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DDX3X overexpression decreases dipeptide repeat proteins in a mouse model of C9ORF72-ALS/FTD
Xiujuan Fu1, Zhe Zhang1, Lindsey R Hayes2
1Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Brain Science Institute, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
Abstract:
Hexanucleotide repeat expansion in C9ORF72 (C9) is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). One of the proposed pathogenic mechanisms is the neurotoxicity arising from dipeptide repeat (DPR) proteins produced by repeat-associated non-AUG (RAN) translation. Therefore, reducing DPR levels emerges as a potential therapeutic strategy for C9ORF72-ALS/FTD. We previously identified an RNA helicase, DEAD-box helicase 3 X-linked (DDX3X), modulates RAN translation. DDX3X overexpression decreases poly-GP accumulation in C9ORF72-ALS/FTD patient-derived induced pluripotent stem cell (iPSC)-differentiated neurons (iPSNs) and reduces the glutamate-induced neurotoxicity. In this study, we examined the in vivo efficacy of DDX3X overexpression using a mouse model. We expressed exogenous DDX3X or GFP in the central nervous system (CNS) of the C9-500 ALS/FTD BAC transgenic or non-transgenic control mice using adeno-associated virus serotype 9 (AAV9). The DPR levels were significantly reduced in the brains of DDX3X-expressing C9-BAC mice compared to the GFP control even twelve months after virus delivery. Additionally, p62 aggregation was also decreased. No neuronal loss or neuroinflammatory response were detected in the DDX3X overexpressing C9-BAC mice. This work demonstrates that DDX3X overexpression effectively reduces DPR levels in vivo without provoking neuroinflammation or neurotoxicity, suggesting the potential of increasing DDX3X expression as a therapeutic strategy for C9ORF72-ALS/FTD.
Insights
Overexpressing DEAD-box helicase 3 X-linked (DDX3X) in mice reduced toxic dipeptide repeat proteins linked to C9ORF72-ALS/FTD without causing harm. This suggests DDX3X as a potential therapeutic target for these neurodegenerative diseases.
Area of Science:
- Neuroscience
- Genetics
- Molecular Biology
Background:
- C9ORF72 repeat expansions cause ALS and FTD.
- Dipeptide repeat proteins (DPRs) from RAN translation are toxic.
- Reducing DPRs is a therapeutic goal for C9ORF72-ALS/FTD.
Purpose of the Study:
- To evaluate the in vivo efficacy of DDX3X overexpression in a mouse model of C9ORF72-ALS/FTD.
- To determine if DDX3X reduces DPR levels and associated pathology in the central nervous system (CNS).
Main Methods:
- Adeno-associated virus serotype 9 (AAV9) delivered exogenous DDX3X or GFP into the CNS of C9-BAC transgenic mice.
- Assessed DPR levels, p62 aggregation, neuronal loss, and neuroinflammation twelve months post-delivery.
Main Results:
- DDX3X overexpression significantly reduced DPR levels in the brains of C9-BAC mice.
- p62 aggregation was also decreased in DDX3X-treated mice.
- No evidence of neuronal loss or neuroinflammation was observed.
Conclusions:
- DDX3X overexpression effectively reduces in vivo DPR levels in a C9ORF72-ALS/FTD mouse model.
- This approach did not induce neurotoxicity or neuroinflammation.
- Increasing DDX3X expression is a promising therapeutic strategy for C9ORF72-ALS/FTD.
