Transcriptional Dysregulation Analysis of Spinocerebellar Ataxia Type 7 in a Human In Vitro Model of the Central Nervous System

Resumen

Introduction
Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disorder caused by the expansion of CAG repeats in the ATXN7 gene, leading to clinical features such as progressive ataxia and retinal degeneration. Although there is evidence supporting transcriptional dysregulation as a key mechanism in polyglutamine diseases, transcriptomic studies in human models of SCA7 remain limited.

Objective
This study aims to investigate the transcriptional alterations associated with SCA7 pathogenesis using a human cellular model, and to explore the potential involvement of nucleolar dysfunction.

Methodology
An inducible human Müller glial cell line model (MIO-M1) was used, with controlled expression of ATXN7 carrying either 10 CAG repeats (Q10, control) or 64 CAG repeats (Q64, mutant). Transcriptomic analysis was performed using Clariom D microarrays (Affymetrix) at days 2, 5, and 7 of induction, followed by qRT-PCR validation of selected genes. Functional analysis was conducted through Ingenuity Pathway Analysis (IPA), focusing on the identification of altered biological pathways. In parallel, nucleolar structure was evaluated by immunofluorescence and ribosomal RNA profiling through electrophoresis.

Results
Differential expression analysis (p < 0.005, |fold-change| > 1.5) revealed a significant number of deregulated genes, highlighting CDKN1B, DCN, DNER, LINC01287, and CCL2, which are associated with neurodegeneration, retinal damage, and autophagy processes. Functional analysis through IPA showed robust enrichment in pathways related to ribosomal RNA processing (z-score = 5.7), suggesting a relevant role of nucleolar dysfunction in the SCA7 model. Morphologically, immunofluorescence assays revealed nucleolar enlargement, perinucleolar aggregation of mutant ataxin-7, and colocalization with the B23 marker, along with alterations in ribosomal RNA profiles. Additionally, progressive cellular and nuclear hypertrophy was observed throughout the induction days, indicating structural impact possibly linked to chronic cellular stress and impaired cellular homeostasis.

Conclusion
These findings confirm significant transcriptional dysregulation and provide the first evidence of nucleolar alteration in a human cellular model of SCA7. The results contribute to a better understanding of the underlying cellular mechanisms in SCA7 and lay the groundwork for future studies on the functional relevance of nucleolar dysfunction in neurodegenerative diseases, opening potential avenues for the development of molecular biomarkers.