Visceral White Adipose Tissue Research Articles

Effects of two types of exercises on MCT1 and GLUT4 expression in visceral white adipose tissue in type I diabetic rats

Effects of two types of exercises on MCT1 and GLUT4 expression in visceral white adipose tissue in type I diabetic rats

Interleukin-16 is increased in obesity and alters adipogenesis and inflammation in vitro.

Obesity is a chronic condition associated with low-grade inflammation mainly due to immune cell infiltration of white adipose tissue (WAT). WAT is distributed into two main depots: subcutaneous WAT (sWAT) and visceral WAT (vWAT), each with different biochemical features and metabolic roles. Proinflammatory cytokines including interleukin (IL)-16 are secreted by both adipocytes and infiltrated immune cells to upregulate inflammation. IL-16 has been widely studied in the peripheral proinflammatory immune response; however, little is known about its role in adipocytes in the context of obesity. We aimed to study the levels of IL-16 in WAT derived from sWAT and vWAT depots of humans with obesity and the role of this cytokine in palmitate-exposed 3T3-L1 adipocytes. The results demonstrated that IL-16 expression was higher in vWAT compared with sWAT in individuals with obesity. In addition, IL-16 serum levels were higher in patients with obesity compared with normal-weight individuals, increased at 6 months after bariatric surgery, and at 12 months after surgery decreased to levels similar to before the intervention. Our in vitro models showed that IL-16 could modulate markers of adipogenesis (Pref1), lipid metabolism (Plin1, Cd36, and Glut4), fibrosis (Hif1a, Col4a, Col6a, and Vegf), and inflammatory signaling (IL6) during adipogenesis and in mature adipocytes. In addition, lipid accumulation and glycerol release assays suggested lipolysis alteration. Our results suggest a potential role of IL-16 in adipogenesis, lipid and glucose homeostasis, fibrosis, and inflammation in an obesity context.

Age-associated accumulation of B cells promotes macrophage inflammation and inhibits lipolysis in adipose tissue during sepsis

Non-canonical lipolysis induced by inflammatory cytokines or Toll-like receptor ligands is required for the regulation of inflammation during endotoxemia and sepsis. Canonical lipolysis induced by catecholamines declines during aging due to factors including an expansion of lymphocytes, pro-inflammatory macrophage polarization, and an increase in chronic low-grade inflammation; however, the extent to which the non-canonical pathway of lipolysis is active and impacted by immune cells during aging remains unclear. Therefore, we aimed to define the extent to which immune cells from old mice influence non-canonical lipolysis during sepsis. We identified age-associated impairments of non-canonical lipolysis and an accumulation of dysfunctional B1 B cells in the visceral white adipose tissue (vWAT) of old mice. Lifelong deficiency of B cells results in restored non-canonical lipolysis and reductions in pro-inflammatory macrophage populations. Our study suggests that targeting the B cell-macrophage signaling axis may resolve metabolic dysfunction in aged vWAT and attenuate septic severity in older individuals.

Claudin-1 as a novel target gene induced in obesity and associated to inflammation, fibrosis, and cell differentiation.

T lymphocytes from visceral and subcutaneous white adipose tissues (vWAT and sWAT, respectively) can have opposing roles in the systemic metabolic changes associated with obesity. However, few studies have focused on this subject. Claudin-1 (CLDN1) is a protein involved canonically in tight junctions and tissue paracellular permeability. We evaluated T-lymphocyte gene expression in vWAT and sWAT and in the whole adipose depots in human samples. A Clariom D-based transcriptomic analysis was performed on T lymphocytes magnetically separated from vWAT and sWAT from patients with obesity (Cohort 1; N = 11). Expression of candidate genes resulting from that analysis was determined in whole WAT from individuals with and without obesity (Cohort 2; patients with obesity: N = 13; patients without obesity: N = 14). We observed transcriptional differences between T lymphocytes from sWAT compared with vWAT. Specifically, CLDN1 expression was found to be dramatically induced in vWAT T cells relative to those isolated from sWAT in patients with obesity. CLDN1 was also induced in obesity in vWAT and its expression correlates with genes involved in inflammation, fibrosis, and adipogenesis. These results suggest that CLDN1 is a novel marker induced in obesity and differentially expressed in T lymphocytes infiltrated in human vWAT as compared with sWAT. This protein may have a crucial role in the crosstalk between T lymphocytes and other adipose tissue cells and may contribute to inflammation, fibrosis, and alter homeostasis and promote metabolic disease in obesity.

Liraglutide induced browning of visceral white adipose through regulation of miRNAs in high-fat-diet-induced obese mice.

Obesity is characterized by excessive accumulation of white adipose tissue (WAT). Conversely, brown adipose tissue is protective against obesity. We recently reported liraglutide, a glucagon-like peptide-1 receptor agonist (GLP-1RA), could inhibit high-fat-diet-induced obesity by browning of WAT. However, the molecular mechanism involved is not well defined. Hence, we aimed to explore whether GLP-1RA could promote brown remodeling in WAT by regulating miRNAs. After the obesity model was successfully constructed, C57BL/6J mice were treated with liraglutide (200 μg/kg/d) or equivoluminal saline subcutaneously for 12 weeks. Then, the deposition of abdominal fat was measured by CT scanning. At the end of the treatments, glucose and insulin tolerance in mice were assessed. Serum lipid levels were monitored and epididymal WAT (eWAT) were collected for analysis. Quantitative real-time PCR and western blot analyses were conducted to evaluate the expression of genes and miRNAs associated with white fat browning. Liraglutide significantly reduced body weight and visceral fat mass. Levels of lipid profile were also improved. Liraglutide upregulated the expression of browning-related genes in eWAT. Meanwhile, the expression level of miRNAs (miR-196a and miR-378a) positively associated with the browning of WAT were increased, while the expression of miR-155, miR-199a, and miR-382 negatively related with browning of WAT were decreased. Our findings suggest that liraglutide could promote brown remodeling of visceral WAT by bi-regulating miRNAs; this might be one of the mechanisms underlying its effect on weight loss.

CDK6 inhibits de novo lipogenesis in white adipose tissues but not in the liver

Increased de novo lipogenesis (DNL) in white adipose tissue is associated with insulin sensitivity. Under both Normal-Chow-Diet and High-Fat-Diet, mice expressing a kinase inactive Cyclin-dependent kinase 6 (Cdk6) allele (K43M) display an increase in DNL in visceral white adipose tissues (VAT) as compared to wild type mice (WT), accompanied by markedly increased lipogenic transcriptional factor Carbohydrate-responsive element-binding proteins (CHREBP) and lipogenic enzymes in VAT but not in the liver. Treatment of WT mice under HFD with a CDK6 inhibitor recapitulates the phenotypes observed in K43M mice. Mechanistically, CDK6 phosphorylates AMP-activated protein kinase, leading to phosphorylation and inactivation of acetyl-CoA carboxylase, a key enzyme in DNL. CDK6 also phosphorylates CHREBP thus preventing its entry into the nucleus. Ablation of runt related transcription factor 1 in K43M mature adipocytes reverses most of the phenotypes observed in K43M mice. These results demonstrate a role of CDK6 in DNL and a strategy to alleviate metabolic syndromes.

Metabolic remodeling of visceral and subcutaneous white adipose tissue during reacclimation of rats after cold.

Deciphering lipid metabolism in white adipose tissue (WAT) depots during weight gain is important to understand the heterogeneity of WAT and its roles in obesity. Here, we examined the expression of key enzymes of lipid metabolism and changes in the morphology of representative visceral (epididymal) and subcutaneous (inguinal) WAT (eWAT and iWAT, respectively)-in adult male rats acclimated to cold (4 ± 1°C) for 45 days and reacclimated to room temperature (RT, 22 ± 1°C) for 1, 3, 7, 12, 21, or 45 days. The relative mass of both depots decreased to a similar extent after cold acclimation. However, fatty acid synthase (FAS), glucose-6-phosphate dehydrogenase (G6PDH), and medium-chain acyl-CoA dehydrogenase (ACADM) protein level increased only in eWAT, whereas adipose triglyceride lipase (ATGL) expression increased only in iWAT. During reacclimation, the relative mass of eWAT reached control values on day 12 and that of iWAT on day 45 of reacclimation. The faster recovery of eWAT mass is associated with higher expression of FAS, acetyl-CoA carboxylase (ACC), G6PDH, and ACADM during reacclimation and a delayed increase in ATGL. The absence of an increase in proliferating cell nuclear antigen suggests that the observed depot-specific mass increase is predominantly due to metabolic adjustments. In summary, this study shows a differential rate of visceral and subcutaneous adipose tissue weight regain during post-cold reacclimation of rats at RT. Faster recovery of the visceral WAT as compared to subcutaneous WAT during reacclimation at RT could be attributed to observed differences in the expression patterns of lipid metabolic enzymes.

LIGHT/TNFSF14 Affects Adipose Tissue Phenotype.

LIGHT/TNFSF14 is linked to several signaling pathways as a crucial member of a larger immunoregulatory network. It is primarily expressed in inflammatory effector cells, and high levels of LIGHT have been reported in obesity. Thus, with the aim of deepening the knowledge of the role of LIGHT on adipose tissue phenotype, we studied wild-type (WT), Tnfsf14-/-, Rag-/- and Rag-/Tnfsf14- (DKO) mice fed a normal diet (ND) or high-fat diet (HFD). Our results show that, although there is no significant weight gain between the mice with different genotypes, it is significant within each of them. We also detected an increase in visceral White Adipose Tissue (vWAT) weight in all mice fed HFD, together with the lowest levels of vWAT weight in Tnfsf14-/- and DKO mice fed ND with respect to the other strain. Inguinal WAT (iWAT) weight is significantly affected by genotype and HFD. The least amount of iWAT was detected in DKO mice fed ND. Histological analysis of vWAT showed that both the genotype and the diet significantly affect the adipocyte area, whereas the number is affected only by the genotype. In iWAT, the genotype and the diet significantly affect mean adipocyte area and number; interestingly, the area with the least adipocyte was detected in DKO mice fed ND, suggesting a potential browning effect due to the simultaneous lack of mature lymphocytes and LIGHT. Consistently, Uncoupling Protein 1 (UCP1) staining of iWAT demonstrated that few positive brown adipocytes appeared in DKO mice. Furthermore, LIGHT deficiency is associated with greater levels of UCP1, highlighting the lack of its expression in Rag-/- mice. Liver examination showed that all mice fed HFD had a steatotic liver, but it was particularly evident for DKO mice. In conclusion, our study demonstrates that the adipose tissue phenotype is affected by LIGHT levels but also much more by mature lymphocytes.

Analysis of tryptophan metabolites and related compounds in human and murine tissue: development and validation of a quantitative and semi-quantitative method using high resolution mass spectrometry.

This study explores the metabolic differences between human and murine plasma in addition to differences between murine subcutaneous and visceral white adipose tissue. A quantitative and semi-quantitative targeted method was developed and validated for this purpose. The quantitative method includes tryptophan and its metabolites in addition to tyrosine, phenylalanine, taurine, B vitamins, neopterin, cystathionine and hypoxanthine. While the semi-quantitative method includes; 3-indoleacetic acid, 5-hydroxyindoleacetic acid, acetylcholine, asymmetric dimethylarginine, citrulline and methionine. Sample preparation was based on protein precipitation, while quantification was conducted using ultrahigh-performance liquid chromatography coupled to a quadrupole Orbitrap tandem mass spectrometer with electrospray ionization in the parallel reaction monitoring (PRM) mode. The low limit of quantification for all metabolites ranged from 1 to 200 ng mL-1. Matrix effects and recoveries for stable isotope labelled internal standards were evaluated, with most having a coefficient of variation (CV) of less than 15%. Results showed that a majority of the analytes passed both the intra- and interday precision and accuracy criteria. The comparative analysis of human and murine plasma metabolites reveals species-specific variations within the tryptophan metabolic pathway. Notably, murine plasma generally exhibits elevated concentrations of most compounds in this pathway, with the exceptions of kynurenine and quinolinic acid. Moreover, the investigation uncovers noteworthy metabolic disparities between murine visceral and subcutaneous white adipose tissues, with the subcutaneous tissue demonstrating significantly higher concentrations of tryptophan, phenylalanine, tyrosine, and serotonin. The findings also show that even a semi-quantitative method can provide comparable results to quantitative methods from other studies and be effective for assessing metabolites in a complex sample. Overall, this study provides a robust platform to compare human and murine metabolism, providing a valuable insight to future investigations.

Diet-Stimulated Marrow Adiposity Fails to Worsen Early, Age-Related Bone Loss

Introduction: Longitudinal effect of diet-induced obesity on bone is uncertain. Prior work showed both no effect and a decrement in bone density or quality when obesity begins prior to skeletal maturity. We aimed to quantify long-term effects of obesity on bone and bone marrow adipose tissue (BMAT) in adulthood. Methods: Skeletally mature, female C57BL/6 mice (n = 70) aged 12 weeks were randomly allocated to low-fat diet (LFD; 10% kcal fat; n = 30) or high-fat diet (HFD; 60% kcal fat; n = 30), with analyses at 12, 15, 18, and 24 weeks (n = 10/group). Tibial microarchitecture was analyzed by µCT, and volumetric BMAT was quantified via 9.4T MRI/advanced image analysis. Histomorphometry of adipocytes and osteoclasts, and qPCR were performed. Results: Body weight and visceral white adipose tissue accumulated in response to HFD started in adulthood. Trabecular bone parameters declined with advancing experimental age. BV/TV declined 22% in LFD (p = 0.0001) and 17% in HFD (p = 0.0022) by 24 weeks. HFD failed to appreciably alter BV/TV and had negligible impact on other microarchitecture parameters. Both dietary intervention and age accounted for variance in BMAT, with regional differences: distal femoral BMAT was more responsive to diet, while proximal femoral BMAT was more attenuated by age. BMAT increased 60% in the distal metaphysis in HFD at 18 and 24 weeks (p = 0.0011). BMAT in the proximal femoral diaphysis, unchanged by diet, decreased 45% due to age (p = 0.0002). Marrow adipocyte size via histomorphometry supported MRI quantification. Osteoclast number did not differ between groups. Tibial qPCR showed attenuation of some adipose, metabolism, and bone genes. A regulator of fatty acid β-oxidation, cytochrome C (CYCS), was 500% more abundant in HFD bone (p < 0.0001; diet effect). CYCS also increased due to age, but to a lesser extent. HFD mildly increased OCN, TRAP, and SOST. Conclusions: Long-term high fat feeding after skeletal maturity, despite upregulation of visceral adiposity, body weight, and BMAT, failed to attenuate bone microarchitecture. In adulthood, we found aging to be a more potent regulator of microarchitecture than diet-induced obesity.

SMYD3: a new regulator of adipocyte precursor proliferation at the early steps of differentiation

BackgroundIn obesity, adipose tissue undergoes a remodeling process characterized by increased adipocyte size (hypertrophia) and number (hyperplasia). The ability to tip the balance toward the hyperplastic growth, with recruitment of new fat cells through adipogenesis, seems to be critical for a healthy adipose tissue expansion, as opposed to a hypertrophic growth that is accompanied by the development of inflammation and metabolic dysfunction. However, the molecular mechanisms underlying the fine-tuned regulation of adipose tissue expansion are far from being understood.MethodsWe analyzed by mass spectrometry-based proteomics visceral white adipose tissue (vWAT) samples collected from C57BL6 mice fed with a HFD for 8 weeks. A subset of these mice, called low inflammation (Low-INFL), showed reduced adipose tissue inflammation, as opposed to those developing the expected inflammatory response (Hi-INFL). We identified the discriminants between Low-INFL and Hi-INFL vWAT samples and explored their function in Adipose-Derived human Mesenchymal Stem Cells (AD-hMSCs) differentiated to adipocytes.ResultsvWAT proteomics allowed us to quantify 6051 proteins. Among the candidates that most differentiate Low-INFL from Hi-INFL vWAT, we found proteins involved in adipocyte function, including adiponectin and hormone sensitive lipase, suggesting that adipocyte differentiation is enhanced in Low-INFL, as compared to Hi-INFL. The chromatin modifier SET and MYND Domain Containing 3 (SMYD3), whose function in adipose tissue was so far unknown, was another top-scored hit. SMYD3 expression was significantly higher in Low-INFL vWAT, as confirmed by western blot analysis. Using AD-hMSCs in culture, we found that SMYD3 mRNA and protein levels decrease rapidly during the adipocyte differentiation. Moreover, SMYD3 knock-down before adipocyte differentiation resulted in reduced H3K4me3 and decreased cell proliferation, thus limiting the number of cells available for adipogenesis.ConclusionsOur study describes an important role of SMYD3 as a newly discovered regulator of adipocyte precursor proliferation during the early steps of adipogenesis.

Activation of a non-neuronal cholinergic system in visceral white adipose tissue of obese mice and humans

Background and objectivesSince white adipose tissue (WAT) lacks parasympathetic cholinergic innervation, the source of the acetylcholine (ACh) acting on white adipocyte cholinergic receptors is unknown. This study was designed to identify ACh-producing cells in mouse and human visceral WAT and to determine whether a non-neuronal cholinergic system becomes activated in obese inflamed WAT. MethodsMouse epididymal WAT (eWAT) and human omental fat were studied in normal and obese subjects. The expression of the key molecules involved in cholinergic signaling was evaluated by qRT-PCR and western blotting whereas their tissue distribution and cellular localization were investigated by immunohistochemistry, confocal microscopy and in situ hybridization. ACh levels were measured by liquid chromatography/tandem mass spectrometry. The cellular effects of ACh were assessed in cultured human multipotent adipose-derived stem cell (hMADS) adipocytes. ResultsIn mouse eWAT, diet-induced obesity modulated the expression of key cholinergic molecular components and, especially, raised the expression of choline acetyltransferase (ChAT), the ACh-synthesizing enzyme, which was chiefly detected in interstitial macrophages, in macrophages forming crown-like structures (CLSs), and in multinucleated giant cells (MGCs). The stromal vascular fraction of obese mouse eWAT contained significantly higher ACh and choline levels than that of control mice. ChAT was undetectable in omental fat from healthy subjects, whereas it was expressed in a number of interstitial macrophages, CLSs, and MGCs from some obese individuals. In hMADS adipocytes stressed with tumor necrosis factor α, ACh, alone or combined with rivastigmine, significantly blunted monocyte chemoattractant protein 1 and interleukin 6 expression, it partially but significantly, restored adiponectin and GLUT4 expression, and promoted glucose uptake. ConclusionsIn mouse and human visceral WAT, obesity induces activation of a macrophage-dependent non-neuronal cholinergic system that is capable of exerting anti-inflammatory and insulin-sensitizing effects on white adipocytes.

The Influence of Maternal High Fat Diet During Lactation on Offspring Hematopoietic Priming.

Obesity and metabolic diseases are rising among women of reproductive age, increasing offspring metabolic risk. Maternal nutritional interventions during lactation present an opportunity to modify offspring outcomes. We previously demonstrated in mice that adult male offspring have metabolic impairments and increased adipose tissue macrophages (ATM) when dams are fed high fat diet (HFD) during the postnatal lactation window (HFD PN). We sought to understand the effect of HFD during lactation on early-life inflammation. HFD PN offspring were evaluated at postnatal day 16 to 19 for tissue weight and gene expression. Profiling of adipose tissue and bone marrow immune cells was conducted through lipidomics, in vitro myeloid colony forming unit assays, and flow cytometry. HFD PN mice had more visceral gonadal white adipose tissue (GWAT) and subcutaneous fat. Adipose tissue RNA sequencing demonstrated enrichment of inflammation, chemotaxis, and fatty acid metabolism and concordant changes in GWAT lipidomics. Bone marrow (BM) of both HFD PN male and female offspring had increased monocytes (CD45+Ly6G-CD11b+CD115+) and B cells (CD45+Ly6G-CD11b-CD19+). Similarly, serum from HFD PN offspring enhanced in vitro BM myeloid colonies in a toll-like receptor 4-dependent manner. We identified that male HFD PN offspring had increased GWAT pro-inflammatory CD11c+ ATMs (CD45+CD64+). Maternal exposure to HFD alters milk lipids enhancing adiposity and myeloid inflammation even in early life. Future studies are needed to understand the mechanisms driving this pro-inflammatory state of both BM and ATMs, the causes of the sexually dimorphic phenotypes, and the feasibility of intervening in this window to improve metabolic health.

Extracellular inflammasome particles promote visceral adipose tissue inflammation

Abstract Background The metabolic syndrome is characterized by a chronic low-grade inflammation that increases the risk for cardiovascular events. With its capability to activate IL-1β, the NLRP3-inflammasome is believed to affect the inflammatory process. When the inflammasome is primed and activated, cytosolic ASC aggregates into the ASC-speck. This inflammasome particle can persist in the extracellular space after the cell it originated from underwent pyroptosis. Purpose We aimed to assess the role of extracellular inflammasome particles as a potential target to reduce chronic inflammation in the metabolic syndrome. Methods Male C57BL6/J mice received either a chow or high-fat-diet (HFD) for 7, 14 or 21 weeks. Flow cytometry and fluorescence microscopy were used to detect inflammasome particles. Adipocytes and stromal vascular fraction (SVF) were isolated from subcutaneous (scWAT) and visceral white adipose tissue (vWAT) using collagenase. Results Mice subjected to HFD show increased NLRP3-inflammasome priming in the SVF of visceral but not subcutaneous WAT (vWAT: 4-fold p&amp;lt;0.001, scWAT: 1-fold). The frequency of ASC-specks induced by the NLRP3-activating agent nigericin correlates with immune cell infiltration (macrophages: r=0.83) and disruption of metabolic homeostasis (bodyweight: r=0.8). Co-staining of nigericin-induced ASC-specks with CD45 and CD11b suggests their derivation from myeloid cells of the SVF. ASC-speck formation can be fully inhibited with the NLRP3-specific inhibitor MCC950. Adipocytes likely do not form ASC-specks as they, despite upregulating the required genes when primed with lipopolysaccharide (e.g. IL-1β: 8-fold), fail to activate the inflammasome in-vitro. In chow-fed mice, cells carrying cytosolic ASC are evenly dispersed in the WAT and can be co-stained with the macrophage marker F4/80. When a metabolic syndrome is acquired, ASC-positive cells form crown-like-structures around dying adipocytes in which ASC-speck formation takes place. In the vWAT of HFD-fed mice, we found ASC-specks that were externalized and also taken up by adipocytes. Co-culture of isolated ASC-specks with adipocytes induced ER-stress and resulted in upregulation of IL-6 (42-fold), CCL2 and TNFα after 24h. In addition, previously undifferentiated bone marrow derived macrophages internalized these particles, which lead to a pro-inflammatory shift. Finally, also human endothelial cells responded to isolated ASC-specks with upregulation of the leukocyte adhesion molecules VCAM1 and ICAM1. Conclusion Our study suggests that extracellular inflammasome particles accumulate in metabolically altered visceral adipose tissue and contribute to a pro-inflammatory environment. The imbalance between pro- and anti-inflammatory immune response is an important contributor to the development of cardiovascular disease. Extracellular inflammasome particles could be an interesting target for novel therapeutic approaches to reduce chronic inflammation.

Abstract 18360: Single-Cell Analysis Reveals Insights Into Visceral Adiposity in Mice With Diabetes-Associated Atherosclerosis

Introduction: - Visceral white adipose tissue (vWAT), once considered passive and uniform, is a dynamic and heterogeneous tissue involved in glucose and lipid metabolism and immune response. Changes in adipose tissue morphology, physiology, and cellular composition occur in response to dietary fat and carbohydrates, associated with insulin resistance, dyslipidemia, and type 2 diabetes. vWAT also has implications for vascular diseases such as atherosclerosis. However, the connection between vWAT metabolism and atherosclerosis in mouse models remains to be fully elucidated. Methods: - vWAT from male Ldlr -/- mice fed either a chow diet or high fat, high sucrose containing (HFSC) diet for 24 weeks were harvested. Single cell RNA sequencing, histology and immunofluorescence were used to analyze the cellular and transcriptomic profiles in the chow and HFSC groups. Results: - We identified distinct subpopulations of vascular endothelial cells (ECs), immune cells, and adipose stem and progenitor cells (ASPCs), revealing differences between healthy and diseased groups. Notably, we observed a significant increase in immune cell composition, accompanied by a decrease in ECs and progenitor cells in HFSC-fed mice. Within the macrophage population, we noted increased activated macrophages, B-cell derived macrophages, and collagen-expressing macrophage subclusters. In ECs, we observed increased lymphatic and vascular EC subgroups. Furthermore, inflammation and altered metabolism pathways were found in both macrophage and ECs. We identified novel markers, such as Lyz2 and Trem2, that were highly associated with diabetes associated atherosclerosis in male Ldlr -/- mice. Through cell-cell interaction analysis (CellChat), we discovered distinct interactions patterns associated with enriched pathways such as chemokine, Wnt, and BMP signaling in multiple cell types, including macrophages, mesothelial cells, ASPCs, pericytes, SMCs, and ECs. Conclusion: Our scRNAseq atlas reveals interactions amongst adipose cell types in lean and obese states, with the chemokine pathway emerging as a prominent player. This dataset serves as a valuable resource for studying genes and cell types involved in vWAT function in diabetes-associated atherosclerosis.

Transcriptional repression of beige fat innervation via a YAP/TAZ-S100B axis

Sympathetic innervation is essential for the development of functional beige fat that maintains body temperature and metabolic homeostasis, yet the molecular mechanisms controlling this innervation remain largely unknown. Here, we show that adipocyte YAP/TAZ inhibit sympathetic innervation of beige fat by transcriptional repression of neurotropic factor S100B. Adipocyte-specific loss of Yap/Taz induces S100b expression to stimulate sympathetic innervation and biogenesis of functional beige fat both in subcutaneous white adipose tissue (WAT) and browning-resistant visceral WAT. Mechanistically, YAP/TAZ compete with C/EBPβ for binding to the zinc finger-2 domain of PRDM16 to suppress S100b transcription, which is released by adrenergic-stimulated YAP/TAZ phosphorylation and inactivation. Importantly, Yap/Taz loss in adipocytes or AAV-S100B overexpression in visceral WAT restricts both age-associated and diet-induced obesity, and improves metabolic homeostasis by enhancing energy expenditure of mice. Together, our data reveal that YAP/TAZ act as a brake on the beige fat innervation by blocking PRDM16-C/EBPβ-mediated S100b expression.

Ablation of diacylglycerol kinase ε promotes whitening of brown adipose tissue under high fat diet feeding

Adipose tissue (AT) comprises distinct fat depots such as white AT and brown AT. White and brown adipocytes exhibit different morphological and physiological properties. White adipocytes containing large single lipid droplet (LD) provide energy on demand whereas brown adipocytes loaded with multilocular LDs consume energy to generate heat or dissipate excess energy. Recent studies have shown that multilocular brown-like cells emerge in white AT under certain conditions. These cells termed beige adipocytes participate in energy expenditure and heat generation. In the process of lipolysis, TG is broken down into free fatty acid and diacylglycerol (DG). In this regard, DG also serves as a signaling molecule activating some proteins such as protein kinase C. Therefore, DG kinase (DGK), an enzyme which phosphorylates DG into phosphatidic acid (PA), plays a pivotal role in integrating energy homeostasis and intracellular signaling. Recently, we described that DGKε-KO mice exhibit increased adiposity in visceral white AT accompanied with impaired glucose tolerance early (40 days) in the course of high fat diet (HFD) feeding, although these mice exhibit “browning or beiging” in visceral white AT associated with improved glucose tolerance after longer term HFD feeding (180 days). This study was conducted to understand the overall features of adipose tissues and investigate changes in subcutaneous (inguinal) white AT and interscapular brown AT of DGKε-KO mice during the course of HFD feeding. Results demonstrated that fat accumulation is promoted in all fat depots under 40 days of HFD feeding conditions. Remarkably, “whitening” of brown adipocytes was identified in DGKε-deficient brown AT during the course of HFD feeding, suggesting brown adipocyte dysfunction. In addition, insulin levels were considerably elevated in DGKε-KO mice under 180 days of HFD feeding conditions. Collectively, these findings suggest that brown adipocytes are dysfunctional in DGKε-KO mice, which promotes browning or beiging in visceral white AT. Beige adipocytes may take over energy disposal and contribute to improving glucose tolerance with the aid of high levels of insulin in DGKε-KO mice upon excess feeding.

Liraglutide modulates morpho-functional and inflammatory gastrointestinal responses in rats.

Obesity impairs homeostatic control of energy and is associated with chronic low-grade inflammation. Effects of glucagon-like peptide-1, the target in the gastrointestinal tract for anti-obesity drugs such as Liraglutide, were not properly associated with inflammation markers. This study investigated the effects of Liraglutide on metabolic and gastrointestinal parameters in a rat model of obesity. Twenty-six Wistar rats with obesity were randomly distributed to receive saline (n = 10), 400 μg (n = 8), or 1200 μg of Liraglutide/kg/day (n = 8), subcutaneously for 30 consecutive days, once a day. Weight gain, feeding efficiency, caloric consumption, gastric motility, adiposity, histomorphometric, murinometric, biochemical parameters and cytokines TNF-α and TGF-β1 in duodenal tissue were measured. Data were analysed by ANOVA, followed by Bonferroni post hoc or Kruskal-Wallis test, followed by Dunn's multiple comparison test. Liraglutide-treated animals had better feeding efficiency and higher caloric intake in a dose-dependent manner. Higher doses slowed gastric emptying and diminished the amplitude of gastric contractions. These effects were accompanied by decreases in intestinal muscle layer thickness and crypt depth. Liraglutide significantly reduced retroperitoneal and visceral white adipose tissue depots. High-dose treatment decreased levels of TNF-α and enhanced levels of TGF-β1 in duodenal tissue. Liraglutide treatment provided significant reductions in total cholesterol, triglyceride and hepatic transaminases. Liraglutide reduced fat accumulation, improved metabolic parameters and downregulated levels of inflammatory signalling in duodenal tissue. Liraglutide at high doses controlled obesity-related outcomes, and such effects seemed to be driven by its action on glucagon-like peptide-1 receptors in the gastrointestinal tract slowing gastric motility.

Blockade of TGF-β signalling alleviates human adipose stem cell senescence induced by native ECM in obesity visceral white adipose tissue

BackgroundAbdominal obesity is appreciated as a major player in insulin resistance and metabolically dysfunctional adipose tissue. Inappropriate extracellular matrix (ECM) remodelling and functional alterations in human adipose stromal/stem cells (hASCs) have been linked with visceral white adipose tissue (vWAT) dysfunction in obesity. Understanding the interactions between hASCs and the native ECM environment in obese vWAT is required for the development of future therapeutic approaches for obesity-associated metabolic complications.MethodsThe phenotypes and transcriptome properties of hASCs from the vWAT of obese patients and lean donors were assessed. The hASC-derived matrix from vWAT of obese or lean patients was generated in vitro using a decellularized method. The topography and the major components of the hASC-derived matrix were determined. The effects of the obese hASC-derived matrix on cell senescence and mitochondrial function were further determined.ResultsWe showed that hASCs derived from the vWAT of obese patients exhibited senescence and were accompanied by the increased production of ECM. The matrix secreted by obese hASCs formed a fibrillar suprastructure with an abundance of fibronectin, type I collagen, and transforming growth factor beta 1 (TGF-β1), which resembles the native matrix microenvironment of hASCs in vWAT derived from obese patients. Furthermore, the obese hASC-derived matrix promoted lean hASC ageing and induced mitochondrial dysfunction compared to the lean hASC-derived matrix. Blockade of TGF-β1 signalling using an anti-TGF-β1 neutralizing antibody alleviated the lean hASC senescence and mitochondrial dysfunction induced by the obese hASC-derived matrix.ConclusionsNative ECM in obesity vWAT initiates hASC senescence through TGF-β1-mediated mitochondrial dysfunction. These data provide a key mechanism for understanding the importance of cell-ECM interactions in hASCs senescence in obesity.

DHA alleviated hepatic and adipose inflammation with increased adipocyte browning in high-fat diet-induced obese mice

Obesity is associated with accumulation of inflammatory immune cells in white adipose tissue, whereas thermogenic browning adipose tissue is inhibited. Dietary fatty acids are important nutritional components and several clinical and experimental studies have reported beneficial effects of docosahexaenoic acid (DHA) on obesity-related metabolic changes. In this study, we investigated effects of DHA on hepatic and adipose inflammation and adipocyte browning in high-fat diet-induced obese C57BL/6J mice, and in vitro 3T3-L1 preadipocyte differentiation. Since visceral white adipose tissue has a close link with metabolic abnormality, epididymal adipose tissue represents current target for evaluation. A course of 8-week DHA supplementation improved common phenotypes of obesity, including improvement of insulin resistance, inhibition of macrophage M1 polarization, and preservation of macrophage M2 polarization in hepatic and adipose tissues. Moreover, dysregulated adipokines and impaired thermogenic and browning molecules, considered obesogenic mechanisms, were improved by DHA, along with parallel alleviation of endoplasmic reticulum (ER) stress, mitochondrial dysfunction, and mitochondrial DNA stress-directed innate immunity. During 3T3-L1 preadipocytes differentiation, DHA treatment decreased lipid droplet accumulation and increased the levels of thermogenic, browning, and mitochondrial biogenesis molecules. Our study provides experimental evidence that DHA mitigates obesity-associated inflammation and induces browning of adipose tissue in visceral epididymal adipose tissue. Since obesity is associated with metabolic abnormalities across tissues, our findings indicate that DHA may have potential as part of a dietary intervention to combat obesity.