Suppressing aberrant GluN3A expression rescues NMDA receptor dysfunction, synapse loss and motor and cognitive decline in Huntington's disease models

Huntington's disease is caused by an expanded polyglutamine repeat in huntingtin (Htt), but the pathophysiological sequence of events that trigger synaptic failure and neuronal loss are not fully understood. Alterations in NMDA-type glutamate receptors (NMDARs) have been implicated, yet it remains unclear how the Htt mutation impacts NMDAR function and direct evidence for a causative role is missing. Here we show that mutant Htt re-directs an intracellular store of juvenile NMDARs to the surface of striatal neurons by sequestering and disrupting the subcellular localization of the GluN3A subunit-specific endocytic adaptor PACSIN1. Overexpressing GluN3A in wild-type striatum mimicked the synapse loss observed in Huntington's disease mouse models, whereas genetic deletion of GluN3A prevented synapse degeneration, ameliorated motor and cognitive decline, and reduced striatal atrophy and neuronal loss in the YAC128 model. Furthermore, GluN3A deletion corrected the abnormally enhanced NMDAR currents, which have been linked to cell death in Huntington's disease and other neurodegenerative conditions. Our findings reveal an early pathogenic role of GluN3A dysregulation in Huntington's disease, and suggest that therapies targeting GluN3A or pathogenic Htt-PACSIN1 interactions might prevent or delay disease progression.