C9orf72 Dipeptide Repeat Proteinopathy Is Linked to Increased Histone H3 Phosphorylation on Serine 10

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are fatal illnesses forming a neurodegenerative disease continuum. While most ALS/FTD cases are sporadic, a small proportion of cases are linked to mutations in many genes. Among these, hexanucleotide repeat expansions in the C9orf72 gene are the most common and lead to the formation of dipeptide repeat proteins (DPRs), including a proline-arginine dipeptide (PR), which aggregate in the cytoplasm of decaying neurons. As genetics alone fails to explain the etiology of ALS/FTD, it is possible that epigenetic mechanisms - such as histone post-translational modifications (PTMs) - are involved in disease processes. A Saccharomyces cerevisiae (PR)₅₀ overexpression model displays overt growth suppression and aggregation. Here, we exploit this model as a discovery platform to comprehensively characterize changes in the levels of PTMs on Histones H3 and H4. We find that overexpression of (PR)₅₀ is associated with increased levels of phosphorylation on Histone H3 at Serine 10 (H3S10ph). Furthermore, (PR)₅₀ overexpression revealed modest increases in the levels of other marks associated with increased gene expression. Remarkably, decreased abundance of Ipl1, the kinase responsible for phosphorylating H3S10 in yeast, leads to amelioration of the growth suppression phenotype and restores H3S10ph levels even in the context of (PR)₅₀ overexpression. Recapitulating our results in yeast, several c9orf72 ALS patient-derived fibroblasts and induced pluripotent stem cell (iPSCs) lines display similar increases in H3S10ph levels. Altogether, these findings reveal a previously undiscovered connection between H3S10ph and c9 ALS/FTD proteinopathy that could reveal novel targets for the treatment of this disease.