Poly-PR in C9ORF72-Related Amyotrophic Lateral Sclerosis/Frontotemporal Dementia Causes Neurotoxicity by Clathrin-Dependent Endocytosis

Human Molecular Genetics

Chung

Park

et al. 2021

RNA-binding proteins (RBPs) play essential roles in diverse cellular processes through post-transcriptional regulation of RNAs. The subcellular localization of RBPs is thus under tight control, the breakdown of which is associated with aberrant cytoplasmic accumulation of nuclear RBPs such as TDP-43 and FUS, well-known pathological markers for amyotrophic lateral sclerosis and frontotemporal dementia (ALS/FTD). Here, we report in Drosophila model for ALS/FTD that nuclear accumulation of a cytoplasmic RBP, Staufen, may be a new pathological feature. We found that in Drosophila C4da neurons expressing PR36, one of the arginine-rich dipeptide repeat proteins (DPRs), Staufen accumulated in the nucleus in Importin- and RNA-dependent manner. Notably, expressing Staufen with exogenous NLS—but not with mutated endogenous NLS—potentiated PR-induced dendritic defect, suggesting that nuclear-accumulated Staufen can enhance PR toxicity. PR36 expression increased Fibrillarin staining in the nucleolus, which was enhanced by heterozygous mutation of stau (stau+/−), a gene that codes Staufen. Furthermore, knockdown of fib, which codes Fibrillarin, exacerbated retinal degeneration mediated by PR toxicity, suggesting that increased amount of Fibrillarin by stau+/− is protective. Stau+/− also reduced the amount of PR-induced nuclear-accumulated Staufen and mitigated retinal degeneration and rescued viability of flies expressing PR36. Taken together, our data show that nuclear accumulation of Staufen in neurons may be an important pathological feature contributing to the pathogenesis of ALS/FTD.

Section: Discussioncontrasting

confidence: 99%

C9orf72-associated arginine-rich dipeptide repeats induce RNA-dependent nuclear accumulation of Staufen in neurons

Human Molecular Genetics

Chung

Park

et al. 2021

“…Based on this study, we speculate that in C4 da neurons expressing V5-PR36, heterozygous stau mutation may have decreased p53 level, with subsequent increased Fibrillarin production. In contrast to our speculation, a previous study showed that treatment of a high dose (10μmol/L) of PR 20 in SH-SY5Y cells led to increased level of p53, albeit with a significant amount of cell death [38]. Thus, further studies are required for a potential role of p53 in mediating Staufen-dependent PR toxicity.…”

Section: Discussioncontrasting

confidence: 97%

C9orf72-associated arginine-rich dipeptide repeats induce RNA-dependent accumulation of Staufen in nucleus

Chung

et al. 2019

Preprint

25Accumulation of RNA in the nucleus is one of the pathological features of C9orf72-associated 26 amyotrophic lateral sclerosis and frontotemporal dementia (C9-ALS/FTD), yet its potential 27 42 Staufen, may also be an important pathological feature of C9-ALS/FTD. 43 44 45 46 47 3 48 Author summary 49 Cytoplasmic accumulation of nuclear RNA-binding proteins (RBPs) is one of the common 50 pathological features of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia 51 (FTD). In C9orf72-associated ALS/FTD fly model, we found that Staufen, a double-stranded 52 (ds) RBP normally localized mostly in cytoplasm, accumulates in the nucleus in an RNA-53 dependent manner. Next, we checked wherein the nucleus Staufen accumulates and found that 54 Staufen partially co-localizes with heterochromatin and nucleolus. Interestingly, the expression 55 of Fibrillarin, a nucleolar protein, was significantly increased by C9orf72-derived PR toxicity 56 and further augmented by reduction in stau dosage, the gene encoding Staufen. When we 57 knocked down fib, the gene encoding Fibrillarin, PR-induced retinal degeneration was 58 exacerbated. This indicates that increased Fibrillarin expression by stau dosage reduction is 59 protective. Furthermore, when we reduced stau dosage in flies presenting PR toxicity, their 60 retinal degeneration and viability were largely rescued. Based on these data, we suggest that 61 nuclear accumulation of Staufen is an important feature of C9-ALS/FTD and suggest that 62 reducing stau dosage is a promising therapeutic target.

“…This in itself is reported to upregulate RAN translation, driving further production of DPRs and becoming a feed-forward loop (Zhang et al, 2014 ). In a different study, expression of synthetic poly(PR) induced ER stress and inhibition of the UPR increased cell survival (Wang et al, 2019 ). Consistent with these reports, RAN translation of the G 4 C 2 expansion was also found to be enhanced by ER stress and overexpression of the repeats impaired global translation, while increasing the formation of stress granules in an eIF2α-dependent manner (Green et al, 2017 ).…”

Section: Upr Activation In Alsmentioning

confidence: 99%

The Role of Mitochondrial Dysfunction and ER Stress in TDP-43 and C9ORF72 ALS

Dafinca

Barbagallo

Talbot

2021

Front. Cell. Neurosci.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease of the motor system with complex determinants, including genetic and non-genetic factors. Despite this heterogeneity, a key pathological signature is the mislocalization and aggregation of specific proteins in the cytoplasm, suggesting that convergent pathogenic mechanisms focusing on disturbances in proteostasis are important in ALS. In addition, many cellular processes have been identified as potentially contributing to disease initiation and progression, such as defects in axonal transport, autophagy, nucleocytoplasmic transport, ER stress, calcium metabolism, the unfolded protein response and mitochondrial function. Here we review the evidence from in vitro and in vivo models of C9ORF72 and TDP-43-related ALS supporting a central role in pathogenesis for endoplasmic reticulum stress, which activates an unfolded protein response (UPR), and mitochondrial dysfunction. Disruption in the finely tuned signaling between the ER and mitochondria through calcium ions may be a crucial trigger of mitochondrial deficits and initiate an apoptotic signaling cascade, thus acting as a point of convergence for multiple upstream disturbances of cellular homeostasis and constituting a potentially important therapeutic target.