A Molecular Determinant of West Nile Virus Secretion and Morphology as a Target for Viral Attenuation.

West Nile virus (WNV), a member of the Flavivirus genus and currently one of the most common arboviruses worldwide, is associated with severe neurological disease in humans. Its high potential to reemerge and rapidly disseminate makes it a bona fide global public health problem. The surface membrane glycoprotein (M) has been associated with Flavivirus-induced pathogenesis. Here, we identified a key amino acid residue at position 36 of the M protein whose mutation impacts WNV secretion and promotes viral attenuation. We also identified a compensatory site at position M-43 whose mutation stabilizes M-36 substitution both in vitro and in vivo Moreover, we found that introduction of the two mutations together confers a full attenuation phenotype and protection against wild-type WNV lethal challenge, eliciting potent neutralizing-antibody production in mice. Our study thus establishes the M protein as a new viral target for rational design of attenuated WNV strains.IMPORTANCE West Nile virus (WNV) is a worldwide (re)emerging mosquito-transmitted Flavivirus causing fatal neurological diseases in humans. However, no human vaccine has been yet approved. One of the most effective live-attenuated vaccines was empirically obtained by serial passaging of wild-type yellow fever Flavivirus However, such an approach is not acceptable nowadays, and the development of a rationally designed vaccine is necessary. Generating molecular infectious clones and mutating specific residues known to be involved in Flavivirus virulence constitute a powerful tool to promote viral attenuation. WNV membrane glycoprotein is thought to carry such essential determinants. Here, we identified two residues of this protein whose substitutions are key to the full and stable attenuation of WNV in vivo, most likely through inhibition of secretion and possible alteration of morphology. Applied to other flaviviruses, this approach should help in designing new vaccines against these viruses, which are an increasing threat to global human health.

EGFR Signaling Is Overactive in Pachyonychia Congenita: Effective Treatment with Oral Erlotinib.

Pachyonychia congenita (PC) is a rare keratinizing disorder characterized by painful palmoplantar keratoderma for which there is no standard current treatment. PC is caused by dominant mutations in keratin (K) K6A, K6B, K6C, K16, or K17 genes involved in stress, wound healing, and epidermal barrier formation. Mechanisms leading to pain and painful palmoplantar keratoderma in PC remain elusive. In this study, we show overexpression of EGFR ligands epiregulin and TGF-α as well as HER1‒EGFR and HER2 in the upper spinous layers of PC lesions. EGFR activation was confirmed by upregulated MAPK/ERK and mTOR signaling. Abnormal late terminal keratinization was associated with elevated TGM1 activity. In addition, the calcium ion permeable channel TRPV3 was significantly increased in PC-lesional skin, suggesting a predominant role of the TRPV3/EGFR signaling complex in PC. We hypothesized that this complex contributes to promoting TGM1 activity and induces the expression and shedding of EGFR ligands. To counteract this biological cascade, we treated three patients with PC with oral erlotinib for 6‒8 months. The treatment was well-tolerated and led to an early, drastic, and sustained reduction of neuropathic pain with a major improvement of QOL. Our study provides evidence that targeted pharmacological inhibition of EGFR is an effective strategy in PC.

Comparison of a human neuronal model proteome upon Japanese encephalitis or West Nile Virus infection and potential role of mosquito saliva in neuropathogenesis.

Neurotropic flavivirus Japanese encephalitis virus (JEV) and West Nile virus (WNV) are amongst the leading causes of encephalitis. Using label-free quantitative proteomics, we identified proteins differentially expressed upon JEV (gp-3, RP9) or WNV (IS98) infection of human neuroblastoma cells. Data are available via ProteomeXchange with identifier PXD016805. Both viruses were associated with the up-regulation of immune response (IFIT1/3/5, ISG15, OAS, STAT1, IRF9) and the down-regulation of SSBP2 and PAM, involved in gene expression and in neuropeptide amidation respectively. Proteins associated to membranes, involved in extracellular matrix organization and collagen metabolism represented major clusters down-regulated by JEV and WNV. Moreover, transcription regulation and mRNA processing clusters were also heavily regulated by both viruses. The proteome of neuroblastoma cells infected by JEV or WNV was significantly modulated in the presence of mosquito saliva, but distinct patterns were associated to each virus. Mosquito saliva favored modulation of proteins associated with gene regulation in JEV infected neuroblastoma cells while modulation of proteins associated with protein maturation, signal transduction and ion transporters was found in WNV infected neuroblastoma cells.

Bioluminescent Ross River Virus Allows Live Monitoring of Acute and Long-Term Alphaviral Infection by In Vivo Imaging.

Arboviruses like chikungunya and Ross River (RRV) are responsible for massive outbreaks of viral polyarthritis. There is no effective treatment or vaccine available against these viruses that induce prolonged and disabling arthritis. To explore the physiopathological mechanisms of alphaviral arthritis, we engineered a recombinant RRV expressing a NanoLuc reporter (RRV-NLuc), which exhibited high stability, near native replication kinetics and allowed real time monitoring of viral spread in an albino mouse strain. During the acute phase of the disease, we observed a high bioluminescent signal reflecting viral replication and dissemination in the infected mice. Using Bindarit, an anti-inflammatory drug that inhibits monocyte recruitment, we observed a reduction in viral dissemination demonstrating the important role of monocytes in the propagation of the virus and the adaptation of this model to the in vivo evaluation of treatment strategies. After resolution of the acute symptoms, we observed an increase in the bioluminescent signal in mice subjected to an immunosuppressive treatment 30 days post infection, thus showing active in vivo replication of remnant virus. We show here that this novel reporter virus is suitable to study the alphaviral disease up to the chronic phase, opening new perspectives for the evaluation of therapeutic interventions.

Comparative Analysis Between Flaviviruses Reveals Specific Neural Stem Cell Tropism for Zika Virus in the Mouse Developing Neocortex.

The recent Zika outbreak in South America and French Polynesia was associated with an epidemic of microcephaly, a disease characterized by a reduced size of the cerebral cortex. Other members of the Flavivirus genus, including West Nile virus (WNV), can cause encephalitis but were not demonstrated to cause microcephaly. It remains unclear whether Zika virus (ZIKV) and other flaviviruses may infect different cell populations in the developing neocortex and lead to distinct developmental defects. Here, we describe an assay to infect mouse E15 embryonic brain slices with ZIKV, WNV and dengue virus serotype 4 (DENV-4). We show that this tissue is able to support viral replication of ZIKV and WNV, but not DENV-4. Cell fate analysis reveals a remarkable tropism of ZIKV infection for neural stem cells. Closely related WNV displays a very different tropism of infection, with a bias towards neurons. We further show that ZIKV infection, but not WNV infection, impairs cell cycle progression of neural stem cells. Both viruses inhibited apoptosis at early stages of infection. This work establishes a powerful comparative approach to identify ZIKV-specific alterations in the developing neocortex and reveals specific preferential infection of neural stem cells by ZIKV.