Streptococcus pneumoniae is one of the most common and most aggressive pathogens of bacterial meningitis. Hippocampal neurons die by apoptosis, which can only partially be inhibited by a caspase-inhibitor or by blocking host inflammation. Our current results show that live pneumococci are indeed potent inducers of apoptosis in vitro. This apoptosis is characterised by early damage of mitochondrial membrane potential and ultrastructure and is dependent on apoptosis-inducing factor (AIF) and on the increase of intracellular Ca2+ . We hypothesised that soluble bacterial factors, Ca2+ , mitochondrial damage, and AIF significantly contribute to brain damage in pneumococcal meningitis.
The proposal aims:
- To identify the bacterial triggers of apoptosis in primary rat hippocampal neurons in vitro by testing
- pneumococcal mutants and
- pneumococcal toxins.
- To determine pro-apoptotic bacterial triggers which induce
- caspase-dependent and -independent apoptosis,
- increases of intracellular Ca2+ and reactive oxygen species (ROS),
- mitochondrial damage,
- translocation of cytochrome C and AIF from mitochondria to the cytosol and AIF- dependent apoptosis.
- To investigate, if overexpression of the mitochondrial anti-apoptotic protein Bcl-2 protects neurons from pneumococcal induced apoptosis.
- To assess the in vivo significance of the two most potent pneumococcal neurotoxins (identified in the aforementioned in vitro experiments) in experimental pneumococcal meningitis by quantification of hippocampal neuronal damage with hematoxylin & eosin (H&E) and TUNELstainings, caspase-3- and AIF-imunohistochemistry. The results of these experiments will help to develop adjunctive therapies to prevent neuronal damage during bacterial meningitis.
Results from this study have been published in scientific journals as follows:
Braun JS, Sublett JE, Freyer D, Mitchell TJ, Cleveland JL, Tuomanen EI, Weber JR,
Pneumococcal pneumolysin and H(2)O(2) mediate brain cell apoptosis during meningitis.
J Clin Invest 2002 Jan;109(1):19-27.
Weber JR, Moreillon P, Tuomanen EI,
Innate sensors for Gram-positive bacteria. Curr Opin
Immunol 2003 Aug;15(4):408-15.
Bermophl D, Halle A, Freyer D, Dagand E, Braun JS, Bechmann I, Schroder NWJ, Weber JR,
Research highlights: Medicine: Barrier grief. Nature 2005 June;435(7044):858. http://www.nature.com/nature/journal/v435858a.html
Bermpohl D, Halle A, Freyer D, Dagand E, Braun JS, Bechmann I, Schroder NW, Weber JR,
Bacterial programmed cell death of cerebral endothelial cells involves dual death pathways.
J Clin Invest 2005 Jun;115(6):1607-15.
Hoffmann O, Zweigner J, Smith SH, Freyer D, Mahrhofer C, Dagand E, Tuomanen EI, Weber JR.
Interplay of pneumococcal hydrogen peroxide and host-derived nitric oxide.
Infect Immun. 2006 Sep;74(9):5058-66
Rueter N, Freyer D, Bert B, Fink H, Weber JR.
Pneumococcal cell wall-induced meningitis impairs adult hippocampal neurogenesis. Hoffmann O, Mahrhofer C, Infect Immun. 2007 Sep;75(9):4289-97. Epub 2007 Jun 25