Depot-specific release of leptin from subcutaneous and omental adipocytes in suspension culture: effect of tumor necrosis factor-alpha and transforming growth factor-beta1

Abstract

Objective: Leptin, the product of the ob gene, is overexpressed in human obesity and increased serum leptin levels are closely correlated with adipose tissue mass, but the regulation of leptin production is not completely understood. The aim of this study was to characterize the role of tumor necrosis factor (TNF)-a and transforming growth factor (TGF)-b1 in depot-specific secretion of leptin from cultured human adipocytes. Design and methods: We measured the leptin concentrations in the culture medium of omental and subcutaneous abdominal adipocytes taken from severely obese individuals and kept in suspension culture, and studied the effect of TNF-a and TGF-b1 on leptin release. Leptin protein was measured by radioimmunoassay, leptin mRNA was assessed by reverse transcriptase (RT)-PCR relative to a housekeeping gene. Results and conclusion: Leptin secretion from subcutaneous fat cells was 2-to 3-fold higher than that from omental fat cells after incubation for 2 and 24 h respectively. A 2-h exposure of adipocytes to 1 nmol/l TNF-a and 400 pmol/l TGF-b1 respectively did not significantly affect leptin secretion. Whereas a 24-h incubation with 1 nmol/l TNF-a also did not influence leptin secretion from fat cells from both depots, exposure of omental fat cells to 400 pmol/l TGF-b1 for 24 h resulted in a significant inhibitory effect (by 33%) on leptin secretion (P<0.05). A 24-and 48-h exposure of in vitro differentiated human adipocytes to TNF-a led to a significant decrease in leptin mRNA levels to 70 Ϯ 8% and 49 Ϯ 13% of controls respectively. Similarly, TGF-b1 decreased leptin mRNA expression in newly differentiated human adipocytes to 77 Ϯ 12% after 24 h and to 54 Ϯ 8% after 48 h compared with control cultures. These data provide evidence that long-term exposure of human fat cells to TNF-a or TGF-b1 may suppress leptin expression in human adipose tissue. The inhibitory effect of TGF-b1 appears to be more pronounced in omental as compared with subcutaneous adipocytes.

No evidence for a direct effect of clozapine on fat-cell formation and production of leptin and other fat-cell-derived factors

“…6 This family apparently supports the locus distally of CHRNA7, since the carrier and the five affected members available for genetic studies share marker alleles between D15S1042 and D15S182, thus…”

“…Additionally, freshly isolated human adipocytes were kept in suspension culture for 24 h as described recently. 6 To study whether clozapine is able to influence adipose differentiation, we added clozapine at concentrations of 10 À9 -10 À5 M to adipocyte precursor cells for 3 and 16 days, respectively, in the presence of adipogenic factors. Clozapine had no significant effect on the percentage of newly developed fat cells as well as on the activity of glycerol-3-phosphate dehydrogenase, a marker enzyme of adipose differentiation, in comparison with control cells.…”

Effects of leptin on the differentiation and metabolism of human adipocytes

“…13 The freshly isolated fat cells were incubated for the time periods indicated in DME=F-12 medium supplemented with 4% BSA, 66 nmol=l insulin, 100 nmol=l cortisol, 50 mg=ml gentamycin and leptin as indicated in a shaking water bath at 37 C. The culture medium was then collected and immediately stored at 780 C until later measurement of glycerol or PAI-1 protein content.…”

Anthropometric, computed tomography and fat cell data in an obese population: relationship with insulin, leptin, tumor necrosis factor-alpha, sex hormone-binding globulin and sex hormones

“…Previous studies on the relationship of hormones and the function and morphology of adipose tissue have shown the in¯uence of these hormones on the accumulation of fat in the adipocytes of different adipose regions (9,10). Although recent adipocyte culture studies provide valuable information on the relationship between hormones and adipose tissue (11,12), including the possible differences in the way this tissue behaves depending on the adipose area studied (13), the very complexity of obesity and the large number of factors which intervene in fat accumulation make it necessary to conduct complete clinical studies in obese individuals. Such studies will include anthropometric data, computed tomography studies, analysis of adipocyte size in different abdominal regions and serum levels of different hormones and cytokines such as insulin, leptin, TNF-a, sex hormones and sex hormone-binding globulin (SHBG), with the aim of determining whether hormones and adipose tissue do interact and, if so, how these interactions differ depending on the different abdominal adipose tissue regions, i.e.…”