Abstract
Recently, we identified a specific extremely low-frequency pulsed electromagnetic field (ELF-PEMF) that supports human osteoblast (hOBs) function in an ERK1/2-dependent manner, suggesting reactive oxygen species (ROS) being key regulators in this process. Thus, this study aimed at investigating how ELF-PEMF exposure can modulate hOBs function via ROS. Our results show that single exposure to ELF-PEMF induced ROS production in hOBs, without reducing intracellular glutathione. Repetitive exposure (>3) to ELF-PEMF however reduced ROS-levels, suggesting alterations in the cells antioxidative stress response. The main ROS induced by ELF-PEMF were •O2− and H2O2, therefore expression/activity of antioxidative enzymes related to these ROS were further investigated. ELF-PEMF exposure induced expression of GPX3, SOD2, CAT and GSR on mRNA, protein and enzyme activity level. Scavenging •O2− and H2O2 diminished the ELF-PEMF effect on hOBs function (AP activity and mineralization). Challenging the hOBs with low amounts of H2O2 on the other hand improved hOBs function. In summary, our data show that ELF-PEMF treatment favors differentiation of hOBs by producing non-toxic amounts of ROS, which induces antioxidative defense mechanisms in these cells. Thus, ELF-PEMF treatment might represent an interesting adjunct to conventional therapy supporting bone formation under oxidative stress conditions, e.g. during fracture healing.
Highlights
In 2000 osteoporosis caused approx. 9 million fractures worldwide[1]
Our preceding study showed that repetitive exposure to ELF-PEMF induced mitochondrial activity and improved human osteoblasts (hOBs) function in an ERK1/2-dependent manner, suggesting that reactive oxygen species (ROS) play a crucial role in this process[12]
Similar to JNK and p38, ERK1/2 is reported to be directly affected by oxidative stress stimuli[23,24], often produced as a by-product of the mitochondrial respiratory of the mitochondrial respiratory chain
Summary
In 2000 osteoporosis caused approx. 9 million fractures worldwide[1]. Due to the anticipated demographic changes, this number is expected to be doubled by 20402,3. ERK1/2 activation was crucial for the observed effects of ELF-PEMF on hOBs12 This observation is supported by the work of Yumoto, showing that EMF exposure induces osteogenic differentiation of MC3T3-E1 cells in an ERK1/2 and p38 dependent manner[17]. The level of EMF-induced ROS showed to be dependent on the field strength and frequency and may trigger diverse cellular responses, ranging from activation of signaling cascades (e.g. ERK1/2, JNK1-3 or p38) to oxidative stress induced cell death[11]. As a by-product of the mitochondrial respiratory chain ROS (superoxide anion (O2−), hydrogen peroxide (H2O2), hydroxyl radicals (HO) and peroxinitrite anion (ONOO−)) are produced In low amounts these ROS trigger various cellular processes, e.g. activation of MAPKinases or cell migration. This way reduction of oxidative stress could improve fracture healing and reduce the postoperative complication rate
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