High-resolution kinetic characterization of the RIG-I-signaling pathway and the antiviral response

RIG-I recognizes viral dsRNA and activates a cell-autonomous antiviral response. Upon stimulation, it triggers a signaling cascade leading to the production of type I and III IFNs. IFNs are secreted and signal to elicit the expression of IFN-stimulated genes, establishing an antiviral state of the cell. The topology of this pathway has been studied intensively, however, its exact dynamics are less understood. Here, we employed electroporation to synchronously activate RIG-I, enabling us to characterize cell-intrinsic innate immune signaling at a high temporal resolution. Employing IFNAR1/IFNLR-deficient cells, we could differentiate primary RIG-I signaling from secondary signaling downstream of the IFN receptors. Based on these data, we developed a comprehensive mathematical model capable of simulating signaling downstream of dsRNA recognition by RIG-I and the feedback and signal amplification by IFN. We further investigated the impact of viral antagonists on signaling dynamics. Our work provides a comprehensive insight into the signaling events that occur early upon virus infection and opens new avenues to study and disentangle the complexity of the host-virus interface.

IL-17-induced dimerization of IL-17RA drives the formation of the IL-17 signalosome to potentiate signaling

Signaling through innate immune receptors such as the Toll-like receptor (TLR)/interleukin-1 receptor (IL-1R) superfamily proceeds via the assembly of large membrane-proximal complexes or “signalosomes.” Although structurally distinct, the IL-17 receptor family triggers cellular responses that are typical of innate immune receptors. The IL-17RA receptor subunit is shared by several members of the IL-17 family. Using a combination of crystallographic, biophysical, and mutational studies, we show that IL-17A, IL-17F, and IL-17A/F induce IL-17RA dimerization. X-ray analysis of the heteromeric IL-17A complex with the extracellular domains of the IL-17RA and IL-17RC receptors reveals that cytokine-induced IL-17RA dimerization leads to the formation of a 2:2:2 hexameric signaling assembly. Furthermore, we demonstrate that the formation of the IL-17 signalosome potentiates IL-17-induced IL-36γ and CXCL1 mRNA expression in human keratinocytes, compared with a dimerization-defective IL-17RA variant.

IL-17RA is the shared co-receptor for several IL-17 family members. Goepfert et al. show that IL-17 induces IL-17RA dimerization, which then drives the formation of a 2:2:2 hexameric signaling assembly with IL-17RC. Furthermore, IL-17RA dimerization potentiates IL-17 signaling in immortalized primary human keratinocytes, compared with cells expressing a dimerization-defective IL-17RA variant.

TNF leads to mtDNA release and cGAS/STING-dependent interferon responses that support inflammatory arthritis

Tumor necrosis factor (TNF) is a key driver of several inflammatory diseases, such as rheumatoid arthritis, inflammatory bowel disease, and psoriasis, in which affected tissues show an interferon-stimulated gene signature. Here, we demonstrate that TNF triggers a type-I interferon response that is dependent on the cyclic guanosine monophosphate-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway. We show that TNF inhibits PINK1-mediated mitophagy and leads to altered mitochondrial function and to an increase in cytosolic mtDNA levels. Using cGAS-chromatin immunoprecipitation (ChIP), we demonstrate that cytosolic mtDNA binds to cGAS after TNF treatment. Furthermore, TNF induces a cGAS-STING-dependent transcriptional response that mimics that of macrophages from rheumatoid arthritis patients. Finally, in an inflammatory arthritis mouse model, cGAS deficiency blocked interferon responses and reduced inflammatory cell infiltration and joint swelling. These findings elucidate a molecular mechanism linking TNF to type-I interferon signaling and suggest a potential benefit for therapeutic targeting of cGAS/STING in TNF-driven diseases.

Identification of Interleukin1β as an Amplifier of Interferon alpha-induced Antiviral Responses

The induction of an interferon-mediated response is the first line of defense against pathogens such as viruses. Yet, the dynamics and extent of interferon alpha (IFNα)-induced antiviral genes vary remarkably and comprise three expression clusters: early, intermediate and late. By mathematical modeling based on time-resolved quantitative data, we identified mRNA stability as well as a negative regulatory loop as key mechanisms endogenously controlling the expression dynamics of IFNα-induced antiviral genes in hepatocytes. Guided by the mathematical model, we uncovered that this regulatory loop is mediated by the transcription factor IRF2 and showed that knock-down of IRF2 results in enhanced expression of early, intermediate and late IFNα-induced antiviral genes. Co-stimulation experiments with different pro-inflammatory cytokines revealed that this amplified expression dynamics of the early, intermediate and late IFNα-induced antiviral genes can also be achieved by co-application of IFNα and interleukin1 beta (IL1β). Consistently, we found that IL1β enhances IFNα-mediated repression of viral replication. Conversely, we observed that in IL1β receptor knock-out mice replication of viruses sensitive to IFNα is increased. Thus, IL1β is capable to potentiate IFNα-induced antiviral responses and could be exploited to improve antiviral therapies.

Innate immune responses contribute to the control of viral infections and the induction of interferon alpha (IFNα)-mediated antiviral responses is an important component. However, IFNα induces a multitude of antiviral response genes and the expression dynamics of these genes can be classified as early, intermediate and late. Here we show, based on a mathematical modeling approach, that mRNA stability as well as the negative regulator IRF2 control the expression dynamics of IFNα-induced antiviral genes. Knock-down of IRF2 resulted in the amplified IFNα-mediated induction of the antiviral genes and this amplified expression of antiviral genes could be functionally mimicked by co-stimulation with IFNα and IL1β. We observed that co-stimulation with IFNα and IL1β enhanced the repression of virus replication and that knock-out of the IL1 receptor in mice resulted in increased replication of a virus sensitive to IFNα. In sum, our studies identified IL1β as an important amplifier of IFNα-induced antiviral responses.

Into the Wild, Out of the Woods: A Systematic Case Study on Facilitating Emotional Change

Cognitive and behavioral treatment programs for individuals who have committed sexual offenses (ISOs) have shown significant but small effect sizes. A growing body of research points toward the importance of difficulties in affect regulation (AR) as a risk factor for sexual recidivism. On this basis, it seems important to target difficulties in AR in treatment. The current systematic case study investigates the potential contribution of emotion-focused therapy (EFT) to changing problematic AR in ISOs. Kevin was a high-risk offender with a traumatic history who met the diagnostic criteria of pedophilic and borderline disorders, with serious AR difficulties. Self-report outcome measures, observation measures, and a biomarker were used to track changes in AR, psychological symptoms, and distress during baseline (Phase A); treatment as usual (Phase B); treatment with an EFT component added (Phase C); and follow-up (Phase A). Statistically significant change was found in AR, psychological symptoms, and distress during treatment (Phase B + C); however, it is not possible to attribute these changes causally to EFT. An examination of the qualitative process data provides deeper insights into how the client reacted to specific EFT interventions. Verbatim clinical vignettes are included to clarify key interventions, hindrances, and mechanisms of change. This study provides preliminary support for the role of therapy to facilitate emotional change in ISOs.

RIPLET, and not TRIM25, is required for endogenous RIG-I-dependent antiviral responses

The innate immune system is our first line of defense against viral pathogens. Host cell pattern recognition receptors sense viral components and initiate immune signaling cascades that result in the production of an array of cytokines to combat infection. Retinoic acid-inducible gene-I (RIG-I) is a pattern recognition receptor that recognizes viral RNA and, when activated, results in the production of type I and III interferons (IFNs) and the upregulation of IFN-stimulated genes. Ubiquitination of RIG-I by the E3 ligases tripartite motif-containing 25 (TRIM25) and Riplet is thought to be requisite for RIG-I activation; however, recent studies have questioned the relative importance of these two enzymes for RIG-I signaling. In this study, we show that deletion of Trim25 does not affect the IFN response to either influenza A virus (IAV), influenza B virus, Sendai virus or several RIG-I agonists. This is in contrast to deletion of either Rig-i or Riplet, which completely abrogated RIG-I-dependent IFN responses. This was consistent in both mouse and human cell lines, as well as in normal human bronchial cells. With most of the current TRIM25 literature based on exogenous expression, these findings provide critical evidence that Riplet, and not TRIM25, is required endogenously for the ubiquitination of RIG-I. Despite this, loss of TRIM25 results in greater susceptibility to IAV infection in vivo, suggesting that it may have an alternative role in host antiviral defense. This study refines our understanding of RIG-I signaling in viral infections and will inform future studies in the field.

Ubiquitin-Dependent and -Independent Roles of E3 Ligase RIPLET in Innate Immunity

The conventional view posits that E3 ligases function primarily through conjugating ubiquitin (Ub) to their substrate molecules. We report here that RIPLET, an essential E3 ligase in antiviral immunity, promotes the antiviral signaling activity of the viral RNA receptor RIG-I through both Ub-dependent and -independent manners. RIPLET uses its dimeric structure and a bivalent binding mode to preferentially recognize and ubiquitinate RIG-I pre-oligomerized on dsRNA. In addition, RIPLET can cross-bridge RIG-I filaments on longer dsRNAs, inducing aggregate-like RIG-I assemblies. The consequent receptor clustering synergizes with the Ub-dependent mechanism to amplify RIG-I-mediated antiviral signaling in an RNA-length dependent manner. These observations show the unexpected role of an E3 ligase as a co-receptor that directly participates in receptor oligomerization and ligand discrimination. It also highlights a previously unrecognized mechanism by which the innate immune system measures foreign nucleic acid length, a common criterion for self versus non-self nucleic acid discrimination.

Phosphorylation of TRIM28 Enhances the Expression of IFN-β and Proinflammatory Cytokines During HPAIV Infection of Human Lung Epithelial Cells

Human infection with highly pathogenic avian influenza viruses (HPAIV) is often associated with severe tissue damage due to hyperinduction of interferons and proinflammatory cytokines. The reasons for this excessive cytokine expression are still incompletely understood, which has hampered the development of efficient immunomodulatory treatment options. The host protein TRIM28 associates to the promoter regions of over 13,000 genes and is recognized as a genomic corepressor and negative immune regulator. TRIM28 corepressor activity is regulated by post-translational modifications, specifically phosphorylation of S473, which modulates binding of TRIM28 to the heterochromatin-binding protein HP1. Here, we identified TRIM28 as a key immune regulator leading to increased IFN-β and proinflammatory cytokine levels during infection with HPAIV. Using influenza A virus strains of the subtype H1N1 as well as HPAIV of subtypes H7N7, H7N9, and H5N1, we could demonstrate that strain-specific phosphorylation of TRIM28 S473 is induced by a signaling cascade constituted of PKR, p38 MAPK, and MSK1 in response to RIG-I independent sensing of viral RNA. Furthermore, using chemical inhibitors as well as knockout cell lines, our results suggest that phosphorylation of S473 facilitates a functional switch leading to increased levels of IFN-β, IL-6, and IL-8. In summary, we have identified TRIM28 as a critical factor controlling excessive expression of type I IFNs as well as proinflammatory cytokines during infection with H5N1, H7N7, and H7N9 HPAIV. In addition, our data indicate a novel mechanism of PKR-mediated IFN-β expression, which could lay the ground for novel treatment options aiming at rebalancing dysregulated immune responses during severe HPAIV infection.

Reovirus intermediate subviral particles constitute a strategy to infect intestinal epithelial cells by exploiting TGF-β dependent pro-survival signaling

Intestinal epithelial cells (IECs) constitute the primary barrier that separates us from the outside environment. These cells, lining the surface of the intestinal tract, represent a major challenge that enteric pathogens have to face. How IECs respond to viral infection and whether enteric viruses have developed strategies to subvert IECs innate immune response remains poorly characterized. Using mammalian reovirus (MRV) as a model enteric virus, we found that the intermediate subviral particles (ISVPs), which are formed in the gut during the natural course of infection by proteolytic digestion of the reovirus virion, trigger reduced innate antiviral immune response in IECs. On the contrary, infection of IECs by virions induces a strong antiviral immune response that leads to cellular death. Additionally, we determined that virions can be sensed by both TLR and RLR pathways while ISVPs are sensed by RLR pathways only. Interestingly, we found that ISVP infected cells secrete TGF-β acting as a pro-survival factor that protects IECs against virion induced cellular death. We propose that ISVPs represent a reovirus strategy to initiate primary infection of the gut by subverting IECs innate immune system and by counteracting cellular-death pathways.

A coding IRAK2 protein variant compromises Toll-like receptor (TLR) signaling and is associated with colorectal cancer survival

Within innate immune signaling pathways, interleukin-1 receptor-associated kinases (IRAKs) fulfill key roles downstream of multiple Toll-like receptors and the interleukin-1 receptor. Although human IRAK4 deficiency was shown to lead to severe immunodeficiency in response to pyogenic bacterial infection during childhood, little is known about the role of human IRAK2. We here identified a non-synonymous IRAK2 variant, rs35060588 (coding R214G), as hypofunctional in terms of NF-κB signaling and Toll-like receptor-mediated cytokine induction. This was due to reduced ubiquitination of TRAF6, a key step in signal transduction. IRAK2 rs35060588 occurs in 3-9% of individuals in different ethnic groups, and our studies suggested a genetic association of rs35060588 with colorectal cancer survival. This for the first time implicates human IRAK2 in a human disease and highlights the R214G IRAK2 variant as a potential novel and broadly applicable biomarker for disease or as a therapeutic intervention point.

Robust RNAi enhancement via human Argonaute-2 overexpression from plasmids, viral vectors and cell lines

As the only mammalian Argonaute protein capable of directly cleaving mRNAs in a small RNA-guided manner, Argonaute-2 (Ago2) is a keyplayer in RNA interference (RNAi) silencing via small interfering (si) or short hairpin (sh) RNAs. It is also a rate-limiting factor whose saturation by si/shRNAs limits RNAi efficiency and causes numerous adverse side effects. Here, we report a set of versatile tools and widely applicable strategies for transient or stable Ago2 co-expression, which overcome these concerns. Specifically, we engineered plasmids and viral vectors to co-encode a codon-optimized human Ago2 cDNA along with custom shRNAs. Furthermore, we stably integrated this Ago2 cDNA into a panel of standard human cell lines via plasmid transfection or lentiviral transduction. Using various endo- or exogenous targets, we demonstrate the potential of all three strategies to boost mRNA silencing efficiencies in cell culture by up to 10-fold, and to facilitate combinatorial knockdowns. Importantly, these robust improvements were reflected by augmented RNAi phenotypes and accompanied by reduced off-targeting effects. We moreover show that Ago2/shRNA-co-encoding vectors can enhance and prolong transgene silencing in livers of adult mice, while concurrently alleviating hepatotoxicity. Our customizable reagents and avenues should broadly improve future in vitro and in vivo RNAi experiments in mammalian systems.

Melatonin treatment in children with therapy-resistant monosymptomatic nocturnal enuresis

OBJECTIVE

To evaluate the effects of exogenous melatonin on the frequency of wet nights, on the sleep-wake cycle, and on the melatonin profile in children with therapy-resistant MNE.

PATIENTS AND METHODS

24 patients were included. Patients had to maintain a diary including time of sleep and arousal, and whether they had a dry or a wet bed in the morning. We measured baseline melatonin profiles in saliva. Hereafter, patients were randomized to synthetic melatonin or placebo. After 3 and 6 months we evaluated the frequency of enuresis and the melatonin profiles.

RESULTS

11 patients were randomized to melatonin, 13 to placebo. We evaluated melatonin profiles of 7 patients in the melatonin group and of 8 in the placebo group. We observed a change in profile in the melatonin group, but we did not observe a difference in the sleep-wake cycle or the frequency of wet nights in either group.

CONCLUSION

This is the first time exogenous melatonin has been evaluated in the treatment of MNE. Although we observed a change in melatonin profile after the use of exogenous melatonin, we did not observe a change in enuresis frequency or in the sleep-wake cycle of this select group of patients.

Vesicoureteral reflux and videourodynamic studies: results of a prospective study

OBJECTIVES

To study the influence of bladder instability on the conservative management and surgical treatment of children with vesicoureteral reflux (VUR), 102 children were included in a prospective study.

METHODS

During a 5-year period all children suspected to have VUR underwent a videourodynamic study to determine VUR grade and bladder function. This resulted in a group of 36 boys and 66 girls who were followed up for well over 5 years.

RESULTS

Bladder instability was found in 41 of 102 children (40%). The 102 children were either treated conservatively or surgically. Of the 77 children who were treated conservatively, bladder instability was found in 35 patients. In the conservatively treated group with bladder instability, reflux resolved in 57%; whereas in those with normal bladder function, reflux resolved in 67%. Of the 25 patients who were treated surgically, the operation was successful in 91%. Breakthrough infections occurred in 22 girls and 3 boys, including 14 of 41 patients with bladder instability (34%) and 11 of 61 patients with normal bladder function (18%).

CONCLUSIONS

Bladder instability is a frequent finding and an important factor in the treatment of children with VUR. To determine if a patient has VUR and bladder instability a videourodynamic study has proved to be an easy and efficient diagnostic tool. When bladder instability is treated with anticholinergic medication, almost the same results can be expected from conservative treatment as from surgical treatment compared to children with a normal bladder function. Breakthrough urinary tract infections occur more often in girls and tend to occur more often in children with bladder instability.

Induction of tyrosine phosphorylation in human MHC class II-positive antigen-presenting cells by stimulation with contact sensitizers

To investigate the intracellular signaling mechanisms involved in the activation of APC by contact sensitizers, we studied the induction of tyrosine phosphorylation by these agents. Selective analysis of phosphotyrosine (p-tyr) in human Langerhans cells and different mononuclear cell types was achieved using a multicolor flow-cytometric technique. Stimulation with contact sensitizers revealed a distinct increase in p-tyr exclusively for MHC class II-positive cells. For different haptens, irritants, as well as activators of distinct signal transduction pathways, it was demonstrated that only strong sensitizers or the protein tyrosine phosphatase inhibitor sodium orthovanadate or cross-linking of MHC class II molecules were able to induce formation of p-tyr in human blood-derived dendritic cells serving as model for the dendritic cell family. This event required physiologic cell culture conditions and was blocked by specific inhibitors of protein tyrosine kinases. No evidence for the inhibition of protein tyrosine phosphatases by haptens was found. Western blot analysis of monocyte-enriched populations revealed an augmented phosphorylation of distinct proteins after hapten stimulation partly resembling the pattern noticed after cross-linking of HLA-DR molecules. In dendritic cells generated from mononuclear progenitors, the protein tyrosine kinase inhibitor genistein was able to block tyrosine phosphorylation as well as production of IL-1beta mRNA transcripts. Our data underline the unique capacity of haptens to activate APC and the important role of tyrosine phosphorylation for this process.

Atrial natriuretic factor potentiates the human forearm vasoconstrictor response to sympathetic stimulation

1. Atrial natriuretic factor has been suggested to affect human sympathetic nervous system activity. The interaction between atrial natriuretic factor and the sympathetic nervous system has not been fully elucidated yet, but may occur at different sites. We studied this modulator effect at the level of the forearm vascular bed: the forearm vasoconstrictor response was examined after alpha-adrenergic sympathetic stimulation in healthy subjects during the locoregional administration of atrial natriuretic factor, sodium nitroprusside and placebo. As a sympathetic stimulation test, the technique of the lower body negative pressure (-20 mmHg) was used. 2. Lower body negative pressure increased the forearm vascular resistance by +37 +/- 8% during concomitant intra-arterial infusion of placebo (n = 10). During a predilator state achieved by infusion of atrial natriuretic factor (10 ng min-1 100 ml-1 forearm volume) into the brachial artery, lower body negative pressure subsequently induced a forearm vasoconstrictor response of +153 +/- 22% (P < 0.05 versus placebo), whereas this was +64 +/- 14% when predilatation was achieved by infusion of an equipotent vasodilator dose of sodium nitroprusside (P > 0.1 versus placebo; P < 0.05 versus atrial natriuretic factor). The potentiation of the forearm vasoconstrictor response to lower body negative pressure by atrial natriuretic factor only occurred in the experimental and not in the contralateral arm. According to calculations on simultaneously sampled arterial and venous plasma catecholamine concentrations, the augmented forearm vasoconstrictor response seemed not to be caused by an increased release of noradrenaline.(ABSTRACT TRUNCATED AT 250 WORDS)

Reproducibility of haemodynamic and plasma catecholamine responses to isometric exercise and mental arithmetic in normo- and hyper-tensive subjects

1. To determine the reproducibility of a mental arithmetic stress test and a handgrip exercise test, we studied the responses of blood pressure, heart rate, forearm blood flow and plasma catecholamines on two occasions, with an interval of at least 1 week, in 24 normotensive and 22 hypertensive subjects. 2. The SE of a single observation of the percentage changes of blood pressure ranged from 3.9 to 9.3% in normotensive subjects and from 3.9 to 7.4% in hypertensive subjects in both tests. For heart rate, these values were 4.9-12.3% in the normotensive subjects and 4.8-5.7% in the hypertensive subjects. However, there was a wide individual scatter of these haemodynamic responses during both tests. The forearm blood flow, only measured during mental arithmetic, had an SE of a single observation of 33.7%. 3. In 10 normotensive subjects the SE of a single observation of the change in plasma noradrenaline was 0.16 nmol/l during handgrip exercise and 0.09 nmol/l during mental arithmetic. The corresponding values for plasma adrenaline were 0.04 and 0.05 nmol/l. 4. In conclusion, although both tests showed a rather low SE of a single observation for the blood pressure and heart rate responses in normo- and hyper-tensive subjects, there was a considerable individual variability. If related to the mean forearm blood flow responses, the SE of a single observation of the forearm blood flow response was of similar magnitude. The limited intra-individual reproducibility of both tests should be borne in mind when interpreting pharmacological intervention studies or studies evaluating sympathoadrenal reactivity in cardiovascular disorders.

Population Dynamics of Percids in Lake IJssel and some Smaller Lakes in The Netherlands

Pikeperch (Stizostedion lucioperca) and Eurasian perch (Perca fluviatilis) in Lake IJssel both prey mainly upon the very abundant smelt (Osmerus eperlanus). But competition for food is of little or no importance and growth is not density-dependent. Growth rates for perch and ruffe (Gymnocephalus cernua) in some lakes are exceptionally rapid, mean lengths after 3 yr being 24 and 18 cm, respectively. Very intensive fishing for pikeperch (total annual mortality 81%) in the season before first spawning removes particularly the fast-growing fish from the population, thus restricting reproduction mainly to the slow-growing pikeperch. Year-class strength of pikeperch is strongly favored by a high summer temperature during the first year of life. Strong year-classes of pikeperch in Lake IJssel are characterized by a mean length of the young-of-the-year of 14.5 cm or more. Migration of pikeperch and perch in Lake IJssel is restricted. When transported to other areas of the lake, both species showed a distinct homing behavior. Key words: Percidae, population dynamics, Stizostedion, Perca, Gymnocephalus

Biology of the Percids

The structure, origin, and spread of the family Percidae are reviewed briefly, and its characteristics compared with those of other families of freshwater fishes. It is suggested that the percids, essentially riverine, have been restricted in their success in North America by the presence of the Centrachidae. Percids are defined as temperate mesothermal fish, and this physiological characteristic together with osmoregulatory capacity and swimming performance is shown to limit the ranges of the perches. The degree of development of the tapetum lucidum in Stizostedion spp. and of the lateral line in all percids is related to differences in pattern of development, feeding behavior, and habitat. Reproductive, feeding and migratory behaviour are also reviewed. Key words: Percidae, structure, origin, biology, morphology, systematics, migration