TRANSCRIPT THERAPY TO REGENERATE VASCULARIZED BONE

Non-healing bone fractures represent a chronic medical condition that not only impairs physical function but also significantly impacts the individual's psychosocial and economic well-being. Current treatment options for these patients are often inadequate. Recombinant human bone morphogenetic protein 2 (BMP-2) and 7 (BMP-7) are well-studied, FDA-approved growth factors with potent osteogenic properties. However, its clinical use is limited by the high costs of recombinant protein production and the need for large doses to achieve therapeutic effects, which further raises costs and increases the risk of side effects. A promising alternative is to deliver those BMPs via chemically modified mRNA (cmRNA), enabling the patient's own cells to produce the protein in situ. We developed BMP-2 and BMP-7 coding cmRNA complexed with a lipid vector for transfection purposes. The complex was loaded in a collagen scaffold for BMP-2 in a critical-size femur study or into fibrin hydrogels containing calcium phosphate granules for a subcutaneous or critical-size femur defect study using BMP-7. The scaffolds were implanted subcutaneously into nude mice to evaluate their osteogenic potential, vascularization, and innervation across three BMP-7 cmRNA doses (0.036, 0.36, and 3.6 μg). The critical-size defect model was performed in rats. We assessed bone volume through micro-computed tomography scans, transcriptomic analysis, and histological staining for key osteogenic, angiogenic, and neurogenic markers. While all scaffolds demonstrated osteoinductive properties, the highest BMP-7 cmRNA dose produced greater bone volumes at earlier time points, with increased secretion of extracellular matrix components such as osteopontin and collagen type I. A high dose of BMP-2 cmRNA consolidated the femur defect between 4 and 8 weeks. Although vascularization and innervation were observed, no significant differences were noted between the cmRNA BMP used nor in between dosages. These findings suggest a promising future for the application of mRNA-based therapies in orthopedics where a complete bone tissue including supporting structures such as vessels and nerves are induced.