Persistent eIF2[alpha](P) is colocalized with cytoplasmic cytochrome c in vulnerable hippocampal neurons after 4 hours of reperfusion following 10-minute complete brain ischemia

• Published in: Acta neuropathologica 2003-07, Vol.106 (1), p.8
• Main Authors: Page, Andrea B, Owen, Cheri R, Kumar, Rita, Miller, Janet M, Rafols, José A, White, Blaine C, DeGracia, Donald J, Krause, Gary S
• Format: Article
• Language: English
• ISSN: 0001-6322; 1432-0533
• DOI: 10.1007/s00401-003-0693-2

Upon brain reperfusion following ischemia, there is widespread inhibition of neuronal protein synthesis that is due to phosphorylation of eukaryotic initiation factor 2[alpha] (eIF2[alpha]), which persists in selectively vulnerable neurons (SVNs) destined to die. Other investigators have shown that expression of mutant eIF2[alpha] (S51D) mimicking phosphorylated eIF2[alpha] induces apoptosis, and expression of non-phosphorylatable eIF2[alpha] (S51A) blocks induction of apoptosis. An early event in initiating apoptosis is the release of cytochrome c from mitochondria, and cytochrome c release corresponds to the selective vulnerability of hippocampal CA1 neurons in rats after transient global cerebral ischemia. At present the signaling pathways leading to this are not well defined. We hypothesized that persistent eIF2[alpha](P) reflects injury mechanisms that are causally upstream of release of cytochrome c and induction of apoptosis. At 4 h of reperfusion following 10-min cardiac arrest, vulnerable neurons in the striatum, hippocampal hilus and CA1 showed colocalized intense immunostaining for both persistent eIF2[alpha](P) and cytoplasmic cytochrome c, while resistant neurons in the dentate gyrus and elsewhere did not immunostain for either. A lower intensity of persistent eIF2[alpha](P) immunostaining was present in cortical layer V pyramidal neurons without cytoplasmic cytochrome c, possibly reflecting the lesser vulnerability of this area to ischemia. We did not observe cytoplasmic cytochrome c in any neurons that did not also display persistent eIF2[alpha](P) immunostaining. Because phosphorylation of eIF2[alpha] during early brain reperfusion is carried out by PERK, these findings suggest that there is prolonged activation of the unfolded protein response in the reperfused brain.