Effects of oxygen on the response of mitochondria to X-irradiation and reactive oxygen species-mediated fibroblast activation

Abstract

Purpose

In living organisms, sensitivity to radiation increases in the presence of oxygen (O₂) compared with that under anoxic or hypoxic conditions. Here, we investigated whether O₂ concentration affected the response of mitochondria to X-rays radiation, which is associated with tumor microenvironment formation via fibroblast activation in radiation-related tumors.

Materials and methods

O₂ concentrations were controlled at <5% (internal environmental oxygen condition) or anoxic levels during culture of normal human diploid lung fibroblasts TIG-3 and MRC-5. Protein expression associated with the response of mitochondria to radiation was assessed using immunostaining or western blotting.

Results

Induction of DNA damage (marker: γ-H2A histone family member X) and mitochondrial signaling (AMP-activated protein kinase), suppression of mitochondrial metabolic activity, and generation of reactive oxygen species occurred with radiation in cells cultured under 5% and 20% O₂ conditions. However, reducing O₂ concentration mitigated the effects of radiation on cell growth, mitochondrial damage (parkin), induction of antioxidant responses (nuclear factor E2-related factor 2), and fibroblast activation (α-smooth muscle actin). Radiation did not affect the markers used in this study in the absence of O₂.

Conclusion

O₂ concentration affected the response of mitochondria to radiation and reactive oxygen species-mediated fibroblast activation. Higher O₂ concentrations enhanced the effects of radiation on mitochondria in human fibroblasts. In vitro studies may overestimate in vivo radiation effects due to high O₂ concentrations.

Keywords:

• Oxygen
• mitochondria
• radiation
• reactive oxygen species (ROS)
• fibroblast activation

Acknowledgments

We thank Drs. Kazuyuki Ishi, Ichiro Takano and Kenji Hattori for their support on this study.

Author contributions

T.S. designed the study, performed most of the experiments and wrote the paper. R.T., H.O. and K.I. helped to analyze the data. M.S., K.K. and A.U. contributed to interpretation of the data and discussion.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data presented in this study are available on request to the corresponding author.

Additional information

Funding

This research was supported by a grant from the JSPS KAKENHI Grant Number 18H03377, Research on Health effects of radiation organized by the Japanese Ministry of the Environment, Industrial Disease Clinical Research Grants from the Japanese Ministry of Health, Labor, and Welfare and in part by NIFS Collaborative Research Program [NIFS13KOBA028]. This work was performed at the Joint Usage/Research Center (Radiation Biology Center), Kyoto University, and the Program of the network-type joint Usage/Research Center for Radiation Disaster Medical Science of Hiroshima University, Nagasaki University, and Fukushima Medical University.

Notes on contributors

Tsutomu Shimura

Tsutomu Shimura, PhD, radiation research scienrist, Chief Senior Researcher, Department of Environmental Health, National Institute of Public Health, Saitama, Japan.

Rina Totani

Rina Totani, Faculty of Pharmaceutical Sciences Student, Meiji Pharmaceutical University, Tokyo, Japan,

Hyougo Ogasawara

Hyougo Ogasawara, Faculty of Pharmaceutical Sciences Student, Meiji Pharmaceutical University, Tokyo, Japan.

Keiki Inomata

Keiki Inomata, Faculty of Pharmaceutical Sciences Student, Meiji Pharmaceutical University, Tokyo, Japan.

Megumi Sasatani

Megumi Sasatani, PhD, radiation research scienrist, associate professor, Department of Experimental Oncology; Research Center for Radiation Genome Medicine; Research Institute for Radiation Biology and Medicine (RIRBM); Hiroshima University. Hiroshima, Japan.

Kenji Kamiya

Kenji Kamiya, MD. PhD. radiation research scienrist professor, Department of Experimental Oncology; Research Center for Radiation Genome Medicine; Research Institute for Radiation Biology and Medicine (RIRBM); Hiroshima University. Hiroshima, Japan.

Akira Ushiyama

Akira Ushiyama, PhD. Director Department of Environmental Health, National Institute of Public Health, Saitama, Japan.