Objective. In experimental collagenase-induced osteoarthritis (OA) in the mouse, synovial lining macrophages are crucial in mediating joint destruction. It was recently shown that adipose-derived stem cells (ASCs) express immunosuppressive characteristics. This study was undertaken to explore the effect of intraarticular injection of ASCs on synovial lining thickness and its relation to joint pathology in experimental mouse OA.Methods. ASCs were isolated from fat surrounding the inguinal lymph nodes and cultured for 2 weeks. Experimental OA was induced by injection of collagenase into the knee joints of C57BL/6 mice. OA phenotypes were measured within 8 weeks after induction. Histologic analysis was performed, and synovial thickening, enthesophyte formation, and cartilage destruction were measured in the knee joint.Results. ASCs were injected into the knee joints of mice 7 days after the induction of collagenase-induced OA. On day 1, green fluorescent protein-labeled ASCs were attached to the lining layer in close contact with macrophages. Thickening of the synovial lining, formation of enthesophytes associated with medial collateral ligaments, and formation of enthesophytes associated with cruciate ligaments were significantly inhibited on day 42 after ASC treatment, by 31%, 89%, and 44%, respectively. Destruction of cartilage was inhibited on day 14 (65%) and day 42 (35%). In contrast to early treatment, injection of ASCs on day 14 after OA induction showed no significant effect on synovial activation or joint pathology on day 42.Conclusion. These findings indicate that a single injection of ASCs into the knee joints of mice with early-stage collagenase-induced OA inhibits synovial thickening, formation of enthesophytes associated with ligaments, and cartilage destruction.

S100A8/A9 regulate joint inflammation and cartilage destruction during antigen-induced arthritis.

Objective. To investigate whether S100A8 is actively involved in matrix metalloproteinase (MMP)-mediated chondrocyte activation.Methods. S100A8 and S100A9 proteins were detected in inflamed knee joints from mice with various forms of murine arthritis, using immunolocalization. Murine chondrocyte cell line H4 was stimulated with proinflammatory cytokines or recombinant S100A8. Messenger RNA (mRNA) and protein levels were measured using reverse transcriptase-polymerase chain reaction and intracellular fluorescence-activated cell sorting (FACS). Breakdown of aggrecan on the pericellular surface of the chondrocytes was measured using VDIPEN and NITEGE antibodies and FACS, and breakdown in patellar cartilage was measured by immunolocalization.Results. S100A8 and S100A9 proteins were abundantly expressed in and around chondrocytes in inflamed knee joints after induction of antigen-induced arthritis or onset of spontaneous arthritis in interleukin-1 (IL-1) receptor antagonist-knockout mice. Stimulation of chondrocytes by the proinflammatory cytokines tumor necrosis factor ␣, IL-1␤, IL-17, and interferon-␥ caused strong up-regulation of S100A8 mRNA and protein levels and up-regulation to a lesser extent of S100A9 levels. Stimulation of chondrocytes with S100A8 induced significant up-regulation of MMP-2, MMP-3, MMP-9, MMP-13, ADAMTS-4, and ADAMTS-5 mRNA levels (up-regulated 4, 4, 3, 16, 8, and 4 times, respectively). VDIPEN and NITEGE neoepitopes were significantly elevated in a concentrationdependent manner in chondrocytes treated with 0.2, 1, or 5 g/ml of S100A8. (VDIPEN levels were elevated 17%, 67%, and 108%, respectively, and NITEGE levels were elevated 8%, 33%, and 67%, respectively.) S100A8 significantly increased the effect of IL-1␤ on MMP-3, MMP-13, and ADAMTS-5. Mouse patellae incubated with both IL-1␤ and S100A8 had elevated levels of NITEGE within the cartilage matrix when compared with patellae incubated with IL-1␤ or S100A8 alone.Conclusion. These findings indicate that S100A8 and S100A9 are found in and around chondrocytes in experimental arthritis. S100A8 up-regulates and activates MMPs and aggrecanase-mediated pericellular matrix degradation.Breakdown of the cartilage matrix is one of the hallmarks of rheumatoid arthritis (RA). Cartilage destruction is predominantly mediated by cytokines, enzymes, and oxygen radicals (1,2). These mediators are released by synovial cells and by chondrocytes. In experimental arthritis, clear pericellular activation of chondrocytes is observed based on expression of large amounts of neoepitopes induced by metalloproteinases, which results in pericellular breakdown of the matrix (3), eventually leading to erosion.

Objective. Rheumatoid arthritis, which is associated with elevated levels of S100A8 and S100A9, is characterized by severe bone erosions caused by enhanced osteoclast formation and activity. The aim of the present study was to investigate the role of S100A8 and S100A9 in osteoclastic bone destruction in murine antigen-induced arthritis (AIA).Methods. Bone destruction was analyzed in the arthritic knee joints of S100A9-deficient mice in which S100A8 protein expression was also lacking, and in wild-type (WT) controls. Osteoclast precursors from S100A9-deficient and WT mice were differentiated into osteoclasts in vitro. Additionally, precursors were stimulated with S100A8, S100A9, or S100A8/A9 during osteoclastogenesis. Receptor involvement was investigated using an anti-receptor for advanced glycation end products (anti-RAGE)-blocking antibody, soluble RAGE, or Toll-like receptor 4 (TLR-4)-deficient osteoclast precursors. The formation of osteoclasts and actin rings, the regulation of osteoclast markers, and bone resorption were analyzed.Results. Bone erosions and cathepsin K staining were significantly suppressed in S100A9-deficient mice after AIA induction. However, osteoclast precursors from S100A9-deficient mice developed normally into functional osteoclasts, which excludes a role for intrinsic S100A8/A9. In contrast to the results observed with S100A9 and S100A8/A9, the addition of S100A8 during osteoclastogenesis resulted in stimulation of osteoclast formation in conjunction with enhanced actin ring formation and increased bone resorption. Analysis of the putative receptor for S100A8 in osteoclastogenesis revealed that osteoclast differentiation and function could not be inhibited by blocking RAGE, whereas the increase in osteoclast numbers and enhanced bone resorption were completely abrogated using TLR-4-deficient osteoclast precursors.Conclusion. These results demonstrate that S100A8 stimulated osteoclast formation and activity and suggest that both S100A8 and TLR-4 are important factors in mediating osteoclastic bone destruction in experimental arthritis.Bone erosions are an important hallmark of rheumatoid arthritis (RA) and typically result from enhanced formation and activity of osteoclasts in affected joints. Osteoclasts originate from hematopoietic precursors of the monocyte/macrophage lineage that differentiate into multinucleated osteoclasts under the

Objective. The levels of both Fc␥ receptor (Fc␥R) 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 Fc␥R 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 Fc␥R 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 Fc␥R 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 Fc␥RI (64-fold increase) and Fc␥RIV (256-fold increase) in the synovium. Stimulation of macrophages with rS100A8 led to significant upregulation of mRNA and protein levels of Fc␥RI and Fc␥RIV, but not Fc␥RIII, 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 Fc␥R expression. Up-regulation of Fc␥RI and Fc␥RIV was abrogated in rS100A8-stimulated macrophages from TLR-4 ؊/؊ mice, indicating that the induction of Fc␥R expression by S100A8 is mediated by TLR-4. Fc␥R 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 metalloproteinasemediated cartilage destruction.Conclusion. S100A8 is a strong promoter of activating Fc␥RI and Fc␥RIV in macrophages through the activation of TLR-4, and acts as a regulator of Fc␥R expression in inflamed synovium in chronic experimental arthritis.

Osteoclasts and macrophages share progenitors that must receive decisive lineage signals driving them into their respective differentiation routes. Macrophage colony stimulation factor M-CSF is a common factor; bone is likely the stimulus for osteoclast differentiation. To elucidate the effect of both, shared mouse bone marrow precursor myeloid blast was pre-cultured with M-CSF on plastic and on bone. M-CSF priming prior to stimulation with M-CSF and osteoclast differentiation factor RANKL resulted in a complete loss of osteoclastogenic potential without bone. Such M-CSF primed cells expressed the receptor RANK, but lacked the crucial osteoclastogenic transcription factor NFATc1. This coincided with a steeply decreased expression of osteoclast genes TRACP and DC-STAMP, but an increased expression of the macrophage markers F4/80 and CD11b. Compellingly, M-CSF priming on bone accelerated the osteoclastogenic potential: M-CSF primed cells that had received only one day M-CSF and RANKL and were grown on bone already expressed an array of genes that are associated with osteoclast differentiation and these cells differentiated into osteoclasts within 2 days. Osteoclastogenesis-insensitive precursors grown in the absence of bone regained their osteoclastogenic potential when transferred to bone. This implies that adhesion to bone dictates the fate of osteoclast precursors. Common macrophage-osteoclast precursors may become insensitive to differentiate into osteoclasts and regain osteoclastogenesis when bound to bone or when in the vicinity of bone.

Activating FcγRs mediate IC-induced inhibition of osteoclastogenesis, which might be overruled in the presence of proinflammatory mediators. This suggests that the balance of FcγR-mediated inflammation, through proinflammatory cytokine production, as well as the direct inhibitory effect of ICs on osteoclastogenesis determines the net effect on bone loss.

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