title: Expression of angiopoietin-1 in osteoblasts and its inhibition by tumor necrosis factor-alpha and interferon-gamma.
abstract: Angiogenesis is a crucial component of bone remodeling under both normal and pathophysiological conditions. Among the various mediators that regulate the angiogenic process is the angiopoietin (Ang) family of growth factors. Ang-1 stabilizes new blood vessels by recruiting surrounding mesenchymal cells and promoting their differentiation into vascular smooth muscle cells, whereas Ang-2 is a natural antagonist of Ang-1 and can inhibit angiogenesis. The expression of Ang-1 and Ang-2 in human osteoblasts (hOBs) isolated from rheumatoid arthritis (RA) and osteoarthritis (OA) patients and from healthy individuals has been examined. After incubation in the presence or absence of tumor necrosis factor-alpha (TNF-alpha) and/or interferon-gamma (IFN-gamma), the culture supernatants were assayed for Ang using an enzyme-linked immunosorbent assay. In addition, expression of Ang protein and mRNA was examined using immunohistochemical techniques and quantitative real-time polymerase chain reaction, respectively. It was found that hOBs expressed Ang-1 but not Ang-2 protein, and cultured hOBs from RA and OA patients and from healthy individuals all spontaneously secreted significant amounts of Ang-1 in the absence of any stimulation. Although stimulation with TNF-alpha or IFN-gamma had little or no effect on Ang-1 secretion, costimulation with IFN-gamma plus TNF-alpha dose- and time-dependently diminished secretion of Ang-1 from hOBs. This inhibitory effect was mediated in part by nuclear factor-kappa B via upregulated expression of inducible nitric oxide synthase and enhanced synthesis of nitric oxide. Taken together, these findings suggest that OBs are an important cellular source of Ang-1 and may modulate bone remodeling through regulation of angiogenesis.
authors.affiliation: Division of Rheumatology and Clinical Immunology, First Department of Internal Medicine, Showa University School of Medicine, Tokyo, Japan. tkasama@med.showa-u.ac.jp
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Kasama
authors.forename: Takeo
authors.initials: T
authors.lastname: Isozaki
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Odai
authors.forename: Mizuho
authors.initials: M
authors.lastname: Matsunawa
authors.forename: Kuninobu
authors.initials: K
authors.lastname: Wakabayashi
authors.forename: Hiroko T
authors.initials: HT
authors.lastname: Takeuchi
authors.forename: Satoshi
authors.initials: S
authors.lastname: Matsukura
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Adachi
authors.forename: Masakazu
authors.initials: M
authors.lastname: Tezuka
authors.forename: Kazuo
authors.initials: K
authors.lastname: Kobayashi
mesh_terms: D042683:Angiopoietin-1 / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D001172:Arthritis, Rheumatoid / Q000378:metabolism*; D002478:Cells, Cultured; D016207:Cytokines / Q000378:metabolism; D015536:Down-Regulation; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology*; D016328:NF-kappa B / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism; D010003:Osteoarthritis / Q000378:metabolism*; D010006:Osteoblasts / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D042683:Angiopoietin-1; D016207:Cytokines; D016328:NF-kappa B; D014409:Tumor Necrosis Factor-alpha; D009569:Nitric Oxide; D007371:Interferon-gamma