The exacerbating roles of CCAAT/enhancer-binding protein homologous protein (CHOP) in the development of bleomycin-induced pulmonary fibrosis and the preventive effects of tauroursodeoxycholic acid (TUDCA) against pulmonary fibrosis in mice

Understanding the impact of ER stress on lung physiology

Human lungs consist of a distinctive array of cell types, which are subjected to persistent challenges from chemical, mechanical, biological, immunological, and xenobiotic stress throughout life. The disruption of endoplasmic reticulum (ER) homeostatic function, triggered by various factors, can induce ER stress. To overcome the elevated ER stress, an adaptive mechanism known as the unfolded protein response (UPR) is activated in cells. However, persistent ER stress and maladaptive UPR can lead to defects in proteostasis at the cellular level and are typical features of the lung aging. The aging lung and associated lung diseases exhibit signs of ER stress-related disruption in cellular homeostasis. Dysfunction resulting from ER stress and maladaptive UPR can compromise various cellular and molecular processes associated with aging. Hence, comprehending the mechanisms of ER stress and UPR components implicated in aging and associated lung diseases could enable to develop appropriate therapeutic strategies for the vulnerable population.

Dissecting causal relationships between immune cells, plasma metabolites, and COPD: a mediating Mendelian randomization study

Objective

This study employed Mendelian Randomization (MR) to investigate the causal relationships among immune cells, COPD, and potential metabolic mediators.

Methods

Utilizing summary data from genome-wide association studies, we analyzed 731 immune cell phenotypes, 1,400 plasma metabolites, and COPD. Bidirectional MR analysis was conducted to explore the causal links between immune cells and COPD, complemented by two-step mediation analysis and multivariable MR to identify potential mediating metabolites.

Results

Causal relationships were identified between 41 immune cell phenotypes and COPD, with 6 exhibiting reverse causality. Additionally, 21 metabolites were causally related to COPD. Through two-step MR and multivariable MR analyses, 8 cell phenotypes were found to have causal relationships with COPD mediated by 8 plasma metabolites (including one unidentified), with 1-methylnicotinamide levels showing the highest mediation proportion at 26.4%.

Conclusion

We have identified causal relationships between 8 immune cell phenotypes and COPD, mediated by 8 metabolites. These findings contribute to the screening of individuals at high risk for COPD and offer insights into early prevention and the precocious diagnosis of Pre-COPD.

Diagnosis and management in Rubinstein-Taybi syndrome: first international consensus statement

Rubinstein-Taybi syndrome (RTS) is an archetypical genetic syndrome that is characterised by intellectual disability, well-defined facial features, distal limb anomalies and atypical growth, among numerous other signs and symptoms. It is caused by variants in either of two genes (CREBBP, EP300) which encode for the proteins CBP and p300, which both have a function in transcription regulation and histone acetylation. As a group of international experts and national support groups dedicated to the syndrome, we realised that marked heterogeneity currently exists in clinical and molecular diagnostic approaches and care practices in various parts of the world. Here, we outline a series of recommendations that document the consensus of a group of international experts on clinical diagnostic criteria for types of RTS (RTS1: CREBBP; RTS2: EP300), molecular investigations, long-term management of various particular physical and behavioural issues and care planning. The recommendations as presented here will need to be evaluated for improvements to allow for continued optimisation of diagnostics and care.

Effects of Natural Products through Inhibiting Endoplasmic Reticulum Stress on Attenuation of Idiopathic Pulmonary Fibrosis

With ever-increasing intensive studies of idiopathic pulmonary fibrosis (IPF), significant progresses have been made. Endoplasmic reticulum stress (ERS)/unfolded protein reaction (UPR) is associated with the development and progression of IPF, and targeting ERS/UPR may be beneficial in the treatment of IPF. Natural product is a tremendous source of new drug discovery, and accumulating studies have reported that many natural products show potential therapeutic effects for IPF via modulating one or more branches of the ERS signaling pathway. Therefore, this review focuses on critical roles of ERS in IPF development, and summarizes herbal preparations and bioactive compounds which protect against IPF through regulating ERS.

Fasudil inhibits the expression of C/EBP homologous protein to protect against liver injury in acetaminophen-overdosed mice

Acetaminophen (APAP) overdoses can cause severe liver injury. In this study, the protective effect of fasudil against APAP-induced liver injury was investigated. APAP (400 mg/kg) was administered to male C57BL/6J mice to induce liver injury, and fasudil (20 or 40 mg/kg) was injected 30 min before APAP administration. Fasudil markedly suppressed APAP-induced elevation in serum transaminase activity and hepatic necrosis and significantly reduced an increase in nitrotyrosine and DNA fragmentation. However, fasudil did not affect cytochrome P450 2E1 expression, N-acetyl-p-benzoquinone imine production or c-jun N-terminal kinase activation. In contrast, fasudil significantly inhibited an APAP-induced increase in expression of the transcription factor C/EBP homologous protein (CHOP) in the liver, accompanied by transcriptional suppression of ER stress-related molecules such as Ero1α, Atf4 and Grp78. These findings indicate that suppression of CHOP expression by fasudil exhibits a remarkable protective effect against APAP liver injury by regulating ER stress. We suggest that fasudil is a promising therapeutic candidate for treating APAP-induced liver injury.

Can endoplasmic reticulum stress observed in the PTZ-kindling model seizures be prevented with TUDCA and 4-PBA?

Epilepsy is a chronic neurological disease with recurrent seizures. Increasing evidence suggests that endoplasmic reticulum (ER) stress may play a role in the pathogenesis of epilepsy. We aimed to investigate the effects of Tauroursodeoxycholic acid (TUDCA) and 4-phenyl-butyric acid (4-PBA), which are known to suppress ER stress, on developed seizures in terms of markers of ER stress, oxidative stress, and apoptosis. The pentylenetetrazole (PTZ) kindling model was induced in Wistar albino rats (n = 48) by administering 35 mg/kg PTZ intraperitoneally (I.P.) every other day for 1 month. TUDCA and 4-PBA were administered via I.P. at a dose of 500 mg/kg dose. ER stress, apoptosis, and oxidative stress were determined in the hippocampus tissues of animals in all groups. Immunohistochemistry, qRT-PCR, ELISA, and Western Blot analyzes were performed to determine the efficacy of treatments. Expressions of ATF4, ATF6, p-JNK1/2, Cleaved-Kaspase3, and Caspase12 significantly increased in PTZ-kindled seizures compared to the control group. Increased NOX2 and MDA activity in the seizures were measured. In addition, stereology analyzes showed an increased neuronal loss in the PTZ-kindled group. qRT-PCR examination showed relative mRNA levels of CHOP. Accordingly, TUDCA and 4-PBA treatment suppressed the expressions of ATF4, ATF6, Cleaved-Caspase3, Kaspase12, NOX2, MDA, and CHOP in TUDCA + PTZ and 4-PBA + PTZ groups. ER stress-induced oxidative stress and apoptosis by reducing neuronal loss and degeneration were also preserved in these groups. Our data show molecularly that TUDCA and 4-PBA treatment can suppress the ER stress process in epileptic seizures.

DNA damage-inducible transcript 3 deficiency promotes bone resorption in murine periodontitis models

BACKGROUND AND OBJECTIVE

Periodontitis is a multifactorial inflammatory disease that leads to the destruction of supporting structures of the teeth. DNA damage-inducible transcript 3 (DDIT3) plays crucial roles in cell survival and differentiation. DDIT3 regulates bone mass and osteoclastogenesis in femur. However, the role of DDIT3 in periodontitis has not been elucidated. This research aimed to explore the role and mechanisms of DDIT3 in periodontitis.

METHODS

DDIT3 gene knockout (KO) mice were generated using a CRISPR/Cas9 system. Experimental periodontitis models were established to explore the role of DDIT3 in periodontitis. The expression of DDIT3 in periodontal tissues was detected by quantitative real-time polymerase chain reaction (qRT-PCR) and immunohistochemistry (IHC). The alveolar bone phenotypes were observed by micro-CT and stereomicroscopy. The inflammation levels and osteoclast activity were examined by histological staining, immunostaining, and qRT-PCR. Bone marrow-derived macrophages (BMMs) were isolated to confirm the effects of DDIT3 on osteoclast formation and function in vitro.

RESULTS

The increased expression of DDIT3 in murine inflamed periodontal tissues was detected. DDIT3 knockout aggravated alveolar bone loss and enhanced expression levels of inflammatory cytokines in murine periodontitis models. Increased osteoclast formation and higher expression levels of osteoclast-specific markers were observed in the inflamed periodontal tissues of KO mice. In vitro, DDIT3 deficiency promoted the formation of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated osteoclasts and the bone resorption activity of mature osteoclasts.

CONCLUSIONS

Our results demonstrate that DDIT3 deletion aggravated alveolar bone loss in experimental periodontitis through enhanced inflammatory reactions and osteoclastogenesis. The anti-inflammation and the inhibition of bone loss by DDIT3 in murine periodontitis provides a potential novel therapeutic strategy for periodontitis.

Molecular Mechanisms Behind the Role of Plasmacytoid Dendritic Cells in Systemic Sclerosis

Systemic sclerosis (SSc) is a debilitating autoimmune disease that affects multiple systems. It is characterized by immunological deregulation, functional and structural abnormalities of small blood vessels, and fibrosis of the skin, and, in some cases, internal organs. Fibrosis has a devastating impact on a patient's life and lung fibrosis is associated with high morbimortality. Several immune populations contribute to the progression of SSc, and plasmacytoid dendritic cells (pDCs) have been identified as crucial mediators of fibrosis. Research on murine models of lung and skin fibrosis has shown that pDCs are essential in the development of fibrosis, and that removing pDCs improves fibrosis. pDCs are a subset of dendritic cells (DCs) that are specialized in anti-viral responses and are also involved in autoimmune diseases, such as SSc, systemic lupus erythematosus (SLE) and psoriasis, mostly due to their capacity to produce type I interferon (IFN). A type I IFN signature and high levels of CXCL4, both derived from pDCs, have been associated with poor prognosis in patients with SSc and are correlated with fibrosis. This review will examine the recent research on the molecular mechanisms through which pDCs impact SSc.

CCAAT/Enhancer-Binding Proteins in Fibrosis: Complex Roles Beyond Conventional Understanding

CCAAT/enhancer-binding proteins (C/EBPs) are a family of at least six identified transcription factors that contain a highly conserved basic leucine zipper domain and interact selectively with duplex DNA to regulate target gene expression. C/EBPs play important roles in various physiological processes, and their abnormal function can lead to various diseases. Recently, accumulating evidence has demonstrated that aberrant C/EBP expression or activity is closely associated with the onset and progression of fibrosis in several organs and tissues. During fibrosis, various C/EBPs can exert distinct functions in the same organ, while the same C/EBP can exert distinct functions in different organs. Modulating C/EBP expression or activity could regulate various molecular processes to alleviate fibrosis in multiple organs; therefore, novel C/EBPs-based therapeutic methods for treating fibrosis have attracted considerable attention. In this review, we will explore the features of C/EBPs and their critical functions in fibrosis in order to highlight new avenues for the development of novel therapies targeting C/EBPs.

Alveolar Epithelial Type 2 Cell Dysfunction in Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive and irreversible pulmonary interstitial disease that seriously affects the patient's quality of life and lifespan. The pathogenesis of IPF has not been clarified, and its treatment is limited to pirfenidone and nintedanib, which only delays the decline of lung function. Alveolar epithelial type 2 (AT2) cells are indispensable in the regeneration and lung surfactant secretion of alveolar epithelial cells. Studies have shown that AT2 cell dysfunction initiates the occurrence and progression of IPF. This review expounds on the AT2 cell dysfunction in IPF, involving senescence, apoptosis, endoplasmic reticulum stress, mitochondrial damage, metabolic reprogramming, and the transitional state of AT2 cells. This article also briefly summarizes potential treatments targeting AT2 cell dysfunction.

ROS and Endoplasmic Reticulum Stress in Pulmonary Disease

Pulmonary diseases are main causes of morbidity and mortality worldwide. Current studies show that though specific pulmonary diseases and correlative lung-metabolic deviance own unique pathophysiology and clinical manifestations, they always tend to exhibit common characteristics including reactive oxygen species (ROS) signaling and disruptions of proteostasis bringing about accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER). ER is generated by the unfolded protein response. When the adaptive unfolded protein response (UPR) fails to preserve ER homeostasis, a maladaptive or terminal UPR is engaged, leading to the disruption of ER integrity and to apoptosis, which is called ER stress. The ER stress mainly includes the accumulation of misfolded and unfolded proteins in lumen and the disorder of Ca²⁺ balance. ROS mediates several critical aspects of the ER stress response. We summarize the latest advances in of the UPR and ER stress in the pathogenesis of pulmonary disease and discuss potential therapeutic strategies aimed at restoring ER proteostasis in pulmonary disease.

Tauroursodeoxycholic Acid Decreases Keloid Formation by Reducing Endoplasmic Reticulum Stress as Implicated in the Pathogenesis of Keloid

Keloids are a common form of pathologic wound healing and are characterized by an excessive production of extracellular matrix. This study examined the major contributing mechanism of human keloid pathogenesis using transcriptomic analysis. We identified the upregulation of mitochondrial oxidative stress response, protein processing in the endoplasmic reticulum, and TGF-β signaling in human keloid tissue samples compared to controls, based on ingenuity pathway and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses. Electron microscopic examinations revealed an increased number of dysmorphic mitochondria and expanded endoplasmic reticulum (ER) in human keloid tissue samples than that in controls. Western blot analysis performed using human tissues suggested noticeably higher ER stress signaling in keloids than in normal tissues. Treatment with tauroursodeoxycholic acid (TUDCA), an ER stress inhibitor, significantly decreased scar formation in rabbit models, compared to normal saline and steroid injections. In summary, our findings demonstrate the contributions of mitochondrial dysfunction and dysregulated ER stress signaling in human keloid formation and the potential of TUDCA in the treatment of keloids.

The role of C/EBP homologous protein (CHOP) in regulating macrophage polarization in RAW264.7 cells

Schistosomiasis is a zoonotic parasitic disease that is endemic in Asia. Macrophages are mainly involved in the inflammatory response of late schistosoma infection. Our previous study found that C/EBP homologous protein (CHOP) expression is significantly increased, and M2 macrophages are activated in schistosome-induced liver fibrosis mice. However, the role of CHOP in the regulation of macrophage polarization remains to be further studied. Western blotting or quantitative PCR revealed that IL-4 increased the expression of arginase-1, macrophage mannose receptor 1, phosphorylation signal transducer and activator of transcription 6 (p-STAT6), Krüppel-like factor 4 (KLF4), CHOP, and IL-13 receptor alpha (IL-13Rα) and induced M2 polarization in RAW264.7 as measured by flow cytometry. Inhibiting STAT6 phosphorylation (AS1517499) reduced the IL-4-induced expression of KLF4, CHOP, and IL-13Rα and also the number of M2 macrophages. The overexpression of CHOP stimulated M2 polarization, but AS1517499 inhibited this effect. CHOP increased the protein expression of KLF4 but did not change the expression of p-STAT6. Soluble egg antigen (SEA) could promote the IL-4-induced protein expression of p-STAT6, CHOP, and KLF4. Overall, the findings show that SEA can promote the activation of M2 macrophages by causing increased CHOP-induced KLF4 levels and activation of STAT6 phosphorylation.

Oxidative Stress and Endoplasmic Reticulum Stress in Rare Respiratory Diseases

Several studies have shown that some rare respiratory diseases, such as alpha-1 antitrypsin deficiency (AATD), idiopathic pulmonary fibrosis (IPF), cystic fibrosis (CF), and primary ciliary dyskinesia (PCD) present oxidative stress (OS) and endoplasmic reticulum (ER) stress. Their involvement in these pathologies and the use of antioxidants as therapeutic agents to minimize the effects of OS are discussed in this review.

Unfolded Protein Response and Crohn’s Diseases: A Molecular Mechanism of Wound Healing in the Gut

Endoplasmic reticulum (ER) stress triggers a series of signaling and transcriptional events termed the unfolded protein response (UPR). Severe ER stress is associated with the development of fibrosis in different organs, including lung, liver, kidney, heart, and intestine. ER stress is an essential response of epithelial and immune cells in the pathogenesis of Inflammatory Bowel Disease (IBD), including Crohn’s disease (CD). Intestinal epithelial cells are susceptible to ER stress-mediated damage due to secretion of a large amount of proteins that are involved in mucosal defense. In other cells, ER stress is linked to myofibroblast activation, extracellular matrix production, macrophage polarization, and immune cell differentiation. This review focuses on the role of the UPR in the pathogenesis in IBD from an immunologic perspective. The roles of macrophage and mesenchymal cells in the UPR from in vitro and in vivo animal models are discussed. The links between ER stress and other signaling pathways, such as senescence and autophagy, are introduced. Recent advances in the understanding of the epigenetic regulation of the UPR signaling are also updated here. The future directions of development of the UPR research and therapeutic strategies to manipulate ER stress levels are also reviewed.

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.

The ER Stress/UPR Axis in Chronic Obstructive Pulmonary Disease and Idiopathic Pulmonary Fibrosis

Cellular protein homeostasis in the lungs is constantly disrupted by recurrent exposure to various external and internal stressors, which may cause considerable protein secretion pressure on the endoplasmic reticulum (ER), resulting in the survival and differentiation of these cell types to meet the increased functional demands. Cells are able to induce a highly conserved adaptive mechanism, known as the unfolded protein response (UPR), to manage such stresses. UPR dysregulation and ER stress are involved in numerous human illnesses, such as metabolic syndrome, fibrotic diseases, and neurodegeneration, and cancer. Therefore, effective and specific compounds targeting the UPR pathway are being considered as potential therapies. This review focuses on the impact of both external and internal stressors on the ER in idiopathic pulmonary fibrosis (IPF) and chronic obstructive pulmonary disease (COPD) and discusses the role of the UPR signaling pathway activation in the control of cellular damage and specifically highlights the potential involvement of non-coding RNAs in COPD. Summaries of pathogenic mechanisms associated with the ER stress/UPR axis contributing to IPF and COPD, and promising pharmacological intervention strategies, are also presented.

Toxicological Property of Acetaminophen: The Dark Side of a Safe Antipyretic/Analgesic Drug?

Acetaminophen (paracetamol, N-acetyl-p-aminophenol; APAP) is the most popular analgesic/antipyretic agent in the world. APAP has been regarded as a safer drug compared with non-steroidal anti-inflammatory drugs (NSAIDs) particularly in terms of lower risks of renal dysfunction, gastrointestinal injury, and asthma/bronchospasm induction, even in high-risk patients such as the elderly, children, and pregnant women. On the other hand, the recent increasing use of APAP has raised concerns about its toxicity. In this article, we review recent pharmacological and toxicological findings about APAP from basic, clinical, and epidemiological studies, including spontaneous drug adverse events reporting system, especially focusing on drug-induced asthma and pre-and post-natal closure of ductus arteriosus. Hepatotoxicity is the greatest fault of APAP and the most frequent cause of drug-induced acute liver failure in Western countries. However, its precise mechanism remains unclear and no effective cure beyond N-acetylcysteine has been developed. Recent animal and cellular studies have demonstrated that some cellular events, such as c-jun N-terminal kinase (JNK) pathway activation, endoplasmic reticulum (ER) stress, and mitochondrial oxidative stress may play important roles in the development of hepatitis. Herein, the molecular mechanisms of APAP hepatotoxicity are summarized. We also discuss the not-so-familiar "dark side" of APAP as an otherwise safe analgesic/antipyretic drug.

The Late-Stage Protective Effect of Mito-TEMPO against Acetaminophen-Induced Hepatotoxicity in Mouse and Three-Dimensional Cell Culture Models

An overdose of acetaminophen (APAP), the most common cause of acute liver injury, induces oxidative stress that subsequently causes mitochondrial impairment and hepatic necroptosis. N-acetyl-L-cysteine (NAC), the only recognized drug against APAP hepatotoxicity, is less effective the later it is administered. This study evaluated the protective effect of mitochondria-specific Mito-TEMPO (Mito-T) on APAP-induced acute liver injury in C57BL/6J male mice, and a three dimensional (3D)-cell culture model containing the human hepatoblastoma cell line HepG2. The administration of Mito-T (20 mg/kg, i.p.) 1 h after APAP (400 mg/kg, i.p.) injection markedly attenuated the APAP-induced elevated serum transaminase activity and hepatic necrosis. However, Mito-T treatment did not affect key factors in the development of APAP liver injury including the activation of c-jun N-terminal kinases (JNK), and expression of the transcription factor C/EBP homologous protein (CHOP) in the liver. However, Mito-T significantly reduced the APAP-induced increase in the hepatic oxidative stress marker, nitrotyrosine, and DNA fragmentation. Mito-T markedly attenuated cytotoxicity induced by APAP in the HepG2 3D-cell culture model. Moreover, liver regeneration after APAP hepatotoxicity was not affected by Mito-T, demonstrated by no changes in proliferating cell nuclear antigen formation. Therefore, Mito-T was hepatoprotective at the late-stage of APAP overdose in mice.

Attenuation of intermittent hypoxia-induced apoptosis and fibrosis in pulmonary tissues via suppression of ER stress activation

Background

Obstructive sleep apnea (OSA) is associated with pulmonary fibrosis and endothelial apoptosis in pulmonary tissues. Chronic intermittent hypoxia (IH) is considered to be the primary player in OSA, but the mechanisms underlying its effect on pulmonary tissues are unknown. Endoplasmic reticulum (ER) stress induced by IH treatment plays an important role in accelerating the process of fibrosis and induction of apoptosis.

Methods

Mice were placed in IH chambers for 4 weeks with an oscillating oxygen (O₂) concentration between 5 and 21%, cycling every 90s for 8 h daily. Mice were randomly divided into four groups: control group (normal oxygen), tauroursodeoxycholic acid (TUDCA) group (normal oxygen intraperitoneally injected with TUDCA), IH group and IH + TUDCA group. After 4 weeks, the proteins in three branch signaling pathways of ER stress, including protein kinase RNA (PKR)-like/Pancreatic ER kinase (PERK), activating transcription factor 6 (ATF-6) and inositol-requiring enzyme 1 (IRE-1), were evaluated. The cleaved caspase-3, caspase-12 and TUNNEL staining was assessed. Furthermore, the expression of transforming growth factor-β1 (TGF-β1) and thrombospondin-1(TSP-1), two extracellular matrix proteins that play critical role in fibrosis, were examined. Finally, Masson’s trichrome staining was performed to detect the expression of collagen.

Results

After 4 weeks of IH treatment, the expressions of two ER stress markers, glucose regulated protein-78 (Grp78) and transcription factor C/EBP homologous protein (CHOP) were increased which was prevented by administration of the ER stress attenuator, TUDCA. The expressions of PERK, but not those of ATF-6 and IRE-1, were increased. The effects of IH were accompanied by an increased number of apoptotic cells and increased expressions of cleaved caspase-3 and caspase-12 in pulmonary tissues. In addition, histological examination suggested the presence of fibrosis after chronic IH treatment, indicated by increased expression of collagen, which was associated with the up-regulation of TGF-β1 and TSP-1 that are known to promote fibrosis. Similarly, TUDCA could reduce the extent of fibrotic area and the expression levels of these proteins.

Conclusions

It reveals the roles of ER stress, especially the PERK pathway, in IH induced apoptosis and fibrosis in pulmonary tissues that might underlie the pulmonary complications observed in OSA.

Tauroursodeoxycholate protects from glycochenodeoxycholate-induced gene expression changes in perfused rat liver

Tauroursodeoxycholate (TUDC) is well known to protect against glycochenodeoxycholate (GCDC)-induced apoptosis in rat hepatocytes. In the present study, we analyzed whether TUDC also exerts protective effects by modulating GCDC-induced gene expression changes. For this, gene array-based transcriptome analysis and quantitative polymerase chain reaction (qPCR) were performed on RNA isolated from rat livers perfused with GCDC, TUDC or a combination of both (each 20 μm for 2 h). GCDC led to a significant increase of lactate dehydrogenase (LDH) into the effluent perfusate, which was prevented by TUDC. GCDC, TUDC and co-perfusion induced distinct gene expression changes. While GCDC upregulated the expression of several pro-inflammatory genes, co-perfusion with TUDC increased the expression of pro-proliferative and anti-apoptotic p53 target genes. In line with this, levels of serine20-phosphorylated p53 and of its target gene p21 were elevated by GCDC in a TUDC-sensitive way. GCDC upregulated the oxidative stress surrogate marker 8OH(d)G and the pro-apoptotic microRNAs miR-15b/16 and these effects were prevented by TUDC. The upregulation of miR-15b and miR-16 in GCDC-perfused livers was accompanied by a downregulation of several potential miR-15b and miR-16 target genes. The present study identified changes in the transcriptome of the rat liver which suggest, that TUDC is hepatoprotective by counteracting GCDC-induced gene expression changes.

C/EBP Homologous Protein (CHOP) Activates Macrophages and Promotes Liver Fibrosis in Schistosoma japonicum-Infected Mice

CCAAT/enhancer-binding homologous protein (CHOP), a transcriptional regulator induced by endoplasmic reticulum stress (ER stress) is a pivotal factor in the ER stress-mediated apoptosis pathway. Previous studies have shown that CHOP is involved in the formation of fibrosis in a variety of tissues and is associated with alternative macrophage activation. The role of CHOP in the pathologic effects of liver fibrosis in schistosomiasis has not been reported, and underlying mechanisms remain unclear. This study is aimed at understanding the effect of CHOP on liver fibrosis induced by Schistosoma japonicum (S. japonicum) in vivo and clarifying its mechanism. C57BL/6 mice were infected with cercariae of S. japonicum through the abdominal skin. The liver fibrosis was examined. The level of IL-13 was observed. The expressions of CHOP, Krüppel-like factor 4 (KLF4), signal transducer and activator of transcription 6 (STAT6), phosphorylation STAT6, interleukin-13 receptor alpha 1 (IL-13Rα1), and interleukin-4 receptor alpha (IL-4Rα) were analysed. The eosinophilic granuloma and collagen deposition were found around the eggs in mice infected for 6 and 10 weeks. IL-13 in plasma and IL-13Rα1 and IL-4Rα in liver tissue were significantly increased. The phosphorylated STAT6 was enhanced while Krüppel-like factor 4 (KLF4) was decreased in liver tissue. The expression of CHOP and colocalization of CHOP and CD206 were increased. Overall, these results suggest that CHOP plays a critical role in hepatic fibrosis induced by S. japonicum, likely through promoting alternative activation of macrophages.

Regulation and role of the ER stress transcription factor CHOP in alveolar epithelial type-II cells

Abstract

Idiopathic pulmonary fibrosis (IPF) is a fatal disease characterized by type-II alveolar epithelial cell (AECII) injury and fibroblast hyperproliferation. Severe AECII endoplasmic reticulum (ER) stress is thought to underlie IPF, but is yet incompletely understood. We studied the regulation of C/EBP homologous protein (CHOP), a proapoptotic ER-stress-related transcription factor (TF) in AECII-like cells. Interestingly, single or combined overexpression of the active ER stress transducers activating transcription factor-4 (Atf4) and activating transcription factor-6 (p50Atf6) or spliced x-box-binding protein-1 (sXbp1) in MLE12 cells did not result in a substantial Chop induction, as compared to the ER stress inducer thapsigargin. Employing reporter gene assays of distinct CHOP promoter fragments, we could identify that, next to the conventional amino acid (AARE) and ER stress response elements (ERSE) within the CHOP promoter, activator protein-1 (AP-1) and c-Ets-1 TF binding sites are necessary for CHOP induction. Serial deletion and mutation analyses revealed that both AP-1 and c-Ets-1 motifs act in concert to induce CHOP expression. In agreement, CHOP promoter activity was greatly enhanced upon combined versus single overexpression of AP-1 and c-Ets-1. Moreover, combined overexpression of AP-1 and c-Ets-1 in MLE12 cells alone in the absence of any other ER stress inducer was sufficient to induce Chop protein expression. Further, AP-1 and c-Ets-1 were upregulated in AECII under ER stress conditions and in human IPF. Finally, Chop overexpression in vitro resulted in AECII apoptosis, lung fibroblast proliferation, and collagen-I production. We propose that CHOP activation by AP-1 and c-Ets-1 plays a key role in AECII maladaptive ER stress responses and consecutive fibrosis, offering new therapeutic prospects in IPF.

Key messages

Overexpression of active ER stress sensors Atf4, Atf6, and Xbp1 does not induce Chop.

AP-1 and c-Ets-1 TFs are necessary for induction of the ER stress factor Chop.

AP-1 and c-Ets-1 alone induce Chop expression in the absence of any ER stress inducers.

AP-1 and c-Ets-1 are induced in AECII under ER stress conditions and in human IPF.

Chop expression alone triggers AECII apoptosis and consecutive profibrotic responses.

Electronic supplementary material

The online version of this article (10.1007/s00109-019-01787-9) contains supplementary material, which is available to authorized users.

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.

Endoplasmic reticulum stress contributes to the pathogenesis of stress urinary incontinence in postmenopausal women

Objective

To investigate the relationship between endoplasmic reticulum stress (ERS) and the pathogenesis of stress urinary incontinence (SUI) in postmenopausal women.

Methods

Anterior vaginal wall tissue was collected from postmenopausal women with SUI and control subjects. Western blotting was performed for glucose-regulated protein (GRP78), inositol-requiring enzyme 1(IRE1), protein kinase-like endoplasmic reticulum kinase (PERK), activating transcription factor 6 (ATF6), C/EBP-homologous protein (CHOP), and B-cell lymphoma 2 (Bcl-2). Additionally, mRNA expression levels of PERK, activating transcription factor 4 (ATF4), and CHOP were examined by real-time polymerase chain reaction.

Results

GRP78 protein and mRNA expression levels were significantly lower in women with SUI, compared with control subjects. PERK and p-PERK expression levels were higher in women with SUI than in control subjects. However, no differences in IRE1 or ATF6 expression levels were observed in either group. Notably, higher CHOP and lower Bcl-2 protein expression levels were detected in women with SUI, compared with control subjects. Furthermore, PERK, ATF4, and CHOP mRNA expression levels were significantly higher in women with SUI than in control subjects.

Conclusions

Alterations of ERS markers in SUI suggest that ERS may be involved in the development of SUI in postmenopausal women.

Heme scavenging reduces pulmonary endoplasmic reticulum stress, fibrosis, and emphysema

Pulmonary fibrosis and emphysema are irreversible chronic events after inhalation injury. However, the mechanism(s) involved in their development remain poorly understood. Higher levels of plasma and lung heme have been recorded in acute lung injury associated with several insults. Here, we provide the molecular basis for heme-induced chronic lung injury. We found elevated plasma heme in chronic obstructive pulmonary disease (COPD) (GOLD stage 4) patients and also in a ferret model of COPD secondary to chronic cigarette smoke inhalation. Next, we developed a rodent model of chronic lung injury, where we exposed C57BL/6 mice to the halogen gas, bromine (Br2) (400 ppm, 30 minutes), and returned them to room air resulting in combined airway fibrosis and emphysematous phenotype, as indicated by high collagen deposition in the peribronchial spaces, increased lung hydroxyproline concentrations, and alveolar septal damage. These mice also had elevated pulmonary endoplasmic reticulum (ER) stress as seen in COPD patients; the pharmacological or genetic diminution of ER stress in mice attenuated Br2-induced lung changes. Finally, treating mice with the heme-scavenging protein, hemopexin, reduced plasma heme, ER stress, airway fibrosis, and emphysema. This is the first study to our knowledge to report elevated heme in COPD patients and establishes heme scavenging as a potential therapy after inhalation injury.

Localized hypoxia links ER stress to lung fibrosis through induction of C/EBP homologous protein

ER stress in type II alveolar epithelial cells (AECs) is common in idiopathic pulmonary fibrosis (IPF), but the contribution of ER stress to lung fibrosis is poorly understood. We found that mice deficient in C/EBP homologous protein (CHOP), an ER stress-regulated transcription factor, were protected from lung fibrosis and AEC apoptosis in 3 separate models where substantial ER stress was identified. In mice treated with repetitive intratracheal bleomycin, we identified localized hypoxia in type II AECs as a potential mechanism explaining ER stress. To test the role of hypoxia in lung fibrosis, we treated mice with bleomycin, followed by exposure to 14% O2, which exacerbated ER stress and lung fibrosis. Under these experimental conditions, CHOP-/- mice, but not mice with epithelial HIF (HIF1/HIF2) deletion, were protected from AEC apoptosis and fibrosis. In vitro studies revealed that CHOP regulates hypoxia-induced apoptosis in AECs via the inositol-requiring enzyme 1α (IRE1α) and the PKR-like ER kinase (PERK) pathways. In human IPF lungs, CHOP and hypoxia markers were both upregulated in type II AECs, supporting a conclusion that localized hypoxia results in ER stress-induced CHOP expression, thereby augmenting type II AEC apoptosis and potentiating lung fibrosis.

Bleomycin Inhibits Proliferation via Schlafen-Mediated Cell Cycle Arrest in Mouse Alveolar Epithelial Cells

Background

Idiopathic pulmonary fibrosis involves irreversible alveolar destruction. Although alveolar epithelial type II cells are key functional participants within the lung parenchyma, how epithelial cells are affected upon bleomycin (BLM) exposure remains unknown. In this study, we determined whether BLM could induce cell cycle arrest via regulation of Schlafen (SLFN) family genes, a group of cell cycle regulators known to mediate growth-inhibitory responses and apoptosis in alveolar epithelial type II cells.

Methods

Mouse AE II cell line MLE-12 were exposed to 1–10 µg/mL BLM and 0.01–100 µM baicalein (Bai), a G1/G2 cell cycle inhibitor, for 24 hours. Cell viability and levels of pro-inflammatory cytokines were analyzed by MTT and enzyme-linked immunosorbent assay, respectively. Apoptosis-related gene expression was evaluated by quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR). Cellular morphology was determined after DAPI and Hoechst 33258 staining. To verify cell cycle arrest, propidium iodide (PI) staining was performed for MLE-12 after exposure to BLM.

Results

BLM decreased the proliferation of MLE-12 cells. However, it significantly increased expression levels of interleukin 6, tumor necrosis factor α, and transforming growth factor β1. Based on Hoechst 33258 staining, BLM induced condensation of nuclear and fragmentation. Based on DAPI and PI staining, BLM significantly increased the size of nuclei and induced G2/M phase cell cycle arrest. Results of qRT-PCR analysis revealed that BLM increased mRNA levels of BAX but decreased those of Bcl2. In addition, BLM/Bai increased mRNA levels of p53, p21, SLFN1, 2, 4 of Schlafen family.

Conclusion

BLM exposure affects pulmonary epithelial type II cells, resulting in decreased proliferation possibly through apoptotic and cell cycle arrest associated signaling.

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.

Autotaxin in Pathophysiology and Pulmonary Fibrosis

Lysophospholipid signaling is emerging as a druggable regulator of pathophysiological responses, and especially fibrosis, exemplified by the relative ongoing clinical trials in idiopathic pulmonary fibrosis (IPF) patients. In this review, we focus on ectonucleotide pyrophosphatase-phosphodiesterase 2 (ENPP2), or as more widely known Autotaxin (ATX), a secreted lysophospholipase D (lysoPLD) largely responsible for extracellular lysophosphatidic acid (LPA) production. In turn, LPA is a bioactive phospholipid autacoid, forming locally upon increased ATX levels and acting also locally through its receptors, likely guided by ATX's structural conformation and cell surface associations. Increased ATX activity levels have been detected in many inflammatory and fibroproliferative conditions, while genetic and pharmacologic studies have confirmed a pleiotropic participation of ATX/LPA in different processes and disorders. In pulmonary fibrosis, ATX levels rise in the broncheoalveolar fluid (BALF) and stimulate LPA production. LPA engagement of its receptors activate multiple G-protein mediated signal transduction pathways leading to different responses from pulmonary cells including the production of pro-inflammatory signals from stressed epithelial cells, the modulation of endothelial physiology, the activation of TGF signaling and the stimulation of fibroblast accumulation. Genetic or pharmacologic targeting of the ATX/LPA axis attenuated disease development in animal models, thus providing the proof of principle for therapeutic interventions.

Endoplasmic reticulum stress in pulmonary fibrosis

Endoplasmic reticulum (ER) stress is associated with development and progression of fibrotic diseases, including idiopathic pulmonary fibrosis (IPF). ER stress was first implicated in the pathogenesis of IPF >15 years ago with the discovery of disease-causing mutations in surfactant protein C, which result in a misfolded gene product in type II alveolar epithelial cells (AECs). ER stress and the unfolded protein response (UPR) have been linked to lung fibrosis through regulation of AEC apoptosis, epithelial-mesenchymal transition, myofibroblast differentiation, and M2 macrophage polarization. Although progress has been made in understanding the causes and consequences of ER stress in IPF and a number of chronic fibrotic disorders, further studies are needed to identify key factors that induce ER stress in important cell types and define critical down-stream processes and effector molecules that mediate ER stress-related phenotypes. This review discusses potential causes of ER stress induction in the lungs and current evidence linking ER stress to fibrosis in the context of individual cell types: AECs, fibroblasts, and macrophages. As our understanding of the relationship between ER stress and lung fibrosis continues to evolve, future studies will examine new strategies to modulate UPR pathways for therapeutic benefit.

Inhibiting Skp2 E3 Ligase Suppresses Bleomycin-Induced Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive disease with poor prognosis and no curative therapies. SCF-Skp2 E3 ligase is a target for cancer therapy, but there have been no reports about Skp2 as a target for IPF. Here we demonstrate that Skp2 is a promising therapeutic target for IPF. We examined whether disrupting Skp2 suppressed pulmonary fibrosis in a bleomycin (BLM)-induced mouse model and found that pulmonary fibrosis was significantly suppressed in Skp2-deficient mice compared with controls. The pulmonary accumulation of fibrotic markers such as collagen type 1 and fibronectin in BLM-infused mice was decreased in Skp2-deficient mice. Moreover, the number of bronchoalveolar lavage fluid cells accompanied with pulmonary fibrosis was significantly diminished. Levels of the Skp2 target p27 were significantly decreased by BLM-administration in wild-type mice, but recovered in Skp2^-/- mice. In vimentin-positive mesenchymal fibroblasts, the decrease of p27-positive cells and increase of Ki67-positive cells by BLM-administration was suppressed by Skp2-deficency. As these results suggested that inhibiting Skp2 might be effective for BLM-induced pulmonary fibrosis, we next performed a treatment experiment using the Skp2 inhibitor SZL-P1-41. As expected, BLM-induced pulmonary fibrosis was significantly inhibited by SZL-P1-41. Moreover, p27 levels were increased by the SZL-P1-41 treatment, suggesting p27 may be an important Skp2 target for BLM-induced pulmonary fibrosis. Our study suggests that Skp2 is a potential molecular target for human pulmonary fibrosis including IPF.

Endoplasmic reticulum stress in the pathogenesis of fibrotic disease

Eukaryotic cells contain an elegant protein quality control system that is crucial in maintaining cellular homeostasis; however, dysfunction of this system results in endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR). Severe or prolonged ER stress is associated with the development of degenerative and fibrotic disorders in multiple organs, as evidenced by the identification of disease-causing mutations in epithelial-restricted genes that lead to protein misfolding or mistrafficking in familial fibrotic diseases. Emerging evidence implicates ER stress and UPR signaling in a variety of profibrotic mechanisms in individual cell types. In epithelial cells, ER stress can induce apoptosis, inflammatory signaling, and epithelial-mesenchymal transition. In other cell types, ER stress is linked to myofibroblast activation, macrophage polarization, and T cell differentiation. ER stress-targeted therapies have begun to emerge using approaches that range from global enhancement of chaperone function to selective targeting of activated ER stress sensors and other downstream mediators. As the complex regulatory mechanisms of this system are further clarified, there are opportunities to develop new disease-modifying therapeutic strategies in a wide range of chronic fibrotic diseases.

Transcription Factor C/EBP Homologous Protein in Health and Diseases

C/EBP homologous protein (CHOP), known also as DNA damage-inducible transcript 3 and as growth arrest and DNA damage-inducible protein 153 (GADD153), is induced in response to certain stressors. CHOP is universally acknowledged as a main conduit to endoplasmic reticulum stress-induced apoptosis. Ongoing research established the existence of CHOP-mediated apoptosis signaling networks, for which novel downstream targets are still being determined. However, there are studies that contradict this notion and assert that apoptosis is not the only mechanism by which CHOP plays in the development of pathologies. In this review, insights into the roles of CHOP in pathophysiology are summarized at the molecular and cellular levels. We further focus on the newest advances that implicate CHOP in human diseases including cancer, diabetes, neurodegenerative disorders, and notably, fibrosis.

Rifampicin-induced injury in HepG2 cells is alleviated by TUDCA via increasing bile acid transporters expression and enhancing the Nrf2-mediated adaptive response

Bile acid transporters and the nuclear factor erythroid 2-related factor (Nrf-2)-mediated adaptive response play important roles in the development of drug-induced liver injury (DILI). However, little is known about the contribution of the adaptive response to rifampicin (RFP)-induced cell injury. In this study, we found RFP decreased the survival rate of HepG2 cells and increased the levels of lactate dehydrogenase (LDH), alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (AKP), γ-glutamyl-transferase (γ-GT), total bilirubin (TBIL), direct bilirubin (DBIL), indirect bilirubin (IBIL), total bile acid (TBA) and adenosine triphosphate (ATP) in the cell culture supernatants in both a concentration- and a time-dependent manner. RFP increased the expression levels of bile acid transporter proteins and mRNAs, such as bile salt export pump (BSEP), multidrug resistance protein 1 (MDR1), multidrug resistance-associated protein 2 (MRP2), Na+/taurocholate cotransporter (NTCP), organic anion transporting protein 2 (OATP2), organic solute transporter β (OSTβ) and Nrf2. Following the transient knockdown of Nrf2 and treatment with RFP, the expression levels of the BSEP, MDR1, MRP2, NTCP, OATP2 and OSTβ proteins and mRNAs were decreased to different degrees. Moreover, the cell survival was decreased, whereas the LDH level in the cell culture supernatant was increased. Overexpression of the Nrf2 gene produced the opposite effects. Treatment with tauroursodeoxycholic acid (TUDCA) increased the expression levels of the bile acid transporters and Nrf2, decreased the expression levels of glucose-regulated protein 78 (GRP78), PKR-like ER kinase (PERK), activating transcription factor 4 (ATF4), and C/EBP-homologous protein (CHOP), and inhibited RFP-induced oxidative stress. Moreover, TUDCA reduced cell apoptosis, increased cell survival and decreased the levels of LDH, ALT, AST, AKP, γ-GT, TBIL, DBIL, IBIL, TBA and ATP in the cell culture supernatant. Therefore, TUDCA alleviates RFP-induced injury in HepG2 cells by enhancing bile acid transporters expression and the Nrf2-mediated adaptive response.

Involvement of ER stress, PI3K/AKT activation, and lung fibroblast proliferation in bleomycin-induced pulmonary fibrosis

Pulmonary fibrosis is characterized by fibroblast proliferation and extracellular matrix remodelling, leading to respiratory insufficiency. The mechanisms underlying this progressive and devastating disease remain unclear. Conditions that can impair the function of the endoplasmic reticulum (ER) cause accumulation of unfolded or misfolded proteins, resulting in ER stress and activation of the unfolded protein response (UPR). ER stress has been implicated in many conditions including cancer, diabetes, obesity, and inflammation. It is also involved in lung fibrosis, through myofibroblastic differentiation of fibroblasts; however, the precise role of ER stress in lung fibrosis is unknown. The current study aimed to investigate the underlying mechanisms of ER stress inhibitors in the treatment of bleomycin-induced lung fibrosis. We demonstrated that bleomycin can activate ER stress associated proteins, including GRP78, CHOP, and ATF-4, both in vitro and in vivo. PI3K/AKT acts upstream of ER stress to affect lung fibroblast proliferation, resulting in bleomycin-induced pulmonary fibrosis. Treatment with ER stress inhibitors or a PI3K inhibitor caused a reduction in fibroblast proliferation and improved pulmonary function. The relationship between PI3K/AKT/mTOR and ER stress in pulmonary fibrosis, and the application of PI3K inhibitors and ER stress inhibitors in the treatment of pulmonary fibrosis require further investigation.

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.

Effect of a chemical chaperone, tauroursodeoxycholic acid, on HDM-induced allergic airway disease

Endoplasmic reticulum (ER) stress-induced unfolded protein response plays a critical role in inflammatory diseases, including allergic airway disease. However, the benefits of inhibiting ER stress in the treatment of allergic airway disease are not well known. Herein, we tested the therapeutic potential of a chemical chaperone, tauroursodeoxycholic acid (TUDCA), in combating allergic asthma, using a mouse model of house dust mite (HDM)-induced allergic airway disease. TUDCA was administered during the HDM-challenge phase (preventive regimen), after the HDM-challenge phase (therapeutic regimen), or therapeutically during a subsequent HDM rechallenge (rechallenge regimen). In the preventive regimen, TUDCA significantly decreased HDM-induced inflammation, markers of ER stress, airway hyperresponsiveness (AHR), and fibrosis. Similarly, in the therapeutic regimen, TUDCA administration efficiently decreased HDM-induced airway inflammation, mucus metaplasia, ER stress markers, and AHR, but not airway remodeling. Interestingly, TUDCA administered therapeutically in the HDM rechallenge regimen markedly attenuated HDM-induced airway inflammation, mucus metaplasia, ER stress markers, methacholine-induced AHR, and airway fibrotic remodeling. These results indicate that the inhibition of ER stress in the lungs through the administration of chemical chaperones could be a valuable strategy in the treatment of allergic airway diseases.

Chronology of UPR activation in skeletal muscle adaptations to chronic contractile activity

The mitochondrial and endoplasmic reticulum unfolded protein responses (UPR(mt) and UPR(ER)) are important for cellular homeostasis during stimulus-induced increases in protein synthesis. Exercise triggers the synthesis of mitochondrial proteins, regulated in part by peroxisome proliferator activator receptor-γ coactivator 1α (PGC-1α). To investigate the role of the UPR in exercise-induced adaptations, we subjected rats to 3 h of chronic contractile activity (CCA) for 1, 2, 3, 5, or 7 days followed by 3 h of recovery. Mitochondrial biogenesis signaling, through PGC-1α mRNA, increased 14-fold after 1 day of CCA. This resulted in 10-32% increases in cytochrome c oxidase activity, indicative of mitochondrial content, between days 3 and 7, as well as increases in the autophagic degradation of p62 and microtubule-associated proteins 1A/1B light chain 3A (LC3)-II protein. Before these adaptations, the UPR(ER) transcripts activating transcription factor-4, spliced X-box-binding protein 1, and binding immunoglobulin protein were elevated (1.3- to 3.8-fold) at days 1-3, while CCAAT/enhancer-binding protein homologous protein (CHOP) and chaperones binding immunoglobulin protein and heat shock protein (HSP) 70 were elevated at mRNA and protein levels (1.5- to 3.9-fold) at days 1-7 of CCA. The mitochondrial chaperones 10-kDa chaperonin, HSP60, and 75-kDa mitochondrial HSP, the protease ATP-dependent Clp protease proteolytic subunit, and the regulatory protein sirtuin-3 of the UPR(mt) were concurrently induced 10-80% between days 1 and 7 To test the role of the UPR in CCA-induced remodeling, we treated animals with the endoplasmic reticulum stress suppressor tauroursodeoxycholic acid and subjected them to 2 or 7 days of CCA. Tauroursodeoxycholic acid attenuated CHOP and HSP70 protein induction; however, this failed to impact mitochondrial remodeling. Our data indicate that signaling to the UPR is rapidly activated following acute contractile activity, that this is attenuated with repeated bouts, and that the UPR is involved in chronic adaptations to CCA; however, this appears to be independent of CHOP signaling.

Role of endoplasmic reticulum stress in drug-induced toxicity

Drug‐induced toxicity is a key issue for public health because some side effects can be severe and life‐threatening. These adverse effects can also be a major concern for the pharmaceutical companies since significant toxicity can lead to the interruption of clinical trials, or the withdrawal of the incriminated drugs from the market. Recent studies suggested that endoplasmic reticulum (ER) stress could be an important event involved in drug liability, in addition to other key mechanisms such as mitochondrial dysfunction and oxidative stress. Indeed, drug‐induced ER stress could lead to several deleterious effects within cells and tissues including accumulation of lipids, cell death, cytolysis, and inflammation. After recalling important information regarding drug‐induced adverse reactions and ER stress in diverse pathophysiological situations, this review summarizes the main data pertaining to drug‐induced ER stress and its potential involvement in different adverse effects. Drugs presented in this review are for instance acetaminophen (APAP), arsenic trioxide and other anticancer drugs, diclofenac, and different antiretroviral compounds. We also included data on tunicamycin (an antibiotic not used in human medicine because of its toxicity) and thapsigargin (a toxic compound of the Mediterranean plant Thapsia garganica) since both molecules are commonly used as prototypical toxins to induce ER stress in cellular and animal models.

The role of Endoplasmic Reticulum (ER) stress in pulmonary fibrosis

The activation of Endoplasmic Reticulum (ER) stress and Unfolded Protein Response (UPR) was first observed in patients with familial interstitial pneumonia (FIP) carrying mutations in the C-terminal BRICHOS domain of surfactant protein C (SFTPC). Here, aggresome formation and severe ER stress was demonstrated in type-II alveolar epithelial cells (AECII), which specifically express this very hydrophobic surfactant protein. In subsequent studies, FIP-patients with mutations in the gene encoding surfactant protein A2 (SFTPA2) were discovered, whose overexpression in epithelial cells in vitro also resulted in significant induction of ER stress. Moreover, prominent ER stress in AECII was also observed in FIP-patients not carrying the SFTPC/SFTPA2 mutations, as well as in patients with the more common sporadic forms of IP. Additionally, cases of adult-onset FIP with mutations in Telomerase genes and other telomereassociated components were reported. These mutations were associated with telomere shortening, which is a potential cause for triggering a persistent DNA damage response and replicative senescence in affected cells. Moreover, shortened telomeres were observed directly in the AECII of FIP-patients, and even sporadic IP cases, in the absence of any gene mutations. Here, we try to figure out the possible origins of ER stress in sporadic IP cases and non-SFTPC/SFTPA2-associated FIP.