Atypical activation of the unfolded protein response in cystic fibrosis airway cells contributes to p38 MAPK-mediated innate immune responses

Role of orphan G-protein coupled receptors in tissue ischemia: A comprehensive review

Ischemic events lead to many diseases and deaths worldwide. Ischemia/reperfusion (I/R) occurs due to reduced blood circulation in tissues followed by blood reflow. Reoxygenation of ischemic tissues is characterized by oxidative stress, inflammation, energy distress, and endoplasmic reticulum stress. There are still no adequate clinical protocols or pharmacological approaches to address the consequences of I/R damage. G protein-coupled receptors (GPCRs) are important therapeutic targets. They compose a large family of seven transmembrane-spanning proteins that are involved in many biological functions. Orphan GPCRs are a large subgroup of these receptors expressed in different organs. In the present review, we summarized the literature regarding the role of orphan GPCRs in I/R in different organs. We focused on the effect of these receptors on modulating cellular and molecular processes underlying ischemia including apoptosis, inflammation, and autophagy. The study showed that GPR3, GPR4, GPR17, GPR30, GPR31, GPR35, GPR37, GPR39, GPR55, GPR65, GPR68, GPR75, GPR81, and GPR91 are involved in ischemic events, mainly in the brain and heart. These receptors offer new possibilities for treating I/R injuries in the body.

Deficiency of flavin-containing monooxygenase 3 protects kidney function after ischemia-reperfusion in mice

The kidney is vulnerable to ischemia and reperfusion (I/R) injury that can be fatal after major surgery. Currently, there are no effective treatments for I/R-induced kidney injury. Trimethylamine N-oxide (TMAO) is a gut-derived metabolite linked to many diseases, but its role in I/R-induced kidney injury remains unclear. Here, our clinical data reveals an association between preoperative systemic TMAO levels and postoperative kidney injury in patients after post-cardiopulmonary bypass surgery. By genetic deletion of TMAO-producing enzyme flavin-containing monooxygenase 3 (FMO3) and dietary supplementation of choline to modulate TMAO levels, we found that TMAO aggravated acute kidney injury through the triggering of endoplasmic reticulum (ER) stress and worsened subsequent renal fibrosis through TGFβ/Smad signaling activation. Together, our study underscores the negative role of TMAO in I/R-induced kidney injury and highlights the therapeutic potential through the modulation of TMAO levels by targeting FMO3, thereby mitigating acute kidney injury and preventing subsequent renal fibrosis.

The Inhibition of the Membrane-Bound Transcription Factor Site-1 Protease (MBTP1) Alleviates the p.Phe508del-Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Defects in Cystic Fibrosis Cells

Cystic Fibrosis (CF) is present due to mutations in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene, the most frequent variant being p.phe508del. The CFTR protein is a chloride (Cl-) channel which is defective and almost absent of cell membranes when the p.Phe508del mutation is present. The p.Phe508del-CFTR protein is retained in the endoplasmic reticulum (ER) and together with inflammation and infection triggers the Unfolded Protein Response (UPR). During the UPR, the Activating Transcription Factor 6 (ATF6) is activated with cleavage and then decreases the expression of p.Phe508del-CFTR. We have previously shown that the inhibition of the activation of ATF6 alleviates the p.Phe508del-CFTR defects in cells overexpressing the mutated protein. In the present paper, our aim was to inhibit the cleavage of ATF6, and thus its activation in a human bronchial cell line with endogenous p.Phe508del-CFTR expression and in bronchial cells from patients, to be more relevant to CF. This was achieved by inhibiting the protease MBTP1 which is responsible for the cleavage of ATF6. We show here that this inhibition leads to increased mRNA and p.Phe508del-CFTR expression and, consequently, to increased Cl-efflux. We also explain the mechanisms linked to these increases with the modulation of genes when MBTP1 is inhibited. Indeed, RT-qPCR assays show that genes such as HSPA1B, CEBPB, VIMP, PFND2, MAPK8, XBP1, INSIG1, and CALR are modulated. In conclusion, we show that the inhibition of MBTP1 has a beneficial effect in relevant models to CF and that this is due to the modulation of genes involved in the disease.

Chronic obstructive pulmonary disease and emerging ER stress-related therapeutic targets

COPD pathogenesis is frequently associated with endoplasmic reticulum stress (ER stress) progression. Targeting the major unfolded protein response (UPR) branches in the ER stress pathway may provide pharmacotherapeutic selection strategies for treating COPD and enable relief from its symptoms. In this study, we aimed to systematically review the potential role of the ER stress inhibitors of major UPR branches (IRE1, PERK, and ATF6) in COPD-related studies and determine the current stage of knowledge in this field. The systematic review was carried out adhering to the PRISMA checklist based on published studies obtained from specific keyword searches of three databases, namely PubMed, ScienceDirect and Springer Database. The search was limited to the year 2000-2022 which includes all in vitro studies, in vivo studies and clinical trials related to the application of ER stress inhibitors toward COPD-induced models and disease. The risk of bias was evaluated using the QUIN, SYRCLE, revised Cochrane risk of bias tool for randomized trials (RoB 2.0) and NIH tool respectively. A total of 7828 articles were screened from three databases and a final total of 37 studies were included in the review. The ER stress and UPR pathways are potentially useful to prevent COPD progression and attenuate the exacerbation of COPD and related symptoms. Interestingly, the off-target effects from inhibition of the UPR pathway may be desirable or undesirable depending on context and therapeutic applications. Targeting the UPR pathway could have complex consequences as the production of ER molecules involved in folding may be impaired which could continuously provoke misfolding of proteins. Although several emerging compounds were noted to be potentially useful for targeted therapy against COPD, clinical studies have yet to be thoroughly explored.

Current evidence on the effect of highly effective CFTR modulation on interleukin-8 in cystic fibrosis

INTRODUCTION

Cystic fibrosis (CF) is a genetically inherited disease, with mortality and morbidity associated with respiratory disease. The inflammatory response in CF is characterized by excessive neutrophil influx to the airways, mainly due to the increased local production and retention of interleukin-8 (IL-8), a potent neutrophil chemoattractant.

AREAS COVERED

We discuss how the chemokine IL-8 dominates the inflammatory profile of the airways in CF lung disease. Cystic fibrosis transmembrane conductance regulator (CFTR) modulator therapies are designed to correct the malfunctioning protein resulting from specific CFTR mutations. This review covers current evidence on the impact of CFTR impairment on levels of IL-8 and outlines the influence of effective CFTR modulation on inflammation in CF with a focus on cytokine production. Review of the literature was carried out using the PUBMED database, Google Scholar, and The Cochrane Library databases, using several appropriate generic terms.

EXPERT OPINION

Therapeutic interventions specifically targeting the defective CFTR protein have improved the outlook for CF. Accumulating studies on the effect of highly effective CFTR modulation on inflammation indicate an impact on IL-8 levels. Further studies are required to increase our knowledge of early onset innate inflammatory dysregulation and on anti-inflammatory mechanisms of CFTR modulators.

The Interplay between the Unfolded Protein Response, Inflammation and Infection in Cystic Fibrosis

In cystic fibrosis (CF), p.Phe508del is the most frequent mutation in the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) gene. The p.Phe508del-CFTR protein is retained in the ER and rapidly degraded. This retention likely triggers an atypical Unfolded Protein Response (UPR) involving ATF6, which reduces the expression of p.Phe508del-CFTR. There are still some debates on the role of the UPR in CF: could it be triggered by the accumulation of misfolded CFTR proteins in the endoplasmic reticulum as was proposed for the most common CFTR mutation p.Phe508del? Or, is it the consequence of inflammation and infection that occur in the disease? In this review, we summarize recent findings on UPR in CF and show how infection, inflammation and UPR act together in CF. We propose to rethink their respective role in CF and to consider them as a whole.

Reciprocal regulation between ER stress and autophagy in renal tubular fibrosis and apoptosis

Both endoplasmic reticulum (ER) stress and autophagy have been implicated in chronic kidney injury and renal fibrosis. However, the relationship and regulatory mechanisms between ER stress and autophagy under this condition remain largely unknown. In this study, we first established a mouse model of ER stress-induced chronic kidney injury by 2 weekly injections of a low dose of tunicamycin (TM), a classical ER stress inducer. This model showed the induction of ER stress, autophagy, fibrosis and apoptosis in kidney tissues. In vitro, TM also induced ER stress, autophagy, fibrosis and apoptosis in HK-2 human kidney proximal tubular cells and BUMPT-306 mouse kidney proximal tubular cells. In these cells, autophagy inhibitor suppressed TM-induced fibrotic changes and apoptosis, suggesting an involvement of autophagy in ER stress-associated chronic kidney injury. PERK inhibitor ameliorated autophagy, fibrotic protein expression and apoptosis in TM-treated cells, indicating a role of the PERK/eIF2α pathway in autophagy activation during ER stress. Similar results were shown in TGF-β1-treated HK-2 cells. Interestingly, in both TM- or TGF-β1-treated kidney proximal tubular cells, inhibition of autophagy exaggerated ER stress, suggesting that autophagy induced by ER stress provides a negative feedback mechanism to reduce the stress. Together, these results unveil a reciprocal regulation between ER stress and autophagy in chronic kidney injury and fibrosis.

The Impact of Endoplasmic Reticulum-Associated Protein Modifications, Folding and Degradation on Lung Structure and Function

The accumulation of unfolded/misfolded proteins in the endoplasmic reticulum (ER) causes ER stress and induces the unfolded protein response (UPR) and other mechanisms to restore ER homeostasis, including translational shutdown, increased targeting of mRNAs for degradation by the IRE1-dependent decay pathway, selective translation of proteins that contribute to the protein folding capacity of the ER, and activation of the ER-associated degradation machinery. When ER stress is excessive or prolonged and these mechanisms fail to restore proteostasis, the UPR triggers the cell to undergo apoptosis. This review also examines the overlooked role of post-translational modifications and their roles in protein processing and effects on ER stress and the UPR. Finally, these effects are examined in the context of lung structure, function, and disease.

Fecal Microbiota Transplantation Shows Marked Shifts in the Multi-Omic Profiles of Porcine Post-weaning Diarrhea

Weaning is the most critical phase in pig production and is generally associated with significant impacts on intestinal morphology, structure, physiology, and immune responses, which can lead to subsequent production inefficiencies such as decreases in growth and intake and increases in morbidity and mortality. In the present study, we attempted to explore the effects of fecal microbiota transplantation (FMT) on the fecal microbiota, fecal metabolites, and transcriptome in the jejunum, colon, liver, spleen, and oral mucosa in piglets with post-weaning diarrhea and to evaluate the therapeutic potential of FMT in piglets with post-weaning diarrhea. We found that FMT partially relieved the symptoms of diarrhea in piglets, and microbiota analysis results indicated that unclassified_f_Prevotellaceae was identified as an FMT-associated bacterial family at 66 day and that the Shannon index in the healthy group at 34, 38, and 66 days were higher than that at 21 day. Functional enrichment analysis of the oral mucosa, liver, jejunum, and colon showed that most of the differentially expressed genes (DEGs) were enriched in the terms metabolic process, immune response, and inflammatory response. Moreover, the enriched fecal metabolites focused mostly on apoptosis, beta-alanine metabolism, glutathione metabolism, and sphingolipid metabolism. We tried to detect specific "metabolite-bacterium" pairs, such as "g_Catenisphaera-stigmastentriol," "p_Bacteroidetes-(6beta,22E)-6-hydroxystigmasta-4,22-dien-3-one," and "g_Prevotellaceae_NK3B31_group-stenocereol." Overall, the present study provides a theoretical basis for the alleviation of weaning stress and contributes to the realization of effective and sustainable application of FMT in the pig production industry in the future.

Exogenous activation of toll-like receptor 5 signaling mitigates acetaminophen-induced hepatotoxicity in mice

Acetaminophen (APAP) poisoning is the most common cause of drug-induced acute liver injury (ALI). Our results showed that toll-like receptor 5 (TLR5) was abundantly expressed in hepatocytes and dramatically downregulated in the toxic mouse livers. Hence, we herein investigated the role of TLR5 signaling after APAP overdose. Mice were intraperitoneally (i.p.) injected with APAP to induce ALI, and then injected with flagellin at one hour after APAP administration. Flagellin attenuated APAP-induced ALI based on decreased histopathologic lesions, serum biochemical, oxidative stress, and inflammation. Furthermore, the protective effects of flagellin were abolished by TH1020 (a TLR5 antagonist) treatment. These results suggest that flagellin exerted protective effects on ALI via TLR5 activation. Mechanistically, flagellin injection promoted the translocation of nuclear factor erythroid 2-related factor 2 (Nrf2) to the nucleus in hepatocytes. Consistent with the in vivo results, flagellin increased the activation of Nrf2 in hepatocytes, resulting in decreased APAP toxicity. ML385, a selective inhibitor of Nrf2, abolished the flagellin-mediated hepatoprotective effects in damaged livers and hepatocytes. Additionally, the flagellin-induced Nrf2 translocation was dependent upon the activation of TLR5-JNK/p38 pathways. These findings suggest that TLR5 signaling-induced Nrf2 activation, at least partially, contributed to the protection against APAP-induced ALI by flagellin treatment.

Pseudomonas aeruginosa induces p38MAP kinase-dependent IL-6 and CXCL8 release from bronchial epithelial cells via a Syk kinase pathway

Pseudomonas aeruginosa (Pa) infection is a major cause of airway inflammation in immunocompromised and cystic fibrosis (CF) patients. Mitogen-activated protein (MAP) and tyrosine kinases are integral to inflammatory responses and are therefore potential targets for novel anti-inflammatory therapies. We have determined the involvement of specific kinases in Pa-induced inflammation. The effects of kinase inhibitors against p38MAPK, MEK 1/2, JNK 1/2, Syk or c-Src, a combination of a p38MAPK with Syk inhibitor, or a novel narrow spectrum kinase inhibitor (NSKI), were evaluated against the release of the proinflammatory cytokine/chemokine, IL-6 and CXCL8 from BEAS-2B and CFBE41o- epithelial cells by Pa. Effects of a Syk inhibitor against phosphorylation of the MAPKs were also evaluated. IL-6 and CXCL8 release by Pa were significantly inhibited by p38MAPK and Syk inhibitors (p<0.05). Phosphorylation of HSP27, but not ERK or JNK, was significantly inhibited by Syk kinase inhibition. A combination of p38MAPK and Syk inhibitors showed synergy against IL-6 and CXCL8 induction and an NSKI completely inhibited IL-6 and CXCL8 at low concentrations. Pa-induced inflammation is dependent on p38MAPK primarily, and Syk partially, which is upstream of p38MAPK. The NSKI suggests that inhibiting specific combinations of kinases is a potent potential therapy for Pa-induced inflammation.

Role of unfolded proteins in lung disease

The lungs are exposed to a range of environmental toxins (including cigarette smoke, air pollution, asbestos) and pathogens (bacterial, viral and fungal), and most respiratory diseases are associated with local or systemic hypoxia. All of these adverse factors can trigger endoplasmic reticulum (ER) stress. The ER is a key intracellular site for synthesis of secretory and membrane proteins, regulating their folding, assembly into complexes, transport and degradation. Accumulation of misfolded proteins within the lumen results in ER stress, which activates the unfolded protein response (UPR). Effectors of the UPR temporarily reduce protein synthesis, while enhancing degradation of misfolded proteins and increasing the folding capacity of the ER. If successful, homeostasis is restored and protein synthesis resumes, but if ER stress persists, cell death pathways are activated. ER stress and the resulting UPR occur in a range of pulmonary insults and the outcome plays an important role in many respiratory diseases. The UPR is triggered in the airway of patients with several respiratory diseases and in corresponding experimental models. ER stress has been implicated in the initiation and progression of pulmonary fibrosis, and evidence is accumulating suggesting that ER stress occurs in obstructive lung diseases (particularly in asthma), in pulmonary infections (some viral infections and in the setting of the cystic fibrosis airway) and in lung cancer. While a number of small molecule inhibitors have been used to interrogate the role of the UPR in disease models, many of these tools have complex and off-target effects, hence additional evidence (eg, from genetic manipulation) may be required to support conclusions based on the impact of such pharmacological agents. Aberrant activation of the UPR may be linked to disease pathogenesis and progression, but at present, our understanding of the context-specific and disease-specific mechanisms linking these processes is incomplete. Despite this, the ability of the UPR to defend against ER stress and influence a range of respiratory diseases is becoming increasingly evident, and the UPR is therefore attracting attention as a prospective target for therapeutic intervention strategies.

Endoplasmic reticulum stress exacerbates inflammation in chronic rhinosinusitis with nasal polyps via the transcription factor XBP1

Endoplasmic reticulum (ER) stress results in the activation of the unfolded protein response (UPR), a process that is involved in the pathogenesis of many inflammatory diseases. However, the role of ER stress in chronic rhinosinusitis with nasal polyps (CRSwNP) has yet to be elucidated. In this study, we found that the protein expression levels of a range of ER stress regulators, including p-PERK, ATF4, ATF6 and XBP1s, were significantly increased in CRSwNP compared to controls. Importantly, the expression of ATF4 and XBP1s was positively correlated with heightened inflammation in CRSwNP. In human nasal epithelial cells, the ER stress inducer tunicamycin (TM) could potentiate Toll-like receptors (TLRs) induced proinflammatory cytokines production. Furthermore, we found that the silencing of XBP1, but not ATF4 or ATF6, abrogated the proinflammatory effect of TM. Mechanistically, ER stress did not affect the NF-κB, MAPK or IRF3 signaling pathways. However, the ER stress regulator XBP1s was able to bind directly to the promoter region of inflammatory genes to modulate gene transcription. Besides, the commensal bacteria Staphylococcus aureus and several inflammatory factors, such as IL4, IL13, IL17 and IFNγ, could induce ER stress in epithelial cells. Collectively, ER stress plays a crucial role in facilitating TLR-induced inflammation. Targeting XBP1 can inhibit the inflammatory response, thus offering a potential approach to treat CRSwNP.

UPR modulation of host immunity by Pseudomonas aeruginosa in cystic fibrosis

Cystic fibrosis (CF) is a progressive multiorgan autosomal recessive disease with devastating impact on the lungs caused by derangements of the CF transmembrane conductance regulator (CFTR) gene. Morbidity and mortality are caused by the triad of impaired mucociliary clearance, microbial infections and chronic inflammation. Pseudomonas aeruginosa is the main respiratory pathogen in individuals with CF infecting most patients in later stages. Despite its recognized clinical impact, molecular mechanisms that underlie P. aeruginosa pathogenesis and the host response to P. aeruginosa infection remain incompletely understood. The nuclear hormone receptor peroxisome proliferator-activated receptor (PPAR) γ (PPARγ), has shown to be reduced in CF airways. In the present study, we sought to investigate the upstream mechanisms repressing PPARγ expression and its impact on airway epithelial host defense. Endoplasmic reticulum-stress (ER-stress) triggered unfolded protein response (UPR) activated by misfolded CFTR and P. aeruginosa infection contributed to attenuated expression of PPARγ. Specifically, the protein kinase RNA (PKR)-like ER kinase (PERK) signaling pathway led to the enhanced expression of the CCAAT-enhancer-binding-protein homologous protein (CHOP). CHOP induction led to the repression of PPARγ expression. Mechanistically, we showed that CHOP induction mediated PPARγ attenuation, impacted the innate immune function of normal and ∆F508 primary airway epithelial cells by reducing expression of antimicrobial peptide (AMP) and paraoxanse-2 (PON-2), as well as enhancing IL-8 expression. Furthermore, mitochondrial reactive oxygen species production (mt-ROS) and ER-stress positive feedforward loop also dysregulated mitochondrial bioenergetics. Additionally, our findings implicate that PPARγ agonist pioglitazone (PIO) has beneficial effect on the host at the multicellular level ranging from host defense to mitochondrial re-energization.

Lung immunoglobulin A immunity dysregulation in cystic fibrosis

BACKGROUND

In cystic fibrosis (CF), recurrent infections suggest impaired mucosal immunity but whether production of secretory immunoglobulin A (S-IgA) is impaired remains elusive. S-IgA is generated following polymeric immunoglobulin receptor (pIgR)-mediated transepithelial transport of dimeric (d-)IgA and represents a major defence through neutralisation of inhaled pathogens like Pseudomonas aeruginosa (Pa).

METHODS

Human lung tissue (n = 74), human sputum (n = 118), primary human bronchial epithelial cells (HBEC) (cultured in air-liquid interface) (n = 19) and mouse lung tissue and bronchoalveolar lavage were studied for pIgR expression, IgA secretion and regulation.

FINDINGS

Increased epithelial pIgR immunostaining was observed in CF lung explants, associated with more IgA-producing plasma cells, sputum and serum IgA, especially Pa-specific IgA. In contrast, pIgR and IgA transport were downregulated in F508del mice, CFTR-inhibited HBEC, and CF HBEC. Moreover, the unfolded protein response (UPR) due to F508del mutation, inhibited IgA transport in Calu-3 cells. Conversely, pIgR expression and IgA secretion were strongly upregulated following Pa lung infection in control and F508del mice, through an inflammatory host response involving interleukin-17.

INTERPRETATION

A complex regulation of IgA secretion occurs in the CF lung, UPR induced by CFTR mutation/dysfunction inhibiting d-IgA transcytosis, and Pa infection unexpectedly unleashing this secretory defence mechanism.

FUNDING

This work was supported by the Forton's grant of the King Baudouin's Foundation, Belgium, the Fondazione Ricerca Fibrosi Cistica, Italy, and the Fonds National de la Recherche Scientifique, Belgium.

The Role of Specialized Pro-Resolving Mediators in Cystic Fibrosis Airways Disease

Cystic Fibrosis (CF) is a recessive genetic disease due to mutations of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene encoding the CFTR chloride channel. The ion transport abnormalities related to CFTR mutation generate a dehydrated airway surface liquid (ASL) layer, which is responsible for an altered mucociliary clearance, favors infections and persistent inflammation that lead to progressive lung destruction and respiratory failure. The inflammatory response is normally followed by an active resolution phase to return to tissue homeostasis, which involves specialized pro-resolving mediators (SPMs). SPMs promote resolution of inflammation, clearance of microbes, tissue regeneration and reduce pain, but do not evoke unwanted immunosuppression. The airways of CF patients showed a decreased production of SPMs even in the absence of pathogens. SPMs levels in the airway correlated with CF patients' lung function. The prognosis for CF has greatly improved but there remains a critical need for more effective treatments that prevent excessive inflammation, lung damage, and declining pulmonary function for all CF patients. This review aims to highlight the recent understanding of CF airway inflammation and the possible impact of SPMs on functions that are altered in CF airways.

Unfolded Protein Response in Lung Health and Disease

The unfolded protein response (UPR) is a complex element, destined to protect the cells against a diverse variety of extracellular and intracellular challenges. UPR activation devises highly efficient responses to counteract cellular threats. If those activities fail, it will dictate cellular execution. The current work focuses on the role of UPR in pulmonary function, by immersing into the highly interrelated network that operates toward the endothelial barrier function. A highly sophisticated UPR manipulation shall reveal new therapeutic possibilities against inflammatory lung disease, such as acute lung injury and acute respiratory distress syndrome.

Systems Biology Approaches to Understanding the Human Immune System

Systems biology is an approach to interrogate complex biological systems through large-scale quantification of numerous biomolecules. The immune system involves >1,500 genes/proteins in many interconnected pathways and processes, and a systems-level approach is critical in broadening our understanding of the immune response to vaccination. Changes in molecular pathways can be detected using high-throughput omics datasets (e.g., transcriptomics, proteomics, and metabolomics) by using methods such as pathway enrichment, network analysis, machine learning, etc. Importantly, integration of multiple omic datasets is becoming key to revealing novel biological insights. In this perspective article, we highlight the use of protein-protein interaction (PPI) networks as a multi-omics integration approach to unravel information flow and mechanisms during complex biological events, with a focus on the immune system. This involves a combination of tools, including: InnateDB, a database of curated interactions between genes and protein products involved in the innate immunity; NetworkAnalyst, a visualization and analysis platform for InnateDB interactions; and MetaBridge, a tool to integrate metabolite data into PPI networks. The application of these systems techniques is demonstrated for a variety of biological questions, including: the developmental trajectory of neonates during the first week of life, mechanisms in host-pathogen interaction, disease prognosis, biomarker discovery, and drug discovery and repurposing. Overall, systems biology analyses of omics data have been applied to a variety of immunology-related questions, and here we demonstrate the numerous ways in which PPI network analysis can be a powerful tool in contributing to our understanding of the immune system and the study of vaccines.

Congenital Tufting Enteropathy-Associated Mutant of Epithelial Cell Adhesion Molecule Activates the Unfolded Protein Response in a Murine Model of the Disease

Congenital tufting enteropathy (CTE) is a rare chronic diarrheal disease of infancy caused by mutations in epithelial cell adhesion molecule (EpCAM). Previously, a murine CTE model showed mis-localization of EpCAM away from the basolateral cell surface in the intestine. Here we demonstrate that mutant EpCAM accumulated in the endoplasmic reticulum (ER) where it co-localized with ER chaperone, GRP78/BiP, revealing potential involvement of ER stress-induced unfolded protein response (UPR) pathway in CTE. To investigate the significance of ER-localized mutant EpCAM in CTE, activation of the three UPR signaling branches initiated by the ER transmembrane protein components IRE1, PERK, and ATF6 was tested. A significant reduction in BLOS1 and SCARA3 mRNA levels in EpCAM mutant intestinal cells demonstrated that regulated IRE1-dependent decay (RIDD) was activated. However, IRE1 dependent XBP1 mRNA splicing was not induced. Furthermore, an increase in nuclear-localized ATF6 in mutant intestinal tissues revealed activation of the ATF6-signaling arm. Finally, an increase in both the phosphorylated form of the translation initiation factor, eIF2α, and ATF4 expression in the mutant intestine provided support for activation of the PERK-mediated pathway. Our results are consistent with a significant role for UPR in gastrointestinal homeostasis and provide a working model for CTE pathophysiology.

Infrared biomarkers of impaired cystic fibrosis transmembrane regulator protein biogenesis

The mid-infrared (IR) spectra of human cystic fibrosis (CF) cells acquired by Fourier transform infrared microspectroscopy were compared with those of non-CF cells. Within the 1700 to 1480 cm^-1 spectral domain of amides, unsupervised explorative principal component analysis identified a few variables reflecting quantitative and qualitative vibrations arising from protein secondary structures and amino acid side chains. Their pattern reflected α-helix to β-sheet transitions in bronchial epithelial cells and in immortalized peripheral blood mononuclear cells from patients with R1162X missense or in-frame F508del mutations in the cystic fibrosis transmembrane regulator gene (Cftr). Similar transitions have been described in IR spectra of cells, tissues and body fluids of patients affected with some neurodegenerative diseases characterized by the accumulation of misfolded protein aggregates. The variables pattern was able to distinguish CF cells from non-CF cells and was modified by molecular compounds used to rescue the unbalanced folding process of mutated cystic fibrosis transmembrane regulator (CFTR) anion channel. To our knowledge, this is the first experimental evidence of spectroscopic biomarkers of the impaired biogenesis of CFTR by IR microanalysis in the spectra of human CF bronchial epithelial and lymphoblastoid cells.

Whole-blood transcriptomic responses to lumacaftor/ivacaftor therapy in cystic fibrosis

BACKGROUND

Cystic fibrosis (CF) remains without a definitive cure. Novel therapeutics targeting the causative defect in the cystic fibrosis transmembrane conductance regulator (CFTR) gene are in clinical use. Lumacaftor/ivacaftor is a CFTR modulator approved for patients homozygous for the CFTR variant p.Phe508del, but there are wide variations in treatment responses preventing prediction of patient responses. We aimed to determine changes in gene expression related to treatment initiation and response.

METHODS

Whole-blood transcriptomics was performed using RNA-Seq in 20 patients with CF pre- and 6 months post-lumacaftor/ivacaftor (drug) initiation and 20 non-CF healthy controls. Correlation of gene expression with clinical variables was performed by stratification via clinical responses.

RESULTS

We identified 491 genes that were differentially expressed in CF patients (pre-drug) compared with non-CF controls and 36 genes when comparing pre-drug to post-drug profiles. Both pre- and post-drug CF profiles were associated with marked overexpression of inflammation-related genes and apoptosis genes, and significant under-expression of T cell and NK cell-related genes compared to non-CF. CF patients post-drug demonstrated normalized protein synthesis expression, and decreased expression of cell-death genes compared to pre-drug profiles, irrespective of clinical response. However, CF clinical responders demonstrated changes in eIF2 signaling, oxidative phosphorylation, IL-17 signaling, and mitochondrial function compared to non-responders. Top overexpressed genes (MMP9 and SOCS3) that decreased post-drug were validated by qRT-PCR. Functional assays demonstrated that CF monocytes normalized calcium (increases MMP9 expression) concentrations post-drug.

CONCLUSIONS

Transcriptomics revealed differentially regulated pathways in CF patients at baseline compared to non-CF, and in clinical responders to lumacaftor/ivacaftor.

Metabolic Reprograming of Cystic Fibrosis Macrophages via the IRE1α Arm of the Unfolded Protein Response Results in Exacerbated Inflammation

Cystic Fibrosis (CF) is a recessive genetic disorder caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR). CFTR mutations cause dysregulation of channel function with intracellular accumulation of misfolded proteins and endoplasmic reticulum (ER) stress, with activation of the IRE1α-XBP1 pathway that regulates a subset of unfolded protein response (UPR) genes. This pathway regulates a group of genes that control proinflammatory and metabolic responses in different immune cells; however, the metabolic state of immune cells and the role of this pathway in CF remain elusive. Our results indicate that only innate immune cells from CF patients present increased levels of ER stress, mainly affecting neutrophils, monocytes, and macrophages. An overactive IRE1α-XBP1 pathway reprograms CF M1 macrophages toward an increased metabolic state, with increased glycolytic rates and mitochondrial function, associated with exaggerated production of TNF and IL-6. This hyper-metabolic state, seen in CF macrophages, is reversed by inhibiting the RNase domain of IRE1α, thereby decreasing the increased glycolic rates, mitochondrial function and inflammation. Altogether, our results indicate that innate immune cells from CF patients are primarily affected by ER stress. Moreover, the IRE1α-XBP1 pathway of the UPR is responsible for the hyper-metabolic state seen in CF macrophages, which is associated with the exaggerated inflammatory response. Modulating ER stress, metabolism and inflammation, by targeting IRE1α, may improve the metabolic fitness of macrophages, and other immune cells in CF and other immune-related disorders.

Functional characterization of an ER-stress responding Crustin gene in Litopenaeus vannamei

Shrimp in culture ponds are challenged by various pathogens as well as harsh water environment. The innate immune system and environmental stress response system of shrimp paly an important role in shrimp survival and growth. For remission the endoplasmic reticulum (ER)-stress caused by environmental stress, unfolded protein response (UPR) may reduce the synthesis of most proteins, including great mass of immune factors, which could weaken the immune function of shrimp. Therefore, how cells keep appropriate amount of immune factor synthesis under such a situation is critical important for shrimp health and growth. In this study, we cloned a new Crustin gene (LvCruU) from Litopenaeus vannamei. We showed that LvCruU has antibacterial activity, and reducing its expression would increase the cumulative mortality of L. vannamei upon the Vibrio parahemolyticus infection. In addition, we found that promoter activity of LvCruU was enhanced not only by the deformed epidermal autoregulatory factor-1 (Deaf1), but also by activating transcription factor 3 (LvATF3) of shrimp UPR. Real-time RT-PCR showed that LvCruU and LvATF3 both were induced upon UPR activation. And moreover, in Thapsigargin plus dsLvCruU injection test, we showed that down-regulation of LvCruU increased the cumulative mortality of V. parahemolyticus-infected shrimp under ER-stress. These results suggest that LvCruU work as a downstream effector of UPR, and contribute to antimicrobic immune response upon ER-stress in L. vannamei.

Modulation of the unfolded protein response pathway as an antiviral approach in airway epithelial cells

INTRODUCTION

Rhinovirus (RV) infection is a major cause of cystic fibrosis (CF) lung morbidity with limited therapeutic options. Various diseases involving chronic inflammatory response and infection are associated with endoplasmic reticulum (ER) stress and subsequent activation of the unfolded protein response (UPR), an adaptive response to maintain cellular homeostasis. Recent evidence suggests impaired ER stress response in CF airway epithelial cells, this might be a reason for recurrent viral infection in CF. Therefore, assuming that ER stress inducing drugs have antiviral properties, we evaluated the activation of the UPR by selected ER stress inducers as an approach to control virus replication in the CF bronchial epithelium.

METHODS

We assessed the levels of UPR markers, namely the glucose-regulated protein 78 (Grp78) and the C/EBP homologous protein (CHOP), in primary CF and control bronchial epithelial cells and in a CF and control bronchial epithelial cell line before and after infection with RV. The cells were also pretreated with ER stress-inducing drugs and RV replication and shedding was measured by quantitative RT-PCR and by a TCID₅₀ assay, respectively. Cell death was assessed by a lactate dehydrogenate (LDH) activity test in supernatants.

RESULTS

We observed a significantly impaired induction of Grp78 and CHOP in CF compare to control cells following RV infection. The ER stress response could be significantly induced in CF cells by pharmacological ER stress inducers Brefeldin A, Tunicamycin, and Thapsigargin. The chemical induction of the UPR pathway prior to RV infection of CF and control cells reduced viral replication and shedding by up to two orders of magnitude and protected cells from RV-induced cell death.

CONCLUSION

RV infection causes an impaired activation of the UPR in CF cells. Rescue of the ER stress response by chemical ER stress inducers reduced significantly RV replication in CF cells. Thus, pharmacological modulation of the UPR might represent a strategy to control respiratory virus replication in the CF bronchial epithelium.

CHAC1 Is Differentially Expressed in Normal and Cystic Fibrosis Bronchial Epithelial Cells and Regulates the Inflammatory Response Induced by Pseudomonas aeruginosa

In cystic fibrosis (CF), Pseudomonas aeruginosa (Pa) colonizes the lungs, leading to chronic inflammation of the bronchial epithelium. ChaC glutathione-specific γ-glutamylcyclotransferase 1 (CHAC1) mRNA is differentially expressed in primary human airway epithelial cells from bronchi (hAECBs) from patients with CF and healthy patients at baseline and upon infection with Pa. CHAC1 degrades glutathione and is associated with ER stress and apoptosis pathways. In this study, we examined the roles of CHAC1 in the inflammatory response and apoptosis in lung epithelial cells. First, we confirmed by reverse transcription quantitative polymerase chain reaction that CHAC1 mRNA was overexpressed in hAECBs from patients without CF compared with the expression in hAECBs from patients with CF upon Pa (PAK strain) infection. Moreover, the Pa virulence factors LPS and flagellin were shown to induce CHAC1 expression in cells from patients without CF. Using NCI-H292 lung epithelial cells, we found that LPS-induced CHAC1 mRNA expression was PERK-independent and involved ATF4. Additionally, using CHAC1 small interfering RNA, we showed that reduced CHAC1 expression in the context of LPS and flagellin stimulation was associated with modulation of inflammatory markers and alteration of NF-κB signaling. Finally, we showed that Pa was not able to induce apoptosis in NCI-H292 cells. Our results suggest that CHAC1 is involved in the regulation of inflammation in bronchial cells during Pa infection and may explain the excessive inflammation present in the respiratory tracts of patients with CF.

The Unfolded Protein Response in Chronic Obstructive Pulmonary Disease

Accumulation of nonfunctional and potentially cytotoxic, misfolded proteins in chronic obstructive pulmonary disease (COPD) is believed to contribute to lung cell apoptosis, inflammation, and autophagy. Because of its fundamental role as a quality control system in protein metabolism, the "unfolded protein response" (UPR) is of potential importance in the pathogenesis of COPD. The UPR comprises a series of transcriptional, translational, and post-translational processes that decrease protein synthesis while enhancing protein folding capacity and protein degradation. Several studies have suggested that the UPR contributes to lung cell apoptosis and lung inflammation in at least some subjects with human COPD. However, information on the prevalence of the UPR in subjects with COPD, the lung cells that manifest a UPR, and the role of the UPR in the pathogenesis of COPD is extremely limited and requires additional study.

Endoplasmic reticulum stress in lung disease

Exposure to inhaled pollutants, including fine particulates and cigarette smoke is a major cause of lung disease in Europe. While it is established that inhaled pollutants have devastating effects on the genome, it is now recognised that additional effects on protein folding also drive the development of lung disease. Protein misfolding in the endoplasmic reticulum affects the pathogenesis of many diseases, ranging from pulmonary fibrosis to cancer. It is therefore important to understand how cells respond to endoplasmic reticulum stress and how this affects pulmonary tissues in disease. These insights may offer opportunities to manipulate such endoplasmic reticulum stress pathways and thereby cure lung disease.

Dysregulated IL-1β Secretion in Autoinflammatory Diseases: A Matter of Stress?

Infectious and sterile inflammation is induced by activation of innate immune cells. Triggering of toll-like receptors by pathogen-associated molecular pattern or damage-associated molecular pattern (PAMP or DAMP) molecules generates reactive oxygen species that in turn induce production and activation of pro-inflammatory cytokines such as IL-1β. Recent evidence indicates that cell stress due to common events, like starvation, enhanced metabolic demand, cold or heat, not only potentiates inflammation but may also directly trigger it in the absence of PAMPs or DAMPs. Stress-mediated inflammation is also a common feature of many hereditary disorders, due to the proteotoxic effects of mutant proteins. We propose that harmful mutant proteins can induce dysregulated IL-1β production and inflammation through different pathways depending on the cell type involved. When expressed in professional inflammatory cells, stress induced by the mutant protein activates in a cell-autonomous way the onset of inflammation and mediates its aberrant development, resulting in the explosive responses that hallmark autoinflammatory diseases. When expressed in non-immune cells, the mutant protein may cause the release of transcellular stress signals that trigger and propagate inflammation.

From the endoplasmic reticulum to the plasma membrane: mechanisms of CFTR folding and trafficking

CFTR biogenesis starts with its co-translational insertion into the membrane of endoplasmic reticulum and folding of the cytosolic domains, towards the acquisition of a fully folded compact native structure. Efficiency of this process is assessed by the ER quality control system that allows the exit of folded proteins but targets unfolded/misfolded CFTR to degradation. If allowed to leave the ER, CFTR is modified at the Golgi and reaches the post-Golgi compartments to be delivered to the plasma membrane where it functions as a cAMP- and phosphorylation-regulated chloride/bicarbonate channel. CFTR residence at the membrane is a balance of membrane delivery, endocytosis, and recycling. Several adaptors, motor, and scaffold proteins contribute to the regulation of CFTR stability and are involved in continuously assessing its structure through peripheral quality control systems. Regulation of CFTR biogenesis and traffic (and its dysregulation by mutations, such as the most common F508del) determine its overall activity and thus contribute to the fine modulation of chloride secretion and hydration of epithelial surfaces. This review covers old and recent knowledge on CFTR folding and trafficking from its synthesis to the regulation of its stability at the plasma membrane and highlights how several of these steps can be modulated to promote the rescue of mutant CFTR.

The burgeoning field of innate immune-mediated disease and autoinflammation

Immune-mediated autoinflammatory diseases are occupying an increasingly prominent position among the pantheon of debilitating conditions that afflict humankind. This review focuses on some of the key developments that have occurred since the original description of autoinflammatory disease in 1999, and focuses on underlying mechanisms that trigger autoinflammation. The monogenic autoinflammatory disease range has expanded considerably during that time, and now includes a broad spectrum of disorders, including relatively common conditions such as cystic fibrosis and subsets of systemic lupus erythematosus. The innate immune system also plays a key role in the pathogenesis of complex inflammatory disorders. We have proposed a new nomenclature to accommodate the rapidly increasing number of monogenic disorders, which predispose to either autoinflammation or autoimmunity or, indeed, combinations of both. This new terminology also encompasses a wide spectrum of genetically determined autoinflammatory diseases, with variable clinical manifestations of immunodeficiency and immune dysregulation/autoimmunity. We also explore some of the ramifications of the breakthrough discovery of the physiological role of pyrin and the search for identifiable factors that may serve to trigger attacks of autoinflammation. The evidence that pyrin, as part of the pyrin inflammasome, acts as a sensor of different inactivating bacterial modification Rho GTPases, rather than interacting directly with these microbial products, sets the stage for a better understanding of the role of microorganisms and infections in the autoinflammatory disorders. Finally, we discuss some of the triggers of autoinflammation as well as potential therapeutic interventions aimed at enhancing autophagy and proteasome degradation pathways. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Endoplasmic Reticulum Stress Is a Danger Signal Promoting Innate Inflammatory Responses in Bronchial Epithelial Cells

Endoplasmic reticulum (ER) stress is associated with chronic pulmonary inflammatory diseases. We hypothesized that the combined activation of both Toll-like receptor (TLR) signaling and ER stress might increase inflammatory reactions in otherwise tolerant airway epithelial cells. Indeed, ER stress resulted in an increased response of BEAS-2B and human primary bronchial epithelial cells to pathogen-associated molecular pattern stimulation with respect to IL6 and IL8 production. ER stress elevated p38 and ERK MAP kinase activation, and pharmacological inhibition of these kinases could inhibit the boosting effect. Knockdown of unfolded protein response signaling indicated that mainly PERK and ATF6 were responsible for the synergistic activity. Specifically, PERK and ATF6 mediated increased MAPK activation, which is needed for effective cytokine secretion. We conclude that within airway epithelial cells the combined activation of TLR signaling and ER stress-mediated MAPK activation results in synergistic proinflammatory activity. We speculate that ER stress, present in various chronic pulmonary diseases, boosts TLR signaling and therefore proinflammatory cytokine production, thus acting as a costimulatory danger signal.

Chemotaxis and Binding of Pseudomonas aeruginosa to Scratch-Wounded Human Cystic Fibrosis Airway Epithelial Cells

Confocal imaging was used to characterize interactions of Pseudomonas aeruginosa (PA, expressing GFP or labeled with Syto 11) with CF airway epithelial cells (CFBE41o-, grown as confluent monolayers with unknown polarity on coverglasses) in control conditions and following scratch wounding. Epithelia and PAO1-GFP or PAK-GFP (2 MOI) were incubated with Ringer containing typical extracellular salts, pH and glucose and propidium iodide (PI, to identify dead cells). PAO1 and PAK swam randomly over and did not bind to nonwounded CFBE41o- cells. PA migrated rapidly (began within 20 sec, maximum by 5 mins) and massively (10–80 fold increase, termed “swarming”), but transiently (random swimming after 15 mins), to wounds, particularly near cells that took up PI. Some PA remained immobilized on cells near the wound. PA swam randomly over intact CFBE41o- monolayers and wounded monolayers that had been incubated with medium for 1 hr. Expression of CFTR and altered pH of the media did not affect PA interactions with CFBE41o- wounds. In contrast, PAO1 swarming and immobilization along wounds was abolished in PAO1 (PAO1ΔcheYZABW, no expression of chemotaxis regulatory components cheY, cheZ, cheA, cheB and cheW) and greatly reduced in PAO1 that did not express amino acid receptors pctA, B and C (PAO1ΔpctABC) and in PAO1 incubated in Ringer containing a high concentration of mixed amino acids. Non-piliated PAKΔpilA swarmed normally towards wounded areas but bound infrequently to CFBE41o- cells. In contrast, both swarming and binding of PA to CFBE41o- cells near wounds were prevented in non-flagellated PAKΔfliC. Data are consistent with the idea that (i) PA use amino acid sensor-driven chemotaxis and flagella-driven swimming to swarm to CF airway epithelial cells near wounds and (ii) PA use pili to bind to epithelial cells near wounds.

Keratin 12 missense mutation induces the unfolded protein response and apoptosis in Meesmann epithelial corneal dystrophy

Meesmann epithelial corneal dystrophy (MECD) is a rare autosomal dominant disorder caused by dominant-negative mutations within the KRT3 or KRT12 genes, which encode the cytoskeletal protein keratins K3 and K12, respectively. To investigate the pathomechanism of this disease, we generated and phenotypically characterized a novel knock-in humanized mouse model carrying the severe, MECD-associated, K12-Leu132Pro mutation. Although no overt changes in corneal opacity were detected by slit-lamp examination, the corneas of homozygous mutant mice exhibited histological and ultrastructural epithelial cell fragility phenotypes. An altered keratin expression profile was observed in the cornea of mutant mice, confirmed by western blot, RNA-seq and quantitative real-time polymerase chain reaction. Mass spectrometry (MS) and immunohistochemistry demonstrated a similarly altered keratin profile in corneal tissue from a K12-Leu132Pro MECD patient. The K12-Leu132Pro mutation results in cytoplasmic keratin aggregates. RNA-seq analysis revealed increased chaperone gene expression, and apoptotic unfolded protein response (UPR) markers, CHOP and Caspase 12, were also increased in the MECD mice. Corneal epithelial cell apoptosis was increased 17-fold in the mutant cornea, compared with the wild-type (P < 0.001). This elevation of UPR marker expression was also observed in the human MECD cornea. This is the first reporting of a mouse model for MECD that recapitulates the human disease and is a valuable resource in understanding the pathomechanism of the disease. Although the most severe phenotype is observed in the homozygous mice, this model will still provide a test-bed for therapies not only for corneal dystrophies but also for other keratinopathies caused by similar mutations.

The Role of Short-Chain Fatty Acids, Produced by Anaerobic Bacteria, in the Cystic Fibrosis Airway

RATIONALE

Anaerobic bacteria are present in large numbers in the airways of people with cystic fibrosis (PWCF). In the gut, anaerobes produce short-chain fatty acids (SCFAs) that modulate immune and inflammatory processes.

OBJECTIVES

To investigate the capacity of anaerobes to contribute to cystic fibrosis (CF) airway pathogenesis via SCFAs.

METHODS

Samples of 109 PWCF were processed using anaerobic microbiological culture with bacteria present identified by 16S RNA sequencing. SCFA levels in anaerobic supernatants and bronchoalveolar lavage (BAL) were determined by gas chromatography. The mRNA and/or protein expression of two SCFA receptors, GPR41 and GPR43, in CF and non-CF bronchial brushings and 16HBE14o(-) and CFBE41o(-) cells were evaluated using reverse transcription polymerase chain reaction, Western blot analysis, laser scanning cytometry, and confocal microscopy. SCFA-induced IL-8 secretion was monitored by ELISA.

MEASUREMENTS AND MAIN RESULTS

Fifty-seven (52.3%) of 109 PWCF were anaerobe positive. Prevalence increased with age, from 33.3% to 57.7% in PWCF younger (n = 24) and older (n = 85) than 6 years of age. All evaluated anaerobes produced millimolar concentrations of SCFAs, including acetic, propionic, and butyric acids. SCFA levels were higher in BAL samples of adults than in those of children. GPR41 levels were elevated in CFBE41o(-) versus 16HBE14o(-) cells; CF versus non-CF bronchial brushings; and 16HBE14o(-) cells after treatment with cystic fibrosis transmembrane conductance regulator inhibitor CFTR(inh)-172, CF BAL, or inducers of endoplasmic reticulum stress. SCFAs induced a dose-dependent and pertussis toxin-sensitive IL-8 response in bronchial epithelial cells, with a higher production of IL-8 in CFBE41o(-) than in 16HBE14o(-) cells.

CONCLUSIONS

This study illustrates that SCFAs contribute to excessive production of IL-8 in CF airways colonized with anaerobes via up-regulated GPR41.

CFTR regulates acute inflammatory responses in macrophages

BACKGROUND

Mutation of cystic fibrosis transmembrane conductance regulator (CFTR) in the airway epithelial cells can lead to recurrent airway inflammation in cystic fibrosis (CF). Dysfunction of CFTR in neutrophils could contribute to LPS-induced acute lung inflammation. Deficiency of CFTR could also facilitate platelet aggregation and neutrophil-platelet interaction and promote inflammation.

AIM

To study whether inhibition or mutation of CFTR in alveolar macrophages (AMs) or peritoneal macrophages (PMs) would promote their proinflammatory responses and whether dysfunction of CFTR would deteriorate acute E. coli-induced lung or peritoneal inflammation.

DESIGN

Laboratory study.

METHODS

ELISA was used to determine production of proinflammatory cytokines in the CFTR inhibited or mutated macrophages under LPS challenge. Lung or peritoneum lavage was used to analyze proinflammatory parameters and cell differentiation. Excess lung water and lung vascular permeability were measured for evaluating severity of acute lung inflammation.

RESULTS

Escherichia coli LPS simulation in AMs increased CFTR expression. Inhibition or mutation of CFTR in both AMs and PMs enhanced production of tumor necrosis factor alpha (TNF-α) and macrophage inflammatory protein-2 (MIP-2). Mutation of CFTR in macrophages exaggerated production of cytokines through NF-kB and p38 MAPK. Inhibition of CFTR by MalH2 or CFTRinh-172 deteriorates E. coli-induced acute lung inflammation. Deficiency of CFTR promotes migration of monocytes and neutrophils in E. coli pneumonia and peritonitis mouse models.

CONCLUSIONS

CFTR expressed by alveolar or peritoneal macrophages regulates acute proinflammatory responses.

Amino Acid-Dependent Attenuation of Toll-like Receptor Signaling by Peptide-Gold Nanoparticle Hybrids

Manipulation of immune responsiveness using nanodevices provides a potential approach to treat human diseases. Toll-like receptor (TLR) signaling plays a central role in the pathophysiology of many acute and chronic human inflammatory diseases, and pharmacological regulation of TLR responses is anticipated to be beneficial in many of these inflammatory conditions. Here we describe the discovery of a unique class of peptide-gold nanoparticle hybrids that exhibit a broad inhibitory activity on TLR signaling, inhibiting signaling through TLRs 2, 3, 4, and 5. As exemplified using TLR4, the nanoparticles were found to inhibit both arms of TLR4 signaling cascade triggered by the prototypical ligand, lipopolysaccharide (LPS). Through structure-activity relationship studies, we identified the key chemical components of the hybrids that contribute to their immunomodulatory activity. Specifically, the hydrophobicity and aromatic ring structure of the amino acids on the peptides were essential for modulating TLR4 responses. This work enhances our fundamental understanding of the role of nanoparticle surface chemistry in regulating innate immune signaling, and identifies specific nanoparticle hybrids that may represent a unique class of anti-inflammatory therapeutics for human inflammatory diseases.

Cell-contact dependent inhibition of monocytes by airway epithelial cells and reversion by infection with Respiratory Syncytial Virus

Airway epithelial cells (AEC) are the first line of defense against airborne infectious microbes and play an important role in regulating the local immune response. However, the interplay of epithelial cells and professional immune cells during both homeostasis and infection has only been partially studied. The present study was performed to determine how bronchial epithelial cells affect the activation of monocytes. Under healthy conditions, AECs were shown to inhibit reactivity of monocytes. We hypothesized that upon infection, monocytes might be released from inhibition by AECs. We report that direct contact of monocytes with unstimulated BEAS2B epithelial cells results in inhibition of TNF secretion by activated monocytes. In addition to the known soluble modulators, we show that cell contacts between epithelial cells and monocytes or macrophages also contribute to homeostatic inhibitory actions. We find AECs to express the inhibitory molecule PD-L1 and blockade of PD-L1 results in increased secretion of pro-inflammatory cytokines from monocytes. Contrary to the inhibitory activities during homeostasis, epithelial cells infected with Respiratory Syncitial Virus (RSV) induce a significant release of inhibition. However, release of inhibition was not due to modulation of PD-L1 expression in AECs. We conclude that airway epithelial cells control the reactivity of monocytes through direct and indirect interactions; however tonic inhibition can be reverted upon stimulation of AECs with RSV and thereof derived molecular patterns. The study confirms the important role of airway epithelial cells for local immune reactions.

Virulence Factors of Pseudomonas aeruginosa Induce Both the Unfolded Protein and Integrated Stress Responses in Airway Epithelial Cells

Pseudomonas aeruginosa infection can be disastrous in chronic lung diseases such as cystic fibrosis and chronic obstructive pulmonary disease. Its toxic effects are largely mediated by secreted virulence factors including pyocyanin, elastase and alkaline protease (AprA). Efficient functioning of the endoplasmic reticulum (ER) is crucial for cell survival and appropriate immune responses, while an excess of unfolded proteins within the ER leads to “ER stress” and activation of the “unfolded protein response” (UPR). Bacterial infection and Toll-like receptor activation trigger the UPR most likely due to the increased demand for protein folding of inflammatory mediators. In this study, we show that cell-free conditioned medium of the PAO1 strain of P. aeruginosa, containing secreted virulence factors, induces ER stress in primary bronchial epithelial cells as evidenced by splicing of XBP1 mRNA and induction of CHOP, GRP78 and GADD34 expression. Most aspects of the ER stress response were dependent on TAK1 and p38 MAPK, except for the induction of GADD34 mRNA. Using various mutant strains and purified virulence factors, we identified pyocyanin and AprA as inducers of ER stress. However, the induction of GADD34 was mediated by an ER stress-independent integrated stress response (ISR) which was at least partly dependent on the iron-sensing eIF2α kinase HRI. Our data strongly suggest that this increased GADD34 expression served to protect against Pseudomonas-induced, iron-sensitive cell cytotoxicity. In summary, virulence factors from P. aeruginosa induce ER stress in airway epithelial cells and also trigger the ISR to improve cell survival of the host.

Pseudomonas aeruginosa causes a devastating infection when it affects patients with cystic fibrosis or other chronic lung diseases. It often causes chronic infection due to its resistance to antibiotic treatment and its ability to form biofilms in these patients. The toxic effects of P. aeruginosa are largely mediated by secreted virulence factors. Efficient functioning of the endoplasmic reticulum is crucial for cell survival and appropriate immune responses, while its dysfunction causes stress and activation of the unfolded protein response. In this study, we found that virulence factors secreted by P. aeruginosa trigger the unfolded protein response in human cells by causing endoplasmic reticulum stress. In addition, secreted virulence factors activate the integrated stress response via a parallel independent pathway. Both stress pathways lead to the induction of the protein GADD34, which appears to provide protection against the toxic effects of the secreted virulence factors.

Early pulmonary inflammation and lung damage in children with cystic fibrosis

Individuals with cystic fibrosis (CF) suffer progressive airway inflammation, infection and lung damage. Airway inflammation and infection are present from early in life, often before children are symptomatic. CF gene mutations cause changes in the CF transmembrane regulator protein that result in an aberrant airway microenvironment including airway surface liquid (ASL) dehydration, reduced ASL acidity, altered airway mucin and a dysregulated inflammatory response. This review discusses how an altered microenvironment drives CF lung disease before overt airway infection, the response of the CF airway to early infection, and methods to prevent inflammation and early lung disease.

Inflammation in cystic fibrosis lung disease: Pathogenesis and therapy

Lung disease is the major cause of morbidity and mortality in patients with cystic fibrosis (CF). Although CF lung disease is primarily an infectious disorder, the associated inflammation is both intense and ineffective at clearing pathogens. Persistent high-intensity inflammation leads to permanent structural damage of the CF airways and impaired lung function that eventually results in respiratory failure and death. Several defective inflammatory responses have been linked to cystic fibrosis transmembrane conductance regulator (CFTR) deficiency including innate and acquired immunity dysregulation, cell membrane lipid abnormalities, various transcription factor signaling defects, as well as altered kinase and toll-like receptor responses. The inflammation of the CF lung is dominated by neutrophils that release oxidants and proteases, particularly elastase. Neutrophil elastase in the CF airway secretions precedes the appearance of bronchiectasis, and correlates with lung function deterioration and respiratory exacerbations. Anti-inflammatory therapies are therefore of particular interest for CF lung disease but must be carefully studied to avoid suppressing critical elements of the inflammatory response and thus worsening infection. This review examines the role of inflammation in the pathogenesis of CF lung disease, summarizes the results of past clinical trials and explores promising new anti-inflammatory options.

Gene expression in transformed lymphocytes reveals variation in endomembrane and HLA pathways modifying cystic fibrosis pulmonary phenotypes

Variation in cystic fibrosis (CF) phenotypes, including lung disease severity, age of onset of persistent Pseudomonas aeruginosa (P. aeruginosa) lung infection, and presence of meconium ileus (MI), has been partially explained by genome-wide association studies (GWASs). It is not expected that GWASs alone are sufficiently powered to uncover all heritable traits associated with CF phenotypic diversity. Therefore, we utilized gene expression association from lymphoblastoid cells lines from 754 p.Phe508del CF-affected homozygous individuals to identify genes and pathways. LPAR6, a G protein coupled receptor, associated with lung disease severity (false discovery rate q value = 0.0006). Additional pathway analyses, utilizing a stringent permutation-based approach, identified unique signals for all three phenotypes. Pathways associated with lung disease severity were annotated in three broad categories: (1) endomembrane function, containing p.Phe508del processing genes, providing evidence of the importance of p.Phe508del processing to explain lung phenotype variation; (2) HLA class I genes, extending previous GWAS findings in the HLA region; and (3) endoplasmic reticulum stress response genes. Expression pathways associated with lung disease were concordant for some endosome and HLA pathways, with pathways identified using GWAS associations from 1,978 CF-affected individuals. Pathways associated with age of onset of persistent P. aeruginosa infection were enriched for HLA class II genes, and those associated with MI were related to oxidative phosphorylation. Formal testing demonstrated that genes showing differential expression associated with lung disease severity were enriched for heritable genetic variation and expression quantitative traits. Gene expression provided a powerful tool to identify unrecognized heritable variation, complementing ongoing GWASs in this rare disease.

Salubrinal acts as a Dusp2 inhibitor and suppresses inflammation in anti-collagen antibody-induced arthritis

Dual-specificity phosphatase 2 (Dusp2; also called phosphatase of activated cells 1, PAC1) is highly expressed in activated immune cells. We examined whether a potential inhibitor of Dusp2, salubrinal, prevents inflammatory cytokine expression in immune cells and arthritic responses in a mouse model of anti-collagen antibody-induced arthritis (CAIA). Salubrinal is a synthetic chemical that inhibits de-phosphorylation of eukaryotic translation initiation factor 2 alpha (eIF2α). In this study, we examined the effects of salubrinal on expression of inflammation linked genes as well as a family of DUSP genes using genome-wide microarrays, qPCR, and RNA interference. We also evaluated the effects of salubrinal on arthritic responses in CAIA mice using clinical and histological scores. The results revealed that salubrinal decreased inflammatory gene expression in macrophages, T lymphocytes, and mast cells. Dusp2 was suppressed by salubrinal in LPS-activated macrophages as well as PMA/ionomycin-activated T lymphocytes and mast cells. Furthermore, a partial silencing of Dusp2 downregulated IL1β and Cox2, and the inflammatory signs of CAIA mice were significantly suppressed by salubrinal. Collectively, this study presents a novel therapeutic possibility of salubrinal for inflammatory arthritis such as RA through inhibition of Dusp2.

Coronavirus-induced ER stress response and its involvement in regulation of coronavirus-host interactions

Coronavirus replication is structurally and functionally associated with the endoplasmic reticulum (ER), a major site of protein synthesis, folding, modification and sorting in the eukaryotic cells. Disturbance of ER homeostasis may occur under various physiological or pathological conditions. In response to the ER stress, signaling pathways of the unfolded protein response (UPR) are activated. UPR is mediated by three ER transmembrane sensors, namely the PKR-like ER protein kinase (PERK), the inositol-requiring protein 1 (IRE1) and the activating transcriptional factor 6 (ATF6). UPR facilitates adaptation to ER stress by reversible translation attenuation, enhancement of ER protein folding capacity and activation of ER-associated degradation (ERAD). In cells under prolonged and irremediable ER stress, UPR can also trigger apoptotic cell death. Accumulating evidence has shown that coronavirus infection causes ER stress and induces UPR in the infected cells. UPR is closely associated with a number of major signaling pathways, including autophagy, apoptosis, the mitogen-activated protein (MAP) kinase pathways, innate immunity and pro-inflammatory response. Therefore, studies on the UPR are pivotal in elucidating the complicated issue of coronavirus-host interaction. In this paper, we present the up-to-date knowledge on coronavirus-induced UPR and discuss its potential involvement in regulation of innate immunity and apoptosis.

Endoplasmic reticulum stress in immunity

Immune responses occur in the midst of a variety of cellular stresses that can severely perturb endoplasmic reticulum (ER) function. The unfolded protein response is a three-pronged signaling axis dedicated to preserving ER homeostasis. In this review, we highlight many important and emerging functional roles for ER stress in immunity, focusing on how the bidirectional cross talk between immunological processes and basic cell biology leads to pleiotropic signaling outcomes and enhanced sensitivity to inflammatory stimuli. We also discuss how dysregulated ER stress responses can provoke many diseases, including autoimmunity, firmly positioning the unfolded protein response as a major therapeutic target in human disease.

Ischemia/reperfusion-induced CHOP expression promotes apoptosis and impairs renal function recovery: the role of acidosis and GPR4

Endoplasmic reticulum (ER) stress-induced apoptosis is implicated in a wide range of diseases, including ischemia/reperfusion injury (IRI). As a common feature of ER stress, the role of CCAT/enhancer-binding protein homologous protein (CHOP) in renal IRI has not been thoroughly investigated. We found that IR led to renal CHOP expression, accompanied by apoptosis induction. Renal IRI was markedly alleviated in CHOP-/- mice. Observations from bone marrow chimeras showed that this was based on CHOP inactivation in renal parenchymal cells rather than inflammatory cells. In vivo and in vitro studies demonstrated that IRI induced CHOP expression in both endothelial and epithelial cells, which was responsible for apoptosis induction. These results were reinforced by the observation that CHOP knockout led to improvement of the postischemic microcirculatory recovery. In vitro studies revealed hypoxia-induced acidosis to be a major inducer of CHOP in endothelial cells, and neutralizing acidosis not only diminished CHOP protein, but also reduced apoptosis. Finally, knockdown of a proton-sensing G protein-coupled receptor GPR4 markedly reduced CHOP expression and endothelial cell apoptosis after hypoxia exposure. These results highlight the importance of hypoxia-acidosis in ER stress signaling regulation in ischemic kidneys and suggest that GPR4 inhibitors or agents targeting CHOP expression may be promising in the treatment of renal IRI.

The integrated stress response in lung disease

Lungs are repeatedly exposed to inhaled toxic insults, such as smoke, diesel exhaust, and microbes, which elicit cellular stress responses. The phosphorylation of eukaryotic translation initiation factor 2α by one of four stress-sensing kinases triggers a pathway called the integrated stress response that helps protect cellular reserves of nutrients and prevents the accumulation of toxic proteins. In this review, we discuss how activation of the integrated stress response has been shown to play an important role in pulmonary pathology, and how its study may help in the development of novel therapies for diverse conditions, from hypoxia to cancer.

Endoplasmic reticulum stress in hepatic steatosis and inflammatory bowel diseases

As an adaptive response to the overloading with misfolded proteins in the endoplasmic reticulum (ER), ER stress plays critical roles in maintaining protein homeostasis in the secretory pathway to avoid damage to the host. Such a conserved mechanism is accomplished through three well-orchestrated pathways known collectively as unfolded protein response (UPR). Persistent and pathological ER stress has been implicated in a variety of diseases in metabolic, inflammatory, and malignant conditions. Furthermore, ER stress is directly linked with inflammation through UPR pathways, which modulate transcriptional programs to induce the expression of inflammatory genes. Importantly, the inflammation induced by ER stress is directly responsible for the pathogenesis of metabolic and inflammatory diseases. In this review, we will discuss the potential signaling pathways connecting ER stress with inflammation. We will also depict the interplay between ER stress and inflammation in the pathogenesis of hepatic steatosis, inflammatory bowel diseases and colitis-associated colon cancer.

Cystic fibrosis bronchial epithelial cells are lipointoxicated by membrane palmitate accumulation

The F508del-CFTR mutation, responsible for Cystic Fibrosis (CF), leads to the retention of the protein in the endoplasmic reticulum (ER). The mistrafficking of this mutant form can be corrected by pharmacological chaperones, but these molecules showed limitations in clinical trials. We therefore hypothesized that important factors in CF patients may have not been considered in the in vitro assays. CF has also been associated with an altered lipid homeostasis, i. e. a decrease in polyunsaturated fatty acid levels in plasma and tissues. However, the precise fatty acyl content of membrane phospholipids from human CF bronchial epithelial cells had not been studied to date. Since the saturation level of phospholipids can modulate crucial membrane properties, with potential impacts on membrane protein folding/trafficking, we analyzed this parameter for freshly isolated bronchial epithelial cells from CF patients. Interestingly, we could show that Palmitate, a saturated fatty acid, accumulates within Phosphatidylcholine (PC) in CF freshly isolated cells, in a process that could result from hypoxia. The observed PC pattern can be recapitulated in the CFBE41o(-) cell line by incubation with 100 µM Palmitate. At this concentration, Palmitate induces an ER stress, impacts calcium homeostasis and leads to a decrease in the activity of the corrected F508del-CFTR. Overall, these data suggest that bronchial epithelial cells are lipointoxicated by hypoxia-related Palmitate accumulation in CF patients. We propose that this phenomenon could be an important bottleneck for F508del-CFTR trafficking correction by pharmacological agents in clinical trials.

Lipopolysaccharide preconditioning protects hepatocytes from ischemia/reperfusion injury (IRI) through inhibiting ATF4-CHOP pathway in mice

Background

Low-dose lipopolysaccharide (LPS) preconditioning-induced liver protection has been demonstrated during ischemia-reperfusion injury (IRI) in several organs but has not been sufficiently elucidated underlying causal mechanism. This study investigated the role of low-dose LPS preconditioning on ATF4-CHOP pathway as well as the effects of the pathway on tissue injury and inflammation in a mouse model of liver partial-warm IRI.

Methods

LPS (100 µg/kg/d) was injected intraperitoneally two days before ischemia. Hepatic injury was evaluated based on serum alanine aminotransferase levels, histopathology, and caspase-3 activity. The ATF4-CHOP pathway and its related apoptotic molecules were investigated after reperfusion. The role of LPS preconditioning on apoptosis and ATF4-CHOP pathway was examined in vitro. Moreover, the effects of the ATF4-CHOP pathway on apoptosis, Caspase-12, and Caspase-3 were determined with ATF4 small interfering RNA (siRNA). Inflammatory cytokine expression was also checked after reperfusion. Inflammatory cytokines and related signaling pathways were analyzed in vitro in macrophages treated by LPS preconditioning or ATF4 siRNA.

Results

LPS preconditioning significantly attenuated liver injury after IRI. As demonstrated by in vitro experiments, LPS preconditioning significantly reduced the upregulation of the ATF4-CHOP pathway and inhibited Caspase-12 and Caspase-3 activation after IRI. Later experiments showed that ATF4 knockdown significantly suppressed CHOP, cleaved caspase-12 and caspase-3 expression, as well as inhibited hepatocellular apoptosis. In addition, in mice pretreated with LPS, TNF-α and IL-6 were inhibited after reperfusion, whereas IL-10 was upregulated. Similarly, low-dose LPS significantly inhibited TNF-α, IL-6, ATF4-CHOP pathway, NF-κB pathway, and ERK1/2 in high-dose LPS-stimulated macrophages, whereas IL-10 and cytokine signaling (SOCS)-3 suppressor were induced. Importantly, ATF4 siRNA is consistent with results of LPS preconditioning in macrophages.

Conclusions

This work is the first time to provide evidence for LPS preconditioning protects hepatocytes from IRI through inhibiting ATF4-CHOP pathway, which may be critical to reducing related apoptosis molecules and modulating innate inflammation.