Treatment of a mouse model of ankylosing spondylitis with exogenous sclerostin has no effect on disease progression.

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.

Quantitative gene profiling of long noncoding RNAs with targeted RNA sequencing.

We compared quantitative RT-PCR (qRT-PCR), RNA-seq and capture sequencing (CaptureSeq) in terms of their ability to assemble and quantify long noncoding RNAs and novel coding exons across 20 human tissues. CaptureSeq was superior for the detection and quantification of genes with low expression, showed little technical variation and accurately measured differential expression. This approach expands and refines previous annotations and simultaneously generates an expression atlas.

Excessive bone formation in a mouse model of ankylosing spondylitis is associated with decreases in Wnt pathway inhibitors.

INTRODUCTION: Ankylosing spondylitis (AS) is unique in its pathology where inflammation commences at the entheses before progressing to an osteoproliferative phenotype generating excessive bone formation that can result in joint fusion. The underlying mechanisms of this progression are poorly understood. Recent work has suggested that changes in Wnt signalling, a key bone regulatory pathway, may contribute to joint ankylosis in AS. Using the proteoglycan-induced spondylitis (PGISp) mouse model which displays spondylitis and eventual joint fusion following an initial inflammatory stimulus, we have characterised the structural and molecular changes that underlie disease progression. METHODS: PGISp mice were characterised 12 weeks after initiation of inflammation using histology, immunohistochemistry (IHC) and expression profiling. RESULTS: Inflammation initiated at the periphery of the intervertebral discs progressing to disc destruction followed by massively excessive cartilage and bone matrix formation, as demonstrated by toluidine blue staining and IHC for collagen type I and osteocalcin, leading to syndesmophyte formation. Expression levels of DKK1 and SOST, Wnt signalling inhibitors highly expressed in joints, were reduced by 49% and 63% respectively in the spine PGISp compared with control mice (P < 0.05) with SOST inhibition confirmed by IHC. Microarray profiling showed genes involved in inflammation and immune-regulation were altered. Further, a number of genes specifically involved in bone regulation including other members of the Wnt pathway were also dysregulated. CONCLUSIONS: This study implicates the Wnt pathway as a likely mediator of the mechanism by which inflammation induces bony ankylosis in spondyloarthritis, raising the potential that therapies targeting this pathway may be effective in preventing this process.