Construction of heterotypic cell sheets by magnetic force-based 3-D coculture of HepG2 and NIH3T3 cells

Heterotypic 3-D coculture is essential to mimic tissues and organs, because cell-cell interaction between various types of cells is believed to be important for the activation of cellular functions. In this study, magnetic force was applied to construct a 3-D coculture system of HepG2 and NIH3T3 cells as a model of hepatocytes and mesenchymal cells. Magnetite cationic liposomes (MCLs) were used to label target cells. NIH3T3 cells labeled with MCLs were seeded onto ultralow-attachment plates, whose surface is composed of a covalently bound hydrogel layer that is hydrophilic and neutrally charged. When a magnet was placed under the plate, cells accumulated on the bottom of the well. After a 24-h incubation period, the cells formed a multilayered cell sheet, which contained the major mesenchymal extracellular matrix (ECM) components (fibronectin and type I collagen), suggesting that the use of stromal NIH3T3 cells gave sufficient strength to cell sheets. Both NIH3T3 and HepG2 cells were labeled with MCLs, and cocultured by two methods: NIH3T3 cell sheets were constructed and HepG2 cells were subsequently seeded onto NIH3T3 cell sheets, and then allowed to form layered cell sheets by applying magnetic force; or NIH3T3 and HepG2 cells were mixed and then allowed to form mixed cell sheets by applying magnetic force. These heterotypic multilayered cell sheets were successfully constructed and an enhanced albumin secretion by HepG2 cells was observed. These results suggest that the new tissue engineering technique using magnetite nanoparticles and magnetic force, to which we refer to as magnetic force-based tissue engineering (Mag-TE), is a promising approach to construct multilayered cell sheets consisting of heterotypic cocultured cells.