Histone Post-translational Modification Dysregulation Contributes to Toxicity in Amyotrophic Lateral Sclerosis Proteinopathy Models
Amyotrophic Lateral Sclerosis (ALS) is the third most common adult onset neurodegenerative disorder worldwide. It is generally characterized by progressive paralysis starting at the limbs ultimately leading to death caused by respiratory failure. There is no cure and current treatments fail to slow the progression of the disease. As such, new treatment options are desperately needed. Epigenetic targets are an attractive possibility because they are reversible. Epigenetics refers to heritable changes in gene expression unrelated to changes in DNA sequence. Histone modifications, a main epigenetic mechanism, occur in many amino acid residues and include phosphorylation, acetylation, methylation as well as other chemical moieties. Recent evidence points to a possible role for epigenetic mechanisms in the etiology of ALS. Here we show that overexpression of the ALS-linked protein FUS in yeast is associated with a strong growth suppression phenotype and decreases in histone acetylation, phosphorylation and methylation. Furthermore, we show that treating these yeast with the Histone Deacetylase inhibitor Trichostatin A improves yeast growth and restores histone acetylation. We then explore how overexpression of FUS alters histone PTMs in yeast. We observed that Ipl1, the histone modifying enzyme responsible for phosphorylation at serine 10 on histone H3, and Rtt109, the histone modifying enzyme responsible for acetylation at lysine 56 on histone H3, are significantly excluded for the nucleus, while the former colocalizes with FUS. We also interrogated the binding partners of FUS by co-immunoprecipitation assays followed by identification by mass spectrometry. We identified that Nop1, a histone methyltransferase involved in rRNA biogenesis, is a binding partner of FUS. We propose that exclusion of Ipl1 from the nucleus is driving the dysregulation of histone PTMs and that reduced levels of H3K56ac and FUS-Nop1 binding are causing reduced total RNA levels, likely representing decreased rRNA which contributing to FUS overexpression toxicity. We next explored the role of histone phosphorylation in the pathology of C9orf72 ALS and identify Ipl1/Aurora B Kinase as a possible therapeutic target. We find that H3S10ph levels are significantly increased in both yeast and human in vitro models of C9orf72 ALS. Furthermore, we show that knocking down Ipl1 in yeast significantly improves growth and that Aurora B Kinase, the human homologue of Ipl1, is enriched in the nucleus of a human in vitro model of C9orf72 ALS. Overall, our results highlight a great need for the inclusion of epigenetic mechanisms in the study of neurodegeneration. We hope our work will pave the way for discovery of more effective therapies to treat patients suffering from ALS and other neurodegenerative diseases.
Biochemistry, Amyotrophic Lateral Sclerosis, FUS, C9orf72, Epigenetics, Histone Post-Translational Modifications, Histone Deacetylase
City University of New York - Graduate Center
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The Graduate School and University Center of The City University of New York