The regeneration of damaged skeletal tissue following traumatic injury involves a complex series of cascades that direct the differentiation of mesenchymal stem cells (MSCs). These signals include a series of key osteogenic growth factors that are actively released within the fracture site. The necessity for controlled and localized expression of these factors has highlighted the role gene therapy may play as a promising treatment option for bone tissue regeneration. Gene transfer applications offer a capacity for sustained, controlled expression of nascent osteogenic factors that can initiate bone repair cascades by guiding MSC differentiation. However, the design of nanocarrier systems that negotiate efficient intracellular trafficking and nuclear delivery represents a significant challenge. Overcoming these hurdles requires a combination of well-controlled materials approaches with techniques to understand and direct cellular delivery.<br/><br/>Recent investigations have highlighted the roles histone tail sequences play in directing nuclear delivery and retention, as well as activating DNA transcription. We previously established the ability to recapitulate these natural histone tail activities within non-viral gene nanocarriers, improving gene transfer and expression in several cell types by enabling effective navigation to the nucleus via retrograde vesicular trafficking. In this current work, we demonstrate that histone-targeting leads to a near three-fold enhancement in osteogenic bone morphogenetic protein 2 (BMP-2) growth factor expression by MSCs, as compared with standard polymeric transfection reagents. This improved expression ultimately augmented chondrogenic differentiation, an essential first step in the fracture healing cascade. Most notably, over 100-fold enhancements in the expression of cartilage-specific extracellular matrix proteins were triggered by histone-targeted gene transfer, as compared with the response to treatment with equivalent amounts of recombinant BMP-2 protein. In fact, a 100-fold dose increase in recombinant BMP-2 was required to achieve similar levels of chondrogenic gene and protein expression. Based on these findings, we aim to examine how histone-targeted gene therapy promotes such substantial reductions in BMP-2 dosing, by investigating the fundamental changes that occur in MSC cellular behavior and biology following gene therapy versus recombinant protein therapy.

Histone-targeted gene nanocarriers enable 100-fold reductions in BMP-2 dosing for bone regenerative applications

254th National Meeting (2017)

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