Cellular-tissue localization and regulation of the GLUT-1 protein in both the embryo and the visceral yolk sac from normal and experimental diabetic rats during the early postimplantation period.

Abstract

We investigated the tissue-specific developmental expression and localization of GLUT-1 protein in the rat embryo and visceral yolk sac (VYS) during the organogenic periods of normal rats. The expression of GLUT-1 protein was then compared to that of experimental diabetic rats to test whether the diabetic state would affect the regulation of the glucose transporter during the early postimplantation periods (9.5-14.5 days), as we have previously demonstrated that GLUT-1 protein in embryo and VYS was down-regulated in culture with hyperglycemic medium. In the embryo, GLUT-1 protein was highly expressed during the early stages of organogenesis (between 9.5-12.5 days) and declined thereafter, whereas in the VYS, its strong expression was observed at the later stages (from 12.5-14.5 days). Immunohistochemical localization of the GLUT-1 protein in the embryo during the main periods of neurulation (9.5-11.5 days) showed that GLUT-1 immunoreactivity was principally observed in the neuroepithelial cells of the neural tube and also noted in the primitive heart, primitive gut, otic, and optic vesicles. At 12.5 days, GLUT-1 protein started to be expressed in the microvessels at the cranial portions of the neural tube, although its expression in the neuroepithelial cells still remained at the caudal (tail) portions of the neural tube. In the later stages (13.5-14.5 days) after completion of neural tube formation, GLUT-1 protein immunoreactivity substantially decreased in the neuroepithelial cells and was found mainly in the microvessels of the brain vesicles and spinal cord, whereas it continued to be expressed in the heart and eyes. In the VYS, its immunoreactivity was noticeably confined to the endodermal layer, which started as a simple layer and developed wave-like folds in the later stages. The levels of GLUT-1 protein in embryo and VYS from diabetic rats, determined by Western blot analysis, were not down-regulated compared to those in control rats at the different gestational days. Likewise, comparison of GLUT-1 protein immunoreactivity of various tissues in embryo and VYS, focusing on the neural tube, also revealed no significant differences between the two groups. We demonstrated that GLUT-1 protein is abundantly expressed in embryonic tissues and VYS during the early periods of organogenesis. The lack of down-regulation and the continuous abundant expression of the GLUT-1 protein despite the diabetic state in embryo and VYS during the early postimplantation periods may increase delivery of glucose from the VYS into various differentiating embryonic cells, leading to diabetes-induced congenital malformations.

Expression of the gene encoding the high-K m glucose transporter 2 by the early postimplantation mouse embryo is essential for neural tube defects associated with diabetic embryopathy

“…Expression of Glut1, Glut2 and Glut3 is suppressed in preimplantation embryos of diabetic mice [46], and expression of Glut1 has been found to be both unchanged or suppressed by maternal diabetes or highglucose culture in postimplantation embryos [21,22]. However, in the present study, expression of Glut2 was unaffected by maternal diabetes.…”

“…However, expression had not been examined during diabetic pregnancy. Whereas expression of Glut1 and Glut3 is not downregulated during maternal hyperglycaemia in the postimplantation embryo [21,22], expression of Glut1, Glut2 and Glut3 has been found to be downregulated by high glucose concentration in the preimplantation embryo [46]. Glut2 mRNA was assayed in embryos recovered on day 7.5, the day of embryonic development that is susceptible to subsequent development of NTD in response to maternal hyperglycaemia [34].…”

“…GLUT12 protein is not detected in early postimplantation embryos, but it is detected later, during fetal development [17,19]. Only expression of Glut1, Glut2 and Glut3 has been detected during the stage of postimplantation development that is susceptible to diabetic embryopathy (day 7.5) [12,13,[20][21][22][23]. Glut1 is expressed primarily in the ectoplacental cone, amnion, chorion and mesodermal layer of the yolk sac, and lower levels are expressed in the embryonic ectoderm.…”

“…Thus, during normal, non-diabetic gestation, glucose transporters with a low K m (high affinity) would transport glucose into the embryo cells more efficiently than the GLUT2 transporter. There have been some reports that GLUT1 and GLUT3, which are produced in the postimplantation embryo during early organogenesis, are not downregulated during exposure to a hyperglycaemic environment, and so could continue to transport glucose even during maternal hyperglycaemia [21,22]. However, the rate of glucose transport by GLUT1 and GLUT3 would saturate during hyperglycaemia.…”

Increased mRNA levels of Mn-SOD and catalase in embryos of diabetic rats from a malformation-resistant strain.

“…downregulated in embryonic tissues despite exposure to a diabetic environment (51), and pyruvate uptake inhibitors decrease glucose-induced malformations in vitro (17). Embryonic rat mitochondria also show high-amplitude swelling in diabetic pregnancy, a phenomenon prevented by maternal antioxidant treatment (52).…”