Journal List > Endocrinol Metab > v.25(3) > 1085821

Bonewald: The Osteocyte Network as a Source and Reservoir of Signaling Factors


Within the past few years, information regarding osteocyte function as been emerging and expanding significantly. No longer is the osteocyte considered a passive cell acting simply as a ‘placeholder’ within mineralized bone. Osteocytes are derived from osteoblast progenitors and in the adult skeleton compose 90–95% of all bone cells. Therefore, the function of these cells in the adult and aging skeleton has become the focus of recent investigation. These cells are proving to be multifunctional, ranging from mechanotransduction, to regulation of mineral homeostasis, to control of bone remodeling. The osteocyte as a source and reservoir of signaling factors important in health and maintenance of the adult skeleton is addressed in this review.


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Fig. 1.
Osteocytes are connected to each other and to cells on the bone surface. Scanning electron micrograph of an acid etched resin embedded bone showing the extensive lacuno-canalicular network. Canaliculi connect to the bone surface and marrow space (right side of figure) (2,000 x-murine bone).
Fig. 2.
Canaliculi bridge the reversal front. This suggests that during the remodeling process, osteocytes can connect their existing dendrites/canaliculi with newly formed dendrites/canaliculi of newly embedded osteocytes. In this manner, the connectivity of the osteocyte lacuno-canalicular network is maintained (1,000 x-human bone).
Table 1.
Osteocyte signaling factors
Factor Target Function
PGE2, ATP, NO Other osteocytes, osteoblasts Anabolic
Sclerostin, Dkk1 Osteoblasts Inhibit bone formation
FGF23 Kidney Phosphate regulation
RANKL, M-CSf Osteoclasts Activates osteoclasts
OPG Osteoclasts Inhibits osteoclast activation

PGE2, prostaglandin E2; ATP, adenosine-5’-triphosphate; NO, Nitric Oxide FEF23, fibroblast growth factor 23; RANKL, receptor activator of NF-B ligand M-CSf, monocyte chemotactic and stimulating factor; OPG, osteoprotegerin.

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