Abstract
Human primary cells, including urine-derived cells (UCs), are an excellent source for generation of pluripotent stem cells (iPSCs) to model disease. However, replicative senescence starts early and shortens the time window for generation of iPSCs. We addressed the question whether combinations of transgenes allows efficient immortalization of UCs, iPSC generation, and differentiation into hepatocyte-like cells (HLCs). Retroviral transfer of three gene cassettes HPVE6E7 (H), hTERT/p53DD (T), cyclinD1/CDK4R24C (C) encoding five genes was established in primary UCs. Long-term cell proliferation was observed in cells carrying transgenes H, HT, HC, and HCT, whereas cells carrying transgenes C, T and CT showed early senescence similar to UCs. iPSCs could be exclusively generated from immortalized UCs transduced with transgenes HCT and HC. iPSC colonies appeared however later and in smaller number as compared to UCs. Using an established hepatic differentiation protocol, HLCs were obtained with high efficacy. Of note, a high expression of individual transgenes was observed in immortalized UCs, which was down-regulated after reprogramming in four out of five genes. One transgene was re-expressed in HLCs as compared to iPSCs. Our data suggest that individual transgene combinations result in advanced growth rates of immortalized cells and do not prevent iPSC formation and HLC differentiation. Retroviral transgene expression is mostly silenced in iPSCs but can be rarely re-expressed after hepatic differentiation. An extended time window for iPSC establishment can be proposed that allows straightforward functional analyses of differentiated cells.