Mitochondria NO

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This article appearsVolume 299, Number 5608, Issue of 7 Feb 2003, p. 838.
Copyright © 2003 by The American Association for the Advancement of Science. All rights reserved.
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CELL BIOLOGY:
Enhanced: NO Says Yes to Mitochondria
Guy C. Brown* [HN17]
Mitochondria [HN1] are the microscopic powerhouses in our cells. They generate almost all of our energy and heat, and consume most of our oxygen and food calories. They are also the central controllers of cellular metabolism and the executioners of programmed cell death (apoptosis) [HN2]. The gas nitric oxide (NO)--identified in 1987 as a vasodilator of blood vessels--undertakes a bewildering array of regulatory tasks in the cell, many [HN3] of which involve mitochondria. On page 896 of this issue, Nisoli et al. [HN4] (1) tie these separate fields together with their finding that NO stimulates the synthesis (biogenesis) of new mitochondria [HN5].
Originally identified as a vasodilator, NO regulates the flow of blood to tissues. This in turn controls the supply of oxygen and respiratory substrates to mitochondria, and the redistribution of heat generated by those mitochondria. More recently, NO has been found to directly regulate the binding and release of oxygen from hemoglobin (2), and in this way controls the supply of oxygen to mitochondria. NO also carries out a very different task for the innate immune system [HN6]: the killing of virally infected cells, tumor cells, and parasitic pathogens (3). The inducible isoform of NO synthase (iNOS) [HN7] produces large quantities of cytotoxic NO, but normally only during inflammation. (If inflammation becomes chronic, then healthy host cells also may be killed by NO, contributing to inflammatory pathologies.) NO is cytotoxic partly because it inactivates the mitochondrial respiratory chain enzymes [HN8] of virally infected cells, tumor cells, and parasites, and partly because it stimulates the mitochondrial pathway of apoptosis (3-5). At high concentrations, NO inhibits many components of the respiratory chain, including the oxygen binding site of cytochrome oxidase [HN9] (4, 5). This ability of NO to reversibly block mitochondrial respiration and oxidative phosphorylation has led to the idea that NO may regulate mitochondrial energy production (3, 4). The finding that mitochondria contain their own isoform of NO synthase, mitochondrial NOS (mtNOS) [HN10], is consistent with direct regulation of mitochondrial energy production by NO (6).------------------------------------------------------------------------
The NO hat trick. Small amounts of NO stimulate mitochondrial biogenesis and boost the supply of oxygen and respiratory substrates to mitochondria. In contrast, high amounts of NO produced by iNOS block mitochondrial respiration, and can be cytotoxic. Cold exposure results in noradrenaline release by sympathetic nerves, which elevates intracellular calcium ions and cAMP (via b3-adrenergic receptors) in brown fat adipocytes. This increase induces NO production by eNOS, which activates cGMP production from soluble guanylate cyclase. Expression of the transcriptional coactivator PGC-1 is enhanced by cGMP, resulting in increased production of NRF-1 and mtTFA, which stimulate mitochondrial biogenesis. Vasodilation of blood vessels (due to the action of NO on vascular smooth muscle) results in an increased supply of oxygen and respiratory substrates to mitochondria. Inflammation enhances iNOS expression, resulting in elevated production of NO, which directly blocks mitochondrial respiration and energy production.
CREDIT: PRESTON MORRIGHAN/SCIENCE
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The ability to regulate the number of mitochondria in our cells is crucial for all sorts of physiological processes, including embryonic development, movement, fat metabolism, and aging. But how do cells control the number of mitochondria they contain? The recent discovery of a master regulator of mitochondrial biogenesis, PGC-1a (peroxisome proliferator-activated receptor g coactivator 1a) [HN11], is beginning to shed light on the underlying mechanisms. Overexpression of PGC-1a in transgenic mice results in increased numbers of mitochondria in cardiac and skeletal muscle (7, 8). PGC-1a is a transcriptional coactivator that increases expression of nuclear respiratory factor-1 (NRF-1) and mitochondrial transcription factor A (mtTFA) [HN12], which in turn promote the expression, respectively, of nuclear and mitochondrial genes that are required for mitochondrial biogenesis (8). PGC-1a is known to be up-regulated under conditions that promote the synthesis of new mitochondria (7, 8), for example, during prolonged exposure of rats to cold temperatures. Cold exposure activates the rat's brown adipose tissue [HN13] through stimulation of b3-adrenergic receptors, leading to an increase in cellular calcium ions and in the signaling molecule, cAMP [HN14] (see the figure). This results in enhanced PGC-1a production and an increase in the numbers of mitochondria in the adipocyte cells of brown fat, which generates body heat (6). Nisoli and colleagues now report the missing link in this causal chain: NO generated by endothelial nitric oxide synthase (eNOS), which may have been activated by calcium ions and/or phosphorylation, increases cGMP [HN15] levels (1). This in turn up-regulates production of PGC-1a and biogenesis of mitochondria. These authors found that overexpression of NO, cGMP, or eNOS dramatically increased the numbers of mitochondria in a range of cell lines and in differentiating brown fat adipocytes. Furthermore, mice lacking functional eNOS exhibited decreased numbers of mitochondria in a wide range of tissues, decreased energy metabolism, and increased weight gain (1). The implication is that NO produced by eNOS is itself a master regulator of mitochondrial number, and thus potentially of aerobic exercise, heat production, and obesity.
This surprising discovery has important implications for understanding energy metabolism and suggests therapeutic interventions for treating obesity. However, a number of questions remain to be answered about NO's ability to stimulate mitochondrial biogenesis. For example, does NO induce mitochondrial biogenesis in all tissues and does it interact with other biogenesis regulators? What is the mechanism of NO/cGMP action? Do iNOS and mtNOS behave in the same way as eNOS? Are the newly formed mitochondria different from their parents? NO can also regulate the proliferation and differentiation of various cell types, including the adipocytes of brown fat (9). The relation between these activities and NO's ability to stimulate mitochondrial biogenesis requires further investigation. The evidence for in vivo regulation of mitochondrial biogenesis by NO, however, remains weak. Encouragingly, Momken and colleagues (10) [HN16] recently reported a decrease in mitochondrial enzymes and oxidative phosphorylation in the aerobic skeletal muscles of mice deficient in eNOS. If NO indeed regulates mitochondrial number in human skeletal muscle, it might be possible to stimulate production of mitochondria in muscles with drugs or gene therapy, in order to increase sports performance, reduce obesity, or even reverse aging. On the downside, mitochondria can themselves contribute to cell death and aging, and NO regulates many other cellular processes (4, 5). But we now know that low levels of NO produced by eNOS can stimulate aerobic metabolism by increasing blood perfusion, unloading oxygen from hemoglobin, inducing growth of new blood vessels, and stimulating the biogenesis of mitochondria. High levels of NO, on the other hand, inhibit mitochondrial oxygen consumption directly. The diverse interactions between NO and mitochondria will continue to fascinate us for some time to come.
References
1. E. Nisoli et al., Science 299, 896 (2003).
2. A. J. Gow, J. S. Stamler, Nature 391, 169 (1998). [Medline]
3. J. B. Hibbs et al., J. Immunol. 138, 550 (1987). [Medline]
4. S. Moncada, J. D. Erusalimsky, Nature Rev. Mol. Cell Biol. 3, 214 (2002). [Medline]
5. G. C. Brown, V. Borutaite, Free Rad. Biol. Med. 33, 1440 (2002). [Medline]
6. S. L. Elfering et al., J. Biol. Chem. 277, 38079 (2002). [Medline] [Full text]
7. J. Lin et al., Nature 418, 797 (2002). [Medline]
8. R. C. Scarpulla, Biochim. Biophys. Acta 1576, 1 (2002). [Medline]
9. E. Nisoli et al., Br. J. Pharmacol. 125, 888 (1998). [Medline]
10. I. Momken et al., Biochem. J. 368, 341 (2002). [Medline] [Full text]
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The author is in the Department of Biochemistry, Cambridge University, Cambridge CB2 1QW, UK. E-mail: gcb@mole.bio.cam.ac.uk
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HyperNotes
Related Resources on the World Wide Web
General Hypernotes
Dictionaries and Glossaries
The xrefer Web site provides a searchable collection of scientific dictionaries and other references.
The On-line Medical Dictionary is provided by CancerWeb.
The Dictionary of Cell and Molecular Biology is made available by the editor J. Dow, Institute for Biomedical and Life Sciences, University of Glasgow.
D. Glick's Glossary of Biochemistry and Molecular Biology is made available by Portland Press.
Web Collections, References, and Resource Lists
The Google Web Directory provides links to Internet resources related to molecular biology and cell biology.
BioNetbook is a directory of Web pages for biology provided by the Institut Pasteur.
HealthWeb is a collaborative project of health sciences libraries to provide access to evaluated Internet resources.
The WWW Virtual Library of Cell Biology is maintained by the Fenteany Lab, Department of Chemistry, University of Illinois at Chicago.
The Nitric Oxide Home Page provides links to Internet resources.
Online Texts and Lecture Notes
The National Academy of Sciences' Beyond Discovery offers a presentation on nitric oxide in biology and medicine.
The Nobel e-Museum offers an illustrated presentation on nitric oxide in connection with the award of the 1998 Nobel Prize in Physiology or Medicine to Robert F. Furchgott, Louis J. Ignarro, and Ferid Murad "for their discoveries concerning nitric oxide as a signalling molecule in the cardiovascular system."
The companion Web site for the third edition of Biochemistry by C. Mathews, K. van Holde, and K. Ahern provides introductions to concepts, molecules, and enzymes.
J. Kimball maintains Kimball's Biology Pages, an online biology textbook and glossary.
Cell Biology Topics are provided by G. Childs, Department of Anatomy and Neurobiology, University of Arkansas for Medical Sciences.
C. Rinehart, Department of Biology, Western Kentucky University, offers lecture notes for a course on molecular and cellular biology.
L. Smart, Faculty of Environmental and Forest Biology, SUNY College of Environmental Science and Forestry, makes available lecture notes for a cell physiology course.
J. Diwan, Department of Biology, Rensselaer Polytechnic Institute, provides lecture notes for a course on the biochemistry of metabolism.
J.A. Illingworth, School of Biochemistry and Molecular Biology, University of Leeds, offers lecture notes on bioenergetics.
General Reports and Articles
The Bookshelf provided by the National Center for Biotechnology Information makes available Molecular Cell Biology by H. Lodish et al., Molecular Biology of the Cell by B. Alberts et al., and The Cell by G. Cooper.
The December 2002 issue of Molecular Pathology had a review article by K. Stuart-Smith titled "Demystified ... Nitric oxide."
W. Xu's Nitric Oxide Page makes available a 1998 review article in PDF format by W. Xu and L. Liu titled "Nitric oxide: From a mysterious labile factor, to the molecule of the Nobel Prize. Recent progress on nitric oxide research."
The 5 March 1999 issue of Science had a review article by M. Yaffe titled "The machinery of mitochondrial inheritance and behavior."
The June 2001 issue of the Journal of Cellular Physiology had a review article by A. Gow and H. Ischiropoulos titled "Nitric oxide chemistry and cellular signaling."
The 19 December 2000 issue of the Proceedings of the National Academy of Sciences had an article by B. Beltrán, A. Mathur, M. Duchen, J. Erusalimsky, and S. Moncada titled "The effects of nitric oxide on cell respiration: A key to understanding its role in cell survival or death."
Nitric oxide was Science's 1992 Molecule of the Year (access to the archive of Science articles provided by JSTOR is available on the AAASMember.org Web site). The 18 December 1992 issue also had an editorial about NO by D. Koshland and an article by J. Stamler, D. Singel, and J. Loscalzo titled "Biochemistry of nitric oxide and its redox-activated forms." Numbered Hypernotes
1. Mitochondria. Cells Alive! provides an introduction to mitochondria. M. Farabee's On-Line Biology Book offers an introduction to mitochondria. G. Childs' Cell Biology Topics include a presentation on mitochondrial structure and function. J. Pérez, Natural Toxins Research Center, Texas A&M University, Kingsville, makes available a student presentation on mitochondrion structure and function.
2. Apoptosis. Apoptosis is defined in xrefer's Dictionary of Biology. The Cell Death Society defines apoptosis and offers a collection of Internet links. A presentation on apoptosis is provided by Horst Ibelgaufts' Cytokines Online Pathfinder Encyclopaedia (COPE). The Reproductive and Cardiovascular Disease Research Group at St. George's Hospital Medical School, London, offers a presentation on apoptosis. Kimball's Biology Pages offer an introduction to apoptosis. R. Keates, Department of Chemistry and Biochemistry, University of Guelph, provides lecture notes on apoptosis for a course on regulation in biological systems. The 28 August 1998 issue of Science had a review article by D. Green and J. Reed titled "Mitochondria and apoptosis." The 27 April 2001 issue had a News Focus article by E. Finkel titled "The mitochondrion: Is it central to apoptosis?"
3. Nitric oxide in cells. The Biochemistry companion Web site offers introductions to nitric oxide and its actions. The Reproductive and Cardiovascular Disease Research Group at St. George's Hospital Medical School offers a presentation on nitric oxide. Kimball's Biology Pages offer an introduction to nitric oxide. L. Buehler, Division of Biological Sciences, University of California, San Diego, offers lecture notes on nitric oxide for a course on metabolic biochemistry. G. Buettner and L. Oberley, Free Radical and Radiation Biology Program, University of Iowa College of Medicine, make available (in PDF format) a student paper on nitric oxide by S. Banulescu, which was prepared for a course on free radicals in biology and medicine. The Brown Lab, Department of Biochemistry, University of Cambridge, offers a presentation on nitric oxide interactions with mitochondria and oxygen metabolism. The January 2001 issue of Physiological Reviews had an article by J. Stamler and G. Meissner titled "Physiology of nitric oxide in skeletal muscle." The 31 August 1999 issue of the Proceedings of the National Academy of Sciences had a commentary by S. Gross and P. Lane titled "Physiological reactions of nitric oxide and hemoglobin: A radical rethink" about an article in that issue by A. Gow et al. titled "The oxyhemoglobin reaction of nitric oxide."
4. E. Nisoli, V. Cozzi, C. Tonello, R. Bracale, and M. Carruba are in the Department of Preclinical Sciences, Lita Vialba, University of Milan. E. Clementi, C. Paolucci, and C. Sciorati are at the Cellular and Molecular Neurobiology Unit, Department of Neuroscience, Scientific Institute San Raffaele, Milan. A. Valerio is in the Department of Biomedical Sciences and Biotechnology, University of Brescia, Italy. M. Francolini is at the CNR Cellular and Molecular Pharmacology Center, Institute of Neurosciences, Milan. S. Moncada is at the Wolfson Institute for Biomedical Research, University College London.
5. Mitochondrial biogenesis. J. Illingworth offers lecture notes on biogenesis of mitochondria. The Journal of Sports Science and Medicine makes available a 1 December 2002 review article by H. Wackerhage and N. Woods titled "Exercise-induced signal transduction and gene regulation in skeletal muscle" that has a section on mitochondrial biogenesis.
6. Innate immunity. Kimball's Biology Pages offer an introduction to innate immunity. J. Decker, Department of Veterinary Science and Microbiology, University of Arizona, provides lecture notes on innate immunity for an immunology course. C. Davis, Department of Biology, Western Kentucky University, provides lecture notes on innate immunity and the inflammatory process for an immunology course. The October 2001 issue of Nature Immunology had a review article by C. Bogdan titled "Nitric oxide and the immune response" (limited access to full text).
7. Inducible nitric oxide synthase (iNOS) and other nitric oxide synthases. The Reproductive and Cardiovascular Disease Research Group at St. George's Hospital Medical School provides an introduction to nitric oxide synthases. Sigma-Aldrich provides introductions to nitric oxide metabolism, inducible nitric oxide synthase (iNOS), epithelial nitric oxide synthase (eNOS), and neuronal nitric oxide synthase (nNOS). The PROMISE Web site offers a presentation on nitric oxide synthases. The 1 August 2001 issue of the Biochemical Journal had a review article by W. Alderton, C. Cooper, and R. Knowles titled "Nitric oxide synthases: Structure, function and inhibition." Online Mendelian Inheritance in Man (OMIM) has entries for inducible NOS, neuronal NOS, and endothelial NOS. The Interactive Fly includes a section on NOS evolutionary homologs in the presentation on nitric oxide synthase gene of Drosophila. The March 2002 issue of Current Drug Targets - Inflammation & Allergy had a review article by P. Lirk, G. Hoffmann, and J. Rieder titled "Inducible nitric oxide synthase - Time for reappraisal" that provides an overview of the NOS family of enzymes.
8. Mitochondrial respiratory chain. The electron transport chain (also known as the respiratory chain) is defined in xrefer's Dictionary of Science. Kimball's Biology Pages offer a presentation on cellular respiration. J. Illingworth offers a presentation on respiratory chain components. A. Crofts, Department of Biochemistry, University of Illinois, provides lecture notes on the mitochondrial respiratory chain for a course on biological energy conversion. K. Redding, Department of Chemistry, University of Alabama, Tuscaloosa, offers lecture notes on the respiratory electron transport chain for a biochemistry course. The December 2001 issue of the American Journal of Physiology - Heart and Circulatory Physiology had an article by V. Borutaite, A. Matthias, H. Harris, S. Moncada, and G. Brown titled "Reversible inhibition of cellular respiration by nitric oxide in vascular inflammation."
9. Cytochrome oxidase is defined in xrefer's Dictionary of Biology. Cytochrome c oxidase was featured as a PDB molecule of the month.
10. Mitochondrial NOS. The 1 May 1998 issue of the Journal of Biological Chemistry had an article by C. Giulivi, J. Poderoso, and A. Boveris titled "Production of nitric oxide by mitochondria." The 11 October 2002 issue had an article by S. Elfering, T. Sarkela, and C. Giulivi titled "Biochemistry of mitochondrial nitric-oxide synthase."
11. PGC-1 alpha. J. Illingworth offers a presentation titled "Peroxisome proliferator-activated receptors and their coactivators." B. Spiegelman, Division of Cell and Molecular Biology, Dana-Farber Cancer Institute, offers introductions to PPAR gamma and PGC-1. Entries for PPARGC1 (peroxisome proliferator activated receptor gamma coactivator 1; PGC-1) are included in the GENATLAS, GeneCards, and OMIN databases. The October 2000 issue of the Journal of Clinical Investigation had an article by J. Lehman et al. titled "Peroxisome proliferator-activated receptor gamma coactivator-1 promotes cardiac mitochondrial biogenesis." The June 2001 issue of Molecular and Cellular Biology had an article by U. Andersson and R. Scarpulla titled "PGC-1-related coactivator: A novel, serum-inducible coactivator of nuclear respiratory factor 1-dependent transcription in mammalian cells." The 12 April 2002 issue of Science had a report by H. Wu et al. titled "Regulation of mitochondrial biogenesis in skeletal muscle by CaMK."
12. NRF-1 and mtTFA. Swiss-Prot has entries for NRF-1 (nuclear respiratory factor-1) and mtTFA (mitochondrial transcription factor A). OMIN has entries for NRF-1 and mtTFA.
13. Brown adipose tissue. Brown adipose tissue is defined in xrefer's Dictionary of Food and Nutrition. A tutorial on adipose tissue is provided by the JEFFLINE Web site, Thomas Jefferson University. The online Encyclopedia of Sports Medicine and Science includes a section on adipose tissue. A presentation on uncoupling proteins made available by the Department of Biology, Arizona State University, includes an illustrated introduction to brown adipose tissue. Colorado State University's Biomedical Hypertexts Web site offers an introduction to brown adipose tissue in the glossary provided.
14. Cyclic AMP (cAMP) is defined in xrefer's Dictionary of Science. The Biochemistry companion Web site offers an introduction to cAMP. L. Farmer, Department of Biology, University of Miami, Coral Gables, offers lecture notes on cAMP and its action for a physiology course.
15. cGMP. The Biochemistry companion Web site includes an entry for cGMP. Kimball's Biology Pages offers an introduction to cAMP and cGMP in a presentation on second messengers. Sigma-Aldrich provides an introduction to cGMP. H. Lodish et al.'s Molecular Cell Biology includes a section titled "Synthesis of cGMP is induced by both peptide hormones and nitric oxide" in the chapter on cell-to-cell signaling. Nitric Oxide, Cyclic GMP and Myocardial Infarction is a Web presentation by L Agulló, Laboratory of Experimental Cardiology, Hospital Vall d'Hebron, Barcelona.
16. The 15 November 2002 issue of the Biochemical Journal had an article by I. Momken et al. titled "Endothelial nitric oxide synthase (NOS) deficiency affects energy metabolism pattern in murine oxidative skeletal muscle." I. Momken, V. Veksler, and colleagues are at Cardiologie Cellulaire et Moléculaire U-446 INSERM, Faculté de Pharmacie, Université Paris-Sud, Châtenay-Malabry, France.
17. G. C. Brown is in the Department of Biochemistry, University of Cambridge.

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Cell Biology Related articles in Science:Mitochondrial Biogenesis in Mammals: The Role of Endogenous Nitric Oxide
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Science 2003 299: 896-899. (in Reports) [Abstract] [Full Text]