کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
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2780467 | 1153299 | 2011 | 8 صفحه PDF | دانلود رایگان |
The aims of the present study were to determine whether prostaglandins (PGs) and PPARγ are involved in the stimulation of tissue-non-specific alkaline phosphatase (TNAP) activity and mineralization by TNF-α in human osteoblasts. We used osteoblasts differentiated from MSCs from three different donors and MG-63 osteoblast-like cells. Inhibition of prostaglandin synthesis with the cyclooxygenase (COX) inhibitor indomethacin or the specific COX-2 blocker NS-398 abolished mineralization in the absence and presence of 1 ng/ml of TNF-α, suggesting that PGs were involved. The TNAP inhibitor levamisole abolished TNF-α effects on mineralization, suggesting that PGs were involved in TNAP expression and mineralization. TNF-α stimulated expression of COX-2 and PG E synthase before that of TNAP, but expression of PG D synthase later suggesting that PGE2 and PGF2α but not 15d-PGJ2 were involved in TNF-α effects. However, both PGE2 and PGF2α dose-dependently inhibited mineralization indicating that endogenous PG are required for mineralization but that TNF-α does not increase mineralization by increasing PG synthesis. Interestingly, TNF-α inhibited PPARγ expression and binding activity to PPRE consensus sequences independently of 15d-PGJ2. Inhibition of PPARγ activity with GW-9662 mimicked TNF-α effects in MG-63 cells, indicating that TNF-α stimulates mineralization by inhibiting PPARγ in osteoblasts. In MSC-derived osteoblast cultures, inhibition of PPARγ dropped TNAP expression and mineralization. Treatment of MG-63 cells with conditioned media from MSC-derived osteoblasts or MSC-derived adipocytes treated or not with GW-9662 revealed that TNF-α inhibition of PPARγ in undifferentiated MSCs and/or adipocytes was responsible for the decreased expression of TNAP in osteoblasts. In conclusion, TNF-α increases TNAP expression and stimulates mineralization by inhibiting PPARγ in osteoblasts, but PPARγ in adipocytes or undifferentiated MSCs controls the secretion of a factor leading to TNAP stimulation in osteoblasts.
Journal: Bone - Volume 48, Issue 2, 1 February 2011, Pages 242–249