The Number of Point Mutations in Induced Pluripotent Stem Cells and Nuclear Transfer Embryonic Stem Cells Depends on the Method and Somatic Cell Type Used for Their Generation

iPS cell generation-associated point mutations include many C > T substitutions via different cytosine modification mechanisms

Genomic aberrations are a critical impediment for the safe medical use of iPSCs and their origin and developmental mechanisms remain unknown. Here we find through WGS analysis of human and mouse iPSC lines that genomic mutations are de novo events and that, in addition to unmodified cytosine base prone to deamination, the DNA methylation sequence CpG represents a significant mutation-prone site. CGI and TSS regions show increased mutations in iPSCs and elevated mutations are observed in retrotransposons, especially in the AluY subfamily. Furthermore, increased cytosine to thymine mutations are observed in differentially methylated regions. These results indicate that in addition to deamination of cytosine, demethylation of methylated cytosine, which plays a central role in genome reprogramming, may act mutagenically during iPSC generation.

Molecular Mechanisms and Clinical Application of Multipotent Stem Cells for Spinal Cord Injury

Spinal Cord Injury (SCI) is a common neurological disorder with devastating psychical and psychosocial sequelae. The majority of patients after SCI suffer from permanent disability caused by motor dysfunction, impaired sensation, neuropathic pain, spasticity as well as urinary complications, and a small number of patients experience a complete recovery. Current standard treatment modalities of the SCI aim to prevent secondary injury and provide limited recovery of lost neurological functions. Stem Cell Therapy (SCT) represents an emerging treatment approach using the differentiation, paracrine, and self-renewal capabilities of stem cells to regenerate the injured spinal cord. To date, multipotent stem cells including mesenchymal stem cells (MSCs), neural stem cells (NSCs), and hematopoietic stem cells (HSCs) represent the most investigated types of stem cells for the treatment of SCI in preclinical and clinical studies. The microenvironment of SCI has a significant impact on the survival, proliferation, and differentiation of transplanted stem cells. Therefore, a deep understanding of the pathophysiology of SCI and molecular mechanisms through which stem cells act may help improve the treatment efficacy of SCT and find new therapeutic approaches such as stem-cell-derived exosomes, gene-modified stem cells, scaffolds, and nanomaterials. In this literature review, the pathogenesis of SCI and molecular mechanisms of action of multipotent stem cells including MSCs, NSCs, and HSCs are comprehensively described. Moreover, the clinical efficacy of multipotent stem cells in SCI treatment, an optimal protocol of stem cell administration, and recent therapeutic approaches based on or combined with SCT are also discussed.

Establishment of a non‐integrated induced pluripotent stem cell line derived from human chorionic villi cells

Background

Few studies have investigated the generation of induced pluripotent stem cells (iPSCs) derived from human primary chorionic villi (CV) cells. The present study aimed to explore an optimal electroporation (EP) condition for generating non‐integrated iPSCs from CV cells (CV‐iPSCs).

Methods

The EGFP plasmid was transfected into CV cells under different EP conditions to evaluate cell adherence and the rate of EGFP positive cells. Subsequently, CV cells were transfected with the pEP4‐E02S‐ET2K and pCEP4‐miR‐302–367 plasmids under optimal EP conditions. Finally, CV‐iPSC pluripotency, karyotype analysis, and differentiation ability were investigated.

Results

Following EP for 48 h under different conditions, different confluency, and transfection efficiency were observed in CV cells. Higher cell density was observed in CV cells exposed to 200 V for 100 s, while higher transfection efficiency was obtained in cells electroporated at a pulse of 300 V for 300 s. To generate typical primitive iPSCs, CV cells were transfected with pEP4‐E02S‐ET2K and pCEP4‐miR‐302–367 plasmids using EP and were then cultured in induction medium for 20 days under selected conditions. Subsequently, monoclonal iPSCs were isolated and were evaluated pluripotency with AP positive staining, the expression of OCT4, SOX2, and NANOG in vitro and the formation of three germ layer teratomas in vivo.

Conclusion

CV‐iPSCs were successfully established under the conditions of 100 μl shock cup and EP pulse of 200 V for 300 s for two times. This may provide a novel strategy for investigating the pathogenesis of several diseases and gene therapy.

Defective chromatin architectures in embryonic stem cells derived from somatic cell nuclear transfer impair their differentiation potentials

Nuclear transfer embryonic stem cells (ntESCs) hold enormous promise for individual-specific regenerative medicine. However, the chromatin states of ntESCs remain poorly characterized. In this study, we employed ATAC-seq and Hi-C techniques to explore the chromatin accessibility and three-dimensional (3D) genome organization of ntESCs. The results show that the chromatin accessibility and genome structures of somatic cells are re-arranged to ESC-like states overall in ntESCs, including compartments, topologically associating domains (TADs) and chromatin loops. However, compared to fertilized ESCs (fESCs), ntESCs show some abnormal openness and structures that have not been reprogrammed completely, which impair the differentiation potential of ntESCs. The histone modification H3K9me3 may be involved in abnormal structures in ntESCs, including incorrect compartment switches and incomplete TAD rebuilding. Moreover, ntESCs and iPSCs show high similarity in 3D genome structures, while a few differences are detected due to different somatic cell origins and reprogramming mechanisms. Through systematic analyses, our study provides a global view of chromatin accessibility and 3D genome organization in ntESCs, which can further facilitate the understanding of the similarities and differences between ntESCs and fESCs.

Insertion/deletion and microsatellite alteration profiles in induced pluripotent stem cells

We here demonstrate that microsatellite (MS) alterations are elevated in both mouse and human induced pluripotent stem cells (iPSCs), but importantly we have now identified a type of human iPSC in which these alterations are considerably reduced. We aimed in our present analyses to profile the InDels in iPSC/ntESC genomes, especially in MS regions. To detect somatic de novo mutations in particular, we generated 13 independent reprogramed stem cell lines (11 iPSC and 2 ntESC lines) from an identical parent somatic cell fraction of a C57BL/6 mouse. By using this cell set with an identical genetic background, we could comprehensively detect clone-specific alterations and, importantly, experimentally validate them. The effectiveness of employing sister clones for detecting somatic de novo mutations was thereby demonstrated. We then successfully applied this approach to human iPSCs. Our results require further careful genomic analysis but make an important inroad into solving the issue of genome abnormalities in iPSCs.

A Comparative Approach of Cellular Reprogramming in the Rodentia Order

Cellular reprogramming mainly involves induction of reactivation of genes responsible for nuclear plasticity, a process that can be performed in vitro through production of cloned embryos by somatic cell nuclear transfer or by induction of cells into the pluripotent state through exogenous transcription factor expression. While these techniques are already well known and utilized in mice and rats, their application in other rodent species would be greatly beneficial, especially for conservation purposes. Within the diverse Rodentia order, wild species stand out as they play an important role in balancing the ecosystem by facilitating seed diversion, soil aeration, and consequently, reforestation. Many of these species are currently approaching extinction, and application of techniques, such as nuclear reprogramming, aimed at species conservation and multiplication and to produce stem cells is of interest. Thus, in this review, we aimed to present the evolution and success of nuclear reprogramming, mainly highlighting its potential application for the conservation of wild rodents.

Genetic aberrations in iPSCs are introduced by a transient G1/S cell cycle checkpoint deficiency

A number of point mutations have been identified in reprogrammed pluripotent stem cells such as iPSCs and ntESCs. The molecular basis for these mutations has remained elusive however, which is a considerable impediment to their potential medical application. Here we report a specific stage at which iPSC generation is not reduced in response to ionizing radiation, i.e. radio-resistance. Quite intriguingly, a G1/S cell cycle checkpoint deficiency occurs in a transient fashion at the initial stage of the genome reprogramming process. These cancer-like phenomena, i.e. a cell cycle checkpoint deficiency resulting in the accumulation of point mutations, suggest a common developmental pathway between iPSC generation and tumorigenesis. This notion is supported by the identification of specific cancer mutational signatures in these cells. We describe efficient generation of human integration-free iPSCs using erythroblast cells, which have only a small number of point mutations and INDELs, none of which are in coding regions.

Point mutations have been found in induced pluripotent stem cells (iPSCs) but when they arise is unclear. Here, the authors show that a G1/S cell cycle checkpoint deficiency transiently occurs early in genome reprogramming, suggesting a common developmental pathway between iPSC and tumorigenesis, and generate genetic burden-free human iPSCs.

Rapid fabrication of reinforced and cell-laden vascular grafts structurally inspired by human coronary arteries

Design strategies for small diameter vascular grafts are converging toward native-inspired tissue engineered grafts. A new automated technology is presented that combines a dip-spinning methodology for depositioning concentric cell-laden hydrogel layers, with an adapted solution blow spinning (SBS) device for intercalated placement of aligned reinforcement nanofibres. This additive manufacture approach allows the assembly of bio-inspired structural configurations of concentric cell patterns with fibres at specific angles and wavy arrangements. The middle and outer layers were tuned to structurally mimic the media and adventitia layers of native arteries, enabling the fabrication of small bore grafts that exhibit the J-shape mechanical response and compliance of human coronary arteries. This scalable automated system can fabricate cellularized multilayer grafts within 30 min. Grafts were evaluated by hemocompatibility studies and a preliminary in vivo carotid rabbit model. The dip-spinning-SBS technology generates constructs with native mechanical properties and cell-derived biological activities, critical for clinical bypass applications.

Biofabrication of Autologous Human Hepatocytes for Transplantation: How Do We Get There?

Directed differentiation of hepatocytes from induced pluripotent stem cells (iPSCs) holds promise as source material for treating some liver disorders. The unlimited availability of perfectly differentiated iPSC-derived hepatocytes will dramatically facilitate cell therapies. While systems to manufacture large quantities of iPSC-derived cells have been developed, we have been unable to generate and maintain stable and mature adult liver cells ex vivo. This short review highlights important challenges and possible solutions to the current state of hepatocyte biofabrication for cellular therapies to treat liver diseases. Successful cell transplantation will require optimizing the best cell function, overcoming limitations to cell numbers and safety, as well as a number of other challenges. Collaboration among scientists, clinicians, and industry is critical for generating new autologous stem cell-based therapies to treat liver diseases.