Story by Song Hye-jin, www.msn.com
WE OFTEN say, “After turning 50, neither the body nor the mind feels the same as before.” A new study has revealed a scientific reason why people feel this way.
As people pass the age of 50, immune cells that originally protected the brain gradually disappear, and other cells that once circulated in the bloodstream take their place.
Researchers from UC San Diego and UC Irvine in the U.S. analyzed brain tissue (from the hippocampus, the brain region responsible for memory) donated by 40 people aged 20 to 100.
Their findings were published in the international journal *Science* at the end of last month.
◇Brain Cells Change After 50
The brain contains special cells called “microglia,” which act as dedicated guards for brain immunity. These cells are known to settle in the brain before birth and remain in place throughout life.
The research team discovered a new fact: after people typically pass 50, microglia gradually disappear, and monocyte-derived cells that once traveled through the bloodstream replace them. By the late 70s, the original immune cells are almost gone, and the newly arrived cells dominate the brain.
The problem is that these new cells are far more sensitive than the original ones and produce more inflammatory substances. This could accelerate brain aging.
◇Gene Structure Loosens
Another change that ages the brain is the reduction of cells that care for it. “Astrocytes” help neurons connect properly and guard the blood-brain barrier. As people age, the number of these cells steadily decreases, and so does the function of mitochondria, which produce energy within cells.
The structure of DNA in the brain also becomes looser after 50. DNA in our bodies is not randomly clumped but folded neatly into sections, like an organized drawer. This allows precise access to necessary genes when needed. With age, these well-divided compartments become increasingly loose, making gene regulation more difficult.
◇Decoding Brain Cells One by One
The researchers uncovered these previously unknown secrets of brain cells using a method called “DNA methylation analysis.” This cutting-edge technique reads individual brain cells to determine their origin and was combined with AI analysis to enhance accuracy.
Reference: https://www.science.org/doi/10.1126/science.adt8307
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