Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) have distinct clinical features but a common pathology—cytoplasmic inclusions rich in TDP43. Rare TDP43 mutations cause ALS or FTD, but abnormal TDP43 levels and localization may cause disease even if TDP43 lacks a mutation. Here we showed that individual neurons vary in their ability to clear TDP43 and are exquisitely sensitive to TDP43 levels. To measure TDP43 clearance, we developed and validated a single-cell optical method that overcomes the confounding effects of aggregation and toxicity, and discovered that pathogenic mutations significantly shorten TDP43 half-life. Novel compounds that stimulate autophagy improved TDP43 clearance and localization, and enhanced survival in primary murine neurons and in human stem cell–derived neurons and astrocytes harboring mutant TDP43. These findings indicate that the levels and localization of TDP43 critically determine neurotoxicity and show that autophagy induction mitigates neurodegeneration by acting directly on TDP43 clearance.

Over 30% of patients with amyotrophic lateral sclerosis (ALS) exhibit cognitive deficits indicative of frontotemporal dementia (FTD), suggesting a common pathogenesis for both diseases. Consistent with this hypothesis, neuronal and glial inclusions rich in TDP43, an essential RNA-binding protein, are found in the majority of those with ALS and FTD, and mutations in TDP43 and a related RNAbinding protein, FUS, cause familial ALS and FTD. TDP43 and FUS affect the splicing of thousands of transcripts, in some cases triggering nonsense-mediated mRNA decay (NMD), a highly conserved RNA degradation pathway. Here, we take advantage of a faithful primary neuronal model of ALS and FTD to investigate and characterize the role of human up-frameshift protein 1 (hUPF1), an RNA helicase and master regulator of NMD, in these disorders. We show that hUPF1 significantly protects mammalian neurons from both TDP43-and FUS-related toxicity. Expression of hUPF2, another essential component of NMD, also improves survival, whereas inhibiting NMD prevents rescue by hUPF1, suggesting that hUPF1 acts through NMD to enhance survival. These studies emphasize the importance of RNA metabolism in ALS and FTD, and identify a uniquely effective therapeutic strategy for these disorders.A myotrophic lateral sclerosis (ALS) is a progressive and lethal motor neuron disease that most often arises sporadically, but can be inherited in 10-15% of patients (1). Many of the genes implicated in familial ALS (fALS) encode RNA-binding proteins, including fused in sarcoma (FUS), transactive response element DNA/RNA-binding protein of 43 kDa (TDP43), and heteronuclear ribonuclear proteins (hnRNPs) (2), emphasizing RNA-based toxicity as a fundamental mechanism contributing to motor neuron degeneration in ALS.More than 40 different mutations in the TDP43 gene (TARDBP) have now been associated with fALS (3). Disease-associated mutations in TARDBP affect the turnover (4), amount (5), and subcellular localization of TDP43 (6, 7), in many cases resulting in cytoplasmic TDP43 inclusions. Affected neurons in sporadic ALS (sALS) exhibit identical inclusions containing wild-type (WT) TDP43 (8), and WT TDP43 accumulation causes neurodegeneration in cellular and animal models (6, 9, 10), providing a pathogenic link between fALS and sALS. FUS mutations have also been linked to fALS (11,12). Unlike TDP43, FUS-related pathology is limited to fALS due to FUS mutations (13). FUS and TDP43 bind largely nonoverlapping RNA targets (14), leading to the unexpected conclusion that, despite their homology and involvement in fALS, TDP43 and FUS have distinct roles in RNA metabolism.TDP43 regulates its own expression through a negative feedback loop (15), but the mechanism by which it does so remains unclear. Conflicting data suggest that TDP43 autoregulation involves nonsense-mediated decay (NMD) (16) or exosome-mediated degradation (15). Excess TDP43 enhances splicing in the TARDBP 3′UTR, potentially targeting the transcript for NMD, whereas deficiencies in human up-frameshift prote...

Abnormalities in nucleic acid processing are associated with the development of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Mutations in Matrin 3 (MATR3), a poorly understood DNA- and RNA-binding protein, cause familial ALS/FTD, and MATR3 pathology is a feature of sporadic disease, suggesting that MATR3 dysfunction is integrally linked to ALS pathogenesis. Using a rat primary neuron model to assess MATR3-mediated toxicity, we noted that neurons were bidirectionally vulnerable to MATR3 levels, with pathogenic MATR3 mutants displaying enhanced toxicity. MATR3’s zinc finger domains partially modulated toxicity, but elimination of its RNA recognition motifs had no effect on survival, instead facilitating its self-assembly into liquid-like droplets. In contrast to other RNA-binding proteins associated with ALS, cytoplasmic MATR3 redistribution mitigated neurodegeneration, suggesting that nuclear MATR3 mediates toxicity. Our findings offer a foundation for understanding MATR3-related neurodegeneration and how nucleic acid binding functions, localization, and pathogenic mutations drive sporadic and familial disease.

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) share key features, including accumulation of the RNA-binding protein TDP-43. TDP-43 regulates RNA homeostasis, but it remains unclear whether RNA stability is affected in these disorders. We use Bru-seq and BruChase-seq to assess genome-wide RNA stability in ALS patient-derived cells, demonstrating profound destabilization of ribosomal and mitochondrial transcripts. This pattern is recapitulated by TDP-43 overexpression, suggesting a primary role for TDP-43 in RNA destabilization, and in postmortem samples from ALS and FTD patients. Proteomics and functional studies illustrate corresponding reductions in mitochondrial components and compensatory increases in protein synthesis. Collectively, these observations suggest that TDP-43 deposition leads to targeted RNA instability in ALS and FTD, and may ultimately cause cell death by disrupting energy production and protein synthesis pathways.

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are progressive neurodegenerative disorders marked in most cases by the nuclear exclusion and cytoplasmic deposition of the RNA binding protein TDP43. We previously demonstrated that ALS–associated mutant TDP43 accumulates within the cytoplasm, and that TDP43 mislocalization predicts neurodegeneration. Here, we sought to prevent neurodegeneration in ALS/FTD models using selective inhibitor of nuclear export (SINE) compounds that target exportin-1 (XPO1). SINE compounds modestly extend cellular survival in neuronal ALS/FTD models and mitigate motor symptoms in an in vivo rat ALS model. At high doses, SINE compounds block nuclear egress of an XPO1 cargo reporter, but not at lower concentrations that were associated with neuroprotection. Neither SINE compounds nor leptomycin B, a separate XPO1 inhibitor, enhanced nuclear TDP43 levels, while depletion of XPO1 or other exportins had little effect on TDP43 localization, suggesting that no single exporter is necessary for TDP43 export. Supporting this hypothesis, we find overexpression of XPO1, XPO7 and NXF1 are each sufficient to promote nuclear TDP43 egress. Taken together, our results indicate that redundant pathways regulate TDP43 nuclear export, and that therapeutic prevention of cytoplasmic TDP43 accumulation in ALS/FTD may be enhanced by targeting several overlapping mechanisms.