Mitochondria-derived reactive oxygen species negatively regulates immune innate signaling pathways triggered by a DNA virus, but not by an RNA virus

Mitochondrial Reactive Oxygen Species Elicit Acute and Chronic Itch via Transient Receptor Potential Canonical 3 Activation in Mice

Mitochondrial reactive oxygen species (mROS) that are overproduced by mitochondrial dysfunction are linked to pathological conditions including sensory abnormalities. Here, we explored whether mROS overproduction induces itch through transient receptor potential canonical 3 (TRPC3), which is sensitive to ROS. Intradermal injection of antimycin A (AA), a selective inhibitor of mitochondrial electron transport chain complex III for mROS overproduction, produced robust scratching behavior in naïve mice, which was suppressed by MitoTEMPO, a mitochondria-selective ROS scavenger, and Pyr10, a TRPC3-specific blocker, but not by blockers of TRPA1 or TRPV1. AA activated subsets of trigeminal ganglion neurons and also induced inward currents, which were blocked by MitoTEMPO and Pyr10. Besides, dry skin-induced chronic scratching was relieved by MitoTEMPO and Pyr10, and also by resveratrol, an antioxidant. Taken together, our results suggest that mROS elicit itch through TRPC3, which may underlie chronic itch, representing a potential therapeutic target for chronic itch.

Binding of a Vitis riparia dehydrin to DNA

Plants must protect themselves from abiotic stresses such as drought, cold, and high salinity. The common thread of all three stresses is that they cause dehydration, which in turn promotes the formation of reactive oxygen species (ROS). Dehydrin proteins (dehydrins) are a large family of proteins that have been identified in nearly all land plants, and whose presence is correlated with plant protection from abiotic stresses. Several dehydrin studies have shown that some dehydrins localize to the nucleus, as well as the cytoplasm, but a functional role for nuclear dehydrins has not yet been determined. We show here that the Vitis riparia dehydrin VrDHN1 localizes to the nucleus and is able to bind to DNA to protect it from damage caused by hydrogen peroxide, an ROS source. We also show that the binding to DNA is not DNA-sequence specific, suggesting that the protein is able to protect any exposed DNA without interfering with its normal function. NMR studies show that the binding is largely driven by the lysine-rich nature of dehydrins located in the conserved K-segments. Unlike other, previously studied dehydrins, VrDHN1 binding to DNA is not enhanced through the presence of metals. Lastly, we demonstrate that the Y-segment does not bind ATP, as has long been proposed.

NF-κB-Dependent Production of ROS and Restriction of HSV-1 Infection in U937 Monocytic Cells

Herpes simplex virus 1 (HSV-1) can infect a wide range of cell types, including cells of the adaptive and innate immunity but, normally, it completes a fully-permissive replication cycle only in epithelial or neural cells. Complex mechanisms controlling this delicate balance in immune cells and consequent restriction of HSV-1 infection in these cells have not been completely elucidated. We have recently demonstrated that the transcription factor nuclear factor kappa B (NF-κB) can act as a main permissiveness regulator of HSV-1 infection in monocytic cells, however, mediators involved in this regulation have not been identified. To better define mechanisms involved in this phenomenon and, particularly, the possible involvement of ROS, wild type U937 cells or U937 cells stably transfected with a dominant-negative (DN) IκB-mutant and selenium-containing compounds, as anti-oxidants, were utilized. The main results can be summarized as follows. HSV-1 infection induces an immediate ROS production in U937 monocytic cells that can efficiently activate NF-κB but not in DN-IκB-mutant cells. Treatment with selenium-containing antioxidants efficiently inhibited HSV-1-induced ROS generation while producing increased levels of HSV-1 replication and a reduction of HSV-1-induced NF-κB activation in U937 monocytic cells. Our results suggest a scenario in which an efficient NF-κB-dependent ROS production in response to infection could contribute in limiting HSV-1 replication in monocytes/macrophages, thus avoiding possible irreparable damage to the innate immune system of the host during HSV-1 infection.

Resveratrol as a Novel Anti-Herpes Simplex Virus Nutraceutical Agent: An Overview

The herpes simplex virus (HSV) is a common human virus affecting many people worldwide. HSV infections manifest with lesions that occur in different parts of the body, including oral, ocular, nasal, and genital skin and mucosa. In rare cases, HSV infections can be serious and lethal. Several anti-HSV drugs have been developed, but the existence of mutant viruses resistant to these drugs led to the individuation of novel antiviral agents. Plant-derived bioactive compounds, and more specifically polyphenols, have been demonstrated to exert marked anti-HSV activity and, among these, resveratrol (RSV) would be considered a good candidate. The purpose of this manuscript is to review the available literature elucidating the efficacy of RSV against HSV and the main demonstrated mechanisms of action.

Redox Biology of Respiratory Viral Infections

Respiratory viruses cause infections of the upper or lower respiratory tract and they are responsible for the common cold—the most prevalent disease in the world. In many cases the common cold results in severe illness due to complications, such as fever or pneumonia. Children, old people, and immunosuppressed patients are at the highest risk and require fast diagnosis and therapeutic intervention. However, the availability and efficiencies of existing therapeutic approaches vary depending on the virus. Investigation of the pathologies that are associated with infection by respiratory viruses will be paramount for diagnosis, treatment modalities, and the development of new therapies. Changes in redox homeostasis in infected cells are one of the key events that is linked to infection with respiratory viruses and linked to inflammation and subsequent tissue damage. Our review summarizes current knowledge on changes to redox homeostasis, as induced by the different respiratory viruses.

Regulation of type I interferon responses by mitochondria-derived reactive oxygen species in plasmacytoid dendritic cells

Mitochondrial reactive oxygen species (mtROS) generated continuously under physiological conditions have recently emerged as critical players in the regulation of immune signaling pathways. In this study we have investigated the regulation of antiviral signaling by increased mtROS production in plasmacytoid dendritic cells (pDCs), which, as major producers of type I interferons (IFN), are the key coordinators of antiviral immunity. The early phase of type I IFN production in pDCs is mediated by endosomal Toll-like receptors (TLRs), whereas the late phase of IFN response can also be triggered by cytosolic retinoic acid-inducible gene-I (RIG-I), expression of which is induced upon TLR stimulation. Therefore, pDCs provide an ideal model to study the impact of elevated mtROS on the antiviral signaling pathways initiated by receptors with distinct subcellular localization. We found that elevated level of mtROS alone did not change the phenotype and the baseline cytokine profile of resting pDCs. Nevertheless increased mtROS levels in pDCs lowered the TLR9-induced secretion of pro-inflammatory mediators slightly, whereas reduced type I IFN production markedly via blocking phosphorylation of interferon regulatory factor 7 (IRF7), the key transcription factor of the TLR9 signaling pathway. The TLR9-induced expression of RIG-I in pDCs was also negatively regulated by enhanced mtROS production. On the contrary, elevated mtROS significantly augmented the RIG-I-stimulated expression of type I IFNs, as well as the expression of mitochondrial antiviral-signaling (MAVS) protein and the phosphorylation of Akt and IRF3 that are essential components of RIG-I signaling. Collectively, our data suggest that increased mtROS exert diverse immunoregulatory functions in pDCs both in the early and late phase of type I IFN responses depending on which type of viral sensing pathway is stimulated.

Bovine herpesviruses induce different cell death forms in neuronal and glial-derived tumor cell cultures

Oncolytic viruses have the ability to infect tumor cells and leave healthy cells intact. In this study, bovine herpesvirus 1 (BHV1; Los Angeles, Cooper, and SV56/90 strains) and bovine herpesvirus 5 (BHV5; SV507/99 and GU9457818 strains) were used to infect two neuronal tumor cell lineages: neuro2a (mouse neuroblastoma cells) and C6 (rat glial cells). BHV1 and BHV5 strains infected both cell lines and positively correlated with viral antigen detection (p < 0.005). When neuro2a cells were infected by Los Angeles, SV507/99, and GU9457818 strains, 40 % of infected cells were under early apoptosis and necroptosis pathways. Infected C6 cells were >40 % in necroptosis phase when infected by BHV5 (GU9457818 strain). Blocking caspase activation did not interfere with cell death. However, when necroptosis was blocked, 60-80 % of both infected cells with either virus switched to early apoptosis pathway with no interference with virus replication. Moreover, reactive oxygen species production and mitochondrial membrane dysfunction were detected at high levels in both infected cell lines. In spite of apoptosis and necroptosis blockage, tumor necrosis factor alpha (TNFA) and virus transcription were positively correlated for all viral strains studied. Thus, these results contribute to the characterization of BHV1 and BHV5 as potential oncolytic viruses for non-human cells. Nonetheless, the mechanisms underlying their oncolytic activity in human cells are still to be determined.

A renewed focus on the interplay between viruses and mitochondrial metabolism

Mitochondria fulfil several key functions within cellular metabolic and antiviral signalling pathways, including their central role in ATP generation. Viruses, as intracellular parasites, require from their cellular host the building blocks for generation of their viral progeny and the energy that drives viral replication and assembly. While some viruses have adopted ways to manipulate the infected cell such that cellular metabolism supports optimal virus production, other viruses simply exhaust cellular resources. The association of viruses with mitochondria is influenced by several important factors such as speed of the viral replication cycle and viral dependence on cellular enzymes and metabolites. This review will highlight the complex interconnectivity of viral life cycles with the three main mitochondrial metabolic pathways, namely β-oxidation, the tricarboxylic (TCA) cycle, and oxidative phosphorylation. This interconnectivity has the potential to reveal interesting points for antiviral therapy with either prometabolites or antimetabolites and highlights the importance of the viral association with mitochondrial metabolism.

Mitochondria: sensors and mediators of innate immune receptor signaling

By integrating stress signals with inputs from other cellular organelles, eukaryotic mitochondria are dynamic sensing systems that can confer substantial impact on innate immune signaling in both health and disease. This review highlights recently discovered elements of innate immune receptor signaling (TLR, RLR, NLR, and CLR) associated with mitochondrial function and discusses the role of mitochondria in the initiation and/or manifestation of inflammatory diseases and disorders. We also highlight the role of mitochondria as therapeutic targets for inflammatory disease.

The case for immunomodulatory approaches in treating HSV encephalitis

HSV encephalitis (HSE) is the most prevalent sporadic viral encephalitis. Although safe and effective antiviral therapies and greatly improved noninvasive diagnostic procedures have significantly improved outcomes, mortality (~20%) and debilitating neurological sequelae in survivors remain unacceptably high. An encouraging new development is that the focus is now shifting away from the virus exclusively, to include consideration of the host immune response to infection in the pathology underlying development of HSE. In this article, the authors discuss results from recent studies in experimental mouse models, as well as clinical reports that demonstrate a role for exaggerated host inflammatory responses in the brain in the development of HSE that is motivating researchers and clinicians to consider new therapeutic approaches for treating HSE. The authors also discuss results from a few studies that have shown that immunomodulatory drugs can be highly protective against HSE, which supports a role for deleterious host inflammatory responses in HSE. The impressive outcomes of some immunomodulatory approaches in mouse models of HSE emphasize the urgent need for clinical trials to rigorously evaluate combination antiviral and immunomodulatory therapy in comparison with standard antiviral therapy for treatment of HSE, and support for such an initiative is gaining momentum.

Sensory nerve terminal mitochondrial dysfunction activates airway sensory nerves via transient receptor potential (TRP) channels

Mitochondrial dysfunction and subsequent oxidative stress has been reported for a variety of cell types in inflammatory diseases. Given the abundance of mitochondria at the peripheral terminals of sensory nerves and the sensitivity of transient receptor potential (TRP) ankyrin 1 (A1) and TRP vanilloid 1 (V1) to reactive oxygen species (ROS) and their downstream products of lipid peroxidation, we investigated the effect of nerve terminal mitochondrial dysfunction on airway sensory nerve excitability. Here we show that mitochondrial dysfunction evoked by acute treatment with antimycin A (mitochondrial complex III Qi site inhibitor) preferentially activated TRPA1-expressing "nociceptor-like" mouse bronchopulmonary C-fibers. Action potential discharge was reduced by the TRPA1 antagonist HC-030031. Inhibition of TRPV1 further reduced C-fiber activation. In mouse dissociated vagal neurons, antimycin A induced Ca(2+) influx that was significantly reduced by pharmacological inhibition or genetic knockout of either TRPA1 or TRPV1. Inhibition of both TRPA1 and TRPV1 was required to abolish antimycin A-induced Ca(2+) influx in vagal neurons. Using an HEK293 cell expression system, antimycin A induced concentration-dependent activation of both hTRPA1 and hTRPV1 but failed to activate nontransfected cells. Myxothiazol (complex III Qo site inhibitor) inhibited antimycin A-induced TRPA1 activation, as did the reducing agent dithiothreitol. Scavenging of both superoxide and hydrogen peroxide inhibited TRPA1 activation following mitochondrial modulation. In conclusion, we present evidence that acute mitochondrial dysfunction activates airway sensory nerves preferentially via TRPA1 through the actions of mitochondrially-derived ROS. This represents a novel mechanism by which inflammation may be transduced into nociceptive electrical signaling.

Inhibition of herpes simplex virus infection by oligomeric stilbenoids through ROS generation

Stilbenoids including resveratrol contain the basic structural unit of 1,2-diphenylethylene. Naturally occurring stilbenoids have broad structural features due to oligomerization and modifications and some have demonstrated potent biological activities. In an effort to identify bioactive stilbenoids, we screened a group of dimeric and oligomeric stilbenoids against HSV-1 and HSV-2 infection. Several trimeric and tetrameric derivatives showed anti-herpetic activity at single digit micromolar concentrations. HSV-1 and HSV-2 replication requires for NF-κB and MAPK activation. The compounds showed no inhibitory activity against NF-κB and Erk/MAPK activation, instead those compounds promoted rapid and transient release of reactive oxygen species (ROS). Addition of N-acetylcysteine (NAC), a scavenger of ROS, reversed the inhibitory effect of those compounds against HSV replication. In addition to the identification of resveratrol derivatives with potent anti-HSV activity, our results uncover a mechanism of polyphenol-mediated anti-HSV response, linking anti-herpetic activity of oligomeric stilbenoids to innate immunity.