Overriding FUS autoregulation in mice triggers gain-of-toxic dysfunctions in RNA metabolism and autophagy-lysosome axis

Abstract

Mutations in coding and non-coding regions of FUS cause amyotrophic lateral sclerosis (ALS). The latter mutations may exert toxicity by increasing FUS accumulation. We show here that broad expression within the nervous system of wild-type or either of two ALS-linked mutants of human FUS in mice produces progressive motor phenotypes accompanied by characteristic ALS-like pathology. FUS levels are autoregulated by a mechanism in which human FUS downregulates endogenous FUS at mRNA and protein levels. Increasing wild-type human FUS expression achieved by saturating this autoregulatory mechanism produces a rapidly progressive phenotype and dose-dependent lethality. Transcriptome analysis reveals mis-regulation of genes that are largely not observed upon FUS reduction. Likely mechanisms for FUS neurotoxicity include autophagy inhibition and defective RNA metabolism. Thus, our results reveal that overriding FUS autoregulation will trigger gain-of-function toxicity via altered autophagy-lysosome pathway and RNA metabolism function, highlighting a role for protein and RNA dyshomeostasis in FUS-mediated toxicity.

Disrupted Autophagy and Neuronal Dysfunction in C. elegans Knock-in Models of FUS Amyotrophic Lateral Sclerosis

“…Consistent with this, overexpression of wild type FUS protein in neuronal cell lines alternately increases and decreases autophagosome and autolysosome levels, respectively [11]. In addition, transgenic mice overexpressing wild type FUS show SQSTM1 accumulation in motor neurons, suggesting autophagy dysfunction [11]. Combined, our results complement previous work in FUS overexpression models and suggest that a gain of toxic function in mutant FUS disrupts neuronal protein homeostasis.…”

“…Consistent with this, overexpression of wild type FUS protein in neuronal cell lines alternately increases and decreases autophagosome and autolysosome levels, respectively [11]. In addition, transgenic mice overexpressing wild type FUS show SQSTM1 accumulation in motor neurons, suggesting autophagy dysfunction [11].…”

“…Recent evidence suggests that wild type FUS overexpression may impair neuronal autophagy [11]. However, it remains unclear whether ALS FUS mutations impair neuronal autophagy.…”

“…Studies in FUS overexpression models have revealed autophagy dysfunction. FUS overexpression perturbs autophagy flux in neuronal cell lines transfected with wild type or mutant FUS [11,23]. Wild type FUS overexpression alters RNA processing, upregulates lysosomal genes, and leads to improper SQSTM1 accumulation in transgenic mice [11].…”

“…FUS overexpression in mice leads to dose-dependent neuromuscular defects and neurodegeneration reminiscent of ALS, with altered RNA transcription and splicing in motor neurons [2]. FUS overexpression impairs synaptic function in mice, flies and nematodes [5][6][7][8][9][10][11]. Furthermore, in fly and mouse ALS FUS overexpression models, neuromuscular dysfunction precedes motor neuron degeneration [12,13], suggesting synaptic dysfunction is an early event in ALS pathogenesis.…”