Loss of the lupus autoantigen Ro52/Trim21 induces tissue inflammation and systemic autoimmunity by disregulating the IL-23-Th17 pathway

Anti-Ro52 Autoantibodies Are Related to Chronic Graft-vs.-Host Disease After Allogeneic Hematopoietic Stem Cell Transplantation

Chronic graft-vs.-host disease (cGVHD) remains a major cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Previous studies have shown that autoantibodies play an important role in the development of cGVHD. Anti-nuclear autoantibodies (ANA) is the most frequently detected autoantibodies in patients with cGVHD, but the role of anti-Ro52 autoantibodies (anti-Ro52) in cGVHD remains largely unknown. In this study, we analyzed autoantibodies from 84 patients after allo-HSCT, including 42 with active cGVHD and 42 without cGVHD. Autoantibodies were found in 36 (42.9%) patients. Among these autoantibody-positive patients, 28 (77.8%) patients had active cGVHD. The most frequent autoantibodies in patients with active cGVHD were ANA (50.0%), anti-Ro52 (28.6%) and anti-mitochondrial autoantibodies type 2 (4.8%). We further explored the association between anti-Ro52 and cGVHD. Patients with active cGVHD had higher anti-Ro52 levels than patients without cGVHD (P < 0.05). The increases of anti-Ro52 levels were more significant in patients with moderate/severe cGVHD compared to those of patients without cGVHD (P < 0.05). Stratified and multivariable logistic regression analysis demonstrated that moderate/severe cGVHD was an independent risk factor for the levels of anti-Ro52 (P < 0.01). ROC analysis confirmed anti-Ro52 as a risk factor for progression of skin cGVHD. Moreover, the anti-Ro52 levels were highly correlated with the levels of B cell-activating factor (BAFF) and IgG1 antibodies. Our study demonstrates that anti-Ro52 is associated with cGVHD. The increased levels of anti-Ro52 were associated with higher levels of BAFF and IgG1 antibodies, suggesting a mechanistic link between elevated anti-Ro52 levels and aberrant B cell homeostasis.

Current State of Knowledge on Primary Sjögren's Syndrome, an Autoimmune Exocrinopathy

Primary Sjögren's syndrome (pSS) is a chronic systemic autoimmune rheumatic disease characterized by lymphoplasmacytic infiltration of the salivary and lacrimal glands, whereby sicca syndrome and/or systemic manifestations are the clinical hallmarks, associated with a particular autoantibody profile. pSS is the most frequent connective tissue disease after rheumatoid arthritis, affecting 0.3-3% of the population. Women are more prone to develop pSS than men, with a sex ratio of 9:1. Considered in the past as innocent collateral passive victims of autoimmunity, the epithelial cells of the salivary glands are now known to play an active role in the pathogenesis of the disease. The aetiology of the "autoimmune epithelitis" still remains unknown, but certainly involves genetic, environmental and hormonal factors. Later during the disease evolution, the subsequent chronic activation of B cells can lead to the development of systemic manifestations or non-Hodgkin's lymphoma. The aim of the present comprehensive review is to provide the current state of knowledge on pSS. The review addresses the clinical manifestations and complications of the disease, the diagnostic workup, the pathogenic mechanisms and the therapeutic approaches.

Negative feedback regulation by HuR controls TRIM21 expression and function in response to UV radiation

The E3 ubiquitin ligase TRIM21 plays a crucial role as a negative regulator of innate immune responses. Recent evidence has also indicated the involvement of TRIM21 in the genotoxic stress response and suppressing tumorigenesis. Our previous work has demonstrated a new function of TRIM21 in inhibiting p53 protein synthesis by degrading the RNA-binding protein HuR in response to UV radiation. This suggested a pro-oncogenic role of TRIM21. In this study, we have shown that TRIM21 enhances the proliferation of MCF7 breast carcinoma cells and counteracts the decrease in cell proliferation and colony formation caused by UV-induced DNA damage. Further, this pro-oncogenic role of TRIM21 in response to DNA damage is mediated by its degradation of HuR. Conversely, we found that HuR binds to a U-rich element in the 3'UTR of TRIM21 mRNA and activates its translation, thereby constituting a negative feedback loop. We found that dihydrotanshinone-I (DHTS-I), a plant-derived product which prevents HuR binding to specific RNAs, prevented HuR-mediated upregulation of TRIM21, while increasing the HuR-mediated upregulation of p53. Together, these findings demonstrate a negative feedback regulation between TRIM21 and HuR, which may play an important role in regulating the level of p53 in the genotoxic stress response.

An integrative Bayesian network approach to highlight key drivers in systemic lupus erythematosus

BACKGROUND

A comprehensive intuition of the systemic lupus erythematosus (SLE), as a complex and multifactorial disease, is a biological challenge. Dealing with this challenge needs employing sophisticated bioinformatics algorithms to discover the unknown aspects. This study aimed to underscore key molecular characteristics of SLE pathogenesis, which may serve as effective targets for therapeutic intervention.

METHODS

In the present study, the human peripheral blood mononuclear cell (PBMC) microarray datasets (n = 6), generated by three platforms, which included SLE patients (n = 220) and healthy control samples (n = 135) were collected. Across each platform, we integrated the datasets by cross-platform normalization (CPN). Subsequently, through BNrich method, the structures of Bayesian networks (BNs) were extracted from KEGG-indexed SLE, TCR, and BCR signaling pathways; the values of the node (gene) and edge (intergenic relationships) parameters were estimated within each integrated datasets. Parameters with the FDR < 0.05 were considered significant. Finally, a mixture model was performed to decipher the signaling pathway alterations in the SLE patients compared to healthy controls.

RESULTS

In the SLE signaling pathway, we identified the dysregulation of several nodes involved in the (1) clearance mechanism (SSB, MACROH2A2, TRIM21, H2AX, and C1Q gene family), (2) autoantigen presentation by MHCII (HLA gene family, CD80, IL10, TNF, and CD86), and (3) end-organ damage (FCGR1A, ELANE, and FCGR2A). As a remarkable finding, we demonstrated significant perturbation in CD80 and CD86 to CD28, CD40LG to CD40, C1QA and C1R to C2, and C1S to C4A edges. Moreover, we not only replicated previous studies regarding alterations of subnetworks involved in TCR and BCR signaling pathways (PI3K/AKT, MAPK, VAV gene family, AP-1 transcription factor) but also distinguished several significant edges between genes (PPP3 to NFATC gene families). Our findings unprecedentedly showed that different parameter values assign to the same node based on the pathway topology (the PIK3CB parameter values were 1.7 in TCR vs - 0.5 in BCR signaling pathway).

CONCLUSIONS

Applying the BNrich as a hybridized network construction method, we highlight under-appreciated systemic alterations of SLE, TCR, and BCR signaling pathways in SLE. Consequently, having such a systems biology approach opens new insights into the context of multifactorial disorders.

Relevance of the Materno-Fetal Interface for the Induction of Antigen-Specific Immune Tolerance

In humans, maternal IgGs are transferred to the fetus from the second trimester of pregnancy onwards. The transplacental delivery of maternal IgG is mediated by its binding to the neonatal Fc receptor (FcRn) after endocytosis by the syncytiotrophoblast. IgGs present in the maternal milk are also transferred to the newborn through the digestive epithelium upon binding to the FcRn. Importantly, the binding of IgGs to the FcRn is also responsible for the recycling of circulating IgGs that confers them with a long half-life. Maternally delivered IgG provides passive immunity to the newborn, for instance by conferring protective anti-flu or anti-pertussis toxin IgGs. It may, however, lead to the development of autoimmune manifestations when pathological autoantibodies from the mother cross the placenta and reach the circulation of the fetus. In recent years, strategies that exploit the transplacental delivery of antigen/IgG complexes or of Fc-fused proteins have been validated in mouse models of human diseases to impose antigen-specific tolerance, particularly in the case of Fc-fused factor VIII (FVIII) domains in hemophilia A mice or pre-pro-insulin (PPI) in the case of preclinical models of type 1 diabetes (T1D). The present review summarizes the mechanisms underlying the FcRn-mediated transcytosis of IgGs, the physiopathological relevance of this phenomenon, and the repercussion for drug delivery and shaping of the immune system during its ontogeny.

Angiopoietin-like protein 2 as a novel marker for patients with primary Sjogren's syndrome-related interstitial lung disease

Angiopoietin-like protein 2 (Angptl2) plays a key role in chronic inflammation and tissue remodeling. We evaluated whether serum Angptl2 is associated with interstitial lung disease (ILD) in primary Sjogren's syndrome (pSS) patients. A total of 158 consecutive pSS patients and 25 normal healthy controls, which completed lung HRCT, were enrolled in our research. The levels of serum Angptl2 and TGF-β1 were measured by enzyme-linked immunosorbent assay. We investigated the correlation between the activity indexes of pSS-ILD patients and the serum Angptl2 levels. There were 71 of 158 (44.94%) patients interpreted pSS-ILD by radiologists at the initial presentation. The median interquartile range for serum Angptl2 was 16.55 ng/mL (range 10.82-41.07) in pSS patients, compared with 6.05 ng/mL (range 3.53-9.91) in normal healthy controls (P < 0.001). Importantly, differences between Angptl2 levels in pSS-ILD patients and pSS-N-ILD patients were also statistically significant [29.80 ng/mL (range 15.42-54.40), 14.75 ng/mL (range 9.85-40.48), P < 0.001]. A logistic regression analysis suggested that anti-Ro52, serum Angptl2 and DLCO were associated with pSS patients with interstitial lung disease, with aORs and 95% CIs of 2.06 (1.14-7.65), 4.13 (1.25-15.89) and 9.51 (2.10-37.74), respectively. Moreover, anti-Ro52 (r_s = 0.48, P = 0.016) and TGF-β1 (r_s = 0.64, P = 0.003) were significantly correlated with the serum Angptl2 in pSS-ILD patients. And, in pulmonary function tests, the serum Angptl2 was significantly correlated with DLCO (r_s = - 0.40, P = 0.009) and FVC (r_s = -0.37, P = 0.020). Serum Angptl2 may display a peculiar role in the pathogenesis of pSS-ILD and might be a potential biomarker.

CIP2A Constrains Th17 Differentiation by Modulating STAT3 Signaling

Cancerous Inhibitor of Protein Phosphatase 2A (CIP2A) is an oncogene and a potential cancer therapy target protein. Accordingly, a better understanding of the physiological function of CIP2A, especially in the context of immune cells, is a prerequisite for its exploitation in cancer therapy. Here, we report that CIP2A negatively regulates interleukin (IL)-17 production by Th17 cells in human and mouse. Interestingly, concomitant with increased IL-17 production, CIP2A-deficient Th17 cells had increased strength and duration of STAT3 phosphorylation. We analyzed the interactome of phosphorylated STAT3 in CIP2A-deficient and CIP2A-sufficient Th17 cells and indicated together with genome-wide gene expression profiling, a role of Acylglycerol Kinase (AGK) in the regulation of Th17 differentiation by CIP2A. We demonstrated that CIP2A regulates the strength of the interaction between AGK and STAT3, and thereby modulates STAT3 phosphorylation and expression of IL-17 in Th17 cells.

B7-H3: A promising therapeutic target for autoimmune diseases

B7-H3 as a newly identified costimulatory molecule that belongs to B7 ligand family, is broadly expressed in both lymphoid and non-lymphoid tissues. The overexpression of B7-H3 has been verified to be correlated with the poor prognosis and poor clinical outcome of several human cancers. In recent years, researchers reveal that B7-H3 is involved in the pathogenesis of various autoimmune diseases, such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), multiple sclerosis (MS), Sjögren's syndrome (SS), ankylosing spondylitis (AS), etc. In this review, we will discuss the biological function of B7-H3 and summarize the progress made over past years regarding its role in the occurrence and development of autoimmune diseases. The insights gained from these findings could serve as the foundation for future therapies of these diseases.

Potential value of autoantibodies as biomarkers of chronic graft-versus-host disease after allogeneic stem cell transplantation

We investigated the value of autoantibodies as biomarkers of chronic graft-versus-host disease (cGVHD) by analyzing the autoantibody profiles of 65 patients (34 cGVHD and 31 non-cGVHD) surviving longer than three months after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Autoantibodies to at least one antigen were detected in 45 patients (70.8%), with multiple autoantibodies detected in 30 patients (46.2%). Antinuclear antibodies (ANAs) were the most frequently detected autoantibodies, with a significantly higher prevalence in non-cGVHD patients and cGVHD patients than that in healthy controls (HCs). ANA-nucleolar (ANA-N) was the main immunofluorescence pattern of ANA-positivity in both the non-cGVHD and cGVHD groups. There was a higher prevalence of anti-Ro52-positivity in non-cGVHD and cGVHD patients than in HC. Liver cGVHD was significantly associated with anti-Ro52-positivity. However, cGVHD activity and severity were not associated with the presence of autoantibodies. Similarly, there were no significant differences in overall survival or relapse among the four groups of patients expressing autoantibodies. Our results suggest that autoantibodies have limited value in predicting cGVHD.

Regulation of bile acid metabolism-related signaling pathways by gut microbiota in diseases

Over the past decade, there has been increasing attention on the interaction between microbiota and bile acid metabolism. Bile acids are not only involved in the metabolism of nutrients, but are also important in signal transduction for the regulation of host physiological activities. Microbial-regulated bile acid metabolism has been proven to affect many diseases, but there have not been many studies of disease regulation by microbial receptor signaling pathways. This review considers findings of recent research on the core roles of farnesoid X receptor (FXR), G protein-coupled bile acid receptor (TGR5), and vitamin D receptor (VDR) signaling pathways in microbial-host interactions in health and disease. Studying the relationship between these pathways can help us understand the pathogenesis of human diseases, and lead to new solutions for their treatments.

Endoplasmic reticulum-associated degradation and beyond: The multitasking roles for HRD1 in immune regulation and autoimmunity

Endoplasmic reticulum (ER)-associated degradation (ERAD) is a mechanism against ER stress, wherein unfolded/misfolded proteins accumulated in the ER are transported to the cytosol for degradation by the ubiquitin-proteasome system. The ER resident E3 ubiquitin ligase HRD1 has been identified as a key ERAD factor that directly catalyzes ubiquitin conjugation onto the unfolded or misfolded proteins for proteasomal degradation. The abnormally increased HRD1 expression was discovered in rheumatoid synovial cells, providing the first evidence for HRD1 dysregulation involved in human inflammatory pathogenesis. Further studies shown that inflammatory cytokines involved in rheumatoid pathogenesis including IL-1β, TNF-α, IL-17 and IL-26 induce HRD1 expression. Recent studies using mice with tissue-specific targeted deletion of HRD1 gene have revealed important functions of HRD1 in immune regulation and inflammatory diseases. HRD1 has been shown critical for dendritic cell expression of antigens to both CD4 and CD8 T cells. Both TCR and costimulatory receptor CD28 signaling induces HRD1 expression, which promotes T cell clonal expansion and IL-2 production. Together with the fact that HRD1 is required for maintaining the stability of regulatory T cell (Treg) stability, HRD1 appears to fine tone T cell immunity. In addition, HRD1 is involved in humoral immune response by regulating early B cell development and maintaining B cell survival upon recognition of specific antigen. HRD1 appears to target its substrates for ubiquitination through, either ERAD-dependent or -independent, at least two distinct molecular mechanisms in a cell or tissue specific manner to achieve its physiological functions. Dysregulation of HRD1 expression and/or it functions are involved in autoimmune inflammatory diseases in particular rheumatoid arthritis and lupus. Here, we review current findings on the mechanism of HRD1 protein in immune regulation and the involvement of HRD1 in the pathogenesis of autoimmune inflammatory diseases.

TRIM21 Dysfunction Enhances Aberrant B-Cell Differentiation in Autoimmune Pathogenesis

TRIM21 is one of the autoantigens that reacts with an anti-SS-A antibody (Ab) present in patients with systemic lupus erythematosus (SLE) and Sjögren's syndrome. TRIM21 is thought to play a role in B-cell proliferation and apoptosis, among other activities. Here we examined a pathological role of TRIM21 in SLE. Trim21-deficient MRL/lpr mice were generated by backcrossing Trim21-deficient C57BL/6 mice to MRL/lpr mice. The levels of serum anti-dsDNA Ab and urine protein at 28 weeks of age were significantly higher in Trim21-deficient MRL/lpr mice as compared to wild-type MRL/lpr mice (p = 0.029 and 0.003, respectively). Resting B cells from Trim21-deficient mice showed significantly higher abilities to differentiate into plasmablasts and to produce Ab as compared with control mice. Due to the reduction of TRIM21-mediated ubiquitylation, IRF5 protein expression was increased in Trim21-deficient MRL/lpr mice (p = 0.021), which correlated with increased plasmablast generation and immunoglobulin production. B cells from SLE patients with anti-TRIM21 Ab seropositivity also showed a significantly higher ability to differentiate into plasmablasts as compared with those without anti-TRIM21 Ab or healthy controls. These results suggest that TRIM21 dysfunction contributes to SLE pathogenesis by promoting B-cell differentiation, for which anti-TRIM21 Ab may be partly responsible.

TRIM21-mediated proteasomal degradation of SAMHD1 regulates its antiviral activity

SAMHD1 possesses multiple functions, but whether cellular factors regulate SAMHD1 expression or its function remains not well characterized. Here, by investigating why cultured RD and HEK293T cells show different sensitivity to enterovirus 71 (EV71) infection, we demonstrate that SAMHD1 is a restriction factor for EV71. Importantly, we identify TRIM21, an E3 ubiquitin ligase, as a key regulator of SAMHD1, which specifically interacts and degrades SAMHD1 through the proteasomal pathway. However, TRIM21 has no effect on EV71 replication itself. Moreover, we prove that interferon production stimulated by EV71 infection induces increased TRIM21 and SAMHD1 expression, whereas increasing TRIM21 overrides SAMHD1 inhibition of EV71 in cells and in a neonatal mouse model. TRIM21-mediated degradation of SAMHD1 also affects SAMHD1-dependent restriction of HIV-1 and the regulation of interferon production. We further identify the functional domains in TRIM21 required for SAMHD1 binding and the ubiquitination site K622 in SAMHD1 and show that phosphorylation of SAMHD1 at T592 also blocks EV71 restriction. Our findings illuminate how EV71 overcomes SAMHD1 inhibition via the upregulation of TRIM21.

To TRIM the Immunity: From Innate to Adaptive Immunity

The tripartite motif (TRIM) proteins have been intensively studied as essential modulators in various biological processes, especially in regulating a wide range of signaling pathways involved in immune responses. Most TRIM proteins have E3 ubiquitin ligase activity, mediating polyubiquitination of target proteins. Emerging evidence demonstrates that TRIM proteins play important roles in innate immunity by regulating pattern recognition receptors, vital adaptor proteins, kinases, and transcription factors in innate immune signaling pathways. Additionally, the critical roles of TRIM proteins in adaptive immunity, especially in T cell development and activation, are increasingly appreciated. In this review, we aim to summarize the studies on TRIMs in both innate and adaptive immunity, focusing on their E3 ubiquitin ligase functions in pattern recognition receptor signaling pathways and T cell functions, shedding light on the developing new strategies for modulating innate and adaptive immune responses against invading pathogens and avoiding autoimmunity.

TRIM21 controls Toll-like receptor 2 responses in bone-marrow-derived macrophages

TRIM21 is an interferon‐stimulated E3 ligase that controls the activity of pattern‐recognition signaling via ubiquitination of interferon regulatory factors and DDX41. Previous studies on the role of TRIM21 in innate immune responses have yielded contradictory results, suggesting that the role of TRIM21 is cell specific. Here, we report that bone‐marrow‐derived macrophages (BMDMs) generated from Trim21^−/− mice have reduced expression of mature macrophage markers. Reflecting their reduced differentiation in response to macrophage colony‐stimulating factor (M‐CSF), Trim21^−/− BMDMs had decreased expression of M‐CSF signature genes. Although Trim21^−/− BMDMs responded normally to Toll‐like receptor 9 (TLR9) activation, they produced lower levels of pro‐inflammatory cytokines in response to the TLR2 agonist PAM3CSK4. In line with this, the response to infection with the Bacillus Calmette–Guérin strain of Mycobacterium bovis was also diminished in Trim21^−/− BMDMs. Our results indicate that TRIM21 controls responses to TLR2 agonists.

TRIM21 Mitigates Human Lung Microvascular Endothelial Cells' Inflammatory Responses to LPS

Endothelial cell (EC) inflammation is regarded as an important pathogenic feature of many inflammatory diseases, including acute lung injury and sepsis. An increase in EC inflammation results in neutrophil infiltration from the blood to the site of inflammation, further promoting EC permeability. The ubiquitin E3 ligase TRIM21 has been implicated in human disorders; however, the roles of TRIM21 in endothelial dysfunction and acute lung injury have not been reported. Here, we reveal an antiinflammatory property of TRIM21 in a mouse model of acute lung injury and human lung microvascular ECs. Overexpression of TRIM21 by lentiviral vector infection effectively dampened LPS-induced neutrophil infiltration, cytokine release, and edema in mice. TRIM21 inhibited human lung microvascular endothelial cell inflammatory responses as evidenced by attenuation of the NF-κB pathway, release of IL-8, expression of intercellular adhesion molecules, and adhesion of monocytes to ECs. Furthermore, we demonstrated that TRIM21 was predominantly degraded by an increase in its monoubiquitination and lysosomal degradation after inflammatory stimuli. Thus, inhibition of vascular endothelial inflammation by TRIM21 provides a novel therapeutic target to lessen pulmonary inflammation.

[Association of polymorphisms of the TRIM21 gene with the severity of dry keratoconjunctivitis in rheumatoid arthritis and Sjogren's disease]

Ophthalmologic manifestation of Sjogren's disease (SD) and rheumatoid arthritis (RA) is dry keratoconjunctivitis (dry eye disease; DED).

PURPOSE

To study the relationship of polymorphic markers rs7947461 (C/T), rs915956 (C/T), rs4144331 (C/A) of the TRIM21 gene with the severity of DED in patients with RA and SD.

MATERIAL AND METHODS

The study included 70 patients with RA (n=27) and SD (n=43). The control group consisted of volunteers without a history of RA or SD (n=35). Alleles of the polymorphic marker C660T rs7947461 of the TRIM21 gene were identified using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method; alleles of the polymorphic marker rs915956 (C/T) and rs4144331 (C/A) of the TRIM21 gene were identified by analyzing DNA melting curves.

RESULTS

An association was found between the predisposing genotype (TT) of rs7947461 polymorphic marker and the risk of developing severe DED. The AA genotype of rs4144331 polymorphic marker was found only in severe DED (c²=7.74; OR=17.46, CI_95%=1.96-318.38, p=0.02).

CONCLUSION

An association was established between rs7947461 (rs660) and rs4144331 and the risk of developing severe DED.

Dual function of miR-1248 links interferon induction and calcium signaling defects in Sjögren's syndrome

BACKGROUND

Sjögren's syndrome (SS) is one of the most common autoimmune disorders leading to exocrine gland dysfunction. Both immune-dependent processes - like Type I Interferon (IFN) signaling and immune-independent processes - such as calcium signaling in epithelial cells - contribute to disease pathophysiology. However, a mechanistic link between these processes has not been demonstrated.

METHODS

Primary human salivary gland cells were used to evaluate the differential expression of miRNAs with smRNA-seq in primary epithelial cells culture and digital PCR was conducted in SS human salivary glands (SG) biopsies to verify the results. With siRNA screening and pull-down assays to establish the role of miRNA in IFN activation.

FINDINGS

Activation of IFN-β by miR-1248 is through the direct association with both RIG-I and AGO2. Further functional studies establish a unique dual functional role of miR-1248 in phSG cells: i) activation of the RIG-I pathway by acting as ligand of this sensor leading to IFN production and ii) regulation of the expression of mRNAs through the canonical microRNA function. Importantly, ITPR3, a key component of calcium signaling in epithelial cells, that has previously shown to be downregulated in SS SG, was directly targeted and downregulated by miR-1248, inducing the same functional calcium signaling changes as observed in SS SGs.

INTERPRETATION

Identification of the first endogenous mammalian microRNA that binds to RIG-I inducing IFN production but also demonstrate a novel pathophysiological underlying mechanism in which miR-1248 overexpression links two major pathways associated with SS, namely activation of IFN production with modulation of calcium signaling. Together, these findings suggest a unifying hypothesis for the immune-independent and -dependent processes contributing to the pathogenesis of SS. FUND: This research was supported by the Intramural Research Program of the National Institutes of Health (NIH), National Institute of Dental and Craniofacial Research (NIDCR).

Enhanced T-cell proliferation and IL-6 secretion mediated by overexpression of TRIM21 in oral lesions of patients with oral lichen planus

BACKGROUNDS

To explore the expression and functions of the tripartite motif-containing protein 21 (TRIM21) in oral lichen planus(OLP) lesions.

METHODS

Paraffin sections of buccal mucosa samples from 15 cases of reticular oral lichen planus (OLP) patients and 10 healthy controls were used for immunohistochemistry to determine expression and distribution of TRIM21. Buccal mucosae from 11 OLP patients and seven healthy controls were analyzed by qPCR to quantify its gene expression. Peripheral blood mononuclear cells and CD3+ cells from four pairs of age- and sex-matched OLP patients and healthy controls were isolated for immunocytochemistry and culture. Following lentivirus-mediated overexpression of TRIM21 gene in CD3+ cells, CCK-8 was applied to evaluate cell proliferation. Cytokines including IL-2, IL-4, IL-5, IL-6, IL-10, TNF-α, and IFN-γ in the supernatants were measured by the cytometric bead array and verified by ELISA.

RESULTS

A larger number of TRIM21-positive cells infiltrating the lamina propria were observed in OLP lesions by immunohistochemistry than those of healthy controls. Significantly higher transcription of TRIM21 was revealed by qPCR. TRIM21 overexpression in CD3+ cells significantly enhanced the proliferation and IL-6 secretion in CD3+ cells from 12 to 72 hours.

CONCLUSION

Overexpressed TRIM21 in OLP may be a primary proinflammatory molecule rather than a secondary and inducible regulatory factor in immunopathogenesis of OLP.

An update on the role of type I interferons in systemic lupus erythematosus and Sjögren's syndrome

PURPOSE OF REVIEW

Systemic lupus erythematosus (SLE) and primary Sjögren's syndrome (pSS) share several clinical and laboratory features, including an overexpression of type I interferon (IFN) regulated genes. The genetic background to this IFN signature and the role of the type I IFN system in the disease process have been partly clarified. Here, we summarize the latest information concerning the type I IFN system in both diseases.

RECENT FINDINGS

A number of gene variants in the type I IFN signalling pathways associate with an increased risk for both SLE and pSS in several ethnicities. The function of some risk gene variants has been elucidated, as well as the importance of epigenetic changes in type I IFN regulated genes. MicroRNA-451 and miR-302d have been shown to target IFN regulatory factor 8 and 9, suggesting that noncoding RNAs can control the IFN system. A prominent type I IFN activation is related to several disease manifestations, and in SLE to a more severe disease phenotype. Phase II studies in SLE suggest beneficial effects of blocking the type I IFN receptor.

SUMMARY

The activated type I IFN system in SLE and pSS has a strong genetic component, is important in the disease etiopathogenesis and can be targeted.

E3 ubiquitin-protein ligase TRIM21-mediated lysine capture by UBE2E1 reveals substrate-targeting mode of a ubiquitin-conjugating E2

The E3 ubiquitin-protein ligase TRIM21, of the RING-containing tripartite motif (TRIM) protein family, is a major autoantigen in autoimmune diseases and a modulator of innate immune signaling. Together with ubiquitin-conjugating enzyme E2 E1 (UBE2E1), TRIM21 acts both as an E3 ligase and as a substrate in autoubiquitination. We here report a 2.82-Å crystal structure of the human TRIM21 RING domain in complex with the human E2-conjugating UBE2E1 enzyme, in which a ubiquitin-targeted TRIM21 substrate lysine was captured in the UBE2E1 active site. The structure revealed that the direction of lysine entry is similar to that described for human proliferating cell nuclear antigen (PCNA), a small ubiquitin-like modifier (SUMO)-targeted substrate, and thus differs from the canonical SUMO-targeted substrate entry. In agreement, we found that critical UBE2E1 residues involved in the capture of the TRIM21 substrate lysine are conserved in ubiquitin-conjugating E2s, whereas residues critical for SUMOylation are not conserved. We noted that coordination of the acceptor lysine leads to remodeling of amino acid side-chain interactions between the UBE2E1 active site and the E2-E3 direct interface, including the so-called "linchpin" residue conserved in RING E3s and required for ubiquitination. The findings of our work support the notion that substrate lysine activation of an E2-E3-connecting allosteric path may trigger catalytic activity and contribute to the understanding of specific lysine targeting by ubiquitin-conjugating E2s.

Augmented Th17 differentiation in Trim21 deficiency promotes a stable phenotype of atherosclerotic plaques with high collagen content

Aims

Patients with hyperlipidemia are at risk of atherosclerosis, but not all develop cardiovascular disease, highlighting the importance of other risk factors such as inflammation. Both the innate and adaptive arms of the immune system have been suggested in the initiation and propagation of plaque formation. Tri-partite motif (TRIM) 21 is a regulator of tissue inflammation and pro-inflammatory cytokine production, and has been implicated in chronic inflammatory disease. Here, we investigate a potential role for TRIM21 in coronary artery disease.

Methods and results

Trim21-deficient or wild-type bone marrow was transplanted into Ldlr-/- mice fed a hypercholesterolemic diet. The Trim21-/-->Ldlr-/- mice developed larger atherosclerotic plaques, with significantly higher collagen content compared to mice transplanted with wild-type cells. High collagen content of the atheroma is stabilizing, and has recently been linked to IL-17. Interestingly, Trim21-/-->Ldlr-/- mice had elevated CD4 and IL-17 mRNA expression in plaques, and increased numbers of activated CD4+ T cells in the periphery. An increased differentiation of naïve T cells lacking Trim21 into Th17 cells was confirmed in vitro, with transcriptomic analysis revealing upregulation of genes of a non-pathogenic Th17 phenotype. Also, decreased expression of matrix metalloproteinases (MMPs) was noted in aortic plaques. Analysis of human carotid plaques confirmed that TRIM21 expression negatively correlates with the expression of key Th17 genes and collagen, but positively to MMPs also in patients, linking our findings to a clinical setting.

Conclusion

In this study, we demonstrate that TRIM21 influences atherosclerosis via regulation of Th17 responses, with TRIM21 deficiency promoting IL-17 expression and a more fibrous, stable, phenotype of the plaques.

Sex Effects on Gene Expression in Lacrimal Glands of Mouse Models of Sjögren Syndrome

Purpose

Sjögren syndrome is an autoimmune disease that occurs primarily in women, and is associated with lacrimal gland inflammation and aqueous-deficient dry eye. We hypothesize that sex-associated differences in lacrimal gland gene expression are very important in promoting lymphocyte accumulation in this tissue and contribute to the onset, progression, and/or severity of the inflammatory disease process. To test our hypothesis, we explored the nature and extent of sex-related differences in gene expression in autoimmune lacrimal glands.

Methods

Lacrimal glands were collected from age-matched, adult, male and female MRL/MpJ-Tnfrsf6^lpr (MRL/lpr) and nonobese diabetic/LtJ (NOD) mice. Glands were processed for the analysis of differentially expressed mRNAs by using CodeLink Bioarrays and Affymetrix GeneChips. Data were evaluated with bioinformatics and statistical software.

Results

Our results show that sex significantly influences the expression of thousands of genes in lacrimal glands of MRL/lpr and NOD mice. The immune nature of this glandular response is very dependent on the Sjögren syndrome model. Lacrimal glands of female, as compared with male, MRL/lpr mice contain a significant increase in the expression of genes related to inflammatory responses, antigen processing, and chemokine pathways. In contrast, it is the lacrimal tissue of NOD males, and not females, that presents with a significantly greater expression of immune-related genes.

Conclusions

These data support our hypothesis that sex-related differences in gene expression contribute to lacrimal gland disease in Sjögren syndrome. Our findings also suggest that factors in the lacrimal gland microenvironment are critically important in mediating these sex-associated immune effects.

Integrated Regulation of HuR by Translation Repression and Protein Degradation Determines Pulsatile Expression of p53 Under DNA Damage

Expression of tumor suppressor p53 is regulated at multiple levels, disruption of which often leads to cancer. We have adopted an approach combining computational systems modeling with experimental validation to elucidate the translation regulatory network that controls p53 expression post DNA damage. The RNA-binding protein HuR activates p53 mRNA translation in response to UVC-induced DNA damage in breast carcinoma cells. p53 and HuR levels show pulsatile change post UV irradiation. The computed model fitted with the observed pulse of p53 and HuR only when hypothetical regulators of synthesis and degradation of HuR were incorporated. miR-125b, a UV-responsive microRNA, was found to represses the translation of HuR mRNA. Furthermore, UV irradiation triggered proteasomal degradation of HuR mediated by an E3-ubiquitin ligase tripartite motif-containing 21 (TRIM21). The integrated action of miR-125b and TRIM21 constitutes an intricate control system that regulates pulsatile expression of HuR and p53 and determines cell viability in response to DNA damage.

Regulating IRFs in IFN Driven Disease

The Interferon regulatory factors (IRFs) are a family of transcription factors that play pivotal roles in many aspects of the immune response, including immune cell development and differentiation and regulating responses to pathogens. Three family members, IRF3, IRF5, and IRF7, are critical to production of type I interferons downstream of pathogen recognition receptors that detect viral RNA and DNA. A fourth family member, IRF9, regulates interferon-driven gene expression. In addition, IRF4, IRF8, and IRF5 regulate myeloid cell development and phenotype, thus playing important roles in regulating inflammatory responses. Thus, understanding how their levels and activity is regulated is of critical importance given that perturbations in either can result in dysregulated immune responses and potential autoimmune disease. This review will focus the role of IRF family members in regulating type I IFN production and responses and myeloid cell development or differentiation, with particular emphasis on how regulation of their levels and activity by ubiquitination and microRNAs may impact autoimmune disease.

Diagnostic Utility of Separate Anti-Ro60 and Anti-Ro52/TRIM21 Antibody Detection in Autoimmune Diseases

Anti-SS-A antibodies are often sought for in autoimmune diseases diagnosis. Two different target proteins have actually been identified: Ro52 and Ro60. Clinical and immunological associations seem different depending on anti-Ro52 or anti-Ro60 antibodies presence. However, due to a heterogeneous presentation in the literature, some immunology laboratories in France have stopped providing anti-Ro52 antibody findings. We report here a new hospital study designed to determine the diagnostic utility of the separate detection of anti-Ro52 and anti-Ro60 antibodies. We conducted a retrospective, observational study, including every adult patient with positive antinuclear antibodies (ANA) tested in our immunology laboratory, and associated with anti-Ro52 and/or anti-Ro60 antibodies, between 2011 and 2014. Out of 13032 sera tested for ANA, 399 adults had antibodies to Ro52 and/or Ro60; 81.7% were female, with a mean age of 54.5 ± 17.0 years. Anti-Ro52 antibodies were found in 75.7% of the patients and anti-Ro60 antibodies in 56.9%. Among them, 43.1% were classified in the Ro52 + Ro60- group, 32.6% in the Ro52 + Ro60 + group and 24.3% in the Ro52-Ro60+ group. In the Ro52-Ro60+ group, systemic lupus was the most frequent diagnosis (48.5%), with a possible association with antiphospholipid antibodies (anti-cardiolipin antibodies: OR 2.5 (CI95 [1.0-5.0], p = 0.05) and lupus anticoagulant {OR 3.6 (CI95 [1.10-10.0] p = 0.02)}. In the Ro52+Ro60+, primary Sjögren Syndrome was the most likely (OR 4.2 95% CI [2.1-8.3] p < 10^-4), especially in patients Ro52+Ro60+La+. Patients with isolated anti-Ro52 had a wider variety of diseases associated, but among auto-immune diseases they were more prone to inflammatory myositis (OR 10.5 [1.4-81.7], p = 0.02) and inflammatory rheumatism (OR 4.6 [1.6-13.8], p = 0.006) in contrast to systemic lupus (OR 0.2 [0.1-0.3], p < 10^-4) or primary Sjögren's syndrome (OR 0.1 [0.06-0.2], p < 10^-4). We therefore suggest that, when anti-ENA antibodies are prescribed, it should include separate anti-Ro52 and anti-Ro60 antibodies determination. To go even further, we would like to suggest a change in ENA nomenclature to avoid confusion, abandoning the anti-SS-A label in favor of the anti-Ro52/TRIM21 or anti-Ro60 antibody for a clearer designation.

Innate immunity and interferons in the pathogenesis of Sjögren's syndrome

Primary SS (pSS) is a rheumatic disease characterized by an immune-mediated exocrinopathy, resulting in severe dryness of eyes and mouth. Systemic symptoms include fatigue and joint pain and a subset of patients develop more severe disease with multi-organ involvement. Accumulating evidence points to involvement of innate immunity and aberrant activity of the type I IFN system in both the initiation and propagation of this disease. Analysis of the activity of IFN-inducible genes has evidenced that more than half of pSS patients present with a so-called 'type I IFN signature'. In this review, we examine activation of the IFN system in pSS patients and how this may drive autoimmunity through various immune cells. We further discuss the clinical value of assessing IFN activity as a biomarker in pSS patients and review novel therapies targeting IFN signalling and their potential use in pSS.

Anti-Ro60 Seropositivity Determines Anti-Ro52 Epitope Mapping in Patients With Systemic Sclerosis

Epitope mapping of anti-Ro52 antibodies (Abs) has been extensively studied in patients with Sjögren's syndrome (SjS) and systemic lupus erythematosus (SLE). Comprehensive epitope mapping in systemic sclerosis (SSc), where anti-Ro52 antibodies are also frequently detected, has not been performed. The aim of the present study was to fully characterize Ro52 epitopes in anti-Ro52-positive SSc using Ro52 fragments spanning the full antigen. Further analysis was made according to anti-Ro60 status. Epitope mapping was performed in 43 anti-Ro52-positive SSc patients. Seventy eight anti-Ro52-positive pathological controls, including 20 patients with SjS, 28 patients with SLE, 15 patients with dermatomyositis (DM), and 15 patients with primary biliary cholangitis (PBC), and 20 anti-Ro52-negative healthy individuals as normal controls were also tested. Five recombinant Ro52 fragments [Ro52-1 (aa 1-127), Ro52-2 (aa 125-268), Ro52-3 (aa 268-475), Ro52-4 (aa 57-180), and Ro52-5 (aa 181-320) were used to test reactivity by line-immunoassay and in house ELISA. Anti-Ro60 reactivity was tested by ELISA. All anti-Ro52 positive sera reacted with Ro52-2; none recognized Ro52-3. Antibodies against Ro52-1 were less frequently found in SSc than in SjS/SLE (11.6 vs. 41.7%, p = 0.001); and antibodies against Ro52-4 were less frequently found in SSc than in SjS/SLE (27.9 vs. 50%, p = 0.03). In SSc patients, reactivity against Ro52-1 was more frequent in anti-Ro52+/anti-Ro60+ than in anti-Ro52+/anti-Ro60-patients (33.3 vs. 0%, p = 0.003). In this comprehensive analysis of Ro52 epitope mapping in SSc, the coiled coil domain remains the predominant epitope on Ro52. Contrary to SjS and SLE, patients with SSc fail to identify epitopic regions within the N-terminus of the protein, especially if they lack con-current anti-Ro60 reactivity.

TRIM21 Restricts Coxsackievirus B3 Replication, Cardiac and Pancreatic Injury via Interacting With MAVS and Positively Regulating IRF3-Mediated Type-I Interferon Production

Tripartite motif-containing 21 (TRIM21) is a regulator of tissue inflammation and pro-inflammatory cytokine production, and has been implicated in negative regulation of IRF3-dependent type I interferon signaling. However, the antiviral activity of TRIM21 varies among diverse viruses and its role on regulation of type I interferon remains inconsistent in different microbial infections. Here, we investigate the potential role for TRIM21 in controlling Coxsackievirus B3 (CVB3) replication and susceptible organ pathology. We found that CVB3 infection up-regulated the expression of TRIM21 in hearts of mice and cardiomyocytes at early phase of infection. Knock-down of TRIM21 resulted in increased viral replication, while overexpression led to increased phosphorylation and dimerization of IRF3, increased IFN-β transcription and reduced viral replication in vitro. We demonstrate that TRIM21 promotes the activation of IRF3 in CVB3-infected cells via interacting with MAVS and catalyzing the K27-linked polyubiquitination of MAVS, thereby enhancing type I interferon signaling. The RING domain of ubiquitin ligase activity and PRY-SPRY domain of TRIM21 are critical for its anti-viral effect. In vivo overexpression of TRIM21 significantly protected mice against viral myocarditis by suppressing CVB3 replication and reducing cardiac inflammatory cytokine production. While TRIM21 deficient mice exhibited a decreased IFN-β production, an increased cardiac and pancreatic CVB3 replication, and aggravated pancreatic injury as well as myocarditis during acute infection. Thus, our results demonstrate TRIM21 as a positive regulator of IFN-β signaling by targeting MAVS during CVB3 infection and suggest it as a potent host defense against CVB3 infection and viral-induced injury in hearts and pancreas.

A novel elastin-like polypeptide drug carrier for cyclosporine A improves tear flow in a mouse model of Sjögren's syndrome

As a potent macrolide immunosuppressant, cyclosporine A (CsA) is used to treat multiple autoimmune diseases, including non-autoimmune and autoimmune-mediated dry eye disease, rheumatoid arthritis and psoriasis. Despite its potency, CsA has poor solubility, poor bioavailability, and can cause serious adverse reactions such as nephrotoxicity and neurotoxicity. To overcome these limitations, we invented a new strategy to carry CsA by fusing its cognate human receptor, cyclophilin A (CypA), to a 73 kDa elastin-like polypeptide (ELP) termed A192 using recombinant protein expression. Derived from human tropoelastin, ELPs are characterized by the ability to phase separate above a temperature that is a function of variables including concentration, molecular weight, and hydrophobicity. The resultant fusion protein, termed CA192, which assembles into a dimeric species in solution, effectively binds and solubilizes CsA with a K_d of 189 nM, comparable to that of endogenous CypA with a K_d of 35.5 nM. The release profile of CsA from CA192 follows a one phase decay model with a half-life of 957.3 h without a burst release stage. Moreover, CA192-CsA inhibited IL-2 expression induced in Jurkat cells through the calcineurin-NFAT signaling pathway with an IC₅₀ of 1.2 nM, comparable to that of free CsA with an IC₅₀ of 0.5 nM. The intravenous pharmacokinetics of CA192 followed a two-compartment model with a mean residence time of 7.3 h. Subcutaneous administration revealed a bioavailability of 30% and a mean residence time of 15.9 h. When given subcutaneously for 2 weeks starting at 14 weeks in male non-obese diabetic (NOD) mice, a model of autoimmune dacryoadenitis used to study Sjögren's syndrome (SS), CA192-CsA (2.5 mg/kg, every other day) significantly (p = 0.014) increased tear production relative to CA192 alone. Moreover, CA192 delivery reduced indications of CsA nephrotoxicity relative to free CsA. CA192 represents a viable new approach to deliver this effective but nephrotoxic agent in a modality that preserves therapeutic efficacy but suppresses drug toxicity.

The Sjögren's syndrome-associated autoantigen Ro52/TRIM21 modulates follicular B cell homeostasis and immunoglobulin production

Systemic rheumatic diseases are characterized by abnormal B cell activation with autoantibody production and hypergammaglobulinaemia. Ro52/SSA, also denoted tripartite motif (TRIM)21, is a major autoantigen in Sjögren's syndrome and systemic lupus erythematosus. Interestingly, TRIM21-deficient mice develop systemic autoimmunity with B cell-driven manifestations such as autoantibodies, hypergammaglobulinaemia and glomerulonephritis following tissue injury. The mechanisms by which TRIM21-deficiency leads to enhanced B cell activation and antibody production are, however, not well understood, and to further elucidate the role of TRIM21 in systemic autoimmunity, we investigated the B cell phenotype and antibody responses of Trim21^-/- mice following immunization with thymus-dependent (TD) and thymus-independent (TI) antigens. We found that TRIM21-deficient mice developed significantly higher specific antibody titres than their wild-type counterparts upon B cell receptor (BCR) engagement by TD and TI type II antigens, and this was accompanied by an altered B cell phenotype. Furthermore, BCR cross-linking, but not anti-CD40 stimulation, in vitro resulted in a significantly higher proliferation of Trim21^-/- cells. We also observed that splenic follicular B cells were expanded not only in immunized mice but also already in young, unmanipulated Trim21^-/- mice, and transcriptomic analysis of these cells revealed an up-regulation of genes associated with B cell differentiation, indicating a role for TRIM21 in their regulation. In conclusion, in this study we describe a link between the rheumatic autoantigen Ro52/TRIM21 and increased antibody production associated with follicular B cell expansion, implicating a potential role for Ro52/TRIM21 in the pathogenesis of systemic autoimmune diseases.

A retrospective analysis of distinguishing features of chest HRCT and clinical manifestation in primary Sjögren's syndrome-related interstitial lung disease in a Chinese population

To characterize the distinctive chest high-resolution computerized tomography (HRCT) features and clinical manifestations of primary Sjögren syndrome (pSS)-related interstitial lung disease (ILD). The demographic data, clinical manifestations, and laboratory and radiological findings of 527 pSS patients were retrospectively analyzed. ILD was defined based on the presences of pulmonary signs in HRCT. Two hundred six of 527 patients were diagnosed as pSS-ILD, and the prevalence was 39.1%. The three most frequent abnormalities in HRCT were reticular pattern (92.7%), ground-glass attenuation (87.4%), and bronchovascular bundle thickening (82%). One hundred twenty-four cases (60.2%) of the pSS-ILD patients had only a single HRCT pattern, which involved 86 non-specific interstitial pneumonitis (NSIP) cases (41.7%), 22 usual interstitial pneumonia (UIP) cases (10.68%), 8 organizing pneumonia (OP) cases (3.9%), and 8 lymphocytic interstitial pneumonia (LIP) cases (3.9%), respectively. Besides, the more important observation was that 82 cases had no less than two HRCT patterns, and NSIP admixed with OP (43.9%), NSIP admixed with UIP (35.4%), and NSIP admixed with LIP (19.5%) were the most frequent. HRCT of pSS-ILD patients demonstrated bilateral infiltrates (99%), with abnormalities predominantly in the lower lobes (89.3%) and subpleural areas (81.1%), and a few lesions were characterized by hilum distributed (8.7%). Pulmonary function tests (PFTs) revealed impaired diffusion capacity for carbon monoxide and total lung capacity, and the rate of small airway lesions in the pSS-ILD patients was 3.5 times higher in patients of pSS. Logistic regression analysis showed that dry cough (OR 59.05), clubbing (OR 6.26), elevated lactate dehydrogenase (OR 21.38) and positive anti-Ro (OR 7.86) were relevant factors of pSS-ILD. ILD is the common pulmonary involvement of pSS and the prevalence of pSS-ILD is 39.1%. The single pattern of NSIP and UIP in HRCT are the commonest, and about 40% of the pSS-ILD patients possess multiple patterns in HRCT. The classification of idiopathic pulmonary fibrosis cannot completely include the pulmonary imaging features of pSS-ILD.

Advances and challenges in targeting IRF5, a key regulator of inflammation

Interferon regulatory factor 5 (IRF5) belongs to a family of transcription factors, originally implicated in antiviral responses and interferon production. However, studies conducted in different laboratories over the last decade have placed IRF5 as a central regulator of the inflammatory response. It has become clear that IRF5 contributes to the pathogenesis of many inflammatory and autoimmune diseases, such as rheumatoid arthritis, inflammatory bowel disease and systemic lupus erythematosus. Given the role of IRF5 in physiology and disease, IRF5 represents a potential therapeutic target. However, despite a significant interest from the pharmaceutical industry, inhibitors that interfere with the IRF5 pathway remain elusive. Here, we review the advances made by various studies in targeting multiple steps of signalling leading to IRF5 activation with their therapeutic potential, and the possible complications of such strategies are discussed.

Na+-Cl- cotransporter-mediated chloride uptake contributes to hypertension and renal damage in aldosterone-infused rats

Recently, in addition to epithelial sodium channel alpha-subunit (αENaC), the thiazide-sensitive sodium-chloride cotransporter (NCC) and pendrin, also known as sodium-independent chloride/iodide transporter, were reported to be activated by aldosterone. Here, we investigated whether chloride (Cl^-) is responsible for hypertension, inflammation, and renal damage in aldosterone-infused rats. Following left nephrectomy, 8-wk-old male Sprague-Dawley rats were allocated into four groups: 1) drinking 1.0% sodium chloride solution with aldosterone infusion (Aldo/NaCl rats); 2) drinking 1.44% sodium bicarbonate solution with aldosterone infusion (Aldo/NaHCO₃ rats); 3) drinking distilled water with aldosterone infusion (Aldo/water rats); and 4) drinking distilled water without aldosterone infusion (sham rats). Additionally, heminephrectomized rats with aldosterone infusion were fed a 0.26% NaCl diet (control); 8.0% NaCl diet (high-Na/high-Cl); or a 4.0% NaCl 6.67% sodium citrate diet (high-Na/half-Cl). Last, Aldo/NaCl rats were treated with or without hydrochlorothiazide. Blood pressure in the Aldo/NaCl rats was significantly higher than in the Aldo/NaHCO₃ rats, which was associated with the increased expression of NCC. Expression of markers of inflammation (CD3, CD68, interleukin-17A) and fibrosis (α-smooth muscle actin, collagen 1) were also increased in Aldo/NaCl rats. Similarly, aldosterone-infused rats fed a high-Na/half-Cl diet had lower blood pressure than those fed a high-Na/high-Cl diet, with a reduction of phosphorylated NCC, but not αENaC and pendrin. NCC inhibition with hydrochlorothiazide attenuated interleukin-17A protein expression along with the phosphorylation of NCC in Aldo/NaCl rats. These findings suggest that NCC-mediated Cl^- uptake plays important roles in the development of aldosterone-induced hypertension and renal injury.

Update on Pathogenesis of Sjogren's Syndrome

Sjogren's syndrome is a common autoimmune disease that presents with sicca symptoms and extraglandular features. Sjogren's syndrome is presumably as common as RA; yet it is poorly understood, underdiagnosed and undertreated. From the usual identity as an autoimmune exocrinopathy to its most recent designate as an autoimmune epithelitis - the journey of SS is complex. We herein review some of the most important milestones that have shed light on different aspects of pathogenesis of this enigmatic disease. This includes role of salivary gland epithelial cells, and their interaction with cells of the innate and adaptive immune system. Non-immune factors acting in concert or in parallel with immune factors may also be important. The risk genes identified so far have only weak association, nevertheless advances in genetics have enhanced understanding of disease mechanisms. Role of epigenetic and environmental role factors is also being explored. SS has also some unique features such as congenital heart block and high incidence of lymphoma; disease mechanisms accounting for these manifestations are also reviewed.

A systematic view on E3 ligase Ring TRIMmers with a focus on cardiac function and disease

Ubiquitination, a post-translational modification via ubiquitin-proteasome-system, is one of the vital cellular processes involved in intracellular signaling, cell death, transcriptional control, etc. Importantly, it prevents the aggregation of non-functional, misfolded or unfolded, potentially toxic proteins to maintain cellular protein homeostasis. Ubiquitination is accomplished by the concerted action of three enzymatic steps involving E1 activating enzymes, E2 conjugating enzymes, and E3 ligases. Tripartite motif-containing (TRIM) proteins are one of the integral members of E3 ubiquitin ligases in metazoans modulating essential cellular pathways. For long, MuRFs (Muscle ring finger proteins) were the most extensively studied TRIMs for their cardiac function. Recent research advances in the field and our analysis presented here, however, demonstrated broader and ever increasing involvement of additional TRIM E3 ligases in the pathophysiology of heart. In this review, we summarize the known cardiac E3 ligases and their targets, and discuss their role and importance in cardiac proteostasis, pathophysiology and potential therapeutic implications with specific focus on TRIM E3 ligases.

Hydroxychloroquine Inhibits the Differentiation of Th17 Cells in Systemic Lupus Erythematosus

Objective.

Hydroxychloroquine (HCQ) is a commonly used medicine for the treatment of systemic lupus erythematosus (SLE), and Th17 cells are closely related to the pathogenesis of SLE. However, the role and mechanism of HCQ on Th17 cell differentiation in SLE is not clearly understood. Here, we investigate the effect of HCQ on Th17 cell differentiation bothin vitroand in patients with SLE.

Methods.

Twenty-five patients with SLE were divided into 2 treatment groups: prednisone alone and HCQ plus prednisone. Interleukin 17 (IL-17) expression was analyzed by ELISA and real-time (RT)-PCR. Th17 were measured in patients with SLE by flow cytometry before and after HCQ treatment.In vitro, naive T cells were cultured in Th17-inducing conditions with or without HCQ. Cell differentiation and IL-17 expression were analyzed. Finally, transcriptome sequencing identified differential gene expression between naive T cells and induced Th17 cells.

Results.

In patients, HCQ plus prednisone treatment inhibited IL-17 production, gene expression, and Th17 cell differentiation.In vitro, HCQ inhibited Th17 cell proliferation and differentiation, as well as IL-17 production. Five microRNA were significantly different in Th17 cells compared with naive T cells, and HCQ treatment reversed this effect.In vivo, microRNA-590 (miR-590) was verified and was significantly decreased in Th17 cells, compared with naive T cells from lupus-prone mice. Moreover, miR-590 was increased in patients treated with HCQ plus prednisone.

Conclusion.

HCQ inhibited Th17 cell differentiation and IL-17 production bothin vitroand in patients with SLE. Our study provides additional evidence for HCQ as a treatment for SLE.

Dysfunction of TRIM21 in interferon signature of systemic lupus erythematosus

OBJECTIVES

TRIM21 is an E3 ubiquitin ligase for interferon regulatory factors (IRFs) that are involved in innate and acquired immunity. Here, we evaluated the role of TRIM21 in the interferon (IFN) signature of systemic lupus erythematosus (SLE).

METHODS

Twenty SLE patients and 24 healthy controls were enrolled in this study. We analyzed mRNA expression of TRIM21, type I IFN, and IFN-inducible genes in peripheral blood mononuclear cell (PBMC). The protein levels of IRFs were assessed by Western blotting in PBMCs cultured with or without MG-132.

RESULTS

The expression of TRIM21 mRNA and protein was significantly higher in SLE PBMCs as compared to healthy controls. There was a correlation between TRIM21 mRNA expression and SLE activities. In contrast to a negative correlation between mRNA expression level of TRIM21 and those of type I IFNs in healthy controls, we found a positive correlation between them in anti-TRIM21 antibody-positive SLE patients. Neither positive nor negative correlation was observed in the autoantibody-negative SLE patients. Western-blotting analysis revealed impaired ubiquitin-dependent proteasomal degradation of IRFs in SLE PBMCs.

CONCLUSION

Our study showed ubiquitin-dependent proteasomal degradation of IRFs was impaired in anti-TRIM21 antibody-dependent and -independent fashions, leading to amplification of IFN signature in SLE.

Intracellular Antiviral Immunity

Innate immunity is traditionally thought of as the first line of defense against pathogens that enter the body. It is typically characterized as a rather weak defense mechanism, designed to restrict pathogen replication until the adaptive immune response generates a tailored response and eliminates the infectious agent. However, intensive research in recent years has resulted in better understanding of innate immunity as well as the discovery of many effector proteins, revealing its numerous powerful mechanisms to defend the host. Furthermore, this research has demonstrated that it is simplistic to strictly separate adaptive and innate immune functions since these two systems often work synergistically rather than sequentially. Here, we provide a broad overview of innate pattern recognition receptors in antiviral defense, with a focus on the TRIM family, and discuss their signaling pathways and mechanisms of action with special emphasis on the intracellular antibody receptor TRIM21.

Rhesus monkey TRIM5α protein SPRY domain contributes to AP-1 activation

TRIM5α is an important host restriction factor that could potently block retrovirus infection. The SPRY domain of TRIM5α mediates post-entry restriction by recognition of and binding to the retroviral capsid. Human TRIM5α also functions as an innate immune sensor to activate AP-1 and NF-κB signaling, which subsequently restrict virus replication. Previous studies have shown that the AP-1 and NF-κB signaling activation relies on the RING motif of TRIM5α. In this study, we have demonstrated that the SPRY domain is essential for rhesus macaque TRIM5α to activate AP-1 but not NF-κB signaling. The AP-1 activation mainly depends on all of the β-sheet barrel on SPRY structure of TRIM5α. Furthermore, the SPRY-mediated auto-ubiquitination of TRIM5α is required for AP-1 activation. This study reports that rhesus macaque TRIM5α mainly undergoes Lys²⁷-linked and Met¹-linked auto-polyubiquitination. Finally, we found that the TRIM5α signaling function was positively correlated with its retroviral restriction activity. This study discovered an important role of the SPRY domain in immune signaling and antiviral activity and further expanded our knowledge of the antiviral mechanism of TRIM5α.

H1N1 vaccination in Sjögren's syndrome triggers polyclonal B cell activation and promotes autoantibody production

OBJECTIVES

Vaccination of patients with rheumatic disease has been reported to result in lower antibody titres than in healthy individuals. However, studies primarily include patients on immunosuppressive therapy. Here, we investigated the immune response of treatment-naïve patients diagnosed with primary Sjögren's syndrome (pSS) to an H1N1 influenza vaccine.

METHODS

Patients with Sjögren's syndrome without immunomodulatory treatment and age-matched and gender-matched healthy controls were immunised with an H1N1 influenza vaccine and monitored for serological and cellular immune responses. Clinical symptoms were monitored with a standardised form. IgG class switch and plasma cell differentiation were induced in vitro in purified naïve B cells of untreated and hydroxychloroquine-treated patients and healthy controls. Gene expression was assessed by NanoString technology.

RESULTS

Surprisingly, treatment-naïve patients with Sjögren's syndrome developed higher H1N1 IgG titres of greater avidity than healthy controls on vaccination. Notably, off-target B cells were also triggered resulting in increased anti-EBV and autoantibody titres. Endosomal toll-like receptor activation of naïve B cells in vitro revealed a greater propensity of patient-derived cells to differentiate into plasmablasts and higher production of class switched IgG. The amplified plasma cell differentiation and class switch could be induced in cells from healthy donors by preincubation with type 1 interferon, but was abolished in hydroxychloroquine-treated patients and after in vitro exposure of naïve B cells to chloroquine.

CONCLUSIONS

This comprehensive analysis of the immune response in autoimmune patients to exogenous stimulation identifies a mechanistic basis for the B cell hyperactivity in Sjögren's syndrome, and suggests that caution is warranted when considering vaccination in non-treated autoimmune patients.

Ubiquitin enzymes in the regulation of immune responses

Ubiquitination plays a central role in the regulation of various biological functions including immune responses. Ubiquitination is induced by a cascade of enzymatic reactions by E1 ubiquitin activating enzyme, E2 ubiquitin conjugating enzyme, and E3 ubiquitin ligase, and reversed by deubiquitinases. Depending on the enzymes, specific linkage types of ubiquitin chains are generated or hydrolyzed. Because different linkage types of ubiquitin chains control the fate of the substrate, understanding the regulatory mechanisms of ubiquitin enzymes is central. In this review, we highlight the most recent knowledge of ubiquitination in the immune signaling cascades including the T cell and B cell signaling cascades as well as the TNF signaling cascade regulated by various ubiquitin enzymes. Furthermore, we highlight the TRIM ubiquitin ligase family as one of the examples of critical E3 ubiquitin ligases in the regulation of immune responses.

Solution NMR structure of the TRIM21 B-box2 and identification of residues involved in its interaction with the RING domain

Tripartite motif-containing (TRIM) proteins are defined by the sequential arrangement of RING, B-box and coiled-coil domains (RBCC), where the B-box domain is a unique feature of the TRIM protein family. TRIM21 is an E3 ubiquitin-protein ligase implicated in innate immune signaling by acting as an autoantigen and by modifying interferon regulatory factors. Here we report the three-dimensional solution structure of the TRIM21 B-box2 domain by nuclear magnetic resonance (NMR) spectroscopy. The structure of the B-box2 domain, comprising TRIM21 residues 86-130, consists of a short α-helical segment with an N-terminal short β-strand and two anti-parallel β-strands jointly found the core, and adopts a RING-like fold. This ββαβ core largely defines the overall fold of the TRIM21 B-box2 and the coordination of one Zn2+ ion stabilizes the tertiary structure of the protein. Using NMR titration experiments, we have identified an exposed interaction surface, a novel interaction patch where the B-box2 is likely to bind the N-terminal RING domain. Our structure together with comparisons with other TRIM B-box domains jointly reveal how its different surfaces are employed for various modular interactions, and provides extended understanding of how this domain relates to flanking domains in TRIM proteins.

New insights into the immunopathogenesis of systemic lupus erythematosus

The aetiology of systemic lupus erythematosus (SLE) is multifactorial, and includes contributions from the environment, stochastic factors, and genetic susceptibility. Great gains have been made in understanding SLE through the use of genetic variant identification, mouse models, gene expression studies, and epigenetic analyses. Collectively, these studies support the concept that defective clearance of immune complexes and biological waste (such as apoptotic cells), neutrophil extracellular traps, nucleic acid sensing, lymphocyte signalling, and interferon production pathways are all central to loss of tolerance and tissue damage. Increased understanding of the pathogenesis of SLE is driving a renewed interest in targeted therapy, and researchers are now on the verge of developing targeted immunotherapy directed at treating either specific organ system involvement or specific subsets of patients with SLE. Accordingly, this Review places these insights within the context of our current understanding of the pathogenesis of SLE and highlights pathways that are ripe for therapeutic targeting.