Characterization of Viral Interference in Aedes albopictus C6/36 Cells Persistently Infected with Dengue Virus 2.

Arboviruses are an important group of pathogens that cause diseases of medical and veterinary concern worldwide. The interactions of these viruses with their host cells are complex, and frequently, the coexistence of two different viruses in the same cell results in the inhibition of replication in one of the viruses, which is a phenomenon called viral interference. This phenomenon can be exploited to develop antiviral strategies. Insect cell lines persistently infected with arboviruses are useful models with which to study viral interference. In this work, a model of C6/36-HT cells (from Aedes albopictus mosquitoes) persistently infected with Dengue virus, serotype 2, was used. Viral interference was evaluated via plaque and flow cytometry assays. The presence of heterotypic interference against the other serotypes of the same virus and homologous interference against yellow fever virus was determined; however, this cell line did not display heterologous viral interference against Sindbis virus. The mechanisms responsible for viral interference have not been fully elucidated, but small RNAs could be involved. However, the silencing of Ago3, a key protein in the genome-derived P-element-induced wimpy testis pathway, did not alter the viral interference process, suggesting that viral interference occurs independent of this pathway.

Differential Gene Expression Pattern of Importin ß3 and NS5 in C6/36 Cells Acutely and Persistently Infected with Dengue Virus 2.

The establishment of persistent dengue virus infection within the cells of the mosquito vector is an essential requirement for viral transmission to a new human host. The mechanisms involved in the establishment and maintenance of persistent infection are not well understood, but it has been suggested that both viral and cellular factors might play an important role. In the present work, we evaluated differential gene expression in Aedes albopictus cells acutely (C6/36-HT) and persistently infected (C6-L) with Dengue virus 2 by cDNA-AFLP. We observed that importin ß3 was upregulated in noninfected cells compared with C6-L cells. Using RT-qPCR and plaque assays, we observed that Dengue virus levels in C6-L cells essentially do not vary over time, and peak viral titers in acutely infected cells are observed at 72 and 120 h postinfection. The expression level of importin ß3 was higher in acutely infected cells than in persistently infected cells; this correlates with higher levels of NS5 in the nucleus of the cell. The differential pattern of importin ß3 expression between acute and persistent infection with Dengue virus 2 could be a mechanism to maintain viral infection over time, reducing the antiviral response of the cell and the viral replicative rate.

Interactions of host miRNAs in the flavivirus 3´UTR genome: From bioinformatics predictions to practical approaches.

The genus Flavivirus of the Flaviviridae family includes important viruses, such as Dengue, Zika, West Nile, Japanese encephalitis, Murray Valley encephalitis, tick-borne encephalitis, Yellow fever, Saint Louis encephalitis, and Usutu viruses. They are transmitted by mosquitoes or ticks, and they can infect humans, causing fever, encephalitis, or haemorrhagic fever. The treatment resources for these diseases and the number of vaccines available are limited. It has been discovered that eukaryotic cells synthesize small RNA molecules that can bind specifically to sequences present in messenger RNAs to inhibit the translation process, thus regulating gene expression. These small RNAs have been named microRNAs, and they have an important impact on viral infections. In this review, we compiled the available information on miRNAs that can interact with the 3' untranslated region (3'UTR) of the flavivirus genome, a conserved region that is important for viral replication and translation.

Association of Genetic Polymorphisms in TLR3, TLR4, TLR7, and TLR8 with the Clinical Forms of Dengue in Patients from Veracruz, Mexico.

Dengue manifestations range from a mild form, dengue fever (DF), to more severe forms such as dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). The ability of the host to present one of these clinical forms could be related to polymorphisms located in genes of the Toll-like receptors (TLRs) which activate the pro-inflammatory response. Therefore, the genotyping of single nucleotide genetic polymorphisms (SNPs) in TLR3 (rs3775291 and rs6552950), TLR4 (rs2737190, rs10759932, rs4986790, rs4986791, rs11536865, and rs10983755), TLR7 (rs179008 and rs3853839), and TLR8 (rs3764880, rs5741883, rs4830805, and rs1548731) was carried out in non-genetically related DHF patients, DF patients, and general population (GP) subjects. The SNPs were analyzed by real-time PCR by genotyping assays from Applied Biosystems®. The codominance model showed that dengue patients had a lower probability of presenting the TLR4-rs2737190-G/G genotype (odds ratio (OR) (95% CI) = 0.34 (0.14-0.8), p = 0.038). Dengue patients showed a lower probability of presenting TLR4-rs11536865-G/C genotype (OR (95% CI) = 0.19 (0.05-0.73), p = 0.0092) and had a high probability of presenting the TACG haplotype, but lower probability of presenting the TGCG haplotype in the TLR4 compared to GP individuals (OR (95% CI) = 0.55 (0.35-0.86), p = 0.0084). In conclusion, the TLR4-rs2737190-G/G and TLR4-rs11536865-G/C genotypes and TGCG haplotype were associated with protection from dengue.

The Regulation of Flavivirus Infection by Hijacking Exosome-Mediated Cell-Cell Communication: New Insights on Virus-Host Interactions.

The arthropod-borne flaviviruses are important human pathogens, and a deeper understanding of the virus-host cell interaction is required to identify cellular targets that can be used as therapeutic candidates. It is well reported that the flaviviruses hijack several cellular functions, such as exosome-mediated cell communication during infection, which is modulated by the delivery of the exosomal cargo of pro- or antiviral molecules to the receiving host cells. Therefore, to study the role of exosomes during flavivirus infections is essential, not only to understand its relevance in virus-host interaction, but also to identify molecular factors that may contribute to the development of new strategies to block these viral infections. This review explores the implications of exosomes in flavivirus dissemination and transmission from the vector to human host cells, as well as their involvement in the host immune response. The hypothesis about exosomes as a transplacental infection route of ZIKV and the paradox effect or the dual role of exosomes released during flavivirus infection are also discussed here. Although several studies have been performed in order to identify and characterize cellular and viral molecules released in exosomes, it is not clear how all of these components participate in viral pathogenesis. Further studies will determine the balance between protective and harmful exosomes secreted by flavivirus infected cells, the characteristics and components that distinguish them both, and how they could be a factor that determines the infection outcome.

miR-927 has pro-viral effects during acute and persistent infection with dengue virus type 2 in C6/36 mosquito cells.

Dengue virus (DENV) is an important flavivirus that is transmitted to humans by Aedes mosquitoes, where it can establish a persistent infection underlying vertical and horizontal transmission. However, the exact mechanism of persistent DENV infection is not well understood. Recently miR-927 was found to be upregulated in C6/36-HT cells at 57 weeks of persistent infection (C6-L57), suggesting its participation during this type of infection. The aim of this study was to determine the role of miR-927 during infection with DENV type 2. The results indicate an overexpression of miR-927 in C6-L57 cells and acutely infected cells according to the time of infection and the m.o.i. used. The downregulation of miR-927 in C6-L57 cells results in a reduction of both viral titre and viral genome copy number. The overexpression of miR-927 in C6-L40 and C6/36 cells infected at an m.o.i. of 0.1 causes an increase in both viral titre and viral genome copy number, suggesting a pro-viral activity of miR-927. In silico prediction analysis reveals target mRNAs for miR-927 are implicated in post-translational modifications (SUMO), translation factors (eIF-2B), the innate immune system (NKIRAS), exocytosis (EXOC-2), endocytosis (APM1) and the cytoskeleton (FLN). The expression levels of FLN were the most affected by both miR-927 overexpression and inhibition, and FLN was determined to be a direct target of miR-927 by a dual-luciferase gene reporter assay. FLN has been associated with the regulation of the Toll pathway and either overexpression or downregulation of miR-927 resulted in expression changes of antimicrobial peptides (Cecropins A and G, and Defensin D) involved in the Toll pathway response.

Isolation and characterization of exosomes released from mosquito cells infected with dengue virus.

Exosomes are endocytic origin small-membrane vesicles secreted to the extracellular space by most cell types. Exosomes released from virus infected-cells can mediate the cell-to-cell communication to promote or modulate viral transmission. Dengue virus (DENV) is an arbovirus transmitted by Aedes mosquitoes bite to humans. Interestingly, the role of exosomes during the DENV infection in mammalian cells has already been described. However, little is known about exosomes derived from infected mosquito cells. Thus, the exosomes released from DENV-infected C6/36 cells were isolated, purified and analyzed using an antibody against the tetraspanin CD9 from human that showed cross-reactivity with the homologs to human CD9 found in Aedes albopictus (AalCD9). The exosomes from DENV infected cells were larger than the exosomes secreted from uninfected cells, contained virus-like particles, and they were able to infect naïve C6/36 cells, suggesting that exosomes are playing a role in virus dissemination.

Mosquito cells persistently infected with dengue virus produce viral particles with host-dependent replication.

Dengue viruses (DENV) are important arboviruses that can establish a persistent infection in its mosquito vector Aedes. Mosquitoes have a short lifetime in nature which makes trying to study the processes that take place during persistent viral infections in vivo. Therefore, C6/36 cells have been used to study this type of infection. C6/36 cells persistently infected with DENV 2 produce virions that cannot infect BHK -21 cells. We hypothesized that the following passages in mosquito cells have a deleterious impact on DENV fitness in vertebrate cells. Here, we demonstrated that the viral particles released from persistently infected cells were infectious to mosquito but not to vertebrate cells. This host restriction occurs at the replication level and is associated with several mutations in the DENV genome. In summary, our findings provide new information about viral replication fitness in a host-dependent manner.

Genotypic variability analysis of DENV-1 in Mexico reveals the presence of a novel Mexican lineage.

Here, we report for the first time the circulation of dengue virus type 1 (DENV-1) belonging to the lineage IV of genotype V (African American genotype) based on phylogenetic analysis of nucleotide sequences from 10 DENV-1-positive samples obtained in Mexico between 2012 and 2014. Our data revealed that the lineages III and IV of DENV-1 genotype V were found circulating during the same period, probably explaining the rise in the number of cases of severe dengue during that period.

Analysis of the miRNA profile in C6/36 cells persistently infected with dengue virus type 2.

Dengue virus (DENV) is the most important arbovirus in the world; DENV is transmitted by the Aedes genus of mosquitoes and can establish a life-long persistent infection in mosquitoes. However, the exact mechanism by which persistent infection is established remains unknown. In this study the differential expression of miRNAs was analysed by deep sequencing and RT-qPCR using a previously established C6/36-HT cell line persistently infected with DENV 2 (C6-L) as a model. miR-927, miR-87, miR-210, miR-2a-3p, miR-190 and miR-970 were up-regulated, whereas miR-252, miR-263a-3p, miR-92b, miR-10-5p miR-9a-5p, miR-9a-1, miR-124, miR-286a and miR-286b were down-regulated in C6-L cells compared with C6/36 cells acutely infected with the same virus or mock-infected cells. Deep sequencing results were validated by RT-qPCR for the highly differentially expressed miR-927 and miR-9a-5p, which were up- and down-regulated, respectively, compared with both acutely and mock-infected C6/36 cells. The putative targets of these miRNAs include components of the ubiquitin conjugation pathway, vesicle-mediated transport, autophagy, and the JAK-STAT cascade as well as proteins with endopeptidase activity. Other putative targets include members of the Toll signalling pathway and proteins with kinase, ATPase, protease, scavenger receptor or Lectin C-type activity or that participate in fatty acid biosynthesis or oxidative stress. Our results suggest that several specific miRNAs help regulate the cellular functions that maintain equilibrium between viral replication and the antiviral response during persistent infection of mosquito cells. This study is the first report of a global miRNA profile in a mosquito cell line persistently infected with DENV.

The Actions of Lyophilized Apple Peel on the Electrical Activity and Organization of the Ventricular Syncytium of the Hearts of Diabetic Rats.

This study was designed to examine the effects of lyophilized red delicious apple peel (RDP) on the action potentials (APs) and the input resistance-threshold current relationship. The experiments were performed on isolated papillary heart muscles from healthy male rats, healthy male rats treated with RDP, diabetic male rats, and diabetic male rats treated with RDP. The preparation was superfused with oxygenated Tyrode's solution at 37°C. The stimulation and the recording of the APs, the input resistance, and the threshold current were made using conventional electrophysiological methods. The RDP presented no significant effect in normal rats. Equivalent doses in diabetic rats reduced the APD and ARP. The relationship between input resistance and threshold current established an inverse correlation. The results indicate the following: (1) The functional structure of the cardiac ventricular syncytium in healthy rats is heterogeneous, in terms of input resistance and threshold current. Diabetes further accentuates the heterogeneity. (2) As a consequence, conduction block occurs and increases the possibility of reentrant arrhythmias. (3) These modifications in the ventricular syncytium, coupled with the increase in the ARP, are the adequate substrate so that, with diabetes, the heart becomes more arrhythmogenic. (4) RDP decreases the APD, the ARP, and most syncytium irregularity caused by diabetes.

Viral Interference and Persistence in Mosquito-Borne Flaviviruses.

Mosquito-borne flaviviruses are important pathogens for humans, and the detection of two or more flaviviruses cocirculating in the same geographic area has often been reported. However, the epidemiological impact remains to be determined. Mosquito-borne flaviviruses are primarily transmitted through Aedes and Culex mosquitoes; these viruses establish a life-long or persistent infection without apparent pathological effects. This establishment requires a balance between virus replication and the antiviral host response. Viral interference is a phenomenon whereby one virus inhibits the replication of other viruses, and this condition is frequently associated with persistent infections. Viral interference and persistent infection are determined by several factors, such as defective interfering particles, competition for cellular factors required for translation/replication, and the host antiviral response. The interaction between two flaviviruses typically results in viral interference, indicating that these viruses share common features during the replicative cycle in the vector. The potential mechanisms involved in these processes are reviewed here.

Large-scale genomic analysis of codon usage in dengue virus and evaluation of its phylogenetic dependence.

The increasing number of dengue virus (DENV) genome sequences available allows identifying the contributing factors to DENV evolution. In the present study, the codon usage in serotypes 1-4 (DENV1-4) has been explored for 3047 sequenced genomes using different statistics methods. The correlation analysis of total GC content (GC) with GC content at the three nucleotide positions of codons (GC1, GC2, and GC3) as well as the effective number of codons (ENC, ENCp) versus GC3 plots revealed mutational bias and purifying selection pressures as the major forces influencing the codon usage, but with distinct pressure on specific nucleotide position in the codon. The correspondence analysis (CA) and clustering analysis on relative synonymous codon usage (RSCU) within each serotype showed similar clustering patterns to the phylogenetic analysis of nucleotide sequences for DENV1-4. These clustering patterns are strongly related to the virus geographic origin. The phylogenetic dependence analysis also suggests that stabilizing selection acts on the codon usage bias. Our analysis of a large scale reveals new feature on DENV genomic evolution.

Surface proteins of C6/36 cells involved in dengue virus 4 binding and entry.

Dengue virus (DENV) is the causative agent of the most important mosquito-borne viral disease, which is endemic to over 100 countries in tropical and subtropical areas of the world. It is transmitted to humans by Aedes mosquitoes. The first step in the viral infection of host cells is virion attachment to the plasma membrane, which is mediated by specific surface molecules. There are several molecules that participate in DENV infection of mosquitoes, but only a few have been identified. In this work, we co-purified 4 proteins from C6/36 cells using a recombinant DENV 4 E protein and identified them as 70 kDa Heat Shock and 70 kDa Heat Shock cognate proteins (HSP70/HSc70), Binding immunoglobulin protein (BiP), Thioredoxin/protein disulphide isomerase (PDI), and 44 kDa Endoplasmic reticulum resident protein (ERp44) via matrix-assisted laser desorption/ionisation time of flight (Maldi-ToF) analysis. Using immunofluorescence and flow cytometry assays, we observed re-localisation of HSP70/HSc70 and, to a lesser extent, BiP to the plasma membrane under stress conditions, such as during DENV infection. By performing binding and infection assays independently, we found that all 4 proteins participate in both processes, but to differing extents: HSP70/HSc70 is the most critical component, while ERp44 is less important. Viral infection was not inhibited when the cells were incubated with antibodies against all of the surface proteins after virus binding, which suggests that DENV entry to C6/36 cells is mediated by these proteins at the same step and not sequentially.

Detection and sequencing of defective viral genomes in C6/36 cells persistently infected with dengue virus 2.

Dengue virus is the most important arbovirus that affects humans, and it can establish persistent infections, especially in insect-derived cell cultures. Defective viral genomes have been implicated in the establishment and maintenance of persistent infections with several flaviviruses; however, there exists almost no information concerning defective dengue virus genomes. Here, we report the detection of defective dengue 2 virus genomes in persistently infected mosquito C6/36 cells. The defective viral genomes were detected at a low ratio compared with the wild-type genome. Deletions of approximately 147 residues (222-368) were found in the E protein, and these mainly affected domain III (73 %) of the protein; deletions of approximately 153 residues (4-156) and 228 residues (597-825) were found in the methyltransferase and polymerase domains, respectively, of the NS5 protein. The truncated versions of NS5 could be detected by western blot only in the protein extracts derived from persistently infected cells.

Distribution of dengue cases in the state of Oaxaca, Mexico, during the period 2004-2006.

BACKGROUND: Dengue virus infection is an emergent viral disease and the most important transmitted by a vector worldwide. In Mexico it has been an important public health problem since 1995 and Oaxaca is one of the most affected states in the country. OBJECTIVE: To determine the geographic distribution of confirmed dengue cases in the state of Oaxaca, Mexico, the serotypes circulating, and the main gender and age groups affected. STUDY DESIGN: Information about confirmed dengue cases obtained by LESPO during the period 2004-2006 was classified, sorted, and analysed. A RT-PCR technique was used to determine the serotype of the virus in serum samples. RESULTS: A substantial increment in the number of dengue cases was noticed during the period of this study. The most affected sanitary jurisdiction was located on the coast where the climatic conditions were ideal for vector development and where there is significant migratory activity. The most affected group was the 11-15-year-old group. Dengue haemorrhagic fever was more frequent in men than in women over 16 years old, with a significant difference evaluated by chi(2)-test (p<0.001). Four serotypes of the virus were detected in the state and two co-infections with DEN2-3 and DEN3-4 were identified. CONCLUSIONS: The increment in the number of dengue cases in the state of Oaxaca could be explained by several factors such as the presence of the four serotypes of the virus, the migratory phenomenon, the climatic conditions and the socioeconomic level of the population.

In vitro interaction of poliovirus with cytoplasmic dynein.

OBJECTIVE: Poliovirus (PV) enters the host by the oral route and can infect the central nervous system (CNS) by two mechanisms: crossing the blood-brain barrier and traveling along the nerves from the muscle to the spinal cord. In the latter mechanism, the PV receptor, CD155, and the motor protein, dynein, have been implicated in the transport of PV to the CNS. In this work we analyzed the possible interaction of PV with dynein. METHODS: PV was bound to a Sepharose 4B beads and they were used to analyze the interaction of PV with cytoplasmic proteins from neuroblastoma cells by affinity chromatography and Western blot. RESULTS: The interaction with cytoplasmic dynein was observed only when the Sepharose beads bound to PV were used and not in the control ones, where proteins from uninfected cells were coupled. CONCLUSION: These preliminary results open the possibility that PV uses the dynein directly in its retrograde axonal transport.

A putative receptor for dengue virus in mosquito tissues: localization of a 45-kDa glycoprotein.

Dengue virus (DENV) infects target cells by attaching to various cell receptors, many of which are still unknown. In C6/36 cells (Aedes albopictus cell line), DENV-4 bound to two glycoproteins of 40 and 45 kDa, located on the cell surface. Preincubation of cells with polyclonal antibody against the 45-kDa protein specifically blocked DENV-4 infection of C6/36 cells. The antibody and purified DENV-4 detected the 45-kDa molecule in total extracts from eggs, larvae, and pupae as well as from the midgut, ovary, and salivary glands from adult-stage Aedes aegypti mosquitoes, whereas in malphigian tubules it was absent. This suggests that the distribution of the 45-kDa protein correlates with tissue tropism of DENV infection in mosquitoes. The 45-kDa molecule was not detected in Anopheles albimanus mosquito. The relevance of our findings is discussed from the pathogenetic and vector competence viewpoints.