editorials May 01, 2018 May 01, 2018

The elusive clinical significance of osteocalcin actions in energy metabolism in humans

DOI: 10.20945/2359-3997000000050

In spite of its stagnant gross appearance, the skeleton is a highly metabolically active organ. The continuous process of bone remodeling, allowing homeostatic availability of calcium and renovation of the important structural material of bone, requires ample energy supply (). Extreme examples of such energy demand had been noticed a long time ago in high bone turnover states, for instance in the cachexia accompanying severe hyperparathyroidism or in slender children with osteogenesis imperfecta, but lacked an explanation. Therefore, when the first mechanistic pieces of evidence linking bone and energy metabolism in animal models started arising (), it not only made sense in physiological terms, but it was also felt as if by identifying these missing links we would potentially be able to tackle simultaneously two major health care concerns, adiposity and osteoporosis.

It has now been more than 10 years since the paramount work of Lee and cols. placed osteocalcin (Oc) as the foremost bone-derived hormone to influence energy metabolism (), rocketing Oc from its role as a (perhaps second rate) bone formation marker to a means by which bone, as an endocrine gland, would direct insulin sensitivity and production, and fat accumulation. From then onwards, subsequent evidence have solidified that, in mice, Oc favors glucose tolerance and insulin sensitivity (,). Its role as an energy metabolism effector in humans, however, remains elusive.

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