Hypothalamic free fatty acid receptor-1 regulates whole-body energy balance.

OBJECTIVE: Free fatty acid receptor-1 (FFAR1) is a medium- and long-chain fatty acid sensing G protein-coupled receptor that is highly expressed in the hypothalamus. Here, we investigated the central role of FFAR1 on energy balance. METHODS: Central FFAR1 agonism and virogenic knockdown were performed in mice. Energy balance studies, infrared thermographic analysis of brown adipose tissue (BAT) and molecular analysis of the hypothalamus, BAT, white adipose tissue (WAT) and liver were carried out. RESULTS: Pharmacological stimulation of FFAR1, using central administration of its agonist TUG-905 in diet-induced obese mice, decreases body weight and is associated with increased energy expenditure, BAT thermogenesis and browning of subcutaneous WAT (sWAT), as well as reduced AMP-activated protein kinase (AMPK) levels, reduced inflammation, and decreased endoplasmic reticulum (ER) stress in the hypothalamus. As FFAR1 is expressed in distinct hypothalamic neuronal subpopulations, we used an AAV vector expressing a shRNA to specifically knockdown Ffar1 in proopiomelanocortin (POMC) neurons of the arcuate nucleus of the hypothalamus (ARC) of obese mice. Our data showed that knockdown of Ffar1 in POMC neurons promoted hyperphagia and body weight gain. In parallel, these mice developed hepatic insulin resistance and steatosis. CONCLUSIONS: FFAR1 emerges as a new hypothalamic nutrient sensor regulating whole body energy balance. Moreover, pharmacological activation of FFAR1 could provide a therapeutic advance in the management of obesity and its associated metabolic disorders.

Pregnancy Protects against Abnormal Gut Permeability Promoted via the Consumption of a High-Fat Diet in Mice.

The consumption of large amounts of dietary fats and pregnancy are independent factors that can promote changes in gut permeability and the gut microbiome landscape. However, there is limited evidence regarding the impact of pregnancy on the regulation of such parameters in females fed a high-fat diet. Here, gut permeability and microbiome landscape were evaluated in a mouse model of diet-induced obesity in pregnancy. The results show that pregnancy protected against the harmful effects of the consumption of a high-fat diet as a disruptor of gut permeability; thus, there was a two-fold reduction in FITC-dextran passage to the bloodstream compared to non-pregnant mice fed a high-fat diet (p < 0.01). This was accompanied by an increased expression of gut barrier-related transcripts, particularly in the ileum. In addition, the beneficial effect of pregnancy on female mice fed the high-fat diet was accompanied by a reduced presence of bacteria belonging to the genus Clostridia, and by increased Lactobacillus murinus in the gut (p < 0.05). Thus, this study advances the understanding of how pregnancy can act during a short window of time, protecting against the harmful effects of the consumption of a high-fat diet by promoting an increased expression of transcripts encoding proteins involved in the regulation of gut permeability, particularly in the ileum, and promoting changes in the gut microbiome.

Maternal emulsifier consumption programs offspring metabolic and neuropsychological health in mice.

Modern lifestyle is associated with a major consumption of ultra-processed foods (UPF) due to their practicality and palatability. The ingestion of emulsifiers, a main additive in UPFs, has been related to gut inflammation, microbiota dysbiosis, adiposity, and obesity. Maternal unbalanced nutritional habits during embryonic and perinatal stages perturb offspring's long-term metabolic health, thus increasing obesity and associated comorbidity risk. However, whether maternal emulsifier consumption influences developmental programming in the offspring remains unknown. Here, we show that, in mice, maternal consumption of dietary emulsifiers (1% carboxymethyl cellulose (CMC) and 1% P80 in drinking water), during gestation and lactation, perturbs the development of hypothalamic energy balance regulation centers of the progeny, leads to metabolic impairments, cognition deficits, and induces anxiety-like traits in a sex-specific manner. Our findings support the notion that maternal consumption of emulsifiers, common additives of UPFs, causes mild metabolic and neuropsychological malprogramming in the progeny. Our data call for nutritional advice during gestation.

Metabolic and feeding adjustments during pregnancy.

Eating behaviours are determined by the integration of interoceptive and environmental inputs. During pregnancy, numerous physiological adaptations take place in the maternal organism to provide an adequate environment for embryonic growth. Among them, whole-body physiological remodelling directly influences eating patterns, commonly causing notable taste perception alterations, food aversions and cravings. Recurrent food cravings for and compulsive eating of highly palatable food can contribute to the development and maintenance of gestational overweight and obesity with potential adverse health consequences for the offspring. Although much is known about how maternal eating habits influence offspring health, the mechanisms that underlie changes in taste perception and food preference during pregnancy (which guide and promote feeding) are only just starting to be elucidated. Given the limited and diffuse understanding of the neurobiology of gestational eating patterns, the aim of this Review is to compile, integrate and discuss the research conducted on this topic in both experimental models and humans. This article sheds light on the mechanisms that drive changes in female feeding behaviours during distinct physiological states. Understanding these processes is crucial to improve gestational parent health and decrease the burden of metabolic and food-related diseases in future generations.

Negative energy balance hinders prosocial helping behavior.

The internal state of an animal, including homeostatic requirements, modulates its behavior. Negative energy balance stimulates hunger, thus promoting a range of actions aimed at obtaining food. While these survival actions are well established, the influence of the energy status on prosocial behavior remains unexplored. We developed a paradigm to assess helping behavior in which a free mouse was faced with a conspecific trapped in a restrainer. We measured the willingness of the free mouse to liberate the confined mouse under diverse metabolic conditions. Around 42% of ad libitum-fed mice exhibited a helping behavior, as evidenced by the reduction in the latencies to release the trapped cagemate. This behavior was independent of subsequent social contact reward and was associated with changes in corticosterone indicative of emotional contagion. This decision-making process was coupled with reduced blood glucose excursions and higher Adenosine triphosphate (ATP):Adenosine diphosphate (ADP) ratios in the forebrain of helper mice, suggesting that it was a highly energy-demanding process. Interestingly, chronic (food restriction and type 2 diabetes) and acute (chemogenetic activation of hunger-promoting AgRP neurons) situations mimicking organismal negative energy balance and enhanced appetite attenuated helping behavior toward a distressed conspecific. To investigate similar effects in humans, we estimated the influence of glycated hemoglobin (a surrogate of long-term glycemic control) on prosocial behavior (namely charity donation) using the Understanding Society dataset. Our results evidenced that organismal energy status markedly influences helping behavior and that hypothalamic AgRP neurons are at the interface of metabolism and prosocial behavior.

Maternal obesity damages the median eminence blood-brain barrier structure and function in the progeny: the beneficial impact of cross-fostering by lean mothers.

Maternal obesity is an important risk factor for obesity, cardiovascular, and metabolic diseases in the offspring. Studies have shown that it leads to hypothalamic inflammation in the progeny, affecting the function of neurons regulating food intake and energy expenditure. In adult mice fed a high-fat diet, one of the hypothalamic abnormalities that contribute to the development of obesity is the damage of the blood-brain barrier (BBB) at the median eminence-arcuate nucleus (ME-ARC) interface; however, how the hypothalamic BBB is affected in the offspring of obese mothers requires further investigation. Here, we used confocal and transmission electron microscopy, transcript expression analysis, glucose tolerance testing, and a cross-fostering intervention to determine the impact of maternal obesity and breastfeeding on BBB integrity at the ME-ARC interface. The offspring of obese mothers were born smaller; conversely, at weaning, they presented larger body mass and glucose intolerance. In addition, maternal obesity-induced structural and functional damage of the offspring's ME-ARC BBB. By a cross-fostering intervention, some of the defects in barrier integrity and metabolism seen during development in an obesogenic diet were recovered. The offspring of obese dams breastfed by lean dams presented a reduction of body mass and glucose intolerance as compared to the offspring continuously exposed to an obesogenic environment during intrauterine and perinatal life; this was accompanied by partial recovery of the anatomical structure of the ME-ARC interface, and by the normalization of transcript expression of genes coding for hypothalamic neurotransmitters involved in energy balance and BBB integrity. Thus, maternal obesity promotes structural and functional damage of the hypothalamic BBB, which is, in part, reverted by lactation by lean mothers.NEW & NOTEWORTHY Maternal dietary habits directly influence offspring health. In this study, we aimed at determining the impact of maternal obesity on BBB integrity. We show that DIO offspring presented a leakier ME-BBB, accompanied by changes in the expression of transcripts encoding for endothelial and tanycytic proteins, as well as of hypothalamic neuropeptides. Breastfeeding in lean dams was sufficient to protect the offspring from ME-BBB disruption, providing a preventive strategy of nutritional intervention during early life.

Food craving-like episodes during pregnancy are mediated by accumbal dopaminergic circuits.

Preparation for motherhood requires a myriad of physiological and behavioural adjustments throughout gestation to provide an adequate environment for proper embryonic development1. Cravings for highly palatable foods are highly prevalent during pregnancy2 and contribute to the maintenance and development of gestational overweight or obesity3. However, the neurobiology underlying the distinct ingestive behaviours that result from craving specific foods remain unknown. Here we show that mice, similarly to humans, experience gestational food craving-like episodes. These episodes are associated with a brain connectivity reorganization that affects key components of the dopaminergic mesolimbic circuitry, which drives motivated appetitive behaviours and facilitates the perception of rewarding stimuli. Pregnancy engages a dynamic modulation of dopaminergic signalling through neurons expressing dopamine D2 receptors in the nucleus accumbens, which directly modulate food craving-like events. Importantly, persistent maternal food craving-like behaviour has long-lasting effects on the offspring, particularly in males, leading to glucose intolerance, increased body weight and increased susceptibility to develop eating disorders and anxiety-like behaviours during adulthood. Our results reveal the cognitively motivated nature of pregnancy food cravings and advocates for moderating emotional eating during gestation to prevent deterioration of the offspring's neuropsychological and metabolic health.

Body mass variability in age-matched outbred male Swiss mice is associated to differential control of food intake by ghrelin.

Swiss mice belong to an outbred strain of mice largely used as a model for experimental obesity induced by high fat diet (HFD). We have previously demonstrated that a given cohort of age-matched Swiss mice is hallmarked by heterogeneous changes in body weight when exposed to HFD. The reasons underlying such variability, however, are not completely understood. Therefore we aimed to clarify the mechanisms underlying the variability in spontaneous weight gain in age-matched male swiss mice. To achieve that, individuals in a cohort of age-matched male Swiss mice were categorized as prone to body mass gain (PBMG) and resistant to body mass gain (RBMG). PBMG animals had higher caloric intake and body mass gain. RBMG and PBMG mice had a similar reduction in food intake when challenged with leptin but only RBMG exhibited a drop in ghrelin concentrations after refeeding. PBMG also showed increased midbrain levels of ghrelin receptor (Ghsr) and Dopamine receptor d2 (Drd2) mRNAs upon refeeding. Pharmacological blockade of GHSR with JMV3002 failed to reduce food intake in PMBG mice as it did in RBMG. On the other hand, the response to JMV3002 seen in PBMG was hallmarked by singular transcriptional response in the midbrain characterized by a simultaneous increase in both tyrosine hydroxylase (Th) and Proopiomelanocortin (Pomc) expressions. In conclusion, our data show that differences in the expression of genes related to the reward system in the midbrain as well as in ghrelin concentrations in serum correlate with spontaneous variability in body mass and food intake seen in age-matched male Swiss mice.

Hypothalamic pregnenolone mediates recognition memory in the context of metabolic disorders.

Obesity and type 2 diabetes are associated with cognitive dysfunction. Because the hypothalamus is implicated in energy balance control and memory disorders, we hypothesized that specific neurons in this brain region are at the interface of metabolism and cognition. Acute obesogenic diet administration in mice impaired recognition memory due to defective production of the neurosteroid precursor pregnenolone in the hypothalamus. Genetic interference with pregnenolone synthesis by Star deletion in hypothalamic POMC, but not AgRP neurons, deteriorated recognition memory independently of metabolic disturbances. Our data suggest that pregnenolone's effects on cognitive function were mediated via an autocrine mechanism on POMC neurons, influencing hippocampal long-term potentiation. The relevance of central pregnenolone on cognition was also confirmed in metabolically unhealthy patients with obesity. Our data reveal an unsuspected role for POMC neuron-derived neurosteroids in cognition. These results provide the basis for a framework to investigate new facets of POMC neuron biology with implications for cognitive disorders.

Cooperative tanycytes fuel the neuronal tank.

Tanycytes are specialized radial glial cells of the hypothalamus that have emerged as important players that sense and respond to fluctuations in whole-body energy status to maintain energy homeostasis. However, the underlying mechanisms by which tanycytes influence energy balance remain incompletely understood. In this issue of the JCI, Lhomme et al. used transgenic mouse models, pharmacological approaches, and electrophysiology to investigate how tanycytes sense glucose availability and integrate metabolic cues into a lactate tanycytic network that fuels pro-opiomelanocortin (POMC) neuronal activity. Notably, the authors found that the tanycytic network relied on monocarboxylate transporters and connexin-43 gap junctions to transfer lactate to POMC neurons. Collectively, this study places tanycytes at the center of the intercellular communication processes governing energy balance.

Interleukin-6 actions in the hypothalamus protects against obesity and is involved in the regulation of neurogenesis.

BACKGROUND: Interleukin-6 (IL6) produced in the context of exercise acts in the hypothalamus reducing obesity-associated inflammation and restoring the control of food intake and energy expenditure. In the hippocampus, some of the beneficial actions of IL6 are attributed to its neurogenesis-inducing properties. However, in the hypothalamus, the putative neurogenic actions of IL6 have never been explored, and its potential to balance energy intake can be an approach to prevent or attenuate obesity. METHODS: Wild-type (WT) and IL6 knockout (KO) mice were employed to study the capacity of IL6 to induce neurogenesis. We used cell labeling with Bromodeoxyuridine (BrdU), immunofluorescence, and real-time PCR to determine the expression of markers of neurogenesis and neurotransmitters. We prepared hypothalamic neuroprogenitor cells from KO that were treated with IL6 in order to provide an ex vivo model to further characterizing the neurogenic actions of IL6 through differentiation assays. In addition, we analyzed single-cell RNA sequencing data and determined the expression of IL6 and IL6 receptor in specific cell types of the murine hypothalamus. RESULTS: IL6 expression in the hypothalamus is low and restricted to microglia and tanycytes, whereas IL6 receptor is expressed in microglia, ependymocytes, endothelial cells, and astrocytes. Exogenous IL6 reduces diet-induced obesity. In outbred mice, obesity-resistance is accompanied by increased expression of IL6 in the hypothalamus. IL6 induces neurogenesis-related gene expression in the hypothalamus and in neuroprogenitor cells, both from WT as well as from KO mice. CONCLUSION: IL6 induces neurogenesis-related gene expression in the hypothalamus of WT mice. In KO mice, the neurogenic actions of IL6 are preserved; however, the appearance of new fully differentiated proopiomelanocortin (POMC) and neuropeptide Y (NPY) neurons is either delayed or disturbed.

Mitochondrial cristae-remodeling protein OPA1 in POMC neurons couples Ca2+ homeostasis with adipose tissue lipolysis.

Appropriate cristae remodeling is a determinant of mitochondrial function and bioenergetics and thus represents a crucial process for cellular metabolic adaptations. Here, we show that mitochondrial cristae architecture and expression of the master cristae-remodeling protein OPA1 in proopiomelanocortin (POMC) neurons, which are key metabolic sensors implicated in energy balance control, is affected by fluctuations in nutrient availability. Genetic inactivation of OPA1 in POMC neurons causes dramatic alterations in cristae topology, mitochondrial Ca2+ handling, reduction in alpha-melanocyte stimulating hormone (α-MSH) in target areas, hyperphagia, and attenuated white adipose tissue (WAT) lipolysis resulting in obesity. Pharmacological blockade of mitochondrial Ca2+ influx restores α-MSH and the lipolytic program, while improving the metabolic defects of mutant mice. Chemogenetic manipulation of POMC neurons confirms a role in lipolysis control. Our results unveil a novel axis that connects OPA1 in POMC neurons with mitochondrial cristae, Ca2+ homeostasis, and WAT lipolysis in the regulation of energy balance.

Pro-opiomelanocortin (POMC) neuron translatome signatures underlying obesogenic gestational malprogramming in mice.

OBJECTIVE: Maternal unbalanced nutritional habits during embryonic development and perinatal stages perturb hypothalamic neuronal programming of the offspring, thus increasing obesity-associated diabetes risk. However, the underlying molecular mechanisms remain largely unknown. In this study we sought to determine the translatomic signatures associated with pro-opiomelanocortin (POMC) neuron malprogramming in maternal obesogenic conditions. METHODS: We used the RiboTag mouse model to specifically profile the translatome of POMC neurons during neonatal (P0) and perinatal (P21) life and its neuroanatomical, functional, and physiological consequences. RESULTS: Maternal high-fat diet (HFD) exposure did not interfere with offspring's hypothalamic POMC neuron specification, but significantly impaired their spatial distribution and axonal extension to target areas. Importantly, we established POMC neuron-specific translatome signatures accounting for aberrant neuronal development and axonal growth. These anatomical and molecular alterations caused metabolic dysfunction in early life and adulthood. CONCLUSIONS: Our study provides fundamental insights on the molecular mechanisms underlying POMC neuron malprogramming in obesogenic contexts.

Hypothalamic expression of the atypical chemokine receptor ACKR2 is involved in the systemic regulation of glucose tolerance.

In experimental obesity, the hypothalamus is affected by an inflammatory response activated by dietary saturated fats. This inflammation is triggered as early as one day after exposure to a high-fat diet, and during its progression, there is recruitment of inflammatory cells from the systemic circulation. The objective of the present study was identifying chemokines potentially involved in the development of hypothalamic diet-induced inflammation. In order to identify chemokines potentially involved in this process, we performed a real-time PCR array that determined Ackr2 as one of the transcripts undergoing differential regulation in obese-prone as compared to obese-resistant mice fed a high-fat diet for three days. ACKR2 is a decoy receptor that acts as an inhibitor of the signals generated by several CC inflammatory chemokines. Our results show that Ackr2 expression is rapidly induced after exposure to dietary fats both in obese-prone and obese-resistant mice. In immunofluorescence studies, ACKR2 was detected in hypothalamic neurons expressing POMC and NPY and also in microglia and astrocytes. The lentiviral overexpression of ACKR2 in the hypothalamus reduced diet-induced hypothalamic inflammation; however, there was no change in spontaneous caloric intake and body mass. Nevertheless, the overexpression of ACKR2 resulted in improvement of glucose tolerance, which was accompanied by reduced insulin secretion and increased whole body insulin sensitivity. Thus, ACKR2 is a decoy chemokine receptor expressed in most hypothalamic cells that is modulated by dietary intervention and acts to reduce diet-induced inflammation, leading to improved glucose tolerance due to improved insulin action.

p53 in AgRP neurons is required for protection against diet-induced obesity via JNK1.

p53 is a well-known tumor suppressor that has emerged as an important player in energy balance. However, its metabolic role in the hypothalamus remains unknown. Herein, we show that mice lacking p53 in agouti-related peptide (AgRP), but not proopiomelanocortin (POMC) or steroidogenic factor-1 (SF1) neurons, are more prone to develop diet-induced obesity and show reduced brown adipose tissue (BAT) thermogenic activity. AgRP-specific ablation of p53 resulted in increased hypothalamic c-Jun N-terminal kinase (JNK) activity before the mice developed obesity, and central inhibition of JNK reversed the obese phenotype of these mice. The overexpression of p53 in the ARC or specifically in AgRP neurons of obese mice decreased body weight and stimulated BAT thermogenesis, resulting in body weight loss. Finally, p53 in AgRP neurons regulates the ghrelin-induced food intake and body weight. Overall, our findings provide evidence that p53 in AgRP neurons is required for normal adaptations against diet-induced obesity.

Mitochondrial Dynamics Mediated by Mitofusin 1 Is Required for POMC Neuron Glucose-Sensing and Insulin Release Control.

Proopiomelanocortin (POMC) neurons are critical sensors of nutrient availability implicated in energy balance and glucose metabolism control. However, the precise mechanisms underlying nutrient sensing in POMC neurons remain incompletely understood. We show that mitochondrial dynamics mediated by Mitofusin 1 (MFN1) in POMC neurons couple nutrient sensing with systemic glucose metabolism. Mice lacking MFN1 in POMC neurons exhibited defective mitochondrial architecture remodeling and attenuated hypothalamic gene expression programs during the fast-to-fed transition. This loss of mitochondrial flexibility in POMC neurons bidirectionally altered glucose sensing, causing abnormal glucose homeostasis due to defective insulin secretion by pancreatic ß cells. Fed mice lacking MFN1 in POMC neurons displayed enhanced hypothalamic mitochondrial oxygen flux and reactive oxygen species generation. Central delivery of antioxidants was able to normalize the phenotype. Collectively, our data posit MFN1-mediated mitochondrial dynamics in POMC neurons as an intrinsic nutrient-sensing mechanism and unveil an unrecognized link between this subset of neurons and insulin release.

Development and Function of the Blood-Brain Barrier in the Context of Metabolic Control.

Under physiological conditions, the brain consumes over 20% of the whole body energy supply. The blood-brain barrier (BBB) allows dynamic interactions between blood capillaries and the neuronal network in order to provide an adequate control of molecules that are transported in and out of the brain. Alterations in the BBB structure and function affecting brain accessibility to nutrients and exit of toxins are found in a number of diseases, which in turn may disturb brain function and nutrient signaling. In this review we explore the major advances obtained in the understanding of the BBB development and how its structure impacts on function. Furthermore, we focus on the particularities of the barrier permeability in the hypothalamus, its role in metabolic control and the potential impact of hypothalamic BBB abnormities in metabolic related diseases.

Leptin, Neuroinflammation and Obesity.

Hypothalamic resistance to adipostatic actions of leptin is a hallmark of obesity. Studies have revealed that hypothalamic inflammation, triggered in response to the consumption of large amounts of dietary fat, is an important mechanism in the development of leptin resistance. In this chapter, we will review the work that paved the way linking neuroinflammation of the hypothalamus and defective leptin action in obesity.

Differential requirements for Gli2 and Gli3 in the regional specification of the mouse hypothalamus.

Secreted protein Sonic hedgehog (Shh) ventralizes the neural tube by modulating the crucial balance between activating and repressing functions (GliA, GliR) of transcription factors Gli2 and Gli3. This balance-the Shh-Gli code-is species- and context-dependent and has been elucidated for the mouse spinal cord. The hypothalamus, a forebrain region regulating vital functions like homeostasis and hormone secretion, shows dynamic and intricate Shh expression as well as complex regional differentiation. Here we asked if particular combinations of Gli2 and Gli3 and of GliA and GliR functions contribute to the variety of hypothalamic regions, i.e., we wanted to approach the question of a possible hypothalamic version of the Shh-Gli code. Based on mouse mutant analysis, we show that: (1) hypothalamic regional heterogeneity is based in part on differentially stringent requirements for Gli2 or Gli3; (2) another source of diversity are differential requirements for Shh of neural vs. non-neural origin; (3) the medial progenitor domain known to depend on Gli2 for its development generates several essential hypothalamic nuclei plus the pituitary and median eminence; (4) the suppression of Gli3R by neural and non-neural Shh is essential for hypothalamic specification. Finally, we have mapped our results on a recent model which considers the hypothalamus as a transverse region with alar and basal portions. Our data confirm the model and are explained by it.