Lipid Regulators of Thermogenic Fat Activation

Adipocyte Mitochondria: Deciphering Energetic Functions across Fat Depots in Obesity and Type 2 Diabetes

Adipose tissue, a central player in energy balance, exhibits significant metabolic flexibility that is often compromised in obesity and type 2 diabetes (T2D). Mitochondrial dysfunction within adipocytes leads to inefficient lipid handling and increased oxidative stress, which together promote systemic metabolic disruptions central to obesity and its complications. This review explores the pivotal role that mitochondria play in altering the metabolic functions of the primary adipocyte types, white, brown, and beige, within the context of obesity and T2D. Specifically, in white adipocytes, these dysfunctions contribute to impaired lipid processing and an increased burden of oxidative stress, worsening metabolic disturbances. Conversely, compromised mitochondrial function undermines their thermogenic capabilities, reducing the capacity for optimal energy expenditure in brown adipocytes. Beige adipocytes uniquely combine the functional properties of white and brown adipocytes, maintaining morphological similarities to white adipocytes while possessing the capability to transform into mitochondria-rich, energy-burning cells under appropriate stimuli. Each type of adipocyte displays unique metabolic characteristics, governed by the mitochondrial dynamics specific to each cell type. These distinct mitochondrial metabolic phenotypes are regulated by specialized networks comprising transcription factors, co-activators, and enzymes, which together ensure the precise control of cellular energy processes. Strong evidence has shown impaired adipocyte mitochondrial metabolism and faulty upstream regulators in a causal relationship with obesity-induced T2D. Targeted interventions aimed at improving mitochondrial function in adipocytes offer a promising therapeutic avenue for enhancing systemic macronutrient oxidation, thereby potentially mitigating obesity. Advances in understanding mitochondrial function within adipocytes underscore a pivotal shift in approach to combating obesity and associated comorbidities. Reigniting the burning of calories in adipose tissues, and other important metabolic organs such as the muscle and liver, is crucial given the extensive role of adipose tissue in energy storage and release.

Mitochondrial function of dairy calf lymphocytes from birth to immunologic maturity

The inability of dairy calves to fully respond to immune stimuli until they reach maturity at 6 mo of age severely limits the use of parenteral vaccines to protect calves against disease. Immune responses are metabolically demanding, and immune cells rely on mitochondrial metabolites for their functionality. Due to the essential role of mitochondria in driving T-cell responses necessary for vaccine efficacy, we hypothesized that the mitochondrial function of dairy calf lymphocytes changes with age, from birth to immunologic maturity. In this cross-sectional study, groups of dairy calves (n = 4/group) were blood sampled at birth before colostrum intake and at 1, 2, 3, 4, 6, 8, 16, and 24 wk of age. Mid-lactation adult cows (n = 4) were also sampled to reference fully mature immune cell populations. B, CD4+, CD8+, and γδ T lymphocytes were enriched using magnetic-activated cell sorting, and their mitochondrial function was assessed with an extracellular flux analyzer. Non-mitochondrial oxygen consumption, basal respiration, maximal respiration, spare respiratory capacity, proton leak, and the oxygen consumption rate (OCR) to extracellular acidification rate (ECAR) ratio were reported. Results were compared among groups using a Kruskal-Wallis test. The OCR to ECAR ratio is an indicator of the relative proportions of oxidative phosphorylation and aerobic glycolysis which is associated with effector functions in lymphocytes. The ratio was lower in 0 wk than adults in CD4+ T-cells. For CD8+ T-cells, the OCR to ECAR ratio for the 2 wk group was lower than the 3 wk group. A lower OCR to ECAR ratio indicates more reliance on glycolytic metabolism than oxidative phosphorylation. Maximal respiration is an indication of mitochondrial efficiency and is often associated with mitochondrial mass. For γδ T-cells, the 3 wk group had higher maximal respiration than the 16 wk group, whereas for B cells maximal respiration was higher in the 1 wk compared with the 16 wk group. Basal respiration indicates all cell functions that require oxygen and was lower in the 0 wk group than the 1 wk and 3 wk groups for CD4+ T-cells. γδ T-cells exhibited lower basal respiration in the 2 wk group than the 24 wk one. Although we found minimal differences in the mitochondrial outcomes reported from non-stimulated lymphocytes from birth through 6 mo of age and mid-lactation adults who served as mature immune cell populations, these results align with previous reports from weaning aged calf and adult CD4+ T-cells. In conclusion, there was insufficient evidence to suggest that the mitochondria in the lymphocytes of dairy calves from birth through immunologic maturity had functional changes associated with age. In conclusion, the capacity of unstimulated calf mitochondria to perform oxidative phosphorylation is not associated with age.

Liver ACOX1 regulates levels of circulating lipids that promote metabolic health through adipose remodeling

The liver gene expression of the peroxisomal β-oxidation enzyme acyl-coenzyme A oxidase 1 (ACOX1), which catabolizes very long chain fatty acids (VLCFA), increases in the context of obesity, but how this pathway impacts systemic energy metabolism remains unknown. Here, we show that hepatic ACOX1-mediated β-oxidation regulates inter-organ communication involved in metabolic homeostasis. Liver-specific knockout of Acox1 (Acox1-LKO) protects mice from diet-induced obesity, adipose tissue inflammation, and systemic insulin resistance. Serum from Acox1-LKO mice promotes browning in cultured white adipocytes. Global serum lipidomics show increased circulating levels of several species of ω-3 VLCFAs (C24-C28) with previously uncharacterized physiological role that promote browning, mitochondrial biogenesis and Glut4 translocation through activation of the lipid sensor GPR120 in adipocytes. This work identifies hepatic peroxisomal β-oxidation as an important regulator of metabolic homeostasis and suggests that manipulation of ACOX1 or its substrates may treat obesity-associated metabolic disorders.

Unravelling the Influence of Endocrine-Disrupting Chemicals on Obesity Pathophysiology Pathways

Obesity represents a global health concern, affecting individuals of all age groups across the world. The prevalence of excess weight and obesity has escalated to pandemic proportions, leading to a substantial increase in the incidence of various comorbidities, such as cardiovascular diseases, type 2 diabetes, and cancer. This chapter seeks to provide a comprehensive exploration of the pathways through which endocrine-disrupting chemicals can influence the pathophysiology of obesity. These mechanisms encompass aspects such as the regulation of food intake and appetite, intestinal fat absorption, lipid metabolism, and the modulation of inflammation. This knowledge may help to elucidate the role of exogenous molecules in both the aetiology and progression of obesity.

Inter-Organ Communication Involved in Brown Adipose Tissue Thermogenesis

Brown and beige adipocytes produce heat from substrates such as fatty acids and glucose. Such heat productions occur in response to various stimuli and are called adaptive non-shivering thermogenesis. This review introduces mechanisms known to regulate brown and beige adipocyte thermogenesis. Leptin and fibroblast growth factor 21 (FGF21) are examples of periphery-derived humoral factors that act on the central nervous system (CNS) and increase brown adipose tissue (BAT) thermogenesis. Additionally, neuronal signals such as those induced by intestinal cholecystokinin and hepatic peroxisome proliferator-activated receptor γ travel through vagal afferent-CNS-sympathetic efferent-BAT pathways and increase BAT thermogenesis. By contrast, some periphery-derived humoral factors (ghrelin, adiponectin, plasminogen activator inhibitor-1, and soluble leptin receptor) act also on CNS but inhibit BAT thermogenesis. Neuronal signals also reduce BAT sympathetic activities and BAT thermogenesis, one such example being signals derived by hepatic glucokinase activation. Beige adipocytes can be induced by myokines (interleukin 6, irisin, and β-aminoisobutyric acid), hepatokines (FGF21), and cardiac-secreted factors (brain natriuretic peptide). Cold temperature and leptin also stimulate beige adipocytes via sympathetic activation. Further investigation on inter-organ communication involving adipocyte thermogenesis may lead to the elucidation of how body temperature is regulated and, moreover, to the development of novel strategies to treat metabolic disorders.

Carbon-based single-atom catalysts in advanced oxidation reactions for water remediation: From materials to reaction pathways

Single-atom catalysts (SACs) have been widely recognized as state-of-the-art catalysts in environment remediation because of their exceptional performance, 100% metal atomic utilization, almost no secondary pollution, and robust structures. Most recently, the activation of persulfate with carbon-based SACs in advanced oxidation processes (AOPs) raises tremendous interest in the degradation of emerging contaminants in wastewater, owning to its efficient and versatile reactive oxidant species (ROS) generation. However, the comprehensive and critical review unraveling the underlying relationship between structures of carbon-based SACs and the corresponding generated ROS is still rare. Herein, we systematically summarize the fundamental understandings and intrinsic mechanisms between single metal atom active sites and produced ROS during AOPs. The types of emerging contaminants are firstly elaborated, presenting the prior pollutants that need to be degraded. Then, the preparation and characterization methods of carbon-based SACs are overviewed. The underlying material structure-ROS type relationship in persulfate-based AOPs is discussed in depth to expound the catalytic mechanisms. Finally, we briefly conclude the current development of carbon-based SACs in AOPs and propose the prospects for rational design and synthesis of carbon-based SACs with on-demand catalytic performances in AOPs in future research.

Loss of Brain Angiogenesis Inhibitor-3 (BAI3) G-Protein Coupled Receptor in Mice Regulates Adaptive Thermogenesis by Enhancing Energy Expenditure

Effective energy expenditure is critical for maintaining body weight (BW). However, underlying mechanisms contributing to increased BW remain unknown. We characterized the role of brain angiogenesis inhibitor-3 (BAI3/ADGRB3), an adhesion G-protein coupled receptor (aGPCR), in regulating BW. A CRISPR/Cas9 gene editing approach was utilized to generate a whole-body deletion of the BAI3 gene (BAI3-/-). In both BAI3-/- male and female mice, a significant reduction in BW was observed compared to BAI3+/+ control mice. Quantitative magnetic imaging analysis showed that lean and fat masses were reduced in male and female mice with BAI3 deficiency. Total activity, food intake, energy expenditure (EE), and respiratory exchange ratio (RER) were assessed in mice housed at room temperature using a Comprehensive Lab Animal Monitoring System (CLAMS). While no differences were observed in the activity between the two genotypes in male or female mice, energy expenditure was increased in both sexes with BAI3 deficiency. However, at thermoneutrality (30 °C), no differences in energy expenditure were observed between the two genotypes for either sex, suggesting a role for BAI3 in adaptive thermogenesis. Notably, in male BAI3-/- mice, food intake was reduced, and RER was increased, but these attributes remained unchanged in the female mice upon BAI3 loss. Gene expression analysis showed increased mRNA abundance of thermogenic genes Ucp1, Pgc1α, Prdm16, and Elov3 in brown adipose tissue (BAT). These outcomes suggest that adaptive thermogenesis due to enhanced BAT activity contributes to increased energy expenditure and reduced BW with BAI3 deficiency. Additionally, sex-dependent differences were observed in food intake and RER. These studies identify BAI3 as a novel regulator of BW that can be potentially targeted to improve whole-body energy expenditure.

Remodeling of Adipose Tissues by Fatty Acids: Mechanistic Update on Browning and Thermogenesis by n-3 Polyunsaturated Fatty Acids

Enhancing thermogenesis by increasing the amount and activity of brown and brite adipocytes is a potential therapeutic target for obesity and its associated diseases. Diet plays important roles in energy metabolism and a myriad of dietary components including lipids are known to regulate thermogenesis through recruitment and activation of brown and brite adipocytes. Depending on types of fatty acids (FAs), the major constituent in lipids, their health benefits differ. Long-chain polyunsaturated FAs (PUFAs), especially n-3 PUFAs remodel adipose tissues in a healthier manner with reduced inflammation and enhanced thermogenesis, while saturated FAs exhibit contrasting effects. Lipid mediators derived from FAs act as autocrine/paracrine as well as endocrine factors to regulate thermogenesis. We discuss lipid mediators that may contribute to the differential effects of FAs on adipose tissue remodeling and hence, cardiometabolic diseases. We also discuss current understanding of molecular and cellular mechanisms through which n-3 PUFAs enhance thermogenesis. Elucidating molecular details of beneficial effects of n-3 PUFAs on thermogenesis is expected to provide information that can be used for development of novel therapeutics for obesity and its associated diseases.

Effects of Fatty Acid Metabolites on Adipocytes Britening: Role of Thromboxane A2

Obesity is a complex disease highly related to diet and lifestyle and is associated with low amount of thermogenic adipocytes. Therapeutics that regulate brown adipocyte recruitment and activity represent interesting strategies to fight overweight and associated comorbidities. Recent studies suggest a role for several fatty acids and their metabolites, called lipokines, in the control of thermogenesis. The purpose of this work was to analyze the role of several lipokines in the control of brown/brite adipocyte formation. We used a validated human adipocyte model, human multipotent adipose-derived stem cell model (hMADS). In the absence of rosiglitazone, hMADS cells differentiate into white adipocytes, but convert into brite adipocytes upon rosiglitazone or prostacyclin 2 (PGI2) treatment. Gene expression was quantified using RT-qPCR and protein levels were assessed by Western blotting. We show here that lipokines such as 12,13-diHOME, 12-HEPE, 15dPGJ2 and 15dPGJ3 were not able to induce browning of white hMADS adipocytes. However, both fatty acid esters of hydroxy fatty acids (FAHFAs), 9-PAHPA and 9-PAHSA potentiated brown key marker UCP1 mRNA levels. Interestingly, CTA2, the stable analog of thromboxane A2 (TXA2), but not its inactive metabolite TXB2, inhibited the rosiglitazone and PGI2-induced browning of hMADS adipocytes. These results pinpoint TXA2 as a lipokine inhibiting brown adipocyte formation that is antagonized by PGI2. Our data open new horizons in the development of potential therapies based on the control of thromboxane A2/prostacyclin balance to combat obesity and associated metabolic disorders.

Isolation and Mass Spectrometry-Based Profiling of Major Lipids in Brown Adipose Tissue

Brown adipose tissue (BAT) is an important regulator of metabolic homeostasis through its role in adaptive thermogenesis and control of whole-body glucose metabolism. Lipids play multiple roles in BAT functions, including serving as a fuel source for thermogenesis, mediating inter-organelle cross talk, and acting as BAT-derived signaling molecules that influence systemic energy metabolism. Profiling of various lipids in BAT under distinct metabolic states could provide new insights into their roles in the biology of the thermogenic fat. In this chapter, we describe a step-by-step workflow starting from sample preparations to mass spectrometry-based analysis of fatty acids and phospholipids in BAT.

VLDL-VLDLR axis facilitates brown fat thermogenesis through replenishment of lipid fuels and PPARβ/δ activation

In mammals, brown adipose tissue (BAT) is specialized to conduct non-shivering thermogenesis for survival under cold acclimation. Although emerging evidence suggests that lipid metabolites are essential for heat generation in cold-activated BAT, the underlying mechanisms of lipid uptake in BAT have not been thoroughly understood. Here, we show that very-low-density lipoprotein (VLDL) uptaken by VLDL receptor (VLDLR) plays important roles in thermogenic execution in BAT. Compared with wild-type mice, VLDLR knockout mice exhibit impaired thermogenic features. Mechanistically, VLDLR-mediated VLDL uptake provides energy sources for mitochondrial oxidation via lysosomal processing, subsequently enhancing thermogenic activity in brown adipocytes. Moreover, the VLDL-VLDLR axis potentiates peroxisome proliferator activated receptor (PPAR)β/δ activity with thermogenic gene expression in BAT. Accordingly, VLDL-induced thermogenic capacity is attenuated in brown-adipocyte-specific PPARβ/δ knockout mice. Collectively, these data suggest that the VLDL-VLDLR axis in brown adipocytes is a key factor for thermogenic execution during cold exposure.

Plasmalogens and platelet-activating factor roles in chronic inflammatory diseases

Fatty acids and phospholipid molecules are essential for determining the structure and function of cell membranes, and they hence participate in many biological processes. Platelet activating factor (PAF) and its precursor plasmalogen, which represent two subclasses of ether phospholipids, have attracted increasing research attention recently due to their association with multiple chronic inflammatory, neurodegenerative, and metabolic disorders. These pathophysiological conditions commonly involve inflammatory processes linked to an excess presence of PAF and/or decreased levels of plasmalogens. However, the molecular mechanisms underlying the roles of plasmalogens in inflammation have remained largely elusive. While anti-inflammatory responses most likely involve the plasmalogen signal pathway; pro-inflammatory responses recruit arachidonic acid, a precursor of pro-inflammatory lipid mediators which is released from membrane phospholipids, notably derived from the hydrolysis of plasmalogens. Plasmalogens per se are vital membrane phospholipids in humans. Changes in their homeostatic levels may alter cell membrane properties, thus affecting key signaling pathways that mediate inflammatory cascades and immune responses. The plasmalogen analogs of PAF are also potentially important, considering that anti-PAF activity has strong anti-inflammatory effects. Plasmalogen replacement therapy was further identified as a promising anti-inflammatory strategy allowing for the relief of pathological hallmarks in patients affected by chronic diseases with an inflammatory component. The aim of this Short Review is to highlight the emerging roles and implications of plasmalogens in chronic inflammatory disorders, along with the promising outcomes of plasmalogen replacement therapy for the treatment of various PAF-related chronic inflammatory pathologies.

Coconut oil and medium-chain fatty acids attenuate high-fat diet-induced obesity in mice through increased thermogenesis by activating brown adipose tissue

Coconut oil (CO) and its main ingredients, medium-chain fatty acids (MCFA), present many benefits. Whether MCFA and CO play an equally valuable role in anti-obesity remains unclear. This study compared the anti-obesity effects of CO and MCFA [octanoic acid (C8:0) and decanoic acid (C10:0)] to gain insight into the underlying mechanism. Male C57BL/6J mice were fed either a low-fat diet (LFD) or high-fat diet (100% HFD) replaced with 2.5% MCFA (97.5% HFD + 2.5% MCFA) or 5% CO (95% HFD + 5% CO) for 17 weeks. CO and MCFA ameliorated the HFD-induced abnormal body and adipose depot weights, insulin sensitivity, and energy expenditure (EE), which was associated with brown adipose tissue (BAT) thermogenesis. Furthermore, CO enhanced the expression of thermogenesis markers in BAT, which was consistent with increased BAT activity. CO showed a better effect than MCFA in activating BAT to increase thermogenesis and energy metabolism to combat obesity, which may be attributed to the cooperation of MCFA and other substances in CO. This work provides evidence for the anti-obesity effects of CO, which could be a better alternative to lard in daily diet, rather than pure MCFA.

Maternal secretin ameliorates obesity by promoting white adipose tissue browning in offspring

Our knowledge of the coordination of intergenerational inheritance and offspring metabolic reprogramming by gastrointestinal endocrine factors is largely unknown. Here, we showed that secretin (SCT), a brain-gut peptide, is downregulated by overnutrition in pregnant mice and women. More importantly, genetic loss of SCT in the maternal gut results in undesirable phenotypes developed in offspring including enhanced high-fat diet (HFD)-induced obesity and attenuated browning of inguinal white adipose tissue (iWAT). Mechanistically, loss of maternal SCT represses iWAT browning in offspring by a global change in genome methylation pattern through upregulation of DNMT1. SCT functions to facilitate ubiquitination and degradation of DNMT1 by activating AMPKα, which contributes to the observed alteration of DNMT1 in progeny. Lastly, we showed that SCT treatment during pregnancy can reduce the development of obesity and improve glucose tolerance and insulin resistance in offspring of HFD-fed females, suggesting that SCT may serve as a novel biomarker or a strategy for preventing metabolic diseases.

Determination of tissue contributions to the circulating lipid pool in cold exposure via systematic assessment of lipid profiles

Plasma lipid levels are altered in chronic conditions such as type 2 diabetes and cardiovascular disease as well as during acute stresses such as fasting and cold exposure. Advances in MS-based lipidomics have uncovered a complex plasma lipidome of more than 500 lipids that serve functional roles, including as energy substrates and signaling molecules. This plasma lipid pool is maintained through regulation of tissue production, secretion, and uptake. A major challenge in understanding the lipidome complexity is establishing the tissues of origin and uptake for various plasma lipids, which is valuable for determining lipid functions. Using cold exposure as an acute stress, we performed global lipidomics on plasma and in nine tissues that may contribute to the circulating lipid pool. We found that numerous species of plasma acylcarnitines (ACars) and ceramides (Cers) were significantly altered upon cold exposure. Through computational assessment, we identified the liver and brown adipose tissue as major contributors and consumers of circulating ACars, in agreement with our previous work. We further identified the kidney and intestine as novel contributors to the circulating ACar pool and validated these findings with gene expression analysis. Regression analysis also identified that the brown adipose tissue and kidney are interactors with the plasma Cer pool. Taken together, these studies provide an adaptable computational tool to assess tissue contribution to the plasma lipid pool. Our findings have further implications in understanding the function of plasma ACars and Cers, which are elevated in metabolic diseases.

Epicardial Adipose Tissue Ceramides Are Related to Lipoprotein Lipase Activity in Coronary Artery Disease: Unfolding a Missing Link

BACKGROUND

Epicardial adipose tissue (EAT) contributes to coronary artery disease (CAD). EAT presents a specific lipidomic signature, showing increased ceramides and other proinflammatory lipids content. Besides, LPL (lipoprotein lipase) activity in EAT would contribute to its expansion, supplying fatty acids to the tissue. Our aim was to evaluate the relations between LPL activity, regulators of LPL, and ceramides in EAT from CAD patients.

METHODS

We studied patients undergoing coronary bypass graft (CAD, n=25) and patients without CAD (no CAD, n=14). EAT and subcutaneous AT (SAT) were obtained, tissue LPL activity and its regulator's expression (ANGPTL4, GPIHBP1 [glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1], and PPARγ [peroxisomal proliferator-activated receptor γ]) were assessed. Tissue lipidomes were evaluated by UHPLC-MS, in positive and negative ionization modes.

RESULTS

LPL activity was higher in EAT from CAD (P<0.001), and in EAT than SAT in both groups (P<0.001). ANGPTL4 levels were lower, GPIHBP1 and PPARγ levels were higher in EAT from CAD (P<0.001). In both groups, EAT exhibited more ceramide (P=0.01), directly associated with LPL activity, being the strongest association with Cer18:1/24:1 (P<0.001). EAT Cer18:1/16:0 to Cer18:1/24:0 and Cer18:1/24:1 to 18:1/24:0 ratios were higher in CAD (P=0.03; P<0.001, respectively), the latter directly associated with LPL activity (r=0.63, P<0.001) GPIHBP1 levels (r=0.68, P<0.001), and inversely to EAT ANGPTL4 expression (r=-0.49, P=0.03). Pairwise partial correlation network showed associations among bioactive lipids and LPL and its regulators (P<0.001 in all cases).

CONCLUSIONS

The association between LPL activity, total ceramide, and the atherogenic ceramide ratios highlights the importance of the enzyme and these bioactive lipids contributing to the different metabolic profile of EAT in CAD.

Browning Epicardial Adipose Tissue: Friend or Foe?

The epicardial adipose tissue (EAT) is the visceral fat depot of the heart which is highly plastic and in direct contact with myocardium and coronary arteries. Because of its singular proximity with the myocardium, the adipokines and pro-inflammatory molecules secreted by this tissue may directly affect the metabolism of the heart and coronary arteries. Its accumulation, measured by recent new non-invasive imaging modalities, has been prospectively associated with the onset and progression of coronary artery disease (CAD) and atrial fibrillation in humans. Recent studies have shown that EAT exhibits beige fat-like features, and express uncoupling protein 1 (UCP-1) at both mRNA and protein levels. However, this thermogenic potential could be lost with age, obesity and CAD. Here we provide an overview of the physiological and pathophysiological relevance of EAT and further discuss whether its thermogenic properties may serve as a target for obesity therapeutic management with a specific focus on the role of immune cells in this beiging phenomenon.

Ether Lipids in Obesity: From Cells to Population Studies

Ether lipids are a unique class of glycero- and glycerophospho-lipid that carry an ether or vinyl ether linked fatty alcohol at the sn-1 position of the glycerol backbone. These specialised lipids are important endogenous anti-oxidants with additional roles in regulating membrane fluidity and dynamics, intracellular signalling, immunomodulation and cholesterol metabolism. Lipidomic profiling of human population cohorts has identified new associations between reduced circulatory plasmalogen levels, an abundant and biologically active sub-class of ether lipids, with obesity and body-mass index. These findings align with the growing body of work exploring novel roles for ether lipids within adipose tissue. In this regard, ether lipids have now been linked to facilitating lipid droplet formation, regulating thermogenesis and mediating beiging of white adipose tissue in early life. This review will assess recent findings in both population studies and studies using cell and animal models to delineate the functional and protective roles of ether lipids in the setting of obesity. We will also discuss the therapeutic potential of ether lipid supplementation to attenuate diet-induced obesity.

Signaling Lipidomic Analysis of Thermogenic Adipocytes

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

Zeaxanthin ameliorates obesity by activating the β3-adrenergic receptor to stimulate inguinal fat thermogenesis and modulating the gut microbiota

The stimulation of fat thermogenesis and modulation of the gut microbiota are promising therapeutic strategies against obesity. Zeaxanthin (ZEA), a carotenoid plant pigment, has been shown to prevent various diseases; however, the therapeutic mechanism for obesity remains unclear. Herein, whether ZEA improves obesity by activating the β3-adrenergic receptor (β3-AR) to stimulate white adipose tissue (WAT) thermogenesis and modulating the gut microbiota was investigated. C57BL6/N mice were fed a high-fat diet (HFD) supplemented with ZEA for 22 weeks. ZEA treatment reduced body weight, fat weight, adipocyte hypertrophy, liver weight, and lipid deposition, and improved dyslipidaemia, serum GPT, GOT, leptin, and irisin levels, glucose intolerance, and insulin resistance in HFD-fed mice. Mechanistically, ZEA treatment induced the expression of β3-AR and thermogenic factors, such as PRDM16, PGC-1α, and UCP1, in inguinal WAT (iWAT) and brown adipose tissue. ZEA treatment stimulated iWAT thermogenesis through the synergistic cooperation of key organelles, which manifested as an increased expression of lipid droplet degradation factors (ATGL, CGI-58 and pHSL), mitochondrial biogenesis factors (Sirt1, Nrf2, Tfam, Nampt and Cyt-C), peroxisomal biogenesis factors (Pex16, Pex19 and Pmp70), and β-oxidation factors (Cpt1, Cpt2, Acadm and Acox1). The thermogenic effect of ZEA was abolished by β3-AR antagonist (SR59230A) treatment. Additionally, dietary supplementation with ZEA reversed gut microbiota dysbiosis by regulating the abundance of Firmicutes, Clostridia, Proteobacteria, and Desulfovibrio, which were associated with the thermogenesis- and obesity-associated indices by Spearman's correlation analysis. Functional analysis of the gut microbiota indicated that ZEA treatment significantly enriched the lipid metabolism pathways. These results demonstrate that ZEA is a promising multi-target functional food for the treatment of obesity by activating β3-AR to stimulate iWAT thermogenesis, and modulating the gut microbiota.

Transcriptional Landscaping Identifies a Beige Adipocyte Depot in the Newborn Mouse

The present study sought to identify gene networks that are hallmarks of the developing inguinal subcutaneous adipose tissue (iWAT) and the interscapular brown adipose tissue (BAT) in the mouse. RNA profiling revealed that the iWAT of postnatal (P) day 6 mice expressed thermogenic and lipid catabolism transcripts, along with the abundance of transcripts associated with the beige adipogenesis program. This was an unexpected finding, as thermogenic BAT was believed to be the only site of nonshivering thermogenesis in the young mouse. However, the transcriptional landscape of BAT in P6 mice suggests that it is still undergoing differentiation and maturation, and that the iWAT temporally adopts thermogenic and lipolytic potential. Moreover, P6 iWAT and adult (P56) BAT were similar in their expression of immune gene networks, but P6 iWAT was unique in the abundant expression of antimicrobial proteins and virus entry factors, including a possible receptor for SARS-CoV-2. In summary, postnatal iWAT development is associated with a metabolic shift from thermogenesis and lipolysis towards fat storage. However, transcripts of beige-inducing signal pathways including β-adrenergic receptors and interleukin-4 signaling were underrepresented in young iWAT, suggesting that the signals for thermogenic fat differentiation may be different in early postnatal life and in adulthood.

Research progress on intervention effect and mechanism of protocatechuic acid on nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) has become a surge burden worldwide due to its high prevalence, with complicated deterioration symptoms such as liver fibrosis and cancer. No effective drugs are available for NALFD so far. The rapid growth of clinical demand has prompted the treatment of NAFLD to become a research hotspot. Protocatechuic acid (PCA) is a natural secondary metabolite commonly found in fruits, vegetables, grains, and herbal medicine. It is also the major internal metabolites of anthocyanins and other polyphenols. In the present manuscript, food sources, metabolic absorption, and efficacy of PCA were summarized while analyzing its role in improving NAFLD, as well as the mechanism involved. The results indicated that PCA could ameliorate NAFLD by regulating glucose and lipid metabolism, oxidative stress and inflammation, gut microbiota and metabolites. It was proposed for the first time that PCA might reduce NAFLD by enhancing the energy consumption of brown adipose tissue (BAT). However, the PCA administration mode and dose for NAFLD remain inconclusive. Fresh insights into the specific molecular mechanisms are required, while clinical trials are essential in the future. This review provides new targets and reasoning for the clinical application of PCA in the prevention and treatment of NAFLD.

Mitochondrial Lipid Signaling and Adaptive Thermogenesis

Thermogenesis is an energy demanding process by which endotherms produce heat to maintain their body temperature in response to cold exposure. Mitochondria in the brown and beige adipocytes play a key role in thermogenesis, as the site for uncoupling protein 1 (UCP1), which allows for the diffusion of protons through the mitochondrial inner membrane to produce heat. To support this energy demanding process, the mitochondria in brown and beige adipocytes increase oxidation of glucose, amino acids, and lipids. This review article explores the various mitochondria-produced and processed lipids that regulate thermogenesis including cardiolipins, free fatty acids, and acylcarnitines. These lipids play a number of roles in thermogenic adipose tissue including structural support of UCP1, transcriptional regulation, fuel source, and activation of cell signaling cascades.

Characterization of the circulating and tissue-specific alterations to the lipidome in response to moderate and major cold stress in mice

This study analyzed the effects of 24 h of cold stress (22°C or 5°C vs. mice maintained at 30 °C) on the plasma, brown adipose tissue (BAT), subcutaneous (SubQ) and epididymal (Epi) white adipose tissue (WAT), liver, and skeletal muscle lipidome of mice. Using mass spectrometry-lipidomics, 624 lipid species were detected, of which 239 were significantly altered in plasma, 134 in BAT, and 51 in the liver. In plasma, acylcarnitines and free fatty acids were markedly increased at 5°C. Plasma triacylglycerols (TGs) were reduced at 22°C and 5°C. We also identified ether lipids as a novel, cold-induced lipid class. In BAT, TGs were the principal lipid class affected by cold stress, being significantly reduced at both 22°C and 5°C. Interestingly, although BAT TG species were uniformly affected at 5°C, at 22°C we observed species-dependent effects, with TGs containing longer and more unsaturated fatty acids particularly sensitive to the effects of cold. In the liver, TGs were the most markedly affected lipid class, increasing in abundance at 5 °C. TGs containing longer and more unsaturated fatty acids accumulated to a greater degree. Our work demonstrates the following: 1) acute exposure to moderate (22°C) cold stress alters the plasma and BAT lipidome; although this effect is markedly less pronounced than at 5°C. 2) Cold stress at 5°C dramatically alters the plasma lipidome, with ether lipids identified as a novel lipid class altered by cold exposure. 3) Cold-induced alterations in liver and BAT TG levels are not uniform, with changes being influenced by acyl chain composition.

Recruitment of Thermogenic Fat: Trigger of Fat Burning

Brown and beige adipose tissues possess the remarkable capacity to convert energy into heat, which potentially opens novel therapeutic perspectives targeting the epidemic of metabolic syndromes such as obesity and type 2 diabetes. These thermogenic fats implement mitochondrial oxidative phosphorylation and uncouple respiration to catabolize fatty acids and glucose, which leads to an increase in energy expenditure. In particular, beige adipocytes that arise in white adipose tissue display their thermogenic capacity through various noncanonical mechanisms. This review aims to summarize the general overview of thermogenic fat, especially including the UCP1-independent adaptive thermogenesis and the emerging mechanisms of "beiging", which may provide more evidence of targeting thermogenic fat to counteract obesity and other metabolic disorders in humans.

Gestational Diabetes Mellitus: A Harbinger of the Vicious Cycle of Diabetes

Gestational diabetes mellitus (GDM), characterized by a transitory form of diabetes induced by insulin resistance and pancreatic β-cell dysfunction during pregnancy, has been identified as one of the major obstacles in achieving improved maternal and child health. Approximately 9-25% of pregnancies worldwide are impacted by the acute, long-term, and transgenerational health complications of this disease. Here, we discuss how GDM affects longstanding maternal and neonatal outcomes, as well as health risks that likely persist into future generations. In addition to the current challenges in the management and diagnosis of and the complications associated with GDM, we discuss current preclinical models of GDM to better understand the underlying pathophysiology of the disease and the timely need to increase our scientific toolbox to identify strategies to prevent and treat GDM, thereby advancing clinical care.

Estrogen-Related Receptor Alpha: An Under-Appreciated Potential Target for the Treatment of Metabolic Diseases

The estrogen-related receptor alpha (ESRRA) is an orphan nuclear receptor (NR) that significantly influences cellular metabolism. ESRRA is predominantly expressed in metabolically-active tissues and regulates the transcription of metabolic genes, including those involved in mitochondrial turnover and autophagy. Although ESRRA activity is well-characterized in several types of cancer, recent reports suggest that it also has an important role in metabolic diseases. This minireview focuses on the regulation of cellular metabolism and function by ESRRA and its potential as a target for the treatment of metabolic disorders.

Untargeted Lipidomics Reveals a Specific Enrichment in Plasmalogens in Epicardial Adipose Tissue and a Specific Signature in Coronary Artery Disease

OBJECTIVE

Epicardial adipose tissue (EAT) is an active endocrine organ that could contribute to the pathophysiology of coronary artery disease (CAD) through the paracrine release of proatherogenic mediators. Numerous works have analyzed the inflammatory signature of EAT, but scarce informations on its lipidome are available. Our objective was first to study the differences between EAT and subcutaneous adipose tissue (SAT) lipidomes and second to identify the specific untargeted lipidomic signatures of EAT and SAT in CAD. Approach and Results: Subcutaneous and EAT untargeted lipidomic analysis was performed in 25 patients with CAD and 14 patients without CAD and compared with paired plasma lipidomic analysis of isolated VLDL (very low-density lipoprotein) and HDL (high-density lipoprotein). Lipidomics was performed on a C18 column hyphenated to a Q-Exactive plus mass spectrometer, using both positive and negative ionization mode. EAT and SAT had independent lipidomic profile, with 95 lipid species differentially expressed and phosphatidylethanolamine 18:1p/22:6 twenty-fold more expressed in EAT compared with SAT false discovery rate =3×10^-4). Patients with CAD exhibited more ceramides (P=0.01), diglycerides (P=0.004; saturated and nonsaturated), monoglycerides (P=0.013) in their EAT than patients without CAD. Conversely, they had lesser unsaturated TG (triglycerides; P=0.02). No difference was observed in the 295 lipid species found in SAT between patients with and without CAD. Fifty-one lipid species were found in common between EAT and plasma lipoproteins. TG 18:0/18:0/18:1 was found positively correlated (r=0.45, P=0.019) in EAT and HDL and in EAT and VLDL (r=0.46, P=0.02).

CONCLUSIONS

CAD is associated with specific lipidomic signature of EAT, unlike SAT. Plasma lipoprotein lipidome only partially reflected EAT lipidome.