Temporary effects of neonatal overfeeding on homeostatic control of food intake involve alterations in POMC promoter methylation in male rats

Early overfeeding and adult anhedonia: Impact of neonatal nutrition on hedonic food regulation in male rats

The aim of our study was to analyze the impact of early-life overnutrition and the exposure in adulthood to a cafeteria diet (CAF) on eating behavior and on the expression of key genes involved in the regulation of food intake. Male Wistar rats were raised in small (SL, 4 pups/dam) or normal litters (NL, 10 pups/dam), fed a control diet (CON) until postnatal day (PND) 90. Then, they received CON or CAF for 11 weeks (NL-CON, NL-CAF, SL-CON, SL-CAF; 12±2 rats/group). Body weight, food intake and behavioral tests (Elevated Plus Maze: EPM, Sensory-specific satiety: SSS) were assessed. At PND167, the rats were euthanized to obtain brain, blood and fat pads. Ventral tegmental area (VTA), Nucleus Accumbens (NAc) and Arcuate Nucleus (Arc), were isolated by micropunch technique for qPCR analysis. Early overfeeding alone had the ability to alter long-term SSS. CAF groups showed increased body weight, adiposity and energy intake; sweet food preference and altered SSS. SL-CAF showed hypophagia, basal hyperglycemia, altered SSS and anxiety-like behavior. Both NL-CAF and SL-CAF showed antidopaminergic effects, but through different pathways: NL-CAF reduced dopamine (DA) production in VTA via decreased tyrosine hydroxylase (TH) expression, while SL-CAF exhibited an increase in dopamine active transporter (DAT) expression in NAc enhancing clearance. SL decreased Neuropeptide Y (NPY) expression in the Arc in adulthood, which has been proposed to be the link between homeostatic and hedonic systems. Our research reveals a key link between early-life overnutrition and adult hedonic feeding control, emphasizing its lasting impact on eating behavior and the potential for innovative therapeutics to combat obesity.

Hypothalamic obesity: from basic mechanisms to clinical perspectives

Despite the diverse nature of obesity, there is compelling genetic, clinical, and experimental evidence that endorses the important contribution of brain circuits to this condition. The hypothalamus contains major regulatory circuits for bodyweight homoeostasis, the deregulation of which can lead to obesity. Although functional perturbation of hypothalamic pathways could lie at the basis of common forms of obesity, the term hypothalamic obesity has been created to define those rare forms of severe obesity where a clear hypothalamic substrate can be identified, either of genetic or acquired origin. An in-depth understanding of the pathogenesis, clinical presentation, and therapeutic targets of hypothalamic obesity relies on the comprehension of the physiological basis of hypothalamic pathways governing bodyweight control, the mechanisms (either genetic or acquired) whereby they are perturbed, and the consequences of such perturbation. In this Review, we provide a synoptic overview of hypothalamic obesity, from basic mechanisms to clinical perspectives, with a major focus on current developments and new avenues for the diagnosis and precise treatment of these rare forms of obesity.

Neonatal overfeeding promotes anxiety, impairs episodic-like memory, and disrupts transcriptional regulation of hippocampal steroidogenic enzymes

The objective of our study was to investigate the impact of neonatal overfeeding on cognitive functions and neurosteroidogenesis in male rats. Offspring were assigned to either small litters (SL; 4 pups/mother), resulting in increased milk intake and body weight gain, or normal litters (NL; 10 pups/mother). On postnatal day (PND) 21, half of the male rats were euthanized, while the remaining were kept under standard conditions (4 rats/cage) until PND70. At this stage, subjects underwent assessments for locomotor activity, anxiety levels via the elevated plus maze, and episodic-like memory (ELM) tests. By PND90, the rats were euthanized for brain dissection. Utilizing micropunch techniques, dentate gyrus (DG), CA1, and CA3 regions were extracted for analysis of mRNA expression and methylation patterns. At PND21, SL rats exhibited increased body and adipose tissue weights, alongside elevated cholesterol, glucose, and triglyceride levels compared to NL counterparts. By PND90, although metabolic disparities were no longer evident, SL rats demonstrated heightened anxiety-like behavior and diminished performance in ELM tests. Early life changes included a decreased expression of aromatase (P450arom) and 3α-HSD in CA1, with increased levels in CA3 and DG among SL rats. Additionally, PND90 rats from SL exhibited increased P450arom and decreased 5α-reductase 1 (5αR-1) expression in DG. Notably, some of these variations were correlated with changes in methylation patterns of their promoter regions. Our findings reveal that neonatal overfeeding exerts a long-term adverse effect on cognitive abilities and neurosteroidogenic pathways, underscoring the lasting impact of nutritional experiences during critical early postnatal development periods.

Swimming training prevents obesity installation and normalizes hypothalamic expressions of GLP1 and leptin receptors in adult offspring born in small litters

OBJECTIVE

Glucagon-like peptide-1 (GLP1) and leptin (Lep) are afferent signals that regulate energy metabolism. Lactational hypernutrition results in hyperphagia and adiposity in adult life, and these events can be prevented by exercise. We evaluated the effects of swimming training on hypothalamic (GLP1-R) and Lep receptor (Lep-R) gene expressions in lactational hypernutrition-induced obesity.

METHODS

On the 3rd postnatal day, the litter sizes of lactating dams were adjusted to small litters (SL; 3 pups/dams) or normal litters (NL; 9 pups/dams). After weaning (21 days), NL and SL male rats were randomly distributed to sedentary (Sed) and exercised (Exe) groups. Exercised mice swam (30 min/3 times/week) for 68 days. Food intake and body weight gain were registered. At 92 days, intraperitoneal glucose and insulin tolerance tests were performed and rats were euthanized at 93 days; adipose tissue depots were weighed, and blood counts and plasma biochemical analyses performed. Hypothalamus were isolated to evaluate Lep-R and GLP1-R gene expressions.

RESULTS

Small litters sedentary rats presented increased body weight gain, adiposity, insulin sensibility and higher fasting values of glucose and triglycerides, besides higher hypothalamic gene expressions of Lep-R and GLP1-R, compared to NLSed animals. SLExe rats did not develop obesity or metabolic abnormalities and Lep-R and GLP1-R hypothalamic gene expressions were normalized.

CONCLUSION

Lactational hypernutrition induces obesity and metabolic dysfunction in adult life, in association with higher hypothalamic expressions of the Lep-R and GLP1-R genes. Exercise prevented obesity and improved metabolic state in SL overnourished rats, and normalized their hypothalamic Lep-R and GLP1-R gene expressions.

Paternal high-fat diet affects weight and DNA methylation of their offspring

Obesity poses a public health threat, reaching epidemic proportions. Our hypothesis suggests that some of this epidemic stems from its transmission across generations via paternal epigenetic mechanisms. To investigate this possibility, we focused on examining the paternal transmission of CpG methylation. First-generation male Wistar rats were fed either a high-fat diet (HF) or chow and were mated with females fed chow. We collected sperm from these males. The resulting offspring were raised on a chow diet until day 35, after which they underwent a dietary challenge. Diet-induced obese (DIO) male rats passed on the obesogenic trait to both male and female offspring. We observed significant hypermethylation of the Pomc promoter in the sperm of HF-treated males and in the hypothalamic arcuate nucleus (Arc) of their offspring at weaning. However, these differences in Arc methylation decreased later in life. This hypermethylation is correlated with increased expression of DNMT3B. Further investigating genes in the Arc that might be involved in obesogenic transgenerational transmission, using reduced representation bisulfite sequencing (RRBS) we identified 77 differentially methylated regions (DMRs), highlighting pathways associated with neuronal development. These findings support paternal CpG methylation as a mechanism for transmitting obesogenic traits across generations.

Neonatal overfeeding alters the functioning of the mesolimbic dopaminergic circuitry involving changes in DNA methylation and effects on feeding behavior

Mesolimbic dopaminergic circuit is essential for food reward and motivational behaviors and can contribute to weight gain and obesity. Litter reduction is a classical model for studying the effects of neonatal overfeeding and overweight. Litters of Wistar rats were reduced to 4 pups/dam for small litter (SL) and 10 pups/dam for normal litter at postnatal day (PND) 4. Immediately after performing the feeding behavior tests, the animals were sacrificed in PND21 and PND90. The ventral tegmental area (VTA), Nucleus Accumbens Core (NAcC) and Shell (NAcSh) were isolated from frozen brain sections using the Palkovits micropunch technique. RNA and DNA were extracted from these areas, gene expression was measured by RT-qPCR and DNA methylation levels were measured by MSRM-qPCR technique. SL-PND21 animals presented increased expression levels of Tyrosine Hydroxylase and Dopamine Receptor D2 in VTA, decreased expression levels of dopamine active transporter (DAT) in VTA, and higher expression levels of DAT in NAcC. On the other hand, SL-PND90 animals showed decreased expression levels of Dopamine Receptor D1 and higher expression of DAT in NAcSh. These animals also evidenced impaired sensory-specific satiety. In addition, altered promoter methylation was observed at weaning, and remained in adulthood. This work demonstrates that neonatal overfeeding induces disruptions in the mesolimbic dopaminergic circuitry and causes alterations in feeding behavior from weaning to adulthood, suggesting that the neonatal period is critical for the normal development of dopaminergic circuit that impact on feeding behavior.

Postnatal Overfeeding during Lactation Induces Endothelial Dysfunction and Cardiac Insulin Resistance in Adult Rats

Early overnutrition is associated with cardiometabolic alterations in adulthood, likely attributed to reduced insulin sensitivity due to its crucial role in the cardiovascular system. This study aimed to assess the long-term effects of early overnutrition on the development of cardiovascular insulin resistance. An experimental childhood obesity model was established using male Sprague Dawley rats. Rats were organized into litters of 12 pups/mother (L12-Controls) or 3 pups/mother (L3-Overfed) at birth. After weaning, animals from L12 and L3 were housed three per cage and provided ad libitum access to food for 6 months. L3 rats exhibited elevated body weight, along with increased visceral, subcutaneous, and perivascular fat accumulation. However, heart weight at sacrifice was reduced in L3 rats. Furthermore, L3 rats displayed elevated serum levels of glucose, leptin, adiponectin, total lipids, and triglycerides compared to control rats. In the myocardium, overfed rats showed decreased IL-10 mRNA levels and alterations in contractility and heart rate in response to insulin. Similarly, aortic tissue exhibited modified gene expression of TNFα, iNOS, and IL-6. Additionally, L3 aortas exhibited endothelial dysfunction in response to acetylcholine, although insulin-induced relaxation remained unchanged compared to controls. At the molecular level, L3 rats displayed reduced Akt phosphorylation in response to insulin, both in myocardial and aortic tissues, whereas MAPK phosphorylation was elevated solely in the myocardium. Overfeeding during lactation in rats induces endothelial dysfunction and cardiac insulin resistance in adulthood, potentially contributing to the cardiovascular alterations observed in this experimental model.

Postnatal Overfeeding in Rodents Induces a Neurodevelopment Delay and Anxious-like Behaviour Accompanied by Sex- and Brain-Region-Specific Synaptic and Metabolic Changes

Nutritional disturbances during the early postnatal period can have long-lasting effects on neurodevelopment and may be related to behavioural changes at adulthood. While such neuronal connection disruption can contribute to social and behaviour alterations, the dysregulation of the neuroendocrine pathways involved in nutrient-sensing balance may also cause such impairments, although the underlying mechanisms are still unclear. We aimed to evaluate sex-specific neurodevelopmental and behavioural changes upon postnatal overfeeding and determine the potential underpinning mechanisms at the central nervous system level, with a focus on the interconnection between synaptic and neuroendocrine molecular alterations. At postnatal day 3 (PND3) litters were culled to three animals (small litter procedure). Neurodevelopmental tests were conducted at infancy, whereas behavioural tests to assess locomotion, anxiety, and memory were performed at adolescence, together with molecular analysis of the hippocampus, hypothalamus, and prefrontal cortex. At infancy, females presented impaired acquisition of an auditory response, eye opening, olfactory discrimination, and vestibular system development, suggesting that female offspring neurodevelopment/maturation was deeply affected. Male offspring presented a transitory delay in locomotor performance., while both offspring had lower upper limb strength. At adolescence, both sexes presented anxious-like behaviour without alterations in short-term memory retention. Both males and females presented lower NPY1R levels in a region-specific manner. Furthermore, both sexes presented synaptic changes in the hippocampus (lower GABAA in females and higher GABAA levels in males), while, in the prefrontal cortex, similar higher GABAA receptor levels were observed. At the hypothalamus, females presented synaptic changes, namely higher vGLUT1 and PSD95 levels. Thus, we demonstrate that postnatal overfeeding modulates offspring behaviour and dysregulates nutrient-sensing mechanisms such as NPY and GABA in a sex- and brain-region-specific manner.

The immediate effect of overnutrition and fluoxetine treatment during the critical period of development on the hippocampus

It is well known that overnutrition, overweight, and obesity in children can modulate brain mechanisms of plasticity, monoaminergic systems, and mitochondrial function. The immediate effect of overnutrition during the developmental period has not been thoroughly examined in rats until the present. This study sought to evaluate the impact on adult rats of early life overfeeding and fluoxetine treatment from post-natal day 1 (PND1) to post-natal day 21 (PND21) relative to mitochondrial function, oxidative balance, and expression of specific monoaminergic genes in the hippocampus. The following were evaluated: mitochondrial function markers, oxidative stress biomarkers, dopamine-and serotonin-related genes, and BDNF mRNA levels. Overfeeding during the lactation period deregulates cellular metabolism and the monoaminergic systems in the hippocampus. Strikingly, serotonin modulation by fluoxetine treatment protected against some of the effects of early overnutrition. We conclude that overfeeding during brain development induce detrimental effects in mitochondria and in the genes that regulate homeostatic status that can be the molecular mechanisms related to neurological diseases.

Litter Size Reduction as a Model of Overfeeding during Lactation and Its Consequences for the Development of Metabolic Diseases in the Offspring

Overfeeding during lactation has a deleterious impact on the baby’s health throughout life. In humans, early overnutrition has been associated with higher susceptibility to obesity and metabolic disorders in childhood and adulthood. In rodents, using a rodent litter size reduction model (small litter) to mimic early overfeeding, the same metabolic profile has been described. Therefore, the rodent small litter model is an efficient tool to investigate the adaptive mechanisms involved in obesogenesis. Besides central and metabolic dysfunctions, studies have pointed to the contribution of the endocrine system to the small litter phenotype. Hormones, especially leptin, insulin, and adrenal hormones, have been associated with satiety, glucose homeostasis, and adipogenesis, while hypothyroidism impairs energy metabolism, favoring obesity. Behavioral modifications, hepatic metabolism changes, and reproductive dysfunctions have also been reported. In this review, we update these findings, highlighting the interaction of early nutrition and the adaptive features of the endocrine system. We also report the sex-related differences and epigenetic mechanisms. This model highlights the intense plasticity during lactation triggering many adaptive responses, which are the basis of the developmental origins of health and disease (DOHaD) concept. Our review demonstrates the complexity of the adaptive mechanisms involved in the obesity phenotype promoted by early overnutrition, reinforcing the necessity of adequate nutritional habits during lactation.

Can breastfeeding affect the rest of our life?

The breastfeeding period is one of the most important critical windows in our development, since milk, our first food after birth, contains several compounds, such as macronutrients, micronutrients, antibodies, growth factors and hormones that benefit human health. Indeed, nutritional, and environmental alterations during lactation, change the composition of breast milk and induce alterations in the child's development, such as obesity, leading to the metabolic dysfunctions, cardiovascular diseases and neurobehavioral disorders. This review is based on experimental animal models, most of them in rodents, and summarizes the impact of an adequate breast milk supply in view of the developmental origins of health and disease (DOHaD) concept, which has been proposed by researchers in the areas of epidemiology and basic science from around the world. Here, experimental advances in understanding the programming during breastfeeding were compiled with the purpose of generating knowledge about the genesis of chronic noncommunicable diseases and to guide the development of public policies to deal with and prevent the problems arising from this phenomenon. This review article is part of the special issue on "Cross talk between periphery and brain".

Long-Term Effects of Maternal Low-Protein Diet and Post-weaning High-Fat Feeding on Glucose Metabolism and Hypothalamic POMC Promoter Methylation in Offspring Mice

Substantial evidence indicated that maternal malnutrition could increase the susceptibility to obesity, insulin resistance, and type 2 diabetes in adulthood. It is increasingly apparent that the brain, especially the hypothalamus, plays a critical role in glucose homeostasis. However, little information is known about the mechanisms linking maternal protein restriction combined with post-weaning high-fat (HF) feeding with altered expression of brain neurotransmitters, and investigations into the epigenetic modifications of hypothalamus in offspring have not been fully elucidated. Our objective was to explore the effects of maternal protein restriction combined with post-weaning HF feeding on glucose metabolism and hypothalamic POMC methylation in male offspring mice. C57/BL6 mice were fed on either low-protein (LP) or normal chow (NC) diet throughout gestation and lactation. Then, the male offspring were randomly weaned to either NC or high-fat (HF) diet until 32 weeks of age. Gene expressions and DNA methylation of hypothalamic proopiomelanocortin (POMC) and melanocortin receptor 4 (MC4R) were determined in male offspring. The results showed that birth weights and body weights at weaning were both significantly lower in male offspring mice of the dams fed with a LP diet. Maternal protein restriction combined with post-weaning high-fat feeding, predisposes higher body weight, persistent glucose intolerance (from weaning to 32 weeks of age), hyperinsulinemia, and hyperleptinemia in male offspring mice. POMC and MC4R expressions were significantly increased in offspring mice fed with maternal LP and postnatal high-fat diet (P < 0.05). Furthermore, maternal protein restriction combined with post-weaning high-fat feeding induced hypomethylation of POMC promoter in the hypothalamus (P < 0.05) and POMC-specific methylation (%) was negatively correlated with the glucose response to a glucose load in male offspring mice (r = -0.42, P = 0.039). In conclusion, maternal LP diet combined with post-weaning high-fat feeding predisposed the male offspring to impaired glucose metabolism and hypothalamic POMC hypomethylation. These findings can advance our thinking about hypothalamic POMC gene methylation between maternal LP diet combined with post-weaning high-fat feeding and metabolic health in offspring.