Infodoc : Sciences, Techniques et Culture

Zika virus (ZIKV) is a mosquito-transmitted flavivirus responsible for worldwide epidemics and constitutes a major public health threat. The majority of ZIKV infections in humans are either asymptomatic or result in a mild febrile illness. However, some patients develop a more severe, sometimes life-threatening, form of the disease. Recent evidence showed that ZIKV infection can trigger Guillain-Barré syndrome and encephalitis in adults, as well as congenital malformations such as microcephaly. The severity of ZIKV disease in humans depends on many factors, likely including host genetic determinants.We investigated how genome-wide variants could impact the susceptibility to ZIKV infection in mice. To this end, we used mouse strains of the Collaborative Cross (CC), a new genetic refere[...]

Zika virus (ZIKV) is a mosquito-transmitted flavivirus responsible for worldwide epidemics and constitutes a major public health threat. The majority of ZIKV infections in humans are either asymptomatic or result in a mild febrile illness. However, some patients develop a more severe, sometimes life-threatening, form of the disease. Recent evidence showed that ZIKV infection can trigger Guillain-Barré syndrome and encephalitis in adults, as well as congenital malformations such as microcephaly. The severity of ZIKV disease in humans depends on many factors, likely including host genetic determinants.We investigated how genome-wide variants could impact the susceptibility to ZIKV infection in mice. To this end, we used mouse strains of the Collaborative Cross (CC), a new genetic reference population encompassing a genetic diversity as broad as that of human populations.First, we described that the susceptibility of Ifnar1 (receptor to type I interferon) knockout mice is largely influenced by their genetic background. We then showed that the genetic diversity of CC mice, which IFNAR was blocked by anti-IFNAR antibody, expressed phenotypes ranging from complete resistance to severe symptoms and death with large variations in the peak and rate of decrease of plasma viral load, in brain viral load, in brain histopathology and in viral replication rate in infected cells. Differences of susceptibility between CC strains were correlated between Zika, Dengue and West Nile viruses. We identified highly susceptible and resistant CC strains as new models to investigate the mechanisms of human ZIKV disease and other flavivirus infections. Genetic analyses revealed that phenotypic variations were driven by multiple genes with small effects, reflecting the complexity of ZIKV disease susceptibility in human population. Notably, our results also ruled out a role of the Oas1b gene in the susceptibility to ZIKV.In a second part, we searched for genes which modify the susceptibility of Ifnar1 knockout mice in an F2 cross between C57BL/6J and 129S2/SvPas mice harboring the mutation. Genetic analysis revealed two Quantitative Trait Locus (QTL) controlling either the peak viremia or the mouse survival. Although these QTLs critical intervals contained hundreds of genes, data mining led us to identify a few candidate causal genes.Then, we investigated how host genetic factors influence viral replication in infected cells using Mouse Embryonic Fibroblasts (MEFs) derived from a series of CC strains with contrasted phenotypes observed in response to ZIKV infection in vivo. MEFs from CC071 strain displayed unique features of increased viral replication rate in late infection. Using transcriptomic analysis, we demonstrated that the phenotype of CC071 infected MEFs resulted from a delayed induction of the type I interferon (IFN) response. Genetic analyses ruled out single gene deficiencies but rather suggested combined effects of multiple factors in the type I IFN induction signaling pathway.Finally, we characterized the ZIKV-induced type I IFN response in MEFs and primary neurons derived from C57BL/6J mouse strain. Primary neurons were less capable than MEFs to control the viral replication due to a delayed IFN response. We later showed that host genetic factors also play a critical role in this context as ZIKV-infected CC071 primary neurons displayed an extreme phenotype compared to neurons from strains that are more resistant.Altogether, our work has unraveled the role of host genes in the pathogeny of ZIKV infection and illustrates the potential of CC mouse strains for genetic studies and as new models of infectious diseases. Extensive analysis of CC strains with extreme phenotypes help us elucidate how genetic variants affect susceptibility as well as immune responses to flaviviral infection and will provide deeper understanding of the pathophysiology of human ZIKV disease.