Chapter 21 - Vitamin D activity in osteoblasts and osteocytes

Abstract

Osteoblasts and osteocytes both derive from the mesenchymal stem cells and are required for processes of bone formation and mineral homeostasis. Osteoblasts produce type I collagen as a major component of the extracellular matrix of bone and control remodeling via induction of receptor activator of NF-κβ ligand. Although the majority of osteoblasts are short-lived, some osteoblasts embed in the matrix and undergo further differentiation to osteocytes, where they reside in bone minerals with a lifespan measured in years. Osteocytes participate in the mineralization of surrounding bone and mediate signaling that regulates bone mineralization and phosphate homeostasis via the secretion of factors such as sclerostin and fibroblast growth factor 23. Multiple osteoblastic and osteocytic processes are regulated by 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). Although large-scale, genome-wide approaches have provided many novel, direct targets of 1,25(OH)2D3 in bone, there remain numerous unanswered questions as to the physiological role of vitamin D within cells of the osteoblast lineage.