Pericyte, but not astrocyte, hypoxia inducible factor-1 (HIF-1) drives hypoxia-induced vascular permeability in vivo

Abstract

Background: Ways to prevent disease-induced vascular modifcations that accelerate brain damage remain largely elusive. Improved understanding of perivascular cell signalling could provide unparalleled insight as these cells impact vascular stability and functionality of the neurovascular unit as a whole. Identifying key drivers of astrocyte and pericyte responses that modify cell–cell interactions and crosstalk during injury is key. At the cellular level, injuryinduced outcomes are closely entwined with activation of the hypoxia-inducible factor-1 (HIF-1) pathway. Studies clearly suggest that endothelial HIF-1 signalling increases blood–brain barrier permeability but the infuence of perivascular HIF-1 induction on outcome is unknown. Using novel mouse lines with astrocyte and pericyte targeted HIF-1 loss of function, we herein show that vascular stability in vivo is diferentially impacted by perivascular hypoxiainduced HIF-1 stabilization.<p> <p>Methods: To facilitate HIF-1 deletion in adult mice without developmental complications, novel Cre-inducible astro‑ cyte-targeted (GFAP-CreER^T2; HIF-1α^f/fl and GLAST-CreER^T2; HIF-1α^f/fl) and pericyte-targeted (SMMHC-CreERT2; HIF-1α^{f/ fl} ) transgenic animals were generated. Mice in their home cages were exposed to either normoxia (21% O₂) or hypoxia (8% O₂) for 96 h in an oxygen-controlled humidifed glove box. All lines were similarly responsive to hypoxic challenge and post-Cre activation showed signifcantly reduced HIF-1 target gene levels in the individual cells as predicted. <p>Results: Unexpectedly, hypoxia-induced vascular remodelling was unafected by HIF-1 loss of function in the two astrocyte lines but efectively blocked in the pericyte line. In correlation, hypoxia-induced barrier permeability and water accumulation were abrogated only in pericyte targeted HIF-1 loss of function mice. In contrast to expectation, brain and serum levels of hypoxia-induced VEGF, TGF-β and MMPs (genes known to mediate vascular remodelling) were unafected by HIF-1 deletion in all lines. However, in agreement with the permeability data, immunofuores‑ cence and electron microscopy showed clear prevention of hypoxia-induced tight junction disruption in the pericyte loss of function line.