Hydroxychloroquine Prevents High-altitude Cerebral Edema by Inhibiting Endothelial Claudin-5 Autophagic Degradation

High-altitude cerebral edema (HACE) is a serious condition caused by prolonged hypobaric hypoxia (HH). Autophagic degradation of Claudin-5 plays a crucial role in HHinduced blood-brain barrier (BBB) damage. Hydroxychloroquine (HCQ), a lysosomal inhibitor used in autophagy treatment, reduces inflammation and BBB damage in traumatic brain injury. However, its effectiveness in preventing HACE is still unknown.

C57BL/6J mice were treated with HCQ and exposed to HH for 24 hrs to study BBB integrity. We evaluated BBB disruption via brain water content, Evans blue, and FITC-dextran assays. Changes in tight junctions (TJs) of cerebrovascular endothelial cells were analyzed using electron microscopy and immunofluorescence. Western blotting quantified autophagy protein levels in brain tissue. Hypoxiamimetic in vitro models were used to explore HCQ's effects on TJs and BBB permeability, confirmed by various assays, including immunofluorescence, electron microscopy, and Western blotting.

HCQ significantly mitigated rapamycin-induced autophagy and Claudin-5 degradation. Prolonged hypoxia exposure promoted lysosomal degradation of Claudin-5, increasing endothelial cell permeability. HCQ inhibited autophagy in bEnd.3 cells via the PI3K-Akt-mTOR and Erk pathway, reducing hypoxia-induced Claudin-5 down-regulation. In mice, HH exposure increased brain autophagy, damaging the vascular endothelial TJs and subsequently increasing endothelial permeability. Pretreatment with HCQ significantly reduced the level of autophagy in the brains of HH-exposed mice, thereby mitigating the HH-induced damage to vascular TJs, alleviating the downregulation of Claudin-5, and enhancing endothelial integrity.

HCQ effectively prevented HACE by inhibiting HH-induced Claudin-5 membrane expression downregulation, thus mitigating BBB damage and brain water content increase in HHexposed mice.