The hidden cross talk between bone and tissues through bone turnover.

Abstract

Bone is more than a reservoir of calcium and phosphorus. Its lacuno-canalicular arrangement provides an important pathway for exchange with circulation and currently, the skeleton is considered a large endocrine organ with actions that go beyond the control of calcium-phosphorus balance mediated by fibroblastic growth factor 23 (FGF23). Parallel to the modulating effect of adipokines on bone turnover, certain bone proteins, such as osteocalcin and sclerostin, play a counter-regulatory role on energy metabolism, probably in an attempt to ensure its high energy requirement for bone turnover. In this crosstalk between bone and other tissues, especially with adipose tissue, canonical Wnt/β-catenin signaling is involved and therefore, sclerostin, an osteocyte derived protein that inhibits this signalling, emerges as a potential biomarker. Furthermore, its involvement in diverse pathologic conditions supports sclerostin as a therapeutic target, with an anti-sclerostin antibody recently approved in our country for the treatment of osteoporosis. This review addresses the endocrine nature of bone, the role of osteocalcin, and specially, the regulatory and modulatory role of sclerostin on bone turnover and energy homeostasis through its inhibitory effect on canonical Wnt/β-catenin signaling, as well as its potential utility as a biomarker.