AQP4-A25Q Point Mutation in Mice Depolymerizes Orthogonal Arrays of Particles and Decreases Polarized Expression of AQP4 Protein in Astrocytic Endfeet at the Blood–Brain Barrier

Abstract

Aquaporin-4 (AQP4) is characterized by the formation of orthogonal arrays of particles (OAPs) comprising its M1 and M23 isoforms in the plasma membrane. However, the biological importance of OAP formation is obscure. Here, we developed an OAP depolymerization male mouse model by transgenic knock-in of an AQP4-A25Q mutation. Analyses of the mutant brain tissue using blue native polyacrylamide gel electrophoresis, super-resolution imaging, and immunogold electron microscopy revealed remarkably reduced OAP structures and glial endfeet localization of the AQP4-A25Q mutant protein without effects on its overall mRNA and protein expression.AQP4A25Q/A25Qmice showed better survival and neurologic deficit scores when cerebral edema was induced by water intoxication or middle cerebral artery occlusion/reperfusion. The brain water content and swelling of pericapillary astrocytic endfeet processes inAQP4A25Q/A25Qmice were significantly reduced, functionally supporting decreased AQP4 protein expression at the blood–brain barrier. The infarct volume and neuronal damage were also reduced inAQP4A25Q/A25Qmice in the middle cerebral artery occlusion/reperfusion model. Astrocyte activation in the brain was alleviated inAQP4A25Q/A25Qmice, which may be associated with decreased cell swelling. We conclude that the OAP structure of AQP4 plays a key role in its polarized expression in astrocytic endfeet processes at the blood–brain barrier. Therefore, our study provided new insights into intervention of cerebral cellular edema caused by stroke and traumatic brain injury through regulating AQP4 OAP formation.SIGNIFICANCE STATEMENTAquaporin-4 (AQP4) is characterized by orthogonal arrays of particles (OAPs) comprising the M1 and M23 isoforms in the membrane. Here, an OAP depolymerization male mouse model induced by AQP4-A25Q mutation was first established, and the functions of OAP depolymerization in cerebral edema have been studied. The results revealed that AQP4 lost its OAP structure without affecting AQP4 mRNA and protein levels in AQP4-A25Q mice. AQP4-A25Q mutation mice has neuroprotective effects on cerebral edema induced by water intoxication and middle cerebral artery occlusion/reperfusion through relieving the activation of astrocytes and suppressed microglia-mediated neuroinflammation. We concluded that the OAP structure of AQP4 plays a key role in its polarized expression in astrocytic endfeet processes at the blood–brain barrier. Therefore, our study provided new insights into intervention of cerebral cellular edema caused by stroke and traumatic brain injury through regulating AQP4 OAP formation.

A year in review: brain barriers and brain fluids research in 2022

“…Aquaporin-4 (AQP4), a water channel, is highly expressed in astrocyte endfeet where it forms large arrays (orthogonal arrays of particles). Zhu et al [ 22 ] have examined the impact of a mutant form of AQP4 (AQP4-A25Q) in mice. They found it greatly reduced the number of arrays without affecting overall mRNA and protein levels.…”

Preconditioned extracellular vesicles from hypoxic microglia reduce poststroke AQP4 depolarization, disturbed cerebrospinal fluid flow, astrogliosis, and neuroinflammation

“…The precise mechanisms that underly the aforementioned AQP4 polarization and glial scar formation under stroke conditions still remain elusive. AQP4 polarization and astrogliosis can either be regulated through direct intercellular contact or through signaling molecules 13 , 14 . As to the latter, additional and novel ways of intercellular communication processes have been elucidated during the last decades, bringing extracellular vesicles (EVs) into the focus of current scientific research.…”