Amyloid-β Slows Cilia Movement Along the Ventricle, Impairs Fluid Flow, and Exacerbates Its Neurotoxicity in Explant Culture

Alzheimer's disease (AD) is characterized by extensive and selective death of neurons and deterioration of synapses and circuits in the brain. The Aβ1-42 concentration is higher in an AD brain than in cognitively normal elderly individuals, and Aβ1-42 exhibits neurotoxicity. Brain-derived Aβ is transported into the cerebrospinal fluid (CSF), and CSF flow is driven in part by the beating of cilia and CSF secretion into ventricles. Ventricles are lined with ependyma whose apical surface is covered with motile cilia. Herein, we constructed an experimental system to measure the movement of ependymal cilia and examined the effects of Aβ1-42 to the beating of cilia and neurons. The circadian rhythm of the beating frequency of ependymal cilia was detected using brain wall explant-cultures containing ependymal cilia and neurons; the beating frequency was high at midday and low at midnight. Aβ1-42 decreased the peak frequency of ciliary beating at midday and slightly increased it at midnight. Aβ1-42 exhibited neurotoxicity to neurons on the non-ciliated side of the explant culture, while the neurotoxicity was less evident in neurons on the ciliated side. The neurotoxic effect of Aβ1-42 was diminished when 1 mPa of shear stress was generated using a flow chamber system that mimicked the flow by cilia. These results indicate that Aβ1-42 affects the circadian rhythm of ciliary beating, decreases the medium flow by the cilia-beating, and enhances the neurotoxic action of Aβ1-42 in the brain explant culture.