Scientists discover a major brain shift between ages 50 and 75 — SkimNews
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- Bing Ren and colleagues at the New York Genome Center published a study in Science using single-cell methods on human hippocampus samples, finding that genome regulation in the brain undergoes sweeping reorganization beginning in midlife — potentially explaining why age is the strongest risk factor for Alzheimer's and other neurodegenerative diseases.
- Microglia — the brain's resident immune cells — declined sharply between approximately ages 50 and 75 and were increasingly replaced by cells with molecular features resembling blood-derived immune cells, challenging the long-standing assumption that embryonic microglia persist for a person's entire life.
- The replacement microglia-like cells showed stronger inflammatory signatures, leading the researchers to raise the possibility that these newcomers could drive chronic inflammation characteristic of the aging brain.
- Blood-brain barrier support cells declined substantially with age, weakening the protective shield that keeps harmful bloodborne substances away from brain tissue.
- Across multiple brain cell types, the team observed broad erosion of the genome's three-dimensional architecture — the organized DNA folding that controls which genes are switched on or off — suggesting structural decay is a fundamental feature of brain aging, not just cellular wear.
- Xiangmin Xu of UC Irvine, a co-corresponding author, framed the findings as showing brain aging involves "coordinated and dynamic remodeling of immune, vascular, and neuronal systems" rather than a simple, steady decline.
- The study is one of six papers released in Science through the NIH's 4D Nucleome Common Fund program, which ran from 2015 to 2025 to map how genome spatial organization changes over time.
Why it matters: By mapping how the aging hippocampus's genome is remodeled between ages 50 and 75 — including the replacement of lifelong microglia with more inflammatory cells and erosion of 3D genome structure — the study hands drug hunters a concrete mechanistic map for the period when Alzheimer's risk begins climbing sharply, potentially opening new therapeutic targets aimed at preserving brain function across the lifespan.
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