TARGETING PARKIN & MITOCHONDRIAL DYNAMICS IN HUNTINGTON'S DISEASE

Lead Research Organisation: University of Leicester
Department Name: Genetics

Abstract

Huntington's disease is an incurable, fatal neurodegenerative disorder that is characterised by the loss of vulnerable neurons in the brains of patients. The disease is caused by an increase in the size of a particular DNA sequence (a trinucleotide CAG repeat) which encodes for the amino acid glutamine in the huntingtin (HTT) gene. If the number of glutamines in the HTT protein increases beyond a critical length it misfolds and forms protein tangles, which can disrupt vital cellular processes. An increased number of CAG repeat units in the HTT gene is associated with an earlier age of Huntington's onset. However, there is substantial variability in the onset of symptoms in individuals with the same number of repeats, and studies have shown that ~40 % of this variation is due to other genes. This suggests that there are many potential therapeutic targets capable of significantly altering age of disease onset in the human genome.

Previous work by our laboratory and others has found that mitochondria - the energy powerhouses of cells - do not function properly in several ways in Huntington's disease. Interestingly, we have recently found that the protein parkin, which is critical for clearing unhealthy mitochondria for the cell, can improve disease symptoms in a fruit fly model of Huntington's. Notably, mutations in the gene encoding parkin cause hereditary forms of Parkinson's disease. Here we propose to dissect the mechanisms underlying parkin protection. As parkin is involved in controlling the shape of mitochondria, we will interrogate mitochondrial morphology using various microscopy-based techniques, in order to see if in the context of Huntington's model flies parkin influences this process. In parallel, we will also study mitochondrial function in these flies using several biochemical approaches. We will also extend this work to systematically test several proteins related to parkin function and mitochondrial dynamics, in order to better understand how parkin is influencing disease "symptoms" in Huntington's flies. In total, this work will inform the mechanisms underlying Huntington's disease, will may ultimately lead to the development of novel therapeutic strategies for this disorder. As mitochondrial dysfunction is linked to several neurodegenerative diseases, any compelling insights may ultimately have broader significance.

Technical Summary

Huntington's disease (HD) is an incurable, fatal neurodegenerative disorder caused by the expansion of a polyglutamine tract in the huntingtin (HTT) protein. This mutation causes HTT to misfold and aggregate, leading to widespread dysfunction and death of vulnerable neurons. As with several other neurodegenerative disorders, the pathogenesis of HD has been closely linked with mitochondrial dysfunction, which includes alterations in mitochondrial dynamics (e.g. increased mitochondrial fragmentation). In preliminary studies we have recently found that the Parkinson's-linked protein parkin alleviates several disease phenotypes in HD flies when overexpressed. Parkin plays a role in clearance of damaged mitochondria (mitophagy), via modulation of mitochondrial dynamics. Here we propose to further investigate the mechanisms underlying parkin protection in HD fruit flies and a PC12 cell model, and also explore the role of mitochondrial dynamics and mitophagy in pathogenesis of this disorder. We will use genetic approaches to modulate parkin expression in HD models - as well as related proteins (e.g. PINK1, Mfn, Opa1, Drp1) - and ascertain the influence upon mitochondrial phenotypes (e.g. mitochondrial morphology, mitochondrial respiration). Relatedly, as parkin has been found to participate in protein degradation and autophagy of aggregated molecules and reduce proteotoxicity, we will also explore the relationship between parkin and HTT. In total, this work will explore the protective role of parkin in HD, and interrogate mitophagy and mitochondrial dynamics in this disorder. These studies may ultimately contribute to therapeutic strategies for HD.

Planned Impact

This proposal has direct implications for individuals suffering from Huntington's disease (HD), and their families. Though several drugs are available for symptomatic management of HD, no treatments are available that halt or delay progression or onset of HD and very few new disease-modifying therapies are in the clinical pipeline. It is estimated that HD costs up to $1 billion per year in medical and nursing costs in the United States alone. Furthermore the common neurodegenerative disorders affect more than 700,000 people in the UK, and cases are predicted to double in the next 25 years, costing the UK economy a staggering £50 billion. In addition to the obvious patient benefits, the identification of an effective treatment for HD and other neurodegenerative disorders could dramatically cut these expenditures world-wide.

We have considerable expertise in the use of fly and mammalian cell models for HD in order to understand the mechanisms underlying this disease, as well as identifying novel candidate therapeutic target. Our previous identification of kynurenine 3-monoxygenase (KMO) as a candidate therapeutic target for Huntington's disease speaks strongly for our approach. Several inhibitors of KMO have been, and are currently being, developed with the aim of entering clinical trials in the near future. Importantly, KMO inhibitors will likely also have relevance for AD and PD. In addition, we have recently found that a compound which mimics the antioxidant activity of glutathione peroxidases is robustly protective in fly and mammalian cell models of HD. Notably, this compound - ebselen - is well-tolerated in humans, giving further impetus for future preclinical analyses. Thus, the proposed research will likely provide additional insights into pathogenesis and treatment for HD, and has a high chance of delivering upon this promise. As mutations in parkin are associated with some familial forms of Parkinson's disease, and alterations in mitochondrial dynamics an mitochondrial impairment are observed in several neurodegenerative disorders, the proposed work may also inform these diseases.

Publications

10 25 50
 
Title Generation of Parkin constructs 
Description We have generated several wild-type and mutant Parkin constructs for expression in both mammalian cells and yeast. These constructs are for overexpression, as well as for bimolecular fluorescence complementation. 
Type Of Material Model of mechanisms or symptoms - in vitro 
Provided To Others? No  
Impact None as of yet. 
 
Description Collaboration with Dr Alex Whitworth (Cambridge) 
Organisation Medical Research Council (MRC)
Department MRC Mitochondrial Biology Unit
Country United Kingdom 
Sector Public 
PI Contribution We established preliminary data looking at mitochondrial dynamics and Parkin in the context of Huntington's disease. This data highlight the importance of this process in pathogenesis of this disorder, and led us to contact Dr Whitworth, who is an expert in this area.
Collaborator Contribution Dr Whitworth has provided expert knowledge on Parkin and mitochondrial dynamics in our collaboration. He addition, he has provided reagents from his lab which will be vital for our future analyses.
Impact No outputs as of yet.
Start Year 2015
 
Description Collaboration with Prof Charalambos Kyriacou 
Organisation University of Leicester
Country United Kingdom 
Sector Academic/University 
PI Contribution I have brought expertise on Huntington's and Parkison's disease models to this project, as well as our knowledge on the study of genetic modifiers of disease.
Collaborator Contribution Prof Kyriacou has advised on the use of fruit fly models in our work.
Impact Several of the publications listed in the portfolio have arisen from our collaboration (as indicated by the presence of Prof Kyriacou on the author list).
Start Year 2008
 
Description Invited seminar, Division of Neuroscience & Experimental Psychology, Faculty of Biology, Medicine and Health, University of Manchester, UK. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Research seminar.
Year(s) Of Engagement Activity 2017
 
Description Brain Awareness Lecture 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact My lecture was part of a wider Brain Awareness Day event which the University of Leicester organized. It was broadly advertised and well attended. My lecture served to spark many questions from the audience how basic research using disease models can lead to advances in medicine and treatment.

The talk led to increased interest in my research, and hopefully emphasized to the audience the translational benefits of our studies.
Year(s) Of Engagement Activity 2015,2016,2017,2018
 
Description GENIE Open Day Events, University of Leicester, UK 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact Open day events organized by GENIE a CETL based at the University of Leicester. ~200 school children per event learning about DNA and genetics, and the use in medicine, etc.

Generated interested in genetics amongst the school children - with greater interest in GCSE and A-level science/biology.
Year(s) Of Engagement Activity 2008,2009,2010,2011,2012
 
Description Inaugural Lecture, University of Leicester 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact This was my inaugural lecture for promotion to professorship, which was a public lecture/event. A mix of individuals from the university and the local community attended. Estimate ~200 people attended.
Year(s) Of Engagement Activity 2017
 
Description Invited seminar, Center for Biostructural Imaging of Neurodegeneration, University Medical Center Goettingen, Germany. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Research seminar.
Year(s) Of Engagement Activity 2018
 
Description Invited seminar, Center for Neuroscience and Cell Biology of the University of Coimbra, Coimbra, Portugal. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact I presented two seminars on Huntington's disease and my research to postgraduate students as part of a course on neurological diseases.
Year(s) Of Engagement Activity 2016
 
Description Invited seminar, Jean-Pierre Aubert Research Centre, UMR Inser-S1172, Univ. Lille-Nord de France, Lille dedex, France 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Research seminar.
Year(s) Of Engagement Activity 2017
 
Description Invited seminar, Living Systems Institute, University of Exeter, UK. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Research seminar.
Year(s) Of Engagement Activity 2018
 
Description Invited talk, Mitochondria Dysfunction in Neurodegeneration Summit, Newcastle University, UK. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact This was a meeting amongst researchers at Newcastle University that are interested in neurodegeneration and mitochondrial dysfunction. I was invited to participate and present our work on mitochondrial dysfunction and Huntington's disease.
Year(s) Of Engagement Activity 2019
 
Description Plenary Speaker; 9th European Huntington's Disease Network (EHDN) Plenary Meeting, The Hague, Netherlands 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Patients, carers and/or patient groups
Results and Impact This was a plenary talk at the EHDN conference on Huntington's disease attended by over 700 individuals - scientists, clinicians, and patients/families.
Year(s) Of Engagement Activity 2016
 
Description Poster presentation at CHDI Therapeutics Conference, Palm Springs, CA Feb 2018 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Poster presentation at research conference.
Year(s) Of Engagement Activity 2018
 
Description University Taster Days 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Undergraduate students
Results and Impact ~100 A-level students contemplating Leicester for undergraduate studies, along with parents/relatives. These talks covered my research, and the students asked several relevant questions, and were interested in how this could tie into their 3rd projects. This has been done 8 times, 7 times in Leicester and once in London.

Impacts will be determined based upon potentially increased applications to the university for study.
Year(s) Of Engagement Activity 2013,2014,2015,2016,2017
 
Description Visit from Mill Lodge Huntington's Disease Inpatient Unit team to our laboratory, Leicester, UK. 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Professional Practitioners
Results and Impact We hosted a visit from the Mill Lodge Huntington's disease team to our laboratory. The activities included HD research talks from our team and a tour of the labs. We also held a discussion over lunch about a future visit to their site, as well additional activities that we can do together.
Year(s) Of Engagement Activity 2018