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

Background: High-altitude cerebral edema (HACE) is a serious condition caused by pro-longed hypobaric hypoxia (HH). Autophagic degradation of Claudin-5 plays a crucial role in HH-induced 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. Methods: C57BL/6J mice were treated with HCQ and exposed to HH for 24 hrs to study BBB integ-rity. 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. Hypoxia-mimetic in vitro models were used to explore HCQ's effects on TJs and BBB per-meability, confirmed by various assays, including immunofluorescence, electron microscopy, and Western blotting. Results: HCQ significantly mitigated rapamycin-induced autophagy and Claudin-5 degradation. Pro-longed 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 au-tophagy, damaging the vascular endothelial TJs and subsequently increasing endothelial permeabil-ity. 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. Conclusion: HCQ effectively prevented HACE by inhibiting HH-induced Claudin-5 membrane ex-pression downregulation, thus mitigating BBB damage and brain water content increase in HH-exposed mice.