Prenatal protein restriction does not affect the proliferation and differentiation of rat preadipocytes

In utero nutritional stress as a cause of obesity: Altered relationship between body fat, leptin levels and caloric intake in offspring into adulthood

AIMS

Emerging evidence suggests that during gestation the in utero environment programs metabolism and can increase risk of obesity in adult offspring. Our aim was to study how alterations in maternal diets during gestation might alter body weight evolution, circulating leptin levels and caloric intake in offspring, leading to changes in body composition.

MATERIALS AND METHODS

We fed gestating rats either a control diet (CD), high fat diet (HFD) or an isocaloric low protein diet (LPD), and examined the repercussions in offspring fed similar diets post-weaning on birth weight, body weight evolution, body composition, insulin sensitivity, glucose tolerance and in the relationship between plasma leptin concentration and caloric intake in offspring during growth and development.

KEY FINDS

Offspring from dams fed LPD maintained reduced body weight with greater % lean mass and consumed fewer calories despite having leptin levels similar to controls. On the other hand, offspring from dams fed a HFD were insulin resistant and maintained increased body weight and % fat mass, while consuming more calories than controls despite elevated leptin concentrations. Therefore the uterine environment, modulated primarily through maternal nutrition, modified the relationship between circulating leptin levels, body fat, and caloric intake in the offspring, and dams fed a HFD produced offspring with excess adiposity, insulin resistance, and leptin resistance into adulthood.

SIGNIFICANCE

Our data indicates that in utero environmental factors affected by maternal diet program alterations in the set point around which leptin regulates body weight in offspring into adulthood contributing to obesity.

Age-Dependent Control of Energy Homeostasis by Brown Adipose Tissue in Progeny Subjected to Maternal Diet-Induced Fetal Programming

Epidemiological and animal studies show that deleterious maternal environments predispose aging offspring to metabolic disorders and type 2 diabetes. Young progenies in a rat model of maternal low-protein (LP) diet are normoglycemic despite collapsed insulin secretion. However, without further worsening of the insulin secretion defect, glucose homeostasis deteriorates in aging LP descendants. Here we report that normoglycemic and insulinopenic 3-month-old LP progeny shows increased body temperature and energy dissipation in association with enhanced brown adipose tissue (BAT) activity. In addition, it is protected against a cold challenge and high-fat diet (HFD)-induced obesity with associated insulin resistance and hyperglycemia. Surgical BAT ablation in 3-month-old LP offspring normalizes body temperature and causes postprandial hyperglycemia. At 10 months, BAT activity declines in LP progeny with the appearance of reduced protection to HFD-induced obesity; at 18 months, LP progeny displays a BAT activity comparable to control offspring and insulin resistance and hyperglycemia occur. Together our findings identify BAT as a decisive physiological determinant of the onset of metabolic dysregulation in offspring predisposed to altered β-cell function and hyperglycemia and place it as a critical regulator of fetal programming of adult metabolic disease.

Maternal nutritional manipulations program adipose tissue dysfunction in offspring

Based on the concept of Developmental Origin of Health and Disease, both human and animal studies have demonstrated a close link between nutrient supply perturbations in the fetus or neonate (i.e., maternal undernutrition, obesity, gestational diabetes and/or rapid catch-up growth) and increased risk of adult-onset obesity. Indeed, the adipose tissue has been recognized as a key target of developmental programming in a sex-and depot-specific manner. Despite different developmental time windows, similar mechanisms of adipose tissue programming have been described in rodents and in bigger mammals (sheep, primates). Maternal nutritional manipulations reprogram offspring's adipose tissue resulting in series of alterations: enhanced adipogenesis and lipogenesis, impaired sympathetic activity with reduced noradrenergic innervations and thermogenesis as well as low-grade inflammation. These changes affect adipose tissue development, distribution and composition predisposing offspring to fat accumulation. Modifications of hormonal tissue sensitivity (i.e., leptin, insulin, glucocorticoids) and/or epigenetic mechanisms leading to persistent changes in gene expression may account for long-lasting programming across generations.

Maternal protein restriction leads to pancreatic failure in offspring: role of misexpressed microRNA-375

The intrauterine environment of the fetus is a preeminent actor in long-term health. Indeed, mounting evidence shows that maternal malnutrition increases the risk of type 2 diabetes (T2D) in progeny. Although the consequences of a disturbed prenatal environment on the development of the pancreas are known, the underlying mechanisms are poorly defined. In rats, restriction of protein during gestation alters the development of the endocrine pancreas and favors the occurrence of T2D later in life. Here we evaluate the potential role of perturbed microRNA (miRNA) expression in the decreased β-cell mass and insulin secretion characterizing progeny of pregnant dams fed a low-protein (LP) diet. miRNA profiling shows increased expression of several miRNAs, including miR-375, in the pancreas of fetuses of mothers fed an LP diet. The expression of miR-375 remains augmented in neoformed islets derived from fetuses and in islets from adult (3-month-old) progeny of mothers fed an LP diet. miR-375 regulates the proliferation and insulin secretion of dissociated islet cells, contributing to the reduced β-cell mass and function of progeny of mothers fed an LP diet. Remarkably, miR-375 normalization in LP-derived islet cells restores β-cell proliferation and insulin secretion. Our findings suggest the existence of a developmental memory in islets that registers intrauterine protein restriction. Hence, pancreatic failure after in utero malnutrition could result from transgenerational transmission of miRNA misexpression in β-cells.

The cellularity of offspring's adipose tissue is programmed by maternal nutritional manipulations

Epidemiological studies initially demonstrated that maternal undernutrition leads to low birth weight with increased risk of adult-onset obesity. Maternal obesity and diabetes associated with high birth weight, excessive nutrition in neonates, and rapid catch-up growth also predispose offspring to fat accumulation. As stated by the Developmental Origin of Health and Disease concept, nutrient supply perturbations in the fetus or neonate result in long-term programming of individual body weight set-point. Adipose tissue is a key fuel storage unit mainly involved in the maintenance of energy homeostasis. Studies in numerous animal models have demonstrated that the adipose tissue is the focus of developmental programming events in a gender- and depot-specific manner. This review summarizes the impact of maternal nutritional manipulations on cellularity (i.e., cell number, size, and type) of adipose tissue in programmed offspring. In rodents, adipose tissue development is particularly active during the perinatal period, especially during the last week of gestation and during early postnatal life. In contrast to rodents, this process essentially takes place before birth in bigger mammals. Despite these different developmental time windows, altricial and precocial species share several mechanisms of adipose tissue programming. Maternal nutritional manipulations result in increased adipogenesis and modified fat distribution and composition. Inflammation changes such as infiltration of macrophages and increased inflammatory markers are also observed. Overall, it may predispose offspring to fat accumulation and obesity. Inappropriate hormone levels, modified tissue sensitivity, and epigenetic mechanisms are key factors involved in the programming of adipose tissue's cellularity during the perinatal period.

Increased susceptibility to streptozotocin and impeded regeneration capacity of beta-cells in adult offspring of malnourished rats

BACKGROUND

Epidemiological studies related poor maternal nutrition and subsequent growth retardation in the progeny to the development of diabetes later in life. Low-protein diet during gestation altered the beta-cell development of the rat progeny by decreasing beta-cell proliferation and increasing their sensitivity to nitric oxide and cytokines in the foetus. This disturbed maternal environment had long-lasting consequences because the higher beta-cell vulnerability was maintained at adulthood.

AIM

The aim of this study was to determine whether early malnutrition influences the vulnerability and the regeneration capacity of beta-cells after streptozotocin (STZ) damage at adulthood.

METHODS

Gestating rats were fed either a control or a low-protein diet until weaning. Adult female offspring received injections of Freund's adjuvant weekly for 5 weeks followed 24 h later by STZ. Half of the cohort was killed at d34, whereas the other half was maintained until d48 to analyse the regeneration capacity of the beta-cells.

RESULTS

Although control and low-protein rats had equivalent pancreatic insulin content and beta-cell volume density at d34, hyperglycaemia appeared earlier and was more dramatic in low-protein rats than in control rats. STZ treatment increased beta-cell proliferation similarly in both groups. At d48, apoptotic rate was higher in the low-protein group. Regeneration appeared in control, but not in the low-protein rats, where beta-cell aggregates/surface area and Reg1-positive area were decreased compared to control.

CONCLUSION

Maternal malnutrition programmes a more vulnerable endocrine pancreas in the progeny which is unable to regenerate after injury, therefore predisposing it to develop glucose intolerance and diabetes later in life.

Nutritional manipulations in the perinatal period program adipose tissue in offspring

Epidemiological studies demonstrated initially that maternal undernutrition results in low birth weight with increased risk for long-lasting energy balance disorders. Maternal obesity and diabetes associated with high birth weight, excessive nutrition in neonates, and rapid catchup growth also increase the risk of adult-onset obesity. As stated by the Developmental Origin of Health and Disease concept, nutrient supply perturbations in the fetus or neonate result in long-term programming of individual body weight set point. Adipose tissue is a key fuel storage unit involved mainly in the maintenance of energy homeostasis. Studies in numerous animal models have demonstrated that the adipose tissue is the focus of developmental programming events in a sex- and depot-specific manner. In rodents, adipose tissue development is particularly active during the perinatal period, especially during the last week of gestation and during early postnatal life. In contrast to rodents, this process essentially takes place before birth in bigger mammals. Despite these different developmental time windows, altricial and precocial species share several mechanisms of adipose tissue programming. Offspring from malnourished dams present adipose tissue with a series of alterations: impaired glucose uptake, insulin and leptin resistance, low-grade inflammation, modified sympathetic activity with reduced noradrenergic innervations, and thermogenesis. These modifications reprogram adipose tissue metabolism by changing fat distribution and composition and by enhancing adipogenesis, predisposing the offspring to fat accumulation. Subtle adipose tissue circadian rhythm changes are also observed. Inappropriate hormone levels, modified tissue sensitivity (especially glucocorticoid system), and epigenetic mechanisms are key factors for adipose tissue programming during the perinatal period.

Early metabolic defects in dexamethasone-exposed and undernourished intrauterine growth restricted rats

Poor fetal growth, also known as intrauterine growth restriction (IUGR), is a worldwide health concern. IUGR is commonly associated with both an increased risk in perinatal mortality and a higher prevalence of developing chronic metabolic diseases later in life. Obesity, type 2 diabetes or metabolic syndrome could result from noxious “metabolic programming.” In order to better understand early alterations involved in metabolic programming, we modeled IUGR rat pups through either prenatal exposure to synthetic glucocorticoid (dams infused with dexamethasone 100 µg/kg/day, DEX) or prenatal undernutrition (dams feeding restricted to 30% of ad libitum intake, UN). Physiological (glucose and insulin tolerance), morphometric (automated tissue image analysis) and transcriptomic (quantitative PCR) approaches were combined during early life of these IUGR pups with a special focus on their endocrine pancreas and adipose tissue development. In the absence of catch-up growth before weaning, DEX and UN IUGR pups both presented basal hyperglycaemia, decreased glucose tolerance, and pancreatic islet atrophy. Other early metabolic defects were model-specific: DEX pups presented decreased insulin sensitivity whereas UN pups exhibited lowered glucose-induced insulin secretion and more marked alterations in gene expression of pancreatic islet and adipose tissue development regulators. In conclusion, these results show that before any catch-up growth, IUGR rats present early physiologic, morphologic and transcriptomic defects, which can be considered as initial mechanistic basis of metabolic programming.

Accumulation capacity of primary cultures of adipocytes for PCB-126: influence of cell differentiation stage and triglyceride levels

Polychlorinated biphenyls (PCBs) are lipophilic persistent organic chemicals that accumulate at high concentrations in the adipose tissue. Recent studies correlate the presence of such contaminants in fat cells to possible alterations in the regulation of energy homeostasis in adipocytes. As the adipose tissue is composed of adipocytes at several stages of differentiation, it is possible that PCBs already accumulate in cells at an early stage, and thereby impair their development. The exact driving force enabling the massive accumulation of PCBs in fat cells remains unclear. The present study investigated the time-course incorporation of (3)H-PCB-126 in primary cultures of rat adipocytes at both early and late differentiation stages and showed that the accumulation of this congener was already significant at an early stage of differentiation. In addition, triglyceride levels in cells were an important parameter governing (3)H-PCB-126's entry. The extent of adipocyte ability to store this pollutant in vitro was also evaluated and revealed that fat cells were able to accumulate (3)H-PCB-126 at extremely high concentrations. A linear relationship was observed between the amount of (3)H-PCB-126 added to the medium and the one accumulated in the cells, which favors a passive diffusion mechanism for the entry of this pollutant into fat cells.

Developmental programming of adult obesity and cardiovascular disease in rodents by maternal nutrition imbalance

Studies on fetal undernutrition have generated the hypothesis that fetal programming corresponds to an attempt of the fetus to adapt to adverse conditions encountered in utero. These adaptations would be beneficial if these conditions prevail later in life, but they become detrimental in the case of normal or plentiful nutrition and favor the appearance of the metabolic syndrome. In this article, the discussion is limited to the developmental programming of obesity and cardiovascular disorders caused by an early mismatched nutrition, particularly intrauterine growth retardation followed by postnatal catch-up growth. Selected data in humans are reviewed before evoking some mechanisms revealed or suggested by experiments in rodents. A variety of physiologic mechanisms are implicated in obesity programming, 2 of which are detailed. In some, but not all observations, hyperphagia resulting namely from perturbed development of the hypothalamic circuitry devoted to appetite regulation may contribute to obesity. Another contribution may be the developmental changes in the population of fat cell precursors in adipose tissue. Even if the link between obesity and cardiovascular disease is well established, alteration of blood pressure regulation may appear independently of obesity. A loss of diurnal variation in heart rate and blood pressure in adulthood has resulted from maternal undernutrition followed by postnatal overnutrition. Further research should clarify the effect of mismatched early nutrition on the development of brain centers regulating energy intake, energy expenditure, and circadian rhythms.

Maternal prenatal undernutrition programs adipose tissue gene expression in adult male rat offspring under high-fat diet

Several studies have shown that maternal undernutrition leading to low birth weight predisposes offspring to the development of metabolic pathologies such as obesity. Using a model of prenatal maternal 70% food restriction diet (FR30) in rat, we evaluated whether postweaning high-fat (HF) diet would amplify the phenotype observed under standard diet. We investigated biological parameters as well as gene expression profile focusing on white adipose tissues (WAT) of adult offspring. FR30 procedure does not worsen the metabolic syndrome features induced by HF diet. However, FR30HF rats displayed catch-up growth to match the body weight of adult control HF animals, suggesting an increase of adiposity while showing hyperleptinemia and a blunted increase of corticosterone. Using quantitative RT-PCR array, we demonstrated that FR30HF rats exhibited leptin and Ob-Rb as well as many peptide precursor and receptor gene expression variations in WAT. We also showed that the expression of genes involved in adipogenesis was modified in FR30HF animals in a depot-specific manner. We observed an opposite variation of STAT3 phosphorylation levels, suggesting that leptin sensitivity is modified in WAT adult FR30 offspring. We demonstrated that 11β-HSD1, 11β-HSD2, GR, and MR genes are coexpressed in WAT and that FR30 procedure modifies gene expression levels, especially under HF diet. In particular, level variation of 11β-HSD2, whose protein expression was detected by Western blotting, may represent a novel mechanism that may affect WAT glucocorticoid sensitivity. Data suggest that maternal undernutrition differently programs the adult offspring WAT gene expression profile that may predispose for altered fat deposition.

The Roles of PPARs in the Fetal Origins of Metabolic Health and Disease

Beyond the short-term effects on fertility, there is increasing evidence that obesity or the consumption of an inappropriate diet by the mother during pregnancy adversely affects the long-term health of her offspring. PPAR and RXR isotypes are widely expressed in reproductive tissues and in the developing fetus. Through their interactions with fatty acids, they may mediate adaptive responses to the changes in the maternal diet. In the maturing follicle, PPAR-γ has an important role in the granulosa cells that surround the maturing oocyte. After fertilisation, PPAR-γ and PPAR-β/δ are essential regulators of placentation and the subsequent development of key metabolic tissues such as skeletal muscle and adipose cells. Activation of PPAR-γ and PPAR-β/δ during fetal development has the potential to modify the growth and development of these tissues. PPAR-α is expressed at low levels in the fetal liver, however, this expression may be important, as changes in the methylation of DNA in its promoter region are reported to take place during this period of development. This epigenetic modification then programmes subsequent expression. These findings suggest that two separate PPAR-dependent mechanisms may be involved in the fetal adaptations to the maternal diet, one, mediated by PPAR-γ and PPAR-β/δ, regulating cell growth and differentiation; and another adapting long-term lipid metabolism via epigenetic changes in PPAR-α to optimise postnatal survival.

Limited and excess protein intake of pregnant gilts differently affects body composition and cellularity of skeletal muscle and subcutaneous adipose tissue of newborn and weanling piglets

AIM

This study investigated whether dietary protein intake less (50%) or greater (250%) than requirements throughout gestation differently affects offspring body composition and cellular properties of skeletal muscle and subcutaneous adipose tissue (SCAT).

METHODS

Primiparous gilts were fed iso-energetic diets containing adequate (22 AP), high (21 HP), or low (19 LP) protein contents. Newborn (n = 166) and weanling piglets cross-fostered to sows fed a standard diet (day 28; n = 83) were examined by morphological, biochemical, histological, and molecular analyses of the body, SCAT, and semitendinosus, longissimus, biceps femoris muscles.

RESULTS

Lowered birth weight (BW) in response to the HP and LP diets (p < 0.01) resulted from decreases in all body constituents in LP, and mainly from reduced body fat in HP piglets (p < 0.05). In the light BW class within litters, HP piglets exhibited a greater percentage of muscle tissue (p < 0.05) than LP piglets. Less SCAT mass in HP and LP piglets resulted from reduced (p < 0.05) number, but not the size of adipocytes. The LP diet adversely affected myogenesis and muscular differentiation derived from less (p < 0.01) primary and secondary myofibers, lower creatine kinase activity (p < 0.05), less IGF2 mRNA (p < 0.10), and greater expression of the embryonic myosin heavy chain isoform (p < 0.01). Catch-up growth of LP but not HP pigs until day 28 increased body fat (p = 0.01). Despite compensated muscle growth in LP piglets, the deficit in myofiber number remained.

CONCLUSION

Poor intrauterine environment by limited and excess protein supply retards fetal growth, but only limited protein supply impairs myogenesis, persistently restricts muscle growth potential, and favors obesity at infancy.

Developmental programming of energy balance and its hypothalamic regulation

Developmental programming is an important physiological process that allows different phenotypes to originate from a single genotype. Through plasticity in early life, the developing organism can adopt a phenotype (within the limits of its genetic background) that is best suited to its expected environment. In humans, together with the relative irreversibility of the phenomenon, the low predictive value of the fetal environment for later conditions in affluent countries makes it a potential contributor to the obesity epidemic of recent decades. Here, we review the current evidence for developmental programming of energy balance. For a proper understanding of the subject, knowledge about energy balance is indispensable. Therefore, we first present an overview of the major hypothalamic routes through which energy balance is regulated and their ontogeny. With this background, we then turn to the available evidence for programming of energy balance by the early nutritional environment, in both man and rodent models. A wealth of studies suggest that energy balance can indeed be permanently affected by the early-life environment. However, the direction of the effects of programming appears to vary considerably, both between and within different animal models. Because of these inconsistencies, a comprehensive picture is still elusive. More standardization between studies seems essential to reach veritable conclusions about the role of developmental programming in adult energy balance and obesity.

Does early mismatched nutrition predispose to hypertension and atherosclerosis, in male mice?

BACKGROUND

A link between early mismatched nutritional environment and development of components of the metabolic syndrome later in life has been shown in epidemiological and animal data. The aim of this study was to investigate whether an early mismatched nutrition produced by catch-up growth after fetal protein restriction could induce the appearance of hypertension and/or atherosclerosis in adult male mice.

METHODOLOGY/PRINCIPAL FINDINGS

Wild-type C57BL6/J or LDLr-/- dams were fed a low protein (LP) or a control (C) diet during gestation. Catch-up growth was induced in LP offspring by feeding dams with a control diet and by culling the litter to 4 pups against 8 in controls. At weaning, male mice were fed either standard chow or an obesogenic diet (OB), leading to 4 experimental groups. Blood pressure (BP) and heart rate (HR) were assessed in conscious unrestrained wild-type mice by telemetry. Atherosclerosis plaque area was measured in aortic root sections of LDLr-/- mice. We found that: (1) postnatal OB diet increased significantly BP (P<0.0001) and HR (P<0.008) in 3-month old OB-C and OB-LP offspring, respectively; (2) that maternal LP diet induced a significant higher BP (P<0.009) and HR (P<0.004) and (3) an altered circadian rhythm in addition to higher plasma corticosterone concentration in 9 months-old LP offspring; (4) that, although LP offspring showed higher plasma total cholesterol than control offspring, atherosclerosis assessed in aortic roots of 6-mo old mice featured increased plaque area due to OB feeding but not due to early mismatched nutrition.

CONCLUSIONS/SIGNIFICANCE

These results indicate a long-term effect of early mismatched nutrition on the appearance of hypertension independently of obesity, while no effect on atherosclerosis was noticed at this age.

Maternal perinatal undernutrition programs a “brown-like” phenotype of gonadal white fat in male rat at weaning

Several studies indicate that maternal undernutrition sensitizes the offspring to the development of metabolic disorders, such as obesity. Using a model of perinatal maternal 50% food-restricted diet (FR50), we recently reported that rat neonates from undernourished mothers exhibit decreased leptin plasma levels associated with alterations of hypothalamic proopiomelanocortin system. The present study aimed at examining the consequences of FR50 on the brain-adipose axis in male rat neonates. Using quantitative RT-PCR array containing 84 obesity-related genes, we demonstrated that most of the genes involved in energy metabolism regulation are expressed in rat gonadal white adipose tissue (WAT) and are sensitive to maternal perinatal undernutrition (MPU). In contrast, hypothalamic gene expression was not substantially affected by MPU. Gene expression of uncoupling protein 1 (UCP1), a marker of brown adipocytes, showed an almost 400-fold stimulation in postnatal day 21 (PND21) FR50 animals, suggesting that their gonadal WAT possesses a brown-like phenotype. This was confirmed by histological and immunoshistochemical procedures, which demonstrated that PND21 FR50 gonadal adipocytes are multilocular, resembling those present in interscapular brown adipose tissue, and exhibit an overexpression of UCP1 and neuropeptide Y (NPY) at the protein level. Control animals contained almost exclusively “classical” unilocular white adipocytes that did not show high UCP1 and NPY labeling. After weaning, FR50 animals exhibited a transient hyperphagia that was associated with the disappearance of brown-like fat pads in PND30 WAT. Our results demonstrate that MPU delays the maturation of gonadal WAT during critical developmental time windows, suggesting that it could have long-term consequences on body weight regulation in the offspring.

Fetal programming: link between early nutrition, DNA methylation, and complex diseases

Complex traits, including those involved in diet-related diseases, are determined by multiple genes and environmental influences. Factors influencing the development of complex traits should be expanded to include epigenetic factors, such as DNA methylation, which occurs in utero. Epigenetic factors regulate gene expression and thereby cell differentiation and organogenesis. The process of epigenotype establishment is sensitive to environmental conditions, with nutrition being one of the most important related factors. For example, DNA methylation depends on the availability of several nutrients including methionine and vitamins B(6), B(12), and folate. Epidemiological studies show that undernutrition during fetal life is associated with increased susceptibility to complex diseases. Numerous studies have been conducted on prenatal caloric and protein undernutrition. A reduction in the number of cells and changes in the structure and functioning of organs, as well as permanent changes in DNA methylation and gene expression, have been considered the molecular mechanisms responsible for metabolism programming.

Forced catch-up growth after fetal protein restriction alters the adipose tissue gene expression program leading to obesity in adult mice

A mismatch between fetal and postnatal environment can permanently alter the body structure and physiology and therefore contribute later to obesity and related disorders, as revealed by epidemiological studies. Early programming of adipose tissue might be central in this observation. Moreover, adipose tissue secretes adipokines that provide a molecular link between obesity and its related disorders. Therefore, our aim was to investigate whether a protein restriction during fetal life, followed by catch-up growth could lead to obesity in 9-mo-old male mice and could alter the adipose tissue gene expression profile. Dams were fed a low-protein (LP) or an isocaloric control (C) diet during gestation. Postnatal catch-up growth was induced in LP offspring by feeding dams with control diet and by culling LP litters to four pups instead of eight in the C group. At weaning, male mice were fed by lab chow alone (C) or supplemented with a hypercaloric diet (HC), to induce obesity (C-C, C-HC, LP-C, and LP-HC groups). At 9 mo, LP offspring featured increased relative fat mass, hyperglycemia, hypercholesterolemia, and hyperleptinemia. Using a microarray designed to study the expression of 89 genes involved in adipose tissue differentiation/function, we demonstrated that the expression profile of several genes were dependent upon the maternal diet. Among the diverse genes showing altered expression, we could identify genes encoding several enzymes involved in lipid metabolism. These results indicated that offspring submitted to early mismatched nutrition exhibited alterations in adipose tissue gene expression that probably increases their susceptibility to overweight when challenged after weaning with a HC diet.

Postnatal catch-up growth after fetal protein restriction programs proliferation of rat preadipocytes

We studied the in vitro proliferation and differentiation of rat preadipocytes to investigate whether catch-up growth after prenatal protein restriction may program adipose precursor cells leading to development of increased adipose tissue mass. Pregnant rat dams were fed either an isocaloric low-protein diet (LP-8%) or control diet (C-20%). During lactation, in order to induce catch-up growth, dams from LP group were fed with the C diet and litter size was reduced to four pups instead of eight. Preadipocytes were isolated from weanling male pups (28 days of age). Differentiation and proliferation were assessed across time. At late stages of preadipocyte differentiation, no difference was observed in lipid accumulation of C or LP cultures but the mRNA expression of leptin was enhanced in LP cells. At early stages of culture, a higher DNA and protein content accompanied by a higher rate of proliferation was measured in adipocytes from LP cultures. Moreover, the mRNA expression of cyclin D1 was increased in these cells whereas the expression of peroxisome proliferators-activated receptor gamma (PPARgamma) and steroyl regulatory element binding protein (SREBP-1c) was significantly reduced during early stages. The results suggest that prenatal exposure to a LP followed by rapid catch-up growth is associated with a higher rate for proliferation in preadipocytes.

Early life programming of obesity and metabolic disease

It is becoming increasingly apparent that conditions experienced in early life play an important role in the long-term health of individuals. Alterations in development due to impaired, excessive or imbalanced growth, both in utero and during critical periods of relative plasticity beyond birth, can lead to the permanent programming of physiological systems. The regulation of energy balance is one area that is receiving particular attention, as rates of obesity and associated metabolic and cardiovascular disease continue to rise. Over recent decades, much progress has been made toward understanding the way in which metabolic tissues and physiological systems develop, and the impact of early life events and nutrition on these processes. It is apparent within human populations that some individuals are better able to maintain an appropriate body weight in the face of an obesogenic environment. Animal models have been widely used for the investigation of differential susceptibility to diet-induced obesity (DIO) and impaired energy balance regulation, and are shedding light on key pathways that may be involved. Alterations in pathways mediating energy homeostasis, outlined below, are likely candidates for programming effects following disturbed growth in early life.

Different mechanisms operating during different critical time-windows reduce rat fetal beta cell mass due to a maternal low-protein or low-energy diet

AIMS/HYPOTHESIS

Adverse events during intra-uterine life may programme organ growth and favour disease later in life. In animals, protein or energy restriction during gestation alters the development of the endocrine pancreas, even though the duration of malnutrition is different. Here, we evaluate the specific effects of both diets during different periods of gestation and the mechanisms underlying the decreased beta cell mass.

METHODS

Pregnant Wistar rats were fed either a low-protein or a low-energy diet during the last week of gestation or throughout gestation. Fetuses and their pancreases were analysed at days 15 and 21 of gestation.

RESULTS

The low-energy diet reduced the beta cell mass from 21-day-old fetuses by 33 or 56% when administered during the last week or throughout gestation, respectively. Fetal corticosterone levels were increased. At 15 days of fetal age, the number of cells producing neurogenin 3 (NEUROG3) or pancreatic and duodenal homeobox gene 1 (PDX-1) was reduced. Neither islet vascularisation nor beta cell proliferation was affected. The low-protein diet, in contrast, was more efficient in decreasing the fetal beta cell mass when given during the last week of gestation (-53%) rather than throughout gestation (-33%). Beta cell proliferation was decreased by 50% by the low-protein diet, independently of its duration, and islet vascularisation was reduced. This diet did not affect NEUROG3- or PDX-1-positive cell numbers.

CONCLUSION/INTERPRETATION

Although both diets reduced the fetal beta cell mass, the cellular mechanisms and the sensitivity windows were different. Early alteration of neogenesis due to elevated corticosterone levels is likely to be responsible for the decreased beta cell mass in low-energy fetuses, whereas impaired beta cell proliferation and islet vascularisation at later stages are implicated in low-protein fetuses.

Diet-induced obesity in gravid rats engenders early hyperadiposity in the offspring

Exposure to a dysmetabolic in utero environment may be one of the mechanisms to explain why individuals with high birth weight are more likely to remain overweight. We explored this hypothesis in an animal model of diet-induced obesity (DIO). We studied adipose tissue development and glucose tolerance in the offspring of rat dams fed a diet rich in milk and sugar from early adulthood until day (d) 2 postpartum. This diet promoted body weight (BW) gain and was previously shown to produce insulin resistance and gestational glucose intolerance. The DIO offspring showed a higher BW in early life (between d7 and d35), with a maximum of 1 SD above the mean BW of controls; however, BW in DIO offspring after d35 was comparable with that of controls. Neonatal DIO offspring also showed larger fat depots, adipocyte hypertrophy (P <or= .001), and more than 2-fold increased tumor necrosis factor alpha messenger RNA levels in subcutaneous adipose tissue (P < .05). In addition, they displayed a higher peak glucose response to a glucose challenge (P < .05). In postpubertal (d56) and adult (d98) offspring, we found differences in fat mass and distribution and glucose tolerance relating to the offspring's sex but not the maternal diet. In conclusion, DIO during pregnancy results in hyperadiposity and reduced glucose tolerance only in their neonatal/weanling but not postpubertal offspring. Future research should disclose whether these early-life effects are reactivated in conditions of heightened insulin resistance.

Maternal protein restriction permanently programs adipocyte growth and development in adult male rat offspring

We previously demonstrated that maternal protein restriction (MPR) during pregnancy and lactation led to fetal growth restriction and development of increased visceral adiposity in adult male rat offspring. Here we studied the rate of proliferation and differentiation of adipocyte precursors (preadipocytes) in vitro to investigate whether MPR may permanently program adipocyte growth and development in adult male offspring. Preadipocytes were isolated from visceral adipose tissue of control and MPR offspring at 130 days of age, and cultured under standard conditions. The rate of proliferation was studied by [(3)H]-thymidine incorporation, and the rate of differentiation assessed with the use of biochemical and morphological markers. Although it did not affect the rate of differentiation, MPR increased the rate of preadipocyte proliferation by almost twofold. To ascertain if the increased proliferation was due to persisting in vivo influences or aberrations inherent in the precursor cells, we studied the rate of preadipocyte proliferation in subcultures. We found that the increased rate of proliferation of MPR preadipocytes persisted throughout the first two subcultures, indicative of an inherent abnormality. In addition, we examined the rate of preadipocyte proliferation under reduced serum conditions. We showed that MPR reduced the rate of preadipocyte proliferation to 56 and 35% of the control in the presence of 5 and 2.5% serum, respectively. Taken together, these results demonstrate that MPR permanently programs adipocyte growth and development such that adipocyte precursors derived from MPR offspring replicate excessively under standard culture conditions but exhibit markedly attenuated growth rate under reduced serum conditions.

Developmental programming of energy balance and the metabolic syndrome

The increasing prevalence of the metabolic syndrome in numerous populations throughout the world is currently of major concern, and presents a huge global health problem. The link between low birth weight and the subsequent development of obesity, disrupted glucose homeostasis and hypertension is now well established, and there is extensive evidence supporting these associations in both epidemiological and experimental studies. Alterations in the secretion of, and responses to, the circulating hormones insulin and leptin are likely candidates in terms of disease development. The aim of current research is to define how the central and peripheral pathways in which these signals exert their effects may be disrupted following poor early growth, and how this disruption contributes to the development of metabolic disease. The present review aims to outline the existing evidence whereby alterations in early growth may programme an individual to be at increased risk of the metabolic syndrome. The development of central appetite and expenditure circuits and of peripheral metabolic tissues, are likely to play a key role in the long-term regulation of energy balance.

The importance of catch-up growth after early malnutrition for the programming of obesity in male rat

OBJECTIVE

To investigate whether catch-up growth after maternal malnutrition would favor the development of obesity in adulthood.

RESEARCH METHODS AND PROCEDURES

Pregnant rats were submitted to protein or calorie restriction during the course of gestation. During lactation, pups were protein-restricted, normally fed, or overfed [reduced litter size, control (C) diet]. At weaning, rats were transferred to chow or to a hypercaloric diet (HCD) known to induce obesity. Body weight, food intake, blood parameters, glucose tolerance, adipocyte cellularity, and adipose factors contributing to cardiovascular disease development were measured.

RESULTS

Protein and calorie restriction during gestation led to growth retardation at birth. If malnutrition was prolonged throughout lactation, adult body weight was permanently reduced. However, growth-retarded offspring overfed during the suckling period underwent a rapid catch-up growth and became heavier than the normally fed Cs. Offspring of calorie-restricted rats gained more weight than those of dams fed protein-restricted diet. Feeding an HCD postnatally amplified the effect of calorie restriction, and offspring that underwent catch-up growth became more obese than Cs. The HCD was associated with hyperphagia, hyperglycemia, hyperinsulinemia, glucose intolerance, insulin resistance, and adipocyte hypertrophy. The magnitude of effects varied depending on the type and the timing of early malnutrition. The expression of genes encoding factors implicated in cardiovascular disease was also modulated differently by early malnutrition and adult obesity.

DISCUSSION

Catch-up growth immediately after early malnutrition should be a key point for the programming of obesity.

Maternal protein intake in the pregnant rat programs the insulin axis and body composition in the offspring

Evidence to support an association between early nutrition and the development of obesity in the rat is equivocal. In this study we have investigated the postnatal growth, glucose tolerance, and adipocyte function of the offspring from pregnant rats fed with diets containing either 20% or 8% protein during gestation. By 25 weeks of age, the female offspring of dams fed with the diet containing 8% protein had a significantly lower adult body weight due in part to a decrease in body fat. The peak concentration of insulin after oral administration of a glucose dose was significantly lower in both the male and female offspring of the dams fed with the diet containing 8% protein. However, the ability of insulin to stimulate lipogenesis or suppress lipolysis in fat cells isolated from the offspring was not influenced by the prenatal diet. Hepatic phosphoenolpyruvate carboxykinase activity was reduced in female offspring of dams fed with the diet containing 8% protein. These results show that adult body composition is determined during the prenatal period as a result of programming of the insulin axis. This metabolic programming influences hepatic metabolism; however, there is no evidence for a programmed change in adipocyte function.

Gene-nutrient interactions during fetal development

Eukaryotic cells have evolved a complex series of nutrient sensors that protect them from damage caused by acute deficiencies and also mediate adaptive responses to prolonged excess or deficiency of particular nutrients. In adults gene expression is regulated by nutrients interacting with pathways involving mammalian target of rapamycin (mTOR), CCAAT/ enhancer-binding proteins (C/EBPs) and peroxisome proliferator activator proteins (PPARs). These systems are also present in key cells of the developing oocyte, embryo and fetus. In this review we will consider the role of interactions between genes and nutrients during reproduction with a particular emphasis on their possible involvement in the prenatal programming of glucose metabolism in the adult.

Programming of obesity and cardiovascular disease

BACKGROUND

There is evidence that malnutrition in early life induces a growth retardation leading, in adult life, to manifest components of the metabolic syndrome. However, the impact on obesity seems less clearly established.

OBJECTIVE

To review the effects of foetal and postnatal malnutrition on the programming of obesity in the context of the metabolic syndrome, as well as the link between central obesity and cardiovascular diseases.

METHODS

Included in the review were recent papers exploring the mechanisms linking maternal nutrition with impaired foetal growth and later obesity, cardiovascular disease, hypertension and diabetes in humans and animals.

RESULTS

The programming of obesity during foetal and early postnatal life depends of the timing of maternal malnutrition as well as the postnatal environment. Obesity arises principally in offspring submitted to malnutrition during early stages of gestation and which presented early catch-up growth. The programming may involve the dysregulation of appetite control or the hormonal environment leading to a context favourable to obesity development (hypersecretion of corticosteroids, hyperinsulinaemia and hyperleptinaemia and anomalies in the IGF axis). Adipose tissue secretes actively several factors implicated in inflammation, blood pressure, coagulation and fibrinolysis. The programmed development of intra-abdominal obesity after early growth restriction may thus favour higher prevalence of hypertension and cardiovascular diseases.

CONCLUSIONS

Abdominal obesity appears in malnourished offspring and is aggravated by early catch-up growth. Higher rates of intra-abdominal obesity observed after growth restriction may participate to hypertension and create atherothrombotic conditions leading to the development of cardiovascular diseases.