Characteristics of enterovirus 71-induced cell death and genome scanning to identify viral genes involved in virus-induced cell apoptosis

Metformin inhibits EV71‑induced pyroptosis by upregulating DEP domain‑containing mTOR‑interacting protein

Enterovirus 71 (EV71) infection is one of the main causes of severe hand, foot and mouth disease (HFMD), which is usually accompanied by a marked inflammatory response. The excessive inflammatory response has been implicated to serve an important role in EV71-caused HFMD. Pyroptosis is a type of inflammatory programmed cell death. Therefore, a novel treatment strategy against EV71 infection could aim to alleviate the inflammatory response through inhibition of EV71-induced pyroptosis. The present study revealed that metformin had this therapeutic potential. A cell model of EV71 infection was established, cell viability was measured by CCK8 assay, cell damage was measured by LDH release kit, and the dead and dying cells were excluded by propidium iodide staining. The intracellular levels of DEP domain-containing mTOR interacting protein (DEPTOR) and pyroptosis-associated molecules were measured by western blot analysis, the NLRP3 expression was assessed by immunofluorescence labeling, and virus titers in cell culture supernatants were determined by a cell culture infectious dose 50 assay. The results demonstrated that EV71 infection could induce pyroptosis in a time- and dose-dependent manner, and metformin could inhibit EV71-induced pyroptosis. The mechanism of metformin inhibiting EV71-induced pyroptosis was explored next. Subsequent experiments indicated that metformin could increase the levels of DEPTOR, which were decreased by EV71. Finally, overexpression of DEPTOR in cells could reduce EV71-induced pyroptosis. Overall, the present study demonstrated that metformin could exert a novel pharmacodynamic anti-pyroptosis effect in the treatment of EV71 infection by upregulating DEPTOR expression.

Children with severe enterovirus A71 infection

BACKGROUND

There are few reports on the timing of onset and the symptoms of enterovirus A71 (EV-A71) infection, which can easily be misdiagnosed. This study aimed to explore the clinical characteristics of children with severe EV-A71 infection.

METHODS

This retrospective observational study included children with severe EV-A71 infection admitted to Hebei Children's Hospital between January 2016 and January 2018.

RESULTS

A total of 101 patients were included: 57 males (56.4%) and 44 females (43.6%). They were 1-13 years of age. The symptoms were fever in 94 patients (93.1%), rash in 46 (45.5%), irritability in 70 (69.3%), and lethargy in 56 (55.4%). There were 19 (59.3%) patients with abnormal neurological magnetic resonance imaging [pontine tegmentum (n = 14, 43.8%), medulla oblongata (n = 11, 34.4%), midbrain (n = 9, 28.1%), cerebellum and dentate nucleus (n = 8, 25.0%), basal ganglia (n = 4, 12.5%), cortex (n = 4, 12.5%), spinal cord (n = 3, 9.3%), and meninges (n = 1, 3.1%)]. There was a positive correlation between the ratio of neutrophil count and white blood cell count in cerebrospinal fluid in the first 3 days of the disease (r = 0.415, P < 0.001).

CONCLUSION

The clinical symptoms of EV-A71 infection are fever and/or skin rash, irritability, and lethargy. Some patients have abnormal neurological magnetic resonance imaging. The white blood cell count in the cerebrospinal fluid of children with EV-A71 infection may increase alongside neutrophil counts.

Enterovirus 71 induces pyroptosis of human neuroblastoma SH-SY5Y cells through miR-146a/ CXCR4 axis

Enterovirus 71 (EV71) is a predominant causative pathogen of hand-foot-and-mouth disease (HFMD) in children. Compared with other HFMD-associated viruses, EV71 tends to induce more severe neurological complications and even death. However, the detailed mechanism of EV71 causes nervous system disorder is still unclear. In this study, we found that EV71 induced the GSDMD/NLRP3-mediated pyroptosis of SH-SY5Y cells through up-regulated miR-146a. Through bioinformatic analysis, we identified C-X-C chemokine receptor type 4 (CXCR4) as the potential target of miR-146a. We noticed that the expression of CXCR4 was regulated by miR-146a during EV71 infection. Moreover, our results show that over-expression of CXCR4 attenuated EV71-induced pyroptosis of SY-SY5Y cells. These results reveal a previously unrecognized mechanism in which EV71 induces nervous system cells damage through regulating miR-146a/CXCR4 mediated pyroptosis.

Gasdermin E is required for induction of pyroptosis and severe disease during enterovirus 71 infection

Pyroptosis is an inflammatory form of programmed cell death that is executed by the gasdermin (GSDM)-N domain of GSDM family proteins, which form pores in the plasma membrane. Although pyroptosis acts as a host defense against invasive pathogen infection, its role in the pathogenesis of enterovirus 71 (EV71) infection is unclear. In the current study, we found that EV71 infection induces cleavage of GSDM E (GSDME) by using western blotting analysis, an essential step in the switch from caspase-3-mediated apoptosis to pyroptosis. We show that this cleavage is independent of the 3C and 2A proteases of EV71. However, caspase-3 activation is essential for this cleavage, as GSDME could not be cleaved in caspase-3-KO cells upon EV71 infection. Further analyses showed that EV71 infection induced pyroptosis in WT cells but not in caspase-3/GSDME double-KO cells. Importantly, GSDME is required to induce severe disease during EV71 infection, as GSDME deficiency in mice was shown to alleviate pathological symptoms. In conclusion, our results reveal that GSDME is important for the pathogenesis of EV71 via mediating initiation of pyroptosis.

Novel strategies for the development of hand, foot, and mouth disease vaccines and antiviral therapies

INTRODUCTION

Hand, foot, and mouth disease (HFMD) poses a great threat to young children in the Asia-Pacific region. HFMD is usually caused by enterovirus A, and infection with enterovirus A71 (EV-A71) is particularly associated with severe complications. However, coxsackievirus CV-A16, CV-A6, and CV-A10 pandemics have been observed in recent HFMD outbreaks. Inactivated monovalent EV-A71 vaccines are available to prevent EV-A71 infection; however, they cannot prevent infections by non-EV-A71 enteroviruses. Anti-enteroviral drugs are still in the developmental stage. Application of novel strategies will facilitate the development of new therapies against these emerging HFMD-associated enteroviruses.

AREAS COVERED

The authors highlight the current approaches for anti-enterovirus therapeutic development and discuss the application of these novel strategies for the discovery of vaccines and antiviral drugs for enteroviruses.

EXPERT OPINION

The maturation of DNA/RNA vaccine technology could be applied for rapid and robust development of multivalent enterovirus vaccines. Structure biology and neutralization antibody studies decipher the immunodominant sites of enteroviruses for vaccine design. Nucleotide aptamer library screening is a novel, fast, and cost-effective strategy for the development of antiviral agents. Animal models carrying viral receptors and attachment factors are required for enterovirus study and vaccine/antiviral development. Currently developed antivirals require effectiveness evaluation in clinical trials.

Isolation and Identification of Andrographis paniculata (Chuanxinlian) and Its Biologically Active Constituents Inhibited Enterovirus 71-Induced Cell Apoptosis

Aim:Andrographis paniculata (Burm. f.) Nees (also known as Chuanxinlian in Chinese) of Acanthaceae family is one of the Chinese herbs reputed to be effective in the treatment of inflammation, infection, cold, and fever. Enterovirus 71 (EV71) is one of the most important enteroviruses that cause hand, foot, and mouth disease (HFMD) accompanied with neurological complication.

Methods: To explore an anti-infective Chinese herb medicine, pure compounds isolated or synthesized analogues from A. paniculata (AP) ethyl acetate (EtOAc) extract are used to explore their anti-EV71-induced cytotoxicity. The antiviral activity was determined by cytopathic effect (CPE) reduction, and sub-G1 assays were used for measuring lysis and apoptosis of EV71-infected rhabdomyosarcoma (RD) cells. IFNγ-driven luciferase reporter assay was used to evaluate their potential roles in activation of immune responses.

Results: Our data showed that EV71-induced sub-G1 phase of RD cells was dose dependently increased. Highly apoptotic EV71-infected RD cells were reduced by AP extract treatment. Ergosterol peroxide (4) has the most anti-apoptotic effect among these seven compounds. In addition, 3,19-O-acetyl-14-deoxy-11,12-didehydroandrographolide (8) synthesized from acetylation of compound 7 showed significantly better antiviral activity and the lowest sub-G1 phase of 6%–18%. Further investigation of IFNγ-inducer activity of these compounds showed that compounds 3, 6, 10, 11, and 12 had significantly higher IFNγ luciferase activities, suggesting their potential to promote IFNγ expression and thus activate immune responses for antivirus function.

Conclusion: Our study demonstrated that bioactive compounds of AP and its derivatives either protecting EV71-infected RD cells from sub-G1 arrest or possessing IFNγ-inducer activity might be feasible for the development of anti-EV71 agents.

Construction and characterization of an infectious cDNA clone of enterovirus 71: a rapid method for rescuing infectious virus based on stable cells expressing T7 polymerase

Enterovirus 71 (EV71) is a causative agent of hand, foot and, mouth disease (HFMD) in young children. It is valuable for virologists to develop a fast method to rescue infectious virus from a viral cDNA clone. Here, we report a method for rapid rescue of infectious EV71 by using cells expressing T7 polymerase. The full-length EV71 genome was amplified in one step by long-distance PCR with a T7 promoter at the 5' end, and the T7 polymerase gene was cloned into a lentivirus vector for construction of a stable cell line expressing T7 polymerase. The infectious virus was rapidly and efficiently rescued by single transfection of cells with the infectious cDNA clone. Further experiments showed that the rescued virus had characteristics similar to those of the parental virus. This method circumvented the difficulty in performing in vitro transcription of a long linear DNA to obtain high-quality RNA. The construction of the viral cDNA clone and the fast rescue of the infectious virus will greatly benefit future investigations.

[Enterovirus 71 can induce autophagy and apoptosis of THP-1 macrophages]

OBJECTIVE

To investigate enterovirus 71 (EV71)-induced of autophagy, apoptosis and the related signaling pathways in THP-1 macrophages.

METHODS

THP-1 macrophages were infected with EV71 at the multiplicity of infection (MOI) of 0.1 for 2, 8 or 16 h, and the cell proliferation and toxicity were analyzed using CCK-8 kit. The intracellular viral nucleic acid in THP-1 macrophages were detected by fluorescence quantitative PCR, and the ultrastructural changes of the cells were observed using transmission electron microscopy. Cell apoptosis induced by EV71 infection was detected using Hoechst 33342 staining and AnnexinV/PI double staining. Western blotting was performed for analysis of changes in autophagy and apoptosis of the cells and in the expressions of the related proteins. The effect of EV71 infection on apoptosis of THP-1 macrophages incubated with 3-MA and Ac-DEVD-CHO inhibitor for 2 h was assessed using Western blotting.

RESULTS

EV71 infection significantly lowered the cell survival rate of THP-1 macrophages at 2, 8 h and 16 h after the infection (P &lt; 0.05). The total copy number of viral nucleic acid in THP-1 macrophages incubated with EV71 increased significantly and progressively over time (P &lt; 0.01). Intracellular autophagosomes and virions could be seen in EV71-infected THP-1 macrophages. The total apoptotic rate of the infected cell also increased significantly over time (P &lt; 0.01). EV71 infection significantly increased LC3 conversion (LC3-Ⅱ/ LC3-I) and the expression of cleaved caspase 3 protein and decreased the protein expressions of p62, Bcl-2 and caspase-3 (P &lt; 0.01) without causing obvious changes in cleaved caspase-8 (P&gt;0.05). 3-MA significantly inhibited the EV71-induced autophagy of THP-1 macrophages and reduced LC3 conversion (LC3-Ⅱ/LC3-I) and p62 protein expression at 8 h after EV71 infection (P &lt; 0.01). Compared with DMSO, Ac-DEVD-CHO significantly inhibited EV71-induced apoptosis of THP-1 macrophages (15.5% vs 7.7%, P &lt; 0.01).

CONCLUSIONS

EV71 not only can infect and replicate in THP-1 macrophages, but also induces autophagy and cell apoptosis possibly by activating LC3/p62 autophagy pathway and caspase apoptosis pathway.

Molecular Pathogenicity of Enteroviruses Causing Neurological Disease

Enteroviruses are single-stranded positive-sense RNA viruses that primarily cause self-limiting gastrointestinal or respiratory illness. In some cases, these viruses can invade the central nervous system, causing life-threatening neurological diseases including encephalitis, meningitis and acute flaccid paralysis (AFP). As we near the global eradication of poliovirus, formerly the major cause of AFP, the number of AFP cases have not diminished implying a non-poliovirus etiology. As the number of enteroviruses linked with neurological disease is expanding, of which many had previously little clinical significance, these viruses are becoming increasingly important to public health. Our current understanding of these non-polio enteroviruses is limited, especially with regards to their neurovirulence. Elucidating the molecular pathogenesis of these viruses is paramount for the development of effective therapeutic strategies. This review summarizes the clinical diseases associated with neurotropic enteroviruses and discusses recent advances in the understanding of viral invasion of the central nervous system, cell tropism and molecular pathogenesis as it correlates with host responses.

Host relieves lnc-IRAK3-3-sequestered miR-891b to attenuate apoptosis in Enterovirus 71 infection

Enterovirus 71 (EV71) is an emerging life-threatening pathogen particularly in the Asia-Pacific region. Apoptosis is a major pathogenic feature in EV71 infection. However, which molecular mechanism participating in EV71-induced apoptosis is not completely understood. Long noncoding RNAs (lncRNAs), a newly discovered class of regulatory RNA molecules, govern a wide range of biological functions through multiple regulatory mechanisms. Whether lncRNAs involved in EV71-induced apoptosis was investigated in this study. We conducted an apoptosis-oriented approach by integrating lncRNA and mRNA profilings. lnc-IRAK3-3 is down-regulated in EV71 infection and plays an important role in EV71 infection-induced apoptosis. Compensation of lnc-IRAK3-3 in EV71 infection promoted cell apoptosis wherein GADD45β expression was increased and further triggered caspase3 and PARP cleavage. Using bioinformatics analysis and functional assays, lnc-IRAK3-3 could functionally sequester miR-891b and GADD45β 3'UTR whereas miR-891b showed the inhibitory activity on GADD45β expression. Taken together, lnc-IRAK3-3 has the ability capturing miR-891b to enforce GADD45β expression and eventually promotes apoptosis. On the contrary, host cells suppress lnc-IRAK3-3 to relieve lnc-IRAK3-3-sequestered miR-891b, restrain GADD45β, and attenuate apoptosis in EV71 infection that prevent host cells from severe damages. We discover a new molecular mechanism by which host cells counteract EV71-induced apoptosis through the lnc-IRAK3-3/miR-891b/GADD45β axis partially.