Common variants near IKZF1 are associated with primary Sjögren's syndrome in Han Chinese

The role of transcription factors in shaping regulatory T cell identity

Forkhead box protein 3-expressing (FOXP3+) regulatory T cells (Treg cells) suppress conventional T cells and are essential for immunological tolerance. FOXP3, the master transcription factor of Treg cells, controls the expression of multiples genes to guide Treg cell differentiation and function. However, only a small fraction (<10%) of Treg cell-associated genes are directly bound by FOXP3, and FOXP3 alone is insufficient to fully specify the Treg cell programme, indicating a role for other accessory transcription factors operating upstream, downstream and/or concurrently with FOXP3 to direct Treg cell specification and specialized functions. Indeed, the heterogeneity of Treg cells can be at least partially attributed to differential expression of transcription factors that fine-tune their trafficking, survival and functional properties, some of which are niche-specific. In this Review, we discuss the emerging roles of accessory transcription factors in controlling Treg cell identity. We specifically focus on members of the basic helix-loop-helix family (AHR), basic leucine zipper family (BACH2, NFIL3 and BATF), CUT homeobox family (SATB1), zinc-finger domain family (BLIMP1, Ikaros and BCL-11B) and interferon regulatory factor family (IRF4), as well as lineage-defining transcription factors (T-bet, GATA3, RORγt and BCL-6). Understanding the imprinting of Treg cell identity and specialized function will be key to unravelling basic mechanisms of autoimmunity and identifying novel targets for drug development.

Ikaros is a principal regulator of Aire+ mTEC homeostasis, thymic mimetic cell diversity, and central tolerance

Mutations in the gene encoding the zinc-finger transcription factor Ikaros (IKZF1) are found in patients with immunodeficiency, leukemia, and autoimmunity. Although Ikaros has a well-established function in modulating gene expression programs important for hematopoietic development, its role in other cell types is less well defined. Here, we uncover functions for Ikaros in thymic epithelial lineage development in mice and show that Ikzf1 expression in medullary thymic epithelial cells (mTECs) is required for both autoimmune regulator-positive (Aire+) mTEC development and tissue-specific antigen (TSA) gene expression. Accordingly, TEC-specific deletion of Ikzf1 in mice results in a profound decrease in Aire+ mTECs, a global loss of TSA gene expression, and the development of autoimmunity. Moreover, Ikaros shapes thymic mimetic cell diversity, and its deletion results in a marked expansion of thymic tuft cells and muscle-like mTECs and a loss of other Aire-dependent mimetic populations. Single-cell analysis reveals that Ikaros modulates core transcriptional programs in TECs that correlate with the observed cellular changes. Our findings highlight a previously undescribed role for Ikaros in regulating epithelial lineage development and function and suggest that failed thymic central tolerance could contribute to the autoimmunity seen in humans with IKZF1 mutations.

Pervasive Sharing of Causal Genetic Risk Factors Contributes to Clinical and Molecular Overlap between Sjögren's Disease and Systemic Lupus Erythematosus

SjD (Sjögren's Disease) and SLE (Systemic Lupus Erythematosus) are similar diseases. There is extensive overlap between the two in terms of both clinical features and pathobiologic mechanisms. Shared genetic risk is a potential explanation of this overlap. In this study, we evaluated whether these diseases share causal genetic risk factors. We compared the causal genetic risk for SLE and SjD using three complementary approaches. First, we examined the published GWAS results for these two diseases by analyzing the predicted causal gene protein-protein interaction networks of both diseases. Since this method does not account for overlapping risk intervals, we examined whether such intervals also overlap. Third, we used two-sample Mendelian randomization (two sample MR) using GWAS summary statistics to determine whether risk variants for SLE are causal for SjD and vice versa. We found that both the putative causal genes and the genomic risk intervals for SLE and SjD overlap 28- and 130-times more than expected by chance (p < 1.1 × 10-24 and p < 1.1 × 10-41, respectively). Further, two sample MR analysis confirmed that alone or in aggregate, SLE is likely causal for SjD and vice versa. [SjD variants predicting SLE: OR = 2.56; 95% CI (1.98-3.30); p < 1.4 × 10-13, inverse-variance weighted; SLE variants predicting SjD: OR = 1.36; 95% CI (1.26-1.47); p < 1.6 × 10-11, inverse-variance weighted]. Notably, some variants have disparate impact in terms of effect size across disease states. Overlapping causal genetic risk factors were found for both diseases using complementary approaches. These observations support the hypothesis that shared genetic factors drive the clinical and pathobiologic overlap between these diseases. Our study has implications for both differential diagnosis and future genetic studies of these two conditions.

Genetics and epigenetics of primary Sjögren syndrome: implications for future therapies

In primary Sjögren syndrome (pSS), chronic inflammation of exocrine glands results in tissue destruction and sicca symptoms, primarily of the mouth and eyes. Fatigue, arthralgia and myalgia are also common symptoms, whereas extraglandular manifestations that involve the respiratory, nervous and vascular systems occur in a subset of patients. The disease predominantly affects women, with an estimated female to male ratio of 14 to 1. The aetiology of pSS, however, remains incompletely understood, and effective treatment is lacking. Large-scale genetic and epigenetic investigations have revealed associations between pSS and genes in both innate and adaptive immune pathways. The genetic variants mediate context-dependent effects, and both sex and environmental factors can influence the outcome. As such, genetic and epigenetic studies can provide insight into the dysregulated molecular mechanisms, which in turn might reveal new therapeutic possibilities. This Review discusses the genetic and epigenetic features that have been robustly connected with pSS, putting them into the context of cellular function, carrier sex and environmental challenges. In all, the observations point to several novel opportunities for early detection, treatment development and the pathway towards personalized medicine.

Genome-wide association study identifies Sjögren's risk loci with functional implications in immune and glandular cells

Sjögren's disease is a complex autoimmune disease with twelve established susceptibility loci. This genome-wide association study (GWAS) identifies ten novel genome-wide significant (GWS) regions in Sjögren's cases of European ancestry: CD247, NAB1, PTTG1-MIR146A, PRDM1-ATG5, TNFAIP3, XKR6, MAPT-CRHR1, RPTOR-CHMP6-BAIAP6, TYK2, SYNGR1. Polygenic risk scores yield predictability (AUROC = 0.71) and relative risk of 12.08. Interrogation of bioinformatics databases refine the associations, define local regulatory networks of GWS SNPs from the 95% credible set, and expand the implicated gene list to >40. Many GWS SNPs are eQTLs for genes within topologically associated domains in immune cells and/or eQTLs in the main target tissue, salivary glands.

Genetics and epigenetics in primary Sjögren's syndrome

Primary Sjögren’s syndrome (pSS) is considered to be a multifactorial disease, where underlying genetic predisposition, epigenetic mechanisms and environmental factors contribute to disease development. In the last 5 years, the first genome-wide association studies in pSS have been completed. The strongest signal of association lies within the HLA genes, whereas the non-HLA genes IRF5 and STAT4 show consistent associations in multiple ethnicities but with a smaller effect size. The majority of the genetic risk variants are found at intergenic regions and their functional impact has in most cases not been elucidated. Epigenetic mechanisms such as DNA methylation, histone modifications and non-coding RNAs play a role in the pathogenesis of pSS by their modulating effects on gene expression and may constitute a dynamic link between the genome and phenotypic manifestations. This article reviews the hitherto published genetic studies and our current understanding of epigenetic mechanisms in pSS.

Ten-year survival analysis of patients with primary Sjögren's syndrome in China: a national prospective cohort study

Aims

To investigate the long-term survival of patients with primary Sjögren's syndrome (pSS) in China.

Methods

Patients with pSS who fulfilled the 2002 American-European Consensus Group classification criteria were prospectively enrolled from 2004 to 2011. Their baseline clinical, laboratory, and therapeutic data were collected. The primary endpoint was all-cause death by January 2018. The standard mortality ratio (SMR) was calculated by comparing with age-matched and sex-matched mortality data of the general population. Kaplan-Meier curves were obtained by time-to-event analysis. Univariate and multivariate Cox hazards regression analyses were performed to identify risk factors for mortality.

Results

A total of 1054 patients were enrolled and 834 patients were followed up for a median of 94.8 months, with 48 confirmed deaths. The total SMR was 3.63 [95% confidence interval (CI) 2.60-4.66]. The 3-, 5-, and 10-year survival rates were 98.4%, 97.5%, and 92.9%, respectively. Infection, malignancy, and respiratory failure were the top three causes of mortality. We identified male sex [hazard ratio (HR) = 3.00, 95% CI 1.23-7.31], age at diagnosis ⩾50 years of age (HR = 7.69, 95% CI 3.01-19.62), thrombocytopenia (HR = 1.93, 95% CI 1.01-3.72), and interstitial lung disease (HR = 5.96, 95% CI 2.24-15.82) as the independent prognostic factors of death.

Conclusions

The mortality rates of Chinese patients with pSS are higher than those of the general population. Male patients of elder age at diagnosis complicated with thrombocytopenia and interstitial lung disease might be suggestive for poorer survival and require closer follow up.

CD4+ T cells require Ikaros to inhibit their differentiation toward a pathogenic cell fate

The production of proinflammatory cytokines, particularly granulocyte-macrophage colony-stimulating factor (GM-CSF), by pathogenic CD4+ T cells is central for mediating tissue injury in inflammatory and autoimmune diseases. However, the factors regulating the T cell pathogenic gene expression program remain unclear. Here, we investigated how the Ikaros transcription factor regulates the global gene expression and chromatin accessibility changes in murine T cells during Th17 polarization and after activation via the T cell receptor (TCR) and CD28. We found that, in both conditions, Ikaros represses the expression of genes from the pathogenic signature, particularly Csf2, which encodes GM-CSF. We show that, in TCR/CD28-activated T cells, Ikaros binds a critical enhancer downstream of Csf2 and is required to regulate chromatin accessibility at multiple regions across this locus. Genome-wide Ikaros binding is associated with more compact chromatin, notably at multiple sites containing NFκB or STAT5 target motifs, and STAT5 or NFκB inhibition prevents GM-CSF production in Ikaros-deficient cells. Importantly, Ikaros also limits GM-CSF production in TCR/CD28-activated human T cells. Our data therefore highlight a critical conserved transcriptional mechanism that antagonizes GM-CSF expression in T cells.

IKZF1 polymorphisms are associated with susceptibility, cytokine levels, and clinical features in systemic lupus erythematosus

Ikaros family zinc finger 1(IKZF1) encodes a lymphoid-restricted zinc finger transcription factor named Ikaros that regulates lymphocyte differentiation and proliferation as well as self-tolerance. Increasing evidence indicates that IKZF1 could contribute to the pathogenesis of autoimmune diseases. Recent research has provided evidence that IKZF1 might correlate with Systemic lupus erythematosus (SLE), but no clear definition has been made yet. In this study, we focus on the relationship between IKZF1 polymorphisms and SLE susceptibility, cytokine levels, and clinical characteristics in the Chinese Han population.One thousand seventy-six subjects, including 400 SLE patients and 676 healthy controls, were included in this study. Three single nucleotide polymorphisms within IKZF1 containing rs4917014, rs11980379, and rs4132601 were genotyped in all subjects by an improved multiplex ligation detection reaction technique. 143 subjects from SLE patients were randomly selected for testing the levels of serum cytokines. The clinical characteristics of SLE patients were gathered and collated from medical records. The data were analyzed mainly using SPSS20.0 (SPSS lnc., Chicago, IL).Significant relationships were observed between rs4132601 and SLE susceptibility, CD40 ligand, and malar rash (P < .001, P = .04, and P = .01, respectively). In addition, significant relationships were observed between rs4917014 and susceptibility, granzyme B level, and hematological disorder in SLE (P = .005, P = .03 and P = .005, respectively).The results further support that IKZF1 may have an important role in the development and pathogenesis of SLE. Allele G of rs4132601 and rs4917014 is related to a decreased risk of SLE occurrence and associated with clinical features in SLE patients, including CD40 ligand level, granzyme B level, malar rash, and hematological disorder, which play important roles in disease progression.

Autoimmune diseases in China

Autoimmune diseases, such as rheumatoid arthritis, systematic lupus erythematosus and Sjögren's syndrome, are a group of diseases characterized by the activation of immune cells and excessive production of autoantibodies. Although the pathogenesis of these diseases is still not completely understood, studies have shown that multiple factors including genetics, environment and immune responses play important roles in the development and progression of the diseases. In China, there are great achievements in the mechanisms of autoimmune diseases during the last decades. These studies provide new insight to understand the diseases and also shed light on the development of novel therapy.

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.

B cells in Sjögren's syndrome: from pathophysiology to therapeutic target

Biological abnormalities associated with B lymphocytes are a hallmark of patients with primary Sjögren's syndrome. Those patients present abnormal distribution of B lymphocytes in peripheral blood and B cells in exocrine glands. B cells produce auto-antibodies, cytokines and present antigens but can also suppressive functions. In this review, we will summarize current knowledge on B cells in primary Sjögren's syndrome patients, demonstrate their critical role in the immunopathology of the disease and describe the past and current trials targeting B cells.

Pathogenesis-based treatments in primary Sjogren's syndrome using artificial intelligence and advanced machine learning techniques: a systematic literature review

Big data analysis has become a common way to extract information from complex and large datasets among most scientific domains. This approach is now used to study large cohorts of patients in medicine. This work is a review of publications that have used artificial intelligence and advanced machine learning techniques to study physio pathogenesis-based treatments in pSS. A systematic literature review retrieved all articles reporting on the use of advanced statistical analysis applied to the study of systemic autoimmune diseases (SADs) over the last decade. An automatic bibliography screening method has been developed to perform this task. The program called BIBOT was designed to fetch and analyze articles from the pubmed database using a list of keywords and Natural Language Processing approaches. The evolution of trends in statistical approaches, sizes of cohorts and number of publications over this period were also computed in the process. In all, 44077 abstracts were screened and 1017 publications were analyzed. The mean number of selected articles was 101.0 (S.D. 19.16) by year, but increased significantly over the time (from 74 articles in 2008 to 138 in 2017). Among them only 12 focused on pSS but none of them emphasized on the aspect of pathogenesis-based treatments. To conclude, medicine progressively enters the era of big data analysis and artificial intelligence, but these approaches are not yet used to describe pSS-specific pathogenesis-based treatment. Nevertheless, large multicentre studies are investigating this aspect with advanced algorithmic tools on large cohorts of SADs patients.