Transcriptional alteration due to protein misfolding during aging
Failure to properly fold proteins results in loss of protein function; accumulation of toxic misfolded intermediates and activates stress response pathways that remodel the transcriptome to adapt cells and restore homeostasis. Dysregulation of protein homeostasis or “proteostasis” is linked to major human disorders such as neurodegenerative diseases including Huntington’s disease (HD). HD is caused by aberrant expansion of polyglutamine repeats (polyQ) within the gene encoding the huntingtin protein. The expanded huntingtin misfolds and accumulates in toxic oligomers/aggregates in cells. Despite its monogenic causative nature, HD remains incurable. At the root of disease onset is a prominent alteration of transcription linked to reduced acetylation of histones and impaired chromatin remodeling. However, dysregulated transcription as a driving force in HD is far from being well understood. Genomic tools available in the budding yeast Saccharomyces cerevisiae provide a powerful approach to systematically explore how polyQ affects the acetylome and its regulation of chromatin to facilitate transcription.
Our central hypothesis is that misfolded polyQ disrupts the function of HAT complexes, leading to changes in the yeast acetylome that affect chromatin structure resulting in dysregulated transcription. In support of this hypothesis, we recently uncovered Tra1 as a new target of toxic polyQ expansions. Tra1 is an evolutionary conserved component of the SAGA and NuA4 histone acetyltransferase (HAT) complexes that regulate gene expression through control of transcriptional activation and nucleosome acetylation. We will exploit the yeast system to comprehensively assess how polyQ expansions alter transcription through chromatin remodeling and changes in the yeast acetylome. We have 3 specific goals:
Aim 1: Determine how misfolded polyQ affects chromatin remodeling and accessibility.
Aim 2: Characterize the effects of polyQ expansions on assembly of HAT complexes.
Aim 3: Identify changes in the yeast acetylome induced by polyQ misfolding.
Upon conclusion, we will understand how HD-causing polyQ expansions affect HAT complex assembly and how polyQ regulates chromatin accessibility and transcription to induce changes in gene expression associated with the disease state. These discoveries using the yeast platform will stimulate new areas for experimental therapeutics in not only HD, but potentially for other protein misfolding diseases.
Yeast cells expressing a sfGFP-tagged version of the ER chaperone Kar2.
PC12 cells expressing Q25 or Q103 mHtt exon1-GFP. Polyglutamine expansion results in increased aggregation of the protein in the cytoplasm of neuronal cells.
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