A new 'crowded uterine horn' mouse model for examining the relationship between foetal growth and adult obesity

Mouse Model of Small for Gestational Age Offspring with Catch-up Growth Failure and Dysregulated Glucose Metabolism in Adulthood

Background

We aimed to build mouse models of small for gestational age (SGA), recapitulating failure of catch-up growth and dysregulated metabolic outcomes in adulthood.

Methods

Pregnant C57BL/6 mice were given a protein-restricted diet (PRD; 6% kcal from protein) during pregnancy without (model 1) or with cross-fostering (model 2). Model 3 extended the PRD to the end of the lactation period. Model 4 changed to a 9% PRD without cross-fostering.

Results

Model 1 yielded a reduced size of offspring with a poor survival rate. Model 2 improved survival but offspring showed early catch-up growth. Model 3 maintained a reduced size of offspring after weaning with a higher body mass index and blood glucose levels in adult stages. Model 4 increased the survival of the offspring while maintaining a reduced size and dysregulated glucose metabolism.

Conclusion

Models 3 and 4 are suitable for studying SGA accompanying adulthood short stature and metabolic disorders.

The Crowded Uterine Horn Mouse Model for Examining Postnatal Metabolic Consequences of Intrauterine Growth Restriction vs. Macrosomia in Siblings

Differential placental blood flow and nutrient transport can lead to both intrauterine growth restriction (IUGR) and macrosomia. Both conditions can lead to adult obesity and other conditions clustered as metabolic syndrome. We previously showed that pregnant hemi-ovariectomized mice have a crowded uterine horn, resulting in siblings whose birth weights differ by over 100% due to differential blood flow based on uterine position. We used this crowded uterus model to compare IUGR and macrosomic male mice and also identified IUGR males with rapid (IUGR-R) and low (IUGR-L) postweaning weight gain. At week 12 IUGR-R males were heavier than IUGR-L males and did not differ from macrosomic males. Rapid growth in IUGR-R males led to glucose intolerance compared to IUGR-L males and down-regulation of adipocyte signaling pathways for fat digestion and absorption and type II diabetes. Macrosomia led to increased fat mass and altered adipocyte size distribution compared to IUGR males, and down-regulation of signaling pathways for carbohydrate and fat digestion and absorption relative to IUGR-R. Clustering analysis of gonadal fat transcriptomes indicated more similarities than differences between IUGR-R and macrosomic males compared to IUGR-L males. Our findings suggest two pathways to adult metabolic disease: macrosomia and IUGR with rapid postweaning growth rate.

Regulation of maternal-fetal metabolic communication

Pregnancy may be the most nutritionally sensitive stage in the life cycle, and improved metabolic health during gestation and early postnatal life can reduce the risk of chronic disease in adulthood. Successful pregnancy requires coordinated metabolic, hormonal, and immunological communication. In this review, maternal-fetal metabolic communication is defined as the bidirectional communication of nutritional status and metabolic demand by various modes including circulating metabolites, endocrine molecules, and other secreted factors. Emphasis is placed on metabolites as a means of maternal-fetal communication by synthesizing findings from studies in humans, non-human primates, domestic animals, rabbits, and rodents. In this review, fetal, placental, and maternal metabolic adaptations are discussed in turn. (1) Fetal macronutrient needs are summarized in terms of the physiological adaptations in place to ensure their proper allocation. (2) Placental metabolite transport and maternal physiological adaptations during gestation, including changes in energy budget, are also discussed. (3) Maternal nutrient limitation and metabolic disorders of pregnancy serve as case studies of the dynamic nature of maternal-fetal metabolic communication. The review concludes with a summary of recent research efforts to identify metabolites, endocrine molecules, and other secreted factors that mediate this communication, with particular emphasis on serum/plasma metabolomics in humans, non-human primates, and rodents. A better understanding of maternal-fetal metabolic communication in health and disease may reveal novel biomarkers and therapeutic targets for metabolic disorders of pregnancy.

Reduced body weight at weaning followed by increased post-weaning growth rate interacts with part-per-trillion fetal serum concentrations of bisphenol A (BPA) to impair glucose tolerance in male mice

There is evidence from longitudinal studies that being light at birth and weaning is associated with subsequent rapid weight gain in infants. This is referred to as “centile crossing”, which can lead to increased risk of lifetime obesity, glucose dysregulation and type 2 diabetes. Here, pregnant CD-1 mice were hemi-ovariectomized so that the entire litter was contained in one uterine horn to increase variability in fetal growth rate. Pregnant females were implanted on gestation day (GD) 9 with a Silastic capsule containing 6, 60 or 600 μg bisphenol A (BPA). On GD 18 the mean fetal serum unconjugated BPA concentrations were 17, 177 and 1858 pg/ml, respectively. Capsules were not removed, to avoid maternal stress, and were predicted to release BPA for at least 3 weeks. Body weight at weaning was strongly negatively correlated with post-weaning weight gain in both control and BPA-treated male mice, consistent with human data; female offspring were excluded, avoiding complications associated with postpubertal estrogens. Within each treatment group, male offspring were sorted into tertiles based on relative weight gain during the two weeks after weaning, designated as having Rapid (R), Medium (M) or Slow (S) growth rate. BPA exposure was associated with altered growth rate between weaning and postnatal week 12 (young adulthood), when a low-dose (20 mg/kg, i.p.) glucose tolerance test (GTT) was performed. We found altered glucose regulation in response to all doses of BPA. However, glucose tolerance was only significantly impaired (blood glucose levels were elevated) compared to controls in males in the rapid post-weaning growth group exposed perinatally to BPA. We conclude that male mice that are light at weaning, but then experience rapid catch-up growth immediately after weaning, represent a sensitive sub-population that is vulnerable to the metabolic disrupting effects of very low pg/ml fetal serum concentrations of BPA.

TRIENNIAL REPRODUCTION SYMPOSIUM: Environmental programming of reproduction during fetal life: Effects of intrauterine position and the endocrine disrupting chemical bisphenol A

During critical periods in fetal life, there is an increased vulnerability to perturbations in endocrine function due to environmental factors. Small shifts in concentrations of hormones that regulate the differentiation of organs, such as estradiol and testosterone, can have permanent effects on morphology, enzymatic activity, and hormone receptors in tissues as well as neurobehavioral effects. These changes can lead to effects throughout life, including impacting the risk for various diseases (referred to as the Developmental Origins of Adult Health and Disease hypothesis). The intrauterine position phenomenon concerns the consequence for fetuses of randomly implanting next to embryos of the same or opposite sex. An intrauterine position next to males vs. females results in small differences in serum testosterone and estradiol during fetal life that are associated with marked effects on life history (such as lifetime fecundity) in both males and females born in litters (mice, rats, gerbils, rabbits, and swine) as well as human twins. Research with mice subsequently demonstrated that a very small experimental change in fetal serum estradiol levels altered organogenesis and caused permanent changes in organ function. Taken together, these findings led to the hypothesis that environmental chemicals that mimic or antagonize hormone action (e.g., endocrine disrupting chemicals) could also be causing harm at very low exposures (the "low dose" hypothesis) within the range of exposure of humans, domesticated animals, and wildlife. There is now extensive evidence from experimental laboratory animals, sheep, and humans that fetal exposure to very low (presumably safe) doses of the endocrine disrupting chemical bisphenol A (BPA), which exhibits estrogenic activity, can cause permanent changes that can increase the risk of a wide array of diseases. The reasons that federal regulatory agencies are ignoring the massive literature showing adverse effects of BPA and other endocrine disrupting chemicals are discussed.

Alcohol-Induced Developmental Origins of Adult-Onset Diseases

Fetal alcohol exposure may impair growth, development, and function of multiple organ systems and is encompassed by the term fetal alcohol spectrum disorders (FASD). Research has so far focused on the mechanisms, prevention, and diagnosis of FASD, while the risk for adult-onset chronic diseases in individuals exposed to alcohol in utero is not well explored. David Barker's hypothesis on Developmental Origins of Health and Disease (DOHaD) suggests that insults to the milieu of the developing fetus program it for adult development of chronic diseases. In the 25 years since the introduction of this hypothesis, epidemiological and animal model studies have made significant advancements in identifying in utero developmental origins of chronic adult-onset diseases affecting cardiovascular, endocrine, musculoskeletal, and psychobehavioral systems. Teratogen exposure is an established programming agent for adult diseases, and recent studies suggest that prenatal alcohol exposure correlates with adult onset of neurobehavioral deficits, cardiovascular disease, endocrine dysfunction, and nutrient homeostasis instability, warranting additional investigation of alcohol-induced DOHaD, as well as patient follow-up well into adulthood for affected individuals. In utero epigenetic alterations during critical periods of methylation are a key potential mechanism for programming and susceptibility of adult-onset chronic diseases, with imprinted genes affecting metabolism being critical targets. Additional studies in epidemiology, phenotypic characterization in response to timing, dose, and duration of exposure, as well as elucidation of mechanisms underlying FASD-DOHaD inter relation, are thus needed to clinically define chronic disease associated with prenatal alcohol exposure. These studies are critical to establish interventional strategies that decrease incidence of these adult-onset diseases and promote healthier aging among individuals affected with FASD.

Novel thromboxane A2 analog-induced IUGR mouse model

Rodents, particularly rats, are used in the majority of intrauterine growth restriction (IUGR) research. An important tool that is lacking in this field is the ability to impose IUGR on transgenic mice. We therefore developed a novel mouse model of chronic IUGR using U-46619, a thromboxane A2 (TXA2) analog, infusion. TXA2 overproduction is prevalent in human pregnancies complicated by cigarette smoking, diabetes mellitus and preeclampsia. In this model, U-46619 micro-osmotic pump infusion in the last week of C57BL/6J mouse gestation caused maternal hypertension. IUGR pups weighed 15% less, had lighter brain, lung, liver and kidney weights, but had similar nose-to-anus lengths compared with sham pups at birth. Metabolically, IUGR pups showed increased essential branched-chain amino acids. They were normoglycemic yet hypoinsulinemic. They showed decreased hepatic mRNA levels of total insulin-like growth factor-1 and its variants, but increased level of peroxisome proliferator-activated receptor-gamma coactivator-1 alpha. IUGR offspring were growth restricted from birth (P1) through postnatal day 21 (P21). IUGR males caught up with sham males in weight by P28, whereas IUGR females caught up with sham females by P77. IUGR males surpassed sham males in weight by P238. In summary, we have a non-brain sparing IUGR mouse model that has a relative ease of surgical IUGR induction and exhibits features similar to the chronic IUGR offspring of humans and other animal models. As transgenic technology predominates in mice, this model now permits the imposition of IUGR on transgenic mice to interrogate mechanisms of fetal origins of adult disease.

Effects of low doses of bisphenol A on the metabolome of perinatally exposed CD-1 mice

BACKGROUND

Bisphenol A (BPA) is a well-known endocrine disruptor used to manufacture polycarbonate plastics and epoxy resins. Exposure of pregnant rodents to low doses of BPA results in pleiotropic effects in their offspring.

OBJECTIVE

We used metabolomics--a method for determining metabolic changes in response to nutritional, pharmacological, or toxic stimuli--to examine metabolic shifts induced in vivo by perinatal exposure to low doses of BPA in CD-1 mice.

METHODS

Male offspring born to pregnant CD-1 mice that were exposed to vehicle or to 0.025, 0.25, or 25 µg BPA/kg body weight/day, from gestation day 8 through day 16 of lactation, were examined on postnatal day (PND) 2 or PND21. Aqueous extracts of newborns (PND2, whole animal) and of livers, brains, and serum samples from PND21 pups were submitted to (1)H nuclear magnetic resonance spectroscopy. Data were analyzed using partial least squares discriminant analysis.

RESULTS

Examination of endogenous metabolic fingerprints revealed remarkable discrimination in whole extracts of the four PND2 newborn treatment groups, strongly suggesting changes in the global metabolism. Furthermore, statistical analyses of liver, serum, and brain samples collected on PND21 successfully discriminated among treatment groups. Variations in glucose, pyruvate, some amino acids, and neurotransmitters (γ-aminobutyric acid and glutamate) were identified.

CONCLUSIONS

Low doses of BPA disrupt global metabolism, including energy metabolism and brain function, in perinatally exposed CD-1 mouse pups. Metabolomics can be used to highlight the effects of low doses of endocrine disruptors by linking perinatal exposure to changes in global metabolism.

Association between body weight at weaning and remodeling in the subcutaneous adipose tissue of obese adult mice with undernourishment in utero

Rapid growth in infancy considerably increases the risk of obesity and metabolic disorders in adulthood especially among neonates born small. To investigate the mechanism involved, we developed an animal model of undernourishment in utero by maternal caloric restriction, in which the Z scores of body weight at weaning (19.5 days) positively correlated with parameters of obesity, metabolic disorders, and remodeling of subcutaneous adipose tissue, such as numbers of macrophages in adipose tissue, the ratio of inflammatory M1 to anti-inflammatory M2 macrophages, estimated by gene expression of specific antigens, and the relative ratio of small adipocytes less than 30 μm in diameter, on a high-fat diet at 17 weeks of age. To our knowledge, this is the first report of a possible connection between infantile body weight and adipose tissue remodeling in obesity after undernourishment in utero.

The estrogenic endocrine disrupting chemical bisphenol A (BPA) and obesity

There is increasing experimental and epidemiological evidence that fetal programming of genetic systems is a contributing factor in the recent increase in adult obesity and other components of metabolic syndrome. In particular, there is evidence that epigenetic changes associated with the use of manmade chemicals may interact with other factors that influence fetal and postnatal growth in contributing to the current obesity epidemic. The focus of this review is on the developmental effects of estrogenic endocrine disrupting chemicals (EDCs), and more specifically on effects of exposure to the estrogenic EDC bisphenol A (BPA), on adipocytes and their function, and the ultimate impact on adult obesity; BPA exposure also results in impaired reproductive capacity. We discuss the interaction of EDCs with other factors that impact growth during fetal and neonatal life, such as placental blood flow and nutrient transport to fetuses, and how these influence fetal growth and abnormalities in homeostatic control systems required to maintain normal body weight throughout life.

Unique in utero identification of fetuses in multifetal mouse pregnancies by placental bidirectional arterial spin labeling MRI

Noninvasive imaging is a critical part of the study of developing embryos/fetuses, particularly in the context of alterations of gene expression in genetically modified animals. However, in litter-bearing animals, such as mice, the inability to accurately identify individual embryo/fetus in utero is a major obstacle to longitudinal, noninvasive in vivo studies. Arterial spin labeling MRI was adopted here to determine the fetal order along the uterine horns in vivo, based on the specific pattern of dual arterial blood supply within the mouse uterine horns. Blood enters the mouse uterus cranially through the ovarian artery and caudally through the uterine artery. Saturation slices were alternately placed on the maternal heart or on the bifurcation point of the common iliac artery, thereby saturating either downward inflow via the ovarian arteries or upward inflow via the uterine arteries, respectively. Saturation maps provided a unique signature with highly significant correlation between the direction-dependent magnetization transfer and the position of the fetuses/placentas along the uterine horns. The bidirectional arterial spin labeling-MRI method reported here opens possibilities to determine and pursue phenotypic alterations in fetuses and placentas in longitudinal studies of transgenic and knockout mice models, and for studying defects in placental vascular architecture.

Fetal signaling through placental structure and endocrine function: illustrations and implications from a nonhuman primate model

The placenta is a transmitter of fetal need and fetal quality, interfacing directly with maternal physiology and ecology. Plasticity of placental structure and function across the developmental timeframe of gestation may serve as an important tool by which a fetus calibrates its growth to shifting maternal ecology and resource availability, and thereby signals its quality and adaptability to a changing environment. Signals of this quality may be conveyed by the size of the placental interface, an important marker of fetal access to maternal resources, or by production of placental insulin-like growth factor-II, a driver of fetoplacental growth. Litter size variation in the common marmoset monkey offers the opportunity to explore intrauterine resource allocation and placental plasticity in an important nonhuman primate model. Triplet marmosets are born at lower birth weights and have poorer postnatal outcomes and survivorship than do twins; triplet placentas differ in placental efficiency, microscopic morphology, and endocrine function. Through placental plasticity, triplet fetuses are able to adjust functional access to maternal resources in a way that allows pregnancy to proceed. However, the costs of such mechanisms may relate to reduced fetal growth and altered postnatal outcomes, with the potential to lead to adverse adult health consequences, suggesting an important link between the placenta itself and the developmental origins of health and disease.