β2-Adrenergic Receptor-Mediated HIF-1α Upregulation Mediates Blood Brain Barrier Damage in Acute Cerebral Ischemia.

Yanyun Sun,Jie Liu,Chun-Feng Liu,Xiaona Wang,Xi Chen,Wenlan Liu,Xinchun Jin,Wen-Cao Liu,Xianzhi Shen,Mengwei Wang,Xinyu Zhang

doi:10.3389/fnmol.2017.00257

Abstract

Disruption of the blood brain barrier (BBB) within the thrombolytic time window is an antecedent event to intracerebral hemorrhage in ischemic stroke. Our recent studies showed that 2-h cerebral ischemia induced BBB damage in non-infarcted area and secreted matrix metalloproteinase-2 (MMP-2) accounted for this disruption. However, the factors that affect MMP-2 secretion and regulate BBB damage remains unknown. Since hypoxia-inducible factor-1 alpha (HIF-1α) was discovered as a mater regulator in hypoxia, we sought to investigate the roles of HIF-1α in BBB damage as well as the factors regulating HIF-1α expression in the ischemic brain. in vivo rat middle cerebral artery occlusion (MCAO) and in vitro oxygen glucose deprivation (OGD) models were used to mimic ischemia. Pretreatment with HIF-1α inhibitor YC-1 significantly inhibited 2-h MCAO-induced BBB damage, which was accompanied by suppressed occludin degradation and vascular endothelial growth factor (VEGF) mRNA upregulation. Interestingly, β2-adrenergic receptor (β2-AR) antagonist ICI 118551 attenuated ischemia-induced BBB damage by regulating HIF-1α expression. Double immunostaining showed that HIF-1α was upregulated in ischemic neurons but not in astrocytes andendothelial cells. Of note, HIF-1α inhibition with inhibitor YC-1 or siRNA significantly prevented OGD-induced VEGF upregulation as well as the secretion of VEGF and MMP-2 in neurons. More importantly, blocking β2-AR with ICI 118551 suppressedHIF-1α upregulation in ischemic neurons and attenuated occludin degradation induced by the conditioned media of OGD-treatedneurons. Taken together, blockade of β2-AR-mediated HIF-1α upregulation mediates BBB damage during acute cerebral ischemia. These findings provide new mechanistic understanding of early BBB damage in ischemic stroke and may help reduce thrombolysis-related hemorrhagic complications.

Highlights

Hemorrhagic transformation (HT), the most serious complication in thrombolytic therapy for acute ischemic stroke (Jin et al, 2015; Wang et al, 2015; Liu H. et al, 2016; Ji et al, 2017), occurs as a result of failure of the blood brain barrier (BBB) integrity (Simard et al, 2007)
hypoxia-inducible factor-1 alpha (HIF-1α) is a key mediator of the adaptive cellular response to hypoxia and vascular endothelial growth factor (VEGF) has been implicated in BBB permeability increase (Schoch et al, 2002; Yan et al, 2011)
The results suggested that 2-h middle cerebral artery occlusion (MCAO) induced VEGF mRNA expression in a HIF-1α-dependent manner

Summary

INTRODUCTION

Hemorrhagic transformation (HT), the most serious complication in thrombolytic therapy for acute ischemic stroke (Jin et al, 2015; Wang et al, 2015; Liu H. et al, 2016; Ji et al, 2017), occurs as a result of failure of the blood brain barrier (BBB) integrity (Simard et al, 2007). Hypoxia-inducible factor alpha (HIF-1α) is constitutively transcribed and translated in most cell types, but the protein has only a half-life of less than 5 min under normoxic conditions (Shi, 2009; Semenza, 2014) It is induced in the brain under hypoxia/ischemia conditions and was discovered as a mater regulator in hypoxia (Bernaudin et al, 2002; Zhang et al, 2014). HIF-1α and downstream vascular endothelial growth factor (VEGF) have been shown to play important roles in ischemia-reperfusion induced BBB damage (Chen et al, 2009, 2010). Our data showed that β2-adrenergic receptor inhibition attenuated HIF-1α upregulation as well as BBB damage within the first several hours of cerebral ischemia

MATERIALS AND METHODS

RESULTS

DISCUSSION