Abstract
Objective: To examine whether exposure of mouse bone marrow stromal cells (BMSC) to 900 MHz radiofrequency fields used in mobile communication devices can induce mitochondrial unfolded protein response (UPRmt).Methods: BMSCs were exposed to continuous wave 900 MHz radiofrequency fields (RF) at 120 μW/cm2 power intensity for 4 h/d for 5 consecutive days. Cells in sham group (SH) were cultured in RF exposure system, but without RF radiation. The positive control cells were irradiated with 6 Gy X-ray at a dose rate of 1.103 Gy/min (XR). To inhibit the upstream molecular JNK2 of UPRmt, cells in siRNA + RF, and siRNA + XR group were also pretreated with 100 nM siRNA-JNK2 for 48 h before RF/XR exposure. Thirty minutes, 4 h, and 24 h post-RF/XR exposure, cells were collected, the level of ROS was measured with flow cytometry, the expression levels of UPRmt-related proteins were detected using western blot analysis.Results: Compared with Sham group, the level of ROS in RF and XR group was significantly increased 30 min and 4 h post-RF/XR exposure (P < 0.05), however, the RF/XR-induced increase of ROS level reversed 24 h post-RF/XR exposure. Compared with Sham group, the expression levels of HSP10/HSP60/ClpP proteins in cells of RF and XR group increased significantly 30 min and 4 h post-RF/XR exposure (P < 0.05), however, the RF/XR-induced increase of HSP10/HSP60/ClpP protein levels reversed 24 h post-RF exposure. After interfering with siRNA-JNK2, the RF/XR exposures could not induce the increase of HSP10/HSP60/ClpP protein levels any more.Conclusions: The exposure of 900 MHz RF at 120 μW/cm2 power flux density could increase ROS level and activate a transient UPRmt in BMSC cells. Mitochondrial homeostasis in term of protein folding ability is restored 24 h post-RF exposure. Exposure to RF in our experimental condition did not cause permanent and severe mitochondrial dysfunctions. However, the detailed underlying molecular mechanism of RF-induced UPRmt remains to be further studied.
Highlights
Non-ionizing radiofrequency fields (RF) are ubiquitous in the environment
Compared with the cells exposed to RF, those exposed to X-ray radiation (XR) showed significant increase in reactive oxygen species (ROS) at 30 min, 4 h (P < 0.05)
These results indicated that both RF and X-ray could induce the production of ROS in bone marrow stem cells (BMSCs) for a certain period of time
Summary
Non-ionizing radiofrequency fields (RF) are ubiquitous in the environment. They are used in military, radio, and television broadcasting, wireless communications systems, industry, and medicine. The newly-synthesized mitochondrial proteins include chaperones HSP10 and HSP60 which facilitate the import and correct folding of unfolded proteins, and proteases ClpP and ClpX which help to degrade the unfolded and misfolded proteins. This process is called mitochondrial unfolded protein response (UPRmt) [3,4,5,6,7]
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