Current perspectives on synovitis

Ginkgolide J protects human synovial cells SW982 via suppression of p38‑dependent production of pro‑inflammatory mediators

Fibroblast-like synoviocytes (FLS) in the synovial lining play a key role in the pathological process of rheumatoid arthritis (RA), which produce pro-inflammatory mediators to perpetuate inflammation and proteases to contribute to cartilage destruction. Ginkgolide J (GJ) is a subclass of ginkgolides (GGs) that exhibits anti-inflammatory activity. In the present study, the protective effect of GJ on lipopolysaccharide (LPS)-treated human synovial cells SW982 and its related mechanisms were investigated using various methods, including ELISA, Griess assay, western blotting, immunofluorescence analysis and p38 kinase activity assay. The results revealed that GJ pretreatment significantly attenuated LPS-induced excess production of pro-inflammatory mediators in SW982 cells via suppression of tumor necrosis factor-α/interleukin (IL)-1β/IL-18/NF-κB/NLR family pyrin domain containing 3, prostaglandin E2/cyclooxygenase-2 and inducible nitric oxide synthase/nitric oxide signaling. Mechanistic studies revealed that p38 activation contributed to the LPS-induced inflammatory response, and GJ pretreatment dose-dependently attenuated p38 activation, indicating that the suppressive effect of GJ was achieved by targeting p38 signaling. These findings may contribute to the prevention and treatment of RA.

MicroRNA-146a governs fibroblast activation and joint pathology in arthritis

Synovial fibroblasts are key cells orchestrating the inflammatory response in arthritis. Here we demonstrate that loss of miR-146a, a key epigenetic regulator of the innate immune response, leads to increased joint destruction in a TNF-driven model of arthritis by specifically regulating the behavior of synovial fibroblasts. Absence of miR-146a in synovial fibroblasts display a highly deregulated gene expression pattern and enhanced proliferation in vitro and in vivo. Deficiency of miR-146a induces deregulation of tumor necrosis factor (TNF) receptor associated factor 6 (TRAF6) in synovial fibroblasts, leading to increased proliferation. In addition, loss of miR-146a shifts the metabolic state of fibroblasts towards glycolysis and augments the ability of synovial fibroblasts to support the generation of osteoclasts by controlling the balance of osteoclastogenic regulatory factors receptor activator of NF-κB ligand (RANKL) and osteoprotegerin (OPG). Bone marrow transplantation experiments confirmed the importance of miR-146a in the radioresistant mesenchymal compartment for the control of arthritis severity, in particular for inflammatory joint destruction. This study therefore identifies microRNA-146a as an important local epigenetic regulator of the inflammatory response in arthritis. It is a central element of an anti-inflammatory feedback loop in resident synovial fibroblasts, who are orchestrating the inflammatory response in chronic arthritis. MiR-146a restricts their activation, thereby preventing excessive tissue damage during arthritis.

Phosphatase and tensin homolog (PTEN) in antigen-presenting cells controls Th17-mediated autoimmune arthritis

INTRODUCTION

Autoreactive T cells are a central element in many systemic autoimmune diseases. The generation of these pathogenic T cells is instructed by antigen-presenting cells (APCs). However, signaling pathways in APCs that drive autoimmune diseases, such as rheumatoid arthritis, are not understood.

METHODS

We measured phenotypic maturation, cytokine production and induction of T cell proliferation of APCs derived from wt mice and mice with a myeloid-specific deletion of PTEN (myeloid PTEN(-/-)) in vitro and in vivo. We induced collagen-induced arthritis (CIA) and K/BxN serum transfer arthritis in wt and myeloid-specific PTEN(-/-) mice. We measured the cellular composition of lymph nodes by flow cytometry and cytokines in serum and after ex vivo stimulation of T cells.

RESULTS

We show that myeloid-specific PTEN(-/-) mice are almost protected from CIA. Myeloid-specific deletion of PTEN leads to a significant reduction of cytokine expression pivotal for the induction of systemic autoimmunity such as interleukin (IL)-23 and IL-6, leading to a significant reduction of a Th17 type of immune response characterized by reduced production of IL-17 and IL-22. In contrast, myeloid-specific PTEN deficiency did not affect K/BxN serum transfer arthritis, which is independent of the adaptive immune system and solely depends on innate effector functions.

CONCLUSIONS

These data demonstrate that the presence of PTEN in myeloid cells is required for the development of CIA. Deletion of PTEN in myeloid cells inhibits the development of autoimmune arthritis by preventing the generation of a pathogenic Th17 type of immune response.

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.

Synovitis score: discrimination between chronic low-grade and high-grade synovitis

AIMS

To standardize the histopathological assessment of synovial membrane specimens in order to contribute to the diagnostics of rheumatic and non-rheumatic joint diseases.

METHODS AND RESULTS

Three features of chronic synovitis (enlargement of lining cell layer, cellular density of synovial stroma, leukocytic infiltrate) were semiquantitatively evaluated (from 0, absent to 3, strong) and each feature was graded separately. The sum provided the synovitis score, which was interpreted as follows: 0-1, no synovitis; 2-4, low-grade synovitis; 5-9, high-grade synovitis. Five hundred and fifty-nine synovectomy specimens were graded by two independent observers. Clinical diagnoses were osteoarthrosis (n=212), post-traumatic arthritis (n=21), rheumatoid arthritis (n=246), psoriatic arthritis (n=22), reactive arthritis (n=9), as well as controls (n=49) from autopsies of patients without joint damage. Median synovitis scores when correlated with clinical diagnoses were: controls 1.0, osteoarthritis 2.0, post-traumatic arthritis 2.0, psoriatic arthritis 3.5, reactive arthritis 5.0 and rheumatoid arthritis 5.0. The scores differed significantly between most disease groups, especially between degenerative and rheumatic diseases. A high-grade synovitis was strongly associated with rheumatic joint diseases (P<0.001, sensitivity 61.7%, specificity 96.1%). The correlation between the two observers was high (r=0.941).

CONCLUSION

The proposed synovitis score is based on well-defined, reproducible histopathological criteria and may contribute to diagnosis in rheumatic and non-rheumatic joint diseases.

Drug delivery strategies for cathepsin inhibitors in joint diseases

Cathepsins play important roles in the development of joint and bone diseases such as osteoporosis, rheumatoid arthritis (RA) and osteoarthritis (OA). Cathepsin inhibitors are presently in development and clinical testing for use as novel disease-modifying drugs for the improved treatment of osteoporosis. They may also be applicable for the treatment of joint diseases. However, some barriers still hamper their clinical applications in these indications. Based on pathophysiological features of RA and OA, the authors discuss six potential drug delivery strategies for the effective delivery of cathepsin inhibitors or other antiarthritic drugs to the arthritic joint tissue. Successful application of these strategies may significantly contribute to a more effective and safe treatment of RA and OA.

Rheumatoid arthritis. From bench to bedside

In the last decade, basic science has unraveled in considerable detail the inflammatory and related processes ongoing in RA synovial membrane. This has translated to cytokine targeting therapies with some effect. How much more can be achieved? It may be argued that the order of improvement obtained thus far obviates further study. This ignores the potential to achieve a far greater magnitude of disease suppression. Our objective in innovating biologic therapies should now be routine achievement of American College of Rheumatology "70% responses" or disease remission and design of patient-specific therapy based on individual disease characteristics. We have not yet explored the potential contained in combination biologic approaches, particularly when different processes within the disease are targeted. Cocktails might target T cells, cytokines, and angiogenic factors, for example. These developments must also be seen in the context of the information soon to be available from the Human Genome Project. The impact of gene array analysis and similar techniques that facilitate simultaneous evaluation of thousands of gene activation events is also awaited. This, in turn, is likely to require considerable development in our use of information technology, because the volume of information will soon (or may already) be prohibitive. Finally, encompassing genomic and bioinformatic approaches should certainly challenge our basic diagnostic criteria such that it ultimately may be necessary to consider our clinical diagnoses on the basis not only of clinical phenotype but of genotype and biologic response profile. Through this rapid evolution, close communication between physician and scientist is essential.