Mycobacterium tuberculosis PE_PGRS1 promotes mycobacteria intracellular survival via reducing the concentration of intracellular free Ca2+ and suppressing endoplasmic reticulum stress.

Mycobacterium tuberculosis (M. tuberculosis) is the causative agent of tuberculosis (TB). And the PE_PGRS family members of M. tuberculosis are closely associated with virulence and antigen presentation but with function largely elusive. PE_PGRS1(Rv0109) contained 7 Ca2+ binding domains of GGXGXD/NXUX (X is any amino acid), which can reduce intracellular Ca2+ surge. In addition, PE_PGRS1 can mitigate the activation of PERK branch in endoplasmic reticulum (ER) stress by down-regulating the expression of CHOP, Bip, p-PERK, p-eIF2α, and ATF4. Interestingly, we found that two splicing variations of Bax/Bcl-2, Baxß, and Bcl-2α, were differentially expressed after infection with Ms_PE_PGRS1, and may be involved in the regulation of apoptosis. Hence, this study identified that PE_PGRS1 is a novel calcium-associated protein that can decrease intracellular Ca2+ levels and the PERK axis. And the weakening of the PERK-eIF2α-ATF4 axis reduces THP-1 macrophages apoptosis, promotes the survival of mycobacteria in macrophages.

Prostaglandin E2-Induced AKT Activation Regulates the Life Span of Short-Lived Plasma Cells by Attenuating IRE1α Hyperactivation.

The mechanism regulating the life span of short-lived plasma cells (SLPCs) remains poorly understood. Here we demonstrated that the EP4-mediated activation of AKT by PGE2 was required for the proper control of inositol-requiring transmembrane kinase endoribonuclease-1α (IRE1α) hyperactivation and hence the endoplasmic reticulum (ER) homeostasis in IgM-producing SLPCs. Disruption of the PGE2-EP4-AKT signaling pathway resulted in IRE1α-induced activation of JNK, leading to accelerated death of SLPCs. Consequently, Ptger4-deficient mice (C57BL/6) exhibited a markedly impaired IgM response to T-independent Ags and increased susceptibility to Streptococcus pneumoniae infection. This study reveals a highly selective impact of the PGE2-EP4 signal on the humoral immunity and provides a link between ER stress response and the life span of SLPCs.

Peptidylarginine deiminase 2 promotes T helper 17-like T cell activation and activated T cell-autonomous death (ACAD) through an endoplasmic reticulum stress and autophagy coupling mechanism.

Peptididylarginine deiminase type 2 (PADI2) catalyzes the conversion of arginine residues to citrulline residues on proteins. We demonstrate that PADI2 induces T cell activation and investigate how PADI2 promotes activated T cell autonomous death (ACAD). In activated Jurkat T cells, overexpression of PADI2 significantly increases citrullinated proteins and induces endoplasmic reticulum (ER) stress and unfolded protein response (UPR) signaling, ultimately resulting in the expression of autophagy-related proteins and autophagy. PADI2 promoted autophagy and resulted in the early degradation of p62 and the light chain 3B (LC3B)-II accumulation. In Jurkat T cells, silencing the autophagy-related gene (Atg) 12 protein inhibits PADI2-mediated autophagy and promotes ER stress and apoptosis, whereas overexpression of Atg12 decreased ER stress and prolonged autophagy to promote cell survival. Additionally, PADI2 regulates T cell activation and the production of Th17 cytokines in Jurkat T cells (interleukins 6, IL-17A, IL-17F, IL-21, and IL-22). In Jurkat T cells, silencing IL-6 promotes autophagy mediated by PADI2 and inhibits PADI2-induced apoptosis, whereas silencing Beclin-1 increases the activation and survival of Th17-like T cells while decreasing autophagy and apoptosis. PADI2 silencing alleviates ER stress caused by PADI2 and decreases cytokine expression associated with Th17-like T cell activation and ACAD. We propose that PADI2 was involved in Th17 lymphocyte ACAD via a mechanism involving ER stress and autophagy that was tightly regulated by PADI2-mediated citrullination. These findings suggest that inhibiting Th17 T cell activation and the development of severe autoimmune diseases may be possible through the use of novel antagonists that specifically target PADI2.

Role of ROS-Induced NLRP3 Inflammasome Activation in the Formation of Calcium Oxalate Nephrolithiasis.

Calcium oxalate nephrolithiasis is a common and highly recurrent disease in urology; however, its precise pathogenesis is still unknown. Recent research has shown that renal inflammatory injury as a result of the cell-crystal reaction plays a crucial role in the development of calcium oxalate kidney stones. An increasing amount of research have confirmed that inflammation mediated by the cell-crystal reaction can lead to inflammatory injury of renal cells, promote the intracellular expression of NADPH oxidase, induce extensive production of reactive oxygen species, activate NLRP3 inflammasome, discharge a great number of inflammatory factors, trigger inflammatory cascading reactions, promote the aggregation, nucleation and growth process of calcium salt crystals, and ultimately lead to the development of intrarenal crystals and even stones. The renal tubular epithelial cells (RTECs)-crystal reaction, macrophage-crystal reaction, calcifying nanoparticles, endoplasmic reticulum stress, autophagy activation, and other regulatory factors and mechanisms are involved in this process.

Mechanisms of liver injury in high fat sugar diet fed mice that lack hepatocyte X-box binding protein 1.

Nonalcoholic fatty liver disease (NAFLD) is one of the most common causes of liver diseases in the United States and can progress to cirrhosis, end-stage liver disease and need for liver transplantation. There are limited therapies for NAFLD, in part, due to incomplete understanding of the disease pathogenesis, which involves different cell populations in the liver. Endoplasmic reticulum stress and its adaptative unfolded protein response (UPR) signaling pathway have been implicated in the progression from simple hepatic steatosis to nonalcoholic steatohepatitis (NASH). We have previously shown that mice lacking the UPR protein X-box binding protein 1 (XBP1) in the liver demonstrated enhanced liver injury and fibrosis in a high fat sugar (HFS) dietary model of NAFLD. In this study, to better understand the role of liver XBP1 in the pathobiology of NAFLD, we fed hepatocyte XBP1 deficient mice a HFS diet or chow and investigated UPR and other cell signaling pathways in hepatocytes, hepatic stellate cells and immune cells. We demonstrate that loss of XBP1 in hepatocytes increased inflammatory pathway expression and altered expression of the UPR signaling in hepatocytes and was associated with enhanced hepatic stellate cell activation after HFS feeding. We believe that a better understanding of liver cell-specific signaling in the pathogenesis of NASH may allow us to identify new therapeutic targets.

The aryl-ureido fatty acid CTU activates endoplasmic reticulum stress and PERK/NOXA-mediated apoptosis in tumor cells by a dual mitochondrial-targeting mechanism.

The cancer cell mitochondrion is functionally different from that in normal cells and could be targeted to develop novel experimental therapeutics. The aryl-ureido fatty acid CTU (16({[4-chloro-3-(trifluoromethyl)phenyl]-carbamoyl}amino)hexadecanoic acid) is the prototype of a new class of mitochondrion-targeted agents that kill cancer cells. Here we show that CTU rapidly depolarized the inner mitochondrial membrane, selectively inhibited complex III of the electron transport chain and increased reactive oxygen species (ROS) production. From RNA-seq analysis, endoplasmic reticulum (ER)-stress was a major activated pathway in CTU-treated cells and in MDA-MB-231 tumor xenografts from CTU-treated nu/nu mice. Mitochondrion-derived ROS activated the PERK-linked ER-stress pathway and induced the BH3-only protein NOXA leading to outer mitochondrial membrane (OMM) disruption. The lipid peroxyl scavenger α-tocopherol attenuated CTU-dependent ER-stress and apoptosis which confirmed the critical role of ROS. Oleic acid protected against CTU-mediated apoptosis by activating Mcl-1 expression, which increased NOXA sequestration and prevented OMM disruption. Taken together, CTU both uncouples mitochondrial electron transport and activates ROS production which promotes ER-stress-dependent OMM disruption and tumor cell death. Dual-mitochondrial targeting agents like CTU offer a novel approach for development of new anti-cancer therapeutics.

Tanshinone IIA alleviates NLRP3 inflammasome-mediated pyroptosis in Mycobacterium tuberculosis-(H37Ra-) infected macrophages by inhibiting endoplasmic reticulum stress.

ETHNOPHARMACOLOGICAL RELEVANCE: Tanshinone IIA (Tan), extracted from Salvia miltiorrhiza Bunge, is a perennial herbal plant widely used as a folk remedy in Asian countries. Several studies have proved that Tanshinone IIA possesses many biological activities, such as anti-inflammatory, free-radical scavenging abilities, antioxidant properties, liver protection, and anti-cancer properties. AIM OF THE STUDY: The objective of the present study was to examine the anti-inflammatory effects of Tan. MATERIALS AND METHODS: The in vitro infection model of Mycobacterium tuberculosis-infected macrophages with the H37Ra strain was established. Murine macrophage Raw 264.7 and human monocyte THP-1 were used for the experiments. Cell viability was determined by the MTT assay. Western blot and lactate dehydrogenase (LDH) activity assays were used to detect the effects of Tan on cell pyroptosis and the level of NLRP3 inflammasome activation. Western blot, Co-immunoprecipitation and Immunofluorescence assays were used to observe the effect of Tan on the expression level of TXNIP. Immunofluorescence assays were applied to explore the effect of Tan on mtROS. Western blot and agarose gel electrophoresis were adopted to observe the effect of Tan on endoplasmic reticulum stress. The siRNA technique was applied to knockdown the expression levels of PERK/peIF2α, IRE1α and ATF6, and Western blot assay was employed to explore the NLRP3 inflammasome activation and possible molecular regulation mechanism of Tan. RESULTS: This study demonstrated that Tan decreased Mtb-induced cell pyroptosis by measuring GSDMD-N and LDH release provoked by NLRP3 inflammasome activation. Additionally, Tan inhibited endoplasmic reticulum stress (ERS), mitochondrial damage, and TXNIP protein expression, all of which acted as upstream signals of NLRP3 inflammasome activation in Mtb-infected macrophages. Significantly, NLRP3 inflammasome activation was suppressed by knocking down ERS pathway proteins, which further clarified that Tan partly targeted ERS to exert anti-inflammatory and immunoregulatory actions. CONCLUSION: This research confirms Tan's anti-inflammatory and immunoregulatory mechanisms in Mtb-infected macrophages by downregulating NLRP3 inflammasome activation-mediated pyroptosis provoked by ERS. Tan may function as an adjuvant drug to treat TB by adjusting host immune responses.

A common approach for fighting tuberculosis and leprosy: controlling endoplasmic reticulum stress in myeloid-derived suppressor cells.

Leprosy and tuberculosis are infectious diseases that are caused by bacteria, and both share primary risk factors. Mediators of these diseases are regulated by a heterogeneous immature population of myeloid cells called myeloid-derived suppressor cells (MDSCs) that exhibit immunosuppressive activity against innate and adaptive immunity. During pathological conditions, endoplasmic reticulum (ER) stress occurs in MDSCs, and high levels of ER stress affect MDSC-linked immunosuppressive activity. Investigating the role of ER stress in regulating immunosuppressive functions of MDSCs in leprosy and tuberculosis may lead to new approaches to treating these diseases. Here the authors discuss the immunoregulatory effects of ER stress in MDSCs as well as the possibility of targeting unfolded protein response elements of ER stress to diminish the immunosuppressive activity of MDSCs and reinvigorate diminished adaptive immune system responses that occur in leprosy and tuberculosis.

Phoenixin-20 ameliorates gestational diabetes mellitus (GDM) symptoms and placental insults in an experimental mouse model.

BACKGROUND AND PURPOSE: Gestational diabetes mellitus (GDM) is a complication commonly observed in pregnancy, closely associated with increased oxidative stress, inflammatory response, and endoplasmic reticulum (ER) stress. Phoenixin-20 (PNX-20) is a newly reproductive hormone from the hypothalamus that has displayed pleiotropic effects. The promising inhibitory effects of PNX-20 on inflammation have recently been widely reported. The present study aims to investigate the protective effect of PNX-20 on GDM induced placental insults. METHODS: A GDM model was established on C57BLKsJ db/+ mice. The expression level of GPR173 was evaluated using RT-PCR and western blotting analysis. The serum level of glucose, insulin, lipid profiles, and oxidative stress indicators were detected with commercial kits. Fetal analysis was performed to evaluate the reproductive ability. ELISA was used to detect the production of inflammatory factors. The expressions of p-eIF-2α, ATF4, and GRP78 were evaluated with western blotting assay. RESULTS: Firstly, we found that GPR173 is expressed in the placenta tissue. Secondly, the elevated blood glucose level and lipid level, declined serum insulin level, fetus alive ratio, fetal and placenta weight, and shorten crown-rump length, were observed in the placenta tissue of GDM mice, which were reversed by treatment with PNX-20. Thirdly, the excessively released inflammatory factors and activated oxidative stress in GDM mice were alleviated by the administration of PNX-20. Lastly, the activated eIF-2α/ATF4 ER stress signaling pathway in GDM mice was dramatically suppressed by PNX-20. CONCLUSION: Our data revealed a protective property of PNX-20 against placental insults resulted from GDM.

Ghrelin Alleviates Endoplasmic Reticulum Stress in MC3T3E1 Cells by Inhibiting AMPK Phosphorylation.

Ghrelin is a gastric endocrine peptide that has been found to be involved in the process of energy homeostasis and bone physiology in recent years. To explore the effects of ghrelin on endoplasmic reticulum stress (ERS) in MC3T3E1 cells and its possible mechanism, an ERS model was induced by tunicamycin (TM) in the osteoblast line MC3T3E1. TM at 1.5 µg/mL was selected as the experimental concentration found by CCK8 assay. Through the determination of apoptosis, reactive oxygen species production, and endoplasmic reticulum stress-related gene expression, we found that ERS induced by TM can be relieved by ghrelin in a concentration-dependent manner (P < 0.001). Compared with the TM group, ghrelin reduced the expression of ERS-related marker genes induced by TM. Compared with the GSK621 + TM group without ghrelin pretreatment, the mRNA expression of genes in the ghrelin pretreatment group decreased significantly (P < 0.001). The results of protein analysis showed that the levels of BIP, p-AMPK, and cleaved-caspase3 in the TM group increased significantly, while the levels decreased after ghrelin pretreatment. In group GSK621 + TM compared with group GSK621 + ghrelin+TM, ghrelin pretreatment significantly reduced the level of p-AMPK, which is consistent with the trend of the ERS-related proteins BIP and cleaved-caspase3. In conclusion, ghrelin alleviates the ERS induced by TM in a concentration-dependent manner and may or at least partly alleviate the apoptosis induced by ERS in MC3T3E1 cells by inhibiting the phosphorylation of AMPK.

XBP-1s Promotes B Cell Pathogenicity in Chronic GVHD by Restraining the Activity of Regulated IRE-1α-Dependent Decay.

Allogeneic hematopoietic cell transplantation (allo-HCT) is an effective therapeutic procedure to treat hematological malignancies. However, the benefit of allo-HCT is limited by a major complication, chronic graft-versus-host disease (cGVHD). Since transmembrane and secretory proteins are generated and modified in the endoplasmic reticulum (ER), the ER stress response is of great importance to secretory cells including B cells. By using conditional knock-out (KO) of XBP-1, IRE-1α or both specifically on B cells, we demonstrated that the IRE-1α/XBP-1 pathway, one of the major ER stress response mediators, plays a critical role in B cell pathogenicity on the induction of cGVHD in murine models of allo-HCT. Endoribonuclease activity of IRE-1α activates XBP-1 signaling by converting unspliced XBP-1 (XBP-1u) mRNA into spliced XBP-1 (XBP-1s) mRNA but also cleaves other ER-associated mRNAs through regulated IRE-1α-dependent decay (RIDD). Further, ablation of XBP-1s production leads to unleashed activation of RIDD. Therefore, we hypothesized that RIDD plays an important role in B cells during cGVHD development. In this study, we found that the reduced pathogenicity of XBP-1 deficient B cells in cGVHD was reversed by RIDD restriction in IRE-1α kinase domain KO mice. Restraining RIDD activity per se in B cells resulted in an increased severity of cGVHD. Besides, inhibition of RIDD activity compromised B cell differentiation and led to dysregulated expression of MHC II and costimulatory molecules such as CD86, CD40, and ICOSL in B cells. Furthermore, restraining the RIDD activity without affecting XBP-1 splicing increased B cell ability to induce cGVHD after allo-HCT. These results suggest that RIDD is an important mediator for reducing cGVHD pathogenesis through targeting XBP-1s.

MKP-1 Overexpression Reduces Postischemic Myocardial Damage through Attenuation of ER Stress and Mitochondrial Damage.

Mitochondrial dysfunction and endoplasmic reticulum (ER) stress contribute to postischemic myocardial damage, but the upstream regulatory mechanisms have not been identified. In this study, we analyzed the role of mitogen-activated protein kinase (MAPK) phosphatase 1 (MKP-1) in the regulation of mitochondrial function and ER stress in hypoxic cardiomyocytes. Our results show that MKP-1 overexpression sustains viability and reduces hypoxia-induced apoptosis among H9C2 cardiomyocytes. MKP-1 overexpression attenuates ER stress and expression of ER stress genes and improves mitochondrial function in hypoxia-treated H9C2 cells. MKP-1 overexpression also increases ATP production and mitochondrial respiration and attenuates mitochondrial oxidative damage in hypoxic cardiomyocytes. Moreover, our results demonstrate that ERK and JNK are the downstream signaling targets of MKP-1 and that MKP-1 overexpression activates ERK, while it inhibits JNK. Inhibition of ERK reduces the ability of MKP-1 to preserve mitochondrial function and ER homeostasis in hypoxic cardiomyocytes. These results show that MKP-1 plays an essential role in the regulation of mitochondrial function and ER stress in hypoxic H9C2 cardiomyocytes through normalization of the ERK pathway and suggest that MKP-1 may serve as a novel target for the treatment of postischemic myocardial injury.

Inhibiting ATG5 mediated autophagy to regulate endoplasmic reticulum stress and CD4+ T lymphocyte differentiation: Mechanisms of acupuncture's effects on asthma.

OBJECTIVE: Asthma is characterized by airway hyperresponsiveness(AHR), inflammation and remodeling. Autophagy and endoplasmic reticulum stress(ERS) are dysregulated in asthma, and ATG5 has attracted wide attentions a representative gene of autophagy. Previous evidence shows that acupuncture may treat asthma by regulating the immune environment.However,the precise mechanism involved in acupuncture's effects on asthma is unclear. Thus, we investigated the inner-relationships of acupuncture and ATG5-mediated autophagy, ERS and CD4+ T lymphocyte differentiation in asthma. METHODS: Ovalbumin (OVA)-sensitized and challenged ATG5+/- and ATG5-/-mice with asthma were treated by acupuncture at Dazhui(GV14),Feishu(BL13) and Zusanli(ST36),and sacrificed the next day.Then blood and bronchoalveolar lavage fluid (BALF)samples were collected to determine inflammatory cell counts and cytokine levels. Lung tissue samples were obtained for histological examination, and the spleen was harvested for flow cytometry. RESULTS: Compared with the untreated group, acupuncture decreased BALF inflammatory cell counts and AHR in OVA-induced mice.Acupuncture decreased autophagy-related protein and mRNA (ATG5,Beclin-1,p62 and LC3B)amounts and ERS-related protein (p-PERK, p-IRE-1,Grp78, and ATF6)levels as well as autophagosome formation in lung tissue, concomitant with increased IFN-γ and decreased IL-4, IL-17 and TGF-ß amounts in BALF.Consistently, the imbalance of CD4+ T lymphocyte subsets(Th1/Th2 and Treg/Th17) was also corrected by acupuncture.Meanwhile, AHR and inflammation were decreased in ATG5-/- mice compared with ATG+/-animals,without affecting the therapeutic effect of acupuncture. CONCLUSION: Acupuncture reduces airway inflammation and AHR in asthma by inhibiting ATG5-mediated autophagy to regulate endoplasmic reticulum stress and CD4+T lymphocyte differentiation.

ROCK1 regulates sepsis-induced acute kidney injury via TLR2-mediated endoplasmic reticulum stress/pyroptosis axis.

BACKGROUND: It has been reported that ROCK1 participates in the progression of multiple diseases, including septic intestinal barrier, cardiac dysfunction and acute lung injury. However, its regulatory role and specific mechanism in sepsis-induced acute kidney injury (AKI) remain unclear. METHODS: Cecal ligation puncture (CLP) was conducted to establish sepsis mouse model, and in vitro model was achieved by lipopolysaccharide (LPS) stimulation. Genes expression was evaluated by qRT-PCR, western blot or ELISA was conducted to assess the levels of proteins. Hoechst staining was performed to evaluate cell pyroptosis. LDH activity assay was detected to assess cytotoxicity. Immunohistochemistry was conducted to detect Ly-6G expression and neutrophils distribution in kidney tissues of mice. H&E and TUNEL staining were carried to evaluate kidney injury of mice. RESULTS: Our findings illuminated that ROCK1 was highly expressed in sepsis-induced AKI, and ROCK1 knockdown inhibited NLRP3-mediated cell pyroptosis in LPS-induced HK-2 cells. Moreover, ROCK1 modulated HK-2 cell pyroptosis by regulating endoplasmic reticulum stress (ERS). TLR2 inhibitor could suppress ERS mediated cell pyroptosis under LPS treatment. Further, TLR2 activator partially reversed the effects of ROCK1 inhibition on ERS mediated pyroptosis in LPS-treated HK-2 cells and CLP mice. CONCLUSION: In conclusion, ROCK1 may regulate sepsis-induced AKI via TLR2-mediated ERS/pyroptosis axis. Our data demonstrated the role and underlying mechanism of ROCK1 in septic AKI, providing theoretical basis for sepsis-induced AKI treatment.

IFN-γ-induced ER stress impairs autophagy and triggers apoptosis in lung cancer cells.

Interferon-gamma (IFN-γ) is a major effector molecule of immunity and a common feature of tumors responding to immunotherapy. Active IFN-γ signaling can directly trigger apoptosis and cell cycle arrest in human cancer cells. However, the mechanisms underlying these actions remain unclear. Here, we report that IFN-γ rapidly increases protein synthesis and causes the unfolded protein response (UPR), as evidenced by the increased expression of glucose-regulated protein 78, activating transcription factor-4, and c/EBP homologous protein (CHOP) in cells treated with IFN-γ. The JAK1/2-STAT1 and AKT-mTOR signaling pathways are required for IFN-γ-induced UPR. Endoplasmic reticulum (ER) stress promotes autophagy and restores homeostasis. Surprisingly, in IFN-γ-treated cells, autophagy was impaired at the step of autophagosome-lysosomal fusion and caused by a significant decline in the expression of lysosomal membrane protein-1 and -2 (LAMP-1/LAMP-2). The ER stress inhibitor 4-PBA restored LAMP expression in IFN-γ-treated cells. IFN-γ stimulation activated the protein kinase-like ER kinase (PERK)-eukaryotic initiation factor 2a subunit (eIF2α) axis and caused a reduction in global protein synthesis. The PERK inhibitor, GSK2606414, partially restored global protein synthesis and LAMP expression in cells treated with IFN-γ. We further investigated the functional consequences of IFN-γ-induced ER stress. We show that inhibition of ER stress significantly prevents IFN-γ-triggered apoptosis. CHOP knockdown abrogated IFN-γ-mediated apoptosis. Inhibition of ER stress also restored cyclin D1 expression in IFN-γ-treated cells. Thus, ER stress and the UPR caused by IFN-γ represent novel mechanisms underlying IFN-γ-mediated anticancer effects. This study expands our understanding of IFN-γ-mediated signaling and its cellular actions in tumor cells.

Granzyme A Produced by γ9δ2 T Cells Activates ER Stress Responses and ATP Production, and Protects Against Intracellular Mycobacterial Replication Independent of Enzymatic Activity.

Mycobacterium tuberculosis (Mtb), the pathological agent that causes tuberculosis (TB) is the number one infectious killer worldwide with one fourth of the world's population currently infected. Data indicate that γ9δ2 T cells secrete Granzyme A (GzmA) in the extracellular space triggering the infected monocyte to inhibit growth of intracellular mycobacteria. Accordingly, deletion of GZMA from γ9δ2 T cells reverses their inhibitory capacity. Through mechanistic studies, GzmA's action was investigated in monocytes from human PBMCs. The use of recombinant human GzmA expressed in a mammalian system induced inhibition of intracellular mycobacteria to the same degree as previous human native protein findings. Our data indicate that: 1) GzmA is internalized within mycobacteria-infected cells, suggesting that GzmA uptake could prevent infection and 2) that the active site is not required to inhibit intracellular replication. Global proteomic analysis demonstrated that the ER stress response and ATP producing proteins were upregulated after GzmA treatment, and these proteins abundancies were confirmed by examining their expression in an independent set of patient samples. Our data suggest that immunotherapeutic host interventions of these pathways may contribute to better control of the current TB epidemic.

Keeping up with the stress of antibody production: BAFF and APRIL maintain memory plasma cells.

Memory plasma cells, also called long-lived plasma cells, provide 'humoral immunity' by continued secretion of protective antibodies against pathogens, which the immune system has once encountered. They are maintained mainly in the bone marrow, docking on to stromal cells individually. In those niches they can apparently persist for decades (Chang et al., 2018 [1]). Integrin-mediated contact to the stromal cell provides an essential survival signal to the plasma cell, activating the PI3K signalling pathway, downregulating FoxO1/3a and repressing the activation of caspases 3 and 7. In a redundant form, the cytokines BAFF and APRIL, ligands of the plasma cell receptors TACI and BCMA, provide a second essential survival signal, preventing activation of caspase 12, as triggered by endoplasmic reticulum stress.

Distinct mechanisms govern populations of myeloid-derived suppressor cells in chronic viral infection and cancer.

Myeloid-derived suppressor cells (MDSCs) are major negative regulators of immune responses in cancer and chronic infections. It remains unclear if regulation of MDSC activity in different conditions is controlled by similar mechanisms. We compared MDSCs in mice with cancer and lymphocytic choriomeningitis virus (LCMV) infection. Chronic LCMV infection caused the development of monocytic MDSCs (M-MDSCs) but did not induce polymorphonuclear MDSCs (PMN-MDSCs). In contrast, both MDSC populations were present in cancer models. An acquisition of immune-suppressive activity by PMN-MDSCs in cancer was controlled by IRE1α and ATF6 pathways of the endoplasmic reticulum (ER) stress response. Abrogation of PMN-MDSC activity by blockade of the ER stress response resulted in an increase in tumor-specific immune response and reduced tumor progression. In contrast, the ER stress response was dispensable for suppressive activity of M-MDSCs in cancer and LCMV infection. Acquisition of immune-suppressive activity by M-MDSCs in spleens was mediated by IFN-γ signaling. However, it was dispensable for suppressive activity of M-MDSCs in tumor tissues. Suppressive activity of M-MDSCs in tumors was retained due to the effect of IL-6 present at high concentrations in the tumor site. These results demonstrate disease- and population-specific mechanisms of MDSC accumulation and the need for targeting different pathways to achieve inactivation of these cells.

ATF6 promotes liver fibrogenesis by regulating macrophage-derived interleukin-1α expression.

Macrophages contribute to liver fibrogenesis by the production of a large variety of cytokines. ATF6 is associated with the activation of macrophages. The present study aimed to investigate the role of ATF6 in the expression of macrophage-derived cytokines and liver fibrogenesis after acute liver injury. Following thioacetamide (TAA)-induced acute liver injury, the characteristics of the occurrence of liver fibrosis and the secretion of cytokines by macrophages were first described. Then, the role of various cytokines secreted by macrophages in activating hepatic stellate cells (HSCs) was tested in vitro. Finally, endoplasmic reticulum stress (ER-stress) signals in macrophages were detected following liver injury. siRNA was used to interfere with the expression of ATF6 in macrophages to verify the influence of ATF6 on cytokine expression and liver fibrogenesis after liver injury. A single intraperitoneal injection of TAA induced acute liver injury. The depletion of macrophages attenuated acute liver injury, while it inhibited liver fibrogenesis. During acute liver injury, macrophages secrete a variety of cytokines. Most of these cytokines promoted the activation of HSCs, but the effect of IL-1α was most significant. In the early stage of acute liver injury, ER-stress signals in macrophages were activated. Interference of ATF6 expression suppressed the secretion of cytokines by macrophages and attenuated liver fibrogenesis. Overall, in the early stage of acute liver injury, ATF6 signals promoted the expression of macrophage-derived cytokines to participate in liver fibrogenesis, and IL-1α exhibited the most significant role in promoting the activation of HSCs and liver fibrogenesis.

Reprogramming of microRNA expression via E2F1 downregulation promotes Salmonella infection both in infected and bystander cells.

Cells infected with pathogens can contribute to clearing infections by releasing signals that instruct neighbouring cells to mount a pro-inflammatory cytokine response, or by other mechanisms that reduce bystander cells' susceptibility to infection. Here, we show the opposite effect: epithelial cells infected with Salmonella Typhimurium secrete host factors that facilitate the infection of bystander cells. We find that the endoplasmic reticulum stress response is activated in both infected and bystander cells, and this leads to activation of JNK pathway, downregulation of transcription factor E2F1, and consequent reprogramming of microRNA expression in a time-dependent manner. These changes are not elicited by infection with other bacterial pathogens, such as Shigella flexneri or Listeria monocytogenes. Remarkably, the protein HMGB1 present in the secretome of Salmonella-infected cells is responsible for the activation of the IRE1 branch of the endoplasmic reticulum stress response in non-infected, neighbouring cells. Furthermore, E2F1 downregulation and the associated microRNA alterations promote Salmonella replication within infected cells and prime bystander cells for more efficient infection.