Analysis of cellular senescence in Spinocerebellar ataxia type 7 using bioinformatics and an inducible cell model

Abstract

Spinocerebellar ataxia type 7 (SCA7) is an autosomal dominant inherited disorder manifested by the inability to coordinate balance, gait, and speech. Some experimental evidence suggests that nuclear inclusion of mutant ataxin-7 (ATX7) is part of the molecular basis of this disease and the origin of oxidative stress. In this thesis, we made a bioinformatic analysis that supports the hypothesis that SCA7 could share some mechanisms that are core features of senescent cells. Senescence is a permanent state of cell-cycle arrest, and core features of this phenotype include the expression of anti-proliferative molecules, the activation of a chronic DNA damage response, altered metabolic rates, and many others. We sought to establish a senescence induction protocol in a human fibroblast cell line as a positive control of senescence and found that induction with H2O2 at 1200 μM resulted in 79% of positive SA-β-gal cells. Afterwards, we were able to validate an inducible cell model of MIO-M1 cells, which were stably transduced to express a mutant ATXN7 gene carrying 64 CAG repeats and 10 CAG repeats. Administration of doxycycline (dox) induced the expression of the mutated protein causing the formation of nuclear aggregates. Furthermore, in a preliminary SA-β-gal assay, we found activity of this enzyme in 64 CAG cells, suggesting the presence of senescence features after the induction of the mutated protein. Based on our findings, we propose that the oxidative stress generated by the accumulation of the mutated protein could be leading to a senescence phenotype. Future evaluation of the Senescence-associated secretory phenotype (SASP) and markers of DNA damage will bring better understanding of the possible role of senescence in SCA7.