Cell differentiation from mesenchymal stem cells (MSCs) to osteoblasts and osteocytes. Parathyroid hormone (PTH) promotes osteoblast proliferation via several mechanisms. PTH stimulates preosteoblasts (PreOBs) and osteoblasts to make growth factors (GFs), which promote proliferation of MSCs to PreOBs. PTH stimulates the conversion of bone-lining cells to osteoblasts, and it prevents osteoblast and osteocyte apoptosis. BMP, bone morphogenetic protein ; FGF, fibroblast growth factor; IGF-1, insulin-like growth factor 1; TGF-β, transforming growth factor β; VEGF, vascular endothelial growth factor. Adapted from Whitfield .