A Critical Role of Mitochondrial Phosphatase Ptpmt1 in Embryogenesis Reveals a Mitochondrial Metabolic Stress-Induced Differentiation Checkpoint in Embryonic Stem Cells

Abstract

Mitochondria are involved in a number of cellular processes and are essential for both life and death. As the site of oxidative phosphorylation, these double-membrane organelles provide a highly efficient route for eukaryotic cells to generate ATP from energy-rich molecules. During the mitochondrial energy production process, reactive oxygen species (ROS), such as superoxide (O 2 Ϫ ) and hydrogen peroxide (H 2 O 2 ), are produced as by-products. In fact, mitochondria are the primary source of a majority of cellular ROS (2). Mitochondria also participate in intermediary metabolism. Under normal oxygen tensions, cells catabolize glucose to pyruvate. Pyruvate is then imported into the mitochondria for further catabolism through the Krebs cycle, which transfers electrons to the respiratory chain for ATP synthesis. In low oxygen tension, or hypoxic conditions in which there is a paucity of oxygen as an electron acceptor, cells are surmised to undergo anaerobic glycolysis as a default mode. Pyruvate is then used for low-efficiency energy production in the cytosol by glycolysis. In addition to metabolism and energy production, mitochondria play important roles in the regulation of apoptosis and intracellular Ca 2ϩ homeostasis. Dysfunction in mitochondria results in severe cellular consequences and is linked to a wide range of human diseases (2, 36, 43). The role of mitochondrial activities in early embryonic development and embryonic stem (ES) cell function is not well defined (20,42). The environment of the uterus before placentation is anaerobic (11). To produce ATP in this environment, early embryonic cells, such as ES cells, rely heavily on glycolysis for ATP production (4) and, thus, do not require a large number of mitochondria. ES cells only have a few mitochondria with poorly developed cristae (21). Effective control of mitochondrial mass and function is critical for the prevention of damage by oxidative stress (ROS) in ES cells. However, when these cells are allowed to differentiate, the resulting cells show numerous large mitochondria with distinct cristae. Thus, mitochondria must undergo robust replication/biogenesis during this short period of time. Earlier studies have shown that the mitochondrial genome undergoes significant replication during implantation of blastocysts (41), and once gastrulation occurs, cells replicate their mitochondrial DNA (mtDNA) to match the energy demand of differentiating cells (39). It has also been demonstrated that mitochondrial metabolic rates correlate inversely with the differentiation capacity of ES cells (37). However, exactly how mitochondria coordinate stem cell behavior during embryogenesis is still not well understood.Mitochondria are highly dynamic organelles that undergo continuous fusion and fission. These mitochondrial processes play important roles in mitochondrial biogenesis/replication.

Phosphatidylinositolphosphate phosphatase activities and cancer

“…The recombinant protein exhibited phosphatase activity against PtdIns(5)P, but no other phosphoinositide ( 80 ). However, other reports have demonstrated that PTPMT1 can dephosphorylate PtdIns(3,5)P 2 , PtdIns(3,4)P 2 , and PtdIns(5) P in vitro ( 81 ). Furthermore, PtdIns(5)P is not dephosphorylated in vivo by this enzyme ( 82 ), but rather phosphatidylglycerolphosphate is the physiological substrate ( 82,83 ); this is a lipid structurally very similar to PtdIns(5)P ( 84 ).…”

Cited2, a Transcriptional Modulator Protein, Regulates Metabolism in Murine Embryonic Stem Cells

“…Ectopic expression of UCP2 in human ESCs reduces glucose oxidation, impairs EB formation, and hampers early differentiation (32). Importantly, the mitochondrial metabolic stress-activated checkpoint in the control of ESC differentiation has been attributed to Ptpmt1 (proteintyrosine phosphatase, mitochondrial 1), a mitochondrial PTEN-like phosphatidylinositol phosphate phosphatase (29); enhanced aerobic glycolysis, decreased oxygen consumption, compromised mitochondrial fusion/dynamics, and blocked differentiation was observed in Ptpmt1 knock-out ESCs (29). This implicates mitochondria as the key player in ESC differentiation and metabolic reprogramming, which may represent a unique way to modulate the fate of ESCs.…”

“…Extinction difference between E1 and E2 was then used to calculate lactate concentration. The relative percentage of glucose metabolized to lactate was utilized for the assessment of glycolytic activity ( ATP Measurement-The total ATP content of ESCs was determined by using an adenosine 5Ј-triphosphate bioluminescent somatic cell assay kit (Sigma) as described elsewhere (29).…”

Cannabinoid receptor activation inhibits cell cycle progression by modulating 14-3-3β

“…These results suggest that CBR activation induces a G 2 /M-phase cell cycle delay in HeLa cells. We consider that this might ultimately induce inhibition of cell proliferation, since there is evidence that cell cycle delay correlates with anti-proliferation [28,29].…”