SREBP2-dependent lipid gene transcription enhances the infection of human dendritic cells by Zika virus

The emergence of Zika virus (ZIKV) as a global health threat has highlighted the unmet need for ZIKV-specific vaccines and antiviral treatments. ZIKV infects dendritic cells (DC), which have pivotal functions in activating innate and adaptive antiviral responses; however, the mechanisms by which DC function is subverted to establish ZIKV infection are unclear. Here we develop a genomics profiling method that enables discrete analysis of ZIKV-infected versus neighboring, uninfected primary human DCs to increase the sensitivity and specificity with which ZIKV-modulated pathways can be identified. The results show that ZIKV infection specifically increases the expression of genes enriched for lipid metabolism-related functions. ZIKV infection also increases the recruitment of sterol regulatory element-binding protein (SREBP) transcription factors to lipid gene promoters, while pharmacologic inhibition or genetic silencing of SREBP2 suppresses ZIKV infection of DCs. Our data thus identify SREBP2-activated transcription as a mechanism for promoting ZIKV infection amenable to therapeutic targeting.

The Ability of Zika virus Intravenous Immunoglobulin to Protect From or Enhance Zika Virus Disease

The closely related flaviviruses, dengue and Zika, cause significant human disease throughout the world. While cross-reactive antibodies have been demonstrated to have the capacity to potentiate disease or mediate protection during flavivirus infection, the mechanisms responsible for this dichotomy are still poorly understood. To understand how the human polyclonal antibody response can protect against, and potentiate the disease in the context of dengue and Zika virus infection we used intravenous hyperimmunoglobulin (IVIG) preparations in a mouse model of the disease. Three IVIGs (ZIKV-IG, Control-Ig and Gamunex®) were evaluated for their ability to neutralize and/or enhance Zika, dengue 2 and 3 viruses in vitro. The balance between virus neutralization and enhancement provided by the in vitro neutralization data was used to predict the IVIG concentrations which could protect or enhance Zika, and dengue 2 disease in vivo. Using this approach, we were able to define the unique in vivo dynamics of complex polyclonal antibodies, allowing for both enhancement and protection from flavivirus infection. Our results provide a novel understanding of how polyclonal antibodies interact with viruses with implications for the use of polyclonal antibody therapeutics and the development and evaluation of the next generation flavivirus vaccines.

Human FcRn expression and Type I Interferon signaling control Echovirus 11 pathogenesis in mice

Neonatal echovirus infections are characterized by severe hepatitis and neurological complications that can be fatal. Here, we show that expression of the human homologue of the neonatal Fc receptor (hFcRn), the primary receptor for echoviruses, and ablation of type I interferon (IFN) signaling are key host determinants involved in echovirus pathogenesis. We show that expression of hFcRn alone is insufficient to confer susceptibility to echovirus infections in mice. However, expression of hFcRn in mice deficient in type I interferon (IFN) signaling, hFcRn-IFNAR-/-, recapitulate the echovirus pathogenesis observed in humans. Luminex-based multianalyte profiling from E11 infected hFcRn-IFNAR-/- mice revealed a robust systemic immune response to infection, including the induction of type I IFNs. Furthermore, similar to the severe hepatitis observed in humans, E11 infection in hFcRn-IFNAR-/- mice caused profound liver damage. Our findings define the host factors involved in echovirus pathogenesis and establish in vivo models that recapitulate echovirus disease in humans.

CD8+ T cells mediate protection against Zika virus induced by an NS3-based vaccine

Zika virus (ZIKV) is associated with congenital malformations in infants born to infected mothers, and with Guillain-Barré syndrome in infected adults. Development of ZIKV vaccines has focused predominantly on the induction of neutralizing antibodies, although a suboptimal antibody response may theoretically enhance disease severity through antibody-dependent enhancement (ADE). Here, we report induction of a protective anti-ZIKV CD8+ T cell response in the HLA-B*0702 Ifnar1-/- transgenic mice using an alphavirus-based replicon RNA vaccine expressing ZIKV nonstructural protein NS3, a potent T cell antigen. The NS3 vaccine did not induce a neutralizing antibody response but elicited polyfunctional CD8+ T cells that were necessary and sufficient for preventing death in lethally infected adult mice and fetal growth restriction in infected pregnant mice. These data identify CD8+ T cells as the major mediators of ZIKV NS3 vaccine-induced protection and suggest a new strategy to develop safe and effective anti-flavivirus vaccines.

CD8+ T cells mediate an NS3-based vaccine protection against Zika virus

Zika virus (ZIKV), a member of the flaviviridae family, is associated with severe congenital malformations in infants born to infected mothers, and with neurological disorders, such as Guillain–Barré syndrome, in infected adults. To date, the development of anti-flavivirus vaccines has focused predominantly on the induction of neutralizing antibodies. Paradoxically, a suboptimal antibody response may enhance disease severity upon subsequent flaviviral infection through a phenomenon known as antibody-dependent enhancement. Thus, alternative approaches to ZIKV vaccine design are necessary. Here, we report induction of a protective anti-ZIKV CD8+ T cell response in the HLA-B*0702 Ifnar1−/− transgenic mouse model using an alphavirus-based replicon RNA vaccine expressing ZIKV nonstructural protein NS3, a potent T cell antigen. The NS3 vaccine did not induce an antibody response, but elicited polyfunctional CD8+ T cells that were necessary and sufficient for controlling viral burden and preventing death in lethally infected adult mice. In addition, the NS3 vaccine prevented fetal growth restriction and death in infected pregnant mice. These data identify CD8+ T cells as the major mediators of the ZIKV NS3 vaccine-induced protection and suggest a new strategy to develop safe and effective anti-flavivirus vaccines that avoid inadvertent antibody-dependent enhancement.

Zika virus suppresses maturation of human dendritic cells

Zika virus (ZIKV) belongs to the genus Flavivirus, which includes several medically relevant viruses, including dengue, yellow fever and Japanese encephalitis viruses. ZIKV causes congenital Zika syndrome in neonates and Guillain-Barré syndrome in adults, and has emerged as a major public health problem worldwide. Dendritic cells (DCs) serve as the major cellular hosts of ZIKV, and T cell responses to flaviviruses may play a dual role in protection and pathogenesis. To decipher the precise interactions between DCs and ZIKV, we profiled the transcriptomic features of ZIKV-infected DCs versus uninfected bystander DCs in primary human blood monocyte-derived DC cultures. RNA sequencing data revealed that the expression of genes related to antigen processing/presentation pathways was reduced in ZIKV-infected DCs relative to uninfected bystander DCs that were exposed to the same environmental stimuli as ZIKV-infected DCs. Flow cytometric analysis of ZIKV-infected DCs for the expression of key DC maturation markers confirmed the RNA sequencing data. Thus, ZIKV hinders DC maturation, suggesting that ZIKV may modulate T cell responses by directly manipulating DC functions. Studies are in progress to determine how ZIKV inhibits DC maturation and influences T cell responses. Results of these studies will provide key insights towards the development of safe and effective vaccines against ZIKV and related flaviviruses.

Human Polyclonal Antibodies Prevent Lethal Zika Virus Infection in Mice

Zika virus (ZIKV) is an emerging mosquito-borne flavivirus that represents a major threat to global health. ZIKV infections in adults are generally asymptomatic or present with mild symptoms. However, recent outbreaks of ZIKV have revealed that it can cause Congenital Zika Syndrome in neonates and Guillain-Barré syndrome in adults. Currently, no ZIKV-specific vaccines or antiviral treatments are available. In this study, we tested the efficacy of convalescent plasma IgG hyperimmune product (ZIKV-IG) isolated from individuals with high neutralizing anti-ZIKV titers as a therapeutic candidate against ZIKV infection using a model of ZIKV infection in Ifnar1^-/- mice. ZIKV-IG successfully protected mice from lethal ZIKV challenge. In particular, ZIKV-IG treatment at 24 hours after lethal ZIKV infection improved survival by reducing weight loss and tissue viral burden and improving clinical score. Additionally, ZIKV-IG eliminated ZIKV-induced tissue damage and inflammation in the brain and liver. These results indicate that ZIKV-IG is efficacious against ZIKV, suggesting this human polyclonal antibody is a viable candidate for further development as a treatment against human ZIKV infection.

Synergism between the tyrosine kinase inhibitor sunitinib and Anti-TNF antibody protects against lethal dengue infection

Dengue virus (DENV) currently circulates in more than 100 countries and causes an estimated 390 million infections per year. While most cases manifest as a self-resolving fever, ∼1.5% of infections develop into a more severe dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS), which causes ∼20,000 deaths annually. The underlying pathological feature of DHF/DSS, also known as Severe Dengue, is an acute increase in vascular permeability leading to hypovolemia and shock. Angiogenic factors and cytokines, such as vascular endothelial growth factor (VEGF) and tumor necrosis factor (TNF), have been implicated in the increased vascular permeability, suggesting a potential therapeutic strategy for Severe Dengue. Here, we employed a mouse model of antibody-dependent enhancement of DENV infection, which recapitulates the fatal capillary leakage and shock of human Severe Dengue, to investigate the effects of approved VEGF- and TNF-targeting drugs. DENV infection caused a significant increase in serum VEGF levels within 2 days and resulted in ∼80% mortality within 8 days of infection. Treatment of mice with sunitinib, a VEGF receptor tyrosine kinase inhibitor, once (day 2) or twice (days 1 and 2) post-infection reduced mortality by 50-80% compared with untreated mice. Notably, sunitinib treatment decreased serum TNF levels, white blood cell counts, and hematocrit levels relative to untreated mice, but had only marginal effects on tissue viral burden. Combination therapy with anti-TNF antibody and sunitinib significantly reduced vascular leakage and synergized to provide superior protection from lethal DENV infection compared with either agent alone. These data suggest that a two-pronged anti-angiogenic and anti-inflammatory approach may be useful for the rapid treatment of DHF/DSS.

Hepatitis C Virus Increases Occludin Expression via the Upregulation of Adipose Differentiation-Related Protein

The hepatitis C virus (HCV) life cycle is closely associated with lipid metabolism. In particular, HCV assembly initiates at the surface of lipid droplets. To further understand the role of lipid droplets in HCV life cycle, we assessed the relationship between HCV and the adipose differentiation-related protein (ADRP), a lipid droplet-associated protein. Different steps of HCV life cycle were assessed in HCV-infected human Huh-7 hepatoma cells overexpressing ADRP upon transduction with a lentiviral vector. HCV infection increased ADRP mRNA and protein expression levels by 2- and 1.5-fold, respectively. The overexpression of ADRP led to an increase of (i) the surface of lipid droplets, (ii) the total cellular neutral lipid content (2.5- and 5-fold increase of triglycerides and cholesterol esters, respectively), (iii) the cellular free cholesterol level (5-fold) and (iv) the HCV particle production and infectivity (by 2- and 3.5-fold, respectively). The investigation of different steps of the HCV life cycle indicated that the ADRP overexpression, while not affecting the viral replication, promoted both virion egress and entry (~12-fold), the latter possibly via an increase of its receptor occludin. Moreover, HCV infection induces an increase of both ADRP and occludin expression. In HCV infected cells, the occludin upregulation was fully prevented by the ADRP silencing, suggesting a specific, ADRP-dependent mechanism. Finally, in HCV-infected human livers, occludin and ADRP mRNA expression levels correlated with each other. Alltogether, these findings show that HCV induces ADRP, which in turns appears to confer a favorable environment to viral spread.

HCV 3a core protein increases lipid droplet cholesteryl ester content via a mechanism dependent on sphingolipid biosynthesis

Hepatitis C virus (HCV) infected patients often develop steatosis and the HCV core protein alone can induce this phenomenon. To gain new insights into the pathways leading to steatosis, we performed lipidomic profiling of HCV core protein expressing-Huh-7 cells and also assessed the lipid profile of purified lipid droplets isolated from HCV 3a core expressing cells. Cholesteryl esters, ceramides and glycosylceramides, but not triglycerides, increased specifically in cells expressing the steatogenic HCV 3a core protein. Accordingly, inhibitors of cholesteryl ester biosynthesis such as statins and acyl-CoA cholesterol acyl transferase inhibitors prevented the increase of cholesteryl ester production and the formation of large lipid droplets in HCV core 3a-expressing cells. Furthermore, inhibition of de novo sphingolipid biosynthesis by myriocin - but not of glycosphingolipid biosynthesis by miglustat - affected both lipid droplet size and cholesteryl ester level. The lipid profile of purified lipid droplets, isolated from HCV 3a core-expressing cells, confirmed the particular increase of cholesteryl ester. Thus, both sphingolipid and cholesteryl ester biosynthesis are affected by the steatogenic core protein of HCV genotype 3a. These results may explain the peculiar lipid profile of HCV-infected patients with steatosis.

PTEN protein phosphatase activity regulates hepatitis C virus secretion through modulation of cholesterol metabolism

BACKGROUND & AIMS

Hepatitis C virus (HCV) infection is dependent on lipid metabolism. Hepatocyte steatosis occurs frequently in HCV infection, but the relationship between steatosis and HCV life cycle is unclear. We showed that HCV induces steatosis via the downregulation of the phosphatase and tensin homolog deleted on chromosome 10 (PTEN). We here investigated how PTEN may affect HCV production.

METHODS

The effect of overexpression or silencing of PTEN on HCV secretion was assessed in genomic-length Jc1 infected HuH7 cells. The role of PTEN protein and lipid phosphatase activities on lipid metabolism and infectious viral particle secretion was investigated using dominant-negative PTEN mutants. The importance of cholesterol metabolism for PTEN-dependent lipid droplet biogenesis and viral particle secretion was examined using statins.

RESULTS

PTEN silencing in Jc1 infected HuH7 cells stimulated HCV particle secretion, while PTEN overexpression decreased virus egress. Viral secretion was also increased by overexpression of protein phosphatase-deleted (PTENY138L), but not lipid phosphatase-deleted (PTENG129E), PTEN mutant, thus indicating that the protein phosphatase activity of PTEN controls viral secretion. Similarly, PTENY138L, but not PTENG129E mutant induced the formation of large lipid droplets. PTENY138L mutant did not affect biosynthesis of triglycerides, but promoted the biosynthesis of cholesterol esters. Consistently, statins prevented the increased cholesterol ester production, large lipid droplet formation, and viral secretion in cells expressing the PTENY138L mutant.

CONCLUSIONS

Downregulation of PTEN protein phosphatase activity by HCV affects cholesterol metabolism, thereby inducing the appearance of large lipid droplets and increasing virion egress.

Role of seipin in lipid droplet morphology and hepatitis C virus life cycle

Infectious hepatitis C virus (HCV) particle assembly starts at the surface of lipid droplets, cytoplasmic organelles responsible for neutral fat storage. We analysed the relationship between HCV and seipin, a protein involved in lipid droplet maturation. Although seipin overexpression did not affect the total mean volume occupied by lipid droplets nor the total triglyceride and cholesterol ester levels per cell, it caused an increase in the mean diameter of lipid droplets by 60 %, while decreasing their total number per cell. The latter two effects combined resulted in a 34 % reduction of the total outer surface area of lipid droplets per cell, with a proportional decrease in infectious viral particle production, probably due to a defect in particle assembly. These results suggest that the available outer surface of lipid droplets is a critical factor for HCV release, independent of the neutral lipid content of the cell.