Recurrent DNA damage is associated with persistent injury in progressive radiation-induced pulmonary fibrosis

Abstract

Purpose: Radiation-induced lung injuries (RILI), namely radiation pneumonitis and/or fibrosis, are dose-limiting outcomes following treatment for thoracic cancers. As part of a search for mitigation targets, we sought to determine if persistent DNA damage is a characteristic of this progressive injury.

Methods: C57BL/6J female mice were sacrificed at 24 h, 1, 4, 12, 16, 24 and 32 weeks following a single dose of 12.5 Gy thorax only gamma radiation; their lungs were compared to age-matched unirradiated animals. Tissues were examined for DNA double-strand breaks (DSBs) (γ-H2A.X and p53bp1), cellular senescence (senescence-associated beta-galactosidase and p21) and oxidative stress (malondialdehyde).

Results: Data revealed consistently higher numbers of DSBs compared to age-matched controls, with increases in γ-H2A.X positivity beyond 24 h post-exposure, particularly during the pathological phases, suggesting periods of recurrent DNA damage. Additional intermittent increases in both cellular senescence and oxidative stress also appeared to coincide with pneumonitis and fibrosis.

Conclusions: These novel, long-term data indicate (a) increased and persistent levels of DSBs, oxidative stress and cellular senescence may serve as bioindicators of RILI, and (b) prevention of genotoxicity, via mitigation of free radical production, continues to be a potential strategy for the prevention of pulmonary radiation injury.

Keywords:

• DNA damage
• DNA damage response (DDR)
• pulmonary fibrosis

Acknowledgments

We gratefully acknowledge Eric Hernady for his work preparing histological sections, and Dr. John Ashton, Michelle Zanche and other staff members of the Genomics Research Center at the University of Rochester Medical Center for their assistance in the RNA sequencing experiment.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research was supported by the National Institute of Allergy and Infectious Diseases [grant number: R01 AI101732-01, U19AI091036]; National Institute of Environmental Health Sciences [grant number: P30 ES-01247]; National Institutes of Health Ruth L. Kirschstein National Research Service Award (NRSA) Institutional Research Training Grant [grant number: ES T32 07026] and National Institutes of Health Multidisciplinary Training in Pulmonary Research [grant number: T32HL066988].

Notes on contributors

Tyler A. Beach

Tyler A. Beach, Jacqueline P. Williams and Jacob N. Finkelstein are members of the University of Rochester School of Medicine and Dentistry, Department of Environmental Medicine.

Angela M. Groves

Angela M. Groves and Carl J. Johnston are members of the Department of Pediatrics and Neonatology at the University of Rochester School of Medicine and Dentistry.