To investigate the direct role of interleukin (IL) 6 in the development of rheumatoid arthritis, IL-6-deficient (IL-6 ؊͞؊) mice were backcrossed for eight generations into C57BL͞6 mice, a strain of mice with a genetic background of susceptibility for antigen-induced arthritis (AIA). Both histological and immunological comparisons were made between IL-6-deficient (IL-6 ؊͞؊) mice and wild-type (IL-6 ؉͞؉) littermates after the induction of AIA. Although all IL-6 ؉͞؉ mice developed severe arthritis, only mild arthritis was observed in IL-6 ؊͞؊ mice. Safranin O staining demonstrated that articular cartilage was well preserved in IL-6 ؊͞؊ mice, whereas it was destroyed completely in IL-6 ؉͞؉ mice. In addition, comparable mRNA expression for both IL-1␤ and tumor necrosis factor ␣, but not for IL-6, was detected in the inf lamed joints of IL-6 ؊͞؊ mice, suggesting that IL-6 may play a more crucial role in cartilage destruction than either IL-1␤ or tumor necrosis factor ␣. In immunological comparisons, both antigen-specific in vitro proliferative response in lymph node cells and in vivo antibody production were elicited in IL-6 ؊͞؊ mice, but they were reduced to less than half of that found in IL-6 ؉͞؉ mice. Lymph node cells of IL-6 ؊͞؊ mice produced many more Th2 cytokines than did IL-6 ؉͞؉ mice with either antigen-specific or nonspecific stimulation in in vitro culture. Taken together, these results indicate that IL-6 may play a key role in the development of AIA at the inductive as well as the effector phase, and the blockade of IL-6 is possibly beneficial in the treatment of rheumatoid arthritis.

Mutations in the TRPS1 gene lead to the tricho-rhino-phalangeal syndrome, which is characterized by skeletal defects and abnormal hair development. The TRPS1 gene encodes an atypical member of the GATA-type family of transcription factors. Here we show that mice with a disrupted Trps1 gene develop a chondrodysplasia characterized by diminished chondrocyte proliferation and decreased apoptosis in growth plates. Our analyses revealed that Trps1 is a repressor of Stat3 expression, which in turn controls chondrocyte proliferation and survival by regulating the expression of cyclin D1 and Bcl2. Our conclusion is supported (i) by siRNA-mediated depletion of Stat3 in Trps1-deficient chondrocytes, which normalized the expression of cyclin D1 and Bcl2, (ii) by overexpression of Trps1 in ATDC5 chondrocytes, which diminished Stat3 levels and increased proliferation and apoptosis, and (iii) by mutational analysis of the GATA-binding sites in the Stat3 gene, which revealed that their integrity is critical for the direct association with Trps1 and for Trps1-mediated repression of Stat3. Altogether our findings identify Trps1 as a novel regulator of chondrocytes proliferation and survival through the control of Stat3 expression.

Objective. To investigate the roles of interleukin-6 (IL-6) in the pathogenesis of rheumatoid arthritis (RA) by studying its effect on murine collagen-induced arthritis (CIA).Methods. IL-6-deficient (IL-6؊/؊) mice with a genetic background of susceptibility to CIA were generated by backcrossing them with DBA/1J mice for 8 generations. Clinical and immunologic features were compared between these mice and IL-6 wild-type (IL-6؉/؉) littermates with CIA.Results. Serum IL-6 levels increased during the development of CIA in IL-6؉/؉ mice. Two prominent peaks were observed. The first was coincident with the onset of arthritis, and the second one was observed during exacerbation of the disease. The onset of arthritis in IL-6؊/؊ mice was delayed for 2 weeks compared with that in IL-6؉/؉ mice, and the severity of arthritis, as indicated by the arthritis score, remained significantly lower in IL-6؊/؊ mice during the entire followup period (14 weeks), although all IL-6؊/؊ mice developed definite arthritis as did the IL-6؉/؉ mice. Histologic severity was also reduced in IL-6؊/؊ mice. In addition, radiologic changes such as osteopenia and bone erosion were reduced significantly in these animals. Both humoral and cellular responses to type II collagen (CII) in IL-6؊/؊ mice were reduced to about half those in IL-6؉/؉ mice. In addition, enhanced production of IL-4 and IL-10 in response to concanavalin A stimulation was observed in IL-6؊/؊ mice.Conclusion. IL-6 plays an important role in the development of CIA, and both suppression of specific immune responses to CII and a tendency to a shift toward a Th2 cytokine profile might contribute in part to the attenuation of CIA in IL-6؊/؊ mice. These findings suggest that blockade of IL-6 might be beneficial in the treatment of RA.

Objective. To investigate the involvement of osteopontin (OPN) in bone destruction in a murine experimental arthritis model of collagen-induced arthritis (CIA).Methods. The expression of OPN was examined at both the messenger RNA (mRNA) and protein levels in various arthritic lesions in mice with CIA by in situ hybridization and immunohistochemistry, respectively. In addition, the expression of ␣v␤3 integrin, a receptor for OPN, the ligation of which is thought to be essential for bone resorption by osteoclasts, was examined by immunohistochemistry. Plasma concentrations of OPN were measured at different time points in the course of CIA by enzyme-linked immunosorbent assay.Results. OPN mRNA was detected mainly at sites of bone erosion in arthritic lesions, where activated osteoclasts were present; OPN protein was also detected at sites of bone erosion. In the arthritic synovium, OPN was predominantly expressed in the synovial lining layer, but not in lymphoid aggregates. In addition, ␣v␤3 integrin was detected coincident with OPN at sites of bone erosion (bone-pannus junction). Plasma OPN levels were markedly elevated at the time points that corresponded to arthritis flares, and higher levels were maintained during the progression of arthritis.Conclusion. OPN may mediate bone resorption by osteoclasts in arthritis through ligation with its receptor, ␣v␤3 integrin. OPN may be a useful therapeutic target molecule in the prevention of bone destruction in arthritis.

Tricho‐rhino‐phalangeal syndrome (TRPS) is an autosomal dominant skeletal disorder caused by mutations of TRPS1. Based on the similar expression patterns of Trps1 and Gdf5, we hypothesized a possible functional interaction between these two molecules. Using a chondrogenic cell line (ATDC5), we investigated the association of Gdf5‐mediated signaling pathways with Trps1 and the phenotypic changes of ATDC5 cells due to over‐expression or suppression of Trps1. Treatment of cells with Gdf5 enhanced Trps1 protein levels and phosphorylation of p38 mitogen‐activated protein kinase (MAPK) in a dose‐dependent manner. Nuclear translocation of Trps1 was also induced by Gdf5. These effects were blocked by a dominant negative form of activin‐linked kinase 6 (dn‐Alk6) and by SB203580, an inhibitor of the p38 MAPK pathway. Conversely, Gdf5 expression was suppressed by the over‐expression of Trps1. Trps1‐overexpressing ATDC5 (O/E) cells differentiated into chondrocytes more quickly than mock‐infected control cells, whereas cells transfected with dn‐Alk6 showed slower differentiation. On the other hand, O/E cells showed an increase of apoptosis along with the up‐regulation of cleaved caspase 3 and down‐regulation of Bcl‐2, whereas dn‐Alk6 cells showed suppression of apoptosis. In conclusion, Trps1 acts downstream of the Gdf5 signaling pathway and promotes the differentiation and apoptosis of ATDC5 cells.