAR dysfunction across the AD spectrum, with a focus on subunit-regulated signalling, subcellular localisation, and subsequent pathological cascades. The effects of Aβ oligomers on NMDAR activity involve multiple mechanisms that disrupt their function, including glutamate dysregulation mediated by GLT-1, redistribution of GluN2B to extrasynaptic areas, and inhibition of JAK2-CREB via activation of extrasynaptic receptors. Tau enhances excitotoxic injury throughdendritic mislocalization, and the tau-Fyn-GluN2B complex, which propels pro-death signalling by DAPK1. This conceptually important prevailing synaptic-extrasynaptic dichotomy is fiercely criticised here, given evidence that synaptic receptors containing GluN2A also mediate pathological signalling during sustained Aß exposure, and that tri-heteromeric receptor populations are problematic for subunit-selective targeting. Neuroinflammation, dysfunction of the blood-brain barrier, and excitotoxic amplification via GluN2C/D-enriched receptor pools in neurons, astrocytes, microglia, oligodendrocytes, and endothelial cells are underexplored therapeutic targets for neurodegenerative disease (non-neuronal NMDARs). Memantine is the only approved NMDAR-targeting agent for AD. Subunit-selective antagonists have not been translated into clinical use, and the positive allosteric modulator dalzanemdor (SAGE-718) did not pass its randomised Phase 2 trial in 2024. The most mechanistically justified approach is to advance subunit-selective, compartment-specific, or protein-complexdisrupting strategies. Although it is not established whether any single NMDAR-targeting intervention will suffice as a disease-modifying therapy, the convergence of molecular, genetic, and clinical evidence positions NMDAR dysfunction as a tractable , if therapeutically demanding , node in the AD pathogenic network, warranting continued, mechanism-informed drug discovery.