Brain immune cells turn inflammatory with age via metabolism

The brain has its own immune system. Microglia are the cells that do the work: they clear waste, monitor connections between neurons, and respond to damage. In youth, they do this efficiently. With age, however, they increasingly shift toward a harmful mode, becoming chronically active and producing inflammatory substances that damage brain tissue. The researchers argue that metabolic changes play a central role in this shift.

Energy drives behavior

Microglia use different energy sources depending on what they are doing. For rapid immune responses, they switch to glycolysis, quickly burning sugar. For quiet maintenance tasks, they use oxidative phosphorylation, a slower but more efficient way to extract energy from oxygen. With aging, this balance is disrupted. Microglia become stuck in the sugar-burning mode, even when there is no acute threat. This leads to persistent production of inflammatory molecules.

The production of reactive oxygen species (unwanted byproducts of energy processes) also increases. These damage surrounding brain tissue and amplify the inflammatory response further. At the same time, the capacity for clearing damaged proteins and cells, a process called phagocytosis, declines.

Sex differences and disease context

The review study, published in Aging Cell, emphasizes that metabolic changes in microglia are not uniform. They differ between males and females, and they progress differently during healthy aging compared to Alzheimer’s or Parkinson’s disease. In Alzheimer’s, specific metabolic pathways related to lipid processing are additionally disrupted. In Parkinson’s, mitochondrial dysfunction and oxidative stress play a larger role.

The researchers emphasize that a better understanding of these metabolic patterns could help develop therapies that return microglia to their healthy, maintenance-oriented behavior. This is early-stage basic research. Concrete treatments do not yet exist.

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