At the crossway of ER-stress and proinflammatory responses

Therapeutic Effect of V8 Affecting Mitophagy and Endoplasmic Reticulum Stress in Acute Myeloid Leukemia Mediated by ROS and CHOP Signaling

Acute myeloid leukemia (AML) is characterized by the malignant proliferation of abnormally or poorly differentiated myeloid cells in the hematopoietic system. However, there is a lack of effective drugs for treating non-M3 AML. V8, a newly synthesized derivative of the natural flavonoid wogonin, which is a potential anticancer drug, has demonstrated significant antitumor activity both in vitro and in vivo. Here, we investigated the effects of V8 on AML cell lines and primary AML cells as well as its underlying mechanisms. Our results showed that V8 exerted significant concentration-dependent growth inhibition and apoptosis induction in AML cells, accompanied by characteristic pathological features including lysosomal functions suppression, mitochondrial dysfunction, and endoplasmic reticulum stress (ERS) activation. Mechanistic investigations revealed that V8 induced mitochondrial membrane potential collapse through elevation of intracellular reactive oxygen species (ROS) levels, while concurrently blocking mitophagy via lysosomal functional inhibition. Furthermore, V8 selectively activated the PERK/p-eIF2α/ATF4 and IRE1α/XBP1 signaling axes of ERS, ultimately triggering CHOP-mediated apoptosis through the ERS-specific pathway. In vivo studies confirmed that V8 treatment significantly prolonged survival duration in NOD/SCID mice bearing primary AML xenografts and suppressed tumor progression in BALB/c nude mice with U937 cell xenografts, with antitumor efficacy closely associated with CHOP-dependent ERS pathway modulation. These findings not only elucidate the multi-targeted mechanism of V8 against AML through coordinated regulation of the ROS-mitochondria-lysosome-ERS signaling network, but also provide critical theoretical foundations for developing natural product-based therapeutics for AML. The multi-pathway synergistic characteristics exhibited by V8 underscore its considerable potential as a clinically translatable candidate drug.

Endoplasmic Reticulum Stress Drives Neuroinflammation Through Lipocalin 2 Upregulation in Retinal Microglia After Optic Nerve Injury

Purpose

This study aims to explore how lipocalin 2 (LCN2) connects endoplasmic reticulum (ER) stress and inflammation in optic nerve injury (ONI) and identify potential therapeutic strategies.

Methods

An optic nerve crush (ONC) mouse model was used to investigate the role of ER stress and LCN2 in ONI. Immunofluorescence, quantitative PCR, and Western blot analyses were performed to assess ER stress markers, LCN2, inflammation-related genes, and retinal ganglion cell (RGC) survival, with or without treatment of 4PBA (an ER stress inhibitor) and TUN (an ER stress activator) in both the ONC model and BV2 cells. Lcn2 knockdown was achieved using small interfering RNA in BV2 cells and adeno-associated virus (AAV)-mediated gene silencing in vivo to explore underlying signaling pathways.

Results

ER stress markers (GRP78, ATF4, CHOP) and LCN2 expression were increased in ONC retinas, accompanied by microglial activation and RGC loss. Inhibition of ER stress using 4PBA effectively decreased LCN2 expression, attenuated microglial activation, and increased RGC survival post-ONC. Intravitreal injection of recombinant LCN2 induced a proinflammatory phenotype in microglia and exacerbated neurotoxicity. AAV-mediated Lcn2 silencing mitigated microglial activation, reduced neuroinflammation, and provided RGC neuroprotection, surpassing 4PBA treatment. In vitro studies further confirmed that Lcn2 knockdown significantly reduced the inflammatory response in BV2 cells by inhibiting NLRP3 inflammasome activation via the TLR4/NF-κB pathway.

Conclusions

This study elucidates the critical role of LCN2 in linking ER stress and inflammation in ONI, offering a promising therapeutic target. AAV-mediated Lcn2 silencing outperforms broad ER stress inhibition, providing a novel strategy for treating optic nerve injuries.

Promoting ER stress in a plasmacytoid dendritic cell line drives fibroblast activation

BACKGROUND

Fibrosis remains a major complication in several chronic diseases, including systemic sclerosis (SSc). Plasmacytoid dendritic cells (pDCs) are innate immune cells that play a key role in the development of fibrosis in SSc patients, through still poorly defined mechanisms. Interestingly, endoplasmic reticulum (ER) stress signaling pathways are dysregulated in pDCs from patients with SSc, but their contribution to fibrosis remains unclear. Thus, this study aimed to unravel the mechanisms behind the involvement of pDCs and ER stress in fibrosis.

METHODS

To address this question, we established an in vitro model designed to study the interactions between pDCs and fibroblasts. More specifically, IMR-90 fibroblasts were co-cultured with CAL-1, a pDC cell line. ER stress was then induced by the bacterial toxin SubAB. Extracellular matrix (ECM) production was assessed using immunoblotting, qPCR and confocal microscopy. The importance of cell-to-cell contact was investigated using conditioned media (CM) and transwell assays.

RESULTS

Direct contact of CAL-1 and IMR-90 cells under ER stress conditions led to increased expression of fibronectin and alpha-smooth muscle actin (α-SMA). This effect required expression of the ER stress signaling sensor protein kinase R-like ER kinase (PERK) in pDCs and was observed only upon direct contact between both cell types.

CONCLUSIONS

Overall, our data suggest that ER stress induction in pDCs promotes fibroblast activation, which may contribute to the development of fibrosis in SSc.

Comparative evaluation of cigarette smoke and a heated tobacco product on microglial toxicity, oxidative stress and inflammatory response

BACKGROUND

Tobacco smoking is the leading cause of preventable death and disease worldwide, with over 8 million annual deaths attributed to cigarette smoking. This study investigates the impact of cigarette smoke and heated tobacco products (HTPs) on microglial function, focusing on toxicological profiles, inflammatory responses, and oxidative stress using ISO standard and clinically relevant conditions of exposure.

METHODS

We assessed cell viability, reactive oxygen species (ROS) production, lipid peroxidation, mitochondrial function, unfolded protein response, and inflammation in human microglial cells (HMC3) exposed to cigarette smoke, HTP aerosol or nicotine.

RESULTS

Our findings show that cigarette smoke significantly reduces microglial viability, increases ROS formation, induces lipid peroxidation, and reduces intracellular glutathione levels. Cigarette smoke also alters the expression of genes involved in mitochondrial dynamics and biogenesis, leading to mitochondrial dysfunction. Additionally, cigarette smoke impairs the unfolded protein response, activates the NF-κB pathway, and induces a pro-inflammatory state characterized by increased TNF and IL-18 expression. Furthermore, cigarette smoke causes DNA damage and decreases the expression of the aging marker Klotho β. In contrast, HTP, exhibited a lesser degree of microglial toxicity, with reduced ROS production, lipid peroxidation, and mitochondrial dysfunction compared to conventional cigarettes.

CONCLUSION

These results highlight the differential toxicological profile of cigarette smoke and HTP on microglial cells, suggesting a potential harm reduction strategy for neurodegenerative disease for smokers unwilling or unable to quit.

ER-transiting bacterial toxins amplify STING innate immune responses and elicit ER stress

The cGAS/STING sensor system drives innate immune responses to intracellular microbial double-stranded DNA (dsDNA) and bacterial cyclic nucleotide second messengers (e.g., c-di-AMP). STING-dependent cell-intrinsic responses can increase resistance to microbial infection and speed pathogen clearance. Correspondingly, STING activation and signaling are known to be targeted for suppression by effectors from several bacterial pathogens. Whether STING responses are also positively regulated through sensing of specific bacterial effectors is less clear. We find that STING activation through dsDNA, by its canonical ligand 2'-3' cGAMP, or the small molecule DMXAA is potentiated following intracellular delivery of the AB5 toxin family member pertussis toxin from Bordetella pertussis or the B subunit of cholera toxin from Vibrio cholerae. Entry of pertussis toxin or cholera toxin B into mouse macrophages triggers markers of endoplasmic reticulum (ER) stress and enhances ligand-dependent STING responses at the level of STING receptor activation in a manner that is independent of toxin enzymatic activity. Our results provide an example in which STING responses integrate information about the presence of relevant ER-transiting bacterial toxins into the innate inflammatory response and may help to explain the in vivo adjuvant effects of catalytically inactive toxins.

Recent progress of endoplasmic reticulum stress in the mechanism of atherosclerosis

The research progress of endoplasmic reticulum (ER) stress in atherosclerosis (AS) is of great concern. The ER, a critical cellular organelle, plays a role in important biological processes including protein synthesis, folding, and modification. Various pathological factors may cause ER stress, and sustained or excessive ER stress triggers the unfolded protein response, ultimately resulting in apoptosis and disease. Recently, researchers have discovered the importance of ER stress in the onset and advancement of AS. ER stress contributes to the occurrence of AS through different pathways such as apoptosis, inflammatory response, oxidative stress, and autophagy. Therefore, this review focuses on the mechanisms of ER stress in the development of AS and related therapeutic targets, which will contribute to a deeper understanding of the disease's pathogenesis and provide novel strategies for preventing and treating AS.

G protein-coupled receptor 84 gene expression is regulated by the ER stress response in the liver

G protein-coupled receptor 84 (Gpr84) is reportedly activated by medium-chain fatty acids and is involved in the pathology of liver fibrosis. Inflammatory stimulants, such as lipopolysaccharide and tumor necrosis factor-α, upregulate Gpr84 expression. However, the detailed molecular mechanism by which Gpr84 is induced remains unknown. Inflammatory stimulation also evokes endoplasmic reticulum (ER) stress, but there has been no direct evidence to link Gpr84 expression and the ER stress response. Administration of tunicamycin (Tm) provokes ER stress and acute steatosis in the liver tissue of mice. Here, in situ hybridization analysis revealed that induction of Gpr84 expression occurred in parenchymal cells in the liver tissue following Tm administration. Gene expression analysis using a reporter assay showed that the intron 1 region of Gpr84 was involved in induction of the gene under ER stress conditions. Furthermore, Tm-dependent upregulation of Gpr84 was blocked by the small chemical compound AEBSF, an inhibitor of ER stress transducers, in vitro and in vivo. In conclusion, the current study marks the discovery that the ER stress agent Tm induces the expression of Gpr84.

Circular RNA HIPK2 Promotes A1 Astrocyte Activation after Spinal Cord Injury through Autophagy and Endoplasmic Reticulum Stress by Modulating miR-124-3p-Mediated Smad2 Repression

Glial scarring formed by reactive astrocytes after spinal cord injury (SCI) is the primary obstacle to neuronal regeneration within the central nervous system, making them a promising target for SCI treatment. Our previous studies have demonstrated the positive impact of miR-124-3p on neuronal repair, but it remains unclear how miR-124-3p is involved in autophagy or ER stress in astrocyte activation. To answer this question, the expression of A1 astrocyte-related markers at the transcriptional and protein levels after SCI was checked in RNA-sequencing data and verified using quantitative polymerase chain reaction (qPCR) and Western blotting in vitro and in vivo. The potential interactions among circHIPK2, miR-124-3p, and Smad2 were analyzed and confirmed by bioinformatics analyses and a luciferase reporter assay. In the end, the role of miR-124-3p in autophagy, ER stress, and SCI was investigated by using Western blotting to measure key biomarkers (C3, LC3, and Chop) in the absence or presence of corresponding selective inhibitors (siRNA, 4-PBA, TG). As a result, SCI caused the increase of A1 astrocyte markers, in which the upregulated circHIPK2 directly targeted miR-124-3p, and the direct downregulating effect of Smad2 by miR-124-3p was abolished, while Agomir-124 treatment reversed this effect. Injury caused a significant change of markers for ER stress and autophagy through the circHIPK2/miR-124-3p/Smad2 pathway, which might activate the A1 phenotype, and ER stress might promote autophagy in astrocytes. In conclusion, circHIPK2 may play a functional role in sequestering miR-124-3p and facilitating the activation of A1 astrocytes through regulating Smad2-mediated downstream autophagy and ER stress pathways, providing a new perspective on potential targets for functional recovery after SCI.

Signaling plasticity in the integrated stress response

The Integrated Stress Response (ISR) is an essential homeostatic signaling network that controls the cell's biosynthetic capacity. Four ISR sensor kinases detect multiple stressors and relay this information to downstream effectors by phosphorylating a common node: the alpha subunit of the eukaryotic initiation factor eIF2. As a result, general protein synthesis is repressed while select transcripts are preferentially translated, thus remodeling the proteome and transcriptome. Mounting evidence supports a view of the ISR as a dynamic signaling network with multiple modulators and feedback regulatory features that vary across cell and tissue types. Here, we discuss updated views on ISR sensor kinase mechanisms, how the subcellular localization of ISR components impacts signaling, and highlight ISR signaling differences across cells and tissues. Finally, we consider crosstalk between the ISR and other signaling pathways as a determinant of cell health.

New insights into the unfolded protein response (UPR)-anterior gradient 2 (AGR2) pathway in the regulation of intestinal barrier function in weaned piglets

Sustained dysfunction of the intestinal barrier caused by early weaning is a major factor that induces postweaning diarrhea in weaned piglets. In both healthy and diseased states, the intestinal barrier is regulated by goblet cells. Alterations in the characteristics of goblet cells are linked to intestinal barrier dysfunction and inflammatory conditions during pathogenic infections. In this review, we summarize the current understanding of the mechanisms of the unfolded protein response (UPR) and anterior gradient 2 (AGR2) in maintaining intestinal barrier function and how modifications to these systems affect mucus barrier characteristics and goblet cell dysregulation. We highlight a novel mechanism underlying the UPR-AGR2 pathway, which affects goblet cell differentiation and maturation and the synthesis and secretion of mucin by regulating epidermal growth factor receptor and mucin 2. This study provides a theoretical basis and new insights into the regulation of intestinal health in weaned piglets.

CXCR3 antagonist rescues ER stress and reduces inflammation and JEV infection in mice brain

The endoplasmic reticulum (ER) is crucial for maintaining cellular homeostasis, and synthesis and folding of proteins and lipids. The ER is sensitive to stresses including viral infection that perturb the intracellular energy level and redox state, and accumulating unfolded/misfolded proteins. Viruses including Japanese encephalitis virus (JEV) activates unfolded protein response (UPR) causing ER stress in host immune cells and promotes inflammation and apoptotic cell death. The chemokine receptor CXCR3 has been reported to play important role in the accumulation of inflammatory immune cells and neuronal cell death in several disease conditions. Recently we described the involvement of CXCR3 in regulating inflammation and JEV infection in mice brain. Supplementation with a CXCR3 antagonist AMG487 significantly reduced JEV infection in the mice brain in conjunction with the downregulation of UPR pathway via PERK:eIF2α:CHOP, and decreased mitochondrial ROS generation, inflammation and apoptotic cell death. Alongside, AMG487 treatment improved interferon (IFN)-α/β synthesis in JEV-infected mice brain. Thus, suggesting a potential therapeutic role of CXCR3 antagonist against JEV infection.

Targeting the tumor microenvironment: Potential strategy for cancer therapeutics

Cellular and stromal components including tumor cells, immune cells, mesenchymal cells, cancer-linked fibroblasts, and extracellular matrix, constituent tumor microenvironment (TME). TME plays a crucial role in reprogramming tumor initiation, uncontrolled proliferation, invasion and metastasis as well as response to therapeutic modalities. In recent years targeting the TME has developed as a potential strategy for treatment of cancer because of its life-threatening functions in restricting tumor development and modulating responses to standard-of-care medicines. Cold atmospheric plasma, oncolytic viral therapy, bacterial therapy, nano-vaccine, and repurposed pharmaceuticals with combination therapy, antiangiogenic drugs, and immunotherapies are among the most effective therapies directed by TME that have either been clinically authorized or are currently being studied. This article discusses above-mentioned therapies in light of targeting TME. We also cover problems related to the TME-targeted therapies, as well as future insights and practical uses in this rapidly growing field.

The molecular link between obesity and genomic instability in cancer development

Obesity has been known to be a major risk factor for various types of cancers for several decades. More recently, the relationship between dysregulated adipokines and cancer development has been the focus of much research. Adipose tissue is an important endocrine organ that secretes adipokines that affect both autocrine and paracrine signaling. These adipokines modulate inflammation, induce insulin resistance, and regulate their own behavior and production. Adipokine-production dysregulation is due to physiological changes in adipose tissue that prompt molecular modifications, including low-grade inflammation and the stimulatory production of reactive oxygen species. Additionally, studies have linked DNA damage response, genomic instability, and the innate immune response to tumorigenesis. Further investigation of adipokines and their role in the promotion of genomic instability may clarify the link between obesity and cancer, as well as elucidate potential pharmaceutical targets. In this review, we discuss the progress of recent literature, focusing on the impact of adipokines, genomic instability, and the innate immune response on increasing the risk of cancer.

IRE1α arm of unfolded protein response in muscle-specific TGF-β signaling-mediated regulation of muscle cell immunological properties

Endoplasmic reticulum stress (ERS) and the unfolded protein response (UPR) are involved in various muscle pathological states. The IRE1α arm of UPR can affect immunological properties of myofiber through restraining p38 mitogen-activated protein kinases (MAPK) activation under inflammatory milieu. However, the relevant pathway molecules regulating the initiation of the IRE1α arm in myofiber remain unclear. In this work, expression of transforming growth factor-beta (TGF-β) and TGF-β receptor II (TGF-βr2), and UPR pathway activation were examined in cardiotoxin (CTX)-damaged mouse muscle, which revealed the activation of TGF-β signaling and UPR in CTX-damaged muscle and in regenerating myofibers. Using control or transgenic mice with TGF-βr2 deleted in skeletal muscle (SM TGF-βr2^-/-) and the derived primary differentiating myogenic precursor cells (MPCs) treated with/without ERS activator or inhibitor, IRE1α pathway inhibitor, or TGF-β signaling activator, this study further revealed an essential role of intrinsic TGF-β signaling in regulating muscle cell to express inflammation-related molecules including H-2K^b, H2-Eα, TLR3, and special myokines. TGF-β signaling prompted UPR IRE1α arm and restrained p38 MAPK activation in myofiber under inflammatory milieu. This study uncovers a previously unrecognized function of TGF-β signaling acting as an upstream factor controlling myofiber immune capacities in the inflamed state through the UPR-IRE1α-p38 MAPK pathway.

Chronic activation of pDCs in autoimmunity is linked to dysregulated ER stress and metabolic responses

Plasmacytoid dendritic cells (pDCs) chronically produce type I interferon (IFN-I) in autoimmune diseases, including systemic sclerosis (SSc) and systemic lupus erythematosus (SLE). We report that the IRE1α-XBP1 branch of the unfolded protein response (UPR) inhibits IFN-α production by TLR7- or TLR9-activated pDCs. In SSc patients, UPR gene expression was reduced in pDCs, which inversely correlated with IFN-I-stimulated gene expression. CXCL4, a chemokine highly secreted in SSc patients, downregulated IRE1α-XBP1-controlled genes and promoted IFN-α production by pDCs. Mechanistically, IRE1α-XBP1 activation rewired glycolysis to serine biosynthesis by inducing phosphoglycerate dehydrogenase (PHGDH) expression. This process reduced pyruvate access to the tricarboxylic acid (TCA) cycle and blunted mitochondrial ATP generation, which are essential for pDC IFN-I responses. Notably, PHGDH expression was reduced in pDCs from patients with SSc and SLE, and pharmacological blockade of TCA cycle reactions inhibited IFN-I responses in pDCs from these patients. Hence, modulating the IRE1α-XBP1-PHGDH axis may represent a hitherto unexplored strategy for alleviating chronic pDC activation in autoimmune disorders.

Cigarette smoke exposed airway epithelial cell-derived EVs promote pro-inflammatory macrophage activation in alpha-1 antitrypsin deficiency

BACKGROUND

Alpha-1 antitrypsin deficiency (AATD) is a genetic disorder most commonly secondary to a single mutation in the SERPINA1 gene (PI*Z) that causes misfolding and accumulation of alpha-1 antitrypsin (AAT) in hepatocytes and mononuclear phagocytes which reduces plasma AAT and creates a toxic gain of function. This toxic gain of function promotes a pro-inflammatory phenotype in macrophages that contributes to lung inflammation and early-onset COPD, especially in individuals who smoke cigarettes. The aim of this study is to determine the role of cigarette exposed AATD macrophages and bronchial epithelial cells in AATD-mediated lung inflammation.

METHODS

Peripheral blood mononuclear cells from AATD and healthy individuals were differentiated into alveolar-like macrophages and exposed to air or cigarette smoke while in culture. Macrophage endoplasmic reticulum stress was quantified and secreted cytokines were measured using qPCR and cytokine ELISAs. To determine whether there is "cross talk" between epithelial cells and macrophages, macrophages were exposed to extracellular vesicles released by airway epithelial cells exposed to cigarette smoke and their inflammatory response was determined.

RESULTS

AATD macrophages spontaneously produce several-fold more pro-inflammatory cytokines as compared to normal macrophages. AATD macrophages have an enhanced inflammatory response when exposed to cigarette smoke-induced extracellular vesicles (EVs) released from airway epithelial cells. Cigarette smoke-induced EVs induce expression of GM-CSF and IL-8 in AATD macrophages but have no effect on normal macrophages. Release of AAT polymers, potent neutrophil chemo attractants, were also increased from AATD macrophages after exposure to cigarette smoke-induced EVs.

CONCLUSIONS

The expression of mutated AAT confers an inflammatory phenotype in AATD macrophages which disposes them to an exaggerated inflammatory response to cigarette smoke-induced EVs, and thus could contribute to progressive lung inflammation and damage in AATD individuals.

T-cell-specific Sel1L deletion exacerbates EAE by promoting Th1/Th17-cell differentiation

Multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE) are demyelinating neuroinflammatory diseases identified by the accumulation and aggregation of misfolded proteins in the brain. The Sel1L-Hrd1 complex comprising endoplasmic reticulum associated degradation (ERAD) is an ER-protein quality control system (ERQC) in the cell. Unfortunately, the contribution of ERAD to the development of these diseases has not been well explored. In this study, we used mice with a conditional deletion (KO) of Sel1L in T cells to dissect the role of ERAD on T cells and its contribution to the development of EAE. The results showed that Sel1L KO mice developed more severe EAE than the control wild type (WT) mice. Although, no obvious effects on peripheral T cells in steady state, more CD44-CD25+ double-negative stage 3 (DN3) cells were detected in the thymus. Moreover, Sel1L deficiency promoted the differentiation of Th1 and Th17 cells and upregulated the proliferation and apoptosis of CD4 T cells in vitro. Regarding the mechanism analyzed by RNA sequencing, 437 downregulated genes and 271 upregulated genes were detected in Sel1L deletion CD4 T cells, which covered the activation, proliferation, differentiation and apoptosis of these T cells. Thus, this study declared that the dysfunction of Sel1L in ERAD in T cells exacerbated the severity of EAE and indicated the important role of ERQC in maintaining immune homeostasis in the central nervous system.

[Estradiol inhibits differentiation of mouse macrophage into a pro-inflammatory phenotype by upregulating the IRE1α-XBP1 signaling axis]

OBJECTIVE

To explore the mechanism by which estradiol modulates the immunophenotype of macrophages through the endoplasmic reticulum stress pathway.

METHODS

Peritoneal macrophages isolated from C57 mice were cultured in the presence of 60 ng/mL interferon-γ (IFN-γ) followed by treatment with estradiol (1.0 nmol/L) alone, estradiol with estrogen receptor antagonist (Acolbifene, 4 nmol/L), estradiol with IRE1α inhibitor (4 μ 8 C), or estradiol with IRE1α agonist. After the treatments, the expression levels of MHC-Ⅱ, iNOS and endoplasmic reticulum stress marker proteins IRE1α, eIF2α and ATF6 in the macrophages were detected with Western blotting, and the mRNA levels of TGF-β, IL-6, IL-10 and TNF-α were detected with RT-PCR.

RESULTS

Estrogen treatment of the macrophages significantly decreased the expressions of M1-related proteins MHC-Ⅱ (P=0.021) and iNOS (P < 0.001) and the mRNA expressions of TNF-α (P=0.003) and IL-6 (P=0.004), increased the mRNA expression of TGF-β (P=0.002) and IL-10 (P=0.008), and up-regulated the protein expressions of IRE1α (P < 0.001) and its downstream transcription factor XBP-1 (P < 0.001). Addition of the estrogen inhibitor obviously blocked the effect of estrogen. Compared with estrogen treatment alone, combined treatment of the macrophages with estrogen and the IRE1α inhibitor 4 μ 8 C significantly up-regulated the protein expressions of MHC-Ⅱ (P=0.002) and iNOS (P=0.003) and the mRNA expressions of TNF-α (P=0.003) and IL-6 (P=0.024), and obviously down-regulated the mRNA expression of TGF-β (P < 0.001) and IL-10 (P < 0.001); these changes were not observed in cells treated with estrogen and the IRE1α agonist.

CONCLUSION

Estrogen can inhibit the differentiation of murine macrophages into a pro-inflammatory phenotype by up-regulating the IRE1α-XBP-1 signaling axis, thereby producing an inhibitory effect on inflammatory response.

Salvianolic Acid B Suppresses ER Stress-Induced NLRP3 Inflammasome and Pyroptosis via the AMPK/FoxO4 and Syndecan-4/Rac1 Signaling Pathways in Human Endothelial Progenitor Cells

Mounting evidence demonstrates uncontrolled endoplasmic reticulum (ER) stress responses can activate the inflammasome, which generally results in endothelial dysfunction, a major pathogenetic factor of chronic inflammatory diseases such as atherosclerosis. Salvianolic acid B (SalB), produced by Radix Salviae, exerts antioxidative and anti-inflammatory activities in multiple cell types. However, SalB's effects on ER stress-related inflammasome and endothelial dysfunction remain unknown. Here, we showed SalB substantially abrogated ER stress-induced cell death and reduction in capillary tube formation, with declined intracellular reactive oxygen species (ROS) amounts and restored mitochondrial membrane potential (MMP), as well as increased expression of HO-1 and SOD2 in bone marrow-derived endothelial progenitor cells (BM-EPCs). ER stress suppression by CHOP or caspase-4 siRNA transfection attenuated the protective effect of SalB. Additionally, SalB alleviated ER stress-mediated pyroptotic cell death via the suppression of TXNIP/NLRP3 inflammasome, as evidenced by reduced cleavage of caspase-1 and interleukin- (IL-) 1β and IL-18 secretion levels. Furthermore, this study provided a mechanistic basis that AMPK/FoxO4/KLF2 and Syndecan-4/Rac1/ATF2 signaling pathway modulation by SalB substantially prevented BM-EPCs damage associated with ER stress by decreasing intracellular ROS amounts and inducing NLRP3-dependent pyroptosis. In summary, our findings identify that ER stress triggered mitochondrial ROS release and NLRP3 generation in BM-EPCs, while SalB inhibits NLRP3 inflammasome-mediated pyroptotic cell death by regulating the AMPK/FoxO4/KLF2 and Syndecan-4/Rac1/ATF2 pathways. The current findings reveal SalB as a potential new candidate for the treatment of atherosclerotic heart disease.

PERK signaling through C/EBPδ contributes to ER stress-induced expression of immunomodulatory and tumor promoting chemokines by cancer cells

Cancer cells experience endoplasmic reticulum (ER) stress due to activated oncogenes and conditions of nutrient deprivation and hypoxia. The ensuing unfolded protein response (UPR) is executed by ATF6, IRE1 and PERK pathways. Adaptation to mild ER stress promotes tumor cell survival and aggressiveness. Unmitigated ER stress, however, will result in cell death and is a potential avenue for cancer therapies. Because of this yin-yang nature of ER stress, it is imperative that we fully understand the mechanisms and dynamics of the UPR and its contribution to the complexity of tumor biology. The PERK pathway inhibits global protein synthesis while allowing translation of specific mRNAs, such as the ATF4 transcription factor. Using thapsigargin and tunicamycin to induce acute ER stress, we identified the transcription factor C/EBPδ (CEBPD) as a mediator of PERK signaling to secretion of tumor promoting chemokines. In melanoma and breast cancer cell lines, PERK mediated early induction of C/EBPδ through ATF4-independent pathways that involved at least in part Janus kinases and the STAT3 transcription factor. Transcriptional profiling revealed that C/EBPδ contributed to 20% of thapsigargin response genes including chaperones, components of ER-associated degradation, and apoptosis inhibitors. In addition, C/EBPδ supported the expression of the chemokines CXCL8 (IL-8) and CCL20, which are known for their tumor promoting and immunosuppressive properties. With a paradigm of short-term exposure to thapsigargin, which was sufficient to trigger prolonged activation of the UPR in cancer cells, we found that conditioned media from such cells induced cytokine expression in myeloid cells. In addition, activation of the CXCL8 receptor CXCR1 during thapsigargin exposure supported subsequent sphere formation by cancer cells. Taken together, these investigations elucidated a novel mechanism of ER stress-induced transmissible signals in tumor cells that may be particularly relevant in the context of pharmacological interventions.

Azithromycin alleviates the severity of rheumatoid arthritis by targeting the UPR component GRP78

BACKGROUND AND PURPOSE

Azithromycin (AZM) is a macrolide antibiotic with well-described anti-inflammatory properties. This study aimed to substantiate the treatment potential of AZM in rheumatoid arthritis (RA).

EXPERIMENTAL APPROACH

Gene expression profiles were collected by RNA sequencing, and the effects of AZM were assessed in functional assays. In vitro and in vivo assays were performed to examine the effects of AZM-mediated blockade of glucose-regulated protein 78 (GRP78). Assays to define the anti-inflammatory activity of AZM using fibroblast-like synoviocytes (FLSs) from RA patients and collagen-induced arthritis (CIA) in DBA/1 mice were performed. Identification and characterization of the binding of AZM to GRP78 was performed using drug affinity responsive target stability assays, proteomics and cellular thermal shift assays. AZM-mediated inhibition of GRP78 and the dependence of the antiarthritic activity of AZM on GRP78 were assessed.

KEY RESULTS

AZM reduced proinflammatory factor production, cell migration, invasion and chemoattraction and enhanced apoptosis, thereby reducing the deleterious inflammatory response of RA FLSs in vitro. AZM ameliorated the severity of CIA lesions as efficiently as the anti-tumour necrosis factor (anti-TNF) biological agent etanercept (ETC). Transcriptional analyses suggested that AZM treatment impairs signalling cascades associated with cholesterol and lipid biosynthetic processes. GRP78 was identified as a novel target of AZM. AZM-mediated activation of the unfolded protein response (UPR) via the inhibition of GRP78 activity is required not only for inducing the expression of C/EBP-homologous protein (ChOP) but also for the activating sterol-regulatory element binding protein (SREBP) and its targeted genes involved in cholesterol and lipid biosynthetic processes. Furthermore, deletion of GRP78 abolished the antiarthritic activity of AZM.

CONCLUSION AND IMPLICATIONS

These findings confirmed that AZM is a therapeutic drug for RA treatment.

Promoting athero-protective immunity by vaccination with low density lipoprotein-derived antigens

Immune responses activated by LDL particles that have been trapped and oxidized in the arterial wall play an important role in atherosclerosis. Some of these immune responses are protective by facilitating the removal of pro-inflammatory and toxic lipid species formed as result of LDL oxidation. However, should these protective immune responses be insufficient, other more potent pro-inflammatory immune responses instead contributing to disease progression will gradually become dominant. The importance of the balance between protective and pathogenic immunity is particularly apparent when it comes to the adaptive immune system where pro-inflammatory T helper 1 (Th1) type T cells aggravate atherosclerosis, while regulatory T cells (Tregs) have an opposing role. As oxidized LDL is a key autoantigen in atherosclerosis, it has become an interesting possibility that immune-modulatory therapy that favors the activity of apolipoprotein B peptide-specific Tregs could be developed into a novel treatment strategy for prevention/stabilization of atherosclerosis and ischemic cardiovascular events. Indeed, several such oxidized LDL tolerance vaccines have shown promising results in animal models of atherosclerosis. This review will discuss the experimental background for development of atherosclerosis vaccines based on LDL-derived antigens as well as the challenges involved in translating these findings into clinical application.

MANF Is Neuroprotective in Early Stages of EAE, and Elevated in Spinal White Matter by Treatment With Dexamethasone

Multiple sclerosis (MS) is a progressive autoimmune disease characterized by T-cell mediated demyelination in central nervous system (CNS). Experimental autoimmune encephalomyelitis (EAE) is a widely used in vivo disease model of MS. Glucocorticoids such as dexamethasone (dex) function as immunosuppressants and are commonly used to treat acute exacerbations of MS. Dex is also often used as a positive control in EAE studies, as it has been shown to promote motor behavior, inhibit immune cell infiltration into the CNS and regulate the activation of glial cell in EAE. This study further validated the effects of intravenously administrated dex by time-dependent fashion in EAE. Dex postponed clinical signs and motor defects in early stages of EAE. Histological analysis revealed that the degeneration of myelin and axons, as well as the infiltration of peripheral immune cells into the white matter of spinal cord was inhibited by dex in early stages of EAE. Additionally, dex-treatment delayed the neuroinflammatory activation of microglia and astrocytes. Furthermore, this study analyzed the expression of the neurotrophic factor mesencephalic astrocyte-derived neurotrophic factor (MANF) in EAE, and the effect of treatment with dex on MANF-expression. We show that in dex-treated EAE mice expression MANF increased within myelinated areas of spinal cord white matter. We also show that intravenous administration with hMANF in EAE mice improved clinical signs and motor behavior in the early stage of EAE. Our report gives insight to the progression of EAE by providing a time-dependent analysis. Moreover, this study investigates the link between MANF and the EAE model, and shows that MANF is a potential drug candidate for MS.

PKC Delta Activation Promotes Endoplasmic Reticulum Stress (ERS) and NLR Family Pyrin Domain-Containing 3 (NLRP3) Inflammasome Activation Subsequent to Asynuclein-Induced Microglial Activation: Involvement of Thioredoxin-Interacting Protein (TXNIP)/Thioredoxin (Trx) Redoxisome Pathway

A classical hallmark of Parkinson's disease (PD) pathogenesis is the accumulation of misfolded alpha-synuclein (αSyn) within Lewy bodies and Lewy neurites, although its role in microglial dysfunction and resultant dopaminergic (DAergic) neurotoxicity is still elusive. Previously, we identified that protein kinase C delta (PKCδ) is activated in post mortem PD brains and experimental Parkinsonism and that it participates in reactive microgliosis; however, the relationship between PKCδ activation, endoplasmic reticulum stress (ERS) and the reactive microglial activation state in the context of α-synucleinopathy is largely unknown. Herein, we show that oxidative stress, mitochondrial dysfunction, NLR family pyrin domain containing 3 (NLRP3) inflammasome activation, and PKCδ activation increased concomitantly with ERS markers, including the activating transcription factor 4 (ATF-4), serine/threonine-protein kinase/endoribonuclease inositol-requiring enzyme 1α (p-IRE1α), p-eukaryotic initiation factor 2 (eIF2α) as well as increased generation of neurotoxic cytokines, including IL-1β in aggregated αSynagg-stimulated primary microglia. Importantly, in mouse primary microglia-treated with αSynagg we observed increased expression of Thioredoxin-interacting protein (TXNIP), an endogenous inhibitor of the thioredoxin (Trx) pathway, a major antioxidant protein system. Additionally, αSynagg promoted interaction between NLRP3 and TXNIP in these cells. In vitro knockdown of PKCδ using siRNA reduced ERS and led to reduced expression of TXNIP and the NLRP3 activation response in αSynagg-stimulated mouse microglial cells (MMCs). Additionally, attenuation of mitochondrial reactive oxygen species (mitoROS) via mito-apocynin and amelioration of ERS via the eIF2α inhibitor salubrinal (SAL) reduced the induction of the ERS/TXNIP/NLRP3 signaling axis, suggesting that mitochondrial dysfunction and ERS may act in concert to promote the αSynagg-induced microglial activation response. Likewise, knockdown of TXNIP by siRNA attenuated the αSynagg-induced NLRP3 inflammasome activation response. Finally, unilateral injection of αSyn preformed fibrils (αSynPFF) into the striatum of wild-type mice induced a significant increase in the expression of nigral p-PKCδ, ERS markers, and upregulation of the TXNIP/NLRP3 inflammasome signaling axis prior to delayed loss of TH+ neurons. Together, our results suggest that inhibition of ERS and its downstream signaling mediators TXNIP and NLRP3 might represent novel therapeutic avenues for ameliorating microglia-mediated neuroinflammation in PD and other synucleinopathies.

The Unfolded Protein Response in Immune Cells as an Emerging Regulator of Neuroinflammation

Immune surveillance is an essential process that safeguards the homeostasis of a healthy brain. Among the increasing diversity of immune cells present in the central nervous system (CNS), microglia have emerged as a prominent leukocyte subset with key roles in the support of brain function and in the control of neuroinflammation. In fact, impaired microglial function is associated with the development of neurodegenerative diseases, including Alzheimer’s disease (AD) and Parkinson’s disease (PD). Interestingly, these pathologies are also typified by protein aggregation and proteostasis dysfunction at the level of the endoplasmic reticulum (ER). These processes trigger activation of the unfolded protein response (UPR), which is a conserved signaling network that maintains the fidelity of the cellular proteome. Remarkably, beyond its role in protein folding, the UPR has also emerged as a key regulator of the development and function of immune cells. However, despite this evidence, the contribution of the UPR to immune cell homeostasis, immune surveillance, and neuro-inflammatory processes remains largely unexplored. In this review, we discuss the potential contribution of the UPR in brain-associated immune cells in the context of neurodegenerative diseases.

ER Stress, UPR Activation and the Inflammatory Response to Viral Infection

The response to invading pathogens such as viruses is orchestrated by pattern recognition receptor (PRR) and unfolded protein response (UPR) signaling, which intersects and converges in the activation of proinflammatory pathways and the release of cytokines and chemokines that harness the immune system in the attempt to clear microbial infection. Despite this protective intent, the inflammatory response, particularly during viral infection, may be too intense or last for too long, whereby it becomes the cause of organ or systemic diseases itself. This suggests that a better understanding of the mechanisms that regulate this complex process is needed in order to achieve better control of the side effects that inflammation may cause while potentiating its protective role. The use of specific inhibitors of the UPR sensors or PRRs or the downstream pathways activated by their signaling could offer the opportunity to reach this goal and improve the outcome of inflammation-based diseases associated with viral infections.

Most non-canonical proteins uniquely populate the proteome or immunopeptidome

Combining RNA sequencing, ribosome profiling, and mass spectrometry, we elucidate the contribution of non-canonical translation to the proteome and major histocompatibility complex (MHC) class I immunopeptidome. Remarkably, of 14,498 proteins identified in three human B cell lymphomas, 2,503 are non-canonical proteins. Of these, 28% are novel isoforms and 72% are cryptic proteins encoded by ostensibly non-coding regions (60%) or frameshifted canonical genes (12%). Cryptic proteins are translated as efficiently as canonical proteins, have more predicted disordered residues and lower stability, and critically generate MHC-I peptides 5-fold more efficiently per translation event. Translating 5' "untranslated" regions hinders downstream translation of genes involved in transcription, translation, and antiviral responses. Novel protein isoforms show strong enrichment for signaling pathways deregulated in cancer. Only a small fraction of cryptic proteins detected in the proteome contribute to the MHC-I immunopeptidome, demonstrating the high preferential access of cryptic defective ribosomal products to the class I pathway.

Oncogenic pathways activated by pro-inflammatory cytokines promote mutant p53 stability: clue for novel anticancer therapies

Inflammation and cancerogenesis are strongly interconnected processes, not only because inflammation promotes DNA instability, but also because both processes are driven by pathways such as NF-kB, STAT3, mTOR and MAPKs. Interestingly, these pathways regulate the release of pro-inflammatory cytokines such as IL-6, TNF-α and IL-1β that in turn control their activation and play a crucial role in shaping immune response. The transcription factor p53 is the major tumor suppressor that is often mutated in cancer, contributing to tumor progression. In this overview, we highlight how the interplay between pro-inflammatory cytokines and pro-inflammatory/pro-oncogenic pathways, regulating and being regulated by UPR signaling and autophagy, affects the stability of mutp53 that in turn is able to control autophagy, UPR signaling, cytokine release and the activation of the same oncogenic pathways to preserve its own stability and promote tumorigenesis. Interrupting these positive feedback loops may represent a promising strategy in anticancer therapy, particularly against cancers carrying mutp53.

Cellular senescence and tumor promotion: Role of the Unfolded Protein Response

Senescence is a cellular state which can be viewed as a stress response phenotype implicated in various physiological and pathological processes, including cancer. Therefore, it is of fundamental importance to understand why and how a cell acquires and maintains a senescent phenotype. Direct evidence has pointed to the homeostasis of the endoplasmic reticulum whose control appears strikingly affected during senescence. The endoplasmic reticulum is one of the sensing organelles that transduce signals between different pathways in order to adapt a functional proteome upon intrinsic or extrinsic challenges. One of these signaling pathways is the Unfolded Protein Response (UPR), which has been shown to be activated during senescence. Its exact contribution to senescence onset, maintenance, and escape, however, is still poorly understood. In this article, we review the mechanisms through which the UPR contributes to the appearance and maintenance of characteristic senescent features. We also discuss whether the perturbation of the endoplasmic reticulum proteostasis or accumulation of misfolded proteins could be possible causes of senescence, and-as a consequence-to what extent the UPR components could be considered as therapeutic targets allowing for the elimination of senescent cells or altering their secretome to prevent neoplastic transformation.

The UPR sensor IRE1α promotes dendritic cell responses to control Toxoplasma gondii infection

The unfolded protein response (UPR) has emerged as a central regulator of immune cell responses in several pathologic contexts including infections. However, how intracellular residing pathogens modulate the UPR in dendritic cells (DCs) and thereby affect T cell-mediated immunity remains uncharacterized. Here, we demonstrate that infection of DCs with Toxoplasma gondii (T. gondii) triggers a unique UPR signature hallmarked by the MyD88-dependent activation of the IRE1α pathway and the inhibition of the ATF6 pathway. Induction of XBP1s controls pro-inflammatory cytokine secretion in infected DCs, while IRE1α promotes MHCI antigen presentation of secreted parasite antigens. In mice, infection leads to a specific activation of the IRE1α pathway, which is restricted to the cDC1 subset. Mice deficient for IRE1α and XBP1 in DCs display a severe susceptibility to T. gondii and succumb during the acute phase of the infection. This early mortality is correlated with increased parasite burden and a defect in splenic T-cell responses. Thus, we identify the IRE1α/XBP1s branch of the UPR as a key regulator of host defense upon T. gondii infection.

Classical swine fever virus employs the PERK- and IRE1-dependent autophagy for viral replication in cultured cells

Endoplasmic reticulum stress (ERS)-mediated autophagy is indispensable for modulation of replication and pathogenesis of numerous mammalian viruses. We have previously shown that classical swine fever virus (CSFV) infection induces ERS-mediated autophagy for maintaining viral replication both in vivo and in vitro, however, the underlying mechanism remains unclarified. Here we found that CSFV infection activates the PERK pathway-dependent complete autophagy to promote viral replication in cultured PK-15 and 3D4/2 cells. Likewise, our results also suggested the essential roles of the IRE1/GRP78-mediated complete autophagy in CSFV replication in vitro. Furthermore, we suggested that CSFV infection induces activation of the PERK and IRE1 pathway for potential immunoregulation via promoting transcription of proinflammatory cytokine (IFN-γ and TNF-α) genes in the CSFV-infected cells. Finally, pharmacological treatment of PERK- or IRE1-pathway regulators, and the corresponding SiRNAs interventions did not affect the viabilities of the cells, excluding the potential interference elicited by altered cell viabilities. Taken together, our results suggest that CSFV infection induces complete autophagy through activation of the PERK and IRE1 pathway to facilitate viral replication in cultured cells, and modulation of proinflammatory cytokines may be a potential mechanism involved in this event. Our findings will open new horizons for molecular mechanisms of sustainable replication and pathogenesis of CSFV, and lay a theoretical foundation for the development of ERS-autophagy-targeting therapeutic strategies for clinical control of CSF.

Proteostasis in dendritic cells is controlled by the PERK signaling axis independently of ATF4

Differentiated dendritic cells display an unusual activation of the integrated stress response, which is necessary for normal type-I Interferon production and cell migration.

In stressed cells, phosphorylation of eukaryotic initiation factor 2α (eIF2α) controls transcriptome-wide changes in mRNA translation and gene expression known as the integrated stress response. We show here that DCs are characterized by high eIF2α phosphorylation, mostly caused by the activation of the ER kinase PERK (EIF2AK3). Despite high p-eIF2α levels, DCs display active protein synthesis and no signs of a chronic integrated stress response. This biochemical specificity prevents translation arrest and expression of the transcription factor ATF4 during ER-stress induction by the subtilase cytotoxin (SubAB). PERK inactivation, increases globally protein synthesis levels and regulates IFN-β expression, while impairing LPS-stimulated DC migration. Although the loss of PERK activity does not impact DC development, the cross talk existing between actin cytoskeleton dynamics; PERK and eIF2α phosphorylation is likely important to adapt DC homeostasis to the variations imposed by the immune contexts.

Protein disulfide isomerase A1 regulates breast cancer cell immunorecognition in a manner dependent on redox state

Oxidoreductase protein disulphide isomerases (PDI) are involved in the regulation of a variety of biological processes including the modulation of endoplasmic reticulum (ER) stress, unfolded protein response (UPR), ER-mitochondria communication and the balance between pro-survival and pro-death pathways. In the current study the role of the PDIA1 family member in breast carcinogenesis was investigated by measuring ROS generation, mitochondrial membrane disruption, ATP production and HLA-G protein levels on the surface of the cellular membrane in the presence or absence of PDIA1. The results showed that this enzyme exerted pro-apoptotic effects in estrogen receptor (ERα)-positive breast cancer MCF-7 and pro-survival in triple negative breast cancer (TNBC) MDA-MB-231 cells. ATP generation was upregulated in PDIA1-silenced MCF-7 cells and downregulated in PDIA1-silenced MDA-MB-231 cells in a manner dependent on the cellular redox status. Furthermore, MCF-7 and MDA-MB-231 cells in the presence of PDIA1 expressed higher surface levels of the non-classical human leukocyte antigen (HLA-G) under oxidative stress conditions. Evaluation of the METABRIC datasets showed that low PDIA1 and high HLA-G mRNA expression levels correlated with longer survival in both ERα-positive and ERα-negative stage 2 breast cancer patients. In addition, analysis of the PDIA1 vs. the HLA-G mRNA ratio in the subgroup of the living stage 2 breast cancer patients exhibiting low PDIA1 and high HLA-G mRNA levels revealed that the longer the survival time of the ratio was high PDIA1 and low HLA-G mRNA and occurred predominantly in ERα-positive breast cancer patients whereas in the same subgroup of the ERα-negative breast cancer mainly this ratio was low PDIA1 and high HLA-G mRNA. Taken together these results provide evidence supporting the view that PDIA1 is linked to several hallmarks of breast cancer pathways including the process of antigen processing and presentation and tumor immunorecognition.

ER Stress Leaves an Inflammatory TRAIL

Cell stress often triggers inflammation as a protective response to tissue damage or infection. In this issue of Developmental Cell, Sullivan et al. (2020) reveal an unexpected role for TRAIL receptors in ER-stress-induced inflammation.

Circulating miRNAs Associated With ER Stress and Organ Damage in a Preclinical Model of Trauma Hemorrhagic Shock

Circulating microRNAs (miRNA) alterations have been reported in severe trauma patients but the pathophysiological relevance of these changes is still unclear. miRNAs are critical biologic regulators of pathological events such as hypoxia and inflammation, which are known to induce endoplasmic reticulum (ER) stress. ER stress is emerging as an important process contributing to the development of single and/or multiple organ dysfunction after trauma hemorrhagic shock (THS) accompanied by impaired tissue microcirculation and inflammation. Here, we aim to bring new insights into the involvement of miRNAs associated with ER stress in THS. THS was induced in rats by a median laparotomy and blood withdrawal until mean arterial pressure (MAP) dropped to 30-35 mmHg followed by a restrictive (40 min) and full reperfusion (60 min) with Ringer's solution. Tunicamycin was used to induce ER stress. Blood samples were collected 24 h after THS for the determination of pathological changes in the blood (PCB) and circulating miRNAs. Plasma levels of circulating miRNAs were compared between THS, tunicamycin, and sham groups and correlated to biomarkers of PCB. MiRNA profile of THS animals showed that 40 out of 91 (44%) miRNAs were significantly upregulated compared to sham (p < 0.01). The data showed a very strong correlation between liver injury and miR−122-5p (r = 0.91, p < 0.00001). MiR-638, miR−135a-5p, miR−135b-5p, miR-668-3p, miR-204-5p, miR−146a-5p, miR−200a-3p, miR−17-5p, miR−30a-5p, and miR−214-3p were found positively correlated with lactate (r > 0.7, p < 0.05), and negatively with base excess (r ≤ 0.8, p < 0.05) and bicarbonate (r ≤ 0.8, p < 0.05), which are clinical parameters that reflected the shock severity. Tunicamycin significantly modified the microRNA profile of the animals, 33 out of 91 miRNAs were found differentially expressed. In addition, principal component analysis revealed that THS and tunicamycin induced similar changes in plasma miRNA patterns. Strikingly, the data showed that 15 (25.9%) miRNAs were regulated by both THS and tunicamycin (p < 0.01). This included miR−122-5p, a liver-specific microRNA, but also miR−17-5p and miR-125b-5p which are miRNAs remarkably involved in unfolded protein response (UPR)-mediating pro-survival signaling (IRE1α). Since miRNAs associated with ER stress are clearly correlated with THS, our data strongly suggest that interaction between miRNAs and ER stress is an important pathologic event occurring during THS. Overall, we consider that the miRNA profile developed in this study can provide a rationale for the development of bench-to-bedside strategies that target miRNAs in critical care diseases or be used as biomarkers in the prognosis of trauma patients.

3'quant mRNA-Seq of Porcine Liver Reveals Alterations in UPR, Acute Phase Response, and Cholesterol and Bile Acid Metabolism in Response to Different Dietary Fats

Animal fats are considered to be unhealthy, in contrast to vegetable fats, which are rich in unsaturated fatty acids. However, the use of some fats, such as coconut oil, is still controversial. In our experiment, we divided experimental animals (domestic pigs) into three groups differing only in the type of fat used in the diet: group R: rapeseed oil (n = 5); group B: beef tallow (n = 5); group C: coconut oil (n = 6). After transcriptomic analysis of liver samples, we identified 188, 93, and 53 DEGs (differentially expressed genes) in R vs. B, R vs. C, and B vs. C comparisons, respectively. Next, we performed a functional analysis of identified DEGs with String and IPA software. We observed the enrichment of genes engaged in the unfolded protein response (UPR) and the acute phase response among genes upregulated in B compared to R. In contrast, cholesterol biosynthesis and cholesterol efflux enrichments were observed among genes downregulated in B when compared to R. Moreover, activation of the UPR and inhibition of the sirtuin signaling pathway were noted in C when compared to R. The most striking difference in liver transcriptomic response between C and B was the activation of the acute phase response and inhibition of bile acid synthesis in the latest group. Our results suggest that excessive consumption of animal fats leads to the activation of a cascade of mutually propelling processes harmful to the liver: inflammation, UPR, and imbalances in the biosynthesis of cholesterol and bile acids via altered organelle membrane composition. Nevertheless, these studies should be extended with analysis at the level of proteins and their function.

Comparison between Single- and Group-housed Pregnant Sows for Direct and Indirect Physiological, Reproductive, Welfare Indicators and Gene Expression Profiling

Single- and group-housed pregnant sows were assessed during 8 weeks (4th and 8th to 14th) with regard to physiological, reproductive, welfare indicators and gene expression profiling. Compared to single-housed sows, group-housed sows had decreased non-return to estrus at 56 days after artificial insemination (AI) (83% vs 92%) and farrowing rate (78% vs 88%), respectively. Furthermore, group-housed sows showed a higher degree (p < 0.01) of advantageous physiological indicators, such as albumin (odds ratio [OR] = 4.4), alkaline phosphatase (OR = 1.5), bactericidal (OR = 3.2) and complement (OR = 24.3), and disadvantageous for alanine amino transferase (OR = 0.5), bilirubin (OR = 0.4), lysozyme (OR = 0.3) and C-reactive protein compared to single-housed. Eighty-seven genes related to immune response were underexpressed (log fold change ≤ 1.5; p < 0.05) during the 8th to 14th weeks in the group compared to single-housed sows, which in turn showed an immunomodulatory reduction on the expression of 43 genes during the 11th to 14th compared to the 4th week. Overall, the results were interpreted as indicative of greater comfort state of the group compared to single-housed sows.

Trophic activities of endoplasmic reticulum proteins CDNF and MANF

Mesencephalic astrocyte-derived neurotrophic factor (MANF) and cerebral dopamine neurotrophic factor (CDNF) are endoplasmic reticulum (ER) luminal proteins that confer trophic activities in a wide range of tissues under diverse pathological conditions. Despite initially being classified as neurotrophic factors, neither protein structurally nor functionally resembles bona fide neurotrophic factors. Their highly homologous structures comprise a unique globular, saposin-like domain within the N-terminus joined by a flexible linker to a C-terminus containing a SAP-like domain, CXXC motif and an ER retention sequence. Neurotrophic factors exert effects by binding to cognate receptors in the plasma membrane; however, no cell surface receptors have been identified for MANF and CDNF. Both can act as unfolded protein response (UPR) genes that modulate the UPR and inflammatory processes. The trophic activity of MANF and CDNF extends beyond the central nervous system with MANF being crucial for the development of pancreatic β cells and both have trophic effects in a variety of diseases related to the liver, heart, skeletal tissue, kidney and peripheral nervous system. In this article, the unique features of MANF and CDNF, such as their structure and mechanisms of action related to ER stress and inflammation, will be reviewed. Recently identified interactions with lipids and membrane trafficking will also be described. Lastly, their function and therapeutic potential in different diseases including a recent clinical trial using CDNF to treat Parkinson's disease will be discussed. Collectively, this review will highlight MANF and CDNF as broad-acting trophic factors that regulate functions of the endoplasmic reticulum.

Endoplasmic Reticulum Stress in Macrophages: The Vicious Circle of Lipid Accumulation and Pro-Inflammatory Response

The endoplasmic reticulum (ER) stress is an important event in the pathogenesis of different human disorders, including atherosclerosis. ER stress leads to disturbance of cellular homeostasis, apoptosis, and in the case of macrophages, to foam cell formation and pro-inflammatory cytokines production. In atherosclerosis, several cell types can be affected by ER stress, including endothelial cells, vascular smooth muscular cells, and macrophages. Modified low-density lipoproteins (LDL) and cytokines, in turn, can provoke ER stress through different processes. The signaling cascades involved in ER stress initiation are complex and linked to other cellular processes, such as lysosomal biogenesis and functioning, autophagy, mitochondrial homeostasis, and energy production. In this review, we discuss the underlying mechanisms of ER stress formation and the interplay of lipid accumulation and pro-inflammatory response. We will specifically focus on macrophages, which are the key players in maintaining chronic inflammatory milieu in atherosclerotic lesions, and also a major source of lipid-accumulating foam cells.

Endoplasmic Reticulum Stress Induced by Toxic Elements-a Review of Recent Developments

Endoplasmic reticulum of all eukaryotic cells is a membrane-bound organelle. Under electron microscope it appears as parallel arrays of "rough membranes" and a maze of "smooth vesicles" respectively. It performs various functions in cell, i.e., synthesis of proteins to degradation of xenobiotics. Bioaccumulation of drugs/chemicals/xenobiotics in the cytosol can trigger ER stress. It is recognized by the accumulation of unfolded or misfolded proteins in the lumen of ER. Present review summarizes the present status of knowledge on ER stress caused by toxic elements, viz arsenic, cadmium, lead, mercury, copper, chromium, and nickel. While inorganic arsenic may induce various glucose-related proteins, i.e., GRP78, GRP94 and CHOP, XBP1, and calpains, cadmium upregulates GRP78. Antioxidants like ascorbic acid, NAC, and Se inhibit the expression of UPR. Exposure to lead also changes ER stress related genes, i.e., GRP 78, GRP 94, ATF4, and ATF6. Mercury too upregulates these genes. Nickel, a carcinogenic element upregulates the expression of Bak, cytochrome C, caspase-3, caspase-9, caspase-12, and GADD 153. Much is not known on ER stress caused by nanoparticles. The review describes inter-organelle association between mitochondria and ER. It also discusses the interdependence between oxidative stress and ER stress. A cross talk amongst different cellular components appears essential to disturb pathways leading to cell death. However, these molecular switches within the signaling network used by toxic elements need to be identified. Nevertheless, ER stress especially caused by toxic elements still remains to be an engaging issue.

NOD1 and NOD2 Activation by Diverse Stimuli: a Possible Role for Sensing Pathogen-Induced Endoplasmic Reticulum Stress

Prompt recognition of microbes by cells is critical to eliminate invading pathogens. Some cell-associated pattern recognition receptors (PRRs) recognize and respond to microbial ligands. However, others can respond to cellular perturbations, such as damage-associated molecular patterns (DAMPs). Nucleotide oligomerization domains 1 and 2 (NOD1/2) are PRRs that recognize and respond to multiple stimuli of microbial and cellular origin, such as bacterial peptidoglycan, viral infections, parasitic infections, activated Rho GTPases, and endoplasmic reticulum (ER) stress. How NOD1/2 are stimulated by such diverse stimuli is not fully understood but may partly rely on cellular changes during infection that result in ER stress. NOD1/2 are ER stress sensors that facilitate proinflammatory responses for pathogen clearance; thus, NOD1/2 may help mount broad antimicrobial responses through detection of ER stress, which is often induced during a variety of infections. Some pathogens may subvert this response to promote infection through manipulation of NOD1/2 responses to ER stress that lead to apoptosis. Here, we review NOD1/2 stimuli and cellular responses. Furthermore, we discuss pathogen-induced ER stress and how it might potentiate NOD1/2 signaling.

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.

Novel Forms of Immunomodulation for Cancer Therapy

In recent years immunotherapy has provided new hope for cancer patients. However, some patients eventually relapse. Immunological responses are thought to underlie the long-term effects of conventional or targeted therapies. Whether this influence emerges from direct effects on cancer cells through immunogenic cell death (ICD) or by modulating the immune environment requires further clarification. ICD-related molecular mechanisms are also shared by cell-intrinsic defense responses that combat foreign intrusions. Indeed, we could potentially mimic and harness these processes to improve cancer immunogenicity. In addition, the microbiome is materializing as a missing factor in the cancer-immune therapy axis. The emerging idea of manipulating the gut microbiota to improve responses to anticancer therapy is becoming increasingly popular, but further clinical authentication is needed.

[Endoplasmic reticulum stress response and pathogenesis of non-alcoholic steatohepatitis]

The incidence of chronic liver disease is constantly increasing, owing to the obesity epidemic. Non-alcoholic fatty liver disease (NAFLD) is currently affecting 20-30% of the general population and 75-100% of obese individuals. NAFLD ranges from simple steatosis to damaging non-alcoholic steatohepatitis (NASH), potentially developing into hepatocellular carcinoma. No efficient pharmacological treatment is yet available. During obesity, the hepatic ER stress response can arise from extracellular stress (lipids, glucose, cytokines) and from intracellular stress including lipid buildup in the hepatocyte (steatosis), a hallmark of NAFLD. The chronic activation of the hepatic ER stress response may be a crucial event in the steatosis-NASH transition, triggering cell death, inflammation and accelerating metabolic disorders. We discuss these aspects and we propose that targeting the ER stress response could be effective in treating NAFLD.

Endoplasmic Reticulum-Associated Degradation-Dependent Processing in Cross-Presentation and Its Potential for Dendritic Cell Vaccinations: A Review

While the success of dendritic cell (DC) vaccination largely depends on cross-presentation (CP) efficiency, the precise molecular mechanism of CP is not yet characterized. Recent research revealed that endoplasmic reticulum (ER)-associated degradation (ERAD), which was first identified as part of the protein quality control system in the ER, plays a pivotal role in the processing of extracellular proteins in CP. The discovery of ERAD-dependent processing strongly suggests that the properties of extracellular antigens are one of the keys to effective DC vaccination, in addition to DC subsets and the maturation of these cells. In this review, we address recent advances in CP, focusing on the molecular mechanisms of the ERAD-dependent processing of extracellular proteins. As ERAD itself and the ERAD-dependent processing in CP share cellular machinery, enhancing the recognition of extracellular proteins, such as the ERAD substrate, by ex vivo methods may serve to improve the efficacy of DC vaccination.

NK cells induce hepatic ER stress to promote insulin resistance in obesity through osteopontin production

High-fat diet (HFD) induced hepatic endoplasmic reticulum (ER) stress drives insulin resistance (IR) and steatosis. NK cells in adipose tissue play an important role in the pathogenesis of IR in obesity. Whether NK cells in the liver can induce hepatic ER stress and thus promote IR in obesity is still unknown. We demonstrate that HFD-fed mice display elevated production of proinflammatory cytokine osteopontin (OPN) in hepatic NK cells, especially in CD49a⁺ DX5^- tissue-resident NK (trNK) cells. Obesity-induced ER stress, IR, and steatosis in the liver are ameliorated by ablating NK cells with neutralizing antibody in HFD-fed mice. OPN treatment enhances the expression of ER stress markers, including p-PERK, p-eIF2, ATF4, and CHOP in both murine liver tissues and HL-7702, a human liver cell line. Pretreatment of HL-7702 cells with OPN promotes hyperactivation of JNK and subsequent decrease of tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1), resulting in impaired insulin signaling, which can be reversed by inhibiting ER stress. Collectively, we demonstrate that hepatic NK cells induce obesity-induced hepatic ER stress, and IR through OPN production.