What happens around an Alzheimer plaque?
July 22, 2020
Science Daily/VIB (the Flanders Institute for Biotechnology)
The brains of people living with Alzheimer's are riddled with plaques: protein aggregates consisting mainly of amyloid beta. Despite decades of research, the real contribution of these plaques to the disease process is still not clear. A research team led by Bart De Strooper and Mark Fiers at the VIB-KU Leuven Center for Brain & Disease Research in Leuven, Belgium used pioneering technologies to study in detail what happens in brain cells in the direct vicinity of plaques. Their findings, published in the prestigious journal Cell, show how different cell types in the brain work together to mount a complex response to amyloid plaques which is likely protective at first, but later on damaging to the brain.
The role of amyloid plaques in Alzheimer's disease has puzzled scientists ever since Alois Alzheimer first described them in the brain of a woman with young onset dementia. Now, over a century later, we have learned a lot about the molecular processes that lead to neurodegeneration and subsequent memory loss, but the relationship between the plaques and the disease process in the brain is still ambiguous.
"Amyloid plaques might act as a trigger or as a driver of disease, and the accumulation of amyloid beta in the brain likely initiates a complex multicellular neurodegenerative process," says professor Bart De Strooper (VIB-KU Leuven). His team set out to map the molecular changes that take place in cells near amyloid plaques.
"We used the latest technologies to analyze genome-wide transcriptomic changes induced by amyloid plaques in hundreds of small tissue domains," explains Mark Fiers, co-lead on the study. "In this way, we could generate a large data set of transcriptional changes that occur in response to increasing amyloid pathology, both in mouse and human brains."
Two co-expression networks
"We focused on the transcriptomic changes in the immediate neighborhood of the amyloid plaques, with a 50 micrometer perimeter," explains Wei-Ting Chen, a postdoc in De Strooper's team. In a well-studied genetic mouse model showing amyloid pathology, the scientists identified two novel gene co-expression networks that appeared highly sensitive to amyloid beta deposition.
Chen: "With increasing amyloid beta deposition, a multicellular co-expressed gene response was established encompassing no less than 57 plaque-induced genes." These genes were mainly expressed in astroglia and microglia, two types of supportive brain cells, and were not co-expressed in the absence of amyloid plaques.
"We also found interesting alterations in a second network, expressed mainly by another type of cells, namely oligodendrocytes," adds Ashley Lu, PhD student in the team. "This gene network was activated under mild amyloid stress but depleted in microenvironments with high amyloid accumulation."
"Many of the genes in both networks show similar alterations in human brain samples, strengthening our observations," adds Fiers.
Targeting plaques
"Our data demonstrate that amyloid plaques are not innocent bystanders of the disease, as has been sometimes suggested, but in fact induce a strong and coordinated response of all surrounding cell types," says De Strooper.
"Further work is needed to understand whether, and when, removal of amyloid plaques -- for instance by antibody therapy currently in development to treat amyloid plaques -- is sufficient to reverse these ongoing cellular processes."
Whether antibody binding to amyloid plaques could also modulate these glial responses remains to be determined. "It would in any case complicate the interpretation of the outcome of clinical trials as these cellular effects might be different between different antibodies," adds De Strooper.
https://www.sciencedaily.com/releases/2020/07/200722134916.htm
Objective subtle cognitive difficulties predict amyloid accumulation and neurodegeneration
December 31, 2019
Science Daily/University of California - San Diego
Writing in the December 30, 2019 online issue of Neurology, researchers at University of California San Diego School of Medicine and Veterans Affairs San Diego Healthcare System report that accumulating amyloid -- an abnormal protein linked to neurodegenerative conditions such as Alzheimer's disease (AD) -- occurred faster among persons deemed to have "objectively-defined subtle cognitive difficulties" (Obj-SCD) than among persons considered to be "cognitively normal."
Classification of Obj-SCD, which has been previously shown to predict progression to mild cognitive impairment (MCI) and dementia, is determined using non-invasive but sensitive neuropsychological measures, including measures of how efficiently someone learns and retains new information or makes certain types of errors.
The new findings, say authors, suggest that Obj-SCD can be detected during the preclinical state of AD when amyloid plaques are accumulating in the brain, neurodegeneration is just starting, but symptoms of impairment on total scores on thinking and memory tests have not yet been recorded.
"The scientific community has long thought that amyloid drives the neurodegeneration and cognitive impairment associated with Alzheimer's disease," said senior author Mark W. Bondi, PhD, professor of psychiatry at UC San Diego School of Medicine and the VA San Diego Healthcare System. "These findings, in addition to other work in our lab, suggest that this is likely not the case for everyone and that sensitive neuropsychological measurement strategies capture subtle cognitive changes much earlier in the disease process than previously thought possible.
"This work, led by Dr. Kelsey Thomas, has important implications for research on treatment targets for AD, as it suggests that cognitive changes may be occurring before significant levels of amyloid have accumulated. It seems like we may need to focus on treatment targets of pathologies other than amyloid, such as tau, that are more highly associated with the thinking and memory difficulties that impact people's lives."
Study participants were enrolled in the Alzheimer's Disease Neuroimaging Initiative (ADNI), an on-going effort (launched in 2003) to test whether regular, repeated brain imaging, combined with other biological markers and clinical assessments, can measure the progression of MCI and early AD. Seven hundred and forty-seven persons were involved in this study: 305 deemed cognitively normal, 153 with Obj-SCD and 289 MCI. All underwent neuropsychological testing and both PET and MRI scans.
The research team found that amyloid accumulation was faster in persons classified with Obj-SCD than in the cognitively normal group. Those classified as Obj-SCD also experienced selective thinning of the entorhinal cortex, a region of the brain impacted very early in Alzheimer's disease and associated with memory, navigation and perception of time. Persons with MCI had more amyloid in their brain at the start of the study, but they did not have faster accumulation of amyloid compared to those with normal cognition. However, those with MCI had more widespread temporal lobe atrophy, including the hippocampus.
Broadly speaking, scientists believe that for most people, AD is likely caused by a combination of genetic, lifestyle and environmental factors. Increasing age is a primary, known risk factor. The amyloid hypothesis or amyloid cascade model posits that accumulating amyloid protein plaques in the brain kill neurons and gradually impair specific cognitive functions, such as memory, resulting in AD dementia. However, many scientists are now questioning the amyloid hypothesis given the large number of clinical trials in which drugs targeted and successfully cleared amyloid from the brain but did not impact the trajectory of cognitive decline.
The ability to identify those at risk for AD before significant impairment and before or during the phase of faster amyloid accumulation would be a clinical boon, said authors, providing both a way to monitor disease progression and a window of opportunity to apply potential preventive or treatment strategies.
Currently, both approaches are limited. Some risk factors for Alzheimer's can be minimized, such as not smoking, managing vascular risk factors such as hypertension or following a healthy diet with regular exercise. There are a handful of medications approved for treating symptoms of AD, but as yet, there is no cure.
"While the emergence of biomarkers of Alzheimer's disease has revolutionized research and our understanding of how the disease progresses, many of these biomarkers continue to be highly expensive, inaccessible for clinical use or not available to those with certain medical conditions," said first author Thomas, PhD, assistant professor of psychiatry at UC San Diego School of Medicine and research health scientist at the VA San Diego Healthcare System.
"A method of identifying individuals at risk for progression to AD using neuropsychological measures has the potential to improve early detection in those who may otherwise not be eligible for more expensive or invasive screening."
https://www.sciencedaily.com/releases/2019/12/191231111811.htm
Dementia study links gene with damage to brain connections
June 27, 2019
Science Daily/University of Edinburgh
Insights into how a gene that increases the risk of Alzheimer's disease disrupts brain cells have been revealed by scientists.
Brain tissue from people with Alzheimer's showed that a protein called clusterin builds up in vital parts of neurons that connect cells and may damage these links.
Scientists say the findings shed light on the causes of the disease and will help to accelerate the search for a treatment.
The study, led by Professor Tara Spires-Jones at the University of Edinburgh, focused on synapses -- connections between brain cells that allow the flow of chemical and electrical signals. These signals are vital for forming memories and are key to brain health, experts say.
Researchers showed that synapses in people who had died with Alzheimer's contained clumps of clusterin, which could contribute to dementia symptoms. These synapses also contained clumps of amyloid beta, the damaging protein that is found in the brains of people with Alzheimer's.
People with a common risk gene, called apolipoprotein E4, had more clusterin and amyloid beta clumps in their synapses than people with Alzheimer's without the risk gene.
Those without dementia symptoms had even less of the damaging proteins in their synapses.
The discovery was made using powerful technology that allowed the scientists to view detailed images of more than one million synapses. Individual synapses are around 5000 times smaller than the thickness of a sheet of paper.
Synapse loss in Alzheimer's disease was previously established, but the clumping of damaging proteins together in synapses was unknown until now because of difficulties in studying them due to their tiny size.
Alzheimer's disease is the most common form of dementia, affecting around 500,000 people in the UK. It can cause severe memory loss and there is no cure.
Professor Spires-Jones, Programme Lead at the UK Dementia Research Institute at the University of Edinburgh, said: "We have identified another player in the host of proteins that damage synapses in Alzheimer's disease. Synapses are essential for thinking and memory, and preventing damage to them is a promising target to help prevent or reverse dementia symptoms. This work gives us a new target to work towards in our goal to develop effective treatments."
https://www.sciencedaily.com/releases/2019/06/190627114025.htm
Scientists propose new theory on Alzheimer's, amyloid connection
April 23, 2019
Science Daily/Florida Atlantic University
Worldwide, 50 million people are living with Alzheimer's disease and other dementias. According to the Alzheimer's Association, every 65 seconds someone in the United States develops this disease, which causes problems with memory, thinking and behavior.
It has been more than 100 years since Alois Alzheimer, M.D., a German psychiatrist and neuropathologist, first reported the presence of senile plaques in an Alzheimer's disease patient brain. It led to the discovery of amyloid precursor protein that produces deposits or plaques of amyloid fragments in the brain, the suspected culprit of Alzheimer's disease. Since then, amyloid precursor protein has been extensively studied because of its association with Alzheimer's disease. However, amyloid precursor protein distribution within and on neurons and its function in these cells remain unclear.
A team of neuroscientists led by Florida Atlantic University's Brain Institute sought to answer a fundamental question in their quest to combat Alzheimer's disease -- "Is amyloid precursor protein the mastermind behind Alzheimer's disease or is it just an accomplice?"
Mutations found in amyloid precursor protein have been linked to rare cases of familial Alzheimer's disease. Although scientists have gained a lot knowledge about how this protein turns into amyloid plaques, little is known about its native function in neurons. In the case of more common sporadic Alzheimer's disease, the highest genetic risk factor is a protein that is involved in cholesterol transportation and not this amyloid precursor protein. Moreover, various clinical trials designed to address Alzheimer's disease by minimizing amyloid plaque formation have failed, including one from Biogen announced last month.
In a study published in the journal Neurobiology of Disease, Qi Zhang, Ph.D., senior author, an investigator at the FAU Brain Institute, and an assistant research professor in FAU's Schmidt College of Medicine, along with collaborators from Vanderbilt University, tackle this Alzheimer's disease mystery by devising a multi-functional reporter for amyloid precursor protein and tracking the protein's localization and mobility using quantitative imaging with unprecedented accuracy.
For the study, Zhang and collaborators genetically disrupted the interaction between cholesterol and amyloid precursor protein. Surprisingly, by disengaging the two, they discovered that this manipulation not only disrupts the trafficking of amyloid precursor protein but also messes up cholesterol distribution at the neuronal surface. Neurons with an altered distribution of cholesterol exhibited swollen synapses and fragmented axons and other early signs of neurodegeneration.
"Our study is intriguing because we noticed a peculiar association between amyloid precursor protein and cholesterol that resides in the cell membrane of synapses, which are points of contact among neurons and the biological basis for learning and memory," said Zhang. "Amyloid precursor protein may just be one of the many accomplices partially contributing to cholesterol deficiency. Strangely, the heart and brain seem to meet again in the fight against bad cholesterol."
Given the broad involvement of cholesterol in almost all aspects of neurons' life, Zhang and collaborators have proposed a new theory about the amyloid precursor protein connection in Alzheimer's disease, especially in the surface of those tiny synapses, which triggers neurodegeneration.
"Although still in early stages, this cutting-edge research by Dr. Zhang and his collaborators at Vanderbilt University may have implications for the millions of people at risk for or suffering with Alzheimer's disease," said Randy D. Blakely, Ph.D., executive director of the FAU Brain Institute and a professor of biomedical science in FAU's Schmidt College of Medicine. "The number of people in Florida alone who are age 65 and older with Alzheimer's disease is expected to increase 41.2 percent by 2025 to a projected 720,000, highlighting the urgency of finding a medical breakthrough."
Locally, Alzheimer's disease affects 11.5 percent of Medicare beneficiaries in Palm Beach County and 12.7 percent of Medicare beneficiaries in Broward County (a nearly 18 percent increase over national average).
According to the Alzheimer's Association, Florida is number one in per capita cases of Alzheimer's disease in the U.S.
https://www.sciencedaily.com/releases/2019/04/190423113951.htm
Cannabinoids remove plaque-forming Alzheimer's proteins from brain cells
June 29, 2016
Science Daily/Salk Institute
Salk Institute scientists have found preliminary evidence that tetrahydrocannabinol (THC) and other compounds found in marijuana can promote the cellular removal of amyloid beta, a toxic protein associated with Alzheimer's disease.
While these exploratory studies were conducted in neurons grown in the laboratory, they may offer insight into the role of inflammation in Alzheimer's disease and could provide clues to developing novel therapeutics for the disorder.
"Although other studies have offered evidence that cannabinoids might be neuroprotective against the symptoms of Alzheimer's, we believe our study is the first to demonstrate that cannabinoids affect both inflammation and amyloid beta accumulation in nerve cells," says Salk Professor David Schubert, the senior author of the paper.
Alzheimer's disease is a progressive brain disorder that leads to memory loss and can seriously impair a person's ability to carry out daily tasks. It affects more than five million Americans according to the National Institutes of Health, and is a leading cause of death. It is also the most common cause of dementia and its incidence is expected to triple during the next 50 years.
It has long been known that amyloid beta accumulates within the nerve cells of the aging brain well before the appearance of Alzheimer's disease symptoms and plaques. Amyloid beta is a major component of the plaque deposits that are a hallmark of the disease. But the precise role of amyloid beta and the plaques it forms in the disease process remains unclear.
In a manuscript published in June 2016's Aging and Mechanisms of Disease, Salk team studied nerve cells altered to produce high levels of amyloid beta to mimic aspects of Alzheimer's disease.
The researchers found that high levels of amyloid beta were associated with cellular inflammation and higher rates of neuron death. They demonstrated that exposing the cells to THC reduced amyloid beta protein levels and eliminated the inflammatory response from the nerve cells caused by the protein, thereby allowing the nerve cells to survive.
"Inflammation within the brain is a major component of the damage associated with Alzheimer's disease, but it has always been assumed that this response was coming from immune-like cells in the brain, not the nerve cells themselves," says Antonio Currais, a postdoctoral researcher in Schubert's laboratory and first author of the paper. "When we were able to identify the molecular basis of the inflammatory response to amyloid beta, it became clear that THC-like compounds that the nerve cells make themselves may be involved in protecting the cells from dying."
Brain cells have switches known as receptors that can be activated by endocannabinoids, a class of lipid molecules made by the body that are used for intercellular signaling in the brain. The psychoactive effects of marijuana are caused by THC, a molecule similar in activity to endocannabinoids that can activate the same receptors. Physical activity results in the production of endocannabinoids and some studies have shown that exercise may slow the progression of Alzheimer's disease.
Schubert emphasized that his team's findings were conducted in exploratory laboratory models, and that the use of THC-like compounds as a therapy would need to be tested in clinical trials.
In separate but related research, his lab found an Alzheimer's drug candidate called J147 that also removes amyloid beta from nerve cells and reduces the inflammatory response in both nerve cells and the brain. It was the study of J147 that led the scientists to discover that endocannabinoids are involved in the removal of amyloid beta and the reduction of inflammation.
Other authors on the paper include Oswald Quehenberger and Aaron Armando at the University of California, San Diego; and Pamela Maher and Daniel Daughtery at the Salk Institute.
The study was supported by the National Institutes of Health, The Burns Foundation and The Bundy Foundation.
https://www.sciencedaily.com/releases/2016/06/160629095609.htm
Marijuana compound may offer treatment for Alzheimer's disease
August 27, 2014
Science Daily/University of South Florida (USF Health)
Extremely low levels of the compound in marijuana known as delta-9-tetrahydrocannabinol, or THC, may slow or halt the progression of Alzheimer's disease, a recent study from neuroscientists at the University of South Florida shows.
Findings from the experiments, using a cellular model of Alzheimer's disease, were reported online in the Journal of Alzheimer's Disease.
Researchers from the USF Health Byrd Alzheimer's Institute showed that extremely low doses of THC reduce the production of amyloid beta, found in a soluble form in most aging brains, and prevent abnormal accumulation of this protein -- a process considered one of the pathological hallmarks evident early in the memory-robbing disease. These low concentrations of THC also selectively enhanced mitochondrial function, which is needed to help supply energy, transmit signals, and maintain a healthy brain.
"THC is known to be a potent antioxidant with neuroprotective properties, but this is the first report that the compound directly affects Alzheimer's pathology by decreasing amyloid beta levels, inhibiting its aggregation, and enhancing mitochondrial function," said study lead author Chuanhai Cao, PhD and a neuroscientist at the Byrd Alzheimer's Institute and the USF College of Pharmacy.
"Decreased levels of amyloid beta means less aggregation, which may protect against the progression of Alzheimer's disease. Since THC is a natural and relatively safe amyloid inhibitor, THC or its analogs may help us develop an effective treatment in the future."
The researchers point out that at the low doses studied, the therapeutic benefits of THC appear to prevail over the associated risks of THC toxicity and memory impairment.
Neel Nabar, a study co-author and MD/PhD candidate, recognized the rapidly changing political climate surrounding the debate over medical marijuana.
"While we are still far from a consensus, this study indicates that THC and THC-related compounds may be of therapeutic value in Alzheimer's disease," Nabar said. "Are we advocating that people use illicit drugs to prevent the disease? No. It's important to keep in mind that just because a drug may be effective doesn't mean it can be safely used by anyone. However, these findings may lead to the development of related compounds that are safe, legal, and useful in the treatment of Alzheimer's disease."
The body's own system of cannabinoid receptors interacts with naturally-occurring cannabinoid molecules, and these molecules function similarly to the THC isolated from the cannabis (marijuana) plant.
Dr. Cao's laboratory at the Byrd Alzheimer's Institute is currently investigating the effects of a drug cocktail that includes THC, caffeine as well as other natural compounds in a cellular model of Alzheimer's disease, and will advance to a genetically-engineered mouse model of Alzheimer's shortly.
"The dose and target population are critically important for any drug, so careful monitoring and control of drug levels in the blood and system are very important for therapeutic use, especially for a compound such as THC," Dr. Cao said.
https://www.sciencedaily.com/releases/2014/08/140827131801.htm