Brown adipose tissue and its therapeutic potential

Reversing Pdgfrβ signaling restores metabolically active beige adipocytes by alleviating ILC2 suppression in aged and obese mice

OBJECTIVE

Platelet Derived Growth Factor Receptor Beta (Pdgfrβ) suppresses the formation of cold temperature-induced beige adipocytes in aged mammals. We aimed to determine if deleting Pdgfrβ in aged mice could rejuvenate metabolically active beige adipocytes by activating group 2 innate lymphoid cells (ILC2), and whether this effect could counteract diet-induced obesity-associated beige fat decline.

METHODS

We employed Pdgfrβ gain-of-function and loss-of-function mouse models targeting beige adipocyte progenitor cells (APCs). Our approach included cold exposure, metabolic cage analysis, and age and diet-induced obesity models to examine beige fat development and metabolic function under varied Pdgfrβ activity.

RESULTS

Acute cold exposure alone enhanced metabolic benefits in aged mice, irrespective of beige fat generation. However, Pdgfrβ deletion in aged mice reestablished the formation of metabolically functional beige adipocytes, enhancing metabolism. Conversely, constitutive Pdgfrβ activation in young mice stymied beige fat development. Mechanistically, Pdgfrβ deletion upregulated IL-33, promoting ILC2 recruitment and activation, whereas Pdgfrβ activation reduced IL-33 levels and suppressed ILC2 activity. Notably, diet-induced obesity markedly increased Pdgfrβ expression and Stat1 signaling, which inhibited IL-33 induction and ILC2 activation. Genetic deletion of Pdgfrβ restored beige fat formation in obese mice, improving whole-body metabolism.

CONCLUSIONS

This study reveals that cold temperature exposure alone can trigger metabolic activation in aged mammals. However, reversing Pdgfrβ signaling in aged and obese mice not only restores beige fat formation but also renews metabolic function and enhances the immunological environment of white adipose tissue (WAT). These findings highlight Pdgfrβ as a crucial target for therapeutic strategies aimed at combating age- and obesity-related metabolic decline.

Differential effects of milk, yogurt, and cheese on energy homeostasis and brown adipose tissue phenotype in high-fat diet-induced obese mice

Aim: We hypothesized that milk, yogurt, and cheese have differential impacts on energy expenditure (EE) and obesity in mice fed a high-fat diet (HFD). Methods: C57BL/6 mice (n = 16 per group) were fed a HFD or a HFD supplemented with fat-free milk (MILK), fat-free plain yogurt (YOG), or reduced-fat cheddar cheese (CHE; 19 kcal% fat), each provided at 10% of the daily energy intake, for 8 weeks. EE was quantified using a metabolic chamber. Metabolic pathways related to BAT mitochondrial function and uncoupling protein 1 (UCP1) abundance were assessed. Serum lipidomic profiles were analyzed to identify potential mediators of the observed effects. Results: MILK supplementation lowered weight gain and fat accumulation and enhanced EE and BAT thermogenesis, perhaps via the SIRT1-AMPK-PGC1α axis in BAT. This led to elevated UCP1 abundance and enhanced the abundance of hormone-sensitive lipase (HSL). MILK also altered serum lipid species, indicating enhanced energy use, and promoted BAT thermogenesis and mitochondrial function pathways. YOG exhibited a similar pattern but a lower magnitude of effects than MILK on reducing weight gain and fat mass, increasing EE, and BAT thermogenic proteins, including AMPK-PGC1α-UCP1. Both MILK and YOG showed a relative increase in serum PC 15:0_15:0 and LPC 15:0. In contrast, CHE reduced weight gain and increased EE without impacting BAT thermogenesis proteins or serum lipid species. Conclusion: Our study showed that MILK, YOG, and CHE reduced weight gain in mice on a HFD by increasing EE. MILK and YOG also up-regulated BAT thermogenesis, while both additionally altered lipids involved in fat metabolism and inflammation. CHE did not affect BAT thermogenesis and lipid species compared to HFD.

Association between total body muscle-fat ratio and risk of thyroid disorders: a cross-sectional study

BACKGROUND

Thyroid disorders(TD) poses a significant health threat to Americans due to its high incidence rate. Obesity, a common factor linked to thyroid disorders, has garnered increasing attention. While Body mass index (BMI) is a widely used obesity index, it fails to account for the distribution of muscle and fat in the body. Recently, tMFR has emerged as a crucial obesity index in clinical research, warranting further investigation into its association with TD.

OBJECTIVE

Exploring the association between tMFR and thyroid disorders.

METHOD

A comprehensive survey and data analysis were conducted using the NHANES database to investigate the relationship between tMFR and the risk of TD. This study utilized multiple logistic regression, smooth curve fitting, and subgroup analysis across four periods from 2011 to 2018.

RESULT

A total of 11,912 subjects were included in the study, showing a prevalence of 7.14% for TD. The research indicated that tMFR had an inverse correlation with the risk of TD in a comprehensive model (OR = 0.90, 95% CI 0.82 to 1.00). When tMFR was divided into quartiles (Q1-Q4), individuals in the highest quartile had a 28% lower risk of TD than those in Q1 (OR = 0.72, 95% CI 0.57 to 0.91). Analysis using smoothed curve fitting demonstrated a nonlinear relationship between tMFR and TD risk, with the inflection point for tMFR saturation effect identified as 1.5. Subgroup analysis further confirmed the strong association between tMFR and TD risk. Receiver operating characteristic (ROC) curve analysis indicated that tMFR exhibited superior predictive ability for TD relative to BMI.

CONCLUSION

The study found a negative association between tMFR and the risk of TD; however, additional prospective studies are required to validate these findings.

Adipose Tissue Dysfunction Related to Climate Change and Air Pollution: Understanding the Metabolic Consequences

Obesity, a global pandemic, poses a major threat to healthcare systems worldwide. Adipose tissue, the energy-storing organ during excessive energy intake, functions as a thermoregulator, interacting with other tissues to regulate systemic metabolism. Specifically, brown adipose tissue (BAT) is positively associated with an increased resistance to obesity, due to its thermogenic function in the presence of uncoupled protein 1 (UCP1). Recently, studies on climate change and the influence of environmental pollutants on energy homeostasis and obesity have drawn increasing attention. The reciprocal relationship between increasing adiposity and increasing temperatures results in reduced adaptive thermogenesis, decreased physical activity, and increased carbon footprint production. In addition, the impact of climate change makes obese individuals more prone to developing type 2 diabetes mellitus (T2DM). An impaired response to heat stress, compromised vasodilation, and sweating increase the risk of diabetes-related comorbidities. This comprehensive review provides information about the effects of climate change on obesity and adipose tissue, the risk of T2DM development, and insights into the environmental pollutants causing adipose tissue dysfunction and obesity. The effects of altered dietary patterns on adiposity and adaptation strategies to mitigate the detrimental effects of climate change are also discussed.

Perivascular Adipose Tissue and Uterine Artery Adaptations to Pregnancy

Pregnancy is characterized by longitudinal maternal, physiological adaptations to support the development of a fetus. One of the cardinal maternal adaptations during a healthy pregnancy is a progressive increase in uterine artery blood flow. This facilitates sufficient blood supply for the development of the placenta and the growing fetus. Regional hemodynamic changes in the uterine circulation, such as a vast reduction in uterine artery resistance, are mainly facilitated by changes in uterine artery reactivity and myogenic tone along with remodeling of the uterine arteries. These regional changes in vascular reactivity have been attributed to pregnancy-induced adaptations of cell-to-cell communication mechanisms, with an emphasis on the interaction between endothelial and vascular smooth muscle cells. Perivascular adipose tissue (PVAT) is considered the fourth layer of the vascular wall and contributes to the regulation of vascular reactivity in most vascular beds and most species. This review focuses on mechanisms of uterine artery reactivity and the role of PVAT in pregnancy-induced maternal vascular adaptations, with an emphasis on the uterine circulation.

Macrophage-derived chemokine CCL22 establishes local LN-mediated adaptive thermogenesis and energy expenditure

There is a regional preference around lymph nodes (LNs) for adipose beiging. Here, we show that local LN removal within inguinal white adipose tissue (iWAT) greatly impairs cold-induced beiging, and this impairment can be restored by injecting M2 macrophages or macrophage-derived C-C motif chemokine (CCL22) into iWAT. CCL22 injection into iWAT effectively promotes iWAT beiging, while blocking CCL22 with antibodies can prevent it. Mechanistically, the CCL22 receptor, C-C motif chemokine receptor 4 (CCR4), within eosinophils and its downstream focal adhesion kinase/p65/interleukin-4 signaling are essential for CCL22-mediated beige adipocyte formation. Moreover, CCL22 levels are inversely correlated with body weight and fat mass in mice and humans. Acute elevation of CCL22 levels effectively prevents diet-induced body weight and fat gain by enhancing adipose beiging. Together, our data identify the CCL22-CCR4 axis as an essential mediator for LN-controlled adaptive thermogenesis and highlight its potential to combat obesity and its associated complications.

Reversing Pdgfrβ Signaling Restores Metabolically Active Beige Adipocytes by Alleviating ILC2 Suppression in Aged and Obese Mice

Objective

Platelet Derived Growth Factor Receptor Beta (Pdgfrβ) suppresses the formation of cold temperature-induced beige adipocytes in aged mammals. We aimed to determine if deleting Pdgfrβ in aged mice could rejuvenate metabolically active beige adipocytes by activating group 2 innate lymphoid cells (ILC2), and whether this effect could counteract diet-induced obesity-associated beige fat decline.

Methods

We employed Pdgfrβ gain-of-function and loss-of-function mouse models targeting beige adipocyte progenitor cells (APCs). Our approach included cold exposure, metabolic cage analysis, and age and diet-induced obesity models to examine beige fat development and metabolic function under varied Pdgfrβ activity.

Results

Acute cold exposure alone enhanced metabolic benefits in aged mice, irrespective of beige fat generation. However, Pdgfrβ deletion in aged mice reestablished the formation of metabolically functional beige adipocytes, enhancing metabolism. Conversely, constitutive Pdgfrβ activation in young mice stymied beige fat development. Mechanistically, Pdgfrβ deletion upregulated IL-33, promoting ILC2 recruitment and activation, whereas Pdgfrβ activation reduced IL-33 levels and suppressed ILC2 activity. Notably, diet-induced obesity markedly increased Pdgfrβ expression and Stat1 signaling, which inhibited IL-33 induction and ILC2 activation. Genetic deletion of Pdgfrβ restored beige fat formation in obese mice, improving whole-body metabolism.

Conclusion

This study reveals that cold temperature exposure alone can trigger metabolic activation in aged mammals. However, reversing Pdgfrβ signaling in aged and obese mice not only restores beige fat formation but also renews metabolic function and enhances the immunological environment of white adipose tissue (WAT). These findings highlight Pdgfrβ as a crucial target for therapeutic strategies aimed at combating age- and obesity-related metabolic decline.

Smooth muscle cell-derived Cxcl12 directs macrophage accrual and sympathetic innervation to control thermogenic adipose tissue

Sympathetic innervation of brown adipose tissue (BAT) controls mammalian adaptative thermogenesis. However, the cellular and molecular underpinnings contributing to BAT innervation remain poorly defined. Here, we show that smooth muscle cells (SMCs) support BAT growth, lipid utilization, and thermogenic plasticity. Moreover, we find that BAT SMCs express and control the bioavailability of Cxcl12. SMC deletion of Cxcl12 fosters brown adipocyte lipid accumulation, reduces energy expenditure, and increases susceptibility to diet-induced metabolic dysfunction. Mechanistically, we find that Cxcl12 stimulates CD301+ macrophage recruitment and supports sympathetic neuronal maintenance. Administering recombinant Cxcl12 to obese mice or leptin-deficient (Ob/Ob) mice is sufficient to boost macrophage presence and drive sympathetic innervation to restore BAT morphology and thermogenic responses. Altogether, our data reveal an SMC chemokine-dependent pathway linking immunological infiltration and sympathetic innervation as a rheostat for BAT maintenance and thermogenesis.

Alternative isoform expression of key thermogenic genes in human beige adipocytes

Background

The beneficial effect of thermogenic adipocytes in maintaining body weight and protecting against metabolic disorders has raised interest in understanding the regulatory mechanisms defining white and beige adipocyte identity. Although alternative splicing has been shown to propagate adipose browning signals in mice, this has yet to be thoroughly investigated in human adipocytes.

Methods

We performed parallel white and beige adipogenic differentiation using primary adipose stem cells from 6 unrelated healthy subjects and assessed differential gene and isoform expression in mature adipocytes by RNA sequencing.

Results

We find 777 exon junctions with robust differential usage between white and beige adipocytes in all 6 subjects, mapping to 562 genes. Importantly, only 10% of these differentially spliced genes are also differentially expressed, indicating that alternative splicing constitutes an additional layer of gene expression regulation during beige adipocyte differentiation. Functional classification of alternative isoforms points to a gain of function for key thermogenic transcription factors such as PPARG and CITED1, and enzymes such as PEMT, or LPIN1. We find that a large majority of the splice variants arise from differential TSS usage, with beige-specific TSSs being enriched for PPARγ and MED1 binding compared to white-specific TSSs. Finally, we validate beige specific isoform expression at the protein level for two thermogenic regulators, PPARγ and PEMT.

Discussion

These results suggest that differential isoform expression through alternative TSS usage is an important regulatory mechanism for human adipocyte thermogenic specification.

Angiostrongylus cantonensis induces energy imbalance and dyskinesia in mice by reducing the expression of melanin-concentrating hormone

BACKGROUND

Infection with Angiostrongylus cantonensis (AC) in humans or mice can lead to severe eosinophilic meningitis or encephalitis, resulting in various neurological impairments. Developing effective neuroprotective drugs to improve the quality of life in affected individuals is critical.

METHODS

We conducted a Gene Ontology enrichment analysis on microarray gene expression (GSE159486) in the brains of AC-infected mice. The expression levels of melanin-concentrating hormone (MCH) were confirmed through real-time quantitative PCR (RT-qPCR) and immunofluorescence. Metabolic parameters were assessed using indirect calorimetry, and mice's energy metabolism was evaluated via pathological hematoxylin and eosin (H&E) staining, serum biochemical assays, and immunohistochemistry. Behavioral tests assessed cognitive and motor functions. Western blotting was used to measure the expression of synapse-related proteins. Mice were supplemented with MCH via nasal administration.

RESULTS

Postinfection, a marked decrease in Pmch expression and the encoded MCH was observed. Infected mice exhibited significant weight loss, extensive consumption of sugar and white fat tissue, reduced movement distance, and decreased speed, compared with the control group. Notably, nasal administration of MCH countered the energy imbalance and dyskinesia caused by AC infection, enhancing survival rates. MCH treatment also increased the expression level of postsynaptic density protein 95 (PSD95) and microtubule-associated protein-2 (MAP2), as well as upregulated transcription level of B cell leukemia/lymphoma 2 (Bcl2) in the cortex.

CONCLUSIONS

Our findings suggest that MCH improves dyskinesia by reducing loss of synaptic proteins, indicating its potential as a therapeutic agent for AC infection.

Human cold adaptation: An unfinished agenda v2.0

BACKGROUND

Research on human extreme cold climate adaptations has benefitted from a recent resurgence since Ted Steegmann laid out his Human Cold Adaptation Agenda in 2007. Human biologists have drastically expanded our knowledge in this area during the last 15 years, but we still have a great deal more work to do to fulfill the cold climate adaptation agenda.

METHODS

Here, I follow Steegmann's example by providing a review of cold climate adaptations and setting forth a new, expanded agenda.

RESULTS

I review the foundational work on cold climate adaptations including classic Bergmann, Allen, and Thomson rules as well as early work assessing metabolic differences among Indigenous cold climate populations. From there, I discuss some of the groundbreaking work currently taking place on cold climate adaptations such as brown adipose tissue (a heat generating organ), physical activity levels, metabolic rates, and behavioral/cultural mechanisms. Finally, I present a path forward for future research with a focus on some of the basic extreme cold adaptations as well as how human biologists should approach the effects of climate change on human health and well-being, particularly within a cold climate context.

CONCLUSION

The Arctic has felt the dramatic effects of climate change sooner and more acutely than other parts of the world, making it an ideal location for studying both cold climate adaptations and climate change resilience. Human biologists have a great deal to contribute to the conversation on not only adaptations to extreme cold, but also the ways in which climate change is being embodied by cold climate populations.

Metformin plus L-carnitine enhances brown/beige adipose tissue activity via Nrf2/HO-1 signaling to reduce lipid accumulation and inflammation in murine obesity

This study investigated how Metformin (Met) combined with L-carnitine (L-car) modulates brown adipose tissue (BAT) to affect obesity. High-fat-induced obese rats received daily oral gavage with Met and/or L-car, followed by serum biochemical analysis, histopathological observation on adipose tissues, and immunochemistry test for the abdominal expression of BAT-specific uncoupling protein 1 (UCP1). Mouse-embryonic-fibroblast cells were induced into adipocytes, during which Met plus L-car was added with/without saturated fatty acid (SFA). The role of nuclear factor erythroid 2-related factor 2 (Nrf2) in adipocyte browning was investigated by gene silencing. Mitochondria biogenesis in adipocytes was inspected by Mitotracker staining. Nrf2/heme oxygenase-1 (HO-1)/BAT-related genes/proinflammatory marker expressions in adipose tissues and/or adipocytes were analyzed by Western blot, qRT-PCR, and/or immunofluorescence test. Met or L-car improved metabolic disorders, reduced adipocyte vacuolization and swelling, upregulated levels of BAT-related genes including UCP1 and downregulated proinflammatory marker expressions, and activated the Nrf2/HO-1 pathway in adipose tissues of obese rats. Met and L-car functioned more strongly than alone. In adipocytes, Met plus L-car upregulated BAT-related gene levels and protected against SFA-caused inflammation promotion and mitochondria degeneration, which yet was attenuated by Nrf2 silencing. Met plus L-car enhances BAT activity and white adipose tissue browning via the Nrf2/HO-1 pathway to reduce lipid accumulation and inflammation in obese rats.

Designer Fat Cells: Adipogenic Differentiation of CRISPR-Cas9 Genome-Engineered Induced Pluripotent Stem Cells

Adipose tissue is an active endocrine organ that can signal bidirectionally to many tissues and organ systems in the body. With obesity, adipose tissue is a source of low-level inflammation that contributes to various co-morbidities and damage to downstream effector tissues. The ability to synthesize genetically engineered adipose tissue could have critical applications in studying adipokine signaling and the use of adipose tissue for novel therapeutic strategies. This study aimed to develop a method for non-viral adipogenic differentiation of genome-edited murine induced pluripotent stem cells (iPSCs) and to test the ability of such cells to engraft in mice in vivo . Designer adipocytes were created from iPSCs, which can be readily genetically engineered using CRISPR-Cas9 to knock out or insert individual genes of interest. As a model system for adipocyte-based drug delivery, an existing iPSC cell line that transcribes interleukin 1 receptor antagonist under the endogenous macrophage chemoattractant protein-1 promoter was tested for adipogenic capabilities under these same differentiation conditions. To understand the role of various adipocyte subtypes and their impact on health and disease, an efficient method was devised for inducing browning and whitening of IPSC-derived adipocytes in culture. Finally, to study the downstream effects of designer adipocytes in vivo , we transplanted the designer adipocytes into fat-free lipodystrophic mice as a model system for studying adipose signaling in different models of disease or repair. This novel translational tissue engineering and regenerative medicine platform provides an innovative approach to studying the role of adipose interorgan communication in various conditions.

A Comprehensive Summary of the Current Understanding of the Relationship between Severe Obesity, Metabolic Syndrome, and Inflammatory Status

At present, obesity, as a part of metabolic syndrome, represents the leading factor for disability, and is correlated with higher inflammation status, morbidity, and mortality. The purpose of our study is to add new insights to the present body of knowledge regarding the correlations between chronic systemic inflammation and severe obesity, which cannot be treated without considering other metabolic syndrome conditions. Biomarkers of high-level chronic inflammation are recognized as important predictors of pro-inflammatory disease. Besides the well-known pro-inflammatory cytokines, such as WBCs (white blood cells), IL-1 (interleukin-1), IL-6 (interleukin-6), TNF-alpha (tumor necrosis factor-alpha), and hsCRP (high-sensitivity C-reactive protein), as well as anti-inflammatory markers, such as adiponectin and systemic inflammation, can be determined by a variety of blood tests as a largely available and inexpensive inflammatory biomarker tool. A few parameters, such as the neutrophil-to-lymphocyte ratio; the level of cholesterol 25-hydroxylase, which is part of the macrophage-enriched metabolic network in adipose tissue; or levels of glutamine, an immune-metabolic regulator in white adipose tissue, are markers that link obesity to inflammation. Through this narrative review, we try to emphasize the influence of the weight-loss process in reducing obesity-related pro-inflammatory status and associated comorbidities. All data from the presented studies report positive results following weight-loss procedures while improving overall health, an effect that lasts over time, as far as the existing research data show.

Ginsenoside Rg1 activates brown adipose tissue to counteract obesity in high-fat diet-fed mice by regulating gut microbes and bile acid composition

Obesity is a global health problem strongly linked to gut microbes and their metabolites. In this study, ginsenoside Rg1 (Rg1) reduced lipid droplet size and hepatic lipid accumulation by activating uncoupling protein 1 expression in brown adipose tissue (BAT), which in turn inhibited high-fat diet (HFD)-induced weight gain in mice. Furthermore, the intestinal flora of mice was altered, the abundance of Lachnoclostridium, Streptococcus, Lactococcus, Enterococcus and Erysipelatoclostridium was upregulated, and the concentrations of fecal bile acids were altered, with cholic acid and taurocholic acid concentrations being significantly increased. In addition, the beneficial effects of Rg1 were eliminated in mice treated with a combination of antibiotics. In conclusion, these results suggest that Rg1 activates BAT to counteract obesity by regulating gut microbes and bile acid composition in HFD-fed mice.

Thermogenic adipose tissue in energy regulation and metabolic health

The ability to generate thermogenic fat could be a targeted therapy to thwart obesity and improve metabolic health. Brown and beige adipocytes are two types of thermogenic fat cells that regulate energy balance. Both adipocytes share common morphological, biochemical, and thermogenic properties. Yet, recent evidence suggests unique features exist between brown and beige adipocytes, such as their cellular origin and thermogenic regulatory processes. Beige adipocytes also appear highly plastic, responding to environmental stimuli and interconverting between beige and white adipocyte states. Additionally, beige adipocytes appear to be metabolically heterogenic and have substrate specificity. Nevertheless, obese and aged individuals cannot develop beige adipocytes in response to thermogenic fat-inducers, creating a key clinical hurdle to their therapeutic promise. Thus, elucidating the underlying developmental, molecular, and functional mechanisms that govern thermogenic fat cells will improve our understanding of systemic energy regulation and strive for new targeted therapies to generate thermogenic fat. This review will examine the recent advances in thermogenic fat biogenesis, molecular regulation, and the potential mechanisms for their failure.

Identification and characterization of the long non-coding RNA NFIA-AS2 as a novel locus for body mass index in American Indians

BACKGROUND

Genome-wide association studies have shown that body mass index (BMI), an estimate of obesity, is highly polygenic. Individual variants typically have small effect sizes, making it challenging to identify unique loci in under-represented ethnic groups which lack statistical power due to their small sample size. Yet obesity is a major health disparity and is particularly prevalent in southwestern American Indians. Here, we identify and characterize a new locus for BMI that was detected by analyzing moderate associations with BMI obtained in a population-based sample of southwestern American Indians together with the well-powered GIANT dataset.

METHODS

Genotypes for 10.5 million variants were tested for association with BMI in 5870 American Indians and 2600 variants that showed an association P < 10^-3 in the American Indian sample were combined in a meta-analysis with the BMI data reported in GIANT (N = 240,608). The newly identified gene, NFIA-AS2 was functionally characterized, and the impact of its lead associated variant rs1777538 was studied both in-silico and in-vitro.

RESULTS

Rs1777538 (T/C; C allele frequency = 0.16 in American Indians and 0.04 in GIANT, meta-analysis P = 5.0 × 10^-7) exhibited a large effect in American Indians (1 kg/m² decrease in BMI per copy of C allele). NFIA-AS2 was found to be a nuclear localized long non-coding RNA expressed in tissues pertinent to human obesity. Analysis of this variant in human brown preadipocytes showed that NFIA-AS2 transcripts carrying the C allele had increased RNA degradation compared to the T allele transcripts (half-lives = 9 h, 13 h respectively). During brown adipogenesis, NFIA-AS2 featured a stage-specific regulation of nearby gene expression where rs1777538 demonstrated an allelic difference in regulation in the mature adipocytes (the strongest difference was observed for L1TD1, P = 0.007).

CONCLUSION

Our findings support a role for NFIA-AS2 in regulating pathways that impact BMI.

Brown adipose tissue and alzheimer's disease

Alzheimer's disease (AD), the most common type of senile dementia, is a chronic neurodegenerative disease characterized by cognitive dysfunction and behavioral disability. The two histopathological hallmarks in this disease are the extraneuronal accumulation of amyloid-β (Aβ) and the intraneuronal deposition of neurofibrillary tangles (NFTs). Despite this, central and peripheral metabolic dysfunction, such as abnormal brain signaling, insulin resistance, inflammation, and impaired glucose utilization, have been indicated to be correlated with AD. There is solid evidence that the age-associated thermoregulatory deficit induces diverse metabolic changes associated with AD development. Brown adipose tissue (BAT) has been known as a thermoregulatory organ particularly vital during infancy. However, in recent years, BAT has been accepted as an endocrine organ, being involved in various functions that prevent AD, such as regulating energy metabolism, secreting hormones, improving insulin sensitivity, and increasing glucose utilization in adult humans. This review focuses on the mechanisms of BAT activation and the effect of aging on BAT production and signaling. Specifically, the evidence demonstrating the effect of BAT on pathological mechanisms influencing the development of AD, including insulin pathway, thermoregulation, and other hormonal pathways, are reviewed in this article.

Nutritional activities of luteolin in obesity and associated metabolic diseases: an eye on adipose tissues

Obesity is characterized by excessive body fat accumulation and is a high-risk factor for metabolic comorbidities, including type 2 diabetes, nonalcoholic fatty liver disease, and cardiovascular disease. In lean individuals, adipose tissue (AT) is not only an important regulatory organ for energy storage and metabolism, but also an indispensable immune and endocrine organ. The sustained energy imbalance induces adipocyte hypotrophy and hyperplasia as well as AT remodeling, accompanied by chronic low-grade inflammation and adipocytes dysfunction in AT, ultimately leading to systemic insulin resistance and ectopic lipid deposition. Luteolin is a natural flavonoid widely distributed in fruits and vegetables and possesses multifold biological activities, such as antioxidant, anticancer, and anti-inflammatory activities. Diet supplementation of this flavonoid has been reported to inhibit AT lipogenesis and inflammation as well as the ectopic lipid deposition, increase AT thermogenesis and systemic energy expenditure, and finally improve obesity and associated metabolic diseases. The purpose of this review is to reveal the nutritional activities of luteolin in obesity and its complications with emphasis on its action on AT energy metabolism, immunoregulation, and endocrine intervention.

Regulation of Adipose Progenitor Cell Expansion in a Novel Micro-Physiological Model of Human Adipose Tissue Mimicking Fibrotic and Pro-Inflammatory Microenvironments

The expansion of adipose progenitor cells (APCs) plays an important role in the regeneration of the adipose tissue in physiological and pathological situations. The major role of CD26-expressing APCs in the generation of adipocytes has recently been highlighted, revealing that the CD26 APC subtype displays features of multipotent stem cells, giving rise to CD54- and CD142-expressing preadipocytes. However, a relevant human in vitro model to explore the regulation of the APC subpopulation expansion in lean and obese adipose tissue microenvironments is still lacking. In this work, we describe a novel adipose tissue model, named ExAdEx, that can be obtained from cosmetic surgery wastes. ExAdEx products are adipose tissue units maintaining the characteristics and organization of adipose tissue as it presents in vivo. The model was viable and metabolically active for up to two months and could adopt a pathological-like phenotype. The results revealed that inflammatory and fibrotic microenvironments differentially regulated the expansion of the CD26 APC subpopulation and its CD54 and CD142 APC progenies. The approach used significantly improves the method of generating adipose tissue models, and ExAdEx constitutes a relevant model that could be used to identify pathways promoting the expansion of APCs in physiological and pathological microenvironments.

A sensitive mitochondrial thermometry 2.0 and the availability of thermogenic capacity of brown adipocyte

The temperature of a living cell is a crucial parameter for cellular events, such as cell division, gene expressions, enzyme activities and metabolism. We previously developed a quantifiable mitochondrial thermometry 1.0 based on rhodamine B methyl ester (RhB-ME) and rhodamine 800 (Rh800), and the theory for mitochondrial thermogenesis. Given that the synthesized RhB-ME is not readily available, thus, a convenient mitochondrial thermometry 2.0 based on tetra-methyl rhodamine methyl ester (TMRM) and Rh800 for the thermogenic study of brown adipocyte was further evolved. The fluorescence of TMRM is more sensitive (∼1.4 times) to temperature than that of RhB-ME, then the TMRM-based mito-thermometry 2.0 was validated and used for the qualitatively dynamic profiles for mitochondrial thermogenic responses and mitochondrial membrane potential in living cells simultaneously. Furthermore, our results demonstrated that the heterogenous thermogenesis evoked by β3 adrenoceptor agonist only used overall up to ∼46% of the thermogenic capacity evoked by CCCP stimulation. On the other hand, the results demonstrated that the maximum thermogenesis evoked by NE and oligomycin A used up to ∼79% of the thermogenic capacity, which suggested the maximum thermogenic capacity under physiological conditions by inhibiting the proton-ATPase function of the mitochondrial complex V, such as under the cold activation of sympathetic nerve and the co-release of sympathetic transmitters.

Drug-Initiated Activity Metabolomics Identifies Myristoylglycine as a Potent Endogenous Metabolite for Human Brown Fat Differentiation

Worldwide, obesity rates have doubled since the 1980s and in the USA alone, almost 40% of adults are obese, which is closely associated with a myriad of metabolic diseases such as type 2 diabetes and arteriosclerosis. Obesity is derived from an imbalance between energy intake and consumption, therefore balancing energy homeostasis is an attractive target for metabolic diseases. One therapeutic approach consists of increasing the number of brown-like adipocytes in the white adipose tissue (WAT). Whereas WAT stores excess energy, brown adipose tissue (BAT) can dissipate this energy overload in the form of heat, increasing energy expenditure and thus inhibiting metabolic diseases. To facilitate BAT production a high-throughput screening approach was developed on previously known drugs using human Simpson-Golabi-Behmel Syndrome (SGBS) preadipocytes. The screening allowed us to discover that zafirlukast, an FDA-approved small molecule drug commonly used to treat asthma, was able to differentiate adipocyte precursors and white-biased adipocytes into functional brown adipocytes. However, zafirlukast is toxic to human cells at higher dosages. Drug-Initiated Activity Metabolomics (DIAM) was used to investigate zafirlukast as a BAT inducer, and the endogenous metabolite myristoylglycine was then discovered to mimic the browning properties of zafirlukast without impacting cell viability. Myristoylglycine was found to be bio-synthesized upon zafirlukast treatment and was unique in inducing brown adipocyte differentiation, raising the possibility of using endogenous metabolites and bypassing the exogenous drugs to potentially alleviate disease, in this case, obesity and other related metabolic diseases.

Nucleophosmin3 carried by small extracellular vesicles contribute to white adipose tissue browning

Background

Browning of white adipose tissue (WAT) is a particularly appealing target for therapeutics in the treatment of obesity and related metabolic diseases. Although small extracellular vesicles (sEVs) released from adipose tissue (sEVs-AT) have emerged as novel player that regulate systemic metabolism by connecting different organs, the role of specific contents in sEVs-AT played in WAT browning has not been clarified.

Results

We revealed Nucleophosmin3 (NPM3), which was mainly transferred by sEVs derived from brown adipose tissue (sEVs-BAT), was served as a batokine that could induce WAT browning by regulating the stability of PRDM16 mRNA. sEVs-BAT enhanced the expressions of browning related genes in 3T3-L1 preadipocytes and WAT while knocking down of NPM3 in BAT impaired sEVs-BAT mediated WAT browning and weight loss in obesity.

Conclusion

These data provided new insight into the role of NPM3 in regulating the browning of WAT. Our study indicated that a supplement of sEVs-BAT might represent a promising therapeutic strategy to promote thermogenesis and energy expenditure in the future.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01381-1.

Topical application of the pharmacological cold mimetic menthol stimulates brown adipose tissue thermogenesis through a TRPM8, UCP1, and norepinephrine dependent mechanism in mice housed at thermoneutrality

Increasing whole-body energy expenditure via the pharmacological activation of uncoupling protein 1 (UCP1)-dependent brown adipose tissue (BAT) thermogenesis is a promising weight management strategy, yet most therapeutics studied in rodents to date either induce compensatory increases in energy intake, have thermogenic effects that are confounded by sub-thermoneutral housing temperatures or are not well tolerated in humans. Here, we sought to determine whether the non-invasive topical application of the pharmacological cold mimetic and transient receptor potential (TRP) cation channel subfamily M member 8 (TRPM8) agonist L-menthol (MNTH), could be used to stimulate BAT thermogenesis and attenuate weight gain in mice housed at thermoneutrality. Using three different strains of mice and multiple complimentary approaches to quantify thermogenesis in vivo, coupled with ex vivo models to quantify direct thermogenic effects, we were able to convincingly demonstrate the following: (1) acute topical MNTH application induces BAT thermogenesis in a TRPM8- and UCP1-dependent manner; (2) MNTH-induced BAT thermogenesis is sufficient to attenuate weight gain over time without affecting energy intake in lean and obese mice; (3) the ability of topical MNTH application to stimulate BAT thermogenesis is mediated, in part, by a central mechanism involving the release of norepinephrine. These data collectively suggest that topical application of MNTH may be a promising weight management strategy.

n-3 polyunsaturated fatty acids in the regulation of adipose tissue browning and thermogenesis in obesity: Potential relationship with gut microbiota

BACKGROUND

Obesity is a worldwide public health problem characterized by fat tissue accumulation, favouring adipose tissue and metabolic alterations. Increasing energy expenditure (EE) through brown adipose tissue activation and white adipose tissue (WAT) browning has gained relevance as a therapeutic approach. Different bioactive compounds, such as n-3 polyunsaturated fatty acids (PUFA), have been shown to induce those thermogenic effects. This process is regulated by the gut microbiota as well. Nevertheless, obesity is characterized by gut microbiota dysbiosis, which can be restored by weight loss and n-3 PUFA intake, among other factors. Knowledge gap: However, the role of the gut microbiota on the n-3 PUFA effect in inducing thermogenesis in obesity has not been fully elucidated.

OBJECTIVE

This review aims to elucidate the potential implications of this interrelation on WAT browning adiposw sittue (BAT), BAT activity, and EE regulation in obesity models.

Global Adipose Tissue Remodeling During the First Month of Postnatal Life in Mice

During the first month of postnatal life, adipose tissue depots of mice go through a drastic, but transient, remodeling process. Between postnatal days 10 and 20, several white fat depots display a strong and sudden surge in beige adipocyte emergence that reverts until day 30. At the same time, brown fat depots appear to undergo an opposite phenomenon. We comprehensively describe these events, their depot specificity and known environmental and genetic interactions, such as maternal diet, housing temperature and mouse strain. We further discuss potential mechanisms and plausible purposes, including the tempting hypothesis that postnatal transient remodeling creates a lasting adaptive capacity still detectable in adult animals. Finally, we propose postnatal adipose tissue remodeling as a model process to investigate mechanisms of beige adipocyte recruitment advantageous to cold exposure or adrenergic stimulation in its entirely endogenous sequence of events without external manipulation.

Insight Into Rho Kinase Isoforms in Obesity and Energy Homeostasis

Obesity and associated complications increasingly jeopardize global health and contribute to the rapidly rising prevalence of type 2 diabetes mellitus and obesity-related diseases. Developing novel methods for the prevention and treatment of excess body adipose tissue expansion can make a significant contribution to public health. Rho kinase is a Rho-associated coiled-coil-containing protein kinase (Rho kinase or ROCK). The ROCK family including ROCK1 and ROCK2 has recently emerged as a potential therapeutic target for the treatment of metabolic disorders. Up-regulated ROCK activity has been involved in the pathogenesis of all aspects of metabolic syndrome including obesity, insulin resistance, dyslipidemia and hypertension. The RhoA/ROCK-mediated actin cytoskeleton dynamics have been implicated in both white and beige adipogenesis. Studies using ROCK pan-inhibitors in animal models of obesity, diabetes, and associated complications have demonstrated beneficial outcomes. Studies via genetically modified animal models further established isoform-specific roles of ROCK in the pathogenesis of metabolic disorders including obesity. However, most reported studies have been focused on ROCK1 activity during the past decade. Due to the progress in developing ROCK2-selective inhibitors in recent years, a growing body of evidence indicates more attention should be devoted towards understanding ROCK2 isoform function in metabolism. Hence, studying individual ROCK isoforms to reveal their specific roles and principal mechanisms in white and beige adipogenesis, insulin sensitivity, energy balancing regulation, and obesity development will facilitate significant breakthroughs for systemic treatment with isoform-selective inhibitors. In this review, we give an overview of ROCK functions in the pathogenesis of obesity and insulin resistance with a particular focus on the current understanding of ROCK isoform signaling in white and beige adipogenesis, obesity and thermogenesis in adipose tissue and other major metabolic organs involved in energy homeostasis regulation.

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.

Repeated Oral Administration of Flavan-3-ols Induces Browning in Mice Adipose Tissues through Sympathetic Nerve Activation

We previously found increases in uncoupling protein (Ucp)-1 transcription in brown adipose tissue (BAT) of mice following a single oral dose of flavan 3-ol (FL)s, a fraction of catechins and procyanidins. It was confirmed that these changes were totally reduced by co-treatment of adrenaline blockers. According to these previous results, FLs possibly activate sympathetic nervous system (SNS). In this study, we confirmed the marked increase in urinary catecholamine (CA) s projecting SNS activity following a single dose of 50 mg/kg FLs. In addition, we examined the impact of the repeated administration of 50 mg/kg FLs for 14 days on adipose tissues in mice. In BAT, FLs tended to increase the level of Ucp-1 along with significant increase of thermogenic transcriptome factors expressions, such as peroxisome proliferator-activated receptor γ coactivator (PGC)-1α and PR domain-containing (PRDM)1. Expression of browning markers, CD137 and transmembrane protein (TMEM) 26, in addition to PGC-1α were increased in epididymal adipose (eWAT) by FLs. A multilocular morphology with cell size reduction was shown in the inguinal adipose (iWAT), together with increasing the level of Ucp-1 by FLs. These results exert that FLs induce browning in adipose, and this change is possibly produced by the activation of the SNS.

Perirenal Adipose Tissue from Healthy Donor: Characteristics and Promise as Potential Therapeutic Cell Source

Perirenal adipose tissue, one of the fat masses surrounding the kidneys, can be obtained from healthy donors during a kidney transplant. Perirenal adipose tissue has only ever been known as a connective tissue to protect the kidneys and renal blood vessels from external physical stimulation. Yet, recently, as adipose tissue has begun to be considered an endocrine organ, and perirenal adipose tissue is now regarded to have a direct effect on metabolic diseases. The characteristics of perirenal adipose tissue from a healthy donor are that: (1) There are a large number of brown adipose cells (70–80% of the total), (2) Most of the brown adipose cells are inactive in the resting cell cycle, (3) Activating factors are constant low-temperature exposure, hormones, metastasis factors, and environmental factors, (4) Anatomically, a large number of brown adipose cells are distributed close to the adrenal glands, (5) Beige cells, produced by converting white adipocytes to brown-like adipocytes, are highly active, (6) Activated cells secrete BATokines, and (7) Energy consumption efficiency is high. Despite these advantages, all of the perirenal adipose tissue from a healthy donor is incinerated as medical waste. With a view to its use, this review discusses the brown adipocytes and beige cells in perirenal adipose tissue from a healthy donor, and proposes opportunities for their clinical application.

Endocrine disrupting chemicals: Friend or foe to brown and beige adipose tissue?

The effects of Endocrine Disrupting Chemicals (EDCs) on the current obesity epidemic is a growing field of interest. Numerous EDCs have shown the potential to alter energy metabolism, which may increase the risk of obesity, in part, through direct actions on adipose tissue. While white adipose tissue has historically been the primary focus of this work, evidence of the EDC-induced disruption of brown and beige adipose tissues continues to build. Both brown and beige fat are thermogenic adipose depots rich in mitochondria that dispense heat when activated. Due to these properties, brown and beige fat are implicated in metabolic diseases such as obesity, diabetes, and cachexia. This review delves into the current literature of different EDCs, including bisphenols, dioxins, air pollutants, phthalates, and phytochemicals. The possible implications that these EDCs have on thermogenic adipose tissues are covered. This review also introduces the possibility of using brown and beige fat as a therapeutic target organ by taking advantage of some of the properties of EDCs. Collectively, we provide a comprehensive discussion of the evidence of EDC disruption in white, brown, and beige fat and highlight gaps worthy of further exploration.

Mouse model of the adipose organ: the heterogeneous anatomical characteristics

Adipose tissue plays a pivotal role in energy storage, hormone secretion, and temperature control. Mammalian adipose tissue is largely divided into white adipose tissue and brown adipose tissue, although recent studies have discovered the existence of beige adipocytes. Adipose tissues are widespread over the whole body and each location shows distinctive metabolic features. Mice are used as a representative experimental model system in metabolic studies due to their numerous advantages. Importantly, the adipose tissues of experimental animals and humans are not perfectly matched, and each adipose tissue exhibits both similar and specific characteristics. Nevertheless, the diversity and characteristics of mouse adipose tissue have not yet been comprehensively summarized. This review summarizes diverse information about the different types of adipose tissue being studied in mouse models. The types and characteristics of adipocytes were described, and each adipose tissue was classified by type, and features such as its distribution, origin, differences from humans, and metabolic characteristics were described. In particular, the distribution of widely studied adipose tissues was illustrated so that researchers can comprehensively grasp its location. Also, the adipose tissues misused or confusingly used among researchers were described. This review will provide researchers with comprehensive information and cautions needed to study adipose tissues in mouse models.

Intermittent cold exposure improves glucose homeostasis despite exacerbating diet-induced obesity in mice housed at thermoneutrality

KEY POINTS

Ambient cold exposure is often regarded as a promising anti-obesity treatment in mice. However, most preclinical studies aimed at treating obesity via cold-induced thermogenesis have been confounded by subthermoneutral housing temperatures. Therefore, the ability of ambient cold to combat diet-induced obesity in mice housed under humanized thermoneutral conditions is currently unknown. Moreover, mammals such as mice are rarely exposed to chronic ambient cold without reprieve, yet mice are often subjected to experimental conditions of chronic rather than intermittent cold exposure (ICE), despite ICE being more physiologically relevant. In the present study, we provide novel evidence that thermoneutral housing uncouples the effects of ICE on glucose and energy homeostasis suggesting that ICE, despite improving glucose tolerance, is not an effective obesity treatment when mice are housed under humanized thermoneutral conditions.

ABSTRACT

The present study examines whether a physiologically relevant model of ambient cold exposure, intermittent cold exposure (ICE), could ameliorate the metabolic impairments of diet-induced obesity in male and female mice housed under humanized thermoneutral conditions. Male and female C57BL/6J mice housed at thermoneutrality (29°C) were fed a low-fat diet or high-fat diet for 6 weeks before being weight matched into groups that remained unperturbed or underwent ICE for 4 weeks (4°C for 60 min day^-1 ; 5 days week^-1 ) when being maintained on their respective diets. ICE induced rapid and persistent hyperphagia exacerbating rather than attenuating high-fat diet-induced obesity over time. These ICE-induced increases in adiposity were found to be energy intake-dependent via pair-feeding. Despite exacerbating high-fat diet-induced obesity, ICE improved glucose tolerance, independent of diet, in a sex-specific manner. The effects of ICE on glucose tolerance were not attributed to improvements in whole-body insulin tolerance, tissue specific insulin action, nor differences in markers of hepatic insulin clearance or pancreatic beta cell proliferation. Instead, ICE increased serum concentrations of insulin and C-peptide in response to glucose, suggesting that ICE may improve glucose tolerance by potentiating pancreatic glucose-stimulated insulin secretion. These data suggest that ICE, despite improving glucose tolerance, is not an effective obesity treatment in mice housed under humanized conditions.

[Comparison of 1H-MRS, Dixon fat-water separation and Z-spectral imaging for quantification of brown adipose tissue in rats]

OBJECTIVE

To evaluate the performance of 1H-magnetic resonance spectroscopy (1H-MRS), Dixon fat-water separation and Z-spectral magnetic resonance imaging (ZS-MRI) for quantification of fat content in phantoms and brown adipose tissues in rats.

OBJECTIVE

First, six water-oil mixture phantoms with different fat fractions (0, 20%, 40%, 60%, 80% and 100%) were prepared and placed in a 50-mL centrifuge tube. ZS-MRI, 1H-MRS and Dixon's method were used to quantitatively evaluate the fat content of the phantom, and the results were compared against the actual fat fractions. Then, ZS-MRI and Dixon's method were used to collect the data in the interscapular region of 6 rats, the fat-water distribution map was calculated, and the results were compared with 1H-MRS.

OBJECTIVE

ZS-MRI accurately quantified fat contents in the phantoms (Y=0.95*X+1.48). ZS-MRI was capable of distinguishing brown adipose tissue from white adipose tissue and defining the spatial distribution of the adipose tissue, and the results were highly consistent with those obtained by Dixon's method. No significant differences were found in the results derived by ZS-MRI and 1H-MRS for quantification of brown adipose tissue (P=0.35).

OBJECTIVE

ZS-MRI can generate an artifact-free fat distribution map for quantitative measurement of the content and distribution of brown adipose tissues in rats.

Mulberry leaf activates brown adipose tissue and induces browning of inguinal white adipose tissue in type 2 diabetic rats through regulating AMP-activated protein kinase signalling pathway

The current epidemic of type 2 diabetes mellitus (T2DM) significantly affects human health worldwide. Activation of brown adipocytes and browning of white adipocytes are considered as a promising molecular target for T2DM treatment. Mulberry leaf, a traditional Chinese medicine, has been demonstrated to have multi-biological activities, including anti-diabetic and anti-inflammatory effects. Our experimental results showed that mulberry leaf significantly alleviated the disorder of glucose and lipid metabolism in T2DM rats. In addition, mulberry leaf induced browning of inguinal white adipose tissue (IWAT) by enhancing the expressions of brown-mark genes as well as beige-specific genes, including uncoupling protein-1 (UCP1), peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α), peroxisome proliferator-activated receptor alpha (PPARα), PRD1-BF-1-RIZ1 homologous domain containing protein 16 (PRDM16), cell death inducing DFFA-like effector A (Cidea), CD137 and transmembrane protein 26 (TMEM26). Mulberry leaf also activated brown adipose tissue (BAT) by increasing the expressions of brown-mark genes including UCP1, PGC-1α, PPARα, PRDM16 and Cidea. Moreover, mulberry leaf enhanced the expression of nuclear respiratory factor 1 (NRF-1) and mitochondrial transcription factor A (TFAM) genes that are responsible for mitochondrial biogenesis in IWAT and BAT. Importantly, mulberry leaf also increased the expression of UCP1 and carnitine palmitoyl transferase 1 (CPT-1) proteins in both IWAT and BAT via a mechanism involving AMP-activated protein kinase (AMPK) and PGC-1α pathway. In conclusion, our findings identify the role of mulberry leaf in inducing adipose browning, indicating that mulberry leaf may be used as a candidate browning agent for the treatment of T2DM.

TFEB deficiency attenuates mitochondrial degradation upon brown adipose tissue whitening at thermoneutrality

OBJECTIVE

Brown adipose tissue (BAT) thermogenesis offers the potential to improve metabolic health in mice and humans. However, humans predominantly live under thermoneutral conditions, leading to BAT whitening, a reduction in BAT mitochondrial content and metabolic activity. Recent studies have established mitophagy as a major driver of mitochondrial degradation in the whitening of thermogenic brite/beige adipocytes, yet the pathways mediating mitochondrial breakdown in whitening of classical BAT remain largely elusive. The transcription factor EB (TFEB), a master regulator of lysosomal biogenesis and autophagy belonging to the MiT family of transcription factors, is the only member of this family that is upregulated during whitening, pointing toward a role of TFEB in whitening-associated mitochondrial breakdown.

METHODS

We generated brown adipocyte-specific TFEB knockout mice, and induced BAT whitening by thermoneutral housing. We characterized gene and protein expression patterns, BAT metabolic activity, systemic metabolism, and mitochondrial localization using in vivo and in vitro approaches.

RESULTS

Under low thermogenic activation conditions, deletion of TFEB preserves mitochondrial mass independently of mitochondriogenesis in BAT and primary brown adipocytes. However, this does not translate into elevated thermogenic capacity or protection from diet-induced obesity. Autophagosomal/lysosomal marker levels are altered in TFEB-deficient BAT and primary adipocytes, and lysosomal markers co-localize and co-purify with mitochondria in TFEB-deficient BAT, indicating trapping of mitochondria in late stages of mitophagy.

CONCLUSION

We identify TFEB as a driver of BAT whitening, mediating mitochondrial degradation via the autophagosomal and lysosomal machinery. This study provides proof of concept that interfering with the mitochondrial degradation machinery can increase mitochondrial mass in classical BAT under human-relevant conditions. However, it must be considered that interfering with autophagy may result in accumulation of non-functional mitochondria. Future studies targeting earlier steps of mitophagy or target recognition are therefore warranted.

Relation of diet-induced thermogenesis to brown adipose tissue activity in healthy men

Human brown adipose tissue (BAT) is a thermogenic tissue activated by the sympathetic nervous system in response to cold exposure. It contributes to energy expenditure (EE) and takes up glucose and lipids from the circulation. Studies in rodents suggest that BAT contributes to the transient rise in EE after food intake, so-called diet-induced thermogenesis (DIT). We investigated the relationship between human BAT activity and DIT in response to glucose intake in 17 healthy volunteers. We assessed DIT, cold-induced thermogenesis (CIT), and maximum BAT activity at three separate study visits within 2 wk. DIT was measured by indirect calorimetry during an oral glucose tolerance test. CIT was assessed as the difference in EE after cold exposure of 2-h duration as compared with warm conditions. Maximal activity of BAT was assessed by 18-F-fluoro-deoxyglucose (¹⁸F-FDG) ¹⁸F-FDG-PET/MRI after cold exposure and concomitant pharmacological stimulation with mirabegron. Seventeen healthy men (mean age = 23.4 yr, mean body mass index = 23.2 kg/m²) participated in the study. EE increased from 1,908 (±181) kcal/24 h to 2,128 (±277) kcal/24 h (P < 0.0001, +11.5%) after mild cold exposure. An oral glucose load increased EE from 1,911 (±165) kcal/24 h to 2,096 (±167) kcal/24 h at 60 min (P < 0.0001, +9.7%). The increase in EE in response to cold was significantly associated with BAT activity (R² = 0.43, P = 0.004). However, DIT was not associated with BAT activity (R² = 0.015, P = 0.64). DIT after an oral glucose load was not associated with stimulated ¹⁸F-FDG uptake into BAT, suggesting that DIT is independent from BAT activity in humans (Clinicaltrials.gov Registration No. NCT03189511).NEW & NOTEWORTHY Cold-induced thermogenesis (CIT) was related to BAT activity as determined by FDG-PET/MRI after stimulation of BAT. Diet-induced thermogenesis (DIT) was not related to stimulated BAT activity. Supraclavicular skin temperature was related to CIT but not to DIT. DIT in humans is probably not a function of BAT.

Visceral adiposity syndrome and cardiometabolism

The distribution of fat in the human body is related to hemodynamic and metabolic homeostasis. Brown fat is inversely related to body mass index and is associated with a lower probability of developing diabetes. Beige adipose tissue shares some functional characteristics with brown adipose tissue. White adipose tissue constitutes the majority of the fatty tissue and is mainly distributed in the subcutaneous and abdominal cavity. Intra-abdominal white fat has gained prominence in recent years for its association with cardiovascular risk factors and higher cardiovascular mortality. This review article discusses the human adaptation in the environment, a sympathovagal and hypothalamic-pituitary-adrenal imbalance as a possible cause of increased visceral adiposity and its consequences on cardiometabolism.

White adipose remodeling during browning in mice involves YBX1 to drive thermogenic commitment

Objective

Increasing adaptive thermogenesis by stimulating browning in white adipose tissue is a promising method of improving metabolic health. However, the molecular mechanisms underlying this transition remain elusive. Our study examined the molecular determinants driving the differentiation of precursor cells into thermogenic adipocytes.

Methods

In this study, we conducted temporal high-resolution proteomic analysis of subcutaneous white adipose tissue (scWAT) after cold exposure in mice. This was followed by loss- and gain-of-function experiments using siRNA-mediated knockdown and CRISPRa-mediated induction of gene expression, respectively, to evaluate the function of the transcriptional regulator Y box-binding protein 1 (YBX1) during adipogenesis of brown pre-adipocytes and mesenchymal stem cells. Transcriptomic analysis of mesenchymal stem cells following induction of endogenous Ybx1 expression was conducted to elucidate transcriptomic events controlled by YBX1 during adipogenesis.

Results

Our proteomics analysis uncovered 509 proteins differentially regulated by cold in a time-dependent manner. Overall, 44 transcriptional regulators were acutely upregulated following cold exposure, among which included the cold-shock domain containing protein YBX1, peaking after 24 h. Cold-induced upregulation of YBX1 also occurred in brown adipose tissue, but not in visceral white adipose tissue, suggesting a role of YBX1 in thermogenesis. This role was confirmed by Ybx1 knockdown in brown and brite preadipocytes, which significantly impaired their thermogenic potential. Conversely, inducing Ybx1 expression in mesenchymal stem cells during adipogenesis promoted browning concurrent with an increased expression of thermogenic markers and enhanced mitochondrial respiration. At a molecular level, our transcriptomic analysis showed that YBX1 regulates a subset of genes, including the histone H3K9 demethylase Jmjd1c, to promote thermogenic adipocyte differentiation.

Conclusion

Our study mapped the dynamic proteomic changes of murine scWAT during browning and identified YBX1 as a novel factor coordinating the genomic mechanisms by which preadipocytes commit to brite/beige lineage.

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Dynamic proteome remodeling occurs in mouse subcutaneous white fat with cold.

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YBX1 acutely increases in response to cold in thermogenic adipose tissues.

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YBX1 is required for the optimal implementation of the early thermogenic program.

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YBX1 promotes metabolic and thermogenic programs and enhances mitochondrial respiration.

TSH promotes adiposity by inhibiting the browning of white fat

Adiposity is caused by an imbalance between energy intake and consumption. Promotion of the browning of white fat increases energy expenditure and could combat adiposity. Thyroid-stimulating hormone (TSH) has been confirmed to positively correlate with adiposity. However, the putative connection between TSH and white adipose browning has never been explored. In this study, we sought to assess the effect of TSH on white adipose tissue browning and energy metabolism. Subclinical hypothyroidism mice, thyroid-specific Tshr-knockout mice injected with TSH, adipocyte-specific and global Tshr-knockout micewere subjected to morphological, physiological, genetic or protein expression analyses and metabolic cages to determine the role of TSH on the browning of white adipose tissue and metabolism. 3T3-L1 and primary SVF cells were used to verify the effects and mechanism of TSH on the browning of white adipocytes. We show that increased circulation TSH level decreases energy expenditure, promotes adiposity, impairs glucose and lipid metabolism. Knockout of Tshr decreases adiposity, increases energy expenditureand markedly promotes the development of beige adipocytesin both epididymal and inguinal subcutaneous white fat via a mechanism that likely involves AMPK/PRDM16/PGC1α. Our results reveal an important role of TSH in regulating energy balance and adiposity by inhibiting the browning of white fat.

Cytochrome P450-derived linoleic acid metabolites EpOMEs and DiHOMEs: a review of recent studies

Linoleic acid (LA) is the most abundant polyunsaturated fatty acid found in the Western diet. Cytochrome P450-derived LA metabolites 9,10-epoxyoctadecenoic acid (9,10-EpOME), 12,13-epoxyoctadecenoic acid (12,13-EpOME), 9,10-dihydroxy-12Z-octadecenoic acid (9,10-DiHOME) and 12,13-dihydroxy-9Z-octadecenoic acid (12,13-DiHOME) have been studied for their association with various disease states and biological functions. Previous studies of the EpOMEs and DiHOMEs have focused on their roles in cytotoxic processes, primarily in the inhibition of the neutrophil respiratory burst. More recent research has suggested the DiHOMEs may be important lipid mediators in pain perception, altered immune response and brown adipose tissue activation by cold and exercise. The purpose of this review is to summarize the current understanding of the physiological and pathophysiological roles and modes of action of the EpOMEs and DiHOMEs in health and disease.

Novel approach to quantify mitochondrial content and intrinsic bioenergetic efficiency across organs

Human disease pathophysiology commonly involves metabolic disruption at both the cellular and subcellular levels. Isolated mitochondria are a powerful model for separating global cellular changes from intrinsic mitochondrial alterations. However, common laboratory practices for isolating mitochondria (e.g., differential centrifugation) routinely results in organelle preparations with variable mitochondrial purity. To overcome this issue, we developed a mass spectrometry-based method that quantitatively evaluates sample-specific percent mitochondrial enrichment. Sample-specific mitochondrial enrichment was then used to correct various biochemical readouts of mitochondrial function to a ‘fixed’ amount of mitochondrial protein, thus allowing for intrinsic mitochondrial bioenergetics, relative to the underlying proteome, to be assessed across multiple mouse tissues (e.g., heart, brown adipose, kidney, liver). Our results support the use of mitochondrial-targeted nLC-MS/MS as a method to quantitate mitochondrial enrichment on a per-sample basis, allowing for unbiased comparison of functional parameters between populations of mitochondria isolated from metabolically distinct tissues. This method can easily be applied across multiple experimental settings in which intrinsic shifts in the mitochondrial network are suspected of driving a given physiological or pathophysiological outcome.

Celastrol alleviates metabolic disturbance in high-fat diet-induced obese mice through increasing energy expenditure by ameliorating metabolic inflammation

Celastrol, a natural triterpene, has been shown to treat obesity and its related metabolic disorders. In this study, we first assessed the relationship between the antiobesity effects of celastrol and its antiinflammatory activities. Our results showed that celastrol can reduce weight gain, ameliorate glucose intolerance, insulin resistance, and dyslipidemia without affecting food intake in high-fat diet-induced obese mice. A CLAMS was used to clarify the improvement of metabolic profiles was attribute to increased adipose thermogenesis after celastrol treatment. Further studies found that celastrol decreased the infiltration of macrophage as well as its inflammatory products (IL-1β, IL-18, MCP-1α, and TNF-α) in liver and adipose tissues, which also displayed an obvious inhibition of TLR3/NLRP3 inflammasome molecules. This study demonstrated that celastrol could be a potential drug for treating metabolic disorders, the underlying mechanism is related to ameliorating metabolic inflammation, thus increasing body energy expenditure.

MiR-92a regulates brown adipocytes differentiation, mitochondrial oxidative respiration, and heat generation by targeting SMAD7

Brown adipocytes are rich in mitochondria and linked to the body's blood fat levels and obesity. MiR-92a is negatively correlated with the activity of brown adipocytes. This study aimed to explore the mechanism of miR-92a on brown adipocytes. The expression of miR-92a in C2C12 cell was detected by a quantitative real-time-polymerase chain reaction (qRT-PCR). C2C12 cells were induced to brown adipocytes. The direct target gene of miR-92a was determined using the dual-luciferase reporter assay. Brown adipocytes were treated with isoprenaline (Iso) and transfected by miR-92a inhibitor and siSMAD7. The expression of heat-producing genes and adipose differentiation genes related to brown adipocytes were detected by qRT-PCR and Western blot analysis. The expression of SMAD7, p-SMAD2, and p-SMAD3 were detected using Western blot analysis. The mitochondrial content was measured by mitotracker fluorescent staining. MiR-92a inhibitor significantly decreased the expression of miR-92a in C2C12 cells. MiR-92a inhibitor could upregulate the expression of Ucp1, Cox7a1, Elovl3, Ppargc1α, PPARγ, and FABP4, and its effect on Ucp1 was increased after the treatment of isoprenaline. Moreover, miR-92a inhibitor increased mitochondrial content, oxygen consumption rate (OCR) and the expression of SMAD7 and suppressed the expressions of p-SMAD2 and p-SMAD3, whereas miR-92a directly targeted SMAD7 to exert its inhibitory effects. SiSMAD7 reversed the effects of the inhibitor on heat-producing genes, mitochondrial content, OCR and the expressions of SMAD7, p-SMAD2, and p-SMAD3 in brown adipocytes. Blocking miR-92a might promote brown adipocytes differentiation, mitochondrial oxidative respiration, and thermogenesis by targeting SMAD7 to inhibit the expressions of p-SMAD2 and p-SMAD3.

Wu-Mei-Wan prevents high-fat diet-induced obesity by reducing white adipose tissue and enhancing brown adipose tissue function

BACKGROUND

Wu-Mei-Wan, a classic traditional Chinese herb medicine, is one of the most important formulations to treat digestive diseases from ancient times to the present. Our previous study showed that WMW treatment can prevent T2DM in db/db mice, which motivating the application of WMW on metabolic disorders.

PURPOSE

Obesity and its comorbid diseases have increased dramatically and are now a worldwide health problem. There is still a lack of satisfactory treatment strategies for obesity. This work was designed to assess the effect and related mechanism of WMW on high fat diet (HFD)-induced obese mice model.

METHODS

Obese mice were induced by HFD. Thetherapeutic effect of WMW were analyzed by examining body and adipose tissue weight, metabolic profile and energy expenditure. Adipose tissue phenotype was determined by histological staining and the mitochondrial content was examined by transmission electron microscopy (TEM). Immunohistochemical and immunofluorescence staining, RT-qPCR and Western blot analysis were used to evaluate expression of key molecules in adipose tissue.

RESULTS

WMW treatment significantly protects HFD-induced obesity. Here we showed that WMW limits weight gain, improves metabolic profile and increases energy expenditure. WMW inhibits the hypertrophy and hyperplasia of white adipocytes, the mechanism involving the inhibition of TLR3/IL-6/JAK1/STAT3 pathway. In brown adipose tissue (BAT), WMW promotes thermogenicprogramme without affecting cell proliferation. The activated BMP7/ Smad1/5/9 pathway is considered to be one of the explanations for the effect of WMW on BAT.

CONCLUSION

Our results suggested that WMW can prevent obesity and its underlying mechanisms are associated with reducing white adipose tissue and enhancing brown adipose tissue function.

Human beige adipocytes for drug discovery and cell therapy in metabolic diseases

Human beige adipocytes (BAs) have potential utility for the development of therapeutics to treat diabetes and obesity-associated diseases. Although several reports have described the generation of beige adipocytes in vitro, their potential utility in cell therapy and drug discovery has not been reported. Here, we describe the generation of BAs from human adipose-derived stem/stromal cells (ADSCs) in serum-free medium with efficiencies >90%. Molecular profiling of beige adipocytes shows them to be similar to primary BAs isolated from human tissue. In vitro, beige adipocytes exhibit uncoupled mitochondrial respiration and cAMP-induced lipolytic activity. Following transplantation, BAs increase whole-body energy expenditure and oxygen consumption, while reducing body-weight in recipient mice. Finally, we show the therapeutic utility of BAs in a platform for high-throughput drug screening (HTS). These findings demonstrate the potential utility of BAs as a cell therapeutic and as a tool for the identification of drugs to treat metabolic diseases.

Methods to generate beige adipocytes from a human cell source are inefficient. Here, the authors present a protocol that efficiently generates beige adipocytes from human adipose-derived stem cells (ADSCs), which have potential utility in therapeutic development relating to metabolic diseases such as type 2 diabetes.

AMPK activation ameliorates fine particulate matter-induced hepatic injury

Both the epidemiological and animal experimental studies have reported the association between PM_2.5 and respiratory, cardiovascular, and metabolic diseases. However, the study linking PM_2.5 and hepatic injury is few, and the relative mechanism has not been fully elucidated. Thirty-two 6-week-old male C57BL/6 mice were exposed to filtered air (FA) or concentrated PM_2.5 for 12 weeks using Shanghai Meteorological and Environmental Animal Exposure System ("Shanghai-METAS"), respectively. At week 11, the mice began to be treated with intraperitoneal injection of normal 0.9% saline or AMPK activator (AICAR). The mRNA levels of IL-6 and TNF-α, and protein expressions of AMPK, GLUT4, NF-κB, p38MAPK, ERK, and JNK in the liver and UCP-1 in brown adipose tissue (BAT) were measured. Meanwhile, histopathological examination both in the liver and BAT was performed to evaluate the histopathological changes. PM_2.5 exposure induced steatosis, hepatocyte ballooning, lobular and portal inflammation in the liver, and the brown adipocyte swelling in BAT. The results found that PM mice displayed higher IL-6, TNF-α, NF-κB, and JNK expression and lower AMPK, GLUT4, and UCP-1 when compared with FA mice. The AICAR injection upregulated the expressions of GLUT4 in the liver of PM-AIC mice when compared with the PM mice. However, there were no significant effects of AICAR on histopathological condition. The current study showed that ambient PM_2.5 exposure might induce the hepatic injury along with the lipid metabolism disorder in BAT. AMPK activation can ameliorate most of the harmful effects and might become the potential target for treating PM_2.5-induced hepatic injury.

A 3D Self-Assembled In Vitro Model to Simulate Direct and Indirect Interactions between Adipocytes and Skeletal Muscle Cells

The molecular mechanisms of the development and progression of diabetes and obesity involve complex interactions between adipocytes and skeletal muscle cells. Although 2D in-vitro models are the gold standard for the mechanistic study of such behaviors, they do not recreate the complexity and dynamics of the interactions between the cell types involved. Alternatively, animal models are used but are expensive, difficult to visualize or analyze, are not completely representative of human physiology or genetic background, and have associated ethical considerations. 3D co-culture systems can be complementary to these approaches. Here, using a newly developed 3D biofabrication method, adipocytes and myoblasts are positioned precisely either in direct physical contact or in close proximity such that the paracrine effects could be systematically studied. Suitable protocols for growth and differentiation of both cells in the co-culture system is also developed. Cells show more restrained lipid and protein production in 3D systems compared to 2D ones and adipocytes show more lipolysis in indirect contact with myoblasts as response to drug treatment. These findings emphasize importance of physical contact between cells that have been overlooked in co-culture systems using transwell inserts and can be used in studies for the development of anti-obesity drugs.