Brain ischemia/reperfusion prevents more than 90 percent of patients resuscitated from cardiac arrest from resuming their normal lives. The long-term goal is sufficient understanding of the injury mechanisms to formulate clinically effective therapy. The inhibition of protein synthesis during brain reperfusion is associated with a rapid increase in alpha-subunit phosphorylated eukaryotic initiation factor 2 [eIF2alpha(P)], which inhibits translation initiation. Insulin administration at resuscitation from cardiac arrest induces dephosphorylation of eIF2alpha(P) and rescue of protein synthesis in vulnerable neurons. Growth factors such as insulin mediate cell survival through the kinase Akt, a downstream affector of the phosphatidylinositol-3 kinase (PI3K). Akt inhibits apoptosis by phosphorylating protein substrates such as the pro-apoptotic protein Bad. Akt is also involved in the regulation of translation initiation, in part through its deactivation of glycogen synthase kinase 3beta (GSK3beta). It is proposed that therapeutic growth factor signaling through the PI3K/Akt signaling system during reperfusion results in both dephosphorylation of eIF2alpha(P) and also activation of cell survival pathways.
Specific Aims are to 1) characterize the effects of 10 min cardiac arrest and various durations of reperfusion on phosphorylation of Akt, GSK3beta, Bad, eIF2alpha and the regulatory subunit of PI3K, 2) investigate the effects of insulin administration at resuscitation after 10 min cardiac arrest on phosphorylation of these proteins during reperfusion, and 3) investigate whether insulin-induced changes in eIF2alpha (P), Akt, Bad and GSK3beta are all PI3K-dependent. A rat model of cardiac arrest and resuscitation will be used to prepare brain tissue for analysis by immunoblotting and immunohistochemistry. Utilizing intracerebroventricular injection of the PI3K inhibitor, wortmannin, followed by cardiac arrest and resuscitation, it will be investigated whether the insulin-induced changes in phosphorylation states of Akt, Bad, GSK3beta and eIF2alpha(P) are all PI3K-dependent. This approach will permit integrated examination of a signaling system that may link growth factor mediated survival and translational competence in the setting of brain reperfusion.
| Sanderson, Thomas H; Kumar, Rita; Murariu-Dobrin, Alina C et al. (2009) Insulin activates the PI3K-Akt survival pathway in vulnerable neurons following global brain ischemia. Neurol Res 31:947-58 |
| Sanderson, Thomas H; Kumar, Rita; Sullivan, Jonathon M et al. (2008) Insulin blocks cytochrome c release in the reperfused brain through PI3-K signaling and by promoting Bax/Bcl-XL binding. J Neurochem 106:1248-58 |
