The Absence of Interferon-β Promotor Stimulator-1 (IPS-1) Predisposes to Bronchiolitis and Asthma-like Pathology in Response to Pneumoviral Infection in Mice

The crucial regulatory role of type I interferon in inflammatory diseases

Type I interferon (IFN-I) plays crucial roles in the regulation of inflammation and it is associated with various inflammatory diseases including systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and periodontitis, impacting people's health and quality of life. It is well-established that IFN-Is affect immune responses and inflammatory factors by regulating some signaling. However, currently, there is no comprehensive overview of the crucial regulatory role of IFN-I in distinctive pathways as well as associated inflammatory diseases. This review aims to provide a narrative of the involvement of IFN-I in different signaling pathways, mainly mediating the related key factors with specific targets in the pathways and signaling cascades to influence the progression of inflammatory diseases. As such, we suggested that IFN-Is induce inflammatory regulation through the stimulation of certain factors in signaling pathways, which displays possible efficient treatment methods and provides a reference for the precise control of inflammatory diseases.

Flaviviridae Nonstructural Proteins: The Role in Molecular Mechanisms of Triggering Inflammation

Members of the Flaviviridae family are posing a significant threat to human health worldwide. Many flaviviruses are capable of inducing severe inflammation in humans. Flaviviridae nonstructural proteins, apart from their canonical roles in viral replication, have noncanonical functions strongly affecting antiviral innate immunity. Among these functions, antagonism of type I IFN is the most investigated; meanwhile, more data are accumulated on their role in the other pathways of innate response. This review systematizes the last known data on the role of Flaviviridae nonstructural proteins in molecular mechanisms of triggering inflammation, with an emphasis on their interactions with TLRs and RLRs, interference with NF-κB and cGAS-STING signaling, and activation of inflammasomes.

MLKL Regulates Rapid Cell Death-independent HMGB1 Release in RSV Infected Airway Epithelial Cells

Respiratory syncytial virus (RSV)-induced bronchiolitis is a significant contributor to infant morbidity and mortality. Previously, we identified that necroptosis, a pro-inflammatory form of cell death mediated by receptor-interacting serine/threonine-protein kinase 1 (RIPK1) and RIPK3, and mixed lineage kinase domain like protein (MLKL), occurs in RSV-infected human airway epithelial cells (hAECs), mediating the release of the alarmin high mobility group box 1 (HMGB1). Here, we show that RSV infection of hAECs induces the biphasic release of HMGB1 at 6 (“early”) and 24 (“late”) hours post infection (hpi). The early phase of HMGB1 release at 6 hpi is cell death-independent, however, this release is nonetheless attenuated by inhibition of MLKL (primarily associated with necroptosis). The early release of HMGB1 promotes the late phase of HMGB1 release via the activation of RAGE (receptor for advanced glycation endproducts) and occurs with cell death. Treatment of hAECS with exogenous HMGB1 combined with a pan-caspase inhibitor induces hAEC necroptosis, and is attenuated by the RAGE antagonist, FPS-ZM1. Together, these findings demonstrate that RSV infection of hAECs leads to the early release of HMGB1, followed by a paracrine feed-forward amplification loop that further increases HMGB1 levels and promotes cell death. As the inhibition of MLKL or targeting of HMGB1/RAGE pathway attenuates the release of pro-inflammatory HMGB1 and decreases viral load, this suggests that the pharmacological targeting of these pathways may be of benefit for the treatment of severe RSV bronchiolitis.

Innate Immune Sensing of Viruses and Its Consequences for the Central Nervous System

Viral infections remain a global public health concern and cause a severe societal and economic burden. At the organismal level, the innate immune system is essential for the detection of viruses and constitutes the first line of defense. Viral components are sensed by host pattern recognition receptors (PRRs). PRRs can be further classified based on their localization into Toll-like receptors (TLRs), C-type lectin receptors (CLR), retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs), NOD-like receptors (NLRs) and cytosolic DNA sensors (CDS). TLR and RLR signaling results in production of type I interferons (IFNα and -β) and pro-inflammatory cytokines in a cell-specific manner, whereas NLR signaling leads to the production of interleukin-1 family proteins. On the other hand, CLRs are capable of sensing glycans present in viral pathogens, which can induce phagocytic, endocytic, antimicrobial, and pro- inflammatory responses. Peripheral immune sensing of viruses and the ensuing cytokine response can significantly affect the central nervous system (CNS). But viruses can also directly enter the CNS via a multitude of routes, such as the nasal epithelium, along nerve fibers connecting to the periphery and as cargo of infiltrating infected cells passing through the blood brain barrier, triggering innate immune sensing and cytokine responses directly in the CNS. Here, we review mechanisms of viral immune sensing and currently recognized consequences for the CNS of innate immune responses to viruses.

DP1 prostanoid receptor activation increases the severity of an acute lower respiratory viral infection in mice via TNF-α-induced immunopathology

Respiratory syncytial virus (RSV) bronchiolitis is a leading cause of infant hospitalization and mortality. We previously identified that prostaglandin D2 (PGD2), released following RSV infection of primary human airway epithelial cells or pneumonia virus of mice (PVM) infection of neonatal mice, elicits pro- or antiviral innate immune responses as a consequence of D-type prostanoid receptor 2 (DP2) or DP1 activation, respectively. Here, we sought to determine whether treatment with the DP1 agonist BW245c decreases the severity of bronchiolitis in PVM-infected neonatal mice. Consistent with previous findings, BW245c treatment increased IFN-λ production and decreased viral load in week 1 of the infection. However, unexpectedly, BW245c treatment increased mortality in week 2 of the infection. This increased morbidity was associated with viral spread to the parenchyma, an increased cellular infiltrate of TNF-α-producing cells (neutrophils, monocytes, and CD4⁺ T cells), and the heightened production of the pro-inflammatory cytokines TNF-α, IL-6, and IL-1β. These phenotypes, as well as the increased mortality, were significantly attenuated following the administration of anti-TNF-α to PVM-infected, BW245c-treated mice. In summary, pharmacological activation of the DP1 receptor in PVM-infected neonatal mice boosts antiviral innate and adaptive immunity, however, this is ultimately detrimental, as a consequence of increased TNF-α-induced morbidity and mortality.

Respiratory Syncytial Virus Infection Promotes Necroptosis and HMGB1 Release by Airway Epithelial Cells

Rationale: Respiratory syncytial virus (RSV) bronchiolitis causes significant infant mortality. Bronchiolitis is characterized by airway epithelial cell (AEC) death; however, the mode of death remains unknown.Objectives: To determine whether necroptosis contributes to RSV bronchiolitis pathogenesis via HMGB1 (high mobility group box 1) release.Methods: Nasopharyngeal samples were collected from children presenting to the hospital with acute respiratory infection. Primary human AECs and neonatal mice were inoculated with RSV and murine Pneumovirus, respectively. Necroptosis was determined via viability assays and immunohistochemistry for RIPK1 (receptor-interacting protein kinase-1), MLKL (mixed lineage kinase domain-like pseudokinase) protein, and caspase-3. Necroptosis was blocked using pharmacological inhibitors and RIPK1 kinase-dead knockin mice.Measurements and Main Results: HMGB1 levels were elevated in nasopharyngeal samples of children with acute RSV infection. RSV-induced epithelial cell death was associated with increased phosphorylated RIPK1 and phosphorylated MLKL but not active caspase-3 expression. Inhibition of RIPK1 or MLKL attenuated RSV-induced HMGB1 translocation and release, and lowered viral load. MLKL inhibition increased active caspase-3 expression in a caspase-8/9-dependent manner. In susceptible mice, Pneumovirus infection upregulated RIPK1 and MLKL expression in the airway epithelium at 8 to 10 days after infection, coinciding with AEC sloughing, HMGB1 release, and neutrophilic inflammation. Genetic or pharmacological inhibition of RIPK1 or MLKL attenuated these pathologies, lowered viral load, and prevented type 2 inflammation and airway remodeling. Necroptosis inhibition in early life ameliorated asthma progression induced by viral or allergen challenge in later life.Conclusions: Pneumovirus infection induces AEC necroptosis. Inhibition of necroptosis may be a viable strategy to limit the severity of viral bronchiolitis and break its nexus with asthma.

HMGB1 amplifies ILC2-induced type-2 inflammation and airway smooth muscle remodelling

Type-2 immunity elicits tissue repair and homeostasis, however dysregulated type-2 responses cause aberrant tissue remodelling, as observed in asthma. Severe respiratory viral infections in infancy predispose to later asthma, however, the processes that mediate tissue damage-induced type-2 inflammation and the origins of airway remodelling remain ill-defined. Here, using a preclinical mouse model of viral bronchiolitis, we find that increased epithelial and mesenchymal high-mobility group box 1 (HMGB1) expression is associated with increased numbers of IL-13-producing type-2 innate lymphoid cell (ILC2s) and the expansion of the airway smooth muscle (ASM) layer. Anti-HMGB1 ablated lung ILC2 numbers and ASM growth in vivo, and inhibited ILC2-mediated ASM cell proliferation in a co-culture model. Furthermore, we identified that HMGB1/RAGE (receptor for advanced glycation endproducts) signalling mediates an ILC2-intrinsic IL-13 auto-amplification loop. In summary, therapeutic targeting of the HMGB1/RAGE signalling axis may act as a novel asthma preventative by dampening ILC2-mediated type-2 inflammation and associated ASM remodelling.

Asthma can start at any time in life, although most often begins in early childhood. Wheezy viral bronchiolitis is a major independent risk factor for subsequent asthma. However, key knowledge gaps exist in relation to the sequelae of severe viral bronchiolitis and the pathogenic processes that promote type-2 inflammation and airway wall remodelling, cardinal features of asthma. Our study addresses this gap by identifying high-mobility group box 1 as a pathogenic cytokine that contributes to group 2 innate lymphoid cell-induced airway smooth muscle growth.

Innate Type 2 Responses to Respiratory Syncytial Virus Infection

Respiratory syncytial virus (RSV) is a common and contagious virus that results in acute respiratory tract infections in infants. In many cases, the symptoms of RSV remain mild, however, a subset of individuals develop severe RSV-associated bronchiolitis. As such, RSV is the chief cause of infant hospitalization within the United States. Typically, the immune response to RSV is a type 1 response that involves both the innate and adaptive immune systems. However, type 2 cytokines may also be produced as a result of infection of RSV and there is increasing evidence that children who develop severe RSV-associated bronchiolitis are at a greater risk of developing asthma later in life. This review summarizes the contribution of a newly described cell type, group 2 innate lymphoid cells (ILC2), and epithelial-derived alarmin proteins that activate ILC2, including IL-33, IL-25, thymic stromal lymphopoietin (TSLP), and high mobility group box 1 (HMGB1). ILC2 activation leads to the production of type 2 cytokines and the induction of a type 2 response during RSV infection. Intervening in this innate type 2 inflammatory pathway may have therapeutic implications for severe RSV-induced disease.

FKBP8 inhibits virus-induced RLR-VISA signaling

The mitochondrial antiviral signal protein mitochondrial antiviral signaling protein, also known as virus-induced signaling adaptor (VISA), plays a key role in regulating host innate immune signaling pathways. This study identifies FK506 binding protein 8 (FKBP8) as a candidate interacting protein of VISA through the yeast two-hybrid technique. The interaction of FKBP8 with VISA, retinoic acid inducible protein 1 (RIG-I), and IFN regulatory factor 3 (IRF3) was confirmed during viral infection in mammalian cells by coimmunoprecipitation. Overexpression of FKBP8 using a eukaryotic expression plasmid significantly attenuated Sendai virus-induced activation of the promoter interferons β (IFN-β), and transcription factors nuclear factor κ-light chain enhancer of activated B cells (NF-κB) and IFN-stimulated response element (ISRE). Overexpression of FKBP8 also decreased dimer-IRF3 activity, but enhanced virus replication. Conversely, knockdown of FKBP8 expression by RNA interference showed opposite effects. Further studies indicated that FKBP8 acts as a negative interacting partner to regulate RLR-VISA signaling by acting on VISA and TANK binding kinase 1 (TBK1). Additionally, FKBP8 played a negative role on virus-induced signaling by inhibiting the formation of TBK1-IRF3 and VISA-TRAF3 complexes. Notably, FKBP8 also promoted the degradation of TBK1, RIG-I, and TRAF3 resulting from FKBP8 reinforced Sendai virus-induced endogenous polyubiquitination of RIG-I, TBK1, and TNF receptor-associated factor 3 (TRAF3). Therefore, a novel function of FKBP8 in innate immunity antiviral signaling regulation was revealed in this study.

MiR-216a-5p protects 16HBE cells from H2O2-induced oxidative stress through targeting HMGB1/NF-kB pathway

Asthma is a complex, chronic inflammatory disorder of the bronchial tree, and can affect patients of all ages including children. High mobility group box 1 (HMGB1) has been proved as a therapeutic target in children with asthma, and was predicted to be the target gene of microRNA-216a-5p (miR-216a-5p). The present study aimed to investigate the function of miR-216a-5p in asthma by creating a human bronchial epithelial cell (16HBE) injury model using H₂O₂. A significantly elevation of HMGB1 protein expression and a reduction of miR-216a-5p expression were observed in children with asthma as well as in H₂O₂ stimulated 16HBE cells. Dual luciferase reporter assays confirmed the target reaction between HMGB1 and miR-216a-5p. MiR-216a-5p repressed HMGB1 protein expression in H₂O₂ induced 16HBE cells. Moreover, miR-216a-5p inhibited H₂O₂ induced cell injury by elevating cell proliferation and decreasing cell apoptosis in 16HBE cells. Furthermore, miR-216a-5p repressed NF-kB pathway activation in H₂O₂ induced 16HBE cells. In conclusion, these results suggested that miR-216a-5p functions as a negative regulator of H₂O₂ induced 16HBE cell injury through targeting HMGB1/NF-kB pathway, provided a potential therapeutic target for asthma.

Rig-I is involved in inflammation through the IPS-1/TRAF6 pathway in astrocytes under chemical hypoxia

The retinoic acid-inducible gene I (RIG-I) is a crucial cytoplasmic pathogen recognition receptor involved in neuroinflammation in degenerative diseases. In the present study, in vitro human astrocytes were subjected to a chemical hypoxia model using cobalt chloride pretreatment. Chemical hypoxia induces the up-regulation of RIG-I in astrocytes and results in the expression of inflammatory cytokines IL-1β, IL-6, and TNF-α in an NF-κB dependent manner. Elevated RIG-I modulates the interaction of interferon-β promoter stimulator-1 (IPS-1) and TNF receptor-associated factor 6 (TRAF6) following chemical hypoxia. Inhibition of IPS-1 or TRAF6 suppresses RIG-I-induced NF-κB activation and inflammatory cytokines in response to chemical hypoxia. These data suggest that chemical hypoxia leads to RIG-I activation and the expression of inflammatory cytokines through the NF-κB pathway. Blocking IPS-1/TRAF6 pathway relieves RIG-I-induced neuroinflammation in astrocytes subjected to hypoxia.

Role of viral infections in the development and exacerbation of asthma in children

Viral infections are closely linked to wheezing illnesses in children of all ages. Respiratory syncytial virus (RSV) is the main causative agent of bronchiolitis, whereas rhinovirus (RV) is most commonly detected in wheezing children thereafter. Severe respiratory illness induced by either of these viruses is associated with subsequent development of asthma, and the risk is greatest for young children who wheeze with RV infections. Whether viral illnesses actually cause asthma is the subject of intense debate. RSV-induced wheezing illnesses during infancy influence respiratory health for years. There is definitive evidence that RSV-induced bronchiolitis can damage the airways to promote airway obstruction and recurrent wheezing. RV likely causes less structural damage and yet is a significant contributor to wheezing illnesses in young children and in the context of asthma. For both viruses, interactions between viral virulence factors, personal risk factors (eg, genetics), and environmental exposures (eg, airway microbiome) promote more severe wheezing illnesses and the risk for progression to asthma. In addition, allergy and asthma are major risk factors for more frequent and severe RV-related illnesses. Treatments that inhibit inflammation have efficacy for RV-induced wheezing, whereas the anti-RSV mAb palivizumab decreases the risk of severe RSV-induced illness and subsequent recurrent wheeze. Developing a greater understanding of personal and environmental factors that promote more severe viral illnesses might lead to new strategies for the prevention of viral wheezing illnesses and perhaps reduce the subsequent risk for asthma.