Hossain Ekhtear, Ota Akinobu, Karnan Sivasundaram, Takahashi Miyuki, Mannan Shahnewaj B, Konishi Hiroyuki, Hosokawa Yoshitaka
Department of Biochemistry, Aichi Medical University School of Medicine, Nagakute, Aichi, Japan.
Mol Cell Biochem. 2015 Feb;400(1-2):29-40. doi: 10.1007/s11010-014-2259-0. Epub 2014 Oct 28.
There is a growing body of evidence supporting an intimate association of immune activation with the pathogenesis of cardiovascular diseases, including atherosclerosis. Uptake of oxidized low-density lipoprotein (oxLDL) through scavenging receptors promotes the formation of mature lipid-laden macrophages, which subsequently leads to exacerbation of regional inflammation and atherosclerotic plaque formation. In this study, we first examined changes in the mRNA level of the lectin-like oxLDL receptor-1 (LOX-1) in the mouse macrophage cell line RAW264.7 and the human PMA-induced macrophage cell line THP-1 after LPS stimulation. LPS significantly up-regulated LOX-1 mRNA in RAW264.7 cells; LOX-1 cell-surface protein expression was also increased. Flow cytometry and fluorescence microscopy analyses showed that cellular uptake of fluorescence (Dil)-labeled oxLDL was significantly augmented with LPS stimulation. The augmented uptake of Dil-oxLDL was almost completely abrogated by treatment with an anti-LOX-1 antibody. Of note, knockdown of Erk1/2 resulted in a significant reduction of LPS-induced LOX-1 up-regulation. Treatment with U0126, a specific inhibitor of MEK, significantly suppressed LPS-induced expression of LOX-1 at both the mRNA and protein levels. Furthermore, LOX-1 promoter activity was significantly augmented by LPS stimulation; this augmentation was prevented by U0126 treatment. Similar results were also observed in human PMA-induced THP-1 macrophages. Taken together, our results indicate that LPS up-regulates LOX-1, at least in part through activation of the Erk1/2 signaling pathway, followed by augmented cellular oxLDL uptake, thus highlighting a critical role of TLR4-mediated aberrant LOX-1 signaling in the pathogenesis of atherosclerosis.
越来越多的证据支持免疫激活与心血管疾病（包括动脉粥样硬化）的发病机制密切相关。通过清道夫受体摄取氧化型低密度脂蛋白（oxLDL）可促进成熟脂质负载巨噬细胞的形成，进而导致局部炎症加剧和动脉粥样硬化斑块形成。在本研究中，我们首先检测了脂多糖（LPS）刺激后小鼠巨噬细胞系RAW264.7和人佛波酯（PMA）诱导的巨噬细胞系THP-1中凝集素样oxLDL受体-1（LOX-1）mRNA水平的变化。LPS显著上调RAW264.7细胞中LOX-1 mRNA的表达；LOX-1细胞表面蛋白表达也增加。流式细胞术和荧光显微镜分析表明，LPS刺激后，荧光（Dil）标记oxLDL的细胞摄取显著增加。用抗LOX-1抗体处理几乎完全消除了Dil-oxLDL摄取的增加。值得注意的是，敲低Erk1/2导致LPS诱导的LOX-1上调显著降低。用MEK的特异性抑制剂U0126处理可显著抑制LPS诱导的LOX-1在mRNA和蛋白水平的表达。此外，LPS刺激显著增强了LOX-1启动子活性；U0126处理可阻止这种增强。在人PMA诱导的THP-1巨噬细胞中也观察到了类似结果。综上所述，我们的结果表明，LPS至少部分通过激活Erk1/2信号通路上调LOX-1，随后增加细胞对oxLDL的摄取，从而突出了TLR4介导的异常LOX-1信号在动脉粥样硬化发病机制中的关键作用。
