BACKGROUND:Preliminary studies of our research group have confirmed that the proliferation of preosteoclasts and the differentiation and function of osteoclasts could be inhibited when they were cultured in lower oxygen tension even hypoxia (2%O 2 ), but the gene expression of osteoclasts cultured in vitro have not been reported.
OBJECTIVE:To examine the effect of oxygen tension on specific gene expression of osteoclasts in vitro and explore the mechanism of osteoclast differentiation influenced by oxygen tension.
METHODS:The preosteoclasts were induced with 10μg/L macrophage colony stimulating facto and 10μg/L soluble receptor activator of nuclear factor-κB ligand into mature osteoclasts. Then the osteoclasts were cultured in normoxia, tissue oxygen and hypoxia (20%, 7%, 2%O 2 ) respectively. cells were then stained for tartarate-resistant acid phosphatase to assess osteoclastic formation. cells were col ected at 1, 2, 3, 4, 5, 6, 7 days after culture respectively. The soluble receptor activator of nuclear factor-κB ligand, tumor necrosis factor receptor-associated factor 6, tartarate-resistant acid phosphatase, and cathepsin K mRNA expression levels were determined using real-time quantitative PCR.
RESULTS AND CONCLUSION:The number of osteoclasts positive for tartarate-resistant acid phosphatase in the hypoxia was significantly lower than that in the tissue oxygen and normoxia (P<0.05). Under different oxygen tension, the mRNA expression levels of soluble receptor activator of nuclear factor-κB ligand in osteoclasts maintained unchanged. The mRNA expression levels of tumor necrosis factor receptor-associated factor 6 reached the peak at 5 days after culture in tissue oxygen and normoxia (P<0.05). The mRNA expression time of tartarate-resistant acid phosphatase and Cathepsin K were delayed accompanied by decreased oxygen tension, but the maximum were maintained in tissue oxygen. Compared with normoxia and hypoxia, osteoclasts cultured in tissue oxygen are more prone to differentiate and maintain the activity and functions.

BACKGROUND:The intracel ular accumulation of reactive oxygen species leads to oxidative stress. Hypoxia is widespread in physiological and pathological condition. Variation of bone proliferation and differentiation when bone tissues cultured or bone cel s induced toxicity by reactive oxygen species under hypoxia have not yet been reported. OBJECTIVE:To observe the biological characteristics of MC3T3-E1 pretreated with different concentrations of hydrogen peroxide (H2O2) in hypoxia, thus understanding the cel mechanism underlying prolonged bone healing in the elderly with osteoporosis and diabetes. METHODS:The MC3T3-E1 cel s pretreated with different concentrations of H2O2 were cultured in different oxygen concentrations. The proliferation of MC3T3-E1 was detected by cel counting kit-8. The cel differentiation was detected through alkaline phosphatase staining and alizarin red staining. Total RNAs were extracted and used for analyzing the mRNA levels of col age type 1, alkaline phosphatase and Cbfa1. RESULTS AND CONCLUSION:When MC3T3-E1 pretreated with 200μmol/L H2O2 for 6 hours, the cel proliferation was increased with time, but lower than that in the control group. The alkaline phosphatase activity was weakened, and the number of mineralized nodes was decreased at the early stage of differentiation. When MC3T3-E1 pretreated with 400μmol/L H2O2 for 6 hours, the cel proliferation was decreased obviously. The alkaline phosphatase activity was stil weakened, and the number of mineralized nodes was decreased further, but not affected by hypoxia. When MC3T3-E1 pretreated with 400μmol/L H2O2 for 6 hours and then cultured in hypoxia, the mRNA expression of Cbfa1 was decreased, but the mRNA expressions of col age type 1 and alkaline phosphatase were significantly increased. These results suggest that MC3T3-E1 pretreated with low concentration of H2O2 show a significant decrease in proliferation, while MC3T3-E1 pretreated with a high concentration of H2O2 and cultured in hypoxia show a decrease in osteogenic differentiation, especial y at the early stage of alkaline phosphatase formation.