High-altitude
cerebral edema (HACE) is a potentially fatal
encephalopathy associated with a time-dependent exposure to the hypobaric
hypoxia of altitude. The formation of HACE is affected by both vasogenic and cytotoxic
edema. The over-activated microglia potentiate the damage of blood-brain barrier (BBB) and exacerbate cytotoxic
edema. In light with the activation of microglia in HACE, we aimed to investigate whether the over-activated microglia were the key turning point of acute
mountain sickness to HACE. In in vivo experiments, by exposing mice to hypobaric
hypoxia (7000 m above sea level) to induce HACE model, we found that microglia were activated and migrated to blood vessels. Microglia depletion by
PLX5622 obviously relieved
brain edema. In in vitro experiments, we found that
hypoxia induced cultured microglial activation, leading to the destruction of endothelial tight junction and astrocyte swelling. Up-regulated
nuclear respiratory factor 1 (NRF1) accelerated pro-inflammatory factors through transcriptional regulation on
nuclear factor kappa B p65 (NF-κB p65) and
mitochondrial transcription factor A (TFAM) in activated microglia under
hypoxia. NRF1 also up-regulated phagocytosis by transcriptional regulation on
caveolin-1 (CAV-1) and
adaptor-related protein complex 2 subunit beta (AP2B1). The present study reveals a new mechanism in HACE:
hypoxia over-activates microglia through up-regulation of NRF1, which both induces inflammatory response through transcriptionally activating NF-κB p65 and TFAM, and enhances phagocytic function through up-regulation of CAV-1 and AP2B1;
hypoxia-activated microglia destroy the integrity of BBB and release pro-inflammatory factors that eventually induce HACE.