Influence of sex hormones on adiponectin expression in human adipocytes

Objectives: Adiponectin is an adipocytokine with profound anti-diabetic and anti-atherogenic effects. Plasma adiponectin concentrations are significantly higher in women than in men. In order to study the molecular aspects of this gender specific dimorphism, we examined the expression of adiponectin under the influence of sex hormones.

Methods: As a model system we have used human SGBS preadipocytes and adipocytes. Differentiating cells (d 8) as well as mature adipocytes (d 14) were incubated with increasing doses of testosterone (1–1000 ng/ml) or estradiol (0.1–100 nM). Adiponectin mRNA expression was determined by RT-PCR using specific primers. Adiponectin secretion into the medium supernatant was measured by ELISA.

Results: Adiponectin mRNA expression was up-regulated during adipogenic differentiation. Adiponectin secretion into the culture medium was detected starting at d 7 (˜ 50 ng/ml). Neither testosterone nor estradiol treatment had an influence on adiponectin mRNA expression in human adipocytes. Adiponectin expression was unaffected even after long incubation periods for up to 7 days. Preliminary data show that secretion of adiponectin was constant upon treatment with both sex hormones. Further experiments using BMI-matched male and female serum samples will provide new insights into regulation of adiponectin expression by systemic humoral factors.

Conclusion: Our data suggest that testosterone and estradiol have no direct influence on the expression of adiponectin mRNA in SGBS adipocytes. Thus, we hypothesize the existence of a systemic factor which is regulated by sex hormones and subsequently causes the sexual dimorphism in adiponectin plasma levels.