211 REPROGRAMMING OF PORCINE NEURAL PROGENITOR CELLS TO INDUCED PLURIPOTENT STEM CELL-LIKE CELLS

Abstract

Human-induced pluripotent stem cells (iPSC) are envisioned to play a vital role in future cell replacement therapy. In this context, porcine iPSC would be highly useful for pre-clinical safety testing by autologous transplantation in a porcine biomedical model. However, a major impediment is that currently, continuous expression of reprogramming factors is required to maintain the pluripotent state of porcine iPSC. In the mouse, neural progenitor cells (NPC) have proved to be highly amenable to reprogramming due to their partly stem-like epigenetic state and expression of pluripotency-related genes such as SOX2. The objective of this study was to establish iPSC from porcine epiblast-derived NPC by use of a tetracycline-inducible Tet-ON approach. A total of 1.5 × 10⁵ porcine NPC at passage 6 (Rasmussen et al. 2011) were transduced O/N with 0.5 mL of active virus containing the following porcine pluripotency genes: pOCT4 (pO); pOCT4 and pKLF4 (pOK); pOCT4 and pC-MYC (pOM); pOCT4, pC-MYC and pKLF4 (pOMK) or polycistronic pOCT4, pSOX2, pC-MYC and pKLF4 (pOSMK); all including 0.25 mL of transactivator (rtTA). After 3 days, the cells were trypsinized and passaged to MEF feeder cells and cultured in iPSC medium containing DMEM/F12, 20% KSR, 1% NEAA, 10 μM β-Me, 20 ng mL^–1 human bFGF and 2 μg mL^–1 doxycycline. On Day 8, tightly packed colonies of cells presenting an embryonic stem cell-like morphology were visible in the pOM, pOMK and pOSMK combinations. In contrast, colonies were not observed with the pO and pOK combination. On Day 14, several iPSC-like colonies were manually picked and subcultured on MEF feeder cells in iPSC medium. Two lines from the pOSMK combination were capable of prolonged clonal propagation while maintaining an ESC-like morphology. However, when doxycycline was removed from the culture medium, growth arrest and spontaneous differentiation occurred. The iPSC-like lines expressed OCT4, SOX2, C-MYC and KLF4, as evaluated by immunocytochemistry and expression of NANOG, SSEA-1 and SSEA-4 was also confirmed, demonstrating activation of endogenous pluripotency genes. The iPSC-like lines were capable of forming embryoid bodies (EB) without addition of doxycycline and in vitro differentiation of EB in medium containing DMEM and 15% FCS confirmed the presence of meso- (SMA) and endodermal (AFP) derivatives by immunocytochemistry. Furthermore, co-culture experiments with MS5 stromal cells in medium containing DMEM, 15% KSR and 150 ng mL^–1 human Noggin resulted in differentiation into neuroectoderm (NESTIN and SOX2), as well as more mature neurons (TUJI and GFAP). The porcine iPSC-like lines could serve as an excellent platform for optimizing culture conditions, which may sustain the pluripotency network in the pig and could be applied for autologous stem cell transplantation in a porcine model for evaluation of safety and efficacy.

The Danish Agency for Science, Technology and Innovation, the Danish National Advanced Technology Foundation as well as the EU projects, EU FP7 (PartnErS, PIAP-GA-2008-218205; PluriSys, HEALTH-2007-B-223485).