Journal Article

S100A9 Increases IL-6 and RANKL Expressions through MAPKs and STAT3 Signaling Pathways in Osteocyte-Like Cells

Yumoto, Hiromichi, Inagaki, Yuji, Kido, Jun-ichi, Naruishi, Koji, Takagi, Ryosuke, Hiroshima, Yuka, Sakamoto, Eijiro

2020

Overview

Objective. Calprotectin is a heterocomplex of S100A8 and S100A9 and is mainly secreted from neutrophils, monocytes, and chondrocytes in inflammatory condition. Calprotectin binds to RAGE and TLR4 and induces the expression of proinflammatory chemokines and cytokines in various cells. Periodontitis is a chronic inflammatory disease that leads to gingival inflammation and alveolar bone resorption. Calprotectin levels in gingival crevicular fluid of periodontitis patients are higher than healthy patients. In the present study, the effects of S100A8 and S100A9 on the expressions of proinflammatory cytokines and bone metabolism-related factors in mouse osteocyte-like cells (MLO-Y4-A2) were investigated. Design. MLO-Y4-A2 cells were treated with S100A8 and S100A9, and the expressions of RAGE, TLR4, RANKL, and several inflammatory cytokines were analyzed by PCR and Western blotting or ELISA methods. To investigate the intracellular signaling pathways, phosphorylation of MAPK and STAT3 was determined by Western blotting, and chemical specific inhibitors and siRNAs were used. Results. Expressions of IL-6 and RANKL were increased by treatment with S100A9 but not S100A8. However, both S100A8 and S100A9 did not change expression of IL-1β, IL-8, and TNF-α. Although RAGE and TLR4 expressions were not upregulated by S100A9 treatment, transfection of siRNA for RAGE and TLR4 significantly decreased IL-6 and RANKL expressions. In addition, S100A9 activated p38, ERK, and STAT3 signaling pathways, and inhibitors for these factors significantly decreased S100A9-induced IL-6 and RANKL expressions. Conclusions. These results indicated that S100A9 induces IL-6 and RANKL production via engagement with RAGE and TLR4 signalings in osteocytes and suggested that S100A9 may play important roles in the periodontal alveolar bone destruction.

• Publisher: Hindawi Publishing Corporation,Hindawi,John Wiley & Sons, Inc
• Subject: Alveolar bone / Animals / Arthritis / Biomedical materials / Bone resorption / Bone turnover / Calgranulin A - metabolism / Calgranulin B - metabolism / Calgranulin B - pharmacology / Cell culture / Cell Survival - drug effects / Chemokines / Chondrocytes / Cytokines / Cytokines - metabolism / Enzyme-linked immunosorbent assay / Inflammation / Inflammatory bowel disease / Inflammatory diseases / Inhibitors / Interleukin 6 / Interleukin 8 / Interleukin-1beta - metabolism / Interleukin-6 - metabolism / Interleukin-8 - metabolism / Intracellular signalling / Kinases / Leukocytes (neutrophilic) / Ligands / MAP kinase / MAP Kinase Signaling System - drug effects / Medical research / Medicine, Experimental / Metabolism / Mice / Monocytes / Organic chemistry / Osteocytes / Osteocytes - drug effects / Osteocytes - metabolism / Penicillin G / Periodontitis / Phosphatase / Phosphorylation / Phosphorylation - drug effects / Proteins / RNA, Small Interfering / Signal transduction / Signal Transduction - drug effects / Signaling / siRNA / Stat3 protein / STAT3 Transcription Factor - drug effects / TLR4 protein / Toll-Like Receptor 4 - metabolism / Toll-like receptors / TRANCE protein / Transfection / Tumor Necrosis Factor-alpha - metabolism / Tumor necrosis factor-TNF / Tumor necrosis factor-α / Up-Regulation - drug effects / Western blotting