Expression of agouti-related peptide, neuropeptide Y, pro-opiomelanocortin and the leptin receptor isoforms in fetal mouse brain from pregnant dams on a protein-restricted diet

Unraveling the Molecular Mechanisms of the Neurodevelopmental Consequences of Fetal Protein Deficiency: Insights From Rodent Models and Public Health Implications

Fetal brain development requires increased maternal protein intake to ensure that offspring reach their optimal cognitive potential in infancy and adulthood. While protein deficiency remains a prevalent issue in developing countries, it is also reemerging in Western societies due to the growing adoption of plant-based diets, some of which are monotonous and may fail to provide sufficient amino acids crucial for the brain's critical developmental phase. Confounding variables in human nutritional research have impeded our understanding of the precise impact of protein deficiency on fetal neurodevelopment, as well as its implications for childhood neurocognitive performance. Moreover, it remains unclear whether such deficiency could predispose to mental health problems in adulthood, mirroring observations in individuals exposed to prenatal famine. In this review, we sought to evaluate mechanistic data derived from rodent models, placing special emphasis on the involvement of neuroendocrine axes, the influence of sex and timing, epigenetic modifications, and cellular metabolism. Despite notable progress, critical knowledge gaps remain, including understanding the long-term reversibility of effects due to fetal protein restriction and the interplay between genetic predisposition and environmental factors. Enhancing our understanding of the precise mechanisms that connect prenatal nutrition to brain development in future research endeavors can be significantly advanced by integrating multiomics approaches and utilizing additional alternative models such as nonhuman primates. Furthermore, it is crucial to investigate potential interventions aimed at alleviating adverse outcomes. Ultimately, this research has profound implications for guiding public health strategies aimed at raising awareness about the crucial role of optimal maternal nutrition in supporting fetal neurodevelopment.

Maternal inulin alleviates high-fat diet-induced lipid disorder in offspring by epigenetically modulating hypothalamus feeding circuit-related genes

Increasing evidence supports the existence of fetal-originated adult diseases. Recent research indicates that the intrauterine environment affects the fetal hypothalamic energy intake center. Inulin is a probiotic that can moderate metabolic disorders, but whether maternal inulin intervention confers long-term metabolic benefits to lipid metabolism in offspring in their adult lives and the mechanism involved are unknown. Here, we used a maternal overnutrition model that was induced by excess energy intake before and during pregnancy and lactation and maternal inulin intervention was performed during pregnancy and lactation. The hypothalamic genome methylation in offspring was analyzed using a methylation array. The results showed that maternal inulin treatment modified the maternal high-fat diet (HFD)-induced increases in body weight, adipose tissue weight, and serum insulin and leptin levels and decreases in serum adiponectin levels. Maternal inulin intervention regulated the impairments in hypothalamic leptin resistance, induced the methylation of Socs3, Npy, and Il6, and inhibited the methylation of Lepr in the hypothalamus of offspring. In conclusion, maternal inulin intervention modifies offspring lipid metabolism, and the underlying mechanism involves the methylation of genes in the hypothalamus feeding circuit.

Long-term effects of pro-opiomelanocortin methylation induced in food-restricted dams on metabolic phenotypes in male rat offspring

Objective

Maternal malnutrition affects the growth and metabolic health of the offspring. Little is known about the long-term effect on metabolic indices of epigenetic changes in the brain caused by maternal diet. Thus, we explored the effect of maternal food restriction during pregnancy on metabolic profiles of the offspring, by evaluating the DNA methylation of hypothalamic appetite regulators at 3 weeks of age.

Methods

Sprague-Dawley rats were divided into 2 groups: a control group and a group with a 50% food-restricted (FR) diet during pregnancy. Methylation and expression of appetite regulator genes were measured in 3-week-old offspring using pyrosequencing, real-time polymerase chain reaction, and western blotting analyses. We analyzed the relationship between DNA methylation and metabolic profiles by Pearson's correlation analysis.

Results

The expression of pro-opiomelanocortin (POMC) decreased, whereas DNA methylation significantly increased in male offspring of the FR dams, compared to the male offspring of control dams. Hypermethylation of POMC was positively correlated with the levels of high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol in 3-week-old male offspring. In addition, there were significant positive correlations between hypermethylation of POMC and the levels of triglycerides, HDL-C, and leptin in 6-month-old male offspring.

Conclusion

Our findings suggest that maternal food restriction during pregnancy influences the expression of hypothalamic appetite regulators via epigenetic changes, leading to the development of metabolic disorders in the offspring.

Diet-induced obesity and prenatal undernutrition lead to differential neuroendocrine gene expression in the hypothalamic arcuate nuclei

Previously we reported that prenatal undernutrition (UN) leads to a dysregulation of appetite suppression through alterations in hypothalamic neuropeptide gene expression. In the current study, we expand our observations and investigate neuroendocrine transcriptional responses and central leptin sensitivity within the arcuate nucleus of rats exposed to prenatal UN or a postnatal high-fat diet (HF). Pregnant Wistar rats were fed a standard chow diet either ad libitum (AD) or at 30 % of AD intake throughout gestation (UN) resulting in either control or intrauterine growth-restricted female offspring. At weaning, AD offspring were fed either a chow (C) or a HF (30 % fat wt/wt) diet ad libitum for the remainder of the study, whereas UN offspring were fed a chow diet only. At ~142 days, AD and UN offspring received either recombinant rat leptin (L) or saline (S) subcutaneously for 14 days. Prenatal UN had a significant effect on hypothalamic NPY (P < 0.0001), AgRP (P < 0.01) and ObRb (P < 0.02) mRNA expression compared to AD chow-fed offspring. A postnatal HF diet had a significant effect on AgRP mRNA expression (P < 0.001), compared to AD chow-fed offspring, but no effect on NPY and ObRb expression. Leptin treatment, in both UN and HF offspring, was ineffective in reducing NPY and AgRP mRNA expression, and had no effect on ObRb expression. These findings suggest that prenatal UN and a postnatal HF diet lead to differential neuroendocrine gene expression in the hypothalamic arcuate nuclei and reduced sensitivity to leptin's anorexigenic effects.

Neurodevelopmental consequences of maternal distress: what do we really know?

A simple internet search of 'maternal stress and pregnancy' turns up hundreds of hits explaining that an adverse intrauterine environment can affect fetal development and potentially lead to various learning, behavioral, and mood disorders in childhood, as well as complex diseases such as obesity and cardiovascular conditions later in life. Indeed, a growing body of literature now links several intrauterine challenges, including maternal obesity and stress, with adverse developmental outcomes in the child. Over the past 5 years, nearly 5000 publications have explored the consequences of maternal distress on young offspring, a marked increase from the 475 published studies over a comparable period 20 years ago. Yet, despite this explosion of research and widespread warnings to pregnant mothers, we still lack a basic understanding of the pathophysiology linking adverse maternal health to the onset of disease in the child, especially regarding how prenatal and perinatal challenges might affect brain development. Recent studies have begun to explore the cellular basis of the abnormal brain cytoarchitecture associated with fetal exposure to intrauterine challenges. Here, our goal is to review the scientific evidence that maternal distress interferes with key neurodevelopmental steps, as an entry point toward mapping the pathophysiology of pre- and perinatal stress on the unborn child's brain.

Developmental changes in embryonic hypothalamic neurons during prenatal fat exposure

Maternal consumption of a fat-rich diet during pregnancy, which causes later overeating and weight gain in offspring, has been shown to stimulate neurogenesis and increase hypothalamic expression of orexigenic neuropeptides in these postnatal offspring. The studies here, using an in vitro model that mimics in vivo characteristics after prenatal high-fat diet (HFD) exposure, investigate whether these same peptide changes occur in embryos and if they are specific to neurons. Isolated hypothalamic neurons were compared with whole hypothalamus from embryonic day 19 (E19) embryos that were prenatally exposed to HFD and were both found to show similar increases in mRNA expression of enkephalin (ENK) and neuropeptide Y (NPY) compared with that of chow-exposed embryos, with no change in melanin-concentrating hormone, orexin, or galanin. Further examination using immunofluorescence cytochemistry revealed an increase in the number of cells expressing ENK and NPY. By plotting the fluorescence intensity of each cell as a probability density function, three different populations of neurons with low, medium, or high levels of ENK or NPY were found in both HFD and chow groups. The prenatal HFD shifted the density of neurons from the population containing low peptide levels to the population containing high peptide levels. This study indicates that neuronal culture is a useful in vitro system for studying diet effects on neuronal development and shows that prenatal HFD exposure alters the population of hypothalamic neurons containing ENK and NPY in the embryo. These changes may contribute to the increase in HFD intake and body weight observed in offspring.

Etiologies of obesity in children: nature and nurture

Childhood obesity is a profoundly complex problem and serves as an example of a biospsychosocial issue. Scientific inquiry has provided incredible insight into the complex etiology of weight gain but must be viewed as an interaction between a human's propensity to conserve calories for survival in a world with an abundance of it. This article provides a brief overview divided between biological (nature) and psychosocial and behavioral (nurture) factors.

Early and post-weaning malnutrition impairs alpha-MSH expression in the hypothalamus: a possible link to long-term overweight

The present study explored the effects of early and post-weaning malnutrition and nutritional rehabilitation on orexigenic (orexin (ORX) and neuropeptide Y (NPY)) and anorexigenic peptides (alpha-melanocyte stimulating hormone (alpha-MSH)) expressed in hypothalamic nuclei. Male Wistar rats were malnourished during gestation-lactation (MGL) or from weaning to post-natal day 55 (MPW; P55). Two groups of rats were rehabilitated with a balanced diet until P90 (MGL-R and MPW-R, respectively). After a glucose tolerance test (GTT) brains were processed for immunohistochemistry. Malnourished groups were hyperglycemic after GTT. ORX expression did not display any difference. Only MGL rats showed increased NPY immunoreactivity in ARC and PVN nuclei, and both malnourished groups showed low alpha-MSH expression in the PVN and DMH, as compared with their controls. After nutritional rehabilitation rats showed normal GTT, increased rate of body and adipose tissue weights and high proportion of food ingestion. Both rehabilitated groups maintained low alpha-MSH expression in the PVN, indicating a deleterious long-lasting effect.

Maternal protein restriction in mice causes adverse metabolic and hypothalamic effects in the F1 and F2 generations

Maternal protein restriction causes metabolic alterations associated with hypothalamic dysfunction. Because the consequences of metabolic programming can be passed transgenerationally, the present study aimed to assess whether maternal protein restriction alters the expression of hypothalamic neuropeptides in offspring and to evaluate hormonal and metabolic changes in male offspring from the F1 and F2 generations. Female Swiss mice (F0) were mated and fed either a normal-protein (NP group; 19 % protein) or a low-protein (LP group; 5 % protein) diet throughout gestation of the F1 generation (NP1 and LP1). At 3 months of age, F1 females were mated to produce the F2 generation (NP2 and LP2). Animals from all groups were evaluated at 16 weeks of age. LP1 offspring had significantly lower weights and shorter lengths than NP1 offspring at birth, but they underwent a phase of rapid catch-up growth. Conversely, the LP2 offspring were not significantly different from the NP2 offspring in either weight or length. At 16 weeks, no differences were found in body mass among any of the groups, although LP1 and LP2 offspring showed hypercholesterolaemia, hypertriacylglycerolaemia, hyperglycaemia, glucose intolerance, insulin resistance, increased levels of insulin, leptin and resistin, decreased endogenous leptin sensitivity, increased adiposity with elevated leptin levels and leptin resistance characterised by altered expression of neuropeptide Y and pro-opiomelanocortin without any changes in the leptin receptor Ob-Rb. We conclude that severe maternal protein restriction promotes metabolic programming in F1 and F2 male offspring due to a dysregulation of the adipoinsular axis and a state of hypothalamic leptin resistance.

Epigenetic changes in the hypothalamic pro-opiomelanocortin gene: a mechanism linking maternal undernutrition to obesity in the offspring?

Maternal undernutrition is associated with programming of obesity in offspring. While previous evidence has linked programming to the hypothalamic, pituitary, and adrenal (HPA) axis it could also affect the hypothalamic neuropeptides which regulate food intake and energy balance. Alpha melanocyte stimulating hormone (αMSH), a key regulator of these neuronal pathways, is derived from pro-opiomelanocortin (POMC) which is therefore a prime target for the programming of obesity. Several models of maternal undernutrition have identified changes in POMC in hypothalami from foetuses or offspring at various ages. These models have also shown that the offspring go on to develop obesity and/or glucose intolerance. It is our hypothesis that programming leads to epigenetic changes in hypothalamic neuropeptide genes. Therefore when there is subsequent increased food availability, the epigenetic changes could cause dysfunctional transcriptional regulation of energy balance. We present evidence of epigenetic changes in the POMC gene promoter in foetal hypothalami after peri-conceptional undernutrition. In this model there are also epigenetic changes in the hypothalamic glucocorticoid receptor with consequent up-regulation of the receptor which could lead to alterations in the regulation of POMC and neuropeptide Y (NPY) in the hypothalamus. Thus maternal undernutrition could cause epigenetic changes in the POMC and glucocorticoid receptor genes, in the foetal hypothalamus, which may predispose the offspring to altered regulation of food intake, energy expenditure and glucose homeostasis, later in life.

The timing of "catch-up growth" affects metabolism and appetite regulation in male rats born with intrauterine growth restriction

Epidemiological studies demonstrated a relationship between low birth weight mainly caused by intrauterine growth restriction (IUGR) and adult metabolic disorders. The concept of metabolic programming centers on the idea that nutritional and hormonal status during the key period of development determines the long-term control of energy balance by programming future feeding behavior and energy expenditure. The present study examined the consequence of early or late "catch-up growth" after IUGR on feeding behavior and metabolic cues of male offspring of rat dams exposed to protein restriction during gestation and/or lactation. Our results suggest that early catch-up growth may be favorable for fasting metabolic parameters at weaning, as no differences were observed on plasma leptin, triglyceride, glucose, and insulin levels compared with controls. In contrast, if pups remained malnourished until weaning, low insulin concentration was detected and was accompanied by hyperphagia associated with a large increase in hypothalamic NPY and AgRP mRNA expression. At adult age, on a regular chow diet, only the meal structure was modified by fetal programming. The two IUGR groups demonstrated a reduced meal duration that enhanced the speed of food ingestion and consequently increased the rest period associated to the satiety state without changes in the hypothalamic expression of appetite neuropeptides. Our findings demonstrate that in IUGR, regardless of postnatal growth magnitude, metabolic programming occurred in utero and was responsible for both feeding behavior alteration and postprandial higher insulin level in adults. Additionally, catch-up growth immediately after early malnutrition could be a key point for the programming of postprandial hyperleptinemia.

Maternal high-fat diet and fetal programming: increased proliferation of hypothalamic peptide-producing neurons that increase risk for overeating and obesity

Recent studies in adult and weanling rats show that dietary fat, in close association with circulating lipids, can stimulate expression of hypothalamic peptides involved in controlling food intake and body weight. In the present study, we examined the possibility that a fat-rich diet during pregnancy alters the development of these peptide systems in utero, producing neuronal changes in the offspring that persist postnatally in the absence of the diet and have long-term consequences. The offspring of dams on a high-fat diet (HFD) versus balanced diet (BD), from embryonic day 6 to postnatal day 15 (P15), showed increased expression of orexigenic peptides, galanin, enkephalin, and dynorphin, in the paraventricular nucleus and orexin and melanin-concentrating hormone in the perifornical lateral hypothalamus. The increased density of these peptide-expressing neurons, evident in newborn offspring as well as P15 offspring cross-fostered at birth to dams on the BD, led us to examine events that might be occurring in utero. During gestation, the HFD stimulated the proliferation of neuroepithelial and neuronal precursor cells of the embryonic hypothalamic third ventricle. It also stimulated the proliferation and differentiation of neurons and their migration toward hypothalamic areas where ultimately a greater proportion of the new neurons expressed the orexigenic peptides. This increase in neurogenesis, closely associated with a marked increase in lipids in the blood, may have a role in producing the long-term behavioral and physiological changes observed in offspring after weaning, including an increase in food intake, preference for fat, hyperlipidemia, and higher body weight.

Chronic consumption of a low-fat diet leads to increased hypothalamic agouti-related protein and reduced leptin

OBJECTIVE

This study examined the hypothesis that dietary fat under ad libitum feeding conditions influences expression levels (mRNA) of the mouse agouti-related protein (AgRP), leptin, leptin receptor (OBRb), and neuropeptide Y (NPY) at early stages of development.

METHODS

C57Bl/6J male mice were placed on a high-fat diet (HFD) or a low-fat diet (LFD) shortly after weaning. Groups of mice were euthanized at various ages and real-time one-step reverse transcriptase polymerase chain reaction was used to analyze gene expression in the hypothalamus (AgRP, NPY, OBRb), the adrenal gland (AgRP), the testis (AgRP), and epididymal fat (leptin).

RESULTS

Leptin expression increased linearly with age but only under the HFD despite body weight gain under both diets. This pattern of expression coincided with reduced expression of hypothalamic AgRP under an HFD, whereas OBRb and NPY did not fluctuate in response to diet. By contrast, consumption of an LFD (i.e., high carbohydrate) increased hypothalamic AgRP and suppressed adipose leptin, which is consistent with the notion that leptin could regulate AgRP centrally. In contrast, AgRP expression in the adrenal gland initially decreased and then increased with age under both diets.

CONCLUSIONS

Dietary fat can have a tissue-dependent effect on AgRP that may be unfettered by leptin under an HFD.

Prenatal programming of childhood overweight and obesity

OBJECTIVE

To review the scientific evidence for prenatal programming of childhood overweight and obesity, and discuss its implications for MCH research, practice, and policy.

METHODS

A systematic review of observational studies examining the relationship between prenatal exposures and childhood overweight and obesity was conducted using MOOSE guidelines. The review included literature posted on PubMed and MDConsult and published between January 1975 and December 2005. Prenatal exposures to maternal diabetes, malnutrition, and cigarette smoking were examined, and primary study outcome was childhood overweight or obesity as measured by body mass index (BMI) for children ages 5 to 21.

RESULTS

Four of six included studies of prenatal exposure to maternal diabetes found higher prevalence of childhood overweight or obesity among offspring of diabetic mothers, with the highest quality study reporting an odds ratio of adolescent overweight of 1.4 (95% CI 1.0-1.9). The Dutch famine study found that exposure to maternal malnutrition in early, but not late, gestation was associated with increased odds of childhood obesity (OR 1.9, 95% CI 1.5-2.4). All eight included studies of prenatal exposure to maternal smoking showed significantly increased odds of childhood overweight and obesity, with most odds ratios clustering around 1.5 to 2.0. The biological mechanisms mediating these relationships are unknown but may be partially related to programming of insulin, leptin, and glucocorticoid resistance in utero.

CONCLUSION

Our review supports prenatal programming of childhood overweight and obesity. MCH research, practice, and policy need to consider the prenatal period a window of opportunity for obesity prevention.