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Defective protein translation as a pathogenic mechanism of peripheral neuropathy

Periodic Reporting for period 3 - CMTaaRS (Defective protein translation as a pathogenic mechanism of peripheral neuropathy)

Reporting period: 2021-06-01 to 2022-11-30

Since the start of the ERC funding, we have (co-)authored the following publications - the scientific problem, the societal relevance and the overall objectives are summarized below each publication:

1. Catinozzi M, Mallik M, Frickenhaus M, Been M, Sijlmans C, Kulshrestha D, Alexopoulos I, Weitkunat M, Schnorrer F, Storkebaum E. The Drosophila FUS ortholog cabeza promotes adult founder myoblast selection by Xrp1-dependent regulation of FGF signaling. PLOS Genetics, 2020; 16(4):e1008731. doi: 10.1371/journal.pgen.1008731.

This paper reports that loss of function of the Drosophila gene cabeza (the Drosophila equivalent of the human FUS gene, mutations in which can cause a familial form of the motor neurodegenerative disease amyotrophic lateral sclerosis or ALS) induces muscle developmental defects. These defects are mediated by increased expression of a protein called Xrp1, which is involved in gene expression regulation. We show that dysregulation of appropriate expression of components of the fibroblast growth factor (FGF) pathway contributes to muscle developmental defects in cabeza mutant Drosophila.

2. Picchiarelli G, Demestre M, Zuko A, Been M, Higelin J, Dieterlé S, Goy M-A, Mallik M, Sellier C, Scekic-Zahirovic J, Zhang L, Rosenbohm A, Sijlmans C, Aly A, Mersmann S, Sanjuan-Ruiz I, Hübers A, Messaddeq N, Wagner M, van Bakel N, Boutillier A-L, Ludolph A, Lagier-Tourenne C, Boeckers T, Dupuis L, Storkebaum E. FUS-mediated transcriptional regulation of acetylcholine receptor at neuromuscular junctions is compromised in amyotrophic lateral sclerosis. Nature Neuroscience, 2019; 22(11):1793-1805.

This paper investigates the molecular mechanisms underlying a familial form of amyotrophic lateral sclerosis (ALS) associated with mutations in FUS. Using a transgenic mouse model in which an ALS-like mutation was introduced in the mouse Fus gene, we could show that ALS pathology starts at the neuromuscular juction (the transition between motor nerves and skeletal muscle cells), long before motor neuron cell bodies in the spinal cord degenerate. Furthermore, we could show that expression of the acetylcholine receptor in skeletal muscles of these mice is affected. The acetylcholine receptor is the receptor that is required for muscle cells to receive signals from the motor nerve. A very important finding reported in this paper is that ALS-mutant FUS protein is toxic to both skeletal muscle cells and motor neurons. This implies that future therapies for ALS-FUS should not only be directed at motor neurons but also at muscle cells.

3. Moens T, Niccoli T, Wilson K, Atilano M, Birsa N, Gittings L, Holbling B, Dyson M, Thoeng A, Neeves J, Glaria I, Yu L, Bussmann J, Storkebaum E, Pardo M, Choudhary J, Fratta P, Partridge L, Isaacs A. C9orf72 arginine-rich dipeptide proteins interact with ribosomal proteins in vivo to induce a toxic translational arrest that is rescued by eIF1A. Acta Neuropathologica 2019; 137(3):487-500.

Hexanucleotide repeat expansions in a gene called C9orf72 are the most prevalent cause of familial ALS. Translation of these hexanucleotide repeat sequences gives rise to dipeptide-repeat proteins, which form intracellular protein aggregates in neuronal and non-neuronal cells of affected patients. This paper reports that certain of these dipeptide repeat proteins interfere with protein synthesis in affected cells, and this molecular derailment may contribute to motor neuron degenetion in C9orf72-ALS patients.

4. Mallik M, Catinozzi M, Clemens H, Zhang L, Wagner M, Bussmann J, Bittern J, Mersmann S, Klämbt C, Drexler H, Huynen M, Vaquerizas J, Storkebaum E. Xrp1 genetically interacts with the ALS-associated FUS ortholog caz and mediates its toxicity. Journal of Cell Biology 2018, 217(11):3947-3964. Cover story.

This paper identifies Xrp1 as genetic interactor of the Drosophila FUS ortholog cabeza. Xrp1 is a DNA-binding protein that is involved in gene expression regulation. We found that Xrp1 expression is increased in cabeza mutant fruit flies, leading to neuronal dysfunction. These findings implicate gene expression dysregulation in the pathogenesis of ALS caused by mutations in FUS.

5. Rode S, Ohm H, Anhäuser L, Wagner M, Rosing M, Deng X, Sin O, Leidel S, Storkebaum E, Rentmeister A, Zhu S, Rumpf S. Differential requirement for translation initiation factor pathways during ecdysone-dependent neuronal remodeling in Drosophila. Cell Reports 2018, 24(9):2287-2299.

This paper reports that proper protein synthesis is required for normal morphology of sensory neurons in the fruit fly Drosophila melanogaster.

6. Naumann M, Pal A, Goswami A, Lojewski X, Japtok J, Vehlow A, Naujock M, Günther R, Jin M, Stanslowsky N, Reinhardt P, Sterneckert J, Frickenhaus M, Pan-Montojo F, Storkebaum E, Poser I, Freischmidt A, Weishaupt J, Holzmann K, Troost D, Ludolph A, Boeckers T, Liebau S, Petri S, Cordes N, Hyman A, Wegner F, Grill S, Weis J, Storch A, Hermann A. Impaired DNA damage response signaling by FUS-NLS mutations leads to neurodegeneration and aggregation formation. Nature Communications 2018, 9(1):335. DOI: 10.1038/s41467-017-02299-1.

In this paper, motor neurons derived from induced pluripotent stem cells are used as a cellular model for ALS associated with mutations in FUS. This paper reports that ALS-causing mutations in FUS lead to an impaired molecular response to DNA damage in affected motor neurons, a mechanism that may contribute to motor neuron degeneration in ALS-FUS patients.
We have studied the molecular mechanisms underlying Charcot-Marie-Tooth disease caused by mutations in tRNA synthetases. Charcot-Marie-Tooth (CMT) disease is characterized by selective degeneration of peripheral motor and sensory neurons, leading to progressive muscle weakness and wasting and sensory dysfunction. Heterozygous mutations in six distinct tRNA synthetase genes have been identified as a genetic cause of CMT. We have previously used the fruit fly Drosophila melanogaster to generate animal models for CMT caused by mutations in the glycyl- and tyrosyl-tRNA synthetase. For this project, we use these Drosophila models to study the role of defective protein synthesis in the pathogenesis of these forms of CMT, along with mouse models and biochemical approaches. We found that inhibtion of protein synthesis may constitute a common pathogenic mechanism underlying CMT caused by mutations in tRNA synthetases. We have made major progress in identifying the molecular mechanism underlying the inhibition of protein synthesis. This has led to a detailed molecular working model that may explain the how the defective protein synthesis comes about.
As indicated above, our results thus far have led to a detailed molecular working model to explain the inhibition of protein synthesis and the induction of peripheral neuropathy phenotypes in Drosophila and mouse for CMT caused by mutant tRNA synthetases. We now wish to validate this working model, and evaluate whether it universally applies to CMT caused by mutant tRNA synthetases. We also wish to study the mechanisms underlying the cell-type-specific nature of these forms of CMT.
Mechanism of tRNA-gly aminoacylation by glycyl-tRNA synthetase (GlyRS)