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Editing-defective tRNA synthetase causes protein misfolding and neurodegeneration

Abstract

Misfolded proteins are associated with several pathological conditions including neurodegeneration. Although some of these abnormally folded proteins result from mutations in genes encoding disease-associated proteins (for example, repeat-expansion diseases), more general mechanisms that lead to misfolded proteins in neurons remain largely unknown. Here we demonstrate that low levels of mischarged transfer RNAs (tRNAs) can lead to an intracellular accumulation of misfolded proteins in neurons. These accumulations are accompanied by upregulation of cytoplasmic protein chaperones and by induction of the unfolded protein response. We report that the mouse sticky mutation, which causes cerebellar Purkinje cell loss and ataxia, is a missense mutation in the editing domain of the alanyl-tRNA synthetase gene that compromises the proofreading activity of this enzyme during aminoacylation of tRNAs. These findings demonstrate that disruption of translational fidelity in terminally differentiated neurons leads to the accumulation of misfolded proteins and cell death, and provide a novel mechanism underlying neurodegeneration.

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Figure 1: Sticky mutant pathology.
Figure 2: The sti mutation is identified in the alanyl-tRNA synthetase ( Aars ) gene.
Figure 3: Mutant fibroblasts are selectively sensitive to serine.
Figure 4: Editing deficiency in sti mutant AlaRS.
Figure 5: Accumulation of misfolded proteins in sti/sti Purkinje cells.

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Acknowledgements

We thank The Jackson Laboratory sequencing, microchemistry, histology, bioimaging and microinjection services for their contributions. We also thank L. Dionne and K. Seburn for rotorod testing and data analysis, J. Szatkiewicz for assistance with statistical analysis, J. Torrance for graphics assistance, P. O'Maille, W. Waas and A. Wolfson for gifts of plasmids, and C. Motta and E. Merriman for facilitating the expression and purification of proteins. We are also grateful to the laboratory of J. Kelly for CD spectrometer assistance and to R. Burgess and P. Nishina for comments on the manuscript. This work was supported by grants from the National Institute of Neurological Disorders and Stroke and the National Institute on Aging to S.L.A., the National Institute of General Medical Sciences and a fellowship from the National Foundation for Cancer Research to P.S., a grant from the National Center for Research Resources to M.T.D., and an institutional National Cancer Institute core grant (JAX). S.L.A. is an investigator of the Howard Hughes Medical Institute. Author Contributions J.W.L. designed and performed mouse and cell culture experiments, K.B. and L.A.N. designed and performed biochemical analyses, J.J. performed mutation analysis, M.T.D. provided the congenic sti mice and oversaw initial mapping experiments, S.A.C. and C.M.L.-G. performed genetic mapping experiments, J.P.S. performed hair pathological analysis, P.S. and S.L.A. designed and supervised experiments. All authors discussed the results and commented on the manuscript, which was written by J.W.L., K.B., P.S. and S.L.A.

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Correspondence to Susan L. Ackerman.

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Competing interests

The sequence for mouse Aars has been deposited in GenBank under the accession number AY223875; sequence-tagged sites (STSs) for D8SlacCA1 (DQ386090), D8SlacCA2 (DQ386088) and D8SlacCA3 (DQ386089) can also be found in GenBank. Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.

Supplementary information

Supplemental Methods

This file contains additional details of the methods used in this study. (DOC 38 kb)

Supplementary Figure 1.

Pathway for acylated tRNAs entering the translational machinery. (PDF 838 kb)

Supplementary Figure 2.

Follicular dystrophy in sti/sti mutant mice. (PDF 3058 kb)

Supplementary Figure 3.

The rotorod latency to fall in sti/sti and wild type mice. (PDF 104 kb)

Supplementary Figure 4.

Genes in the sti critical region. (PDF 162 kb)

Supplementary Figure 5.

The sti mutation is in the alanyl-tRNA synthetase (Aars) gene. (PDF 862 kb)

Supplementary Figure 6.

Secondary structure analysis of mutant and wild type human AlaRS. (PDF 88 kb)

Supplementary Figure 7

Normal aminoacylation of tRNAAla by A734E AlaRS. (PDF 89 kb)

Supplementary Figure 8.

Normal deacylation of Ala-tRNAAla by A734E AlaRS (PDF 132 kb)

Supplementary Figure 9.

Inherent misacylation with serine and glycine by mouse AlaRS (PDF 172 kb)

Supplementary Figure 10.

Accumulation of misfolded proteins in sti/sti Purkinje cells. (PDF 1318 kb)

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Lee, J., Beebe, K., Nangle, L. et al. Editing-defective tRNA synthetase causes protein misfolding and neurodegeneration. Nature 443, 50–55 (2006). https://doi.org/10.1038/nature05096

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