Adverse Outcomes Associated with Cigarette Smoke Radicals Related to Damage to Protein-disulfide Isomerase

The Multifaceted Role of Glutathione S-Transferases in Health and Disease

In humans, the cytosolic glutathione S-transferase (GST) family of proteins is encoded by 16 genes presented in seven different classes. GSTs exhibit remarkable structural similarity with some overlapping functionalities. As a primary function, GSTs play a putative role in Phase II metabolism by protecting living cells against a wide variety of toxic molecules by conjugating them with the tripeptide glutathione. This conjugation reaction is extended to forming redox sensitive post-translational modifications on proteins: S-glutathionylation. Apart from these catalytic functions, specific GSTs are involved in the regulation of stress-induced signaling pathways that govern cell proliferation and apoptosis. Recently, studies on the effects of GST genetic polymorphisms on COVID-19 disease development revealed that the individuals with higher numbers of risk-associated genotypes showed higher risk of COVID-19 prevalence and severity. Furthermore, overexpression of GSTs in many tumors is frequently associated with drug resistance phenotypes. These functional properties make these proteins promising targets for therapeutics, and a number of GST inhibitors have progressed in clinical trials for the treatment of cancer and other diseases.

Protein disulfide isomerase A1 as a novel redox sensor in VEGFR2 signaling and angiogenesis

VEGFR2 signaling in endothelial cells (ECs) is regulated by reactive oxygen species (ROS) derived from NADPH oxidases (NOXs) and mitochondria, which plays an important role in postnatal angiogenesis. However, it remains unclear how highly diffusible ROS signal enhances VEGFR2 signaling and reparative angiogenesis. Protein disulfide isomerase A1 (PDIA1) functions as an oxidoreductase depending on the redox environment. We hypothesized that PDIA1 functions as a redox sensor to enhance angiogenesis. Here we showed that PDIA1 co-immunoprecipitated with VEGFR2 or colocalized with either VEGFR2 or an early endosome marker Rab5 at the perinuclear region upon stimulation of human ECs with VEGF. PDIA1 silencing significantly reduced VEGF-induced EC migration, proliferation and spheroid sprouting via inhibiting VEGFR2 signaling. Mechanistically, VEGF stimulation rapidly increased Cys-OH formation of PDIA1 via the NOX4-mitochondrial ROS axis. Overexpression of "redox-dead" mutant PDIA1 with replacement of the active four Cys residues with Ser significantly inhibited VEGF-induced PDIA1-CysOH formation and angiogenic responses via reducing VEGFR2 phosphorylation. Pdia1+/- mice showed impaired angiogenesis in developmental retina and Matrigel plug models as well as ex vivo aortic ring sprouting model. Study using hindlimb ischemia model revealed that PDIA1 expression was markedly increased in angiogenic ECs of ischemic muscles, and that ischemia-induced limb perfusion recovery and neovascularization were impaired in EC-specific Pdia1 conditional knockout mice. These results suggest that PDIA1 can sense VEGF-induced H2O2 signal via CysOH formation to promote VEGFR2 signaling and angiogenesis in ECs, thereby enhancing postnatal angiogenesis. The oxidized PDIA1 is a potential therapeutic target for treatment of ischemic vascular diseases.

Endoplasmic Reticulum Stress in Chronic Obstructive Pulmonary Disease: Mechanisms and Future Perspectives

The endoplasmic reticulum (ER) is an integral organelle for maintaining protein homeostasis. Multiple factors can disrupt protein folding in the lumen of the ER, triggering ER stress and activating the unfolded protein response (UPR), which interrelates with various damage mechanisms, such as inflammation, apoptosis, and autophagy. Numerous studies have linked ER stress and UPR to the progression of chronic obstructive pulmonary disease (COPD). This review focuses on the mechanisms of other cellular processes triggered by UPR and summarizes drug intervention strategies targeting the UPR pathway in COPD to explore new therapeutic approaches and preventive measures for COPD.

A Synthetic Small RNA Homologous to the D-Loop Transcript of mtDNA Enhances Mitochondrial Bioenergetics

Mitochondrial malfunction is a hallmark of many diseases, including neurodegenerative disorders, cardiovascular and lung diseases, and cancers. We previously found that alveolar progenitor cells, which are more resistant to cigarette smoke-induced injury than the other cells of the lung parenchyma, upregulate the mtDNA-encoded small non-coding RNA mito-ncR-805 after exposure to smoke. The mito-ncR-805 acts as a retrograde signal between the mitochondria and the nucleus. Here, we identified a region of mito-ncR-805 that is conserved in the mammalian mitochondrial genomes and generated shorter versions of mouse and human transcripts (mmu-CR805 and hsa-LDL1, respectively), which differ in a few nucleotides and which we refer to as the "functional bit". Overexpression of mouse and human functional bits in either the mouse or the human lung epithelial cells led to an increase in the activity of the Krebs cycle and oxidative phosphorylation, stabilized the mitochondrial potential, conferred faster cell division, and lowered the levels of proapoptotic pseudokinase, TRIB3. Both oligos, mmu-CR805 and hsa-LDL1 conferred cross-species beneficial effects. Our data indicate a high degree of evolutionary conservation of retrograde signaling via a functional bit of the D-loop transcript, mito-ncR-805, in the mammals. This emphasizes the importance of the pathway and suggests a potential to develop this functional bit into a therapeutic agent that enhances mitochondrial bioenergetics.

Acid-Catalyzed Isomerization of Carbonyls-2,4- dinitrophenylhydrazone in Mainstream Smoke of Heat-Not-Burn Tobacco Product for HPLC Analysis

Carbonyls (such as acrolein, acetaldehyde, and formaldehyde) are the critical type of carcinogens and toxicants contained within the heat-not-burn (HNB) tobacco products. Using HNB products can have negative effects on human health; therefore, it is important to measure carbonyl contents within the HNB mainstream smoke. Typically, the 2,4-dinitrophenylhydrazine (DNPH) approach involves forming the 2,4-dinitrophenylhydrazone derivatives, which is the most extensively adopted approach to qualitatively and quantitatively analyze carbonyl compounds. However, the approach can result in analytical error because 2,4-dinitrophenylhydrazones contains the E-stereoisomer as well as the Z-stereoisomer. Only an E-isomers exists in the purified carbonyls-2,4-dinitrophenylhydrazone, but when acid is added, the E-isomer and Z-isomer can be observed. For propionaldehyde-, acetaldehyde-, crotonaldehyde-, acrolein-, and 2-butanone-2,4-dinitrophenylhydrazones, their equilibrium Z/E isomer ratios are 0.143, 0.309, 0.093, 0.028, and 0.154. In the case of adding trace water into hydrazone derivatives dissolved within the acetonitrile solution, the derivative contents decrease, whereas the free DNPH content increases. Therefore, catalytic acid should be added in the low content. To determine carbonyls-2,4-dinitrophenylhydrazones through HPLC, the optimal approach is adding phosphoric acid into the samples and the standard reference solution to form the 0.02–1.0% acid solution.

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.

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.

Ischemic stroke disrupts the endothelial glycocalyx through activation of proHPSE via acrolein exposure

Infiltration of peripheral immune cells after blood-brain barrier dysfunction causes severe inflammation after a stroke. Although the endothelial glycocalyx, a network of membrane-bound glycoproteins and proteoglycans that covers the lumen of endothelial cells, functions as a barrier to circulating cells, the relationship between stroke severity and glycocalyx dysfunction remains unclear. In this study, glycosaminoglycans, a component of the endothelial glycocalyx, were studied in the context of ischemic stroke using a photochemically induced thrombosis mouse model. Decreased levels of heparan sulfate and chondroitin sulfate and increased activity of hyaluronidase 1 and heparanase (HPSE) were observed in ischemic brain tissues. HPSE expression in cerebral vessels increased after stroke onset and infarct volume greatly decreased after co-administration of N-acetylcysteine + glycosaminoglycan oligosaccharides as compared with N-acetylcysteine administration alone. These results suggest that the endothelial glycocalyx was injured after the onset of stroke. Interestingly, scission activity of proHPSE produced by immortalized endothelial cells and HEK293 cells transfected with hHPSE1 cDNA were activated by acrolein (ACR) exposure. We identified the ACR-modified amino acid residues of proHPSE using nano LC-MS/MS, suggesting that ACR modification of Lys139 (6-kDa linker), Lys107, and Lys161, located in the immediate vicinity of the 6-kDa linker, at least in part is attributed to the activation of proHPSE. Because proHPSE, but not HPSE, localizes outside cells by binding with heparan sulfate proteoglycans, ACR-modified proHPSE represents a promising target to protect the endothelial glycocalyx.

Retrograde signaling by a mtDNA-encoded non-coding RNA preserves mitochondrial bioenergetics

Alveolar epithelial type II (AETII) cells are important for lung epithelium maintenance and function. We demonstrate that AETII cells from mouse lungs exposed to cigarette smoke (CS) increase the levels of the mitochondria-encoded non-coding RNA, mito-RNA-805, generated by the control region of the mitochondrial genome. The protective effects of mito-ncR-805 are associated with positive regulation of mitochondrial energy metabolism, and respiration. Levels of mito-ncR-805 do not relate to steady-state transcription or replication of the mitochondrial genome. Instead, CS-exposure causes the redistribution of mito-ncR-805 from mitochondria to the nucleus, which correlated with the increased expression of nuclear-encoded genes involved in mitochondrial function. These studies reveal an unrecognized mitochondria stress associated retrograde signaling, and put forward the idea that mito-ncRNA-805 represents a subtype of small non coding RNAs that are regulated in a tissue- or cell-type specific manner to protect cells under physiological stress.

Protein thiol oxidation in the rat lung following e-cigarette exposure

E-cigarette (e-cig) aerosols are complex mixtures of various chemicals including humectants (propylene glycol (PG) and vegetable glycerin (VG)), nicotine, and various flavoring additives. Emerging research is beginning to challenge the "relatively safe" perception of e-cigarettes. Recent studies suggest e-cig aerosols provoke oxidative stress; however, details of the underlying molecular mechanisms remain unclear. Here we used a redox proteomics assay of thiol total oxidation to identify signatures of site-specific protein thiol modifications in Sprague-Dawley rat lungs following in vivo e-cig aerosol exposures. Histologic evaluation of rat lungs exposed acutely to e-cig aerosols revealed mild perturbations in lung structure. Bronchoalveolar lavage (BAL) fluid analysis demonstrated no significant change in cell count or differential. Conversely, total lung glutathione decreased significantly in rats exposed to e-cig aerosol compared to air controls. Redox proteomics quantified the levels of total oxidation for 6682 cysteine sites representing 2865 proteins. Protein thiol oxidation and alterations by e-cig exposure induced perturbations of protein quality control, inflammatory responses and redox homeostasis. Perturbations of protein quality control were confirmed with semi-quantification of total lung polyubiquitination and 20S proteasome activity. Our study highlights the importance of redox control in the pulmonary response to e-cig exposure and the utility of thiol-based redox proteomics as a tool for elucidating the molecular mechanisms underlying this response.

The integrated stress response in pulmonary disease

The respiratory tract and its resident immune cells face daily exposure to stress, both from without and from within. Inhaled pathogens, including severe acute respiratory syndrome coronavirus 2, and toxins from pollution trigger a cellular defence system that reduces protein synthesis to minimise viral replication or the accumulation of misfolded proteins. Simultaneously, a gene expression programme enhances antioxidant and protein folding machineries in the lung. Four kinases (PERK, PKR, GCN2 and HRI) sense a diverse range of stresses to trigger this “integrated stress response”. Here we review recent advances identifying the integrated stress response as a critical pathway in the pathogenesis of pulmonary diseases, including pneumonias, thoracic malignancy, pulmonary fibrosis and pulmonary hypertension. Understanding the integrated stress response provides novel targets for the development of therapies.

Cellular stress responses and dysfunctional Mitochondrial-cellular senescence, and therapeutics in chronic respiratory diseases

The abnormal inflammatory responses due to the lung tissue damage and ineffective repair/resolution in response to the inhaled toxicants result in the pathological changes associated with chronic respiratory diseases. Investigation of such pathophysiological mechanisms provides the opportunity to develop the molecular phenotype-specific diagnostic assays and could help in designing the personalized medicine-based therapeutic approaches against these prevalent diseases. As the central hubs of cell metabolism and energetics, mitochondria integrate cellular responses and interorganellar signaling pathways to maintain cellular and extracellular redox status and the cellular senescence that dictate the lung tissue responses. Specifically, as observed in chronic obstructive pulmonary disease (COPD) and pulmonary fibrosis, the mitochondria-endoplasmic reticulum (ER) crosstalk is disrupted by the inhaled toxicants such as the combustible and emerging electronic nicotine-delivery system (ENDS) tobacco products. Thus, the recent research efforts have focused on understanding how the mitochondria-ER dysfunctions and oxidative stress responses can be targeted to improve inflammatory and cellular dysfunctions associated with these pathologic illnesses that are exacerbated by viral infections. The present review assesses the importance of these redox signaling and cellular senescence pathways that describe the role of mitochondria and ER on the development and function of lung epithelial responses, highlighting the cause and effect associations that reflect the disease pathogenesis and possible intervention strategies.

Multi-omics systems toxicology study of mouse lung assessing the effects of aerosols from two heat-not-burn tobacco products and cigarette smoke

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Multi-omics systems toxicology study, comprising five omics data modalities.

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Multi-Omics Factor Analysis and multi-modality functional network interpretation.

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Cigarettes smoke (CS) induced complex immunoregulatory interactions across molecular layers.

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Aerosols from two heat-not-burn tobacco products had less impact on lungs than CS.

Cigarette smoke (CS) causes adverse health effects and, for smoker who do not quit, modified risk tobacco products (MRTPs) can be an alternative to reduce the risk of developing smoking-related diseases. Standard toxicological endpoints can lack sensitivity, with systems toxicology approaches yielding broader insights into toxicological mechanisms. In a 6-month systems toxicology study on ApoE^−/− mice, we conducted an integrative multi-omics analysis to assess the effects of aerosols from the Carbon Heated Tobacco Product (CHTP) 1.2 and Tobacco Heating System (THS) 2.2—a potential and a candidate MRTP based on the heat-not-burn (HnB) principle—compared with CS at matched nicotine concentrations. Molecular exposure effects in the lungs were measured by mRNA/microRNA transcriptomics, proteomics, metabolomics, and lipidomics. Integrative data analysis included Multi-Omics Factor Analysis and multi-modality functional network interpretation. Across all five data modalities, CS exposure was associated with an increased inflammatory and oxidative stress response, and lipid/surfactant alterations. Upon HnB aerosol exposure these effects were much more limited or absent, with reversal of CS-induced effects upon cessation and switching to CHTP 1.2. Functional network analysis revealed CS-induced complex immunoregulatory interactions across the investigated molecular layers (e.g., itaconate, quinolinate, and miR-146) and highlighted the engagement of the heme–Hmox–bilirubin oxidative stress axis by CS. This work exemplifies how multi-omics approaches can be leveraged within systems toxicology studies and the generated multi-omics data set can facilitate the development of analysis methods and can yield further insights into the effects of toxicological exposures on the lung of mice.

Role of the ERO1-PDI interaction in oxidative protein folding and disease

Protein folding in the endoplasmic reticulum is an oxidative process that relies on protein disulfide isomerase (PDI) and endoplasmic reticulum oxidase 1 (ERO1). Over 30% of proteins require the chaperone PDI to promote disulfide bond formation. PDI oxidizes cysteines in nascent polypeptides to form disulfide bonds and can also reduce and isomerize disulfide bonds. ERO1 recycles reduced PDI family member PDIA1 using a FAD cofactor to transfer electrons to oxygen. ERO1 dysfunction critically affects several diseases states. Both ERO1 and PDIA1 are overexpressed in cancers and implicated in diabetes and neurodegenerative diseases. Cancer-associated ERO1 promotes cell migration and invasion. Furthermore, the ERO1-PDIA1 interaction is critical for epithelial-to-mesenchymal transition. Co-expression analysis of ERO1A gene expression in cancer patients demonstrated that ERO1A is significantly upregulated in lung adenocarcinoma (LUAD), glioblastoma and low-grade glioma (GBMLGG), pancreatic ductal adenocarcinoma (PAAD), and kidney renal papillary cell carcinoma (KIRP) cancers. ERO1Α knockdown gene signature correlates with knockdown of cancer signaling proteins including IGF1R, supporting the search for novel, selective ERO1 inhibitors for the treatment of cancer. In this review, we explore the functions of ERO1 and PDI to support inhibition of this interaction in cancer and other diseases.

Redox Regulation of Mitochondrial Fission Protein Drp1 by Protein Disulfide Isomerase Limits Endothelial Senescence

Mitochondrial dynamics are tightly controlled by fusion and fission, and their dysregulation and excess reactive oxygen species (ROS) contribute to endothelial cell (EC) dysfunction. How redox signals regulate coupling between mitochondrial dynamics and endothelial (dys)function remains unknown. Here, we identify protein disulfide isomerase A1 (PDIA1) as a thiol reductase for the mitochondrial fission protein Drp1. A biotin-labeled Cys-OH trapping probe and rescue experiments reveal that PDIA1 depletion in ECs induces sulfenylation of Drp1 at Cys⁶⁴⁴, promoting mitochondrial fragmentation and ROS elevation without inducing ER stress, which drives EC senescence. Mechanistically, PDIA1 associates with Drp1 to reduce its redox status and activity. Defective wound healing and angiogenesis in diabetic or PDIA1^+/- mice are restored by EC-targeted PDIA1 or the Cys oxidation-defective mutant Drp1. Thus, this study uncovers a molecular link between PDIA1 and Drp1 oxidoreduction, which maintains normal mitochondrial dynamics and limits endothelial senescence with potential translational implications for vascular diseases associated with diabetes or aging.

Oxidative Stress Mechanisms in the Pathogenesis of Environmental Lung Diseases

Globally, respiratory diseases are major cause of disability and mortality, and more alarmingly, it disproportionately affects developing countries, which is largely attributed to poor quality of air. Tobacco smoke and emissions from combustion of fossil fuel and biomass fuel are the major airborne pollutants affecting human lung health. Oxidative stress is the dominant driving force by which the airborne pollutants exert their toxicity in lungs and cause respiratory diseases. Most airborne pollutants are associated with intrinsic oxidative potential and, additionally, stimulate endogenous production of reactive oxygen species (ROS) and reactive nitrogen species (RNS). Elevated ROS and RNS in lungs modulate redox signals and cause irreversible damage to critical biomolecules (lipids, proteins and DNA) and initiate various pathogenic cellular process. This chapter provides an insight into oxidative stress-linked pathogenic cellular process such as lipid peroxidation, inflammation, cell death, mitochondrial dysfunction, endoplasmic reticulum stress, epigenetic changes, profibrotic signals and mucus hypersecretion, which drive the development and progression of lung diseases. Lungs are associated with robust enzymatic and non-enzymatic (GSH, ascorbic acid, uric acid, vitamin E) antioxidant defences. However, sustained production of free radicals due to continuous exposures to airborne pollutants overwhelms lung antioxidant defences and causes oxidative injury. Preclinical studies have demonstrated the critical roles and therapeutic potential of upregulating lung antioxidants for intervention of respiratory diseases; however, so far clinical benefits in antioxidant supplementation trials have been minimal and conflicting. Antioxidants alone may not be effective in treatment of respiratory diseases; however it could be a promising adjunctive therapy.

Pulmonary endoplasmic reticulum stress-scars, smoke, and suffocation

Protein misfolding within the endoplasmic reticulum (ER stress) can be a cause or consequence of pulmonary disease. Mutation of proteins restricted to the alveolar type II pneumocyte can lead to inherited forms of pulmonary fibrosis, but even sporadic cases of pulmonary fibrosis appear to be strongly associated with activation of the unfolded protein response and/or the integrated stress response. Inhalation of smoke can impair protein folding and may be an important cause of pulmonary ER stress. Similarly, tissue hypoxia can lead to impaired protein homeostasis (proteostasis). But the mechanisms linking smoke and hypoxia to ER stress are only partially understood. In this review, we will examine the role of ER stress in the pathogenesis of lung disease by focusing on fibrosis, smoke, and hypoxia.

Acrolein, a commonly found environmental toxin, causes oocyte mitochondrial dysfunction and negatively affects embryo development

Recent studies have revealed that acrolein, a commonly found toxin and a potent metabolite of cyclophosphamide (CTX), can cause deterioration of mouse oocyte quality through a mechanism involving the generation of reactive oxygen species (ROS). We extend these studies to evaluate the effects of acrolein, in varying concentrations, on the oocyte mitochondrial membrane and oocyte apoptosis and its effect on embryo development in vitro. Metaphase II mouse oocytes were exposed for 45 minutes to acrolein and CTX (10 & 25 µM) and mitochondrial dysfunction, a major source of ROS overproduction, was evaluated by the 5,5,6,6-tetrachloro-1,1,3,3-tetraethyl-β-benzimidazolylcarbocyanine iodide (JC-10) mitochondrial membrane potential assay. Treatment with acrolein led to mitochondrial membrane damage as well as induction of apoptosis compared to untreated control (p < 0.05). Similar results were obtained when oocytes were exposed to CTX (p < .05). Subsequently, the effect of acrolein exposure was evaluated by observing in vitro development of embryos after exposure. Acrolein treatment caused higher proportions of arrested and poor-quality embryos, evidenced by irregular cleavage, severe asymmetry of blastomeres, presence of large percentage of anuclear fragments, and dark granularity of the cytoplasm. Development at various durations in culture revealed that optimal embryo growth was significantly inhibited in a dose dependent manner, when compared to control (p < .05). A global model that links acrolein accumulation, generation of ROS, and mitochondrial dysfunction and their effect on oocyte and embryo quality is discussed further. Collectively, understanding the mechanism by which CTX and acrolein impact fertility is helpful in finding potential alternative or supplemental treatment options.

Combined expression of protein disulfide isomerase and endoplasmic reticulum oxidoreductin 1-α is a poor prognostic marker for non-small cell lung cancer

Protein disulfide isomerase (PDI) is one of the most abundant proteins in the endoplasmic reticulum (ER) and is known as a primary ER resident target of cigarette smoke-induced oxidation. PDI dysfunction triggers unfolded protein response and ER stress. Endoplasmic reticulum oxidoreductin 1-α (ERO1A) is a major regulator of PDI, and recent evidence implicates PDI and ERO1A as tumor prognostic factors. However, the associated role of PDI and ERO1A and their prognostic impact in non-small cell lung cancers (NSCLCs) remains unknown. The present study investigated the expression of PDI and ERO1A using immunohistochemistry and examined its association with smoking status and their prognostic impact in 198 NSCLCs. PDI and ERO1A expression were observed in 71.2 and 69.2% of NSCLCs, respectively, and their expressions were significantly associated with each other (P<0.001). Individual PDI (P=0.001) and ERO1A (P=0.005) expression were significantly associated with shorter overall survival (OS) in univariate analysis. PDI expression was significantly associated with never smoking (P=0.003). PDI expression (P<0.001) and the co-expression of PDI and ERO1A (P<0.001) were independent poor prognostic factors for OS in patients with NSCLC in multivariate analysis. Individual expression and co-expression of PDI and ERO1A may be used as novel prognostic indicators of NSCLC outcome.

Oxidative and endoplasmic reticulum stress in respiratory disease

Oxidative stress and endoplasmic reticulum (ER) stress are related states that can occur in cells as part of normal physiology but occur frequently in diseases involving inflammation. In this article, we review recent findings relating to the role of oxidative and ER stress in the pathophysiology of acute and chronic nonmalignant diseases of the lung, including infections, cystic fibrosis, idiopathic pulmonary fibrosis and asthma. We also explore the potential of drugs targeting oxidative and ER stress pathways to alleviate disease.

Cigarette smoke modifies and inactivates SPLUNC1, leading to airway dehydration

Chronic obstructive pulmonary disease (COPD) is a growing cause of morbidity and mortality worldwide. Cigarette smoke (CS) exposure, a major cause of COPD, dysregulates airway epithelial ion transport and diminishes airway surface liquid (ASL) volume. Short palate lung and nasal epithelial clone 1 (SPLUNC1) is secreted into the airway lumen where it maintains airway hydration via interactions with the epithelial Na+ channel (ENaC). Although ASL hydration is dysregulated in CS-exposed/COPD airways, effects of CS on SPLUNC1 have not been elucidated. We hypothesized that CS alters SPLUNC1 activity, therefore contributing to ASL dehydration. CS exposure caused irreversible SPLUNC1 aggregation and prevented SPLUNC1 from internalizing ENaC and maintaining ASL hydration. Proteomic analysis revealed αβ-unsaturated aldehyde modifications to SPLUNC1's cysteine residues. Removal of these cysteines prevented SPLUNC1 from regulating ENaC/ASL volume. In contrast, SPX-101, a peptide mimetic of natural SPLUNC1, that internalizes ENaC, but does not contain cysteines was unaffected by CS. SPX-101 increased ASL hydration and attenuated ENaC activity in airway cultures after CS exposure and prolonged survival in a chronic airway disease model. These findings suggest that the CS-induced defects in SPLUNC1 can be circumvented, thus making SPX-101 a novel candidate for the treatment of mucus dehydration in COPD. -Moore, P. J., Reidel, B., Ghosh, A., Sesma, J., Kesimer, M., Tarran, R. Cigarette smoke modifies and inactivates SPLUNC1, leading to airway dehydration.

Acrolein Disrupts Tight Junction Proteins and Causes Endoplasmic Reticulum Stress-Mediated Epithelial Cell Death Leading to Intestinal Barrier Dysfunction and Permeability

Increasing evidence suggests that environmental and dietary factors can affect intestinal epithelial integrity leading to gut permeability and bacterial translocation. Intestinal barrier dysfunction is a pathogenic process associated with many chronic disorders. Acrolein is an environmental and dietary pollutant and a lipid-derived endogenous metabolite. The impact of acrolein on the intestine has not been investigated before and is evaluated in this study, both in vitro and in vivo. Our data demonstrate that oral acrolein exposure in mice caused damage to the intestinal epithelial barrier, resulting in increased permeability and subsequently translocation of bacterial endotoxin-lipopolysaccharide into the blood. Similar results were seen in vitro using established Caco-2 cell monolayers wherein acrolein decreased barrier function and increased permeability. Acrolein also caused the down-regulation and/or redistribution of three representative tight junction proteins (ie, zonula occludens-1, Occludin, Claudin-1) that critically regulate epithelial paracellular permeability. In addition, acrolein induced endoplasmic reticulum stress-mediated death of epithelial cells, which is an important mechanism contributing to intestinal barrier damage/dysfunction, and gut permeability. Overall, we demonstrate that exposure to acrolein affects the intestinal epithelium by decrease/redistribution of tight junction proteins and endoplasmic reticulum stress-mediated epithelial cell death, thereby resulting in loss of barrier integrity and function. Our findings highlight the adverse consequences of environmental and dietary pollutants on intestinal barrier integrity/function with relevance to gut permeability and the development of disease.

Cyclophosphamide and acrolein induced oxidative stress leading to deterioration of metaphase II mouse oocyte quality

Cyclophosphamide (CTX) is a chemotherapeutic agent widely used to treat ovarian, breast, and hematological cancers as well as autoimmune disorders. Such chemotherapy is associated with reproductive failure and premature ovarian insufficiency. The mechanism by which CTX and/or its main metabolite, acrolein, affect female fertility remains unclear, but it is thought to be caused by an overproduction of reactive oxygen species (ROS). Here, we investigated the effect of CTX on metaphase II mouse oocytes obtained from treated animals (120mg/kg, 24h of single treatment), and oocytes directly exposed to increasing concentrations of CTX and acrolein (n=480; 0, 5, 10, 25, 50, and 100μM) with and without cumulus cells (CCs) for 45min which correlates to the time of maximum peak plasma concentrations after administration. Oocytes were fixed and subjected to indirect immunofluorescence and were scored based on microtubule spindle structure (MT) and chromosomal alignment (CH). Generation of ROS was evaluated using the Cellular Reactive Oxygen Species Detection Assay Kit. Deterioration of oocyte quality was noted when oocytes were obtained from CTX treated mice along with CTX and acrolein treated oocytes in a dose-dependent manner as shown by an increase in poor scores. Acrolein had an impact at a significantly lower level as compared to CTX, plateau at 10μM versus 50μM, respectively. These variation is are associated with the higher amount of ROS generated with acrolein exposure as compared to CTX (p<0.05). Utilization of antioxidant therapy and acrolein scavengers may mitigate the damaging effects of these compounds and help women undergoing such treatment.

Disruption of the structural and functional features of surfactant protein A by acrolein in cigarette smoke

The extent to which defective innate immune responses contribute to chronic obstructive pulmonary disease (COPD) is not fully understood. Pulmonary surfactant protein A (SP-A) plays an important role in regulating innate immunity in the lungs. In this study, we hypothesised that cigarette smoke (CS) and its component acrolein might influence pulmonary innate immunity by affecting the function of SP-A. Indeed, acrolein-modified SP-A was detected in the lungs of mice exposed to CS for 1 week. To further confirm this finding, recombinant human SP-A (hSP-A) was incubated with CS extract (CSE) or acrolein and then analysed by western blotting and nanoscale liquid chromatography-matrix-assisted laser desorption/ionisation time-of-flight tandem mass spectrometry. These analyses revealed that CSE and acrolein induced hSP-A oligomerisation and that acrolein induced the modification of six residues in hSP-A: His39, His116, Cys155, Lys180, Lys221, and Cys224. These modifications had significant effects on the innate immune functions of hSP-A. CSE- or acrolein-induced modification of hSP-A significantly decreased hSP-A's ability to inhibit bacterial growth and to enhance macrophage phagocytosis. These findings suggest that CS-induced structural and functional defects in SP-A contribute to the dysfunctional innate immune responses observed in the lung during cigarette smoking.

Cigarette smoke extract induced exosome release is mediated by depletion of exofacial thiols and can be inhibited by thiol-antioxidants

INTRODUCTION

Airway epithelial cells have been described to release extracellular vesicles (EVs) with pathological properties when exposed to cigarette smoke extract (CSE). As CSE causes oxidative stress, we investigated whether its oxidative components are responsible for inducing EV release and whether this could be prevented using the thiol antioxidants N-acetyl-l-cysteine (NAC) or glutathione (GSH).

METHODS

BEAS-2B cells were exposed for 24h to CSE, H₂O₂, acrolein, 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB), bacitracin, rutin or the anti-protein disulfide isomerase (PDI) antibody clone RL90; with or without NAC or GSH. EVs in media were measured using CD63⁺CD81⁺ bead-coupled flow cytometry or tunable resistive pulse sensing (TRPS). For characterization by Western Blotting, cryo-transmission electron microscopy and TRPS, EVs were isolated using ultracentrifugation. Glutathione disulfide and GSH in cells were assessed by a GSH reductase cycling assay, and exofacial thiols using Flow cytometry.

RESULTS

CSE augmented the release of the EV subtype exosomes, which could be prevented by scavenging thiol-reactive components using NAC or GSH. Among thiol-reactive CSE components, H₂O₂ had no effect on exosome release, whereas acrolein imitated the NAC-reversible exosome induction. The exosome induction by CSE and acrolein was paralleled by depletion of cell surface thiols. Membrane impermeable thiol blocking agents, but not specific inhibitors of the exofacially located thiol-dependent enzyme PDI, stimulated exosome release.

SUMMARY/CONCLUSION

Thiol-reactive compounds like acrolein account for CSE-induced exosome release by reacting with cell surface thiols. As acrolein is produced endogenously during inflammation, it may influence exosome release not only in smokers, but also in ex-smokers with chronic obstructive pulmonary disease. NAC and GSH prevent acrolein- and CSE-induced exosome release, which may contribute to the clinical benefits of NAC treatment.

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.

Genetic susceptibility for air pollution-induced airway inflammation in the SALIA study

BACKGROUND

Long-term air pollution exposure has been associated with chronic inflammation providing a link to the development of chronic health effects. Furthermore, there is evidence that pathways activated by endoplasmatic reticulum (ER) stress induce airway inflammation and thereby play an important role in the pathogenesis of inflammatory diseases.

OBJECTIVE

We investigated the role of genetic variation of the ER stress pathway on air pollution-induced inflammation.

METHODS

We used the follow-up examination of the German SALIA study (N=402, age 68-79 years). Biomarkers of inflammation were determined in induced sputum. We calculated biomarker-specific weighted genetic risk scores (GRS) out of eight ER stress related single nucleotide polymorphisms and tested their interaction with PM_2.5, PM_2.5 absorbance, PM₁₀ and NO₂ exposure on inflammation by adjusted linear regression.

RESULTS

Genetic variation of the ER stress pathway was associated with higher concentration of inflammation-related biomarkers (levels of leukotriene (LT)B₄, tumor necrosis factor-α (TNF-α), the total number of cells and nitric oxide (NO) derivatives). Furthermore, we observed a significant interaction between air pollution exposure and the ER stress risk score on the concentration of inflammation-related biomarkers. The strongest gene-environment interaction was found for LTB₄ (PM_2.5: p-value=0.002, PM_2.5 absorbance: p-value=0.002, PM₁₀: p-value=0.001 and NO₂: p-value=0.004). Women with a high GRS had a 38% (95%-CI: 16-64%) higher LTB₄ level for an increase of 2.06μg/m³(IQR) in PM_2.5 (no associations in women with a low GRS).

CONCLUSION

These results indicate that genetic variation in the ER stress pathway might play a role in air pollution induced inflammation in the lung.

Protein disulfide isomerases: Redox connections in and out of the endoplasmic reticulum

Protein disulfide isomerases are thiol oxidoreductase chaperones from thioredoxin superfamily. As redox folding catalysts from the endoplasmic reticulum (ER), their roles in ER-related redox homeostasis and signaling are well-studied. PDIA1 exerts thiol oxidation/reduction and isomerization, plus chaperone effects. Also, substantial evidence indicates that PDIs regulate thiol-disulfide switches in other cell locations such as cell surface and possibly cytosol. Subcellular PDI translocation routes remain unclear and seem Golgi-independent. The list of signaling and structural proteins reportedly regulated by PDIs keeps growing, via thiol switches involving oxidation, reduction and isomerization, S-(de)nytrosylation, (de)glutathyonylation and protein oligomerization. PDIA1 is required for agonist-triggered Nox NADPH oxidase activation and cell migration in vascular cells and macrophages, while PDIA1-dependent cytoskeletal regulation appears a converging pathway. Extracellularly, PDIs crucially regulate thiol redox signaling of thrombosis/platelet activation, e.g., integrins, and PDIA1 supports expansive caliber remodeling during injury repair via matrix/cytoskeletal organization. Some proteins display regulatory PDI-like motifs. PDI effects are orchestrated by expression levels or post-translational modifications. PDI is redox-sensitive, although probably not a mass-effect redox sensor due to kinetic constraints. Rather, the "all-in-one" organization of its peculiar redox/chaperone properties likely provide PDIs with precision and versatility in redox signaling, making them promising therapeutic targets.