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Osteologie 2016; 25(02): 62-68
DOI: 10.1055/s-0037-1619003
Osteocyte: Morphology & Function
Schattauer GmbH

Endocrine function of osteocytes

Die endokrine Funktion der Osteozyten
T. Yorgan
1   Department of Osteology and Biomechanics, University Medical Center Hamburg Eppendorf, Hamburg, Germany
,
T. Schinke
1   Department of Osteology and Biomechanics, University Medical Center Hamburg Eppendorf, Hamburg, Germany
› Author Affiliations
Further Information

Publication History

received: 23 February 2016

accepted after revision: 22 March 2016

Publication Date:
22 December 2017 (online)

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Summary

Osteocytes represent the most abundant cell type of the skeletal system. They have access to a large cellular surface area within the lacuno-canalicular network. This network additionally provides connection to the vascular system, a prerequisite for secretion of endocrine regulators into the circulation. The best established endocrine function of the osteocyte network is the regulation of phosphate homeostasis by secretion of Fgf23, a hormone inhibiting renal phosphate reabsorption. Recently, several additional osteocyte-derived factors have been suggested to influence phosphate homeostasis, either directly or in an Fgf23-dependent manner. Moreover, osteocytes are also the major producers of Wnt signaling modulators, such as Sclerostin or Dkk1. Since these molecules primarily act as inhibitors of bone formation, there might be an additional influence of osteocyte-derived molecules on glucose handling and energy metabolism. In fact, osteocalcin, a long-known bone matrix protein and biomarker of bone formation, is now considered to act as a hormone controlling insulin production by pancreatic β-cells and insulin sensitivity of target organs. Since the endocrine functions of osteocytes are only beginning to be uncovered, it appears likely that additional osteocyte-derived molecules with systemic influences on whole body homeostasis might be identified in the future.

Zusammenfassung

Osteozyten sind über das lakuno-kanalikuläre Netzwerk mit dem vaskulären System verbunden, wodurch die Grundvoraussetzung für die Sekretion endokriner Regulatoren gegeben ist. Die am besten etablierte endokrine Funktion des Osteozyten-Netzwerks ist die Regulation der Phosphat-Homöostase durch die Sezernierung von Fgf23, einem Hormon, das u. a. die renale Phosphat-Resorption inhibiert. Zudem wurden weitere Faktoren osteozytären Ursprungs identifiziert, welche die Phosphat-Homöostase direkt oder Fgf23-abhängig beeinflussen. Des Weiteren bilden Osteozyten auch Modulatoren der Wnt-Signaltransduktion, z. B. Sklerostin oder Dkk1. Da diese Moleküle als Inhibitoren der Knochenbildung wirken, könnte ein zusätzlicher Einfluss von Osteozyten auf den Glukose- und Energiestoffwechsel vorhanden sein. In der Tat gibt es Hinweise darauf, dass die Insulinproduktion im Pankreas sowie die Insulinsensitivität peripherer Organe durch Osteokalzin, einem Marker der Knochenbildung, reguliert werden. Somit ist es nicht unwahrscheinlich, dass zukünftig weitere Moleküle osteozytären Ursprungs entdeckt werden, die einen systemischen Einfluss auf die Homöostase des Gesamtorganismus haben.

Keywords

Osteocytes - endocrine function - Fgf23

Schlüsselwörter

Osteozyten - endokrine Funktion - Fgf23
 

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