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Accumulating evidence continues to underpin the role of the innate immune system in pathologies associated with neuroinflammation. Innate immunity is regulated by pattern recognition receptors that detect pathogens, and in the case of Gram-positive bacteria, binding of bacterial lipopeptides to toll-like receptor (TLR)2 is emerging as an important mechanism controlling glial cell activation. In the present study, we employed the use of the synthetic bacterial lipoprotein and a selective TLR2 agonist, Pam3CSK4, to induce inflammatory signaling in microglia and astrocytes. The adaptor proteins, downstream of kinase (Dok)1 and Dok2, are known to have a role in negatively regulating the Ras-ERK signaling cascade, with downstream consequences on pro-inflammatory cytokine expression. Data presented herein demonstrate that TLR2 enhanced the tyrosine phosphorylation of Dok1 and Dok2 in astrocytes and microglia, and that knockdown of these adaptors using small interfering RNA robustly elevated TLR2-induced ERK activation. Importantly, TLR2-induced NF-κB activation, and IL-6 production was exacerbated in astrocytes transfected with Dok1 and Dok2 siRNA, indicating that both Dok proteins negatively regulate TLR2-induced inflammatory signaling in astrocytes. In contrast, Dok1 knockdown attenuated TLR2-induced NF-κB activation and IL-6 production in microglia, while Dok2 siRNA failed to affect TLR2-induced NF-κB activity and subsequent cytokine expression in this cell type. Overall, this indicates that Dok1 and Dok2 are novel adaptors for TLR2 in glial cells and importantly indicates that Dok1 and Dok2 differentially regulate TLR2-induced pro-inflammatory signaling in astrocytes and microglia.

Original publication

DOI

10.1016/j.mcn.2013.04.007

Type

Journal article

Journal

Mol Cell Neurosci

Publication Date

09/2013

Volume

56

Pages

148 - 158

Keywords

AD, Alzheimer's disease, CNS, DAMPs, Dok, EMSA, ERK, GM-CSF, Glia, HBSS, Hanks' balanced salt solution buffered, IFN, Inflammation, Innate immunity, M-CSF, MAPK, MS, Mal, MyD88, MyD88-adaptor like, NF-κB, PAMPs, PD, PH, PPRs, PTK, Parkinson's disease, SH, SLAM, Src homology, TIR, TLR, TRAM, TRIF, TRIF-related adaptor molecule, Toll-interleukin-1 receptor, Toll-interleukin-1 receptor (TIR)-domain-containing adaptor-inducing IFN-β, Toll-like receptor, central nervous system, damage-associated molecular patterns, downstream of kinase, electrophoretic mobility shift assay, extracellular signal-regulated kinase, granulocyte macrophage colony stimulating factor, interferon, macrophage colony stimulating factor, mitogen-activated protein kinase, multiple sclerosis, myeloid differentiation factor 88, nuclear factor-κB, pathogen-associated molecular patterns, pattern recognition receptors, pleckstrin homology, protein tyrosine kinase, siRNA, signaling lymphocyte activation molecule, small interfering RNA, Adaptor Proteins, Signal Transducing, Animals, Astrocytes, Cells, Cultured, DNA-Binding Proteins, Inflammation, Interleukin-6, Lipopeptides, MAP Kinase Signaling System, Mice, Mice, Inbred C57BL, Microglia, NF-kappa B, Phosphoproteins, RNA-Binding Proteins, Toll-Like Receptor 2