Quantitative Modelling of Amyloid-β Dynamics in Brain, CSF, and Plasma During Sleep and Wakefulness

Amyloid-beta (A{beta}) accumulation in the brain is linked to Alzheimer's disease. In healthy individuals, A{beta} rises during wakefulness and is cleared during sleep, yet the effects of sleep disturbances on the A{beta} dynamics are unclear. We developed a model, incorporating brain, cerebrospinal fluid (CSF), and plasma, to investigate the A{beta} dynamics along the sleep-wake cycles. The model reproduces the experimentally observed 24-hour A{beta}42 oscillations in CSF (660-760 pg/mL) and plasma (15-19 pg/mL) and predicts brain A{beta} dynamics. Indwelling lumbar catheter data show elevated CSF A{beta}42 levels on the second morning after a full night of sleep compared to first morning. The model predicts this increased level is due to repeated CSF sampling, which affects A{beta} levels through pressure-mediated changes in CSF, impaired sleep associated clearance, or their synergistic effect. These findings provide a framework for understanding A{beta} regulation, highlighting sleep's protective role and the need for non-invasive measurement approaches.