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Figure 3. The glymphatic system in association with the clearance of neurodegenerative disease proteins. The glymphatic system is a perivascular network that has lymphatic functions. Driven by arterial pulsation, the CSF flows into the brain along periarterial spaces surrounding cerebral arteries and arterioles, running in the same direction as blood flow. The CSF enters the brain parenchyma mediated by the aquaporin (AQP-4) water channel on the perivascular end-foot processes of astrocytes. Mixtures of CSF and ISF with interstitial solutes outflow along the perivenous space and drain out of the brain, which can clear Aβ in the ISF. The glymphatic system depends on AQP-4 on astrocytes. Sleep enhances glymphatic system function to promote the clearance of Aβ and other disease proteins in the brain. CSF: Cerebral spinal fluid; ISF: interstitial fluid; Aβ: amyloid-β.