title: Lipopolysaccharide increases IL-6 secretion via activation of the ERK1/2 signaling pathway to up-regulate RANKL gene expression in MLO-Y4 cells.
abstract: 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.
authors: State Key Laboratory of Oral Diseases, Sichuan University, Chengdu, 610041, China.|West China College of Stomatology, Sichuan University, Chengdu, 610041, China.|College of Stomatology, Hospital of Stomatology, Southwest Medical University, Luzhou, 646000, China.
authors: Ke
authors: K
authors: Yu
authors: Guanghua School of Stomatology, Hospital of Stomatology, Sun Yat-Sen University, Guangzhou, 510055, China.
authors: Yuanyuan
authors: Y
authors: Ma
authors: Sichuan Academy of Medical Sciences and Sichuan Provincial People's Hospital, Chengdu, 610041, China.
authors: Xianxian
authors: X
authors: Li
authors: State Key Laboratory of Oral Diseases, Sichuan University, Chengdu, 610041, China.|West China College of Stomatology, Sichuan University, Chengdu, 610041, China.
authors: Xiangnan
authors: X
authors: Wu
authors: State Key Laboratory of Oral Diseases, Sichuan University, Chengdu, 610041, China.|West China College of Stomatology, Sichuan University, Chengdu, 610041, China.
authors: Wenjia
authors: W
authors: Liu
authors: State Key Laboratory of Oral Diseases, Sichuan University, Chengdu, 610041, China.
authors: Xiaoyu
authors: X
authors: Li
authors: State Key Laboratory of Oral Diseases, Sichuan University, Chengdu, 610041, China.|West China College of Stomatology, Sichuan University, Chengdu, 610041, China.
authors: Jiefei
authors: J
authors: Shen
authors: State Key Laboratory of Oral Diseases, Sichuan University, Chengdu, 610041, China.|West China College of Stomatology, Sichuan University, Chengdu, 610041, China.
authors: Hang
authors: H
authors: Wang
mesh_terms: D000818:Animals; D015153:Blotting, Western; D004789:Enzyme Activation / Q000187:drug effects; D004797:Enzyme-Linked Immunosorbent Assay; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D015850:Interleukin-6 / Q000235:genetics / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D008822:Mice, Transgenic; D010766:Phosphorylation / Q000187:drug effects; D053245:RANK Ligand / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D050796:STAT3 Transcription Factor / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects*
chemical_list: D015850:Interleukin-6; D008070:Lipopolysaccharides; D053245:RANK Ligand; D012333:RNA, Messenger; D050796:STAT3 Transcription Factor; D048049:Extracellular Signal-Regulated MAP Kinases
keywords: ERK1/2; RANKL; interleukin-6; lipopolysaccharide; osteocyte