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Distinct single-cell signaling characteristics are conferred by the MyD88 and TRIF pathways during TLR4 activation.

ABSTRACT: Toll-like receptors (TLRs) recognize specific pathogen-associated molecular patterns and initiate innate immune responses through signaling pathways that depend on the adaptor proteins MyD88 (myeloid differentiation marker 88) or TRIF (TIR domain-containing adaptor protein-inducing interferon-?). TLR4, in particular, uses both adaptor proteins to activate the transcription factor nuclear factor ?B (NF-?B); however, the specificity and redundancy of these two pathways remain to be elucidated. We developed a mathematical model to show how each pathway encodes distinct dynamical features of NF-?B activity and makes distinct contributions to the high variability observed in single-cell measurements. The assembly of a macromolecular signaling platform around MyD88 associated with receptors at the cell surface determined the timing of initial responses to generate a reliable, digital NF-?B signal. In contrast, ligand-induced receptor internalization into endosomes produced noisy, delayed, yet sustained NF-?B signals through TRIF. With iterative mathematical model development, we predicted the molecular mechanisms by which the MyD88- and TRIF-mediated pathways provide ligand concentration-dependent signaling dynamics that transmit information about the pathogen threat.

SUBMITTER: Cheng Z

PROVIDER: S-EPMC6764925 | biostudies-literature | 2015 Jul

REPOSITORIES: biostudies-literature

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Distinct single-cell signaling characteristics are conferred by the MyD88 and TRIF pathways during TLR4 activation.

Cheng Zhang Z Taylor Brooks B Ourthiague Diana R DR Hoffmann Alexander A

Science signaling 20150714 385

Toll-like receptors (TLRs) recognize specific pathogen-associated molecular patterns and initiate innate immune responses through signaling pathways that depend on the adaptor proteins MyD88 (myeloid differentiation marker 88) or TRIF (TIR domain-containing adaptor protein-inducing interferon-β). TLR4, in particular, uses both adaptor proteins to activate the transcription factor nuclear factor κB (NF-κB); however, the specificity and redundancy of these two pathways remain to be elucidated. We ...[more]

PMID: 26175492

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Project description:Binge/moderate alcohol suppresses TLR4-MyD88 proinflammatory cytokines; however, alcohol's effects on TLR-TRIF signaling, especially after in vivo exposure in humans, are unclear. We performed a comparative analysis of the TLR4-MyD88, TLR4-TRIF, and TLR3-TRIF pathways in human monocytes following binge alcohol exposure. Mechanistic regulation of TLR-TRIF signaling by binge alcohol was evaluated by analyzing IRF3 and TBK1, upstream regulator protein phosphatase 1 (PP1), and immunoregulatory stress proteins HspA1A and XBP-1 in alcohol-treated human and mouse monocytes/macrophages. Two approaches for alcohol exposure were used: in vivo exposure of primary monocytes in binge alcohol-consuming human volunteers or in vitro exposure of human monocytes/murine macrophages to physiological alcohol concentrations (25-50 mM ethanol), followed by LPS (TLR4) or polyinosinic-polycytidylic acid (TLR3) stimulation ex vivo. In vivo and in vitro binge alcohol exposure significantly inhibited the TLR4-MyD88 cytokines TNF-? and IL-6, as well as the TLR4-TRIF cytokines/chemokines IFN-?, IP-10, and RANTES, in human monocytes, but not TLR3-TRIF-induced cytokines/chemokines, as detected by quantitative PCR and ELISA. Mechanistic analyses revealed TBK-1-independent inhibition of the TLR4-TRIF effector IRF3 in alcohol-treated macrophages. Although stress protein XBP-1, which is known to regulate IRF3-mediated IFN-? induction, was not affected by alcohol, HspA1A was induced by in vivo alcohol in human monocytes. Alcohol-induced HspA1A was required for inhibition of TLR4-MyD88 signaling but not TLR4-TRIF cytokines in macrophages. In contrast, inhibition of PP1 prevented alcohol-mediated TLR4-TRIF tolerance in macrophages. Collectively, our results demonstrate that in vivo and in vitro binge alcohol exposure in humans suppresses TLR4-MyD88 and TLR4-TRIF, but not TLR3-TRIF, responses. Whereas alcohol-mediated effects on the PP1-IRF3 axis inhibit the TLR4-TRIF pathway, HspA1A selectively suppresses the TLR4-MyD88 pathway in monocytes/macrophages.

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Distinct single-cell signaling characteristics are conferred by the MyD88 and TRIF pathways during TLR4 activation.

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Distinct single-cell signaling characteristics are conferred by the MyD88 and TRIF pathways during TLR4 activation.

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