In contrast, mature cells in children and adults depend more on cell mitochondria to convert sugar and oxygen into carbon dioxide and water during a high energy-producing process called oxidative phosphorylation for their metabolic needs.
How cells progress from one form of energy production to another during development is unknown, although a finding by UCLA stem cell researchers provides new insight for this transition that may have implications for using these cells for therapies in the clinic.
Based mostly on visual appearance, it had been assumed that pluripotent stem cells contained undeveloped and inactive mitochondria, which are the energy-producing power plants that drive most cell functions. It was thought that stem cell mitochondria could not respire, or convert sugar and oxygen into carbon dioxide and water with the production of energy. This led most scientists to expect that mitochondria matured and gained the ability to respire during the transition from pluripotent stem cells into differentiated body cells over time.
Surprisingly, UCLA stem cell researchers discovered that pluripotent stem cell mitochondria respire at roughly the same level as differentiated body cells, although they produced very little energy, thereby uncoupling the consumption of sugar and oxygen from energy generation. Rather than finding that mitochondria matured with cell differentiation, as was anticipated, the researchers uncovered a mechanism by which the stem cells converted from glucose fermentation to oxygen-dependent respiration to achieve full differentiation potential.
The four-year study appears in the Nov. 15, 2011 issue of The EMBO Journal, a peer-reviewed journal of the European Molecular Biology Organization. Teitell collaborated with Carla Koehler, a UCLA professor of chemistry and biochemistry, for the study.
“A lot of attention is being paid to the role of metabolism in pluripotent stem cells for making properly differentiated cell lineages for research and potential clinical uses,” said study senior author Dr. Michael Teitell, a researcher with the Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research at UCLA and a professor of pediatrics, pathology and laboratory medicine, and bioengineering.
The initial question prompting our study was whether metabolism in pluripotent stem cells and cancer cells, which also rely heavily on glycolysis, were molecularly similar,” he said. “This question led us to study the details of energy-generation by mitochondria in pluripotent stem cells.”
Cells make energy in the form of ATP mainly in two ways, by glucose uptake and fermentation in the cytoplasm or by using respiration, in which glucose and oxygen are consumed to make carbon dioxide and water to fuel cell functions. Teitell and his team expected that pluripotent stem cells could not respire because of prior reports on the immature appearance and paucity of mitochondria.
Teitell’s team found that the molecular complexes responsible for respiration, called the electron transport chain, in the mitochondria of pluripotent stem cells were functional, and yet the cells instead relied on glycolysis for energy production. The researchers speculated that there were one or more unknown regulators that kept the stem cells from respiring, since the electron transport chain was functional.
Jin Zhang, a graduate student and first author of the study, discovered that a protein called uncoupling protein 2 (UCP2), was highly expressed in the stem cells. He also found that UCP2 blocked respiration substrates derived from sugar from gaining access to the mitochondria, instead shunting them to the glycolytic and biosynthesis pathways located in the cytoplasm, inhibiting the stem cell’s ability to respire as a method for generating energy.
As pluripotent stem cells were driven to develop into mature cell types, UCP2 expression was shut off, allowing respiration substrates to enter the mitochondria for energy generation, switching the cells from glycolysis to oxidative phosphorylation. Manipulating UCP2 expression, by keeping it switched on in differentiating cells, disturbed their maturation, a finding that could make them unsuitable for clinical use and also pointing to the importance of properly functioning metabolism for generating safe, high quality cells.
Teitell and his team confirmed these findings in both human embryonic stem cells and in induced pluripotent stem cells, which are mature body cells that are genetically reprogrammed to have similar abilities and attributes as the pluripotent embryonic stem cells.
“A main question that evolved during the study was whether it was the process of pluripotent stem cell differentiation that was altering the pattern of metabolism, or was it the change in the pattern of metabolism that altered the process of differentiation, a typical chicken-or-the-egg question,” Teitell said. “We over-expressed UCP2 in the stem cells and showed that metabolism patterns changed before markers of pluripotency or cell maturation changed, indicating that changes in metabolism affect changes in differentiation and not the other way around, at least for UCP2. This was important, to show causation for metabolic changes in driving the process of cell differentiation. However, it still leaves open the key question of exactly how manipulating cell metabolism controls cell differentiation, a question we are working hard to address.”
Since metabolism in pluripotent stem cells and cancer cells appear quite similar, Teitell said the finding could potentially be used to target UCP2 in malignant tumors that express it, of which there are many. Silencing UCP2 could force cancer cells to respire, which might impair their ability to grow quickly.
The study was supported in part by the California Institute for Regenerative Medicine, an Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research training grant, the National Institutes of Health and the National Center for Research Resources.
The stem cell center was launched in 2005 with a UCLA commitment of $20 million over five years. A $20 million gift from the Eli and Edythe Broad Foundation in 2007 resulted in the renaming of the center. With more than 200 members, the Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research is committed to a multi-disciplinary, integrated collaboration of scientific, academic and medical disciplines for the purpose of understanding adult and human embryonic stem cells. The center supports innovation, excellence and the highest ethical standards focused on stem cell research with the intent of facilitating basic scientific inquiry directed towards future clinical applications to treat disease. The center is a collaboration of the David Geffen School of Medicine, UCLA’s Jonsson Cancer Center, the Henry Samueli School of Engineering and Applied Science and the UCLA College of Letters and Science. To learn more about the center, visit our web site at http://www.stemcell.ucla.edu. To learn more about the center, visit our web site at http://www.stemcell.ucla.edu.
Further reports about: > Broad Institute > Human vaccine > Medicine > Regenerative Therapien > Stem cell innovation > UCLA > UCP2 > cancer cells > carbon dioxide > cell death > cell function > cell type > clinical application > embryonic stem > embryonic stem cell > energy generation > energy production > human embryonic stem cell > mechanism > metabolism > pluripotent > pluripotent stem > pluripotent stem cells > power plant > stem cell research > stem cells
A room with a view - or how cultural differences matter in room size perception
25.04.2017 | Max-Planck-Institut für biologische Kybernetik
Studying a catalyst for blood cancers
25.04.2017 | University of Miami Miller School of Medicine
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
20.04.2017 | Event News
18.04.2017 | Event News
03.04.2017 | Event News
25.04.2017 | Earth Sciences
25.04.2017 | Life Sciences
25.04.2017 | Earth Sciences