Nobiletin Alleviates Non-alcoholic Steatohepatitis in MCD-Induced Mice by Regulating Macrophage Polarization.

Si-Wei Wang,Tian Lan,Hang-Fei Chen,Chun-Yi Xu,Mei-Kang Lei,Li-Xia Wang,Hao Sheng,Feng Zhang,Fang Zheng

doi:10.3389/fphys.2021.687744

Abstract

Non-alcoholic steatohepatitis (NASH) is an inflammatory disorder that is characterized by chronic activation of the hepatic inflammatory response and subsequent liver damage. The regulation of macrophage polarization in liver is closely related to the progression of NASH. The orphan nuclear receptor retinoic-acid-related orphan receptor α (RORα) and Krüppel-like factor 4 (KLF4) are key regulators which promote hepatic macrophages toward M2 phenotype and protect against NASH in mice. Nobiletin (NOB), a natural polymethoxylated flavone, is previously reported as a RORα regulator in diet-induced obese mice. However, it is still unclear whether NOB has the protective effect on NASH. In this study, we investigated the role of NOB in NASH using a methionine and choline deficient (MCD)-induced NASH mouse model. Our results showed that NOB ameliorated hepatic damage and fibrosis in MCD fed mice. NOB treatment reduced the infiltration of macrophages and neutrophils in the liver in MCD-fed mice. Of importance, NOB significantly increased the proportion of M2 macrophages and the expression of anti-inflammatory factors in vivo and in vitro. Meanwhile, NOB also decreased the population of M1 macrophages and the expression of proinflammatory cytokines. Mechanistically, NOB elevated KLF4 expression in macrophages. Inhibition of KLF4 abolished NOB regulated macrophage polarization. Furthermore, the regulation of NOB in KLF4 expression was dependent on RORα.

Highlights

Non-alcoholic steatohepatitis (NASH), the progressive form of non-alcoholic fatty liver disease (NAFLD), is an inflammatory disorder that is characterized by liver inflammation, fibrosis and hepatocellular injury (Han et al, 2017; Kong et al, 2019; Xu et al, 2020)
We evaluated the effect of NOB on NASH using methionine and choline deficient (MCD)-induced mouse model
We found M2 type macrophages were significantly increased in the livers of NOB treated NASH mice accompanied by elevated expression of anti-inflammatory cytokine interleukin 10 (IL-10)

Summary

Introduction

Non-alcoholic steatohepatitis (NASH), the progressive form of non-alcoholic fatty liver disease (NAFLD), is an inflammatory disorder that is characterized by liver inflammation, fibrosis and hepatocellular injury (Han et al, 2017; Kong et al, 2019; Xu et al, 2020). It has been known that macrophage plays a critical role in hepatic immune homeostasis by releasing cytokines and modulating immune cell response in NASH (Han et al, 2019). The M1 macrophage phenotype is characterized by the production of high levels of pro-inflammatory cytokines such as tumor necrosis factor α (TNF-α) and interleukin 1β (IL-1β). Phenotypically M2 macrophages have been characterized as anti-inflammatory cytokines such as interleukin 10 (IL-10) and arginase-1 (Arg-1) (Murray, 2017). Increasing evidence has suggested that targeting M1/M2 polarization of macrophages could be effective strategy to alleviate NASH (Wan et al, 2014; Han et al, 2017, 2019; Kong et al, 2019)

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