Endoplasmic reticulum aminopeptidase 1 and interleukin-23 receptor in ankylosing spondylitis

JAK inhibition and axial spondyloarthritis: new steps on the path to understanding pathophysiology

Axial spondyloarthritis (axSpA) is a chronic inflammatory disease that predominantly affects the sacroiliac joints and spine. Tumor necrosis factor (TNF) and interleukin (IL)-17A are key cytokines in disease pathogenesis and are established axSpA treatment targets. Recently, axSpA treatment options have been complemented by Janus kinase inhibitors (JAKi), which inhibit various cytokines without directly impacting TNF or IL-17 signaling. The effect of JAKi on axSpA remains under investigation: besides a JAK2-mediated (and potentially tyrosine kinase 2 [TYK2]-mediated) effect on the IL-23/IL-17 axis, emerging evidence suggests γδ T cells, type 3 innate lymphoid cells, and mucosa-associated invariant T cells, which are dependent on IL-7 and/or IL-15 and thus on JAK1, are strongly inhibited by JAKi used to treat axSpA. This review summarizes potential effects of JAKi on axSpA and shows evidence from pre-clinical/clinical studies. Greater understanding of the mechanisms of action of available treatments may improve knowledge of axSpA and pave the road for future therapies.

The Role of Aminopeptidase ERAP1 in Human Pathology-A Review

Aminopeptidases are a group of enzymatic proteins crucial for protein digestion, catalyzing the cleavage of amino acids at the N-terminus of peptides. Among them are ERAP1 (coding for endoplasmic reticulum aminopeptidase 1), ERAP2 (coding for endoplasmic reticulum aminopeptidase 2), and LNPEP (coding for leucyl and cystinyl aminopeptidase). These genes encoding these enzymes are contiguous and located on the same chromosome (5q21); they share structural homology and functions and are associated with immune-mediated diseases. These aminopeptidases play a key role in immune pathology by cleaving peptides to optimal sizes for binding to the major histocompatibility complex (MHC) and contribute to cellular homeostasis. By their ability to remove the extracellular region of interleukin 2 and 6 receptors (IL2, IL6) and the tumor necrosis factor receptor (TNF), ERAP1 and ERAP2 are involved in regulating the innate immune response and, finally, in blood pressure control and angiogenesis. The combination of specific genetic variations in these genes has been linked to various conditions, including autoimmune and autoinflammatory diseases and cancer, as well as hematological and dermatological disorders. This literature review aims to primarily explore the impact of ERAP1 polymorphisms on its enzymatic activity and function. Through a systematic examination of the available literature, this review seeks to provide valuable insights into the role of ERAP1 in the pathogenesis of various diseases and its potential implications for targeted therapeutic interventions. Through an exploration of the complex interplay between ERAP1 and various disease states, this review contributes to the synthesis of current biomedical research findings and their implications for personalized medicine.

Investigating the causal relationship between ankylosing spondylitis and osteoporosis in the European population: a bidirectional Mendelian randomization study

Background

Ankylosing Spondylitis (AS) is an inflammatory condition affecting the spine, which may lead to complications such as osteoporosis (OP). Many observational studies have demonstrated a close relationship with strong evidence between OP and AS. The combination of AS and OP is already an indisputable fact, but the exact mechanism of AS complicated with OP is unclear. To better prevent and treat OP in patients with AS, it is necessary to understand the specific mechanism of OP in these patients. In addition, there is a study showing that OP is a risk factor for AS, but the causal relationship between them is not yet clear. Therefore, we conducted a bidirectional Mendelian randomization (MR) analysis to determine whether there is a direct causal effect between AS and OP and to investigate the co-inherited genetic information between the two.

Methods

Bone mineral density (BMD) was used as a phenotype for OP. The AS dataset was taken from the IGAS consortium and included people of European ancestry (9,069 cases and 13,578 controls). BMD datasets were obtained from the GEFOS consortium, a large GWAS meta-analysis study, and the UK Biobank and were categorized based on site (total body (TB): 56,284 cases; lumbar spine (LS): 28,498 cases; femoral neck (FN): 32,735 cases; forearm (FA): 8,143 cases; and heel: 265,627 cases) and age (0-15: 11,807 cases; 15-30: 4,180 cases; 30-45: 10,062 cases; 45-60: 18,062 cases; and over 60: 22,504 cases).To obtain the casual estimates, the inverse variant weighted (IVW) method was mainly used due to its good statistical power and robustness. The presence of heterogeneity was evaluated using Cochran's Q test. Pleiotropy was assessed utilizing MR-Egger regression and MR-pleiotropy residual sum and outlier (MR-PRESSO).

Results

Generally, there were no significant causal associations between genetically predicted AS and decreased BMD levels. The results of MR-Egger regression, Weighted Median, and Weighted Mode methods were consistent with those of the IVW method. However, there was a sign of a connection between genetically elevated BMD levels and a decreased risk of AS (Heel-BMD: OR = 0.879, 95% CI: 0.795-0.971, P = 0.012; Total-BMD: OR = 0.948, 95% CI: 0.907-0.990, P = 0.017; LS-BMD: OR = 0.919, 95% CI: 0.861-0.980, P = 0.010). The results were confirmed to be reliable by sensitivity analysis.

Conclusion

This MR study found that the causal association between genetic liability to AS and the risk of OP or lower BMD in the European population was not evident, which highlights the second effect (e.g., mechanical reasons such as limited movement) of AS on OP. However, genetically predicted decreased BMD/OP is a risk factor for AS with a causal relationship, implying that patients with OP should be aware of the potential risk of developing AS. Moreover, OP and AS share similar pathogenesis and pathways.

Aberrant antigen processing and presentation: Key pathogenic factors leading to immune activation in Ankylosing spondylitis

The strong association of HLA-B*27 with ankylosing spondylitis (AS) was first reported nearly 50 years ago. However, the mechanistic link between HLA-B*27 and AS has remained an enigma. While 85-90% of AS patients possess HLA-B*27, majority of HLA-B*27 healthy individuals do not develop AS. This suggests that additional genes and genetic regions interplay with HLA-B*27 to cause AS. Previous genome-wide association studies (GWAS) identified key genes that are distinctively expressed in AS, including the Endoplasmic Reticulum Aminopeptidase (ERAP) 1 and ERAP2. As these gene-encoding molecules are primarily implicated in the process of peptide processing and presentation, potential pathological interaction of these molecules with HLA-B*27 may operate to cause AS by activating downstream immune responses. The aberrant peptide processing also gives rise to the accumulation of unstable protein complex in endoplasmic reticulum (ER), which drives endoplasmic reticulum-associated protein degradation (ERAD) and unfolded protein response (UPR) and activates autophagy. In this review, we describe the current hypotheses of AS pathogenesis, focusing on antigen processing and presentation operated by HLA-B*27 and associated molecules that may contribute to the disease initiation and progression of AS.

Discovery of Potential Serum Protein Biomarkers in Ankylosing Spondylitis Using Tandem Mass Tag-Based Quantitative Proteomics

Ankylosing spondylitis (AS) is a systemic, chronic, and inflammatory rheumatic disease that affects 0.2% of the population. Current diagnostic criteria for disease activity rely on subjective Bath Ankylosing Spondylitis Disease Activity Index scores. Here, we aimed to discover a panel of serum protein biomarkers. First, tandem mass tag (TMT)-based quantitative proteomics was applied to identify differential proteins between 15 pooled active AS and 60 pooled healthy subjects. Second, cohort 1 of 328 humans, including 138 active AS and 190 healthy subjects from two independent centers, was used for biomarker discovery and validation. Finally, biomarker panels were applied to differentiate among active AS, stable AS, and healthy subjects from cohort 2, which enrolled 28 patients with stable AS, 26 with active AS, and 28 healthy subjects. From the proteomics study, a total of 762 proteins were identified and 46 proteins were up-regulated and 59 proteins were down-regulated in active AS patients compared to those in healthy persons. Among them, C-reactive protein (CRP), complement factor H-related protein 3 (CFHR3), α-1-acid glycoprotein 2 (ORM2), serum amyloid A1 (SAA1), fibrinogen γ (FG-γ), and fibrinogen β (FG-β) were the most significantly up-regulated inflammation-related proteins and S100A8, fatty acid-binding protein 5 (FABP5), and thrombospondin 1 (THBS1) were the most significantly down-regulated inflammation-related proteins. From the cohort 1 study, the best panel for the diagnosis of active AS vs healthy subjects is the combination of CRP and SAA1. The area under the receiver operating characteristic (ROC) curve was nearly 0.900, the sensitivity was 0.970%, and the specificity was 0.805% at a 95% confidence interval from 0.811 to 0.977. Using 0.387 as the cutoff value, the predictive values reached 92.00% in the internal validation set (62 with active AS vs 114 healthy subjects) and 97.50% in the external validation phase (40 with active AS vs 40 healthy subjects). From the cohort 2 study, a panel of CRP and SAA1 can differentiate well among active AS, stable AS, and healthy subjects. For active AS vs stable AS, the area under the ROC curve was 0.951, the sensitivity was 96.43%, the specificity was 88.46% at a 95% confidence interval from 0.891 to 1, and the coincidence rate was 92.30%. For stable AS vs healthy humans, the area under the ROC curve was 0.908, the sensitivity was 89.29%, the specificity was 78.57% at a 95% confidence interval from 0.836 to 0.980, and the coincidence rate was 83.93%. For active AS vs healthy subjects, the predictive value was 94.44%. The results indicated that the CRP and SAA1 combination can potentially diagnose disease status, especially for active or stable AS, which will be conducive to treatment recommendation for patients with AS.

HLA-B*27 subtypes and their implications in the pathogenesis of ankylosing spondylitis

Ankylosing spondylitis (AS) is a highly heritable kind of arthritis that affects the vertebral column. AS risk has been associated strongly with Human leukocyte antigen (HLA)-B*27. In fact, some HLA-B*27 subtypes have been associated with the increased disease risk, although some specific subtypes have not shown such associations. It is supposed that HLA-B*27 plays a major role in the etiopathogenesis of the disease. However, the difference in pathogenic outcomes of HLA-B*27 certain subtypes needs to be clarified. The purpose of this review article is to overview on the detailed implications of the HLA-B*27 subtypes in the etiopathogenesis of AS. Moreover, the role of ERAP1 in AS and its epistasis with HLA-B*27 have been reviewed.

Bioinformatics analysis of genetic variants of endoplasmic reticulum aminopeptidase 1 in ankylosing spondylitis

According to the results of the first genome-wide association study of ankylosing spondylitis (AS), endoplasmic reticulum aminopeptidase 1 (ERAP1) may serve an important role. However, a number of case-control studies have not been able to replicate this result using the same genetic markers. In the present study, the role of common genetic variants of ERAP1 in AS was investigated using two-stage bioinformatics analysis. In the first stage, a classical meta-analysis was performed to assess AS susceptibility markers in ERAP1 using data from available published case-control association studies. The summary odds ratios for 10 single nucleotide polymorphisms (SNPs) were observed to be statistically significant in different studies. In the second stage, the functional effects of these genetic ERAP1 variants were investigated using prediction tools and structural analyses. The K528R (rs30187) substitution SNP in ERAP1 was termed as likely damaging by PolyPhen-2 software, was observed to be located close to the entrance of the substrate pocket, and was predicted to contribute to reduced ERAP1 aminopeptidase activity. In addition, the R725Q (rs17482078) SNP, which was an additional potentially damaging substitution, was suggested to decrease the enzymatic activity of ERAP1, as this substitution may lead to the loss of two hydrogen bonds between R725 and D766 and affect the stability of the C-terminus of ERAP1. In conclusion, the results of the two-stage bioinformatics analysis supported the hypothesis that ERAP1 may present an important susceptibility gene for AS. In addition, the results revealed that two functional SNPs (rs30187 and rs17482078) demonstrated the potential to decrease the enzymatic activity of ERAP1 by affecting its protein structure. Further protein structure-guided studies of the specificity and activity of these ERAP1 variants are therefore warranted.

Interleukin-23R rs7517847 T/G Polymorphism Contributes to the Risk of Crohn's Disease in Caucasians: A Meta-Analysis

The association between Interleukin-23R gene polymorphism and Crohn's disease (CD) in Caucasians is still controversial. Thus, a meta-analysis was performed to evaluate the correlation between this gene variant and CD risk. We retrieved the available data from EMBASE and PUBMED until May 1, 2014, and evaluated the effect of rs7517847 in Caucasians. The significant associations were confirmed between rs7517847 and CD risk in dominant models (TT/TG versus GG: OR = 1.652, 95% CI 1.277, 2.137), allelic model (T allele versus G allele: OR = 1.327, 95% CI 1.198, 1.469), homozygote comparison (TT versus GG: OR = 1.890, 95% CI 1.465, 2.437), heterozygote comparison (TG versus GG: OR = 1.509, 95% CI 1.161, 1.960), and recessive model (TT versus TG/GG: OR = 1.409, 95% CI 1.279, 1.552). In conclusion, this meta-analysis demonstrates that rs7517847 is associated with the risk of CD in Caucasians. These findings show that IL-23R genes confer susceptibility to CD in the Caucasians.

Mutations in the B30.2 domain of pyrin and the risk of ankylosing spondylitis in the Chinese Han population: a case-control study

Ankylosing spondylitis (AS) and familial Mediterranean fever (FMF) are a common autoimmune disease and a classic autoinflammatory disease, respectively. Mediterranean fever (MEFV) encodes the pyrin protein and is the causal disease gene in FMF. This protein is an important regulator of innate immunity and may play a key role in the development of AS. To identify the mutations in the B30.2 domain of pyrin and to uncover the relationships between these mutations and AS risk in the Chinese Han population, we extracted genomic DNA from the peripheral blood of 200 AS patients and 200 matched controls and performed polymerase chain reactions (PCRs) and direct sequencing on those samples. Statistical analysis indicated that only Met694Val (rs61752717) in the B30.2 domain of pyrin could affect the risk of AS (P = 0.042; odds ratio [OR] = 5.103; 95% confidence interval [CI] = 1.111-23.437 for the model of Met (M) vs. Val (V), P = 0.040; OR = 5.211; 95% CI = 1.127-24.091 for the model of MM vs. MV+VV). Moreover, M694V is significantly associated with a higher level of erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) in AS patients. Our results are the first to suggest that the M694V allele of the pyrin was associated with AS risk in the Chinese Han population and that this mutation may be associated with the inflammatory response in the development of AS.

The genetic basis of ankylosing spondylitis: new insights into disease pathogenesis

Ankylosing spondylitis (AS) is a complex disease involving multiple risk factors, both genetic and environmental. AS patients are predominantly young men, and the disease is characterized by inflammation and ankylosis, mainly at the cartilage–bone interface and enthesis. HLA-B27 has been known to be the major AS-susceptibility gene for more than 40 years. Despite advances made in the past few years, progress in the search for non-human leukocyte antigen susceptibility genes has been hampered by the heterogeneity of the disease. Compared to other complex diseases, such as inflammatory bowel disease (IBD), fewer susceptibility loci have been identified in AS. Furthermore, non-major histocompatibility-complex susceptibility loci discovered, such as ERAP1 and IL23R, are likely contributors to joint inflammation. Identification and confirmation of functional variants remains a significant challenge of investigations involving genome-wide association studies (GWAS). It remains unclear why none of the AS-susceptibility genes identified in GWAS appear to be directly involved in the ankylosing process. Numerous reviews have recently been published on the genetics of AS. Therefore, aside from a brief summary of what AS GWAS has successfully achieved thus far, this review will focus on directions that could address unanswered questions raised by GWAS.

Polymorphism of HLA-B27: 105 subtypes currently known

HLA-B27 has a high degree of genetic polymorphism, with 105 known subtypes, named HLA-B*27:01 to HLA-B*27:106, encoded by 132 alleles. The most common subtypes associated with ankylosing spondylitis are HLA-B*27:05 (Caucasians), HLA-B*27:04 (Chinese), and HLA-B*27:02 (Mediterranean populations). For Chinese populations, HLA-B*27:04 is associated with a greater ankylosing spondylitis risk than HLA-B*27:05. Two subtypes, HLA-B27*06 and HLA-B27*09, seem to have no disease association. These differential disease associations of HLA-B27 subtypes, and the recent discovery that ERAP1 is associated with ankylosing spondylitis for patients with HLA-B27, have increased attempts to determine the function of HLA-B27 in disease pathogenesis by studying hemodynamic features of its protein structure, alterations of its peptidome, aberrant peptide handling, and associated molecular events. However, after 40 years we still do not fully know how HLA-B27 predisposes to ankylosing spondylitis and related spondyloarthritis.