Abstract
Spinocerebellar ataxia 3 (SCA3, also known as Machado Joseph disease) is a fatal neurodegenerative disease caused by expansion of the trinucleotide repeat region within the ATXN3/MJD gene. Mutation of ATXN3 causes formation of ataxin-3 protein aggregates, neurodegeneration and motor deficits. Here we investigated the therapeutic potential and mechanistic activity of sodium butyrate (SB), the sodium salt of butyric acid, a metabolite naturally produced by gut microbiota, on cultured SH-SY5Y cells and transgenic zebrafish expressing human ataxin-3 containing 84 glutamine (Q) residues to model SCA3. SCA3 SH-SY5Y cells were found to contain ataxin-3 oligomeric species and protein aggregates. Treatment with SB increased activity of the autophagy protein quality control pathway in the SCA3 cells, decreased presence of ataxin-3 aggregates and presence of ataxin-3 oligomers in an autophagy-dependent manner. Treatment with SB was also beneficial in vivo, improving swimming performance, increasing activity of the autophagy pathway and decreasing presence of insoluble ataxin-3 protein species in the transgenic SCA3 zebrafish. Co-treating the SCA3 zebrafish with SB and chloroquine, an autophagy inhibitor, prevented the beneficial effects of SB on the zebrafish swimming, indicating that the improved swimming performance was autophagy-dependent. To understand the mechanism by which SB induces autophagy we performed proteomic analysis of protein lysates from the SB treated and untreated SCA3 SH-SY5Y cells. We found that SB treatment had increased activity of Protein Kinase A and AMPK signalling, with immunoblot analysis confirming that SB treatment had increased levels of AMPK protein and its substrates. Together our findings indicate that treatment with SB can increase activity of the autophagy pathway through a PKA/AMPK-dependent process and that this has beneficial effects in vitro and in vivo. We propose that treatment with sodium butyrate warrants further investigation as a potential treatment for neurodegenerative diseases underpinned by mechanisms relating to protein aggregation including SCA3.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
updated text and figures.
Abbreviations
- MJD
- Machado-Joseph disease
- SCA3
- spinocerebellar ataxia type 3
- HDAC
- histone deacetylase
- polyQ
- polyglutamine
- SB
- sodium butyrate
- dpf
- days post fertilization
- EGFP
- enhanced green fluorescent protein
- FSC
- forward scatter signal
- H3K9
- acetylated histone 3 at lysine 9
- H4K5
- acetylated histone 4 at lysine 5