Role of calcium in Parkinson’s disease

The international team, led by the University of Cambridge found that excess levels of calcium in brain cells may lead to the formation of toxic clusters that are the hallmark of Parkinson’s disease. Their research found that calcium can mediate the interaction between small membranous structures inside nerve endings, which are important for neuronal signalling in the brain, and alpha-synuclein, the protein associated with Parkinson’s disease. Excess levels of either calcium or alpha-synuclein may be what starts the chain reaction that leads to the death of brain cells.

Credit: Janin Lautenschläger

The findings, reported in the journal Nature Communications, represent another step towards understanding how and why people develop Parkinson’s. According to the charity Parkinson’s UK, one in every 350 adults in the UK currently has the condition. Parkinson’s disease is one of a number of neurodegenerative diseases caused  by amyloid deposits of aggregated alpha-synuclein. These deposits also known as Lewy bodies, are the sign of Parkinson’s disease.

Curiously, it hasn’t been clear until now what alpha-synuclein actually does in the cell: why it’s there and what it’s meant to do. It is implicated in various processes, such as the smooth flow of chemical signals in the brain and the movement of molecules in and out of nerve endings, but exactly how it does is unclear.

Thanks to super-resolution microscopy techniques, it is now possible to look inside cells to understand role of alpha-synuclein. To do so researchers isolated synaptic vesicles, part of the nerve cells that store the neurotransmitters which send signals from one nerve cell to another.

In neurons, calcium plays a role in the release of neurotransmitters. The researchers observed that when calcium levels in the nerve cell increase, such as upon neuronal signalling, the alpha-synuclein binds to synaptic vesicles at multiple points causing the vesicles to come together. This may indicate that the normal role of alpha-synuclein is to help the chemical transmission of information across nerve cells.

“This is the first time we’ve seen that calcium influences the way alpha-synuclein interacts with synaptic vesicles,” said Dr Janin Lautenschläger, the paper’s first author. “We think that alpha-synuclein is almost like a calcium sensor. In the presence of calcium, it changes its structure and how it interacts with its environment, which is likely very important for its normal function.”

“There is a fine balance of calcium and alpha-synuclein in the cell, and when there is too much of one or the other, the balance is tipped and aggregation begins, leading to Parkinson’s disease,” said co-first author Dr Amberley Stephens.

The imbalance can be caused by a genetic doubling of the amount of alpha-synuclein (gene duplication), by an age-related slowing of the breakdown of excess protein, by an increased level of calcium in neurons that are sensitive to Parkinson’s, or an associated lack of calcium buffering capacity in these neurons.

Understanding the role of alpha-synuclein in physiological or pathological processes may aid in the development of new treatments for Parkinson’s disease. One possibility is that drug candidates developed to block calcium, for use in heart disease for instance, might also have potential against Parkinson’s disease.

Citation: Lautenschläger, Janin, Amberley D. Stephens, Giuliana Fusco, Florian Ströhl, Nathan Curry, Maria Zacharopoulou, Claire H. Michel, Romain Laine, Nadezhda Nespovitaya, Marcus Fantham, Dorothea Pinotsi, Wagner Zago, Paul Fraser, Anurag Tandon, Peter St George-Hyslop, Eric Rees, Jonathan J. Phillips, Alfonso De Simone, Clemens F. Kaminski, and Gabriele S. Kaminski Schierle. “C-terminal calcium binding of α-synuclein modulates synaptic vesicle interaction.” Nature Communications 9, no. 1 (2018). doi:10.1038/s41467-018-03111-4.

Adapted from press release by University of Cambridge.

Protein Wnt5a is important in sustaining adult neuron structure in mice hippocampus

Humans and other vertebrates depend on a portion of the brain called the hippocampus for learning, memory and their sense of location. Nerve cell structures in the adult hippocampus are sustained by factors whose identities have remained largely mysterious so far.

Now, research led by a Johns Hopkins University biologist Dr. Kuruvilla sheds light on the subject, potentially pointing the way to a better understanding of how the structure of nerve cells in the adult hippocampus may deteriorate, which can lead to Alzheimer’s disease and other neurological disorders.

In a paper in the journal Proceedings of the National Academy of Sciences, Kuruvilla and eight other scientists from two research institutions report that a protein that has primarily been studied for its role in early animal development also plays a surprising role in maintaining the structure of hippocampal neurons in adult mice.

The team studied a protein called Wnt5a, which belongs to a family of proteins that have been studied primarily for their functions during embryonic development and in nurturing neurons as the young brain forms. Using mice genetically altered to remove Wnt5a from the hippocampus, the team showed that the protein’s absence did not affect hippocampus development in young mice, but instead resulted in striking degradation of specific nerve cell structures called dendrites, which resemble clusters of tree branches, in adult mice. These findings suggest that the protein plays an important role in maintaining dendrite structures as the mouse ages.

The team went further by showing that when the Wnt5a protein was reintroduced after the dendrites had started to deteriorate in aged mice, the nerve cell structures were restored – to a degree the scientists did not expect.

The team also tested the ability of mice lacking Wnt5a in the hippocampus to perform learning and memory tasks. Behavior tests were run in a Morris Water Maze designed to show how well mice use spatial cues to navigate in a water pool and how long it takes them to learn to use a hidden platform to escape. They found that mutant mice – those without Wnt5a – were poor learners and had attenuated memory; their performance in behavioral tasks became progressively worse with age.

“Together, the findings from the Morris Water Maze test support an essential role for Wnt5a in the acquisition of spatial learning and memory storage in adult animals,” the authors wrote.
In the brain, the hippocampus is the seat of short- and long-term memory and governs spatial orientation. Studies have shown that the brains of people with Alzheimer’s disease have structural alterations in dendrites, particularly in the hippocampus.

Kuruvilla said the experiments suggest avenues for further research on what may cause shrinkage of dendrites during neurological disorders. She emphasized, however, that it is premature to extrapolate these results in mice to humans.

While Kuruvilla was careful not to overstate the significance of the findings or how they may apply to cognitive disorders in humans, she said the results at least bring attention to the significance of studying molecular signals that maintain neurons in the adult brain. Compared to the wealth of information on signals that help in formation of neuronal connections in the developing brain, we know far less of how brain structure is sustained in adult life, she said.

Citation: Chih-Ming Chena,  Lauren L. Oreficeb,  Shu-Ling Chiuc,  Tara A. LeGatesa,  Samer Hattara,  Richard L. Huganirc,  Haiqing Zhaoa,  Baoji Xub, and  Rejji Kuruvillaa. “Wnt5a is essential for hippocampal dendritic maintenance and spatial learning and memory in adult mice.” PNAS 2017.
DOI: 10.1073/pnas.1615792114
Research funding: National Institutes of Health.
Adapted from press release by Johns Hopkins University.

Squalamine shows promise as potential treatment for Parkinson’s disease in lab studies

A naturally-occurring compound has been found to block a molecular process thought to underlie Parkinson’s Disease and to suppress its toxic products, scientists have reported. The findings, although only preliminary, suggest that the compound, called squalamine, could be exploited in various ways as the basis of a potential treatment for Parkinson’s Disease.

Credit: Geralt/pixabay

The study was led by academics from the Centre for Misfolding Diseases, based in the Chemistry Department at the University of Cambridge in the United Kingdom, and Georgetown University and the National Institutes of Health in the United States. Scientists from the Netherlands, Italy, and Spain also played key roles. The findings are published in Proceedings of The National Academy of Sciences.

In the new study, the researchers explored squalamine’s capacity to displace alpha-synuclein from cell membranes – a phenomenon that was first observed in the laboratory headed by another co-author, Dr. Ad Bax, in the National Institutes of Health in Bethesda, USA. This finding has significant implications for Parkinson’s Disease because alpha-synuclein works by binding to the membranes of tiny, bubble-like structures called synaptic vesicles, which help to transfer neurotransmitters between neurons.

Under normal circumstances, the protein thus aids the effective flow of chemical signals, but in some instances, it malfunctions and instead begins to clump together, creating toxic particles harmful to brain cells. This clustering is the hallmark of Parkinson’s Disease.

The researchers carried out a series of experiments which analyzed the interaction between squalamine, alpha-synuclein and lipid vesicles, building on earlier work from Cambridge scientists which showed the vital role that vesicles play in initiating the aggregation. They found that squalamine inhibits the aggregation of the protein by competing for binding sites on the surfaces of synthetic vesicles. By displacing the protein in this way, it significantly reduces the rate at which toxic particles form. Further tests, carried out with human neuronal cells, then revealed another key factor – that squalamine also suppresses the toxicity of these particles.

Finally, the group tested the impact of squalamine in an animal model of Parkinson’s Disease, by using nematode worms genetically programmed to overexpress alpha-synuclein in their muscle cells. As the worms develop, alpha-synuclein aggregation causes them to become paralyzed, but squalamine prevented the paralysis from taking effect.

Together, the results imply that squalamine could be used as the basis of a treatment targeting at least some of the symptoms of Parkinson’s Disease. Researchers are now planning a clinical trial with squalamine in Parkinson’s Disease patients in the US.

Citation: Michele Perni, Céline Galvagnion, Alexander Maltsev, Georg Meisl, Martin B. D. Müller, Pavan K. Challa, Julius B. Kirkegaard, Patrick Flagmeier, Samuel I. A. Cohen, Roberta Cascella, Serene W. Chen, Ryan Limboker, Pietro Sormanni, Gabriella T. Heller, Francesco A. Aprile, Nunilo Cremades, Cristina Cecchi, Fabrizio Chiti, Ellen A. A. Nollen, Tuomas P. J. Knowles, Michele Vendruscolo, Adriaan Bax, Michael Zasloff, and Christopher M. Dobson. “A natural product inhibits the initiation of α-synuclein aggregation and suppresses its toxicity.” PNAS 2017
DOI: 10.1073/pnas.1610586114
Adapted from press release by University of Cambridge.

Concussion and Alzheimer’s disease link

New research has found concussions accelerate Alzheimer’s disease-related brain atrophy and cognitive decline in people who are at genetic risk for the condition. The findings, which appear in the journal Brain, show promise for detecting the influence of concussion on neurodegeneration.

Brain. Ashton University

Moderate-to-severe traumatic brain injury is one of the strongest environmental risk factors for developing neurodegenerative diseases such as late-onset Alzheimer’s disease, although it is unclear whether mild traumatic brain injury or concussion also increases this risk.

Researchers from Boston University School of Medicine (BUSM) studied 160 Iraq and Afghanistan war veterans, some who had suffered one or more concussions and some who had never had a concussion. Using MRI imaging, the thickness of their cerebral cortex was measured in seven regions that are the first to show atrophy in Alzheimer’s disease, as well as seven control regions.

We found that having a concussion was associated with lower cortical thickness in brain regions that are the first to be affected in Alzheimer’s disease,” explained corresponding author Jasmeet Hayes, PhD, assistant professor of psychiatry at BUSM and research psychologist at the National Center for PTSD, VA Boston Healthcare System. “Our results suggest that when combined with genetic factors, concussions may be associated with accelerated cortical thickness and memory decline in Alzheimer’s disease relevant areas.”

Of particular note was that these brain abnormalities were found in a relatively young group, with the average age being 32 years old. “These findings show promise for detecting the influence of concussion on neurodegeneration early in one’s lifetime, thus it is important to document the occurrence and subsequent symptoms of a concussion, even if the person reports only having their “bell rung” and is able to shake it off fairly quickly, given that when combined with factors such as genetics, the concussion may produce negative long-term health consequences,” said Hayes.

The researchers hope that others can build upon these findings to find the precise concussion-related mechanisms that accelerate the onset of neurodegenerative diseases such as Alzheimer’s disease, chronic traumatic encephalopathy, Parkinson’s and others. “Treatments may then one day be developed to target those mechanisms and delay the onset of neurodegenerative pathology,” she added.

Citation: Hayes, Jasmeet P., Mark W. Logue, Naomi Sadeh, Jeffrey M. Spielberg, Mieke Verfaellie, Scott M. Hayes, Andrew Reagan, David H. Salat, Erika J. Wolf, Regina E. McGlinchey, William P. Milberg, Annjanette Stone, Steven A. Schichman and Mark W. Miller. ” Mild traumatic brain injury is associated with reduced cortical thickness in those at risk for Alzheimer’s disease.” Brain 2017 vol: 83 pp: aww344.
DOI: 10.1093/brain/aww344
Research funding: US Department of Veterans Affairs, NIH/National Institute of Mental Health.
Adapted from press release by Boston University School of Medicine.

Early detection of Alzheimer’s disease using tau protein biomarker in platelets

Researchers have pioneered the technology that detects pathological oligomeric forms of brain tau protein levels in platelets to diagnose Alzheimer’s disease (AD) and other neurodegenerative disorders.  More importantly, the ratio between this anomalous tau and the normal tau protein can discriminate Alzheimer’s disease patients from normal controls, and are associated with decreased cognitive impairment. This discovery is published in Journal of Alzheimer’s Disease (JAD). The research findings stems from a fruitful collaboration between the neuroscience laboratory from the International Center for Biomedicine (ICC) under the leadership of Dr. Ricardo Maccioni and the research teams of Drs. Andrea Slachevsky, Faculty of Medicine, University of Chile, together with Drs. Oscar Lopez and James Becker from University of Pittsburgh, School of Medicine, USA.

Credit: IOS press.

These studies open a new avenue in the development of highly sensitive and efficient biomarkers for neurodegenerative disorders. The fact that pathological forms of tau proteins in platelets correlated with decreased brain volume in areas known to be associated with Alzheimer’s disease pathology in the brain is one step forward for the use of peripheral biomarkers, not only for clinical purposes, but also for research studies oriented to understand the complexity of Alzheimer’s disease pathology.

This article, highlighted by Journal of Alzheimer’s Disease, proved that the relationship between the pathological and normal variants of tau were associated with the reduction of cerebral volume in key structures linked with the disease. These structures included the left medial and right anterior cingulate gyri, right cerebellum, right thalamus (pulvinar), left frontal cortex, and right parahippocampal region, in agreement with MRI neuroimaging approaches.

In addition to the enormous utility of this non-invasive technology for the detection and progression of Alzheimer’s disease, the use of a tau biomarker could lead to the identification of Alzheimer’s disease pathology before the clinical symptoms are evident, and it could play an essential role in the development of preventive therapies. Moreover, the determination of peripheral tau markers in platelets can contribute to the understanding of the pathophysiology of multiple neurodegenerative processes where tau proteins play a critical role.

Citation: Slachevsky, Andrea, Leonardo Guzmán-Martínez, Carolina Delgado, Pablo Reyes, Gonzalo A. Farías, Carlos Muñoz-Neira, Eduardo Bravo et al. “Tau Platelets Correlate with Regional Brain Atrophy in Patients with Alzheimer’s Disease.” Journal of Alzheimer’s Disease vol. 55, no. 4, pp. 1595-1603, 2017.
DOI: 10.3233/JAD-160652
Adapted from press release by IOS press.

NeuroVascular Unit on a chip created to mimic functions of Blood-brain barrier

The blood-brain barrier is a network of specialized cells that surrounds the arteries and veins within the brain. It forms a unique gateway that both provides brain cells with the nutrients they require and protects them from potentially harmful compounds.

This is an illustration of the neurovascular unit on a chip.
Credit: Dominic Doyle, Vanderbilt University

An interdisciplinary team of researchers from the Vanderbilt Institute for Integrative Biosystems Research and Education (VIIBRE) headed by Gordon A. Cain University Professor John Wikswo report that they have developed a microfluidic device that overcomes the limitations of previous models of this key system and have used it to study brain inflammation, dubbed the “silent killer” because it doesn’t cause pain but contributes to neurodegenerative conditions such as Alzheimer’s and Parkinson’s diseases. Recent research also suggests that it may underlie a wider range of problems from impaired cognition to depression and even schizophrenia.

The project is part of a $70 million “Tissue Chip for Drug Testing Program” funded by the National Institutes of Health’s National Center for Advancing Translational Sciences. Its purpose is to develop human organ-on-a-chip technology in order to assess the safety and efficacy of new drugs in a faster, cheaper, more effective and more reliable fashion.

The importance of understanding how the blood-brain barrier works have increased in recent years as medical researchers have found that this critical structure is implicated in a widening range of brain disorders, extending from stroke to Alzheimer’s and Parkinson’s disease to blunt force trauma and brain inflammation.

Despite its importance, scientists have had considerable difficulty creating faithful laboratory models of the complex biological system that protects the brain. Previous models have either been static and so have not reproduced critical blood flow effects or they have not supported all the cell types found in human blood-brain barriers.

The new device, which the researchers call a NeuroVascular Unit (NVU) on a chip, overcomes these problems. It consists of a small cavity that is one-fifth of an inch long, one-tenth of an inch wide and three-hundredths of an inch thick – giving it a total volume of about one-millionth of a human brain. The cavity is divided by a thin, porous membrane into an upper chamber that acts as the brain side of the barrier and a lower chamber that acts as the blood or vascular side. Both chambers are connected to separate microchannels hooked to micropumps that allow them to be independently perfused and sampled.

To create an artificial blood-brain barrier, the researchers first flip the device over so the vascular chamber is on top and inject specialized human endothelial cells. They found that if they maintain a steady fluid flow through the chamber during this period, the endothelial cells, which left to themselves form shapeless blobs, consistently orient themselves parallel to the direction of flow. This orientation, which is a characteristic of the endothelial cells in human blood-brain barrier, has been lacking in many previous models.

After a day or two, when the endothelial cells have attached themselves to the membrane, the researchers flip the device and inject the two other human cell types that form the barrier — star-shaped astrocytes and pericytes that wrap around endothelial cells — as well as excitatory neurons that may regulate the barrier. These all go into the brain chamber that is now on top. The porous membrane allows the new cells to make physical and chemical contact with the endothelial cells just as they do in the brain.

The researchers were able to purchase the human endothelial cells, astrocytes and pericytes that they need from commercial sources. For the excitatory neurons required, they turned to Vanderbilt University Medical Center collaborators M. Diana Neely, research associate professor of pediatrics, and Aaron Bowman, associate professor of pediatrics, neurology and biochemistry. Starting with human induced pluripotent stem cells that are generated directly from adult cells they were able to produce the specialized neurons that the project needed.

“This is one of the most exciting projects I’m involved with,” said Neely. “Although it’s still in its infancy, it has tremendous potential.” According to Bowman, one potential application is to develop tissue chips that contain cells from individual patients, making it possible to predict their personal reactions to different drugs.

“Once we had successfully created the artificial barrier, we subjected it to a series of basic tests and it passed them all with flying colors. This gives us the confidence to state that we have developed a fully functional model of the human blood-brain barrier,” said VIIBRE staff scientist Jacquelyn Brown, who is first author of the paper “Recreating blood-brain barrier physiology and structure on chip: A novel neurovascular microfluidic bioreactor” that described this achievement in the journal Biomicrofluidics.

“The NeuroVascular Unit (NVU) on a chip has reached the point where we can begin using it to test different drugs and compounds,” observed team member Donna Webb, associate professor of biological sciences who is interested in studying how different substances affect synapses — the junctions between neurons. “There is an urgent need for us to understand how various substances affect cognitive processes. When we do, we will be in for a number of surprises!

Already, the VIBRE team has used the NeuroVascular Unit (NVU) on a chip to overcome a basic limitation of existing studies of brain inflammation, which have only produced snapshots of the process at various stages. Because the NeuroVascular Unit (NVU) on a chip can be continuously monitored, it has provided the first dynamic view of how the brain and blood-brain barrier respond to systemic inflammation.

These results are summarized in a paper titled “Metabolic consequences of inflammatory disruption of the blood-brain barrier in an organ-on-chip model of the human neurovascular unit” accepted for publication in the Journal of Neuroinflammation.

The scientists exposed the NeuroVascular Unit (NVU) on a chip to two different compounds known to induce brain inflammation: a large molecule found on the surface of certain bacteria called lipopolysaccharide and a “cocktail” of small proteins called cytokines that play an important role in immune response to inflammation.

“One of our biggest surprises was the discovery that a critical component in the blood-brain barrier’s response to these compounds was to begin increasing protein synthesis,” said Brown. “Next will be to find out which proteins it is making and what they do.”

The researchers also found that the blood vessels in the barrier respond to inflammation by pumping up their metabolic rate while the metabolism of the brain cells slows down. According to Brown, “It might be that the vasculature is trying to respond while the brain is trying to protect itself.”

Citation: “Metabolic consequences of inflammatory disruption of the blood-brain barrier in an organ-on-chip model of the human neurovascular unit” accepted in Journal of Neuroinflammation.
Research funding: NIH

Adapted from press release by Vanderbilt University.

Computer models to analyze Huntington disease pathology

Rice University scientists have uncovered new details about how a repeating nucleotide sequence in the gene for a mutant protein may trigger Huntington’s and other neurological diseases. Researchers used computer models to analyze proteins suspected of misfolding and forming plaques in the brains of patients with neurological diseases. Their simulations confirmed experimental results by other labs that showed the length of repeating polyglutamine sequences contained in proteins is critical to the onset of disease. The study led by Rice bioscientist Peter Wolynes appears in the Journal of the American Chemical Society.

Glutamine is the amino acid coded for by the genomic trinucleotide CAG. Repeating glutamines, called polyglutamines, are normal in huntingtin proteins, but when the DNA is copied incorrectly, the repeating sequence of glutamines can become too long. The result can be diseases like Huntington’s or spinocerebellar ataxia.

Simulations at Rice show how a repeating sequence in a mutant
 protein may trigger Huntington’s and other neurological diseases.
Credit:Mingchen Chen/Rice University

The number of repeats of glutamine can grow as the genetic code information is passed down through generations. That means a healthy parent whose huntingtin gene encodes proteins with 35 repeats may produce a child with 36 repeats. A person having the longer repeat is likely to develop Huntington’s disease.

Aggregation in Huntington’s typically begins only when polyglutamine chains reach a critical length of 36 repeats. Studies have demonstrated that longer repeat chains can make the disease more severe and its onset earlier.

The paper builds upon techniques used in an earlier study of amyloid beta proteins. That study was the lab’s first attempt to model the energy landscape of amyloid aggregation, which has been implicated in Alzheimer’s disease.  This time, Wolynes and his team were interested in knowing how the varying length of repeats, as few as 20 and as many as 50 influenced how aggregates form.

The Rice team found that at intermediate lengths between 20 and 30 repeats, polyglutamine sequences can choose between straight or hairpin configurations. While longer and shorter sequences form aligned fiber bundles, simulations showed intermediate sequences are more likely to form disordered, branched structures.

Mutations that would encourage polyglutamine sequences to remain unfolded would raise the energy barrier to aggregation, they found. “What’s ironic is that while Huntington’s has been classified as a misfolding disease, it seems to happen because the protein, in the bad case of longer repeats, carries out an extra folding process that it wasn’t supposed to be doing,” Wolynes said.

The team’s ongoing study is now looking at how the complete huntingtin protein, which contains parts in addition to the polyglutamine repeats, aggregates.

Citation: Chen, Mingchen, MinYeh Tsai, Weihua Zheng, and Peter G. Wolynes. “The Aggregation Free Energy Landscapes of Polyglutamine Repeats.” Journal of the American Chemical Society (2016).
DOI: 10.1021/jacs.6b08665
Research funding: NIH/National Institute of General Medical Sciences, Ministry of Science and Technology of Taiwan
Adapted from press release by Rice University.

Research finds role of Messenger RNA in Huntington’s disease patholgy

A research effort at the Centre for Genomic Regulation in Barcelona, Spain, reveals new molecular mechanisms of Huntington’s disease. The results, published in The Journal of Clinical Investigation, question the approaches used up to now for treatment of the disease. They also point to messenger RNA as a key pathogenic component that will make it possible to define new therapeutic strategies.

Fluorescent detection of foci in red fibroblasts of patients with
Huntington’s disease. Up: cells showing mutated RNA foci.
Down: Cells with blocked RNA do not show foci.
Credit: Centre for Genoic Regulation

Huntington’s disease is a neurodegenerative disease that is presently incurable. Scientists around the world are researching its causes and molecular processes in the attempt to find a treatment. Huntington’s disease is caused by the excessive repetition of a nucleotide triplet (CAG) in the Huntingtin gene. The number of CAG repetitions varies from person to person. Healthy individuals can have up to 36 repetitions. Nevertheless, as of 36 repetitions, Huntington’s disease develops. The direct consequence of this excess of repetitions is the synthesis of a mutated protein–different from what would be obtained without the additional CAG repetitions–which has been considered the main cause of the disease for the past 20 years.

The research by a group of scientists from the Centre for Genomic Regulation (CRG) led by Eulàlia Martí, in cooperation with researchers from the University of Barcelona (UB) and August Pi i Sunyer Biomedical Research Institute (IDIBAPS), has brought to light new information on the molecular mechanisms that cause Huntington’s disease, and defines new pathways to therapy discovery.

What we have observed in our study is that the mutated fragment acting as a conveyor–the so-called messenger RNA–is key in the pathogenesis,” says Dr. Eulàlia Martí, lead author of the research project, together with Xavier Estivill, and acting group leader of the Genes and Disease laboratory at the Centre for Genomic Regulation. “The research on this disease being done by most groups around the world seeking new therapeutic strategies focuses on trying to prevent expression of the mutated protein. Our work suggests that blocking the activity of messenger RNA (the “conveyor”), would be enough to revert the alterations associated with Huntington’s disease. We hope this will contribute to improving the strategies in place to find a cure,” states the researcher.

Going deeper in molecular mechanisms enables progress to future applications. This work underscores the importance of rethinking the mechanisms behind illnesses in order to find new treatments. The work of scientists at the CRG has helped explore the molecular mechanisms that cause the disease. Now, their results will contribute to better delimit research efforts towards a cure.

As opposed to most other research groups, Eulàlia Martí’s team has sought to identify whether the problem resided in the messenger RNA – which would be the copy responsible for manufacturing the protein – or in the resulting protein. Prior work indicated that mRNA produced, in addition to defective protein, other damages. This previous work was the starting point for Martí and her fellow researchers, who have finally demonstrated that mRNA has a key role in the pathogenesis of Huntington’s chorea. “The research we have just published points to RNA’s clear role in Huntington’s disease. This information is very important in translational research to take on new treatments,” says the researcher.

More in-depth studies on these mechanisms are yet to be done. For example, research must explore whether it will be possible to revert the effects of Huntington’s disease in patients, just as researchers have demonstrated in mouse models. It also remains to be seen whether the proposal of the CRG researchers can be used in a preventive way, as the disease does not generally appear until after 40 years of age (in humans). Despite the remaining gaps, the published work makes for a key step in knowledge of the mechanisms of this neurodegenerative disease that, as of today, remains incurable.

Citation: Rué, Laura, Mónica Bañez-Coronel, Jordi Creus-Muncunill, Albert Giralt, Rafael Alcalá-Vida, Gartze Mentxaka, Birgit Kagerbauer et al. “Targeting CAG repeat RNAs reduces Huntington’s disease phenotype independently of huntingtin levels.” The Journal of Clinical Investigation 126, no. 11 (2016).
DOI: http://dx.doi.org/10.1172/JCI83185
Adapted from press release by Centre for Genomic Regulation

Research finds that disruption of mitochondria-associated membrane in neurons as a possible pathological basis for Amyotrophic lateral sclerosis

A schematic illustration for MAM disruption in ALS. IP3R3, a MAM specific Ca2+ channel (an orange arrow, left), was
mislocalized from the MAM in the ALS model mice (white arrow heads, right). Credit: Koji Yamanaka laboratory

Amyotrophic lateral sclerosis (ALS) is an adult onset, fetal neurodegenerative disease that selectively affects motor neurons. To date, more than 20 genes are identified as a causative of inherited Amyotrophic lateral sclerosis. A research team led by Prof. Koji Yamanaka (Nagoya University) found that collapse of the mitochondria-associated membrane is a common pathological hallmark to two distinct inherited forms of ALS: SOD1– and SIGMAR1– linked Amyotrophic lateral sclerosis. The research findings were reported in EMBO Molecular Medicine.

The researchers focused on the mitochondria-associated membrane (MAM), which is a contacting site of mitochondria and endoplasmic reticulum (ER). Recent studies have revealed that the mitochondria-associated membrane plays a key role in cellular homeostasis, such as lipid synthesis, protein degradation, and energy metabolism. Intriguingly, a recessive mutation in SIGMAR1 gene, which encodes sigma 1 receptor (Sig1R), a chaperone enriched in the mitochondria-associated membrane, is causative for a juvenile ALS. In this study, the researchers identified a novel Amyotrophic lateral sclerosis linked SIGMAR1 mutation, c.283dupC/p.L95fs in a juvenile-onset Amyotrophic lateral sclerosis case. Moreover, Amyotrophic lateral sclerosis linked Sig1R mutant proteins were unstable and non-functional, indicating a loss-of function mechanism in SIGMAR1-linked Amyotrophic lateral sclerosis.

A loss of Sig1R function induced mitochondria-associated membrane disruption in neurons. However, it was still unknown whether the mitochondria-associated membrane alternation was also involved in the other Amyotrophic lateral sclerosis cases. To address this question, the researchers cross-bred SIGMAR1 deficient mice with the other inherited Amyotrophic lateral sclerosis mice which overexpress a mutant form of SOD1 gene. SIGMAR1 deficiency accelerated disease onset of SOD1-Amyotrophic lateral sclerosis mice by more than 20 %. In those mice, inositol triphosphate receptor type-3 (IP3R3), a mitochondria-associated membrane enriched calcium ion (Ca2+) channel on ER, was disappeared from the mitochondria-associated membrane. The loss of proper localization of IP3R3 led to Ca2++ dysregulation to exacerbate the neurodegeneration. The researchers also found that IP3R3 was selectively enriched in motor neurons, suggesting that integrity of the mitochondria-associated membrane is crucial for the selective vulnerability in Amyotrophic lateral sclerosis.

These results provide us with new perspectives regarding future therapeutics, especially focused on preventing the mitochondria-associated membrane disruption for Amyotrophic lateral sclerosis patients. Together with the research from other groups, collapse of the mitochondria-associated membrane is widely observed in the other genetic causes of Amyotrophic lateral sclerosis, and therefore it may be applicable to sporadic Amyotrophic lateral sclerosis patients.

Citation: Seiji Watanabe, Hristelina Ilieva, Hiromi Tamada, Hanae Nomura, Okiru Komine, Fumito Endo, Shijie Jin, Pedro Mancias, View ORCID ProfileHiroshi Kiyama, Koji Yamanaka. “Mitochondria‐associated membrane collapse is a common pathomechanism in SIGMAR1‐ and SOD1‐linked ALS” EMBO Molecular Medicine  2016 vol: 34 (36) pp: 12093-1210
DOI: http://dx.doi.org/10.15252/emmm.201606403
Research funding: Japan Ministry for Education, Culture and Sports, Science and Technology, Japan Agency for Medical Research and Development, Naito Foundation, Uehara Memorial Foundation, Japan ALS Association, Hori Science and Arts Foundation.
Press release by Nagoya University