Reactive astrocytes are thought to protect the penumbra during
brain ischemia, but direct evidence has been lacking due to the absence of suitable experimental models. Previously, we generated mice deficient in two intermediate filament (IF)
proteins,
glial fibrillary acidic protein (GFAP) and
vimentin, whose upregulation is the hallmark of reactive astrocytes. GFAP(-/-)Vim(-/-) mice exhibit attenuated posttraumatic reactive
gliosis, improved integration of neural grafts, and posttraumatic regeneration. Seven days after middle cerebral artery (MCA) transection,
infarct volume was 210 to 350% higher in GFAP(-/-)Vim(-/-) than in wild-type (WT) mice; GFAP(-/-), Vim(-/-) and WT mice had the same
infarct volume.
Endothelin B receptor (ET(B)R) immunoreactivity was strong on cultured astrocytes and reactive astrocytes around
infarct in WT mice but undetectable in GFAP(-/-)Vim(-/-) astrocytes. In WT astrocytes, ET(B)R colocalized extensively with bundles of IFs. GFAP(-/-)Vim(-/-) astrocytes showed attenuated endothelin-3-induced blockage of gap junctions. Total and
glutamate transporter-1 (GLT-1)-mediated
glutamate transport was lower in GFAP(-/-)Vim(-/-) than in WT mice.
DNA array analysis and quantitative real-time PCR showed downregulation of
plasminogen activator inhibitor-1 (PAI-1), an inhibitor of
tissue plasminogen activator. Thus, reactive astrocytes have a protective role in
brain ischemia, and the absence of astrocyte IFs is linked to changes in
glutamate transport, ET(B)R-mediated control of gap junctions, and
PAI-1 expression.