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Biomedical subjects

G Ailhaud

Publications and source records attributed to G Ailhaud.

At least 145 records · Page 8Linked to original sources
PubMed1985

[Lipoprotein lipase and adipocyte differentiation].

Some hormonal factors, possibly involved in the proliferation and differentiation of adipose precursor cells in vivo, have been characterized in vitro using different preadipocyte cell lines established from rodent adipose tissue. The process of adipose conversion has also been studied using these cell lines; in this process, stem cells (adipoblasts) were committed at any cell division during the growth phase. At confluence, committed cells (preadipocytes) underwent a limited number of mitoses and differentiated into adipose cells, whereas the uncommitted cells remained as stem cells in the cell population. This stochastic model could be extended to the development of rat adipose tissue in vivo. The study of adipose conversion showed the early emergence of lipoprotein lipase (LPL) and monoglyceride lipase (MGL). LPL activity appeared in the cells before any triglyceride accumulation. In contrast, this accumulation seemed dependent upon the emergence of glycerol-3-phosphate dehydrogenase. In vitro experiments clearly established that LPL-containing (differentiating) cells underwent postconfluent mitoses. This limited proliferation was in agreement with previous data obtained in vivo and indicates that only triglyceride-containing (mature) cells could not divide.

Adipose Tissue↗
PubMed1985

Adipose conversion of ob17 cells and hormone-related events.

The ob17 preadipocyte clonal line has been established from the adipocyte fraction of the epididymal fat pads of adult C57 BL/6J ob/ob mice. In vivo, injection of ouabain-resistant mutant cells (ob 17OR11 cell line) into athymic mice is followed by the formation of fat pads containing ouabain-resistant mature fat cells. In vitro, ob17 cells develop after confluence biochemical and morphological characteristics of adipocytes. The adipose conversion process is best represented by a stochastic model in which a pool of stem cells (adipoblasts) give rise to clusters of adipose cells and to additional stem cells that remain in the population. The role of the different factors involved in such conversion is discussed; (1) factors that enhance the number of susceptible cells (ACF or ACF-like compounds), (2) factors without which no adipose conversion takes place (triiodothyronine, growth hormone and other factors still to be characterized), (3) factors that enhance the expression of the differentiation program (insulin). The early emergence of lipoprotein lipase occurs normally in insulin-depleted medium. The separation of ob17 cells by isopycnic centrifugation shows that lipoprotein lipase is present at high levels in early differentiating cells which are still devoid of late markers, ie glycerol-3-phosphate dehydrogenase and triglycerides. These results are discussed with respect to the determination of cellularity during development of adipose tissue in vivo.

Adipose Tissue↗
PubMed1984

Growth of preadipocyte cell lines and cell strains from rodents in serum-free hormone-supplemented medium.

Ob17 is a clonal cell line isolated from the epididymal fat pad of C57 BL/6J ob/ob mouse that differentiates into adiposelike cells in serum-supplemented medium. In serum-free medium, this cell line shows increased growth under the addition of insulin, transferrin, fibroblast growth factor (FGF), and a factor present in extract of rat submaxillary gland (SMGE). This medium is referred to as 4F. Epidermal growth factor or nerve growth factor cannot replace SMGE, whereas partially purified platelet extract can substitute for FGF but only partially for SMGE. 4F Medium is able to support the proliferation of cells from other established preadipocyte clonal lines, HGFu and 3T3-F442A, and also of preadipocyte cells isolated from the stromal-vascular fraction of rat and mouse adipose tissues. In each case 4F medium is insufficient to support the differentiation of these cells into adipocytes. Ob17 cells grown and maintained in serum-free hormone-supplemented medium retain the ability to convert to adiposelike cells after serum addition. This serum requirement for differentiation cannot be substituted by the addition of growth hormone or of other putative adipogenic factors, or both. The results are discussed with respect to the requirements for growth and differentiation of the 3T3-L1 and 1246 preadipocyte cell lines previously described.

Adipose Tissue↗
PubMed1984

Adipose conversion of ob17 cells. Insulin acts solely as a modulator in the expression of the differentiation program.

Adipose conversion of ob17 preadipocyte cells was studied in insulin-depleted (less than 0.2 pM), serum-supplemented medium. The results show that insulin is neither required for the commitment of stem cells ( adipoblasts ) to preadipocytes nor for the onset of the differentiation program and the post-confluent mitoses of preadipocytes to adipocyte-like cells. No unmasking of insulin 'super' receptors and no cellular production of insulin can be detected in cells exposed to insulin-depleted medium. Insulin enhances only the rate of the lipid-filling process of differentiating cells and thus the number of fat cell clusters visible after staining for neutral lipids. Therefore, in the light of these and previous results [17, 18], the role of insulin is only to act as a modulator in the expression of the differentiation program.

Adipose Tissue↗
PubMed1984

ob17 cells transformed by the middle-T-only gene of polyoma virus differentiate in vitro and in vivo into adipose cells.

Cell lines were derived from ob17 preadipocyte cells by focus formation after transfer of the complete early region of polyoma virus (ob17PY) or of a modified genome encoding only the middle T protein (ob17MT). Both ob17PY and ob17MT cell lines exhibited a high cloning efficiency in agarose medium containing 10% fetal bovine serum. Fully transformed ob17PY cells grew to high saturation densities and did not differentiate in vitro and in vivo. ob17MT cells and derived subclones did not grow in the absence of serum and were able to differentiate in vitro and to give rise in vivo to adipose tumors. Among these different clones an inverse relationship was observed in culture between their potentiality to overproliferate at low serum and their potentiality to convert into adipose cells. The expression of enzyme markers of adipose conversion was strictly dependent upon the presence of growth hormone. In addition, the hormonal requirements for differentiation were simpler than those of the original ob17 cells and the adipose conversion could take place in serum-free hormone-supplemented medium.

Adipose Tissue↗
PubMed1983

Modulation of lipid-synthesizing enzymes by insulin in differentiated ob17 adipose-like cells.

ob17 cells convert into adipose-like cells when maintained in the presence of physiological concentrations of insulin and tri-iodothyronine. After this conversion, insulin removal from differentiated ob17 cells gives within 24-48 h a large decrease in fatty acid synthetase, glycerol 3-phosphate dehydrogenase and acid:CoA ligase activities, as well as in the rate of fatty acid synthesis determined by [14C]acetate incorporation into lipids. All parameters are restored by insulin addition to initial values within 24-48 h. Dose-response curves of insulin on the restoration of glycerol 3-phosphate dehydrogenase activity and of fatty acid synthesis give half-maximally effective concentrations close to 1 nM, in agreement with the affinity for insulin of the insulin receptors previously characterized in these cells. Immunotitration experiments indicate that the changes in the specific activity of fatty acid synthetase are due to parallel changes in the cellular enzyme content. Therefore the ob17 cell line should be a useful model to study the long-term effects of insulin on the modulation of lipid synthesis in adipose cells.

Acetates↗
PubMed1983

Establishment of a preadipocyte cell line from the epididymal fat pad of the lean C57 BL/6J mouse--long term effects of insulin and triiodothyronine on adipose conversion.

A clonal cell line has been established from the epididymal fat pad of the C57 BL/6J +/? mouse. This line, designated HGFu, is aneuploid and exhibits both morphological and biochemical properties characteristic of mature adipocytes. Adipose conversion begins after confluence and is accompanied by (a) an early emergence of lipoprotein lipase, (b) an increase in the incorporation of [14C]acetate into lipids and in the activities of acid:CoA ligase and glycerol-3-phosphate dehydrogenase, (c) a 27- to 35-fold increase in the average triglyceride content per cell. In the presence of a beta-agonist (isoproterenol) a full lipolytic response (measured by fatty acid release) is observed with differentiated cells, whereas the responsiveness examined by cyclic AMP (cAMP) production is present both in undifferentiated and differentiated cells. Adipose conversion, estimated by activities of enzyme markers, is accelerated by the continuous presence in the culture medium of insulin and triiodothyronine both within their physiological range of concentrations, whereas insulin at supraphysiological concentrations shows a growth promoting activity. The concentrations of insulin and triiodothyronine required for half-maximal lipogenic effects are in agreement with the Kd values of their respective high affinity binding sites present in HGFu cells. The HGFu cell line seems to be a useful model for the study on a long term basis of the mechanisms of action both of insulin and triiodothyronine. Moreover it will make it possible to realize comparative studies between clonal lines established from the lean adult mouse (HGFu line) and from the genetically obese adult mouse (Ob17 line).

Adipose Tissue↗
PubMed1983

Establishment and characterization of an epithelial intestinal cell line from rat fetus.

An epithelial intestinal cell line has been established from explants of fetal rat small intestine. After the 9th passage (approx. 25 population doublings) epithelial-like cells acquired the properties of a permanent cell line. The epithelial nature of this cell line, and of clone IRD 98 subsequently isolated, is supported by morphological and ultrastructural criteria, and also by the presence of enzymes characteristic of enterocytes, such as aminopeptidase, alkaline phosphatase, gamma-glutamyl transferase, lactase and maltase. The occurrence of the triglyceride pathway enzyme monoacylglycerol acyltransferase and of apoproteins (Apo A1 and Apo E) can also be demonstrated. Taken together, the results presented here provide evidence that clone IRD 98 is an epithelial cell line, most likely originating from the relatively differentiated cell layer of fetal rat small intestine.

Acyltransferases↗
PubMed1983

Lipogenic and mitogenic effects of insulin during conversion of Ob17 cells to adipose-like cells.

Chronic exposure to insulin of confluent cells of a preadipocyte clonal line (Ob17) leads to an acceleration of their development into adipose cells. The short-term effects of insulin have been examined by the stimulation of [14C] alpha-aminoisobutyrate uptake and the long-term effects by the increase in the activity levels of several lipogenic enzymes and in the intracellular triacylglycerol content. These metabolic effects of insulin occur within a physiological range of concentrations (EC50 congruent to 1 nM). As compared to insulin, dose-response curves obtained with proinsulin on these parameters show at least a 10-fold decrease in sensitivity of the cells. In contrast, the growth-promoting effects of both insulin and proinsulin occur at supraphysiological concentrations (EC50 greater than 300 nM). This mitogenic response is likely mediated through binding to receptors of insulin-like growth factors. Our data demonstrate that long-term effects of insulin on lipid synthesis can be dissociated from its effect on cell growth. Therefore the Ob17 cell line should be a useful model to study the role of insulin in the regulation of lipid synthesis in adipose cells.

Adipose Tissue↗
PubMed1983

Establishment of a human cell line after transformation by a plasmid containing the early region of the SV40 genome.

A human clonal cell line, designated TAH9, has been established from cells of adipose tissue by fusion with E. coli protoplasts containing a recombinant plasmid carrying the early genes of Simian virus 40. The establishment of the cell line is preceeded by a delayed growth crisis. The results indicate that, after cell transformation, another event(s) of low frequency is required for cell immortalization. Some biological properties of TAH9 cells are also described.

Adipose Tissue↗
PubMed1983

[Long-term effects of insulin on the adipocyte conversion of Ob17-line cells].

The Ob17 cell line was established from the epididymal fat pad of ob/ob mice. Chronic exposure to physiological concentrations of insulin led to a net increase in lipogenic enzyme activities (EC50 = 1 to 3 nM). Proinsulin exerted the same effects at higher concentrations (EC50 = 10 to 30 nM). The mitogenic effects of both hormones appeared only at supraphysiological concentrations (EC50 = 300 nM). We conclude this was a net dissociation between the lipogenic and mitogenic effects of insulin during differentiation of the Ob17 cells.

Adipose Tissue↗
PubMed1982

Differentiation of Ob17 preadipocytes to adipocytes: requirement of adipose conversion factor(s) for fat cell cluster formation.

An active fraction present in fetal calf serum (adipose conversion factor(s) or ACF) controls the formation of fat cell clusters observed during the adipose conversion of Ob17 cells. This conclusion is based upon microscopic examinations, autoradiographic experiments, and activity levels of characteristic enzyme markers. ACF has no effect on the doubling time of exponentially-growing cells but is required in the first few days of the resting phase. ACF has been partially purified; it is a low mol. wt. component (less than 6000-8000), proteas -insensitive, thermostable at neutral pH but not at strongly acidic pH. An active fraction recovered from bovine pituitary extract shows properties similar to those of ACF. Therefore, ACF plays the role of a mitogenic factor specific for cells susceptible to conversion to adipose cells.

Adipose Tissue↗