Bacterial programmed cell death of cerebral endothelial cells involves dual death pathways
Daniela Bermpohl, Annett Halle, Dorette Freyer, Emilie Dagand, Johann S. Braun, Ingo Bechmann, Nicolas W.J. Schröder, Joerg R. Weber
Daniela Bermpohl, Annett Halle, Dorette Freyer, Emilie Dagand, Johann S. Braun, Ingo Bechmann, Nicolas W.J. Schröder, Joerg R. Weber
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Research Article Infectious disease

Bacterial programmed cell death of cerebral endothelial cells involves dual death pathways

Abstract

Major barriers separating the blood from tissue compartments in the body are composed of endothelial cells. Interaction of bacteria with such barriers defines the course of invasive infections, and meningitis has served as a model system to study endothelial cell injury. Here we report the impressive ability of Streptococcus pneumoniae, clinically one of the most important pathogens, to induce 2 morphologically distinct forms of programmed cell death (PCD) in brain-derived endothelial cells. Pneumococci and the major cytotoxins H202 and pneumolysin induce apoptosis-like PCD independent of TLR2 and TLR4. On the other hand, pneumococcal cell wall, a major proinflammatory component, causes caspase-driven classical apoptosis that is mediated through TLR2. These findings broaden the scope of bacterial-induced PCD, link these effects to innate immune TLRs, and provide insight into the acute and persistent phases of damage during meningitis.

Authors

Daniela Bermpohl, Annett Halle, Dorette Freyer, Emilie Dagand, Johann S. Braun, Ingo Bechmann, Nicolas W.J. Schröder, Joerg R. Weber

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Figure 1

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Pneumococci and PCW trigger PCD in BMECs. (A and C) Unchallenged BMECs. ...
Pneumococci and PCW trigger PCD in BMECs. (A and C) Unchallenged BMECs. Living pneumococci (R6, 107 CFU/ml, 12 hours) induced the appearance of TUNEL-positive BMECs (B) and shrinkage and condensation of the nuclei by ethidium bromide/acridine orange staining (D). (E) BMECs incubated with PCW (107 CFU equivalents, 72 hours) underwent shrinkage, condensation, and fragmentation of the nuclei by ethidium bromide/acridine orange staining. Arrows indicate apoptotic bodies. (F) Pneumococci (D39) induced nuclear fragmentation (arrow) in endothelial cells of the vessel wall of capillaries in experimental mouse meningitis. (G) Electron microscopy showed a normal nucleus in the control culture. (H) Shrinkage and condensation of the nucleus occurred after challenge with living pneumococci (R6, 107 CFU/ml, 4 hours). (I) Nuclear fragmentation characterized PCD by PCW (107 CFU equivalents, 72 hours). Scale bars: 10 μm (A–F) and 1 μm (G–I). (J) Pneumococci (D39) caused dose- and time-dependent PCD in BMECs. No BMECs survived 18 hours after pneumococcal challenge. Co, control; n.d., not done. (K) PCW triggered a dose- and time-dependent protracted PCD. (L) The absence of 1 toxin, either pneumolysin (plnA–) or H2O2 (spxB–), did not prevent PCD compared with wild-type D39. Absence of both toxins significantly decreased PCD. Addition of catalase (Cat; 1,250 U/ml) to plnA– resulted in only a minor enhancement of protection of BMECs compared with plnA–spxB– after 12 hours. All data are presented as mean ± SD. *P < 0.05 (ANOVA and Student-Newman-Keuls test).