How immunity contributes to ageing and neurodegeneration

As we age, our bodies undergo various changes that can impact our overall health and make us more susceptible to diseases. One common factor in the ageing process is low-grade inflammation, which contributes to age-related decline and impairment. However, the precise pathways responsible for this inflammation and their impact on natural ageing have remained elusive until now.

A new study now shows that a molecular signaling pathway called cGAS/STING, plays a critical role in driving chronic inflammation and functional decline during aging. By blocking the STING protein, the researchers were able to suppress inflammatory responses in senescent cells and tissues, leading to improvements in tissue function.

cGAS/STING is a molecular signaling pathway that detects the presence of DNA in cells. It involves two proteins, cyclic GMP–AMP synthase (cGAS) and Stimulator of Interferon Genes (STING). When activated, cGAS/STING triggers an immune response to defend against viral and bacterial infections.

Previous work has linked cGAS/STING to a number of biological processes, including cellular senescence, a hallmark of aging. Based on this, the researchers investigated whether it might underlie maladapted immune responses during ageing.

The research found that activating the STING protein triggers specific patterns of gene activity in microglia, the brain’s first-line-of-defense immune cells. These gene-activation patterns matched those arising in microglia in distinct neurodegenerative conditions, such as Alzheimer`s disease and ageing.

“In search for a mechanism that would engage the cGAS-STING pathway in ageing, we considered aberrant mitochondrial DNA species,” says the author. “Mitochondria, the organelles that are responsible for energy production are well-known for disturbed functioning in ageing and disease. Indeed, in microglia from old, but not young mice, DNA from mitochondria accumulated in the cell cytoplasm, suggesting a possible mechanism by which the cGAS-STING pathway contributes to inflammation in the ageing brain.”

The researchers studied the effects of blocking the STING protein in aged mice. As expected by its central role in driving inflammation, inhibiting STING alleviated markers of inflammation both in the periphery and in the brain. More importantly, animals receiving STING inhibitors displayed significant enhancements in spatial and associative memory. STING blockade also affected physical function with improved muscle strength and endurance.

The study advances our understanding of ageing-related inflammation and also offers potential strategies for slowing cognitive deterioration in age-associated neurodegenerative conditions. The precise elucidation of the neuroimmune crosstalk governing microglial-dependent neurotoxicity also holds promise for the future study of neurodegenerative diseases.