Projects / Programmes
Pathogenic mechanism of the C9orf72 expanded hexanucleotide repeat mutation in neurodegeneration
| Code |
Science |
Field |
Subfield |
| 3.03.00 |
Medical sciences |
Neurobiology |
|
| Code |
Science |
Field |
| B640 |
Biomedical sciences |
Neurology, neuropsychology, neurophysiology |
| Code |
Science |
Field |
| 3.01 |
Medical and Health Sciences |
Basic medicine |
Frontotemporal dementia, amyotrophic lateral sclerosis, neurodegeneration, C9orf72, GGGGCC, RAN translation, RNA binding proteins, G-quadruplexes, TDP-43
Researchers (23)
Organisations (4)
Abstract
Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) are devastating neurodegenerative diseases that form two ends of a complex disease spectrum. Aggregation of RNA binding proteins is one of the hallmark pathological features of ALS and FTDL, and suggests perturbance of the RNA metabolism in their aetiology. In 95% of all ALS and 60% of FTLD patients the aggregating protein is TDP-43, thus defining the major part of the disease spectrum as TDP-43 proteinopathies. However, only a very small percent of aggregation is caused by TDP-43 mutations. Therefore, the main questions in the field are what makes ‘normal’ TDP-43 aggregate in ALS and FTLD and what is the role of perturbed RNA metabolism in these diseases. Recent identification of the disease-associated expansions of the intronic hexanucleotide repeat GGGGCC (G4C2) in the C9orf72 gene further substantiates the case for RNA involvement. This hexanucleotide repeat expansion mutation (HREM) has turned out to be the single most common genetic cause of ALS and FTLD and also presents itself as TDP-43 proteinopathy. HREM may enable the formation of complex DNA and RNA structures, changes in RNA transcription and processing and formation of toxic RNA foci, which may sequester and inactivate RNA binding proteins. This complexity is furtherer increased by the fact that expanded repeat is also transcribed in the antisense direction forming the CCCCGG (C4G2) repeat. According to some reports the antisense HREM transcript is even more abundant than the sense transcript. Additionally, the transcribed expanded repeats from both directions can undergo repeat-associated non-ATG-initiated (RAN) translation resulting in accumulation and aggregation of a series of dipeptide repeat proteins. Finally, HREM may also lead to haploinsufficiency of the C9orf72 protein. As it is a newly discovered protein it has not been well characterized to date. There are very recent publications linking it to endosomal trafficking. Of importance, it has also been recently reported that C9orf72 protein associates with RNA binding proteins.
As C9orf72 repeat expansion is the biggest single contributing cause of TDP-43 proteinopathies, it is very important to resolve which of the possible mechanism of pathogenicity are leading to the TDP-43 proteinopathy. Therefore, increased characterization and understanding of these mechanisms is a pre-requirement in order to find ways of delaying onset or progression of ALS and FTLD.
Thus, this project aims to contribute to the understanding of the pathological role of expanded hexanucleotide repeat in the gene C9orf72 with the focus on RNA toxicity and characterization of the C9orf72 protein.
Recent publications, including ours, have identified a set of proteins that bind to the (G4C2)n RNA and colocalize with RNA foci, therefore in the proposed project we will focus on the disease relevance of the antisense transcript and characterization of the C9orf72 protein in light of its association with RNA binding proteins. The disease relevance of these findings will be tested on inducible pluripotent stem cells containing C9orf72 mutations and postmortem CNS brain and spinal cord tissue from ALS and FTLD patients with C9orf72 mutations.
Significance for science
ALS and FTD are terminal neurological disorders for which there is no known cure. Recent findings strongly implicate disturbances in RNA processes in this spectrum disorder. Numerous other high-impact publications suggest the arising importance of RNA-related processes in understanding other complex diseases and in the development of novel therapies. The main aim of this project was to investigate the disease mechanisms of the hexanucleotide repeat expansion mutation (HREM) in C9orf72, which is the most common genetic cause of ALS and FTD and is also associated with some other neurodegenerative disorders. The three most likely hypotheses are: RNA toxicity from the transcribed HREM, toxicity from overaccumulation and aggregation of dipeptide repeats translated from the HREM, and haploinsufficeincy of the C9orf72 protein. We published four original articles directly related to the topic of the project, as well as five articles on a wider theme of ALS and FTD and three review articles. The significance of the achieved results is also reflected in 324 citations (information on the publications attributed to this project and calculated up to the moment of writing this report; source: Scopus). The most important achievements have been reported on the topology of different lengths of the sense and the antisense DNA strands of the hexanucleotide repreats and the role of dipeptide repeats in toxicity. The publication that had the highest impact was carried out in collaboration with a large international consortium, and we reported on new genes, gene regions that are associated with the emergence of ALS. It was published in the journal Nature Genetics (IF 31.6) and has received a considerable response in the foreign and domestic public. At the time of publication, we had signifcant media attention with television, radio and newspaper articles or interviews.
Significance for the country
Neurodegenerative disorders are one of the largest threats to public health and the economy in developed countries. Despite half a century of advances in neuroscience there are no drugs that significantly improve the course of any neurodegenerative disorder. Therefore, there is a pressing need to discover therapies that can slow or prevent disease progression. Advances in our understanding of the molecular basis of these diseases present an imperative and exciting opportunity to identify novel druggable targets and develop more effective interventions. Beside the already mentioned publication achievements, the project enabled continuation of cutting-edge in molecular neurodegeneration in Slovenia and ensured continuation of very fruitful collaboration between the applicant institutions in Slovenia with the Centre for Neurodegeneration Research from King's College London (prof Shaw), UK, as well as introduced collaboration with another top level institution – Institute of Neurology, University College London (prof Ule). It will also bring together top Slovenian neuroscientists (Zorec and Rogelj) and promote setting up regional collaboration with University of Maribor (Potočnik). We also obtained three bilateral projects, namely with prof. dr. Don Cleveland and prof. dr. Robert Brown from the USA and prof. dr. Pavle Andjus from Serbia. Young researchers in our group received the Ad Futura scholarship, which allowed them to research and gain valuable experience at King's College in London and UCSD. We attended several international conferences and participated in the organizing committees of the three conferences that were held in Slovenia (SBD, Sinapsa and ENCALS). At the SBD 2017 conference, the leader of the group was awarded the Lapanje Prize for top achievements in biochemical science.
Most important scientific results
Annual report
2014,
2015,
final report
Most important socioeconomically and culturally relevant results
Annual report
2015,
final report
