Histone-Targeted Gene Delivery Carriers for Bone Regeneration

Gene therapy has emerged as a promising treatment option for the regeneration of damaged skeletal tissue. Gene transfer applications offer non-invasive, low cost alternatives to conventional bone grafting procedures, with a capacity for sustained, controlled expression of nascent proteins that can initiate bone repair. However, the design of synthetic delivery systems that negotiate efficient intracellular trafficking and controllably bind and release DNA within the nucleus represents a significant challenge. Overcoming these hurdles requires a combination of well-controlled materials approaches with techniques to understand and direct cellular delivery.

Recent investigations have highlighted the roles histone tail sequences play in directing nuclear delivery, nuclear retention, and DNA transcription in chromatin. In this work, we establish the ability to recapitulate these natural histone tail activities within non-viral gene carriers to improve gene transfer and expression of exogenous factors. We demonstrate that histone-targeted carriers employ vesicular retrograde trafficking pathways to reach the nucleus without endosomal escape, and we identify their key interactions with native histone effectors that initiate nuclear targeting and enhance gene expression. We also show that histone-targeting leads to improved osteogenic growth factor expression in mesenchymal stem cells, ultimately enhancing differentiation along cellular lineages essential to endochondral ossification and fracture healing. Most notably, we demonstrate that histone-targeted growth factor expression can trigger similar levels of differentiation as topically applied growth factors, yet requires only 1/100th the quantity of growth factor. Future work seeks to further enhance growth factor delivery and expression capabilities through the development of a tunable delivery scaffold designed to mimic additional aspects of the natural histone octamer architecture.