Skeletal energy homeostasis: a paradigm of endocrine discovery.

Throughout the last decade, significant developments in cellular, molecular and mouse models have revealed major endocrine functions of the skeleton. More recent studies have evolved the interplay between bone-specific hormones, the skeleton, marrow adipose tissue, muscle and the brain. This review focuses on literature from the last decade, addressing the endocrine regulation of global energy metabolism via the skeleton.

A novel promoter for the 11beta-hydroxysteroid dehydrogenase type 1 gene is active in lung and is C/EBPalpha independent.

11Beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) increases intracellular glucocorticoid action by converting inactive to active glucocorticoids (cortisol, corticosterone) within cells. It is highly expressed in glucocorticoid target tissues including liver and lung, and at modest levels in adipose tissue and brain. A selective increase in adipose 11beta-HSD1 expression occurs in obese humans and rodents and is likely to be of pathogenic importance in the metabolic syndrome.

Glucocorticoids and 11beta-hydroxysteroid dehydrogenase in adipose tissue.

The highly prevalent metabolic syndrome (insulin resistance, type 2 diabetes, dyslipidemia, hypertension, along with abdominal obesity) resembles Cushing's syndrome. However, in simple obesity, plasma cortisol levels are not elevated. 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1), at least in mature adipocytes and hepatocytes, converts inactive circulating 11-keto steroids into active glucocorticoids, amplifying local glucocorticoid action.