Scientists discover a hidden brain shift that begins around age 50
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- NIH-funded researchers found that microglia in the hippocampus gradually decline from about age 50 to 75 and are replaced by cells with stronger inflammatory signals that resemble peripheral blood immune cells.
- The study analyzed postmortem hippocampal tissue from 40 neurologically healthy adults aged 20 to 95 using single-cell methods that combined gene activity with 3D genome mapping and epigenome analysis.
- The discovery challenges the long-standing belief that microglia—which first develop during embryonic growth—remain in the brain and renew themselves throughout a person's life.
- Researchers from UC San Diego, the New York Genome Center, and UC Irvine also identified age-related decline in cells maintaining the blood-brain barrier and widespread coordinated changes in the genome's physical organization across multiple brain cell types.
- NIA Director Richard Hodes called the "previously hidden microglial shift" an "important clue" linking aging to dementia, noting that aging is the single largest risk factor for the disease.
- The study, published in Science (DOI: 10.1126/science.adt8307), will inform future research into whether this immune cell transition directly contributes to Alzheimer's disease and other age-related neurological conditions.
Why it matters: This finding gives researchers a concrete midlife cellular event—microglia being replaced by inflammatory cells starting around age 50—that could become a target for interventions aimed at delaying Alzheimer's and other neurodegenerative diseases. It reframes age 50 as a potential neurological inflection point rather than just a demographic milestone.
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