Inhibitor of DNA binding/differentiation 2 induced by hypoxia promotes synovial fibroblast–dependent osteoclastogenesis

Abstract

Objective. To map hypoxic areas in arthritic synovium and to establish the relevance of low oxygen levels to the phenotype of synovial fibroblasts, with special focus on bone degradation.Methods. To analyze the distribution of hypoxia in arthritic joints, the hypoxia marker EF5 was administered to mice with collagen-induced arthritis (CIA). To evaluate the effect of hypoxia on rheumatoid arthritis synovial fibroblasts (RASFs), reverse suppression subtractive hybridization and complementary DNA array were used. Real-time polymerase chain reaction, Western blotting, and immunohistochemistry were used to evaluate the expression of inhibitor of DNA binding/ differentiation 2 (ID-2). To investigate the function of ID-2 in RASFs, cells were transfected either with ID-2 vector or with ID-2-specific small interfering RNA.Results. EF5 staining showed the presence of hypoxia in arthritic joints, particularly at sites of synovial invasion into bone. Differential expression analysis revealed that ID-2 was strongly induced by hypoxia in RASFs. Immunohistochemical analysis of CIA mouse synovium and human RA synovium showed a strong expression of ID-2 by RASFs at sites of synovial invasion into bone. Overexpression of ID-2 in RASFs significantly induced the expression of several factors promoting osteoclastogenesis. The biologic relevance of the potent osteoclastogenesis-promoting effects was shown by coculture assays of ID-2-overexpressing RASFs with bone marrow cells, leading to an increased differentiation of osteoclasts from bone marrow precursors.Conclusion. The data show that hypoxic conditions are present at sites of inflammation and synovial invasion into bone in arthritic synovium. Hypoxiainduced ID-2 may contribute to joint destruction in RA patients by promoting synovial fibroblast-dependent osteoclastogenesis.

Dual Functions of Histone-Lysine N-Methyltransferase Setdb1 Protein at Promyelocytic Leukemia-Nuclear Body (PML-NB)

“…Id2, inhibitor of DNA binding 2 (42), a transcriptional regulator containing a helix-loop-helix (HLH) domain but not a basic domain, inhibits the functions of basic HLH transcription factors in a dominant-negative manner by suppressing their heterodimerizing partners through the HLH domain. We next examined Id2 downstream genes such as M-CSF and collagen 1a1 genes in Set-R cells, which were previously shown to be positively regulated by Id2 (43,44), and clearly found their expressions markedly augmented in Set-R cells (Fig. 4B).…”

Negative regulation of osteoclastogenesis and bone resorption by cytokines and transcriptional repressors

“…Thus, the role of Ids seems to be more complex in vivo . Hypoxia-induced Id2 expression is found in rheumatoid arthritis synovial fibroblasts, and promotes synovial fibroblast-dependent osteoclastogenesis [61]. Another study showed that overexpression of Id1 in prostate cancer cells has an important role in promoting prostate cancer-mediated osteoclast differentiation, probably via certain secreted factors [62].…”

Osteogenic differentiation of human ligament fibroblasts induced by conditioned medium of osteoclast-like cells

“…The current study has shown that conditioned medium of osteoclastlike cells can influence the adhesion molecule pathway of fibroblasts. Hypoxia-induced ID-2 may contribute to joint destruction in RA patients by promoting synovial fibroblast-dependent osteoclastogenesis (10). Moreover, oestrogen can inhibit osteoclast formation induced by periodontal ligament fibroblasts (11).…”