Embryonic stem cell-derived neural progenitors as non-tumorigenic source for dopaminergic neurons

The growth of endothelial-like cells in zebrafish embryoid body culture

There is increasing interest in the possibility of culturing organ-like tissues (organoids) in vitro for biomedical applications. The ability to culture organoids would be greatly enhanced by having a functional circulation in vitro. The endothelial cell is the most important cell type in this context. Endothelial cells can be derived from pluripotent embryonic blastocyst cells in aggregates called embryoid bodies. Here, we examine the yield of endothelial-like cells in embryoid bodies (EBs) developed from transgenic zebrafish fli:GFP and kdrl:GFP blastocyst embryos. The isolated blastocyst cells developed into EBs within the first 24 h of culture and contained fli:GFP⁺ (putative endothelial, hematopoietic and other cell types); or kdrl:GFP⁺ (endothelial) cells. The addition of endothelial growth supplements to the media and culture on collagen type-I substratum increased the percentages of fli:GFP⁺ and kdrl:GFP⁺ cells in culture. We found that EBs developed in hanging-drop cultures possessed a higher percentage of fli:GFP⁺ (45.0 ± 3.1%) and kdrl:GFP⁺ cells (8.7 ± 0.7%) than those developed on conventional substrata (34.5 ± 1.4% or 5.2 ± 0.4%, respectively). The transcriptome analysis showed a higher expression of VEGF and TGFβ genes in EB cultures compared to the adherent cultures. When transferred to conventional culture, the percentage of fli:GFP⁺ or kdrl:GFP⁺ cells declined significantly over subsequent days in the EBs. The fli:GFP⁺ cells formed a monolayer around the embryoid bodies, while the kdrl:GFP⁺ cells formed vascular network-like structures in the embryoid bodies. Differences were observed in the spreading of fli:GFP⁺ cells, and network formation of kdrl:GFP⁺ cells on different substrates. The fli:GFP⁺ cells could be maintained in primary culture and sub-cultures. By contrast, kdrl:GFP⁺ cells were almost completely absent at 8d of primary culture. Our culture model allows real-time observation of fli:GFP⁺ and kdrl:GFP⁺ cells in culture. The results obtained from this study will be important for the development of vascular and endothelial cell culture using embryonic cells.

Influencing the Fate of Cardiac and Neural Stem Cell Differentiation Using Small Molecule Inhibitors of ALK5

In this study, 50 tri-substituted imidazoles (TIs), which are analogs of the small molecules TA-01 and SB203580, were synthesized and screened for cardiomyogenic activities. Several TIs displayed cardiomyogenic activities when applied during the differentiation from days 3-5. The TIs did not affect the Wnt/β-catenin pathway during cardiomyogenesis and the likely mechanism of action is through the inhibition of ALK5 of the TGFβ pathway. Interestingly, these TIs promoted the neural differentiation of human pluripotent stem cells (hPSCs) with a similar potency to that of the dual SMAD inhibitors SB431542/LDN-193189 when dosed from days 1 to 9. The neural induction activities of the TIs correlated with their ALK5 inhibitory activities. This study reports the discovery of small molecule inhibitors of ALK5, which can promote the differentiation of hPSCs into cardiomyocytes or neural cells depending on the time of dosing, showing potential for the production of clinical-grade cardiac/neural cells for regenerative therapy. Stem Cells Translational Medicine 2018;7:709-720.

Transplantation of iPS cell-derived neural progenitors overexpressing SDF-1α increases regeneration and functional recovery after ischemic stroke

Ischemic stroke is a leading cause of human death and disability while clinical treatments are limited. The adult brain possesses endogenous regenerative activities that may benefit tissue repair after stroke. Trophic factors such as stromal cell-derived factor 1 alpha (SDF-1α) are upregulated in the ischemic brain, which promote endogenous regeneration. The regenerative response, however, is normally insufficient. Transplantation of exogenous cells has been explored as regenerative therapies. One promising cell type for transplantation is induced pluripotent stem (iPS) cells which are cells genetically reprogrammed from adult somatic cells. We hypothesized that transplanting neural progenitor cells derived from iPS cells (iPS-NPCs) could provide cell replacement and trophic support. The trophic factor SDF-1α was overexpressed in iPS-NPCs by lentiviral transduction to test if SDF-1α could increase regeneration in the ischemic brain. These SDF-1α-iPS-NPCs were differentiated in vitro to express mature neuronal and synaptic markers. Differentiated cells expressed functional Na+ and K+ channels, and fired action potentials. In the oxygen glucose deprivation (OGD) test, SDF-1α-iPS-NPCs survived significantly better compared to control iPS-NPCs. In mice subjected to focal cerebral ischemia in the sensorimotor cortex, iPS-NPCs and SDF-1α-iPS-NPCs were intracranially transplanted into the ischemic cortex 7 days after stroke. Neuronal differentiation of transplanted cells was identified using NeuN 14 days after transplantation. Mice that received SDF-1α-iPS-NPCs had greater numbers of NeuN/BrdU and Glut-1/BrdU co-labeled cells in the peri-infarct area and improved locomotion compared to the control iPS-NPC transplantation. Thus, SDF-1α upregulation in transplanted cells may be a therapeutic strategy to enhance endogenous neurovascular repair after ischemic stroke in adult mice.

Efficient Killing of Murine Pluripotent Stem Cells by Natural Killer (NK) Cells Requires Activation by Cytokines and Partly Depends on the Activating NK Receptor NKG2D

Natural killer (NK) cells play an important role as cytotoxic effector cells, which scan the organism for infected or tumorigenic cells. Conflicting data have been published whether NK cells can also kill allogeneic or even autologous pluripotent stem cells (PSCs) and which receptors are involved. A clarification of this question is relevant since an activity of NK cells against PSCs could reduce the risk of teratoma growth after transplantation of PSC-derived grafts. Therefore, the hypothesis has been tested that the activity of NK cells against PSCs depends on cytokine activation and specifically on the activating NK receptor NKG2D. It is shown that a subcutaneous injection of autologous iPSCs failed to activate NK cells against these iPSCs and can give rise to teratomas. In agreement with this result, several PSC lines, including two iPSC, two embryonic stem cell (ESC), and two so-called multipotent adult germline stem cell (maGSC) lines, were largely resistant against resting NK cells although differences in killing were found at low level. All PSC lines were killed by interleukin (IL)-2-activated NK cells, and maGSCs were better killed than the other PSC types. The PSCs expressed ligands of the activating NK receptor NKG2D and NKG2D-deficient NK cells from Klrk1^-/- mice were impaired in their cytotoxic activity against PSCs. The low-cytotoxic activity of resting NK cells was almost completely dependent on NKG2D. The cytotoxic activity of IL-2-activated NKG2D-deficient NK cells against PSCs was reduced, indicating that also other activating receptors on cytokine-activated NK cells must be engaged by ligands on PSCs. Thus, NKG2D is an important activating receptor involved in killing of murine PSCs. However, NK cells need to be activated by cytokines before they efficiently target PSCs and then also other NK receptors become relevant. These features of NK cells might be relevant for transplantation of PSC-derived grafts since NK cells have the capability to kill undifferentiated cells, which might be present in grafts in trace amounts.

Self-regulatory factors of embryonic stem cells in co-culture with stromal cells enhance neural differentiation

Embryonic stem cells (ESCs), due to their intrinsic capability to generate somatic cells of all three germ layers, are potential sources of neural cells for cell replacement therapies. However, the empirical differentiation protocols and the lack of mechanistic understanding of the neural differentiation of ESCs have limited the utility of ESCs as a developmental model or as a cell source for neural cell populations for replacement therapies. Co-culturing ESCs with stromal cells is one of the extensively used methods to induce neural differentiation. Despite several studies to identify neural inducing factors in stromal cell induced neural differentiation, the self-regulatory effects of ESCs in the neural differentiation process remain unexplored. For the first time, we elucidate the self-regulatory role of mESCs in their neural cell differentiation by supplementing conditioned media from differentiating mESCs to mESC-PA6 co-cultures and quantitatively evaluating the change in neural differentiation. Moreover, we use statistical tools to analyze the expression of various growth and trophic factors and distinguish the factors produced primarily by PA6 cells versus mESCs in co-culture. We observe that addition of the medium containing mESC-secreted factors to a single mESC colony co-cultured with PA6 cells significantly enhances the neural differentiation of mESCs compares to the medium extracted from the stromal cells only. Hierarchical clustering of gene expression data from PA6 and co-cultured mESCs segregates two groups of factors that are produced by the stromal cells and differentiating mESCs. Identifying the major soluble factors that drive and regulate the neural differentiation process in the mESC-PA6 co-culture niche will help understand molecular mechanisms of neural development. Moreover, it can be a major step toward developing novel protocols to differentiate stem cells with mESC derived factor supplementation without using feeder cells and with greater efficiency compared to existing approaches.

Molecular Analysis of Stromal Cells-Induced Neural Differentiation of Mouse Embryonic Stem Cells

Deriving specific neural cells from embryonic stem cells (ESCs) is a promising approach for cell replacement therapies of neurodegenerative diseases. When co-cultured with certain stromal cells, mouse ESCs (mESCs) differentiate efficiently to neural cells. In this study, a comprehensive gene and protein expression analysis of differentiating mESCs is performed over a two-week culture period to track temporal progression of cells from a pluripotent state to specific terminally-differentiated neural cells such as neurons, astrocytes, and oligodendrocytes. Expression levels of 26 genes consisting of marker genes for pluripotency, neural progenitors, and specific neuronal, astroglial, and oligodendrocytic cells are tracked using real time q-PCR. The time-course gene expression analysis of differentiating mESCs is combined with the hierarchal clustering and functional principal component analysis (FPCA) to elucidate the evolution of specific neural cells from mESCs at a molecular level. These statistical analyses identify three major gene clusters representing distinct phases of transition of stem cells from a pluripotent state to a terminally-differentiated neuronal or glial state. Temporal protein expression studies using immunohistochemistry demonstrate the generation of neural stem/progenitor cells and specific neural lineages and show a close agreement with the gene expression profiles of selected markers. Importantly, parallel gene and protein expression analysis elucidates long-term stability of certain proteins compared to those with a quick turnover. Describing the molecular regulation of neural cells commitment of mESCs due to stromal signaling will help identify major promoters of differentiation into specific cell types for use in cell replacement therapy applications.

hiPSC-derived iMSCs: NextGen MSCs as an advanced therapeutically active cell resource for regenerative medicine

Mesenchymal stem cells (MSCs) are being assessed for ameliorating the severity of graft‐versus‐host disease, autoimmune conditions, musculoskeletal injuries and cardiovascular diseases. While most of these clinical therapeutic applications require substantial cell quantities, the number of MSCs that can be obtained initially from a single donor remains limited. The utility of MSCs derived from human‐induced pluripotent stem cells (hiPSCs) has been shown in recent pre‐clinical studies. Since adult MSCs have limited capability regarding proliferation, the quantum of bioactive factor secretion and immunomodulation ability may be constrained. Hence, the alternate source of MSCs is being considered to replace the commonly used adult tissue‐derived MSCs. The MSCs have been obtained from various adult and foetal tissues. The hiPSC‐derived MSCs (iMSCs) are transpiring as an attractive source of MSCs because during reprogramming process, cells undergo rejuvination, exhibiting better cellular vitality such as survival, proliferation and differentiations potentials. The autologous iMSCs could be considered as an inexhaustible source of MSCs that could be used to meet the unmet clinical needs. Human‐induced PSC‐derived MSCs are reported to be superior when compared to the adult MSCs regarding cell proliferation, immunomodulation, cytokines profiles, microenvironment modulating exosomes and bioactive paracrine factors secretion. Strategies such as derivation and propagation of iMSCs in chemically defined culture conditions and use of footprint‐free safer reprogramming strategies have contributed towards the development of clinically relevant cell types. In this review, the role of iPSC‐derived mesenchymal stromal cells (iMSCs) as an alternate source of therapeutically active MSCs has been described. Additionally, we also describe the role of iMSCs in regenerative medical applications, the necessary strategies, and the regulatory policies that have to be enforced to render iMSC's effectiveness in translational medicine.

iPSC Transplantation increases regeneration and functional recovery after ischemic stroke in neonatal rats

Limited treatments are available for perinatal/neonatal stroke. Induced pluripotent stem cells (iPSCs) hold therapeutic promise for stroke treatment, but the benefits of iPSC transplantation in neonates are relatively unknown. We hypothesized that transplanted iPSC-derived neural progenitor cells (iPSC-NPCs) would increase regeneration after stroke. Mouse pluripotent iPSCs were differentiated into neural progenitors using a retinoic acid protocol. Differentiated neural cells were characterized by using multiple criteria and assessments. Ischemic stroke was induced in postnatal day 7 (P7) rats by occluding the right middle cerebral artery and right common carotid artery. iPSC-NPCs (400,000 in 4 µl) were transplanted into the penumbra via intracranial injection 7 days after stroke. Trophic factor expression in the peri-infarct tissue was measured using Western blot analysis. Animals received daily bromodeoxyuridine (BrdU) injections and were sacrificed 21 days after stroke for immunohistochemistry. The vibrissae-elicited forelimb placement test was used to evaluate functional recovery. Differentiated iPSCs expressed mature neuronal markers, functional sodium and potassium channels, and fired action potentials. Several angiogenic and neurogenic trophic factors were identified in iPSC-NPCs. Animals that received iPSC-NPC transplantation had greater expression of stromal cell-derived factor 1-α (SDF-1α) and vascular endothelial growth factor (VEGF) in the peri-infarct region. iPSC-NPCs stained positive for neuronal nuclei (NeuN) or glial fibrillary acidic protein (GFAP) 14 days after transplantation. iPSC-NPC-transplanted animals showed greater numbers of BrdU/NeuN and BrdU/Collagen IV colabeled cells in the peri-infarct area compared with stroke controls and performed better in a sensorimotor functional test after stroke. iPSC-NPC therapy may play multiple therapeutic roles after stroke by providing trophic factors, increasing angiogenesis and neurogenesis, and providing new cells for tissue repair.

Human Induced Pluripotent Stem Cells Are Targets for Allogeneic and Autologous Natural Killer (NK) Cells and Killing Is Partly Mediated by the Activating NK Receptor DNAM-1

Human induced pluripotent stem cells (hiPSCs) could be used to generate autologous cells for therapeutic purposes, which are expected to be tolerated by the recipient. However, iPSC-derived grafts are at risk of giving rise to teratomas in the host, if residuals of tumorigenic cells are not rejected by the recipient. We have analyzed the susceptibility of hiPSC lines to allogeneic and autologous natural killer (NK) cells. IL-2-activated, in contrast to resting NK cells killed hiPSC lines efficiently (P = 1.69 x 10(-39)). Notably, the specific lysis of the individual hiPSC lines by IL-2-activated NK cells was significantly different (P = 1.72 x 10(-6)) and ranged between 46 % and 64 % in 51Cr-release assays when compared to K562 cells. The hiPSC lines were killed by both allogeneic and autologous NK cells although autologous NK cells were less efficient (P=8.63 x 10(-6)). Killing was partly dependent on the activating NK receptor DNAM-1 (P = 8.22 x 10(-7)). The DNAM-1 ligands CD112 and CD155 as well as the NKG2D ligands MICA and MICB were expressed on the hiPSC lines. Low amounts of human leukocyte antigen (HLA) class I proteins, which serve as ligands for inhibitory and activating NK receptors were also detected. Thus, the susceptibility to NK cell killing appears to constitute a common feature of hiPSCs. Therefore, NK cells might reduce the risk of teratoma formation even after autologous transplantations of pluripotent stem cell-derived grafts that contain traces of pluripotent cells.