Transient upregulation of translational efficiency in prodromal and early symptomatic Tg2576 mice contributes to Aβ pathology

• Published in: Neurobiology of disease 2020-06, Vol.139, p.104787-104787, Article 104787
• Main Authors: Borreca, Antonella, Valeri, Francesco, De Luca, Mariassunta, Ernst, Lysianne, Russo, Arianna, Nobili, Annalisa, Cordella, Alberto, Corsetti, Veronica, Amadoro, Giuseppina, Mercuri, Nicola Biagio, D'Amelio, Marcello, Ammassari-Teule, Martine
• Format: Article
• Language: English
• Subjects: Alzheimer Disease - metabolism; Alzheimer's disease; Amyloid beta-Peptides; Amyloid beta-Protein Precursor - metabolism; Amyloid Precursor Protein Secretases - metabolism; Animals; Cognition; Disease Models, Animal; eIF2α; Eukaryotic Initiation Factor-2 - metabolism; Female; Fragile X Mental Retardation Protein; hAPP mRNA; Hippocampus - metabolism; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Neurons - metabolism; Phosphorylation; Pre-symptomatic markers; Prodromal Symptoms; RNA, Messenger - metabolism; Salubrinal; Synapses - metabolism; Synaptic plasticity; Tg2576 mice; Translational control; Up-Regulation
• ISSN: 0969-9961; 1095-953X
• DOI: 10.1016/j.nbd.2020.104787

TG2576 mice show highest levels of the full length mutant Swedish Human Amyloid Precursor Protein (APPKM670/671LN) during prodromal and early sympotomatic stages. Interestingly, this occurs in association with the unbalanced expression of two of its RNA Binding proteins (RBPs) opposite regulators, the Fragile-X Mental Retardation Protein (FMRP) and the heteronuclear Ribonucleoprotein C (hnRNP C). Whether an augmentation in overall translational efficiency also contributes to the elevation of APP levels at those early developmental stages is currently unknown. We investigated this possibility by performing a longitudinal polyribosome profiling analysis of APP mRNA and protein in total hippocampal extracts from Tg2576 mice. Results showed that protein polysomal signals were exclusively detected in pre-symptomatic (1 months) and early symptomatic (3 months) mutant mice. Differently, hAPP mRNA polysomal signals were detected at any age, but a peak of expression was found when mice were 3-month old. Consistent with an early but transient rise of translational efficiency, the phosphorylated form of the initial translation factor eIF2α (p-eIF2α) was reduced at pre-symptomatic and early symptomatic stages, whereas it was increased at the fully symptomatic stage. Pharmacological downregulation of overall translation in early symptomatic mutants was then found to reduce hippocampal levels of full length APP, Aβspecies, BACE1 and Caspase-3, to rescue predominant LTD at hippocampal synapses, to revert dendritic spine loss and memory alterations, and to reinstate memory-induced c-fosactivation. Altogether, our findings demonstrate that overall translation is upregulated in prodromal and early symptomatic Tg2576 mice, and that restoring proper translational control at the onset of AD-like symptoms blocks the emergence of the AD–like phenotype. [Display omitted] •The shift of APP mRNA in polysomal fraction found in AD mice reveals that APP is more prone to be translated when mice are pre- and early symptomatic.•Early enhancement of APP translation associates with decreased levels of eIF2aphosphorylation (p-eIF2a).•Salubrinal-induced inhibition of eIF2ade-phosphorylation in early symptomatic mutant mice globally rescues the AD phenotype.•Opposite dysregulation of APP and p-eIF2alevels in association with mild cognitive impairment should reliably predictfuture AD.