Osteocyte signaling in bone

Abstract

Osteocytes, the cells residing within the bone matrix and comprising 90% to 95% of the all bone cells, have long been considered quiescent bystander cells compared to the osteoblasts and osteoclasts whose activities cause bone gain and loss, and whose dysfunction lead to growth defects and osteoporosis. However, recent studies show that osteocytes play a crucial, central role in regulating the dynamic nature of bone in all its diverse functions. Osteocytes are now known to be the principal sensors for mechanical loading of bone. They produce the soluble factors that regulate the onset of both bone formation and resorption. Osteocytes regulate local mineral deposition and chemistry at the bone matrix level, and they also function as endocrine cells producing factors that target distant organs such as the kidney to regulate phosphate transport. Osteocytes appear to be the major local orchestrator of many of bone's functions.

Figure 1. Recent insights in osteocyte signaling and regulation in bone function

DMP1—dentin matrix protein 1; FGF 23—fibroblast growth factor 23; MEPE—matrix extracellular phosphoglycoprotein; PHEX—phosphate-regulating neutral endopeptidase on chromosome X; PTH—parathyroid hormone; RANKL—receptor activator of nuclear factor-κB ligand.