High-mobility group box-B1 (HMGB1) mediates the hypoxia-induced mesenchymal transition of osteoblast cells via activating ERK/JNK signaling

High-mobility group box 1 (HMGB1) is a nuclear protein that involves the binding with DNA and influences chromatin regulation and transcription. HMGB1 activates monocytes and neutrophils, which are involved in inflammation during wounding. In this study, we investigated the promotion of HMGB1 under hypoxia and determined the regulatory role of HMGB1 on the fibrosis of mouse osteoblast-like MC3T3-E1 cells or of human osteoblast MG-63 cells. Results demonstrated that HMGB1 expression was significantly upregulated in MC3T3-E1 or MG-63 cells under hypoxia. We also found that treatment with 10 and 100 ng/mL of HMGB1 significantly promoted the fibrosis-associated markers such as Collagen I, a-SMA, whereas downregulated the E-cadherin, indicating the differentiation of MC3T3-E1 or MG-63 cells into fibroblast cells. Further investigation indicated that the HMGB1 treatment markedly activated the mitogen-activated protein kinases (MAPKs), including extracellular signal-related kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (p38) phosphorylation, as well as nuclear factor (NF)-kappa B nuclear translocation. On the other side, using specific inhibitors and shRNAs of protein kinases, we observed that repression of ERK, JNK, p38, and NF-kappa B all inhibited HMGB1-induced cellular differentiation and migration of MC3T3-E1 cells. In addition, knocking down of advanced glycation end products (RAGE) but not Toll-like receptor (TLR) 2 and TLR4 by shRNAs attenuated HMGB1-induced myofibroblast differentiation and migration. In conclusion, our study demonstrated that HMGB1 induced the fibrosis of osteoblasts in vitro via activating the RAGE-MAPK and NF-kappa B interaction signaling pathways.