Finally we demonstrate here that PML

Finally, we demonstrate here that PML promotes iPSC generation by facilitating the early activation steps. Our proposed model for its contribution to reprogramming is that PML activates mesenchymal marker activation (EMT), which in turn enhances epithelial (MET) and pluripotent gene activation, resulting in an increase of reprogramming efficiency. In agreement with recent publications (Liu et al., 2013), we detect an initial EMT step in the reprogramming process that is compromised by PML loss. Additionally it is well established that PML is a crucial regulator of transforming growth factor β (TGF-β) signaling, since Pml−/− MEF showed a significant reduction of p-Smad2/3 and impaired npy receptor of TGF-β target genes including mesenchymal-specific genes (Lin et al., 2004). Consequently, Pml−/− iPSC showed reduced pluripotency as manifested by the generation of smaller and more differentiated teratomas. This effect may be also attributed to telomere dysfunction that was reported in PML KD ESC (Chang et al., 2013). Functional telomeres are essential for pluripotency, and telomere shortening causes impaired teratoma formation (Huang et al., 2011). Collectively, we present evidence that PML preserves mESC naive pluripotency and facilitates the reprogramming ability of mouse fibroblasts. This action may be related to the recently described pro-survival action of PML in breast cancer (Carracedo et al., 2012) and the involvement of PML in cancer stem cell maintenance in leukemia (Ito et al., 2008) and glioma (Zhou et al., 2015).
Experimental Procedures
Author Contributions
Acknowledgments We would like to thank G. Vretzos and D. Tsoukatou for technical assistance, as well as D. Vassou for her contribution in gene expression profiling (IMBB), E. Deligianni for her involvement in TMRE-stained figures analysis, T. Kosteas for help with the isolation of mouse blastocysts, and Prof. C. Spilianakis for critical suggestions. We also thank Prof. N. Tavernarakis for providing reagents for monitoring oxygen consumption and mitochondria function. This work was funded by Thalis-MIS380247-MIREG (NSRF 2007-2013), Umbistem11SYN_10_668, Fondation Sante, “PROGRAMMATIC AGREEMENTS BETWEEN RESEARCH CENTRES – GSRT 2015-2017” (SIEMENS Biology Activity -Biophotonics) and IMBB internal funding.
Introduction The discovery that development is not a one-way street but can be reverted by nuclear reprogramming leading to induced pluripotent stem cells (iPSCs) is one of the most promising recent discoveries in translational medicine (Larribere and Utikal, 2014; Tabar and Studer, 2014). Patient-specific iPSCs not only allow for the modeling of distinct diseases and testing of novel drugs, but also provide unique resources for regenerative medicine (Galach and Utikal, 2011). The possibility to differentiate human iPSCs (hiPSCs) into distinct neuronal cells is already beginning to revolutionize research in the neurodegenerative disease field, indicated by the escalating number of publications focusing on hiPSC-derived neurodegenerative disease models (Lojewski et al., 2014; Stanslowsky et al., 2014; Japtok et al., 2015). Nevertheless, the full potential of hiPSCs is not yet utilized. Using hiPSCs to study the influence of the differentiation state on disease-associated mutations is still in its infancy. Nuclear reprogramming is initiated by ectopic expression of the four transcription factors OCT4, SOX2, KLF4, and MYC. During this process the epigenetic profile of a somatic cell is reverted in stepwise fashion to the profile of pluripotent stem cells (PSCs), which are able to differentiate into any cell of the three germ layers (Takahashi and Yamanaka, 2006; Maherali et al., 2007; Takahashi et al., 2007). Using patient-derived somatic cells, the initiation of even genetically complex diseases such as Alzheimer’s disease (Yagi et al., 2011), multiple sclerosis (reviewed in Di Ruscio et al., 2015), or early events in tumor initiation (Kim et al., 2013) can be modeled. Therefore, iPSC technology enables investigation not only of early events during the onset of a disease but also the influence of the epigenetic status on the disease. Although previous studies successfully demonstrated reprogramming of cancer cells, reprogramming barriers prevent the successful induction of pluripotency in the majority of tumor cells (Utikal et al., 2009; Bernhardt et al., 2012; Kim et al., 2013).