Early foetal programming of hepatic gluconeogenesis: Glucocorticoids strike back

Epigenetic changes of hepatic glucocorticoid receptor in sheep male offspring undernourished in utero

The aim of this study was to characterise the effects of maternal undernutrition during gestation on hepatic gluconeogenic enzyme gene expression and to determine whether such effects are mediated through epigenetic changes in the glucocorticoid receptor (GR). Pregnant ewes were fed a 50% nutrient-restricted diet from Day 0 to 30 (R1) or from Day 31 to 100 of gestation (R2) or a 100% diet throughout gestation (Control). After parturition lambs were fed to appetite. At 10 months of age offspring were euthanised and livers were removed. Maternal undernutrition did not affect offspring bodyweight at birth or at 10 months of age. However, liver weight of males of the R2 group was lower (P<0.05) in relation to other groups. A significant (P<0.05) hypomethylation of the hepatic GR promoter was revealed in males of the R2 group and a tendency towards the same in the R1 group, along with increased (P<0.001) GR gene expression in both restricted groups. A significant increase (P<0.05) in hepatic phosphoenolpyruvate carboxykinase (PEPCK) gene expression was found in male lambs of both undernourished groups, accompanied by increased (P<0.01) protein levels, while no differences were detected for glucose-6-phosphatase (G6Pase) mRNA abundance and protein levels. In female lambs, no differences between groups were observed for any parameter studied. These data represent potential mechanisms by which insults in early life may lead to persistent physiological changes in the offspring.

H19 lncRNA alters methylation and expression of Hnf4α in the liver of metformin-exposed fetuses

Metformin is the most widely used anti-diabetic medication worldwide. However, human and animal studies suggest that prenatal metformin exposure may increase the risk of metabolic disorders in adult offspring, yet the underpinning mechanism remains unclear. Here we report that metformin-exposed mouse fetuses exhibit elevated expression of the H19 long noncoding RNA, which induces hypomethylation and increased expression of hepatocyte nuclear factor 4α (HNF4α). As a transcription factor essential for morphological and functional differentiation of hepatocytes, HNF4α also has an indispensable role in the regulation of expression of gluconeogenic genes. Consistently, H19 overexpression in a human liver cell line leads to decreased methylation and increased expression of Hnf4α, with concomitant activation of the gluconeogenic program. Mechanistically, we show that the methylation change of Hnf4α is induced by H19-mediated regulation of S-adenosylhomocysteine hydrolase. We also provide evidence that altered H19 expression is a direct effect of metformin in the fetal liver. Our results suggest that metformin from the mother can directly act upon the fetal liver to modify Hnf4α expression, a key factor for both liver development and function, and that perturbation of this H19/Hnf4α-mediated pathway may contribute to the fetal origin of adult metabolic abnormalities.

Energy metabolism in the newborn farm animal with emphasis on the calf: endocrine changes and responses to milk-born and systemic hormones

Neonatal mammals need adaption to changes in nutrient supply because energy intake shifts from continuous parenteral supply of nutrients (mainly glucose, lactate, and amino acids) via the placenta to discontinuous colostrum and milk intake with lactose and fat as main energy sources. Besides ingested lactose, endogenous glucose production is essential in the neonate to assure sufficient glucose availability. Fetal endogenous glucose production is low, but endocrine changes (especially the prenatal rise of glucocorticoid production) promote maturation of metabolic pathways that enable marked glycogen synthesis before and enhanced gluconeogenesis after birth to establish an adequate glucose status during postnatal maturation. In preterm born farm animals gluconeogenic activity is low, mainly because of a low glucocorticoid and thyroid status. In full-term neonates, endogenous glucose production increases with age. Colostral bioactive components (such as growth factors, hormones, bioactive peptides, and cytokines) do not have a direct effect on endogenous glucose production. However, colostrum feeding stimulates intestinal growth and development, an effect at least in part mediated by bioactive substances. Increased nutrient and glucose absorption thus allows increased glucose supply and hepatic glycogen storage, which improves the glucose status. The improved energetic status of colostrum-fed neonates is reflected by an accelerated maturation of the somatotropic axis, leading especially to enhanced production of IGF-I in the neonate. Secretion and production of hormones involved in the regulation of glucose and fat metabolism in neonates depend on the developmental stage and the response to feeding. In addition, many such hormones have actions in the neonate that differ from adult animals. Endocrine action to support endogenous energy supply in neonates is probably not fully established, and therefore, needs postnatal maturation. Therefore, our knowledge on energy metabolism in the neonate needs to be extended to better understand the function and the failure and to assess endocrine responses during the neonatal period.

Maturation of endogenous glucose production in preterm and term calves

Glucose disposability is often impaired in neonatal calves and even more in preterm calves. The objective of this study was to investigate ontogenic maturation of endogenous glucose production (eGP) in calves and its effects on postnatal glucose homeostasis. Calves (n = 7 per group) were born preterm (PT; delivered by section 9 d before term) or at term (T; spontaneous vaginal delivery), or spontaneously born and fed colostrum for 4 d (TC). Blood samples were taken immediately after birth and before and 2h after feeding at 24h after birth (PT; T) or on d 4 of life (TC) to determine metabolic and endocrine changes. After birth (PT and T) or on d 3 of life (TC), fasted calves were gavaged with deuterium-labeled water to determine gluconeogenesis (GNG) and intravenously infused with [U(13)C]-glucose to measure eGP and glucose oxidation (GOx) in blood plasma. After slaughter at 26h after birth (PT, T) or on d 4 of life (TC), glycogen concentrations in liver and hepatic mRNA concentrations and enzyme activities of pyruvate carboxylase, phosphoenolpyruvate carboxykinase (PEPCK), and glucose-6-phosphatase were measured. Preterm calves had the lowest plasma concentrations of cortisol and 3,5,3'-triiodothyronine at birth. Plasma glucose concentrations from d 1 to 2 decreased more, but plasma concentrations of lactate and urea and glucagon:insulin ratio were higher in PT than in T and TC calves. The eGP, GNG, GOx, as well as hepatic glycogen concentrations and PEPCK activities, were lowest in PT calves. Results indicate impaired glucose homeostasis due to decreased eGP in PT calves and maturation of eGP with ontogenic development.

Effects of ewe size and nutrition during pregnancy on glucose metabolism, fat metabolism and adrenal function of postpubertal female twin offspring

Little is known about the long-term metabolic effects of maternal constraint on the offspring and whether a possible interaction of dam size and nutrition during gestation exists, affecting postnatal metabolic functions in the offspring. Four hundred and fifty heavy (H) (60.8 ± 0.18 kg) and 450 light (L) (42.5 ± 0.17 kg) Romney dams were allocated to ad libitum (A) or maintenance (M) nutritional regimens under New Zealand pastoral grazing conditions, from Day 21 to 140 after insemination. One week before lambing, all dams and offspring were managed as one group and provided with ad libitum feeding. At 16 months of age, female twin-born offspring (n = 12 per size by nutrition group) were catheterised and given intravenous insulin (0.15 IU/kg) (ITT), glucose (0.17 g/kg) (GTT) and epinephrine (1 μg/kg) (ETT) challenges to assess their glucose and fat metabolism and adrenal function. No effects of dam size or interactions between dam size and dam nutrition were found on glucose or fat metabolism or adrenal function. In response to the ETT, M-dam offspring showed greater (P < 0.05) peak glucose concentrations, increased (P < 0.05) glucose area under the curve and tended (P < 0.10) to have increased maximum change in glucose and non-esterified free fatty acid concentrations compared with A-ewes. No effects of dam nutrition were found on glucose tolerance, insulin resistance or adrenal function in response to GTT and ITT. In conclusion, dam size had no effect on glucose metabolism, adrenal function or fat metabolism in 16-month-old female twin offspring. Dam nutrition during pregnancy from Day 21 to 140 had no major effect on glucose metabolism, adrenal function or lipolysis; however, it did potentially affect gluconeogenesis and/or glycogenolysis, as increased glucose concentrations in ewes born to M-fed dams were observed in response to ETT. These results indicate that M-ewes could have an advantage over A-ewes in physiological stressful situations in life (e.g. pregnancy, lactation) as their liver may be able to supply more glucose to support their growing conceptus and milk production to increase the chances of survival of their offspring.

Maternal high-fat diet triggers lipotoxicity in the fetal livers of nonhuman primates

Maternal obesity is thought to increase the offspring's risk of juvenile obesity and metabolic diseases; however, the mechanism(s) whereby excess maternal nutrition affects fetal development remain poorly understood. Here, we investigated in nonhuman primates the effect of chronic high-fat diet (HFD) on the development of fetal metabolic systems. We found that fetal offspring from both lean and obese mothers chronically consuming a HFD had a 3-fold increase in liver triglycerides (TGs). In addition, fetal offspring from HFD-fed mothers (O-HFD) showed increased evidence of hepatic oxidative stress early in the third trimester, consistent with the development of nonalcoholic fatty liver disease (NAFLD). O-HFD animals also exhibited elevated hepatic expression of gluconeogenic enzymes and transcription factors. Furthermore, fetal glycerol levels were 2-fold higher in O-HFD animals than in control fetal offspring and correlated with maternal levels. The increased fetal hepatic TG levels persisted at P180, concurrent with a 2-fold increase in percent body fat. Importantly, reversing the maternal HFD to a low-fat diet during a subsequent pregnancy improved fetal hepatic TG levels and partially normalized gluconeogenic enzyme expression, without changing maternal body weight. These results suggest that a developing fetus is highly vulnerable to excess lipids, independent of maternal diabetes and/or obesity, and that exposure to this may increase the risk of pediatric NAFLD.