A study published in Nature Communications challenges the long-held belief that mitochondrial-derived hydrogen peroxide (H₂O₂) directly damages chromosomal DNA. The research, led by Daan M. K. van Soest and colleagues, investigates the effects of H₂O₂ released by mitochondria or produced at nucleosomes using a chemogenetic approach. The findings reveal that mitochondrial H₂O₂ release does not cause DNA damage or mutations, even at levels much higher than normally produced. In contrast, H₂O₂ generated near nuclear DNA leads to DNA damage, mutations, and activation of the DNA damage response (DDR), resulting in cell cycle arrest and senescence. The study concludes that mitochondrial H₂O₂ is unlikely to directly damage nuclear DNA, limiting its contribution to oncogenic transformation and aging. The study highlights that while reactive oxygen species (ROS), including H₂O₂, are produced by mitochondria, they do not directly damage nuclear DNA under physiological conditions. This is because H₂O₂ is rapidly scavenged by peroxidases, preventing it from diffusing into the nucleus. Additionally, the study shows that even when H₂O₂ is produced at high levels, it does not lead to DNA damage unless it is generated in close proximity to DNA. The research also demonstrates that mitochondrial H₂O₂ release does not activate the DDR or cause DNA mutations, even at supraphysiological levels. These findings challenge the assumption that mitochondrial ROS are a major contributor to DNA damage and mutations, and suggest that the DNA damage response is more likely triggered by exogenous ROS or other sources of oxidative stress. The study underscores the importance of understanding the role of mitochondrial ROS in cellular processes and highlights the need for further research to clarify the mechanisms by which mitochondrial ROS contribute to DNA damage and disease.A study published in Nature Communications challenges the long-held belief that mitochondrial-derived hydrogen peroxide (H₂O₂) directly damages chromosomal DNA. The research, led by Daan M. K. van Soest and colleagues, investigates the effects of H₂O₂ released by mitochondria or produced at nucleosomes using a chemogenetic approach. The findings reveal that mitochondrial H₂O₂ release does not cause DNA damage or mutations, even at levels much higher than normally produced. In contrast, H₂O₂ generated near nuclear DNA leads to DNA damage, mutations, and activation of the DNA damage response (DDR), resulting in cell cycle arrest and senescence. The study concludes that mitochondrial H₂O₂ is unlikely to directly damage nuclear DNA, limiting its contribution to oncogenic transformation and aging. The study highlights that while reactive oxygen species (ROS), including H₂O₂, are produced by mitochondria, they do not directly damage nuclear DNA under physiological conditions. This is because H₂O₂ is rapidly scavenged by peroxidases, preventing it from diffusing into the nucleus. Additionally, the study shows that even when H₂O₂ is produced at high levels, it does not lead to DNA damage unless it is generated in close proximity to DNA. The research also demonstrates that mitochondrial H₂O₂ release does not activate the DDR or cause DNA mutations, even at supraphysiological levels. These findings challenge the assumption that mitochondrial ROS are a major contributor to DNA damage and mutations, and suggest that the DNA damage response is more likely triggered by exogenous ROS or other sources of oxidative stress. The study underscores the importance of understanding the role of mitochondrial ROS in cellular processes and highlights the need for further research to clarify the mechanisms by which mitochondrial ROS contribute to DNA damage and disease.