Downregulation of Iduna is associated with AIF nuclear translocation in neonatal brain after hypoxia-ischemia

In adult stroke models, the neuroprotective protein, Iduna, inhibits poly (ADP-ribose) polymerase-1 (PARP-1)-dependent cell death by decreasing apoptosis-inducing factor (AIF) nuclear translocation. Because the PARP1-dependent pathway and Iduna, which promotes AIF degradation, contribute to hypoxic-ischemic (HI) brain damage in the immature brain, we examined the relationship between Iduna expression and AIF nuclear translocation in the cerebral cortex of postnatal day 7 rats after HI. Ninety rats were divided into three groups: sham, 1-h hypoxia and 2-h hypoxia. The HI insult was induced by permanent ligation of the left common carotid artery plus 1 or 2h of hypoxia. Brain damage pathological features were evaluated by hematoxylin and eosin staining, Nissl staining, transmission electron microscopy, TUNEL staining and immunofluorescence. Immunohistochemistry and western blot analysis were used to assess protein expression and ubiquitination status of AIF. The interaction between Iduna and AIF was tested by co-immunoprecipitation. Learning and memory were analyzed by the Morris water maze test. Compared with sham animals, the number of surviving neurons in the cerebral cortex decreased, and cell damage and DNA breakage were severe in rats with HI, with worse damage in the 2-h group. Iduna expression significantly decreased, whereas nuclear AIF expression increased. Furthermore, Iduna downregulation negatively correlated with nuclear AIF abundance in the 2-h HI group (r=-0.950; P<0.0001). Additionally, learning and memory ability decreased with hypoxic time. These results suggest that AIF nuclear translocation and neuronal cell death are associated with Iduna loss after severe HI in the immature brain.