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At least 55 records · Page 3Linked to original sources
PubMed2000

A selective peroxisome proliferator-activated receptor-gamma (PPARgamma) modulator blocks adipocyte differentiation but stimulates glucose uptake in 3T3-L1 adipocytes.

Peroxisome proliferator-activated receptor-gamma (PPARgamma) agonists such as the thiazolidinediones are insulin sensitizers used in the treatment of type 2 diabetes. These compounds induce adipogenesis in cell culture models and increase weight gain in rodents and humans. We have identified a novel PPARgamma ligand, LG100641, that does not activate PPARgamma but selectively and competitively blocks thiazolidinedione-induced PPARgamma activation and adipocyte conversion. It also antagonizes target gene activation as well as repression in agonist-treated 3T3-L1 adipocytes. This novel PPARgamma antagonist does not block adipocyte differentiation induced by a ligand for the retinoid X receptor (RXR), the heterodimeric partner for PPARgamma, or by a differentiation cocktail containing insulin, dexamethasone, and 1-methyl-3-isobutylxanthine. Surprisingly, LG100641, like the PPARgamma agonist rosiglitazone, increases glucose uptake in 3T3-L1 adipocytes. Such selective PPARgamma antagonists may help determine whether insulin sensitization by thiazolidinediones is mediated solely through PPARgamma activation, and whether there are PPARgamma-ligand-independent pathways for adipocyte differentiation. If selective PPARgamma modulators block adipogenesis in vivo, they may prevent obesity, lower insulin resistance, and delay the onset of type 2 diabetes.

1-Methyl-3-isobutylxanthine↗
PubMed2002

IGF-binding protein-1 inhibits IGF effects on adipocyte function: implications for insulin-like actions at the adipocyte.

IGF action in vivo is acutely regulated by IGF-binding protein-1 (IGFBP-1) and its phosphorylation state is implicated in modulating these effects. Since IGFs have an important regulatory role in adipocyte function, we investigated the effects of phosphorylated IGFBP-1 (pIGFBP-1) and non-phosphorylated IGFBP-1 (npIGF BP-1) on 3T3-L1 preadipocyte proliferation and adipocyte metabolism. IGFs stimulated clonal expansion of 3T3-L1 cells (IGF-I more potently than IGF-II (EC(50): 30 nM and 50 nM)). npIGFBP-1 inhibited IGF-I (50 nM) clonal expansion at a 5:1 molar ratio (P<0.01), whereas pIGFBP-1 (purified from HepG2 cell medium) abolished clonal expansion at a 1:1 molar ratio (P<0.005). In contrast, IGF-II-induced clonal expansion was inhibited 100% at a 1:1 molar ratio of npIGFBP-1. In mature adipocytes, IGF-I was equipotent with insulin in stimulating glucose uptake (EC(50): 10 nM) and inhibiting isoproterenol-induced lipolysis (EC(50): 15 nM). npIGFBP-1 completely reversed IGF-I effects at a 1:1 molar ratio (P<0.01). In summary, IGFs rather than insulin are potent regulators of clonal expansion in 3T3-L1 preadipocytes. Importantly, IGFs are equipotent with insulin in regulating adipocyte metabolism. IGFBP-1 inhibits IGF effects on preadipocyte proliferation and adipocyte metabolism, with pIGFBP-1 being more potent than npIGFBP-1 at inhibiting mitogenic actions. Since IGFBP-1 is acutely regulated by insulin, this could have important consequences in hyperinsulinaemic and insulin-resistant states.

3T3 Cells↗
PubMed1999

Functional antagonism between inhibitor of DNA binding (Id) and adipocyte determination and differentiation factor 1/sterol regulatory element-binding protein-1c (ADD1/SREBP-1c) trans-factors for the regulation of fatty acid synthase promoter in adipocytes.

We show that Id (inhibitor of DNA binding) 2 and Id3, dominant negative members of the helix-loop-helix (HLH) family, interact with the adipocyte determination and differentiation factor 1 (ADD1)/sterol regulatory element-binding protein (SREBP) 1c, a transcription factor of the basic HLH-leucine zipper family that controls the expression of several key genes of adipose metabolism. Gel mobility-shift assays performed with in vitro-translated ADD1, Id2 or Id3 proteins and a fatty acid synthase (FAS) promoter oligonucleotide showed evidence for a marked inhibition of the formation of DNA-ADD1 complexes by Id2 or Id3 proteins. Co-immunoprecipitation studies using in vitro-translated proteins demonstrated further the physical interaction of Id and ADD1/SREBP-1c proteins in the absence of DNA. Using the FAS gene as a model of an ADD1-regulated promoter in transiently transfected isolated rat adipocytes or mature 3T3-L1 adipocytes, a potent inhibition of the activity of the FAS-chloramphenicol acetyltransferase reporter gene was observed by overexpression of Id2 or Id3. Reciprocally, co-transfection of Id3 antisense and ADD1 expression vectors in preadipocytes potentiated the ADD1/SREBP-1c effect on the FAS promoter activity. Finally, in the non adipogenic NIH-3T3 cell line, most of the ADD1-mediated trans-activation of the FAS promoter was counteracted by co-transfection of Id2 or Id3 expression vectors. Previous studies have indicated Id gene expression to be down-regulated during adipogenesis [Moldes, Lasnier, Fève, Pairault and Djian (1997) Mol. Cell. Biol. 17, 1796-1804]. We here demonstrated that there was a dramatic rise of Id2 and Id3 mRNA levels when 3T3-L1 adipocytes or isolated rat fat cells were exposed to lipolytic and anti-lipogenic agents, forskolin and isoproterenol. Taken together, our data show that Id products are functionally involved in modulating ADD1/SREBP-1c transcriptional activity, and thus lipogenesis in adipocytes.

3T3 Cells↗
PubMed1984

Infusion of insulin impairs human adipocyte glucose metabolism in vitro without decreasing adipocyte insulin receptor binding.

To determine whether hyperinsulinaemia can cause insulin resistance in man and, if so, whether this occurs at a receptor or post-receptor site, nine normal volunteers were infused with insulin for 6 h at a rate (2 mU X kg-1 X min-1) which resulted in steady-state plasma insulin concentrations of 140 +/- 13 mU/l and four subjects were infused with saline (0.45%). Isolated adipocytes and monocytes were used as models for studying insulin binding, while adipocytes were also used to study insulin action in vitro. Adipocyte insulin binding did not decrease following infusion of insulin (4.6 +/- 0.5 versus 4.4 +/- 0.4% per 2 X 10(5) cells, before and after, respectively), whereas monocyte insulin binding did (7.2 +/- 0.6 versus 6.2 +/- 0.6% per 10(7) cells, p less than 0.05). Initial rates of adipocyte 3-0-methyl glucose transport were decreased in the absence of insulin (basal) and at submaximally effective (33.3 pmol/l) but not at maximally effective insulin concentrations. At all insulin concentrations and in the absence of insulin, rates of glucose conversion to lipids were decreased more than 50% (p less than 0.05), whereas rates of glucose oxidation were unaffected. This decrease in the rates of conversion of glucose to lipids could not be accounted for by the decrease in rates of glucose transport. These results suggest that hyperinsulinaemia can cause insulin resistance in man and that, at least initially, this occurs at a post-receptor site. Furthermore, the discordant effect of hyperinsulinaemia on monocyte and adipocyte insulin binding indicates that monocyte insulin binding may not always reflect insulin binding in insulin-sensitive tissues.

3-O-Methylglucose↗
PubMed1985

Differential effects of insulin, antibodies against rat adipocyte plasma membranes, and other agents that mimic insulin action in rat adipocytes.

The effects of insulin and several insulin-mimetic agents on rat adipocyte D-glucose metabolism were studied in an effort to determine if any of the insulin-mimetic agents could be used to define the mechanism of insulin action. Antibodies against rat adipocyte plasma membranes have been characterized as having insulin-mimetic effects on glucose transport and these effects may be caused by divalent clustering of cell surface antigens. In contrast to insulin, antimembrane antibodies had little stimulatory effect on D-glucose conversion to lipids in isolated rat adipocytes, under conditions where both reagents stimulated D-glucose oxidation. Among other insulin-mimetic agents tested, the reagents hydrogen peroxide and concanavalin A most closely resembled insulin in their ability to increase both [14C]-CO2 and [14C]-lipid formation from [14C]D-glucose in rat adipocytes. Vitamin K5 and diamide had the unusual effect of inhibiting [1-14C]D-glucose conversion to [14C]-lipids at a concentration that gave maximal stimulation of glucose oxidation by rat adipocytes. Analysis of the lipid components into which glucose derivatives were incorporated revealed that insulin increased D-glucose incorporation into both nonesterified fatty acids and triglycerides and H2O2 and concanavalin A had similar effects. These findings argue against the possibility that insulin and the antimembrane antibodies or the insulin-mimetic agents other than H2O2 and concanavalin A share the same mechanism of action.

Adipose Tissue↗
PubMed1985

Uptake studies in adipocytes isolated from rainbow trout (Salmo gairdnerii). A comparison with adipocytes from rat and cat.

Adipocytes were isolated from mesenteric adipose tissue of rainbow trout (Salmo gairdnerii) by incubation of tissue slices at 20 degrees C in a buffer containing 3 mg collagenase per ml. These cells were compared to adipocytes from the cat and the rat, isolated by conventional technique (1 mg collagenase per ml buffer, incubation temperature 37 degrees C). Uptake studies of some metabolites were performed with fish, rat and in some cases cat adipocytes. At a glucose concentration of 0.33 mM, the glucose uptake into rat cells was more than twice as fast as in cells from the cat, and more than five times as fast as in trout cells. 2-Amino butyrate resembled glucose in relative uptake rates between species. Metabolite uptake into rat cells was specific, with different uptake rates for different metabolites. The uptake into trout adipocytes proceeded at similar rates for all metabolites tested, provided the concentrations were the same. The uptake rate of glucose into rat cells was stimulated by insulin. Insulin had no effect on glucose uptake into adipocytes from trout.

Adipose Tissue↗
PubMed1981

The effect of glucocorticoids on adipocyte corticotropin receptors and adipocyte responses.

A specific and sensitive assay for determining the binding of adrenocorticotropin (ACTH) to isolated rat adipocytes has been developed and utilized to study the effect of glucocorticoids on ACTH receptor. Measurement of the binding of tritiated ACTH (spec. act. 90 Ci/mmol) to adipocytes isolated from normal, adrenalectomized, and adrenalectomized dexamethasone-treated rats indicated that there are no differences among these three populations in either the magnitude or the affinity of the binding reaction. The binding interaction was found to be of high affinity (Kd = 5.23 + 1.92 . 10(-9) M and paralleled closely the stimulation of lipolysis (Km = 2.09 +/- 0.35 . 10(-9) M. About 16,300 receptors were calculated to be presented per adipocyte. Hormone-induced cyclic 3',5'-adenosine monophosphate production remained intact after adrenalectomy, thereby confirming that receptors are not lost during steroid deprivation. The lipolytic response did, however, become less sensitive to both ACTH and epinephrine following adrenalectomy. Pre-treatment of adrenalectomized rats with dexamethasone resulted in an increase in basal and hormone-stimulated levels of cyclic AMP and glycerol production to super-normal values. In adipocyte ghost preparations, ACTH and epinephrine sensitive adenylate cyclase activity was not decreased by adrenalectomy and dexamethasone administration did not result in a selective enhancement of ACTH sensitive adenylate cyclase activity. Our results indicate that glucocorticoids do not cause their permissive effects by specific regulation of the ACTH receptor on the adipocyte.

Adipose Tissue↗
PubMed2001

Fatty acids modulate porcine adipocyte differentiation and transcripts for transcription factors and adipocyte-characteristic proteins*

Porcine stromal-vascular cells (S/V cells) differentiate into adipocytes in vitro when presented with appropriate hormones and growth factors. Porcine S/V cells were differentiated in vitro in serum-free media with or without fatty acids to determine the effect of fatty acids on differentiation and on transcripts for peroxisome proliferator-activated receptor gamma (PPARgamma), CCAAT/enhancer binding protein alpha (C/EBPalpha), lipoprotein lipase (LPL) and adipocyte fatty acid binding protein (aP2). Differentiation was measured by Oil Red O staining and transcript concentrations were measured by Northern analysis using porcine riboprobes. Addition of 100 µM oleic acid (C18:1) for 5 days increased differentiation and the mRNA levels for PPARgamma, C/EBPalpha, LPL and aP2. Other medium- and long-chain fatty acids were less active. Adipocyte differentiation and transcript concentrations for PPARgamma, C/EBPalpha, LPL and aP2 were increased by C18:1 in a dose-related manner. Differentiation was greater at 10 days than at 5 days than at 1 day, and C18:1 increased differentiation at each time. Transcript concentrations were increased by C18:1 at 1 and 5 days, but not at 10 days. These results suggest that the main effect of C18:1 is on regulating gene expression (an acute or drug-like effect) rather than changing the membrane fluidity as a result of changing membrane fatty acid composition (a chronic or nutrient-like effect). Taken together, these results indicate that selected fatty acids modulate porcine adipocyte differentiation and transcripts for adipocyte differentiation-related proteins such as PPARgamma, C/EBPalpha, LPL and aP2.

Journal Article↗
PubMed2000

Nutritional deprivation reduces the transcripts for transcription factors and adipocyte-characteristic proteins in porcine adipocytes.

For an organism to survive during nutritional deprivation, it must be able to regulate the genes involved in energy metabolism. White adipose tissue is an energy source during fasting conditions. In adipose tissue, transcription factors regulate several adipocyte-characteristic proteins involved in differentiation and energy metabolism. We investigated the transcript concentrations of two key transcription factors, as well as the transcript concentrations of several adipocyte-characteristic proteins, and genes involved in adipocyte energy metabolism in the adipose tissue of pigs fasted for 72 hours. Nutritional deprivation resulted in decreased transcript concentrations of the transcription factors, peroxisome proliferator-activated receptor gamma, and CCAAT-enhancer-binding protein alpha. The transcript concentrations of several adipocyte-characteristic proteins, fatty acid synthase, glucose transporter 4, lipoprotein lipase, leptin, and adipocyte fatty acid binding protein were also significantly reduced. The insulin receptor transcript concentration did not change. We conclude that these transcript concentration changes are aimed collectively at adjusting energy partitioning to conserve energy during nutritional deprivation, thereby enabling survival.

Journal Article↗
PubMed1991

Characterization of the adipocyte ghost (Na+,K+) pump. Insights into the insulin regulation of the adipocyte (Na+,K+) pump.

The (Na+,K+) ATPase in plasma membranes isolated from rat adipocytes is insensitive to insulin (Lytton J., Lin, J.C., and Guidotti, G. (1985) J. Biol. Chem. 260, 1177-1184). For this reason, the characteristics of the (Na+,K+) pump in adipocyte ghosts, prepared by hypotonic lysis of adipocytes (Rodbell, M. (1967) J. Biol. Chem. 242, 5744-5750), were studied. Herein it is demonstrated that the (Na+,K+) pump in ghosts is identical to that described in isolated plasma membranes, sharing the following characteristics: 1) the Ki values for ouabain are 1.3 x 10(-7) M and 4.5 x 10(-5) M for the alpha 2 and alpha 1 isozymes, respectively; 2) the K0.5 values for sodium are 11.4 +/- 1.6 and 7.2 +/- 3.8 mM for the alpha 2 and alpha 1 isozymes, respectively; 3) both forms of the (Na+,K+) pump are insensitive to insulin stimulation, presumably because the activities are already maximal. The ghosts are not in an insulin-stimulated state because the activity of the glucose transporter is not increased as it is in ghosts prepared from insulin-treated cells. In addition, presented evidence demonstrates that ghost internal sodium concentration, [Na+]i, is very sensitive to changes in the activity of the (Na+,K+) pump. If the [Na+]i, of adipocytes is also very sensitive to the activity of the (Na+,K+) pump, the mechanism of insulin stimulation of the adipocyte (Na+,K+) pump requires reexamination.

Adipose Tissue↗
PubMed2006

Nitric oxide production from rat adipocytes is modulated by beta3-adrenergic receptor agonists and is involved in a cyclic AMP-dependent lipolysis in adipocytes.

It is established that the modulation of beta(3)-adrenoceptor function could be associated with impairment of lipolysis in white fat and be responsible for disturbed lipid metabolism. Though two isoforms of nitric oxide synthase (NOS) were reported in adipocytes, the role of nitric oxide (NO) in adipose tissue is still ambiguous. The present work was directed to study the interplay between NO production and beta-adrenoceptor/cyclic AMP (cAMP) pathway on lipid mobilization (glycerol and nonesterified fatty acids, NEFA) in cultures of rat adipocytes isolated from epididymal white adipose tissue. beta-Nonselective (isoprenaline) and beta(3)-selective (BRL-37344) agonists and the postadrenoceptor agents such as dibutyryl-cAMP, forskolin, and 3-isobutyl-1-methylxanthine significantly increased nitrite, glycerol, and NEFA levels with BRL-37344 being the most potent. Conversely, addition of beta-nonselective (propranolol) or beta(3)-selective (bupranolol) antagonist or the adenylyl cyclase inhibitor (SQ 22,536) significantly reduced beta-agonist-induced NO production and lipolysis. For beta-adrenoceptor agonists, antagonists, and their pairs, there was a positive correlation between medium nitrite and glycerol or NEFA with r(2) being 0.90 and 0.84, respectively. The possible relationship between NO and lipolysis was revealed after adipocyte treatment with nonspecific (N(omega)-nitro-l-arginine methyl ester, l-NAME) and specific (aminoguanidine) NOS inhibitors. Both l-NAME and aminoguanidine significantly inhibited the lipolytic effect of BRL-37344. Moreover, NO-donor (S-nitroso-N-acetylpenicillamine) at higher concentration increased basal glycerol and NEFA levels. 8-bromo-cyclic GMP had no effect on adipocyte lipolysis. These data suggest that beta-adrenergic lipolysis, specifically beta(3)-adrenoceptor effect, which is realized via the adenylyl cyclase/cAMP/protein kinase A signaling cascade, involves NO production downstream of beta(3)-adrenoceptor/cAMP pathway.

1-Methyl-3-isobutylxanthine↗
PubMed2001

Emergence during development of the white-adipocyte cell phenotype is independent of the brown-adipocyte cell phenotype.

In mammals, two types of adipose tissue are present, brown and white. They develop sequentially, as brown fat occurs during late gestation whereas white fat grows mainly after birth. However, both tissues have been shown to have great plasticity. Thus an apparent transformation of brown fat into white fat takes place during post-natal development. This observation raises questions about a possible conversion of brown into white adipocytes during development, although indirect data argue against this hypothesis. To investigate such questions in vivo, we generated two types of transgenic line. The first carried a transgene expressing Cre recombinase specifically in brown adipocytes under the control of the rat UCP1 promoter. The second corresponded to an inactive lacZ gene under the control of the human cytomegalovirus promoter. This dormant gene is inducible by Cre because it contains a Stop sequence between two loxP sequences, separating the promoter from the coding sequence. Adipose tissues of progeny derived by crossing independent lines established from both constructs were investigated. LacZ mRNA corresponding to the activated reporter gene was easily detected in brown fat and not typically in white fat, even by reverse transcriptase PCR experiments. These data represent the first direct experimental proof that, during normal development, most white adipocytes do not derive from brown adipocytes.

Adipocytes↗
PubMed2004

Mest/Peg1 imprinted gene enlarges adipocytes and is a marker of adipocyte size.

Obesity is a common and serious metabolic disorder in the developed world that is occasionally accompanied by type II diabetes, atherosclerosis, hypertension, and hyperlipidemia. We have found that mesoderm-specific transcript (Mest)/paternally expressed gene 1 (Peg1) gene expression was markedly enhanced in white adipose tissue of mice with diet-induced and genetically caused obesity/diabetes but not with streptozotocin-induced diabetes, which does not cause obesity. Administration of pioglitazone, a drug for type II diabetes and activator of peroxisome proliferator-activated receptor (PPAR)gamma, in obese db/db mice reduced the enhanced expression of Mest mRNA in adipose tissue, concomitant with an increase in body weight and a decrease in the size of adipose cells. Ectopic expression of Mest in 3T3-L1 cells caused increased gene expression of adipose markers such as PPARgamma, CCAAT/enhancer binding protein (C/EBP)alpha, and adipocyte fatty acid binding protein (aP)2. In transgenic mice overexpressing Mest in adipose tissue, enhanced expression of the adipose genes was observed. Moreover, adipocytes were markedly enlarged in the transgenic mice. Thus Mest appears to enlarge adipocytes and could be a novel marker of the size of adipocytes.

3T3-L1 Cells↗
PubMed2001

A novel potent antagonist of peroxisome proliferator-activated receptor gamma blocks adipocyte differentiation but does not revert the phenotype of terminally differentiated adipocytes.

The antidiabetic thiazolidinediones, which include troglitazone and rosiglitazone, are ligands for the nuclear receptor peroxisome proliferator-activated receptor gamma (PPARgamma). Their antihyperglycemic effects seem to be linked to the regulation of PPARgamma-responsive genes. Here, we report the characterization of a specific PPARgamma antagonist that blocks several of the biological activities of the PPARgamma agonist rosiglitazone. PD068235 inhibited rosiglitazone-dependent PPARgamma transcriptional activity with an IC(50) of 0.8 microM and rosiglitazone-stimulated in vitro coactivator association. The role of PPARgamma in the initiation of differentiation is well documented. In this study, we used PD068235 as a tool to evaluate the functional role of PPARgamma in the maintenance of the terminally differentiated state. Treatment of confluent, growth-arrested 3T3-L1 preadipocytes with PD068235 blocked adipocyte differentiation induced by the standard adipogenic hormonal mixture (insulin/dexamethasone/isobutylmethylxanthin) and fully antagonized rosiglitazone-induced adipogenesis. In contrast, long-term treatment of terminally differentiated 3T3-L1 adipocytes with PD068235 did not induce any obvious morphological changes and had no effect on basal lipolysis rates. In addition, in fully differentiated adipocytes PD068235 did not alter the basal expression of PPARgamma target genes aP2 and CAP, but it effectively blocked rosiglitazone-induced expression of both genes. These results suggest that in terminally differentiated adipocytes, the PPARgamma activity is minimal and may not be required for the maintenance of PPARgamma target gene expression.

3T3 Cells↗
PubMed2005

Dynamics of lipid droplet-associated proteins during hormonally stimulated lipolysis in engineered adipocytes: stabilization and lipid droplet binding of adipocyte differentiation-related protein/adipophilin.

In mature adipocytes, triglyceride is stored within lipid droplets, which are coated with the protein perilipin, which functions to regulate lipolysis by controlling lipase access to the droplet in a hormone-regulatable fashion. Adipocyte differentiation-related protein (ADRP) is a widely expressed lipid droplet binding protein that is coexpressed with perilipin in differentiating fat cells but is minimally present in fully differentiated cultured adipocytes. We find that fibroblasts ectopically expressing C/EBPalpha (NIH-C/EBPalpha cells) differentiate into mature adipocytes that simultaneously express perilipin and ADRP. In response to isoproterenol, perilipin is hyperphosphorylated, lipolysis is enhanced, and subsequently, ADRP expression increases coincident with it surrounding intracellular lipid droplets. In the absence of lipolytic stimulation, inhibition of proteasomal activity with MG-132 increased ADRP levels to those of cells treated with 10 mum isoproterenol, but ADRP does not surround the lipid droplet in the absence of lipolytic stimulation. We overexpressed a perilipin A construct in NIH-C/EBPalpha cells where the six serine residues known to be phosphorylated by protein kinase A were changed to alanine (Peri A Delta1-6). These cells show no increase in ADRP expression in response to isoproterenol. We propose that ADRP can replace perilipin on existing lipid droplets or those newly formed as a result of fatty acid reesterification, under dynamic conditions of hormonally stimulated lipolysis, thus preserving lipid droplet morphology/structure.

Adipocytes↗
PubMed2005

Effect of docosahexaenoic acid and arachidonic acid on the expression of adipocyte determination and differentiation-dependent factor 1 in differentiating porcine adipocytes.

Adipocyte determination and differentiation-dependent factor 1 (ADD1) drives the expression of several lipogenic genes in mammals. Polyunsaturated fatty acids decrease ADD1 mRNA abundance in differentiating porcine adipocytes. The current study was designed to explore the mechanisms by which PUFA inhibit the expression of ADD1 in porcine adipocytes. Porcine preadipocytes were differentiated for 24 h with 0 or 100 microM of docosahexaenoic acid (DHA) and mixtures of different concentrations of antioxidants to investigate the effect of DHA and antioxidants on the ADD1 mRNA abundance. We found the relative mRNA abundance was decreased by the addition of 100 microM DHA to the medium for porcine differentiating adipocytes, and adding an antioxidant mixture to the medium prevented part of the decrease in ADD1 mRNA abundance. These data suggest that DHA decreased the steady-state transcription factor ADD1 mRNA through a mechanism related to fatty acid peroxidation. Indeed, adding 7.5 microM vitamin E (a natural antioxidant) also restored the concentrations of ADD1 and fatty acid synthase mRNA, which were decreased by DHA treatment; however, the DHA or the antioxidant treatment did not change the expression of antioxidation genes (superoxide dismutase 1 and glutathione peroxidase 1) in porcine stromal vascular cells. When supplemented with the eicosanoid synthesis pathway inhibitors, the inhibition of the expression of ADD1 by arachidonic acid was partially recovered. These results suggest that the mechanism by which PUFA decrease ADD1 mRNA is due to the metabolic product of eicosanoids and peroxidation of these PUFA.

Adipocytes↗
PubMed1991

The CCAAT/enhancer binding protein and its role in adipocyte differentiation: evidence for direct involvement in terminal adipocyte development.

During the course of differentiation of preadipocytes into adipocytes, several differentiation-linked genes are activated synchronously with morphological changes. To follow this process we have used 3T3-F442A cells, known to undergo adipocyte conversion with high frequency. Accumulation of lipid droplets in the cytoplasm constitutes an easily visualized sign of the terminally differentiated phenotype. In this report we demonstrate that expression of the CCAAT/enhancer binding protein (C/EBP) is an important factor in determining the ability to accumulate lipid droplets in terminally differentiated adipocytes. In one experiment we can suppress C/EBP expression through administration of hydrocortisone to differentiating 3T3-F442A cells, which is accompanied by an inability of the cells to accumulate lipid. In another experiment a C/EBP antisense expression vector has been stably introduced into 3T3-F442A cells and as compared with control cells, a 62% decrease of C/EBP mRNA (p less than 0.01) is demonstrated. This decrease of C/EBP mRNA is accompanied by a change in cellular morphology characterized by a reduced ability to form lipid droplets. We can also demonstrate a correlation between the degree of reduction of C/EBP mRNA and the amount of lipid present in the cells. These findings strongly support the view that C/EBP is a necessary component of terminal adipocyte differentiation.

3T3 Cells↗
PubMed1975

Permeability characteristics of the adipocyte cell membrane and partitioning characteristics of the adipocyte triglyceride core.

The unidirectional rates of passive permeation of a homologous series of saturated fatty acids and bile acids into rat epididymal adipocytes were measured to determine the permeability characteristics of this mammalian cell membrane. For fatty acids containing 5 to 12 carbon atoms the logarithm of the permeability coefficient was a linear function of the number of carbons in the fatty acid chain: fatty acids with less than five carbon atoms showed anomalously high permeabilities. Using the data for the fatty acids with 5 to 12 carbon atoms, the incremental free energy of transfer (delta delta F w leads to l) of the -CH2 moiety from the aqueous environment into the fat cell was calculated to equal -547 cal mole-1. The delta delta F w leads to l of the -OH moiety calculated from data using bile acids as the probe molecules was +1,225 cal mole-1. After rupturing the fat cells by freeze-thawing, partition ratios also were measured between bubber and the lipid phase of the adipocyte core using both the fatty acid series and a series of terminal diols as probe molecules. Using these partition ratios delta delta F w leads to l for the -CH2 and -OH substituent groups was calculated to equal -830 and +2,070 cal mole-1, respectively. On the basis of these studies, two conclusions were drawn. First, like many epithelial surfaces and the erythrocyte membrane, the fat cell membrane exhibits anomalously high permeabilities to small molecular weight, polar compounds. Since this behavior in the adipocyte, as in the erythrocyte, cannot be attributed to structures such as tight junctions, it must be explained on the basis of some physico-chemical feature of the cell membrane itself. Secondly, the values of the delta delta F w leads to l indicate that the adipocyte membrane is less polar than the intestinal and gallbladder membranes but more polar than the membranes of Nitella and the erythrocyte.

Adipose Tissue↗