Switching on the furnace: Regulation of heat production in brown adipose tissue

Fibroblast growth factor receptor signaling in metabolic dysfunction-associated fatty liver disease: Pathogenesis and therapeutic targets

Metabolic dysfunction-associated fatty liver disease (MAFLD) has emerged as a significant hepatic manifestation of metabolic syndrome, with its prevalence increasing globally alongside the epidemics of obesity and diabetes. MAFLD represents a continuum of liver damage, spanning from uncomplicated steatosis to metabolic dysfunction-associated steatohepatitis (MASH). This condition can advance to more severe outcomes, including fibrosis and cirrhosis. Fibroblast growth factor receptors (FGFRs) are a family of four receptor tyrosine kinases (FGFR1-4) that interact with both paracrine and endocrine fibroblast growth factors (FGFs). This interaction activates the phosphorylation of tyrosine kinase residues, thereby triggering downstream signaling pathways, including RAS-MAPK, JAK-STAT, PI3K-AKT, and PLCγ. In the context of MAFLD, paracrine FGF-FGFR signaling is predominantly biased toward the development of liver fibrosis and carcinogenesis. In contrast, endocrine FGF-FGFR signaling is primarily biased toward regulating the metabolism of bile acids, carbohydrates, lipids, and phosphate, as well as maintaining the overall balance of energy metabolism in the body. The interplay between these biased signaling pathways significantly influences the progression of MAFLD. This review explores the critical functions of FGFR signaling in MAFLD from three perspectives: first, it examines the primary roles of FGFRs relative to their structure; second, it summarizes FGFR signaling in hepatic lipid metabolism, elucidating mechanisms underlying the occurrence and progression of MAFLD; finally, it highlights recent advancements in drug development aimed at targeting FGFR signaling for the treatment of MAFLD and its associated diseases.

Z-Spectral MRI Quantifies the Mass and Metabolic Activity of Adipose Tissues With Fat-Water-Fraction and Amide-Proton-Transfer Contrasts

BACKGROUND

Brown adipose tissue (BAT) is metabolically activatable and plays an important role in obesity and metabolic diseases. With reduced fat-water-fraction (FWF) compared with white adipose tissue (WAT), BAT mass and its functional activation may be quantified with Z-spectra MRI, with built-in FWF and the metabolic amide proton transfer (APT) contrasts.

PURPOSE

To investigate if Z-spectral MRI can quantify the mass and metabolic activity of adipose tissues.

STUDY TYPE

Prospective.

SUBJECTS

Seven groups of 8-week-old male rats, including two groups (n = 7 per group) for in vivo MRI study and five groups (n = 5 per group) for ex vivo validation; 12 young and healthy volunteers with 6 male and 6 female.

FIELD STRENGTH/SEQUENCE

The 7 T small animal and 3 T clinical systems, T2-weighted imaging, Rapid Acquisition with Relaxation Enhancement (RARE) readout based chemical exchange saturation transfer (CEST) Z-spectral MRI sequence.

ASSESSMENT

Quantified FWF and APT from Z-spectra in rats before and after norepinephrine (NE) stimulation and in healthy human subjects; ex vivo measurements of total proteins in BAT from rats.

STATISTICAL TESTS

Two-tailed unpaired Student's t-tests and repeated measures ANOVA. P-value <0.05 was considered significant.

RESULTS

Decreased FWF (from 39.6% ± 7.2% before NE injection to 16.4% ± 7.2% 120 minutes after NE injection, P < 0.0001) and elevated APT (from 1.1% ± 0.5% before NE injection to 2.9% ± 0.5% 120 minutes after NE injection, P < 0.0001) signals in BAT were observed with in vivo Z-spectral MRI in rats injected with NE at 7 T MRI. At clinical 3 T, Z-spectral MRI was used to quantify the FWF (58.5% ± 7.2% in BAT and 73.7% ± 6.5% in WAT with P < 0.0001) and APT (2.6% ± 0.8% in BAT and 0.9% ± 0.3% in WAT with P < 0.0001) signals in healthy volunteers. APT signals of BAT were negatively correlated with the BMI in humans (r = 0.71).

DATA CONCLUSION

Endogenous Z-spectral MRI was demonstrated to simultaneously quantify BAT mass and function based on its FWF and APT contrasts.

LEVEL OF EVIDENCE: 2

TECHNICAL EFFICACY STAGE

1.

Deciphering significances of autophagy in the development and metabolism of adipose tissue

The mechanisms of adipose tissue activation and inactivation have been a hot topic of research in the last decade, from which countermeasures have been attempted to be found against obesity as well as other lipid metabolism-related diseases, such as type 2 diabetes mellitus and non-alcoholic fatty liver disease. Autophagy has been shown to be closely related to the regulation of adipocyte activity, which is involved in the whole process including white adipocyte differentiation/maturation and brown or beige adipocyte generation/activation. Dysregulation of autophagy in adipose tissue has been demonstrated to be associated with obesity. On this basis, we summarize the pathways and mechanisms of autophagy involved in the regulation of lipid metabolism and present a review of its pathophysiological roles in lipid metabolism-related diseases, in the hope of providing ideas for the treatment of these diseases.

Response to Food Restriction, but Not Social Information Use, Varies Seasonally in Captive Cardueline Finches

Temperate winters can impose severe conditions on songbirds that threaten survival, including shorter days and often lower temperatures and food availability. One well-studied mechanism by which songbirds cope with such conditions is seasonal acclimatization of thermal metabolic traits, with strong evidence for both preparative and responsive changes in thermogenic capacity (i.e., the ability to generate heat) to low winter temperatures. However, a bird's ability to cope with seasonal extremes or unpredictable events is likely dependent on a combination of behavioral and physiological traits that function to maintain allostatic balance. The ability to cope with reduced food availability may be an important component of organismal response to temperate winters in songbirds. Here, we compare responses to experimentally reduced food availability at different times of year in captive red crossbills (Loxia curvirostra) and pine siskins (Spinus pinus)-two species that cope with variable food resources and live in cold places-to investigate seasonal changes in the organismal response to food availability. Further, red crossbills are known to use social information to improve responses to reduced food availability, so we also examine whether the use of social information in this context varies seasonally in this species. We find that pine siskins and red crossbills lose less body mass during time-restricted feedings in late winter compared to summer, and that red crossbills further benefit from social information gathered from observing other food-restricted red crossbills in both seasons. Observed changes in body mass were only partially explained by seasonal differences in food intake. Our results demonstrate seasonal acclimation to food stress and social information use across seasons in a controlled captive environment and highlight the importance of considering diverse physiological systems (e.g., thermogenic, metabolic, digestive, etc.) to understand organismal responses to environmental challenges.

Characteristics of T2* and anisotropy parameters in inguinal and epididymal adipose tissues after cold exposure in mice

White adipose tissue (WAT) in mice undergoes browning in response to cold exposure. Brown and beige adipocytes contain multilocular lipid droplets and abundant iron-containing mitochondria expressing uncoupling protein 1 (UCP-1). Cold exposure-induced browning WAT is accompanied by increased density of blood vessels and sympathetic nerve fibres. A previous study reported a more than threefold increase in sympathetic nerve dendritic tone in inguinal white adipose tissue (iWAT) after cold exposure. Therefore, we hypothesized that water molecule diffusion would be more restricted in brown and beige adipocytes compared to white adipocytes. The characteristics of T2* values and anisotropy parameters by diffusion tensor imaging (DTI) in browning WAT are unclear. The aim of the present study was to investigate the effect of cold exposure on T2* values and anisotropy parameters (fractional anisotropy [FA], apparent diffusion coefficient [ADC], radial diffusivity [RD] and eigenvalues λ1, λ2, λ3) in brown adipose tissue (BAT), iWAT and epididymal white adipose tissue (epiWAT). Furthermore, these parameters were investigated in vivo through additional validation experiments in three control mice. Mice in the cold exposure (CE) group were exposed to a cold environment at 4 °C for 10 days, while these in the control (C) group were maintained at 22 °C throughout the experiment. T2* values, FA, ADC, RD and eigenvalues (λ1, λ2, λ3) were measured in BAT, iWAT and epiWAT using a 9.4T magnetic resonance scanner (Bruker Biospin AG). T2* values of epiWAT in the C group were significantly higher than these of BAT in the C group and iWAT in the CE group. No significant differences were observed between groups for FA, ADC, RD, λ1 and λ2 of iWAT and epiWAT. However, the λ3 values of iWAT and epiWAT in the CE group were significantly higher than these of iWAT, epiWAT and BAT in the C group. Compared to ex vivo measurements, in vivo measurements in control mice showed higher T2* values with reduced intertissue variability while maintaining tissue-specific patterns. These results suggest that T2* values and anisotropy parameters might serve as potential markers for the assessment of adipose tissue plasticity. Further studies are required to investigate their utility as non-invasive indicators of browning WAT.

Short-Term Effects of Poly-L-Lactic Acid-b-Polyethylene Glycol Microsphere Injection on Different Adipose Tissue Types in Rats

Background

Wrinkles and sagging, characteristics of aging, are associated with reductions in collagen and fat. Poly-L-lactic acid (PLLA) is widely used clinically as a tissue filler owing to its good biocompatibility and ability to improve wrinkles and signs of aging. Despite extensive studies of the mechanism of action of PLLA when used as a dermal filler, few studies have examined its effects on adipose tissue.

Objectives

The short-term effects of PLLA-b-polyethylene glycol (PEG) microspheres implanted in subcutaneous back adipose tissue (BAT) and visceral epididymal adipose tissue (EAT) of rats were examined.

Methods

The authors divided 15 male Sprague-Dawley rats into 5 groups based on implantation time, and PLLA-b-PEG microspheres were implanted into the BAT (3 groups were sampled at 6, 8, and 12 weeks) and EAT (2 groups were sampled at 6 and 12 weeks) of rats. Tissue samples were collected at different time points postimplantation and subjected to histological analyses using hematoxylin and eosin, Masson's trichrome, and immunofluorescence staining.

Results

Implantation of PLLA-b-PEG microspheres into different adipose tissues resulted in a mild and persistent inflammatory reaction, increased fibrous connective tissue, and noticeable collagen regeneration. Immunofluorescence showed the upregulation of uncoupling protein (UCP) 1 and UCP2 in the visceral adipose tissue surrounding the implant.

Conclusions

PLLA-b-PEG microspheres exhibited good tissue compatibility and induced an increase in fibrous connective tissue postimplantation, potentially mitigating oxidative damage and improving adipose tissue quality.

Level of Evidence 5 Therapeutic

The function of brown adipose tissue at different sites of the body in Brandt's voles during cold acclimation

Ambient temperatures have great impacts on thermoregulation of small mammals. Brown adipose tissue (BAT), an obligative thermogenic tissue for small mammals, is localized not only in the interscapular depot (iBAT), but also in supraclavicular, infra/subscapular, cervical, paravertebral, and periaortic depots. The iBAT is known for its cold-induced thermogenesis, however, less has been paid attention to the function of BAT at other sites. Here, we investigated the function of BAT at different sites of the body during cold acclimation in a small rodent species. As expected, Brandt's voles (Lasiopodomys brandtii) consumed more food and reduced the body mass gain when they were exposed to cold. The voles increased resting metabolic rate and maintained a relatively lower body temperature in the cold (36.5 ± 0.27 °C) compared to those in the warm condition (37.1 ± 0.36 °C). During cold acclimation, the uncoupling protein 1 (UCP1) increased in aBAT (axillary), cBAT (anterior cervical), iBAT (interscapular), nBAT (supraclavicular), and sBAT (suprascapular). The levels of proliferating cell nuclear antigen (PCNA), a marker for cell proliferation, were higher in cBAT and iBAT in the cold than in the warm group. The pAMPK/AMPK and pCREB/CREB were increased in cBAT and iBAT during cold acclimation, respectively. These data indicate that these different sites of BAT play the cold-induced thermogenic function for small mammals.

Non-invasive mapping of brown adipose tissue activity with magnetic resonance imaging

Thermogenic brown adipose tissue (BAT) has a positive impact on whole-body metabolism. However, in vivo mapping of BAT activity typically relies on techniques involving ionizing radiation, such as [18F]fluorodeoxyglucose ([18F]FDG) positron emission tomography (PET) and computed tomography (CT). Here we report a noninvasive metabolic magnetic resonance imaging (MRI) approach based on creatine chemical exchange saturation transfer (Cr-CEST) contrast to assess in vivo BAT activity in rodents and humans. In male rats, a single dose of the β3-adrenoceptor agonist (CL 316,243) or norepinephrine, as well as cold exposure, triggered a robust elevation of the Cr-CEST MRI signal, which was consistent with the [18F]FDG PET and CT data and 1H nuclear magnetic resonance measurements of creatine concentration in BAT. We further show that Cr-CEST MRI detects cold-stimulated BAT activation in humans (both males and females) using a 3T clinical scanner, with data-matching results from [18F]FDG PET and CT measurements. This study establishes Cr-CEST MRI as a promising noninvasive and radiation-free approach for in vivo mapping of BAT activity.

MHO or MUO? White adipose tissue remodeling

In this review, we delve into the intricate relationship between white adipose tissue (WAT) remodeling and metabolic aspects in obesity, with a specific focus on individuals with metabolically healthy obesity (MHO) and metabolically unhealthy obesity (MUO). WAT is a highly heterogeneous, plastic, and dynamically secreting endocrine and immune organ. WAT remodeling plays a crucial role in metabolic health, involving expansion mode, microenvironment, phenotype, and distribution. In individuals with MHO, WAT remodeling is beneficial, reducing ectopic fat deposition and insulin resistance (IR) through mechanisms like increased adipocyte hyperplasia, anti-inflammatory microenvironment, appropriate extracellular matrix (ECM) remodeling, appropriate vascularization, enhanced WAT browning, and subcutaneous adipose tissue (SWAT) deposition. Conversely, for those with MUO, WAT remodeling leads to ectopic fat deposition and IR, causing metabolic dysregulation. This process involves adipocyte hypertrophy, disrupted vascularization, heightened pro-inflammatory microenvironment, enhanced brown adipose tissue (BAT) whitening, and accumulation of visceral adipose tissue (VWAT) deposition. The review underscores the pivotal importance of intervening in WAT remodeling to hinder the transition from MHO to MUO. This insight is valuable for tailoring personalized and effective management strategies for patients with obesity in clinical practice.

Insulin at the intersection of thermoregulation and glucose homeostasis

Mammals are protected from changes in environmental temperature by altering energetic processes that modify heat production. Insulin is the dominant stimulus of glucose uptake and metabolism, which are fundamental for thermogenic processes. The purpose of this work was to determine the interaction of ambient temperature induced changes in energy expenditure (EE) on the insulin sensitivity of glucose fluxes. Short-term and adaptive responses to thermoneutral temperature (TN, ∼28 °C) and room (laboratory) temperature (RT, ∼22 °C) were studied in mice. This range of temperature does not cause detectable changes in circulating catecholamines or shivering and postabsorptive glucose homeostasis is maintained. We tested the hypothesis that a decrease in EE that occurs with TN causes insulin resistance and that this reduction in insulin action and EE is reversed upon short term (<12h) transition to RT. Insulin-stimulated glucose disposal (Rd) and tissue-specific glucose metabolic index were assessed combining isotopic tracers with hyperinsulinemic-euglycemic clamps. EE and insulin-stimulated Rd are both decreased (∼50%) in TN-adapted vs RT-adapted mice. When RT-adapted mice are switched to TN, EE rapidly decreases and Rd is reduced by ∼50%. TN-adapted mice switched to RT exhibit a rapid increase in EE, but whole-body insulin-stimulated Rd remains at the low rates of TN-adapted mice. In contrast, whole body glycolytic flux rose with EE. This higher EE occurs without increasing glucose uptake from the blood, but rather by diverting glucose from glucose storage to glycolysis. In addition to adaptations in insulin action, 'insulin-independent' glucose uptake in brown fat is exquisitely sensitive to thermoregulation. These results show that insulin action adjusts to non-stressful changes in ambient temperature to contribute to the support of body temperature homeostasis without compromising glucose homeostasis.

The Metabolic Syndrome, a Human Disease

This review focuses on the question of metabolic syndrome (MS) being a complex, but essentially monophyletic, galaxy of associated diseases/disorders, or just a syndrome of related but rather independent pathologies. The human nature of MS (its exceptionality in Nature and its close interdependence with human action and evolution) is presented and discussed. The text also describes the close interdependence of its components, with special emphasis on the description of their interrelations (including their syndromic development and recruitment), as well as their consequences upon energy handling and partition. The main theories on MS's origin and development are presented in relation to hepatic steatosis, type 2 diabetes, and obesity, but encompass most of the MS components described so far. The differential effects of sex and its biological consequences are considered under the light of human social needs and evolution, which are also directly related to MS epidemiology, severity, and relations with senescence. The triggering and maintenance factors of MS are discussed, with especial emphasis on inflammation, a complex process affecting different levels of organization and which is a critical element for MS development. Inflammation is also related to the operation of connective tissue (including the adipose organ) and the widely studied and acknowledged influence of diet. The role of diet composition, including the transcendence of the anaplerotic maintenance of the Krebs cycle from dietary amino acid supply (and its timing), is developed in the context of testosterone and β-estradiol control of the insulin-glycaemia hepatic core system of carbohydrate-triacylglycerol energy handling. The high probability of MS acting as a unique complex biological control system (essentially monophyletic) is presented, together with additional perspectives/considerations on the treatment of this 'very' human disease.

Intestinal mucosal microbiota mediate amino acid metabolism involved in the gastrointestinal adaptability to cold and humid environmental stress in mice

Growing evidence has demonstrated that cold and humid environmental stress triggers gastrointestinal (GI) disorders. In this study, we explored the effects of intestinal microbiota homeostasis on the intestinal mucus barrier and GI disorders by cold and humid environmental stress. Moreover, the inner link between the intestinal mucosal microbiota and metabolites in mice with cold and humid environmental stress was interpreted by integrative analysis of PacBio HiFi sequencing microbial genomics and targeted metabolomics. In the current study, we found (1) after the cold and wet cold and humid environmental stress intervened in the intestinal microbiota disorder and homeostasis mice respectively, the bacterial culturing and fluorescein diacetate (FDA) microbial activity detection of intestinal microbiota including feces, intestinal contents, and intestinal mucosa suggested that the cold and humid environmental stress decreased the colony of culturable bacteria and microbial activity, in which intestinal microbiota disorder aggravated the injury of the intestinal mucus barrier and the GI symptoms related to cold and humid environmental stress; (2) the serum amino acid transferases such as glutamate pyruvic transa (GPT), and glutamic oxaloacetic transaminase (GOT) in cold and humid environmental stressed mice increased significantly, indicating that the intestinal microbiota adapted to cold and humid environmental stress by regulating the host's amino acid metabolism; (3) the integrative analysis of multi-omics illustrated a prediction model based on the microbiota Lactobacillus reuteri abundance and host amino acid level that can predict intestinal mucoprotein Muc2 with an adjusted R2 of 75.0%. In conclusion, the cold and humid environmental stress regulates the neurotransmitter amino acids metabolic function both in intestinal mucosal microbiota and host serum by adjusting the composition of the dominant bacterial population Lactobacillus reuteri, which contributes to the intestinal mucus barrier injury and GI disorders caused by cold and humid environmental stress.

SGLT2 inhibitor improves the prognosis of patients with coronary heart disease and prevents in-stent restenosis

Coronary heart disease is a narrowing or obstruction of the vascular cavity caused by atherosclerosis of the coronary arteries, which leads to myocardial ischemia and hypoxia. At present, percutaneous coronary intervention (PCI) is an effective treatment for coronary atherosclerotic heart disease. Restenosis is the main limiting factor of the long-term success of PCI, and it is also a difficult problem in the field of intervention. Sodium-glucose cotransporter 2 (SGLT2) inhibitor is a new oral glucose-lowering agent used in the treatment of diabetes in recent years. Recent studies have shown that SGLT2 inhibitors can effectively improve the prognosis of patients after PCI and reduce the occurrence of restenosis. This review provides an overview of the clinical studies and mechanisms of SGLT2 inhibitors in the prevention of restenosis, providing a new option for improving the clinical prognosis of patients after PCI.

Cancer cachexia: Focus on cachexia factors and inter-organ communication

ABSTRACT

Cancer cachexia is a multi-organ syndrome and closely related to changes in signal communication between organs, which is mediated by cancer cachexia factors. Cancer cachexia factors, being the general name of inflammatory factors, circulating proteins, metabolites, and microRNA secreted by tumor or host cells, play a role in secretory or other organs and mediate complex signal communication between organs during cancer cachexia. Cancer cachexia factors are also a potential target for the diagnosis and treatment. The pathogenesis of cachexia is unclear and no clear effective treatment is available. Thus, the treatment of cancer cachexia from the perspective of the tumor ecosystem rather than from the perspective of a single molecule and a single organ is urgently needed. From the point of signal communication between organs mediated by cancer cachexia factors, finding a deeper understanding of the pathogenesis, diagnosis, and treatment of cancer cachexia is of great significance to improve the level of diagnosis and treatment. This review begins with cancer cachexia factors released during the interaction between tumor and host cells, and provides a comprehensive summary of the pathogenesis, diagnosis, and treatment for cancer cachexia, along with a particular sight on multi-organ signal communication mediated by cancer cachexia factors. This summary aims to deepen medical community's understanding of cancer cachexia and may conduce to the discovery of new diagnostic and therapeutic targets for cancer cachexia.

Brown adipose tissue but not tibia exhibits a dramatic response to acute reduction in environmental temperature in growing male mice

Mice are typically housed at room temperature (∼22 °C), which is well below their thermoneutral zone and results in cold stress. Chronic cold stress leads to increased adaptive thermogenesis and reductions in cancellous bone volume and bone marrow adipose tissue mass in long bones of growing mice. There is strong evidence that increased neuronal activity initiates the metabolic response of intrascapular brown adipose tissue (BAT) to cold stress, but it is less clear whether bone is regulated through a similar mechanism. Therefore, we compared the short-term response of BAT and whole tibia to a reduction in environmental temperature. To accomplish this, we transferred a group of 6-week-old male mice from 32 °C to 22 °C housing and sacrificed the mice 24 h later. Age-matched controls were maintained at 32 °C. We then evaluated expression levels of a panel of genes related to adipocyte differentiation and fat metabolism in BAT and tibia, and a panel of genes related to bone metabolism in tibia. The decrease in housing temperature resulted in changes in expression levels for 47/86 genes related to adipocyte differentiation and fat metabolism in BAT, including 9-fold and 17-fold increases in Ucp1 and Dio2, respectively. In contrast, only 1/86 genes related to adipocyte differentiation and fat metabolism and 4/84 genes related to bone metabolism were differentially expressed in tibia. These findings suggest that bone, although innervated with sensory and sympathetic neurons, does not respond as rapidly as BAT to changes in environmental temperature.

Insulin at the Intersection of Thermoregulation and Glucose Homeostasis

Mammals are protected from changes in environmental temperature by altering energetic processes that modify heat production. Insulin is the dominant stimulus of glucose uptake and metabolism, which are fundamental for thermogenic processes. The purpose of this work was to determine the interaction of ambient temperature induced changes in energy expenditure (EE) on the insulin sensitivity of glucose fluxes. Short-term and adaptive responses to thermoneutral temperature (TN, ~28°C) and room (laboratory) temperature (RT, ~22°C) were studied in mice. This range of temperature does not cause detectable changes in circulating catecholamines or shivering and postabsorptive glucose homeostasis is maintained. We tested the hypothesis that a decrease in EE that occurs with TN causes insulin resistance and that this reduction in insulin action and EE is reversed upon short term (<12h) transition to RT. Insulin-stimulated glucose disposal (Rd) and tissue specific glucose uptake were assessed combining isotopic tracers with hyperinsulinemic-euglycemic clamps. EE and insulin-stimulated Rd are both decreased (~50%) in TN-adapted vs RT-adapted mice. When RT-adapted mice are switched to TN, EE rapidly decreases and Rd is reduced by ~50%. TN-adapted mice switched to RT exhibit a rapid increase in EE, but whole body insulin-stimulated Rd remains at the low rates of TN-adapted mice. In contrast, whole body glycolytic flux rose with EE. This higher EE occurs without increasing glucose uptake from the blood, but rather by diverting glucose from glucose storage to glycolysis. In addition to adaptations in insulin action, 'insulin-independent' glucose uptake in brown fat is exquisitely sensitive to thermoregulation. These results show that insulin action adjusts to non-stressful changes in ambient temperature to contribute to the support of body temperature homeostasis without compromising glucose homeostasis.

Progress in the contrary effects of glucagon-like peptide-1 and chemerin on obesity development

Glucagon-like peptide-1 (GLP-1), secreted by intestinal L-cells, plays a pivotal role in the modulation of β-cell insulin secretion in a glucose-dependent manner, concurrently promoting β-cell survival and β-cell mass. Notably, GLP-1 has emerged as an effective second-line treatment for type 2 diabetes mellitus, gaining further prominence for its pronounced impact on body weight reduction, positioning it as a potent antiobesity agent. However, the mechanism by which GLP-1 improves obesity remains unclear. Some reports suggest that this mechanism may be associated with the regulation of adipokine synthesis within adipose tissue. Chemerin, a multifunctional adipokine and chemokine, has been identified as a pivotal player in adipocyte differentiation and the propagation of systemic inflammation, a hallmark of obesity. This review provides a comprehensive overview of the mechanisms by which GLP-1 and chemerin play crucial roles in obesity and obesity-related diseases. It discusses well-established aspects, such as their effects on food intake and glycolipid metabolism, as well as recent insights, including their influence on macrophage polarization and adipose tissue thermogenesis. GLP-1 has been shown to increase the population of anti-inflammatory M2 macrophages, promote brown adipose tissue thermogenesis, and induce the browning of white adipose tissue. In contrast, chemerin exhibits opposite effects in these processes. In addition, recent research findings have demonstrated the promising potential of GLP-1-based therapies in directly or indirectly regulating chemerin expression. In an intriguing reciprocal relationship, chemerin has also been newly identified as a negative regulator of GLP-1 in vivo. This review delineates the intricate interplay between GLP-1 and chemerin, unraveling their mutual inhibitory interactions. To the best of our knowledge, no previous reviews have focused on this specific topic, making this review particularly valuable in expanding our understanding of the endocrine mechanisms of obesity and providing potential strategies for the treatment of obesity and related diseases.

Mother's warmth from maternal genes: genomic imprinting of brown adipose tissue

Background and objectives

Brown adipose tissue (BAT) plays key roles in mammalian physiology, most notably with regard to thermoregulation in infants and juveniles. Previous studies have suggested that intragenomic conflict, in the form of genomic imprinting, mediates BAT thermogenesis, because it represents a public good for groups of siblings, or a mother with her offspring, who huddle together to conserve warmth. By this hypothesis, maternally expressed imprinted genes should promote BAT, while paternally expressed genes should repress it.

Methodology

We systematically searched the literature using two curated lists of genes imprinted in humans and/or mice, in association with evidence regarding effects of perturbation to imprinted gene expression on BAT development or activity.

Results

Overall, enhanced BAT was associated with relatively higher expression of maternally expressed imprinted genes, and relatively lower expression of paternally expressed imprinted genes; this pattern was found for 16 of the 19 genes with sufficient information for robust ascertainment (Binomial test, P < 0.005, 2-tailed).

Conclusions and implications

These results support the kinship theory of imprinting and indicate that future studies of BAT, and its roles in human health and disease, may usefully focus on effects of imprinted genes and associated genomic conflicts.

The Role of Brown Adipose Tissue and Energy Metabolism in Mammalian Thermoregulation during the Perinatal Period

Hypothermia is one of the most common causes of mortality in neonates, and it could be developed after birth because the uterus temperature is more elevated than the extrauterine temperature. Neonates use diverse mechanisms to thermoregulate, such as shivering and non-shivering thermogenesis. These strategies can be more efficient in some species, but not in others, i.e., altricials, which have the greatest difficulty with achieving thermoneutrality. In addition, there are anatomical and neurological differences in mammals, which may present different distributions and amounts of brown fat. This article aims to discuss the neuromodulation mechanisms of thermoregulation and the importance of brown fat in the thermogenesis of newborn mammals, emphasizing the analysis of the biochemical, physiological, and genetic factors that determine the distribution, amount, and efficiency of this energy resource in newborns of different species. It has been concluded that is vital to understand and minimize hypothermia causes in newborns, which is one of the main causes of mortality in neonates. This would be beneficial for both animals and producers.

Proline hydroxylase 2 (PHD2) promotes brown adipose thermogenesis by enhancing the hydroxylation of UCP1

OBJECTIVE

Brown adipose tissue (BAT) plays a crucial role in regulating non-shivering thermogenesis under cold exposure. Proline hydroxylases (PHDs) were found to be involved in adipocyte differentiation and lipid deposition. However, the effects of PHDs on regulatory mechanisms of BAT thermogenesis are not fully understood.

METHODS

We detected the expression of PHDs in different adipose tissues by using immunoblotting and real-time PCR. Further, immunoblotting, real-time PCR, and immunostaining were performed to determine the correlation between proline hydroxylase 2 (PHD2) and UCP1 expression. Inhibitor of PHDs and PHD2-sgRNA viruses were used to construct the PHD2-deficiency model in vivo and in vitro to investigate the impacts of PHD2 on BAT thermogenesis. Afterward, the interaction between UCP1 and PHD2 and the hydroxylation modification level of UCP1 were verified by Co-IP assays and immunoblotting. Finally, the effect of specific proline hydroxylation on the expression/activity of UCP1 was further confirmed by site-directed mutation of UCP1 and mass spectrometry analysis.

RESULTS

PHD2, but not PHD1 and PHD3, was highly enriched in BAT, colocalized, and positively correlated with UCP1. Inhibition or knockdown of PHD2 significantly suppressed BAT thermogenesis under cold exposure and aggravated obesity of mice fed HFD. Mechanistically, mitochondrial PHD2 bound to UCP1 and regulated the hydroxylation level of UCP1, which was enhanced by thermogenic activation and attenuated by PHD2 knockdown. Furthermore, PHD2-dependent hydroxylation of UCP1 promoted the expression and stability of UCP1 protein. Mutation of the specific prolines (Pro-33, 133, and 232) in UCP1 significantly mitigated the PHD2-elevated UCP1 hydroxylation level and reversed the PHD2-increased UCP1 stability.

CONCLUSIONS

This study suggested an important role for PHD2 in BAT thermogenesis regulation by enhancing the hydroxylation of UCP1.

Progress and obstacles in transplantation of brown adipose tissue or engineered cells with thermogenic potential for metabolic benefits

Transplantation of brown adipose tissue (BAT), engineered thermogenic progenitor cells, and adipocytes have received much attention for the improvement of obesity and metabolic disorders. However, even though the thermogenic and metabolic potential exists early after transplantation, the whitening of the brown fat graft occurs with metabolic function significantly impaired. In this review, specific experiment designs, graft outcomes, and metabolic benefits for the transplantation of BAT or engineered cells will be discussed. The current advancements will offer guidance to further investigation, and the obstacles appearing in previous studies will require innovation of BAT transplantation methods.

Effects of Essential Oils and Fragrant Compounds on Appetite: A Systematic Review

Appetite dysregulation is one of the factors contributing to anorexia, bulimia nervosa, obesity, and diabetes. Essential oils or fragrant compounds have been proven to regulate food intake and energy expenditure; hence, this study aimed to summarize their effects on appetite and the underlying mechanisms. The PubMed and Web of Science databases were searched until July 2022. Only two of the 41 studies were performed clinically, and the remaining 39 used animal models. Oral administration was the most common route, and a dosage range of 100-2000 mg/kg for mice or 2-32 mg/kg for rats was applied, with a duration of 12 days to 4 weeks, followed by inhalation (10^-6-10^-3 mg/cage or 10^-9-10^-2 mg/cm³ within 1 h). Approximately 11 essential oil samples and 22 fragrant compounds were found to increase appetite, while 12 essential oils and seven compounds decreased appetite. These fragrant components can exert appetite-regulating effects via leptin resistance, the activity of sympathetic/parasympathetic nerves, or the mRNA expression of neuropeptide Y (NPY)/agouti-related protein (AgRP), cocaine- and amphetamine-regulated transcript (CART)/proopiomelanocortin (POMC) in the hypothalamus. Fragrance memory and cognitive processes may also play roles in appetite regulation. The findings of this study accentuate the potential of essential oils and fragrant compounds to regulate appetite and eating disorders.

Nicotinamide mononucleotide alters body composition and ameliorates metabolic disorders induced by a high-fat diet

Obesity is caused by an imbalance between calorie intake and energy expenditure, leading to excessive adipose tissue accumulation. Nicotinamide adenine dinucleotide (NAD⁺ ) is an important molecule in energy and signal transduction, and NAD⁺ supplementation therapy is a new treatment for obesity in recent years. Liver kinase B1 (LKB1) is an energy metabolism regulator. The relationship between NAD⁺ and LKB1 has only been studied in the heart and has not yet been reported in obesity. Nicotinamide mononucleotide (NMN), as a direct precursor of NAD⁺ , can effectively enhance the level of NAD⁺ . In the current study, we showed that NMN intervention altered body composition in obese mice, characterized by a reduction in fat mass and an increase in lean mass. NMN reversed high-fat diet-induced blood lipid levels then contributed to reducing hepatic steatosis. NMN also improved glucose tolerance and alleviated adipose tissue inflammation. Moreover, our data suggested that NMN supplementation may be depends on the NAD⁺ /SIRT6/LKB1 pathway to regulate brown adipose metabolism. These results provided new evidence for NMN in obesity treatment.

Astragalus polysaccharide prevents heart failure-induced cachexia by alleviating excessive adipose expenditure in white and brown adipose tissue

BACKGROUND

Astragalus polysaccharide (APS) is a key active ingredient isolated from Astragalus membranaceus that has been reported to be a potential treatment for obesity and diabetes by regulating lipid metabolism and adipogenesis, alleviating inflammation, and improving insulin resistance. However, whether APS regulates lipid metabolism in the context of cachexia remains unclear. Therefore, this study analysed the effects of APS on lipid metabolism and adipose expenditure in a heart failure (HF)-induced cardiac cachexia rat model.  METHODS: A salt-sensitive hypertension-induced cardiac cachexia rat model was used in the present study. Cardiac function was detected by echocardiography. The histological features and fat droplets in fat tissue and liver were observed by H&E staining and Oil O Red staining. Immunohistochemical staining, Western blotting and RT‒qPCR were used to detect markers of lipolysis and adipose browning in white adipose tissue (WAT) and thermogenesis in brown adipose tissue (BAT). Additionally, sympathetic nerve activity and inflammation in adipose tissue were detected.

RESULTS

Rats with HF exhibited decreased cardiac function and reduced adipose accumulation as well as adipocyte atrophy. In contrast, administration of APS not only improved cardiac function and increased adipose weight but also prevented adipose atrophy and FFA efflux in HF-induced cachexia. Moreover, APS inhibited HF-induced lipolysis and browning of white adipocytes since the expression levels of lipid droplet enzymes, including HSL and perilipin, and beige adipocyte markers, including UCP-1, Cd137 and Zic-1, were suppressed after administration of APS. In BAT, treatment with APS inhibited PKA-p38 MAPK signalling, and these effects were accompanied by decreased thermogenesis reflected by decreased expression of UCP-1, PPAR-γ and PGC-1α and reduced FFA β-oxidation in mitochondria reflected by decreased Cd36, Fatp-1 and Cpt1. Moreover, sympathetic nerve activity and interleukin-6 levels were abnormally elevated in HF rats, and astragalus polysaccharide could inhibit their activity.

CONCLUSION

APS prevented lipolysis and adipose browning in WAT and decreased BAT thermogenesis. These effects may be related to suppressed sympathetic activity and inflammation. This study provides a potential approach to treat HF-induced cardiac cachexia.

Regulatory role of atrial natriuretic peptide in brown adipose tissue: A narrative review

Atrial natriuretic peptide (ANP) has been considered to exert an essential role as a cardiac secretory hormone in the regulation of hemodynamic homeostasis. As the research progresses, the role of ANP in the crosstalk between heart and lipid metabolism has become an interesting topic that is attracting the interest of researchers. The regulation of ANP in lipid metabolism shows favorable effects, particularly the activation of brown adipose tissue (BAT). The complex regulatory network of ANP on BAT has not been fully outlined. This narrative review critically evaluated the existing literature on the regulatory effects of ANP on BAT. In general, we have summarized the expression of ANP and its receptors in various human tissues, analyzed the progress of research on the relationship between the ANP and BAT, and described several potential pathways of ANP to BAT. Exogenous ANP, natriuretic peptide receptor C (NPRC) deficiency, cold exposure, bariatric surgery, and cardiac or renal insufficiency could all contribute to BAT expression by increasing circulating ANP levels.

A Review of Structural Features, Biological Functions and Biotransformation Studies in Adipose Tissues and an Assessment of Progress and Implications

Roles for adipose tissues in energy metabolism, health maintenance and disease onset have been established. Evidence indicates that white, brown and beige fats are quite different in terms of their cellular origin and biological characteristics. These differences are significant in targeting adipocytes to study the pathogenesis and prevention strategies of related diseases. The biotransformations of white, brown and beige fat cells constitute an intriguing topic worthy of further study, and the molecular mechanisms underlying the biotransformations of white, brown and beige fat cells remain to be elucidated. Hence, we herein collected evidence from studies on adipose tissue or adipocytes, and we extracted the structural features, biologic functions, and biotransformations of adipose tissue/adipocytes. The present review aimed to summarize the latest research progress and propose novel research directions with respect to adipose tissue and adipocytes. We posit that this work will provide new insights and opportunities in the effective treatment strategies for obesity, diabetes and other lipid-related diseases. It will also contribute to our knowledge of the basic biologic underpinnings of adipocyte biology.

The evolving view of thermogenic fat and its implications in cancer and metabolic diseases

The incidence of metabolism-related diseases like obesity and type 2 diabetes mellitus has reached pandemic levels worldwide and increased gradually. Most of them are listed on the table of high-risk factors for malignancy, and metabolic disorders systematically or locally contribute to cancer progression and poor prognosis of patients. Importantly, adipose tissue is fundamental to the occurrence and development of these metabolic disorders. White adipose tissue stores excessive energy, while thermogenic fat including brown and beige adipose tissue dissipates energy to generate heat. In addition to thermogenesis, beige and brown adipocytes also function as dynamic secretory cells and a metabolic sink of nutrients, like glucose, fatty acids, and amino acids. Accordingly, strategies that activate and expand thermogenic adipose tissue offer therapeutic promise to combat overweight, diabetes, and other metabolic disorders through increasing energy expenditure and enhancing glucose tolerance. With a better understanding of its origins and biological functions and the advances in imaging techniques detecting thermogenesis, the roles of thermogenic adipose tissue in tumors have been revealed gradually. On the one hand, enhanced browning of subcutaneous fatty tissue results in weight loss and cancer-associated cachexia. On the other hand, locally activated thermogenic adipocytes in the tumor microenvironment accelerate cancer progression by offering fuel sources and is likely to develop resistance to chemotherapy. Here, we enumerate current knowledge about the significant advances made in the origin and physiological functions of thermogenic fat. In addition, we discuss the multiple roles of thermogenic adipocytes in different tumors. Ultimately, we summarize imaging technologies for identifying thermogenic adipose tissue and pharmacologic agents via modulating thermogenesis in preclinical experiments and clinical trials.

Browning of the white adipose tissue regulation: new insights into nutritional and metabolic relevance in health and diseases

Adipose tissues are dynamic tissues that play crucial physiological roles in maintaining health and homeostasis. Although white adipose tissue and brown adipose tissue are currently considered key endocrine organs, they differ functionally and morphologically. The existence of the beige or brite adipocytes, cells displaying intermediary characteristics between white and brown adipocytes, illustrates the plastic nature of the adipose tissue. These cells are generated through white adipose tissue browning, a process associated with augmented non-shivering thermogenesis and metabolic capacity. This process involves the upregulation of the uncoupling protein 1, a molecule that uncouples the respiratory chain from Adenosine triphosphate synthesis, producing heat. β-3 adrenergic receptor system is one important mediator of white adipose tissue browning, during cold exposure. Surprisingly, hyperthermia may also induce beige activation and white adipose tissue beiging. Physical exercising copes with increased levels of specific molecules, including Beta-Aminoisobutyric acid, irisin, and Fibroblast growth factor 21 (FGF21), which induce adipose tissue browning. FGF21 is a stress-responsive hormone that interacts with beta-klotho. The central roles played by hormones in the browning process highlight the relevance of the individual lifestyle, including circadian rhythm and diet. Circadian rhythm involves the sleep-wake cycle and is regulated by melatonin, a hormone associated with UCP1 level upregulation. In contrast to the pro-inflammatory and adipose tissue disrupting effects of the western diet, specific food items, including capsaicin and n-3 polyunsaturated fatty acids, and dietary interventions such as calorie restriction and intermittent fasting, favor white adipose tissue browning and metabolic efficiency. The intestinal microbiome has also been pictured as a key factor in regulating white tissue browning, as it modulates bile acid levels, important molecules for the thermogenic program activation. During embryogenesis, in which adipose tissue formation is affected by Bone morphogenetic proteins that regulate gene expression, the stimuli herein discussed influence an orchestra of gene expression regulators, including a plethora of transcription factors, and chromatin remodeling enzymes, and non-coding RNAs. Considering the detrimental effects of adipose tissue browning and the disparities between adipose tissue characteristics in mice and humans, further efforts will benefit a better understanding of adipose tissue plasticity biology and its applicability to managing the overwhelming burden of several chronic diseases.

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.

Thyroid Hormone Abuse in Elite Sports: The Regulatory Challenge

Abuse of androgens and erythropoietin has led to hormones being the most effective and frequent class of ergogenic substances prohibited in elite sports by the World Anti-Doping Agency (WADA). At present, thyroid hormone (TH) abuse is not prohibited, but its prevalence among elite athletes and nonprohibited status remains controversial. A corollary of prohibiting hormones for elite sports is that endocrinologists must be aware of a professional athlete's risk of disqualification for using prohibited hormones and/or to certify Therapeutic Use Exemptions, which allow individual athletes to use prohibited substances for valid medical indications. This narrative review considers the status of TH within the framework of the WADA Code criteria for prohibiting substances, which requires meeting 2 of 3 equally important criteria of potential performance enhancement, harmfulness to health, and violation of the spirit of sport. In considering the valid clinical uses of TH, the prevalence of TH use among young adults, the reason why some athletes seek to use TH, and the pathophysiology of sought-after and adverse effects of TH abuse, together with the challenges of detecting TH abuse, it can be concluded that, on the basis of present data, prohibition of TH in elite sport is neither justified nor feasible.

Effects of ambient temperatures between 5 and 35 oC on energy balance, body mass and body composition in mice

Background

Considerable attention is currently focused on the potential to switch on brown adipose tissue (BAT), or promote browning of white adipose tissue, to elevate energy expenditure and thereby reduce obesity levels. These processes are already known to be switched on by cold exposure. Yet humans living in colder regions do not show lower levels of obesity. This could be because humans shield themselves from external temperatures, or because the resultant changes in BAT and thermogenesis are offset by elevated food intake, or reductions in other components of expenditure.

Scope of Review

We exposed mice to 11 different ambient temperatures between 5 and 35 °C and characterized their energy balance and body weight/composition. As it got colder mice progressively increased their energy expenditure coincident with changes in thyroid hormone levels and increased BAT activity. Simultaneously, these increases in expenditure were matched by elevated food intake, and body mass remained stable. Nevertheless, within this envelope of unchanged body mass there were significant changes in body composition – with increases in the sizes of the liver and small intestine, presumably to support the greater food intake, and reductions in the level of stored fat – maximally providing about 10% of the total elevated energy demands.

Major Conclusions

Elevating activity of BAT may be a valid strategy to reduce fat storage even if overall body mass is unchanged but if it is mostly offset by elevated food intake, as found here, then the impacts may be small.

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Male and female mice were exposed to 11 different ambient temperatures between 5 and 35 °C.

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As it got colder mice increased both energy expenditure and food intake.

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Increased energy expenditure was coincident with increased THs and BAT activity.

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Stored fat was considerably reduced in colder conditions, providing about 10% of the elevated energy requirements.

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Elevating activity of BAT may be a valid strategy to reduce fat storage.

Brown adipose tissue activation by ginsenoside compound K treatment ameliorates polycystic ovary syndrome

BACKGROUND AND PURPOSE

Polycystic ovary syndrome (PCOS) is a common metabolic and endocrine disease affecting women of reproductive age. Due to its complex etiology, there is no effective cure for PCOS currently. Brown adipose tissue (BAT) activity is significantly decreased in PCOS patients and BAT activation has beneficial effects on PCOS animal models. Here, we investigated the therapeutic effect of ginsenoside compound K (CK) on an animal model of PCOS and its mechanism of BAT activation EXPERIMENTAL APPROACH: Primary brown adipocyte, Db/Db mice and dehydroepiandrosterone (DHEA)-induced PCOS rats were used. The core body temperature, oxygen consumption, energy metabolism related gene and protein expression were assessed to identify the function of CK on energy metabolism. Estrous cycle, serum sex hormone, ovarian steroidogenic enzyme gene expression and ovarian morphology were evaluated following CK treatment.

KEY RESULTS

Our results indicated that CK treatment could significantly protect against body weight gain in Db/Db mice via BAT activation. Furthermore, we found that CK treatment could normalize hyperandrogenism, estrous cyclicity, normalize steroidogenic enzyme expression and decrease the number of cystic follicles in PCOS rats. Interestingly, as a potential endocrine intermediate, C-X-C motif chemokine ligand-14 protein (CXCL14) was significantly upregulated following CK administration. In addition, exogenous CXC14 supplementation was found to reverse DHEA-induced PCOS in a phenotypically similar manner to CK treatment.

CONCLUSION AND IMPLICATIONS

In summary, CK treatment significantly activates BAT, increases CXCL14 expression and ameliorates PCOS. These findings suggest that CK might be a potential drug candidate for PCOS treatment.

p53 Regulates a miRNA-Fructose Transporter Axis in Brown Adipose Tissue Under Fasting

Active thermogenic adipocytes avidly consume energy substrates like fatty acids and glucose to maintain body temperature upon cold exposure. Despite strong evidence for the involvement of brown adipose tissue (BAT) in controlling systemic energy homeostasis upon nutrient excess, it is unclear how the activity of brown adipocytes is regulated in times of nutrient scarcity. Therefore, this study aimed to scrutinize factors that modulate BAT activity to balance thermogenic and energetic needs upon simultaneous fasting and cold stress. For an unbiased view, we performed transcriptomic and miRNA sequencing analyses of BAT from acutely fasted (24 h) mice under mild cold exposure. Combining these data with in-depth bioinformatic analyses and in vitro gain-of-function experiments, we define a previously undescribed axis of p53 inducing miR-92a-1-5p transcription that is highly upregulated by fasting in thermogenic adipocytes. p53, a fasting-responsive transcription factor, was previously shown to control genes involved in the thermogenic program and miR-92a-1-5p was found to negatively correlate with human BAT activity. Here, we identify fructose transporter Slc2a5 as one direct downstream target of this axis and show that fructose can be taken up by and metabolized in brown adipocytes. In sum, this study delineates a fasting-induced pathway involving p53 that transactivates miR-92a-1-5p, which in turn decreases Slc2a5 expression, and suggests fructose as an energy substrate in thermogenic adipocytes.

Smilax china Polyphenols Stimulate Browning via [Formula: see text]3-Adrenergic Receptor/AMP-Activated Protein Kinase [Formula: see text] Signaling Pathway in 3T3-L1 Adipocytes

The aim of this study is to investigate the molecular mechanism of Smilax china L. polyphenols (SCLPs) in enhancing lipid metabolism and stimulating browning to reduce lipid accumulation in 3T3-L1 adipocytes. SCLP treatment obviously decreased lipid content in a dose-dependent manner (10-40 μg/mL) in adipocytes. SCLP treatment cooperated with noradrenalin to increase lipolysis. SCLPs reduced the gene expressions of C/EBP[Formula: see text] and Ap2 and enhanced the expressions of ACO, CPT, pHSL/HSL, ATGL, and PKA in adipocytes. Furthermore, SCLPs increased mRNA and protein expressions of brown adipocyte-specific factors (UCP-1, PRDM16, PGC-1α, and PPARγ) and mRNA expressions of beige adipocyte-specific markers (CD137, Tbx1, and Tmem26) in 3T3-L1 adipocytes, as well as mitochondrial biogenesis genes (Nrf1 and Tfam). In addition, according to the immunofluorescence staining, the mitochondria number was increased by SCLP. Moreover, β3-AR or AMPK agonist synergistic SCLPs enhanced the expressions of UCP-1, PRDM16, and PGC-1α. While β3-AR or AMPK antagonist significantly decreased the expressions of these brown adipocyte-specific factors, SCLP treatment inhibited the effect of antagonist to improve the expression of UCP-1, PRDM16, and PGC-1α. These results indicated that SCLPs may regulate lipid metabolism and stimulate browning via the β3-AR/AMPKα signaling pathway. Thus, SCLPs likely have potential therapeutic effects on obesity.

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.

Cold exposure prevents fat accumulation in striped hamsters refed a high-fat diet following food restriction

Background

In mammals, body mass lost during food restriction is often rapidly regained, and fat is accumulated when ad libitum feeding is resumed. Studies in small cold-acclimated mammals have demonstrated significant mobilization of fat deposits during cold exposure to meet the energy requirements of metabolic thermogenesis. However, no studies to our knowledge have examined the effect of cold exposure on fat accumulation during body mass recovery when refed ad libitum. In this study, striped hamsters restricted to 80% of their regular food intake were then refed ad libitum and exposed to one of three conditions: Intermittent cold temperature (5 °C) for 2 h per day (ICE-2 h/d), intermittent cold temperature (5 °C) for 12 h per day (ICE-12 h/d), or persistent cold exposure (PCE) for four weeks. We measured energy intake, fat deposit mass, serum thyroid hormone levels, and uncoupling protein 1 expression in brown adipose tissue.

Results

There was no significant effect of intermittent or persistent cold exposure on body mass regain, whereas energy intake increased significantly and total fat deposit decreased in the ICE-12 h/d and PCE groups compared to the ICE-2 h/d group and control group maintained at 23 °C (CON). In the ICE-12 h/d and PCE groups, hamsters had 39.6 and 38.3% higher serum 3,3′,5-triiodothyronine levels, respectively, and 81.6 and 71.3% up-regulated expression of uncoupling protein 1, respectively, in brown adipose tissue compared to their counterparts in the CON group. The rate of mitochondrial state III and state IV respiration O2 consumption and the activity of cytochrome c oxidase in BAT and liver were significantly higher in the ICE-12 h/d and PCE groups than in the ICE-2 h/d and CON groups.

Conclusions

Our findings suggest thyroid hormone-mediated heat production in brown adipose tissue and liver may be involved in preventing fat accumulation during refeeding in animals frequently or persistently exposed to cold conditions.

Three-dimensional visualization of electroacupuncture-induced activation of brown adipose tissue via sympathetic innervation in PCOS rats

Background

Low-frequency electroacupuncture (EA) has been shown to ameliorate obesity and reproductive dysfunctions in patients with polycystic ovary syndrome (PCOS), and further explorations in PCOS-like rats showed that EA could affect white adipose tissue. However, the function and neuromodulation of brown adipose tissue (BAT) in PCOS and after EA treatment have remained unknown. The present study focused on the role of BAT in PCOS-like rats and its relationship with EA and characterized the three-dimensional (3D) innervation of BAT associated with activation molecules.

Methods

Female rats (21 days old) were implanted with dihydrotestosterone or fed with a high fat diet to establish PCOS-like and obesity models, respectively, and then EA treatment at “Guilai” (ST 29) and “Sanyinjiao” (SP 6) was carried out for 4 weeks. In the present study, morphological analysis, 3D imaging, molecular biology, and other experimental techniques were used to study the sympathetic nerves and activity of BAT.

Results

PCOS-like rats showed both obvious weight gain and reproductive dysfunction, similar to what was seen in obese rats except for the absence of reproductive dysfunction. The body weight gain was mainly caused by an increase in white adipose tissue, and there was an abnormal decrease in BAT. Because both the lipid metabolism and reproductive disorders could be improved with bilateral EA at “Guilai” (ST 29) and “Sanyinjiao” (SP 6), especially the restoration of BAT, we further investigated the neuromodulation and inflammation in BAT and identified the sympathetic marker tyrosine hydroxylase as one of the key factors of sympathetic nerves. Modified adipo-clearing technology and 3D high-resolution imaging showed that crooked or dispersed sympathetic nerves, but not the twisted vasculature, were reconstructed and associated with the activation of BAT and are likely to be the functional target for EA treatment.

Conclusion

Our study highlights the significant role of BAT and its sympathetic innervations in PCOS and in EA therapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13020-022-00603-w.

Impacts of essential amino acids on energy balance

BACKGROUND

Obesity develops due to an imbalance in energy homeostasis, wherein energy intake exceeds energy expenditure. Accumulating evidence shows that manipulations of dietary protein and their component amino acids affect the energy balance, resulting in changes in fat mass and body weight. Amino acids are not only the building blocks of proteins but also serve as signals regulating multiple biological pathways.

SCOPE OF REVIEW

We present the currently available evidence regarding the effects of dietary alterations of a single essential amino acid (EAA) on energy balance and relevant signaling mechanisms at both central and peripheral levels. We summarize the association between EAAs and obesity in humans and the clinical use of modifying the dietary EAA composition for therapeutic intervention in obesity. Finally, similar mechanisms underlying diets varying in protein levels and diets altered of a single EAA are described. The current review would expand our understanding of the contribution of protein and amino acids to energy balance control, thus helping discover novel therapeutic approaches for obesity and related diseases.

MAJOR CONCLUSIONS

Changes in circulating EAA levels, particularly increased branched-chain amino acids (BCAAs), have been reported in obese human and animal models. Alterations in dietary EAA intake result in improvements in fat and weight loss in rodents, and each has its distinct mechanism. For example, leucine deprivation increases energy expenditure, reduces food intake and fat mass, primarily through regulation of the general control nonderepressible 2 (GCN2) and mammalian target of rapamycin (mTOR) signaling. Methionine restriction by 80% decreases fat mass and body weight while developing hyperphagia, primarily through fibroblast growth factor 21 (FGF-21) signaling. Some effects of diets with different protein levels on energy homeostasis are mediated by similar mechanisms. However, reports on the effects and underlying mechanisms of dietary EAA imbalances on human body weight are few, and more investigations are needed in future.

Adipocyte-specific deletion of PIP5K1c reduces diet-induced obesity and insulin resistance by increasing energy expenditure

Background

Phosphatidylinositol 4-phosphate 5-kinase type I c (PIP5K1c) catalyses the synthesis of phospholipid phosphatidylinositol 4,5-bisphosphate (PIP2) by phosphorylating phosphatidylinositol 4 phosphate, which plays multiple roles in regulating focal adhesion formation, invasion, and cell migration signal transduction cascades. Here, a new physiological mechanism of PIP5K1c in adipocytes and systemic metabolism is reported.

Methods

Adipose-specific conditional knockout mice were generated to delete the PIP5K1c gene in adipocytes. In addition, in vitro research investigated the effect of PIP5K1c deletion on adipogenesis.

Results

Deletion of PIP5K1c in adipocytes significantly alleviated high fat diet (HFD)-induced obesity, hyperlipidaemia, hepatic steatosis, and insulin resistance. PIP5K1c deficiency in adipocytes also decreased adipocyte volume in HFD-induced obese mice, whereas no significant differences were observed in body weight and adipose tissue weight under normal chow diet conditions. PIP5K1c knockout in adipocytes significantly enhanced energy expenditure, which protected mice from HFD-induced weight gain. In addition, adipogenesis was markedly impaired in mouse stromal vascular fraction (SVF) from PIP5K1c-deleted mice.

Conclusion

Under HFD conditions, PIP5K1c regulates adipogenesis and adipose tissue homeostasis. Together, these data indicate that PIP5K1c could be a novel potential target for regulating fat accumulation, which could provide novel insight into the treatment of obesity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12944-021-01616-4.

Signaling Lipidomic Analysis of Thermogenic Adipocytes

Brown adipose tissue is a thermogenic organ that possesses anti-diabetic and anti-obesogenic potential. There has recently been growing interest on the secretory role of brown adipose tissue in regulating whole-body metabolism. Several signaling lipids, including 12-HEPE and 12,13-diHOME, have been shown to be secreted by brown adipose tissue and have demonstrated roles in regulating whole-body energy metabolism. Lipidomics platforms that broadly characterize the signaling lipidome can deconvolute the underlying biology of the lipid metabolites having a broad systemic impact on physiology. Herein, we describe how to perform and analyze LC-MS/MS signaling lipidomics on mature brown adipocytes.

Blowing Hot and Cold: Body Temperature and the Microbiome

The intestinal microbiome influences host health, and its responsiveness to diet and disease is increasingly well studied. However, our understanding of the factors driving microbiome variation remain limited. Temperature is a core factor that controls microbial growth, but its impact on the microbiome remains to be fully explored. Although commonly assumed to be a constant 37°C, normal body temperatures vary across the animal kingdom, while individual body temperature is affected by multiple factors, including circadian rhythm, age, environmental temperature stress, and immune activation. Changes in body temperature via hypo- and hyperthermia have been shown to influence the gut microbiota in a variety of animals, with consistent effects on community diversity and stability. It is known that temperature directly modulates the growth and virulence of gastrointestinal pathogens; however, the effect of temperature on gut commensals is not well studied. Further, body temperature can influence other host factors, such as appetite and immunity, with indirect effects on the microbiome. In this minireview, we discuss the evidence linking body temperature and the intestinal microbiome and their implications for microbiome function during hypothermia, heat stress, and fever.

Physical Activity Attenuates the Obesity-Induced Dysregulated Expression of Brown Adipokines in Murine Interscapular Brown Adipose Tissue

In recent years, brown adipose tissue (BAT), which has a high heat-producing capacity, has been confirmed to exist even in adults, and it has become a focal point for the prevention and the improvement of obesity and lifestyle-related diseases. However, the influences of obesity and physical activity (PA) on the fluid factors secreted from BAT (brown adipokines) are not well understood. In this study, therefore, we focused on brown adipokines and investigated the effects of obesity and PA. The abnormal expressions of gene fluid factors such as galectin-3 (Lgals3) and Lgals3 binding protein (Lgals3bp), whose proteins are secreted from HB2 brown adipocytes, were observed in the interscapular BAT of obese mice fed a high-fat diet for 4 months. PA attenuated the abnormalities in the expressions of these genes. Furthermore, although the gene expressions of factors related to brown adipocyte differentiation such as peroxisome proliferator-activated receptor gamma coactivator 1-α were also down-regulated in the BAT of the obese mice, PA suppressed the down-regulation of these factors. On the other hand, lipogenesis was increased more in HB2 cells overexpressing Lgals3 compared with that in control cells, and the overexpression of Lgals3bp decreased the mitochondrial mass. These results indicate that PA attenuates the obesity-induced dysregulated expression of brown adipokines and suggests that Lgals3 and Lgals3bp are involved in brown adipocyte differentiation.

Brown adipose tissue is the key depot for glucose clearance in microbiota depleted mice

Gut microbiota deficient mice demonstrate accelerated glucose clearance. However, which tissues are responsible for the upregulated glucose uptake remains unresolved, with different studies suggesting that browning of white adipose tissue, or modulated hepatic gluconeogenesis, may be related to enhanced glucose clearance when the gut microbiota is absent. Here, we investigate glucose uptake in 22 different tissues in 3 different mouse models. We find that gut microbiota depletion via treatment with antibiotic cocktails (ABX) promotes glucose uptake in brown adipose tissue (BAT) and cecum. Nevertheless, the adaptive thermogenesis and the expression of uncoupling protein 1 (UCP1) are dispensable for the increased glucose uptake and clearance. Deletion of Ucp1 expressing cells blunts the improvement of glucose clearance in ABX-treated mice. Our results indicate that BAT and cecum, but not white adipose tissue (WAT) or liver, contribute to the glucose uptake in the gut microbiota depleted mouse model and this response is dissociated from adaptive thermogenesis.

The effect of aggression II: Acclimation to a high ambient temperature reduces territorial aggression in male striped hamsters (Cricetulus barabensis)

Thyroid hormones have a profound influence on development, cellular differentiation and metabolism, and are also suspected of playing a role in aggression. We measured territorial aggression, body temperature (T_b) and serum thyroid hormones levels of male striped hamsters (Cricetulus barabensis) acclimated to either cold (5 °C), cool (21 °C) or hot (34 °C) ambient temperatures. The effects of methimazole on territorial aggression, food intake, metabolic rate and serum thyroid hormone levels, were also examined. Territorial aggression was significantly lower in male hamsters acclimated to the hot temperature compared to those acclimated to the cool or cold temperatures. T_b significantly increased during aggressive territorial interactions with intruders but did not significantly differ among the three temperature treatments. Serum T₃, T₄ and cortisol levels of hamsters acclimated to 34 °C were significantly lower than those acclimated to 21 °C. In addition to significantly reducing territorial aggression, treatment with methimazole also significantly reduced serum T₃ and T₄ levels, T_b and metabolic rate. These results suggest that exposure to high temperatures reduces the capacity of hamsters to dissipate heat causing them to lower their metabolic rate, which, in turn, causes them to reduce territorial aggression to prevent hyperthermia. The lower metabolic rate mediated by down-regulated thyroid hormones inhibits territorial aggression and could thereby determine the outcome of territorial conflicts.

Sesamol promotes browning of white adipocytes to ameliorate obesity by inducing mitochondrial biogenesis and inhibition mitophagy via β3-AR/PKA signaling pathway

Background

Obesity is defined as an imbalance between energy intake and expenditure, and it is a serious risk factor of non-communicable diseases. Recently many studies have shown that promoting browning of white adipose tissue (WAT) to increase energy consumption has a great therapeutic potential for obesity. Sesamol, a lignan from sesame oil, had shown potential beneficial functions on obesity treatment.

Objective

In this study, we used C57BL/6J mice and 3T3-L1 adipocytes to investigate the effects and the fundamental mechanisms of sesamol in enhancing the browning of white adipocytes to ameliorate obesity.

Methods

Sixteen-week-old C57BL/6J male mice were fed high-fat diet (HFD) for 8 weeks to establish the obesity models. Half of the obese mice were administered with sesamol (100 mg/kg body weight [b.w.]/day [d] by gavage for another 8 weeks. Triacylglycerol (TG) and total cholesterol assay kits were used to quantify serum TG and total cholesterol (TC). Oil red O staining was used to detect lipid droplet in vitro. Mito-Tracker Green was used to detect the mitochondrial content. Quantitative reverse transcription-polymerase chain reaction (RT-PCR) was used to detect the levels of beige-specific genes. Immunoblotting was used to detect the proteins involved in beige adipocytes formation.

Results

Sesamol decreased the content of body fat and suppressed lipid accumulation in HFD-induced obese mice. In addition, sesamol significantly upregulated uncoupling protein-1 (UCP1) protein in adipose tissue. Further research found that sesamol also significantly activated the browning program in mature 3T3-L1 adipocytes, manifested by the increase in beige-specific genes and proteins. Moreover, sesamol greatly increased mitochondrial biogenesis, as proved by the upregulated protein levels of mitochondrial biogenesis, and the inhibition of the proteins associated with mitophagy. Furthermore, β3-adrenergic receptor (β3-AR), protein kinase A-C (PKA-C) and Phospho-protein kinase A (p-PKA) substrate were elevated by sesamol, and these effects were abolished by the pretreatment of antagonists β3-AR.

Conclusion

Sesamol promoted browning of white adipocytes by inducing mitochondrial biogenesis and inhibiting mitophagy through the β3-AR/PKA pathway. This preclinical data promised the potential to consider sesamol as a metabolic modulator of HFD-induced obesity.

Mitochondrial proton leaks and uncoupling proteins

Non-shivering thermogenesis in brown adipose tissue is mediated by uncoupling protein 1 (UCP1), which provides a carefully regulated proton re-entry pathway across the mitochondrial inner membrane operating in parallel to the ATP synthase and allowing respiration, and hence thermogenesis, to be released from the constraints of respiratory control. In the 40 years since UCP1 was first described, an extensive, and frequently contradictory, literature has accumulated, focused on the acute physiological regulation of the protein by fatty acids, purine nucleotides and possible additional factors. The purpose of this review is to examine, in detail, the experimental evidence underlying these proposed mechanisms. Emphasis will be placed on the methodologies employed and their relation to the physiological constraints under which the protein functions in the intact cell. The nature of the endogenous, UCP1-independent, proton leak will also be discussed. Finally, the troubled history of the putative novel uncoupling proteins, UCP2 and UCP3, will be evaluated.

Contribution of thermogenic mechanisms by male and female mice lacking pituitary adenylate cyclase-activating polypeptide in response to cold acclimation

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide critical to the regulation of the stress response, including having a role in energy homeostasis. Mice lacking PACAP are cold-sensitive and have impaired adrenergic-induced thermogenesis. Interestingly, Pacap null mice can survive cold housing if acclimated slowly, similar to observations in uncoupling protein 1 (UCP1)-deficient mice. We hypothesized that Pacap null mice use alternate thermogenic pathways to compensate for impaired adaptive thermogenesis when acclimated to cold. Observations of behavior and assessment of fiber type in skeletal muscles did not show evidence of prolonged burst shivering or changes in oxidative metabolism in male or female Pacap^-/- mice during cold acclimation compared with Pacap^+/+ mice. Despite previous work that has established impaired capacity for adaptive thermogenesis in Pacap null mice, adaptive thermogenesis can be induced in mice lacking PACAP to support survival with cold housing. Interestingly, sex-specific morphological and molecular differences in adipose tissue remodeling were observed in Pacap null mice compared with controls. Thus, sexual dimorphisms are highlighted in adipose tissue remodeling and thermogenesis with cold acclimation in the absence of PACAP.NEW & NOTEWORTHY This manuscript adds to the literature of endocrine regulation of adaptive thermogenesis and energy balance. It specifically describes the role of pituitary adenylate cyclase-activating polypeptide on the regulation of brown adipose tissue via the sympathetic nervous system with a focus on compensatory mechanisms of thermogenesis. We highlight sex-specific differences in energy metabolism.

Network pharmacology-based research uncovers cold resistance and thermogenesis mechanism of Cinnamomum cassia

BACKGROUND

Cinnamomum cassia (L.) J.Presl (Cinnamon) was known as a kind of hot herb, improved circulation and warmed the body. However, the active components and mechanisms of dispelling cold remain unknown.

METHODS

The effects of several Chinses herbs on thermogenesis were evaluated on body temperature and activation of brown adipose tissue. After confirming the effect, the components of cinnamon were identified using HPLC-Q-TOF/MS and screened with databases. The targets of components were obtained with TCMSP, SymMap, Swiss and STITCH databases. Thermogenesis genes were predicted with DisGeNET and GeneCards databases. The protein-protein interaction network was constructed with Cytoscape 3.7.1 software. GO enrichment analysis was accomplished with STRING databases. KEGG pathway analysis was established with Omicshare tools. The top 20 targets for four compounds were obtained according to the number of edges of PPI network. In addition, the network results were verified with experimental research for the effects of extracts and major compounds.

RESULTS

Cinnamon extract significantly upregulated the body temperature during cold exposure.121 components were identified in HPLC-Q-TOF/MS. Among them, 60 compounds were included in the databases. 116 targets were obtained for the compounds, and 41 genes were related to thermogenesis. The network results revealed that 27 active ingredients and 39 target genes. Through the KEGG analysis, the top 3 pathways were PPAR signaling pathway, AMPK signaling pathway, thermogenesis pathway. The thermogenic protein PPARγ, UCP1 and PGC1-α was included in the critical targets of four major compounds. The three major compounds increased the lipid consumption and activated the brown adipocyte. They also upregulated the expression of UCP1, PGC1-α and pHSL, especially 2-methoxycinnamaldehyde was confirmed the effect for the first time. Furthermore, cinnamaldehyde and cinnamon extract activated the expression of TRPA1 on DRG cells.

CONCLUSION

The mechanisms of cinnamon on cold resistance were investigated with network pharmacology and experiment validation. This work provided research direction to support the traditional applications of thermogenesis.