Analysis of macrophage apoptosis induced by Brucella melitensis and the effects of caspases 3, 8 and 9

Abstract

Objective To determine the difference of macrophage RAW264.7 apoptosis induced by Brucella melitensis virulent strain 16M and attenuated strain M5-90 and elucidate the regulatory role of caspases 3,8 and 9.Methods The best multiplicity of infection (MOI) was determined through kinetic analysis of Brucella melitensis strain 16M and M5-90 induced mouse macrophages apoptosis(bacterium ∶ cell =100 ∶ 1,50 ∶ 1,10 ∶1).The infection model was established using the best MOI =50 ∶ 1.The numbers of in vivo bacteria by colony formation units were calculated after macrophages were infected for different times,including 2,4,8,12,24 and 48 h,and the infected cells were collected.The ratios of apoptosis were detected and the regulation of caspases 3,8 and 9 in apoptosis pathway was elucidated by flow cytometry.Results The numbers of 16M in vivo bacteria were 105.4,104.8,105.8,106.5,108.0 and 109.0,respectively and of M5-90 were 106.1,106.2,106.4,106.3,106.1 and 105.0,respectively.The number of in vivo bacteria of 16M was significantly increased than that of M5-90 after infected for 24 h to 48 h.The ratios of apoptosis induced by 16M after infected for 2,4,8,12,24 and 48 h was (2.67 ± 0.09)％,(13.13 ± 0.30)％,(6.56 ± 0.42)％,(6.49 ± 0.28)％,(16.07 ± 0.86)％ and (24.23 ± 1.67)％,respectively,and by M5-90 was (3.62 ± 0.02)％,(32.01 ± 2.59)％,(17.58 ± 0.44)％,(16.09 ± 0.10)％,(62.53 ± 2.70)％ and (85.53 ± 0.15)％,respectively,and by control group was [(1.90 ± 0.20)％,(1.92 ±0.16)％,(1.99 ± 0.03)％,(2.48 ± 0.11)％,(3.56 ± 0.07)％,(5.26 ± 0.33)％].The differences were statistically between groups in same time.The Brucella melitensis vaccine strain M5-90 was more powerful than virulent strain 16M in respect of inducing macrophage apoptosis after infected for 24 to 48 h.Twenty-four hours after infection,the expression of caspases 3,8 and 9 was (1.47 ± 0.05)％,(1.52 ± 0.02)％ and (2.47 ± 0.12)％,respectively,in control group and the expression was (9.70 ± 0.46)％,(6.08 ± 0.56)％ and (35.08 ± 1.64)％,respectively,after infected for 24 h induced by M5-90.The expression of caspases 3,8 and 9 was significantly higher than that control group (P ＜ 0.01).Twenty-four hours after given caspases 3,8 and 9 inhibitor,apoptosis rate in control group was (66.72 ± 1.28)％,in M5-90 group was (22.58 ± 0.55)％,(53.15 ± 1.85)％ and (29.18 ± 0.23)％,respectively,and compared with control group,apoptosis rate of caspases 3,8 and 9 was significantly lower(P ＜ 0.01).Conclusions Apoptosis of macrophage can be induced by Brucella melitensis virulent vaccine strain 16M and attenuated strain M5-90.M5-90 is stronger than that of strain 16M.Caspases 3,8 and 9 can regulate macrophage apoptosis after M5-90 infection. Key words: Brucella melitensis ; Macrophage ; Apoptosis ; Caspase