Current and Emerging Evidence for Toll-Like Receptor Activation in Sjögren's Syndrome

Primary Sjögren's syndrome independently promotes premature subclinical atherosclerosis

OBJECTIVES

Cardiovascular comorbidities are common in patients with autoimmune diseases. This study investigates the extent of subclinical atherosclerosis in patients with primary Sjögren's syndrome (pSS). Correlations with clinical factors such as organ involvement (OI) or disease activity were analysed and oxLDL antibodies (oxLDL ab) were measured as potential biomarkers of vascular damage.

METHODS

Patients with pSS were consecutively included from the rheumatology outpatient clinic. Age- and sex-matched controls were recruited (2:1 ratio). Data collection was performed by a standardised questionnaire and Doppler ultrasound to evaluate the plaque extent and carotid intima-media thickness (cIMT). Propensity score matching included all cardiovascular risk (CVR) factors and corresponding laboratory markers.

RESULTS

Data were available for 299 participants (199 pSS/100 controls), aged 59.4 years (50.6-65.0), 19.1% male. After matching, the pSS cohort had greater cIMT (p<0.001) and plaque extent (OR=1.82; 95% CI 1.14 to 2.95). Subgroup analyses of patients with pSS revealed that OI was associated with increased cIMT (p=0.025) and increased plaque occurrence compared with patients without OI (OR=1.74; 95% CI 1.02 to 3.01). OxLDL ab tended to be lower in patients with plaque (p=0.052). Correlations of higher Oxidized Low Density Lipoprotein (oxLDL) ab with EULAR Sjögren's Syndrome Disease Activity Index (p<0.001) and anti-Sjögren's-syndrome-related antigen A autoantibodies (SSA/Ro antibodies) (p=0.026) were observed.

CONCLUSIONS

Subclinical atherosclerosis occurs earlier and more severely in patients with pSS. The difference in cIMT between pSS and controls seems mainly driven by patients with OI, suggesting that this subgroup is particularly at risk. OxLDL ab might protect against atherosclerotic progression in patients with pSS. CVR stratification and preventive medications such as Hydroxymethylglutaryl-CoA (HMG-CoA) reductase inhibitors should be discussed and further longitudinal studies are needed.

Computational inhibition of S100A8 (calgranulin A) as a potential non-invasive biomarker for rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic joint pain and inflammation, loss of mobility, which affects the quality of life. The etiology of RA is unknown, and there is no isolated cause for the development of this illness. Synovial inflammation, autoantibody generation and bone degradation leading to deformity are classic characteristics of RA. The search for a non-invasive biomarker is crucial for helping patients receive standard therapies leading to faster treatments, as diagnosis depends on invasive biopsies. Therefore, in the present investigation, using transcriptomics and proteomic approaches, potential genes involved in crucial networks in RA were identified. Gene expression datasets of two tissue types i.e. whole blood and synovial tissue were retrieved from the GEO database and used for transcriptomic analyses. Using SWATH-MS analysis, differentially expressed proteins were identified from collected saliva of RA patients. Through bioinformatics analysis, S100A8, also known as Calprotectin (a complex of S100A8/A9) or Calgranulin A, was found to be common among all tissue types. S100A8 was then further quantified in saliva of healthy volunteers and RA patients, where it was found that the protein's level in healthy controls was lowered when compared to RA patients. Through in-silico characterization, potential plant-based inhibitors of S100A8 were also identified, to reduce its pro-inflammatory effects. Thus, it may be important in the pathophysiology of RA and, in the future, might help guide targeted treatment. as well as act as a non-invasive diagnostic biomarker platform.

Identification and verification of inflammatory biomarkers for primary Sjögren's syndrome

INTRODUCTION

Primary Sjögren's syndrome (pSS) is an autoimmune disease characterized by inflammatory infiltration, and dysfunction of the salivary and lacrimal glands. This research aimed to explore the disease pathogenesis and improve the diagnosis and treatment of pSS by mining inflammation-associated biomarkers.

METHODS

Five pSS-related datasets were retrieved from the Gene Expression Omnibus (GEO) database. Inflammation-associated biomarkers were determined by the least absolute shrinkage and selection operator (LASSO) and support vector machines recursive feature elimination (SVM-RFE). Single sample gene set enrichment analysis (ssGSEA) was implemented to profile the infiltration levels of immune cells. Real-time quantitative PCR (RT-qPCR) verified the expression of biomarkers in clinical samples.

RESULTS

Four genes (LY6E, EIF2AK2, IL15, and CXCL10) were screened as inflammation-associated biomarkers in pSS, the predictive performance of which were determined among three pSS-related datasets (AUC > 0.7). Functional enrichment results suggested that the biomarkers were involved in immune and inflammation-related pathways. Immune infiltration analysis revealed that biomarkers were notably connected with type 2 T helper cells, regulatory T cells which were significantly expressed between pSS and control. TESTOSTERONE and CYCLOSPORINE were predicted to take effect by targeting CXCL10 and IL15 in pSS, respectively.

CONCLUSION

Four inflammation-associated biomarkers (LY6E, EIF2AK2, IL15, and CXCL10) were explored, and the underlying regulatory mechanisms and targeted drugs associated with these biomarkers were preliminarily investigated according to a series of bioinformatics methods based on the online datasets of pSS, which provided a reference for understanding the pathogenesis of pSS. Key Points • Inflammation-associated biomarkers (LY6E, EIF2AK2, IL15, and CXCL10) were firstly identified in Sjögren's syndrome based on LASSO and SVM-RFE analyses. • CXCL10, EIF2AK2 and LY6E were prominently positively correlated with immature B cells, while IL15 were significantly negatively correlated with memory B cells in Sjögren's syndrome. • LY6E, EIF2AK2, IL15, and CXCL10 were significantly more highly expressed in clinical Sjögren's syndrome samples compared to healthy control samples, which was consistent with the analysis results of the GEO database. •LY6E, EIF2AK2, IL15, and CXCL10 might be used as the biomarkers for the treatment and diagnosis of Sjögren's syndrome.

TLR7 activation of age-associated B cells mediates disease in a mouse model of primary Sjögren's disease

Primary Sjögren's disease (pSD) (also referred to as Sjögren's syndrome) is an autoimmune disease that primarily occurs in women. In addition to exocrine gland dysfunction, pSD patients exhibit B cell hyperactivity. B cell-intrinsic TLR7 activation is integral to the pathogenesis of systemic lupus erythematosus, a disease that shares similarities with pSD. The role of TLR7-mediated B cell activation in pSD, however, remains poorly understood. We hypothesized that age-associated B cells (ABCs) were expanded in pSD and that TLR7-stimulated ABCs exhibited pathogenic features characteristic of disease. Our data revealed that ABC expansion and TLR7 expression were enhanced in a pSD mouse model in a Myd88-dependent manner. Splenocytes from pSD mice showed enhanced sensitivity to TLR7 agonism as compared with those derived from control animals. Sort-purified marginal zone B cells and ABCs from pSD mice showed enhanced inflammatory cytokine secretion and were enriched for antinuclear autoantibodies following TLR7 agonism. Finally, IgG from pSD patient sera showed elevated antinuclear autoantibodies, many of which were secreted preferentially by TLR7-stimulated murine marginal zone B cells and ABCs. These data indicate that pSD B cells are hyperresponsive to TLR7 agonism and that TLR7-activated B cells contribute to pSD through cytokine and autoantibody production. Thus, therapeutics that target TLR7 signaling cascades in B cells may have utility in pSD patients.

The Role of Regulatory T Cells in the Onset and Progression of Primary Sjögren's Syndrome

Regulatory T cells (Tregs) play a key role in maintaining immune balance and regulating the loss of self-tolerance mechanisms in various autoimmune diseases, including primary Sjögren's syndrome (pSS). With the development of pSS primarily in the exocrine glands, lymphocytic infiltration occurs in the early stages, mainly due to activated CD4⁺ T cells. Subsequently, in the absence of rational therapy, patients develop ectopic lymphoid structures and lymphomas. While the suppression of autoactivated CD4⁺ T cells is involved in the pathological process, the main role belongs to Tregs, making them a target for research and possible regenerative therapy. However, the available information about their role in the onset and progression of this disease seems unsystematized and, in certain aspects, controversial. In our review, we aimed to organize the data on the role of Tregs in the pathogenesis of pSS, as well as to discuss possible strategies of cell therapy for this disease. This review provides information on the differentiation, activation, and suppressive functions of Tregs and the role of the FoxP3 protein in these processes. It also highlights data on various subpopulations of Tregs in pSS, their proportion in the peripheral blood and minor salivary glands of patients as well as their role in the development of ectopic lymphoid structures. Our data emphasize the need for further research on Tregs and highlight their potential use as a cell-based therapy.

Relationship between Chinese Herbal Medicine Use and Risk of Sjögren’s Syndrome in Patients with Rheumatoid Arthritis: A Retrospective, Population-Based, Nested Case-Control Study

Background and Objectives: Sjögren’s Syndrome (SS) is a common extra-articular feature among subjects with rheumatoid arthritis (RA). While Chinese herbal medicine (CHM) has been used to treat symptoms of RA for many years, few studies have examined its efficacy in guarding against the SS onset. This study aimed to compare risk of SS for RA patients with and without use of CHM. Materials and Methods: Data obtained for this nested case-control study were retrieved from Taiwanese nationwide insurance database from 2000–2013. Cases with SS claims were defined and matched to two randomly selected controls without SS from the recruited RA cohorts. Risk of SS in relation to CHM use was estimated by fitting multiple conditional logistic regression. Results: Patients aged between 20 and 80 years were included and 916 patients with incident SS were matched to 1832 non-SS controls by age, sex and index year. Among them, 28.1% and 48.4% cases ever received CHM therapy, respectively. After adjusting for baseline characteristics, CHM use was found to be related to a lower risk of SS among them (adjusted odds ratio = 0.40, 95% confidence interval: 0.34–0.47). A dose-dependent, reverse association, was further detected between the cumulative duration of CHM use and SS risk. Those receiving CHM therapy for more than 730 days showed a significantly reduced risk of SS by 83%. Conclusions: Findings of this study indicated that the add-on CHM formula, as part of RA care, may be a beneficial treatment for prevention against the incident SS.

Melatonin: a potential therapeutic approach for the management of primary Sjögren's syndrome

Primary Sjögren's syndrome (pSS) is an autoimmune disease that primarily affects the exocrine glands and is mainly characterized by sicca symptoms of the eyes and mouth. Approximately 30-50% of pSS patients develop systemic multi-organ disorders including malignant lymphoma. The etiology of pSS is not well understood; growing evidence suggests that uncontrolled immune/inflammatory responses, excessive oxidative stress, defected apoptosis, dysregulated autophagy, exosomes, and exogenous virus infections may participate in the pathogenesis of pSS. There is no ideal therapeutic method for pSS; the management of pSS is mainly palliative, which aims to alleviate sicca symptoms. Melatonin, as the main secretory product of the pineal gland, has been evidenced to show various physiological functions, including effects of immunoregulation, capability of antioxidation, moderation of autophagy, suppressive activities of apoptosis, regulative capacity of exosomes, properties of anti-infection, and improvement of sleep. The beneficial effects of melatonin have been already validated in some autoimmune diseases such as multiple sclerosis (MS), type 1 diabetes mellitus (T1DM), systemic lupus erythematosus (SLE), and inflammatory bowel disease (IBD). However, our previous research firstly revealed that melatonin might inhibit pathogenic responses of peripheral Th17 and double-negative (DN) T cells in pSS. More importantly, melatonin administration alleviated the development of pSS in animal models with reduced infiltrating lymphocytes, improved functional activity of salivary gland, and decreased production of inflammatory factors as well as autoantibodies. Owing to the important biological properties reported in melatonin are characteristics closely related to the treatment of pSS; the potential role and underlying mechanisms of melatonin in the administration of pSS are certainly worth further investigations. Consequently, the aim of this review is to give a deep insight to the therapeutic potency of melatonin for pSS.

An Overview of the Dry Eye Disease in Sjögren's Syndrome Using Our Current Molecular Understanding

Sjögren's syndrome is a chronic and insidious auto-immune disease characterized by lymphocyte infiltration of exocrine glands. The patients typically present with ocular surface diseases related to dry eye and other systemic manifestations. However, due to the high prevalence of dry eye disease and the lack of objective and clinically reliable diagnostic tools, discriminating Sjögren's syndrome dry eye (SSDE) from non-Sjögren's syndrome dry eye (NSSDE) remains a challenge for clinicians. Diagnosing SS is important to improve the quality of life of patients through timely referral for systemic workups, as SS is associated with serious systemic complications such as lymphoma and other autoimmune diseases. The purpose of this article is to describe the current molecular understanding of Sjögren's syndrome and its implications for novel diagnostic modalities on the horizon. A literature review of the pre-clinical and clinical studies published between 2016 and 2022 was conducted. The SSDE pathophysiology and immunology pathways have become better understood in recent years. Novel diagnostic modalities, such as tear and saliva proteomics as well as exosomal biomarkers, provide hope on the horizon.

TLR7 agonism accelerates disease in a mouse model of primary Sjögren's syndrome and drives expansion of T-bet+ B cells

Primary Sjögren's syndrome (pSS) is a systemic autoimmune disease characterized by chronic inflammation of exocrine tissue, resulting in loss of tears and saliva. Patients also experience many extra-glandular disease manifestations. Treatment for pSS is palliative, and there are currently no treatments available that target disease etiology. Previous studies in our lab demonstrated that MyD88 is crucial for pSS pathogenesis in the NOD.B10Sn-H2^b (NOD.B10) pSS mouse model, although the way in which MyD88-dependent pathways become activated in disease remains unknown. Based on its importance in other autoimmune diseases, we hypothesized that TLR7 activation accelerates pSS pathogenesis. We administered the TLR7 agonist Imiquimod (Imq) or sham treatment to pre-disease NOD.B10 females for 6 weeks. Parallel experiments were performed in age and sex-matched C57BL/10 controls. Imq-treated pSS animals exhibited cervical lymphadenopathy, splenomegaly, and expansion of TLR7-expressing B cells. Robust lymphocytic infiltration of exocrine tissues, kidney and lung was observed in pSS mice following treatment with Imq. TLR7 agonism also induced salivary hypofunction in pSS mice, which is a hallmark of disease. Anti-nuclear autoantibodies, including Ro (SSA) and La (SSB) were increased in pSS mice following Imq administration. Cervical lymph nodes from Imq-treated NOD.B10 animals demonstrated an increase in the percentage of activated/memory CD4+ T cells. Finally, T-bet⁺ B cells were expanded in the spleens of Imq-treated pSS mice. Thus, activation of TLR7 accelerates local and systemic disease and promotes expansion of T-bet-expressing B cells in pSS.

Nucleic acid-sensing toll-like receptors: Important players in Sjögren’s syndrome

Sjögren’s syndrome (SS) is a chronic systemic autoimmune disease that affects the salivary and lacrimal glands, as well as other organ systems like the lungs, kidneys and nervous system. SS can occur alone or in combination with another autoimmune disease, such as systemic lupus erythematosus (SLE) or rheumatoid arthritis. The etiology of SS is unknown but recent studies have revealed the implication of the activation of innate immune receptors, including Toll-like receptors (TLRs), mainly through the detection of endogenous nucleic acids, in the pathogenesis of systemic autoimmune diseases. Studies on SS mouse models suggest that TLRs and especially TLR7 that detects single-stranded RNA of microbial or endogenous origin can drive the development of SS and findings in SS patients corroborate those in mouse models. In this review, we will give an overview of the function and signaling of nucleic acid-sensing TLRs, the interplay of TLR7 with TLR8 and TLR9 in the context of autoimmunity, summarize the evidence for the critical role of TLR7 in the pathogenesis of SS and present a possible connection between SARS-CoV-2 and SS.

Bone marrow-derived macrophages from a murine model of Sjögren's syndrome demonstrate an aberrant, inflammatory response to apoptotic cells

Sjögren's syndrome (SjS) is a female-dominated autoimmune disease involving lymphocytic infiltration of the exocrine glands. We have previously demonstrated cleavage of the TAM (Tyro3, Axl, Mer) receptor Mer is enhanced in SjS, leading to defective efferocytosis. Mer also plays a role in modulating phagocyte inflammatory response to apoptotic cells. Here we investigated the SjS macrophage response to apoptotic cells (AC). Bone marrow-derived macrophages (BMDMs) from SjS-susceptible (SjS^s) C57BL/6.NOD-Aec1Aec2 mice and C57BL/6 (B6) controls were treated with either AC or CpG-oligodeoxynucleotides. RNA was collected from macrophages and bulk sequencing was performed to analyze transcripts. Cytokine expression was confirmed by Bio-plex. RT-qPCR was used to determine toll-like receptor (TLR) 7 and 9 involvement in BMDM inflammatory response to apoptotic cells. SjS^S BMDMs exhibited a distinct transcriptional profile involving upregulation of a broad array of inflammatory genes that were not elevated in B6 BMDMs by AC. Inhibition of TLR 7 and 9 was found to limit the inflammatory response of SjS^S BMDMs to ACs. ACs elicit an inflammatory reaction in SjS^S BMDMs distinct from that observed in B6 BMDMs. This discovery of aberrant macrophage behavior in SjS in conjunction with previously described efferocytosis defects suggests an expanded role for macrophages in SjS, where uncleared dead cells stimulate an inflammatory response through macrophage TLRs recruiting lymphocytes, participating in co-stimulation and establishing an environment conducive to autoimmunity.

Research on primary Sjögren's syndrome in 2004-2021: a Web of Science-based cross-sectional bibliometric analysis

The extent, range, and nature of available research in the field of primary Sjögren's syndrome (pSS) have not been understood fully. This study aimed to map the literature available on pSS, and identify global hotspots and trends in the research. Papers on pSS published between 2004 and 2021 were searched from Web of Science Core Collection. The quantity and citations of publications, and the research hotspots and trends in the field of pSS were analyzed and presented visually by Microsoft Excel and Citespace software. A total of 3606 papers mainly from 526 institutions in 83 countries/regions were included for analysis. The number of publications presented an overall upward trend in the field of pSS from 2004 to 2021. The USA ranked first in the number of publications (n = 661), followed by China (n = 491), Italy (n = 405), France (n = 351), and Japan (n = 292). Moreover, seven of the top ten countries by the number of publications on pSS were from Europe. The University of Groningen (n = 661), Xavier Mariette (n = 95), and Clinical and Experimental Rheumatology (n = 184) were the most prolific affiliation, author, and journal, respectively. Vitali C (n = 2009) and Arthritis and Rheumatism (n = 3918) held the record for the most cited papers by an author and journal, respectively. At present, the hot keywords in the field of pSS include disease activity, ultrasonography, management, consensus, and data-driven. Lymphoid organization, clinical phenotypes outcome, salivary gland ultrasonography, and Toll-like receptor are the emerging research trends in pSS. Research on pSS is flourishing. Current research of pSS mainly focuses on disease activity, ultrasonography, and management. While, the emerging research trends in pSS are lymphoid organization, clinical phenotypes outcome, salivary gland ultrasonography, and Toll-like receptor.

Promising novel biomarkers and candidate drugs or herbs in Osteoarthritis: Evidence from bioinformatics analysis of high‐throughput data

Background:

The most common joint illness is osteoarthritis (OA). The goal of this work was to find changes in gene signatures between normal knee joints and OA tissue samples and look for prospective gene targets for OA.

Methods:

The gene expression profiles of GSE12021, GSE51588, and GSE55457 were downloaded from Gene Expression Omnibus (GEO). Total 64 samples (40 OA and 24 standard control samples) were used. The limma program was used to find differentially expressed genes (DEGs) in OA versus NC. Functional annotation and protein-protein interaction (PPI) network construction of OA-specific DEGs were performed. Finally, the candidate drugs and herbs as potential drugs to treat OA were predicted in the DGIdb and TCMIO databases.

Results:

19 upregulated and 27 downregulated DEGs between OA and NC samples. DEGs such as PTN, COMP, NELL1 and MN1 have shown a significant correlation with OA and are expected to become new biomarkers. Cellular senescence,Positive regulation of ossification and Vascular endothelial growth factor (VEGF) were significantly enriched for OA‐specific DEGs.In cell composition analysis, DEGs were also found to be highly enriched in the cytosol.We have identified a total of 68 types of drugs or molecular compounds that are promising to reverse OA-related DEGs.Honeycomb and cinnamon oil have the possibility of treating OA.

Conclusion:

Our findings suggest new biomarkers that can be used to diagnose OA. Furthermore, we tried to find drugs and traditional Chinese medicine that may improve the progress of OA. This research may improve the identification and treatment of these uncontrollable chronic diseases.

Salivary Gland Function, Development and Regeneration

Salivary glands produce and secrete saliva, which is essential for maintaining oral health and overall health. Understanding both the unique structure and physiological function of salivary glands, as well as how they are affected by disease and injury will direct the development of therapy to repair and regenerate them. Significant recent advances, particularly in the OMICS field, increase our understanding of how salivary glands develop at the cellular, molecular and genetic levels; the signaling pathways involved, the dynamics of progenitor cell lineages in development, homeostasis and regeneration and the role of the extracellular matrix microenvironment. These provide a template for cell and gene therapies as well as bioengineering approaches to repair or regenerate salivary function.

Why Should We Consider Potential Roles of Oral Bacteria in the Pathogenesis of Sjögren Syndrome?

Sjögren syndrome (SS) is a chronic autoimmune disorder that primarily targets the salivary and lacrimal glands. The pathology of these exocrine glands is characterized by periductal focal lymphocytic infiltrates, and both T cell-mediated tissue injury and autoantibodies that interfere with the secretion process underlie glandular hypofunction. In addition to these adaptive mechanisms, multiple innate immune pathways are dysregulated, particularly in the salivary gland epithelium. Our understanding of the pathogenetic mechanisms of SS has substantially improved during the past decade. In contrast to viral infection, bacterial infection has never been considered in the pathogenesis of SS. In this review, oral dysbiosis associated with SS and evidence for bacterial infection of the salivary glands in SS were reviewed. In addition, the potential contributions of bacterial infection to innate activation of ductal epithelial cells, plasmacytoid dendritic cells, and B cells and to the breach of tolerance via bystander activation of autoreactive T cells and molecular mimicry were discussed. The added roles of bacteria may extend our understanding of the pathogenetic mechanisms and therapeutic approaches for this autoimmune exocrinopathy.

Transcriptomic and Single-Cell Analysis Reveals Regulatory Networks and Cellular Heterogeneity in Mouse Primary Sjögren's Syndrome Salivary Glands

Sjögren’s Syndrome (SS) is a chronic autoimmune disease of unknown etiology which primarily affects the salivary and lacrimal glands resulting in the loss of secretory function. Treatment options for SS have been hampered due to the lack of a better understanding of the underlying gene regulatory circuitry and the interplay between the myriad pathological cellular states that contribute to salivary gland dysfunction. To better elucidate the molecular nature of SS, we have performed RNA-sequencing analysis of the submandibular glands (SMG) of a well-established primary Sjögren’s Syndrome (pSS) mouse model. Our comprehensive examination of global gene expression and comparative analyses with additional SS mouse models and human datasets, have identified a number of important pathways and regulatory networks that are relevant in SS pathobiology. To complement these studies, we have performed single-cell RNA sequencing to examine and identify the molecular and cellular heterogeneity of the diseased cell populations of the mouse SMG. Interrogation of the single-cell transcriptomes has shed light on the diversity of immune cells that are dysregulated in SS and importantly, revealed an activated state of the salivary gland epithelial cells that contribute to the global immune mediated responses. Overall, our broad studies have not only revealed key pathways, mediators and new biomarkers, but have also uncovered the complex nature of the cellular populations in the SMG that are likely to drive the progression of SS. These newly discovered insights into the underlying molecular mechanisms and cellular states of SS will better inform targeted therapeutic discoveries.

Targeting Gut–Liver Axis for Treatment of Liver Fibrosis and Portal Hypertension

Antifibrotic therapies for the treatment of liver fibrosis represent an unconquered area of drug development. The significant involvement of the gut microbiota as a driving force in a multitude of liver disease, be it pathogenesis or fibrotic progression, suggest that targeting the gut–liver axis, relevant signaling pathways, and/or manipulation of the gut’s commensal microbial composition and its metabolites may offer opportunities for biomarker discovery, novel therapies and personalized medicine development. Here, we review potential links between bacterial translocation and deficits of host-microbiome compartmentalization and liver fibrosis that occur in settings of advanced chronic liver disease. We discuss established and emerging therapeutic strategies, translated from our current knowledge of the gut–liver axis, targeted at restoring intestinal eubiosis, ameliorating hepatic fibrosis and rising portal hypertension that characterize and define the course of decompensated cirrhosis.

Integrated analysis of transcriptomics to identify hub genes in primary Sjögren's syndrome

OBJECTIVE

The treatment of patients with primary Sjögren's syndrome is a clinical challenge. Gene expression profile analysis and comprehensive network methods for complex diseases can provide insight into molecular characteristics in the clinical context.

MATERIALS AND METHODS

We downloaded gene expression datasets from the Gene Expression Omnibus (GEO) database. We screened differentially expressed genes (DEG) between the pSS patients and the controls by the robust rank aggregation (RRA) method. We explored DEGs' potential function using gene function annotation and PPI network analysis.

RESULTS

GSE23117 GSE40611 GSE80805 and GSE127952were included, including 38 patients and 30 controls. The RRA integrated analysis determined 294 significant DEGs (241 upregulated and 53 downregulated), and the most significant gene aberrantly expressed in SS was CXCL9 (p = 6.39E-15), followed by CXCL13 (p = 1.53E-13). Immune response (GO:0006955; p = 4.29E-32) was the most significantly enriched biological process in GO (gene ontology) analysis. KEGG pathway enrichment analysis showed that cytokine-cytokine receptor interaction (hsa04060; p = 6.46E-10) and chemokine signaling pathway (hsa04062; p = 9.54E-09) were significantly enriched. We defined PTPRC, CD86, and LCP2 as the hub genes based on the PPI results.

CONCLUSION

Our integrated analysis identified gene signatures and helped understand molecular changes in pSS.

Management of Sjögren's Syndrome: Present Issues and Future Perspectives

In view of the new possibilities for the treatment of primary Sjögren's syndrome (pSS) given by the availability of new biotechnological agents targeting the various molecular and cellular actors of the pathological process of the disease, classification criteria aimed at selecting patients to be enrolled in therapeutic trials, and validated outcome measures to be used as response criteria to these new therapies, have been developed and validated in the last decades. Unfortunately, the therapeutic trials so far completed with these new treatments have yielded unsatisfactory or only partially positive results. The main issues that have been evoked to justify the poor results of the new therapeutic attempts are: (i) the extreme variability of the disease phenotypes of the patients enrolled in the trials, which are dependent on different underlying patterns of biological mechanisms, (ii) the fact that the disease has a long indolent course, and that most of the enrolled patients might already have irreversible clinical features. The advances in the research of new disease biomarkers that can better distinguish the different clinical phenotypes of patients and diagnose the disease in an earlier phase are also discussed.

TLR7 Signaling Drives the Development of Sjögren's Syndrome

Sjögren’s syndrome (SS) is a chronic systemic autoimmune disease that affects predominately salivary and lacrimal glands. SS can occur alone or in combination with another autoimmune disease like systemic lupus erythematosus (SLE). Here we report that TLR7 signaling drives the development of SS since TLR8-deficient (TLR8ko) mice that develop lupus due to increased TLR7 signaling by dendritic cells, also develop an age-dependent secondary pathology similar to associated SS. The SS phenotype in TLR8ko mice is manifested by sialadenitis, increased anti-SSA and anti-SSB autoantibody production, immune complex deposition and increased cytokine production in salivary glands, as well as lung inflammation. Moreover, ectopic lymphoid structures characterized by B/T aggregates, formation of high endothelial venules and the presence of dendritic cells are formed in the salivary glands of TLR8ko mice. Interestingly, all these phenotypes are abrogated in double TLR7/8-deficient mice, suggesting that the SS phenotype in TLR8-deficient mice is TLR7-dependent. In addition, evaluation of TLR7 and inflammatory markers in the salivary glands of primary SS patients revealed significantly increased TLR7 expression levels compared to healthy individuals, that were positively correlated to TNF, LT-α, CXCL13 and CXCR5 expression. These findings establish an important role of TLR7 signaling for local and systemic SS disease manifestations, and inhibition of such will likely have therapeutic value.

Tissue-specific activation of Myd88-dependent pathways governs disease severity in primary Sjögren's syndrome

Myd88 activation is an important driver of autoimmunity. Primary Sjögren's syndrome (pSS) is an autoimmune disease characterized by exocrine gland dysfunction in combination with serious systemic disease manifestations. Myd88-dependent signaling networks remain incompletely understood in the context of pSS. The objective of this study was to establish the contribution of tissue-specific Myd88 activation to local (exocrine) and systemic pSS manifestations. To this end, we generated two novel conditional knockout pSS mouse models; one lacking Myd88 in hematopoietic cells and a second strain in which Myd88 was deleted in the stromal compartment. Spontaneous production of inflammatory mediators was altered in salivary tissue, and nephritis was diminished in both conditional knockout strains. In contrast, pulmonary inflammation was increased in mice lacking Myd88 in hematopoietic cells and was reduced when Myd88 was ablated in stromal cells. Finally, anti-nuclear autoantibodies (ANAs) were attenuated in pSS mice lacking Myd88 in immune cells. Additionally, the ANA-specific B cell repertoire was skewed in the Myd88-deficient strains. Collectively, these data demonstrate that Myd88 activation in specific cell types is essential for distinct aspects of pSS pathology.

Making Sense of Intracellular Nucleic Acid Sensing in Type I Interferon Activation in Sjögren's Syndrome

Primary Sjögren's syndrome (pSS) is a systemic autoimmune rheumatic disease characterized by dryness of the eyes and mucous membranes, which can be accompanied by various extraglandular autoimmune manifestations. The majority of patients exhibit persistent systemic activation of the type I interferon (IFN) system, a feature that is shared with other systemic autoimmune diseases. Type I IFNs are integral to anti-viral immunity and are produced in response to stimulation of pattern recognition receptors, among which nucleic acid (NA) receptors. Dysregulated detection of endogenous NAs has been widely implicated in the pathogenesis of systemic autoimmune diseases. Stimulation of endosomal Toll-like receptors by NA-containing immune complexes are considered to contribute to the systemic type I IFN activation. Accumulating evidence suggest additional roles for cytosolic NA-sensing pathways in the pathogenesis of systemic autoimmune rheumatic diseases. In this review, we will provide an overview of the functions and signaling of intracellular RNA- and DNA-sensing receptors and summarize the evidence for a potential role of these receptors in the pathogenesis of pSS and the sustained systemic type I IFN activation.

The Involvement of Innate and Adaptive Immunity in the Initiation and Perpetuation of Sjögren's Syndrome

Sjogren’s syndrome (SS) is a chronic autoimmune disease characterized by the infiltration of exocrine glands including salivary and lachrymal glands responsible for the classical dry eyes and mouth symptoms (sicca syndrome). The spectrum of disease manifestations stretches beyond the classical sicca syndrome with systemic manifestations including arthritis, interstitial lung involvement, and neurological involvement. The pathophysiology underlying SS is not well deciphered, but several converging lines of evidence have supported the conjuncture of different factors interplaying together to foster the initiation and perpetuation of the disease. The innate and adaptive immune system play a cardinal role in this process. In this review, we discuss the inherent parts played by both the innate and adaptive immune system in the pathogenesis of SS.

Transcriptomic and Network Analysis of Minor Salivary Glands of Patients With Primary Sjögren's Syndrome

Primary Sjögren’s syndrome (pSS) is a systemic autoimmune disease characterized primarily by immune-mediated destruction of exocrine tissues, such as those of the salivary and lacrimal glands, resulting in the loss of saliva and tear production, respectively. This disease predominantly affects middle-aged women, often in an insidious manner with the accumulation of subtle changes in glandular function occurring over many years. Patients commonly suffer from pSS symptoms for years before receiving a diagnosis. Currently, there is no effective cure for pSS and treatment options and targeted therapy approaches are limited due to a lack of our overall understanding of the disease etiology and its underlying pathology. To better elucidate the underlying molecular nature of this disease, we have performed RNA-sequencing to generate a comprehensive global gene expression profile of minor salivary glands from an ethnically diverse cohort of patients with pSS. Gene expression analysis has identified a number of pathways and networks that are relevant in pSS pathogenesis. Moreover, our detailed integrative analysis has revealed a primary Sjögren’s syndrome molecular signature that may represent important players acting as potential drivers of this disease. Finally, we have established that the global transcriptomic changes in pSS are likely to be attributed not only to various immune cell types within the salivary gland but also epithelial cells which are likely playing a contributing role. Overall, our comprehensive studies provide a database-enriched framework and resource for the identification and examination of key pathways, mediators, and new biomarkers important in the pathogenesis of this disease with the long-term goals of facilitating earlier diagnosis of pSS and to mitigate or abrogate the progression of this debilitating disease.

Toll-Like Receptor 7 Is Required for Lacrimal Gland Autoimmunity and Type 1 Diabetes Development in Male Nonobese Diabetic Mice

Sjögren syndrome (SS) is an immunologically complex, chronic autoimmune disease targeting lacrimal and salivary glands. Nonobese diabetic (NOD) mice spontaneously develop inflammation of lacrimal and salivary glands with histopathological features similar to SS in humans including focal lymphocytic infiltrates in the affected glands. The innate immune signals driving lymphocytic infiltration of these glands are not well-defined. Here we evaluate the role of Toll-like receptor (TLR) 7 in the development of SS-like manifestations in NOD mice. We created a Tlr7 knockout NOD mouse strain and performed histological and gene expression studies to characterize the effects of TLR7 on autoimmunity development. TLR7 was required for male-specific lacrimal gland inflammation but not for female-specific salivary gland inflammation. Moreover, TLR7 was required for type 1 diabetes development in male but not female NOD mice. RNA sequencing demonstrated that TLR7 was associated with a type I interferon (IFN) response and a type I IFN-independent B cell response in the lacrimal glands. Together these studies identify a previously unappreciated pathogenic role for TLR7 in lacrimal gland autoimmunity and T1D development in male NOD mice adding to the growing body of evidence supporting sex differences in mechanisms of autoimmune disease in NOD mice.

Revisiting B cell tolerance and autoantibodies in seropositive and seronegative autoimmune rheumatic disease (AIRD)

Autoimmune rheumatic diseases (AIRD) are categorized seropositive or seronegative, dependent upon the presence or absence of specific autoreactive antibodies, including rheumatoid factor and anti-citrullinated protein antibodies. Autoantibody-based diagnostics have proved helpful in patient care, not only for diagnosis but also for monitoring of disease activity and prediction of therapy responsiveness. Recent work demonstrates that AIRD patients develop autoantibodies beyond those contained in the original categorization. In this study we discuss key mechanisms that underlie autoantibody development in AIRD: defects in early B cell development, genetic variants involved in regulating B cell and T cell tolerance, environmental triggers and antigen modification. We describe how autoantibodies can directly contribute to AIRD pathogenesis through innate and adaptive immune mechanisms, eventually culminating in systemic inflammation and localized tissue damage. We conclude by discussing recent insights that suggest distinct AIRD have incorrectly been denominated seronegative.

Understanding the Complexity of Sjögren's Syndrome: Remarkable Progress in Elucidating NF-κB Mechanisms

Sjögren’s syndrome (SS) is a systemic autoimmune inflammatory disease with a poorly defined aetiology, which targets exocrine glands (particularly salivary and lachrymal glands), affecting the secretory function. Patients suffering from SS exhibit persistent xerostomia and keratoconjunctivitis sicca. It is now widely acknowledged that a chronic grade of inflammation plays a central role in the initiation, progression, and development of SS. Consistent with its key role in organizing inflammatory responses, numerous recent studies have shown involvement of the transcription factor nuclear factor κ (kappa)-light-chain-enhancer of activated B cells (NF-κB) in the development of this disease. Therefore, chronic inflammation is considered as a critical factor in the disease aetiology, offering hope for the development of new drugs for treatment. The purpose of this review is to describe the current knowledge about the NF-κB-mediated molecular events implicated in the pathogenesis of SS.

The dark side of Sjögren's syndrome: the possible pathogenic role of infections

PURPOSE OF REVIEW

To highlight recent findings on pathogenic mechanisms and clinical associations which characterize the role of infectious agents as triggers for Sjögren's syndrome development.

RECENT FINDINGS

Several candidate infectious agents have been identified to induce the autoimmune and inflammatory pathways leading to Sjögren's syndrome clinical appearance in the setting of a genetic background. This is reinforced by the demonstration that Sjögren's syndrome patients are characterized by higher prevalence of seropositivity to virus and bacterial agents in comparison with general population. Moreover, these agents may infect salivary gland epithelial cells. Stronger evidence confirmed the role of some viruses, like Epstein-Barr, as triggers of the disease and different mechanisms have been demonstrated to interplay. Recent experimental and clinical studies supported the adjunctive role of an altered buccal and intestinal microbial composition and chronic inflammatory response to Helicobacter pylori in disease induction. Finally, latent viral infections and immune system chronic stimulation induced by persistent infections may participate in disease lymphoproliferative evolution.

SUMMARY

Different viral and bacterial agents have been identified as triggers in Sjögren's syndrome induction and contributors to the chronic immune system stimulation underlying lymphoproliferative complication. Deeper knowledge of involved microbial agents and pathogenic mechanisms linking Sjögren's syndrome and infections may help the identification of preventive therapeutic strategy.

Genes that escape from X-chromosome inactivation: Potential contributors to Klinefelter syndrome

One of the two X chromosomes in females is epigenetically inactivated, thereby compensating for the dosage difference in X-linked genes between XX females and XY males. Not all X-linked genes are completely inactivated, however, with 12% of genes escaping X chromosome inactivation and another 15% of genes varying in their X chromosome inactivation status across individuals, tissues or cells. Expression of these genes from the second and otherwise inactive X chromosome may underlie sex differences between males and females, and feature in many of the symptoms of XXY Klinefelter males, who have both an inactive X and a Y chromosome. We review the approaches used to identify genes that escape from X-chromosome inactivation and discuss the nature of their sex-biased expression. These genes are enriched on the short arm of the X chromosome, and, in addition to genes in the pseudoautosomal regions, include genes with and without Y-chromosomal counterparts. We highlight candidate escape genes for some of the features of Klinefelter syndrome and discuss our current understanding of the mechanisms underlying silencing and escape on the X chromosome as well as additional differences between the X in males and females that may contribute to Klinefelter syndrome.

Inhibitory Effects of Dietary N-Glycans From Bovine Lactoferrin on Toll-Like Receptor 8; Comparing Efficacy With Chloroquine

Toll-like receptor 8 (TLR-8) plays a role in the pathogenesis of autoimmune disorders and associated gastrointestinal symptoms that reduce quality of life of patients. Dietary interventions are becoming more accepted as mean to manage onset, progression, and treatment of a broad spectrum of inflammatory conditions. In this study, we assessed the impact of N-glycans derived from bovine lactoferrin (bLF) on the inhibition of TLR-8 activation. We investigated the effects of N-glycans in their native form, as well as in its partially demannosylated and partially desialylated form, on HEK293 cells expressing TLR-8, and in human monocyte-derived dendritic cells (MoDCs). We found that in HEK293 cells, N-glycans strongly inhibited the ssRNA40 induced TLR-8 activation but to a lesser extent the R848 induced TLR-8 activation. The impact was compared with a pharmaceutical agent, i.e., chloroquine (CQN), that is clinically applied to antagonize endosomal TLR- activation. Inhibitory effects of the N-glycans were not influenced by the partially demannosylated or partially desialylated N-glycans. As the difference in charge of the N-glycans did not influence the inhibition capacity of TLR-8, it is possible that the inhibition mediated by the N-glycans is a result of a direct interaction with the receptor rather than a result of pH changes in the endosome. The inhibition of TLR-8 in MoDCs resulted in a significant decrease of IL-6 when cells were treated with the unmodified (0.5-fold, p < 0.0001), partially demannosylated (0.3-fold, p < 0.0001) and partially desialylated (0.4-fold, p < 0.0001) N-glycans. Furthermore, the partially demannosylated and partially desialylated N-glycans showed stronger inhibition of IL-6 production compared with the native N-glycans. This provides evidence that glycan composition plays a role in the immunomodulatory activity of the isolated N-glycans from bLF on MoDCs. Compared to CQN, the N-glycans are specific inhibitors of TLR-8 activation and of IL-6 production in MoDCs. Our findings demonstrate that isolated N-glycans from bLF have attenuating effects on TLR-8 induced immune activation in HEK293 cells and human MoDCs. The inhibitory capacity of N-glycans isolated from bLF onTLR-8 activation may become a food-based strategy to manage autoimmune, infections or other inflammatory disorders.

Activation of Myd88-Dependent TLRs Mediates Local and Systemic Inflammation in a Mouse Model of Primary Sjögren's Syndrome

Toll-like receptors (TLRs) are important mediators of chronic inflammation in numerous autoimmune diseases, although the role of these receptors in primary Sjögren's syndrome (pSS) remains incompletely understood. Previous studies in our laboratory established Myd88 as a crucial mediator of pSS, although the disease-relevant ligands and the upstream signaling events that culminate in Myd88 activation have yet to be established. The objective of this study was to identify specific Myd88-dependent TLR-related pathways that are dysregulated both locally and systemically in a mouse model of pSS [NOD.B10Sn-H2^b/J (NOD.B10)]. We performed RNA-sequencing on spleens derived from NOD.B10 mice. We then harvested salivary tissue and spleens from Myd88-sufficient and deficient C57BL/10 (BL/10) and NOD.B10 mice and performed flow cytometry to determine expression of Myd88-dependent TLRs. We cultured splenocytes with TLR2 and TLR4 agonists and measured production of inflammatory mediators by ELISA. Next, we evaluated spontaneous and TLR4-mediated inflammatory cytokine secretion in NOD.B10 salivary tissue. Finally, we assessed spontaneous Myd88-dependent cytokine secretion by NOD.B10 salivary cells. We identified dysregulation of numerous TLR-related networks in pSS splenocytes, particularly those employed by TLR2 and TLR4. We found upregulation of TLRs in both the splenic and salivary tissue from pSS mice. In NOD.B10 splenic tissue, robust expression of B cell TLR1 and TLR2 required Myd88. Splenocytes from NOD.B10 mice were hyper-responsive to TLR2 ligation and the endogenous molecule decorin modulated inflammation via TLR4. Finally, we observed spontaneous secretion of numerous inflammatory cytokines and this was enhanced following TLR4 ligation in female NOD.B10 salivary tissue as compared to males. The spontaneous production of salivary IL-6, MCP-1 and TNFα required Myd88 in pSS salivary tissue. Thus, our data demonstrate that Myd88-dependent TLR pathways contribute to the inflammatory landscape in pSS, and inhibition of such will likely have therapeutic utility.

B cell dysregulation in primary Sjögren's syndrome: A review

Primary Sjögren’s syndrome is a chronic autoimmune disorder of unknown etiology and is characterized by progressive focal lymphocytic infiltration of the lacrimal and salivary glands. Comparison of B cell subsets from the peripheral blood and salivary glands of patients with primary Sjögren’s syndrome and those from healthy individuals shows dysregulation and derangement of B cell subsets in both peripheral circulation and in inflamed glandular tissues. This dysregulation is expressed as a decrease in the percentage of CD27+ memory B cells in peripheral blood and an increase in the CD27+ memory B cells in the affected glands. Further, the overall percentage of long-lived autoantibodies-producing plasma cells within the affected glands is increased. In the last two decades, several studies have shown growing evidences that B cells play multiple roles in primary Sjögren’s syndrome pathophysiology, and that dysregulation of these cells may actually play a central role in the disease development.

MicroRNA-130a Contributes to Type-2 Classical DC-activation in Sjögren's Syndrome by Targeting Mitogen- and Stress-Activated Protein Kinase-1

Objectives: Considering the critical role of microRNAs (miRNAs) in regulation of cell activation, we investigated their role in circulating type-2 conventional dendritic cells (cDC2s) of patients with primary Sjögren's syndrome (pSS) compared to healthy controls (HC). Methods: CD1c-expressing cDC2s were isolated from peripheral blood. A discovery cohort (15 pSS, 6 HC) was used to screen the expression of 758 miRNAs and a replication cohort (15 pSS, 11 HC) was used to confirm differential expression of 18 identified targets. Novel targets for two replicated miRNAs were identified by SILAC in HEK-293T cells and validated in primary cDC2s. Differences in cytokine production between pSS and HC cDC2s were evaluated by intracellular flow-cytometry. cDC2s were cultured in the presence of MSK1-inhibitors to investigate their effect on cytokine production. Results: Expression of miR-130a and miR-708 was significantly decreased in cDC2s from pSS patients compared to HC in both cohorts, and both miRNAs were downregulated upon stimulation via endosomal TLRs. Upstream mediator of cytokine production MSK1 was identified as a novel target of miR-130a and overexpression of miR-130a reduced MSK1 expression in cDC2s. pSS cDC2s showed higher MSK1 expression and an increased fraction of IL-12 and TNF-α-producing cells. MSK1-inhibition reduced cDC2 activation and production of IL-12, TNF-α, and IL-6. Conclusions: The decreased expression of miR-130a and miR-708 in pSS cDC2s seems to reflect cell activation. miR-130a targets MSK1, which regulates pro-inflammatory cytokine production, and we provide proof-of-concept for MSK1-inhibition as a therapeutic avenue to impede cDC2 activity in pSS.