Antioxidant status alters levels of fas-associated death domain-like IL-1B-converting enzyme inhibitory protein following neonatal hypoxia-ischemia

Activation of Fas death receptor (Fas DR) signaling cascade is seen after neonatal hypoxia-ischemia (HI). Cell survival is favored when signaling through the death-inducing signaling complex and cleavage of caspase 8 to its active form is blocked by FLIP, a dominant negative of caspase 8. H₂O ₂ quickly downregulates expression of FLIP. Neonatal mice overexpressing glutathione peroxidase (GPx) have less injury and less H ₂O₂ accumulation compared with neonatal mice overexpressing superoxide dismutase (SOD) or wild-type (WT) littermates. Expression of both FLIP_L and FLIP_S is increased in GPx-oxerexpressing mice relative to WT mice at 24 h and relative to SOD-overexpressing mice at 2 and 24 h following neonatal HI (ANOVA, p < 0.05). There is an increase in Fas DR expression at 24 h in both WT and GPx-overexpressing mice and significant differences between WT and SOD-overexpressing mice (ANOVA, p < 0.01). There is no difference in FADD expression among the 3 groups 24 h after HI. At 24 h following HI, the ratio of FLIP to Fas DR expression supports a significant negative correlation with injury score (r² = 0.99, slope = -4.01), and expression of both the active fragment of caspase 8 and caspase 8 activity is increased in SOD overexpressors compared to GPx overexpressors at 24 h after HI (ANOVA, p < 0.05). The overall degree of injury previously seen in these 3 strains correlates well with changes in expression of Fas DR signaling proteins favoring neuroprotection in the GPx-overexpressing mice, i.e. increased FLIP expression and decreased caspase 8 activity compared to SODtg mice. The mechanism by which antioxidant status alters FLIP levels following neonatal HI may be related to the ability to detoxify H₂O₂ produced following neonatal HI.