genetics
Case Study Unlocks Clues to Rare Resilience to Alzheimer’s Disease
Posted on by Lawrence Tabak, D.D.S., Ph.D.
Biomedical breakthroughs most often involve slow and steady research in studies involving large numbers of people. But sometimes careful study of even just one truly remarkable person can lead the way to fascinating discoveries with far-reaching implications.
An NIH-funded case study published recently in the journal Nature Medicine falls into this far-reaching category [1]. The report highlights the world’s second person known to have an extreme resilience to a rare genetic form of early onset Alzheimer’s disease. These latest findings in a single man follow a 2019 report of a woman with similar resilience to developing symptoms of Alzheimer’s despite having the same strong genetic predisposition for the disease [2].
The new findings raise important new ideas about the series of steps that may lead to Alzheimer’s and its dementia. They’re also pointing the way to key parts of the brain for cognitive resilience—and potentially new treatment targets—that may one day help to delay or even stop progression of Alzheimer’s.
The man in question is a member of a well-studied extended family from the country of Colombia. This group of related individuals, or kindred, is the largest in the world with a genetic variant called the “Paisa” mutation (or Presenilin-1 E280A). This Paisa variant follows an autosomal dominant pattern of inheritance, meaning that those with a single altered copy of the rare variant passed down from one parent usually develop mild cognitive impairment around the age of 44. They typically advance to full-blown dementia around the age of 50 and rarely live past the age of 60. This contrasts with the most common form of Alzheimer’s, which usually begins after age 65.
The new findings come from a team led by Yakeel Quiroz, Massachusetts General Hospital, Boston; Joseph Arboleda-Velasquez, Massachusetts Eye and Ear, Boston; Diego Sepulveda-Falla, University Medical Center Hamburg-Eppendorf, Hamburg, Germany; and Francisco Lopera, University of Antioquia, Medellín, Colombia. Lopera first identified this family more than 30 years ago and has been studying them ever since.
In the new case report, the researchers identified a Colombian man who’d been married with two children and retired from his job as a mechanic in his early 60s. Despite carrying the Paisa mutation, his first cognitive assessment at age 67 showed he was cognitively intact, having limited difficulties with verbal learning skills or language. It wasn’t until he turned 70 that he was diagnosed with mild cognitive impairment—more than 20 years later than the expected age for this family—showing some decline in short-term memory and verbal fluency.
At age 73, he enrolled in the Colombia-Boston biomarker research study (COLBOS). This study is a collaborative project between the University of Antioquia and Massachusetts General Hospital involving approximately 6,000 individuals from the Paisa kindred. About 1,500 of those in the study carry the mutation that sets them up for early Alzheimer’s. As a member of the COLBOS study, the man underwent thorough neuroimaging tests to look for amyloid plaques and tau tangles, both of which are hallmarks of Alzheimer’s.
While this man died at age 74 with Alzheimer’s, the big question is: how did he stave off dementia for so long despite his poor genetic odds? The COLBOS study earlier identified a woman with a similar resilience to Alzheimer’s, which they traced to two copies of a rare, protective genetic variant called Christchurch. This variant affects a gene called apolipoprotein E (APOE3), which is well known for its influence on Alzheimer’s risk. However, the man didn’t carry this same protective variant.
The researchers still thought they’d find an answer in his genome and kept looking. While they found several variants of possible interest, they zeroed in on a single gene variant that they’ve named Reelin-COLBOS. What helped them to narrow it down to this variant is the man also had a sister with the Paisa mutation who only progressed to advanced dementia at age 72. It turned out, in addition to the Paisa variant, the siblings also shared an altered copy of the newly discovered Reelin-COLBOS variant.
This Reelin-COLBOS gene is known to encode a protein that controls signals to chemically modify tau proteins, which form tangles that build up over time in the Alzheimer’s brain and have been linked to memory loss. Reelin is also functionally related to APOE, the gene that was altered in the woman with extreme Alzheimer’s protection. Reelin and APOE both interact with common protein receptors in neurons. Together, the findings add to evidence that signaling pathways influencing tau play an important role in Alzheimer’s pathology and protection.
The neuroimaging exams conducted when the man was age 73 have offered further intriguing clues. They showed that his brain had extensive amyloid plaques. He also had tau tangles in some parts of his brain. But one brain region, called the entorhinal cortex, was notable for having a very minimal amount of those hallmark tau tangles.
The entorhinal cortex is a hub for memory, navigation, and the perception of time. Its degeneration also leads to cognitive impairment and dementia. Studies of the newly identified Reelin-COLBOS variant in Alzheimer’s mouse models also help to confirm that the variant offers its protection by diminishing the pathological modifications of tau.
Overall, the findings in this one individual and his sister highlight the Reelin pathway and brain region as promising targets for future study and development of Alzheimer’s treatments. Quiroz and her colleagues report that they are actively exploring treatment approaches inspired by the Christchurch and Reelin-COLBOS discoveries.
Of course, there’s surely more to discover from continued study of these few individuals and others like them. Other as yet undescribed genetic and environmental factors are likely at play. But the current findings certainly offer some encouraging news for those at risk for Alzheimer’s disease—and a reminder of how much can be learned from careful study of remarkable individuals.
References:
[1] Resilience to autosomal dominant Alzheimer’s disease in a Reelin-COLBOS heterozygous man. Lopera F, Marino C, Chandrahas AS, O’Hare M, Reiman EM, Sepulveda-Falla D, Arboleda-Velasquez JF, Quiroz YT, et al. Nat Med. 2023 May;29(5):1243-1252.
[2] Resistance to autosomal dominant Alzheimer’s disease in an APOE3 Christchurch homozygote: a case report. Arboleda-Velasquez JF, Lopera F, O’Hare M, Delgado-Tirado S, Tariot PN, Johnson KA, Reiman EM, Quiroz YT et al. Nat Med. 2019 Nov;25(11):1680-1683.
Links:
Alzheimer’s Disease & Related Dementias (National Institute on Aging/NIH)
“NIH Support Spurs Alzheimer’s Research in Colombia,” Global Health Matters, January/February 2014, Fogarty International Center/NIS
“COLBOS Study Reveals Mysteries of Alzheimer’s Disease,” NIH Record, August 19, 2022.
Yakeel Quiroz (Massachusetts General Hospital, Harvard Medical School, Boston)
Joseph Arboleda-Velasquez (Massachusetts Eye and Ear, Harvard Medical School, Boston)
Diego Sepulveda-Falla Lab (University Medical Center Hamburg-Eppendorf, Hamburg, Germany)
Francisco Lopera (University of Antioquia, Medellín, Colombia)
NIH Support: National Institute on Aging; National Eye Institute; National Institute of Neurological Disorders and Stroke; Office of the Director
All of Us Research Program Participants Fuel Both Scientific and Personal Discovery
Posted on by Josh Denny, M.D., M.S., All of Us Research Program
The NIH’s All of Us Research Program is a historic effort to create an unprecedented research resource that will speed biomedical breakthroughs, transform medicine and advance health equity. To create this resource, we are enrolling at least 1 million people who reflect the diversity of the United States.
At the program’s outset, we promised to make research a two-way street by returning health information to our participant partners. We are now delivering on that promise. We are returning personalized health-related DNA reports to participants who choose to receive them.
That includes me. I signed up to receive my “Medicine and Your DNA” and “Hereditary Disease Risk” reports along with nearly 200,000 other participant partners. I recently read my results, and they hit home, revealing an eye-opening connection between my personal and professional lives.
First, the professional. Before coming to All of Us, I was a practicing physician and researcher at Vanderbilt University, Nashville, TN, where I studied how a person’s genes might affect his or her response to medications. One of the drug-gene interactions that I found most interesting is related to clopidogrel, a drug commonly prescribed to keep arteries open after a major cardiovascular event, like a heart attack, stroke, or placement of a stent.
People with certain gene variations are not able to process this medication well, leaving them in a potentially risky situation. The patient and their health care provider may think the condition is being managed. But, since they can’t process the medication, the patient’s symptoms and risks are likely to increase.
The impact on patients has been seen in numerous studies, including one that I published with colleagues last year in the Journal of Stroke and Cerebrovascular Disease [1]. We found that stroke risk is three times higher in patients who were poor responders to clopidogrel and treated with the drug following a “mini-stroke”—also known as a transient ischemic attack. Other studies have shown that major cardiovascular events were 50 percent more common in individuals who were poor responders to clopidogrel [2]. Importantly, there are alternative therapies that work well for people with this genetic variant.
Now, the personal. Reading my health-related results, I learned that I carry some of these very same gene variations. So, if I ever needed a medicine to manage my risk of blood clots, clopidogrel would not likely work well for me.
Instead, should I ever need treatment, my provider and I could bypass this common first-line therapy and choose an alternate medicine. Getting the right treatment on the first try could cut my chances of a heart attack in half. The benefits of this knowledge don’t stop with me. By choosing to share my findings with family members who may have inherited the same genetic variations, they can discuss it with their health care teams.
Other program participants who choose to receive results will experience the same process of learning more about their health. Nearly all will get actionable information about how their body may process certain medications. A small percentage, 2 to 3 percent, may learn they’re at higher risk of developing several severe hereditary health conditions, such as certain preventable heart diseases and cancers. The program will provide a genetic counselor at no cost to all participants to discuss their results.
To enroll participants who reflect the country’s diverse population, All of Us partners with trusted community organizations around the country. Inclusion is vitally important in the field of genomics research, where available data have long originated mostly from people of European ancestry. In contrast, about 50 percent of the All of Us’ genomic data come from individuals who self-identify with a racial or ethnic minority group.
More than 3,600 research projects are already underway using data contributed by participants from diverse backgrounds. What’s especially exciting about this “ecosystem” of discovery between participants and researchers is that, by contributing their data, participants are helping researchers decode what our DNA is telling us about health across all types of conditions. In turn, those discoveries will deepen what participants can learn.
Those who have stepped up to join All of Us are the heartbeat of this historic research effort to advance personalized approaches in medicine. Their contributions are already fueling new discoveries in numerous areas of health.
At the same time, making good on our promises to our participant partners ensures that the knowledge gained doesn’t only accumulate in a database but is delivered back to participants to help advance their own health journeys. If you’re interested in joining All of Us, we welcome you to learn more.
References:
[1] CYP2C19 loss-of-function is associated with increased risk of ischemic stroke after transient ischemic attack in intracranial atherosclerotic disease. Patel PD, Vimalathas P, Niu X, Shannon CN, Denny JC, Peterson JF, Chitale RV, Fusco MR. J Stroke Cerebrovasc Dis. 2021 Feb;30(2):105464.
[2] Predicting clopidogrel response using DNA samples linked to an electronic health record. Delaney JT, Ramirez AH, Bowton E, Pulley JM, Basford MA, Schildcrout JS, Shi Y, Zink R, Oetjens M, Xu H, Cleator JH, Jahangir E, Ritchie MD, Masys DR, Roden DM, Crawford DC, Denny JC. Clin Pharmacol Ther. 2012 Feb;91(2):257-263.
Links:
Join All of Us (All of Us/NIH)
NIH’s All of Us Research Program returns genetic health-related results to participants, NIH News Release, December 13, 2022.
NIH’s All of Us Research Program Releases First Genomic Dataset of Nearly 100,000 Whole Genome Sequences, NIH News Release, March 17, 2022.
Funding and Program Partners (All of Us)
Medicine and Your DNA (All of Us)
Clopidogrel Response (National Library of Medicine/NIH)
Hereditary Disease Risk (All of Us)
Preparing for DNA Results: What Is a Genetic Counselor? (All of Us)
Research Projects Directory (All of Us)
Note: Dr. Lawrence Tabak, who performs the duties of the NIH Director, has asked the heads of NIH’s Institutes, Centers, and Offices to contribute occasional guest posts to the blog to highlight some of the interesting science that they support and conduct. This is the 24th in the series of NIH guest posts that will run until a new permanent NIH director is in place.
NCI Support for Basic Science Paves Way for Kidney Cancer Drug Belzutifan
Posted on by Norman "Ned" Sharpless, M.D., National Cancer Institute
There’s exciting news for people with von Hippel-Lindau (VHL) disease, a rare genetic disorder that can lead to cancerous and non-cancerous tumors in multiple organs, including the brain, spinal cord, kidney, and pancreas. In August 2021, the U.S. Food and Drug Administration (FDA) approved belzutifan (Welireg), a new drug that has been shown in a clinical trial led by National Cancer Institute (NCI) researchers to shrink some tumors associated with VHL disease [1], which is caused by inherited mutations in the VHL tumor suppressor gene.
As exciting as this news is, relatively few people have this rare disease. The greater public health implication of this advancement is for people with sporadic, or non-inherited, clear cell kidney cancer, which is by far the most common subtype of kidney cancer, with more than 70,000 cases and about 14,000 deaths per year. Most cases of sporadic clear cell kidney cancer are caused by spontaneous mutations in the VHL gene.
This advancement is also a great story of how decades of support for basic science through NCI’s scientists in the NIH Intramural Research Program and its grantees through extramural research funding has led to direct patient benefit. And it’s a reminder that we never know where basic science discoveries might lead.
Belzutifan works by disrupting the process by which the loss of VHL in a tumor turns on a series of molecular processes. These processes involve the hypoxia-inducible factor (HIF) transcription factor and one of its subunits, HIF-2α, that lead to tumor formation.
The unraveling of the complex relationship among VHL, the HIF pathway, and cancer progression began in 1984, when Bert Zbar, Laboratory of Immunobiology, NCI-Frederick; and Marston Linehan, NCI’s Urologic Oncology Branch, set out to find the gene responsible for clear cell kidney cancer. At the time, there were no effective treatments for advanced kidney cancer, and 80 percent of patients died within two years.
Zbar and Linehan started by studying patients with sporadic clear cell kidney cancer, but then turned their focus to investigations of people affected with VHL disease, which predisposes a person to developing clear cell kidney cancer. By studying the patients and the genetic patterns of tumors collected from these patients, the researchers hypothesized that they could find genes responsible for kidney cancer.
Linehan established a clinical program at NIH to study and manage VHL patients, which facilitated the genetic studies. It took nearly a decade, but, in 1993, Linehan, Zbar, and Michael Lerman, NCI-Frederick, identified the VHL gene, which is mutated in people with VHL disease. They soon discovered that tumors from patients with sporadic clear cell kidney cancer also have mutations in this gene.
Subsequently, with NCI support, William G. Kaelin Jr., Dana-Farber Cancer Institute, Boston, discovered that VHL is a tumor suppressor gene that, when inactivated, leads to the accumulation of HIF.
Another NCI grantee, Gregg L. Semenza, Johns Hopkins School of Medicine, Baltimore, identified HIF as a transcription factor. And Peter Ratcliffe, University of Oxford, United Kingdom, discovered that HIF plays a role in blood vessel development and tumor growth.
Kaelin and Ratcliffe simultaneously showed that the VHL protein tags a subunit of HIF for destruction when oxygen levels are high. These results collectively answered a very old question in cell biology: How do cells sense the intracellular level of oxygen?
Subsequent studies by Kaelin, with NCI’s Richard Klausner and Linehan, revealed the critical role of HIF in promoting the growth of clear cell kidney cancer. This work ultimately focused on one member of the HIF family, the HIF-2α subunit, as the key mediator of clear cell kidney cancer growth.
The fundamental work of Kaelin, Semenza, and Ratcliffe earned them the 2019 Nobel Prize in Physiology or Medicine. It also paved the way for drug discovery efforts that target numerous points in the pathway leading to clear cell kidney cancer, including directly targeting the transcriptional activity of HIF-2α with belzutifan.
Clinical trials of belzutifan, including several supported by NCI, demonstrated potent anti-cancer activity in VHL-associated kidney cancer, as well as other VHL-associated tumors, leading to the aforementioned recent FDA approval. This is an important development for patients with VHL disease, providing a first-in-class therapy that is effective and well-tolerated.
We believe this is only the beginning for belzutifan’s use in patients with cancer. A number of trials are now studying the effectiveness of belzutifan for sporadic clear cell kidney cancer. A phase 3 trial is ongoing, for example, to look at the effectiveness of belzutifan in treating people with advanced kidney cancer. And promising results from a phase 2 study show that belzutifan, in combination with cabozantinib, a widely used agent to treat kidney cancer, shrinks tumors in patients previously treated for metastatic clear cell kidney cancer [2].
This is a great scientific story. It shows how studies of familial cancer and basic cell biology lead to effective new therapies that can directly benefit patients. I’m proud that NCI’s support for basic science, both intramurally and extramurally, is making possible many of the discoveries leading to more effective treatments for people with cancer.
References:
[1] Belzutifan for Renal Cell Carcinoma in von Hippel-Lindau Disease. Jonasch E, Donskov F, Iliopoulos O, Rathmell WK, Narayan VK, Maughan BL, Oudard S, Else T, Maranchie JK, Welsh SJ, Thamake S, Park EK, Perini RF, Linehan WM, Srinivasan R; MK-6482-004 Investigators. N Engl J Med. 2021 Nov 25;385(22):2036-2046.
[2] Phase 2 study of the oral hypoxia-inducible factor 2α (HIF-2α) inhibitor MK-6482 in combination with cabozantinib in patients with advanced clear cell renal cell carcinoma (ccRCC). Choueiri TK et al. J Clin Oncol. 2021 Feb 20;39(6_suppl): 272-272.
Links:
Von Hippel-Lindau Disease (Genetic and Rare Diseases Information Center/National Center for Advancing Translational Sciences/NIH)
Clear Cell Renal Cell Carcinoma (National Cancer Institute/NIH)
Belzutifan Approved to Treat Tumors Linked to Inherited Disorder VHL, Cancer Currents Blog, National Cancer Institute, September 21, 2021.
The Long Road to Understanding Kidney Cancer (Intramural Research Program/NIH)
[Note: Acting NIH Director Lawrence Tabak has asked the heads of NIH’s institutes and centers to contribute occasional guest posts to the blog as a way to highlight some of the cool science that they support and conduct. This is the first in the series of NIH institute and center guest posts that will run until a new permanent NIH director is in place.]
A Race-Free Approach to Diagnosing Chronic Kidney Disease
Posted on by Dr. Francis Collins
Race has a long and tortured history in America. Though great strides have been made through the work of leaders like Dr. Martin Luther King, Jr. to build an equal and just society for all, we still have more work to do, as race continues to factor into American life where it shouldn’t. A medical case in point is a common diagnostic tool for chronic kidney disease (CKD), a condition that affects one in seven American adults and causes a gradual weakening of the kidneys that, for some, will lead to renal failure.
The diagnostic tool is a medical algorithm called estimated glomerular filtration rate (eGFR). It involves getting a blood test that measures how well the kidneys filter out a common waste product from the blood and adding in other personal factors to score how well a person’s kidneys are working. Among those factors is whether a person is Black. However, race is a complicated construct that incorporates components that go well beyond biological and genetic factors to social and cultural issues. The concern is that by lumping together Black people, the algorithm lacks diagnostic precision for individuals and could contribute to racial disparities in healthcare delivery—or even runs the risk of reifying race in a way that suggests more biological significance than it deserves.
That’s why I was pleased recently to see the results of two NIH-supported studies published in The New England Journal of Medicine that suggest a way to take race out of the kidney disease equation [1, 2]. The approach involves a new equation that swaps out one blood test for another and doesn’t ask about race.
For a variety of reasons, including socioeconomic issues and access to healthcare, CKD disproportionately affects the Black community. In fact, Blacks with the condition are also almost four times more likely than whites to develop kidney failure. That’s why Blacks with CKD must visit their doctors regularly to monitor their kidney function, and often that visit involves eGFR.
The blood test used in eGFR measures creatinine, a waste product produced from muscle. For about the past 20 years, a few points have been automatically added to the score of African Americans, based on data showing that adults who identify as Black, on average, have a higher baseline level of circulating creatinine. But adjusting the score upward toward normal function runs the risk of making the kidneys seem a bit healthier than they really are and delaying life-preserving dialysis or getting on a transplant list.
A team led by Chi-yuan Hsu, University of California, San Francisco, took a closer look at the current eGFR calculations. The researchers used long-term data from the Chronic Renal Insufficiency Cohort (CRIC) Study, an NIH-supported prospective, observational study of nearly 4,000 racially and ethnically diverse patients with CKD in the U.S. The study design specified that about 40 percent of its participants should identify as Black.
To look for race-free ways to measure kidney function, the researchers randomly selected more than 1,400 of the study’s participants to undergo a procedure that allows kidney function to be measured directly instead of being estimated based on blood tests. The goal was to develop an accurate approach to estimating GFR, the rate of fluid flow through the kidneys, from blood test results that didn’t rely on race.
Their studies showed that simply omitting race from the equation would underestimate GFR in Black study participants. The best solution, they found, was to calculate eGFR based on cystatin C, a small protein that the kidneys filter from the blood, in place of the standard creatinine. Estimation of GFR using cystatin C generated similarly accurate results but without the need to factor in race.
The second NIH-supported study led by Lesley Inker, Tufts Medical Center, Boston, MA, came to similar conclusions. They set out to develop new equations without race using data from several prior studies. They then compared the accuracy of their new eGFR equations to measured GFR in a validation set of 12 other studies, including about 4,000 participants.
Their findings show that currently used equations that include race, sex, and age overestimated measured GFR in Black Americans. However, taking race out of the equation without other adjustments underestimated measured GFR in Black people. Equations including both creatinine and cystatin C, but omitting race, were more accurate. The new equations also led to smaller estimated differences between Black and non-Black study participants.
The hope is that these findings will build momentum toward widespread adoption of cystatin C for estimating GFR. Already, a national task force has recommended immediate implementation of a new diagnostic equation that eliminates race and called for national efforts to increase the routine and timely measurement of cystatin C [3]. This will require a sea change in the standard measurements of blood chemistries in clinical and hospital labs—where creatinine is routinely measured, but cystatin C is not. As these findings are implemented into routine clinical care, let’s hope they’ll reduce health disparities by leading to more accurate and timely diagnosis, supporting the goals of precision health and encouraging treatment of CKD for all people, regardless of their race.
References:
[1] Race, genetic ancestry, and estimating kidney function in CKD. Hsu CY, Yang W, Parikh RV, Anderson AH, Chen TK, Cohen DL, He J, Mohanty MJ, Lash JP, Mills KT, Muiru AN, Parsa A, Saunders MR, Shafi T, Townsend RR, Waikar SS, Wang J, Wolf M, Tan TC, Feldman HI, Go AS; CRIC Study Investigators. N Engl J Med. 2021 Sep 23.
[2] New creatinine- and cystatin C-based equations to estimate GFR without race. Inker LA, Eneanya ND, Coresh J, Tighiouart H, Wang D, Sang Y, Crews DC, Doria A, Estrella MM, Froissart M, Grams ME, Greene T, Grubb A, Gudnason V, Gutiérrez OM, Kalil R, Karger AB, Mauer M, Navis G, Nelson RG, Poggio ED, Rodby R, Rossing P, Rule AD, Selvin E, Seegmiller JC, Shlipak MG, Torres VE, Yang W, Ballew SH,Couture SJ, Powe NR, Levey AS; Chronic Kidney Disease Epidemiology Collaboration. N Engl J Med. 2021 Sep 23.
[3] A unifying approach for GFR estimation: recommendations of the NKF-ASN Task Force on Reassessing the Inclusion of Race in Diagnosing Kidney Disease. Delgado C, Baweja M, Crews DC, Eneanya ND, Gadegbeku CA, Inker LA, Mendu ML, Miller WG, Moxey-Mims MM, Roberts GV, St Peter WL, Warfield C, Powe NR. Am J Kidney Dis. 2021 Sep 22:S0272-6386(21)00828-3.
Links:
Chronic Kidney Disease (National Institute of Diabetes and Digestive and Kidney Diseases/NIH)
Explaining Your Kidney Test Results: A Tool for Clinical Use (NIDDK)
Chronic Renal Insufficiency Cohort Study
Chi-yuan Hsu (University of California, San Francisco)
Lesley Inker (Tufts Medical Center, Boston)
NIH Support: National Institute of Diabetes and Digestive and Kidney Diseases
First Comprehensive Census of Cell Types in Brain Area Controlling Movement
Posted on by Dr. Francis Collins
The primary motor cortex is the part of the brain that enables most of our skilled movements, whether it’s walking, texting on our phones, strumming a guitar, or even spiking a volleyball. The region remains a major research focus, and that’s why NIH’s Brain Research Through Advancing Innovative Neurotechnologies® (BRAIN) Initiative – Cell Census Network (BICCN) has just unveiled two groundbreaking resources: a complete census of cell types present in the mammalian primary motor cortex, along with the first detailed atlas of the region, located along the back of the frontal lobe in humans (purple stripe above).
This remarkably comprehensive work, detailed in a flagship paper and more than a dozen associated articles published in the journal Nature, promises to vastly expand our understanding of the primary motor cortex and how it works to keep us moving [1]. The papers also represent the collaborative efforts of more than 250 BICCN scientists from around the world, teaming up over many years.
Started in 2013, the BRAIN Initiative is an ambitious project with a range of groundbreaking goals, including the creation of an open-access reference atlas that catalogues all of the brain’s many billions of cells. The primary motor cortex was one of the best places to get started on assembling an atlas because it is known to be well conserved across mammalian species, from mouse to human. There’s also a rich body of work to aid understanding of more precise cell-type information.
Taking advantage of recent technological advances in single-cell analysis, the researchers categorized into different types the millions of neurons and other cells in this brain region. They did so on the basis of morphology, or shape, of the cells, as well as their locations and connections to other cells. The researchers went even further to characterize and sort cells based on: their complex patterns of gene expression, the presence or absence of chemical (or epigenetic) marks on their DNA, the way their chromosomes are packaged into chromatin, and their electrical properties.
The new data and analyses offer compelling evidence that neural cells do indeed fall into distinct types, with a high degree of correspondence across their molecular genetic, anatomical, and physiological features. These findings support the notion that neural cells can be classified into molecularly defined types that are also highly conserved or shared across mammalian species.
So, how many cell types are there? While that’s an obvious question, it doesn’t have an easy answer. The number varies depending upon the method used for sorting them. The researchers report that they have identified about 25 classes of cells, including 16 different neuronal classes and nine non-neuronal classes, each composed of multiple subtypes of cells.
These 25 classes were determined by their genetic profiles, their locations, and other characteristics. They also showed up consistently across species and using different experimental approaches, suggesting that they have important roles in the neural circuitry and function of the motor cortex in mammals.
Still, many precise features of the cells don’t fall neatly into these categories. In fact, by focusing on gene expression within single cells of the motor cortex, the researchers identified more potentially important cell subtypes, which fall into roughly 100 different clusters, or distinct groups. As scientists continue to examine this brain region and others using the latest new methods and approaches, it’s likely that the precise number of recognized cell types will continue to grow and evolve a bit.
This resource will now serve as a springboard for future research into the structure and function of the brain, both within and across species. The datasets already have been organized and made publicly available for scientists around the world.
The atlas also now provides a foundation for more in-depth study of cell types in other parts of the mammalian brain. The BICCN is already engaged in an effort to generate a brain-wide cell atlas in the mouse, and is working to expand coverage in the atlas for other parts of the human brain.
The cell census and atlas of the primary motor cortex are important scientific advances with major implications for medicine. Strokes commonly affect this region of the brain, leading to partial or complete paralysis of the opposite side of the body.
By considering how well cell census information aligns across species, scientists also can make more informed choices about the best models to use for deepening our understanding of brain disorders. Ultimately, these efforts and others underway will help to enable precise targeting of specific cell types and to treat a wide range of brain disorders that affect thinking, memory, mood, and movement.
Reference:
[1] A multimodal cell census and atlas of the mammalian primary motor cortex. BRAIN Initiative Cell Census Network (BICCN). Nature. Oct 6, 2021.
Links:
NIH Brain Research Through Advancing Innovative Neurotechnologies® (BRAIN) Initiative (NIH)
BRAIN Initiative – Cell Census Network (BICCN) (NIH)
NIH Support: National Institute of Mental Health; National Institute of Neurological Disorders and Stroke
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