“…22 It is produced by a multitude of cells, including osteoblasts, epithelial cells, 23 vascular endothelial cells, 24 smooth muscle cells, 25,26,27 fibroblasts, and cancer cells. 28 In addition to the regulation of bone integrity, OPG has been shown to play a significant role in arthritis, 29,30 cancer, 31,32 and vascularization. Furthermore, OPG levels can be induced by several factors other than estradiol and TGF, such as vascular endothelial growth factor and stromal cell-derived factor-1 in endothelial colony forming cells, and interleukin-13 in fibroblasts.…”