Mitochondrial H₂O₂release does not directly cause genomic DNA damage

Abstract

Reactive Oxygen Species (ROS) derived from mitochondrial respiration are frequently cited as a major source of genomic DNA damage and subsequent mutations that contribute to cancer development and aging. However, experimental evidence showing that ROS released by mitochondrial can directly damage nuclear DNA under (patho)physiological conditions has been largely lacking. In this study we modeled the effects of mitochondrial H2O2 release and compared this to H2O2 production at the nucleosomes in an untransformed human cell line. We used a chemogenetic approach to produce localized H2O2 and combined it with a new method we developed to directly quantify the amount of H2O2 produced. This enabled us to precisely investigate to what extent DNA damage occurs downstream of near- and supraphysiological amounts of localized H2O2 generation. Nuclear H2O2 production gives rise to DNA strand breaks, subsequent activation of the DNA damage response, cell cycle arrest and eventually senescence. Release of H2O2 from mitochondria on the other hand shows none of these effects, even at levels that are orders of magnitude higher than what mitochondria normally produce. Artificially high levels of mitochondrial H2O2 release do result in DNA strand breaks, but in parallel invariably cause ferroptosis-mediated cell death, preventing propagation of DNA damage-induced mutations. This study shows that H2O2 released from mitochondria is unlikely to directly damage genomic DNA, limiting its contribution to oncogenic transformation and aging.