EV71 is a positive-sense single-stranded RNA virus that belongs to the Picornaviridae family. EV71 infection may cause various symptoms ranging from hand-foot-and-mouth disease to neurological pathological conditions such as aseptic meningitis, ataxia, and acute transverse myelitis. There is currently no effective treatment or vaccine available. Various compounds have been examined for their ability to restrict EV71 replication. However, most experiments have been performed in rhabdomyosarcoma or Vero cells. Since the gastrointestinal tract is the entry site for this pathogen, we anticipated that orally ingested agents may exert beneficial effects by decreasing virus replication in intestinal epithelial cells. In this study, curcumin (diferuloylmethane, C21H20O6), an active ingredient of turmeric (Curcuma longa Linn) with anti-cancer properties, was investigated for its anti-enterovirus activity. We demonstrate that curcumin treatment inhibits viral translation and increases host cell viability. Curcumin does not exert its anti-EV71 effects by modulating virus attachment or virus internal ribosome entry site (IRES) activity. Furthermore, curcumin-mediated regulation of mitogen-activated protein kinase (MAPK) signaling pathways is not involved. We found that protein kinase C delta (PKCδ) plays a role in virus translation in EV71-infected intestinal epithelial cells and that curcumin treatment decreases the phosphorylation of this enzyme. In addition, we show evidence that curcumin also limits viral translation in differentiated human intestinal epithelial cells. In summary, our data demonstrate the anti-EV71 properties of curcumin, suggesting that ingestion of this phytochemical may protect against enteroviral infections.

Abstract Background Enterovirus A71 (EV-A71) has been noted for its tendency to lead to neurological manifestations in young children and infants. Although the alimentary tract has been identified as the primary replication site of this virus, how EV-A71 replicates in the gut and is transmitted to other organs remains unclear. Methods By using differentiated C2BBe1 cells as a model, we observed that intestinal epithelial cells (IECs) were permissive to EV-A71 infection, and viral particles were released in a nonlytic manner. Results The coexistence of active caspase 3 and EV-A71 protein was observed in the infected undifferentiated C2BBe1 and RD cells but not in the infected differentiated C2BBe1 cells. Furthermore, EV-A71 infection caused differentiated C2BBe1 and intestinal organoids to secrete exosomes containing viral components and have the ability to establish active infection. Inhibition of the exosome pathway decreased EV-A71 replication and release in IECs and increased the survival rates of infected animals. Conclusions Our findings showed that EV-A71 is able to be actively replicated in enterocytes, and that the exosome pathway is involved in the nonlytic release of viral particles, which may be useful for developing antiviral strategies.

Neural progenitor cells (NPCs) are stem cells that can differentiate into various neural lineage cells. The damage and loss of NPCs are associated with neurological conditions such as cognitive deficits and memory impairment. In a long-term study of patients with EV71, cognitive disorders were observed. Therefore, we hypothesized that NPCs may be permissive to EV71 infection. We demonstrated that NPCs are prone to EV71 infection and that these stem cells can support the active replication of this virus. Furthermore, EV71 infection triggers apoptosis, resulting in significant cell death in infected NPCs. However, EV71 did not replicate in the differentiated cell types that were tested. Our findings suggest that EV71 can infect NPCs and cause the depletion of these cells.

BackgroundNeural stem cells (NSCs) residing in the central nervous system play an important role in neurogenesis. Several viruses can infect these neural progenitors and cause severe neurological diseases. The innate immune responses against the neurotropic viruses in these tissue-specific stem cells remain unclear.MethodsHuman NSCs were transfected with viral RNA mimics or infected with neurotropic virus for detecting the expression of antiviral interferons (IFNs) and downstream IFN-stimulated antiviral genes.ResultsNSCs are able to produce interferon-β (IFN-β) (type I) and λ1 (type III) after transfection with poly(I:C) and that downstream IFN-stimulated antiviral genes, such as ISG56 and MxA, and the viral RNA sensors RIG-I, MDA5, and TLR3, can be expressed in NSCs under poly(I:C) or IFN-β stimulation. In addition, our results show that the pattern recognition receptors RIG-I and MDA5, as well as the endosomal pathogen recognition receptor TLR3, but not TLR7 and TLR8, are involved in the activation of IFN-β transcription in NSCs. Furthermore, NSCs infected with the neurotropic viruses, Zika and Japanese encephalitis viruses, are able to induce RIG-I-mediated IFN-β expression.ConclusionHuman NSCs have the ability to activate IFN signals against neurotropic viral pathogens.

Enterovirus 71 (EV71) can invade the central nervous system (CNS) and cause neurological disease. Accumulating evidence indicates that EV71 can directly infect neurons in the CNS. Innate immune responses in the CNS have been known to play an essential role in limiting pathogen infections. Thus, investigating the effects of EV71 infection of neural cells is important for understanding disease pathogenesis. In this study, human neural cells were infected with EV71, and interferonβ (IFNβ) expression was examined. Our results show that IFNβ expression was upregulated in EV71-infected neural cells via pattern recognition receptors (PRRs) sensing of virus RNA. The PRRs Toll-like receptor 3 (TLR3), Toll-like receptor 8 (TLR8), and melanoma differentiation-associated gene-5 (MDA-5), but not retinoic acid-inducible gene-I (RIG-I) and Toll-like receptor 7 (TLR7), were found to be EV71-mediated IFNβ induction. Although viral proteins exhibited the ability to cleave mitochondrial antiviral signaling protein (MAVS) and Toll/IL-1 receptor (TIR) domain-containing adaptor-inducing IFN-β (TRIF) in neural cells, levels of viral protein expression were low in these cells. Furthermore, neural cells efficiently produced IFNβ transcripts upon EV71 vRNA stimulation. Treating infected cells with anti-IFNβ antibodies resulted in increased virus replication, indicating that IFNβ release may play a role in limiting viral growth. These results indicate that EV71 infection can induce IFNβ expression in neural cells through PRR pathways.