ESPE Abstracts

Background: Leptin is produced by adipocytes and regulates central hunger and satiety sensation. While the central leptin effects are well understood, little is known about the regulation of peripheral leptin production. Clinical data demonstrate that leptin levels are rapidly declining upon fasting, suggesting that leptin secretion is acutely regulated by nutrient availability. Although it has been previously shown that leptin secretion is under control by glucocorticoids (GC) in human adipocytes, the interplay between nutrients and GC in this context has not been studied. Our aim was therefore to investigate leptin expression and secretion in response to GC and glucose in a human adipocyte cell model.

Methods: Human SGBS preadipocytes were differentiated into adipocytes for 14 days. The expression of leptin in response to different stimuli were determined by qRT-PCR and Western Blot. Secretion of leptin to the cell culture medium was measured by ELISA after 48 hours. ATP production rates were quantified by quantified using a Seahorse XFe96 bioanalyzer. RNA sequencing was used to investigate transcriptomic changes due to glucose and GC treatment.

Results: As expected, both leptin expression and secretion were strongly enhanced by cortisol (100 nM) treatment (approx. 10-fold and 3.2-fold (111+/-26 vs. 353+/-31 pg/ml) in mature adipocytes. Treatment with different glucose concentrations (0-10 mM) revealed a dose-dependent effect on GC-induced leptin secretion, which peaked at physiological glucose levels (5.5mM). Complete glucose deprivation or inhibition of glycolysis by 2-desoxy-glucose blocked GC-induced leptin expression and secretion, indicating that glucose metabolism is a driver of leptin production. Remarkably, compared to the expression of other known adipokines, leptin was the one most strongly induced by glucose in presence of GC, suggesting a specific influence of glucose on leptin expression under these conditions. As expected, cellular ATP production was lower in absence of glucose (reduction by approx. 40%), thus we were interested whether leptin secretion by GC and glucose was mediated via common energy sensing pathways. We therefore either activated AMP-dependent protein kinase by AICAR or inhibited mTOR activity using rapamycin. Indeed, both treatments resulted in an inhibition of GC-stimulated leptin expression and secretion, indicating that leptin production is dependent on glycolytic energy supply.

Conclusion: Our data indicate that GC-induced leptin production in human adipocytes is mediated by intracellular glucose availability, suggesting a direct link between glycolytic energy supply and leptin production. These findings may contribute to understand the rapid regulation of leptin levels upon fasting.