Genetic removal of eIF2α kinase PERK in mice enables hippocampal L‐LTP independent of mTORC1 activity

Abstract

Characterization of the molecular signaling pathways underlying protein synthesis-dependent forms of synaptic plasticity, such as late long-term potentiation (L-LTP), can provide insights not only into memory expression/maintenance under physiological conditions but also potential mechanisms associated with the pathogenesis of memory disorders. Here, we report in mice that L-LTP failure induced by the mammalian (mechanistic) target of rapamycin complex 1 (mTORC1) inhibitor rapamycin is reversed by brain-specific genetic deletion of PKR-like ER kinase, PERK (PERK KO), a kinase for eukaryotic initiation factor 2α (eIF2α). In contrast, genetic removal of general control non-derepressible-2, GCN2 (GCN2 KO), another eIF2α kinase, or treatment of hippocampal slices with the PERK inhibitor GSK2606414, does not rescue rapamycin-induced L-LTP failure, suggesting mechanisms independent of eIF2α phosphorylation. Moreover, we demonstrate that phosphorylation of eukaryotic elongation factor 2 (eEF2) is significantly decreased in PERK KO mice but unaltered in GCN2 KO mice or slices treated with the PERK inhibitor. Reduction in eEF2 phosphorylation results in increased general protein synthesis, and thus could contribute to the mTORC1-independent L-LTP in PERK KO mice. We further performed experiments on mutant mice with genetic removal of eEF2K (eEF2K KO), the only known kinase for eEF2, and found that L-LTP in eEF2K KO mice is insensitive to rapamycin. These data, for the first time, connect reduction in PERK activity with the regulation of translation elongation in enabling L-LTP independent of mTORC1. Thus, our findings indicate previously unrecognized levels of complexity in the regulation of protein synthesis-dependent synaptic plasticity. Read the Editorial Highlight for this article on page 119. Cover Image for this issue: doi: 10.1111/jnc.14185.

Brain-specific repression of AMPKα1 alleviates pathophysiology in Alzheimer’s model mice

“…Markedly, AD-associated eEF2 hyperphosphorylation was restored with selective AMPKα1, but not AMPKα2, suppression ( Figure 5A). To directly measure de novo protein synthesis, we used the surface sensing of translation (SUnSET, a nonradioactive puromycin end-labeling assay) on living acute hippocampal slices (42,43). In agreement with previous studies (44), de novo protein synthesis in hippocampal slices (assessed by puromycin labeling) was reduced in Tg mice as compared with WT controls ( Figure 5B).…”

“…Tissues were removed from appropriate structures and flash frozen on dry ice. Tissues were then homogenized in an appropriate lysis buffer and quantified as previously described (43). Samples were loaded on 4% to 15% TGX Precast Gels (Bio-Rad) and transferred to nitrocellulose membranes.…”

Genetic reduction of eEF2 kinase alleviates pathophysiology in Alzheimer’s disease model mice

“…Mounting evidence suggests an important role for elongation regulation in cognition, with recent studies linking dysregulation of elongation factors with AD pathophysiology (15,(44)(45)(46)(47). Of note, a recent study showed a connection between eIF2 signaling and eEF2 phosphorylation in neurons (48). While additional studies are warranted to evaluate ADassociated dysregulation of initiation and elongation separately, there is evidence for crosstalk between these 2 phases of translation via eIF2 and eEF2.…”

The Unfolded Protein Response and Autophagy as Drug Targets in Neuropsychiatric Disorders

“…Hippocampus late long-term potentiation (L-LTP), inhibited by rapamycin acting on the mammalian target of rapamycin complex 1 (mTORC1), was reversed in the PERK KO mice. Mechanistically, the PERK KO mice displayed no alterations in mTORC1 signaling but showed reduced phosphorylation of eukaryotic elongation factor 2 (eEF2) with increased protein translation (Zimmermann et al, 2018 ). These results point to the role of PERK in mTORC1-independent L-LTP via its effects on eEF2-mediated translation.…”