Blood brain barrier (BBB) disruption occurring within the first few hours of ischemic stroke onset is closely associated with hemorrhagic transformation following thrombolytic therapy. However, the mechanism of this acute BBB disruption remains unclear. In the neurovascular unit, neurons do not have direct contact with the endothelial barrier, however they are highly sensitive and vulnerable to ischemic injury, and may act as the initiator for disrupting BBB when cerebral ischemia occurs. Herein we employed oxygen-glucose deprivation (OGD) and an in vitro BBB system consisting of brain microvascular cells and astrocytes to test this hypothesis. Neurons (CATH.a cells) were exposed to OGD for 3-hours before co-culturing with endothelial monolayer (bEnd 3 cells), or endothelial cells plus astrocytes (C8-D1A cells). Incubation of OGD-treated neurons with endothelial monolayer alone did not increase endothelial permeability. However, when astrocytes were present, the endothelial permeability was significantly increased, which was accompanied by loss of occludin and claudin-5 proteins as well as increased VEGF secretion into the conditioned medium. Importantly, all these changes were abolished when VEGF was knocked down in astrocytes by siRNA. Our findings suggest that ischemic neurons activate astrocytes to increase VEGF production, which in turn induces endothelial barrier disruption.

No abstract

Stroke is deemed a worldwide leading cause of neurological disability and death, however, there is currently no promising pharmacotherapy for acute ischemic stroke aside from intravenous or intra-arterial thrombolysis. Yet because of the narrow therapeutic time window involved, thrombolytic application is very restricted in clinical settings. Accumulating data suggest that non-pharmaceutical therapies for stroke might provide new opportunities for stroke treatment. Here we review recent research progress in the mechanisms and clinical implications of non-pharmaceutical therapies, mainly including neuroprotective approaches such as hypothermia, ischemic/hypoxic conditioning, acupuncture, medical gases, transcranial laser therapy, etc. In addition, we briefly summarize mechanical endovascular recanalization devices and recovery devices for the treatment of the chronic phase of stroke and discuss the relative merits of these devices.

Autophagy, an important intracellular degradation pathway, has been reported to clear impaired mitochondria and reduce mitochondria-mediated injury in ischemic disease. Our study and other recent investigations have shown that AKT-dependent autophagy contributes to the neuroprotection afforded by limb remote ischemic conditioning (RIC) in experimental stroke. However, how AKT triggers RIC-based autophagy and whether RIC-afforded autophagy is beneficial for mitochondrial function after cerebral ischemia remains unclear. The disruption of the Bcl-2/Beclin1 complex has been reported to trigger autophagy formation in the condition of Bcl-2 phosphorylation at Ser70. We investigated whether Bcl-2 phosphorylation triggers RIC-based autophagy and thereby confers RIC-induced neuroprotection against mitochondrial injury, using a transient cerebral ischemic rat model. We demonstrated that rats undergoing RIC treatment 30 min after the onset of ischemia (I-30) and at reperfusion (R-0) significantly upregulated Bcl-2 phosphorylation. Immunoprecipitation revealed that RIC increased dissociation of the Bcl-2/Beclin1 complex, leading to a higher level of autophagy than in ischemia/reperfusion rats. Furthermore, AKT activation was shown to play a critical role in regulating Bcl-2-mediated autophagy, as an AKT inhibitor (LY294002, AKTi) administered 30 min prior to ischemia significantly suppressed Bcl-2 phosphorylation and Bcl-2/Beclin1 complex dissociation, thereby reducing autophagy in RIC rats. Blocking Bcl-2 phosphorylation-dependent autophagy with AKTi suppressed RIC-afforded protection on mitochondrial potential and mitochondrial-dependent cell death effector pathway. These findings indicate that Bcl-2 phosphorylation and thereby Bcl-2/Beclin1 complex disruption play a crucial role in triggering autophagy and reducing mitochondrial damage in RIC rats after cerebral ischemia and require the involvement of the AKT activation.

These results aid optimization of the time window for RIPostC use and offer novel insight into, and a better understanding of, the protective mechanism of autophagy in limb RIPostC.