PRECOMPACTION MOUSE EMBRYOS SHOW METABOLIC PLASTICITY BY UPREGULATING GLUT1 EXPRESSION UNDER ANOXIC CONDITIONS.

Precompaction embryos essentially utilize aerobic respiration rather than anaerobic glycolysis for energy production. They do not use glucose because the phosphofructokinase (Pfk) enzyme is inhibited, and glucose transporter proteins (Gluts) are not located in the cell membrane. Cells use anaerobic glycolysis only in the absence of O2. In contrast, cancer cells prefer to use glycolysis by shifting their metabolism from oxidative phosphorylation to aerobic glycolysis by up-regulating Hif-1 (hypoxia-inducible factor) expression of Glut1 and Pfk under hypoxic conditions. Similar pathways also regulate Hif-1 mediated metabolic switch in the blastocyst. However, it is not known whether this metabolic switch can also occur in precompaction embryos. The purpose of this study was to investigate the potential of metabolic plasticity in mouse precompaction embryos under anoxic conditions by up-regulating their membranous Glut1 expression. Two-cell embryos obtained from Balb/c mice were distributed into control (5% O2), chemical anoxia (using FCCP as a mitochondrial uncoupler), and anoxia (0% O2) groups. Around 75 embryos were used in each group. Two cell, 4 cell, 8 cell embryos, morula, and blastocyst were evaluated for their developmental potency at 6th, 12th, 24th, 36th, and 60th hours. Mitochondrial activity and mitochondrial membrane potential (MMP) of the embryos were determined by assessing the autofluorescence FAD level and Rhodamine/Mitotracker ratio using confocal microscopy. The distribution pattern of Glut1 was determined by immunofluorescence. Comparisons between groups were performed by t-test. P values <0.05 were considered as statistically significant. In the chemical anoxia group, 100% of 4 cell embryos, morula, and blastocyst and 91,6% of 8 cell embryos underwent at least 2-3 cell divisions. In the anoxia group, 35,7% of 4 cell embryos, 76,9% of 8 cell embryos, 66,6% of morula, and 50% of blastocyst underwent at least 2-3 cell divisions. FAD levels increased significantly in 2 cell, 4 cell, and 8 cell embryos in the anoxia groups. MMP decreased significantly in 4 cell embryos in the chemical anoxia group. FAD and MMP levels decreased significantly in morula embryos in the anoxia group. MMP levels decreased significantly in blastocysts in the chemical anoxia group. FAD levels decreased significantly in blastocysts in both anoxia groups. Glut1 was found up-regulated in the cell membrane of precompaction embryos under anoxic conditions. Precompaction mouse embryos can show metabolic plasticity by up-regulating Glut1 expression under anoxic conditions. Moreover, FAD levels can be used as a non-invasive technique to reveal detailed information about mitochondria during the development of the preimplantation embryos.