Glucagon-like peptide-1 regulates brown adipose tissue thermogenesis via the gut-brain axis in rats

Glucagon-Like Peptide-1 Links Ingestion, Homeostasis, and the Heart

Glucagon-like peptide-1 (GLP-1), a hormone released from enteroendocrine cells in the distal small and large intestines in response to nutrients and other stimuli, not only controls eating and insulin release, but is also involved in drinking control as well as renal and cardiovascular functions. Moreover, GLP-1 functions as a central nervous system peptide transmitter, produced by preproglucagon (PPG) neurons in the hindbrain. Intestinal GLP-1 inhibits eating by activating vagal sensory neurons directly, via GLP-1 receptors (GLP-1Rs), but presumably also indirectly, by triggering the release of serotonin from enterochromaffin cells. GLP-1 enhances glucose-dependent insulin release via a vago-vagal reflex and by direct action on beta cells. Finally, intestinal GLP-1 acts on the kidneys to modulate electrolyte and water movements, and on the heart, where it provides numerous benefits, including anti-inflammatory, antiatherogenic, and vasodilatory effects, as well as protection against ischemia/reperfusion injury and arrhythmias. Hindbrain PPG neurons receive multiple inputs and project to many GLP-1R-expressing brain areas involved in reward, autonomic functions, and stress. PPG neuron-derived GLP-1 is involved in the termination of large meals and is implicated in the inhibition of water intake. This review details GLP-1's roles in these interconnected systems, highlighting recent findings and unresolved issues, and integrating them to discuss the physiological and pathological relevance of endogenous GLP-1 in coordinating these functions. As eating poses significant threats to metabolic, fluid, and immune homeostasis, the body needs mechanisms to mitigate these challenges while sustaining essential nutrient intake. Endogenous GLP-1 plays a crucial role in this "ingestive homeostasis."

The Chimeric Peptide (GEP44) Reduces Body Weight, Energy Intake, and Energy Expenditure in Diet-Induced Obese Rats

We recently reported that a chimeric peptide (GEP44) targeting the glucagon-like peptide-1 receptor (GLP-1R) and neuropeptide Y1- and Y2-receptors decreased body weight (BW), energy intake and core temperature in diet-induced obese (DIO) male and female mice. Given that GEP44 was found to reduce core temperature (surrogate measure of energy expenditure (EE)) in DIO mice, we hypothesized that GEP44 would reduce EE in male and female high fat diet (HFD)-fed rats. To test this, rats were maintained on a HFD for at least 4 months to elicit DIO prior to undergoing a sequential 2-day vehicle period, 2-day GEP44 (50 nmol/kg) period and a minimum 2-day washout period and detailed measures of energy homeostasis. GEP44 (50 nmol/kg) reduced EE (indirect calorimetry), respiratory exchange ratio (RER), core temperature, activity, energy intake and BW in male and female rats. As in our previous study in mice, GEP44 reduced BW in male and female HFD-fed rats by 3.8 ± 0.2% and 2.3 ± 0.4%, respectively. These effects appear to be mediated by increased lipid oxidation and reductions of energy intake as GEP44 reduced RER and cumulative energy intake in male and female HFD-fed rats. The strong reduction of body weight in response to GEP44 is related to a robust reduction of energy intake, but not to stimulation of EE. The paradoxical finding that GEP44 reduced EE might be secondary to a reduction of diet-induced thermogenesis or might indicate an important mechanism to limit the overall efficacy of GEP44 to prevent further weight loss.

Cross-talk between adipose tissue and microbiota-gut-brain-axis in brain development and neurological disorder

The gut microbiota is an important factor responsible for the physiological processes as well as pathogenesis of host. The communication between central nervous system (CNS) and microbiota occurs by different pathways i.e., chemical, neural, immune, and endocrine. Alteration in gut microbiota i.e., gut dysbiosis causes alteration in the bidirectional communication between CNS and gut microbiota and linked to the pathogenesis of neurological and neurodevelopmental disorder. Therefore, now-a-days microbiota-gut-brain-axis (MGBA) has emerged as therapeutic target for the treatment of metabolic disorder. But, experimental data available on MGBA from basic research has limited application in clinical study. In present study we first summarized molecular mechanism of microbiota interaction with brain physiology and pathogenesis via collecting data from different sources i.e., PubMed, Scopus, Web of Science. Furthermore, evidence shows that adipose tissue (AT) is active during metabolic activities and may also interact with MGBA. Hence, in present study we have focused on the relationship among MGBA, brown adipose tissue, and white adipose tissue. Along with this, we have also studied functional specificity of AT, and understanding heterogeneity among MGBA and different types of AT. Therefore, molecular interaction among them may provide therapeutic target for the treatment of neurological disorder.

Glucagon-like Peptide 1 Receptor Agonists in Cardio-Oncology: Pathophysiology of Cardiometabolic Outcomes in Cancer Patients

Cancer patients, especially long cancer survivors, are exposed to several cardio-metabolic diseases, including diabetes, heart failure, and atherosclerosis, which increase their risk of cardiovascular mortality. Therapy with glucagon-like peptide 1 (GLP1) receptor agonists demonstrated several beneficial cardiovascular effects, including atherosclerosis and heart failure prevention. Cardiovascular outcome trials (CVOTs) suggest that GLP-1 RA could exert cardiorenal benefits and systemic anti-inflammatory effects in patients with type-2 diabetes through the activation of cAMP and PI3K/AkT pathways and the inhibition of NLRP-3 and MyD88. In this narrative review, we highlight the biochemical properties of GLP-1 RA through a deep analysis of the clinical and preclinical evidence of the primary prevention of cardiomyopathies. The overall picture of this review encourages the study of GLP-1 RA in cancer patients with type-2 diabetes, as a potential primary prevention strategy against heart failure and atherosclerosis.

The novel chimeric multi-agonist peptide (GEP44) reduces energy intake and body weight in male and female diet-induced obese mice in a glucagon-like peptide-1 receptor-dependent manner

We recently reported that a novel chimeric peptide (GEP44) targeting both the glucagon-like peptide-1 receptor (GLP-1R) and neuropeptide Y1- and Y2 receptor (Y1R and Y2R) reduced energy intake and body weight (BW) in diet-induced obese (DIO) rats. We hypothesized that GEP44 reduces energy intake and BW primarily through a GLP-1R dependent mechanism. To test this hypothesis, GLP-1R+/+ mice and GLP-1R null (GLP-1R-/-) mice were fed a high fat diet for 4 months to elicit diet-induced obesity prior to undergoing a sequential 3-day vehicle period, 3-day drug treatment (5, 10, 20 or 50 nmol/kg; GEP44 vs the selective GLP-1R agonist, exendin-4) and a 3-day washout. Energy intake, BW, core temperature and activity were measured daily. GEP44 (10, 20 and 50 nmol/kg) reduced BW after 3-day treatment in DIO male GLP-1R+/+ mice by -1.5 ± 0.6, -1.3 ± 0.4 and -1.9 ± 0.4 grams, respectively (P<0.05), with similar effects being observed in female GLP-1R+/+ mice. These effects were absent in male and female DIO GLP-1R-/- mice suggesting that GLP-1R signaling contributes to GEP44-elicited reduction of BW. Further, GEP44 decreased energy intake in both male and female DIO GLP-1R+/+ mice, but GEP44 appeared to produce more consistent effects across multiple doses in males. In GLP-1R-/- mice, the effects of GEP44 on energy intake were only observed in males and not females, suggesting that GEP44 may reduce energy intake, in part, through a GLP-1R independent mechanism in males. In addition, GEP44 reduced core temperature and activity in both male and female GLP-1R+/+ mice suggesting that it may also reduce energy expenditure. Lastly, we show that GEP44 reduced fasting blood glucose in DIO male and female mice through GLP-1R. Together, these findings support the hypothesis that the chimeric peptide, GEP44, reduces energy intake, BW, core temperature, and glucose levels in male and female DIO mice primarily through a GLP-1R dependent mechanism.

Dual glucagon-like peptide-1 and glucagon receptor agonism reduces energy intake in type 2 diabetes with obesity

AIMS

To establish which components of energy balance mediate the clinically significant weight loss demonstrated with use of cotadutide, a glucagon-like peptide-1 (GLP-1)/glucagon receptor dual agonist, in early-phase studies.

MATERIALS AND METHODS

We conducted a phase 2a, single-centre, randomized, placebo-controlled trial in overweight and obese adults with type 2 diabetes. Following a 16-day single-blind placebo run-in, participants were randomized 2:1 to double-blind 42-day subcutaneous treatment with cotadutide (100-300 μg daily) or placebo. The primary outcome was percentage weight change. Secondary outcomes included change in energy intake (EI) and energy expenditure (EE).

RESULTS

A total of 12 participants (63%) in the cotadutide group and seven (78%) in the placebo group completed the study. The mean (90% confidence interval [CI]) weight change was -4.0% (-4.9%, -3.1%) and -1.4% (-2.7%, -0.1%) for the cotadutide and placebo groups, respectively (p = 0.011). EI was lower with cotadutide versus placebo (-41.3% [-66.7, -15.9]; p = 0.011). Difference in EE (per kJ/kg lean body mass) for cotadutide versus placebo was 1.0% (90% CI -8.4, 10.4; p = 0.784), assessed by doubly labelled water, and -6.5% (90% CI -9.3, -3.7; p < 0.001), assessed by indirect calorimetry.

CONCLUSION

Weight loss with cotadutide is primarily driven by reduced EI, with relatively small compensatory changes in EE.

The interplay between leptin, glucocorticoids, and GLP1 regulates food intake and feeding behaviour

Nutritional, endocrine, and neurological signals converge in multiple brain centres to control feeding behaviour and food intake as part of the allostatic regulation of energy balance. Among the several neuroendocrine systems involved, the leptin, glucocorticoid, and glucagon-like peptide 1 (GLP1) systems have been extensively researched. Leptin is at the top hierarchical level since its complete absence is sufficient to trigger severe hyperphagia. Glucocorticoids are key regulators of the energy balance adaptation to stress and their sustained excess leads to excessive adiposity and metabolic perturbations. GLP1 participates in metabolic adaptation to food intake, regulating insulin secretion and satiety by parallel central and peripheral signalling systems. Herein, we review the brain and peripheral targets of these three hormone systems that integrate to regulate food intake, feeding behaviour, and metabolic homeostasis. We examine the functional relationships between leptin, glucocorticoids, and GLP1 at the central and peripheral levels, including the cross-regulation of their circulating levels and their cooperative or antagonistic actions at different brain centres. The pathophysiological roles of these neuroendocrine systems in dysregulated intake are explored in the two extremes of body adiposity - obesity and lipodystrophy - and eating behaviour disorders.

Role of incretins and glucagon receptor agonists in metabolic dysfunction-associated steatotic liver disease: Opportunities and challenges

Metabolic dysfunction-associated steatotic liver disease (MASLD) has become the most common chronic liver disease worldwide, paralleling the rising pandemic of obesity and type 2 diabetes. Due to the growing global health burden and complex pathogenesis of MASLD, a multifaceted and innovative therapeutic approach is needed. Incretin receptor agonists, which were initially developed for diabetes management, have emerged as promising candidates for MASLD treatment. This review describes the pathophysiological mechanisms and action sites of three major classes of incretin/glucagon receptor agonists: glucagon-like peptide-1 receptor agonists, glucose-dependent insulinotropic polypeptide receptor agonists, and glucagon receptor agonists. Incretins and glucagon directly or indirectly impact various organs, including the liver, brain, pancreas, gastrointestinal tract, and adipose tissue. Thus, these agents significantly improve glycemic control and weight management and mitigate MASLD pathogenesis. Importantly, this study provides a summary of clinical trials analyzing the effectiveness and safety of incretin receptor agonists in MASLD management and provides an in-depth analysis highlighting their beneficial effects on improving liver function, hepatic steatosis, and intrahepatic inflammation. There are emerging challenges associated with the use of these medications in the real world, particularly adverse events, drug-drug interactions, and barriers to access, which are discussed in detail. Additionally, this review highlights the evolving role of incretin receptor agonists in MASLD management and suggests future research directions.

The Novel Chimeric Multi-Agonist Peptide (GEP44) Reduces Energy Intake and Body Weight in Male and Female Diet-Induced Obese Mice in a Glucagon-Like Peptide-1 Receptor-Dependent Manner

We recently reported that a novel chimeric peptide (GEP44) targeting both the glucagon-like peptide-1 receptor (GLP-1R) and neuropeptide Y1- and Y2 receptor (Y1R and Y2R) reduced energy intake and body weight (BW) in diet-induced obese (DIO) rats. We hypothesized that GEP44 reduces energy intake and BW primarily through a GLP-1R dependent mechanism. To test this hypothesis, GLP-1R +/+ mice and GLP-1R null (GLP-1R -/- ) mice were fed a high fat diet for 4 months to elicit diet-induced obesity prior to undergoing a sequential 3-day vehicle period, 3-day drug treatment (5, 10, 20 or 50 nmol/kg; GEP44 vs the selective GLP-1R agonist, exendin-4) and a 3-day washout. Energy intake, BW, core temperature and activity were measured daily. GEP44 (10, 20 and 50 nmol/kg) reduced BW after 3-day treatment in DIO male GLP-1R +/+ mice by - 1.5±0.6, -1.3±0.4 and -1.9±0.4 grams, respectively ( P <0.05), with similar effects being observed in female GLP-1R +/+ mice. These effects were absent in male and female DIO GLP-1R -/- mice suggesting that GLP-1R signaling contributes to GEP44-elicited reduction of BW. Further, GEP44 decreased energy intake in both male and female DIO GLP-1R +/+ mice, but GEP44 appeared to produce more consistent effects across multiple doses in males. In GLP-1R -/- mice, the effects of GEP44 on energy intake were only observed in males and not females, suggesting that GEP44 may reduce energy intake, in part, through a GLP-1R independent mechanism in males. In addition, GEP44 reduced core temperature and activity in both male and female GLP-1R +/+ mice suggesting that it may also reduce energy expenditure. Lastly, we show that GEP44 reduced fasting blood glucose in DIO male and female mice through GLP-1R. Together, these findings support the hypothesis that the chimeric peptide, GEP44, reduces energy intake, BW, core temperature, and glucose levels in male and female DIO mice primarily through a GLP-1R dependent mechanism.

Molecular and cellular regulation of thermogenic fat

Thermogenic fat, consisting of brown and beige adipocytes, dissipates energy in the form of heat, in contrast to the characteristics of white adipocytes that store energy. Increasing energy expenditure by activating brown adipocytes or inducing beige adipocytes is a potential therapeutic strategy for treating obesity and type 2 diabetes. Thus, a better understanding of the underlying mechanisms of thermogenesis provides novel therapeutic interventions for metabolic diseases. In this review, we summarize the recent advances in the molecular regulation of thermogenesis, focusing on transcription factors, epigenetic regulators, metabolites, and non-coding RNAs. We further discuss the intercellular and inter-organ crosstalk that regulate thermogenesis, considering the heterogeneity and complex tissue microenvironment of thermogenic fat.

Impact of short and long exposure to cafeteria diet on food intake and white adipose tissue lipolysis mediated by glucagon-like peptide 1 receptor

Introduction

The modern food environment facilitates excessive calorie intake, a major driver of obesity. Glucagon-like peptide 1 (GLP1) is a neuroendocrine peptide that has been the basis for developing new pharmacotherapies against obesity. The GLP1 receptor (GLP1R) is expressed in central and peripheral tissues, and activation of GLP1R reduces food intake, increases the expression of thermogenic proteins in brown adipose tissue (BAT), and enhances lipolysis in white adipose tissue (WAT). Obesity decreases the efficiency of GLP1R agonists in reducing food intake and body weight. Still, whether palatable food intake before or during the early development of obesity reduces the effects of GLP1R agonists on food intake and adipose tissue metabolism remains undetermined. Further, whether GLP1R expressed in WAT contributes to these effects is unclear.

Methods

Food intake, expression of thermogenic BAT proteins, and WAT lipolysis were measured after central or peripheral administration of Exendin-4 (EX4), a GLP1R agonist, to mice under intermittent-short exposure to CAF diet (3 h/d for 8 days) or a longer-continuous exposure to CAF diet (24 h/d for 15 days). Ex-vivo lipolysis was measured after EX4 exposure to WAT samples from mice fed CAF or control diet for 12 weeks. .

Results

During intermittent-short exposure to CAF diet (3 h/d for 8 days), third ventricle injection (ICV) and intra-peritoneal administration of EX4 reduced palatable food intake. Yet, during a longer-continuous exposure to CAF diet (24 h/d for 15 days), only ICV EX4 administration reduced food intake and body weight. However, this exposure to CAF diet blocked the increase in uncoupling protein 1 (UCP1) caused by ICV EX4 administration in mice fed control diet. Finally, GLP1R expression in WAT was minimal, and EX4 failed to increase lipolysis ex-vivo in WAT tissue samples from mice fed CAF or control diet for 12 weeks. .

Discussion

Exposure to a CAF diet during the early stages of obesity reduces the effects of peripheral and central GLP1R agonists, and WAT does not express a functional GLP1 receptor. These data support that exposure to the obesogenic food environment, without the development or manifestation of obesity, can alter the response to GLP1R agonists. .

Mode of action of Akkermansia muciniphila in the intestinal dialogue: role of extracellular proteins, metabolites and cell envelope components

Akkermansia muciniphila is a promising next-generation beneficial microbe due to its natural presence in the mucus layer of the gut, its symbiotic ability to degrade mucus, and its capacity to improve the intestinal barrier function. A. muciniphila is able to counteract weight gain and immuno-metabolic disturbances in several animal models. Many of these disorders, including obesity and auto-immune diseases, have been associated with decreased gut barrier function and consequent increased inflammation. Since A. muciniphila was found to normalize these changes and strengthen the gut barrier function, it is hypothesized that other beneficial effects of A. muciniphila might be caused by this restoration. In search for A. muciniphila's mode of action in enhancing the gut barrier function and promoting health, we reasoned that secreted components or cell envelope components of A. muciniphila are interesting candidates as they can potentially reach and interact with the epithelial barrier. In this review, we focus on the potential mechanisms through which A. muciniphila can exert its beneficial effects on the host by the production of extracellular and secreted proteins, metabolites and cell envelope components. These products have been studied in isolation for their structure, signaling capacity, and in some cases, also for their effects in preclinical models. This includes the protein known as Amuc_1100, which we here rename as pilus-associated signaling (PAS) protein , the P9 protein encoded by Amuc_1631, the short-chain fatty acids acetate and propionate, and cell envelope components, such as phosphatidylethanolamine and peptidoglycan.

Brown Adipose Tissue-A Translational Perspective

Brown adipose tissue (BAT) displays the unique capacity to generate heat through uncoupled oxidative phosphorylation that makes it a very attractive therapeutic target for cardiometabolic diseases. Here, we review BAT cellular metabolism, its regulation by the central nervous and endocrine systems and circulating metabolites, the plausible roles of this tissue in human thermoregulation, energy balance, and cardiometabolic disorders, and the current knowledge on its pharmacological stimulation in humans. The current definition and measurement of BAT in human studies relies almost exclusively on BAT glucose uptake from positron emission tomography with 18F-fluorodeoxiglucose, which can be dissociated from BAT thermogenic activity, as for example in insulin-resistant states. The most important energy substrate for BAT thermogenesis is its intracellular fatty acid content mobilized from sympathetic stimulation of intracellular triglyceride lipolysis. This lipolytic BAT response is intertwined with that of white adipose (WAT) and other metabolic tissues, and cannot be independently stimulated with the drugs tested thus far. BAT is an interesting and biologically plausible target that has yet to be fully and selectively activated to increase the body's thermogenic response and shift energy balance. The field of human BAT research is in need of methods able to directly, specifically, and reliably measure BAT thermogenic capacity while also tracking the related thermogenic responses in WAT and other tissues. Until this is achieved, uncertainty will remain about the role played by this fascinating tissue in human cardiometabolic diseases.

Mechanisms linking bariatric surgery to adipose tissue, glucose metabolism, fatty liver disease and gut microbiota

PURPOSE

In the last 20 years, bariatric surgery has achieved an important role in translational and clinical research because of obesity comorbidities. Initially, a tool to lose weight, bariatric surgery now has been shown to be involved in several metabolic pathways.

METHODS

We conducted a narrative review discussing the underlying mechanisms that could explain the impact of bariatric surgery and the relationship between obesity and adipose tissue, T2D, gut microbiota, and NAFLD.

RESULTS

Bariatric surgery has an impact in the relation between obesity and type 2 diabetes, but in addition  it induces the white-to-brown adipocyte trans-differentiation, by enhancing thermogenesis. Another issue is the connection of bariatric surgery with the gut microbiota and its role in the complex mechanism underlying weight gain.

CONCLUSION

Bariatric surgery modifies gut microbiota, and these modifications influence lipid metabolism, leading to improvement of non-alcoholic fatty liver disease.

Paraventricular nucleus-Medullary interactions: How they help enable endocrine responses to metabolic stress

The paraventricular hypothalamic nucleus (PVH) organizes neuroendocrine and autonomic responses to rapidly and slowly developing metabolic stressors that limit their impact on energy balance. The PVH together with the lateral hypothalamic area, and the arcuate and dorsomedial nuclei form a network that is defined by its inputs from medullary catecholamine neurons. These medullary neurons convey important glycemia and glucocorticoid feedback information that is integrated by the PVH and the rest of this network to control a variety of responses to metabolic stressors that have rapid (hypoglycemia) or slow onsets (eating a high calorie diet). This review focuses on how the responses to these two challenges are enabled by these catecholamine neurons, and the integrative nature of the network into which they project.

Different Protein Sources Enhance 18FDG-PET/MR Uptake of Brown Adipocytes in Male Subjects

Background: The unique ability of brown adipocytes to increase metabolic rate suggests that they could be targeted as an obesity treatment. Objective: The objective of the study was to search for new dietary factors that may enhance brown adipose tissue (BAT) activity. Methods: The study group comprised 28 healthy non-smoking males, aged 21–42 years old. All volunteers underwent a physical examination and a 75 g oral glucose tolerance test (75g-OGTT). Serum atrial and brain natriuretic peptide (ANP, BNP), PRD1-BF1-RIZ1 homologous domain containing 16 (PRDM16) and eukaryotic translation initiation factor 4E (eIF4E) measurements were taken, and 3-day food intake diaries were completed. Body composition measurements were assessed using dual-energy X-ray absorptiometry (DXA) scanning and bioimpedance methods. An fluorodeoxyglucose-18 (FDG-18) uptake in BAT was assessed by positron emission tomography/magnetic resonance (PET/MR) in all participants after 2 h cold exposure. The results were adjusted for age, daily energy intake, and DXA lean mass. Results: Subjects with detectable BAT (BAT⁽⁺⁾) were characterized by a higher percentage of energy obtained from dietary protein and fat and higher muscle mass (p = 0.01, p = 0.02 and p = 0.04, respectively). In the BAT⁽⁺⁾ group, animal protein intake was positively associated (p= 0.04), whereas the plant protein intake negatively correlated with BAT activity (p = 0.03). Additionally, the presence of BAT was inversely associated with BNP concentration in the 2 h of cold exposure (p = 0.002). Conclusion: The outcomes of our study suggest that different macronutrient consumption may be a new way to modulate BAT activity leading to weight reduction.

Beige Adipocyte as the Flame of White Adipose Tissue: Regulation of Browning and Impact of Obesity

Beige adipocyte, the third and relatively new type of adipocyte, can emerge in white adipose tissue (WAT) under thermogenic stimulations that is termed as browning of WAT. Recent studies suggest that browning of WAT deserves more attention and therapies targeting browning of WAT can be helpful for reducing obesity. Beyond the major inducers of browning, namely cold and β 3-adrenergic stimulation, beige adipocytes are affected by several factors, and excess adiposity per se may also influence the browning process. The objective of the present review is to provide an overview of recent clinical and preclinical studies on the hormonal and nonhormonal factors that affect the browning of WAT. This review further focuses on the role of obesity per se on browning process.

The physiological control of eating: signals, neurons, and networks

During the past 30 yr, investigating the physiology of eating behaviors has generated a truly vast literature. This is fueled in part by a dramatic increase in obesity and its comorbidities that has coincided with an ever increasing sophistication of genetically based manipulations. These techniques have produced results with a remarkable degree of cell specificity, particularly at the cell signaling level, and have played a lead role in advancing the field. However, putting these findings into a brain-wide context that connects physiological signals and neurons to behavior and somatic physiology requires a thorough consideration of neuronal connections: a field that has also seen an extraordinary technological revolution. Our goal is to present a comprehensive and balanced assessment of how physiological signals associated with energy homeostasis interact at many brain levels to control eating behaviors. A major theme is that these signals engage sets of interacting neural networks throughout the brain that are defined by specific neural connections. We begin by discussing some fundamental concepts, including ones that still engender vigorous debate, that provide the necessary frameworks for understanding how the brain controls meal initiation and termination. These include key word definitions, ATP availability as the pivotal regulated variable in energy homeostasis, neuropeptide signaling, homeostatic and hedonic eating, and meal structure. Within this context, we discuss network models of how key regions in the endbrain (or telencephalon), hypothalamus, hindbrain, medulla, vagus nerve, and spinal cord work together with the gastrointestinal tract to enable the complex motor events that permit animals to eat in diverse situations.

Food phenolics stimulate adipocyte browning via regulating gut microecology

Fat browning has piqued the interest of researchers as a potential target for treating obesity and related metabolic disorders. Recruitment of brown adipocytes leads to enhanced energy dissipation and reduced adiposity, thus facilitating the maintenance of metabolic homeostasis. Evidence is increasing to support the crucial roles of polyphenols and gut microecology in turning fat "brown". However, it is not clear whether the intestinal microecology is involved in polyphenol-mediated regulation of adipose browning, so this concept is worthy of exploration. In this review, we summarize the current knowledge, mostly from studies with murine models, supporting the concept that the effects of food phenolics on brown fat activation and white fat browning can be attributed to their regulatory actions on gut microecology, including microbial community profile, gut metabolites, and gut-derived hormones. Furthermore, the potential underlying pathways involved are also discussed. Basically, understanding gut microecology paves the way to determine the underlying roles and mechanisms of food phenolics in adipose browning.

Neuro-immune-metabolism: The tripod system of homeostasis

Homeostatic regulation of cellular and molecular processes is essential for the efficient physiological functioning of body organs. It requires an intricate balance of several networks throughout the body, most notable being the nervous, immune and metabolic systems. Several studies have reported the interactions between neuro-immune, immune-metabolic and neuro-metabolic pathways. Current review aims to integrate the information and show that neuro, immune and metabolic systems form the triumvirate of homeostasis. It focuses on the cellular and molecular interactions occurring in the extremities and intestine, which are innervated by the peripheral nervous system and for the intestine in particular the enteric nervous system. While the interdependence of neuro-immune-metabolic pathways provides a fallback mechanism in case of disruption of homeostasis, in chronic pathologies of continued disequilibrium, the collapse of one system spreads to the other interacting networks as well. Current review illustrates this domino-effect using diabetes as the main example. Together, this review attempts to provide a holistic picture of the integrated network of neuro-immune-metabolism and attempts to broaden the outlook when devising a scientific study or a treatment strategy.

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

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

Obesity and Cardiomyopathy

While much has been written about the syndrome of diabetic cardiomyopathy, clinicians and research scientists are now beginning to realize that an entirely unique syndrome exists, albeit with several commonalities to the diabetic syndrome, that being obesity cardiomyopathy. This syndrome develops independent of such comorbidities as hypertension, myocardial infarction and coronary artery disease; and it is characterized by specific alterations in adipose tissue function, inflammation and metabolism. Recent insights into the etiology of the syndrome and its consequences have focused on the roles played by altered intracellular calcium homeostasis, reactive oxygen species, and mitochondrial dysfunction. A timely and comprehensive review by Ren, Wu, Wang, Sowers and Zhang (1) identifies unique mechanisms underlying this syndrome, its relationship to heart failure and the recently identified incidence of COVID-19-related cardiovascular mortality. Importantly, the review concludes by advancing recommendations for novel approaches to the clinical management of this dangerous form of cardiomyopathy.

Therapeutic Perspectives of Thermogenic Adipocytes in Obesity and Related Complications

There is a rapidly increasing prevalence of obesity and related metabolic disorders such as type 2 diabetes worldwide. White adipose tissue (WAT) stores excess energy, whereas brown and beige adipose tissues consume energy to generate heat in the process of thermogenesis. Adaptive thermogenesis occurs in response to environmental cues as a means of generating heat by dissipating stored chemical energy. Due to its cumulative nature, very small differences in energy expenditure from adaptive thermogenesis can have a significant impact on systemic metabolism over time. Targeting brown adipose tissue (BAT) activation and converting WAT to beige fat as a method to increase energy expenditure is one of the promising strategies to combat obesity. In this review, we discuss the activation of the thermogenic process in response to physiological conditions. We highlight recent advances in harnessing the therapeutic potential of thermogenic adipocytes by genetic, pharmacological and cell-based approaches in the treatment of obesity and metabolic disorders in mice and the human.

Akkermansia muciniphila secretes a glucagon-like peptide-1-inducing protein that improves glucose homeostasis and ameliorates metabolic disease in mice

The gut microbiota, which includes Akkermansia muciniphila, is known to modulate energy metabolism, glucose tolerance, immune system maturation and function in humans^1-4. Although A. muciniphila is correlated with metabolic diseases and its beneficial causal effects were reported on host metabolism^5-8, the molecular mechanisms involved have not been identified. Here, we report that A. muciniphila increases thermogenesis and glucagon-like peptide-1 (GLP-1) secretion in high-fat-diet (HFD)-induced C57BL/6J mice by induction of uncoupling protein 1 in brown adipose tissue and systemic GLP-1 secretion. We apply fast protein liquid chromatography and liquid chromatography coupled to mass spectrophotometry analysis to identify an 84 kDa protein, named P9, that is secreted by A. muciniphila. Using L cells and mice fed on an HFD, we show that purified P9 alone is sufficient to induce GLP-1 secretion and brown adipose tissue thermogenesis. Using ligand-receptor capture analysis, we find that P9 interacts with intercellular adhesion molecule 2 (ICAM-2). Interleukin-6 deficiency abrogates the effects of P9 in glucose homeostasis and downregulates ICAM-2 expression. Our results show that the interactions between P9 and ICAM-2 could be targeted by therapeutics for metabolic diseases.

The Medullary Targets of Neurally Conveyed Sensory Information from the Rat Hepatic Portal and Superior Mesenteric Veins

Vagal and spinal sensory endings in the wall of the hepatic portal and superior mesenteric veins (PMV) provide the brain with chemosensory information important for energy balance and other functions. To determine their medullary neuronal targets, we injected the transsynaptic anterograde viral tracer HSV-1 H129-772 (H129) into the PMV wall or left nodose ganglion (LNG) of male rats, followed by immunohistochemistry (IHC) and high-resolution imaging. We also determined the chemical phenotype of H129-infected neurons, and potential vagal and spinal axon terminal appositions in the dorsal motor nucleus of the vagus (DMX) and the nucleus of the solitary tract (NTS). PMV wall injections generated H129-infected neurons in both nodose ganglia and in thoracic dorsal root ganglia (DRGs). In the medulla, cholinergic preganglionic parasympathetic neurons in the DMX were virtually the only targets of chemosensory information from the PMV wall. H129-infected terminal appositions were identified on H129-infected somata and dendrites in the DMX, and on H129-infected DMX dendrites that extend into the NTS. Sensory transmission via vagal and possibly spinal routes from the PMV wall therefore reaches DMX neurons via axo-somatic appositions in the DMX and axo-dendritic appositions in the NTS. However, the dearth of H129-infected NTS neurons indicates that sensory information from the PMV wall terminates on DMX neurons without engaging NTS neurons. These previously underappreciated direct sensory routes into the DMX enable a vago-vagal and possibly spino-vagal reflexes that can directly influence visceral function.

The metabolic impact of small intestinal nutrient sensing

The gastrointestinal tract maintains energy and glucose homeostasis, in part through nutrient-sensing and subsequent signaling to the brain and other tissues. In this review, we highlight the role of small intestinal nutrient-sensing in metabolic homeostasis, and link high-fat feeding, obesity, and diabetes with perturbations in these gut-brain signaling pathways. We identify how lipids, carbohydrates, and proteins, initiate gut peptide release from the enteroendocrine cells through small intestinal sensing pathways, and how these peptides regulate food intake, glucose tolerance, and hepatic glucose production. Lastly, we highlight how the gut microbiota impact small intestinal nutrient-sensing in normal physiology, and in disease, pharmacological and surgical settings. Emerging evidence indicates that the molecular mechanisms of small intestinal nutrient sensing in metabolic homeostasis have physiological and pathological impact as well as therapeutic potential in obesity and diabetes.

The gastrointestinal tract participates in maintaining metabolic homeostasis in part through nutrient-sensing and subsequent gut-brain signalling. Here the authors review the role of small intestinal nutrient-sensing in regulation of energy intake and systemic glucose metabolism, and link high-fat diet, obesity and diabetes with perturbations in these pathways.

Amino Acid Sensing in Metabolic Homeostasis and Health

Sensing and responding to changes in nutrient levels, including those of glucose, lipids, and amino acids, by the body is necessary for survival. Accordingly, perturbations in nutrient sensing are tightly linked with human pathologies, particularly metabolic diseases such as obesity, type 2 diabetes mellitus, and other complications of metabolic syndromes. The conventional view is that amino acids are fundamental elements for protein and peptide synthesis, while recent studies have revealed that amino acids are also important bioactive molecules that play key roles in signaling pathways and metabolic regulation. Different pathways that sense intracellular and extracellular levels of amino acids are integrated and coordinated at the organismal level, and, together, these pathways maintain whole metabolic homeostasis. In this review, we discuss the studies describing how important sensing signals respond to amino acid availability and how these sensing mechanisms modulate metabolic processes, including energy, glucose, and lipid metabolism. We further discuss whether dysregulation of amino acid sensing signals can be targeted to promote metabolic disorders, and discuss how to translate these mechanisms to treat human diseases. This review will help to enhance our overall understanding of the correlation between amino acid sensing and metabolic homeostasis, which have important implications for human health.

Incretin Hormones in Obesity and Related Cardiometabolic Disorders: The Clinical Perspective

The prevalence of obesity continues to grow rapidly worldwide, posing many public health challenges of the 21st century. Obese subjects are at major risk for serious diet-related noncommunicable diseases, including type 2 diabetes mellitus, cardiovascular disease, and non-alcoholic fatty liver disease. Understanding the mechanisms underlying obesity pathogenesis is needed for the development of effective treatment strategies. Dysregulation of incretin secretion and actions has been observed in obesity and related metabolic disorders; therefore, incretin-based therapies have been developed to provide new therapeutic options. Incretin mimetics present glucose-lowering properties, together with a reduction of appetite and food intake, resulting in weight loss. In this review, we describe the physiology of two known incretins—glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), and their role in obesity and related cardiometabolic disorders. We also focus on the available and incoming incretin-based medications that can be used in the treatment of the above-mentioned conditions.

Dissecting the Role of Subtypes of Gastrointestinal Vagal Afferents

Gastrointestinal (GI) vagal afferents convey sensory signals from the GI tract to the brain. Numerous subtypes of GI vagal afferent have been identified but their individual roles in gut function and feeding regulation are unclear. In the past decade, technical approaches to selectively target vagal afferent subtypes and to assess their function has significantly progressed. This review examines the classification of GI vagal afferent subtypes and discusses the current available techniques to study vagal afferents. Investigating the distribution of GI vagal afferent subtypes and understanding how to access and modulate individual populations are essential to dissect their fundamental roles in the gut-brain axis.

Adipose Tissue Composition in Obesity and After Bariatric Surgery

The adipose tissue is a complex organ that regulates food intake and energy expenditure as well as induces low-grade inflammation. This review deals with changes in the composition and activity of the adipose organ after bariatric surgery, focusing on epicardial and ectopic fat and on relationships between white and brown adipose tissues. Postoperative improvements of ectopic fat and epicardial fat size and composition account for the metabolic recovery and the decreased cardiovascular risk. Following Roux-en-Y gastric bypass or biliopancreatic diversion, a proportional increase in the size and activity of the metabolically active brown adipose tissue was observed, most likely related to the postoperative rearrangement of the entero-hormonal pattern with an increase of GLP-1 production: this aspect would promote the postoperative weight loss and maintenance of post-surgery benefits.

Ileal transposition: A non-restrictive bariatric surgical procedure that reduces body fat and increases ingestion-related energy expenditure

BACKGROUND

Ileal Transposition (IT) was developed as a model to study body weight reduction without the restrictive or malabsorptive aspects of other bariatric surgeries, but the exact mechanisms of the alterations in body weight after IT are not completely understood.

OBJECTIVE

To provide a detailed description of the surgical procedure of IT, and describe its effect on energy balance parameters.

METHODS

Adult male Lewis rats underwent either IT (IT+) or sham (IT-) surgery. Following surgery body weight and energy intake were monitored. After attaining weight stability (> 30 days), energy expenditure and its components were assessed using indirect calorimetry at a day of fasting, limited intake, and ad libitum intake. At the end of the study body composition analysis was performed.

RESULTS

IT+ resulted in transiently reduced energy intake, increased ingestion-related energy expenditure (IEE) and decreased body and adipose tissue weight when compared to IT-. At weight stability, neither energy budget (i.e., energy intake - energy expenditure), nor energy efficiency was different in IT+ rats compared to IT-.

CONCLUSION

Our data show that the primary cause of weight reduction following IT+ is a transient reduction in energy intake. If the increased IEE is related to a higher level of satiety, compensatory feeding to bridge body weight difference between IT+ and IT- rats is less likely to occur.

A compendium of G-protein-coupled receptors and cyclic nucleotide regulation of adipose tissue metabolism and energy expenditure

With the ever-increasing burden of obesity and Type 2 diabetes, it is generally acknowledged that there remains a need for developing new therapeutics. One potential mechanism to combat obesity is to raise energy expenditure via increasing the amount of uncoupled respiration from the mitochondria-rich brown and beige adipocytes. With the recent appreciation of thermogenic adipocytes in humans, much effort is being made to elucidate the signaling pathways that regulate the browning of adipose tissue. In this review, we focus on the ligand-receptor signaling pathways that influence the cyclic nucleotides, cAMP and cGMP, in adipocytes. We chose to focus on G-protein-coupled receptor (GPCR), guanylyl cyclase and phosphodiesterase regulation of adipocytes because they are the targets of a large proportion of all currently available therapeutics. Furthermore, there is a large overlap in their signaling pathways, as signaling events that raise cAMP or cGMP generally increase adipocyte lipolysis and cause changes that are commonly referred to as browning: increasing mitochondrial biogenesis, uncoupling protein 1 (UCP1) expression and respiration.

A systematic review on the role of infrared thermography in the Brown adipose tissue assessment

Brown adipose tissue (BAT) is an endocrine adipose tissue with attributes to dissipate energy as heat in response to changes in temperature and diet. Infrared thermography (IRT) has been studied in recent years in the assessment of BAT thermogenesis, as an option to positron emission tomography - computed tomography (PET-CT), because of several advantages. We performed a systematic review on the use of IRT in BAT assessment. Comprehensive online search was performed in different databases. The QUADAS 2 tool was used to evaluate studies' quality. 12 studies fit the inclusion criteria, whereas only one of these was considered of low risk of bias. 10 studies were favorable to IRT appliance in BAT evaluation, observing elevation of supraclavicular skin temperature correlated with BAT activity. Studies were heterogeneous in design, and a meta-analysis was precluded. Further studies with similar methodologies are needed. Conclusion: Despite the large number of published methodologies, IRT is a promising method for detecting BAT activation. Current knowledge already allows a better understanding of thermography to improve and standardize the technique.

Proglucagon-Derived Peptides, Glucose-Dependent Insulinotropic Polypeptide, and Dipeptidyl Peptidase-4-Mechanisms of Action in Adipose Tissue

Proglucagon-derived peptides (PGDPs) and related gut hormones exemplified by glucose-dependent insulinotropic polypeptide (GIP) regulate energy disposal and storage through actions on metabolically sensitive organs, including adipose tissue. The actions of glucagon, glucagon-like peptide (GLP)-1, GLP-2, GIP, and their rate-limiting enzyme dipeptidyl peptidase-4, include direct and indirect regulation of islet hormone secretion, food intake, body weight, all contributing to control of white and brown adipose tissue activity. Moreover, agents mimicking actions of these peptides are in use for the therapy of metabolic disorders with disordered energy homeostasis such as diabetes, obesity, and intestinal failure. Here we highlight current concepts and mechanisms for direct and indirect actions of these peptides on adipose tissue depots. The available data highlight the importance of indirect peptide actions for control of adipose tissue biology, consistent with the very low level of endogenous peptide receptor expression within white and brown adipose tissue depots. Finally, we discuss limitations and challenges for the interpretation of available experimental observations, coupled to identification of enduring concepts supported by more robust evidence.

Inhibition of Hepatic Bile Acid Uptake by Myrcludex B Promotes Glucagon-Like Peptide-1 Release and Reduces Obesity

BACKGROUND & AIMS

Bile acids are important metabolic signaling molecules. Bile acid receptor activation promotes body weight loss and improves glycemic control. The incretin hormone GLP-1 and thyroid hormone activation of T4 to T3 have been suggested as important contributors. Here, we identify the hepatic bile acid uptake transporter Na⁺ taurocholate co-transporting polypeptide (NTCP) as target to prolong postprandial bile acid signaling.

METHODS

Organic anion transporting polypeptide (OATP)1a/1b KO mice with or without reconstitution with human OATP1B1 in the liver were treated with the NTCP inhibitor Myrcludex B for 3.5 weeks after the onset of obesity induced by high fat diet-feeding. Furthermore, radiolabeled T4 was injected to determine the role of NTCP and OATPs in thyroid hormone clearance from plasma.

RESULTS

Inhibition of NTCP by Myrcludex B in obese Oatp1a/1b KO mice inhibited hepatic clearance of bile acids from portal and systemic blood, stimulated GLP-1 secretion, reduced body weight, and decreased (hepatic) adiposity. NTCP inhibition did not affect hepatic T4 uptake nor lead to increased thyroid hormone activation. Myrcludex B treatment increased fecal energy output, explaining body weight reductions amongst unaltered food intake and energy expenditure.

CONCLUSIONS

Pharmacologically targeting hepatic bile acid uptake to increase bile acid signaling is a novel approach to treat obesity and induce GLP1- secretion.

Obesity: a neuroimmunometabolic perspective

Neuroimmunology and immunometabolism are burgeoning topics of study, but the intersection of these two fields is scarcely considered. This interplay is particularly prevalent within adipose tissue, where immune cells and the sympathetic nervous system (SNS) have an important role in metabolic homeostasis and pathology, namely in obesity. In the present Review, we first outline the established reciprocal adipose-SNS relationship comprising the neuroendocrine loop facilitated primarily by adipose tissue-derived leptin and SNS-derived noradrenaline. Next, we review the extensive crosstalk between adipocytes and resident innate immune cells as well as the changes that occur in these secretory and signalling pathways in obesity. Finally, we discuss the effect of SNS adrenergic signalling in immune cells and conclude with exciting new research demonstrating an immutable role for SNS-resident macrophages in modulating SNS-adipose crosstalk. We posit that the latter point constitutes the existence of a new field - neuroimmunometabolism.

Nonclassical Islet Peptides: Pancreatic and Extrapancreatic Actions

The pancreas has physiologically important endocrine and exocrine functions; secreting enzymes into the small intestine to aid digestion and releasing multiple peptide hormones via the islets of Langerhans to regulate glucose metabolism, respectively. Insulin and glucagon, in combination with ghrelin, pancreatic polypeptide and somatostatin, are the main classical islet peptides critical for the maintenance of blood glucose. However, pancreatic islets also synthesis numerous ‘nonclassical’ peptides that have recently been demonstrated to exert fundamental effects on overall islet function and metabolism. As such, insights into the physiological relevance of these nonclassical peptides have shown impact on glucose metabolism, insulin action, cell survival, weight loss, and energy expenditure. This review will focus on the role of individual nonclassical islet peptides to stimulate pancreatic islet secretions as well as regulate metabolism. In addition, the more recognised actions of these peptides on satiety and energy regulation will also be considered. Furthermore, recent advances in the field of peptide therapeutics and obesity-diabetes have focused on the benefits of simultaneously targeting several hormone receptor signalling cascades. The potential for nonclassical islet hormones within such combinational approaches will also be discussed.

Glucagon-like peptide 1 (GLP-1)

BACKGROUND

The glucagon-like peptide-1 (GLP-1) is a multifaceted hormone with broad pharmacological potential. Among the numerous metabolic effects of GLP-1 are the glucose-dependent stimulation of insulin secretion, decrease of gastric emptying, inhibition of food intake, increase of natriuresis and diuresis, and modulation of rodent β-cell proliferation. GLP-1 also has cardio- and neuroprotective effects, decreases inflammation and apoptosis, and has implications for learning and memory, reward behavior, and palatability. Biochemically modified for enhanced potency and sustained action, GLP-1 receptor agonists are successfully in clinical use for the treatment of type-2 diabetes, and several GLP-1-based pharmacotherapies are in clinical evaluation for the treatment of obesity.

SCOPE OF REVIEW

In this review, we provide a detailed overview on the multifaceted nature of GLP-1 and its pharmacology and discuss its therapeutic implications on various diseases.

MAJOR CONCLUSIONS

Since its discovery, GLP-1 has emerged as a pleiotropic hormone with a myriad of metabolic functions that go well beyond its classical identification as an incretin hormone. The numerous beneficial effects of GLP-1 render this hormone an interesting candidate for the development of pharmacotherapies to treat obesity, diabetes, and neurodegenerative disorders.

Metabolic control via nutrient-sensing mechanisms: role of taste receptors and the gut-brain neuroendocrine axis

Nutrient sensing plays an important role in ensuring that appropriate digestive or hormonal responses are elicited following the ingestion of fuel substrates. Mechanisms of nutrient sensing in the oral cavity have been fairly well characterized and involve lingual taste receptors. These include heterodimers of G protein-coupled receptors (GPCRs) of the taste receptor type 1 (T1R) family for sensing sweet (T1R2-T1R3) and umami (T1R1-T1R3) stimuli, the T2R family for sensing bitter stimuli, and ion channels for conferring sour and salty tastes. In recent years, several studies have revealed the existence of additional nutrient-sensing mechanisms along the gastrointestinal tract. Glucose sensing is achieved by the T1R2-T1R3 heterodimer on enteroendocrine cells, which plays a role in triggering the secretion of incretin hormones for improved glycemic and lipemic control. Protein hydrolysates are detected by Ca²⁺-sensing receptor, the T1R1-T1R3 heterodimer, and G protein-coupled receptor 92/93 (GPR92/93), which leads to the release of the gut-derived satiety factor cholecystokinin. Furthermore, several GPCRs have been implicated in fatty acid sensing: GPR40 and GPR120 respond to medium- and long-chain fatty acids, GPR41 and GPR43 to short-chain fatty acids, and GPR119 to endogenous lipid derivatives. Aside from the recognition of fuel substrates, both the oral cavity and the gastrointestinal tract also possess T2R-mediated mechanisms of recognizing nonnutrients such as environmental contaminants, bacterial toxins, and secondary plant metabolites that evoke a bitter taste. These gastrointestinal sensing mechanisms result in the transmission of neuronal signals to the brain through the release of gastrointestinal hormones that act on vagal and enteric afferents to modulate the physiological response to nutrients, particularly satiety and energy homeostasis. Modulating these orally accessible nutrient-sensing pathways using particular foods, dietary supplements, or pharmaceutical compounds may have therapeutic potential for treating obesity and metabolic diseases.

Central nervous system circuits that control body temperature

Maintenance of mammalian core body temperature within a narrow range is a fundamental homeostatic process to optimize cellular and tissue function, and to improve survival in adverse thermal environments. Body temperature is maintained during a broad range of environmental and physiological challenges by central nervous system circuits that process thermal afferent inputs from the skin and the body core to control the activity of thermoeffectors. These include thermoregulatory behaviors, cutaneous vasomotion (vasoconstriction and, in humans, active vasodilation), thermogenesis (shivering and brown adipose tissue), evaporative heat loss (salivary spreading in rodents, and human sweating). This review provides an overview of the central nervous system circuits for thermoregulatory reflex regulation of thermoeffectors.

TMEM16B determines cholecystokinin sensitivity of intestinal vagal afferents of nodose neurons

The satiety effects and metabolic actions of cholecystokinin (CCK) have been recognized as potential therapeutic targets in obesity for decades. We identified a potentially novel Ca2+-activated chloride (Cl-) current (CaCC) that is induced by CCK in intestinal vagal afferents of nodose neurons. The CaCC subunit Anoctamin 2 (Ano2/TMEM16B) is the dominant contributor to this current. Its expression is reduced, as is CCK current activity in obese mice on a high-fat diet (HFD). Reduced expression of TMEM16B in the heterozygote KO of the channel in sensory neurons results in an obese phenotype with a loss of CCK sensitivity in intestinal nodose neurons, a loss of CCK-induced satiety, and metabolic changes, including decreased energy expenditure. The effect on energy expenditure is further supported by evidence in rats showing that CCK enhances sympathetic nerve activity and thermogenesis in brown adipose tissue, and these effects are abrogated by a HFD and vagotomy. Our findings reveal that Ano2/TMEM16B is a Ca2+-activated chloride channel in vagal afferents of nodose neurons and a major determinant of CCK-induced satiety, body weight control, and energy expenditure, making it a potential therapeutic target in obesity.

Diversity of enteroendocrine cells investigated at cellular and subcellular levels: the need for a new classification scheme

Enteroendocrine cells were historically classified by a letter code, each linked to a single hormone, deduced to be the only hormone produced by the cell. One type, the L cell, was recognised to store and secrete two products, peptide YY (PYY) and glucagon-related peptides. Many other exceptions to the one-cell one-hormone classifications have been reported over the last 40 years or so, and yet the one-hormone dogma has persisted. In the last 6 years, a plethora of data has appeared that makes the concept unviable. Here, we describe the evidence that multiple hormone transcripts and their products reside in single cells and evidence that the hormones are often, but not always, processed into separate storage vesicles. It has become clear that most enteroendocrine cells contain multiple hormones. For example, most secretin cells contain 5-hydroxytryptamine (5-HT), and in mouse many of these also contain cholecystokinin (CCK). Furthermore, CCK cells also commonly store ghrelin, glucose-dependent insulinotropic peptide (GIP), glucagon-like peptide-1 (GLP-1), neurotensin, and PYY. Several hormones, for example, secretin and 5-HT, are in separate storage vesicles at a subcellular level. Hormone patterns can differ considerably between species. Another complication is that relative levels of expression vary substantially. This means that data are significantly influenced by the sensitivities of detection techniques. For example, a hormone that can be detected in storage vesicles by super-resolution microscopy may not be above threshold for detection by conventional fluorescence microscopy. New nomenclature for cell clusters with common attributes will need to be devised and old classifications abandoned.

Involvement of TRPV1 Channels in Energy Homeostasis

The ion channel TRPV1 is involved in a wide range of processes including nociception, thermosensation and, more recently discovered, energy homeostasis. Tightly controlling energy homeostasis is important to maintain a healthy body weight, or to aid in weight loss by expending more energy than energy intake. TRPV1 may be involved in energy homeostasis, both in the control of food intake and energy expenditure. In the periphery, it is possible that TRPV1 can impact on appetite through control of appetite hormone levels or via modulation of gastrointestinal vagal afferent signaling. Further, TRPV1 may increase energy expenditure via heat production. Dietary supplementation with TRPV1 agonists, such as capsaicin, has yielded conflicting results with some studies indicating a reduction in food intake and increase in energy expenditure, and other studies indicating the converse. Nonetheless, it is increasingly apparent that TRPV1 may be dysregulated in obesity and contributing to the development of this disease. The mechanisms behind this dysregulation are currently unknown but interactions with other systems, such as the endocannabinoid systems, could be altered and therefore play a role in this dysregulation. Further, TRPV1 channels appear to be involved in pancreatic insulin secretion. Therefore, given its plausible involvement in regulation of energy and glucose homeostasis and its dysregulation in obesity, TRPV1 may be a target for weight loss therapy and diabetes. However, further research is required too fully elucidate TRPV1s role in these processes. The review provides an overview of current knowledge in this field and potential areas for development.