Activation of pluripotency genes by a nanotube-mediated protein delivery system

The overexpression of cell reprogramming factors (Oct4, Sox2, Klf4, Nanog, and c-Myc) allows differentiated cells to revertto an earlier developmental stage. Differentiated cells can also be reprogrammed by directly delivering reprogramming proteins tagged with cell-penetrating peptides, which allow the proteins to pass through the cell membrane and into the cytoplasm-although this method has been an inefficient process. Here, we describe a novel technique for delivering reprogramming proteins into cells using titanium oxide (TiO₂) nanotubes, which show no cytotoxic effects and do not affect cell proliferation. TiO₂ nanotubes successfully transferred the above-mentioned reprogramming factors into differentiated somatic cells. After 3 weeks of treatment with protein-conjugated nanotubes, the somatic cells adopted an embryonic stem cell-like morphology and expressed activated Oct4-green fluorescent protein, a pluripotency biomarker. Our results indicate that TiO₂ nanotubes can be used to directly deliver reprogramming factors into somatic cells to induce pluripotency.