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According to the “developmental origin of health and disease” hypothesis, the metabolic set points of glucose and lipid metabolism are determined prenatally. In the case of a diabetic pregnancy, the embryo is exposed to higher glucose and lipid concentrations as early as during preimplantation development. We used the rabbit to study the effect of maternal diabetes type 1 on lipid accumulation and expression of lipogenic markers in preimplantation blastocysts. Accompanied by elevated triglyceride and glucose levels in the maternal blood, embryos from diabetic rabbits showed a massive intracellular lipid accumulation and increased expression of fatty acid transporter 4, fatty acid–binding protein 4, perilipin/adipophilin, and maturation of sterol-regulated element binding protein. However, expression of fatty acid synthase, a key enzyme for de novo synthesis of fatty acids, was not altered in vivo. During a short time in vitro culture of rabbit blastocysts, the accumulation of lipid droplets and expression of lipogenic markers were directly correlated with increasing glucose concentration, indicating that hyperglycemia leads to increased lipogenesis in the preimplantation embryo. Our study shows the decisive effect of glucose as the determining factor for fatty acid metabolism and intracellular lipid accumulation in preimplantation embryos.

Intoxication by dioxins such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) leads, among other damages, to early embryo loss, fetal malformations, and cardiovascular toxicity. Apart from binding to the arylhydrocarbon receptor (AhR), the mechanism of TCDD-mediated embryo toxicity is still unclear. We investigated possible modes of a TCDD-mediated toxicity, particularly in glucose metabolism, in pluripotent P19 mouse embryonic carcinoma cells. Undifferentiated P19 cells were exposed to 1–100 nm TCDD and characterized for AhR signaling. For studying cell differentiation, P19 cells were exposed to 10 nm TCDD at stage of embryoid body formation, and analyzed on glucose metabolism and cardiac differentiation during the next 3 wk. TCDD treatment activated the AhR-signaling cascade within 1 h, confirmed by AhR translocation, induction of cytochrome P450 1A1 expression, and activation of the xenobiotic response element. Although cell viability and transcription of the cardiac marker protein α-myosin heavy chain were affected, TCDD did not inhibit the differentiation of P19 cells to pulsating cardiomyocytes. TCDD significantly down-regulated the expression levels of the glucose transporter (GLUT) isoforms 1 and 3. After 24-h TCDD treatment, GLUT1 was no longer localized in the plasma membrane of P19 cells. The impaired GLUT expression correlated with a lower glucose uptake in 5-d-old embryoid bodies. The TCDD effects were mediated by AhR, as shown by preculture with the AhR antagonist α-naphthoflavone. Our data demonstrate that an AhR-mediated disturbance in GLUT expression and insufficient glucose uptake may be major mechanisms in TCDD embryo toxicity.

The insulin/IGF system plays a critical role in embryo growth and development. We have investigated the expression of insulin receptor (IR) and IGF-I receptor (IGF-IR) and the activation of their downstream pathways in rabbit 6-d-old blastocysts. IR was expressed in embryoblast (Em, inner cell mass) and trophoblast (Tr) cells, whereas IGF-IR was localized mainly in Em. Isoform A (IR-A) represents the main insulin isoform in blastocysts and was found in Em and Tr cells. IR-B was detectable only in Tr. IR/IGF-IR signaling pathways were analyzed after stimulation with insulin (17 nm) or IGF-I (1.3 nm) in cultured blastocysts. Insulin stimulated Erk1/2 in Em and Tr and Akt in Tr but not in Em. IGF-I activated both kinases exclusively in Em. The target genes c-fos (for MAPK kinase-1/Erk signaling) and phosphoenolpyruvate carboxykinase (PEPCK, for PI3K/Akt signaling) were also specifically regulated. Insulin down-regulated PEPCK RNA amounts in Tr by activation of the phosphatidylinositol 3-kinase/Akt pathway. Expression of c-fos by insulin and IGF-I was different with respect to time and fortitude of expression, mirroring again the specific IR and IGF-IR expression patterns in Em and Tr. Taken together, we show that IGF-I acts primarily mitogenic, an effect that is cell lineage-specifically restricted to the Em. By contrast, insulin is the growth factor of the Tr stimulating mitogenesis and down-regulating metabolic responses. As soon as blastocyst differentiation in Em and Tr has been accomplished, insulin and IGF-I signaling is different in both cell lineages, implying a different developmental impact of both growth factors.