Role of toll-like receptor 3, RIG-I, and MDA5 in the expression of mesothelial IL-8 induced by viral RNA

Mechanisms of mesothelial cell response to viral infections: HDAC1-3 inhibition blocks poly(I:C)-induced type I interferon response and modulates the mesenchymal/inflammatory phenotype

Infectious peritonitis is a leading cause of peritoneal functional impairment and a primary factor for therapy discontinuation in peritoneal dialysis (PD) patients. Although bacterial infections are a common cause of peritonitis episodes, emerging evidence suggests a role for viral pathogens. Toll-like receptors (TLRs) specifically recognize conserved pathogen-associated molecular patterns (PAMPs) from bacteria, viruses, and fungi, thereby orchestrating the ensuing inflammatory/immune responses. Among TLRs, TLR3 recognizes viral dsRNA and triggers antiviral response cascades upon activation. Epigenetic regulation, mediated by histone deacetylase (HDAC), has been demonstrated to control several cellular functions in response to various extracellular stimuli. Employing epigenetic target modulators, such as epidrugs, is a current therapeutic option in several cancers and holds promise in treating viral diseases. This study aims to elucidate the impact of TLR3 stimulation on the plasticity of human mesothelial cells (MCs) in PD patients and to investigate the effects of HDAC1-3 inhibition. Treatment of MCs from PD patients with the TLR3 agonist polyinosinic:polycytidylic acid (Poly(I:C)), led to the acquisition of a bona fide mesothelial-to-mesenchymal transition (MMT) characterized by the upregulation of mesenchymal genes and loss of epithelial-like features. Moreover, Poly(I:C) modulated the expression of several inflammatory cytokines and chemokines. A quantitative proteomic analysis of MCs treated with MS-275, an HDAC1-3 inhibitor, unveiled altered expression of several proteins, including inflammatory cytokines/chemokines and interferon-stimulated genes (ISGs). Treatment with MS-275 facilitated MMT reversal and inhibited the interferon signature, which was associated with reduced STAT1 phosphorylation. However, the modulation of inflammatory cytokine/chemokine production was not univocal, as IL-6 and CXCL8 were augmented while TNF-α and CXCL10 were decreased. Collectively, our findings underline the significance of viral infections in acquiring a mesenchymal-like phenotype by MCs and the potential consequences of virus-associated peritonitis episodes for PD patients. The observed promotion of MMT reversal and interferon response inhibition by an HDAC1-3 inhibitor, albeit without a general impact on inflammatory cytokine production, has translational implications deserving further analysis.

Epidemiology of pleural empyema in English hospitals and the impact of influenza

Pleural empyema represents a significant healthcare burden due to extended hospital admissions and potential requirement for surgical intervention. This study aimed to assess changes in incidence and management of pleural empyema in England over the past 10 years and the potential impact of influenza on rates.Hospital Episode Statistics data were used to identify patients admitted to English hospitals with pleural empyema between 2008 and 2018. Linear regression was used to analyse the relationship between empyema rates and influenza incidence recorded by Public Health England. The relationship between influenza and empyema was further explored using serological data from a prospective cohort study of patients presenting with pleural empyema.Between April 2008 and March 2018 there were 55 530 patients admitted with pleural empyema. There was male predominance (67% versus 33%), which increased with age. Cases have increased significantly from 4447 in 2008 to 7268 in 2017. Peaks of incidence correlated moderately with rates of laboratory-confirmed influenza in children and young adults (r=0.30). For nine of the 10 years studied, the highest annual point incidence of influenza coincided with the highest admission rate for empyema (with a 2-week lag). In a cohort study of patients presenting to a single UK hospital with pleural empyema/infection, 24% (17 out of 72) had serological evidence of recent influenza infection, compared to 7% in seasonally matched controls with simple parapneumonic or cardiogenic effusions (p<0.001).Rates of empyema admissions in England have increased steadily with a seasonal variation that is temporally related to influenza incidence. Patient-level serological data from a prospective study support the hypothesis that influenza may play a pathogenic role in empyema development.

Mesopolysaccharides: The extracellular surface layer of visceral organs

The mesothelium is a dynamic and specialized tissue layer that covers the somatic cavities (pleural, peritoneal, and pericardial) as well as the surface of the visceral organs such as the lung, heart, liver, bowel and tunica vaginalis testis. The potential therapeutic manipulation of visceral organs has been complicated by the carbohydrate surface layer-here, called the mesopolysaccharide (MPS)-that coats the outer layer of the mesothelium. The traditional understanding of MPS structure has relied upon fixation techniques known to degrade carbohydrates. The recent development of carbohydrate-preserving fixation for high resolution imaging techniques has provided an opportunity to re-examine the structure of both the MPS and the visceral mesothelium. In this report, we used high pressure freezing (HPF) as well as serial section transmission electron microscopy to redefine the structure of the MPS expressed on the murine lung, heart and liver surface. Tissue preserved by HPF and examined by transmission electron microscopy demonstrated a pleural MPS layer 13.01±1.1 um deep-a 100-fold increase in depth compared to previously reported data obtained with conventional fixation techniques. At the base of the MPS were microvilli 1.1±0.35 um long and 42±5 nm in diameter. Morphological evidence suggested that the MPS was anchored to the mesothelium by microvilli. In addition, membrane pits 97±17 nm in diameter were observed in the apical mesothelial membrane. The spatial proximity and surface density (29±4.5%) of the pits suggested an active process linked to the structural maintenance of the MPS. The striking magnitude and complex structure of the MPS indicates that it is an important consideration in studies of the visceral mesothelium.

Porcine circovirus type 2 upregulates endothelial-derived IL-8 production in porcine iliac artery endothelial cells via the RIG-I/MDA-5/MAVS/JNK signaling pathway

Background

Dysfunction of endothelial cells and vascular system is one of the most important pathological changes of porcine circovirus disease (PCVD) caused by porcine circovirus type 2 (PCV2). PCV2-infected endothelial cells can upregulate the production of endothelial-derived IL-8, which can inhibit the maturation of dendritic cells. Endothelial-derived IL-8 has different structural and biological characteristics compared with monocyte-derived IL-8. However, the mechanism of endothelial-derived IL-8 production is still unclear.

Results

Key molecules of RIG-I-like signaling pathway RIG-I, MDA-5, MAVS and a key molecule of JNK signaling pathway c-Jun in PCV2-infected porcine iliac artery endothelial cells (PIECs) were upregulated significantly detected with quantitative PCR, Western blot and fluorescence confocal microscopy, while no significant changes were found in NF-κB signaling pathway. Meanwhile, the expression of endothelial-derived IL-8 was downregulated after RIG-I, MDA-5, or MAVS genes in PIECs were knocked down and PIECs were treated by JNK inhibitor.

Conclusions

PCV2 can activate RIG-I/MDA-5/MAVS/JNK signaling pathway to induce the production of endothelial-derived IL-8 in PIECs, which provides an insight into the further study of endothelial dysfunction and vascular system disorder caused by PCV2.

Critical role of RIG-I-like receptors in inflammation in chronic obstructive pulmonary disease

INTRODUCTION

Viral infection is a significant cause of chronic obstructive pulmonary disease (COPD) and acute exacerbation of COPD. Retinoic acid inducible gene I (RIG-I)-like receptors (RLRs), including RIG-I and melanoma differentiation associated gene 5 (MDA-5), are important pattern recognition receptors for viral elimination.

OBJECTIVE

The study aims to investigate the role of RIG-I and MDA-5 in COPD pathogenesis.

METHODS

We examined the expression of RIG-I and MDA-5 by immunohistochemistry, real-time PCR and Western blots in COPD patients and control subjects.

RESULTS

Our results showed that MDA-5 expression was upregulated in lung tissues and peripheral blood mononuclear cells of COPD patients and there was a negative correlation between MDA-5 mRNA levels and forced expiratory volume in 1 s %pred. COPD patients had higher interleukin (IL)-1 and IL-8 mRNA expression levels, and these inflammatory cytokines positively correlate with MDA-5 levels. However, there was no difference in the expression of RIG-I between COPD patients and control subjects.

CONCLUSION

Our results suggested that MDA-5, but not RIG-I, may play a critical role in airway inflammation in COPD.

TLR3 activation increases chemokine expression in human fetal airway smooth muscle cells

Viral infections, such as respiratory syncytial virus and rhinovirus, adversely affect neonatal and pediatric populations, resulting in significant lung morbidity, including acute asthma exacerbation. Studies in adults have demonstrated that human airway smooth muscle (ASM) cells modulate inflammation through their ability to secrete inflammatory cytokines and chemokines. The role of ASM in the developing airway during infection remains undefined. In our study, we used human fetal ASM cells as an in vitro model to examine the effect of Toll-like receptor (TLR) agonists on chemokine secretion. We found that fetal ASM express multiple TLRs, including TLR3 and TLR4, which are implicated in the pathogenesis of respiratory syncytial virus and rhinovirus infection. Cells were treated with TLR agonists, polyinosinic-polycytidylic acid [poly(I:C)] (TLR3 agonist), lipopolysaccharide (TLR4 agonist), or R848 (TLR7/8 agonist), and IL-8 and chemokine (C-C motif) ligand 5 (CCL5) secretion were evaluated. Interestingly, poly(I:C), but neither lipopolysaccharide nor R848, increased IL-8 and chemokine (C-C motif) ligand 5 secretion. Examination of signaling pathways suggested that the poly(I:C) effects in fetal ASM involve TLR and ERK signaling, in addition to another major inflammatory pathway, NF-κB. Moreover, there are variations between fetal and adult ASM with respect to poly(I:C) effects on signaling pathways. Pharmacological inhibition suggested that ERK pathways mediate poly(I:C) effects. Overall, our data show that poly(I:C) initiates activation of proinflammatory pathways in developing ASM, which may contribute to immune responses to infection and exacerbation of asthma.

Mammalian target of rapamycin (mTOR) regulates TLR3 induced cytokines in human oral keratinocytes

Recent studies implicate the mammalian target of rapamycin (mTOR) pathway in the control of inflammatory responses following Toll-like receptor (TLR) stimulation in myeloid cells but its role in non-myeloid cells such as human keratinocytes is unknown. Here we show that TLR3 signaling can induce robust cytokine secretion including interleukin 1 beta (IL-1β), tumor necrosis factor alpha (TNFα), IL-12p70 and interferon beta (IFN-β), and our data reveal for the first time that inhibiting mTOR with rapamycin, suppresses these TLR3 induced responses but actually enhances bioactive IL-12p70 production in human oral keratinocytes. Rapamycin inhibited the phosphorylation of the 70-kDa ribosomal protein S6 kinase (p70S6K) and the 4E binding protein 1 (4EBP-1), and suppressed the mitogen activated protein kinase (MAPK) pathway by decreasing phosphorylation of c-Jun N-terminal kinase (JNK). We also show that TLR3 induces interferon regulatory factor 3 (IRF3) activation by Akt via an mTOR-p70S6K-4EBP1 pathway. Furthermore, we provide evidence that Poly I:C induced expression of IL-1β, TNFα, IL-12p70 and IFN-β was blocked by JNK inhibitor SP600125. TLR3 preferentially phosphorylated IKKα through mTOR to activate nuclear factor kappa beta (NF-κB) in human oral keratinocytes. Taken together, these data demonstrate p70S6K, p4EBP1, JNK, NF-κB and IRF3 are involved in the regulation of inflammatory mediators by TLR3 via the mTOR pathway. mTOR is a novel pathway modulating TLR3 induced inflammatory and antiviral responses in human oral keratinocytes.

Rhinovirus-induced exacerbations of asthma: How is the {beta}2-adrenoceptor implicated?

Rhinovirus (RV) infections are the major cause of asthma exacerbations in children and adults. Under normal circumstances, asthmatic airway obstruction improves spontaneously or characteristically briskly in response to inhaled beta(2)-adrenergic receptor (beta(2)AR) agonists. During virus-associated exacerbations, an impaired response to beta(2)AR agonists is observed; the reason for this is not known. The objective of this study was to determine the effect of RV infection on airway smooth muscle beta(2)AR function. The human cell line Beas-2B and primary human bronchial epithelial cells (HBECs) were infected with RV (multiplicity of infection = 1). After 1 or 5 days for primary and Beas-2B cells, respectively, cell culture supernatants were harvested, UV-irradiated to inactivate RV, and applied to human airway smooth muscle cells for 3 days to assess modifications of beta(2)AR function. RV conditioned medium from Beas-2B and HBECs decreased beta(2)AR agonist-induced cAMP by 50 and 65%, respectively (n = 5; P < 0.05). When cAMP was induced independently of the beta(2)AR using forskolin, no impairment was found. Using flow cytometry, we demonstrated that this decrease was likely the result of beta(2)AR desensitization because membrane but not total cell receptor beta(2)AR was decreased. Pretreatment of HBECs and Beas-2B cells but not human airway smooth muscle cells with the corticosteroids dexamethasone or fluticasone abolished virus-mediated beta(2)AR loss of function. This study shows that epithelial infection with RV induces a decrease of beta(2)AR function on airway smooth muscle cells, potentially explaining the clinical observation of loss of beta(2)AR agonist function during RV-induced asthma exacerbations.