Insulin signaling in chick embryos exposed to alcohol

The avian embryo as a model for fetal alcohol spectrum disorder

Prenatal alcohol exposure (PAE) remains a leading preventable cause of structural birth defects and permanent neurodevelopmental disability. The chicken (Gallus gallus domesticus) is a powerful embryological research model, and was possibly the first in which the teratogenicity of alcohol was demonstrated. Pharmacologically relevant exposure to alcohol in the range of 20-70 mmol/L (20-80 mg/egg) disrupt the growth of chicken embryos, morphogenesis, and behavior, and the resulting phenotypes strongly parallel those of mammalian models. The avian embryo's direct accessibility has enabled novel insights into the teratogenic mechanisms of alcohol. These include the contribution of IGF1 signaling to growth suppression, the altered flow dynamics that reshape valvuloseptal morphogenesis and mediate its cardiac teratogenicity, and the suppression of Wnt and Shh signals thereby disrupting the migration, expansion, and survival of the neural crest, and underlie its characteristic craniofacial deficits. The genetic diversity within commercial avian strains has enabled the identification of unique loci, such as ribosome biogenesis, that modify vulnerability to alcohol. This venerable research model is equally relevant for the future, as the application of technological advances including CRISPR, optogenetics, and biophotonics to the embryo's ready accessibility creates a unique model in which investigators can manipulate and monitor the embryo in real-time to investigate the effect of alcohol on cell fate.

Increased intracellular localization of brain GLUT-1 transporter in response to ethanol during chick embryogenesis

Fetal exposure to ethanol is associated with growth retardation of the developing central nervous system. We have previously described a chick model to study the molecular mechanism of ethanol effects on glucose metabolism in ovo. Total membrane fractions were prepared from day 4, day 5, and day 7 chick embryos exposed in ovo to ethanol or to vehicle. By Western blotting analysis, ethanol exposure caused a mean 7- to 10-fold increase in total GLUT-1 and a 2-fold increase in total GLUT-3. However, glucose uptake by ethanol-treated cells increased by only 10%. Analysis of isolated plasma (PM) and intracellular (IM) membranes from day 5 cranial tissue revealed a mean 25% decrease in GLUT-1 in the PM and a 66% increase in the IM in the ethanol group vs. control. The amount of PM GLUT-3 was unchanged but that of IM GLUT-3 was significantly decreased. The data suggest that GLUT-3 cell surface expression may be resistant to the suppressive effects of ethanol in the developing brain of ethanol-treated embryos. The overall increase in GLUT-1 may reflect a deregulation of the transporter induced by ethanol exposure. The increased IM localization and decreased amount of PM GLUT-1 may be a mechanism used by the ethanol-treated cell to maintain normal glucose uptake despite the overall increased level of the transporter.

[The action of insulin in the morphogenesis of Gallus gallus domesticus embryos]

Aspects concerned with morphogenesis of Gallus gallus domesticus, avail studies related to the action of the insulin in the topography and embryonic structures. At the temperature of 37.5 degrees C, eggs were incubated during 24 h, injected with 5 ml of swine insulin in three concentrations and reincubated for more 72 h. The morphological characteristics of 80 embryos were evaluated and, according to the presented organization, classified in 5 morphogenetic levels. It was registered generalized dysmorphism (4th level) in 21 embryos that went through the tests with insulin. Standard morphogenesis (1st level) and located dysmorphism (3rd level) were verified among those from the control experiments. Those individuals concerned with the 4th level, showed reduced dimension of the body and were characterized by anterior-dorsal limits organized in a cephalic projection, and also presented alterations in the posterior-ventral region. These features evidence a pattern of abnormality in the determination of the cephalic-caudal axis and indicate a specific action of the insulin in the embryonic morphogenesis, in the period of 96 hours of incubation.

Changes in brain glucose levels and glucose transporter protein isoforms in alcohol- or nicotine-treated chick embryos

Suppression of fetal brain growth during pregnancy as the result of maternal smoking or alcohol consumption leads to significant problems for the offspring as well as for the society who must care for these individuals. Chronic maternal intake of cigarette smoke is frequently observed in humans and studies using animal models suggest that in utero nicotine exposure is an important component of the growth suppression that results. Similarly, maternal consumption of alcohol (ethanol) has a profound, negative effect on fetal growth. The developing fetal central nervous system (CNS) is sensitive to the growth inhibitory effect of nicotine or alcohol and morphological as well as functional CNS deficits may result from fetal exposure. Using an embryonic chick model which minimizes drug-induced changes in maternal nutrition and behavior, the studies presented here indicate that nicotine or alcohol exposure during early embryonic development inhibits brain growth to a degree comparable to that seen in the rest of the organism, i.e., there was no 'brain sparing' in this model. Glucose content per milligram tissue was markedly decreased in brains of the nicotine-treated embryos but was not significantly different in the alcohol-exposed embryos. Western blots of fetal brain glucose transporter protein isoforms showed no change in the Glut 3 transporter content in the growth suppressed brains compared to vehicle-treated brains. The Glut 1 55 kilodalton (kd) isoform protein content was significantly decreased in the nicotine-treated brains but unchanged in the ethanol-treated brains, while the reverse was true for the Glut 1 45 kd isoform. Thus, the changes in the 55 kd isoform protein content were correlated with tissue glucose levels in the ethanol- and nicotine-treated embryos.

Ethanol differentially affects metabolic and mitotic processes in chick embryonic cells

Our laboratory has been investigating the mechanisms by which ethanol-induced growth inhibition occurs in a developing embryo, and our studies have focused on disruption of cellular signaling pathways. Previous work on ethanol-induced changes in signaling systems that regulate ornithine decarboxylase activity indicated that the pathways containing protein kinase A, protein kinase C (PKC), and insulin-dependent tyrosine kinase were important for the control of ornithine decarboxylase in chick embryonic cells. Herein, we report ethanol's effect on the regulation of glucose uptake and thymidine uptake by these same kinase pathways. A pronounced increase in glucose uptake was associated with PKC downregulation in both vehicle- and ethanol-exposed cells, with the larger increase occurring in ethanol-exposed cells. An increase in thymidine uptake was associated with an activation of all three kinases, as well as with downregulation of PKC. Because previous work on signaling pathways has looked for changes in the insulin signaling pathway, the work herein focuses on the signaling pathways involving protein kinase A and PKC. cAMP levels were increased by ethanol treatment, but the increase was relatively small. Analysis of changes in PKC activity induced by ethanol exposure showed a significant suppression of PKC activity in the ethanol-treated cells and suggested that, overall, ethanol treatment affects the regulation of glucose uptake in embryonic cells predominantly by PKC downregulation.

Increase in vasoactive prostaglandin E production after perfusion in human placental cotyledons

Studies from our laboratory indicate that prostaglandins may be mediators of at least some of the teratogenic actions of ethanol in both mouse and human tissue model systems. The present studies were designed to evaluate the relationship between ethanol and prostaglandin E (PGE) production in isolated human placental cotyledons. Placentas were obtained immediately after cesarean section delivery. A fetal artery supplying a single cotyledon was identified and cannulated, and the isolated cotyledon was placed in a perfusion chamber where maternal circulation was established and dual circulation continued throughout the perfusion procedure. Antipyrine clearance, oxygen consumption, and placental production of human chorionic gonadotropin were measured to verify tissue viability. PGE levels of the perfusate were measured by radioimmunoassay. Study 1 evaluates the effect of perfusion with 25 and 100 mM ethanol on placental PGE production. It was found that PGE production increased after perfusion with 25 mM ethanol, but not during the perfusion period per se. The paradigm for study 2 was identical to that of study 1, with the addition of a buffer washout period after 100-mM ethanol perfusion. Again, results indicate that perfusate PGE levels were increased in the buffer washout periods after the 25-mM and the 100-mM ethanol perfusions. The effect was not concentration dependent. An increase in circulating PGE associated with ethanol administration may be teratogenic actions and represent a potential mechanism underlying at least some aspects of fetal alcohol syndrome.