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RNA sequencing of human fibroblasts after SUPT4H1 siRNA treatment

ABSTRACT: Asses the transcriptome-wide changes associated with depletion of transcription elongation factor, SUPT4H1, in human fibroblasts. An expanded hexanucleotide repeat in C9orf72 is the most common genetic cause of amyotrophic lateral sclerosis and frontotemporal dementia (c9FTD/ALS). Therapeutics (e.g., antisense oligonucleotides) are being developed to target RNAs containing the expanded repeat sequence (GGGGCC); however, this approach is complicated by the presence of antisense strand transcription of expanded GGCCCC repeats. We found that targeting the transcription elongation factor, Spt4, selectively decreased production of both sense and antisense expanded transcripts, as well as their translated dipeptide repeat (DPR) products, and also mitigated degeneration in animal models. Inhibition of SUPT4H1, the human ortholog of Spt4, similarly decreased production of sense and antisense RNA foci as well as DPR proteins in c9ALS patient fibroblasts and neurons from patient-derived induced pluripotent stem cells, consistent with our finding that cerebellar DPR protein levels correlate with SUPT4H1 expression in c9FTD/ALS patients. Therapeutic targeting of a single factor to eliminate pathological features of c9FTD/ALS offers advantages over approaches that require targeting sense and antisense repeats separately.

ORGANISM(S): Homo sapiens

PROVIDER: GSE83484 | GEO | 2016/09/09

SECONDARY ACCESSION(S): PRJNA326113

REPOSITORIES: GEO

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Project description:G4C2 hexanucleotide repeat expansions in a non-coding region of the C9orf72 gene are the most common cause of familial amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). G4C2 insertion length is variable, and patients can carry up to several thousand repeats. Dipeptide repeat proteins (DPR) translated from G4C2 transcripts are thought to be a main driver of toxicity. Experiments in model organisms with relatively short DPR have shown that arginine-rich DPR are most toxic, while polyGlycine-Alanine (GA) DPRs cause only mild toxicity. However, GA is the most abundant DPR in patient brains, and experimental work in animals has generally relied on the use of low numbers of repeats, with DPRs often tagged for in vivo tracking. Whether repeat length, or tagging, affect the toxicity of GA has not been systematically assessed. Therefore, we generated Drosophila fly lines expressing GA100, GA200 or GA400 specifically in adult neurons. Consistent with previous studies, expression of GA100 and GA200 caused only mild toxicity. In contrast, neuronal expression of GA400 drastically reduced climbing ability and survival of the flies, indicating that long GA DPRs can be highly toxic in vivo. This toxicity could be abolished by tagging GA400. Proteomics analysis of fly brains showed a repeat-length-dependent modulation of the brain proteome, with GA400 causing earlier and stronger changes than shorter GA proteins. PolyGA expression up-regulated proteins involved in ER to Golgi trafficking, and down-regulated proteins involved in insulin signalling. Experimental down-regulation of Tango1, a highly conserved regulator of ER-to Golgi transport, partially rescued GA400 toxicity, suggesting that misregulation of this process contributes to polyGA toxicity. Experimentally increasing insulin signaling also rescued GA toxicity. In summary, our data show that long polyGA proteins can be highly toxic in vivo, and that they may therefore contribute to ALS/FTD pathogenesis in humans patients.

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RNA sequencing of human fibroblasts after SUPT4H1 siRNA treatment

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