Neutrophil-Macrophage Communication via Extracellular Vesicle Transfer Promotes Itaconate Accumulation and Ameliorates Cytokine Storm Syndrome

This report is based on the following research article: “neutrophil–macrophage communication via extracellular vesicle transfer promotes itaconate accumulation and ameliorates cytokine storm syndrome”, written by Haixia Kang, Ting Liu, Yuanyuan Wang, Wenjuan Bai, Yan Luo, and Jing Wang, published in the journal “Cellular & Molecular Immunology” in 2024. The article mainly explores how neutrophils communicate with macrophages through extracellular vesicles to promote itaconic acid accumulation, thereby alleviating Cytokine Storm Syndrome.

Background

Cytokine Storm Syndrome (CSS) is a systemic inflammatory syndrome involving excessive activation of the innate immune system, often triggered by various treatments, infections, and autoimmune diseases. CSS causes excessive production of pro-inflammatory cytokines, directly associated with tissue damage, multiple organ failure, and even death. Understanding the potential interactions between immune cells is crucial for CSS research. However, current understanding of the possible biological consequences between innate immune cells is still limited, and researchers need to further investigate the mechanisms of influence between immune cells.

Research Source and Purpose

This article was co-authored by a team of scientists from the Department of Immunology and Microbiology at the Shanghai Institute of Immunology, Shanghai Jiao Tong University School of Medicine, and the Department of Anesthesiology at Shanghai Ruijin Hospital. The project aims to explore the protective role of neutrophils in suppressing macrophage pro-inflammatory responses by establishing various animal models of cytokine storm induction, and to discover how neutrophils regulate macrophages through extracellular vesicle-mediated molecular signaling to produce the anti-inflammatory metabolite itaconic acid.

Research Methods

Establishment of Animal Models

The study established animal cytokine storm models by injecting various immune stimulants, including the TLR3 agonist poly I:C and TLR4 agonist LPS. The role of neutrophils and their derived vesicles in macrophage activation and anti-inflammatory responses was investigated.

Image Observation and Metabolic Analysis

The authors observed vesicles produced by neutrophils in the liver and spleen through in vivo imaging techniques and tracked their movement pathways in the body. Metabolomic analysis was performed on macrophages treated with neutrophil extracellular vesicles, revealing significantly elevated levels of the anti-inflammatory metabolite itaconic acid.

Gene Function Verification

The study further verified the key role of the IRG1 gene (encoding AcoD1) in macrophages through gene knockout techniques, exploring the mechanism by which neutrophil extracellular vesicles carry miR-27a-3p to inhibit the expression of succinyl-CoA ligase (SUCLG1), leading to itaconic acid accumulation in macrophages.

Research Results

High Inflammatory Phenotype in Macrophages

Animal model studies found that macrophages in mice exhibited a pronounced high inflammatory phenotype after injection of TNF-α and IFN-γ or poly I:C/LPS, with significantly increased production of pro-inflammatory cytokines in the spleen and liver, especially IL-6, IL-1β, and TNF-α.

Neutrophil Inhibition of Macrophages

Further studies showed that the absence of neutrophils led to a significant increase in various pro-inflammatory cytokines, suggesting an inhibitory role of neutrophils in regulating macrophage pro-inflammatory responses. In vitro co-culture experiments found that neutrophil extracellular vesicles effectively inhibited the gene expression of pro-inflammatory cytokines in macrophages.

Characteristics and Functions of Neutrophil Extracellular Vesicles

The diameter and concentration distribution of neutrophil extracellular vesicles were determined through transmission electron microscopy and nanoparticle tracking analysis (NTA). Isolation and infusion experiments revealed that neutrophil extracellular vesicles significantly improved the survival rate of mice in animal models and were preferentially phagocytosed by macrophages in the liver and spleen.

Itaconic Acid Metabolic Pathway

Metabolomic analysis showed significantly elevated levels of itaconic acid in macrophages treated with neutrophil extracellular vesicles, while other key intermediates in the metabolic cycle, such as cis-aconitate, did not change significantly, suggesting that neutrophil extracellular vesicles mainly function by regulating the itaconic acid metabolic pathway.

miR-27a-3p Mechanism of Action

The study showed that neutrophil extracellular vesicles inhibited the expression of SUCLG1 in macrophages by delivering miR-27a-3p, thereby reducing the metabolic breakdown of itaconic acid and allowing it to accumulate in cells to exert anti-inflammatory effects. In vitro experiments further confirmed the direct targeting regulatory effect of miR-27a-3p on SUCLG1 mRNA.

Conclusion and Significance

This study reveals a novel mechanism of neutrophil communication with macrophages through extracellular vesicle delivery of miR-27a-3p, leading to itaconic acid accumulation in macrophages and countering severe pro-inflammatory responses. This discovery provides new ideas and potential clinical applications for the treatment of CSS, suggesting that regulating neutrophil extracellular vesicles and their contents could become a new approach to prevent and treat inflammatory diseases.

Research Highlights

• The study reveals a new function of neutrophils in suppressing inflammatory responses by regulating communication between neutrophils and macrophages through extracellular vesicles.
• Discovered that miR-27a-3p carried by neutrophil extracellular vesicles inhibits SUCLG1 expression, leading to itaconic acid accumulation in macrophages, thus exerting anti-inflammatory effects.
• The research results provide new ideas for the treatment of cytokine storm syndrome, with significant scientific value and potential clinical applications.

This study expands our understanding of the mechanisms of interaction between innate immune cells and provides new directions for regulating inflammatory responses. Future research should continue to explore the role and mechanisms of neutrophil extracellular vesicles in other inflammation-related diseases, with the aim of achieving greater breakthroughs in clinical applications.