The Development of Cancer through the Transient Overexpression of Reprogramming Factors

Retention of Somatic Memory Associated with Cell Identity, Age and Metabolism in Induced Pluripotent Stem (iPS) Cells Reprogramming

The discovery of induced pluripotent stem (iPS) cells in 2006 marked a major breakthrough in regenerative medicine, enabling reversal of terminally differentiated somatic cells into pluripotent stem cells. The embryonic stem (ES) cells-like pluripotency and unlimited self-renewal capability of iPS cells have granted them enormous potential in many applications, particularly regenerative therapy. Unlike ES cells, however, iPS cells exhibit somatic memories which were carried over from the tissue of origin thus limited its translation in clinical applications. This review provides an updated overview of the retention of various somatic memories associated with the cellular identity, age and metabolism of tissue of origin in iPS cells. The influence of cell types, stage of maturation, age and various other factors on the retention of somatic memory has been discussed. Recent evidence of somatic memory in the form of epigenetic, transcriptomic, metabolic signatures and its functional manifestations in both in vitro and in vivo settings also have been reviewed. The increasing number of studies which had adopted isogenic cell lines for comparisons in recent years had facilitated the identification of genuine somatic memories. These memories functionally affect iPS cells and its derivatives and are potentially tumorigenic thus, raising concerns on their safety in clinical application. Various approaches for memory erasure had since being reported and their efficacies were highlighted in this review.

Gene Expression in Pancreatic Cancer-Like Cells and Induced Pancreatic Stem Cells Generated by Transient Overexpression of Reprogramming Factors

We previously reported that transient overexpression of reprogramming factors can be used to generate induced pluripotent stem (iPS) cells, induced tissue-specific stem (iTS) cells, and fibroblast-like (iF) cells from pancreatic tissue. iF cells have tumorigenic ability and behave similarly to pancreatic cancer cells. In this study, we analyzed gene expression in iF cells and iTS-P cells (iTS cells from pancreatic tissue) via microarray analysis and quantitative reverse transcription-polymerase chain reaction (qRT-PCR). The expression levels of the Mybl2 and Lyn genes, which are reported to be oncogenes, were significantly higher in iF cells than in iTS-P cells. The expression level of Nestin, which is expressed in not only pancreatic progenitor cells but also pancreatic ductal adenocarcinomas, was also higher in iF cells than in iTS-P cells. Itgb6 and Fgf13, which are involved in the pathogenesis of diseases such as cancer, exhibited higher expression levels in iF cells than in iTS-P cells. Unexpectedly, the expression levels of genes related to epithelial-mesenchymal transition (EMT), except Bmp4, were lower in iF cells than in iTS-P cells. These data suggest that the Mybl2, Lyn, Nestin, Itgb6, and Fgf13 genes could be important biomarkers to distinguish iTS-P cells from iF cells.

Induction of Expandable Adipose-Derived Mesenchymal Stem Cells from Aged Mesenchymal Stem Cells by a Synthetic Self-Replicating RNA

Adipose-derived mesenchymal stem cells (ADSCs) have attracted attention due to their potential for use in the treatment of various diseases. However, the self-renewal capacity of ADSCs is restricted and their function diminishes during passage. We previously generated induced tissue-specific stem cells from mouse pancreatic cells using a single synthetic self-replicating Venezuelan Equine Encephalitis (VEE)-reprogramming factor (RF) RNA replicon (SR-RNA) expressing the reprogramming factors POU class 5 homeobox 1 (OCT4), Krueppel-like factor 4 (KLF4), Sex determining region Y-box 2 (SOX2), and Glis Family Zinc Finger 1 (GLIS1). This vector was used to generate induced pluripotent stem (iPS) cells. Here, we applied this SR-RNA vector to generate human iTS cells from aged mesenchymal stem cells (hiTS-M cells) deficient in self-renewal that were derived from adipose tissue. These hiTS-M cells transfected with the SR-RNA vector survived for 15 passages. The hiTS-M cells expressed cell surface markers similar to those of human adipose-derived mesenchymal stem cells (hADSCs) and differentiated into fat cells and osteoblasts. Global gene expression profiling showed that hiTS-M cells were transcriptionally similar to hADSCs. These data suggest that the generation of iTS cells has important implications for the clinical application of autologous stem cell transplantation.