Insulin and dexamethasone dynamically regulate adipocyte 11β-hydroxysteroid dehydrogenase type 1

The adipocyte enzyme 11 beta-hydroxysteroid dehydrogenase type 1 (11 beta-HSD1) amplifies local glucocorticoid action by generating active glucocorticoids from inactive metabolites and has emerged as a key player in the pathogenesis of central obesity and metabolic syndrome. However, the regulation of adipocyte 11 beta-HSD1 is incompletely understood. Therefore, the present study was designed to investigate the effects of insulin and glucocorticoid as well as their underlying molecular mechanisms on 11 beta-HSD1 activity and expression in 3T3-L1 adipocytes and determine whether the in vitro findings could be confirmed in vivo. Our main in vitro findings are 1) insulin stimulated whereas dexamethasone inhibited 11 beta-HSD1 activity and expression in a time-and concentration-dependent manner; 2) the effect of dexamethasone was mimicked by both cortisol and corticosterone but blocked by the glucocorticoid receptor antagonist RU486; 3) the p38 MAPK inhibitor SB220025, but not the ERK inhibitor U0126 or the phosphatidylinositol 3-kinase inhibitor LY294002, prevented insulin stimulation of 11 beta-HSD1 activity; and 4) although dexamethasone did not alter the half-life of 11 beta-HSD1 mRNA, insulin doubled it. Taken together, these in vitro results demonstrate that insulin stimulates adipocyte 11 beta-HSD1 through a posttranscriptional mechanism that involves activation of the p38 MAPK signaling pathway, whereas dexamethasone exerts an opposite effect by a glucocorticoid receptor-mediated transcriptional mechanism. In contrast, both insulin and dexamethasone augmented 11 beta-HSD1 activity and expression in rat white adipose tissue in vivo, thus confirming the role of insulin but revealing a fundamental difference regarding the role of dexamethasone in regulating adipocyte 11 beta-HSD1 between the two model systems.