Huntington's disease (HD) is one of several progressive and fatal neurodegenerative diseases. Selective neuronal loss is driven by genetic and environmental factors exacerbated by advancing age. Transcriptional dysregulation is central to many neurodegenerative diseases (HD among them) and to normal aging. We are interested in neuronal death in HD, a process driven by abnormal polyglutamine expansions in the huntingtin protein (Htt). Our studies have demonstrated a central role for the serine/threonine kinase Rip2 in HD pathogenesis. Rip2 also drives neuronal death elicited by other apoptotic stimuli, suggesting that Rip2 kinase is a common mediator of diverse neurological insults. To understand the molecular mechanism of Rip2's pro-apoptotic effects, we performed a yeast two-hybrid screen using Rip2 as bait. We found that Rip2 directly binds EED, a component of the major epigenetic regulator PRC2. PRC2 tri-methylates histone H3 at lysine 27 (H3-K27me3), thereby remodeling chromatin and repressing gene transcription. This activity of EED suggests that Rip2 may cause cell death by altering an epigenetic pathway controlling gene transcription. We will study the molecular regulation of the PRC2 epigenetic pathway as a putative mechanism by which Rip2 affects HD and aging. We envision that our findings will suggest novel targets for therapies for HD and potentially for other neurological diseases and aging.
Aim 1 : To determine how Rip2 regulates the EED-containing histone H3-K27 methyltransferase, PRC2. Approaches include in vitro methyltransferase and kinase assays, mass spectroscopic analysis of phosphorylation, RNA interference (RNAi), and protein biochemistry.
Aim 2 : To determine the role of PRC2 in neuronal cell death induced by mutant Htt and oxidative stress. Approaches include apoptosis assays, RNAi, gene structure-function analysis, and immunocytochemistry.
Aim 3 : To identify gene targets of PRC2 and H3-K27me3 in HD and aged brains. Approaches include target gene chromatin immunoprecipitation (ChIP) and cutting-edge ChlP-sequencing to identify gene targets on the genome-wide scale.
Epigenetic transcriptional changes involving histone modification play a critical role in aging and age- associated neurodegenerative diseases. Findings in this proposal will identify specific signaling pathways that lead to aberrant gene transcription. The pathways identified will aid in the development of novel therapeutics, which may potentially retard aging and slow neurodegeneration.
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