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G Ailhaud

Publications and source records attributed to G Ailhaud.

At least 55 records · Page 3Linked to original sources
PubMed1996

Modulation of vascular tone and glycerol levels measured by in situ microdialysis in rat adipose tissue.

Changes in blood flow induced by the beta-adrenoceptor agonist isoproterenol (Iso) and a stable analogue of the major metabolite of arachidonic acid in adipose tissue, carbaprostacyclin (cPGI2), have been studied in rat periepididymal fat pad with in situ microdialysis measuring the distribution ratio of 0.2% ethanol in the dialysate (outflow) to that in the perfusate (inflow) (O/I ratio). Local perfusions of 1 microM cPGI2 or 1 microM Iso led to reversible decreases of the O/I ratio that were similar to the decrease induced by the vasodilating reference drug hydralazine (Hydra, 630 microM). Interestingly, a continuous perfusion of Hydra at a submaximal vasodilating concentration (63 microM) was sufficient to prevent further vasodilatation induced by Iso or cPGI2. To take advantage of this observation, experiments were designed to evaluate the influence of the vasodilating effect of Iso or cPGI2 on the ability of either to induce lipolysis in vivo. The results showed that the vasodilating effect of Iso could contribute to glycerol removal from the extracellular fluid and demonstrate that cPGI2 was devoid of lipolytic activity.

Adipose Tissue↗
PubMed1995

Increased expression in adipocytes of ob RNA in mice with lesions of the hypothalamus and with mutations at the db locus.

The gene product of the recently cloned mouse obese gene (ob) is important in regulating adipose tissue mass. ob RNA is expressed specifically by mouse adipocytes in vivo in each of several different fat cell depots, including brown fat. ob RNA is also expressed in cultured 3T3-442A preadipocyte cells that have been induced to differentiate. Mice with lesions of the hypothalamus, as well as mice mutant at the db locus, express a 20-fold higher level of ob RNA in adipose tissue. These data suggest that both the db gene and the hypothalamus are downstream of the ob gene in the pathway that regulates adipose tissue mass and are consistent with previous experiments suggesting that the db locus encodes the ob receptor. In db/db and lesioned mice, quantitative differences in expression level of ob RNA correlated with adipocyte lipid content. The molecules that regulate expression level of the ob gene in adipocytes probably are important in determining body weight, as are the molecules that mediate the effects of ob at its site of action.

Adipocytes↗
PubMed1995

Cloning of a protein that mediates transcriptional effects of fatty acids in preadipocytes. Homology to peroxisome proliferator-activated receptors.

Exposure of preadipocytes to long chain fatty acids induces expression of several gene markers of adipocyte differentiation. This report describes the cloning, from a preadipocyte library, of a cDNA encoding a fatty acid-activated receptor, FAAR. The cDNA had the characteristics and ligand-binding domains of nuclear hormone receptors and encoded a 440 amino acid protein related to peroxisome proliferator-activated receptors, PPAR. The deduced protein sequence was 88% homologous to that of hNUC I, isolated from human osteosarcoma cells. FAAR mRNA was abundant in adipose tissue, intestine, brain, heart, and skeletal muscles and less abundant in kidney, liver, testis, and spleen. The mRNA was undetectable in growing Ob1771 and 3T3-F442A preadipocytes, was strongly induced early during differentiation, and was increased by fatty acid. Transcription assays using hybrid receptor showed strong stimulation by fatty acid and weaker induction by fibrates. Transfection of 3T3-C2 fibroblasts, with a FAAR expression vector, conferred fatty acid inducibility of the adipocyte lipid-binding protein and the fatty acid transporter. Transcriptional induction of these genes exhibited inducer specificity identical to that described in preadipocytes. In summary, the data indicate that FAAR is likely a mediator of fatty acid transcriptional effects in preadipocytes.

Adipocytes↗
PubMed1995

[Adipose tissue. Hidden aspects].

Adipose differentiation is a sequential process (adipoblasts-->preadipocytes-->adipocytes). Adipogenic factors are only involved in the terminal differentiation of preadipocytes to adipocytes by means of circulating hormones (growth hormone, glucocorticoids, insulin, triiodothyronine) and locally produced hormones (prostacyclin, IGF-I). Fatty acids also behave as hormones and act as transcriptional regulators of lipid-related genes. Once differentiated, adipocytes become secretory cells able to synthetize and release numerous peptide and nonpeptide compounds, suggesting a potential link between excess of adipose tissue mass and various physiopathologic consequences.

Adipocytes↗
PubMed1995

Cholesteryl ester transfer protein (CETP) mRNA abundance in human adipose tissue: relationship to cell size and membrane cholesterol content.

Cholesteryl ester transfer protein (CETP) has a well-defined role in plasma neutral lipid transport. CETP synthesized by human adipose tissue may contribute to the plasma CETP pool. CETP mRNA abundance increases in subcutaneous adipose tissue in response to cholesterol feeding and we have hypothesized that CETP gene expression is regulated by a specific pool of cellular sterol. In the present study, we have quantified CETP mRNA levels in subcutaneous adipose tissue of 10 female subjects using a solution hybridization RNase protection assay. Particulate (membrane cholesterol) and lipid droplet cholesterol (core cholesterol) were determined by gas chromatography. CETP mRNA abundance in these adipose tissue specimens correlated significantly with membrane cholesterol expressed as a fraction of membrane protein (r = 0.67, P = 0.031). There was also a linear relationship between CETP mRNA abundance and membrane cholesterol to core triglyceride ratio (r = 0.77, P = 0.009) and a strong correlation between the percentage of cellular cholesterol in the membrane fraction (ratio of membrane to core cholesterol) and CETP mRNA abundance (r = 0.91, P = 0.0002). In contrast, there was a negative relationship between each of lipid droplet cholesterol and triglyceride and CETP mRNA levels. Human adipose tissue maintained in organ culture for several days was shown to secrete CETP into the culture medium. Incubation with cholesterol-rich chylomicron remnants elicited a dose-dependent increase in both membrane and core cholesterol and a concomitant increase in the level of CETP mRNA. These studies demonstrate that adipose tissue CETP mRNA abundance is a function of membrane cholesterol concentration rather than lipid droplet cholesterol and that CETP mRNA increases with adipocyte cholesterol enrichment via chylomicron remnants. CETP gene expression is highest in small lipid-poor adipocytes, suggesting that CETP synthesized and secreted by adipocytes may have a role in promoting cellular cholesterol accumulation.

Adipose Tissue↗
PubMed1994

Fatty acids and retinoids act synergistically on adipose cell differentiation.

Fatty acids and retinoids have been recently reported to act as positive effectors of adipose cell differentiation. Treatment of Ob1771 preadipose cells with selective agonists of retinoic acid receptors (RARs) in the presence of alpha-bromopalmitate, a non-metabolized fatty acid, led to a potent synergy in regard to the differentiation process, as assayed by the activity of glycerol-3-phosphate dehydrogenase. The most potent synergy was observed with compound CD 367, a potent agonist of RARs as well as with compound Am 580, a specific agonist of RAR alpha. Northern blot analysis of poly(A)+ mRNA from cells treated with compound CD 367, alpha-bromopalmitate, or a combination of both agonists, did not show a dramatic effect, if any, on the expression of RAR alpha, RAR gamma, RXR alpha and RXR beta genes. The results are discussed in light of the formation of heterodimers between RARs, RXRs and members of the family of peroxisome proliferator-activated receptors (PPARs).

Adipocytes↗
PubMed1994

Rise in cytosolic Ca2+ abolishes in preadipose cells the expression of lipoprotein lipase stimulated by growth hormone.

Lipoprotein lipase (LPL) is known to be an early marker of adipose cell differentiation. Growth hormone (GH) stimulates in preadipose Ob1771 cells the expression of LPL gene and this effect is mediated at least in part by c-fos protooncogene, the expression of which is transiently activated by a protein kinase C-dependent pathway (Barcellini-Couget et al., Endocrinology, 1993, 132: 55-60). Since GH stimulates the formation of diacylglycerol from phosphatidylcholine independently of Ca2+ mobilization, the role of Ca2+ was studied in regard to LPL gene expression stimulated by GH. The results obtained in the presence of Ca2+ ionophores show that a rise in intracellular free Ca2+ abolishes this expression but has no effect on the expression of various adipose-related genes, including the transient expression of c-fos protooncogene. Therefore, the inability of preadipose cells to mobilize Ca2+ in response to GH, at an early stage of the differentiation process, appears as a prerequisite for the maximal expression of LPL.

Adipocytes↗
PubMed1994

Prostacyclin as an indicator of preadipocyte transformation: studies in vivo by microdialysis and in vitro.

Nontransformed (Ob1771) and polyoma virus-transformed (Ob17PY) mouse cells from the preadipocyte Ob17 clonal line have been compared in their ability to release prostaglandins in vitro as well as in vivo as assayed by in situ microdialysis. Prostaglandin FE2, prostaglandin-2 alpha and mainly prostacyclin are released in larger amounts (4- to 10-fold) by Ob17PY cells in vitro and Ob17PY-induced tumors in vivo as compared to Ob1771 preadipocytes in vitro and periepididymal adipose tissue in vivo. In contrast to Ob1771 preadipocytes, none of these prostanoids appear to be involved in the control of proliferation or differentiation of Ob17PY cells in serum-free culture medium. However, prostacyclin, the level of which is the most affected by transformation, might be considered as a valuable indicator of fibrosarcoma development.

Adipocytes↗
PubMed1994

Proliferation and differentiation of rat adipose precursor cells in chemically defined medium: differential action of anti-adipogenic agents.

Primary rat adipose precursor cells, maintained in the minimal chemically defined medium (ITT medium) able to promote differentiation, have been used to investigate the ability of several agents to modulate their proliferation and their differentiation. Fetuin and fibroblast growth factor (FGF), which exhibited a strong and a weak mitogenic activity, respectively, do not significantly affect the proportion of differentiated cells as indicated by glycerol-3-phosphate dehydrogenase (GPDH) activity values. In contrast, carbaprostacyclin (cPGI2), a stable analogue of prostacyclin, behaves as a true adipogenic factor leading to a 4 to 5-fold increase in GPDH-specific activities with no significant effect on cell growth. Submaxillary gland kallikrein (SMGK), transforming growth factor-beta (TGF-beta) and tumor necrosis factor-alpha (TNF-alpha) behave as growth-promoting agents but at the same time elicit a dose-dependent inhibition of differentiation. Epidermal growth factor (EGF) and prostaglandin F2 alpha (PGF2 alpha) do not show any effect on cell proliferation at concentrations which exert a maximal inhibitory action on differentiation. Upon removal of EGF from the culture medium, complete resumption of differentiation occurs, whereas upon removal of PGF2 alpha or SMGK, complete resumption only takes place when differentiation is triggered by cPGI2. Upon removal of TNF-alpha, a partial resumption of differentiation is observed, whereas no subsequent differentiation is observed upon TGF-beta removal. These results emphasize the adipogenic, nonmitogenic role of cPGI2 and also allow the distinction between the various adipogenic/mitogenic factors which affect adipose cell differentiation.

Adipocytes↗
PubMed1994

Retinoids are positive effectors of adipose cell differentiation.

Retinoids, especially all-trans retinoic acid (t-RA), have been reported in the last decade to inhibit the differentiation of preadipose cells. In those studies, however, the concentrations of t-RA were supraphysiological (0.1-10 microM range). In contrast we show that, when present at concentrations below or close to the Kd values of retinoic acid receptors, retinoids behave as potent adipogenic hormones (1 pM to 10 nM range). As shown by the use of specific ligands for each RAR subtype, these positive effects on adipose differentiation involve in particular the RAR alpha subtype, and have been observed in Ob17 cells exposed to serum-supplemented or serum-free medium, and in rat preadipocytes exposed to serum-free medium. Among the two classes of retinoid acid receptors (RARs) and retinoid X receptors (RXRs), RAR alpha, RAR gamma, RXR alpha and RXR beta mRNAs could be detected in growing adipoblasts and were found to be increased in committed preadipocytes and differentiated cells upon retinoid treatment. Like other adipogenic hormones, retinoids were only effective in the terminal differentiation process leading from preadipocytes to adipocytes.

Adipocytes↗
PubMed1994

Differentiation of preadipose cells: paracrine role of prostacyclin upon stimulation of adipose cells by angiotensin-II.

Prostacyclin (PGI2), the major metabolite of arachidonic acid in adipose tissue, has been shown to play a key role in the process of preadipose cell differentiation in vitro. Moreover, angiotensin-II (Ang II) is able to induce the production of PGI2 in suspensions of isolated adipocytes as well as in the interstitial fluid of rat adipose tissue. A possible role of Ang II in the control of the autocrine-paracrine adipogenic effect of PGI2 has been investigated, using cells of the Ob1771 preadipocyte clonal line cultured in serum-free chemically defined medium. Whereas both preadipose and adipose cells were able to produce PGI2 upon exposure to arachidonic acid, only adipose cells were able to do so when challenged with Ang II. In agreement with this observation, the ability of Ang II to induce preadipose cells to differentiate required the simultaneous presence of differentiated cells. Such coculture experiments show that the promoting effect of Ang II on preadipose cell differentiation was strongly reduced by aspirin, antibodies able to neutralize PGI2, and the AT2 receptor antagonist PD123177, but not by the AT1 receptor antagonist losartan. Together, these results support Ang II as being able, by means of binding to a receptor of the AT2 subtype present in adipose cells, to control the adipogenic effect of PGI2 through a paracrine mode of action.

Adipocytes↗
PubMed1994

Evidence for a common mechanism of action for fatty acids and thiazolidinedione antidiabetic agents on gene expression in preadipose cells.

In diabetic rodents, thiazolidinediones are able to improve insulin sensitivity of target tissues and to reverse, at least partially, the diabetic state. The effects of these drugs on phenotypic expression in various tissues, including adipose tissue, have been reported. We report here that a new thiazolidinedione compound, BRL 49653, exerts, in preadipose cells, potent effects on the expression of genes encoding proteins involved in fatty acid metabolism. These effects of BRL 49653 in Ob 1771 preadipose cells are similar, in terms of kinetics, reversibility, specificity of genes affected, and requirement for protein synthesis, to those already described for natural or nonmetabolizable fatty acids. Moreover, when used at submaximally effective concentrations, BRL49653 and 2-bromopalmitate act in an additive manner to induce gene expression in preadipose cells, but this additivity of effects is lost when one of the compounds is used at a maximally effective concentration. These observations, suggesting similar mechanisms of action for thiazolidinediones and fatty acids, are strongly supported by the demonstration that (i) both molecules activate, in a heterogolous trans-activation assay, the same nuclear receptor of the steroid/thyroid hormone nuclear receptor superfamily and (ii) transfection of 3T3-C2 fibroblasts with an expression vector for this nuclear receptor confers thiazolidinedione inducibility of adipocyte lipid-binding protein gene expression.

3T3 Cells↗
PubMed1994

In situ microdialysis of prostaglandins in adipose tissue: stimulation of prostacyclin release by angiotensin II.

In order to clarify the physiological roles that PGE2 and PGI2, the two major metabolites of arachidonic acid in adipose tissue could play in vivo, their measurements have been undertaken in the interstitial fluid of rat periepididymal adipose tissue using in situ microdialysis. This technique appears suitable with a rather high dialysis yield (70%) for the measurement of prostaglandins. The basal equilibrium extracellular concentrations of 6-keto-PGF1 alpha (the stable metabolite of PGI2) and PGE2 can be estimated to 1 and 0.3 nM, respectively. Experiments designed to study the hormonal regulation of in situ PGI2 and PGE2 production show that (i) lipolysis induced by local perfusion of 10(-6) M isoproterenol is not accompanied by an increase of either 6-keto-PGF1 alpha or PGE2 in the dialysate but, in contrast (ii) perfusion of angiotensin II (10(-7)-10(-5) M) leads, independently of triacylglycerol hydrolysis, to a transient dose-dependent and indomethacin-sensitive increase of released 6-keto-PGF1 alpha with no change in released PGE2. Therefore, in vivo PGI2 appears as the major hormonally regulated prostaglandin in rat adipose tissue, and angiotensin II appears as a physiological effector of its extracellular release.

Adipose Tissue↗
PubMed1994

Fatty acids as signal transducing molecules: involvement in the differentiation of preadipose to adipose cells.

Fatty acids are important metabolic substrates for adipose tissue and act, in preadipose cells, as potent inducers of various proteins directly involved in their metabolism. We have investigated the long-term effects of fatty acids on the conversion process of preadipose Ob1771 cells to adipose cells. Chronic exposure of cells to palmitate led, in a dose-dependent manner, to a strong stimulation of cell differentiation; this effect was confined to terminal events whereas fatty acids did not affect expression of early genes related to commitment of adipoblasts to preadipose cells. Adipogenic action of fatty acids did not require their metabolism as 2-bromopalmitate, which is not metabolized by preadipose cells, was more effective than palmitate in inducing differentiation. The critical role of fatty acids occurred during the first 3 days of the differentiation process and led subsequently to an increase in the number of differentiated cells by means of enhancement of post-confluent mitoses and over-expression of terminal differentiation-related genes. These results thus provide, at the molecular level, a potential link observed in vivo between an increase in fatty acid supply induced by high-fat or high-carbohydrate diets and the hyperplastic development of adipose tissue.

Adipocytes↗
PubMed1993

Differential expression of adenosine A1 and A2 receptors in preadipocytes and adipocytes.

Multiple physiological functions have been described to be affected by adenosine in numerous cell types. A comparative study of the expression of adenosine receptors has been performed in preadipocytes and adipocytes from rat epididymal fat pad. The results show that, in agreement with its well known antilipolytic effect, adenosine induces a negative modulation of adenylate cyclase via the A1 receptor present in adipocytes. By contrast, the A2 receptor subtype, which is positively coupled to adenylate cyclase, is herein demonstrated to be only expressed in adipose precursor cells. This expression allows, in chemically defined medium, the adenosine analogue NECA, by means of its ability to elevate cAMP concentration, to potentiate differentiation. These findings emphasize the role that adenosine might play as a bimodal regulatory extracellular signal in adipose tissue development.

Adenosine↗
PubMed1993

Interaction of reconstituted high density lipoprotein discs containing human apolipoprotein A-I (ApoA-I) variants with murine adipocytes and macrophages. Evidence for reduced cholesterol efflux promotion by apoA-I(Pro165-->Arg).

Interaction of cells with both native and reconstituted high density lipoproteins (rHDL) containing apolipoprotein (apo) A-I mediates efflux of cellular cholesterol. To characterize structural requirements for this activity in apoA-I, six different genetic apoA-I variants and the corresponding normal allele products were isolated from heterozygous carriers, reconstituted with dimyristoylphosphatidylcholine (DMPC) into discoidal HDL and compared with regard to their ability to release intracellular cholesterol from murine adipocytes and peritoneal macrophages. In previous studies we determined the amino acid changes of these variants: Pro3-->Arg, Pro4-->Arg, Lys107-->0, Lys107-->Met, Pro165-->Arg, and Glu198-->Lys (von Eckardstein, A., Funke, H., Walter, M., Altland, K., Benninghoven, A., and Assmann, G. (1990) J. Biol. Chem. 265, 8610-8617) and demonstrated that all apoA-I variants except apoA-I(Lys107-->0) form discoidal HDL particles with phosphatidylcholine analogues indistinguishable from normal apoA-I (Jonas, A., von Eckardstein, A., Kezdy, K. E., Steinmetz, A., and Assmann, G. (1991) J. Lipid Res. 32, 95-106). In the present study, all apoA-I.DMPC complexes except those containing apoA-I(Pro165-->Arg) promoted cholesterol efflux as effectively as those containing normal apoA-I. Cholesterol efflux from adipocytes obtained after 180 min of incubation with apoA-I(Pro165-->Arg).DMPC complexes was decreased by 30% although this variant was bound to adipocytes with normal affinity. By contrast, apoA-I(Lys107-->Met).DMPC complexes were decreased in their binding affinity compared to normal apoA-I.DMPC complexes but normally promoted cholesterol efflux. Incubation of mouse peritoneal macrophages with apoA-I(Pro165-->Arg).DMPC complexes did also result in a 30% decreased efflux of radiolabeled cholesterol if compared to rHDL with the normal allele product from the same donor. Together the observations suggest that the substitution of proline at residue 165 interferes with the formation of a structural domain in apoA-I that is crucial for cellular cholesterol efflux stimulation. Furthermore, our results suggest that binding of HDL to adipocytes and cholesterol efflux promotion by HDL requires different structural domains.

Adipose Tissue↗
PubMed1993

Cloning of alpha 2 chain of type VI collagen and expression during mouse development.

We have previously described the molecular cloning of a cDNA probe which detects a 6 kb mRNA termed pOb24. pOb24 mRNA appeared to be a marker of the preadipose state both in vitro and in vivo. A pOb24 genomic fragment was isolated and used to screen cDNA libraries in order to isolate the full-length pOb24 cDNA and to identify the corresponding protein. The screening yielded a new cDNA clone which detected a 3.7 kb mRNA species in addition to the 6 kb mRNA species. Sequences at the 3' end of the 6 kb and 3.7 kb mRNAs indicate that both mRNAs are generated from the same gene through the use of two different polyadenylation sites. The protein encoded by the 3.7 kb mRNA appeared to be homologous to the human alpha 2 chain of type VI collagen (A2COL6). The expression of the A2COL6 gene was not confined to adipose tissue; mRNA species can be detected in ovaries, adrenal glands and lungs but not in liver and skeletal muscle. The expression appeared specific for initial phase(s) of cell differentiation since it is parallel to that of the MyoD1 gene during muscle embryogenesis in vivo. In the myogenic C2C12 cell line, the A2COL6 gene exhibited the same regulation as MyoD1 and myogenin genes. These results indicate that A2COL6 gene expression is a marker of the preadipose state, but may also be a marker of other differentiation programmes such as that of muscle.

Amino Acid Sequence↗