Primary Sjögren's syndrome: pathophysiological, clinical and therapeutic advances

Mitochondrial Dysfunction and Fatigue in Sjögren's Disease

Objectives

Sjögren's disease (SjD) is a common exocrine disorder typified by chronic inflammation and dryness, but also profound fatigue, suggesting a pathological basis in cellular bioenergetics. In healthy states, damaged or dysfunctional mitochondrial components are broken down and recycled by mitophagy, a specialized form of autophagy. In many autoimmune disorders, however, evidence suggests that dysfunctional mitophagy allows poorly functioning mitochondria to persist and contribute to a cellular milieu with elevated reactive oxygen species. We hypothesized that mitophagic processes are dysregulated in SjD and that dysfunctional mitochondria contribute to overall fatigue. We sought to link fatigue with mitochondrial dysfunction directly in SjD, heretofore unexamined, and further sought to assess the pathogenic extent and implications of dysregulated mitophagy in SjD.

Methods

We isolated pan T cells via negative selection from the peripheral blood mononuclear cells of 17 SjD and 8 age-matched healthy subjects, all of whom completed fatigue questionnaires prior to phlebotomy. Isolated T cells were analyzed for mitochondrial oxygen consumption rate (OCR) and glycolysis using Seahorse, and linear correlations with fatigue measures were assessed. A mitophagy transcriptional signature in SjD was identified by reanalysis of whole-blood microarray data from 190 SjD and 32 healthy subjects. Differential expression analyses were performed by case/control and subgroup analyses comparing SjD patients by mitophagy transcriptional cluster against healthy subjects followed by bioinformatic interpretation using gene set enrichment analysis.

Results

Basal OCR, ATP-linked respiration, maximal respiration, and reserve capacity were significantly lower in SjD compared to healthy subjects with no observed differences in non-mitochondrial respiration, basal glycolysis, or glycolytic stress. SjD lymphocytic mitochondria show structural alterations compared to healthy subjects. Fatigue scores related to pain/discomfort in SjD correlated with the altered OCR. Results from subgroup analyses by mitophagic SjD clusters revealed highly variable inter-cluster differentially expressed genes (DEGs) and expanded the number of SjD-associated gene targets by tenfold within the same dataset.

Conclusion

Mitochondrial dysfunction, associated with fatigue, is a significant problem in SjD and warrants further investigation.

Sjögren's syndrome: a systemic autoimmune disease

Sjögren's syndrome is a chronic autoimmune disease characterized by ocular and oral dryness resulting from lacrimal and salivary gland dysfunction. Besides, a variety of systemic manifestations may occur, involving virtually any organ system. As a result, the disease is characterized by pleomorphic clinical manifestations whose characteristics and severity may vary greatly from one patient to another. Sjögren's syndrome can be defined as primary or secondary, depending on whether it occurs alone or in association with other systemic autoimmune diseases, respectively. The pathogenesis of Sjögren's syndrome is still elusive, nevertheless, different, not mutually exclusive, models involving genetic and environmental factors have been proposed to explain its development. Anyhow, the emergence of aberrant autoreactive B-lymphocytes, conducting to autoantibody production and immune complex formation, seems to be crucial in the development of the disease. The diagnosis of Sjögren's syndrome is based on characteristic clinical signs and symptoms, as well as on specific tests including salivary gland histopathology and autoantibodies. Recently, new classification criteria and disease activity scores have been developed primarily for research purposes and they can also be useful tools in everyday clinical practice. Treatment of Sjögren's syndrome ranges from local and symptomatic therapies aimed to control dryness to systemic medications, including disease-modifying agents and biological drugs. The objective of this review paper is to summarize the recent literature on Sjögren's syndrome, starting from its pathogenesis to current therapeutic options.

Significance of Sjögren's syndrome and anti-cN1A antibody in myositis patients

OBJECTIVE

We recently recorded a high prevalence of inclusion body myositis (IBM) in patients with Sjögren's syndrome (SS). Whether myositis patients with SS differ from myositis patients without SS in terms of the characteristics of the myositis is currently unknown. Anti-cytosolic 5'-nucleotidase 1 A (cN1A) has recently been proposed as a biomarker for IBM but is also frequent in SS. Whether anti-cN1A is independently associated with IBM is still an open question. We aimed to assess the significance of SS and anti-cN1A in myositis patients.

METHODS

Cumulative data on all myositis patients (EULAR/ACR 2017 criteria) screened for SS (ACR/EULAR 2016 criteria) in a single center were analyzed. Ninety-nine patients were included, covering the whole spectrum of EULAR/ACR 2017 myositis subgroups and with a median follow-up of 6 years [range 1.0-37.5]. The 34 myositis patients with SS (myositis/SS+) were compared with the 65 myositis patients without SS (myositis/SS-).

RESULTS

IBM was present in 24% of the myositis/SS+ patients vs 6% of the myositis/SS- group (p = 0.020). None of the IBM patients responded to treatment, whether they had SS or not. Anti-cN1A was more frequent in myositis/SS+ patients (38% vs 6%, p = 0.0005), independently of the higher prevalence of IBM in this group (multivariate p-value: 0.02). Anti-cN1A antibody specificity for IBM was 0.96 [95% CI, 0.87-0.99] in the myositis SS- group but dropped to 0.70 [95% CI, 0.48-0.85] in the myositis SS/+ group.

INTERPRETATION

In myositis patients, SS is associated with IBM and with anti-cN1A antibodies, independently of the IBM diagnosis. As a consequence, anti-cN1A has limited specificity for IBM in myositis patients with SS.

Increased B-cell activating factor, interleukin-6, and interleukin-8 in induced sputum from primary Sjögren's syndrome patients

OBJECTIVE

Small airway disease and chronic obstructive pulmonary disease are common in primary Sjögren's syndrome (pSS). However, the underlying inflammatory mechanisms behind pSS-associated airway disease have not been studied in detail. We therefore wanted to study cytokine and leucocyte levels in induced sputum in never-smoking patients with pSS.

METHOD

Induced sputum cytokines and leucocytes were assessed in 20 never-smoking patients with pSS and 19 age- and gender-matched population-based controls. In addition, pulmonary function, disease activity, respiratory symptoms, and inflammatory and serological features of pSS were assessed.

RESULTS

B-cell activating factor (BAFF), interleukin-6 (IL-6) and IL-8 were significantly increased in induced sputum in pSS patients compared to population-based controls, while IL-1β, interferon-α, and tumour necrosis factor-α levels and leucocytes were not. The proportion of lymphocytes and BAFF levels in induced sputum correlated significantly in pSS patients. However, cytokine levels in induced sputum were not associated with pulmonary function tests, disease activity, respiratory symptoms, or serological features of pSS.

CONCLUSION

The increase in BAFF, IL-6, and IL-8 in induced sputum suggests a specific ongoing inflammatory disease process in the airways in pSS patients. Its association with pSS-associated airway disease needs to be further examined in future larger studies.

Women With Primary Sjögren Syndrome and With Non-Sjögren Sicca Syndrome Show Similar Vulvar Histopathologic and Immunohistochemical Changes

The goal of this study was to evaluate the characteristics and the prevalence of histopathologic and immunohistochemical changes in vulvar biopsies, in women with Primary Sjögren Syndrome (pSS) and non-Sjögren Sicca Syndrome (nS-SS). Twenty-one women with pSS and 11 with nS-SS (investigated by xerophtalmia and xerostomia tests, biopsy of minor salivary glands, gynecological history, and gynecologic symptoms score) underwent vulvar biopsies, evaluated for histopathologic and immunohistochemicalchanges, and compared with those obtained from 26 patients with lichen sclerosus. An inflammatory infiltrate was present in 31/32 biopsies (96.9%); biopsies from pSS patients showed a mild infiltrate in 10 cases and a moderate infiltrate in 11 cases; and patients with nS-SS had a mild infiltrate in 8 biopsies and moderate infiltrate in the other 2 biopsies. By immunohistochemistry, the infiltrate was composed predominantly of T lymphocytes (CD3), CD20 B cells were sparse and mean CD4:CD8 T-cell ratio was 1.5. No differences were observed between the grading of the inflammatory infiltrate in nS-SS and pSS; no correlation was shown between vulvar inflammatory infiltrate score (mild or moderate) and salivary glands inflammatory score. No differences were found in gynecologic symptoms, as well as in clinical and demographical characteristics between patients with mild and those with moderate vulvar inflammatory score. A higher prevalence of moderate inflammatory infiltrate was observed in biopsies from women with lichen sclerosus than in pSS and nS-SS patients (61.5% vs. 27.5%, P=0.02). Women with pSS and nS-SS show a high and similar prevalence of vulvar inflammatory infiltrate. A gynecologic evaluation is needed both in pSS and nS-SS to assess genital involvement and, eventually, to address a therapy targeted to genital symptoms.

Fingolimod efficacy in multiple sclerosis associated with Sjogren syndrome

BACKGROUND

Sjogren syndrome (SS) is a common autoimmune disease characterized by lymphocytic infiltration of the exocrine glands with neurological involvement in about 20% of patients. The neurological manifestations in the central nervous system CNS may vary and include a multiple sclerosis (MS)-like disease, and the treatments with immunosuppressive drugs have been undertaken.

CASE PRESENTATION

We describe a case of 40-year-old woman with clinical and instrumental evidence of an MS characterized by numerous relapses and demyelinating lesions prevailing in the infratentorial and spinal cord. Immunological analysis showed biological data that were consistent with an SS. The treatment with fingolimod showed not only an optimal response to the demyelinating events but also biological parameters.

CONCLUSION

These data allow us to hypothesize possible combined efficacy of treatment with fingolimod in SS associated with definite MS.

Immunomodulatory drugs: oral and systemic adverse effects

OBJECTIVE

The main objectives are to present the different adverse effects of the immunomodulatory drugs that can impair the quality of life of the immunosuppressed patients and study the impact of immunomodulation on oral diseases. Immunomodulatory drugs have changed the treatment protocols of many diseases where immune functions play a central role, such as rheumatic diseases. Their effect on oral health has not been systematically investigated, however.

STUDY DESIGN

We review current data on the new immunomodulatory drugs from the oral health perspective based on open literature search of the topic.

RESULTS

These target specific drugs appear to have less drug interactions than earlier immunomodulating medicines but have nevertheless potential side effects such as activating latent infections. There are some data showing that the new immunomodulatory drugs may also have a role in the treatment of certain oral diseases such as lichen planus or ameliorating symptoms in Sjögren's syndrome, but the results have not been overly promising.

CONCLUSION

In general, data are sparse of the effect of these new drugs vs. oral diseases and there are no properly powered randomized controlled trials published on this topic.

Advances in understanding the pathogenesis of primary Sjögren's syndrome

Primary Sjögren's syndrome (pSS) is a prototypic autoimmune disorder, management of which has long suffered from a lack of knowledge of the underlying pathophysiological mechanisms; however, over the past decade major advances have been made in understanding the pathogenesis of pSS. The innate immune system has been demonstrated to have an important role at the early stage of the disease, notably through activation of the type I interferon (IFN) system. In addition, mechanisms of B-cell activation in pSS have become clearer, particularly owing to recognition of the involvement of the TNF family cytokine B-cell-activating factor, production of which is highly dependent on expression of type I and type II IFNs. Moreover, key inroads have been made in understanding lymphomagenesis, the most severe complication of pSS. IL-12 production and subsequent T-cell activation, mainly IFN-γ-secreting type 1 T-helper cells, have also been implicated in disease pathogenesis. Furthermore, evidence implicates neuroendocrine system dysfunction in pSS pathogenesis. These pathophysiological advances open new avenues of investigation. Indeed, the increased understanding of pSS pathogenesis has already led to the development of promising novel therapeutic strategies. This article summarizes recent findings regarding the pathogenic mechanisms involved in pSS and their implications.

Proteomic analysis of saliva: a unique tool to distinguish primary Sjögren's syndrome from secondary Sjögren's syndrome and other sicca syndromes

Introduction

A growing interest has arisen in salivary proteomics as a tool for the identification of biomarkers for primary Sjögren's syndrome (pSS). Nonetheless, only a limited number of preclinical validation studies have been performed, limiting the possibility of translating proteomic results into clinical practice. The primary aim of this study was to refine the diagnostic power of a panel of candidate salivary biomarkers described in pSS with respect to both healthy volunteers and pathological controls. We also explored the pathogenetic function of the detected putative biomarkers both in the local exocrinopathy and in the systemic inflammatory processes of SS.

Methods

One hundred and eighty patients were included in the study overall. In the first "exploratory phase", we enrolled 40 females with pSS, 40 sex- and age-matched healthy volunteers, 10 patients with sicca non-SS and 15 secondary SS (sSS) patients. The testing cohort of the second "challenge phase" of the study was represented by 75 unselected, consecutive subjects: 19 pSS, 21 healthy volunteers, 10 sicca non-SS and 25 sSS patients. Salivary proteomic analysis was performed combining two-dimensional electrophoresis (2DE) and matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF-MS). Western blot (WB) analysis and enzyme-linked immunosorbent assay (ELISA) were employed to validate 2DE results. Ingenuity Pathway Analysis (IPA) Knowledge base was adopted to associate candidate biomarkers in a signalling pathogenetic network.

Results

A total of 28, 6, 7 and 12 protein spots were found to be significantly different in pSS samples with respect to healthy volunteers, non-SS sicca syndrome, SSc-sSS and rheumatoid arthritis-sSS, leading to the identification of 15 differently expressed proteins. Among them, α-amylases precursor, carbonic anhydrase VI, β-2 microglobulin, glyceraldehydes-3-phosphate dehydrogenase (G3PDH), epidermal fatty acid binding protein (E-FABP) and immunoglobulin k light chain (IGK-light chain) apparently showed the most significant differences in pSS when compared to healthy volunteers and non-SS pathological controls. On the other hand, as expected, pSS and sSS salivary profiles shared a great number of similarities.

Conclusions

This study demonstrated that salivary fluid might represent a novel ideal milieu for the detection of a diagnostic panel of candidate biomarkers for pSS, and to gain an insight into the pathogenetic processes underlying glandular and systemic autoimmune disorders.

Activation of innate immunity accelerates sialoadenitis in a mouse model for Sjögren's syndrome-like disease

OBJECTIVE

Sjögren's syndrome is a chronic autoimmune disorder characterized by progressive lymphocytic infiltration within the salivary and lacrimal glands. This study was undertaken to investigate the effects of innate immunity activation on sialoadenitis in a mouse strain genetically susceptible for development of SS-like disease.

METHODS

Female New Zealand Black X New Zealand White F1 mice were repeatedly treated with toll-like 3 receptor agonist poly(I:C). Submandibular glands were investigated at different time points for sialoadenitis by immunohistochemistry and for gene expression of different chemokines by quantitative PCR. Submandibular gland-infiltrating cells were characterized by flow cytometry.

RESULTS

Poly(I:C) treatment significantly upregulated the expression of multiple chemokines within the submandibular glands. The severity and incidence of sialoadenitis was considerably higher in poly(I:C)-treated mice. There was a preponderance of dendritic cells and NK cells in the initial inflammatory cell infiltrates, and these were followed by CD4+ T cells.

CONCLUSIONS

Our data clearly demonstrate that systemic activation of innate immunity accelerates sialoadenitis in a mouse model for SS-like disease. These findings suggest that chronic activation of innate immunity can influence certain features of SS.

Genetics and genomics of Sjögren's syndrome: research provides clues to pathogenesis and novel therapies

PURPOSE

Although the key inciting events that drive the progression from autoantibodies to clinical disease remain to be clarified, new light has been shed on the factors contributing to disease susceptibility and the role of genetic factors in determining Sjögren's syndrome (SS) disease phenotypes. The purpose of this article is to provide an update on the role of genetic markers in the susceptibility to and pathogenesis of SS. This article also discusses how genomic and proteomic technology can help in the design of specific therapeutics.

KEY FINDINGS

Recent evidence suggests that inflammatory genes associated with interferon pathways, and specific regulatory genes that control the maturation and proliferation of B cells, contribute to the pathogenesis of SS. Both gene expression profiling technology and gene association studies have been used to identify these key biological pathways. Molecularly, defined subsets of pSS patients are also being revealed by these studies. Previously, identified gene loci that predispose to multiple autoimmune disorders have been confirmed supporting the paradigm of "general" autoimmune disease genes. Association of SS with many additional susceptibility loci are likely to be established through ongoing genome-wide association scans (GWAS). Clues from genetic studies suggest that targeting B cells will prove to be an effective way of reducing the systemic manifestations of pSS and are supported by early clinical trials.

SUMMARY

Genome-wide technologies are likely to identify new genes and molecular pathways in the pathogenesis of SS that will be useful not only to identify patients at risk for SS, but also to identify subsets of patients at risk for variable levels of disease severity. In the future, these studies could identify novel biomarkers that will lead to significant advances in management by providing the means to tailor therapeutic strategies to individual patients.