Glucocorticoids, bone and energy metabolism

- Prolonged circulating glucocorticoid excess has significant adverse effects on body composition and systemic fuel metabolism.
- The action of glucocorticoids on body composition and systemic fuel metabolism is, at least in part, mediated through the osteoblast.
- Osteocalcin is the bone derived substance most likely to link glucocorticoid action in osteoblasts to changes in body composition.

Prolonged exposure to excessive levels of endogenous or exogenous glucocorticoids is associated with serious clinical features including altered body composition and the development of insulin resistance, impaired glucose tolerance and diabetes. It had been assumed that these adverse effects were mediated by direct effects of glucocorticoids on tissues such as adipose or liver. Recent studies have however indicated that these effects are, at least in part, mediated through the actions of glucocorticoids on bone and specifically the osteoblast. In mice, targeted abrogation of glucocorticoid signalling in osteoblasts significantly attenuated the changes in body composition and systemic fuel metabolism seen during glucocorticoid treatment. Heterotopic expression of osteocalcin in the liver of normal mice was also able to protect against the metabolic changes induced by glucocorticoids indicating that osteocalcin was the likely factor connecting bone osteoblasts to systemic fuel metabolism. Studies are now needed in humans to determine the extent to which glucocorticoid induced changes in body composition and systemic fuel metabolism are mediated through bone.This article is part of a Special Issue entitled Bone and diabetes.