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Generation of Directly Converted Human Osteoblasts That Are Free of Exogenous Gene and Xenogenic Protein

Generation of osteoblasts from human somatic cells may be applicable in an effective transplantation therapy against bone diseases. Recently we established a procedure to directly convert human fibroblasts into osteoblasts by transducing some transcription factor genes via retroviral vectors. However, retroviral vector‐mediated transduction may potentially cause tumor formation from the infected cells, thus a non‐viral gene transfection method may be more preferable for preparation of osteoblasts to be used for transplantation therapy. Here, we constructed a plasmid vector encoding Oct4, Osterix, and L‐Myc that were an appropriate combination of transcription factors for this purpose. Osteoblast‐like phenotypes including high alkaline phosphatase (ALP) activity, bone matrix production and osteoblast‐specific gene expression were induced in normal human fibroblasts that were transfected with the plasmid followed by culturing in osteogenic medium. The plasmid‐driven directly converted osteoblasts (p‐dOBs) were obtained even in the absence of a xenogenic protein. The plasmid vector sequence had fallen out of the p‐dOBs. The cells formed deposition of calcified bodies in situ after transplantation into mice. These results strongly suggest that p‐dOBs can be put into practical use for a novel cell‐based therapy against bone diseases. J. Cell. Biochem. 117: 2538–2545, 2016. © 2016 Wiley Periodicals, Inc.