Irradiation inhibits the maturation and mineralization of osteoblasts via the activation of Nrf2/HO-1 pathway.
Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) regulates the induction of antioxidant gene expression and protects cells against oxidative injury. However, there are controversial findings regarding the roles of Nrf2 on bone metabolism under oxidative stress. The role of Nrf2 on the differentiation of radiation-exposed osteoblasts is also unclear. We investigated whether Nrf2 negatively or positively affects osteoblast differentiation in response to irradiation. Irradiation inhibited osteoblast differentiation of MC3T3-E1 cells in a dose-dependent manner. This inhibition was evidenced by the irradiation-mediated decreases in bone-like nodule formation, alkaline phosphatase (ALP) activity, calcium accumulation, and expression of osteoblast markers, such as ALP, osteocalcin, osteopontin, bone sialoprotein, osterix, and Runx2. These reductions were accompanied by increased induction of Nrf2 and heme oxygenase-1 (HO-1), accumulation of cellular oxidants, and depletion of antioxidant defense enzymes. siRNA-mediated silencing of Nrf2 markedly reversed the negative effect of irradiation on osteoblast differentiation of the cells, leading to a decrease in HO-1 and an increase in Runx2 levels. Irradiation-mediated decreases in the levels of Runx2 and osteocalcin mRNA, but not of Nrf2 protein, were also significantly inhibited by HO-1 inhibitor, zinc protoporphyrin IX. Furthermore, N-acetyl cysteine restored all of the changes induced by irradiation to near-normal levels in the cells. These results demonstrate that irradiation inhibits osteoblast differentiation and mineralization of MC3T3-E1 cells through the oxidative stress-mediated activation of Nrf2/HO-1 pathway.
Institute of Oral Biosciences and School of Dentistry, Chonbuk National University, Jeonju, 561-756, South Korea.|Research Center of Bioactive Materials and Institute of Molecular Biology and Genetics, Chonbuk National University, Jeonju, 561-756, South Korea.
Sung-Ho
SH
Kook
Institute of Oral Biosciences and School of Dentistry, Chonbuk National University, Jeonju, 561-756, South Korea.|Department of Oral and Maxillofacial Radiology and Research Institute of Clinical Medicine, Chonbuk National University, Jeonju, 561-756, South Korea.
Kyoung-A
KA
Kim
Institute of Oral Biosciences and School of Dentistry, Chonbuk National University, Jeonju, 561-756, South Korea.
Hyeok
H
Ji
Institute of Oral Biosciences and School of Dentistry, Chonbuk National University, Jeonju, 561-756, South Korea.
Daewoo
D
Lee
Institute of Oral Biosciences and School of Dentistry, Chonbuk National University, Jeonju, 561-756, South Korea. leejc88@jbnu.ac.kr.|Research Center of Bioactive Materials and Institute of Molecular Biology and Genetics, Chonbuk National University, Jeonju, 561-756, South Korea. leejc88@jbnu.ac.kr.|Department of Orthodontics and Institute of Oral Biosciences, Research Center of Bioactive Materials, Chonbuk National University, Jeonju, 561-756, South Korea. leejc88@jbnu.ac.kr.
Jeong-Chae
JC
Lee
D016475:3T3 Cells; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D015415:Biomarkers / Q000378:metabolism; D002113:Calcification, Physiologic / Q000187:drug effects / Q000528:radiation effects*; D002118:Calcium / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D004790:Enzyme Induction; D004791:Enzyme Inhibitors / Q000494:pharmacology; D051547:Heme Oxygenase-1 / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics; D051379:Mice; D051267:NF-E2-Related Factor 2 / Q000235:genetics / Q000378:metabolism*; D010006:Osteoblasts / Q000187:drug effects / Q000201:enzymology / Q000473:pathology / Q000528:radiation effects*; D010012:Osteogenesis / Q000187:drug effects / Q000528:radiation effects*; D018384:Oxidative Stress / Q000528:radiation effects; D034622:RNA Interference; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000528:radiation effects; D014162:Transfection
D000975:Antioxidants; D015415:Biomarkers; D004791:Enzyme Inhibitors; D008565:Membrane Proteins; D051267:NF-E2-Related Factor 2; C495636:Nfe2l2 protein, mouse; D017382:Reactive Oxygen Species; D051547:Heme Oxygenase-1; C496542:Hmox1 protein, mouse; D002118:Calcium
HO-1; Irradiation; Nrf2; Osteoblast differentiation; Runx2