Luteolin transforms the polarity of bone marrow-derived macrophages to regulate the cytokine storm

Shuxia Wang,Shuhang Xu,Xiaoming Yao,Jing Zhou,Chao Liu,Li Zhang,Xiaodong Mao

doi:10.1186/s12950-021-00285-5

Abstract

BackgroundMacrophages are indispensable regulators of inflammatory responses. Macrophage polarisation and their secreted inflammatory factors have an association with the outcome of inflammation. Luteolin, a flavonoid abundant in plants, has anti-inflammatory activity, but whether luteolin can manipulate M1/M2 polarisation of bone marrow-derived macrophages (BMDMs) to suppress inflammation is still unclear. This study aimed to observe the effects of luteolin on the polarity of BMDMs derived from C57BL/6 mice and the expression of inflammatory factors, to explore the mechanism by which luteolin regulates the BMDM polarity.MethodsM1-polarised BMDMs were induced by lipopolysaccharide (LPS) + interferon (IFN)-γ and M2-polarisation were stimulated with interleukin (IL)-4. BMDM morphology and phagocytosis were observed by laser confocal microscopy; levels of BMDM differentiation and cluster of differentiation (CD)11c or CD206 on the membrane surface were assessed by flow cytometry (FCM); mRNA and protein levels of M1/M2-type inflammatory factors were performed by qPCR and ELISA, respectively; and the expression of p-STAT1 and p-STAT6 protein pathways was detected by Western-blotting.ResultsThe isolated mouse bone marrow cells were successfully differentiated into BMDMs, LPS + IFN-γ induced BMDM M1-phenotype polarisation, and IL-4 induced M2-phenotype polarisation. After M1-polarised BMDMs were treated with luteolin, the phagocytosis of M1-polarized BMDMs was reduced, and the M1-type pro-inflammatory factors including IL-6, tumour necrosis factor (TNF)-α, inducible nitric oxide synthase (iNOS), and CD86 were downregulated while the M2-type anti-inflammatory factors including IL-10, IL-13, found in inflammatory zone (FIZZ)1, Arginase (Arg)1 and CD206 were upregulated. Additionally, the expression of M1-type surface marker CD11c decreased. Nevertheless, the M2-type marker CD206 increased; and the levels of inflammatory signalling proteins phosphorylated signal transducer and activator of transcription (p-STAT)1 and p-STAT6 were attenuated and enhanced, respectively.ConclusionsOur study suggests that luteolin may transform BMDM polarity through p-STAT1/6 to regulate the expression of inflammatory mediators, thereby inhibiting inflammation. Naturally occurring luteolin holds promise as an anti-inflammatory and immunomodulatory agent.

Highlights

Macrophages are indispensable regulators of inflammatory responses
Our study suggests that luteolin may transform bone marrow-derived macrophages (BMDMs) polarity through p-STAT1/6 to regulate the expression of inflammatory mediators, thereby inhibiting inflammation
It is well known that pathogenic agents such as viral or bacterial infections incur the pathological process of sepsis, which is characterised by an overwhelming generation of pro-inflammatory cytokines

Summary

Introduction

Macrophages are indispensable regulators of inflammatory responses. Macrophage polarisation and their secreted inflammatory factors have an association with the outcome of inflammation. A flavonoid abundant in plants, has anti-inflammatory activity, but whether luteolin can manipulate M1/M2 polarisation of bone marrow-derived macrophages (BMDMs) to suppress inflammation is still unclear. Inflammation is the immune system’s response to invading pathogens, but aberrant inflammatory responses lead to a “cytokine storm” that worsens a patient’s condition [1]. If immune cells and pro-inflammatory cytokines are overproduced, cytokine cascades occur, called a “cytokine storm” or “inflammatory storm”, leading to sepsis, acute respiratory distress syndrome (ARDS) and even multipleorgan failure (MOF) [3]. The immunomodulatory therapy for inflammation is crucial for maintaining homeostasis [5]

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