Insulin-independent reversal of type 1 diabetes in nonobese diabetic mice with brown adipose tissue transplant

Thermogenic Fat as a New Obesity Management Tool: From Pharmaceutical Reagents to Cell Therapies

Obesity is a complex medical condition caused by a positive imbalance between calorie intake and calorie consumption. Brown adipose tissue (BAT), along with the newly discovered "brown-like" adipocytes (called beige cells), functions as a promising therapeutic tool to ameliorate obesity and metabolic disorders by burning out extra nutrients in the form of heat. Many studies in animal models and humans have proved the feasibility of this concept. In this review, we aim to summarize the endeavors over the last decade to achieve a higher number/activity of these heat-generating adipocytes. In particular, pharmacological compounds, especially agonists to the β3 adrenergic receptor (β3-AR), are reviewed in terms of their feasibility and efficacy in elevating BAT function and improving metabolic parameters in human subjects. Alternatively, allograft transplantation of BAT and the transplantation of functional brown or beige adipocytes from mesenchymal stromal cells or human induced pluripotent stem cells (hiPSCs) make it possible to increase the number of these beneficial adipocytes in patients. However, practical and ethical issues still need to be considered before the therapy can eventually be applied in the clinical setting. This review provides insights and guidance on brown- and beige-cell-based strategies for the management of obesity and its associated metabolic comorbidities.

An update on the secretory functions of brown, white, and beige adipose tissue: Towards therapeutic applications

Adipose tissue, including white adipose tissue (WAT), brown adipose tissue (BAT), and beige adipose tissue, is vital in modulating whole-body energy metabolism. While WAT primarily stores energy, BAT dissipates energy as heat for thermoregulation. Beige adipose tissue is a hybrid form of adipose tissue that shares characteristics with WAT and BAT. Dysregulation of adipose tissue metabolism is linked to various disorders, including obesity, type 2 diabetes, cardiovascular diseases, cancer, and infertility. Both brown and beige adipocytes secrete multiple molecules, such as batokines, packaged in extracellular vesicles or as soluble signaling molecules that play autocrine, paracrine, and endocrine roles. A greater understanding of the adipocyte secretome is essential for identifying novel molecular targets in treating metabolic disorders. Additionally, microRNAs show crucial roles in regulating adipose tissue differentiation and function, highlighting their potential as biomarkers for metabolic disorders. The browning of WAT has emerged as a promising therapeutic approach in treating obesity and associated metabolic disorders. Many browning agents have been identified, and nanotechnology-based drug delivery systems have been developed to enhance their efficacy. This review scrutinizes the characteristics of and differences between white, brown, and beige adipose tissues, the molecular mechanisms involved in the development of the adipocytes, the significant roles of batokines, and regulatory microRNAs active in different adipose tissues. Finally, the potential of WAT browning in treating obesity and atherosclerosis, the relationship of BAT with cancer and fertility disorders, and the crosstalk between adipose tissue with circadian system and circadian disorders are also investigated.

Use of brown adipose tissue transplantation and engineering as a thermogenic therapy in obesity and metabolic disease

The induction of thermogenesis in brown adipose tissue is emerging as an attractive therapy for obesity and metabolic syndrome. However, the long-term efficacy and safety of clinical pharmaceutical agents have yet to be fully characterized. The transplantation of brown adipose tissue represents an alternative approach that might have a therapeutic effect by inducing a long-term increase in energy expenditure. However, limited tissue resources hinder the development of transplantation. Stem cell-based therapy and brown adipose tissue engineering, in addition to transplantation, represent alternative approaches that might resolve this problem. In this article, we discuss recent advances in understanding the mechanisms and applications of brown adipose tissue transplantation in the treatment of obesity and related metabolic disorders. Specifically, the induction of brown adipocytes and the fabrication of engineered brown adipose tissue as novel transplantation resources have long-term effects on ameliorating metabolic defects in rodent models. Additionally, we explore future prospects regarding the development of three-dimensional engineered brown adipose tissue and the associated challenges.

Transplantation of committed pre-adipocytes from brown adipose tissue improves whole-body glucose homeostasis

Obesity and its co-morbidities including type 2 diabetes are increasing at epidemic rates in the U.S. and worldwide. Brown adipose tissue (BAT) is a potential therapeutic to combat obesity and type 2 diabetes. Increasing BAT mass by transplantation improves metabolic health in rodents, but its clinical translation remains a challenge. Here, we investigated if transplantation of 2-4 million differentiated brown pre-adipocytes from mouse BAT stromal fraction (SVF) or human pluripotent stem cells (hPSCs) could improve metabolic health. Transplantation of differentiated brown pre-adipocytes, termed "committed pre-adipocytes" from BAT SVF from mice or derived from hPSCs improves glucose homeostasis and insulin sensitivity in recipient mice under conditions of diet-induced obesity, and this improvement is mediated through the collaborative actions of the liver transcriptome, tissue AKT signaling, and FGF21. These data demonstrate that transplantation of a small number of brown adipocytes has significant long-term translational and therapeutic potential to improve glucose metabolism.

An orally available compound suppresses glucagon hypersecretion and normalizes hyperglycemia in type 1 diabetes

Suppression of glucagon hypersecretion can normalize hyperglycemia during type 1 diabetes (T1D). Activating erythropoietin-producing human hepatocellular receptor type-A4 (EphA4) on α cells reduced glucagon hypersecretion from dispersed α cells and T1D islets from both human donor and mouse models. We synthesized a high-affinity small molecule agonist for the EphA4 receptor, WCDD301, which showed robust plasma and liver microsome metabolic stability in both mouse and human preparations. In islets and dispersed islet cells from nondiabetic and T1D human donors, WCDD301 reduced glucagon secretion comparable to the natural EphA4 ligand, Ephrin-A5. In diabetic NOD and streptozotocin-treated mice, once-daily oral administration of WCDD301 formulated with a time-release excipient reduced plasma glucagon and normalized blood glucose for more than 3 months. These results suggest that targeting the α cell EphA4 receptor by sustained release of WCDD301 is a promising pharmacologic pathway for normalizing hyperglycemia in patients with T1D.

Sweet triterpenoid glycoside from Cyclocarya paliurus ameliorates obesity-induced insulin resistance through inhibiting the TLR4/NF-κB/NLRP3 inflammatory pathway

Our prophase studies have manifested that the sweet triterpenoid glycoside from the leaves of Cyclocarya paliurus (CPST) effectively improved the disorders of glucolipid metabolism in vitro and in patients. The current purpose was to further detect its mechanisms involved. The results demonstrated that CPST could ameliorate high-fat diet (HFD)-induced insulin resistance (IR), which was linked to reducing HFD-induced mice's body weight, serum glucose (GLUO), triglyceride (TG), total cholesterol (T-CHO) and low-density lipoprotein cholesterol (LDL-C), lowering the area under the oral glucose tolerance curve and insulin tolerance, elevating the percentage of brown adipose, high-density lipoprotein cholesterol (HDL-C), reducing fat droplets of adipocytes in interscapular brown adipose tissue (iBAT) and cross-sectional area of adipocytes. Further studies manifested that CPST obviously downregulated TLR4, MyD88, NLRP3, ASC, caspase-1, cleased-caspase-1, IL-18, IL-1β, TXNIP, and GSDMD protein expressions and p-NF-кB/NF-кB ratio in iBAT. These aforementioned findings demonstrated that CPST ameliorated HFD induced IR by regulating TLR4/NF-κB/NLRP3 signaling pathway, which in turn enhancing insulin sensitivity and glucose metabolism.

Brown adipose tissue-derived metabolites and their role in regulating metabolism

The discovery and rejuvenation of metabolically active brown adipose tissue (BAT) in adult humans have offered a new approach to treat obesity and metabolic diseases. Beyond its accomplished role in adaptive thermogenesis, BAT secretes signaling molecules known as "batokines", which are instrumental in regulating whole-body metabolism via autocrine, paracrine, and endocrine action. In addition to the intrinsic BAT metabolite-oxidizing activity, the endocrine functions of these molecules may help to explain the association between BAT activity and a healthy systemic metabolic profile. Herein, we review the evidence that underscores the significance of BAT-derived metabolites, especially highlighting their role in controlling physiological and metabolic processes involving thermogenesis, substrate metabolism, and other essential biological processes. The conversation extends to their capacity to enhance energy expenditure and mitigate features of obesity and its related metabolic complications. Thus, metabolites derived from BAT may provide new avenues for the discovery of metabolic health-promoting drugs with far-reaching impacts. This review aims to dissect the complexities of the secretory role of BAT in modulating local and systemic metabolism in metabolic health and disease.

Cutaneous changes in diabetic patients: Primed for aberrant healing?

Cutaneous manifestations affect most patients with diabetes mellitus, clinically presenting with numerous dermatologic diseases from xerosis to diabetic foot ulcers (DFUs). Skin conditions not only impose a significantly impaired quality of life on individuals with diabetes but also predispose patients to further complications. Knowledge of cutaneous biology and the wound healing process under diabetic conditions is largely limited to animal models, and studies focusing on biology of the human condition of DFUs remain limited. In this review, we discuss the critical molecular, cellular, and structural changes to the skin in the hyperglycaemic and insulin-resistant environment of diabetes with a focus specifically on human-derived data. Elucidating the breadth of the cutaneous manifestations coupled with effective diabetes management is important for improving patient quality of life and averting future complications including wound healing disorders.

Adipose Tissue and Metabolic Health

In this review, we provide a brief synopsis of the connections between adipose tissue and metabolic health and highlight some recent developments in understanding and exploiting adipocyte biology. Adipose tissue plays critical roles in the regulation of systemic glucose and lipid metabolism and secretes bioactive molecules possessing endocrine, paracrine, and autocrine functions. Dysfunctional adipose tissue has a detrimental impact on metabolic health and is intimately involved in key aspects of metabolic diseases such as insulin resistance, lipid overload, inflammation, and organelle stress. Differences in the distribution of fat depots and adipose characteristics relate to divergent degrees of metabolic dysfunction found in metabolically healthy and unhealthy obese individuals. Thermogenic adipocytes increase energy expenditure via mitochondrial uncoupling or adenosine triphosphate-consuming futile substrate cycles, while functioning as a metabolic sink and participating in crosstalk with other metabolic organs. Manipulation of adipose tissue provides a wealth of opportunities to intervene and combat the progression of associated metabolic diseases. We discuss current treatment modalities for obesity including incretin hormone analogs and touch upon emerging strategies with therapeutic potential including exosome-based therapy, pharmacological activation of brown and beige adipocyte thermogenesis, and administration or inhibition of adipocyte-derived factors.

Farrell, Li L, Tseng YH, Profeta G, Buys ES, Bloch DB, Scherrer-Crosbie M. Brown Adipose Tissue and BMP3b Decrease Injury in Cardiac Ischemia-Reperfusion

BACKGROUND

Despite advances in treatment, myocardial infarction (MI) is a leading cause of heart failure and death worldwide, with both ischemia and reperfusion (I/R) causing cardiac injury. A previous study using a mouse model of nonreperfused MI showed activation of brown adipose tissue (BAT). Recent studies showed that molecules secreted by BAT target the heart. We investigated whether BAT attenuates cardiac injury in I/R and sought to identify potential cardioprotective proteins secreted by BAT.

METHODS

Myocardial I/R surgery with or without BAT transplantation was performed in wild-type (WT) mice and in mice with impaired BAT function (uncoupling protein 1 [Ucp1]-deficient mice). To identify potential cardioprotective factors produced by BAT, RNA-seq (RNA sequencing) was performed in BAT from WT and Ucp1-/- mice. Subsequently, myocardial I/R surgery with or without BAT transplantation was performed in Bmp3b (bone morphogenetic protein 3b)-deficient mice, and WT mice subjected to myocardial I/R were treated using BMP3b.

RESULTS

Dysfunction of BAT in mice was associated with larger MI size after I/R; conversely, augmenting BAT by transplantation decreased MI size. We identified Bmp3b as a protein secreted by BAT after I/R. Compared with WT mice, Bmp3b-deficient mice developed larger MIs. Increasing functional BAT by transplanting BAT from WT mice to Bmp3b-deficient mice reduced I/R injury whereas transplanting BAT from Bmp3b-deficient mice did not. Treatment of WT mice with BMP3b before reperfusion decreased MI size. The cardioprotective effect of BMP3b was mediated through SMAD1/5/8. In humans, the plasma level of BMP3b increased after MI and was positively correlated with the extent of cardiac injury.

CONCLUSIONS

The results of this study suggest a cardioprotective role of BAT and BMP3b, a protein secreted by BAT, in a model of I/R injury. Interventions increasing BMP3b levels or targeting Smad 1/5 may represent novel therapeutic approaches to decrease myocardial damage in I/R injury.

The effect of Xuezhikang capsule on gene expression profile in brown adipose tissue of obese spontaneously hypertensive rats

ETHNOPHARMACOLOGICAL RELEVANCE

Obesity is a critical threat to global health, and brown adipose tissue (BAT) is a potential target for the treatment of obesity and comorbidities. Xuezhikang Capsule (XZK), an extract of red yeast rice, has remarkable clinical efficacy and is widely used for the treatment of hyperlipidemia and coronary heart disease. However, its modulatory effect on BAT remains unknown.

AIM OF THIS STUDY

The aim of this study was to investigate the protective mechanism of XZK in the obese spontaneously hypertensive rat (SHR) model by evaluating the regulatory effect of XZK on the BAT gene profile through transcriptome sequencing.

MATERIALS AND METHODS

The SHRs were randomly divided into four groups: the standard chow diet (STD) group, the STD supplemented with 126 mg/kg of XZK group, the high-fat diet (HFD) group, and the HFD supplemented with 126 mg/kg of XZK group. All SHRs were fed for 18 weeks. The metabolic phenotypes, including body weight, fat mass, oral glucose tolerance test (OGTT), and serum glucose and lipid levels, was evaluated, and hematoxylin and eosin staining (H&E) staining was performed to evaluate the adipose tissue histopathological phenotype. Transcriptome sequencing was performed to determine the mechanism by which XZK improves the metabolic phenotype and the expression of key differential expression genes was verified by real-time quantitative polymerase chain reaction (qRT-PCR).

RESULTS

XZK inhibited HFD-induced weight gain and adipose tissue remodeling in SHRs and prevented hypertrophy of epididymal adipocytes and maintained the brown fat phenotype. XZK intervention also improved glucose and lipid metabolism in SHRs, as suggested by a reduction in serum triglyceride (TG), low-density cholesterol (LDL-C), and fasting blood glucose (FBG) levels as well as increasing in serum high-density cholesterol (HDL-C) levels. Transcriptome sequencing analysis confirmed the regulatory effect of XZK on the gene expression profile of BAT, and the expression patterns of 45 genes were reversed by the XZK intervention. Additionally, the results of the transcriptome analysis of 10 genes that are important for brown fat function were in line with the results of qRT-PCR.

CONCLUSIONS

XZK protected SHRs from HFD-induced obesity, inhibited fat accumulation and improved glucolipid metabolism. Additionally, the protective effect of XZK on the overall metabolism of obese SHRs might partly be related to its regulatory effect on the BAT gene expression profile. These findings might provide novel therapeutic strategies for obesity-related metabolic diseases in traditional Chinese medicine (TCM).

Role of Hormones During Gestation and Early Development: Pathways Involved in Developmental Programming

Accumulating evidence suggests that an altered maternal milieu and environmental insults during the intrauterine and perinatal periods of life affect the developing organism, leading to detrimental long-term outcomes and often to adult pathologies through programming effects. Hormones, together with growth factors, play critical roles in the regulation of maternal-fetal and maternal-neonate interfaces, and alterations in any of them may lead to programming effects on the developing organism. In this chapter, we will review the role of sex steroids, thyroid hormones, and insulin-like growth factors, as crucial factors involved in physiological processes during pregnancy and lactation, and their role in developmental programming effects during fetal and early neonatal life. Also, we will consider epidemiological evidence and data from animal models of altered maternal hormonal environments and focus on the role of different tissues in the establishment of maternal and fetus/infant interaction. Finally, we will identify unresolved questions and discuss potential future research directions.

Fabricating 3-dimensional human brown adipose microtissues for transplantation studies

Transplanting cell cultured brown adipocytes (BAs) represents a promising approach to prevent and treat obesity (OB) and its associated metabolic disorders, including type 2 diabetes mellitus (T2DM). However, transplanted BAs have a very low survival rate in vivo. The enzymatic dissociation during the harvest of fully differentiated BAs also loses significant cells. There is a critical need for novel methods that can avoid cell death during cell preparation, transplantation, and in vivo. Here, we reported that preparing BAs as injectable microtissues could overcome the problem. We found that 3D culture promoted BA differentiation and UCP-1 expression, and the optimal initial cell aggregate size was 100 μm. The microtissues could be produced at large scales via 3D suspension assisted with a PEG hydrogel and could be cryopreserved. Fabricated microtissues could survive in vivo for long term. They alleviated body weight and fat gain and improved glucose tolerance and insulin sensitivity in high-fat diet (HFD)-induced OB and T2DM mice. Transplanted microtissues impacted multiple organs, secreted protein factors, and influenced the secretion of endogenous adipokines. To our best knowledge, this is the first report on fabricating human BA microtissues and showing their safety and efficacy in T2DM mice. The proposal of transplanting fabricated BA microtissues, the microtissue fabrication method, and the demonstration of efficacy in T2DM mice are all new. Our results show that engineered 3D human BA microtissues have considerable advantages in product scalability, storage, purity, safety, dosage, survival, and efficacy.

The relationship of antipsychotic treatment with reduced brown adipose tissue activity in patients with schizophrenia

BACKGROUND

Antipsychotic drug (APD) treatment has been associated with metabolic abnormalities. Brown adipose tissue (BAT) is the main site of adaptive thermogenesis and secretes various metabolism-improving factors known as batokines. We explored the association of BAT activity with APD treatment and metabolic abnormalities in patients with schizophrenia by measuring the blood levels of bone morphogenetic protein 8b (BMP8b), a batokine secreted by mature BAT.

METHODS

BMP8b levels were compared among 50 drug-free, 32 aripiprazole-treated, and 91 clozapine-treated patients with schizophrenia. Regression analysis was used to explore factors, including APD types, that might be associated with BMP8b levels and the potential effect of BMP8b on metabolic syndrome (MS).

RESULTS

APD-treated patients had decreased BMP8b levels relative to drug-free patients. The difference still existed after adjustment for body mass index and Brief Psychiatric Rating Scale scores. Among APD-treated group, clozapine was associated with even lower BMP8b levels than the less obesogenic APD, aripiprazole. Furthermore, higher BMP8b levels were associated with lower risks of MS after adjustment for BMI and APD treatment.

CONCLUSION

Using drug-free patients as the comparison group to understand the effect of APDs, this is the first study to show APD treatment is associated with reduced BAT activity that is measured by BMP8b levels, with clozapine associated a more significant reduction than aripiprazole treatment. BMP8b might have a beneficial effect against metabolic abnormalities and this effect is independent of APD treatment. Future studies exploring the causal relationship between APD treatment and BMP8b levels and the underlying mechanisms are warranted.

Brown adipose tissue: a protective mechanism in "pre-prediabetes"?

Brown adipose tissue (BAT) is present in a significant number of adult humans and has been postulated to exert beneficial metabolic effects. Lean, non-diabetic patients undergoing clinical positron emission tomography (PET)/computed tomography (CT) imaging are more likely to exhibit incidental BAT activation. The aim of this study was to assess metabolic changes associated with the cold-activation of BAT and to compare baseline blood metabolites in participants with varying amounts of active BAT. Methods: Serum blood samples were collected from healthy adult volunteers (body mass index 18.0-25.0 and age≤35 years) before and after 2 h cold exposure. ¹⁸F-flurodeoxyglucose (FDG) PET/CT imaging was performed immediately following cold exposure. Activated BAT was segmented and fasting glucose, insulin, lipid, and other blood metabolite levels were correlated with volume and intensity of active BAT. Using a median cutoff, subjects were classified as BATHIGH or BATLOW. Results: A higher volume of activated BAT was associated with significantly higher pre-cooling glucose and insulin levels (P<0.001 for each). Pre-cooling thyroid stimulating hormone (TSH) and triglyceride levels were significantly higher in the BATHIGH than in the BATLOW group (P = 0.002 and P<0.001, respectively). Triglyceride levels tended to increase over the cooling period in both BAT groups, but increased significantly more in the BATHIGH group (15.7±13.2 md/dl; P<0.001) than in the BATLOW group (4.5±12.2 mg/dl; P = 0.061). Conclusion: These findings may indicate that BAT is recruited to counteract incipient "pre-prediabetic" states, potentially serving as a first-line protective mechanism against very early metabolic or hormonal variations.

Transplantation of fat tissues and iPSC-derived energy expenditure adipocytes to counteract obesity-driven metabolic disorders: Current strategies and future perspectives

Several therapeutic options have been developed to address the obesity epidemic and treat associated metabolic diseases. Despite the beneficial effects of surgery and drugs, effective therapeutic solutions have been held back by the poor long-term efficiency and detrimental side effects. The development of alternative approaches is thus urgently required. Fat transplantation is common practice in many surgical procedures, including aesthetic and reconstructive surgery, and is a budding future direction for treating obesity-related metabolic defects. This review focuses on adipose tissue transplantation and the recent development of cell-based therapies to boost the mass of energy-expenditure cells. Brown adipocyte transplantation is a promising novel therapy to manage obesity and associated metabolic disorders, but the need to have an abundant and relevant source of brown fat tissue or brown adipocytes for transplantation is a major hurdle to overcome. Current studies have focused on the rodent model to obtain a proof of concept of a tissue-transplantation strategy able to achieve effective long-term effects to reverse metabolic defects in obese patients. Future perspectives and opportunities to develop innovative human fat tissue models and 3D engineered hiPSC-adipocytes are discussed.

An update on brown adipose tissue and obesity intervention: Function, regulation and therapeutic implications

Overweight and obesity have become a world-wide problem. However, effective intervention approaches are limited. Brown adipose tissue, which helps maintain body temperature and contributes to thermogenesis, is dependent on uncoupling protein1. Over the last decade, an in-creasing number of studies have found that activating brown adipose tissue and browning of white adipose tissue can protect against obesity and obesity-related metabolic disease. Brown adipose tissue has gradually become an appealing therapeutic target for the prevention and re-versal of obesity. However, some important issues remain unresolved. It is not certain whether increasing brown adipose tissue activity is the cause or effect of body weight loss or what the risks might be for sympathetic nervous system-dependent non-shivering thermogenesis. In this review, we comprehensively summarize approaches to activating brown adipose tissue and/or browning white adipose tissue, such as cold exposure, exercise, and small-molecule treatment. We highlight the functional mechanisms of small-molecule treatment and brown adipose tissue transplantation using batokine, sympathetic nervous system and/or gut microbiome. Finally, we discuss the causality between body weight loss induced by bariatric surgery, exercise, and brown adipose tissue activity.

Skeletal muscle provides a pro-browning microenvironment for transplanted brown adipose tissue to maintain its effect to ameliorate obesity in ob/ob mice

Brown adipose tissue (BAT) transplantation is a promising means of increasing whole-body energy metabolism to ameliorate obesity. However, the changes in BAT following transplantation and the effects of the microenvironment of the recipient site on graft function have yet to be fully characterized. Therefore, we aimed to determine the effects of transplanting BAT from C57BL/6 mice into the dorsal subcutaneous region or deep to the quadriceps femoris muscle of leptin-deficient ob/ob mice. Subcutaneously transplanted BAT lost features of BAT and demonstrated greater inflammatory cell infiltration and more oil cysts 16 weeks following transplantation. By contrast, the sub-muscularly transplanted BAT maintained features of BAT and was more highly vascularized. Interestingly, sub-muscular BAT transplantation led to a significant increase in oxygen consumption and less inflammation in subcutaneous fat, which was associated with long-term reductions in insulin resistance and body mass gain, whereas the subcutaneous transplants failed after 16 weeks. These results demonstrate that the beneficial effects of BAT transplantation depend upon the microenvironment of the recipient site. Skeletal muscle may provide a microenvironment that maintains the inherent features of BAT grafts over a long period of time, which facilitates a reduction in obesity and improvements in glucose homeostasis.

Metabolic determinants of Alzheimer's disease: A focus on thermoregulation

Alzheimer's disease (AD) is a complex age-related neurodegenerative disease, associated with central and peripheral metabolic anomalies, such as impaired glucose utilization and insulin resistance. These observations led to a considerable interest not only in lifestyle-related interventions, but also in repurposing insulin and other anti-diabetic drugs to prevent or treat dementia. Body temperature is the oldest known metabolic readout and mechanisms underlying its maintenance fail in the elderly, when the incidence of AD rises. This raises the possibility that an age-associated thermoregulatory deficit contributes to energy failure underlying AD pathogenesis. Brown adipose tissue (BAT) plays a central role in thermogenesis and maintenance of body temperature. In recent years, the modulation of BAT activity has been increasingly demonstrated to regulate energy expenditure, insulin sensitivity and glucose utilization, which could also provide benefits for AD. Here, we review the evidence linking thermoregulation, BAT and insulin-related metabolic defects with AD, and we propose mechanisms through which correcting thermoregulatory impairments could slow the progression and delay the onset of AD.

Brown and beige adipose tissue: a novel therapeutic strategy for obesity and type 2 diabetes mellitus

Mammalian adipose tissue can be divided into two major types, namely, white adipose tissue (WAT) and brown adipose tissue (BAT). According to classical view, the main function of WAT is to store excess energy in the form of triglycerides, while BAT is a thermogenic tissue that acts a pivotal part in maintaining the core body temperature. White adipocytes display high plasticity and can transdifferentiate into beige adipocytes which have many similar morphological and functional properties with brown adipocytes under the stimulations of exercise, cold exposure and other factors. This phenomenon is also known as 'browning of WAT'. In addition to transdifferentiation, beige adipocytes can also come from de novo differentiation from tissue-resident progenitors. Activating BAT and inducing browning of WAT can accelerate the intake of glycolipids and reduce the insulin secretion requirement, which may be a new strategy to improve glycolipids metabolism and insulin resistance of obese and type 2 diabetes mellitus (T2DM) patients. This review mainly discusses the significance of brown and beige adipose tissues in the treatment of obesity and T2DM, and focuses on the effect of the browning agent on obesity and T2DM, which provides a brand-new theoretical reference for the prevention and treatment of obesity and T2DM.

Preconditioning improves muscle regeneration after ischemia-reperfusion injury

Ischemia-reperfusion injury (IRI) is a critical condition associated with serious clinical manifestations. Extensive research has focused on the strategies increasing organ tolerance to IRI. Preconditioning (PC) has been shown to provide protection to various organs toward IRI. However, the underlying mechanisms remain unknown. This study aimed to evaluate the role of PC on muscle regeneration after IRI and the potential underlying mechanisms. Three-month-old male UCP-1 reporter mice underwent unilateral hindlimb IRI with or without PC, the tissue viability and injury index were measured at 24 h after IRI. Hindlimb gait, muscle contractility, muscle histology were analyzed at 2 weeks after IRI. In another group of animals, β3 adrenergic receptor (β3AR) agonist amibegron and β3AR antagonist SR-59230A were administrated before PC/IRI, the hindlimb function and muscle regeneration were evaluated at 2 weeks after IRI. Our results showed that PC has little effect on improving the tissue viability at the acute phase of IRI, but it showed a long-term beneficial role of improving hindlimb function and muscle regeneration as evidenced by increased central nuclei regenerating myofibers. The effects of PC are related to inducing muscle fibro-adipogenic progenitor (FAP) brown/beige-like adipocyte (BAT) differentiation. Amibegron treatment displayed a similar role of PC while SR-59230A abolished the effect of PC. This study suggests PC has a beneficial role in promoting muscle regeneration after IRI through β3AR signaling pathway-stimulated FAP-BAT differentiation.

Obeticholic acid ameliorates obesity and hepatic steatosis by activating brown fat

Obeticholic acid (OCA) is exemplified as a potent drug for treating primary biliary cirrhosis and nonalcoholic fatty liver disease by inhibiting bile acid synthesis. However, it remains unclear whether the effect of OCA is mediated by the function of brown adipose tissue (BAT). In the present study, brown adipogenesis differentiation in vitro and db/db mouse model treated with OCA were used to assess the anti-obesity function by body weight tracking, O₂ consumption, food intake, physical activity, glucose tolerance tests. In addition, uncoupling protein 1 (Ucp1) protein expression in brown adipose tissue was measured by western blotting, morphometry of brown adipose tissue was analyzed by hematoxylin and eosin staining. Hepatic steatosis was detected by Oil-Red O staining and serological analysis was performed to assess the effect of OCA on hyperlipidemia. OCA treatment enhanced brown adipocyte cell differentiation and upregulated the expression of the BAT-specific gene Ucp1) in C3H10T1/2 cells in vitro. Consistent with these findings, OCA increased whole-body energy metabolism and glucose homeostasis by enhancing BAT activity in vivo, and ultimately decreased body weight gain in db/db mice. In addition, the results demonstrated that spontaneous hepatic steatosis in db/db mice was ameliorated following OCA treatment. In summary, OCA functioned as a BAT activator to help ameliorate obesity and maintain glucose homeostasis in db/db mice. The present results may provide a novel potential therapeutic approach to activate brown fat in patients with obesity and other metabolic disorders.

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.

Thermogenic Fat: Development, Physiological Function, and Therapeutic Potential

The concerning worldwide increase of obesity and chronic metabolic diseases, such as T2D, dyslipidemia, and cardiovascular disease, motivates further investigations into preventive and alternative therapeutic approaches. Over the past decade, there has been growing evidence that the formation and activation of thermogenic adipocytes (brown and beige) may serve as therapy to treat obesity and its associated diseases owing to its capacity to increase energy expenditure and to modulate circulating lipids and glucose levels. Thus, understanding the molecular mechanism of brown and beige adipocytes formation and activation will facilitate the development of strategies to combat metabolic disorders. Here, we provide a comprehensive overview of pathways and players involved in the development of brown and beige fat, as well as the role of thermogenic adipocytes in energy homeostasis and metabolism. Furthermore, we discuss the alterations in brown and beige adipose tissue function during obesity and explore the therapeutic potential of thermogenic activation to treat metabolic syndrome.

Reduced brown adipose tissue-associated skin temperature following cold stimulation in children and adolescents with type 1 diabetes

BACKGROUND

Brown adipose tissue (BAT) is essential to maintain body temperature. Its ability to convert chemical energy in glucose and free fatty acids to heat is conferred by a unique protein, UCP-1. BAT activity is greatest in children and adolescents, declining through adulthood. Blood glucose concentrations outside the normal nondiabetic range are common in type 1 diabetes and hyperglycaemia leads to insulin resistance in muscle and white adipose tissue, but whether this applies to BAT, is not known.

METHOD

To investigate the effect of type 1 diabetes on BAT activity, we measured the supraclavicular temperature of 20 children with type 1 diabetes and compared them to 20 age-matched controls, using infrared thermography.

RESULTS

The diabetes group had lower stimulated supraclavicular temperatures (diabetes group: 35.03 (34.76-35.30)°C; control group: 35.42 (35.16-35.69)°C; p = 0.037) and a reduced response in relative temperature following cold stimulation, after adjusting for BMI (diabetes group: 0.11 (0.03-0.18)°C; control group: 0.22 (0.15-0.29)°C; p = 0.034). In the diabetes group, there was no association between glycaemic measures and supraclavicular temperatures, but the method of insulin delivery may significantly affect the change in supraclavicular temperature with stimulation (injections: 0.01 (-0.07-0.09)°C; pump: 0.15 (0.04-0.26)°C; p = 0.028).

CONCLUSIONS

While further work is needed to better understand the glucose-insulin-BAT relationship, one possible explanation for the reduced supraclavicular temperature is that exogenous, unlike endogenous, insulin, is not suppressed by the activity of the sympathetic nervous system, preventing lipolysis-driven activation of BAT.

Brown Adipose Tissue Heterogeneity, Energy Metabolism, and Beyond

Brown adipocyte in brown adipose tissue (BAT) specializes in expending energy through non-shivering thermogenesis, a process that produces heat either by uncoupling protein 1 (UCP1) dependent uncoupling of mitochondrial respiration or by UCP1 independent mechanisms. Apart from this, there is ample evidence suggesting that BAT has an endocrine function. Studies in rodents point toward its vital roles in glucose and lipid homeostasis, making it an important therapeutic target for treating metabolic disorders related to morbidities such as obesity and type 2 diabetes. The rediscovery of thermogenically active BAT depots in humans by several independent research groups in the last decade has revitalized interest in BAT as an even more promising therapeutic intervention. Over the last few years, there has been overwhelming interest in understanding brown adipocyte's developmental lineages and how brown adipocyte uniquely utilizes energy beyond UCP1 mediated uncoupling respiration. These new discoveries would be leveraged for designing novel therapeutic interventions for metabolic disorders.

The Causes of Insulin Resistance in Type 1 Diabetes Mellitus: Is There a Place for Quaternary Prevention?

Diabetes mellitus was the first non-communicable disease that was recognized by the United Nations as a 21st-century pandemic problem. Recent scientific reports suggest that people with type 1 diabetes mellitus also develop insulin resistance, which is generally considered to be a distinctive feature of type 2 diabetes mellitus. The causes of insulin resistance in type 1 diabetes mellitus were explored, but there was a lack of publications that connected the risk factors of insulin resistance in type 1 diabetes mellitus with the proposition of repair mechanisms that are offered by quaternary prevention. Toward this end, the present review is an attempt to combine the previous reports on the causes of insulin resistance in type 1 diabetes mellitus and a brief review of quaternary prevention. The destructive effect of insulin resistance on many physiological processes that predisposes the individual to chronic diabetes complications creates an urgent need to introduce effective therapeutic methods for preventing the development and progression of this pathology.

Brown Adipose Tissue: A Potential Site for Islet Transplantation

BACKGROUND

Islet transplantation is a promising treatment in patients with complicated diabetes. The ideal transplant site that can extend islet graft survival and reduce the required number of engrafted islets remains to be established.

METHODS

Donor islets were isolated from red fluorescent protein (RFP) mice and transplanted into interscapular brown adipose tissue (BAT) or unilateral inguinal white adipose tissue of age-matched diabetic RFP mice. Blood glucose and body weight of the mice were monitored, and vitality and function of ectopic RFP islets were detected by fluorescence imaging, histological examination, and intraperitoneal glucose tolerance test (GTT).

RESULTS

BAT enabled the marginal number of grafted islets (80 islets) to restore blood glucose, insulin level, and GTT to normal values in all diabetic recipient mice in the short term after graft, and maintained these values for 1 year at the end of the experiment. Importantly, in the short term after transplantation, abundant extra- and intraislet neovasculatures were observed in BAT, but not in white adipose tissue, which allowed the ectopic islets to retain typical architecture and morphology and contributed to the normal GTT. Moreover, the islet-engrafted BAT displayed normal structure and morphology without significant immunocyte infiltration, and the recipient mice also showed normal lipid levels in the blood.

CONCLUSIONS

BAT remarkably enhances the viability and biological function of the transplanted ectopic islets. Moreover, the anatomical location of BAT lends itself to biopsy, removal, and islet retransplantation, which strongly suggests the BAT as a potential desirable site for islet transplantation in basic and clinical research.

Long-term exercise-secreted extracellular vesicles promote browning of white adipocytes by suppressing miR-191a-5p

AIMS

The purpose of the study is to explore the mechanism of transdifferentiation from white adipose tissue (WAT) to Brown adipose tissue (BAT).

MATERIALS AND METHOD

In this study, we established a model of mouse obesity induced by a high-fat diet (HFD) before 30 days of forced exercise or sedentary mice. Then, we isolated extracellular vesicles (EVs) from plasma and identified them by transmission electron microscope, dynamic light scattering and western blot analysis. Body temperature and body weight were utilized for assessment of thermogenesis in vivo. Oil red O staining was used to measure triglyceride in vitro. Luciferase reporter assay was applied for the relationship between miR-191a-5p and Prdm16.

KEY FINDINGS

As a result, mice that exercised for a long period time exhibited higher caloric expenditure, better weight maintenance and more WAT browning, as well as better resistance to obesity associated with a high-fat diet, compared to mice that lacked exercise. MircoRNA-191-5p (miR-191-5p) was found to be lowly expressed in the EVs from mice with long-term exercise (Exe-EVs). Functional experiments revealed that Exe-EVs promoted WAT browning by the silencing of miR-191-5p. At the molecular level, siRNA-mediated PRDM16 partly inhibited uncoupling protein-1(UCP-1) expression by miR-191-5p inhibitor in white adipocytes. Here, we observed that the lowly expressed miR-191-5p in Exe-EVs promoted the browning of WAT by negatively targeting the PRDM16-3'-untranslated region (PRDM16-3'UTR), thereby enhancing heat production and reducing obesity.

SIGNIFICANCE

MiR-191-5p may serve as a potential target for the identification and treatment of obesity.

Brown adipose tissue transplantation as a novel alternative to obesity treatment: a systematic review

BACKGROUND

Obesity, a global challenge, is a complex disorder linked to various diseases. Different kinds of treatments are currently used to treat or control this pandemic. Despite their positive effects on controlling obesity, they still have limitations and side effects including digestive problems, difficulties of daily infusion of some drugs, surgical complications, and weight regain. All these issues cause these conventional methods not to have desirable efficacy. In this regard, brown adipose tissue (BAT) transplantation as a new investigational treatment is proposed, which has beneficial effects with no documented side effect in studies up to now.

METHODS

This systematic review protocol was registered in the International Prospective Register of Systematic Reviews (Registration Number: CRD42018110045). The systematical search was conducted on Web of Science, Scopus, PubMed, Embase, and ProQuest databases. The quality assessments in the included studies and data gathering were conducted independently by two authors. The main variables were anthropometric indices including body weight, levels of leptin, IGF-1, glucagon, adiponectin, fasting blood glucose, and UCP-1.

RESULTS

Following the search in mentioned databases, ten articles were entered into this systematic review. In most studies, weight gain and white adipocyte size were reduced in the BAT transplant group. It seems that the transplantation leads to the regeneration of healthy adipose tissue by activating the endogenous BAT.

CONCLUSIONS

Since BAT transplantation is one of the possible future treatments of obesity, many studies are conducted to evaluate the outcomes and related procedures precisely, so it can finally step into clinical application.

Inflammatory Signaling and Brown Fat Activity

Obesity is characterized by a state of chronic inflammation in adipose tissue mediated by the secretion of a range of inflammatory cytokines. In comparison to WAT, relatively little is known about the inflammatory status of brown adipose tissue (BAT) in physiology and pathophysiology. Because BAT and brown/beige adipocytes are specialized in energy expenditure they have protective roles against obesity and associated metabolic diseases. BAT appears to be is less susceptible to developing inflammation than WAT. However, there is increasing evidence that inflammation directly alters the thermogenic activity of brown fat by impairing its capacity for energy expenditure and glucose uptake. The inflammatory microenvironment can be affected by cytokines secreted by immune cells as well as by the brown adipocytes themselves. Therefore, pro-inflammatory signals represent an important component of the thermogenic potential of brown and beige adipocytes and may contribute their dysfunction in obesity.

Investigation of the Relationship between MR-Based Supraclavicular Fat Fraction and Thyroid Hormones

PURPOSE

Brown adipose tissue (BAT) plays a potential role in energy and glucose metabolism in humans. Thyroid hormones (TH) are main regulators of BAT development and function. However, it remains unknown how the magnetic resonance (MR)-based proton density fat fraction (PDFF) of supraclavicular adipose tissue used as a surrogate marker for BAT presence relates to TH. Therefore, the purpose of this analysis was to investigate the relationship between supraclavicular PDFF and serum levels of TH.

METHODS

In total, 96 adult volunteers from a large cross-sectional study who underwent additional MR examination of the neck and pelvis were included in this analysis. Segmented PDFF maps of the supraclavicular and gluteal subcutaneous adipose tissue were generated. Delta PDFF was calculated as the difference between gluteal and supraclavicular PDFF and grouped as high (≥12%) or low (<12%) based on the median and the clinical rationale of a high versus low probability of BAT being present. Thyroid-stimulating hormone (mIU/L), free triiodothyronine (FT3, pg/mL) and free thyroxine (FT4, ng/dL) levels were determined in blood samples. Body mass index (BMI) was calculated as weight (kg)/height (m)2. Statistical analyses included the use of paired samples ttest, simple linear regression analysis and a multivariable linear regression analysis.

RESULTS

The median age of the subjects (77% female) was 33 years, BMI ranged from 17.2 to 43.1 kg/m2. Supraclavicular and gluteal PDFF differed significantly (76.5 ± 4.8 vs. 89.4 ± 3.5 %, p < 0.01). Supraclavicular PDFF was associated with FT3 in subjects with high delta PDFF (R2 = 0.17, p < 0.01), with higher FT3 being associated with lower supraclavicular PDFF (y = 85.2 + -3.6 x). In a multivariable linear regression analysis considering further potential prognostic factors, the interaction between the delta PDFF group and FT3 remained a predictor for supraclavicular PDFF (B = -4.65, p < 0.01).

DISCUSSION/CONCLUSIONS

Supraclavicular PDFF corresponds to the presence of BAT. In the present analysis, supraclavicular PDFF is correlated with FT3 in subjects with high delta PDFF. Therefore, the present findings suggest that biologically active T3 may be involved in the development of supraclavicular BAT.

Metabolically Active Brown Adipose Tissue Is Found in Adult Subjects with Type 1 Diabetes

Type 1 diabetes (T1D) is characterized by the loss of insulin-producing cells and hence insulin secretion and metabolic control. In addition to insulin, there are a number of hormones and cytokines that influence metabolism, and many of these can be secreted from brown adipose tissue (BAT). However, the presence and activity of BAT in T1D have not been studied, despite the fact that preclinical studies have shown that transplantation of BAT in mouse models of T1D can restore metabolic control. The metabolic activity of BAT, white adipose tissue (WAT), and skeletal muscle was investigated in patients with T1D (n = 11) by 2-deoxy-2-(¹⁸F)fluoro-D-glucose PET/CT after cold stimulation. Functional BAT was detected in 4 out of 11 individuals with T1D with a prevalence of 36%. The glucose utilization rate in the supraclavicular BAT regions ranged from 0.75–38.7 µmol × min⁻¹ × 100 g⁻¹. The glucose utilization per gram tissue was higher in BAT when compared with both WAT (p = 0.049) and skeletal muscle (p = 0.039). However, no correlation between BAT activity and metabolic control or insulin requirements was found. In conclusion, for the first time, cold-induced BAT was detected in patients with T1D with a wide range in metabolic activity. Contrary to findings in animal models, the metabolic activity of BAT had negligible impact on insulin requirements or metabolic control in T1D under normal physiological conditions.

Mechanistic Links Between Obesity, Diabetes, and Blood Pressure: Role of Perivascular Adipose Tissue

Obesity is increasingly prevalent and is associated with substantial cardiovascular risk. Adipose tissue distribution and morphology play a key role in determining the degree of adverse effects, and a key factor in the disease process appears to be the inflammatory cell population in adipose tissue. Healthy adipose tissue secretes a number of vasoactive adipokines and anti-inflammatory cytokines, and changes to this secretory profile will contribute to pathogenesis in obesity. In this review, we discuss the links between adipokine dysregulation and the development of hypertension and diabetes and explore the potential for manipulating adipose tissue morphology and its immune cell population to improve cardiovascular health in obesity.

Insulin-Independent Reversal of Type-1 Diabetes Following Transplantation of Adult Brown Adipose Tissue Supplemented With IGF-1

As our previous publications show, it is feasible to reverse type 1 diabetes (T1D) without insulin in multiple mouse models, through transplantation of embryonic brown adipose tissue (BAT) in the subcutaneous space. Embryonic BAT transplants result in rapid and long-lasting euglycemia accompanied by decreased inflammation and regenerated healthy white adipose tissue, with no detectable increase in insulin. To translate this approach to human patients, it is necessary to establish practical alternatives for embryonic tissue. Adult adipose tissue transplants or BAT-derived stem cell lines alone fail to reverse T1D. A likely reason is transplant failure resulting from lack of growth factors abundant in embryonic tissue. Adding growth factors may enable transplants to survive and vascularize as well as stimulate adipogenesis and decrease inflammation in the surrounding host tissue. Previous data points to insulin like growth factor 1 (IGF-1) as the most likely candidate. Embryonic BAT abundantly expresses IGF-1, and embryonic BAT transplant recipients exhibit increased plasma levels of IGF-1. Therefore, we tested the ability of temporary administration of exogenous IGF-1 to enable adult BAT transplants to correct T1D.

Methods

Fresh BAT from healthy adult CB7BL/6 donors were transplanted in the subcutaneous space of hyperglycemic nonobese diabetic recipients. Exogenous IGF-1 was administered daily for a week following transplant, at 100 µg/kg SC.

Results

Adult BAT transplants with IGF-1 supplementation produced rapid long-lasting euglycemia at a 57% success rate, in contrast with no recovery in the control groups who received adult BAT alone, IGF-1 alone, or no treatment.

Conclusions

Temporary supplementation with IGF-1 enables adult BAT transplants to correct T1D phenotypes independent of insulin, providing a possible route to translate this treatment to human patients.

The endocrine function of adipose tissues in health and cardiometabolic disease

In addition to their role in glucose and lipid metabolism, adipocytes respond differentially to physiological cues or metabolic stress by releasing endocrine factors that regulate diverse processes, such as energy expenditure, appetite control, glucose homeostasis, insulin sensitivity, inflammation and tissue repair. Both energy-storing white adipocytes and thermogenic brown and beige adipocytes secrete hormones, which can be peptides (adipokines), lipids (lipokines) and exosomal microRNAs. Some of these factors have defined targets; for example, adiponectin and leptin signal through their respective receptors that are expressed in multiple organs. For other adipocyte hormones, receptors are more promiscuous or remain to be identified. Furthermore, many of these hormones are also produced by other organs and tissues, which makes defining the endocrine contribution of adipose tissues a challenge. In this Review, we discuss the functional role of adipose tissue-derived endocrine hormones for metabolic adaptations to the environment and we highlight how these factors contribute to the development of cardiometabolic diseases. We also cover how this knowledge can be translated into human therapies. In addition, we discuss recent findings that emphasize the endocrine role of white versus thermogenic adipocytes in conditions of health and disease.

ComBATing aging-does increased brown adipose tissue activity confer longevity?

Brown and its related beige adipose tissue (BAT) play a definitive role in maintaining body temperature by producing heat through uncoupling protein 1 (UCP1), which acts by dissociating oxidative phosphorylation from ATP production, resulting in the release of heat. Therefore, in order to maintain high thermogenic capacity, BAT must act as a metabolic sink by taking up vast amounts of circulating glucose and lipids for oxidation. This, along with the rediscovery of BAT in adult humans, has fueled the study of BAT as a putative therapeutic approach to manage the growing rates of obesity and metabolic syndromes. Notably, many of the beneficial consequences of BAT activity overlap with metabolic biomarkers of extended lifespan and healthspan. In this review, we provide background about BAT including the thermogenic program, BAT's role as a secretory organ, and differences between BAT in mice and humans. We also provide details on BAT during aging, and perspectives on the potential of targeting BAT to promote lifespan and healthspan.

The beneficial effects of brown adipose tissue transplantation

Obesity is a disease that results from an imbalance between energy intake and energy expenditure. Brown adipose tissue (BAT) is a potential therapeutic target to improve the comorbidities associated with obesity due to its inherent thermogenic capacity and its ability to improve glucose metabolism. Multiple studies have shown that activation of BAT using either pharmacological treatments or cold exposure had an acute effect to increase metabolic function and reduce adiposity. Recent preclinical investigations have explored whether increasing BAT mass or activation through transplantation models could improve glucose metabolism and metabolic health. Successful BAT transplantation models have shown improvements in glucose metabolism and insulin sensitivity, as well as reductions in body mass and decreased adiposity in recipients. BAT transplantation may confer its beneficial effects through several different mechanisms, including endocrine effects via the release of 'batokines'. More recent studies have demonstrated that beige and brown adipocytes isolated from human progenitor cells and transplanted into mouse models result in metabolic improvements similar to transplantation of whole BAT; this could represent a clinically translatable model. In this review we will discuss the impetus for both early and recent investigations utilizing BAT transplantation models, the outcomes of these studies, and review the mechanisms associated with the beneficial effects of BAT transplant to confer improvements in metabolic health.

Adipose Tissue-Derived Signatures for Obesity and Type 2 Diabetes: Adipokines, Batokines and MicroRNAs

: Obesity is one of the main risk factors for type 2 diabetes mellitus (T2DM). It is closely related to metabolic disturbances in the adipose tissue that primarily functions as a fat reservoir. For this reason, adipose tissue is considered as the primary site for initiation and aggravation of obesity and T2DM. As a key endocrine organ, the adipose tissue communicates with other organs, such as the brain, liver, muscle, and pancreas, for the maintenance of energy homeostasis. Two different types of adipose tissues-the white adipose tissue (WAT) and brown adipose tissue (BAT)-secrete bioactive peptides and proteins, known as "adipokines" and "batokines," respectively. Some of them have beneficial anti-inflammatory effects, while others have harmful inflammatory effects. Recently, "exosomal microRNAs (miRNAs)" were identified as novel adipokines, as adipose tissue-derived exosomal miRNAs can affect other organs. In the present review, we discuss the role of adipose-derived secretory factors-adipokines, batokines, and exosomal miRNA-in obesity and T2DM. It will provide new insights into the pathophysiological mechanisms involved in disturbances of adipose-derived factors and will support the development of adipose-derived factors as potential therapeutic targets for obesity and T2DM.

Ectopic brown adipose tissue formation within skeletal muscle after brown adipose progenitor cell transplant augments energy expenditure

Brown adipose tissue (BAT) thermogenesis increases energy expenditure (EE). Expanding the volume of active BAT via transplantation holds promise as a therapeutic strategy for morbid obesity and diabetes. Brown adipose progenitor cells (BAPCs) can be isolated and expanded to generate autologous brown adipocyte implants. However, the transplantation of brown adipocytes is currently impeded by poor efficiency of BAT tissue formation in vivo and undesirably short engraftment time. In this study, we demonstrated that transplanting BAPCs into limb skeletal muscles consistently led to the ectopic formation of uncoupling protein 1 (UCP1)^+pos adipose tissue with long-term engraftment (>4 mo). Combining VEGF with the BAPC transplant further improved BAT formation in muscle. Ectopic engraftment of BAPC-derived BAT in skeletal muscle augmented the EE of recipient mice. Although UCP1 expression declined in long-term BAT grafts, this deterioration can be reversed by swimming exercise because of sympathetic activation. This study suggests that intramuscular transplantation of BAPCs represents a promising approach to deriving functional BAT engraftment, which may be applied to therapeutic BAT transplantation and tissue engineering.-Liu, Y., Fu, W., Seese, K., Yin, A., Yin, H. Ectopic brown adipose tissue formation within skeletal muscle after brown adipose progenitor cell transplant augments energy expenditure.

Differentiating supraclavicular from gluteal adipose tissue based on simultaneous PDFF and T2 * mapping using a 20-echo gradient-echo acquisition

Background

Adipose tissue (AT) can be classified into white and brown/beige subtypes. Chemical shift encoding‐based water–fat MRI‐techniques allowing simultaneous mapping of proton density fat fraction (PDFF) and T₂* result in a lower PDFF and a shorter T₂* in brown compared with white AT. However, AT T₂* values vary widely in the literature and are primarily based on 6‐echo data. Increasing the number of echoes in a multiecho gradient‐echo acquisition is expected to increase the precision of AT T₂* mapping.

Purpose

1) To mitigate issues of current T₂*‐measurement techniques through experimental design, and 2) to investigate gluteal and supraclavicular AT T₂* and PDFF and their relationship using a 20‐echo gradient‐echo acquisition.

Study Type

Prospective.

Subjects

Twenty‐one healthy subjects.

Field Strength/Sequence Assessment

First, a ground truth signal evolution was simulated from a single‐T₂* water–fat model. Second, a time‐interleaved 20‐echo gradient‐echo sequence with monopolar gradients of neck and abdomen/pelvis at 3 T was performed in vivo to determine supraclavicular and gluteal PDFF and T₂*. Complex‐based water–fat separation was performed for the first 6 echoes and the full 20 echoes. AT depots were segmented.

Statistical Tests

Mann‐Whitney test, Wilcoxon signed‐rank test and simple linear regression analysis.

Results

Both PDFF and T₂* differed significantly between supraclavicular and gluteal AT with 6 and 20 echoes (PDFF: P < 0.0001 each, T₂*: P = 0.03 / P < 0.0001 for 6/20 echoes). 6‐echo T₂* demonstrated higher standard deviations and broader ranges than 20‐echo T₂*. Regression analyses revealed a strong relationship between PDFF and T₂* values per AT compartment (R² = 0.63 supraclavicular, R² = 0.86 gluteal, P < 0.0001 each).

Data Conclusion

The present findings suggest that an increase in the number of sampled echoes beyond 6 does not affect AT PDFF quantification, whereas AT T₂* is considerably affected. Thus, a 20‐echo gradient‐echo acquisition enables a multiparametric analysis of both AT PDFF and T₂* and may therefore improve MR‐based differentiation between white and brown fat.

Level of Evidence: 2

Technical Efficacy: Stage 2

J. Magn. Reson. Imaging 2019;50:424–434.

Brown Adipokines

Brown adipokines are regulatory factors secreted by brown and beige adipocytes that exhibit endocrine, paracrine, and autocrine actions. Peptidic and non-peptidic molecules, including miRNAs and lipids, are constituents of brown adipokines. Brown adipose tissue remodeling to meet thermogenic needs is dependent on the secretory properties of brown/beige adipocytes. The association between brown fat activity and a healthy metabolic profile, in relation to energy balance and glucose and lipid homeostasis, is influenced by the endocrine actions of brown adipokines. A comprehensive knowledge of the brown adipocyte secretome is still lacking. Advancements in the identification and characterization of brown adipokines will facilitate therapeutic interventions for metabolic diseases, as these molecules are obvious candidates to therapeutic agents. Moreover, identification of brown adipokines as circulating biomarkers of brown adipose tissue activity may be particularly useful for noninvasive assessment of brown adipose tissue alterations in human pathologies.

ErbB4 deletion predisposes to development of metabolic syndrome in mice

ErbB4, a member of the EGF receptor family, plays a variety of roles in physiological and pathological states. Genetic studies have indicated a link between ErbB4 and type 2 diabetes and obesity, but its role in metabolic syndrome (MetS) has not been reported. In the current study we found that mice with ErbB4 deletion developed MetS after 24 wk on a medium-fat diet (MFD), as indicated by development of obesity, dyslipidemia, hepatic steatosis, hyperglycemia, hyperinsulinemia, and insulin resistance, compared with wild-type mice. ErbB4 deletion mice also exhibited increased amounts of subcutaneous and visceral fat, with increased serum leptin levels, compared with wild-type mice, whereas levels of adiponectin were not significantly different. Histologically, severe inflammation, indicated by F4/80 immunostaining and M1 macrophage polarization, was detected in inguinal and epididymal white adipose tissue in ErbB4 deletion mice. ErbB4 expression decreased during 3T3-L1 preadipocyte differentiation. Administration of neuroregulin 4, a specific ligand for ErbB4, to 3T3-L1 adipocytes had no effect on adipogenesis and lipolysis but significantly inhibited lipogenesis, promoted browning, induced GLUT4 redistribution to the cell membrane, and increased glucose uptake. Neuroregulin 4 also significantly increased glucose uptake in adipocytes isolated from wild-type mice, while these effects were significantly decreased in adipocytes isolated from ErbB4 deletion mice. In conclusion, our results indicate that ErbB4 may play an important role in glucose homeostasis and lipogenesis. ErbB4 deficiency-related obesity and adipose tissue inflammation may contribute to the development of MetS.

Adipose Tissue and Modulation of Hypertension

PURPOSE OF REVIEW

Obesity is a major risk factor for the development of hypertension (HTN), a leading cause of cardiovascular morbidity and mortality. Growing body of research suggests that adipose tissue function is directly associated with the pathogenesis of obesity-related HTN. In this review, we will discuss recent research on the role of adipose tissue in blood pressure (BP) regulation and activation of brown adipose tissue (BAT) as a potentially new therapeutic means for obesity-related HTN.

RECENT FINDINGS

Adipose tissue provides mechanical protection of the blood vessels and plays a role in regulation of vascular tone. Exercise and fasting activate BAT and induce browning of white adipose tissue (WAT). BAT-secreted FGF21 lowers BP and protects against HTN. Browning of perivascular WAT improves HTN. New insights on WAT browning and BAT activation can open new avenues of potential therapeutic interventions to treat obesity-related HTN.

Regulation of islet glucagon secretion: Beyond calcium

The islet of Langerhans plays a key role in glucose homeostasis through regulated secretion of the hormones insulin and glucagon. Islet research has focused on the insulin-secreting β-cells, even though aberrant glucagon secretion from α-cells also contributes to the aetiology of diabetes. Despite its importance, the mechanisms controlling glucagon secretion remain controversial. Proper α-cell function requires the islet milieu, where β- and δ-cells drive and constrain α-cell dynamics. The response of glucagon to glucose is similar between isolated islets and that measured in vivo, so it appears that the glucose dependence requires only islet-intrinsic factors and not input from blood flow or the nervous system. Elevated intracellular free Ca²⁺ is needed for α-cell exocytosis, but interpreting Ca²⁺ data is tricky since it is heterogeneous among α-cells at all physiological glucose levels. Total Ca²⁺ activity in α-cells increases slightly with glucose, so Ca²⁺ may serve a permissive, rather than regulatory, role in glucagon secretion. On the other hand, cAMP is a more promising candidate for controlling glucagon secretion and is itself driven by paracrine signalling from β- and δ-cells. Another pathway, juxtacrine signalling through the α-cell EphA receptors, stimulated by β-cell ephrin ligands, leads to a tonic inhibition of glucagon secretion. We discuss potential combinations of Ca²⁺ , cAMP, paracrine and juxtacrine factors in the regulation of glucagon secretion, focusing on recent data in the literature that might unify the field towards a quantitative understanding of α-cell function.

New approaches targeting brown adipose tissue transplantation as a therapy in obesity

Brown adipose tissue (BAT) is raising high expectations as a potential target in the fight against metabolic disorders such as obesity and type 2 diabetes. BAT utilizes fuels such as fatty acids to maintain body temperature by uncoupling mitochondrial electron transport to produce heat instead of ATP. This process is called thermogenesis. BAT was considered to be exclusive to rodents and human neonates. However, in the last decade several studies have demonstrated that BAT is not only present but also active in adult humans and that its activity is reduced in several pathological conditions, such as aging, obesity, and diabetes. Thus, tremendous efforts are being made by the scientific community to enhance either BAT mass or activity. Several activators of thermogenesis have been described, such as natriuretic peptides, bone morphogenic proteins, or fibroblast growth factor 21. Furthermore, recent studies have tested a therapeutic approach to directly increase BAT mass by the implantation of either adipocytes or fat tissue. This approach might have an important future in regenerative medicine and in the fight against metabolic disorders. Here, we review the emerging field of BAT transplantation including the various sources of mesenchymal stem cell isolation in rodents and humans and the described metabolic outcomes of adipocyte cell transplantation and BAT transplantation in obesity.

Cyanidin-3-O-β-glucoside regulates the activation and the secretion of adipokines from brown adipose tissue and alleviates diet induced fatty liver

AIM

Cyanidin-3-O-β-glucoside (Cy-3-G) the most abundant monomer of anthocyanins has multiple protective effects on many diseases. To date, whether Cy-3-G could regulate the function of brown adipose tissue (BAT) is still unclear and whether this regulation could influence the secretion of adipokines from BAT to prevent non-alcoholic fatty liver disease (NAFLD) indirectly remains to be explored. In this study we investigated the effect of Cy-3-G on BAT and the potential role of Cy-3-G to prevent fatty liver through regulating the secretion of BAT.

METHODS

Male C57BL/6 J mice were fed with a high fat high cholesterol (HFC) diet with or without 200 mg/kg B.W Cy-3-G for 8 weeks. In in vitro experiments, the differentiated brown adipocytes (BAC) and C3H10T1/2 clone8 cells were treated with 0.2 mM palmitate with or without Cy-3-G for 72 or 96 h. Then the culture media of C3H10T1/2 clone8 cells were collected for measuring the adipokines secretion by immunoblot assay and were applied to culture HepG2 cells or LO2 cells for 24 h. Lipid accumulation in HepG2 cells or LO2 cells were evaluated by oil red O staining.

RESULTS

Here we found that Cy-3-G regulated the activation of BAT and the expression of adipokines in BAT which were disrupted by HFC diet and alleviated diet induced fatty liver in mice. In in vitro experiments, Cy-3-G inhibited the release of adipokines including extracellular nicotinamide phosphoribosyltransferase (eNAMPT) and fibroblast growth factor 21 (FGF21) from differentiated C3H10T1/2 clone8 cells induced by palmitate, which was accompanied by a reduction of lipid accumulation in HepG2 cells and LO2 cells cultured by the corresponding collected media of C3H10T1/2 clone8 cells.

CONCLUSIONS

These results indicate that Cy-3-G can regulate the thermogenic and secretory functions of BAT. Furthermore, our data suggest that the protective effect of Cy-3-G on hepatic lipid accumulation is probably via regulating the secretion of adipokines from BAT.