Depot-specific release of leptin from subcutaneous and omental adipocytes in suspension culture:: effect of tumor necrosis factor-α and transforming growth factor-β1

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)-alpha and transforming growth factor (TGF)-beta 1 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-alpha and TGF-beta 1 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-alpha and 400 pmol/l TGF-beta 1 respectively did not significantly affect leptin secretion. Whereas a 24-h incubation with 1 nmol/l TNF-alpha also did not influence leptin secretion from fat cells from both depots, exposure of omental Fat cells to 400 pmol/l TGF-beta 1 for 24h 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-alpha led to a significant decrease in leptin mRNA levels to 70 +/- 8% and 49 +/- 13% of controls respectively Similarly TCF-beta 1 decreased leptin mRNA expression in newly differentiated human adipocytes to 77 +/- 12% after 24 h and to 54 +/- 8% after 48 h compared with control cultures. These data provide evidence that long-term exposure of human fat cells to TNF-alpha or TGF-beta 1 may suppress leptin expression in human adipose tissue. The inhibitory effect of TGF-BT appears to be more pronounced in omental as compared with subcutaneous adipocytes.