Transcriptional dysregulation in the spinal cord of SCA3 provides insights into disease mechanisms

Spinocerebellar ataxia type 3 (SCA3) is a neurodegenerative disease caused by polyglutamine repeat expansion in the ATXN3 gene. Despite the ubiquitous expression of ATXN3 throughout the body, SCA3 pathology is pronounced in select, vulnerable regions within the central nervous system (CNS). Notably, imaging studies of SCA3 patients have revealed spinal cord atrophy prior to ataxia symptom onset and progressing with disease severity. However, the molecular mechanisms underlying SCA3 pathology in the spinal cord remain largely unexplored. Here, we present, for the first time, a comprehensive analysis of the spinal cord transcriptome using SCA3 tissue from humans and mouse models. Our data demonstrates both early and progressive transcriptional dysregulation in the spinal cord, impacting key biological processes such as lipid metabolism, inflammation, cellular structure, and nucleic acid processing. Transcriptomic profiling of Atxn3 knockout mice revealed only weak transcriptional changes in the spinal cord, with minimal overlap compared to the robust alterations observed in SCA3 knock-in mice, indicating that the molecular signature of the disease in the spinal cord is likely not driven by ATXN3 loss of function. In addition, we identified aberrant RNA splicing, particularly affecting genes involved in cytoskeletal organization. Collectively, our findings indicate that SCA3-associated transcriptional dysregulation in the spinal cord contributes to canonical pathological mechanisms of SCA3 both early and progressively. These results underscore the central role of the spinal cord in SCA3 pathogenesis and advocate for its inclusion as a key therapeutic target.