Scientists discover a major brain shift between ages 50 and 75 — SkimNews
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- Bing Ren's team at the New York Genome Center used single-cell methods to map how gene regulation and 3D genome organization shift in the human hippocampus across the lifespan, with the largest changes landing between ages 50 and 75.
- Microglia — the brain's resident immune cells — declined sharply in that 50-to-75 window and were replaced by cells whose molecular features resemble blood immune cells, a turnover that challenges the long-standing assumption that microglia established in the embryo persist for life.
- The replacement cells carried stronger inflammatory signatures, raising the possibility that they drive chronic inflammation in the aging brain, according to co-author Bing Ren.
- Researchers also detected a substantial decline in cell populations that maintain the blood-brain barrier, the layer that shields the brain from harmful substances circulating in the bloodstream.
- Across multiple brain cell types, the team observed broad erosion of the genome's three-dimensional architecture — the folded DNA structure that determines which genes are switched on or off — suggesting structural decay is a fundamental feature of brain aging.
- The 4D Nucleome program, a decade-long NIH initiative that ran from 2015 to 2025, produced six papers in Science; this study is one of four by Ren's group examining genome architecture across cell types and timescales.
Why it matters: Age is the strongest risk factor for Alzheimer's and other neurodegenerative diseases, and this study pinpoints a specific biological window — roughly 50 to 75 — where inflammation-linked immune cells displace the brain's original microglia and blood-brain barrier support collapses. That midlife turnaround gives drug hunters a concrete cellular target and timeframe to study, rather than a vague 'old age' decline.
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