Brain Aging Study Reveals Coordinated Cellular Remodeling in the Hippocampus Between Ages 50 and 75
核心洞察
A single-cell analysis of the human hippocampus reveals that microglia undergo a major shift between ages 50 and 75, with embryonic-derived cells declining and being replaced by cells resembling blood-borne immune cells with stronger inflammatory signatures.
Genome three-dimensional organization progressively weakens across multiple brain cell types with age, suggesting declining genome architecture may be a fundamental feature of brain aging.
Cell populations maintaining the blood-brain barrier also decline substantially during this midlife window, potentially compromising the brain's protective boundary.
A comprehensive single-cell analysis of the human hippocampus has uncovered a striking biological transition occurring between roughly ages 50 and 75, revealing coordinated changes across immune cells, genome organization, and gene regulation that may help explain why advancing age is the strongest risk factor for neurodegenerative diseases (搜索) such as Alzheimer's.
The study, published in Science, is one of six papers released through the National Institutes of Health's 4D Nucleome (4DN) Common Fund program, a decade-long initiative mapping how the genome's three-dimensional architecture changes across space and time.
Midlife Immune Shift in the Brain
The most pronounced transition appeared in microglia, the resident immune cells that maintain and protect brain tissue. Between approximately ages 50 and 75, microglia formed during embryonic development declined sharply. In their place, researchers detected cells whose molecular profiles resembled immune cells circulating in the blood.
This turnover challenges the long-held assumption that microglia established before birth remain in the brain throughout a person's life. The replacement microglia-like cells carried stronger inflammatory signatures, raising the possibility that they contribute to the persistent neuroinflammation associated with brain aging.
"Microglia are critical for maintaining brain homeostasis," said Bing Ren, PhD, a corresponding author of the study, Scientific Director and CEO of the New York Genome Center, and Professor at Columbia University. "When these cells fail to perform their housekeeping duties, toxic materials accumulate that can trigger inflammatory processes that may contribute to neurodegenerative diseases (搜索)."
The analysis also revealed that cell populations involved in maintaining the blood-brain barrier declined substantially. This protective boundary helps prevent harmful substances in the bloodstream from entering brain tissue, and its deterioration may represent another pathway through which aging increases vulnerability to neurological disease.
Genome Architecture Erodes With Age
Beyond immune and vascular changes, researchers found that the genome's three-dimensional structure became progressively less organized across several types of brain cells. DNA is not stored inside the nucleus as a loose strand but folds into a carefully arranged structure that helps determine which genes a cell can use. The widespread erosion of that architecture suggests that declining genome organization may be a basic feature of brain aging.
"This work represents a major step forward in understanding how aging reshapes the human genome in brain cells," said Nathan Zemke, Director of Single-cell Genomics at the Center for Epigenomics at UC San Diego. "These findings demonstrate a critical need for studying gene regulation and genome organization to gain a mechanistic understanding of the aging process."
Coordinated Remodeling, Not Gradual Decline
The results indicate that brain aging involves more than a slow accumulation of damage. Instead, immune, vascular, and neuronal systems appear to undergo coordinated changes as people grow older.
"Importantly, this study reveals that aging is not simply a gradual decline, but involves coordinated and dynamic remodeling of immune, vascular, and neuronal systems," said Xiangmin Xu, PhD, Chancellor's Professor and Director of the Center for Neural Circuit Mapping at the University of California, Irvine, and a co-corresponding author of the study. "These findings open the door to identifying new therapeutic targets aimed at preserving circuit integrity and brain function across the lifespan."
To trace this process, researchers analyzed individual cells from human hippocampal tissue collected across the adult lifespan. The hippocampus is a brain region essential for learning and memory. Using advanced single-cell methods, they mapped both gene regulation and three-dimensional genome architecture, producing one of the most detailed accounts yet of how these features change as the human brain ages.
The 4D Nucleome program, which ran from 2015 to 2025, united interdisciplinary research groups from across the United States to examine how the spatial arrangement of the genome shapes biological activity. Together, the six studies establish a broad resource for researchers investigating how failures in genome organization relate to development, aging, and disease, including neurodegenerative disease.