Biomarkers

Area of Science:

• Neuroscience
• Sleep Medicine
• Gerontology

Background:

• Sleep is crucial for brain health, regulating the clearance of Alzheimer's disease (AD) hallmarks like beta-amyloid (Aβ) and tau proteins.
• Sleep disturbances can precede cognitive symptoms in AD by decades, but specific sleep characteristics predicting post-onset changes are unclear.

Purpose of the Study:

• To investigate the association between non-rapid eye-movement sleep spindles, slow oscillations (SO), and neurodegenerative/cognitive changes in mild-to-moderate AD patients.
• To determine if sleep characteristics predict changes in AD biomarkers and cognitive function over a three-year period.

Main Methods:

• Prospective cohort study of 60 mild-to-moderate AD patients in Spain.
• Polysomnography (PSG) for sleep spindle and SO analysis, cerebrospinal fluid (CSF) and blood tests for Aβ and tau biomarkers, and neuropsychological assessments (MMSE, CVLT, ROCF, ADAS-Cog) at baseline and 36-month follow-up.
• Generalized linear models were used to analyze associations, controlling for age, sex, and apnea-hypopnea index.

Main Results:

• Higher spindle and SO density, duration, amplitude, and power were significantly associated with changes in Aβ42, phosphorylated tau (pTau-181), total tau, and the tau/Aβ42 ratio.
• Enhanced sleep activity predicted significantly better cognitive performance, indicated by lower ADAS-Cog and higher MMSE scores, and improved verbal and visual memory.
• Sleep spindles and SO activity mediated the effect of pTau181/Aβ42 on cognition, and pTau181/Aβ42 moderated the effect of sleep activity on cognition.

Conclusions:

• Sleep spindle and SO activity serve as predictive, non-invasive biomarkers for neurodegeneration and cognitive status in AD patients.
• These sleep characteristics represent novel therapeutic targets for potentially delaying cognitive decline and slowing AD progression.