MiRNAs perform gene regulation that can target approximately 60% of human protein coding genes. Along with many cellular processes, miRNAs have been implicated in stem cell differentiation. Osterix (Osx), which is inhibited by mir-31, is required by MSCs for early osteoblast differentiation resulting in bone formation further downstream. We used antagomir functionalised gold nanoparticles (AuNPs) to block mir-31, which resulted in upregulation of Osx in pre-osteoblastic MG63 cells and human mesenchymal stem cells (MSCs).

We used MG63 pre-osteoblastic cell line and human MSCs. Cytotoxicity of AuNPs was assessed by MTT, and cellular uptake of AuNPs was verified by TEM and ICP-MS. Osx RNA levels were determined by Fluidigm analysis and protein expression by In Cell Western analysis.

Antagomir-functionalised AuNPs were incubated with cells for an initial 48 hours. (1) No cytotoxic effects were noted in either cell type. (2) Fluidigm analysis identified a varied gene response to antagomir delivery in both cell types, with MSCs recording a reduction of stem cell marker genes nestin, alcam, CD63, and CD44 at day 5 (indicating differentiation). (3) Osx protein levels were increased in both cell types after 48 hour incubation. (4) Downstream MSC analysis demonstrated accelerated osteogenesis at week 3 and 5 (verified by osteocalcin nodule formation) following 48 hour AuNP incubation.

RNA analysis in both cell types suggested a shift away from proliferation towards osteoblastic differentiation. This was supported by Osx protein expression, which was increased in both MG63 cells and MSCs. Finally, an increase in the late osteogenic marker (osteocalcin) was verified at weeks 3 and 5 in MSCs after AuNP incubation for 48 hours. These results collectively infer successful delivery of mir-31 antagomirs, which are blocking mir-31-mediated suppression of Osx, resulting in an early increase in Osx, which accelerates MSC osteogenesis downstream.