Effects of leptin on the differentiation and metabolism of human adipocytes

BACKGROUND: Leptin is an adipose protein regulating food intake in the hypothalamus. Animal studies have suggested that leptin also acts in an auto-/paracrine fashion on adipose cell function. OBJECTIVE: The aim of this study was to investigate the effects of leptin on the differentiation and metabolism of cultured human adipocytes. MATERIAL: Adipose tissue from young healthy, lean women (body mass index (BMI) < 27kg/m(2)) undergoing elective mammary reduction surgery and young obese individuals (BMI > 40kg/m(2)) undergoing laparoscopic gastric banding. METHODS: Human preadipocytes in primary culture were induced to undergo differentiation by defined adipogenic factors. Mature adipocytes were isolated by collagenase digestion and kept in culture suspension. Glycero-3-phosphate dehydrogenase (GPDH) activity was used as a marker of adipose differentiation; glucose uptake, lipolysis and PAI-1 secretion were measured as parameters of fat cell function. RESULTS: Human preadipocytes and adipocytes from lean and obese subjects expressed the long leptin receptor isoform and two of the three short forms as assessed by polymerase chain reaction (PCR). Leptin at a supraphysiological concentration induced a transient increase of GPDH activity, but had no effect on glucose uptake and PAI-1 secretion from human adipocytes. In addition, basal and isoproterenol-stimulated lipolysis as well as the antilipolytic action of insulin in human adipocytes was not significantly affected by leptin exposure. CONCLUSION: In contrast to animal data, the results of our experiments do not demonstrate significant effects of leptin on main metabolic functions of human adipocytes arguing against a local auto-/paracrine action of leptin in human adipose tissue.