ER stress-induced inflammation: does it aid or impede disease progression?

Engineering nanomedicines through boosting immunogenic cell death for improved cancer immunotherapy

Current cancer immunotherapy has limited response rates in a large variety of solid tumors partly due to the low immunogenicity of the tumor cells and the immunosuppressive tumor microenvironment (ITM). A number of clinical cancer treatment modalities, including radiotherapy, chemotherapy, photothermal and photodynamic therapy, have been shown to elicit immunogenicity by inducing immunogenic cell death (ICD). However, ICD-based immunotherapy is restricted by the ITM limiting its efficacy in eliciting a long-term antitumor immune response, and by severe systemic toxicity. To address these challenges, nanomedicine-based drug delivery strategies have been exploited for improving cancer immunotherapy by boosting ICD of the tumor cells. Nanosized drug delivery systems are promising for increasing drug accumulation at the tumor site and codelivering ICD inducers and immune inhibitors to simultaneously elicit the immune response and relieve the ITM. This review highlights the recent advances in nanomedicine-based immunotherapy utilizing ICD-based approaches. A perspective on the clinical translation of nanomedicine-based cancer immunotherapy is also provided.

Endoplasmic reticulum stress-dependent activation of iNOS/NO-NF-κB signaling and NLRP3 inflammasome contributes to endothelial inflammation and apoptosis associated with microgravity

Exposure to microgravity results in vascular remodeling and cardiovascular dysfunction. To elucidate the mechanism involved in this condition, we investigated whether endoplasmic reticulum (ER) stress during simulated microgravity induced endothelial inflammation and apoptosis in human umbilical vein endothelial cells (HUVECs). Microgravity was simulated by clinorotation in the current study. We examined markers of ER stress, inducible nitric oxide (NO) synthase (iNOS)/NO content, proinflammatory cytokine production, nuclear factor kappa B (NF-κB)/IκB signaling, NLRP3 inflammasome, and detected apoptosis in HUVECs. We found that the levels of C/EBP homologous protein and glucose-regulated protein 78, pro-inflammatory cytokines (IL-6, TNF-α, IL-8, and IL-1β), and iNOS/NO content were upregulated by clinorotation. ER stress inhibition with tauroursodeoxycholic acid or 4-phenylbutyric acid and iNOS inhibition with 1400 W dramatically suppressed activation of the NF-κB/IκB pathway and the NLRP3 inflammasome, and decreased the production of pro-inflammatory cytokines. The increase of apoptosis in HUVECs during clinorotation was significantly suppressed by inhibiting ER stress, iNOS activity, NF-κB/IκB, and the NLRP3 inflammasome signaling pathway. Therefore, simulated microgravity causes ER stress in HUVECs, and subsequently activates iNOS/NO-NF-κB/IκB and the NLRP3 inflammasome signaling pathway, which have key roles in the induction of endothelial inflammation and apoptosis.

Crosstalk between ER stress, NLRP3 inflammasome, and inflammation

Endoplasmic reticulum stress (ERS) is a protective response to restore protein homeostasis by activating the unfolded protein response (UPR). However, UPR can trigger cell death under severe and/or persistently high ERS. The NLRP3 inflammasome is a complex of multiple proteins that activates the secretion of the proinflammatory cytokine IL-1β in a caspase-1-dependent manner to participate in the regulation of inflammation. The NLRP3 inflammasome involvement in ERS-induced inflammation has not been completely described. The intersection of ERS with multiple inflammatory pathways can initiate and aggravate chronic diseases. Accumulating evidence suggests that ERS-induced activation of NLRP3 inflammasome is the pathological basis of various inflammatory diseases. In this review, we have discussed the networks between ERS and NLRP3 inflammasome, with the view to identifying novel therapeutic targets in inflammatory diseases. KEY POINTS: • Endoplasmic reticulum stress (ERS) is an important factor for the activation of the NLRP3 inflammasomes that results in pathological processes. • ERS can activate the NLRP3 inflammasome to induce inflammatory responses via oxidative stress, calcium homeostasis, and NF-κB activation. • The interactions between ERS and NLRP3 inflammasome are associated with inflammation, which represent a potential therapeutic opportunity of inflammatory diseases.

Exosomes derived from endoplasmic reticulum-stressed liver cancer cells enhance the expression of cytokines in macrophages via the STAT3 signaling pathway

Previous studies have shown that endoplasmic reticulum (ER) stress serves an important role in shaping the immunosuppressive microenvironment by modulating resident immune cells. However, the communication between ER-stressed tumor cells and immune cells is not fully understood. Exosomes have been reported to play a vital role in intercellular communication. Therefore, in order to investigate the role of ER stress-related exosomes in liver cancer cells mediated macrophage function remodeling, immunohistochemical analysis, western-blotting immunofluorescence and cytokine bead array analyses were performed. The results demonstrated that glucose-regulated protein 78 (GRP78) expression was upregulated in human liver cancer tissue. Moreover, 69.09% of GRP78-positive liver cancer tissues possessed macrophages expressing CD68⁺ (r=0.55; P<0.001). In addition to these CD68⁺ macrophages, interleukin (IL)-10 and IL-6 expression levels were increased in liver cancer tissues. It was also demonstrated that exosomes released by ER-stressed HepG2 cells significantly enhanced the expression levels of several cytokines, including IL-6, monocyte chemotactic protein-1, IL-10 and tumor necrosis factor-α in macrophages. Furthermore, incubation of cells with ER stress-associated exosomes resulted inactivation of the Janus kinase 2/STAT3 pathway, and inhibition of STAT3 using S3I-201 in RAW264.7 cells significantly reduced cytokine production. Collectively, the present study identified a novel function of ER stress-associated exosomes in mediating macrophage cytokine secretion in the liver cancer microenvironment, and also indicated the potential of treating liver cancer via an ER stress-exosomal-STAT3 pathway.

Assistance for Folding of Disease-Causing Plasma Membrane Proteins

An extensive catalog of plasma membrane (PM) protein mutations related to phenotypic diseases is associated with incorrect protein folding and/or localization. These impairments, in addition to dysfunction, frequently promote protein aggregation, which can be detrimental to cells. Here, we review PM protein processing, from protein synthesis in the endoplasmic reticulum to delivery to the PM, stressing the main repercussions of processing failures and their physiological consequences in pathologies, and we summarize the recent proposed therapeutic strategies to rescue misassembled proteins through different types of chaperones and/or small molecule drugs that safeguard protein quality control and regulate proteostasis.

GRP78 expression in peripheral blood mononuclear cells is a new predictive marker for the benefit of taxanes in breast cancer neoadjuvant treatment

BACKGROUND

Breast cancer treatment is tailored to the specific cancer subtype. Often, systemic treatment is given prior to surgery. Chemotherapy induces significant endoplasmic reticulum (ER) stress-mediated cell death and upregulation of 78-kDa glucose-regulated protein (GRP78). We hypothesized that chemotherapy induces ER stress not only in the tumor tissue but also in immune cells, which may affect the response to anti-cancer treatment.

METHODS

We determined the surface expression of GRP78 on 15 different peripheral blood mononuclear cell (PBMC) subpopulations in 20 breast cancer patients at three time points of the neoadjuvant treatment, i.e., at baseline, after anthracycline treatment, and after taxanes treatment. For this purpose, we performed flow cytometric analyses and analyzed the data using ANOVA and the Tukey test. Serum cytokine levels were also evaluated, and their levels were correlated with response to treatment using the t-test after log transformation and Mann-Whitney U Wilcoxon W test.

RESULTS

A significant increase in GRP78 expression in PBMCs was documented during the taxane phase, only in patients who achieved pathological complete response (pCR). GRP78-positive clones correlated with increased serum levels of interferon gamma (IFNγ).

CONCLUSIONS

The presence of GRP78-positive clones in certain PBMC subpopulations in pCR patients suggests a dynamic interaction between ER stress and immune responsiveness. The correlation of GRP78-positive clones with increased levels of IFNγ supports the idea that GRP78 expression in PBMCs might serve as a new predictive marker to identify the possible benefits of taxanes in the neoadjuvant setting.

Elevation of the unfolded protein response increases RANKL expression

Increased production of the osteoclastogenic cytokine RANKL is a common feature of pathologic bone loss, but the underlying cause of this increase is poorly understood. The unfolded protein response (UPR) is activated in response to accumulation of misfolded proteins in the endoplasmic reticulum (ER). Failure to resolve misfolding results in excess UPR signaling that stimulates cytokine production and cell death. We therefore investigated whether RANKL is one of the cytokines stimulated in response to elevated UPR in bone cells. Pharmacologic induction of UPR with tunicamycin (Tm)-stimulated RANKL expression in cultures of primary osteoblastic cells and in osteoblast and osteocyte cell lines. Pharmacologic inhibition of the UPR blunted Tm-induced RANKL production. Silencing Edem1 or Sel1l, proteins that aid in degradation of misfolded proteins, also induced UPR and increased RANKL mRNA. Moreover, Tm or hypoxia increased RANKL and bone resorption in cultures of neonatal murine calvaria. Administration of Tm to adult mice caused dilation of ER in osteoblasts and osteocytes, elevated the UPR, and increased RANKL expression and osteoclast number. These findings support the hypothesis that excessive UPR signaling stimulates the expression of RANKL by osteoblasts and osteocytes, and thereby facilitates excessive bone resorption and bone loss in pathologic conditions.

Vitamin D Receptor Activation in Liver Macrophages Protects Against Hepatic Endoplasmic Reticulum Stress in Mice

BACKGROUND AND AIMS

Hepatic endoplasmic reticulum (ER) stress, whether triggered by intrinsic or extrinsic factors, can be resolved by the unfolded protein response (UPR). Sustained UPR activation leads to cell death and inflammatory response and contributes to liver disease progression. Hepatic tissue macrophages are key players in orchestrating liver inflammation, and ER stress can enhance macrophage activation. However, it is not well defined how the interplay between ER stress and inflammation is regulated during hepatic stress response.

APPROACH AND RESULTS

Here we demonstrate that vitamin D receptor (VDR) activation mitigates hepatic ER stress response, whereas VDR knockout mice undergo persistent UPR activation and apoptosis in response to chemical ER stress inducer. Moreover, VDR deficiency promotes hepatic macrophage infiltration and increases gene expression and systematic levels of proinflammatory cytokines, including interleukin (IL)-1β, IL-6, and tumor necrosis factor α. VDR expression is induced in hepatic macrophages by ER stress, and VDR plays a dual regulatory role in macrophages by protecting against ER stress and promoting anti-inflammatory polarization. Co-culture with VDR-activated bone marrow-derived macrophages suppresses UPR target genes in primary hepatocytes treated with ER stress inducers. Thus, the immunomodulatory functions of VDR in macrophages are critical in hepatic ER stress resolution in mice.

CONCLUSIONS

VDR signaling in macrophages regulates a shift between proinflammatory and anti-inflammatory activation during ER stress-induced inflammation to promote hepatic ER stress resolution.

Inhibition of protein disulfide isomerase has neuroprotective effects in a mouse model of experimental autoimmune encephalomyelitis

Endoplasmic reticulum (ER) stress is strictly linked to neuroinflammation and involves in the development of neurodegenerative disorders. Protein disulfide isomerase (PDI) is an enzyme that catalyzes formation and isomerization of disulfide bonds and also acts as a chaperone that survives the cells against cell death by removal of misfolded proteins. Our previous work revealed that PDI is explicitly upregulated in response to myelin oligodendrocyte glycoprotein (MOG)-induced ER stress in the brain of experimental autoimmune encephalomyelitis (EAE) mice. The significance of overexpression of PDI in the apoptosis of neural cells prompted us to study the effect of CCF642, efficient inhibitor of PDI, in the recovery of EAE clinical symptoms. Using this in vivo model, we characterized the ability of CCF642 to decrease the expression of ER stress markers and neuroinflammation in the hippocampus of EAE mice. Our observations suggested that CCF642 administration attenuates EAE clinical symptomsand the expression of ER stress-related proteins. Further, it suppressed the inflammatory infiltration of CD4 + T cells and the activation of hippocampus-resident microglia and Th17 cells. We reported here that the inhibition of PDI protected EAE mice against neuronal apoptosis induced by prolonged ER stress and resulted in neuroprotection.

Protective effect of caffeic acid phenethyl ester against imidacloprid-induced hepatotoxicity by attenuating oxidative stress, endoplasmic reticulum stress, inflammation and apoptosis

Imidacloprid (IMI) is a widely used neonicotinoid pesticide in the world, its environmental and human health risk has particularly attracted the attention of researchers. Caffeic acid phenethyl ester (CAPE), an active polyphenol of propolis, has many pharmacological activities including free radical scavenger, anti-inflammatory, and anti-oxidant. In this study, protective effect of CAPE against IMI induced liver injury in mice was performed. Administration of 1 and 2.5 mg/kg CAPE markedly prevented serum AST and ALT increase in 5 mg/kg IMI-induced mice. CAPE significantly downregulated liver NO generation and lipid peroxidation, and upregulated glutathione, catalase, superoxide dismutase and glutathione peroxidase in a dose-dependent manner in liver of IMI-induced mice. Endoplasmic reticulum stress represented by the swelling of endoplasmic reticulum was observed by transmission electron microscope in IMI group. Pretreatment of 2.5 mg/kg CAPE significantly attenuated the endoplasmic reticulum stress induced by IMI in liver. Western blot analysis illustrated that pretreatment of CAPE downregulated the upregulation of TNF-α and IFN-γ induced by IMI in liver of mice. Moreover, the increase of positive apoptotic hepatocytes further suggested apoptosis might be involved in IMI-induced hepatotoxicity. Pretreatment of 1 and 2.5 mg/kg CAPE significantly decreased positive apoptotic hepatocytes, suggested that CAPE prevented apoptosis in liver of IMI-induced mice. In conclusion, CAPE prevented liver injury in IMI-induced mice via attenuation of oxidative stress, endoplasmic reticulum stress, inflammation and apoptosis. Our findings may have broad biological and environmental implications for future research on the therapeutic strategy to prevent liver injury induced by pesticides.

Perturbation of bulk and selective macroautophagy, abnormal UPR activation and their interplay pave the way to immune dysfunction, cancerogenesis and neurodegeneration in ageing

A plethora of studies has indicated that ageing is characterized by an altered proteostasis, ROS accumulation and a status of mild/chronic inflammation, in which macroautophagy reduction and abnormal UPR activation play a pivotal role. The dysregulation of these inter-connected processes favors immune dysfunction and predisposes to a variety of several apparently unrelated pathological conditions including cancer and neurodegeneration. Given the progressive ageing of the population, a better understanding of the mechanisms regulating autophagy, UPR and their interplay is needed in order to design new therapeutic strategies able to counteract the effects of ageing and concomitantly restrain the onset/progression of age-related diseases that represent a private and public health problem.

Catestatin improves insulin sensitivity by attenuating endoplasmic reticulum stress: In vivo and in silico validation

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An endogenous peptide catestatin alleviates obesity-induced ER stress.

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Alleviation of ER stress by catestatin improves insulin sensitivity.

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PID controller based model of ER stress is supported by experimental findings.

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It predicts AKT phosphorylation achieves insulin sensitivity overcoming ER stress.

Obesity is characterized by a state of chronic, unresolved inflammation in insulin-targeted tissues. Obesity-induced inflammation causes accumulation of proinflammatory macrophages in adipose tissue and liver. Proinflammatory cytokines released from tissue macrophages inhibits insulin sensitivity. Obesity also leads to inflammation-induced endoplasmic reticulum (ER) stress and insulin resistance. In this scenario, based on the data (specifically patterns) generated by our in vivo experiments on both diet-induced obese (DIO) and normal chow diet (NCD) mice, we developed an in silico state space model to integrate ER stress and insulin signaling pathways. Computational results successfully followed the experimental results for both DIO and NCD conditions. Chromogranin A (CgA) peptide catestatin (CST: hCgA352-372) improves obesity-induced hepatic insulin resistance by reducing inflammation and inhibiting proinflammatory macrophage infiltration. We reasoned that the anti-inflammatory effects of CST would alleviate ER stress. CST decreased obesity-induced ER dilation in hepatocytes and macrophages. On application of Proportional-Integral-Derivative (PID) controllers on the in silico model, we checked whether the reduction of phosphorylated PERK resulting in attenuation of ER stress, resembling CST effect, could enhance insulin sensitivity. The simulation results clearly pointed out that CST not only decreased ER stress but also enhanced insulin sensitivity in mammalian cells. In vivo experiment validated the simulation results by depicting that CST caused decrease in phosphorylation of UPR signaling molecules and increased phosphorylation of insulin signaling molecules. Besides simulation results predicted that enhancement of AKT phosphorylation helps in both overcoming ER stress and achieving insulin sensitivity. These effects of CST were verified in hepatocyte culture model.

Modification of lung endoplasmic reticulum genes expression and NF-kB protein levels in obese ovalbumin-sensitized male and female rats

AIMS

Previous studies showed a close relationship between obesity and asthma. In this study, we investigated the expression of endoplasmic reticulum (ER) stress genes in the lung tissue of obese ovalbumin (OVA)-sensitized male and female rats.

MAIN METHODS

The rats were divided into eight groups (n = 5 per group) as follows: female and male rats fed with normal diet (FND and MND, respectively), female and male OVA-sensitized rats fed with normal diet (F-OND and M-OND, respectively), female and male rats fed with high-fat diet (F-HFD and M-HFD, respectively), female and male OVA-sensitized rats fed with high-fat diet (F-OHFD and M-OHFD, respectively). All rats were fed with a high-fat diet or standard pelts for 8 weeks, and for another 4 weeks, they were sensitized by OVA or saline. At the end of the study, lung tissue NF-kB protein level was assessed, and ER stress markers genes expression was determined by Real Time-PCR.

KEY FINDING

OVA-sensitization and diet-induced obesity caused the curve of methacholine concentration-response to shift to the left. In addition, the results indicated that the EC50 (the effective concentration of methacholine generating 50% of peak response) in F-OHFD rats was statistically lower than that of the M-OHFD group (p < 0.05). Moreover, the results showed that diet-induced obesity increased the expression of ATF4, ATF6, GRP78, XBP-1, and CHOP as well as the protein level of NF-kB in this experimental model of asthma, markedly in the F-OHFD group.

SIGNIFICANCE

The results suggest that ER stress may be involved in the pathogenesis of asthma observed in obese OVA-sensitized rats, especially in the female animals.

Inhibition of Endoplasmic Reticulum Stress Attenuated Ethanol-Induced Exosomal miR-122 and Acute Liver Injury in Mice

AIMS

In acute alcoholic liver injury, alcohol can directly or indirectly induce endoplasmic reticulum stress (ERS) to participate in liver injury, and it is found that the expression of serum exosomal miR-122 is significantly affected. Therefore, the present study investigated the effects of endoplasmic reticulum stress inhibition on the expression of serum exosomal miR-122 and acute liver injury.

METHODS

The acute alcoholic liver injury models were established by the intragastric administration of ethanol (5 g/kg) in ICR mice. Intervention group received 4-phenylbutyric acid (PBA, endoplasmic reticulum stress inhibitor; 75 mg/kg and 150 mg/kg, intraperitoneal) 12 and 24 hours before intragastric administration. Mice treated with saline were used as controls.

RESULTS

The ethanol treated mice exhibited significantly elevated hepatosomatic index (liver weight/body weight) and alanine aminotransferase (ALT), compared with those in the control group (P < 0.05). The ERS inhibitor 4-phenylbutyric acid protected against ethanol induced acute liver injury and hepatocyte necrosis, and PBA 150 mg/kg significantly attenuated ethanol induced hepatic ER stress-related proteins (GRP78, pIRE1α and pIF2α) (P < 0.05). Moreover, PBA 150 mg/kg markedly alleviated ethanol induced elevation of hepatic and serum exosomal miR-122 and pri-miR-122 (P < 0.05).

CONCLUSIONS

These findings suggest that ER stress inhibitor PBA attenuated ethanol induced acute liver injury and serum exosomal miR-122, and provides a potential therapy strategy for acute alcoholic liver injury.

Endoplasmic reticulum stress and pulmonary hypertension

Pulmonary hypertension is a fatal disease of which pulmonary vasculopathy is the main pathological feature resulting in the mean pulmonary arterial pressure higher than 25 mmHg. Moreover, pulmonary hypertension remains a tough problem with unclear molecular mechanisms. There have been dozens of studies about endoplasmic reticulum stress during the onset of pulmonary hypertension in patients, suggesting that endoplasmic reticulum stress may have a critical effect on the pathogenesis of pulmonary hypertension. The review aims to summarize the rationale to elucidate the role of endoplasmic reticulum stress in pulmonary hypertension. Started by reviewing the mechanisms responsible for the unfolded protein response following endoplasmic reticulum stress, the potential link between endoplasmic reticulum stress and pulmonary hypertension were introduced, and the contributions of endoplasmic reticulum stress to different vascular cells, mitochondria, and inflammation were described, and finally the potential therapies of attenuating endoplasmic reticulum stress for pulmonary hypertension were discussed.

Endoplasmic reticulum stress and focused drug discovery in cardiovascular disease

Endoplasmic reticulum (ER) is an intracellular membranous organelle involved in the synthesis, folding, maturation and post-translation modification of secretory and transmembrane proteins. Therefore, ER is closely related to the maintenance of intracellular homeostasis and the good balance between health and diseases. Endoplasmic reticulum stress (ERS) occurs when unfolded/misfolded proteins accumulate after disturbance of ER environment. In response to ERS, cells trigger an adaptive response called the Unfolded protein response (UPR), which helps cells cope with the stress. In recent years, a large number of studies show that ERS can aggravate cardiovascular diseases. ERS-related proteins expression in cardiovascular diseases is on the rise. Therefore, down-regulation of ERS is critical for alleviating symptoms of cardiovascular diseases, which may be used in the near future to treat cardiovascular diseases. This article reviews the relationship between ERS and cardiovascular diseases and drugs that inhibit ERS. Furthermore, we detail the role of ERS inhibitors in the treatment of cardiovascular disease. Drugs that inhibit ERS are considered as promising strategies for the treatment of cardiovascular diseases.

Elevated expression of unfolded protein response genes in the prefrontal cortex of depressed subjects: Effect of suicide

BACKGROUND

Major Depressive Disorder (MDD) is a leading cause of mental disability worldwide. Despite many studies, the pathophysiology associated with MDD brain is not very clear. It is reported that cellular stress is related to depressive symptoms. Under stressful conditions, intracellular homeostasis processes can be disrupted, which can induce a process of unfolded protein response (UPR) in the subcellular lumen of endoplasmic reticulum (ER). The purpose of this study is to elucidate whether UPR is active in the depressed brain.

METHODS

The dorsolateral prefrontal cortex (dlPFC) was used from 23 non-psychiatric controls and 43 MDD subjects. The expression levels of UPR associated genes (GRP78, GRP94, XBP-1, CHOP, ATF4C, and ATF6C) were measured by qRT-PCR.

RESULTS

The level of mRNA expression in MDD subjects was significantly higher for GRP78 (p = 0.008), GRP94 (p = 0.018), and ATF4C (p = 0.03) compared to non-psychiatric controls. Further analysis suggested that changes in the expression of these genes were specifically higher only in those MDD subjects who died by suicide but not in those who died by causes other than suicide when compared with non-psychiatric controls (GRP78, p = 0.007; GRP94, p = 0.041; ATF4C, p = 0.037).

LIMITATIONS

This study was performed only in MDD subjects who had died by suicide. Suicide subjects with other psychiatric illnesses need to be included.

CONCLUSIONS

Given that UPR is involved in many physiological processes in the brain, including inflammatory response as well as apoptosis, increased expression of UPR genes indicates that ER stress and mediated UPR may be critical factors in suicidality among depressed patients.

Endoplasmic Reticulum Stress and Mitochondrial Function in Airway Smooth Muscle

Inflammatory airway diseases such as asthma affect more than 300 million people world-wide. Inflammation triggers pathophysiology via such as tumor necrosis factor α (TNFα) and interleukins (e.g., IL-13). Hypercontraction of airway smooth muscle (ASM) and ASM cell proliferation are major contributors to the exaggerated airway narrowing that occurs during agonist stimulation. An emergent theme in this context is the role of inflammation-induced endoplasmic reticulum (ER) stress and altered mitochondrial function including an increase in the formation of reactive oxygen species (ROS). This may establish a vicious cycle as excess ROS generation leads to further ER stress. Yet, it is unclear whether inflammation-induced ROS is the major mechanism leading to ER stress or the consequence of ER stress. In various diseases, inflammation leads to an increase in mitochondrial fission (fragmentation), associated with reduced levels of mitochondrial fusion proteins, such as mitofusin 2 (Mfn2). Mitochondrial fragmentation may be a homeostatic response since it is generally coupled with mitochondrial biogenesis and mitochondrial volume density thereby reducing demand on individual mitochondrion. ER stress is triggered by the accumulation of unfolded proteins, which induces a homeostatic response to alter protein balance via effects on protein synthesis and degradation. In addition, the ER stress response promotes protein folding via increased expression of molecular chaperone proteins. Reduced Mfn2 and altered mitochondrial dynamics may not only be downstream to ER stress but also upstream such that a reduction in Mfn2 triggers further ER stress. In this review, we summarize the current understanding of the link between inflammation-induced ER stress and mitochondrial function and the role played in the pathophysiology of inflammatory airway diseases.

TNFα selectively activates the IRE1α/XBP1 endoplasmic reticulum stress pathway in human airway smooth muscle cells

Airway inflammation is a key aspect of diseases such as asthma. Proinflammatory cytokines such as TNFα mediate the inflammatory response. In various diseases, inflammation leads to endoplasmic reticulum (ER) stress, the accumulation of unfolded proteins, which triggers homeostatic responses to restore normal cellular function. We hypothesized that TNFα triggers ER stress through an increase in reactive oxygen species generation in human airway smooth muscle (hASM) with a downstream effect on mitofusin 2 (Mfn2). In hASM cells isolated from lung specimens incidental to patient surgery, dose- and time-dependent effects of TNFα exposure were assessed. Exposure of hASM to tunicamycin was used as a positive control. Tempol (500 μM) was used as superoxide scavenger. Activation of three ER stress pathways were evaluated by Western blotting: 1) autophosphorylation of inositol-requiring enzyme1 (IRE1α) leading to splicing of X-box binding protein 1 (XBP1); 2) autophosphorylation of protein kinase RNA-like endoplasmic reticulum kinase (PERK) leading to phosphorylation of eukaryotic initiation factor 2α; and 3) translocation and cleavage of activating transcription factor 6 (ATF6). We found that exposure of hASM cells to tunicamycin activated all three ER stress pathways. In contrast, TNFα selectively activated the IRE1α/XBP1 pathway in a dose- and time-dependent fashion. Our results indicate that TNFα does not activate the PERK and ATF6 pathways. Exposure of hASM cells to TNFα also decreased Mfn2 protein expression. Concurrent exposure to TNFα and tempol reversed the effect of TNFα on IRE1α phosphorylation and Mfn2 protein expression. Selective activation of the IRE1α/XBP1 pathway in hASM cells after exposure to TNFα may reflect a unique homeostatic role of this pathway in the inflammatory response of hASM cells.

Does perturbation in the mitochondrial protein folding pave the way for neurodegeneration diseases?

Mitochondria, which are cell compartments that are widely present in eukaryotic cells, have been shown to be involved in a variety of synthetic, metabolic, and signaling processes, thereby playing a vital role in cells. The mitochondrial unfolded protein response (mtUPR) is a response in which mitochondria reverse the signal to the nucleus and maintain mitochondrial protein homeostasis when unfolded and misfolded proteins continue to accumulate. Multiple neurodegeneration diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), and familial amyotrophic lateral sclerosis (fALS), are public health challenges. Every year, countless efforts are expended trying to clarify the pathogenesis and treatment of neurological disorders, which are associated with mitochondrial dysfunction to some extent. Numerous studies have shown that mtUPR is involved in and plays an important role in the pathogenesis of neurological disorders, but the exact mechanism of the disorders is still unclear. Further study of the process of mtUPR in neurological disorders can help us more accurately understand their pathogenesis in order to provide new therapeutic targets. In this paper, we briefly review mtUPR signaling in Caenorhabditis elegans (C. elegans) and mammals and summarize the role of mtUPR in neurodegeneration diseases, including AD, PD and fALS.

What Is the Sweetest UPR Flavor for the β-cell? That Is the Question

Unfolded protein response (UPR) is a process conserved from yeasts to mammals and, based on the generally accepted dogma, helps the secretory performance of a cell, by improving its capacity to cope with a burden in the endoplasmic reticulum (ER). The ER of β-cells, "professional secretory cells", has to manage tremendous amounts of insulin, which elicits a strong pressure on the ER intrinsic folding capacity. Thus, the constant demand for insulin production results in misfolded proinsulin, triggering a physiological upregulation of UPR to restore homeostasis. Most diabetic disorders are characterized by the loss of functional β-cells, and the pathological side of UPR plays an instrumental role. The transition from a homeostatic to a pathological UPR that ultimately leads to insulin-producing β-cell decay entails complex cellular processes and molecular mechanisms which remain poorly described so far. Here, we summarize important processes that are coupled with or driven by UPR in β-cells, such as proliferation, inflammation and dedifferentiation. We conclude that the UPR comes in different "flavors" and each of them is correlated with a specific outcome for the cell, for survival, differentiation, proliferation as well as cell death. All these greatly depend on the way UPR is triggered, however what exactly is the switch that favors the activation of one UPR as opposed to others is largely unknown. Substantial work needs to be done to progress the knowledge in this important emerging field as this will help in the development of novel and more efficient therapies for diabetes.

Endoplasmic reticulum targeting fluorescent probes to image mobile Zn2

Zn2+ plays an important role in the normal function of the endoplasmic reticulum (ER) and its deficiency can cause ER stress, which is related to a wide range of diseases. In order to provide tools to better understand the role of mobile Zn2+ in ER processes, the first custom designed ER-localised fluorescent Zn2+ probes have been developed through the introduction of a cyclohexyl sulfonylurea as an ER-targeting unit with different Zn2+ receptors. Experiments in vitro and in cellulo show that both probes have a good fluorescence switch on response to Zn2+, high selectivity over other cations, low toxicity, ER-specific targeting ability and are efficacious imaging agents for mobile Zn2+ in four different cell lines. Probe 9 has been used to detect mobile Zn2+ changes under ER stress induced by both tunicamycin or thapsigargin, which indicates that the new probes should allow a better understanding of the mechanisms cells use to respond to dysfunction of zinc homeostasis in the ER and its role in the initiation and progression of diseases to be developed.

Immunogenic cell death induced by a new photodynamic therapy based on photosens and photodithazine

Background

Anti-cancer therapy is more successful when it can also induce an immunogenic form of cancer cell death (ICD). Therefore, when developing new treatment strategies, it is extremely important to choose methods that induce ICD and thereby activate anti-tumor immune response leading to the most effective destruction of tumor cells. The aim of this work was to analyze whether the clinically widely used photosensitizers, photosens (PS) and photodithazine (PD), can induce ICD when used in photodynamic therapy (PDT).

Methods

Cell death in murine glioma GL261 or fibrosarcoma MCA205 cells was induced by PS- or PD-PDT and cell death was analyzed by MTT or flow cytometry. Intracellular distribution of PS and PD was studied by using the laser scanning microscope. Calreticulin exposure and HMGB1 and ATP release were detected by flow cytometry, ELISA and luminescence assay, respectively. Immunogenicity in vitro was analyzed by co-culturing of dying cancer cells with bone-marrow derived dendritic cells (BMDCs) and rate of phagocytosis and maturation (CD11c⁺CD86⁺, CD11c⁺CD40⁺) of BMDCs and production of IL-6 in the supernatant were measured. In vivo immunogenicity was analyzed in mouse tumor prophylactic vaccination model.

Results

We determined the optimal concentrations of the photosensitizers and found that at a light dose of 20 J/cm² (λex 615–635 nm) both PS and PD efficiently induced cell death in glioma GL261 and fibrosarcoma MCA205 cells. We demonstrate that PS localized predominantly in the lysosomes and that the cell death induced by PS-PDT was inhibited by zVAD-fmk (apoptosis inhibitor) and by ferrostatin-1 and DFO (ferroptosis inhibitors), but not by the necroptosis inhibitor necrostatin-1 s. By contrast, PD accumulated in the endoplasmic reticulum and Golgi apparatus, and the cell death induced by PD-PDT was inhibited only by z-VAD-fmk. Dying cancer cells induced by PS-PDT or PD-PDT emit calreticulin, HMGB1 and ATP and they were efficiently engulfed by BMDCs, which then matured, became activated and produced IL-6. Using dying cancer cells induced by PS-PDT or PD-PDT, we demonstrate the efficient vaccination potential of ICD in vivo.

Conclusions

Altogether, these results identify PS and PD as novel ICD inducers that could be effectively combined with PDT in cancer therapy.

Mechanisms Underlying Bone Loss Associated with Gut Inflammation

Patients with gastrointestinal diseases frequently suffer from skeletal abnormality, characterized by reduced bone mineral density, increased fracture risk, and/or joint inflammation. This pathological process is characterized by altered immune cell activity and elevated inflammatory cytokines in the bone marrow microenvironment due to disrupted gut immune response. Gastrointestinal disease is recognized as an immune malfunction driven by multiple factors, including cytokines and signaling molecules. However, the mechanism by which intestinal inflammation magnified by gut-residing actors stimulates bone loss remains to be elucidated. In this article, we discuss the main risk factors potentially contributing to intestinal disease-associated bone loss, and summarize current animal models, illustrating gut-bone axis to bridge the gap between intestinal inflammation and skeletal disease.

Pas de Deux: Control of Anti-tumor Immunity by Cancer-Associated Inflammation

In many settings, tumor-associated inflammation, supported mainly by innate immune cells, contributes to tumor growth. Initial innate activation triggers secretion of inflammatory, regenerative, and anti-inflammatory cytokines, which in turn shape the adaptive immune response to the tumor. Here, we review the current understanding of the intricate dialog between cancer-associated inflammation and anti-tumor immunity. We discuss the changing nature of these interactions during tumor progression and the impact of the tissue environment on the anti-tumor immune response. In this context, we outline important gaps in current understanding by considering basic research and findings in the clinic. The future of cancer immunotherapy and its utility depend on improved understanding of these interactions and the ability to manipulate them in a predictable and beneficial manner.

The active nuclear form of SREBP1 amplifies ER stress and autophagy via regulation of PERK

Endoplasmic reticulum (ER) stress and autophagy dysfunction contribute to the establishment and progression of diverse pathologies. Proteolytic activation of the transcription factor nSREBP1 is induced under ER stress; however, little is known about how SREBP1 and its nuclear active form nSREBP1 influence autophagy and unfolded protein response (UPR) activation in osteosarcoma cells. Our research focused on the effect of SREBP1/nSREBP1 upon apoptosis and autophagy during ER stress and the molecular mechanisms involved. Here, we showed that nSREBP1 binds to the promoter of protein kinase RNA-like endoplasmic reticulum kinase (PERK) and then regulates ER stress, cell growth, cell apoptosis, and autophagy through the PERK signaling pathway. nSREBP1 increased PERK gene expression and phosphorylation. nSREBP1 was further demonstrated to activate ER stress response through stimulatory effects on PERK signaling. Overexpression of SREBP1 increased its cleavage and release of nSREBP1; therefore, the effect of SREBP1 is achieved through the enhancement of the expression of nSREBP1. Overexpression of SREBP1/nSREBP1 amplifies PERK-associated cell cycle stagnation with G1 phase arresting, S phase reducing, and G2-M phase delaying. LV-SREBP1/nSREBP1 can also bolster PERK's ER stress-associated pro-apoptotic effects. LV-SREBP1/nSREBP1 and LV-PERK can activate autophagy in ER stress response, along with the overexpression of SREBP1/nSREBP1 and PERK. This resulted in amplification of PERK-related changes to cell proliferation and ER stress-mediated apoptosis and autophagy, with the biological effect of nSREBP1 relying on PERK, which makes up one of the three branches of the UPR signaling pathway. This study reveals important roles for SREBP1/nSREBP1 in PERK signaling under ER stress. Furthermore, nSREBP1, the nuclear active form of SREBP1, is able to robustly augment the effects of PERK. Description of the link between PERK and SREBP1/nSREBP1 function offers an improved understanding of the ER stress response and insight into the biological function of SREBP1/nSREBP1.

Pyroptosis is a critical inflammatory pathway in the placenta from early onset preeclampsia and in human trophoblasts exposed to hypoxia and endoplasmic reticulum stressors

Systemic manifestation of preeclampsia (PE) is associated with circulating factors, including inflammatory cytokines and damage-associated molecular patterns (DAMPs), or alarmins. However, it is unclear whether the placenta directly contributes to the increased levels of these inflammatory triggers. Here, we demonstrate that pyroptosis, a unique inflammatory cell death pathway, occurs in the placenta predominantly from early onset PE, as evidenced by elevated levels of active caspase-1 and its substrate or cleaved products, gasdermin D (GSDMD), IL-1β, and IL-18. Using cellular models mimicking pathophysiological conditions (e.g., autophagy deficiency, hypoxia, and endoplasmic reticulum (ER) stress), we observed that pyroptosis could be induced in autophagy-deficient human trophoblasts treated with sera from PE patients as well as in primary human trophoblasts exposed to hypoxia. Exposure to hypoxia elicits excessive unfolded protein response (UPR) and ER stress and activation of the NOD-like receptor pyrin-containing 3 (NLRP3) inflammasome in primary human trophoblasts. Thioredoxin-interacting protein (TXNIP), a marker for hyperactivated UPR and a crucial signaling molecule linked to NLRP3 inflammasome activation, is significantly increased in hypoxia-treated trophoblasts. No evidence was observed for necroptosis-associated events. Importantly, these molecular events in hypoxia-treated human trophoblasts are significantly observed in placental tissue from women with early onset PE. Taken together, we propose that placental pyroptosis is a key event that induces the release of factors into maternal circulation that possibly contribute to severe sterile inflammation and early onset PE pathology.

Grade II/III Glioma Microenvironment Mining and Its Prognostic Merit

OBJECTIVE

The tumor microenvironment greatly influences tumor formation, invasion, and progression. The ESTIMATE (Estimation of STromal and Immune cells in MAlignant Tumor tissues) algorithm quantifies stromal and immune components in a tumor, reflecting the tumor microenvironment. This study aimed to explore key prognostic genes in a grade II/III glioma microenvironment.

METHODS

We obtained stromal/immune scores for the Cancer Genome Atlas (TCGA) grade II/III glioma cohort from the online ESTIMATE portal. The associations of stromal/immune scores with clinicopathologic characteristics and overall survival of patients with grade II/III glioma were assessed by the Mann-Whitney U test and the Kaplan-Meier method, respectively. Functional enrichment analysis and protein-protein interaction network assessments were employed to analyze differentially expressed genes (DEGs). The top 7 genes with 5 or more edges in the protein-protein interaction network were selected. For validation, CGGA grade II/III glioma data were analyzed.

RESULTS

The results showed that elevated stromal/immune/ESTIMATE score was significantly associated with poor survival of patients with TCGA grade II/III glioma. Functional enrichment analysis showed that DEGs were associated with immune cell regulation, extracellular matrix, cytokine activation, and receptor binding. The selected DEGs (interleukin-10, beta-2 microglobulin, C-C motif chemokine ligand 5, cluster of differentiation 74, human leukocyte antigen-DRA, lymphocyte cytosolic protein 2, and myxovirus resistance protein 1) showed prognostic values in patients with grade II/III glioma of the TCGA and CGGA database.

CONCLUSIONS

Stromal/immune/ESTIMATE scores have prognostic values in patients with grade II/III glioma. The selected DEGs, including interleukin-10, beta-2 microglobulin, C-C motif chemokine ligand 5, cluster of differentiation 74, human leukocyte antigen-DRA, lymphocyte cytosolic protein 2, and myxovirus resistance protein 1, associated with tumor immunity and microenvironment, have prognostic values in grade II/III glioma. Further investigation of these genes could provide novel insights into the tumor microenvironment of glioma.

Is Alzheimer's disease an inflammasomopathy?

Alzheimer's disease (AD) is the most common form of dementia in the elderly and, despite the tremendous efforts researchers have put into AD research, there are no effective options for prevention and treatment of the disease. The best way to reach this goal is to clarify the mechanisms involved in the onset and progression of AD. In the last few years the views about the drivers of AD have been changing and nowadays it is believed that neuroinflammation takes center stage in disease pathogenesis. Herein, we provide an overview about the role of neuroinflammation in AD describing the role of microglia and astroglia is this process. Then, we will debate the NLRP3 inflammasome putting the focus on its activation through the canonical, non-canonical and alternative pathways and the triggers involved herein namely endoplasmic reticulum stress, mitochondrial dysfunction, reactive oxygen species and amyloid β peptide. Data supporting the hypothesis that inflammasome-mediated peripheral inflammation may contribute to AD pathology will be presented. Finally, a brief discussion about the therapeutic potential of NLRP3 inflammasome modulation is also provided.

Angiotensin-converting enzyme 2 regulates endoplasmic reticulum stress and mitochondrial function to preserve skeletal muscle lipid metabolism

Objective

Endoplasmic reticulum (ER) stress and mitochondrial function affected intramuscular fat accumulation. However, there is no clear evident on the effect of the regulation of ER stress and mitochondrial function by Angiotensin-converting enzyme 2 (ACE2) on the prevention of intramuscular fat metabolism. We investigated the effects of ACE2 on ER stress and mitochondrial function in skeletal muscle lipid metabolism.

Methods

The triglyceride (TG) content in skeletal muscle of ACE2 knockout mice and Ad-ACE2-treated db/db mice were detected by assay kits. Meanwhile, the expression of lipogenic genes (ACCα, SREBP-1c, LXRα, CPT-1α, PGC-1α and PPARα), ER stress and mitochondrial function related genes (GRP78, eIF2α, ATF4, BCL-2, and SDH6) were analyzed by RT-PCR. Lipid metabolism, ER stress and mitochondrial function related genes were analyzed by RT-PCR in ACE2-overexpression C2C12 cell. Moreover, the IKKβ/NFκB/IRS-1 pathway was determined using lysate sample from skeletal muscle of ACE2 knockout mice.

Results

ACE2 deficiency in vivo is associated with increased lipid accumulation in skeletal muscle. The ACE2 knockout mice displayed an elevated level of ER stress and mitochondrial dysfunctions in skeletal muscle. In contrast, activation of ACE2 can ameliorate ER stress and mitochondrial function, which slightly accompanied by reduced TG content and down-regulated the expression of skeletal muscle lipogenic proteins in the db/db mice. Additionally, ACE2 improved skeletal muscle lipid metabolism and ER stress genes in the C2C12 cells. Mechanistically, endogenous ACE2 improved lipid metabolism through the IKKβ/NFκB/IRS-1 pathway in skeletal muscle.

Conclusions

ACE2 was first reported to play a notable role on intramuscular fat regulation by improving endoplasmic reticulum and mitochondrial function. This study may provide a strategy for treating insulin resistance in skeletal muscle.

Type I interferons and endoplasmic reticulum stress in health and disease

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

Resveratrol treatment in patients with polycystic ovary syndrome decreased pro-inflammatory and endoplasmic reticulum stress markers

PROBLEM

Polycystic ovary syndrome (PCOS) is associated with endoplasmic reticulum (ER) stress and pro-inflammatory condition. The aim of the present study was to evaluate the effect of resveratrol treatment on pro-inflammatory and ER stress markers in patients with PCOS.

METHOD OF STUDY

Cumulus cells were obtained from 40 patients with PCOS who were divided into two groups: placebo and resveratrol treatment (receiving 800 mg/d for 40 days) groups. Blood samples were obtained from all patients before and after the procedure to evaluate interleukin (IL)-6, IL-1β, IL-18, TNF-α, NF-κB, and C-reactive protein (CRP). Total RNA was extracted from cumulus cells, and cDNA was synthesized by reverse transcription. Expressions of five genes in ER stress response pathway (ATF4, ATF6, CHOP, GRP78, and XBP1s) were assessed with quantitative real-time PCR. Statistical analysis was performed with Student's t test.

RESULTS

After treatment with resveratrol, it was found that serum levels of IL-6, IL-1β, TNF-α, IL-18, NF-κB, and CRP decreased in the treatment group. In addition, gene expression results showed that the expression levels of ATF4 (P < .05) and ATF6 (P < .001) significantly increased in the resveratrol treatment group, while the expression levels of CHOP, GRP78, and XBP1 (P < .001 for all) significantly decreased.

CONCLUSION

Results demonstrated that resveratrol has anti-inflammatory effects through the suppression of NF-κB and NF-κB-regulated gene products. On the other hand, resveratrol can modulate ER stress in granulosa cells (GCs) by altering the expression of genes involved in unfolding protein response (UPR) process. Our findings suggest that ER stress is a potential therapeutic target for patients with PCOS.

Dynamics of Genomic, Epigenomic, and Transcriptomic Aberrations during Stepwise Hepatocarcinogenesis

Hepatocellular carcinoma (HCC) undergoes a stepwise progression from liver cirrhosis to low-grade dysplastic nodule (LGDN), high-grade dysplastic nodule (HGDN), early HCC (eHCC), and progressed HCC (pHCC). Here, we profiled multilayered genomic, epigenomic, and transcriptomic aberrations in the stepwise hepatocarcinogenesis. Initial DNA methylation was observed in eHCC (e.g., DKK3, SALL3, and SOX1) while more extensive methylation was observed in pHCC. In addition, eHCCs showed an initial loss of DNA copy numbers of tumor suppressor genes in the 4q and 13q regions, thereby conferring survival benefits to cancer cells. Transcriptome analysis revealed that HGDNs expressed endoplasmic reticulum (ER) stress-related genes, while eHCC started to express oncogenes. Furthermore, integrative analysis indicated that expression of the serine peptidase inhibitor, Kazal type 1 (SPINK1), played a pivotal role in eHCC development. Significant demethylation of SPINK1 was observed in eHCC compared to HGDN. The study also demonstrated that ER stress may induce SPINK1 demethylation and expression in liver cancer cells. In conclusion, these results reveal the dynamics of multiomic aberrations during malignant conversion of liver cancer, thus providing novel pathobiological insights into hepatocarcinogenesis. SIGNIFICANCE: Multiomics profiling and integrative analyses of stepwise hepatocarcinogenesis reveal novel mechanistic and clinical insights into hepatocarcinogenesis.

Methanol extract of Iphiona aucheri ameliorates CCl4 induced hepatic injuries by regulation of genes in rats

We have investigated the protective potential of methanol extract of Iphiona aucheri (IAM) on the expression of endoplasmic reticulum (ER) stress associated genes and inflammatory genes on carbon tetrachloride (CCl4) induced hepatic toxicity in rats. Hepatic damage markers: aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP) and bilirubin were elevated while the content of antioxidants: catalase (CAT), superoxide dismutase (SOD), peroxidase (POD) and reduced glutathione (GSH) were decreased significantly (p < 0.05) in CCl4 treated rats as compared to the control group. The CCl4 intoxication induced a higher expression of glucose-regulated protein 78 kDa (GRP78), X-box-binding protein 1 total (XBP1t), spliced X-box-binding protein 1 (XBP1s), unspliced X-box-binding protein 1 (XBP1u), C/EBP homologous protein (CHOP) and genes involved in inflammation and fibrosis: tumor necrosis factor alpha (TNF-α), transforming growth factor-beta (TGF-β), mothers against DPP homolog 3 (SMAD3), alpha skeletal muscle actin (αSMA) and collagen type I alpha 1 chain (COL1A1). The intoxicated rats showed a low expression of the glutamate-cysteine ligase catalytic subunit (GCLC), protein disulfide isomerase (PDI) and nuclear factor (erythroid-derived 2) like-2 (Nrf2). The administration of IAM to intoxicated rats restored the expression of ER stress, inflammatory, fibrosis and antioxidant genes in a dose dependent manner. Our results indicated that IAM can impede the ER stress and inflammatory genes and it could be a complementary and alternative therapeutic agent for oxidative stress associated disorders.

Drug-induced PD-L1 expression and cell stress response in breast cancer cells can be balanced by drug combination

The impact of chemotherapy on tumor-immune system interaction can be either beneficial or harmful, which is represented by the immunogenic cell death (ICD) paradigm or overexpression of the immunosuppressive protein – programmed death ligand 1 (PD-L1). In this study we explore the impact of steroid receptor coactivator inhibitor, other targeted anti-cancer compounds and traditional chemotherapeutic agents on the expression of PD-L1 in four breast cancer (BC) cell lines. Our results show that these agents induce PD-L1 expression, yet the magnitude of this induction varies substantially across the different compounds. In addition, we utilized the E0771 ER + BC cells as a model to examine in greater detail the relationship between pharmacological pressure, cell stress and the induction of PD-L1. Our results imply that drug induced PD-L1 expression occurs in the broader context of cell-stress, without conferring acquired drug-resistance. Furthermore, a balance between BC cytotoxicity, induction of cell-stress and the overexpression of PD-L1 can be achieved through the selection of appropriate combinations of anti-cancer compounds. Therefore, we propose that drug combination can be employed not only for increasing the direct kill of cancer cells, but also as a strategy to minimize the activation of immunosuppressive and cancer cell pro-survival program responses during drug treatment.

ADP-dependent glucokinase regulates energy metabolism via ER-localized glucose sensing

Modulation of energy metabolism to a highly glycolytic phenotype, i.e. Warburg effect, is a common phenotype of cancer and activated immune cells allowing increased biomass-production for proliferation and cell division. Endoplasmic reticulum (ER)-localized ADP-dependent glucokinase (ADPGK) has been shown to play a critical role in T cell receptor activation-induced remodeling of energy metabolism, however the underlying mechanisms remain unclear. Therefore, we established and characterized in vitro and in vivo models for ADPGK-deficiency using Jurkat T cells and zebrafish. Upon activation, ADPGK knockout Jurkat T cells displayed increased cell death and ER stress. The increase in cell death resulted from a metabolic catastrophe and knockout cells displayed severely disturbed energy metabolism hindering induction of Warburg phenotype. ADPGK knockdown in zebrafish embryos led to short, dorsalized body axis induced by elevated apoptosis. ADPGK hypomorphic zebrafish further displayed dysfunctional glucose metabolism. In both model systems loss of ADPGK function led to defective N- and O-glycosylation. Overall, our data illustrate that ADPGK is part of a glucose sensing system in the ER modulating metabolism via regulation of N- and O-glycosylation.

Obesity in mares promotes uterine inflammation and alters embryo lipid fingerprints and homeostasis

Maternal body composition can be an important determinant for development of obesity and metabolic syndrome in adult offspring. Obesity-related outcomes in offspring may include epigenetic alterations; however, mechanisms of fetal programming remain to be fully elucidated. This study was conducted to determine the impact of maternal obesity in the absence of a high fat diet on equine endometrium and preimplantation embryos. Embryos were collected from normal and obese mares at 8 and 16 days and a uterine biopsy at 16 days (0 day = ovulation). With the exception of 8 day embryos, each sample was divided into two pieces. One piece was analyzed for gene expression markers related to carbohydrate metabolism, lipid homeostasis, inflammation, endoplasmic reticulum stress, oxidative stress, mitochondrial stress, and components of the insulin-like growth factor (IGF) system. The second piece was analyzed for lipid content using matrix-assisted laser desorption/ionization mass spectrometry. Obese mares had elevated concentrations of insulin, leptin, and total cholesterol, and they tended to have increased triglycerides and decreased insulin sensitivity. Embryos from obese mares had altered transcript abundance in genes for inflammation and lipid homeostasis, as well as endoplasmic reticulum, oxidative and mitochondrial stress and altered lipid fingerprints. Endometrium from obese mares had increased expression of inflammatory cytokines, lipid homeostasis regulation, mitochondrial stress, and the IGF2 system. This study demonstrates that increased adiposity in mares alters the uterine environment, transcript abundance of genes for cellular functions, and lipid profiles of embryos. These alterations could affect prenatal programming, with potential long-term effects in offspring.

ER stress response mediates diabetic microvascular complications

Endoplasmic reticulum (ER) homeostasis orchestrates the folding, modification, and trafficking of secretory and membrane proteins to the Golgi compartment, thus governing cellular functions. Alterations in ER homeostasis result in the activation of signaling pathways, such as the unfolded protein response (UPR), to regain ER homeostasis. Nevertheless, failure of UPR leads to activation of autophagy-mediated cell death. Several recent studies emphasized the association of the ER stress (ERS) response with the initiation and progression of diabetes. In this review, we highlight the contribution of the ERS response, such as UPR and autophagy, in the initiation and progression of diabetes and associated microvascular complications, including diabetic nephropathy (DN), retinopathy, and neuropathy, in various experimental models, as well as in humans. We highlight the ERS as a putative therapeutic target for the treatment of diabetic microvascular complications and, thus, the urgent need for the development of improved synthetic and natural inhibitors of ERS.

Renal tubular cell spliced X-box binding protein 1 (Xbp1s) has a unique role in sepsis-induced acute kidney injury and inflammation

Sepsis is a systemic inflammatory state in response to infection, and concomitant acute kidney injury (AKI) increases mortality significantly. Endoplasmic reticulum stress is activated in many cell types upon microbial infection and modulates inflammation. The role of endoplasmic reticulum signaling in the kidney during septic AKI is unknown. Here we tested the role of the spliced X-box binding protein 1 (Xbp1s), a key component of the endoplasmic reticulum stress-activated pathways, in the renal response to sepsis in the lipopolysaccharide (LPS) model. Xbp1s was increased in the kidneys of mice treated with LPS but not in other models of AKI, or several chronic kidney disease models. The functional significance of Xbp1s induction was examined by genetic manipulation in renal tubules. Renal tubule-specific overexpression of Xbp1s caused severe tubule dilation and vacuolation with expression of the injury markers Kim1 and Ngal, the pro-inflammatory molecules interleukin-6 (Il6) and Toll-like receptor 4 (Tlr4), decreased kidney function and 50% mortality in five days. Renal tubule-specific genetic ablation of Xbp1 had no phenotype at baseline. However, after LPS, Xbp1 knockdown mice displayed lower renal NGAL, pro-apoptotic factor CHOP, serum creatinine levels, and a tendency towards lower Tlr4 compared to LPS-treated mice with intact Xbp1s. LPS treatment in Xbp1s-overexpressing mice caused a mild increase in NGAL and CHOP compared to LPS-treated mice without genetic Xbp1s overexpression. Thus, increased Xbp1s signaling in renal tubules is unique to sepsis-induced AKI and contributes to renal inflammation and injury. Inhibition of this pathway may be a potential portal to alleviate injury.

PRKCSH contributes to tumorigenesis by selective boosting of IRE1 signaling pathway

Unfolded protein response (UPR) is an adaptive mechanism that aims at restoring ER homeostasis under severe environmental stress. Malignant cells are resistant to environmental stress, which is largely due to an activated UPR. However, the molecular mechanisms by which different UPR branches are selectively controlled in tumor cells are not clearly understood. Here, we provide evidence that PRKCSH, previously known as glucosidase II beta subunit, functions as a regulator for selective activation of the IRE1α branch of UPR. PRKCSH boosts ER stress–mediated autophosphorylation and oligomerization of IRE1α through mutual interaction. PRKCSH contributes to the induction of tumor-promoting factors and to tumor resistance to ER stress. Increased levels of PRKCSH in various tumor tissues are positively correlated with the expression of XBP1-target genes. Taken together, our data provide a molecular rationale for selective activation of the IRE1α branch in tumors and adaptation of tumor cells to severe environmental stress.

Cancer cells utilise the unfolded protein response (UPR) to adapt to environmental and ER stress. Here, the authors show that the glycosidase II beta subunit, PRKSCH, protects cancer cells from ER stress, by interacting with IRE1α and activating the IRE1α-XBP1 branch of the UPR.

Deficiency of fibroblast growth factor 21 aggravates obesity-induced atrophic responses in skeletal muscle

Background

Obesity-induced skeletal muscle inflammation is a major contributor of skeletal muscle loss/atrophy and is implicated in metabolic complications such as insulin resistance. Fibroblast growth factor 21 (FGF21) is known to be an important metabolic regulator with anti-inflammatory properties. However, the effect of FGF21 on skeletal muscle atrophy is unclear. In this study, we investigated the effect of FGF21 deficiency on obesity-induced skeletal muscle inflammation and atrophy in mice.

Results

The expression of atrophic factors (MuRF1 and Atrogin-1) was upregulated at the mRNA and/or protein levels in the skeletal muscle of FGF21-deficient obese mice compared with wild type obese control mice. This was accompanied by an increase in levels of inflammatory cytokines (TNFα and MCP-1) and a reduction in AMPK phosphorylation. FGF21 treatment markedly suppressed TNFα-mediated inflammatory and atrophic responses in cultured myotubes, and the actions of FGF21 were blunted by the AMPK inhibitor compound C.

Conclusion

These findings suggest that FGF21 deficiency aggravates obesity-induced inflammation and atrophic responses in the skeletal muscle of obese mice, and FGF21 may protect inflammation-mediated atrophy through the AMPK pathway.

A Novel Animal Model for Studying Depression Featuring the Induction of the Unfolded Protein Response in Hippocampus

Depression is the leading cause of disability worldwide with global distribution of 322 million people suffering from the disease. While much is understood about depression, the underlying pathophysiology is yet to be fully characterized. Recently, the unfolded protein response (UPR) has been shown to be involved in regulating key aspects like inflammation, cell death, and behavioral depression. The UPR is an evolutionarily conserved ancient response system that reacts to the stressful environmental impact on a cell; the net effect of stress to a cell is that the quality of protein folding is diminished. The UPR responds by repairing and removing misfolded proteins and, if necessary, initiates apoptosis. Here, we demonstrate that the UPR is not only involved in depression, but that its activation causes a depressive phenotype. The hippocampi of rats were directly infused with 500 ng of tunicamycin (TM), an agent that initiates the UPR by blocking N-terminal glycosylation. Three to 8 days post-surgery, the rats showed depressive behavior in escape latency, forced swim despair, sucrose preference anhedonia, and also physiological signs of depression like decreased weight. Further, these behavioral changes were associated with enhanced expression of key UPR genes and proteins in the hippocampus. We propose that this model will make an excellent tool for studying depression and for understanding pathways that are affected by the UPR which directly causes depressive behavior.

Resveratrol alleviates nuclear factor-κB-mediated neuroinflammation in vasculitic peripheral neuropathy induced by ischaemia-reperfusion via suppressing endoplasmic reticulum stress

Vasculitic peripheral neuropathy (VPN) arises from an inflammatory obstruction in the blood vessels supplying peripheral nerves and subsequent ischaemic insults, which exhibits the clinical features of neuropathic pain and impaired peripheral nerve function. VPN induced by ischaemia-reperfusion (IR) has been reported to involve nuclear factor-κB (NF-κB)-mediated neuroinflammation. Recent studies have suggested that endoplasmic reticulum (ER) stress has been implicated in the development of peripheral neuropathies. Resveratrol possesses a potent anti-inflammatory capacity. We hypothesized that resveratrol may exert a protective effect against VPN through modulating the interrelated ER stress and NF-κB pathways. Male Sprague-Dawley rats were allocated into five groups: sham, sham + resveratrol 40 mg/kg (R40), IR, IR + R20 and IR + R40. VPN was induced by occluding the right femoral artery for 4 hours followed by reperfusion. Our data have shown that VPN induced by IR led to hind paw mechanical allodynia, heat hyperalgaesia, and impaired motor nerve conduction velocity (MNCV). With resveratrol intervention, the behavioural parameters were improved in a dose-dependent manner and the MNCV levels were increased as well. The molecular data revealed that VPN induced by IR significantly increased the expression of NF-κB as well as the ER stress sensor proteins, protein kinase RNA-like endoplasmic reticulum kinase, inositol-requiring enzyme 1 and activating transcription factor 6 in the sciatic nerves. More importantly, resveratrol significantly attenuated the expression of NF-κB and the ER stress sensor proteins after IR. In conclusion, resveratrol alleviates VPN induced by IR. The mechanisms may involve modulating NF-κB-mediated neuroinflammation via suppressing ER stress.

KHG21834 attenuates glutamate-induced mitochondrial damage, apoptosis, and NLRP3 inflammasome activation in SH-SY5Y human neuroblastoma cells

New compounds were screened to develop effective drugs against glutamate-induced toxicity. The present study assessed the effects of the novel thiazole derivative KHG21834 against glutamate-induced toxicity in human neuroblastoma SH-SY5Y cell cultures. Treatment of SH-SY5Y cells with KHG21834 significantly protected cells against glutamate-induced toxicity in a dose-dependent manner, with an optimum concentration of 50 μM. KHG21834 protected SH-SY5Y cells against glutamate toxicity by suppressing glutamate-induced oxidative stress by 50%. KHG21834 also attenuated glutamate-induced mitochondrial membrane potential, ATP level reductions, and intracellular Ca²⁺ influx. Furthermore, KHG21834 efficiently reduced glutamate-induced ER stress and NLRP3 inflammasome activation (59% and 65% of glutamate group, respectively). In addition, KHG21834 effectively attenuated glutamate-induced levels of Bax, Bcl-2, cleaved caspase-3, p-p38, p-JNK proteins, and TUNEL positive cells. To our knowledge, this is the first study showing that KHG21834 can effectively protect SH-SY5Y cells against glutamate toxicity, suggesting that this compound may be a valuable therapeutic agent for the treatment of glutamate toxicity.

Curcumin Inhibits the PERK-eIF2α-CHOP Pathway through Promoting SIRT1 Expression in Oxidative Stress-induced Rat Chondrocytes and Ameliorates Osteoarthritis Progression in a Rat Model

Oxidative stress plays a crucial role in the occurrence and development of osteoarthritis (OA) through the activation of endoplasmic reticulum (ER) stress. Curcumin is a polyphenolic compound with significant antioxidant and anti-inflammatory activity among various diseases. To elucidate the role of curcumin in oxidative stress-induced chondrocyte apoptosis, this study investigated the effect of curcumin on ER stress-related apoptosis and its potential mechanism in oxidative stress-induced rat chondrocytes. The results of flow cytometry and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) staining showed that curcumin can significantly attenuate ER stress-associated apoptosis. Curcumin inhibited the expression of cleaved caspase3, cleaved poly (ADP-ribose) polymerase (PARP), C/EBP homologous protein (CHOP), and glucose-regulated protein78 (GRP78) and upregulated the chondroprotective protein Bcl2 in TBHP-treated chondrocytes. In addition, curcumin promoted the expression of silent information regulator factor 2-related enzyme 1 (SIRT1) and suppressed the expression of activating transcription factor 4 (ATF4), the ratio of p-PERK/PERK, p-eIF2α/eIF2α. Our anterior cruciate ligament transection (ACLT) rat OA model research demonstrated that curcumin (50 mg/kg and 150 mg/kg) ameliorated the degeneration of articular cartilage and inhibited chondrocyte apoptosis in ACLT rats in a dose-dependent manner. By applying immunohistochemical analysis, we found that curcumin enhanced the expression of SIRT1 and inhibited the expression of CHOP and cleaved caspase3 in ACLT rats. Taken together, our present findings firstly indicate that curcumin could inhibit the PERK-eIF2α-CHOP axis of the ER stress response through the activation of SIRT1 in tert-Butyl hydroperoxide- (TBHP-) treated rat chondrocytes and ameliorated osteoarthritis development in vivo.

The characteristics of the ancient cell death suppressor, TMBIM6, and its related signaling pathways after endoplasmic reticulum stress

Activation of the unfolded protein response in combination with generation of reactive oxygen species, from cytochrome P450 members and NADPH-P450 reductases, are two major consequences of Endoplasmic Reticulum (ER) stress that cause oxidative damage and cell death. Herein, we reviewed the role of Bax Inhibitor-1 (BI-1), an evolutionarily conserved protein encoded by the Transmembrane Bax inhibitor Motif Containing 6 gene, in protection from ER stress. As BI-1 has multimodal properties that can target a wide array of pathophysiological consequences after injury, our main objective was to explore BI-1's protective role in ER stress and its potential signaling pathways.