Posts Tagged ‘neurodegeneration’

New evidence suggests a mechanism by which progressive accumulation of Tau protein in brain cells may lead to Alzheimer’s disease. Scientists studied more than 600 human brains and fruit fly models of Alzheimer’s disease and found the first evidence of a strong link between Tau protein within neurons and the activity of particular DNA sequences called transposable elements, which might trigger neurodegeneration. The study appears in the journal Cell Reports.

“One of the key characteristics of Alzheimer’s disease is the accumulation of Tau protein within brain cells, in combination with progressive cell death,” said corresponding author Dr. Joshua Shulman, associate professor of neurology, neuroscience and molecular and human genetics at Baylor College of Medicine and investigator at the Jan and Dan Duncan Neurological Research Institute at Texas Children’s Hospital. “In this study we provide novel insights into how accumulation of Tau protein may contribute to the development of Alzheimer’s disease.”

Although scientists have studied for years what happens when Tau forms aggregates inside neurons, it still is not clear why brain cells ultimately die. One thing that scientists have noticed is that neurons affected by Tau accumulation also appear to have genomic instability.

“Genomic instability refers to an increased tendency to have alterations in the genetic material, DNA, such as mutations or other impairments. This means that the genome is not functioning correctly. Genomic instability is known to be a major driving force behind other diseases such as cancer,” Shulman said. “Our study focused on a new possible causal connection between Tau accumulation within neurons and the resulting genomic instability in Alzheimer’s disease.”

Enter transposable elements
Previous studies of brain tissues from patients with other neurologic diseases and of animal models have suggested that the neurons not only present with genomic instability, but also with activation of transposable elements.

“Transposable elements are short pieces of DNA that do not seem to contribute to the production of proteins that make cells function. They behave in a way similar to viruses; they can make copies of themselves that are inserted within the genome and this can create mutations that lead to disease,” Shulman said. “Although most transposable elements are dormant or dysfunctional, some may become active in human brains late in life or in disease. That’s what led us to look specifically at Alzheimer’s disease and the possible association between Tau accumulation and activated transposable elements.”

Shulman and his colleagues began their investigations by studying more than 600 human brains from a population study run by co-author Dr. David Bennett at Rush University Medical Center in Chicago. This population study follows participants throughout their lives and at death, allowing the researchers to examine their brains in detail postmortem. One of the evaluations is the amount of Tau accumulation across many brain regions. In addition, co-author Dr. Philip De Jager at the Broad Institute and Columbia University comprehensively profiled gene expression in the same brains.

“With this large amount of data, we looked to identify signatures of active transposable elements, but this was not easy,” Shulman said. “We therefore reached out to Dr. Zhandong Liu, a co-author in this study, and together we developed a new software tool to detect signatures of active transposable elements from postmortem human brains. Then we conducted a statistical analysis in which we compared the amount of active transposable elements signatures with the amount of Tau accumulation, brain by brain.” Liu also is assistant professor of pediatrics – neurology at Baylor and a member of the Dan L Duncan Comprehensive Cancer Center.

The researchers found a strong link between the amount of Tau accumulation in neurons and detectable activity of transposable elements.

“We identified individual transposable elements that were active when Tau aggregates were present. Surprisingly, we also found evidence that the activation of transposable elements was quite broad across the genome,” Shulman said.

Other research has shown that Tau may disrupt the tightly packed architecture of the genome. It is believed that tightly packed DNA limits gene activation, while opening up the DNA may promote it. Keeping the DNA tightly packed may be an important mechanism to suppress the activity of transposable elements that lead to disease.

“The fact that Tau aggregates can affect that architecture of the genome may be one possible mechanism by which transposable elements are activated in Alzheimer’s disease,” Shulman said. “However, our studies in human brains only establish an association between Tau accumulation and activation of transposable elements. To determine whether Tau accumulation could in fact cause transposable element activation, we conducted studies with a fruit fly model of Alzheimer’s disease.”

In this fruit fly model of the disease, the researchers found that triggering Tau changes similar to those observed in human brains resulted in the activation of fruit fly transposable elements, strongly suggesting that Tau aggregates that disrupt the architecture of the genome can potentially mediate the activation of transposable elements and ultimately cause neurodegeneration.

“We think our experiments reveal new and potentially important insights relevant for understanding Alzheimer’s disease mechanisms,” Shulman said. “There is still a lot of work to be done, but by presenting our results we hope we can stimulate others in the research community to help work on this problem.”

https://www.bcm.edu/news/neurology/research-links-tau-aggregates-cell-death

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The majority of the cells in the brain are no neurons, but Glia (from “glue”) cells, that support the structure and function of the brain. Astrocytes (“start cells”) are star-shaped glial cells providing many supportive functions for the neurons surrounding them, such as the provision of nutrients and the regulation of their chemical environment. Newer studies showed that astrocytes also monitor and modulate neuronal activity. For example, these studies have shown that astrocytes are necessary for the ability of neurons to change the strength of the connections between them, the process underlying learning and memory, and indeed astrocytes are also necessary for normal cognitive function. However, it is still unknown whether astrocytic activity is only necessary, or is it may also be sufficient to induce synaptic potentiation and enhance cognitive performance.

In a new study published in Cell, two graduate students, Adar Adamsky and Adi Kol, from Inbal Goshen’s lab, employed chemogenetic and optogenetic tools that allow specific activation of astrocytes in behaving mice, to explore their role in synaptic activity and memory performance. They found that astrocytic activation in the hippocampus, a brain region that plays an important role in memory acquisition and consolidation, potentiated the synaptic connections in this region, measured in brain slices. Moreover, in the intact brain, astrocytic activation enhanced hippocampal neuronal activity in a task-dependent way: i.e. only during when it was combined with memory acquisition, but not when mice were at their home cage with no meaningful stimuli. The ability of astrocytes to increase neuronal activity during memory acquisition had a significant effect on cognitive function: Specifically, astrocytic activation during learning resulted in enhanced memory in two memory tests. In contrast, direct neuronal activation in the hippocampus induced a non-selective increase in activity (during learning or in the home cage), and thus resulted in drastic memory impairment.

The results suggest that the memory enhancement induced by astrocytic activation during learning is not simply a result of a general increase in hippocampal neuronal activity. Rather, the astrocytes, which sense and respond to changes in the surrounding neuronal activity, can detect and specifically enhance only the neuronal activity involved in learning, without affecting the general activity. This may explain why general astrocytic activation improves memory performance, whereas a similar activation of neurons impairs it.

Memory is not a binary process (remember/don’t remember); the strength of a memory can vary greatly, either for the same memory or between different memories. Here, we show that activating astrocytes in mice with intact cognition improves their memory performance. This finding has important clinical implications for cognitive augmentation treatments. Furthermore, the ability of astrocytes to strengthen neuronal communication and improve memory performance supports the claim that astrocytes are able to take an active part in the neuronal processes underlying cognitive function. This perspective expands the definition of the role of astrocytes, from passive support cells to active cells that can modulate neural activity and thus shape behavior.

Link: https://www.cell.com/cell/pdf/S0092-8674(18)30575-0.pdf

https://elsc.huji.ac.il/content/article-month-june-2018-goshens-lab

Psychologists at the University of Sussex have found a link between depression and an acceleration of the rate at which the brain ages. Although scientists have previously reported that people with depression or anxiety have an increased risk of dementia in later life, this is the first study that provides comprehensive evidence for the effect of depression on decline in overall cognitive function (also referred to as cognitive state), in a general population.

For the study, published today, Thursday 24 May 2018, in the journal Psychological Medicine, researchers conducted a robust systematic review of 34 longitudinal studies, with the focus on the link between depression or anxiety and decline in cognitive function over time. Evidence from more than 71,000 participants was combined and reviewed. Including people who presented with symptoms of depression as well as those that were diagnosed as clinically depressed, the study looked at the rate of decline of overall cognitive state – encompassing memory loss, executive function (such as decision making) and information processing speed – in older adults.

Importantly, any studies of participants who were diagnosed with dementia at the start of study were excluded from the analysis. This was done in order to assess more broadly the impact of depression on cognitive ageing in the general population. The study found that people with depression experienced a greater decline in cognitive state in older adulthood than those without depression. As there is a long pre-clinical period of several decades before dementia may be diagnosed, the findings are important for early interventions as currently there is no cure for the disease.

Lead authors of the paper, Dr Darya Gaysina and Amber John from the EDGE (Environment, Development, Genetics and Epigenetics in Psychology and Psychiatry) Lab at the University of Sussex, are calling for greater awareness of the importance of supporting mental health to protect brain health in later life.

Dr Gaysina, a Lecturer in Psychology and EDGE Lab Lead, comments: “This study is of great importance – our populations are ageing at a rapid rate and the number of people living with decreasing cognitive abilities and dementia is expected to grow substantially over the next thirty years.

“Our findings should give the government even more reason to take mental health issues seriously and to ensure that health provisions are properly resourced. We need to protect the mental wellbeing of our older adults and to provide robust support services to those experiencing depression and anxiety in order to safeguard brain function in later life.”

Researcher Amber John, who carried out this research for her PhD at the University of Sussex adds: “Depression is a common mental health problem – each year, at least 1 in 5 people in the UK experience symptoms. But people living with depression shouldn’t despair – it’s not inevitable that you will see a greater decline in cognitive abilities and taking preventative measures such as exercising, practicing mindfulness and undertaking recommended therapeutic treatments, such as Cognitive Behaviour Therapy, have all been shown to be helpful in supporting wellbeing, which in turn may help to protect cognitive health in older age.”

The research paper, ‘Affective problems and decline in cognitive state in older adults’ will be available at: https:// doi.org/10.1017/S0033291718001137 from Thursday 24 May 2018.

http://www.sussex.ac.uk/broadcast/read/44977

by Leigh Hopper

Tnew stroke-healing gel created by UCLA researchers helped regrow neurons and blood vessels in mice whose brains had been damaged by strokes. The finding is reported May 21 in Nature Materials.

“We tested this in laboratory mice to determine if it would repair the brain and lead to recovery in a model of stroke,” said Dr. S. Thomas Carmichael, professor of neurology at the David Geffen School of Medicine at UCLA. “The study indicated that new brain tissue can be regenerated in what was previously just an inactive brain scar after stroke.”

The results suggest that such an approach could some day be used to treat people who have had a stroke, said Tatiana Segura, a former professor of chemical and biomolecular engineering at UCLA who collaborated on the research. Segura is now a professor at Duke University.

The brain has a limited capacity for recovery after stroke. Unlike the liver, skin and some other organs, the brain does not regenerate new connections, blood vessels or tissue structures after it is damaged. Instead, dead brain tissue is absorbed, which leaves a cavity devoid of blood vessels, neurons or axons — the thin nerve fibers that project from neurons.

To see if healthy tissue surrounding the cavity could be coaxed into healing the stroke injury, Segura engineered a hydrogel that, when injected into the cavity, thickens to create a scaffolding into which blood vessels and neurons can grow. The gel is infused with medications that stimulate blood vessel growth and suppress inflammation, since inflammation results in scars and impedes functional tissue from regrowing.

After 16 weeks, the stroke cavities contained regenerated brain tissue, including new neuronal connections — a result that had not been seen before. The mice’s ability to reach for food improved, a sign of improved motor behavior, although the exact mechanism for the improvement wasn’t clear.

“The new axons could actually be working,” Segura said. “Or the new tissue could be improving the performance of the surrounding, unharmed brain tissue.”

The gel was eventually absorbed by the body, leaving behind only new tissue.

The research was designed to explore recovery in acute stroke, the period immediately following a stroke — in mice, that period lasts five days; in humans, it’s two months. Next, Carmichael and Segura plan to investigate whether brain tissue can be regenerated in mice long after the stroke injury. More than 6 million Americans are living with long-term effects of stroke, which is known as chronic stroke.

The other authors of the paper are Lina Nih and Shiva Gojgini, both of UCLA.

The study was supported by the National Institutes of Health.

http://newsroom.ucla.edu/releases/biomaterial-ucla-regrow-brain-tissue-after-stroke-mice

Scientists have just discovered that a small region of a cellular protein that helps long-term memories form also drives the neurodegeneration seen in motor neuron disease (MND). This small part of the Ataxin-2 protein thus works for good and for bad. When a version of the protein lacking this region was substituted for the normal form in fruit flies (model organisms), the animals could not form long-term memories – but, surprisingly, the same flies showed a remarkable resistance to neurodegeneration.

The popular “ice bucket challenge” highlighted the social significance of MND, as well as the need to better understand and treat neurodegenerative conditions. This new research identifies a very specific basic mechanism that facilitates progression of neuronal loss in an animal model of MND, and, by shedding light on a potential way to protect against cell death in MND, it should inform strategies for the development of therapeutics to treat or manage these devastating conditions, which are currently incurable.

The Science Foundation Ireland-funded research, involving scientists from the Trinity College Institute of Neuroscience, NCBS Bangalore and HMMI, University of Colorado, Boulder, has just been published in the leading international journal Neuron.

Professor of Neurogenetics at Trinity College Dublin, Mani Ramaswami, said: “This work, by collaborating young researchers based in Irish, Indian and American laboratories, provides a great example of the ability of fundamental research in model organisms to produce biologically and clinically interesting information.”

A common feature of neurodegenerative diseases is the presence of specific protein aggregates in nerve cells, which accumulate and clump together — usually as protein fibres called amyloid filaments. Such aggregates are believed to trigger processes that cause the neuronal death associated with these debilitating diseases. For example, amyloid-beta (Aβ) aggregates are associated with Alzheimer’s disease, while TDP-43, FUS and Ataxin-2 proteins are commonly found in MND patients.

The scientists behind the current study set out to test this “amyloid hypothesis” to see whether it may explain how MND develops. The scientists genetically engineered fruit flies with mutations designed to reduce Ataxin-2 protein assembly into aggregates without affecting other functions of the protein.

Arnas Petrauskas, Trinity, said: “The flies with this altered, non-aggregating version of the protein showed a striking resistance to neurodegeneration. This suggests the normal Ataxin-2 protein and its ability to form aggregates is required for the progression of at least some forms of MND, which means these results provide support for the amyloid hypothesis.”

“What really surprised us though was that this same protein region seems to be required for the flies to develop long-term memory, as those with the altered version of Ataxin-2 showed normal short-term but defective long-term memories.”

Fruit flies normally respond strongly to new odorants, but weakly to familiar odorants through a process called habituation. This memory of the familiar can be of the short-term kind – to an odorant encountered for half-an-hour, or of the long-term kind, to odorants encountered for days (think of it as remembering a phone number of a new acquaintance versus remembering your own phone number). Flies lacking this small domain of Ataxin-2 showed greatly reduced long-term memory.

So how is long-term memory formation and disease progression connected? It turns out that proteins like the TDP-43, FUS and Ataxin-2 found in MND are also involved in the natural control and management of protein expression in the cell. The very same region of Ataxin-2 is needed to form RNP granules that store RNAs (essentially blueprints, or recipes for specific proteins) in a silent form until they are unpackaged by a signal and used to produce molecules when they are required. This local control of RNAs is required for long-term changes at neuronal synapses that underlie long-term memory.

The new discovery shows that Ataxin-2 concentrates several RNA-binding proteins used in the process of memory storing, but in doing so, it creates a biological environment that can help these proteins aggregate into disease-causing amyloids. A “trade-off” therefore exists in nature where the Ataxin-2 gene increases the danger of neurodegeneration, but helps our cells control RNA and form long-term memories.

In a commentary on the research published in the same issue of the journal Neuron, Aaron Gitler, Professor of Genetics in the Stanford Neuroscience Institute, an independent expert in MND research said: “This data suggest that manipulating RNP granule formation by genetically manipulating ataxin-2’s IDRs, or by other means could be therapeutic in ALS. Beyond ataxin-2, the race is now on to discover additional proteins that help build RNP granules.”

https://www.tcd.ie/news_events/articles/link-between-long-term-memory-and-neurodegenerative-disease/8941

Brown University researchers studying the biology of aging have demonstrated a new strategy for stimulating autophagy, the process by which cells rebuild themselves by recycling their own worn-out parts.

In a study published in the journal Cell Reports, the researchers show that the approach increased the lifespans of worms and flies, and experiments in human cells hint that the strategy could be useful in future treatments for Alzheimer’s disease, ALS and other age-related neurodegenerative conditions.

“Autophagy dysfunction is present across a range of age-related diseases including neurodegeneration,” said Louis Lapierre, an assistant professor of molecular biology, cell biology and biochemistry at Brown who led the work. “We and others think that by learning how to influence this process pharmacologically, we might be able to affect the progression of these diseases. What we’ve shown here is a new and conserved entry point for stimulating autophagy.”

Autophagy has become a hot topic in recent years, earning its discoverer the Nobel Prize in Physiology and Medicine in 2016. The process involves the rounding up of misfolded proteins and obsolete organelles within a cell into vesicles called autophagosomes. The autophagosomes then fuse with a lysosome, an enzyme-containing organelle that breaks down those cellular macromolecules and converts it into components the cell can re-use.

Lapierre and his colleagues wanted to see if they could increase autophagy by manipulating a transcription factor (a protein that turns gene expression on and off) that regulates autophagic activity. In order for the transcription factor to switch autophagic activity on, it needs to be localized in the nucleus of a cell. So Lapierre and his team screened for genes that enhance the level of the autophagy transcription factor, known as TFEB, within nuclei.

Using the nematode C. elegans, the screen found that reducing the expression of a protein called XPO1, which transports proteins out of the nucleus, leads to nuclear accumulation of the nematode version of TFEB. That accumulation was associated with an increase in markers of autophagy, including increased autophagosome, autolysosomes as well as increased lysosome biogenesis. There was also a marked increase in lifespan among the treated nematodes of between about 15 and 45 percent.

“What we showed was that by blocking the escape of this transcription factor from the nucleus, we could not only influence autophagy but we could get an increase in lifespan as well,” Lapierre said.

The next step was to see if there were drugs that could mimic the effect of the gene inhibition used in the screening experiment. The researchers found that selective inhibitors of nuclear export (SINE), originally developed to inhibit XPO1 to treat cancers, had a similar effect — increasing markers of autophagy and significantly increasing lifespan in nematodes.

The researchers then tested SINE on a genetically modified fruit fly that serves as a model organism for the neurodegenerative disease ALS. Those experiments showed a small but significant increase in the lifespans of the treated flies. “Our data suggests that these compounds can alleviate some of the neurodegeneration in these flies,” Lapierre said.

As a final step, the researchers set out to see if XPO1 inhibition had similar effects on autophagy in human cells as it had in the nematodes. After treating a culture of human HeLa cells with SINE, the researchers found that, indeed, TFEB concentrations in nuclei increased, as did markers of autophagic activity and lysosomal biogenesis.

“Our study tells us that the regulation of the intracellular partitioning of TFEB is conserved from nematodes to humans and that SINE could stimulate autophagy in humans,” Lapierre said. “SINE have been recently shown in clinical trials for cancer to be tolerated, so the potential for using SINE to treat other age-related diseases is there.”

Future research, Lapierre said, will focus on testing these drugs in more clinically relevant models of neurodegenerative diseases. But this initial research is a proof of concept for this strategy as a means to increase autophagy and potentially treat age-related diseases.

Lapierre is a faculty member in the newly approved Center on the Biology of Aging within the Brown Institute for Translational Science. This center, led by Professor of Biology John Sedivy, studies the biological mechanisms of aging. The center’s mission is to expand biomedical research and education programs in the emerging discipline of biogerontology, and to bring forth scientific discoveries related to aging and associated disorders.

A study by scientists of the German Center for Neurodegenerative Diseases (DZNE) points to a novel potential approach against Alzheimer’s disease. In studies in mice, the researchers were able to show that blocking a particular receptor located on astrocytes normalized brain function and improved memory performance. Astrocytes are star-shaped, non-neuronal cells involved in the regulation of brain activity and blood flow. The findings are published in the Journal of Experimental Medicine (JEM).

Alzheimer’s disease is a common and currently incurable brain disorder leading to dementia, whose mechanisms remain incompletely understood. The disease appears to be sustained by a combination of factors that include pathological changes in blood flow, neuroinflammation and detrimental changes in brain cell activity.

“The brain contains different types of cells including neurons and astrocytes”, explains Dr. Nicole Reichenbach, a postdoc researcher at the DZNE and first author of the paper published in JEM. “Astrocytes support brain function and shape the communication between neurons, called synaptic transmission, by releasing a variety of messenger proteins. They also provide metabolic and structural support and contribute to the regulation of blood flow in the brain.”

Glitches in network activity

Similar to neurons, astrocytes are organized into functional networks that may involve thousands of cells. “For normal brain function, it is crucial that networks of brain cells coordinate their firing rates. It’s like in a symphony orchestra where the instruments have to be correctly tuned and the musicians have to stay in synchrony in order to play the right melody”, says Professor Gabor Petzold, a research group leader at the DZNE and supervisor of the current study. “Interestingly, one of the main jobs of astrocytes is very similar to this: to keep neurons healthy and to help maintain neuronal network function. However, in Alzheimer’s disease, there is aberrant activity of these networks. Many cells are hyperactive, including neurons and astrocytes. Hence, understanding the role of astrocytes, and targeting such network dysfunctions, holds a strong potential for treating Alzheimer’s.”

Astrocyte-targeted treatment alleviated memory impairment

Petzold and colleagues tested this approach in an experimental study involving mice. Due to a genetic disposition, these rodents exhibited certain symptoms of Alzheimer’s similar to those that manifest in humans with the disease. In the brain, this included pathological deposits of proteins known as “Amyloid-beta plaques” and aberrant network activity. In addition, the mice showed impaired learning ability and memory.

In their study, the DZNE scientists targeted a cell membrane receptor called P2Y1R, which is predominately expressed by astrocytes. Previous experiments by Petzold and colleagues had revealed that activation of this receptor triggers cellular hyperactivity in mouse models of Alzheimer’s. Therefore, the researchers treated groups of mice with different P2Y1R antagonists. These chemical compounds can bind to the receptor, thus switching it off. The treatment lasted for several weeks.

“We found that long-term treatment with these drugs normalized the brain’s network activity. Furthermore, the mice’s learning ability and memory greatly improved”, Petzold says. On the other hand, in a control group of wild type mice this treatment had no significant effect on astrocyte activity. “This indicates that P2Y1R inhibition acts quite specifically. It does not dampen network activity when pathological hyperactivity is absent.”

New approaches for research and therapies?

Petzold summarizes: “This is an experimental study that is currently not directly applicable to human patients. However, our results suggest that astrocytes, as important safeguards of neuronal health and normal network function, may hold the potential for novel treatment options in Alzheimer’s disease.” In future studies, the scientists intend to identify additional novel pathways in astrocytes and other cells as potential drug targets.

Reference:
Reichenbach, N., Delekate, A., Breithausen, B., Keppler, K., Poll, S., Schulte, T., . . . Petzold, G. C. (2018). P2Y1 receptor blockade normalizes network dysfunction and cognition in an Alzheimer’s disease model. The Journal of Experimental Medicine. doi:10.1084/jem.20171487

https://www.dzne.de/en/news/public-relations/press-releases/press/detail/the-brains-rising-stars-new-options-against-alzheimers/