Endothelial Phenotypic Transition Contributes to Cerebral Ischemia-Reperfusion Injury and Repair

Background: Long-term ischemia leads to insufficient cerebral microvascular perfusion and dysfunction. Reperfusion restores physiological fluid shear stress but leads to serious injury. The mechanism of FSS-induced endothelial injury in ischemia-reperfusion injury remains poorly understood. Methods: In this study, a rat model of middle cerebral artery occlusion was constructed in vivo and the endothelial phenotype factor VE-cadherin and mesenchymal phenotype factor N-cadherin, Snail1, α-SMA, and slug were detected by Immunofluorescence to research the change of endothelial phenotypic. The cerebrovascular endothelial function and endothelial inflammation factors were detected by Evans Blue (EB) Staining and Quantitative real-time PCR. Additionally, the rat brain microvascular endothelial cells were exposed to a laminar fluid shear stress of 0.5 dyn/cm 2 for 6h and subsequently restored to physiological fluid shear stress level (2 dyn/cm 2 ) for 2h and 12h in vitro, to simulate the fluid shear stress environments in early and late reperfusion. Then we detect the change of endothelial phenotype factor VE-cadherin and mesenchymal phenotype factor N-cadherin, Snail1, and slug by western blot. What’s more, inflammation factors and the blood-brain barrier were also detected by Quantitative real-time PCR and Transmission Electron Microscope, respectively. After that, Yes related protein (YAP) was Knockdown and actin polymerization was inhibited to research the change of endothelial-to-mesenchymal transition in rat brain microvascular endothelial cells. Results We found that reperfusion-induced endothelial-to-mesenchymal transition in endothelial cells leads to serious blood-brain barrier damage and endothelial inflammation, accompanied by the nuclear accumulation of YAP. In the later stage of reperfusion, cerebral endothelium was restored to the endothelial phenotype with a distinct change of mesenchymal-to-endothelial transition, while YAP was translocated and phosphorylated in the cytoplasm. More importantly, the knockdown of YAP or inhibition of actin polymerization markedly impairs the endothelial-to-mesenchymal transition in rat brain microvascular endothelial cells. Conclusions These results suggested that ischemia-reperfusion increased intensity of fluid shear stress triggered an endothelial-to-mesenchymal transition process and thus resulted in endothelial inflammation and tissue injury, whereas continuous FSS may lead to a reversal mesenchymal-to-endothelial transition event in a time-dependent way that contributed to the endothelial repair. This study is helpful to provide new enlightenment for the therapy of ischemia-reperfusion injury.