A changing of the guard in immune cells could make the older brain more vulnerable to Alzheimer’s and other dementias.
A series of silent transformations that the human brain undergoes between the ages of 50 and 75 could explain why aging is a factor that markedly increases the risk of Alzheimer’s and other neurodegenerative diseases.
A research published on has brought these changes of pace to light Sciencewho studied how gene regulation (i.e. the process that activates or deactivates specific genes in response to the organism’s needs and which is the basis of cellular differentiation) changes with advancing age. The analysis concerns cells of the hippocampus, a brain structure crucial for memory.
The decline of microglia
The most obvious changes were detected in microglia, the collection of cells responsible for immune surveillance of the central nervous system.
The scientists at the New York Genome Center who signed the study realized that, between the ages of 50 and 75, these cells face a marked decline, and are progressively replaced by other cells, with molecular characteristics more similar to those of blood immune cells.
These new “replacement” cells send stronger inflammatory signals and could contribute to the inflammatory processes also thought to be implicated in dementia.
A more porous shield
The second change detected by the study is a decline in cells that help maintain the blood-brain barrier, which regulates the passage of chemicals through the blood to and from the brain, and protects the nervous system from poisoning and intoxication. The progressive weakening of these two lines of protection could expose the brain to the accumulation of toxins and more intense inflammatory processes.
A more chaotic genome structure
Within the nuclei of several types of brain cells, scientists ultimately observed a deterioration in the three-dimensional structure of DNA, which could contribute to changes in gene expression and be a typical feature of brain aging.
These transformations help to understand how brain aging is a complex process, which involves immune actors and not just vascular or neural ones. Knowing how the spatial arrangement of DNA influences gene regulation, or how immune changes can impact inflammatory processes in the brain, will help refine research to protect the nervous system from degenerative conditions.
