CAG repeat expansion in the Huntington's disease gene shapes linear and circular RNAs biogenesis.

Alternative splicing (AS) appears to be altered in Huntington's disease (HD), but its significance for early, pre-symptomatic disease stages has not been inspected. Here, taking advantage of Htt CAG knock-in mouse in vitro and in vivo models, we demonstrate a correlation between Htt CAG repeat length and increased aberrant linear AS, specifically affecting neural progenitors and, in vivo, the striatum prior to overt behavioral phenotypes stages. Remarkably, a significant proportion (36%) of the aberrantly spliced isoforms are not-functional and meant to non-sense mediated decay (NMD). The expanded Htt CAG repeats further reflect on a previously neglected, global impairment of back-splicing, leading to decreased circular RNAs production in neural progenitors. Integrative transcriptomic analyses unveil a network of transcriptionally altered micro-RNAs and RNA-binding proteins (CELF, hnRNPS, PTBP, SRSF, UPF1, YTHD2) which might influence the AS machinery, primarily in neural cells. We suggest that this unbalanced expression of linear and circular RNAs might alter neural fitness, contributing to HD pathogenesis. Author summary: This study establishes the first evidence for a direct correlation between Htt CAG repeat expansion and altered RNA splicing in neurons. Specifically, we demonstrate that accurate murine model systems, mimicking the human HD mutation, exhibit a mis-shaped repertoire of linear and back-spliced circular RNA isoforms. Mechanistically, our integrative analysis points to aberrantly regulated miRNAs and RNA-binding proteins implicated in NMD, M6A modification and splicing regulation, thus unveiling a possible new angle of HD biology. To conclude, this work contributes to the understanding of neuronal and striatal vulnerability in HD pathogenesis and delineates new potential molecular targets for therapeutic intervention. [ABSTRACT FROM AUTHOR]