Lifespan extension with preservation of hippocampal function in aged system x_c^--deficient male mice

The cystine/glutamate antiporter system x_c^- has been identified as the major source of extracellular glutamate in several brain regions as well as a modulator of neuroinflammation, and genetic deletion of its specific subunit xCT (xCT^-/-) is protective in mouse models for age-related neurological disorders. However, the previously observed oxidative shift in the plasma cystine/cysteine ratio of adult xCT^-/- mice led to the hypothesis that system x_c^- deletion would negatively affect life- and healthspan. Still, till now the role of system x_c^- in physiological aging remains unexplored. We therefore studied the effect of xCT deletion on the aging process of mice, with a particular focus on the immune system, hippocampal function, and cognitive aging. We observed that male xCT^-/- mice have an extended lifespan, despite an even more increased plasma cystine/cysteine ratio in aged compared to adult mice. This oxidative shift does not negatively impact the general health status of the mice. On the contrary, the age-related priming of the innate immune system, that manifested as increased LPS-induced cytokine levels and hypothermia in xCT^+/+ mice, was attenuated in xCT^-/- mice. While this was associated with only a very moderate shift towards a more anti-inflammatory state of the aged hippocampus, we observed changes in the hippocampal metabolome that were associated with a preserved hippocampal function and the retention of hippocampus-dependent memory in male aged xCT^-/- mice. Targeting system x_c^- is thus not only a promising strategy to prevent cognitive decline, but also to promote healthy aging.