Alzheimer risk genes converge on microglia
March 18, 2020
Science Daily/VIB (the Flanders Institute for Biotechnology)
Our DNA determines a large part of our risk for Alzheimer's disease, but it remained unclear how many genetic risk factors contribute to disease. A team led by Prof. Bart De Strooper (VIB-KU Leuven) and Dr. Mark Fiers now show that many of risk factors affect brain maintenance cells called microglia, and more particularly their response to amyloid-beta, one of the proteins aggregating in the brains of Alzheimer patients. The individual effects of small genetic variations are likely small, but the combination of hundreds of such subtle alterations might tip the balance and cause disease.
Why do some people get Alzheimer's disease while others do not, even when growing very old? Despite decades of research, we still don't know the full answer to this question. Epidemiological studies show that about two-thirds of a person's risk for Alzheimer's disease is genetically determined. A few dozen risk genes have been identified, however, recent evidence shows that there could be hundreds of additional genetic variants that each contribute in a small but significant way to disease risk.
From risk gene to disease mechanism
Bart De Strooper (VIB-KU Leuven) has been studying the mechanisms of Alzheimer's disease for decades. His team tries to find out what this combined genetic risk can teach us about how the disease develops in our brain: "Two crucial questions arise from the myriad of genetic studies. First, what is the link between these Alzheimer risk genes and the amyloid-beta plaques or tau tangles we find in Alzheimer brains; and second, are they all involved in one central cellular or molecular pathway, or do they define many parallel pathways that all lead to Alzheimer's?"
The researchers set out to understand when these genes are expressed and in particular, whether they respond to tau or amyloid?beta pathology. "When it comes to risk, you always need to take the context into account," explain Mark Fiers, co-lead author of the study. "If you don't wear your seatbelt in the car, there is no problem as long as you don't have an accident."
With this in mind, the researchers aimed to understand under which circumstances genetic risk for Alzheimer's comes into play. Fiers: "Almost every person develops some degree of Alzheimer pathology in the brain, i.e. amyloid-beta plaques and tau tangles. However, some people remain cognitively healthy despite a high pathology load, while others develop Alzheimer symptoms quite rapidly."
"To gain more insight we checked gene expression in two different mouse models of Alzheimer's, one displaying amyloid-beta and the other tau pathology, at different ages," says Annerieke Sierksma, a postdoctoral researcher in De Strooper's lab. "We identified that many of the genes linked to Alzheimer's risk are particularly responsive to amyloid-beta but not to tau pathology."
Microglia activation
The team identified 11 new risk genes that are significantly upregulated when facing increased amyloid-beta levels. All these genes are expressed in microglia, cells that play a key role in brain maintenance.
Ashley Lu, a PhD student closely involved in the analysis: "We could confirm that microglia exposed to amyloid-beta drastically switch to an activated status, something that occurs to a much lesser extent in the tau mice. These new insights indicate that a large part of the genetic risk of Alzheimer's disease involves the microglial response to amyloid-beta."
Understanding genetic risk
Should we rethink the classical gene?based view, where certain mutations or genetic variants lead to disease? De Strooper thinks so: "One single genetic variant within a functional network will not lead to disease. However, multiple variants within the same network may tip the balance to a disease?causing disturbance. Such a hypothesis could also explain the conundrum that some /individuals with a lot of amyloid-beta in their brain do not develop clinical symptoms."
"While amyloid-beta might be the trigger of the disease, it is the genetic make?up of the microglia, and possibly other cell types, which determines whether a pathological response is induced," adds Fiers. "Identifying which genetic variants are crucial to such network disturbances and how they lead to altered gene expression will be the next big challenge."
Why mice?
"Profiling of postmortem brain tissue only provides insights into the advanced stages of the disease and does not allow to delineate cause-consequence relationships," explains De Strooper. "Genetically modified mouse models on the other hand only partially recapitulate the disease, but they allow for detailed insights into the initial steps of disease, which is of high relevance for preventative therapeutic interventions."
https://www.sciencedaily.com/releases/2020/03/200318104501.htm
How a protein in your brain could protect against Alzheimer's disease
New research sets the stage for new therapeutic strategies for Alzheimer's disease
December 13, 2019
University of Alberta
Research shows that white blood cells in the human brain are regulated by a protein called CD33--a finding with important implications in the fight against Alzheimer's disease, according to a new study.
"Immune cells in the brain, called microglia, play a critical role in Alzheimer's disease," explained Matthew Macauley, assistant professor in theDepartment of Chemistry and co-author on the paper. "They can be harmful or protective. Swaying microglia from a harmful to protective state could be the key to treating the disease."
Scientists have identified the CD33 protein as a factor that may decrease a person's likelihood of Alzheimer's disease. Less than 10 percent of the population have a version of CD33 that makes them less likely to get Alzheimer's disease. "The fact that CD33 is found on microglia suggests that immune cells can protect the brain from Alzheimer's disease under the right circumstances," said Abhishek Bhattacherjee, first author and postdoctoral fellow in the Macauley lab.
Now, Macauley's research shows that the most common type of CD33 protein plays a crucial role in modulating the function of microglia.
"These findings set the stage for future testing of a causal relationship between CD33 and Alzheimer's Disease, as well as testing therapeutic strategies to sway microglia from harmful to protecting against the disease -- by targeting CD33," said Macauley. "Microglia have the potential to 'clean up' the neurodegenerative plaques, through a process called phagocytosis -- so a therapy to harness this ability to slow down or reverse Alzheimer's disease can be envisioned."
Macauley is an investigator with GlycoNet, a Canada-wide network of researchers based at the University of Alberta that is working to further our understanding of biological roles for sugars. GlycoNet provided key funding to get this project off the ground in the Macauley lab and continues to support the ongoing applications of the project.
According to the Alzheimer's Association, 747,000 Canadians are currently living with Alzheimer's or another form of dementia. The disease affects more than 44 million people around the world.
https://www.sciencedaily.com/releases/2019/12/191213124921.htm
The night gardeners: Immune cells rewire, repair brain while we sleep
October 21, 2019
Science Daily/University of Rochester Medical Center
Science tells us that a lot of good things happen in our brains while we sleep -- learning and memories are consolidated and waste is removed, among other things. New research shows for the first time that important immune cells called microglia -- which play an important role in reorganizing the connections between nerve cells, fighting infections, and repairing damage -- are also primarily active while we sleep.
The findings, which were conducted in mice and appear in the journal Nature Neuroscience, have implications for brain plasticity, diseases like autism spectrum disorders, schizophrenia, and dementia, which arise when the brain's networks are not maintained properly, and the ability of the brain to fight off infection and repair the damage following a stroke or other traumatic injury.
"It has largely been assumed that the dynamic movement of microglial processes is not sensitive to the behavioral state of the animal," said Ania Majewska, Ph.D., a professor in the University of Rochester Medical Center's (URMC) Del Monte Institute for Neuroscience and lead author of the study. "This research shows that the signals in our brain that modulate the sleep and awake state also act as a switch that turns the immune system off and on."
Microglia serve as the brain's first responders, patrolling the brain and spinal cord and springing into action to stamp out infections or gobble up debris from dead cell tissue. It is only recently that Majewska and others have shown that these cells also play an important role in plasticity, the ongoing process by which the complex networks and connections between neurons are wired and rewired during development and to support learning, memory, cognition, and motor function.
In previous studies, Majewska's lab has shown how microglia interact with synapses, the juncture where the axons of one neuron connects and communicates with its neighbors. The microglia help maintain the health and function of the synapses and prune connections between nerve cells when they are no longer necessary for brain function.
The current study points to the role of norepinephrine, a neurotransmitter that signals arousal and stress in the central nervous system. This chemical is present in low levels in the brain while we sleep, but when production ramps up it arouses our nerve cells, causing us to wake up and become alert. The study showed that norepinephrine also acts on a specific receptor, the beta2 adrenergic receptor, which is expressed at high levels in microglia. When this chemical is present in the brain, the microglia slip into a sort of hibernation.
The study, which employed an advanced imaging technology that allows researchers to observe activity in the living brain, showed that when mice were exposed to high levels of norepinephrine, the microglia became inactive and were unable to respond to local injuries and pulled back from their role in rewiring brain networks.
"This work suggests that the enhanced remodeling of neural circuits and repair of lesions during sleep may be mediated in part by the ability of microglia to dynamically interact with the brain," said Rianne Stowell, Ph.D. a postdoctoral associate at URMC and first author of the paper. "Altogether, this research also shows that microglia are exquisitely sensitive to signals that modulate brain function and that microglial dynamics and functions are modulated by the behavioral state of the animal."
The research reinforces to the important relationship between sleep and brain health and could help explain the established relationship between sleep disturbances and the onset of neurodegenerative conditions like Alzheimer's and Parkinson's.
https://www.sciencedaily.com/releases/2019/10/191021111835.htm
Link between brain immune cells and Alzheimer's disease development identified
Absence of microglia prevents plaque formation
August 21, 2019
Science Daily/University of California - Irvine
Scientists from the University of California, Irvine School of Biological Sciences have discovered how to forestall Alzheimer's disease in a laboratory setting, a finding that could one day help in devising targeted drugs that prevent it.
The researchers found that by removing brain immune cells known as microglia from rodent models of Alzheimer's disease, beta-amyloid plaques -- the hallmark pathology of AD -- never formed. Their study will appear Aug. 21 in the journal Nature Communications.
Previous research has shown most Alzheimer's risk genes are turned on in microglia, suggesting these cells play a role in the disease. "However, we hadn't understood exactly what the microglia are doing and whether they are significant in the initial Alzheimer's process," said Kim Green, associate professor of neurobiology & behavior. "We decided to examine this issue by looking at what would happen in their absence."
The researchers used a drug that blocks microglia signaling that is necessary for their survival. Green and his lab have previously shown that blocking this signaling effectively eliminates these immune cells from the brain. "What was striking about these studies is we found that in areas without microglia, plaques didn't form," Green said. "However, in places where microglia survived, plaques did develop. You don't have Alzheimer's without plaques, and we now know microglia are a necessary component in the development of Alzheimer's."
The scientists also discovered that when plaques are present, microglia perceive them as harmful and attack them. However, the attack also switches off genes in neurons needed for normal brain functioning. "This finding underlines the crucial role of these brain immune cells in the development and progression of Alzheimer's," said Green.
Professor Green and colleagues say their discovery holds promise for creating future drugs that prevent the disease. "We are not proposing to remove all microglia from the brain," Professor Green said, noting the importance of microglia in regulating other brain functions. "What could be possible is devising therapeutics that affect microglia in targeted ways."
He also believes the project's research approach offers an avenue for better understanding other brain disorders.
"These immune cells are involved in every neurological disease and even in brain injury," Professor Green said. "Removing microglia could enable researchers working in those areas to determine the cells' role and whether targeting microglia could be a potential treatment."
https://www.sciencedaily.com/releases/2019/08/190821082236.htm
New way to think about brain's link to postpartum depression
Research in animals shows brain's immune system is activated by stress during pregnancy
October 21, 2019
Science Daily/Ohio State University
Chronic stress during pregnancy triggers an immune response in the brain that has potential to alter brain functions in ways that could contribute to postpartum depression, new research in animals suggests.
The study is the first to show evidence of this gestational stress response in the brain, which is unexpected because the immune system in both the body and the brain is suppressed during a normal pregnancy.
The Ohio State University researchers who made the discovery have been studying the brain biology behind postpartum depression for several years, creating depressive symptoms in pregnant rats by exposing them to chronic stress. Chronic stress during pregnancy is a common predictor of postpartum depression, which is characterized by extreme sadness, anxiety and exhaustion that can interfere with a mother's ability to care for herself or her baby.
Stress is known to lead to inflammation, which prompts an immune response to protect against inflammation's harmful effects. Based on what they already know about compromised brain signaling in rats stressed during pregnancy, the scientists suspect the immune cells in the brain responding to stress may be involved. If that's the case, the immune changes may create circumstances in the brain that increase susceptibility to depression.
In unstressed pregnant rats, the normal suppression of the immune system in the body and the brain remained intact throughout pregnancy. In contrast, stressed rats showed evidence of neuroinflammation. The study also showed that the stressed rats' immune response in the rest of their bodies was not active.
"That suggests there's this disconnect between what's happening in the body and what's happening in the brain," said Benedetta Leuner, associate professor of psychology at Ohio State and lead author of the study. She speculated that the signaling changes her lab has seen before in the brain and this immune response are happening in parallel, and may be directly related.
Leuner presented the findings Saturday (Oct. 19, 2019) at the Society for Neuroscience meeting in Chicago.
In this work, rats are exposed to unpredictable and varied stressful events throughout their pregnancies, a practice that adds a component of psychological stress but does not harm the health of the mother or her offspring.
In the stressed animals, the researchers found numerous pro-inflammatory compounds that indicated there was an increase in the number and activity levels of the primary immune cells in the brain called microglia. Their findings also suggested the microglia were affecting brain cells in the process.
Leuner's lab previously determined in rats that chronic stress during pregnancy prevented motherhood-related increases in dendritic spines, which are hair-like growths on brain cells that are used to exchange information with other neurons. These same rats behaved in ways similar to what is seen in human moms with postpartum depression: They had less physical interaction with their babies and showed depressive-like symptoms.
Leuner and colleagues now plan to see whether the brain immune cells activated during gestational stress are responsible for the dendritic spine elimination. They suspect that microglia might be clearing away synaptic material on dendrites.
Leuner has partnered on this research with Kathryn Lenz, assistant professor of psychology at Ohio State, whose work explores the role of the immune system in brain development.
Though pregnancy was known to suppress the body's immune system, Lenz and Leuner showed in a previous study that the same suppression of the immune system happens in the brain during pregnancy -- the number of microglia in the brain decreases.
"By layering gestational stress onto a normal pregnancy, we're finding this normal immunosuppression that should happen during pregnancy doesn't occur, and in fact there's evidence of inflammatory signaling in the brain that could be bad for dendritic spines and synapses," Lenz said. "But we've also found changes in the microglia's appetite. Every characteristic we've looked at in these cells has changed as a result of this stress."
The researchers are now trying to visualize microglia while they're performing their cleanup to see if they are eating synaptic material. They are also manipulating inflammatory changes in the brain to see if that reverses postpartum depression-like behavior in rats.
"We've seen the depressive-like symptoms and neural changes in terms of dendritic spines and synapses, and now we have neuroimmune changes suggesting that those microglia could be contributing to the neural changes -- which we think ultimately underlie the behaviors," Leuner said.
The research was supported by the National Institutes of Health
https://www.sciencedaily.com/releases/2019/10/191021151538.htm
Call it Mighty Mouse: Breakthrough leaps Alzheimer's research hurdle
Study reveals crucial mechanisms contributing to the disease
July 31, 2019
Science Daily/University of California - Irvine
University of California, Irvine researchers have made it possible to learn how key human brain cells respond to Alzheimer's, vaulting a major obstacle in the quest to understand and one day vanquish it. By developing a way for human brain immune cells known as microglia to grow and function in mice, scientists now have an unprecedented view of crucial mechanisms contributing to the disease.
The team, led by Mathew Blurton-Jones, associate professor of neurobiology & behavior, said the breakthrough also holds promise for investigating many other neurological conditions such as Parkinson's, traumatic brain injury, and stroke. The details of their study have just been published in the journal Neuron.
The scientists dedicated four years to devising the new rodent model, which is considered "chimeric." The word, stemming from the mythical Greek monster Chimera that was part goat, lion and serpent, describes an organism containing at least two different sets of DNA.
To create the specialized mouse, the team generated induced pluripotent stem cells, or iPSCs, using cells donated by adult patients. Once created, iPSCs can be turned into any other type of cell. In this case, the researchers coaxed the iPSCs into becoming young microglia and implanted them into genetically-modified mice. Examining the rodents several months later, the scientists found about 80-percent of the microglia in their brains was human, opening the door for an array of new research.
"Microglia are now seen as having a crucial role in the development and progression of Alzheimer's," said Blurton-Jones. "The functions of our cells are influenced by which genes are turned on or off. Recent research has identified over 40 different genes with links to Alzheimer's and the majority of these are switched on in microglia. However, so far we've only been able to study human microglia at the end stage of Alzheimer's in post-mortem tissues or in petri dishes."
In verifying the chimeric model's effectiveness for these investigations, the team checked how its human microglia reacted to amyloid plaques, protein fragments in the brain that accumulate in people with Alzheimer's. They indeed imitated the expected response by migrating toward the amyloid plaques and surrounding them.
"The human microglia also showed significant genetic differences from the rodent version in their response to the plaques, demonstrating how important it is to study the human form of these cells," Blurton-Jones said.
"This specialized mouse will allow researchers to better mimic the human condition during different phases of Alzheimer's while performing properly-controlled experiments," said Jonathan Hasselmann, one of the two neurobiology & behavior graduate students involved in the study. Understanding the stages of the disease, which according to the Alzheimer's Association can last from two to 20 years, has been among the challenges facing researchers.
Neurobiology & behavior graduate student and study co-author Morgan Coburn said: "In addition to yielding vital information about Alzheimer's, this new chimeric rodent model can show us the role of these important immune cells in brain development and a wide range of neurological disorders."
https://www.sciencedaily.com/releases/2019/07/190731125448.htm
Raising eyebrows on neuroinflammation: Study finds novel role for 'skin plumping' molecule
Neuroscientists identify surprising brain action of cartilage component hyaluronic acid
July 11, 2019
Science Daily/Florida Atlantic University
Scientists have discovered a novel mechanism and role in the brain for hyaluronic acid -- a clear, gooey substance popularized by cosmetic and skin care products. Hyaluronic acid may be the key in how an immune signal moves from the blood stream to the brain, activating the brain's resident immune cells, the microglia. Findings from this study have important implications for better treatments for stroke, neurodegenerative diseases, as well as head injuries.
This clear, gooey substance, which is naturally produced by the human body, has been popularized by cosmetic and skin care products that promote healthier, plumper and more supple skin. Also recognized for its abilities to speed up wound healing, reduce joint pain from osteoarthritis, and relieve dry eye and discomfort, a neuroscientist at Florida Atlantic University's Brain Institute (I-BRAIN) and Schmidt College of Medicine, has discovered a novel mechanism and role in the brain for hyaluronic acid.
In a study published in the journal Brain, Behavior and Immunity, Ning Quan, Ph.D., lead author, a professor of biomedical science in FAU's Schmidt College of Medicine and a member of I-BRAIN, and collaborators, have discovered that hyaluronic acid may be the key in how an immune signal moves from the blood stream to the brain, activating the brain's resident immune cells, the microglia.
This unsuspected molecule may be the main signal passed between these cells, and this new discovery could lead to novel opportunities to shut down brain inflammatory responses. Findings from this study have important implications for better treatments for stroke, neurodegenerative diseases, as well as head injuries.
"We normally think of hyaluronic acid with respect to cartilage formation and also for its role in many processes including cancer progression and metastasis," said Quan. "However, what we have uncovered in our study is a completely unique role for this molecule. We have been able to document a connection between the blood cells and the brain cells, showing that the activating signal passed between these cells is hyaluronic acid."
Quan and collaborators from the Sichuan University, The Ohio State University, and the University of Illinois Urbana-Champaign, demonstrate that inflammation in the central nervous system is oftentimes quenched or restricted, as neurons are extremely vulnerable to inflammation-caused damages. However, this inflammation can be aberrantly amplified through endothelial cell-microglia crosstalk when the brain constantly receives inflammatory signals. Quan's work identified hyaluronic acid as the key signal released by endothelial cells to stimulate microglia and promote oxidative damage.
"To prevent the inflammation from being intensified in the brain, you have to stop the communication between the two cell types," said Xiaoyu Liu, Ph.D., another corresponding author of the study in FAU's Schmidt College of Medicine and I-BRAIN. "We found ascorbyl palmitate, also known as 'Vitamin C Ester,' to be quite effective in inhibiting microglia and reducing the production of inflammatory hyaluronic acid."
In the past, Vitamin C Ester has been widely used as a source of vitamin C and an antioxidant food additive. Now, this latest discovery suggests a novel function of Vitamin C Ester: treating central nervous system inflammation.
"As the newest addition to our Department of Biomedical Science, Dr. Quan's work already is making an important impact on our mission to advance understanding of human health and disease," said Janet Robishaw, Ph.D., senior associate dean for research and chair of the Department of Biomedical Science in FAU's Schmidt College of Medicine. "Long known as a popular skin and joint supplement, this discovery identifies a novel role for hyaluronic acid to potentially treat conditions caused by inflammation in the central nervous system."
Inflammation can occur in the central nervous system as a result of head trauma or stroke, or as part of a systemic immune response. Inflammation within the central nervous system has been associated with chronic neurodegenerative diseases including Alzheimer's disease, Parkinson's disease and multiple sclerosis.
"Neurological disorders such as Parkinson's disease and Alzheimer's disease impact all races, genders, and geographical backgrounds," said Randy Blakely, Ph.D., executive director of FAU's I-BRAIN. "Findings from this study may thus have global implications for how we treat neurodegeneration arising from traumatic brain injuries and brain changes associated with aging and dementia. This exceptional research by Dr. Quan and his colleagues is a testament to the cutting-edge work that is being conducted by our Brain Institute members and the research faculty in FAU's Schmidt College of Medicine."
https://www.sciencedaily.com/releases/2019/07/190711141439.htm
Native California medicinal plant may hold promise for treating Alzheimer's
Salk scientists identify possible healing compound in Yerba santa
February 20, 2019
Science Daily/Salk Institute
The medicinal powers of aspirin, digitalis, and the anti-malarial artemisinin all come from plants. A discovery of a potent neuroprotective and anti-inflammatory chemical in a native California shrub may lead to a treatment for Alzheimer's disease based on a compound found in nature.
"Alzheimer's disease is a leading cause of death in the United States," says Senior Staff Scientist Pamela Maher, a member of Salk's Cellular Neurobiology Laboratory, run by Professor David Schubert. "And because age is a major risk factor, researchers are looking at ways to counter aging's effects on the brain. Our identification of sterubin as a potent neuroprotective component of a native California plant called Yerba santa (Eriodictyon californicum) is a promising step in that direction."
Native California tribes, which dubbed the plant "holy herb" in Spanish, have long used Yerba santa for its medicinal properties. Devotees brew its leaves to treat respiratory ailments, fever and headaches; and mash it into a poultice for wounds, sore muscles and rheumatism.
To identify natural compounds that might reverse neurological disease symptoms, Maher applied a screening technique used in drug discovery to a commercial library of 400 plant extracts with known pharmacological properties. The lab had previously used this approach to identify other chemicals (called flavonoids) from plants that have anti-inflammatory and neuroprotective properties.
Through the screen, the lab identified a molecule called sterubin as Yerba santa's most active component. The researchers tested sterubin and other plant extracts for their impact on energy depletion in mouse nerve cells, as well as other age-associated neurotoxicity and survival pathways directly related to the reduced energy metabolism, accumulation of misfolded, aggregated proteins and inflammation seen in Alzheimer's. Sterubin had a potent anti-inflammatory impact on brain cells known as microglia. It was also an effective iron remover -- potentially beneficial because iron can contribute to nerve cell damage in aging and neurodegenerative diseases. Overall, the compound was effective against multiple inducers of cell death in the nerve cells, according to Maher.
"This is a compound that was known but ignored," Maher says. "Not only did sterubin turn out to be much more active than the other flavonoids in Yerba santa in our assays, it appears as good as, if not better than, other flavonoids we have studied."
Next, the lab plans to test sterubin in an animal model of Alzheimer's, then determine its drug-like characteristics and toxicity levels in animals. With that data, Maher says, it might be possible to test the compound in humans, although it would be critical to use sterubin derived from plants grown under standardized, controlled conditions. She says the team will likely generate synthetic derivatives of sterubin.
https://www.sciencedaily.com/releases/2019/02/190220174105.htm