Direct Reprogramming of Fibroblasts to Osteoblasts: Techniques and Methodologies

Direct reprogramming (DR) is an emerging technique that can be applied to convert fibroblasts into osteoblast-like cells, promoting bone formation and regeneration. We review the current methodology of DR in relation to the creation of induced osteoblasts, including a comparison of transcription factor-mediated reprogramming and nontranscription factor-mediated reprogramming. We review the selection of reprogramming factors and delivery systems required. Transcription factor cocktails, such as the RXOL cocktail (Runx2, Osx, OCT3/4, and L-MYC), have shown promise in inducing osteogenic differentiation in fibroblasts. Alterations to the original cocktail, such as the addition of Oct9 and N-myc, have resulted in improved reprogramming efficiency. Transcription factor delivery includes integrative and nonintegrative systems which encompass viral vectors and nonviral methods such as synthetic RNA. Recently, an integrative approach using self-replicating RNA has been developed to achieve a longer and more sustained transcription factor expression. Nontranscription factor-mediated reprogramming using small molecules, proteins, inhibitors, and agonists has also been explored. For example, IGFBP7 protein supplementation and ALK5i-II inhibitor treatment have shown potential in enhancing osteoblast reprogramming. Direct reprogramming methods hold great promise for advancing bone regeneration and tissue repair, providing a potential therapeutic approach for fracture healing and the repair of bone defects. Multiple obstacles and constraints need to be addressed before a clinically significant level of cell therapy will be reached. Further research is needed to optimize the efficiency of the reprogramming cocktails, delivery methods, and safety profile of the reprogramming process.