Glycoxidative stress–induced mitophagy modulates mitochondrial fatesLo, Mei‐Chen; Lu, Chin‐I; Chen, Ming‐Hong; Chen, Chun‐Da; Lee, Horng‐Mo; Kao, Shu‐Huei
doi: 10.1111/j.1749-6632.2010.05630.xpmid: 20649531
Diabetes mellitus (DM), a state of chronic hyperglycemia, is associated with a variety of serious complications. Hyperglycemia‐induced advanced glycation end products (AGEs) play an important role in the development of diabetic complications. In vivo, we demonstrated that disrupted mitochondria and autophagy was elevated in type II DM db/db mice. Mitophagy was evidenced by increased autophagosome formation in the β‐islet cells. The adducts of Nɛ‐(carboxymethyl) lysine (CML), a major AGE, and bovine serum albumin (CML‐BSA) stimulated the conversion of microtubule‐associated protein 1 light chain 3‐I (LC3‐I) to LC3‐II in rat insulinoma cells (RIN‐m5F). CML‐BSA increased ROS generation as demonstrated in a time‐dependent manner. Experiments with mitochondrial targeted enhanced yellow fluorescent protein transfected RIN‐m5F cells, massive fragmented mitochondria were visualized in the CML‐BSA treated cells. Taken together, these data suggested that AGEs may cause mitochondrial dysfunction and mitophagosome formation, and AGEs‐induced glycoxidative stress may trigger mitophagic process to modulate mitochondrial fates leading to either cell survival or cell death.
Advantages and considerations in the confirmation of mitochondrial DNA mutations by denaturing HPLC and pyrosequencingYen, Hsiu‐Chuan; Hsu, Wei‐Chien; Lin, Chih‐Lung; Chen, Guang‐Wu; Huang, Yu‐Hsiang
doi: 10.1111/j.1749-6632.2010.05626.xpmid: 20649533
Human mitochondrial DNA (mtDNA) encodes 13 polypeptides essential for oxidative phosphorylation. Because of the unique features of “replicative segregation” and “threshold expression” of mtDNA genetics, identification of homoplasmy versus heteroplasmy status is critical. Results from various detection methods may lead to different interpretations on formation or outcome of mtDNA mutations, such as the conclusion of somatic mutation versus genetic drift in cancers. Denaturing high‐performance liquid chromatography (DHPLC) and pyrosequencing (PSQ) have recently been employed to confirm the presence of heteroplasmy of mtDNA because of their high sensitivity in detecting heteroplasmic mutations compared with direct sequencing. Moreover, PSQ has superior ability in quantifying percentage of heteroplasmy. However, there could be disagreement between these two techniques and several issues specific for mtDNA should be taken into consideration. Particularly, DHPLC analysis should be more prone to be interfered by nuclear mitochondrial sequences (Numts), if it is coamplified with mtDNA, than PSQ analysis.
Physiological functions of mitochondrial fusionChen, Hsiuchen; Chan, David C.
doi: 10.1111/j.1749-6632.2010.05615.xpmid: 20649534
In recent years, the dynamic nature of mitochondria has been discovered to be critical for their function. Here we discuss the molecular basis of mitochondrial fusion, its protective role in neurodegeneration, and its importance in cellular function. The mitofusins Mfn1 and Mfn2, GTPases localized to the outer membrane, mediate outer‐membrane fusion. OPA1, a GTPase associated with the inner membrane, mediates subsequent inner‐membrane fusion. Mutations in Mfn2 or OPA1 cause neurodegenerative diseases. Mouse models with defects in mitochondrial fusion genes have provided important avenues for understanding how fusion maintains mitochondrial physiology and neuronal function. Mitochondrial fusion enables content mixing within a mitochondrial population, thereby preventing permanent loss of essential components. Cells with reduced mitochondrial fusion, as a consequence, show a subpopulation of mitochondria that lack mtDNA nucleoids. Such mtDNA defects lead to respiration‐deficient mitochondria, and their accumulation in neurons leads to impaired outgrowth of cellular processes and ultimately neurodegeneration.
Dynamic regulation of mitochondrial fission through modification of the dynamin‐related protein Drp1Chang, Chuang‐Rung; Blackstone, Craig
doi: 10.1111/j.1749-6632.2010.05629.xpmid: 20649536
Mitochondria in cells comprise a tubulovesicular network shaped continuously by complementary fission and fusion events. The mammalian Drp1 protein plays a key role in fission, while Mfn1, Mfn2, and OPA1 are required for fusion. Shifts in the balance between these opposing processes can occur rapidly, indicating that modifications to these proteins may regulate mitochondrial membrane dynamics. We highlight posttranslational modifications of the mitochondrial fission protein Drp1, for which these regulatory mechanisms are best characterized. This dynamin‐related GTPase undergoes a number of steps to mediate mitochondrial fission, including translocation from cytoplasm to the mitochondrial outer membrane, higher‐order assembly into spirals, GTP hydrolysis associated with a conformational change and membrane deformation, and ultimately disassembly. Many of these steps may be influenced by covalent modification of Drp1. We discuss the dynamic nature of Drp1 modifications and how they contribute not only to the normal regulation of mitochondrial division, but also to neuropathologic processes.
A novel function of mtDNA: its involvement in metastasisIshikawa, Kaori; Hayashi, Jun‐Ichi
doi: 10.1111/j.1749-6632.2010.05616.xpmid: 20649537
It has been controversial whether mtDNA mutations are responsible for oncogenic transformation (normal cells to develop tumors) and for malignant progression (tumor cells to develop metastases). To clarify this issue, we created transmitochondrial cybrids with mtDNA exchanged between mouse tumor cells that express different metastatic phenotypes. The G13997A mutation in the ND6 gene of mtDNA from high‐metastatic tumor cells reversibly controlled development of metastases by overproduction of reactive oxygen species (ROS). The mtDNA‐mediated reversible control of metastasis reveals a novel function of mtDNA, and suggests that ROS scavengers may be therapeutically effective in suppressing metastasis.
The NADH‐fumarate reductase system, a novel mitochondrial energy metabolism, is a new target for anticancer therapy in tumor microenvironmentsTomitsuka, Eriko; Kita, Kiyoshi; Esumi, Hiroyasu
doi: 10.1111/j.1749-6632.2010.05620.xpmid: 20649538
Since deficiencies of critical nutrients and hypoxia are observed in hypovascular tumors, glycolysis alone cannot explain how cancer cells maintain their required energy levels. To study energy metabolism in cancer cells within such tumor microenvironments, we examined the NADH‐fumarate reductase system, which is found in anaerobic organisms, such as parasitic helminthes. In human cancer cells cultured under tumor microenvironment‐mimicking conditions, mitochondrial NADH‐fumarate reductase activity increased in parallel with an increase in fumarate reductase activity, which is the reverse reaction of succinate‐ubiquinone reductase and is regulated by the phosphorylation of its subunit. Pyrvinium pamoate, an anthelmintic drug, has an anticancer effect within tumor‐mimicking microenvironments. We found that one of the biological mechanisms of pyrvinium is the inhibition of the NADH‐fumarate reductase system. Therefore, the NADH‐fumarate reductase system might be important for maintaining mitochondrial energy metabolism within the tumor microenvironments and might represent a novel target for anticancer therapies.
Bioenergetics and cell deathKushnareva, Yulia; Newmeyer, Donald D.
doi: 10.1111/j.1749-6632.2010.05633.xpmid: 20649539
Mitochondrial bioenergetic function is a key to cell life and death. Cells need energy not only to support their vital functions but also to die gracefully. Execution of an apoptotic program includes energy‐dependent steps, including kinase signaling, formation of the apoptosome, and effector caspase activation. Under conditions of bioenergetic collapse, cells are diverted toward necrotic demise. Mitochondrial outer membrane permeabilization (MOMP) is a decisive event in the execution of apoptosis. It is also causally linked to a decline in bioenergetic function via different mechanisms, not merely due to cytochrome c dispersion. MOMP‐induced bioenergetic deficiency is usually irreversible and commits cells to die, even when caspases are inactive. Here, we discuss the mechanisms by which MOMP impacts bioenergetics in different cell death paradigms.
A role for the CISD2 gene in lifespan control and human diseaseChen, Yi‐Fan; Wu, Chia‐Yu; Kirby, Ralph; Kao, Cheng‐Heng; Tsai, Ting‐Fen
doi: 10.1111/j.1749-6632.2010.05619.xpmid: 20649540
CISD2, the causative gene for Wolfram syndrome 2 (WFS2), is an evolutionarily conserved novel gene. Recently, we have demonstrated that CISD2 is involved in mammalian lifespan control; this work also establishes WFS2 as a mitochondria‐mediated disorder and effectively links CISD2 gene function, mitochondrial integrity, and aging in mammals. In wild‐type mice, the expression levels of CISD2 decrease in an age‐dependent manner during the naturally aging process; this correlates with mitochondrial breakdown and parallels the development of an aged phenotype. Future work will examine how the CISD2 knockout mouse helps us to understand WFS2 pathogenesis, as well as exploring the potential effects of increased CISD2 expression. In addition, it will be of great interest to compare gene activity and/or protein function between normal human populations and long‐lived centenarian groups. Together, human and mouse genetic studies should provide evidence as to whether CISD2 is a “master gene” for extreme old age.