The Common and Distinct Features of Brown and Beige Adipocytes

Targeting Adipokines: A Promising Therapeutic Strategy for Epilepsy

Epilepsy affects 65 million people globally and causes neurobehavioral, cognitive, and psychological defects. Although research on the disease is progressing and a wide range of treatments are available, approximately 30% of people have refractory epilepsy that cannot be managed with conventional medications. This underlines the importance of further understanding the condition and exploring cutting-edge targets for treatment. Adipokines are peptides secreted by adipocyte's white adipose tissue, involved in controlling food intake and metabolism. Their regulatory functions in the central nervous system (CNS) are multifaceted and identified in several physiology and pathologies. Adipokines play a role in oxidative stress and neuroinflammation which are associated with brain degeneration and connected neurological diseases. This review aims to highlight the potential impacts of leptin, adiponectin, apelin, vaspin, visfatin, and chimerin in the pathogenesis of epilepsy.

Dietary Pectin from Premna microphylla Turcz Leaves Prevents Obesity by Regulating Gut Microbiota and Lipid Metabolism in Mice Fed High-Fat Diet

The present study was designed to investigate the protective effects of pectin extracted from Premna microphylla Turcz leaves (PTP) against high-fat-diet (HFD)-induced lipid metabolism disorders and gut microbiota dysbiosis in obese mice. PTP was made using the acid extraction method, and it was found to be an acidic pectin that had relative mole percentages of 32.1%, 29.2%, and 26.2% for galacturonic acid, arabinose, and galactose, respectively. The administration of PTP in C57BL/6J mice inhibited the HFD-induced abnormal weight gain, visceral obesity, and dyslipidemia, and also improved insulin sensitivity, as revealed by the improved insulin tolerance and the decreased glucose levels during an insulin sensitivity test. These effects were linked to increased energy expenditure, as demonstrated by the upregulation of thermogenesis-related protein UCP1 expression in the brown adipose tissue (BAT) of PTP-treated mice. 16S rRNA gene sequencing revealed that PTP dramatically improved the HFD-induced gut dysbiosis by lowering the ratio of Firmicutes to Bacteroidetes and the quantity of potentially harmful bacteria. These findings may provide a theoretical basis for us to understand the functions and usages of PTP in alleviating obesity.

Recent advances on cyanidin-3-O-glucoside in preventing obesity-related metabolic disorders: A comprehensive review

Anthocyanins, found in various pigmented plants as secondary metabolites, represent a class of dietary polyphenols known for their bioactive properties, demonstrating health-promoting effects against several chronic diseases. Among these, cyanidin-3-O-glucoside (C3G) is one of the most prevalent types of anthocyanins. Upon consumption, C3G undergoes phases I and II metabolism by oral epithelial cells, absorption in the gastric epithelium, and gut transformation (phase II & microbial metabolism), with limited amounts reaching the bloodstream. Obesity, characterized by excessive body fat accumulation, is a global health concern associated with heightened risks of disability, illness, and mortality. This comprehensive review delves into the biodegradation and absorption dynamics of C3G within the gastrointestinal tract. It meticulously examines the latest research findings, drawn from in vitro and in vivo models, presenting evidence underlining C3G's bioactivity. Notably, C3G has demonstrated significant efficacy in combating obesity, by regulating lipid metabolism, specifically decreasing lipid synthesis, increasing fatty acid oxidation, and reducing lipid accumulation. Additionally, C3G enhances energy homeostasis by boosting energy expenditure, promoting the activity of brown adipose tissue, and stimulating mitochondrial biogenesis. Furthermore, C3G shows potential in managing various prevalent obesity-related conditions. These include cardiovascular diseases (CVD) and hypertension through the suppression of reactive oxygen species (ROS) production, enhancement of endogenous antioxidant enzyme levels, and inhibition of the nuclear factor-kappa B (NF-κB) signaling pathway and by exercising its cardioprotective and vascular effects by decreasing pulmonary artery thickness and systolic pressure which enhances vascular relaxation and angiogenesis. Type 2 diabetes mellitus (T2DM) and insulin resistance (IR) are also managed by reducing gluconeogenesis via AMPK pathway activation, promoting autophagy, protecting pancreatic β-cells from oxidative stress and enhancing glucose-stimulated insulin secretion. Additionally, C3G improves insulin sensitivity by upregulating GLUT-1 and GLUT-4 expression and regulating the PI3K/Akt pathway. C3G exhibits anti-inflammatory properties by inhibiting the NF-κB pathway, reducing pro-inflammatory cytokines, and shifting macrophage polarization from the pro-inflammatory M1 phenotype to the anti-inflammatory M2 phenotype. C3G demonstrates antioxidative effects by enhancing the expression of antioxidant enzymes, reducing ROS production, and activating the Nrf2/AMPK signaling pathway. Moreover, these mechanisms also contribute to attenuating inflammatory bowel disease and regulating gut microbiota by decreasing Firmicutes and increasing Bacteroidetes abundance, restoring colon length, and reducing levels of inflammatory cytokines. The therapeutic potential of C3G extends beyond metabolic disorders; it has also been found effective in managing specific cancer types and neurodegenerative disorders. The findings of this research can provide an important reference for future investigations that seek to improve human health through the use of naturally occurring bioactive compounds.

Brown Adipose Tissue as a Unique Niche for Islet Organoid Transplantation: Insights From In Vivo Imaging

Background

Transplantation of human-induced pluripotent stem cell (hiPSC)-derived islet organoids is a promising cell replacement therapy for type 1 diabetes (T1D). It is important to improve the efficacy of islet organoids transplantation by identifying new transplantation sites with high vascularization and sufficient accommodation to support graft survival with a high capacity for oxygen delivery.

Methods

A human-induced pluripotent stem cell line (hiPSCs-L1) was generated constitutively expressing luciferase. Luciferase-expressing hiPSCs were differentiated into islet organoids. The islet organoids were transplanted into the scapular brown adipose tissue (BAT) of nonobese diabetic/severe combined immunodeficiency disease (NOD/SCID) mice as the BAT group and under the left kidney capsule (KC) of NOD/SCID mice as a control group, respectively. Bioluminescence imaging (BLI) of the organoid grafts was performed on days 1, 7, 14, 28, 35, 42, 49, 56, and 63 posttransplantation.

Results

BLI signals were detected in all recipients, including both the BAT and control groups. The BLI signal gradually decreased in both BAT and KC groups. However, the graft BLI signal intensity under the left KC decreased substantially faster than that of the BAT. Furthermore, our data show that islet organoids transplanted into streptozotocin-induced diabetic mice restored normoglycemia. Positron emission tomography/MRI verified that the islet organoids were transplanted at the intended location in these diabetic mice. Immunofluorescence staining revealed the presence of functional organoid grafts, as confirmed by insulin and glucagon staining.

Conclusions

Our results demonstrate that BAT is a potentially desirable site for islet organoid transplantation for T1D therapy.

A novel fatty acid mimetic with pan-PPAR partial agonist activity inhibits diet-induced obesity and metabolic dysfunction-associated steatotic liver disease

OBJECTIVE

The prevalence of metabolic diseases is increasing globally at an alarming rate; thus, it is essential that effective, accessible, low-cost therapeutics are developed. Peroxisome proliferator-activated receptors (PPARs) are transcription factors that tightly regulate glucose homeostasis and lipid metabolism and are important drug targets for the treatment of type 2 diabetes and dyslipidemia. We previously identified LDT409, a fatty acid-like compound derived from cashew nut shell liquid, as a novel pan-active PPARα/γ/δ compound. Herein, we aimed to assess the efficacy of LDT409 in vivo and investigate the molecular mechanisms governing the actions of the fatty acid mimetic LDT409 in diet-induced obese mice.

METHODS

C57Bl/6 mice (6-11-month-old) were fed a chow or high fat diet (HFD) for 4 weeks; mice thereafter received once daily intraperitoneal injections of vehicle, 10 mg/kg Rosiglitazone, 40 mg/kg WY14643, or 40 mg/kg LDT409 for 18 days while continuing the HFD. During treatments, body weight, food intake, glucose and insulin tolerance, energy expenditure, and intestinal lipid absorption were measured. On day 18 of treatment, tissues and plasma were collected for histological, molecular, and biochemical analysis.

RESULTS

We found that treatment with LDT409 was effective at reversing HFD-induced obesity and associated metabolic abnormalities in mice. LDT409 lowered food intake and hyperlipidemia, while improving insulin tolerance. Despite being a substrate of both PPARα and PPARγ, LDT409 was crucial for promoting hepatic fatty acid oxidation and reducing hepatic steatosis in HFD-fed mice. We also highlighted a role for LDT409 in white and brown adipocytes in vitro and in vivo where it decreased fat accumulation, increased lipolysis, induced browning of WAT, and upregulated thermogenic gene Ucp1. Remarkably, LDT409 reversed HFD-induced weight gain back to chow-fed control levels. We determined that the LDT409-induced weight-loss was associated with a combination of increased energy expenditure (detectable before weight loss was apparent), decreased food intake, increased systemic fat utilization, and increased fecal lipid excretion in HFD-fed mice.

CONCLUSIONS

Collectively, LDT409 represents a fatty acid mimetic that generates a uniquely favorable metabolic response for the treatment of multiple abnormalities including obesity, dyslipidemia, metabolic dysfunction-associated steatotic liver disease, and diabetes. LDT409 is derived from a highly abundant natural product-based starting material and its development could be pursued as a therapeutic solution to the global metabolic health crisis.

Mouse vascularized adipose spheroids: an organotypic model for thermogenic adipocytes

Adipose tissues, particularly beige and brown adipose tissue, play crucial roles in energy metabolism. Brown adipose tissues' thermogenic capacity and the appearance of beige cells within white adipose tissue have spurred interest in their metabolic impact and therapeutic potential. Brown and beige fat cells, activated by environmental factors like cold exposure or by pharmacology, share metabolic mechanisms that drive non-shivering thermogenesis. Understanding these two cell types requires advanced, yet broadly applicable in vitro models that reflect the complex microenvironment and vasculature of adipose tissues. Here we present mouse vascularized adipose spheroids of the stromal vascular microenvironment from inguinal white adipose tissue, a tissue with 'beiging' capacity in mice and humans. We show that adding a scaffold improves vascular sprouting, enhances spheroid growth, and upregulates adipogenic markers, thus reflecting increased adipocyte maturity. Transcriptional profiling via RNA sequencing revealed distinct metabolic pathways upregulated in our vascularized adipose spheroids, with increased expression of genes involved in glucose metabolism, lipid metabolism, and thermogenesis. Functional assessment demonstrated increased oxygen consumption in vascularized adipose spheroids compared to classical 2D cultures, which was enhanced by β-adrenergic receptor stimulation correlating with elevated β-adrenergic receptor expression. Moreover, stimulation with the naturally occurring adipokine, FGF21, induced Ucp1 mRNA expression in the vascularized adipose spheroids. In conclusion, vascularized inguinal white adipose tissue spheroids provide a physiologically relevant platform to study how the stromal vascular microenvironment shapes adipocyte responses and influence activated thermogenesis in beige adipocytes.

Molecular Regulation of Thermogenic Mechanisms in Beige Adipocytes

Adipose tissue is conventionally recognized as a metabolic organ responsible for storing energy. However, a proportion of adipose tissue also functions as a thermogenic organ, contributing to the inhibition of weight gain and prevention of metabolic diseases. In recent years, there has been significant progress in the study of thermogenic fats, particularly brown adipose tissue (BAT). Despite this progress, the mechanism underlying thermogenesis in beige adipose tissue remains highly controversial. It is widely acknowledged that beige adipose tissue has three additional thermogenic mechanisms in addition to the conventional UCP1-dependent thermogenesis: Ca2+ cycling thermogenesis, creatine substrate cycling thermogenesis, and triacylglycerol/fatty acid cycling thermogenesis. This paper delves into these three mechanisms and reviews the latest advancements in the molecular regulation of thermogenesis from the molecular genetic perspective. The objective of this review is to provide readers with a foundation of knowledge regarding the beige fats and a foundation for future research into the mechanisms of this process, which may lead to the development of new strategies for maintaining human health.

Dynamics of the Trypanosoma cruzi infection in adipose tissue: Assessing gene expression of PNPLA2, FASN, and ACAT1 under Benzonidazole treatment and indirect mononuclear immune cells interaction

Trypanosoma cruzi is a parasite with a high capacity to adapt to the host. Animal models have already demonstrated that the tropism of this parasite occurs not only in cardiac/digestive tissues but also in adipose tissue (AT). That said, the consequences ofT. cruziinfection for AT and the implications of treatment with Benzonidazole in this tissue are under discussion. Here, we tested the hypothesis that T. cruzi infection in adipose tissue upon treatment with Benzonidazole (Bz) and the interaction of mononuclear immune cells (PBMC) influences the relative expression of ACAT1, FASN, and PNPLA2 genes. Thus, stem cells derived from adipose tissue (ADSC) after adipogenic differentiation were indirectly cultivated with PBMC after infection with the T. cruzi Y strain and treatment with Bz. We use the TcSAT-IAM system and RT-qPCR to evaluate the parasite load and the relative quantification (ΔCt) of the ACAT1, FASN, and PNPLA2 genes. Our results demonstrate that treatment with Bz did not reduce adipocyte infection in the presence (p-value: 0.5796) or absence (p-value: 0.1854) of cultivation with PBMC. In addition, even though there is no statistical difference when compared to the control group (AT), T. cruzi induces the FASN expression (Rq: 14.00). However, treatment with Bz in AT suggests the increases of PNPLA2 expression levels (Rq: 12.58), even in the absence of T. cruzi infection. During indirect cultivation with PBMC, T. cruzi smooths the expression of PNPLA2 (Rq: 0.824) and instigates the expression of ACAT1 (Rq: 1.632) and FASN (Rq: 1.394). Furthermore, the treatment with Bz during infection induces PNPLA2 expression (Rq: 1.871), maintaining FASN expression levels (Rq: 1.334). Given this, our results indicate that treatment with Benzonidazole did not decrease T. cruzi infection in adipose tissue. However, treating the adipocyte cells with Bz during the interaction with PBMC cells influences the lipid pathways scenario, inducing lipolytic metabolism through the expression of PNPLA2.

Developing MiR-133a Zipper Nanoparticles for Targeted Enhancement of Thermogenic Adipocyte Generation

Existing delivery methods for RNAi therapeutics encounter challenges, including stability, specificity, and off-target effects, which restrict their clinical effectiveness. In this study, a novel miR-133a zipper nanoparticle (NP) system that integrates miRNA zipper technology with rolling circle transcription (RCT) to achieve targeted delivery and specific regulation of miR-133a in adipocytes, is presented. This innovative approach can greatly enhance the delivery and release of miR-133a zippers, increasing the expression of thermogenic genes and mitochondrial biogenesis. he miR-133a zipper NP is utilized for the delivery of miRNA zipper-blocking miR-133a, an endogenous inhibitor of Prdm16 expression, to enhance the thermogenic activity of adipocytes by modulating their transcriptional program. Inhibition of miR-133a through the miR-133a zipper NP leads to more significant upregulation of thermogenic gene expression (Prdm16 and Ucp1) than with the free miR-133a zipper strand. Furthermore, miR-133a zipper NPs increase the number of mitochondria and induce heat production, reducing the size of 3D adipose spheroids. In short, this study emphasizes the role of RNA NPs in improving RNAi stability and specificity and paves the way for broader applications in gene therapy. Moreover, this research represents a significant advancement in RNAi-based treatments, pointing toward a promising direction for future therapeutic strategies.

The dairy-derived peptide Miltin exerts anti-obesity effects by increasing adipocyte thermogenesis

Growing research has highlighted that the consumption of dairy products improves the metabolic health in obese individuals by functioning as regulatory modulators. However, the molecular basis of this effect remains largely unknown. Herein, we report a dairy-derived peptide, which we named Miltin, that activates the thermogenesis of brown adipocytes and increases white adipocyte browning. Previously, Miltin was merely identified for its antioxidant capacity, although it is commonly present in different dairy products. In this study, we revealed the effect of Miltin in modulating adipose thermogenesis and further explored its potential in treating obesity through in vivo and in vitro strategies. The administration of Miltin in mice fed with a high-fat diet resulted in enhanced thermogenesis, improved glucose homeostasis, and reduced body mass and lipid accumulation, indicating the anti-obesity effect of Miltin. Genomic analysis revealed that Miltin modulates thermogenesis by inducing the activation of the MAPK signaling pathway by preferentially interacting with GADD45γ to promote its stability. Together, our findings indicate that Miltin's role in initiating the thermogenesis of adipocytes makes it a potential anti-obesity therapy for future development.

Adipose tissue rearrangement in cancer cachexia: The involvement of β3-adrenergic receptor associated pathways

Cancer-associated cachexia (CAC) is a complex multiple organ syndrome that significantly contributes to reduced quality of life and increased mortality among many cancer patients. Its multifactorial nature makes its early diagnosis and effective therapeutic interventions challenging. Adipose tissue is particularly impacted by cachexia, typically through increased lipolysis, browning and thermogenesis, mainly at the onset of the disease. These processes lead to depletion of fat mass and contribute to the dysfunction of other organs. The β-adrenergic signalling pathways are classical players in the regulation of adipose tissue metabolism. They are activated upon sympathetic stimulation inducing lipolysis, browning and thermogenesis, therefore contributing to energy expenditure. Despite accumulating evidence suggesting that β3-adrenergic receptor stimulation may be crucial to the adipose tissue remodelling during cachexia, the literature remains controversial. Moreover, there is limited knowledge regarding sexual dimorphism of adipose tissue in the context of cachexia. This review paper aims to present the current knowledge regarding adipose tissue wasting during CAC, with a specific focus on the role of the β3-adrenergic receptor, placing it as a potential therapeutic target against cachexia.

Ginsenoside Rg3, enriched in red ginseng extract, improves lipopolysaccharides-induced suppression of brown and beige adipose thermogenesis with mitochondrial activation

Brown adipose tissue (BAT) which is a critical regulator of energy homeostasis, and its activity is inhibited by obesity and low-grade chronic inflammation. Ginsenoside Rg3, the primary constituent of Korean red ginseng (steamed Panax ginseng CA Meyer), has shown therapeutic potential in combating inflammatory and metabolic diseases. However, it remains unclear whether Rg3 can protect against the suppression of browning or activation of BAT induced by inflammation. In this study, we conducted a screening of ginsenoside composition in red ginseng extract (RGE) and explored the anti-adipogenic effects of both RGE and Rg3. We observed that RGE (exist 0.25 mg/mL of Rg3) exhibited significant lipid-lowering effects in adipocytes during adipogenesis. Moreover, treatment with Rg3 (60 μM) led to the inhibition of triglyceride accumulation, subsequently promoting enhanced fatty acid oxidation, as evidenced by the conversion of radiolabeled 3H-fatty acids into 3H-H2O with mitochondrial activation. Rg3 alleviated the attenuation of browning in lipopolysaccharide (LPS)-treated beige adipocytes and primary brown adipocytes by recovered by uncoupling protein 1 (UCP1) and the oxygen consumption rate compared to the LPS-treated group. These protective effects of Rg3 on inflammation-induced inhibition of beige and BAT-derived thermogenesis were confirmed in vivo by treating with CL316,243 (a beta-adrenergic receptor agonist) and LPS to induce browning and inflammation, respectively. Consistent with the in vitro data, treatment with Rg3 (2.5 mg/kg, 8 weeks) effectively reversed the LPS-induced inhibition of brown adipocyte features in C57BL/6 mice. Our findings confirm that Rg3-rich foods are potential browning agents that counteract chronic inflammation and metabolic complications.

Involution of brown adipose tissue through a Syntaxin 4 dependent pyroptosis pathway

Aging, chronic high-fat diet feeding, or housing at thermoneutrality induces brown adipose tissue (BAT) involution, a process characterized by reduction of BAT mass and function with increased lipid droplet size. Single nuclei RNA sequencing of aged mice identifies a specific brown adipocyte population of Ucp1-low cells that are pyroptotic and display a reduction in the longevity gene syntaxin 4 (Stx4a). Similar to aged brown adipocytes, Ucp1-STX4KO mice display loss of brown adipose tissue mass and thermogenic dysfunction concomitant with increased pyroptosis. Restoration of STX4 expression or suppression of pyroptosis activation protects against the decline in both mass and thermogenic activity in the aged and Ucp1-STX4KO mice. Mechanistically, STX4 deficiency reduces oxidative phosphorylation, glucose uptake, and glycolysis leading to reduced ATP levels, a known triggering signal for pyroptosis. Together, these data demonstrate an understanding of rapid brown adipocyte involution and that physiologic aging and thermogenic dysfunction result from pyroptotic signaling activation.

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.

Effect of lanthanum nitrate on adipogenesis in mice

Lanthanum (La) is widely used in modern industry and agriculture because of its unique physicochemical properties and is broadly exposed in the population. Some studies have shown that La may have some effects on adipogenesis, but there is a lack of related in vivo evidence. In this study, the effects of La(NO3 )3 on adipogenesis and its associated mechanism were studied using C57BL/6J mouse model. The results showed that La(NO3 )3 exposure caused a decrease in body weight and the percentage of fat content in mice. In addition, the adipose marker molecules and specific adipogenic transcription factors decreased in both white adipose tissue (WAT) and brown adipose tissue (BAT). Detection of signaling pathway-related molecules revealed that canonical wnt/β-catenin pathway-related molecules were upregulated in both adipose tissues. In summary, in vivo exposure to La(NO3 )3 might inhibited adipogenesis in mice, possibly through upregulation of the canonical Wnt/β-catenin signaling pathway.

Beyond the Cold: Activating Brown Adipose Tissue as an Approach to Combat Obesity

With a dramatic increase in the number of obese and overweight people, there is a great need for new anti-obesity therapies. With the discovery of the functionality of brown adipose tissue in adults and the observation of beige fat cells among white fat cells, scientists are looking for substances and methods to increase the activity of these cells. We aimed to describe how scientists have concluded that brown adipose tissue is also present and active in adults, to describe where in the human body these deposits of brown adipose tissue are, to summarize the origin of both brown fat cells and beige fat cells, and, last but not least, to list some of the substances and methods classified as BAT promotion agents with their benefits and side effects. We summarized these findings based on the original literature and reviews in the field, emphasizing the discovery, function, and origins of brown adipose tissue, BAT promotion agents, and batokines. Only studies written in English and with a satisfying rating were identified from electronic searches of PubMed.

The Impact of Excessive Fructose Intake on Adipose Tissue and the Development of Childhood Obesity

Worldwide, childhood obesity cases continue to rise, and its prevalence is known to increase the risk of non-communicable diseases typically found in adults, such as cardiovascular disease and type 2 diabetes mellitus. Thus, comprehending its multiple causes to build healthier approaches and revert this scenario is urgent. Obesity development is strongly associated with high fructose intake since the excessive consumption of this highly lipogenic sugar leads to white fat accumulation and causes white adipose tissue (WAT) inflammation, oxidative stress, and dysregulated adipokine release. Unfortunately, the global consumption of fructose has increased dramatically in recent years, which is associated with the fact that fructose is not always evident to consumers, as it is commonly added as a sweetener in food and sugar-sweetened beverages (SSB). Therefore, here, we discuss the impact of excessive fructose intake on adipose tissue biology, its contribution to childhood obesity, and current strategies for reducing high fructose and/or free sugar intake. To achieve such reductions, we conclude that it is important that the population has access to reliable information about food ingredients via food labels. Consumers also need scientific education to understand potential health risks to themselves and their children.

The potential of therapeutic strategies targeting mitochondrial biogenesis for the treatment of insulin resistance and type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a persistent metabolic disorder marked by deficiencies in insulin secretion and/or function, affecting various tissues and organs and leading to numerous complications. Mitochondrial biogenesis, the process by which cells generate new mitochondria utilizing existing ones plays a crucial role in energy homeostasis, glucose metabolism, and lipid handling. Recent evidence suggests that promoting mitochondrial biogenesis can alleviate insulin resistance in the liver, adipose tissue, and skeletal muscle while improving pancreatic β-cell function. Moreover, enhanced mitochondrial biogenesis has been shown to ameliorate T2DM symptoms and may contribute to therapeutic effects for the treatment of diabetic nephropathy, cardiomyopathy, retinopathy, and neuropathy. This review summarizes the intricate connection between mitochondrial biogenesis and T2DM, highlighting the potential of novel therapeutic strategies targeting mitochondrial biogenesis for T2DM treatment and its associated complications. It also discusses several natural products that exhibit beneficial effects on T2DM by promoting mitochondrial biogenesis.

Regulation of adipogenesis by histone methyltransferases

Epigenetic regulation is a critical component of lineage determination. Adipogenesis is the process through which uncommitted stem cells or adipogenic precursor cells differentiate into adipocytes, the most abundant cell type of the adipose tissue. Studies examining chromatin modification during adipogenesis have provided further understanding of the molecular blueprint that controls the onset of adipogenic differentiation. Unlike histone acetylation, histone methylation has context dependent effects on the activity of a transcribed region of DNA, with individual or combined marks on different histone residues providing distinct signals for gene expression. Over half of the 42 histone methyltransferases identified in mammalian cells have been investigated in their role during adipogenesis, but across the large body of literature available, there is a lack of clarity over potential correlations or emerging patterns among the different players. In this review, we will summarize important findings from studies published in the past 15 years that have investigated the role of histone methyltransferases during adipogenesis, including both protein arginine methyltransferases (PRMTs) and lysine methyltransferases (KMTs). We further reveal that PRMT1/4/5, H3K4 KMTs (MLL1, MLL3, MLL4, SMYD2 and SET7/9) and H3K27 KMTs (EZH2) all play positive roles during adipogenesis, while PRMT6/7 and H3K9 KMTs (G9a, SUV39H1, SUV39H2, and SETDB1) play negative roles during adipogenesis.

Fatty Acids and their Proteins in Adipose Tissue Inflammation

Chronic low-grade adipose tissue inflammation is associated with metabolic disorders. Inflammation results from the intertwined cross-talks of pro-inflammatory and anti-inflammatory pathways in the immune response of adipose tissue. In addition, adipose FABP4 levels and lipid droplet proteins are involved in systemic and tissue inflammation. Dysregulated adipocytes help infiltrate immune cells derived from bone marrow responsible for producing cytokines and chemokines. When adipose tissue expands in excess, adipocyte exhibits increased secretion of adipokines and is implicated in metabolic disturbances due to the release of free fatty acids. This review presents an emerging concept in adipose tissue fat metabolism, fatty acid handling and binding proteins, and lipid droplet proteins and their involvement in inflammatory disorders.

Brown adipose tissue evaluation using water and triglyceride as indices by diffuse reflectance spectroscopy

Brown adipose tissue (BAT) is related to lipid and glucose metabolism, and BAT evaluation is expected to contribute to disease prevention and treatment. We aimed to establish a BAT evaluation method using simple and non-invasive diffuse reflectance spectroscopy (DRS). We acquired diffuse reflectance spectra of BAT using DRS from rats with cold stimulation and analyzed the second-derivative spectra. To predict the amount of triglyceride in BAT from the second-derivative spectra, partial least-squares regression analysis was performed, and we examined whether BAT weight can be predicted from the amount of triglyceride by single regression analysis. By focusing on changes in the amount of triglyceride in BAT with cold stimulation, it was suggested that this amount could be predicted spectroscopically, and the predicted amount of triglyceride could be used to estimate the BAT weight with cold stimulation. If these results can be translated into humans, they may contribute to preventing metabolic disorders.

A newly identified compound activating UCP1 inhibits obesity and its related metabolic disorders

OBJECTIVE

Promoting thermogenesis in adipose tissue has been a promising strategy against obesity and related metabolic complications. We aimed to identify compounds that promote thermogenesis in adipocytes and to elucidate their functions and roles in metabolism.

METHODS

To identify compounds that directly promote thermogenesis from a structurally diverse set of 4800 compounds, we utilized a cell-based platform for high-throughput screening that induces uncoupling protein 1 (Ucp1) expression in adipocytes.

RESULTS

We identified one candidate compound that activates UCP1. Additional characterization of this compound revealed that it induced cellular thermogenesis in adipocytes with negligible cytotoxicity. In a subsequent diet-induced obesity model, mice treated with this compound exhibited a slower rate of weight gain, improved insulin sensitivity, and increased energy expenditure. Mechanistic studies have revealed that this compound increases mitochondrial biogenesis by elevating maximal respiration, which is partly mediated by the protein kinase A (PKA)-p38 mitogen-activated protein kinase (MAPK) signaling pathway. A further comprehensive genetic analysis of adipocytes treated with these compounds identified two novel UCP1-dependent thermogenic genes, potassium voltage-gated channel subfamily C member 2 (Kcnc2) and predicted gene 5627 (Gm5627).

CONCLUSIONS

The identified compound can serve as a potential therapeutic drug for the treatment of obesity and its related metabolic disorders. Furthermore, our newly clarified thermogenic genes play an important role in UCP1-dependent thermogenesis in adipocytes.

A Study on the Acquisition and Identification of Beige Adipocytes and Exosomes as Well as Their Inflammatory Regulation by Promoting Macrophage Polarization

BACKGROUND

The fat retention rate is associated with postoperative inflammation. However, fat survival is still unpredictable even when supplemented with adipose-derived stem cells (ADSCs). Beige adipocytes play a role in regulating pathological inflammation. Thus, we assumed that exosomes may promote macrophage polarization to regulate inflammation when we simulated postgrafted inflammation by lipopolysaccharide (LPS) induction.

METHODS

3T3-L1 preadipocytes were used to differentiate into beige adipocytes, which were stimulated by special culture media, and then, exosomes were isolated from the supernatant. We identified them by morphology, protein and gene expression, or size distribution. Next, we utilized exosomes to stimulate LPS-induced macrophages and evaluated the changes in inflammatory cytokines and macrophage polarization.

RESULTS

The induced cells contained multilocular lipid droplets and expressed uncoupling protein 1 (UCP1) and beige adipocyte-specific gene. The exosomes, which were approximately 111.5 nm and cup-like, were positive for surface markers. Additionally, the levels of proinflammatory-related indicators in the LPS+exosomes (LPS+Exos) group were increased after inflammation was activated for 6 h. When inflammation lasted 16 h, exosomes decreased the expression of proinflammatory-related indicators and increased the expression of anti-inflammatory-related indicators compared with the group without exosomes.

CONCLUSION

The method described in this article can successfully obtain beige adipocytes and exosomes. The results suggest that beige adipocyte exosomes can promote inflammatory infiltration and polarize more macrophages to the M1 type in the early period of inflammation, accelerating the occurrence of the inflammation endpoint and the progression of macrophage switching from M1 to M2, while inflammation develops continuously.

NO LEVEL ASSIGNED

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Environmental factor reversibly determines cellular identity through opposing Integrators that unify epigenetic and transcriptional pathways

Organisms must adapt to environmental stresses to ensure their survival and prosperity. Different types of stresses, including thermal, mechanical, and hypoxic stresses, can alter the cellular state that accompanies changes in gene expression but not the cellular identity determined by a chromatin state that remains stable throughout life. Some tissues, such as adipose tissue, demonstrate remarkable plasticity and adaptability in response to environmental cues, enabling reversible cellular identity changes; however, the mechanisms underlying these changes are not well understood. We hypothesized that positive and/or negative "Integrators" sense environmental cues and coordinate the epigenetic and transcriptional pathways required for changes in cellular identity. Adverse environmental factors such as pollution disrupt the coordinated control contributing to disease development. Further research based on this hypothesis will reveal how organisms adapt to fluctuating environmental conditions, such as temperature, extracellular matrix stiffness, oxygen, cytokines, and hormonal cues by changing their cellular identities.

Ubiquitin ligase RNF20 coordinates sequential adipose thermogenesis with brown and beige fat-specific substrates

In mammals, brown adipose tissue (BAT) and inguinal white adipose tissue (iWAT) execute sequential thermogenesis to maintain body temperature during cold stimuli. BAT rapidly generates heat through brown adipocyte activation, and further iWAT gradually stimulates beige fat cell differentiation upon prolonged cold challenges. However, fat depot-specific regulatory mechanisms for thermogenic activation of two fat depots are poorly understood. Here, we demonstrate that E3 ubiquitin ligase RNF20 orchestrates adipose thermogenesis with BAT- and iWAT-specific substrates. Upon cold stimuli, BAT RNF20 is rapidly downregulated, resulting in GABPα protein elevation by controlling protein stability, which stimulates thermogenic gene expression. Accordingly, BAT-specific Rnf20 suppression potentiates BAT thermogenic activity via GABPα upregulation. Moreover, upon prolonged cold stimuli, iWAT RNF20 is gradually upregulated to promote de novo beige adipogenesis. Mechanistically, iWAT RNF20 mediates NCoR1 protein degradation, rather than GABPα, to activate PPARγ. Together, current findings propose fat depot-specific regulatory mechanisms for temporal activation of adipose thermogenesis.

Neuregulin 4 mediates the metabolic benefits of mild cold exposure by promoting beige fat thermogenesis

Interorgan crosstalk via secreted hormones and metabolites is a fundamental aspect of mammalian metabolic physiology. Beyond the highly specialized endocrine cells, peripheral tissues are emerging as an important source of metabolic hormones that influence energy and nutrient metabolism and contribute to disease pathogenesis. Neuregulin 4 (Nrg4) is a fat-derived hormone that protects mice from nonalcoholic steatohepatitis (NASH) and NASH-associated liver cancer by shaping hepatic lipid metabolism and the liver immune microenvironment. Despite its enriched expression in brown fat, whether NRG4 plays a role in thermogenic response and mediates the metabolic benefits of cold exposure are areas that remain unexplored. Here we show that Nrg4 expression in inguinal white adipose tissue (iWAT) is highly responsive to chronic cold exposure. Nrg4 deficiency impairs beige fat induction and renders mice more susceptible to diet-induced metabolic disorders under mild cold conditions. Using mice with adipocyte and hepatocyte-specific Nrg4 deletion, we reveal that adipose tissue-derived NRG4, but not hepatic NRG4, is essential for beige fat induction following cold acclimation. Furthermore, treatment with recombinant NRG4-Fc fusion protein promotes beige fat induction in iWAT and improves metabolic health in mice with diet-induced obesity. These findings highlight a critical role of NRG4 in mediating beige fat induction and preserving metabolic health under mild cold conditions.

Zinc homeostasis and redox alterations in obesity

Impairment of both cellular zinc and redox homeostasis is a feature of several chronic diseases, including obesity. A significant two-way interaction exists between redox metabolism and the relatively redox-inert zinc ion. Redox metabolism critically influences zinc homeostasis and controls its cellular availability for various cellular functions by regulating zinc exchange from/to zinc-binding proteins. Zinc can regulate redox metabolism and exhibits multiple pro-antioxidant properties. On the other hand, even minor disturbances in zinc status and zinc homeostasis affect systemic and cellular redox homeostasis. At the cellular level, zinc homeostasis is regulated by a multi-layered machinery consisting of zinc-binding molecules, zinc sensors, and two selective families of zinc transporters, the Zinc Transporter (ZnT) and Zrt, Irt-like protein (ZIP). In the present review, we summarize the current state of knowledge on the role of the mutual interaction between zinc and redox homeostasis in physiology and pathophysiology, pointing to the role of zinc in the alterations responsible for redox stress in obesity. Since zinc transporters primarily control zinc homeostasis, we describe how changes in the expression and activity of these zinc-regulating proteins are associated with obesity.

Senescent adipocytes and type 2 diabetes - current knowledge and perspective concepts

Among civilization diseases, the number of individuals suffering from type 2 diabetes (T2DM) is expected to increase to more than a billion in less than 20 years, which is associated with, e.g., populational aging, poor diet, sedentary lifestyle, genetic predispositions, and immunological factors. T2DM affects many organs and is characterized by insulin resistance, high glucose levels, and adipocyte dysfunction, which are related to senescence. Although this type of cellular aging has beneficial biological functions, it can also act unfavorable since senescent adipocytes resist apoptosis, enhance cytokine secretion, downregulate cell identity genes, and acquire the senescence-associated secretory phenotype that renders a more oxidative environment. Opposing T2DM is possible via a wide variety of senotherapies, including senolytics and senomorphics; nevertheless, further research is advised to expand therapeutic possibilities and benefits. Consequences that ought to be deeply researched include secretory phenotype, chronic inflammation, increasing insulin resistance, as well as impairment of adipogenesis and functioning of adipocyte cells. Herein, despite reviewing T2DM and fat tissue senescence, we summarized the latest adipocyte-related anti-diabetes solutions and suggested further research directions.

The Emerging Role of SIRT7 in Glucose and Lipid Metabolism

Sirtuins (SIRT1-7 in mammals) are a family of NAD+-dependent lysine deacetylases and deacylases that regulate diverse biological processes, including metabolism, stress responses, and aging. SIRT7 is the least well-studied member of the sirtuins, but accumulating evidence has shown that SIRT7 plays critical roles in the regulation of glucose and lipid metabolism by modulating many target proteins in white adipose tissue, brown adipose tissue, and liver tissue. This review focuses on the emerging roles of SIRT7 in glucose and lipid metabolism in comparison with SIRT1 and SIRT6. We also discuss the possible implications of SIRT7 inhibition in the treatment of metabolic diseases such as type 2 diabetes and obesity.

miR-889-3p Facilitates the Browning Process of White Adipocyte Precursors by Targeting the SON Gene

It is well-established that beige/brown adipose tissue can dissipate stored energy through thermogenesis; hence, the browning of white adipocytes (WAT) has garnered significant interest in contemporary research. Our preceding investigations have identified a marked downregulation of miR-889-3p concurrent with the natural maturation of brown adipose tissue. However, the specific role and underlying molecular mechanisms of miR-889-3p in the browning process of white adipose tissue warrant further elucidation. In this research, we initially delved into the potential role of miR-889-3p in preadipocyte growth via flow cytometry and CCK-8 assay, revealing that miR-889-3p can stimulate preadipocyte growth. To validate the potential contribution of miR-889-3p in the browning process of white adipose tissue, we established an in vitro rabbit white adipocyte browning induction, which exhibited a significant upregulation of miR-889-3p during the browning process. RT-qPCR and Western blot analysis indicated that miR-889-3p overexpression significantly amplified the mRNA levels of UCP1, PRDM16, and CIDEA, as well as UCP1 protein levels. Furthermore, miR-889-3p overexpression fostered intracellular triglyceride accumulation. Conversely, the downregulation of miR-889-3p hindered the browning of rabbit preadipocytes. Subsequently, based on target gene prediction and luciferase reporter gene determination, we demonstrated that miR-889-3p directly targets the 3'-UTR region of SON. Lastly, we observed that inhibiting SON could facilitate the browning of rabbit preadipocytes. In conclusion, our findings suggest that miR-889-3p facilitates the browning process of white adipocyte precursors by specifically targeting the SON gene.

[Cold stimulation promotes interleukin-4 secretion by mucosal-associated invariant T cells in the adipose tissue to promote adipose browning in mice]

OBJECTIVE

To investigate the role of mucosal-associated invariant T (MAIT) cells in the regulatory mechanism of adipose browning.

METHODS

A mouse model with functional deficiency of MAIT cells was established for comparison with the wild-type mice for levels of brown adipose tissue markers in response to cold stimulation using Western blotting and RT-PCR. Flow cytometry was used to analyze the changes in the number, activation level and cytokine secretion ability of MAIT cells in mouse adipose tissue after cold stimulation. In a co-culture system of MAIT cells and adipocytes, the effect of interleukin-4 (IL-4) blocking antibodies on the expressions of brown adipose tissue markers in the adipocytes was evaluated using Western blotting and RT-PCR. In a mouse model of MAIT cell deficiency, the changes in adipose browning-related indicators in response to cold stimulation were analyzed using metabolic cages, immunohistochemistry, Western blotting and the Seahorse method.

RESULTS

In both the mouse models of functional deficiency of MAIT cells and wild-type mice, cold stimulation significantly increased the expression levels of brown adipose tissue markers UCP-1 and PGC1-α and upregulated CD69 and IL-4 expressions in the adipose tissue without significantly affecting the number of MAIT cells in the adipose tissue. In the coculture experiment, the adipocytes showed obviously increased browning level after co-culture with MAIT cells (P < 0.05), but blocking IL-4 signaling strongly downregulated the browning level (P < 0.05). The MAIT cell-deficient mice showed obviously lower levels of energy expenditure, adipose browning and metabolism of the adipocytes compared with the wild-type mice in response to cold stimulation (P < 0.05).

CONCLUSION

MAIT cells participate in adipose browning in mice, and cold stimulation promotes MAIT cell secretion of IL-4 to positively regulate adipose browning.

Adipose Tissue Metabolism in Response to Food Intake

The quality and quantity of the food we consume have a major impact on our general health and longevity [...].

Placental extract suppresses lipid droplet accumulation by autophagy during the differentiation of adipose-derived mesenchymal stromal/stem cells into mature adipocytes

OBJECTIVE

Placental extract, which contains various bioactive compounds, has been used as traditional medicine. Many studies have demonstrated additional applications of placental extract and provided a scientific basis for the broad spectrum of its effects. We have previously reported that porcine placental extract (PPE) strongly suppresses adipogenesis in a 3T3-L1 preadipocyte cell line, inhibiting differentiation. This study aimed to examine the effect of PPE on the accumulation of lipid droplets (LD) in adipose-derived mesenchymal stromal/stem cells (ASC).

RESULTS

The study findings revealed that PPE decreased the size of LD during the differentiation of ASC into mature adipocytes. RT-qPCR analysis revealed that PPE increased the gene expression of lysosomal acid lipase A (Lipa), a lipolysis-related gene, in ASC-differentiated adipocytes. However, no differences were noted in the adipocyte differentiation markers (Pparg, Cebpa, and Adipoq), or the adipogenesis-related genes (Dgat1, Dgat2, Fasn, Soat1, and Soat2). In addition, PPE promoted autophagosome formation, which was partially co-localized with the LD, indicating that PPE accelerated the degradation of LD by inducing autophagy (termed lipophagy) during the differentiation of ASC into mature adipocytes. These results suggest that the use of PPE may be a potential novel treatment for regulating adipogenesis for the treatment of obesity.

Branched-chain amino acid modulation of lipid metabolism, gluconeogenesis, and inflammation in a finishing pig model: targeting leucine and valine

Branched-chain amino acids (BCAAs) play a regulatory role in adipogenesis and energy balance. Therefore, this study aimed to investigate the impact of BCAA supplements, especially leucine (Leu) and valine (Val) supplementation, on lipid metabolism and related disorders in a finishing pig model. The results demonstrated that Leu (1%) and Val decreased serum as well as hepatic lipid accumulation. Moreover, metabolomics and lipidomics analyses revealed that Leu and Val markedly downregulated the level of various lipid species in the liver. This outcome may be explained by Leu and Val promoting cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA)/hormone-sensitive triglyceride lipase (HSL) signaling pathways. Leu and Val altered the fatty acid composition in distinct adipose tissues and decreased the levels of inflammatory factors. Additionally, they significantly decreased back fat thickness, and the results of the fatty acid profiles demonstrated that Leu and Val significantly increased the levels of monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs) while decreasing those of saturated fatty acids (SFAs), especially in back fat and abdominal fat. Besides, Leu and Val restored glucose homeostasis by suppressing gluconeogenesis through the serine/threonine protein kinase (AKT)/transcription factor forkhead box O1 (FOXO1) signaling pathway in the liver and back fat. In summary, these results suggest that Leu and Val may serve as key regulators for modulating lipid metabolism and steatosis.

Standardized In Vitro Models of Human Adipose Tissue Reveal Metabolic Flexibility in Brown Adipocyte Thermogenesis

Functional human brown and white adipose tissue (BAT and WAT) are vital for thermoregulation and nutritional homeostasis, while obesity and other stressors lead, respectively, to cold intolerance and metabolic disease. Understanding BAT and WAT physiology and dysfunction necessitates clinical trials complemented by mechanistic experiments at the cellular level. These require standardized in vitro models, currently lacking, that establish references for gene expression and function. We generated and characterized a pair of immortalized, clonal human brown (hBA) and white (hWA) preadipocytes derived from the perirenal and subcutaneous depots, respectively, of a 40-year-old male individual. Cells were immortalized with hTERT and confirmed to be of a mesenchymal, nonhematopoietic lineage based on fluorescence-activated cell sorting and DNA barcoding. Functional assessments showed that the hWA and hBA phenocopied primary adipocytes in terms of adrenergic signaling, lipolysis, and thermogenesis. Compared to hWA, hBA were metabolically distinct, with higher rates of glucose uptake and lactate metabolism, and greater basal, maximal, and nonmitochondrial respiration, providing a mechanistic explanation for the association between obesity and BAT dysfunction. The hBA also responded to the stress of maximal respiration by using both endogenous and exogenous fatty acids. In contrast to certain mouse models, hBA adrenergic thermogenesis was mediated by several mechanisms, not principally via uncoupling protein 1 (UCP1). Transcriptomics via RNA-seq were consistent with the functional studies and established a molecular signature for each cell type before and after differentiation. These standardized cells are anticipated to become a common resource for future physiological, pharmacological, and genetic studies of human adipocytes.

Pharmacological modulation of adaptive thermogenesis: new clues for obesity management?

BACKGROUND

Adaptive thermogenesis represents the main mechanism through which the body generates heat in response to external stimuli, a phenomenon that includes shivering and non-shivering thermogenesis. The non-shivering thermogenesis is mainly exploited by adipose tissue characterized by a brown aspect, which specializes in energy dissipation. A decreased amount of brown adipose tissue has been observed in ageing and chronic illnesses such as obesity, a worldwide health problem characterized by dysfunctional adipose tissue expansion and associated cardiometabolic complications. In the last decades, the discovery of a trans-differentiation mechanism ("browning") within white adipose tissue depots, leading to the generation of brown-like cells, allowed to explore new natural and synthetic compounds able to favour this process and thus enhance thermogenesis with the aim of counteracting obesity. Based on recent findings, brown adipose tissue-activating agents could represent another option in addition to appetite inhibitors and inhibitors of nutrient absorption for obesity treatment.

PURPOSE

This review investigates the main molecules involved in the physiological (e.g. incretin hormones) and pharmacological (e.g. β3-adrenergic receptors agonists, thyroid receptor agonists, farnesoid X receptor agonists, glucagon-like peptide-1, and glucagon receptor agonists) modulation of adaptive thermogenesis and the signalling mechanisms involved.

A PPARγ/long noncoding RNA axis regulates adipose thermoneutral remodeling in mice

Interplay between energy-storing white adipose cells and thermogenic beige adipocytes contributes to obesity and insulin resistance. Irrespective of specialized niche, adipocytes require the activity of the nuclear receptor PPARγ for proper function. Exposure to cold or adrenergic signaling enriches thermogenic cells though multiple pathways that act synergistically with PPARγ; however, the molecular mechanisms by which PPARγ licenses white adipose tissue to preferentially adopt a thermogenic or white adipose fate in response to dietary cues or thermoneutral conditions are not fully elucidated. Here, we show that a PPARγ/long noncoding RNA (lncRNA) axis integrates canonical and noncanonical thermogenesis to restrain white adipose tissue heat dissipation during thermoneutrality and diet-induced obesity. Pharmacologic inhibition or genetic deletion of the lncRNA Lexis enhances uncoupling protein 1-dependent (UCP1-dependent) and -independent thermogenesis. Adipose-specific deletion of Lexis counteracted diet-induced obesity, improved insulin sensitivity, and enhanced energy expenditure. Single-nuclei transcriptomics revealed that Lexis regulates a distinct population of thermogenic adipocytes. We systematically map Lexis motif preferences and show that it regulates the thermogenic program through the activity of the metabolic GWAS gene and WNT modulator TCF7L2. Collectively, our studies uncover a new mode of crosstalk between PPARγ and WNT that preserves white adipose tissue plasticity.

Mulberry leaf flavonoids activate BAT and induce browning of WAT to improve type 2 diabetes via regulating the AMPK/SIRT1/PGC-1α signaling pathway

Mulberry (Morus alba L.) leaf is a well-established traditional Chinese botanical and culinary resource. It has found widespread application in the management of diabetes. The bioactive constituents of mulberry leaf, specifically mulberry leaf flavonoids (MLFs), exhibit pronounced potential in the amelioration of type 2 diabetes (T2D). This potential is attributed to their ability to safeguard pancreatic β cells, enhance insulin resistance, and inhibit α-glucosidase activity. Our antecedent research findings underscore the substantial therapeutic efficacy of MLFs in treating T2D. However, the precise mechanistic underpinnings of MLF's anti-T2D effects remain the subject of inquiry. Activation of brown/beige adipocytes is a novel and promising strategy for T2D treatment. In the present study, our primary objective was to elucidate the impact of MLFs on adipose tissue browning in db/db mice and 3T3-L1 cells and elucidate its underlying mechanism. The results manifested that MLFs reduced body weight and food intake, alleviated hepatic steatosis, improved insulin sensitivity, and increased lipolysis and thermogenesis in db/db mice. Moreover, MLFs activated brown adipose tissue (BAT) and induced the browning of inguinal white adipose tissue (IWAT) and 3T3-L1 adipocytes by increasing the expressions of brown adipocyte marker genes and proteins such as uncoupling protein 1 (UCP1) and beige adipocyte marker genes such as transmembrane protein 26 (Tmem26), thereby promoting mitochondrial biogenesis. Mechanistically, MLFs facilitated the activation of BAT and the induction of WAT browning to ameliorate T2D primarily through the activation of AMP-activated protein kinase (AMPK)/sirtuin 1 (SIRT1)/peroxisome proliferator-activated receptor-gamma coactivator 1α (PGC-1α) signaling pathway. These findings highlight the unique capacity of MLF to counteract T2D by enhancing BAT activation and inducing browning of IWAT, thereby ameliorating glucose and lipid metabolism disorders. As such, MLFs emerge as a prospective and innovative browning agent for the treatment of T2D.

Echinacoside Induces UCP1- and ATP-Dependent Thermogenesis in Beige Adipocytes via the Activation of Dopaminergic Receptors

Echinacoside (ECH) is a naturally occurring phenylethanoid glycoside, isolated from Echinacea angustifolia, and this study aimed to analyze its effect on thermogenesis and its interaction with dopaminergic receptors 1 and 5 (DRD1 and DRD5) in 3T3-L1 white adipocytes and mice models. We employed RT-PCR, immunoblot, immunofluorescence, a staining method, and an assay kit to determine its impact. ECH showed a substantial increase in browning signals in vitro and a decrease in adipogenic signals in vivo. Additionally, analysis of the iWAT showed that the key genes involved in beiging, mitochondrial biogenesis, and ATP-dependent thermogenesis were upregulated while adipogenesis and lipogenesis genes were downregulated. OXPHOS complexes, Ca2+ signaling proteins as well as intracellular Ca2+ levels were also upregulated in 3T3-L1 adipocytes following ECH treatment. This was collectively explained by mechanistic studies which showed that ECH mediated the beiging process via the DRD1/5-cAMP-PKA and subsequent downstream molecules, whereas it co-mediated the α1-AR-signaling thermogenesis via the DRD1/5/SERCA2b/RyR2/CKmt pathway in 3T3-L1 adipocytes. Animal experiments revealed that there was a 12.28% reduction in body weight gain after the ECH treatment for six weeks. The effects of ECH treatment on adipose tissue can offer more insights into the treatment of obesity and metabolic syndrome.

Adipose tissue‑derived extracellular vesicles: Systemic messengers in health and disease (Review)

Adipose tissue (AT) is a complicated metabolic organ consisting of a heterogeneous population of cells that exert wide‑ranging effects on the regulation of systemic metabolism and in maintaining metabolic homeostasis. Various obesity‑related complications are associated with the development of dysfunctional AT. As an essential transmitter of intercellular information, extracellular vesicles (EVs) have recently been recognized as crucial in regulating multiple physiological functions. AT‑derived extracellular vesicles (ADEVs) have been shown to facilitate cellular communication both inside and between ATs and other peripheral organs. Here, the role of EVs released from ATs in the homeostasis of metabolic and cardiovascular diseases, cancer, and neurological disorders by delivering lipids, proteins, and nucleic acids between different cells is summarized. Furthermore, the differences in the sources of ADEVs, such as adipocytes, AT macrophages, AT‑derived stem cells, and AT‑derived mesenchymal stem cells, are also discussed. This review may provide valuable information for the potential application of ADEVs in metabolic syndrome, cardiovascular diseases, cancer, and neurological disorders.

Brown Fat and Nutrition: Implications for Nutritional Interventions

Brown and beige adipocytes are renowned for their unique ability to generate heat through a mechanism known as thermogenesis. This process can be induced by exposure to cold, hormonal signals, drugs, and dietary factors. The activation of these thermogenic adipocytes holds promise for improving glucose metabolism, reducing fat accumulation, and enhancing insulin sensitivity. However, the translation of preclinical findings into effective clinical therapies poses challenges, warranting further research to identify the molecular mechanisms underlying the differentiation and function of brown and beige adipocytes. Consequently, research has focused on the development of drugs, such as mirabegron, ephedrine, and thyroid hormone, that mimic the effects of cold exposure to activate brown fat activity. Additionally, nutritional interventions have been explored as an alternative approach to minimize potential side effects. Brown fat and beige fat have emerged as promising targets for addressing nutritional imbalances, with the potential to develop strategies for mitigating the impact of metabolic diseases. Understanding the influence of nutritional factors on brown fat activity can facilitate the development of strategies to promote its activation and mitigate metabolic disorders.

Extracellular thiamine concentration influences thermogenic competency of differentiating neck area-derived human adipocytes

Introduction

Brown adipose tissue (BAT) dissipates energy in the form of heat majorly via the mitochondrial uncoupling protein 1 (UCP1). The activation of BAT, which is enriched in the neck area and contains brown and beige adipocytes in humans, was considered as a potential therapeutic target to treat obesity. Therefore, finding novel agents that can stimulate the differentiation and recruitment of brown or beige thermogenic adipocytes are important subjects for investigation. The current study investigated how the availability of extracellular thiamine (vitamin B1), an essential cofactor of mitochondrial enzyme complexes that catalyze key steps in the catabolism of nutrients, affects the expression of thermogenic marker genes and proteins and subsequent functional parameters during ex vivo adipocyte differentiation.

Methods

We differentiated primary human adipogenic progenitors that were cultivated from subcutaneous (SC) or deep neck (DN) adipose tissues in the presence of gradually increasing thiamine concentrations during their 14-day differentiation program. mRNA and protein expression of thermogenic genes were analyzed by RT-qPCR and western blot, respectively. Cellular respiration including stimulated maximal and proton-leak respiration was measured by Seahorse analysis.

Results

Higher thiamine levels resulted in increased expression of thiamine transporter 1 and 2 both at mRNA and protein levels in human neck area-derived adipocytes. Gradually increasing concentrations of thiamine led to increased basal, cAMP-stimulated, and proton-leak respiration along with elevated mitochondrial biogenesis of the differentiated adipocytes. The extracellular thiamine availability during adipogenesis determined the expression levels of UCP1, PGC1a, CKMT2, and other browning-related genes and proteins in primary SC and DN-derived adipocytes in a concentration-dependent manner. Providing abundant amounts of thiamine further increased the thermogenic competency of the adipocytes.

Discussion

Case studies in humans reported that thiamine deficiency was found in patients with type 2 diabetes and obesity. Our study raises the possibility of a novel strategy with long-term thiamine supplementation, which can enhance the thermogenic competency of differentiating neck area-derived adipocytes for preventing or combating obesity.

Ageing-associated phenotypes in mice

Ageing is a continuous process in life featuring progressive damage accumulation that leads to physiological decline, functional deterioration and ultimately death of an organism. Based on the relatively close anatomical and physiological similarity to humans, the mouse has been proven as a valuable model organism in ageing research over the last decades. In this review, we survey methods and tools currently in use to assess ageing phenotypes in mice. We summarize a range of ageing-associated alterations detectable at two major levels of analysis: (1) physiology and pathophysiology and (2) molecular biomarkers. Age-sensitive phenotypes provided in this article may serve to inform future studies targeting various aspects of organismal ageing in mice. In addition, we discuss conceptual and technical challenges faced by previous ageing studies in mice and, where possible, provide recommendations on how to resolve some of these issues.

The Role of Proton-Coupled Amino Acid Transporter 2 (SLC36A2) in Cold-Induced Thermogenesis of Mice

Brown adipocytes mainly utilize glucose and fatty acids to produce energy, which play key roles in thermogenesis. Furthermore, brown adipocytes also utilize other substrates, such as amino acids, for energy expenditure in various conditions. Here, we report the new physiological roles of proton-coupled amino acid transporters, SLC36A2 and SLC36A3, on global energy metabolism. The relative mRNA expression levels of both Slc36a2 and Slc36a3 were all highest in brown adipose tissue. We then generated global Slc36a2 and Slc36a3 knockout mice to investigate their functions in metabolism. Neither loss of Slc36a2 nor Slc36a3 affected the body weight and body composition of the mice. Slc36a2 knockout mice exhibited increased oxygen consumption during the daytime. After cold treatment, inhibition of Slc36a2 significantly decreased the mass of brown adipose tissue compared to wildtype mice, while it lowered the expression level of Cpt1a. Moreover, the serum lipid levels and liver mass were also decreased in Slc36a2 knockout mice after cold treatment. On the contrary, Slc36a3 knockout impaired glucose tolerance and up-regulated serum LDL-cholesterol concentration. Thus, SLC36A2 and SLC36A3 play central and different roles in the energy metabolism of the mice.

The muscle-enriched myokine Musclin impairs beige fat thermogenesis and systemic energy homeostasis via Tfr1/PKA signaling in male mice

Skeletal muscle and thermogenic adipose tissue are both critical for the maintenance of body temperature in mammals. However, whether these two tissues are interconnected to modulate thermogenesis and metabolic homeostasis in response to thermal stress remains inconclusive. Here, we report that human and mouse obesity is associated with elevated Musclin levels in both muscle and circulation. Intriguingly, muscle expression of Musclin is markedly increased or decreased when the male mice are housed in thermoneutral or chronic cool conditions, respectively. Beige fat is then identified as the primary site of Musclin action. Muscle-transgenic or AAV-mediated overexpression of Musclin attenuates beige fat thermogenesis, thereby exacerbating diet-induced obesity and metabolic disorders in male mice. Conversely, Musclin inactivation by muscle-specific ablation or neutralizing antibody treatment promotes beige fat thermogenesis and improves metabolic homeostasis in male mice. Mechanistically, Musclin binds to transferrin receptor 1 (Tfr1) and antagonizes Tfr1-mediated cAMP/PKA-dependent thermogenic induction in beige adipocytes. This work defines the temperature-sensitive myokine Musclin as a negative regulator of adipose thermogenesis that exacerbates the deterioration of metabolic health in obese male mice and thus provides a framework for the therapeutic targeting of this endocrine pathway.

Physiological Approaches Targeting Cellular and Mitochondrial Pathways Underlying Adipose Organ Senescence

The adipose organ is involved in many metabolic functions, ranging from the production of endocrine factors to the regulation of thermogenic processes. Aging is a natural process that affects the physiology of the adipose organ, leading to metabolic disorders, thus strongly impacting healthy aging. Cellular senescence modifies many functional aspects of adipose tissue, leading to metabolic alterations through defective adipogenesis, inflammation, and aberrant adipocytokine production, and in turn, it triggers systemic inflammation and senescence, as well as insulin resistance in metabolically active tissues, leading to premature declined physiological features. In the various aging fat depots, senescence involves a multiplicity of cell types, including mature adipocytes and immune, endothelial, and progenitor cells that are aging, highlighting their involvement in the loss of metabolic flexibility, one of the common features of aging-related metabolic disorders. Since mitochondrial stress represents a key trigger of cellular senescence, and senescence leads to the accumulation of abnormal mitochondria with impaired dynamics and hindered homeostasis, this review focuses on the beneficial potential of targeting mitochondria, so that strategies can be developed to manage adipose tissue senescence for the treatment of age-related metabolic disorders.

Effect of Supplementation with Coffee and Cocoa By-Products to Ameliorate Metabolic Syndrome Alterations Induced by High-Fat Diet in Female Mice

Coffee and cocoa manufacturing produces large amounts of waste. Generated by-products contain bioactive compounds with antioxidant and anti-inflammatory properties, suitable for treating metabolic syndrome (MetS). We aimed to compare the efficacy of aqueous extracts and flours from coffee pulp (CfPulp-E, CfPulp-F) and cocoa shell (CcShell-E, CcShell-F) to ameliorate MetS alterations induced by a high-fat diet (HFD). Bioactive component content was assessed by HPLC/MS. C57BL/6 female mice were fed for 6 weeks with HFD followed by 6 weeks with HFD plus supplementation with one of the ingredients (500 mg/kg/day, 5 days/week), and compared to non-supplemented HFD and Control group fed with regular chow. Body weight, adipocyte size and browning (Mitotracker, confocal microscopy), plasma glycemia (basal, glucose tolerance test-area under the curve, GTT-AUC), lipid profile, and leptin were compared between groups. Cocoa shell ingredients had mainly caffeine, theobromine, protocatechuic acid, and flavan-3-ols. Coffee pulp showed a high content in caffeine, protocatechuic, and chlorogenic acids. Compared to Control mice, HFD group showed alterations in all parameters. Compared to HFD, CcShell-F significantly reduced adipocyte size, increased browning and high-density lipoprotein cholesterol (HDL), and normalized basal glycemia, while CcShell-E only increased HDL. Both coffee pulp ingredients normalized adipocyte size, basal glycemia, and GTT-AUC. Additionally, CfPulp-E improved hyperleptinemia, reduced triglycerides, and slowed weight gain, and CfPulp-F increased HDL. In conclusion, coffee pulp ingredients showed a better efficacy against MetS, likely due to the synergic effect of caffeine, protocatechuic, and chlorogenic acids. Since coffee pulp is already approved as a food ingredient, this by-product could be used in humans to treat obesity-related MetS alterations.

Increasing adipocyte number and reducing adipocyte size: the role of retinoids in adipose tissue development and metabolism

The rising prevalence of obesity is a grave public health threat. In response to excessive energy intake, adipocyte hypertrophy impairs cellular function and leads to metabolic dysfunctions while de novo adipogenesis leads to healthy adipose tissue expansion. Through burning fatty acids and glucose, the thermogenic activity of brown/beige adipocytes can effectively reduce the size of adipocytes. Recent studies show that retinoids, especially retinoic acid (RA), promote adipose vascular development which in turn increases the number of adipose progenitors surrounding the vascular vessels. RA also promotes preadipocyte commitment. In addition, RA promotes white adipocyte browning and stimulates the thermogenic activity of brown/beige adipocytes. Thus, vitamin A is a promising anti-obesity micronutrient.

Effects of multi-organ crosstalk on the physiology and pathology of adipose tissue

In previous studies, adipocytes were found to play an important role in regulating whole-body nutrition and energy balance, and are also important in energy metabolism, hormone secretion, and immune regulation. Different adipocytes have different contributions to the body, with white adipocytes primarily storing energy and brown adipocytes producing heat. Recently discovered beige adipocytes, which have characteristics in between white and brown adipocytes, also have the potential to produce heat. Adipocytes interact with other cells in the microenvironment to promote blood vessel growth and immune and neural network interactions. Adipose tissue plays an important role in obesity, metabolic syndrome, and type 2 diabetes. Dysfunction in adipose tissue endocrine and immune regulation can cause and promote the occurrence and development of related diseases. Adipose tissue can also secrete multiple cytokines, which can interact with organs; however, previous studies have not comprehensively summarized the interaction between adipose tissue and other organs. This article reviews the effect of multi-organ crosstalk on the physiology and pathology of adipose tissue, including interactions between the central nervous system, heart, liver, skeletal muscle, and intestines, as well as the mechanisms of adipose tissue in the development of various diseases and its role in disease treatment. It emphasizes the importance of a deeper understanding of these mechanisms for the prevention and treatment of related diseases. Determining these mechanisms has enormous potential for identifying new targets for treating diabetes, metabolic disorders, and cardiovascular diseases.

Multifaceted mitochondrial quality control in brown adipose tissue

Brown adipose tissue (BAT) controls mammalian core body temperature by non-shivering thermogenesis. BAT is extraordinarily rich in mitochondria, which have the peculiarity of generating heat by uncoupled respiration. Since the mitochondrial activity of BAT is subject to cycles of activation and deactivation in response to environmental temperature changes, an integrated mitochondrial quality control (MQC) system is of fundamental importance to ensure BAT physiology. Here, we provide an overview of the conventional and alternative mechanisms through which thermogenic adipocytes selectively remove damaged parts of mitochondria and how macrophages participate in the MQC system by removing extracellular mitochondrial waste to maintain the thermogenic function of BAT.