Challenges in nourishing the intrauterine growth-restricted foetus - Lessons learned from studies in the intrauterine growth-restricted foetal sheep

Mitochondrial respiration is lower in the intrauterine growth-restricted fetal sheep heart

Fetuses affected by intrauterine growth restriction have an increased risk of developing heart disease and failure in adulthood. Compared with controls, late gestation intrauterine growth-restricted (IUGR) fetal sheep have fewer binucleated cardiomyocytes, reflecting a more immature heart, which may reduce mitochondrial capacity to oxidize substrates. We hypothesized that the late gestation IUGR fetal heart has a lower capacity for mitochondrial oxidative phosphorylation. Left (LV) and right (RV) ventricles from IUGR and control (CON) fetal sheep at 90% gestation were harvested. Mitochondrial respiration (states 1-3, LeakOmy, and maximal respiration) in response to carbohydrates and lipids, citrate synthase (CS) activity, protein expression levels of mitochondrial oxidative phosphorylation complexes (CI-CV), and mRNA expression levels of mitochondrial biosynthesis regulators were measured. The carbohydrate and lipid state 3 respiration rates were lower in IUGR than CON, and CS activity was lower in IUGR LV than CON LV. However, relative CII and CV protein levels were higher in IUGR than CON; CV expression level was higher in IUGR than CON. Genes involved in lipid metabolism had lower expression in IUGR than CON. In addition, the LV and RV demonstrated distinct differences in oxygen flux and gene expression levels, which were independent from CON and IUGR status. Low mitochondrial respiration and CS activity in the IUGR heart compared with CON are consistent with delayed cardiomyocyte maturation, and CII and CV protein expression levels may be upregulated to support ATP production. These insights will provide a better understanding of fetal heart development in an adverse in utero environment. KEY POINTS: Growth-restricted fetuses have a higher risk of developing and dying from cardiovascular diseases in adulthood. Mitochondria are the main supplier of energy for the heart. As the heart matures, the substrate preference of the mitochondria switches from carbohydrates to lipids. We used a sheep model of intrauterine growth restriction to study the capacity of the mitochondria in the heart to produce energy using either carbohydrate or lipid substrates by measuring how much oxygen was consumed. Our data show that the mitochondria respiration levels in the growth-restricted fetal heart were lower than in the normally growing fetuses, and the expression levels of genes involved in lipid metabolism were also lower. Differences between the right and left ventricles that are independent of the fetal growth restriction condition were identified. These results indicate an impaired metabolic maturation of the growth-restricted fetal heart associated with a decreased capacity to oxidize lipids postnatally.

Effect of Genetically Reduced Maternal Myostatin on Late Gestation Maternal, Fetal, and Placental Metabolomes in Mice

Myostatin (gene symbol: Mstn) is an autocrine and paracrine inhibitor of muscle growth. Pregnant mice with genetically reduced levels of myostatin give birth to offspring with greater adult muscle mass and bone biomechanical strength. However, maternal myostatin is not detectable in fetal circulations. Fetal growth is dependent on the maternal environment, and the provisioning of nutrients and growth factors by the placenta. Thus, this study examined the effect of reduced maternal myostatin on maternal and fetal serum metabolomes, as well as the placental metabolome. Fetal and maternal serum metabolomes were highly distinct, which is consistent with the role of the placenta in creating a specific fetal nutrient environment. There was no effect from myostatin on maternal glucose tolerance or fasting insulin. In comparisons between pregnant control and Mstn+/- mice, there were more significantly different metabolite concentrations in fetal serum, at 50, than in the mother's serum at 33, confirming the effect of maternal myostatin reduction on the fetal metabolic milieu. Polyamines, lysophospholipids, fatty acid oxidation, and vitamin C, in fetal serum, were all affected by maternal myostatin reduction.

Impact of Placental SLC2A3 Deficiency during the First-Half of Gestation

In the ruminant placenta, glucose uptake and transfer are mediated by facilitative glucose transporters SLC2A1 (GLUT1) and SLC2A3 (GLUT3). SLC2A1 is located on the basolateral trophoblast membrane, whereas SLC2A3 is located solely on the maternal-facing, apical trophoblast membrane. While SLC2A3 is less abundant than SLC2A1, SLC2A3 has a five-fold greater affinity and transport capacity. Based on its location, SLC2A3 likely plays a significant role in the uptake of glucose into the trophoblast. Fetal hypoglycemia is a hallmark of fetal growth restriction (FGR), and as such, any deficiency in SLC2A3 could impact trophoblast glucose uptake and transfer to the fetus, thus potentially setting the stage for FGR. By utilizing in vivo placenta-specific lentiviral-mediated RNA interference (RNAi) in sheep, we were able to significantly diminish (p ≤ 0.05) placental SLC2A3 concentration, and determine the impact at mid-gestation (75 dGA). In response to SLC2A3 RNAi (n = 6), the fetuses were hypoglycemic (p ≤ 0.05), exhibited reduced fetal growth, including reduced fetal pancreas weight (p ≤ 0.05), which was associated with reduced umbilical artery insulin and glucagon concentrations, when compared to the non-targeting sequence (NTS) RNAi controls (n = 6). By contrast, fetal liver weights were not impacted, nor were umbilical artery concentrations of IGF1, possibly resulting from a 70% increase (p ≤ 0.05) in umbilical vein chorionic somatomammotropin (CSH) concentrations. Thus, during the first half of gestation, a deficiency in SLC2A3 results in fetal hypoglycemia, reduced fetal development, and altered metabolic hormone concentrations. These results suggest that SLC2A3 may be the rate-limiting placental glucose transporter during the first-half of gestation in sheep.

Fetal Sex Does Not Impact Placental Blood Flow or Placental Amino Acid Transfer in Late Gestation Pregnant Sheep With or Without Placental Insufficiency

Pregnant sheep have been used to model complications of human pregnancies including placental insufficiency and intrauterine growth restriction. Some of the hallmarks of placental insufficiency are slower uterine and umbilical blood flow rates, impaired placental transport of oxygen and amino acids, and lower fetal arterial concentrations of anabolic growth factors. An impact of fetal sex on these outcomes has not been identified in either human or sheep pregnancies. This is likely because most studies measuring these outcomes have used small numbers of subjects or animals. We undertook a secondary analysis of previously published data generated by our laboratory in late-gestation (gestational age of 133 ± 0 days gestational age) control sheep (n = 29 male fetuses; n = 26 female fetuses; n = 3 sex not recorded) and sheep exposed to elevated ambient temperatures to cause experimental placental insufficiency (n = 23 male fetuses; n = 17 female fetuses; n = 1 sex not recorded). The primary goal was to determine how fetal sex modifies the effect of the experimental insult on outcomes related to placental blood flow, amino acid and oxygen transport, and fetal hormones. Of the 112 outcomes measured, we only found an interaction between fetal sex and experimental insult for the uterine uptake rates of isoleucine, phenylalanine, and arginine. Additionally, most outcomes measured did not show a difference based on fetal sex when adjusting for the impact of placental insufficiency. Exceptions included fetal norepinephrine and cortisol concentrations, which were higher in female compared to male fetuses. For the parameters measured in the current analysis, the impact of fetal sex was not widespread.

Long-Term Consequences of Adaptive Fetal Programming in Ruminant Livestock

Environmental perturbations during gestation can alter fetal development and postnatal animal performance. In humans, intrauterine growth restriction (IUGR) resulting from adaptive fetal programming is known as a leading cause of perinatal morbidity and mortality and predisposes offspring to metabolic disease, however, the prevalence and impact in livestock is not characterized as well. Multiple animal models have been developed as a proxy to determine mechanistic changes that underlie the postnatal phenotype resulting from these programming events in humans but have not been utilized as robustly in livestock. While the overall consequences are similar between models, the severity of the conditions appear to be dependent on type, timing, and duration of insult, indicating that some environmental insults are of more relevance to livestock production than others. Thus far, maternofetal stress during gestation has been shown to cause increased death loss, low birth weight, inefficient growth, and aberrant metabolism. A breadth of this data comes from the fetal ruminant collected near term or shortly thereafter, with fewer studies following these animals past weaning. Consequently, even less is known about how adaptive fetal programming impacts subsequent progeny. In this review, we summarize the current knowledge of the postnatal phenotype of livestock resulting from different models of fetal programming, with a focus on growth, metabolism, and reproductive efficiency. We further describe what is currently known about generational impacts of fetal programming in production systems, along with gaps and future directions to consider.

Lower citrate synthase activity, mitochondrial complex expression, and fewer oxidative myofibers characterize skeletal muscle from growth-restricted fetal sheep

Skeletal muscle from the late gestation sheep fetus with intrauterine growth restriction (IUGR) has evidence of reduced oxidative metabolism. Using a sheep model of placental insufficiency and IUGR, we tested the hypothesis that by late gestation, IUGR fetal skeletal muscle has reduced capacity for oxidative phosphorylation because of intrinsic deficits in mitochondrial respiration. We measured mitochondrial respiration in permeabilized muscle fibers from biceps femoris (BF) and soleus (SOL) from control and IUGR fetal sheep. Using muscles including BF, SOL, tibialis anterior (TA), and flexor digitorum superficialis (FDS), we measured citrate synthase (CS) activity, mitochondrial complex subunit abundance, fiber type distribution, and gene expression of regulators of mitochondrial biosynthesis. Ex vivo mitochondrial respiration was similar in control and IUGR muscle. However, CS activity was lower in IUGR BF and TA, indicating lower mitochondrial content, and protein expression of individual mitochondrial complex subunits was lower in IUGR TA and BF in a muscle-specific pattern. IUGR TA, BF, and FDS also had lower expression of type I oxidative fibers. Fiber-type shifts that support glycolytic instead of oxidative metabolism may be advantageous for the IUGR fetus in a hypoxic and nutrient-deficient environment, whereas these adaptions may be maladaptive in postnatal life.

Maternal Lipid Profile as a Risk Factor for Gestational Diabetes Mellitus in Obese Women

As dyslipidemia is frequently associated with gestational diabetes mellitus, the aim of this study was to establish a correlation between the evolution of the maternal lipid profile evaluated in the first and third pregnancy trimester for a series of parameters: triglycerides, cholesterol, high-density lipoprotein cholesterol (HDL-C), blood sugar fasting (BSF), triglyceride-glucose index (TyG index), TG/HDL-C ratio, leptin and the risk of gestational diabetes mellitus occurrence. The results were statistically interpreted, establishing the mean value of the obtained results and the standard deviation. From the studied parameters, only HDL-C and Tyg were statistically significant different in the  first trimester for the two study groups, while in the third trimester statistically significant differences were observed also for triglycerides, blood sugar fasting and the TG/HDL-C ratio.

Treadmill Running of Mouse as a Model for Studying Influence of Maternal Exercise on Offspring

Epidemiological studies robustly show the beneficial effects of maternal exercise in reducing maternal birth complications and improving neonatal outcomes, though underlying mechanisms remain poorly understood. To facilitate mechanistic exploration, a protocol for maternal exercise of mice is established, with the regimen following the exercise guidelines for pregnant women. Compared to volunteer wheel running, treadmill running allows precise control of exercise intensity and duration, dramatically reducing variations among individual mouse within treatments and facilitating translation into maternal exercise in humans. Based on the maximal oxygen consumption rate (VO₂max) before pregnancy, the treadmill exercise protocol is separated into three stages: early stage (E1.5 to E7.5 at 40% VO₂max), mid stage (E8.5 to E14.5 at 65% VO₂max), and late stage of pregnancy (E15.5 to birth at 50% VO₂max), which demonstrated persistent beneficial effects on maternal health and fetal development. This protocol can be useful for standardizing maternal treadmill exercise using mice as an experimental model.

Effects of birth weight and dietary fat on intake, body composition, and plasma thyroxine in neonatal lambs

Intrauterine growth restriction (IUGR) is often observed in one of the fetuses carried by well-fed prolific ewes. This condition is the result of an insufficient placental size to cover the nutritional needs of the fetus during the near exponential growth phase of the last trimester. After birth, these IUGR offspring have an elevated appetite and lower maintenance energy requirements, suggesting dysregulation of homeostatic systems governing energy metabolism. It is also unknown whether the consequent increase in fatness occurs similarly in both visceral and carcass fractions. To address these questions, lambs differing in birth size (BS, IUGR vs. Normal, 2.6 ± 0.05 vs. 4.2 ± 0.07 kg, P < 0.001) were offered unlimited amounts of a low fat [LF; 22% of dry matter (DM)] or a high fat (HF; 38% of DM) milk replacer and slaughtered on day 14 of postnatal age (n = 7 to 8 for each BS × Diet); a second group of IUGR lambs (n = 3 for each diet) was slaughtered when they reached 8.5 kg, corresponding to the weight of Normal lambs on day 14. When normalized to body weight (BW), the DM and energy intake of IUGR lambs were higher than those of Normal lambs over the first 14 d of life (BS, P < 0.01), but contrary to expectations, the HF diet did not exacerbate these effects of the IUGR condition. Intrauterine growth restricted lambs had increased viscera fat with both diets (BS and Diet, P < 0.05) but increased carcass fat only with the LF diet (BS × Diet, P = 0.08); the fatness promoting effect of the IUGR condition was increased in both body fractions when lamb groups were compared at the fixed BW of 8.5 kg. A subset of metabolic hormones was analyzed, including the metabolic rate-setting hormone thyroxine (T4) and its possible positive regulator leptin. Plasma T4 was lower in IUGR than in Normal lambs at birth (P < 0.05) but then disappeared by day 7 of postnatal life (BS × Day, P < 0.01). On the other hand, the HF diet had no effect on plasma T4 over the first 3 d but caused an increase, irrespective of BS by day 11 (Diet × Day, P < 0.001). Plasma leptin increased with dietary fat and time (P < 0.06) but bore no relation to the effects of BS or Diet on plasma T4. These data show that IUGR and Normal lambs are similarly unable to adjust caloric intake in early life and that the fatness promoting effects of the IUGR condition are more pronounced in the viscera than in the carcass. These data also reveal dynamic regulation of plasma T4 by BS and Diet in neonatal lambs.

Differentially expressed genes in cotyledon of ewes fed mycotoxins

BACKGROUND

Ergot alkaloids (E+) are mycotoxins produced by the endophytic fungus, Epichloë coenophiala, in tall fescue that are associated with ergotism in animals. Exposure to ergot alkaloids during gestation reduces fetal weight and placental mass in sheep. These reductions are related to vasoconstrictive effects of ergot alkaloids and potential alterations in nutrient transport to the fetus. Cotyledon samples were obtained from eight ewes that were fed E+ (n = 4; E+/E+) or E- (endophyte-free without ergot alkaloids; n = 4; E-/E-) seed during both mid (d 35 to 85) and late (d 85-133) gestation to assess differentially expressed genes associated with ergot alkaloid induced reductions in placental mass and fetal weight, and discover potential adaptive mechanisms to alter nutrient supply to fetus.

RESULTS

Ewes fed E+/E+ fescue seed during both mid and late gestation had 20% reduction in fetal body weight and 33% reduction in cotyledon mass compared to controls (E-/E-). Over 13,000 genes were identified with 110 upregulated and 33 downregulated. Four genes had a |log2FC| > 5 for ewes consuming E+/E+ treatment compared to controls: LECT2, SLC22A9, APOC3, and MBL2. REViGO revealed clusters of upregulated genes associated glucose, carbohydrates, lipid, protein, macromolecular and cellular metabolism, regulation of wound healing and response to starvation. For downregulated genes, no clusters were present, but all enriched GO terms were associated with anion and monocarboxylic acid transport. The complement and coagulation cascade and the peroxisome proliferator-activated receptor signaling pathway were found to be enriched for ewes consuming E+/E+ treatment.

CONCLUSIONS

Consumption of ergot alkaloids during gestation altered the cotyledonary transcriptome specifically related to macronutrient metabolism, wound healing and starvation. These results show that ergot alkaloid exposure upregulates genes involved in nutrient metabolism to supply the fetus with additional substrates in attempts to rescue fetal growth.

Sex Differences Across the Lifespan: A Focus on Cardiometabolism

Women's health and sex differences research remain understudied. In 2016, to address the topic of sex differences, the Center for Women' s Health Research (CWHR) at the University of Colorado (cwhr@ucdenver.edu) held its inaugural National Conference, "Sex Differences Across the Lifespan: A Focus on Metabolism" and published a report summarizing the presentations. Two years later, in 2018, CWHR organized the 2nd National Conference. The research presentations and discussions from the 2018 conference also addressed sex differences across the lifespan with a focus on cardiometabolism and expanded the focus by including circadian physiology and effects of sleep on cardiometabolic health. Over 100 participants, including basic scientists, clinicians, policymakers, advocacy group leaders, and federal agency leadership participated. The meeting proceedings reveal that although exciting advances in the area of sex differences have taken place, significant questions and gaps remain about women's health and sex differences in critical areas of health. Identifying these gaps and the subsequent research that will result may lead to important breakthroughs.

Prolonged amino acid infusion into intrauterine growth-restricted fetal sheep increases leucine oxidation rates

Overcoming impaired growth in an intrauterine growth-restricted (IUGR) fetus has potential to improve neonatal morbidity, long-term growth, and metabolic health outcomes. The extent to which fetal anabolic capacity persists as the IUGR condition progresses is not known. We subjected fetal sheep to chronic placental insufficiency and tested whether prolonged amino acid infusion would increase protein accretion in these IUGR fetuses. IUGR fetal sheep were infused for 10 days with either mixed amino acids providing ~2 g·kg^-1·day^-1 (IUGR-AA) or saline (IUGR-Sal) during late gestation. At the end of the infusion, fetal plasma leucine, isoleucine, lysine, methionine, and arginine concentrations were higher in the IUGR-AA than IUGR-Sal group ( P < 0.05). Fetal plasma glucose, oxygen, insulin, IGF-1, cortisol, and norepinephrine concentrations were similar between IUGR groups, but glucagon concentrations were fourfold higher in the IUGR-AA group ( P < 0.05). Net umbilical amino acid uptake rate did not differ between IUGR groups; thus the total amino acid delivery rate (net umbilical amino acid uptake + infusion rate) was higher in the IUGR-AA than IUGR-Sal group (30 ± 4 vs. 19 ± 1 μmol·kg^-1·min^-1, P < 0.05). Net umbilical glucose, lactate, and oxygen uptake rates were similar between IUGR groups. Fetal leucine oxidation rate, measured using a leucine tracer, was higher in the IUGR-AA than IUGR-Sal group (2.5 ± 0.3 vs. 1.7 ± 0.3 μmol·kg^-1·min^-1, P < 0.05). Fetal protein accretion rate was not statistically different between the IUGR groups (1.6 ± 0.4 and 0.8 ± 0.3 μmol·kg^-1·min^-1 in IUGR-AA and IUGR-Sal, respectively) due to variability in response to amino acids. Prolonged amino acid infusion into IUGR fetal sheep increased leucine oxidation rates with variable anabolic response.

Atypical fetal development: Fetal alcohol syndrome, nutritional deprivation, teratogens, and risk for neurodevelopmental disorders and psychopathology

Accumulating evidence indicates that the fetal environment plays an important role in brain development and sets the brain on a trajectory across the life span. An abnormal fetal environment results when factors that should be present during a critical period of development are absent or when factors that should not be in the developing brain are present. While these factors may acutely disrupt brain function, the real cost to society resides in the long-term effects, which include important mental health issues. We review the effects of three factors, fetal alcohol exposure, teratogen exposure, and nutrient deficiencies, on the developing brain and the consequent risk for developmental psychopathology. Each is reviewed with respect to the evidence found in epidemiological and clinical studies in humans as well as preclinical molecular and cellular studies that explicate mechanisms of action.

Fetal adaptations in insulin secretion result from high catecholamines during placental insufficiency

Placental insufficiency and intrauterine growth restriction (IUGR) of the fetus affects approximately 8% of all pregnancies and is associated with short- and long-term disturbances in metabolism. In pregnant sheep, experimental models with a small, defective placenta that restricts delivery of nutrients and oxygen to the fetus result in IUGR. Low blood oxygen concentrations increase fetal plasma catecholamine concentrations, which lower fetal insulin concentrations. All of these observations in sheep models with placental insufficiency are consistent with cases of human IUGR. We propose that sustained high catecholamine concentrations observed in the IUGR fetus produce developmental adaptations in pancreatic β-cells that impair fetal insulin secretion. Experimental evidence supporting this hypothesis shows that chronic elevation in circulating catecholamines in IUGR fetuses persistently inhibits insulin concentrations and secretion. Elevated catecholamines also allow for maintenance of a normal fetal basal metabolic rate despite low fetal insulin and glucose concentrations while suppressing fetal growth. Importantly, a compensatory augmentation in insulin secretion occurs following inhibition or cessation of catecholamine signalling in IUGR fetuses. This finding has been replicated in normally grown sheep fetuses following a 7-day noradrenaline (norepinephrine) infusion. Together, these programmed effects will potentially create an imbalance between insulin secretion and insulin-stimulated glucose utilization in the neonate which probably explains the transient hyperinsulinism and hypoglycaemia in some IUGR infants.

RNA Sequencing Exposes Adaptive and Immune Responses to Intrauterine Growth Restriction in Fetal Sheep Islets

The risk of type 2 diabetes is increased in children and adults who exhibited fetal growth restriction. Placental insufficiency and intrauterine growth restriction (IUGR) are common obstetrical complications associated with fetal hypoglycemia and hypoxia that reduce the β-cell mass and insulin secretion. In the present study, we have defined the underlying mechanisms of reduced growth and proliferation, impaired metabolism, and defective insulin secretion previously established as complications in islets from IUGR fetuses. In an IUGR sheep model that recapitulates human IUGR, high-throughput RNA sequencing showed the transcriptome of islets isolated from IUGR and control sheep fetuses and identified the transcripts that underlie β-cell dysfunction. Functional analysis expanded mechanisms involved in reduced proliferation and dysregulated metabolism that include specific cell cycle regulators and growth factors and mitochondrial, antioxidant, and exocytotic genes. These data also identified immune responses, wnt signaling, adaptive stress responses, and the proteasome as mechanisms of β-cell dysfunction. The reduction of immune-related gene expression did not reflect a change in macrophage density within IUGR islets. The present study reports the islet transcriptome in fetal sheep and established processes that limit insulin secretion and β-cell growth in fetuses with IUGR, which could explain the susceptibility to premature islet failure in adulthood. Islet dysfunction formed by intrauterine growth restriction increases the risk for diabetes.

Metabolomic profiling in umbilical venous plasma reveals effects of dietary rumen-protected arginine or N-carbamylglutamate supplementation in nutrient-restricted Hu sheep during pregnancy

Maternal nutrient restriction during pregnancy is a major problem worldwide for human and animal production. Arginine (Arg) is critical to health, growth and reproduction. N-carbamylglutamate (NCG), a key enzyme in arginine synthesis, is not extensively degraded in rumen. The aim of this study was to investigate ameliorating effects of rumen-protected arginine (RP-Arg) and NCG supplementation on dietary in undernourished Hu sheep during gestation. From day 35 to 110 of gestation, 32 Hu ewes carrying twin foetuses were randomly divided into four groups: a control (CG) group (n = 8; fed 100% National Research Council (NRC) requirements for pregnant sheep), a nutrient-restricted (RG) group (n = 8; fed 50% NRC requirements, which included 50% mineral-vitamin mixture) and two treatment (Arg and NCG) groups (n = 8; fed 50% NRC requirements supplemented with 20 g/day RP-Arg or 5 g/day NCG, which included 50% mineral-vitamin mixture). The umbilical venous plasma samples of foetus were tested by ¹ H-nuclear magnetic resonance. Thirty-two differential metabolites were identified, indicating altered metabolic pathways of amino acid, carbohydrate and energy, lipids and oxidative stress metabolism among the four groups. Our results demonstrate that the beneficial effect of dietary RP-Arg and NCG supplementation on mammalian reproduction is associated with complex metabolic networks.