Astrocytes are abundant cells in the central nervous system (CNS) that provide trophic support for neurons, promote formation and function of synapses, and prune synapses by phagocytosis, in addition to fulfilling a range of other homeostatic maintenance functions1–4. Astrocytes undergo a dramatic transformation called “reactive astrocytosis” after brain injury and disease and up-regulate many genes5,6 and form a glial scar after acute CNS trauma1,6,7. Functions of reactive astrocytes have been a subject of some debate, with previous studies showing they both hinder and support CNS recovery1,6–9. It has not been clear under what contexts they may be helpful or harmful and many questions remain about their functions.
