Neural Plast. 2015;2015:825157. doi: 10.1155/2015/825157.

Limited effects of an eIF2αS51A allele on neurological impairments in the 5xFAD mouse model of Alzheimer’s disease.

 

Paesler K1, Xie K1, Hettich MM1, Siwek ME2, Ryan DP1, Schröder S1, Papazoglou A2, Broich K2, Müller R3, Trog A4, Garthe A5, Kempermann G5, Weiergräber M2, Ehninger D1.
  • 1German Center for Neurodegenerative Diseases (DZNE), Ludwig Erhard Allee 2, 53175 Bonn, Germany.
  • 2Federal Institute for Drugs and Medical Devices (BfArM), Kurt Georg Kiesinger Allee 3, 53175 Bonn, Germany.
  • 3Department of Psychiatry and Psychotherapy, University of Cologne, Kerpener Straße 62, 50937 Köln, Germany.
  • 4Institute of Molecular Psychiatry, University of Bonn, Sigmund Freud Straße 25, 53125 Bonn, Germany.
  • 5German Center for Neurodegenerative Diseases (DZNE), Fetscherstraße 105, 01307 Dresden, Germany.

 

Abstract

Alzheimer’s disease (AD) has been associated with increased phosphorylation of the translation initiation factor 2α (eIF2α) at serine 51. Increased phosphorylation of eIF2α alters translational control and may thereby have adverse effects on synaptic plasticity, learning, and memory. To analyze if increased levels of p-eIF2α indeed promote AD-related neurocognitive impairments, we crossed 5xFAD transgenic mice with an eIF2α(S51A) knock-in line that expresses the nonphosphorylatable eIF2α variant eIF2α(S51A). Behavioral assessment of the resulting mice revealed motor and cognitive deficits in 5xFAD mice that were, with the possible exception of locomotor hyperactivity, not restored by the eIF2α(S51A) allele. Telemetric intracranial EEG recordings revealed no measurable effects of the eIF2α(S51A) allele on 5xFAD-associated epileptic activity. Microarray-based transcriptome analyses showed clear transcriptional alterations in 5xFAD hippocampus that were not corrected by the eIF2α(S51A) allele. In contrast to prior studies, our immunoblot analyses did not reveal increased levels of p-eIF2α in the hippocampus of 5xFAD mice, suggesting that elevated p-eIF2α levels are not a universal feature of AD models. Collectively, our data indicate that 5xFAD-related pathologies do not necessarily require hyperphosphorylation of eIF2α to emerge; they also show that heterozygosity for the nonphosphorylatable eIF2α(S51A) allele has limited effects on 5xFAD-related disease manifestations.

PMID: 25883808

 

Supplementary text

The eukaryotic translation initiation factor 2α (eIF2α) is an essential factor for protein synthesis. Its phosphorylation at serine residue 51 is associated with a downregulation of global protein synthesis and a translational upregulation of specific transcripts, such as the activating transcription factor 4 (ATF4) [1-3]. Hyperphosphorylation of eIF2α has been observed in human postmortem brain tissue, as well as in mouse models of Alzheimer’s disease (AD) [4-7] and might contribute to altered plasticity and cognitive dysfunction in AD.

In order to address whether eIF2α hyperphosphorylation plays a role in diseases progression in mouse models of familial AD, we crossed the 5xFAD mouse model with heterozygous eIF2αS51A knock-in mice that express a non-phosphorylatable eIF2α variant. We then tested the resulting mice for a range of disease outcomes, including neurological phenotypes, electrophysiological alterations, as well as biochemical and transcriptome changes.

We observed a number of disease phenotypes in 5xFAD mice, including reduced body weight and body length and a number of neurological alterations. These included the presence of a pathological hindlimb clasping reflex, as well as deficits in muscle strength and motor coordination. 5xFAD mice showed an impaired performance on hippocampus-dependent learning and memory tasks, such as contextual fear conditioning and spatial learning in the Morris water maze. Additionally, 5xFAD animals showed pronounced motor hyperactivity in an open field assay and epileptic seizures observed by telemetric intracranial electroencephalogram recordings. The neurobehavioral phenotype was associated with increased levels of amyloid-β and C-terminals fragments, as well as transcriptional alterations that featured a substantial enrichment of immune response-related genes among transcripts differentially expressed in the hippocampus of 5xFAD mice. Unexpectedly, the extent of eIF2α phosphorylation was unaltered in 5xFAD mice.

 

 

DE Figure 1

Figure 1: The eIF2αS51A allele had limited effects on a range of neurological phenotypes in 5xFAD mice, including pathological reflexes, impaired motor behavior and deficient contextual fear conditioning.

 

Overall, the non-phosphorylatable eIF2α variant (eIF2αS51A) had few measurable effects on the 5xFAD phenotypes described above, including impaired motor strength and coordination, as well as learning and memory deficits. The eIF2αS51A allele did, however, appear to restore locomotor hyperactivity in the open field in 5xFAD mice. We considered the possibility that the eIF2αS51A allele rescued hyperactivity in 5xFAD mice by preventing the degeneration of the cholinergic system in these animals, which may contribute to hyperlocomotion in this and related models [8-13]. Stereological cell counting analyses revealed only limited loss of cholinergic neurons in 5xFAD mice, whereas immunoblot analyses were sensitive enough to pick up clear 5xFAD-related reductions in ChAT (choline acetyltransferase, a marker of cholinergic neurons) protein levels in one of the target areas of basal forebrain cholinergic nuclei, namely the hippocampus. However, the eIF2αS51A allele did not rescue the aberrant cholinergic system of 5xFAD mice, indicating that the neurobiology underlying the eIF2αS51A-mediated rescue of 5xFAD-related hyperactivity remains to be elucidated.

In conclusion, our data suggest that an excessive eIF2α phosphorylation is not a universal feature of AD mouse models and that heterozygosity for the non-phosphorylatable eIF2αS51A allele has limited effects on 5xFAD-related disease manifestations.

 

DE Figure 2

Figure 2: 5xFAD-related hyperactivity appeared to be restored by the non-phosphorylatable eIF2αS51A allele.

 

References

  1. Harding HP, Zhang Y, Ron D: Protein translation and folding are coupled by an endoplasmic-reticulum-resident kinase. Nature 1999, 397(6716):271-274.
  2. Blais JD, Filipenko V, Bi M, Harding HP, Ron D, Koumenis C, Wouters BG, Bell JC: Activating transcription factor 4 is translationally regulated by hypoxic stress. Mol Cell Biol 2004, 24(17):7469-7482.
  3. Costa-Mattioli M, Gobert D, Harding H, Herdy B, Azzi M, Bruno M, Bidinosti M, Ben Mamou C, Marcinkiewicz E, Yoshida M et al: Translational control of hippocampal synaptic plasticity and memory by the eIF2alpha kinase GCN2. Nature 2005, 436(7054):1166-1173.
  4. Chang RC, Wong AK, Ng HK, Hugon J: Phosphorylation of eukaryotic initiation factor-2alpha (eIF2alpha) is associated with neuronal degeneration in Alzheimer’s disease. Neuroreport 2002, 13(18):2429-2432.
  5. Kim HS, Choi Y, Shin KY, Joo Y, Lee YK, Jung SY, Suh YH, Kim JH: Swedish amyloid precursor protein mutation increases phosphorylation of eIF2alpha in vitro and in vivo. Journal of neuroscience research 2007, 85(7):1528-1537.
  6. O’Connor T, Sadleir KR, Maus E, Velliquette RA, Zhao J, Cole SL, Eimer WA, Hitt B, Bembinster LA, Lammich S et al: Phosphorylation of the translation initiation factor eIF2alpha increases BACE1 levels and promotes amyloidogenesis. Neuron 2008, 60(6):988-1009.
  7. Mouton-Liger F, Paquet C, Dumurgier J, Bouras C, Pradier L, Gray F, Hugon J: Oxidative stress increases BACE1 protein levels through activation of the PKR-eIF2alpha pathway. Biochim Biophys Acta 2012, 1822(6):885-896.
  8. Boncristiano S, Calhoun ME, Kelly PH, Pfeifer M, Bondolfi L, Stalder M, Phinney AL, Abramowski D, Sturchler-Pierrat C, Enz A et al: Cholinergic changes in the APP23 transgenic mouse model of cerebral amyloidosis. J Neurosci 2002, 22(8):3234-3243.
  9. Bellucci A, Luccarini I, Scali C, Prosperi C, Giovannini MG, Pepeu G, Casamenti F: Cholinergic dysfunction, neuronal damage and axonal loss in TgCRND8 mice. Neurobiology of disease 2006, 23(2):260-272.
  10. Perez SE, Dar S, Ikonomovic MD, DeKosky ST, Mufson EJ: Cholinergic forebrain degeneration in the APPswe/PS1DeltaE9 transgenic mouse. Neurobiology of disease 2007, 28(1):3-15.
  11. Christensen DZ, Bayer TA, Wirths O: Intracellular Ass triggers neuron loss in the cholinergic system of the APP/PS1KI mouse model of Alzheimer’s disease. Neurobiology of aging 2010, 31(7):1153-1163.
  12. Devi L, Ohno M: Phospho-eIF2alpha level is important for determining abilities of BACE1 reduction to rescue cholinergic neurodegeneration and memory defects in 5XFAD mice. PloS one 2010, 5(9):e12974.
  13. Whishaw IQ, O’Connor WT, Dunnett SB: Disruption of central cholinergic systems in the rat by basal forebrain lesions or atropine: effects on feeding, sensorimotor behaviour, locomotor activity and spatial navigation. Behav Brain Res 1985, 17(2):103-115.

 

 

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