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. Author manuscript; available in PMC: 2014 Jun 1.
Published in final edited form as: Metabolism. 2013 Jan 30;62(6):768–777. doi: 10.1016/j.metabol.2013.01.003

Figure 2. Vitamin D metabolism, regulation, and action in hMSCs.

Figure 2

Vitamin D3 (cholecalciferol) is hydroxylated at carbon-25 by CYP27A1 to 25(OH)D3 (calcidiol), which downregulates CYP27A1 and upregulates CYP27B1 and, at higher concentrations, upregulates CYP24A1. In a dose-dependent manner, 25(OH)D3 is hydroxylated at carbon-1α by CYP27B1 to 1α,25(OH)2D3 (calcitriol). Higher concentrations of 1α,25(OH)2D3 downregulate CYP27B1 and upregulate CYP24A1. Both 25(OH)D3 and 1α,25(OH)2D3 upregulate IGF-I which mediates their stimulation of osteoblast differentiation in hMSCs. These findings indicate an autocrine/paracrine role for vitamin D metabolism in human osteoblastogenesis in hMSCs.