TIA1 variant drives myodegeneration in multisystem proteinopathy with SQSTM1 mutations
YouJin Lee, … , Conrad C. Weihl, Bjarne Udd
YouJin Lee, … , Conrad C. Weihl, Bjarne Udd
Published February 19, 2018
Citation Information: J Clin Invest. 2018;128(3):1164-1177. https://doi.org/10.1172/JCI97103.
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Research Article Genetics Muscle biology

TIA1 variant drives myodegeneration in multisystem proteinopathy with SQSTM1 mutations

Abstract

Multisystem proteinopathy (MSP) involves disturbances of stress granule (SG) dynamics and autophagic protein degradation that underlie the pathogenesis of a spectrum of degenerative diseases that affect muscle, brain, and bone. Specifically, identical mutations in the autophagic adaptor SQSTM1 can cause varied penetrance of 4 distinct phenotypes: amyotrophic lateral sclerosis (ALS), frontotemporal dementia, Paget’s disease of the bone, and distal myopathy. It has been hypothesized that clinical pleiotropy relates to additional genetic determinants, but thus far, evidence has been lacking. Here, we provide evidence that a TIA1 (p.N357S) variant dictates a myodegenerative phenotype when inherited, along with a pathogenic SQSTM1 mutation. Experimentally, the TIA1-N357S variant significantly enhances liquid-liquid–phase separation in vitro and impairs SG dynamics in living cells. Depletion of SQSTM1 or the introduction of a mutant version of SQSTM1 similarly impairs SG dynamics. TIA1-N357S–persistent SGs have increased association with SQSTM1, accumulation of ubiquitin conjugates, and additional aggregated proteins. Synergistic expression of the TIA1-N357S variant and a SQSTM1-A390X mutation in myoblasts leads to impaired SG clearance and myotoxicity relative to control myoblasts. These findings demonstrate a pathogenic connection between SG homeostasis and ubiquitin-mediated autophagic degradation that drives the penetrance of an MSP phenotype.

Authors

YouJin Lee, Per Harald Jonson, Jaakko Sarparanta, Johanna Palmio, Mohona Sarkar, Anna Vihola, Anni Evilä, Tiina Suominen, Sini Penttilä, Marco Savarese, Mridul Johari, Marie-Christine Minot, David Hilton-Jones, Paul Maddison, Patrick Chinnery, Jens Reimann, Cornelia Kornblum, Torsten Kraya, Stephan Zierz, Carolyn Sue, Hans Goebel, Asim Azfer, Stuart H. Ralston, Peter Hackman, Robert C. Bucelli, J. Paul Taylor, Conrad C. Weihl, Bjarne Udd

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Figure 2

TIA1-N357S variant promotes LLPS and disrupts SG dynamics.

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TIA1-N357S variant promotes LLPS and disrupts SG dynamics. (A) Phase di...
(A) Phase diagram of TIA1-WT, -EK, and -NS mapped at physiological conditions. The mean concentration of the light phase (protein depleted phase) and SE are plotted. A quadratic equation was used to fit the trendlines (R2, WT, and NS = 0.99, EK = 0.98; P < 0.003 for NS vs. WT and P < 0.0002 for EK vs. WT, by χ2 test). Insets show characteristic DIC images of light, diffused phase, and dense phase droplets, respectively. (B) Thioflavin T fluorescence intensity of amyloid fibrils at 2.5 μM TIA1-WT, -EK, and -NS variants at the indicated time points. The spectrum of BSA (nonamyloid fibril–forming) was measured as a baseline. That baseline was subtracted from all the WT, EK and NS spectra at each time point. ***P < 0.001, by 2-way ANOVA with Tukey’s multiple comparisons test (NS, P > 0.1). (C) IF images of MEFs expressing GFP-TIA1-WT, -NS, or -EK immunostained with anti-G3BP1 (red) prior to 1 hour HS at 42°C, immediately after HS, or following a 30-minute HS recovery at 37°C. DAPI nuclear staining is shown in blue. Scale bars: 5 μm. (D) Bar graph of the percentage of cells containing TIA1/G3BP1-positive SGs under the conditions described in C. Individual transfected cells were counted and are indicated as the total number of cells. Representative data were pooled from 3 independent experiments (n = 150~200). rec, recovery. (E) Graphical representation of the average relative fluorescence intensity (RFI) following photobleaching of individual SGs from MEFs expressing GFP-TIA1-WT, -NS, or -EK and treated for 1 hour with 0.5 mM arsenite. Representative data were pooled from 3 independent experiments (n = 20~30). Error bars represent the mean ± SEM. (D and E) *P < 0.05, by 2-way ANOVA and 2-tailed Student’s t test.