Afferent regulation of chicken auditory brainstem neurons: Rapid changes in phosphorylation of elongation factor 2

• Published in: Journal of comparative neurology (1911) Vol. 521; no. 5; pp. 1165 - 1183
• Main Authors: McBride, Ethan G., Rubel, Edwin W, Wang, Yuan
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01.04.2013; Wiley Subscription Services, Inc
• Subjects: afferent deprivation; Animals; Animals, Newborn; apoptosis; Auditory Pathways - physiology; Brain stem; Brain Stem - cytology; Brain Stem - growth & development; Brain Stem - metabolism; cell death; Cell Line, Transformed; Cell Survival; Chickens; Cochlea - physiology; cochlea removal; Gene Expression Regulation - physiology; HEK293 Cells - drug effects; HEK293 Cells - metabolism; Humans; Microtubule-Associated Proteins - metabolism; Neurons - physiology; nucleus magnocellularis; Peptide Elongation Factor 2 - metabolism; Phosphoric Monoester Hydrolases - pharmacology; Phosphorylation - physiology; protein synthesis; RNA - metabolism; Sensory Deprivation - physiology; Time Factors
• ISSN: 0021-9967; 1096-9861
• DOI: 10.1002/cne.23227

The relationships between protein synthesis and neuronal survival are poorly understood. In chicken nucleus magnocellularis (NM), significant alterations in overall protein synthesis precede neuronal death induced by deprivation of excitatory afferent activity. Previously we demonstrated an initial reduction in the overall rate of protein synthesis in all deprived NM neurons, followed by quick recovery (starting at 6 hours) in some, but not all, neurons. Neurons with recovered protein synthesis ultimately survive, whereas others become “ghost” cells (no detectable Nissl substance) at 12–24 hours and die within 48 hours. To explore the mechanisms underlying this differential influence of afferent input on protein synthesis and cell survival, the current study investigates the involvement of eukaryotic translation elongation factor 2 (eEF2), the phosphorylation of which reduces overall protein synthesis. Using immunocytochemistry for either total or phosphorylated eEF2 (p‐eEF2), we found significant reductions in the level of phosphorylated, but not total, eEF2 in NM neurons as early as 0.5–1 hour following cochlea removal. Unexpectedly, neurons with low levels of p‐eEF2 show reduced protein synthesis at 6 hours, indicated by a marker for active ribosomes. At 12 hours, all “ghost” cells exhibited little or no p‐eEF2 staining, although not every neuron with a comparable low level of p‐eEF2 was a “ghost” cell. These observations demonstrate that a reduced level of p‐eEF2 is not responsible for immediate responses (including reduced overall protein synthesis) of a neuron to compromised afferent input but may impair the neuron's ability to initiate recovery signaling for survival and make the neuron more vulnerable to death. J. Comp. Neurol. 521:1165–1183, 2013. © 2012 Wiley Periodicals, Inc. Following afferent deprivation, 30% of chicken nucleus magnocellularis (NM) die within 48h. The role of eukaryotic elongation factor 2 (eEF2) phosphorylation in this cell death was examined by double‐labeling NM neurons for Nissl substance (red) and phosphorylated eEF2 (p‐eEF2; green). Dying neurons are marked 12h after deprivation by low cytoplasmic and high nuclear levels of Nissl labeling. Dying neurons are also devoid of p‐eEF2 labeling, demonstrating that low p‐eEF2 levels indicate a fate of cell death. Scale bar is 10μm.