Tongxinluo protects against hypoxia-induced breakdown of the endothelial barrier through inducing tight junction protein expression

The hypoxia can cause abnormal expression of tight junction proteins, leading to disruption of tight junctions (TJs) and increasing permeability of the endothelial barrier. Tongxinluo (TXL) can improve endothelial cell function and protect the brain against blood-brain barrier disruption. However, it remains unclear whether there is a direct relationship between protective effect of TXL on endothelial functions and TXL-induced tight junction protein expression. The aim of present study was to investigate the mechanism of TXL actions whereby TXL protects against hypoxia-induced tight junction disruption. We found that hypoxia disrupted, while TXL treatment protected the TJs in the microvasculature of the mouse brain, and that TXL promoted the expressions of TJ proteins VE-cadherin, beta-catenin and ZO-1 in human cardiac microvascular endothelial cells (HCMECs) under hypoxia conditions. Mechanistic studies suggested that upregulation of TJ protein expressions is attributable to KLF4 phosphorylation at sites Ser444 and Ser415 induced by TXL. Furthermore, our study shows that Akt signaling plays a key role in TXL-induced KLF4 phosphorylation. In conclusion, the results of our study reveal a novel mechanism whereby TXL protects against hypoxia-induced tight junction disruption through promoting KLF4 phosphorylation and inducing tight junction protein expression.