Neuronal death in pneumococcal meningitis is triggered by pneumolysin and RrgA interactions with β-actin

Neuronal damage is a major consequence of bacterial meningitis, but little is known about mechanisms of bacterial interaction with neurons leading to neuronal cell death. Streptococcus pneumoniae (pneumococcus) is a leading cause of bacterial meningitis and many survivors develop neurological sequelae after the acute infection has resolved, possibly due to neuronal damage. Here, we studied mechanisms for pneumococcal interactions with neurons. Using human primary neurons, pull-down experiments and mass spectrometry, we show that pneumococci interact with the cytoskeleton protein beta-actin through the pilus-1 adhesin RrgA and the cytotoxin pneumolysin (Ply), thereby promoting adhesion and invasion of neurons, and neuronal death. Using our bacteremia-derived meningitis mouse model, we observe that RrgA- and Ply-expressing pneumococci co-localize with neuronal beta-actin. Using purified proteins, we show that Ply, through its cholesterol-binding domain 4, interacts with the neuronal plasma membrane, thereby increasing the exposure on the outer surface of beta-actin filaments, leading to more beta-actin binding sites available for RrgA binding, and thus enhanced pneumococcal interactions with neurons. Pneumococcal infection promotes neuronal death possibly due to increased intracellular Ca2+ levels depending on presence of Ply, as well as on actin cytoskeleton disassembly. STED super-resolution microscopy showed disruption of beta-actin filaments in neurons infected with pneumococci expressing RrgA and Ply. Finally, neuronal death caused by pneumococcal infection could be inhibited using antibodies against beta-actin. The generated data potentially helps explaining mechanisms for why pneumococci frequently cause neurological sequelae. Author summary Neuronal damage is a major consequence of meningitis. Streptococcus pneumoniae (pneumococcus) is the leading etiological cause of bacterial meningitis, yet how pneumococci interact with neurons and cause neuronal death is poorly understood. Using human neurons in vitro and our established bacteremia-derived meningitis mouse model in vivo, we found that pneumococci use the pilus-1 adhesin RrgA and the cytotoxin pneumolysin (Ply) to interact with neuronal beta-actin expressed on the plasma membrane. Also, we demonstrate that Ply interaction with the neuronal plasma membrane increase the exposure of beta-actin on the neuronal plasma membrane, allowing more pneumococci to adhere to neurons through RrgA-beta-actin interaction. Moreover, neurons infected with RrgA- and Ply-expressing pneumococci showed increased intracellular Ca2+ levels and disruption of beta-actin filaments, possibly leading to neuronal death. Importantly, by blocking pneumococcal-beta-actin interaction using antibodies, we could reduce neuronal cell death after pneumococcal infection.

Automated summary

Neuronal damage is a major consequence of bacterial meningitis, with Streptococcus pneumoniae playing a prominent role in causing neurological sequelae. This study investigated mechanisms by which pneumococci interact with neurons, leading to neuronal death. The findings suggest that pneumococci utilize specific proteins to bind to neurons, ultimately causing neuronal cell death through intracellular calcium levels and disruption of the actin cytoskeleton. Antibodies against beta-actin may serve as a potential therapy to prevent neuronal death caused by pneumococcal infection.