The neuronal damage caused by ischemic brain injury is associated with increased apoptosis. IGF-I exposure promotes neuronal defense and survival against ischemic insult by inhibiting apoptotic processes. We investigated the role of prostate apoptosis response-4 (Par-4), a proapoptotic gene the expression of which is increased after ischemic injury, in IGF-I-mediated inhibition of apoptosis using PC12 cells exposed to oxygen-glucose deprivation (OGD). The OGD insult resulted in significant

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... ases in apoptotic cell death and Par-4 expression, which were prevented by the treatment of cells with an antisense oligonucleotide of Par-4. IGF-I treatment prior to OGD insult significantly reduced the number of apoptotic cells and the OGD-induced increase in Par-4 expression. OGD-induced nuclear translocation of Par-4 was also attenuated by IGF-I treatment. In addition, we demonstrated that the anti-apoptotic effect of IGF-I was blocked by chemical inhibition of a mitogen activated protien kinase (MAPK), phosphatidylinositol 3-kinase (PI3K), or protein kinase A (PKA), but not by a protein kinase C inhibitor. Finally, pretreatment of cells with a MAPK or PI3K inhibitor attenuated IGF-I-induced inhibition of Par-4 expression, suggesting that the MAPK and PI3K pathways contribute to IGF-I-induced Par-4 suppression. In contrast, a PKA inhibitor failed to alter the inhibitory effect of IGF-I on Par-4. These findings indicate that in PC12 cells exposed to OGD insult, IGF-I protects cells from apoptosis, at least in part through the inhibition of Par-4 expression. . (nZ4). Each experiment was repeated twice. *P!0 . 05 versus vehicle-treated cells exposed to OGD; † P!0 . 05 versus Par-4 antisense oligonucleotide-treated cells. Figure 5 PI3K and MAPK pathways are involved in IGF-I-induced inhibition of Par-4 induced by OGD. PC12 cells were preincubated with (A) 200 nM wortmannin for 30 min, (B) 2 mM LY294002 for 30 min, (C) 50 mM PD98059 for 1 h, or (D) 5 mM H89 for 30 min and then treated with IGF-I (10 K8 M) for 24 h, and then cells were exposed to OGD for 3 h followed by 24-h reoxygenation. Par-4 protein levels were assessed by western blot analysis. Values are the meanGS.E.M. (nZ4). Each experiment was repeated twice. Group means that do not share a common letter (a and b) are significantly different (P!0 . 05).