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Structure-function dissection of huntingtin exon 1 identifies a PRD-driven modifier of neuronal toxicity in Huntington's disease

Cattaneo, E.; Iennaco, R.; Maffezzini, C.; Maestri, S.; Scolz, A.; Moia, L.; Cattaneo, A.; Murgia, A.; Trovesi, C.; Cammarota, E.; Cordiglieri, C.; Vezzoli, E.; Falqui, A.; Felsenfeld, D. P.; Vogt, T. F.; Bachi, A.; Zuccato, C.

2026-07-27 neuroscience
10.64898/2026.07.23.740298 bioRxiv
Show abstract

The Huntingtin gene (HTT) contains a conserved, yet expandable CAG repeat within exon 1. While the pathogenic expansion in Huntingtons Disease (HD) is well studied, the role of surrounding domains remains unclear. Using genome-edited mini-organoids and neurons, we dissected HTT exon 1 and found species-specific toxicity: the human variant caused more severe deficits than the mouse. Swapping the proline-rich domain (PRD) - the most divergent region - revealed its key role: the mouse PRD mitigated, while the human PRD worsened neuronal phenotypes. Omics profiling showed that pathogenic human exon 1 induced broad protein dysregulation, largely reversed by mouse PRD replacement. Bioinformatics implicated the actin cytoskeleton and transcriptional coactivator MKL2/MRTFB. We validated MKL2/MRTFB dysregulation in HD models and showed that restoring its expression rescued neuronal abnormalities. These findings highlight the PRDs contribution to HD toxicity and point to MKL2/MRTFB and the cytoskeleton as candidate mediators.

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