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  • Title: Dkk-1-mediated inhibition of Wnt signaling in bone ameliorates osteoarthritis in mice.
    Author: Funck-Brentano T, Bouaziz W, Marty C, Geoffroy V, Hay E, Cohen-Solal M.
    Journal: Arthritis Rheumatol; 2014 Nov; 66(11):3028-39. PubMed ID: 25080367.
    Abstract:
    OBJECTIVE: Wnt signaling is a master regulator of joint homeostasis, but its role in osteoarthritis (OA) remains unclear. This study was undertaken to characterize the activation of Wnt/β-catenin in knee joints of mice with OA and to assess how inhibiting this pathway in bone could affect cartilage. METHODS: OA was induced by partial meniscectomy in Topgal mice and in transgenic mice overexpressing Dkk-1 under the control of the 2.3-kb Col1a1 promoter (Col1a1-Dkk-1-Tg mice). Wnt/β-catenin activation was assessed by X-Gal staining at baseline and at weeks 4, 6, and 9. Cartilage and bone damage was analyzed in Col1a1-Dkk-1-Tg mice with OA at week 6. Primary chondrocytes and cartilage explants were used to assess the effect of Dkk-1 on cartilage catabolism. RESULTS: In meniscectomized Topgal mice, Wnt was mainly activated in osteocytes from the subchondral bone at week 6 after OA induction, as well as in osteophytes and synovium at week 4. Chondrocytes from damaged zones expressed X-Gal from week 4. Dkk-1 expression was high in chondrocytes in control mouse knees (mean ± SEM 84.2 ± 3.1%) but decreased greatly in knees of meniscectomized mice from week 4 (mean ± SEM 14.4 ± 3.8%). The OA score was lower in meniscectomized Col1a1-Dkk-1-Tg mice at week 6 compared with wild-type mice (5.1 ± 0.6 versus 8.4 ± 0.6; P = 0.002). Subchondral bone fraction and osteophyte volume were decreased. However, cartilage explants from Col1a1-Dkk-1-Tg mice showed proteoglycan loss and increased NITEGE expression. Expression of vascular endothelial growth factor (VEGF) was reduced in osteoblasts from Col1a1-Dkk-1-Tg mice, thereby decreasing expression of messenger RNA for matrix metalloproteinases in chondrocytes. CONCLUSION: Wnt activation in OA affects the whole joint, particularly bone. Selective inhibition of this pathway in bone by Dkk-1 decreased OA severity through VEGF inhibition.
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