Immunoproteasome subunit LMP2 expression is deregulated in Sjogren's syndrome but not in other autoimmune disorders

Proteomics profiling of CD4 + T-cell-derived exosomes from patients with rheumatoid arthritis

OBJECTIVES

Our study profiled the CD4 + T-cell-derived exosomes from patients with rheumatoid arthritis (RA) using proteomics.

METHODS

Proteomic analysis of CD4 + T-cell-derived exosomes was performed by tandem mass tags (TMT) combined with LC-MS/MS. We validated the most significantly upregulated and downregulated proteins using ELISA and WB.

RESULTS

The proteomic results showed that there were 3 upregulated differentially expressed proteins and 31 downregulated differentially expressed proteins in the RA group. The results indicated that dihydropyrimidinase-related protein 3 (DPYSL3) was significantly upregulated in CD4 + T-cell-derived exosomes, whereas proteasome activator complex subunit 1 (PSME1) was significantly downregulated in the RA group. Bioinformatics analysis showed that proteins were enriched in "positive regulation of gene expression", "antigen processing and presentation", "acute-phase response" and "PI3K-AKT signaling" pathways. ELISA verified that compared to the control group, the RA group showed significant upregulation of DPYSL3, and downregulation of PSME1 in CD4 + T-cell-derived exosomes.

CONCLUSIONS

The proteomic analysis results of CD4 + T-cell-derived exosomes from patients with RA suggest that these differentially expressed proteins may be involved in RA pathogenesis. DPYSL3 and PSME1 may become useful biomarkers for RA.

Blood Immunoproteasome Activity Is Regulated by Sex, Age and in Chronic Inflammatory Diseases: A First Population-Based Study

Dysfunction of the immunoproteasome has been implicated in cardiovascular and pulmonary diseases. Its potential as a biomarker for predicting disease stages, however, has not been investigated so far and population-based analyses on the impact of sex and age are missing. We here analyzed the activity of all six catalytic sites of the proteasome in isolated peripheral blood mononuclear cells obtained from 873 study participants of the KORA FF4 study using activity-based probes. The activity of the immuno- and standard proteasome correlated clearly with elevated leukocyte counts of study participants. Unexpectedly, we observed a strong sex dimorphism for proteasome activity with significantly lower immunoproteasome activity in women. In aging, almost all catalytic activities of the proteasome were activated in aged women while maintained upon aging in men. We also noted distinct sex-related activation patterns of standard and immunoproteasome active sites in chronic inflammatory diseases such as diabetes, cardiovascular diseases, asthma, or chronic obstructive pulmonary disease as determined by multiple linear regression modeling. Our data thus provides a conceptual framework for future analysis of immunoproteasome function as a bio-marker for chronic inflammatory disease development and progression.

Role of Proteasomes in Inflammation

The ubiquitin–proteasome system (UPS) is involved in multiple cellular functions including the regulation of protein homeostasis, major histocompatibility (MHC) class I antigen processing, cell cycle proliferation and signaling. In humans, proteasome loss-of-function mutations result in autoinflammation dominated by a prominent type I interferon (IFN) gene signature. These genomic alterations typically cause the development of proteasome-associated autoinflammatory syndromes (PRAAS) by impairing proteasome activity and perturbing protein homeostasis. However, an abnormal increased proteasomal activity can also be found in other human inflammatory diseases. In this review, we cast a light on the different clinical aspects of proteasomal activity in human disease and summarize the currently studied therapeutic approaches.

Response to abatacept is associated with the inhibition of proteasome β1i expression in T cells of patients with rheumatoid arthritis

Objective

Abatacept is a biological disease-modifying antirheumatic drug (DMARD) used for the treatment of rheumatoid arthritis (RA) and modulates the costimulatory signal by cluster of differentiation (CD)28:CD80/CD86 interaction required for T cell activation. Since CD28-mediated signalling regulates many T cell functions including cytokine production of, for example, interferons (IFNs), it is of interest to clarify, whether response to abatacept has an effect on the IFN inducible immunoproteasome, as a central regulator of the immune response.

Methods

Effects of abatacept on the proteasome were investigated in 39 patients with RA over a period of 24 weeks. Using real-time PCR, transcript levels of constitutive and corresponding immunoproteasome catalytic subunits were investigated at baseline (T0), week 16 (T16) and week 24 (T24) in sorted blood cells. Proteasomal activity and induction of apoptosis after proteasome inhibition were also evaluated.

Results

Abatacept achieved remission or low disease activity in 55% of patients at T16 and in 70% of patients at T24. By two-way analysis of variance (ANOVA), a significant reduction of proteasome immunosubunit β1i was shown only in CD4+ and CD8+ T cells of sustained responders at both T16 and T24. One-way ANOVA analysis for each response group confirmed the results and showed a significant reduction at T24 in CD4+ and CD8+ T cells of the same group. Abatacept did not influence chymotrypsin-like activity of proteasome and had no effect on induction of apoptosis under exposure to a proteasome inhibitor in vitro.

Conclusion

The reduction of proteasome immunosubunit β1i in T cells of patients with RA with sustained response to abatacept suggests association of the immunoproteasome of T cells with RA disease activity.

Shared and Unique Patterns of DNA Methylation in Systemic Lupus Erythematosus and Primary Sjögren's Syndrome

Objectives: To perform a cross-comparative analysis of DNA methylation in patients with systemic lupus erythematosus (SLE), patients with primary Sjögren's syndrome (pSS), and healthy controls addressing the question of epigenetic sharing and aiming to detect disease-specific alterations.

Methods: DNA extracted from peripheral blood from 347 cases with SLE, 100 cases with pSS, and 400 healthy controls were analyzed on the Human Methylation 450k array, targeting 485,000 CpG sites across the genome. A linear regression model including age, sex, and blood cell type distribution as covariates was fitted, and association p-values were Bonferroni corrected. A random forest machine learning classifier was designed for prediction of disease status based on DNA methylation data.

Results: We established a combined set of 4,945 shared differentially methylated CpG sites (DMCs) in SLE and pSS compared to controls. In pSS, hypomethylation at type I interferon induced genes was mainly driven by patients who were positive for Ro/SSA and/or La/SSB autoantibodies. Analysis of differential methylation between SLE and pSS identified 2,244 DMCs with a majority of sites showing decreased methylation in SLE compared to pSS. The random forest classifier demonstrated good performance in discerning between disease status with an area under the curve (AUC) between 0.83 and 0.96.

Conclusions: The majority of differential DNA methylation is shared between SLE and pSS, however, important quantitative differences exist. Our data highlight neutrophil dysregulation as a shared mechanism, emphasizing the role of neutrophils in the pathogenesis of systemic autoimmune diseases. The current study provides evidence for genes and molecular pathways driving common and disease-specific pathogenic mechanisms.

The ubiquitin proteasome system as a potential therapeutic target for systemic sclerosis

The present review aims to summarize available knowledge on the role of the ubiquitin-proteasome system (UPS) in the pathogenesis of scleroderma and scleroderma-related disease mechanisms. This will provide the reader with a more mechanistic understanding of disease pathogenesis and help to identify putative novel targets within the UPS for potential therapeutic intervention. Because of the heterogenous manifestations of scleroderma, we will primarily focus on conserved mechanisms that are involved in the development of lung scleroderma phenotypes.

Hepatic expression profiles in retroviral infection: relevance to drug hypersensitivity risk

HIV‐infected patients show a markedly increased risk of delayed hypersensitivity (HS) reactions to potentiated sulfonamide antibiotics (trimethoprim/sulfamethoxazole or TMP/SMX). Some studies have suggested altered SMX biotransformation in HIV infection, but hepatic biotransformation pathways have not been evaluated directly. Systemic lupus erythematosus (SLE) is another chronic inflammatory disease with a higher incidence of sulfonamide HS, but it is unclear whether retroviral infection and SLE share risk factors for drug HS. We hypothesized that retroviral infection would lead to dysregulation of hepatic pathways of SMX biotransformation, as well as pathway alterations in common with SLE that could contribute to drug HS risk. We characterized hepatic expression profiles and enzymatic activities in an SIV‐infected macaque model of retroviral infection, and found no evidence for dysregulation of sulfonamide drug biotransformation pathways. Specifically, NAT1,NAT2,CYP2C8,CYP2C9,CYB5R3,MARC1/2, and glutathione‐related genes (GCLC,GCLM,GSS,GSTM1, and GSTP1) were not differentially expressed in drug naïve SIVmac239‐infected male macaques compared to age‐matched controls, and activities for SMX N‐acetylation and SMX hydroxylamine reduction were not different. However, multiple genes that are reportedly over‐expressed in SLE patients were also up‐regulated in retroviral infection, to include enhanced immunoproteasomal processing and presentation of antigens as well as up‐regulation of gene clusters that may be permissive to autoimmunity. These findings support the hypothesis that pathways downstream from drug biotransformation may be primarily important in drug HS risk in HIV infection.

Knockout of immunoproteasome subunit β2i ameliorates cardiac fibrosis and inflammation in DOCA/Salt hypertensive mice

The immunoproteasome is a multicatalytic protease complex in all eukaryotic cells, which plays a key role in regulating essential cellular processes. However, the role of immunoproteasome subunit β2i in regulation of cardiac fibrosis and inflammation in deoxycorticosterone-acetate (DOCA)/salt mice remains unknown. Wild-type (WT) and β2i knockout (KO) mice were subjected to uninephrectomy and DOCA/salt treatment for 21 days. Blood pressure was measured by the tail-cuff system. Cardiac function and remodeling were examined by echocardiography, hematoxylin-eosin (H&E) and Masson's trichrome staining. The gene and protein expressions were detected by quantitative real-time PCR, and Western blot analysis. After 21 days, DOCA/salt treatment significantly up-regulated the expression of β2i mRNA and protein in the hearts. Moreover, systolic blood pressure and heart weight/body weight (HW/BW) ratio were significantly higher in DOCA/salt mice than in sham groups, and these effects were markedly reversed in β2i knockout mice. Importantly, DOCA/salt-induced cardiac fibrosis, inflammation and the expression of collagen I, collagen III, α-SMA, IL-1β, IL-6 and TNF-α in the wild-type hearts, which were markedly attenuated by β2i knockout. These beneficial effects were due, at least in part, to the inhibition of IκBα/NF-κB and TGF-β1/Smad2/3 signaling pathways. Collectively, these findings indicate that knockout of β2i ameliorates DOCA/salt-induced cardiac fibrosis and inflammation, and may be a novel potential therapeutic target for hypertensive heart diseases.

The proteasome - victim or culprit in autoimmunity

The ubiquitin proteasome system is closely connected to apoptosis, autophagy, signaling of inflammatory cytokines and generation of ligands for MHC class I antigen presentation. Proteasome function in the innate immune response becomes particularly evident in patients with proteasome-associated autoinflammatory syndromes (PRAAS), where disease causing mutations result in reduced proteasome activity. PRAAS can be classified as a novel type of interferonopathy, however the molecular mechanism and signaling pathways leading from impaired proteasome capacity, the accumulation of damaged proteins, and the induction of type I IFN-genes remain to be determined. In contrast, several studies have confirmed an up-regulation of inducible subunits of the proteasome in systemic autoimmune diseases. Since proteasome inhibition was shown to be efficacious in several in-vitro studies and animal models of autoimmune diseases, it is justified to investigate the application of proteasome inhibitors in human disease. In this context, a number of available proteasome inhibitors has been characterized as potent immune-suppressants. The mode of action of proteasome inhibition interferes with the quality control of the huge amounts of synthetized antibodies causing an unfolded protein response. Further effects of proteasome inhibition includes inhibition of NFκB activation as well as direct activation of intrinsic and extrinsic pathways of apoptosis. The preliminary clinical work on proteasome inhibition in autoimmune diseases comprises only few studies in small cohorts with promising effects, which needs to be confirmed in controlled clinical trials.

Pro-inflammatory cytokines enhance ERAD and ATF6α pathway activity in salivary glands of Sjögren's syndrome patients

Salivary gland (SG) acinar-cells are susceptible to endoplasmic reticulum (ER) stress related to their secretory activity and the complexity of synthesized secretory products. SGs of Sjögren's syndrome patients (SS)-patients show signs of inflammation and altered proteostasis, associated with low IRE1α/XBP-1 pathway activity without avert increases in apoptosis. Acinar-cells may avoid apoptosis by activation of the ATF6α pathway and ER-associated protein degradation (ERAD). The aim of this study was to evaluate the role of pro-inflammatory cytokines in ATF6α pathway/ERAD activation and cell viability in labial salivary glands (LSG) of SS-patients. In biopsies from SS-patients increased ATF6α signaling pathway activity, as evidenced by generation of the ATF6f cleavage fragment, and increased expression of ERAD machinery components, such as EDEM1, p97, SEL1L, gp78, UBE2J1, UBE2G2, HERP and DERLIN1, were observed compared to controls. Alternatively, for pro- (active-caspase-3) and anti-apoptotic (cIAP2) markers no significant difference between the two experimental groups was detected. Increased presence of ATF6f and ERAD molecules correlated significantly with increased expression of pro-inflammatory cytokines. These observations were corroborated in vitro in 3D-acini treated with TNF-α and/or IFN-γ, where an increase in the expression and activation of the ATF6α sensor and ERAD machinery components was detected under ER stress conditions, while changes in cell viability and caspase-3 activation were not observed. Cytokine stimulation protected cells from death when co-incubated with an ERAD machinery inhibitor. Alternatively, when cytokines were eliminated from the medium prior to ERAD inhibition, cell death increased, suggesting that the presence of pro-inflammatory cytokines in the medium is essential to maintain cell viability. In conclusion, the ATF6α pathway and the ERAD machinery are active in LSG of SS-patients. Both were also activated by TNF-α and IFN-γ in vitro in 3D-acini and aided in preventing apoptosis. IFN-γ levels were elevated in SS-patients and UPR responses triggered in vitro by this cytokine closely matched those observed in LSG from SS-patients, suggesting that cytokines may induce ER stress.

Silencing of Inducible Immunoproteasome Subunit Expression by Chemically Modified siRNA and shRNA

Overexpression of inducible subunits of immunoproteasome is related to pathogenesis of some chronic diseases. Specific inhibition of the immunosubunits may be used for the treatment of these diseases and RNA interference is one of the potent methods used in this area. We designed 2'-O-methyl modified siRNAs with selectively protected nuclease-sensitive sites, which efficiently silence LMP2, LMP7, and MECL-1 genes expression. To provide stable long-lasting inhibition of target genes, short-hairpin RNAs (shRNA) expressed by lentiviral vectors were constructed. Our results demonstrated that chemically modified siRNAs inhibited the expression of target genes with similar efficiency or with efficiency exceeding that of corresponding shRNAs and provide silencing effect for 5 days.

Proteasome function shapes innate and adaptive immune responses

The proteasome system degrades more than 80% of intracellular proteins into small peptides. Accordingly, the proteasome is involved in many essential cellular functions, such as protein quality control, transcription, immune responses, cell signaling, and apoptosis. Moreover, degradation products are loaded onto major histocompatibility class I molecules to communicate the intracellular protein composition to the immune system. The standard 20S proteasome core complex contains three distinct catalytic active sites that are exchanged upon stimulation with inflammatory cytokines to form the so-called immunoproteasome. Immunoproteasomes are constitutively expressed in immune cells and have different proteolytic activities compared with standard proteasomes. They are rapidly induced in parenchymal cells upon intracellular pathogen infection and are crucial for priming effective CD8(+) T-cell-mediated immune responses against infected cells. Beyond shaping these adaptive immune reactions, immunoproteasomes also regulate the function of immune cells by degradation of inflammatory and immune mediators. Accordingly, they emerge as novel regulators of innate immune responses. The recently unraveled impairment of immunoproteasome function by environmental challenges and by genetic variations of immunoproteasome genes might represent a currently underestimated risk factor for the development and progression of lung diseases. In particular, immunoproteasome dysfunction will dampen resolution of infections, thereby promoting exacerbations, may foster autoimmunity in chronic lung diseases, and possibly contributes to immune evasion of tumor cells. Novel pharmacological tools, such as site-specific inhibitors of the immunoproteasome, as well as activity-based probes, however, hold promises as innovative therapeutic drugs for respiratory diseases and biomarker profiling, respectively.

Modified siRNA effectively silence inducible immunoproteasome subunits in NSO cells

The pathogenesis of autoimmune and neurodegenerative diseases involves overexpression of inducible subunits of the immunoproteasome. However, the clinical application of inhibitors to inducible subunits of the immunoproteasome has been limited due to systemic toxicity. Here, we designed siRNAs that efficiently silence LMP2, LMP7 and MECL-1 gene expression. Inducible subunits of the immunoproteasome are complex siRNA targets because they have a long half-life; therefore, we introduced 2'-O-methyl modifications into nuclease-sensitive sites. This led to 90-95% silencing efficiency and prolonged silencing, eliminating the need for multiple transfections. Furthermore, we showed that in the absence of transfection reagent, siRNAs with lipophilic residues were able to penetrate cells more effectively and decrease the expression of inducible immunoproteasome subunits by 35% after 5 days. These results show that siRNA targeted to inducible immunoproteasome subunits have great potential for the development of novel therapeutics for autoimmune and neurodegenerative diseases.

Dysfunction in protein clearance by the proteasome: impact on autoinflammatory diseases

During innate immune responses, proteostasis is greatly impacted by synthesis of pathogen proteins as well as by inflammatory tissue damage through radicals or other damaging molecules released by phagocytes. An adequate adaptation of cellular clearance pathways to the increased burden of damaged proteins is thus of fundamental importance for cells and tissues to prevent protein aggregation, inclusion body formation, and ultimately cell death. We here review the current understanding of the pivotal role of the ubiquitin proteasome system (UPS) in this proteostasis network. The proteolytic capacity of the UPS can be adjusted by differential gene expression, the incorporation and maturation kinetics of alternative active sites, and the attachment of different regulators. Dysregulation of this fine-tuning is likely to induce cell death but seen more often to promote inflammation as well. The link between proteostasis impairment and inflammation may play a crucial role in autoinflammation as well as in age-related diseases and currently uncharacterized diseases. Recent studies on proteasome-associated autoinflammatory syndromes (PRAAS) discovered that IFN signaling drives the inflammation caused by reduction of degradation capacity. Elucidation of these syndromes will reveal further insights in the understanding of inadequate immune responses. Knowledge related to the diversity of this degradation system will raise the awareness of potential pitfalls in the molecular diagnostics of autoinflammatory syndromes and may help to identify novel drug targets.

Increased proteasome activator 28 gamma (PA28γ) levels are unspecific but correlate with disease activity in rheumatoid arthritis

BACKGROUND

PA28γ (also known as Ki, REG gamma, PMSE3), a member of the ubiquitin-and ATP-independent proteasome activator family 11S, has been proved to show proteasome-dependent and -independent effects on several proteins including tumor suppressor p53, cyclin-dependent kinase inhibitor p21 and steroid receptor co-activator 3 (SCR-3). Interestingly, PA28γ is overexpressed in pathological tissue of various cancers affecting e. g. breast, bowl and thyroids. Furthermore, anti-PA28γ autoantibodies have been linked to several autoimmune disorders. The aim of this study was to develop and evaluate a novel and sensitive PA28γ sandwich ELISA for the quantification of PA28γ serum levels in patients with cancer and autoimmune diseases for diagnostic and prognostic purposes.

METHODS

PA28γ-specific polyclonal antibodies and recombinant His-tagged PA28γ were purified and used to develop a sandwich ELISA for the detection of circulating PA28γ. With this new assay, PA28γ serum levels of patients with various cancers, rheumatoid arthritis (RA), Sjögren's syndrome (SS), adult-onset Still's disease (AOSD) and different connective-tissue diseases (CTD) were compared with healthy control subjects. Anti-PA28γ autoantibodies were additionally confirmed using a newly developed microbead assay.

RESULTS

The developed PA28γ sandwich ELISA showed a high specificity with a detection limit of 3 ng/ml. A significant up-regulation of circulating PA28γ was detected in the sera of patients with cancer, RA, SS and CTD. A significant correlation was observed dependent on age as well as anti-PA28γ autoantibody levels with circulating PA28γ protein levels. Furthermore, PA28γ serum levels showed a correlation with disease activity in patients with RA under treatment with the T-cell directed biological compound abatacept according to disease activity score 28 (DAS28) and erythrocyte sedimentation rate (ESR).

CONCLUSION

The application of PA28γ as a novel biomarker for diagnostic purposes of a specific disease is limited, since elevated levels were observed in different disorders. However, the correlation with disease activity in patients with RA suggests a prognostic value, which needs to be addressed by further studies. Therefore our results show that PA28γ is a useful marker which should be included in studies related to novel treatments, e.g. abatacept.

Interferon-γ induces immunoproteasomes and the presentation of MHC I-associated peptides on human salivary gland cells

A prominent histopathological feature of Sjögren's syndrome, an autoimmune disease, is the presence of lymphocytic infiltrates in the salivary and lachrymal glands. Such infiltrates are comprised of activated lymphocytes and macrophages, and known to produce multiple cytokines including interferon-gamma (IFN-γ). In this study, we have demonstrated that IFN-γ strongly induces the expression of immunoproteasome beta subunits (β1i, β2i and β5i) and immunoproteasome activity but conversely inhibits the expression of proteasome beta subunits (β1, β2 and β5) in human salivary gland (HSG) cells. Mass spectrometric analysis has revealed potential MHC I-associated peptides on the HSG cells, including a tryptic peptide derived from salivary amylase, due to IFN-γ stimulation. These results suggest that IFN-γ induces immunoproteasomes in HSG cells, leading to enhanced presentation of MHC I-associated peptides on cell surface. These peptide-presenting salivary gland cells may be recognized and targeted by auto-reactive T lymphocytes. We have also found that lactacystin, a proteasome inhibitor, inhibits the expression of β1 subunit in HSG cells and blocks the IFN-γ-induced expression of β1i and immunoproteasome activity. However, the expression of β2i and β5i in HSG cells is not affected by lactacystin. These results may add new insight into the mechanism regarding how lactacystin blocks the action of proteasomes or immunoproteasomes.

Upregulation of immunoproteasome subunits in myositis indicates active inflammation with involvement of antigen presenting cells, CD8 T-cells and IFNΓ

Objective

In idiopathic inflammatory myopathies (IIM) infiltration of immune cells into muscle and upregulation of MHC-I expression implies increased antigen presentation and involvement of the proteasome system. To decipher the role of immunoproteasomes in myositis, we investigated individual cell types and muscle tissues and focused on possible immune triggers.

Methods

Expression of constitutive (PSMB5, -6, -7) and corresponding immunoproteasomal subunits (PSMB8, -9, -10) was analyzed by real-time RT-PCR in muscle biopsies and sorted peripheral blood cells of patients with IIM, non-inflammatory myopathies (NIM) and healthy donors (HD). Protein analysis in muscle biopsies was performed by western blot. Affymetrix HG-U133 platform derived transcriptome data from biopsies of different muscle diseases and from immune cell types as well as monocyte stimulation experiments were used for validation, coregulation and coexpression analyses.

Results

Real-time RT-PCR revealed significantly increased expression of immunoproteasomal subunits (PSMB8/-9/-10) in DC, monocytes and CD8+ T-cells in IIM. In muscle biopsies, the immunosubunits were elevated in IIM compared to NIM and exceeded levels of matched blood samples. Proteins of PSMB8 and -9 were found only in IIM but not NIM muscle biopsies. Reanalysis of 78 myositis and 20 healthy muscle transcriptomes confirmed these results and revealed involvement of the antigen processing and presentation pathway. Comparison with reference profiles of sorted immune cells and healthy muscle confirmed upregulation of PSMB8 and -9 in myositis biopsies beyond infiltration related changes. This upregulation correlated highest with STAT1, IRF1 and IFNγ expression. Elevation of T-cell specific transcripts in active IIM muscles was accompanied by increased expression of DC and monocyte marker genes and thus reflects the cell type specific involvement observed in peripheral blood.

Conclusions

Immunoproteasomes seem to indicate IIM activity and suggest that dominant involvement of antigen processing and presentation may qualify these diseases exemplarily for the evolving therapeutic concepts of immunoproteasome specific inhibition.

TNF Receptor 2 and Disease: Autoimmunity and Regenerative Medicine

The regulatory cytokine tumor necrosis factor (TNF) exerts its effects through two receptors: TNFR1 and TNFR2. Defects in TNFR2 signaling are evident in a variety of autoimmune diseases. One new treatment strategy for autoimmune disease is selective destruction of autoreactive T cells by administration of TNF, TNF inducers, or TNFR2 agonism. A related strategy is to rely on TNFR2 agonism to induce T-regulatory cells (T_regs) that suppress cytotoxic T cells. Targeting TNFR2 as a treatment strategy is likely superior to TNFR1 because of its more limited cellular distribution on T cells, subsets of neurons, and a few other cell types, whereas TNFR1 is expressed throughout the body. This review focuses on TNFR2 expression, structure, and signaling; TNFR2 signaling in autoimmune disease; treatment strategies targeting TNFR2 in autoimmunity; and the potential for TNFR2 to facilitate end organ regeneration.

Gene expression of catalytic proteasome subunits and resistance toward proteasome inhibition of B lymphocytes from patients with primary sjogren syndrome

OBJECTIVE

Dysregulation of proteasome subunit β1i expression has been shown in total blood mononuclear cells (PBMC) from patients with primary Sjögren syndrome (pSS), a B cell-driven systemic autoimmune disorder.

METHODS

Proteasome activation was investigated in sorted blood cells from patients with pSS and controls by measuring transcript levels of constitutive (β1/β2/β5) and corresponding immunoproteasome catalytic subunits (β1i/β2i/β5i) using real-time PCR. At protein level, β1i protein expression was analyzed by immunoblotting. Functional effects of proteasome inhibition on proteolytic activity and induction of apoptosis were also evaluated in cellular subsets.

RESULTS

The proteasome was found to be activated in pSS, with upregulation of gene expression of catalytic proteasome subunits. Western blot analysis revealed decreased β1i protein expression in pSS B lymphocytes, with decreased protein despite increased messenger RNA (mRNA) levels. After proteasome inhibition in vitro, proteolytic activity was less reduced and resistance to apoptosis was increased in B lymphocytes compared to other cells.

CONCLUSION

In pSS, catalytic subunits of the proteasome are upregulated at the mRNA level, while dysregulation of subunit β1i is attributed to B lymphocytes. B cell resistance after proteasome inhibition differs from the classical concept of increased susceptibility toward inhibition in activated cells, supporting the novel notion that susceptibility depends on cellular intrinsic factors and on proteasome activation.

Proteomic identification of immunoproteasome accumulation in formalin-fixed rodent spinal cords with experimental autoimmune encephalomyelitis

Clinically relevant formalin-fixed and paraffin-embedded (FFPE) tissues have not been widely used in neuroproteomic studies because many proteins are presumed to be degraded during tissue preservation. Recent improvements in proteomics technologies, from the 2D gel analysis of intact proteins to the "shotgun" quantification of peptides and the use of isobaric tags for absolute and relative quantification (iTRAQ) method, have made the analysis of FFPE tissues possible. In recent years, iTRAQ has been one of the main methods of choice for high throughput quantitative proteomics analysis, which enables simultaneous comparison of up to eight samples in one experiment. Our objective was to assess the relative merits of iTRAQ analysis of fresh frozen versus FFPE nervous tissues by comparing experimental autoimmune encephalomyelitis (EAE)-induced proteomic changes in FFPE rat spinal cords and frozen tissues. EAE-induced proteomic changes in FFPE tissues were positively correlated with those found in the frozen tissues, albeit with ∼50% less proteome coverage. Subsequent validation of the enrichment of immunoproteasome (IP) activator 1 in EAE spinal cords led us to evaluate other proteasome and IP-specific proteins. We discovered that many IP-specific (as opposed to constitutive) proteasomal proteins were enriched in EAE rat spinal cords, and EAE-induced IP accumulation also occurred in the spinal cords of an independent mouse EAE model in a disability score-dependent manner. Therefore, we conclude that it is feasible to generate useful information from iTRAQ-based neuroproteomics analysis of archived FFPE tissues for studying neurological disease tissues.

Vasoactive intestinal peptide/vasoactive intestinal peptide receptor relative expression in salivary glands as one endogenous modulator of acinar cell apoptosis in a murine model of Sjögren's syndrome

Sjögren's syndrome (SS) is a chronic autoimmune disease characterized by a progressive oral and ocular dryness that correlates poorly with the autoimmune damage of the glands. It has been proposed that a loss of homeostatic equilibrium in the glands is partly responsible for salivary dysfunction with acinar cells involved actively in the pathogenesis of SS. The non-obese diabetic (NOD) mouse model of Sjögren's syndrome develops secretory dysfunction and early loss of glandular homeostatic mechanisms, with mild infiltration of the glands. Based on the vasodilator, prosecretory and trophic effects of the vasoactive intestinal peptide (VIP) on acini as well as its anti-inflammatory properties we hypothesized that the local expression of VIP/vasoactive intestinal peptide receptor (VPAC) system in salivary glands could have a role in acinar cell apoptosis and macrophage function thus influencing gland homeostasis. Here we show a progressive decline of VIP expression in submandibular glands of NOD mice with no changes in VPAC receptor expression compared with normal mice. The deep loss of endogenous VIP was associated with a loss of acinar cells through apoptotic mechanisms that could be induced further by tumour necrosis factor (TNF)-α and reversed by VIP through a cyclic adenosine-5'-monophosphate (cAMP)/protein kinase A (PKA)-mediated pathway. The clearance of apoptotic acinar cells by macrophages was impaired for NOD macrophages but a shift from inflammatory to regulatory phenotype was induced in macrophages during phagocytosis of apoptotic acinar cells. These results support that the decline in endogenous VIP/VPAC local levels might influence the survival/apoptosis intracellular set point in NOD acinar cells and their clearance, thus contributing to gland homeostasis loss.

Structure of the proteasome

The ubiquitin-proteasomal system is an essential element of the protein quality control machinery in cells. The central part of this system is the 20S proteasome. The proteasome is a barrel-shaped multienzyme complex, containing several active centers hidden at the inner surface of the hollow cylinder. So, the regulation of the substrate entry toward the inner proteasomal surface is a key control mechanism of the activity of this protease. This chapter outlines the knowledge on the structure of the subunits of the 20S proteasome, the binding and structure of some proteasomal regulators and inducible proteasomal subunits. Therefore, this chapter imparts the knowledge on proteasomal structure which is required for the understanding of the following chapters.

Aging and calorie restriction modulate yeast redox state, oxidized protein removal, and the ubiquitin-proteasome system

The ubiquitin-proteasome system governs the half-life of most cellular proteins. Calorie restriction (CR) extends the maximum life span of a variety of species and prevents oxidized protein accumulation. We studied the effects of CR on the ubiquitin-proteasome system and protein turnover in aging Saccharomyces cerevisiae. CR increased chronological life span as well as proteasome activity compared to control cells. The levels of protein carbonyls, a marker of protein oxidation, and those of polyubiquitinated proteins were modulated by CR. Controls, but not CR cells, exhibited a significant increase in oxidized proteins. In keeping with decreased proteasome activity, polyubiquitinated proteins were increased in young control cells compared to time-matched CR cells, but were profoundly decreased in aged control cells despite decreased proteasomal activity. This finding is related to a decreased polyubiquitination ability due to the impairment of the ubiquitin-activating enzyme in aged control cells, probably related to a more oxidative microenvironment. CR preserves the ubiquitin-proteasome system activity. Overall, we found that aging and CR modulate many aspects of protein modification and turnover.

Association analysis of polymorphisms of porcine LMP2 and LMP7 genes with haematological traits

Low molecular weight polypeptides 2 (LMP2) and low molecular weight polypeptides 7 (LMP7) are located within the major histocompatibility complex and have been associated with autoimmune disease. In this study, polymorphisms of porcine LMP2 and LMP7 genes were analyzed by PCR-SSCP and DNA sequencing methods. Four SNPs (DQ659151:g.2115T>C; DQ659151:g.4343A>G; DQ872631:g.1232C>G; DQ872631:g.2847C>T) were identified. Four SNPs of genes were analyzed for association with 22 haematological traits in Large White (n = 195), Landrace (n = 84) and Songliao Black (n = 86) pig population. Of all the 22 traits, seven were significant associated with the SNPs of LMP2/LMP7 gene (P < 0.05). They included white blood cell count (WBC) (P = 0.028), neutrophilic granulocyte count (GRAN) (P = 0.037), monocytes percentage (MO%) (P = 0.015), red blood cell (RBC) (P = 0.004), red blood cell volume distribution width (RDW) (P = 0.004), mean platelet volume (MPV) (P = 0.016) and CD4(+)CD8(+)% (P = 0.045). These results suggest LMP2/LMP7 gene should be regarded as molecular marker to estimate animal's immune status for their effects on hematological traits.

TNF receptor 2 pathway: drug target for autoimmune diseases

Although drug development has advanced for autoimmune diseases, many current therapies are hampered by adverse effects and the frequent destruction or inactivation of healthy cells in addition to pathological cells. Targeted autoimmune therapies capable of eradicating the rare autoreactive immune cells that are responsible for the attack on the body's own cells are yet to be identified. This Review presents a new emerging approach aimed at selectively destroying autoreactive immune cells by specific activation of tumour necrosis factor receptor 2 (TNFR2), which is found on autoreactive and normal T lymphocytes, with the potential of avoiding or reducing the toxicity observed with existing therapies.

Potential roles for PA28beta in gastric adenocarcinoma development and diagnosis

PURPOSE

This study aimed to investigate the expression level of human proteasome activator PA28beta subunit (PA28beta) in gastric adenocarcinomas (GA) tissues and investigate its potential role in GA carcinogenesis.

METHODS

To investigate the expression profile of PA28beta in patients with GA, we employed immunohistochemistry for detection of 287 cases of paired GA and adjacent non-neoplastic tissues. To evaluate the role of PA28beta in GA cells, we measured cell growth, colony formation, soft agar, and nude mice tumorigenicity assays in MKN-45 GA cells pre- and post-PA28beta transfection.

RESULTS

PA28beta had lower expression in 183 of 287 GA cases compared to paired normal samples (63.76%; P < or = 0.001). Decreased expression was dependent on histological type, TNM stage, and differentiation grade. Significantly decreased expression was correlated with a diffuse histological type (88/116, 75.86%) compared to an intestinal type (84/152, 55.26%; P < or = 0.001), with advanced TNM stages (T3: 44/59, 74.58%; T4:25/32, 78.13%) compared to earlier stages (T1: 25/47, 53.19%; T2: 90/149, 60.40%; P = 0.004), and poorer differentiation grade (poor: 68/90, 75.56%) compared to a higher grade (high: 9/18, 50%, moderate: 74/134, 55.22%) (P = 0.006). Over-expression of PA28beta inhibited cell growth, proliferation, and tumorigenicity of MKN-45 GA cells.

CONCLUSIONS

These results indicated that PA28beta might participate in the origin and progression of GA cancer through changes to cell proliferation activity and tumorigenicity. Therefore, PA28beta might be a novel biomarker for GA.

Immunoproteasome overexpression underlies the pathogenesis of thyroid oncocytes and primary hypothyroidism: studies in humans and mice

Background

Oncocytes of the thyroid gland (Hürthle cells) are found in tumors and autoimmune diseases. They have a unique appearance characterized by abundant granular eosinophilic cytoplasm and hyperchromatic nucleus. Their pathogenesis has remained, thus far, unknown.

Methodology/Principal Findings

Using transgenic mice chronically expressing IFNγ in thyroid gland, we showed changes in the thyroid follicular epithelium reminiscent of the human oncocyte. Transcriptome analysis comparing transgenic to wild type thyrocytes revealed increased levels of immunoproteasome subunits like LMP2 in transgenics, suggesting an important role of the immunoproteasome in oncocyte pathogenesis. Pharmacologic blockade of the proteasome, in fact, ameliorated the oncocytic phenotype. Genetic deletion of LMP2 subunit prevented the development of the oncocytic phenotype and primary hypothyroidism. LMP2 was also found expressed in oncocytes from patients with Hashimoto thyroiditis and Hürthle cell tumors.

Conclusions/Significance

In summary, we report that oncocytes are the result of an increased immunoproteasome expression secondary to a chronic inflammatory milieu, and suggest LMP2 as a novel therapeutic target for the treatment of oncocytic lesions and autoimmune hypothyroidism.

Expression of proteasomal immunosubunit beta1i is dysregulated in inflammatory infiltrates of minor salivary glands in Sjogren's syndrome

OBJECTIVE

Minor salivary gland specimens were analyzed to investigate dysregulation of the proteasome system in patients with Sjögren's syndrome (SS) and patients with sicca syndrome.

METHODS

Labial biopsy specimens from 17 patients with SS and 11 patients with non-autoimmunesicca syndrome were analyzed by immunohistochemistry for expression of the inducible proteasomal subunits ss1i, ss2i, and ss5i. The infiltrating subsets of lymphocytes were characterized using immunofluorescence stainings against the cell-surface markers CD20 and CD27. Two-dimensional electrophoresis and immunoblotting were used for detection of the proteasomal subunits ss1 and ss1i in peripheral blood monocyte cells. Gene expression of the constitutive subunits ss1, ss2, and ss5 and the corresponding inducible subunits ss1i, ss2i, and ss5i was further investigated at the mRNA level in small lip biopsies using real-time polymerase chain reaction.

RESULTS

The expression of ss1i in infiltrating and peripheral immune cells was altered in patients with SS compared to patients with non-autoimmune sicca syndrome and healthy controls. No significant differences were found in ss2i and ss5i expression between the same groups in small lip biopsies. Chisholm-Mason grade and ss1i expression were found to be inversely correlated (Spearman r = -0.461, p = 0.014). The phenotype and distribution of the lymphocytic infiltrate showed no differences between patients with primary and secondary SS regardless of ss1i expression.

CONCLUSION

The proteasomal ss1i subunit is dysregulated in peripheral white blood cells and in inflammatory infiltrates of minor salivary glands in patients with SS.

Systems biology analysis of Sjögren's syndrome and mucosa-associated lymphoid tissue lymphoma in parotid glands

OBJECTIVE

To identify key target genes and activated signaling pathways associated with the pathogenesis of Sjögren's syndrome (SS) by conducting a systems analysis of parotid glands manifesting primary SS or primary SS/mucosa-associated lymphoid tissue (MALT) lymphoma phenotypes.

METHODS

A systems biology approach was used to analyze parotid gland tissue samples obtained from patients with primary SS, patients with primary SS/MALT lymphoma, and subjects without primary SS (non-primary SS controls). The tissue samples were assessed concurrently by gene-expression microarray profiling and proteomics analysis, followed by weighted gene-coexpression network analysis.

RESULTS

Gene-coexpression modules related to primary SS and primary SS/MALT lymphoma were significantly enriched with genes known to be involved in the immune/defense response, apoptosis, cell signaling, gene regulation, and oxidative stress. Detailed functional pathway analyses indicated that primary SS-associated modules were enriched with genes involved in proteasome degradation, apoptosis, signal peptides of the class I major histocompatibility complex (MHC), complement activation, cell growth and death, and integrin-mediated cell adhesion, while primary SS/MALT lymphoma-associated modules were enriched with genes involved in translation, ribosome biogenesis and assembly, proteasome degradation, class I MHC signal peptides, the G13 signaling pathway, complement activation, and integrin-mediated cell adhesion. Combined analyses of gene expression and proteomics data implicated 6 highly connected "hub" genes for distinguishing primary SS from non-primary SS, and 8 hub genes for distinguishing primary SS/MALT lymphoma from primary SS.

CONCLUSION

Systems biology analyses of the parotid glands from patients with primary SS and those with primary SS/MALT lymphoma revealed pathways and molecular targets associated with disease pathogenesis. The identified gene modules/pathways provide further insights into the molecular mechanisms of primary SS and primary SS/MALT lymphoma. The identified disease-hub genes represent promising targets for therapeutic intervention, diagnosis, and prognosis.

Upregulation of the immunoproteasome in peripheral blood mononuclear cells of patients with IgA nephropathy

In order to present an antigen to T-cells, the antigen must first be degraded by proteasomes. Following exposure to interferons, some proteasome subunits (ss1,ss2,ss5) are replaced by others (LMP2, LMP7, MECL-1) that have more optimal catalytic properties for peptide presentation; this more efficient organelle is termed the immuno-proteasome. Here we measured gene expression of various subunits in peripheral mononuclear cells of patients with IgA nephropathy, a disease with features of immune dysregulation. We used quantitative PCR to measure the expression of proteasomal subunit mRNA in mononuclear cells from IgA nephropathy patients, a group of proteinuric control patients with idiopathic nephrotic syndromes, and healthy controls. A significant switch in the expression of trypsin- and chymotrypsin-like proteasome subunits to corresponding immuno-proteasome subunits was found in patients as compared to healthy controls. Further, we found that nuclear translocation of NF-kappaB p50 and p65 was significantly greater in the IgA nephropathy patients, but this did not correlate with the switch to the immuno-proteasome phenotype. Patients with proteinuria greater than 0.5 g/1.73 m(2)/day had a significant switch of the chymotryptic-like beta5 protease to the LMP7 subunit, but this did not occur in patients with idiopathic nephrotic syndrome. The switch to an immuno-proteasome in peripheral blood mononuclear cells of patients with IgA nephropathy suggests an increased efficiency of antigen processing and presentation. This switch appears to be independent of a coincidental activation of the NF-kappaB pathway but is associated with high levels of proteinuria, a well known risk factor for progression of IgA nephropathy.

Selective death of autoreactive T cells in human diabetes by TNF or TNF receptor 2 agonism

Human autoimmune (AI) diseases are difficult to treat, because immunosuppressive drugs are nonspecific, produce high levels of adverse effects, and are not based on mechanistic understanding of disease. Destroying the rare autoreactive T lymphocytes causing AI diseases would improve treatment. In animal models, TNF selectively kills autoreactive T cells, thereby hampering disease onset or progression. Here, we seek to determine, in fresh human blood, whether TNF or agonists of TNF selectively kill autoreactive T cells, while sparing normal T cells. We isolated highly pure CD4 or CD8 T cells from patients with type 1 diabetes (n = 675), other AI diseases, and healthy controls (n = 512). Using two cell death assays, we found that a subpopulation of CD8, but not CD4, T cells in patients' blood was vulnerable to TNF or TNF agonist-induced death. One agonist for the TNFR2 receptor exhibited a dose-response pattern of killing. In type 1 diabetes, the subpopulation of T cells susceptible to TNF or TNFR2 agonist-induced death was traced specifically to autoreactive T cells to insulin, a known autoantigen. Other activated and memory T cell populations were resistant to TNF-triggered death. This study shows that autoreactive T cells, although rare, can be selectively destroyed in isolated human blood. TNF and a TNFR2 agonist may offer highly targeted therapies, with the latter likely to be less systemically toxic.

Role of proteasomes in disease

A functional ubiquitin proteasome system is essential for all eukaryotic cells and therefore any alteration to its components has potential pathological consequences. Though the exact underlying mechanism is unclear, an age-related decrease in proteasome activity weakens cellular capacity to remove oxidatively modified proteins and favours the development of neurodegenerative and cardiac diseases. Up-regulation of proteasome activity is characteristic of muscle wasting conditions including sepsis, cachexia and uraemia, but may not be rate limiting. Meanwhile, enhanced presence of immunoproteasomes in aging brain and muscle tissue could reflect a persistent inflammatory defence and anti-stress mechanism, whereas in cancer cells, their down-regulation reflects a means by which to escape immune surveillance. Hence, induction of apoptosis by synthetic proteasome inhibitors is a potential treatment strategy for cancer, whereas for other diseases such as neurodegeneration, the use of proteasome-activating or -modulating compounds could be more effective. Publication history: Republished from Current BioData's Targeted Proteins database (TPdb; http://www.targetedproteinsdb.com).

Reversal of Sjogren's-like syndrome in non-obese diabetic mice

BACKGROUND

Non-obese diabetic (NOD) mice exhibit autoimmune diabetes and Sjögren's-like syndrome.

OBJECTIVE

To test whether a treatment that reverses end-stage diabetes in the NOD mouse would affect their Sjögren's-like syndrome.

METHODS

NOD mice have a proteasome defect. Improperly selected naive T cells escape, but can be killed by reintroducing major histocompatibility complex class I self-peptides on matched normal splenocytes. The proteasome defect also impairs nuclear factor kB, a transcription factor in pathogenic memory T cells, increasing their susceptibility to tumour necrosis factor-induced apoptosis stimulated through complete Freund's adjuvant (CFA). The impact of this two-limb therapy (injections of matched normal splenocytes and CFA) on the autoimmune salivary gland disease of the NOD mice was studied.

RESULTS

All NOD mice receiving the above treatment had a complete recovery of salivary flow and were protected from diabetes. Restoration of salivary flow could be the result of a combination of rescue and regeneration of the gland, as confirmed by immunohistochemical analysis. All untreated NOD mice showed a continuous decline in salivary flow, followed by hyperglycaemia and death.

CONCLUSION

This study establishes that a brief intervention in NOD mice with Sjögren's-like syndrome can reverse salivary gland dysfunction.

A role for transcription factor NF-kappaB in autoimmunity: possible interactions of genes, sex, and the immune response

Sex hormones have long been implicated in autoimmune diseases because women account for 80% of cases. The mechanism of hormonal action in autoimmunity is unknown. Drawing on genetic studies of autoimmune disease, this article discusses how both genes and sex hormones may exert their effects through the same general mechanism, dysregulation of transcription factor NF-kappaB, an immunoregulatory protein. Gene and hormone alterations of the NF-kappaB signaling cascade provide a unifying hypothesis to explain the wide-ranging human and murine autoimmune disease phenotypes regulated by NF-kappaB, including cytokine balance, antigen presentation, lymphoid development, and lymphoid repertoire selection by apoptosis.