Bone morphogenetic proteins 2 and 6, expressed in arthritic synovium, are regulated by proinflammatory cytokines and differentially modulate fibroblast-like synoviocyte apoptosis.
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 transcription-polymerase 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-1beta and tumor necrosis factor alpha, but not interferon-gamma, 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.


CONCLUSIONS
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.
Lories
Rik J U
RJ
Katholieke Universiteit Leuven, Leuven, Belgium.
Derese
Inge
I
Ceuppens
Jan L
JL
Luyten
Frank P
FP
D000328:Adult; D000368:Aged; D000970:Antineoplastic Agents / Q000276:immunology / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000276:immunology*; D001172:Arthritis, Rheumatoid / Q000276:immunology / Q000473:pathology / Q000503:physiopathology*; D055396:Bone Morphogenetic Protein 2; D055418:Bone Morphogenetic Protein 6; D019485:Bone Morphogenetic Proteins / Q000235:genetics* / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects / Q000276:immunology; D002478:Cells, Cultured; D005260:Female; D005347:Fibroblasts / Q000473:pathology; D015870:Gene Expression / Q000276:immunology; D006801:Humans; D007371:Interferon-gamma / Q000276:immunology / Q000494:pharmacology; D007375:Interleukin-1 / Q000276:immunology* / Q000494:pharmacology; D008297:Male; D008875:Middle Aged; D009569:Nitric Oxide / Q000378:metabolism; D015398:Signal Transduction / Q000276:immunology; D013583:Synovial Membrane / Q000276:immunology / Q000473:pathology / Q000503:physiopathology*; D016212:Transforming Growth Factor beta; D014409:Tumor Necrosis Factor-alpha / Q000276:immunology / Q000494:pharmacology; D015854:Up-Regulation / Q000276:immunology
D000970:Antineoplastic Agents; C525718:BMP2 protein, human; C525816:BMP6 protein, human; D055396:Bone Morphogenetic Protein 2; D055418:Bone Morphogenetic Protein 6; D019485:Bone Morphogenetic Proteins; D007375:Interleukin-1; D016212:Transforming Growth Factor beta; D014409:Tumor Necrosis Factor-alpha; D009569:Nitric Oxide; D007371:Interferon-gamma