Hallmark Of Endoplasmic Reticulum Stress Research Articles

Exploring Endocannabinoid System: Unveiling New Roles in Modulating ER Stress

The endoplasmic reticulum (ER) is the organelle mainly involved in maintaining cellular homeostasis and driving correct protein folding. ER-dependent defects or dysfunctions are associated with the genesis/progression of several pathological conditions, including cancer, inflammation, and neurodegenerative disorders, that are directly or indirectly correlated to a wide set of events collectively named under the term “ER stress”. Despite the recent increase in interest concerning ER activity, further research studies are needed to highlight all the mechanisms responsible for ER failure. In this field, recent discoveries paved the way for the comprehension of the strong interaction between ER stress development and the endocannabinoid system. The activity of the endocannabinoid system is mediated by the activation of cannabinoid receptors (CB), G protein-coupled receptors that induce a decrease in cAMP levels, with downstream anti-inflammatory effects. CB activation drives, in most cases, the recovery of ER homeostasis through the regulation of ER stress hallmarks PERK, ATF6, and IRE1. In this review, we focus on the CB role in modulating ER stress, with particular attention to the cellular processes leading to UPR activation and oxidative stress response extinguishment, and to the mechanisms underlying natural cannabinoids’ modulation of this complex cellular machine.

Sphingosine-1-Phosphate Inhibition Increases Endoplasmic Reticulum Stress to Enhance Oxaliplatin Sensitivity in Pancreatic Cancer.

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive cancer resistant to current therapies, including oxaliplatin (Oxa). Growing evidence supports the ability of cancers to harness sphingolipid metabolism for survival. Sphingosine-1-phosphate (S1P) is an anti-apoptotic, pro-survival mediator that can influence cellular functions such as endoplasmic reticulum (ER) stress. We hypothesize that PDAC drives dysregulated sphingolipid metabolism and that S1P inhibition can enhance ER stress to improve therapeutic response to Oxa in PDAC. RNA sequencing data of sphingolipid mediators from The Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression Project (GTEx) datasets were analyzed. Murine and human PDAC cell lines were treated with small interfering RNA (siRNA) against sphingosine kinase-2 (SPHK2) or ABC294640 (ABC) and incubated with combinations of vehicle control or Oxa. In an orthotopic syngeneic KPC PDAC model, tumors were treated with either vehicle control, Oxa, ABC, or combination therapy. RNA sequencing analysis revealed multiple significantly differentially expressed sphingolipid mediators (P < 0.05). In vitro, both siRNA knockdown of SPHK2 and ABC sensitized cells to Oxa therapy (P < 0.05), and induced eukaryotic initiation factor 2α (eIF2α) and protein kinase RNA-like endoplasmic reticulum kinase (PERK) phosphorylation, hallmarks of ER stress. In vitro therapy also increased extracellular high mobility group box 1 (HMGB1) release (P < 0.05), necessary for immunogenic cell death (ICD). In vivo combination therapy increased apoptotic markers as well as the intensity of HMGB1 staining compared to control (P < 0.05). Our evidence suggests that sphingolipid metabolism is dysregulated in PDAC. Furthermore, S1P inhibition can sensitize PDAC to Oxa therapy through increasing ER stress and can potentiate ICD induction. This highlights a potential therapeutic target for chemosensitizing PDAC as well as an adjunct for future chemoimmunotherapy strategies.

Endoplasmic reticulum stress mediates environmental particle-induced inflammatory response in bronchial epithelium

While the detailed mechanisms for how particulate matter (PM) causes adverse health effects in the lungs remain largely unknown, endoplasmic reticulum (ER) stress has been implicated in PM-induced lung injury. The present study was undertaken to examine how/if ER stress might regulate PM-induced inflammation, and to begin to define potential underlying molecular mechanisms. Here, ER stress hallmarks were examined in human bronchial epithelial (HBE) cells exposed to PM. To confirm roles of certain pathways, siRNA targeting ER stress genes and an ER stress inhibitor were employed. Expression of select inflammatory cytokines and related signaling pathway components by the cells were assessed as well. The results showed that PM exposure induced elevations in two ER stress hallmarks, i.e. GRP78 and IRE1α, in time-and/or dose-related manners in the HBE cells. Inhibition of ER stress by siRNA for GRP78 or IRE1α significantly alleviated the PM-induced effects. Further, ER stress appeared to regulate PM-induced inflammation – likely through downstream autophagy and NF-κB pathways – as implied by studies showing that inhibition of ER stress by siRNA of GRP78 or IRE1α caused significant amelioration of PM-induced autophagy and subsequent activation of NF-κB pathways. Moreover, the ER stress inhibitor 4-PBA were used to confirm the protective effects against PM-induced outcomes. Together, the results suggest ER stress plays a deleterious role in PM-induced airway inflammation, possibly through activation of autophagy and NF-κB signaling. Accordingly, protocols/treatments that could lead to inhibited ER stress could potentially be effective for treatment of PM-related airway disorders.

Trehalose Attenuates Oxidative Stress and Endoplasmic Reticulum Stress-Mediated Apoptosis in IPEC-J2 Cells Subjected to Heat Stress.

Simple SummaryAs global warming continues, the increased frequency and intensity of high ambient temperatures imposes heat stress (HS) on farm animals and human beings. Pigs are susceptible to heat exposure; decreased performance and increased morbidity due to HS give rise to economic losses for the swine industry. HS induces oxidative stress and apoptosis, both of which are associated with compromised intestinal barrier integrity. Trehalose (Tre) is a natural disaccharide that is considered a health-promoting food owing to its antioxidant and anti-inflammatory effects and its molecular chaperone ability to inhibit protein denaturation. The present study aimed to determine the optimum trehalose level for alleviating HS-induced intestinal porcine epithelial cell (IPEC-J2) insults and to uncover the molecular mechanism of the protective effects of Tre. This study demonstrated that 10 mM trehalose can significantly attenuate HS-induced IPEC-J2 cell impairment and that the mechanism is related to trehalose alleviating oxidative stress and endoplasmic reticulum stress-mediated apoptosis.This study was carried out to investigate the effects of trehalose (Tre) on antioxidant capacity, endoplasmic reticulum stress (ERS) response and apoptosis of heat-stressed intestinal porcine epithelial cells (IPEC-J2). IPEC-J2 cells were cultured at 37 °C until the end of the experiment (control, CON); exposed to heat stress for 2 h (43 °C, HS); or pretreated with 0.1, 1, 5, 10, and 15 mM trehalose at 37 °C for 4 h prior to heat stress exposure for 2 h. The optimum level of trehalose for protecting against HS-induced cell injuries was determined to be 10 mM, as evidenced by the highest cellular viability and lowest malondialdehyde (MDA) content and lactate dehydrogenase (LDH) activity. Based on these, IPEC-J2 cells were divided into three groups: the first group was cultured at 37 °C until the end of the experiment (control, CON); the second group was exposed to heat stress for 2 h (43 °C, HS); the third group was pretreated with 10 mM trehalose for 4 h at 37 °C prior to heat stress exposure for 2 h (Tre + HS). The reactive oxygen species (ROS) content, superoxide dismutase (SOD) activity, mitochondrial membrane potential (MMP) changes, and expressions of the manganese superoxide dismutase (SOD2), ERS and apoptosis-related proteins were determined. Compared to the CON group, HS significantly increased ROS generation (p < 0.01), decreased SOD activity (p < 0.05), and downregulated protein expression of SOD2 (p < 0.01). Compared to the HS group, Tre supplementation reduced ROS levels and increased SOD activity and SOD2 expression to the levels that were comparable to the control (p < 0.05). The HS-induced ERS response was evidenced by the increased protein expressions of glucose-regulated protein 78 (GRP78) (p < 0.01), eukaryotic translation initiation factor 2α (p-eif2α) (p < 0.01), transcription activator 4 (ATF4) (p < 0.01), and the protein expression of C/EBP homologous protein (CHOP) (p < 0.01), which were the four hallmarks of ERS. The Tre + HS group showed lower expressions of GRP78 (p < 0.01), p-eif2α (p < 0.01), ATF4 (p < 0.01), and CHOP (p < 0.01) than that of the HS group. Tre pretreatment attenuated HS-induced mitochondrial apoptosis in IPEC-J2 cells, demonstrated by the increased MMP and decreased proapoptotic proteins active caspase 3, Bax, and cytochrome c (Cyt c). Taken together, trehalose can protect against HS-induced oxidative damage and endoplasmic reticulum stress-mediated apoptosis in IPEC-J2 cells. These data may provide a nutritional strategy for alleviating heat stress in pig production.

A Pipeline for Natural Small Molecule Inhibitors of Endoplasmic Reticulum Stress.

The homeostasis of eukaryotic cells is inseverable of that of the endoplasmic reticulum (ER). The main function of this organelle is the synthesis and folding of a significant portion of cellular proteins, while it is also the major calcium reservoir of the cell. Upon unresolved ER stress, a set of stress response signaling pathways that are collectively labeled as the unfolded protein response (UPR) is activated. Prolonged or intense activation of this molecular machinery may be deleterious. It is known that compromised ER homeostasis, and consequent UPR activation, characterizes the pathogenesis of neurodegenerative diseases. In an effort to discover new small molecules capable of countering ER stress, we subjected a panel of over 100 natural molecules to a battery of assays designed to evaluate several hallmarks of ER stress. The protective potential of these compounds against ER stress was evaluated at the levels of calcium homeostasis, key gene and protein expression, and levels of protein aggregation in fibroblasts. The most promising compounds were subsequently tested in neuronal cells. This framework resulted in the identification of several bioactive molecules capable of countering ER stress and deleterious events associated to it. Delphinidin stands out as the most promising candidate against neurodegeneration. This compound significantly inhibited the expression of UPR biomarkers, and displayed a strong potential to inhibit protein aggregation in the two aforementioned cell models. Our results indicate that natural products may be a valuable resource in the development of an effective therapeutic strategy against ER stress-related diseases.

Caffeine alleviates acute liver injury by inducing the expression of NEDD4L and deceasing GRP78 level via ubiquitination.

Acute liver injury is liver cell injury that occurs rapidly in a short period of time. Caffeine has been shown to maintain hepatoprotective effect with an unclear mechanism. Endoplasmic reticulum stress (ERS) has significant effects in acute liver injury. Induction of GRP78 is a hallmark of ERS. Whether or not caffeine's function is related to GRP78 remains to be explored. Acute liver injury model was established by LPS-treated L02 cells and in vivo administration of LPS/D-Gal in mice. Caffeine was pre-treated in L02 cells or mice. Gene levels was determined by real-time PCR and western blot. Cell viability was tested by CCK-8 assay and cell apoptosis was tested by flow cytometry. The interaction of GRP78 and NEDD4L was determined by Pull-down and co-immunoprecipitation (Co-IP) assay. The ubiquitination by NEDD4L on GRP78 was validated by in vitro ubiquitination assay. Caffeine protected liver cells against acute injury induced cell apoptosis and ERS both in vitro and in vivo. Suppression of GRP78 could block the LPS-induced cell apoptosis and ERS. NEDD4L was found to interact with GRP78 and ubiquitinate its lysine of 324 site directly. Caffeine treatment induced the expression of NEDD4L, resulting in the ubiquitination and inhibition of GRP78. Caffeine mitigated the acute liver injury by stimulating NEDD4L expression, which inhibited GRP78 expression via ubiquitination at its K324 site. Low dose of caffeine could be a promising therapeutic treatment for acute liver injury.

Induction of endoplasmic reticulum stress markers in an acromegaly model.

Acromegaly is a growth hormone (GH) excess pathological condition in humans. Acromegaly is associated with somatic disfigurement and a wide range of systemic manifestations such as arthritis, neuropathy, carpal tunnel syndrome, reproductive disorders, metabolic disorders, and gastrointestinal complications. The influence of excess GHon the cellular level could aid in understanding the root causes of acromegaly-related health complications. Previously, we found that GH excess induces DNA damage to somatic cells and reduces the stem cells number and causes premature aging. In this study, an in-depth analysis of the acromegaly RNAseq data revealed the disruption of important biological cellular processes. Gene set enrichment analysis, heatmap, and enrichment analysis of acromegaly RNAseq data revealed induction of endoplasmic reticulum (ER) stress markers in various organs. Interestingly, the induction of ER stress was even more apparent than in aged zebrafish. Splicing of box-binding protein-1 (XBP1) mRNA is a hallmark of ER stress. Therefore, we quantified spliced XBP1 mRNA in different organs of our acromegaly model. Thus, our study emphasizes the importance of ER stress in GH oversecretion, which is important for understanding the health complications of acromegaly.

ERK5 Inhibition Induces Autophagy-Mediated Cancer Cell Death by Activating ER Stress.

Autophagy is a highly conserved intracellular process that preserves cellular homeostasis by mediating the lysosomal degradation of virtually any component of the cytoplasm. Autophagy is a key instrument of cellular response to several stresses, including endoplasmic reticulum (ER) stress. Cancer cells have developed high dependency on autophagy to overcome the hostile tumor microenvironment. Thus, pharmacological activation or inhibition of autophagy is emerging as a novel antitumor strategy. ERK5 is a novel member of the MAP kinase family that is activated in response to growth factors and different forms of stress. Recent work has pointed ERK5 as a major player controlling cancer cell proliferation and survival. Therefore small-molecule inhibitors of ERK5 have shown promising therapeutic potential in different cancer models. Here, we report for the first time ERK5 as a negative regulator of autophagy. Thus, ERK5 inhibition or silencing induced autophagy in a panel of human cancer cell lines with different mutation patterns. As reported previously, ERK5 inhibitors (ERK5i) induced apoptotic cancer cell death. Importantly, we found that autophagy mediates the cytotoxic effect of ERK5i, since ATG5ˉ/ˉ autophagy-deficient cells viability was not affected by these compounds. Mechanistically, ERK5i stimulated autophagic flux independently of the canonical regulators AMPK or mTORC1. Moreover, ERK5 inhibition resulted in ER stress and activation of the Unfolded Protein Response (UPR) pathways. Specifically, ERK5i induced expression of the ER luminal chaperone BiP (a hallmark of ER stress), the UPR markers CHOP and ATF4, and the spliced form of XBP1. Pharmacological inhibition of UPR with chemical chaperone TUDC, or ATF4 silencing, resulted in impaired ERK5i-mediated UPR, autophagy and cytotoxicity. Overall, our results suggest that ERK5 inhibition induces autophagy-mediated cancer cell death by activating ER stress. Since ERK5 inhibition sensitizes cancer cells and tumors to chemotherapy, future work will determine the relevance of UPR and autophagy in the combined use of chemotherapy and ERK5i to tackle Cancer.

EETs/sEHi alleviates nociception by blocking the crosslink between endoplasmic reticulum stress and neuroinflammation in a central poststroke pain model

BackgroundCentral post-stroke pain (CPSP) is a chronic and intolerable neuropathic pain syndrome following a cerebral vascular insult, which negatively impacts the quality of life of stroke survivors but currently lacks efficacious treatments. Though its underlying mechanism remains unclear, clinical features of hyperalgesia and allodynia indicate central sensitization due to excessive neuroinflammation. Recently, the crosslink between neuroinflammation and endoplasmic reticulum (ER) stress has been identified in diverse types of diseases. Nevertheless, whether this interaction contributes to pain development remains unanswered. Epoxyeicosatrienoic acids (EETs)/soluble epoxy hydrolase inhibitors (sEHi) are emerging targets that play a significant role in pain and neuroinflammatory regulation. Moreover, recent studies have revealed that EETs are effective in attenuating ER stress. In this study, we hypothesized that ER stress around the stroke site may activate glial cells and lead to further inflammatory cascades, which constitute a positive feedback loop resulting in central sensitization and CPSP. Additionally, we tested whether EETs/sEHi could attenuate CPSP by suppressing ER stress and neuroinflammation, as well as their vicious cycle, in a rat model of CPSP.MethodsYoung male SD rats were used to induce CPSP using a model of thalamic hemorrhage and were then treated with TPPU (sEHi) alone or in combination with 14,15-EET or 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE, the EET antagonist), tunicamycin (Tm, ER stress inducer), or 4-PBA (ER stress inhibitor). Nociceptive behaviors, ER stress markers, JNK and p38 (two well-recognized inflammatory kinases of mitogen-activated protein kinase (MAPK) signaling) expression, and glial cell activation were assessed. In addition, some healthy rats were intrathalamically microinjected with Tm or lipopolysaccharide (LPS) to test the interaction between ER stress and neuroinflammation in central pain.ResultsAnalysis of the perithalamic lesion tissue from the brain of CPSP rats demonstrated decreased soluble epoxy hydrolase (sEH) expression, which was accompanied by increased expression of ER stress markers, including BIP, p-IRE, p-PERK, and ATF6. In addition, inflammatory kinases (p-p38 and p-JNK) were upregulated and glial cells were activated. Intrathalamic injection of sEHi (TPPU) increased the paw withdrawal mechanical threshold (PWMT), reduced hallmarks of ER stress and MAPK signaling, and restrained the activation of microglia and astrocytes around the lesion site. However, the analgesic effect of TPPU was completely abolished by 14,15-EEZE. Moreover, microinjection of Tm into the thalamic ventral posterior lateral (VPL) nucleus of healthy rats induced mechanical allodynia and activated MAPK-mediated neuroinflammatory signaling; lipopolysaccharide (LPS) administration led to activation of ER stress along the injected site in healthy rats.ConclusionsThe present study provides evidence that the interaction between ER stress and neuroinflammation is involved in the mechanism of CPSP. Combined with the previously reported EET/sEHi effects on antinociception and neuroprotection, therapy with agents that target EET signaling may serve as a multi-functional approach in central neuropathic pain by attenuating ER stress, excessive neuroinflammation, and subsequent central sensitization. The use of these agents within a proper time window could not only curtail further nerve injury but also produce an analgesic effect.

Role of Src‐Dependent Phosphorylation of Mitofusin 2 in Endoplasmic Reticulum‐Mitochondria Tethering

Introduction : Contact sites between the mitochondria and endoplasmic reticulum (ER) are one of the key structures involved in regulating lipid, Ca2+ and reactive oxygen species exchange across the two organelles which is critical for the maintenance of mitochondrial bioenergetics. Recent studies have reported that a major component of the tethering structures between the two organelles is mitofusin 2 (Mfn2), a GTPase associated with fusion of the outer mitochondrial membrane (OMM) as well as the activities of mitophagy and ER stress. While several post-translational modifications (PTMs) that influence the fusion and mitophagy functions of Mfn2 have been identified, it remains unclear whether there are PTMs that can regulate its tethering function. Data from mass spectroscopy reveals that there is basal tyrosine phosphorylation (P-Tyr) of Mfn2, but it is unknown whether Mfn2 is a substrate of mitochondria-localized tyrosine kinases (proline rich tyrosine kinase 2 [Pyk2] and proto-oncogene Src kinase [Src]). Objective : To determine whether P-Tyr of Mfn2 regulates Mfn2 functions. Methods HEK293T cells stably overexpressing shRNA targeted to a specific negative regulator of Src, C-terminal Src kinase (CSK) or a control vector were subjected to several biochemical (Fluorescent western blotting), cell biological (Transmission electron microscopy [TEM], Förster Resonance Energy Transfer [FRET] between cyan-fluorescent protein targeted to the OMM and yellow-fluorescent protein targeted to the ER membrane observed under confocal microscopy) and physiological (mitochondrial calcium [mtCa2+] uptake measurements using a mitochondria-targeted Ca2+ biosensor, mt-RCaMp1h) assays. Results Overexpression of Pyk2 and Src lead to P-Tyr of Mfn2 with Src having greater P-Tyr levels of Mfn2. Generation of a HEK293T cell line with stable knockdown of CSK reveals that CSK knockdown promotes Src activation in the mitochondria and increases P-Tyr of Mfn2 without changing expression levels of Src and Mfn2. CSK knockdown (CSK-KD) cells showed decreased distance between the ER and OMM as assessed by FRET measurement under confocal microscopy. This change was abolished by pretreatment with a Src-specific inhibitor, PP2. TEM images also showed that CSK knockdown decreases the distance between OMM and ER without changing the length of interface. To assess the impact of changes in the physical interaction between ER and mitochondria, mtCa2+ uptake profiles in CSK-KD cells were observed. In CSK-KD cells, mtCa2+ uptake in response to cytosolic Ca2+ elevation induce by Gq-protein coupled receptor stimulation was enhanced with faster kinetics compared to that in control cells. While physical coupling between ER and mitochondria increased, we found that hallmarks of ER stress and mitophagy were not altered in CSK-KD cells compared to control cells. Conclusion : Src-dependent phosphorylation of Mfn2 decreased the distance between the OMM and ER and lead to increased Ca2+ exchange between ER and mitochondria.

A mechanism of perhexiline's cytotoxicity in hepatic cells involves endoplasmic reticulum stress and p38 signaling pathway

Perhexiline is a coronary vasodilator for angina treatment that was first developed in the 1960s. Perhexiline enjoyed worldwide success before reports of severe side effects, such as hepatotoxicity and neurotoxicity, caused its withdrawal from most of the markets. The underlying mechanism of the cytotoxicity of perhexiline, however, is not yet well understood. Here we demonstrated that perhexiline induced cellular damage in primary human hepatocytes, HepaRG cells and HepG2 cells. Analysis of gene and protein expression levels of endoplasmic reticulum (ER) stress markers showed that perhexiline caused ER stress in primary human hepatocytes and HepG2 cells. The splicing of XBP1 mRNA, a hallmark of ER stress, was observed upon perhexiline treatment. Using Gluc-Fluc-HepG2 cell line, we demonstrated that protein secretion was impaired upon perhexiline treatment, suggesting functional deficits in ER. Inhibition of ER stress using ER inhibitor 4-PBA or salubrinal attenuated the cytotoxicity of perhexiline. Directly knocking down ATF4 using siRNA also partially rescued HepG2 cells upon perhexiline exposure. In addition, inhibition of ER stress using either inhibitors or siRNA transfection attenuated perhexiline-induced increase in caspase 3/7 activity, indicating that ER stress contributed to perhexiline-induced apoptosis. Moreover, perhexiline treatment resulted in activation of p38 and JNK signaling pathways, two branches of MAPK cascade. Pre-treating HepG2 cells with p38 inhibitor SB239063 attenuated perhexiline-induced apoptosis and cell death. The inhibitor also prevented the activation of CHOP and ATF4. Overall, our study demonstrated that ER stress is one important mechanism underlying the hepatotoxicity of perhexiline, and p38 signaling pathway contributes to this process. Our finding shed light on the role of both ER stress and p38 signaling pathway in drug-induced liver injury.

Celecoxib-Dependent Neuroprotection in a Rat Model of Transient Middle Cerebral Artery Occlusion (tMCAO) Involves Modifications in Unfolded Protein Response (UPR) and Proteasome.

Stroke is one of the main causes of death and disability worldwide. Ischemic stroke results in unfolded/misfolded protein accumulation in endoplasmic reticulum (ER), a condition known as ER stress. We hypothesized that previously reported neuroprotection of celecoxib, a selective inhibitor of cyclooxygenase-2, in transient middle cerebral artery occlusion (tMCAO) model, relies on the ER stress decrease. To probe this hypothesis, Sprague-Dawley rats were subjected to 1h of tMCAO and treated with celecoxib or vehicle 1 and 24h after ischemia. Protein and mRNA levels of the main hallmarks of ER stress, unfolded protein response (UPR) activation, UPR-induced cell death, and ubiquitin proteasome system (UPS) and autophagy, the main protein degradation pathways, were measured at 12 and 48h of reperfusion. Celecoxib treatment decreased polyubiquitinated protein load and ER stress marker expression such as glucose-related protein 78 (GRP78), C/EBP (CCAAT/enhancer-binding protein) homologous protein (CHOP), and caspase 12 after 48h of reperfusion. Regarding the UPR activation, celecoxib promoted inositol-requiring enzyme 1 (IRE1) pathway instead of double-stranded RNA-activated protein kinase-like ER kinase (PERK) pathway. Furthermore, celecoxib treatment increased proteasome catalytic subunits transcript levels and decreased p62 protein levels, while the microtubule-associated protein 1 light chain 3 (LC3B) II/I ratio remained unchanged. Thus, the ability of celecoxib treatment on reducing the ER stress correlates with the enhancement of IRE1-UPR pathway and UPS degradation. These data support the ability of anti-inflammatory therapy in modulating ER stress and reveal the IRE1 pathway as a promising therapeutic target in stroke therapy.Graphical abstract.

The Role of eIF2α in the Collagen Production in Hepatic Stellate Cell is Associated with Autophagic and Apoptotic Signaling

Background &amp; AimsStudies have documented cellular apoptosis, autophagy and endoplasmic reticulum (ER) stress participate in the liver fibrogenesis. However, the specific mechanism remains unclear. This study was aimed to determine whether and how eIF2α protein play a role in the collagen generation in hepatic stellate cell (HSC) via autophagic signaling events.MethodsHSC‐LX2 cell line was activated by transforming growth factor beta1 (TGF‐β1) in the presence of eIF2α plasmid or vehicle control. Real‐time fluorescence quantitative PCR was then performed to compare the differential mRNA level of COL1, eIF2α, CHOP, Bcl‐2 and Bax. Western Blot was performed to analyze the protein expression of α‐SMA, COL1, LC3, P62, eIF2α, P‐eIF2α and Bcl‐2 in LX2 cells. Meanwhile, the numbers of apoptotic cells were measured by flow cytometry.ResultsCompare to vehicle control, the ER stress hallmarks of eIF2α, CHOP were at lower level in HSC‐LX2 cells in TGF‐β1 treated condition. While transfected eIF2α plasmid in HSC‐LX2 cells, it was found that CHOP and BAX significantly increased in these cells but substantial reduction in LC3, P62, Bcl‐2, α‐SMA and COL1 v.s. control(&lt;0.05). Moreover, thus exogenously enhancing of eIF2α gene was found to induce apoptosis of HSC‐LX2 cells with a 50% increment (&lt;0.05).ConclusionsOverexpression of eIF2α in HSCs may trigger autophagy inhibition and apoptosis promotion, thereby reduce collagen production in these cells, which provide a potential therapeutic strategy for hepatic fibrosis.Support or Funding InformationSupported by NSFC Grants 81360077, 81860654, 30630145, 81172260 and GXNSFC Grants 2015GXNSFDA139022 to Guo ZhangThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Insights into the role of endoplasmic reticulum stress in skin function and associated diseases.

Endoplasmic reticulum (ER) stress is a mechanism that allows the protection of normal cellular functions in response to both internal perturbations, such as accumulation of unfolded proteins, and external perturbations, for example redox stress, UVB irradiation, and infection. A hallmark of ER stress is the accumulation of misfolded and unfolded proteins. Physiological levels of ER stress trigger the unfolded protein response (UPR) that is required to restore normal ER functions. However, the UPR can also initiate a cell death program/apoptosis pathway in response to excessive or persistent ER stress. Recently, it has become evident that chronic ER stress occurs in several diseases, including skin diseases such as Darier's disease, rosacea, vitiligo and melanoma; furthermore, it is suggested that ER stress is directly involved in the pathogenesis of these disorders. Here, we review the role of ER stress in skin function, and discuss its significance in skin diseases.

Endoplasmic Reticulum Stress Is Involved in Baicalin Protection on Chondrocytes From Patients With Osteoarthritis.

Osteoarthritis (OA) affects elderly population worldwide and endoplasmic reticulum (ER) stress is known to be positively correlated with OA development. Previous reports prove the cytoprotective effects of baicalin on chondrocytes, whereas the mechanisms are hardly reported. Hence, we aimed to investigate the links between OA, ER stress, and baicalin. Chondrocytes from patients with OA were subjected to H2O2 treatment with or without baicalin pretreatment, and cell viability was assessed via Cell Counting Kit-8. Messenger RNA (mRNA) amounts of apoptosis-related genes (Bax, Bcl-2, and Caspase-3), extracellular matrix (ECM)-related genes (Collange I, Collange II, Aggrecan, and Sox9) and ER stress hallmarks (binding immunoglobulin protein [BiP] C/EBP homologous protein [CHOP]) were evaluated via quantitative real-time PCR. Bax, Bcl-2, BiP, and CHOP protein levels were analyzed via Western blot. Baicalin suppressed the changes in cell viability and apoptosis-related gene expressions caused by H2O2. Reactive oxygen species and glutathione/oxidized glutathione assay showed that H2O2 enhanced oxidative stress. Baicalin suppressed H2O2-induced downregulation of mRNA expression of ECM-related genes. Moreover, baicalin reduced H2O2-stimulated increase in oxidative stress and the expression of ER stress hallmarks. Endoplasmic reticulum stress inducer abolished the protective activities, whereas ER stress inhibitor did not exhibit extra protective effects. Baicalin pretreatment protected patient-derived chondrocytes from H2O2 through ER stress inhibition.

Curcumin mitigates axonal injury and neuronal cell apoptosis through the PERK/Nrf2 signaling pathway following diffuse axonal injury.

Diffuse axonal injury (DAI) accounts for more than 50% of all traumatic brain injury. In response to the mechanical damage associated with DAI, the abnormal proteins produced in the neurons and axons, namely, β-APP and p-tau, induce endoplasmic reticulum (ER) stress. Curcumin, a major component extracted from the rhizome of Curcuma longa, has shown potent anti-inflammatory, antioxidant, anti-infection, and antitumor activity in previous studies. Moreover, curcumin is an activator of nuclear factor-erythroid 2-related factor 2 (Nrf2) and promotes its nuclear translocation. In this study, we evaluated the therapeutic potential of curcumin for the treatment of DAI and investigated the mechanisms underlying the protective effects of curcumin against neural cell death and axonal injury after DAI. Rats subjected to a model of DAI by head rotational acceleration were treated with vehicle or curcumin to evaluate the effect of curcumin on neuronal and axonal injury. We observed that curcumin (20 mg/kg intraperitoneal) administered 1 h after DAI induction alleviated the aggregation of p-tau and β-APP in neurons, reduced ER-stress-related cell apoptosis, and ameliorated neurological deficits. Further investigation showed that the protective effect of curcumin in DAI was mediated by the PERK/Nrf2 pathway. Curcumin promoted PERK phosphorylation, and then Nrf2 dissociated from Keap1 and was translocated to the nucleus, which activated ATF4, an important bZIP transcription factor that maintains intracellular homeostasis, but inhibited the CHOP, a hallmark of ER stress and ER-associated programmed cell death. In summary, we demonstrate for the first time that curcumin confers protection against abnormal proteins and neuronal apoptosis after DAI, that the process is mediated by strengthening of the unfolded protein response to overcome ER stress, and that the protective effect of curcumin against DAI is dependent on the activation of Nrf2.

Ginkgo biloba Leaf Extract Protects against Myocardial Injury via Attenuation of Endoplasmic Reticulum Stress in Streptozotocin-Induced Diabetic ApoE-/- Mice.

Diabetes was induced in high-fat diet-fed ApoE−/− mice via administration of low-dose streptozotocin (STZ) for five days. Mice were then treated with GBE (200 or 400 mg/kg) by gastric gavage daily for 12 weeks. Mice in the untreated diabetic group received saline instead, and nondiabetic C57BL/6J mice served as controls. Collagen І and ІІІ mRNA expression was measured by real-time PCR. TNF-α, IL-1β mRNA levels, and NF-κB expression were determined to analyze intramyocardial inflammation. Hallmarks of endoplasmic reticulum stress- (ERS-) related apoptosis pathways, including phosphorylated c-Jun N-terminal kinase (p-JNK), C/EBP homologous protein (CHOP), caspase-12, and cleaved caspase-3, were analyzed by Western blotting. Diabetic ApoE−/− myocardial injury was associated with increased cardiomyocyte apoptosis (increased expression of p-JNK, CHOP, caspase-12, and cleaved caspase-3), interstitial fibrosis (increased mRNA levels of collagen І and ІІІ), and inflammation (increased mRNA levels of TNF-α and IL-1β, and NF-κB expression). GBE at 200 and 400 mg/kg/day significantly attenuated cardiomyocyte apoptosis, collagen deposition, and inflammation in diabetic mice via inhibition of the p-JNK, CHOP, and caspase-12 pathways. Serum levels of the proinflammatory cytokines (IL-6, IL-1β, and TNF-α), blood glucose, and lipid profiles were also regulated by GBE treatment. GBE might be beneficial in the treatment of diabetic myocardial injury.

Melatonin ameliorates myocardial apoptosis by suppressing endoplasmic reticulum stress in rats with long‑term diabetic cardiomyopathy.

The effects of melatonin (MLT), which exerts cardioprotective effects against myocardial apoptosis, in long‑term diabetic cardiomyopathy are not currently well defined. The present study aimed to investigate how MLT protects the heart through modulating myocardial apoptosis in rats with type 2 diabetes mellitus (DM). In total, 36 rats were randomly divided into three groups, including control (n=12), DM (n=12) and DM+MLT (n=12) groups. The results demonstrated that, in DM rats, a significant increase was observed in the serum fasting blood glucose and lipid levels, in addition to insulin resistance and cardiac dysfunction, which were attenuated in DM rats treated with MLT. Additionally, cellular apoptosis in rats with DM was increased, and the expression of Bcl‑2 was downregulated, while levels of Bcl‑2‑associated X and caspase‑3 were upregulated, and these observations were reversed by MLT, as determined by TUNEL and western blot analysis, respectively. As increased endoplasmic reticulum (ER) stress induced by hyperglycemia is reported to be a factor for apoptosis, the present study also determined the expression of proteins associated with ER stress in cardiac tissues following MLT treatment by western blotting. The results further indicated that MLT decreased the expression of ER stress hallmarks, including CCAAT/enhancer‑binding protein homologous protein, glucose‑regulated protein 78, protein kinase RNA‑like endoplasmic reticulum kinase (PERK) and activating transcription factor 6α in cardiac tissues. In conclusion, the results of the present study indicate that MLT may protect heart by ameliorating cardiac ER stress‑induced apoptosis in diabetic cardiomyopathy.

Mycobacterium bovis Induces Endoplasmic Reticulum Stress Mediated-Apoptosis by Activating IRF3 in a Murine Macrophage Cell Line

Mycobacterium bovis (M. bovis) is highly adapted to macrophages and has developed multiple mechanisms to resist intracellular assaults. However, the host cells in turn deploy a multipronged defense mechanism to control bacterial infection. Endoplasmic reticulum (ER) stress-mediated apoptosis is one such primary defense mechanism. However, the role of interferon regulatory factor 3 (IRF3) between ER stress and apoptosis during M. bovis infection is unknown. Here, we demonstrate that M. bovis effectively induced apoptosis in murine macrophages. Caspase-12, caspase-9, and caspase-3 were activated over a 48 h infection period. The splicing of XBP-1 mRNA and the level of phosphorylation of eIF2α, indicators of ER stress, significantly increased at early time points after M. bovis infection. The expansion of the ER compartment, a morphological hallmark of ER stress, was observed at 6 h. Pre-treatment of Raw 264.7 cells with 4-PBA (an ER stress-inhibitor) reduced the activation of the ER stress indicators, caspase activation and its downstream poly (ADP-ribose) polymerase (PARP) cleavage, phosphorylation of TBK1 and IRF3 and cytoplasmic co-localization of STING and TBK1. M. bovis infection led to the interaction of activated IRF3 and cytoplasmic Bax leading to mitochondrial damage. Role of IRF3 in apoptosis was further confirmed by blocking this molecule with BX-795 that showed significant reduction expression of caspase-8 and caspase-3. Intracellular survival of M. bovis increased in response to 4-PBA and BX-795. These findings indicate that STING-TBK1-IRF3 pathway mediates a crosstalk between ER stress and apoptosis during M. bovis infection, which can effectively control intracellular bacteria.

Increased phosphorylation of eIF2α in chronic myeloid leukemia cells stimulates secretion of matrix modifying enzymes.

Recent studies underscore the role of the microenvironment in therapy resistance of chronic myeloid leukemia (CML) cells and leukemia progression. We previously showed that sustained mild activation of endoplasmic reticulum (ER) stress in CML cells supports their survival and resistance to chemotherapy. We now demonstrate, using dominant negative non-phosphorylable mutant of eukaryotic initiation factor 2 α subunit (eIF2α), that phosphorylation of eIF2α (eIF2α-P), which is a hallmark of ER stress in CML cells, substantially enhances their invasive potential and modifies their ability to secrete extracellular components, including the matrix-modifying enzymes cathepsins and matrix metalloproteinases. These changes are dependent on the induction of activating transcription factor-4 (ATF4) and facilitate extracellular matrix degradation by CML cells. Conditioned media from CML cells with constitutive activation of the eIF2α-P/ATF4 pathway induces invasiveness of bone marrow stromal fibroblasts, suggesting that eIF2α-P may be important for extracellular matrix remodeling and thus leukemia cells-stroma interactions. Our data show that activation of stress response in CML cells may contribute to the disruption of bone marrow niche components by cancer cells and in this way support CML progression.