Mitochondrial HO release does not directly cause damage to chromosomal DNA.

Reactive Oxygen Species (ROS) derived from mitochondrial respiration are frequently cited as a major source of chromosomal DNA mutations that contribute to cancer development and aging. However, experimental evidence showing that ROS released by mitochondria can directly damage nuclear DNA is largely lacking. In this study, we investigated the effects of HO released by mitochondria or produced at the nucleosomes using a titratable chemogenetic approach. This enabled us to precisely investigate to what extent DNA damage occurs downstream of near- and supraphysiological amounts of localized HO. Nuclear HO gives rise to DNA damage and mutations and a subsequent p53 dependent cell cycle arrest. Mitochondrial HO release shows none of these effects, even at levels that are orders of magnitude higher than what mitochondria normally produce. We conclude that HO released from mitochondria is unlikely to directly damage nuclear genomic DNA, limiting its contribution to oncogenic transformation and aging.