Effects of intrauterine and early postnatal growth restriction on hypothalamic somatostatin gene expression in the rat

Changes in cardiovascular responses to chemoreflex activation of rats recovered from protein restriction are not related to AT1 receptors

NEW FINDINGS

What is the central question of this study? In this study, we sought to investigate whether cardiovascular responses to peripheral chemoreflex activation of rats recovered from protein restriction are related to activation of AT₁ receptors. What is the main finding and its importance? This study highlights the fact that angiotensinergic mechanisms activated by AT₁ receptors do not support increased responses to peripheral chemoreflex activation by KCN in rats recovered from protein restriction. Also, we found that protein restriction led to increased resting ventilation in adult rats, even after recovery. The effects of a low-protein diet followed by recovery on cardiorespiratory responses to peripheral chemoreflex activation were tested before and after systemic angiotensin II type 1 (AT₁ ) receptor antagonism. Male Fischer rats were divided into control and recovered (R-PR) groups after weaning. The R-PR rats were fed a low-protein (8%) diet for 35 days and recovered with a normal protein (20%) diet for 70 days. Control rats received a normal protein diet for 105 days (CG₁₀₅ ). After cannulation surgery, mean arterial pressure, heart rate, respiratory frequency, tidal volume and minute ventilation were acquired using a digital recording system in freely moving rats. The role of angintensin II was evaluated by systemic antagonism of AT₁ receptors with losartan (20 mg kg^-1 i.v.). The peripheral chemoreflex was elicited by increasing doses of KCN (20-160 μg kg min^-1 , i.v.). At baseline, R-PR rats presented increased heart rate and minute ventilation (372 ± 34 beats min^-1 and 1.274 ± 377 ml kg^-1  min^-1 ) compared with CG₁₀₅ animals (332 ± 22 beats min^-1 and 856 ± 112 ml kg^-1  min^-1 ). Mean arterial pressure was not different between the groups. Pressor and bradycardic responses evoked by KCN (60 μg kg^-1 ) were increased in R-PR (+45 ± 13 mmHg and -77 ± 47 beats min^-1 ) compared with CG₁₀₅ rats (+25 ± 17 mmHg and -27 ± 28 beats min^-1 ), but no difference was found in the tachypnoeic response. These differences were preserved after losartan. The data suggest that angiotensin II acting on AT₁ receptors may not be associated with the increased heart rate, increased minute ventilation and acute cardiovascular responses to peripheral chemoreflex activation in rats that underwent postweaning protein restriction followed by recovery.

Bilateral uterine vessel ligation as a model of intrauterine growth restriction in mice

BACKGROUND

Intrauterine growth restriction (IUGR) occurs in up to 10% of pregnancies and is considered as a major risk to develop various diseases in adulthood, such as cardiovascular diseases, insulin resistance, hypertension or end stage kidney disease. Several IUGR models have been developed in order to understand the biological processes linked to fetal growth retardation, most of them being rat or mouse models and nutritional models. In order to reproduce altered placental flow, surgical models have also been developed, and among them bilateral uterine ligation has been frequently used. Nevertheless, this model has never been developed in the mouse, although murine tools display multiple advantages for biological research. The aim of this work was therefore to develop a mouse model of bilateral uterine ligation as a surgical model of IUGR.

RESULTS

In this report, we describe the set up and experimental data obtained from three different protocols (P1, P2, P3) of bilateral uterine vessel ligation in the mouse. Ligation was either performed at the cervical end of each uterine horn (P1) or at the central part of each uterine horn (P2 and P3). Time of surgery was E16 (P1), E17 (P2) or E16.5 (P3). Mortality, maternal weight and abortion parameters were recorded, as well as placentas weights, fetal resorption, viability, fetal weight and size. Results showed that P1 in test animals led to IUGR but was also accompanied with high mortality rate of mothers (50%), low viability of fetuses (8%) and high resorption rate (25%). P2 and P3 improved most of these parameters (decreased mortality and improved pregnancy outcomes; improved fetal viability to 90% and 27%, respectively) nevertheless P2 was not associated to IUGR contrary to P3. Thus P3 experimental conditions enable IUGR with better pregnancy and fetuses outcomes parameters that allow its use in experimental studies.

CONCLUSIONS

Our results show that bilateral uterine artery ligation according to the protocol we have developed and validated can be used as a surgical mouse model of IUGR.

Non-coding RNA and DNA as epigenetic biomarkers for pre-eclampsia

The human genome contains a hidden and large layer of biologic information that is not accessible by proteomic or metabolic methods. Insight into the nature, size, function and importance of this information is increasing rapidly. This additional layer of information includes non-coding RNA and DNA and can be retrieved and analyzed using nucleic acids that circulate in the maternal plasma during pregnancy, originate from the developing placenta and provide information on fetal well being. This review explains why, when and how fetal information as carried on and provided by the placental DNA and RNA molecules circulating in the plasma of pregnant women can be explored to understand and to analyze the primary placental processes, that underlie pre-eclampsia and related disorders.

Continuity between fetal and neonatal neurobehavior

The human brain is very sensitive to environmental changes affecting its growth and development. Environmental changes influence neonatal behavior after birth, enabling continuity between prenatal and postnatal behavior, but postnatal adaptation could be considered as discontinuity. Thus there is the question of environmental discontinuity between intrauterine conditions characterized by existence of microgravity and extrauterine life with gravity as a developmental condition sine qua non. Four-dimensional ultrasound is currently being assessed as a functional prenatal screening test for detection of neurological impairment in utero. The Kurjak Antenatal Neurodevelopmental Test (KANET) combines the assessment of fetal behavior, general movements, and three out of four signs that have been postnatally considered as symptoms of possible neurodevelopmental impairment (neurological thumb, overlapping sutures and small head circumference). Although the KANET has been tested on normal and high-risk pregnancies, the significance of the test for detection and prevention of neurodevelopmental disability is still questionable.

Neurobehavioral continuity from fetus to neonate

Neurobehavior represents development of the central nervous system (CNS). Fetuses and newborns exhibit a large number of endogenously generated motor patterns, among which general movements are often investigated pre- and post-natally. Spontaneous activity is probably a more sensitive indicator of brain dysfunction than reactivity to sensory stimuli while testing reflexes. Nutritional stress at critical times during fetal development can have persistent and potentially irreversible effects particularly on brain growth and function. Unfavorable intrauterine environment can affect adversely brain growth. All endogenously generated movement patterns from un-stimulated CNS might be observed as early as from the seven to eight weeks' gestation, with a rich repertoire of movements within the next two or three weeks, continuing for five to six months postnatally. It is still uncertain whether a new scoring system for prenatal neurological assessment will be adequate for the distinction between normal and abnormal fetuses in low-risk pregnancies. The continuity of behavioral patterns from prenatal to postnatal life might answer these intriguing questions.

Maternal undernutrition and endocrine development

Maternal undernutrition, whether it occurs before conception, throughout gestation or during lactation, may lead to physiological adaptations in the fetus that will affect the health of the offspring in adult life. The timing, severity, duration and nature of the maternal nutritional insult may affect the offspring differently. Other factors determining outcome following maternal undernutrition are fetal number and gender. Importantly, effects of maternal undernutrition may be carried over into subsequent generations. This review examines the endocrine pathways disrupted by maternal undernutrition that affect the long-term postnatal health of the offspring. Maternal and childhood undernutrition are highly prevalent in low- and middle-income countries, and, in developed countries, unintentional undernutrition may arise from maternal dieting. It is, therefore, important that we better understand the mechanisms driving the long-term effects of maternal undernutrition, as well as identifying treatments to ameliorate the associated mortality and morbidity.

Gene expression in the placenta: maternal stress and epigenetic responses

Successful placental development is crucial for optimal growth, development, maturation and survival of the embryo/fetus into adulthood. Numerous epidemiologic and experimental studies have demonstrated the profound influence of intrauterine environment on life, and the diseases to which one is subject as an adult. For the most part, these invidious influences, whether maternal hypoxia, protein or caloric deficiency or excess, and others, represent types of maternal stress. In the present review, we examine certain aspects of gene expression in the placenta as a consequence of maternal stressors. To examine these issues in a controlled manner, and in a species in which the genome has been sequenced, most of these reported studies have been performed in the mouse. Although each individual maternal stress is characterized by up- or down-regulation of specific genes in the placenta, functional analysis reveals some patterns of gene expression common to the several forms of stress. Of critical importance, these genes include those involved in DNA methylation and histone modification, cell cycle regulation, and related global pathways of great relevance to epigenesis and the developmental origins of adult health and disease.

Placental gene expression responses to maternal protein restriction in the mouse

OBJECTIVE

Maternal protein restriction has been shown to have deleterious effects on placental development, and has long-term consequences for the progeny. We tested the hypothesis that, by the use of microarray technology, we could identify specific genes and cellular pathways in the developing placenta that are responsive to maternal protein deprivation, and propose a potential mechanism for observed gene expression changes.

METHODS

We fed pregnant FVB/NJ mice from day post-coitum 10.5 (DPC10.5) to DPC17.5, an isocaloric diet containing 50% less protein than normal chow. We used the Affymetrix Mouse 430A_2.0 array to measure gene expression changes in the placenta. We functionally annotated the regulated genes, and examined over-represented functional categories and performed pathway analysis. For selected genes, we confirmed the microarray results by use of qPCR.

RESULTS

We observed 244 probe sets, corresponding to 235 genes, regulated by protein restriction (p<0.001), with ninety-one genes being up-regulated, and 153 down-regulated. Up-regulated genes included those involved in the p53 pathway, apoptosis, negative regulators of cell growth, negative regulators of cell metabolism and genes related to epigenetic control. Down-regulated genes included those involved in nucleotide metabolism.

CONCLUSIONS

Microarray analysis has allowed us to describe the genetic response to maternal protein deprivation in the mouse placenta. We observed that negative regulators of cell growth and metabolism in conjunction with genes involved in epigenesis were up-regulated, suggesting that protein deprivation may contribute to growth restriction and long-term epigenetic changes in stressed tissues and organs. The challenge will be to understand the cellular and molecular mechanisms of these gene expression responses.

Early postnatal nutrition determines somatotropic function in mice

Increasing evidence suggests a developmental origin for a number of human diseases, notably after intrauterine or postnatal nutrient deprivation. Nutritional changes readily translate into alterations of somatic growth. However, whereas intrauterine growth retardation often shows postnatal catch-up growth, recovery from food restriction immediately after birth is limited. Therefore, we investigated whether early postnatal nutrition (undernutrition and overfeeding) modifies plasticity of growth through developmental control of the somatotropic hormone axis. We used cross-fostering in mice to induce changes in early nutrition, and examined endocrine growth regulation and the development of specific disease phenotypes in adults. We showed that underfeeding during the early postnatal period delayed growth, whereas overfeeding accelerated it. In both cases, final body size was permanently altered. We found coordinated alterations in pituitary GH, plasma IGF-I and acid labile subunit, and gene expression of hypothalamic GHRH during postnatal development. These changes were consistent with the observed phenotypes. Alterations in the somatotropic axis persisted throughout adulthood. Although limited to the early postnatal period, both underfeeding and overfeeding led to reduced glucose tolerance later in life. These metabolic abnormalities were in line with defective insulin secretion in restricted mice and insulin resistance in overfed mice. Moreover, both restricted and overfed mice had increased arterial blood pressure, suggestive of vascular impairment. Our findings indicate a significant link between early postnatal diet, somatotropic development, and specific late onset diseases in mice. We suggest that, together with other hormones like leptin, IGF-I may play a role in modulating hypothalamic stimulation of the developing somatotropic function.

Pituitary mRNA expression of the growth hormone axis in the 1-year-old intrauterine growth restricted rat

Intrauterine growth restriction (IUGR) is one of the major causes of short stature in childhood. Abnormalities in the growth hormone (GH) axis have frequently been observed in children who are born intrauterine growth restricted and GH treatment is effective to improve final height. However, the way that the GH axis is involved is not fully understood. Previously, when investigating the effect of IUGR on the central somatotrophic axis, a hypothalamic effect was discovered with elevated somatostatin and decreased neuropeptide Y mRNA expression levels, whereas serum GH and insulin-like growth factor I (IGFI) were unaltered. These findings were thought to indicate a hypothalamic alteration of the GH axis due to IUGR, probably to compensate pituitary output, thereby normalising peripheral values of GH and IGFI. Therefore, the present study aimed to evaluate the effect of IUGR on the pituitary GH axis in this rat model. Pups from rats that underwent bilateral uterine artery ligation at day 17 of pregnancy were studied. Pituitary glands were collected from 1-year-old offspring for quantitative measurements of GH, GH-receptor (GH-R), GH-releasing hormone receptor (GHRH-R), somatostatin receptor subtype 2 and 5, IGFI and IGFI receptor mRNA levels using a real-time reverse transcriptase-polymerase chain reaction. In addition, liver GH-R and IGFI mRNA expression levels were measured and a radioimmunoassay was performed to determine serum IGFI levels. In the IUGR rat, levels of pituitary GH, GH-R and GHRH-R relative gene expression (RGE) were increased. No differences were found in the RGE level of all other pituitary growth factors, liver GH-R and IGFI, and serum IGFI concentration between IUGR and control rats. The present data show that intrauterine growth failure leads to changes in the pituitary that might counterbalance the effects found previously in the hypothalamus.

Impact of intrauterine growth restriction and glucocorticoids on brain development: insights using advanced magnetic resonance imaging

There are now a number of evidences showing that the developing organism adapts to the environment it finds itself. Short- and long-term adjustments, referred as "programming", take place and will initially induce intrauterine growth retardation but will also have consequences that will appear later in life. The use of magnetic resonance imaging (MRI) techniques in IUGR babies has delineated changes in the central nervous system (CNS) development that correlate with altered neurodevelopment and could be implicated in the development of neuropsychiatric disorders in adult life. Similarly, the use of corticosteroid treatment in preterm infants has also been implicated in abnormal CNS development. In this review, we will focus on the modifications of CNS development that occur after exposition to adverse environment such as undernutrition or corticosteroid treatment that can now be studied in vivo with advanced MRI technology.

Ligation of the Uterine Artery and Early Postnatal Food Restriction – Animal Models for Growth Retardation

Intrauterine growth restriction (IUGR) is one of the major causes of short stature in child- and adulthood. The cause of IUGR is unknown, however, an impaired uteroplacental function during the second half of human pregnancy might be an important factor, by affecting the programming of somatotropic axis and leading to postnatal growth failure into adulthood. Two rat models with perinatally induced growth retardation were used to examine the long-term effects of perinatal insults on growth. IUGR rats were prepared from pregnant dams, with a bilateral uterine artery ligation at day 17 of their pregnancy. Since the rat is relatively immature at birth, an early postnatal food restriction model was included as another model to broaden the time window of sensitive period of organogenesis. An individual growth curve was calculated of each animal (n = 813). From these individual growth curves the predicted growth curve for each experimental group was calculated by multilevel analysis. The proposed mathematical model allows us to estimate the growth potentials of these rat models with precision and could provide basic information to investigate the relationships among a number of other variables in future studies. Furthermore, we concluded that both pre- and early postnatal malnutrition leads to irreversible slowing down of postnatal growth.

Effects of perinatal maternal food restriction on pituitary-gonadal axis and plasma leptin level in rat pup at birth and weaning and on timing of puberty

The effects of maternal 50% food restriction (FR) during the last week of gestation and/or lactation on pituitary-gonadal axis (at birth and weaning), on circulating levels of leptin (at weaning), and on the onset of puberty have been determined in rats at birth and at weaning. Maternal FR during pregnancy has no effect at term on the litter size, on the basal level of testosterone in male pups, and on the drastic surge of circulating testosterone that occurs 2 h after birth. At weaning, similar retardation of body growth is observed in male and female pups from mothers exposed to FR. This undernutrition induces the most drastic effects when it is performed during both gestation and lactation or during lactation alone. Drastic retardation of testicle growth with reduction of cross-sectional area and intratubular lumen of the seminiferous tubules is observed in male pups from mothers exposed to undernutrition during both gestation and lactation or during lactation alone. Maternal FR during the perinatal period reduces circulating levels of FSH in male pups without affecting LH and testosterone concentrations. Maternal FR does not affect circulating levels of LH, estradiol, and progesterone in female pups. Female pups from mothers exposed to FR during both gestation and lactation show a significant increase of plasma FSH as well as a drastic retardation of ovarian growth. The follicular population was also altered. The number of antral follicles of small size (vesicular follicles) was increased, although the number of antral follicles of large size (graafian follicles) was reduced. Maternal FR occurring during both late gestation and lactation (male and female pups), during lactation alone (male and female pups), or during late gestation (female pups) induces a drastic reduction of plasma leptin and fat mass in pups at weaning. The onset of puberty is delayed in pups of both sexes from mothers exposed to FR during lactation and during both gestation and lactation. In conclusion, these data demonstrate that a perinatal growth retardation induced by maternal FR has long-term consequences on both size and histology of the genitals, on plasma gonadotropins and leptin levels, on fat stores at weaning, and on the onset of puberty.