Negative regulation of type I interferon signaling by integrin-linked kinase permits dengue virus replication.

Dengue virus (DENV) infection can induce life-threatening dengue hemorrhagic fever/dengue shock syndrome in infected patients. DENV is a threat to global health due to its growing numbers and incidence of infection in the last 50 years. During infection, DENV expresses ten structural and nonstructural proteins modulating cell responses to benefit viral replication. However, the lack of knowledge regarding the cellular proteins and their functions in enhancing DENV pathogenesis impedes the development of antiviral drugs and therapies against fatal DENV infection. Here, we identified that integrin-linked kinase (ILK) is a novel enhancing factor for DENV infection by suppressing type I interferon (IFN) responses. Mechanistically, ILK binds DENV NS1 and NS3, activates Akt and Erk, and induces NF-κB-driven suppressor of cytokine signaling 3 (SOCS3) expression. Elevated SOCS3 in DENV-infected cells inhibits phosphorylation of STAT1/2 and expression of interferon-stimulated genes (ISGs). Inhibiting ILK, Akt, or Erk activation abrogates SOCS3 expression. In DENV-infected mice, the treatment of an ILK inhibitor significantly reduces viral loads in the brains, disease severity, and mortality rate. Collectively, our results show that ILK is a potential therapeutic target against DENV infection.

Suppression of annexin A1 and its receptor reduces herpes simplex virus 1 lethality in mice.

Herpes simplex virus 1 (HSV-1)-induced encephalitis is the most common cause of sporadic, fatal encephalitis in humans. HSV-1 has at least 10 different envelope glycoproteins, which can promote virus infection. The ligands for most of the envelope glycoproteins and the significance of these ligands in virus-induced encephalitis remain elusive. Here, we show that glycoprotein E (gE) binds to the cellular protein, annexin A1 (Anx-A1) to enhance infection. Anx-A1 can be detected on the surface of cells permissive for HSV-1 before infection and on virions. Suppression of Anx-A1 or its receptor, formyl peptide receptor 2 (FPR2), on the cell surface and gE or Anx-A1 on HSV-1 envelopes reduced virus binding to cells. Importantly, Anx-A1 knockout, Anx-A1 knockdown, or treatments with the FPR2 antagonist reduced the mortality and tissue viral loads of infected mice. Our results show that Anx-A1 is a novel enhancing factor of HSV-1 infection. Anx-A1-deficient mice displayed no evident physiology and behavior changes. Hence, targeting Anx-A1 and FPR2 could be a promising prophylaxis or adjuvant therapy to decrease HSV-1 lethality.

Absence of the lectin-like domain of thrombomodulin reduces HSV-1 lethality of mice with increased microglia responses.

BACKGROUND: Herpes simplex virus 1 (HSV-1) can induce fatal encephalitis. Cellular factors regulate the host immunity to affect the severity of HSV-1 encephalitis. Recent reports focus on the significance of thrombomodulin (TM), especially the domain 1, lectin-like domain (TM-LeD), which modulates the immune responses to bacterial infections and toxins and various diseases in murine models. Few studies have investigated the importance of TM-LeD in viral infections, which are also regulated by the host immunity. METHODS: In vivo studies comparing wild-type and TM-LeD knockout mice were performed to determine the role of TM-LeD on HSV-1 lethality. In vitro studies using brain microglia cultured from mice or a human microglia cell line to investigate whether and how TM-LeD affects microglia to reduce HSV-1 replication in brain neurons cultured from mice or in a human neuronal cell line. RESULTS: Absence of TM-LeD decreased the mortality, tissue viral loads, and brain neuron apoptosis of HSV-1-infected mice with increases in the number, proliferation, and phagocytic activity of brain microglia. Moreover, TM-LeD deficiency enhanced the phagocytic activity of brain microglia cultured from mice or of a human microglia cell line. Co-culture of mouse primary brain microglia and neurons or human microglia and neuronal cell lines revealed that TM-LeD deficiency augmented the capacity of microglia to reduce HSV-1 replication in neurons. CONCLUSIONS: Overall, TM-LeD suppresses microglia responses to enhance HSV-1 infection.

Doxycycline Ameliorates the Severity of Experimental Proliferative Vitreoretinopathy in Mice.

After successful surgeries for patients with rhegmatogenous retinal detachment, the most common cause of retinal redetachment is proliferative vitreoretinopathy (PVR), which causes severe vision impairment and even blindness worldwide. Until now, the major treatment for PVR is surgical removal of the epiretinal membrane, while effective treatment to prevent PVR is still unavailable. Therefore, we investigated the potential of doxycycline, an antibiotic in the tetracycline class, to treat PVR using a mouse model. We used the human retinal pigment epithelial cell line, ARPE-19, for in vitro and in vivo studies to test doxycycline for PVR treatment. We found that doxycycline suppressed the migration, proliferation, and contraction of ARPE-19 cells with reduced p38 MAPK activation and total MMP activity. Intravitreal doxycycline and topical tetracycline treatment significantly ameliorated the PVR severity induced by ARPE-19 cells in mice. PVR increased the expression of MMP-9 and IL-4 and p38 MAPK phosphorylation and modestly decreased IL-10. These effects were reversed by doxycycline and tetracycline treatment in the mouse retina. These results suggest that doxycycline will be a potential treatment for PVR in the future.

Microglia Reduce Herpes Simplex Virus 1 Lethality of Mice with Decreased T Cell and Interferon Responses in Brains.

Herpes simplex virus 1 (HSV-1) infects the majority of the human population and can induce encephalitis, which is the most common cause of sporadic, fatal encephalitis. An increase of microglia is detected in the brains of encephalitis patients. The issues regarding whether and how microglia protect the host and neurons from HSV-1 infection remain elusive. Using a murine infection model, we showed that HSV-1 infection on corneas increased the number of microglia to outnumber those of infiltrating leukocytes (macrophages, neutrophils, and T cells) and enhanced microglia activation in brains. HSV-1 antigens were detected in brain neurons, which were surrounded by microglia. Microglia depletion increased HSV-1 lethality of mice with elevated brain levels of viral loads, infected neurons, neuron loss, CD4 T cells, CD8 T cells, neutrophils, interferon (IFN)-ß, and IFN-γ. In vitro studies demonstrated that microglia from infected mice reduced virus infectivity. Moreover, microglia induced IFN-ß and the signaling pathway of signal transducer and activator of transcription (STAT) 1 to inhibit viral replication and damage of neurons. Our study reveals how microglia protect the host and neurons from HSV-1 infection.

Thymidine Kinase-Negative Herpes Simplex Virus 1 Can Efficiently Establish Persistent Infection in Neural Tissues of Nude Mice.

Herpes simplex virus 1 (HSV-1) establishes latency in neural tissues of immunocompetent mice but persists in both peripheral and neural tissues of lymphocyte-deficient mice. Thymidine kinase (TK) is believed to be essential for HSV-1 to persist in neural tissues of immunocompromised mice, because infectious virus of a mutant with defects in both TK and UL24 is detected only in peripheral tissues, but not in neural tissues, of severe combined immunodeficiency mice (T. Valyi-Nagy, R. M. Gesser, B. Raengsakulrach, S. L. Deshmane, B. P. Randazzo, A. J. Dillner, and N. W. Fraser, Virology 199:484-490, 1994, https://doi.org/10.1006/viro.1994.1150). Here we find infiltration of CD4 and CD8 T cells in peripheral and neural tissues of mice infected with a TK-negative mutant. We therefore investigated the significance of viral TK and host T cells for HSV-1 to persist in neural tissues using three genetically engineered mutants with defects in only TK or in both TK and UL24 and two strains of nude mice. Surprisingly, all three mutants establish persistent infection in up to 100% of brain stems and 93% of trigeminal ganglia of adult nude mice at 28 days postinfection, as measured by the recovery of infectious virus. Thus, in mouse neural tissues, host T cells block persistent HSV-1 infection, and viral TK is dispensable for the virus to establish persistent infection. Furthermore, we found 30- to 200-fold more virus in neural tissues than in the eye and detected glycoprotein C, a true late viral antigen, in brainstem neurons of nude mice persistently infected with the TK-negative mutant, suggesting that adult mouse neurons can support the replication of TK-negative HSV-1. IMPORTANCE: Acyclovir is used to treat herpes simplex virus 1 (HSV-1)-infected immunocompromised patients, but treatment is hindered by the emergence of drug-resistant viruses, mostly those with mutations in viral thymidine kinase (TK), which activates acyclovir. TK mutants are detected in brains of immunocompromised patients with persistent infection. However, answers to the questions as to whether TK-negative (TK-) HSV-1 can establish persistent infection in brains of immunocompromised hosts and whether neurons in vivo are permissive for TK- HSV-1 remain elusive. Using three genetically engineered HSV-1 TK- mutants and two strains of nude mice deficient in T cells, we found that all three HSV-1 TK- mutants can efficiently establish persistent infection in the brain stem and trigeminal ganglion and detected glycoprotein C, a true late viral antigen, in brainstem neurons. Our study provides evidence that TK- HSV-1 can persist in neural tissues and replicate in brain neurons of immunocompromised hosts.

Suppression of interleukin-6 increases enterovirus A71 lethality in mice.

BACKGROUND: Enterovirus A71 (EV-A71) infection can induce fatal encephalitis in young children. Clinical reports show that interleukin-6 (IL-6) levels in the serum and cerebrospinal fluid of infected patients with brainstem encephalitis are significantly elevated. We used a murine model to address the significance of endogenous IL-6 in EV-A71 infection. RESULTS: EV-A71 infection transiently increased serum and brain IL-6 protein levels in mice. Most importantly, absence of IL-6 due to gene knockout or depletion of IL-6 using neutralizing monoclonal antibody enhanced the mortality and tissue viral load of infected mice. Absence of IL-6 increased the damage in the central nervous system and decreased the lymphocyte and virus-specific antibody responses of infected mice. CONCLUSIONS: Endogenous IL-6 functions to clear virus and protect the host from EV-A71 infection. Our study raises caution over the use of anti-IL-6 antibody or pentoxifylline to reduce IL-6 for patient treatment.

Enterovirus 71 Proteins 2A and 3D Antagonize the Antiviral Activity of Gamma Interferon via Signaling Attenuation.

UNLABELLED: Enterovirus 71 (EV71) infection causes severe mortality involving multiple possible mechanisms, including cytokine storm, brain stem encephalitis, and fulminant pulmonary edema. Gamma interferon (IFN-γ) may confer anti-EV71 activity; however, the claim that disease severity is highly correlated to an increase in IFN-γ is controversial and would indicate an immune escape initiated by EV71. This study, investigating the role of IFN-γ in EV71 infection using a murine model, showed that IFN-γ was elevated. Moreover, IFN-γ receptor-deficient mice showed higher mortality rates and more severe disease progression with slower viral clearance than wild-type mice. In vitro results showed that IFN-γ pretreatment reduced EV71 yield, whereas EV71 infection caused IFN-γ resistance with attenuated IFN-γ signaling in IFN regulatory factor 1 (IRF1) gene transactivation. To study the immunoediting ability of EV71 proteins in IFN-γ signaling, 11 viral proteins were stably expressed in cells without cytotoxicity; however, viral proteins 2A and 3D blocked IFN-γ-induced IRF1 transactivation following a loss of signal transducer and activator of transcription 1 (STAT1) nuclear translocation. Viral 3D attenuated IFN-γ signaling accompanied by a STAT1 decrease without interfering with IFN-γ receptor expression. Restoration of STAT1 or blocking 3D activity was able to rescue IFN-γ signaling. Interestingly, viral 2A attenuated IFN-γ signaling using another mechanism by reducing the serine phosphorylation of STAT1 following the inactivation of extracellular signal-regulated kinase without affecting STAT1 expression. These results demonstrate the anti-EV71 ability of IFN-γ and the immunoediting ability by EV71 2A and 3D, which attenuate IFN-γ signaling through different mechanisms. IMPORTANCE: Immunosurveillance by gamma interferon (IFN-γ) may confer anti-enterovirus 71 (anti-EV71) activity; however, the claim that disease severity is highly correlated to an increase in IFN-γ is controversial and would indicate an immune escape initiated by EV71. IFN-γ receptor-deficient mice showed higher mortality and more severe disease progression, indicating the anti-EV71 property of IFN-γ. However, EV71 infection caused cellular insusceptibility in response to IFN-γ stimulation. We used an in vitro system with viral protein expression to explore the novel IFN-γ inhibitory properties of the EV71 2A and 3D proteins through the different mechanisms. According to this study, targeting either 2A or 3D pharmacologically and/or genetically may sustain a cellular susceptibility in response to IFN-γ, particularly for IFN-γ-mediated anti-EV71 activity.

Miltefosine reduces coxsackievirus B3 lethality of mice with enhanced STAT3 activation.

Coxsackievirus B3 (CVB3), one serotype of enteroviruses, can induce fatal myocarditis and hepatitis in neonates, but both treatment and vaccine are unavailable. Few reports tested antivirals to reduce CVB3. Several antivirals were developed against other enterovirus serotypes, but these antivirals failed in clinical trials due to side effects and drug resistance. Repurposing of clinical drugs targeting cellular factors, which enhance viral replication, may be another option. Parasite and cancer studies showed that the cellular protein kinase B (Akt) decreases interferon (IFN), apoptosis, and interleukin (IL)-6-induced STAT3 responses, which suppress CVB3 replication. Furthermore, miltefosine, the Akt inhibitor used in the clinic for parasite infections, enhances IL-6, IFN, and apoptosis responses in treated patients, suggesting that miltefosine could be the potential antiviral for CVB3. This study was therefore designated to test the antiviral effects of miltefosine against CVB3 in vitro and especially, in mice, as few studies test miltefosine in vitro, but not in vivo. In vitro results showed that miltefosine inhibited viral replication with enhanced activation of the cellular transcription factor, STAT3, which is reported to reduce CVB3 both in vitro and in mice. Notably, STAT3 knockdown abolished the anti-CVB3 activity of miltefosine in vitro. Mouse studies demonstrated that miltefosine pretreatment reduced CVB3 lethality of mice with decreased virus loads, organ damage, and apoptosis, but enhanced STAT3 activation. Miltefosine could be prophylaxis for CVB3 by targeting Akt to enhance STAT3 activation in the mechanism, which is independent of IFN responses and hardly reported in pathogen infections.

Enterovirus 71 infection increases expression of interferon-gamma-inducible protein 10 which protects mice by reducing viral burden in multiple tissues.

Enterovirus 71 (EV71) infection has induced fatal encephalitis in thousands of young children in the Asia-Pacific region over the last decade. EV71 infection continues to cause serious problems in areas with outbreaks, because vaccines and antiviral therapies are not available. Lymphocytes are present in the brains of infected patients and mice, and they protect mice from infection by decreasing the viral burden. The chemokines responsible for recruiting lymphocytes to infected organs are yet to be identified. Among the lymphocyte chemokines detected, high levels of interferon-gamma-inducible protein-10 (IP-10) are found in the plasma and cerebral spinal fluid of patients with brainstem encephalitis as compared with the levels of a monokine induced by gamma interferon (Mig). Using a murine model to investigate the induction of IP-10 by EV71 infection, we observed that EV71 infection significantly enhanced IP-10 protein expression in the serum and brain, with kinetics similar to viral titres in the blood and brain. Brain neurons of infected mice expressed IP-10. Using wild-type mice and IP-10 gene knockout mice to investigate the role of IP-10 in EV71 infection, we found that IP-10 deficiency significantly reduced levels of Mig in serum, and levels of gamma interferon and the number of CD8 T cells in the mouse brain. Absence of IP-10 significantly increased the mortality of infected mice by 45%, with slow virus clearance in several vital tissues. Our observations are consistent with a model where EV71 infection boosts IP-10 expression to increase gamma interferon and Mig levels, infiltration of CD8 T cells, virus clearance in tissues and the survival of mice.

Antiviral and immunoregulatory effects of curcumin on coxsackievirus B3-infected hepatitis.

Fulminant hepatitis is a life-threatening complication of coxsackievirus B (CVB) 3 infections. The condition may deteriorate to disseminated intravascular coagulopathy with markedly increased liver enzymes, inflammatory cytokines, and chemokines, which significantly induce local and systemic inflammation. Curcumin exhibits anti-inflammatory and antiviral characteristics in inflammatory and infectious diseases. Here we determined effects of curcumin on viral replications, cytokine and chemokine expressions, and liver damage in CVB3-infected Huh-7 cells. The mouse-adapted CVB3 strain was used to investigate the antiviral and anti-inflammatory effects of curcumin on CVB3-induced hepatitis in a mouse model. In vitro studies showed that curcumin reduced viral protein and titer levels and increased cell viability. Curcumin enhanced the heme oxygenase-1 (HO-1) protein level and decreased the levels of cleaved caspase-3 protein and mRNA of gene encoding C-X-C motif chemokine 10 in infected cells. In vivo studies showed that curcumin improved the survival rate and clinical scores in mice and reduced the viral titer in the liver during CVB3 infection. Moreover, the HO-1 levels were increased, and the cleaved caspase-3 levels were diminished in the CVB3-infected liver. Curcumin reduced the levels of interferon (IFN)-γ and monokine induced by IFN-γ in liver and levels of interleukin (IL)-8 in serum, but increased levels of regulated activation, normal T cell expression in liver and levels of IL-10 in serum of CVB3-infected mice. In summary, curcumin presents antiviral and anti-inflammation efficacies in CVB3 infection in vitro and in vivo; these results provide potential evidence on the feasibility of curcumin for clinical treatment.

CD4 T-cell-independent antibody response reduces enterovirus 71 lethality in mice by decreasing tissue viral loads.

Enterovirus 71 (EV71) has induced fatal encephalitis in hundreds of thousands of infants and young children in the Asia-Pacific region since the past decade. Lymphocyte and antibody responses have been suspected to aggravate EV71-induced neurological symptoms, so anti-inflammatory agents have been used to treat patients with neurological symptoms. In the present study, we found that mice deficient in CD4(+) T cells were resistant to EV71 infection as wild-type mice, whereas mice deficient in B cells were highly susceptible to viral infection. Compensation of CD4 T-cell function by other immune cells was not likely, because wild-type mice depleted of CD4(+) T cells were also resistant to viral infection. Infected CD4 T-cell-deficient mice produced virus-specific neutralizing antibodies, IgM and IgG. Moreover, adoptive transfer of the virus-specific antibody produced by infected CD4 T-cell-deficient mice protected B-cell-deficient mice from infection by reducing tissue viral loads. Collectively, our results show that the CD4 T-cell-independent antibody response promotes the survival of EV71-infected mice and suggest great potential for the use of vaccines and neutralizing antibodies to reduce fatal symptoms in patients.

Integrin-Linked Kinase Reduces H3K9 Trimethylation to Enhance Herpes Simplex Virus 1 Replication.

Histone modifications control the lytic gene expression of herpes simplex virus 1 (HSV-1). The heterochromatin mark, trimethylation of histone H3 on lysine (K) 9 (H3K9me3), is detected on HSV-1 genomes at early phases of infection to repress viral gene transcription. However, the components and mechanisms involved in the process are mostly unknown. Integrin-linked kinase (ILK) is activated by PI3K to phosphorylate Akt and promote several RNA virus infections. Akt has been shown to enhance HSV-1 infection, suggesting a pro-viral role of ILK in HSV-1 infection that has not been addressed before. Here, we reveal that ILK enhances HSV-1 replication in an Akt-independent manner. ILK reduces the accumulation of H3K9me3 on viral promoters and replication compartments. Notably, ILK reduces H3K9me3 in a manner independent of ICP0. Instead, we show an increased binding of H3K9 methyltransferase SUV39H1 and corepressor TRIM28 on viral promoters in ILK knockdown cells. Knocking down SUV39H1 or TRIM28 increases HSV-1 lytic gene transcription in ILK knockdown cells. These results show that ILK antagonizes SVU39H1- and TRIM28-mediated repression on lytic gene transcription. We further demonstrate that ILK knockdown reduces TRIM28 phosphorylation on serine 473 and 824 in HSV-1-infected cells, suggesting that ILK facilitates TRIM28 phosphorylation to abrogate its inhibition on lytic gene transcription. OSU-T315, an ILK inhibitor, suppresses HSV-1 replication in cells and mice. In conclusion, we demonstrate that ILK decreases H3K9me3 on HSV-1 DNA by reducing SUV39H1 and TRIM28 binding. Moreover, our results suggest that targeting ILK could be a broad-spectrum antiviral strategy for DNA and RNA virus infections, especially for DNA viruses controlled by histone modifications.

Therapeutics for fulminant hepatitis caused by enteroviruses in neonates.

Neonatal infection with nonpolio enteroviruses (EVs) causes nonspecific febrile illnesses and even life-threatening multiorgan failure. Hepatitis, which often results in hepatic necrosis followed by disseminated intravascular coagulopathy, is one of the most severe and frequent fatal neonatal EV infection complications. Coxsackievirus B (CVB) 1-5 and many echoviruses have been most commonly identified. Neonatal EV infection treatment has usually involved initial supportive care. Studies for CVB and echovirus infection treatments were developed for more than thirty years. Intravenous immunoglobulin and pleconaril therapy was performed in some clinical trials. Additionally, other studies demonstrated antiviral and/or anti-inflammatory pathogenesis mechanisms of neonatal EV hepatitis in in vitro or in vivo models. These treatments represented promising options for the clinical practice of neonatal EV hepatitis. However, further investigation is needed to elucidate the whole therapeutic potential and safety problems.

Bortezomib induces HSV-1 lethality in mice with neutrophil deficiency.

Bortezomib suppressing NF-κB activity is an effective therapy for patients with myeloma or lymphoma. However, this drug can cause adverse effects, neutropenia, and recurrent infections of herpes viruses. Among herpes viruses, HSV-1 can reactivate to induce mortality. The important issues regarding how bortezomib diminishes neutrophils, whether bortezomib can induce HSV-1 reactivation, and how bortezomib exacerbates HSV-1 infection, need investigation. Using the murine model, we found that bortezomib induced HSV-1 reactivation. Bortezomib diminished neutrophil numbers in organs of uninfected and HSV-1-infected mice and turned a nonlethal infection to lethal with elevated tissue viral loads. In vitro results showed that bortezomib and HSV-1 collaborated to enhance the death and apoptosis of mouse neutrophils. The leukocyte deficiency induced by chemotherapies is generally believed to be the cause for aggravating virus infections. Here we show the potential of pathogen to exacerbate chemotherapy-induced leukocyte deficiency.

Flt3 ligand treatment reduces enterovirus A71 lethality in mice with enhanced B cell responses.

Enterovirus A71 (EV-A71) infection can induce encephalitis, which causes death or long-term neurological sequelae, especially in young children. Using a murine infection model, we searched for anti-EV-A71 agents, because effective therapies are not available to control fatal infection. In EV-A71-infected mice, treatment with the hematopoietic growth factor, Fms-like tyrosine-kinase 3 ligand (Flt3 ligand) before infection reduced the lethality and tissue viral loads. Flt3 ligand failed to enhance the production of type I interferons. Instead, Flt3 ligand boosted the numbers of dendritic cells and, particularly lymphocytes in infected organs with an expansion of spleen B cells, and resulted in an increased titer of virus-specific antibody with neutralizing activity in the serum. The protective effect of Flt3 ligand was abolished in B cell-deficient mice. Our findings revealed that Flt3 ligand administration promotes resistance to EV-A71 infection with enhanced B cell response in a mechanism rarely reported before.