Amplification and propagation of interleukin-1β signaling by murine brain endothelial and glial cells

Background: during acute infections and chronic illnesses,the pro-inflammatory cytokine interleukin-1β (il-1β) acts within the brain to elicit metabolic derangements and sickness behaviors. it is unknown which cells in the brain are the proximal targets for il-1β with respect to the generation of these illness responses. we performed a series of in vitro experiments to (1) investigate which brain cell populations exhibit inflammatory responses to il-1β and (2) examine the interactions between different il-1β-responsive cell types in various co-culture combinations. methods: we treated primary cultures of murine brain microvessel endothelial cells (bmec),astrocytes,and microglia with pbs or il-1β,and then performed qpcr to measure inflammatory gene expression or immunocytochemistry to evaluate nuclear factor kappa-light-chain-enhancer of activated b cells (nf-κb) activation. to evaluate whether astrocytes and/or bmec propagate inflammatory signals to microglia,we exposed microglia to astrocyte-conditioned media and co-cultured endothelial cells and glia in transwells. treatment groups were compared by student's t tests or by anova followed by bonferroni-corrected t tests. results: il-1β increased inflammatory gene expression and nf-κb activation in primary murine-mixed glia,enriched astrocyte,and bmec cultures. although il-1β elicited minimal changes in inflammatory gene expression and did not induce the nuclear translocation of nf-κb in isolated microglia,these cells were more robustly activated by il-1β when co-cultured with astrocytes and/or bmec. we observed a polarized endothelial response to il-1β,because the application of il-1β to the abluminal endothelial surface produced a more complex microglial inflammatory response than that which occurred following luminal il-1β exposure. conclusions: inflammatory signals are detected,amplified,and propagated through the cns via a sequential and reverberating signaling cascade involving communication between brain endothelial cells and glia. we propose that the brain's innate immune response differs depending upon which side of the blood-brain barrier the inflammatory stimulus arises,thus allowing the brain to respond differently to central vs. peripheral inflammatory insults. © 2017 the author(s).