A needle in a haystack: focus on “Proteomic alterations of distinct mitochondrial subpopulations in the type 1 diabetic heart”
2010; American Physiological Society; Volume: 300; Issue: 2 Linguagem: Inglês
10.1152/ajpregu.00751.2010
ISSN1522-1490
Autores Tópico(s)Adipose Tissue and Metabolism
ResumoCall for PapersMitochondrial Function/Dysfunction in Health and DiseaseA needle in a haystack: focus on “Proteomic alterations of distinct mitochondrial subpopulations in the type 1 diabetic heart”Sean M. DavidsonSean M. DavidsonThe Hatter Cardiovascular Institute, University College London, London, United KingdomPublished Online:01 Feb 2011https://doi.org/10.1152/ajpregu.00751.2010This is the final version - click for previous versionMoreSectionsPDF (341 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat diabetes mellitus is increasingly common throughout the world, due to both an increase in incidence and to decreased mortality of those with diabetes. Unfortunately, diabetes more than doubles the risk of cardiovascular disease in adults, and it even causes its own peculiar form of “diabetic” cardiomyopathy. These facts are conspiring, in turn, to increase the prevalence of heart failure (reviewed in Ref. 2). In fact, cardiovascular disease is now the leading cause of morbidity and mortality among individuals with diabetes, which raises the importance of understanding the mechanism of diabetic cardiomyopathy.Proteomics is a very appealing tool for the of study of complicated disease processes, such as diabetes, since it allows one to compare the protein expression profile of tissues, cells, or even organelles harvested from normal and diseased hearts. With luck, this unbiased approach might reveal the proverbial “needle in a haystack”—a specifically altered protein or pathway offering a potential therapeutic angle. However, as the results reported in the accompanying article by Baseler et al. (1) demonstrate, it is important to be certain that one is searching in the right “haystack.” Then, once the “needle” is found, there is also the not-insignificant task of working out what it means.Whereas the more common type II diabetes is due to loss of insulin sensitivity (“insulin resistance”), up to 10% of cases are due to insufficient insulin production and are categorized as type I. In both types, there is a progressive increase in blood glucose concentration which defines the disease. Paradoxically, despite the plentiful glucose, glucose oxidation rates actually decrease in the diabetic heart, and fatty acid oxidation increases (2). This method of ATP production is less efficient, and contributes to the development of heart failure. Diabetes can, therefore, be considered a metabolic disease, which naturally raises the possible involvement of the mitochondria in diabetic cardiomyopathy.Previous proteomic investigations of the ventricular myocardium of type I diabetic mouse models have detected an increase in mitochondrial proteins involved in fatty acid oxidation (2, 8, 19). Interpretation is complicated, though, by a potentially confounding increase in mitochondrial volume in the diabetic hearts (19). A subsequent proteomic analysis of mitochondria purified from type I diabetic rat hearts apparently confirmed an increase in proteins involved in fatty acid β-oxidation, with little change in tricarboxylic acid cycle proteins and a modest decrease in electron transport proteins (21). However, in all studies of cardiac mitochondria, a critical factor is the method used for their separation and purification, since there are at least two distinct populations of mitochondria that require different techniques for their isolation. The mitochondria purified most easily, by simple cellular lysis and centrifugation, are the subsarcolemmal mitochondria (SSM), positioned just beneath the sarcolemma (Fig. 1A). These are believed to be specialized for their role in producing ATP for ion pumps, and hence provide energy for the maintenance of the plasma membrane potential and generation of the cardiac action potential (10% of all cellular energy expenditure) and maintenance of internal stores of calcium (15% energy expenditure) (10). In the above study by Turko and Murad (21), the mitochondria are likely to have been mainly of subsarcolemmal origin, raising the possibility that differences might be detected in other mitochondrial subpopulations (other “haystacks”). The ideal arrangement on a farm, presumably, is to locate the haystacks close to the livestock, i.e., the source of energy is close to its site of utilization. Indeed, one finds just such an arrangement in the cardiomyocyte, wherein the majority of mitochondria are positioned immediately adjacent to the myofibrillar contractile units, providing the energy for contractile force production, which, in itself, accounts for 75% of energy expenditure (10). The close physical association with these interfibrillar mitochondria (IFM) is important for efficient cardiac energy utilization and function (22).Fig. 1.A: transmission electron micrograph of rat myocardium illustrating the three subpopulations of mitochondria: subsarcolemmal mitochondria (SSM); interfibrillar mitochondria (IFM); and perinuclear mitochondria (PNM). B: cristae are typically more lamelliform in SSM (top) and more tubular in IFM (bottom).Download figureDownload PowerPointWhen an additional, mild proteolysis step is used to release the IFM from the myofibrils (15), they are found to have an innately higher respiratory rate than the SSM (15). Importantly, these differences are not an artefact of the isolation procedure, since the differences persist even if SSM are exposed to protease (15). On the other hand, a recent study suggesting that mitochondrial respiratory defects only become apparent in aged skeletal muscle after mitochondrial isolation and are not present in the original myofibers, may be cause for concern about the isolation procedure (16).The mitochondrial subpopulations also exhibit differences in internal structure, with the cristae of the IFM being relatively more tubular than the lamelliform cristae of the SSM (Fig. 1B), and these differences are reasonably well preserved during isolation (17). Though the IFM were believed to be relatively “fixed” in place due to the physical constraint of the sarcomeres, recent evidence suggests that they are able fuse into elongated, “thread”-like mitochondria under certain conditions (14). Conversely, in pathological situations, such as ischemia, hypertrophy, and diabetes, they may fragment into smaller individual units, though whether this reflects an injury or a protective, “defense” mechanism, remains uncertain. IFM also appear to be more sensitive to various pathologies, such as aging, cardiomyopathy, and diabetes, although ischemia preferentially affects SSM, depleting cardiolipin, decreasing membrane fluidity, causing ultrastructural damage, and decreased oxidative capacity (1, 9).In addition to being sites of energy production, there is increasing realization that mitochondria have additional roles such as Ca2+ buffering (20), and there is evidence that mitochondria accumulate Ca2+ with each cardiomyocyte contraction, effectively integrating over time the fluctuating [Ca2+]cyto. A cleverly designed experiment to “shock-freeze” cardiomyocytes at a specific stage of the action potential showed that [Ca2+]mito increases higher in SSM than in IFM mitochondria, which was ascribed to microdomains of elevated Ca2+ and Na+ generated during contraction (7). This reflects growing awareness that [Ca2+]mito is differentially regulated according to subcellular localization in numerous cell types (20). A close physical association between endoplasmic reticulum/sarcoplasmic reticulum, and mitochondria is important in Ca2+ regulation in other cell types, and this may well vary between SSM and IFM.The authors of the accompanying article by Baseler et al. (1) previously confirmed that the streptozotocin type I diabetic model resulted in the expected cardiac contractile abnormalities in their hands (5). Furthermore, they found that the IFM were more susceptible than SSM, decreasing in size and complexity, with respiration more severely decreased (5) and with a concomitant decrease in membrane potential (23). The IFM produced more superoxide, resulting in oxidative damage of proteins and lipids in IFM and were more susceptible to opening of the mitochondrial permeability transition pore under certain conditions (23). Here, Baseler et al. (1) report the results of the first proteomic investigation using this model, which separates the IFM and SSM populations of myocardial mitochondria. Comparing these two “haystacks,” they found a number of “needles,” i.e., changes occurring preferentially in the IFM. These include a decrease in the content of proteins involved in fatty acid oxidation, electron transport chain activity, cristae morphology (mitofilin), and, interestingly, mitochondrial HSP70 (involved in mitochondrial protein import). Following this thread of investigation, they went on to examine the efficiency of mitochondrial protein import in the subpopulations and identified a selective deficiency in IFM mitochondria. This, in turn, may be due to a decrease in IFM membrane potential (which drives mitochondrial protein uptake). Thus, a defect in the respiratory capability to generate a membrane potential may be self-reenforcing, as it diminishes the ability of the mitochondria to import replacement proteins. At the risk of overextending the barnyard analogies, it then becomes a matter of “the chicken and the egg,” in terms of which is the initial damage responsible for the mitochondrial changes.The question remains as to why the IFM are more susceptible than SSM to injury in type I diabetes. One possibility is that their higher respiratory rates generate more damaging oxygen free radicals. Some of the observed posttranslational protein modifications were suggestive of oxidative damage (1), and a more extensive proteomic examination might confirm specific oxidative damage in components of fatty acid oxidation and respiration. Knowing the primary defect raises therapeutic possibilities. For example, overexpression of mitochondrial antioxidants may prevent diabetic cardiomyopathy (2). A therapeutic approach might make use of the emerging class of mitochondrially targeted reactive oxygen species scavengers, such as mitoQ (6). Indeed, this has recently been shown to be beneficial in type I diabetic mice (3). Overexpression of mitochondrial translocases, such as Tim44, is another interesting approach (13).The observed difference may depend upon the diabetic model. The same group has previously performed a similar study in db/db mice as a model for type II diabetes (4). In these mice, SSM had decreased size and internal complexity, while IFM had increased internal complexity. Though IFM were relatively unchanged, SSM had decreased respiratory rates, lower membrane potential, and increased oxidative damage, with corresponding decreases in mitochondrial protein import machinery and IMM proteins in SSM (4). This suggests insulin resistance may affect SSM specifically, although an early study also observed impaired fatty acid oxidation in IFM of type II diabetic mice (2, 11).There are, of course, limitations to the proteomic approach. There are increasing numbers of reports of signaling proteins being localized to mitochondria, and even proteins such as connexin-43, proposed as mediating cardioprotection selectively via the SSM (18). Unfortunately, the standard proteomic approach is unlikely to detect these changes, as it is limited to proteins of high abundance, although an interesting extension to the current study would be to examine posttranslational modifications related to activity. Other “haystacks” may merit investigation. For example, there is an unexplored, third population of mitochondria in a sarcomere-free region near the nuclei (Fig. 1A) (12), which presumably provide ATP for transcription and translation. Furthermore, mitochondria in other cell types, particularly the endothelium may be important in diabetic cardiomyopathy (6). In conclusion, the authors may have succeeded in finding a needle in a haystack, but diabetic cardiomyopathy is not yet sewn up.DISCLOSURESNo conflicts of interest, financial or otherwise, are declared by the author.REFERENCES1. Baseler WA , Dabkowski ER , Williamson CL , Croston TL , Thapa D , Powell MJ , Razunguzwa TT , Hollander JM. Proteomic alterations of distinct mitochondrial subpopulations in the type 1 diabetic heart: contribution of protein import dysfunction. Am J Physiol Regul Integr Comp Physiol (November 3, 2010). 10.1152/ajpregu.00423.2010.PubMed | ISI | Google Scholar2. Bugger H , Abel ED. Mitochondria in the diabetic heart. Cardiovasc Res 88: 229–240, 2010.Crossref | PubMed | ISI | Google Scholar3. Chacko BK , Reily C , Srivastava A , Johnson MS , Ye Y , Ulasova E , Agarwal A , Zinn KR , Murphy MP , Kalyanaraman B , Darley-Usmar V. Prevention of diabetic nephropathy in Ins2+/−AkitaJ mice by the mitochondria-targeted therapy MitoQ. Biochem J 432: 9–19, 2010.Crossref | PubMed | ISI | Google Scholar4. Dabkowski ER , Baseler WA , Williamson CL , Powell M , Razunguzwa TT , Frisbee JC , Hollander JM. Mitochondrial dysfunction in the Type 2 diabetic heart is associated with alterations in spatially-distinct mitochondrial proteomes. Am J Physiol Heart Circ Physiol 299: H529–H540, 2010.Link | ISI | Google Scholar5. Dabkowski ER , Williamson CL , Bukowski VC , Chapman RS , Leonard SS , Peer CJ , Callery PS , Hollander JM. Diabetic cardiomyopathy-associated dysfunction in spatially distinct mitochondrial subpopulations. Am J Physiol Heart Circ Physiol 296: H359–H369, 2009.Link | ISI | Google Scholar6. Davidson SM. Endothelial mitochondria and heart disease. Cardiovasc Res 88: 58–66, 2010.Crossref | PubMed | ISI | Google Scholar7. Gallitelli MF , Schultz M , Isenberg G , Rudolf F. Twitch-potentiation increases calcium in peripheral more than in central mitochondria of guinea-pig ventricular myocytes. J Physiol 518: 433–447, 1999.Crossref | PubMed | ISI | Google Scholar8. Hamblin M , Friedman DB , Hill S , Caprioli RM , Smith HM , Hill MF. Alterations in the diabetic myocardial proteome coupled with increased myocardial oxidative stress underlies diabetic cardiomyopathy. J Mol Cell Cardiol 42: 884–895, 2007.Crossref | PubMed | ISI | Google Scholar9. Hoppel CL , Tandler B , Fujioka H , Riva A. Dynamic organization of mitochondria in human heart and in myocardial disease. Int J Biochem Cell Biol 41: 1949–1956, 2009.Crossref | PubMed | ISI | Google Scholar10. Katz AM. Physiology of the Heart. Baltimore, MD: Lippincott Williams and Wilkins, 2005.Google Scholar11. Kuo TH , Giacomelli F , Wiener J. Oxidative metabolism of Polytron versus Nagarse mitochondria in hearts of genetically diabetic mice. Biochim Biophys Acta 806: 9–15, 1985.Crossref | PubMed | ISI | Google Scholar12. Lukyanenko V , Chikando A , Lederer WJ. Mitochondria in cardiomyocyte Ca2+ signaling. Int J Biochem Cell Biol 41: 1957–1971, 2009.Crossref | PubMed | ISI | Google Scholar13. Matsuoka T , Wada J , Hashimoto I , Zhang Y , Eguchi J , Ogawa N , Shikata K , Kanwar YS , Makino H. Gene delivery of Tim44 reduces mitochondrial superoxide production and ameliorates neointimal proliferation of injured carotid artery in diabetic rats. Diabetes 54: 2882–2890, 2005.Crossref | PubMed | ISI | Google Scholar14. Ong SB , Subrayan S , Lim SY , Yellon DM , Davidson SM , Hausenloy DJ. Inhibiting mitochondrial fission protects the heart against ischemia/reperfusion injury. Circulation 121: 2012–2022, 2010.Crossref | PubMed | ISI | Google Scholar15. Palmer JW , Tandler B , Hoppel CL. Biochemical properties of subsarcolemmal and interfibrillar mitochondria isolated from rat cardiac muscle. J Biol Chem 252: 8731–8739, 1977.Crossref | PubMed | ISI | Google Scholar16. Picard M , Ritchie D , Wright KJ , Romestaing C , Thomas MM , Rowan SL , Taivassalo T , Hepple RT. Mitochondrial functional impairment with aging is exaggerated in isolated mitochondria compared to permeabilized myofibers. Aging Cell 9: 1032–1046, 2010.Crossref | PubMed | Google Scholar17. Riva A , Tandler B , Loffredo F , Vazquez E , Hoppel C. Structural differences in two biochemically defined populations of cardiac mitochondria. Am J Physiol Heart Circ Physiol 289: H868–H872, 2005.Link | ISI | Google Scholar18. Rottlaender D , Boengler K , Wolny M , Michels G , Endres-Becker J , Motloch LJ , Schwaiger A , Buechert A , Schulz R , Heusch G , Hoppe UC. Connexin 43 acts as a cytoprotective mediator of signal transduction by stimulating mitochondrial KATP channels in mouse cardiomyocytes. J Clin Invest 120: 1441–1453, 2010.Crossref | PubMed | ISI | Google Scholar19. Shen X , Zheng S , Thongboonkerd V , Xu M , Pierce WM , Klein JB , Epstein PN. Cardiac mitochondrial damage and biogenesis in a chronic model of type 1 diabetes. Am J Physiol Endocrinol Metab 287: E896–E905, 2004.Link | ISI | Google Scholar20. Szabadkai G , Duchen MR. Mitochondria: the hub of cellular Ca2+ signaling. Physiology 23: 84–94, 2008.Link | ISI | Google Scholar21. Turko IV , Murad F. Quantitative protein profiling in heart mitochondria from diabetic rats. J Biol Chem 278: 35844–35849, 2003.Crossref | PubMed | ISI | Google Scholar22. Wilding JR , Joubert F , de Araujo C , Fortin D , Novotova M , Veksler V , Ventura-Clapier R. Altered energy transfer from mitochondria to sarcoplasmic reticulum after cytoarchitectural perturbations in mice hearts. J Physiol 575: 191–200, 2006.Crossref | PubMed | ISI | Google Scholar23. Williamson CL , Dabkowski ER , Baseler WA , Croston TL , Alway SE , Hollander JM. Enhanced apoptotic propensity in diabetic cardiac mitochondria: influence of subcellular spatial location. Am J Physiol Heart Circ Physiol 298: H633–H642, 2010.Link | ISI | Google ScholarAUTHOR NOTESAddress for reprint requests and other correspondence: The Hatter Cardiovascular Institute, Univ. College London, 67 Chenies Mews, London, WC1E 6HX, UK (e-mail: S.[email protected]ac.uk). Download PDF Back to Top Next FiguresReferencesRelatedInformationCited ByMitochondrial proteome design: From molecular identity to pathophysiological regulation28 May 2012 | The Journal of General Physiology, Vol. 139, No. 6 More from this issue > Volume 300Issue 2February 2011Pages R183-R185 Copyright & PermissionsCopyright © 2011 the American Physiological Societyhttps://doi.org/10.1152/ajpregu.00751.2010PubMed21123761History Received 12 November 2010 Accepted 29 November 2010 Published online 1 February 2011 Published in print 1 February 2011 Metrics
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