Bone morphogenetic proteins 2 and 6, expressed in arthritic synovium, are regulated by proinflammatory cytokines and differentially modulate fibroblast‐like synoviocyte apoptosis

Abstract

Objective. To examine the expression, regulation, and potential roles of bone morphogenetic proteins (BMPs) in arthritic synovium.Methods. Expression of BMPs in arthritic synovium from patients with rheumatoid arthritis (RA) or spondylarthropathy (SpA) and in noninflamed synovium from patients undergoing diagnostic or therapeutic arthroscopies was studied by reverse transcriptionpolymerase chain reaction (RT-PCR), Western blot, immunohistochemistry, and 2-color immunofluorescence. In vitro regulation of gene expression in fibroblast-like synoviocytes (FLS) was determined by real-time quantitative RT-PCR and immunohistochemistry. We used 3 H-thymidine incorporation after serum deprivation-induced growth arrest to examine effects on FLS proliferation. FLS apoptosis was evaluated by flow cytometry cell cycle analysis. Apoptotic cells in synovial tissue were detected by TUNEL staining.Results. Transcripts of different BMPs, most strikingly BMP-2 and BMP-6, were detected in synovial tissues. By Western blot, BMP-2 and BMP-6 precursor protein was found in RA and SpA synovial tissue extracts, but not in extracts of noninflamed synovial tissue. By immunohistochemistry, BMP-2 and BMP-6 were detected in the hyperplastic lining and the sublining layer of synovium from RA and SpA patients, both in CD90؉ cells (FLS) and in some CD68؉ cells (macrophages). Proinflammatory cytokines, such as interleukin-1␤ and tumor necrosis factor ␣, but not interferon-␥, enhanced the expression of BMP-2 and BMP-6 transcripts in FLS in vitro. Neither BMP-2 nor BMP-6 affected FLS proliferation. BMP-2 promoted FLS apoptosis, whereas BMP-6 protected against nitric oxide-induced FLS apoptosis. BMP-2-positive apoptotic cells were found in arthritic synovium.Conclusion. BMP-2 and BMP-6 are expressed in arthritic synovium and are strongly up-regulated by proinflammatory cytokines. Although BMP signaling has been proposed to be involved in cartilage and bone repair in arthritis, this pathway may be equally important in modulating FLS cell populations in inflamed synovium.

Expression and Synthesis of Bone Morphogenetic Proteins by Osteoclasts: A Possible Path to Anabolic Bone Remodeling

“…Our finding of higher molecular forms of BMPs in osteoclasts might reflect the presence of proteolytically uncleaved precursor forms of BMPs or bands generated from posttranslational modifications such as glycosylation (partial or complete), as seen in other studies reporting BMP protein expression Kochanowska et al 2002;Wordinger et al 2002;Lories et al 2003;Schwalbe et al 2003). Another reason might be insufficient reduction by dithiotheritol of BMP multimers, at a concentration of 1 mM, which is routinely used in denaturing SDS gels.…”

Linkage and Association Studies of Joint Morbidity from Rheumatoid Arthritis

“…Cheng, et al 24 demonstrated a specific role for osteoblasts during mesenchymal stem cell differentiation. Further, work by Lories, et al 25 supported the hypothesis that BMP6 could be a potent regulator of bone and cartilage repair in arthritis. Based on these results, we postulate that BMP6 may be responsible for helping to regulate joint motion and alignment during the progression of RA.…”

Biophysical Comparison of BMP-2, ProBMP-2, and the Free Pro-peptide Reveals Stabilization of the Pro-peptide by the Mature Growth Factor

“…Sequential cleavage at two distinct sites within the pro-domain by furin or furin-like proteases is required for the activation of the BMP-4 precursor (20,21). Furthermore, proBMP-2 and proBMP-6 have been detected in arthritic synovial tissue (22). Whereas these results suggest a function of the pro-peptides in modulation of BMP activities, no specific function of the pro-peptide of BMP-2 could be assigned as yet.…”