Abstract
Fused in sarcoma (FUS) is an RNA-binding protein that is genetically and pathologically associated with rare and aggressive forms of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). To explore the mechanisms by which mutant FUS causes neurodegeneration in ALS-FTD, we generated a series of FUS knock-in mouse lines that express the equivalent of ALS-associated mutant FUSP525L and FUSΔEX14 protein. In FUS mutant mice, we show progressive, age-dependent motor neuron loss as a consequence of a dose-dependent gain of toxic function, associated with the insolubility of FUS and related RNA-binding proteins. In this disease-relevant mouse model of ALS-FUS, we show that ION363, a non-allele-specific FUS antisense oligonucleotide, efficiently silences Fus and reduces postnatal levels of FUS protein in the brain and spinal cord, delaying motor neuron degeneration. In a patient with ALS with a FUSP525L mutation, we provide preliminary evidence that repeated intrathecal infusions of ION363 lower wild-type and mutant FUS levels in the central nervous system, resulting in a marked reduction in the burden of FUS aggregates that are a pathological hallmark of disease. In mouse genetic and human clinical studies, we provide evidence in support of FUS silencing as a therapeutic strategy in FUS-dependent ALS and FTD.
Highlights
Mutations in Fused in sarcoma (FUS) are associated with the most aggressive, early-onset forms of ALS5,6 as well as rare forms of FTD7,8
We provide genetic evidence that, despite a partial loss of function associated with the equivalents of the human FUSP525L mutation and a truncation mutation (G466VfsX14 or Δ14) associated with rapidly progressive, juvenile-onset ALS15, expression of these mutant forms of FUS in vivo at physiological levels leads to progressive, age-dependent MN degeneration that is dose dependent and selective for MN subpopulations known to be preferentially vulnerable in patients with amyotrophic lateral sclerosis (ALS) and related mouse models of familial ALS
Using choline acetyl transferase (ChAT) as an MN marker, we found no MN loss in the lumbar spinal cord at 6 months or 1 year of age in either the P517L/WT or Δ14/WT mice (Extended Data Fig. 1f); at 1.5 years, we observed approximately 11% fewer MNs in both mutants compared to the wild-type animals (Fig. 1c)
Summary
Mutations in FUS are associated with the most aggressive, early-onset forms of ALS5,6 as well as rare forms of FTD7,8. We provide genetic evidence that, despite a partial loss of function associated with the equivalents of the human FUSP525L mutation (mFusP517L) and a truncation mutation (G466VfsX14 or Δ14) associated with rapidly progressive, juvenile-onset ALS15, expression of these mutant forms of FUS in vivo at physiological levels leads to progressive, age-dependent MN degeneration that is dose dependent and selective for MN subpopulations known to be preferentially vulnerable in patients with ALS and related mouse models of familial ALS. Using a conditional allele of Δ14, we show that FUS-dependent MN degeneration is a cell-autonomous process, driving secondary inflammatory changes that do not depend on mutant FUS expression in the reactive cells but might contribute to neurodegeneration In these knock-in mouse models of ALS-FUS, toxicity correlates with the degree of insolubility of FUS and other RBPs, which is associated with functional deficiency of these related, phase-separating proteins. We provide evidence to support the clinical application of ION363 in the treatment of ALS-FUS and related FUS-dependent proteinopathies
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