Genetic, genomic and epigenetic studies as tools for elucidating disease pathogenesis in primary Sjögren's syndrome

Moving towards a molecular taxonomy of autoimmune rheumatic diseases

Autoimmune rheumatic diseases pose many problems that have, in general, already been solved in the field of cancer. The heterogeneity of each disease, the clinical similarities and differences between different autoimmune rheumatic diseases and the large number of patients that remain without a diagnosis underline the need to reclassify these diseases via new approaches. Knowledge about the molecular basis of systemic autoimmune diseases, along with the availability of bioinformatics tools capable of handling and integrating large volumes of various types of molecular data at once, offer the possibility of reclassifying these diseases. A new taxonomy could lead to the discovery of new biomarkers for patient stratification and prognosis. Most importantly, this taxonomy might enable important changes in clinical trial design to reach the expected outcomes or the design of molecularly targeted therapies. In this Review, we discuss the basis for a new molecular taxonomy for autoimmune rheumatic diseases. We highlight the evidence surrounding the idea that these diseases share molecular features related to their pathogenesis and development and discuss previous attempts to classify these diseases. We evaluate the tools available to analyse and combine different types of molecular data. Finally, we introduce PRECISESADS, a project aimed at reclassifying the systemic autoimmune diseases.

Current views on the pathogenesis of Sjögren's syndrome

PURPOSE OF REVIEW

The purpose of this review is to provide an insight into the pathophysiological mechanisms involved in the pathogenesis of primary Sjögren's Syndrome (pSS), highlighting recent findings with potential therapeutic repercussions.

RECENT FINDINGS

In the last 2 years, epigenetic analyses provided new insights into pSS pathogenesis. Characterization of DNA methylation patterns, chromatin structures and microRNA confirmed the importance of aberrant interferon and B-cell responses in the development of the disease. The formation of ectopic B-cell follicles with germinal centers is now a well recognized pathogenic mechanism within salivary glands of pSS. In the context of ectopic germinal centers reaction, T/B-cell interactions, that is regarding T-helper 17 and T-follicular helper cells, and their respective counterparts, T-regulatory and T-follicular regulatory cells, appear particularly relevant in pSS pathogenesis as their imbalance is associated with a dysregulation of B-cell dynamics and the production of autoantibodies.

SUMMARY

Advances in the understanding of pSS pathogenesis have paved the way for clinical trials with novel biologic agents targeting immune pathways regulating T/B-cell interactions and downstream B-cell activation. Reverse translation from these studies provides invaluable novel information of the mechanisms sustaining autoimmunity and chronic inflammation in pSS.

The Neonatal Salivary Transcriptome

The ability to noninvasively assess the physical and developmental status of a neonate is a goal of modern medicine. In recent years, technological advances have permitted the high-throughput analysis of saliva for thousands of genes, proteins, and metabolites from a single sample source. Saliva is an ideal biofluid to assess health, disease, and development in the newborn. It may be harnessed repeatedly, even in the most vulnerable patients, without risk of harm. Translating novel information about an infant's global development and risk of disease to the neonatal bedside through the salivary transcriptome has the potential to significantly improve clinical care and outcomes in this at-risk population.

Reevaluation for clinical manifestations of HTLV-I-seropositive patients with Sjögren's syndrome

Background

The aim of the study was to reassess the prevalence and characteristics of human T lymphotropic virus type I (HTLV-I)-associated Sjögren’s syndrome (SS) and SS in HTLV-I-associated myelopathy (HAM) based on the American European Consensus Group (AECG) criteria in HTLV-I endemic area, Nagasaki prefecture.

Methods

The 349 patients who underwent a minor salivary gland biopsy (MSGB) for suspected SS were retrospectively classified by AECG classification criteria and divided with or without anti-HTLV-I antibody.

Results

The HTLV-I data-available 294 patients were investigated. One hundred-seventy patients were classified as SS and 26.5 % were HTLV-I-seropositive. We have included 26 patients with HTLV-I-associated myelopathy (HAM) and 38.5 % were classified as having SS. The prevalences of ANA and anti-SS-A/Ro antibody of HAM + SS were significantly low compared to the HTLV-I asymptomatic carriers (AC) with SS and the HTLV-I-seronegative SS patients, although lacrimal dysfunction tended to be high in HAM + SS and significantly high in AC + SS patients compared with the patients with HTLV-I-seronegative SS. The focus scores of MSGB in the HAM + SS patients were similar to those of the AC + SS patients and the HTLV-I-seronegative patients with SS. Among the MSGB-positive patients, there was a low prevalence of ANA in the HAM + SS patients. Similar results were obtained in case of anti-SS-A/Ro or SS-B/La antibody.

Conclusion

In HTLV-I endemic area, high prevalence of anti-HTLV-I antibody among SS as well as the characteristics of HAM + SS and AC + SS was still determined by AECG classification criteria.

Contribution of Genetic Factors to Sjögren's Syndrome and Sjögren's Syndrome Related Lymphomagenesis

We aimed to summarize the current evidence related to the contributory role of genetic factors in the pathogenesis of Sjögren's syndrome (SS) and SS-related lymphoma. Genes within the major histocompatibility complex (MHC) locus previously considered conferring increased susceptibility to SS development have been also revealed as important contributors in recent genome wide association studies. Moreover, genetic variations outside the MHC locus involving genes in type I interferon pathway, NF-κB signaling, B- and T-cell function and methylation processes have been shown to be associated with both SS and SS-related lymphoma development. Appreciating the functional implications of SS-related genetic variants could provide further insights into our understanding of SS heterogeneity, allowing the design of tailored therapeutic interventions.

Overlap between differentially methylated DNA regions in blood B lymphocytes and genetic at-risk loci in primary Sjögren's syndrome

BACKGROUND

Beyond genetics, epigenetics alterations and especially those related to DNA methylation, play key roles in the pathogenesis of autoimmune diseases such as primary Sjögren's syndrome (pSS) and systemic lupus erythematosus. This study aimed to assess the role of methylation deregulation in pSS pathogeny through a genome-wide methylation approach.

PATIENTS AND METHODS

26 female patients with pSS and 22 age-matched controls were included in this study. CD4+ T cells and CD19+ B cells were isolated from peripheral blood mononuclear cells by magnetic microbeads and their genome-wide DNA methylation profiles were analysed using Infinium Human Methylation 450 K BeadChips. Probes with a median DNA methylation difference of at least 7% and p<0.01 between patients and controls were considered significantly differentially methylated.

RESULTS

Methylation alterations were mainly present in B cells compared with T cells. In B cells, an enrichment of genes with differentially methylated probes in genetic at-risk loci was observed, suggesting involvement of both genetic and epigenetic abnormalities in the same genes. Methylation alterations in B cells were more frequent in some specific pathways including Interferon Regulated Genes, mainly among patients who were autoantibody positive. Moreover, genes with differentially methylated probes were over-represented in B cells from patients with active disease.

CONCLUSIONS

This study demonstrated more important deregulation of DNA methylation patterns in B cells compared with T cells, emphasising the importance of B cells in the pathogenesis of the disease. Overlap between genes with differentially methylated probes in B lymphocytes and genetic at-risk loci is a new finding highlighting their importance in pSS.

Towards inhibition of morbidity and mortality in Sjögren's syndrome: opportunities and challenges

In recent years considerable progress has been made in our understanding of the immunopathology of primary Sjögren's syndrome. Several genetic and environmental risk factors as well as cellular and molecular pathways have been identified, providing multiple targets for therapeutic strategies. Establishment of disease activity scores allows careful monitoring of therapeutic strategies and has set the stage for definition of clinical response criteria. Early detection of autoimmune symptoms before the onset of primary Sjögren's syndrome might trigger early intervention strategies to prevent immunopathology. New studies that indicated a strong association between lymphoid neogenesis and development of lymphoma and extra-glandular manifestations indicate that future therapeutic strategies should perhaps be directed at patients at risk for more severe disease. Several challenges remain, such as dissecting the causes and consequences of several types of IFN signatures or elucidating how viral triggering of the immune system is involved and could be targeted. The biggest challenge may be prevention of dryness since the causes of dryness remain elusive and could include non-immunological ones. In the coming years it will become clear to what extent novel drugs can prevent immunopathology and clinical symptoms like dryness and fatigue.