Adipocyte Physiology Research Articles

Selenium and Selenoproteins in Adipose Tissue Physiology and Obesity.

Selenium (Se) homeostasis is tightly related to carbohydrate and lipid metabolism, but its possible roles in obesity development and in adipocyte metabolism are unclear. The objective of the present study is to review the current data on Se status in obesity and to discuss the interference between Se and selenoprotein metabolism in adipocyte physiology and obesity pathogenesis. The overview and meta-analysis of the studies on blood Se and selenoprotein P (SELENOP) levels, as well as glutathione peroxidase (GPX) activity in obese subjects, have yielded heterogenous and even conflicting results. Laboratory studies demonstrate that Se may modulate preadipocyte proliferation and adipogenic differentiation, and also interfere with insulin signaling, and regulate lipolysis. Knockout models have demonstrated that the selenoprotein machinery, including endoplasmic reticulum-resident selenoproteins together with GPXs and thioredoxin reductases (TXNRDs), are tightly related to adipocyte development and functioning. In conclusion, Se and selenoproteins appear to play an essential role in adipose tissue physiology, although human data are inconsistent. Taken together, these findings do not support the utility of Se supplementation to prevent or alleviate obesity in humans. Further human and laboratory studies are required to elucidate associations between Se metabolism and obesity.

Angiopoietin-1 protects 3T3-L1 preadipocytes from saturated fatty acid–induced cell death

Cross talk between endothelial cells and adipocytes is vital to adipocyte functions, but little is known about the mechanisms or factors controlling the process. Angiogenesis is a critical component linking the endothelium to healthy adipogenesis, yet it is not known if or how it is involved in adipocyte physiology. Therefore, the purpose of this study was to determine the effect of angiopoietin-1 (Ang-1) and -2 (Ang-2) as well as their receptor, Tie-2, on adipocyte physiology. 3T3-L1 pre- and mature adipocytes were found to express Ang-1, Ang-2, and Tie-2, which decrease upon polyunsaturated fatty acid treatment. Furthermore, 3T3-L1 cells treated with recombinant Ang-1 or Ang-2 increased expression of the antiapoptotic gene Bcl-x and decreased expression of the proapoptotic gene Casp-8. Next, preadipocytes were treated with saturated fatty acids (SFAs) to induce cell stress. SFA-mediated splicing of X-box-binding protein-1 was reduced by co-treatment with Ang-1, and cell viability was improved in the presence of SFAs + Ang-1. Taken together, these results indicate that Ang-1 may protect preadipocytes from SFA-induced apoptosis and endoplasmic reticulum stress.

Transcriptome Modifications in the Porcine Intramuscular Adipocytes during Differentiation and Exogenous Stimulation with TNF-α and Serotonin.

Adipocytes are dynamic cells that have critical functions to maintain body energy homeostasis. Adipocyte physiology is affected by the adipogenic differentiation, cell program, as well as by the exogenous stimulation of biochemical factors, such as serotonin and TNF-α. In this work, we investigated the global transcriptome modifications when porcine intramuscular preadipocyte (PIP) was differentiated into porcine mature adipocyte (pMA). Moreover, we studied transcriptome changes in pMA after stimulation with serotonin or TNF-α by using a microarray approach. Transcriptome analysis revealed that the expression of 270, 261, and 249 genes were modified after differentiation, or after serotonin and TNF-α stimulation, respectively. Expression changes in APP, HNF4A, ESR1, EGR1, SRC, HNF1A, FN1, ALB, STAT3, CBL, CEBPB, AR, FOS, CFTR, PAN2, PTPN6, VDR, PPARG, STAT5A and NCOA3 genes which are enriched in the ‘PPAR signaling’ and ‘insulin resistance’ pathways were found in adipocytes during the differentiation process. Dose-dependent serotonin stimulation resulted in a decreased fat accumulation in pMAs. Serotonin-induced differentially expressed genes in pMAs were found to be involved in the significant enrichment of ′GPCR ligand-binding′, ‘cell chemotaxis’, ‘blood coagulation and complement’, ‘metabolism of lipid and lipoproteins’, ‘regulation of lipid metabolism by PPARA’, and ‘lipid digestion, mobilization and transport’ pathways. TNF-α stimulation also resulted in transcriptome modifications linked with proinflammatory responses in the pMA of intramuscular origin. Our results provide a landscape of transcriptome modifications and their linked-biological pathways in response to adipogenesis, and exogenous stimulation of serotonin- and TNF-α to the pMA of intramuscular origin.

Differential effects of EPA and DHA on plasma and adipose tissue lipid mediators: the ComparED study

AbstractOxylipins and endocannabinoids (eCBs) both belong to superclasses of lipid mediators with potent inflammation modulatory activities. The adipose tissue (AT) plays a key role in metabolic syndrome-related inflammation, via altered adipocyte physiology, infiltrated macrophages and altered profile of eCBs. We previously reported that DHA is more potent than EPA at modulating systemic inflammation, but the underlying mechanisms remain unclear. The objective of this study was to compare the individual effect of high-dose DHA and of EPA on circulating lipid mediators, i.e. plasma oxylipins and eCBs, and AT-related inflammation. In a randomized double-blind crossover trial, 154 volunteers with abdominal obesity and low-grade inflammation were subjected to three 10-wk supplementation phases: 1- EPA (2.7 g/d); 2- DHA (2.7 g/d); 3- corn oil (control), each separated by a 9-wk washout. Supplements were provided as re-esterified triacylglycerols. Profiling of plasma oxylipins and eCBs was performed on 58 subjects after each phase. Abdominal subcutaneous AT biopsies were also obtained from 13 individuals after each phase. Plasma DHA-, EPA-, arachidonic acid-derived oxylipins were analyzed by LC-MS. eCBs and some of their bioactive congeners were analyzed in plasma and AT by LC-APCI-MS. Adipocyte diameter was determined by histological analysis and AT macrophage infiltration was quantified by double immunofluorescence. Compared with EPA, DHA increased plasma levels of hydroxy-docosahexaenoic acids (7-, 11-, 14-, 4-, 17-HDOHE; P < 0.0001) and palmitoylethanolamide (PEA; P = 0.04). Compared with DHA, EPA led to higher plasma level of hydroxy-eicosapentaenoic acids (12-, 15-, 5-HEPE; P < 0.0001). In the AT, EPA increased the level of oleoylethanolamide (OEA; P = 0.01) compared with DHA, but no other difference was observed between treatments in adipose eCBs and eCB-related lipids. DHA and EPA did not differentially modify adipocyte size distributions (P > 0.50) and proportions of M1-type and M2-type macrophages (P > 0.30). In conclusion, increased plasma levels of anti-inflammatory DHA-derived oxylipins and plasma PEA may be responsible, at least to some extent, for the more potent anti-inflammatory effects of DHA compared with EPA observed in the ComparED study. Conversely, subcutaneous AT does not seem to be involved in explaining such differences between EPA and DHA.

Abstract 277: Neonatal Cardiomyocyte-Released Signaling Protein Reduces Adipocyte Differentiation

The heart continuously cycles through periods of muscle contraction and relaxation to pump blood throughout the body, which requires a constant supply of metabolic substrates to the heart to power these contractile cycles. To ensure adequate energy availability, the heart must communicate with other organ systems to maintain global metabolic energy homeostasis. In addition to the role of the sympathetic nervous system in global metabolic regulation, mounting evidence suggests cardiomyocytes can release signaling factors that alter global energy balance through communication with other organ systems, including the liver and adipose tissue. To identify potential cardiomyocyte-released circulating factors, we collected media conditioned by neonatal rat ventricular myocytes (NRVM-CM) and screened for released-factor activity using an in vitro adipocyte differentiation assay. Treatment of differentiating 3T3-L1 adipocytes reduced lipid accumulation and decreased expression of adipocyte proteins, demonstrating NRVM-released factor activity. Released factor activity was also under the control of regulators of GPCR signaling as overexpression of G-protein coupled receptor kinase 2 (GRK2) further enhanced the NRVM-released factor activity. We further determined that NRVM released-factor activity was abolished by trypsin treatment and could be segregated into >30kDa CM fractions using centrifugal filter units. To identify proteins responsible for the NRVM-released factor activity, NRVM-CM retained in the 30kDA centrifugal filter units (containing all proteins >30kDa) was analyzed by mass spectrometry. This revealed a number of signaling proteins with known adipocyte regulatory roles that could potentially regulate adipocyte physiology. We confirmed these results by examining NRVM cell lysate and concentrated NRVM-CM by Western blot to test for the presence of decorin, one of the proteins identified by mass spectrometry known to have adipocyte regulatory roles. These results provide a framework to identify potential in vivo cardiomyocyte-released factors that regulate global energy balance.

1786-P: ACSL1 Contributes to Thermogenesis and Differentiation of Brown Adipose Tissue

Long chain acyl-CoA synthetases (ACSLs) convert fatty acids (FA) to fatty acyl-CoAs that are utilized for various cellular processes, including triglyceride synthesis, activation of transcription factors, signal transduction, and providing energy sources via oxidation. Among 5 isotypes (ACSL1, 3, 4, 5, and 6), ACSL1 is the predominant isotype in adipocytes, and it is known to play important roles in adipocyte physiology, including FA uptake, triglyceride (TG) synthesis, thermogenesis, and FA oxidation. However, the roles of ACSL1 in brown adipocyte differentiation is incompletely understood. During the in vitro differentiation of brown adipocytes from stromal vascular cells (SVC), mRNA expression of ACSL1 was drastically increased. Pharmacological inhibition of ACSLs by triacsin C suppressed the differentiation of brown adipocytes. Interestingly, triacsin C inhibited the expression of uncoupled protein 1 (UCP1), which plays the major role in thermogenesis in mitochondria. Thus, we hypothesize that ACSL1 regulates thermogenesis and energy utilization by regulation of brown adipocyte differentiation. To examine the role of ACSL1 in brown adipose tissue (BAT), we generated BAT specific ACSL1 knockout mice by breeding UCP1-Cre with ACSL1 flox/flox mice (ACSL1BATKO). ACSL1 deficiency in BAT reduced the weight gain and glucose intolerance in high fat diet (HFD)-fed mice. ACSL1BATKO mice were severely cold intolerant. Furthermore, ACSL1BATKO mice were resistant to beta 3-agonist (CL-316243)-stimulated weight loss. Fat mass in HFD-fed ACSL1BATKO was lower than HFD-fed wild type mice. These data suggest that ACSL1 in BAT contributes to BAT differentiation, which causes the impairment of FA utilization. However, the mechanisms by which deficiency of ACSL1 in BAT reduces HFD-induced weight gain need to be further investigated. Disclosure G. Ren: None. J. Kim: None. Funding National Institutes of Health (R01HL128695R03AG058078)

1970-P: Epinephrine and Insulin Stimulates White Adipocyte Secretion of Diverse Adiponectin Forms

The white adipocyte hormone adiponectin is released in different molecular forms and a reduction of high-molecular weight (HMW) adiponectin has specifically been associated with the development of metabolic disease. We have recently shown that adiponectin is released via cAMP/epinephrine-stimulated exocytosis, involving activation of beta 3 adrenergic receptors (beta3ARs). However, a number of studies have, seemingly incompatible with the catecholamine-triggered release, reported that insulin (lowers cAMP) increases adiponectin secretion. Here we have pinpointed the differences between insulin- and catecholamine-stimulated short-term adiponectin secretion. Using a combination of biophysical and biochemical techniques applied to mouse and human adipocytes as well as whole animal studies, we show that catecholamines specifically stimulate the rapid exocytosis of high-molecular weight (HMW) adiponectin. In contrast, insulin induces secretion of smaller adiponectin forms only, with slower time kinetics. The catecholamine-stimulated secretion of HMW adiponectin is blunted in adipocytes isolated from obese and diabetic mice (8 weeks high-fat diet) and this secretory defect is paralleled by a ∼50% reduction of serum HMW adiponectin. The insulin-induced release of smaller adiponectin forms is also abrogated i adipocytes from obese/diabetic mice. However, the total serum adiponectin level remains unaltered, likely due to enhanced basal (unstimulated) release of smaller adiponectin forms. Our findings suggest that insulin and catecholamines have entirely different roles in the regulation of adiponectin secretion and demonstrate a previously unknown role of beta3ARs for human white adipocyte physiology. We propose that the reduced levels of HMW adiponectin observed in diabetic individuals, and that have been linked to the development of metabolic disease, is a result of a secretory disturbance largely depending on disrupted adrenergic signaling. Disclosure S. Musovic: None. A.M. Komai: None. E. Banke Nordbeck: None. U.A. Noor: None. I. Wernstedt Asterholm: None. C.S. Olofsson: None. Funding Swedish Diabetes Foundation; Knut and Alice Wallenberg Foundation; Swedish Medical Research Council

Angiopoietin‐1 Protects 3T3‐L1 Pre‐Adipocytes from Saturated Fatty Acid‐Induced Cell Death

Crosstalk between endothelial cells and adipocytes is vital to adipocyte functions, but little is known about the mechanisms or factors controlling the process. Angiogenesis is a critical component linking the endothelium to healthy adipogenesis, yet it is not known if or how it is involved in adipocyte physiology. Therefore, the purpose of this study was to determine the effect of Angiopoietin‐1 (Ang‐1) and ‐2 (Ang‐2) as well as their receptor, Tie‐2, on adipocyte physiology. 3T3‐L1 pre‐ and mature adipocytes were found to express Ang‐1, Ang‐2, and Tie‐2 which decrease upon PUFA‐treatment. Furthermore, 3T3‐L1 cells treated with recombinant Ang‐1 or Ang‐2 increased expression of the anti‐apoptotic gene Bcl‐x and decreased expression of the pro‐apoptotic gene Casp‐8. Next, pre‐adipocytes were treated with saturated fatty acids (SFA) to induce cell stress. SFA‐mediated splicing of X‐box‐binding protein‐1 (Xbp‐1s) was reduced by co‐treatment with Ang‐1 and cell viability was improved in the presence of SFA + Ang‐1. Taken together, these results indicate that Ang‐1 may protect pre‐adipocytes from SFA‐induced apoptosis and ER stress.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Lrp4 expression by adipocytes and osteoblasts differentially impacts sclerostin’s endocrine effects on body composition and glucose metabolism

Sclerostin exerts profound local control over bone acquisition and also mediates endocrine communication between fat and bone. In bone, sclerostin's anti-osteoanabolic activity is enhanced by low-density lipoprotein receptor-related protein 4 (Lrp4), which facilitates its interaction with the Lrp5 and Lrp6 Wnt co-receptors. To determine whether Lrp4 similarly affects sclerostin's endocrine function, we examined body composition as well as glucose and fatty acid metabolism in mice rendered deficient of Lrp4 in the adipocyte (AdΔLrp4) or the osteoblast (ObΔLrp4). AdΔLrp4 mice exhibit a reduction in adipocyte hypertrophy and improved glucose and lipid homeostasis, marked by increased glucose and insulin tolerance and reduced serum fatty acids, and mirror the effect of sclerostin deficiency on whole-body metabolism. Indeed, epistasis studies place adipocyte-expressed Lrp4 and sclerostin in the same genetic cascade that regulates adipocyte function. Intriguingly, ObΔLrp4 mice, which exhibit dramatic increases in serum sclerostin, accumulate body fat and develop impairments in glucose tolerance and insulin sensitivity despite development of a high bone mass phenotype. These data indicate that expression of Lrp4 by both the adipocyte and osteoblast is required for normal sclerostin endocrine function and that the impact of sclerostin deficiency on adipocyte physiology is distinct from the effect on osteoblast function.

Technical note: Bovine adipocyte and preadipocyte co-culture as an efficient adipogenic model

Reductionist studies of adipose tissue biology require reliable in vitro adipocyte culturing models. Current protocols for adipogenesis induction in stromal vascular fraction-derived preadipocytes require extended culturing periods and have low adipogenic rates. We compared the adipogenic efficiency of a 7-d co-culture model of visceral (VIS) and subcutaneous (SC) stromal vascular fraction-derived preadipocytes with mature adipocytes with a 14-d standard adipocyte differentiation protocol. We obtained preadipocytes and mature adipocytes from SC and VIS adipose tissue of nonlactating, nongestating Holstein cows (n = 6). Adipogenesis induction was performed using a standard protocol for 7 (SD7; control) or 14 d (SD14), and a co-culture model for 7 d (CC7). Culture conditions, including medium composition, were the same for all treatments. For CC7, 900 primary adipocytes/cm2 were placed in 0.4-μm transwell inserts and co-cultured with preadipocytes for adipogenesis induction. Both CC7 and SD14 similarly stimulated gene expression of adipogenic genes such as ADIPOQ, CEBPA, and CEBPB in VIS and SC. The CC7 increased triacylglycerol accumulation compared with SD14 and SD7. CC7 augmented triacylglycerol accumulation by 40- and 16-fold in SC and VIS compared with 22- and 4-fold increment in SD14, respectively. Lipolytic responses to 2-h β-adrenergic stimulation with 1 µM isoproterenol were higher in CC7 and SD14 than SD7 in SC; CC7 increased glycerol release compared with SD7 in VIS but SD7 and SD14 had similar responses. Overall, CC7 was more efficient in inducing adipogenesis in preadipocytes from VIS and SC than SD14. Furthermore, CC7 stimulated similar lipolysis and lipogenic responses than SD14 but in a shorter time. The adipogenic approach of co-culturing preadipocytes with mature adipocytes will improve the use of reductionist models to study adipocyte physiology in dairy cows and the assessment of pharmacological or nutritional interventions for enhancing dairy cow health and production.

Caveolar Kv1.3 Targeting Participates in the Adipocyte Physiology

The voltage-gated potassium channel Kv1.3 contributes to peripheral insulin sensitivity. KO mice for Kv1.3 are resistant to diet-induced weight gain. Therefore, this protein is being considered as a pharmacological target for obesity and associated type II diabetes. However, the expression of Kv1.3 in adipocytes generates controversy. Here, we found that Kv1.3 is present in white adipose tissue from humans and rodents. In addition, Kv1.1, Kv1.2, Kv1.4 and especially Kv1.5, from the same Shaker family are also present. Although elevated insulin levels and adipogenesis remodeled the Kv phenotype, which could trigger to numerous hybrid complexes, Kv1.3 noticeably participated in the insulin-dependent regulation of glucose transport in differentiated adipocytes. Adipogenesis increased the expression of Kv1.3 into caveolae by molecular interactions with caveolin 1. In a caveolin 1-deficient 3T3-L1 adipocyte cell line, we verified that the localization of Kv1.3 in caveolar lipid raft structures is necessary for proper insulin signaling. Insulin-dependent phosphorylation of the Kv1.3 occurs at the beginning of insulin-mediated signaling. However, when Kv1.3 localized out of these lipid microdomains, reduced phosphorylation was demonstrated. Our data contribute to the knowledge of the putative role of Kv1.3 in adipocyte physiology. Supported by the Ministerio de Ciencia, Innovación y Universidades, Spain (BFU2014-54928-R and BFU2017-87104-R) and Fondo Europeo de Desarrollo Regional (FEDER).

MicroRNAs and other non-coding RNAs in adipose tissue and obesity: emerging roles as biomarkers and therapeutic targets.

Obesity is a metabolic condition usually accompanied by insulin resistance (IR), type 2 diabetes (T2D), and dyslipidaemia, which is characterised by excessive fat accumulation and related to white adipose tissue (WAT) dysfunction. Enlargement of WAT is associated with a transcriptional alteration of coding and non-coding RNAs (ncRNAs). For many years, big efforts have focused on understanding protein-coding RNAs and their involvement in the regulation of adipocyte physiology and subsequent role in obesity. However, diverse findings have suggested that a dysfunctional adipocyte phenotype in obesity might be also dependent on specific alterations in the expression pattern of ncRNAs, such as miRNAs. The aim of this review is to update current knowledge on the physiological roles of miRNAs and other ncRNAs in adipose tissue function and their potential impact on obesity. Therefore, we examined their regulatory role on specific WAT features: adipogenesis, adipokine secretion, inflammation, glucose metabolism, lipolysis, lipogenesis, hypoxia and WAT browning. MiRNAs can be released to body fluids and can be transported (free or inside microvesicles) to other organs, where they might trigger metabolic effects in distant tissues, thus opening new possibilities to a potential use of miRNAs as biomarkers for diagnosis, prognosis, and personalisation of obesity treatment. Understanding the role of miRNAs also opens the possibility of using these molecules on individualised dietary strategies for precision weight management. MiRNAs should be envisaged as a future therapeutic approach given that miRNA levels could be modulated by synthetic molecules (f.i. miRNA mimics and inhibitors) and/or specific nutrients or bioactive compounds.

Mechanisms of obesity-induced metabolic and vascular dysfunctions.

Obesity has reached epidemic proportions and its prevalence is climbing. Obesity is characterized by hypertrophied adipocytes with a dysregulated adipokine secretion profile, increased recruitment of inflammatory cells, and impaired metabolic homeostasis that eventually results in the development of systemic insulin resistance, a phenotype of type 2 diabetes. Nitric oxide synthase (NOS) is an enzyme that converts L-arginine to nitric oxide (NO), which functions to maintain vascular and adipocyte homeostasis. Arginase is a ureohydrolase enzyme that competes with NOS for L-arginine. Arginase activity/expression is upregulated in obesity, which results in diminished bioavailability of NO, impairing both adipocyte and vascular endothelial cell function. Given the emerging role of NO in the regulation of adipocyte physiology and metabolic capacity, this review explores the interplay between arginase and NO, and their effect on the development of metabolic disorders, cardiovascular diseases, and mitochondrial dysfunction in obesity. A comprehensive understanding of the mechanisms involved in the development of obesity-induced metabolic and vascular dysfunction is necessary for the identification of more effective and tailored therapeutic avenues for their prevention and treatment.

Evidence of functional bile acid signaling pathways in adipocytes

Background and aimBile acids (BA) are increasingly recognized as pleiotropic and hormone-like signaling molecules with metabolic and endocrine functions. However, the role of BA in white adipocyte physiology remains somewhat obscure. It was the aim to investigate the BA receptors (FXR, TGR5) and FGFR1 (Fibroblast growth factor receptor 1) as well as Bsep (bile salt export pump) in white adipocytes and in murine and human adipose tissue (AT) and to investigate effects of different BA species in adipocyte physiology. Patients, material and methodsReceptor mRNA expression was quantified by real-time PCR in mice, humans and during 3T3-L1 pre-adipocyte differentiation. Adipokines were measured by ELISA upon stimulation by several BA. Effects of BA on TNF- and LPS-induced MCP-1 secretion and lipolysis were analyzed. TNF-induced lipolysis was investigated by glycerol assay. ResultsThe present data provide for the first time a detailed expression profile of FXR, TGR5, FGFR1, and Bsep during adipocyte differentiation and in murine and human AT. FGFR1 expression is upregulated in adipose tissue of LPS-injected animals. Several BA regulate secretion of adipokines such as adiponectin and resistin differentially. Importantly, TNF- and LPS-induced MCP-1 release from adipocytes as well as TNF-induced lipolysis can be antagonized by cholic acid (CA) and deoxycholic acid (DCA). ConclusionsThe present data provide evidence of functional BA signaling pathways in adipocytes and argue for certain MCP-1 related anti-inflammatory effects of BA in TNF- and LPS-induced inflammation, whereas pro-inflammatory resistin is induced by CA and glycocholic acid (GCA). Systemic bile acids might represent a hormonal network regulating white adipocyte physiology including lipolysis.

Fighting obesity by targeting factors regulating beige adipocytes.

The current review provides an update on secreted factors and mechanisms that promote a thermogenic program in beige adipocytes, and their potential roles as therapeutic targets to fight obesity. We outline recent studies revealing unrecognized mechanisms controlling beige adipocyte physiology, and summarize in particular those that underlie beige thermogenesis independently of classical uncoupling. We also update strategies aimed at fostering beige adipogenesis and white-to beige adipocyte conversion. Finally, we summarize newly identified endogenous secreted factors that promote the thermogenic activation of beige adipocytes and discuss their therapeutic potential. The identification of novel endogenous factors that promote beiging and regulate beige adipocyte-specific physiological pathways opens up new avenues for therapeutic engineering targeting obesity and related metabolic disorders.

Adipose tissue, fillers, and skin tightening.

The role of adipose tissue has long been underestimated in esthetic dermatology. With the development of liposculpture and lipolysis, subcutaneous adipose tissue has gained an increasing interest. Harvested tissue has been used for lipofilling. In recent years, a better understanding of adipocyte physiology and its role in aging opened a new road for targeted treatments. Subcutaneous adipose tissue is no longer an innocent bystander in the combat of aging and the correction in esthetics. Adipose tissue is of importance for metabolic function and thermoregulation. Adipose tissue is involved in inflammation. Adipose tissue is heterogeneous in sense of function, color and size of adipocytes. The tissue is an important source of somatic stem cells.

Caveolar targeting links Kv1.3 with the insulin-dependent adipocyte physiology.

The voltage-dependent potassium channel Kv1.3 participates in peripheral insulin sensitivity. Genetic ablation of Kv1.3 triggers resistance to diet-induced weight gain, thereby pointing to this protein as a pharmacological target for obesity and associated type II diabetes. However, this role is under intense debate because Kv1.3 expression in adipose tissue raises controversy. We demonstrated that Kv1.3 is expressed in white adipose tissue from humans and rodents. Moreover, other channels, such as Kv1.1, Kv1.2, Kv1.4 and especially Kv1.5, from the same Shaker family are also present. Although elevated insulin levels and adipogenesis remodel the Kv phenotype, which could lead to multiple heteromeric complexes, Kv1.3 markedly participates in the insulin-dependent regulation of glucose uptake in mature adipocytes. Adipocyte differentiation increased the expression of Kv1.3, which is targeted to caveolae by molecular interactions with caveolin 1. Using a caveolin 1-deficient 3T3-L1 adipocyte cell line, we demonstrated that the localization of Kv1.3 in caveolar raft structures is important for proper insulin signaling. Insulin-dependent phosphorylation of the channel occurs at the onset of insulin-mediated signaling. However, when Kv1.3 was spatially outside of these lipid microdomains, impaired phosphorylation was exhibited. Our data shed light on the putative role of Kv1.3 in weight gain and insulin-dependent responses contributing to knowledge about adipocyte physiology.

Chronic phosphodiesterase type 5 inhibition has beneficial effects on subcutaneous adipose tissue plasticity in type 2 diabetic mice.

Different adipose tissue (AT) depots are associated with multiple metabolic risks. Phosphodiesterase type 5 (PDE5) is involved in adipocyte physiology and PDE5 inhibition may affect adipogenesis and ameliorate white AT quality. The aim of this study is to investigate the distribution of AT and the composition of the stroma-vascular fraction (SVF) of subcutaneous AT (SAT) in type 2 diabetic mice after prolonged treatment with a PDE5 inhibitor, Sildenafil. 18 db/db mice were treated with Sildenafil or vehicle for 12 weeks. AT distribution was monitored and SAT was processed for isolation of SVF by flow cytometry. Sildenafil induced an overall reduction in AT, mainly in visceral AT (VAT), compared with SAT. In Sildenafil-treated mice, the mean change in body weight from baseline positively correlated with VAT, but not with SAT. Characterization of SVF of SAT showed an increase in the frequency of M2 macrophages and endothelial cells in treated mice. Sildenafil improved the maintenance of SAT homeostasis and distribution.

Distinct macrophage populations direct inflammatory versus physiological changes in adipose tissue

Obesity is characterized by an accumulation of macrophages in adipose, some of which form distinct crown-like structures (CLS) around fat cells. While multiple discrete adipose tissue macrophage (ATM) subsets are thought to exist, their respective effects on adipose tissue, and the transcriptional mechanisms that underlie the functional differences between ATM subsets, are not well understood. We report that obese fat tissue of mice and humans contain multiple distinct populations of ATMs with unique tissue distributions, transcriptomes, chromatin landscapes, and functions. Mouse Ly6c ATMs reside outside of CLS and are adipogenic, while CD9 ATMs reside within CLS, are lipid-laden, and are proinflammatory. Adoptive transfer of Ly6c ATMs into lean mice activates gene programs typical of normal adipocyte physiology. By contrast, adoptive transfer of CD9 ATMs drives gene expression that is characteristic of obesity. Importantly, human adipose tissue contains similar ATM populations, including lipid-laden CD9 ATMs that increase with body mass. These results provide a higher resolution of the cellular and functional heterogeneity within ATMs and provide a framework within which to develop new immune-directed therapies for the treatment of obesity and related sequela.

Collagen overlays can inhibit leptin and adiponectin secretion but not lipid accumulation in adipocytes.

BackgroundWhite adipose tissue (WAT) is essential for energy storage as well as being an active endocrine organ. The secretion of adipokines by adipocytes can affect whole body metabolism, appetite, and contribute to overall health. WAT is comprised of lipid-laden mature adipocytes, as well as immune cells, endothelial cells, pre-adipocytes, and adipose-derived stem cells. In addition, the presence of extracellular matrix (ECM) proteins in WAT can actively influence adipocyte differentiation, growth, and function. Type I collagen is an abundant fibrous ECM protein in WAT that is secreted by developing adipocytes. However, the extent and overall effect of Type I collagen on adipokine secretion in mature adipocytes when added exogenously has not been established.MethodsWe characterized the effects of Type I collagen overlays prepared using two different buffers on adipocyte physiology and function when added at different times during differentiation. In addition, we compared the effect of collagen overlays when adipocytes were cultured on two different tissue culture plastics that have different adherent capabilities. Triglyceride accumulation was analyzed to measure adipocyte physiology, and leptin and adiponectin secretion was determined to analyze effects on adipokine secretion.ResultsWe found that collagen overlays, particularly when added during the early differentiation stage, impaired adipokine secretion from mature adipocytes. Collagen prepared using PBS had a greater suppression of leptin than adiponectin while collagen prepared using HANKS buffer suppressed the secretion of both adipokines. The use of CellBind plates further suppressed leptin secretion. Triglyceride accumulation was not substantially impacted with any of the collagen overlays.DiscussionAdipokine secretion can be selectively altered by collagen overlays. Thus, it is feasible to selectively manipulate the secretion of adipokines by adipocytes in vitro by altering the composition or timing of collagen overlays. The use of this technique could be applied to studies of adipokine function and secretion in vitro as well as having potential therapeutic implications to specifically alter adipocyte functionality in vivo.