Extracellular CIRP induces macrophage endotoxin tolerance through IL-6R-mediated STAT3 activation.

Mian Zhou,Gaifeng Ma,Monowar Aziz,Ping Wang,Hao-Ting Yen,Naomi-Liza Denning

doi:10.1172/jci.insight.133715

Mian Zhou, Gaifeng Ma + Show 4 more

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https://doi.org/10.1172/jci.insight.133715

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Journal: JCI insight	Publication Date: Mar 12, 2020
Citations: 34	License type: CC BY 4.0

Affiliation: Feinstein Institute for Medical Research

Abstract

Extracellular cold-inducible RNA-binding protein (eCIRP) is a damage-associated molecular pattern, whose effect on macrophages is not entirely elucidated. Here we identified that eCIRP promotes macrophage endotoxin tolerance. Septic mice had higher serum levels of eCIRP; this was associated with a reduced ex vivo immune response of their splenocytes to LPS. Pretreatment of macrophages with recombinant murine CIRP (rmCIRP) resulted in a tolerance to LPS stimulation as demonstrated by a reduction of TNF-α production. We found that eCIRP increased phosphorylated STAT3 (p-STAT3) in macrophages. A STAT3 inhibitor, Stattic, rescued macrophages from rmCIRP-induced tolerance by restoring the release of TNF-α in response to LPS stimulation. We discovered strong binding affinity between eCIRP and IL-6 receptor (IL-6R) as revealed by Biacore, fluorescence resonance energy transfer (FRET), and their colocalization in macrophages by immunostaining assays. Blockade of IL-6R with its neutralizing Ab inhibited eCIRP-induced p-STAT3 and restored LPS-stimulated TNF-α release in macrophages. Incubation of macrophages with rmCIRP skewed them toward an M2 phenotype, while treatment with anti–IL-6R Ab prevented rmCIRP-induced M2 polarization. Thus, we have demonstrated that eCIRP activates p-STAT3 via a novel receptor, IL-6R, to promote macrophage endotoxin tolerance. Targeting eCIRP appears to be a new therapeutic option to correct immune tolerance in sepsis.

Highlights

Macrophage “endotoxin tolerance” is defined as a state of LPS hyporesponsiveness, in which macrophages preexposed to endotoxin produce decreased levels of inflammatory mediators upon restimulation with LPS [1, 2]
We discovered a new receptor of Extracellular cold-inducible RNA-binding protein (eCIRP), IL-6 receptor (IL-6R), which played a critical role in macrophage tolerance
We found a dramatic increase in the expression of IL-6R in recombinant murine CIRP (rmCIRP)-treated macrophages

Summary

Introduction

Macrophage “endotoxin tolerance” is defined as a state of LPS hyporesponsiveness, in which macrophages preexposed to endotoxin produce decreased levels of inflammatory mediators upon restimulation with LPS [1, 2]. Tolerant macrophages produce lower levels of the inflammatory cytokine tumor necrosis factor–α (TNF-α) and increased levels of the antiinflammatory cytokines IL-10 and transforming growth factor–β (TGF-β) as compared with their nonsensitized counterparts [1, 2, 5,6,7,8]. Macrophage endotoxin tolerance has been associated with decreased Toll-like receptor 4–myeloid differentiation factor 88 (TLR4-MyD88) complex formation [9], defects in the activation of mitogen-activated protein kinases (MAPKs) and NF-κB [1, 10], and the upregulation of negative regulators like IL-1 receptor associated kinase-M (IRAK-M) [11], ST2 [12], and suppressor of cytokine signaling 1 (SOCS1) [13]. M2 macrophages, like endotoxin-tolerant macrophages, produce fewer proinflammatory cytokines (e.g., IL-12, TNF-α) and more antiinflammatory cytokines (e.g., IL-10) [1, 14, 15].

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