Liang-Ge-San inhibits dengue virus serotype 2 infection by reducing caveolin1-induced cytoplasmic heat shock protein 70 translocation into the plasma membrane

BACKGROUND

Dengue virus (DENV) is a major public health threat. However, there are no specific therapeutic drugs for DENV. Many Chinese heat-cleaning formulas, such as Liang-Ge-San (LGS), have been frequently used in the virus-induced diseases. The antiviral effect of LGS has not been reported yet.

PURPOSE

In this study, the effect of LGS on the inhibition of dengue virus serotype 2 (DENV-2) was investigated and the relevant mechanism was explored.

METHODS

High-performance liquid chromatography was applied to analyze the chemical characterization of LGS. The in vitro antiviral activities of LGS against DENV-2 were evaluated by time-of-drug-addition assay. The binding of heat shock protein 70 (Hsp70) and envelope (E) protein or caveolin1 (Cav1) were analyzed by immunofluorescence and immunoprecipitation assays. Then the role of Cav1 in the anti-DENV-2 effects of LGS was further examined. DENV-2 infected Institute of Cancer Research suckling mice (n = 10) and AG129 mice (n = 8) were used to examine the protective effects of LGS.

RESULTS

It was found that geniposide, liquiritin, forsythenside A, forsythin, baicalin, baicalein, rhein, and emodin maybe the characteristic components of LGS. LGS inhibited the early stage of DENV-2 infection, decreased the expression levels of viral E and non-structural protein 1 (NS1) proteins. LGS also reduced E protein and Hsp70 binding and attenuated the translocation of Hsp70 from cytoplasm to the cell membrane. Moreover, LGS decreased the binding of Hsp70 to Cav1. Further study showed that the overexpression of Cav1 reversed LGS-mediated E protein and Hsp70 inhibition in the plasma membrane. In the in vivo study, LGS was highly effective in prolonging the survival time, reducing viral loads.

CONCLUSION

This work demonstrates for the first time that LGS exerts anti-DENV-2 activity in vitro and in vivo. LGS decreases DENV-2-stimulated cytoplasmic Hsp70 translocation into the plasma membrane by Cav1 inhibition, thereby inhibiting the early stage of virus infection. These findings indicate that LGS may be a candidate for the treatment of DENV.

Transcriptome analysis of Aedes albopictus midguts infected by dengue virus identifies a gene network module highly associated with temperature

BACKGROUND

Dengue is prevalent worldwide and is transmitted by Aedes mosquitoes. Temperature is a strong driver of dengue transmission. However, little is known about the underlying mechanisms.

METHODS

Aedes albopictus mosquitoes exposed or not exposed to dengue virus serotype 2 (DENV-2) were reared at 23 °C, 28 °C and 32 °C, and midguts and residual tissues were evaluated at 7 days after infection. RNA sequencing of midgut pools from the control group, midgut breakthrough group and midgut nonbreakthrough group at different temperatures was performed. The transcriptomic profiles were analyzed using the R package, followed by weighted gene correlation network analysis (WGCNA) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis to identify the important molecular mechanisms regulated by temperature.

RESULTS

The midgut infection rate and midgut breakthrough rate at 28 °C and 32 °C were significantly higher than those at 23 °C, which indicates that high temperature facilitates DENV-2 breakthrough in the Ae. albopictus midgut. Transcriptome sequencing was performed to investigate the antiviral mechanism in the midgut. The midgut gene expression datasets clustered with respect to temperature, blood-feeding and midgut breakthrough. Over 1500 differentially expressed genes were identified by pairwise comparisons of midguts at different temperatures. To assess key molecules regulated by temperature, we used WGCNA, which identified 28 modules of coexpressed genes; the ME3 module correlated with temperature. KEGG analysis indicated that RNA degradation, Toll and immunodeficiency factor signaling and other pathways are regulated by temperature.

CONCLUSIONS

Temperature affects the infection and breakthrough of Ae. albopictus midguts invaded by DENV-2, and Ae. albopictus midgut transcriptomes change with temperature. The candidate genes and key pathways regulated by temperature provide targets for the prevention and control of dengue.

Circulation of genotypes of dengue virus serotype 2 in Guangzhou over a period of 20 years

Background

The dengue epidemic in Guangzhou has imposed a rising burden on society and health infrastructure. Here, we present the genotype data for dengue virus serotype 2 (DENV-2) to improve understanding of this dengue epidemic.

Methods

We sequenced the envelope gene of DENV-2 obtained from patient serum samples and subsequently performed maximum-likelihood phylogenetic analysis using PhyMLv3.1, maximum clade credibility analysis using BEAST v.1.10.4, and selection pressure analysis using Datamonkey 2.0.

Results

The prevalent DENV-2 strains identified in Guangzhou region are related to those in Southeast Asian countries. In particular, the Malaysia/Indian subcontinent genotype is prevailing in Guangzhou with no apparent genotype shift having occurred over the past 20 years. However, episodic positive selection was detected at one site.

Conclusions

Local control of the DENV-2 epidemic in Guangzhou requires effective measures to prevent and monitor imported cases. Moreover, the shift between the Malaysia/Indian subcontinent genotype lineages, which originated at different time points, may account for the rise in DENV-2 cases in Guangzhou. Meanwhile, the low rate of dengue haemorrhagic fever in Guangzhou may be explained by the dominance of the less virulent Malaysia/Indian subcontinent genotype.

Construction of Genomic and Sub-Genomic Dengue Infectious Replicons

Dengue replicons are powerful tools used in studying virus biology as well as in high-throughput screening of drug candidates. Replicon constructs are developed as genomic (consists of all the viral protein genes) or sub-genomic (consists of only nonstructural protein genes) and are used to study various aspects of the virus life cycle such as genome replication and virus assembly. In addition, a replicon usually includes a reporter gene used in monitoring virus replication. In this chapter, we provide methods to develop both genomic and sub-genomic dengue replicons with a luciferase reporter and describe different assays to utilize these systems.

Comparative whole genome analysis of dengue virus serotype-2 strains differing in trans-endothelial cell leakage induction in vitro

The role of genetic differences among dengue virus (DENV) in causing increased microvascular permeability is less explored. In the present study, we compared two closely related DENV serotype-2 strains of Cosmopolitan genotype for their in vitro infectivity phenotype and ability to induce trans-endothelial leakage. We found that these laboratory strains differed significantly in infecting human microvascular endothelial cells (HMEC-1) and hepatocytes (Huh7), two major target cells of DENV in in vivo infections. There was a reciprocal correlation in infectivity and vascular leakage induced by these strains, with the less infective strain inducing more trans-endothelial cell leakage in HMEC-1 monolayer upon infection. The cells infected with the strain capable of inducing more permeability were found to secrete more Non-Structural protein (sNS1) into the culture supernatant. A whole genome analysis revealed 37 predicted amino acid changes and changes in the secondary structure of 3' non-translated region between the strains. But none of these changes involved the signal sequence coded by the C-terminal of the Envelope protein and the two glycosylation sites within the NS1 protein critical for its secretion, and the N-terminal NS2A sequence important for surface targeting of NS1. The strain that secreted lower levels of NS1 and caused less leakage had two mutations within the NS1 protein coding region, F103S and T146I that significantly changed amino acid properties. A comparison of the sequences of the two strains with published sequences of various DENV strains known to cause clinically severe dengue identified a number of amino acid changes which could be implicated as possible key genetic differences. Our data supports the earlier observations that the vascular leakage induction potential of DENV strains is linked to the sNS1 levels. The results also indicate that viral genetic determinants, especially the mutations within the NS1 coding region, could affect this critical phenotype of DENV strains.

Genomic studies of envelope gene sequences from mosquito and human samples from Bangkok, Thailand

Dengue virus (DENV) is an RNA virus showing a high degree of genetic variation as a consequence of its proofreading inability. This variation plays an important role in virus evolution and pathogenesis. Although levels of within-host genetic variation are similar following equilibrium, variation among different hosts is frequently different. To identify dengue quasispecies present among two hosts, we collected patient samples from six acute DENV cases and two pools of Aedes aegypti mosquitoes and analyzed the genetic variation of regions of the viral envelope gene. Among human and mosquito samples, we found three major clusters originating from two subpopulations. Although several shared lineages were observed in the two hosts, only one lineage showing evidence of neutral selection was observed among two hosts. Taken together, our data provide evidence for the existence of a DENV quasispecies, with less genetic variation observed in mosquitoes than humans and with circulating lineages found in both host types.

Analysis of genotype diversity and evolution of Dengue virus serotype 2 using complete genomes

BACKGROUND

Dengue is one of the most common arboviral diseases prevalent worldwide and is caused by Dengue viruses (genus Flavivirus, family Flaviviridae). There are four serotypes of Dengue Virus (DENV-1 to DENV-4), each of which is further subdivided into distinct genotypes. DENV-2 is frequently associated with severe dengue infections and epidemics. DENV-2 consists of six genotypes such as Asian/American, Asian I, Asian II, Cosmopolitan, American and sylvatic. Comparative genomic study was carried out to infer population structure of DENV-2 and to analyze the role of evolutionary and spatiotemporal factors in emergence of diversifying lineages.

METHODS

Complete genome sequences of 990 strains of DENV-2 were analyzed using Bayesian-based population genetics and phylogenetic approaches to infer genetically distinct lineages. The role of spatiotemporal factors, genetic recombination and selection pressure in the evolution of DENV-2 is examined using the sequence-based bioinformatics approaches.

RESULTS

DENV-2 genetic structure is complex and consists of fifteen subpopulations/lineages. The Asian/American genotype is observed to be diversified into seven lineages. The Asian I, Cosmopolitan and sylvatic genotypes were found to be subdivided into two lineages, each. The populations of American and Asian II genotypes were observed to be homogeneous. Significant evidence of episodic positive selection was observed in all the genes, except NS4A. Positive selection operational on a few codons in envelope gene confers antigenic and lineage diversity in the American strains of Asian/American genotype. Selection on codons of non-structural genes was observed to impact diversification of lineages in Asian I, cosmopolitan and sylvatic genotypes. Evidence of intra/inter-genotype recombination was obtained and the uncertainty in classification of recombinant strains was resolved using the population genetics approach.

DISCUSSION

Complete genome-based analysis revealed that the worldwide population of DENV-2 strains is subdivided into fifteen lineages. The population structure of DENV-2 is spatiotemporal and is shaped by episodic positive selection and recombination. Intra-genotype diversity was observed in four genotypes (Asian/American, Asian I, cosmopolitan and sylvatic). Episodic positive selection on envelope and non-structural genes translates into antigenic diversity and appears to be responsible for emergence of strains/lineages in DENV-2 genotypes. Understanding of the genotype diversity and emerging lineages will be useful to design strategies for epidemiological surveillance and vaccine design.