Does transcription factor induced pluripotency accurately mimic embryo derived pluripotency?

Human induced pluripotent stem cells generated neural cells behaving like brain and spinal cord cells: An insight into the involvement of retinoic acid and sonic hedgehog proteins

OBJECTIVES

The previous studies generated neural progenitor cells (NPCs) from human induced pluripotent stem cells (hiPSCs) using different protocols. However, the nature of the temporal or regional specificity of NPCs derived using these protocols is not well defined. Therefore, this study aimed to generate age- and region-specific NPCs from hiPSCs, which mimic in vivo fetal brain (FNPC-B) or spinal cord (FNPC-SC) tissues, in the absence or presence of retinoic acid (RA) and sonic hedgehog (SHH).

MATERIALS AND METHODS

Ventral, caudal and posterior neural cells were generated from hiPSCs with morphogens (RA and SHH), or dorsal, rostral, and anterior neural cells by the withdrawal of these morphogens from the NPC-media. NPCs generated from hiPSCs were compared to FNPC-B or FNPC-SC using immunocytochemical staining assays and global microarray for the evaluations of general and region-specific neural cells markers of neural induction, differentiation, and maturation. Microarray profiling results were analyzed using quantitative unpaired t-test (P < 0.05).

RESULTS

Immunocytochemical analyzes showed that generated NPCs expressed general neural cells markers (PAX6 and MUSASHI-2). Furthermore, FNPC-B and anterior NPCs were characterized with marked expression of cortical neural cells marker (SOX1) when compared to FNPC-SC and posterior NPCs. Microarray profiling results showed the up-regulation of brain cells markers (EMX2 and PAX6) in FNPC-B and anterior NPCs. Similarly, spinal cord cells markers (COL5A2, HOXB5, HOXB7, HOXB8, HOXC4, and HOXD4) were up-regulated in FNPC-SC and posterior NPCs.

CONCLUSION

NPCs that mimic in vivo brain and spinal cord cells can be generated from hiPSCs in the absence or presence of RA and SHH.

Discovery of consensus gene signature and intermodular connectivity defining self-renewal of human embryonic stem cells

Molecular markers defining self-renewing pluripotent embryonic stem cells (ESCs) have been identified by relative comparisons between undifferentiated and differentiated cells. Most of analysis has been done under a specific differentiation condition that may present significantly different molecular changes over others. Therefore, it is currently unclear if there are true consensus markers defining undifferentiated human ESCs (hESCs). To identify a set of key genes consistently altered during differentiation of hESCs regardless of differentiation conditions, we have performed microarray analysis on undifferentiated hESCs (H1 and H9) and differentiated EBs and validated our results using publicly available expression array datasets. We constructed consensus modules by Weighted Gene Coexpression Network Analysis and discovered novel markers that are consistently present in undifferentiated hESCs under various differentiation conditions. We have validated top markers (downregulated: LCK, KLKB1, and SLC7A3; upregulated: RhoJ, Zeb2, and Adam12) upon differentiation. Functional validation analysis of LCK in self-renewal of hESCs using LCK inhibitor or gene silencing with siLCK resulted in a loss of undifferentiation characteristics-morphological change, reduced alkaline phosphatase activity, and pluripotency gene expression, demonstrating a potential functional role of LCK in self-renewal of hESCs. We have designated hESC markers to interactive networks in the genome, identifying possible interacting partners and showing how new markers relate to each other. Furthermore, comparison of these datasets with available datasets from induced pluripotent stem cells (iPSCs) revealed that the level of these newly identified markers was correlated to the establishment of iPSCs, which may imply a potential role of these markers in gaining of cellular potency.

Inhibition of stearoyl-coA desaturase selectively eliminates tumorigenic Nanog-positive cells: improving the safety of iPS cell transplantation to myocardium

Induced pluripotent stem cells (iPS) can differentiate into cardiomyocytes (CM) and represent a promising form of cellular therapy for heart regeneration. However, residual undifferentiated iPS derivates (iPSD), which are not fully eliminated by cell differentiation or purification protocols, may form tumors after transplantation, thus compromising therapeutic application. Inhibition of stearoyl-coA desaturase (SCD) has recently been reported to eliminate undifferentiated human embryonic stem cells, which share many features with iPSD. Here, we tested the effects of PluriSin#1, a small-molecule inhibitor of SCD, on iPS-derived CM. We found that plurisin#1 treatment significantly decreased the mRNA and protein level of Nanog, a marker for both cell pluripotency and tumor progression; importantly, we provide evidence that PluriSin#1 treatment at 20 µM for 1 day significantly induces the apoptosis of Nanog-positive iPSD. In addition, PluriSin#1 treatment at 20 µM for 4 days diminished Nanog-positive stem cells in cultured iPSD while not increasing apoptosis of iPS-derived CM. To investigate whether PluriSin#1 treatment prevents tumorigenicity of iPSD after cell transplantation, we intramyocardially injected PluriSin#1- or DMSO-treated iPSD in a mouse model of myocardial infarction (MI). DMSO-treated iPSD readily formed Nanog-expressing tumors 2 weeks after injection, which was prevented by treatment with PluriSin#1. Moreover, treatment with PluriSin#1 did not change the expression of cTnI, α-MHC, or MLC-2v, markers of cardiac differentiation (P>0.05, n = 4). Importantly, pluriSin#1-treated iPS-derived CM exhibited the ability to engraft and survive in the infarcted myocardium. We conclude that inhibition of SCD holds the potential to enhance the safety of therapeutic application of iPS cells for heart regeneration.

Epigenetics of reprogramming to induced pluripotency

Reprogramming to induced pluripotent stem cells (iPSCs) proceeds in a stepwise manner with reprogramming factor binding, transcription, and chromatin states changing during transitions. Evidence is emerging that epigenetic priming events early in the process may be critical for pluripotency induction later. Chromatin and its regulators are important controllers of reprogramming, and reprogramming factor levels, stoichiometry, and extracellular conditions influence the outcome. The rapid progress in characterizing reprogramming is benefiting applications of iPSCs and is already enabling the rational design of novel reprogramming factor cocktails. However, recent studies have also uncovered an epigenetic instability of the X chromosome in human iPSCs that warrants careful consideration.