Self-assembly of FUS through its low-complexity domain contributes to neurodegeneration

Abstract

Aggregation of fused in sarcoma (FUS) protein, and mutations in FUS gene, are causative to a range of neurodegenerative disorders including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia. To gain insights into the molecular mechanism whereby FUS causes neurodegeneration, we generated transgenic Drosophila melanogaster overexpressing human FUS in the photoreceptor neurons, which exhibited mild retinal degeneration. Expression of familial ALS-mutant FUS aggravated the degeneration, which was associated with an increase in cytoplasmic localization of FUS. A carboxy-terminally truncated R495X mutant FUS also was localized in cytoplasm, whereas the degenerative phenotype was diminished. Double expression of R495X and wild-type FUS dramatically exacerbated degeneration, sequestrating wild-type FUS into cytoplasmic aggregates. Notably, replacement of all tyrosine residues within the low-complexity domain, which abolished self-assembly of FUS, completely eliminated the degenerative phenotypes. Taken together, we propose that self-assembly of FUS through its low-complexity domain contributes to FUS-induced neurodegeneration.

In VivoValidation of Bimolecular Fluorescence Complementation (BiFC) to Investigate Aggregate Formation in Amyotrophic Lateral Sclerosis (ALS)

“…To verify if BiFC can be used to study the process of aggregate formation in zebrafish, we expressed both TDP-43 and Fus BiFC fusion proteins transiently in zebrafish embryos. Our study revealed fluorescence complementation of wild-type TDP-43 and wild-type Fus and the development of intra-nuclear aggregates, whilst mutant Fus BiFC fusion proteins demonstrated fluorescence complementation in cytoplasmic aggregates as previously reported in cell culture BiFC experiments [75],[77]. Interestingly, co-expression of wild-type and mutant Fus BiFC fusion proteins resulted in fluorescence complementation in intra-nuclear aggregates, not cytoplasmic aggregates, contrary to previously reported findings from cell culture studies and post-mortem tissue [77],[78].…”

“…Our study revealed fluorescence complementation of wild-type TDP-43 and wild-type Fus and the development of intra-nuclear aggregates, whilst mutant Fus BiFC fusion proteins demonstrated fluorescence complementation in cytoplasmic aggregates as previously reported in cell culture BiFC experiments [75],[77]. Interestingly, co-expression of wild-type and mutant Fus BiFC fusion proteins resulted in fluorescence complementation in intra-nuclear aggregates, not cytoplasmic aggregates, contrary to previously reported findings from cell culture studies and post-mortem tissue [77],[78]. However, the Matsumoto et al cell culture study did not use a BiFC approach and one possibility is that the intra-nuclear aggregation could represent an early phenomenon (nuclear maturation of the protein followed by cytoplasmic shuttling) that is too late to observe in post-mortem tissue or cell culture models.…”

“…This approach revealed that tau aggregation is favored when tau is phosphorylated at S396/S404 in the presence of increased GSK3beta activity [54]. A similar approach has identified that specific amino-acids in the head and tail portions of the N-terminal domain of TDP-43 (E17A; E21A; R52A; R55A) mediate the interactions necessary for its self-assembly [75] and that the self-assembly of FUS is mediated through its low-complexity domain (amino acids 1-214) [76],[77]. BiFC approaches have also been adapted to in vivo systems to study morphogen gradients and protein interactions in developmental biology pathways [56],[57],[58],[59].…”

Big data of clinical manifestations combined with neuroelectrophysiologic features in the early diagnosis of motor neuron disease

“…FUS is physiologically involved in RNA metabolism and DNA repair, and there are indications that DNA damage is apparent in FUS-ALS. FUS is normally shuttled between the nucleus and cytoplasm, mainly in the nucleus, and nuclear transport is impaired in patients with FUS-ALS, resulting in mislocalization of FUS in the cytoplasm, self-assembly in the cytoplasm and subsequent neurodegeneration and FUS aggregate formation (Matsumoto et al 2018;De Santis et al 2017). FUS aggregates promote the secretion of tumor necrosis factor-Alpha (TNFα) and thus alter the expression level of AMPA receptors (which mediates glutamate excitatory overexpression), making motoneurons more sensitive to stimuli and leading to excitotoxic damage and cell death, the AMPA-mediated excitotoxic component pathway serves as a potential therapeutic target for FUS-ALS (Kia et al 2018).…”

Dynamics of Ischemia-Dependence as Neurodegeneration

“…Provocation of the indeterminate accumulation of multiple protein molecular species characterize essential attributes of a neurodegenerative cascade in terms of accumulated biophysical dimensions for further driven protein unfolding and misfolding. Aggregation of fused in sarcoma (FUS) protein and mutated FUS gene induce neurodegeneration that includes amyotrophic lateral sclerosis and frontotemporal dementia [11]. Nicotinamide function includes the general maintenance of cellular energy levels and the more specific inhibition of nicotinamide adenine dinucleotide-dependent deacetylase sirtuin 1 [12].…”