Noggin haploinsufficiency differentially affects tissue responses in destructive and remodeling arthritis

Assessment of radiographic progression in the spines of patients with ankylosing spondylitis treated with adalimumab for up to 2 years

Introduction

Ankylosing spondylitis (AS) is a chronic rheumatic disease associated with spinal inflammation that subsequently leads to progression of structural damage and loss of function. The fully human anti-tumor necrosis factor (anti-TNF) antibody adalimumab reduces the signs and symptoms and improves overall quality of life in patients with active AS; these benefits have been maintained through 2 years of treatment. Our objective was to compare the progression of structural damage in the spine in patients with AS treated with adalimumab for up to 2 years versus patients who had not received TNF antagonist therapy.

Methods

Radiographs from patients with AS who received adalimumab 40 mg every other week subcutaneously were pooled from the Adalimumab Trial Evaluating Long-Term Efficacy and Safety for Ankylosing Spondylitis (ATLAS) study and a Canadian AS study (M03-606). Radiographic progression from baseline to 2 years in the spine of adalimumab-treated patients from these two studies (adalimumab cohort, n = 307) was compared with an historic anti-TNF-naïve cohort (Outcome in AS International Study [OASIS], n = 169) using the modified Stoke AS Spine Score (mSASSS) method.

Results

mSASSS results were not significantly different between the adalimumab cohort and the OASIS cohort, based on baseline and 2-year radiographs. Mean changes in mSASSS from baseline to 2 years were 0.9 for the OASIS cohort and 0.8 for the adalimumab cohort (P = 0.771), indicating similar radiographic progression in both groups. When results for patients in the OASIS cohort who met the baseline disease activity criteria for the ATLAS and Canadian studies (OASIS-Eligible cohort) were analyzed, there was no significant difference in mean change in mSASSS from baseline to 2 years between OASIS-Eligible patients and adalimumab-treated patients; the mean changes in mSASSS were 0.9 for the OASIS-Eligible cohort and 0.8 for the adalimumab cohort (P = 0.744).

Conclusions

Two years of treatment with adalimumab did not slow radiographic progression in patients with AS, as assessed by the mSASSS scoring system, when compared with radiographic data from patients naïve to TNF antagonist therapy.

Trial registration

Canadian study (M03-606) ClinicalTrials.gov identifier: NCT00195819; ATLAS study (M03-607) ClinicalTrials.gov identifier: NCT00085644.

Progress in spondylarthritis. Mechanisms of new bone formation in spondyloarthritis

Targeted therapies that neutralize tumour necrosis factor are often able to control the signs and symptoms of spondyloarthritis. However, recent animal model data and clinical observations indicate that control of inflammation may not be sufficient to impede disease progression toward ankylosis in these patients. Bone morphogenetic proteins and WNTs (wingless-type like) are likely to play an important role in ankylosis and could be therapeutic targets. The relationship between inflammation and new bone formation is still unclear. This review summarizes progress made in our understanding of ankylosis and offers an alternative view of the relationship between inflammation and ankylosis.

Dynamic activation of bone morphogenetic protein signaling in collagen-induced arthritis supports their role in joint homeostasis and disease

Introduction

Rheumatoid arthritis is a chronic systemic autoimmune disease affecting peripheral joints and leading to loss of joint function. The severity and outcome of disease are dependent on the balance between inflammatory/destructive and homeostatic or repair pathways. Increasing evidence suggests a role for bone morphogenetic protein (BMP) signaling in joint homeostasis and disease.

Methods

Activation of BMP signaling in collagen-induced arthritis as a model of rheumatoid arthritis was studied by immunohistochemistry and Western blot for phosphorylated SMAD1/5 at different time points. Expression of different BMP ligands and noggin, a BMP antagonist, was determined on synovium and cartilage extracts of arthritic knees, at different time points, with quantitative polymerase chain reaction. At the protein level, BMP2 and BMP7 were studied with immunohistochemistry. Finally, the effect of anti-tumor necrosis factor-alpha (TNFα) treatment on the expression of BMP2, BMP7, and growth and differentiation factor-5 (GDF5) in synovium and cartilage of arthritic knees was investigated.

Results

A time-dependent activation of the BMP signaling pathway in collagen-induced arthritis was demonstrated with a dynamic and characteristic expression pattern of different BMP subfamily members in synovium and cartilage of arthritic knees. As severity increases, the activation of BMP signaling becomes more prominent in the invasive pannus tissue. BMP2 is present in cartilage and the hyperplastic lining layer. BMP7 is found in the sublining zone and inflammatory infiltrate. Treatment with etanercept slowed down progression of disease, but no change in expression of GDF5, BMP2, and BMP7 in synovium was found; in the cartilage, however, blocking of TNFα increased the expression of BMP7.

Conclusions

BMP signaling is dynamically activated in collagen-induced arthritis and is partly TNFα-independent. TNFα blocking increased the expression of BMP7 in the articular cartilage, possibly enhancing anabolic mechanisms. Different types of source and target cells are recognized. These data further support a role for BMP signaling in arthritis.

Joint homeostasis, restoration, and remodeling in osteoarthritis

Osteoarthritis is the major cause of joint failure. The outcome of the disease process is determined by complex interactions between cells and molecules steering homeostasis, destruction, restoration, and remodeling. The articular cartilage has a limited restoration and repair capacity. Genetic studies in humans and the development of mouse models have identified the role of signaling pathways that are important for skeletal development in the postnatal biology and pathology of articular cartilage. These include bone morphogenetic protein, transforming growth factor beta, fibroblast growth factor, wingless-type signaling, and their respective antagonists such as noggin and frizzled related protein. The synovium is prone to inflammation and emerging evidence suggests that innate and adaptive immune responses are important. Bone and cartilage form a biomechanical unit; stiffer bones might impair cartilage homeostasis. The biology of frizzled related protein provides a basis for the hypothesized inverse relationship between osteoarthritis and osteoporosis.

Radiographic progression of ankylosing spondylitis after up to two years of treatment with etanercept

OBJECTIVE

To investigate the effect of etanercept therapy on radiographic progression in patients with ankylosing spondylitis (AS).

METHODS

Patients with AS who had previously participated in a 24-week randomized, double-blind, placebo-controlled trial of etanercept therapy were enrolled in a 72-week open-label extension. Radiographs of the cervical and lumbar spine from patients who received etanercept (25 mg twice weekly) for up to 96 weeks were compared with radiographs from patients in a large prevalence cohort (Outcome Assessments in Ankylosing Spondylitis International Study [OASIS]) who had not been treated with anti-tumor necrosis factor alpha (anti-TNFalpha) agents. Radiographs obtained at 2 time points up to 96 weeks apart from patients in both study populations were digitized and read by 2 independent readers who were blinded with regard to patient group and sequence. The primary end point was the 96-week change in the modified Stoke AS Spine Score (mSASSS).

RESULTS

A total of 257 patients treated with etanercept were compared with 175 unselected patients from the OASIS study. There was no significant difference in the change in the mSASSS from baseline among patients who received etanercept (mean +/- SD 0.91 +/- 2.45) versus those from the OASIS group (0.95 +/- 3.18).

CONCLUSION

Unlike other inflammatory rheumatic diseases such as rheumatoid arthritis and psoriatic arthritis, structural progression in AS seems to be independent of TNF, despite the fact that TNF is responsible for the signs and symptoms due to inflammation in this disease.

Bone morphogenetic proteins in destructive and remodeling arthritis

Joint destruction and tissue responses determine the outcome of chronic arthritis. Joint inflammation and damage are often the dominant clinical presentation. However, in some arthritic diseases, in particular the spondyloarthritides, joint remodeling is a prominent feature, with new cartilage and bone formation leading to ankylosis and contributing to loss of function. A role for bone morphogenetic proteins in joint remodeling has been demonstrated in the formation of both enthesophytes and osteophytes. Data from genetic models support a role for bone morphogenetic protein signaling in cartilage homeostasis. Finally, this signaling pathway is likely to play a steering role in the synovium.

Mesenchymal stem cells in rheumatology: a regenerative approach to joint repair

The advent of biologics in rheumatology has considerably changed the evolution and prognosis of chronic inflammatory arthritis. The success of these new treatments has contributed to steering more attention to research focussed on repair and remodelling of joint tissues. Indeed, when the tissue damage is established, treatment options are very limited and the risk of progression towards joint destruction and failure remains high. Increasing evidence indicates that mesenchymal stem cells persist postnatally within joint tissues. It is postulated that they would function to safeguard joint homoeostasis and guarantee tissue remodelling and repair throughout life. Alterations in mesenchymal stem cell biology in arthritis have indeed been reported but a causal relationship has not been demonstrated, mainly because our current knowledge of mesenchymal stem cell niches and functions within the joint in health and disease is very limited. Nonetheless, mesenchymal stem cell technologies have attracted the attention of the biomedical research community as very promising tools to achieve the repair of joint tissues such as articular cartilage, subchondral bone, menisci and tendons. This review will outline stem-cell-mediated strategies for the repair of joint tissues, spanning from the use of expanded mesenchymal stem cell populations to therapeutic targeting of endogenous stem cells, resident in their native tissues, and related reparative signals in traumatic, degenerative and inflammatory joint disorders.

Structure-function relationships of entheses in relation to mechanical load and exercise

Entheses are regions of high-stress concentration that are commonly affected by overuse injuries in sport. This review summarizes current knowledge of their structure-function relationships - at the macroscopic, microscopic and molecular levels. Consideration is given to how stress concentration is reduced at fibrocartilaginous entheses by various adaptations which ensure that stress is dissipated away from the hard-soft tissue interface. The fundamental question of how a tendon or ligament is anchored to bone is addressed - particularly in relation to the paucity of compact bone at fibrocartilaginous entheses. The concept of an "enthesis organ" is reviewed - i.e. the idea of a collection of tissues adjacent to the enthesis itself, which jointly serve a common function - stress dissipation. The archetypal enthesis organ is that of the Achilles tendon and the functional importance of its subtendinous bursa, with its fibrocartilaginous walls and protruding fat pad, is emphasized. The distribution of adipose tissue elsewhere at entheses is also explained and possible functions of insertion-site fat are evaluated. Finally, a brief consideration is given to enthesopathies, with attention drawn to the possibility of degenerative changes affecting other regions of an enthesis organ, besides the enthesis itself.

Interaction of interleukin-6 and the BMP pathway in pulmonary smooth muscle

The majority of familial pulmonary arterial hypertension (PAH) cases are caused by mutations in the type 2 bone morphogenetic protein receptor (BMPR2). However, less than one-half of BMPR2 mutation carriers develop PAH, suggesting that the most important function of BMPR2 mutation is to cause susceptibility to a "second hit." There is substantial evidence from the literature implicating dysregulated inflammation, in particular the cytokine IL-6, in the development of PAH. We thus hypothesized that the BMP pathway regulates IL-6 in pulmonary tissues and conversely that IL-6 regulates the BMP pathway. We tested this in vivo using transgenic mice expressing an inducible dominant negative BMPR2 in smooth muscle, using mice injected with an IL-6-expressing virus, and in vitro using small interfering RNA (siRNA) to BMPR2 in human pulmonary artery smooth muscle cells (PA SMC). Consistent with our hypothesis, we found upregulation of IL-6 in both the transgenic mice and in cultured PA SMC with siRNA to BMPR2; this could be abolished with p38(MAPK) inhibitors. We also found that IL-6 in vivo caused a twofold increase in expression of the BMP signaling target Id1 and caused increased BMP activity in a luciferase-reporter assay in PA SMC. Thus we have shown both in vitro and in vivo a complete negative feedback loop between IL-6 and BMP, suggesting that an important consequence of BMPR2 mutations may be poor regulation of cytokines and thus vulnerability to an inflammatory second hit.

Mechanisms of pathologic new bone formation

Pathologic new bone formation occurs in response to a variety of stimuli. Heterotopic and orthotopic bone formation can interfere with the normal function of the joint and can contribute to disability in inflammatory joint diseases. Syndesmophyte formation and progressive ankylosis are characteristic features of spondyloarthropathies, including psoriatic arthritis and ankylosing spondylitis, and they can be regarded as abnormal bone remodeling. Successful blocking of inflammation in patients with spondyloarthropathy apparently fails to halt progression of ankylosis in cohort studies. This suggests that though they may be linked in some way, bone formation and inflammation are largely independent phenomena. Indeed, new bone formation also occurs in diseases such as osteoarthritis and diffuse idiopathic skeletal hyperostosis. Therefore, therapeutic strategies in spondyloarthropathy ideally should control both inflammation and bone formation.