ERAP2 functional knockout in humans does not alter surface heavy chains or HLA-B27, inflammatory cytokines or endoplasmic reticulum stress markers

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.

Psoriatic arthritis

Psoriatic arthritis (PsA) is a type of inflammatory arthritis that is included within the spondyloarthritis, a group of rheumatological diseases characterized by different clinical manifestations and associated comorbidities, that can compromise the quality of life of patients. The diagnosis of PsA is sometimes difficult due to an enormous clinical and radiological variability, including six different domains of involvement: peripheral joint, axial skeleton, skin psoriasis, nail psoriasis, enthesitis and dactylitis. Currently, there are no biomarkers that allow the detection of PsA in patients with psoriasis, so a high level of suspicion is important, mainly by dermatologists, but also by other specialists, such as family doctors. Advances in the knowledge of new immunological mechanisms and joint management by rheumatologists and dermatologists have made it possible to improve the therapeutic approach in patients with PsA.

Association of the genetic variants in the endoplasmic reticulum aminopeptidase 2 gene with ankylosing spondylitis susceptibility

BACKGROUND

Genetic polymorphisms in the endoplasmic reticulum aminopeptidase gene ERAP2 has been attributed with the etiopathogenesis of ankylosing spondylitis (AS). Here we assessed the association of ERAP2 gene single nucleotide polymorphisms (SNPs) with AS predisposition in Iranian patients and determined their effect on the inflammatory state of the patients.

METHODS

For genotyping of rs2548538, rs2287988, and rs17408150 SNPs using a real-time allelic discrimination approach, DNA was extracted from the whole blood of 250 AS patients and 250 healthy individuals. RNA of the peripheral blood mononuclear cells was separated, cDNA was synthesized, and transcriptional levels of cytokines, including interleukin (IL)-17A, IL-23, IL-10, and transforming growth factor-β, were measured. Enzyme-linked immunosorbent assay was used to measure the serum concentration on the cytokines.

RESULTS

Three ERAP2 gene SNPs were not associated significantly with AS risk. Nonetheless, rs2287988 and rs17408150 SNPs showed statistically significant association with susceptibility to the disease in those AS patients who were positive for human leukocyte antigen (HLA)-B27. Transcriptional level and serum concentration of IL-17A and IL-23 were higher, but those of IL-10 were lower in both AS patients and the HLA-B27-positive patient group relative to the control group. Nevertheless, ERAP2 gene SNPs in the HLA-B27-positive AS patients did not affect the transcription level and serum concentration of cytokines.

CONCLUSIONS

ERAP2 gene rs2287988 and rs17408150 SNPs are associated with susceptibility to AS, but they are probably not determining the levels of IL-17A, IL-23, and IL-10 in this disease.

The IL-17/IL-23 Axis and Its Genetic Contribution to Psoriatic Arthritis

Psoriatic arthritis (PsA) is a chronic inflammatory disease belonging to the family of spondyloarthropathies (SpA). PsA commonly aggravates psoriasis of the skin and frequently manifests as an oligoarthritis with axial skeletal involvement and extraarticular manifestations including dactylitis, enthesitis, and uveitis. The weight of genetic predisposition to psoriasis and PsA is illustrated by the concordance rates in monozygotic twins which clearly demonstrate that genomics is insufficient to induce the clinical phenotype. The association of PsA with several single nucleotide polymorphisms (SNPs) at the IL23R locus and the involvement of Th17 cells in the immunopathogenesis of PsA clearly put the IL-23/IL-17 axis in the spotlight. The IL-23 and IL-17 cytokines have a pivotal role in the chronic inflammation of the synovium in PsA and are also prominent in the skin lesions of those with PsA. In this review, we focus on the genetic association of the IL-23/IL-17 axis with PsA and the contribution of these master cytokines in the pathophysiology of the disease, highlighting the main cell types incriminated in PsA and their specific role in the peripheral blood, lesional skin and joints of patients. We then provide an overview of the approved biologic drugs targeting the IL-23/IL-17 axis and discuss the advantages of genetic stratification to enhance personalized therapies in PsA.

Understanding the Pathogenesis of Spondyloarthritis

Spondyloarthritis comprises a group of inflammatory diseases of the joints and spine, with various clinical manifestations. The group includes ankylosing spondylitis, reactive arthritis, psoriatic arthritis, arthritis associated with inflammatory bowel disease, and undifferentiated spondyloarthritis. The exact etiology and pathogenesis of spondyloarthritis are still unknown, but five hypotheses explaining the pathogenesis exist. These hypotheses suggest that spondyloarthritis is caused by arthritogenic peptides, an unfolded protein response, HLA-B*27 homodimer formation, malfunctioning endoplasmic reticulum aminopeptidases, and, last but not least, gut inflammation and dysbiosis. Here we discuss the five hypotheses and the evidence supporting each. In all of these hypotheses, HLA-B*27 plays a central role. It is likely that a combination of these hypotheses, with HLA-B*27 taking center stage, will eventually explain the development of spondyloarthritis in predisposed individuals.

Identification of Prognostic Immune-Related Genes in Pancreatic Adenocarcinoma and Establishment of a Prognostic Nomogram: A Bioinformatic Study

BACKGROUND

The prognosis of pancreatic adenocarcinoma (PAAD) is extremely poor and has not been improved. Thus, an effective method to assess the prognosis of patients must be established to improve their survival rate.

METHOD

This study investigated immune-related genes that could be used as potential therapeutic targets for PAAD. Level 3 gene expression data from the PAAD cohort and the relevant clinical information were obtained from The Cancer Genome Atlas (TCGA) database. For validation, other PAAD datasets (DSE62452) were downloaded from the Gene Expression Omnibus (GEO) database. The PAAD datasets from TCGA and GEO were used to screen immune-related genes through the Molecular Signatures Database using gene set enrichment analysis. Then, the overlapping immune-related genes of the two datasets were identified. Coexpression networks of the immune-related genes were constructed.

RESULTS

A signature of three immune-related genes (CKLF, ERAP2, and EREG) was identified in patients with PAAD. The signature could be used to divide the patients with PAAD into high- and low-risk groups based on their median risk score. Multivariate Cox regression analysis was performed to determine the independent prognostic factors of PAAD. Time-dependent receiver operating characteristic (ROC) curve analysis was conducted to assess the prediction accuracy of the prognostic signature. Last, a nomogram was established to assess the individualized prognosis prediction model based on the clinical characteristics and risk score of the TCGA PAAD dataset. The accuracy of the prognostic signature was further evaluated through functional evaluation and principal component analysis.

CONCLUSIONS

The results indicated that the signature of three immune-related genes had excellent predictive value for PAAD. These findings might help improve personalized treatment and medical decisions.

Identification of an Unconventional Subpeptidome Bound to the Behçet's Disease-associated HLA-B*51:01 that is Regulated by Endoplasmic Reticulum Aminopeptidase 1 (ERAP1)

Human leukocyte antigen (HLA) B*51:01 and endoplasmic reticulum aminopeptidase 1 (ERAP1) are strongly genetically associated with Behçet's disease (BD). Previous studies have defined two subgroups of HLA-B*51 peptidome containing proline (Pro) or alanine (Ala) at position 2 (P2). Little is known about the unconventional non-Pro/Ala2 HLA-B*51-bound peptides. We aimed to study the features of this novel subpeptidome, and investigate its regulation by ERAP1. CRISPR-Cas9 was used to generate an HLA-ABC-triple knockout HeLa cell line (HeLa.ABC-KO), which was subsequently transduced to express HLA-B*51:01 (HeLa.ABC-KO.B51). ERAP1 was silenced using lentiviral shRNA. Peptides bound to HLA-B*51:01 were eluted and analyzed by mass spectrometry. The characteristics of non-Pro/Ala2, Pro2, and Ala2 peptides and their alteration by ERAP1 silencing were investigated. Effects of ERAP1 silencing on cell surface expression of HLA-B*51:01 were studied using flow cytometry. More than 20% of peptides eluted from HLA-B*51:01 lacked Pro or Ala at P2. This unconventional group of HLA-B*51:01-bound peptides was relatively enriched for 8-mers (with relatively fewer 9-mers) compared with the Pro2 and Ala2 subpeptidomes and had similar N-terminal and C-terminal residue usages to Ala2 peptides (with the exception of the less abundant leucine at position Ω). Knockdown of ERAP1 increased the percentage of non-Pro/Ala2 from 20% to ∼40%, increased the percentage of longer (10-mer and 11-mer) peptides eluted from HLA-B*51:01 complexes, and abrogated the predominance of leucine at P1. Interestingly knockdown of ERAP1 altered the length and N-terminal residue usage of non-Ala2&Pro2 and Ala2 but not the Pro2 peptides. Finally, ERAP1 silencing regulated the expression levels of cell surface HLA-B*51 in a cell-type-dependent manner. In conclusion, we have used a novel methodology to identify an unconventional but surprisingly abundant non-Pro/Ala2 HLA-B*51:01 subpeptidome. It is increased by knockdown of ERAP1, a gene affecting the risk of developing BD. This has implications for theories of disease pathogenesis.

Stress proteins in the pathogenesis of spondyloarthritis

Spondyloarthritis is an autoinflammatory rheumatic disease in which arthritis and osteoproliferation lead the patients who suffer from it to chronic disability. This disease is associated with the expression of class I MHC molecule HLA-B27, which tends to be misfolded in the endoplasmic reticulum and, therefore, expressed in aberrant forms. This phenomena lead to endoplasmic reticulum stress, which in time, evokes a whole response to cellular injury. Under these conditions, the molecules involved in restoring cell homeostasis play a key role. Such is the case of the "heat-shock proteins", which usually regulate protein folding, but also have important immunomodulatory functions, as well as some roles in tissue modeling. In this review, we attempt to summarize the involvement of cell stress and heat-shock proteins in the homeostatic disturbances and pathological conditions associated with this disease.

The interplay between HLA-B27 and ERAP1/ERAP2 aminopeptidases: from anti-viral protection to spondyloarthritis

The human leukocyte antigen class I gene HLA-B27 is the strongest risk factor for ankylosing spondylitis (AS), a chronic inflammatory arthritic disorder. More recently, the Endoplasmic Reticulum Aminopeptidase (ERAP) 1 and 2 genes have been identified by genome wide association studies (GWAS) as additional susceptibility factors. In the ER, these aminopeptidases trim the peptides to a length suitable to fit into the groove of the major histocompatibility complex (MHC) class I molecules. It is noteworthy that an epistatic interaction between HLA-B27 and ERAP1, but not between HLA-B27 and ERAP2, has been highlighted. However, these observations suggest a paramount centrality for the HLA-B27 peptide repertoire that determines the natural B27 immunological function, i.e. the T cell antigen presentation and, as a by-product, elicits HLA-B27 aberrant behaviours: (i) the misfolding leading to ER stress responses and autophagy and (ii) the surface expression of homodimers acting as ligands for innate immune receptors. In this context, it has been observed that the HLA-B27 carriers, besides being prone to autoimmunity, display a far better surveillance to some viral infections. This review focuses on the ambivalent role of HLA-B27 in autoimmunity and viral protection correlating its functions to the quantitative and qualitative effects of ERAP1 and ERAP2 polymorphisms on their enzymatic activity.

Functional Interaction of the Ankylosing Spondylitis-Associated Endoplasmic Reticulum Aminopeptidase 2 With the HLA-B*27 Peptidome in Human Cells

OBJECTIVE

To determine the influence of endoplasmic reticulum aminopeptidase 2 (ERAP-2) expression on the HLA-B*27 peptidome in live cells.

METHODS

Using immunoaffinity chromatography and acid extraction, HLA-B*27:05-bound peptides were isolated from 2 ERAP-2-negative lymphoblastoid cell lines and 1 ERAP-2-positive lymphoblastoid cell line expressing functionally indistinguishable ERAP-1 variants. More than 2,000-4,000 B*27:05 ligands were identified from each cell line, and their relative abundance was established by quantitative tandem mass spectrometry and MaxQuant-based peptide analyses. Pairwise comparisons were used to determine the structural features of peptides whose relative abundance was dependent on the presence of ERAP-2. Synthetic peptide digestions were performed with recombinant ERAP-1 and ERAP-2. Peptide affinity was estimated with standard algorithms.

RESULTS

The B*27:05 peptidome from ERAP-2-positive cells showed 3-4% fewer peptides with N-terminal basic residues than did the peptidome from ERAP-2-negative cells. Among the shared peptides, those most abundant in the presence of ERAP-2 included more nonamers, fewer decamers, and fewer N-terminal basic residues than the peptides predominant in ERAP-2-negative cells. These ERAP-2-dependent changes did not alter the global affinity of the B*27:05 peptidome.

CONCLUSION

ERAP-2 significantly influences the B*27:05-bound peptidome by destroying some ligands and decreasing the abundance of many more ligands with N-terminal basic residues, while increasing the abundance of nonamers. The former effects are best explained by direct ERAP-2 trimming. The effects on peptide length might be attributed to ERAP-2-induced activation of ERAP-1 trimming. These data support the notion of a peptide-mediated mechanism as the basis for the association of ERAP-2 with ankylosing spondylitis. Analogous effects on other major histocompatibility complex class I peptidomes might explain the involvement of ERAP-2 in HLA-B27-negative spondyloarthritis.

Pathogenesis of ankylosing spondylitis - recent advances and future directions

Over the past 5 years, advances in high-throughput techniques and studies involving large cohorts of patients have led to considerable advances in the identification of novel genetic associations and immune pathways involved in ankylosing spondylitis (AS). These discoveries include genes encoding cytokine receptors, transcription factors, signalling molecules and transport proteins. Although progress has been made in understanding the functions and potential pathogenic roles of some of these molecules, much work remains to be done to comprehend their complex interactions and therapeutic potential in AS. In this Review, we outline the current knowledge of AS pathogenesis, including genetic risk associations, HLA-B27-mediated pathology, perturbations in antigen-presentation pathways and the contribution of the type 3 immune response.

Genetic association of ankylosing spondylitis with TBX21 influences T-bet and pro-inflammatory cytokine expression in humans and SKG mice as a model of spondyloarthritis

OBJECTIVES

Ankylosing spondylitis (AS) is a highly heritable immune-mediated arthropathy. Inflammation in AS is poorly understood. TBX21 encodes T-bet, a transcription factor, lying within a locus with genome-wide significant association with AS. T-bet is implicated in innate and adaptive immunity. However, the role of T-bet in AS pathogenesis is unclear.

METHODS

We assessed the importance of T-bet in disease development and progression in peripheral blood mononuclear cells from 172 AS cases and 83 healthy controls carrying either risk or protective alleles of the peak AS-associated TBX21 single nucleotide polymorphism. Kinetics and localisation of T-bet expression in the SKG mouse model of spondyloarthropathy was examined, along with the impact of Tbx21 knockout on arthritis development in SKG mice.

RESULTS

Patients with AS had higher T-bet expression than healthy individuals, driven predominantly by natural killer and CD8+ T cells, with expression levels in CD8+ T cells completely distinguishing AS cases from healthy controls. T-bet expression was increased in AS cases carrying risk compared with protective alleles of rs11657479. In curdlan-treated SKG mice, T-bet expression increased early after disease initiation and persisted throughout the course of disease. There was marked reduction in gut and peripheral joint inflammation, and less IFNγ-producing and IL-17-producing CD8+ T cells, in Tbx21-/- compared with wild-type SKG mice.

CONCLUSIONS

AS-associated variants in TBX21 influence T-bet expression. T-bet+ innate and adaptive immune cells have altered IL-17 and IFNγ, and early activation marker CD69 expression than T-bet cells. This indicates that T-bet is a major component of inflammatory pathways of spondyloarthropathy in humans and mice.