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Looking for Answers to Epilepsy in a Blood Test

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Gemma Carvill and lab members
Gemma Carvill (second from right) with members of her lab. Courtesy of Gemma Carvill

Millions of people take medications each day for epilepsy, a diverse group of disorders characterized by seizures. But, for about a third of people with epilepsy, current drug treatments don’t work very well. What’s more, the medications are designed to treat symptoms of these disorders, basically by suppressing seizure activity. The medications don’t really change the underlying causes, which are wired deep within the brain.

Gemma Carvill, a researcher at Northwestern University Feinberg School of Medicine, Chicago, wants to help change that in the years ahead. She’s dedicated her research career to discovering the genetic causes of epilepsy in hopes of one day designing treatments that can control or even cure some forms of the disorder [1].

It certainly won’t be easy. A recent paper put the number of known genes associated with epilepsy at close to 1,000 [2]. However, because some disease-causing genetic variants may arise during development, and therefore occur only within the brain, it’s possible that additional genetic causes of epilepsy are still waiting to be discovered within the billions of cells and their trillions of interconnections.

To find these new leads, Carvill won’t have to rely only on biopsies of brain tissue. She’s received a 2018 NIH Director’s New Innovator Award in search of answers hidden within “liquid biopsies”—tiny fragments of DNA that research in other forms of brain injury and neurological disease [3] suggests may spill into the bloodstream and cerebrospinal fluid (CSF) from dying neurons or other brain cells following a seizure.

Carvill and team will start with mouse models of epilepsy to test whether it’s possible to detect DNA fragments from the brain in bodily fluids after a seizure. They’ll also attempt to show DNA fragments carry telltale signatures indicating from which cells and tissues in the brain those molecules originate. The hope is these initial studies will also tell them the best time after a seizure to collect blood samples.

In people, Carvill’s team will collect the DNA fragments and begin searching for genetic alterations to explain the seizures, capitalizing on Carvill’s considerable expertise in the use of next generation DNA sequencing technology for ferreting out disease-causing variants. Importantly, if this innovative work in epilepsy pans out, it also can be applied to any other neurological condition in which DNA spills from dying brain cells, including Alzheimer’s disease and Parkinson’s disease.

References:

[1] Unravelling the genetic architecture of autosomal recessive epilepsy in the genomic era. Calhoun JD, Carvill GL. J Neurogenet. 2018 Sep 24:1-18.

[2] Epilepsy-associated genes. Wang J, Lin ZJ, Liu L, Xu HQ, Shi YW, Yi YH, He N, Liao WP. Seizure. 2017 Jan;44:11-20.

[3] Identification of tissue-specific cell death using methylation patterns of circulating DNA. Lehmann-Werman R, Neiman D, Zemmour H, Moss J, Magenheim J, Vaknin-Dembinsky A, Rubertsson S, Nellgård B, Blennow K, Zetterberg H, Spalding K, Haller MJ, Wasserfall CH, Schatz DA, Greenbaum CJ, Dorrell C, Grompe M, Zick A, Hubert A, Maoz M, Fendrich V, Bartsch DK, Golan T, Ben Sasson SA, Zamir G, Razin A, Cedar H, Shapiro AM, Glaser B, Shemer R, Dor Y. Proc Natl Acad Sci U S A. 2016 Mar 29;113(13):E1826-34.

Links:

Epilepsy Information Page (National Institute of Neurological Disorders and Stroke/NIH)

Gemma Carvill Lab (Northwestern University Feinberg School of Medicine, Chicago)

Carvill Project Information (NIH RePORTER)

NIH Director’s New Innovator Award (Common Fund)

NIH Support: Common Fund; National Institute of Neurological Disorders and Stroke


Largest-Ever Alzheimer’s Gene Study Brings New Answers

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Alzheimer's Risk Genes

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


Sleep Loss Encourages Spread of Toxic Alzheimer’s Protein

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Man sleeping
Credit: iStock/bowdenimages

In addition to memory loss and confusion, many people with Alzheimer’s disease have trouble sleeping. Now an NIH-funded team of researchers has evidence that the reverse is also true: a chronic lack of sleep may worsen the disease and its associated memory loss.

The new findings center on a protein called tau, which accumulates in abnormal tangles in the brains of people with Alzheimer’s disease. In the healthy brain, active neurons naturally release some tau during waking hours, but it normally gets cleared away during sleep. Essentially, your brain has a system for taking the garbage out while you’re off in dreamland.

The latest findings in studies of mice and people further suggest that sleep deprivation upsets this balance, allowing more tau to be released, accumulate, and spread in toxic tangles within brain areas important for memory. While more study is needed, the findings suggest that regular and substantial sleep may play an unexpectedly important role in helping to delay or slow down Alzheimer’s disease.

It’s long been recognized that Alzheimer’s disease is associated with the gradual accumulation of beta-amyloid peptides and tau proteins, which form plaques and tangles that are considered hallmarks of the disease. It has only more recently become clear that, while beta-amyloid is an early sign of the disease, tau deposits track more closely with disease progression and a person’s cognitive decline.

Such findings have raised hopes among researchers including David Holtzman, Washington University School of Medicine, St. Louis, that tau-targeting treatments might slow this devastating disease. Though much of the hope has focused on developing the right drugs, some has also focused on sleep and its nightly ability to reset the brain’s metabolic harmony.

In the new study published in Science, Holtzman’s team set out to explore whether tau levels in the brain naturally are tied to the sleep-wake cycle [1]. Earlier studies had shown that tau is released in small amounts by active neurons. But when neurons are chronically activated, more tau gets released. So, do tau levels rise when we’re awake and fall during slumber?

The Holtzman team found that they do. The researchers measured tau levels in brain fluid collected from mice during their normal waking and sleeping hours. (Since mice are nocturnal, they sleep primarily during the day.) The researchers found that tau levels in brain fluid nearly double when the animals are awake. They also found that sleep deprivation caused tau levels in brain fluid to double yet again.

These findings were especially interesting because Holtzman’s team had already made a related finding in people. The team found that healthy adults forced to pull an all-nighter had a 30 percent increase on average in levels of unhealthy beta-amyloid in their cerebrospinal fluid (CSF).

The researchers went back and reanalyzed those same human samples for tau. Sure enough, the tau levels were elevated on average by about 50 percent.

Once tau begins to accumulate in brain tissue, the protein can spread from one brain area to the next along neural connections. So, Holtzman’s team wondered whether a lack of sleep over longer periods also might encourage tau to spread.

To find out, mice engineered to produce human tau fibrils in their brains were made to stay up longer than usual and get less quality sleep over several weeks. Those studies showed that, while less sleep didn’t change the original deposition of tau in the brain, it did lead to a significant increase in tau’s spread. Intriguingly, tau tangles in the animals appeared in the same brain areas affected in people with Alzheimer’s disease.

Another report by Holtzman’s team appearing early last month in Science Translational Medicine found yet another link between tau and poor sleep. That study showed that older people who had more tau tangles in their brains by PET scanning had less slow-wave, deep sleep [2].

Together, these new findings suggest that Alzheimer’s disease and sleep loss are even more intimately intertwined than had been realized. The findings suggest that good sleep habits and/or treatments designed to encourage plenty of high quality Zzzz’s might play an important role in slowing Alzheimer’s disease. On the other hand, poor sleep also might worsen the condition and serve as an early warning sign of Alzheimer’s.

For now, the findings come as an important reminder that all of us should do our best to get a good night’s rest on a regular basis. Sleep deprivation really isn’t a good way to deal with overly busy lives (I’m talking to myself here). It isn’t yet clear if better sleep habits will prevent or delay Alzheimer’s disease, but it surely can’t hurt.

References:

[1] The sleep-wake cycle regulates brain interstitial fluid tau in mice and CSF tau in humans. Holth JK, Fritschi SK, Wang C, Pedersen NP, Cirrito JR, Mahan TE, Finn MB, Manis M, Geerling JC, Fuller PM, Lucey BP, Holtzman DM. Science. 2019 Jan 24.

[2] Reduced non-rapid eye movement sleep is associated with tau pathology in early Alzheimer’s disease. Lucey BP, McCullough A, Landsness EC, Toedebusch CD, McLeland JS, Zaza AM, Fagan AM, McCue L, Xiong C, Morris JC, Benzinger TLS, Holtzman DM. Sci Transl Med. 2019 Jan 9;11(474).

Links:

Alzheimer’s Disease and Related Dementias (National Institute on Aging/NIH)

Accelerating Medicines Partnership: Alzheimer’s Disease (NIH)

Holtzman Lab (Washington University School of Medicine, St. Louis)

NIH Support: National Institute on Aging; National Institute of Neurological Disorders and Stroke; National Center for Advancing Translational Sciences; National Cancer Institute; National Institute of Biomedical Imaging and Bioengineering


Connecting Senescent Cells to Obesity and Anxiety

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Graphical Abstract
Adapted from Ogrodnik et al., 2019, Cell Metabolism.

Obesity—which affects about 4 in 10 U.S. adults—increases the risk for lots of human health problems: diabetes, heart disease, certain cancers, and even anxiety and depression [1]. It’s also been associated with increased accumulation of senescent cells, which are older cells that resist death even as they lose the ability to grow and divide.

Now, NIH-funded researchers have found that when lean mice are fed a high-fat diet that makes them obese, they also have more senescent cells in their brain and show more anxious behaviors [2]. The researchers could reduce this obesity-driven anxiety using so-called senolytic drugs that cleared away the senescent cells. These findings are among the first to provide proof-of-concept that senolytics may offer a new avenue for treating an array of neuropsychiatric disorders, in addition to many other chronic conditions.

As we age, senescent cells accumulate in many parts of the body [3]. But cells can also enter a senescent state at any point in life in response to major stresses, such as DNA damage or chronic infection. Studies suggest that having lots of senescent cells around, especially later in life, is associated with a wide variety of chronic conditions, including osteoporosis, osteoarthritis, vascular disease, and general frailty.

Senescent cells display a “zombie”-like behavior known as a senescence-associated secretory phenotype (SASP). In this death-defying, zombie-like state, the cells ramp up their release of proteins, bioactive lipids, DNA, and other factors that, like a zombie virus, induce nearby healthy cells to join in the dysfunction.

In fact, the team behind this latest study, led by James Kirkland, Mayo Clinic, Rochester, MN, recently showed that transplanting small numbers of senescent cells into young mice is enough to cause them weakness, frailty, and persistent health problems. Those ill effects were alleviated with a senolytic cocktail, including dasatinib (a leukemia drug) and quercetin (a plant compound). This drug cocktail overrode the zombie-like SASP phenotype and forced the senescent cells to undergo programmed cell death and finally die.

Previous research indicates that senescent cells also accumulate in obesity, and not just in adipose tissues. Moreover, recent studies have linked senescent cells in the brain to neurodegenerative conditions, including Alzheimer’s disease, and showed in mice that dasatinib and quercetin helps to alleviate neurodegenerative disease [4,5]. In the latest paper, published in the journal Cell Metabolism, Kirkland and colleagues asked whether senescent cells in the brain also could explain anxiety-like behavior in obesity.

The answer appears to be “yes.” The researchers showed that lean mice, if allowed to feast on a high-fat diet, grew obese and became more anxious about exploring open spaces and elevated mazes.

The researchers also found that the obese mice had an increase in senescent cells in the white matter near the lateral ventricle, a part of the brain that offers a pathway for cerebrospinal fluid. Those senescent cells also contained an excessive amount of fat. Could senolytic drugs clear those cells and make the obesity-related anxiety go away?

To find out, the researchers treated lean and obese mice with a senolytic drug for 10 weeks. The treatment didn’t lead to any changes in body weight. But, as senescent cells were cleared from their brains, the obese mice showed a significant reduction in their anxiety-related behavior. They lost their anxiety without losing the weight!

More preclinical study is needed to understand more precisely how the treatment works. But, it’s worth noting that clinical trials testing a variety of senolytic drugs are already underway for many conditions associated with senescent cells, including chronic kidney disease [6,7], frailty [8], and premature aging associated with bone marrow transplant [9].

As a matter of fact, just after the Cell Metabolism paper came out, Kirkland’s team published encouraging though preliminary, first-in-human results of the previously mentioned senolytic drug dasatinib in 14 people with age-related idiopathic pulmonary fibrosis, a condition in which lung tissue becomes damaged and scarred [10]. Caution is warranted as we learn more about the associated risks and benefits, but it’s safe to say we’ll be hearing a lot more about senolytics in the years ahead.

References:

[1] Adult obesity facts (Centers for Disease Control and Prevention)

[2] Obesity-induced cellular senescence drives anxiety and impairs neurogenesis. Ogrodnik M et al. Cell Metabolism. 2019 Jan 3.

[3] Aging, Cell Senescence, and Chronic Disease: Emerging Therapeutic Strategies. Tchkonia T, Kirkland JL. JAMA. 2018 Oct 2;320(13):1319-1320.

[4] Tau protein aggregation is associated with cellular senescence in the brain. Musi N, Valentine JM, Sickora KR, Baeuerle E, Thompson CS, Shen Q, Orr ME. Aging Cell. 2018 Dec;17(6):e12840.

[5] Clearance of senescent glial cells prevents tau-dependent pathology and cognitive decline. Bussian TJ, Aziz A, Meyer CF, Swenson BL, van Deursen JM, Baker DJ. Nature. 2018 Oct;562(7728):578-582.

[6] Inflammation and Stem Cells in Diabetic and Chronic Kidney Disease. ClinicalTrials.gov, Sep 2018.

[7] Senescence in Chronic Kidney Disease. Clinicaltrials.gov, Sep 2018.

[8] Alleviation by Fisetin of Frailty, Inflammation, and Related Measures in Older Adults (AFFIRM-LITE). Clinicaltrials.gov, Dec 2018.

[9] Hematopoietic Stem Cell Transplant Survivors Study (HTSS Study). Clinicaltrials.gov, Sep 2018.

[10] Senolytics in idiopathic pulmonary fibrosis: Results from a first-in-human, open-label, pilot study. Justice JN, Nambiar AN, Tchkonia T, LeBrasseur K, Pascual R, Hashmi SK, Prata L, Masternak MM, Kritchevsky SB, Musi N, Kirkland JL. EBioMed. 5 Jan. 2019. [Epub ahead of print]

Links:

Healthy Aging (National Institute on Aging/NIH)

Video: Vail Scientific Summit James Kirkland Interview (Youtube)

James Kirkland (Mayo Clinic, Rochester, MN)

NIH Support: National Institute on Aging; National Institute of Neurological Disorders and Stroke


A New Piece of the Alzheimer’s Puzzle

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A couple enjoying a hot drink

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.


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