Long-term consequences of the absence of leptin signaling in early life

Leptin receptor reactivation restores brain function in early-life Lepr-deficient mice

Obesity is a chronic disease caused by excessive fat accumulation that impacts the body and brain health. Insufficient leptin or leptin receptor (LepR) is involved in the disease pathogenesis. Leptin is involved with several neurological processes, and it has crucial developmental roles. We have previously demonstrated that leptin deficiency in early life leads to permanent developmental problems in young adult mice, including an imbalance in energy homeostasis, alterations in melanocortin and the reproductive system and a reduction in brain mass. Given that in humans, obesity has been associated with brain atrophy and cognitive impairment, it is important to determine the long-term consequences of early-life leptin deficiency on brain structure and memory function. Here, we demonstrate that leptin-deficient (LepOb) mice exhibit altered brain volume, decreased neurogenesis and memory impairment. Similar effects were observed in animals that do not express the LepR (LepRNull). Interestingly, restoring the expression of LepR in 10-week-old mice reverses brain atrophy, in addition to neurogenesis and memory impairments in older animals. Our findings indicate that leptin deficiency impairs brain development and memory, which are reversible by restoring leptin signalling in adulthood.

Central leptin signaling deficiency induced by leptin receptor antagonist leads to hypothalamic proteomic remodeling

AIMS

Leptin irresponsiveness, which is often associated with obesity, can have significant impacts on the hypothalamic proteome of individuals, including those who are lean. While mounting evidence on leptin irresponsiveness has focused on obese individuals, understanding the early molecular and proteomic changes associated with deficient hypothalamic leptin signaling in lean individuals is essential for early intervention and prevention of metabolic disorders. Leptin receptor antagonists block the binding of leptin to its receptors, potentially reducing its effects and used in cases where excessive leptin activity might be harmful.

MATERIALS AND METHODS

In this work, we blocked the central actions of leptin in lean male adult Wistar rat by chronically administering intracerebroventricularly the superactive leptin receptor antagonist (SLA) (D23L/L39A/D40A/F41A) and investigated its impact on the hypothalamic proteome using label-free sequential window acquisition of all theoretical fragment ion spectra mass spectrometry (SWATH-MS) for quantitative proteomics.

KEY FINDINGS

Our results show an accumulation of proteins involved in mRNA processing, mRNA stability, and translation in the hypothalamus of SLA-treated rats. Conversely, hypothalamic leptin signaling deficiency reduces the representation of proteins implicated in energy metabolism, neural circuitry, and neurotransmitter release.

SIGNIFICANCE

The alterations in the adult rat hypothalamic proteome contribute to dysregulate appetite, metabolism, and energy balance, which are key factors in the development and progression of obesity and related metabolic disorders. Additionally, using bioinformatic analysis, we identified a series of transcription factors that are potentially involved in the upstream regulatory mechanisms responsible for the observed signature.

New findings on brain actions of growth hormone and potential clinical implications

Growth hormone (GH) is secreted by somatotropic cells of the anterior pituitary gland. The classical effects of GH comprise the stimulation of cell proliferation, tissue and body growth, lipolysis, and insulin resistance. The GH receptor (GHR) is expressed in numerous brain regions. Notably, a growing body of evidence indicates that GH-induced GHR signaling in specific neuronal populations regulates multiple physiological functions, including energy balance, glucose homeostasis, stress response, behavior, and several neurological/cognitive aspects. The importance of central GHR signaling is particularly evident when the organism is under metabolic stress, such as pregnancy, chronic food deprivation, hypoglycemia, and prolonged exercise. These particular situations are associated with elevated GH secretion. Thus, central GH action represents an internal signal that coordinates metabolic, neurological, neuroendocrine, and behavioral adaptations that are evolutionarily advantageous to increase the chances of survival. This review summarizes and discusses recent findings indicating that the brain is an important target of GH, and GHR signaling in different neuronal populations regulates essential physiological functions.

The Pattern of GH Action in the Mouse Brain

GH acts in numerous organs expressing the GH receptor (GHR), including the brain. However, the mechanisms behind the brain's permeability to GH and how this hormone accesses different brain regions remain unclear. It is well-known that an acute GH administration induces phosphorylation of the signal transducer and activator of transcription 5 (pSTAT5) in the mouse brain. Thus, the pattern of pSTAT5 immunoreactive cells was analyzed at different time points after IP or intracerebroventricular GH injections. After a systemic GH injection, the first cells expressing pSTAT5 were those near circumventricular organs, such as arcuate nucleus neurons adjacent to the median eminence. Both systemic and central GH injections induced a medial-to-lateral pattern of pSTAT5 immunoreactivity over time because GH-responsive cells were initially observed in periventricular areas and were progressively detected in lateral brain structures. Very few choroid plexus cells exhibited GH-induced pSTAT5. Additionally, Ghr mRNA was poorly expressed in the mouse choroid plexus. In contrast, some tanycytes lining the floor of the third ventricle expressed Ghr mRNA and exhibited GH-induced pSTAT5. The transport of radiolabeled GH into the hypothalamus did not differ between wild-type and dwarf Ghr knockout mice, indicating that GH transport into the mouse brain is GHR independent. Also, single-photon emission computed tomography confirmed that radiolabeled GH rapidly reaches the ventral part of the tuberal hypothalamus. In conclusion, our study provides novel and valuable information about the pattern and mechanisms behind GH transport into the mouse brain.

Neuroendocrinological and Clinical Aspects of Leptin

Obesity is characterized by an abnormal increase in adipose tissue mass and is regarded as a neurobehavioral as well as a metabolic disorder. Increases in body fat are caused by even slight, long-term discrepancies between energy intake and energy expenditure. It is a chronic condition linked to the metabolic syndrome, a spectrum of risky conditions, such as diabetes, high blood pressure, and heart disease. With a swiftly rising prevalence, obesity has emerged as a significant global health concern. Leptin influences the brain's neuroendocrine and metabolic processes, which is important for maintaining energy homeostasis. White adipose tissue secretes the majority of leptin, and there is a positive correlation between leptin levels in the blood and body fat percentages. The central nervous system is also modulated by leptin levels to modify energy intake and usage. The idea of an obesity cure sparked excitement after it was discovered more than 25 years ago. However, the leptin medication only effectively reduces weight in patients with congenital leptin insufficiency and not in patients with typical obesity who may also have leptin resistance. Recent research has focused on the role of leptin in managing weight reduction and preventing "yo-yo dieting". This review concentrates on the neurological effects of leptin with a focus on therapeutic and diagnostic applications, particularly for childhood obesity.

Elderly rats fed with a high-fat high-sucrose diet developed sex-dependent metabolic syndrome regardless of long-term metformin and liraglutide treatment

Aim/Introduction

The study aimed to determine the effectiveness of early antidiabetic therapy in reversing metabolic changes caused by high-fat and high-sucrose diet (HFHSD) in both sexes.

Methods

Elderly Sprague-Dawley rats, 45 weeks old, were randomized into four groups: a control group fed on the standard diet (STD), one group fed the HFHSD, and two groups fed the HFHSD along with long-term treatment of either metformin (HFHSD+M) or liraglutide (HFHSD+L). Antidiabetic treatment started 5 weeks after the introduction of the diet and lasted 13 weeks until the animals were 64 weeks old.

Results

Unexpectedly, HFHSD-fed animals did not gain weight but underwent significant metabolic changes. Both antidiabetic treatments produced sex-specific effects, but neither prevented the onset of prediabetes nor diabetes.

Conclusion

Liraglutide vested benefits to liver and skeletal muscle tissue in males but induced signs of insulin resistance in females.

Neonatal Leptin Levels Predict the Early Childhood Developmental Assessment Scores of Preterm Infants

Preterm infants have low circulating levels of leptin, a key trophic hormone that influences growth and development. While the clinical importance of prematurity-associated leptin deficiency is undefined, recent preclinical and clinical investigations have shown that targeted enteral leptin supplementation can normalize neonatal leptin levels. We tested the hypothesis that, independent of growth velocity, prematurity-related neonatal leptin deficiency predicts adverse cardiovascular and neurodevelopmental outcomes. In a planned 2-year longitudinal follow-up of 83 preterm infants born at 22 to 32 weeks' gestation, we obtained blood pressures from 58 children and the Ages & Stages Questionnaire (ASQ-3) for 66 children. Based on univariate analysis, blood pressures correlated with gestational age at birth (R = 0.30, p < 0.05) and weight gain since discharge (R = 0.34, p < 0.01). ASQ-3 scores were significantly higher in female than male children. Utilizing best subset regression with Mallows' C_p as the criterion for model selection, higher systolic blood pressure was predicted by rapid postnatal weight gain, later gestation at delivery and male sex (C_p = 3.0, R = 0.48). Lower ASQ-3 was predicted by lower leptin levels at 35 weeks postmenstrual age, earlier gestation at delivery and male sex (C_p = 2.9, R = 0.45). Children that had leptin levels above 1500 pg/mL at 35 weeks postmenstrual age had the highest ASQ-3 scores at 2 years. In conclusion, independent of growth velocity, higher leptin levels at 35 weeks' gestation are associated with better developmental assessment scores in early childhood. While longer-term follow-up of a larger cohort is needed, these findings support investigations that have suggested that targeted neonatal leptin supplementation could improve the neurodevelopmental outcomes of preterm infants.

Programming of metabolism by adipokines during development

The intrauterine and early postnatal periods represent key developmental stages in which an organism is highly susceptible to being permanently influenced by maternal factors and nutritional status. Strong evidence indicates that either undernutrition or overnutrition during development can predispose individuals to disease later in life, especially type 2 diabetes mellitus and obesity, a concept known as metabolic programming. Adipose tissue produces important signalling molecules that control energy and glucose homeostasis, including leptin and adiponectin. In addition to their well-characterized metabolic effects in adults, adipokines have been associated with metabolic programming by affecting different aspects of development. Therefore, alterations in the secretion or signalling of adipokines, caused by nutritional insults in early life, might lead to metabolic diseases in adulthood. This Review summarizes and discusses the potential role of several adipokines in inducing metabolic programming through their effects during development. The identification of the endocrine factors that act in early life to permanently influence metabolism represents a key step in understanding the mechanisms behind metabolic programming. Thus, future strategies aiming to prevent and treat these metabolic diseases can be designed, taking into consideration the relationship between adipokines and the developmental origins of health and disease.

A critical update on the leptin-melanocortin system

The discovery of leptin in 1994 was an "eureka moment" in the field of neurometabolism that provided new opportunities to better understand the central control of energy balance and glucose metabolism. Rapidly, a prevalent model in the field emerged that pro-opiomelanocortin (POMC) neurons were key in promoting leptin's anorexigenic effects and that the arcuate nucleus of the hypothalamus (ARC) was a key region for the regulation of energy homeostasis. While this model inspired many important discoveries, a growing body of literature indicates that this model is now outdated. In this review, we re-evaluate the hypothalamic leptin-melanocortin model in light of recent advances that directly tackle previous assumptions, with a particular focus on the ARC. We discuss how segregated and heterogeneous these neurons are, and examine how the development of modern approaches allowing spatiotemporal, intersectional, and chemogenetic manipulations of melanocortin neurons has allowed a better definition of the complexity of the leptin-melanocortin system. We review the importance of leptin in regulating glucose homeostasis, but not food intake, through direct actions on ARC POMC neurons. We further highlight how non-POMC, GABAergic neurons mediate leptin's direct effects on energy balance and influence POMC neurons.

Chronic Leptin Deficiency Improves Tolerance of Physiological Damage and Host-Pathogen Cooperation during Yersinia pseudotuberculosis Infection

To combat infections, hosts employ a combination of antagonistic and cooperative defense strategies. The former refers to pathogen killing mediated by resistance mechanisms, while the latter refers to physiological defense mechanisms that promote host health during infection independent of pathogen killing, leading to an apparent cooperation between the host and the pathogen. Previous work has shown that Leptin, a pleiotropic hormone that plays a central role in regulating appetite and energy metabolism, is indispensable for resistance mechanisms, while a role for Leptin signaling in cooperative host-pathogen interactions remains unknown. Using a mouse model of Yersinia pseudotuberculosis (Yptb) infection, an emerging pathogen that causes fever, diarrhea, and mesenteric lymphadenitis in humans, we found that the physiological effects of chronic Leptin-signaling deficiency conferred protection from Yptb infection due to increased host-pathogen cooperation rather than greater resistance defenses. The protection against Yptb infection was independent of differences in food consumption, lipolysis, or fat mass. Instead, we found that the chronic absence of Leptin signaling protects from a shift to lipid utilization during infection that contributes to Yptb lethality. Furthermore, we found that the survival advantage conferred by Leptin deficiency was associated with increased liver and kidney damage. Our work reveals an additional level of complexity for the role of Leptin in infection defense and demonstrates that in some contexts, in addition to tolerating the pathogen, tolerating organ damage is more beneficial for survival than preventing the damage.

Characterization of the metabolic differences between male and female C57BL/6 mice

AIMS

The present study aims to compare the responses between male and female C57BL/6 mice to multiple metabolic challenges to understand the importance of sex in the control of energy homeostasis.

MAIN METHODS

Male and female C57BL/6 mice were subjected to nutritional and hormonal challenges, such as food restriction and refeeding, diet-induced obesity, feeding response to ghrelin and leptin, ghrelin-induced growth hormone secretion, and central responsiveness to ghrelin and leptin. The hypothalamic expression of transcripts that control energy homeostasis was also evaluated.

KEY FINDINGS

Male mice lost more weight and lean body mass in response to food restriction, compared to females. During refeeding, males accumulated more body fat and exhibited lower energy expenditure and glycemia, as compared to females. Additionally, female mice exhibited a higher protection against diet-induced obesity and related metabolic imbalances in comparison to males. Low dose ghrelin injection elicited higher food intake and growth hormone secretion in male mice, whereas the acute anorexigenic effect of leptin was more robust in females. However, the sex differences in the feeding responses to ghrelin and leptin were not explained by variations in the central responsiveness to these hormones nor by differences in the fiber density from arcuate nucleus neurons. Female, but not male, mice exhibited compensatory increases in hypothalamic Pomc mRNA levels in response to diet-induced obesity.

SIGNIFICANCE

Our findings revealed several sexually differentiated responses to metabolic challenges in C57BL/6 mice, highlighting the importance of taking into account sex differences in metabolic studies.

Early Life Stress, Brain Development, and Obesity Risk: Is Oxytocin the Missing Link?

Obesity disease results from a dysfunctional modulation of the energy balance whose master regulator is the central nervous system. The neural circuitries involved in such function complete their maturation during early postnatal periods, when the brain is highly plastic and profoundly influenced by the environment. This phenomenon is considered as an evolutionary strategy, whereby metabolic functions are adjusted to environmental cues, such as food availability and maternal care. In this timeframe, adverse stimuli may program the body metabolism to maximize energy storage abilities to cope with hostile conditions. Consistently, the prevalence of obesity is higher among individuals who experienced early life stress (ELS). Oxytocin, a hypothalamic neurohormone, regulates the energy balance and modulates social, emotional, and eating behaviors, exerting both central and peripheral actions. Oxytocin closely cooperates with leptin in regulating energy homeostasis. Both oxytocin and leptin impact the neurodevelopment during critical periods and are affected by ELS and obesity. In this review article, we report evidence from the literature describing the effect of postnatal ELS (specifically, disorganized/inconstant maternal care) on the vulnerability to obesity with a focus on the role of oxytocin. We emphasize the existing research gaps and highlight promising directions worthy of exploration. Based on the available data, alterations in the oxytocin system may in part mediate the ELS-induced susceptibility to obesity.

Mechanisms mediating the impact of maternal obesity on offspring hypothalamic development and later function

As obesity rates have risen around the world, so to have pregnancies complicated by maternal obesity. Obesity during pregnancy is not only associated with negative health outcomes for the mother and the baby during pregnancy and birth, there is also strong evidence that exposure to maternal obesity causes an increased risk to develop obesity, diabetes and cardiovascular disease later in life. Animal models have demonstrated that increased weight gain in offspring exposed to maternal obesity is usually preceded by increased food intake, implicating altered neuronal control of food intake as a likely area of change. The hypothalamus is the primary site in the brain for maintaining energy homeostasis, which it coordinates by sensing whole body nutrient status and appropriately adjusting parameters including food intake. The development of the hypothalamus is plastic and regulated by metabolic hormones such as leptin, ghrelin and insulin, making it vulnerable to disruption in an obese in utero environment. This review will summarise how the hypothalamus develops, how maternal obesity impacts on structure and function of the hypothalamus in the offspring, and the factors that are altered in an obese in utero environment that may mediate the permanent changes to hypothalamic function in exposed individuals.

Metabolic-endocrine disruption due to preterm birth impacts growth, body composition, and neonatal outcome

Despite optimized nutrition, preterm-born infants grow slowly and tend to over-accrete body fat. We hypothesize that the premature dissociation of the maternal-placental-fetal unit disrupts the maintenance of physiological endocrine function in the fetus, which has severe consequences for postnatal development. This review highlights the endocrine interactions of the maternal-placental-fetal unit and the early perinatal period in both preterm and term infants. We report on hormonal levels (including tissue, thyroid, adrenal, pancreatic, pituitary, and placental hormones) and nutritional supply and their impact on infant body composition. The data suggest that the premature dissociation of the maternal-placental-fetal unit leads to a clinical picture similar to panhypopituitarism. Further, we describe how the premature withdrawal of the maternal-placental unit, neonatal morbidities, and perinatal stress can cause differences in the levels of growth-promoting hormones, particularly insulin-like growth factors (IGF). In combination with the endocrine disruption that occurs following dissociation of the maternal-placental-fetal unit, the premature adaptation to the extrauterine environment leads to early and fast accretion of fat mass in an immature body. In addition, we report on interventional studies that have aimed to compensate for hormonal deficiencies in infants born preterm through IGF therapy, resulting in improved neonatal morbidity and growth. IMPACT: Preterm birth prematurely dissociates the maternal-placental-fetal unit and disrupts the metabolic-endocrine maintenance of the immature fetus with serious consequences for growth, body composition, and neonatal outcomes. The preterm metabolic-endocrine disruption induces symptoms resembling anterior pituitary failure (panhypopituitarism) with low levels of IGF-1, excessive postnatal fat mass accretion, poor longitudinal growth, and failure to thrive. Appropriate gestational age-adapted nutrition alone seems insufficient for the achievement of optimal growth of preterm infants. Preliminary results from interventional studies show promising effects of early IGF-1 supplementation on postnatal development and neonatal outcomes.

Leptin Receptor Expression in GABAergic Cells is Not Sufficient to Normalize Metabolism and Reproduction in Mice

Previous studies indicate that leptin receptor (LepR) expression in GABAergic neurons is necessary for the biological effects of leptin. However, it is not clear whether LepR expression only in GABAergic neurons is sufficient to prevent the metabolic and neuroendocrine imbalances caused by LepR deficiency. In the present study, we produced mice that express the LepR exclusively in GABAergic cells (LepRVGAT mice) and compared them with wild-type (LepR+/+) and LepR-deficient (LepRNull/Null) mice. Although LepRVGAT mice showed a pronounced reduction in body weight and fat mass, as compared with LepRNull/Null mice, male and female LepRVGAT mice exhibited an obese phenotype relative to LepR+/+ mice. Food intake was normalized in LepRVGAT mice; however, LepRVGAT mice still exhibited lower energy expenditure in both sexes and reduced ambulatory activity in the females, compared with LepR+/+ mice. The acute anorexigenic effect of leptin and hedonic feeding were normalized in LepRVGAT mice despite the hyperleptinemia they present. Although LepRVGAT mice showed improved glucose homeostasis compared with LepRNull/Null mice, both male and female LepRVGAT mice exhibited insulin resistance. In contrast, LepR expression only in GABAergic cells was sufficient to normalize the density of agouti-related peptide (AgRP) and α-MSH immunoreactive fibers in the paraventricular nucleus of the hypothalamus. However, LepRVGAT mice exhibited reproductive dysfunctions, including subfertility in males and alterations in the estrous cycle of females. Taken together, our findings indicate that LepR expression in GABAergic cells, although critical to the physiology of leptin, is insufficient to normalize several metabolic aspects and the reproductive function in mice.

Glucagon-like peptide-1 (GLP-1) signalling in the brain: From neural circuits and metabolism to therapeutics

Glucagon‐like‐peptide‐1 (GLP‐1) derived from gut enteroendocrine cells and a discrete population of neurons in the caudal medulla acts through humoral and neural pathways to regulate satiety, gastric motility and pancreatic endocrine function. These physiological attributes contribute to GLP‐1 having a potent therapeutic action in glycaemic regulation and chronic weight management. In this review, we provide an overview of the neural circuits targeted by endogenous versus exogenous GLP‐1 and related drugs. We also highlight candidate subpopulations of neurons and cellular mechanisms responsible for the acute and chronic effects of GLP‐1 and GLP‐1 receptor agonists on energy balance and glucose metabolism. Finally, we present potential future directions to translate these findings towards the development of effective therapies for treatment of metabolic disease.

Fasting reduces the number of TRH immunoreactive neurons in the hypothalamic paraventricular nucleus of male rats, but not in mice

During fasting or weight loss, the fall in leptin levels leads to suppression of thyrotropin-releasing hormone (TRH) expression in the paraventricular nucleus of the hypothalamus (PVH) and, consequently, inhibition of the hypothalamic-pituitary-thyroid (HPT) axis. However, differently than rats, just few PVH^TRH neurons express the leptin receptor in mice. In the present study, male adult rats and mice were submitted to 48 -h fasting to evaluate the consequences on proTRH peptide expression at the PVH level. Additionally, the proTRH peptide expression was also assessed in the brains of leptin-deficient (Lep^ob/ob) mice. We observed that approximately 50 % of PVH^TRH neurons of leptin-injected rats exhibited phosphorylation of the signal transducer and activator of transcription 3 (pSTAT3), a marker of leptin receptor activation. In contrast, very few PVH^TRH neurons of leptin-injected mice exhibited pSTAT3. Rats submitted to 48 -h fasting showed a significant reduction in the number of PVH^TRH immunoreactive neurons, as compared to fed rats. On the other hand, no changes in the number of PVH^TRH immunoreactive neurons were observed between fasted and fed mice. Next, the number of TRH immunoreactive cells was determined in the PVH, dorsomedial nucleus of the hypothalamus and nucleus raphe pallidus of Lep^ob/ob and wild-type mice and no significant differences were observed, despite reduced plasma T4 levels in Lep^ob/ob mice. Taken together, these findings provide additional evidence of the important species-specific differences in the mechanisms used by fasting and/or leptin to regulate the HPT axis.

The Importance of Leptin to Reproduction

A healthy nutritional state is required for all aspects of reproduction and is signaled by the adipokine leptin. Leptin acts in a relatively narrow concentration range: too much or too little will compromise fertility. The leptin signal timing is important to prepubertal development in both sexes. In the brain, leptin acts on ventral premammillary neurons which signal kisspeptin (Kiss1) neurons to stimulate gonadotropin releasing hormone (GnRH) neurons. Suppression of Kiss1 neurons occurs when agouti-related peptide neurons are activated by reduced leptin, because leptin normally suppresses these orexigenic neurons. In the pituitary, leptin stimulates production of GnRH receptors (GnRHRs) and follicle-stimulating hormone at midcycle, by activating pathways that derepress actions of the messenger ribonucleic acid translational regulatory protein Musashi. In females, rising estrogen stimulates a rise in serum leptin, which peaks at midcycle, synchronizing with nocturnal luteinizing hormone pulses. The normal range of serum leptin levels (10-20 ng/mL) along with gonadotropins and growth factors promote ovarian granulosa and theca cell functions and oocyte maturation. In males, the prepubertal rise in leptin promotes testicular development. However, a decline in leptin levels in prepubertal boys reflects inhibition of leptin secretion by rising androgens. In adult males, leptin levels are 10% to 50% of those in females, and high leptin inhibits testicular function. The obesity epidemic has elucidated leptin resistance pathways, with too much leptin in either sex leading to infertility. Under conditions of balanced nutrition, however, the secretion of leptin is timed and regulated within a narrow level range that optimizes its trophic effects.

Central Regulation of Metabolism by Growth Hormone

Growth hormone (GH) is secreted by the pituitary gland, and in addition to its classical functions of regulating height, protein synthesis, tissue growth, and cell proliferation, GH exerts profound effects on metabolism. In this regard, GH stimulates lipolysis in white adipose tissue and antagonizes insulin's effects on glycemic control. During the last decade, a wide distribution of GH-responsive neurons were identified in numerous brain areas, especially in hypothalamic nuclei, that control metabolism. The specific role of GH action in different neuronal populations is now starting to be uncovered, and so far, it indicates that the brain is an important target of GH for the regulation of food intake, energy expenditure, and glycemia and neuroendocrine changes, particularly in response to different forms of metabolic stress such as glucoprivation, food restriction, and physical exercise. The objective of the present review is to summarize the current knowledge about the potential role of GH action in the brain for the regulation of different metabolic aspects. The findings gathered here allow us to suggest that GH represents a hormonal factor that conveys homeostatic information to the brain to produce metabolic adjustments in order to promote energy homeostasis.

Impact of Early Nutrition, Physical Activity and Sleep on the Fetal Programming of Disease in the Pregnancy: A Narrative Review

Early programming is the adaptation process by which nutrition and environmental factors alter development pathways during prenatal growth, inducing changes in postnatal metabolism and diseases. The aim of this narrative review, is evaluating the current knowledge in the scientific literature on the effects of nutrition, environmental factors, physical activity and sleep on development pathways. If in utero adaptations were incorrect, this would cause a mismatch between prenatal programming and adulthood. Adequate caloric intake, protein, mineral, vitamin, and long-chain fatty acids, have been noted for their relevance in the offspring brain functions and behavior. Fetus undernutrition/malnutrition causes a delay in growth and have detrimental effects on the development and subsequent functioning of the organs. Pregnancy is a particularly vulnerable period for the development of food preferences and for modifications in the emotional response. Maternal obesity increases the risk of developing perinatal complications and delivery by cesarean section and has long-term implications in the development of metabolic diseases. Physical exercise during pregnancy contributes to overall improved health post-partum. It is also interesting to highlight the relevance of sleep problems during pregnancy, which influence adequate growth and fetal development. Taking into account these considerations, we conclude that nutrition and metabolic factors during early life play a key role of health promotion and public health nutrition programs worldwide to improve the health of the offspring and the health costs of hospitalization.

Leptin Receptor Signaling Regulates Protein Synthesis Pathways and Neuronal Differentiation in Pluripotent Stem Cells

The role of leptin receptor (OB-R) signaling in linking pluripotency with growth and development and the consequences of dysfunctional leptin signaling on progression of metabolic disease is poorly understood. Using a global unbiased proteomics approach we report that embryonic fibroblasts (MEFs) carrying the db/db mutation exhibit metabolic abnormalities, while their reprogrammed induced pluripotent stem cells (iPSCs) show altered expression of proteins involved in embryonic development. An upregulation in expression of eukaryotic translation initiation factor 4e (Eif4e) and Stat3 binding to the Eif4e promoter was supported by enhanced protein synthesis in mutant iPSCs. Directed differentiation of db/db iPSCs toward the neuronal lineage showed defects. Gene editing to correct the point mutation in db/db iPSCs using CRISPR-Cas9, restored expression of neuronal markers and protein synthesis while reversing the metabolic defects. These data imply a direct role for OB-R in regulating metabolism in embryonic fibroblasts and key developmental pathways in iPSCs.

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Pluripotency markers are decreased in db/db iPSCs (lacking functional OB-R)

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Mouse db/db iPSCs exhibit higher protein synthesis mediated by the Stat3/Eif4e axis

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OB-R signaling regulates neuronal development markers—NOGGIN, NESTIN, GFAP

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CRISPR correction reverses defects in db/db iPSCs

Temporal Leptin to Determine Cardiovascular and Metabolic Fate throughout the Life

Leptin links peripheral adiposity and the central nervous system (CNS) to regulate cardiometabolic physiology. Within the CNS, leptin receptor-expressing cells are a counterpart to circulating leptin, and leptin receptor-mediated neural networks modulate the output of neuroendocrine and sympathetic nervous activity to balance cardiometabolic homeostasis. Therefore, disrupted CNS leptin signaling is directly implicated in the development of metabolic diseases, such as hypertension, obesity, and type 2 diabetes. Independently, maternal leptin also plays a central role in the development and growth of the infant during gestation. Accumulating evidence points to the dynamic maternal leptin environment as a predictor of cardiometabolic fate in their offspring as it is directly associated with infant metabolic parameters at birth. In postnatal life, the degree of serum leptin is representative of the level of body adiposity/weight, a driving factor for cardiometabolic alterations, and therefore, the levels of blood leptin through the CNS mechanism, in a large part, are a strong determinant for future cardiometabolic fate. The current review focuses on highlighting and discussing recent updates for temporal dissection of leptin-associated programing of future cardiometabolic fate throughout the entire life.

Leptin signaling in vagal afferent neurons supports the absorption and storage of nutrients from high-fat diet

Objective:

Activation of vagal afferent neurons (VAN) by postprandial gastrointestinal signals terminates feeding and facilitates nutrient digestion and absorption. Leptin modulates responsiveness of VAN to meal-related gastrointestinal signals. Rodents with high-fat diet (HF) feeding develop leptin resistance that impairs responsiveness of VAN. We hypothesized that lack of leptin signaling in VAN reduces responses to meal-related signals, which in turn decreases absorption of nutrients and energy storage from high-fat, calorically dense food.

Methods:

Mice with conditional deletion of the leptin receptor from VAN (Nav1.8-Cre/LepR^fl/fl; KO) were used in this study. Six-week-old male mice were fed a 45% HF for 4 weeks; metabolic phenotype, food intake, and energy expenditure were measured. Absorption and storage of nutrients were investigated in the refed state.

Results:

After 4 weeks of HF feeding, KO mice gained less body weight and fat mass that WT controls, but this was not due to differences in food intake or energy expenditure. KO mice had reduced expression of carbohydrate transporters and absorption of carbohydrate in the jejunum. KO mice had fewer hepatic lipid droplets and decreased expression of de novo lipogenesis-associated enzymes and lipoproteins for endogenous lipoprotein pathway in liver, suggesting decreased long-term storage of carbohydrate in KO mice.

Conclusions:

Impairment of leptin signaling in VAN reduces responsiveness to gastrointestinal signals, which reduces intestinal absorption of carbohydrates and de novo lipogenesis resulting in reduced long-term energy storage. This study reveals a novel role of vagal afferents to support digestion and energy storage that may contribute to the effectiveness of vagal blockade to induce weight loss.

Differences between rats and mice in the leptin action on the paraventricular nucleus of the hypothalamus: Implications for the regulation of the hypothalamic-pituitary-thyroid axis

Previous studies indicate that leptin regulates the hypothalamic-pituitary-thyroid (HPT) axis via direct and indirect mechanisms. The indirect mechanism involves leptin action in pro-opiomelanocortin (POMC)- and agouti-related peptide (AgRP)-expressing neurones. These cells innervate the paraventricular nucleus of the hypothalamus (PVH) where they modulate hypophysiotrophic thyrotrophin-releasing hormone (TRH)-producing neurones. The direct mechanism involves the expression of leptin receptor (LepR) in a subpopulation of PVH TRH neurones. However, to our knowledge, the existence of LepR in PVH TRH neurones of mice has not been clearly confirmed. Therefore, we investigated possible species-specific differences between rats and mice with respect to the mechanisms recruited by leptin to regulate the HPT axis. We observed that an acute leptin injection induced phosphorylated signal transducer and activator of transcription 3 (pSTAT3), a marker of leptin-responsive cells, in 46.2 ± 8.0% of PVH proTRH immunoreactive neurones in rats. By contrast, an insignificant number of proTRH positive neurones in the mouse PVH co-expressed leptin-induced pSTAT3 or LepR. Similarly, central leptin injection increased the percentage of PVH proTRH neurones containing cAMP response element-binding protein phosphorylation in rats, but not in mice. We investigated the innervation of AgRP and POMC axons in the PVH and observed that rats exhibited a denser POMC innervation in the PVH compared to mice, whereas rats and mice showed similar density of AgRP axons in the PVH. In conclusion, rats and mice exhibit important species-specific differences in the direct and indirect mechanisms used by leptin to regulate the HPT axis.

Chronic Gq signaling in AgRP neurons does not cause obesity

Maintaining energy homeostasis requires coordinating physiology and behavior both on an acute timescale to adapt to rapid fluctuations in caloric intake and on a chronic timescale to regulate body composition. Hypothalamic agouti-related peptide (AgRP)-expressing neurons are acutely activated by caloric need, and this acute activation promotes increased food intake and decreased energy expenditure. On a longer timescale, AgRP neurons exhibit chronic hyperactivity under conditions of obesity and high dietary fat consumption, likely due to leptin resistance; however, the behavioral and metabolic effects of chronic AgRP neuronal hyperactivity remain unexplored. Here, we use chemogenetics to manipulate Gq signaling in AgRP neurons in mice to explore the hypothesis that chronic activation of AgRP neurons promotes obesity. Inducing chronic Gq signaling in AgRP neurons initially increased food intake and caused dramatic weight gain, in agreement with published data; however, food intake returned to baseline levels within 1 wk, and body weight returned to baseline levels within 60 d. Additionally, we found that, when mice had elevated body weight due to chronic Gq signaling in AgRP neurons, energy expenditure was not altered but adiposity and lipid metabolism were both increased, even under caloric restriction. These findings reveal that the metabolic and behavioral effects of chronic Gq signaling in AgRP neurons are distinct from the previously reported effects of acute Gq signaling and also of leptin insensitivity.

Conditional knockout of leptin receptor in neural stem cells leads to obesity in mice and affects neuronal differentiation in the hypothalamus early after birth

Leptin, secreted by peripheral adipocytes, binds the leptin receptor (Lepr) in the hypothalamus, thereby contributing to the regulation of satiety and body weight. Lepr is expressed in the embryonic brain as early as embryonic day 12.5. However, the function of Lepr in neural precursor cells in the brain has not been resolved. To address this issue, we crossed the Lepr^flox/flox mice with each of Shh-Cre mice (Shh, sonic hedgehog) and Nestin (Nes)-Cre mice. We found that deletion of Lepr specifically in nestin-expressing cells led to extreme obesity, but the conditional null of Lepr in Shh-expressing cells had no obvious phenotype. Moreover, the level of leptin-activated pSTAT3 decreased in the anterior and central subregions of the arcuate hypothalamus of Shh-Cre; Lepr^flox/flox mice compared with the controls. By contrast, in Nes-Cre; Lepr^flox/flox mice, the level of leptin-activated pSTAT3 decreased in all subregions including the anterior, central, and posterior arcuate hypothalamus as well as the dorsomedial, ventromedial, and median eminence of the hypothalamus, revealing that the extensive lack of Lepr in the differentiated neurons of the hypothalamus in the conditional null mice. Notably, conditional deletion of Lepr in nestin-expressing cells enhanced the differentiation of neural precursor cells into neurons and oligodendroglia but inhibited differentiation into astrocytes early in postnatal development of hypothalamus. Our results suggest that Lepr expression in neural precursor cells is essential for maintaining normal body weight as well as the differentiation of neural precursor cells to the neural/glial fate in the hypothalamus shortly after birth.

Prolonged fasting induces long-lasting metabolic consequences in mice

To endure prolonged fasting, animals undergo important acute physiological adjustments. However, whether severe fasting also leads to long-term metabolic adaptations is largely unknown. Forty-eight-hour fasting caused a pronounced weight loss in adult C57BL/6 male mice. Seven days of refeeding increased body adiposity to levels above baseline, whereas fasting-induced reductions in lean body mass and energy expenditure were not fully recovered. Respiratory exchange ratio and locomotor activity also remained altered. A fasting/refeeding cycle led to persistent suppression of Pomc mRNA levels and significant changes in the expression of histone deacetylases and DNA methyltransferases in the hypothalamus. Additionally, histone acetylation in the ventromedial nucleus of the hypothalamus was reduced by prolonged fasting and remained suppressed after refeeding. Mice subjected to 48-h fasting 30 days earlier exhibited higher body weight and fat mass compared to aged-matched animals that were never food-deprived. Furthermore, a previous fasting experience altered the changes in body weight, lean mass, energy expenditure and locomotor activity induced by a second cycle of fasting and refeeding. Notably, when acutely exposed to high-palatable/high-fat diet, mice that went through cumulative fasting episodes presented higher calorie intake and reduced energy expenditure and fat oxidation, compared to mice that had never been subjected to fasting. When chronically exposed to high-fat diet, mice that experienced cumulative fasting episodes showed higher gain of body and fat mass and reduced energy expenditure and calorie intake. In summary, cumulative episodes of prolonged fasting lead to hypothalamic epigenetic changes and long-lasting metabolic adaptations in mice.

Growth Hormone Receptor Deletion Reduces the Density of Axonal Projections from Hypothalamic Arcuate Nucleus Neurons

The arcuate nucleus (ARH) is an important hypothalamic area for the homeostatic control of feeding and other metabolic functions. In the ARH, proopiomelanocortin- (POMC) and agouti-related peptide (AgRP)-expressing neurons play a key role in the central regulation of metabolism. These neurons are influenced by circulating factors, such as leptin and growth hormone (GH). The objective of the present study was to determine whether a direct action of GH on ARH neurons regulates the density of POMC and AgRP axonal projections to major postsynaptic targets. We studied POMC and AgRP axonal projections to the hypothalamic paraventricular (PVH), lateral (LHA) and dorsomedial (DMH) nuclei in leptin receptor (LepR)-deficient mice (Lepr^db/db), GH-deficient mice (Ghrhr^lit/lit) and in mice carrying specific ablations of GH receptor (GHR) either in LepR- or AgRP-expressing cells. Lepr^db/db mice presented reduction in the density of POMC innervation to the PVH compared to wild-type and Ghrhr^lit/lit mice. Additionally, both Lepr^db/db and Ghrhr^lit/lit mice showed reduced AgRP fiber density in the PVH, LHA and DMH. LepR GHR knockout mice showed decreased density of POMC innervation in the PVH and DMH, compared to control mice, whereas a reduction in the density of AgRP innervation was observed in all areas analyzed. Conversely, AgRP-specific ablation of GHR led to a significant reduction in AgRP projections to the PVH, LHA and DMH, without affecting POMC innervation. Our findings indicate that GH has direct trophic effects on the formation of POMC and AgRP axonal projections and provide additional evidence that GH regulates hypothalamic neurocircuits controlling energy homeostasis.

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.

Fasting induces remodeling of the orexigenic projections from the arcuate nucleus to the hypothalamic paraventricular nucleus, in a growth hormone secretagogue receptor-dependent manner

Objective

Arcuate nucleus (ARC) neurons producing Agouti-related peptide (AgRP) and neuropeptide Y (NPY; ARC^AgRP/NPY neurons) are activated under energy-deficit states. ARC^AgRP/NPY neurons innervate the hypothalamic paraventricular nucleus (PVH), and ARC→PVH projections are recognized as key regulators of food intake. Plasma ghrelin levels increase under energy-deficit states and activate ARC^AgRP/NPY neurons by acting on the growth hormone secretagogue receptor (GHSR). Here, we hypothesized that activation of ARC^AgRP/NPY neurons in fasted mice would promote morphological remodeling of the ARC^AgRP/NPY→PVH projections in a GHSR-dependent manner.

Methods

We performed 1) fluorescent immunohistochemistry, 2) imaging of green fluorescent protein (GFP) signal in NPY-GFP mice, and 3) DiI axonal labeling in brains of ad libitum fed or fasted mice with pharmacological or genetic blockage of the GHSR signaling and then estimated the density and strength of ARC^AgRP/NPY→PVH fibers by assessing the mean fluorescence intensity, the absolute area with fluorescent signal, and the intensity of the fluorescent signal in the fluorescent area of the PVH.

Results

We found that 1) the density and strength of ARC^AgRP/NPY fibers increase in the PVH of fasted mice, 2) the morphological remodeling of the ARC^AgRP/NPY→PVH projections correlates with the activation of PVH neurons, and 3) PVH neurons are not activated in ARC-ablated mice. We also found that fasting-induced remodeling of ARC^AgRP/NPY→PVH fibers and PVH activation are impaired in mice with pharmacological or genetic blockage of GHSR signaling.

Conclusion

This evidence shows that the connectivity between hypothalamic circuits controlling food intake can be remodeled in the adult brain, depending on the energy balance conditions, and that GHSR activity is a key regulator of this phenomenon.

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The density and strength of ARC^AgRP/NPY→PVH fibers increase in fasted mice.

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Remodeling of ARC^AgRP/NPY→PVH projections correlates with the activation of PVH neurons.

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GHSR signaling is required for fasting-induced ARC^AgRP/NPY→PVH projection remodeling.

Brain STAT5 Modulates Long-Term Metabolic and Epigenetic Changes Induced by Pregnancy and Lactation in Female Mice

Several metabolic and behavioral adaptations that emerge during pregnancy remain present after weaning. Thus, reproductive experience causes long-lasting metabolic programming, particularly in the brain. However, the isolate effects of pregnancy or lactation and the molecular mechanisms involved in these long-term modifications are currently unknown. In the current study, we investigated the role of brain signal transducer and activator of transcription-5 (STAT5), a key transcription factor recruited by hormones highly secreted during gestation or lactation, for the long-term adaptations induced by reproductive experience. In control mice, pregnancy followed by lactation led to increased body adiposity and reduced ambulatory activity later in life. Additionally, pregnancy+lactation induced long-term epigenetic modifications in the brain: we observed upregulation in hypothalamic expression of histone deacetylases and reduced numbers of neurons with histone H3 acetylation in the paraventricular, arcuate, and ventromedial nuclei. Remarkably, brain-specific STAT5 ablation prevented all metabolic and epigenetic changes observed in reproductively experienced control female mice. Nonetheless, brain-specific STAT5 knockout (KO) mice that had the experience of pregnancy but did not lactate showed increased body weight and reduced energy expenditure later in life, whereas pregnancy KO and pregnancy+lactation KO mice exhibited improved insulin sensitivity compared with virgin KO mice. In summary, lactation is necessary for the long-lasting metabolic effects observed in reproductively experienced female mice. In addition, epigenetic mechanisms involving histone acetylation in neuronal populations related to energy balance regulation are possibly associated with these long-term consequences. Finally, our findings highlighted the key role played by brain STAT5 signaling for the chronic metabolic and epigenetic changes induced by pregnancy and lactation.

Growth hormone/STAT5 signaling in proopiomelanocortin neurons regulates glucoprivic hyperphagia

Several hypothalamic neuronal populations are directly responsive to growth hormone (GH) and central GH action regulates glucose and energy homeostasis. However, the potential role of GH signaling in proopiomelanocortin (POMC) neurons has not been studied yet. Thus, we investigated whether POMC neurons are responsive to GH and if ablation of GH receptor (GHR) or STAT5 in POMC cells leads to metabolic imbalances. Approximately 60% of POMC neurons of the arcuate nucleus exhibited STAT5 phosphorylation after intracerebroventricular GH injection. Ablation of GHR or STAT5 in POMC cells did not affect energy or glucose homeostasis. However, glucoprivic hyperphagia was blunted in male and female GHR knockout mice, and in male POMC-specific STAT5 knockout mice. Additionally, the absence of GHR in POMC neurons decreased glycemia during prolonged food restriction in male mice. Thus, GH action in POMC neurons regulates glucoprivic hyperphagia as well as blood glucose levels during prolonged food restriction.