Histological staining reveals that axonal myelination is reduced in APOE4 human brains compared to APOE3/3. Each image is a representative image from different individuals.
UNDER EMBARGO UNTIL
Wednesday, November 16 at 11am EST
Newswise — New York, NY (November 11, 2022) – A gene recognized as the strongest risk factor for Alzheimer’s disease (AD) alters the way cholesterol moves around the brain and as we age, this altered movement likely contributes to loss of learning and memory, a team of researchers from the Icahn School of Medicine at Mount Sinai and the Massachusetts Institute of Technology (MIT) reports.
The change in cholesterol processing brought about by the gene, APOE4, may play a central role in Alzheimer’s disease-related cognitive impairments, and pharmacological intervention to reduce this effect improved learning and memory in mice with APOE4 Alzheimer’s disease, the researchers said. The study was published online November 16 in Nature.
“Since APOE4 is present in aproximately 50 percent of people with Alzheimer’s, we realized that deciphering its molecular and cellular pathways could help us to better understand the pathogenesis of the disease and reveal new therapeutic strategies for a large portion of the AD population,” says co-lead author Joel Blanchard, PhD, Assistant Professor of Neuroscience, and Cell, Developmental and Regenerative Biology, at Icahn Mount Sinai. “We learned that APOE4 causes gene expression changes across all cell types of the human brain and significantly alters signaling pathways associated with cholesterol balance and transport.”
The study was initiated while Dr. Blanchard was a postdoctoral fellow at The Picower Institute for Learning and Memory in the laboratory of Li-Huei Tsai, PhD, Picower Professor of Neuroscience at MIT and senior author of the paper. They continued the work as a collaboration when Dr. Blanchard joined Mount Sinai as a faculty member in 2021.
“Mounting evidence shows that APOE4 disrupts how different brain cells process lipids including cholesterol and that this underlying biology may contribute significantly to the pathology of Alzheimer’s disease,” Dr. Tsai said. “This insight suggests that in a large population of patients, lipid regulation may be a worthwhile target in the urgent search for potential interventions.”
Dr. Blanchard and co-lead authors Leyla Akay, and Djuna von Maydell, graduate students at MIT, and Jose Davila Velderrain, PhD, research group leader at Human Technopole, performed single-nuclei RNA sequencing of the postmortem prefrontal cortex of 32 human brains from individuals with and without APOE4. The researchers found that in patients with APOE4, cholesterol was aberrantly deposited in oligodendrocytes, the cells responsible for producing myelin, a fatty insulating structure that sheaths neurons and facilitates electrical communication between different parts of the brain. This accumulation of cholesterol in APOE4 oligodendrocytes led to reduced myelination, hindering electrical communitation within the brain and potentially leading to learning and memory dysfunction.
Previous studies have documented myelin damage in many individuals before the onset of Alzheimer’s disease symptoms, and found that reduced myelin volume in the fourth and fifth decades of life predicts a higher probability of cognitive impairment decades later. The Mount Sinai-MIT team is the first to establish a functional link between APOE4, myelination, and memory loss.
“It’s interesting to speculate from our work that dysregulation of cholesterol-related processes in the oligodendrocytes causes a reduction in myelin early in the lives of APOE4 carriers, rendering them particularly vulnerable to amyloid and tau-mediated neurotoxicity that accumulates later on. This has clear implications for treating and also identifying those at risk for developing AD,” says Dr. Blanchard, who is an investigator in the Black Family Stem Cell Institute, The Friedman Brain Institute, and The Ronald M. Loeb Center for Alzheimer’s Disease at Mount Sinai.
APOE4 is associated with increased deposition of amyloid-β proteins that clump together to form plaques, and neurofibrillary tangles of the tau protein, both of which collect between neurons and disrupt their communications function. While prior research has suggested a link between Alzheimer’s disease and the interaction of abnormal tau and amyloid-β, it is still not known if these proteins are the cause or the consequence of AD.
The connection uncovered by Mount Sinai and MIT researchers between APOE4 and cholesterol imbalance could potentially open the door to new therapeutic solutions for a disease known to afflict one in ten Americans over the age of 65.
Dr. Blanchard said that in addition to drugs that facilitate cholesterol transport, other interventions designed to restore cholesterol equilibrium in the brain—including dietary and lifestyle—might also increase cognitive reserves in individuals with the APOE4 gene. “By identifying ways APOE4 mediates the risk of Alzheimer’s,” he says, “we’ve opened new pathways to both treat and prevent the disease through a much-needed non-amyloid strategy.”
About the Icahn School of Medicine at Mount Sinai
The Icahn School of Medicine at Mount Sinai is internationally renowned for its outstanding research, educational, and clinical care programs. It is the sole academic partner for the eight member hospitals* of the Mount Sinai Health System, one of the largest academic health systems in the United States, providing care to a large and diverse patient population.
Ranked 14th nationwide in National Institutes of Health (NIH) funding and among the 99th percentile in research dollars per investigator according to the Association of American Medical Colleges, Icahn Mount Sinai has a talented, productive, and successful faculty. More than 3,000 full-time scientists, educators and clinicians work within and across 34 academic departments and 35 multidisciplinary institutes, a structure that facilitates tremendous collaboration and synergy. Our emphasis on translational research and therapeutics is evident in such diverse areas as genomics/big data, virology, neuroscience, cardiology, geriatrics, as well as gastrointestinal and liver diseases.
Icahn Mount Sinai offers highly competitive MD, PhD, and Master’s degree programs, with current enrollment of approximately 1,300 students. It has the largest graduate medical education program in the country, with more than 2,000 clinical residents and fellows training throughout the Health System. In addition, more than 550 postdoctoral research fellows are in training within the Health System.
A culture of innovation and discovery permeates every Icahn Mount Sinai program. Mount Sinai’s technology transfer office, one of the largest in the country, partners with faculty and trainees to pursue optimal commercialization of intellectual property to ensure that Mount Sinai discoveries and innovations translate into healthcare products and services that benefit the public.
Icahn Mount Sinai’s commitment to breakthrough science and clinical care is enhanced by academic affiliations that supplement and complement the School’s programs.
Through the Mount Sinai Innovation Partners (MSIP), the Health System facilitates the real-world application and commercialization of medical breakthroughs made at Mount Sinai. Additionally, MSIP develops research partnerships with industry leaders such as Merck & Co., AstraZeneca, Novo Nordisk, and others.
The Icahn School of Medicine at Mount Sinai is located in New York City on the border between the Upper East Side and East Harlem and classroom teaching takes place on a campus facing Central Park. Icahn Mount Sinai’s location offers many opportunities to interact with and care for diverse communities. Learning extends well beyond the borders of our physical campus, to the eight hospitals of the Mount Sinai Health System, our academic affiliates, and globally.
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* Mount Sinai Health System Member Hospitals: The Mount Sinai Hospital; Mount Sinai Queens; Mount Sinai Beth Israel; Mount Sinai West; Mount Sinai Morningside; Mount Sinai Brooklyn; New York Eye and Ear Infirmary of Mount Sinai; and Mount Sinai South Nassau.
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