Oxidative damage to mtDNA increases ROS

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Abstracts / Mitochondrion 6 (2006) 263–288

diffusion-weighted imaging correlated with decreased signal intensity on apparent diffusion coefficient maps. MRS showed diffuse lactate peaks. After two months on supplements with clinical improvement, repeat MRI showed markedly diminished white matter signal abnormality; MRS showed diminished lactate peaks. Conclusions: MRI and MRS can help assess central nervous system disease activity, and may offer an objective measure of response to medical management in mitochondrial cytopathies. doi:10.1016/j.mito.2006.08.007

Oxidative damage to mtDNA increases ROS Yudong Wang *, Jing Fang, Chunhao Li, Stephen S. Leonard, K. Shih-Hong Young, Jerry Roberts, Terence Meighan, K. Murali Krishna Rao University of Pittsburgh School of Medicine, Children’s Hospital of Pittsburgh, Department of Pediatrics, Pittsburgh, PA 15213, USA Mitochondria are the main source of reactive oxygen species (ROS) in cells. Accumulation of ROS leads to damage of proteins along with both nuclear and mitochondrial DNA and can decrease the function of the mitochondrial respiratory chain. Disorders of mitochondrial function associated with aging and many other mitochondrial diseases, in turn, can be expected to increase ROS production establishing a hypothetical ‘‘vicious cycle.’’ Such a cycle has been offered as one explanation for the exponential increase in ROS generation seen in the mitochondria of old animals; however, there is little experimental data to support it. To examine this phenomenon directly, we have developed an external ‘mild oxidative-exposure’ protocol that causes damage to mitochondrial DNA (mtDNA) but not to the nuclear DNA (nDNA) in actively growing tissue culture cells. Following exposure to oxidative stress, cells are returned to normal culture conditions and ROS generation is measured in the growing culture over time. Under these conditions, offspring cells showed an exponential increase in internal ROS generation similar to that described in the aging process. Electron spin resonance magnetic trapping studies identified that this was mainly due to inactivation of complex I of the respiratory chain. The increased ROS generation resulted in mtDNA damage including induction of mitochondrial chromosome deletions, and later nuclear DNA fragmentation and cellular apoptosis. In mtDNA the COX and ribosomal RNA genes were more frequently affected than other portions of the mitochondrial chromosome. Complex III activity was reduced by 40% in these cells. Thus, we conclude that mild oxidative stress preferentially induces mtDNA damage and decreased complex III activity. This in turn leads to the generation of more free radicals and increased ROS. These observations provide experimental support for the

mechanism of a ‘vicious cycle’ for the accumulation of mitochondrial damage due to ROS. doi:10.1016/j.mito.2006.08.008

Overcoming mitochondrial respiratory inhibition Guy C. Brown University of Cambridge, UK Inhibition of the mitochondrial respiratory chain can result from mitochondrial disease, hypoxia, inflammation or apoptosis. In turn, this respiratory inhibition can impair heart/brain function, block cell proliferation and induce cell death. These may feedforward to cause more hypoxia, inflammation and mitochondrial damage. We find that the nitric oxide produced from iNOS during inflammation inhibits mitochondrial respiration in competition with oxygen, and greatly sensitises the aorta and neurons to hypoxic death. This can be overcome by iNOS inhibitors. The block of cell proliferation induced by respiratory inhibition may be important to many pathologies. We find that the block of cell proliferation induced by respiratory chain inhibitors rotenone, myxothiazol or cyanide is reversed by uridine plus pyruvate. Respiratory inhibition can induce cell death by multiple mechanisms. We find that respiratory inhibition in the heart causes mitochondrial permeability transition, cytochrome c release, caspase activation, nuclear apoptosis, followed by necrosis. All of this can be blocked by low levels of nitric oxide or specific inhibitors of permeability transition. Respiratory inhibition in brain neurons results in glutamate release and excitotoxicity. This can be blocked by NMDA antagonists, calpain inhibitors or c-secretase inhibitors. Respiratory inhibition itself can be overcome with TMPD (tetra-methyl-phenylene-diamine), and we find that this is surprisingly protective, by a variety of mechanisms that will be discussed. doi:10.1016/j.mito.2006.08.009

Quantitation of heteroplasmy of mtDNA sequence variants identified in a population of AD patients and unaffected controls by array-based resequencing Keith D. Coon a,*, Jon Valla b,f, Szabolics Szelinger a, Lonnie E. Schneider b,f, Tracy L. Niedzielko b,f, Kevin M. Brown a, John V. Pearson a, Rebecca Halperin a, Phillip Stafford a, Andreas Papassotiropoulos a,c, Richard J. Casseli d, Eric M. Reiman a,e,f, Dietrich A. Stephan a a Neurogenomics Division, Translational Genomics Research Institute, Phoenix, AZ 85004, USA; b Cognitive Neurometabolism Laboratory, Barrow Neurological Institute, Phoenix, AZ 85013, USA; c Division of Psychiatry Research, University of Zurich, Zurich, Switzerland; d Department of Neurology, Mayo Clinic Scottsdale, USA; e PET Center, Banner Good Samaritan Medical Center, USA; f Department of Psychiatry, University of Arizona, USA