Overexpression of α5β1 integrin and angiopoietin-1 co-operatively promote blood-brain barrier integrity and angiogenesis following ischemic stroke

Abstract

We previously demonstrated that cross-talk between α5β1 integrin and the angiopoietin-1 (Ang1) / Tie2 receptor plays an important role in regulating brain endothelial angiogenic responses in the ischemic penumbra following cerebral ischemic stroke (CIS). However, a recent study suggested that stimulation of the α5β1 integrin also has the potential of increasing blood-brain barrier (BBB) permeability after CIS, raising doubt about whether α5β1 integrin stimulation by itself will protect against ischemic injury. In light of these conflicting roles, the goal of this study was to evaluate the impact of co-overexpression of α5 integrin and Ang1 on vascular remodeling and repair under cerebral ischemic conditions both in vivo following 90 min of ischemia by temporary occlusion of the middle cerebral artery, and in vitro. Our results demonstrate that as compared to mock-transfected controls, overexpression of α5 integrin alone didn't improve the outcomes in neurological score and size of infarct and caused worse BBB breakdown in the ischemic hemisphere, offsetting its beneficial angiogenic effects during the early stages of CIS. However, co-overexpression of α5 integrin with Ang1 led to smaller infarcts and improved neurological deficits, which at the molecular level was underpinned by reduced BBB breakdown and increased expression of endothelial tight junction proteins in the ischemic penumbra during the early stages of CIS. Furthermore, co-overexpression of α5 integrin and Ang1 synergistically promoted BEC proliferation during the early stage of CIS, resulting in increased blood vessel density at later stages. Positive effects of α5 integrin and Ang1 co-overexpression on endothelial proliferation and tight junction protein expression were also confirmed in vitro. Collectively, these data indicate that co-overexpression of Ang-1 and α5 integrin in combination confers synergistic vascular protection against cerebral ischemic injury without the negative side effects on BBB permeability, suggesting a novel combinatorial approach for the treatment of CIS.