Dendritic cells (DCs) are specialized APCs that can be activated upon pathogen recognition as well as recognition of endogenous ligands, which are released during inflammation and cell stress. The recognition of exogenous and endogenous ligands depends on TLRs, which are abundantly expressed in synovial tissue from rheumatoid arthritis (RA) patients. Furthermore TLR ligands are found to be present in RA serum and synovial fluid and are significantly increased, compared with serum and synovial fluid from healthy volunteers and patients with systemic sclerosis and systemic lupus erythematosus. Identification of novel endogenous TLR ligands might contribute to the elucidation of the role of TLRs in RA and other autoimmune diseases. In this study, we investigated whether five members of the small heat shock protein (HSP) family were involved in TLR4-mediated DC activation and whether these small HSPs were present in RA synovial tissue. In vitro, monocyte-derived DCs were stimulated with recombinant αA crystallin, αB crystallin, HSP20, HSPB8, and HSP27. Using flow cytometry and multiplex cytokine assays, we showed that both αA crystallin and HSPB8 were able to activate DCs and that this activation was TLR4 dependent. Furthermore, Western blot and immunohistochemistry showed that HSPB8 was abundantly expressed in synovial tissue from patients with RA. With these experiments, we identified sHSP αA crystallin and HSPB8 as two new endogenous TLR4 ligands from which HSPB8 is abundantly expressed in RA synovial tissue. These findings suggest a role for HSPB8 during the inflammatory process in autoimmune diseases such as RA.

Objective: Wnt signaling pathway proteins are involved in embryonic development of cartilage and bone, and, interestingly, developmental processes appear to be recapitulated in osteoarthritic (OA) cartilage. The present study was undertaken to characterize the expression pattern of Wnt and Fz genes during experimental OA and to determine the function of selected genes in experimental and human OA.Methods: Longitudinal expression analysis was performed in 2 models of OA. Levels of messenger RNA for genes from the Wnt/β‐catenin pathway were determined in synovium and cartilage, and the results were validated using immunohistochemistry. Effects of selected genes were assessed in vitro using recombinant protein, and in vivo by adenoviral overexpression.Results: Wnt‐induced signaling protein 1 (WISP‐1) expression was strongly increased in the synovium and cartilage of mice with experimental OA. Wnt‐16 and Wnt‐2B were also markedly up‐regulated during the course of disease. Interestingly, increased WISP‐1 expression was also found in human OA cartilage and synovium. Stimulation of macrophages and chondrocytes with recombinant WISP‐1 resulted in interleukin‐1–independent induction of several matrix metalloproteinases (MMPs) and aggrecanase. Adenoviral overexpression of WISP‐1 in murine knee joints induced MMP and aggrecanase expression and resulted in cartilage damage.Conclusion: This study included a comprehensive characterization of Wnt and Frizzled gene expression in experimental and human OA articular joint tissue. The data demonstrate, for the first time, that WISP‐1 expression is a feature of experimental and human OA and that WISP‐1 regulates chondrocyte and macrophage MMP and aggrecanase expression and is capable of inducing articular cartilage damage in models of OA.

Knee arthrocentesis is a commonly performed diagnostic and therapeutic procedure in rheumatology and orthopedic surgery. Classic teaching of arthrocentesis skills relies on hands-on practice under supervision. Video-based online teaching is an increasingly utilized educational tool in higher and clinical education. YouTube is a popular video-sharing Web site that can be accessed as a teaching source. The objective of this study was to assess the educational value of YouTube videos on knee arthrocentesis posted by health professionals and institutions during the period from 2008 to 2012. The YouTube video database was systematically searched using 5 search terms related to knee arthrocentesis. Two independent clinical reviewers assessed videos for procedural technique and educational value using a 5-point global score, ranging from 1 = poor quality to 5 = excellent educational quality. As validated international guidelines are lacking, we used the guidelines of the Swiss Society of Rheumatology as criterion standard for the procedure. Of more than thousand findings, 13 videos met the inclusion criteria. Of those, 2 contained additional animated video material: one was purely animated, and one was a check list. The average length was 3.31 ± 2.28 minutes. The most popular video had 1388 hits per month. Our mean global score for educational value was 3.1 ± 1.0. Eight videos (62 %) were considered useful for teaching purposes. Use of a "no-touch" procedure, meaning that once disinfected the skin remains untouched before needle penetration, was present in all videos. Six videos (46%) demonstrated full sterile conditions. There was no clear preference of a medial (n = 8) versus lateral (n = 5) approach. A discreet number of YouTube videos on knee arthrocentesis appeared to be suitable for application in a Web-based format for medical students, fellows, and residents. The low-average mean global score for overall educational value suggests an improvement of future video-based instructional materials on YouTube would be necessary before regular use for teaching could be recommended.

Subchondral osteosclerosis, characterized by an increase of hypomineralized bone material, is a pathological hallmark of osteoarthritis. The cellular components in the subchondral marrow compartment that participate in this aberrant bone remodeling process remain to be elucidated. This study assessed the presence of marrow inflammatory cells and their relative abundance between nonsclerotic and sclerotic tissues in knee osteoarthritis. Bone samples from osteoarthritic knee tibial plateaus were stratified for histological analyses using computed tomography osteoabsorptiometry. Immunohistological analysis revealed the presence of CD20 (B‐lymphocyte) and CD68 (macrophage), but not CD3 (T‐lymphocyte) immunoreactive mononuclear cells in subchondral marrow tissues and their relative abundance was significantly increased in sclerotic compared with nonsclerotic bone samples. Multinucleated osteoclasts that stained positive for CD68 and tartrate‐resistant acid phosphatase, predominantly associated with CD34‐positive blood vessels and their abundance was strongly increased in sclerotic samples. Bone‐specific alkaline phosphatase activity in outgrowth osteoblasts was induced by conditioned medium from nonsclerotic, but not sclerotic, bone pieces. These results suggest that an interaction between bone‐resident cells and marrow inflammatory cells might play a role in aberrant bone remodeling leading to subchondral osteosclerosis. Elevated osteoclast activity in sclerotic bone suggests that bone formation and resorption activities are increased, yet uncoupled, in human knee osteoarthritis. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:262–269, 2016.

Osteoarthritis (OA) is a major health burden of our time. Age is the most prominent risk factor for the development and progression of OA. The mechanistic influence of aging on OA has different facets. On a molecular level, matrix proteins such as collagen or proteoglycans are modified, which alters cartilage function. Collagen cross-linking within the bone results in impaired plasticity and increased stiffness. Synovial or fat tissue, menisci but also ligaments and muscles play an important role in the pathogenesis of OA. In the elderly, sarcopenia or other causes of muscle atrophy are frequently encountered, leading to a decreased stability of the joint. Inflammation in form of cellular infiltration of synovial tissue or subchondral bone and expression of inflammatory cytokines is more and more recognized as trigger of OA. It has been demonstrated that joint movement can exhibit anti-inflammatory mechanisms. Therefore physical activity or physiotherapy in the elderly should be encouraged, also in order to increase the muscle mass. A reduced stem cell capacity in the elderly is likely associated with a decrease of repair mechanisms of the musculoskeletal system. New treatment strategies, for example with mesenchymal stem cells (MSC) are investigated, despite clear evidence for their efficacy is lacking.

Objective: The levels of both Fcγ receptor (FcγR) and the alarmins S100A8 and S100A9 are correlated with the development and progression of cartilage destruction during antigen‐induced arthritis (AIA). This study was undertaken to study the active involvement of S100A8, S100A9, and S100A8/S100A9 in FcγR regulation in murine macrophages and synovium during AIA.Methods: Recombinant murine S100A8 (rS100A8) was injected into normal mouse knee joints, and the synovium was isolated for analysis of FcγR messenger RNA (mRNA) expression by reverse transcription–polymerase chain reaction (RT‐PCR). Macrophages, including bone marrow macrophages derived from Toll‐like receptor 4–deficient (TLR‐4^−/−) mice, and polymorphonuclear cells (PMNs) were stimulated with S100 proteins, and levels of FcγR mRNA and protein were measured using RT‐PCR and fluorescence‐activated cell sorting analyses. AIA was induced in the knee joints of S100A9‐deficient (S100A9^−/−) mice, compared with wild‐type (WT) controls, and the extent of cartilage destruction was determined using immunohistochemical analysis.Results: Intraarticular injection of rS100A8 into the knee joints of normal mice caused a strong up‐regulation of mRNA levels of activating FcγRI (64‐fold increase) and FcγRIV (256‐fold increase) in the synovium. Stimulation of macrophages with rS100A8 led to significant up‐regulation of mRNA and protein levels of FcγRI and FcγRIV, but not FcγRIII, while the effects of S100A9 or S100A8/S100A9 complexes were less potent. Stimulation of PMNs (32Dcl3 cell line) with S100 proteins had no effect on FcγR expression. Up‐regulation of FcγRI and FcγRIV was abrogated in rS100A8‐stimulated macrophages from TLR‐4^−/− mice, indicating that the induction of FcγR expression by S100A8 is mediated by TLR‐4. FcγR expression in the inflamed synovium of S100A9^−/− mice was significantly lower on day 14 after arthritis induction when compared with WT controls, and these findings correlated with reduced severity of matrix metalloproteinase–mediated cartilage destruction.Conclusion: S100A8 is a strong promoter of activating FcγRI and FcγRIV in macrophages through the activation of TLR‐4, and acts as a regulator of FcγR expression in inflamed synovium in chronic experimental arthritis.