Kallol Dutta

RIG-I Mediates Innate Immune Response in Mouse Neurons Following Japanese Encephalitis Virus Infection

Background Neuroinflammation associated with Japanese encephalitis (JE) is mainly due to the activation of glial cells with subsequent release of proinflammatory mediators from them. The recognition of viral RNA, in part, by the pattern recognition receptor retinoic acid-inducible gene I (RIG-I) has been indicated to have a role in such processes. Even though neurons are also known to express this receptor, its role after JE virus (JEV) infections is yet to be elucidated. Methodology/Principal Findings Upon infecting murine neuroblastoma cells and primary cortical neurons with JEV the expression profile of key proinflammatory cyto/chemokines were analyzed by qRT-PCR and bead array, both before and after ablation of RIG-I. Immunoblotting was performed to evaluate the levels of key molecules downstream to RIG-I leading to production of proinflammatory mediators. Changes in the intracellular viral antigen expression were confirmed by intracellular staining and immunoblotting. JEV infection induced neuronal expression of IL-6, IL-12p70, MCP-1, IP-10 and TNF-α in a time-dependent manner, which showed significant reduction upon RIG-I ablation. Molecules downstream to RIG-I showed significant changes upon JEV-infection, that were modulated following RIG-I ablation. Ablation of RIG-I in neurons also increased their susceptibility to JEV. Conclusions/Significance In this study we propose that neurons are one of the potential sources of proinflammatory cyto/chemokines in JEV-infected brain that are produced via RIG-I dependent pathways. Ablation of RIG-I in neurons leads to increased viral load and reduced release of the cyto/chemokines.

Understanding the molecular mechanism of blood–brain barrier damage in an experimental model of Japanese encephalitis: Correlation with minocycline administration as a therapeutic agent

The blood-brain barrier (BBB) serves to protect the central nervous system (CNS) from damage by exogenous molecules. Japanese encephalitis (JE), caused by a neurotropic flavivirus, leads to inflammation in the CNS, neuronal death and also compromises the structural and functional integrity of the BBB. Minocycline, a semisynthetic tetracycline, has been found to be broadly protective in neurological disease models featuring inflammation and cell death and at present, is being evaluated in clinical trials. In the present study, we propose that the neuroprotective role of minocycline in experimental models of JE extends also to the protection of the BBB. Damage to the BBB was assessed by Evans blue dye exclusion test after minocycline treatment following Japanese encephalitis virus (JEV) infection. A breakdown of the BBB occurred in mice inoculated intravenously with JEV. This resulted in leakage of protein-bound Evans blue dye into the brain tissue. Semi-quantitative RT-PCR revealed an up-regulation of chemokine receptors and adhesion molecules following JEV infection. Immunostaining showed leukocyte and neutrophil infiltration following JEV infection. Intraperitoneal injection of minocycline, beginning 24h post-JEV infection, abrogated the effects by reducing BBB damage, decreasing expression of iNOS, Cox-2, VEGF and also by reducing the elevated level of transcript of chemokine receptors and adhesion molecules in the brain. Matrix metalloproteinases (MMPs) are known to disrupt the BBB and minocycline was found to significantly decrease the activity of MMP-9 in brain tissue homogenates. Thus, minocycline, administered at a clinically relevant time, appears to maintain blood-brain barrier integrity following JEV infection.

Curcumin Protects Neuronal Cells from Japanese Encephalitis Virus-Mediated Cell Death and also Inhibits Infective Viral Particle Formation by Dysregulation of Ubiquitin–Proteasome System

Japanese encephalitis (JE) is an arboviral disease common in Southeast Asia encompassing a population of 3 billion people. Periodic outbreak of JE takes hundreds of lives. Children are major victims of JE. About one third of JE patients die, and many of the survivors suffer from permanent neuropsychiatric sequel, owing to the lack of specific therapeutic measure. Curcumin is a naturally occurring phenolic compound extracted from Curcuma longa L. Previous studies have reported that curcumin possesses strong antioxidant, anti-inflammatory, antiviral activity. We used Neuro2a cell line and infected them with JE virus. The infected cells were treated with varying doses of curcumin. Cell viability, reactive oxygen species (ROS) production within the cells, and change in cellular membrane integrity were studied. The changes in expression of some signaling and stress-related proteins were also assessed. We also studied the inhibitory role of curcumin on the production of infective viral particles by dysregulation of the ubiquitin–proteasome system. In this study, we found that curcumin imparts neuroprotection in vitro, probably by decreasing cellular reactive oxygen species level, restoration of cellular membrane integrity, decreasing pro-apoptotic signaling molecules, and modulating cellular levels of stress-related proteins. We have also shown that curcumin, by inhibition of ubiquitin–proteasome system causes reduction in infective viral particle production from previously infected neuroblastoma cells.

A Common Carcinogen Benzo[a]pyrene Causes Neuronal Death in Mouse via Microglial Activation

Background Benzo[a]pyrene (B[a]P) belongs to a class of polycyclic aromatic hydrocarbons that serve as micropollutants in the environment. B[a]P has been reported as a probable carcinogen in humans. Exposure to B[a]P can take place by ingestion of contaminated (especially grilled, roasted or smoked) food or water, or inhalation of polluted air. There are reports available that also suggests neurotoxicity as a result of B[a]P exposure, but the exact mechanism of action is unknown. Methodology/Principal Findings Using neuroblastoma cell line and primary cortical neuron culture, we demonstrated that B[a]P has no direct neurotoxic effect. We utilized both in vivo and in vitro systems to demonstrate that B[a]P causes microglial activation. Using microglial cell line and primary microglial culture, we showed for the first time that B[a]P administration results in elevation of reactive oxygen species within the microglia thereby causing depression of antioxidant protein levels; enhanced expression of inducible nitric oxide synthase, that results in increased production of NO from the cells. Synthesis and secretion of proinflammatory cytokines were also elevated within the microglia, possibly via the p38MAP kinase pathway. All these factors contributed to bystander death of neurons, in vitro. When administered to animals, B[a]P was found to cause microglial activation and astrogliosis in the brain with subsequent increase in proinflammatory cytokine levels. Conclusions/Significance Contrary to earlier published reports we found that B[a]P has no direct neurotoxic activity. However, it kills neurons in a bystander mechanism by activating the immune cells of the brain viz the microglia. For the first time, we have provided conclusive evidence regarding the mechanism by which the micropollutant B[a]P may actually cause damage to the central nervous system. In todays perspective, where rising pollution levels globally are a matter of grave concern, our study throws light on other health hazards that such pollutants may exert.

Abrogated Inflammatory Response Promotes Neurogenesis in a Murine Model of Japanese Encephalitis

Background Japanese encephalitis virus (JEV) induces neuroinflammation with typical features of viral encephalitis, including inflammatory cell infiltration, activation of microglia, and neuronal degeneration. The detrimental effects of inflammation on neurogenesis have been reported in various models of acute and chronic inflammation. We investigated whether JEV-induced inflammation has similar adverse effects on neurogenesis and whether those effects can be reversed using an anti-inflammatory compound minocycline. Methodology/Principal Findings Here, using in vitro studies and mouse models, we observed that an acute inflammatory milieu is created in the subventricular neurogenic niche following Japanese encephalitis (JE) and a resultant impairment in neurogenesis occurs, which can be reversed with minocycline treatment. Immunohistological studies showed that proliferating cells were replenished and the population of migrating neuroblasts was restored in the niche following minocycline treatment. In vitro, we checked for the efficacy of minocycline as an anti-inflammatory compound and cytokine bead array showed that production of cyto/chemokines decreased in JEV-activated BV2 cells. Furthermore, mouse neurospheres grown in the conditioned media from JEV-activated microglia exhibit arrest in both proliferation and differentiation of the spheres compared to conditioned media from control microglia. These effects were completely reversed when conditioned media from JEV-activated and minocycline treated microglia was used. Conclusion/Significance This study provides conclusive evidence that JEV-activated microglia and the resultant inflammatory molecules are anti-proliferative and anti-neurogenic for NSPCs growth and development, and therefore contribute to the viral neuropathogenesis. The role of minocycline in restoring neurogenesis may implicate enhanced neuronal repair and attenuation of the neuropsychiatric sequelae in JE survivors.

STING Mediates Neuronal Innate Immune Response Following Japanese Encephalitis Virus Infection

Flavivirus-mediated inflammation causes neuronal death, but whether the infected neurons can evoke an innate immune response to elicit their own protection, is unknown. In an earlier study we have shown that neuronal RIG-I, play a significant role in inducing production and release of molecules that are related to inflammation. In this study, using a neuronal cell line, we show that RIG-I acts with STING in a concerted manner following its interaction with Japanese encephalitis viral RNA to induce a type 1 interferon response. Knock-down of STING showed that the expressions of various inflammatory signaling molecules were down-regulated along with increased intracellular viral load. Alternatively, over-expressing STING decreased intracellular viral load. Our results indicate that at the sub-cellular level, interaction between the pattern recognition receptor RIG-I and the adapter molecule STING, is a major contributor to elicit immunological responses involving the type 1 interferons in neurons following JEV infections.

Antiviral and Neuroprotective Role of Octaguanidinium Dendrimer-Conjugated Morpholino Oligomers in Japanese Encephalitis

Background Japanese encephalitis (JE), caused by a mosquito-borne flavivirus, is endemic to the entire south-east Asian and adjoining regions. Currently no therapeutic interventions are available for JE, thereby making it one of the most dreaded encephalitides in the world. An effective way to counter the virus would be to inhibit viral replication by using anti-sense molecules directed against the viral genome. Octaguanidinium dendrimer-conjugated Morpholino (or Vivo-Morpholino) are uncharged anti-sense oligomers that can enter cells of living organisms by endocytosis and subsequently escape from endosomes into the cytosol/nuclear compartment of cells. We hypothesize that Vivo-Morpholinos generated against specific regions of 3′ or 5′ untranslated regions of JEV genome, when administered in an experimental model of JE, will have significant antiviral and neuroprotective effect. Methodology/Principal Findings Mice were infected with JEV (GP78 strain) followed by intraperitoneal administration of Morpholinos (5 mg/kg body weight) daily for up to five treatments. Survivability of the animals was monitored for 15 days (or until death) following which they were sacrificed and their brains were processed either for immunohistochemical staining or protein extraction. Plaque assay and immunoblot analysis performed from brain homogenates showed reduced viral load and viral protein expression, resulting in greater survival of infected animals. Neuroprotective effect was observed by thionin staining of brain sections. Cytokine bead array showed reduction in the levels of proinflammatory cytokines in brain following Morpholino treatment, which were elevated after infection. This corresponded to reduced microglial activation in brain. Oxidative stress was reduced and certain stress-related signaling molecules were found to be positively modulated following Morpholino treatment. In vitro studies also showed that there was decrease in infective viral particle production following Morpholino treatment. Conclusions/Significance Administration of Vivo-Morpholino effectively resulted in increased survival of animals and neuroprotection in a murine model of JE. Hence, these oligomers represent a potential antiviral agent that merits further evaluation.

Minocycline differentially modulates macrophage mediated peripheral immune response following Japanese encephalitis virus infection.

Japanese encephalitis virus (JEV) is a neurotropic flavivirus that is the causative agent of a major mosquito-borne encephalitis in the world. Evasion of peripheral immune system facilitates the entry of the virus into the central nervous system (CNS) where it causes extensive neuronal inflammatory damage that leads to death or severe neuropschychiatric sequel in survivors. It has been proposed that after entry into the body, the virus is carried into the CNS by peripheral immune cells that act as Trojan horses. In this study we investigate whether macrophages can be considered as such a Trojan horse. We also investigate the role of minocycline, a synthetic tetracycline, in such processes. Minocycline has been found to be broadly protective in neurological disease models featuring inflammation and cell death but there has been no report of it having any modulatory role in peripheral macrophage-mediated immune response against viral infection. Persistence of internalized virus within macrophages was visualized by immunofluorescent staining. Cytotoxicity assay revealed that there was no significant cell death after 24 h and 72 h infection with JEV. Proinflammatory cytokine levels were elevated in cells that were infected with JEV but it was abrogated following minocycline treatment. Reactive oxygen species level was also increased after JEV infection. Nitric oxide level was found to increase after 72 h post infection but remained unchanged after 24h. The cellular levels of signaling molecules such as PI3 kinase, phophoAkt and phospho p38MAP kinase were found to be altered after JEV infection and minocycline treatment. JEV infection also affected the VEGF-MMP pathway. Increased activity of MMP-9 was detected from JEV-infected macrophage culture supernatants after 72 h; minocycline treatment resulted in reduced activity. Thus it seems that minocycline dampens peripheral immune reactions by decreasing proinflammatory cytokine release from infected macrophages and the virus survives within macrophages long enough to be carried into the CNS, even though minocycline inhibits cell survival.

Gentamicin in Combination with Ascorbic Acid Regulates the severity of Staphylococcus aureus Infection–Induced Septic Arthritis in Mice

To study the effects of gentamicin in combination with ascorbic acid on septic arthritis, mice were infected with Staphylococcus aureus (S. aureus) and treated with gentamicin, which was given at 5 mg/kg after 24 h of infection, followed by ascorbic acid, given at 20 mg/kg body weight after 2 h of gentamicin treatment. Mice were sacrificed at 3, 9, 15 days post‐infection (dpi). Combined treatment of infected mice with gentamicin and ascorbic acid eradicated the bacteria from the blood, spleen and synovial tissue and showed a significant gross reduction in arthritis, reduced serum levels of tumour necrosis factor alpha (TNF‐α) and interferon gamma (IFN‐γ). S. aureus‐infected mice have demonstrated the disturbed antioxidant status measured in terms of cellular antioxidants like reduced glutathione and antioxidant enzymes such as superoxide dismutase (SOD) and catalase. The same were ameliorated when the animals were co‐treated with gentamicin along with ascorbic acid.

Neurons under viral attack: victims or warriors?

Abstract When the central nervous system (CNS) is under viral attack, defensive antiviral responses must necessarily arise from the CNS itself to rapidly and efficiently curb infections with minimal collateral damage to the sensitive, specialized and non-regenerating neural tissue. This presents a unique challenge because an intact blood–brain barrier (BBB) and lack of proper lymphatic drainage keeps the CNS virtually outside the radar of circulating immune cells that are at constant vigilance for antigens in peripheral tissues. Limited antigen presentation skills of CNS cells in comparison to peripheral tissues is because of a total lack of dendritic cells and feeble expression of major histocompatibility complex (MHC) proteins in neurons and glia. However, research over the past two decades has identified immune effector mechanisms intrinsic to the CNS for immediate tackling, attenuating and clearing of viral infections, with assistance pouring in from peripheral circulation in the form of neutralizing antibodies and cytotoxic T cells at a later stage. Specialized CNS cells, microglia and astrocytes, were regarded as sole sentinels of the brain for containing a viral onslaught but neurons held little recognition as a potential candidate for protecting itself from the proliferation and pathogenesis of neurotropic viruses. Accumulating evidence however indicates that extracellular insult causes neurons to express immune factors characteristic of lymphoid tissues. This article aims to comprehensively analyze current research on this conditional alteration in the protein expression repertoire of neurons and the role it plays in CNS innate immune response to counter viral infections.