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Lipopolysaccharide increases IL‐6 secretion via activation of the ERK1/2 signaling pathway to up‐regulate RANKL gene expression in MLO‐Y4 cells
Author(s) -
Yu Ke,
Ma Yuanyuan,
Li Xianxian,
Wu Xiangnan,
Liu Wenjia,
Li Xiaoyu,
Shen Jiefei,
Wang Hang
Publication year - 2017
Publication title -
cell biology international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.932
H-Index - 77
eISSN - 1095-8355
pISSN - 1065-6995
DOI - 10.1002/cbin.10696
Subject(s) - rankl , phosphorylation , blot , signal transduction , secretion , bone resorption , chemistry , kinase , mapk/erk pathway , lipopolysaccharide , extracellular , microbiology and biotechnology , endocrinology , medicine , biology , receptor , activator (genetics) , biochemistry , gene
Lipopolysaccharide (LPS) plays an important role in bone resorption, which involves numerous cytokines through various signaling pathways. RANKL and interleukin (IL)‐6 are two important cytokines that are involved in bone remodeling. The aim of this study was to evaluate the effect of LPS on RANKL and IL‐6 gene expression, the relationship of RANKL and IL‐6, and the role of extracellular signal‐regulated kinases 1/2 (ERK1/2) on IL‐6 secretion induced by LPS in MLO‐Y4 cells. The cells were stimulated by LPS at different concentrations (1, 10, 100, 500, and 1000 ng/mL) for different durations (0.5, 1, 2, 4, and 8 h and 0.5, 1, 1.5, 2, and 4 h), and the mRNA expressions of RANKL and IL‐6 were determined by PCR. In the presence of 100 ng/mL LPS at different time points (0.5, 1, 1.5, 2, and 4 h), IL‐6 secretion and ERK1/2 phosphorylation in the cells were determined by ELISA and western blotting, respectively. STAT3 phosphorylation in cells simulated by 100 ng/mL LPS at different time points (0.5, 1, 2, 4, and 8 h) was assessed by western blotting. We found that LPS significantly up‐regulated RANKL expression and activated the ERK1/2 pathway to induce IL‐6 mRNA expression and protein synthesis in MLO‐Y4 cells. However, the increased IL‐6 was blocked by pre‐treatment of MLO‐Y4 cells with the ERK1/2 inhibitor U0126 (10 µM), and the enhanced RANKL was blocked by the STAT3 inhibitor S3I‐201 (100 µM). Our results indicate that LPS up‐regulates osteocyte expression of RANKL and IL‐6, and the increased RANKL is associated with the up‐regulation of IL‐6, which involves the ERK1/2 pathway.