Cholesterol effectively blocks entry of flavivirus

NRF2-mediated regulation of lipid pathways in viral infection

The first line of defense against viral infection of the host cell is the cellular lipid membrane, which is also a crucial first site of contact for viruses. Lipids may sometimes be used as viral receptors by viruses. For effective infection, viruses significantly depend on lipid rafts during the majority of the viral life cycle. It has been discovered that different viruses employ different lipid raft modification methods for attachment, internalization, membrane fusion, genome replication, assembly, and release. To preserve cellular homeostasis, cells have potent antioxidant, detoxifying, and cytoprotective capabilities. Nuclear factor erythroid 2-related factor 2 (NRF2), widely expressed in many tissues and cell types, is one crucial component controlling electrophilic and oxidative stress (OS). NRF2 has recently been given novel tasks, including controlling inflammation and antiviral interferon (IFN) responses. The activation of NRF2 has two effects: it may both promote and prevent the development of viral diseases. NRF2 may also alter the host's metabolism and innate immunity during viral infection. However, its primary function in viral infections is to regulate reactive oxygen species (ROS). In several research, the impact of NRF2 on lipid metabolism has been examined. NRF2 is also involved in the control of lipids during viral infection. We evaluated NRF2's function in controlling viral and lipid infections in this research. We also looked at how lipids function in viral infections. Finally, we investigated the role of NRF2 in lipid modulation during viral infections.

Current Advances in Japanese Encephalitis Virus Drug Development

Japanese encephalitis virus (JEV) belongs to the Flaviviridae family and is a representative mosquito-borne flavivirus responsible for acute encephalitis and meningitis in humans. Despite the availability of vaccines, JEV remains a major public health threat with the potential to spread globally. According to the World Health Organization (WHO), there are an estimated 69,000 cases of JE each year, and this figure is probably an underestimate. The majority of JE victims are children in endemic areas, and almost half of the surviving patients have motor or cognitive sequelae. Thus, the absence of a clinically approved drug for the treatment of JE defines an urgent medical need. Recently, several promising and potential drug candidates were reported through drug repurposing studies, high-throughput drug library screening, and de novo design. This review focuses on the historical aspects of JEV, the biology of JEV replication, targets for therapeutic strategies, a target product profile, and drug development initiatives.

Wolbachia interferes with Zika virus replication by hijacking cholesterol metabolism in mosquito cells

IMPORTANCE

Arthropod-borne viruses are emerging pathogens that are spread widely by mosquitos. Zika virus is an arbovirus that can infect humans and be transmitted from an infected mother to the fetus, potentially leading to microcephaly in infants. One promising strategy to prevent disease caused by arboviruses is to target the insect vector population. Recent field studies have shown that mosquito populations infected with Wolbachia bacteria suppress arbovirus replication and transmission. Here, we describe how intracellular bacteria redirect resources within their host cells and suppress Zika virus replication at the cellular level. Understanding the mechanism behind Wolbachia-induced interference of arbovirus replication could help advance strategies to control arbovirus pathogens in insect vectors and human populations.

Conessine inhibits enveloped viruses replication through up-regulating cholesterol level

Dengue virus (DENV) is one of the most prevalent arthropod-borne diseases. It may cause dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS), while no effective vaccines and drugs are available. Our study demonstrated that conessine exhibits broad antiviral activity against several enveloped viruses, including DENV, vesicular stomatitis virus, and herpes simplex virus. In addition, conessine has no direct destructive effect on the integrity or infectivity of virions. Both pre-treatment and post-treatment with conessine significantly reduce DENV replication. Pre-treatment with conessine disrupts the endocytosis of enveloped viruses, while post-treatment disturbs DENV RNA replication or translation at an early stage. Through screening differentially expressed genes by transcriptome sequencing, we found that conessine may affect cholesterol biosynthesis, metabolism or homeostasis. Finally, we confirmed that conessine inhibits virus replication through up-regulating cholesterol levels. Our work suggests that conessine could be developed as a prophylactic and therapeutic treatment for infectious diseases caused by enveloped viruses.

Profiling lipidomic changes in dengue-resistant and dengue-susceptible strains of Colombian Aedes aegypti after dengue virus challenge

The mosquito Aedes aegypti is the primary vector for all four serotypes of dengue viruses (DENV1-4), which infect millions across the globe each year. Traditional insecticide programs have been transiently effective at minimizing cases; however, insecticide resistance and habitat expansion have caused cases of DENV to surge over the last decade. There is an urgent need to develop novel vector control measures, but these are contingent on a detailed understanding of host-parasite interactions. Here, we have utilized lipidomics to survey the profiles of naturally DENV-resistant (Cali-MIB) or susceptible (Cali-S) populations of Ae. aegypti, isolated from Cali, Colombia, when fed on blood meals containing DENV. Control insects were fed on a DENV-free blood meal. Midguts were dissected from Cali-MIB and Cali-S females at three time points post-infectious blood meal, 18, 24 and 36h, to identify changes in the lipidome at key times associated with the entry, replication and exit of DENV from midgut cells. We used principal component analysis to visualize broad patterns in lipidomic profiles between the treatment groups, and significance analysis of microarray to determine lipids that were altered in response to viral challenge. These data can be used to identify molecules or metabolic pathways particular to the susceptible or refractory phenotypes, and possibly lead to the generation of stable, DENV-resistant strains of Ae. aegypti.

The roles of different microRNAs in the regulation of cholesterol in viral hepatitis

Cholesterol plays a significant role in stabilizing lipid or membrane rafts, which are specific cellular membrane structures. Cholesterol is involved in numerous cellular processes, including regulating virus entry into the host cell. Multiple viruses have been shown to rely on cholesterol for virus entry and/or morphogenesis. Research indicates that reprogramming of the host's lipid metabolism is associated with hepatitis B virus (HBV) and hepatitis C virus (HCV) infections in the progression to severe liver disease for viruses that cause chronic hepatitis. Moreover, knowing the precise mode of viral interaction with target cells sheds light on viral pathogenesis and aids in the development of vaccines and therapeutic targets. As a result, the area of cholesterol-lowering therapy is quickly evolving and has many novel antiviral targets and medications. It has been shown that microRNAs (miRNAs) either directly or indirectly target the viral genome, preventing viral replication. Moreover, miRNAs have recently been shown to be strong post-transcriptional regulators of the genes involved in lipid metabolism, particularly those involved in cholesterol homeostasis. As important regulators of lipid homeostasis in several viral infections, miRNAs have recently come to light. In addition, multiple studies demonstrated that during viral infection, miRNAs modulate several enzymes in the mevalonate/cholesterol pathway. As cholesterol metabolism is essential to the life cycle of viral hepatitis and other viruses, a sophisticated understanding of miRNA regulation may contribute to the development of a novel anti-HCV treatment. The mechanisms underlying the effectiveness of miRNAs as cholesterol regulators against viral hepatitis are explored in this review. Video Abstract.

Repurposing Amphotericin B and Its Liposomal Formulation for the Treatment of Human Mpox

Mpox (monkeypox) is a zoonotic viral disease caused by the mpox virus (MPXV). Recently in 2022, a multi-country Mpox outbreak has determined great concern as the disease rapidly spreads. The majority of cases are being noticed in European regions and are unrelated to endemic travel or known contact with infected individuals. In this outbreak, close sexual contact appears to be important for MPXV transmission, and an increasing prevalence in people with multiple sexual partners and in men who have sex with men has been observed. Although Vaccinia virus (VACV)-based vaccines have been shown to induce a cross-reactive and protective immune response against MPXV, limited data support their efficacy against the 2022 Mpox outbreak. Furthermore, there are no specific antiviral drugs for Mpox. Host-cell lipid rafts are small, highly dynamic plasma-membrane microdomains enriched in cholesterol, glycosphingolipids and phospholipids that have emerged as crucial surface-entry platforms for several viruses. We previously demonstrated that the antifungal drug Amphotericin B (AmphB) inhibits fungal, bacterial and viral infection of host cells through its capacity to sequester host-cell cholesterol and disrupt lipid raft architecture. In this context, we discuss the hypothesis that AmphB could inhibit MPXV infection of host cells through disruption of lipid rafts and eventually through redistribution of receptors/co-receptors mediating virus entry, thus representing an alternative or additional therapeutic tool for human Mpox.

The buzz in the field: the interaction between viruses, mosquitoes, and metabolism

Among many medically important pathogens, arboviruses like dengue, Zika and chikungunya cause severe health and economic burdens especially in developing countries. These viruses are primarily vectored by mosquitoes. Having surmounted geographical barriers and threat of control strategies, these vectors continue to conquer many areas of the globe exposing more than half of the world's population to these viruses. Unfortunately, no medical interventions have been capable so far to produce successful vaccines or antivirals against many of these viruses. Thus, vector control remains the fundamental strategy to prevent disease transmission. The long-established understanding regarding the replication of these viruses is that they reshape both human and mosquito host cellular membranes upon infection for their replicative benefit. This leads to or is a result of significant alterations in lipid metabolism. Metabolism involves complex chemical reactions in the body that are essential for general physiological functions and survival of an organism. Finely tuned metabolic homeostases are maintained in healthy organisms. However, a simple stimulus like a viral infection can alter this homeostatic landscape driving considerable phenotypic change. Better comprehension of these mechanisms can serve as innovative control strategies against these vectors and viruses. Here, we review the metabolic basis of fundamental mosquito biology and virus-vector interactions. The cited work provides compelling evidence that targeting metabolism can be a paradigm shift and provide potent tools for vector control as well as tools to answer many unresolved questions and gaps in the field of arbovirology.

Differences in gene expression in field populations of Wolbachia-infected Aedes aegypti mosquitoes with varying release histories in northern Australia

Aedes aegypti is the principal mosquito vector of dengue, yellow fever, Zika and chikungunya viruses. The wMel strain of the endosymbiotic bacteria Wolbachia pipientis was introduced into the vector as a novel biocontrol strategy to stop transmission of these viruses. Mosquitoes with Wolbachia have been released in the field in Northern Queensland, Australia since 2011, at various locations and over several years, with populations remaining stably infected. Wolbachia infection is known to alter gene expression in its mosquito host, but whether (and how) this changes over the long-term in the context of field releases remains unknown. We sampled mosquitoes from Wolbachia-infected populations with three different release histories along a time gradient and performed RNA-seq to investigate gene expression changes in the insect host. We observed a significant impact on gene expression in Wolbachia-infected mosquitoes versus uninfected controls. Fewer genes had significantly upregulated expression in mosquitoes from the older releases (512 and 486 from the 2011 and 2013/14 release years, respectively) versus the more recent releases (1154 from the 2017 release year). Nonetheless, a fundamental signature of Wolbachia infection on host gene expression was observed across all releases, comprising upregulation of immunity (e.g. leucine-rich repeats, CLIPs) and metabolism (e.g. lipid metabolism, iron transport) genes. There was limited downregulation of gene expression in mosquitoes from the older releases (84 and 71 genes from the 2011 and 2013/14 release years, respectively), but significantly more in the most recent release (509 from the 2017 release year). Our findings indicate that at > 8 years post-introgression into field populations, Wolbachia continues to profoundly impact expression of host genes, such as those involved in insect immune response and metabolism. If Wolbachia-mediated virus blocking is underpinned by these differential gene expression changes, our results suggest it may remain stable long-term.

Japanese Encephalitis Virus: An Update on the Potential Antivirals and Vaccines

Japanese encephalitis virus (JEV) is the causal agent behind Japanese encephalitis (JE), a potentially severe brain infection that spreads through mosquito bites. JE is predominant over the Asia-Pacific Region and has the potential to spread globally with a higher rate of morbidity and mortality. Efforts have been made to identify and select various target molecules essential in JEV’s progression, but until now, no licensed anti-JEV drug has been available. From a prophylactic point of view, a few licensed JE vaccines are available, but various factors, viz., the high cost and different side effects imposed by them, has narrowed their global use. With an average occurrence of >67,000 cases of JE annually, there is an urgent need to find a suitable antiviral drug to treat patients at the acute phase, as presently only supportive care is available to mitigate infection. This systematic review highlights the current status of efforts put in to develop antivirals against JE and the available vaccines, along with their effectiveness. It also summarizes epidemiology, structure, pathogenesis, and potential drug targets that can be explored to develop a new range of anti-JEV drugs to combat JEV infection globally.

The Current Landscape of Bioactive Molecules against DENV: A Systematic Review

With a 30-fold increase in incidence over the previous 50 years, dengue fever is now the most widespread viral disease transmitted by mosquitoes in the world. The intricate interaction of the human defense system, hereditary predisposition, and specific bitterness elements is more likely to be the pathogenesis of dengue. There are presently no viable treatments for dengue. Synthetic drugs which are used against this ailment also show major side effects. There must be a deeper understanding of the underlying mechanism generating severe symptoms to develop auguring markers, cutting-edge diagnostics, and treatments and finally a well-rounded and secure antiserum. Hence, the aim is to search for safer and more potent drugs derived from plants. Plants or herbs are mainly targeting replication or its enzyme or specific stereotypes, though an exact mechanism of phytoconstituents interfering with the viral replication is still undiscovered. The present attempt provided the update with the objective to bringing up forward pathophysiological eventualities involved in dengue virus along with the naturally derived treatment relevant to provide the impregnable therapy by evading the noxious symptoms for dengue fever. Governor's plum, Cryptocarya chartacea, magnolia berry, and Chinese ginger are such plants exhibiting many effective phytoconstituents against DENV and can be further explored for novel drug discovery by medicinal scientists.

Chronic depletion of vertebrate lipids in Aedes aegypti cells dysregulates lipid metabolism and inhibits innate immunity without altering dengue infectivity

Aedes aegypti is the primary vector of dengue virus (DENV) and other arboviruses. Previous literature suggests that vertebrate and invertebrate lipids and the nutritional status of mosquitoes modify virus infection. Here, we developed a vertebrate lipid-depleted Ae. aegypti cell line to investigate if chronic depletion of vertebrate lipids normally present in a blood meal and insect cell culture medium would impact cell growth and virus infection. Chronic depletion of vertebrate lipids reduced cell size and proliferation, although cells retained equivalent total intracellular lipids per cell by reducing lipolysis and modifying gene expression related to sugar and lipid metabolism. Downregulation of innate immunity genes was also observed. We hypothesized that chronic depletion of vertebrate lipids would impact virus infection; however, the same amount of DENV was produced per cell. This study reveals how Ae. aegypti cells adapt in the absence of vertebrate lipids, and how DENV can replicate equally well in cells that contain predominately vertebrate or invertebrate lipids.

Aedes aegypti is a major threat to public health. Ae. aegypti is the primary vector of dengue virus types 1–4 (DENV 1–4), zika virus (ZIKV), chikungunya virus (CHIKV), and yellow fever virus (YFV). Ae. aegypti acquires arboviruses from a vertebrate host during blood feeding. Blood feeding introduces vertebrate-specific factors into the mosquito that may be important for both mosquito and virus. This study reveals that Ae. aegypti adapts to depletion of vertebrate lipids by inhibiting lipolysis and promoting de novo synthesis of invertebrate lipids, and that DENV can replicate equally well without high concentrations of cholesterol and other vertebrate lipid species. Understanding how disease vectors adapt to nutritional changes will identify novel strategies for vector control and disease mitigation.

Identification of a βCD-Based Hyper-Branched Negatively Charged Polymer as HSV-2 and RSV Inhibitor

Cyclodextrins and cyclodextrin derivatives were demonstrated to improve the antiviral potency of numerous drugs, but also to be endowed with intrinsic antiviral action. They are suitable building blocks for the synthesis of functionalized polymer structures with potential antiviral activity. Accordingly, four water-soluble hyper-branched beta cyclodextrin (βCD)-based anionic polymers were screened against herpes simplex virus (HSV-2), respiratory syncytial virus (RSV), rotavirus (HRoV), and influenza virus (FluVA). They were characterized by FTIR-ATR, TGA, elemental analyses, zeta-potential measurements, and potentiometric titrations, while the antiviral activity was investigated with specific in vitro assays. The polymer with the highest negative charge, pyromellitic dianhydride-linked polymer (P_PMDA), showed significant antiviral action against RSV and HSV-2, by inactivating RSV free particles and by altering HSV-2 binding to the cell. The polymer fraction with the highest molecular weight showed the strongest antiviral activity and both P_PMDA and its active fractions were not toxic for cells. Our results suggest that the polymer virucidal activity against RSV can be exploited to produce new antiviral materials to counteract the virus dissemination through the air or direct contact. Additionally, the strong HSV-2 binding inhibition along with the water solubility of P_PMDA and the acyclovir complexation potential of βCD are attractive features for developing new therapeutic topical options against genital HSV-2 infection.

Role of Lipid Rafts in Pathogen-Host Interaction - A Mini Review

Lipid rafts, also known as microdomains, are important components of cell membranes and are enriched in cholesterol, glycophospholipids and receptors. They are involved in various essential cellular processes, including endocytosis, exocytosis and cellular signaling. Receptors are concentrated at lipid rafts, through which cellular signaling can be transmitted. Pathogens exploit these signaling mechanisms to enter cells, proliferate and egress. However, lipid rafts also play an important role in initiating antimicrobial responses by sensing pathogens via clustered pathogen-sensing receptors and triggering downstream signaling events such as programmed cell death or cytokine production for pathogen clearance. In this review, we discuss how both host and pathogens use lipid rafts and associated proteins in an arms race to survive. Special attention is given to the involvement of the major vault protein, the main constituent of a ribonucleoprotein complex, which is enriched in lipid rafts upon infection with vaccinia virus.

Lipid Interactions Between Flaviviruses and Mosquito Vectors

Mosquito-borne flaviviruses, such as dengue (DENV), Zika (ZIKV), yellow fever (YFV), West Nile (WNV), and Japanese encephalitis (JEV) viruses, threaten a large part of the human populations. In absence of therapeutics and effective vaccines against each flaviviruses, targeting viral metabolic requirements in mosquitoes may hold the key to new intervention strategies. Development of metabolomics in the last decade opened a new field of research: mosquito metabolomics. It is now clear that flaviviruses rely on mosquito lipids, especially phospholipids, for their cellular cycle and propagation. Here, we review the biosyntheses of, biochemical properties of and flaviviral interactions with mosquito phospholipids. Phospholipids are structural lipids with a polar headgroup and apolar acyl chains, enabling the formation of lipid bilayer that form plasma- and endomembranes. Phospholipids are mostly synthesized through the de novo pathway and remodeling cycle. Variations in headgroup and acyl chains influence phospholipid physicochemical properties and consequently the membrane behavior. Flaviviruses interact with cellular membranes at every step of their cellular cycle. Recent evidence demonstrates that flaviviruses reconfigure the phospholipidome in mosquitoes by regulating phospholipid syntheses to increase virus multiplication. Identifying the phospholipids involved and understanding how flaviviruses regulate these in mosquitoes is required to design new interventions.

Anti-flavivirus Properties of Lipid-Lowering Drugs

Although Flaviviruses such as dengue (DENV) and zika (ZIKV) virus are important human pathogens, an effective vaccine or antiviral treatment against them is not available. Hence, the search for new strategies to control flavivirus infections is essential. Several studies have shown that the host lipid metabolism could be an antiviral target because cholesterol and other lipids are required during the replicative cycle of different Flaviviridae family members. FDA-approved drugs with hypolipidemic effects could be an alternative for treating flavivirus infections. However, a better understanding of the regulation between host lipid metabolism and signaling pathways triggered during these infections is required. The metabolic pathways related to lipid metabolism modified during DENV and ZIKV infection are analyzed in this review. Additionally, the role of lipid-lowering drugs as safe host-targeted antivirals is discussed.

Antiviral strategies targeting host factors and mechanisms obliging +ssRNA viral pathogens

The ongoing COVID-19 pandemic, periodic recurrence of viral infections, and the emergence of challenging variants has created an urgent need of alternative therapeutic approaches to combat the spread of viral infections, failing to which may pose a greater risk to mankind in future. Resilience against antiviral drugs or fast evolutionary rate of viruses is stressing the scientific community to identify new therapeutic approaches for timely control of disease. Host metabolic pathways are exquisite reservoir of energy to viruses and contribute a diverse array of functions for successful replication and pathogenesis of virus. Targeting the host factors rather than viral enzymes to cease viral infection, has emerged as an alternative antiviral strategy. This approach offers advantage in terms of increased threshold to viral resistance and can provide broad-spectrum antiviral action against different viruses. The article here provides substantial review of literature illuminating the host factors and molecular mechanisms involved in innate/adaptive responses to viral infection, hijacking of signalling pathways by viruses and the intracellular metabolic pathways required for viral replication. Host-targeted drugs acting on the pathways usurped by viruses are also addressed in this study. Host-directed antiviral therapeutics might prove to be a rewarding approach in controlling the unprecedented spread of viral infection, however the probability of cellular side effects or cytotoxicity on host cell should not be ignored at the time of clinical investigations.

The novel therapeutic target and inhibitory effects of PF-429242 against Zika virus infection

Zika virus (ZIKV) is a re-emerging mosquito-borne flavivirus of African origin that is transmitted by Aedes mosquitoes. ZIKV was historically limited to Africa and Asia, where mild cases were reported. However, ZIKV has recently been responsible for major global outbreaks associated with a wide range of neurological complications. Since no antiviral therapy exists for ZIKV, drug discovery research for ZIKV is crucial. Intracellular lipids regulated by sterol regulatory element-binding proteins (SREBPs) are important in flavivirus pathogenesis. PF-429242 has been reported to inhibit the activity of site-1 protease (S1P), which regulates the expression of SREBP target genes. Our primary objective in this study is to elucidate the mechanism of the antiviral activity of PF-429242 against the African genotype (ZIKV_MR-766) and Asian genotypes (ZIKV _{H/PF 2013} and ZIKV _PRVABC59) using several primate-derived cell lines. The virus titer was determined via a focus-forming assay; we used flow cytometry to quantify intracellular lipids in ZIKV-infected and mock-treated cells. The PF-429242 molecule effectively suppressed ZIKV infection in neuronal cell lines; T98G, U-87MG, SK-N-SH and primary monocytes cell, indicating that PF-429242 molecule can be used therapeutically. A strong reduction in ZIKV replication was observed at 12 μM and 30 μM in in neuronal cell lines and primary monocytes, respectively. Interestingly, the inhibitory effects of the PF-429242 molecule were observed when it was tested on various ZIKV-lineage infections. Lipid quantification reveals that ZIKV increases lipogenesis in infected cells, while the exogenous addition of cholesterol effectively blocks ZIKV replication. Furthermore, the supplementation of oleic acid increases the ZIKV titer. Fenofibrate, an inhibitor of lipid droplet formation, reduces the ZIKV titer. Collectively, our results demonstrate that the development of antiviral drugs against ZIKV could be based on key regulators of lipid metabolism. In addition, this study reveals that the mechanism of the PF-429242-mediated suppression among flavivirus infections is not entirely identical. Our results warrant further evaluation of PF-429242 as a prospective antiviral drug, given the multiple advantageous properties of this compound, such as its limited toxicity, neuroprotective properties, and broad spectrum of capabilities.

Using Wolbachia to Eliminate Dengue: Will the Virus Fight Back?

Recent field trials have demonstrated that dengue incidence can be substantially reduced by introgressing strains of the endosymbiotic bacterium Wolbachia into Aedes aegypti mosquito populations. This strategy relies on Wolbachia reducing the susceptibility of Ae. aegypti to disseminated infection by positive-sense RNA viruses like dengue. However, RNA viruses are well known to adapt to antiviral pressures. Here, we review the viral infection stages where selection for Wolbachia-resistant virus variants could occur. We also consider the genetic constraints imposed on viruses that alternate between vertebrate and invertebrate hosts, and the likely selection pressures to which dengue virus might adapt in order to be effectively transmitted by Ae. aegypti that carry Wolbachia. While there are hurdles to dengue viruses developing resistance to Wolbachia, we suggest that long-term surveillance for resistant viruses should be an integral component of Wolbachia-introgression biocontrol programs.

Compartmentalized replication organelle of flavivirus at the ER and the factors involved

Flaviviruses are positive-sense single-stranded RNA viruses that pose a considerable threat to human health. Flaviviruses replicate in compartmentalized replication organelles derived from the host endoplasmic reticulum (ER). The characteristic architecture of flavivirus replication organelles includes invaginated vesicle packets and convoluted membrane structures. Multiple factors, including both viral proteins and host factors, contribute to the biogenesis of the flavivirus replication organelle. Several viral nonstructural (NS) proteins with membrane activity induce ER rearrangement to build replication compartments, and other NS proteins constitute the replication complexes (RC) in the compartments. Host protein and lipid factors facilitate the formation of replication organelles. The lipid membrane, proteins and viral RNA together form the functional compartmentalized replication organelle, in which the flaviviruses efficiently synthesize viral RNA. Here, we reviewed recent advances in understanding the structure and biogenesis of flavivirus replication organelles, and we further discuss the function of virus NS proteins and related host factors as well as their roles in building the replication organelle.

Cyclodextrins in Antiviral Therapeutics and Vaccines

The present review describes the various roles of cyclodextrins (CDs) in vaccines against viruses and in antiviral therapeutics. The first section describes the most commonly studied application of cyclodextrins—solubilisation and stabilisation of antiviral drugs; some examples also refer to their beneficial taste-masking activity. The second part of the review describes the role of cyclodextrins in antiviral vaccine development and stabilisation, where they are employed as adjuvants and cryopreserving agents. In addition, cyclodextrin-based polymers as delivery systems for mRNA are currently under development. Lastly, the use of cyclodextrins as pharmaceutical active ingredients for the treatment of viral infections is explored. This new field of application is still taking its first steps. Nevertheless, promising results from the use of cyclodextrins as agents to treat other pathologies are encouraging. We present potential applications of the results reported in the literature and highlight the products that are already available on the market.

DHA attenuated Japanese Encephalitis virus infection-induced neuroinflammation and neuronal cell death in cultured rat Neuron/glia

Japanese Encephalitis Virus (JEV) is a neurotropic virus and its Central Nervous System (CNS) infection causes fatal encephalitis with high mortality and morbidity. Microglial activation and consequences of bystander damage appear to be the dominant mechanisms for Japanese Encephalitis and complications. Docosahexaenoic acid (DHA), an essential fatty acid and a major component of brain cell membranes, possesses additional biological activities, including anti-apoptosis, anti-inflammation, and neuroprotection. Through this study, we have provided experimental evidence showing the anti-inflammatory, neuroprotective, and anti-viral effects of DHA against JEV infection in rat Neuron/glia cultures. By Neuron/glia and Neuron cultures, DHA protected against neuronal cell death upon JEV infection and reduced JEV amplification. In Neuron/glia and Microglia cultures, the effects of DHA were accompanied by the downregulation of pro-inflammatory M1 microglia, upregulation of anti-inflammatory M2 microglia, and reduction of neurotoxic cytokine expression, which could be attributed to its interference in the Toll-Like Receptor (TLR), Mitogen-Activated Protein Kinase (MAPK), and Interferon/Janus Kinase/Signal Transducers and Activators of Transcription (Stat), along with the NF-κB, AP-1, and c-AMP Response Element Binding Protein (CREB) controlled transcriptional programs. Parallel anti-inflammatory effects against JEV infection were duplicated by G Protein-Coupled Receptor (GPR120) and GPR40 agonists and a reversal of DHA-mediated anti-inflammation was seen in the presence of GPR120 antagonist, while the GPR40 was less effectiveness. Since increasing evidence indicates its neuroprotection against neurodegenerative diseases, DHA is a proposed anti-inflammatory and neuroprotective candidate for the treatment of neuroinflammation-accompanied viral pathogenesis such as Japanese Encephalitis.

Porcine Circovirus Type 3 Enters Into PK15 Cells Through Clathrin- and Dynamin-2-Mediated Endocytosis in a Rab5/Rab7 and pH-Dependent Fashion

Porcine circovirus type 3 (PCV3) invades multiple tissues and organs of pigs of different ages and are widely spread throughout pig farms, emerging as an important viral pathogen that can potentially damage the pig industry worldwide. Since PCV3 is a newly discovered virus, many aspects of its life cycle remain unknown. Porcine kidney epithelial cells are important host targets for PCV3. Here, we used systematic approaches to dissect the molecular mechanisms underlying the cell entry and intracellular trafficking of PCV3 in PK15 cells, a cell line of porcine kidney epithelial origin. A large number of PCV3 viral particles were found to colocalize with clathrin but not caveolin-1 after entry, and PCV3 infection was significantly decreased when treated with chlorpromazine, dynasore, knockdown of clathrin heavy chain expression via RNA interference, or overexpression of a dominant-negative mutant of EPS15 in PCV3-infected cells. After internalization, the viral particles were further observed to colocalize with Rab5 and Rab7, and knockdown of both expression by RNA interference significantly inhibited PCV3 replication. We also found that PCV3 infection was impeded by ammonium chloride treatment, which indicated the requirement of an acidic environment for viral entry. Taken together, our findings demonstrate that PCV3 enters PK15 cells through a clathrin- and dynamin-2-mediated endocytic pathway, which requires early and late endosomal trafficking, as well as an acidic environment, providing an insightful theoretical basis for further understanding the PCV3 life cycle and its pathogenesis.

Dissecting lipid metabolism alterations in SARS-CoV-2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause of the COVID-19 pandemic that has infected over a hundred million people globally. There have been more than two million deaths recorded worldwide, with no end in sight until a widespread vaccination will be achieved. Current research has centred on different aspects of the virus interaction with cell surface receptors, but more needs to be done to further understand its mechanism of action in order to develop a targeted therapy and a method to control the spread of the virus. Lipids play a crucial role throughout the viral life cycle, and viruses are known to exploit lipid signalling and synthesis to affect host cell lipidome. Emerging studies using untargeted metabolomic and lipidomic approaches are providing new insight into the host response to COVID-19 infection. Indeed, metabolomic and lipidomic approaches have identified numerous circulating lipids that directly correlate to the severity of the disease, making lipid metabolism a potential therapeutic target. Circulating lipids play a key function in the pathogenesis of the virus and exert an inflammatory response. A better knowledge of lipid metabolism in the host-pathogen interaction will provide valuable insights into viral pathogenesis and to the development of novel therapeutic targets.

Membrane Rafts: Portals for Viral Entry

Membrane rafts are dynamic, small (10-200 nm) domains enriched with cholesterol and sphingolipids that compartmentalize cellular processes. Rafts participate in roles essential to the lifecycle of different viral families including virus entry, assembly and/or budding events. Rafts seem to participate in virus attachment and recruitment to the cell surface, as well as the endocytic and non-endocytic mechanisms some viruses use to enter host cells. In this review, we will introduce the specific role of rafts in viral entry and define cellular factors implied in the choice of one entry pathway over the others. Finally, we will summarize the most relevant information about raft participation in the entry process of enveloped and non-enveloped viruses.

Dengue virus dominates lipid metabolism modulations in Wolbachia-coinfected Aedes aegypti

Competition between viruses and Wolbachia for host lipids is a proposed mechanism of Wolbachia-mediated virus blocking in insects. Yet, the metabolomic interaction between virus and symbiont within the mosquito has not been clearly defined. We compare the lipid profiles of Aedes aegypti mosquitoes bearing mono- or dual-infections of the Wolbachia wMel strain and dengue virus serotype 3 (DENV3). We found metabolic signatures of infection-induced intracellular events but little evidence to support direct competition between Wolbachia and virus for host lipids. Lipid profiles of dual-infected mosquitoes resemble those of DENV3 mono-infected mosquitoes, suggesting virus-driven modulation dominates over that of Wolbachia. Interestingly, knockdown of key metabolic enzymes suggests cardiolipins are host factors for DENV3 and Wolbachia replication. These findings define the Wolbachia-DENV3 metabolic interaction as indirectly antagonistic, rather than directly competitive, and reveal new research avenues with respect to mosquito × virus interactions at the molecular level.

Koh, Islam, Ye et al. describe lipid profiles of Aedes aegypti mosquitoes bearing mono- or dual-infections of Wolbachia (wMel) and dengue virus serotype 3 (DENV3), finding that virus modulation dominates the dual-infection lipid profile and that cardiolipins support DENV3 and Wolbachia replication. This study suggests that direct competition for lipids do not underlie Wolbachia-mediated virus blocking.

Recent advances in antiviral drug development towards dengue virus

Despite the high disease burden of dengue virus, there is no approved antiviral treatment or broadly applicable vaccine to treat or prevent dengue virus infection. In the last decade, many antiviral compounds have been identified but only few have been further evaluated in pre-clinical or clinical trials. This review will give an overview of the direct-acting and host-directed antivirals identified to date. Furthermore, important parameters for further development that is, drug properties including efficacy, specificity and stability, pre-clinical animal testing, and combinational drug therapy will be discussed.

Coronavirus Interplay With Lipid Rafts and Autophagy Unveils Promising Therapeutic Targets

Coronaviruses are enveloped, single-stranded, positive-sense RNA viruses that can infect animal and human hosts. The infection induces mild or sometimes severe acute respiratory diseases. Nowadays, the appearance of a new, highly pathogenic and lethal coronavirus variant, SARS-CoV-2, responsible for a pandemic (COVID-19), represents a global problem for human health. Unfortunately, only limited approaches are available to treat coronavirus infections and a vaccine against this new coronavirus variant is not yet available. The plasma membrane microdomain lipid rafts have been found by researchers to be involved in the replication cycle of numerous viruses, including coronaviruses. Indeed, some pathogen recognition receptors for coronaviruses as for other viruses cluster into lipid rafts, and it is therefore conceivable that the first contact between virus and host cells occurs into these specialized regions, representing a port of cell entry for viruses. Recent data highlighted the peculiar pro-viral or anti-viral role played by autophagy in the host immune responses to viral infections. Coronaviruses, like other viruses, were reported to be able to exploit the autophagic machinery to increase their replication or to inhibit the degradation of viral products. Agents known to disrupt lipid rafts, such as metil-β-cyclodextrins or statins, as well as autophagy inhibitor agents, were shown to have an anti-viral role. In this review, we briefly describe the involvement of lipid rafts and autophagy in coronavirus infection and replication. We also hint how lipid rafts and autophagy may represent a potential therapeutic target to be investigated for the treatment of coronavirus infections.

Characterization of Zika Virus Endocytic Pathways in Human Glioblastoma Cells

Zika virus (ZIKV) infections can cause microcephaly and neurological disorders. However, the early infection events of ZIKV in neural cells remain to be characterized. Here, by using a combination of pharmacological and molecular approaches and the human glioblastoma cell T98G as a model, we first observed that ZIKV infection was inhibited by chloroquine and NH₄Cl, indicating a requirement of low intracellular pH. We further showed that dynamin is required as the ZIKV entry was affected by the specific inhibitor dynasore, small interfering RNA (siRNA) knockdown of dynamin, or by expressing the dominant-negative K44A mutant. Moreover, the ZIKV entry was significantly inhibited by chlorpromazine, pitstop2, or siRNA knockdown of clathrin heavy chain, indicating an involvement of clathrin-mediated endocytosis. In addition, genistein treatment, siRNA knockdown of caveolin-1, or overexpression of a dominant-negative caveolin mutant impacted the ZIKV entry, with ZIKV particles being observed to colocalize with caveolin-1, implying that caveola endocytosis can also be involved. Furthermore, we found that the endocytosis of ZIKV is dependent on membrane cholesterol, microtubules, and actin cytoskeleton. Importantly, ZIKV infection was inhibited by silencing of Rab5 and Rab7, while confocal microscopy showed that ZIKV particles localized in Rab5- and Rab7-postive endosomes. These results indicated that, after internalization, ZIKV likely moves to Rab5-positive early endosome and Rab7-positive late endosomes before delivering its RNA into the cytoplasm. Taken together, our study, for the first time, described the early infection events of ZIKV in human glioblastoma cell T98G.

Extracellular vesicles restrict dengue virus fusion in Aedes aegypti cells

Aedes aegypti is the primary vector of dengue virus (DENV), and acquires this virus from a vertebrate host during blood feeding. Previous literature has shown that vertebrate blood factors such as complement protein C5a and low-density lipoprotein (LDL) influence DENV acquisition in the mosquito. Here, we show that extracellular vesicles in cell culture medium inhibit DENV infection in mosquito cells. Specifically, extracellular vesicles enter into mosquito cells and inhibit an early stage of infection. Extracellular vesicles had no effect on virus cell attachment or entry. Instead, extracellular vesicles restricted virus membrane fusion. Extracellular vesicles only inhibited DENV infection in mosquito cells and not vertebrate cells. These data highlight a novel virus-vector-host interaction that limits virus infection in mosquito cells by restricting virus membrane fusion.

Cyclodextrins: Emerging Medicines of the New Millennium

Cyclodextrins, since their discovery in the late 19th century, were mainly regarded as excipients. Nevertheless, developments in cyclodextrin research have shown that some of these hosts can capture and include biomolecules, highlighting fatty acids and cholesterol, which implies that they are not inert and that their action may be used in specific medicinal purposes. The present review, centered on literature reports from the year 2000 until the present day, presents a comprehensive description of the known biological activities of cyclodextrins and their implications for medicinal applications. The paper is divided into two main sections, one devoted to the properties and applications of cyclodextrins as active pharmaceutical ingredients in a variety of pathologies, from infectious ailments to cardiovascular dysfunctions and metabolic diseases. The second section is dedicated to the use of cyclodextrins in a range of biomedical technologies.

Lipophilic statins inhibit Zika virus production in Vero cells

Zika virus (ZIKV) is a mosquito-borne member of the Flaviviridae family. ZIKV infection has been associated with neurological complications such as microcephaly in newborns and Guillain-Barré syndrome in adults; thus, therapeutic agents are urgently needed. Statins are clinically approved for lowering cholesterol levels to prevent cardiovascular disease but have shown potential as antiviral drugs. In this study, we explored the possibility of utilizing statins as anti-ZIKV drugs. We found that, generally, lipophilic statins (atorvastatin, cerivastatin, fluvastatin, lovastatin, mevastatin, and simvastatin) could reduce ZIKV production in vitro and result in smaller foci of infection. Time-of-drug-addition assay revealed that early treatment with statins is more beneficial than late treatment; however, statins could not completely inhibit the entry stage of ZIKV infection. Furthermore, individual lipophilic statins differed in anti-ZIKV capacity, with fluvastatin being the most efficient at low concentrations. Taken together, this study shows that statins or their derivatives have the potential to be used as anti-ZIKV therapeutic agents.

Curious entanglements: interactions between mosquitoes, their microbiota, and arboviruses

Mosquitoes naturally harbor a diverse community of microorganisms that play a crucial role in their biology. Mosquito-microbiota interactions are abundant and complex. They can dramatically alter the mosquito immune response, and impede or enhance a mosquito's ability to transmit medically important arboviral pathogens. Yet critically, given the massive public health impact of arboviral disease, few such interactions have been well characterized. In this review, we describe the current state of knowledge of the role of microorganisms in mosquito biology, how microbial-induced changes to mosquito immunity moderate infection with arboviruses, cases of mosquito-microbial-virus interactions with a defined mechanism, and the molecular interactions that underlie the endosymbiotic bacterium Wolbachia's ability to block virus infection in mosquitoes.

Dual targeting of dengue virus virions and NS1 protein with the heparan sulfate mimic PG545

Dengue virus (DENV) is the most prevalent mosquito-borne flavivirus that infects humans. At present, there are no specific antiviral drugs to treat DENV infection and vaccine development has met with challenges. DENV encodes two glycosaminoglycan (GAG) binding proteins; Envelope (E) and non-structural protein 1 (NS1). While previous work has validated the use of GAG analogues as inhibitors of E mediated virus-cell attachment, their potential for antiviral intervention in NS1 protein toxicity has not yet been explored. Here, we investigate the potential of the heparan sulfate mimetic PG545 as a dual purpose compound to target both DENV virion infectivity and NS1 function. In comparison to a non-sulfated analogue, we show that PG545 potently inhibits DENV infectivity with no cytotoxic effect. Against NS1, PG545 completely blocks the induction of cellular activation and abolishes NS1-mediated disruption of endothelial monolayer integrity. Furthermore, PG545 treatment moderately improves survival from lethal DENV challenge in a murine model. At peak disease, PG545-treated mice have lower viremia, circulating NS1 and serum TNF-α. Consistent with anti-NS1 activity, PG545 treatment also reduces systemic vascular leakage caused by DENV infection in vivo. Taken together, these findings demonstrate that the dual targeting of DENV virions and NS1 using GAG analogues offers a new avenue for DENV drug development.

Dengue virus reduces expression of low-density lipoprotein receptor-related protein 1 to facilitate replication in Aedes aegypti

Aedes aegypti is the primary vector of a number of viruses pathogenic to humans including dengue virus (DENV). DENV infection leads to widespread transcriptomic and proteomic alterations in mosquito cells. Here we identified alterations to the mosquito cell secretome during DENV infection by performing liquid chromatography tandem mass spectrometry. We found that an extracellular fragment of low-density lipoprotein receptor-related protein 1 (LRP-1) was present during infection. Previous literature suggests that LRP-1 regulates cholesterol homeostasis. Therefore, we hypothesized that DENV modifies LRP-1 protein expression to maintain host-derived intracellular cholesterol, which would facilitate virus replication within membrane-associated replication compartments. Accordingly, stimuli that are present during flavivirus infection reduced LRP-1 protein expression. We also found that dsRNA knockdown of LRP-1 increased intracellular cholesterol and DENV viral RNA. Further, depletion of intracellular lipids reduced infection. Together, these data suggest that DENV reduces LRP-1 protein expression, possibly through regulated intramembrane proteolysis (RIP), to increase intracellular cholesterol and facilitate replication in Ae. aegypti.

Engagement of cellular cholesterol in the life cycle of classical swine fever virus: its potential as an antiviral target

Classical swine fever virus (CSFV), the etiological agent of classical swine fever in pigs, is a member of the Pestivirus genus within the Flaviviridae family. It has been proposed that CSFV infection is significantly inhibited by methyl-β-cyclodextrin (MβCD) treatment. However, the exact engagement of cellular cholesterol in the life cycle of CSFV remains unclear. Here, we demonstrated that pretreatment of PK-15 cells with MβCD significantly decreased the cellular cholesterol level and resulted in the inhibition of CSFV infection, while replenishment of exogenous cholesterol in MβCD-treated cells recovered the cellular cholesterol level and restored the viral infection. Moreover, we found that depletion of cholesterol acted on the early stage of CSFV infection and blocked its internalization into the host cells. Furthermore, we showed that 25-hydroxycholesterol, a regulator of cellular cholesterol biosynthesis, exhibited a potent anti-CSFV activity by reducing cellular cholesterol level. Taken together, our findings highlight the engagement of cholesterol in the life cycle of CSFV and its potential use as an antiviral target.

The Role of Host Cholesterol During Flavivirus Infection

In recent years the emergence and resurgence of arboviruses have generated a global health alert. Among arboviruses, Dengue (DENV), Zika (ZIKV), Yellow Fever (YFV), and West Nile (WNV) virus, belong to the genus Flavivirus, cause high viremia and occasionally fatal clinical disease in humans. Given the genetic austerity of the virus, they depend on cellular factors and organelles to complete its replication. One of the cellular components required for flavivirus infection is cholesterol. Cholesterol is an abundant lipid in biomembranes of eukaryotes cells and is necessary to maintain the cellular homeostasis. Recently, it has been reported, that cholesterol is fundamental during flavivirus infection in both mammal and insect vector models. During infection with DENV, ZIKV, YFV, and WNV the modulation of levels of host-cholesterol facilitates viral entry, replicative complexes formation, assembly, egress, and control of the interferon type I response. This modulation involves changes in cholesterol uptake with the concomitant regulation of cholesterol receptors as well as changes in cholesterol synthesis related to important modifications in cellular metabolism pathways. In view of the flavivirus dependence of cholesterol and the lack of an effective anti-flaviviral treatment, this cellular lipid has been proposed as a therapeutic target to treat infection using FDA-approved cholesterol-lowering drugs. This review aims to address the dependence of cholesterol by flaviviruses as well as the basis for anti flaviviral therapy using drugs which target is cholesterol synthesis or uptake.

Flavivirus Receptors: Diversity, Identity, and Cell Entry

Flaviviruses are emerging and re-emerging arthropod-borne pathogens responsible for significant mortality and morbidity worldwide. The genus comprises more than seventy small, positive-sense, single-stranded RNA viruses, which are responsible for a spectrum of human and animal diseases ranging in symptoms from mild, influenza-like infection to fatal encephalitis and haemorrhagic fever. Despite genomic and structural similarities across the genus, infections by different flaviviruses result in disparate clinical presentations. This review focusses on two haemorrhagic flaviviruses, dengue virus and yellow fever virus, and two neurotropic flaviviruses, Japanese encephalitis virus and Zika virus. We review current knowledge on host-pathogen interactions, virus entry strategies and tropism.

Shaping the flavivirus replication complex: It is curvaceous!

Flavivirus replication is intimately involved with remodelled membrane organelles that are compartmentalised for different functions during their life cycle. Recent advances in lipid analyses and gene depletion have identified a number of host components that enable efficient virus replication in infected cells. Here, we describe the current understanding on the role and contribution of host lipids and membrane bending proteins to flavivirus replication, with a particular focus on the components that bend and shape the membrane bilayer to induce the flavivirus-induced organelles characteristic of infection.

Zika Virus and the Metabolism of Neuronal Cells

Zika virus (ZIKV) infection is associated with abnormal functions of neuronal cells causing neurological disorders such as microcephaly in the newborns and Guillain-Barré syndrome in the adults. Typically, healthy brain growth is associated with normal neural stem cell proliferation, differentiation, and maturation. This process requires a controlled cellular metabolism that is essential for normal migration, axonal elongation, and dendrite morphogenesis of newly generated neurons. Thus, the remarkable changes in the cellular metabolism during early stages of neuronal stem cell differentiation are crucial for brain development. Recent studies show that ZIKV directly infects neuronal stem cells in the fetus and impairs brain growth. In this review, we highlighted the fact that the activation of P53 and inhibition of the mTOR pathway by ZIKV infection to neuronal stem cells induces early shifting from glycolysis to oxidative phosphorylation (OXPHOS) may induce immature differentiation, apoptosis, and stem cell exhaustion. We hypothesize that ZIKV infection to mature myelin-producing cells and resulting metabolic shift may lead to the development of neurological diseases, such as Guillain-Barré syndrome. Thus, the effects of ZIKV on the cellular metabolism of neuronal cells may lead to the incidence of neurological disorders as observed recently during ZIKV infection.

Conflict in the Intracellular Lives of Endosymbionts and Viruses: A Mechanistic Look at Wolbachia-Mediated Pathogen-blocking

At the forefront of vector control efforts are strategies that leverage host-microbe associations to reduce vectorial capacity. The most promising of these efforts employs Wolbachia, a maternally transmitted endosymbiotic bacterium naturally found in 40% of insects. Wolbachia can spread through a population of insects while simultaneously inhibiting the replication of viruses within its host. Despite successes in using Wolbachia-transfected mosquitoes to limit dengue, Zika, and chikungunya transmission, the mechanisms behind pathogen-blocking have not been fully characterized. Firstly, we discuss how Wolbachia and viruses both require specific host-derived structures, compounds, and processes to initiate and maintain infection. There is significant overlap in these requirements, and infection with either microbe often manifests as cellular stress, which may be a key component of Wolbachia’s anti-viral effect. Secondly, we discuss the current understanding of pathogen-blocking through this lens of cellular stress and develop a comprehensive view of how the lives of Wolbachia and viruses are fundamentally in conflict with each other. A thorough understanding of the genetic and cellular determinants of pathogen-blocking will significantly enhance the ability of vector control programs to deploy and maintain effective Wolbachia-mediated control measures.

Dynamic remodeling of lipids coincides with dengue virus replication in the midgut of Aedes aegypti mosquitoes

We describe the first comprehensive analysis of the midgut metabolome of Aedes aegypti, the primary mosquito vector for arboviruses such as dengue, Zika, chikungunya and yellow fever viruses. Transmission of these viruses depends on their ability to infect, replicate and disseminate from several tissues in the mosquito vector. The metabolic environments within these tissues play crucial roles in these processes. Since these viruses are enveloped, viral replication, assembly and release occur on cellular membranes primed through the manipulation of host metabolism. Interference with this virus infection-induced metabolic environment is detrimental to viral replication in human and mosquito cell culture models. Here we present the first insight into the metabolic environment induced during arbovirus replication in Aedes aegypti. Using high-resolution mass spectrometry, we have analyzed the temporal metabolic perturbations that occur following dengue virus infection of the midgut tissue. This is the primary site of infection and replication, preceding systemic viral dissemination and transmission. We identified metabolites that exhibited a dynamic-profile across early-, mid- and late-infection time points. We observed a marked increase in the lipid content. An increase in glycerophospholipids, sphingolipids and fatty acyls was coincident with the kinetics of viral replication. Elevation of glycerolipid levels suggested a diversion of resources during infection from energy storage to synthetic pathways. Elevated levels of acyl-carnitines were observed, signaling disruptions in mitochondrial function and possible diversion of energy production. A central hub in the sphingolipid pathway that influenced dihydroceramide to ceramide ratios was identified as critical for the virus life cycle. This study also resulted in the first reconstruction of the sphingolipid pathway in Aedes aegypti. Given conservation in the replication mechanisms of several flaviviruses transmitted by this vector, our results highlight biochemical choke points that could be targeted to disrupt transmission of multiple pathogens by these mosquitoes.

Low density lipopolyprotein inhibits flavivirus acquisition in Aedes aegypti

Aedes aegypti is the primary vector of a number of human pathogens including dengue virus (DENV) and Zika virus (ZIKV). Ae. aegypti acquires these viruses during the processing of bloodmeals obtained from an infected vertebrate host. Vertebrate blood contains a number of factors that have the potential to modify virus acquisition in the mosquito. Interestingly, low density lipopolyprotein (LDL) levels are decreased during severe DENV infection. Accordingly, we hypothesized that LDL is a modifiable factor that can influence flavivirus acquisition in the mosquito. We found that LDL is endocytosed by Ae. aegypti cells in a dynamin-dependent manner. LDL is also endocytosed by midgut epithelial cells and accumulates at the luminal midgut epithelium during bloodmeal digestion. Importantly, pretreatment with LDL, but not high density lipopolyprotein (HDL), significantly inhibited both DENV and ZIKV infection in vitro, and LDL inhibited ZIKV infection in vivo. This study identifies human LDL or 'bad cholesterol' as a modifiable factor that can inhibit flavivirus acquisition in Ae. aegypti. Identification of modifiable blood factors and critical cellular interactions that mediate pathogen acquisition may lead to novel strategies to disrupt the transmission cycle of vector-borne diseases.

Perturbed cholesterol and vesicular trafficking associated with dengue blocking in Wolbachia-infected Aedes aegypti cells

Wolbachia are intracellular maternally inherited bacteria that can spread through insect populations and block virus transmission by mosquitoes, providing an important approach to dengue control. To better understand the mechanisms of virus inhibition, we here perform proteomic quantification of the effects of Wolbachia in Aedes aegypti mosquito cells and midgut. Perturbations are observed in vesicular trafficking, lipid metabolism and in the endoplasmic reticulum that could impact viral entry and replication. Wolbachia-infected cells display a differential cholesterol profile, including elevated levels of esterified cholesterol, that is consistent with perturbed intracellular cholesterol trafficking. Cyclodextrins have been shown to reverse lipid accumulation defects in cells with disrupted cholesterol homeostasis. Treatment of Wolbachia-infected Ae. aegypti cells with 2-hydroxypropyl-β-cyclodextrin restores dengue replication in Wolbachia-carrying cells, suggesting dengue is inhibited in Wolbachia-infected cells by localised cholesterol accumulation. These results demonstrate parallels between the cellular Wolbachia viral inhibition phenotype and lipid storage genetic disorders.

Wolbachia infection of mosquitoes can block dengue virus infection and is tested in field trials, but the mechanism of action is unclear. Using proteomics, Geoghegan et al. here identify effects of Wolbachia on cholesterol homeostasis and dengue virus replication in Aedes aegypti.

Imipramine Inhibits Chikungunya Virus Replication in Human Skin Fibroblasts through Interference with Intracellular Cholesterol Trafficking

Chikungunya virus (CHIKV) is an emerging arbovirus of the Togaviridae family that poses a present worldwide threat to human in the absence of any licensed vaccine or antiviral treatment to control viral infection. Here, we show that compounds interfering with intracellular cholesterol transport have the capacity to inhibit CHIKV replication in human skin fibroblasts, a major viral entry site in the human host. Pretreatment of these cells with the class II cationic amphiphilic compound U18666A, or treatment with the FDA-approved antidepressant drug imipramine resulted in a near total inhibition of viral replication and production at the highest concentration used without any cytotoxic effects. Imipramine was found to affect both the fusion and replication steps of the viral life cycle. The key contribution of cholesterol availability to the CHIKV life cycle was validated further by the use of fibroblasts from Niemann-Pick type C (NPC) patients in which the virus was unable to replicate. Interestingly, imipramine also strongly inhibited the replication of several Flaviviridae family members, including Zika, West Nile and Dengue virus. Together, these data show that this compound is a potential drug candidate for anti-arboviral treatment.

DENV up-regulates the HMG-CoA reductase activity through the impairment of AMPK phosphorylation: A potential antiviral target

Dengue is the most common mosquito-borne viral disease in humans. Changes of lipid-related metabolites in endoplasmic reticulum of dengue virus (DENV) infected cells have been associated with replicative complexes formation. Previously, we reported that DENV infection inhibits HMGCR phosphorylation generating a cholesterol-enriched cellular environment in order to favor viral replication. In this work, using enzymatic assays, ELISA, and WB we found a significant higher activity of HMGCR in DENV infected cells, associated with the inactivation of AMPK. AMPK activation by metformin declined the HMGCR activity suggesting that AMPK inactivation mediates the enhanced activity of HMGCR. A reduction on AMPK phosphorylation activity was observed in DENV infected cells at 12 and 24 hpi. HMGCR and cholesterol co-localized with viral proteins NS3, NS4A and E, suggesting a role for HMGCR and AMPK activity in the formation of DENV replicative complexes. Furthermore, metformin and lovastatin (HMGCR inhibitor) altered this co-localization as well as replicative complexes formation supporting that active HMGCR is required for replicative complexes formation. In agreement, metformin prompted a significant dose-dependent antiviral effect in DENV infected cells, while compound C (AMPK inhibitor) augmented the viral genome copies and the percentage of infected cells. The PP2A activity, the main modulating phosphatase of HMGCR, was not affected by DENV infection. These data demonstrate that the elevated activity of HMGCR observed in DENV infected cells is mediated through AMPK inhibition and not by increase in PP2A activity. Interestingly, the inhibition of this phosphatase showed an antiviral effect in an HMGCR-independent manner. These results suggest that DENV infection increases HMGCR activity through AMPK inactivation leading to higher cholesterol levels in endoplasmic reticulum necessary for replicative complexes formation. This work provides new information about the mechanisms involved in host lipid metabolism during DENV replicative cycle and identifies new potential antiviral targets for DENV replication.

DENV replicative complexes formation is associated with changes of lipid-related metabolites in endoplasmic reticulum, such as an increase in cholesterol synthesis. This increase correlates with a significant augment in the activity of HMGCoA reductase (the limiting enzyme in cholesterol synthesis), favoring a cholesterol-enriched cellular environment. The augment in the activity of the HMGCR observed in infected cells is caused by a decrease in the phosphorylation level of the HMGCR, associated with the inactivation of AMPK. In agreement, AMPK activation by metformin reduces HMGCR activity and affects viral replication. The role HMGCR and AMPK activity in DENV replicative complexes formation was confirmed by the co-localization of HMGCR and cholesterol with the viral proteins NS3, NS4A and E. Furthermore, metformin and lovastatin (HMGCR inhibitor) treatments altered this co-localization as well as replicative complexes formation supporting that active HMGCR is required for replicative complexes formation. The results show that during DENV infection, an increase in the HMGCR activity occurs through AMPK inactivation, leading to higher cholesterol levels in endoplasmic reticulum necessary for replicative complexes formation. This work provides new information about the mechanisms involved in host lipid metabolism during DENV replicative cycle and identifies potential new antiviral targets for DENV replication.

Antiviral activity of peptide inhibitors derived from the protein E stem against Japanese encephalitis and Zika viruses

Japanese encephalitis virus (JEV) and Zika virus (ZIKV) are mosquito-borne viruses of the Flavivirus genus that cause viral encephalitis and congenital microcephaly, respectively, in humans, and thus present a risk to global public health. The envelope glycoprotein (E protein) of flaviviruses is a class II viral fusion protein that mediates host cell entry through a series of conformational changes, including association between the stem region and domain II leading to virion-target cell membrane fusion. In this study, peptides derived from the JEV E protein stem were investigated for their ability to block JEV and ZIKV infection. Peptides from stem helix 2 inhibit JEV infection with the 50% inhibitory concentration (IC₅₀) in the nanomolar range. One of these peptides (P5) protected mice against JEV-induced lethality by decreasing viral load, while abrogating histopathological changes associated with JEV infection. We also found that P5 blocked ZIKV infection with IC₅₀ at the micromolar level. Moreover, P5 was proved to reduce the histopathological damages in brain and testes resulting from ZIKV infection in type I and II interferon receptor-deficient (AG6) mice. These findings provide a basis for the development of peptide-based drugs against JEV and ZIKV.