Toxic effect of Brucella outer membrane protein 16 on osteoblasts / 中华地方病学杂志

ABSTRACT

Objective:This study is designed to investigate the toxicity of lipoprotein (L16) and non-lipoprotein (U16) of Brucella outer membrane protein (OMP) 16 on osteoblasts. Methods:Recombinant L16 and U16 proteins were prepared by using prokaryotic expression system of Escherichia coli ( E. coli) BL21 (DE3) and purified by Ni column. Using group design, mouse osteoblasts (MC3T3 cells) were co-incubated with L16 and U16, respectively. Brucella lipopolysaccharide (LPS) stimulus was used as the positive control, and cells without any stimulation were used as the negative control. Incubation time was 24 h. The activity of co-incubated MC3T3 cells were detected by CCK-8; the supernatant of cultured cells was collected and the release rate of lactate dehydrogenase (LDH) in the supernatant was detected by bioluminescence, and the virulence of L16 and U16 on MC3T3 cells was evaluated. Annexin Ⅴ-PE/7-AAD double staining flow cytometry was further used to analyze the apoptosis rate of MC3T3 cells, and the activation level of apoptosis executive protein Caspase-3 was detected by Western blotting (WB). Results:The activity of MC3T3 cells in L16 group [(56.16±1.63)%] was significantly lower than that in U16 and LPS groups [(97.02±1.44)%, (98.64±0.90)%, P < 0.01], the LDH release rate [(84.64±0.96)%] was significantly higher than that in U16 and LPS groups [(34.82±3.41)%, (26.75±1.95)%, P < 0.01]. Annexin Ⅴ-PE/7-AAD double staining results showed that the apoptosis rate was (46.45±2.19)% in L16 group, while the remaining groups were all less than 1%. WB results showed that activated Caspase-3 (cleaved-Caspase-3) existed in L16 stimulated cells, but not in U16 stimulated cells and LPS control cells. Conclusion:L16 can induce the apoptosis of osteoblasts and inhibit the proliferation of osteoblasts, but U16 has no obvious effect indicating that Brucella L16 with complete lipid structure is necessary for virulence effect.