Surrogates of glymphatic metrics decline and coupled sleep rhythms disruption in Alzheimer’s disease

BACKGROUND: Sleep is essential for brain homeostasis, in part by supporting glymphatic clearance through sleep-related oscillations. However, the relationship between putative glymphatic metrics and coupled sleep rhythm disruption, and their combined role in Alzheimer's disease (AD) progression, remains poorly understood. METHODS: We analyzed data from 75 individuals, 54 with AD and 21 cognitively normal (CN) controls, including sleep electroencephalography (EEG), magnetic resonance imaging (MRI), cerebrospinal fluid (CSF) AD biomarkers, and two-year longitudinal cognitive assessments. Putative glymphatic metrics was evaluated using choroid plexus (CP) volume, perivascular spaces (PVSs), diffusion tensor imaging along the perivascular space (DTI-ALPS) index, and blood oxygen level-dependent signal coupled to CSF signal (BOLD-CSF coupling). Coupled sleep rhythm was assessed via slow oscillation (SO)-theta and SO-spindle couplings. Correlation and mediation analyses explored associations between these MRI-derived indices and coupled sleep oscillations, and least absolute shrinkage and selection operator (LASSO) regression was used to predict AD progression. RESULTS: Compared to CN controls, individuals with AD had reduced DTI-ALPS index and BOLD-CSF coupling (p < 0.05), along with disrupted SO-spindle coupling (p = 0.029). Across all participants, lower global BOLD-CSF coupling correlated with misaligned SO-theta burst coupling (r = 0.311, p = 0.018), and reduced DTI-ALPS was associated with misaligned SO-spindle coupling (r = 0.370, p = 0.008). In the AD group, DTI-ALPS remained correlated with SO-spindle misalignment (r = 0.376, p = 0.028). Mediation analysis revealed that SO-spindle misalignment contributed to cognitive decline through its effect on DTI-ALPS. Importantly, combining putative glymphatic and sleep EEG metrics effectively predicted AD progression. CONCLUSIONS: Our findings suggest that disruptions in surrogates marker of glymphatic clearance and coupled sleep rhythms are jointly associated with AD-related cognitive decline. These metrics offer a promising framework for predicting disease progression and understanding neurodegenerative mechanisms in AD.