Tag Archives: Research

New research shows for the first time that PET scans can track the progressive stages of Alzheimer’s disease in cognitively normal adults, a key advance in the early diagnosis and staging of the neurodegenerative disorder.

In the process, the scientists also obtained important clues about two Alzheimer’s-linked proteins – tau and beta-amyloid – and how they relate to each other.

The findings, published in the journal Neuron, come from positron emission tomography (PET) of 53 adults. Five were young adults aged 20-26, 33 were cognitively healthy adults aged 64-90 and 15 were patients aged 53-77 who had been diagnosed with probable Alzheimer’s dementia.

PET scans are used to detect early signs of disease by looking at cellular-level changes in organs and tissue. The results of the scans in this study paralleled Braak neuropathological stages, which range from one to six, describing the degree of tau protein accumulation in the brain.

The findings also shed light on the nature of tau and amyloid protein deposits in the aging brain. For many years, the accumulation of beta amyloid plaques was considered the primary culprit in Alzheimer’s disease. Over the past decade, however, tau, a microtubule protein important in maintaining the structure of neurons, has emerged as a major player. When the tau protein gets tangled and twisted, its ability to support synaptic connections becomes impaired.

While a number of symptoms exist that signal Alzheimer’s disease, a definitive diagnosis has been possible only through an examination of the brain after the patient has died. The availability of amyloid imaging for the past decade has improved this situation, but how Alzheimer’s developed as a result of amyloid remains a mystery. Studies done in autopsies linked the development of symptoms to the deposition of the tau protein.

Through the PET scans, the researchers confirmed that with advancing age, tau protein accumulated in the medial temporal lobe — home to the hippocampus and the memory center of the brain.

The study revealed that higher levels of tau in the medial temporal lobe was associated with greater declines in episodic memory, the type of memory used to code new information. The researchers tested episodic memory by asking subjects to recall a list of words viewed 20 minutes earlier.

One question yet to be answered is why so many people have tau in their medial temporal lobe yet never go on to develop Alzheimer’s. Likewise, adults may have beta amyloid in their brains and yet be cognitively healthy.

While higher levels of tau in the medial temporal lobe was linked to more problems with episodic memory, it was when tau spread outside this region to other parts of the brain, such as the neocortex, that researchers saw more serious declines in global cognitive function. Significantly, they found that tau’s spread outside the medial temporal lobe was connected to the presence of amyloid plaques in the brain.

What the study does indicate is that tau imaging could become an important tool in helping to develop therapeutic approaches that target the correct protein — either amyloid or tau — depending on the disease stage.

Source: Sarah Yang, UC Berkeley

Protein aggregates are deemed to be one reason for the death of nerve cells in disorders such as Alzheimer’s or Huntington’s disease. As researchers report in the current issue of Nature, they have now decoded a new cellular mechanism for the development of aggregates. Missing stop signals in the production of proteins lead erroneously to long lysine chains at the end of the protein. This in turn blocks the ribosomes, the cell’s protein factory. Healthy cells detect blocked ribosomes and rapidly destroy useless proteins. If the necessary quality control machinery does not function properly, defective proteins accumulate and form toxic aggregates.

In order to be able to treat neurodegenerative disorders in future, researchers have for many years been studying the cellular causes for the death of nerve cells. A determining cause is believed to be protein deposits – aggregates of misfolded proteins.

In each cell, proteins perform vital functions, acting as small molecular machines. The mRNA contains a start signal, the information about the protein structure, a stop signal and, at the end, a poly(A) tail. If the blueprint is damaged, for example due to radiation or mutagenic substances, this can lead to the loss of this stop signal. As a result, once the protein has been manufactured in the ribosomes, the completed protein cannot be released. Instead, the poly(A) tail is interpreted as the blueprint and additional amino acids are attached. The lysine chain that is positively charged as a result blocks the protein factory and the manufacture of protein comes to a standstill.

Healthy cells have a very efficient quality control process when it comes to the manufacture of protein. Misfolded and useless proteins are selected, repaired or rapidly destroyed.

Using a mouse model, the researchers can now demonstrate the fatal consequences of a quality control malfunction. Animals with the relevant mutation show symptoms of advanced neurodegeneration and a restricted ability to move.

The protein aggregates that develop have a sticky surface and act as a seed. They ultimately also bind functioning proteins, which are free of defects and vital for the cell. As a result, the cell is destabilized and, in the long run, is damaged.

Source: Max Planck Institute of Biochemistry

The body has a variety of natural defences to protect itself against neurodegeneration, but as we age, these defences become progressively impaired and can get overwhelmed.

Researchers have identified a drug that targets the first step in the toxic chain reaction leading to the death of brain cells, suggesting that treatments could be developed to protect against Alzheimer’s disease, in a similar way to how statins are able to reduce the risk of developing heart disease.

The drug, which is an approved anti-cancer treatment, has been shown to delay the onset of Alzheimer’s disease, both in a test tube and in nematode worms. It has previously been suggested that statin-like drugs – which are safe and can be taken widely by those at risk of developing disease – might be a prospect, but this is the first time that a potential ‘neurostatin’ has been reported.

When the drug was given to nematode worms genetically programmed to develop Alzheimer’s disease, it had no effect once symptoms had already appeared. But when the drug was given to the worms before any symptoms became apparent, no evidence of the condition appeared, raising the possibility that this drug, or other molecules like it, could be used to reduce the risk of developing Alzheimer’s disease. The results are reported in the journal Science Advances.

By analysing the way the drug, called bexarotene, works at the molecular level, the international team of researchers, from the University of Cambridge, Lund University and the University of Groningen, found that it stops the first step in the molecular cascade that leads to the death of brain cells. This step, called primary nucleation, occurs when naturally occurring proteins in the body fold into the wrong shape and stick together with other proteins, eventually forming thin filament-like structures called amyloid fibrils. This process also creates smaller clusters called oligomers, which are highly toxic to nerve cells and are thought to be responsible for brain damage in Alzheimer’s disease.

For the past two decades, researchers have attempted to develop treatments for Alzheimer’s that could stop the aggregation and proliferation of oligomers. However, these attempts have all failed, in part because there was not a precise knowledge of the mechanics of the disease’s development.

The researchers were able to determine what happens during each stage of the disease’s development, and also what might happen if one of those stages was somehow switched off.

The researchers assembled a library of more than 10,000 small molecules that interact in some way with amyloid-beta, a molecule that plays a vital role in Alzheimer’s disease. They first analysed molecules that were either drugs already approved for some other purpose, or drugs developed for Alzheimer’s disease or other similar conditions which had failed clinical trials.

The first successful molecule they identified was bexarotene, which is approved by the US Food and Drug Administration for the treatment of lymphoma. One of the key advances of the current work is that by understanding the mechanisms of how Alzheimer’s disease develops in the brain, the researchers were able to target

Earlier studies of bexarotene had suggested that the drug could actually reverse Alzheimer’s symptoms by clearing amyloid-beta aggregates in the brain, which received a great deal of attention. However, the earlier results, which were later called into question, were based on a completely different mode of action – the clearance of aggregates – than the one reported in the current study. By exploiting their novel approach, which enables them to carry out highly quantitative analysis of the aggregation process, the researchers have now shown that compounds such as bexarotene could instead be developed as preventive drugs, because its primary action is to inhibit the crucial first step in the aggregation of amyloid-beta.

Source: University of Cambridge

Scientists have developed a new optical technique to study how information is transmitted in the brains of mice. Using this method, they found that only a small portion of synapses — the connections between cells that control brain activity — may be active at any given time.

The study was published in the latest issue of Nature Neuroscience.

To obtain a detailed view of synaptic activity, the researchers developed a novel compound called fluorescent false neurotransmitter 200 (FFN200). When added to brain tissue or nerve cells from mice, FFN200 mimics the brain’s natural neurotransmitters and allows researchers to spy on chemical messaging in action.

Using a fluorescence microscope, the researchers were able to view the release and reuptake of dopamine — a neurotransmitter involved in motor learning, habit formation, and reward-seeking behavior — in individual synapses. When all the neurons were electrically stimulated in a sample of brain tissue, the researchers expected all the synapses to release dopamine. Instead, they found that less than 20 percent of dopaminergic synapses were active following a pulse of electricity.

“This particular study didn’t explain what’s causing most of the synapses to remain silent,” said David Sulzer, a co-author of the paper. “If we can work this out, we may learn a lot more about how alterations in dopamine levels are involved in brain disorders such as Parkinson’s disease, addiction, and schizophrenia.”

Source: Columbia University Medical Center

Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease, is a devastating progressive neurodegenerative disease that results in the death of motor neurons, the nerve cells that control muscles. Eventually, individuals with ALS will lose their ability to walk, move, swallow and breathe.

Until recently, the role of astrocytes, glial cells that normally support motor neurons, in motor neuron death has been a mystery, but new research sheds new light on molecular mechanisms responsible for motor neuron death in ALS. In a study published in Nature Medicine, researchers demonstrate the explicit loss of major histocompatibility complex I (MHCI) expression in the outer membrane of motor neurons in ALS, leading to motor neuron vulnerability to ALS astrocyte toxicity.

For each subtype of MHCI protein, there is a receptor that binds to it, much like a lock and key. If MCHI proteins are the keys, then killer inhibitory receptors (KIRs) are the locks. In their study, the researchers not only provide evidence of the protective effect of MHCI against astrocyte toxicity in ALS but also identify the killer inhibitory receptors (KIRs) associated with the specific subclass of MHCI (HLA-F) involved in human motor neurons.

According to the study, a dramatic loss of MHCI (HLA-F) from motor neurons is observed in the spinal cords of subjects affected by ALS. This finding is supported by evidence obtained in animal models and in vitro experiments using animal and human cells, which give insight on the protective nature of MHCI (HLA-F). Specifically, MHCI expression in the animal model was modulated using adeno-associated viral vector serotype 9 (AAV9), resulting in increased expression of MHCI and markedly extended survival.

The protective nature of MHCI (HLA-F) points to a potential translational target to delay the progression of ALS, since HLA-F expression may significantly impact disease progression in patients. In the in vitro experiments, human motor neurons expressing higher levels of HLA-F experienced reduced astrocyte toxicity. However, it remains to be seen whether or not this can be translated into a clinical trial and meaningful therapy for patients.

Source: Nationwide Children’s Hospital

Accumulation of amyloid beta in the brain impairs memory and cognitive ability in people with Alzheimer’s. New findings published in Nature Communications show that the cause of amyloid beta pathology might be more versatile than previously known. Researchers believe that these new findings may be of significance to the development of new medications.

The accumulation of the protein amyloid beta in the brain is a sign of Alzheimer’s disease. Sufficiently large quantities cause plaque, which blocks the function of the nerve cells and thereby impair the patient’s memory and cognitive ability.

A small proportion of Alzheimer’s patients have a hereditary risk gene, which causes overproduction of amyloid beta in the brain. In all other cases, the cause of the disease has so far been explained by the body’s lack of ability to break down and remove amyloid beta. However, these new findings provide a more nuanced picture:

“In our study, we show that accumulation of amyloid in the brain is associated with high levels of specific amyloid peptides in the cerebrospinal fluid. This means that overproduction of amyloid beta may contribute to development of Alzheimer’s disease in some people, even if they do not carry the hereditary risk gene for Alzheimer’s. The fact that the disease in these individuals can be attributed to both the overproduction of and problems in breaking down amyloid beta may be of significance to the future development of drugs and treatments”, explained Niklas Mattsson, a researcher at Lund University and specialist physician at Skåne University Hospital.

The study noted increased levels of amyloid beta in a large group of patients with no hereditary risk gene. More than 330 people from Sweden participated in the study, some of whom suffered from mild cognitive disorders (which may be an early sign of Alzheimer’s), while others were part of a control group of healthy individuals.

Source: Lund University

An innovative tool allows researchers to observe protein aggregation throughout the life of a worm. The development of these aggregates, which play a role in the onset of a number of neurodegenerative diseases, can now be monitored automatically and in real time. This breakthrough was made possible by isolating worms in tiny microfluidic chambers.

Biologists and microfluidics specialists have joined forces and developed a highly innovative research tool: a 2cm by 2cm ‘chip’ with 32 independent compartments, each of which is designed to hold a nematode – a widely used worm in the research world. The device is described in the journal Molecular Neurodegeneration.

Each of these ‘cells’ is fed by microfluidic channels. These allow variable concentrations of nutrients or therapeutic molecules to be injected with precision. The ambient temperature can also be adjusted. Each worm is observed through a microscope throughout its life. However, for more detailed investigations and very high resolution images, the worms need to be immobilized.

This method is fully reversible and does not affect the nematode’s development. Using it, researchers can observe the formation of protein aggregates linked to several neurodegenerative diseases like Alzheimer’s, Parkinson’s and Huntington’s. The same worm can be photographed several times, as the clusters develop.

Nematodes are very useful models for studying a number of human diseases. In many cases, they obviate the need to experiment on rodents. But until now, handling nematodes was a delicate affair. By simplifying the process, this new technology should accelerate research on numerous afflictions and how they are treated.

Source: Emmanuel Barraud, École polytechnique fédérale de Lausanne

A new study in the journal Nature Communications shows that cells normally associated with protecting the brain from infection and injury also play an important role in rewiring the connections between nerve cells. While this discovery sheds new light on the mechanics of neuroplasticity, it could also help explain diseases like autism spectrum disorders, schizophrenia, and dementia, which may arise when this process breaks down and connections between brain cells are not formed or removed correctly.

While the constant reorganization of neural networks – called neuroplasticity – has been well understood for some time, the basic mechanisms by which connections between brain cells are made and broken have eluded scientists.

Performing experiments in mice, the researchers employed a well-established model of measuring neuroplasticity by observing how cells reorganize their connections when visual information received by the brain is reduced from two eyes to one.

The researchers found that in the mice’s brains microglia responded rapidly to changes in neuronal activity as the brain adapted to processing information from only one eye. They observed that the microglia targeted the synaptic cleft – the business end of the connection that transmits signals between neurons. The microglia “pulled up” the appropriate connections, physically disconnecting one neuron from another, while leaving other important connections intact.

The researchers also pinpointed one of the key molecular mechanisms in this process and observed that when a single receptor – called P2Y12 – was turned off the microglia ceased removing the connections between neurons.

These findings may provide new insight into disorders that are the characterized by sensory or cognitive dysfunction, such as autism spectrum disorders, schizophrenia, and dementia. It is possible that when the microglia’s synapse pruning function is interrupted or when the cells mistakenly remove the wrong connections – perhaps due to genetic factors or because the cells are too occupied elsewhere fighting an infection or injury – the result is impaired signaling between brain cells.

Source: University of Rochester Medical Center (URMC)

The European Medicines Agency (EMA) has released draft revised guidelines on medicines for the treatment of Alzheimer’s disease and other types of dementias for a six-month public consultation.

EMA follows a multi-stakeholder approach to facilitate research and development of more effective medicines. The revised guidelines take into account comments received at EMA’s workshop on the clinical investigation of medicines for the treatment of Alzheimer’s disease in November 2014. This workshop brought together a wide range of stakeholders, including patient representatives, regulators, pharmaceutical industry and independent experts. The aim of the workshop was to ensure that during the revision of its guidelines, EMA would be able to consider the most up-to-date scientific developments in understanding and treating Alzheimer’s disease and views from experts in the field. The revised guidelines also build on EMA scientific advice provided for a number of specific development plans for Alzheimer’s disease in recent years, as well as the qualification of several biomarkers for the selection of patients in clinical trials.

The revised guideline specifically addresses the:

impact of new diagnostic criteria for Alzheimer’s disease, including early and even asymptomatic disease stages, on clinical trial design
choice of parameters to measure trial outcomes and the need for distinct assessment tools for the different disease stagesin Alzheimer’s (different signs and symptoms, differences in changes over time, severity)
potential use of biomarkers and their temporal relationship with the different phases of Alzheimer’s disease at different stages of medicine development (mechanism of action, use as diagnostic test, enrichment of study populations, stratification of subgroups, safety and efficacy markers etc.)
design of long-term efficacy and safety studies

Comments received during the consultation will be taken into account in the finalisation of the guideline.

Stakeholders are invited to send their comments by 31 July 2016. To learn more, visit the EMA website.

Source: EMA

Scientists have solved a longstanding problem with modeling Parkinson’s disease in animals. Using newfound insights, they improve both cell and animal models for the disease, which can propel research and drug development.

Parkinson’s disease is characterized by the appearance of protein clumps within neurons in the brain, called Lewy bodies. Reproducing Lewy bodies in animals in order to model the disease for research and drug screening has proven notoriously difficult, leaving a gap in Parkinson’s research and treatment. Scientists have now shown where the discrepancy between humans and animals lies. Using the knowledge, the scientists have produced cellular and mouse models that reproduce the evolution of Parkinson’s disease more accurately for both fundamental research and drug development. The work is published in PNAS.

In humans, Lewy bodies form when the brain produces twice the normal amount of alpha-synuclein. When mice, which are often used to model human diseases, are used to model Parkinson’s, they are genetically engineered to overproduce it. But human alpha-synuclein does not form fibrils and Lewy bodies when produced in mice.

Mice produce three types of their own synuclein, which are similar to human alpha-synuclein. Because of this, they are referred to as its “homologues”. The researchers found that human alpha-synuclein does not form Lewy bodies in mice because its homologues in the animal prevent it from doing so. This discovery explains why it is so difficult to model Parkinson’s disease in normal mice, which have all of their synuclein homologues. In other words, the key to successfully modeling the disease in mice is to genetically suppress their homologues of human alpha-synuclein.

Working off their genetically engineered mice and neuronal cultures, the team developed and characterized new models for Lewy bodies for the scientific and medical community. Hilal Lashuel expects that the new insights will advance the development of neuronal and in vivo models that reproduce features of Parkinson’s disease, and allow screening for new drugs. “We now have a very well-characterized model that offers a powerful tool for rapid screening of molecular pathways involved in Parkinson’s disease,” he says.

Source: École polytechnique fédérale de Lausanne