Investigating the Roles of Aquaporin 4 in Intracellular and Extracellular Vesicles in Models of Traumatic Injury

Abstract

Recent findings indicate that Aquaporins (AQP) play important roles in intracellular and extracellular Vesicles (EV). Intracellular vesicular trafficking of vesicles causes increased AQP concentration in the plasma membrane and increased water uptake by cells. It has recently been shown that AQP are released in EV, multiple roles for AQP in EV have been suggested, such as volumetric control of cells, uptake of AQP by recipient cells, and more. Both mechanisms have been identified in cells expressing AQP4 and have been linked to the pathological uptake and accumulation of water (oedema) in the central nervous system following injury. This study aims to understand the role of AQP4 in intracellular and extracellular vesicles. We ask: 1) Does AQP4 traffic to the endfeet of astrocytes following injury? 2) Does extracellular hypotonicity (as seen in CNS oedema) promote EV release? 3) Is AQP4 present in these EV? and 4) what is the role of AQP4 in these EV? A rat spinal crush injury model was used to investigate the role of calmodulin (CaM) and protein kinase A (PKA) in AQP4 trafficking to astrocytic endfeet in vivo, a mechanism previously only investigated in an in vitro model. Inhibition of CaM and PKA reduced AQP4 expression and trafficking to endfeet. An EV release model was developed to produced AQP4-positive EV in vitro, using stably transfected cell lines expressing AQP4, changes in extracellular tonicity impacted both EV release and EV cargo. Changes in EV populations were measured using ultraviolet side scatter flow cytometry and western blotting. These results indicate that AQP4 plays an important role in astrocytic vesicles and could be a therapeutic target to cerebral oedema.