Hypoxia-induced HMGB1 in would tissues promotes the osteoblast cell proliferation via activating ERK/JNK signaling.

High mobility group box-B1 (HMGB1) is upregulated in tumors, inflammations, and other injuries. However, its extracellular role and signaling in wound healing remains unclear. In the present study, we examined the HMGB1 levels in hematoma samples in fractured bones and in human macrophagy U937 cells under hypoxia with enzyme-linked immunosorbent assay (ELISA) and western blotting. Then we investigated the activation of the extracellular signal-regulated kinases (ERK) and c-Jun N-terminal kinases (JNK) signaling western blotting in osteoblast MG-63 cells under hypoxia, with or without HMGB1 treatment. And then we assessed the effects of extracellular HMGB1 on cell proliferation of MG-63 cells with CCK-8 assay. It was demonstrated that HMGB1 expression was significantly up regulated in hematoma samples in fractured bones and in U937 cells under hypoxia. MG-63 cells under hypoxia showed an increased HMGB1 in the cytoplasm rather than in nuclei. And the extracellular HMGB1 ameliorated the hypoxia-induced viability reduction and promoted the proliferation of MG-63 cells. Moreover, the MG-63 cells incubated with HMGB1 had increased ERK1/2 phosphorylation, whereas such effect was blocked by the TLR-4 knockout with SIRNA-TLR-4 transfection. In conclusion, we found the up regulation HMGB1 in the hematoma of fractured bones and in macrophage U937 cells under hypoxia, and the hypoxia-up regulated HMGB1 promoted the proliferation of osteoblast MG-63 cells and activated the phosphorylation of ERK and JNK. And the proliferation promotion and the activation of ERK/JNK signaling was TLR-4-dependent.