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International Journal of Endocrinology
Volume 2013 (2013), Article ID 846480, 10 pages
http://dx.doi.org/10.1155/2013/846480
Review Article

Endocrine Actions of Osteocalcin

Department of Clinical, Surgical and Neurological Sciences, University of Siena, 53100 Siena, Italy

Received 28 December 2012; Revised 1 April 2013; Accepted 2 April 2013

Academic Editor: Yuichiro Nishida

Copyright © 2013 Aurora Patti et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Osteocalcin is the most abundant noncollagenous protein of bone matrix. Once transcribed, this protein undergoes posttranslational modifications within osteoblastic cells before its secretion, including the carboxylation of three glutamic residues in glutamic acid, which is essential for hydroxyapatite binding and deposition in the extracellular matrix of bone. Recent provocative data from experimental observations in mice showed that the circulating undercarboxylated fraction of osteocalcin increases insulin secretion and sensitivity, lowers blood glucose, and decreases visceral fat in both genders, while it enhances testosterone production by the testes in males. Moreover, both total and undercarboxylated osteocalcins increase following physical activity with potential positive effects on glucose tolerance. Despite that these evidences have been only in part confirmed in humans, further prospective investigations are needed to definitively establish the endocrine role of osteocalcin both in the general population and cohorts of patients with diabetes or other metabolic disorders.