Summaries of 2015 HDSA-Funded HD Human Biology Projects

Ultrasensitve detection of huntingtin protein in cerebrospinal fluid

Amber Southwell, Postdoctoral Fellow, University of British Columbia:
Dr. Janis Brown Memorial Award Winner

amber2Huntingtin, the protein that when mutated causes HD, accumulates within cells and engages in a variety of aberrant interactions. Reducing the levels of this toxic protein should prevent all subsequent pathology and prevent or delay the onset of HD. In fact, several huntingtin lowering therapies are being developed through animal studies and rapidly approaching trials in humans. However, what is missing is a method to measure huntingtin protein levels in the human brain, a necessary pre-requisite to evaluating the success of huntingtin lowering therapies. We have overcome this obstacle using a technique called IP-FCM to measure mutant huntingtin protein in the fluid that bathes the brain, the cerebrospinal fluid (CSF) and have shown that mutant huntingtin protein in the CSF originates in the brain and is released by injured or dying brain cells. Levels of mutant huntingtin protein in the CSF increase with worsening HD symptoms, suggesting that this approach will be useful as a measure of disease progression in HD. Additionally, lowering mutant huntingtin in the brain using gene-silencing treatments results in a measurable reduction of mutant huntingtin in the CSF, indicating that IP-FCM could be used to verify and quantify changes in brain mutant huntingtin in response to experimental therapies. In ongoing work, we will continue to study our IP-FCM method to learn more about how it works and continue to use IP-FCM to learn about HD by measuring mutant huntingtin in CSF from the same patients over time to see how it changes in individuals. Additionally, we will develop similar quantitative methods to measure huntingtin protein that cannot be quantified with the current method, such as the normal huntingtin protein, allowing comparison of mutant and normal protein levels over time in patients.

 

Investigating the toxicity of mutant huntingtin in human induced pluripotent stem cells (iPSCs) derived from gut epithelial cell models

Ali Khoshnan, Senior Research Scientist, California Institute of Technology

 

Ali2The age of disease onset is variable among HD patients with similar polyglutamine (polyQ) length. Thus, in addition to polyQ expansion, environmental factors may accelerate the progression of symptoms. Inflammation is a potential modifier of HD pathology. The intestinal microbes contain compounds, which are known to induce inflammation and disrupt the normal function of intestinal epithelium. The expression of mutant huntingtin (mHTT) in the gastrointestinal (GI) tract cells may increase the susceptibility of intestinal epithelium to microbial insults. We propose that the inflammatory components of gut microbes enhance the toxicity of mHTT in intestinal cells and contribute to GI abnormalities in HD patients. Our preliminary data support this hypothesis. To expand on these findings and to establish a connection between gut microbes and HD pathology, we plan to develop intestinal models using patient-derived stem cells. These innovative approaches may identify novel biomarkers for diagnosis and provide strategies to develop safe biotherapies for GI-associated symptoms in HD.

 

Study of CAG repeat expansion impact on huntingtin mRNA cellular localization for a rational design of next generation oligonucleotide-based therapeutics

Marie Didiot, Postdoctoral Fellow, University of Massachusetts Medical School 

marie2Oligonucleotide-based therapy that enables the direct silencing of HTT mRNA, is one of the most promising therapeutic approaches for the treatment of Huntington’s disease (HD). Our laboratory is focused on the development of novel hydrophobically modified, small-interfering RNA (hsiRNA) for the treatment of HD. We observed that any RNA-interfering (RNAi) reagents targeting HTT mRNA reach a plateau of 50-70% silencing, while the targeting of other genes usually results in more than 95% knockdown. Understanding this phenomenon is critical for the development of HTT-targeting oligonucleotide therapeutics. Based on preliminary data, we suspect that a significant fraction of Htt mRNA is nuclear (in nucleus of cell) and thus is inaccessible to regular RNAi reagents. Understanding the potential functional role of nuclear HTT mRNA is essential for a rational design of next-generation oligonucleotide therapeutics. The goal of this proposal is to investigate the impact of CAG repeat expansion on HTT mRNA intracellular localization in human-derived primary fibroblasts from healthy and HD subjects. We hope to understand how the CAG repeat expansion impacts the sub-cellular localization of HTT mRNA that impairs the silencing efficiency of oligonucleotide therapeutics. This study will also contribute to the validation of oligonucleotide therapeutics against HTT mRNA in a human HD context. Finally, we also aim to better understand the role of HTT mRNA CAG repeat expansions in HD pathogenesis.

 

Exercise and brain stimulation as modifiers of neuroplasticity in Huntington’s disease

Sophie Andrews, Research Fellow, Monash University (Australia)

sophie2Huntington’s disease is a devastating genetic condition with no cure. Drugs can lessen the symptoms but have little effect on disease progression. It has been observed that disease onset is delayed in patients with more active lifestyles. This suggests exercise is a lifestyle factor with exciting potential to delay the symptoms of neurodegenerative disease. Researchers investigating HD in mice have shown that exercise can increase brain plasticity, the brain’s ability to change and adapt. It is not yet known whether the same is true in humans, or what ‘dose’ (intensity) of exercise is optimal, and therefore studies are needed to determine how best to use exercise to improve brain function. We propose to address this important gap by undertaking two studies. First, we will examine the effect of exercise intensity on brain plasticity in pre-symptomatic individuals who are predisposed genetically to HD, as well as healthy control participants. We will measure brain plasticity using a safe, non-invasive and painless way to stimulate the brain (‘transcranial magnetic stimulation’). Second, we will assess whether exercise can enhance the learning of new motor skills, and whether this effect can be increased using another type of non-invasive brain stimulation (‘transcranial direct current stimulation’). This research is the first step towards providing individuals that are predisposed genetically to HD with evidence based advice to change their lifestyles before symptoms develop. The knowledge generated from this research will also be used to design new non-medication interventions that are most likely to be effective.

 

Molecular and cellular assessment of huntingtin lowering in differentiated patient-derived HD iPSCs.

Lisa Salazar, Assistant Project Scientist, University of California at Irvine

 lisa salazarHuntington’s disease (HD) is a devastating neurodegenerative disease that strikes in the prime of life. Patients experience progressive impairment of motor and cognitive function, as well as other symptoms, and treatments to slow disease progression remain elusive. Because disease is caused by mutation of the huntingtin (HTT) gene, one strategy for disease intervention, now in clinical trials, is to reduce production of the HTT protein. Using HD patient-derived stem cells, we are generating cell lines in which total or mutant HTT levels can be reduced at the stem cell stage, or any time during their development into mature neurons. This will allow us to evaluate the consequences of reducing total HTT compared to those of preferentially lowering mutant HTT. This is important because the question remains whether decreasing expression of wild-type HTT will have more subtle adverse effects. This strategy will further enable us to begin to identify which disease characteristics can be rescued, especially when intervention is given to more mature cells, as it would be in patients. Specifically for the proposed studies, we will examine the ability of HTT lowering to rescue gene expression, cell viability and metabolic function, resulting in the identification of relationships between gene expression and cell function that might inform benefits and side effects of HTT lowering treatments and provide signatures amenable to rescue that can be targeted in small molecule screens.

 

Investigation of epigenetic mechanisms in Huntington’s disease patients quantified by non-invasive PET imaging

Changning Wang, Instructor, Massachusetts General Hospital/Harvard Medical School

cwang 2To date, our understanding of HD has been dominated by HD animal model data and without tools to ‘see’ into the living brain, it is impossible to visualize the molecular changes that precede disease onset. Molecular imaging with techniques like positron emission tomography (PET) has proven valuable at measuring disease after onset. A key subset of this family, the class 1 Histone deacetylase (HDAC) isoforms, has been shown to be dysregulated in the brains of animal models with remarkable therapeutic potential for improving cognitive function that results from early neurodegeneration. Our lab has developed the first, and to date only, imaging agent for class 1 HDACs and has successfully progressed the imaging agent to first-in-human trials. Our experiments will answer the question, is HDAC expression altered in the human HD brain? Importantly, either positive OR negative outcomes will provide an immediate step forward in understanding HD and motivate novel drug trials.

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