Background

Atherosclerosis is a chronic inflammatory disease. Although Toll-like receptor 4 (TLR4) has been involved in inflammatory atherosclerosis, the exact mechanisms by which oxidized-low-density lipoproteins (ox-LDL) activates TLR4 and elicits inflammatory genesis are not fully known. Myeloid differentiation factor 2 (MD2) is an extracellular molecule indispensable for lipopolysaccharide recognition of TLR4.

Method

Apoe^−/−Md2^−/− mice and pharmacological inhibitor of MD2 were used in this study. We also reconstituted Apoe^−/− mice with either Apoe^−/− or Apoe^−/−Md2^−/− marrow-derived cells. Mechanistic studies were performed in primary macrophages, HEK-293T cells, and cell-free system.

Finding

MD2 levels are elevated in atherosclerotic lesion macrophages, and MD2 deficiency or pharmacological inhibition in mice reduces the inflammation and stunts the development of atherosclerotic lesions in Apoe^−/− mice fed with high-fat diet. Transfer of marrow-derived cells from Apoe-Md2 double knockout mice to Apoe knockout mice confirmed the critical role of bone marrow-derived MD2 in inflammatory factor induction and atherosclerosis development. Mechanistically, we show that MD2 does not alter ox-LDL uptake by macrophages but is required for TLR4 activation and inflammation via directly binding to ox-LDL, which triggers MD2/TLR4 complex formation and TLR4-MyD88-NFκB pro-inflammatory cascade.

Interpretation

We provide a mechanistic basis of ox-LDL-induced macrophage inflammation, illustrate the role of macrophage-derived MD2 in atherosclerosis, and support the therapeutic potential of MD2 targeting in atherosclerosis-driven cardiovascular diseases.

Funding

This work was supported by the National Key Research Project of China (2017YFA0506000), National Natural Science Foundation of China (21961142009, 81930108, 81670244, and 81700402), and Natural Science Foundation of Zhejiang Province (LY19H020004).

中文翻译：

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巨噬细胞源性骨髓分化蛋白2在ox-LDL诱导的炎症和动脉粥样硬化中起重要作用

背景

动脉粥样硬化是一种慢性炎性疾病。尽管Toll样受体4（TLR4）已参与炎症性动脉粥样硬化，但氧化的低密度脂蛋白（ox-LDL）激活TLR4并引起炎症发生的确切机制尚不完全清楚。髓样分化因子2（MD2）是脂多糖识别TLR4所必需的细胞外分子。

方法

本研究使用Apoe ^-/- Md2 ^-//小鼠和MD2的药理抑制剂。我们还用Apoe ^-/-或Apoe ^-/- Md2 ^-/-骨髓来源的细胞重建了Apoe ^-/-小鼠。在原代巨噬细胞，HEK-293T细胞和无细胞系统中进行了机理研究。

寻找

动脉粥样硬化病变巨噬细胞中的MD2水平升高，小鼠的MD2缺乏或药理抑制作用减轻了炎症，并阻碍了高脂饮食喂养的Apoe ^-/-小鼠的动脉粥样硬化病变的发展。骨髓来源的细胞从Apoe-Md2双敲除小鼠转移到Apoe基因敲除小鼠证实了骨髓来源的MD2在炎症因子诱导和动脉粥样硬化发展中的关键作用。从机制上讲，我们显示MD2不会改变巨噬细胞对ox-LDL的摄取，而是通过直接结合到ox-LDL来激活TLR4激活和炎症所必需的，这会触发MD2 / TLR4复合物形成和TLR4-MyD88-NFκB促炎性级联反应。

解释

我们提供了ox-LDL诱导巨噬细胞炎症的机制基础，阐明了巨噬细胞衍生的MD2在动脉粥样硬化中的作用，并支持以MD2为靶标的动脉粥样硬化驱动的心血管疾病的治疗潜力。

资金

这项工作得到了国家重点研究项目（2017YFA0506000），国家自然科学基金（21961142009、81930108、81670244和81700402）和浙江省自然科学基金（LY19H020004）的支持。