Key laboratory of Endocrinology, Ministry of Health, Department of Endocrinology, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China.
Acta Biochim Biophys Sin (Shanghai). 2011 Dec;43(12):940-7. doi: 10.1093/abbs/gmr093. Epub 2011 Oct 19.
Macrophage foam cells formation is the most important process in atherosclerotic plaque formation and development. Toll-like receptor 4 (TLR4) is one of the important innate immune sensors of endogenous damage signals and crucial for regulating inflammation. Growing evidence indicates that TLR4 plays a very important role in macrophage foam cells formation. However, the underlying mechanisms regulating TLR4 expression in macrophage are not fully understood. In this study, we induced THP-1 macrophage foam cells formation with oxidative modified low-density lipoprotein (ox-LDL). We observed that TLR4 mRNA and protein expression were markedly up-regulated, and the phosphorylation of mammalian target of rapamycin (mTOR) and its downstream target p70S6K were promoted during foam cells formation. The mTOR inhibitor rapamycin blocked mTOR phosphorylation and inhibited TLR4 expression induced by ox-LDL. Silencing mTOR, rictor or raptor protein expression by small interfering RNA, also inhibited the up-regulation of TLR4 expression, respectively. Inhibition of mTOR with rapamycin reversed the down-regulation of cellular lipid efflux mediator ABCA1, which resulted from the activation of TLR4 by ligands. These data suggested that TRL4 expression was up-regulated by a mechanism dependent on mTOR signal pathway activation during THP-1 macrophage foam cells formation. Inhibition of ox-LDL induced mTOR activation reduced TLR4 expression, and improved the impaired lipid efflux.
泡沫细胞的形成是动脉粥样硬化斑块形成和发展过程中的最重要的过程。Toll 样受体 4（TLR4）是内源性损伤信号的重要固有免疫传感器之一，对于调节炎症至关重要。越来越多的证据表明 TLR4 在泡沫细胞形成中起着非常重要的作用。然而，调节巨噬细胞中 TLR4 表达的潜在机制尚不完全清楚。在本研究中，我们用氧化修饰的低密度脂蛋白（ox-LDL）诱导 THP-1 巨噬细胞泡沫细胞形成。我们观察到 TLR4mRNA 和蛋白表达明显上调，并且在泡沫细胞形成过程中促进了哺乳动物雷帕霉素靶蛋白（mTOR）及其下游靶标 p70S6K 的磷酸化。mTOR 抑制剂雷帕霉素阻断 mTOR 磷酸化并抑制 ox-LDL 诱导的 TLR4 表达。通过小干扰 RNA 沉默 mTOR、rictor 或 raptor 蛋白表达，也分别抑制了 TLR4 表达的上调。用雷帕霉素抑制 mTOR 逆转了 TLR4 配体激活引起的细胞脂质流出介质 ABCA1 的下调。这些数据表明，在 THP-1 巨噬细胞泡沫细胞形成过程中，TLR4 表达的上调是通过依赖于 mTOR 信号通路激活的机制介导的。抑制 ox-LDL 诱导的 mTOR 激活可降低 TLR4 表达，并改善受损的脂质流出。
