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.

Maternal AMPK pathway activation with uterine artery blood flow and fetal growth maintenance during hypoxia.

High altitude (HA) hypoxia lowers uterine artery (UtA) blood flow during pregnancy and birth weight. Adenosine monophosphate kinase (AMPK) activation has selective, uteroplacental vasodilator effects which lessen hypoxia-associated birth weight reductions. In this study, we determined the relationship between AMPK-pathway gene expression and metabolites in the maternal circulation during HA pregnancy as well as with the maintenance of UtA blood flow and birth weight at HA. HA (2793 m) vs low altitude (LA; 1640 m) residents had smaller UtA diameters at weeks 20 and 34, lower UtA blood flow at week 20, and lower birth weight babies. At week 34, HA vs LA women had decreased expression of up- and down-stream AMPK-pathway genes. Expression of the a-1 AMPK catalytic subunit, PRKAA1, correlated positively with UtA diameter and blood flow at week 20 (HA) and 34 (LA). Downstream AMPK-pathway gene expression positively correlated with week 20 fetal biometry at both altitudes and with UtA diameter and birth weight at LA. Reduced gene expression of AMPK activators and downstream targets in HA versus LA women, together with positive correlations between PRKAA1 gene expression, UtA diameter, and blood flow suggest that greater sensitivity to AMPK activation at mid-gestation at HA may help offset later depressant effects of hypoxia on fetal growth.

Initiation of Metformin in Early Pregnancy Results in Fetal Bioaccumulation, Growth Restriction & Renal Dysmorphology in a Primate Model.

BACKGROUND: In recent years, pragmatic metformin use in pregnancy has stretched to include prediabetes, type 2 diabetes, gestational diabetes and (most recently) pre-eclampsia. With its expanded use, however, concerns of unintended harm have been raised. OBJECTIVE: We developed an experimental primate model and applied triple-quadruple pole LC mass spectrometry (UHPLC-QQQ) for direct quantitation of maternal and fetal tissue metformin levels with detailed fetal biometry and histopathology. STUDY DESIGN: Within 30 days of confirmed conception (defined as early pregnancy), n=13 time-bred (TMB) Rhesus dams with gestations designated for fetal necropsy were initiated on twice daily human dose-equivalent 10 mg/kg metformin or vehicle control. Pregnant dams were maintained as pairs and fed either a control chow or 36% fat Western-style diet (WSD). Metformin or placebo vehicle control were delivered in a variety of treats while animals were separated via a slide. A Cesarean was performed at G145, and amniotic fluid and blood were collected and the fetus and placenta were delivered. The fetus was immediately necropsied by trained primate center personnel. All fetal organs were dissected, measured, sectioned, and processed per clinical standards. Fluid and tissue metformin levels were assayed using validated UHPLC-QQQ in SRM against standard curves. RESULTS: Among the n=13 G145 pregnancies with fetal necropsy, n=1 dam and its fetal tissues had detectable metformin levels despite being allocated to the vehicle control group (>1 µM metformin/kg maternal weight or fetal/placental tissue), while a second fetus allocated to the vehicle control group had severe fetal growth restriction (birthweight 248.32 g, <1%) and was suspected of having a fetal congenital condition. After excluding these two fetal gestations from further analyses, 11 fetuses from dams initiated on either vehicle control (n=4, 3 female, 1 male fetuses) or 10 mg/kg metformin (n=7, 5 female, 2 male fetuses) were available for analyses. Among dams initiated on metformin by G30 (regardless of maternal diet), we observed significant bioaccumulation within the fetal kidney (0.78-6.06 µmol/kg, mean 2.48 µmol/kg) , liver (0.16-0.73 µmol/kg, mean 0.38 µmol/kg), fetal gut (0.28-1.22 µmol/kg, mean 0.70 µmol/kg), amniotic fluid (0.43-3.33 µmol/L, mean 1.88 µmol/L), placenta (0.16-1.0 µmol/kg , mean 0.50 µmol/kg) and fetal serum (0 -0.66 µmol/L , mean 0.23 µmol/L ), and fetal urine (4.1-174.1 µmol/L mean 38.5 µmol/L ), with fetal levels near biomolar equivalent to maternal levels (maternal serum 0.18-0.86 µmol/L , mean 0.46 µmol/L; maternal urine 42.6-254.0 µmol/L , mean 149.3 µmol/L). WSD feeding neither accelerated nor reduced metformin bioaccumulations in maternal or fetal serum, urine, amniotic fluid, placenta nor fetal tissues. In these 11 animals, fetal bioaccumulation of metformin was associated with less fetal skeletal muscle (57% lower cross-sectional area of gastrocnemius) and decreased liver, heart, and retroperitoneal fat masses (p<0.05), collectively driving lower delivery weight (p<0.0001) without changing the crown-rump length. Sagittal sections of fetal kidneys demonstrated delayed maturation, with disorganized glomerular generations and increased cortical thickness; this renal dysmorphology was not accompanied by structural nor functional changes indicative of renal insufficiency. CONCLUSIONS: We demonstrate fetal bioaccumulation of metformin with associated fetal growth restriction and renal dysmorphology following maternal initiation of the drug within 30 days of conception in primates. Given these results and the prevalence of metformin use during pregnancy, additional investigation of any potential immediate and enduring effects of prenatal metformin use is warranted.

Adaptive responses in uteroplacental metabolism and fetoplacental nutrient shuttling and sensing during placental insufficiency.

Glucose, lactate, and amino acids are major fetal nutrients. During placental insufficiency-induced intrauterine growth restriction (PI-IUGR), uteroplacental weight-specific oxygen consumption rates are maintained, yet fetal glucose and amino acid supply is decreased and fetal lactate concentrations are increased. We hypothesized that uteroplacental metabolism adapts to PI-IUGR by altering nutrient allocation to maintain oxidative metabolism. Here, we measured nutrient flux rates, with a focus on nutrients shuttled between the placenta and fetus (lactate-pyruvate, glutamine-glutamate, and glycine-serine) in a sheep model of PI-IUGR. PI-IUGR fetuses weighed 40% less and had decreased oxygen, glucose, and amino acid concentrations and increased lactate and pyruvate versus control (CON) fetuses. Uteroplacental weight-specific rates of oxygen, glucose, lactate, and pyruvate uptake were similar. In PI-IUGR, fetal glucose uptake was decreased and pyruvate output was increased. In PI-IUGR placental tissue, pyruvate dehydrogenase (PDH) phosphorylation was decreased and PDH activity was increased. Uteroplacental glutamine output to the fetus and expression of genes regulating glutamine-glutamate metabolism were lower in PI-IUGR. Fetal glycine uptake was lower in PI-IUGR, with no differences in uteroplacental glycine or serine flux. These results suggest increased placental utilization of pyruvate from the fetus, without higher maternal glucose utilization, and lower fetoplacental amino acid shuttling during PI-IUGR. Mechanistically, AMP-activated protein kinase (AMPK) activation was higher and associated with thiobarbituric acid-reactive substances (TBARS) content, a marker of oxidative stress, and PDH activity in the PI-IUGR placenta, supporting a potential link between oxidative stress, AMPK, and pyruvate utilization. These differences in fetoplacental nutrient sensing and shuttling may represent adaptive strategies enabling the placenta to maintain oxidative metabolism.NEW & NOTEWORTHY These results suggest increased placental utilization of pyruvate from the fetus, without higher maternal glucose uptake, and lower amino acid shuttling in the placental insufficiency-induced intrauterine growth restriction (PI-IUGR) placenta. AMPK activation was associated with oxidative stress and PDH activity, supporting a putative link between oxidative stress, AMPK, and pyruvate utilization. These differences in fetoplacental nutrient sensing and shuttling may represent adaptive strategies enabling the placenta to maintain oxidative metabolism at the expense of fetal growth.

Maternal Western-style diet in nonhuman primates leads to offspring islet adaptations including altered gene expression and insulin hypersecretion.

Maternal overnutrition is associated with increased susceptibility to type 2 diabetes in the offspring. Rodent models have shown that maternal overnutrition influences islet function in offspring. To determine whether maternal Western-style diet (WSD) alters prejuvenile islet function in a model that approximates that of human offspring, we utilized a well-characterized Japanese macaque model. We compared islet function from offspring exposed to WSD throughout pregnancy and lactation and weaned to WSD (WSD/WSD) compared with islets from offspring exposed only to postweaning WSD (CD/WSD) at 1 yr of age. WSD/WSD offspring islets showed increased basal insulin secretion and an exaggerated increase in glucose-stimulated insulin secretion, as assessed by dynamic ex vivo perifusion assays, relative to CD/WSD-exposed offspring. We probed potential mechanisms underlying insulin hypersecretion using transmission electron microscopy to evaluate ß-cell ultrastructure, qRT-PCR to quantify candidate gene expression, and Seahorse assay to assess mitochondrial function. Insulin granule density, mitochondrial density, and mitochondrial DNA ratio were similar between groups. However, islets from WSD/WSD male and female offspring had increased expression of transcripts known to facilitate stimulus-secretion coupling and changes in the expression of cell stress genes. Seahorse assay revealed increased spare respiratory capacity in islets from WSD/WSD male offspring. Overall, these results show that maternal WSD feeding confers changes to genes governing insulin secretory coupling and results in insulin hypersecretion as early as the postweaning period. The results suggest a maternal diet leads to early adaptation and developmental programming in offspring islet genes that may underlie future ß-cell dysfunction.NEW & NOTEWORTHY Programed adaptations in islets in response to maternal WSD exposure may alter ß-cell response to metabolic stress in offspring. We show that islets from maternal WSD-exposed offspring hypersecrete insulin, possibly due to increased components of stimulus-secretion coupling. These findings suggest that islet hyperfunction is programed by maternal diet, and changes can be detected as early as the postweaning period in nonhuman primate offspring.

Chronic Fetal Leucine Infusion Increases Rate of Leucine Oxidation but Not of Protein Synthesis in Late Gestation Fetal Sheep.

BACKGROUND: Leucine increases protein synthesis rates in postnatal animals and adults. Whether supplemental leucine has similar effects in the fetus has not been determined. OBJECTIVE: To determine the effect of a chronic leucine infusion on whole-body leucine oxidation and protein metabolic rates, muscle mass, and regulators of muscle protein synthesis in late gestation fetal sheep. METHODS: Catheterized fetal sheep at ∼126 d of gestation (term = 147 d) received infusions of saline (CON, n = 11) or leucine (LEU; n = 9) adjusted to increase fetal plasma leucine concentrations by 50%-100% for 9 d. Umbilical substrate net uptake rates and protein metabolic rates were determined using a 1-13C leucine tracer. Myofiber myosin heavy chain (MHC) type and area, expression of amino acid transporters, and abundance of protein synthesis regulators were measured in fetal skeletal muscle. Groups were compared using unpaired t tests. RESULTS: Plasma leucine concentrations were 75% higher in LEU fetuses compared with CON by the end of the infusion period (P < 0.0001). Umbilical blood flow and uptake rates of most amino acids, lactate, and oxygen were similar between groups. Fetal whole-body leucine oxidation was 90% higher in LEU (P < 0.0005) but protein synthesis and breakdown rates were similar. Fetal and muscle weights and myofiber areas were similar between groups, however, there were fewer MHC type IIa fibers (P < 0.05), greater mRNA expression levels of amino acid transporters (P < 0.01), and a higher abundance of signaling proteins that regulate protein synthesis (P < 0.05) in muscle from LEU fetuses. CONCLUSIONS: A direct leucine infusion for 9 d in late gestation fetal sheep does not increase protein synthesis rates but results in higher leucine oxidation rates and fewer glycolytic myofibers. Increasing leucine concentrations in the fetus stimulates its own oxidation but also increases amino acid transporter expression and primes protein synthetic pathways in skeletal muscle.

Tissue-specific responses that constrain glucose oxidation and increase lactate production with the severity of hypoxemia in fetal sheep.

Fetal hypoxemia decreases insulin and increases cortisol and norepinephrine concentrations and may restrict growth by decreasing glucose utilization and altering substrate oxidation. Specifically, we hypothesized that hypoxemia would decrease fetal glucose oxidation and increase lactate and pyruvate production. We tested this by measuring whole body glucose oxidation and lactate production, and molecular pathways in liver, muscle, adipose, and pancreas tissues of fetuses exposed to maternal hypoxemia for 9 days (HOX) compared with control fetal sheep (CON) in late gestation. Fetuses with more severe hypoxemia had lower whole body glucose oxidation rates, and HOX fetuses had increased lactate production from glucose. In muscle and adipose tissue, expression of the glucose transporter GLUT4 was decreased. In muscle, pyruvate kinase (PKM) and lactate dehydrogenase B (LDHB) expression was decreased. In adipose tissue, LDHA and lactate transporter (MCT1) expression was increased. In liver, there was decreased gene expression of PKLR and MPC2 and phosphorylation of PDH, and increased LDHA gene and LDH protein abundance. LDH activity, however, was decreased only in HOX skeletal muscle. There were no differences in basal insulin signaling across tissues, nor differences in pancreatic tissue insulin content, ß-cell area, or genes regulating ß-cell function. Collectively, these results demonstrate coordinated metabolic responses across tissues in the hypoxemic fetus that limit glucose oxidation and increase lactate and pyruvate production. These responses may be mediated by hypoxemia-induced endocrine responses including increased norepinephrine and cortisol, which inhibit pancreatic insulin secretion resulting in lower insulin concentrations and decreased stimulation of glucose utilization.NEW & NOTEWORTHY Hypoxemia lowered fetal glucose oxidation rates, based on severity of hypoxemia, and increased lactate production. This was supported by tissue-specific metabolic responses that may result from increased norepinephrine and cortisol concentrations, which decrease pancreatic insulin secretion and insulin concentrations and decrease glucose utilization. This highlights the vulnerability of metabolic pathways in the fetus and demonstrates that constrained glucose oxidation may represent an early event in response to sustained hypoxemia and fetal growth restriction.

Why is human uterine artery blood flow during pregnancy so high?

In healthy near-term women, blood flow to the uteroplacental circulation is estimated as 841 mL/min, which is greater than in other mammalian species. We argue that as uterine venous Po2 sets the upper limit for O2 diffusion to the fetus, high uterine artery blood flow serves to narrow the maternal arterial-to-uterine venous Po2 gradient and thereby raise uterine vein Po2. In support, we show that the reported levels for uterine artery blood flow agree with what is required to maintain normal fetal growth. Although residence at high altitudes (>2,500 m) depresses fetal growth, not all populations are equally affected; Tibetans and Andeans have higher levels of uterine artery blood flow than newcomers and exhibit normal fetal growth. Estimates of uterine venous Po2 from the umbilical blood-gas data available from healthy Andean pregnancies indicate that their high levels of uterine artery blood flow are consistent with their reported, normal birth weights. Unknown, however, are the effects on placental gas exchange of the lower levels of uterine artery blood flow seen in high-altitude newcomers or hypoxia-associated pregnancy complications. We speculate that, by widening the maternal artery to uterine vein Po2 gradient, lower levels of uterine artery blood flow prompt metabolic changes that slow fetal growth to match O2 supply.

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.

Late gestation fetal hyperglucagonaemia impairs placental function and results in diminished fetal protein accretion and decreased fetal growth.

KEY POINTS: Fetal glucagon concentrations are elevated in the setting of placental insufficiency, hypoxia and elevated stress hormones. Chronically elevated glucagon concentrations in the adult result in profound decreases in amino acid concentrations and lean body mass. Experimental elevation of fetal glucagon concentrations in a late-gestation pregnant sheep results in lower fetal amino acid concentrations, lower protein accretion and lower fetal weight, in addition to decreased placental function. This study demonstrates a negative effect of glucagon on fetal protein accretion and growth, and also provides the first example of a fetal hormone that negatively regulates placental nutrient transport and blood flow. ABSTRACT: Fetal glucagon concentrations are elevated in the setting of placental insufficiency and fetal stress. Postnatal studies have demonstrated the importance of glucagon in amino acid metabolism, and limited fetal studies have suggested that glucagon inhibits umbilical uptake of certain amino acids. We hypothesized that chronic fetal hyperglucagonaemia would decrease amino acid transfer and increase amino acid oxidation by the fetus. Late gestation singleton fetal sheep received a direct intravenous infusion of glucagon (GCG; 5 or 50 ng/kg/min; n = 7 and 5, respectively) or a vehicle control (n = 10) for 8-10 days. Fetal and maternal nutrient concentrations, uterine and umbilical blood flows, fetal leucine flux, nutrient uptake rates, placental secretion of chorionic somatomammotropin (CSH), and targeted placental gene expression were measured. GCG fetuses had 13% lower fetal weight compared to controls (P = 0.0239) and >28% lower concentrations of 16 out of 21 amino acids (P < 0.02). Additionally, protein synthesis was 49% lower (P = 0.0005), and protein accretion was 92% lower in GCG fetuses (P = 0.0006). Uterine blood flow was 33% lower in ewes with GCG fetuses (P = 0.0154), while umbilical blood flow was similar. Fetal hyperglucagonaemia lowered uterine uptake of 10 amino acids by >48% (P < 0.05) and umbilical uptake of seven amino acids by >29% (P < 0.04). Placental secretion of CSH into maternal circulation was reduced by 80% compared to controls (P = 0.0080). This study demonstrates a negative effect of glucagon on fetal protein accretion and growth. It also demonstrates that glucagon, a hormone of fetal origin, negatively regulates maternal placental nutrient transport function, placental CSH production and uterine blood flow.

Reduced glucose-stimulated insulin secretion following a 1-wk IGF-1 infusion in late gestation fetal sheep is due to an intrinsic islet defect.

Insulin and insulin-like growth factor-1 (IGF-1) are fetal hormones critical to establishing normal fetal growth. Experimentally elevated IGF-1 concentrations during late gestation increase fetal weight but lower fetal plasma insulin concentrations. We therefore hypothesized that infusion of an IGF-1 analog for 1 wk into late gestation fetal sheep would attenuate fetal glucose-stimulated insulin secretion (GSIS) and insulin secretion in islets isolated from these fetuses. Late gestation fetal sheep received infusions with IGF-1 LR3 (IGF-1, n = 8), an analog of IGF-1 with low affinity for the IGF binding proteins and high affinity for the IGF-1 receptor, or vehicle control (CON, n = 9). Fetal GSIS was measured with a hyperglycemic clamp (IGF-1, n = 8; CON, n = 7). Fetal islets were isolated, and insulin secretion was assayed in static incubations (IGF-1, n = 8; CON, n = 7). Plasma insulin and glucose concentrations in IGF-1 fetuses were lower compared with CON (P = 0.0135 and P = 0.0012, respectively). During the GSIS study, IGF-1 fetuses had lower insulin secretion compared with CON (P = 0.0453). In vitro, glucose-stimulated insulin secretion remained lower in islets isolated from IGF-1 fetuses (P = 0.0447). In summary, IGF-1 LR3 infusion for 1 wk into fetal sheep lowers insulin concentrations and reduces fetal GSIS. Impaired insulin secretion persists in isolated fetal islets indicating an intrinsic islet defect in insulin release when exposed to IGF-1 LR3 infusion for 1 wk. We speculate this alteration in the insulin/IGF-1 axis contributes to the long-term reduction in ß-cell function in neonates born with elevated IGF-1 concentrations following pregnancies complicated by diabetes or other conditions associated with fetal overgrowth.NEW & NOTEWORTHY After a 1-wk infusion of IGF-1 LR3, late gestation fetal sheep had lower plasma insulin and glucose concentrations, reduced fetal glucose-stimulated insulin secretion, and decreased fractional insulin secretion from isolated fetal islets without differences in pancreatic insulin content.

IGF-1 infusion to fetal sheep increases organ growth but not by stimulating nutrient transfer to the fetus.

Insulin-like growth factor-1 (IGF-1) is an important fetal growth factor. However, the role of fetal IGF-1 in increasing placental blood flow, nutrient transfer, and nutrient availability to support fetal growth and protein accretion is not well understood. Catheterized fetuses from late gestation pregnant sheep received an intravenous infusion of LR3 IGF-1 (LR3 IGF-1; n = 8) or saline (SAL; n = 8) for 1 wk. Sheep then underwent a metabolic study to measure uterine and umbilical blood flow, nutrient uptake rates, and fetal protein kinetic rates. By the end of the infusion, fetal weights were not statistically different between groups (SAL: 3.260 ± 0.211 kg, LR3 IGF-1: 3.682 ± 0.183; P = 0.15). Fetal heart, adrenal gland, and spleen weights were higher (P < 0.05), and insulin was lower in LR3 IGF-1 (P < 0.05). Uterine and umbilical blood flow and umbilical uptake rates of glucose, lactate, and oxygen were similar between groups. Umbilical amino acid uptake rates were lower in LR3 IGF-1 (P < 0.05) as were fetal concentrations of multiple amino acids. Fetal protein kinetic rates were similar. LR3 IGF-1 skeletal muscle had higher myoblast proliferation (P < 0.05). In summary, LR3 IGF-1 infusion for 1 wk into late gestation fetal sheep increased the weight of some fetal organs. However, because umbilical amino acid uptake rates and fetal plasma amino acid concentrations were lower in the LR3 IGF-1 group, we speculate that animals treated with LR3 IGF-1 can efficiently utilize available nutrients to support organ-specific growth in the fetus rather than by stimulating placental blood flow or nutrient transfer to the fetus.NEW & NOTEWORTHY After a 1-wk infusion of LR3 IGF-1, late gestation fetal sheep had lower umbilical uptake rates of amino acids, lower fetal arterial amino acid and insulin concentrations, and lower fetal oxygen content; however, LR-3 IGF-1-treated fetuses were still able to effectively utilize the available nutrients and oxygen to support organ growth and myoblast proliferation.

Anemic hypoxemia reduces myoblast proliferation and muscle growth in late-gestation fetal sheep.

Fetal skeletal muscle growth requires myoblast proliferation, differentiation, and fusion into myofibers in addition to protein accretion for fiber hypertrophy. Oxygen is an important regulator of this process. Therefore, we hypothesized that fetal anemic hypoxemia would inhibit skeletal muscle growth. Studies were performed in late-gestation fetal sheep that were bled to anemic and therefore hypoxemic conditions beginning at ∼125 days of gestation (term = 148 days) for 9 ± 0 days (n = 19) and compared with control fetuses (n = 16). A metabolic study was performed on gestational day ∼134 to measure fetal protein kinetic rates. Myoblast proliferation and myofiber area were determined in biceps femoris (BF), tibialis anterior (TA), and flexor digitorum superficialis (FDS) muscles. mRNA expression of muscle regulatory factors was determined in BF. Fetal arterial hematocrit and oxygen content were 28% and 52% lower, respectively, in anemic fetuses. Fetal weight and whole body protein synthesis, breakdown, and accretion rates were not different between groups. Hindlimb length, however, was 7% shorter in anemic fetuses. TA and FDS muscles weighed less, and FDS myofiber area was smaller in anemic fetuses compared with controls. The percentage of Pax7+ myoblasts that expressed Ki67 was lower in BF and tended to be lower in FDS from anemic fetuses indicating reduced myoblast proliferation. There was less MYOD and MYF6 mRNA expression in anemic versus control BF consistent with reduced myoblast differentiation. These results indicate that fetal anemic hypoxemia reduced muscle growth. We speculate that fetal muscle growth may be improved by strategies that increase oxygen availability.

Chronic Fetal Leucine Infusion Does Not Potentiate Glucose-Stimulated Insulin Secretion or Affect Pancreatic Islet Development in Late-Gestation Growth-Restricted Fetal Sheep.

BACKGROUND: Growth-restricted fetuses have attenuated glucose-stimulated insulin secretion (GSIS), smaller pancreatic islets, less pancreatic ß-cells, and less pancreatic vascularization compared with normally growing fetuses. Infusion of leucine into normal late-gestation fetal sheep potentiates GSIS, as well as increases pancreatic islet size, the proportion of the pancreas and islet comprising ß-cells, and pancreatic and islet vascularity. In addition, leucine stimulates hepatocyte growth factor (HGF ) mRNA expression in islet endothelial cells isolated from normal fetal sheep. OBJECTIVE: We hypothesized that a 9-d leucine infusion would potentiate GSIS and increase pancreatic islet size, ß-cells, and vascularity in intrauterine fetal growth restriction (IUGR) fetal sheep. We also hypothesized that leucine would stimulate HGF mRNA in islet endothelial cells isolated from IUGR fetal sheep. METHODS: Late-gestation Columbia-Rambouillet IUGR fetal sheep (singleton or twin) underwent surgeries to place vascular sampling and infusion catheters. Fetuses were randomly allocated to receive a 9-d leucine infusion to achieve a 50-100% increase in leucine concentrations or a control saline infusion. GSIS was measured and pancreas tissue was processed for histologic analysis. Pancreatic islet endothelial cells were isolated from IUGR fetal sheep and incubated with supplemental leucine. Data were analyzed by mixed-models ANOVA; Student, Mann-Whitney, or a paired t test; or a test of equality of proportions. RESULTS: Chronic leucine infusion in IUGR fetuses did not affect GSIS, islet size, the proportion of the pancreas comprising ß-cells, or pancreatic or pancreatic islet vascularity. In isolated islet endothelial cells from IUGR fetuses, HGF mRNA expression was not affected by supplemental leucine. CONCLUSIONS: IUGR fetal sheep islets are not responsive to a 9-d leucine infusion with respect to insulin secretion or any histologic features measured. This is in contrast to the response in normally growing fetuses. These results are important when considering nutritional strategies to prevent the adverse islet and ß-cell consequences in IUGR fetuses.

Effects of chronic hyperinsulinemia on metabolic pathways and insulin signaling in the fetal liver.

The effect of chronic of hyperinsulinemia in the fetal liver is poorly understood. Here, we produced hyperinsulinemia with euglycemia for ∼8 days in fetal sheep [hyperinsulinemic (INS)] at 0.9 gestation. INS fetuses had increased insulin and decreased oxygen and amino acid (AA) concentrations compared with saline-infused fetuses [control (CON)]. Glucose (whole body) utilization rates were increased, as expected, in INS fetuses. In the liver, however, there were few differences in genes and metabolites related to glucose and lipid metabolism and no activation of insulin signaling proteins (Akt and mTOR). There was increased p-AMPK activation and decreased mitochondrial mass (PGC1A expression, mitochondrial DNA content) in INS livers. Using an unbiased multivariate analysis with 162 metabolites, we identified effects on AA and one-carbon metabolism in the INS liver. Expression of the transaminase BCAT2 and glutaminase genes GLS1 and GLS2 was decreased, supporting decreased AA utilization. We further evaluated the roles of hyperinsulinemia and hypoxemia, both present in INS fetuses, on outcomes in the liver. Expression of PGC1A correlated only with hyperinsulinemia, p-AMPK correlated only with hypoxemia, and other genes and metabolites correlated with both hyperinsulinemia and hypoxemia. In fetal hepatocytes, acute treatment with insulin activated p-Akt and decreased PGC1A, whereas hypoxia activated p-AMPK. Overall, chronic hyperinsulinemia produced greater effects on amino acid metabolism compared with glucose and lipid metabolism and a novel effect on one-carbon metabolism in the fetal liver. These hepatic metabolic responses may result from the downregulation of insulin signaling and antagonistic effects of hypoxemia-induced AMPK activation that develop with chronic hyperinsulinemia.

A Chronic Fetal Leucine Infusion Potentiates Fetal Insulin Secretion and Increases Pancreatic Islet Size, Vascularity, and ß Cells in Late-Gestation Sheep.

BACKGROUND: Infusion of a complete amino acid mixture into normal late-gestation fetal sheep potentiates glucose-stimulated insulin secretion (GSIS). Leucine acutely stimulates insulin secretion in late-gestation fetal sheep and isolated fetal sheep islets in vitro. OBJECTIVES: We hypothesized that a 9-d leucine infusion would potentiate GSIS in fetal sheep. METHODS: Columbia-Rambouillet fetal sheep at 126 days of gestation received a 9-d leucine infusion to achieve a 50%-100% increase in leucine concentrations or a control infusion. At the end of the infusion we measured GSIS, pancreatic morphology, and expression of pancreatic mRNAs. Pancreatic islet endothelial cells (ECs) were isolated from fetal sheep and incubated with supplemental leucine or vascular endothelial growth factor A (VEGFA) followed by collection of mRNA. Data measured at multiple time points were compared with a repeated-measures 2-factor ANOVA. Data measured at 1 time point were compared using Student's t test or the Mann-Whitney test. RESULTS: Glucose-stimulated insulin concentrations were 80% higher in leucine-infused (LEU) fetuses than in controls (P < 0.05). In the pancreas, LEU fetuses had a higher proportion of islets >5000 µm2 than controls (75% more islets >5000 µm2; P < 0.05) and a larger proportion of the pancreas that stained for ß cells (12% greater; P < 0.05). Pancreatic and pancreatic islet vascularity were both 25% greater in LEU fetuses (P < 0.05). Pancreatic VEGFA and hepatocyte growth factor (HGF) mRNA expressions were 38% and 200% greater in LEU fetuses than in controls (P < 0.05), respectively. In isolated islet ECs, HGF mRNA was 20% and 50% higher after incubation in supplemental leucine (P < 0.05) or VEGFA (P < 0.01), respectively. CONCLUSIONS: A 9-d leucine infusion potentiates fetal GSIS, demonstrating that glucose and leucine act synergistically to stimulate insulin secretion in fetal sheep. A greater proportion of the pancreas being comprised of ß cells and higher pancreatic vascularity contributed to the higher GSIS.

Normalizing adiponectin levels in obese pregnant mice prevents adverse metabolic outcomes in offspring.

Infants of obese mothers have an increased risk of developing obesity, insulin resistance, and type 2 diabetes. The underlying mechanisms remain elusive, and no effective interventions to limit the transmission of metabolic disease from the obese mother to her infant are currently available. Obese pregnant women have decreased circulating levels of adiponectin, which is associated with increased placental nutrient transport and fetal overgrowth. We have reported that normalization of adiponectin levels during late gestation reversed placental dysfunction and fetal overgrowth in a mouse model of maternal obesity in pregnancy. In the current study, we hypothesized that adiponectin supplementation during pregnancy in obese mice attenuates the adverse metabolic outcomes in adult offspring. Adult male offspring of obese mice developed obesity, fatty liver, and insulin resistance, with adult female offspring of obese mice having a less pronounced metabolic phenotype. These metabolic abnormalities in offspring born to obese mice were largely prevented by normalization of maternal adiponectin levels in late pregnancy. We provide evidence that low circulating maternal adiponectin is a critical mechanistic link between maternal obesity and the development of metabolic disease in offspring. Strategies aimed at improving maternal adiponectin levels may prevent long-term metabolic dysfunction in offspring of obese mothers.-Paulsen, M. E., Rosario, F. J., Wesolowski, S. R., Powell, T. L., Jansson, T. Normalizing adiponectin levels in obese pregnant mice prevents adverse metabolic outcomes in offspring.

Sustained hypoxemia in late gestation potentiates hepatic gluconeogenic gene expression but does not activate glucose production in the ovine fetus.

Fetal hypoxemia is associated with pregnancy conditions that cause an early activation of fetal glucose production. However, the independent role of hypoxemia to activate this pathway is not well understood. We hypothesized that fetal hypoxemia would activate fetal glucose production by decreasing umbilical glucose uptake and increasing counter-regulatory hormone concentrations. We induced hypoxemia for 9 days with maternal tracheal N2 gas insufflation to reduce maternal and fetal arterial Po2 by ~20% (HOX) compared with fetuses from ewes receiving intratracheal compressed air (CON). At 0.9 of gestation, fetal metabolic studies were performed (n = 7 CON, 11 HOX). Umbilical blood flow rates, net fetal oxygen and glucose uptake rates, and fetal arterial plasma glucose concentrations were not different between the two groups. Fetal glucose utilization rates were lower in HOX versus CON fetuses but not different from umbilical glucose uptake rates, demonstrating the absence of endogenous glucose production. In liver tissue, mRNA expression of gluconeogenic genes G6PC (P < 0.01) and PCK1 (P = 0.06) were six- and threefold greater in HOX fetuses versus CON fetuses. Increased fetal norepinephrine and cortisol concentrations and hepatic G6PC and PCK1 expression were inversely related to fetal arterial Po2. These findings support a role for fetal hypoxemia to act with counter-regulatory hormones to potentiate fetal hepatic gluconeogenic gene expression. However, in the absence of decreased net fetal glucose uptake rates and plasma glucose concentrations, hypoxemia-induced gluconeogenic gene activation is not sufficient to activate fetal glucose production.

Differential effects of intrauterine growth restriction and a hypersinsulinemic-isoglycemic clamp on metabolic pathways and insulin action in the fetal liver.

Intrauterine growth-restricted (IUGR) fetal sheep have increased hepatic glucose production (HGP) that is resistant to suppression during a hyperinsulinemic-isoglycemic clamp (insulin clamp). We hypothesized that the IUGR fetal liver would have activation of metabolic and signaling pathways that support HGP and inhibition of insulin-signaling pathways. To test this, we used transcriptomic profiling with liver samples from control (CON) and IUGR fetuses receiving saline or an insulin clamp. The IUGR liver had upregulation of genes associated with gluconeogenesis/glycolysis, transcription factor regulation, and cytokine responses and downregulation of genes associated with cholesterol synthesis, amino acid degradation, and detoxification pathways. During the insulin clamp, genes associated with cholesterol synthesis and innate immune response were upregulated in CON and IUGR. There were 20-fold more genes differentially expressed during the insulin clamp in IUGR versus CON. These genes were associated with proteasome activation and decreased amino acid and lipid catabolism. We found increased TRB3, JUN, MYC, and SGK1 expression and decreased PTPRD expression as molecular targets for increased HGP in IUGR. As candidate genes for resistance to insulin's suppression of HGP, expression of JUN, MYC, and SGK1 increased more during the insulin clamp in CON compared with IUGR. Metabolites were measured with 1H-nuclear magnetic resonance and support increased amino acid concentrations, decreased mitochondria activity and energy state, and increased cell stress in the IUGR liver. These results demonstrate a robust response, beyond suppression of HGP, during the insulin clamp and coordinate responses in glucose, amino acid, and lipid metabolism in the IUGR fetus.

Skeletal muscle amino acid uptake is lower and alanine production is greater in late gestation intrauterine growth-restricted fetal sheep hindlimb.

In a sheep model of intrauterine growth restriction (IUGR) produced from placental insufficiency, late gestation fetuses had smaller skeletal muscle mass, myofiber area, and slower muscle protein accretion rates compared with normally growing fetuses. We hypothesized that IUGR fetal muscle develops adaptations that divert amino acids (AAs) from protein accretion and activate pathways that conserve substrates for other organs. We placed hindlimb arterial and venous catheters into late gestation IUGR (n = 10) and control (CON, n = 8) fetal sheep and included an external iliac artery flow probe to measure hindlimb AA uptake rates. Arterial and venous plasma samples and biceps femoris muscle were analyzed by mass spectrometry-based metabolomics. IUGR fetuses had greater abundance of metabolites enriched within the alanine, aspartate, and glutamate metabolism pathway compared with CON. Net uptake rates of branched-chain AA (BCAA) were lower by 42%-73%, and muscle ammoniagenic AAs (alanine, glycine, and glutamine) were lower by 107%-158% in IUGR hindlimbs versus CON. AA uptake rates correlated with hindlimb weight; the smallest hindlimbs showed net release of ammoniagenic AAs. Gene expression levels indicated a decrease in BCAA catabolism in IUGR muscle. Plasma purines were lower and plasma uric acid was higher in IUGR versus CON, possibly a reflection of ATP conservation. We conclude that IUGR skeletal muscle has lower BCAA uptake and develops adaptations that divert AAs away from protein accretion into alternative pathways that sustain global energy production and nitrogen disposal in the form of ammoniagenic AAs for metabolism in other organs.