aging brain
Largest-Ever Alzheimer’s Gene Study Brings New Answers
Posted on by Dr. Francis Collins
Predicting whether someone will get Alzheimer’s disease (AD) late in life, and how to use that information for prevention, has been an intense focus of biomedical research. The goal of this work is to learn not only about the genes involved in AD, but how they work together and with other complex biological, environmental, and lifestyle factors to drive this devastating neurological disease.
It’s good news to be able to report that an international team of researchers, partly funded by NIH, has made more progress in explaining the genetic component of AD. Their analysis, involving data from more than 35,000 individuals with late-onset AD, has identified variants in five new genes that put people at greater risk of AD [1]. It also points to molecular pathways involved in AD as possible avenues for prevention, and offers further confirmation of 20 other genes that had been implicated previously in AD.
The results of this largest-ever genomic study of AD suggests key roles for genes involved in the processing of beta-amyloid peptides, which form plaques in the brain recognized as an important early indicator of AD. They also offer the first evidence for a genetic link to proteins that bind tau, the protein responsible for telltale tangles in the AD brain that track closely with a person’s cognitive decline.
The new findings are the latest from the International Genomics of Alzheimer’s Project (IGAP) consortium, led by a large, collaborative team including Brian Kunkle and Margaret Pericak-Vance, University of Miami Miller School of Medicine, Miami, FL. The effort, spanning four consortia focused on AD in the United States and Europe, was launched in 2011 with the aim of discovering and mapping all the genes that contribute to AD.
An earlier IGAP study including about 25,500 people with late-onset AD identified 20 common gene variants that influence a person’s risk for developing AD late in life [2]. While that was terrific progress to be sure, the analysis also showed that those gene variants could explain only a third of the genetic component of AD. It was clear more genes with ties to AD were yet to be found.
So, in the study reported in Nature Genetics, the researchers expanded the search. While so-called genome-wide association studies (GWAS) are generally useful in identifying gene variants that turn up often in association with particular diseases or other traits, the ones that arise more rarely require much larger sample sizes to find.
To increase their odds of finding additional variants, the researchers analyzed genomic data for more than 94,000 individuals, including more than 35,000 with a diagnosis of late-onset AD and another 60,000 older people without AD. Their search led them to variants in five additional genes, named IQCK, ACE, ADAM10, ADAMTS1, and WWOX, associated with late-onset AD that hadn’t turned up in the previous study.
Further analysis of those genes supports a view of AD in which groups of genes work together to influence risk and disease progression. In addition to some genes influencing the processing of beta-amyloid peptides and accumulation of tau proteins, others appear to contribute to AD via certain aspects of the immune system and lipid metabolism.
Each of these newly discovered variants contributes only a small amount of increased risk, and therefore probably have limited value in predicting an average person’s risk of developing AD later in life. But they are invaluable when it comes to advancing our understanding of AD’s biological underpinnings and pointing the way to potentially new treatment approaches. For instance, these new data highlight intriguing similarities between early-onset and late-onset AD, suggesting that treatments developed for people with the early-onset form also might prove beneficial for people with the more common late-onset disease.
It’s worth noting that the new findings continue to suggest that the search is not yet over—many more as-yet undiscovered rare variants likely play a role in AD. The search for answers to AD and so many other complex health conditions—assisted through collaborative data sharing efforts such as this one—continues at an accelerating pace.
References:
[1] Genetic meta-analysis of diagnosed Alzheimer’s disease identifies new risk loci and implicates Aβ, tau, immunity and lipid processing. Kunkle BW, Grenier-Boley B, Sims R, Bis JC, et. al. Nat Genet. 2019 Mar;51(3):414-430.
[2] Meta-analysis of 74,046 individuals identifies 11 new susceptibility loci for Alzheimer’s disease. Lambert JC, Ibrahim-Verbaas CA, Harold D, Naj AC, Sims R, Bellenguez C, DeStafano AL, Bis JC, et al. Nat Genet. 2013 Dec;45(12):1452-8.
Links:
Alzheimer’s Disease Genetics Fact Sheet (National Institute on Aging/NIH)
Genome-Wide Association Studies (NIH)
Margaret Pericak-Vance (University of Miami Health System, FL)
NIH Support: National Institute on Aging; National Heart, Lung, and Blood Institute; National Human Genome Research Institute; National Institute of Allergy and Infectious Diseases; Eunice Kennedy Shriver National Institute of Child Health and Human Development; National Institute of Diabetes and Digestive and Kidney Disease; National Institute of Neurological Disorders and Stroke
A New Piece of the Alzheimer’s Puzzle
Posted on by Dr. Francis Collins
Credit: National Institute on Aging, NIH
For the past few decades, researchers have been busy uncovering genetic variants associated with an increased risk of Alzheimer’s disease (AD) [1]. But there’s still a lot to learn about the many biological mechanisms that underlie this devastating neurological condition that affects as many as 5 million Americans [2].
As an example, an NIH-funded research team recently found that AD susceptibility may hinge not only upon which gene variants are present in a person’s DNA, but also how RNA messages encoded by the affected genes are altered to produce proteins [3]. After studying brain tissue from more than 450 deceased older people, the researchers found that samples from those with AD contained many more unusual RNA messages than those without AD.
Unlocking the Brain’s Memory Retrieval System
Posted on by Dr. Francis Collins
Credit:Sahay Lab, Massachusetts General Hospital, Boston
Play the first few bars of any widely known piece of music, be it The Star-Spangled Banner, Beethoven’s Fifth, or The Rolling Stones’ (I Can’t Get No) Satisfaction, and you’ll find that many folks can’t resist filling in the rest of the melody. That’s because the human brain thrives on completing familiar patterns. But, as we grow older, our pattern completion skills often become more error prone.
This image shows some of the neural wiring that controls pattern completion in the mammalian brain. Specifically, you’re looking at a cross-section of a mouse hippocampus that’s packed with dentate granule neurons and their signal-transmitting arms, called axons, (light green). Note how the axons’ short, finger-like projections, called filopodia (bright green), are interacting with a neuron (red) to form a “memory trace” network. Functioning much like an online search engine, memory traces use bits of incoming information, like the first few notes of a song, to locate and pull up more detailed information, like the complete song, from the brain’s repository of memories in the cerebral cortex.
New Evidence Suggests Aging Brains Continue to Make New Neurons
Posted on by Dr. Francis Collins
Caption: Mammalian hippocampal tissue. Immunofluorescence microscopy showing neurons (blue) interacting with neural astrocytes (red) and oligodendrocytes (green).
Credit: Jonathan Cohen, Fields Lab, Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH
There’s been considerable debate about whether the human brain has the capacity to make new neurons into adulthood. Now, a recently published study offers some compelling new evidence that’s the case. In fact, the latest findings suggest that a healthy person in his or her seventies may have about as many young neurons in a portion of the brain essential for learning and memory as a teenager does.
As reported in the journal Cell Stem Cell, researchers examined the brains of healthy people, aged 14 to 79, and found similar numbers of young neurons throughout adulthood [1]. Those young neurons persisted in older brains that showed other signs of decline, including a reduced ability to produce new blood vessels and form new neural connections. The researchers also found a smaller reserve of quiescent, or inactive, neural stem cells in a brain area known to support cognitive-emotional resilience, the ability to cope with and bounce back from stressful circumstances.
While more study is clearly needed, the findings suggest healthy elderly people may have more cognitive reserve than is commonly believed. However, the findings may also help to explain why even perfectly healthy older people often find it difficult to face new challenges, such as travel or even shopping at a different grocery store, that wouldn’t have fazed them earlier in life.
Creative Minds: Mapping the Biocircuitry of Schizophrenia and Bipolar Disorder
Posted on by Dr. Francis Collins
Bruce Yankner
As a graduate student in the 1980s, Bruce Yankner wondered what if cancer-causing genes switched on in non-dividing neurons of the brain. Rather than form a tumor, would those genes cause neurons to degenerate? To explore such what-ifs, Yankner spent his days tinkering with neural cells, using viruses to insert various mutant genes and study their effects. In a stroke of luck, one of Yankner’s insertions encoded a precursor to a protein called amyloid. Those experiments and later ones from Yankner’s own lab showed definitively that high concentrations of amyloid, as found in the brains of people with Alzheimer’s disease, are toxic to neural cells [1].
The discovery set Yankner on a career path to study normal changes in the aging human brain and their connection to neurodegenerative diseases. At Harvard Medical School, Boston, Yankner and his colleague George Church are now recipients of an NIH Director’s 2016 Transformative Research Award to apply what they’ve learned about the aging brain to study changes in the brains of younger people with schizophrenia and bipolar disorder, two poorly understood psychiatric disorders.
Creative Minds: Reprogramming the Brain
Posted on by Dr. Francis Collins
Caption: Neuronal circuits in the mouse retina. Cone photoreceptors (red) enable color vision; bipolar neurons (magenta) relay information further along the circuit; and a subtype of bipolar neuron (green) helps process signals sensed by other photoreceptors in dim light.
Credit: Brian Liu and Melanie Samuel, Baylor College of Medicine, Houston.
When most people think of reprogramming something, they probably think of writing code for a computer or typing commands into their smartphone. Melanie Samuel thinks of brain circuits, the networks of interconnected neurons that allow different parts of the brain to work together in processing information.
Samuel, a researcher at Baylor College of Medicine, Houston, wants to learn to reprogram the connections, or synapses, of brain circuits that function less well in aging and disease and limit our memory and ability to learn. She has received a 2016 NIH Director’s New Innovator Award to decipher the molecular cues that encourage the repair of damaged synapses or enable neurons to form new connections with other neurons. Because extensive synapse loss is central to most degenerative brain diseases, Samuel’s reprogramming efforts could help point the way to preventing or correcting wiring defects before they advance to serious and potentially irreversible cognitive problems.
Creative Minds: A Transcriptional “Periodic Table” of Human Neurons
Posted on by Dr. Francis Collins
Caption: Mouse fibroblasts converted into induced neuronal cells, showing neuronal appendages (red), nuclei (blue) and the neural protein tau (yellow).
Credit: Kristin Baldwin, Scripps Research Institute, La Jolla, CA
Writers have The Elements of Style, chemists have the periodic table, and biomedical researchers could soon have a comprehensive reference on how to make neurons in a dish. Kristin Baldwin of the Scripps Research Institute, La Jolla, CA, has received a 2016 NIH Director’s Pioneer Award to begin drafting an online resource that will provide other researchers the information they need to reprogram mature human skin cells reproducibly into a variety of neurons that closely resemble those found in the brain and nervous system.
These lab-grown neurons could be used to improve our understanding of basic human biology and to develop better models for studying Alzheimer’s disease, autism, and a wide range of other neurological conditions. Such questions have been extremely difficult to explore in mice and other animal models because they have shorter lifespans and different brain structures than humans.
Antibody Makes Alzheimer’s Protein Detectable in Blood
Posted on by Dr. Francis Collins
Caption: The protein tau (green) aggregates abnormally in a brain cell (blue). Tau spills out of the cell and enters the bloodstream (red). Research shows that antibodies (blue) can capture tau in the blood that reflect its levels in the brain.
Credit: Sara Moser
Age can bring moments of forgetfulness. It can also bring concern that the forgetfulness might be a sign of early Alzheimer’s disease. For those who decide to have it checked out, doctors are likely to administer brief memory exams to assess the situation, and medical tests to search for causes of memory loss. Brain imaging and spinal taps can also help to look for signs of the disease. But an absolutely definitive diagnosis of Alzheimer’s disease is only possible today by examining a person’s brain postmortem. A need exists for a simple, less-invasive test to diagnose Alzheimer’s disease and similar neurodegenerative conditions in living people, perhaps even before memory loss becomes obvious.
One answer may lie in a protein called tau, which accumulates in abnormal tangles in the brains of people with Alzheimer’s disease and other “tauopathy” disorders. In recent years, researchers have been busy designing an antibody to target tau in hopes that this immunotherapy approach might slow or even reverse Alzheimer’s devastating symptoms, with promising early results in mice [1, 2]. Now, an NIH-funded research team that developed one such antibody have found it might also open the door to a simple blood test [3].
Aging Research: Plasma Protein Revitalizes the Brain
Posted on by Dr. Francis Collins
For centuries, people have yearned for an elixir capable of restoring youth to their aging bodies and minds. It sounds like pure fantasy, but, in recent years, researchers have shown that the blood of young mice can exert a regenerative effect when transfused into older animals. Now, one of the NIH-funded teams that brought us those exciting findings has taken an early step toward extending them to humans.
In their latest work published in Nature, the researchers showed that blood plasma collected from the umbilical cords of newborn infants possesses some impressive rejuvenating effects [1]. When the human plasma was infused into the bloodstream of old mice, it produced marked improvements in learning and memory. Additional experiments traced many of those cognitive benefits to a specific protein called TIMP2—an unexpected discovery that could pave the way for the development of brain-boosting drugs to slow the effects of aging.
LabTV: Curious about the Aging Brain
Posted on by Dr. Francis Collins
This LabTV video takes us to the West Coast to meet Saul Villeda, a creative young researcher who’s exploring ways to reduce the effects of aging on the human brain. Thanks to a 2012 NIH Director’s Early Independence award, Villeda set up his own lab at the University of California, San Francisco to study how age-related immune changes may affect the ability of brain cells to regenerate. By figuring out exactly what’s going on, Villeda and his team hope to devise ways to counteract such changes, possibly preventing or even reversing the cognitive declines that all too often come with age.
Villeda is the first person in his family to become a scientist. His parents immigrated to the United States from Guatemala, settled into a working-class neighborhood in Pasadena, CA, and enrolled their kids in public schools. While he was growing up, Villeda says he’d never even heard of a Ph.D. and thought all doctors were M.D.’s who wore stethoscopes. But he did have a keen mind and a strong sense of curiosity—gifts that helped him become the valedictorian of his high school class and find his calling in science. Villeda went on to earn an undergraduate degree in physiological science from the University of California, Los Angeles and a Ph.D. in neurosciences from Stanford University Medical School, Palo Alto, CA, as well as to publish his research findings in several influential scientific journals.
