snRNA-seq reveals a subpopulation of adipocytes that regulates thermogenesis.

Adipose tissue is usually classified on the basis of its function as white, brown or beige (brite)1. It is an important regulator of systemic metabolism, as shown by the fact that dysfunctional adipose tissue in obesity leads to a variety of secondary metabolic complications2,3. In addition, adipose tissue functions as a signalling hub that regulates systemic metabolism through paracrine and endocrine signals4. Here we use single-nucleus RNA-sequencing (snRNA-seq) analysis in mice and humans to characterize adipocyte heterogeneity. We identify a rare subpopulation of adipocytes in mice that increases in abundance at higher temperatures, and we show that this subpopulation regulates the activity of neighbouring adipocytes through acetate-mediated modulation of their thermogenic capacity. Human adipose tissue contains higher numbers of cells of this subpopulation, which could explain the lower thermogenic activity of human compared to mouse adipose tissue and suggests that targeting this pathway could be used to restore thermogenic activity.

Unlocking the paracrine crosstalk: adipocyte-derived factors affect carbonic anhydrase IX expression in colon and breast cancer cells.

Obesity is a major public health concern because it increases the risk of several diseases, including cancer. Crosstalk between obesity and cancer seems to be very complex, and the interaction between adipocytes and cancer cells leads to changes in adipocytes' function and their paracrine signaling, promoting a microenvironment that supports tumor growth. Carbonic anhydrase IX (CA IX) is a tumor-associated enzyme that not only participates in pH regulation but also facilitates metabolic reprogramming and supports the migration, invasion, and metastasis of cancer cells. In addition, CA IX expression, predominantly regulated via hypoxia-inducible factor (HIF-1), serves as a surrogate marker of hypoxia. In this study, we investigated the impact of adipocytes and adipocyte-derived factors on the expression of CA IX in colon and breast cancer cells. We observed increased expression of CA9 mRNA as well as CA IX protein in the presence of adipocytes and adipocyte-derived conditioned medium. Moreover, we confirmed that adipocytes affect the hypoxia signaling pathway and that the increased CA IX expression results from adipocyte-mediated induction of HIF-1α. Furthermore, we demonstrated that adipocyte-mediated upregulation of CA IX leads to increased migration and decreased adhesion of colon cancer cells. Finally, we brought experimental evidence that adipocytes, and more specifically leptin, upregulate CA IX expression in cancer cells and consequently promote tumor progression.

Enantioselective Total Syntheses of Cassane Furanoditerpenoids and Their Stimulation of Cellular Respiration in Brown Adipocytes.

We report the first and enantioselective total syntheses of (+)-1-deacetylcaesalmin C, (+)-δ-caesalpin, (+)-norcaesalpinin MC, and (+)-norcaesalpinin P. Salient features of the synthetic strategy are an exo-selective intramolecular Diels-Alder reaction of a furanoquinone monoketal and subsequent chemoselective reduction of the resulting pentacyclic furfuryl ketal, furnishing a keystone intermediate. The latter enables access to the collection of natural products through implementation of stereoselective oxidations. Having accessed the cassane furanoditerpenoids, we unveil previously unknown bioactivity: (+)-1-deacetylcaesalmin C stimulates respiration in brown adipocytes, which has been suggested to play a central role in treatment of obesity.

Plasma Leptin Reflects Progression of Neurofibrillary Pathology in Animal Model of Tauopathy.

The close relationship between Alzheimer's disease (AD) and obesity was recognized many years ago. However, complete understanding of the pathological mechanisms underlying the interactions between degeneration of CNS and fat metabolism is still missing. The leptin a key adipokine of white adipose tissue has been suggested as one of the major mediators linking the obesity and AD. Here we investigated the association between peripheral levels of leptin, general metabolic status and stage of the pathogenesis in rat transgenic model of AD. We demonstrate significantly decreased levels of plasma leptin in animals with experimentally induced progressive neurofibrillary pathology, which represents only 62.3% (P = 0.0015) of those observed in normal wild type control animals. More detailed analysis showed a strong and statistically significant inverse correlation between the load of neurofibrillary pathology and peripheral levels of leptin (r = - 0.7248, P = 0.0177). We also observed a loss of body weight during development of neurodegeneration (about 14% less than control animals, P = 0.0004) and decrease in several metabolic parameters such as glucose, insulin, triglycerides and VLDL in plasma of the transgenic animals. Our data suggest that plasma leptin could serve as a convenient peripheral biomarker for tauopathies and Alzheimer's disease. Decrease in gene expression of leptin in fat tissue and its plasma level was found as one of the consequences of experimentally induced neurodegeneration. Our data may help to design rational diagnostic and therapeutic strategies for patients suffering from Alzheimer's disease or other forms of tauopathy.

Plasma proteome alterations in prediabetic, obese Zucker rats - possible cardiovascular risk implications.

Hyperphagia and obesity, which underlie metabolic syndrome, have been linked to multiple health complications and increased mortality. Here, we investigate the differences in plasma proteome between obese and lean Zucker rats in order to identify circulating proteins involved in obesity-related conditions. Plasma samples of male Zucker fatty (obese) rats carrying fatty fa/fa mutation (-/-) and their lean controls were enriched using ProteoMiner technology and labeled with isobaric tags (iTRAQ) for mass spectrometry-based quantitation. We found elevation in levels of coagulation factors whereas levels of serine protease inhibitors were decreased. Levels of acute phase proteins were also altered, as well as complement components. We also noticed differences in the abundance of apolipoproteins. In summary, quantitative proteomic assessment of plasma protein composition in obese Zucker rats revealed a profound landscape of changes, reflecting altered hemostasis, disturbed metabolic processes involving insulin resistance and lipid metabolism and ongoing low-grade inflammation.

Hypertension does not alter disturbances in leptin signalling observed in experimental model of tauopathy.

Neurodegeneration is associated with hypertension and disturbance in fat metabolism. The complex interaction of neurodegenerative processes with both metabolic changes and blood pressure is still not fully elucidated. Here we demonstrate that the experimentally induced tauopathy in hypertensive transgenic animals causes significant downregulation of plasma leptin (53% of control), reduction of body weight by 11%, a 1.2-fold drop of adiposity index, and decrease in HDL cholesterol level, while the fasting glucose and insulin concentration remain unchanged. Despite of these alterations we found the leptin projection circuit including the arcuate nucleus, paraventricular nucleus in hypothalamus, and nucleus tractus solitarius in the brainstem not affected by neurofibrillary pathology. Furthermore, hypertension does not alter disturbances in leptin signalling. The presented data provide further insight into neurodegeneration-induced metabolic alterations relevant for human tauopathies.

Obesity- and age-related alterations in FAT/CD36 translocation and lipin-1 subcellular localization in skeletal muscle of the Zucker rats.

Fatty acid (FA) uptake and/or intramuscular triglyceride (TG) accumulation in skeletal muscle are increased in obesity, type 2 diabetes and aging. FA translocase (FAT/CD36) translocation, lipin-1 subcellular localization and nuclear factor kappa B (NF-κB) p65 protein content in quadriceps muscle of young and old obese Zucker fa/fa rats and their lean controls were analyzed by immunoblot to define obesity- and aging-related alterations in FA uptake, their subsequent metabolic fate and potential to activate pro-inflammatory signaling. As expected, obesity increased FAT/CD36 content in plasma membrane in quadriceps muscle of fa/fa rats. Aging increased cytosolic lipin-1 content in both, obese rats and their lean controls. Also, old obese rats had decreased level of nuclear extract lipin-1compared to that in old lean rats. Neither obesity nor age altered NF-κB p65 protein content in cytosol and nuclear extract of quadriceps muscle suggesting that obesity/aging-induced changes in FA handling are not accompanied by NF-κB-mediated inflammation. Increase in plasma membrane FAT/CD36 content in obese rats and failure in lipin-1 export to nucleus with progression of obesity, implying an increase in FA uptake and their different channeling into lipid intermediates synthesis pathway in old fa/fa rats versus FA usage in lean rats of the same age.

Lactacystin-Induced Model of Hypertension in Rats: Effects of Melatonin and Captopril.

Lactacystin is a proteasome inhibitor that interferes with several factors involved in heart remodelling. The aim of this study was to investigate whether the chronic administration of lactacystin induces hypertension and heart remodelling and whether these changes can be modified by captopril or melatonin. In addition, the lactacystin-model was compared with NG-nitro-l-arginine-methyl ester (L-NAME)- and continuous light-induced hypertension. Six groups of three-month-old male Wistar rats (11 per group) were treated for six weeks as follows: control (vehicle), L-NAME (40 mg/kg/day), continuous light (24 h/day), lactacystin (5 mg/kg/day) alone, and lactacystin with captopril (100 mg/kg/day), or melatonin (10 mg/kg/day). Lactacystin treatment increased systolic blood pressure (SBP) and induced fibrosis of the left ventricle (LV), as observed in L-NAME-hypertension and continuous light-hypertension. LV weight and the cross-sectional area of the aorta were increased only in L-NAME-induced hypertension. The level of oxidative load was preserved or reduced in all three models of hypertension. Nitric oxide synthase (NOS) activity in the LV and kidney was unchanged in the lactacystin group. Nuclear factor-kappa B (NF-κB) protein expression in the LV was increased in all treated groups in the cytoplasm, however, in neither group in the nucleus. Although melatonin had no effect on SBP, only this indolamine (but not captopril) reduced the concentration of insoluble and total collagen in the LV and stimulated the NO-pathway in the lactacystin group. We conclude that chronic administration of lactacystin represents a novel model of hypertension with collagenous rebuilding of the LV, convenient for testing antihypertensive drugs or agents exerting a cardiovascular benefit beyond blood pressure reduction.

Inhibition of AXL receptor tyrosine kinase enhances brown adipose tissue functionality in mice.

The current obesity epidemic and high prevalence of metabolic diseases necessitate efficacious and safe treatments. Brown adipose tissue in this context is a promising target with the potential to increase energy expenditure, however no pharmacological treatments activating brown adipose tissue are currently available. Here, we identify AXL receptor tyrosine kinase as a regulator of adipose function. Pharmacological and genetic inhibition of AXL enhance thermogenic capacity of brown and white adipocytes, in vitro and in vivo. Mechanistically, these effects are mediated through inhibition of PI3K/AKT/PDE signaling pathway, resulting in induction of nuclear FOXO1 localization and increased intracellular cAMP levels via PDE3/4 inhibition and subsequent stimulation of the PKA-ATF2 pathway. In line with this, both constitutive Axl deletion as well as inducible adipocyte-specific Axl deletion protect animals from diet-induced obesity concomitant with increases in energy expenditure. Based on these data, we propose AXL receptor as a target for the treatment of obesity.

FAM3D: A gut secreted protein and its potential in the regulation of glucose metabolism.

The number of diabetic patients is rising globally and concomitantly so do the diabetes associated complications. The gut secretes a variety of proteins to control blood glucose levels and/or food intake. As the drug class of GLP-1 agonists is based on a gut secreted peptide and the positive metabolic effects of bariatric surgery are at least partially mediated by gut peptides, we were interested in other gut secreted proteins which have yet to be explored. In this respect we identified the gut secreted protein FAM3D by analyzing sequencing data from L- and epithelial cells of VSG and sham operated as well as chow and HFD fed mice. FAM3D was overexpressed in diet induced obese mice via an adeno-associated virus (AAV), which resulted in a significant improvement of fasting blood glucose levels, glucose tolerance and insulin sensitivity. The liver lipid deposition was reduced, and the steatosis morphology was improved. Hyperinsulinemic clamps indicated that FAM3D is a global insulin sensitizer and increases glucose uptake into various tissues. In conclusion, the current study demonstrated that FAM3D controls blood glucose levels by acting as an insulin sensitizing protein and improves hepatic lipid deposition.

Mitochondrial transformation occurs in cultured adipocytes, but fails to increase adipose tissue metabolic activity in mice in vivo.

A large number of studies in recent years have aimed to devise novel therapeutic strategies to increase adipose tissue metabolic activity and fight the global obesity epidemics. Growing evidence suggests that cells are able to accept isolated mitochondria by a simple coincubation in a process known as mitochondrial transformation. Therefore, we aimed to test whether mitochondrial transformation occurs in mature adipocytes, and whether this phenomenon could be utilized as a therapeutic approach to increase adipose tissue mitochondrial content and improve metabolic control. We provide evidence that both brown and white adipocytes are able to rapidly accept a large amount of brown adipocyte-derived mitochondria, which remain functional for several days and significantly contribute to cellular respiration in vitro. However, we did not find any evidence that internalization of exogenous mitochondria would trigger transcriptional changes in the recipient cells. Moreover, injection of a large amount of brown adipocyte-derived mitochondria into the inguinal fat of C57BL/6 mice failed to increase whole-body energy expenditure, and reduce body weight gain under obesogenic conditions. This might be due to activation of immune response and rapid removal of administered mitochondria. Altogether, our study adds information on the usability of mitochondrial transformation in the treatment of metabolic disease.

Identification of a regulatory pathway inhibiting adipogenesis via RSPO2.

Healthy adipose tissue remodeling depends on the balance between de novo adipogenesis from adipogenic progenitor cells and the hypertrophy of adipocytes. De novo adipogenesis has been shown to promote healthy adipose tissue expansion, which confers protection from obesity-associated insulin resistance. Here, we define the role and trajectory of different adipogenic precursor subpopulations and further delineate the mechanism and cellular trajectory of adipogenesis, using single-cell RNA-sequencing datasets of murine adipogenic precursors. We identify Rspo2 as a functional regulator of adipogenesis, which is secreted by a subset of CD142+ cells to inhibit maturation of early progenitors through the receptor Lgr4. Increased circulating RSPO2 in mice leads to adipose tissue hypertrophy and insulin resistance and increased RSPO2 levels in male obese individuals correlate with impaired glucose homeostasis. Taken together, these findings identify a complex cellular crosstalk that inhibits adipogenesis and impairs adipose tissue homeostasis.

GPR180 is a component of TGFß signalling that promotes thermogenic adipocyte function and mediates the metabolic effects of the adipocyte-secreted factor CTHRC1.

Activation of thermogenic brown and beige adipocytes is considered as a strategy to improve metabolic control. Here, we identify GPR180 as a receptor regulating brown and beige adipocyte function and whole-body glucose homeostasis, whose expression in humans is associated with improved metabolic control. We demonstrate that GPR180 is not a GPCR but a component of the TGFß signalling pathway and regulates the activity of the TGFß receptor complex through SMAD3 phosphorylation. In addition, using genetic and pharmacological tools, we provide evidence that GPR180 is required to manifest Collagen triple helix repeat containing 1 (CTHRC1) action to regulate brown and beige adipocyte activity and glucose homeostasis. In this work, we show that CTHRC1/GPR180 signalling integrates into the TGFß signalling as an alternative axis to fine-tune and achieve low-grade activation of the pathway to prevent pathophysiological response while contributing to control of glucose and energy metabolism.

Insulin-Regulated Aminopeptidase Inhibition Ameliorates Metabolism in Obese Zucker Rats.

The aim of our study was to determine the influence of inhibition of insulin-regulated aminopeptidase/oxytocinase (IRAP) on glucose tolerance and metabolism of skeletal muscle and visceral adipose tissue in obese Zucker rats. Obese Zucker rats administered with IRAP inhibitor-HFI-419 at a dose of 29 µg/100 g BW/day by osmotic minipumps implanted subcutaneously for 2 weeks. Two-hour intraperitoneal glucose tolerance test (ipGTT) was performed in fasting rats. Plasma oxytocin levels were measured by enzyme immunoassay after plasma extraction. In the musculus quadriceps and epididymal adipose tissue, the expression of factors affecting tissue oxidative status and metabolism was determined by real-time qPCR and/or Western blot analysys. The plasma and tissue enzymatic activities were determined by colorimetric or fluorometric method. Circulated oxytocin levels in obese animals strongly tended to increase after HFI-419 administration. This was accompanied by significantly improved glucose utilization during ipGTT and decreased area under the curve (AUC) for glucose. In skeletal muscle IRAP inhibitor treatment up-regulated enzymes of antioxidant defense system - superoxide dismutase 1 and 2 and improved insulin signal transduction pathway. HFI-419 increased skeletal muscle aminopeptidase A expression and activity and normalized its plasma levels in obese animals. In epididymal adipose tissue, gene expression of markers of inflammation and adipocyte hypertrophy was down-regulated in obese rats after HFI-419 treatment. Our results demonstrate that IRAP inhibition improves whole-body glucose tolerance in insulin-resistant Zucker fatty rats and that this metabolic effect of HFI-419 involves ameliorated redox balance in skeletal muscle.

AVE0991, a Nonpeptide Angiotensin 1-7 Receptor Agonist, Improves Glucose Metabolism in the Skeletal Muscle of Obese Zucker Rats: Possible Involvement of Prooxidant/Antioxidant Mechanisms.

Angiotensin 1-7 (Ang 1-7) enhances insulin signaling and glucose transport activity in the skeletal muscle. The aim of our study was to evaluate the effect of AVE0991, a nonpeptide Mas receptor agonist, on the metabolic parameters, expression of RAS components and markers of oxidative stress, and insulin signaling in the skeletal morbidly obese rats. 33-week-old male obese Zucker rats were treated with vehicle and AVE0991 (0.5 mg/kg BW/day) via osmotic minipumps for two weeks. Gene expressions were determined by qPCR and/or Western blot analysis in musculus quadriceps. The enzymatic activities were detected flourometrically (aminopeptidase A) or by colorimetric assay kit (protein tyrosine phosphatase 1B). Administration of AVE0991 enhanced insulin signaling cascade in the skeletal muscle, reflected by improved whole-body glucose tolerance. It has been shown that reactive oxygen species (ROS) have insulin-mimetic action in muscle. The expression of renin receptor, transcription factor PLZF, and prooxidant genes was upregulated by AVE0991 accompanied by elevated expression of genes coding enzymes with antioxidant action. Our results show that AVE0991 administration activates genes involved in both ROS generation and clearance establishing a new prooxidant/antioxidant balance on a higher level, which might contribute to the improved insulin signaling pathway and glucose tolerance of obese Zucker rats.

Obesity and aging affects skeletal muscle renin-angiotensin system and myosin heavy chain proportions in pre-diabetic Zucker rats.

There is a gap in the knowledge regarding regulation of local renin-angiotensin system (RAS) in skeletal muscle during development of obesity and insulin resistance in vivo. This study evaluates the obesity- and age-related changes in the expression of local RAS components. Since RAS affects skeletal muscle remodelling, we also evaluated the muscle fibre type composition, defined by myosin heavy chain (MyHC) mRNAs and protein content. Gene expressions were determined by qPCR and/or Western blot analysis in musculus quadriceps of 3- and 8-month-old male obese Zucker rats and their lean controls. The enzymatic activity of aminopeptidase A (APA) was determined flourometrically. Activation of renin receptor (ReR)/promyelocytic leukaemia zinc finger (PLZF) negative feedback mechanism was observed in obesity. The expression of angiotensinogen and AT1 was downregulated by obesity, while neutral endopeptidase and AT2 expressions were upregulated in obese rats with aging. Skeletal muscle APA activity was decreased by obesity, which negatively correlated with the increased plasma APA activity and plasma cholesterol. The expression of angiotensin-converting enzyme (ACE) positively correlated with MyHC mRNAs characteristic for fast-twitch muscle fibres. The obesity- and age-related alterations in the expression of both classical and alternative RAS components suggest an onset of a new equilibrium between ACE/AngII/AT1 and ACE2/Ang1-7/Mas at lower level accompanied by increased renin/ReR/PLZF activation. Increased APA release from the skeletal muscle in obesity might contribute to increased plasma APA activity. There is a link between reduced ACE expression and altered muscle MyHC proportion in obesity and aging.

Inhibition of Mevalonate Pathway Prevents Adipocyte Browning in Mice and Men by Affecting Protein Prenylation.

Recent research focusing on brown adipose tissue (BAT) function emphasizes its importance in systemic metabolic homeostasis. We show here that genetic and pharmacological inhibition of the mevalonate pathway leads to reduced human and mouse brown adipocyte function in vitro and impaired adipose tissue browning in vivo. A retrospective analysis of a large patient cohort suggests an inverse correlation between statin use and active BAT in humans, while we show in a prospective clinical trial that fluvastatin reduces thermogenic gene expression in human BAT. We identify geranylgeranyl pyrophosphate as the key mevalonate pathway intermediate driving adipocyte browning in vitro and in vivo, whose effects are mediated by geranylgeranyltransferases (GGTases), enzymes catalyzing geranylgeranylation of small GTP-binding proteins, thereby regulating YAP1/TAZ signaling through F-actin modulation. Conversely, adipocyte-specific ablation of GGTase I leads to impaired adipocyte browning, reduced energy expenditure, and glucose intolerance under obesogenic conditions, highlighting the importance of this pathway in modulating brown adipocyte functionality and systemic metabolism.

Weight Loss and Adipose Tissue Browning in Humans: The Chicken or the Egg?

Recruitment of thermogenic adipocytes within white fat depots represents a promising strategy to increase energy expenditure. Negative energy balance has been reported to promote adipose tissue browning in rodents. In a recent issue of Cell Reports, Barquissau et al. show that caloric restriction-associated weight loss does not induce browning of subcutaneous abdominal white fat in obese humans.

Author Correction: Cold-induced epigenetic programming of the sperm enhances brown adipose tissue activity in the offspring.

In the version of this article originally published, the months on the axis labeled projected month of conception in Fig. 1a were out of order. April and March should have been the first and last months listed, respectively. The error has been corrected in the print, PDF and HTML versions of this article.

Publisher Correction: Cold-induced epigenetic programming of the sperm enhances brown adipose tissue activity in the offspring.

In the version of this article originally published, the bars in the mean temperature graph in Fig. 1a were incorrectly aligned. The left-most bar should have been aligned with the Apr label on the projected month of conception axis. The error has been corrected in the print, PDF and HTML versions of this article.