Histones of Neutrophil Extracellular Traps (NETs) Activate Brain Pericyte via Dectin-1 in Traumatic Brain Injury

Abstract

BackgroundBlood-brain barrier (BBB) disruption and leukocyte infiltration are two pathological features post traumatic brain injury (TBI). However, the role of circulating leukocytes in BBB disruption and the crosstalk between them are not fully elucidated. Neutrophil is the most abundant circulating cell type that migrates into brain tissue when TBI occurs instantly, while brain pericyte occupies a strategic position between circulating cell and interstitial space in BBB. Understanding their interactions is essential to provide insight into the intrinsic relationship and identify biological targets for TBI treatments. MethodsBy analyzing brain tissues from TBI patients and mouse TBI model through immunohistochemical method and flow cytometry, we build the relationship between neutrophils, neutrophil extracellular traps (NETs) and brain pericyte. The components of NETs-related medium were investigated by proteomics and metabolomics to decipher the factors directly regulating pericytes. The molecular mechanisms were deeply explored by WB/CHIP/RT-PCR in primary brain pericyte/pericyte cell line MBVP treated with NETs-formed medium or specific NETs components. In mice TBI model, we also explored the possible therapeutic approaches for TBI treatment that targeting at the axis of neutrophil-NETs-pericyte. ResultsNETs formation is highly enhanced post TBI, inducing the appearance of CD11b expressing brain pericyte simultaneously. This novel CD11b+ pericyte subset is characterized with increased permeability and pro-inflammatory profiles. Mechanistically, recognition of histones from NETs by Dectin-1 on pericyte contributes to CD11b induction in protein kinase C (PKC)-c-Jun-dependent manner. Transcription factor c-Jun directly binds to the promoter sequence of CD11b to enhance its expression in pericyte, conferring pericyte activation, BBB disruption and aggravated neutrophil infiltration post TBI. Either inhibiting NETs formation by Cl-Amidine or blocking Dectin-1 by Laminarin are both beneficial for decreasing neutrophil infiltration and brain pericyte activation post TBI. ConclusionsThese results unfold that “neutrophil-NETs-pericyte” and “histones-Dectin-1-CD11b” are possible cellular and molecular mechanisms for building connection between BBB damage and neutrophil infiltration. Targeting at NETs formation and Dectin-1 are promising treatments for improving neurological outcomes of TBI patients.