Revisiting MHC Genes in Spondyloarthritis

TGFβ signaling pathway is altered by HLA-B27 expression, resulting in pathogenic consequences relevant for spondyloarthritis

BACKGROUND

Association of HLA-B27 with spondyloarthritis (SpA) has been known for 50 years, but still remains unexplained. We recently showed that HLA-B27 expressed in wing imaginal disc from HLA-B27/human-β2 microglobulin (hβ2m) transgenic Drosophila deregulated bone morphogenetic protein (BMP) pathway by interacting physically with type I BMP receptor (BMPR1) Saxophone (Sax), leading to crossveinless phenotype.

METHODS

Genetic interaction was studied between activin/transforming growth factor β (TGFβ) pathway and HLA-B27/hβ2m in transgenic Drosophila wings. The HLA-B27-bound peptidome was characterized in wing imaginal discs. In mesenteric lymph node (mLN) T cells from HLA-B27/hβ2m rat (B27 rat), physical interaction between HLA-B27 and activin receptor-like kinase-2 (ALK2), ALK3 and ALK5 BMPR1s, phosphorylation of small mothers against decapentaplegic (SMADs) and proteins of the non-canonical BMP/TGFβ pathways induced by its ligands, and the transcript level of target genes of the TGFβ pathway, were evaluated.

RESULTS

In HLA-B27/hβ2m transgenic Drosophila, inappropriate signalling through the activin/TGFβ pathway, involving Baboon (Babo), the type I activin/TGFβ receptor, contributed to the crossveinless phenotype, in addition to deregulated BMP pathway. We identified peptides bound to HLA-B27 with the canonical binding motif in HLA-B27/hβ2m transgenic Drosophila wing imaginal disc. We demonstrated specific physical interaction, between HLA-B27/hβ2m and mammalian orthologs of Sax and Babo, i.e. ALK2 and ALK5 (i.e. TGFβ receptor I), in the mLN cells from B27 rat. The magnitude of phosphorylation of SMAD2/3 in response to TGFβ1 was increased in T cells from B27 rats, showing evidence for deregulated TGFβ pathway. Accordingly, expression of several target genes of the pathway was increased in T cells from B27 rats, in basal conditions and/or after TGFβ exposure, including Foxp3, Rorc, Runx1 and Maf. Interestingly, Tgfb1 expression was reduced in naive T cells from B27 rats, even premorbid, an observation consistent with a pro-inflammatory pattern.

CONCLUSIONS

This study shows that HLA-B27 alters the TGFβ pathways in Drosophila and B27 rat. Given the importance of this pathway in CD4 + T cells differentiation and regulation, its disturbance could contribute to the abnormal expansion of pro-inflammatory T helper 17 cells and altered regulatory T cell phenotype observed in B27 rats.

CD8+ T and NK cells characterized by upregulation of NPEPPS and ABHD17A are associated with the co-occurrence of type 2 diabetes and coronary artery disease

Background

Coronary artery disease (CAD) and type 2 diabetes mellitus (T2DM) are closely related. The function of immunocytes in the pathogenesis of CAD and T2DM has not been extensively studied. The quantitative bioinformatics analysis of the public RNA sequencing database was applied to study the key genes that mediate both CAD and T2DM. The biological characteristics of associated key genes and mechanism of CD8+ T and NK cells in CAD and T2DM are our research focus.

Methods

With expression profiles of GSE66360 and GSE78721 from the Gene Expression Omnibus (GEO) database, we identified core modules associated with gene co-expression relationships and up-regulated genes in CAD and T2DM using Weighted Gene Co-expression Network Analysis (WGCNA) and the 'limma' software package. The enriched pathways of the candidate hub genes were then explored using GO, KEGG and GSEA in conjunction with the immune gene set (from the MSigDB database). A diagnostic model was constructed using logistic regression analysis composed of candidate hub genes in CAD and T2DM. Univariate Cox regression analysis revealed hazard ratios (HRs), 95% confidence intervals (CIs), and p-values for candidate hub genes in diagnostic model, while CIBERSORT and immune infiltration were used to assess the immune microenvironment. Finally, monocytes from peripheral blood samples and their immune cell ratios were analyzed by flow cytometry to validate our findings.

Results

Sixteen candidate hub genes were identified as being correlated with immune infiltration. Univariate Cox regression analysis revealed that NPEPPS and ABHD17A were highly correlated with the diagnosis of CAD and T2DM. The results indicate that CD8+ T cells (p = 0.04) and NKbright cells (p = 3.7e-3) are significantly higher in healthy controls than in individuals with CAD or CAD combined with T2DM. The bioinformatics results on immune infiltration were well validated by flow cytometry.

Conclusions

A series of bioinformatics studies have shown ABHD17A and NPEPPS as key genes for the co-occurrence of CAD and T2DM. Our study highlights the important effect of CD8+ T and NK cells in the pathogenesis of both diseases, indicating that they may serve as viable targets for diagnosis and therapeutic intervention.

Human Leukocyte Antigen B*27-Negative Spondyloarthritis: Clinical, Serological, and Radiological Features of a Single-Center Cohort

The strong genetic association between HLA-B*27 and spondyloarthritis (SpA) accounts for about 90% of the susceptibility to axial SpA (axSpA), and the presence of HLA-B*27 is helpful in classifying patients according to the Assessment of SpondyloArthritis International Society (ASAS) classification criteria. However, over the years, other HLA-B alleles have been associated with an increased risk of developing SpA; on this basis, the aim of our study was to describe the demographic, clinical, and radiological characteristics of a cohort of SpA patients who were negative for HLA-B*27. We identified 85 patients with a clinical diagnosis of SpA displaying HLA-B alleles other than HLA-B*27; HLA-B*51 emerged as the most prevalent allele (N = 33, 39%), regardless of the fulfilment of either the axial or the peripheral ASAS criteria. The second most prevalent allele in the full cohort (N = 16, 19%) and in the patients fulfilling either the axial or the peripheral criteria was HLA-B*35. The third most prevalent allele in the full cohort was HLA-B*18 (N = 12, 15%), which was also the second most prevalent allele in the patients fulfilling neither of the two sets of criteria. Overall, the clinical picture was similar across the subgroups fulfilling the different sets of ASAS criteria; however, the patients not fulfilling any ASAS criteria had a higher likelihood of having arthritis compared to the patients fulfilling the axial criteria, whereas the Bath Ankylosing Spondylitis Functional Index was significantly higher in those patients fulfilling the axial criteria compared to those who did not fulfill any criteria. Our results indicate that other HLA alleles, beyond HLA-B*27, could be useful in facilitating SpA diagnosis, particularly in patients with a clinical picture which is consistent with SpA but does not fulfill the ASAS classification criteria.

Genetics, Epigenetics, and Gender Impact in Axial-Spondyloarthritis Susceptibility: An Update on Genetic Polymorphisms and Their Sex Related Associations

Spondyloarthritis (SpA) is a group of chronic inflammatory rheumatic disease that can be divided into predominantly axial or predominantly peripheral involvement, with or without associated psoriasis, inflammatory bowel disease or previous infection. Axial SpA (axSpA) encompasses ankylosing spondylitis (AS) with radiological sacroiliitis, and a type without radiographic sacroiliitis, called “non-radiographic axial SpA” (nr-axSpA). Males and females show large differences in their susceptibility to SpA, such as distinctions in clinical patterns, phenotypes and in therapeutical response, particularly to TNF inhibitors (TNFi). Several studies indicate that AS women have doubled risk to failure TNFi compared with males. This diversity in drugs’ efficacy among women and men may be caused by differences in the balance of sex hormones and in gene-specific expression likely triggered by X-chromosome instability and gene-specific epigenetic modifications. Evidence reported that polymorphisms in microRNAs on X- and other chromosomes, such as miR-146a, miR-155, miR-125a-5p, miR-151a-3p and miR-22-3p, miR-199a-5p could be involved in the different clinical presentation of SpA, as well as disease activity. In addition, association with non−response to TNFi treatment and presence of IRAK3 and CHUCK genes in SpA patients was recently detected. Finally, polymorphisms in genes involved in IL-23/IL-17 pathway, such as in drug pharmacodynamics and pharmacokinetics may have a role in response to TNFi, IL17i, and IL23i. A major understanding of genomic variability could help in the development of new therapeutic targets or in taking advantages of different mechanisms of action of biological drugs. Moving from the multifactorial etiology of disease, the present review aims at evaluating genetic and epigenetic factors and their relationship with sex and bDMARDs response, helping to investigate the different expression among males and females of genes on X- and other chromosomes, as well as mi-RNA, to highlight relationships between sex and occurrence of specific phenotypes and symptoms of the disease. Moreover, the role of the epigenetic modification in relation to immune-regulatory mechanisms will be evaluated.

Intestinal dysbiosis in spondyloarthritis - chicken or egg?

PURPOSE OF REVIEW

The well-established link between intestinal inflammation and spondyloarthritis (SpA) remains largely unexplained. Recent sequencing technologies have given access to a thorough characterization of the gut microbiota in healthy and disease conditions. This showed that inflammatory bowel disease (IBD) is associated with dysbiosis - i.e., disturbed gut microbiota composition - which may contribute to disease pathogenesis. Whether gut dysbiosis exists in SpA and could contribute to disease development or be a bystander consequence of chronic inflammation is a question of major interest.

RECENT FINDINGS

Several metagenomic studies have been performed in SpA. Most of them concerned faecal samples and showed dysbiosis consisting in a reduction of microbial biodiversity in a way similar to what has been described in IBD. They also highlighted changes in microbial taxa composition that could contribute to the inflammatory process. Likewise, healthy carriers of human leukocyte antigen (HLA)-B27 exhibited gut dysbiosis, indicating that this predisposing allele could exert its pathogenic effect by influencing microbiota composition, and possibly by driving antigen-specific cross-reactive immune response. On the other hand, SpA treatments were associated with a reduction of dysbiosis, showing that it is at least in part a consequence of inflammation.

SUMMARY

Recent insights from metagenomic studies warrant further investigations to identify the mechanisms by which microbial dysbiosis could contribute to SpA development. This would bring novel therapeutic opportunities aiming at correcting detrimental changes.

The Association of Fecal Microbiota in Ankylosing Spondylitis Cases with C-Reactive Protein and Erythrocyte Sedimentation Rate

The purpose of this work was to identify the features of the gut microbiome in cases of ankylosing spondylitis (AS) testing positive for human leukocyte antigen- (HLA-) B27 and healthy controls (HCs) as well as to determine how bacterial populations were correlated with C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR). Fecal DNA extracted from fecal samples from 10 AS cases and 12 HCs was subjected to 16S rRNA gene sequencing. The two research groups did not differ significantly regarding alpha diversity. By comparison to HCs, AS cases displayed a lower relative level of Bacteroidetes (P < 0.05), but a higher level of Firmicutes and Verrucomicrobia (P < 0.05). Furthermore, the correlation between the specific gut bacteria and ESR or CRP was investigated. At the phylum level, Firmicutes and Verrucomicrobia had a positive association with ESR and CRP, while Bacteroidetes exhibited an inverse correlation with ESR and CRP. Meanwhile, in terms of genus, Bacteroides had a positive association with ESR and CRP, whereas Ruminococcus and Parasutterella had an inverse correlation with ESR and CRP, and Helicobacter also displayed an inverse correlation with CRP. Such findings indicated dissimilarities between AS cases and HCs regarding the gut microbiome, as well as the existence of correlations between bacterial populations and both ESR and CRP.

HLA-B27 Subtypes Predisposing to Ankylosing Spondylitis Accumulate in an Endoplasmic Reticulum-Derived Compartment Apart From the Peptide-Loading Complex

OBJECTIVE

It was previously shown that HLA-B27 subtypes predisposing to spondyloarthritis (SpA), i.e., B*27:02, B*27:05, and B*27:07, displayed an increased propensity to form intracellular oligomers and to accumulate at a high density in cytoplasmic vesicles, as compared to the non-SpA-associated HLA-B*07:02 and HLA-B*27:06. This study was undertaken to characterize the nature and content of HLA-B-containing vesicles and to further examine their relevance to SpA predisposition.

METHODS

Vesicles containing HLA-B proteins were detected in transfected HeLa cells and in cells from SpA patients or HLA-B27/human β₂ -microglobulin (hβ₂ m)-transgenic rats, by microscopy. The nature and content of HLA-B-containing vesicles were characterized in colocalization experiments with appropriate markers.

RESULTS

The SpA-associated HLA-B*27:04 subtype accumulated at higher levels (P < 10^-5 ) in cytoplasmic vesicles compared to HLA-B*27:06, from which it differs only by 2 substitutions, reinforcing the correlation between vesicle formation and SpA predisposition. Colocalization studies showed that those vesicles contained misfolded HLA-B heavy chain along with β₂ m and endoplasmic reticulum (ER) chaperones (calnexin, calreticulin, BiP, glucose-regulated protein 94-kd) and belonged to the ER but were distinct from the peptide-loading complex (PLC). Similar vesicles were observed in immune cells from HLA-B27+ SpA patients, in greater abundance than in healthy controls (P < 0.01), and in dendritic cells from HLA-B27/hβ₂ m transgenic rats, correlating with SpA susceptibility.

CONCLUSION

Accumulation of misfolded HLA-B heavy chain along with β₂ m and ER chaperones into ER-derived vesicles distinct from the PLC is a characteristic feature of HLA-B27 subtypes predisposing to SpA. This phenomenon could contribute to HLA-B27 pathogenicity, via a noncanonical mechanism.

Genetics and Functional Genomics of Spondyloarthritis

Spondyloarthritis (SpA) is a chronic inflammatory disorder with high heritability but with complex genetics. It encompasses several entities that share common clinical features. Most of the genetic studies in SpA have been restricted to ankylosing spondylitis (AS), the prototypical form of SpA. However, there is growing evidence of shared genetic background between all the SpA subtypes and also with some other immune-mediated diseases. The most important part of SpA heritability comes from the HLA-B27 allele in the major histocompatibility complex (MHC) that explains around 25% of the attributable heredity. Several other loci outside of the MHC have been shown to be involved in the disease. However, all these non-MHC loci explain only a small additional fraction of disease predisposition. Thus, a substantial fraction of SpA genetic basis remains poorly understood. Gene expression profiling is a complementary approach to elucidate the underlying mechanisms and pathways that drive the disease. Several expression profiling studies have been undertaken in SpA. However, results have been quite disappointing with little overlap between the studies largely due to the small sample sizes, resulting in limited power to discover small effects. In this review, we summarize current knowledge on genetic findings concerning SpA and we describe strategic approaches for identification of additional variants, with a focus on rare variants in familial forms. We also provide an overview of gene expression studies in SpA and discuss the possibilities offered by high-throughput RNA sequencing technologies, in particular in sorted cells. Finally, issues in establishing molecular mechanisms underlying genetic association hits and potential translational applications will be addressed.

Contribution of ancient human remains analysis to the understanding of the variability in HLA-B gene variants in relation to the diagnosis of spondyloarthropathies

Genetic investigations on ancient human remains affected by rheumatological pathologies are a research field of particular interest for identifying the pathogenesis of diseases, especially those having an autoimmune background such as spondyloarthopaties (SpA). Reliable studies concerning this topic require collaboration between multiple disciplines, usually starting from paleopathologic observations up to molecular genetic screening. Here, we focused our investigation in a medieval necropolis in the Basque Country (13th-15th century, N = 163), which presents a high frequency of joint pathologies through two approaches: on the one hand, the analysis of joint manifestations for the differential diagnosis of the SpA and, on the other hand, the determination of the alleles of the HLA-B gene. The morphological analysis allowed determining that 30% of the individuals had rheumatic bone manifestations, with SpA being the most frequent (45%). The genetic analysis of individuals with and without pathologies, based on the study of the HLA-B gene, allowed finding 17 alleles for this gene, with HLA-B40, HLA-B27 and HLA-B35 being the most frequent. Although these alleles have been traditionally described as genetic markers associated to the development of SpA, in this study they were also found in individuals with other rheumatic diseases (osteoarthritis and rheumatoid arthritis) and even in individuals without pathologies. These data confirm the complexity of the relationship of the HLA-B gene variants with SpA, since it is not possible to establish a diagnosis of SpA with these variants alone. However, we suggest that allele HLA-B40, in combination with some specific rheumatic bone manifestations, facilitates the diagnosis of SpA.

Faecal microbiota study reveals specific dysbiosis in spondyloarthritis

OBJECTIVE

Altered microbiota composition or dysbiosis is suspected to be implicated in the pathogenesis of chronic inflammatory diseases, such as spondyloarthritis (SpA) and rheumatoid arthritis (RA).

METHODS

16S ribosomal RNA gene sequencing was performed on faecal DNA isolated from stool samples in two consecutive cross-sectional cohorts, each comprising three groups of adult volunteers: SpA, RA and healthy controls (HCs). In the second study, HCs comprised a majority of aged-matched siblings of patients with known HLA-B27 status. Alpha and beta diversities were assessed using QIIME, and comparisons were performed using linear discriminant analysis effect size to examine differences between groups.

RESULTS

In both cohorts, dysbiosis was evidenced in SpA and RA, as compared with HCs, and was disease specific. A restriction of microbiota biodiversity was detected in both disease groups. The most striking change was a twofold to threefold increased abundance of Ruminococcus gnavus in SpA, as compared with both RA and HCs that was significant in both studies and positively correlated with disease activity in patients having a history of inflammatory bowel disease (IBD). Among HCs, significant difference in microbiota composition were also detected between HLA-B27+ and HLA-B27 negative siblings, suggesting that genetic background may influence gut microbiota composition.

CONCLUSION

Our results suggest that distinctive dysbiosis characterise both SpA and RA and evidence a reproducible increase in R. gnavus that appears specific for SpA and a marker of disease activity. This observation is consistent with the known proinflammatory role of this bacteria and its association with IBD. It may provide an explanation for the link that exists between SpA and IBD.

Association of HLA-DP/DQ and STAT4 polymorphisms with ankylosing spondylitis in Southwest China

Ankylosing spondylitis (AS) is a highly heritable complex inflammatory arthritis disease. Genetic factors are thought to be crucial in the pathogenesis of AS. However, few data are available on the relationship between HLA-DP/DQ and STAT4 polymorphisms and AS susceptibility in the Chinese population. Therefore, we examined HLA-DP/DQ and STAT4 polymorphisms (rs3077, rs9277535, rs7453920 and rs7574865) in a total of 779 subjects, including 400 AS and 379 age- and sex-matched healthy controls in Chinese. No significant difference was observed between AS patients and healthy controls in the allele frequency of rs3077, rs9277535 and rs7574865. However, there was a significant association between the HLA-DQ rs7453920 G/A variant and AS patients, with minor allele A correlated with a reduced risk of AS (allelic frequency, adjusted OR=0.66, 95% CI=0.55-0.78, p=4.0E-06; dominant model, adjusted OR=0.75, 95% CI=0.66-0.85, p=1.1E-05). Moreover, the haplotypes block AAA and GGA in the HLA gene significantly correlated with reduced risk of AS. This is the first study demonstrating the significant associations of SNP rs7453920 and the haplotypes in the HLA gene with the risk of AS in Southwest Chinese population. This research sheds new light on the significant relationship between HLA polymorphisms and AS.

Genetics of autoimmune diseases: perspectives from genome-wide association studies

Genome-wide association studies (GWASs) for autoimmune diseases (ADs) have identified many risk loci and have provided insights into the etiology of each disease. Some of these loci, such asPTPN22,IL23RandSTAT4, are shared among different ADs, and the combination of risk loci may determine an individual's susceptibility for a disease. The majority of GWAS loci are expression quantitative trait loci (eQTLs), where disease-causing variants regulate expression of neighboring (or sometimes distant) genes. Because the eQTL effects are often cell type-specific, the incorporation of epigenetic data from disease-related cell types and tissues is expected to refine the identification of causal variants. The cumulative eQTL effects in multiple genes may influence the activity or fate of immune cells, which in turn may affect the function of the immune system in individuals. In this paper, I review the etiology of ADs by focusing on important immune cells (Th1 cells, Th17 cells and regulatory T cells), important pathways (antigen-receptor signaling and type I interferon signaling) and relevant genes identified in GWASs.