Declines in Drp1 and parkin expression underlie DNA damage-induced changes in mitochondrial length and neuronal death

Maintaining proper mitochondrial length is essential for normal mitochondrial function in neurons. Mitochondrial fragmentation has been associated with neuronal cell death caused by a variety of experimental toxic stressors. Despite the fact that oxidative stress is a hallmark of neurodegenerative conditions and aging and the resulting activation of p53 is believed to contribute to the neuropathology, little is still known regarding changes in mitochondrial morphology in p53-dependent neuronal death. Therefore, we specifically addressed the relationship between genotoxic stress, p53 activation, and the regulation of mitochondrial morphology in neurons. In cultured postnatal mouse cortical neurons, treatment with the DNA-damaging agent camptothecin (CPT) resulted in elongated mitochondria, in contrast to fragmented mitochondria observed upon staurosporine and glutamate treatment. In fibroblasts, however, CPT resulted in fragmented mitochondria. CPT treatment in neurons suppressed expression of the mitochondrial fission protein Drp1 and the E3 ubiquitin ligase parkin. The presence of elongated mitochondria and the declines in Drp1 and parkin expression occurred before the commitment point for apoptosis. The CPT-induced changes in Drp1 and parkin were not observed in p53-deficient neurons, while p53 overexpression alone was sufficient to reduce the expression of the two proteins. Elevating Drp1 or parkin expression before CPT treatment enhanced neuronal viability and restored a normal pattern of mitochondrial morphology. The present findings demonstrate that genotoxic stress in neurons results in elongated mitochondria in contrast to fission induced by other forms of stress, and p53-dependent declines in Drp1 and parkin levels contribute to altered mitochondrial morphology and cell death.