Closing the door on toxic proteins – new clues in understanding a genetic form of MND

The defects in the C9orf72 gene are known to cause motor neurone disease, but researchers don’t understand why. Defective copies of this gene are passed down in some families affected by the rare, inherited form of MND. This week MND Association grantees Drs Guillaume Hautbergue, Lydia Castelli and colleagues, based at the Sheffield Institute of Translational Neuroscience have published their research study providing some important clues about the toxicity of C9orf72. Their research is published in the prestigious journal Nature Communications. Continue reading

Exploring the interaction between TDP-43 and RNA

In light of the upcoming Biomedical Research Advisory Panel meeting happening on Friday 7 April that will discuss which new research projects the MND Association will fund, we are pleased to report on the progress of one of our already-funded researchers. In their three year project, funded by the MND Association, Prof Annalisa Pastore (King’s College London) and Prof Gian Tartaglia (University Pompeu Fabra, Barcelona) are investigating the process by which TDP-43 binds to RNA. Below is a summary of the progress they made during their first year.

Background to the project

Alumni Board Meeting 2008

Annalisa Pastore, King’s College London

One of the causes of amyotrophic lateral sclerosis (ALS), the most common type of motor neurone disease (MND), is related to faulty functioning of the TDP-43 protein, a component that is naturally present in all of our cells. In healthy cells, TDP-43 resides in the centre of a cell (the nucleus) where it attaches to RNA and supports correct gene expression – that is, it helps to extract information carried by a gene to form proteins, the main building blocks of our bodies.

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Motor neurone signalling and the effects of RNA in MND

Dr Pietro Fratta completed his first MRC-MND Association Clinical Research Training Fellowship in 2014. Last year he was awarded a new £1.16 million Clinician Scientist Fellowship to continue his research at University College London, studying the earliest physical changes that affect motor neurons in MND (our reference 946-795). Our contribution to this four year research fellowship is £280,000.

Pietro Fratta

Dr Pietro Fratta, University College London

As his first Fellowship progressed, Dr Fratta became more interested in the field of RNA biology, where he is rapidly establishing himself as an expert. His latest project aims to see whether RNA plays a pivotal role in the earliest signs of cellular damage that occur in MND.

RNA is the cell’s copy of our genetic material known as DNA; Dr Fratta is hoping to establish if the transport of RNA molecules along the nerve fibres is impaired and if so, whether there are particular versions of RNA that are particularly important for motor neurone health and survival.

Several lab studies have shown that the process of transporting things up and down the motor neurones is impaired long before the physical signs of damage are seen. His research will seek to find out what RNA molecules are present in both the cell body of the motor neuron and the nerve fibres. Continue reading

The MND Researchers Bake off Champion!

As well as helping out with our ‘blog a day’ during MND Awareness Month, we also asked our researchers to get involved in ‘baking’ to become our first ‘MND Researchers Bake off Champion’. We received some great science-themed cakes, from zebrafish biscuits to a Nuclear Magnetic Resonance(NMR) machine cake!

Our Director of Research, Dr Brain Dickie said: “It was really tough to judge, they were all great entries! (might need to taste next year though…!). Of the seven entrants there was one that I think wins by a short head, scoring on appearance, originality and relevance to MND research, with an extra mark for sheer wackiness – the ribosome translating a C9orf72 repeat expansion cake!”

The winning cake was by Jenn Dodd, a PhD student at the Sheffield Institute for Translational Neuroscience (SITraN)! Here Jenn describes her cake and how it feels to be the MND Researchers Bake off Champion!

Jenn Dodd's winning ribosome translating C9orf72 cake!

Jenn Dodd’s winning ribosome translating C9orf72 cake!

The winner’s speech:

I decided to bake the cake, as at SITraN we have a weekly cake club and it was my turn to bake in June. I thought entering the competition would be a good way to get involved in MND awareness month and thought it would make cake club a bit different!

Small structural units called cells make up the human body. They convert food and oxygen into energy to produce chemically reactive machines and building blocks called proteins. There are thousands of different proteins made and so special templates called RNA are sent to a protein-making factory in cells called the ribosome. The ribosome makes proteins from the RNA templates in a process called translation (Read more about how cells make proteins here).

The cake shows a ribosome (yellow) translating RNA (the stripey sweets) to make a protein (the flying saucer chains). The protein that is being made is C9ORF72, a protein with an unknown function that is involved in some cases of MND.

I’d like to say thank you and I am really please to have won the bake off with my cake experiment!

What’s all the ‘FUS’ about?

Prof Vladimir Buchman (Cardiff University)’s research was selected as one of the best research studies, as decided by the journal editors, published in the Journal of Biological Chemistry in 2013. He is building on this research in his Association-funded project, which began on 1 April 2014.

The background to FUS:

In 2009 an international team of scientists, including researchers funded by the Association, identified the FUS gene as a cause of approximately 4% of inherited MND cases (5-10% of total MND cases).

The FUS protein formed by this gene is usually found in the nucleus or ‘control centre of the cell’. A change in the structure and/ or function of the FUS protein leads to motor neurone damage and the development of MND. This change causes the FUS protein to ‘wander’ outside of the cell nucleus and form protein ‘clumps’ within the cell.

These protein clumps, as well as being found in 4% of inherited MND cases, are found in many cases of MND and the related disease, frontotemporal dementia. At present it is still not clear how this happens and how these clumps of FUS protein cause MND.

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Of yeast and men: reducing toxic effects of TDP-43 as a potential treatment for MND

A collaborative American research group, led by Prof Aaron Gitler from Stanford University School of Medicine in California, has identified a potential therapeutic target for MND using yeast.

The toxic activity of the MND-linked protein TDP-43 was suppressed when a gene called DBR1 was deleted from yeast and mammal cells.

The study marks the first steps in the identification of a treatment that can target TDP-43, which is found to clump together in over 90% of cases of MND.

The study was published in the prestigious journal Nature Genetics.

Toxic tangle of TDP-43

To develop effective treatments for MND, we need to find ways of targeting the systems that go wrong to cause the disease.

One hallmark of MND is the accumulation of tangled lumps of protein – including TDP-43.

For years, researchers didn’t know whether the clumps of TDP-43 they could see was a by-product of MND, or a cause of the disease. That was of course, until researchers identified that mistakes in the TDP-43 gene can cause inherited MND in 2008. Since then, researchers have been busy creating new disease models to learn more about how TDP-43 can cause MND.

So far, at least 400 studies have been published to better understand TDP-43 in MND (search terms ALS, FTD, variations of TDP-43 on Pubmed).

Yet we still don’t know whether TDP-43 is doing harm by being over active or under active. We do however know that it’s found in the ‘factory floor’ of the cell, called the cytoplasm, when it’s normally found in the control centre. Using this information, it’s possible to focus on therapies that decrease the toxic effect of TDP-43 rather than to increase or decrease the amount of TDP-43.

This is exactly what a collaborative American research group, led by Prof Aaron Gitler has done.

Using yeast, Prof Gitler and colleagues performed two unbiased genetic screens in different laboratories using different techniques. By doing this, they verified a list of genes that can modify the effects of TDP-43 when deleted – by either enhancing the toxic effect or suppressing it.

Out of the list of resulting modifiers, the research group chose to investigate a suppressor of TDP-43 toxicity, a gene called DBR1.

DBR1

Far from a classic Aston Martin sports racing car (also named DBR1), DBR1 in biological terms is an ‘RNA lariat de-branching enzyme’. It plays an important role in recycling genetic ‘junk’.

Our genes are split into segments within our genetic code, separated by what’s often referred to as ‘junk’ DNA. These sections of junk, known as introns, don’t code for anything, but often perform other important roles.

When a gene is copied into its intermediate form of RNA (before these instructions are used to create a functional protein), it needs to be edited to remove the introns, leaving the vital instructions intact. This involves the introns forming loops of RNA – called lariats – which cut away from the rest of the copy. This leaves only the instructions for the gene product. These lariats then move away from the control centre of the cell (the nucleus) to be recycled.

DBR1’s role normally cuts these lariats open into strings, which can then be recycled. When in a lariat form, RNA is resilient to being recycled. DBR1 therefore plays an important role in recycling intronic RNA in the cell.

What happens when DBR1 is deleted?

When the research group deleted DBR1, intronic lariats accumulated in the factory floor of the cell (the cytoplasm). These lariats then competed to bind to TDP-43, acting as a decoy. This stopped TDP-43 from performing its dastardly deeds when faulty – chopping up essential RNAs within the cell –which could be contributing to the cause of MND.

By deleting DBR1 in yeast and in rat neurones grown in a dish, the research group identified that it increased the chance of neurone survival by nearly 20%.

This means that identifying a therapy that can decrease the amount of DBR1 could be a potential treatment for MND.

Reliability

Prof Gitler and colleagues independently verified their results from the genetic screen in yeast using different laboratories and different methods.

This is significant in terms of its reliability, as this often has huge repercussions for future research.

This topic was recently discussed in the popular science magazine New Scientist in an article called ‘Is medical science built on shaky foundations?’ In the article, the writer explains that a number of pharmaceutical companies have recently announced their failure to replicate a large number of promising results of potential drug targets from published studies.

It’s vital that if we are to identify a treatment for MND that works, that the evidence that led it to be tested in humans is solid. Gaining evidence to suggest the effectiveness of a treatment means replicating the results using independent researchers and using different methods to put an idea through its paces. This ensures that the original results aren’t identified as a coincidence and can be relied upon.

The decision by Prof Aaron Gitler’s group to reproduce their genetic screen independently, using different methods should be applauded. It means their findings are unlikely to be added to the heap of potential targets that cannot be reproduced in other studies.

Being thorough to identify potential targets may take more time, but it’s likely to produce more fruitful results in the long haul.

Looking forward

There are many steps left to climb with the development of a treatment that targets TDP-43. For example, the research group will need to determine whether stopping DBR1 could itself be toxic due to side effects. They also need to determine where the ‘therapeutic window’ is with this therapy – where it’s both effective and safe.

This study also identified many other modifying factors for TDP-43, which can begin to be investigated by other research groups for their potential as a therapy for MND.

As this is the beginning of the story of TDP-43 specific treatments for MND, it will inevitably be a long journey to answer these questions and to bring treatments to the doctor’s prescription pad.

Hopefully, the beacon of rigor and scientific righteousness that this study symbolises will continue and we will see the first TDP-43 therapy being developed for MND in the coming years.

References:

Maria Armakola et al Inhibition of RNA lariat debranching enzyme suppresses TDP-43 toxicity in ALS disease models. Nature Genetics 2012; doi:10.1038/ng.2434

http://www.newscientist.com/article/mg21528826.000-is-medical-science-built-on-shaky-foundations.html

Learning about genetic messages and their potential role in MND

Talks on RNA biology are new to the symposium this year as it is the newest puzzle piece to the expanding list of possible cellular causes of MND.

So why is RNA biology important to MND and what is it all about? RNA stands for ‘ribonucleic acid’ and plays a vital role in the creation of proteins that play day-to-day roles in our bodies. Two MND causing genes – TDP-43 and FUS, have been found to have a role in the processing of RNA and so understanding more about the link between these genes and RNA processing is of growing importance in order to find out more about the causes of MND.

So what does RNA processing mean? Our genetic code is over three billion letters long and holds the instructions for how to build everything in our bodies but in this form, it’s nonsense. ‘Editors’ are a type of RNA processers and are needed to copy and ‘tidy’ short sections of code to produce instructions that can then be used to build new proteins. This session was therefore dedicated to our growing understanding of how TDP-43 and FUS may be involved in RNA processing and how this may be affected in MND.

The first talk was given by one of the researchers that we fund– Prof Tom Maniatis from Colombia University in America. In his talk, he gave an enthralling overview of his current study to develop a human ‘in a dish’ model of MND following the success of a recent ‘proof of principle’ study in mice. This new and exciting method of studying live human motor neurones and support cells called ‘glia’ uses stem cell technology to ‘turn back the clock’ on skin cells donated by people living with MND. 

In his current study, alongside Prof Chris Shaw from King’s College London and Prof Siddharthan Chandran from Edinburgh University, Prof Maniatis is studying the effect of a ‘sandwich’ of glia and motor neurones on the amount of proteins being made. The preliminary results from the human study have found that there are hundreds of other genes that are found in higher and lower quantities than normal in motor neurones as compared to healthy motor neurones. Of these, a large number are involved with many different processes that are known to be involved with the degeneration of motor neurones. These findings are still preliminary as the study is ongoing – but it’ll certainly be interesting to find out more in the future!

As the session continued, we heard from a number of speakers who are also working to find out how TDP-43 is involved with RNA processing and how this causes motor neurones to degenerate.

The ‘take home’ message from these talks is that we are learning more about what TDP-43 interacts with through its role in RNA processing, and we are now moving closer to learn how it can cause MND.