Glucose regulated proteins 78 protects insulinoma cells (NIT-1) from death induced by streptozotocin, cytokines or cytotoxic T lymphocytes

Adoptive transfer of GRP78-treated dendritic cells alleviates insulitis in NOD mice

The 78-kDa glucose-regulated protein (GRP78) has extracellular, anti-inflammatory properties that can aid resolving inflammation. It has been established previously that GRP78 induced myeloid CD11c⁺ cell differentiation into distinct tolerogenic cells. This tolerance induction makes GRP78 a potential therapeutic agent for transplanted allogeneic grafts and autoimmune diseases, such as type 1 diabetes. In this research, it is revealed that rmGRP78-treated NOD mice bone marrow-derived CD11c⁺ cells (GRP78-DCs) highly expressed B7-H4 but down-regulated CD86 and CD40, and retained a tolerogenic signature even after stimulation by LPS. In the assessment of in vivo therapeutic efficacy after the adoptive transfer of GRP78-DCs into NOD mice, fluorescent imaging analyses revealed that the transfer specifically homed in inflamed pancreases, promoting β-cell survival and alleviating insulitis in NOD mice. The adoptive transfer of GRP78-DCs also helped reduce Th1, Th17, and CTL, suppressing inflammatory cytokine production in vivo. The findings suggest that adoptive GRP78-DC transfer is critical to resolving inflammation in NOD mice and may have relevance in a clinical setting.

Thioredoxin-1 Is a Target to Attenuate Alzheimer-Like Pathology in Diabetic Encephalopathy by Alleviating Endoplasmic Reticulum Stress and Oxidative Stress

Varying degrees of central nervous system neuropathy induced by diabetes mellitus (DM) contribute to a cognitive disorder known as diabetic encephalopathy (DE), which is also one of the independent risk factors for Alzheimer's disease (AD). Endoplasmic reticulum stress (ERS) plays a critical role in the occurrence and development of DE and AD. However, its molecular mechanism remains largely unknown. This study aims to investigate whether thioredoxin-1 (Trx-1) could alleviate DE and AD through ERS, oxidative stress (OS) and apoptosis signaling pathways. Mice were randomly divided into a wild-type group (WT-NC), a streptozotocin (STZ)-treated DM group (WT-DM), a Trx-1-TG group (TG-NC) and a Trx-1-TG DM group (TG-DM). Diabetic animals showed an increase in the time spent in the target quadrant and the number of platform crossings as well as AD-like behavior in the water maze experiment. The immunocontent of the AD-related protein Tau and the levels of cell apoptosis, β-amyloid (Aβ) plaque formation and neuronal degeneration in the hippocampus of the diabetic group were increased. Some key factors associated with ERS, such as protein disulfide isomerase (PDI), glucose-regulated protein 78 (GRP78), inositol-requiring enzyme 1α (IRE1α), tumor necrosis factor receptor-associated factor 2 (TRAF2), apoptosis signal-regulating kinase-1 (ASK1), c-Jun N-terminal kinase (JNK), protein kinase RNA (PKR)-like ER kinase (PERK), and C/EBP homologous protein (CHOP), were upregulated, and other factors related to anti-oxidant stress, such as nuclear factor erythroid 2-related factor (Nrf2), were downregulated in the DM group. Moreover, DM caused an increase in the immunocontents of caspase-3 and caspase-12. However, these changes were reversed in the Trx-1-tg DM group. Therefore, we conclude that Trx-1 might be a key factor in alleviating DE and AD by regulating ERS and oxidative stress response, thus preventing apoptosis.

Cambogin exerts anti-proliferative and pro-apoptotic effects on breast adenocarcinoma through the induction of NADPH oxidase 1 and the alteration of mitochondrial morphology and dynamics

Cambogin, a bioactive polycyclic polyprenylated acylphoroglucinol (PPAP) derived from the Garcinia genus, possesses proapoptotic effect in medulloblastoma and breast cancer cells. We have previously demonstrated that the proapoptotic effect of cambogin is driven by the production of reactive oxygen species (ROS). Here we have shown that the inhibitory effect of cambogin on cell proliferation is associated with the loss of mitochondrial transmembrane potential (ΔΨ_m) and mitochondrial fragmentation. Cambogin also promotes the mutual complex formation of the membrane-bound subunit p22^phox of NADPH oxidase 1 (NOX1), as well as the phosphorylation of the cytosolic subunit p47^phox, subsequently enhancing membrane-bound NOX1 activity, which leads to increases in intracellular and mitochondrial levels of O₂^.- and H₂O₂. Pharmacological inhibition of NOX1 using apocynin (pan-NOX inhibitor), ML171 (NOX1 inhibitor) or siRNA against NOX1 prevents the increases in O₂^.- and H₂O₂ levels and the anti-proliferative effect of cambogin. Antioxidants, including SOD (superoxide dismutase), CAT (catalase) and EUK-8, are also able to restore cell viability in the presence of cambogin. Besides, cambogin increases the dissociation of thioredoxin-1 (Trx1) from ASK1, switching the inactive form of ASK1 to the active kinase, subsequently leads to the phosphorylation of JNK/SAPK, which is abolished upon ML171 treatment. The proapoptotic effect of cambogin in breast cancer cells is also aggravated upon knocking down Trx1 in MCF-7 cells. Taken in conjunction, these data indicate that the anti-proliferative and pro-apoptotic effect of cambogin is mediated via inducing NOX1-dependent ROS production and the dissociation of ASK1 and Trx1.

GRP78 Impairs Production of Lipopolysaccharide-Induced Cytokines by Interaction with CD14

The 78-kDa glucose-regulated protein (GRP78) is a stress-inducible chaperone that resides primarily in the endoplasmic reticulum. GRP78 has been described to be released at times of cellular stress and as having extracellular properties that are anti-inflammatory or favor the resolution of inflammation. In the current study, we confirmed that GRP78 impaired the production of lipopolysaccharide-induced pro-inflammatory cytokines in GRP78-treated bone-marrow-derived dendritic cells (DCs). To explore the underlying mechanism, first of all, GRP78 was checked to be bound to the plasma membrane. Interestingly, such binding promoted endocytosis of toll-like receptor (TLR) 4 and reduction in TLR4 on the plasma surface had a key role in desensitization of GRP78-treated DCs to lipopolysaccharide. Given that cluster of differentiation (CD)14 is a crucial regulator of TLR4 endocytosis, interaction of GRP78 with CD14 was investigated next. Data showed that GRP78 co-localized with CD14 on the plasma membrane and glutathione-S-transferase-GRP78 precipitated CD14. In CD14 knockout mice, down-regulation of tumor necrosis factor-α and reduction in TLR4 on the plasma surface were abrogated in GRP78-treated DCs. Overall, these data suggested that GRP78 mediates endocytosis of TLR4 by targeting CD14 to favor the resolution of inflammation.

Glucose-Regulated Protein 78-Induced Myeloid Antigen-Presenting Cells Maintained Tolerogenic Signature upon LPS Stimulation

The 78-kDa glucose-regulated protein (Grp78) is stress-inducible chaperone that mostly reside in the endoplasmic reticulum. Grp78 has been described to be released at times of cellular stress and as having extracellular properties that are anti-inflammatory or favor the resolution of inflammation. As antigen-presenting cells (APCs) play a critical role in both the priming of adaptive immune responses and the induction of self-tolerance, herein, we investigated the effect of Grp78 on the maturation of murine myeloid APCs (CD11c⁺ cells). Results showed that CD11c⁺ cells could be bound by AF488-labeled Grp78 and that Grp78 treatment induced a tolerogenic phenotype comparable to immature cells. Furthermore, when exposed to lipopolysaccharide, Grp78-treated CD11c⁺ cells (DC_Grp78) did not adopt a mature dendritic cell phenotype. DC_Grp78-primed T cells exhibited reduced proliferation along with a concomitant expansion of CD4⁺CD25⁺FoxP3⁺ cells in pancreaticoduodenal lymph nodes and induction of T cell apoptosis in vitro and ex vivo. The above work suggests that Grp78 is an immunomodulatory molecule that could aid resolution of inflammation. It may thus contribute to induce durable tolerance to be of potential therapeutic benefit in transplanted allogeneic grafts and autoimmune diseases such as type I diabetes.

Overexpression of GRP78 enhances survival of CHO cells in response to serum deprivation and oxidative stress

Chinese hamster ovary (CHO) cells are regarded as one of the most commonly used mammalian hosts, which decreases the productivity due to loss in culture viability. Overexpressing antiapoptosis genes in CHO cells was developed as a means of limiting cell death upon exposure to environmental insults. Glucose-regulated protein 78 (GRP78) is traditionally regarded as a major ER chaperone that participates in protein folding and other cell processes. It is also a potent antiapoptotic protein and plays a critical role in cell survival, proliferation, and metastasis. In this study, the impact of GRP78 on CHO cells in response to environmental insults such as serum deprivation and oxidative stress was investigated. First, it was confirmed that CHO cells were very sensitive to environmental insults. Then, GRP78 overexpressing CHO cell line was established and exposed to serum deprivation and H₂O₂. Results showed that GRP78 engineering increased the viability and decreased the apoptosis of CHO cells. The survival advantage due to GRP78 engineering could be mediated by suppression of caspase-3 involved in cell death pathways in stressed cells. Besides, GRP78 engineering also enhanced yields of antibody against transferrin receptor in CHO cells. GRP78 should be a potential application in the biopharmaceutical industries.

Immunomodulation by MYB is associated with tumor relapse in patients with early stage colorectal cancer

The presence of tumor immune infiltrating cells (TILs), particularly CD8⁺ T-cells, is a robust predictor of outcome in patients with colorectal cancer (CRC). We revisited TIL abundance specifically in patients with microsatellite stable (MSS) CRC without evidence of lymph node or metastatic spread. Examination of the density of CD8⁺ T-cells in primary tumors in the context of other pro-oncogenic markers was performed to investigate potential regulators of TILs. Two independent cohorts of patients with MSS T2-4N0M0 CRC, enriched for cases with atypical relapse, were investigated. We quantified CD8⁺ and CD45RO⁺ -TILs, inflammatory markers, NFkBp65, pStat3, Cyclo-oxygenase-2 (COX2) and GRP78 as well as transcription factors (TF), β-catenin and MYB. High CD8⁺ TILs correlated with a better relapse-free survival in both cohorts (p = 0.002) with MYB and its target gene, GRP78 being higher in the relapse group (p = 0.001); no difference in pSTAT3 and p65 was observed. A mouse CRC (CT26) model was employed to evaluate the effect of MYB on GRP78 expression as well as T-cell infiltration. MYB over-expressing in CT26 cells increased GRP78 expression and the analysis of tumor-draining lymph nodes adjacent to tumors showed reduced T-cell activation. Furthermore, MYB over-expression reduced the efficacy of anti-PD-1 to modulate CT26 tumor growth. This high MYB and GRP78 show a reciprocal relationship with CD8⁺ TILs which may be useful refining the prediction of patient outcome. These data reveal a new immunomodulatory function for MYB suggesting a basis for further development of anti-GRP78 and/or anti-MYB therapies.

Hepatitis B virus enhances cisplatin-induced hepatotoxicity via a mechanism involving suppression of glucose-regulated protein of 78 Kda

Cisplatin is a classical platinum-based chemotherapeutic drug used in the treatment of many cancer types, including hepatocellular carcinoma (HCC). The application of cisplatin is significantly limited by its toxicity, which may be affected by various biological factors. Persistence of Hepatitis B virus (HBV) infection leads to HCC development and may be associated with higher incidence of severe hepatitis during chemotherapy. However, whether HBV alters the susceptibility of hepatocytes to cisplatin remains poorly understood. Here, we demonstrate that HBV transfection enhanced cisplatin-induced hepatotoxicity via a mechanism involving suppression of glucose-regulated protein of 78 KDa (Grp78), a major stress-induced chaperone that localizes to the endoplasmic reticulum. Silencing Grp78 gene increased the susceptibility of HepG2 to cisplatin by activating caspase-3. Grp78 expression was down-regulated by HBV infection both in vitro and in liver tissues of patients. We compared the cisplatin sensitivity of hepatoma cells either expressing (HepG2.2.15 cells) or not expressing the entire Hepatitis B Virus genome (HepG2). HepG2.2.15 cells showed increased sensitivity to cisplatin and a higher apoptosis rate. Overexpression of Grp78 counteracted the increase of sensitivity of HepG2.215 cells to cisplatin. Furthermore, we found that HBV disrupted Grp78 synthesis in response to cisplatin stimulation, which may trigger severe and prolonged endoplasmic reticulum (ER) stress that can induce cellular apoptosis. Our findings provide new information into the effect of HBV in the modulation of Grp78 expression, and, consequently on cisplatin-induced hepatotoxicity during viral infection.

Cytokines and Pancreatic β-Cell Apoptosis

The discovery 30 years ago that inflammatory cytokines cause a concentration, activity, and time-dependent bimodal response in pancreatic β-cell function and viability has been a game-changer in the fields of research directed at understanding inflammatory regulation of β-cell function and survival and the causes of β-cell failure and destruction in diabetes. Having until then been confined to the use of pathophysiologically irrelevant β-cell toxic chemicals as a model of β-cell death, researchers could now mimic endocrine and paracrine effects of the cytokine response in vitro by titrating concentrations in the low to the high picomolar-femtomolar range and vary exposure time for up to 14-16h to reproduce the acute regulatory effects of systemic inflammation on β-cell secretory responses, with a shift to inhibition at high picomolar concentrations or more than 16h of exposure to illustrate adverse effects of local, chronic islet inflammation. Since then, numerous studies have clarified how these bimodal responses depend on discrete signaling pathways. Most interest has been devoted to the proapoptotic response dependent upon mainly nuclear factor κ B and mitogen-activated protein kinase activation, leading to gene expressional changes, endoplasmic reticulum stress, and triggering of mitochondrial dysfunction. Preclinical studies have shown preventive effects of cytokine antagonism in animal models of diabetes, and clinical trials demonstrating proof of concept are emerging. The full clinical potential of anticytokine therapies has yet to be shown by testing the incremental effects of appropriate dosing, timing, and combinations of treatments. Due to the considerable translational importance of enhancing the precision, specificity, and safety of antiinflammatory treatments of diabetes, we review here the cellular, preclinical, and clinical evidence of which of the death pathways recently proposed in the Nomenclature Committee on Cell Death 2012 Recommendations are activated by inflammatory cytokines in the pancreatic β-cell to guide the identification of antidiabetic targets. Although there are still scarce human data, the cellular and preclinical studies point to the caspase-dependent intrinsic apoptosis pathway as the prime effector of inflammatory β-cell apoptosis.

Pancreatic beta cells are highly susceptible to oxidative and ER stresses during the development of diabetes

The complex interplay of many cell types and the temporal heterogeneity of pancreatic islet composition obscure the direct role of resident alpha and beta cells in the development of Type 1 diabetes. Therefore, in addition to studying islets isolated from non-obese diabetic mice, we analyzed homogeneous cell populations of murine alpha (αTC-1) and beta (NIT-1) cell lines to understand the role and differential survival of these two predominant islet cell populations. A total of 56 proteins in NIT-1 cells and 50 in αTC-1 cells were differentially expressed when exposed to proinflammatory cytokines. The major difference in the protein expression between cytokine-treated NIT-1 and αTC-1 cells was free radical scavenging enzymes. A similar observation was made in cytokine-treated whole islets, where a comprehensive analysis of subcellular fractions revealed that 438 unique proteins were differentially expressed under inflammatory conditions. Our data indicate that beta cells are relatively susceptible to ER and oxidative stress and reveal key pathways that are dysregulated in beta cells during cytokine exposure. Additionally, in the islets, inflammation also leads to enhanced antigen presentation, which completes a three-way insult on beta cells, rendering them targets of infiltrating T lymphocytes.

Ventricular hypertrophy blocked delayed anesthetic cardioprotection in rats by alteration of iNOS/COX-2 signaling

The aim of the current study was to determine whether ventricular hypertrophy affects the delayed isoflurane preconditioning against myocardial ischemia-reperfusion (IR) injury. Transverse aortic constriction (TAC) was performed on male Sprague-Dawley rats to induce left ventricular (LV) hypertrophy, then sham-operated or hypertrophied rat hearts were subjected to isoflurane preconditioning (2.1% v/v, 1 h). 24 h after exposure, the hearts were isolated and perfused retrogradely by the Langendorff for 30 min (equilibration) followed by 40 min of ischemia and then 120 min of reperfusion. The hemodynamics, infarct size, apoptosis, nitric oxide synthase (NOS), cyclooxygenase-2 (COX-2), Cleaved Caspase-3 and production of NO were determined. We found that the hemodynamic parameters were all markedly improved during the reperfusion period and the myocardial infarct size and apoptosis was significantly reduced by delayed isoflurane preconditioning in sham-operated rats. However, such cardiac improvement induced by delayed isoflurane preconditioning was not observed in hypertrophied hearts. The expression of iNOS, COX-2 and NO was markedly enhanced, whereas Cleaved Caspase-3 activity was inhibited by delayed isoflurane preconditioning in sham-operated rats, a phenomenon was not found in TAC-control groups pretreated with isoflurane. Our results demonstrated that ventricular hypertrophy abrogated isoflurane-induced delayed cardioprotection by alteration of iNOS/COX-2 pathway.

β-Cell responses to nitric oxide

Autoimmune diabetes is characterized by the selective destruction of insulin-secreting β-cells that occurs during an inflammatory reaction in and around pancreatic islets of Langerhans. Cytokines such as interleukin-1, released by activated immune cells, have been shown to inhibit insulin secretion from pancreatic β-cells and cause islet destruction. In response to cytokines, β-cells express inducible nitric oxide synthase and produce micromolar levels of the free radical nitric oxide. Nitric oxide inhibits the mitochondrial oxidation of glucose resulting in an impairment of insulin secretion. Nitric oxide is also responsible for cytokine-mediated DNA damage in β-cells. While nitric oxide mediates the inhibitory and toxic effects of cytokines, it also activates protective pathways that allow β-cells to recover from this damage. This review will focus on the dual role of nitric oxide as a mediator of cytokine-induced damage and the activator of repair mechanisms that protect β-cells from cytokine-mediated injury.

Update on the protective molecular pathways improving pancreatic beta-cell dysfunction

The primary function of pancreatic beta-cells is to produce and release insulin in response to increment in extracellular glucose concentrations, thus maintaining glucose homeostasis. Deficient beta-cell function can have profound metabolic consequences, leading to the development of hyperglycemia and, ultimately, diabetes mellitus. Therefore, strategies targeting the maintenance of the normal function and protecting pancreatic beta-cells from injury or death might be crucial in the treatment of diabetes. This narrative review will update evidence from the recently identified molecular regulators preserving beta-cell mass and function recovery in order to suggest potential therapeutic targets against diabetes. This review will also highlight the relevance for novel molecular pathways potentially improving beta-cell dysfunction.

Signalling danger: endoplasmic reticulum stress and the unfolded protein response in pancreatic islet inflammation

Protein synthesis is increased by several-fold in stimulated pancreatic beta cells. Synthesis and folding of (pro)insulin takes place in the endoplasmic reticulum (ER), and beta cells trigger the unfolded protein response (UPR) to upgrade the functional capacity of the ER. Prolonged or excessive UPR activation contributes to beta cell dysfunction and death in type 2 diabetes, but there is another side of the UPR that may be of particular relevance for autoimmune type 1 diabetes, namely, the cross-talk between the UPR and innate immunity/inflammation. Recent evidence, discussed in this review, indicates that both saturated fats and inflammatory mediators such as cytokines trigger the UPR in pancreatic beta cells. The UPR potentiates activation of nuclear factor κB, a key regulator of inflammation. Two branches of the UPR, namely IRE1/XBP1s and PERK/ATF4/CHOP, mediate the UPR-induced sensitisation of pancreatic beta cells to the proinflammatory effects of cytokines. This can contribute to the upregulation of local inflammatory mechanisms and the aggravation of insulitis. The dialogue between the UPR and inflammation may provide an explanation for the parallel increase in the prevalence of childhood obesity and type 1 diabetes.

Endoplasmic reticulum chaperone GRP78 suppresses the aggregation of proteins containing expanded polyglutamine tract

Polyglutamine (polyQ) diseases are inherited neurodegenerative diseases characterized by the aggregation of proteins containing expanded polyQ tract. It has been shown that expanded polyQ tract-containing proteins impair the functions of other cellular proteins. However, quantitative changes of cellular proteins in cells expressing expanded polyQ tract-containing proteins have not been performed. Here, we performed proteomic analysis of cells expressing expanded polyQ tract-containing proteins, and showed that GRP78, the endoplasmic reticulum (ER) chaperone, was significantly decreased in the cells expressing enhanced green fluorescent protein with a pathological-length polyQ tract (EGFP-polyQ97), but not with a non-pathological-length polyQ tract (EGFP-polyQ24). In addition, we revealed that down-regulation of GRP78 expression resulted in increase of the aggregation of EGFP-polyQ97. Conversely, the aggregation of EGFP-polyQ97 was suppressed by the overexpression of GRP78 in the cells. Furthermore, it seemed that the decreased GRP78 expression in the cells expressing EGFP-polyQ97 was due to the enhanced protein degradation of GRP78 through the ubiquitin-proteasome pathway. These findings indicated that GRP78, which has an inhibitory effect on the aggregation of proteins containing expanded polyQ tract, may be an effective target for the treatment of polyQ diseases.

Co-silencing of Birc5 (survivin) and Hspa5 (Grp78) induces apoptosis in hepatoma cells more efficiently than single gene interference

Birc5 (previously known as survivin) is a cancer-specific protein. Due to the upregulation of its expression in various human malignancies and its key role in apoptosis, proliferation and angiogenesis, Birc5 has attracted attention as a target for anticancer therapies. In this study, when Birc5 was silenced in HepG2 cells, 29.7±3.3% cells underwent apoptosis as expected. It was found that the expression levels of glucose-regulated protein 78 (Hspa5, previously known as Grp78) was increased by almost 3-fold in Birc5-silenced HepG2 cells. Hspa5, a master regulator of the anti-apoptotic unfolded protein response signalling network, can also promote tumor proliferation, survival and metastasis. Hence, we hypothesized that the co-silencing of Birc5 and Hspa5 may exert a stronger apoptosis-inducing effect than single gene interference. To verify this, the expression levels of Birc5 and Hspa5 in human hepatocellular carcinoma tissues were determined. Immunohistochemical staining showed that the expression of Birc5 and Hspa5 was elevated in 28 out of 31 samples. Additionally, plasmid-based siRNA against Birc5 and/or Hspa5 were constructed and transfected into the human hepatocellular liver carcinoma cell line, HepG2. Compared with the HepG2 cells, in which Birc5 or Hspa5 were silenced alone, only 44.2±3.4% of the co-silenced cells proliferated, and 40.3±3.7% co-silenced cells underwent apoptosis (p<0.05). Furthermore, tumor formation from inoculated subcutaneous co-silenced cells in nude mice was inhibited significantly. The current study suggests that Birc5 and Hspa5 could be important survival factors for hepatoma carcinoma cells and that the simultaneous knockdown of Birc5 and Hspa5 is more effective in inducing apoptosis in HepG2 cells than the knockdown of Birc5 or Hspa5 alone. The co-silencing of Birc5 and Hspa5 could be warranted for cancer therapy.

XJP-1, a novel ACEI, with anti-inflammatory properties in HUVECs

AIM

We investigated whether 8-dihydroxy-3-methyl-isochromanone (XJP-1), a novel angiotensin-converting enzyme inhibitor (ACEI), exhibited inhibitory activity to lipopolysaccharide (LPS)-accelerated vascular inflammation.

METHODS

Human umbilical vein endothelial cells (HUVECs) were isolated from human umbilical cords and cultured. The direct effect of XJP-1 on the activation of endothelial cells was measured using MTT assay. Nitric oxide (NO) in the culture medium was measured using Griess method. The expression of cell adhesion molecules (ICAM-1 and VCAM-1) was determined by flow cytometry and RT-PCR. The protein expression levels of tumor necrosis factor-α (TNF-α), monocyte chemotactic protein (MCP)-1, and endothelin-1 (ET-1) secretion were measured using ELISA. Quantitative analysis of eNOS, iNOS, inhibitory factor NF-κB (IκB) and MAPKs were determined using Western blot analysis. The translocation of NF-κB from the cytoplasm to the nucleus was determined using immunofluorescence.

RESULTS

XJP-1 significantly inhibited LPS-mediated endothelial cell dysfunction, as measured by NO production, iNOS expression, adhesion molecule (ICAM-1, VCAM-1) expression, and chemokine (TNF-α, MCP-1) production in vitro. It up-regulated eNOS expression in the same experimental setting. XJP-1 alone was found non-cytotoxic at the concentration up to 1000μM. The mechanistic investigations of XJP-1 suppression LPS-induced inflammation in HUVECs revealed that XJP-1 blocked NF-κB nuclear entry in an IκB-dependent manner, as well as inhibited MAPK activation induced by LPS. XJP-1 reduced endothelin-1 secretion and increased nitric oxide metabolite production by HUVECs. However, the effect of XJP-1 on nitric oxide and endothelin-1 metabolite production is mediated by the activation of bradykinin B(2) receptor being counteracted, at least in part, by a specific antagonist.

CONCLUSION

XJP-1 inhibited LPS-induced cytotoxicity and inflammatory response. The mechanism underlying this protective effect might be related to the inhibition of MAPK and NF-κB signaling pathway activation, suggesting the potential inhibition of the atherosclerotic process by suppressing the expression of chemoattractant molecules and monocyte adhesion. XJP-1 also has an effect in improving endothelin-1 through activating bradykinin B(2) receptor. These findings indicated that XJP-1 is potentially a novel therapeutic candidate for the treatment of atherosclerosis.

Differential effects of proinflammatory cytokines on cell death and ER stress in insulin-secreting INS1E cells and the involvement of nitric oxide

Proinflammatory cytokines produced by immune cells destroy pancreatic beta cells in type 1 diabetes. The aim of this study was to investigate the cytokine network and its effects in insulin-secreting cells. INS1E cells were exposed to different combinations of proinflammatory cytokines. Cytokine toxicity was estimated by MTT assay and caspase activation measurements. The NFκB-iNOS pathway was analyzed by a SEAP reporter gene assay, Western-blotting and nitrite measurements. Gene expression analyses of ER stress markers, Chop and Bip, were performed by real-time RT-PCR. Cytokines tested in this study, namely IL-1β, TNFα and IFNγ, had deleterious effects on beta cell viability. The most potent toxicity exhibited IL-1β and its combinations with other cytokines. The toxic effects of IL-1β towards cell viability, caspase activation and iNOS activity were dependent on nitric oxide and abolished by an iNOS blocker. IL-1β was the strongest inducer of the NFκB activation. An iNOS blocker inhibited IL-1β-mediated NFκB activation in the first, initial phase of cytokine action, but did not affect significantly NFκB activation after prolonged incubation. Interestingly iNOS protein expression was induced predominantly by IL-1β and decreased in the presence of an iNOS blocker in the case of a short time exposure. The changes in the expression of ER stress markers were also almost exclusively dependent on the IL-1β presence and counteracted by iNOS blockade. Thus cytokine-induced beta cell death is primarily IL-1β mediated with a NO-independent enhancement by TNFα and IFNγ. The deleterious effects on cell viability and function are crucially dependent on IL-1β-induced nitric oxide formation.

Sustained production of spliced X-box binding protein 1 (XBP1) induces pancreatic beta cell dysfunction and apoptosis

AIMS/HYPOTHESIS

Pro-inflammatory cytokines involved in the pathogenesis of type 1 diabetes deplete endoplasmic reticulum (ER) Ca2+ stores, leading to ER-stress and beta cell apoptosis. However, the cytokine-induced ER-stress response in beta cells is atypical and characterised by induction of the pro-apoptotic PKR-like ER kinase (PERK)-C/EBP homologous protein (CHOP) branch of the unfolded protein response, but defective X-box binding protein 1 (XBP1) splicing and activating transcription factor 6 activation. The purpose of this study was to overexpress spliced/active Xbp1 (XBP1s) to increase beta cell resistance to cytokine-induced ER-stress and apoptosis.

METHODS

Xbp1s was overexpressed using adenoviruses and knocked down using small interference RNA in rat islet cells. In selected experiments, Xbp1 was also knocked down in FACS-purified rat beta cells and rat fibroblasts. Expression and production of XBP1s and key downstream genes and proteins was measured and beta cell function and viability were evaluated.

RESULTS

Adenoviral-mediated overproduction of Xbp1s resulted in increased XBP1 activity and induction of several XBP1s target genes. Surprisingly, XBP1s overexpression impaired glucose-stimulated insulin secretion and increased beta cell apoptosis, whereas it protected fibroblasts against cell death induced by ER-stress. mRNA expression of Pdx1 and Mafa was inhibited in cells overproducing XBP1s, leading to decreased insulin expression. XBP1s knockdown partially restored cytokine/ER-stress-driven insulin and Pdx1 inhibition but had no effect on cytokine-induced ER-stress and apoptosis.

CONCLUSIONS/INTERPRETATION

XBP1 has a distinct inhibitory role in beta cell as compared with other cell types. Prolonged XBP1s production hampers beta cell function via inhibition of insulin, Pdx1 and Mafa expression, eventually leading to beta cell apoptosis.

Insights into modeling streptozotocin-induced diabetes in ICR mice

Streptozotocin (STZ)-induced diabetes in ICR mice is often used to model diabetes mellitus and its complications, as well as other pathologies. In studies of diabetes progression and effects of newly developed treatments, experimental results may be difficult to interpret because blood glucose levels (BGLs) of untreated diabetic control animals tend to decline substantially during typical experimental time spans of 8-11 h. To address this problem, the authors examined several experimental conditions that might affect BGL stability, including STZ dose, initial mouse weight, fasting regimen and light:dark cycle. The authors found that diabetes severity was dependent on initial mouse weight and that weight loss after diabetes induction was less severe in heavier mice. Furthermore, a dose of 150 mg STZ per kg body weight was sufficient to induce stabilized acute diabetes without causing many complications. Finally, BGL could be stabilized in diabetic mice that were not treated with insulin by avoiding pre-fasting before an 8-h experiment and by allowing mice limited access to food during the experiment.

The altered expression of glucose-regulated proteins 78 in different phase of streptozotocin-affected pancreatic beta-cells

Endoplasmic reticulum (ER) stress-mediated apoptosis plays an important role in the destruction of pancreatic beta-cells and contributes to the development of type 1 diabetes. The chaperone molecule, glucose-regulated proteins 78 (Grp78), is required to maintain ER function during toxic insults. In this study, we investigated the changes of Grp78 expression in different phases of streptozotocin (STZ)-affected beta-cells to explore the relationship between Grp78 and the response of beta-cells to ER stress. An insulinoma cell line (NIT-1) treated with STZ for different time periods and STZ-induced diabetic Balb/C mice at different time points were used as the model system. The level of Grp78 and C/EBP homologous protein (CHOP) mRNA were detected by real-time polymerase chain reaction and their protein by immunoblot. Apoptosis and necrosis was measured by flow cytometry. In addition, the changes of Grp78 protein in STZ-treated nondiabetic mice were also detected by immunoblot. Grp78 expression significantly increased in the early phase but decreased in the later phase of affected beta-cells, while CHOP was induced and apoptosis occurred along with the decrease of Grp78. Interestingly, the Grp78 protein of STZ-treated nondiabetic mice increased stably compared with that of the control. From the results, we can conclude that Grp78 may contribute to the response of beta-cells to ER stress, and more attention should be paid to Grp78 in the improvement of diabetes.

GRP78, but Not Protein-disulfide Isomerase, Partially Reverses Hyperglycemia-induced Inhibition of Insulin Synthesis and Secretion in Pancreatic {beta}-Cells

Chronic hyperglycemia contributes to pancreatic beta-cell dysfunction during the development of type 2 diabetes. Treatment of pancreatic beta-cells with prolonged high glucose concentrations has been shown to reduce insulin promoter activity and insulin gene expression. Here, we examined the effect of high glucose on endoplasmic reticulum (ER) stress pathway activation and insulin production in INS-1 832/13 pancreatic beta-cells. Treatment of cells with 25 mm glucose for 24-48 h decreased insulin mRNA and protein levels and reduced the proinsulin translation rate, which was accompanied by enhanced unfolded protein response pathway activation (XBP-1 mRNA splicing and increased phospho-eIF2alpha, CHOP, and active ATF6 levels). Overexpressing the ER chaperone GRP78 partially rescued high glucose-induced suppression of proinsulin levels and improved glucose-stimulated insulin secretion with no effect on insulin 2 mRNA levels. Under these conditions, there was little effect of GRP78 overexpression on ER stress markers. Knockdown of GRP78 expression under basal glucose conditions reduced cellular insulin levels and glucose-stimulated insulin secretion. Thus, GRP78 is essential for insulin biosynthesis, and enhancing chaperone capacity can improve beta-cell function in the presence of prolonged hyperglycemia. In contrast, overexpression of the ER chaperone and oxidoreductase protein-disulfide isomerase (PDI) reduced glucose-stimulated insulin secretion and induced ER stress resulting from the accumulation of proinsulin in the ER. These results suggest a role for both GRP78 and PDI in insulin biosynthesis, although an excess of PDI disrupts normal proinsulin processing.

Cytokine-induced beta-cell death is independent of endoplasmic reticulum stress signaling

OBJECTIVE

Cytokines contribute to beta-cell destruction in type 1 diabetes. Endoplasmic reticulum (ER) stress-mediated apoptosis has been proposed as a mechanism for beta-cell death. We tested whether ER stress was necessary for cytokine-induced beta-cell death and also whether ER stress gene activation was present in beta-cells of the NOD mouse model of type 1 diabetes.

RESEARCH DESIGN AND METHODS

INS-1 beta-cells or rat islets were treated with the chemical chaperone phenyl butyric acid (PBA) and exposed or not to interleukin (IL)-1beta and gamma-interferon (IFN-gamma). Small interfering RNA (siRNA) was used to silence C/EBP homologous protein (CHOP) expression in INS-1 beta-cells. Additionally, the role of ER stress in lipid-induced cell death was assessed.

RESULTS

Cytokines and palmitate triggered ER stress in beta-cells as evidenced by increased phosphorylation of PKR-like ER kinase (PERK), eukaryotic initiation factor (EIF)2alpha, and Jun NH(2)-terminal kinase (JNK) and increased expression of activating transcription factor (ATF)4 and CHOP. PBA treatment attenuated ER stress, but JNK phosphorylation was reduced only in response to palmitate, not in response to cytokines. PBA had no effect on cytokine-induced cell death but was associated with protection against palmitate-induced cell death. Similarly, siRNA-mediated reduction in CHOP expression protected against palmitate- but not against cytokine-induced cell death. In NOD islets, mRNA levels of several ER stress genes were reduced (ATF4, BiP [binding protein], GRP94 [glucose regulated protein 94], p58, and XBP-1 [X-box binding protein 1] splicing) or unchanged (CHOP and Edem1 [ER degradation enhancer, mannosidase alpha-like 1]).

CONCLUSIONS

While both cytokines and palmitate can induce ER stress, our results suggest that, in contrast to lipoapoptosis, the PERK-ATF4-CHOP ER stress-signaling pathway is not necessary for cytokine-induced beta-cell death.

JunB Inhibits ER Stress and Apoptosis in Pancreatic Beta Cells

Cytokines contribute to pancreatic β-cell apoptosis in type 1 diabetes (T1D) by modulation of β-cell gene expression networks. The transcription factor Activator Protein-1 (AP-1) is a key regulator of inflammation and apoptosis. We presently evaluated the function of the AP-1 subunit JunB in cytokine-mediated β-cell dysfunction and death. The cytokines IL-1β+IFN-γ induced an early and transitory upregulation of JunB by NF-κB activation. Knockdown of JunB by RNA interference increased cytokine-mediated expression of inducible nitric oxide synthase (iNOS) and endoplasmic reticulum (ER) stress markers, leading to increased apoptosis in an insulin-producing cell line (INS-1E) and in purified rat primary β-cells. JunB knockdown β-cells and junB^−/− fibroblasts were also more sensitive to the chemical ER stressor cyclopiazonic acid (CPA). Conversely, adenoviral-mediated overexpression of JunB diminished iNOS and ER markers expression and protected β-cells from cytokine-induced cell death. These findings demonstrate a novel and unexpected role for JunB as a regulator of defense mechanisms against cytokine- and ER stress-mediated apoptosis.

The role for endoplasmic reticulum stress in diabetes mellitus

Accumulating evidence suggests that endoplasmic reticulum (ER) stress plays a role in the pathogenesis of diabetes, contributing to pancreatic beta-cell loss and insulin resistance. Components of the unfolded protein response (UPR) play a dual role in beta-cells, acting as beneficial regulators under physiological conditions or as triggers of beta-cell dysfunction and apoptosis under situations of chronic stress. Novel findings suggest that "what makes a beta-cell a beta-cell", i.e., its enormous capacity to synthesize and secrete insulin, is also its Achilles heel, rendering it vulnerable to chronic high glucose and fatty acid exposure, agents that contribute to beta-cell failure in type 2 diabetes. In this review, we address the transition from physiology to pathology, namely how and why the physiological UPR evolves to a proapoptotic ER stress response and which defenses are triggered by beta-cells against these challenges. ER stress may also link obesity and insulin resistance in type 2 diabetes. High fat feeding and obesity induce ER stress in liver, which suppresses insulin signaling via c-Jun N-terminal kinase activation. In vitro data suggest that ER stress may also contribute to cytokine-induced beta-cell death. Thus, the cytokines IL-1beta and interferon-gamma, putative mediators of beta-cell loss in type 1 diabetes, induce severe ER stress through, respectively, NO-mediated depletion of ER calcium and inhibition of ER chaperones, thus hampering beta-cell defenses and amplifying the proapoptotic pathways. A better understanding of the pathways regulating ER stress in beta-cells may be instrumental for the design of novel therapies to prevent beta-cell loss in diabetes.