Scientists discover a hidden brain shift that begins around age 50
Beginning around age 50, the brain’s memory center appears to lose many of its longtime immune cells and replace them with more inflammatory ones. This surprising shift may help explain how normal aging sets the stage for Alzheimer’s disease and dementia.
A recent NIH-funded study has revealed a significant change in the immune system of the hippocampus, a brain region crucial for learning and memory, particularly in individuals over 50 years old. This shift, which marks a substantial departure from previous assumptions about microglia, the brain's primary immune cells, could shed light on how aging contributes to neurodegenerative diseases like Alzheimer's.
Led by researchers from UC San Diego, the New York Genome Center, and UC Irvine, the team employed advanced single-cell techniques to analyze postmortem hippocampal tissue from 40 adults aged 20 to 95. Their findings indicate that microglia decline from around age 50 to 75, replaced by cells with heightened inflammatory markers and traits akin to peripheral blood immune cells. This discovery contradicts the long-held belief that microglia continuously renew themselves throughout a person's life.
By integrating gene expression data with genome structure and epigenetic modifications, the researchers uncovered a profound transformation in the identity and lineage of these immune cells. These insights were only possible through the combined analysis of gene activity and epigenetic signatures, techniques that allowed them to detect changes in cell identity and origin that would have been missed by examining gene expression alone.
The study also uncovered signs of aging-related deterioration in cells that maintain the blood-brain barrier, the protective shield regulating the transfer of substances from the bloodstream to the brain. Additionally, aging was associated with widespread, coordinated changes in the brain's genome organization, which were linked to shifts in gene regulation and cell identity.
The researchers, including Dr. Bing Ren from the New York Genome Center, are now investigating why these microglia are lost with age and whether the newly discovered immune cell transition directly contributes to Alzheimer's disease and other age-related neurological conditions. By understanding these cellular transitions, the team hopes to develop interventions that preserve brain function and reduce vulnerability to neurodegenerative diseases, potentially altering the course of aging-related cognitive decline.
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