Ageing: Immune invasion in the ageing brain

Observations of age-dependent changes in the collection of cells that contribute to the production of new neurons (the neurogenic niche) in mice are reported in Nature. The study identifies a role for the immune system in the age-related decline of the neurogenic niche. These findings may help to inform strategies for countering the decline of neuron precursor cells in the ageing mammalian brain.

Mammalian brains are capable of generating new neurons within neurogenic niches, which are made up of neural stem cells, neural progenitors and several other cell types. The function of this niche and its ability to create new neurons declines with age, an effect that is thought to contribute to cognitive decline. However, it is unclear how this niche changes with age or what causes these changes.

To compare the composition of cells in young and old neurogenic niches, Anne Brunet and colleagues profile cells the brains of three young (3 months old) and three old (28 - 29 months old) mice. Analyses of RNA sequences from 14,685 single cells reveals age-dependent changes in the neurogenic niche, including a decrease in activated neural stem cells and progenitors, and the infiltration of T cells (a type of immune cell) in the older brains. The T cells from old brains release a signalling molecule called interferon gamma, which is shown to reduce the proliferation of neural stem cells grown in cultures. These results identify a possible cause for a decline in neuron replenishment during ageing, and may pave the way for immune-based strategies to address age-related cognitive impairment, the authors conclude.