Endothelial tPA-dependent recruitment of microglia to vessels protects the blood-brain barrier after stroke.

Abstract

BACKGROUND: Ischemic stroke is one of the leading causes of death and disability worldwide and thrombolysis, with tissue-type plasminogen activator (tPA) or its mutants, remains the only pharmacological treatment available for the acute phase. In this study, we hypothesised that endothelial tPA plays a key role in modulating the microglial response and maintaining blood brain barrier (BBB) integrity after stroke. METHODS: Using a mouse model with endothelial-specific deletion of tPA (VeCad- tPA), combined with a thrombotic stroke model and high-resolution imaging, we investigated the effects of endothelial tPA on vascular inflammation and microglial activation. RESULTS: Our results demonstrate that microglia-vessel contacts increase post-stroke. Notably, deletion of endothelial tPA reduces vascular cell adhesion molecule 1 (VCAM1) expression and is associated with decreased microglial activation and fewer microglia-vessel contacts. Interestingly, endothelial tPA deletion also leads to increased BBB permeability and a heightened risk of haemorrhagic transformation following stroke. CONCLUSIONS: Collectively, these findings indicate that endothelial tPA promotes microglial recruitment to blood vessels and plays a protective role in preserving BBB integrity after ischemic stroke.