Induced pluripotent stem cells: past, present, and future

3-D bioprinting technologies in tissue engineering and regenerative medicine: Current and future trends

Advances in three-dimensional (3D) printing have increased feasibility towards the synthesis of living tissues. Known as 3D bioprinting, this technology involves the precise layering of cells, biologic scaffolds, and growth factors with the goal of creating bioidentical tissue for a variety of uses. Early successes have demonstrated distinct advantages over conventional tissue engineering strategies. Not surprisingly, there are current challenges to address before 3D bioprinting becomes clinically relevant. Here we provide an overview of 3D bioprinting technology and discuss key advances, clinical applications, and current limitations. While 3D bioprinting is a relatively novel tissue engineering strategy, it holds great potential to play a key role in personalized medicine.

Generation of human-induced pluripotent stem cells from burn patient-derived skin fibroblasts using a non-integrative method

Patient specific induced pluripotent stem cells (iPSCs) have been recognized as a possible source of cells for skin tissue engineering. They have the potential to greatly benefit patients with large areas of burned skin or skin defects. However, the integration virus-based reprogramming method is associated with a high risk of genetic mutation and mouse embryonic fibroblast feeder-cells may be a pollutant. In the present study, human skin fibroblasts (HSFs) were successfully harvested from patients with burns and patient-specific iPSCs were generated using a non-integration method with a feeder-free approach. The octamer-binding transcription factor 4 (OCT4), sex-determining region Y box 2 (SOX2) and NANOG transcription factors were delivered using Sendai virus vectors. iPSCs exhibited representative human embryonic stem cell-like morphology and proliferation characteristics. They also expressed pluripotent markers, including OCT4, NANOG, SOX2, TRA181, stage-specific embryonic antigen 4 and TRA-160, and exhibited a normal karyotype. Teratoma and embryoid body formation revealed that iPSCs were able to differentiate into cells of all three germ layers in vitro and in vivo. The results of the present study demonstrate that HSFs derived from patients with burns, may be reprogrammed into stem cells with pluripotency, which provides a basis for cell-based skin tissue engineering in the future.

Effects of Klf4 and c-Myc Knockdown on Pluripotency Maintenance in Porcine Induced Pluripotent Stem Cell

Objective

The importance of Oct4 and Sox2 in maintaining pluripotency and self-renewal is well-understood, but the functions of Klf4 and c-Myc has not been fully investigated. In the present study, we attempted to determine the roles of Klf4 and c-Myc on pluripotency maintenance of porcine induced pluripotent stem (piPS) cells.

Materials and Methods

In this experimental study, we performed short hairpin RNA (shRNA) to knock down the Klf4 and c-Myc functions of piPS cells and examined pluripotency markers and teratoma formation to evaluate piPS cell pluripotency. The shRNA-Klf4 and shRNA-c-Myc vectors containing a reporter gene, TagFP635, were transfected into piPS cells by lentivirus infection. The piPS cells fully expressing infrared fluorescence were selected to confirm gene knockdown of Klf4 and c-Myc reverse transcription-polymerase chain reaction (RT-PCR). Next, for pluripotency evaluation, expression of pluripotency markers was detected by immunocytochemical staining, and capability of teratoma formation was investigated by piPS cell transplantation into nonobese diabetic-severe combined immunodeficiency (NOD-SCID) mice.

Results

Our findings indicated that Klf4 and c-Myc functions of piPS cells were knocked down by shRNA transfection, and knockdown of Klf4 and c-Myc functions impaired expression of pluripotency markers such as Oct4, AP, SSEA-3, SSEA-4, TRA-1-6, and TRA-1-81. Furthermore, piPS cells without Klf4 and c-Myc expression failed to form teratomas.

Conclusion

The pluripotency of piPS cells are crucially dependent upon Klf4 and c-Myc expression. These findings, suggesting potential mechanisms of Klf4 and c-Myc contribution to piPS cell formation, have important implications for application, regulation, and tumorigenesis of piPS cells.

A Simple and Robust Method for Culturing Human-Induced Pluripotent Stem Cells in an Undifferentiated State Using Botulinum Hemagglutinin

Clinical and industrial applications of human-induced pluripotent stem cells (hiPSCs) is hindered by the lack of robust culture strategies capable of sustaining a culture in an undifferentiated state. Here, a simple and robust hiPSC-culture-propagation strategy incorporating botulinum hemagglutinin (HA)-mediated selective removal of cells deviating from an undifferentiated state is developed. After HA treatment, cell-cell adhesion is disrupted, and deviated cells detached from the central region of the colony to subsequently form tight monolayer colonies following prolonged incubation. The authors find that the temporal and dose-dependent activity of HA regulated deviated-cell removal and recoverability after disruption of cell-cell adhesion in hiPSC colonies. The effects of HA are confirmed under all culture conditions examined, regardless of hiPSC line and feeder-dependent or -free culture conditions. After routine application of our HA-treatment paradigm for serial passages, hiPSCs maintains expression of pluripotent markers and readily forms embryoid bodies expressing markers for all three germ-cell layers. This method enables highly efficient culturing of hiPSCs and use of entire undifferentiated portions without having to pick deviated cells manually. This simple and readily reproducible culture strategy is a potentially useful tool for improving the robust and scalable maintenance of undifferentiated hiPSC cultures.

Detailed Characterization of Human Induced Pluripotent Stem Cells Manufactured for Therapeutic Applications

We have recently described manufacturing of human induced pluripotent stem cells (iPSC) master cell banks (MCB) generated by a clinically compliant process using cord blood as a starting material (Baghbaderani et al. in Stem Cell Reports, 5(4), 647-659, 2015). In this manuscript, we describe the detailed characterization of the two iPSC clones generated using this process, including whole genome sequencing (WGS), microarray, and comparative genomic hybridization (aCGH) single nucleotide polymorphism (SNP) analysis. We compare their profiles with a proposed calibration material and with a reporter subclone and lines made by a similar process from different donors. We believe that iPSCs are likely to be used to make multiple clinical products. We further believe that the lines used as input material will be used at different sites and, given their immortal status, will be used for many years or even decades. Therefore, it will be important to develop assays to monitor the state of the cells and their drift in culture. We suggest that a detailed characterization of the initial status of the cells, a comparison with some calibration material and the development of reporter sublcones will help determine which set of tests will be most useful in monitoring the cells and establishing criteria for discarding a line.

Lung development, regeneration and plasticity: From disease physiopathology to drug design using induced pluripotent stem cells

Lungs have a complex structure composed of different cell types that form approximately 17 million airway branches of gas-delivering bronchioles connected to 500 million gas-exchanging alveoli. Airways and alveoli are lined by epithelial cells that display a low rate of turnover at steady-state, but can regenerate the epithelium in response to injuries. Here, we review the key points of lung development, homeostasis and epithelial cell plasticity in response to injury and disease, because this knowledge is required to develop new lung disease treatments. Of note, canonical signaling pathways that are essential for proper lung development during embryogenesis are also involved in the pathophysiology of most chronic airway diseases. Moreover, the perfect control of these interconnected pathways is needed for the successful differentiation of induced pluripotent stem cells (iPSC) into lung cells. Indeed, differentiation of iPSC into airway epithelium and alveoli is based on the use of biomimetics of normal embryonic and fetal lung development. In vitro iPSC-based models of lung diseases can help us to better understand the impaired lung repair capacity and to identify new therapeutic targets and new approaches, such as lung cell therapy.

Large-scale mapping of mammalian transcriptomes identifies conserved genes associated with different cell states

Distinguishing cell states based only on gene expression data remains a challenging task. This is true even for analyses within a species. In cross-species comparisons, the results obtained by different groups have varied widely. Here, we integrate RNA-seq data from more than 40 cell and tissue types of four mammalian species to identify sets of associated genes as indicators for specific cell states in each species. We employ a statistical method, TROM, to identify both protein-coding and non-coding indicators. Next, we map the cell states within each species and also between species using these indicator genes. We recapitulate known phenotypic similarity between related cell and tissue types and reveal molecular basis for their similarity. We also report novel associations between several tissues and cell types with functional support. Moreover, our identified conserved associated genes are found to be a good resource for studying cell differentiation and reprogramming. Lastly, long non-coding RNAs can serve well as associated genes to indicate cell states. We further infer the biological functions of those non-coding associated genes based on their co-expressed protein-coding genes. This study demonstrates that combining statistical modeling with public RNA-seq data can be powerful for improving our understanding of cell identity control.

Elongation of Axon Extension for Human iPSC-Derived Retinal Ganglion Cells by a Nano-Imprinted Scaffold

Optic neuropathies, such as glaucoma and Leber's hereditary optic neuropathy (LHON) lead to retinal ganglion cell (RGC) loss and therefore motivate the application of transplantation technique into disease therapy. However, it is a challenge to direct the transplanted optic nerve axons to the correct location of the retina. The use of appropriate scaffold can promote the proper axon growth. Recently, biocompatible materials have been integrated into the medical field, such as tissue engineering and reconstruction of damaged tissues or organs. We, herein, utilized nano-imprinting to create a scaffold mimicking the in vitro tissue microarchitecture, and guiding the axonal growth and orientation of the RGCs. We observed that the robust, long, and organized axons of human induced pluripotent stem cell (iPSC)-derived RGCs projected axially along the scaffold grooves. The RGCs grown on the scaffold expressed the specific neuronal biomarkers indicating their proper functionality. Thus, based on our in vitro culture system, this device can be useful for the neurophysiological analysis and transplantation for ophthalmic neuropathy treatment.

Patient- and Cell Type-Specific Heterogeneity of Metformin Response

Most FDA-approved drugs are not equally effective in all patients, suggesting that identification of biomarkers to predict responders to a chemoprevention agent will be needed to stratify patients and achieve maximum benefit. The goal of this study was to investigate both patient-specific and cell context-specific heterogeneity of metformin response, using fibroblast cell lines and induced pluripotent stem cells differentiated into lung epithelial lineages. We performed cell survival analysis, transcriptome and whole exome sequencing analysis on both patient-derived cell lines and cancer cell lines to assess differential metformin response and identify response genes. We found differences in response to metformin treatment across a variety of cell lines and cellular contexts, suggesting that heterogeneity may be patient- and cell type-specific. Gene expression profiling and analysis of metformin-sensitive and metformin-resistant cells identified differentially expressed genes that may be able to stratify patients into metformin responders and non-responders. Sequencing analysis found genomic alterations that correlated with metformin response. These results suggest that the identification of genomic biomarkers for patients who may respond to metformin treatment can provide an opportunity for individualizing metformin chemoprevention in the clinical setting.

Effects of RPE-conditioned medium on the differentiation of hADSCs into RPE cells, and their proliferation and migration

Age-related macular degeneration (AMD) is associated with the dysfunction and death of the retinal pigment epithelium (RPE). Recently, there has been increasing interest in stem cell-derived RPE cells for cell replacement therapies, such as those for AMD. The present study investigated whether RPE-conditioned medium (RPECM) could promote the differentiation of human adipose tissue-derived mesenchymal stromal cells (hADSCs) into RPE cells, and enhance the proliferation and migration of these cells. Reverse-transcription quantitative polymerase chain reaction analysis demonstrated that RPECM induced hADSCs to differentiate into cells expressing RPE markers, including retinoid isomerohydrolase (RPE65), cytokeratin (CK8) and Bestrophin, which were identified to be significantly upregulated by ~10-fold, 3.5-fold and 2.4-fold, respectively, compared with the control group [hADSCs cultured in ADSC-conditioned medium (ADSCCM)]. The immunocytochemistry and western blot analysis results demonstrated that the protein levels of RPE65, CK8 and Bestrophin were significantly increased in RPECM-treated hADSCs. In addition, Cell Counting Kit-8 analysis demonstrated that RPECM promoted the proliferation of induced cells. RPECM also increased the expression level of the cell proliferative marker Ki-67. Furthermore, to evaluate the migration potential, cell migration assays were performed. These assays demonstrated that following RPECM treatment hADSCs migrated more quickly compared with the control group. The results of the present study suggest that RPECM induces hADSCs to differentiate into RPE cells with higher proliferative and migratory potentials, which may aid in applications for hADSCs in RPE regenerative therapy.

Piwil2-transfected human fibroblasts are cancer stem cell-like and genetically unstable

Uncontrolled cell proliferation and inhibition of apoptosis are considered to be vital for cancer initiation, maintenance, infiltration, metastasis and recurrence after anti-cancer therapy. Here we report the generation of a novel cell line by reprogramming child foreskin fibroblast with the full length apoptosis inhibitor gene PIWIL2. The fibroblasts transfected with PIWIL2 expressed the stem cell markers OCT-4, NANOG, SOX-2, KLF-4 and C-MYC; endoderm marker AFP and GATA6; mesoderm markers ACTA2 and BRACHYURY; and ectoderm markers NESTIN and TUBB3. The karyotype was found to be hyperdiploid. The PIWIL2 transfected fibroblast cells grew into tumorous masses within 5 weeks of subcutaneous injection into adult nude mice. Although the injected cell expressed markers for all three germlines, ectoderm, mesoderm, and endoderm, they did not form teratomas in vivo. This study indicates that the PIWIL2 gene could play a key role in cancer induction and maintenance. This method for generating induced tumorigenic cells (ITGC) provides a new research tool to study oncogenesis that in turn may lead to a better understanding of cancer etiology and the development of novel anti-cancer therapies.

Beyond organoids: In vitro vasculogenesis and angiogenesis using cells from mammals and zebrafish

The ability to culture complex organs is currently an important goal in biomedical research. It is possible to grow organoids (3D organ-like structures) in vitro; however, a major limitation of organoids, and other 3D culture systems, is the lack of a vascular network. Protocols developed for establishing in vitro vascular networks typically use human or rodent cells. A major technical challenge is the culture of functional (perfused) networks. In this rapidly advancing field, some microfluidic devices are now getting close to the goal of an artificially perfused vascular network. Another development is the emergence of the zebrafish as a complementary model to mammals. In this review, we discuss the culture of endothelial cells and vascular networks from mammalian cells, and examine the prospects for using zebrafish cells for this objective. We also look into the future and consider how vascular networks in vitro might be successfully perfused using microfluidic technology.

Engineering cell identity: establishing new gene regulatory and chromatin landscapes

Cellular reprogramming can be achieved by ectopically expressing transcription factors that directly convert one differentiated cell type into another, bypassing embryonic states. A number of different cell types have been generated by such 'direct lineage reprogramming' methods, but their practical utility has been limited because, in most protocols, the resulting populations are often partially differentiated or incompletely specified. Here, we review mechanisms of lineage reprogramming by pioneer transcription factors, a unique class of transcriptional regulators that has the capacity to engage with silent chromatin to activate target gene regulatory networks. We assess the possible barriers to successful reprogramming in the context of higher-order chromatin landscape, considering how the mechanistic relationship between nuclear organization and cell identity will be crucial to unlocking the full potential of cell fate engineering.

No fuzzy space for intracellular Na+ in healthy ventricular myocytes

Sachse et al. highlight work that reveals a Na⁺-dependent inactivation mechanism in the Na⁺/K⁺ pump.

Modeling Keratoconus Using Induced Pluripotent Stem Cells

PURPOSE

To model keratoconus (KC) using induced pluripotent stem cells (iPSC) generated from fibroblasts of both KC and normal human corneal stroma by a viral method.

METHODS

Both normal and KC corneal fibroblasts from four human donors were reprogramed directly by delivering reprogramming factors in a single virus using 2A "self-cleaving" peptides, using a single polycistronic lentiviral vector coexpressing four transcription factors (Oct 4, Sox2, Klf4, and Myc) to yield iPSC. These iPS cells were characterized by immunofluorescence detection using of stem cell markers (SSEA4, Oct4, and Sox2). The mRNA sequencing was performed and the datasets were analyzed using ingenuity pathways analysis (IPA) software.

RESULTS

The generated stem cell-like clones expressed the pluripotency markers, SSEA4, Oct4, Sox2, Tra-1-60, and also expressed pax6. Our transcriptome analysis showed 4300 genes, which had 2-fold change and 870 genes with a q-value of <0.05 in keratoconus iPSC compared to normal iPSC. One of the genes that showed difference in KC iPSC was FGFR2 (down-regulated by 2.4 fold), an upstream target of Pi3-Kinase pathway, was further validated in keratoconus corneal sections and also KC iPSC-derived keratocytes (down regulated by 2.0-fold). Both normal and KC-derived keratocytes expressed keratocan, signature marker for keratocytes. KC iPSC-derived keratocytes showed adverse growth and proliferation and was further confirmed by using Ly2924002, a PI3k inhibitor, which severely affected the growth and differentiation in normal iPSC.

CONCLUSIONS

Based on our result, we propose a model for KC in which inhibition FGFR2-Pi3-Kinase pathway affects the AKT phosphorylation, and thus affecting the keratocytes survival signals. This inhibition of the survival signals could be a potential mechanism for the KC-specific decreased cell survival and apoptosis of keratocytes.

Transcriptional Addiction in Cancer

Cancer arises from genetic alterations that invariably lead to dysregulated transcriptional programs. These dysregulated programs can cause cancer cells to become highly dependent on certain regulators of gene expression. Here, we discuss how transcriptional control is disrupted by genetic alterations in cancer cells, why transcriptional dependencies can develop as a consequence of dysregulated programs, and how these dependencies provide opportunities for novel therapeutic interventions in cancer.

The potential of induced pluripotent stem cells as a tool to study skeletal dysplasias and cartilage-related pathologic conditions

The development of induced pluripotent stem cells (iPSCs) technology has opened up new horizons for development of new research tools especially for skeletal dysplasias, which often lack human disease models. Regenerative medicine and tissue engineering could be the next areas to benefit from refinement of iPSC methods to repair focal cartilage defects, while applications for osteoarthritis (OA) and drug screening have evolved rather slowly. Although the advances in iPSC research of skeletal dysplasias and repair of focal cartilage lesions are not directly relevant to OA, they can be considered to pave the way to future prospects and solutions to OA research, too. The same problems which face the present cell-based treatments of cartilage injuries concern also the iPSC-based ones. However, established iPSC lines, which have no genomic aberrations and which efficiently differentiate into extracellular matrix secreting chondrocytes, could be an invaluable cell source for cell transplantations in the future. The safety issues concerning the recipient risks of teratoma formation and immune response still have to be solved before the potential use of iPSCs in cartilage repair of focal cartilage defects and OA.

ATP-Binding Cassette Transporter A1 Deficiency in Human Induced Pluripotent Stem Cell-Derived Hepatocytes Abrogates HDL Biogenesis and Enhances Triglyceride Secretion

Despite the recognized role of the ATP-binding Cassette Transporter A1 (ABCA1) in high-density lipoprotein (HDL) metabolism, our understanding of ABCA1 deficiency in human hepatocytes is limited. To define the functional effects of human hepatocyte ABCA1 deficiency, we generated induced pluripotent stem cell (iPSC)-derived hepatocyte-like cells (HLCs) from Tangier disease (TD) and matched control subjects. Control HLCs exhibited robust cholesterol efflux to apolipoprotein A-I (apoA-I) and formed nascent HDL particles. ABCA1-deficient HLCs failed to mediate lipid efflux or nascent HDL formation, but had elevated triglyceride (TG) secretion. Global transcriptome analysis revealed significantly increased ANGPTL3 expression in ABCA1-deficient HLCs. Angiopoietin-related protein 3 (ANGPTL3) was enriched in plasma of TD relative to control subjects. These results highlight the required role of ABCA1 in cholesterol efflux and nascent HDL formation by hepatocytes. Furthermore, our results suggest that hepatic ABCA1 deficiency results in increased hepatic TG and ANGPTL3 secretion, potentially underlying the elevated plasma TG levels in TD patients.

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ABCA1 deficiency in human hepatocytes abolishes nascent HDL formation, but elevates triglyceride secretion

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ABCA1 deficiency increases hepatic ANGPTL3 expression and secretion

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Tangier disease patients display higher plasma ANGPTL3 levels relative to normal HDL control subjects

ATP-Binding Cassette Transporter A1 (ABCA1) is a key regulator of high-density lipoprotein metabolism, but the intrinsic functional impact of human hepatocyte ABCA1 deficiency is yet to be defined. We generated hepatocyte-like cells (HLCs) from induced pluripotent stem cell (iPSC) of patients with Tangier disease (TD), a rare genetic disorder caused by mutations in ABCA1. ABCA1 deficiency in HLCs abrogates lipid efflux and nascent HDL formation but increases triglyceride secretion. ANGPTL3 has also been uncovered as a potential mediator of hypertriglyceridemia in TD. This study thus highlights the utility of iPSC-derived cells in disease modeling.

Mechanisms Regulating Stemness and Differentiation in Embryonal Carcinoma Cells

Just over ten years have passed since the seminal Takahashi-Yamanaka paper, and while most attention nowadays is on induced, embryonic, and cancer stem cells, much of the pioneering work arose from studies with embryonal carcinoma cells (ECCs) derived from teratocarcinomas. This original work was broad in scope, but eventually led the way for us to focus on the components involved in the gene regulation of stemness and differentiation. As the name implies, ECCs are malignant in nature, yet maintain the ability to differentiate into the 3 germ layers and extraembryonic tissues, as well as behave normally when reintroduced into a healthy blastocyst. Retinoic acid signaling has been thoroughly interrogated in ECCs, especially in the F9 and P19 murine cell models, and while we have touched on this aspect, this review purposely highlights how some key transcription factors regulate pluripotency and cell stemness prior to this signaling. Another major focus is on the epigenetic regulation of ECCs and stem cells, and, towards that end, this review closes on what we see as a new frontier in combating aging and human disease, namely, how cellular metabolism shapes the epigenetic landscape and hence the pluripotency of all stem cells.

DNA repair and replication links to pluripotency and differentiation capacity of pig iPS cells

Pigs are proposed to be suitable large animal models for test of the efficacy and safety of induced pluripotent stem cells (iPSCs) for stem cell therapy, but authentic pig ES/iPS cell lines with germline competence are rarely produced. The pathways or signaling underlying the defective competent pig iPSCs remain poorly understood. By improving induction conditions using various small chemicals, we generated pig iPSCs that exhibited high pluripotency and differentiation capacity that can contribute to chimeras. However, their potency was reduced with increasing passages by teratoma formation test, and correlated with declined expression levels of Rex1, an important marker for naïve state. By RNA-sequencing analysis, genes related to WNT signaling were upregulated and MAPK signaling and TGFβ pathways downregulated in pig iPSCs compared to fibroblasts, but they were abnormally expressed during passages. Notably, pathways involving in DNA repair and replication were upregulated at early passage, but downregulated in iPSCs during prolonged passage in cluster with fibroblasts. Our data suggests that reduced DNA repair and replication capacity links to the instability of pig iPSCs. Targeting these pathways may facilitate generation of truly pluripotent pig iPSCs, with implication in translational studies.

Concise Review: Induced Pluripotent Stem Cell Research in the Era of Precision Medicine

Recent advances in DNA sequencing technologies are revealing how human genetic variations associate with differential health risks, disease susceptibilities, and drug responses. Such information is now expected to help evaluate individual health risks, design personalized health plans and treat patients with precision. It is still challenging, however, to understand how such genetic variations cause the phenotypic alterations in pathobiologies and treatment response. Human induced pluripotent stem cell (iPSC) technologies are emerging as a promising strategy to fill the knowledge gaps between genetic association studies and underlying molecular mechanisms. Breakthroughs in genome editing technologies and continuous improvement in iPSC differentiation techniques are particularly making this research direction more realistic and practical. Pioneering studies have shown that iPSCs derived from a variety of monogenic diseases can faithfully recapitulate disease phenotypes in vitro when differentiated into disease-relevant cell types. It has been shown possible to partially recapitulate disease phenotypes, even with late onset and polygenic diseases. More recently, iPSCs have been shown to validate effects of disease and treatment-related single nucleotide polymorphisms identified through genome wide association analysis. In this review, we will discuss how iPSC research will further contribute to human health in the coming era of precision medicine. Stem Cells 2017;35:545-550.

Induced pluripotent stem cell technology: a decade of progress

Since the advent of induced pluripotent stem cell (iPSC) technology a decade ago, enormous progress has been made in stem cell biology and regenerative medicine. Human iPSCs have been widely used for disease modelling, drug discovery and cell therapy development. Novel pathological mechanisms have been elucidated, new drugs originating from iPSC screens are in the pipeline and the first clinical trial using human iPSC-derived products has been initiated. In particular, the combination of human iPSC technology with recent developments in gene editing and 3D organoids makes iPSC-based platforms even more powerful in each area of their application, including precision medicine. In this Review, we discuss the progress in applications of iPSC technology that are particularly relevant to drug discovery and regenerative medicine, and consider the remaining challenges and the emerging opportunities in the field.

Preferential Lineage-Specific Differentiation of Osteoblast-Derived Induced Pluripotent Stem Cells into Osteoprogenitors

While induced pluripotent stem cells (iPSCs) hold great clinical promise, one hurdle that remains is the existence of a parental germ-layer memory in reprogrammed cells leading to preferential differentiation fates. While it is problematic for generating cells vastly different from the reprogrammed cells' origins, it could be advantageous for the reliable generation of germ-layer specific cell types for future therapeutic use. Here we use human osteoblast-derived iPSCs (hOB-iPSCs) to generate induced osteoprogenitors (iOPs). Osteoblasts were successfully reprogrammed and demonstrated by endogenous upregulation of Oct4, Sox2, Nanog, TRA-1-81, TRA-16-1, SSEA3, and confirmatory hPSC Scorecard Algorithmic Assessment. The hOB-iPSCs formed embryoid bodies with cells of ectoderm and mesoderm but have low capacity to form endodermal cells. Differentiation into osteoprogenitors occurred within only 2-6 days, with a population doubling rate of less than 24 hrs; however, hOB-iPSC derived osteoprogenitors were only able to form osteogenic and chondrogenic cells but not adipogenic cells. Consistent with this, hOB-iOPs were found to have higher methylation of PPARγ but similar levels of methylation on the RUNX2 promoter. These data demonstrate that iPSCs can be generated from human osteoblasts, but variant methylation patterns affect their differentiation capacities. Therefore, epigenetic memory can be exploited for efficient generation of clinically relevant quantities of osteoprogenitor cells.

The impact of Zika virus in the brain

The recent outbreak of ZIKV in Brazil called the attention of the world because the effects of viral infection in the brain under development in fetuses. Consequences of vertical infection comprise brain malformation, especially microcephaly, eye and musculoskeletal abnormalities, among others. In adults, outcomes of infection include meningoencephalitis and Guillain-Barré Syndrome. Recent data specific suggest that neural progenitor cells are the main targets of ZIKV infection, causing massive cellular death and impairment in the neurogenesis process. Here we review the fetal and adult brain damage after ZIKV exposure, exploring models to study the mechanisms underlying the pathways related to microcephaly and cell death.

Culture substrates made of elastomeric micro-tripod arrays for long-term expansion of human pluripotent stem cells

Elastomeric micro-tripod arrays were used as novel substrates for culturing and long-term expansion of human pluripotent stem cells.

Human iPSC-derived cardiomyocytes and tissue engineering strategies for disease modeling and drug screening

Improved methodologies for modeling cardiac disease phenotypes and accurately screening the efficacy and toxicity of potential therapeutic compounds are actively being sought to advance drug development and improve disease modeling capabilities. To that end, much recent effort has been devoted to the development of novel engineered biomimetic cardiac tissue platforms that accurately recapitulate the structure and function of the human myocardium. Within the field of cardiac engineering, induced pluripotent stem cells (iPSCs) are an exciting tool that offer the potential to advance the current state of the art, as they are derived from somatic cells, enabling the development of personalized medical strategies and patient specific disease models. Here we review different aspects of iPSC-based cardiac engineering technologies. We highlight methods for producing iPSC-derived cardiomyocytes (iPSC-CMs) and discuss their application to compound efficacy/toxicity screening and in vitro modeling of prevalent cardiac diseases. Special attention is paid to the application of micro- and nano-engineering techniques for the development of novel iPSC-CM based platforms and their potential to advance current preclinical screening modalities.

Therapeutic Application of Placental Mesenchymal Stem Cells Reprogrammed Neurospheres in Spinal Cord Injury of SCID

Mesenchymal stromal cells (MSCs) and induced pluripotent stem cells (iPSCs) have stimulated much interest in the scientific community and hopes among the general public since their discovery in 1966 due to a variety of potential applications it has in the field of regenerative medicine. Copious amount of literature, as well as long-term animal and human clinical trials, indicates that MSCs can be successfully used for therapeutic purpose without any extreme adversities. MSCs have been isolated from adult and fetal tissues. Recently, MSCs from placenta have generated much inquisitiveness. In this article, we will demonstrate the step-by-step procedure for isolating human placental MSCs from term placenta, reprogramming of placental MSCs into iPSCs using plasmid vectors, evaluation of functional recovery in mice spinal cord injury models, and in vivo tracking of the transplanted cells.

Gene Addition Strategies for β-Thalassemia and Sickle Cell Anemia

Beta-thalassemia and sickle cell anemia are two of the most common diseases related to the hemoglobin protein. In these diseases, the beta-globin gene is mutated, causing severe anemia and ineffective erythropoiesis. Patients can additionally present with a number of life-threatening co-morbidities, such as stroke or spontaneous fractures. Current treatment involves transfusion and iron chelation; allogeneic bone marrow transplant is the only curative option, but is limited by the availability of matching donors and graft-versus-host disease. As these two diseases are monogenic diseases, they make an attractive setting for gene therapy. Gene therapy aims to correct the mutated beta-globin gene or add back a functional copy of beta- or gamma-globin. Initial gene therapy work was done with oncoretroviral vectors, but has since shifted to lentiviral vectors. Currently, there are a few clinical trials underway to test the curative potential of some of these lentiviral vectors. This review will highlight the work done thus far, and present the challenges still facing gene therapy, such as genome toxicity concerns and achieving sufficient transgene expression to cure those with the most severe forms of thalassemia.

Epigenetic Modifiers Facilitate Induction and Pluripotency of Porcine iPSCs

Inadequate silencing of exogenous genes represents a major obstacle to complete epigenetic reprogramming of porcine-induced pluripotent stem cells (piPSCs) by conventional pluripotency transcription factors (OSKM). We tested the hypothesis that epigenetic modification by active DNA or histone demethylation or by inhibition of histone deacetylase would enhance reprogramming and exogenous gene silencing in piPSCs. piPSCs induced by OSKM in combination with epigenetic factors, specifically Ten-Eleven Translocation (Tet1 or Tet3) or lysine (K)-specific demethylase 3A (Kdm3a), expressed higher levels of Rex1 and other genes representing naive state and exhibited more open chromatin status, compared with those of OSKM controls. Tet1 also improved differentiation capacity. Conversion with inhibitors of histone deacetylases (HDACi), NaB, TSA, or VPA, further increased Rex1 expression, while decreasing expression of exogenous genes. piPSCs induced by Tet1+OSKM followed by conversion with HDACi show high pluripotency. Together, epigenetic modifiers enhance generation of piPSCs and reduce their reliance on exogenous genes.

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Epigenetic modifiers facilitate induction and quality of porcine iPSCs

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Tet1, Tet3, or Kdm3a increases naive pluripotency network in association with Rex1

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Unlike cytoplasmic Rex1, nuclear expression of Rex1 is associated with high pluripotency

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HDAC inhibitors further activate Rex1 and reduce reliance on the exogenous genes

Integrating Gene Correction in the Reprogramming and Transdifferentiation Processes: A One-Step Strategy to Overcome Stem Cell-Based Gene Therapy Limitations

The recent advent of induced pluripotent stem cells (iPSCs) and gene therapy tools has raised the possibility of autologous cell therapy for rare genetic diseases. However, cellular reprogramming is inefficient in certain diseases such as ataxia telangiectasia, Fanconi anemia, LIG4 syndrome, and fibrodysplasia ossificans progressiva syndrome, owing to interference of the disease-related genes. To overcome these therapeutic limitations, it is necessary to fundamentally correct the abnormal gene during or prior to the reprogramming process. In addition, as genetic etiology of Parkinson's disease, it has been well known that induced neural stem cells (iNSCs) were progressively depleted by LRRK2 gene mutation, LRRK2 (G2019S). Thus, to maintain the induced NSCs directly derived from PD patient cells harboring LRRK2 (G2019S), it would be ideal to simultaneously treat the LRRK2 (G2019S) fibroblast during the process of TD. Therefore, simultaneous reprogramming (or TD) and gene therapy would provide the solution for therapeutic limitation caused by vulnerability of reprogramming or TD, in addition to being suitable for general application to the generation of autologous cell-therapy products for patients with genetic defects, thereby obviating the need for the arduous processes currently required.

Pluripotent stem cells: the last 10 years

Pluripotent stem cells (PSCs) can differentiate into virtually any cell type in the body, making them attractive for both regenerative medicine and drug discovery. Over the past 10 years, technological advances and innovative platforms have yielded first-in-man PSC-based clinical trials and opened up new approaches for disease modeling and drug development. Induced PSCs have become the foremost alternative to embryonic stem cells and accelerated the development of disease-in-a-dish models. Over the years and with each new discovery, PSCs have proven to be extremely versatile. This review article highlights key advancements in PSC research, from 2006 to 2016, and how they will guide the direction of the field over the next decade.

Critical roles of Cyclin D1 in mouse embryonic fibroblast cell reprogramming

Although pluripotent stem cells hold great promise in the fields of human disease modeling and regenerative medicine, the molecular basis of Oct-4, Sox2, Klf4, and c-Myc (OSKM)-induced cellular reprogramming remains unclear. To investigate the molecular mechanisms involved in cellular reprogramming, we studied the immediate effects of expression of the OSKM reprogramming factors on mouse embryonic fibroblasts (MEFs) in this study. Induction of the OSKM reprogramming factors significantly altered primary MEF growth properties. Although MEFs not expressing the reprogramming factors underwent replicative senescence within 9-12 days in culture, MEFs expressing the four reprogramming factors proliferated continuously throughout the duration of the experiment, suggesting that the expression of the OSKM reprogramming factors inhibits or delays replicative senescence. Cell cycle progression by the reprogramming factors was accompanied by the accumulation of Cyclin D1 through the early stages of reprogramming in MEFs, leading us to hypothesize that it might play a positive role in cellular reprogramming. Consistent with this hypothesis, forced Cyclin D1 expression enhanced reprogramming if administered concomitant with expression of the OSKM reprogramming factors. Most importantly, unlike wild-type MEFs expressing reprogramming factors, the number of emerging alkaline phosphatase-positive cyclin D1-null colonies was significantly reduced and cyclin D1-null MEFs were unable to initiate mesenchymal-to-epithelial transition. Our studies demonstrate that cyclin D1 is an essential gene in the reprogramming process and that activation of cyclin D1 by reprogramming factors is an important process for somatic cell reprogramming.

Investigating Leber's hereditary optic neuropathy: Cell models and future perspectives

Leber's hereditary optic neuropathy (LHON) was the first human disease found to be associated with a mitochondrial DNA (mtDNA) point mutation. The most common LHON mutations are 11778G>A, 3460G>A or 14484T>C. The most common clinical features of LHON are optic nerve and retina atrophy. The affected tissue is not available for studies, therefore a variety of other cell types are used. However, all models face difficulties and limitations in mitochondrial disease research. The advantages and disadvantages of different cell models used to study LHON, recent advances in animal model generation and novel approaches in this field are discussed.

Application of induced pluripotent stem cells in cholangiopathies

Induced pluripotent stem cells (iPSCs) are similar to embryonic stem cells (ESCs) in morphology, gene expression, cell self-renewal and differentiation potential. They avoid the problem of immune rejection and ethical issues associated with the application of ESCs. The application of iPSCs in a variety of diseases provides favorable experiences to the research of liver diseases. Cholangiopathies, such as primary biliary cirrhosis and primary sclerosing cholangitis, refer to a category of uncommon diseases that possess unclear pathogenesis, lack effective treatment and have a poor prognosis. Hence, investigating cholangiopathies-derived, individualized iPSCs and their differentiation into functional cells can mimic the disease phenotype and pathological process in vitro. The application of these cells has great significance for pathogenesis exploration, drug screening and therapeutic evaluation.

Neurotrophin Signaling and Stem Cells-Implications for Neurodegenerative Diseases and Stem Cell Therapy

Neurotrophins (NTs) are members of a neuronal growth factor protein family whose action is mediated by the tropomyosin receptor kinase (TRK) receptor family receptors and the p75 NT receptor (p75NTR), a member of the tumor necrosis factor (TNF) receptor family. Although NTs were first discovered in neurons, recent studies have suggested that NTs and their receptors are expressed in various types of stem cells mediating pivotal signaling events in stem cell biology. The concept of stem cell therapy has already attracted much attention as a potential strategy for the treatment of neurodegenerative diseases (NDs). Strikingly, NTs, proNTs, and their receptors are gaining interest as key regulators of stem cells differentiation, survival, self-renewal, plasticity, and migration. In this review, we elaborate the recent progress in understanding of NTs and their action on various stem cells. First, we provide current knowledge of NTs, proNTs, and their receptor isoforms and signaling pathways. Subsequently, we describe recent advances in the understanding of NT activities in various stem cells and their role in NDs, particularly Alzheimer's disease (AD) and Parkinson's disease (PD). Finally, we compile the implications of NTs and stem cells from a clinical perspective and discuss the challenges with regard to transplantation therapy for treatment of AD and PD.

Lesch-Nyhan Syndrome: Models, Theories, and Therapies

Lesch-Nyhan syndrome (LNS) is a rare X-linked disorder caused by mutations in HPRT1, an important enzyme in the purine salvage pathway. Symptoms of LNS include dystonia, gout, intellectual disability, and self-mutilation. Despite having been characterized over 50 years ago, it remains unclear precisely how deficits in hypoxanthine and guanine recycling can lead to such a profound neurological phenotype. Several studies have proposed different hypotheses regarding the etiology of this disease, and several treatments have been tried in patients, though none have led to a satisfactory explanation of the disease. New technologies such as next-generation sequencing, optogenetics, genome editing, and induced pluripotent stem cells provide a unique opportunity to map the precise sequential pathways leading from genotype to phenotype.

Stem cell therapy for acute respiratory distress syndrome: a promising future?

PURPOSE OF REVIEW

Acute respiratory distress syndrome (ARDS) is a devastating disease process with a 40% mortality rate, and for which there is no therapy. Stem cells are an exciting potential therapy for ARDS, and are currently the subject of intensive ongoing research efforts. We review data concerning the therapeutic promise of cell-based therapies for ARDS.

RECENT FINDINGS

Recent experimental studies suggest that cell-based therapies, particularly mesenchymal stem/stromal cells (MSCs), endothelial progenitor cells, and embryonic or induced pluripotent stem cells all offer considerable promise for ARDS. Of these cell types, mesenchymal stromal cells offer the greatest potential for allogeneic therapy, given the large body of preclinical data supporting their use, and the advanced state of our understanding of their diverse mechanisms of action. Although other stem cells such as EPCs also have therapeutic potential, greater barriers exist, particularly the requirement for autologous EPC therapy. Other stem cells, such as ESCs and iPSCs, are at an earlier stage in the translational process, but offer the hope of directly replacing injured lung tissue. Ultimately, lung-derived stem cells may offer the greatest hope for lung diseases, given their homeostatic role in replacing and repairing damaged native lung tissues.MSCs are currently in early phase clinical trials, the results of which will be of critical importance to subsequent translational efforts for MSCs in ARDS. A number of translational challenges exist, including minimizing variability in cell batches, developing standard tests for cell potency, and producing large amounts of clinical-grade cells for use in patients.

SUMMARY

Cell-based therapies, particularly MSCs, offer considerable promise for the treatment of ARDS. Overcoming translational challenges will be important to fully realizing their therapeutic potential for ARDS.

Zika Virus Infection in Pregnancy, Microcephaly, and Maternal and Fetal Health: What We Think, What We Know, and What We Think We Know

CONTEXT

-The global epidemic of Zika virus (ZIKV) infection has emerged as an important public health problem affecting pregnant women and their infants.

OBJECTIVES

-To review the causal association between ZIKV infection during pregnancy and intrauterine fetal infection, microcephaly, brain damage, congenital malformation syndrome, and experimental laboratory models of fetal infection. Many questions remain regarding the risk factors, pathophysiology, epidemiology, and timing of maternal-fetal transmission and disease. These include mechanisms of fetal brain damage and microcephaly; the role of covariables, such as viral burden, duration of viremia, and host genetics, on vertical transmission; and the clinical and pathologic spectrum of congenital Zika syndrome. Additional questions include defining the potential long-term physical and neurobehavioral outcomes for infected infants, whether maternal or fetal host genetics influence the clinical outcome, and whether ZIKV infection can cause maternal morbidity. Finally, are experimental laboratory and animal models of ZIKV infection helpful in addressing maternal-fetal viral transmission and the development of congenital microcephaly? This communication provides current information and attempts to address some of these important questions.

DATA SOURCES

-Comprehensive review of published scientific literature.

CONCLUSIONS

-Recent advances in epidemiology, clinical medicine, pathology, and experimental studies have provided a great amount of new information regarding vertical ZIKV transmission and the mechanisms of congenital microcephaly, brain damage, and congenital Zika syndrome in a relatively short time. However, much work still needs to be performed to more completely understand the maternal and fetal aspects of this new and emerging viral disease.

Studying the pathophysiologic connection between cardiovascular and nervous systems using stem cells

The cardiovascular and nervous systems are deeply connected during development, health, and disease. Both systems affect and regulate the development of each other during embryogenesis and the early postnatal period. Specialized neural crest cells contribute to cardiac structures, and a number of growth factors released from the cardiac tissue (e.g., glial cell line-derived neurotrophic factor, neurturin, nerve growth factor, Neurotrophin-3) ensure proper maturation of the incoming parasympathetic and sympathetic neurons. Physiologically, the cardiovascular and nervous systems operate in harmony to adapt to various physical and emotional conditions to maintain homeostasis through sympathetic and parasympathetic nervous systems. Moreover, neurocardiac regulation involves a neuroaxis consisting of cortex, amygdala, and other subcortical structures, which have the ability to modify lower-level neurons in the hierarchy. Given the interconnectivity of cardiac and neural systems, when one undergoes pathological changes, the other is affected to a certain extent. In addition, there are specific neurocardiac diseases that affect both systems simultaneously, such as Huntington disease, Lewy body diseases, Friedreich ataxia, congenital heart diseases, Danon disease, and Timothy syndrome. Over the last decade, in vitro modeling of neurocardiac diseases using induced pluripotent stem cells (iPSCs) has provided an invaluable opportunity to elevate our knowledge about the brain-heart connection, since previously primary cardiomyocytes and neurons had been extremely difficult to maintain long-term in vitro. Ultimately, the ability of iPSC technology to model abnormal functional phenotypes of human neurocardiac disorders, combined with the ease of therapeutic screening using this approach, will transform patient care through personalized medicine in the future. © 2016 Wiley Periodicals, Inc.

Bioprinting and Differentiation of Stem Cells

The 3D bioprinting of stem cells directly into scaffolds offers great potential for the development of regenerative therapies; in particular for the fabrication of organ and tissue substitutes. For this to be achieved; the lineage fate of bioprinted stem cell must be controllable. Bioprinting can be neutral; allowing culture conditions to trigger differentiation or alternatively; the technique can be designed to be stimulatory. Such factors as the particular bioprinting technique; bioink polymers; polymer cross-linking mechanism; bioink additives; and mechanical properties are considered. In addition; it is discussed that the stimulation of stem cell differentiation by bioprinting may lead to the remodeling and modification of the scaffold over time matching the concept of 4D bioprinting. The ability to tune bioprinting properties as an approach to fabricate stem cell bearing scaffolds and to also harness the benefits of the cells multipotency is of considerable relevance to the field of biomaterials and bioengineering.