Linus Wiora

Spinocerebellar ataxia type 3 (SCA3), also called Machado-Joseph disease, the most common form of autosomal dominant cerebellar ataxia, is caused by a CAG repeat expansion in ATXN3 . The mutant protein is prone to aggregation and exerts toxic gain-of-function effects, whereas the wild-type protein has important neuroprotective roles as a deubiquitinase. Current treatment strategies for SCA3 lack specificity for the mutant allele. Identifying genetic variants such as single-nucleotide polymorphisms (SNPs) in linkage with the pathogenic CAG expansion offers a promising avenue to develop allele-specific therapeutic interventions, like antisense oligonucleotides (ASOs). To address this, we conducted allele-specific, targeted, multiplexed nanopore sequencing on 79 patients with SCA3 from Germany, UK, and Portugal. We identified almost 200 polymorphisms and grouped them into three haplotype blocks on the basis of linkage disequilibrium. These SNPs were strongly associated with the CAG expansion. Genotypic modeling of our subcohorts indicated that targeting only two SNPs from different blocks could enable allele-specific treatment of the majority of European patients with SCA3. We evaluated 17 candidate ASOs targeting SNPs from different haplotype blocks. Seven of these ASOs caused allele-preferential reduction of more than 65%. A single ASO application in two SCA3 iPSC-derived cortical neurons (AX1, AX2) achieved up to 90% reduction of mutant ATXN3. Toxicity assessments together with RNA sequencing analyses in AX1 did not indicate evidence of toxicity or widespread transcriptional perturbations. These findings highlight that characterizing heterozygosity rates offers valuable opportunities for selective ASO therapies. Our proof-of-principle targeting with ASOs demonstrates the feasibility of haplotype-informed allele-specific silencing in ATXN3 .

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Recombinant Adeno-associated viruses (AAVs) are widely used for gene delivery in the central nervous system and have become central tools in both gene therapy and basic neuroscience research. However, although AAV serotypes have been extensively characterized in rodent models, their performance in human neurons, particularly those derived from induced pluripotent stem cells (iPSCs), remains poorly characterized. While human iPSC-derived neurons are increasingly used for disease modeling and drug screening, their susceptibility to viral transduction varies and remains difficult to predict. In this study, we systematically evaluated the transduction efficiency and toxicity profiles of 18 wild-type and engineered AAV serotypes across three distinct types of iPSC-derived neurons, relevant to disease modeling and drug discovery: cortical projection neurons, NGN2- induced forebrain-like neurons, and dopaminergic neurons and four doses (1E3, 1E4, 1E5 and 2E5 genome copies per cell). Using automated high-throughput confocal imaging and quantification of reporter gene expression, we identified several serotypes with robust and efficient transduction across all neuronal subtypes. Among these, three serotypes AAV6, AAV6.2 and AAV2.7m8 showed consistently high performance. To assess safety, we quantified cell number and neurite morphology, finding that while high transduction and gene expression correlate with toxicity, sensitivity varied across neuronal subtypes, with NGN2 neurons being most vulnerable and dopaminergic neurons most resilient. Finally, we validated our findings in a more complex 3D model by testing one of the best-performing serotypes, AAV2.7m8, in both whole and dissociated human cerebellar organoids. Together, our results establish a benchmark dataset for AAV performance in human iPSC- derived neurons and provide practical guidance for AAV based gene delivery in human in vitro neural models. This resource will be valuable for both basic research and preclinical applications aiming to manipulate gene expression in human neurons and understanding AAV tropism in disease-relevant cell types.