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-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 developed a mathematical model to show how each pathway encodes distinct dynamical features of NF-κB 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-κB signal. In contrast, ligand-induced receptor internalization into endosomes produced noisy, delayed, yet sustained NF-κB 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.

Activator of G-Protein Signaling 3–Induced Lysosomal Biogenesis Limits Macrophage Intracellular Bacterial Infection

“…The loss of MyD88 or TRIF also impaired the induction of LAMP-1 expression following LPS stimulation. The combined role of MyD88 and TRIF in the early induction and sustained activity of NF-κB activity TLR4 signaling (46) suggests that AGS3 may be a NF-κB target gene in macrophages. An involvement of NF-κB in the induction of AGS3 is also consistent with the increase in AGS3 noted in lymphocytes following antigen receptor crosslinking (26).…”

Redefining Signaling Pathways with an Expanding Single-Cell Toolbox

“…To explore extrinsic noise sources influencing NF-κB translocation dynamics, Cheng and colleagues measured and modeled FP-RelA nuclear translocation in RAW 264.7 mouse macrophages following lipopolysaccharide (LPS) stimulation. They found that intracellular protein abundance regulated two distinct signaling paths downstream of LPS respectively contributing to variations in initiation timing and duration of NF-κB nuclear localization [30]. …”

The rise in computational systems biology approaches for understanding NF-κB signaling dynamics

“…The fi rst widely used model was developed in 2002 by Hoffmann et al (7), and since then, the Hoffmann group has extensively used a computational systems biology approach to further our understanding of NF-κB dynamics. Their latest study, by Cheng et al (8), describes the distinct signaling characteristics conferred by the MyD88-controlled and TRIF-dependent pathways in the TLR4-stimulated activation of NF-κB.…”