Effects of the obese gene product on body weight regulation in ob/ob mice

Astrocytes of the hippocampus and responses to periprandial neuroendocrine hormones

Astrocytes have risen as stars in the field of energy homeostasis and neurocognitive function, acting as a bridge of communication between the periphery and the brain, providing metabolic support, signaling via gliotransmitters, and altering synaptic communication. Dietary factors and energy state have a profound influence on hippocampal function, and the hippocampus is critical for appropriate behavioral responses associated with feeding and internal hunger cues (being in the fasted or full state), but how the hippocampus senses periprandial status and is impacted by diet is largely unknown. Periprandial hormones act within the hippocampus to modulate processes involved in hippocampal-dependent learning and memory function and astrocytes likely play an important role in modulating this signaling. In addition to periprandial hormones, astrocytes are positioned to respond to changes in circulating nutrients like glucose. Here, we review literature investigating how astrocytes mediate changes in hippocampal function, highlighting astrocyte location, morphology, and function in the context of integrating glucose metabolism, neuroendocrine hormone action, and/or cognitive function in the hippocampus. Specifically, we discuss research findings on the effects of insulin, ghrelin, leptin, and GLP-1 on glucose homeostasis, neural activity, astrocyte function, and behavior in the hippocampus. Because obesogenic diets impact neuroendocrine hormones, astrocytes, and cognitive function, we also discuss the effects of diet and diet-induced obesity on these parameters.

AgRP neuron hyperactivity drives hyperglycemia in a mouse model of type 2 diabetes

Growing evidence suggests that the pathogenesis of type 2 diabetes (T2D) involves dysfunctional central mechanisms, and, hence, the brain can be targeted to treat this disease. As an example, a single intracerebroventricular (icv) injection of fibroblast growth factor 1 (FGF1) can normalize hyperglycemia for weeks or months in rodent models of T2D. Convergent evidence implicates inhibition of a particular subset of neurons as a mediator of this FGF1 effect. Specifically, AgRP neurons, which are located in the hypothalamic arcuate nucleus (ARC) and are hyperactive in Lepob/ob mice and other rodent models of T2D. To investigate whether chronic AgRP neuron inactivation mimics the antidiabetic action of FGF1, we directed an adeno-associated virus (AAV) containing a cre-inducible tetanus toxin-GFP (TeTx-GFP) cassette (or cre-inducible AAV GFP control) to the ARC of obese, diabetic male Lepob/ob mice in which cre recombinase is expressed solely by AgRP neurons (Lepob/ob AgRP-Cre mice). We report that over a 10-wk period of observation, hyperglycemia was fully normalized by AgRP neuron inactivation. In contrast, changes in energy homeostasis parameters (food intake, energy expenditure, body weight, and fat mass) were not observed. We conclude that in diabetic male Lepob/ob mice, AgRP neuron hyperactivity is required for hyperglycemia but is dispensable for obesity.

White adipose tissue in type 2 diabetes and the effect of antidiabetic drugs

White adipose tissue (WAT) is highly flexible and was previously considered a passive location for energy storage. Its endocrine function has been established for several years, earning it the title of an "endocrine organ" due to its ability to secrete many adipokines that regulate metabolism. WAT is one of the core tissues that influence insulin sensitivity. Its dysfunction enhances insulin resistance and type 2 diabetes (T2D) progression. However, T2D may cause WAT dysfunction, including changes in distribution, metabolism, adipocyte hypertrophy, inflammation, aging, and adipokines and free fatty acid levels, which may exacerbate insulin resistance. This review used PubMed to search WAT dysfunction in T2D and the effects of these changes on insulin resistance. Additionally, we described and discussed the effects of antidiabetic drugs, including insulin therapy, sulfonylureas, metformin, glucose-like peptide-1 receptor agonists, thiazolidinediones, and sodium-dependent glucose transporters-2 inhibitors, on WAT parameters under T2D conditions.

ExermiR-129-3p Enhances Muscle Function by Improving Mitochondrial Activity Through PARP1 Inhibition

BACKGROUND

Physical exercise has beneficial effects on various organs, including skeletal muscle. However, not all patients are capable of engaging in exercise to maintain muscle function, which underscores the importance of identifying molecular mechanisms of physical training that could lead to the discovery of exercise-mimicking molecules.

METHODS

This study sought to identify molecular mediators of exercise that could improve muscle function. We focused on the exercise-induced microRNA (miR)-129-3p, investigating its role and effects on mitochondrial activity both in vivo and in vitro. The expression of miR-129-3p was analysed in skeletal muscle following exercise, and its downstream effects on the poly (ADP-ribose) polymerase-1 (Parp1)-SIRT1-PGC1α signalling pathway were elucidated. Functional studies were conducted using muscle-specific overexpression of miR-129-3p in adult mice and intramuscular injection of AAV9-miR-129-3p in obese mice to assess exercise capacity and muscle strength.

RESULTS

Exercise was found to upregulate miR-129-3p in skeletal muscle (p < 0.05), which directly inhibits Parp1, a major NAD+-consuming enzyme. This inhibition leads to increased NAD+ levels (p < 0.05), activating SIRT1 and subsequently reducing the acetylation of PGC1α, thereby enhancing mitochondrial function. Muscle-specific overexpression of miR-129-3p in adult mice significantly enhanced exercise capacity (> 130%, p < 0.0001), while AAV9-miR-129-3p injections ameliorated muscle weakness (twitch force, > 140%, p < 0.05; tetanic force, > 160%, p < 0.01) in obese mice. In human skeletal muscle myoblasts, miR-129-3p improved mitochondrial function via the PARP1-SIRT1-PGC1α signalling pathway.

CONCLUSION

Our findings suggest that miR-129-3p, induced by exercise, can mimic the beneficial effects of physical exercise. This highlights miR-129-3p as a potential therapeutic target for improving muscle health, especially in individuals unable to exercise.

Leptin enhances the intracellular thyroid hormone activation in skeletal muscle to boost energy balance

Thyroid hormones (THs) are key modulators of energy metabolism and cross-talk with other endocrine and metabolic factors. Notably, leptin can increase hypothalamic control of TH synthesis as an adaptive metabolic response regulating body weight. In this study, we found that the TH signal is heightened in overweight humans and is lost with obesity. In mice, systemic and intracerebroventricular leptin injection induces the expression of type 2 deiodinase (D2), the TH-activating enzyme, in skeletal muscle. Mechanistically, leptin enhances the transcription of D2 by a STAT3- and α-melanocyte-stimulating hormone (α-MSH)/cyclic AMP (cAMP)-dependent regulation. Notably, mice lacking D2 or with a mutation in the TH receptor do not exhibit the metabolic effects of leptin, such as increased insulin sensitivity and oxygen consumption, indicating that leptin's peripheral metabolic effects in skeletal muscle are mediated by TH. These findings underscore the critical role of leptin in integrating the TH-induced metabolic activation, while also contributing to appetite suppression in response to perceived fat stores.

Leptin activates dopamine and GABA neurons in the substantia nigra via a local pars compacta-pars reticulata circuit

Adipose-derived leptin contributes to energy homeostasis by balancing food intake and motor output, but how leptin acts in brain motor centers remains poorly understood. We investigated the influence of leptin on neuronal activity in two basal ganglia nuclei involved in motor control: the substantia nigra pars compacta (SNc) and pars reticulata (SNr). Using a mouse reporter line to identify cells expressing leptin receptors (LepRs), we found that in both sexes, a majority of SNc dopamine neurons express a high level of LepR. Whole-cell recording in ex vivo midbrain slices from male wild-type mice showed that leptin activates SNc dopamine neurons directly and increases somatodendritic dopamine release. Although LepR expression in SNr GABA output neurons was low, leptin also activated these cells. Additional experiments showed that the influence of leptin on SNr neurons is indirect and involves D1 dopamine receptors and TRPC3 channels. Administration of leptin to male mice increased locomotor activity, consistent with activation of dopamine neurons in the SNc coupled to previously reported amplification of axonal dopamine release by leptin in striatal slices. These findings indicate that in addition to managing energy homeostasis through its actions as a satiety hormone, leptin also promotes axonal and somatodendritic dopamine release that can influence motor output.Significance statement Dopamine neurons regulate motivated behaviors, but how they are influenced by metabolic hormones, like leptin, is incompletely understood. We show here that leptin increases the activity of substantia nigra (SN) pars compacta dopamine neurons directly, and that this enhances somatodendritic dopamine release. Leptin also increases the activity of GABAergic neurons in the SN pars reticulata, but does so indirectly via D1 dopamine receptors activated by locally released dopamine. Consistent with increased nigral dopamine neuron activity and previous evidence showing that leptin amplifies striatal dopamine release, systemic leptin increases locomotor behavior. This increase in motor activity complements the well-established inhibitory effect of leptin on food intake and adds an additional dimension to the regulation of energy balance by this hormone.

Blocking the SIRPα-CD47 axis promotes macrophage phagocytosis of exosomes derived from visceral adipose tissue and improves inflammation and metabolism in mice

BACKGROUND

Adipose tissue plays a pivotal role in systemic metabolism and maintaining bodily homeostasis. Exosomes from adipose tissues, known as AT-Exos, are recognized as important messengers in the communication between adipose tissue and other organs. Despite this, the alterations in exosome composition and the functional disparities among depot-specific AT-Exos in obesity remain elusive.

METHODS

In this work, we utilized lipidomics and microRNA (miRNA) sequencing to elucidate the lipid and miRNA profiles of AT-Exos in a diet-induced obesity model. We identified obesity-related miRNAs in AT-Exos and further explored their mechanisms using gain- and loss-of-function experiments. To evaluate the metabolic effects of AT-Exos on adipocytes, we conducted RNA-sequencing (RNA-seq) and confirmed our findings through Quantitative Real-time PCR (qPCR) and Western bolt analyses. Meanwhile, a mouse model with intraperitoneal injections was utilized to validate the role of exosomes derived from visceral white adipose tissue (vWAT-Exos) in obesity progression in vivo. Finally, we explored potential therapeutic intervention strategies targeting AT-Exos, particularly focusing on modulating the SIRPα-CD47 axis to enhance macrophage phagocytosis using Leptin-deficient (ob/ob) mice and SIRPα knock-out mice.

RESULTS

Our study revealed that obesity-related metabolism affects the biological processes of AT-Exos, with depot-specific secretion patterns. In obesity, the lipidome profile of AT-Exos was significantly altered, and diet can modify the miRNA content and function within these exosomes, influencing lipid metabolism and inflammatory pathways that contribute to metabolic dysregulation. Specifically, we identified that miR-200a-3p and miR-200b-3p promoted lipid accumulation in 3T3L1 cells partly through the PI3K/AKT/mTOR pathway. RNA-Seq analysis revealed that AT-Exos from different fat depots exerted distinct effects on adipocyte metabolism, with obese vWAT-Exos being notably potent in triggering inflammation and lipid accumulation in diet-induced obesity. Additionally, we found that inhibiting the SIRPα-CD47 axis can mitigate metabolic disorders induced by obese vWAT-Exos or ob/ob mice, partly due to the enhanced clearance of vWAT-Exos. Consistent with this, SIRPα-deficient mice exhibited a reduction in vWAT-Exos and displayed greater resistance to obesity.

CONCLUSIONS

This study elucidates that diet-induced obesity altered the lipid and miRNA profiles of AT-Exos, which involved in modulating adipocyte inflammation and metabolic balance. The SIRPα-CD47 axis emerges as a potential therapeutic target for obesity and its associated complications.

Leptin and Leptin Signaling in Multiple Sclerosis: A Narrative Review

Obesity, a pandemic health problem, is now considered as a chronic inflammatory state, related to many autoimmune diseases, such as multiple sclerosis. Thus, adipokines, inflammatory mediators secreted by adipose tissue, play an important role modulating the immune response. In this context, obesity, especially during adolescent age, seems to be a key factor for the development of multiple sclerosis. Leptin, the main pro-inflammatory adipokine secreted by the adipose tissue, has been found increased in patients with multiple sclerosis and is able to regulate the immune system promoting a pro-inflammatory response. Leptin signaling in both innate and adaptative immune cells might have immunomodulatory effects in the context of multiple sclerosis. In this way, leptin has been found to produce a Th1 and Th17 response, increasing M1 macrophages and decreasing regulatory T cells and Th2 response. Moreover, circulating inflammatory adipokines, such as leptin, have been found in people with multiple sclerosis. In the present work, we are reviewing literature to update the body of knowledge regarding the role of obesity and leptin in multiple sclerosis.

Leptin receptor neurons in the dorsomedial hypothalamus require distinct neuronal subsets for thermogenesis and weight loss

The dorsomedial hypothalamus (DMH) receives inputs from the preoptic area (POA), where ambient temperature mediates physiological adaptations of energy expenditure and food intake. Warm-activated POA neurons suppress energy expenditure via brown adipose tissue (BAT) projecting neurons in the dorsomedial hypothalamus/dorsal hypothalamic area (dDMH/DHA). Our earlier work identified leptin receptor (Lepr)-expressing, BAT-projecting dDMH/DHA neurons that mediate metabolic leptin effects. Yet, the neurotransmitter (glutamate or GABA) used by dDMH/DHALepr neurons remains unexplored and was investigated in this study using mice. We report that dDMH/DHALepr neurons represent equally glutamatergic and GABAergic neurons. Surprisingly, chemogenetic activation of glutamatergic and/or GABAergic dDMH/DHA neurons were capable to increase energy expenditure and locomotion, but neither reproduced the beneficial metabolic effects observed after chemogenetic activation of dDMH/DHALepr neurons. We clarify that BAT-projecting dDMH/DHA neurons that innervate the raphe pallidus (RPa) are exclusively glutamatergic Lepr neurons. In contrast, projections of GABAergic or dDMH/DHALepr neurons overlapped in the ventromedial arcuate nucleus (vmARC), suggesting distinct energy expenditure pathways. Brain slice patch clamp recordings further demonstrate a considerable proportion of leptin-inhibited dDMH/DHALepr neurons, while removal of pre-synaptic (indirect) effects with synaptic blocker increased the proportion of leptin-activated dDMH/DHALepr neurons, suggesting that pre-synaptic Lepr neurons inhibit dDMH/DHALepr neurons. We conclude that stimulation of BAT-related, GABA- and glutamatergic dDMH/DHALepr neurons in combination mediate the beneficial metabolic effects. Our data support the idea that dDMH/DHALepr neurons integrate upstream Lepr neurons (e.g., originating from POA and ARC). We speculate that these neurons manage dynamic adaptations to a variety of environmental changes including ambient temperature and energy state. SIGNIFICANCE STATEMENT: Our earlier work identified leptin receptor expressing neurons in the dDMH/DHA as an important thermoregulatory site. Dorsomedial hypothalamus (DMH) Lepr neurons participate in processing and integration of environmental exteroceptive signals like ambient temperature and circadian rhythm, as well as interoceptive signals including leptin and the gut hormone glucagon-like-peptide-1 (GLP1). The present work further characterizes dDMH/DHALepr neurons as a mixed glutamatergic and GABAergic population, but with distinct axonal projection sites. Surprisingly, select activation of glutamatergic and/or GABAergic populations are all able to increase energy expenditure, but are unable to replicate the beneficial metabolic effects observed by Lepr activation. These findings highlighting dDMH/DHA Lepr neurons as a distinct subgroup of glutamatergic and GABAergic neurons that are under indirect and direct influence of the interoceptive hormone leptin and if stimulated are uniquely capable to mediate beneficial metabolic effects. Our work significantly expands our knowledge of thermoregulatory circuits and puts a spotlight onto DMH-Lepr neurons for the integration into whole body energy and body weight homeostasis.

Regulation of energy balance by leptin as an adiposity signal and modulator of the reward system

BACKGROUND

Leptin is an adipose tissue-derived hormone that plays a crucial role in body weight, appetite, and behaviour regulation. Leptin controls energy balance as an indicator of adiposity levels and as a modulator of the reward system, which is associated with liking palatable foods. Obesity is characterized by expanded adipose tissue mass and consequently, elevated concentrations of leptin in blood. Leptin's therapeutic potential for most forms of obesity is hampered by leptin resistance and a narrow dose-response window.

SCOPE OF REVIEW

This review describes the current knowledge of the brain regions and intracellular pathways through which leptin promotes negative energy balance and restrains neural circuits affecting food reward. We also describe mechanisms that hinder these biological responses in obesity and highlight potential therapeutic interventions.

MAJOR CONCLUSIONS

Additional research is necessary to understand how pathways engaged by leptin in different brain regions are interconnected in the control of energy balance.

Interplay between the brain and adipose tissue: a metabolic conversation

The central nervous system and adipose tissue interact through complex communication. This bidirectional signaling regulates metabolic functions. The hypothalamus, a key homeostatic brain region, integrates exteroceptive and interoceptive signals to control appetite, energy expenditure, glucose, and lipid metabolism. This regulation is partly achieved via the nervous modulation of white (WAT) and brown (BAT) adipose tissue. In this review, we highlight the roles of sympathetic and parasympathetic innervation in regulating WAT and BAT activities, such as lipolysis and thermogenesis. Adipose tissue, in turn, plays a dual role as an energy reservoir and an endocrine organ, secreting hormones that influence brain function and metabolic health. In addition, this review focuses on recently uncovered communication pathways, including extracellular vesicles and neuro-mesenchymal units, which add new layers of regulation and complexity to the brain-adipose tissue interaction. Finally, we also examine the consequences of disrupted communication between the brain and adipose tissue in metabolic disorders like obesity and type-2 diabetes, emphasizing the potential for new therapeutic strategies targeting these pathways to improve metabolic health.

History and future of leptin: Discovery, regulation and signaling

The cloning of leptin 30 years ago in 1994 was an important milestone in obesity research. Prior to the discovery of leptin, obesity was stigmatized as a condition caused by lack of character and self-control. Mutations in either leptin or its receptor were the first single gene mutations found to cause severe obesity, and it is now recognized that obesity is caused mostly by a dysregulation of central neuronal circuits. Since the discovery of the leptin-deficient obese mouse (ob/ob) the cloning of leptin (ob aka lep) and leptin receptor (db aka lepr) genes, we have learned much about leptin and its action in the central nervous system. The first hope that leptin would cure obesity was quickly dampened because humans with obesity have increased leptin levels and develop leptin resistance. Nevertheless, leptin target sites in the brain represent an excellent blueprint to understand how neuronal circuits control energy homeostasis. Our expanding understanding of leptin function, interconnection of leptin signaling with other systems and impact on distinct physiological functions continues to guide and improve the development of safe and effective interventions to treat metabolic illnesses. This review highlights past concepts and current emerging concepts of the hormone leptin, leptin receptor signaling pathways and central targets to mediate distinct physiological functions.

Leptin physiology and pathophysiology in energy homeostasis, immune function, neuroendocrine regulation and bone health

Since its discovery and over the past thirty years, extensive research has significantly expanded our understanding of leptin and its diverse roles in human physiology, pathophysiology and therapeutics. A prototypical adipokine initially identified for its critical function in appetite regulation and energy homeostasis, leptin has been revealed to also exert profound effects on the hypothalamic-pituitary-gonadal, thyroid, adrenal and growth hormone axis, differentially between animals and humans, as well as in regulating immune function. Beyond these roles, leptin plays a pivotal role in significantly affecting bone health by promoting bone formation and regulating bone metabolism both directly and indirectly through its neuroendocrine actions. The diverse actions of leptin are particularly notable in leptin-deficient animal models and in conditions characterized by low circulating leptin levels, such as lipodystrophies and relative energy deficiency. Conversely, the effectiveness of leptin is attenuated in leptin-sufficient states, such as obesity and other high-adiposity conditions associated with hyperleptinemia and leptin tolerance. This review attempts to consolidate 30 years of leptin research with an emphasis on its physiology and pathophysiology in humans, including its promising therapeutic potential. We discuss preclinical and human studies describing the pathophysiology of energy deficiency across organ systems and the significant role of leptin in regulating neuroendocrine, immune, reproductive and bone health. We finally present past proof of concept clinical trials of leptin administration in leptin-deficient subjects that have demonstrated positive neuroendocrine, reproductive, and bone health outcomes, setting the stage for future phase IIb and III randomized clinical trials in these conditions.

Targeting the Brain Leptin-Melanocortin Pathway to Treat Heart Failure

PURPOSE OF THE REVIEW

The role of leptin in regulating cardiac function is still controversial with conflicting results in clinical and preclinical studies. However, most previous studies have not considered leptin's powerful cardiac effects that are mediated via activation of central nervous system (CNS) leptin receptors (LepRs) which, in turn, elicit major improvements in cardiac metabolism. In this review, we focus mainly on the role of leptin in regulating cardiac function via its CNS LepRs and downstream signaling pathways, such as the brain melanocortin system.

RECENT FINDINGS

Studies from our laboratory showed that CNS LepR activation, without raising plasma leptin levels, has remarkable beneficial effects on cardiac metabolism and function that protect the heart during pathological conditions, including heart failure (HF) induced by myocardial infarction (MI). These cardioprotective effects of leptin appear to be mediated by stimulation of CNS proopiomelanocortin neurons and subsequent activation of melanocortin 4 receptors (MC4R) in the brain. Chronic activation of the brain leptin-melanocortin pathway improves cardiac function and metabolism following myocardial infarction. However, the mechanism underlying this brain-heart crosstalk remains unclear and may have important implications for the development of new therapies for MI and HF.

Leptin Activation of Dorsal Raphe Neurons Inhibits Feeding Behavior

Leptin is a homeostatic regulatory element that signals the presence of adipocyte energy stores, reduces food intake, and increases energy expenditure. Similarly, serotonin (5-HT), a signaling molecule found in both the central and peripheral nervous systems, also controls food intake. Using neuronal tract tracing, pharmacologic and optogenetic approaches, and in vivo microdialysis, combined with behavioral end points, we tested the hypothesis that leptin controls food intake not only by activating hypothalamic leptin receptors (LepRs) but also through activation of LepRs expressed by serotonergic raphe neurons that send projections to the arcuate (ARC). We showed that microinjection of leptin directly into the dorsal raphe nucleus (DRN) reduced food intake in rats. This effect was mediated by LepR-expressing neurons in the DRN, because selective optogenetic activation of these neurons at either their DRN cell bodies or their ARC terminals reduced food intake. Anatomically, we identified a unique population of serotonergic raphe neurons expressing LepRs that send projections to the ARC. Finally, by using in vivo microdialysis, we showed that leptin administration to the DRN increased 5-HT efflux into the ARC, and specific antagonism of the 5-HT2C receptors in the ARC diminished the leptin anorectic effect. Overall, this study identified a novel circuit for leptin-mediated control of food intake through a DRN-ARC pathway, identifying a new level of interaction between leptin and serotonin to control food intake. Characterization of this new pathway creates opportunities for understanding how the brain controls eating behavior and opens alternative routes for the treatment of eating disorders.

ARTICLE HIGHLIGHTS

Increased serum leptin levels are associated with metabolic syndrome and semen parameters in patients with infertility

This study aims to ascertain the associations between serum leptin levels and metabolic syndrome and semen parameters in patients with infertility. A total of 200 patients who were diagnosed as primary infertility in our hospital were enrolled in this study, and they were divided into MetS group and non-MetS group. About 30 healthy men were enrolled as the control group. The general information, blood lipids, reproductive hormones and semen parameters were collected. We used the Student t test, the Chi-square test, the Kruskal-Wallis test, and the spearman correlation analysis to analyze their relationships. BMI, glucose, TG, follicle-stimulating hormone (FSH), and leptin were significantly higher in MetS infertile patients (P < .001; P < .005; P < .001; P < .001; and P < .001, respectively). While T and high-density lipoprotein (HDL) were significantly lower in MetS infertile patients (P < .01, and P < .001, respectively). Leptin was correlated with sperm progressive motility (R = -0.312, P < .01), and normal morphology (R = -0.458, P < .001). Moreover, sperm concentration was correlated with FSH (R = -0.268, P < .001) and inhibin B (R = 0.401, P < .001), and normal morphology was correlated with HDL (R = 0.233, P < .001) and TG (R = -0.182, P < .01). In primary infertile patients, sperm normal morphology were found to be depressed and related to MetS. Leptin was increased in patients diagnosed with MetS and associated with semen parameters.

Study on the Function of Leptin Nutrient Acquisition and Energy Metabolism of Zebrafish (Danio rerio)

Leptin plays an indispensable role in energy homeostasis, and its involvement in metabolic activities has been extensively explored in fish. We generated mutant lines of leptina (-5 bp) and leptinb (+8 bp) in zebrafish using CRISPR/Cas9 technology to explore the metabolic characteristics of lepa and lepb mutant zebrafish in response to high glucose nutritional stress induced by high levels of carbohydrates. The results were as follows: the body weight and food intake of adult zebrafish of the two mutant species were increased; the visceral fat accumulation, whole-body crude lipid, and crude protein contents of lepb-/- were increased; and the visceral fat accumulation and crude lipid in lepa-/- zebrafish were decreased. The blood glucose levels of the two mutant zebrafish were increased, the mRNA expression levels of glycolytic genes pk and gck were decreased in the two mutant zebrafish, and there were differences between lepa-/- and lepb-/- zebrafish. The expressions of glycogen synthesis and decomposition genes were inhibited and promoted, respectively. The expression of adipose synthesis genes in the liver and muscle was stimulated in lepb-/- zebrafish but suppressed in lepa-/- zebrafish. Lipolysis and oxidation genes were also stimulated in lepa-/- zebrafish livers, while the livers of lepb-/- zebrafish were stimulated but muscle was inhibited. In conclusion, the results indicate that lepa plays a major role in glucose metabolism, which is conducive to promoting glucose utilization and lipogenesis, while lepb mainly promotes lipolysis and oxidation, regulates protein generation, and plays a minor role in glucose metabolism.

Mitochondrial Function and Dysfunction in White Adipocytes and Therapeutic Implications

For a long time, white adipocytes were thought to function as lipid storages due to the sizeable unilocular lipid droplet that occupies most of their space. However, recent discoveries have highlighted the critical role of white adipocytes in maintaining energy homeostasis and contributing to obesity and related metabolic diseases. These physiological and pathological functions depend heavily on the mitochondria that reside in white adipocytes. This article aims to provide an up-to-date overview of the recent research on the function and dysfunction of white adipocyte mitochondria. After briefly summarizing the fundamental aspects of mitochondrial biology, the article describes the protective role of functional mitochondria in white adipocyte and white adipose tissue health and various roles of dysfunctional mitochondria in unhealthy white adipocytes and obesity. Finally, the article emphasizes the importance of enhancing mitochondrial quantity and quality as a therapeutic avenue to correct mitochondrial dysfunction, promote white adipocyte browning, and ultimately improve obesity and its associated metabolic diseases. © 2024 American Physiological Society. Compr Physiol 14:5581-5640, 2024.

Leptin receptor Gln223Arg and Lys109Arg polymorphisms may be associated with HBV-related hepatocellular carcinoma risk: A system review and meta-analysis

Increasing evidence has suggested a strong association of hepatocellular carcinoma (HCC) susceptibility and Gln223Arg (rs1137101) and Lys109Arg (rs1137100) polymorphisms in leptin receptor (LEPR) genes. To provide a quantitative assessment for such correlation, we reviewed all related systems and conducted meta-analysis for case and control researches. A literature search of Web of Science, EMBASE, PubMed, Scopus as well as China National Knowledge Infrastructure databases was collected. 95% confidence intervals (95% CIs) together with odds ratios (ORs) were calculated. Five case-control researches consisting of 1323 cases and 1919 control cases were incorporated into meta-analysis. Researches indicated A-allelic and AA genotype of rs1137101 were substantially related to boosted susceptibility of hepatitis B virus (HBV)-related HCC (mutant model, OR = 1.81, 95% CI = 1.36-2.41, p < .001; allelic model, OR = 1.55, 95% CI = 1.32-1.83, p < .001). On the contrary, we observed GG genotype of rs1137101 substantially related to reduced risk of HBV-related HCC (wild model, OR 0.59, 95%CI = 0.46-0.75, p < .001). We observed AA genotype of rs1137100 relevant to boosted HCC risk (mutant model, OR = 1.51, 95%CI = 1.14-2.01, p = .005) as well as in those with HBV-related HCCs (homozygous model, OR = 2.12, 95%CI = 1.49-3.02, p < .001; mutant model, OR = 1.67, 95%CI = 1.23-2.26, p = .001). G-allele and AA genotype of rs1137101 might be in connection with boosted HBV-related HCC susceptibility, and wild-type GG genotype might prevent diseases. AA genotype of rs1137100 might also improve HBV-related HCC susceptibility. Such conclusions ought to be validated by larger and better-designed researches.

The gut-brain axis in appetite, satiety, food intake, and eating behavior: Insights from animal models and human studies

The gut-brain axis plays a pivotal role in the finely tuned orchestration of food intake, where both homeostatic and hedonic processes collaboratively control our dietary decisions. This interplay involves the transmission of mechanical and chemical signals from the gastrointestinal tract to the appetite centers in the brain, conveying information on meal arrival, quantity, and chemical composition. These signals are processed in the brain eventually leading to the sensation of satiety and the termination of a meal. However, the regulation of food intake and appetite extends beyond the realms of pure physiological need. Hedonic mechanisms, including sensory perception (i.e., through sight, smell, and taste), habitual behaviors, and psychological factors, exert profound influences on food intake. Drawing from studies in animal models and human research, this comprehensive review summarizes the physiological mechanisms that underlie the gut-brain axis and its interplay with the reward network in the regulation of appetite and satiety. The recent advancements in neuroimaging techniques, with a focus on human studies that enable investigation of the neural mechanisms underpinning appetite regulation are discussed. Furthermore, this review explores therapeutic/pharmacological strategies that hold the potential for controlling food intake.

Progress in the Study of Animal Models of Metabolic Dysfunction-Associated Steatotic Liver Disease

Metabolic dysfunction-associated steatotic liver disease (MASLD) has recently been proposed as an alternative term to NAFLD. MASLD is a globally recognized chronic liver disease that poses significant health concerns and is frequently associated with obesity, insulin resistance, and hyperlipidemia. To better understand its pathogenesis and to develop effective treatments, it is essential to establish suitable animal models. Therefore, attempts have been made to establish modelling approaches that are highly similar to human diet, physiology, and pathology to better replicate disease progression. Here, we reviewed the pathogenesis of MASLD disease and summarised the used animal models of MASLD in the last 7 years through the PubMed database. In addition, we have summarised the commonly used animal models of MASLD and describe the advantages and disadvantages of various models of MASLD induction, including genetic models, diet, and chemically induced models, to provide directions for research on the pathogenesis and treatment of MASLD.

Translational potential of mouse models of human metabolic disease

Obesity causes significant morbidity and mortality globally. Research in the last three decades has delivered a step-change in our understanding of the fundamental mechanisms that regulate energy homeostasis, building on foundational discoveries in mouse models of metabolic disease. However, not all findings made in rodents have translated to humans, hampering drug discovery in this field. Here, we review how studies in mice and humans have informed our current framework for understanding energy homeostasis, discuss their challenges and limitations, and offer a perspective on how human studies may play an increasingly important role in the discovery of disease mechanisms and identification of therapeutic targets in the future.

Nutrition, Other Environmental Influences, and Genetics in the Determination of Human Stature

Linear growth during three distinct stages of life determines attained stature in adulthood: namely, in utero, early postnatal life, and puberty and the adolescent period. Individual host factors, genetics, and the environment, including nutrition, influence attained human stature. Each period of physical growth has its specific biological and environmental considerations. Recent epidemiologic investigations reveal a strong influence of prenatal factors on linear size at birth that in turn influence the postnatal growth trajectory. Although average population height changes have been documented in high-income regions, stature as a complex human trait is not well understood or easily modified. This review summarizes the biology of linear growth and its major drivers, including nutrition from a life-course perspective, the genetics of programmed growth patterns or height, and gene-environment interactions that determine human stature in toto over the life span. Implications for public health interventions and knowledge gaps are discussed.

Navigating Lipodystrophy: Insights from Laminopathies and Beyond

Recent research into laminopathic lipodystrophies-rare genetic disorders caused by mutations in the LMNA gene-has greatly expanded our knowledge of their complex pathology and metabolic implications. These disorders, including Hutchinson-Gilford progeria syndrome (HGPS), Mandibuloacral Dysplasia (MAD), and Familial Partial Lipodystrophy (FPLD), serve as crucial models for studying accelerated aging and metabolic dysfunction, enhancing our understanding of the cellular and molecular mechanisms involved. Research on laminopathies has highlighted how LMNA mutations disrupt adipose tissue function and metabolic regulation, leading to altered fat distribution and metabolic pathway dysfunctions. Such insights improve our understanding of the pathophysiological interactions between genetic anomalies and metabolic processes. This review merges current knowledge on the phenotypic classifications of these diseases and their associated metabolic complications, such as insulin resistance, hypertriglyceridemia, hepatic steatosis, and metabolic syndrome, all of which elevate the risk of cardiovascular disease, stroke, and diabetes. Additionally, a range of published therapeutic strategies, including gene editing, antisense oligonucleotides, and novel pharmacological interventions aimed at addressing defective adipocyte differentiation and lipid metabolism, will be explored. These therapies target the core dysfunctional lamin A protein, aiming to mitigate symptoms and provide a foundation for addressing similar metabolic and genetic disorders.

The Intersection of the Pathogenic Processes Underlying Psoriasis and the Comorbid Condition of Obesity

In the past decade, our understanding of psoriasis pathogenesis has made significant steps forward, leading to the development of multiple game-changing therapies. While psoriasis primarily affects the skin, it is increasingly recognized as a systemic disease that can have effects beyond the skin. Obesity is associated with more severe forms of psoriasis and can potentially worsen the systemic inflammation and metabolic dysfunction seen in psoriatic patients. The exact mechanisms underlying the link between these two conditions are not fully understood, but it is believed that chronic inflammation and immune dysregulation play a role. In this review, we examine the existing body of knowledge regarding the intersection of pathogenic processes responsible for psoriasis and obesity. The ability of biological therapies to reduce systemic and obesity-related inflammation in patients with psoriasis will be also discussed.

Transient loss of satiety effects of leptin in middle-aged male mice

Extensive research is undertaken in rodents to determine the mechanism underlying obesity-induced leptin resistance. While body weight is generally tightly controlled in these studies, the effect of age of experimental animals has received less attention. Specifically, there has been little investigation into leptin regulation of food intake in middle-aged animals, which is a period of particular relevance for weight gain in humans. We investigated whether the satiety effects of leptin remained constant in young (3 months), middle-aged (12 months) or aged (18-22 months) male mice. Although mean body weight increased with age, leptin concentrations did not significantly increase in male mice beyond 12 months of age. Exogenous leptin administration led to a significant reduction in food intake in young mice but had no effect on food intake in middle-aged male mice. This loss of the satiety effect of leptin appeared to be transient, with leptin administration leading to the greatest inhibition of food intake in the aged male mice. Subsequently, we investigated whether these differences were due to changes in leptin transport into the brain with ageing. No change in leptin clearance from the blood or transport into the brain was observed, suggesting the emergence of central resistance to leptin in middle age. These studies demonstrate the presence of dynamic and age-specific changes in the satiety effects of leptin in male mice and highlight the requirement for age to be carefully considered when undertaking metabolic studies in rodents.

Hippo-YAP/TAZ signalling coordinates adipose plasticity and energy balance by uncoupling leptin expression from fat mass

Adipose tissues serve as an energy reservoir and endocrine organ, yet the mechanisms that coordinate these functions remain elusive. Here, we show that the transcriptional coregulators, YAP and TAZ, uncouple fat mass from leptin levels and regulate adipocyte plasticity to maintain metabolic homeostasis. Activating YAP/TAZ signalling in adipocytes by deletion of the upstream regulators Lats1 and Lats2 results in a profound reduction in fat mass by converting mature adipocytes into delipidated progenitor-like cells, but does not cause lipodystrophy-related metabolic dysfunction, due to a paradoxical increase in circulating leptin levels. Mechanistically, we demonstrate that YAP/TAZ-TEAD signalling upregulates leptin expression by directly binding to an upstream enhancer site of the leptin gene. We further show that YAP/TAZ activity is associated with, and functionally required for, leptin regulation during fasting and refeeding. These results suggest that adipocyte Hippo-YAP/TAZ signalling constitutes a nexus for coordinating adipose tissue lipid storage capacity and systemic energy balance through the regulation of adipocyte plasticity and leptin gene transcription.

Repeated photodynamic therapy using a chlorin e6-embedded device to prolong the therapeutic effects on obesity

OBJECTIVE

This study aimed to investigate the efficacy and safety of repeated photodynamic therapy (PDT) with a chlorin e6 (Ce6)-embedded intragastric satiety-inducing device (ISD) to maintain therapeutic effects of obesity in a juvenile pig.

METHODS

The Ce6-embedded ISD was fabricated with a dipping method. Twelve pigs were divided into four groups of three and were administered control, single, biweekly, or weekly PDT, respectively. The therapeutic effects were assessed by comparing the results of phototoxicity, endoscopy, fluoroscopy, hormone and weight changes, and histological examination.

RESULTS

The percentage of total body weight gain was significantly suppressed in PDT-treated pigs compared with control pigs (all p < 0.001). This suppression persisted in the repeated PDT groups, but percentage of total body weight gain gradually increased when PDT was stopped. Ghrelin levels in the PDT-treated groups were significantly lower and leptin levels were significantly higher than those in the control group (all p < 0.05). Inflammatory cell infiltration, collagen, TUNEL, and anti-ghrelin-positive deposition in the weekly group were significantly higher than those in the control, single, and biweekly groups (all p < 0.01).

CONCLUSIONS

Repeated and periodic PDT was technically feasible and safe and successfully maintained the therapeutic effects against obesity while eliminating the indwelling time and reducing ISD-related complications in pigs.

Neuroendocrine and cellular mechanisms in stress resilience: From hormonal influence in the CNS to mitochondrial dysfunction and oxidative stress

Recent advancements in neuroendocrinology challenge the long-held belief that hormonal effects are confined to perivascular tissues and do not extend to the central nervous system (CNS). This paradigm shift, propelled by groundbreaking research, reveals that synthetic hormones, notably in anti-inflammatory medications, significantly influence steroid psychosis, behavioural, and cognitive impairments, as well as neuropeptide functions. A seminal development in this field occurred in 1968 with McEven's proposal that rodent brains are responsive to glucocorticoids, fundamentally altering the understanding of how anxiety impacts CNS functionality and leading to the identification of glucocorticosteroids and mineralocorticoids as distinct corticotropic receptors. This paper focuses on the intricate roles of the neuroendocrine, immunological, and CNS in fostering stress resilience, underscored by recent animal model studies. These studies highlight active, compensatory, and passive strategies for resilience, supporting the concept that anxiety and depression are systemic disorders involving dysregulation across both peripheral and central systems. Resilience is conceptualized as a multifaceted process that enhances psychological adaptability to stress through adaptive mechanisms within the immunological system, brain, hypothalamo-pituitary-adrenal axis, and ANS Axis. Furthermore, the paper explores oxidative stress, particularly its origin from the production of reactive oxygen species (ROS) in mitochondria. The mitochondria's role extends beyond ATP production, encompassing lipid, heme, purine, and steroidogenesis synthesis. ROS-induced damage to biomolecules can lead to significant mitochondrial dysfunction and cell apoptosis, emphasizing the critical nature of mitochondrial health in overall cellular function and stress resilience. This comprehensive synthesis of neuroendocrinological and cellular biological research offers new insights into the systemic complexity of stress-related disorders and the imperative for multidisciplinary approaches in their study and treatment.

Intergenerational inheritance induced by a high-fat diet causes hyperphagia and reduced hypothalamic sensitivity to insulin and leptin in the second-generation of rats

OBJECTIVE

The aim was to investigate the intergenerational inheritance induced by a high-fat diet on sensitivity to insulin and leptin in the hypothalamic control of satiety in second-generation offspring, which were fed a control diet.

METHODS

Progenitor rats were fed a high-fat or a control diet for 59 d until weaning. The first-generation and second-generation offspring were fed the control diet until 90 d of age. Body mass and adiposity index of the progenitors fed the high-fat diet and the second-generation offspring from progenitors fed the high-fat diet were evaluated as were the gene expression of DNA methyltransferase 3a, angiotensin-converting enzyme type 2, angiotensin II type 2 receptor, insulin and leptin signaling pathway (insulin receptor, leptin receptor, insulin receptor substrate 2, protein kinase B, signal transducer and transcriptional activator 3, pro-opiomelanocortin, and neuropeptide Agouti-related protein), superoxide dismutase activity, and the concentration of carbonyl protein and satiety-regulating neuropeptides, pro-opiomelanocortin and neuropeptide Agouti-related protein, in the hypothalamus.

RESULTS

The progenitor group fed a high-fat diet showed increased insulin resistance and reduced insulin-secreting beta-cell function and reduced food intake, without changes in caloric intake. The second-generation offspring from progenitors fed a high-fat diet, compared with second-generation offspring from progenitors fed a control diet group, had decreased insulin-secreting beta-cell function and increased food and caloric intake, insulin resistance, body mass, and adiposity index. Furthermore, second-generation offspring from progenitors fed a high-fat diet had increased DNA methyltransferase 3a, neuropeptide Agouti-related protein, angiotensin II type 1 receptor, and nicotinamide adenine dinucleotide phosphate oxidase p47phox gene expression, superoxide dismutase activity, and neuropeptide Agouti-related protein concentration in the hypothalamus. In addition, there were reduced in gene expression of the insulin receptor, leptin receptor, insulin receptor substrate 2, pro-opiomelanocortin, angiotensin II type 2 receptor, angiotensin-converting enzyme type 2, and angiotensin-(1-7) receptor and pro-opiomelanocortin concentration in the second-generation offspring from progenitors fed the high-fat diet.

CONCLUSIONS

Overall, progenitors fed a high-fat diet induced changes in the hypothalamic control of satiety of the second-generation offspring from progenitors fed the high-fat diet through intergenerational inheritance. These changes led to hyperphagia, alterations in the hypothalamic pathways of insulin, and leptin and adiposity index increase, favoring the occurrence of different cardiometabolic disorders in the second-generation offspring from progenitors fed the high-fat diet fed only with the control diet.

Meta-analysis investigating the impact of the LEPR rs1137101 (A>G) polymorphism on obesity risk in Asian and Caucasian ethnicities

Obesity is a chronic condition which is identified by the buildup of excess body fat caused by a combination of various factors, including genetic predisposition and lifestyle choices. rs1137101 (A > G) polymorphism in the CHR1 domain of LEPR protein linked to different diseases including obesity. Nevertheless, the connection between this polymorphism and the likelihood of developing obesity has not been determined definitively. Therefore, a meta-analysis was conducted to assess the relationship between rs1137101 and the risk of obesity. The meta-analysis included all studies meeting pre-defined criteria, found through searching databases up until February 2023. A combined odds ratio with a 95% confidence interval was estimated as overall and in continent subgroups for homozygous, heterozygous, recessive, dominant and allelic models using the fixed or the random-effects model. The meta-analysis identified 39 eligible studies with cases and controls (6099 cases/6711 controls) in 38 articles under different ethnic backgrounds. The results indicated a significant relationship between rs1137101 and the likelihood of developing obesity in each of the genetic models [the homozygous model (GG vs. AA: 95% Confidence Interval = 1.12-1.73, Odds Ratio = 1.39, P value = 0.003); the heterozygous model (AG vs. AA: 95% Confidence Interval = 1.07-1.42, Odds Ratio = 1.23, P value = 0.005); the dominant model (AG/GG vs AA: 95% Confidence Interval = 1.10-1.49, Odds Ratio = 1.28, P value = 0.001); the recessive model (GG vs AA/AG: 95% Confidence Interval = 1.02-1.45, Odds Ratio = 1.21, P value = 0.03); and the allelic model (G vs A; 95% Confidence Interval = 1.07-1.33, Odds Ratio = 1.19, P value = 0.002)] tested. Additionally, with an FDR <0.05, all genotypic models demonstrated statistical significance. The association remained significant among subgroups of Asian and Caucasian populations, although analysis in some genetic models did not show a significant association. Begg's and Egger's tests did not show publication biases. In sensitivity analysis, one particular study was found to have an impact on the Recessive model's significance, but other models remained unaffected. The current meta-analysis found significant indications supporting the association between rs1137101 and obesity. To avail a deeper understanding of this association, future research should include large-scale studies conducted in diverse ethnic populations.

Novel insights into metabolic-associated steatotic liver disease preclinical models

Metabolic-associated steatotic liver disease (MASLD) encompasses a wide spectrum of metabolic conditions associated with an excess of fat accumulation in the liver, ranging from simple hepatic steatosis to cirrhosis and hepatocellular carcinoma. Finding appropriate tools to study its development and progression is essential to address essential unmet therapeutic and staging needs. This review discusses advantages and shortcomings of different dietary, chemical and genetic factors that can be used to mimic this disease and its progression in mice from a hepatic and metabolic point of view. Also, this review will highlight some additional factors and considerations that could have a strong impact on the outcomes of our model to end up providing recommendations and a checklist to facilitate the selection of the appropriate MASLD preclinical model based on clinical aims.

Hypothalamic AMP-Activated Protein Kinase as a Whole-Body Energy Sensor and Regulator

5´-Adenosine monophosphate (AMP)-activated protein kinase (AMPK), a cellular energy sensor, is an essential enzyme that helps cells maintain stable energy levels during metabolic stress. The hypothalamus is pivotal in regulating energy balance within the body. Certain neurons in the hypothalamus are sensitive to fluctuations in food availability and energy stores, triggering adaptive responses to preserve systemic energy equilibrium. AMPK, expressed in these hypothalamic neurons, is instrumental in these regulatory processes. Hypothalamic AMPK activity is modulated by key metabolic hormones. Anorexigenic hormones, including leptin, insulin, and glucagon-like peptide 1, suppress hypothalamic AMPK activity, whereas the hunger hormone ghrelin activates it. These hormonal influences on hypothalamic AMPK activity are central to their roles in controlling food consumption and energy expenditure. Additionally, hypothalamic AMPK activity responds to variations in glucose concentrations. It becomes active during hypoglycemia but is deactivated when glucose is introduced directly into the hypothalamus. These shifts in AMPK activity within hypothalamic neurons are critical for maintaining glucose balance. Considering the vital function of hypothalamic AMPK in the regulation of overall energy and glucose balance, developing chemical agents that target the hypothalamus to modulate AMPK activity presents a promising therapeutic approach for metabolic conditions such as obesity and type 2 diabetes mellitus.

Methylation of the leptin gene promoter is associated with a negative correlation between leptin concentration and body fat in Tupaia belangeri

AIMS

Leptin is a signaling protein secreted by white adipose tissue encoded by the obesity gene, and its main function is to regulate the food intake and energy metabolism in mammals. Previous studies had found that animal leptin concentration was positively correlated with its body fat, but the leptin concentration of Tupaia belangeri was negatively correlated with its body fat mass. The present study attempted to investigate the mechanisms of leptin concentration negatively correlated with its body fat mass in T. belangeri.

MATERIAL AND METHODS

We measured the leptin concentration of the two groups of animals by enzyme linked immunosorbent assay (ELISA) and quantified the leptin mRNA expression by qPCR. Then, the histological, transcriptomic, and bisulfite sequencing of the two groups of animals were studied. Moreover, to investigate the energy metabolism under the negative correlation, we also analyzed the metabolomics and metabolic rate in T. belangeri.

KEY FINDINGS

We revealed the negative correlation was mediated by leptin gene methylation of subcutaneous adipose tissue. Further, we also found that T. belangeri increased energy metabolism with leptin decreased.

SIGNIFICANCE

We challenge the traditional view that leptin concentration was positively correlated with body fat mass, and further revealed its molecular mechanism and energy metabolism strategy. This special leptin secretion mechanism and energy metabolism strategy enriched our understanding of energy metabolism of animals, which provided an opportunity for the clinical transformation of metabolic diseases.

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.

Leptin and energy balance: exploring Leptin's role in the regulation of energy intake and energy expenditure

Leptin is a tonic appetite-regulating hormone, which is integral for the long-term regulation of energy balance. The current evidence suggests that the typical orexigenic or anorexigenic response of many of these appetite-regulating hormones, most notably ghrelin and cholecystokinin (CCK), require leptin to function whereas glucagon-like peptide-1 (GLP-1) is required for leptin to function, and these responses are altered when leptin injection or gene therapy is administered in combination with these same hormones or respective agonists. The appetite-regulatory pathway is complex, thus peptide tyrosine tyrosine (PYY), brain-derived neurotrophic factor (BDNF), orexin-A (OXA), and amylin also maintain ties to leptin, however these are less well understood. While reviews to date have focused on the existing relationships between leptin and the various neuropeptide modulators of appetite within the central nervous system (CNS) or it's role in thermogenesis, no review paper has synthesised the information regarding the interactions between appetite-regulating hormones and how leptin as a chronic regulator of energy balance can influence the acute appetite-regulatory response. Current evidence suggests that potential relationships exist between leptin and the circulating peripheral appetite hormones ghrelin, GLP-1, CCK, OXA and amylin to exhibit either synergistic or opposing effects on appetite inhibition. Though more research is warranted, leptin appears to be integral in both energy intake and energy expenditure. More specifically, functional leptin receptors appear to play an essential role in these processes.

DNA methylation regulates pancreatic gene expression and links maternal high-fat diet to the offspring glucose metabolism

Maternal high-fat diet (HFD) is related to an increased risk of glucose metabolism disorders throughout the whole life of offspring. The pancreas is a glucose homeostasis regulator. Accumulating evidence has revealed that maternal HFD affects offspring pancreas structure and function. However, the potential mechanism remains unclear. In this study, the mouse dam was fed with HFD or control diet (CD) during prepregnancy, pregnancy and lactation. The pancreatic insulin secretion function and islet genome methylome of offspring were analyzed. Pancreatic islet specific gene methylation was detected by using MeDIP qPCR. The results showed that body weight, blood glucose after oral glucose loads, fasting serum insulin, and HOMA-IR index values were significantly higher in male 12-week-old offspring from HFD dams than in the offspring from CD dams. Maternal HFD induced insulin secretion defects in male offspring. Compared with that in maternal CD group, methylation of the Abcc8 and Kcnj11 genes was increased in maternal HFD group in male offspring pancreatic islets. Furthermore, the expression levels of Abcc8 and Kcnj11 were downregulated by intrauterine exposure to a maternal HFD. In summary, maternal HFD results in a long-term functional disorder of the pancreas that is involved in insulin secretion-related gene DNA hypermethylation.

CRISPR/Cas9 Technology: A Novel Approach to Obesity Research

Gene editing technology, particularly Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) has transformed medical research. As a newly developed genome editing technique, CRISPR technology has strongly assisted scientists in enriching their comprehension of the roles of individual genes and their influences on a vast spectrum of human malignancies. Despite considerable progress in elucidating obesity's molecular pathways, current anti-obesity medications fall short in effectiveness. A thorough understanding of the genetic foundations underlying various neurobiological pathways related to obesity, as well as the neuro-molecular mechanisms involved, is crucial for developing effective obesity treatments. Utilizing CRISPR-based technologies enables precise determination of the roles of genes that encode transcription factors or enzymes involved in processes, such as lipogenesis, lipolysis, glucose metabolism, and lipid storage within adipose tissue. This innovative approach allows for the targeted suppression or activation of genes regulating obesity, potentially leading to effective weight management strategies. In this review, we have provided a detailed overview of obesity's molecular genetics, the fundamentals of CRISPR/Cas9 technology, and how this technology contributes to the discovery and therapeutic targeting of new genes associated with obesity.

Preclinical, randomized phase 1, and compassionate use evaluation of REGN4461, a leptin receptor agonist antibody for leptin deficiency

Deficiency in the adipose-derived hormone leptin or leptin receptor signaling causes class 3 obesity in individuals with genetic loss-of-function mutations in leptin or its receptor LEPR and metabolic and liver disease in individuals with hypoleptinemia secondary to lipoatrophy such as in individuals with generalized lipodystrophy. Therapies that restore leptin-LEPR signaling may resolve these metabolic sequelae. We developed a fully human monoclonal antibody (mAb), REGN4461 (mibavademab), that activates the human LEPR in the absence or presence of leptin. In obese leptin knockout mice, REGN4461 normalized body weight, food intake, blood glucose, and insulin sensitivity. In a mouse model of generalized lipodystrophy, REGN4461 alleviated hyperphagia, hyperglycemia, insulin resistance, dyslipidemia, and hepatic steatosis. In a phase 1, randomized, double-blind, placebo-controlled two-part study, REGN4461 was well tolerated with an acceptable safety profile. Treatment of individuals with overweight or obesity with REGN4461 decreased body weight over 12 weeks in those with low circulating leptin concentrations (<8 ng/ml) but had no effect on body weight in individuals with higher baseline leptin. Furthermore, compassionate-use treatment of a single patient with atypical partial lipodystrophy and a history of undetectable leptin concentrations associated with neutralizing antibodies to metreleptin was associated with noteable improvements in circulating triglycerides and hepatic steatosis. Collectively, these translational data unveil an agonist LEPR mAb that may provide clinical benefit in disorders associated with relatively low leptin concentrations.

Unripe fruits of Litchi chinensis (Gaertn.) Sonn.: An overview of its toxicity

Litchi (Litchi chinensis) is a widely consumed fruit that has been used in many food and health-promoting products worldwide. Litchi is a good source of nutrients including vitamin and minerals, dietary fibers, proteins, and carbohydrates. Of note, several studies have reported that the constituents of litchi fruits elicit antioxidant properties and help to maintain blood pressure, and reduce the risk of stroke and heart attack. An unclearly explained outbreak occurred in June 2019 in Muzaffarpur (Bihar), India resulted in the death of more than 150 children in a week, followed by a total of 872 cases and 176 deaths. This outbreak was associated with the consumption of Litchi fruits and the occurrence of acute encephalitis syndrome. In this high Litchi production region, a huge number of acute encephalitis syndrome cases have been registered in children in the past two decades with high mortality due to these neurological disorders linked to the consumption of litchi. While finding out the causes for this recurrent outbreak, whether or not it is caused by a virus or the phytotoxins of litchi is to be considered critical. Amongst the probable causes were observed to be methylene cyclopropyl acetic acid and hypoglycin-A found in unripe Litchi fruits which can cause hypoglycemia and as a plausible cause of AES outbreaks. This review addresses this recurrent outbreak in-depth exploring the possible causes and discusses the possible mechanisms by which phytotoxins of litchi such as hypoglycin A and methylene cyclopropylglycine which may elicit such toxic effects.

Serum Leptin Receptor and the rs1137101 Variant of the LEPR Gene Are Associated with Bladder Cancer

Globally, bladder cancer (BC) is one of the ten most common tumors. Obesity is a worldwide problem associated with an increased BC risk. Considering that levels of leptin and/or its receptor are often deregulated in obese individuals, we hypothesized that they could contribute to BC. To test this hypothesis, we utilized a case-control study in which 116 patients with a confirmed diagnosis of BC and 116 controls were recruited. The serum levels of leptin and leptin receptor were measured. Patients and controls were also genotyped for SNPs in the LEP (rs7799039, rs791620, and rs2167270) and LEPR genes (rs1137100, rs1137101, and rs1805094). The univariate analysis indicated that BC patients had significantly higher levels of leptin and lower levels of leptin receptor (p < 0.05). Moreover, rs7799039 of LEP and rs1137101 of LEPR were associated with BC (p < 0.05). In the multivariate analysis, leptin receptor levels were protective (OR: 0.98, 95% CI = 0.97-0.99, p = 0.002) while the GG genotype of rs1137101 of LEPR increased BC risk (OR: 3.42, 95% CI = 1.27-9.20, p = 0.02). These findings highlight that lifestyle changes could be useful in preventing BC and that disturbances in energy metabolism could play a role in the pathobiology of BC.

Highly recruited brown adipose tissue does not in itself protect against obesity

OBJECTIVE

The possibility to counteract the development of obesity in humans by recruiting brown or brite/beige adipose tissue (and thus UCP1) has attracted much attention. Here we examine if a diet that can activate diet-induced thermogenesis can exploit pre-enhanced amounts of UCP1 to counteract the development of diet-induced obesity.

METHODS

To investigate the anti-obesity significance of highly augmented amounts of UCP1 for control of body energy reserves, we physiologically increased total UCP1 amounts by recruitment of brown and brite/beige tissues in mice. We then examined the influence of the augmented UCP1 levels on metabolic parameters when the mice were exposed to a high-fat/high-sucrose diet under thermoneutral conditions.

RESULTS

The total UCP1 levels achieved were about 50-fold higher in recruited than in non-recruited mice. Contrary to underlying expectations, in the mice with highly recruited UCP1 and exposed to a high-fat/high-sucrose diet the thermogenic capacity of this UCP1 was completely inactivate. The mice even transiently (in an adipostat-like manner) demonstrated a higher metabolic efficiency and fat gain than did non-recruited mice. This was accomplished without altering energy expenditure or food absorption efficiency. The metabolic efficiency here was indistinguishable from that of mice totally devoid of UCP1.

CONCLUSIONS

Although UCP1 protein may be available, it is not inevitably utilized for diet-induced thermogenesis. Thus, although attempts to recruit UCP1 in humans may become successful as such, it is only if constant activation of the UCP1 is also achieved that amelioration of obesity development could be attained.

Leptin deficiency impairs adipogenesis and browning response in mouse mesenchymal progenitors

Although phenotypically different, brown adipose tissue (BAT) and inguinal white adipose tissue (iWAT) are able to produce heat through non-shivering thermogenesis due to the presence of mitochondrial uncoupling protein 1 (UCP1). The appearance of thermogenically active beige adipocytes in iWAT is known as browning. Both brown and beige cells originate from mesenchymal stem cells (MSCs), and in culture conditions a browning response can be induced with hypothermia (i.e. 32 °C) during which nuclear leptin immunodetection was observed. The central role of leptin in regulating food intake and energy consumption is well recognised, but its importance in the browning process at the cellular level is unclear. Here, immunocytochemical analysis of MSC-derived adipocytes established nuclear localization of both leptin and leptin receptor suggesting an involvement of the leptin pathway in the browning response. In order to elucidate whether leptin modulates the expression of brown and beige adipocyte markers, BAT and iWAT samples from leptin-deficient (ob/ob) mice were analysed and exhibited reduced brown/beige marker expression compared to wild-type controls. When MSCs were isolated and differentiated into adipocytes, leptin deficiency was observed to induce a white phenotype, especially when incubated at 32 °C. These adaptations were accompanied with morphological signs of impaired adipogenic differentiation. Overall, our results indicate that leptin supports adipocyte browning and suggest a potential role for leptin in adipogenesis and browning.

Isoform-specific disruption of the TP73 gene reveals a critical role for TAp73γ in tumorigenesis via leptin

TP73, a member of the p53 family, is expressed as TAp73 and ΔNp73 along with multiple C-terminal isoforms (α-η). ΔNp73 is primarily expressed in neuronal cells and necessary for neuronal development. Interestingly, while TAp73α is a tumor suppressor and predominantly expressed in normal cells, TAp73 is found to be frequently altered in human cancers, suggesting a role of TAp73 C-terminal isoforms in tumorigenesis. To test this, the TCGA SpliceSeq database was searched and showed that exon 11 (E11) exclusion occurs frequently in several human cancers. We also found that p73α to p73γ isoform switch resulting from E11 skipping occurs frequently in human prostate cancers and dog lymphomas. To determine whether p73α to p73γ isoform switch plays a role in tumorigenesis, CRISPR technology was used to generate multiple cancer cell lines and a mouse model in that Trp73 E11 is deleted. Surprisingly, we found that in E11-deificient cells, p73γ becomes the predominant isoform and exerts oncogenic activities by promoting cell proliferation and migration. In line with this, E11-deficient mice were more prone to obesity and B-cell lymphomas, indicating a unique role of p73γ in lipid metabolism and tumorigenesis. Additionally, we found that E11-deficient mice phenocopies Trp73-deficient mice with short lifespan, infertility, and chronic inflammation. Mechanistically, we showed that Leptin, a pleiotropic adipocytokine involved in energy metabolism and oncogenesis, was highly induced by p73γ,necessary for p73γ-mediated oncogenic activity, and associated with p73α to γ isoform switch in human prostate cancer and dog lymphoma. Finally, we showed that E11-knockout promoted, whereas knockdown of p73γ or Leptin suppressed, xenograft growth in mice. Our study indicates that the p73γ-Leptin pathway promotes tumorigenesis and alters lipid metabolism, which may be targeted for cancer management.

Genome-wide association studies of human and rat BMI converge on synapse, epigenome, and hormone signaling networks

A vexing observation in genome-wide association studies (GWASs) is that parallel analyses in different species may not identify orthologous genes. Here, we demonstrate that cross-species translation of GWASs can be greatly improved by an analysis of co-localization within molecular networks. Using body mass index (BMI) as an example, we show that the genes associated with BMI in humans lack significant agreement with those identified in rats. However, the networks interconnecting these genes show substantial overlap, highlighting common mechanisms including synaptic signaling, epigenetic modification, and hormonal regulation. Genetic perturbations within these networks cause abnormal BMI phenotypes in mice, too, supporting their broad conservation across mammals. Other mechanisms appear species specific, including carbohydrate biosynthesis (humans) and glycerolipid metabolism (rodents). Finally, network co-localization also identifies cross-species convergence for height/body length. This study advances a general paradigm for determining whether and how phenotypes measured in model species recapitulate human biology.

Positive effect of leptin substitution on mood and behaviour in patients with congenital leptin deficiency

BACKGROUND

States of starvation are characterized by reduced physical activity and social withdrawal. This has been suggested to be mediated at least in part via reduced leptin concentrations.

OBJECTIVE

We therefore aimed to ascertain if leptin substitution in patients with congenital leptin deficiency (CLD) can improve physical activity and mood.

METHODS

Seven patients with CLD were filmed prior to and after short- and long-term substitution (2-21 days; 3-4 months) in a play situation. Six independent, blinded investigators ranked each video according to specifically developed scales concerning motor activity, social interaction, emotionality, and mood with higher scores representing improvements.

RESULTS

Short term metreleptin substitution significantly increased mean total score from 17.7 ± 4.1 to 22.6 ± 6.6 (p = 0.039), and mean scores for motor activity (4.1 ± 1.1 to 5.1 ± 1.5, p = 0.023) and social interaction (4.6 ± 1.1 to 6.2 ± 1.7, p = 0.016). After long term substitution means of all four single scales and of total score were even higher than at short-term follow-up. During a treatment pause of 3 months in two children, all four scale scores fell below substitution levels and rose again after restart.

CONCLUSIONS

Metreleptin substitution improved indices of physical activity and psychological wellbeing in patients with CLD. This suggests that reduced leptin concentrations might be in part responsible for emotional and behavioural changes seen during starvation.

Low-dose peripheral leptin infusion produces selective activation of ventromedial hypothalamic and hindbrain STAT3

Previous studies have shown that very low dose, acute, single peripheral leptin injections fully activate arcuate nucleus signal transducer and activator of transcription 3 (STAT3), but ventromedial hypothalamus (VMH) pSTAT3 continues to increase with higher doses of leptin that inhibit food intake. The lowest dose that inhibited intake increased circulating leptin 300-fold whereas food intake is inhibited by chronic peripheral leptin infusions that only double circulating leptin. This study examined whether the pattern of hypothalamic pSTAT3 was the same in leptin-infused rats as in leptin-injected rats. Male Sprague-Dawley rats received intraperitoneal infusions of 0, 5, 10, 20, or 40 µg leptin/day for 9 days. The highest dose of leptin increased serum leptin by 50-100%, inhibited food intake for 5 days, but inhibited weight gain and retroperitoneal fat mass for 9 days. Energy expenditure, respiratory exchange ratio, and brown fat temperature did not change. pSTAT3 was quantified in hypothalamic nuclei and the nucleus of the solitary tract (NTS) when food intake was inhibited and when it had returned to control levels. There was no effect of leptin on pSTAT3 in the medial or lateral arcuate nucleus or in the dorsomedial nucleus of the hypothalamus. VMH pSTAT3 was increased only at day 4 when food intake was inhibited, but NTS pSTAT3 was increased at both 4 and 9 days of infusion. These results suggest that activation of leptin VMH receptors contributes to the suppression of food intake, but that hindbrain receptors contribute to a sustained change in metabolism that maintains a reduced weight and fat mass.NEW & NOTEWORTHY Low-dose, chronic peripheral infusions of leptin produced an initial, transient inhibition of food intake that correlated with signal transducer and activator of transcription 3 (STAT3) activation in the ventromedial hypothalamus (VMH) and nucleus of the solitary tract (NTS). When intake normalized, but weight remained suppressed, the NTS was the only area that remained activated. These data suggest that leptin's primary function is to reduce body fat, that hypophagia is a means of achieving this and that different areas of the brain are responsible for the progressive response.

Creativity in energy balance, obesity and feeding behavior research, some thoughts

This review provides an overview of examples of especially creative work related to the fields of ingestive behavior, energetics (defined as the study of the acquisition, storage, and use of metabolizable energy by biological organisms and the causes and consequences of such acquisition, storage, and use), and nutrition, focusing on both individual works and discoveries, as well as bodies of works and in some cases the working styles of particular scientists. The paper then discusses some principles extracted from our observations as well as from the literature on creativity pointing out some factors that seem to make for more creative science and that can be done by individuals to promote creativity in their own work. Finally, we end with a short set of tips for the field in general to promote creativity among our ranks broadly.

The Neurobiology of Eating Behavior in Obesity: Mechanisms and Therapeutic Targets: A Report from the 23rd Annual Harvard Nutrition Obesity Symposium

Obesity is increasing at an alarming rate. The effectiveness of currently available strategies for the treatment of obesity (including pharmacologic, surgical, and behavioral interventions) is limited. Understanding the neurobiology of appetite and the important drivers of energy intake (EI) can lead to the development of more effective strategies for the prevention and treatment of obesity. Appetite regulation is complex and is influenced by genetic, social, and environmental factors. It is intricately regulated by a complex interplay of endocrine, gastrointestinal, and neural systems. Hormonal and neural signals generated in response to the energy state of the organism and the quality of food eaten are communicated by paracrine, endocrine, and gastrointestinal signals to the nervous system. The central nervous system integrates homeostatic and hedonic signals to regulate appetite. Although there has been an enormous amount of research over many decades regarding the regulation of EI and body weight, research is only now yielding potentially effective treatment strategies for obesity. The purpose of this article is to summarize the key findings presented in June 2022 at the 23rd annual Harvard Nutrition Obesity Symposium entitled "The Neurobiology of Eating Behavior in Obesity: Mechanisms and Therapeutic Targets." Findings presented at the symposium, sponsored by NIH P30 Nutrition Obesity Research Center at Harvard, enhance our current understanding of appetite biology, including innovative techniques used to assess and systematically manipulate critical hedonic processes, which will shape future research and the development of therapeutics for obesity prevention and treatment.