̽��ֱ�� of Cambridge - motor neurone disease

Gene discovery indicates motor neurone diseases caused by abnormal lipid processing in cells

Anonymous — Mon, 20 Jun 2022 01:35:50 +0000

Motor neurone degenerative diseases (MNDs) are a large family of neurological disorders. Currently, there are no treatments available to prevent onset or progression of the condition. MNDs are caused by changes in one of numerous different genes. Despite the number of genes known to cause MNDs, many patients remain without a much-needed genetic diagnosis.

̽��ֱ��team behind the current work developed a hypothesis to explain a common cause of MNDs stemming from their discovery of 15 genes responsible for MNDs. ̽��ֱ��genes they identified are all involved in processing lipids - in particular cholesterol – inside brain cells. Their new hypothesis, published in the journal Brain, describes the specific lipid pathways that the team believe are important in the development of MNDs.

Now, the team has identified a further new gene – named TMEM63C – which causes a degenerative disease that affects the upper motor neurone cells in the nervous system. Also published in Brain, their latest discovery is important as the protein encoded by TMEM63C is located in the region of the cell where the lipid processing pathways they identified operate. This further bolsters the hypothesis that MNDs are caused by abnormal processing of lipids including cholesterol.

“This new gene finding is consistent with our hypothesis that the correct maintenance of specific lipid processing pathways is crucial for the way brain cells function, and that abnormalities in these pathways are a common linking theme in motor neurone degenerative diseases,” said study co-author Professor Andrew Crosby from the ̽��ֱ�� of Exeter. “It also enables new diagnoses and answers to be readily provided for families affected by some forms of MND”

MNDs affect the nerve cells that control voluntary muscle activity such as walking, speaking and swallowing. There are many different forms of MNDs that have different clinical features and severity. As the condition progresses, the motor neurone cells become damaged and may eventually die. This leads to the muscles, which rely on those nerve messages, gradually weakening and wasting away.

If confirmed, the theory could lead to scientists to use patient samples to predict the course and severity of the condition in an individual, and to monitor the effect of potential new drugs developed to treat these disorders.

In the latest research, the team used cutting-edge genetic sequencing techniques to investigate the genome of three families with individuals affected by hereditary spastic paraplegia – a large group of MNDs in which the motor neurons in the upper part of the spinal cord miscommunicate with muscle fibres, leading to symptoms including muscle stiffness, weakness and wasting. These investigations showed that changes in the TMEM63C gene were the cause of the disease. In collaboration with the group led by Dr Julien Prudent at the Medical Research Council Mitochondrial Biology Unit at the ̽��ֱ�� of Cambridge, the team also undertook studies to learn more about the functional relevance of the TMEM63C protein inside the cell.

Using state-of-the-art microscopy methods, the Cambridge team’s work showed that a subset of TMEM63C is localised at the interface between two critical cellular organelles, the endoplasmic reticulum and the mitochondria, a region of the cell required for lipid metabolism homeostasis and proposed by the Exeter team to be important for the development of MNDs.

In addition to this specific localisation, Dr Luis-Carlos Tabara Rodriguez, a Postdoctoral Fellow in Prudent’s lab, also uncovered that TMEM63C controls the morphology of both the endoplasmic reticulum and mitochondria, which may reflect its role in the regulation of the functions of these organelles, including lipid metabolism homeostasis.

“From a mitochondrial cell biologist point of view, identification of TMEM63C as a new motor neurone degenerative disease gene and its importance to different organelle functions reinforce the idea that the capacity of different cellular compartments to communicate together, by exchanging lipids for example, is critical to ensure cellular homeostasis required to prevent disease,” said Prudent.

“Understanding precisely how lipid processing is altered in motor neurone degenerative diseases is essential to be able to develop more effective diagnostic tools and treatments for a large group of diseases that have a huge impact on people’s lives,” said study co-author Dr Emma Baple from the ̽��ֱ�� of Exeter. “Finding this gene is another important step towards these important goals.”

̽��ֱ��Halpin Trust, a charity who support projects which deliver a powerful and lasting impact in healthcare, nature conservation and the environment, part-funded this research. Claire Halpin, who co-founded the charity with her husband Les, said “ ̽��ֱ��Halpin Trust are extremely proud of the work ongoing in Exeter, and the important findings of this highly collaborative international study. We’re delighted that the Trust has contributed to this work, which forms part of Les’s legacy. He would also have been pleased, I know.”

Reference:
Luis-Carlos Tábara et al. ‘TMEM63C mutations cause mitochondrial morphology defects and underlie hereditary spastic paraplegia.’ Brain (2022). DOI: 10.1093/brain/awac123

Adapted from a ̽��ֱ�� of Exeter press release.

A new genetic discovery adds weight to a theory that motor neurone degenerative diseases are caused by abnormal lipid (fat) processing pathways inside brain cells. This theory will help pave the way to new diagnostic approaches and treatments for this group of conditions. ̽��ֱ��discovery will provide answers for certain families who have previously had no diagnosis.

Andriy Onufriyenko via Getty Images

Neuron

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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Lab-grown ‘mini brains’ hint at treatments for neurodegenerative diseases

cjb250 — Thu, 21 Oct 2021 15:00:41 +0000

A common form of motor neurone disease, amyotrophic lateral sclerosis, often overlaps with frontotemporal dementia (ALS/FTD) and can affect younger people, occurring mostly after the age of 40-45. These conditions cause devastating symptoms of muscle weakness with changes in memory, behaviour and personality. Being able to grow small organ-like models (organoids) of the brain allows the researchers to understand what happens at the earliest stages of ALS/FTD, long before symptoms begin to emerge, and to screen for potential drugs.

In general, organoids, often referred to as ‘mini organs’, are being used increasingly to model human biology and disease. At the ̽��ֱ�� of Cambridge alone, researchers use them to repair damaged livers, study SARS-CoV-2 infection of the lungs and model the early stages of pregnancy, among many other areas of research.

Typically, researchers take cells from a patient’s skin and reprogramme the cells back to their stem cell stage – a very early stage of development at which they have the potential to develop into most types of cell. These can then be grown in culture as 3D clusters that mimic particular elements of an organ. As many diseases are caused in part by defects in our DNA, this technique allows researchers to see how cellular changes – often associated with these genetic mutations – lead to disease.

Scientists at the John van Geest Centre for Brain Repair, ̽��ֱ�� of Cambridge, used stem cells derived from patients suffering from ALS/FTD to grow brain organoids that are roughly the size of a pea. These resemble parts of the human cerebral cortex in terms of their embryonic and fetal developmental milestones, 3D architecture, cell-type diversity and cell-cell interactions.

Although this is not the first time scientists have grown mini brains from patients with neurodegenerative diseases, most efforts have only been able to grow them for a relatively short time frame, representing a limited spectrum of dementia-related disorders. In findings published today in Nature Neuroscience, the Cambridge team reports growing these models for 240 days from stem cells harbouring the commonest genetic mutation in ALS/FTD, which was not previously possible – and in unpublished work the team has grown them for 340 days.

Dr András Lakatos, the senior author who led the research in Cambridge’s Department of Clinical Neurosciences, said: “Neurodegenerative diseases are very complex disorders that can affect many different cell types and how these cells interact at different times as the diseases progress.

“To come close to capturing this complexity, we need models that are more long-lived and replicate the composition of those human brain cell populations in which disturbances typically occur, and this is what our approach offers. Not only can we see what may happen early on in the disease – long before a patient might experience any symptoms – but we can also begin to see how the disturbances change over time in each cell.”

While organoids are usually grown as balls of cells, first author Dr Kornélia Szebényi generated patient cell-derived organoid slice cultures in Dr Lakatos’ laboratory. This technique ensured that most cells within the model could receive the nutrients required to keep them alive.

Dr Szebényi said: “When the cells are clustered in larger spheres, those cells at the core may not receive sufficient nutrition, which may explain why previous attempts to grow organoids long term from patients’ cells have been difficult.”

Using this approach, Dr Szebényi and colleagues observed changes occurring in the cells of the organoids at a very early stage, including cell stress, damage to DNA and changes in how the DNA is transcribed into proteins. These changes affected those nerve cells and other brain cells known as astroglia, which orchestrate muscle movements and mental abilities.

“Although these initial disturbances were subtle, we were surprised at just how early changes occurred in our human model of ALS/FTD,” added Dr Lakatos. “This and other recent studies suggest that the damage may begin to accrue as soon as we are born. We will need more research to understand if this is in fact the case, or whether this process is brought forward in organoids by the artificial conditions in the dish.”

As well as being useful for understanding disease development, organoids can be a powerful tool for screening potential drugs to see which can prevent or slow disease progression. This is a crucial advantage of organoids, as animal models often do not show the typical disease-relevant changes, and sampling the human brain for this research would be unfeasible.

̽��ֱ��team showed that a drug, GSK2606414, was effective at relieving common cellular problems in ALS/FTD, including the accumulation of toxic proteins, cell stress and the loss of nerve cells, hence blocking one of the pathways that contributes to disease. Similar drugs that are more suitable as medications and approved for human use are now being tested in clinical trials for neurodegenerative diseases.

Dr Gabriel Balmus from the UK Dementia Research Institute at the ̽��ֱ�� of Cambridge, collaborating senior author, said: “By modelling some of the mechanisms that lead to DNA damage in nerve cells and showing how these can lead to various cell dysfunctions, we may also be able to identify further potential drug targets.”

Dr Lakatos added: “We currently have no very effective options for treating ALS/FTD, and while there is much more work to be done following our discovery, it at least offers hope that it may in time be possible to prevent or to slow down the disease process.

“It may also be possible in future to be able to take skin cells from a patient, reprogramme them to grow their ‘mini brain’ and test which unique combination of drugs best suits their disease.”

̽��ֱ��study was primarily funded by the Medical Research Council UK, Wellcome Trust and the Evelyn Trust.

Reference

Szebényi, K et al. Human ALS/FTD Brain Organoid Slice Cultures Display Distinct Early Astrocyte and Targetable Neuronal Pathology. Nature Neuroscience; 21 Oct 2021; DOI: 10.1038/s41593-021-00923-4

Cambridge researchers have developed ‘mini brains’ that allow them to study a fatal and untreatable neurological disorder causing paralysis and dementia – and for the first time have been able to grow these for almost a year.

Not only can we see what may happen early on in the disease – long before a patient might experience any symptoms – but we can also begin to see how the disturbances change over time in each cell

András Lakatos

Andras Lakatos

Mini brain organoids showing cortical-like structures

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Mechanism behind neuron death in motor neurone disease and frontotemporal dementia discovered

cjb250 — Fri, 20 Apr 2018 13:14:58 +0000

Writing in Cell, the researchers from the ̽��ֱ�� of Cambridge and ̽��ֱ�� of Toronto also identify potential therapeutic targets for these currently incurable diseases.

ALS is a progressive and terminal disease that damages the function of nerves and muscle, affecting up to 5,000 adults in the UK at any one time. Frontotemporal dementia is a form of dementia that causes changes in personality and behaviour, and language difficulties.

A common characteristic of ALS and frontotemporal dementia is the build-up of clumps of misfolded RNA-binding proteins, including a protein called FUS, in the brain and spinal cord. This leads to the death of neurons, which stops them from communicating with each other and from reaching the muscles.

FUS proteins can change back and forth from small liquid droplets (resembling oil droplets in water) to small gels (like jelly) inside nerve cells. As the FUS protein condenses (from droplets to gel) it captures RNA and transfers it to remote parts of the neuron that are involved in making connections (known as synapses) with other neurons. Here, the protein ‘melts’ and releases the RNA. ̽��ֱ��RNA are then used to create new proteins in the synapses, which are essential for keeping the synapses working properly, especially during memory formation and learning.

In frontotemporal dementia and ALS, the proteins become permanently stuck as abnormally dense gels, trapping the RNA and making it unavailable for use. This damages nerve cells by blocking their ability to make the proteins needed for synaptic function and leads to the death of neurons in the brain and spinal cord.

In research funded by Wellcome, scientists used human cells that resembled neurons and neurons from frogs to investigate how the change in FUS from liquid droplets to small gels process is regulated and what makes it go awry. They found that this reversible process was tightly controlled by enzymes which chemically alter FUS making it able or unable to form droplets and gels. In frontotemporal dementia, the abnormal gelling was found to be caused by defects in the chemical modification of FUS. In motor neuron disease, it was caused by mutations in the FUS protein itself which meant it was no longer able to change form.

This research provides new ideas and tools to find ways to prevent or reverse the abnormal gelling of FUS as a treatment for these devastating diseases. Potential therapeutic targets identified by the researchers are the enzymes that regulate the chemical modification of FUS and the molecular chaperones that facilitate FUS proteins to change its form. These treatments would need to allow FUS to continue moving between safe reversible states (liquid droplets and reversible gels) but prevent FUS from dropping into the dense, irreversible gel states that cause disease.

Professor Peter St George-Hyslop from the Cambridge Institute for Medical Research said: “This was a very exciting set of experiments where we were able to apply cutting edge tools from physics, chemistry and neurobiology to understand how the FUS protein normally works in nerve cells, and how it goes wrong in motor neurone disease and dementia. It now opens up a new avenue of work to use this knowledge to identify ways to prevent the abnormal gelling of FUS in motor neurone disease and dementia.”

Dr Giovanna Lalli, from Wellcome’s Neuroscience and Mental Health team, said: “Motor neurone disease and frontotemporal dementia are devastating diseases that affect thousands of people across the UK, resulting in severe damage to the brain and spinal cord. By bringing together an interdisciplinary team of researchers, this study provides important new insights into a fundamental process underlying neurodegeneration. Through their research, the team have uncovered promising new ways to tackle these diseases.”

Reference
Qamar, S et al. FUS Phase Separation Is Modulated by a Molecular Chaperone and Methylation of Arginine Cation-π Interactions. Cell; 19 Apr 2018; DOI: 10.1016/j.cell.2018.03.056

Adapted from a press release by Wellcome

Scientists have identified the molecular mechanism that leads to the death of neurons in amyotrophic lateral sclerosis (also known as ALS or motor neurone disease) and a common form of frontotemporal dementia.

This was a very exciting set of experiments where we were able to apply cutting edge tools from physics, chemistry and neurobiology to understand how the FUS protein normally works in nerve cells, and how it goes wrong in motor neurone disease and dementia

Peter St George-Hyslop

ColiN00B

Nerve cells

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Breaking the mould: Untangling the jelly-like properties of diseased proteins

cjb250 — Thu, 29 Oct 2015 16:30:11 +0000

A common characteristic of neurodegenerative diseases – such as Alzheimer’s, Parkinson’s and Huntington’s disease – is the build-up of ‘misfolded’ proteins, which cause irreversible damage to the brain. For example, Alzheimer’s disease sees the build-up of beta-amyloid ‘plaques’ and tau ‘tangles’.

In the case of some forms of motor neurone disease (also known as amyotrophic lateral sclerosis, or ALS) and frontotemporal dementia, it is the build up of ‘assemblies’ of misshapen FUS protein and several other RNA-binding proteins that is associated with disease. However, the assembly of these RNA binding proteins has several differences to conventional protein aggregates seen in Alzheimer’s disease and Parkinson’s disease and as a result, the significance of the build-up of these proteins and how it occurs has until now been unclear.

FUS is an RNA-binding protein, which has a number of important functions in regulating RNA transcription (the first step in DNA expression) and splicing in the nucleus of cells. FUS also has functions in the cytoplasm of cells involved in regulating the translation of RNA into proteins. There are several other similar RNA binding proteins: a common feature of all of them is that in addition to having domains to bind RNA they also have domains where the protein appears to be unfolded or unstructured.

In a study published today in the journal Neuron, scientists at the ̽��ֱ�� of Cambridge examined FUS’s physical properties to demonstrate how the protein’s unfolded domain enables it to undergo reversible ‘phase transitions’. In other words, it can change back and forth from a fully soluble ‘monomer’ form into distinct localised accumulations that resemble liquid droplets and then further condense into jelly-like structures that are known as hydrogels. During these changes, the protein ‘assemblies’ capture and release RNA and other proteins. In essence this process allows cellular machinery for RNA transcription and translation to be condensed in high concentrations within restricted three-dimensional space without requiring a limiting membrane, thereby helping to easily regulate these vital cellular processes.

Using the nematode worm C. elegans as a model of ALS and frontotemporal dementia, the team was then able to also show that this process can become irreversible. Mutated FUS proteins cause the condensation process to go too far, forming thick gels that are unable to return to their soluble state. As a result, these irreversible gel-like assemblies trap other important proteins, preventing them carrying out their usual functions. One consequence is that it affects the synthesis of new proteins in nerve cell axons (the trunk of a nerve cell).

Importantly, the researchers also showed that by disrupting the formation of these irreversible assemblies (for example, by targeting with particular small molecules), it is possible to rescue the impaired motility and prolong the worm’s lifespan.

Like jelly on a plate

̽��ֱ��behaviour of FUS can be likened to that of a jelly, explains Professor Peter St George Hyslop from the Cambridge Institute for Medical Research.

When first made, jelly is runny, like a liquid. As it cools the fridge, it begins to set, initially becoming slightly thicker than water, but still runny as the gelatin molecules forms into longer, fibre-like chains known as fibrils. If you dropped a droplet of this nearly-set jelly into water, it would (at least briefly) remain distinct from the surrounding water – a ‘liquid droplet’ within a liquid.

As the jelly cools further in the fridge, the gelatin fibres condense more, and it eventually becomes a firmly set jelly that can be flipped out of the mould onto a plate. This set jelly is a ‘hydrogel’, a loose meshwork of protein (gelatin) fibrils that is dense enough to hold the water inside the spaces between its fibres. ̽��ֱ��set jelly holds the water in a constrained 3D space – and depending on the recipe, there may be some other ‘cargo’ suspended within the jelly, such as bits of fruit (in the case of FUS this ‘cargo’ might be ribosomes, other proteins, enzymes or RNA, for example).

When the jelly is stored in a cool room, the fruit is retained in the jelly. This means the fruit (or ribosomes, etc) can be moved around the house and eventually put on the dinner table (or in the case of FUS, be transported to parts of a cell with unique protein synthesis requirements).

If the jelly is re-warmed, it melts and releases its fruit, which then float off‎. But if the liquid molten jelly is put back in the fridge and re-cooled, it re-makes a firm hydrogel again, and the fruit is once again trapped. In theory, this cycle of gel-melt-gel-melt can be repeated endlessly.

However, if the jelly is left out, the water will slowly evaporate, and the jelly condenses down, changing from a soft, easily-melted jelly to a thick, rubbery jelly. (In fact, jelly is often sold as a dense cube like this.) In this condensed jelly, the meshwork of protein fibrils are much closer together and it becomes increasingly difficult to get the condensed jelly to melt (you would have to pour boiling water on it to get it to melt). Because the condensed jelly is not easily meltable when it gets to this state, any cargo (fruit, ribosomes, etc.) within the jelly essentially becomes irreversibly trapped.

In the case of FUS and other RNA binding proteins, the ‘healthy’ proteins only very rarely spontaneously over-condense. However, disease-causing mutations make these proteins much more prone to spontaneously ‎condense down into thick fibrous gels, trapping their cargo (in this case the ribosomes, etc), which then become unavailable for use.

So essentially, this new research shows that the ability of some proteins to self-assemble into liquid droplets and (slightly more viscous) jellies/hydrogel is a useful property that allows cells to transiently concentrate cellular machinery into a constrained 3D space in order to perform key tasks, and then disassemble and disperse the machinery when not needed. It is probably faster and less energy-costly than doing the same thing inside intracellular membrane-bound vesicles – but that same property can go too far, leading to disease.

Professor St George Hyslop says: “We’ve shown that a particular group of proteins can regulate vital cellular processes by their distinct ability to transition between different states. But this essential property also makes them vulnerable to forming more fixed structures if mutated, disrupting their normal function and causing disease.

“ ̽��ֱ��same principles are likely to be at play in other more common forms of these diseases due to mutation in other related binding proteins. Understanding what is in these assemblies should provide further targets for disease treatments.

“Our approach shows the importance of considering the mechanisms of diseases as not just biological, but also physical processes. By bringing together people from the biological and physical sciences, we’ve been able to better understand how misshapen proteins build up and cause disease.”

̽��ֱ��research was funded by in the UK by the Wellcome Trust, Medical Research Council and National Institutes of Health Research, in Canada by Canadian Institutes of Health Research, and in the US by National Institutes of Health.

Reference
Murakami, T et al. ALS/FTD mutation-induced phase transition of FUS liquid droplets and reversible hydrogels into irreversible hydrogels impairs RNP granule function. Neuron; 29 Oct 2015

Scientists at the ̽��ֱ�� of Cambridge have identified a new property of essential proteins which, when it malfunctions, can cause the build up, or ‘aggregation’, of misshaped proteins and lead to serious diseases.

Our approach shows the importance of considering the mechanisms of diseases as not just biological, but also physical processes

Peter St George-Hyslop

Steven Depolo

Jello Cubes

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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