Investigating the use of hydrogel matrix systems to generate 3D cultures of induced neural precursor cells for transplantation therapy

Abstract

With recent and ongoing developments within the field of cell reprogramming, the generation and transplantation of induced neural stem/precursor cells (iNSPCs) are gaining traction as a promising treatment strategy for focal neurodegenerative disease. However, optimisation of protocols is currently needed for issues in cell survival, differentiation and functional integration post-transplantation. Hydrogel matrix systems is a potential solution, with recent animal studies reporting promising results with hydrogels encapsulated iNSPCs compared to more traditional liquid vehicles for transplantation in vivo. This study first investigated the potential of gelatin methacryloyl (GelMA) and hyaluronan methylcellulose (HAMC) hydrogels for use in 3D culturing of SOX2/PAX6 reprogrammed iNSPCs in vitro compared to traditional 2D cell cultures. GelMA encapsulation was shown to bias SOX2/PAX6 iNSPCs towards neuronal differentiation and significantly increased TUJ1+ neuronal yields over standard 2D culturing. Further work is required to overcome technical difficulties that have limited the complete and thorough analysis of encapsulated cells in this study, due to the inability to visualise neurites within the GelMA hydrogel. An interesting finding was that HAMC hydrogels do not gelate at physiological temperatures, making them unfeasible for use in 3D culturing in vitro despite prior reports of successful transplantation into rodent models in vivo. Next, SOX2/PAX6 iNSPCs were transplanted into ex vivo rat organotypic slice cultures modelling excitotoxic lesions. Differentiation into neuron-like morphologies was only seen when transplanted cells were encapsulated in HAMC hydrogel, compared to GelMA encapsulation or use of culture media for transplantation. However, these transplanted cells failed to express neuronal markers despite their suggestive morphologies. Analysis was marred by very low efficiencies of zsGreen transduction, resulting in a potentially unrepresentative population of transplanted cells being observed within the ex vivo slices. Due to the novel undertaking of this study, further work is required to fully characterise the differentiated iNSPC population. Despite shortcomings, our results do suggest the use of a hydrogel matrix system can improve neuronal differentiation and survival over more traditional methodologies, with GelMA as a promising option for use in vitro and HAMC for ex vivo transplantation. Our findings are an essential first step in the development of a reliable 3D culture system in vitro and transplantation methodology ex vivo for iNSPCs.