Extracellular CIRP Induces Inflammation in Alveolar Type II Cells via TREM-1.

Chuyi Tan,Steven D Gurien,Ping Wang,William Royster,Monowar Aziz

doi:10.3389/fcell.2020.579157

Abstract

Extracellular cold-inducible RNA-binding protein (eCIRP) induces acute lung injury (ALI) in sepsis. Triggering receptor expressed on myeloid cells-1 (TREM-1) serves as a receptor for eCIRP to induce inflammation in macrophages and neutrophils. The effect of eCIRP on alveolar epithelial cells (AECs) remains unknown. We hypothesize that eCIRP induces inflammation in AECs through TREM-1. AECs were isolated from C57BL/6 mice and freshly isolated AECs were characterized as alveolar type II (ATII) cells by staining AECs with EpCAM, surfactant protein-C (SP-C), and T1 alpha (T1α) antibodies. AECs were stimulated with recombinant murine (rm) CIRP and assessed for TREM-1 by flow cytometry. ATII cells from WT and TREM-1–/– mice were stimulated with rmCIRP and assessed for interleukin-6 (IL-6) and chemokine (C-X-C motif) ligand 2 (CXCL2) in the culture supernatants. ATII cells from WT mice were pretreated with vehicle (PBS), M3 (TREM-1 antagonist), and LP17 (TREM-1 antagonist) and then after stimulating the cells with rmCIRP, IL-6 and CXCL2 levels in the culture supernatants were assessed. All of the freshly isolated AECs were ATII cells as they expressed EpCAM and SP-C, but not T1α (ATI cells marker). Treatment of ATII cells with rmCIRP significantly increased TREM-1 expression by 56% compared to PBS-treated ATII cells. Stimulation of WT ATII cells with rmCIRP increased IL-6 and CXCL2 expression, while the expression of IL-6 and CXCL2 in TREM-1–/– ATII cells were reduced by 14 and 23%, respectively. Pretreatment of ATII cells with M3 and LP17 significantly decreased the expression of IL-6 by 30 and 47%, respectively, and CXCL2 by 27 and 34%, respectively, compared to vehicle treated ATII cells after stimulation with rmCIRP. Thus, eCIRP induces inflammation in ATII cells via TREM-1 which implicates a novel pathophysiology of eCIRP-induced ALI and directs a possible therapeutic approach targeting eCIRP-TREM-1 interaction to attenuate ALI.

Highlights

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are life-threatening complications of critically ill patients
alveolar epithelial cells (AECs) were stained with antibodies against epithelial cell adhesion molecule (EpCAM), an epithelial cell-specific marker and analyzed by flow cytometry, which revealed the purity of sorted AECs to be 83% (Figure 1A)
We found that after 7 days of culture of extracellular cold-inducible RNA-binding protein (eCIRP) and Type II Pneumocytes freshly isolated alveolar type II (ATII) cells, these cells differentiated into type I phenotype (ATI) as determined by their increased expression of T1α, but not surfactant protein-C (SP-C) (Figure 1C)

Summary

Introduction

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are life-threatening complications of critically ill patients. They are characterized by severe inflammation, injury to the lungs, acute non-cardiogenic pulmonary edema, and hypoxemia (Ranieri et al, 2012). Pathological specimens from patients with ALI and laboratory studies have demonstrated diffuse alveolar capillary barrier injury, increased permeability to liquids and proteins, and subsequent respiratory failure (Matthay et al, 2019). The ATII cells secrete surfactant, a critical factor that reduces alveolar surface tension, allowing the alveoli to remain open, facilitating gas exchange (Ward and Nicholas, 1984). Injury to ATII cells results in decreased production of surfactant, which causes reduced lung compliance, leading to respiratory failure. The lung epithelium can be injured by pathogen-associated molecular patterns (PAMPs) such as bacterial products, viruses, and nucleic acids as well as damageassociated molecular patterns (DAMPs) which are endogenous danger molecules released by cells in states of stress such as hypoxia, mechanical force, sepsis, pancreatitis and other diseases (Saffarzadeh et al, 2012; Short et al, 2016; Matthay et al, 2019)

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