| [ Summary ] |
Osteocytes compose over 90% of all bone cells in the bone tissue. Osteocytes are embedded within the bone matrix in the bone lacuna, and connected to each other by gap junctions. Therefore, these cells are believed to respond to mechanical stress to regulate bone metabolism. On the other hand, FGF23 was discovered as a factor, which decreases serum phosphate levels through controlling the renal expression of Type II sodium-dependent phosphate transporters. In addition, PHEX and DMP1, which are responsible for vitamin D-resistant rickets/osteomalacia, have been shown to down-regulate the expression of FGF23. Interestingly, all of these factors (FGF23, PHEX and DMP1) are expressed by osteocytes. Similarly, it was shown that osteocytes specifically express sclerostin, an inhibitor of bone formation, which acts as an antagonist of canonical Wnt/β-catenin signaling. These results suggest that osteocytes regulate bone metabolism through multiple pathways. Clarifying the precise role of osteocytes is necessary to fully understand the regulation of bone metabolism. |