Powell, T., Lager, S., Aye, I., Gaccioli, F., Fredrick, R., and Jansson, T.
Nearly two-thirds of American women enter pregnancy overweight or obese and the prevalence of maternal overweight and obesity is increasing rapidly in many other countries, including the UK. The obese mother is at higher risk for many pregnancy complications and fetal overgrowth is common in these pregnancies. Fetal overgrowth increases the risk for perinatal complications and predisposes the child for obesity, diabetes and hypertension later in life. The mechanisms underlying increased fetal growth in overweight and obese women are poorly understood. Since fetal growth largely depends on the transfer of nutrients across the placenta, we hypothesize that altered placental function in obese women may lead to fetal overgrowth and its' associated long term health consequences. We are exploring the role of altered maternal metabolism associated with obesity in regulating placental nutrient transport. The placenta, uniquely juxtapositioned between the maternal and fetal blood supplies, must integrate both maternal supply and fetal demand signals. In cases of maternal obesity the signals impinging on the placenta are diverse and include high levels of macronutrients (glucose, amino acids, fatty acids), hyperinsulinemia, elevated adipokines (leptin, TNF-alpha, IL1-beta) and low levels of adiponectin. We evaluated alterations in placental nutrient transport capacity and multiple placental signaling pathways including 1) Toll Like Receptor 4 (TLR4), 2) insulin/IGF-I 3) mammalian target of rapamycin and 4) PPARs in term placentas from women of varying pre-pregnant body mass index (BMI). We found mTOR and inflammasome pathway activation, decreased PPARgamma activation and increased expression of amino acid and fatty acid transporters in placentas of high BMI women. Additionally, we developed a model of obesity without diabetes in mice based on feeding a highly palatable high-fat and high-sugar diet. The maternal metabolic phenotype resembles that of obese women with increased leptin and decreased adiponectin. Our model results in increased fetal growth and the placentas of obese mice were found to have an activation of insulin/IGF-I and mTOR signaling and a greater nutrient transport capacity. We used cultured primary human trophoblast cells to directly study regulation of placental nutrient transporters and demonstrated that saturated and monounsaturated fatty acids stimulate trophoblast System A amino acid uptake in a TLR4 dependent manner while omega3 long chain polyunsaturated fatty acids inhibit amino acid uptake by System A. Insulin, leptin and pro-inflammatory cytokines also increased trophoblast amino acid uptake. These data suggest that in obese mothers with high leptin, insulin resistance, and chronic proinflammatory activation, the placenta is stimulated by the maternal metabolic environment to deliver excess nutrients to the fetus. Adiponectin is insulin sensitizing in some tissues however elevated adiponectin, a feature of lean women, inhibits placental insulin signaling at the level of IRS-1 in cultured trophoblast cells. This would tend to decrease amino acid uptake in normal healthy pregnancies. In contrast, low adiponectin, which is associated with obesity, would promote insulin stimulated amino acid transfer across the placenta. Our experiments in cultured trophoblast cells indicate that adiponectin treatment leads to PPARalpha and p38 MAPK activation and increased ceramide biosynthesis, resulting in decreased insulin sensitivity. Additionally, we performed chronic infusion of full-length adipoenctin in normal mice and found an inhibition of placental insulin/IGF-I and mTOR signaling along with decreased fetal growth (-20%). These studies have identified mechanistic links between the perturbed maternal metabolism in pregnancies complicated by obesity and changes in placental signaling and nutrient transport capacity that likely lead to increased nutrient delivery to the fetus. We have discovered that adiponectin constitutes an endocrine link between maternal adipose tissue and placental function, supporting our hypothesis that the maternal metabolic environment is of key importance in regulating placental function. The role of the placenta in integrating signals from both the mother and fetus involves a complex interaction of extrinsic signals such as hormones, cytokines, maternal nutrient and energy levels with intrinsic placental signaling pathways for nutrient sensing, inflammation, and growth. Understanding the complex placental signaling pathways that lead to alterations in fetal growth will allow for the development of strategies to prevent short- and long-term health consequences of pathological fetal growth. [ABSTRACT FROM AUTHOR]