Targeting Aquaporin-4 Subcellular Localization to Treat Central Nervous System Edema

Swelling of the brain or spinal cord (CNS edema) affects millions of people every year. All potential pharmacological interventions have failed in clinical trials, meaning that symptom management is the only treatment option. The water channel protein aquaporin-4 (AQP4) is expressed in astrocytes and mediates water flux across the blood-brain and blood-spinal cord barriers. Here we show that AQP4 cell-surface abundance increases in response to hypoxia-induced cell swelling in a calmodulin-dependent manner. Calmodulin directly binds the AQP4 carboxyl terminus, causing a specific conformational change and driving AQP4 cell-surface localization. Inhibition of calmodulin in a rat spinal cord injury model with the licensed drug trifluoperazine inhibited AQP4 localization to the blood-spinal cord barrier, ablated CNS edema, and led to accelerated functional recovery compared with untreated animals. We propose that targeting the mechanism of calmodulin-mediated cell-surface localization of AQP4 is a viable strategy for development of CNS edema therapies. [Display omitted] •Hypoxia triggers an increase in AQP4-mediated flux of water into astrocytes•Translocation of AQP4 to the astrocyte cell surface drives increased water flux•AQP4 cell-surface localization is mediated by a CaM- and PKA-dependent mechanism•Inhibition of AQP4 localization with the licensed drug TFP halts CNS edema in rats Modulating the subcellular localization of the water channel protein AQP4 may be a therapeutic option for treatment of brain and spinal cord edemas.