Bone Regulates Glucose Metabolism as an Endocrine Organ through Osteocalcin

Figure 3

Endocrine actions of osteocalcin. Circulating OCN and particularly ucOCN (released during bone resorption activity) have direct effects on β cells, stimulating insulin synthesis. Meanwhile it affects adipocytes and stimulates adiponectin secretion. Adiponectin upregulates insulin sensitivity. In turn, insulin binds to insulin receptor of osteoblasts and affects osteoblasts; then OPG expression will be upregulated and in turn suppress the activity of osteoclasts. Osteoclast stimulates bone resorption with subsequent release of ucOCN in blood circulation. OCN also functions on leydig cells. It can increase their activity and testosterone production. OCN, osteocalcin; ucOCN, uncarboxylated osteocalcin; OPG, osteoprotegerin; InsR, insulin receptor.