Anca Irinel Catrina

Induction of osteoclastogenesis and bone loss by human autoantibodies against citrullinated vimentin

Autoimmunity is complicated by bone loss. In human rheumatoid arthritis (RA), the most severe inflammatory joint disease, autoantibodies against citrullinated proteins are among the strongest risk factors for bone destruction. We therefore hypothesized that these autoantibodies directly influence bone metabolism. Here, we found a strong and specific association between autoantibodies against citrullinated proteins and serum markers for osteoclast-mediated bone resorption in RA patients. Moreover, human osteoclasts expressed enzymes eliciting protein citrullination, and specific N-terminal citrullination of vimentin was induced during osteoclast differentiation. Affinity-purified human autoantibodies against mutated citrullinated vimentin (MCV) not only bound to osteoclast surfaces, but also led to robust induction of osteoclastogenesis and bone-resorptive activity. Adoptive transfer of purified human MCV autoantibodies into mice induced osteopenia and increased osteoclastogenesis. This effect was based on the inducible release of TNF-α from osteoclast precursors and the subsequent increase of osteoclast precursor cell numbers with enhanced expression of activation and growth factor receptors. Our data thus suggest that autoantibody formation in response to citrullinated vimentin directly induces bone loss, providing a link between the adaptive immune system and bone.

Smoking increases peptidylarginine deiminase 2 enzyme expression in human lungs and increases citrullination in BAL cells

Objectives: A gene–environment interaction between HLA-DR shared epitope genes and smoking in anti-cyclic citrullinated peptide antibody-positive rheumatoid arthritis (RA) has been reported. Identification of citrullinated proteins in bronchoalveolar lavage (BAL) cells from smokers has led to the suggestion that citrullination induced by smoking might be the first step in the pathogenic chain of RA. Objective: To confirm and extend these findings. Methods: Immunohistochemistry was performed on BAL cells and bronchial mucosal biopsy sections obtained through bronchoscopy from 14 healthy smokers and 16 healthy non-smokers. Two antibodies recognising citrullinated proteins, two antibodies recognising peptidylarginine deiminase (PAD)2 enzyme and one recognising PAD4 enzyme were used. Results: Citrullinated proteins are upregulated in BAL cells of healthy smokers compared with healthy non-smokers. This was associated with higher expression of the PAD2 enzyme. The same level of citrullinated proteins was present in bronchial mucosal biopsy specimens of healthy smokers and non-smokers, despite higher expression of PAD2 in smokers. Conclusion: This study provides evidence that smoking enhances PAD2 expression in the bronchial mucosal and alveolar compartment, with consequent generation of citrullinated proteins in the latter. Smoking is an environmental factor that may lead to citrulline autoimmunity in genetically susceptible subjects.

Stabilization of HIF-1α is critical to improve wound healing in diabetic mice

Relative hypoxia is essential in wound healing since it normally plays a pivotal role in regulation of all the critical processes involved in tissue repair. Hypoxia-inducible factor (HIF) 1α is the critical transcription factor that regulates adaptive responses to hypoxia. HIF-1α stability and function is regulated by oxygen-dependent soluble hydroxylases targeting critical proline and asparaginyl residues. Here we show that hyperglycemia complexly affects both HIF-1α stability and activation, resulting in suppression of expression of HIF-1 target genes essential for wound healing both in vitro and in vivo. However, by blocking HIF-1α hydroxylation through chemical inhibition, it is possible to reverse this negative effect of hyperglycemia and to improve the wound healing process (i.e., granulation, vascularization, epidermal regeneration, and recruitment of endothelial precursors). Local adenovirus-mediated transfer of two stable HIF constructs demonstrated that stabilization of HIF-1α is necessary and sufficient for promoting wound healing in a diabetic environment. Our findings outline the necessity to develop specific hydroxylase inhibitors as therapeutic agents for chronic diabetes wounds. In conclusion, we demonstrate that impaired regulation of HIF-1α is essential for the development of diabetic wounds, and we provide evidence that stabilization of HIF-1α is critical to reverse the pathological process.

Monoclonal IgG antibodies generated from joint-derived B cells of RA patients have a strong bias toward citrullinated autoantigen recognition

Synovial IgG-expressing B cells from patients with rheumatoid arthritis show specificity for citrullinated autoantigens.

Multinational evidence-based recommendations for the diagnosis and management of gout: integrating systematic literature review and expert opinion of a broad panel of rheumatologists in the 3e initiative

We aimed to develop evidence-based multinational recommendations for the diagnosis and management of gout. Using a formal voting process, a panel of 78 international rheumatologists developed 10 key clinical questions pertinent to the diagnosis and management of gout. Each question was investigated with a systematic literature review. Medline, Embase, Cochrane CENTRAL and abstracts from 2010–2011 European League Against Rheumatism and American College of Rheumatology meetings were searched in each review. Relevant studies were independently reviewed by two individuals for data extraction and synthesis and risk of bias assessment. Using this evidence, rheumatologists from 14 countries (Europe, South America and Australasia) developed national recommendations. After rounds of discussion and voting, multinational recommendations were formulated. Each recommendation was graded according to the level of evidence. Agreement and potential impact on clinical practice were assessed. Combining evidence and clinical expertise, 10 recommendations were produced. One recommendation referred to the diagnosis of gout, two referred to cardiovascular and renal comorbidities, six focused on different aspects of the management of gout (including drug treatment and monitoring), and the last recommendation referred to the management of asymptomatic hyperuricaemia. The level of agreement with the recommendations ranged from 8.1 to 9.2 (mean 8.7) on a 1–10 scale, with 10 representing full agreement. Ten recommendations on the diagnosis and management of gout were established. They are evidence-based and supported by a large panel of rheumatologists from 14 countries, enhancing their utility in clinical practice.

Structural Changes and Antibody Enrichment in the Lungs Are Early Features of Anti–Citrullinated Protein Antibody–Positive Rheumatoid Arthritis

It has been suggested that immunologic events in the lungs may be involved in triggering immunity, in particular production of anti–citrullinated protein antibodies (ACPAs) during early phases of rheumatoid arthritis (RA). The aim of this study was to investigate the structural and immunologic features of the lungs in incident cases of early RA in relation to ACPA presence and smoking status.

B lymphocyte autoimmunity in rheumatoid synovitis is independent of ectopic lymphoid neogenesis

B lymphocyte autoimmunity plays a crucial role in the pathogenesis of rheumatoid arthritis. The local production of autoantibodies and the presence of ectopic lymphoid neogenesis in the rheumatoid synovium suggest that these dedicated microenvironments resembling canonical lymphoid follicles may regulate the initiation and maturation of B cell autoimmunity. In this study, we assessed experimentally the relevance of ectopic lymphoid neogenesis for B cell autoimmunity by a detailed structural, molecular, and serological analysis of seropositive and seronegative human synovitis. We demonstrate that synovial lymphoid neogenesis is a reversible process associated with inflammation which is neither restricted to nor preferentially associated with autoantibody positive rheumatic conditions. Despite the abundant expression of key chemokines and cytokines required for full differentiation toward germinal center reactions, synovial lymphoid neogenesis in rheumatoid arthritis only occasionally progresses toward fully differentiated follicles. In agreement with that observation, we could not detect Ag-driven clonal expansion and affinity maturation of B lymphocytes. Furthermore, ectopic lymphoid neogenesis is not directly associated with local production of anti-citrullinated protein Abs and rheumatoid factor in the rheumatoid joint. Therefore, we conclude that synovial lymphoid neogenesis is not a major determinant of these rheumatoid arthritis-specific autoantibody responses.

Identification of a novel chemokine-dependent molecular mechanism underlying rheumatoid arthritis-associated autoantibody-mediated bone loss

Objectives Rheumatoid arthritis (RA)-specific anti-citrullinated protein/peptide antibodies (ACPAs) appear before disease onset and are associated with bone destruction. We aimed to dissect the role of ACPAs in osteoclast (OC) activation and to identify key cellular mediators in this process. Methods Polyclonal ACPA were isolated from the synovial fluid (SF) and peripheral blood of patients with RA. Monoclonal ACPAs were isolated from single SF B-cells of patients with RA. OCs were developed from blood cell precursors with or without ACPAs. We analysed expression of citrullinated targets and peptidylarginine deiminases (PAD) enzymes by immunohistochemistry and cell supernatants by cytometric bead array. The effect of an anti-interleukin (IL)-8 neutralising antibody and a pan-PAD inhibitor was tested in the OC cultures. Monoclonal ACPAs were injected into mice and bone structure was analysed by micro-CT before and after CXCR1/2 blocking with reparixin. Results Protein citrullination by PADs is essential for OC differentiation. Polyclonal ACPAs enhance OC differentiation through a PAD-dependent IL-8-mediated autocrine loop that is completely abolished by IL-8 neutralisation. Some, but not all, human monoclonal ACPAs derived from single SF B-cells of patients with RA and exhibiting distinct epitope specificities promote OC differentiation in cell cultures. Transfer of the monoclonal ACPAs into mice induced bone loss that was completely reversed by the IL-8 antagonist reparixin. Conclusions We provide novel insights into the key role of citrullination and PAD enzymes during OC differentiation and ACPA-induced OC activation. Our findings suggest that IL8-dependent OC activation may constitute an early event in the initiation of the joint specific inflammation in ACPA-positive RA.

Delays in assessment of patients with rheumatoid arthritis: variations across Europe

Objective The first 3 months after symptom onset represent an important therapeutic window for rheumatoid arthritis (RA). This study investigates the extent and causes of delay in assessment of patients with RA in eight European countries. Method Data on the following levels of delay were collected from 10 centres (Berlin, Birmingham, Heraklion, Lund, Prague, Stockholm, Umeå, Vienna, Warsaw and Zurich): (1) from onset of RA symptoms to request to see healthcare professional (HCP); (2) from request to see HCP to assessment by that HCP; (3) from initial assessment by HCP to referral to rheumatologist; and (4) from referral to rheumatologist to assessment by that rheumatologist. Results Data were collected from 482 patients with RA. The median delay across the 10 centres from symptom onset to assessment by the rheumatologist was 24 weeks, with the percentage of patients seen within 12 weeks of symptom onset ranging from 8% to 42%. There were important differences in the levels underlying the total delays at individual centres. Conclusions This research highlights the contribution of patients, professionals and health systems to treatment delay for patients with RA in Europe. Although some centres have strengths in minimising certain types of delay, interventions are required in all centres to ensure timely treatment for patients.

Autoantibodies to citrullinated proteins induce joint pain independent of inflammation via a chemokine-dependent mechanism

Objective An interesting and so far unexplained feature of chronic pain in autoimmune disease is the frequent disconnect between pain and inflammation. This is illustrated well in rheumatoid arthritis (RA) where pain in joints (arthralgia) may precede joint inflammation and persist even after successful anti-inflammatory treatment. In the present study, we have addressed the possibility that autoantibodies against citrullinated proteins (ACPA), present in RA, may be directly responsible for the induction of pain, independent of inflammation. Methods Antibodies purified from human patients with RA, healthy donors and murinised monoclonal ACPA were injected into mice. Pain-like behaviour was monitored for up to 28 days, and tissues were analysed for signs of pathology. Mouse osteoclasts were cultured and stimulated with antibodies, and supernatants analysed for release of factors. Mice were treated with CXCR1/2 (interleukin (IL) 8 receptor) antagonist reparixin. Results Mice injected with either human or murinised ACPA developed long-lasting pronounced pain-like behaviour in the absence of inflammation, while non-ACPA IgG from patients with RA or control monoclonal IgG were without pronociceptive effect. This effect was coupled to ACPA-mediated activation of osteoclasts and release of the nociceptive chemokine CXCL1 (analogue to human IL-8). ACPA-induced pain-like behaviour was reversed with reparixin. Conclusions The data suggest that CXCL1/IL-8, released from osteoclasts in an autoantibody-dependent manner, produces pain by activating sensory neurons. The identification of this new pain pathway may open new avenues for pain treatment in RA and also in other painful diseases associated with autoantibody production and/or osteoclast activation.