ERp29 deficiency affects sensitivity to apoptosis via impairment of the ATF6-CHOP pathway of stress response. Apoptosis. 2014;19:801-815. [PMID: 24370996 DOI: 10.1007/s10495-013-0961-0]

ERP29 regulates the proliferation of endometrial carcinoma via M6A modification

AIMS

Endoplasmic reticulum protein 29 (ERP29) is crucial for endoplasmic reticulum stress (ERS). M6A plays an important role in the progression of endometrial cancer (EC). The study investigated the role of ERS-related gene (ERP29) and m6A in EC.

MATERIALS AND METHODS

We screened ERS-related genes based on the GEO dataset, GSEA dataset and TCGA-UCEC database using WGCNA and two machine learning algorithms. The m6A-related GEO dataset was employed to identify the ERS-related hub genes with m6A. Expression of hub genes in different cell types were visualize through scRNA-seq data analyzing. Using qPCR, Western blot, and Immunohistochemical assays to detect the expression of ERP29, the effect of ERP29 on cancer cell proliferation was investigated through CCK8, EdU and clone formation experiments. M6A modifications were studied using m6A Dot blot and MeRIP-qPCR. Finally, we conducted rescue experiments.

KEY FINDINGS

Ten ERS-related hub genes with m6A were identified. ERP29 is highly expressed in EC. ERP29 knockdown inhibits EC cell proliferation. METTL3 overexpression increases the ERP29 mRNA m6A and decreases the expression of ERP29. Cycloleucine (Cyc), a nucleic acid methylation inhibitor, treatment reduces ERP29 mRNA m6A and increases the expression of ERP29. Cyc rescue the low expression of ERP29 caused by overexpression of METTL3 through m6A. ERP29 knockdown rescued the increased proliferation of EC cells caused by low m6A.

SIGNIFICANCE

ERP29 is highly expressed in EC. m6A regulates ERP29 expression and affects the proliferation of endometrial cancer cells. This represents the premise for applying ERP29 and m6A modifications in diagnosing and treating EC.

Crosstalk between autophagy and ferroptosis mediate injury in ischemic stroke by generating reactive oxygen species

Stroke represents a significant threat to global human health, characterized by high rates of morbidity, disability, and mortality. Predominantly, strokes are ischemic in nature. Ischemic stroke (IS) is influenced by various cell death pathways, notably autophagy and ferroptosis. Recent studies have increasingly highlighted the interplay between autophagy and ferroptosis, a process likely driven by the accumulation of reactive oxygen species (ROS). Post-IS, either the inhibition of autophagy or its excessive activation can escalate ROS levels. Concurrently, the interaction between ROS and lipids during ferroptosis further augments ROS accumulation. Elevated ROS levels can provoke endoplasmic reticulum stress-induced autophagy and, in conjunction with free iron (Fe2+), can trigger ferroptosis. Moreover, ROS contribute to protein and lipid oxidation, endothelial dysfunction, and an inflammatory response, all of which mediate secondary brain injury following IS. This review succinctly explores the mechanisms of ROS-mediated crosstalk between autophagy and ferroptosis and the detrimental impact of increased ROS on IS. It also offers novel perspectives for IS treatment strategies.

Mechanisms of intermittent theta-burst stimulation attenuating nerve injury after ischemic reperfusion in rats through endoplasmic reticulum stress and ferroptosis

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) exerts neuroprotective effects early in cerebral ischemia/reperfusion (I/R) injury. Intermittent theta-brust stimulation (iTBS), a more time-efficient modality of rTMS, improves the efficiency without at least decreasing the efficacy of the therapy. iTBS elevates cortical excitability, and in recent years it has become increasingly common to apply iTBS to patients in the early post-IS period. However, little is known about the neuroprotective mechanisms of iTBS. Endoplasmic reticulum stress (ERS), and ferroptosis have been shown to be involved in the development of I/R injury. We aimed to investigate the potential regulatory mechanisms by which iTBS attenuates neurological injury after I/R in rats.

METHODS

Rats were randomly divided into three groups: sham-operated group, MCAO/R group, and MCAO/R + iTBS group, and were stimulated with iTBS 36 h after undergoing middle cerebral artery occlusion (MCAO) or sham-operated. The expression of ERS, ferroptosis, and apoptosis-related markers was subsequently detected by western blot assays. We also investigated the mechanism by which iTBS attenuates nerve injury after ischemic reperfusion in rats by using the modified Neurological Severity Score (mNSS) and the balance beam test to measure nerve function.

RESULTS

iTBS performed early in I/R injury attenuated the levels of ERS, ferroptosis, and apoptosis, and improved neurological function, including mNSS and balance beam experiments. It is suggested that this mode of stimulation reduces the cost per treatment by several times without compromising the efficacy of the treatment and could be a practical and less costly intervention.

Participation of WD repeat-containing protein 54 (WDR54) in rat sperm-oocyte fusion through interaction with both IZUMO1 and JUNO

Fertilization is a complex process that depends on the fusion of the cell membrane of sperm with that of oocyte, and it involves sperm-oocyte recognition, binding, and fusion, which are mediated by multiple proteins. Among those proteins, IZUMO1 and its receptor JUNO have been identified as essential factors for sperm-oocyte recognition and fusion. However, the interaction between IZUMO1 and JUNO alone does not lead to cell membrane fusion, suggesting the involvement of additional proteins in sperm-oocyte membrane fusion. In this study, we have discovered that a protein called WDR54, which consists of WD-repeat modules, is located on the cell membrane of sperm, as well as on the cell membrane and in the cytoplasm of the oocyte. We have found that WDR54 is involved in sperm-oocyte fertilization. When sperm and oocyte were treated with anti-WDR54 ascites, the in vitro fertilization (IVF) rate significantly decreased. Furthermore, our research has shown that WDR54 interacts with both IZUMO1 and JUNO, and it colocalizes with IZUMO1 on the surface of the sperm head and with JUNO on the oocyte surface. Through structural analysis of the putative complexes of WDR54-IZUMO1 and WDR54-JUNO, we infer that these three proteins could form a complex of JUNO-WDR54-IZUMO1-JUNO (referred to as the "JWIJ complex") on the oocyte surface. Our findings suggest that WDR54 is an important factor involved in sperm-oocyte adhesion and fusion. This discovery provides new insight into the mechanisms of mammalian sperm-oocyte adhesion and fusion.

TRAPPC1 is essential for the maintenance and differentiation of common myeloid progenitors in mice

Myeloid cell development in bone marrow is essential for the maintenance of peripheral immune homeostasis. However, the role of intracellular protein trafficking pathways during myeloid cell differentiation is currently unknown. By mining bioinformatics data, we identify trafficking protein particle complex subunit 1 (TRAPPC1) as continuously upregulated during myeloid cell development. Using inducible ER-TRAPPC1 knockout mice and bone marrow chimeric mouse models, we demonstrate that TRAPPC1 deficiency causes severe monocyte and neutrophil defects, accompanied by a selective decrease in common myeloid progenitors (CMPs) and subsequent cell subsets in bone marrow. TRAPPC1-deleted CMPs differentiate poorly into monocytes and neutrophils in vivo and in vitro, in addition to exhibiting enhanced endoplasmic reticulum stress and apoptosis via a Ca2+ -mitochondria-dependent pathway. Cell cycle arrest and senescence of TRAPPC1-deleted CMPs are mediated by the activation of pancreatic endoplasmic reticulum kinase and the upregulation of cyclin-dependent kinase inhibitor p21. This study reveals the essential role of TRAPPC1 in the maintenance and differentiation of CMPs and highlights the significance of protein processing and trafficking processes in myeloid cell development.

The Regulation of Endoplasmic Reticulum Stress in Cancer: Special Focuses on Luteolin Patents

Cancer is a major health problem across the globe, and is expeditiously growing at a faster rate worldwide. The endoplasmic reticulum (ER) is a membranous cell organelle having inextricable links in cellular homeostasis. Altering ER homeostasis initiates various signaling events known as the unfolded protein response (UPR). The basic purpose of the UPR is to reinstate the homeostasis; however, a continuous UPR can stimulate pathways of cell death, such as apoptosis. As a result, there is great perturbation to target particular signaling pathways of ER stress. Flavonoids have gained significant interest as a potential anticancer agent because of their considerable role in causing cytotoxicity of the cancerous cells. Luteolin, a flavonoid isolated from natural products, is a promising phytochemical used in the treatment of cancer. The current study is designed to review the different endoplasmic reticulum stress pathways involved in the cancer, mechanistic insights of luteolin as an anticancer agent in modulating ER stress, and the available luteolin patent formulations were also highlighted. The patents were selected on the basis of pre-clinical and/or clinical trials, and established antitumor effects using patent databases of FPO IP and Espacenet. The patented formulation of luteolin studied so far has shown promising anticancer potential against different cancer cell lines. However, further research is still required to determine the molecular targets of such bioactive molecules so that they can be used as anticancer drugs.

Cellular stress signaling and the unfolded protein response in retinal degeneration: mechanisms and therapeutic implications

Background

The retina, as part of the central nervous system (CNS) with limited capacity for self-reparation and regeneration in mammals, is under cumulative environmental stress due to high-energy demands and rapid protein turnover. These stressors disrupt the cellular protein and metabolic homeostasis, which, if not alleviated, can lead to dysfunction and cell death of retinal neurons. One primary cellular stress response is the highly conserved unfolded protein response (UPR). The UPR acts through three main signaling pathways in an attempt to restore the protein homeostasis in the endoplasmic reticulum (ER) by various means, including but not limited to, reducing protein translation, increasing protein-folding capacity, and promoting misfolded protein degradation. Moreover, recent work has identified a novel function of the UPR in regulation of cellular metabolism and mitochondrial function, disturbance of which contributes to neuronal degeneration and dysfunction. The role of the UPR in retinal neurons during aging and under disease conditions in age-related macular degeneration (AMD), retinitis pigmentosa (RP), glaucoma, and diabetic retinopathy (DR) has been explored over the past two decades. Each of the disease conditions and their corresponding animal models provide distinct challenges and unique opportunities to gain a better understanding of the role of the UPR in the maintenance of retinal health and function.

Method

We performed an extensive literature search on PubMed and Google Scholar using the following keywords: unfolded protein response, metabolism, ER stress, retinal degeneration, aging, age-related macular degeneration, retinitis pigmentosa, glaucoma, diabetic retinopathy.

Results and conclusion

We summarize recent advances in understanding cellular stress response, in particular the UPR, in retinal diseases, highlighting the potential roles of UPR pathways in regulation of cellular metabolism and mitochondrial function in retinal neurons. Further, we provide perspective on the promise and challenges for targeting the UPR pathways as a new therapeutic approach in age- and disease-related retinal degeneration.

How Cells Deal with the Fluctuating Environment: Autophagy Regulation under Stress in Yeast and Mammalian Systems

Eukaryotic cells frequently experience fluctuations of the external and internal environments, such as changes in nutrient, energy and oxygen sources, and protein folding status, which, after reaching a particular threshold, become a type of stress. Cells develop several ways to deal with these various types of stress to maintain homeostasis and survival. Among the cellular survival mechanisms, autophagy is one of the most critical ways to mediate metabolic adaptation and clearance of damaged organelles. Autophagy is maintained at a basal level under normal growing conditions and gets stimulated by stress through different but connected mechanisms. In this review, we summarize the advances in understanding the autophagy regulation mechanisms under multiple types of stress including nutrient, energy, oxidative, and ER stress in both yeast and mammalian systems.

Effects of Escitalopram on Endoplasmic Reticulum Stress and Oxidative Stress Induced by Tunicamycin

Background: Major depressive disorder (MDD) was reported to be associated with endoplasmic reticulum stress (ERS) combined with oxidative stress (OS) (ERS/OS). Here, we aimed to investigate the effects of escitalopram (ESC) on blood-brain barrier (BBB) permeability and ERS/OS-related pathways in brain microvascular endothelial cells (bEnd.3 cells) induced by tunicamycin (TM).

Methods: bEnd.3 cells were divided into four groups: control, TM, ESC, and ESC + TM groups. CCK-8 and flow cytometry were used to detect cell survival and apoptosis, respectively. The expression levels of proteins involved in cell permeability and ERS/OS-related pathways were assessed by western blot and immunofluorescence. Malondialdehyde (MDA) concentration and superoxide dismutase (SOD) activity were determined by commercial kits.

Results: We revealed that TM-induced bEnd.3 cells exhibited remarkably decreased viability and increased apoptosis rate, while ESC treatment reversed these changes. Additionally, TM treatment resulted in markedly increased PERK, GRP78, ATF6, XBP1, and CHOP protein expression levels. On the contrary, the expression of PERK, GRP78, XBP1, and CHOP was obviously reduced in TM-induced bEnd.3 cells after ESC treatment. Moreover, TM significantly reduced the expression of p-eNOS and P-gp and increased the expression of CaMKII and MMP9 compared with the control group. However, ESC reversed these changes in TM-induced bEnd.3 cells. Furthermore, the expression of SOD was significantly decreased, while MDA was significantly increased by TM treatment. In contrast, the expression of SOD was dramatically increased, while MDA was remarkably decreased by ESC treatment.

Conclusion: Our results demonstrated that ESC can inhibit ERS/OS and BBB permeability of TM-induced bEnd.3 cells. ESC may alleviate cognitive impairment and prevent comorbidities in MDD patients through ERS/OS.

Antioxidant Role of Kaempferol in Prevention of Hepatocellular Carcinoma

Reactive oxygen species (ROS) are noxious to cells because their increased level interacts with the body's defense mechanism. These species also cause mutations and uncontrolled cell division, resulting in oxidative stress (OS). Prolonged oxidative stress is responsible for incorrect protein folding in the endoplasmic reticulum (ER), causing a stressful condition, ER stress. These cellular stresses (oxidative stress and ER stress) are well-recognized biological factors that play a prominent role in the progression of hepatocellular carcinoma (HCC). HCC is a critical global health problem and the third leading cause of cancer-related mortality. The application of anti-oxidants from herbal sources significantly reduces oxidative stress. Kaempferol (KP) is a naturally occurring, aglycone dietary flavonoid that is present in various plants (Crocus sativus, Coccinia grandis, Euphorbia pekinensis, varieties of Aloe vera, etc.) It is capable of interacting with pleiotropic proteins of the human body. Efforts are in progress to develop KP as a potential candidate to prevent HCC with no adverse effects. This review emphasizes the molecular mechanism of KP for treating HCC, targeting oxidative stress.

The Dual Regulation of Apoptosis by Flavivirus

Apoptosis is a form of programmed cell death, which maintains cellular homeostasis by eliminating pathogen-infected cells. It contains three signaling pathways: death receptor pathway, mitochondria-mediated pathway, and endoplasmic reticulum pathway. Its importance in host defenses is highlighted by the observation that many viruses evade, hinder or destroy apoptosis, thereby weakening the host’s immune response. Flaviviruses such as Dengue virus, Japanese encephalitis virus, and West Nile virus utilize various strategies to activate or inhibit cell apoptosis. This article reviews the research progress of apoptosis mechanism during flaviviruses infection, including flaviviruses proteins and subgenomic flaviviral RNA to regulate apoptosis by interacting with host proteins, as well as various signaling pathways involved in flaviviruses-induced apoptosis, which provides a scientific basis for understanding the pathogenesis of flaviviruses and helps in developing an effective antiviral therapy.

Exosomes Derived from Human Urine-Derived Stem Cells Inhibit Intervertebral Disc Degeneration by Ameliorating Endoplasmic Reticulum Stress

Objective

This study is aimed at determining the effects of human urine-derived stem cell-derived exosomes (USCs-exos) on pressure-induced nucleus pulposus cell (NPC) apoptosis and intervertebral disc degeneration (IDD) and on the ERK and AKT signaling pathways.

Methods

The NPCs were obtained from patients with herniated lumbar discs. Western blot analysis (WB) and quantitative real-time polymerase chain reaction (qRT-PCR) were used to determine endoplasmic reticulum (ER) stress levels of NPCs under stress. Human USCs were identified using an inverted microscope, three-line differentiation experiments, and flow cytometry. A transmission microscope, nanoparticle size analysis, and WB procedures were used to identify the extracted exosomes and observe NPC uptake. A control group, a 48 h group, and a USCs-exos group were established. The control group was untreated, and the 48 h group was pressure-trained for 48 h, while the USCs-exos group was pressure-trained for 48 h and treated with USCs-exos. WB, qRT-PCR, and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) analysis were used to determine the ER stress levels in stress conditions and after exosomal treatment. The AKT and ERK pathways were partially detected. Magnetic Resonance Imaging (MRI) and computed tomography (CT) were used to evaluate cell degeneration while exosomal effects on the intervertebral disc (IVD) tissue were determined by hematoxylin and eosin (HE) staining, Safranin O-fast green staining, immunohistochemical staining (IHC), nuclear magnetic resonance (NMR), spectrometric detection, and total correlation spectroscopy (TOCSY). IVD metabolites were also identified and quantified.

Results

After pressure culture, ER stress markers (GRP78 and C/EBP homologous protein (CHOP)) in the NPCs were significantly elevated with time (p < 0.05). Human USCs are short and spindle-shaped. They can successfully undergo osteogenic, adipogenic, and chondrogenic differentiation. In this study, these stem cells were found to be positive for CD29, CD44, and CD73. The exosomes were centrally located with a diameter of 50-100 nm. CD63 and Tsg101 were highly expressed while the expression of Calnexin was suppressed. The exosomes can be ingested by NPCs. USCs-exos significantly improved ER stress responses and inhibited excessive activation of the unfolded protein response (UPR) as well as cell apoptosis and disc degeneration through the AKT and ERK signaling pathways (p < 0.05).

Conclusion

Through the AKT and ERK signaling pathways, USCs-exos significantly inhibit ER stress-induced cell apoptosis and IDD under pressure conditions. It is, therefore, a viable therapeutic strategy.

Endoplasmic Reticulum Stress Provocation by Different Nanoparticles: An Innovative Approach to Manage the Cancer and Other Common Diseases

A proper execution of basic cellular functions requires well-controlled homeostasis including correct protein folding. Endoplasmic reticulum (ER) implements such functions by protein reshaping and post-translational modifications. Different insults imposed on cells could lead to ER stress-mediated signaling pathways, collectively called the unfolded protein response (UPR). ER stress is also closely linked with oxidative stress, which is a common feature of diseases such as stroke, neurodegeneration, inflammation, metabolic diseases, and cancer. The level of ER stress is higher in cancer cells, indicating that such cells are already struggling to survive. Prolonged ER stress in cancer cells is like an Achilles' heel, if aggravated by different agents including nanoparticles (NPs) may be exhausted off the pro-survival features and can be easily subjected to proapoptotic mode. Different types of NPs including silver, gold, silica, graphene, etc. have been used to augment the cytotoxicity by promoting ER stress-mediated cell death. The diverse physico-chemical properties of NPs play a great role in their biomedical applications. Some special NPs have been effectively used to address different types of cancers as these particles can be used as both toxicological or therapeutic agents. Several types of NPs, and anticancer drug nano-formulations have been engineered to target tumor cells to enhance their ER stress to promote their death. Therefore, mitigating ER stress in cancer cells in favor of cell death by ER-specific NPs is extremely important in future therapeutics and understanding the underlying mechanism of how cancer cells can respond to NP induced ER stress is a good choice for the development of novel therapeutics. Thus, in depth focus on NP-mediated ER stress will be helpful to boost up developing novel pro-drug candidates for triggering pro-death pathways in different cancers.

Role of a genetic variation in the microRNA-4421 binding site of ERP29 regarding risk of oropharynx cancer and prognosis

We conducted a two-stage association study on patients with oropharynx (OP) squamous cell carcinoma (SCC) and healthy controls to identify single nucleotide variants (SNVs) located at the microRNA (miR)-binding sites of carcinogenesis genes associated with risk and prognosis of the disease. In stage 1, 49 patients and 49 controls were analyzed using Genome-Wide Human SNV Arrays to identify variants in the 3′-untranslated region (3′-UTR) of carcinogenesis-related genes, and one SNV was selected for data validation in stage 2 by TaqMan assays in 250 OPSCC patients and 250 controls. The ERP29 c.*293A > G (rs7114) SNV located at miR-4421 binding site was selected for data validation among 46 SNVs. The ERp29 and miR-4421 levels were evaluated by quantitative-PCR and Western blotting. Interaction between miR-4421 with 3′-UTR of ERP29 was evaluated by luciferase reporter assay. Event-free survival (EFS) was calculated by Kaplan–Meier and Cox methods. ERP29 GG variant genotype was more common in OPSCC patients than in controls (6.4% vs 3.6%, p = 0.02; odds ratio: 5.67; 95% confidence interval (CI) 1.27–25.26). Shorter EFS were seen in the base of tongue (BT) SCC patients with GG genotype (0.0% vs 36.2%, p = 0.01; hazard ratio: 2.31; 95% CI: 1.03–5.15). Individuals with ERP29 AG or GG genotypes featured lower levels of ERP29 mRNA (p = 0.005), ERp29 protein (p < 0.001) and higher levels of miR-4421 (p = 0.02). The miR-4421 showed more efficient binding with 3′-UTR of the variant G allele when compared with wild-type allele A (p = 0.001). Our data suggest that ERP29 rs7114 SNV may alter the risk and prognosis of OPSCC due to variation in the ERp29 production possibly modulated by miR-4421.

Endoplasmic reticulum stress and protein degradation in chronic liver disease

Endoplasmic reticulum (ER) stress is easily observed in chronic liver disease, which often causes accumulation of unfolded or misfolded proteins in the ER, leading to unfolded protein response (UPR). Regulating protein degradation is an integral part of UPR to relieve ER stress. The major protein degradation system includes the ubiquitin-proteasome system (UPS) and autophagy. All three arms of UPR triggered in response to ER stress can regulate UPS and autophagy. Accumulated misfolded proteins could activate these arms, and then generate various transcription factors to regulate the expression of UPS-related and autophagy-related genes. The protein degradation process regulated by UPR has great significance in many chronic liver diseases, including non-alcoholic fatty liver disease (NAFLD), alcoholic liver disease (ALD), viral hepatitis, liver fibrosis, and hepatocellular carcinoma(HCC). In most instances, the degradation of excessive proteins protects cells with ER stress survival from apoptosis. According to the specific functions of protein degradation in chronic liver disease, choosing to promote or inhibit this process is promising as a potential method for treating chronic liver disease.

The Probable, Possible, and Novel Functions of ERp29

The luminal endoplasmic reticulum (ER) protein of 29 kDa (ERp29) is a ubiquitously expressed cellular agent with multiple critical roles. ERp29 regulates the biosynthesis and trafficking of several transmembrane and secretory proteins, including the cystic fibrosis transmembrane conductance regulator (CFTR), the epithelial sodium channel (ENaC), thyroglobulin, connexin 43 hemichannels, and proinsulin. ERp29 is hypothesized to promote ER to cis-Golgi cargo protein transport via COP II machinery through its interactions with the KDEL receptor; this interaction may facilitate the loading of ERp29 clients into COP II vesicles. ERp29 also plays a role in ER stress (ERS) and the unfolded protein response (UPR) and is implicated in oncogenesis. Here, we review the vast array of ERp29’s clients, its role as an ER to Golgi escort protein, and further suggest ERp29 as a potential target for therapies related to diseases of protein misfolding and mistrafficking.

Heat shock protein 5 and inflammatory bowel disease

Inflammatory bowel disease is a kind of chronic recurrent intestinal inflammatory disease whose occurrence and development are affected by the integrity of the mucosal barrier. As the main component of the mucosal barrier, intestinal epithelial cells mainly include Paneth cells, goblet cells, etc. Heat shock protein 5 is a key factor for endoplasmic reticulum stress, and it affects the survival and apoptosis of intestinal epithelial cells mainly through endoplasmic reticulum stress pathways, and then participates in the process of inflammatory bowel disease.

Serum Protein Changes in Pediatric Sepsis Patients Identified With an Aptamer-Based Multiplexed Proteomic Approach

OBJECTIVES

Sepsis, a life-threatening organ dysfunction caused by a dysregulated host response to infection, is a leading cause of death and disability among children worldwide. Identifying sepsis in pediatric patients is difficult and can lead to treatment delay. Our objective was to assess the host proteomic response to infection utilizing an aptamer-based multiplexed proteomics approach to identify novel serum protein changes that might help distinguish between pediatric sepsis and infection-negative systemic inflammation and hence can potentially improve sensitivity and specificity of the diagnosis of sepsis over current clinical criteria approaches.

DESIGN

Retrospective, observational cohort study.

SETTING

PICU and cardiac ICU, Seattle Children's Hospital, Seattle, WA.

PATIENTS

A cohort of 40 children with clinically overt sepsis and 30 children immediately postcardiopulmonary bypass surgery (infection-negative systemic inflammation control subjects) was recruited. Children with sepsis had a confirmed or suspected infection, two or more systemic inflammatory response syndrome criteria, and at least cardiovascular and/or pulmonary organ dysfunction.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Serum samples from 35 of the sepsis and 28 of the bypass surgery subjects were available for screening with an aptamer-based proteomic platform that measures 1,305 proteins to search for large-scale serum protein expression pattern changes in sepsis. A total of 111 proteins were significantly differentially expressed between the sepsis and control groups, using the linear models for microarray data (linear modeling) and Boruta (decision trees) R packages, with 55 being previously identified in sepsis patients. Weighted gene correlation network analysis helped identify 76 proteins that correlated highly with clinical sepsis traits, 27 of which had not been previously reported in sepsis.

CONCLUSIONS

The serum protein changes identified with the aptamer-based multiplexed proteomics approach used in this study can be useful to distinguish between sepsis and noninfectious systemic inflammation.

Endoplasmic reticulum stress and the protein degradation system in ophthalmic diseases

Objective

Endoplasmic reticulum (ER) stress is involved in the pathogenesis of various ophthalmic diseases, and ER stress-mediated degradation systems play an important role in maintaining ER homeostasis during ER stress. The purpose of this review is to explore the potential relationship between them and to find their equilibrium sites.

Design

This review illustrates the important role of reasonable regulation of the protein degradation system in ER stress-mediated ophthalmic diseases. There were 128 articles chosen for review in this study, and the keywords used for article research are ER stress, autophagy, UPS, ophthalmic disease, and ocular.

Data sources

The data are from Web of Science, PubMed, with no language restrictions from inception until 2019 Jul.

Results

The ubiquitin proteasome system (UPS) and autophagy are important degradation systems in ER stress. They can restore ER homeostasis, but if ER stress cannot be relieved in time, cell death may occur. However, they are not independent of each other, and the relationship between them is complementary. Therefore, we propose that ER stability can be achieved by adjusting the balance between them.

Conclusion

The degradation system of ER stress, UPS and autophagy are interrelated. Because an imbalance between the UPS and autophagy can cause cell death, regulating that balance may suppress ER stress and protect cells against pathological stress damage.

Type I interferons and endoplasmic reticulum stress in health and disease

Type I interferons (IFNs) comprise of pro-inflammatory cytokines created, as well as sensed, by all nucleated cells with the main objective of blocking pathogens-driven infections. Owing to this broad range of influence, type I IFNs also exhibit critical functions in many sterile inflammatory diseases and immunopathologies, especially those associated with endoplasmic reticulum (ER) stress-driven signaling pathways. Indeed, over the years accumulating evidence has indicated that the presence of ER stress can influence the production, or sensing of, type I IFNs induced by perturbations like pattern recognition receptor (PRR) agonists, infections (bacterial, viral or parasitic) or autoimmunity. In this article we discuss the link between type I IFNs and ER stress in various diseased contexts. We describe how ER stress regulates type I IFNs production or sensing, or how type I IFNs may induce ER stress, in various circumstances like microbial infections, autoimmunity, diabetes, cancer and other ER stress-related contexts.

Endoplasmic Reticulum Stress Activates Unfolded Protein Response Signaling and Mediates Inflammation, Obesity, and Cardiac Dysfunction: Therapeutic and Molecular Approach

Obesity has been implicated as a risk factor for insulin resistance and cardiovascular diseases (CVDs). Although the association between obesity and CVD is a well-established phenomenon, the precise mechanisms remain incompletely understood. This has led to a relative paucity of therapeutic measures for the prevention and treatment of CVD and associated metabolic disorders. Recent studies have shed light on the pivotal role of prolonged endoplasmic reticulum stress (ERS)-initiated activation of the unfolded protein response (UPR), the ensuing chronic low-grade inflammation, and altered insulin signaling in promoting obesity-compromised cardiovascular system (CVS). In this aspect, potential ways of attenuating ERS-initiated UPR signaling seem a promising avenue for therapeutic interventions. We review intersecting role of obesity-induced ERS, chronic inflammation, insulin resistance, and oxidative stress in the discovery of targeted therapy. Moreover, this review highlights the current progress and strategies on therapeutics being explored in preclinical and clinical research to modulate ERS and UPR signaling.

Exosomes from mesenchymal stem cells modulate endoplasmic reticulum stress to protect against nucleus pulposus cell death and ameliorate intervertebral disc degeneration in vivo

Objectives: Intervertebral disc degeneration (IDD) is widely accepted as a cause of low back pain and related degenerative musculoskeletal disorders. Nucleus pulposus (NP) cell apoptosis which is related to excessive endoplasmic reticulum (ER) stress in the intervertebral disc (IVD) could aggravate IDD progression. Many studies have shown the therapeutic potential of exosomes derived from bone marrow mesenchymal stem cells (MSC-exos) in degenerative diseases. We hypothesized that the delivery of MSC-exos could modulate ER stress and inhibit excessive NP cell apoptosis during IDD.

Methods: The ER stress levels were measured in normal or degenerative NP tissues for contrast. The effects of MSC-exos were testified in advanced glycation end products (AGEs) -induced ER stress in human NP cells. The mechanism involving AKT and ERK signaling pathways was investigated using RNA interference or signaling inhibitors. Histological or immunohistochemical analysis and TUNEL staining were used for evaluating MSC-exos therapeutic effects in vivo.

Results: The ER stress level and apoptotic rate was elevated in degenerative IVD tissues. MSC-exos could attenuate ER stress-induced apoptosis by activating AKT and ERK signaling. Moreover, delivery of MSC-exos in vivo modulated ER stress-related apoptosis and retarded IDD progression in a rat tail model.

Conclusions: These results highlight the therapeutic effects of exosomes in preventing IDD progression. Our work is the first to demonstrate that MSC-exos could modulate ER stress-induced apoptosis during AGEs-associated IVD degeneration.

Stressed: The Unfolded Protein Response in T Cell Development, Activation, and Function

The unfolded protein response (UPR) is a highly conserved pathway that allows cells to respond to stress in the endoplasmic reticulum caused by an accumulation of misfolded and unfolded protein. This is of great importance to secretory cells because, in order for proteins to traffic from the endoplasmic reticulum (ER), they need to be folded appropriately. While a wealth of literature has implicated UPR in immune responses, less attention has been given to the role of UPR in T cell development and function. This review discusses the importance of UPR in T cell development, homeostasis, activation, and effector functions. We also speculate about how UPR may be manipulated in T cells to ameliorate pathologies.

Liver proteomics unravel the metabolic pathways related to Feed Efficiency in beef cattle

Improving nutrient utilization efficiency is essential for livestock, given the current scenario of increasing demand for animal protein and sustainable resource use. In this context, understanding the biology of feed efficiency (FE) in beef cattle allows the development of markers for identification and selection of best animals for animal production. Thus, 98 young Nellore bulls were evaluated for FE and at the end of the experiment liver samples from six High Feed Efficient (HFE) and six Low Feed Efficient (LFE) animals were collected for protein extraction, digestion and analysis by HPLC-MS/MS. Data were analyzed for differential abundant proteins (DAPs), protein networks, and functional enrichment. Serum endotoxin was also quantified. We found 42 DAPs and 3 protein networks significantly related to FE. The main pathways associated with FE were: microbial metabolism; biosynthesis of fatty acids, amino acids and vitamins; glycolysis/gluconeogenesis; xenobiotic metabolism and; antigen processing and presentation. Serum endotoxins were significantly higher in LFE animals supporting the results. Therefore, the findings presented here confirmed the altered hepatic metabolism and pronounced hepatic inflammation in LFE animals supporting that the increased bacterial load is at least in part responsible for the hepatic lesions and inflammation in LFE animals.

Endoplasmic reticulum protein 29 (ERp29) as a novel prognostic marker and tumor suppressor in osteosarcoma

Background

Diverse aberrancy in genetic background, protein profiling, and biological pathways have emerged as important factors hindering discovery of effective treatment of osteosarcoma. In a previous study, we used a proteomic approach to identify some osteosarcoma-related proteins by analysis of protein profiling in individual patients through primary cell culture. Endoplasmic reticulum protein 29 (ERp29) emerged as a protein of interest for further study since accumulating evidence suggests it has broad functions in tumorigenesis of different types of cancer. Importantly, until now no report on examination of the expression patterns of ERp29 in osteosarcoma has been published.

Methods

In this study, an expression of ERp29 was examined in patient-derived osteosarcoma cells (7 cases) and normal bone graft-derived osteoblasts (7 cases) using western blotting. Expression profile of ERp29 in 94 osteosarcoma cases was investigated using immunohistochemically stained on formalin-fixed paraffin-embedded biopsied tissue. An association with clinicopathologic parameters and the patient survival was evaluated. The doubling time of five osteosarcoma cells lines expressing different levels of ERp29 was determined by a cell number along the exponential phase of the growth curve.

Results

The results substantiate the outcome from the proteomic study in which ERp29 expression was significantly higher in primary osteosarcoma cells compared to osteoblastic cells. Immunohistochemical analysis found that expression of ERp29 was low in 79% of the cases (immunoreactive score (IRS) <6). A significant correlation was observed between expression of ERp29 and patient survival. Lower expression of ERp29 (IRS<6) was statistically significantly associated with shorter overall survival of the patients (P = 0.041). In addition, we found that osteosarcoma cells with low ERp29 expression had a higher growth rate compared with high-ERp29-expressing cells.

Conclusions

These findings suggest a tumor suppressive role of ERp29 in osteosarcoma. In addition, ERp29 might potentially be applied as a prognostic indicator in patients with osteosarcoma.

Interactions Between Autophagy and the Unfolded Protein Response: Implications for Inflammatory Bowel Disease

Inflammatory bowel disease (IBD), which includes Crohn's disease (CD) and ulcerative colitis, is characterized by chronic inflammation of the gastrointestinal tract. The etiology involves a combination of genetic and environmental factors resulting in abnormal immune responses to intestinal microbiota. Genetic studies have strongly linked genes involved in autophagy to CD, and genes involved in the unfolded protein response (UPR) to IBD. The UPR is triggered in response to accumulation of misfolded proteins in the endoplasmic reticulum (ER), and autophagy plays a key role in relieving ER stress and restoring homeostasis. This review summarizes the known interactions between autophagy and the UPR and discusses the impact of these converging pathways on IBD pathogenesis. With a paucity of effective long-term treatments for IBD, targeting of synergistic pathways may provide novel and more effective therapeutic options.

Role of Endoplasmic Reticulum Stress in the Anticancer Activity of Natural Compounds

Cancer represents a serious global health problem, and its incidence and mortality are rapidly growing worldwide. One of the main causes of the failure of an anticancer treatment is the development of drug resistance by cancer cells. Therefore, it is necessary to develop new drugs characterized by better pharmacological and toxicological profiles. Natural compounds can represent an optimal collection of bioactive molecules. Many natural compounds have been proven to possess anticancer effects in different types of tumors, but often the molecular mechanisms associated with their cytotoxicity are not completely understood. The endoplasmic reticulum (ER) is an organelle involved in multiple cellular processes. Alteration of ER homeostasis and its appropriate functioning originates a cascade of signaling events known as ER stress response or unfolded protein response (UPR). The UPR pathways involve three different sensors (protein kinase RNA(PKR)-like ER kinase (PERK), inositol requiring enzyme1α (IRE1) and activating transcription factor 6 (ATF6)) residing on the ER membranes. Although the main purpose of UPR is to restore this organelle's homeostasis, a persistent UPR can trigger cell death pathways such as apoptosis. There is a growing body of evidence showing that ER stress may play a role in the cytotoxicity of many natural compounds. In this review we present an overview of different plant-derived natural compounds, such as curcumin, resveratrol, green tea polyphenols, tocotrienols, and garcinia derivates, that exert their anticancer activity via ER stress modulation in different human cancers.

ERp29 counteracts the suppression of malignancy mediated by endoplasmic reticulum stress and promotes the metastasis of colorectal cancer

Endoplasmic reticulum protein 29 (ERp29), an endoplasmic reticulum (ER) protein, participates in ER stress (ERS), but little is known about the association of ERp29 with ERS in the metastasis and prognosis of cancerous diseases. The present study revealed that ERp29 was important to ERS and interfered with the malignant behaviors of colorectal cancer (CRC). Experiments in in vitro and in animal models revealed that ERS inhibited the cell growth and suppressed the metastatic capacity of CRC cells, but ERp29 counteracted these effects. Furthermore, it was demonstrated that ERp29 recovered the migration and metastatic behaviors of CRC cells suppressed by ERS, mediated only when it combined with cullin5 (CUL5). ERp29 also relied on CUL5 to promote epithelial-mesenchymal transition. From the immunohistochemical examination of CRC tissues, the high expression of ERp29 was revealed to predict the poor prognosis of 457 CRC cases. The retrospective analysis of the clinicopathological data of patients with CRC was consistent with the results of the in vitro and in vivo experiments. Thus, ERp29 protected CRC cells from ERS-mediated reduction of malignancy to promote metastasis and may be a potential target of medical intervention for CRC therapy.

Mechanisms of disordered neurodegenerative function: concepts and facts about the different roles of the protein kinase RNA-like endoplasmic reticulum kinase (PERK)

Neurodegenerative diseases, such as Alzheimer's disease, Huntington's disease, Parkinson's disease, prion disease, and amyotrophic lateral sclerosis, are a dissimilar group of disorders that share a hallmark feature of accumulation of abnormal intraneuronal or extraneuronal misfolded/unfolded protein and are classified as protein misfolding disorders. Cellular and endoplasmic reticulum (ER) stress activates multiple signaling cascades of the unfolded protein response (UPR). Consequently, translational and transcriptional alterations in target gene expression occur in response directed toward restoring the ER capacity of proteostasis and reestablishing the cellular homeostasis. Evidences from in vitro and in vivo disease models indicate that disruption of ER homeostasis causes abnormal protein aggregation that leads to synaptic and neuronal dysfunction. However, the exact mechanism by which it contributes to disease progression and pathophysiological changes remains vague. Downstream signaling pathways of UPR are fully integrated, yet with diverse unexpected outcomes in different disease models. Three well-identified ER stress sensors have been implicated in UPR, namely, inositol requiring enzyme 1, protein kinase RNA-activated-like ER kinase (PERK), and activating transcription factor 6. Although it cannot be denied that each of the involved stress sensor initiates a distinct downstream signaling pathway, it becomes increasingly clear that shared pathways are crucial in determining whether or not the UPR will guide the cells toward adaptive prosurvival or proapoptotic responses. We review a body of work on the mechanism of neurodegenerative diseases based on oxidative stress and cell death pathways with emphasis on the role of PERK.

Apelin-13 Alleviates Early Brain Injury after Subarachnoid Hemorrhage via Suppression of Endoplasmic Reticulum Stress-mediated Apoptosis and Blood-Brain Barrier Disruption: Possible Involvement of ATF6/CHOP Pathway

Neuronal apoptosis plays important roles in the early brain injury after subarachnoid hemorrhage (SAH). This study first showed that inhibition of activating transcription factor 6 (ATF6) by apelin-13 could reduce endoplasmic reticulum (ER)-stress-mediated apoptosis and blood-brain-barrier (BBB) disruption after SAH. We chose apelin-13, ATF6 and CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP) siRNAs to verify the hypothesis. Brain water content, neurological behavior and Evans Blue (EB) were assessed at 24 h after SAH. Western blot analysis and reverse transcription-polymerase chain reaction (RT-PCR) were applied to evaluate the expression of targets in both protein and mRNA levels. Neuronal apoptosis was assessed with Terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) and caspase-3 staining. The results showed that the levels of ATF6, and its downstream protein, CHOP were upregulated and reached the peak at 24 h after SAH. ATF6 was highly expressed in neurons. The administration of apelin-13 could significantly reduce the mRNA and protein levels of ATF6, and its downstream targets, CHOP and caspase-3, but increase the Bcl-2/Bax ratio, Claudin-5, Occludin and ZO-1. What's more, the administration of apelin-13 could reduce brain edema, ameliorate BBB disruption and improve neurological functions. However, the CHOP siRNA could significantly reverse the pro-apoptotic effect induced by the increased ATF6 level after SAH. Apelin-13 could exert its neuroprotective effects via suppression of ATF6/CHOP arm of ER-stress-response pathway in the early brain injury after SAH.

IRE1α deficiency promotes tumor cell death and eIF2α degradation through PERK dipendent autophagy

Sensors of endoplasmic reticulum (ER) stress function in a co-ordinated manner. In the present study we investigated the relationship between IRE1α and PERK pathways and survival of ER stressed U937 cells and BC3 cells. To this end, we investigated the effects of a subcytotoxic concentration of Tunicamycin in IRE1α-proficient and in IRE1α-deficient cells, by pharmacological inhibition with 4μ8 C or down-regulation by specific siRNA. We show that either type of IRE1α deficiency affects eIF2α expression and causes cell death increase. GSK2606414, a PERK inhibitor, and PERK specific siRNA prevent eIF2α down-regulation and restore cell survival. Degradation of this protein is due to autophagy, as it is prevented by bafilomycin and not by proteasome inhibition. Furthermore, activation of the autophagy flux is PERK dependent. Also the Cathepsin B inhibitor CA074 prevents eIF2α from degradation and reduces cell death. Altogether, these results show that IRE1α deficiency in ER stressed cells leads to an unexpected decrease of eIF2α, an important molecule for protein translation, through PERK dependent autophagy. Thus, IRE1/XBP1 inhibitors may represent a feasible strategy for tumor therapy, while PERK inhibitors may vanish the goal.

Molecular Chaperone ERp29: A Potential Target for Cellular Protection in Retinal and Neurodegenerative Diseases

The molecular chaperone endoplasmic reticulum protein 29 (ERp29) plays a critical role in protein folding, trafficking, and secretion. Though ubiquitously expressed, ERp29 is upregulated in response to ER stress and is found at higher levels in certain cell types such as secretory epithelial cells and neurons. As an ER resident protein, ERp29 shares many structural and functional similarities with protein disulfide isomerases, but is not regarded as part of this family due to several key differences. The broad expression and myriad roles of ERp29 coupled with its upregulation via the unfolded protein response (UPR) upon ER stress have implicated ERp29 in a range of cellular processes and diseases. We summarize the diverse activities of ERp29 in protein trafficking, cell survival and apoptosis, and ER homeostasis and highlight a potential role of ERp29 in neuroprotection in retinal and neurodegenerative diseases.

Crosstalk of ER stress-mediated autophagy and ER-phagy: Involvement of UPR and the core autophagy machinery

Endoplasmic reticulum (ER) stress, a common cellular stress response, is closely related to the activation of autophagy that is an important and evolutionarily conserved mechanism for maintaining cellular homeostasis. Autophagy induced by ER stress mainly includes the ER stress-mediated autophagy and ER-phagy. The ER stress-mediated autophagy is characterized by the generation of autophagosomes that include worn-out proteins, protein aggregates, and damaged organelles. While the autophagosomes of ER-phagy selectively include ER membranes, and the double membranes also derive, at least in part, from the ER. The signaling pathways of IRE1α, PERK, ATF6, and Ca²⁺ are necessary for the activation of ER stress-mediated autophagy, while the receptor-mediated selective ER-phagy degrades the ER is Atg40/FAM134B. The ER stress-mediated autophagy and ER-phagy not only have differences, but also have connections. The activation of ER-phagy requires the core autophagy machinery, and the ER-phagy may be a branch of ER stress-mediated autophagy that selectively targets the ER. However, the determined factors that control the changeover switch between ER stress-mediated autophagy and ER-phagy are largely obscure, which may be associated with the type of cells and the extent of stimulation. This review summarized the crosstalk between ER stress-mediated autophagy and ER-phagy and their signaling networks. Additionally, we discussed the possible factors that influence the type of autophagy induced by ER stress.

A review of endoplasmic reticulum (ER) stress and nanoparticle (NP) exposure

Understanding the mechanism of nanoparticle (NP) induced toxicity is important for nanotoxicological and nanomedicinal studies. Endoplasmic reticulum (ER) is a crucial organelle involved in proper protein folding. High levels of misfolded proteins in the ER could lead to a condition termed as ER stress, which may ultimately influence the fate of cells and development of human diseases. In this review, we summarized studies about effects of NP exposure on ER stress. A variety of NPs, especially metal-based NPs, could induce morphological changes of ER and activate ER stress pathway both in vivo and in vitro. In addition, modulation of ER stress by chemicals has been shown to alter the toxicity of NPs. These studies in combination suggested that ER stress could be the mechanism responsible for NP induced toxicity. Meanwhile, nanomedicinal studies also used ER stress inducing NPs or NPs loaded with ER stress inducer to selectively induce ER stress mediated apoptosis in cancer cells for cancer therapy. In contrast, alleviation of ER stress by NPs has also been shown as a strategy to cure metabolic diseases. In conclusion, exposure to NPs may modulate ER stress, which could be a target for future nanotoxicological and nanomedicinal studies.

Molecular signal networks and regulating mechanisms of the unfolded protein response

Within the cell, several mechanisms exist to maintain homeostasis of the endoplasmic reticulum (ER). One of the primary mechanisms is the unfolded protein response (UPR). In this review, we primarily focus on the latest signal webs and regulation mechanisms of the UPR. The relationships among ER stress, apoptosis, and cancer are also discussed. Under the normal state, binding immunoglobulin protein (BiP) interacts with the three sensors (protein kinase RNA-like ER kinase (PERK), activating transcription factor 6 (ATF6), and inositol-requiring enzyme 1α (IRE1α)). Under ER stress, misfolded proteins interact with BiP, resulting in the release of BiP from the sensors. Subsequently, the three sensors dimerize and autophosphorylate to promote the signal cascades of ER stress. ER stress includes a series of positive and negative feedback signals, such as those regulating the stabilization of the sensors/BiP complex, activating and inactivating the sensors by autophosphorylation and dephosphorylation, activating specific transcription factors to enable selective transcription, and augmenting the ability to refold and export. Apart from the three basic pathways, vascular endothelial growth factor (VEGF)-VEGF receptor (VEGFR)-phospholipase C-γ (PLCγ)-mammalian target of rapamycin complex 1 (mTORC1) pathway, induced only in solid tumors, can also activate ATF6 and PERK signal cascades, and IRE1α also can be activated by activated RAC-alpha serine/threonine-protein kinase (AKT). A moderate UPR functions as a pro-survival signal to return the cell to its state of homeostasis. However, persistent ER stress will induce cells to undergo apoptosis in response to increasing reactive oxygen species (ROS), Ca²⁺ in the cytoplasmic matrix, and other apoptosis signal cascades, such as c-Jun N-terminal kinase (JNK), signal transducer and activator of transcription 3 (STAT3), and P38, when cellular damage exceeds the capacity of this adaptive response.

The impact of growth hormone on proteomic profiles: a review of mouse and adult human studies

Growth hormone (GH) is a protein that is known to stimulate postnatal growth, counter regulate insulin's action and induce expression of insulin-like growth factor-1. GH exerts anabolic or catabolic effects depending upon on the targeted tissue. For instance, GH increases skeletal muscle and decreases adipose tissue mass. Our laboratory has spent the past two decades studying these effects, including the effects of GH excess and depletion, on the proteome of several mouse and human tissues. This review first discusses proteomic techniques that are commonly used for these types of studies. We then examine the proteomic differences found in mice with excess circulating GH (bGH mice) or mice with disruption of the GH receptor gene (GHR^-/-). We also describe the effects of increased and decreased GH action on the proteome of adult patients with either acromegaly, GH deficiency or patients after short-term GH treatment. Finally, we explain how these proteomic studies resulted in the discovery of potential biomarkers for GH action, particularly those related with the effects of GH on aging, glucose metabolism and body composition.

Endoplasmic Reticulum (ER) Stress and Endocrine Disorders

The endoplasmic reticulum (ER) is the organelle where secretory and membrane proteins are synthesized and folded. Unfolded proteins that are retained within the ER can cause ER stress. Eukaryotic cells have a defense system called the “unfolded protein response” (UPR), which protects cells from ER stress. Cells undergo apoptosis when ER stress exceeds the capacity of the UPR, which has been revealed to cause human diseases. Although neurodegenerative diseases are well-known ER stress-related diseases, it has been discovered that endocrine diseases are also related to ER stress. In this review, we focus on ER stress-related human endocrine disorders. In addition to diabetes mellitus, which is well characterized, several relatively rare genetic disorders such as familial neurohypophyseal diabetes insipidus (FNDI), Wolfram syndrome, and isolated growth hormone deficiency type II (IGHD2) are discussed in this article.

Agglutinin isolated from Arisema heterophyllum Blume induces apoptosis and autophagy in A549 cells through inhibiting PI3K/Akt pathway and inducing ER stress

Arisaema heterophyllum Blume is one of the three medicinal plants known as traditional Chinese medicine Rhizoma Arisaematis (RA). RA has been popularly used to treat patients with convulsions, inflammation, and cancer for a long time. However, the underlying mechanisms for RA effects are still unclear. The present study was designed to determine the cytotoxicity of agglutinin isolated from Arisema heterophyllum Blume (AHA) and explore the possible mechanisms in human non-small-cell lung cancer A549 cells. AHA with purity up to 95% was isolated and purified from Arisaema heterophyllum Blume using hydrophobic interaction chromatography. AHA dose-dependently inhibited the proliferation of A549 cells and induced G₁ phase cell cycle arrest. AHA induced apoptosis by up-regulating pro-apoptotic Bax, decreasing anti-apoptotic Bcl-2, and activating caspase-9 and caspase-3. In A549 cells treated with AHA, the PI3K/Akt pathway was inhibited. Furthermore, AHA induced increase in the levels of ER stress markers such as phosphorylated eukaryotic initiation factor 2α (p-eIF2α), C/EBP-homologous protein (CHOP), inositol-requiring enzyme 1α (IRE1α), and phosphorylated c-Jun NH₂-terminal kinase (p-JNK). AHA also induced autophagy in A549 cells. Staining of acidic vesicular organelles (AVOs) and increase in the levels of LC3II and ATG7 were observed in AHA-treated cells. These findings suggested that AHA might be one of the active components with anti-cancer effects in Arisaema heterophyllum Blume. In conclusion, cytotoxicity of AHA on cancer cells might be related to its effects on apoptosis and autophagy through inhibition of PI3K/Akt pathway and induction of ER stress.

ALS-linked protein disulfide isomerase variants cause motor dysfunction

Disturbance of endoplasmic reticulum (ER) proteostasis is a common feature of amyotrophic lateral sclerosis (ALS). Protein disulfide isomerases (PDIs) areERfoldases identified as possibleALSbiomarkers, as well as neuroprotective factors. However, no functional studies have addressed their impact on the disease process. Here, we functionally characterized fourALS-linked mutations recently identified in two majorPDIgenes,PDIA1 andPDIA3/ERp57. Phenotypic screening in zebrafish revealed that the expression of thesePDIvariants induce motor defects associated with a disruption of motoneuron connectivity. Similarly, the expression of mutantPDIs impaired dendritic outgrowth in motoneuron cell culture models. Cellular and biochemical studies identified distinct molecular defects underlying the pathogenicity of thesePDImutants. Finally, targetingERp57 in the nervous system led to severe motor dysfunction in mice associated with a loss of neuromuscular synapses. This study identifiesERproteostasis imbalance as a risk factor forALS, driving initial stages of the disease.

Asymmetric dimethylarginine (ADMA) treatment induces apoptosis in cultured rat mesangial cells via endoplasmic reticulum stress activation

Asymmetric dimethylarginine (ADMA), a high risk factor for endothelial dysfunction and cardiovascular disease (CVD), has been reported to promote cellular dysfunction via endoplasmic reticulum (ER) stress activation in various cells. Additionally, increased serum ADMA levels have been observed in incipient kidney diseases. Previously, we reported that activated ER stress is associated with mesangial cell apoptosis, observed mainly in overt nephropathy or chronic kidney disease (CKD). However, the effect of ADMA on mesangial cell apoptosis is unknown. Thus, we investigated the effects of ADMA on mesangial cell apoptosis and ER stress signaling. ADMA treatment increased caspase-3 activity and activated three branches of ER stress signaling (PERK, IRE1, and ATF6) that induce mesangial cell apoptosis. Pharmacological inhibitors of ER stress (inhibitors of PERK, IRE1, and S1P) attenuated ADMA-induced cleavage of caspase-3 and induced a decrease in the mitochondrial membrane potential. Furthermore, these inhibitors diminished the number of apoptotic cells induced by ADMA treatment. Taken together, our results indicated that ADMA treatment induces mesangial cell apoptosis via ER stress signaling. These results suggest that ADMA-induced mesangial cell apoptosis could contribute to the progression of overt nephropathy and CKD.

Erp29 Attenuates Cigarette Smoke Extract-Induced Endoplasmic Reticulum Stress and Mitigates Tight Junction Damage in Retinal Pigment Epithelial Cells

PURPOSE

Endoplasmic reticulum protein 29 (ERp29) is a novel chaperone that was recently found decreased in human retinas with AMD. Herein, we examined the effect of ERp29 on cigarette smoke-induced RPE apoptosis and tight junction disruption.

METHODS

Cultured human RPE (HRPE) cells (ARPE-19) or mouse RPE eyecup explants were exposed to cigarette smoke extract (CSE) for short (up to 24 hours) or long (up to 3 weeks) periods. Expression of ERp29 was up- and downregulated by adenovirus and siRNA, respectively. Endoplasmic reticulum stress markers, apoptosis, and cell death, the expression and distribution of tight junction protein ZO-1, transepithelial electrical resistance (TEER), and F-actin expression were examined.

RESULTS

Endoplasmic reticulum protein 29 was significantly increased by short-term exposure to CSE in ARPE-19 cells or eyecup explants but was reduced after 3-week exposure. Overexpression of ERp29 increased the levels of GRP78, p58(IPK), and Nrf-2, while reducing p-eIF2α and C/EBP homologous protein (CHOP), and protected RPE cells from CSE-induced apoptosis. In contrast, knockdown of ERp29 decreased the levels of p58(IPK) and Nrf2, but increased p-eIF2α and CHOP and exacerbated CSE-triggered cell death. In addition, overexpression of ERp29 attenuated CSE-induced reduction in ZO-1 and enhanced the RPE barrier function, as measured by TEER. Knockdown of ERp29 decreased the level of ZO-1 protein. These effects were associated with changes in the expression of cytoskeleton F-actin.

CONCLUSIONS

Endoplasmic reticulum protein 29 attenuates CSE-induced ER stress and enhances cell viability and barrier integrity of RPE cells, and therefore may act as a protective mechanism for RPE survival and activity.

Changes of TRB3 and CHOP expression in nonalcoholic fatty liver disease in rats

AIM: To investigate the changes of Tribbles related protein 3 (TRB3) and CCAAT/enhancer-binding protein homologous protein (CHOP) expression in nonalcoholic fatty liver disease (NAFLD) in rats.

METHODS: Thirty Wistar rats were randomly divided into a normal control group and an NAFLD group. The rats of the NAFLD group were given a high-fat, high-glucose diet for 16 weeks to induce NAFLD, while the normal control group was given an ordinary diet. The levels of total cholesterol (TC), triglyceride (TG), low-density lipoprotein (LDL) and high-density lipoprotein (HDL) were detected with an automatic biochemical analyzer. The expression of TRB3 and CHOP mRNAs in the liver was detected by real-time quantitative PCR. The expression of TRB3 and CHOP proteins in liver tissue was detected by immunohistochemistry. Cell apoptosis was detected by flow cytometry.

RESULTS: The levels of TC, TG, and LDL in the NAFLD group were significantly higher than those in the normal control group (P < 0.05), while the level of HDL was lower than that in the normal control group (P < 0.05). Compared with the normal group, levels of TRB3 and CHOP mRNAs and proteins in the NAFLD group were significantly increased (mRNA: P < 0.05 or P < 0.01; protein: P < 0.01). Flow cytometry analysis showed that the apoptosis in the NAFLD group was higher than that in the normal control group.

CONCLUSION: The changes of TRB3 and CHOP expression may play important roles in the development of NAFLD.

Functional Role of the Disulfide Isomerase ERp57 in Axonal Regeneration

ERp57 (also known as grp58 and PDIA3) is a protein disulfide isomerase that catalyzes disulfide bonds formation of glycoproteins as part of the calnexin and calreticulin cycle. ERp57 is markedly upregulated in most common neurodegenerative diseases downstream of the endoplasmic reticulum (ER) stress response. Despite accumulating correlative evidence supporting a neuroprotective role of ERp57, the contribution of this foldase to the physiology of the nervous system remains unknown. Here we developed a transgenic mouse model that overexpresses ERp57 in the nervous system under the control of the prion promoter. We analyzed the susceptibility of ERp57 transgenic mice to undergo neurodegeneration. Unexpectedly, ERp57 overexpression did not affect dopaminergic neuron loss and striatal denervation after injection of a Parkinson’s disease-inducing neurotoxin. In sharp contrast, ERp57 transgenic animals presented enhanced locomotor recovery after mechanical injury to the sciatic nerve. These protective effects were associated with enhanced myelin removal, macrophage infiltration and axonal regeneration. Our results suggest that ERp57 specifically contributes to peripheral nerve regeneration, whereas its activity is dispensable for the survival of a specific neuronal population of the central nervous system. These results demonstrate for the first time a functional role of a component of the ER proteostasis network in peripheral nerve regeneration.

Protein kinase R-like ER kinase and its role in endoplasmic reticulum stress-decided cell fate

Over the past few decades, understandings and evidences concerning the role of endoplasmic reticulum (ER) stress in deciding the cell fate have been constantly growing. Generally, during ER stress, the signal transductions are mainly conducted by three ER stress transducers: protein kinase R-like endoplasmic reticulum kinase (PERK), inositol-requiring kinase 1 (IRE1) and activating transcription factor 6 (ATF6). Consequently, the harmful stimuli from the ER stress transducers induce apoptosis and autophagy, which share several crosstalks and eventually decide the cell fate. The dominance of apoptosis or autophagy induced by ER stress depends on the type and degree of the stimuli. When ER stress is too severe and prolonged, apoptosis is induced to eliminate the damaged cells; however, when stimuli are mild, cell survival is promoted to maintain normal physiological functions by inducing autophagy. Although all the three pathways participate in ER stress-induced apoptosis and autophagy, PERK shows several unique characteristics by interacting with some specific downstream effectors. Notably, there are some preliminary findings on PERK-dependent mechanisms switching autophagy and apoptosis. In this review, we particularly focused on the novel, intriguing and complicated role of PERK in ER stress-decided cell fate, and also discussed more roles of PERK in restoring cellular homeostasis. However, more in-depth knowledge of PERK in the future would facilitate our understanding about many human diseases and benefit in searching for new molecular therapeutic targets.

Friend or foe: Endoplasmic reticulum protein 29 (ERp29) in epithelial cancer

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ERp29 regulates epithelial cell plasticity and the mesenchymal–epithelial transition.

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ERp29 shows a tumor suppressive function in primary tumor development.

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ERp29 is potentially associated with distant metastasis in cancer.

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ERp29 modulates cell survival against genotoxic stress.

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Thus, ERp29 displays dual functions as a “friend or foe” in epithelial cancer.

The endoplasmic reticulum (ER) protein 29 (ERp29) is a molecular chaperone that plays a critical role in protein secretion from the ER in eukaryotic cells. Recent studies have also shown that ERp29 plays a role in cancer. It has been demonstrated that ERp29 is inversely associated with primary tumor development and functions as a tumor suppressor by inducing cell growth arrest in breast cancer. However, ERp29 has also been reported to promote epithelial cell morphogenesis, cell survival against genotoxic stress and distant metastasis. In this review, we summarize the current understanding on the biological and pathological functions of ERp29 in cancer and discuss the pivotal aspects of ERp29 as “friend or foe” in epithelial cancer.