Therapeutic targeting of DNA methyltransferases in Huntington's disease

Huntington’s disease (HD) is a devastating and invariably fatal neurodegenerative disease caused by an abnormal expansion of polyglutamine repeat in the protein called huntingtin (Htt). HD is characterized by progressive loss of selective neurons in the striatum and cortex, but the precise mechanisms underlying neuronal dysfunction and death are not fully understood, and no disease-modifying treatment is currently available. Thus, there is an urgent need to identify critical therapeutic targets and establish effective neuroprotective treatments for HD. One of the major challenges in developing effective treatments lies in the complexity of the brain and our incomplete mechanistic understanding of the disease, The brain comprises diverse cell types, each with distinct vulnerabilities in HD, which complicates treatment approaches. Understanding the individual responses of these brain cell types to the treatment would be crucial for maximizing the effectiveness of the treatment. Transcriptional dysregulation is one of the early molecular abnormalities found in the course of HD and is thought to play a central role in disease pathogenesis. Accumulating evidence suggests that genome-wide perturbations of DNA methylation may drive alterations in gene expression in HD. The fundamental objective of this proposal is to determine the effect of a DNA demethylating agent on gene expression, behavior, and pathology of HD in vivo using two different mouse models. The molecular impact of the treatment on individual cell types in the brain, including neurons and glial cells, in particular, in the striatum, the most vulnerable brain region in HD, will be determined. The underlying hypothesis is that treatment with the hypomethylating agent protects HD brain by inhibiting specific DNA methylation-mediated transcriptional alterations critical for neuronal function and survival, thereby attenuating disease progression. Importantly, therapeutic manipulation of DNA methylation has not been clinically used for neurodegenerative diseases, including HD. To test our hypothesis, the following specific aims will be pursued: 1) Determine the impact of a DNA methylation inhibitor on altered gene expression in individual cell types in HD mouse brains and 2) Determine the effectiveness of the DNA methylation inhibitor on behavior and pathology of HD mice. Given that both neurons and glia contribute to HD pathogenesis, it is crucial to understand the transcriptional responses of individual brain cell types to the treatment. The impact of the demethylating agent in multiple cell types in the striatum of HD model mice will be determined by innovative single-nucleus RNA-seq analysis. If successful, the proposed study will lay the foundation for the development of a new class of disease-modifying treatment for HD. It will also provide a mechanistic understanding of neuroprotection in vivo by this manipulation.