Regulation of Osteoblast Differentiation and Iron Content in MC3T3-E1 Cells by Static Magnetic Field with Different Intensities

Many studies have indicated that static magnetic fields (SMFs) have positive effects on bone tissue, including bone formation and bone healing process. Evaluating the effects of SMFs on bone cell (especially osteoblast) function and exploring the mechanism, which is critical for understanding the possible risks or benefits from SMFs to the balance of bone remodeling. Iron and magnetic fields have the natural relationship, and iron is an essential element for normal bone metabolism. Iron overload or deficiency can cause severe bone disorders including osteoporosis. However, there are few reports regarding the role of iron in the regulation of bone formation under SMFs. In this study, hypomagnetic field (HyMF) of 500 nT, moderate SMF (MMF) of 0.2 T, and high SMF (HiMF) of 16 T were used to investigate how osteoblast (MC3T3-E1) responses to SMFs and iron metabolism of osteoblast under SMFs. The results showed that SMFs did not pose severe toxic effects on osteoblast growth. During cell proliferation, iron content of osteoblast MC3T3-E1 cells was decreased in HyMF, but was increased in MMF and HiMF after exposure for 48 h. Compared to untreated control (i.e., geomagnetic field, GMF), HyMF and MMF exerted deleterious effects on osteoblast differentiation by simultaneously retarding alkaline phosphatase (ALP) activity, mineralization and calcium deposition. However, when exposed to HiMF of 16 T, the differentiation potential showed the opposite tendency with enhanced mineralization. Iron level was increased in HyMF, constant in MMF and decreased in HiMF during cell differentiation. In addition, the mRNA expression of transferrin receptor 1 (TFR1) was promoted by HyMF but was inhibited by HiMF. At the same time, HiMF of 16 T and MMF of 0.2 T increased the expression of ferroportin 1 (FPN1). In conclusion, these results indicated that osteoblast differentiation can be regulated by altering the strength of the SMF, and iron is possibly involved in this process.