The hyperglycemia of maternal diabetes suppresses the glucose transporter-1 (GLUT1) facilitative glucose transporter 49 -66% in preimplantation embryos. Glucose uptake is reduced and apoptosis is activated. We hypothesized that the reduction of embryonic GLUT1 may play a key role in the malformations of diabetic embryopathy. Therefore, we produced GLUT1-deficient transgenic mice [i.e., antisense-GLUT1 (GT1AS)] to determine whether GLUT1 deficiency alone could reproduce the growth defects. Early cell division of fertilized mouse eggs injected with GT1AS was markedly impaired, P < 0.001 vs. controls. Two populations of preimplantation embryos obtained from GT1AS ؋ GT1AS heterozygote matings exhibited reduction of the 2-deoxyglucose uptake rate: one by 50% (presumed heterozygotes, P < 0.001 vs. control) and the other by 95% (presumed homozygotes, P < 0.001 vs. heterozygotes). Embryonic GLUT1 deficiency in the range reported with maternal diabetes was associated with growth retardation and developmental malformations similar to those described in diabetes-exposed embryos: intrauterine growth retardation (31.1%), caudal regression (9.8%), anencephaly with absence of the head (6.6%), microphthalmia (4.9%), and micrognathia (1.6%). Reduced body weight (small embryos, <70% of the nontransgenic body weight) was accompanied by other malformations and a 56% reduction of GLUT1 protein, P < 0.001 vs. nonsmall embryos (body weight >70% normal). The heart, brain, and kidneys of embryonic day 18.5 GT1AS embryos exhibited 24 -51% reductions of GLUT1 protein. The homozygous GT1AS genotype was lethal during gestation. Reduced embryonic GLUT1 was associated with the appearance of apoptosis. Therefore, GLUT1 deficiency may play a role in producing embryonic malformations resulting from the hyperglycemia of maternal diabetes. Late gestational macrosomia was absent, apparently requiring a different mechanism.embryo ͉ antisense ͉ transgenic ͉ development ͉ apoptosis

Glucose transporter protein type 1 (GLUT1) is a major glucose transporter of the fertilized egg and preimplantation embryo. Haploinsufficiency for GLUT1 causes the GLUT1 deficiency syndrome in humans, however the embryo appears unaffected. Therefore, here we produced heterozygous GLUT1 knockout murine embryonic stem cells (GT1؉/؊) to study the role of GLUT1 deficiency in their growth, glucose metabolism, and survival in response to hypoxic stress. GT1(؊/؊) cells were determined to be nonviable. Both the GLUT1 and GLUT3 high-affinity, facilitative glucose transporters were expressed in GT1(؉/؉) and GT1(؉/؊) embryonic stem cells. GT1(؉/؊) demonstrated 49 ؎ 4% reduction of GLUT1 mRNA. This induced a posttranscriptional, GLUT1 compensatory response resulting in 24 ؎ 4% reduction of GLUT1 protein. GLUT3 was unchanged. GLUT8 and GLUT12 were also expressed and unchanged in GT1(؉/؊). Stimulation of glycolysis by azide inhibition of oxidative phosphorylation was impaired by 44% in GT1(؉/؊), with impaired up-regulation of GLUT1 protein. Hypoxia for up to 4 hours led to 201% more apoptosis in GT1(؉/؊) than in GT1(؉/؉) controls. Caspase-3 activity was 76% higher in GT1(؉/؊) versus GT1(؉/؉) at 2 hours. Heterozygous knockout of GLUT1 led to a partial GLUT1 compensatory response protecting nonstressed cells. However, inhibition of oxidative phosphorylation and hypoxia both exposed their increased susceptibility to these stresses.