Hong Dan, Li Ling-Fang, Gao Hai-Chao, Wang Xiang, Li Chuan-Chang, Luo Ying, Bai Yong-Ping, Zhang Guo-Gang
Department of Cardiovascular Medicine, Xiangya Hospital, Central South University, Changsha, Hunan, China.
Department of Cardiovascular Medicine, The Affiliated Hospital of Chengde Medical College, Hebei, China.
PLoS One. 2015 Apr 29;10(4):e0124285. doi: 10.1371/journal.pone.0124285. eCollection 2015.
Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) is a specific cell-surface receptor for oxidized-low-density lipoprotein (ox-LDL). The impact of high-density lipoprotein (HDL) on endoplasmic reticulum (ER) stress-mediated alteration of the LOX-1 level in hepatocytes remains unclear. We aimed to investigate the impact on LOX-1 expression by tunicamycin (TM)-induced ER stress and to determine the effect of HDL on TM-affected LOX-1 expression in hepatic L02 cells. Overexpression or silencing of related cellular genes was conducted in TM-treated cells. mRNA expression was evaluated using real-time polymerase chain reaction (PCR). Protein expression was analyzed by western blot and immunocytochemistry. Lipid uptake was examined by DiI-ox-LDL, followed by flow cytometric analysis. The results showed that TM induced the upregulation of ER chaperone GRP78, downregulation of LOX-1 expression, and lipid uptake. Knock down of IRE1 or XBP-1 effectively restored LOX-1 expression and improved lipid uptake in TM-treated cells. HDL treatment prevented the negative impact on LOX-1 expression and lipid uptake induced by TM. Additionally, 1-10 μg/mL HDL significantly reduced the GRP78, IRE1, and XBP-1 expression levels in TM-treated cells. Our findings reveal that HDL could prevent the TM-induced reduction of LOX-1 expression via inhibiting the IRE1/XBP-1 pathway, suggesting a new mechanism for beneficial roles of HDL in improving lipid metabolism.
凝集素样氧化低密度脂蛋白受体1（LOX-1）是氧化型低密度脂蛋白（ox-LDL）的特异性细胞表面受体。高密度脂蛋白（HDL）对内质网（ER）应激介导的肝细胞中LOX-1水平变化的影响尚不清楚。我们旨在研究衣霉素（TM）诱导的内质网应激对LOX-1表达的影响，并确定HDL对TM影响的肝L02细胞中LOX-1表达的作用。在TM处理的细胞中进行相关细胞基因的过表达或沉默。使用实时聚合酶链反应（PCR）评估mRNA表达。通过蛋白质印迹和免疫细胞化学分析蛋白质表达。用DiI-ox-LDL检测脂质摄取，然后进行流式细胞术分析。结果表明，TM诱导内质网伴侣GRP78上调、LOX-1表达下调以及脂质摄取增加。敲低IRE1或XBP-1可有效恢复TM处理细胞中LOX-1的表达并改善脂质摄取。HDL处理可防止TM对LOX-1表达和脂质摄取的负面影响。此外，1-10μg/mL HDL可显著降低TM处理细胞中GRP78、IRE1和XBP-1的表达水平。我们的研究结果表明，HDL可通过抑制IRE1/XBP-1途径防止TM诱导的LOX-1表达降低，提示HDL在改善脂质代谢中的有益作用的新机制。
