Crosstalk between astrocytes and neutrophils via S100B/RAGE/NETs exacerbates secondary injury following traumatic brain injury.

Astrocytes and neutrophils are crucial cells that migrate to the injured site in the early stages following traumatic brain injury (TBI), and their crosstalk may facilitate the transition to a pro-inflammatory phenotype and function in each other, contributing to secondary injury. However, the regulatory mechanism under the crosstalk is still poorly understood. Our previous work showed that TBI-induced activated astrocytes mediate endothelial injury through the S100B/RAGE pathway. In the present study, the RAGE knockout mice were utilized to demonstrate that RAGE signaling upregulated A1 reactive astrocytes and S100B expression and release following TBI. An in vitro model of TBI was established by stimulating neutrophils with TBI mouse serum or recombinant S100B, along with the use of a RAGE inhibitor. Our findings showed that S100B/RAGE signaling mediates the N1 phenotype and mitochondrial ROS-dependent NET production in neutrophils after TBI. Further study revealed that S100B enhances ICAM-1 expression and intracellular signaling in neutrophils, while also synergistically activating RAGE and CD11b to amplify inflammatory response. In addition, activated neutrophils or isolated NETs in vitro also result in elevated A1 reactivity and S100B levels in astrocytes. Finally, in TBI mouse models, we confirmed that inhibiting RAGE signaling indeed reduces N1 neutrophils and NETs in brain and lung tissues, alleviating secondary lung injury after TBI. Overall, the present study reveals the regulatory mechanisms of the S100B/RAGE/NETs signaling in the crosstalk between astrocytes and neutrophils, offering new approaches for preventing secondary injuries after TBI.