All oligonucleotide sequences and modification patterns synthesized in-house are summarized in Supplementary Table S1. Accell siRNA (Thermo Fisher) targeting HTT was purchased and used without further purification. Clonidine (Sigma–Aldrich), Retro-1 (Sigma–Aldrich) and Salubrinal (Sigma–Aldrich) were dissolved in DMSO and stored as 10 mM stock solutions at −20°C. Unless otherwise specified, all oligonucleotides and small molecules were diluted in OptiMEM (Gibco) prior to administration in vitro.