Deficiency of IRE1 and PERK signal pathways in systemic lupus erythematosus

Deletion of mesencephalic astrocyte-derived neurotrophic factor delays and damages the development of white pulp in spleen

Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an endoplasmic reticulum (ER) stress-induced protein, and it has been reported that ER stress and unfolded protein response (UPR) are closely related to the immune system. The spleen is an important immune organ and we have shown in our previous research that MANF is expressed in human spleen tissues. However, there have been limited studies about the effect of MANF on spleen development. In this study, we detected MANF expression in spleen tissues and found that MANF was expressed in the red pulp and marginal zone. Additionally, MANF was localized in the CD68+ and CD138+ cells of adult rat spleen tissues, but not in the CD3+ cells. We performed immunohistochemical staining to detect MANF expression in the spleen tissues of rats that were different ages, and we found that MANF+ cells were localized together in the spleen tissues of rats that were 1-4 weeks old. MANF was also expressed in CD68+ cells in the spleen tissues of rats and mice. Furthermore, we found that MANF deficiency inhibited white pulp development in MANF knockout mice, thus indicating that MANF played an important role in the white pulp development of rodent spleen tissues.

Loss of function of XBP1 splicing activity of IRE1α favors B cell tolerance breakdown

Anti-nuclear antibodies are the hallmark of autoimmune diseases such as systemic lupus erythematosus (SLE) and scleroderma. However, the molecular mechanisms of B cell tolerance breakdown in these pathological contexts are poorly known. The study of rare familial forms of autoimmune diseases could therefore help to better describe common biological mechanisms leading to B cell tolerance breakdown. By Whole-Exome Sequencing, we identified a new heterozygous mutation (p.R594C) in ERN1 gene, encoding IRE1α (Inositol-Requiring Enzyme 1α), in a multiplex family with several members presenting autoantibody-mediated autoimmunity. Using human cell lines and a knock-in (KI) transgenic mouse model, we showed that this mutation led to a profound defect of IRE1α ribonuclease activity on X-Box Binding Protein 1 (XBP1) splicing. The KI mice developed a broad panel of autoantibodies, however in a subclinical manner. These results suggest that a decrease of spliced form of XBP1 (XBP1s) production could contribute to B cell tolerance breakdown and give new insights into the function of IRE1α which are important to consider for the development of IRE1α targeting strategies.

Endoplasmic reticulum stress in T cell-mediated diseases

T cells synthesize a large number of proteins during their development, activation, and differentiation. The build-up of misfolded and unfolded proteins in the endoplasmic reticulum, however, causes endoplasmic reticulum (ER) stress. Thus, T cells can maintain ER homeostasis via endoplasmic reticulum-associated degradation, unfolded protein response, and autophagy. In T cell-mediated diseases, such as rheumatoid arthritis, systemic lupus erythematosus, Sjogren's syndrome, type 1 diabetes and vitiligo, ER stress caused by changes in the internal microenvironment can cause disease progression by affecting T cell homeostasis. This review discusses ER stress in T cell formation, activation, differentiation, and T cell-mediated illnesses, and may offer new perspectives on the involvement of T cells in autoimmune disorders and cancer.

Endoplasmic Reticulum Stress in Systemic Lupus Erythematosus and Lupus Nephritis: Potential Therapeutic Target

Systemic lupus erythematosus (SLE) is a complex autoimmune disease. Approximately one-third to two-thirds of the patients with SLE progress to lupus nephritis (LN). The pathogenesis of SLE and LN has not yet been fully elucidated, and effective treatment for both conditions is lacking. The endoplasmic reticulum (ER) is the largest intracellular organelle and is a site of protein synthesis, lipid metabolism, and calcium storage. Under stress, the function of ER is disrupted, and the accumulation of unfolded or misfolded proteins occurs in ER, resulting in an ER stress (ERS) response. ERS is involved in the dysfunction of B cells, macrophages, T cells, dendritic cells, neutrophils, and other immune cells, causing immune system disorders, such as SLE. In addition, ERS is also involved in renal resident cell injury and contributes to the progression of LN. The molecular chaperones, autophagy, and proteasome degradation pathways inhibit ERS and restore ER homeostasis to improve the dysfunction of immune cells and renal resident cell injury. This may be a therapeutic strategy for SLE and LN. In this review, we summarize advances in this field.

Increased serum concentrations of Mesencephalic astrocyte-derived neurotrophic factor in patients and rats with ischemic stroke

OBJECTIVES

Although Mesencephalic astrocyte-derived neurotrophic factor (MANF) shows protection in multiple cells, the role of circulating MANF in patients with acute ischemic stroke (AIS) and transient ischemic attack (TIA) remains unclear. Here, we aimed to explore the value of circulating MANF levels in cerebral ischemic events.

MATERIALS AND METHODS

Using a rat cerebral ischemic model, MANF expression in ischemic brains and serum was detected. 50 AIS patients, 56 TIA patients and 48 controls were enrolled, and MANF mRNA, inflammatory cytokines and MANF concentrations in serum and different blood cell types were detected. The National Institutes of Health Stroke Scale (NIHSS) score and Alberta Stroke Program Early CT Score (ASPECTS) were used to evaluate stroke severity. Cerebrovascular recurrence within 90 d was documented during TIA follow-up.

RESULTS

MANF expression increased at 2h, peaking at 24h and decreased to baseline at 7d in rat ischemic brains and serum. Serum MANF concentrations increased at 24h and 7d in AIS patients compared to controls and were correlated with NIHSS score, ASPECTS and inflammatory cytokines. MANF protein was present in blood cells, while MANF mRNA levels did not differ between AIS patients and controls. MANF levels revealed a good value to diagnose TIA with area under the curve (AUC) of 0.949 (95% CI: 0.9093-0.9892). MANF levels were lower in TIA patients with recurrence compared to non-recurrence patients. The AUC for MANF to predict a re-event was 0.80 (95% CI: 0.6746-0.9282).

CONCLUSIONS

Serum MANF levels correlate with neuroprotection, stroke severity, inflammation, and TIA recurrence.

Endoplasmic Reticulum Stress, Oxidative Stress, and Rheumatic Diseases

BACKGROUND

The endoplasmic reticulum (ER) is a multi-functional organelle responsible for cellular homeostasis, protein synthesis, folding and secretion. It has been increasingly recognized that the loss of ER homeostasis plays a central role in the development of autoimmune inflammatory disorders, such as rheumatic diseases. Purpose/Main contents: Here, we review current knowledge of the contribution of ER stress to the pathogenesis of rheumatic diseases, with a focus on rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). We also review the interplay between protein folding and formation of reactive oxygen species (ROS), where ER stress induces oxidative stress (OS), which further aggravates the accumulation of misfolded proteins and oxidation, in a vicious cycle. Intervention studies targeting ER stress and oxidative stress in the context of rheumatic diseases are also reviewed.

CONCLUSIONS

Loss of ER homeostasis is a significant factor in the pathogeneses of RA and SLE. Targeting ER stress, unfolded protein response (UPR) pathways and oxidative stress in these diseases both in vitro and in animal models have shown promising results and deserve further investigation.

JM, Zhang K, Fang D. Inositol-Requiring Enzyme 1α-Mediated Synthesis of Monounsaturated Fatty Acids as a Driver of B Cell Differentiation and Lupus-like Autoimmune Disease

OBJECTIVE

To explore the molecular mechanisms underlying dysregulation of lipid metabolism in the pathogenesis of systemic lupus erythematosus (SLE).

METHODS

B cells in peripheral blood from patients with SLE and healthy controls were stained with BODIPY dye for detection of lipids. Mice with targeted knockout of genes for B cell-specific inositol-requiring enzyme 1α (IRE-1α) and stearoyl-coenzyme A desaturase 1 (SCD-1) were used for studying the influence of the IRE-1α/SCD-1/SCD-2 pathway on B cell differentiation and autoantibody production. The preclinical efficacy of IRE-1α suppression as a treatment for lupus was tested in MRL.Faslpr mice.

RESULTS

In cultures with mouse IRE-1α-null B cells, supplementation with monounsaturated fatty acids largely rescued differentiation of plasma cells from B cells, indicating that the compromised capacity of B cell differentiation in the absence of IRE-1α may be attributable to a defect in monounsaturated fatty acid synthesis. Moreover, activation with IRE-1α/X-box binding protein 1 (XBP-1) was required to facilitate B cell expression of SCD-1 and SCD-2, which are 2 critical enzymes that catalyze monounsaturated fatty acid synthesis. Mice with targeted Scd1 gene deletion displayed a phenotype that was similar to that of IRE-1α-deficient mice, with diminished B cell differentiation into plasma cells. Importantly, in B cells from patients with lupus, both IRE-1α expression and Xbp1 messenger RNA splicing were significantly increased, and this was positively correlated with the expression of both Scd1 and Scd2 as well as with the amount of B cell lipid deposition. In MRL.Faslpr mice, both genetic and pharmacologic suppression of IRE-1α protected against the pathologic development and progression of lupus-like autoimmune disease.

CONCLUSION

The results of this study reveal a molecular link in the dysregulation of lipid metabolism in the pathogenesis of lupus, demonstrating that the IRE-1α/XBP-1 pathway controls plasma cell differentiation through SCD-1/SCD-2-mediated monounsaturated fatty acid synthesis. These findings provide a rationale for targeting IRE-1α and monounsaturated fatty acid synthesis in the treatment of patients with SLE.

Endoplasmic reticulum stress sensor IRE1α propels neutrophil hyperactivity in lupus

Neutrophils amplify inflammation in lupus through the release of neutrophil extracellular traps (NETs). The endoplasmic reticulum stress sensor inositol-requiring enzyme 1 α (IRE1α) has been implicated as a perpetuator of inflammation in various chronic diseases; however, IRE1α has been little studied in relation to neutrophil function or lupus pathogenesis. Here, we found that neutrophils activated by lupus-derived immune complexes demonstrated markedly increased IRE1α ribonuclease activity. Importantly, in neutrophils isolated from patients with lupus, we also detected heightened IRE1α activity that was correlated with global disease activity. Immune complex-stimulated neutrophils produced both mitochondrial ROS (mitoROS) and the activated form of caspase-2 in an IRE1α-dependent fashion, whereas inhibition of IRE1α mitigated immune complex-mediated NETosis (in both human neutrophils and a mouse model of lupus). Administration of an IRE1α inhibitor to lupus-prone MRL/lpr mice over 8 weeks reduced mitoROS levels in peripheral blood neutrophils, while also restraining plasma cell expansion and autoantibody formation. In summary, these data identify a role for IRE1α in the hyperactivity of lupus neutrophils and show that this pathway is upstream of mitochondrial dysfunction, mitoROS formation, and NETosis. We believe that inhibition of the IRE1α pathway is a novel strategy for neutralizing NETosis in lupus, and potentially other inflammatory conditions.

The aftermath of the interplay between the endoplasmic reticulum stress response and redox signaling

The endoplasmic reticulum (ER) is an essential organelle of eukaryotic cells. Its main functions include protein synthesis, proper protein folding, protein modification, and the transportation of synthesized proteins. Any perturbations in ER function, such as increased demand for protein folding or the accumulation of unfolded or misfolded proteins in the ER lumen, lead to a stress response called the unfolded protein response (UPR). The primary aim of the UPR is to restore cellular homeostasis; however, it triggers apoptotic signaling during prolonged stress. The core mechanisms of the ER stress response, the failure to respond to cellular stress, and the final fate of the cell are not yet clear. Here, we discuss cellular fate during ER stress, cross talk between the ER and mitochondria and its significance, and conditions that can trigger ER stress response failure. We also describe how the redox environment affects the ER stress response, and vice versa, and the aftermath of the ER stress response, integrating a discussion on redox imbalance-induced ER stress response failure progressing to cell death and dynamic pathophysiological changes.

The endoplasmic reticulum (ER), a cellular organelle responsible for protein folding, is sensitive to chemical imbalances that can induce stress, leading to cell death and disease. Researchers in South Korea, led by Han-Jung Chae from Jeonbuk National University in Jeonju and Hyung-Ryong Kim from Dankook University in Cheonan, review how the ER counters changes in its environment that spur protein folding defects by activating a series of signaling pathways, known collectively as the unfolded protein response. Redox imbalance, may fail adaptive ER stress response that can damage the ER and surrounding mitochondria by modifying cysteine residues. The interaction between the two stress systems, ER stress and oxidative stress, has profound negative impacts on normal physiology. Targeting one or both of these stress mechanisms may therefore be an effective means of treating disease.

Gene expression signatures of target tissues in type 1 diabetes, lupus erythematosus, multiple sclerosis, and rheumatoid arthritis

Autoimmune diseases are typically studied with a focus on the immune system, and less attention is paid to responses of target tissues exposed to the immune assault. We presently evaluated, based on available RNA sequencing data, whether inflammation induces similar molecular signatures at the target tissues in type 1 diabetes, systemic lupus erythematosus, multiple sclerosis, and rheumatoid arthritis. We identified confluent signatures, many related to interferon signaling, indicating pathways that may be targeted for therapy, and observed a high (>80%) expression of candidate genes for the different diseases at the target tissue level. These observations suggest that future research on autoimmune diseases should focus on both the immune system and the target tissues, and on their dialog. Discovering similar disease-specific signatures may allow the identification of key pathways that could be targeted for therapy, including the repurposing of drugs already in clinical use for other diseases.

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.

Mesencephalic Astrocyte-Derived Neurotrophic Factor Inhibits Liver Cancer Through Small Ubiquitin-Related Modifier (SUMO)ylation-Related Suppression of NF-κB/Snail Signaling Pathway and Epithelial-Mesenchymal Transition

BACKGROUND AND AIMS

Endoplasmic reticulum (ER) stress is associated with liver inflammation and hepatocellular carcinoma (HCC). However, how ER stress links inflammation and HCC remains obscure. Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an ER stress-inducible secretion protein that inhibits inflammation by interacting with the key subunit of nuclear factor kappa light chain enhancer of activated B cells (NF-κB) p65. We hypothesized that MANF may play a key role in linking ER stress and inflammation in HCC.

APPROACH AND RESULTS

Here, we found that MANF mRNA and protein levels were lower in HCC tissues versus adjacent noncancer tissues. Patients with high levels of MANF had better relapse-free survival and overall survival rates than those with low levels. MANF levels were also associated with the status of liver cirrhosis, advanced tumor-node-metastasis (TNM) stage, and tumor size. In vitro experiments revealed that MANF suppressed the migration and invasion of hepatoma cells. Hepatocyte-specific deletion of MANF accelerated N-nitrosodiethylamine (DEN)-induced HCC by up-regulating Snail1+2 levels and promoting epithelial-mesenchymal transition (EMT). MANF appeared in the nuclei and was colocalized with p65 in HCC tissues and in tumor necrosis factor alpha (TNF-α)-treated hepatoma cells. The interaction of p65 and MANF was also confirmed by coimmunoprecipitation experiments. Consistently, knockdown of MANF up-regulated NF-κB downstream target genes TNF-α, interleukin (IL)-6 and IL-1α expression in vitro and in vivo. Finally, small ubiquitin-related modifier 1 (SUMO1) promoted MANF nuclear translocation and enhanced the interaction of MANF and p65. Mutation of p65 motifs for SUMOylation abolished the interaction of p65 and MANF.

CONCLUSIONS

MANF plays an important role in linking ER stress and liver inflammation by inhibiting the NF-κB/Snail signal pathway in EMT and HCC progression. Therefore, MANF may be a cancer suppressor and a potential therapeutic target for HCC.

Type I interferons and endoplasmic reticulum stress in health and disease

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

Increased Serum Levels of Mesencephalic Astrocyte-Derived Neurotrophic Factor in Subjects With Parkinson's Disease

Background

Mesencephalic astrocyte-derived neurotrophic factor (MANF) and cerebral dopamine neurotrophic factor (CDNF) promote the survival of midbrain dopamine neurons in animal models of Parkinson’s disease (PD). However, little is known about endogenous concentrations of MANF and CDNF in human PD patients, and their relation to PD pathogenesis. Our main objective was to study whether circulating concentrations of MANF and CDNF differ between PD patients and controls, and if they correlate with clinical parameters. Levels of circulating CDNF were studied for the first time.

Methods

MANF and CDNF levels were measured from serum samples of 34 PD patients and 35 controls using validated in-lab-designed enzyme-linked immunosorbent assay (ELISAs). MANF and CDNF mRNA levels in whole blood samples of 60 PD patients and 30 controls were measured by quantitative real time polymerase chain reaction (qRT-PCR). MANF concentrations in different blood cell types were measured by ELISA.

Results

Circulating MANF concentrations were significantly higher in PD patients compared to controls (P < 0.001) and were positively correlated with Beck Depression Inventory (BDI) depression rating. MANF protein was present in blood cells, however, MANF mRNA levels in the blood did not differ between PD patients and controls (P = 0.44). The mean concentration of serum CDNF was 33 pg/ml in the controls. CDNF levels were not altered in PD patients (P = 0.25).

Conclusion

MANF but not CDNF level was increased in the blood of PD patients. It would be interesting to examine the blood level of MANF from early stage PD patients in future studies to test whether MANF can be used as a clinical marker of PD.

Stressed: The Unfolded Protein Response in T Cell Development, Activation, and Function

The unfolded protein response (UPR) is a highly conserved pathway that allows cells to respond to stress in the endoplasmic reticulum caused by an accumulation of misfolded and unfolded protein. This is of great importance to secretory cells because, in order for proteins to traffic from the endoplasmic reticulum (ER), they need to be folded appropriately. While a wealth of literature has implicated UPR in immune responses, less attention has been given to the role of UPR in T cell development and function. This review discusses the importance of UPR in T cell development, homeostasis, activation, and effector functions. We also speculate about how UPR may be manipulated in T cells to ameliorate pathologies.

Sodium 4-phenylbutyrate treatment protects against renal injury in NZBWF1 mice

Systemic lupus erythematosus (SLE) is an autoimmune disease predominantly affecting women and often leading to lupus nephritis and kidney damage. Endoplasmic reticulum (ER) stress has been implicated in several forms of kidney disease, but whether ER stress contributes to renal injury in SLE is unknown. To investigate this, a small molecule chaperone, sodium 4-phenylbutyrate (4-PBA), was administered to the New Zealand Black x New Zealand White F₁ hybrid (NZBWF1) mouse model of SLE. In a prevention study, treatment with 4-PBA from 20 weeks of age (prior to the development of renal injury) delayed the onset of albuminuria and significantly reduced additional indices of renal injury compared with vehicle-treated NZBWF1 mice at 36 weeks of age, including collagen deposition, tubular casts, renal cell apoptosis, and blood urea nitrogen (BUN) concentration. To test whether ER stress contributes to the progression of renal injury once albuminuria has developed, mice were monitored for the onset of albuminuria (3+ or ≥300 mg/dl by dipstick measurement of 24-h urine sample) and once established, were either killed (onset group), or underwent 4-PBA or vehicle treatment for 4 weeks. Treatment with 4-PBA blocked the worsening of glomerular injury, reduced the number of dilated or cast-filled tubules, and reduced the number of apoptotic cells compared with vehicle-treated mice. BUN and left ventricle to bodyweight ratio (LV:BW) were also reduced by 4-PBA treatment. Renal expression of the endogenous chaperones, protein disulphide isomerase (PDI), and 78 kDa glucose-regulated protein (GRP78, also known as binding Ig protein (BiP)), were increased in 4-PBA-treated mice. Together, these results suggest a therapeutic potential for agents like 4-PBA in combating renal injury in SLE.

Crosstalk of oxidative damage, apoptosis, and autophagy under endoplasmic reticulum (ER) stress involved in thifluzamide-induced liver damage in zebrafish (Danio rerio)

Although the hepatotoxicity of thifluzamide in zebrafish has been characterized, its toxic mechanisms have not been fully explored. The present study demonstrated that thifluzamide damaged the zebrafish liver and endoplasmic reticulum (ER). In addition, thifluzamide significantly changed the expression of genes encoding antioxidant proteins and increased the malondialdehyde (MDA) content, leading to oxidative damage in zebrafish liver. Additionally, the autophagic ultrastructure was observed by transmission electron microscopy (TEM), and LC3-I/LC3-II conversion was obviously upregulated under western blotting (WB) measurements, verifying that autophagy was induced by thifluzamide. Moreover, the activities of Caspase-3 and Caspase-9 were obviously decreased, indicating that apoptosis was inhibited in adult zebrafish exposed to a higher concentration of thifluzamide. In summary, oxidative damage and autophagy but not apoptosis under ER injury might lead to the hepatotoxicity of thifluzamide in zebrafish. Our findings provide a new mechanistic insight into the toxicity of thifluzamide in zebrafish.

Trophic Factors in Inflammation and Regeneration: The Role of MANF and CDNF

Regeneration is an important process in multicellular organisms, responsible for homeostatic renewal and repair of different organs after injury. Immune cell activation is observed at early stages of the regenerative response and its regulation is essential for regenerative success. Thus, immune regulators play central roles in optimizing regenerative responses. Neurotrophic factors (NTFs) are secreted molecules, defined by their ability to support neuronal cell types. However, emerging evidence suggests that they can also play important functions in the regulation of immune cell activation and tissue repair. Here we discuss the literature supporting a role of NTFs in the regulation of inflammation and regeneration. We will focus, in particular, in the emerging roles of mesencephalic astrocyte-derived neurotrophic factor (MANF) and cerebral dopamine neurotrophic factor (CDNF) in the regulation of immune cell function and in the central role that immune modulation plays in their biological activity in vivo. Finally, we will discuss the potential use of these factors to optimize regenerative success in vivo, both within and beyond the nervous system.

Activator protein‑1 is a novel regulator of mesencephalic astrocyte‑derived neurotrophic factor transcription

Mesencephalic astrocyte‑derived neurotrophic factor (MANF) is an endoplasmic reticulum stress‑inducible protein, which has been suggested to be upregulated in inflammatory diseases; however, how inflammation regulates its transcription remains unclear. Activator protein‑1 (AP‑1), which is a transcription factor complex composed of c‑Fos and c‑Jun, is activated during the inflammatory process. The present study aimed to investigate whether the AP‑1 complex regulates MANF transcription. The results of a luciferase reporter assay revealed that one of three putative AP‑1 binding sites in the MANF promoter region is essential for enhancement of MANF transcription. Mechanistically, AP‑1 was revealed to directly bind to the promoter region of the MANF gene by chromatin immunoprecipitation assay. Furthermore, MANF was strongly expressed in the liver tissues of patients with hepatitis B virus (HBV) infection, compared with in normal liver tissues from patients with hepatic hemangioma. Furthermore, c‑Fos and c‑Jun were also upregulated in the nuclei of hepatocytes from patients with HBV infection. In mice treated with carbon tetrachloride, the expression patterns of MANF, c‑Fos and c‑Jun were similar to those in patients with HBV. These results suggested that the AP‑1 complex may be a novel regulator of MANF transcription, which may be involved in liver inflammation and fibrosis.

Interferon-α Triggers Autoimmune Thyroid Diseases via Lysosomal-Dependent Degradation of Thyroglobulin

CONTEXT

Autoimmune thyroid diseases (AITDs) arise from complex interactions among genetic, epigenetic, and environmental factors. Thyroglobulin (TG) is a major susceptibility gene for both Graves disease and Hashimoto thyroiditis. Interferon-α (IFNα), a cytokine secreted during viral infections, has emerged as a key trigger of AITD. We have shown that IFNα upregulates TG transcription; however, how the upregulation of TG transcription by IFNα triggers AITD is still unknown.

OBJECTIVE

To evaluate how IFNα triggers AITD by testing its effects on TG processing.

DESIGN

We exposed human thyroid cells to IFNα and evaluated its effects on TG expression and processing.

RESULTS

Human thyroid cells exposed to INFα had increased levels of TG mRNA but reduced TG protein levels, indicating TG protein degradation. IFNα induced endoplasmic reticulum stress, but surprisingly, neither the use of chemical chaperones nor proteasome inhibitor prevented IFNα-induced TG degradation. IFNα also increased LysoTracker staining and autophagy flux measured by net light chain 3 (LC3)-II and p62 fluxes. In addition, expression of autophagy markers LC3 and autophagy-related gene 5 was higher in thyroid tissues from patients with AITD. Finally, blocking lysosomal degradation prevented IFNα-induced degradation of TG.

CONCLUSION

We have shown in this study IFNα-induced lysosomal-dependent degradation of TG in human thyroid cells. Our findings suggest that during viral infections, local thyroidal IFNα production can lead to lysosomal TG degradation, releasing pathogenic TG peptides that can trigger AITD.

Endoplasmic reticulum stress in autoimmune diseases: Can altered protein quality control and/or unfolded protein response contribute to autoimmunity? A critical review on Sjögren's syndrome

For many years, researchers in the field of autoimmunity have focused on the role of the immune components in the etiopathogenesis of autoimmune diseases. However, some studies have demonstrated the importance of target tissues in their pathogenesis and the breach of immune tolerance. The immune system as well as target tissue cells (plasmatic, β-pancreatic, fibroblast-like synoviocytes, thyroid follicular and epithelial cells of the lachrymal glands, salivary glands, intestine, bronchioles and renal tubules) share the characteristic of secretory cells with an extended endoplasmic reticulum (ER). The function of these cells depends considerably on a normal ER function and calcium homeostasis, so they can produce and secrete their main components, which include glycoproteins involved in antigenic presentation such as major histocompatibility complex (MHC) class I and II. All these proteins are synthesized and modified in the ER, and for this reason disturbances in the normal functions of this organelle such as protein folding, protein quality control, calcium homeostasis and redox balance, promote accumulation of unfolded or misfolded proteins, a condition known as ER stress. Autoimmune diseases are characterized by inflammation, which has been associated with an ER stress condition. Interestingly, patients with these diseases contain circulating auto-antibodies against chaperone proteins (such as Calnexin and GRP94), thus affecting the folding and assembly of MHC class I and II glycoproteins and their loading with peptide. The main purpose of this article is to review the involvement of the protein quality control and unfolded protein response (UPR) in the ER protein homeostasis (proteostasis) and their alterations in autoimmune diseases. In addition, we describe the interaction between ER stress and inflammation and evidences are shown of how autoimmune diseases are associated with an ER stress condition, with a special emphasis on the second most prevalent autoimmune rheumatic disease, Sjögren's syndrome.

IRE1α Implications in Endoplasmic Reticulum Stress-Mediated Development and Pathogenesis of Autoimmune Diseases

Inositol-requiring transmembrane kinase/endoribonuclease 1α (IRE1α) is the most prominent and evolutionarily conserved endoplasmic reticulum (ER) membrane protein. This transduces the signal of misfolded protein accumulation in the ER, named as ER stress, to the nucleus as “unfolded protein response (UPR).” The ER stress-mediated IRE1α signaling pathway arbitrates the yin and yang of cell life. IRE1α has been implicated in several physiological as well as pathological conditions, including immune disorders. Autoimmune diseases are caused by abnormal immune responses that develop due to genetic mutations and several environmental factors, including infections and chemicals. These factors dysregulate the cell immune reactions, such as cytokine secretion, antigen presentation, and autoantigen generation. However, the mechanisms involved, in which these factors induce the onset of autoimmune diseases, are remaining unknown. Considering that these environmental factors also induce the UPR, which is expected to have significant role in secretory cells and immune cells. The role of the major UPR molecule, IRE1α, in causing immune responses is well identified, but its role in inducing autoimmunity and the pathogenesis of autoimmune diseases has not been clearly elucidated. Hence, a better understanding of the role of IRE1α and its regulatory mechanisms in causing autoimmune diseases could help to identify and develop the appropriate therapeutic strategies. In this review, we mainly center the discussion on the molecular mechanisms of IRE1α in the pathophysiology of autoimmune diseases.

Regulation of Cytokine Production by the Unfolded Protein Response; Implications for Infection and Autoimmunity

Protein folding in the endoplasmic reticulum (ER) is an essential cell function. To safeguard this process in the face of environmental threats and internal stressors, cells mount an evolutionarily conserved response known as the unfolded protein response (UPR). Invading pathogens induce cellular stress that impacts protein folding, thus the UPR is well situated to sense danger and contribute to immune responses. Cytokines (inflammatory cytokines and interferons) critically mediate host defense against pathogens, but when aberrantly produced, may also drive pathologic inflammation. The UPR influences cytokine production on multiple levels, from stimulation of pattern recognition receptors, to modulation of inflammatory signaling pathways, and the regulation of cytokine transcription factors. This review will focus on the mechanisms underlying cytokine regulation by the UPR, and the repercussions of this relationship for infection and autoimmune/autoinflammatory diseases. Interrogation of viral and bacterial infections has revealed increasing numbers of examples where pathogens induce or modulate the UPR and implicated UPR-modulated cytokines in host response. The flip side of this coin, the UPR/ER stress responses have been increasingly recognized in a variety of autoimmune and inflammatory diseases. Examples include monogenic disorders of ER function, diseases linked to misfolding protein (HLA-B27 and spondyloarthritis), diseases directly implicating UPR and autophagy genes (inflammatory bowel disease), and autoimmune diseases targeting highly secretory cells (e.g., diabetes). Given the burgeoning interest in pharmacologically targeting the UPR, greater discernment is needed regarding how the UPR regulates cytokine production during specific infections and autoimmune processes, and the relative place of this interaction in pathogenesis.

Role of endoplasmic reticulum stress in the protective effects of PPARβ/δ activation on endothelial dysfunction induced by plasma from patients with lupus

Background

We tested whether GW0742, a peroxisome proliferator-activated receptor beta/delta (PPARβ/δ) agonist, improves endothelial dysfunction induced by plasma from patients with systemic lupus erythematosus (SLE) involving the inhibition of endoplasmic reticulum (ER) stress.

Methods

A total of 12 non-pregnant women with lupus and 5 non-pregnant healthy women (controls) participated in the study. Cytokines and double-stranded DNA autoantibodies (anti-dsDNA) were tested in plasma samples. Endothelial cells, isolated from human umbilical cord veins (HUVECs), were used to measure nitric oxide (NO), intracellular reactive oxygen species (ROS) production, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity, and ER stress markers.

Results

Interferon-γ, interleukin-6, and interleukin-12 levels were significantly increased in plasma from patients with SLE with active nephritis (AN), as compared to both patients with SLE with inactive nephritis (IN) and the control group. The NO production stimulated by both the calcium ionophore A23187 and insulin was significantly reduced in HUVECs incubated with plasma from patients with AN-SLE as compared with the control group. Plasma from patients with IN-SLE did not modify A23187-stimulated NO production. Increased ROS production and NADPH oxidase activity were found in HUVECs incubated with plasma from patients with AN-SLE, which were suppressed by the ER stress inhibitor 4-PBA and the NADPH oxidase inhibitors, apocynin and VAS2870. GW0742 incubation restored the impaired NO production, the increased ROS levels, and the increased ER stress markers induced by plasma from patients with AN-SLE. These protective effects were abolished by the PPARβ/δ antagonist GSK0660 and by silencing PPARβ/δ.

Conclusions

PPARβ/δ activation may be an important target to control endothelial dysfunction in patients with SLE.

Novel risk genes for systemic lupus erythematosus predicted by random forest classification

Genome-wide association studies have identified risk loci for SLE, but a large proportion of the genetic contribution to SLE still remains unexplained. To detect novel risk genes, and to predict an individual's SLE risk we designed a random forest classifier using SNP genotype data generated on the "Immunochip" from 1,160 patients with SLE and 2,711 controls. Using gene importance scores defined by the random forest classifier, we identified 15 potential novel risk genes for SLE. Of them 12 are associated with other autoimmune diseases than SLE, whereas three genes (ZNF804A, CDK1, and MANF) have not previously been associated with autoimmunity. Random forest classification also allowed prediction of patients at risk for lupus nephritis with an area under the curve of 0.94. By allele-specific gene expression analysis we detected cis-regulatory SNPs that affect the expression levels of six of the top 40 genes designed by the random forest analysis, indicating a regulatory role for the identified risk variants. The 40 top genes from the prediction were overrepresented for differential expression in B and T cells according to RNA-sequencing of samples from five healthy donors, with more frequent over-expression in B cells compared to T cells.

Causes and consequences of endoplasmic reticulum stress in rheumatic disease

Rheumatic diseases represent a heterogeneous group of inflammatory conditions, many of which involve chronic activation of both innate and adaptive immune responses by multiple genetic and environmental factors. These immune responses involve the secretion of excessive amounts of cytokines and other signalling mediators by activated immune cells. The endoplasmic reticulum (ER) is the cellular organelle that directs the folding, processing and trafficking of membrane-bound and secreted proteins, including many key components of the immune response. Maintaining homeostasis in the ER is critical to cell function and survival. Consequently, elaborate mechanisms have evolved to sense and respond to ER stress through three main signalling pathways that together comprise the unfolded protein response (UPR). Activation of the UPR can rapidly resolve the accumulation of misfolded proteins, direct permanent changes in the size and function of cells during differentiation, and critically influence the immune response and inflammation. Recognition of the importance of ER stress and UPR signalling pathways in normal and dysregulated immune responses has greatly increased in the past few years. This Review discusses several settings in which ER stress contributes to the pathogenesis of rheumatic diseases and considers some of the therapeutic opportunities that these discoveries provide.

Increased circulating concentrations of mesencephalic astrocyte-derived neurotrophic factor in children with type 1 diabetes

Mesencephalic astrocyte-derived neurotrophic factor (MANF) was recently shown to be essential for the survival and proliferation of pancreatic β-cells in mice, where deletion of MANF resulted in diabetes. The current study aimed at determining whether the concentration of circulating MANF is associated with the clinical manifestation of human type 1 diabetes (T1D). MANF expression in T1D or MANF levels in serum have not been previously studied. We developed an enzyme-linked immunosorbent assay (ELISA) for MANF and measured serum MANF concentrations from 186 newly diagnosed children and adolescents and 20 adults with longer-term T1D alongside with age-matched controls. In healthy controls the mean serum MANF concentration was 7.0 ng/ml. High MANF concentrations were found in children 1–9 years of age close to the diagnosis of T1D. The increased MANF concentrations were not associated with diabetes-predictive autoantibodies and autoantibodies against MANF were extremely rare. Patients with conspicuously high MANF serum concentrations had lower C-peptide levels compared to patients with moderate MANF concentrations. Our data indicate that increased MANF concentrations in serum are associated with the clinical manifestation of T1D in children, but the exact mechanism behind the increase remains elusive.

Endoplasmic Reticulum Stress Interacts With Inflammation in Human Diseases

The endoplasmic reticulum (ER) is a critical organelle for normal cell function and homeostasis. Disturbance in the protein folding process in the ER, termed ER stress, leads to the activation of unfolded protein response (UPR) that encompasses a complex network of intracellular signaling pathways. The UPR can either restore ER homeostasis or activate pro-apoptotic pathways depending on the type of insults, intensity and duration of the stress, and cell types. ER stress and the UPR have recently been linked to inflammation in a variety of human pathologies including autoimmune, infectious, neurodegenerative, and metabolic disorders. In the cell, ER stress and inflammatory signaling share extensive regulators and effectors in a broad spectrum of biological processes. In spite of different etiologies, the two signaling pathways have been shown to form a vicious cycle in exacerbating cellular dysfunction and causing apoptosis in many cells and tissues. However, the interaction between ER stress and inflammation in many of these diseases remains poorly understood. Further understanding of the biochemistry, cell biology, and physiology may enable the development of novel therapies that spontaneously target these pathogenic pathways.

A pathogenic role for ER stress-induced autophagy and ER chaperone GRP78/BiP in T lymphocyte systemic lupus erythematosus

Abnormal regulation of ER stress and apoptosis has been implicated in autoimmune disorders. Particularly, ER stress-induced autophagy and the role of GRP78, or BiP in T lymphocyte survival and death in SLE are poorly understood. This study investigated the pathogenic roles of ER stress-induced autophagy and GRP78/BiP in apoptosis of T lymphocytes. We compared spontaneous and induced autophagy and apoptosis of T lymphocytes in healthy donors and patients with SLE. The molecular mechanism of altered autophagy and apoptosis was investigated in T lymphocytes transfected with siRNA for beclin 1 and CHOP and T lymphocytes overexpressing GRP78. Decreased autophagy and increased apoptosis in response to TG-induced ER stress were observed in lupus T lymphocytes. GRP78 and ER stress-signaling molecules, such as PERK, p-eIF2α, IRE1, and ATF6 decreased, whereas CHOP levels increased in lupus T cells in response to TG. The levels antiapoptotic molecules, Bcl-2 and Bcl-XL decreased, whereas the proapoptotic molecules, Bax and caspase 6, increased in lupus T cells. The TG-induced ER stress altered autophagy and apoptosis, which in turn, led to abnormal T cell homeostasis with increased apoptotic T cell death. We hypothesize that aberrant autophagy of T lymphocytes as a result of ER stress and decreased GRP78 expression is involved in the pathogenesis of SLE and might serve as important therapeutic targets.