We sought to determine whether T cell derived iPSCs

We sought to determine whether T cell-derived iPSCs (TiPSCs) could be used to analyze neurological diseases. Several issues regarding the utilization of TiPSCs in neurological studies remain unresolved. First, previous studies indicated that each iPSC clone retains an epigenetic memory relating to the cell type from which they are derived, even after their re-differentiation into somatic cells, and this restricts their differentiation potential (Kim et al., 2010, 2011; Panopoulos et al., 2012; Polo et al., 2010). Kim et al. reported that there are distinct differences in the genome-wide DNA methylation profiles of iPSCs derived from cord blood PalMitoyl Tripeptide-1 (CB-iPSCs) and iPSCs derived from neonate keratinocytes (K-iPSCs), and that these differences are closely related to their differentiation potentials. K-iPSCs had an enhanced potential to differentiate into keratinocytes in comparison with CB-iPSCs, even though both types of iPSCs were established from the same donor. Second, rearrangement of T cell receptor (TCR) chain genes in mature T cells indicates that they are not identical to naive lymphocytes at the genomic level. Although such rearrangements are reportedly retained in TiPSCs (Seki et al., 2010), it is unknown whether they affect the neural differentiation and function of TiPSCs.
Results
Discussion hiPSCs can be used to generate neuronal cells in vitro, which has widened the application of these cells. However, the requirement for skin biopsies to be performed must be overcome before iPSC technologies are widely adopted. Seki et al. (2010) developed TiPSCs, which enabled iPSCs to be obtained more easily and with less invasive methods. The current study shows that TiPSCs can differentiate into functional neurons, including dopaminergic, GABAergic, and glutamatergic subtypes, using an optimized differentiation protocol, dNS method. Moreover, these cells could be used to study the mechanisms underlying neuronal diseases, although there are some differences between TiPSCs and aHDF-iPSCs. Furthermore, the neurons differentiated from TiPSCs derived from a PARK2 patient exhibited several Parkinson\'s disease phenotypes, including an impairment of mitochondrial functions, dopaminergic neuron-specific cell death, and increased ROS production. Some studies indicate that iPSCs retain a transient transcriptional and epigenetic memory of their cell types of origin, which can substantially affect their potential to differentiate into various cell types, even among iPSCs that are genetically identical (Kim et al., 2010, 2011; Polo et al., 2010). Two independent studies of genetically matched hiPSC clones established from skin or blood cells examined how their differentiation potential is influenced by their cell types of origin. Daley and colleagues reported that blood cell-derived iPSCs differentiate into blood cells more efficiently than keratinocyte-derived iPSCs, and the latter iPSCs efficiently differentiate into keratinocytes (Kim et al., 2011). They concluded that the differentiation potential of hiPSCs is influenced by a residual epigenetic memory of the tissue from which they are derived. They also showed that extended passage of most iPSC lines reduced the effect of cell origin by erasing the cells\' epigenetic memory, although some clones failed to erase the epigenetic memory, even after recurrent passaging. It is possible that our protocol could minimize the differences stemming from differences in epigenetic status after any passage of iPSCs, which we will address in a future study. However, a study by Yamanaka and colleagues reported that blood cell-derived iPSCs and skin cell-derived iPSCs can both differentiate into the hepatic lineage if they are established from the same donor (Kajiwara et al., 2012). They concluded that variations in hepatic differentiation are largely owing to differences in the donors, rather than to the cell types from which iPSCs are derived. Although these two conclusions seem contradictory, it is possible that the influences of epigenetic memory and donor differences vary according to the lineage along which cells differentiate. Here, we showed that TiPSCs failed to differentiate along the neural lineage using the EB formation protocol. The increased expression of mesendodermal and endodermal markers in TiPSC-derived EBs suggests that TiPSCs preferentially differentiated into the mesendodermal lineage, rather than the ectodermal lineage. Our single-cell dissociation protocol enabled TiPSCs to differentiate into functional neuronal cells with a similar efficiency as aHDF-iPSCs. Furthermore, TiPSC-derived neuronal cells generated from a Parkinson\'s disease patient exhibited abnormal mitochondrial degradation similar to aHDF-iPSC-derived neuronal cells. Our results suggest that this robust directed differentiation protocol can overcome the biased differentiation of iPSCs owing to epigenetic memory of the original cells. Our results also suggest that TCR rearrangement does not affect the differentiation efficiency when a directed neural differentiation method is used. EBs contain cells that have differentiated from PSCs into the three germ cell lineages in a spontaneous and unbiased manner (Itskovitz-Eldor et al., 2000). However, TiPSC-derived EBs contained few neural cells due to their reduced potential to differentiate into the neural lineage. By contrast, our differentiation protocol facilitated directed neural differentiation by removing extracellular signals. In relation to genetic background, Yamanaka and colleagues suggested that the propensity for hepatic differentiation of iPSCs is affected by differences in the donor, rather than in the original cell types (Kajiwara et al., 2012). Our results suggest that differences in the donors, original cell types, and iPSC generation methods can be minimalized by using this differentiation protocol.