Loss of aquaporin-4 impairs cerebrospinal fluid solute clearance through cerebrospinal fluid drainage pathways

The aquaporin-4 (AQP4) water channel is essential in neurofluid dynamics. AQP4 loss impairs solute exchange between the cerebrospinal fluid (CSF) and interstitial fluid (ISF). However, whether AQP4 expression affects solute clearance from the CSF space to the extracranial space remains unclear. This study aimed to investigate this using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) following the intrathecal administration of gadolinium-based contrast agents (GBCAs) to AQP4 knockout (KO) rats. AQP4 KO rats showed reduced efflux of intrathecal GBCAs to the extracranial spaces through CSF drainage pathways and increased retention of intrathecal GBCAs in the CSF space compared with the controls. These results suggest that AQP4 loss impairs solute clearance from the CSF space to the extracranial spaces via the CSF drainage pathways. This study revealed a close relationship between AQP4 expression and CSF solute clearance, contributing to a better understanding of the function of AQP4 in neurofluid dynamics.