Aging triggers an upregulation of a multitude of cytokines in the male and especially the female rodent hippocampus but more discrete changes in other brain regions

Background Despite widespread acceptance that neuroinflammation contributes to age-related cognitive decline, studies comparing protein expression of cytokines in the young versus old brains are surprisingly limited in terms of the number of cytokines and brain regions studied. Complicating matters, discrepancies abound-particularly for interleukin 6 (IL-6)-possibly due to differences in sex, species/strain, and/or the brain regions studied. Methods As such, we clarified how cytokine expression changes with age by using a Bioplex and Western blot to measure multiple cytokines across several brain regions of both sexes, using 2 mouse strains bred in-house as well as rats obtained from NIA. Parametric and nonparametric statistical tests were used as appropriate. Results In the ventral hippocampus of C57BL/6J mice, we found age-related increases in IL-1 alpha, IL-1 beta, IL-2, IL-3, IL-4, IL-6, IL-9, IL-10, IL-12p40, IL-12p70, IL-13, IL-17, eotaxin, G-CSF, interfeuron delta, KC, MIP-1a, MIP-1b, rantes, and TNF alpha that are generally more pronounced in females, but no age-related change in IL-5, MCP-1, or GM-CSF. We also find aging is uniquely associated with the emergence of a module (a.k.a. network) of 11 strongly intercorrelated cytokines, as well as an age-related shift from glycosylated to unglycosylated isoforms of IL-10 and IL-1 beta in the ventral hippocampus. Interestingly, age-related increases in extra-hippocampal cytokine expression are more discreet, with the prefrontal cortex, striatum, and cerebellum of male and female C57BL/6J mice demonstrating robust age-related increase in IL-6 expression but not IL-1 beta. Importantly, we found this widespread age-related increase in IL-6 also occurs in BALB/cJ mice and Brown Norway rats, demonstrating conservation across species and rearing environments. Conclusions Thus, age-related increases in cytokines are more pronounced in the hippocampus compared to other brain regions and can be more pronounced in females versus males depending on the brain region, genetic background, and cytokine examined.

Automated summary

Despite the wide acceptance of neuroinflammation contributing to age-related cognitive decline, studies on cytokine protein expression in young versus old brains are limited. Age-related increases in cytokines are more pronounced in the hippocampus, especially in females, with a shift in glycosylated forms of IL-10 and IL-1 beta in this brain region. Age-related increases in IL-6 expression are also seen in extra-hippocampal regions but are more discreet.