Tethered growth factors on biocompatible scaffolds improve stemness of cultured rat and human neural stem cells and growth of oligodendrocyte progenitors.

ABSTRACT

Currently, there is no widely accepted technique to efficiently and reproducibly grow stem and progenitor cells in vitro. Stem cells require contact with extracellular matrices as well as signals from growth factors to proliferate and to retain their stemness. We have shown a novel tissue culture platform (StemTrix cultureware) that transforms standard tissue culture plasticware into a multi-functional chitosan-based scaffold that supports the expansion of neural stem cells. The StemTrix scaffold is comprised of chitosan with immobilized heparin which in turn tethers heparin-binding growth factors. The scaffold is also coated with an adhesive ECM protein. Here we demonstrate that fibronectin or the RGD peptide contained in fibronectin are equally effective in promoting the adhesion, viability and growth of rat and human neural stem cells. When FGF-2 and heparin-binding EGF are tethered to the StemTrix cultureware neural stem cells grow ∼3 times faster and remain in a more primitive state as determined by both Western Blot and gene expression analyses. Another important feature of this new culture platform is that the NSCs remain in a primitive and proliferative state for 4days without refreshing the culture medium or providing new growth factors, which represents a 20-fold extension of FGF-2's biological activity vs when it is freely soluble in the medium. To test the utility of this scaffold for propagating other types of stem cells and progenitors we tethered platelet-derived growth factor (PDGF) and FGF-2 alone and in combination to the scaffold and tested the efficacy of this platform to maintain primary oligodendrocyte progenitors or the CG-4 cell line in a primitive state. Oligodendrocyte progenitors plated onto this multifunctional film proliferated for at least 3days without providing soluble growth factors while inhibiting the expression of the differentiation marker myelin-basic protein. Oligodendrocyte progenitors proliferated 3 times more rapidly than cells maintained on fibronectin-coated culture substrates in culture medium supplemented with soluble FGF-2 and PDGF. Finally, we show that StemTrix cultureware can be produced using clinical grade components, providing users with a fully defined platform suitable for clinical use that maintains stem cells or progenitors in a more uniform and primitive state.