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

Abstract

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. 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. 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. 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.