Occludin Degradation Mediated by Autophagy Leads to Blood-Brain Barrier Disruption in Ischemic Stroke

Abstract

The integrity of blood-brain barrier (BBB), which shows selective permeability for substances to brain, is significantly damaged under ischemic stroke amplifying ischemic neuronal damage. There have been attempts to identify the exact mechanism of ischemic BBB disruption to minimize brain damage. Autophagy is a catabolic process which involves degradation and recycling of damaged or unnecessary organelles, but excessive autophagy can induce cell damage and death under pathological conditions such as ischemia. Here, we evaluated if autophagy plays a key role in BBB dysfunction under ischemic stroke. In vitro BBB model of bEnd.3 cells were exposed to oxygen-glucose deprivation (OGD), an in vitro ischemic condition. After exposure to OGD for 18 hours, cell viability was significantly decreased and cellular permeability was impaired. The conversion of LC3-I to LC3-II and puncta of LC3 in bEnd.3 were increased, demonstrating that autophagy is induced under ischemic condition. Modulation of autophagy by 3-methyladenine, an autophagy inhibitor, reversed the conversion of LC3, and restored the impairment of cell permeability induced by OGD. The protein level of occludin, a tight junction protein in BBB, was significantly decreased following OGD exposure, and reversed by 3-MA. Also, immunofluorescence showed occludin was dispersed from cell membrane and co-localized with LC3 puncta in bEnd.3 after OGD. Our findings showed that induction of autophagy might contribute to increased permeability through occludin degradation in brain endothelial cells under ischemia, providing a new mechanism of BBB disruption in ischemic stroke.