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Expression of FSHD-related DUX4-FL alters proteostasis and induces TDP-43 aggregation
Sachiko Homma1, Mary Lou Beermann1, Frederick M Boyce2
1Neuromuscular Biology & Disease Group, Departments of Neurology and Physiology & Biophysics, Boston University School of Medicine Boston, Massachusetts, 02118.
Objective:
Pathogenesis in facioscapulohumeral muscular dystrophy (FSHD) appears to be due to aberrant expression, particularly in skeletal muscle nuclei, of the full-length isoform of DUX4 (DUX4-FL). Expression of DUX4-FL is known to alter gene expression and to be cytotoxic, but cell responses to DUX4-FL are not fully understood. Our study was designed to identify cellular mechanisms of pathogenesis caused by DUX4-FL expression.
Methods:
We used human myogenic cell cultures to analyze the effects of DUX4-FL when it was expressed either from its endogenous promoter in FSHD cells or by exogenous expression using BacMam vectors. We focused on determining the effects of DUX4-FL on protein ubiquitination and turnover and on aggregation of TDP-43.
Results:
Human FSHD myotubes with endogenous DUX4-FL expression showed both altered nuclear and cytoplasmic distributions of ubiquitinated proteins and aggregation of TDP-43 in DUX4-FL-expressing nuclei. Similar changes were found upon exogenous expression of DUX4-FL, but were not seen upon expression of the non-toxic short isoform DUX4-S. DUX4-FL expression also inhibited protein turnover in a model system and increased the amounts of insoluble ubiquitinated proteins and insoluble TDP-43. Finally, inhibition of the ubiquitin-proteasome system with MG132 produced TDP-43 aggregation similar to DUX4-FL expression.
Interpretations:
Our results identify DUX4-FL-induced inhibition of protein turnover and aggregation of TDP-43, which are pathological changes also found in diseases such as amyotrophic lateral sclerosis and inclusion body myopathy, as potential pathological mechanisms in FSHD.
Insights
Facioscapulohumeral muscular dystrophy (FSHD) pathogenesis involves DUX4-FL protein, which impairs protein turnover and causes TDP-43 aggregation. These findings offer new insights into FSHD cellular mechanisms.
Area of Science:
- Molecular Biology
- Cellular Biology
- Genetics
Background:
- Facioscapulohumeral muscular dystrophy (FSHD) is linked to aberrant expression of the DUX4-FL protein.
- The precise cellular mechanisms underlying DUX4-FL-induced pathogenesis remain incompletely understood.
- DUX4-FL expression is known to alter gene expression and induce cytotoxicity.
Purpose of the Study:
- To elucidate the cellular mechanisms driving pathogenesis in FSHD.
- To investigate the effects of DUX4-FL expression on protein ubiquitination, turnover, and TDP-43 aggregation.
Main Methods:
- Utilized human myogenic cell cultures to study DUX4-FL effects.
- Analyzed DUX4-FL expression from endogenous promoters in FSHD cells and via exogenous BacMam vector delivery.
- Focused on protein ubiquitination, turnover, and TDP-43 aggregation.
Main Results:
- DUX4-FL expression in FSHD myotubes altered ubiquitinated protein distribution and induced TDP-43 aggregation.
- Exogenous DUX4-FL expression mimicked these effects, unlike the DUX4-S isoform.
- DUX4-FL inhibited protein turnover and increased insoluble ubiquitinated proteins and TDP-43.
Conclusions:
- DUX4-FL-induced protein turnover inhibition and TDP-43 aggregation are identified as key pathological mechanisms in FSHD.
- These mechanisms are shared with other neurodegenerative diseases like ALS and inclusion body myopathy.
- This research provides critical insights into FSHD cellular pathology.
