Integrin Alpha 5 Beta 1-Ang1/Tie2 Receptor Cross-Talk Regulates Brain Endothelial Cell Responses Following Cerebral Ischemia

We have previously demonstrated that in response to cerebral ischemia (CI), the growth factor angiopoietin-1 (Angl) and alpha 5 beta 1 integrin are both induced in cerebral vessels, which likely provide positive signals driving the endogenous angiogenic response and vascular protection after CI. However, the precise relationship between endothelial Ang1 and alpha 5 beta 1 integrin after CI remains poorly understood. Here, we investigated the effects of the interaction between the Angl/Tie2 system and alpha 5 beta 1 integrin on brain endothelial cells (BECs) under cerebral ischemic conditions in vivo and in vitro. lmmunofluorescence analysis demonstrated that integrin alpha 5 beta 1 co-localized with Tie2/phosphorylated Tie2 on cerebral vessels in the penumbra. The in vitro study showed that oxygen-glucose deprivation/restoration (OGD/R) induced the expression of the Angl receptor Tie2 on BECs in a manner similar to that for integrin alpha 5 and Angl in response to OGD/R, accompanied by increased activation of Tie2 and its downstream effectors focal adhesion kinase (FAK) and Akt. Knockdown of alpha 5 integrin markedly suppressed OGD/R-induced Tie2 receptor activation in BECs, while in contrast, priming BECs with Angl promoted the expression of alpha 5 integrin as well as the Tie2 downstream transcription factor Ets-1 in OGD-treated BECs. In line with this, Ets-1 knockdown significantly attenuated Anglmediated upregulation of alpha 5 integrin. Functionally, Angl induced cell migration and tube formation of BECs after OGD, but this effect was inhibited by diminishment of the levels of alpha 5 integrin in BECs. Taken together, our data indicate that the Angl/Tie2 system cross-talks with integrin alpha 5 beta 1 in BECs after CI, which may contribute to the endogenous angiogenic vascular protective response following CI.