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N Moustaid

Publications and source records attributed to N Moustaid.

10 recordsLinked to original sources
PubMed1999

The agouti gene product stimulates pancreatic [beta]-cell Ca2+ signaling and insulin release.

Ubiquitous expression of the mouse agouti gene results in obesity and hyperinsulinemia. Human agouti is expressed in adipose tissue, and we found recombinant agouti protein to stimulate lipogenesis in adipocytes in a Ca(2+)-dependent fashion. However, adipocyte-specific agouti transgenic mice only became obese in the presence of hyperinsulinemia. Because intracellular Ca(2+) concentration ([Ca(2+)](i)) is a primary signal for insulin release, and we have shown agouti protein to increase [Ca(2+)](i) in several cell types, we examined the effects of agouti on [Ca(2+)](i) and insulin release. We demonstrated the expression of agouti in human pancreas and generated recombinant agouti to study its effects on Ca(2+) signaling and insulin release. Agouti (100 nM) stimulated Ca(2+) influx, [Ca(2+)](i) increase, and a marked stimulation of insulin release in two beta-cell lines (RIN-5F and HIT-T15; P < 0. 05). Agouti exerted comparable effects in isolated human pancreatic islets and beta-cells, with a 5-fold increase in Ca(2+) influx (P < 0.001) and a 2.2-fold increase in insulin release (P < 0.01). These data suggest a potential role for agouti in the development of hyperinsulinemia in humans.

Agouti Signaling Protein↗
PubMed1998

Effects of a potent melanocortin agonist on the diabetic/obese phenotype in yellow mice.

OBJECTIVE: To test the hypothesis that a melanocortin agonist can reverse obesity and insulin resistance in mice overexpressing the agouti protein. EXPERIMENTAL MODEL: Mice overexpressing the agouti protein either by transgene introduction (beta-actin promotor) or by mutation (Ay). DESIGN: NDPMSH was tested for pharmacokinetic suitability. NDPMSH at various doses was administered subcutaneously twice a day for 2-3 weeks. MEASUREMENTS: Fur pigmentation, various fatness parameters (core temperature, fat pad weight and body weight), blood glucose and hormones, fatty acid synthase measurement. RESULTS: NDPMSH caused fur pigmentation and core temperature changes, but failed to affect any metabolic parameters in agouti-dependent manner. CONCLUSION: NDPMSH, as a representation melanocortin agonist, does not compete with agouti in reversing agouti-dependent metabolic effects. This suggests that 1) agouti works via a receptor other than a melanocortin receptor to mediate its metabolic effects, 2) agouti-dependent metabolic effects are mediated through melanocortin receptors but not via antagonism of these receptors, or 3) NDPMSH is pharmacodynamically an inappropriate molecule for these types of studies.

Agouti Signaling Protein↗
PubMed1997

Angiotensin II increases lipogenesis in 3T3-L1 and human adipose cells.

Angiotensin II (Ang II) is one of numerous hormones recently shown to be synthesized and secreted by adipose cells. Although the function of Ang II in adipose tissue is unknown, several studies indirectly suggest that it may be involved in control of adiposity. Little is known, however, about direct actions of Ang II in adipose cells. To further investigate this issue, we first characterized the type of Ang II receptors in 3T3-L1 adipocytes. We then tested the hypothesis that Ang II exerted direct actions on adipocyte metabolism using both 3T3-L1 and human adipocyte models. We report here that Ang II significantly increased triglyceride content and the activities of two key lipogenic enzymes (fatty acid synthase, FAS and glycerol-3-phosphate dehydrogenase, GPDH) in 3T3-L1 adipocytes, and that these effects were mediated through the type-2 Ang II receptor. We also report that Ang II exerted similar effects in human adipose cells maintained in primary culture. Finally, we demonstrate that Ang II increased the transcription rate of the FAS and ob genes in 3T3-L1 and human adipose cells. These results indicate that Ang II may be involved in control of adiposity through regulation of lipid synthesis and storage in adipocytes.

3T3 Cells↗
PubMed1996

Upregulation of adipocyte metabolism by agouti protein: possible paracrine actions in yellow mouse obesity.

Mutations leading to ectopic expression of the murine agouti gene (a) result in progressive obesity. To further characterize this model, we analyzed adipose and hepatic mRNA levels for fatty acid synthase (FAS) and stearoyl-CoA desaturase (SCD), two key enzymes in de novo fatty acid synthesis and desaturation, respectively. FAS and SCD mRNA in both tissues of obese (Avy) mice were dramatically increased relative to lean (ala) controls. Excessive expression of these genes in this model could be due to direct effects of the agouti gene product; to test this possibility we treated 3T3-L1 adipocytes in vitro with recombinant agouti protein. Agouti treatment increased FAS and SCD mRNA levels by 1.5- and 4-fold, respectively. In addition, FAS activity and triglyceride content were 3-fold higher in agoutitreated 3T3-L1 cells relative to controls; these effects were attenuated by simultaneous treatment with a calcium channel blocker (nitrendipine). These data demonstrate that the agouti protein can directly increase lipogenesis in adipocytes and suggest that these effects are mediated through an intracellular calcium-dependent mechanism.

Adipocytes↗
PubMed1996

The effects of calcium channel blockade on agouti-induced obesity.

We have previously observed that obese viable yellow (Avy/a) mice exhibit increased intracellular Ca2+ ([Ca2+]i) and fatty acid synthase (FAS) gene expression; further, recombinant agouti protein increases in cultured adipocytes and these effects are inhibited by Ca2+ channel blockade. Accordingly, we determined the effect of Ca2+ channel blockade (nifedipine for 4 wk) on FAS and obesity in transgenic mice expressing the agouti gene in a ubiquitous manner. The transgenic mice initially were significantly heavier (30.5+/-0.6 vs. 27.3+/-0.3 g; P<0.001) and exhibited a 0.81 degrees C lower initial core temperature (P<0.0005), an approximately twofold increase in fat pad weights (P=0.002), a sevenfold increase in adipose FAS activity (P=0.009), and a twofold increase in plasma insulin level (P<0.05) compared to control mice. Nifedipine treatment resulted in an 18% decrease in fat pad weights (P<0.007) and a 74% decrease in adipose FAS activity (P=0.03), normalized circulating insulin levels and insulin sensitivity (P<0.05), and transiently elevated core temperature in the transgenic mice, but was without effect in the control mice. These data suggest that agouti regulates FAS, fat storage, and possibly thermogenesis, at least partially, via a [Ca2+]i-dependent mechanism, and that Ca2+ channel blockade may partially attenuate agouti-induced obesity.

Adipose Tissue↗
PubMed1990

Long term regulation of glucose transporters by insulin in mature 3T3-F442A adipose cells. Differential effects on two glucose transporter subtypes.

The question of a long term regulatory role of insulin on adipocyte glucose transporter content was addressed using the differentiating or fully mature 3T3-F442A adipocytes. Glucose transport was measured in intact cells. Glucose transporter content in plasma membranes and low density microsomes (LDM) was assessed by cytochalasin B binding and Western analysis. In insulin- versus spontaneously differentiated adipocytes, glucose transport and glucose transporters content of plasma membranes and LDM were increased 5-, 4-, and 2-fold, respectively. Insulin deprivation for 24 h induced a redistribution of glucose transporters in those cells which then displayed 2-fold higher glucose transport and glucose transporter content in plasma membranes than spontaneously differentiated cells and 3-fold more glucose transporters in LDM. When fully insulin-differentiated adipocytes were insulin-deprived for 4 days, there was a marked decrease in glucose transporters in both membrane fractions that was fully reversible by reexposing the cells to insulin for 4 days. Glucose uptake changes were closely proportionate to changes in glucose transporter content of plasma membranes as assessed by an antiserum to the C-terminal peptide of the erythrocyte/HepG2/brain-type glucose transporter. When Western blots were immunoblotted with 1F8 monoclonal antibody, specific for glucose transporter in insulin responsive tissues, an abundant immunoreactive protein was detected in both plasma membranes and LDM but the amount of this glucose transporter did not change with insulin exposure in any membrane fractions. In conclusion, insulin plays a long term regulatory role on cultured adipocyte glucose transporter content through a selective effect on the erythrocyte/HepG2/brain-type glucose transporter.

Adipose Tissue↗
PubMed1990

Analysis of gene expression during adipogenesis in 3T3-F442A preadipocytes: insulin and dexamethasone control.

In the present study, we have investigated dexamethasone and insulin regulation of the expression of adipose-specific mRNA, namely, glycerophosphate dehydrogenase (G3PDH) and adipsin, at different stages of differentiation. During adipose conversion, insulin promotes an accumulation of G3PDH mRNA which is linked to cell differentiation; in fully differentiated cells, insulin is not required to maintain G3PDH gene expression. Differentiating cells in serum deprived medium already exhibit, at day 1, a maximal amount of mRNA encoding for adipsin, which is tenfold decreased by 10 nM of insulin; insulin also exerts a negative effect on the abundance of adipsin mRNA in mature cells. This result indicates that adipsin appears to be a very early marker of adipose conversion, the gene expression of which is down-regulated by the presence of insulin. Dexamethasone (DEX) decreases the G3PDH message at all stages of adipose conversion, while it promotes the accumulation of adipsin mRNA mainly in differentiating cells. In DEX-treated adipocytes, the transcription efficiency of the G3PDH gene is not altered, and reduction to 50% of the message is due essentially to an approximately twofold decrease in its half-life.

Adipose Tissue↗
PubMed1990

Analysis of the glucocorticoid receptor during differentiation of 3T3-F442A preadipocyte cell line in culture.

A pure glucocorticoid agonist RU 28362 and the potent antagonist RU 38486 were compared with dexamethasone for the evolution and the molecular nature of the GR during insulin-dependent conversion of 3T3-F442A preadipocytes into mature cells. In the whole cell assay system, the affinity for preadipocyte GR was observed in the order RU 38486 greater than RU 28362 greater than dexamethasone. The GR complex was most stable in presence of dexamethasone followed by the antagonist RU 38486 = the agonist RU 28362. Similar results were obtained in mature adipocytes but the binding of RU 38486 was more equivocal. An insulin-dependent differentiation process did not alter any of these parameters but increased the number of GR nearly fivefold over a 2-week period. Ion-exchange analysis of the cytosolic receptor revealed that the differentiation process was not accompanied by the appearance of any novel or new forms of GR, contrary to the situation in the liver, since both RU 38486 and dexamethasone were bound to identical molecular species of GR. These data provide a defined system for further analysis of cellular receptor as a function of steroid, tissue, and species, contrary to the classical dogma where GR is generally thought to be identical as a passive vehicle for the steroid in all circumstances, and affinity for steroid is generally equated with receptor stability.

Adipose Tissue↗
PubMed1987

Glucocorticoid binding during the differentiation of 3T3-F442A fibroblasts into adipocytes. A possible regulatory effect of insulin.

Until recently, few studies had been carried out on receptors for glucocorticoids in adipocytes, although the role of these steroids is considerable. In the present studies, we chose the pre-adipocyte line 3T3-F442A, which constitutes an excellent model for investigating the differentiation and function of adipocytes. Using a whole cell assay system, we showed the existence of a homogenous class of sites with the characteristics of glucocorticoid receptors, that is, high-affinity binding which is reversible, specific and saturable. Whatever the state of cellular differentiation, the affinity of the receptor for dexamethasone did not vary, although we observed an increase in the number of sites during differentiation. When cells were differentiated in the presence of insulin, there was a further increase in the binding capacity; moreover, insulin deprivation of such adipocytes caused a decrease in the number of sites. Our results therefore suggest that factors other than the glucocorticoids themselves influence dexamethasone binding. It is suggested that insulin plays a role in the regulation of the number of glucocorticoid receptors.

Adipose Tissue↗