Small Fat Cells Research Articles

Red mold rice prevents the development of obesity, dyslipidemia and hyperinsulinemia induced by high-fat diet

To investigate the influences of red mold rice (RMR) on obesity and related metabolic abnormalities. The 3T3-L1 cell line was used to examine the effects of RMR extracts on preadipocytes and on mature adipocytes. Both water and ethanol extracts of RMR had inhibitory effects on 3T3-L1 preadipocyte proliferation and differentiation. Water extracts of RMR enhanced the lipolysis activity in mature adipocytes, which negatively correlated with the triglyceride content within cells. RMR treatment did not affect heparin-releasable lipoprotein lipase activity in mature adipocytes. Furthermore, animal studies were carried out to explore the antiobesity effects of RMR. The control group of male Wistar rats were fed regular laboratory feed, whereas the other groups were fed the high-fat (HF) diet supplemented with lovastatin, rice or RMR (0.4 and 2%, w w(-1)). The relative caloric intakes of the control and HF groups were 3.34 and 4.85 kcal g(-1), respectively. After 6 weeks, rats treated with RMR at the 0.4 and 2% doses had lower weight gain and less fat pads mass accompanied with smaller fat cells than did the HF-diet rats. These effects probably resulted from an increase in the lipolysis activity of adipose tissue and a reduction in food/energy consumption. On the other hand, the RMR supplement significantly reduced serum total cholesterol, serum low-density lipoprotein (LDL) cholesterol, the ratio of LDL to high-density lipoprotein (HDL) cholesterol and serum insulin in the HF group. Moreover, the 2% RMR treatment significantly increased serum HDL cholesterol. This study reveals for the first time that RMR can prevent body fat accumulation and improve dyslipidemia. The antiobesity effects of RMR mainly derive from the lipolytic activity and mild antiappetite potency of RMR. In addition, extracts of RMR suppressed the proliferation and differentiation in 3T3-L1 preadipocytes, which might have contributed to the inhibition of new adipocyte formation or hyperplasia in adipose tissue.

Monomeric tartrate resistant acid phosphatase induces insulin sensitive obesity.

BackgroundObesity is associated with macrophage infiltration of adipose tissue, which may link adipose inflammation to insulin resistance. However, the impact of inflammatory cells in the pathophysiology of obesity remains unclear. Tartrate resistant acid phosphatase (TRAP) is an enzyme expressed by subsets of macrophages and osteoclasts that exists either as an enzymatically inactive monomer or as an active, proteolytically processed dimer.Principal FindingsUsing mice over expressing TRAP, we show that over-expression of monomeric, but not the dimeric form in adipose tissue leads to early onset spontaneous hyperplastic obesity i.e. many small fat cells. In vitro, recombinant monomeric, but not proteolytically processed TRAP induced proliferation and differentiation of mouse and human adipocyte precursor cells. In humans, monomeric TRAP was highly expressed in the adipose tissue of obese individuals. In both the mouse model and in the obese humans the source of TRAP in adipose tissue was macrophages. In addition, the obese TRAP over expressing mice exhibited signs of a low-grade inflammatory reaction in adipose tissue without evidence of abnormal adipocyte lipolysis, lipogenesis or insulin sensitivity.ConclusionMonomeric TRAP, most likely secreted from adipose tissue macrophages, induces hyperplastic obesity with normal adipocyte lipid metabolism and insulin sensitivity.

Dissection of the Insulin-Sensitizing Effect of Liver X Receptor Ligands

The liver X receptors (LXRalpha and beta) are nuclear receptors that coordinate carbohydrate and lipid metabolism. Treatment of insulin-resistant mice with synthetic LXR ligands enhances glucose tolerance, inducing changes in gene expression expected to decrease hepatic gluconeogenesis (via indirect suppression of gluconeogenic enzymes) and increase peripheral glucose disposal (via direct up-regulation of glut4 in fat). To evaluate the relative contribution of each of these effects on whole-body insulin sensitivity, we performed hyperinsulinemic-euglycemic clamps in high-fat-fed insulin-resistant rats treated with an LXR agonist or a peroxisome proliferator-activated receptor gamma ligand. Both groups showed significant improvement in insulin action. Interestingly, rats treated with LXR ligand had lower body weight and smaller fat cells than controls. Insulin-stimulated suppression of the rate of glucose appearance (Ra) was pronounced in LXR-treated rats, but treatment failed to enhance peripheral glucose uptake (R'g), despite increased expression of glut4 in epididymal fat. To ascertain whether LXR ligands suppress hepatic gluconeogenesis directly, mice lacking LXRalpha (the primary isotype in liver) were treated with LXR ligand, and gluconeogenic gene expression was assessed. LXR activation decreased expression of gluconeogenic genes in wild-type and LXRbeta null mice, but failed to do so in animals lacking LXRalpha. Our observations indicate that despite inducing suggestive gene expression changes in adipose tissue in this model of diet-induced insulin resistance, the antidiabetic effect of LXR ligands is primarily due to effects in the liver that appear to require LXRalpha. These findings have important implications for clinical development of LXR agonists as insulin sensitizers.

New Scanning Electron Microscopic Method for Determination of Adipocyte Size in Humans and Mice*

To evaluate a new scanning electronic microscopic (EM) method for assessing fat cell sizes and compare fat cell size distribution in human adipose tissue from different fat depots before and after weight loss. Identical human fat tissue biopsies were separated into two fractions: one used to prepare a fat cell suspension by collagenase digestion followed by photomicrography (collagenase method) and the other fixed in formalin for EM analysis. The EM method was evaluated further by determining fat cell sizes from lean and ob/ob mice. Finally, the EM method was used to assess fat cell sizes in biopsies of different human depots from before and after weight loss. Fat cell size distributions measured by the two methods were not identical, but differences were generally small. The EM method reproduced the well-documented fat cell size difference between lean and ob/ob mice. Large variation was detected in fat cell distributions among three depots in humans. Weight loss reduced fat cell sizes in subjects with large baseline fat cells but had no effect in subjects with small baseline fat cell sizes. Our results suggest that the EM method may be a useful alternative for fat cell size analysis of clinical samples.

Insulin-induced GLUT4 translocation to the plasma membrane is blunted in large compared with small primary fat cells isolated from the same individual

Several studies have suggested that large fat cells are less responsive to insulin than small fat cells. However, in these studies, large fat cells from obese individuals were compared with smaller fat cells from leaner participants, in effect making it impossible to draw conclusions about whether there is a causal relationship between fat cell size and insulin sensitivity. We hypothesised that small fat cells might be more insulin-responsive than large adipocytes when obtained from the same individual. We developed a method of sorting isolated primary human fat cells by using nylon filters of two different pore sizes. The cells were stained to visualise DNA, which allowed discrimination from artefacts such as lipid droplets. The sorted cells were left to recover overnight, since we had previously demonstrated that this is necessary for correct assessment of insulin response. We found similar amounts of the insulin receptor (IR), IRS-1 and GLUT4 when we compared small and large adipocytes from the same volunteer by immunoblotting experiments using the same total cell volume from both cell populations. Activation of IR, IRS-1 and Akt1 (also known as protein kinase B) by insulin was similar in the two cell populations. However, immunofluorescence confocal microscopy of plasma membrane sheets did not reveal any increase in the amount of GLUT4 in the plasma membrane following insulin stimulation in the large fat cells, whereas we saw a twofold increase in the amount of GLUT4 in the small fat cells. Our results support a causal relationship between the accumulation of large fat cells in obese individuals and reduced insulin responsiveness.

Congenital Combined Orbito-Nasal Lipoblastoma: Clinico-Pathologic Study

The authors present the clinical picture, histopathologic findings and surgical treatment of an infant born with a lipoblastoma involving an unusual combined orbito-nasal location. To the best of our knowledge, this is the first report of congenital lipoblastoma extension from orbit to the nasal cavity. Transconjunctival orbitotomy with excisional biopsy of tumor was performed. Histology specimen that demonstrates the small embryonal fat cells in different stages of maturation and the characteristic lobulation of the fat tissue are presented. The embryonic origin, timing of development of the tumor during gestation, as well as the route of propagation from orbit to nose are discussed. The authors conclude that complete excision of this tumor, with preservation of normal tissue, may bring cure to the young patient without gross functional deformity.

Recent findings concerning thiazolidinediones in the treatment of diabetes

Thiazolidinediones (TZDs) are peroxisomal proliferator-activated receptor (PPAR)-γ agonists. They increase insulin action through several mechanisms including: stimulation of the expression of genes that increase fat oxidation and lower plasma free fatty acid levels; increased expression, synthesis and release of adiponectin; and stimulation of adipocyte differentiation resulting in more and smaller fat cells. TZDs lower blood sugar comparably to sulfonylureas and metformin. The clinical use of TZDs is limited due to the long duration of time required before they reach their full blood sugar-lowering action (3 – 4 months) and adverse effects such as fluid retention, resulting in excessive weight gain and occasionally in peripheral and/or pulmonary oedema and congestive heart failure. Troglitazone, a TZD that has since been removed from the market because of hepatoxicity, has been demonstrated to decrease the progression from normal or impaired glucose tolerance to overt Type 2 diabetes mellitus. Pioglitazone, another TZD, marginally decreased the incidence of cardiovascular complications in patients with Type 2 diabetes mellitus (PROactive trial). Other, as yet, unapproved uses of TZDs include: non-alcoholic fatty liver disease, in which TZDs reduced hepatic fat accumulation and improved liver function tests; polycystic ovary syndrome, where TZDs improved ovulation, hirsutism and endothelial dysfunction; and lipodystrophies, where TZDs increased body fat (marginally) and decrease liver size. Lastly, because PPAR-α and -γ agonists improve atherosclerotic vascular disease and insulin sensitivity, respectively, dual PPAR-α/γ agonists, which are currently undergoing clinical trials, may be useful in treating patients with the metabolic syndrome.

Long-Term Prospective and Controlled Studies Demonstrate Adipose Tissue Hypercellularity and Relative Leptin Deficiency in the Postobese State

Enlarged fat cells and leptin hypersecretion are hallmarks of common obesity. The objective of this study was to investigate fat cell size and leptin production in the basal state after long-term steady-state weight reduction to the nonobese state. This prospective case-control study had a duration of 3 +/- 1 (mean +/- sd) yr. Twenty-five obese women (cases) were studied. Each case was compared with a control subject matched for age, sex, and body mass index (BMI) at nadir of weight for the cases. This study was conducted at Karolinska University Hospital (Stockholm, Sweden). The subjects were followed until they reached a steady-state weight reduction after lifestyle modification or bariatric surgery (cases). Treatment target was the nonobese state (BMI < 30 kg/m2). Subcutaneous adipose tissue secretion of leptin, serum leptin levels, and fat cell volume were determined after an overnight fast. Ten obese women (40%) reached the nonobese state. This was accompanied by marked decreases in fat cell volume, leptin secretion, and serum leptin concentrations (P < 0.0001). The postobese cases had 43% smaller fat cell volume (P = 0.0008), 68% lower adipocyte leptin production (P = 0.001), and 54% lower serum leptin levels (P = 0.0007) than control subjects, despite almost identical percent body fat in the two groups. Fat cell volume, but not percent body fat or BMI, was directly proportional to leptin secretion and serum leptin concentrations. Adipose tissue hyperplasia (too many small fat cells) and low leptin production resulting in relative hypoleptinemia in the fasting (basal) state are common features of the postobese state in women.

Histological investigation of liposuctioned fat for injection laryngoplasty

Purpose There are a few injectable biomaterials used in vocal-fold–augmentation surgery. In this study, liposuctioned autologous fat, used as the injection material, was investigated histologically. Materials and methods Liposuctioned fat, which was harvested from 13 patients during injection laryngoplasty, was examined by light and electron microscopy. Results The cell membranes of most of the liposuctioned fat had not been damaged during harvesting and microinjection by our method. The harvested liposuctioned fat was a group of unilocular fat cells. Each cell was surrounded by a meshwork of fine reticular fibers. The cells were spherical and about 30 to 130 μm in diameter. The cells size and density were different from individual to individual. The diameters of liposuctioned fat cells were correlated with the body mass index. Dense and small fat cells were able to maintain graft volume. Sparse and large fat cells tended to not be able to maintain graft volume. There was little proliferation of unilocular fat cells, which were not able to maintain graft volume. Conclusion The structure consisting of a unilocular cell, containing a single droplet of lipid, surrounded by a meshwork of delicate reticular fiber is one of the reasons why autologous fat has viscous properties similar to those of human lamina propria. Autologous fat was not damaged by our harvesting and microinjection method. The size, density and proliferation of fat cells, and ground substance around them may be related to resorption and a decrease in surviving graft volume.

Genetic Modulation of PPARγ Phosphorylation Regulates Insulin Sensitivity

Obesity-associated diabetes is epidemic in industrialized societies. The nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ) is highly expressed in adipose tissue and the presumed molecular target for antidiabetic thiazolidinedione drugs that reverse insulin resistance but also promote weight gain. Phosphorylation reduces the activity of PPARγ in vitro, but physiological relevance has not been demonstrated. We have studied mice homozygous for a mutation (S112A) that prevents PPARγ phosphorylation. Surprisingly, the weights and adipose mass of PPARγ-S112A mice are not greater than wild-type. Remarkably, however, genetic prevention of PPARγ phosphorylation preserves insulin sensitivity in the setting of diet-induced obesity. Underlying this protection are smaller fat cells, elevated serum adiponectin, and reduced free fatty acid levels. Thus, the phosphorylation state of PPARγ modulates insulin sensitivity. Compounds that prevent PPARγ phosphorylation or ligands that induce the conformation of nonphosphorylated PPARγ may selectively enhance insulin sensitivity without increasing body weight.

Adipocyte functions are modulated by cell size change: potential involvement of an integrin/ERK signalling pathway.

Adipocyte is the only cell whose size may vary dramatically in physiological conditions. We hypothesized that increase in fat cell size per se could modulate several signalling pathways by changing the relationships between the cell and the extracellular matrix. The aim of the current study was (i). to examine whether within the same fat depot, metabolic functions of adipocyte were modified by cell size and (ii). if such an adaptation exists, to look for an integrin/extracellular-signal-regulated kinases (ERKs) signalling pathway. We isolated two populations of adipocytes with different volumes (67 and 22 x 10(3) microm(3)) within the same adipose location. In large compared to small fat cells, fatty acid synthase and lipoprotein lipase activities were increased two- and seven-fold, respectively; GLUT4 protein concentration and leptin expression were increased three-fold; lipolytic capacity was increased four-fold. The integrin/ERK signalling pathway could be the one responsible for the adaptation of adipose functions to cell size. In large compared with small adipocytes, we showed that beta(1)-integrins are present in adipose membranes and at a higher concentration in large than in small cells. In isolated adipocytes, stimulation of beta(1)-integrins with a specific monoclonal antibody results in ERK(1) and ERK(2) activation. In large compared to small cells, cytoplasmic concentrations of these two mitogen-activated protein kinases were increased two-fold, whereas their activities were increased 10-fold. A beta(1)-integrin/ERKs signalling pathway is present in mature adipocyte. Increase in cell size, by modifying the relationships between cell and extracellular matrix, could turn on this pathway. Since ERKs can modulate transcription factors and subsequently modulate gene expression important for adipose function, this pathway could play an important role in the adaptation of adipose functions to cell size.

Reply to:LeptinIs a Hypoxia-Inducible Gene

In their letter, Guerre-Millo et al. ((1)) provide explanation for the different results reported earlier by us ((2)). To discuss the control of leptin production by adipocytes under hypoxic conditions, one should focus on two issues. The first is hypoxia itself. Grosfeld et al. ((3)) reported recently that hypoxia increases leptin gene expression, through activation of the leptin gene promoter, and leptin production by human PAZ6 adipocytes. With consideration to the fact that leptin has a direct ((4)) or synergistic effect ((5)) on angiogenesis and vascular permeability, it is reasonable to consider that leptin is a hypoxia-inducible gene. In this regard, hypoxia can up-regulate leptin production in PAZ6 adipocytes, as well as human trophoblastic cell line (BeWo cells) ((6)). Second, it seems that cell size is an important determinant of leptin expression. Adipocytes can markedly change their own cell size according to lipid (mainly triglyceride) content, which is regulated by a balance between lipogenic and lipolytic functions of these cells, and insulin plays a central role in regulating metabolic pathways associated with energy storage and use of adipocytes. This rapid change in cell size is seldom seen in other cell types. Clinically, leptin may function as part of the signaling pathway from adipose tissue, regulate the size of the body fat depot ((7)), and serve as a useful marker of adiposity, reflecting the total lipid content in humans ((8)). In vitro, small fat cells express less obese (ob) mRNA than large fat cells even when obtained from the same individual ((9)), and exogenously applied tension to the plasma membrane leads to the induction of gene expression in other cell systems ((10)). Therefore, a change in adipocyte cell size serves as an important signal for induction of leptin expression even under hypoxic conditions. Hypoxic stress increases the expression of a variety of genes with products that act in concert, both systematically and at hypoxic sites, to facilitate the supply of metabolic energy. Zelzer et al. ((11)) reported that insulin induces the genes of glycolytic enzymes, glucose transporters Glut-1 and Glut-3, and VEGF in Hep-G2 hepatoma through the hypoxia-inducible factor-1 (HIF-1) pathway, similar to the action of cobalt chloride (CoCl2). Similar data in adipocytes were recently confirmed by Mick et al. ((12)), i.e., VEGF production is up-regulated by insulin and this effect is additive with CoCl2. Taken together, it is conceivable that CoCl2 or desferrioxamine (DFO) increases leptin release from primary rat adipocytes through the HIF-1 pathway ((3)) because leptin secretion is regulated by adipocyte–glucose use in response to insulin ((13)). We speculate that CoCl2 or DFO exerts insulin-like actions through the HIF-1 pathway ((11)) and that these agents induce the products associated with energy influx and storage of adipocytes, including glycolytic enzymes, glucose transporters Glut-1 and Glut-3, VEGF ((12)), and also leptin ((3)). However, the question arises as to why leptin accumulation was not enhanced but rather decreased when primary rat adipocytes were cultured under hypoxia((1),(2)). Hypoxia activates transcription through a mitochondria-dependent signaling process that involves increased reactive oxygen species (ROS), whereas CoCl2 activates transcription by stimulating ROS generation through a mitochondria-independent mechanism ((14)). These different mechanisms of cellular O2 sensing during hypoxia and in response to CoCl2 may be a key factor in explaining the discrepancy in leptin production by primary rat adipocytes in response to hypoxia and chemical hypoxia (CoCl2 and DFO) ((1),(3)). We speculate that during hypoxia, primary rat adipocytes induce several glycolytic enzymes and glucose transporters Glut-1 and Glut-3, through the HIF-1 pathway and facilitate the production of glycolytic adenosine triphosphate (ATP) to compensate for the low-energy state. The adipocytes cannot support the accumulation of triglycerides. Despite up-regulating leptin expression through the HIF-1 pathway, the signal invoked by a change in adipocyte cell size may not be potent enough to up-regulate the pathways that induce leptin expression. Consequently, hypoxia inhibits leptin production by primary rat adipocytes. Then, the question arises as to why hypoxia can stimulate leptin secretion in human PAZ6 brown adipose cells ((3)) and another leptin-producing cell type, the choriocarcinoma BeWo cells ((6)). These cells are a family of cancer cells, i.e., tumor, known to be the most pro-angiogenic. Because of progressive tumor growth, these cells are under persistent hypoxia, which stimulates angiogenesis and serves to relieve hypoxia through reoxygenation of tissues ((15)). If the size of PAZ6 adipocytes cultured under hypoxia does not significantly change relative to that under normoxia—attributable to the immortalized feature of PAZ6 adipocytes ((16)) and/or culture conditions (medium and supplements including insulin), i.e., under the same level of cell-size-dependent signals in the adipocyte—then hypoxia should increase leptin production through the HIF-1 pathway in human PAZ6 adipose cells.

Monounsaturated canola oil reduces fat deposition in growing female rats fed a high or low fat diet

The purpose of this study was to determine whether canola oil (monounsaturated fatty acids) and corn oil (polyunsaturated fatty acids) compared to coconut oil (saturated fatty acids) had a differential effect on adipose tissue deposition in growing female rats fed high (40% kcal) (HF) or low fat (6% kcal) (LF) diets. Body weight, total body fat content, and adipose tissue depots were greater in the HF fed groups compared to the LF fed groups. In the LF fed rats, body weight, body weight gain, and total body fat were higher in the rats fed corn oil (COR) compared to rats fed canola oil (CAN) or coconut oil (COC). Fat source affected adipose tissue fat cell size and number differentially. In the HF groups, fat cell size was larger for COR fed rats than for CAN or COC fed rats, but fat cell number was greater for COC fed rats than for corn and CAN fed rats. CAN had a positive advantage over COR since rats fed the LFCAN had a lower body weight gain, HFCAN rats maintained a smaller fat cell size than HFCOR and HFCOC fed rats, and plasma lipids were lower in CAN fed rats than for COR fed rats.

Cholesterol, a Cell Size-dependent Signal That Regulates Glucose Metabolism and Gene Expression in Adipocytes

Enlarged fat cells exhibit modified metabolic capacities, which could be involved in the metabolic complications of obesity at the whole body level. We show here that sterol regulatory element-binding protein 2 (SREBP-2) and its target genes are induced in the adipose tissue of several models of rodent obesity, suggesting cholesterol imbalance in enlarged adipocytes. Within a particular fat pad, larger adipocytes have reduced membrane cholesterol concentrations compared with smaller fat cells, demonstrating that altered cholesterol distribution is characteristic of adipocyte hypertrophy per se. We show that treatment with methyl-beta-cyclodextrin, which mimics the membrane cholesterol reduction of hypertrophied adipocytes, induces insulin resistance. We also produced cholesterol depletion by mevastatin treatment, which activates SREBP-2 and its target genes. The analysis of 40 adipocyte genes showed that the response to cholesterol depletion implicated genes involved in cholesterol traffic (caveolin 2, scavenger receptor BI, and ATP binding cassette 1 genes) but also adipocyte-derived secretion products (tumor necrosis factor alpha, angiotensinogen, and interleukin-6) and proteins involved in energy metabolism (fatty acid synthase, GLUT 4, and UCP3). These data demonstrate that altering cholesterol balance profoundly modifies adipocyte metabolism in a way resembling that seen in hypertrophied fat cells from obese rodents or humans. This is the first evidence that intracellular cholesterol might serve as a link between fat cell size and adipocyte metabolic activity.

AP2 Protein Expression as a Diagnostic Marker in Soft Tissue Tumours

Purpose/Methods: The aP2 gene product (aP2 protein) is known to be expressed by preadipocytes and other immature fat cells in vitro. A mouse monoclonal antibody raised against an 18 amino acid segment of the aP2 protein was found to react with lipoblasts and fetal fat cells in paraffin sections of soft tissue tumours of adipose differentiation. In this immunohistochemical study, we have further examined the diagnostic utility of aP2 expression in distinguishing tumours of adipose differentiation from other benign and malignant soft tissue tumours. Result and discussion aP2 was strongly expressed by lipoblasts in lipoblastomas and all types of liposarcoma as well as brown fat cells in hibernomas. Optimal conditions for immunohistochemical identification of lipoblasts in tumours of adipose differentiation was noted when the antibody was diluted 1:30 to 1:50. Small lipoblast-like fat cells in pleomorphic lipoma and spindle cell lipoma also showed variable staining for aP2 at this dilution of the antibody. Most benign and malignant soft tissue tumours were distinguished by their absence of staining for aP2 protein, but some cases of myxoma, malignant fibrous histiocytoma, synovial sarcoma and leiomyosarcoma contained tumour cells which reacted for aP2. aP2 protein expression is likely to prove a useful means of distinguishing lipoblasts in liposarcoma but it should be used as part of a tumour panel to exclude expression in other forms of mesenchymal tumour.

The Expression of Insulin-like Growth Factor-1 during Adipogenesisin Vivo:Effect of Thyroxine

The expression of insulin-like growth factor-1 (IGF-1) was examined in subcutaneous (SQ) adipose tissue from 105-day pig fetuses by ribonuclease protection assays andin situhybridization using a porcine IGF-1 riboprobe. Fetuses were hypophysectomized (hypox) at 70 days of gestation and at 90 days thyroxine (T4) pellets were implanted into some of the hypox fetuses. Fetuses were removed and SQ tissues collected on day 105 of gestation. RNase protection assays followed by scanning laser densitometry revealed that IGF-1 mRNA in SQ adipose tissue in hypox fetuses was significantly decreased to 19.8 ± 1.2% of control values. T4 treatment increased the expression of IGF-1 by 174 ± 26.6% of values for hypox fetuses. Usingin situhybridization we showed that fetal hypophysectomy reduced and T4 treatment increased expression of IGF-1 mRNA in the outer SQ adipose tissue layer (P<0.05). However, T4 treatment after hypox did not influence IGF-1 expression in the inner SQ layer (P>0.05). IGF-1 was expressed around capillaries, in small fat cells, and in fibroblasts in loose and dense connective tissue. Large fat cells, however, did not express IGF-1. Collectively, we concluded that (1) IGF-1 mRNA was decreased after hypox and increased by T4 treatment in SQ tissue of 105-day fetuses; (2) The expression of the IGF-1 gene was more sensitive to T4 treatment after hypox in outer SQ tissue than in inner SQ tissue; (3) Most stromal cells produced IGF-1 mRNA, and as a result they may influence adipogenesis in the outer layer of SQ adipose tissue; and (4) Once fat cells enlarged, expression of IGF-1 was not detected. Therefore, these studies provide evidence that IGF-1 may mediate the influence of T4 on fetal adipogenesis.

Preferential expression of cholesteryl ester transfer protein mRNA by stromal-vascular cells of human adipose tissue

Cholesteryl ester transfer protein (CETP) mRNA is more abundantly expressed in small mature adipocytes as compared to large, lipid-rich adipocytes [Radeau et al., J. Lipid Res. 36 (1995) 2552–2561]. In the present study, the stromal vascular fraction (SVF) of human adipose tissue was isolated and the presence of very small fat cells in this fraction confirmed by electron microscopy and by demonstrating the presence of mRNA for adipsin and for CCAAT enhancer binding protein α (C/EBPα), a marker of adipocyte differentiation. sn-Glycerol 3-phosphate dehydrogenase (GPDH) activity was present in the SVF but not in the preadipocyte fraction. Northern blot analysis of human adipose tissue demonstrated that CETP mRNA expression was significantly greater (+96%, P<0.03) in stromal-vascular cells (SVC) as compared to mature fat cells. By comparison, lipoprotein lipase mRNA expression was lower (−75%, P<0.03) in SVC while apolipoprotein E mRNA expression was not significantly different in SVC as compared to isolated adipocytes. By RT-PCR analysis, we demonstrated that CETP mRNA was expressed by human pre-adipocytes at levels less than those of SVC and adipocytes. The absence of monocytes/macrophages in SVC was confirmed by the absence of FcγRIII (CD16) mRNA in these fractions. These data demonstrate that CETP mRNA is most highly expressed in the immature fat cells of human adipose tissue, consistent with other experiments from this laboratory demonstrating that CETP plays an important local role in adipocyte cholesterol accumulation.

Hormonal regulation of leptin mRNA expression and preadipocyte recruitment and differentiation in porcine primary cultures of S-V cells.

The hormonal regulation of leptin mRNA expression and the association between leptin expression and adipocyte differentiation were examined in primary cultures of porcine S-V cells with Northern blot and immunocytochemical analysis. Seeding for 3 days with fetal bovine serum (FBS) with varying levels of dexamethasone (Dex) increased levels of leptin mRNA in a dose-dependent manner in parallel with increases in the proportion of preadipocytes (AD-3 positive cells; AD-3, a preadipocyte marker). Six-day treatment with 10 or 850 nM insulin after FBS+Dex treatment resulted in a similar increase in leptin mRNA expression and morphological differentiation. However, significantly lower levels of leptin mRNA and smaller fat cells were observed in cultures treated with 1 nM insulin or 10 nM insulin-like growth factor-I (IGF-I). Dex-induced increases in leptin mRNA levels and AD-3 cell numbers were blocked completely by the addition of transforming growth factor-beta (TGF-beta) to FBS+Dex-treated cultures. However TGF-beta significantly increased fat cell size and leptin mRNA expression when added to ITS (insulin, 850 nM; transferrin, 5 microg/ml; and selenium, 5 microg/mL) treated cultures during the lipid-filling stage. When added with FBS+DEX for the first 3 days, growth hormone (GH) did not influence the Dex-induced increase in AD-3 cells and leptin mRNA expression, but GH reduced leptin mRNA levels when added with insulin for 6 days after FBS+Dex. These results demonstrated that regulation of leptin mRNA expression by Dex, insulin, IGF-I, TGF-beta, and GH may be associated with changes in preadipocyte number and fat cell size.

Proliferation of Small Fat Cells Derived from Unilocular Fat Cells of Rats in Collagen Gel Matrix Culture.

The proliferative ability of fat cells has been studied both in the adipose tissue in vivo and in culture. We studied the proliferation of unilocular fat cells of young rats in a threedimensional collagen gel matrix culture, which provides a physiological environment for fat cells. In this setting, the unilocular fat cells were able to maintain their cellular functions and actively proliferate. In this study using cells derived from 3 to 6-week-old rats, we observed the appearance of very small fat cells at the surface of unilocular fat cells following the division of the nucleus. We concluded that small fat cells were created mostly in a “budding” manner, and then proliferated. Insulin accelerated both the budding and proliferation process. In other unilocular fat cells, lipid droplets divided after the division of the nucleus, and very small fat cells appeared within the unilocular fat cells in a “sharing” manner. Adenosine deaminase, a potent lipolytic factor, accelerated this process. An analysis of the cellular volume by a Coulter counter confirmed the proliferation of small fat cells derived from the unilocular fat cells. These small fat cells grew and developed into unilocular fat cells. It is supposed that not all unilocular fat cells are terminally differentiated, nor do they lose their proliferative activity.

Age-Related Changes in Rat Adipose Tissue Cellularity Are Altered by Dietary Restriction and Exercise

AbstractThis study examined the effects of diet restriction and exercise training during aging on adipocyte size and number in male Wistar rats. An average of 30 weanling rats each were assigned to one of four experimental groups: ad libitum access to food, nonexercised; diet restricted, nonexercised; ad libitum access to food, exercised; diet restricted, exercised. Diet-restricted groups were allowed free access to food every other day, and, over the course of the study, they consumed 18–25% less than the groups allowed ad libitum access. Exercise training consisted of swimming on alternate days for up to 3 h per exercise period. Fat cell size, number and fat depot mass were determined in the inguinal, epididymal and perirenal fat depots at 12 mo of age and every 4 mo thereafter until 28 mo of age. Fat cell number was not influenced by age, exercise or food restriction in the epididymal or perirenal fat depots. Inguinal cell number was lower (P < 0.05) in the diet-restricted, exercised group at all ages compared with all other treatments. Dietary restriction and exercise training significantly decreased fat depot mass and fat cell size, with dietary restriction having the greatest effect. A bimodal distribution of adipocytes was observed in the epididymal, perirenal and inguinal depots of animals allowed ad libitum access to food. The presence of a large population of small fat cells (<35 μm) indicated that even in the very aged animal there was the propensity for large variations in fat pad mass. The influence of diet restriction, exercise and aging on adipocyte cell size was highly variable and these effects were dependent on adipose tissue depot location