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Human pluripotent stem cells decouple respiration from energy production

2011; Springer Nature; Volume: 30; Issue: 24 Linguagem: Inglês

10.1038/emboj.2011.436

1460-2075

Ng Shyh‐Chang, Yu-Xiang Zheng, Jason W. Locasale, Lewis C. Cantley,

Gene Regulatory Network Analysis

Have you seen?14 December 2011free access Human pluripotent stem cells decouple respiration from energy production Ng Shyh-Chang Ng Shyh-Chang Stem Cell Program, Children's Hospital Boston, Boston, MA, USA Division of Signal Transduction, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, MA, USA Department of Systems Biology, Harvard Medical School, Boston, MA, USA Search for more papers by this author Yuxiang Zheng Yuxiang Zheng Division of Signal Transduction, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, MA, USA Department of Systems Biology, Harvard Medical School, Boston, MA, USA Search for more papers by this author Jason W Locasale Corresponding Author Jason W Locasale Division of Signal Transduction, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, MA, USA Department of Systems Biology, Harvard Medical School, Boston, MA, USA Search for more papers by this author Lewis C Cantley Corresponding Author Lewis C Cantley Division of Signal Transduction, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, MA, USA Department of Systems Biology, Harvard Medical School, Boston, MA, USA Search for more papers by this author Ng Shyh-Chang Ng Shyh-Chang Stem Cell Program, Children's Hospital Boston, Boston, MA, USA Division of Signal Transduction, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, MA, USA Department of Systems Biology, Harvard Medical School, Boston, MA, USA Search for more papers by this author Yuxiang Zheng Yuxiang Zheng Division of Signal Transduction, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, MA, USA Department of Systems Biology, Harvard Medical School, Boston, MA, USA Search for more papers by this author Jason W Locasale Corresponding Author Jason W Locasale Division of Signal Transduction, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, MA, USA Department of Systems Biology, Harvard Medical School, Boston, MA, USA Search for more papers by this author Lewis C Cantley Corresponding Author Lewis C Cantley Division of Signal Transduction, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, MA, USA Department of Systems Biology, Harvard Medical School, Boston, MA, USA Search for more papers by this author Author Information Ng Shyh-Chang1,2,3, Yuxiang Zheng2,3, Jason W Locasale 2,3 and Lewis C Cantley 2,3 1Stem Cell Program, Children's Hospital Boston, Boston, MA, USA 2Division of Signal Transduction, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, MA, USA 3Department of Systems Biology, Harvard Medical School, Boston, MA, USA *Correspondence to: [email protected]@hms.harvard.edu The EMBO Journal (2011)30:4851-4852https://doi.org/10.1038/emboj.2011.436 There is an Article (December 2011) associated with this Have you seen?. PDFDownload PDF of article text and main figures. ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InMendeleyWechatReddit Figures & Info Human pluripotent stem cells (hPSCs) rely heavily on glycolysis for energy metabolism, and because their mitochondria appear poorly developed, hPSCs have been assumed to be incapable of using oxidative phosphorylation (OxPhos). In this issue, Zhang et al (2011) demonstrate that hPSCs actually possess functional OxPhos machinery, but that the mitochondrial protein UCP2 decouples OxPhos from glycolysis. The study further suggests that regulation of glucose metabolism by UCP2 facilitates hPSC pluripotency and controls hPSC differentiation. Pluripotent embryonic stem cells require an exceptionally high flux of glucose uptake and lactate production, even when these cells grow in aerobic conditions outside the hypoxic blastocyst (aerobic glycolysis) (Prigione et al, 2010). In contrast, differentiated cells often require lower rates of aerobic glycolysis and shunt most of the cytosolic pyruvate into mitochondria where it is oxidized via the Krebs cycle and the electron transport chain (ETC) to synthesize ATP, a process collectively known as OxPhos. Consistent with these observations, hPSC mitochondria possess poorly developed cristae that only enlarge to form a densely tubular structure upon differentiation, which led some to conclude that hPSCs lack functional mitochondria (Facucho-Oliveira et al, 2007). However, how this switch occurs and whether a specific mitochondrial physiology is required for maintenance of the pluripotent state remained unclear. Zhang et al (2011) now show that hPSCs actually possess functional OxPhos machinery. In fact, hPSC mitochondria consume oxygen at rates similar to differentiated cell mitochondria. Unlike that of differentiated cells, glucose uptake is less coupled to OxPhos in hPSCs, and instead hPSCs predominantly use glycolysis to generate ATP. Furthermore, the authors inferred that ATP synthesis is also less coupled to the ETC in hPSCs and that ATP synthase may even be hydrolyzing ATP. Although more work is needed to establish this claim, it raises the intriguing possibility that ATP consumption in hPSCs is supporting an optimal membrane potential that promotes biosynthetic growth, just like in cancer cells (Racker 1976; Vander Heiden et al, 2010). Yet how is OxPhos decoupled from glycolysis in hPSCs? Zhang et al (2011) found that ectopic expression of UCP2 suppressed OxPhos during hPSC differentiation, while UCP2 knockdown decreased lactate production (Figure 1). Importantly, ectopic UCP2 also impeded hPSC differentiation, suggesting that relieving UCP2-mediated suppression of OxPhos is required for differentiation. Figure 1.Decoupling of respiration from ATP synthesis in hPSCs. The high glycolytic flux in hPSCs generates cytosolic pyruvate and ATP. High levels of UCP2 (bold) in hPSCs suppress the channelling of glycolytic flux into the Krebs cycle (grey). Pyruvate is converted to lactate instead. Upon differentiation of hPSCs, UCP2 levels decline (grey), thus increasing the interaction between glycolysis and the Krebs cycle (bold). Lactate production (grey) drops and OxPhos increases. The fully active ETC is also less coupled to ATP synthesis in hPSCs, but coupling of this step increases with hPSC differentiation. Download figure Download PowerPoint UCP2 belongs to the uncoupling protein (UCP) family. UCP1 transports protons to dissipate the membrane potential and uncouples ATP synthesis from the ETC. In contrast, UCP2 is still a subject of controversy. UCP2 transports protons in vitro, but apparently not in vivo (Couplan et al, 2002). Instead, studies have shown that UCP2 decreases pyruvate oxidation, suggesting that UCP2 decouples glycolysis from OxPhos by shunting pyruvate out of the mitochondria (Emre and Nubel, 2010). Zhang et al (2011) provide evidence to support this view. By using 13C-isotope tracing, the authors show that ectopic expression of UCP2 decreases glycolytic flux to the Krebs cycle in differentiating hPSCs. However, whether this reflects a bona fide pyruvate transport activity in UCP2 remains to be tested. Glycolysis has recently been studied during the reprogramming of human fibroblasts into induced hPSCs (Zhu et al, 2010; Folmes et al, 2011). Although c-Myc is a well-known pluripotency factor that also promotes aerobic glycolysis, these studies have shown that aerobic glycolysis in hPSCs can be enhanced by factors other than c-Myc. It would be interesting to examine which pluripotency factors regulate UCP2 expression to control hPSC bioenergetics. Zhang et al (2011) also showed that ectopic expression of UCP2 prevented hPSC differentiation, but UCP2 knockdown failed to impair self-renewal or induce differentiation, suggesting that other mechanisms exist to suppress OxPhos or coordinate OxPhos with differentiation in hPSCs. In addition, it is still unclear why or how the ETC is operating at maximal capacity, when ATP synthesis appears to be less coupled to the ETC in hPSCs. One possibility is that it is operating to recycle NAD and keep the Krebs cycle turning to generate biosynthetic intermediates. Another complementary possibility is that the high glycolytic ATP is forcing some ETC reactions to run in reverse, a phenomenon first observed in the 1960s (Forman and Wilson, 1982). This then functions to engage the ETC in an ATP-consuming futile cycle to maintain an optimal membrane potential. The study by Zhang et al (2011) raises many interesting questions with implications for understanding the bioenergetics in PSCs and perhaps also in other settings such as those found in cancer metabolism. Conflict of Interest The authors declare that they have no conflict of interest. References Couplan E, del Mar Gonzalez-Barroso M, Alves-Guerra MC, Ricquier D, Goubern M, Bouillaud F (2002) No evidence for a basal, retinoic, or superoxide-induced uncoupling activity of the uncoupling protein 2 present in spleen or lung mitochondria. J Biol Chem 277: 26268–26275CrossrefCASPubMedWeb of Science®Google Scholar Emre Y, Nubel T (2010) Uncoupling protein UCP2: when mitochondrial activity meets immunity. FEBS Lett 584: 1437–1442Wiley Online LibraryCASPubMedWeb of Science®Google Scholar Facucho-Oliveira JM, Alderson J, Spikings EC, Egginton S, St John JC (2007) Mitochondrial DNA replication during differentiation of murine embryonic stem cells. 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J Cell Physiol 89: 697–700Wiley Online LibraryCASPubMedWeb of Science®Google Scholar Vander Heiden MG, Locasale JW, Swanson KD, Sharfi H, Heffron GJ, Amador-Noguez D, Christofk HR, Wagner G, Rabinowitz JD, Asara JM, Cantley LC (2010) Evidence for an alternative glycolytic pathway in rapidly proliferating cells. Science 329: 1492–1499CrossrefCASPubMedWeb of Science®Google Scholar Zhang J, Khvorostov I, Hong JS, Oktay Y, Vergnes L, Nuebel E, Wahjudi PN, Setoguchi K, Wang G, Do A, Jung H-J, McCaffery JM, Kurland IJ, Reue K, Lee W-NP, Koehler CM, Teitell MA (2011) UCP2 regulates energy metabolism and differentiation potential of human pluripotent stem cells. EMBO J 30: 4860–4873Wiley Online LibraryCASPubMedWeb of Science®Google Scholar Zhu S, Li W, Zhou H, Wei W, Ambasudhan R, Lin T, Kim J, Zhang K, Ding S (2010) Reprogramming of human primary somatic cells by OCT4 and chemical compounds. Cell Stem Cell 7: 651–655CrossrefCASPubMedWeb of Science®Google Scholar Previous ArticleNext Article Read MoreAbout the coverClose modalView large imageVolume 30,Issue 24,December 14, 2011Voronoi Treemap Visualization of transcription 60 min after onset of glucose starvation in Bacillus subtilis 168. Individual genes (small polygons) are grouped according to operon membership (next higher level) and those again by their dependency on a regulator. Orange indicates induction, light grey no change, and dark blue repression. This image, submitted by Jörg Bernhardt from the University of Greifswald, Germany, was one of the finalists in the scientific section of the EMBO Journal Cover Contest 2011. Visit http://covercontest.embo.org for an online gallery of some of the other high-scoring images. If you would like to take part in the 2012 contest yourself, submit your (scientific or non-scientific) images through the contest website by 17 January, 2012. 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