Our analysis revealed that ZIKV

Our analysis revealed that ZIKV strongly impairs cell cycle progression of RGP cells, consistent with recent reports (Qian et al., 2016; Li et al., 2016). Surprisingly, WNV-infected RGP cells did not show such cell cycle abnormalities. Our comparative analysis should therefore prove very powerful to identify the molecular pathways responsible for ZIKV\'s specific anti-mitotic activity. It will also be important to test if non-microcephaly-associated ZIKV strains from the African lineage may have different effect and tropism of infection in the developing neocortex, compared to the Pf13 strain from the Asian lineage used in this study (Cugola et al., 2016). We focused here on the early stages of neocortex infection (24h, representing a full replication cycle of the virus) and observed a reduction of apoptotic cell death, which may represent a crucial step for ZIKV infection of the developing brain. Recent studies have reported increased apoptosis several days post-infection with ZIKV (Li et al., 2016; Qian et al., 2016; Garcez et al., 2016). The development of methods to cultivate infected diazoxide cost slices for multiple days (5–7days) will therefore be critical to identify the long-term consequences of ZIKV infection and to describe if a switch from reduced to increased apoptosis indeed occurs during the course of ZIKV infection. Our work establishes a framework to identify ZIKV-specific processes leading to microcephaly. While our approach does not address the critical steps by which the virus reaches the brain, it allows to precisely characterize the molecular and cellular alterations caused by different flaviviruses. We show that ZIKV, but not other closely related flaviviruses, has a strong tropism of infection for the neural stem cells. ZIKV impairs cell cycle progression of neural stem cells and inhibits apoptotic cell death at early stages of brain infection, which may represent two crucial events in the route leading to microcephaly. The development of similar assays to infect human fetal developing brain is now of urgent need and will be crucial to fully understand congenital Zika syndrome (Check Hayden, 2016).
Acknowledgments & Funding We are grateful to Joseph J. Cockburn and Renata Basto for helpful comments and suggestions on the manuscript. We thank Valérie Caro, Laure Diancourt and Meriadeg Ar Gouilh for assistance with the phylogenetic tree. The Baffet and Goud labs are part of the Labex CelTisPhyBio (11-LBX-0038) and the Idex Paris Sciences et Lettres (ANR-10-IDEX-0001-02 PSL). Seventh Framework Programme (FP7) provided funding under grant number 278433-PREDEMICS to NP, JB and MPF. Ministry of Defence/Direction Générale de l’Armement (DGA) provided funding to CK. This work was supported by the European Research Council advanced grants (project 339847 ‘MYODYN’ to B.G.). We acknowledge the Curie Cell and Tissue Imaging Platform—PICT-IBiSA (member of France–Bioimaging) for technical assistance.
Conflict of Interest Statement
Author Contribution
Introduction Community-acquired meningitis is a life-threatening infection of the membranes surrounding the brain and spinal cord. Pneumococcal meningitis is the most common and severe form of bacterial meningitis. Fatality rates are substantial, and long-term sequelae develop in about half of survivors (Brouwer et al., 2010; Schut et al., 2012; van de Beek et al., 2012; van de Beek et al., 2004; Zoons et al., 2008). Vaccination has decreased the incidence of invasive pneumococcal disease in infants and recently also in the adult population (Bijlsma et al., 2016; McIntyre et al., 2012; Tsai et al., 2008). Streptococcus pneumoniae is a human commensal strain adapted to colonize the nasopharynx (Brown et al., 2015). However, after asymptomatic colonization translocation of the pneumococcus to the respiratory tract, sinuses and nasal cavity, S. pneumoniae can cause pneumonia, acute sinusitis, otitis media, bacteremia, sepsis and meningitis (Brown et al., 2015; Mook-Kanamori et al., 2011; van de Beek et al., 2006). One of the first host determinants of developing an infection is the recognition and clearance of the pneumococcal strains with initiation of an inflammatory response by the innate immune response. The innate immune response depends on specific pathogen-associated molecular pattern molecules (PAMPS) of the pneumococcus. For example, peptidoglycan and lipoteichoic acid (LTA), are recognized by membrane surface and intracellular Toll-like receptors (TLRs) found on leukocyte cells (Santos-Sierra et al., 2006). After PAMP recognition, intracellular signaling initiates the activation of transcription factors. This leads to the induction of small cell signaling proteins, called cytokines, which are responsible for the inflammatory response and attracts immune cells to the site of infection (Akira et al., 2006). TLRs, like TLR2, TLR4, TLR9 and NOD-like receptors (NLRs) as NOD2 are known to be important in the recognition of invasive pneumococcal strains (Koppe et al., 2012). Differences within these or underlying signaling proteins, caused by genetic variations, can contribute to differences in the immune response affecting the susceptibility to disease and its severity.