Maternal nutrient restriction and the fetal left ventricle: decreased angiotensin receptor expression

Animal Foetal Models of Obesity and Diabetes - From Laboratory to Clinical Settings

The prenatal period, during which a fully formed newborn capable of surviving outside its mother's body is built from a single cell, is critical for human development. It is also the time when the foetus is particularly vulnerable to environmental factors, which may modulate the course of its development. Both epidemiological and animal studies have shown that foetal programming of physiological systems may alter the growth and function of organs and lead to pathology in adulthood. Nutrition is a particularly important environmental factor for the pregnant mother as it affects the condition of offspring. Numerous studies have shown that an unbalanced maternal metabolic status (under- or overnutrition) may cause long-lasting physiological and behavioural alterations, resulting in metabolic disorders, such as obesity and type 2 diabetes (T2DM). Various diets are used in laboratory settings in order to induce maternal obesity and metabolic disorders, and to alter the offspring development. The most popular models are: high-fat, high-sugar, high-fat-high-sugar, and cafeteria diets. Maternal undernutrition models are also used, which results in metabolic problems in offspring. Similarly to animal data, human studies have shown the influence of mothers' diets on the development of children. There is a strong link between the maternal diet and the birth weight, metabolic state, changes in the cardiovascular and central nervous system of the offspring. The mechanisms linking impaired foetal development and adult diseases remain under discussion. Epigenetic mechanisms are believed to play a major role in prenatal programming. Additionally, sexually dimorphic effects on offspring are observed. Therefore, further research on both sexes is necessary.

Caloric Restriction and Cardiovascular Health: the Good, the Bad, and the Renin-Angiotensin System

Much excitement exists over the cardioprotective and life-extending effects of caloric restriction (CR). This review integrates population studies with experimental animal research to address the positive and negative impact of mild and severe CR on cardiovascular physiology and pathophysiology, with a particular focus on the renin-angiotensin system (RAS). We also highlight the gaps in knowledge and areas ripe for future physiological research.

Sexual dimorphism in the fetal cardiac response to maternal nutrient restriction

Poor maternal nutrition causes intrauterine growth restriction (IUGR); however, its effects on fetal cardiac development are unclear. We have developed a baboon model of moderate maternal undernutrition, leading to IUGR. We hypothesized that the IUGR affects fetal cardiac structure and metabolism. Six control pregnant baboons ate ad-libitum (CTRL)) or 70% CTRL from 0.16 of gestation (G). Fetuses were euthanized at C-section at 0.9G under general anesthesia. Male but not female IUGR fetuses showed left ventricular fibrosis inversely correlated with birth weight. Expression of extracellular matrix protein TSP-1 was increased (p<0.05) in male IUGR. Expression of cardiac fibrotic markers TGFβ, SMAD3 and ALK-1 were downregulated in male IUGRs with no difference in females. Autophagy was present in male IUGR evidenced by upregulation of ATG7 expression and lipidation LC3B. Global miRNA expression profiling revealed 56 annotated and novel cardiac miRNAs exclusively dysregulated in female IUGR, and 38 cardiac miRNAs were exclusively dysregulated in males (p<0.05). Fifteen (CTRL) and 23 (IUGR) miRNAs, were differentially expressed between males and females (p<0.05) suggesting sexual dimorphism, which can be at least partially explained by differential expression of upstream transcription factors (e.g. HNF4α, and NFκB p50). Lipidomics analysis of fetal cardiac tissue exhibited a net increase in diacylglycerol and plasmalogens and a decrease in triglycerides and phosphatidylcholines. In summary, IUGR resulting from decreased maternal nutrition is associated with sex-dependent dysregulations in cardiac structure, miRNA expression, and lipid metabolism. If these changes persist postnatally, they may program offspring for higher later life cardiac risk.

Nutrient-restricted fetus and the cardio–renal connection in hypertensive offspring

A suboptimal intrauterine environment has a number of deleterious effects on fetal development and postpartum health outcomes. Epidemiological studies on several human populations have linked socioeconomic status and low birth weight to an increased incidence of diseases such as hypertension, diabetes, obesity and cardiovascular disease. A growing number of experimental studies in a variety of animal models demonstrate that maternal stressors, such as nutrition and reduced uterine perfusion, affect the intrauterine milieu and result in increased blood pressure in offspring. Several mechanisms appear to contribute to hypertension, including vascular dysfunction and increased peripheral resistance, altered cardio-renal structure and alterations in cardio-renal function. Although many studies have characterized models of developmentally generated hypertension, few have begun to seek therapeutic modalities to ameliorate its incidence. This review discusses recent work that refines hypotheses linking a suboptimal intrauterine environment to cardiovascular and renal phenotypes that have increased susceptibility to cardiovascular disease and hypertension.

The frail renin-angiotensin system

Over the last few decades, the understanding of the renin-angiotensin system (RAS) has advanced dramatically. RAS is now thought to play a crucial role in physiologic and pathophysiologic mechanisms in almost every organ system and is a key regulator of hypertension, cardiovascular disease, and renal function. Angiotensin II (Ang II) promotes inflammation and the generation of reactive oxygen species and governs onset and progression of vascular senescence, which are all associated with functional and structural changes, contributing to age-related diseases. Although the vast majority of the actions of Ang II, including vascular senescence, are mediated by the Ang II type 1 receptor (AT1R), the identification, characterization, and cloning of the angiotensin type 2 receptor has focused attention on this receptor and to its antagonistic effect on the detrimental effects of AT1R. This review provides an overview of the changes in RAS with aging and age-disease interactions culminating in the development of frailty.

Maternal nutrition, low nephron number and arterial hypertension in later life

A potential role of the intrauterine environment in the development of low nephron number and hypertension in later life has been recently recognized in experimental studies and is also postulated in certain conditions in human beings. Nephrogenesis is influenced by genetic as well as by environmental and in particular maternal factors. In man nephrogenesis, i.e. the formation of nephrons during embryogenesis, takes place from weeks 5 to 36 of gestation with the most rapid phase of nephrogenesis occurring from the mid-2nd trimester until 36 weeks. This 16 week period is a very vulnerable phase where genetic and environmental factors such as maternal diet or medication could influence and disturb nephron formation leading to lower nephron number. Given a constant rise in body mass until adulthood lower nephron number may become "nephron underdosing" and result in maladaptive glomerular changes, i.e. glomerular hyperfiltration and glomerular enlargement. These maladaptive changes may then eventually lead to the development of glomerular and systemic hypertension and renal disease in later life. It is the purpose of this review to discuss the currently available experimental and clinical evidence for factors and mechanisms that could interfere with nephrogenesis with particular emphasis on maternal nutrition. In addition, we discuss the emerging concept of low nephron number being a new cardiovascular risk factor in particular for essential hypertension in later life.

Impact of maternal undernutrition on diabetes and cardiovascular disease risk in adult offspring

Epidemiological, clinical, and experimental observations have led to the hypothesis that the risk of developing chronic diseases in adulthood is influenced not only by genetic and adult lifestyle factors, but also by environmental factors during early life. Low birth weight, a marker of intrauterine stress, has been linked to predisposition to cardiovascular disease (CVD) and diabetes. The compelling animal evidence and significant human data to support this conclusion are reviewed. Specifically, the review discusses the role of maternal nutrition before and during pregnancy, placental insufficiencies and epigenetic changes in the increased predisposition to diabetes and CVD in adult life. The impact of low birth weight and catch-up growth as they pertain to risk of disease in adult life is also discussed. In addition, adult disease risk in the overnourished fetus is also mentioned. Reference is made to some of the mechanisms of the induction of diabetes and CVD phenotype. It is proposed that fetal nutrition, growth and development through efficient maternal nutrition before and during pregnancy could constitute the basis for nutritional strategies for the primary prevention of diabetes and CVD.

Sex differences in the developmental origins of hypertension and cardiorenal disease

The "developmental origins of health and disease" (DOHAD) hypothesis derives from clinical observations, indicating long-term health consequences for persons of low birth weight. There is growing evidence, primarily from animal studies, that supports the idea that processes put in motion during development that contribute to DOHAD do not necessarily reflect as significantly compromised growth and altered birth weight. Throughout the body of work investigating the DOHAD hypothesis, several themes have emerged; the importance of the placenta, the presence of critical periods of vulnerability, the involvement of the kidney in programmed hypertension, the presence of sex differences in the progression and development of adult diseases. Despite compelling findings in recent studies, much remains unclear regarding the impact of biological sex in the progression of human diseases, in general, and in the mechanisms underlying developmentally programmed responses, in particular. Although the contribution of biological sex to DOHAD is increasingly recognized, it also appears that it may exert distinctly different influences during fetal and adult life. The mechanisms by which biological sex contributes to these processes remains nebulous at present; nevertheless, several intriguing mechanistic candidates have been proposed ranging from differences in the amounts of sex hormones (e.g., estrogens, androgens) to recently described sexual dimorphism in the transcriptome of a variety of mammalian tissues. Recognizing the influences of biological sex or sex hormones on DOHAD uniquely situates research in this area to provide significant insights into the development and progression of many diseases, recent examples of which are the subject of this review.

Early origins of cardiac hypertrophy: does cardiomyocyte attrition programme for pathological 'catch-up' growth of the heart?

1. Epidemiological and experimental evidence suggests that adult development of cardiovascular disease is influenced by events of prenatal and early postnatal life. Cardiac hypertrophy is recognized as an important predictor of cardiovascular morbidity and mortality, but the developmental origins of this condition are not well understood. 2. In the heart, a switch from hyperplastic to hypertrophic cellular growth occurs during late prenatal or early postnatal life. Postnatal growth of the heart is almost entirely reliant on hypertrophy of individual cardiomyocytes, and damage to heart muscle in adulthood is typically not reparable by cell replacement. Therefore, a reduced number of cardiomyocytes may render the heart more vulnerable in situations where an increased workload is required. 3. A number of different animal models have been used to study fetal programming of adult diseases, including nutritional, hypoxic, maternal/neonatal endocrine stress and genetic models. Although studies investigating the cellular basis of myocardial disease in growth-restricted models are limited, a reduction in cardiomyocyte number through either reduced cellular proliferation or increased apoptosis appears to be a central feature. 4. The mechanisms responsible for the programming of adult cardiovascular disease are poorly understood. We hypothesize that cardiac hypertrophy can have a developmental origin in excess cardiomyocyte attrition during a critical perinatal growth window. Findings that have directly assessed the impact of fetal growth restriction on the myocardium are considered and cellular and molecular mechanisms involved in the potential pathological 'catch-up' growth of the heart during later maturation are identified.

Prenatal origins of adult disease

PURPOSE OF REVIEW

Human epidemiological and animal studies show that many chronic adult conditions have their antecedents in compromised fetal and early postnatal development. Developmental programming is defined as the response by the developing mammalian organism to a specific challenge during a critical time window that alters the trajectory of development with resulting persistent effects on phenotype. Mammals pass more biological milestones before birth than any other time in their lives. Each individual's phenotype is influenced by the developmental environment as much as their genes. A better understanding is required of gene-environment interactions leading to adult disease.

RECENT FINDINGS

During development, there are critical periods of vulnerability to suboptimal conditions when programming may permanently modify disease susceptibility. Programming involves structural changes in important organs; altered cell number, imbalance in distribution of different cell types within the organ, and altered blood supply or receptor numbers. Compensatory efforts by the fetus may carry a price. Effects of programming may pass across generations by mechanisms that do not necessarily involve structural gene changes. Programming often has different effects in males and females.

SUMMARY

Developmental programming shows that epigenetic factors play major roles in development of phenotype and predisposition to disease in later life.

Spontaneously occurring differences in fetal weight do not affect blood pressure, the hypothalamic-pituitary-adrenal axis or the renin-angiotensin system in the late-gestation ovine fetus

Fetal growth restriction (FGR) has been associated with an increased incidence of cardiovascular disease in adult life. Animal models of restricted fetal growth often cause FGR over discrete periods of gestation and hence may not be applicable to individuals with low birthweight but who are not clinically growth-restricted. Our aim was to determine whether spontaneously occurring differences in fetal growth influence the functional development of the hypothalamic-pituitary-adrenal (HPA) axis or the renin-angiotensin system (RAS), both of which are involved in arterial pressure regulation. Using sheep, arterial pressure and heart rate were monitored in chronically catheterised singleton and twin fetuses at 130, 134 and 137 days of gestation (term approximately 147 days). Fetuses were challenged, at different times, with exogenous angiotensin (Ang) II, combined administration of arginine vasopressin and corticotrophin releasing hormone (AVP+CRH) and adrenocorticotrophic hormone (ACTH); fetal cardiovascular responses and circulating cortisol concentrations were measured. In all fetuses Ang II and AVP+CRH altered cardiovascular function (increase in mean arterial pressure and decrease in heart rate); both AVP+CRH and ACTH increased circulating cortisol concentrations. Responses were not related to fetal bodyweight. We conclude that naturally occurring differences in growth do not influence the development of the HPA axis or RAS function in fetal sheep.

Periconceptional Nutrient Restriction in the Ewe Alters MAPK/ERK1/2 and PI3K/Akt Growth Signaling Pathways and Vascularity in the Placentome

This study evaluated the role of MAPK/ERK1/2 and/or PI3K/Akt signaling pathways in modulating ovine placentomal vascularity in response to periconceptional maternal nutrient restriction. Ewes were randomly assigned to be nutrient restricted (NR, 50% NRC recommendation, N=7) or control fed (CF, 100% NRC recommendation, N=7) from 60 +/- 2 days before to 30 days after conception (day 0). From day 31 of gestation, all ewes (CF and NR) were fed the control diet until necropsy on day 78. On day 78 of gestation, NR ewes exhibited greater vascularity in both caruncular (CAR) and cotyledon (COT) tissues than CF ewes. Akt or ERK1/2 content in CAR and COT arterial tissue did not differ across dietary treatment. The activated forms, phosphorylated Akt and phosphorylated ERK1/2, were significantly increased in COT but not CAR arterial tissues of NR ewes compared to those of CF ewes (P<0.05). For both CF and NR ewes, phosphorylated Akt and phosphorylated ERK1/2 content in COT are higher (P<0.05) than those in CAR arterial tissues. Immunohistochemical staining revealed cytoplasmic and nuclear localization of Akt, phosphorylated Akt, ERK1/2 and phosphorylated ERK1/2, with phosphorylated Akt and phosphorylated-ERK1/2 specifically localized in trophoblast cells, while binucleate cells remained unstained. In placentomal blood vessels, Akt, phosphorylated Akt, ERK1/2 and phosphorylated ERK1/2 were localized to both endothelium and smooth muscle cells. These findings demonstrate for the first time that periconceptional NR increases vascular density in both COT than CAR tissues of the ovine placentome, and that the MAPK/ERK1/2 and/or PI3K/Akt signaling pathways are increased in NR COT but not NR CAR arterial tissues.

Evaluation of gene expression through qRT-PCR in cyclically loaded tendons: an in vivo model

An in vivo rabbit animal model for the tendinopathy, epicondylitis, was used to examine the effects of repetitive load on the expression of various genes associated with matrix remodeling. Following 80 h of cumulative load, tissue from the distal and proximal regions of the flexor digitorum profundus tendon was collected. Quantitative RT-PCR was used to asses mRNA levels of collagenase-1 (MMP-1), stromelysin (MMP-3), vascular endothelial growth factor (VEGF), connective tissue growth factor (CTGF), cyclooxygenase-2 (COX-2), interleukin-1beta (IL-1beta), type III collagen (COL-III) and fibronectin (FBRN). No significant differences in expression levels were found between loaded and unloaded limbs at either region of the tendon. The findings were unexpected as the same model has already demonstrated an increase in the density of cells staining for VEGF and CTGF. Different regulatory mechanisms between mRNA and protein expression or localized changes missed due to homogenization of the tissue samples, may explain the discrepancy in findings.

Nutrient restriction impairs nephrogenesis in a gender-specific manner in the ovine fetus

Inadequate nutrition compromises fetal development and poses long-term health risks for the offspring, even without decreased birth weight. The present study sought to 1) establish the ontogeny of fetal renal glomerulus number (GN) in sheep and 2) evaluate the effects of 50% global nutrient restriction (NR) during early to midgestation on GN and the renin-angiotensin system in the fetal kidney. GN increased from 78 dG (68,560 +/- 3802) to 135 dG (586,118 +/- 25,792). NR increased combined kidney weight (29 +/- 0.6 g versus 23 +/- 1.1 g), whereas decreased GN relative to right kidney weight approached significance in males (26,000 +/- 5300 versus 39,000 +/- 2800 GN/g) compared with control (C) males and females. NR decreased immunoreactive angiotensin II (Ang II) type 1 receptor (AT1) in the NR kidneys at 78 dG and increased renin at 135 dG. Immunoreactive renin decreased from 78 to 135 dG. Female fetuses had more immunoreactive Ang II type 2 receptor (AT2) than male fetuses at 78 dG and males had more AT1 at 135 dG. The present study demonstrates gender-specific differences in fetal growth and development and in fetal kidney development in pregnancies affected by NR.

A Thin Phenotype Is Protective for Impaired Glucose Tolerance and Related to Low Birth Weight in Mice

BACKGROUND

Low birth weight is an independent risk factor for impaired glucose tolerance (IGT) and diabetes in adult life. This risk extends to both preterm and term infants, a particularly important finding given the increased survival of low-birth-weight infants with improvements in neonatal care. One potential strategy for prevention of low-birth-weight-associated glucose intolerance is postnatal nutritional modification and prevention of early postnatal weight gain. To determine the efficacy of this approach, we utilized our mouse model of low birth weight related to maternal undernutrition during the third week of pregnancy.

METHODS

We studied three experimental groups of offspring mice: controls (C), undernutrition with low birth weight (UN) fed ad lib postnatally, and undernutrition with food restriction continued in postnatal life (UN-UN). Mean birth weight was significantly reduced in both groups of undernutrition offspring in utero (C: 1.86 +/- 0.03 vs. UN: 1.37 +/- 0.04 and UN-UN: 1.32 +/- 0.06, p <0.001). As expected, and in accord with human data, differences in weight between C and UN mice disappeared by week 2 of life, indicating catch-up growth in the UN group.

RESULTS

Body weight was similar in all groups until 4 months of age, after which the UN-UN group had reduced body weight as compared with controls (p <0.05 at 6 months). Insulin tolerance test (1 U/kg), glucose tolerance test (2 g/kg) and glucose-stimulated insulin secretion test (3 g/kg) at 2 months of age were identical among C, UN, and UN-UN groups. By age 6 months, IGT had developed in the UN mice (p <0.05 vs. C). By contrast, UN offspring with caloric restriction postnatally (UN-UN) were protected from the development of glucose intolerance, with glucose levels identical to that of control mice. These differences appeared to be related to improved insulin sensitivity in the UN-UN mice as compared with UN mice, although data did not reach statistical significance.

CONCLUSIONS

Our data suggest that alterations in early postnatal nutrition are associated with prevention of weight gain and the development of IGT in low-birth-weight mice.

Maternal nutrient restriction upregulates growth signaling pathways in the cotyledonary artery of cow placentomes

This study evaluated the role of MAPK/ERK1/2 and/or PI3-K/Akt signaling pathways in modulating bovine placentomal vascularity in response to maternal nutrient restriction. Beef cows were randomly assigned to control fed (Control, n=15, 100% of requirements) or nutrient restricted (NR, n=15, 50% requirements) diets from day 30 to day 125 of gestation. Ten cows from each dietary group were necropsied on day 125 (approximately 45% gestation), and the remaining cows in each diet group were then fed control diets and necropsied on day 250 (approximately 90% gestation). At day 125 of gestation, NR cows exhibited increased (P=0.06) COT vascularity, improved (P<0.05) placentome efficiency (fetal weight/placentomal weight), and increased (P<0.05) phosphorylated Akt and ERK1/2 in COT arteries compared to Control cows. By day 250, however, treatment differences in COT vascularity and phosphorylated Akt and ERK1/2 in COT arteries were lost. On both gestational days, no treatment difference was observed in the levels of phosphorylated Akt or ERK1/2 in CAR arteries. CAR vascularity was similar across treatment on day 125, but tended to be greater (P<0.10) in NR than Control cows on day 250. These data suggest that conceptuses react to an early gestational nutrient restriction by up-regulating COT growth signaling pathways associated with angiogenesis, and that these compensations do not persist to term.

Role of nutrition in the development of the fetal cardiovascular system

Emerging evidence demonstrates that heart disease may originate during fetal development. This review will focus on the role of maternal nutrition in the development of the fetal cardiovascular system. Emphasis will be placed upon the concept that nutritional inadequacies during gestation may be major programming stimuli that alter fetal cardiac, as well as vascular, physiology and predispose an individual to cardiovascular abnormalities in postnatal life. It is hypothesized that this research area will yield new information, resulting in improved fetal nutrition, growth and development through efficient maternal nutrition before and during pregnancy and will form the basis for nutritional strategies for the primary prevention of cardiovascular disease.