Spreading the seeds of an idea: MND disease pathology

With motor neurone disease (MND), the muscle weakness almost always starts in a single part of the body, with the weakness then spreading to other muscles in an orderly fashion. Neurologists are usually quite good at predicting which muscles will be affected next, slightly less so at predicting when this will happen.

The physical changes on the outside will be reflecting events occurring in the ‘closed box’ that is the brain and spinal cord. The latest imaging techniques are starting to give us more of a picture of what’s happening in the central nervous system as the disease progresses, but further technological advances will still need to be made. The clearest picture still comes from the study of generously donated and incredibly valuable post-mortem tissue.

The second day of the Symposium saw researchers present in the Clinical-Pathological Correlates of Disease Progression session, focussing on how to understand disease progression, the role of prions in neurodegenerative diseases and the relationship between MND and frontotemporal dementia.Read More »

The 11th Annual ENCALS meeting highlights how TDP-43 spreads in MND

The European Network for a cure of ALS (ENCALS) held its 11th Annual meeting in Sheffield from 31 May to the 2 June. The weekend was full of glorious British sunshine and more than 200 international scientists and clinicians were also able to enjoy a range of incredibly interesting talks about the latest developments in MND research.

A particular talk caught my attention on the first day by Dr Johannes Brettschneider from the University of Ulm in Germany. Dr Brettschneider explained how his research had shown the stages and spread of the protein TDP-43 in ALS (the commonest form of MND).

Dr Brian Dickie, Director of Research Development, said: “The key to defeating MND lies in fostering strong collaborations between neurologists, healthcare professionals, research scientists, early career investigators and students in the field of MND and the 11th Annual ENCALS meeting in Sheffield provided that opportunity. The MND Association was proud to support this event.”

‘Special’ staining

At the end of an afternoon of talks on the MND- causing genes C9orf72, FUS and SOD1, Dr Brettschneider engrossed over 200 delegates with his talk on the TDP-43 protein and how it spreads in ALS.

Although TDP-43 genetic mistakes are a rare cause of MND, scientists are especially interested in the TDP-43 protein because in the vast majority of cases of MND (irrespective of whether it was caused by an inherited genetic mistake), TDP-43 protein forms pathological clumps inside motor neurons.

The study (which is a collaboration between Dr. John Trojanowski and Dr. Virginia Lee from the Penn University Center of Neurodegenerative Disease Research in Philadelphia, America and the group of Dr. Heiko Braak in Ulm) used a technique known as ‘immunohistochemistry’.  This technique involves taking tissue samples of the brain and spinal cord from people who have died from ALS. The researchers would then make extremely thin slices of the tissue, which could then be stained using a ‘special stain’ and viewed under a microscope.

The stain used by Dr Brettschneider only ‘stained’ the TDP-43 protein in the samples, meaning that he could see the amount of TDP-43 in different areas of the brain and spinal cord.

Using the clinical information and TDP-43 staining this would allow Dr Brettschneider to stage the disease.

Image kindly provided by Dr Robin Highley, SITraN: (top left) a motor neurone with a skein-like neuronal cytoplasmic inclusion, next to a normal motor neurone (bottom left) on TDP-43 immunohistochemistry.
Image kindly provided by Dr Robin Highley, SITraN: (top left) a motor neurone with a skein-like neuronal cytoplasmic inclusion, next to a normal motor neurone (bottom left) on TDP-43 immunohistochemistry.

Axonal ‘telephone wires’ do more than just talking

Dr Brettschneider showed that TDP-43 increased in different areas of the brain and spinal cord during different stages of the disease. Amazingly, he also showed how ALS (characterized by clumps of TDP-43) spreads from one are of the body to another.

A motor neurone consists of three parts; the cell body, axon and nerve ending. The cell body contains the nucleus, or the control centre of the cell. When a message travels from the brain the cell body sends the message down the axon. Like telephone wires, the axon carries the message to the muscle, where the nerve endings cause the muscle to move.

However, in ALS it seems that these ‘telephone wires’ do more than just carry a message. The protein TDP-43 forms ‘clumps’ in the motor neurones and it seems that these clumps use the axon to travel from one motor neurone to the next (possibly explaining why someone get’s weakness in their arm and then their hand).

Another key finding was that TDP-43 clumps develop in the front part of the brain (prefrontal cortex), which is responsible for personality and may explain the development of cognitive symptoms.

Dr Brettschneider explained the importance of this research While spreading of disease-related proteins has been described for other neurodegenerative diseases like Alzheimer’s disease or Parkinson’s disease, this had not been previously shown in ALS. Now, we can show evidence that supports a spreading of the major disease protein TDP-43 in ALS across specific regions of the brain and spinal cord with ongoing disease.

 If these findings can be confirmed (for example in cell culture or mouse model studies) then this could lead to the design of new treatments specifically aiming to impair the spread of TDP-43 protein clumps.

Dr Johannes Brettschneider from the University of Ulm in Germany at ENCALS
Dr Johannes Brettschneider from the University of Ulm in Germany at ENCALS

Furthermore, we believe that our findings offer a better understanding of disease progression in ALS.  Our data implies that TDP-43 spreads throughout the prefrontal cortex with ongoing disease, thereby lending support to the idea that all ALS patients could eventually develop “frontal type” cognitive deficits.”

The future

Dr Brettschneider commented why this research is important to people living with MND explaining that “If these stages can be reproduced in patients with ALS they could offer a new way to assess disease progression and response to new treatments. We hope that our study provides the essential groundwork for strategies designed to prevent pTDP-43 spread.”

This research is only the beginning and more work is needed, Dr Brettschneider also explained what he hoped to do next with these exciting results. “There were restrictions in time and availability of the tissue samples during this study, so we were unable to determine how and where exactly ALS begins in the very early stage of the disease. Therefore, an important next step in our work would be to analyze very early cases with ALS to look at TDP -43 spread as this offers the most promising window for therapeutic intervention.”

Reference

Brettschneider J, Del Tredici K, Toledo JB, Robinson JL, Irwin DJ, Grossman M, Suh E, Van Deerlin VM, Wood EM, Baek Y, Kwong L, Lee EB, Elman L, McCluskey L, Fang L, Feldengut S, Ludolph AC, Lee VM, Braak H, Trojanowski JQ. Stages of pTDP-43 pathology in amyotrophic lateral sclerosis. Ann Neurol. 2013 May 20. doi: 10.1002/ana.23937. [Epub ahead of print]

Finding the key to why TDP-43 accumulates in MND

A study, part funded by the MND Association and led by Prof Chris Shaw from King’s College London has been published in the June edition of the scientific journal Brain. As we part-funded this study, Prof Shaw sent us the resulting paper from his research yesterday. So, this morning after reading the paper, we thought we’d share with you what they were looking to answer and what they found!

First, a bit of background: One thing that we’ve known for a long time about MND is that by looking through a microscope at an affected motor neurone, brown blobs of proteins that stick together can be seen. It wasn’t until a few years ago that we finally identified a component of the blobs as a protein called TDP-43 that accumulates in around 90% of cases of MND. In 2008, a fundamental breakthrough occurred in that the second causative genetic mistake was discovered in a gene which codes for TDP-43. This was found to be responsible for the cause of between 4-5% of cases of the inherited form of MND and forged a new understanding that the brown blobs containing TDP-43 may have something do to with the cause of MND as opposed to a possible ‘side effect’ of the disease.

TDP-43 is also now recognised to be a cause of a related disease called fronto-temporal dementia (often called FTD). So, by learning more about TDP-43 we can try to identify how it can go wrong in cells to cause both of these diseases.

One mechanism that has been proposed to trigger the accumulation of TDP-43 which may lead to the cause of MND is a defective transport system of the protein into the nucleus – the control centre of the cell. Without TDP-43 having the right ‘key’ to get into the nucleus, it is left to accumulate outside outside of the nucleus. This can have a negative impact on the neurone as TDP-43 cannot perform its regular function and it can cause ‘pile-ups’ within the neurone. What we don’t understand, is what makes TDP-43 not find the right ‘key’ to enter the nucleus. This is the question that this research group set to answer.

What did the research group find?
The research group first silenced (quite literally stopping the function) 82 proteins that are known to be involved with the transport of cargo, such as TDP-43 into the nucleus. From this they identified five proteins that when silenced result in an accumulation of TDP-43 outside of the nucleus. However, three of these are known to be involved in the general transport of all proteins into the nucleus and so were discarded from the study. To make sure the results were not a fluke they repeated their experiments in a total of three cellular models originating from humans and mice. The two proteins that were found to cause an accumulation of TDP-43 outside of the nucleus are called CAS (which stands for Cellular Apoptosis Susceptibility) and Karopherin-β1.

They then went on to see whether the levels of these two proteins are altered in people who have sporadic ALS (the most common form of MND) with TDP-43 clumps (so called TDP-43 positive) or TDP-43 positive FTD. They used brain and spinal cords that had been kindly donated for use in research from people with FTD, people with ALS and healthy controls.

From this, they found that the protein CAS is found in lesser quantities than normal for people who have FTD but did find any differences in samples from people with ALS. Neither FTD nor ALS samples had any significant difference in the level of Karopherin-β1 as compared to the healthy controls.

This means that CAS may play a causative role in FTD but not in ALS. For ALS, this suggests that something else may be going wrong to cause TDP-43 to accumulate outside of the nucleus.

What does this mean for the future of MND research?
From this research project, we now know that although the lack of CAS protein can lead to TDP-43 accumulation in a cell, this is not what causes the accumulation of TDP-43 in MND but may cause the accumulation in FTD. Learning more about how TDP-43 works is important in order for us to understand what the consequences may be if it goes wrong. This research project is a good stepping stone in learning more about TDP-43 and the causes of MND.

The search will now continue to find out what causes TDP-43 to go wrong in MND which may lead to the discovery of a new target for treatments.

We’re currently funding a number of studies relating to TDP-43 to learn more about what it does and how it may cause MND – visit our causes research projects we fund and look out for TDP-43 in the titles!

Link to abstract for scientific paper published in Brain.