Deletion of aquaporin‐4 improves capillary blood flow distribution in brain edema

Brain edema is a feared complication to disorders and insults affecting the brain. It can be fatal if the increase in intracranial pressure is sufficiently large to cause brain herniation. Moreover, accruing evidence suggests that even slight elevations of intracranial pressure have adverse effects, for instance on brain perfusion. The water channel aquaporin‐4 (AQP4), densely expressed in perivascular astrocytic endfeet, plays a key role in brain edema formation. Using two‐photon microscopy, we have studied AQP4‐mediated swelling of astrocytes affects capillary blood flow and intracranial pressure (ICP) in unanesthetized mice using a mild brain edema model. We found improved regulation of capillary blood flow in mice devoid of AQP4, independently of the severity of ICP increase. Furthermore, we found brisk AQP4‐dependent astrocytic Ca2+ signals in perivascular endfeet during edema that may play a role in the perturbed capillary blood flow dynamics. The study suggests that astrocytic endfoot swelling and pathological signaling disrupts microvascular flow regulation during brain edema formation. Main Points Capillary flow dynamics are perturbed in mild brain edema. Mice devoid of aquaporin‐4 display improved capillary flow regulation in edema. Endfoot Ca2+ signaling in edema is increased in wildtype, but not in aquaporin‐4 knockouts.