Remote activation of Frizzled receptors using magnetic nanoparticles for bone tissue engineering

Abstract

The Wnt signalling pathways play crucial roles in development, tissue patterning, and stem cell fate determination. These pathways are therefore an attractive therapeutic target in the field of regenerative medicine and tissue engineering. Magnetic nanoparticles (MNP) are useful tools in bio-engineering. Previous work from our group has demonstrated the efficacy of targeting and activating cell signalling pathways using MNP functionalised with targeting proteins coupled with magnetic fields to remotely torque the MNP. Using this approach, in this work MNP were functionalised with ligands targeted to cell surface Frizzled receptors which are involved in Wnt signal transduction. The effects of remote stimulation with MNP on Wnt pathway activity were then assessed in human mesenchymal stem cells (hMSC). Results demonstrated that targeting of Frizzled receptors with MNP and remote stimulation using magnetic fields remotely activated Wnt signalling pathways. This was indicated by nuclear mobilisation of ß-catenin and activation of a TCF/LEF luciferase reporter. The effect of remote Wnt pathway activation on hMSC osteogenesis was subsequently assessed. Activation was shown to augment hMSC differentiation in monolayer experiments where expression of osteogenic markers increased. This strategy also had beneficial effects on bone formation in an ex vivo foetal chick femur model as indicated by µCT and histology. The role of spatial Wnt gradients on bone formation is also important in development and was investigated using a tissue engineering platform utilising immobilised Wnt protein. In conclusion, these studies demonstrate the use of MNP to remotely activate Wnt signalling pathways and have shown potential in directing hMSC differentiation. This provides proof of concept for new injectable therapies that modulate cell signalling pathways with applications in regenerative medicine.