Salubrinal protects against cigarette smoke extract-induced HBEpC apoptosis likely via regulating the activity of PERK-eIF2α signaling pathway

N-acetylcysteine Attenuates Cigarette Smoke-induced Alveolar Epithelial Cell Apoptosis through Reactive Oxygen Species Depletion and Glutathione Replenish In vivo and In vitro

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is the third leading cause of death worldwide. N-acetylcysteine (NAC) is well known for its antioxidant properties, along with potential protective effects on COPD. However, the molecular mechanism of NAC against the apoptosis of alveolar epithelial cells (AECs) in COPD remains unclear.

OBJECTIVE

This study aimed to explore the anti-apoptosis effect of NAC in COPD mice and alveolar epithelial cells.

METHODS

In the present study, the mouse model of COPD was established by cigarette smoke (CS), and mouse alveolar epithelial (MLE-12) cells were treated with cigarette smoke extract (CSE). TdT-mediated dUTP nick-end labeling (TUNEL) assay, reverse transcription polymerase chain reaction (RT-PCR), and western blot were performed to evaluate the effects of NAC on apoptosis, endoplasmic reticulum (ER) stress, and mitochondrial dysfunction. Meanwhile, Lbuthionine- sulfoximine (BSO), a glutathione (GSH) inhibitor, was used to uncover the mechanism of COPD treatment by NAC.

RESULTS

We found that NAC pretreatment could attenuate the protein levels of apoptosis, ER stress, and mitochondrial dysfunction-related genes caused by CS in vivo. Meanwhile, CSE could decrease MLE-12 cell viability, which was prevented by apoptosis inhibitor ZVAD-FMK but not necroptosis inhibitor necrostatin-1. Pretreatment of MLE-12 cells with NAC increased cellular GSH levels, inhibited cellular and mitochondrial reactive oxygen species (ROS) accumulation, and decreased protein level of apoptosis, ER stress, and mitochondrial dysfunction-related genes. Moreover, experiment results showed that BSO could completely reverse the beneficial effects of NAC.

CONCLUSION

Our study confirmed that NAC can attenuate CS-induced AEC apoptosis via alleviating ROS-mediated ER stress and mitochondrial dysfunction pathway, and the mechanism was found to be related to replenishing the cellular GSH content.

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

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

Identification and Analysis of Necroptosis-Related Genes in COPD by Bioinformatics and Experimental Verification

Chronic obstructive pulmonary disease (COPD) is a heterogeneous and complex progressive inflammatory disease. Necroptosis is a newly identified type of programmed cell death. However, the role of necroptosis in COPD is unclear. This study aimed to identify necroptosis-related genes in COPD and explore the roles of necroptosis and immune infiltration through bioinformatics. The analysis identified 49 differentially expressed necroptosis-related genes that were primarily engaged in inflammatory immune response pathways. The infiltration of CD8+ T cells and M2 macrophages in COPD lung tissue was relatively reduced, whereas that of M0 macrophages was increased. We identified 10 necroptosis-related hub genes significantly associated with infiltrated immune cells. Furthermore, 7 hub genes, CASP8, IL1B, RIPK1, MLKL, XIAP, TNFRSF1A, and CFLAR, were validated using an external dataset and experimental mice. CFLAR was considered to have the best COPD-diagnosing capability. TF and miRNA interactions with common hub genes were identified. Several related potentially therapeutic molecules for COPD were also identified. The present findings suggest that necroptosis occurs in COPD pathogenesis and is correlated with immune cell infiltration, which indicates that necroptosis may participate in the development of COPD by interacting with the immune response.

Complement component 3 protects human bronchial epithelial cells from cigarette smoke-induced oxidative stress and prevents incessant apoptosis

The complement component 3 (C3) is a pivotal element of the complement system and plays an important role in innate immunity. A previous study showed that intracellular C3 was upregulated in airway epithelial cells (AECs) from individuals with end-stage chronic obstructive pulmonary disease (COPD). Accumulating evidence has shown that cigarette smoke extract (CSE) induces oxidative stress and apoptosis in AECs. Therefore, we investigated whether C3 modulated cigarette smoke-induced oxidative stress and apoptosis in AECs and participated in the pathogenesis of COPD. We found increased C3 expression, together with increased oxidative stress and apoptosis, in a cigarette smoke-induced mouse model of COPD and in AECs from patients with COPD. Different concentrations of CSEinduced C3 expression in 16HBE cells in vitro. Interestingly, C3 knockdown (KD) exacerbated oxidative stress and apoptosis in 16HBE cells exposed to CSE. Furthermore, C3 exerted its pro-survival effects through JNK inhibition, while exogenous C3 partially rescued CSE-induced cell death and oxidative stress in C3 KD cells. These data indicate that locally produced C3 is an important pro-survival molecule in AECs under cigarette smoke exposure, revealing a potentially novel mechanism in the pathogenesis of COPD.

Mangiferin attenuates cigarette smoke-induced chronic obstructive pulmonary disease in male albino rats

We analyzed the ability of mangiferin to suppress cigarette smoke-induced chronic obstructive pulmonary disease. Control rats showed a marked decrease in the ratio of the forced expiratory volume at 0.1 s to forced vital capacity. The decreases in the peak expiratory flow and maximal mid-expiratory flow indicated airway remodeling and enlargement. The expression levels of superoxide dismutase (SOD), heme oxygenase-1 (HO-1), γ-glutamylcysteine synthetase, nuclear factor erythroid 2-related factor 2, and activating transcription factor 4 were increased in the control rats. The levels of oxidative stress, malondialdehyde, and reactive oxygen species peaked after 24 weeks, whereas the SOD and HO-1 levels and the total antioxidant capacity were reduced in control rats. Mangiferin restored the levels of reactive oxygen species, malondialdehyde, SOD, HO-1, and T-AOC to near normal. Increased numbers of infiltrating inflammatory cells were observed in control rats but were significantly reduced by mangiferin. In addition, edema and airway inflammation were reduced by mangiferin.

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 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.

Titanium dioxide nanoparticles induce endoplasmic reticulum stress-mediated apoptotic cell death in liver cancer cells

Objective

Titanium oxide (TiO₂) acts as a photosensitizer in photodynamic therapy by mediating reactive oxygen species (ROS)-induced endoplasmic reticulum (ER) stress. This study aimed to investigate the effect of TiO₂ on ER stress in liver cancer cells.

Methods

Normal human liver and human hepatocarcinoma cell lines were incubated with various concentrations of TiO₂ nanotubes for 48 hours. Cell growth, apoptosis, cell cycle, and cellular ROS were detected. Expression levels of ER stress sensors (PERK and ATF6) and Bax were evaluated by western blot. The effect of TiO₂ on liver cancer growth was also investigated in mice in vivo.

Results

TiO₂ inhibited cell growth, increased apoptosis and cellular ROS levels, and arrested the cell cycle in G1 stage in liver cancer cells. TiO₂ also increased PERK, ATF6, and Bax expression levels in liver cancer cells in dose-dependent manners. TiO₂ had no significant effect on cell growth, apoptosis, ROS level, cell cycle distribution, or PERK, ATF6, or Bax expression in normal liver cells. TiO₂ administration reduced tumor volume and increased PERK, Bax, and ATF6 expression levels in tumor tissues in vivo.

Conclusions

TiO₂ nanoparticles increased ROS-induced ER stress and activated the PERK/ATF6/Bax axis in liver cancer cells in vitro and in vivo.

SIRT1 attenuates endoplasmic reticulum stress and apoptosis in rat models of COPD

The present study aimed to investigate the protective role of sirtuin 1 (SIRT1) and oxygen regulated protein 150 (ORP150) in a rat COPD model by inducing changes in ER stress and apoptosis. We separated 48 Sprague Dawley (SD) rats into four groups randomly: the control group, resveratrol group, COPD group and the resveratrol intervention group. Rats were challenged with cigarette smoke and lipopolysaccharide with resveratrol (a selective activator of SIRT1). The lung functions of the rats were measured and recorded. The expression levels of SIRT1 and ORP150 in lung tissues were examined by western blot and RTq PCR. The expression levels of the ER stress apoptosis-associated protein were determined .The apoptotic level of lung tissues was analyzed. The results suggest that SIRT1 attenuated apoptosis and ER stress in the lung tissues of rats with COPD. During this process, a positive correlation was identified between SIRT1 and ORP150.

Astragalus Polysaccharides Protects Thapsigargin-induced Endoplasmic Reticulum Stress in HT29 Cells

Aim

This study investigates the effect of astragalus polysaccharides (APS) in protecting against thapsigargin-induced endoplasmic reticulum (ER) stress in HT29 cells by suppressing the PERK-eIF2a signaling pathway.

Methods

HT29 cells were induced by thapsigargin for 12 hours, then treated with APS for 24 hours, and the gene expressions of GRP78, CHOP and eIF2a were quantified by reverse transcription quantitative polymerase chain reaction (RT-qPCR). The expression of GRP78, CHOP, PERK, p-PERK, eIF2a, and p-eIF2a were detected by Western blot.

Results

The ER stress caused by thapsigargin strongly up-regulated the expression of GRP78 and CHOP in HT29 cells, which activated the PERK-eIF2a pathway. There was an increase in PERK phosphorylation, and induction of eIF2a in HT29 cells. Thapsigargin caused significant ER expansion in HT29 cells due to the 12-hour ER stress. Importantly, Astragalus polysaccharide significantly inhibited the phosphorylation of PERK and eIF2a, which reduced the mRNA levels of GRP78, CHOP, PERK and eIF2a, and inhibited the ER expansion in HT29 cells after 24 hours of treatment.

Conclusion

The results indicate that APS reduces the expression of GRP78 and CHOP in HT29 cells, at least in part, by preventing the activation of the PERK-eIF2a signaling pathway.

Ergosterol attenuates cigarette smoke extract-induced COPD by modulating inflammation, oxidative stress and apoptosis in vitro and in vivo

Cigarette smoke (CS) is the major cause of chronic obstructive pulmonary disease (COPD). CS heightens inflammation, oxidative stress and apoptosis. Ergosterol is the main bioactive ingredient in Cordyceps sinensis (C. sinensis), a traditional medicinal herb for various diseases. The objective of this work was to investigate the effects of ergosterol on anti-inflammatory and antioxidative stress as well as anti-apoptosis in a cigarette smoke extract (CSE)-induced COPD model both in vitro and in vivo Our results demonstrate that CSE induced inflammatory and oxidative stress and apoptosis with the involvement of the Bcl-2 family proteins via the nuclear factor kappa B (NF-κB)/p65 pathway in both 16HBE cells and Balb/c mice. CSE induced epithelial cell death and increased the expression of nitric oxide (NO), interleukin-6 (IL-6), tumor necrosis factor α (TNF-α), malondialdehyde (MAD) and the apoptosis-related proteins cleaved caspase 3/7/9 and cleaved-poly-(ADP)-ribose polymerase (PARP) both in vitro and in vivo, whereas decreased the levels of superoxide dismutase (SOD) and catalase (CAT). Treatment of 16HBE cells and Balb/c mice with ergosterol inhibited CSE-induced inflammatory and oxidative stress and apoptosis by inhibiting the activation of NF-κB/p65. Ergosterol suppressed apoptosis by inhibiting the expression of the apoptosis-related proteins both in vitro and in vivo Moreover, the usage of QNZ (an inhibitor of NF-κB) also partly demonstrated that NF-κB/p65 pathway was involved in the ergosterol protective progress. These results show that ergosterol suppressed COPD inflammatory and oxidative stress and apoptosis through the NF-κB/p65 pathway, suggesting that ergosterol may be partially responsible for the therapeutic effects of cultured C. sinensis on COPD patients.

Ursolic Acid Protected Lung of Rats From Damage Induced by Cigarette Smoke Extract

Background: We found previously that ursolic acid (UA) administration could alleviate cigarette smoke-induced emphysema in rats partly through the unfolded protein response (UPR) PERK-CHOP and Nrf2 pathways, thus alleviating endoplasmic reticulum stress (ERS)-associated oxidative stress and cell apoptosis. We hypothesized that other UPR pathways may play similar roles in cigarette smoke extract (CSE)-induced emphysema. So, we sought to investigate the dynamic changes and effects of UPR and the downstream apoptotic pathways. Further, we investigated whether UA could alleviate CSE-induced emphysema and airway remodelling in rats, whether and when it exerts its effects through UPR pathways as well as Smads pathways.

Methods: One hundred eight Sprague Dawley (SD) rats were randomly divided into three groups: Sham group, CSE group, and UA group, and each group was further divided into three subgroups, administered CSE (vehicle) for 2, 3, or 4 weeks; each subgroup had 12 rats. We examined pathological changes, analyzed the three UPR signaling pathways and subsequent ERS, intrinsic and extrinsic apoptotic pathway indicators, as well as activation of Smad2,3 molecules in rat lungs.

Results: Exposure to CSE for 3 or 4 weeks could apparently induce emphysema and airway remodeling in rats, including gross and microscopic changes, alteration of mean alveolar number (MAN), mean linear intercept (MLI), and mean airway thickness in lung tissue sections. UA intervention could significantly alleviate CSE-induced emphysema and airway remodeling in rats. UA exerted its effects through ameliorating apoptosis by down regulating UPR signalling pathways and subsequent apoptosis pathways, as well as, downregulating p-Smad2 and p-Smad3 molecules.

Conclusions: UA attenuated CSE-induced emphysema and airway remodeling, exerting its effects partly through regulation of three UPR pathways, amelioration downstream apoptotic pathways, and alleviating activation of Smad2 and Smad3.

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.

Role of reciprocal interaction between autophagy and endoplasmic reticulum stress in apoptosis of human bronchial epithelial cells induced by cigarette smoke extract

Endoplasmic reticulum stress (ERS)-induced apoptosis of airway epithelial cells plays an important role in the pathogenesis of chronic obstructive pulmonary disease (COPD). Furthermore, autophagy is closely related to ERS under apoptosis. Here, this study aimed to investigate the role of the reciprocal interaction between autophagy and ERS in the cigarette smoke extract (CSE)-induced apoptosis of human bronchial epithelial (HBE) cells. Cell apoptosis was detected by flow cytometry analysis. Protein expression was examined by Western blot. The mRNA expression was detected using real-time quantitative reverse transcription PCR (qRT-PCR). The results showed that CSE treatment induced apoptosis, autophagy, and expression of ERS-related proteins in HBE cells. Furthermore, autophagy inhibition by 3-MA significantly decreased protein expression of GRP78, p-PERK, and p-eIF2α and increased CHOP, ATF4, and caspase-4, whereas ERS inhibition by 4-PBA led to autophagy suppression. Moreover, the CSE-induced autophagy was diminished by knockdown of GRP78, PERK, or eIF2α but enhanced by knockdown of ATF4 or CHOP; however, the CSE-induced HBE apoptosis was enhanced by knockdown of GRP78, PERK, or eIF2α but was attenuated by knockdown of ATF4 or CHOP. Additionally, both sodium hydrosulfide (NaHS) and melatonin attenuated the CSE-induced apoptosis, enhanced the CSE-induced autophagy, increased GRP78, p-PERK, and p-eIF2α, and decreased CHOP, ATF4, and caspase-4, via SIRT1/ORP150 pathway. Collectively, this study provided evidence about the role of the reciprocal interaction between autophagy and ERS in CSE-induced apoptosis of HBE cells. © 2018 IUBMB Life, 71(1):66-80, 2019.

Propofol inhibited autophagy through Ca2+/CaMKKβ/AMPK/mTOR pathway in OGD/R-induced neuron injury

Background

The neuroprotective role of propofol (PPF) in cerebral ischemia-reperfusion (I/R) has recently been highlighted. This study aimed to explore whether the neuroprotective mechanisms of PPF were linked to its regulation of Ca²⁺/CaMKKβ (calmodulin-dependent protein kinase kinase β)/AMPK (AMP-activated protein kinase)/mTOR (mammalian target of rapamycin)/autophagy pathway.

Methods

Cultured primary rat cerebral cortical neurons were treated with oxygen-glucose deprivation and re-oxygenation (OGD/R) to mimic cerebral I/R injury in vitro.

Results

Compared with the control neurons, OGD/R exposure successfully induced neuronal I/R injury. Furthermore, OGD/R exposure notably caused autophagy induction, reflected by augmented LC3-II/LC3-I ratio and Beclin 1 expression, decreased p62 expression, and increased LC3 puncta formation. Moreover, OGD/R exposure induced elevation of intracellular Ca²⁺ concentration ([Ca²⁺]i). However, PPF treatment significantly antagonized OGD/R-triggered cell injury, autophagy induction, and [Ca²⁺]i elevation. Further investigation revealed that both autophagy induction by rapamycin and [Ca²⁺]i elevation by the Ca²⁺ ionophore ionomycin significantly reversed the PPF-mediated amelioration of OGD/R-triggered cell injury. Importantly, ionomycin also significantly abrogated the PPF-mediated suppression of autophagy and CaMKKβ/AMPK/mTOR signaling in OGD/R-exposed neurons. Additionally, activation of CaMKKβ/AMPK/mTOR signaling abrogated the PPF-mediated autophagy suppression.

Conclusion

Our findings demonstrate that PPF antagonized OGD/R-triggered neuronal injury, which might be mediated, at least in part, via inhibition of autophagy through Ca²⁺/CaMKKβ/AMPK/mTOR pathway.

Electronic supplementary material

The online version of this article (10.1186/s10020-018-0054-1) contains supplementary material, which is available to authorized users.

Knockdown of TRPV4 suppresses osteoclast differentiation and osteoporosis by inhibiting autophagy through Ca2+ -calcineurin-NFATc1 pathway

The aim of this study is to evaluate the effect of transient receptor potential vanilloid 4 (TRPV4) on osteoclast differentiation and osteoporosis, and to investigate the underlying mechanism. The results showed that TRPV4 expression and intracellular Ca²⁺ concentration were significantly upregulated in macrophage colony-stimulating factor (M-CSF)-stimulated and receptor activator of nuclear factor κΒ ligand (RANKL)-stimulated RAW264.7 cells. Furthermore, TRPV4 overexpression further increased the M-CSF- and RANKL-induced number of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts and expression of osteoclastogenesis-related genes (TRAP, c-Fos, and nuclear factor of activated T cells [NFATc1]), activated the Ca ²⁺ -calcineurin-NFATc1 signaling and increased autophagy-related proteins (light chain [LC] 3II and Beclin-1) during osteoclast differentiation. In contrast, TRPV4 knockdown exerted the opposite effects. Mechanically, inhibition of Ca ²⁺ -calcineurin-NFATc1 signaling by FK506 or 11R-VIVIT abrogated the TRPV4 overexpression-induced osteoclast differentiation and autophagy induction. Moreover, suppression of autophagy by 3-methyladenine attenuated the TRPV4-induced osteoclast differentiation. In addition, short hairpin RNA TRPV4-lentivirus administration significantly diminished the increased levels of several osteoclastogenesis-related genes (RANKL, TRAP, and tumor necrosis factor-α), alleviated the disturbed microarchitecture of lumbar vertebrae, restored the decreased bone mineral density, ratio of bone volume to total tissue volume, trabecular thickness, and trabecular number, and diminished the increased trabecular separation, in ovariectomy (OVX)-induced osteoporosis mice. Consistent with the in vitro data, TRPV4 knockdown significantly decreased the induced number of TRAP-positive osteoclasts, the increased LC3 and NFATc1 expression in the lumbar vertebrae of OVX mice. In conclusion, TRPV4 knockdown suppresses osteoclast differentiation and osteoporosis by inhibiting autophagy through Ca ²⁺ -calcineurin-NFATc1 pathway.

AMPK alleviates endoplasmic reticulum stress by inducing the ER-chaperone ORP150 via FOXO1 to protect human bronchial cells from apoptosis

Chronic obstructive pulmonary disease (COPD), is characterized by inflammation of airways accompanied by a progressive destruction of lung parenchyma. This process is initiated in most cases by cigarette smoking. In this study we investigated the role of AMP activated protein kinase (AMPK) in cigarette smoke extract (CSE)-induced airway epithelial cell apoptosis as a consequence of endoplasmic reticulum stress (ER stress). Exposure of human bronchial epithelial cells (HBEpC) to CSE resulted in apoptosis as detected using Annexin V-PI flow cytometry. However, co-treatment with N1-(β-d-ribofuranosyl)-5-aminoimidazole-4-carboxamide (AICAR), a pharmacological activator of AMPK, significantly increased cell protection against ER stress-induced apoptosis by upregulating the 150 kDa oxygen-regulated protein (ORP150), which functions as an ER-associated chaperone, with concomitant elevation of FOXO1, a critical transcription factor regulating ORP150 expression. Lentiviral silencing of AMPK or FOXO1 using short hairpin (sh) RNA resulted in a significant decrease of ORP150 and an elevation of CCAAT/enhancer-binding protein-homologous protein (CHOP) resulting in ER stress and apoptosis of HBEpC. Together, our results strongly suggest that AMPK can activate ORP150 through FOXO1 pathway and confer protection against ER stress-induced apoptosis of airway epithelial cells following exposure to CSE. Thus, AMPK may serve as a likely therapeutic target for clinical and sub-clinical interventions in COPD.

Adaptive unfolded protein response promotes cell survival in rifampicin-treated L02 cells

An important concept in drug-induced liver injury (DILI) is adaptation, which means the injury reverses with the continuation of the drug. The mechanism of adaption of drugs remains enigmatic, adaptive unfolded protein response (UPR) is possibly involved. We once observed adaptation phenomenon of rifampicin (RFP) in animal models, in this study, we investigate the effects of RFP on adaptive UPR in L02 cells, and after inhibiting UPR by using 4-phenylbutyrate (4-PBA), the change of cell viability and cell apoptosis in RFP-treated cells. We found that with the concentration of RFP increased and the treatment time was prolonged, the glucose-regulated protein 78 (GRP78), a hallmark of the UPR, was upregulated, and was dose- and time-dependent. RFP also activates the p-eukaryotic initiation factor 2α (eIF2α) protein expression. 4-PBA decreased GRP78 and p-eIF2α protein expression levels. Moreover, FCA showed that cell apoptosis rate obviously increased, and MTT assay showed that cell survival rate obviously decreased, this indicates that after inhibiting the UPR, the cell damage increased, which shows that the UPR is an adaptation mechanism to protect cells against injury induced by RFP. This also proves that when the degree of UPR induced by RFP is relatively mild, adaptive UPR is helpful for cell survival.

Eukaryotic translation initiation factor 2 subunit α (eIF2α) inhibitor salubrinal attenuates paraquat-induced human lung epithelial-like A549 cell apoptosis by regulating the PERK-eIF2α signaling pathway

Paraquat (PQ), as one of the most widely used herbicides in the world, can cause severe lung damage in humans and animals. This study investigated the underlying molecular mechanism of PQ-induced lung cell damage and the protective role of salubrinal. Human lung epithelial-like A549 cells were treated with PQ for 24h and were pre-incubated with salubrinal for 2h, followed by 500μM of PQ treatment. Silencing eIF2α gene of the A549 cells with siRNA interference method was conducted. Cell morphology, cell viability, apoptosis and caspase-3 activity were assessed by different assays accordingly thereafter. The expression of PERK, p-PERK, ATF6, c-ATF6, IRE1α, p-IRE1α, CHOP, GRP78, p-eIF2α and β-actin was assayed by western blot. The data showed that PQ significantly reduced A549 cell viability, changed cell morphology, induced cell apoptosis and significantly upregulated the levels of GRP78, CHOP, p-PERK, c-ATF6 and p-IRE1α. However, 30μM salubrinal could attenuate the effects of PQ on damages to A549 cells through upregulating p-eIF2α. In contrast, knocking down eIF2α gene inhabited the effects of salubrinal. These results suggest that PQ-induced A549 cell apoptosis involved endoplasmic reticulum (ER) stress, specially the PERK-eIF2α pathway. Salubrinal attenuated A549 cells from PQ-induced damages through regulation of the PERK-eIF2α signaling.

Mechanical and hypoxia stress can cause chondrocytes apoptosis through over-activation of endoplasmic reticulum stress

OBJECTIVE

To examine the role of mechanical force and hypoxia on chondrocytes apoptosis and osteoarthritis (OA)-liked pathological change on mandibular cartilage through over-activation of endoplasmic reticulum stress (ERS).

METHODS

We used two in vitro models to examine the effect of mechanical force and hypoxia on chondrocytes apoptosis separately. The mandibular condylar chondrocytes were obtained from three-week-old male Sprague-Dawley rats. Flexcell 5000T apparatus was used to produce mechanical forces (12%, 0.5Hz, 24h vs 20%, 0.5Hz, 24h) on chondrocytes. For hypoxia experiment, the concentration of O₂ was down regulated to 5% or 1%. Cell apoptosis rates were quantified by annexin V and propidium iodide (PI) double staining and FACS analysis. Quantitative real-time PCR and western blot were performed to evaluate the activation of ERS and cellular hypoxia. Then we used a mechanical stress loading rat model to verify the involvement of ERS in OA-liked mandibular cartilage pathological change. Histological changes in mandibular condylar cartilage were assessed via hematoxylin & eosin (HE) staining. Immunohistochemistry of GRP78, GRP94, HIF-1α, and HIF-2α were performed to evaluate activation of the ERS and existence of hypoxia. Apoptotic cells were detected by the TUNEL method.

RESULTS

Tunicamycin, 20% mechanical forces and hypoxia (1% O₂) all significantly increased chondrocytes apoptosis rates and expression of ERS markers (GRP78, GRP94 and Caspase 12). However, 12% mechanical forces can only increase the apoptotic sensitivity of chondrocytes. Mechanical stress resulted in OA-liked pathological change on rat mandibular condylar cartilage which included thinning cartilage and bone erosion. The number of apoptotic cells increased. ERS and hypoxia markers expressions were also enhanced. Salubrinal, an ERS inhibitor, can reverse these effects in vitro and in vivo through the down-regulation of ERS markers and hypoxia markers.

CONCLUSION

We confirmed that mechanical stress and local hypoxia both contributed to the chondrocytes apoptosis. Mechanical stress can cause OA-like pathological change in rat mandibular condylar cartilage via ERS activation and hypoxia existed in the meantime. Both mechanical forces and hypoxia can induce ERS and cause chondrocytes apoptosis only if the stimulate was in higher level. Salubrinal can protect chondrocytes from apoptosis, and relieve OA-liked pathological change on mandibular condylar cartilage under mechanical stress stimulation.

IL-17A deficiency mitigates bleomycin-induced complement activation during lung fibrosis

Interleukin 17A (IL-17A) and complement (C') activation have each been implicated in the pathogenesis of idiopathic pulmonary fibrosis (IPF). We have reported that IL-17A induces epithelial injury via TGF-β in murine bronchiolitis obliterans; that TGF-β and the C' cascade present signaling interactions in mediating epithelial injury; and that the blockade of C' receptors mitigates lung fibrosis. In the present study, we investigated the role of IL-17A in regulating C' in lung fibrosis. Microarray analyses of mRNA isolated from primary normal human small airway epithelial cells indicated that IL-17A (100 ng/ml; 24 h; n = 5 donor lungs) induces C' components (C' factor B, C3, and GPCR kinase isoform 5), cytokines (IL8, -6, and -1B), and cytokine ligands (CXCL1, -2, -3, -5, -6, and -16). IL-17A induces protein and mRNA regulation of C' components and the synthesis of active C' 3a (C3a) in normal primary human alveolar type II epithelial cells (AECs). Wild-type mice subjected to IL-17A neutralization and IL-17A knockout (il17a^-/- ) mice were protected against bleomycin (BLEO)-induced fibrosis and collagen deposition. Further, BLEO-injured il17a^-/- mice had diminished levels of circulating Krebs Von Den Lungen 6 (alveolar epithelial injury marker), local caspase-3/7, and local endoplasmic reticular stress-related genes. BLEO-induced local C' activation [C3a, C5a, and terminal C' complex (C5b-9)] was attenuated in il17a^-/- mice, and IL-17A neutralization prevented the loss of epithelial C' inhibitors (C' receptor-1 related isoform Y and decay accelerating factor), and an increase in local TUNEL levels. RNAi-mediated gene silencing of il17a in fibrotic mice arrested the progression of lung fibrosis, attenuated cellular apoptosis (caspase-3/7) and lung deposition of collagen and C' (C5b-9). Compared to normals, plasma from IPF patients showed significantly higher hemolytic activity. Our findings demonstrate that limiting complement activation by neutralizing IL-17A is a potential mechanism in ameliorating lung fibrosis.-Cipolla, E., Fisher, A. J., Gu, H., Mickler, E. A., Agarwal, M., Wilke, C. A., Kim, K. K., Moore, B. B., Vittal, R. IL-17A deficiency mitigates bleomycin-induced complement activation during lung fibrosis.

Ursolic acid attenuates cigarette smoke-induced emphysema in rats by regulating PERK and Nrf2 pathways

OBJECTIVE

Ursolic acid (UA) is widely distributed in natural plants to against oxidation, virus, inflammation, tumor, and has been widely used in the pharmaceutical and cosmetics. However, its effect on emphysema of chronic obstructive pulmonary disease (COPD) is unknown. Unfolded protein response is involved in pathogenesis of COPD through PERK pathway. Nuclear erythroid-related factor 2 (Nrf2) regulates antioxidant defensive mechanism in COPD. This study was to explore effect and mechanism of UA on cigarette smoke (CS)-induced rat emphysema.

MATERIALS AND METHODS

50 Wistar rats were divided into 5 groups (n = 10 each): rats were exposed to CS for 12 weeks in absence (CS group) or presence of UA at different doses. Control group was treated with UA vehicle only. Histopathology, apoptosis, key protein expression of PERK and Nrf2 pathway were determined in lung tissues. Oxidative stress levels in lung were represented by 8-OHdG, MDA and GSH levels.

RESULTS

Emphysema-related pathology, based on inter-alveolar wall distance and alveolar density, was less severe in UA groups than in CS group. Compared with CS group, UA treatment down-regulated PERK pathway protein expression, up-regulated expression of Bcl-2 and down-regulated expression of Bax, Cleaved-Caspase3 and Cleaved-Caspase12. Moreover, UA decreased number of apoptotic cells in rat lungs. UA also up-regulated protein expression of Nrf2/ARE pathway and GSH level, decreased expression of oxidant stress factor 8-OHdG and MDA. These improvements were in accordance with attenuation of severity of emphysema.

CONCLUSIONS

UA attenuates CS-induced rat emphysema by down-regulating PERK pathway to alleviate CS-induced apoptosis in lung, and up-regulating Nrf2 pathway to improve cigarette smoke-induced oxidant stress in rat lungs.

PCSK9 regulates apoptosis in human lung adenocarcinoma A549 cells via endoplasmic reticulum stress and mitochondrial signaling pathways

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a member of the subtilisin family of PCs that encodes a neural apoptosis-regulated convertase 1. However, the precise role of PCSK9 in lung cancer cell apoptosis has remained elusive. In the present study, A549 human lung adenocarcinoma cells were transfected with PCSK9 small interfering (si)RNA to investigate the underlying mechanisms of apoptosis. The results indicated that PCSK9 siRNA exhibited anti-tumor activity by inducing apoptosis as determined by a Cell Counting Kit-8 and Hoechst staining analysis. In addition, PCSK9 siRNA significantly increased apoptosis of A549 cells in part via activation of caspase-3 and downregulation of the anti-apoptotic proteins survivin and X-linked inhibitor of apoptosis protein. Moreover, the results demonstrated that perturbations in the mitochondrial membrane were associated with the deregulation of the Bax/Bcl-2 ratio, which led to the release of cytochrome c after PCSK9 siRNA transfection. In addition, PCSK9 siRNA also induced endoplasmic reticulum stress (ERS) by increasing the levels of 78 kDa glucose-regulated protein (GRP78), GRP94, phosphorylated protein kinase R-like ER kinase and phosphorylated eukaryotic initiation factor 2α. Therefore, these results demonstrated that PCSK9 siRNA may exert its anti-tumor activity through inducing mitochondrial dysfunction and ERS-associated cell death in A549 cells.

Protective effect of mild endoplasmic reticulum stress on radiation-induced bystander effects in hepatocyte cells

Radiation-induced bystander effect (RIBE) has important implications for secondary cancer risk assessment during cancer radiotherapy, but the defense and self-protective mechanisms of bystander normal cells are still largely unclear. The present study found that micronuclei (MN) formation could be induced in the non-irradiated HL-7702 hepatocyte cells after being treated with the conditioned medium from irradiated hepatoma HepG2 cells under either normoxia or hypoxia, where the ratio of the yield of bystander MN induction to the yield of radiation-induced MN formation under hypoxia was much higher than that of normoxia. Nonetheless, thapsigargin induced endoplasmic reticulum (ER) stress and dramatically suppressed this bystander response manifested as the decrease of MN and apoptosis inductions. Meanwhile, the interference of BiP gene, a major ER chaperone, amplified the detrimental RIBE. More precisely, thapsigargin provoked ER sensor of PERK to initiate an instantaneous and moderate ER stress thus defensed the hazard form RIBE, while BiP depletion lead to persistently destroyed homeostasis of ER and exacerbated cell injury. These findings provide new insights that the mild ER stress through BiP-PERK-p-eIF2α signaling pathway has a profound role in protecting cellular damage from RIBE and hence may decrease the potential secondary cancer risk after cancer radiotherapy.

5-Hydroxymethylfurfural protects against ER stress-induced apoptosis in GalN/TNF-α-injured L02 hepatocytes through regulating the PERK-eIF2α signaling pathway

5-Hydroxymethylfurfural (5-HMF), a water-soluble compound extracted from wine-processed Fructus corni, is a novel hepatic protectant for treating acute liver injury. The present study was designed to investigate the protective effect of 5-HMF in human L02 hepatocytes injured by D-galactosamine (GalN) and tumor necrosis factor-α (TNF-α) in vitro and to explore the underlying mechanisms of action. Our results showed that 5-HMF caused significant increase in the viability of L02 cells injured by GalN/TNF-α, in accordance with a dose-dependent decrease in apoptotic cell death confirmed by morphological and flow cytometric analyses. Based on immunofluorescence and Western blot assays, we found that GalN/TNF-α induced ER stress in the cells, as indicated by the disturbance of intracellular Ca(2+) concentration, the activation of protein kinase RNA (PKR)-like ER kinase (PERK), phosphorylation of eukaryotic initiation factor 2 alpha (eIF2α), and expression of ATF4 and CHOP proteins, which was reversed by 5-HMF pre-treatment in a dose-dependent manner. The anti-apoptotic effect of 5-HMF was further evidenced by balancing the expression of Bcl-2 family members. In addition, the knockdown of PERK suppressed the expression of phospho-PERK, phospho-eIF2α, ATF4, and CHOP, resulting in a significant decrease in cell apoptosis after the treatment with GalN/TNF-α. 5-HMF could enhance the effects of PERK knockdown, protecting the cells against the GalN/TNF-α insult. In conclusion, these findings demonstrate that 5-HMF can effectively protect GalN/TNF-α-injured L02 hepatocytes against ER stress-induced apoptosis through the regulation of the PERK-eIF2α signaling pathway, suggesting that it is a possible candidate for liver disease therapy.

Role of Cigarette Smoke-Induced Aggresome Formation in Chronic Obstructive Pulmonary Disease-Emphysema Pathogenesis

Cigarette smoke (CS) exposure is known to induce proteostasis imbalance that can initiate accumulation of ubiquitinated proteins. Therefore, the primary goal of this study was to determine if first- and secondhand CS induces localization of ubiquitinated proteins in perinuclear spaces as aggresome bodies. Furthermore, we sought to determine the mechanism by which smoke-induced aggresome formation contributes to chronic obstructive pulmonary disease (COPD)-emphysema pathogenesis. Hence, Beas2b cells were treated with CS extract (CSE) for in vitro experimental analysis of CS-induced aggresome formation by immunoblotting, microscopy, and reporter assays, whereas chronic CS-exposed murine model and human COPD-emphysema lung tissues were used for validation. In preliminary analysis, we observed a significant (P < 0.01) increase in ubiquitinated protein aggregation in the insoluble protein fraction of CSE-treated Beas2b cells. We verified that CS-induced ubiquitin aggregrates are localized in the perinuclear spaces as aggresome bodies. These CS-induced aggresomes (P < 0.001) colocalize with autophagy protein microtubule-associated protein 1 light chain-3B(+) autophagy bodies, whereas U.S. Food and Drug Administration-approved autophagy-inducing drug (carbamazepine) significantly (P < 0.01) decreases their colocalization and expression, suggesting CS-impaired autophagy. Moreover, CSE treatment significantly increases valosin-containing protein-p62 protein-protein interaction (P < 0.0005) and p62 expression (aberrant autophagy marker; P < 0.0001), verifying CS-impaired autophagy as an aggresome formation mechanism. We also found that inhibiting protein synthesis by cycloheximide does not deplete CS-induced ubiquitinated protein aggregates, suggesting the role of CS-induced protein synthesis in aggresome formation. Next, we used an emphysema murine model to verify that chronic CS significantly (P < 0.0005) induces aggresome formation. Moreover, we observed that autophagy induction by carbamazepine inhibits CS-induced aggresome formation and alveolar space enlargement (P < 0.001), confirming involvement of aggresome bodies in COPD-emphysema pathogenesis. Finally, significantly higher p62 accumulation in smokers and severe COPD-emphysema lungs (Global Initiative for Chronic Obstructive Lung Disease Stage III/IV) as compared with normal nonsmokers (Global Initiative for Chronic Obstructive Lung Disease Stage 0) substantiates the pathogenic role of autophagy impairment in aggresome formation and COPD-emphysema progression. In conclusion, CS-induced aggresome formation is a novel mechanism involved in COPD-emphysema pathogenesis.

Experimental Evidence Shows Salubrinal, an eIF2α Dephosphorylation Inhibitor, Reduces Xenotoxicant-Induced Cellular Damage

Accumulating evidence indicates that endoplasmic reticulum (ER) stress and the subsequent unfolded protein response (UPR) are involved in the pathogenesis of not only the protein misfolding disorders such as certain neurodegenerative and metabolic diseases, but also in the cytotoxicity of environmental pollutants, industrial chemicals, and drugs. Thus, the modulation of ER stress signaling pathways is an important issue for protection against cellular damage induced by xenotoxicants. The substance salubrinal has been shown to prevent dephosphorylation of the eukaryotic translation initiation factor 2 alpha (eIF2α). The phosphorylation of eIF2α appears to be cytoprotective during ER stress, because inhibition of the translation initiation activity of eIF2α reduces global protein synthesis. In addition, the expression of activating transcription factor 4 (ATF4), a transcription factor that induces the expression of UPR target genes, is up-regulated through alternative translation. This review shows that salubrinal can protect cells from the damage induced by a wide range of xenotoxicants, including environmental pollutants and drugs. The canonical and other possible mechanisms of cytoprotection by salubrinal from xenotoxicant-induced ER stress are also discussed.

Decreased proteasomal function accelerates cigarette smoke-induced pulmonary emphysema in mice

Chronic obstructive pulmonary disease (COPD) is a disease common in elderly people, characterized by progressive destruction of lung parenchyma and chronic inflammation of the airways. The pathogenesis of COPD remains unclear, but recent studies suggest that oxidative stress-induced apoptosis in alveolar cells contributes to emphysematous lung destruction. The proteasome is a multicatalytic enzyme complex that plays a critical role in proteostasis by rapidly destroying misfolded and modified proteins generated by oxidative and other stresses. Proteasome activity decreases with aging in many organs including lungs, and an age-related decline in proteasomal function has been implicated in various age-related pathologies. However, the role of the proteasome system in the pathogenesis of COPD has not been investigated. Recently, we have established a transgenic (Tg) mouse model with decreased proteasomal chymotrypsin-like activity, showing age-related phenotypes. Using this model, we demonstrate here that decreased proteasomal function accelerates cigarette smoke (CS)-induced pulmonary emphysema. CS-exposed Tg mice showed remarkable airspace enlargement and increased foci of inflammation compared with wild-type controls. Importantly, apoptotic cells were found in the alveolar walls of the affected lungs. Impaired proteasomal activity also enhanced apoptosis in cigarette smoke extract (CSE)-exposed fibroblastic cells derived from mice and humans in vitro. Notably, aggresome formation and prominent nuclear translocation of apoptosis-inducing factor were observed in CSE-exposed fibroblastic cells isolated from Tg mice. Collective evidence suggests that CS exposure and impaired proteasomal activity coordinately enhance apoptotic cell death in the alveolar walls that may be involved in the development and progression of emphysema in susceptible individuals such as the elderly.

Resveratrol exerts an anti-apoptotic effect on human bronchial epithelial cells undergoing cigarette smoke exposure

Cigarette smoke can cause endoplasmic reticulum stress and induce apoptosis, both of which are important pathogenic factors contributing to chronic obstructive pulmonary disease. The aim of the present study was to produce a cigarette smoke extract (CSE)-induced apoptosis human bronchial epithelial cell (HBEpC) model, to investigate the protective effects of resveratrol (RES). The role of oxygen-regulated protein 150 (ORP150) in the RES-induced activation of Sirtuin 1 (SIRT1) was additionally studied. Cultured HBEpCs were initially treated with CSE to induce apoptosis, followed by an incubation either with or without RES. Numerous techniques were used to evaluate the outcomes of the present study, including cell counting kit-8 assay, quantitative polymerase chain reaction, western blotting, Hoechst 33342 staining and AnnexinV-PI flow cytometry apoptosis analyses, and gene knockdown. It was identified that 24 h 2% CSE incubation induced apoptosis in HBEpC, accompanied by an overexpression of the apoptosis molecular markers CCAAT-enhancer-binding protein homologous protein, caspase 4 and caspase 3. Pre-treatment of the cells with RES markedly alleviated the severity of apoptosis, as confirmed by apoptosis analyses and the expression levels of the apoptosis molecular markers. SIRT1 was shown to be overexpressed following RES treatment. However, following the gene knockdown of ORP150, the anti-apoptotic effects of RES were significantly attenuated. The results of the present study demonstrate that RES may have a protective effect against CSE-induced apoptosis, and a molecular pathway involving SIRT1 and ORP150 may be associated with the anti-apoptotic functions of RES in HBEpC.

S-oxygenation of thiocarbamides V: oxidation of tetramethylthiourea by chlorite in slightly acidic media

The reaction between tetramethylthiourea (TTTU) and slightly acidic chlorite has been studied. The reaction is much faster than comparable oxidations of the parent thiourea compound as well as other substituted thioureas. The stoichiometry of the reaction in excess oxidant showed a complete desulfurization of the thiocarbamide to yield the corresponding urea and sulfate: 2ClO2(-) + (Me2N)2C ═ S + H2O → (Me2N)2C ═ O + SO4(2-) + 2Cl(-) + 2H(+). The reaction mechanism is unique in that the most stable metabolite before formation of the corresponding urea is the S-oxide. This is one of the rare occasions in which a low-molecular-weight S-oxide has been stabilized without the aid of large steric groups. ESI-MS data show almost quantitative formation of the S-oxide and negligible formation of the sulfinic and sulfonic acids. TTTU, in contrast to other substituted thioureas, can only stabilize intermediate oxoacids, before formation of sulfate, in the form of zwitterions. With a stoichiometric excess of TTTU over oxidant, the TTTU dimer is the predominant product. Chlorine dioxide, which is formed from the reaction of excess chlorite and HOCl, is a very important reactant in the overall mechanism. It reacts rapidly with TTTU to reform ClO2(-). Oxidation of TTTU by chlorite has a complex dependence on acid as a result of chlorous acid dissociation and protonation of the thiol group on TTTU in high-acid conditions, which renders the thiol center a less effective nucleophile.

The PERK-eIF2α signaling pathway is involved in TCDD-induced ER stress in PC12 cells

Studies have shown that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induces apoptotic cell death in neuronal cells. However, whether this is the result of endoplasmic reticulum (ER) stress-mediated apoptosis remains unknown. In this study, we determined whether ER stress plays a role in the TCDD-induced apoptosis of pheochromocytoma (PC12) cells and primary neurons. PC12 cells were exposed to different TCDD concentrations (1, 10, 100, 200, or 500nM) for varying lengths of time (1, 3, 6, 12, or 24h). TCDD concentrations much higher than 10nM (100, 200, or 500nM) markedly increased glucose-regulated protein (GRP78) and C/EBP homologous protein (CHOP) levels, which are hallmarks of ER stress. We also evaluated the effects of TCDD on ER morphology in PC12 cells and primary neurons that were treated with different TCDD concentrations (1, 10, 50, or 200nM) for 24h. Ultrastructural ER alterations were observed with transmission electron microscopy in PC12 cells and primary neurons treated with high concentrations of TCDD. Furthermore, TCDD-induced ER stress significantly promoted the activation of the PKR-like ER kinase (PERK), a sensor for the unfolded protein response (UPR), and its downstream target eukaryotic translation initiation factor 2 α (eIF2α); in contrast, TCDD did not appear to affect inositol-requiring enzyme 1 (IRE1) and activating transcription factor 6 (ATF6), two other UPR sensors. Importantly, TCDD significantly inhibited eIF2α phosphorylation and triggered apoptosis in PC12 cells after 6-24h of treatment. Salubrinal, which activates the PERK-eIF2α pathway, significantly enhanced eIF2α phosphorylation in PC12 cells and attenuated the TCDD-induced cell death. In contrast, knocking down eIF2α using small interfering RNA markedly enhanced TCDD-induced cell death. Together, these results indicate that the PERK-eIF2α pathway plays an important role in TCDD-induced ER stress and apoptosis in PC12 cells.

Inhibition of serine/threonine protein phosphatase PP1 protects cardiomyocytes from tunicamycin-induced apoptosis and I/R through the upregulation of p-eIF2α

The serine/threonine protein phosphatase PP1 mediates the dephosphorylation of phosphorylated eukaryotic translation initiation factor 2 subunit α (p-eIF2α), which is a central regulator of protein synthesis. In the present study, we examined the protective effects of PP1-12 (an inhibitor of the serine/threonine protein phosphatase PP1) against tunicamycin (TM)-induced apoptosis in cultured cardiomyocytes in vitro, as well as in an in vivo model of ischemia/reperfusion (I/R) injury in rat hearts. Neonatal cardiomyocytes cultured from the ventricles of the hearts of 1-day-old Wistar rats were exposed to various concentrations of PP1-12 (0.3, 1 and 3 µmol/l) for 30 min, followed by treatment with TM for 36 h. Cell viability was assessed by adenosine triphosphate (ATP) bioluminescence, and the results revealed that pre-treatment with PP1-12 protected cell viability. Western blot analysis revealed that PP1-12 induced eIF2α phosphorylation and immuncytochemistry indicated that PP1-12 downregulated the expression of C/EBP homologous protein (CHOP), which is related to apoptosis. PP1-12 suppressed cell apoptosis, with maximum protective effects displayed at the concentration of 3 µmol/l. For the in vivo experiments, male Sprague-Dawley rats were randomly divided into 5 groups: i) sham-operated; ii) vehicle (I/R + DMSO); iii) I/R + 1 mg/kg/day PP1-12; iv) I/R + 3 mg/kg/day PP1-12; and v) I/R + 10 mg/kg/day PP1-12. PP1-12 reduced the expression of cleaved caspase-12 and increased the phosphorylation of eIF2α, as revealed by western blot analysis. By calculating the apoptotic index (AI), we found that 10 mg/kg/day PP1-12 exerted the most pronounced anti-apoptotic effect. The infarction area was significantly decreased following treatment with this concentration of PP1-12, as revealed by 2,3,5-triphenyltetrazolium chloride (TTC) staining. Taken together, these data suggest that PP1-12 protects cardiomyocytes from TM- and I/R-induced apoptosis, and this effect is achieved at least in part through the inhibition of cell apoptosis and the induction of eIF2α phosphorylation.

Cigarette smoke extract induces the expression of GRP78 in A549 cells via the p38/MAPK pathway

Apoptosis of alveolar epithelial cells has been implicated in the pathogenesis of chronic obstructive pulmonary disease. To determine the involvement of glucose‑regulated protein 78 (GRP78) in the cigarette smoke extract (CSE)‑induced apoptosis of alveolar epithelial cells and the potential mechanisms underlying this effect, A549 cells that originate from alveolar type II epithelial cells were exposed to various CSE conditions in the present study. GRP78 expression and its effect on the apoptosis of A549 cells were investigated using techniques such as RT-PCR, western blot analysis, gene knockdown by GRP78 siRNA interference and the terminal deoxynucleotidyl transferase dUTP nick‑end labeling assay. The activity of the p38/mitogen‑activated protein kinase (MAPK) pathway and its involvement in GRP78 expression were also analyzed using SB203580, a p38/MAPK pathway inhibitor. It was demonstrated that GRP78 expression in the cells was significantly upregulated following CSE exposure and a 12‑h exposure of 5% CSE was the most efficient in inducing GRP78 expression. This CSE‑induced GRP78 expression was significantly attenuated by GRP78 siRNA or by the use of SB203580. The downregulation of GRP78 expression by GRP78 siRNA also led to the increased expression of caspase-3 and an increased apoptotic index (AI, P<0.05 vs. other groups). These results suggested that CSE induced GRP78 expression in A549 cells. This study demonstrated that upregulated GRP78 expression may be anti‑apoptotic effects and the p38/MAPK pathway was involved in the process of CSE‑induced GRP78 expression in A549 cells.

Is there a therapeutic role for selenium in alpha-1 antitrypsin deficiency?

Selenium is an essential trace mineral of fundamental importance to human health. Much of its beneficial influence is attributed to its presence within selenoproteins, a group of proteins containing the rare amino acid selenocysteine. There are 25 known human selenoproteins including glutathione peroxidases, thioredoxin reductases and selenoproteins. Selenoprotein S (SEPS1) is an endoplasmic reticulum (ER) resident selenoprotein involved in the removal of misfolded proteins from the ER. SEPS1 expression can be induced by ER stress, an event that is associated with conformational disorders and occurs due to accumulation of misfolded proteins within the ER. Alpha-1 antitrypsin (AAT) deficiency, also known as genetic emphysema, is a conformational disorder in which the roles of ER stress, SEPS1 and selenium have been investigated. SEPS1 can relieve ER stress in an in vitro model of AAT deficiency by reducing levels of active ATF6 and inhibiting grp78 promoter- and NFκB activity; some of these effects are enhanced in the presence of selenium supplementation. Other studies examining the molecular mechanisms by which selenium mediates its anti-inflammatory effects have identified a role for prostaglandin 15d-PGJ₂ in targeting NFκB and PPARγ. Together these ER stress-relieving and anti-inflammatory properties suggest a therapeutic potential for selenium supplementation in genetic emphysema.