Role of astrogial Connexin 43 in pneumococcal meningitis and pneumolysin cytotoxicity

Introductory paragraph Streptococcus pneumoniae or pneumococcus (PN) is a major causative agent of bacterial meningitis with high mortality in young infants and elderly people. The mechanism underlying PN crossing of the blood brain barrier (BBB) remains poorly understood. Here, we show that the gap junctional component connexin 43 expressed in astrocytes (aCx43) plays a major role in PN meningitis. Following intravenous PN challenge, mice deficient for aCx43 developed milder symptoms and showed severely reduced bacterial counts in the brain. We show a role for aCx43 in the PN-induced fragmentation of astrocytic GFAP filaments associated with bacterial translocation across endothelial vessels and replication in the brain cortex. aCx43 triggers the PN- and Ply-dependent GFAP fragmentation and nuclear shrinkage in in vitro cultured astrocytes. We showed that purified pneumolysin (Ply) co-opted Cx43 to promote the permeabilization and cytosolic calcium (Ca 2+ ) increase of host cells, a process sensitive to extracellular ATP depletion. These results point to aCx43 as a major player during bacterial meningitis and extend cytolytic mechanisms implicating other host cell plasma membrane channels proposed for small pore-forming toxins, to Ply, a cholesterol-dependent cytolysin, at concentrations relevant to bacterial infection.