Altered mechanisms of protein synthesis in frontal cortex in Alzheimer disease and a mouse model

Abstract

Expression of the nucleolar chaperones nucleolin (NCL) and nucleophosmin (NPM1), upstream binding transcription factor (UBTF), rRNA18S, rRNA28S, and several genes encoding ribosomal proteins (RPs) is decreased in frontal cortex area 8 at advanced stages of Alzheimer's disease (AD). This is accompanied by reduced protein levels of elongation factors eEF1A and eEF2. Changes are more marked in AD cases with rapid course (rpAD), as initiation factor eIF3η is significantly down-regulated and several RP genes up-regulated in rpAD when compared with typical AD. These changes contrast with those seen in APP/PS1 transgenic mice used as a model of AD-like β-amyloidopathy; Ncl mRNA, rRNA18S, rRNA28S and seven out of fifteen assessed RP genes are up-regulated in APP/PS1 mice aged 20 months; only eEF2 protein levels are reduced in transgenic mice. Our findings show marked altered expression of molecules linked to the protein synthesis machinery from the nucleolus to the ribosome in frontal cortex at terminal stages of AD which differs from that seen in APP/PS1 transgenic mice, thus further suggesting that molecular signals in mouse models do not apply to real human disease counterparts.

Keywords: APP/PS1 transgenic mouse; Alzheimer’s disease; nucleolar chaperones; protein synthesis; rRNAs; transcription; translation.

Figure 1

Protein expression levels of eukaryotic initiation factors eIF2α, phospho-eIF2α, eIF3η and eIF5, and eukaryotic elongation factors, eEF1A and eEF2 as revealed with gel electrophoresis and western blotting in frontal cortex area 8 in MA, AD and rpAD, and corrected with β-actin. Densitometry of western blot bands was assessed with the TotalLab program and subsequently analyzed with GraphPad Prism and Statgraphics Statistical Analysis, and Data Visualization Software version 5.1 with one-way ANOVA with post-hoc Tukey’s range test for multiple comparisons: *P<0.05; **P<0.01; ***P<0.001.

Figure 2

Western blots of the somatosensory cortex of WT and APP/PS1 transgenic mice at the ages of 3, 12 and 20 months showing the expression of eIF2α, eIF3η, eIF5, eEF1a and eEF2 proteins.

Figure 3

Protein expression levels of eukaryotic initiation factors eIF2α, eIF3η and eIF5, and eukaryotic elongation factors, eEF1A and eEF2 as revealed with gel electrophoresis and western blotting in somatosensory cortex of WT and APP/PS1 transgenic mice at the ages of 3, 12 and 20 months. Densitometry of western blot bands was assessed with the TotalLab program and subsequently analyzed with GraphPad Prism and Statgraphics Statistical Analysis, and Data Visualization Software version 5.1 with one-way ANOVA with post-hoc Tukey’s range test for multiple comparisons: *P<0.05, **P<0.01 comparison with age-matched WT; §P<0.01, §§P<0.01, §§§P<0.001, comparison with mice aged 3 months; #P<0.05, ##P<0.01, comparison with mice aged 12 months.