11β-HYDROXYSTEROID DEHYDROGENASE TYPE 1 IN DIFFERENTIATING OMENTAL HUMAN PREADIPOCYTES: FROM DE-ACTIVATION TO GENERATION OF CORTISOL

Abstract

In humans, glucocorticoids are important regulators of adipose tissue distribution and function but circulating cortisol concentrations are normal in most patients with obesity. However, intracellular glucocorticoid levels can be modified by a microsomal enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) expressed mainly in the liver and adipose tissue. Locally generated cortisol within human adipose tissue can induce preadipocyte differentiation, but the relationship between 11β-HSD1 expression and adipogenesis is unknown. Our present study has shown that in intact, undifferentiated omental (OM) but not subcutaneous (SC) preadipocytes, 11β-HSD1 acts primarily as a dehydrogenase inactivating cortisol to cortisone. When preadipocytes become “committed” to adipocyte differentiation, oxo-reductase activity predominates generating cortisol. Since glucocorticoids are not only essential for OM preadipocyte differentiation but also inhibit cell proliferation, we postulate that 11β-HSD1 dehydrogenase activity in “uncommitted” OM preadipocytes may provide an autocrine mechanism to protect preadipocytes from differentiation, in turn facilitating their proliferation. Once early differentiation is initiated, a “switch” to 11β-HSD1 oxo-reductase activity generates cortisol, thus promoting adipogenesis. The differences in set-point of 11β-HSD1 activity between OM and SC human adipose tissue may be an important factor in the pathogenesis of visceral obesity.

Acknowledgments

We would like to thank MRC for the financial support (P. M. Stewart is a MRC Senior Clinical Fellow) and the surgeons and theatre staff of the Queen Elizabeth and Women's Hospitals in Birmingham for their help in collecting tissue samples.