Timothy R. H. Regnault

In Utero Programming of Later Adiposity: The Role of Fetal Growth Restriction

Intrauterine growth restriction (IUGR) is strongly associated with obesity in adult life. The mechanisms contributing to the onset of IUGR-associated adult obesity have been studied in animal models and humans, where changes in fetal adipose tissue development, hormone levels and epigenome have been identified as principal areas of alteration leading to later life obesity. Following an adverse in utero development, IUGR fetuses display increased lipogenic and adipogenic capacity in adipocytes, hypoleptinemia, altered glucocorticoid signalling, and chromatin remodelling, which subsequently all contribute to an increased later life obesity risk. Data suggest that many of these changes result from an enhanced activity of the adipose master transcription factor regulator, peroxisome proliferator-activated receptor-γ (PPARγ) and its coregulators, increased lipogenic fatty acid synthase (FAS) expression and activity, and upregulation of glycolysis in fetal adipose tissue. Increased expression of fetal hypothalamic neuropeptide Y (NPY), altered hypothalamic leptin receptor expression and partitioning, reduced adipose noradrenergic sympathetic innervations, enhanced adipose glucocorticoid action, and modifications in methylation status in the promoter of hepatic and adipose adipogenic and lipogenic genes in the fetus also contribute to obesity following IUGR. Therefore, interventions that inhibit these fetal developmental changes will be beneficial for modulation of adult body fat accumulation.

Altered placental and fetal expression of IGFS and IGF-binding proteins associated with intrauterine growth restriction in fetal sheep during early and mid-pregnancy

The insulin-like growth factors (IGFs) are postulated to be altered in association with the development of intrauterine growth restriction (IUGR). The present studies examined placental and fetal hepatic mRNA concentration of components of the IGF system at two time points (55 and 90 d gestational age, dGA; Term 147 dGA) in a hyperthermia (HT)-induced sheep model of placental insufficiency-IUGR. Maternal plasma insulin and IGF-I were constant at 55 and 90 dGA and were unaffected by treatment. Umbilical vein insulin concentrations tended to be reduced at 90 dGA following HT exposure. Caruncle IGF-I mRNA was increased at 90 dGA in HT placentae (p < 0.05), while cotyledon concentrations were constant over gestation and unaltered by treatment. In control cotyledons, IGF-II mRNA concentration increased (p < 0.01) and IGFBP-3 decreased between 55 and 90 dGA (p < 0.01). Cotyledon IGF-II and caruncle IGFBP-4 mRNA were elevated at 55 dGA in HT placentae compared with control (p < 0.01 and p < 0.05 respectively). Fetal hepatic IGF-I, IGFBP-2, -3 and -4 concentrations rose over gestation (p < 0.05), but there were no treatment effects. These data suggest that changes in placental IGF expression in early and mid gestation may predispose the pregnancy to placental insufficiency, resulting in inadequate substrate supply to the developing fetus later in gestation.

In Utero Origins of Adult Insulin Resistance and Vascular Dysfunction

The metabolic syndrome (or syndrome X) is a constellation of risk factors including insulin resistance, hypertension, dyslipidemia, and central obesity that predispose to the development of cardiovascular disease and type 2 diabetes in adult life. Insulin resistance is believed to be a critical pathophysiological event early in the disease process, impacting both skeletal muscle metabolic function and vascular responses. Adverse changes in insulin sensitivity have been found to originate in utero; for instance, prenatal events such as placental insufficiency/oxidative stress leading to altered fetal growth trajectories are associated with increased rates of metabolic syndrome in adult life. Such intrauterine insults result in reduced skeletal muscle mass in conjunction with altered insulin signaling, decreased oxidative fibers, and impaired mitochondrial function. These developmental disturbances set the stage for development of muscle triglyceride accumulation and depressed insulin sensitivity in childhood. Abnormalities of vascular structure and function arising from deprived intrauterine conditions that are exacerbated by insulin resistance account for the progression of hypertension from childhood to adulthood. Arterial changes initiated in utero include reduced endothelial nitric oxide (NO) bioavailability, vascular smooth muscle cell proliferation and inflammation, events leading to endothelial dysfunction, and atherosclerosis that are present in those destined for metabolic syndrome. In addition, the hypertensive phenotype that is a hallmark of metabolic syndrome may also be traced to blunted kidney development and renin-angiotensin system activation in growth-restricted offspring. The summative impact of these intrauterine programmed changes in terms of influencing adult health and disease encompasses dietary and lifestyle factors introduced postnatally. Establishing novel therapeutic interventions aimed at preventing and/or reducing in utero-induced insulin resistance and vascular dysfunction warrants investigation because the numbers of low birthweight babies continue to increase.

Fructose, pregnancy and later life impacts

Fructose is an increasingly common constituent of the Westernized diet due to cost and production efficiencies. Although an integral component of our pre‐industrial revolution diet, over the past two decades human and animal studies have highlighted that excessive fructose intake appears to be associated with adverse metabolic effects. Excessive intake of fructose is the combined result of increased total energy consumption and increased portion sizes of foods, which often incorporate the fructose‐containing sugars sucrose and high‐fructose corn‐syrup (HFCS). The adverse metabolic effects following excessive fructose consumption have become a hot topic in mainstream media and there is now rigorous scientific debate regarding periods of exposure, dosage levels, interactive effects with other sugars and fats and mechanisms underlying the actions of fructose. There is still a degree of controversy regarding the extent to which sugars such as sucrose and HFCS have contributed to the current epidemic of obesity and diabetes. Furthermore, an increasing number of infants are being exposed to sugar‐sweetened food and beverages before birth and during early postnatal life, highlighting the importance of determining the long‐term effects of this perinatal exposure on the developing offspring. There are limited human observational and controlled studies identifying associations of excessive sweetened food and beverage consumption with poor pregnancy outcomes. Animal research has demonstrated an increased incidence of gestational diabetes as well as altered maternal, fetal and offspring metabolic function, although the long‐term effects and the mechanism underlying these perturbations are ill defined. This review aims to understand the role of early life fructose exposure in modifying postnatal risk of disease in the offspring, focusing on fructose intake during pregnancy and in early postnatal life.

Chronic intrauterine hypoxia interferes with aortic development in the late gestation ovine fetus

Non‐technical summary  It is now known that adverse events in the womb leading to fetal growth impairment increase the risk of cardiovascular disease (CVD) in adulthood. We show perturbed arterial development in sheep fetuses subjected to oxygen deprivation by placental dysfunction, which accounts for the majority of fetal growth restriction in developed countries. The altered structure and composition of the vascular wall exhibited by growth restricted sheep fetuses are akin to those changes present in the preclinical stage of CVD. Therefore, we reveal a plausible mechanism of CVD susceptibility in individuals growth restricted by placental dysfunction. In addition, we identified molecular factors involved in aberrant arterial formation and thus highlight the need for further investigation into these molecular pathways and possible prenatal interventions such as antioxidants.

Placental expression of angiopoietin-1, angiopoietin-2 and tie-2 during placental development in an ovine model of placental insufficiency-fetal growth restriction.

Fetal growth restriction (FGR) is associated with increased perinatal morbidity and mortality, and often results from functional placental insufficiency. Placentation requires extensive vasculogenesis and subsequent angiogenesis, in both maternal and fetal tissues. Angiopoietin-1 (Ang-1) and Angiopoietin-2 (Ang-2) are angiogenic growth factors expressed in the placenta, and compete for binding to a common receptor, Tunica interna endothelial cell kinase-2 (Tie-2). Our objective was to examine Ang-1, Ang-2 and Tie-2 expression in ovine placental tissue obtained from normal and FGR pregnancies throughout gestation. Fetal cotyledon and maternal caruncle tissue concentrations of Ang-1, Ang-2 and Tie-2 mRNA were assessed by real-time reverse transcriptase-polymerase chain reaction and protein concentrations were assessed by Western immunoblot analysis, at 55, 90 and 135 d gestational age (dGA). Concentrations of Ang-1, Ang-2 and Tie-2 mRNA in FGR fetal cotyledons were increased at 55 dGA, and Tie-2 mRNA concentrations were decreased in FGR fetal cotyledons and maternal caruncles at 135 dGA. Immunoblot analysis demonstrated increased concentrations of Ang-2 in the fetal cotyledon at 55 dGA, and lower concentrations at 135 dGA. In contrast, concentrations of Tie-2 were increased at 90 dGA, but tended to decrease at 135 dGA in FGR maternal caruncles. The changes observed during early- to mid-gestation may result in increased branching angiogenesis, but may also set the stage for increased nonbranching angiogenesis during late gestation, altered placental architecture and placental insufficiency that result in FGR.

The expression of ovine placental lactogen, StAR and progesterone-associated steroidogenic enzymes in placentae of overnourished growing adolescent ewes

Overnourishing pregnant adolescent sheep promotes maternal growth but reduces placental mass, lamb birth weight and circulating progesterone. This study aimed to determine whether altered progesterone reflected transcript abundance for StAR (cholesterol transporter) and the steroidogenic enzymes (Cyp11A1, Hsd3b and Cyp17). Circulating and placental expression of ovine placental lactogen (oPL) was also investigated. Adolescent ewes with singleton pregnancies were fed high (H) or moderate (M) nutrient intake diets to restrict or support placental growth. Experiment 1: peripheral progesterone and oPL concentrations were measured in H (n=7) and M (n=6) animals across gestation (days 7-140). Experiment 2: progesterone was measured to mid- (day 81; M: n=11, H: n=13) or late gestation (day 130; M: n=21, H: n=22), placental oPL, StAR and steroidogenic enzymes were measured by qPCR and oPL protein by immunohistochemistry. Experiment 1: in H vs M animals, term placental (P<0.05), total cotyledon (P<0.01) and foetal size (P<0.05) were reduced. Circulating oPL and progesterone were reduced at mid- (P<0.001, P<0.01) and late gestation (P<0.01, P<0.05) and oPL detection was delayed (P<0.01). Experiment 2: placental oPL was not altered by nutrition. In day 81 H animals, progesterone levels were reduced (P<0.001) but not related to placental or foetal size. Moreover, placental steroidogenic enzymes were unaffected. Day 130 progesterone (P<0.001) and Cyp11A1 (P<0.05) were reduced in H animals with intrauterine growth restriction (H+IUGR). Reduced mid-gestation peripheral oPL and progesterone may reflect altered placental differentiation and/or increased hepatic clearance respectively. Restricted placental growth and reduced biosynthesis may account for reduced progesterone in day 130 H+IUGR ewes.

Umbilical uptakes and transplacental concentration ratios of amino acids in severe fetal growth restriction.

Background:This study examines the relationship between placental amino acid (AA) transport and fetal AA demand in an ovine fetal growth restriction (FGR) model in which placental underdevelopment induces fetal hypoxemia and hypoglycemia.Methods:Umbilical uptakes of AA, oxygen, glucose, and lactate were measured near term in eight experimental ewes (FGR group) and in eight controls (C group).Results:The FGR group demonstrated significantly reduced umbilical uptakes of oxygen, glucose, lactate, and 11 AAs per kg fetus. The combined uptake of glucose, lactate, and AAs, expressed as nutrient/oxygen quotients, was reduced almost to 1.00 (FGR: 1.05 vs. C: 1.32, P ≤ 0.02). In contrast to a decrease in umbilical glucose concentration, all but one of the AAs that were transported from placenta to fetus demonstrated normal or elevated fetal concentrations, and five of the essential AAs were transported against a significantly higher feto/maternal (F/M) concentration ratio. This ratio peaked at the lowest fetal oxygen levels.Conclusion:We conclude that, in the hypoxic FGR fetus, the reduction in AA uptake is not due to a disproportionally small placental AA transport capacity. It is the consequence of decreased fetal oxidative metabolism and growth rate, which together reduce fetal AA demand.

The Long and Short of It: The Role of Telomeres in Fetal Origins of Adult Disease

Placental insufficiency, maternal malnutrition, and other causes of intrauterine growth restriction (IUGR) can significantly affect short-term growth and long-term health. Following IUGR, there is an increased risk for cardiovascular disease and Type 2 Diabetes. The etiology of these diseases is beginning to be elucidated, and premature aging or cellular senescence through increased oxidative stress and DNA damage to telomeric ends may be initiators of these disease processes. This paper will explore the areas where telomere and telomerase biology can have significant effects on various tissues in the body in IUGR outcomes.

Central stiffening in adulthood linked to aberrant aortic remodeling under suboptimal intrauterine conditions

This study examined perturbed aortic development and subsequent wall stiffening as a link to later cardiovascular disease. Placental insufficiency was induced in pregnant guinea pigs at midgestation by uterine artery ligation. Near term, fetuses were killed and defined as normal birth weight (NBW), low birth weight (LBW), and intrauterine growth restricted (IUGR). Offspring were classified according to birth weight and killed in adulthood. Collagen and elastin content of aortas were analyzed using Sirius red and orcein staining, respectively. Immunofluorescence was used for detection of α-actin and nonmuscle myosin heavy chain (MHC-B), a marker of synthetic-type vascular smooth muscle cells (VSMCs). Ex vivo generation of length-tension curves was performed with aortic rings from adult offspring. Relative elastic fiber content was decreased by 10% in LBW and 14% in IUGR compared with NBW fetuses. In adulthood, relative elastic fiber content was 51% lower in LBW vs. NBW, and the number of elastic laminae adjusted for wall thickness was 25% lower in LBW (P < 0.01). The percent area stained for MHC-B was sixfold higher in LBW vs. NBW fetuses (P < 0.0001) and threefold higher in LBW vs. NBW adult offspring (P < 0.05). The increase in MHC-B in LBW offspring concurred with a 41% increase in total collagen content and a 33 and 56% increase in relative and total α-actin content, respectively (P < 0.05). Thus aortic wall stiffening in adulthood can be traced to altered matrix composition established under suboptimal intrauterine conditions that is amplified postnatally by the activity of synthetic VSMCs.