The Antiviral Potential of AdipoRon, an Adiponectin Receptor Agonist, Reveals the Ability of Zika Virus to Deregulate Adiponectin Receptor Expression.

Zika virus (ZIKV) is a pathogenic member of the flavivirus family, with several unique characteristics. Unlike any other arbovirus, ZIKV can be transmitted sexually and maternally, and thus produce congenital syndromes (CZS) due to its neurotropism. This challenges the search for safe active molecules that can protect pregnant women and their fetuses. In this context, and in the absence of any existing treatment, it seemed worthwhile to test whether the known cytoprotective properties of adiponectin and its pharmacological analog, AdipoRon, could influence the outcome of ZIKV infection. We showed that both AdipoRon and adiponectin could significantly reduce the in vitro infection of A549 epithelial cells, a well-known cell model for flavivirus infection studies. This effect was particularly observed when a pre-treatment was carried out. Conversely, ZIKV revealed an ability to downregulate adiponectin receptor expression and thereby limit adiponectin signaling.

Genomic evolution of SARS-CoV-2 in Reunion Island.

Island communities are interesting study sites for microbial evolution during epidemics, as their insular nature reduces the complexity of the population's connectivity. This was particularly true on Reunion Island during the first half of 2021, when international travel was restricted in order to mitigate the risk for SARS-CoV-2 introductions. Concurrently, the SARS-CoV-2 Beta variant became dominant and started to circulate at high levels for several months before being completely replaced by the Delta variant as of October 2021. Here, we explore some of the particularities of SARS-CoV-2 genomic evolution within the insular context of Reunion Island. We show that island isolation allowed the amplification and expansion of unique genetic lineages that remained uncommon across the globe. Islands are therefore potential hotspots for the emergence of new genetic variants, meaning that they will play a key role in the continued evolution and propagation of COVID-19 as the pandemic persists.

Evidence of RedOX Imbalance during Zika Virus Infection Promoting the Formation of Disulfide-Bond-Dependent Oligomers of the Envelope Protein.

Flaviviruses replicate in membrane factories associated with the endoplasmic reticulum (ER). Significant levels of flavivirus viral protein accumulation contribute to ER stress. As a consequence, the host cell exhibits an Unfolded Protein Response (UPR), subsequently stimulating appropriate cellular responses such as adaptation, autophagy or apoptosis. The correct redox conditions of this compartment are essential to forming native disulfide bonds in proteins. Zika virus (ZIKV) has the ability to induce persistent ER stress leading to the activation of UPR pathways. In this study, we wondered whether ZIKV affects the redox balance and consequently the oxidative protein folding in the ER. We found that ZIKV replication influences the redox state, leading to the aggregation of the viral envelope protein as amyloid-like structures in the infected cells.

Apoptosis during ZIKA Virus Infection: Too Soon or Too Late?

Cell death by apoptosis is a major cellular response in the control of tissue homeostasis and as a defense mechanism in the case of cellular aggression such as an infection. Cell self-destruction is part of antiviral responses, aimed at limiting the spread of a virus. Although it may contribute to the deleterious effects in infectious pathology, apoptosis remains a key mechanism for viral clearance and the resolution of infection. The control mechanisms of cell death processes by viruses have been extensively studied. Apoptosis can be triggered by different viral determinants through different pathways as a result of virally induced cell stresses and innate immune responses. Zika virus (ZIKV) induces Zika disease in humans, which has caused severe neurological forms, birth defects, and microcephaly in newborns during the last epidemics. ZIKV also surprised by revealing an ability to persist in the genital tract and in semen, thus being sexually transmitted. Mechanisms of diverting antiviral responses such as the interferon response, the role of cytopathic effects and apoptosis in the etiology of the disease have been widely studied and debated. In this review, we examined the interplay between ZIKV infection of different cell types and apoptosis and how the virus deals with this cellular response. We illustrate a duality in the effects of ZIKV-controlled apoptosis, depending on whether it occurs too early or too late, respectively, in neuropathogenesis, or in long-term viral persistence. We further discuss a prospective role for apoptosis in ZIKV-related therapies, and the use of ZIKV as an oncolytic agent.

Zika E Glycan Loop Region and Guillain-Barré Syndrome-Related Proteins: A Possible Molecular Mimicry to Be Taken in Account for Vaccine Development.

The neurological complications of infection by the mosquito-borne Zika virus (ZIKV) include Guillain-Barré syndrome (GBS), an acute inflammatory demyelinating polyneuritis. GBS was first associated with recent ZIKV epidemics caused by the emergence of the ZIKV Asian lineage in South Pacific. Here, we hypothesize that ZIKV-associated GBS relates to a molecular mimicry between viral envelope E (E) protein and neural proteins involved in GBS. The analysis of the ZIKV epidemic strains showed that the glycan loop (GL) region of the E protein includes an IVNDT motif which is conserved in voltage-dependent L-type calcium channel subunit alpha-1C (Cav1.2) and Heat Shock 70 kDa protein 12A (HSP70 12A). Both VSCC-alpha 1C and HSP70 12A belong to protein families which have been associated with neurological autoimmune diseases in central nervous system. The purpose of our in silico analysis is to point out that IVNDT motif of ZIKV E-GL region should be taken in consideration for the development of safe and effective anti-Zika vaccines by precluding the possibility of adverse neurologic events including autoimmune diseases such as GBS through a potent mimicry with Heat Shock 70 kDa protein 12A (HSP70 12A).

CHOP Pro-Apoptotic Transcriptional Program in Response to ER Stress Is Hacked by Zika Virus.

Zika virus (ZIKV) is an emerging mosquito-borne flavivirus considered as a threat to human health due to large epidemics and serious clinical outcomes such as microcephaly in new-borns. Like all flaviviruses, ZIKV relies on the cellular machinery to complete its viral cycle, with the endoplasmic reticulum (ER) being the critical site of viral replication factories. The sudden high protein load in the ER induces an ER stress to which the cell responds with an appropriate unfolded protein response (UPR) in an attempt to restore its disturbed homeostasis. When the restoration fails, the cell signalling leads to a programmed cell death by apoptosis with the upregulation of the UPR-induced C/EBP homologous protein (CHOP) which acts as the main trigger for this fatal outcome. Our previous studies have shown the ability of ZIKV to manipulate various cellular responses in order to optimize virus production. ZIKV is able to delay apoptosis to its benefit and although ER stress is induced, the UPR is not complete. Here we discovered that ZIKV impairs the expression of CHOP/DDIT3, the main factor responsible of ER-stress driven apoptosis. Surprisingly, the mechanism does not take place at the transcriptional level but at the translational level.

Improvement of immunodetection of the transcription factor C/EBP homologous protein by western blot.

Accumulation of misfolded proteins within the endoplasmic reticulum (ER) induces an unfolded protein response (UPR) that either restores homeostasis or triggers apoptosis in case of adaptation failure. The three activated branches of UPR lead to IRE1-, PERK- and ATF6- dependent transcriptional induction of the gene encoding the transcription factor C/EBP homologous protein (CHOP) which plays an important role in apoptosis induction. In conventional immunoblotting conditions, detection of CHOP is a difficult task. Using a fixation step, we have optimized the detection of CHOP and this method provides a valuable tool to decipher CHOP involvement in UPR.

Zika virus subversion of chaperone GRP78/BiP expression in A549 cells during UPR activation.

Flaviviruses replicate in membranous factories associated with the endoplasmic reticulum (ER). Significant levels of flavivirus polyprotein integration contribute to ER stress and the host cell may exhibit an Unfolded Protein Response (UPR) to this protein accumulation, stimulating appropriate cellular responses such as adaptation, autophagy or cell death. These different stress responses support other antiviral strategies initiated by infected cells and can help to overcome viral infection. In epithelial A549 cells, a model currently used to study the flavivirus infection cycle and the host cell responses, all three pathways leading to UPR are activated during infection by Dengue virus (DENV), Yellow Fever virus (YFV) or West Nile virus (WNV). In the present study, we investigated the capacity of ZIKA virus (ZIKV) to induce ER stress in A549 cells. We observed that the cells respond to ZIKV infection by implementing an UPR through activation of the IRE1 and PERK pathway without activation of the ATF6 branch. By modulating the ER stress response, we found that UPR inducers significantly inhibit ZIKV replication. Interestingly, our findings provide evidence that ZIKV could manipulate the UPR to escape this host cell defence system by downregulating GRP78/BiP expression. This subversion of GRP78 expression could lead to unresolved and persistent ER stress which can be a benefit for virus growth.

The ZIKA Virus Delays Cell Death Through the Anti-Apoptotic Bcl-2 Family Proteins.

Zika virus (ZIKV) is an emerging human mosquito-transmitted pathogen of global concern, known to be associated with complications such as congenital defects and neurological disorders in adults. ZIKV infection is associated with induction of cell death. However, previous studies suggest that the virally induced apoptosis occurs at a slower rate compared to the course of viral production. In this present study, we investigated the capacity of ZIKV to delay host cell apoptosis. We provide evidence that ZIKV has the ability to interfere with apoptosis whether it is intrinsically or extrinsically induced. In cells expressing viral replicon-type constructions, we show that this control is achieved through replication. Finally, our work highlights an important role for anti-apoptotic Bcl-2 family protein in the ability of ZIKV to control apoptotic pathways, avoiding premature cell death and thereby promoting virus replication in the host-cell.

The epidemic of Dengue virus type-2 Cosmopolitan genotype on Reunion Island relates to its active circulation in the Southwestern Indian Ocean neighboring islands.

Reunion Island is currently experiencing an epidemic caused by Dengue virus type-2 (DENV-2) resulting in over 6,763 cases from austral summer 2017 to winter 2018. Phylogenetic analyses on two non-imported cases of dengue infection from Reunion Island highlight a regional circulation of DENV-2 Cosmopolitan lineage 1 virus on both Reunion Island and the Seychelles.

Subversion of the Heme Oxygenase-1 Antiviral Activity by Zika Virus.

Heme oxygenase-1 (HO-1), a rate-limiting enzyme involved in the degradation of heme, is induced in response to a wide range of stress conditions. HO-1 exerts antiviral activity against a broad range of viruses, including the Hepatitis C virus, the human immunodeficiency virus, and the dengue virus by inhibiting viral growth. It has been reported that HO-1 displays antiviral activity against the Zika virus (ZIKV) but the mechanisms of viral inhibition remain largely unknown. Using a ZIKV RNA replicon with the Green Fluorescent Protein (GFP) as a reporter protein, we were able to show that HO-1 expression resulted in the inhibition of viral RNA replication. Conversely, we observed a decrease in HO-1 expression in cells replicating the ZIKV RNA replicon. The study of human cells infected with ZIKV showed that the HO-1 expression level was significantly lower once viral replication was established, thereby limiting the antiviral effect of HO-1. Our work highlights the capacity of ZIKV to thwart the anti-replicative activity of HO-1 in human cells. Therefore, the modulation of HO-1 as a novel therapeutic strategy against ZIKV infection may display limited effect.

The structural proteins of epidemic and historical strains of Zika virus differ in their ability to initiate viral infection in human host cells.

Mosquito-borne Zika virus (ZIKV) recently emerged in South Pacific islands and Americas where large epidemics were documented. In the present study, we investigated the contribution of the structural proteins C, prM and E in the permissiveness of human host cells to epidemic strains of ZIKV. To this end, we evaluated the capacity of the epidemic strain BeH819015 to infect epithelial A549 and neuronal SH-SY5Y cells in comparison to the African historical MR766 strain. For that purpose, we generated a molecular clone of BeH819015 and a chimeric clone of MR766 which contains the BeH819015 structural protein region. We showed that ZIKV containing BeH819015 structural proteins was much less efficient in cell-attachment leading to a reduced susceptibility of A549 and SH-SY5Y cells to viral infection. Our data illustrate a previously underrated role for C, prM, and E in ZIKV epidemic strain ability to initiate viral infection in human host cells.