Wang, Yi, Wang, Haiyan, Ye, Qingsong, Ye, Jie, Xu, Chunyan, Lin, Leilei, Deng, Hui, and Hu, Rongdang (2013) Co-regulation of LPS and tensile strain downregulating osteogenicity via c-fos expression. Life Sciences, 93 (1). pp. 38-43.

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Abstract

Aims: Orthodontic forces are known to aggravate inflammation-induced destruction of the periodontium, but the underlying mechanism has not been elucidated. The present study investigates how inflammation and forces co-regulate periodontium damage.

Main methods: Cultures of MC3T3-E1 osteoblasts were pre-treated with conditioned medium from RAW264.7 macrophages exposed to 100 ng/ml Porphyromonas gingivalis (Pg)-LPS. Conditioned medium was analyzed by ELISA for interleukin-1 beta (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α). Osteoblasts were then subjected to tensile strain (0.5 Hz; 1000 μ or 3000 μ) for 0 min, 5 min, 15 min, 30 min, 1 h, 3 h, and 6 h. The cultures were analyzed for mRNA and protein levels of c-fos. Cells were also analyzed for alkaline phosphatase (ALP) activity.

Key findings: (Pg)-LPS stimulated the secretion of all three cytokines from RAW264.7 cells in a dose- and time-dependent manner. Medium from (Pg)-LPS stimulated cells induced a 10-fold increase in c-fos expression, which decreased to a 4-fold plateau after 3 h. In contrast, ALP activity of control osteoblasts decreased during the first 60 min, then recovered over the next 4 h. Pretreatment with conditioned medium generated the same initial decrease during tensile strain but prevented the recovery.

Significance: Our study showed, for the first time, that the inhibitory effect of inflammation and tensile strain on osteogenicity is associated with the upregulation in c-fos expression. In addition, inflammation may reduce the ability of osteoblasts to restore their osteogenic capacity during sustained tensile stress and contribute to periodontium damage.

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