Adipose Conversion Research Articles

Mandibular bone is protected against microarchitectural alterations and bone marrow adipose conversion in ovariectomized rats

Osteoporosis is a disease that leads to a loss of bone mass and to alterations in the bone microarchitecture that occur in a site-specific manner; however it remains controversial in the jaw. The involvement of bone marrow adipose tissue (BMAT) in the bone metabolism has been suggested in several physiopathological contexts, such as in aging and osteoporosis. To test whether the BMAT content is related to mandibular bone loss, this study aimed to investigate the potential correlations between the trabecular bone microarchitecture on one hand and BMAT content and its spatial distribution in relation to bone surface on the other hand during aging and ovariectomy (OVX) during a long-term follow-up in a mature rat model. No age-related microarchitectural or BMAT changes were observed in the mandible. The OVX-induced bone loss was three-fold lower in the mandible than in the tibia and was observed only in the alveolar bone (not in the condyle). We also report a delayed increase in the mandibular BMAT content that remained 4-6-fold lower compared to tibia. This low BMAT content in the mandible was located at a distance from the trabecular bone surface (only 5% in contact with the bone surface versus 87% in the tibia). These findings highlight a specific mandibular response to OVX, in particular fewer microarchitectural alterations compared to that in the tibia. For the latter, the trabecular bone thickness and surface were correlated with the BMAT content. Oral functions may have a protective effect on the mandibular BMAT conversion in an OVX context.

Promotion of lipid storage rather than of thermogenic competence by fetal versus newborn calf serum in primary cultures of brown adipocytes

ABSTRACTMuch current understanding of brown adipocyte development comes from in-vitro cell models. Serum type may affect the behavior of cultured cells and thus conclusions drawn. Here, we investigate effects of serum type (“fetal bovine” versus “newborn calf”) on responses to differentiation inducers (the PPARγ agonist rosiglitazone or the neurotransmitter norepinephrine) in cultured primary brown adipocytes. Lipid storage was enhanced by fetal versus newborn serum. However, molecular adipose conversion (Pparg2 and Fabp4 expression) was not affected by serum type. Rosiglitazone-induced (7-days) expression of thermogenic genes (i.e. Ucp1, Pgc1a, Dio2 and Elovl3) was not systematically affected by serum type. However, importantly, acute (2 h) norepinephrine-induced thermogenic gene expression was overall markedly higher (and adipose genes somewhat lower) in cells cultured in newborn serum. Thus, newborn serum promotes thermogenic competence, and the use of fetal serum in brown adipocyte cultures (as is often routine) counteracts adequate differentiation. Agents that counteract this inhibition may therefore confoundingly be ascribed genuine thermogenic competence-inducing properties.

The effects of knee immobilization on marrow adipocyte hyperplasia and hypertrophy at the proximal rat tibia epiphysis

Marrow adipose deposition is observed during aging and in association with extended periods of immobility. The objective of this study was to determine the contribution of adipocyte hypertrophy and hyperplasia to bone marrow fat deposition induced by immobilization of the rat knee joint for 2, 4, 16 or 32 weeks. Histomorphometric analyses compared immobilized to sham-operated proximal tibia from age and gender matched rats to assess the contribution of aging and duration of immobilization on the number and size of marrow adipocytes. Results indicated that marrow adipose tissue increased with the duration of immobilization and was significant larger at 16 weeks compared to the sham-operated group (0.09956±0.13276mm2 vs 0.01990±0.01100mm2, p=0.047). The marrow adipose tissue was characterized by hyperplasia of adipocytes with a smaller average size after 2 and 4 weeks of immobilization (at 2 weeks hyperplasia: 68.86±33.62 vs 43.57±24.47 adipocytes/mm2, p=0.048; at 4 weeks hypotrophy: 0.00036±0.00019 vs 0.00046±0.00023mm2, p=0.027), and by adipocyte hypertrophy after 16 weeks of immobilization (0.00083±0.00049 vs 0.00046±0.00028mm2, p=0.027) compared to sham-operated. Both immobilized and sham-operated groups showed marrow adipose conversion with age; immobilized (p=0.008; sham: p=0.003). Overall, fat deposition in the bone marrow of the proximal rat tibia epiphysis and induced by knee joint immobilization was characterized by hyperplasia of small adipocytes in the early phase and by adipocyte hypertrophy in the later phase. Mediators of marrow fat deposition after immobilization and preventive countermeasures need to be investigated.

DbcAMP regulates adipogenesis in sheep inguinal preadipocytes

BackgroundThe cyclic adenosine-monophosphate (cAMP) pathway is generally recognized as one of the essential pathways for the adipose conversion of rodent preadipocytes in vitro. However, divergent effects of cAMP on adipocyte differentiation have also been reported. Since there is very little data on non-rodent preadipose cells, the aim of the present work was to analyze the effects of one classic activator (dbcAMP) of the cAMP pathway on the proliferation and differentiation of sheep preadipocytes grown.MethodWe retrospectively analyzed the regulation of dbcAMP on the proliferation and differentiation of sheep preadipocytes through observation on cell dynamic morphology, drawing on the growth curve, Oil Red O staining and induction of cell differentiation.Results1) During first 5 days of treatment, at lower levels of dbcAMP (1 nmol/L to 1 × 104 nmol/L), sheep cells were not increased, but at higher levels (1 × 105 nmol/l to 1 × 106 nmol/l), they were significantly increased (P < 0.05); 2) dbcAMP had the trendency to promote cell differentition, but it was not significant (P > 0.05); 3) treated for 4 days, dbcAMP at the levels of 1 nmol/L, 1 × 104 nmol/L and 1 × 106 nmol/L increased C20:0 abundance (P < 0.05), but other fatty acids had no significant changes; 4) treated for 4 days, expression of SCD mRNA had no significant change (P > 0.05), but expression of HSL mRNA increased at the level of 1 × 106 nmol/L dbcAMP (P < 0.05).ConclusionThis study demonstrated that the mechanisms by which of the cAMP pathway affects on preadipocytes between sheep and rodent animals was different.

Retinoic Acid Inhibits Adipogenesis Modulating C/EBPβ Phosphorylation and Down Regulating Srebf1a Expression.

Adipogenesis comprises a complex network of signaling pathways and transcriptional cascades; the GSK3β-C/EBPβ-srebf1a axis is a critical signaling pathway at early stages leading to the expression of PPARγ2, the master regulator of adipose differentiation. Previous work has demonstrated that retinoic acid inhibits adipogenesis affecting different signaling pathways. Here, we evaluated the anti-adipogenic effect of retinoic acid on the adipogenic transcriptional cascade, and the expression of adipogenic genes cebpb, srebf1a, srebf1c, pparg2, and cebpa. Our results demonstrate that retinoic acid blocks adipose differentiation during commitment, returning cells to an apparent non-committed state, since they have to be newly induced to adipose conversion after the retinoid is removed from the culture medium. Retinoic acid down regulates the expression of the adipogenic genes, srebf1a, srebf1c, pparg2, and cebpa; however, it did not down regulate the expression of cebpb, but it inhibited C/EBPβ phosphorylation at Thr188, a critical step for the progression of the adipogenic program. We also found that RA inhibition of adipogenesis did not increase the expression of dlk1, the gene encoding for Pref1, a well-known anti-adipogenic factor.

Characterization of PSPA Cell Differentiation,an Established Pig Preadipocyte Cell Line as an In Vitro Model for Pig Fat Development

We have established a clonal porcine subcutaneous preadipocyte cell line for the first time. This cell line, named PSPA, shows a fibroblast-like phenotype and keeps on growing under growth medium even after reaching confluence. Adipose conversion occurs only when confluent cultures are stimulated with insulin, dexamethasone, biotin, pantothenate, and octanoate. Following exposure to this differentiation medium, growth was arrested immediately without mitotic expansion and PSPA cells exhibited a marked increase in intracellular lipid accumulation accompanied by changes in gene expressions directly related to fat metabolism and also in extracellular environments. Since PSPA cells were established, it has become possible to end the discussion over whether there is species specificity in the adipose conversion between pig and mouse by comparing PSPA cells and 3T3-L1 cells, the most widely studied preadipocyte cell line. Consequently, we demonstrated that responsiveness to inducers and fatty acid composition was unequal, despite being treated with the same media. Thus, species-specific differences indeed exist in adipogenesis between these two, meaning that PSPA cells would be an in vitro model specialized to improve understanding of pig adipocyte growth and differentiation in controlling the carcass fat content of pigs.

Spatiotemporal lipid profiling during early embryo development of Xenopus laevis using dynamic ToF-SIMS imaging

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) imaging has been used for the direct analysis of single intact Xenopus laevis embryo surfaces, locating multiple lipids during fertilization and the early embryo development stages with subcellular lateral resolution (∼4 μm). The method avoids the complicated sample preparation for lipid analysis of the embryos, which requires selective chemical extraction of a pool of samples and chromatographic separation, while preserving the spatial distribution of biological species. The results show ToF-SIMS is capable of profiling multiple components (e.g., glycerophosphocholine, SM, cholesterol, vitamin E, diacylglycerol, and triacylglycerol) in a single X. laevis embryo. We observe lipid remodeling during fertilization and early embryo development via time course sampling. The study also reveals the lipid distribution on the gamete fusion site. The methodology used in the study opens the possibility of studying developmental biology using high resolution imaging MS and of understanding the functional role of the biological molecules.

The impact of dietary fat and thyroid function on adipose conversion in male Sprague Dawley rats (1160.10)

The thyroid hormones (THs) play critical roles in differentiation, growth and metabolism and are critical for the normal function of nearly all tissues, with major roles in regulating energy balance, metabolism of glucose, and lipids and metabolic rate. The two functionally different types of fat in mammals are: brown adipose tissue (BAT), containing specialized thermogenic brown adipocytes, and white adipose tissue (WAT), containing white adipocytes specialized in triglyceride metabolism. Both tissues are strongly involved in energy balance. The objective of this study was to evaluate and compare physiological and histological effects of saturated and unsaturated fats in periadrenal BAT and thyroid gland of euthyroid and thyroid altered rats. Adult male Sprague Dawley rats (n=100) were exposed to a control or one of four test diets; 25% and 27% (saturated or unsaturated) for 8 weeks. A chemically reduced thyroid state was obtained through the addition of .05% propylthioracil (PTU) in drinking water. The body weights of the normal animals were significantly higher than in the altered thyroid groups. Histopathological evaluations confirmed damage to thyroid tissue in the altered thyroid groups and revealed an increase in BAT to WAT conversion in the thyroid gland and periadrenal BAT. Gene expression of FABP and LXR was generally higher in thyroid altered animals compared to the euthyroid group. In conclusion, chemically induced hypothyroidism negatively impacted fat metabolism, which contributed to increased BAT to WAT conversion and increased expression of FABP and LXR.

High density lipoproteins improve insulin sensitivity in high-fat diet-fed mice by suppressing hepatic inflammation

Obesity-induced liver inflammation can drive insulin resistance. HDL has anti-inflammatory properties, so we hypothesized that low levels of HDL would perpetuate inflammatory responses in the liver and that HDL treatment would suppress liver inflammation and insulin resistance. The aim of this study was to investigate the effects of lipid-free apoAI on hepatic inflammation and insulin resistance in mice. We also investigated apoAI as a component of reconstituted HDLs (rHDLs) in hepatocytes to confirm results we observed in vivo. To test our hypothesis, C57BL/6 mice were fed a high-fat diet (HFD) for 16 weeks and administered either saline or lipid-free apoAI. Injections of lipid-free apoAI twice a week for 2 or 4 weeks with lipid-free apoAI resulted in: i) improved insulin sensitivity associated with decreased systemic and hepatic inflammation; ii) suppression of hepatic mRNA expression for key transcriptional regulators of lipogenic gene expression; and iii) suppression of nuclear factor κB (NF-κB) activation. Human hepatoma HuH-7 cells exposed to rHDLs showed suppressed TNFα-induced NF-κB activation, correlating with decreased NF-κB target gene expression. We conclude that apoAI suppresses liver inflammation in HFD mice and improves insulin resistance via a mechanism that involves a downregulation of NF-κB activation.

Bone marrow uptake of ferumoxytol: A preliminary study in healthy human subjects

To characterize the uptake and elimination of ferumoxytol, an ultrasmall superparamagnetic iron oxide (USPIO) agent, in bone marrow of healthy human subjects. Four men and two postmenopausal women, aged 22 to 57 years, were prospectively included. Simultaneous fat, water, and T2* mapping of the proximal femora was performed at 1.5 Tesla using a three-dimensional multiple gradient echo sequence. After baseline imaging, ferumoxytol (Feraheme/Rienso) was injected intravenously at a dose of 5 mg Fe/kg body weight. Imaging was repeated at 3 days, 1 month, 3 months, and 5 months after administration. Imaging at 3 days revealed large increases in R2* ( =1/T2*) in hematopoietic marrow and lower average responses in fatty marrow, consistent with macrophage-specific uptake. However, certain regions of the diaphysis exhibited substantial R2* enhancement despite having very high fat content. This suggests the persistence of residual marrow stroma following adipose conversion, and may reflect the ability of diaphyseal marrow to adapt dynamically to fluctuating demand for hematopoiesis. Follow-up imaging demonstrated almost complete R2* recovery within 3 months. The observed R2* enhancement characteristics support applications for ferumoxytol in distinguishing normal or hypercellular marrow from neoplasms, infection and inflammation. Further studies are warranted in specific patient populations.

Glucocorticoid Paradoxically Recruits Adipose Progenitors and Impairs Lipid Homeostasis and Glucose Transport in Mature Adipocytes

Chronic treatment with glucocorticoids increases the mass of adipose tissue and promotes metabolic syndrome. However little is known about the molecular effects of dexamethasone on adipose biology. Here, we demonstrated that dexamethasone induces progenitor cells to undergo adipogenesis. In the adipogenic pathway, at least two cell types are found: cells with the susceptibility to undergo staurosporine-induced adipose conversion and cells that require both staurosporine and dexamethasone to undergo adipogenesis. Dexamethasone increased and accelerated the expression of main adipogenic genes such as pparg2, cebpa and srebf1c. Also, dexamethasone altered the phosphorylation pattern of C/EBPβ, which is an important transcription factor during adipogenesis. Dexamethasone also had effect on mature adipocytes mature adipocytes causing the downregulation of some lipogenic genes, promoted a lipolysis state, and decreased the uptake of glucose. These paradoxical effects appear to explain the complexity of the action of glucocorticoids, which involves the hyperplasia of adipose cells and insulin resistance.

Effects of Parabens on Adipocyte Differentiation

Parabens are a group of alkyl esters of p-hydroxybenzoic acid that include methylparaben, ethylparaben, propylparaben, butylparaben, and benzylparaben. Paraben esters and their salts are widely used as preservatives in cosmetics, toiletries, food, and pharmaceuticals. Humans are exposed to parabens through the use of such products from dermal contact, ingestion, and inhalation. However, research on the effects of parabens on health is limited, and the effects of parabens on adipogenesis have not been systematically studied. Here, we report that (1) parabens promote adipogenesis (or adipocyte differentiation) in murine 3T3-L1 cells, as revealed by adipocyte morphology, lipid accumulation, and mRNA expression of adipocyte-specific markers; (2) the adipogenic potency of parabens is increased with increasing length of the linear alkyl chain in the following potency ranking order: methyl- < ethyl- < propyl- < butylparaben. The extension of the linear alkyl chain with an aromatic ring in benzylparaben further augments the adipogenic ability, whereas 4-hydroxybenzoic acid, the common metabolite of all parabens, and the structurally related benzoic acid (without the OH group) are inactive in promoting 3T3-L1 adipocyte differentiation; (3) parabens activate glucocorticoid receptor and/or peroxisome proliferator-activated receptor γ in 3T3-L1 preadipocytes; however, no direct binding to, or modulation of, the ligand binding domain of the glucocorticoid receptor by parabens was detected by glucocorticoid receptor competitor assays; and lastly, (4) parabens, butyl- and benzylparaben in particular, also promote adipose conversion of human adipose-derived multipotent stromal cells. Our results suggest that parabens may contribute to obesity epidemic, and the role of parabens in adipogenesis in vivo needs to be examined further.

The influence of mechanical stretching on mitosis, growth, and adipose conversion in adipocyte cultures

The mechanotransduction of adipocytes is not well characterized in the literature. In this study, we employ stochastic modeling fitted to experiments for characterizing the influence of mechanical stretching delivered to adipocyte monolayers on the probabilities of commitment to the adipocyte lineage, mitosis, and growth after mitosis in 3T3-L1 adipocytes. We found that the probability of a cell to become committed to the adipocyte lineage in a single division when cultured on an elastic substrate was 0.025, which was indistinguishable between cultures that were radially stretched (to 12% strain) and control cultures. The probability of undergoing mitosis however was different between the groups, being 0.4 in the stretched cultures and 0.6 in the controls. The probability of growing after mitosis was affected by the stretching as well and was 0.9 and 0.8 in the stretched and control groups, respectively. We conclude that static stretching of the substrate of adipocyte cultures influences the mitotic potential of the cells as well as the growth potential post-mitosis. The present work provides better understanding of the mechanotransduction of adipocytes and in particular quantify how stretching influences the likelihood of cell proliferation and differentiation and, consequently, adipogenesis in the adipocyte cultures.

(−)-Epigallocatechin-3-gallate blocks 3T3-L1 adipose conversion by inhibition of cell proliferation and suppression of adipose phenotype expression

AimsA major objective in the treatment of obese individuals is the development of agents that reduce body fat and improve metabolic homeostasis. Among a variety of biological effects, green tea exerts an anti-obesity effect; however, the mechanisms behind its activity on adipose tissue are uncertain. Tea contains high levels of (−)-epigallocatechin-3-gallate (EGCG), which is one of its main bioactive substances. Therefore, we studied the effects of EGCG on mouse embryonic fibroblast-adipose like cell line (3T3-L1) preadipocyte proliferation and differentiation. Main methods3T3-L1 cells were incubated with physiologically attainable (0.1–1μM) and pharmacological (5μM, 10μM) concentrations of EGCG for various lengths of time. Cell proliferation was assessed by cell counting and cell cycle analysis. Adipose conversion was evaluated by lipid accumulation and expression of CCAAT/enhancer binding protein alpha (C/EBPα) and peroxisome proliferator-activated receptor gamma (PPARγ) transcription factors. Key findingsA dose dependent suppressive effect on preadipocyte proliferation was observed, with the highest reduction in cell number at 10μM EGCG. On the other hand, adipose conversion was fully inhibited with 10μM EGCG. Flow-cytometric analysis showed that 3T3-L1 cells treated with EGCG underwent an arrest of cell cycle at G2/M. The inhibition of the expression of C/EBPα and PPARγ was accompanied by the inhibitory effect of EGCG. Microscopic observation showed that 3T3-L1 cells treated with EGCG maintained the fibroblastic shape and failed to accumulate cytoplasmic fat droplets even after the induction of differentiation. SignificanceOur results suggest that EGCG reduces adipogenesis through an arrest of cell cycle and a blockage of adipose phenotype expression. These results also suggest that the anti-obesity activity of green tea may be partially attributed to its suppressive effects in adipogenesis.

Adipocyte expression of the glucose-dependent insulinotropic polypeptide receptor involves gene regulation by PPARγ and histone acetylation

Glucose-dependent insulinotropic polypeptide (GIP) is a gastrointestinal hormone that exerts insulinotropic and growth and survival effects on pancreatic β-cells. Additionally, there is increasing evidence supporting an important role for GIP in the regulation of adipocyte metabolism. In the current study we examined the molecular mechanisms involved in the regulation of GIP receptor (GIPR) expression in 3T3-L1 cells. GIP acted synergistically with insulin to increase neutral lipid accumulation during progression of 3T3-L1 preadipocytes to the adipocyte phenotype. Both GIPR protein and mRNA expression increased during 3T3-L1 cell differentiation, and this increase was associated with upregulation of nuclear levels of sterol response element binding protein 1c (SREBP-1c) and peroxisome proliferator-activated receptor γ (PPARγ), as well as acetylation of histones H3/H4. The PPARγ receptor agonists LY171883 and rosiglitazone increased GIPR expression in differentiated 3T3-L1 adipocytes, whereas the antagonist GW9662 ablated expression. Additionally, both PPARγ and acetylated histones H3/H4 were shown to bind to a region of the GIPR promoter containing the peroxisome proliferator response element (PPRE). Knockdown of PPARγ in differentiated 3T3-L1 adipocytes, using RNA interference, reduced GIPR expression, supporting a functional regulatory role. Taken together, these studies show that GIP and insulin act in a synergistic manner on 3T3-L1 cell development and that adipocyte GIPR expression is upregulated through a mechanism involving interactions between PPARγ and a GIPR promoter region containing an acetylated histone region.

Reorganization of the nuclear lamina and cytoskeleton in adipogenesis

A thorough understanding of fat cell biology is necessary to counter the epidemic of obesity. Although molecular pathways governing adipogenesis are well delineated, the structure of the nuclear lamina and nuclear-cytoskeleton junction in this process are not. The identification of the ‘linker of nucleus and cytoskeleton’ (LINC) complex made us consider a role for the nuclear lamina in adipose conversion. We herein focused on the structure of the nuclear lamina and its coupling to the vimentin network, which forms a cage-like structure surrounding individual lipid droplets in mature adipocytes. Analysis of a mouse and human model system for fat cell differentiation showed fragmentation of the nuclear lamina and subsequent loss of lamins A, C, B1 and emerin at the nuclear rim, which coincides with reorganization of the nesprin-3/plectin/vimentin complex into a network lining lipid droplets. Upon 18 days of fat cell differentiation, the fraction of adipocytes expressing lamins A, C and B1 at the nuclear rim increased, though overall lamin A/C protein levels were low. Lamin B2 remained at the nuclear rim throughout fat cell differentiation. Light and electron microscopy of a subcutaneous adipose tissue specimen showed striking indentations of the nucleus by lipid droplets, suggestive for an increased plasticity of the nucleus due to profound reorganization of the cellular infrastructure. This dynamic reorganization of the nuclear lamina in adipogenesis is an important finding that may open up new venues for research in and treatment of obesity and nuclear lamina-associated lipodystrophy.Electronic supplementary materialThe online version of this article (doi:10.1007/s00418-011-0792-4) contains supplementary material, which is available to authorized users.

Antiadipogenic Effects of the Mineralocorticoid Receptor Antagonist Drospirenone: Potential Implications for the Treatment of Metabolic Syndrome

The mineralocorticoid receptor (MR) mediates aldosterone- and glucocorticoid-induced adipocyte differentiation. Drospirenone (DRSP) is a potent synthetic antimineralocorticoid with progestogenic and antiandrogenic properties, which is widely used for contraception and hormone replacement therapy. We investigated its potential role on adipocyte differentiation. The effects of DRSP were studied in murine preadipocyte cell lines and primary cultures of human preadipocytes. Differentiation markers and mechanisms underlying phenotypic variations in response to DRSP were explored. Early exposure to DRSP during differentiation led to a marked dose-dependent inhibition of adipose differentiation and triglyceride accumulation in 3T3-L1 and 3T3-F442A cells. DRSP also markedly inhibited adipose conversion of human primary preadipocytes derived from visceral (mesenteric and epicardial) and subcutaneous fat. This effect was MR-dependent and did not involve the glucocorticoid, androgen, or progesterone receptors. DRSP inhibited clonal expansion of pre-adipocytes and decreased expression of PPARγ, a key transcriptional mediator of adipogenesis, but had no effect on lipolysis, glucose uptake, and PPARγ binding to its ligands. DRSP exerts a potent antiadipogenic effect that is related to an alteration of the transcriptional control of adipogenesis via an antagonistic effect on the MR. Selective MR blockade therefore has promise as a novel therapeutic option for the control of excessive adipose tissue deposition and its related metabolic complications.

Antiadipogenic Effects of the Mineralocorticoid Receptor Antagonist Drospirenone: Potential Implications for the Treatment of Metabolic Syndrome

The mineralocorticoid receptor (MR) mediates aldosterone- and glucocorticoid-induced adipocyte differentiation. Drospirenone (DRSP) is a potent synthetic antimineralocorticoid with progestogenic and antiandrogenic properties, which is widely used for contraception and hormone replacement therapy. We investigated its potential role on adipocyte differentiation. The effects of DRSP were studied in murine preadipocyte cell lines and primary cultures of human preadipocytes. Differentiation markers and mechanisms underlying phenotypic variations in response to DRSP were explored. Early exposure to DRSP during differentiation led to a marked dose-dependent inhibition of adipose differentiation and triglyceride accumulation in 3T3-L1 and 3T3-F442A cells. DRSP also markedly inhibited adipose conversion of human primary preadipocytes derived from visceral (mesenteric and epicardial) and subcutaneous fat. This effect was MR-dependent and did not involve the glucocorticoid, androgen, or progesterone receptors. DRSP inhibited clonal expansion of preadipocytes and decreased expression of PPARγ, a key transcriptional mediator of adipogenesis, but had no effect on lipolysis, glucose uptake, and PPARγ binding to its ligands. DRSP exerts a potent antiadipogenic effect that is related to an alteration of the transcriptional control of adipogenesis via an antagonistic effect on the MR. Selective MR blockade therefore has promise as a novel therapeutic option for the control of excessive adipose tissue deposition and its related metabolic complications.

The effect of squalane-dissolved fullerene-C60 on adipogenesis-accompanied oxidative stress and macrophage activation in a preadipocyte-monocyte co-culture system

Effects of squalane-dissolved fullerene-C60 (Sql-fullerene) on macrophage activation and adipose conversion with oxidative stress were studied using an inflammatory adipose-tissue equivalent (ATE) and OP9 mouse stromal preadipocyte-U937 lymphoma cell co-culture systems. Differentiation of OP9 cells was initiated by insulin-rich serum replacement (SR) as an adipogenic stimulant, and then followed by accumulation of intracellular lipid droplets and reactive oxygen species (ROS), both of which were significantly inhibited by Sql-fullerene. In the OP9-U937 cell co-culture system, U937 cells rapidly differentiated to macrophage-like cells during SR-induced adipogenesis in OP9 cells. The ROS accumulation was in the co-culture more marked than in OP9 cells alone, suggesting that the interaction between adipocytes and monocytes/macrophages promotes inflammatory responses. Sql-fullerene significantly inhibited macrophage activation and low-grade adipogenesis in the OP9-U937 co-culture system. We developed a three-dimensional inflammatory adipose-tissue model “ATE” consisting of, characteristically, U937 cells in the culture-wells, and, in addition, mounted a culture insert containing OP9 cells-populated collagen gel. ATE is enabled with suitable stimulation to represent the pathology of inflammatory disorders, such as macrophage infiltration in adipose tissue. Five-day culturing of ATE in SR medium occurred U937 macrophage migration and intracellular oil-droplet accumulation that were significantly inhibited by Sql-fullerene. Our results suggest that Sql-fullerene might be explored as a potential medicine for the treatment of metabolic syndrome or other obesity-related disorders.

Ras signalling regulates differentiation and UCP1 expression in models of brown adipogenesis

Background The Ras/Raf/MEK/ERK pathway has been recognised as an important signalling module in adipogenesis and adipocyte function, but whether it promotes or inhibits the formation of fat cells has not been reconciled. Methods Here we investigate the significance of Ras signalling intensity on two unrelated models of mouse brown adipocyte differentiation. Results A constitutively active H-Ras mutant (Ras V12) caused a complete block of adipose conversion, as manifested by a lack of both lipid accumulation and induction of adipocyte gene expression. The Ras V12-mediated impediment of differentiation was inefficiently rescued by forced expression of the adipogenic transcription factors C/EBPα and PPARγ. However, the defective differentiation was alleviated by MEK inhibitors, suggesting that the obstruction of differentiation was dependent on activation of ERK. A dominant interfering H-Ras mutant (Ras N17) did not inhibit differentiation, but led to increased expression of genes important for energy dissipation in brown fat cells, including UCP1. General significance These data suggest that the intensity of Ras signalling is important for differentiation and UCP1 expression in models of brown adipogenesis.