Department of Physical Therapy, Graduate Institute of Rehabilitation Science, China Medical University, and Department of Obstetrics and Gynecology, China Medical University Hospital, 91 Hsueh-Shih Road, Taichung 40202, Taiwan.
J Appl Physiol (1985). 2010 Jun;108(6):1745-56. doi: 10.1152/japplphysiol.00879.2009. Epub 2010 Mar 4.
Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), originally identified as the major receptor for oxidized low-density lipoprotein (oxLDL) in endothelial cells, plays a major role in the pathology of vascular diseases. Green tea consumption is associated with reduced cardiovascular mortality in some epidemiological studies. In the present study, we hypothesized that the most abundant polyphenolic compound in tea, epigallocatechin-3-gallate (EGCG), can downregulate parameters of endothelial dysfunction by modulating LOX-1-regulated cell signaling. In cultured human umbilical vein endothelial cells (HUVECs), exposure to oxLDL (130 microg/ml), which led to an increase in LOX-1 expression at the RNA and protein levels, was abrogated by addition of EGCG or DPI, a well-known inhibitor of flavoproteins, suggesting the involvement of NADPH oxidase. Furthermore, oxLDL rapidly activated the membrane translocation of Rac-1 and p47phox and the subsequent induction of ROS generation, which was suppressed markedly by pretreatment with EGCG or anti-LOX-1 monoclonal antibody. OxLDL also increased p38 MAPK phosphorylation and decreased phosphorylation of the amino-terminal region of Akt, with maximal induction at about 30 min, and NF-kappaB phosphorylation within 1 h, resulting in redox-sensitive signaling. In addition, oxLDL diminished the expression of endothelial nitric oxide synthase (eNOS), enhanced the expression of endothelin-1 and adhesion molecules (ICAM, E-selectin, and monocyte chemoattractant protein-1), and increased the adherence of monocytic THP-1 cells to HUVECs. Pretreatment with EGCG, however, exerted significant cytoprotective effects in all events. These data suggest that EGCG inhibits the oxLDL-induced LOX-1-mediated signaling pathway, at least in part, by inhibiting NADPH oxidase and consequent ROS-enhanced LOX-1 expression, which contributes to further ROS generation and the subsequent activation of NF-kappaB via the p38 MAPK pathway. Results from this study may provide insight into a possible molecular mechanism by which EGCG suppresses oxLDL-mediated vascular endothelial dysfunction.
凝集素样氧化低密度脂蛋白受体-1（LOX-1）最初被鉴定为内皮细胞中氧化低密度脂蛋白（oxLDL）的主要受体，在血管疾病的病理中起着重要作用。一些流行病学研究表明，绿茶的消费与心血管死亡率的降低有关。在本研究中，我们假设茶叶中最丰富的多酚化合物表没食子儿茶素没食子酸酯（EGCG）可以通过调节 LOX-1 调节的细胞信号来下调内皮功能障碍的参数。在培养的人脐静脉内皮细胞（HUVEC）中，添加 EGCG 或 flavoproteins 的已知抑制剂 DPI 可阻断 oxLDL（130μg/ml）导致的 LOX-1 在 RNA 和蛋白质水平表达的增加，表明 NADPH 氧化酶的参与。此外，oxLDL 可迅速激活 Rac-1 和 p47phox 的膜易位，并随后诱导 ROS 的产生，而 EGCG 或抗 LOX-1 单克隆抗体的预处理可显著抑制其产生。oxLDL 还增加了 p38 MAPK 的磷酸化，降低了 Akt 的氨基末端区域的磷酸化，最大诱导作用约为 30 分钟，NF-κB 的磷酸化在 1 小时内，导致氧化还原敏感的信号转导。此外，oxLDL 降低了内皮型一氧化氮合酶（eNOS）的表达，增强了内皮素-1 和粘附分子（ICAM、E-选择素和单核细胞趋化蛋白-1）的表达，并增加了单核细胞 THP-1 细胞对 HUVEC 的粘附。然而，EGCG 的预处理在所有事件中都发挥了显著的细胞保护作用。这些数据表明，EGCG 通过抑制 NADPH 氧化酶和随后的 ROS 增强的 LOX-1 表达来抑制 oxLDL 诱导的 LOX-1 介导的信号通路，这有助于通过 p38 MAPK 途径进一步产生 ROS 和随后激活 NF-κB。本研究的结果可能为 EGCG 抑制 oxLDL 介导的血管内皮功能障碍的分子机制提供一些启示。
