The Role of Polyamines in SCA7

Abstract

Introduction: Spinocerebellar ataxia type 7 (SCA7) is a hereditary neurodegenerative disorder characterized by the accumulation of neurotoxic aggregates of mutant ataxin-7 (Atxn7). Autophagy, a crucial process for clearing such aggregates, is impaired in SCA7. Among the many molecules regulating this process, polyamines, a group of small polycationic molecules (putrescine, spermidine, and spermine), have been shown to modulate autophagy, through the regulation of transcription factor EB (TFEB), a key regulator of autophagy.

Objective: This study aimed to explore the role of polyamines in SCA7 and their relationship with autophagy on both plasma from SCA7 patients as well as in a cellular inducible model for the pathological phenotype.

Methods: Our experiments were performed in a Tet-on system in a Mio-M1 inducible cell model to mimic the pathological phenotype of SCA7 (64Q vs10Q/control cells). For total polyamine quantification on both plasma from patients and from the cell model, a commercial assay kit was used according to manufacturer instructions. The specific quantification of the polyamine spermidine in plasm was performed through HPLC. Additionally, we assessed protein expression of autophagy proteins as well as the ornithine decarboxylase 1 (ODC1-involved on polyamines biosynthesis) through SDS-PAGE and immunofluorescence.

Results: Total polyamine levels were significantly reduced in both SCA7 patient plasma as well as in the cells exhibiting the pathological phenotype of SCA7, compared with their respective control conditions. Notably, spermidine - the principal polyamine involved in autophagy - was decreased in SCA7 patients compared to control. Evaluation of the protein levels of the ornithine decarboxylase 1 (ODC1), the rate-limiting enzyme in polyamine biosynthesis, demonstrated significantly elevated levels SCA7 phenotype cells (64Q) compared to control cells (10Q). This upregulation may reflect a compensatory mechanism to restore the polyamine levels.

Autophagy analysis revealed impaired autophagosome formation and altered LC3 protein levels in 64Q cells compared to 10Q. Additionally, TFEB exhibited elevated protein levels and altered subcellular in 64Q cells compared to control, indicating a potential cellular attempt to counteract autophagic dysfunction.

Importantly, supplementation of the polyamine spermidine, the principal polyamine involved in autophagy regulation, restore the protein levels of TFEB on 64Q cells similar to those observed in control.  These results support the idea about the potential of spermidine to ameliorate the autophagy-related deficits in SCA7 cells.

Conclusions: Our findings highlight a complex interplay between polyamines and autophagy in SCA7, suggesting novel therapeutic targets for modulating disease progression.