Involvement of apoptosis‐inducing factor in neuronal death after hypoxia‐ischemia in the neonatal rat brain

Abstract Apoptosis‐inducing factor (AIF) triggers apoptosis in a caspase‐independent manner. Here we report for the first time involvement of AIF in neuronal death induced by cerebral ischemia. Unilateral cerebral hypoxia‐ischemia (HI) was induced in 7‐day‐old rats by ligation of the left carotid artery and hypoxia (7.7% O 2 ) for 55 min. AIF release from mitochondria and AIF translocation to nuclei was detected immediately after HI, and only in damaged areas, as judged by the concurrent loss of MAP‐2. AIF release was detected earlier than that of cytochrome c . Cells with AIF‐positive nuclei displayed nuclear condensation and signs of DNA damage. The number of AIF‐positive nuclei showed a positive correlation with the infarct volume 72 h post‐HI, and this was not changed by treating the animals with boc‐Asp‐fmk (BAF), a multicaspase inhibitor. BAF treatment reduced the activity of caspase‐3, ‐2 and ‐9 (78, 73 and 33%, respectively), and prevented caspase‐dependent fodrin cleavage in vivo , but did not affect AIF release from mitochondria or the frequency of positive nuclear AIF or DNA damage 72 h post‐HI, indicating that these processes occurred in a caspase‐independent fashion. In summary, AIF‐mediated cell death may be an important mechanism of HI‐induced neuronal loss in the immature brain.