Abstract

Hypoxia is linked to changes in blood brain barrier (BBB) permeability and loss of BBB integrity is characteristic of many pathological brain diseases including stroke. In particular astrocytes play a central role in brain homeostasis and BBB function. We investigated how hypoxia affects astrocyte survival and assessed whether VEGF release through Hif-1alpha induction plays a role in the tolerance of these cells to insult. Thus primary astrocytes were subjected to normoxic (21% O2), hypoxic (1% O2) or near anoxic (<0.1% O2) conditions in presence or absence of glucose. Cell death was significantly initiated after combined oxygen glucose deprivation and surprisingly, astrocyte proliferation increased concomitantly. Near anoxic, but not hypoxic, conditions stabilised HIF-1alpha protein and provoked DNA binding activity whereas oxygen and glucose deprivation accelerated HIF-1alpha accumulation. Unexpectedly HIF-1alpha knockdown studies showed that elevated VEGF levels following increased insult was only partially due to HIF-1alpha induction suggesting alternative mechanisms of VEGF regulation. Notably, endogenous VEGF signalling during insult was essential for cell fate since VEGF inhibition appreciably augmented cell death and reduced proliferation. These data suggest Hif-1 only partially contributes to the VEGF-mediated astrocyte responses during chronic injury (as occurs in clinical hypoxic/ischemic insults) that may ultimately be responsible for disrupting BBB integrity. Key words: oxygen deprivation, blood brain barrier, glucose deprivation, permeability, glial scarring.