Cell cycle arrest by transforming growth factor beta1 enhances replication of respiratory syncytial virus in lung epithelial cells

RNA-RNA interactions between respiratory syncytial virus and miR-26 and miR-27 are associated with regulation of cell cycle and antiviral immunity

microRNAs (miRNAs) regulate nearly all physiological processes but our understanding of exactly how they function remains incomplete, particularly in the context of viral infections. Here, we adapt a biochemical method (CLEAR-CLIP) and analysis pipeline to identify targets of miRNAs in lung cells infected with Respiratory syncytial virus (RSV). We show that RSV binds directly to miR-26 and miR-27 through seed pairing and demonstrate that these miRNAs target distinct gene networks associated with cell cycle and metabolism (miR-27) and antiviral immunity (miR-26). Many of the targets are de-repressed upon infection and we show that the miR-27 targets most sensitive to miRNA inhibition are those associated with cell cycle. Finally, we demonstrate that high confidence chimeras map to long noncoding RNAs (lncRNAs) and pseudogenes in transcriptional regulatory regions. We validate that a proportion of miR-27 and Argonaute 2 (AGO2) is nuclear and identify a long non-coding RNA (lncRNA) as a miR-27 target that is linked to transcriptional regulation of nearby genes. This work expands the target networks of miR-26 and miR-27 to include direct interactions with RSV and lncRNAs and implicate these miRNAs in regulation of key genes that impact the viral life cycle associated with cell cycle, metabolism, and antiviral immunity.

A map of signaling responses in the human airway epithelium

Receptor-mediated signaling plays a central role in tissue regeneration, and it is dysregulated in disease. Here, we build a signaling-response map for a model regenerative human tissue: the airway epithelium. We analyzed the effect of 17 receptor-mediated signaling pathways on organotypic cultures to determine changes in abundance and phenotype of epithelial cell types. This map recapitulates the gamut of known airway epithelial signaling responses to these pathways. It defines convergent states induced by multiple ligands and diverse, ligand-specific responses in basal cell and secretory cell metaplasia. We show that loss of canonical differentiation induced by multiple pathways is associated with cell-cycle arrest, but that arrest is not sufficient to block differentiation. Using the signaling-response map, we show that a TGFB1-mediated response underlies specific aberrant cells found in multiple lung diseases and identify interferon responses in COVID-19 patient samples. Thus, we offer a framework enabling systematic evaluation of tissue signaling responses. A record of this paper's transparent peer review process is included in the supplemental information.

Neuropilin 1 is an entry receptor for KSHV infection of mesenchymal stem cell through TGFBR1/2-mediated macropinocytosis

Kaposi's sarcoma-associated herpesvirus (KSHV) has been implicated in the pathogenesis of Kaposi's sarcoma (KS) and other malignancies. The cellular origin of KS has been suggested to be either mesenchymal stem cells (MSCs) or endothelial cells. However, receptor(s) for KSHV to infect MSCs remains unknown. By combining bioinformatics analysis and shRNA screening, we identify neuropilin 1 (NRP1) as an entry receptor for KSHV infection of MSCs. Functionally, NRP1 knockout and overexpression in MSCs significantly reduce and promote, respectively, KSHV infection. Mechanistically, NRP1 facilitated the binding and internalization of KSHV by interacting with KSHV glycoprotein B (gB), which was blocked by soluble NRP1 protein. Furthermore, NRP1 interacts with TGF-β receptor type 2 (TGFBR2) through their respective cytoplasmic domains and thus activates the TGFBR1/2 complex, which facilitates the macropinocytosis-mediated KSHV internalization via the small GTPases Cdc42 and Rac1. Together, these findings implicate that KSHV has evolved a strategy to invade MSCs by harnessing NRP1 and TGF-beta receptors to stimulate macropinocytosis.

Canine Distemper Virus Alters Defense Responses in an Ex Vivo Model of Pulmonary Infection

Canine distemper virus (CDV), belonging to the genus Morbillivirus, is a highly contagious pathogen. It is infectious in a wide range of host species, including domestic and wildlife carnivores, and causes severe systemic disease with involvement of the respiratory tract. In the present study, canine precision-cut lung slices (PCLSs) were infected with CDV (strain R252) to investigate temporospatial viral loads, cell tropism, ciliary activity, and local immune responses during early infection ex vivo. Progressive viral replication was observed during the infection period in histiocytic and, to a lesser extent, epithelial cells. CDV-infected cells were predominantly located within the bronchial subepithelial tissue. Ciliary activity was reduced in CDV-infected PCLSs, while viability remained unchanged when compared to controls. MHC-II expression was increased in the bronchial epithelium on day three postinfection. Elevated levels of anti-inflammatory cytokines (interleukin-10 and transforming growth factor-β) were observed in CDV-infected PCLSs on day one postinfection. In conclusion, the present study demonstrates that PCLSs are permissive for CDV. The model reveals an impaired ciliary function and an anti-inflammatory cytokine response, potentially fostering viral replication in the lung during the early phase of canine distemper.

The role of transforming growth factor beta-1 protein in Escherichia coli secondary infection induced by H9N2 avian influenza virus in chickens

The H9N2 subtype of avian influenza virus (AIV) is common in poultry production. It causes mild clinical signs but rarely leads to poultry mortalities. However, higher mortality can occur in chickens with co-infections, especially avian pathogenic Escherichia coli (APEC), which results in huge economic losses for the poultry industry. Unfortunately, the mechanism of co-infection remains unknown. Our previous studies screened several proteins associated with bacterial adhesion, including transforming growth factor beta-1 (TGF-β1), integrins, cortactin, E-cadherin, vinculin, and fibromodulin. Herein, we investigated the contribution of TGF-β1 to APEC adhesion after H9N2 infection. We first infected H9N2 and APEC in chicken, chicken embryo and DF-1 cells, and demonstrated that H9N2 infection promotes APEC adhesion to hosts in vitro and in vivo by plate count method. Through real-time fluorescence quantification and enzyme-linked immunosorbent assay, it was demonstrated that H9N2 infection not only increases TGF-β1 expression but also its activity in a time-dependent manner. Then, through exogenous addition of TGF-β1 and overexpression, we further demonstrated that TGF-β1 can increase the adhesion of endothelial cells to DF-1 cells. Furthermore, the capacity of APEC adhesion to DF-1 cells was significantly decreased either by adding a TGF-β1 receptor inhibitor or using small interfering RNAs to interfere with the expression of TGF-β1. To sum up, H9N2 infection can promote the upregulation of TGF-β1 and then increase the adhesion ability of APEC. Targeting TGF-β1 and its associated pathway will provide valuable insights into the clinical treatment of E. coli secondary infection induced by H9N2 infection.

A map of signaling responses in the human airway epithelium

Receptor-mediated signaling plays a central role in tissue regeneration, and it is dysregulated in disease. Here, we build a signaling-response map for a model regenerative human tissue: the airway epithelium. We analyzed the effect of 17 receptor-mediated signaling pathways on organotypic cultures to determine changes in abundance and phenotype of all epithelial cell types. This map recapitulates the gamut of known airway epithelial signaling responses to these pathways. It defines convergent states induced by multiple ligands and diverse, ligand-specific responses in basal-cell and secretory-cell metaplasia. We show that loss of canonical differentiation induced by multiple pathways is associated with cell cycle arrest, but that arrest is not sufficient to block differentiation. Using the signaling-response map, we show that a TGFB1-mediated response underlies specific aberrant cells found in multiple lung diseases and identify interferon responses in COVID-19 patient samples. Thus, we offer a framework enabling systematic evaluation of tissue signaling responses.

Modeling explains prolonged SARS-CoV-2 nasal shedding relative to lung shedding in remdesivir treated rhesus macaques

In clinical trials, remdesivir decreased recovery time in hospitalized patients with SARS- CoV-2 and prevented hospitalization when given early during infection, despite not reducing nasal viral loads. In rhesus macaques, early remdesivir prevented pneumonia and lowered lung viral loads, but viral loads increased in nasal passages after five days. We developed mathematical models to explain these results. Our model raises the hypotheses that: 1) in contrast to nasal passages viral load monotonically decreases in lungs during therapy because of infection-dependent generation of refractory cells, 2) slight reduction in lung viral loads with an imperfect agent may result in a substantial decrease in lung damage, and 3) increases in nasal viral load may occur due to a blunting of peak viral load which decreases the intensity of the innate immune response. We demonstrate that a higher potency drug could lower viral loads in nasal passages and lung.

The Role of Defective Epithelial Barriers in Allergic Lung Disease and Asthma Development

The respiratory epithelium constitutes the physical barrier between the human body and the environment, thus providing functional and immunological protection. It is often exposed to allergens, microbial substances, pathogens, pollutants, and environmental toxins, which lead to dysregulation of the epithelial barrier and result in the chronic inflammation seen in allergic diseases and asthma. This epithelial barrier dysfunction results from the disturbed tight junction formation, which are multi-protein subunits that promote cell-cell adhesion and barrier integrity. The increasing interest and evidence of the role of impaired epithelial barrier function in allergy and asthma highlight the need for innovative approaches that can provide new knowledge in this area. Here, we review and discuss the current role and mechanism of epithelial barrier dysfunction in developing allergic diseases and the effect of current allergy therapies on epithelial barrier restoration.

Respiratory syncytial virus infection induces the release of transglutaminase 2 from human airway epithelial cells

Respiratory syncytial virus (RSV) is an important human pathogen that causes severe lower respiratory tract infections in young children, the elderly, and the immunocompromised, yet no effective treatments or vaccines are available. The precise mechanism underlying RSV-induced acute airway disease and associated sequelae are not fully understood; however, early lung inflammatory and immune events are thought to play a major role in the outcome of the disease. Moreover, oxidative stress responses in the airways play a key role in the pathogenesis of RSV. Oxidative stress has been shown to elevate cytosolic calcium (Ca²⁺) levels, which in turn activate Ca²⁺-dependent enzymes, including transglutaminase 2 (TG2). Transglutaminase 2 is a multifunctional cross-linking enzyme implicated in various physiological and pathological conditions; however, its involvement in respiratory virus-induced airway inflammation is largely unknown. In this study, we demonstrated that RSV-induced oxidative stress promotes enhanced activation and release of TG2 from human lung epithelial cells as a result of its translocation from the cytoplasm and subsequent release into the extracellular space, which was mediated by Toll-like receptor (TLR)-4 and NF-κB pathways. Antioxidant treatment significantly inhibited RSV-induced TG2 extracellular release and activation via blocking viral replication. Also, treatment of RSV-infected lung epithelial cells with TG2 inhibitor significantly reduced RSV-induced matrix metalloprotease activities. These results suggested that RSV-induced oxidative stress activates innate immune receptors in the airways, such as TLRs, that can activate TG2 via the NF-κB pathway to promote cross-linking of extracellular matrix proteins, resulting in enhanced inflammation.

Multiple RNA virus matrix proteins interact with SLD5 to manipulate host cell cycle

The matrix protein of many enveloped RNA viruses regulates multiple stages of viral life cycle and has the characteristics of nucleocytoplasmic shuttling. We have previously demonstrated that matrix protein 1 (M1) of an RNA virus, influenza virus, blocks host cell cycle progression by interacting with SLD5, a member of the GINS complex, which is required for normal cell cycle progression. In this study, we found that M protein of several other RNA viruses, including VSV, SeV and HIV, interacted with SLD5. Furthermore, VSV/SeV infection and M protein of VSV/SeV/HIV induced cell cycle arrest at G0/G1 phase. Importantly, overexpression of SLD5 partially rescued the cell cycle arrest by VSV/SeV infection and VSV M protein. In addition, SLD5 suppressed VSV replication in vitro and in vivo, and enhanced type Ⅰ interferon signalling. Taken together, our results suggest that targeting SLD5 by M protein might be a common strategy used by multiple enveloped RNA viruses to block host cell cycle. Our findings provide new mechanistic insights for virus to manipulate cell cycle progression by hijacking host replication factor SLD5 during infection.

Reversible disruption of XPO1-mediated nuclear export inhibits respiratory syncytial virus (RSV) replication

Respiratory syncytial virus (RSV) is the primary cause of serious lower respiratory tract disease in infants, young children, the elderly and immunocompromised individuals. Therapy for RSV infections is limited to high risk infants and there are no safe and efficacious vaccines. Matrix (M) protein is a major RSV structural protein with a key role in virus assembly. Interestingly, M is localised to the nucleus early in infection and its export into the cytoplasm by the nuclear exporter, exportin-1 (XPO1) is essential for RSV assembly. We have shown previously that chemical inhibition of XPO1 function results in reduced RSV replication. In this study, we have investigated the anti-RSV efficacy of Selective Inhibitor of Nuclear Export (SINE) compounds, KPT-335 and KPT-185. Our data shows that therapeutic administration of the SINE compounds results in reduced RSV titre in human respiratory epithelial cell culture. Within 24 h of treatment, RSV replication and XPO1 expression was reduced, M protein was partially retained in the nucleus, and cell cycle progression was delayed. Notably, the effect of SINE compounds was reversible within 24 h after their removal. Our data show that reversible inhibition of XPO1 can disrupt RSV replication by affecting downstream pathways regulated by the nuclear exporter.

RSV attenuates epithelial cell restitution by inhibiting actin cytoskeleton-dependent cell migration

The airway epithelium's ability to repair itself after injury, known as epithelial restitution, is an essential mechanism enabling the respiratory tract's normal functions. Respiratory Syncytial Virus (RSV) is the leading cause of lower respiratory tract infections worldwide. We sought to determine whether RSV delays the airway epithelium wound repair process both in vitro and in vivo. We found that RSV infection attenuated epithelial cell migration, a step in wound repair, promoted stress fiber formation, and mediated assembly of large focal adhesions (FA). Inhibition of Rho kinase (ROCK), a master regulator of actin function, reversed these effects. There was increased RhoA and phospho-myosin light chain (pMLC2) following RSV infection. In vivo, mice were intraperitoneally inoculated with naphthalene to induce lung injury, followed by RSV infection. RSV infection delayed re-epithelialization. There were increased concentrations of pMLC2 in day 7 naphthalene plus RSV animals which normalized by day 14. This study suggests a key mechanism by which RSV infection delays wound healing.

TGF-β1 signaling inhibit the in vitro apoptotic, infection and stimulatory cell response induced by influenza H1N1 virus infection on A549 cells

Influenza A virus (IAV) infection induces host cell responses that could derive in inflammatory and apoptotic response. In this respect, in multiple pathological situations, TGF-β1 has shown anti-inflammatory effect, but its role during IAV infection is poorly understood. Interestingly, recent profiling expression studies have suggested that the TGF-β1 pathway could be functionally related to the IAV infection's host response. To gain an understanding of the involvement of TGF-β1's signaling pathway during IAV infection, we compared different apoptotic proteins such as TNFR1, Fas ligand, XIAP, cIAP, among others proteins, and pro-inflammatory elements like IL-1β in the A549 cells during IAV infection (H1N1/NC/99), with and without 1 h of pre-treatment with TGF-β1. Pre-incubation with TGF-β1 significantly inhibited apoptosis and the presence of pro-apoptotic factors. Moreover, the relative abundance of immunodetected IAV M1 protein along 24 -h post-infection period was abridged, which correlated with a disminished infectious viral progeny Additionally, caspase 1 activation and increase of IL-1β induced by IAV infection was also reduced by TGF-β1 signaling activation. Whereas IAV infection increase of Smad-7 and, as consequence, partially inhibiting Smad2/3 phosphorylation, pre-treatment with TGF-β1 blocked IAV-dependent Smad7 induction and prevented Smad2/3 signaling shutdown. All these data suggest the role of TGF-β1 signaling pathway in the control of host cell response induced by the IAV infection and identify a potential clinical target to modulate acute cell death.

Alternative mRNA Processing of Innate Response Pathways in Respiratory Syncytial Virus (RSV) Infection

The innate immune response (IIR) involves rapid genomic expression of protective interferons (IFNs) and inflammatory cytokines triggered by intracellular viral replication. Although the transcriptional control of the innate pathway is known in substantial detail, little is understood about the complexity of alternative splicing (AS) and alternative polyadenylation (APA) of mRNAs underlying the cellular IIR. In this study, we applied single-molecule, real-time (SMRT) sequencing with mRNA quantitation using short-read mRNA sequencing to characterize changes in mRNA processing in the epithelial response to respiratory syncytial virus (RSV) replication. Mock or RSV-infected human small-airway epithelial cells (hSAECs) were profiled using SMRT sequencing and the curated transcriptome analyzed by structural and quality annotation of novel transcript isoforms (SQANTI). We identified 113,082 unique isoforms; 28,561 represented full splice matches, and 45% of genes expressed six or greater AS mRNA isoforms. Identification of differentially expressed AS isoforms was accomplished by mapping a short-read RNA sequencing expression matrix to the curated transcriptome, and 905 transcripts underwent differential polyadenylation site analysis enriched in protein secretion, translation, and mRNA degradation. We focused on 355 genes showing differential isoform utilization (DIU), indicating where a new AS isoform becomes a major fraction of mRNA isoforms expressed. In pathway and network enrichment analyses, we observed that DIU transcripts are substantially enriched in cell cycle control and IIR pathways. Interestingly, the RelA/IRF7 innate regulators showed substantial DIU where major transcripts included distinct isoforms with exon occlusion, intron inclusion, and alternative transcription start site utilization. We validated the presence of RelA and IRF7 AS isoforms as well as their induction by RSV using eight isoform-specific RT-PCR assays. These isoforms were identified in both immortalized and primary small-airway epithelial cells. We concluded that the cell cycle and IIR are differentially spliced in response to RSV. These data indicate that substantial post-transcriptional complexity regulates the antiviral response.

Interferon-Induced Protein 44 and Interferon-Induced Protein 44-Like Restrict Replication of Respiratory Syncytial Virus

RSV infects all children under 2 years of age, but only a subset of children get severe disease. We hypothesize that susceptibility to severe RSV necessitating hospitalization in children without predefined risk factors is, in part, mediated at the antiviral gene level. However, there is a large array of antiviral genes, particularly in the ISG family, the mechanism of which is poorly understood. Having previously identified IFI44 and IFI44L as possible genes of interest in a bioinformatic screen, we dissected the function of these two genes in the control of RSV. Through a range of overexpression and knockout studies, we show that the genes are antiviral and antiproliferative. This study is important because IFI44 and IFI44L are upregulated after a wide range of viral infections, and IFI44L can serve as a diagnostic biomarker of viral infection.

Cellular intrinsic immunity, mediated by the expression of an array of interferon-stimulated antiviral genes, is a vital part of host defense. We have previously used a bioinformatic screen to identify two interferon-stimulated genes (ISG) with poorly characterized function, interferon-induced protein 44 (IFI44) and interferon-induced protein 44-like (IFI44L), as potentially being important in respiratory syncytial virus (RSV) infection. Using overexpression systems, CRISPR-Cas9-mediated knockout, and a knockout mouse model, we investigated the antiviral capability of these genes in the control of RSV replication. Overexpression of IFI44 or IFI44L was sufficient to restrict RSV infection at an early time postinfection. Knocking out these genes in mammalian airway epithelial cells increased levels of infection. Both genes express antiproliferative factors that have no effect on RSV attachment but reduce RSV replication in a minigenome assay. The loss of Ifi44 was associated with a more severe infection phenotype in a mouse model of infection. These studies demonstrate a function for IFI44 and IFI44L in controlling RSV infection.

IMPORTANCE RSV infects all children under 2 years of age, but only a subset of children get severe disease. We hypothesize that susceptibility to severe RSV necessitating hospitalization in children without predefined risk factors is, in part, mediated at the antiviral gene level. However, there is a large array of antiviral genes, particularly in the ISG family, the mechanism of which is poorly understood. Having previously identified IFI44 and IFI44L as possible genes of interest in a bioinformatic screen, we dissected the function of these two genes in the control of RSV. Through a range of overexpression and knockout studies, we show that the genes are antiviral and antiproliferative. This study is important because IFI44 and IFI44L are upregulated after a wide range of viral infections, and IFI44L can serve as a diagnostic biomarker of viral infection.

Network pharmacology to dissect the mechanisms of Yinlai Decoction for pneumonia

BACKGROUND

Pneumonia is a common respiratory disorder, which brings an enormous financial burden to the medical system. However, the current treatment options for pneumonia are limited because of drug resistance and side effects. Our previous study preliminarily confirmed that Yinlai Decoction (YD), a common prescription for pneumonia in clinical practice, can regulate the expression of inflammatory factors, but the mechanisms are unknown yet.

METHODS

In our work, a method named network pharmacology was applied, which investigated the underlying mechanisms of herbs based on a variety of databases. We obtained bioactive ingredients of YD on TCMSP database and collected potential targets of these ingredients by target fishing. Then the pneumonia-related targets database was built by TTD, Drugbank, HPO, OMIM, and CTD. Based on the matching targets between YD and pneumonia, the PPI network was built by STRING to analyze the interactions among these targets and then input into Cytoscape for further topological analysis. DAVID and KEGG were utilized for GO and pathway enrichment analysis. Then rat model based on LPS stimulated pneumonia was used to verify the possible mechanism of YD in treating pneumonia.

RESULTS

Sixty-eight active ingredients, 103 potential targets and 8 related pathways, which likely exert a number of effects, were identified. Three networks were constructed using Cytoscape, which were herb-component-network, YD-pneumonia target network, and herb-component-YD target-pneumonia network. YD was verified to treat LPS-induced pneumonia by regulating the inflammatory factor IL-6, which was a predicted target.

CONCLUSION

Network analysis indicated that YD could alleviate the symptoms and signs of pneumonia through regulating host immune inflammatory response, angiogenesis and vascular permeability, the barrier function of the airway epithelial cells, hormone releasing and cell growth, proliferation, and apoptosis.

Non-Coding RNAs and Their Role in Respiratory Syncytial Virus (RSV) and Human Metapneumovirus (hMPV) Infections

Recent high-throughput sequencing revealed that only 2% of the transcribed human genome codes for proteins, while the majority of transcriptional products are non-coding RNAs (ncRNAs). Herein, we review the current knowledge regarding ncRNAs, both host- and virus-derived, and their role in respiratory syncytial virus (RSV) and human metapneumovirus (hMPV) infections. RSV is known as the most common cause of lower respiratory tract infection (LRTI) in children, while hMPV is also a significant contributor to LRTI in the pediatrics population. Although RSV and hMPV are close members, belonging to the Pneumoviridae family, they induce distinct changes in the ncRNA profile. Several types of host ncRNAs, including long ncRNA (lncRNA), microRNAs (miRNAs), and transfer RNA (tRNA)-derived RNA fragments (tRFs), are involved as playing roles in RSV and/or hMPV infection. Given the importance of ncRNAs in regulating the expression and functions of genes and proteins, comprehensively understanding the roles of ncRNAs in RSV/hMPV infection could shed light upon the disease mechanisms of RSV and hMPV, potentially providing insights into the development of prevention strategies and antiviral therapy. The presence of viral-derived RNAs and the potential of using ncRNAs as diagnostic biomarkers are also discussed in this review.

How the Respiratory Epithelium Senses and Reacts to Influenza Virus

The human lung is constantly exposed to the environment and potential pathogens. As the interface between host and environment, the respiratory epithelium has evolved sophisticated sensing mechanisms as part of its defense against pathogens. In this review, we examine how the respiratory epithelium senses and responds to influenza A virus, the biggest cause of respiratory viral deaths worldwide.

Determining Immune and miRNA Biomarkers Related to Respiratory Syncytial Virus (RSV) Vaccine Types

Respiratory Syncytial Virus (RSV) causes serious respiratory tract illness and substantial morbidity and some mortality in populations at the extremes of age, i.e., infants, young children, and the elderly. To date, RSV vaccine development has been unsuccessful, a feature linked to the lack of biomarkers available to assess the safety and efficacy of RSV vaccine candidates. We examined microRNAs (miR) as potential biomarkers for different types of RSV vaccine candidates. In this study, mice were vaccinated with a live attenuated RSV candidate that lacks the small hydrophobic (SH) and attachment (G) proteins (CP52), an RSV G protein microparticle (GA2-MP) vaccine, a formalin-inactivated RSV (FI-RSV) vaccine or were mock-treated. Several immunological endpoints and miR expression profiles were determined in mouse serum and bronchoalveolar lavage (BAL) following vaccine priming, boost, and RSV challenge. We identified miRs that were linked with immunological parameters of disease and protection. We show that miRs are potential biomarkers providing valuable insights for vaccine development.

Airway Epithelial Derived Cytokines and Chemokines and Their Role in the Immune Response to Respiratory Syncytial Virus Infection

The airway epithelium is the primary target of respiratory syncytial virus infection. It is an important component of the antiviral immune response. It contributes to the recruitment and activation of innate immune cells from the periphery through the secretion of cytokines and chemokines. This paper provides a broad review of the cytokines and chemokines secreted from human airway epithelial cell models during respiratory syncytial virus (RSV) infection based on a comprehensive literature review. Epithelium-derived chemokines constitute most inflammatory mediators secreted from the epithelium during RSV infection. This suggests chemo-attraction of peripheral immune cells, such as monocytes, neutrophils, eosinophils, and natural killer cells as a key function of the epithelium. The reports of epithelium-derived cytokines are limited. Recent research has started to identify novel cytokines, the functions of which remain largely unknown in the wider context of the RSV immune response. It is argued that the correct choice of in vitro models used for investigations of epithelial immune functions during RSV infection could facilitate greater progress in this field.

Regulatory cytokine function in the respiratory tract

The respiratory tract is an important site of immune regulation; required to allow protective immunity against pathogens, while minimizing tissue damage and avoiding aberrant inflammatory responses to inhaled allergens. Several cell types work in concert to control pulmonary immune responses and maintain tolerance in the respiratory tract, including regulatory and effector T cells, airway and interstitial macrophages, dendritic cells and the airway epithelium. The cytokines transforming growth factor β, interleukin (IL-) 10, IL-27, and IL-35 are key coordinators of immune regulation in tissues such as the lung. Here, we discuss the role of these cytokines during respiratory infection and allergic airway disease, highlighting the critical importance of cellular source and immunological context for the effects of these cytokines in vivo.

Louis I, Schiff LA, Bohjanen PR. Reovirus infection induces stabilization and up-regulation of cellular transcripts that encode regulators of TGF-β signaling

Reovirus infection induces dramatic changes in host mRNA expression. We utilized oligonucleotide microarrays to measure cellular mRNA decay rates in mock- or reovirus-infected murine L929 cells to determine if changes in host mRNA expression are a consequence of reovirus-induced alterations in cellular mRNA stability. Our analysis detected a subset of cellular transcripts that were coordinately induced and stabilized following infection with the reovirus isolates c87 and c8, strains that led to an inhibition of cellular translation, but not following infection with Dearing, a reovirus isolate that did not negatively impact cellular translation. The induced and stabilized transcripts encode multiple regulators of TGF- β signaling, including components of the Smad signaling network and apoptosis/survival pathways. The coordinate induction, through mRNA stabilization, of multiple genes that encode components of TGF-β signaling pathways represents a novel mechanism by which the host cell responds to reovirus infection.

Human lung epithelial cells support human metapneumovirus persistence by overcoming apoptosis

Human metapneumovirus (hMPV) has been identified as a major cause of lower respiratory tract infection in children. Epidemiological and molecular evidence has highlighted an association between severe childhood respiratory viral infection and chronic lung diseases, such as asthma and chronic obstructive pulmonary disease. Currently, animal models have demonstrated the ability of hMPV to persist in vivo suggesting a role of the virus in asthma development in children. However, mechanisms involved in hMPV persistence in the respiratory tract are not yet understood. In the present study we monitored hMPV infection in human alveolar epithelial A549 cells in order to understand if the virus is able to persist in these cells upon acute infection. Our data show that hMPV initially induces an apoptotic process in A549 cells through poly (ADP-ribose) polymerase 1 cleavage, caspase-3/7 activation and Wee1 activity. The hMPV-infected cells were then able to overcome the apoptotic pathway and cell cycle arrest in G2/M by expressing B-cell lymphoma 2 and to acquire a reservoir cell phenotype with constant production of infectious virus. These findings provide evidence of the ability of hMPV to persist in alveolar epithelial cells and help in understanding the mechanisms responsible for hMPV persistence in the human respiratory tract.

The role of respiratory epithelium in host defence against influenza virus infection

The respiratory epithelium is the major interface between the environment and the host. Sophisticated barrier, sensing, anti-microbial and immune regulatory mechanisms have evolved to help maintain homeostasis and to defend the lung against foreign substances and pathogens. During influenza virus infection, these specialised structural cells and populations of resident immune cells come together to mount the first response to the virus, one which would play a significant role in the immediate and long term outcome of the infection. In this review, we focus on the immune defence machinery of the respiratory epithelium and briefly explore how it repairs and regenerates after infection.

Epithelial-derived TGF-β1 acts as a pro-viral factor in the lung during influenza A infection

Mucosal surfaces are under constant bombardment from potentially antigenic particles and so must maintain a balance between homeostasis and inappropriate immune activation and consequent pathology. Epithelial cells have a vital role orchestrating pulmonary homeostasis and defense against pathogens. TGF-β regulates an array of immune responses-both inflammatory and regulatory-however, its function is highly location- and context-dependent. We demonstrate that epithelial-derived TGF-β acts as a pro-viral factor suppressing early immune responses during influenza A infection. Mice specifically lacking bronchial epithelial TGF-β1 (epTGFβKO) displayed marked protection from influenza-induced weight loss, airway inflammation, and pathology. However, protection from influenza-induced pathology was not associated with a heightened lymphocytic immune response. In contrast, the kinetics of interferon beta (IFNβ) release into the airways was significantly enhanced in epTGFβKO mice compared with control mice, with elevated IFNβ on day 1 in epTGFβKO compared with control mice. This induced a heighted antiviral state resulting in impaired viral replication in epTGFβKO mice. Thus, epithelial-derived TGF-β acts to suppress early IFNβ responses leading to increased viral burden and pathology. This study demonstrates the importance of the local epithelial microenvironmental niche in shaping initial immune responses to viral infection and controlling host disease.

Safer approaches to therapeutic modulation of TGF-β signaling for respiratory disease

The transforming growth factor (TGF)-β cytokines play a central role in development and progression of chronic respiratory diseases. TGF-β overexpression in chronic inflammation, remodeling, fibrotic process and susceptibility to viral infection is established in the most prevalent chronic respiratory diseases including asthma, COPD, lung cancer and idiopathic pulmonary fibrosis. Despite the overwhelming burden of respiratory diseases in the world, new pharmacological therapies have been limited in impact. Although TGF-β inhibition as a therapeutic strategy carries great expectations, the constraints in avoiding compromising the beneficial pleiotropic effects of TGF-β, including the anti-proliferative and immune suppressive effects, have limited the development of effective pharmacological modulators. In this review, we focus on the pathways subserving deleterious and beneficial TGF-β effects to identify strategies for selective modulation of more distal signaling pathways that may result in agents with improved safety/efficacy profiles. Adverse effects of TGF-β inhibitors in respiratory clinical trials are comprehensively reviewed, including those of the marketed TGF-β modulators, pirfenidone and nintedanib. Precise modulation of TGF-β signaling may result in new safer therapies for chronic respiratory diseases.

In the Shadow of Fibrosis: Innate Immune Suppression Mediated by Transforming Growth Factor-β

Transforming growth factor-β (TGFB) regulates cell proliferation, differentiation, apoptosis, and matrix homeostasis and is intimately involved in fibrosis. TGFB expression is increased in fibrotic lung diseases, such as idiopathic pulmonary fibrosis, and in chronic inflammatory conditions, such as chronic obstructive pulmonary disease and asthma. In addition to exhibiting profibrotic activities, the protein exhibits profound immune-suppressive actions involving both innate and adaptive responses, but often this aspect of TGFB biology is overlooked. Recent investigations have demonstrated that TGFB causes wide-ranging immune suppression, including blunting of pivotal early innate IFN responses. These activities permit severe virus infections, often followed by secondary bacterial infections, which may last longer, with augmented inflammation, scarring, fibrosis, and loss of lung function. Strategies to oppose TGFB actions or to enhance IFN responses may help ameliorate the detrimental consequences of infection in patients with diseases characterized by TGFB overexpression, inflammation, and fibrosis.

A comparison of host gene expression signatures associated with infection in vitro by the Makona and Ecran (Mayinga) variants of Ebola virus

The Ebola virus (EBOV) variant Makona (which emerged in 2013) was the causative agent of the largest outbreak of Ebola Virus Disease recorded. Differences in virus-host interactions between viral variants have potential consequences for transmission, disease severity and mortality. A detailed profile of the cellular changes induced by the Makona variant compared with other Ebola virus variants was lacking. In this study, A549 cells, a human cell line with a robust innate response, were infected with the Makona variant or with the Ecran variant originating from the 1976 outbreak in Central Africa. The abundance of viral and cellular mRNA transcripts was profiled using RNASeq and differential gene expression analysis performed. Differences in effects of each virus on the expression of interferon-stimulated genes were also investigated in A549 NPro cells where the type 1 interferon response had been attenuated. Cellular transcriptomic changes were compared with those induced by human respiratory syncytial virus (HRSV), a virus with a similar genome organisation and replication strategy to EBOV. Pathway and gene ontology analysis revealed differential expression of functionally important genes; including genes involved in the inflammatory response, cell proliferation, leukocyte extravasation and cholesterol biosynthesis. Whilst there was overlap with HRSV, there was unique commonality to the EBOV variants.

C-phycocyanin suppresses transforming growth factor-β1-induced epithelial mesenchymal transition in human epithelial cells

BACKGROUND

Epithelial mesenchymal transition (EMT) is a process through which epithelial cells undergo multiple biochemical changes, causing them to differentiate into a mesenchymal-cell phenotype. This process has been shown to contribute to the development of fibrotic diseases. C-phycocyanin (C-PC) is a phycobiliprotein extracted from Spirulina platensis. This study was done to investigate the effect of C-PC on transforming growth factor-β1 (TGF-β1)-induced EMT and an EMT associated proliferation in human epithelial cell lines.

METHODS

Human adenocarcinoma cell line, A549 and breast cancer cell line, MCF-7 were treated with TGF-β1, and EMT-related genes expression, cell proliferation and cell cycle arrest were examined.

RESULTS

C-PC suppressed the EMT as assessed by reduced expression of vimentin, type-1-collagen and fibronectin, and increased E-cadherin expression in TGF-β1 treated cells. Further, TGF-β1 treatment induced cell cycle arrest in S and G2/M phase in A549 cells. However, TGF-β1-mediated cell cycle arrest was significantly reversed by combined treatment with C-PC.

CONCLUSIONS

The overall data suggested that C-PC suppresses TGF- β1-induced EMT and warrants further in vivo studies for future evaluation of C-PC as a potential antifibrotic agent.

Glucocorticoid Insensitivity in Virally Infected Airway Epithelial Cells Is Dependent on Transforming Growth Factor-β Activity

Asthma and chronic obstructive pulmonary disease (COPD) exacerbations are commonly associated with respiratory syncytial virus (RSV), rhinovirus (RV) and influenza A virus (IAV) infection. The ensuing airway inflammation is resistant to the anti-inflammatory actions of glucocorticoids (GCs). Viral infection elicits transforming growth factor-β (TGF-β) activity, a growth factor we have previously shown to impair GC action in human airway epithelial cells through the activation of activin-like kinase 5 (ALK5), the type 1 receptor of TGF-β. In the current study, we examine the contribution of TGF-β activity to the GC-resistance caused by viral infection. We demonstrate that viral infection of human bronchial epithelial cells with RSV, RV or IAV impairs GC anti-inflammatory action. Poly(I:C), a synthetic analog of double-stranded RNA, also impairs GC activity. Both viral infection and poly(I:C) increase TGF-β expression and activity. Importantly, the GC impairment was attenuated by the selective ALK5 (TGFβRI) inhibitor, SB431542 and prevented by the therapeutic agent, tranilast, which reduced TGF-β activity associated with viral infection. This study shows for the first time that viral-induced glucocorticoid-insensitivity is partially mediated by activation of endogenous TGF-β.

In this study, we investigate how respiratory viral infection interferes with the anti-inflammatory actions of glucocorticoid (GC) drugs, which are a highly effective group of anti-inflammatory agents widely used in the treatment of chronic inflammatory airway diseases, including asthma and chronic obstructive pulmonary disease (COPD). Exacerbations of both asthma (“asthma attacks”) and COPD are often caused by viral infection, which does not respond well to GC therapy. Patients are often hospitalized placing a large burden on healthcare systems around the world, with the young, elderly, and those with a poor immune system particularly at risk. We show that viral infection of airway epithelial cells causes increased expression and activity of transforming growth factor-beta (TGF-β), which interferes with GC drug action. Importantly, we have shown for the first time that inhibiting TGF-β activity in the airways could serve as a new strategy to prevent and/or treat viral exacerbations of chronic airway diseases.

Autophagy, TGF-β, and SMAD-2/3 Signaling Regulates Interferon-β Response in Respiratory Syncytial Virus Infected Macrophages

Human respiratory syncytial virus (RSV) is a lung tropic virus causing severe airway diseases including bronchiolitis and pneumonia among infants, children, and immuno-compromised individuals. RSV triggers transforming growth factor-β (TGF-β) production from lung epithelial cells and TGF-β facilitates RSV infection of these cells. However, it is still unknown whether RSV infected myeloid cells like macrophages produce TGF-β and the role of TGF-β if any during RSV infection of these cells. Our study revealed that RSV infected macrophages produce TGF-β and as a consequence these cells activate TGF-β dependent SMAD-2/3 signaling pathway. Further mechanistic studies illustrated a role of autophagy in triggering TGF-β production from RSV infected macrophages. In an effort to elucidate the role of TGF-β and SMAD-2/3 signaling during RSV infection, we surprisingly unfolded the requirement of TGF-β—SMAD2/3 signaling in conferring optimal innate immune antiviral response during RSV infection of macrophages. Type-I interferon (e.g., interferon-β or IFN-β) is a critical host factor regulating innate immune antiviral response during RSV infection. Our study revealed that loss of TGF-β—SMAD2/3 signaling pathway in RSV infected macrophages led to diminished expression and production of IFN-β. Inhibiting autophagy in RSV infected macrophages also resulted in reduced production of IFN-β. Thus, our studies have unfolded the requirement of autophagy—TGF-β—SMAD2/3 signaling network for optimal innate immune antiviral response during RSV infection of macrophages.

The genetic and epigenetic landscapes of the epithelium in asthma

Asthma is a global health problem with increasing prevalence. The airway epithelium is the initial barrier against inhaled noxious agents or aeroallergens. In asthma, the airway epithelium suffers from structural and functional abnormalities and as such, is more susceptible to normally innocuous environmental stimuli. The epithelial structural and functional impairments are now recognised as a significant contributing factor to asthma pathogenesis. Both genetic and environmental risk factors play important roles in the development of asthma with an increasing number of genes associated with asthma susceptibility being expressed in airway epithelium. Epigenetic factors that regulate airway epithelial structure and function are also an attractive area for assessment of susceptibility to asthma. In this review we provide a comprehensive discussion on genetic factors; from using linkage designs and candidate gene association studies to genome-wide association studies and whole genome sequencing, and epigenetic factors; DNA methylation, histone modifications, and non-coding RNAs (especially microRNAs), in airway epithelial cells that are functionally associated with asthma pathogenesis. Our aims were to introduce potential predictors or therapeutic targets for asthma in airway epithelium. Overall, we found very small overlap in asthma susceptibility genes identified with different technologies. Some potential biomarkers are IRAKM, PCDH1, ORMDL3/GSDMB, IL-33, CDHR3 and CST1 in airway epithelial cells. Recent studies on epigenetic regulatory factors have further provided novel insights to the field, particularly their effect on regulation of some of the asthma susceptibility genes (e.g. methylation of ADAM33). Among the epigenetic regulatory mechanisms, microRNA networks have been shown to regulate a major portion of post-transcriptional gene regulation. Particularly, miR-19a may have some therapeutic potential.

Expression of the NS5 (VPg) Protein of Murine Norovirus Induces a G1/S Phase Arrest

Murine norovirus-1 (MNV-1) is known to subvert host cell division inducing an accumulation of cells in the G₀/G₁ phase, creating conditions where viral replication is favored. This study identified that NS5 (VPg), is capable of inducing cell cycle arrest in the absence of viral replication or other viral proteins in an analogous manner to MNV-1 infection. NS5 expression induced an accumulation of cells in the G₀/G₁ phase in an asynchronous population by inhibiting progression at the G₁/S restriction point. Furthermore, NS5 expression resulted in a down-regulation of cyclin A expression in asynchronous cells and inhibited cyclin A expression in cells progressing from G₁ to S phase. The activity of NS5 on the host cell cycle occurs through an uncharacterized function. Amino acid substitutions of NS5(Y26A) and NS5(F123A) that inhibit the ability for NS5 to attach to RNA and recruit host eukaryotic translation initiation factors, respectively, retained the ability to induce an accumulation of cells in the G₀/G₁ phase as identified for wild-type NS5. To the best of our knowledge, this is the first report of a VPg protein manipulating the host cell cycle.

Regulation of group 2 innate lymphoid cells

Group 2 innate lymphoid cells (ILC2) exert critical roles in type 2 immune responses, epithelial repair at mucosal tissues and metabolic homeostasis. ILC2 rapidly provide large amounts of type 2 signature cytokines, thereby driving type 2 immune responses such as the defense against helminths. However, if deregulated, ILC2 facilitate tissue fibrosis and trigger unwanted type 2 immunopathologies such as allergies, asthma and atopic dermatitis. Therefore, ILC2 need to be tightly regulated and we are just beginning to understand which mediators activate or inhibit this rare but important cell population. In this review, we summarize current knowledge about positive and negative regulation of ILC2 and discuss its immunological consequences.

Human respiratory syncytial virus non-structural protein NS1 modifies miR-24 expression via transforming growth factor-β

Human respiratory syncytial virus (RSV) is a major health challenge in the young and elderly owing to the lack of a safe and effective vaccine and proven antiviral drugs. Understanding the mechanisms by which viral genes and proteins modulate the host response to infection is critical for identifying novel disease intervention strategies. In this study, the RSV non-structural protein NS1 was shown to suppress miR-24 expression during infection. Lack of NS1 was linked to increased expression of miR-24, whilst NS1 overexpression suppressed miR-24 expression. NS1 was found to induce Kruppel-like factor 6 (KLF6), a transcription factor that positively regulates the transforming growth factor (TGF)-b pathway to induce cell cycle arrest. Silencing of KLF6 led to increased miR-24 expression via downregulation of TGF-β. Treatment with exogenous TGF-β suppressed miR-24 expression and induced KLF6. Confocal microscopy showed co-localization of KLF6 and RSV NS1. These findings indicated that RSV NS1 interacts with KLF6 and modulates miR-24 expression and TGF-β, which facilitates RSV replication.

Induction of DNA double-strand breaks and cellular senescence by human respiratory syncytial virus

Human respiratory syncytial virus (HRSV) accounts for the majority of lower respiratory tract infections during infancy and childhood and is associated with significant morbidity and mortality. HRSV provokes a proliferation arrest and characteristic syncytia in cellular systems such as immortalized epithelial cells. We show here that HRSV induces the expression of DNA damage markers and proliferation arrest such as P-TP53, P-ATM, CDKN1A and γH2AFX in cultured cells secondary to the production of mitochondrial reactive oxygen species (ROS). The DNA damage foci contained γH2AFX and TP53BP1, indicative of double-strand breaks (DSBs) and could be reversed by antioxidant treatments such as N-Acetylcysteine (NAC) or reduced glutathione ethyl ester (GSHee). The damage observed is associated with the accumulation of senescent cells, displaying a canonical senescent phenotype in both mononuclear cells and syncytia. In addition, we show signs of DNA damage and aging such as γH2AFX and CDKN2A expression in the respiratory epithelia of infected mice long after viral clearance. Altogether, these results show that HRSV triggers a DNA damage-mediated cellular senescence program probably mediated by oxidative stress. The results also suggest that this program might contribute to the physiopathology of the infection, tissue remodeling and aging, and might be associated to long-term consequences of HRSV infections.

A Recombinant G Protein Plus Cyclosporine A-Based Respiratory Syncytial Virus Vaccine Elicits Humoral and Regulatory T Cell Responses against Infection without Vaccine-Enhanced Disease

Respiratory syncytial virus (RSV) infection can cause severe disease in the lower respiratory tract of infants and older people. Vaccination with a formalin-inactivated RSV vaccine (FI-RSV) and subsequent RSV infection has led to mild to severe pneumonia with two deaths among vaccinees. The vaccine-enhanced disease (VED) was recently demonstrated to be due to an elevated level of Th2 cell responses following loss of regulatory T (Treg) cells from the lungs. To induce high levels of neutralizing Abs and minimize pathogenic T cell responses, we developed a novel strategy of immunizing animals with a recombinant RSV G protein together with cyclosporine A. This novel vaccine induced not only a higher level of neutralizing Abs against RSV infection, but, most importantly, also significantly higher levels of Treg cells that suppressed VED in the lung after RSV infection. The induced responses provided protection against RSV challenge with no sign of pneumonia or bronchitis. Treg cell production of IL-10 was one of the key factors to suppress VED. These finding indicate that G protein plus cyclosporine A could be a promising vaccine against RSV infection in children and older people.

Pulmonary Epithelial Cell-Derived Cytokine TGF-β1 Is a Critical Cofactor for Enhanced Innate Lymphoid Cell Function

Epithelial cells orchestrate pulmonary homeostasis and pathogen defense and play a crucial role in the initiation of allergic immune responses. Maintaining the balance between homeostasis and inappropriate immune activation and associated pathology is particularly complex at mucosal sites that are exposed to billions of potentially antigenic particles daily. We demonstrated that epithelial cell-derived cytokine TGF-β had a central role in the generation of the pulmonary immune response. Mice that specifically lacked epithelial cell-derived TGF-β1 displayed a reduction in type 2 innate lymphoid cells (ILCs), resulting in suppression of interleukin-13 and hallmark features of the allergic response including airway hyperreactivity. ILCs in the airway lumen were primed to respond to TGF-β by expressing the receptor TGF-βRII and ILC chemoactivity was enhanced by TGF-β. These data demonstrate that resident epithelial cells instruct immune cells, highlighting the central role of the local environmental niche in defining the nature and magnitude of immune reactions.

Modulation of host adaptive immunity by hRSV proteins

Globally, the human respiratory syncytial virus (hRSV) is the major cause of lower respiratory tract infections (LRTIs) in infants and children younger than 2 years old. Furthermore, the number of hospitalizations due to LRTIs has shown a sustained increase every year due to the lack of effective vaccines against hRSV. Thus, this virus remains as a major public health and economic burden worldwide. The lung pathology developed in hRSV-infected humans is characterized by an exacerbated inflammatory and Th2 immune response. In order to rationally design new vaccines and therapies against this virus, several studies have focused in elucidating the interactions between hRSV virulence factors and the host immune system. Here, we discuss the main features of hRSV biology, the processes involved in virus recognition by the immune system and the most relevant mechanisms used by this pathogen to avoid the antiviral host response.

Influenza viral neuraminidase primes bacterial coinfection through TGF-β-mediated expression of host cell receptors

Influenza infection predisposes the host to secondary bacterial pneumonia, which is a major cause of mortality during influenza epidemics. The molecular mechanisms underlying the bacterial coinfection remain elusive. Neuraminidase (NA) of influenza A virus (IAV) enhances bacterial adherence and also activates TGF-β. Because TGF-β can up-regulate host adhesion molecules such as fibronectin and integrins for bacterial binding, we hypothesized that activated TGF-β during IAV infection contributes to secondary bacterial infection by up-regulating these host adhesion molecules. Flow cytometric analyses of a human lung epithelial cell line indicated that the expression of fibronectin and α5 integrin was up-regulated after IAV infection or treatment with recombinant NA and was reversed through the inhibition of TGF-β signaling. IAV-promoted adherence of group A Streptococcus (GAS) and other coinfective pathogens that require fibronectin for binding was prevented significantly by the inhibition of TGF-β. However, IAV did not promote the adherence of Lactococcus lactis unless this bacterium expressed the fibronectin-binding protein of GAS. Mouse experiments showed that IAV infection enhanced GAS colonization in the lungs of wild-type animals but not in the lungs of mice deficient in TGF-β signaling. Taken together, these results reveal a previously unrecognized mechanism: IAV NA enhances the expression of cellular adhesins through the activation of TGF-β, leading to increased bacterial loading in the lungs. Our results suggest that TGF-β and cellular adhesins may be potential pharmaceutical targets for the prevention of coinfection.

Marked induction of matrix metalloproteinase-10 by respiratory syncytial virus infection in human nasal epithelial cells

Respiratory syncytial virus (RSV) is an important pathogen of bronchiolitis, asthma, and severe lower respiratory tract disease in infants and young children. Matrix metalloproteinases (MMPs) play key roles in viral infection, inflammation and remodeling of the airway. However, the roles and regulation of MMPs in human nasal epithelial cells (HNECs) after RSV infection remain unclear. To investigate the regulation of MMP induced after RSV infection in HNECs, an RSV-infected model of HNECs in vitro was used. It was found that mRNA of MMP-10 was markedly increased in HNECs after RSV infection, together with induction of mRNAs of MMP-1, -7, -9, and -19. The amount of MMP-10 released from HNECs was also increased in a time-dependent manner after RSV infection as was that of chemokine RANTES. The upregulation of MMP-10 in HNECs after RSV infection was prevented by inhibitors of NF-κB and pan-PKC with inhibition of RSV replication, whereas it was prevented by inhibitors of JAK/STAT, MAPK, and EGF receptors without inhibition of RSV replication. In lung tissue of an infant with severe RSV infection in which a few RSV antibody-positive macrophages were observed, MMP-10 was expressed at the apical side of the bronchial epithelial cells and alveolar epithelial cells. In conclusion, MMP-10 induced by RSV infection in HNECs is regulated via distinct signal transduction pathways with or without relation to RSV replication. MMP-10 may play an important role in the pathogenesis of RSV diseases and it has the potential to be a novel marker and therapeutic target for RSV infection.

Viral degradasome hijacks mitochondria to suppress innate immunity

The balance between the innate immunity of the host and the ability of a pathogen to evade it strongly influences pathogenesis and virulence. The two nonstructural (NS) proteins, NS1 and NS2, of respiratory syncytial virus (RSV) are critically required for RSV virulence. Together, they strongly suppress the type I interferon (IFN)-mediated innate immunity of the host cells by degrading or inhibiting multiple cellular factors required for either IFN induction or response pathways, including RIG-I, IRF3, IRF7, TBK1 and STAT2. Here, we provide evidence for the existence of a large and heterogeneous degradative complex assembled by the NS proteins, which we named "NS-degradasome" (NSD). The NSD is roughly ∼300-750 kD in size, and its degradative activity was enhanced by the addition of purified mitochondria in vitro. Inside the cell, the majority of the NS proteins and the substrates of the NSD translocated to the mitochondria upon RSV infection. Genetic and pharmacological evidence shows that optimal suppression of innate immunity requires mitochondrial MAVS and mitochondrial motility. Together, we propose a novel paradigm in which the mitochondria, known to be important for the innate immune activation of the host, are also important for viral suppression of the innate immunity.

Human but Not Laboratory Borna Disease Virus Inhibits Proliferation and Induces Apoptosis in Human Oligodendrocytes In Vitro

Borna disease virus (BDV) is a neurotropic virus that produces neuropsychiatric dysfunction in a wide range of warm-blooded species. Several studies have associated BDV with human psychiatric illness, but the findings remain controversial. Although oligodendrocytes are a major glial component of brain white matter and play a pivotal role in neuronal cell function, BDV's effects on human oligodendrocytes have not been clarified. Here, the effects of two BDV strains, Hu-H1 (isolated from a bipolar patient) and Strain V (a laboratory strain), on the proliferation and apoptosis of human oligodendrocytes were investigated. Three experimental cell lines were constructed: Hu-H1-infected oligodendroglioma (Hu-H1) cells, Strain V-infected oligodendroglioma (Strain V) cells, and non-infected oligodendroglioma (control) cells. BDV infection was assayed by BDV nucleoprotein (p40) immunofluorescence, cell proliferation was assayed by Cell Counting Kit-8 (CCK8), and cell cycle phases and apoptosis were assayed by flow cytometry. Expressions of the apoptosis-related proteins Bax and Bcl-2 were measured by Western blotting. p40 expression was confirmed in Hu-H1 and Strain V on and after day three post-infection. Strain V cells showed significantly greater cellular proliferation than Hu-H1 cells on and after day three post-infection. In Hu-H1 cells, Bax and Bcl-2 expression were significantly increased and decreased, respectively, on and after day three post-infection. In contrast, in Strain V cells, Bax and Bcl-2 expression were significantly decreased and increased, respectively, on and after day three post-infection. In conclusion, Hu-H1 inhibits cellular proliferation and promotes apoptosis in human oligodendrocytes via Bax upregulation and Bcl-2 downregulation. In contrast, Strain V promotes cellular proliferation and inhibits apoptosis in human oligodendrocytes via Bax downregulation and Bcl-2 upregulation. The effects of the Hu-H1 strain (isolated from a bipolar patient) are opposite from those of Strain V (a laboratory strain), thereby providing a proof of authenticity for both.

Activation of TGF-β1 promoter by hepatitis C virus-induced AP-1 and Sp1: role of TGF-β1 in hepatic stellate cell activation and invasion

Our previous studies have shown the induction and maturation of transforming growth factor-beta 1 (TGF-β1) in HCV-infected human hepatoma cells. In this study, we have investigated the molecular mechanism of TGF-β1 gene expression in response to HCV infection. We demonstrate that HCV-induced transcription factors AP-1, Sp1, NF-κB and STAT-3 are involved in TGF-β1 gene expression. Using chromatin immunoprecipitation (ChIP) assay, we further show that AP-1 and Sp1 interact with TGF-b1 promoter in vivo in HCV-infected cells. In addition, we demonstrate that HCV-induced TGF-β1 gene expression is mediated by the activation of cellular kinases such as p38 MAPK, Src, JNK, and MEK1/2. Next, we determined the role of secreted bioactive TGF-β1 in human hepatic stellate cells (HSCs) activation and invasion. Using siRNA approach, we show that HCV-induced bioactive TGF-β1 is critical for the induction of alpha smooth muscle actin (α-SMA) and type 1 collagen, the markers of HSCs activation and proliferation. We further demonstrate the potential role of HCV-induced bioactive TGF-β1 in HSCs invasion/cell migration using a transwell Boyden chamber. Our results also suggest the role of HCV-induced TGF-β1 in HCV replication and release. Collectively, these observations provide insight into the mechanism of TGF-β1 promoter activation, as well as HSCs activation and invasion, which likely manifests in liver fibrosis associated with HCV infection.

Induction of apoptosis-resistant and TGF-β-insensitive murine CD8(+) cytotoxic T lymphocytes specific for HIV-1 gp160

Although TGF-β and IL-6 would turn CD8(+) T cells to differentiate into non-cytotoxic state, these treated cells were converted to cytolytic phenotypes after re-exposure to their antigenic epitope in vitro. Here, using spleen cells from TCR transgenic mice expressing TCRαβ genes of clone RT1 recognizing an epitope peptide (P18-I10: RGPGRAFVTI) of HIV-1 gp160, we generated CD8(+) cytotoxic T lymphocytes (CTLs) activated by re-exposure to P18-I10 after primarily cultured with TGF-β and IL-6 in vitro to examine their effector function. The CTLs, having strong cytotoxic activity in vitro, were not only resistant to Fas-FasL mediated apoptosis, but also insensitive to the suppression of their cytotoxicity by re-exposure to TGF-β in vitro. Moreover, adoptive transfer experiments indicated that the CTLs are capable of eliminating recombinant vaccinia virus expressing HIV-1 gp160 in vivo. Taken together, our data suggest that TGF-β and IL-6 may play pivotal roles in inducing apoptosis-resistant and TGF-β-insensitive CTLs in vitro.

Respiratory syncytial virus mechanisms to interfere with type 1 interferons

Respiratory syncytial virus (RSV) is a member of the Paramyxoviridae family that consists of viruses with nonsegmented negative-strand RNA genome. Infection by these viruses triggers the innate antiviral response of the host, mainly type I interferon (IFN). Essentially all other viruses of this family produce IFN suppressor functions by co-transcriptional RNA editing. In contrast, RSV has evolved two unique nonstructural proteins, NS1 and NS2, to effectively serve this purpose. Together, NS1 and NS2 degrade or sequester multiple signaling proteins that affect both IFN induction and IFN effector functions. While the mechanism of action of NS1 and NS2 is a subject of active research, their effect on adaptive immunity is also being recognized. In this review, we discuss various aspects of NS1 and NS2 function with implications for vaccine design.

Transforming growth factor-beta promotes rhinovirus replication in bronchial epithelial cells by suppressing the innate immune response

Rhinovirus (RV) infection is a major cause of asthma exacerbations which may be due to a deficient innate immune response in the bronchial epithelium. We hypothesized that the pleiotropic cytokine, TGF-β, influences interferon (IFN) production by primary bronchial epithelial cells (PBECs) following RV infection. Exogenous TGF-β₂ increased RV replication and decreased IFN protein secretion in response to RV or double-stranded RNA (dsRNA). Conversely, neutralizing TGF-β antibodies decreased RV replication and increased IFN expression in response to RV or dsRNA. Endogenous TGF-β₂ levels were higher in conditioned media of PBECs from asthmatic donors and the suppressive effect of anti-TGF-β on RV replication was significantly greater in these cells. Basal SMAD-2 activation was reduced when asthmatic PBECs were treated with anti-TGF-β and this was accompanied by suppression of SOCS-1 and SOCS-3 expression. Our results suggest that endogenous TGF-β contributes to a suppressed IFN response to RV infection possibly via SOCS-1 and SOCS-3.

Respiratory syncytial virus modifies microRNAs regulating host genes that affect virus replication

Respiratory syncytial virus (RSV) causes substantial morbidity and life-threatening lower respiratory tract disease in infants, young children and the elderly. Understanding the host response to RSV infection is critical for developing disease-intervention approaches. The role of microRNAs (miRNAs) in post-transcriptional regulation of host genes responding to RSV infection is not well understood. In this study, it was shown that RSV infection of a human alveolar epithelial cell line (A549) induced five miRNAs (let-7f, miR-24, miR-337-3p, miR-26b and miR-520a-5p) and repressed two miRNAs (miR-198 and miR-595), and showed that RSV G protein triggered let-7f expression. Luciferase–untranslated region reporters and miRNA mimics and inhibitors validated the predicted targets, which included cell-cycle genes (CCND1, DYRK2 and ELF4), a chemokine gene (CCL7) and the suppressor of cytokine signalling 3 gene (SOCS3). Modulating let-7 family miRNA levels with miRNA mimics and inhibitors affected RSV replication, indicating that RSV modulates host miRNA expression to affect the outcome of the antiviral host response, and this was mediated in part through RSV G protein expression.