A recent study reveals a significant shift in the brain’s memory center around age 50. The discovery indicates that the brain starts replacing its long-standing immune cells with more inflammatory ones. This change might provide insights into how normal aging contributes to the onset of dementia, particularly Alzheimer’s disease.
Surprising Findings
Furhan Qureshi, a board-certified internal medicine physician, noted that the findings were unexpected. Medical education has long taught that the brain’s primary immune cells remain lifelong, appearing before birth and renewing within the brain. However, the study shows that at about 50, the hippocampus begins exchanging these cells for more inflammatory ones, possibly recruited from the bloodstream. This change represents a significant shift in understanding the brain’s immune environment.
Qureshi highlighted that this could alter scientific perspectives on diseases like Alzheimer’s. Inflammation has been widely observed in Alzheimer’s-affected brains, but its origin was unclear. The study suggests that normal aging might initiate inflammation in midlife, long before symptoms appear. The brain undergoes decades of quiet immune changes.
Study Details
The research was funded by the National Institutes of Health.
Scientists from the University of California, San Diego, the New York Genome Center, and the University of California, Irvine, participated. They used advanced single-cell techniques on postmortem hippocampal tissue from 40 neurologically healthy adults aged 20 to 95.
Findings showed that microglia, the brain’s primary immune cells, decline steadily between ages 50 and 75. As they diminish, cells with stronger inflammatory traits, resembling blood-circulating monocytes, replace them. This discovery challenges the longstanding belief that microglia appear during embryonic development and self-renew in the brain throughout life.
Researchers combined traditional gene-activity measures with newer tools mapping the genome’s 3D structure and chemical modifications, called the epigenome. This approach revealed cell identity and origin changes that gene activity alone couldn’t detect. Additionally, early signs of decline were found in cells maintaining the blood-brain barrier, the critical boundary controlling substances entering the brain from the bloodstream.
Implications for Aging
Aging is the primary risk factor for neurodegenerative diseases, with the hippocampus being particularly susceptible. An estimated 42% of Americans over 55 will eventually develop some form of dementia.
The study acknowledges that while previous research linked aging to increased inflammatory gene activity, gene expression alone provided an incomplete view of the decline’s cause. Ankit Chawla, a longevity and functional medicine physician, noted that the findings align with his field’s observations. The immune system is vital in aging processes, including in the brain.
The research also discovered that aging weakens the genome’s 3D organization across brain cell types and leads to a significant loss of astrocytes, essential cells for supporting brain signaling and metabolism.
For more information, Newsweek reached out to the study’s authors.
Reference:
Zemke, N. R., et al. (2026). Epigenetic and 3D genome reprogramming during the aging of the human hippocampus. Science. https://doi.org/10.1126/science.adt8307