Die feineren Veränderungen des Gelenkknorpels bei fungöser Synovitis und Caries der Gelenkenden

Mast cell chymase in synovial fluid of collagen-induced-arthritis rats regulates gelatinase release and promotes synovial fibroblasts proliferation via FAK/p21 signaling pathway

Mast cells (MCs) were accumulated in synovial tissue of rheumatoid arthritis (RA) patients. MC activation releases numerous mediators including MC-chymase. Synovial fibroblast shows a dramatic hyperplasia in RA articular cavity, but the effects of MC-chymase on synovial fibroblast are unknown. In this study, the collagen-induced-arthritis (CIA) rat model was employed to evaluate the dynamic changes of MC-chymase activity and other inflammatory factors during CIA development in-vivo. The fresh primary synovial fibroblasts from normal or CIA rats were extracted to compare the differences of these two cell-types, and to investigate the effects of MC-chymase on both-types of synovial fibroblast. The data showed that the dynamic changes in chymase activity in synovial fluids of CIA rats before and after immunizations were companied with the changes of tryptase, MMP-2/-9, TNF-α, IL-6, Co-II IgG, total protein, paw-thickness and body weight in-vivo. The baseline differences in cell grow rates, expression levels of p21, FAK, MMP-9 between normal and CIA-SFB have been seen. Compared to the normal synovial fibroblasts, CIA-SFB increased the percentage of the cells transferred to S or G2/M phases in cell cycle in-vivo; CIA-SFB become more proliferative with high-expression MMP-2/9 during CIA development. MC-chymase in-vitro promoted both types of synovial fibroblast proliferation and induced cell cycle changes, but CIA-synovial fibroblasts exhibited much stronger responses to MC-chymase stimulation by increased expression levels of p21, FAK, MMP-9 which associated with cell adhesion and migration. This study might give a new insight that the activated mast cell can be an important target cell for RA treatment and suggest that MC-chymase needs well attention for therapeutic aims.

Animal Models of Bone Loss in Inflammatory Arthritis: from Cytokines in the Bench to Novel Treatments for Bone Loss in the Bedside-a Comprehensive Review

Throughout life, bone is continuously remodelled. Bone is formed by osteoblasts, from mesenchymal origin, while osteoclasts induce bone resorption. This process is tightly regulated. During inflammation, several growth factors and cytokines are increased inducing osteoclast differentiation and activation, and chronic inflammation is a condition that initiates systemic bone loss. Rheumatoid arthritis (RA) is a chronic inflammatory auto-immune disease that is characterised by active synovitis and is associated with early peri-articular bone loss. Peri-articular bone loss precedes focal bone erosions, which may progress to bone destruction and disability. The incidence of generalised osteoporosis is associated with the severity of arthritis in RA and increased osteoporotic vertebral and hip fracture risk. In this review, we will give an overview of different animal models of inflammatory arthritis related to RA with focus on bone erosion and involvement of pro-inflammatory cytokines. In addition, a humanised endochondral ossification model will be discussed, which can be used in a translational approach to answer osteoimmunological questions.

Mechanisms of tissue damage in arthritis

The destruction of articular structures in the course of inflammatory arthritides such as rheumatoid arthritis (RA) or seronegative spondyloarthropathies is the most serious direct consequence of these diseases. Indeed, joint damage constitutes the "organ damage" of RA and-just like in all other diseases with organ involvement-such damage will usually be irreversible, cause permanent loss of function and subsequent disability. Research has identified a number of mechanisms and mediators of damage to articular structures such as bone and cartilage, ranging from proinflammatory cytokines, signal transduction pathways and cells types, which will be discussed in this review.

Bone erosion in rheumatoid arthritis: mechanisms, diagnosis and treatment

Bone erosion is a central feature of rheumatoid arthritis and is associated with disease severity and poor functional outcome. Erosion of periarticular cortical bone, the typical feature observed on plain radiographs in patients with rheumatoid arthritis, results from excessive local bone resorption and inadequate bone formation. The main triggers of articular bone erosion are synovitis, including the production of proinflammatory cytokines and receptor activator of nuclear factor κB ligand (RANKL), as well as antibodies directed against citrullinated proteins. Indeed, both cytokines and autoantibodies stimulate the differentiation of bone-resorbing osteoclasts, thereby stimulating local bone resorption. Although current antirheumatic therapy inhibits both bone erosion and inflammation, repair of existing bone lesions, albeit physiologically feasible, occurs rarely. Lack of repair is due, at least in part, to active suppression of bone formation by proinflammatory cytokines. This Review summarizes the substantial progress that has been made in understanding the pathophysiology of bone erosions and discusses the improvements in the diagnosis, monitoring and treatment of such lesions.

The role of RANK ligand/osteoprotegerin in rheumatoid arthritis

In the complex system of bone remodeling, the receptor activator of nuclear factor κB ligand (RANKL)/osteoprotegerin (OPG) pathway is the coupling factor between bone formation and bone resorption. RANKL binds to the RANK receptor of pre-osteoclasts and mature osteoclasts and stimulates their activation and differentiation. The production of RANKL/OPG by osteoblasts is influenced by hormones, growth factors and cytokines, which each have a different effect on the production of RANKL and OPG. Ultimately, the balance between RANKL and OPG determines the degree of proliferation and activity of the osteoclasts. In rheumatoid arthritis (RA), bone erosions are the result of osteoclastic bone resorption at the sites of synovitis, where RANKL expression is also found. Furthermore, magnetic resonance imaging (MRI) bone edema in RA indicates the presence of active inflammation within bone and the presence of osteitis, which is also associated with the expression of RANKL. Bone loss has been documented in the cortical and trabecular bone in the joints of the hand of RA patients. Both synovitis and periarticular bone involvement (osteitis and bone loss) are essential components of RA: they occur early in the disease and both are predictive for the occurrence and progression of bone damage. RANKL knockout mice and mice treated with OPG did not develop focal bone loss, in spite of persistent joint inflammation. Inhibition of osteoclasts by denosumab, a humanized antibody that selectively binds RANKL, has revealed in patients with RA that the occurrence of erosions and periarticular bone loss can be halted, however without affecting synovial inflammation. This disconnect between inflammation and bone destruction opens new ways to separately focus treatment on inflammation and osteoclastogenesis for preventing and/or minimizing the connection between joints and subchondral bone and bone marrow.

Pathogenesis of rheumatoid arthritis: targeting cytokines

Although considerable progress has been made by adequate treatment with traditional disease-modifying antirheumatic drugs (DMARDs), therapy of rheumatoid arthritis (RA) still remains difficult. The discovery of the importance of cytokines such as tumor necrosis factor (TNF), interleukin-1 (IL-1), interleukin-6 (IL-6), and interleukin-15 (IL-15), which are also stimulated by consequences of autoimmune responses, has led to the development of anticytokine therapies ("biologicals"). Blocking TNF or also, to some extent, IL-1 has proved beneficial in DMARD-resistant RA patients in multiple clinical trials. Along with clinical improvement, TNF blockade has been shown to halt radiographic disease progression, a major risk factor for disability. Recently, clinical trials have shown a significant therapeutic benefit of biological inhibitors of IL-6, and also of IL-15, with an efficacy comparable to that of TNF blockers. All these agents are particularly efficacious when combined with methotrexate. Although clinical remission is difficult to achieve even with anticytokine treatment, these drugs offer the potential to decrease disease activity and improve quality of life in a majority of RA patients, and it is conceivable that combinations of biological therapies may pave the path to even better success, which ultimately is remission or even cure.

Mechanisms of Disease: the link between RANKL and arthritic bone disease

Chronic inflammation and bone loss are closely linked pathophysiologic events. The most typical example of inflammatory bone loss is seen in patients with rheumatoid arthritis who develop systemic osteopenia as well as local breakdown of bone in the direct vicinity of inflamed joints. Understanding the mechanisms of arthritic bone degradation is crucial for designing therapies that can specifically protect joints from structural damage. Since osteoclast differentiation and activity are key events in arthritic bone damage, the signals that trigger osteoclastogenesis are potential therapeutic targets. Receptor activator of nuclear factor-kappaB (RANK) is activated by its ligand, RANKL, an essential molecule for osteoclast development: in the absence of RANKL or RANK, osteoclast differentiation from monocyte precursors does not occur. RANKL is expressed on T cells and fibroblasts within the synovial inflammatory tissue of patients with RA and its expression is regulated by proinflammatory cytokines. In animal models of arthritis, blockade of RANKL-RANK interactions, or a genetic absence of RANKL or RANK, protects against joint damage despite the presence of joint inflammation. Therefore, inhibition of RANKL is regarded as a promising future strategy for inhibiting inflammatory bone loss in patients with chronic inflammatory arthritis.

Interaction between Synovial Inflammatory Tissue and Bone Marrow in Rheumatoid Arthritis

Rheumatoid arthritis (RA) leads to destruction of cartilage and bone. Whether rheumatoid arthritis also affects the adjacent bone marrow is less clear. In this study, we investigated subcortical bone marrow changes in joints from patients with RA. We describe penetration of the cortical barrier by synovial inflammatory tissue, invasion into the bone marrow cavity and formation of mononuclear cell aggregates with B cells as the predominant cell phenotype. B cells expressed common B cell markers, such as CD20, CD45RA, and CD79a, and were mature B cells, as indicated by CD27 expression. Plasma cells were also present and were enriched in the regions between aggregates and inflammatory tissue. Moreover, molecules for B cell chemoattraction, such as BCA-1 and CCL-21, homing, mucosal addressin cell adhesion molecule-1 and survival, BAFF, were expressed. Endosteal bone next to subcortical bone marrow aggregates showed an accumulation of osteoblasts and osteoid deposition. In summary, we show that synovial inflammatory tissue can reach the adjacent bone marrow by fully breaking the cortical barrier, which results in formation of B cell-rich aggregates as well as increased formation of new bone. This suggests that bone marrow is an additional compartment in the disease process of RA.