Transcriptome Analysis of an Aedes albopictus Cell Line Single- and Dual-Infected with Lammi Virus and WNV

Understanding the flavivirus infection process in mosquito hosts is important and fundamental in the search for novel control strategies that target the mosquitoes’ ability to carry and transmit pathogenic arboviruses. A group of viruses known as insect-specific viruses (ISVs) has been shown to interfere with the infection and replication of a secondary arbovirus infection in mosquitoes and mosquito-derived cell lines. However, the molecular mechanisms behind this interference are unknown. Therefore, in the present study, we infected the Aedes albopictus cell line U4.4 with either the West Nile virus (WNV), the insect-specific Lammi virus (LamV) or an infection scheme whereby cells were pre-infected with LamV 24 h prior to WNV challenge. The qPCR analysis showed that the dual-infected U4.4 cells had a reduced number of WNV RNA copies compared to WNV-only infected cells. The transcriptome profiles of the different infection groups showed a variety of genes with altered expression. WNV-infected cells had an up-regulation of a broad range of immune-related genes, while in LamV-infected cells, many genes related to stress, such as different heat-shock proteins, were up-regulated. The transcriptome profile of the dual-infected cells was a mix of up- and down-regulated genes triggered by both viruses. Furthermore, we observed an up-regulation of signal peptidase complex (SPC) proteins in all infection groups. These SPC proteins have shown importance for flavivirus assembly and secretion and could be potential targets for gene modification in strategies for the interruption of flavivirus transmission by mosquitoes.

Small RNA Response to Infection of the Insect-Specific Lammi Virus and Hanko Virus in an Aedes albopictus Cell Line

RNA interference (RNAi)-mediated antiviral immunity is believed to be the primary defense against viral infection in mosquitoes. The production of virus-specific small RNA has been demonstrated in mosquitoes and mosquito-derived cell lines for viruses in all of the major arbovirus families. However, many if not all mosquitoes are infected with a group of viruses known as insect-specific viruses (ISVs), and little is known about the mosquito immune response to this group of viruses. Therefore, in this study, we sequenced small RNA from an Aedes albopictus-derived cell line infected with either Lammi virus (LamV) or Hanko virus (HakV). These viruses belong to two distinct phylogenetic groups of insect-specific flaviviruses (ISFVs). The results revealed that both viruses elicited a strong virus-derived small interfering RNA (vsiRNA) response that increased over time and that targeted the whole viral genome, with a few predominant hotspots observed. Furthermore, only the LamV-infected cells produced virus-derived Piwi-like RNAs (vpiRNAs); however, they were mainly derived from the antisense genome and did not show the typical ping-pong signatures. HakV, which is more distantly related to the dual-host flaviviruses than LamV, may lack certain unknown sequence elements or structures required for vpiRNA production. Our findings increase the understanding of mosquito innate immunity and ISFVs’ effects on their host.

Expression profile of the PIWI mRNAs protein family in human cells experimentally infected with Dengue Virus 4

Objective: Evaluate the messenger RNAs (mRNA) PIWI proteins expression during infection with VDEN 4 in human hepatocyte cells. Materials and Methods: VDEN4 strain H778494 (JQ513335) was used, which was stored in Aedes albopictus cell culture (Clone C6 / 36) at the Arbovirology and Hemorrhagic Fevers section of the Evandro Chagas Institute. The techniques of cell cultures, stock (C6/36), inoculation, extraction, viral load quantification, RTqPCR and statistical analyzes were performed at the Viral Biogenesis Laboratory. Results: According to the results obtained, two cells (HepG2 and Huh7.5) demonstrated a higher level of viral replication at 72 hours post infection (hpi). The PIWI 2 target alter its mRNA expression during VDEN4 infection. The PIWI 4 target expression, was observed an altered expression in the infected cells. Thus, it was found that they are in different poles, while the viral load in the first three days showed high expression. The expression of mRNA was low in relation to the normal rate given by the uninfected cells. Conclusion: In our findings, it was observed that PIWI2 and 4 proteins have an inverse relationship to the viral infection process by VDEN4, when there is an increase in viral replication, these two proteins end up having a significant reduction in their expression. Probably, this reduction of expression is involved with the biogenesis process of apoptosis-regulating microRNAs.

Transfection and colonization of Tetranychus truncatus Wolbachia strain wTtru in cell lines of the mosquito Aedes albopictus

Wolbachia are endosymbiotic bacteria that commonly infect arthropods and cause reproductive manipulations in hosts. Artificial transfection is one of the best methods for the study of Wolbachia-induced reproductive manipulations and its application in production practice. However, the low success rate of artificial transfection laid burden for investigation. The success rate of artificial transfection of Wolbachia between closely related hosts is usually higher than distant hosts, but the mechanism of transfection is unknown. In our study, the wTtru strain (supergroup B) infecting the Arachnida Tetranychus truncatus was transfected into the Aedes albopictus cell line (native-infected with wAlB strain from supergroup B). The wTtru strain was quantified and localized in the cell line to observe dynamic changes after transfection. A phylogenetic analysis of the relationship between the wTtru strain and the wAlB strain showed that the wTtru (ST=278) strain belonged to supergroup B and was closely related to the mosquitoes native Wolbachia wAlbB (ST=464), so we speculate that successful transfection was related to the Wolbachia strain, and furthermore, Wolbachia strain may be more important than host relationship. Our results provide a factual basis for studying artificial transfection of Wolbachia, and show that Wolbachia transfection between distant hosts can be achieved.

Infection, growth and maintenance of Wolbachia pipientis in clonal and non-clonal Aedes albopictus cell cultures

Insect cell lines provide useful in vitro models for studying biological systems, including interactions between mosquitoes and obligate intracellular endosymbionts such as Wolbachia pipientis. The Aedes albopictus Aa23 cell line was the first cell line developed to allow examination of Wolbachia infections. However, Wolbachia studies using Aa23 can be complicated by the presence of different cell types in the cell line and the substantial temporal variation in infection level. Two approaches were examined to ameliorate infection variability. In the first approach, multiple Aa23 passaging regimes were tested for an effect on infection variability. Fluorescence in situ hybridization (FISH) staining was used to characterize Wolbachia infection level over time. The results demonstrate an impact of passaging method on Wolbachia infection level, with some methods resulting in loss of infection. None of the passaging methods succeeded in effectively mitigating infection level variation. In a second approach, the clonal C7-10 A. albopictus cell line was infected with Wolbachia from Aa23 cells and Drosophila simulans (Riverside), resulting in cell lines designated C7-10B and C7-10R, respectively. Characterization via FISH staining showed greater stability and uniformity of Wolbachia infection in C7-10R relative to the infection in C7-10B. Characterization of the Aa23, C7-10B and C7-10R lines is discussed as a tool for the study of Wolbachia-host cell interactions.

First isolation of dengue 4 in the state of São Paulo, Brazil, 2011

We report the first isolation of Dengue virus 4 (DENV-4) in the state of São Paulo, from two patients - one living in São José do Rio Preto and the other one in Paulo de Faria, both cities located in the Northwest region of the state. The virus isolations were accomplished in the clone C6/36 Aedes albopictus cell line, followed by indirect immunofluorescence assays, performed with type-specific monoclonal antibodies that showed positive reactions for DENV-4. The results were confirmed by Nested RT-PCR and Real-Time RT-PCR assays. The introduction of DENV-4 in a country that already has to deal with the transmission of three other serotypes increases the possibility of the occurrence of more severe cases of the disease. The importance of early detection of dengue cases, before the virus spreads and major outbreaks occur, should be emphasized.