Mitochondrial reactive oxygen species impact human fibroblast responses to protracted γ-ray exposures

Abstract

Purpose: Continuous exposure to ionizing radiation at a low dose rate poses significant health risks to humans on deep space missions, prompting the need for mechanistic studies to identify countermeasures against its deleterious effects. Mitochondria are a major subcellular locus of radiogenic injury, and may trigger secondary cellular responses through the production of reactive oxygen species (mtROS) with broader biological implications. Methods and Materials: To determine the contribution of mtROS to radiation-induced cellular responses, we investigated the impacts of protracted γ-ray exposures (IR; 1.1 Gy delivered at 0.16 mGy/min continuously over 5 days) on mitochondrial function, gene expression, and the protein secretome of human HCA2-hTERT fibroblasts in the presence and absence of a mitochondria-specific antioxidant mitoTEMPO (MT; 5 µM). Results: IR increased fibroblast mitochondrial oxygen consumption (JO₂) and H₂O₂ release rates (JH₂O₂) under energized conditions, which corresponded to higher protein expression of NADPH Oxidase (NOX) 1, NOX4, and nuclear DNA-encoded subunits of respiratory chain Complexes I and III, but depleted mtDNA transcripts encoding subunits of the same complexes. This was associated with activation of gene programs related to DNA repair, oxidative stress, and protein ubiquination, all of which were attenuated by MT treatment along with radiation-induced increases in JO₂ and JH₂O₂. IR also increased secreted levels of interleukin-8 and Type I collagens, while decreasing Type VI collagens and enzymes that coordinate assembly and remodeling of the extracellular matrix. MT treatment attenuated many of these effects while augmenting others, revealing complex effects of mtROS in fibroblast responses to IR. Conclusion: These results implicate mtROS production in fibroblast responses to protracted radiation exposure, and suggest potentially protective effects of mitochondrial-targeted antioxidants against radiogenic tissue injury in vivo.

Keywords:

• Mitochondria
• oxidative stress
• fibroblasts
• space radiation

Disclosure statement

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

Additional information

Funding

This work is supported by the Translational Research Institute for Space Health through NASA Cooperative Agreement NNX16AO69A (AJC, JCW, MMW), NASA grant 80ARC022CA003 (JCW), and National Institutes of Health R01 HL171102 (JCW).

Notes on contributors

Luke A. Whitcomb

Luke A. Whitcomb, MS, is a research associate in the Department of Biomedical Sciences at Colorado State University and an incoming MD-PhD student. His research has explored mitochondrial responses to physiological stressors such as protracted irradiation and hypobaric hypoxia.

Xu Cao

Xu Cao, PhD, is a postdoctoral research associate at the Stanford Cardiovascular Institute at Stanford University School of Medicine in California, USA. His research interests include the use of induced pluripotent stem cells (iPSC)-derived cardiac organoids and engineered heart tissues to study the effects of radiation on the human heart.

Dilip Thomas

Dilip Thomas, PhD, is an instructor at the Stanford Cardiovascular Institute at Stanford University in Palo Alto, California, USA. His research interests include the use of induced pluripotent stem cells (iPSC)-derived cardiac organoids and engineered heart tissues for cardiovascular disease modeling and drug testing.

Claudia Wiese

Claudia Wiese, PhD, is an Associate Professor of Radiation Cancer Biology in the Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, CO, USA. Her laboratory studies the mechanisms of DNA damage repair and how the inactivation of such mechanisms leads to genome instability and disease.

Alissa S. Pessin

Alissa S. Pessin, BS, is a research assistant and nursing student at the University of Utah in Salt Lake City, Utah, USA.

Robert Zhang

Robert Zhang, BS, is a research assistant in the Department of Biomedical Sciences at Colorado State University in Fort Collins, Colorado, USA.

Joseph C. Wu

Joseph C. Wu, MD, PhD, is a Director of the Stanford Cardiovascular Institute and Professor of Medicine and Radiology at Stanford University School of Medicine in California, USA. His lab works on utilizing patient-specific and disease-specific induced pluripotent stem cells (iPSCs) and engineered tissues to study and treat human diseases.

Michael M. Weil

Michael M. Weil, PhD, is a professor in the Department of Environmental and Radiological Health Sciences at Colorado State University in Fort Collins, Colorado, USA. His research is focused on understanding how radiation exposure can lead to cancer and why some individuals may be more susceptible than others.

Adam J. Chicco

Adam J. Chicco, PhD, is a Professor of Biomedical Sciences and Director of the Cardiovascular Research Center and Colorado State University in Fort Collins, Colorado, USA. His research is focused on understanding the roles of mitochondria and lipid metabolism in physiological responses to environmental stress and the pathogenesis of cardiometabolic diseases.