Subchronic exposure of hsp70.1-deficient mice to radiofrequency radiation

Abstract

PURPOSE: Heat shock protein 70 (HSP70) is one of the most inducible proteins to play a cytoprotective role under stressful conditions. Previously we generated hsp70.1-deficient mice to elucidate the in vivo function of HSP70 in detail. The renal tissues and embryonic fibroblasts of these mice were shown to be more vulnerable to hyperosmotic stress. Since RF (radiofrequency) energy has been suggested to be an environmental stressor, we carried out a study to determine whether sub-chronic RF exposure can cause constitutive induction of a stress response at a cellular and/or molecular level in hsp70.1-deficient mice due to repeated stimulation. MATERIALS AND METHODS: Eight-week-old hsp70.1-deficient mice were exposed twice daily for 45 min, with a 15 min interval, 5 days a week for 10 weeks. Whole-body average specific absorption rate was 0.4 W/Kg for fields of both 849 MHz and 1763 MHz. Major tissues were histopathologically analysed, and immunocytochemically evaluated for cell proliferative activity. Apoptosis was investigated by TdT-mediated dUTP nick-end labeling (TUNEL) assay. To determine whether RF radiation elicits a stress response, the expression level of heat shock proteins (HSP) and phosphorylation of the stress-activated kinases were also observed by western blots. RESULTS: No difference was observed in the histopathological analysis between sham- and RF-exposed mice. There was no evidence of increased proliferative and apoptotic activities. The levels of HSP90, HSP70, and HSP25 showed no obvious changes. RF exposure did not affect the phosphorylation status of the major stress-activated kinase (MAPK); extracellular signal-regulated kinase 1/2 (ERK1/2), C-Jun N-terminal kinase 1/2 (JNK1/2) or p38 MAPK. CONCLUSION: The hsp70.1-deficient mice did not show any significant changes in terms of cell proliferation, apoptosis, or stress response due to exposure of 849 or 1,763 MHz RF fields.