Promoting effect of 1,25(OH)(2) vitamin D(3) in osteogenic differentiation from induced pluripotent stem cells to osteocyte-like cells

We recently reported a new method to purify the induced pluripotent stem (iPS)-derived osteoprogenitors (iPSop). In this paper, we optimized the procedure and characterized cells at each process step. We observed that 10 days of treatment with FGF-2, IGF-1 and TGF-β (FIT) resulted in early-phase osteoblasts and 14 days of treatment resulted in late-phase osteoblasts. We found that treatment with 1,25(OH)(2) vitamin D(3) increased expression of osteocalcin and decreased expression of tissue-non-specific alkaline phosphatase and runt-related transcription factor 2 (RUNX2) in iPSop-day14 cells (cells treated with FIT for 14 days). Therefore, iPSop-day14 cells were promoted to mature osteoblasts by 1,25(OH)(2) vitamin D(3) treatment. In addition, we found that 1,25(OH)(2) vitamin D(3) treatment for 14 days enhanced not only mineralization but also expression of osteocyte markers, including dentin matrix protein-1 and fibroblast growth factor-23, in iPSop cells. Therefore, 1,25(OH)(2) vitamin D(3) is a potent promoter of osteoblast–osteocyte transition. The results of this study suggest that it is possible to evaluate both early- and late-phase osteoblasts and to apply cells to drug screening for anabolic drugs that stimulate bone formation.