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An intronic (G 4 C 2 ) n expansion in C9orf72 causes amyotrophic lateral sclerosis and frontotemporal dementia primarily through gain-of-function mechanisms: the accumulation of sense and antisense repeat RNA foci and dipeptide repeat (DPR) proteins (poly-GA/GP/GR/PA/PR) translated from repeat RNA. To therapeutically block this pathway, we screen a library of 1,430 approved drugs and known bioactive compounds in patient-derived induced pluripotent stem cell-derived neurons (iPSC-Neurons) for inhibitors of DPR expression. The clinically used guanosine/cytidine analogs decitabine, entecavir, and nelarabine reduce poly-GA/GP expression, with decitabine being the most potent. Hit compounds nearly abolish sense and antisense RNA foci and reduce expression of the repeat-containing nascent C9orf72 RNA transcript and its mature mRNA with minimal effects on global gene expression, suggesting that they specifically act on repeat transcription. Importantly, decitabine treatment reduces (G 4 C 2 ) n foci and DPRs in C9orf72 BAC transgenic mice. Our findings suggest that nucleoside analogs are a promising compound class for therapeutic development in C9orf72 repeat-expansion-associated disorders., Competing Interests: Declaration of interests T.K. and J.M. are employees of Orion Pharma. The other authors declare no competing interests., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Manual culture and differentiation protocols for human induced pluripotent stem cells (hiPSC) are difficult to standardize, show high variability and are prone to spontaneous differentiation into unwanted cell types. The methods are labor-intensive and are not easily amenable to large-scale experiments. To overcome these limitations, we developed an automated cell culture system coupled to a high-throughput imaging system and implemented protocols for maintaining multiple hiPSC lines in parallel and neuronal differentiation. We describe the automation of a short-term differentiation protocol using Neurogenin-2 (NGN2) over-expression to produce hiPSC-derived cortical neurons within 6‒8 days, and the implementation of a long-term differentiation protocol to generate hiPSC-derived midbrain dopaminergic (mDA) neurons within 65 days. Also, we applied the NGN2 approach to a small molecule-derived neural precursor cells (smNPC) transduced with GFP lentivirus and established a live-cell automated neurite outgrowth assay. We present an automated system with protocols suitable for routine hiPSC culture and differentiation into cortical and dopaminergic neurons. Our platform is suitable for long term hands-free culture and high-content/high-throughput hiPSC-based compound, RNAi and CRISPR/Cas9 screenings to identify novel disease mechanisms and drug targets.