Abstract
Recent advances in tissue engineering that combine an extracellular matrix–like scaffold with therapeutic molecules, cells, DNA encoding therapeutic proteins, or a combination of the three hold promise for treating defects in the brain resulting from a penetrating injury or tumor resection. The purpose of this study was to investigate a porous sponge-like collagen scaffold for non-viral delivery of a plasmid encoding for glial cell line–derived neurotrophic factor (pGDNF) to rat marrow stromal stem cells (also referred to as mesenchymal stem cells, MSCs). The effects of the following parameters on GDNF synthesis in the three-dimensional (3D) constructs were evaluated and compared with results in monolayer culture: initial plasmid load (2–50 μg pGDNF), ratio of a lipid transfection reagent to plasmid (5:10), culture environment during the transfection (static and dynamic), and cell density. The level of gene expression in the collagen scaffolds achieved therapeutic levels that had previously been found to support survival of dopaminergic and trigeminal neurons in vitro. For the highest loading of plasmid (50 μg), the level of GDNF protein remained six to seven times above the control level after 2 weeks, a significant difference. Cell density in the scaffold was of importance for an early increase in GDNF production, with accumulated GDNF being approximately 60% greater after 9 days of culture when scaffolds were initially seeded with 2 million rat MSCs compared to 500,000 cells. Application of orbital shaking during the 4 h of transfection had a positive effect on the production of GDNF on 3D constructs but not of the same magnitude as reported in monolayer studies. Overall, these results demonstrate that the combination of tissue engineering and non-viral transfection of MSCs for the over-expression of GDNF is a promising approach for the long-term production of GDNF and probably for neurotrophic factors in general.