The human placenta, a tissue primarily of fetal origin, is the critical maternal/fetal interface. Fetal growth and development depend upon normal placental function. Chronic ethanol abuse during pregnancy causes impaired fetal growth and development, a characteristic of the Fetal Alcohol Syndrome. Ethanol which freely crosses the placenta, has direct effects upon the fetus, but adversely affects placental function as well. The mechanisms by which ethanol diminishes tissue growth and alters cellular physiologic function are incompletely understood. In the placenta, one mechanism may be interference with the action of insulin (insulin) and insulin like growth factor 1 (IGF-1). Placental trophoblasts (like other fetal tissues) are responsive to insulin and IGF-1. Impairment of these hormone response systems would alter placental function. To better understand mechanisms for the cellular and molecular effects of ethanol, experiments are proposed to evaluate the action of ethanol on insulin and IGF-1 signal transduction. Using cultured human trophoblasts (normal first trimester, term, and choriocarcinoma) we will assess the effect of ethanol upon insulin and IGF-1 receptor concentrations and affinity; receptor tyrosine kinase; expression and tyrosyl phosphorylation of human insulin receptor substrate-1 (IRS-1); association of IRS-1 with other cell proteins; IRS-1 tyrosyl phosphorylation in relation to activation of Pl-3 kinase and Ras. To complement these studies we will evaluate several downstream physiologic responses to insulin and IGF-1 signal transduction, such as DNA synthesis; amino acid uptake; upregulation of the insulin responsive gene, glyceraldehyde-3-phosphate dehydrogenase (GAPDH); production and secretion of IGF-1 and IGF-1 binding proteins in response to insulin. In preliminary studies, the presence of several sequential components of insulin mediated signal transduction have been demonstrated in human placenta trophoblasts; this is coupled with ethanol induced reduction in amino acid uptake by cultured trophoblasts (in response to both insulin and IGF-1) and diminished IRS-1 tyrosyl phosphorylation. These data strongly suggest that ethanol interferes with insulin/IGF-1 signal transduction. The studies should provide important information on the molecular effects of ethanol on placental function and, hence, advance our understanding of the pathophysiology of the Fetal Alcohol Syndrome. The findings should also contribute to the general understanding of the mechanisms by which ethanol affects the biology of many human tissues, including those of the fetus.
