Streptococcus oralis, an oral commensal, belongs to the mitis group of streptococci and occasionally causes opportunistic infections, such as bacterial endocarditis and bacteremia. Recently, we found that the hydrogen peroxide (H2O2) produced by S. oralis is sufficient to kill human monocytes and epithelial cells, implying that streptococcal H2O2 is a cytotoxin. In the present study, we investigated whether streptococcal H2O2 impacts lysosomes, organelles of the intracellular digestive system, in relation to cell death. S. oralis infection induced the death of RAW 264 macrophages in an H2O2-dependent manner, which was exemplified by the fact that exogenous H2O2 also induced cell death. Infection with either a mutant lacking spxB, which encodes pyruvate oxidase responsible for H2O2 production, or Streptococcus mutans, which does not produce H2O2, showed less cytotoxicity. Visualization of lysosomes with LysoTracker revealed lysosome deacidification after infection with S. oralis or exposure to H2O2, which was corroborated by acridine orange staining. Similarly, fluorescent labeling of lysosome-associated membrane protein-1 gradually disappeared during infection with S. oralis or exposure to H2O2. The deacidification and the following induction of cell death were inhibited by chelating iron in lysosomes. Moreover, fluorescent staining of cathepsin B indicated lysosomal destruction. However, treatment of infected cells with a specific inhibitor of cathepsin B had negligible effects on cell death; instead, it suppressed the detachment of dead cells from the culture plates. These results suggest that streptococcal H2O2 induces cell death with lysosomal destruction and then the released lysosomal cathepsins contribute to the detachment of the dead cells.
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机译：口腔链球菌是口腔链球菌，属于链球菌的微生物群，偶尔引起机会性感染，例如细菌性心内膜炎和菌血症。最近，我们发现口头链球菌产生的过氧化氢（H 2 O 2 ）足以杀死人单核细胞和上皮细胞，这暗示链球菌H 2 O 2 是一种细胞毒素。在本研究中，我们调查了链球菌H 2 O 2 是否会影响溶酶体，细胞内消化系统的细胞器以及细胞死亡。口腔链球菌感染以H 2 O 2 依赖性方式诱导RAW 264巨噬细胞死亡，外源性H 2 事实证明了这一点。 sub> O 2 也诱导细胞死亡。感染缺少 spxB 的突变体（其编码负责H 2 O 2 产生的丙酮酸氧化酶）或不产生H的变形链球菌的感染 2 O 2 ，表现出较低的细胞毒性。用LysoTracker可视化溶酶体显示口腔链球菌感染或暴露于H 2 O 2 后溶酶体脱酸，这通过a啶橙染色得到证实。同样，溶酶体相关膜蛋白1的荧光标记在口腔链球菌感染或暴露于H 2 O 2 期间逐渐消失。通过溶酶体中的铁螯合抑制脱酸和随后的细胞死亡诱导。此外，组织蛋白酶B的荧光染色表明溶酶体破坏。但是，用组织蛋白酶B的特异性抑制剂处理受感染的细胞对细胞死亡的影响可忽略不计。相反，它抑制了死细胞从培养板上的脱落。这些结果表明，链球菌H 2 O 2 诱导细胞死亡并导致溶酶体破坏，然后释放的溶酶体组织蛋白酶促进了死细胞的脱离。
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