TNF-α-sensitive brain pericytes activate microglia by releasing IL-6 through cooperation between Iκβ-NFκB and JAK-STAT3 pathways

Interleukin (IL)-6 is an important mediator of neurovascular dysfunction, neurodegeneration and/or neuroinflammation. We previously reported that brain pericytes released higher levels of IL-6 than did glial cells (astrocytes and microglia) in response to tumor necrosis factor (TNF)-alpha. Moreover, pericytes stimulated with TNF-alpha enhanced activation of BV-2 microglia. In this study, we investigated the mechanisms of TNF-alpha mediated induction of IL-6 release from brain pericytes and astrocytes and whether pericyte-derived IL-6 would facilitate activation of BV-2 microglia. Using rat brain pericyte and astrocyte primary cultures and pharmacological inhibitors, we found that, TNF-alpha induced the highest levels of IL-6 release from pericytes by activating the inhibitor kappa B (I kappa beta)-nuclear factor kappa-light-chain-enhancer of activated B cells (NF kappa B) and Janus family of tyrosine kinase (JAK)-signal transducer and activator of transcription (STAT)3 pathways. STAT3 contributed to INF-alpha induced nuclear translocation of phospho-NF kappa B in pericytes. INF-alpha-induced IL-6 release in astrocytes was mediated by NFKB but not by STAT3. The presence of pericytes amplified TNF-alpha-induced iNOS mRNA expression in BV-2 microglia. This effect was blocked by a neutralizing antibody for IL-6. These findings indicated that crosstalk between the I kappa beta-NF kappa B and JAK-STAT3 pathways is a pericyte specific mechanism, not occurring in astrocytes, for TNF-alpha-induced IL-6 release. IL-6 derived from pericytes enhanced microglial activation. Our findings increase understanding of the role of pericyte-microglia crosstalk in the brain under neuroinflammatory conditions and suggest a potentially attractive therapeutic target for brain inflammation. (C) 2018 Elsevier B.V. All rights reserved.