Dysregulation of ubiquitin homeostasis and β-catenin signaling promote spinal muscular atrophy
Thomas M. Wishart, … , Brunhilde Wirth, Thomas H. Gillingwater
Thomas M. Wishart, … , Brunhilde Wirth, Thomas H. Gillingwater
Published March 3, 2014
Citation Information: J Clin Invest. 2014;124(4):1821-1834. https://doi.org/10.1172/JCI71318.
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Research Article Neuroscience

Dysregulation of ubiquitin homeostasis and β-catenin signaling promote spinal muscular atrophy

Abstract

The autosomal recessive neurodegenerative disease spinal muscular atrophy (SMA) results from low levels of survival motor neuron (SMN) protein; however, it is unclear how reduced SMN promotes SMA development. Here, we determined that ubiquitin-dependent pathways regulate neuromuscular pathology in SMA. Using mouse models of SMA, we observed widespread perturbations in ubiquitin homeostasis, including reduced levels of ubiquitin-like modifier activating enzyme 1 (UBA1). SMN physically interacted with UBA1 in neurons, and disruption of Uba1 mRNA splicing was observed in the spinal cords of SMA mice exhibiting disease symptoms. Pharmacological or genetic suppression of UBA1 was sufficient to recapitulate an SMA-like neuromuscular pathology in zebrafish, suggesting that UBA1 directly contributes to disease pathogenesis. Dysregulation of UBA1 and subsequent ubiquitination pathways led to β-catenin accumulation, and pharmacological inhibition of β-catenin robustly ameliorated neuromuscular pathology in zebrafish, Drosophila, and mouse models of SMA. UBA1-associated disruption of β-catenin was restricted to the neuromuscular system in SMA mice; therefore, pharmacological inhibition of β-catenin in these animals failed to prevent systemic pathology in peripheral tissues and organs, indicating fundamental molecular differences between neuromuscular and systemic SMA pathology. Our data indicate that SMA-associated reduction of UBA1 contributes to neuromuscular pathogenesis through disruption of ubiquitin homeostasis and subsequent β-catenin signaling, highlighting ubiquitin homeostasis and β-catenin as potential therapeutic targets for SMA.

Authors

Thomas M. Wishart, Chantal A. Mutsaers, Markus Riessland, Michell M. Reimer, Gillian Hunter, Marie L. Hannam, Samantha L. Eaton, Heidi R. Fuller, Sarah L. Roche, Eilidh Somers, Robert Morse, Philip J. Young, Douglas J. Lamont, Matthias Hammerschmidt, Anagha Joshi, Peter Hohenstein, Glenn E. Morris, Simon H. Parson, Paul A. Skehel, Thomas Becker, Iain M. Robinson, Catherina G. Becker, Brunhilde Wirth, Thomas H. Gillingwater

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Figure 6

Amelioration of neuromuscular pathology in zebrafish and Drosophila models of SMA following pharmacological inhibition of β-catenin signaling.

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Amelioration of neuromuscular pathology in zebrafish and Drosophila mode...
(A) Representative confocal micrographs of motor axons growing out from the spinal cord in a SMA zebrafish 34 hours after fertilization (top panel) as well as an SMA zebrafish treated with 50 μM quercetin (bottom panel). Note the abnormal outgrowth and branching of motor axons in SMA zebrafish absent in the SMA zebrafish treated with quercetin. Scale bar: 100 μm. (B and C) Significant improvement in the number of truncated motor axons (B) and abnormally branched motor axons (C) in SMA zebrafish treated with 50 μM quercetin (Kruskal-Wallis test with Dunn’s post hoc test; n = 31 animals, control; n = 32 SMA; n = 30 SMA + 50 μM quercetin). (D) Representative confocal micrographs of NMJs in WT Drosophila (w1118), SMA Drosophila without quercetin, and SMA Drosophila fed 50 μM quercetin. NMJs were stained with anti-HRP to visualize axons and anticysteine string protein to identify synaptic boutons. Scale bar: 10 μm. (E and F) Feeding SMA Drosophila 50 μM quercetin restored bouton size (E) and rescued synaptic overgrowth (F) (n = 8 larvae per treatment; ANOVA with Tukey’s post test). *P < 0.05; **P < 0.01; ***P < 0.001.