A Novel Cell Therapy via Direct Reprogramming Of Human Fibroblasts into Functional Osteoblasts for Bone Regeneration

Nova Southeastern University, Davie, Florida, USA

Objective: Osteoblasts (OBs) play a central role in osteogenesis. It is thought that autologous somatic stem cells or iPS cells represents the sufficiently efficient bone regenerative therapy. This approach is, however, limited by the number of available authentic stem cells as well as cost- and time-consuming procedures. In this study, we developed a novel method of directly reprogramming human fibroblasts which are abundantly available from patients into functional OBs. Methods: Normal human fibroblasts were transfected with a panel of selected genes using retroviral vectors or polycistronic plasmid vector, and then cultured in osteogenic medium. The resultant cells were tested in vitro for expressions of OB-specific genes, the production of calcified bone matrix, and the epigenetic status of the cells. To assess in vivo function, the reprogramed OBs were transplanted to the bone defect generated in immune-deficient mice. Results: Gene-transfection of fibroblasts using retroviral vector induced osteocalcin- and ALP-positive OB-like cells which produced mineralized bone matrix at high efficiency, while polycistronic plasmid vector showed modest efficiency. Such reprogrammed OB-like cells demonstrated distinctly different methylation status from original fibroblasts, while displaying the gene-expression profile similar to normal OBs. Directly reprogrammed OBs, further, facilitated sufficient bone regeneration in vivo. These results suggest the direct transformation of fibroblasts can generate functional OBs. Conclusion: We developed a novel technique to directly reprogram human somatic cells, i.e., fibroblasts, into functional OBs by transfection with defined genes, offering an alternative cell therapy for bone regeneration in some patients, e.g. elderlies, who have limited number of stem cells. Grants: NSU HPD grant, Osteology foundation research grant