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Objective: Endoplasmic reticulum aminopeptidase 1 (ERAP‐1) and ERAP‐2, encoded on chromosome 5q15, trim endogenous peptides for HLA‐mediated presentation to the immune system. Polymorphisms in ERAP1 and/or ERAP2 are strongly associated with several immune‐mediated diseases with specific HLA backgrounds, implicating altered peptide handling and presentation as prerequisites for autoreactivity against an arthritogenic peptide. Given the thorough characterization of disease risk–associated polymorphisms that alter ERAP activity, this study aimed instead to interrogate the expression effect of chromosome 5q15 polymorphisms to determine their effect on ERAP isoform and protein expression. Methods: RNA sequencing and genotyping across chromosome 5q15 were performed to detect genetic variants in ERAP1 and ERAP2 associated with altered total gene and isoform‐specific expression. The functional implication of a putative messenger RNA splice‐altering variant on ERAP‐1 protein levels was validated using mass spectrometry. Results: Polymorphisms associated with ankylosing spondylitis (AS) significantly influenced the transcript and protein expression of ERAP‐1 and ERAP‐2. Disease risk–associated polymorphisms in and around both genes were also associated with increased gene expression. Furthermore, key risk‐associated ERAP1 variants were associated with altered transcript splicing, leading to allele‐dependent alternate expression of 2 distinct isoforms and significant differences in the type of ERAP‐1 protein produced. Conclusion: In accordance with studies demonstrating that polymorphisms that increase aminopeptidase activity predispose to immune disease, the increased risk also attributed to increased expression of ERAP1 and ERAP2 supports the notion of using aminopeptidase inhibition to treat AS and other ERAP‐associated conditions. [ABSTRACT FROM AUTHOR]

Background: Ankylosing spondylitis (AS) is characterised by immune-mediated arthritis and osteoproliferation, ultimately leading to joint ankylosis. Whether inflammation is necessary for osteoproliferation is controversial, fuelled by the unclear efficacy of anti-inflammatory treatments on radiographic progression. In proteoglycan-induced spondylitis (PGISp), a mouse model of AS, inflammation is the prerequisite for osteoproliferation as osteoproliferation was only observed following inflammation-driven intervertebral disc (IVD) destruction. We hypothesised that early intervention with a potent anti-inflammatory therapy would protect IVD integrity and consequently alter disease progression.Methods: PGISp mice received vehicle or a combination of etanercept (ETN) plus prednisolone (PRD) therapy for 2 or 6 weeks initiated at an early disease stage. Peripheral arthritis was scored longitudinally. Spinal disease was assessed using a semi-quantitative histological scoring regimen including inflammation, joint destruction and excessive tissue formation.Results: ETN + PRD therapy significantly delayed the onset of peripheral arthritis. IVD integrity was significantly protected when treatment was commenced in early disease. Six-weeks of treatment resulted in trends towards reductions in intervertebral joint damage and excessive tissue formation. IVD score distribution was dichotomized, likely reflecting the extent of axial disease at initiation of therapy. In the sub-group of mice with high IVD destruction scores, ETN + PRD treatment significantly reduced IVD destruction severity, inflammation and bone erosion and reduced cartilage damage and excessive tissue formation.Conclusions: Early intervention with anti-inflammatory treatment not only improved inflammatory symptoms but also ameliorated structural damage of spine in PGISp mice. This preclinical observation suggests that early anti-inflammatory intervention may slow radiographic progression in AS patients. [ABSTRACT FROM AUTHOR]

Background: No treatment to date is available which specifically targets bone formation in ankylosing spondylitis (AS). Several recent studies have shown that sclerostin (SOST), a Wnt inhibitor specific to osteocytes and chondrocytes, is down-regulated in AS patients. This suggests Wnt signalling may be upregulated, and application of exogenous recombinant SOST (rSOST) may inhibit Wnt signalling and slow pathological bone formation.Methods: The proteoglycan-induced spondylitis (PGISp) mouse model in which we have previously demonstrated downregulated SOST expression, was used for this study. Mice were injected with 2.5 ug rSOST/day for a period of 8 weeks following induction of disease. Axial skeleton disease development was assessed by histology and skeletal changes examined using DEXA.Results: rSOST treatment had no effect on peripheral or axial disease development, bone density or disease severity. Injected rSOST was stable over 8 h and residual levels were evident 24 h after injection, resulting in a cumulative increase in SOST serum levels over the treatment time course. Immunohistochemical examination of SOST levels within the joints in non-rSOST treated PGISp mice showed a significant decrease in the percentage of positive osteocytes in the unaffected joints compared to the affected joints, while no difference was seen in rSOST treated mice. This suggests that rSOST treatment increases the number of SOST-positive osteocytes in unaffected joints but not affected joints, despite having no impact on the number of joints affected by disease.Conclusions: Although not disease-modifying, rSOST treatment did appear to regulate SOST levels in the joints suggesting biological activity. Further dose response studies are required and SOST may require modifications to improve its bone targeting ability in order to affect tissue formation to a meaningful level in this model. [ABSTRACT FROM AUTHOR]

Background In the spondyloarthropathies, the underlying molecular and cellular pathways driving disease are poorly understood. By undertaking a study in knee synovial biopsies from spondyloarthropathy (SpA) and ankylosing spondylitis (AS) patients we aimed to elucidate dysregulated genes and pathways. Methods RNA was extracted from six SpA, two AS, three osteoarthritis (OA) and four normal control knee synovial biopsies. Whole genome expression profiling was undertaken using the Illumina DASL system, which assays 24000 cDNA probes. Differentially expressed candidate genes were then validated using quantitative PCR and immunohistochemistry. Results Four hundred and sixteen differentially expressed genes were identified that clearly delineated between AS/SpA and control groups. Pathway analysis showed altered gene-expression in oxidoreductase activity, B-cell associated, matrix catabolic, and metabolic pathways. Altered "myogene" profiling was also identified. The inflammatory mediator, MMP3, was strongly upregulated (5-fold) in AS/SpA samples and the Wnt pathway inhibitors DKK3 (2.7-fold) and Kremen1 (1.5-fold) were downregulated. Conclusions Altered expression profiling in SpA and AS samples demonstrates that disease pathogenesis is associated with both systemic inflammation as well as local tissue alterations that may underlie tissue damaging modelling and remodelling outcomes. This supports the hypothesis that initial systemic inflammation in spondyloarthropathies transfers to and persists in the local joint environment, and might subsequently mediate changes in genes directly involved in the destructive tissue remodelling. [ABSTRACT FROM AUTHOR]

Ankylosing spondylitis is a common form of inflammatory arthritis predominantly affecting the spine and pelvis that occurs in approximately 5 out of 1,000 adults of European descent. Here we report the identification of three variants in the RUNX3, LTBR-TNFRSF1A and IL12B regions convincingly associated with ankylosing spondylitis (P < 5 × 10?8 in the combined discovery and replication datasets) and a further four loci at PTGER4, TBKBP1, ANTXR2 and CARD9 that show strong association across all our datasets (P < 5 × 10?6 overall, with support in each of the three datasets studied). We also show that polymorphisms of ERAP1, which encodes an endoplasmic reticulum aminopeptidase involved in peptide trimming before HLA class I presentation, only affect ankylosing spondylitis risk in HLA-B27-positive individuals. These findings provide strong evidence that HLA-B27 operates in ankylosing spondylitis through a mechanism involving aberrant processing of antigenic peptides. [ABSTRACT FROM AUTHOR]

Ankylosing spondylitis (AS) is a common, highly heritable arthropathy, the pathogenesis of which is poorly understood. The mechanism by which the main gene for the disease, HLA-B27, leads to AS is unknown. Genetic and genomic studies have demonstrated involvement of the interleukin-23 (IL-23) signaling pathway in AS, a finding which has stimulated much new research into the disease and has led to therapeutic trials. Several other genes and genetic regions, including further major histocompatibility complex (MHC) and non-MHC loci, have been shown to be involved in the disease, but it is not clear yet how they actually induce the condition. These findings have shown that there is a strong genetic overlap between AS and Crohn’s disease in particular, although there are also major differences in the genes involved in the two conditions, presumably explaining their different presentations. Genomic and proteomic studies are in an early phase but have potential both as diagnostic/prognostic tools and as a further hypothesis-free tool to investigate AS pathogenesis. Given the slow progress in studying the mechanism of association of HLA-B27 with AS, these may prove to be more fruitful approaches to investigating the pathogenesis of the disease. [ABSTRACT FROM AUTHOR]