The role of nuclear factor-E2-related factor 1 in oxidative stress response in osteoblast cells

Abstract

[한글]

[영문]Oxidative stress and antioxidants have been shown to regulate cellular function and metabolism. A normal balance between oxidants and antioxidants is needed for the maintenance of equilibrium between osteoblast-osteoclast. Excessive oxidants induce many defense mechanisms such as antioxidant enzymes. The antioxidant response element (ARE) is found in the promoters of antioxidant genes and has been reported to bind diverse transcriptional factors.Nuclear factor-E2-related factor 1 (Nrf1, NFE2L1), a member of the Cap’n’Collar-basic leucine zipper protein family, is known to bind the ARE and regulate the expression of a number of genes involved in oxidative stress, cellular differentiation and inflammation.The purpose of this study was to examine the effects of Nrf1 on the response to oxidative stress in osteoblastic MC3T3E1 cells. This study also examined the effects of Nrf1 on osteoblastic proliferation and differentiation under unstimulated and oxidative stress conditions.The expression of Nrf1 mRNA was upregulated with lipopolysaccharide (LPS) treatment in MC3T3E1 cells. LPS induced formation of intracellular reactive oxygen species (ROS) in MC3T3E1 cells. Transfection with siRNA against Nrf1 suppressed the expression of antioxidant genes including metallothionein 2 (MT2), glutamate-cysteine ligase catalytic subunit (GCLC), and glutathione peroxidase 1 (GPx1) in LPS-treated MC3T3E1 cells. Knockdown of Nrf1 expression was not sensitized to MC3T3E1 cells proliferation under unstimulated or oxidative stress conditions. In contrast to previous studies, knockdown of Nrf1 expression did not affect osteoblast differentiation in MC3T3E1 cells. However, knockdown of Nrf1 expression showed increased cartilage nodules in embryonal mesenchymal cells.In conclusion, Nrf1 contributes to the expression of several antioxidant genes such as MT2, GCLC, and GPx1 in osteoblasts under oxidative stress. This in vitro study suggests that Nrf1 alone does not have a decisive effect on regulating osteoblast proliferation or differentiation. However, Nrf1 might have a variable effect on cellular differentiation according to the stage of development. Further study is needed to evaluate the comprehensive mechanisms of the Nrf1-antioxidant pathway in various pathologic conditions.