Pro-inflammatory hepatic macrophages generate ROS through NADPH oxidase 2 via endocytosis of monomeric TLR4\u2013MD2 complex

So Yeon Kim,Ho Min Kim,Sun Chang Kim,Jun Hee Lee ,Wonbeak Yoo,George Kunos,Bin Gao,Young Ri Shim ,Wonhyo Seo,Won Mook Choi ,Young Sun Lee ,Jong Min Jeong ,Kwangsik Chun,Byung Seok Lee,Hyon‐Seung Yi ,Hyuk Soo Eun,Myung Ho Kim ,Sang-Won Kang ,Won Il Jeong

doi:10.1038/s41467-017-02325-2

Abstract

Reactive oxygen species (ROS) contribute to the development of non-alcoholic fatty liver disease. ROS generation by infiltrating macrophages involves multiple mechanisms, including Toll-like receptor 4 (TLR4)-mediated NADPH oxidase (NOX) activation. Here, we show that palmitate-stimulated CD11b+F4/80low hepatic infiltrating macrophages, but not CD11b+F4/80high Kupffer cells, generate ROS via dynamin-mediated endocytosis of TLR4 and NOX2, independently from MyD88 and TRIF. We demonstrate that differently from LPS-mediated dimerization of the TLR4–MD2 complex, palmitate binds a monomeric TLR4–MD2 complex that triggers endocytosis, ROS generation and increases pro-interleukin-1β expression in macrophages. Palmitate-induced ROS generation in human CD68lowCD14high macrophages is strongly suppressed by inhibition of dynamin. Furthermore, Nox2-deficient mice are protected against high-fat diet-induced hepatic steatosis and insulin resistance. Therefore, endocytosis of TLR4 and NOX2 into macrophages might be a novel therapeutic target for non-alcoholic fatty liver disease.

Highlights

Reactive oxygen species (ROS) contribute to the development of non-alcoholic fatty liver disease
We have demonstrated that palmitate binds a monomeric Toll-like receptor 4 (TLR4)–MD2 complex in CD11b+F4/80high and CD68lowCD14high macrophages of mice and humans, respectively, which leads to NOX2-mediated ROS generation by dynamin-mediated endocytosis of the TLR4–MD2 complex
Another striking finding was that the high-fat diet (HFD) or palmitateinduced ROS generation and pro-inflammatory changes selectively appeared in transmigrating liver macrophages and not in resident Kupffer cells

Summary

Introduction

Reactive oxygen species (ROS) contribute to the development of non-alcoholic fatty liver disease. Diet-induced obesity is commonly associated with nonalcoholic fatty liver disease (NAFLD) and insulin resistance, in which recruited immune cells such as macrophages, neutrophils, lymphocytes, mast cells and eosinophils contribute to a pro-inflammatory environment[1, 2] Of these cells, recruited macrophages and resident Kupffer cells secrete diverse cytokines including tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and IL-1β, which contribute to insulin resistance in hepatocytes by upregulating the activation of inhibitor of κB kinase-β/nuclear factor-κB (NF-κB) and c-Jun Nterminal kinase (JNK)/activator protein-12–4. We report that in CD11b+F4/80low hepatic macrophages, palmitate triggers the endocytosis of a monomeric TLR4–MD2 complex, leading to NOX2 activation and ROS generation, which play an obligatory role in diet-induced hepatic steatosis and insulin resistance These findings provide novel pathophysiological insights and therapeutic targets for NAFLD

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Results

Conclusion