title: Visualizing common deletion of mitochondrial DNA-augmented mitochondrial reactive oxygen species generation and apoptosis upon oxidative stress.
abstract: Common deletion (CD) 4977 bp of mitochondrial DNA (mtDNA) disrupt specifically mitochondrial complex I, IV and V on the electron transport chain (ETC) and is closely associated with wide spectrums of clinical manifestations. To quantitatively investigate how CD-induced ETC defect alters mitochondrial reactive oxygen species (mROS) generation as well as down stream apoptotic signaling, we employed an established array of human CD cytoplasmic hybrids (cybrids) harboring 0%-80% of CD. Pathological effects of CD on the mitochondria were visualized at single cell level by the application of fluorescent probes coupled with conventional and multiphoton imaging microscopy. Intriguingly, we observed CD-augmented mROS generation omitted "threshold effect". CD-augmented mROS generation was associated with depolarized mitochondrial membrane potential (DeltaPsi(m)). Upon oxidative stress, the amount of CD-augmented mROS generation was greatly enhanced to cause pathological apoptotic deterioration including opening of the mitochondrial permeability transition, cytochrome c release, phosphatidylserine externalization and DNA fragmentation. In addition, heterogeneous mitochondrial dysfunctions were found in cybrids containing 80% of CD (D cybrids), i.e., low sensitive-D (LS-D, roughly 80%) and a super sensitive-D (SS-D, 20%). As compared to LS-D, SS-D had higher resting mROS level but slightly hyperpolarized DeltaPsi(m). Upon H2O2 treatment, much faster generation of mROS was observed which induced a faster depolarization of DeltaPsi(m) and later apoptotic deterioration in SS-D. We proposed a dose-dependent, feed-forward and self-accelerating vicious cycle of mROS production might be initiated in CD-induced ETC defect without threshold effect. As CD-augmented mROS generation is obligated to cause an enhanced pathological apoptosis, precise detection of CD-augmented mROS generation and their degree of heterogeneity in single cells may serve as sensitive pathological indexes for early diagnosis, prognosis and treatment of CD-associated diseases.
authors.affiliation: Department of Neurology, Lin-Kou Medical Center, Chang Gung Memorial Hospital, Tao-Yuan, Taiwan.
authors.forename: Tsung-I
authors.initials: TI
authors.lastname: Peng
authors.forename: Pei-Ru
authors.initials: PR
authors.lastname: Yu
authors.forename: Jing-Yi
authors.initials: JY
authors.lastname: Chen
authors.forename: Hung-Li
authors.initials: HL
authors.lastname: Wang
authors.forename: Hong-Yeuh
authors.initials: HY
authors.lastname: Wu
authors.forename: Yau-Huei
authors.initials: YH
authors.lastname: Wei
authors.forename: Mei-Jie
authors.initials: MJ
authors.lastname: Jou
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002478:Cells, Cultured; D045304:Cytochromes c / Q000378:metabolism; D004272:DNA, Mitochondrial / Q000235:genetics*; D004789:Enzyme Activation / Q000187:drug effects; D017353:Gene Deletion; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008928:Mitochondria / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D008933:Mitochondrial Swelling / Q000187:drug effects; D018384:Oxidative Stress; D017382:Reactive Oxygen Species / Q000378:metabolism*; D017384:Sequence Deletion / Q000235:genetics*
chemical_list: D004272:DNA, Mitochondrial; D017382:Reactive Oxygen Species; D045304:Cytochromes c; D006861:Hydrogen Peroxide; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases