The influence of ERAP1 gene variants on clinical phenotype in ankylosing spondylitis

Association of Endoplasmic Reticulum Aminopeptidase 1 Gene Polymorphism with Susceptibility and Severity of Axial Spondyloarthritis in Egyptian Population: A Single-center Case-Control Study

BACKGROUND

Axial spondyloarthritis (axSpA) is a systemic, progressive, autoimmune disease. Complex interactions between environmental factors and host immune responses are the origin of axSpA. Together with human leukocyte antigen (HLA-B27), endoplasmic reticulum aminopeptidase 1 (ERAP1) gene is a potential non-HLA contributor to axSpA susceptibility.

AIM

This study aimed to identify the role of ERAP1 single-nucleotide polymorphisms (SNPs) (rs30187, rs27044, and rs27037) in susceptibility to and severity of axSpA in Egyptian patients.

METHODS

In this case-control study, we enrolled 120 patients with axSpA and 120 healthy individuals as controls. Real-time polymerase chain reaction was used to identify ERAP1 polymorphisms.

RESULTS

The present study revealed no significant association between ERAP1 SNPs (rs30187, rs27044, and rs27037) and axSpA susceptibility in Egyptian patients. A significant relationship was found only between the ERAP1 SNP rs27037 "GT" genotype and axSpA HLA-B27-positive cases, demonstrating a functional interaction between ERAP1 and HLA-B27-positive cases. Our analysis revealed a significant association between the ERAP1 SNP rs27037 "GT and TT" genotypes and Bath Ankylosing Spondylitis Disease Activity Index, in addition to an association between the ERAP1 SNP rs27037 "TT" genotype and active enthesitis. The ERAP1 SNP rs27044 "GG" genotype was significantly associated with active enthesitis, but not with clinical axial involvement. Finally, we did not observe a significant relationship between HLA-B27 positivity and disease severity in the studied cases.

CONCLUSION

Three SNPs (rs30187, rs27044, and rs27037) in ERAP1 do not confer susceptibility to axSpA in Egyptian patients. This association existed exclusively between the ERAP1 SNP (rs27037) "GT" genotype and axSpA HLA-B27-positive cases.

Shedding Light on the Role of ERAP1 in Axial Spondyloarthritis

Spondyloarthritis (SpA) is a multifactorial chronic inflammatory disease affecting the axial skeleton (axSpA) and/or peripheral joints (p-SpA) and entheses. The disease's pathogenesis depends on genetic, immunological, mechanical, and environmental factors. Endoplasmic reticulum aminopeptidase 1 (ERAP1) is a multifunctional enzyme that shapes the peptide repertoire presented by major histocompatibility complex (MHC) class I molecules. Genome-wide association studies (GWAS) have identified different single nucleotide polymorphisms (SNPs) in ERAP1 that are associated with several autoimmune diseases, including axSpA. Therefore, a deeper understanding of the ERAP1 role in axSpA could make it a potential therapeutic target for this disease and offer greater insight into its impact on the immune system. Here, we review the biological functions and structure of ERAP1, discuss ERAP1 polymorphisms and their association with axSpA, highlight the interaction between ERAP1 and human leukocyte antigen (HLA)-B27, and review the association between ERAP1 SNPs and axSpA clinical parameters.

EULAR study group on ‘MHC-I-opathy’: identifying disease-overarching mechanisms across disciplines and borders

The ‘MHC-I (major histocompatibility complex class I)-opathy’ concept describes a family of inflammatory conditions with overlapping clinical manifestations and a strong genetic link to the MHC-I antigen presentation pathway. Classical MHC-I-opathies such as spondyloarthritis, Behçet’s disease, psoriasis and birdshot uveitis are widely recognised for their strong association with certain MHC-I alleles and gene variants of the antigen processing aminopeptidases ERAP1 and ERAP2 that implicates altered MHC-I peptide presentation to CD8+T cells in the pathogenesis. Progress in understanding the cause and treatment of these disorders is hampered by patient phenotypic heterogeneity and lack of systematic investigation of the MHC-I pathway.

Here, we discuss new insights into the biology of MHC-I-opathies that strongly advocate for disease-overarching and integrated molecular and clinical investigation to decipher underlying disease mechanisms. Because this requires transformative multidisciplinary collaboration, we introduce the EULAR study group on MHC-I-opathies to unite clinical expertise in rheumatology, dermatology and ophthalmology, with fundamental and translational researchers from multiple disciplines such as immunology, genomics and proteomics, alongside patient partners. We prioritise standardisation of disease phenotypes and scientific nomenclature and propose interdisciplinary genetic and translational studies to exploit emerging therapeutic strategies to understand MHC-I-mediated disease mechanisms. These collaborative efforts are required to address outstanding questions in the etiopathogenesis of MHC-I-opathies towards improving patient treatment and prognostication.

Searching for New Genetic Biomarkers of Axial Spondyloarthritis

Background: Axial spondyloarthritis (axSpA) is a chronic inflammatory condition of the spine. In addition to musculoskeletal symptoms, there are also extra-articular manifestations. The aim of this study was to search for new biomarkers associated with the clinical presentation and treatment response in axSpA patients. Methods: In this study, 106 axSpA patients and 110 healthy controls were enrolled. Six single-nucleotide polymorphisms (SNPs) were selected for genotyping: ERAP1 rs2287987, ERAP2 rs2549782, TNF rs1800629, TNFRSF1A rs767455, TNFRSF1B rs1061622, and FCGR2A rs1801274. Participants were examined at baseline and after 12 and 24 weeks of anti-TNF therapy. Results: SNPs associated with high axSpA initial activity were TNFRSF1A rs767455 and TNFRSF1B rs1061622 (p < 0.008). The ERAP1 rs2287987 AA genotype was more frequently observed in patients with enthesitis (AA vs. G+, p = 0.049), while the TNFRSF1B rs1061622 GG genotype was more common in participants with uveitis (GG vs. TT, p = 0.042). Potential in predicting anti-TNF treatment response was demonstrated by ERAP1 rs2287987, ERAP2 rs2549782, TNFRSF1B rs1061622, and FCGR2A rs1801274. Conclusions: SNPs can be used to identify patients at risk of severe disease to initiate treatment earlier. Genetic testing will allow clinicians to choose the right drug for the patient.

Disease Activity and Patient-Reported Health Measures in Relation to Cytokine Levels in Ankylosing Spondylitis

INTRODUCTION

Ankylosing spondylitis (AS) is a lifelong condition where spinal inflammation causes chronic back pain and restriction of spinal function. While proinflammatory cytokines participate in the disease process, their relation with disease activity, spinal function, and quality of life is less well understood.

METHODS

Cross-sectional study of serum levels of four inflammatory cytokines (IL-6, TNF, IL-23, and IL-17A) in AS patients not on biologics. Disease characteristics and simultaneous spinal function tests and patient-reported health measures (Bath Functional Index (BASFI), Dougados Functional Index (DFI), Modified Health Assessment Questionnaire (MHAQ), and routine laboratory parameters were recorded. The composite ASDAS-CRP score was used to classify disease activity as absent, low, or high.

RESULTS

In 164 AS patients (age 46 years, 70.1% males, 90.9% HLAB27 positive, ASDAS-CRP 1.8), disease activity was classified as inactive in 14%, low in 54%, and high in 31%. ASDAS-CRP correlated well with MHAQ, DFI, BASFI, and spinal mobility across patients with low and high disease activity (all p < 0.05). Cytokine levels did not correlate with ASDAS-CRP, ESR, BASFI, or spinal mobility scores and were comparable between patients with no, low, or high disease activity regardless of gender or disease duration (all p > 0.2).

CONCLUSIONS

A large proportion of AS not on biologics have active disease far into the disease course. This impacts negatively on quality of life, work ability, and spinal mobility. Serum cytokine levels are poor markers for these central disease features in AS management.

FUNDING

Abbott Norway AS and Arthritis Foundation of Western Australia.

Functionally distinct ERAP1 and ERAP2 are a hallmark of HLA-A29-(Birdshot) Uveitis

Birdshot Uveitis (Birdshot) is a rare eye condition that affects HLA-A29-positive individuals and could be considered a prototypic member of the recently proposed 'MHC-I (major histocompatibility complex class I)-opathy' family. Genetic studies have pinpointed the endoplasmic reticulum aminopeptidase (ERAP1) and (ERAP2) genes as shared associations across MHC-I-opathies, which suggests ERAP dysfunction may be a root cause for MHC-I-opathies. We mapped the ERAP1 and ERAP2 haplotypes in 84 Dutch cases and 890 controls. We identified association at variant rs10044354, which mediated a marked increase in ERAP2 expression. We also identified and cloned an independently associated ERAP1 haplotype (tagged by rs2287987) present in more than half of the cases; this ERAP1 haplotype is also the primary risk and protective haplotype for other MHC-I-opathies. We show that the risk ERAP1 haplotype conferred significantly altered expression of ERAP1 isoforms in transcriptomic data (n = 360), resulting in lowered protein expression and distinct enzymatic activity. Both the association for rs10044354 (meta-analysis: odds ratio (OR) [95% CI]=2.07[1.58-2.71], P = 1.24 × 10(-7)) and rs2287987 (OR[95% CI]: =2.01[1.51-2.67], P = 1.41 × 10(-6)) replicated and showed consistent direction of effect in an independent Spanish cohort of 46 cases and 2103 controls. In both cohorts, the combined rs2287987-rs10044354 haplotype associated with Birdshot more strongly than either variant alone [meta-analysis: P=3.9 × 10(-9)]. Finally, we observed that ERAP2 protein expression is dependent on the ERAP1 background across three European populations (n = 3353). In conclusion, a functionally distinct combination of ERAP1 and ERAP2 are a hallmark of Birdshot and provide rationale for strategies designed to correct ERAP function for treatment of Birdshot and MHC-I-opathies more broadly.

Epistatic Interaction of ERAP1 and HLA-B*51 in Iranian Patients with Behçet's Disease

Behçet's Disease (BD) pathogenesis remains unclear, but some genetic loci and environmental factors are proposed to play a role. Here, we investigate the association of the endoplasmic reticulum aminopeptidase-1 (ERAP1) gene variants and HLA-B*51 with BD susceptibility and clinical manifestations in Iranian patients. In the study, 748 BD patients and 776 healthy individuals were included. The MGB-TaqMan Allelic Discrimination method was used to genotype 10 common missense single nucleotide polymorphisms (SNPs) and one intronic SNP in the ERAP1 gene region. We found no significant association between the 11 SNPs and BD in allelic and genotypic association tests. However, rs30187 showed the strongest association with BD in the recessive genotype model of the risk T allele in HLA-B*51 carriers. Although this became insignificant after correcting for multiple comparisons, the homozygous rs30187 risk allele genotype (TT) increased disease susceptibility in HLA-B*51 carriers in epistasis analysis, and the rs30187 TT recessive genotype showed a significant association with risk of cardiac involvement in the all patients and articular involvements in HLA-B*51 positive patients. Our findings suggest that gene-gene interactions between HLA-B*51 and ERAP1 variants is important for BD development, however, ERAP1 variants which interact with HLA-B*51 may differ among disease phenotypes or populations.

Association of polymorphisms in ERAP1 and risk of ankylosing spondylitis in a Chinese population

To explore the association between five polymorphisms in endoplasmic reticulum associated aminopeptidase 1 (ERAP1) gene and risk of ankylosing spondylitis (AS) in a Chinese population. A case-control study enrolled 250 AS patients and 250 healthy controls was carried out. The genotypes of involved polymorphisms (rs27037, rs27038, rs469876, rs27044 and rs27980) in ERAP1 were detected by Sequenom Mass-Array platform. There were significant differences of the level of WBC (white blood cell), Platelets, CRP (C-reactive protein) and ESR (erythrocyte sedimentation rate) between AS patients and controls (P_all<0.05). There was statistically association between ERAP1 rs27044 polymorphism and risk of AS, and the carriers with rs27044 CG genotype have an increased the risk for AS (CG versus GG, OR=1.70, 95% CI=1.10-2.62, P=0.015). However, we found no evidence for the association of rs27037, rs469876, and rs27980 polymorphisms in ERAP1 with AS risk. Our findings indicated that ERAP1 rs27044 polymorphism was associated with the susceptibility of AS.