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 4

The presence of aggregated proteins increases TIA SG persistence in the presence of TIA1 mutations or loss of SQSTM1.

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The presence of aggregated proteins increases TIA SG persistence in the ...
(A) Immunofluorescence images of control or p62–/– MEFs labeled with Alexa Fluor 594–azide (red) to detect DRiPs after incubation at 42°C for 1 hour and following a 30-minute HS recovery. Representative data were pooled from 3 independent experiments (n = 350~450). Scale bars: 5 μm. (B) Graph of the percentage of TIA1 SGs labeled with Alexa Fluor 594–azide (red) detecting DRiPs in control or SQSTM1-knockout MEFs (p62–/–), incubated at 42°C for 1 hour and returned to 37°C for 30 minutes. Individual TIA1 SGs (green) were counted and are indicated as the total number of TIA1 SGs. Representative data were pooled from 3 independent experiments (n = 350~450). (C) IF images of MEFs expressing GFP-TIA1-WT, -NS, or -EK and labeled with Alexa Fluor 594–azide (red) to detect DRiPs before HS, after incubation at 42°C for 1 hour, and following a 30-minute HS recovery period. Representative data were pooled from 3 independent experiments (n = 350~450). (D) Bar graph of the percentage of TIA1 SGs labeled with DRiPs as in C. Individual TIA1 SGs (green) were counted and are indicated as the total number of TIA1 SGs. *P < 0.05 by 2-way ANOVA and 2-tailed Student’s t test.