Posts tagged neurodegeneration
Articles and news from the latest research reports.
(Image caption: A daydreaming brain: the yellow areas depict the default mode network from three different perspectives; the coloured fibres show the connections amongst each other and with the remainder of the brain.)
The structure of the human brain is complex, reminiscent of a circuit diagram with countless connections. But what role does this architecture play in the functioning of the brain? To answer this question, researchers at the Max Planck Institute for Human Development in Berlin, in cooperation with colleagues at the Free University of Berlin and University Hospital Freiburg, have for the first time analysed 1.6 billion connections within the brain simultaneously. They found the highest agreement between structure and information flow in the “default mode network,” which is responsible for inward-focused thinking such as daydreaming.
Everybody’s been there: You’re sitting at your desk, staring out the window, your thoughts wandering. Instead of getting on with what you’re supposed to be doing, you start mentally planning your next holiday or find yourself lost in a thought or a memory. It’s only later that you realize what has happened: Your brain has simply “changed channels”—and switched to autopilot.
For some time now, experts have been interested in the competition among different networks of the brain, which are able to suppress one another’s activity. If one of these approximately 20 networks is active, the others remain more or less silent. So if you’re thinking about your next holiday, it is almost impossible to follow the content of a text at the same time.
To find out how the anatomical structure of the brain impacts its functional networks, a team of researchers at the Max Planck Institute for Human Development in Berlin, in cooperation with colleagues at the Free University of Berlin and the University Hospital Freiburg, have analysed the connections between a total of 40,000 tiny areas of the brain. Using functional magnetic resonance imaging, they examined a total of 1.6 billion possible anatomical connections between these different regions in 19 participants aged between 21 and 31 years. The research team compared these connections with the brain signals actually generated by the nerve cells.
Their results showed the highest agreement between brain structure and brain function in areas forming part of the “default mode network“, which is associated with daydreaming, imagination, and self-referential thought. “In comparison to other networks, the default mode network uses the most direct anatomical connections. We think that neuronal activity is automatically directed to level off at this network whenever there are no external influences on the brain,” says Andreas Horn, lead author of the study and researcher in the Center for Adaptive Rationality at the Max Planck Institute for Human Development in Berlin.
Living up to its name, the default mode network seems to become active in the absence of external influences. In other words, the anatomical structure of the brain seems to have a built-in autopilot setting. It should not, however, be confused with an idle state. On the contrary, daydreaming, imagination, and self-referential thought are complex tasks for the brain.
“Our findings suggest that the structural architecture of the brain ensures that it automatically switches to something useful when it is not being used for other activities,” says Andreas Horn. “But the brain only stays on autopilot until an external stimulus causes activity in another network, putting an end to the daydreaming. A buzzing fly, a loud bang in the distance, or focused concentration on a text, for example.”
The researchers hope that their findings will contribute to a better understanding of brain functioning in healthy people, but also of neurodegenerative disorders such as Alzheimer’s disease and psychiatric conditions such as schizophrenia. In follow-up studies, the research team will compare the brain structures of patients with neurological disorders with those of healthy controls.
Brain repair after injury and Alzheimer’s disease
Researchers at Penn State University have developed an innovative technology to regenerate functional neurons after brain injury, and also in model systems used for research on Alzheimer’s disease. The scientists have used supporting cells of the central nervous system, glial cells, to regenerate healthy, functional neurons, which are critical for transmitting signals in the brain.
Gong Chen, a professor of biology, the Verne M. Willaman Chair in Life Sciences at Penn State, and the leader of the research team, calls the method a breakthrough in the long journey toward brain repair. “This technology may be developed into a new therapeutic treatment for traumatic brain and spinal cord injuries, stroke, Alzheimer’s disease, Parkinson’s disease, and other neurological disorders,” Chen said. The research will be posted online by the journal Cell Stem Cell on 19 December 2013.
When the brain is harmed by injury or disease, neurons often die or degenerate, but glial cells become more branched and numerous. These “reactive glial cells” initially build a defense system to prevent bacteria and toxins from invading healthy tissues, but this process eventually forms glial scars that limit the growth of healthy neurons. “A brain-injury site is like a car-crash site,” Chen explained. “Reactive glial cells are like police vehicles, ambulances, and fire trucks immediately rushing in to help — but these rescue vehicles can cause problems if too many of them get stuck at the scene. The problem with reactive glial cells is that they often stay at the injury site, forming a glial scar and preventing neurons from growing back into the injured areas,” he explained.
So several years ago, Chen’s lab tested new ways to transform glial scar tissue back to normal neural tissue. “There are more reactive glial cells and fewer functional neurons in the injury site,” Chen said, “so we hypothesized that we might be able to convert glial cells in the scar into functional neurons at the site of injury in the brain. This research was inspired by the Nobel prize-winning technology of induced pluripotent stem cells (iPSCs) developed in Shinya Yamanaka’s group, which showed how to reprogram skin cells into stem cells,” Chen recalled.
Chen and his team began by studying how reactive glial cells respond to a specific protein, NeuroD1, which is known to be important in the formation of nerve cells in the hippocampus area of adult brains. They hypothesized that expressing NeuroD1 protein into the reactive glial cells at the injury site might help to generate new neurons — just as it does in the hippocampus. To test this hypothesis, his team infected reactive glial cells with a retrovirus that specifies the genetic code for the NeuroD1 protein. “The retrovirus we used is replication-deficient and thus cannot kill infected cells like other viruses found in the wild,” Chen said. “More importantly, a retrovirus can infect only dividing cells such as reactive glial cells, but it does not affect neurons, which makes it ideal for therapeutic use with minimal side effect on normal brain functions.”
In a first test, Chen and his team investigated whether reactive glial cells can be converted into functional neurons after injecting NeuroD1 retrovirus into the cortex area of adult mice. The scientists found that two types of reactive glial cells — star-shaped astroglial cells and NG2 glial cells — were reprogrammed into neurons within one week after being infected with the NeuroD1 retrovirus. “Interestingly, the reactive astroglial cells were reprogrammed into excitatory neurons, whereas the NG2 cells were reprogrammed into both excitatory and inhibitory neurons, making it possible to achieve an excitation-inhibition balance in the brain after reprogramming,” Chen said. His lab also performed electrophysiological tests, which demonstrated that the new neurons converted by the NeuroD1 retrovirus could receive neurotransmitter signals from other nerve cells, suggesting that the newly converted neurons had successfully integrated into local neural circuits.
In a second test, Chen and his team used a transgenic-mouse model for Alzheimer’s disease, and demonstrated that reactive glial cells in the mouse’s diseased brain also can be converted into functional neurons. Furthermore, the team demonstrated that even in 14-month-old mice with Alzheimer’s disease — an age roughly equivalent to 60 years old for humans — injection of the NeuroD1 retrovirus into a mouse cortex can still induce a large number of newborn neurons reprogrammed from reactive glial cells. “Therefore, the conversion technology that we have demonstrated in the brains of mice potentially may be used to regenerate functional neurons in people with Alzheimer’s disease,” Chen said.
To ensure that the glial cell-to-neuron conversion method is not limited to rodent animals, Chen and his team further tested the method on cultured human glial cells. “Within 3 weeks after expression of the NeuroD1 protein, we saw in the microscope that human glial cells were reinventing themselves: they changed their shape from flat sheet-like glial cells into normal-looking neurons with axon and dendritic branches,” Chen said. The scientists further tested the function of these newly converted human neurons and found that, indeed, they were capable of both releasing and responding to neurotransmitters.
"Our dream is to develop this in vivo conversion method into a useful therapy to treat people suffering from neural injury or neurological disorders," Chen said. "Our passionate motivation for this research is the idea that an Alzheimer’s patient, who for a long time was not able to remember things, could start to have new memories after regenerating new neurons as a result of our in vivo conversion method, and that a stroke victim who could not even move his legs might start to walk again."
A New—and Reversible—Cause of Aging
Researchers have discovered a cause of aging in mammals that may be reversible.
The essence of this finding is a series of molecular events that enable communication inside cells between the nucleus and mitochondria. As communication breaks down, aging accelerates. By administering a molecule naturally produced by the human body, scientists restored the communication network in older mice. Subsequent tissue samples showed key biological hallmarks that were comparable to those of much younger animals.
“The aging process we discovered is like a married couple—when they are young, they communicate well, but over time, living in close quarters for many years, communication breaks down,” said Harvard Medical School Professor of Genetics David Sinclair, senior author on the study. “And just like with a couple, restoring communication solved the problem.”
This study was a joint project between Harvard Medical School, the National Institute on Aging, and the University of New South Wales, Sydney, Australia, where Sinclair also holds a position.
The findings are published Dec. 19 in Cell.
Communication breakdown
Mitochondria are often referred to as the cell’s “powerhouse,” generating chemical energy to carry out essential biological functions. These self-contained organelles, which live inside our cells and house their own small genomes, have long been identified as key biological players in aging. As they become increasingly dysfunctional overtime, many age-related conditions such as Alzheimer’s disease and diabetes gradually set in.
Researchers have generally been skeptical of the idea that aging can be reversed, due mainly to the prevailing theory that age-related ills are the result of mutations in mitochondrial DNA—and mutations cannot be reversed.
Sinclair and his group have been studying the fundamental science of aging—which is broadly defined as the gradual decline in function with time—for many years, primarily focusing on a group of genes called sirtuins. Previous studies from his lab showed that one of these genes, SIRT1, was activated by the compound resveratrol, which is found in grapes, red wine and certain nuts.
Ana Gomes, a postdoctoral scientist in the Sinclair lab, had been studying mice in which this SIRT1 gene had been removed. While they accurately predicted that these mice would show signs of aging, including mitochondrial dysfunction, the researchers were surprised to find that most mitochondrial proteins coming from the cell’s nucleus were at normal levels; only those encoded by the mitochondrial genome were reduced.
“This was at odds with what the literature suggested,” said Gomes.
As Gomes and her colleagues investigated potential causes for this, they discovered an intricate cascade of events that begins with a chemical called NAD and concludes with a key molecule that shuttles information and coordinates activities between the cell’s nuclear genome and the mitochondrial genome. Cells stay healthy as long as coordination between the genomes remains fluid. SIRT1’s role is intermediary, akin to a security guard; it assures that a meddlesome molecule called HIF-1 does not interfere with communication.
For reasons still unclear, as we age, levels of the initial chemical NAD decline. Without sufficient NAD, SIRT1 loses its ability to keep tabs on HIF-1. Levels of HIF-1 escalate and begin wreaking havoc on the otherwise smooth cross-genome communication. Over time, the research team found, this loss of communication reduces the cell’s ability to make energy, and signs of aging and disease become apparent.
“This particular component of the aging process had never before been described,” said Gomes.
While the breakdown of this process causes a rapid decline in mitochondrial function, other signs of aging take longer to occur. Gomes found that by administering an endogenous compound that cells transform into NAD, she could repair the broken network and rapidly restore communication and mitochondrial function. If the compound was given early enough—prior to excessive mutation accumulation—within days, some aspects of the aging process could be reversed.
Cancer connection
Examining muscle from two-year-old mice that had been given the NAD-producing compound for just one week, the researchers looked for indicators of insulin resistance, inflammation and muscle wasting. In all three instances, tissue from the mice resembled that of six-month-old mice. In human years, this would be like a 60-year-old converting to a 20-year-old in these specific areas.
One particularly important aspect of this finding involvesHIF-1. More than just an intrusive molecule that foils communication, HIF-1 normally switches on when the body is deprived of oxygen. Otherwise, it remains silent. Cancer, however, is known to activate and hijack HIF-1. Researchers have been investigating the precise role HIF-1 plays in cancer growth.
“It’s certainly significant to find that a molecule that switches on in many cancers also switches on during aging,” said Gomes. “We’re starting to see now that the physiology of cancer is in certain ways similar to the physiology of aging. Perhaps this can explain why the greatest risk of cancer is age.”
“There’s clearly much more work to be done here, but if these results stand, then certain aspects of aging may be reversible if caught early,” said Sinclair.
The researchers are now looking at the longer-term outcomes of the NAD-producing compound in mice and how it affects the mouse as a whole. They are also exploring whether the compound can be used to safely treat rare mitochondrial diseases or more common diseases such as Type 1 and Type 2 diabetes. Longer term, Sinclair plans to test if the compound will give mice a healthier, longer life.
(Source: hms.harvard.edu)
Brain Area Attacked by Alzheimer’s Links Learning and Rewards
One of the first areas of the brain to be attacked by Alzheimer’s disease is more active when the brain isn’t working very hard, and quiets down during the brain’s peak performance.
The question that Duke University graduate student Sarah Heilbronner wanted to resolve was whether this brain region, called the posterior cingulate cortex, or PCC, actively dampens cognitive performance, say by allowing the mind to wander, or is instead monitoring performance and trying to improve it when needed.
If the PCC were monitoring and improving performance, increased activity there would be the result of poor performance, not the cause of it.
The PCC connects to both learning and reward systems, Heilbronner said, and is a part of the “default mode network.” It lies along a mid-line between the ears, where many structures related to rewards can be found. “It’s kind of a nexus for multiple systems,” said Heilbronner, who is currently a postdoctoral researcher in neuroanatomy at the University of Rochester.
"As this area begins to deteriorate, people begin to show the early signs of cognitive decline — problems learning and remembering things, getting lost, trouble planning — that ultimately manifest as outright dementia," said Michael Platt, director of the Duke Institute for Brain Sciences, who supervised Heilbronner’s 2012 dissertation. Their findings appear Dec. 18 in the journal Neuron.
Heilbronner’s experiment to better understand the PCC’s role in learning and remembering relied on two rhesus macaque monkeys fitted with electrodes to read out the activity of individual neurons in their brains. Their task was akin to playing video games with their eyes. The monkeys were shown a series of photographs each day marked with dots at the upper left and lower right corners. To get a rewarding squirt of juice, they had to move their gaze to the correct target dot on a photo, and they learned by trial and error which dot would yield the reward for each photo.
Each day, they were shown up to 12 photos from an assortment of Heilbronner’s vacation snaps at Yellowstone National Park and the Grand Canyon. Some of each day’s images were familiar with a known reward target, and others were new. As the monkeys responded with their gaze, the researchers watched the activity of dozens of neurons in each monkey’s brain immediately following correct and incorrect responses. They also altered the amount of juice dispensed in some cases, creating a sense of high-reward and low-reward answers.
If the PCC actively dampened performance, the researchers would expect to see it active before a choice is made or the feedback is received. Instead, they saw it working after the feedback, lasting sometimes until the next image was presented. Neurons in the PCC responded strongly when the monkeys needed to learn something new, especially when they made errors or didn’t earn enough reward to keep motivated.
The researchers also ran the task after administering a drug, muscimol, that impaired the function of the PCC temporarily during testing. With the center inactivated by the drug, the monkeys could recall earlier learning regardless of the size of the reward. Learning a new item was still possible when the reward was large, but the monkeys couldn’t learn anything new when rewards were small. “Maybe it didn’t seem worth it,” Heilbronner said.
The dampening experiment also reinforced what the researchers had seen in the timing of the PCC’s response. If this center’s role is to let the mind wander, performance should have improved when the muscimol was administered, but the opposite was true.
Heilbronner concludes that the PCC summons more resources for a challenging cognitive task. So rather than being the cause of poor performance on a task, PCC actually steps in during a challenge to improve the situation.
"This study tells us that a healthy PCC is required for monitoring performance and keeping motivated during learning, particularly when problems are challenging," Platt said.
Heilbronner is now interested in finding out whether the PCC is more important to learning than it is to recall, and how motivation interacts with PCC abnormalities seen in Alzheimer’s disease.
Study provides new insights into cause of human neurodegenerative disease
A recent study led by scientists from the National University of Singapore (NUS) opens a possible new route for treatment of Spinal Muscular Atrophy (SMA), a devastating disease that is the most common genetic cause of infant death and also affects young adults. As there is currently no known cure for SMA, the new discovery gives a strong boost to the fight against SMA.
SMA is caused by deficiencies in the Survival Motor Neuron (SMN) gene. This gene controls the activity of various target genes. It has long been speculated that deregulation of some of these targets contributes to SMA, yet their identity remained unknown.
Using global genome analysis, the research team, led by Associate Professor Christoph Winkler of the Department of Biological Sciences at the NUS Faculty of Science and Dr Kelvin See, a former A*STAR graduate scholar in NUS who is currently a Research Fellow at the Genome Institute of Singapore (GIS), found that deficiency in the SMN gene impairs the function of the Neurexin2 gene. This in turn limits the neurotransmitter release required for the normal function of nerve cells. The degeneration of motor neurons in the spinal cord causes SMA. This is the first time that scientists establish an association between Neurexin2 and SMA.
Preliminary experimental data also showed that a restoration of Neurexin2 activity can partially recover neuron function in SMN deficient zebrafish. This indicates a possible new direction for therapy of neurodegeneration.
Collaborating with Assoc Prof Winkler and the NUS researchers are Dr S. Mathavan and his team at GIS, as well as researchers from the University of Wuerzburg in Germany. The breakthrough discovery was first published in scientific journal Human Molecular Genetics last month.
Small zebrafish provides insights into human neurodegenerative disease
SMA is a genetic disease that attacks a distinct type of nerve cells called motor neurons in the spinal cord. The disease has been found to be caused by a defect in the SMN gene, a widely used gene that is responsible for normal motor functions in the body.
To study how defects in SMN cause neuron degeneration, the scientists utilised a zebrafish model, as the small fish has a relatively simple nervous system that allows detailed imaging of neuron behaviour.
In laboratory experiments, the researchers showed when SMN activity in zebrafish was reduced to levels found in human SMA patients, Neurexin2 function was impaired. This novel disease mechanism was also discovered in other in vivo models, suggesting that it is applicable to mammals and possibly human patients.
When the scientists measured the activity of nerve cells in zebrafish using laser imaging, they found that nerve cells deficient for Neurexin2 or SMN could not be activated to the same level as healthy nerve cells. This impairment consequently led to the reduction of muscular activity. Interestingly, preliminary data showed that a restoration of Neurexin2 activity can partially recover neuron function in SMN deficient zebrafish.
Further studies
Assoc Prof Winkler, who is also with the NUS Centre for Biolmaging Sciences, explained, “These findings significantly advance our understanding of how the loss of SMN leads to neurodegeneration. A better understanding of these mechanisms will lead to novel therapeutic strategies that could aim at restoring and maintaining functions in deficient nerve cells of SMA patients.”
Dr See added, “Our study provides a link between SMN deficiency and its effects on a critical gene important for neuronal function. It would be interesting to perform follow up studies in clinical samples to further investigate the role of Neurexin2 in SMA pathophysiology.”
Moving forward, the team of scientists will conduct further research to determine if Neurexin2 is an exclusive mediator of SMN induced defects and hence can be used as a target for future drug designs. They hope their findings will contribute towards treatment of neurodegeneration.
Repairing mitochondria in neurodegenerative disease
The relationship between fine-scale structure and function in the brain is perhaps best explored today by the study of neurodegenerative disease. Disorders like Rett syndrome may be considered developmental in origin—and defined by exotic mechanisms including X-linked inactivation, DNA methylation, and genomic imprinting—but even here, its larger physical pathology evolves through the course of life and continues to be revealed in almost any place that researchers look. When diseases directly involve inputs to the brain like vitamin or diet, and can also be controlled by them, things get even more interesting. More often than not, these disorders have a clear genetic component, are frequently linked to the mitochondria, and lead to progressive and often perplexing deficits of movement. One such enigma is known as pantothenate kinase-associated neurodegeneration, or PKAN syndrome, in its the most frequent form. A recent open paper in the journal Brain explains.
This particular syndrome can be caused by any number of a hundred or so mutations in the PANK2 gene, which codes for the mitochondrial enzyme pantothenate kinase 2. Of the four nuclear-coded PANK genes, only PANK2 is targeted to the mitochondria. Its protein product is involved in co-enzyme A biosynthesis and catalyzes the phosphorylation of pantothenate (vitamin B5). The hallmark pathology, as defined by T2-weighted MRI, can be seen in the globus pallidus and even has its own unique name— the Eye-of-the-Tiger sign.
The researchers used a mouse model of the disease with a Pank2 double gene knockout. On a standard diet, the mice showed growth issues, azoospermia (lack of sperm) and minor mitochondrial dysfunction, but not some of the other typical issues like iron accumulation in the brain or retinal degeneration. Since co-enzyme A is crucial to several metabolic pathways, the researchers also tested the mice on a high fat ketogenic diet. Under these conditions, ketone bodies produced through fatty acid oxidation bypass the normal glycolytic pathways and proceed directly to the citric acid acid.
On the ketogenic diet, the mitochondria, which were already ailing with abnormal, swollen cristae, fared much worse, losing some cristae entirely. Extensive lipofuschin deposits were also found in these mice, and movement issues were amplified. It had previously been established in other organisms like flies, that panthethine (a dimeric form of vitamin B5 linked by cysteamine bridging groups) could counteract these issues. When the mice were given panthethine, the general pathology was resolved. In particular, the mitochondria were completely rescued, presumably restored to health, or otherwise replaced in the natural course of events.
The researchers also evaluated mitochondrial membrane potential using dye staining methods. In the knockout mice, membrane potential was compromised, however it was completely restored by the panthethine. At present there is no definitive way to predict functional variables, like membrane potential, from the morphology as it is seen on processed EM tissue. In a recent review of new brain mapping techniques, we discussed this issue, and also pointed to new technologies which may permit closer examinations.
On EM images, one of the most striking features in the interior of mitochondria is the crista junction. This protein structure functionally divides the inner and intermembrane spaces, and controls exchanges between them. While mitochondria come in a variety of forms, the junctions generally converge on a preferred shape and size. Efforts to thermodynamically characterize them in terms of shape entropy have been initiated, as have conceptions of how they evolve as conditions in the mitochondria change mechanically. The so-called “baffle model” of mitochondrial has been entirely replaced by the new cristae junction model which aims to relate structure to function for these organelles, just as we seek it on larger scales for the brain.
Several issues in PNAK style neurodegeneration still stand out like a sore thumb. The iron accumulation is still unexplained, but may be related to another unexplained issue: namely, not only does panthethine fail to cross the BBB, it does not even appear to be working through a vitamin B5 function. When panthethine is metabolized into two pantothenic acid molecules, it also forms two cysteamines. While cysteamine is associated with various side effects, and it can bind and inactivate certain liver enzymes, it also can cross the BBB, perhaps as seen here, to great effect.
The doses necessary for vitamin B5 function are far below those needed here for restorative function. More work is needed to constrain the range of possible mechanisms at play here, but in addition to finding cures for the disease, it will also help cure our ignorance as far as structure-function relations.
New gene discovery sheds more light on Alzheimer’s risk
A research team from The University of Nottingham has helped uncover a second rare genetic mutation which strongly increases the risk of Alzheimer’s disease in later life.
In an international collaboration, the University’s Translational Cell Sciences Human Genetics research group has pinpointed a rare coding variation in the Phospholipase D3 (PLD3) gene which is more common in people with late-onset Alzheimer’s than non-sufferers.
The discovery is an important milestone on the road to early diagnosis of the disease and eventual improved treatment. Having surveyed the human genome for common variants associated with Alzheimer’s, geneticists are now turning the spotlight on rare mutations which may be even stronger risk factors.
More than 820,000 people in the UK have dementia and the number is rising as the population ages. The condition, of which Alzheimer’s disease is the predominant cause, costs the UK economy £23 billion per year, much more than other diseases like cancer and heart disease.
Nottingham’s genetic experts have been working with long-term partners from Washington University, St Louis, USA and University College, London, to carry out next-generation whole exome sequencing on families where Alzheimer’s affects several members.
Earlier this year the collaboration uncovered the first ever rare genetic mutation implicated in disease risk, linking the TREM2 gene to a higher risk of Alzheimer’s (published in the New England Journal of Medicine). Now, in a new study published today in the international journal, Nature, the team reveal that after analysis of the genes of around 2,000 people with Alzheimer’s, a second genetic variation has been found, in the PLD3 gene.
PLD3 influences processing of amyloid precursor protein which results in the generation of the characteristic amyloid plaques seen in AD brain tissue, suggesting that it may be a potential therapeutic target.
The international research team used Nottingham’s Alzheimer’s Research UK DNA bank, one of the largest collections of DNA from Alzheimer’s patients, to completely sequence the entire coding region (exome) of the PLD3 gene. The results showed several mutations in the gene occurred more frequently in people who had the disease than in non-sufferers. Carriers of PLD3 coding variants showed a two-fold increased risk for the disease.
Leading the team at Nottingham, Professor of Human Genomics and Molecular Genetics, Kevin Morgan, said:
“This second crucial discovery has confirmed that this latest scientific approach does deliver, it is able to find these clues. However, it is also inferring that there are lots more AD-significant variations out there and before we can use it for diagnosis we need to find all of the other genetic variations involved in Alzheimer’s too.
“Our research is forming the basis of potential diagnostics later on and more importantly it shows pathways that can be diagnostic targets which could lead to therapeutic interventions in the future.
“The next step will be to examine how this particular rare gene variant functions in the cell and see if it can be targeted, to see if there are any benefits to finding out how this gene operates in both normal and diseased cells. If we can do this, we may be able eventually to correct the defect with drug therapy. Here in Nottingham we will keep looking for more rare gene variations.
“Even if we could eventually slow or halt the progress of the disease with new drugs rather than curing it completely, the benefits would be huge in terms of the real impact on patients’ lives and also in vast savings to the health economy. The group The University of Nottingham has played a significant role in all of the recent AD genetics discoveries that have highlighted 20 new regions of interest in the genome in the last five years and we will continue to do so into the future.”
Rebecca Wood, Chief Executive of Alzheimer’s Research UK, the UK’s leading dementia research charity, said: “Advances in genetic technology are allowing researchers to understand more than ever about the genetic risk factors for the most common form of Alzheimer’s. This announcement, made just off the back of the G8 dementia research summit, is a timely reminder of the progress that can be made by worldwide collaboration. We know that late-onset Alzheimer’s is caused by a complex mix of risk factors, including both genetic and lifestyle. Understanding all of these risk factors and how they work together to affect someone’s likelihood of developing Alzheimer’s is incredibly important for developing interventions to slow the onset of the disease. Alzheimer’s Research UK is proud to have contributed to this discovery, both by funding researchers and through the establishment of a DNA collection that has been used in many of the recent genetic discoveries in Alzheimer’s.”
(Source: nottingham.ac.uk)
Staying ahead of Huntington’s disease
Huntington’s disease is a devastating, incurable disorder that results from the death of certain neurons in the brain. Its symptoms show as progressive changes in behavior and movements.
The neurodegenerative disease is caused by a defect in the huntingtin gene (Htt) that causes an abnormal expansion in a part of DNA, called a CAG codon or triplet that codes for the amino acid glutamine. A healthy version of the Htt gene has between 20 and 23 CAG triplets. The mutational expansion in Htt can lead to long repeats of the CAG triplet, resulting in the mutant protein having a long sequence of several glutamine residues called a polyglutamine tract. This CAG triplet expansion in unrelated genes is the root of at least nine neurodegenerative disorders, including Huntington’s disease.
Rohit Pappu, PhD, professor of biomedical engineering at Washington University in St. Louis, and his colleagues in the School of Engineering & Applied Science and in the School of Medicine, are working to understand how expanded polyglutamine tracts form the types of supramolecular structures that are presumed to be toxic to neurons – a feature that polyglutamine expansions share with proteins associated with Alzheimer’s disease and Parkinson’s disease.
In recent work, Pappu and his research team showed that the amino acid sequences on either side of the polyglutamine tract within Htt can act as natural gatekeepers because they control the fundamental ability of polyglutamine tracts to form structures that are implicated in cellular toxicity. The results were published in PNAS Early Edition Nov.25.
“These are progressive onset disorders,” Pappu says. “The longer the polyglutamine tract gets, the more severe the disease, and the symptoms worsen with age. Our results are exciting because it means that any success we have in mimicking the effects of naturally occurring gatekeepers would be a significant step forward. And mechanistic studies are important in this regard because they enable us to learn from nature’s own strategies.
“Previous studies from other labs showed that the toxic effects of polyglutamine expansions are tempered by the sequence contexts of polyglutamine tracts in Htt, not just the lengths of the polyglutamine tracts”, Pappu says.
He and his research team focused on understanding the effects of sequence stretches that lie on either side of the polyglutamine tract in Htt. The results show that the N-terminal stretch accelerates the formation of ordered structures that are presumed to be benign to cells, whereas the C-terminal stretch slows the overall transition into structures that are expected to create trouble for cells, suggesting that these naturally occurring sequences behave as gatekeepers.
“It appears that where polyglutamine stretches are of functional importance, nature has ensured that they are flanked by gatekeeping sequences,” Pappu says.
Pappu and his team are now working to find way s to mimic the effects of the N- and C-terminal flanking sequences from Htt. His team is working closely with Marc Diamond, MD, the David Clayson Professor of Neurology at the School of Medicine, to understand how naturally occurring proteins interact with flanking sequences and see if they can coopt them to ameliorate the toxic functions in the polyglutamine expansions.
(Source: engineering.wustl.edu)
Human Stem Cells Predict Efficacy of Alzheimer Drugs
Researchers from the University of Bonn use reprogrammed patient neurons for drug testing
Why do certain Alzheimer medications work in animal models but not in clinical trials in humans? A research team from the University of Bonn and the biomedical enterprise LIFE & BRAIN GmbH has been able to show that results of established test methods with animal models and cell lines used up until now can hardly be translated to the processes in the human brain. Drug testing should therefore be conducted with human nerve cells, conclude the scientists. The results are published by Cell Press in the journal “Stem Cell Reports”.
In the brains of Alzheimer patients, deposits form that consist essentially of beta-amyloid and are harmful to nerve cells. Scientists are therefore searching for pharmaceutical compounds that prevent the formation of these dangerous aggregates. In animal models, certain non-steroidal anti-inflammatory drugs (NSAIDs) were found to a reduced formation of harmful beta-amyloid variants. Yet, in subsequent clinical studies, these NSAIDs failed to elicit any beneficial effects.
"The reasons for these negative results have remained unclear for a long time", says Prof. Dr. Oliver Brüstle, Director of the Institute for Reconstructive Neurobiology of the University of Bonn and CEO of LIFE & BRAIN GmbH. "Remarkably, these compounds were never tested directly on the actual target cells – the human neuron", adds lead author Dr. Jerome Mertens of Prof. Brüstle’s team, who now works at the Laboratory of Genetics in La Jolla (USA). This is because, so far, living human neurons have been extremely difficult to obtain. However, with the recent advances in stem cell research it has become possible to derive limitless numbers of brain cells from a small skin biopsy or other adult cell types.
Scientists transform skin cells into nerve cells
Now a research team from the Institute for Reconstructive Neurobiology and the Department of Neurology of the Bonn University Medical Center together with colleagues from the LIFE & BRAIN GmbH and the University of Leuven (Belgium) has obtained such nerve cells from humans. The researchers used skin cells from two patients with a familial form of Alzheimer’s Disease to produce so-called induced pluripotent stem cells (iPS cells), by reprogramming the body’s cells into a quasi-embryonic stage. They then transformed the resulting so-called “jack-of-all-trades cells” into nerve cells.
Using these human neurons, the scientists tested several compounds in the group of non-steroidal anti-inflammatory drugs. As control, the researchers used nerve cells they had obtained from iPS cells of donors who did not have the disease. Both in the nerve cells obtained from the Alzheimer patients and in the control cells, the NSAIDs that had previously tested positive in the animal models and cell lines typically used for drug screening had practically no effect: The values for the harmful beta-amyloid variants that form the feared aggregates in the brain remained unaffected when the cells were treated with clinically relevant dosages of these compounds.
Metabolic processes in animal models differ from humans
"In order to predict the efficacy of Alzheimer drugs, such tests have to be performed directly on the affected human nerve cells", concludes Prof. Brüstle’s colleague Dr. Philipp Koch, who led the study. Why do NSAIDs decrease the risk of aggregate formation in animal experiments and cell lines but not in human neurons? The scientists explain this with differences in metabolic processes between these different cell types. "The results are simply not transferable", says Dr. Koch.
The scientists now hope that in the future, testing of potential drugs for the treatment of Alzheimer’s disease will be increasingly conducted using neurons obtained from iPS cells of patients. “The development of a single drug takes an average of ten years”, says Prof. Brüstle. “By using patient-specific nerve cells as a test system, investments by pharmaceutical companies and the tedious search for urgently needed Alzheimer medications could be greatly streamlined”.
(Source: www3.uni-bonn.de)
Study Treats Alzheimer’s by Delivering Protein Across Blood-Brain Barrier
The body is structured to ensure that any invading organisms have a tough time reaching the brain, an organ obviously critical to survival. Known as the blood-brain barrier, cells that line the brain and spinal cord are tightly packed, making it difficult for anything besides very small molecules to cross from the bloodstream into the central nervous system. While beneficial, this blockade also stands in the way of delivering drugs intended to treat neurological disorders, such as Alzheimer’s.
In a new study published in the journal Molecular Therapy, University of Pennsylvania researchers have found a way of traversing the blood-brain barrier, as well as a similar physiological obstacle in the eye, the retinal-blood barrier. By pairing a receptor that targets neurons with a molecule that degrades the main component of Alzheimer’s plaques, the biologists were able to substantially dissolve these plaques in mice brains and human brain tissue, offering a potential mechanism for treating the debilitating disease, as well as other conditions that involve either the brain or the eyes.
The work was led by Henry Daniell, a professor in Penn’s School of Dental Medicine’s departments of biochemistry and pathology and director of translational research. The research team included Penn Dental Medicine’s Neha Kohli, Donevan R. Westerveld, Alexandra C. Ayache and Sich L. Chan. Co-authors at the University of Florida College of Medicine, including Amrisha Verma, Pollob Shil, Tuhina Prasad, Ping Zhu and Quihong Li, analyzed retinal tissues.
The researchers began their work by considering how they might breach the blood-brain barrier. Daniell hypothesized that a molecule might be permitted to cross if it was attached to a carrier that is able to pass over, as a sort of molecular crossing guard. The protein cholera toxin B, or CTB, a non-toxic carrier currently approved for use in humans by the Food and Drug Administration, is used in this study to traverse the blood-brain barrier.
They next identified a protein that could clear the plaques that are found in the brains of Alzheimer’s patients. These plaques, which are believed to cause the dementia associated with the disease, are made up of tangles of amyloid beta (Aβ), a protein that is found in soluble form in healthy individuals. Noting that myelin basic protein (MBP) has been shown to degrade Aβ chains, the team decided to couple it with CTB to see if MBP would be permitted to cross.
“These tangles of beta amyloid are known to be the problem in Alzheimer’s,” says Daniell. “So our idea was to chop the protein back to their normal size so they wouldn’t form these tangles.”
To test this idea, the Penn-led team first exposed healthy mice to the CTB-MBP compound by feeding them capsules of freeze-dried leaves that had been genetically engineered to express the fused proteins, a method developed and perfected by Daniell over many years as a means of orally administering various drugs and vaccines. Adding a green-fluorescent protein to the CTB carrier, the researchers tracked the “glow” to see where the mice took up the protein. They found the glowing protein in both the brain and retina.
“When we found the glowing protein in the brain and the retina we were quite thrilled,” said Daniell. “If the protein could cross the barrier in healthy mice, we thought it was likely that it could cross in Alzheimer’s patients brains, because their barrier is somewhat impaired.”
When CTB was not part of the fused protein, they did not see this expression, suggesting that their carrier protein, the crossing guard, was an essential part of delivering their protein of interest.
To then see what MBP would do once it got to the brain, Daniell and colleagues exposed the CTB-MBP protein to the brains of mice bred to have an Alzheimer’s disease. They used a stain that binds to the brain plaques and found that exposure to the CTB-MBP compound resulted in reductions of staining up to 60 percent, indicating that the plaques were dissolving.
Gaining confidence that their compound was appropriately targeting the plaques, the researchers worked with the National Institutes of Health to obtain brain tissue from people who died of Alzheimer’s and performed the same type of staining. Their results showed a 47 percent decrease in staining in the inferior parietal cortex, a portion of the brain found to play an important role in the development of Alzheimer’s-associated dementia.
As a final step, the researchers fed the CTB-MBP-containing capsules to 15-month-old mice, the equivalent of 80 or more human years, bred to develop Alzheimer’s disease. After three months of feeding, the mice had reductions in Aβ plaques of up to 70 percent in the hippocampus and up to 40 percent in the cortex, whereas mice fed capsules that contained lettuce leaves without CTB-MBP added and mice that were not fed any capsules did not have any reduction in evidence of brain plaques.
Because Alzheimer’s patients have also been found to have plaques in their eyes, the researchers examined the eyes of the mice fed the protein. They found that, indeed, the Alzheimer’s-mice did have retinal plaques, but those fed the CBP-MBP compound had undetectable Aβ plaques in their retinae.
“Really no one knows whether the memory problems that people who have Alzheimer’s disease are due to the dementia or problems with their eyes,” Daniell said. “Here we show it may be both, and that we can dissolve the plaques through an oral route.”
Daniell hopes that this technique of delivering proteins across the blood-brain and blood-retina barriers could serve to treat a variety of diseases beyond Alzheimer’s. Several current clinical trials have failed because of an inability to deliver drugs to the brain. Currently, treatments of some eye conditions must physically penetrate the retina with an injection, an approach that requires anesthesia and risks retinal detachment. Treatment with an ingestible capsule would be safer, easier, and more cost-effective.
As a next step, Daniell hopes to collaborate with Alzheimer’s experts at Penn to advance these studies and add a behavioral component to determine whether the CBP-MBP compound not only removes plaques but also improves the memory and functioning of mice with the Alzheimer’s disease.