Effects of glucose and fatty acids on human trophoblasts in primary culture

Abstract

Background: Diabetes in pregnancy is a major cause of maternal and neonatal complications, which also places the new born at risk of developing metabolic syndrome in adult life. Dyslipidaemia often accompanies hyperglycaemia in diabetic pregnancy. Hyperglycaemia has been shown to enhance the toxic effects of fatty acids in other tissues, a process termed glucolipotoxicity. Glucolipotoxicity therefore could contribute to the adverse outcomes of diabetic pregnancy, particularly if it were to occur at the feto-placental interphase. The aim of this study was to characterise the effects of elevated glucose, elevated fatty acids and their interactions on human trophoblast metabolism, function and morphology. Experimental approach: Human trophoblasts were isolated from term, normal placentae and established in culture over 16 h prior to experiments. Assessments of trophoblasts were carried out following their short and long-term exposure to various concentrations of glucose and fatty acids. Metabolic studies were carried out using radio-labeled tracers to determine the rates of glucose utilization, fatty acid oxidation and fatty acid esterification. Morphological changes examined were formation of lipid droplets, cell aggregation and syncytialisation. Cell viability, proliferation and apoptosis were assessed. Secretory function was assessed by measuring the levels of hormones and cytokines secreted into the culture media. Results: Glucose utilisation via glycolysis was near maximal at a low glucose concentration of 4 mM and maximal at 8 mM glucose. Esterification of fatty acids into triacylglycerols and diacylglycerols increased with increasing fatty acid levels without showing any evidence of plateau. Furthermore, pre-incubation of trophoblasts in fatty acids for 24 h caused up-regulation of fatty acid esterification and down-regulation of fatty acid oxidation and lipolysis processes. Trophoblasts avidly formed lipid droplets when exposed to fatty acids, however, their accumulation appeared to be less in cells cultured at 10 mM compared to 1 mM glucose. Fatty acids promoted trophoblast aggregation and syncytia formation and enhanced the secretion of TNF-alpha and IL-1beta. Elevated glucose did not alter trophoblast metabolism and function significantly except to increase glycogen accumulation as seen by electron microscopy. Glucose, fatty acids or their combination did not affect cell viability, apoptosis or hormone secretory function. Conclusions: The finding that fatty acids enhance their own storage into lipid droplets is indicative of up-regulation of a buffering mechanism to protect the fetus from excess lipid. The novel findings that fatty acids promote syncytialisation and cytokine production may be indicative of harmful effects of dyslipidaemia via effects on placental structure and inflammation. It was remarkable how little effect glucose had on trophoblasts compared to the effects of fatty acids. Glucose did not alter fatty acid partitioning as was predicted by the glucolipotoxicity hypothesis. Dyslipidaemia, therefore, may have greater pathogenic significance than hyperglycaemia at the level of trophoblast in diabetic pregnancy. Show more