Perinatal overfeeding in rats results in increased levels of plasma leptin but unchanged cerebrospinal leptin in adulthood

Prolonged breastfeeding protects from obesity by hypothalamic action of hepatic FGF21

Early-life determinants are thought to be a major factor in the rapid increase of obesity. However, while maternal nutrition has been extensively studied, the effects of breastfeeding by the infant on the reprogramming of energy balance in childhood and throughout adulthood remain largely unknown. Here we show that delayed weaning in rat pups protects them against diet-induced obesity in adulthood, through enhanced brown adipose tissue thermogenesis and energy expenditure. In-depth metabolic phenotyping in this rat model as well as in transgenic mice reveals that the effects of prolonged suckling are mediated by increased hepatic fibroblast growth factor 21 (FGF21) production and tanycyte-controlled access to the hypothalamus in adulthood. Specifically, FGF21 activates GABA-containing neurons expressing dopamine receptor 2 in the lateral hypothalamic area and zona incerta. Prolonged breastfeeding thus constitutes a protective mechanism against obesity by affecting long-lasting physiological changes in liver-to-hypothalamus communication and hypothalamic metabolic regulation.

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.

Obesity induces resistance to central action of BMP8B through a mechanism involving the BBSome

Objective

Bone morphogenetic protein 8B (BMP8B) plays a major role in the regulation of energy homeostasis by modulating brown adipose tissue (BAT) thermogenesis and white adipose tissue (WAT) browning. Here, we investigated whether BMP8B's role in metabolism is affected by obesity and the possible molecular mechanisms underlying that action.

Methods

Central treatments with BMP8B were performed in rats fed a standard (SD) and high-fat diet (HFD), as well as in genetically modified mice. Energy balance studies, infrared thermographic analysis of BAT and molecular analysis of the hypothalamus, BAT and WAT were carried out.

Results

We show for the first time that HFD-induced obesity elicits resistance to the central actions of BMP8B on energy balance. This obesity-induced BMP8B resistance is explained by i) lack of effects on AMP-activated protein kinase (AMPK) signaling, ii) decreased BMP receptors signaling and iii) reduced expression of Bardet-Biedl Syndrome 1 (BBS1) protein, a key component of the protein complex BBSome in the ventromedial nucleus of the hypothalamus (VMH). The possible mechanistic involvement of BBS1 in this process is demonstrated by lack of a central response to BMP8B in mice carrying a single missense disease-causing mutation in the Bbs1 gene.

Conclusions

Overall, our data uncover a new mechanism of central resistance to hormonal action that may be of relevance in the pathophysiology of obesity.

•

Central BMP8B induces BAT activation and browning through hypothalamic AMPK.

•

Obesity elicits resistance to the central effects of BMP8B on energy balance.

•

Obesity impairs the effect of BMP8B on AMPK, BMP Type I receptors signaling and BBS1 in the hypothalamus.

•

Lack of BBS1 function recapitulates the thermogenic-induced resistance to central BMP8B.

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

A small litter (SL) model was used to determine how neonatal overfeeding affects the homeostatic control of food intake in male rats at weaning and postnatal day (PND) 90. At PND4, litters were reduced to small (4 pups/dam) or normal (10 pups/dam) litters. At weaning, SL rats showed higher body weight and characteristic features of the metabolic syndrome. Gene expression of pro-opiomelanocortin (POMC), cocaine and amphetamine regulated transcript, neuropeptide Y (NPY) and leptin and ghrelin (GHSR) receptors were increased and POMC promoter was hypomethylated in arcuate nucleus, indicating that the early development of obesity may involve the GHSR/NPY system and changes in POMC methylation state. At PND90, body weight, metabolic parameters and gene expression were restored; however, POMC methylation state remained altered. This work provides insight into the effects of neonatal overfeeding, showing the importance of developmental plasticity in restoring early changes in central pathways involved in metabolic programming.

Consequences of early life overfeeding for microglia - Perspectives from rodent models

The early life period is crucially important to how the individual develops, and environmental and lifestyle challenges during this time can lead to lasting programming effects on the brain and immune system. In particular, poor diet in early development can lead to long-term negative metabolic and cognitive outcomes, with those who over-eat in early development being at risk of obesity and poor learning and memory throughout their adult lives. Current research has identified a neuroinflammatory component to this metabolic and cognitive programming that can potentially be manipulated to restore a healthy phenotype. Thus, early life over-feeding in a rat model leads to microglial priming and an exacerbated microglial response to immune challenge when the rats reach adulthood. Microglial responses to a learning task are also impaired. To specifically investigate the role of microglia in these programming effects our group has developed a novel transgenic rat with a diphtheria toxin receptor insertion in the promoter region for the Cx3cr1 gene, expressed on microglia and monocytes; allowing us to conditionally ablate microglia throughout the brain. With this model we reveal that microglia have a direct role in regulating feeding behavior and modifying cognition, but are not likely to be the sole mechanism by which early life overfeeding confers lasting neuroimmune and cognitive effects. Additional work implicates changes to the hypothalamic-pituitary-adrenal axis in this. Together these data highlight the importance of dietary choices in early life and the potential for positive interventions targeting the neuroimmune and neuroendocrine stress systems to reverse such programming damage.

Perinatal over- and underfeeding affect hypothalamic leptin and ghrelin neuroendocrine responses in adult rats

BACKGROUND

Changes in the nutritional supply during the perinatal period can lead to metabolic disturbances and obesity in adulthood.

OBJECTIVE

The divergent litter size model was used to investigate the hypothalamic sensitivity to leptin and ghrelin as well as the mechanisms involved in the disruption of food intake and energy expenditure.

METHODS

On postnatal day 3 (P3), male Wistar rats were divided into 3 groups: small litter (SL - 3 pups), normal litter (NL - 10 pups), and large litter (LL - 16 pups). Animals at P60 were intraperitoneally treated with leptin (500 µg/Kg), ghrelin (40 µg/Kg), or vehicle (0.9% NaCl) at 5 pm and the following parameters were assessed: food intake and body weight; immunostaining of p-STAT-3 in the hypothalamus; Western Blotting analysis of p-AMPKα and UCP2 in the mediobasal hypothalamus (MBH), and UCP1 in the interscapular brown adipose tissue (BAT); or heat production, VO₂, VCO₂, and locomotor activity.

RESULTS

SL rats had earlier leptin and ghrelin surges, while LL rats had no variations. At P60, after leptin treatment, LL rats showed hypophagia and increased p-STAT-3 expression in the arcuate nucleus, but SL rats had no response. After ghrelin treatment, LL rats did not have the orexigenic response or AMPKα phosphorylation in the MBH, while SL animals, unexpectedly, decreased body weight gain, without changes in food intake, and increased metabolic parameters and UCP1 expression in the BAT.

CONCLUSIONS

Changes in the nutritional supply at early stages of life modify leptin and ghrelin responsiveness in adulthood, programming metabolic and central mechanisms, which contribute to overweight and obesity in adulthood.

Peptides from Natural or Rationally Designed Sources Can Be Used in Overweight, Obesity, and Type 2 Diabetes Therapies

Overweight and obesity are among the most prominent health problems in the modern world, mostly because they are either associated with or increase the risk of other diseases such as type 2 diabetes, hypertension, and/or cancer. Most professional organizations define overweight and obesity according to individual body-mass index (BMI, weight in kilograms divided by height squared in meters). Overweight is defined as individuals with BMI from 25 to 29, and obesity as individuals with BMI ≥30. Obesity is the result of genetic, behavioral, environmental, physiological, social, and cultural factors that result in energy imbalance and promote excessive fat deposition. Despite all the knowledge concerning the pathophysiology of obesity, which is considered a disease, none of the existing treatments alone or in combination can normalize blood glucose concentration and prevent debilitating complications from obesity. This review discusses some new perspectives for overweight and obesity treatments, including the use of the new orally active cannabinoid peptide Pep19, the advantage of which is the absence of undesired central nervous system effects usually experienced with other cannabinoids.

Differential effects of leptin administration on feeding and HPT axis function in early-life overfed adult rats

Early-life overfeeding (OF) disrupts neuroendocrine systems, energy homeostasis and food intake regulation inducing overeating and overweight in adults. Adult rats raised in small litters during lactation, display hyperphagia and overweight since weaning and exhibit a decrease in thyrotropin-releasing hormone (TRH) mRNA expression in hypothalamic paraventricular nucleus (PVN). This is counterintuitive because TRH expression should increase to activate the hypothalamic-pituitary-thyroid (HPT) axis and promote energy expenditure, thus, HPT axis seems inhibited in OF rats. Leptin, an adipocyte-synthesized hormone that stimulates hypothalamic TRH expression, enhances both TRH anorectic effects and HPT axis-induced metabolic rate. To evaluate hypothalamic resistance to the anorectic and HPT axis stimulatory actions of leptin, we injected leptin i.p. to ad libitum fed and to 48-h fasted adult control (reared in normal litters) and to small-litter reared (OF) male Wistar rats. Findings showed that HPT axis was still responsive to leptin, since PVN TRH mRNA levels, median eminence TRH release and T4 serum concentration increased in both, ad libitum and fasted OF rats after leptin administrations. Leptin was ineffective to reduce feeding of OF animals. By comparing leptin receptor (ObRb) expression changes between arcuate and PVN nuclei, we observed that arcuate ObRb was not modified in response to leptin administrations in OF rats, likely accounting for the differential effects in feeding and HPT axis function. Nevertheless, ObRb expression was modified by leptin in the PVN of OF rats to the same extent as controls; this supports the hormone's role as a therapeutic agent for early onset obesity in adults.

Feeding circuit development and early-life influences on future feeding behaviour

A wide range of maternal exposures - undernutrition, obesity, diabetes, stress and infection - are associated with an increased risk of metabolic disease in offspring. Developmental influences can cause persistent structural changes in hypothalamic circuits regulating food intake in the service of energy balance. The physiological relevance of these alterations has been called into question because maternal impacts on daily caloric intake do not persist to adulthood. Recent behavioural and epidemiological studies in humans provide evidence that the relative contribution of appetitive traits related to satiety, reward and the emotional aspects of food intake regulation changes across the lifespan. This Opinion article outlines a neurodevelopmental framework to explore the possibility that crosstalk between developing circuits regulating different modalities of food intake shapes future behavioural responses to environmental challenges.

Orexins/Hypocretins: Key Regulators of Energy Homeostasis

Originally described to be involved in feeding regulation, orexins/hypocretins are now also considered as major regulatory actors of numerous biological processes, such as pain, sleep, cardiovascular function, neuroendocrine regulation, and energy expenditure. Therefore, they constitute one of the most pleiotropic families of hypothalamic neuropeptides. Although their orexigenic effect is well documented, orexins/hypocretins also exert central effects on energy expenditure, notably on the brown adipose tissue (BAT) thermogenesis. A better comprehension of the underlying mechanisms and potential interactions with other hypothalamic molecular pathways involved in the modulation of food intake and thermogenesis, such as AMP-activated protein kinase (AMPK) and endoplasmic reticulum (ER) stress, is essential to determine the exact implication and pathophysiological relevance of orexins/hypocretins on the control of energy balance. Here, we will review the actions of orexins on energy balance, with special focus on feeding and brown fat function.

Effects of a High-Fat Diet on Adipose Tissue CD8+ T Cells in Young vs. Adult Mice

T cells are involved in chronic inflammation of adipose tissue in obese conditions. However, the impact of age on the adipose T cells remains unknown. In this study, we investigated T cells in the white adipose tissue of young and adult mice. Obesity was induced in the mice using a high-fat diet (HFD) for 14 weeks. The young mice were fed an HFD at 3 weeks old, and adult mice were fed the HFD at 12 weeks old. Relative to adult mice, the young mice gained less fat and exhibited better glucose tolerance. Their adipose tissue contained more CD8+ T cells and higher levels of pro-inflammatory cytokines. Young mice showed a larger increase in CD4+ T cells. The young and adult mice showed similar insulin tolerance. HFD reduced the colon muscle layer, which was more obvious in the young mice. These data suggested that young and adult mice exhibit different responses to an HFD in terms of adipose tissue, glucose tolerance, and the colon muscle layer. The increase in CD8+ T cells and CD4+ T cells, together with higher levels of pro-inflammatory cytokines, suggested elevated inflammation in the presence of less fat gain in the young mice, which was unexpected. The significance of this inflammation remains unknown. We propose that inflammation might inhibit energy storage in the adipose tissue to provide more energy to the lean body mass in favor of growth in the young mice. The present study provides another example of the beneficial effect of inflammation in physiological conditions.

Hypothalamic effects of neonatal diet: reversible and only partially leptin dependent

Early life diet influences metabolic programming, increasing the risk for long-lasting metabolic ill health. Neonatally overfed rats have an early increase in leptin that is maintained long term and is associated with a corresponding elevation in body weight. However, the immediate and long-term effects of neonatal overfeeding on hypothalamic anorexigenic pro-opiomelanocortin (POMC) and orexigenic agouti-related peptide (AgRP)/neuropeptide Y (NPY) circuitry, and if these are directly mediated by leptin, have not yet been examined. Here, we examined the effects of neonatal overfeeding on leptin-mediated development of hypothalamic POMC and AgRP/NPY neurons and whether these effects can be normalised by neonatal leptin antagonism in male Wistar rats. Neonatal overfeeding led to an acute (neonatal) resistance of hypothalamic neurons to exogenous leptin, but this leptin resistance was resolved by adulthood. While there were no effects of neonatal overfeeding on POMC immunoreactivity in neonates or adults, the neonatal overfeeding-induced early increase in arcuate nucleus (ARC) AgRP/NPY fibres was reversed by adulthood so that neonatally overfed adults had reduced NPY immunoreactivity in the ARC compared with controls, with no further differences in AgRP immunoreactivity. Short-term neonatal leptin antagonism did not reverse the excess body weight or hyperleptinaemia in the neonatally overfed, suggesting factors other than leptin may also contribute to the phenotype. Our findings show that changes in the availability of leptin during early life period influence the development of hypothalamic connectivity short term, but this is partly resolved by adulthood indicating an adaptation to the metabolic mal-programming effects of neonatal overfeeding.

The cellular and molecular bases of leptin and ghrelin resistance in obesity

Obesity, a major risk factor for the development of diabetes mellitus, cardiovascular diseases and certain types of cancer, arises from a chronic positive energy balance that is often due to unlimited access to food and an increasingly sedentary lifestyle on the background of a genetic and epigenetic vulnerability. Our understanding of the humoral and neuronal systems that mediate the control of energy homeostasis has improved dramatically in the past few decades. However, our ability to develop effective strategies to slow the current epidemic of obesity has been hampered, largely owing to the limited knowledge of the mechanisms underlying resistance to the action of metabolic hormones such as leptin and ghrelin. The development of resistance to leptin and ghrelin, hormones that are crucial for the neuroendocrine control of energy homeostasis, is a hallmark of obesity. Intensive research over the past several years has yielded tremendous progress in our understanding of the cellular pathways that disrupt the action of leptin and ghrelin. In this Review, we discuss the molecular mechanisms underpinning resistance to leptin and ghrelin and how they can be exploited as targets for pharmacological management of obesity.

Sequential Exposure to Obesogenic Factors in Females Rats: From Physiological Changes to Lipid Metabolism in Liver and Mesenteric Adipose Tissue

During their lifetime, females are subjected to different nutritional and hormonal factors that could increase the risk of obesity and associated comorbidities. From early postnatal periods until the postmenopausal phase, exposure to over nutrition, high-energy diet and oestrogen deficiency, are considered as significant obesity risk factors in women. In this study, we assessed how key transitional life events and exposure to different nutrition influence energy homeostasis in a rat model. Specifically, we assessed the sequential exposure to postnatal over nutrition, high-fat diet (HFD) after weaning, followed later by ovariectomy (OVX; as a model of menopause). Each obesity risk factor increased significantly body weight (BW) and adiposity, with additive effects after sequential exposure. Increased energy intake in both HFD and/or OVX groups, and decreased locomotor activity and energy expenditure after OVX can explain these metabolic changes. Our study also documents decreased lipogenic pathway in mesenteric adipose tissue after HFD and/or OVX, independent of previous postnatal programming, yet only HFD evoked this effect in liver. In addition, we report an increase in the expression of the hepatic PEPCK depending on previous metabolic status. Overall, our results identify the impact of different risk factors, which will help in understanding the development of obesity in females.

Neonatal overfeeding disrupts pituitary ghrelin signalling in female rats long-term; Implications for the stress response

The hypothalamic-pituitary-adrenal (HPA) axis responses to psychological stress are exacerbated in adult female but not male rats made obese due to overfeeding in early life. Ghrelin, traditionally known for its role in energy homeostasis, has been recently recognised for its role in coordinating the HPA responses to stress, particularly by acting directly at the anterior pituitary where the growth hormone secretagogue receptor (GHSR), the receptor for acyl ghrelin, is abundantly expressed. We therefore hypothesised that neonatal overfeeding in female rats would compromise pituitary responsiveness to ghrelin, contributing to a hyperactive central stress responsiveness. Unlike in males where hypothalamic ghrelin signalling is compromised by neonatal overfeeding, there was no effect of early life diet on circulating ghrelin or hypothalamic ghrelin signalling in females, indicating hypothalamic feeding and metabolic ghrelin circuitry remains intact. However, neonatal overfeeding did lead to long-term alterations in the pituitary ghrelin system. The neonatally overfed females had increased neonatal and reduced adult expression of GHSR and ghrelin-O-acyl transferase (GOAT) in the pituitary as well as reduced pituitary responsiveness to exogenous acyl ghrelin-induced adrenocorticotropic hormone (ACTH) release in vitro. These data suggest that neonatal overfeeding dysregulates pituitary ghrelin signalling long-term in females, potentially accounting for the hyper-responsive HPA axis in these animals. These findings have implications for how females may respond to stress throughout life, suggesting the way ghrelin modifies the stress response at the level of the pituitary may be less efficient in the neonatally overfed.

Hyperleptinemia in Neonatally Overfed Female Rats Does Not Dysregulate Feeding Circuitry

Neonatal overfeeding during the first weeks of life in male rats is associated with a disruption in the peripheral and central leptin systems. Neonatally overfed male rats have increased circulating leptin in the first 2 weeks of life, which corresponds to an increase in body weight compared to normally fed counterparts. These effects are associated with a short-term disruption in the connectivity of neuropeptide Y (NPY), agouti-related peptide (AgRP), and pro-opiomelanocortin (POMC) neurons within the regions of the hypothalamus responsible for control of energy balance and food intake. Female rats that are overfed during the first weeks of their life experience similar changes in circulating leptin levels as well as in their body weight. However, it has not yet been studied whether these metabolic changes are associated with the same central effects as observed in males. Here, we hypothesized that hyperleptinemia associated with neonatal overfeeding would lead to changes in central feeding circuitry in females as it does in males. We assessed hypothalamic NPY, AgRP, and POMC gene expression and immunoreactivity at 7, 12, or 14 days of age, as well as neuronal activation in response to exogenous leptin in neonatally overfed and control female rats. Neonatally overfed female rats were hyperleptinemic and were heavier than controls. However, these metabolic changes were not mirrored centrally by changes in hypothalamic NPY, AGRP, and POMC fiber density. These findings are suggestive of sex differences in the effects of neonatal overfeeding and of differences in the ability of the female and male central systems to respond to changes in the early life nutritional environment.

Orexins (hypocretins) and energy balance: More than feeding

Initially implicated in the regulation of feeding, orexins/hypocretins are now acknowledged to play a major role in the control of a wide variety of biological processes, such as sleep, energy expenditure, pain, cardiovascular function and neuroendocrine regulation, a feature that makes them one of the most pleiotropic families of hypothalamic neuropeptides. While the orexigenic effect of orexins is well described, their central effects on energy expenditure and particularly on brown adipose tissue (BAT) thermogenesis are not totally unraveled. Better understanding of these actions and their possible interrelationship with other hypothalamic systems controlling thermogenesis, such as AMP-activated protein kinase (AMPK) and endoplasmic reticulum (ER) stress, will help to clarify the exact role and pathophysiological relevance of these neuropeptides have on energy balance.

Use of a stair-step compensatory gain nutritional regimen to program the onset of puberty in beef heifers

It was hypothesized that metabolic programming of processes underlying puberty can be shifted temporally through the use of a stair-step compensatory growth model such that puberty is optimally timed to occur at 11 to 12 mo of age. Forty crossbred beef heifers were weaned at approximately 3.5 mo of age and, after a 2-wk acclimation period, were assigned randomly to 1 of 4 nutritional groups: 1) low control (LC), restricted feed intake of a forage-based diet to promote BW gain of 0.5 kg/d until 14 mo of age, 2) high control (HC), controlled feed intake of a high-concentrate diet to promote BW gain of 1 kg/d until 14 mo of age, 3) stair-step 1 (SS-1), ad libitum feed intake of a high-concentrate diet until 6.5 mo of age followed by restricted access to a high-forage diet to promote BW gain of 0.35 kg/d until 9 mo of age, ad libitum feed intake of a high-concentrate diet until 11.5 mo of age, and restricted intake of a high-forage diet to promote BW gain of 0.35 kg/d until 14 mo of age, and 4) stair-step 2 (SS-2), reverse sequence of SS-1, beginning with restricted access to a high-forage diet. Body weight (every 2 wk) and circulating concentrations of leptin (monthly) were determined throughout the experiment. Concentrations of progesterone in blood samples collected twice weekly beginning at 8 mo of age were used to determine pubertal status. Body weight gain followed a pattern similar to that proposed in our experimental design. Circulating concentrations of leptin increased following distinct elevations in BW but decreased abruptly after feed intake restriction. Survival analysis indicated that the percentage of pubertal heifers in the LC group was lower (P < 0.05) than all other groups throughout the experiment. Although heifers in SS-1 were nutritionally restricted between 6.5 and 9 mo of age, the proportion pubertal by 12 mo of age did not differ (P = 0.36) from that of the HC group, with 80% and 70% pubertal in SS-1 and HC, respectively. In contrast, the proportion of heifers pubertal by 12 mo of age in the SS-2 group (40%) was lower (P < 0.05) than both HC and SS-1. However, by 14 mo of age, 90% of heifers in the SS-2 group had also attained puberty compared to only 40% of the LC group. In summary, these data provide evidence that changes in the nutritional and metabolic status during the early juvenile period can program the onset of puberty that occurs months later, allowing optimal timing of sexual maturation in replacement beef heifers.

Neonatal events, such as androgenization and postnatal overfeeding, modify the response to ghrelin

It is currently accepted that ambient, non-genetic factors influence perinatal development and evoke structural and functional changes that may persist throughout life. Overfeeding and androgenization after birth are two of these key factors that could result in “metabolic imprinting” of neuronal circuits early in life and, thereby, increase the body weight homeostatic “set point”, stimulate appetite, and result in obesity. Our aim was to determine the influence of these obesogenic factors on the response to ghrelin. We observed the expected orexigenic effect of ghrelin regardless of the nutritional or hormonal manipulations to which the animals were subjected to at early postnatal development and this effect remained intact at later stages of development. In fact, ghrelin responses increased significantly when the animals were subjected to one of the two manipulations, but not when both were combined. An increased response to ghrelin could explain the obese phenotype displayed by individuals with modified perinatal environment.

Nicotine improves obesity and hepatic steatosis and ER stress in diet-induced obese male rats

Nicotine, the main addictive component of tobacco, promotes body weight reduction in humans and rodents. Recent evidence has suggested that nicotine acts in the central nervous system to modulate energy balance. Specifically, nicotine modulates hypothalamic AMP-activated protein kinase to decrease feeding and to increase brown adipose tissue thermogenesis through the sympathetic nervous system, leading to weight loss. Of note, most of this evidence has been obtained in animal models fed with normal diet or low-fat diet (LFD). However, its effectiveness in obese models remains elusive. Because obesity causes resistance towards many factors involved in energy homeostasis, the aim of this study has been to compare the effect of nicotine in a diet-induced obese (DIO) model, namely rats fed a high-fat diet, with rats fed a LFD. Our data show that chronic peripheral nicotine treatment reduced body weight by decreasing food intake and increasing brown adipose tissue thermogenesis in both LFD and DIO rats. This overall negative energy balance was associated to decreased activation of hypothalamic AMP-activated protein kinase in both models. Furthermore, nicotine improved serum lipid profile, decreased insulin serum levels, as well as reduced steatosis, inflammation, and endoplasmic reticulum stress in the liver of DIO rats but not in LFD rats. Overall, this evidence suggests that nicotine diminishes body weight and improves metabolic disorders linked to DIO and might offer a clear-cut strategy to develop new therapeutic approaches against obesity and its metabolic complications.

Hypothalamic KLF4 mediates leptin's effects on food intake via AgRP

Krüppel-like factor 4 (KLF4) is a zinc-finger-type transcription factor expressed in a range of tissues that plays multiple functions. We report that hypothalamic KLF4 represents a new transcription factor specifically modulating agouti-related protein (AgRP) expression in vivo. Hypothalamic KLF4 colocalizes with AgRP neurons and is modulated by nutritional status and leptin. Over-expression of KLF4 in the hypothalamic arcuate nucleus (ARC) induces food intake and increases body weight through the specific stimulation of AgRP, as well as blunting leptin sensitivity in lean rats independent of forkhead box protein 01 (FoxO1). Down-regulation of KLF4 in the ARC inhibits fasting-induced food intake in both lean and diet-induced obese (DIO) rats. Silencing KLF4, however, does not, on its own, enhance peripheral leptin sensitivity in DIO rats.

Pro-TRH and pro-CRF expression in paraventricular nucleus of small litter-reared fasted adult rats

Neuroendocrine axes adapt to nutrient availability. During fasting, the function of the hypothalamus-pituitary-thyroid axis (HPT) is reduced, whereas that of the hypothalamus-pituitary-adrenal axis (HPA) is increased. Overfeeding-induced hyperleptinemia during lactation may alter the regulatory set point of neuroendocrine axes and their adaptability to fasting in adulthood. Hyperleptinemia is developed in rodents by litter size reduction during lactation; adult rats from small litters become overweight, but their paraventricular nucleus (PVN) TRH synthesis is unchanged. It is unclear whether peptide expression still responds to nutrient availability. PVN corticotropin-releasing factor (CRF) expression has not been evaluated in this model. We analyzed adaptability of HPT and HPA axes to fasting-induced low leptin levels of reduced-litter adult rats. Offspring litters were reduced to 2-3/dam (early-overfed) or maintained at 8/dam (controls, C). At 10 weeks old, a subset of animals from each group was fasted for 48 h and leptin, corticosterone, and thyroid hormones serum levels were analyzed. In brain, expressions of leptin receptor, NPY and SOCS3, were evaluated in arcuate nucleus, and those of proTRH and proCRF in PVN by real-time PCR. ProTRH expression in anterior and medial PVN subcompartments was assayed by in situ hybridization. Early-overfed adults developed hyperphagia and excessive weight, together with decreased proTRH expression in anterior PVN, supporting the anorexigenic effects of TRH. Early-overfed rats presented low PVN proTRH synthesis, whereas fasting did not induce a further reduction. Fasting-induced stress was unable to increase corticosterone levels, contributing to reduced body weight loss in early-overfed rats. We concluded that early overfeeding impaired the adaptability of HPT and HPA axes to excess weight and fasting in adults.

Hypothalamic inflammation without astrogliosis in response to high sucrose intake is modulated by neonatal nutrition in male rats

Hypothalamic inflammation and gliosis are proposed to participate in the pathogenesis of high-fat diet-induced obesity. Because other factors and nutrients also induce weight gain and adiposity, we analyzed the inflammatory and glial responses to a sucrose (S)-enriched diet. Neonatal overnutrition (NON) exacerbates weight gain in response to metabolic challenges; thus, we compared the inflammatory response of male Wistar rats with NON (4 pups/litter) and controls (12 pups/litter) to increased S intake. At weaning rats received water or a 33% sucrose solution and normal chow ad libitum for 2 months. Sucrose increased serum IL-1β and -6 and hypothalamic IL-6 mRNA levels in NON and TNFα mRNA levels in control and NON rats, whereas NON alone had no effect. The astrocyte marker glial fibrillary acidic protein was increased by NON but decreased by S. This was associated with hypothalamic nuclei specific changes in glial fibrillary acidic protein-positive cell number and morphology. Sucrose increased the number of microglia and phosphorylation of inhibitor of -κB and c-Jun N-terminal kinase in control but not NON rats, with no effect on microglia activation markers. Proteins highly expressed in astrocytes (glutamate, glucose, and lactate transporters) were increased by NON but not S, with no increase in vimentin expression in astrocytes, further suggesting that S-induced adiposity is not associated with hypothalamic astrogliosis. Hence, activation of hypothalamic inflammatory processes and gliosis depend not only on weight gain but also on the diet inducing this weight gain and the early nutritional status. These diverse inflammatory processes could indicate a differential disposition to obesity-induced pathologies.

Effects of coronary ischemia-reperfusion in a rat model of early overnutrition. Role of angiotensin receptors

Background

Obesity during childhood has dramatically increased worldwide in the last decades. Environmental factors acting early in life, including nutrition, play an important role in the pathogenesis of obesity and cardiovascular diseases in adulthood.

Aims

To analyze the effects of early overfeeding on the heart and coronary circulation, the effect of ischemia-reperfusion (I/R) and the role of the renin-angiotensin system (RAS) were studied in isolated hearts from control and overfed rats during lactation.

Methods and Results

On the day of birth litters were adjusted to twelve pups per mother (control) or to three pups per mother (overfed). At weaning (21 days) the rats were killed and the heart perfused in a Langendorff system and subjected to 30 min of ischemia followed by 15 min of reperfusion. The contractility (left developed intraventricular pressure) was lower in the hearts from overfed rats, and was reduced by I/R in hearts from control but not from overfed rats. I/R also reduced the coronary vasoconstriction to angiotensin II more in hearts from control than from overfed rats, and the vasodilatation to bradykinin similarly in both experimental groups. The expression of both angiotensin AGTRa and AGTR2 receptors was increased in the myocardium of overfed rats, and I/R increased the expression of both receptors in control rats but reduced it in overfed rats. The expression of apoptotic and antiapoptotic markers was increased in hearts of overfed rats compared with control, and further increased by I/R.

Conclusions

These results suggest that both overfeeding and I/R impair cardiac and coronary function due, at least in part, to activation of the angiotensin pathway. However, overfeeding may reduce the impairment of ventricular contractility by I/R.

Effects of neonatal overfeeding on juvenile and adult feeding and energy expenditure in the rat

Overfeeding during perinatal life leads to an overweight phenotype that persists throughout the juvenile stage and into adulthood, however, the mechanim(s) underlying this effect are poorly understood. We hypothesized that obesity due to neonatal overfeeding is maintained by changes in energy expenditure and that these changes differ between males and females. We investigated feeding, physical activity, hormonal and metabolic alterations that occur in adult rats made obese by having been nursed in small litters (SL) compared with those from control litters (CL). There were no differences in absolute food intake between the groups, and juvenile and adult SL rats ate less chow per gram body weight than the CL did in the dark (active) phase. Juvenile, but not adult SL rats did have reduced whole body energy expenditure, but there were no differences between the groups by the time they reached adulthood. Adult SL females (but not males) had reduced brown adipose tissue (BAT) temperatures compared with CL in the first half of the dark phase. Our results indicate a persistent overweight phenotype in rats overfed as neonates is not associated with hyperphagia at any stage, but is reflected in reduced energy expenditure into the juvenile phase. The reduced dark phase BAT activity in adult SL females is not sufficient to reduce total energy expenditure at this stage of life and there is an apparently compensatory effect that prevents SL and CL from continuing to diverge in weight that appears between the juvenile and adult stages.

Leptin as mediator of the effects of developmental programming

Considerable epidemiological, experimental and clinical data have amassed showing that the risk of developing disease in later life is dependent upon early life conditions. In particular, altered maternal nutrition, including undernutrition and overnutrition, can lead to metabolic disorders in offspring characterised by obesity and leptin resistance. The adipokine leptin has received significant interest as a potential programming factor; alterations in the profile of leptin in early life are associated with altered susceptibility to obesity and metabolic disorders in adulthood. Maintenance of a critical leptin level during early development facilitates the normal maturation of tissues and signalling pathways involved in metabolic homeostasis. A period of relative hypo- or hyperleptinemia during this window of development will induce some of the metabolic adaptations which underlie developmental programming. However, it remains unclear whether leptin alone is a critical factor for the programming of obesity. At least in animal experimental studies, developmental programming is potentially reversible by manipulating the concentration of circulating leptin during a critical window of developmental plasticity and offers an exciting new approach for therapeutic intervention.

Strategies for reversing the effects of metabolic disorders induced as a consequence of developmental programming

Obesity and the metabolic syndrome have reached epidemic proportions worldwide with far-reaching health care and economic implications. The rapid increase in the prevalence of these disorders suggests that environmental and behavioral influences, rather than genetic causes, are fueling the epidemic. The developmental origins of health and disease hypothesis has highlighted the link between the periconceptual, fetal, and early infant phases of life and the subsequent development of metabolic disorders in later life. In particular, the impact of poor maternal nutrition on susceptibility to later life metabolic disease in offspring is now well documented. Several studies have now shown, at least in experimental animal models, that some components of the metabolic syndrome, induced as a consequence of developmental programming, are potentially reversible by nutritional or targeted therapeutic interventions during windows of developmental plasticity. This review will focus on critical windows of development and possible therapeutic avenues that may reduce metabolic and obesogenic risk following an adverse early life environment.

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.

Hyperphagia and central mechanisms for leptin resistance during pregnancy

The purpose of this work was to study the central mechanisms involved in food intake regulation and leptin resistance during gestation in the rat. Sprague Dawley rats of 7, 13, and 18 d of pregnancy [days of gestation (G) 7, G13, and G18] were used and compared with nonpregnant animals in diestrus-1. Food intake was already increased in G7, before hyperleptinemia and central leptin resistance was established in midpregnancy. Leptin resistance was due to a reduction in leptin transport through the blood-brain barrier (BBB) and to alterations in leptin signaling within the hypothalamus based on an increase in suppressor of cytokine signaling 3 levels and a blockade of signal transducer and activator of transcription-3 phosphorylation (G13), followed by a decrease in LepRb and of Akt phosphorylation (G18). In early gestation (G7), no change in hypothalamic neuropeptide Y (NPY), agouti-related peptide (AgRP), or proopiomelanocortin (POMC) expression was shown. Nevertheless, an increase in NPY and AgRP and a decrease in POMC mRNA were observed in G13 and G18 rats, probably reflecting the leptin resistance. To investigate the effect of maternal vs. placental hormones on these mechanisms, we used a model of pseudogestation. Rats of 9 d of pseudogestation were hyperphagic, showing an increase in body and adipose tissue weight, normoleptinemia, and normal responses to iv/intracerebroventricular leptin on hypothalamic leptin signaling, food intake, and body weight. Leptin transport through the BBB, and hypothalamic NPY, AgRP and POMC expression were unchanged. Finally, the transport of leptin through the BBB was assessed using a double-chamber culture system of choroid plexus epithelial cells or brain microvascular endothelial cells. We found that sustained high levels of prolactin significantly reduced leptin translocation through the barrier, whereas progesterone and β-estradiol did not show any effect. Our data demonstrate a dual mechanism of leptin resistance during mid/late-pregnancy, which is not due to maternal hormones and which allows the maintenance of hyperphagia in the presence of hyperleptinemia driven by an increase in NPY and AgRP and a decrease in POMC mRNA. By contrast, in early pregnancy maternal hormones induce hyperphagia without the regulation of hypothalamic NPY, AgRP, or POMC and in the absence of leptin resistance.

Cross-talk between orexins (hypocretins) and the neuroendocrine axes (hypothalamic-pituitary axes)

Lesioning and electrical stimulation experiments carried out during the first half of the twentieth century showed that the lateral hypothalamic area (LHA) is involved in the neuroendocrine control of hormone secretion. However, the molecular basis of this phenomenon remained unclear until fifty years later when in 1998, two different laboratories discovered a new family of hypothalamic neuropeptides, the orexins or hypocretins (OX-A/Hcrt1 and OX-B/Hcrt2). Since then, remarkable evidence has revealed that orexins/hypocretins play a prominent role in regulating virtually all the neuroendocrine axes, acting as pivotal signals in the coordination of endocrine responses with regards to sleep, arousal and energy homeostasis. The clinical relevance of these actions is supported by human data showing impairment of virtually all the neuroendocrine axes in orexin/hypocretin-deficient narcoleptic patients. Here, we summarize more than ten years of knowledge about the orexins/hypocretins with particular focus on their role as neuroendocrine regulators. Understanding this aspect of orexin/hypocretin physiology could open new therapeutic possibilities in the treatment of sleep, energy homeostasis and endocrine pathologies.

Early overnutrition results in early-onset arcuate leptin resistance and increased sensitivity to high-fat diet

Childhood obesity increases the risk of adult obesity and diabetes, suggesting that early overnutrition permanently programs altered energy and glucose homeostasis. In the present studies, we used a mouse model to investigate whether early overnutrition increases susceptibility to obesity and insulin resistance in response to a high-fat diet (HFD). Litters from Swiss Webster dams were culled to three [chronic postnatal overnutrition (CPO)] or 10 (control) pups and then weaned onto standard chow at postnatal day (P) 23. At 6 wk of age, a subset of mice was placed on HFD, and glucose and insulin tolerance were examined at 16-17 wk of age. Leptin sensitivity was determined by hypothalamic phosphorylated signal transducer and activator of transcription-3 immunoreactivity at P16 and adulthood after ip leptin. CPO mice exhibited accelerated body weight gain and hyperleptinemia during the preweaning period but only a slightly heavier body weight and normal glucose tolerance in adulthood on standard chow diet. Importantly, CPO mice exhibited significant leptin resistance in the arcuate nucleus, demonstrated by reduced activation of phospho-signal transducer and activator of transcription-3, as early as P16 and throughout life, despite normalized leptin levels. In response to HFD, CPO but not control mice displayed insulin resistance in response to an insulin tolerance test. In conclusion, CPO mice exhibited early and persistent leptin resistance in the arcuate nucleus and, in response to HFD, rapid development of obesity and insulin resistance. These studies suggest that early overnutrition can permanently alter energy homeostasis and significantly increase susceptibility to obesity and insulin resistance.

Postnatal early overfeeding induces hypothalamic higher SOCS3 expression and lower STAT3 activity in adult rats

Postnatal early overnutrition (EO) is a risk factor for future obesity and metabolic disorders. Rats raised in small litters (SLs) develop overweight, hyperphagia, hyperleptinemia, hyperinsulinemia and hypertension when adults. As obesity is related to hyperleptinemia, leptin resistance and metabolic syndrome, we aimed to investigate body composition, plasma hormone levels, glucose tolerance and the leptin signaling pathway in hypothalamus from early overfed animals at weaning and adulthood. To induce postnatal EO, we reduced litter size to three pups/litter (SL), and the groups with normal litter size (10 pups/litter) were used as control. Rats had free access to standard diet and water postweaning. Body weight and food intake were monitored daily, and offspring were killed at 21 (weaning) and 180 days old (adulthood). Postnatal EO group had higher body weight and total and visceral fat mass at both periods. Lean mass and serum high-density lipoprotein cholesterol (HDL-C) were higher at 21 days and lower at 180 days. Small litter rats presented higher levels of globulins at both periods, while albumin levels were higher at weaning and lower at adulthood. There was higher leptin, insulin and glucose serum concentrations at 21 days old, while no glucose intolerance was observed in adulthood. Leptin signaling pathway was unaffected at weaning. However, postnatal EO induced lower JAK2 and p-STAT3, and higher SOCS3 expression in adult animals, indicating central leptin resistance in adulthood. In conclusion, postnatal EO induces obesity, higher total and visceral fat mass, lower HDL-C and central leptin resistance in adult life.

Postnatal early overnutrition changes the leptin signalling pathway in the hypothalamic-pituitary-thyroid axis of young and adult rats

Postnatal early overnutrition (EO) is a risk factor for obesity in adult life. Rats raised in a small litter can develop hyperinsulinaemia, hyperphagia, hyperleptinaemia and hypertension as adults. Since leptin regulates the hypothalamic-pituitary-thyroid axis and the metabolism of thyroid hormones, we studied the leptin signalling pathway in pituitary and thyroid glands of the postnatal EO model. To induce EO, at the third day of lactation the litter size was reduced to three pups per litter (SL group). In control litters (NL group), the litter size was adjusted to 10 pups per litter. Body weight and food intake were monitored. Rat offspring were killed at 21 (weaning) and 180 days old (adulthood). Plasma thyroid hormones, thyroid-stimulating hormone (TSH) and leptin were measured by radioimmunoassay. Proteins of the leptin signalling pathway were analysed by Western blotting. Body weight of offspring in the SL group was higher from the seventh day of lactation (+33%, P < 0.05) until 180 days old (+18%, P < 0.05). Offspring in the SL group showed higher visceral fat mass at 21 and 180 days old (+176 and +52%, respectively, P < 0.05), but plasma leptin was higher only at 21 days (+88%, P < 0.05). The SL offspring showed higher plasma TSH, 3,5,3'-triiodothronine (T(3)) and thyroxine (T(4)) at 21 days (+60, +91 and +68%, respectively, P < 0.05), while the opposite was observed at 180 days regarding thyroid hormones (T(3), -10%; and T(4), -30%, P < 0.05), with no difference in TSH levels. In hypothalamus, no change was observed in the leptin signalling pathway at 21 days. However, lower janus thyrosine kinase 2 (JAK2) and phosphorilated-signal transducer and activator of transcription-3 (p-STAT3) content were detected in adulthood. In pituitary, the SL group presented higher leptin receptors (Ob-R), JAK2 and p-STAT3 content at 21 days and lower JAK2 and STAT3 content at 180 days old. In contrast, in thyroid, the Ob-R expression was lower in young SL rats, while the adult SL group presented higher Ob-R and JAK2 content. We showed that postnatal EO induces short- and long-term effects upon the hypothalamic-pituitary-thyroid axis. These changes may help to explain future development of metabolic and endocrine dysfunctions, such as metabolic syndrome and hypothyroidism.

Leptin transport in the central nervous system

Synthesized and released by the adipose tissue, leptin is the widely studied 167-amino acid hormonal protein product of the obesity gene. Originally leptin was defined in association with satiety and energy balance and claimed to be an anti-obesity factor that functioned via a feedback effect from adipocytes to hypothalamus. There is a growing body of evidence that emphasizes the importance of leptin in the regulation of food intake and body weight in animals and humans, alike. Other research findings point out that it plays a role in the regulation of the metabolism, sexual development, reproduction, hematopoiesis, immunity, gastrointestinal functions, sympathetic activation, and angiogenesis. The aim of this review is to evaluate the relation between leptin and the central nervous system (CNS).

Hypothalamic neuropeptide expression of juvenile and middle-aged rats after early postnatal food restriction

Rats subjected to early postnatal food restriction (FR) show persistent changes in energy balance. The hypothalamus plays a major role in the regulation of energy balance. Therefore, we hypothesized that early postnatal food restriction induces developmental programming of hypothalamic gene expression of neuropeptides involved in this regulation. In the hypothalamus of juvenile and middle-aged rats that were raised in control (10 pups) or FR litters (20 pups), gene expression was investigated for neuropeptide Y (NPY), agouti-related protein (AgRP), proopiomelanocortin (POMC), and cocaine- and amphetamine-regulated transcript (CART) in the arcuate nucleus (ARC); CRH and TRH in the paraventricular nucleus; and melanin-concentrating hormone (MCH) and orexin in the lateral hypothalamic area. Early postnatal FR acutely and persistently reduced body size. Juvenile FR rats had significantly reduced CART gene expression and increased MCH expression. In middle-aged FR rats, POMC and CART mRNA levels were significantly reduced. The ratio between expression of the ARC orexigenic peptides (NPY and AgRP) and anorexigenic peptides (POMC and CART) was increased in juvenile, but not in middle-aged, FR rats. These results suggest that in neonatal rats, FR already triggers the ARC, and to a lesser extent the lateral hypothalamic area, but not the paraventricular nucleus, to increase expression of orexigenic relative to anorexigenic peptides. In addition, with enduring small body size and normalized hypothalamic gene expression, the adult FR rats appeared to have accepted this smaller body size as normal. This suggests that the body weight set-point was differently programmed in animals with early postnatal FR.

Pathophysiology of the blood-brain barrier: animal models and methods

The specialized cerebral microvascular endothelium interacts with the cellular milieu of the brain and extracellular matrix to form a neurovascular unit, one aspect of which is a regulated interface between the blood and central nervous system (CNS). The concept of this blood-brain barrier (BBB) as a dynamically regulated system rather than a static barrier has wide-ranging implications for pathophysiology of the CNS. While in vitro models of the BBB are useful for screening drugs targeted to the CNS and indispensable for studies of cerebral endothelial cell biology, the complex interactions of the neurovascular unit make animal-based models and methods essential tools for understanding the pathophysiology of the BBB. BBB dysfunction is a complication of neurodegenerative disease and brain injury. Studies on animal models have shown that diseases of the periphery, such as diabetes and inflammatory pain, have deleterious effects on the BBB which may contribute to neurological complications associated with these conditions. Furthermore, genetic and/or epigenetic abnormalities in constituents of the BBB may be significant contributing factors in disease etiology. Research that approaches the BBB as a dynamic system integrated with both the CNS and the periphery is therefore critical to understanding and treating diseases of the CNS. Herein, we review various methodological approaches used to study BBB function in the context of disease. These include measurement of transport between blood and brain, imaging-based technologies, and genomic/proteomic approaches.