LPS at low concentration promotes the fracture healing through regulating the autophagy of osteoblasts via NF-κB signal pathway

M.-X. Xu, X.-X. Sun, W. Li, G. Xie, Q. Yang, Z.-W. Qu, Q.-G. Meng

Harbin Medical University, Harbin, China. Plasone66@126.com

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• Orthopedics

OBJECTIVE: To investigate the effect of low-concentration lipopolysaccharide (LPS) on proliferation and apoptosis of osteoblasts and to discover the mechanism of low-concentration LPS in facilitating the proliferation of osteoblasts.

MATERIALS AND METHODS: MC3T3-E1 osteoblasts were treated with LPS, 3-methyladenine (3-MA, autophagy inhibitor), and BAY11-7082 (inhibitor of nuclear factor-kappa b, NF-κB), respectively. The cell cycles were detected using a flow cytometer. Cell proliferation and activity of MC3T3-E1 osteoblasts were explored by cell counting kit-8. Western blotting and immunofluorescence assay were performed to detect the protein level. RNA expression was measured through polymerase chain reaction (PCR) and immunofluorescence assay.

RESULTS: At the third day after cell culture, cell infusion reached 80%, and cells were taken as the subjects. At 6 h after treatment with low-concentration LPS, the proliferation and activity of cells were higher than those at 1 h and 12 h after treatment, and the apoptotic level was significantly lower than that in cells at 12 h after treatment. The proliferation and activity of cells in the low-concentration LPS group were significantly higher than those in the control group, 3-MA group and BAY11-7082 group, and the apoptotic level was lower than those in these groups. Compared with those of cells in control group and BAY11-7082 group, the messenger RNA (mRNA) and protein expressions and nuclear transfer of cells in low-concentration LPS group were significantly elevated, but there were no statistically significant differences in comparisons with the 3-MA group. In the experiment of cell autophagy, the autophagic level in cells in low-concentration LPS group was higher than those in the control group, 3-MA group and BAY11-7082 group.

CONCLUSIONS: Through the NF-κB signaling pathway in osteoblasts, low-concentration LPS can activate the autophagy and promote cell proliferation, thereby inhibiting cell apoptosis and accelerating the fracture healing.

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