Resumo

For decades, astrocytes have been considered to be non-excitable support cells that are relatively resistant to brain injury. This view has changed radically during the past twenty years. Multiple essential functions are performed by astrocytes in normal brain. Astrocytes are dynamically involved in synaptic transmission, metabolic and ionic homeostasis, and inflammatory maintenance of the blood brain barrier. Advances in our understanding of astrocytes include new observations about their structure, organization, and function. Astrocytes also contribute significantly to brain antioxidant defense with evidence they can upregulate endothelial cell antioxidant protection. Recent works have demonstrated a protective role for reactive astrocytes after brain injury. Nevertheless, others have pointed to an inhibitory role for astrocytes in axonal regeneration after injury. Reactive astrogliosis is a complex phenomenon that includes a mixture of positive and negative responses for neuronal survival and regeneration. Reactive astroglia maintains the integrity of the blood-brain barrier and the survival of the perilesional tissue, but may prevent axonal and damaged tissue regeneration. My talk will focus on those astrocytic mechanisms evolved to protect the brain against the consequences of an ischemic injury, contrasting with their key role in regeneration failure. In this context we will consider particularly the two-sided role of reactive astrocytes, which is an experimental paradigm helpful in discriminating destructive from protective mechanisms after brain injury.