Pneumococcal pneumolysin and H2O2 mediate brain cell apoptosis during meningitis
Johann S. Braun, Jack E. Sublett, Dorette Freyer, Tim J. Mitchell, John L. Cleveland, Elaine I. Tuomanen, Joerg R. Weber
Johann S. Braun, Jack E. Sublett, Dorette Freyer, Tim J. Mitchell, John L. Cleveland, Elaine I. Tuomanen, Joerg R. Weber
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Pneumococcal pneumolysin and H2O2 mediate brain cell apoptosis during meningitis

Abstract

Pneumococcus is the most common and aggressive cause of bacterial meningitis and induces a novel apoptosis-inducing factor–dependent (AIF–dependent) form of brain cell apoptosis. Loss of production of two pneumococcal toxins, pneumolysin and H2O2, eliminated mitochondrial damage and apoptosis. Purified pneumolysin or H2O2 induced microglial and neuronal apoptosis in vitro. Both toxins induced increases of intracellular Ca2+ and triggered the release of AIF from mitochondria. Chelating Ca2+ effectively blocked AIF release and cell death. In experimental pneumococcal meningitis, pneumolysin colocalized with apoptotic neurons of the hippocampus, and infection with pneumococci unable to produce pneumolysin and H2O2 significantly reduced damage. Two bacterial toxins, pneumolysin and, to a lesser extent, H2O2, induce apoptosis by translocation of AIF, suggesting new neuroprotective strategies for pneumococcal meningitis.

Authors

Johann S. Braun, Jack E. Sublett, Dorette Freyer, Tim J. Mitchell, John L. Cleveland, Elaine I. Tuomanen, Joerg R. Weber

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Inactivation of pneumolysin and blocking H2O2 inhibits apoptosis induced...
Inactivation of pneumolysin and blocking H2O2 inhibits apoptosis induced by live pneumococci. (a and b) Human microglia incubated with wild-type pneumococci D39 (107 CFU/ml, 6 hours) in the absence or presence of NAC (10 mM) underwent massive shrinkage and condensation of their nuclei by AO/EB staining, whereas NAC effectively impaired changes in nuclear morphology and cell membrane damage in cells exposed to plnA– (107 CFU/ml, 6 hours). Bars = 10 μm. (b) Quantification of apoptotic microglia after exposure to wild-type (D39) or mutant pneumococci defective in pneumolysin (plnA–) or H2O2 production (spxB–) or both (plnA–/spxB–). Shown are the results (means + SD) of three independent experiments after 6 hours of incubation. Addition of the antioxidant NAC prevented apoptosis induced by plnA–, but not that induced by D39 or spxB– (b). plnA– in the presence of NAC or catalase (Cat) (1,250 U/ml) and plnA–/spxB–were significantly different compared with all others (P < 0.05). plnA– combined with NAC or catalase was more efficient to prevent apoptosis than was the double mutant plnA–/spxB– (P < 0.05). ANOVA and Student-Newman-Keuls test were used. WT, wild-type.