Hippocampal Hap1 down-regulation impairs glucocorticoid receptor nuclear translocation and exacerbates Alzheimer’s disease-related neuropathology in APP/PS1 mice

Impaired nuclear translocation of glucocorticoid receptor (GR) has been implicated in hippocampal vulnerability in Alzheimer's disease (AD), yet the molecular basis of this defect remains poorly understood. This study identified Huntingtin-associated protein 1 (Hap1) as a critical regulator of GR nuclear translocation in the hippocampus. Specifically, Hap1 expression progressively declined in the hippocampus of APP/PS1 mice with advancing age and pathological burden. Hippocampal Hap1 knockdown induced pronounced cognitive deficits and synaptic deterioration, as indicated by reduced dendritic arborization, decreased spine density, impaired long-term potentiation, and exacerbated amyloid-β deposition. Mechanistic analyses showed that Hap1 deficiency increased GR ubiquitination and proteasomal degradation and, more importantly, disrupted ligand-dependent GR translocation to the nucleus, thereby attenuating GR-dependent brain-derived neurotrophic factor transcription. In parallel, Hap1 knockdown elevated corticosterone concentration and induced depression-like behavior, consistent with hypothalamic-pituitary-adrenal axis dysregulation. Collectively, these findings establish defective GR nuclear trafficking driven by loss of Hap1 function as a key pathomechanism linking intracellular transport failure to synaptic dysfunction in AD and highlight Hap1 as a potential therapeutic target.