[Effects of acupuncture intervention on expression of glucose-regulated protein 78 and C/EBP homologous protein in hippocampal CA 1 region in rats with hyperspasmia]

OBJECTIVE

To observe the effect of acupuncture intervention on expression of glucose-regulated protein 78 (Grp 78) and C/EBP homologous protein (CHOP) in the hippocampus in epilepsy rats so as to explore its mechanism underlying improvement of hyperspasmia-induced brain injury.

METHODS

Forty-two SD rats were randomly divided into normal control group (n = 6), model group (n = 18), and acupuncture group (n = 18). The epileptic seizure model was established by intraperitonel injection of Pentylenetetrazol (50 mg/kg, 2 mL). Manual acupuncture stimulation of "Baihui" (GV 20) and "Dazhui" (GV 14) was conducted for rats of the acupuncture group for 30 min. Two hours (h), 12 h and 48 h after acupuncture intervention, the hippocampal tissue was sampled (6 rats at each time-point). The expression levels of Grp 78 and CHOP proteins in the hippocampal CA 1 region were detected by immunohistochemistry.

RESULTS

Compared with the normal group, the expression levels of Grp 78 protein at time-points of 2 h and 12 h, and those of CHOP protein at 2 h, 12 h and 48 h after epilpeptic seizure were significantly increased in the model group (P < 0.01). After acupuncture treatment, the expression levels of Grp 78 at 12 and 48 h were significantly increased, and those of CHOP protein at 2 h, 12 h and 24 h in the acupuncture group were considerably downregulated (P < 0.05, P < 0.01).

CONCLUSION

Acupuncture treatment can up-regulate Grp 78 protein expression and down-regulate CHOP protein expression level in epilepsy rats , which may contribute to its protective effect on seizure-induced brain injury.

New insights into the roles of CHOP-induced apoptosis in ER stress

Endoplasmic reticulum stress (ER stress) is triggered due to a loss of homeostasis in the ER, resulting in accumulation of misfolded proteins in the ER lumen. ER stress activates a series of adaptive mechanisms known as the unfolded protein response. Perturbation of the ER is a powerful inducer of the transcription factor C/EBP homologous protein (CHOP). Although it has been proved that excessive or adverse stress to the ER triggers apoptosis, the specific mechanisms underlying these processes induced by CHOP remain unclear. By now, CHOP-induced apoptosis in ER stress has been implicated in numerous human diseases, such as neurodegenerative diseases, diabetes, ischemic diseases, tumor, and so on. In this review, we summarized the current understanding of the roles of CHOP in the development of several diseases from the laboratory to the clinic.

Advanced glycation end-products induce endoplasmic reticulum stress in human aortic endothelial cells

BACKGROUND

Advanced glycation end products (AGEs), the final products of the Maillard reaction, have been shown to impair endothelial proliferation and function, thus contributing to endothelial cell injury present in diabetes, inflammatory and cardiovascular diseases. Endoplasmic reticulum (ER) stress triggered under hyperglycemic, hypoxic and oxidative conditions has been implicated in endothelial dysfunction through activation of the unfolded protein response (UPR). The present study investigates the role of AGEs in ER stress induction in human aortic endothelial cells exposed to variable AGE treatments.

METHODS

Human aortic endothelial cells (HAEC) were treated with increasing concentrations (100, 200 μg/mL) of AGE-bovine serum albumin (AGE-BSA) at different time-points (24, 48, 72 h). The induction of ER stress and the involved UPR components were investigated on mRNA and protein levels. Apoptosis was quantitatively determined by flow cytometry detecting propidium iodide expression and annexin V binding simultaneously.

RESULTS

AGEs administration significantly reduced HAEC proliferation in a time- and dose-dependent manner. An immediate induction of the ER chaperones GRP78, GRP94 and the transcriptional activator, XBP-1 was observed at 24 h and 48 h. A later induction of the phospho-elF2α and proapoptotic transcription factor CHOP was observed at 48 h and 72 h, being correlated with elevated early apoptotic cell numbers at the same time-points.

CONCLUSIONS

The present study demonstrates that AGEs directly induce ER stress in human aortic endothelial cells, playing an important role in endothelial cell apoptosis. Targeting AGEs signaling pathways in order to alleviate ER stress may prove of therapeutic potential to endothelial dysfunction-related disorders.

Protein degradation and quality control in cells from laforin and malin knockout mice

Lafora disease is a progressive myoclonus epilepsy caused by mutations in the EPM2A or EPM2B genes that encode a glycogen phosphatase, laforin, and an E3 ubiquitin ligase, malin, respectively. Lafora disease is characterized by accumulation of insoluble, poorly branched, hyperphosphorylated glycogen in brain, muscle, heart, and liver. The laforinmalin complex has been proposed to play a role in the regulation of glycogen metabolism and protein quality control. We evaluated three arms of the protein degradation/ quality control process (the autophago-lysosomal pathway, the ubiquitin-proteasomal pathway, and the endoplasmic reticulum (ER) stress response) in mouse embryonic fibroblasts from Epm2a(-/-), Epm2b(-/-), and Epm2a(-/-) Epm2b(-/-) mice. The levels of LC3-II, a marker of autophagy, were decreased in all knock-out cells as compared with wild type even though they still showed a slight response to starvation and rapamycin. Furthermore, ribosomal protein S6 kinase and S6 phosphorylation were increased. Under basal conditions there was no effect on the levels of ubiquitinated proteins in the knock-out cells, but ubiquitinated protein degradation was decreased during starvation or stress. Lack of malin (Epm2b(-/-) and Epm2a(-/-) Epm2b(-/-) cells) but not laforin (Epm2a(-/-) cells) decreased LAMP1, a lysosomal marker. CHOP expression was similar in wild type and knock-out cells under basal conditions or with ER stress-inducing agents. In conclusion, both laforin and malin knock-out cells display mTOR-dependent autophagy defects and reduced proteasomal activity but no defects in the ER stress response. We speculate that these defects may be secondary to glycogen overaccumulation. This study also suggests a malin function independent of laforin, possibly in lysosomal biogenesis and/or lysosomal glycogen disposal.

Chaperones ameliorate beta cell dysfunction associated with human islet amyloid polypeptide overexpression

In type 2 diabetes, beta-cell dysfunction is thought to be due to several causes, one being the formation of toxic protein aggregates called islet amyloid, formed by accumulations of misfolded human islet amyloid polypeptide (hIAPP). The process of hIAPP misfolding and aggregation is one of the factors that may activate the unfolded protein response (UPR), perturbing endoplasmic reticulum (ER) homeostasis. Molecular chaperones have been described to be important in regulating ER response to ER stress. In the present work, we evaluate the role of chaperones in a stressed cellular model of hIAPP overexpression. A rat pancreatic beta-cell line expressing hIAPP exposed to thapsigargin or treated with high glucose and palmitic acid, both of which are known ER stress inducers, showed an increase in ER stress genes when compared to INS1E cells expressing rat IAPP or INS1E control cells. Treatment with molecular chaperone glucose-regulated protein 78 kDa (GRP78, also known as BiP) or protein disulfite isomerase (PDI), and chemical chaperones taurine-conjugated ursodeoxycholic acid (TUDCA) or 4-phenylbutyrate (PBA), alleviated ER stress and increased insulin secretion in hIAPP-expressing cells. Our results suggest that the overexpression of hIAPP induces a stronger response of ER stress markers. Moreover, endogenous and chemical chaperones are able to ameliorate induced ER stress and increase insulin secretion, suggesting that improving chaperone capacity can play an important role in improving beta-cell function in type 2 diabetes.

Role of endoplasmic reticulum stress in atherosclerosis and diabetic macrovascular complications

Age-related changes in endoplasmic reticulum (ER) are associated with stress of this cell organelle. Unfolded protein response (UPR) is a normal physiological reaction of a cell in order to prevent accumulation of unfolded and misfolded proteins in the ER and improve the normal ER function. However, in pathologic conditions such as atherosclerosis, obesity, and diabetes, ER function becomes impaired, leading to the development of ER stress. In chronic ER stress, defective posttranslational protein folding results in deposits of aberrantly folded proteins in the ER and the induction of cell apoptosis mediated by UPR sensors C/EBPα-homologous protein (CHOP) and inositol requiring protein-1 (IRE1). Since ER stress and ER-induced cell death play a nonredundant role in the pathogenesis of atherosclerosis and diabetic macrovascular complications, pharmaceutical targeting of ER stress components and pathways may be beneficial in the treatment and prevention of cardiovascular pathology.

The effects and underlying mechanism of excessive iodide on excessive fluoride-induced thyroid cytotoxicity

In many regions, excessive fluoride and excessive iodide coexist in groundwater, which may lead to biphasic hazards to human thyroid. To explore fluoride-induced thyroid cytotoxicity and the mechanism underlying the effects of excessive iodide on fluoride-induced cytotoxicity, a thyroid cell line (Nthy-ori 3-1) was exposed to excessive fluoride and/or excessive iodide. Cell viability, lactate dehydrogenase (LDH) leakage, reactive oxygen species (ROS) formation, apoptosis, and the expression levels of inositol-requiring enzyme 1 (IRE1) pathway-related molecules were detected. Fluoride and/or iodide decreased cell viability and increased LDH leakage and apoptosis. ROS, the expression levels of glucose-regulated protein 78 (GRP78), IRE1, C/EBP homologous protein (CHOP), and spliced X-box-binding protein-1 (sXBP-1) were enhanced by fluoride or the combination of the two elements. Collectively, excessive fluoride and excessive iodide have detrimental influences on human thyroid cells. Furthermore, an antagonistic interaction between fluoride and excessive iodide exists, and cytotoxicity may be related to IRE1 pathway-induced apoptosis.

Dual role for CHOP in the crosstalk between autophagy and apoptosis to determine cell fate in response to amino acid deprivation

CHOP encodes a ubiquitous transcription factor that is one of the most important components in the network of stress-inducible transcription. In particular, this factor is known to mediate cell death in response to stress. The focus of this work is to study its pivotal role in the control of cell viability according to the duration of a stress like amino acid starvation. We show that during the first 6h of starvation, CHOP upregulates a number of autophagy genes but is not involved in the first steps of the autophagic process. By contrast, when the amino acid starvation is prolonged (16-48h), we demonstrated that CHOP has a dual role in both inducing apoptosis and limiting autophagy through the transcriptional control of specific target genes. Overall, this study reveals a novel regulatory role for CHOP in the crosstalk between autophagy and apoptosis in response to stress.

DHA-mediated enhancement of TRAIL-induced apoptosis in colon cancer cells is associated with engagement of mitochondria and specific alterations in sphingolipid metabolism

Docosahexaenoic acid (DHA), an n-3 polyunsaturated fatty acid present in fish oil, may exert cytotoxic and/or cytostatic effects on colon cancer cells when applied individually or in combination with some anticancer drugs. Here we demonstrate a selective ability of subtoxic doses of DHA to enhance antiproliferative and apoptotic effects of clinically useful cytokine TRAIL (tumor necrosis factor-related apoptosis inducing ligand) in cancer but not normal human colon cells. DHA-mediated stimulation of TRAIL-induced apoptosis was associated with extensive engagement of mitochondrial pathway (Bax/Bak activation, drop of mitochondrial membrane potential, cytochrome c release), activation of endoplasmic reticulum stress response (CHOP upregulation, changes in PERK level), decrease of cellular inhibitor of apoptosis protein (XIAP, cIAP1) levels and significant changes in sphingolipid metabolism (intracellular levels of ceramides, hexosyl ceramides, sphingomyelines, sphingosines; HPLC/MS/MS). Interestingly, we found significant differences in representation of various classes of ceramides (especially C16:0, C24:1) between the cancer and normal colon cells treated with DHA and TRAIL, and suggested their potential role in the regulation of the cell response to the drug combination. These study outcomes highlight the potential of DHA for a new combination therapy with TRAIL for selective elimination of colon cancer cells via simultaneous targeting of multiple steps in apoptotic pathways.

DDIT3 overexpression increases odontoblastic potential of human dental pulp cells

OBJECTIVES

Human dental pulp cells (HDPCs) with multi-potential differentiational capacity can undergo odontoblastic differentiation when stimulated with proinflammatory cytokines. However, factors linking proinflammatory stimuli and their odontoblastic differentiation have, as yet, not been completely understood. As an apoptotic transcription factor, DDIT3 plays a crucial role in the inflammatory reaction and in osteogenic differentiation. Thus, we hypothesized that DDIT3 may participate in odontoblastic differentiation of HDPCs.

MATERIALS AND METHODS

Immunofluorescent staining was used to detect expression of DDIT3 in HDPCs and effects of TNFα, on its nuclear accumulation. HDPCs that overexpressed DDIT3 were developed and their proliferation and odontoblastic differentiation abilities were examined. qRT-PCR was employed to detect mineralization-related genes, including ALP, runt-related transcription factor-2 (Runx2), osterix (OSX), dentin sialophosphoprotein (DSPP), dentin matrix acidic phosphoprotein 1 (DMP1) and osteocalcin (OCN). Western blot analysis was performed to detect expression of DSPP protein.

RESULTS

DDIT3 was expressed in HDPCs. TNFα treatment enhanced mRNA expression as well as nuclear accumulation of DDIT3 (slightly). DDIT3 overexpression reduced HDPC proliferation, however, it increased their calcium nodule formation and expression of OSX, DSPP, DMP1 and OCN.

CONCLUSIONS

DDIT3 may be a factor that links proinflammatory stimuli and differentiation of HDPCs.

The relationship between anticancer effect of metformin and the transcriptional regulation of certain genes (CHOP, CAV-1, HO-1, SGK-1 and Par-4) on MCF-7 cell line

BACKGROUND

1,1-dimethylbiguanide hydrochloride (biguanide metformin) is a hypoglycemic agent that is widely used in the treatment of Type 2 diabetes. Use of metformin was found to be associated with the lower risk of cancer. It is suggested that metformin has an anticancer and antiproliferative effect and affects the apoptosis by activating the AMPK and inhibiting the mammalian target of rapamycin (mTOR). Although the effects of metformin treatment of various types of cancers are defined with many mechanisms, the literature provides only sufficient information about how it affects the SGK-1, Par-4 and Cav-1 mRNA expressions and the impact of this effect on cytotoxicity. The breast cancer is globally one of the most important causes of cancer-related mortality for women. We, therefore investigated the possible effects of metmorfin on proliferation, cytotoxicity and some unfolded protein response (UPR) genes in the breast cancer cells (MCF-7).

MATERIALS AND METHODS

We administrated 0.31 mM, 2.5 mM and 10 mM of metformin alone and in combination with 2-DG to the MCF-7 cells and monitored the cell viability and proliferation with real-time cell analyzer system for 48 hours. We also measured CHOP, Cav-1, HO-1, SGK-1 and Par-4 genes mRNA expression levels using Real Time-Polymerase Chain Reaction (RT-PCR). We considered the GAPDH gene as reference gene and the control groups as calibrator. We performed an analysis for relative gene expressions of the study groups.

RESULTS

Metformin caused transcriptional regulation of UPR and tumor-related genes in MCF-7 cells and inhibited the proliferation depending on the dose, resulting in cytotoxic effect.

CONCLUSIONS

We consider that administration of metformin with chemotherapeutic agents could be an effective method in treatment of breast cancer through mechanisms such as reduced resistance to chemotherapy and increased cytotoxic activity.

Smoke exposure causes endoplasmic reticulum stress and lipid accumulation in retinal pigment epithelium through oxidative stress and complement activation

Age-related macular degeneration (AMD) is a complex disease caused by genetic and environmental factors, including genetic variants in complement components and smoking. Smoke exposure leads to oxidative stress, complement activation, endoplasmic reticulum (ER) stress, and lipid dysregulation, which have all been proposed to be associated with AMD pathogenesis. Here we examine the effects of smoke exposure on the retinal pigment epithelium (RPE). Mice were exposed to cigarette smoke or filtered air for 6 months. RPE cells grown as stable monolayers were exposed to 5% cigarette smoke extract (CSE). Effects of smoke were determined by biochemical, molecular, and histological measures. Effects of the alternative pathway (AP) of complement and complement C3a anaphylatoxin receptor signaling were analyzed using knock-out mice or specific inhibitors. ER stress markers were elevated after smoke exposure in RPE of intact mice, which was eliminated in AP-deficient mice. To examine this relationship further, RPE monolayers were exposed to CSE. Short term smoke exposure resulted in production and release of complement C3, the generation of C3a, oxidative stress, complement activation on the cell membrane, and ER stress. Long term exposure to CSE resulted in lipid accumulation, and secretion. All measures were reversed by blocking C3a complement receptor (C3aR), alternative complement pathway signaling, and antioxidant therapy. Taken together, our results provide clear evidence that smoke exposure results in oxidative stress and complement activation via the AP, resulting in ER stress-mediated lipid accumulation, and further suggesting that oxidative stress and complement act synergistically in the pathogenesis of AMD.

Luteolin modulates 6-hydroxydopamine-induced transcriptional changes of stress response pathways in PC12 cells

The neurotoxin 6-hydroxydopamine (6-OHDA), which causes transcriptional changes associated with oxidative and proteotoxic stress, has been widely used to generate an experimental model of Parkinson's disease. The food-derived compound luteolin has multi-target actions including antioxidant, anti-inflammatory and neurotrophic activities. The aim of this study is to investigate how luteolin affects 6-OHDA-mediated stress response pathways. The results showed that when PC12 cells were pre-treated with luteolin (20 µM) 30 min prior to 6-OHDA (100 µM) exposure, 6-OHDA-induced ROS overproduction, cytotoxicity, caspase-3 activation, and mRNA expression of BIM, TRB3 and GADD34 were significantly attenuated. Moreover, 6-OHDA-mediated cell cycle arrest and transcription of p53 target genes, p21, GADD45α and PUMA, were reduced by luteolin. Luteolin also significantly down-regulated 6-OHDA-mediated unfolded protein response (UPR), leading to decreases in phospho-eIF2α, ATF4, GRP78 and CHOP. In addition, luteolin attenuated 6-OHDA-induced Nrf2-mediated HO-1 and GCLC. Taken together, these results suggest that diminishing intracellular ROS formation and down-regulation of p53, UPR and Nrf2-ARE pathways may be involved in the neuroprotective effect of luteolin.

The transcription factor CHOP, a central component of the transcriptional regulatory network induced upon CCl4 intoxication in mouse liver, is not a critical mediator of hepatotoxicity

Since xenobiotics enter the organism via the liver, hepatocytes must cope with numerous perturbations, including modifications of proteins leading to endoplasmic reticulum stress (ER-stress). This triggers a signaling pathway termed unfolded protein response (UPR) that aims to restore homeostasis or to eliminate disturbed hepatocytes by apoptosis. In the present study, we used the well-established CCl4 hepatotoxicity model in mice to address the questions whether CCl4 induces ER-stress and, if so, whether the well-known ER-stress effector CHOP is responsible for CCl4-induced apoptosis. For this purpose, we treated mice with a high dose of CCl4 injected i.p. and followed gene expression profile over time using Affymetrix gene array analysis. This time resolved gene expression analysis allowed the identification of gene clusters with overrepresented binding sites for the three most important ER-stress induced transcription factors, CHOP, XBP1 and ATF4. Such result was confirmed by the demonstration of CCl4-induced XBP1 splicing, upregulation of CHOP at mRNA and protein levels, and translocation of CHOP to the nucleus. Two observations indicated that CHOP may be responsible for CCl4-induced cell death: (1) Nuclear translocation of CHOP was exclusively observed in the pericentral fraction of hepatocytes that deteriorate in response to CCl4 and (2) CHOP-regulated genes with previously reported pro-apoptotic function such as GADD34, TRB3 and ERO1L were induced in the pericentral zone as well. Therefore, we compared CCl4 induced hepatotoxicity in CHOP knockout versus wild-type mice. Surprisingly, genetic depletion of CHOP did not afford protection against CCl4-induced damage as evidenced by serum GOT and GPT as well as quantification of dead tissue areas. The negative result was obtained at several time points (8, 24 and 72 h) and different CCl4 doses (1.6 and 0.132 g/kg). Overall, our results demonstrate that all branches of the UPR are activated in mouse liver upon CCl4 treatment. However, CHOP does not play a critical role in CCl4-induced cell death and cannot be considered as a biomarker strictly linked to hepatotoxicity. The role of alternative UPR effectors such as XBP1 remains to be investigated.

Endoplasmic reticulum stress response as a possible mechanism of cyclooxygenase-2-independent anticancer effect of celecoxib

BACKGROUND

We investigated whether the endoplasmic reticulum (ER) stress response could be a cyclooxygenase-2 (COX2)-independent mechanism of growth inhibition by celecoxib in a head and neck squamous cell carcinoma (HNSCC) cell line.

MATERIALS AND METHODS

We performed western blotting and reverse transcription polymerase chain reaction to analyze the expression of ER stress response-associated proteins C/EBP homologous protein (CHOP), glucose-regulated protein (GRP)-78 and X-box binding protein-1 (XBP1), after treatment of celecoxib in the SNU-1041 cell line. A 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was performed to determine the change in growth inhibition by celecoxib after inhibition of the ER stress pathway by CHOP small-interfering RNA (siRNA).

RESULTS

Celecoxib triggered an ER stress response in this HNSCC cell line as shown by activation of CHOP, GRP78 and XBP1. The inhibition of cell proliferation by celecoxib was effectively hindered with CHOP siRNA.

CONCLUSION

ER stress response could be a COX2-independent anticancer mechanism of celecoxib.

Ocular-specific ER stress reduction rescues glaucoma in murine glucocorticoid-induced glaucoma

Administration of glucocorticoids induces ocular hypertension in some patients. If untreated, these patients can develop a secondary glaucoma that resembles primary open-angle glaucoma (POAG). The underlying pathology of glucocorticoid-induced glaucoma is not fully understood, due in part to lack of an appropriate animal model. Here, we developed a murine model of glucocorticoid-induced glaucoma that exhibits glaucoma features that are observed in patients. Treatment of WT mice with topical ocular 0.1% dexamethasone led to elevation of intraocular pressure (IOP), functional and structural loss of retinal ganglion cells, and axonal degeneration, resembling glucocorticoid-induced glaucoma in human patients. Furthermore, dexamethasone-induced ocular hypertension was associated with chronic ER stress of the trabecular meshwork (TM). Similar to patients, withdrawal of dexamethasone treatment reduced elevated IOP and ER stress in this animal model. Dexamethasone induced the transcriptional factor CHOP, a marker for chronic ER stress, in the anterior segment tissues, and Chop deletion reduced ER stress in these tissues and prevented dexamethasone-induced ocular hypertension. Furthermore, reduction of ER stress in the TM with sodium 4-phenylbutyrate prevented dexamethasone-induced ocular hypertension in WT mice. Our data indicate that ER stress contributes to glucocorticoid-induced ocular hypertension and suggest that reducing ER stress has potential as a therapeutic strategy for treating glucocorticoid-induced glaucoma.

[Effect of curcumin in inducing apoptosis of MDA-MB-213 cells by activating endoplasmic reticulum stress]

OBJECTIVE

To explore the possible mechanism of curcumin in inducing the apoptosis of breast cancer cell MDA-MB-231.

METHOD

Curcumin of different concentrations at 0, 10 25, 50, 100, 150, 200 micromol x L(-1) were used to intervene breast cancer cells MDA-MB-231 for 24 hours. MTT was used to observe its effect on the proliferation of breast cancer cells. The flow cytometry was used to detect its effect on the cell apoptosis. The real-time quantitative PCR and Western blot was used to assess the expression levels of GRP78 and CHOP in breast cancer cells.

RESULT

Curcumin could inhibit the proliferative ability of breast cancer cells by inducing them in a concentration-dependent manner. Curcumin could significantly increase the expression levels of GRP78 and CHOP in breast cancer cells.

CONCLUSION

Curcumin could induce the apoptosis of breast cancer cells MDA-MB-231 by activating endoplasmic reticulum stress.

Proteasome dysfunction mediates high glucose-induced apoptosis in rodent beta cells and human islets

The ubiquitin/proteasome system (UPS), a major cellular protein degradation machinery, plays key roles in the regulation of many cell functions. Glucotoxicity mediated by chronic hyperglycaemia is detrimental to the function and survival of pancreatic beta cells. The aim of our study was to determine whether proteasome dysfunction could be involved in beta cell apoptosis in glucotoxic conditions, and to evaluate whether such a dysfunction might be pharmacologically corrected. Therefore, UPS activity was measured in GK rats islets, INS-1E beta cells or human islets after high glucose and/or UPS inhibitor exposure. Immunoblotting was used to quantify polyubiquitinated proteins, endoplasmic reticulum (ER) stress through CHOP expression, and apoptosis through the cleavage of PARP and caspase-3, whereas total cell death was detected through histone-associated DNA fragments measurement. In vitro, we found that chronic exposure of INS-1E cells to high glucose concentrations significantly decreases the three proteasome activities by 20% and leads to caspase-3-dependent apoptosis. We showed that pharmacological blockade of UPS activity by 20% leads to apoptosis in a same way. Indeed, ER stress was involved in both conditions. These results were confirmed in human islets, and proteasome activities were also decreased in hyperglycemic GK rats islets. Moreover, we observed that a high glucose treatment hypersensitized beta cells to the apoptotic effect of proteasome inhibitors. Noteworthily, the decreased proteasome activity can be corrected with Exendin-4, which also protected against glucotoxicity-induced apoptosis. Taken together, our findings reveal an important role of proteasome activity in high glucose-induced beta cell apoptosis, potentially linking ER stress and glucotoxicity. These proteasome dysfunctions can be reversed by a GLP-1 analog. Thus, UPS may be a potent target to treat deleterious metabolic conditions leading to type 2 diabetes.

Abnormal chondrocyte apoptosis in the cartilage growth plate is influenced by genetic background and deletion of CHOP in a targeted mouse model of pseudoachondroplasia

Pseudoachondroplasia (PSACH) is an autosomal dominant skeletal dysplasia caused by mutations in cartilage oligomeric matrix protein (COMP) and characterised by short limbed dwarfism and early onset osteoarthritis. Mouse models of PSACH show variable retention of mutant COMP in the ER of chondrocytes, however, in each case a different stress pathway is activated and the underlying disease mechanisms remain largely unknown. T585M COMP mutant mice are a model of moderate PSACH and demonstrate a mild ER stress response. Although mutant COMP is not retained in significant quantities within the ER of chondrocytes, both BiP and the pro-apoptotic ER stress-related transcription factor CHOP are mildly elevated, whilst bcl-2 levels are decreased, resulting in increased and spatially dysregulated chondrocyte apoptosis. To determine whether the abnormal chondrocyte apoptosis observed in the growth plate of mutant mice is CHOP-mediated, we bred T585M COMP mutant mice with CHOP-null mice to homozygosity, and analysed the resulting phenotype. Although abnormal apoptosis was alleviated in the resting zone following CHOP deletion, the mutant growth plates were generally more disorganised. Furthermore, the bone lengths of COMP mutant CHOP null mice were significantly shorter at 9 weeks of age when compared to the COMP mutant mice, including a significant difference in the skull length. Overall, these data demonstrate that CHOP-mediated apoptosis is an early event in the pathobiology of PSACH and suggest that the lack of CHOP, in conjunction with a COMP mutation, may lead to aggravation of the skeletal phenotype via a potentially synergistic effect on endochondral ossification.

Hydrogen sulfide [corrected] increases survival during sepsis: protective effect of CHOP inhibition

Sepsis is a major cause of mortality, and dysregulation of the immune response plays a central role in this syndrome. H2S, a recently discovered gaso-transmitter, is endogenously generated by many cell types, regulating a number of physiologic processes and pathophysiologic conditions. We report that H2S increased survival after experimental sepsis induced by cecal ligation and puncture (CLP) in mice. Exogenous H2S decreased the systemic inflammatory response, reduced apoptosis in the spleen, and accelerated bacterial eradication. We found that C/EBP homologous protein 10 (CHOP), a mediator of the endoplasmic reticulum stress response, was elevated in several organs after CLP, and its expression was inhibited by H2S treatment. Using CHOP-knockout (KO) mice, we demonstrated for the first time, to our knowledge, that genetic deletion of Chop increased survival after LPS injection or CLP. CHOP-KO mice displayed diminished splenic caspase-3 activation and apoptosis, decreased cytokine production, and augmented bacterial clearance. Furthermore, septic CHOP-KO mice treated with H2S showed no additive survival benefit compared with septic CHOP-KO mice. Finally, we showed that H2S inhibited CHOP expression in macrophages by a mechanism involving Nrf2 activation. In conclusion, our findings show a protective effect of H2S treatment afforded, at least partially, by inhibition of CHOP expression. The data reveal a major negative role for the transcription factor CHOP in overall survival during sepsis and suggest a new target for clinical intervention, as well potential strategies for treatment.

Ampelopsin induces cell growth inhibition and apoptosis in breast cancer cells through ROS generation and endoplasmic reticulum stress pathway

Ampelopsin (AMP), a major bioactive constituent of Ampelopsis grossedentata, exerts a number of biological effects. In this study, we investigated its anti-cancer activity in human breast cancer cell lines, and explored the underlying mechanism of this action. Our results showed that treatment with AMP dose-dependently inhibited cell viability and induced apoptosis in MCF-7 and MDA-MB-231 breast cancer cells without cytotoxicity in human normal breast epithelial cells MCF-10A. Meanwhile, AMP dose- dependently triggered reactive oxygen species (ROS) generation in both breast cancer cells. The ROS scavenger N-acetyl-L-cysteine (NAC) strongly attenuated AMP-induced ROS production, along with cell growth inhibition and apoptosis. Furthermore, AMP was observed to activate endoplasmic reticulum (ER) stress, as evidenced by the up-regulation of ER stress-related proteins, including GRP78, p-PERK, p-elF2α, cleaved ATF6α and CHOP, while knockdown of ATF6α or PERK markedly down-regulated AMP-induced CHOP expression. Blocking ER stress using 4-phenylbutyric acid not only down-regulated AMP-induced GRP78 and CHOP expression, but also significantly decreased AMP-induced cell growth inhibition and apoptosis, whereas ER stress inducer thapsigargin played opposing effects. Additionally, NAC inhibited AMP-induced ER stress by down-regulating GRP78 and CHOP expression. Conversely, blocking ER stress using CHOP siRNA decreased AMP-induced ROS production and cell apoptosis. Taken together, these results demonstrate that AMP has anti-tumor effects against breast cancer cells through ROS generation and ER stress pathway, which therefore provide experimental evidences for developing AMP as a new therapeutic drug for breast cancer.

Anti-inflammatory effect of unsaturated fatty acids and Ergosta-7,22-dien-3-ol from Marthasterias glacialis: prevention of CHOP-mediated ER-stress and NF-κB activation

There has been increasing awareness to the potential interest of drug discovery from marine natural products to treat several pathological conditions, including inflammation. In this work we describe the anti-inflammatory activity of several compounds present in the echinoderm Marthasterias glacialis (spiny sea-star), using the inflammatory model RAW 264.7 cells challenged with LPS. Lipidomic profiling of the organism revealed two major classes of compounds: fatty acids and sterols. Among these, the predominant compounds cis 11-eicosenoic and cis 11,14 eicosadienoic acids and the unsaturated sterol ergosta-7,22-dien-3-ol were evaluated. The mechanism of action of the compounds was distinct as they modulated different levels of the inflammation pathway. Classical inflammatory markers, such as COX-2, iNOS, IL-6 and NF-κB, were evaluated. We also studied the contribution of the CHOP pathway-mediated ER-stress to the inflammatory process. Overall, the sterol ergosta-7,22-dien-3-ol was the most active compound, however maximum activity was obtained when all compounds were tested in combination, thus suggesting a potentially synergistic activity of both classes of metabolites. This work establishes the echinoderm M. glacialis as an interesting source of anti-inflammatory molecules.

Ablation of the proapoptotic genes CHOP or Ask1 does not prevent or delay loss of visual function in a P23H transgenic mouse model of retinitis pigmentosa

The P23H mutation in rhodopsin (Rho(P23H)) is a prevalent cause of autosomal dominant retinitis pigmentosa. We examined the role of the ER stress proteins, Chop and Ask1, in regulating the death of rod photoreceptors in a mouse line harboring the Rho(P23H) rhodopsin transgene (GHL(+)). We used knockout mice models to determine whether Chop and Ask1 regulate rod survival or retinal degeneration. Electrophysiological recordings showed similar retinal responses and sensitivities for GHL(+), GHL(+)/Chop(-/-) and GHL(+)/Ask1(-/-) animals between 4-28 weeks, by which time all three mouse lines exhibited severe loss of retinal function. Histologically, ablation of Chop and Ask1 did not rescue photoreceptor loss in young animals. However, in older mice, a regional protective effect was observed in the central retina of GHL(+)/Chop(-/-) and GHL(+)/Ask1(-/-), a region that was severely degenerated in GHL(+) mice. Our results show that in the presence of the Rho(P23H) transgene, the rate of decline in retinal sensitivity is similar in Chop or Ask1 ablated and wild-type retinas, suggesting that these proteins do not play a major role during the acute phase of photoreceptor loss in GHL(+) mice. Instead they may be involved in regulating secondary pathological responses such as inflammation that are upregulated during later stages of disease progression.

Bufalin induces the interplay between apoptosis and autophagy in glioma cells through endoplasmic reticulum stress

Malignant gliomas are common primary tumors of the central nervous system. The prognosis of patients with malignant glioma is poor in spite of current intensive therapy and thus novel therapeutic modalities are necessary. Bufalin is the major component of Chan-Su (a traditional Chinese medicine) extracts from the venom of Bufo gargarizan. In this study, we evaluated the growth inhibitory effect of bufalin on glioma cells and explored the underlying molecular mechanisms. Our results showed that bufalin inhibited the growth of glioma cells significantly. Mechanistic studies demonstrated that bufalin induced apoptosis through mitochondrial apoptotic pathway. In addition, bufalin was also found to induce ER stress-mediated apoptosis, which was supported by the up- regulation of ER stress markers, CHOP and GRP78, and augmented phosphorylation of PERK and eIF2α as well as cleavage of caspase-4. Downregulation of CHOP using siCHOP RNA attenuated bufalin-induced apoptosis, further confirming the role of ER stress response in mediating bufalin-induced apoptosis. Evidence of bufalin-induced autophagy included formation of the acidic vesicular organelles, increase of autophagolysosomes and LC3-II accumulation. Further experiments showed that the mechanism of bufalin-induced autophagy associated with ATP deleption involved an increase in the active form of AMPK, decreased phosphorylation levels of mTOR and its downstream targets 4EBP1 and p70S6K1. Furthermore, TUDC and silencing of eIF2α or CHOP partially blocked bufalin-induced accumulation of LC3-II, which indicated that ER stress preceded bufalin-induced autophagy and PERK/eIF2α/CHOP signaling pathway played a major part in the process. Blockage of autophagy increased expression of ER stress associated proteins and the ratio of apoptosis, indicating that autophagy played a cytoprotective role in bufalin induced ER stress and cell death. In conclusion, bufalin inhibits glioma cell growth and induces interplay between apoptosis and autophagy through endoplasmic reticulum stress. It will provide molecular bases for developing bufalin into a drug candidate for the treatment of maglinant glioma.

The role of thioredoxin-1 in suppression of endoplasmic reticulum stress in Parkinson disease

Endoplasmic reticulum (ER) stress has been implicated in Parkinson disease. We previously reported that thioredoxin 1 (Trx-1) suppressed the ER stress caused by 1-methy-4-phenyl-1,2,3,6-tetrahydropyridine; however, its molecular mechanism remains largely unknown. In the present study, we showed that 1-methyl-4-phenylpyridinium ion (MPP(+)) induced ER stress by activating glucose-regulated protein 78 (GRP78), inositol-requiring enzyme 1α (IRE1α), tumor necrosis factor receptor-associated factor 2 (TRAF2), c-Jun N-terminal kinase (JNK), caspase-12, and C/EBP homologous protein (CHOP) in PC12 cells. The downregulation of Trx-1 aggravated the ER stress and further increased the expression of the above molecules induced by MPP(+). In contrast, overexpression of Trx-1 attenuated the ER stress and repressed the expression of the above molecules induced by MPP(+). More importantly, the overexpression of Trx-1 in transgenic mice suppressed ER stress by inhibiting the activation of these molecules. We present, for the first time, the molecular mechanism of Trx-1 suppression of endoplasmic reticulum stress in Parkinson disease in vitro and in vivo. Based on our findings, we conclude that Trx-1 plays a neuroprotective role in Parkinson disease by suppressing ER stress by regulating the activation of GRP78, IRE1α, TRAF2, JNK, caspase-12, and CHOP.