Poster Presentation The 3rd Prato Conference on Pore Forming Proteins 2015

Pneumolysin disrupts the regulation of glutamate in the brain, leading to synaptic damage during Streptococcus pneumonaie meningitis (#43)

C Wippel 1 , J Maurer 1 , C Förtsch 1 , S Hupp 1 , A Bohl 1 , J Ma 2 , T.J. Mitchell 2 , S Bunkowski 3 , W Brück 3 , R Nau 3 4 , A.I. Iliev 1 5
  1. Department of Pharmacology and Toxicology, University of Würzburg, Germany
  2. School of Immunity and Infection, College of Medical and Dental Sciences, University of Birmingham, United Kingdom
  3. Department of Neuropathology, University of Göttingen, Germany
  4. Geriatrics Department, Weende Hospital, Göttingen, Germany
  5. Department of Anatomy, University of Bern, Switzerland

Streptococcus pneumoniae is the most common cause of bacterial meningitis in the world and is accompanied with high lethality and serious disability in survivors. The cholesterol-dependent cytolysin pneumolysin represents a key factor, determining the neuropathogenic potential of the pneumococci. Removal of pneumolysin correlates with much milder disease course in experimental pneumococcal meningitis model. In the current poster, we present evidence for selective synaptic loss within the superficial layers of the frontal neocortex of post-mortem brain samples from individuals with pneumococcal meningitis. This is the first description of synaptic loss in bacterial meningitis, which gives an explanation for the long-term cognitive alterations in survivors. 

Next, to clarify the molecular factors involved in this process, we analyzed mice with experimental pneumococcal meningitis. A similar synaptic loss was observed in mice with pneumococcal meningitis only when the bacteria expressed the pore-forming cholesterol-dependent cytolysin pneumolysin. Exposure of acute mouse brain slices to only pore-competent pneumolysin at disease-relevant, non-lytic concentrations caused permanent dendritic swelling, dendritic spine elimination and synaptic loss (as assessed by PSD95 and synapsin staining). The NMDA glutamate receptor antagonists MK801 and D-AP5 reduced this pathology, indicative of excessive glutamatergic activation (excitotoxicity). This was surprising, since the toxin apparently altered the synapses not directly, but via glutamate. Pneumolysin increased glutamate levels in acute mouse brain slices within 30 min after exposure. In mouse astrocytes, pneumolysin initiated the release of glutamate in a calcium-dependent manner. We propose that pneumolysin plays a significant synapto- and dendritotoxic role in pneumococcal meningitis by initiating glutamate release from astrocytes, leading to subsequent glutamate-dependent synaptic damage. We outline for the first time the occurrence of synaptic pathology in pneumococcal meningitis and demonstrate that a bacterial cytolysin can dysregulate the control of glutamate in the brain, inducing excitotoxic damage.