Cell-free chromatin particles released from dying cells inflict mitochondrial damage and ROS production in living cells

Several hundred billion to a trillion cells die in the body every day and release cell free chromatin particles (cfChPs) which enter into the circulation, or are released locally into extracellular compartments of the body. We have reported that cfChPs from the dying cells can readily enter into living cells and damage their DNA. To test the hypothesis that internalised cfChPs might also inflict mitochondrial damage, we treated NIH3T3 mouse fibroblast cells with cfChPs isolated from sera of healthy individuals (10ng), or co-cultured the cells with hypoxia induced dying NIH3T3 cells. Abundant cfChPs could be detected in the cytoplasm of the treated cells by 4h. The latter was associated with evidence of mitochondrial damage in the form of ultra-structural changes, increased mitochondrial mass, alterations in mitochondrial shape, upregulation of the mitochondrial outer membrane protein TOM20, and changes in mitochondrial membrane potential. We also detected increased fluorescence signals of gamma-H2AX and p-ATM signifying double-strand breaks in mitochondrial DNA. There was marked increase in production of mitochondrial superoxide (ROS) as detected by MitoSOX Red, and activation of the intracellular antioxidant enzyme superoxide dismutase-1. Mitochondrial damage and ROS production could be inhibited by a cfChPs deactivating agent viz. anti-histone antibody complexed nanoparticles. Given that 1x109-1x1012 cells die in the body every day, we propose that cfChPs are major physiological triggers for mitochondrial damage and ROS production with an important bearing on human health and disease. Deactivation of cfChPs may provide a novel therapeutic approach to retard ageing and associated degenerative conditions that have been linked to oxidative stress.