Ischemia-induced apoptosis in primary cultures of astrocytes

Astrocytes participate in a wide variety of important physiological processes and pathological insults, including ischemia. Information on the mechanism of astroglial injury and death during ischemic insult, however, is scarce. In this study, we investigated the mode of astrocytic cell death using an in vitro ischemic model. Cultured astrocytes exhibited several distinct morphological and biochemical features of apoptosis under ischemia. At 4 h of ischemia, Annexin V staining demonstrated an early commitment of some astrocytes to apoptosis. Condensed nuclei became visible from 4 h and the number increased with ischemic incubation time. Electron microscopy showed compacted and segregated chromatin along the edges of nuclear membranes. The number of TUNEL-positive nuclei and the degree of DNA laddering increased with ischemic incubation. Caspase-3, but not caspase-1, activity was increased in ischemia-injured astrocytes. Swollen mitochondria and vacuoles found in some cells with chromatin condensation indicated that these apoptotic-like cells might die of necrosis. The results imply that astrocytes are capable of undergoing apoptosis without the presence of other cell types, such as neurons. Ischemia can induce apoptosis in astrocytes contributing to the pathogenesis of ischemic injury in the CNS.