Induction of pluripotent stem cells from adult somatic cells by protein-based reprogramming without genetic manipulation

Possible Strategies to Reduce the Tumorigenic Risk of Reprogrammed Normal and Cancer Cells

The reprogramming of somatic cells to pluripotent stem cells has immense potential for use in regenerating or redeveloping tissues for transplantation, and the future application of this method is one of the most important research topics in regenerative medicine. These cells are generated from normal cells, adult stem cells, or neoplastic cancer cells. They express embryonic stem cell markers, such as OCT4, SOX2, and NANOG, and can differentiate into all tissue types in adults, both in vitro and in vivo. However, tumorigenicity, immunogenicity, and heterogeneity of cell populations may hamper the use of this method in medical therapeutics. The risk of cancer formation is dependent on mutations of these stemness genes during the transformation of pluripotent stem cells to cancer cells and on the alteration of the microenvironments of stem cell niches at genetic and epigenetic levels. Recent reports have shown that the generation of induced pluripotent stem cells (iPSCs) derived from human fibroblasts could be induced using chemicals, which is a safe, easy, and clinical-grade manufacturing strategy for modifying the cell fate of human cells required for regeneration therapies. This strategy is one of the future routes for the clinical application of reprogramming therapy. Therefore, this review highlights the recent progress in research focused on decreasing the tumorigenic risk of iPSCs or iPSC-derived organoids and increasing the safety of iPSC cell preparation and their application for therapeutic benefits.

Induced-pluripotent stem cells and neuroproteomics as tools for studying neurodegeneration

The investigation of neurodegenerative diseases advanced significantly with the advent of cell-reprogramming technology, leading to the creation of new models of human illness. These models, derived from induced pluripotent stem cells (iPSCs), facilitate the study of sporadic as well as hereditary diseases and provide a comprehensive understanding of the molecular mechanisms involved with neurodegeneration. Through proteomics, a quantitative tool capable of identifying thousands of proteins from small sample volumes, researchers have attempted to identify disease mechanisms by detecting differentially expressed proteins and proteoforms in disease models, biofluids, and postmortem brain tissue. The integration of these two technologies allows for the identification of novel pathological targets within the realm of neurodegenerative diseases. Here, we highlight studies from the past 5 years on the contributions of iPSCs within neuroproteomic investigations, which uncover the molecular mechanisms behind these illnesses.

Application Prospect of Induced Pluripotent Stem Cells in Organoids and Cell Therapy

Since its inception, induced pluripotent stem cell (iPSC) technology has been hailed as a powerful tool for comprehending disease etiology and advancing drug screening across various domains. While earlier iPSC-based disease modeling and drug assessment primarily operated at the cellular level, recent years have witnessed a significant shift towards organoid-based investigations. Organoids derived from iPSCs offer distinct advantages, particularly in enabling the observation of disease progression and drug metabolism in an in vivo-like environment, surpassing the capabilities of iPSC-derived cells. Furthermore, iPSC-based cell therapy has emerged as a focal point of clinical interest. In this review, we provide an extensive overview of non-integrative reprogramming methods that have evolved since the inception of iPSC technology. We also deliver a comprehensive examination of iPSC-derived organoids, spanning the realms of the nervous system, cardiovascular system, and oncology, as well as systematically elucidate recent advancements in iPSC-related cell therapies.

Recent advances in the application of induced pluripotent stem cell technology to the study of myeloid malignancies

Acquired myeloid malignancies are a spectrum of clonal disorders known to be caused by sequential acquisition of genetic lesions in hematopoietic stem and progenitor cells, leading to their aberrant self-renewal and differentiation. The increasing use of induced pluripotent stem cell (iPSC) technology to study myeloid malignancies has helped usher a paradigm shift in approaches to disease modeling and drug discovery, especially when combined with gene-editing technology. The process of reprogramming allows for the capture of the diversity of genetic lesions and mutational burden found in primary patient samples into individual stable iPSC lines. Patient-derived iPSC lines, owing to their self-renewal and differentiation capacity, can thus be a homogenous source of disease relevant material that allow for the study of disease pathogenesis using various functional read-outs. Furthermore, genome editing technologies like CRISPR/Cas9 enable the study of the stepwise progression from normal to malignant hematopoiesis through the introduction of specific driver mutations, individually or in combination, to create isogenic lines for comparison. In this review, we survey the current use of iPSCs to model acquired myeloid malignancies including myelodysplastic syndromes (MDS), myeloproliferative neoplasms (MPN), acute myeloid leukemia and MDS/MPN overlap syndromes. The use of iPSCs has enabled the interrogation of the underlying mechanism of initiation and progression driving these diseases. It has also made drug testing, repurposing, and the discovery of novel therapies for these diseases possible in a high throughput setting.

Overcoming the Variability of iPSCs in the Manufacturing of Cell-Based Therapies

Various factors are known to contribute to the diversity of human induced pluripotent stem cells (hiPSCs). Among these are the donor's genetic background and family history, the somatic cell source, the iPSC reprogramming method, and the culture system of choice. Moreover, variability is seen even in iPSC clones, generated in a single reprogramming event, where the donor, somatic cell type, and reprogramming platform are the same. The diversity seen in iPSC lines often translates to epigenetic differences, as well as to differences in the expansion rate, iPSC line culture robustness, and their ability to differentiate into specific cell types. As such, the diversity of iPSCs presents a hurdle to standardizing iPSC-based cell therapy manufacturing. In this review, we will expand on the various factors that impact iPSC diversity and the strategies and tools that could be taken by the industry to overcome the differences amongst various iPSC lines, therefore enabling robust and reproducible iPSC-based cell therapy manufacturing processes.

Aryl Hydrocarbon Receptor: From Homeostasis to Tumor Progression

Transcription factor aryl hydrocarbon receptor (AHR) has emerged as one of the main regulators involved both in different homeostatic cell functions and tumor progression. Being a member of the family of basic-helix-loop-helix (bHLH) transcriptional regulators, this intracellular receptor has become a key member in differentiation, pluripotency, chromatin dynamics and cell reprogramming processes, with plenty of new targets identified in the last decade. Besides this role in tissue homeostasis, one enthralling feature of AHR is its capacity of acting as an oncogene or tumor suppressor depending on the specific organ, tissue and cell type. Together with its well-known modulation of cell adhesion and migration in a cell-type specific manner in epithelial-mesenchymal transition (EMT), this duality has also contributed to the arise of its clinical interest, highlighting a new potential as therapeutic tool, diagnosis and prognosis marker. Therefore, a deregulation of AHR-controlled pathways may have a causal role in contributing to physiological and homeostatic failures, tumor progression and dissemination. With that firmly in mind, this review will address the remarkable capability of AHR to exert a different function influenced by the phenotype of the target cell and its potential consequences.

RNA-Based Strategies for Cell Reprogramming toward Pluripotency

Cell therapy approaches to treat a wide range of pathologies have greatly benefited from cell reprogramming techniques that allow the conversion of a somatic cell into a pluripotent cell. Many technological developments have been made since the initial major discovery of this biological process. Recently reprogramming methods based on the use of RNA have emerged and seem very promising. Thus, in this review we will focus on presenting the interest of such methods for cell reprogramming but also how these RNA-based strategies can be extended to eventually lead to medical applications to improve healthspan and longevity.

Induced Pluripotent Stem Cells for Treatment of Alzheimer’s and Parkinson’s Diseases

Neurodegenerative diseases are a group of debilitating pathologies in which neuronal tissue dies due to the buildup of neurotoxic plaques, resulting in detrimental effects on cognitive ability, motor control, and everyday function. Stem cell technology offers promise in addressing this problem on multiple fronts, but the conventional sourcing of pluripotent stem cells involves harvesting from aborted embryonic tissue, which comes with strong ethical and practical concerns. The keystone discovery of induced pluripotent stem cell (iPSC) technology provides an alternative and endless source, circumventing the unfavorable issues with embryonic stem cells, and yielding fundamental advantages. This review highlights iPSC technology, the pathophysiology of two major neurodegenerative diseases, Alzheimer’s and Parkinson’s, and then illustrates current state-of-the-art approaches towards the treatment of the diseases using iPSCs. The technologies discussed in the review emphasize in vitro therapeutic neural cell and organoid development for disease treatment, pathological modeling of neurodegenerative diseases, and 3D bioprinting as it applies to both.

OUP accepted manuscript

Discovering cell–surface markers based on a comprehensive understanding of development is utilized to isolate a particular cell type with high purity for therapeutic purposes. Given that latrophilin-2 (Lphn2) substantially contributes to cardiac differentiation, we examined whether Lphn2 regulates functional significance in heart development and repair. We performed whole-mount immunostaining followed by clearing technique of embryo, RNA sequencing related to Lphn2-knockout (KO) embryo, and in vivo functional analyses of Lphn2+ cells using echocardiography. After immunostaining the cleared embryo sample, Lphn2 was exclusively observed in cardiac cells expressing α-sarcomeric actinin at embryonic days E9.5 and E10.5. Homozygous Lphn2-KO mice were embryonically lethal and showed underdevelopment of the ventricular myocardium. However, Lphn2 was not required to develop vessels, including endothelial cells and smooth muscle cells. For the purpose of cardiac regeneration, we transplanted pluripotent stem cell (PSC)–derived Lphn2+ cells into the infarcted heart. PSC–derived Lphn2+ cells differentiated into cardiomyocytes and regenerated the myocardium when transplanted into the infarcted heart, unlike Lphn2− cells. Transplanted Lphn2+ cells improved left-ventricle systolic function and reduced infarct size. We demonstrated that Lphn2 exhibits potential as a cardiomyogenic marker to facilitate targeted stem cell therapy for heart repair in clinical practice.

Cardiovascular Regeneration via Stem Cells and Direct Reprogramming: A Review

Despite recent advancements in treatment strategies, cardiovascular disease such as heart failure remains a significant source of global mortality. Stem cell technology and cellular reprogramming are rapidly growing fields that will continue to prove useful in cardiac regenerative therapeutics. This review provides information on the role of human pluripotent stem cells (hPSCs) in cardiac regeneration and discusses the practical applications of hPSC-derived cardiomyocytes (CMCs). Moreover, we discuss the practical applications of hPSC-derived CMCs while outlining the relevance of directly-reprogrammed CMCs in regenerative medicine. This review critically summarizes the most recent advances in the field will help to guide future research in this developing area.

Cardiovascular disease (CVD) is the leading causes of morbidity and death globally. In particular, a heart failure remains a major problem that contributes to global mortality. Considerable advancements have been made in conventional pharmacological therapies and coronary intervention surgery for cardiac disorder treatment. However, more than 15% of patients continuously progress to end-stage heart failure and eventually require heart transplantation. Over the past year, numerous numbers of protocols to generate cardiomyocytes (CMCs) from human pluripotent stem cells (hPSCs) have been developed and applied in clinical settings. Number of studies have described the therapeutic effects of hPSCs in animal models and revealed the underlying repair mechanisms of cardiac regeneration. In addition, biomedical engineering technologies have improved the therapeutic potential of hPSC-derived CMCs in vivo. Recently substantial progress has been made in driving the direct differentiation of somatic cells into mature CMCs, wherein an intermediate cellular reprogramming stage can be bypassed. This review provides information on the role of hPSCs in cardiac regeneration and discusses the practical applications of hPSC-derived CMCs; furthermore, it outlines the relevance of directly reprogrammed CMCs in regenerative medicine.

Safe and stable generation of induced pluripotent stem cells using doggybone DNA vectors

The application of induced pluripotent stem cells (iPSCs) in advanced therapies is increasing at pace, but concerns remain over their clinical safety profile. We report the first-ever application of doggybone DNA (dbDNA) vectors to generate human iPSCs. dbDNA vectors are closed-capped linear double-stranded DNA gene expression cassettes that contain no bacterial DNA and are amplified by a chemically defined, current good manufacturing practice (cGMP)-compliant methodology. We achieved comparable iPSC reprogramming efficiencies using transiently expressing dbDNA vectors with the same iPSC reprogramming coding sequences as the state-of-the-art OriP/EBNA1 episomal vectors but, crucially, in the absence of p53 shRNA repression. Moreover, persistent expression of EBNA1 from bacterially derived episomes resulted in stimulation of the interferon response, elevated DNA damage, and increased spontaneous differentiation. These cellular activities were diminished or absent in dbDNA-iPSCs, resulting in lines with a greater stability and safety potential for cell therapy.

Plant callus-derived shikimic acid regenerates human skin through converting human dermal fibroblasts into multipotent skin-derived precursor cells

Background

The human skin-derived precursors (SKPs) are a good cell source for regeneration. However, the isolation of SKP from human skin is limited. To overcome this drawback, we hypothesized that the component of plant stem cells could convert human fibroblasts to SKPs.

Methods

Human dermal fibroblasts were treated with shikimic acid, a major component of Sequoiadendron giganteum callus extract. The characteristics of these reprogrammed cells were analyzed by qPCR, western blot, colony-forming assay, and immunofluorescence staining. Artificial human skin was used for CO₂ laser-induced wound experiments. Human tissues were analyzed by immunohistochemistry.

Results

The reprogrammed cells expressed nestin (a neural precursor-specific protein), fibronectin, and vimentin and could differentiate into the ectodermal and mesodermal lineage. Nestin expression was induced by shikimic acid through the mannose receptor and subsequent MYD88 activation, leading to P38 phosphorylation and then CREB binding to the nestin gene promoter. Finally, we confirmed that shikimic acid facilitated the healing of cut injury and enhanced dermal reconstruction in a human artificial skin model. Moreover, in a clinical study with healthy volunteers, plant callus extracts increased the expression of stem cell markers in the basal layer of the epidermis and collagen deposit in the dermis.

Conclusions

These results indicate that shikimic acid is an effective agent for tissue regeneration.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02409-3.

Induced Pluripotent Stem Cells for Ischemic Stroke Treatment

Ischemic stroke is one of the main central nervous system diseases and is associated with high disability and mortality rates. Recombinant tissue plasminogen activator (rt-PA) and mechanical thrombectomy are the optimal therapies available currently to restore blood flow in patients with stroke; however, their limitations are well recognized. Therefore, new treatments are urgently required to overcome these shortcomings. Recently, stem cell transplantation technology, involving the transplantation of induced pluripotent stem cells (iPSCs), has drawn the interest of neuroscientists and is considered to be a promising alternative for ischemic stroke treatment. iPSCs are a class of cells produced by introducing specific transcription factors into somatic cells, and are similar to embryonic stem cells in biological function. Here, we have reviewed the current applications of stem cells with a focus on iPSC therapy in ischemic stroke, including the neuroprotective mechanisms, development constraints, major challenges to overcome, and clinical prospects. Based on the current state of research, we believe that stem cells, especially iPSCs, will pave the way for future stroke treatment.

Potential of Induced Pluripotent Stem Cells for Use in Gene Therapy: History, Molecular Bases, and Medical Perspectives

Induced pluripotent stem cells (iPSCs) are defined as reprogrammed somatic cells exhibiting embryonic stem cell characteristics. Since their discovery in 2006, efforts have been made to utilize iPSCs in clinical settings. One of the promising fields of medicine, in which genetically patient-specific stem cells may prove themselves useful, is gene therapy. iPSCs technology holds potential in both creating models of genetic diseases and delivering therapeutic agents into the organism via auto-transplants, which reduces the risk of rejection compared to allotransplants. However, in order to safely administer genetically corrected stem cells into patients’ tissues, efforts must be made to establish stably pluripotent stem cells and reduce the risk of insertional tumorigenesis. In order to achieve this, optimal reprogramming factors and vectors must be considered. Therefore, in this review, the molecular bases of reprogramming safe iPSCs for clinical applications and recent attempts to translate iPSCs technology into the clinical setting are discussed.

Generation of biologically active recombinant human OCT4 protein from E. coli

Octamer-binding transcription factor 4 (OCT4) is vital for early embryonic development and is a master regulator of pluripotency in embryonic stem cells. Notably, OCT4 is a key reprogramming factor to derive induced pluripotent stem cells, which have tremendous prospects in regenerative medicine. In the current study, we report heterologous expression and purification of human OCT4 in E. coli to produce pure recombinant protein under native conditions. To achieve this, the 1083 bp coding sequence of the human OCT4 gene was codon-optimized for heterologous expression in E. coli. The codon-optimized sequence was fused with fusion tags, namely a cell-penetrating peptide sequence for intracellular delivery, a nuclear localization sequence for intranuclear delivery, and a His-tag for affinity purification. Subsequently, the codon-optimized sequence and the fusion tags were cloned in the protein expression vector, pET28a(+), and transformed into E. coli strain BL21(DE3) for expression. The recombinant OCT4 protein was purified from the soluble fraction under native conditions using immobilized metal ion affinity chromatography in a facile manner, and its identity was confirmed by Western blotting and mass spectrometry. Furthermore, the secondary structure of the recombinant protein was analyzed using far ultraviolet circular dichroism spectroscopy, which confirmed that the purified fusion protein maintained a secondary structure conformation, and it predominantly composed of α-helices. Next, the recombinant OCT4 protein was applied to human cells, and was found that it was able to enter the cells and translocate to the nucleus. Furthermore, the biological activity of the transduced OCT4 protein was also demonstrated on human cells. This recombinant tool can substitute for genetic and viral forms of OCT4 to enable the derivation of integration-free pluripotent cells. It can also be used to elucidate its biological role in various cellular processes and diseases and for structural and biochemical studies.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02758-z.

Adhesion GPCR Latrophilin-2 Specifies Cardiac Lineage Commitment through CDK5, Src, and P38MAPK

Identifying lineage-specific markers is pivotal for understanding developmental processes and developing cell therapies. Here, we investigated the functioning of a cardiomyogenic cell-surface marker, latrophilin-2 (LPHN2), an adhesion G-protein-coupled receptor, in cardiac differentiation. LPHN2 was selectively expressed in cardiac progenitor cells (CPCs) and cardiomyocytes (CMCs) during mouse and human pluripotent stem cell (PSC) differentiation; cell sorting with an anti-LPHN2 antibody promoted the isolation of populations highly enriched in CPCs and CMCs. Lphn2 knockdown or knockout PSCs did not express cardiac genes. We used the Phospho Explorer Antibody Array, which encompasses nearly all known signaling pathways, to assess molecular mechanisms underlying LPHN2-induced cardiac differentiation. LPHN2-dependent phosphorylation was the strongest for cyclin-dependent kinase 5 (CDK5) at Tyr15. We identified CDK5, Src, and P38MAPK as key downstream molecules of LPHN2 signaling. These findings provide a valuable strategy for isolating CPCs and CMCs from PSCs and insights into the still-unknown cardiac differentiation mechanisms.

Lysophosphatidic Acid Receptor 4 Is Transiently Expressed during Cardiac Differentiation and Critical for Repair of the Damaged Heart

Efficient differentiation of pluripotent stem cells (PSCs) into cardiac cells is essential for the development of new therapeutic modalities to repair damaged heart tissue. We identified a novel cell surface marker, the G protein-coupled receptor lysophosphatidic acid receptor 4 (LPAR4), specific to cardiac progenitor cells (CPCs) and determined its functional significance and therapeutic potential. During in vitro differentiation of mouse and human PSCs toward cardiac lineage, LPAR4 expression peaked after 3−7 days of differentiation in cardiac progenitors and then declined. In vivo, LPAR4 was specifically expressed in the early stage of embryonal heart development, and as development progressed, LPAR4 expression decreased and was non-specifically distributed. We identified the effective agonist octadecenyl phosphate and a p38 MAPK blocker as the downstream signal blocker. Sequential stimulation and inhibition of LPAR4 using these agents enhanced the in vitro efficiency of cardiac differentiation from mouse and human PSCs. Importantly, in vivo, this sequential stimulation and inhibition of LPAR4 reduced the infarct size and rescued heart dysfunction in mice. In conclusion, LPAR4 is a novel CPC marker transiently expressed only in heart during embryo development. Modulation of LPAR4-positive cells may be a promising strategy for repairing myocardium after myocardial infarction.

Generation of a Recombinant Stem Cell-Specific Human SOX2 Protein from Escherichia coli Under Native Conditions

The stem cell-specific SOX2 transcription factor is critical for early embryonic development and the maintenance of embryonic and neural stem cell identity. It is also crucial for the generation of induced pluripotent and neural stem cells, thus providing immense prospect in patient-specific therapies. Here, we report soluble expression and purification of human SOX2 protein under native conditions from a bacterial system. To generate this macromolecule, we codon-optimized the protein-coding sequence and fused it to a nuclear localization signal, a protein transduction domain, and a His-tag. This was then cloned into a protein expression vector and was expressed in Escherichia coli. Subsequently, we have screened and identified the optimal expression conditions to obtain recombinant fusion protein in a soluble form and studied its expression concerning the position of fusion tags at either terminal. Furthermore, we purified two versions of recombinant SOX2 fusion proteins to homogeneity under native conditions and demonstrated that they maintained their secondary structure. This molecular tool can substitute genetic and viral forms of SOX2 to facilitate the derivation of integration-free induced pluripotent and neural stem cells. Furthermore, it can be used in elucidating its role in stem cells, various cellular processes and diseases, and for structural and biochemical studies.

Expression of Recombinant Human Octamer-Binding Transcription Factor 4 in Rice Suspension Cells

The rice cell suspension culture system is a good way to produce recombinant human proteins, owing to its high biosafety and low production cost. Human Octamer-binding Transcription Factor 4 (Oct4) is a fundamental transcription factor responsible for maintaining human pluripotent embryonic stem cells. Recombinant Oct4 protein has been used to induce pluripotent stem cells. In this study, recombinant Oct4 proteins are produced via a sugar starvation-inducible αAmy3/RAmy3D promoter-signal peptide-based rice recombinant protein expression system. Oct4 mRNAs accumulate in the transgenic rice suspension cells under sugar starvation. The Oct4 recombinant protein is detected in the transgenic rice suspension cells, and its highest yield is approximately 0.41% of total cellular soluble proteins after one day of sugar starvation. The rice cell-synthesized recombinant human Oct4 protein show DNA-binding activity in vitro, which implies that the protein structure is correct for enabling specific binding to the target DNA motif.

A Concise Review on Induced Pluripotent Stem Cell-Derived Cardiomyocytes for Personalized Regenerative Medicine

The induced pluripotent stem cells (iPSCs) are derived from somatic cells by using reprogramming factors such as Oct4, Sox2, Klf4, and c-Myc (OSKM) or Oct4, Sox2, Nanog and Lin28 (OSNL). They resemble embryonic stem cells (ESCs) and have the ability to differentiate into cell lineage of all three germ-layer, including cardiomyocytes (CMs). The CMs can be generated from iPSCs by inducing embryoid bodies (EBs) formation and treatment with activin A, bone morphogenic protein 4 (BMP4), and inhibitors of Wnt signaling. However, these iPSC-derived CMs are a heterogeneous population of cells and require purification and maturation to mimic the in vivo CMs. The matured CMs can be used for various therapeutic purposes in regenerative medicine by cardiomyoplasty or through the development of tissue-engineered cardiac patches. In recent years, significant advancements have been made in the isolation of iPSC and their differentiation, purification, and maturation into clinically usable CMs. Newer small molecules have also been identified to substitute the reprogramming factors for iPSC generation as well as for direct differentiation of somatic cells into CMs without an intermediary pluripotent state. This review provides a concise update on the generation of iPSC-derived CMs and their application in personalized cardiac regenerative medicine. It also discusses the current limitations and challenges in the application of iPSC-derived CMs. Graphical abstract.

An Insight into DNA-free Reprogramming Approaches to Generate Integration-free Induced Pluripotent Stem Cells for Prospective Biomedical Applications

More than a decade ago, a pioneering study reported generation of induced Pluripotent Stem Cells (iPSCs) by ectopic expression of a cocktail of reprogramming factors in fibroblasts. This study has revolutionized stem cell research and has garnered immense interest from the scientific community globally. iPSCs hold tremendous potential for understanding human developmental biology, disease modeling, drug screening and discovery, and personalized cell-based therapeutic applications. The seminal study identified Oct4, Sox2, Klf4 and c-Myc as a potent combination of genes to induce reprogramming. Subsequently, various reprogramming factors were identified by numerous groups. Most of these studies have used integrating viral vectors to overexpress reprogramming factors in somatic cells to derive iPSCs. However, these techniques restrict the clinical applicability of these cells as they may alter the genome due to random viral integration resulting in insertional mutagenesis and tumorigenicity. To circumvent this issue, alternative integration-free reprogramming approaches are continuously developed that eliminate the risk of genomic modifications and improve the prospects of iPSCs from lab to clinic. These methods establish that integration of transgenes into the genome is not essential to induce pluripotency in somatic cells. This review provides a comprehensive overview of the most promising DNA-free reprogramming techniques that have the potential to derive integration-free iPSCs without genomic manipulation, such as sendai virus, recombinant proteins, microRNAs, synthetic messenger RNA and small molecules. The understanding of these approaches shall pave a way for the generation of clinical-grade iPSCs. Subsequently, these iPSCs can be differentiated into desired cell type(s) for various biomedical applications.

Induced Pluripotent Stem Cells: Reprogramming Platforms and Applications in Cell Replacement Therapy

The generation of induced pluripotent stem cells (iPSCs) from differentiated mature cells is one of the most promising technologies in the field of regenerative medicine. The ability to generate patient-specific iPSCs offers an invaluable reservoir of pluripotent cells, which could be genetically engineered and differentiated into target cells to treat various genetic and degenerative diseases once transplanted, hence counteracting the risk of graft versus host disease. In this context, we review the scientific research streams that lead to the emergence of iPSCs, the roles of reprogramming factors in reprogramming to pluripotency, and the reprogramming strategies. As iPSCs serve tremendous correction potentials for various diseases, we highlight the successes and challenges of iPSCs in cell replacement therapy and the synergy of iPSCs and clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 gene editing tools in therapeutics research.

Methods of Generation of Induced Pluripotent Stem Cells and Their Application for the Therapy of Central Nervous System Diseases

The use of induced pluripotent stem cells (IPSC) is a promising approach to the therapy of CNS diseases. The undeniable advantage of IPSC technology is the possibility of obtaining practically all types of somatic cells for autologous transplantation bypassing bioethical problems. The review presents integrative and non-integrative methods for obtaining IPSC and the ways of their in vitro and in vivo application for the study and treatment of neurological diseases.

Non-viral reprogramming and induced pluripotent stem cells for cardiovascular therapy

Despite significant effort devoted to developing new treatments and procedures, cardiac disease is still one of the leading causes of death in the world. The loss of myocytes due to ischemic injury remains a major therapeutic challenge. However, cell-based therapy to repair the injured heart has shown significant promise in basic and translation research and in clinical trials. Embryonic stem cells have been successfully used to improve cardiac outcomes. Unfortunately, treatment with these cells is complicated by ethical and legal issues. Recent progress in developing induced pluripotent stem cells (iPSCs) using non-viral vectors has made it possible to derive cardiomyocytes for therapy. This review will focus on these non-integration-based approaches for reprogramming and their therapeutic advantages for cardiovascular medicine.

NFATc1+CD31+CD45- circulating multipotent stem cells derived from human endocardium and their therapeutic potential

Many studies have shown the existence of cardiac stem cells in the myocardium and epicardial progenitor cells in the epicardium. However, the characteristics of stem cells in the endocardium has not been fully elucidated. In this study, we investigated the origin of newly identified cells in the blood and their therapeutic potential. The new population of cells, identified from human peripheral blood, was quite different from previously reported stem cells. These newly identified cells, which we named Circulating Multipotent Stem (CiMS) cells, were multipotent, and therefore differentiated into multiple lineages in vitro and in vivo. In order to determine the origin of these cells, we collected peripheral blood from a group of patients who underwent bone marrow, liver, heart, or kidney transplantation. We identified the endocardium as the origin of these cells because the Short Tandem Repeat profile of CiMS cells from the recipient had changed from the recipient's profile to the donor's profile after heart transplantation. CiMS cells significantly increased after stimuli to the endocardium, such as catheter ablation for arrhythmia or acute myocardial infarction. CiMS cells circulate in human peripheral blood and are easily obtainable, suggesting that these cells could be a promising tool for cell therapy.

Successful Derivation of an Induced Pluripotent Stem Cell Line from a Genetically Nonpermissive Enhanced Green Fluorescent Protein-Transgenic FVB/N Mouse Strain

The embryonic stem cell line derivation from nonpermissive mouse strains is a challenging and highly inefficient process. The cellular reprogramming strategy provides an alternative route for generating pluripotent stem cell (PSC) lines from such strains. In this study, we successfully derived an enhanced green fluorescent protein (EGFP)-transgenic "N9" induced pluripotent stem cell (iPS cell, iPSC) line from the FVB/N strain-derived mouse embryonic fibroblasts (MEFs). The exposure of MEFs to human OCT4, SOX2, KLF4, and c-MYC (OSKM) transgenes via lentiviral transduction resulted in complete reprogramming. The N9 iPS cell line demonstrated all the criteria of a typical mouse PSC line, including normal colony morphology and karyotype (40,XY), high replication and propagation efficiencies, expression of the pluripotency-associated genes, spontaneous differentiation to three germ lineage-derived cell types, and robust potential of chimeric blastocyst formation. Taken together, using human OSKM genes for transduction, we report, for the first time, the successful derivation of an EGFP-expressing iPS cell line from a genetically nonpermissive transgenic FVB/N mouse. This cell line could provide opportunities for designing protocols for efficient derivation of PSC lines from other nonpermissive strains and developing mouse models of human diseases.

Modeling blood diseases with human induced pluripotent stem cells

Induced pluripotent stem cells (iPSCs) are derived from somatic cells through a reprogramming process, which converts them to a pluripotent state, akin to that of embryonic stem cells. Over the past decade, iPSC models have found increasing applications in the study of human diseases, with blood disorders featuring prominently. Here, we discuss methodological aspects pertaining to iPSC generation, hematopoietic differentiation and gene editing, and provide an overview of uses of iPSCs in modeling the cell and gene therapy of inherited genetic blood disorders, as well as their more recent use as models of myeloid malignancies. We also discuss the strengths and limitations of iPSCs compared to model organisms and other cellular systems commonly used in hematology research.

Imprinted gene Zinc finger protein 127 is a novel regulator of master pluripotency transcription factor, Oct4

Induced pluripotent stem cells (iPSCs) show great promise for replacing current stem cell therapies in the field of regenerative medicine. However, the original method for cellular reprogramming, involving four exogenous transcription factors, is characterized by low efficiency. Here, we focused on using epigenetic modifications to enhance the reprogramming efficiency. We hypothesized that there would be a new reprogramming factor involved in DNA demethylation, acting on the promoters of pluripotency-related genes. We screened proteins that bind to the methylated promoter of Oct4 and identified Zinc finger protein 127 (Zfp127), the functions of which have not yet been identified. We found that Zfp127 binds to the Oct4 promoter. Overexpression of Zfp127 in fibroblasts induced demethylation of the Oct4 promoter, thus enhancing Oct4 promoter activity and gene expression. These results demonstrate that Zfp127 is a novel regulator of Oct4, and may become a potent target to improve cellular reprogramming. [BMB Reports 2018; 51(5): 242-248].

Intracellular Delivery by Membrane Disruption: Mechanisms, Strategies, and Concepts

Intracellular delivery is a key step in biological research and has enabled decades of biomedical discoveries. It is also becoming increasingly important in industrial and medical applications ranging from biomanufacture to cell-based therapies. Here, we review techniques for membrane disruption-based intracellular delivery from 1911 until the present. These methods achieve rapid, direct, and universal delivery of almost any cargo molecule or material that can be dispersed in solution. We start by covering the motivations for intracellular delivery and the challenges associated with the different cargo types-small molecules, proteins/peptides, nucleic acids, synthetic nanomaterials, and large cargo. The review then presents a broad comparison of delivery strategies followed by an analysis of membrane disruption mechanisms and the biology of the cell response. We cover mechanical, electrical, thermal, optical, and chemical strategies of membrane disruption with a particular emphasis on their applications and challenges to implementation. Throughout, we highlight specific mechanisms of membrane disruption and suggest areas in need of further experimentation. We hope the concepts discussed in our review inspire scientists and engineers with further ideas to improve intracellular delivery.

Gata6 in pluripotent stem cells enhance the potential to differentiate into cardiomyocytes

Pluripotent stem cell (PSC) variations can cause significant differences in the efficiency of cardiac differentiation. This process is unpredictable, as there is not an adequate indicator at the undifferentiated stage of the PSCs. We compared global gene expression profiles of two PSCs showing significant differences in cardiac differentiation potential. We identified 12 up-regulated genes related to heart development, and we found that 4 genes interacted with multiple genes. Among these genes, Gata6 is the only gene that was significantly induced at the early stage of differentiation of PSCs to cardiomyocytes. Gata6 knock-down in PSCs decreased the efficiency of cardiomyocyte production. In addition, we analyzed 6 mESC lines and 3 iPSC lines and confirmed that a positive correlation exists between Gata6 levels and efficiency of differentiation into cardiomyocytes. In conclusion, Gata6 could be utilized as a biomarker to select the best PSC lines to produce PSC-derived cardiomyocytes for therapeutic purposes. [BMB Reports 2018; 51(2): 85-91].

The march of pluripotent stem cells in cardiovascular regenerative medicine

Cardiovascular disease (CVD) continues to be the leading cause of global morbidity and mortality. Heart failure remains a major contributor to this mortality. Despite major therapeutic advances over the past decades, a better understanding of molecular and cellular mechanisms of CVD as well as improved therapeutic strategies for the management or treatment of heart failure are increasingly needed. Loss of myocardium is a major driver of heart failure. An attractive approach that appears to provide promising results in reducing cardiac degeneration is stem cell therapy (SCT). In this review, we describe different types of stem cells, including embryonic and adult stem cells, and we provide a detailed discussion of the properties of induced pluripotent stem cells (iPSCs). We also present and critically discuss the key methods used for converting somatic cells to pluripotent cells and iPSCs to cardiomyocytes (CMs), along with their advantages and limitations. Integrating and non-integrating reprogramming methods as well as characterization of iPSCs and iPSC-derived CMs are discussed. Furthermore, we critically present various methods of differentiating iPSCs to CMs. The value of iPSC-CMs in regenerative medicine as well as myocardial disease modeling and cardiac regeneration are emphasized.

Embryonic germ cell extracts erase imprinted genes and improve the efficiency of induced pluripotent stem cells

Patient-specific induced pluripotent stem cells (iPSCs) have the potential to be useful in the treatment of human diseases. While prior studies have reported multiple methods to generate iPSCs, DNA methylation continues to limit the totipotency and reprogramming efficiency of iPSCs. Here, we first show the competency of embryonic germ cells (EGCs) as a reprogramming catalyst capable of effectively promoting reprogramming induced by four defined factors, including Oct4, Sox2, Klf4 and c-Myc. Combining EGC extracts with these four factors resulted in formation of more embryonic stem cell-like colonies than did factors alone. Notably, expression of imprinted genes was higher with combined induction than with factors alone. Moreover, iPSCs derived from the combined inductors tended to have more global hypomethylation. Our research not only provides evidence that EGC extracts could activate DNA demethylation and reprogram imprinted genes, but also establishes a new way to enhance reprogramming of iPSCs, which remains a critical safety concern for potential use of iPSCs in regenerative medicine.

Regenerating β cells of the pancreas - potential developments in diabetes treatment

INTRODUCTION

The etiology of diabetes is mainly attributed to insulin deficiency due to the lack of β cells (type 1), or to insulin resistance that eventually results in β cell dysfunction (type 2). Therefore, an ultimate cure for diabetes requires the ability to replace the lost insulin-secreting β cells. Strategies for regenerating β cells are under extensive investigation.

AREAS COVERED

Herein, the authors first summarize the mechanisms underlying embryonic β cell development and spontaneous adult β cell regeneration, which forms the basis for developing β cell regeneration strategies. Then the rationale and progress of each β cell regeneration strategy is reviewed. Current β cell regeneration strategies can be classified into two main categories: in vitro β cell regeneration using pluripotent stem cells and in vivo reprogramming of non-β cells into β cells. Each has its own advantages and disadvantages.

EXPERT OPINION

Regenerating β cells has shown its potential as a cure for the treatment of insulin-deficient diabetes. Much progress has been made, and β cell regeneration therapy is getting closer to a clinical reality. Nevertheless, more hurdles need to be overcome before any of the strategies suggested can be fully translated from bench to bedside.

Nuclear delivery of recombinant OCT4 by chitosan nanoparticles for transgene-free generation of protein-induced pluripotent stem cells

Protein-based reprogramming of somatic cells is a non-genetic approach for the generation of induced pluripotent stem cells (iPSCs), whereby reprogramming factors, such as OCT4, SOX2, KLF4 and c-MYC, are delivered as functional proteins. The technique is considered safer than transgenic methods, but, unfortunately, most protein-based protocols provide very low reprogramming efficiencies. In this study, we developed exemplarily a nanoparticle (NP)-based delivery system for the reprogramming factor OCT4. To this end, we expressed human OCT4 in Sf9 insect cells using a baculoviral expression system. Recombinant OCT4 showed nuclear localization in Sf9 cells indicating proper protein folding. In comparison to soluble OCT4 protein, encapsulation of OCT4 in nuclear-targeted chitosan NPs strongly stabilized its DNA-binding activity even under cell culture conditions. OCT4-loaded NPs enabled cell treatment with high micromolar concentrations of OCT4 and successfully delivered active OCT4 into human fibroblasts. Chitosan NPs therefore provide a promising tool for the generation of transgene-free iPSCs.

Extract of mouse embryonic stem cells induces the expression of pluripotency genes in human adipose tissue-derived stem cells

Objective(s):

In some previous studies, the extract of embryonic carcinoma cells (ECCs) and embryonic stem cells (ESCs) have been used to reprogram somatic cells to more dedifferentiated state. The aim of this study was to investigate the effect of mouse ESCs extract on the expression of some pluripotency markers in human adipose tissue-derived stem cells (ADSCs).

Materials and Methods:

Human ADSCs were isolated from subcutaneous abdominal adipose tissue and characterized by flow cytometric analysis for the expression of some mesenchymal stem cell markers and adipogenic and osteogenic differentiation. Frequent freeze-thaw technique was used to prepare cytoplasmic extract of ESCs. Plasma membranes of the ADSCs were reversibly permeabilized by streptolysin-O (SLO). Then the permeabilized ADSCs were incubated with the ESC extract and cultured in resealing medium. After reprogramming, the expression of some pluripotency genes was evaluated by RT-PCR and quantitative real-time PCR (qPCR) analyses.

Results:

Third-passaged ADSCs showed a fibroblast-like morphology and expressed mesenchymal stem cell markers. They also showed adipogenic and osteogenic differentiation potential. QPCR analysis revealed a significant upregulation in the expression of some pluripotency genes including OCT4, SOX2, NANOG, REX1 and ESG1 in the reprogrammed ADSCs compared to the control group.

Conclusion:

These findings showed that mouse ESC extract can be used to induce reprogramming of human ADSCs. In fact, this method is applicable for reprogramming of human adult stem cells to a more pluripotent sate and may have a potential in regenerative medicine.

CRISPR Genome Engineering for Human Pluripotent Stem Cell Research

The emergence of targeted and efficient genome editing technologies, such as repurposed bacterial programmable nucleases (e.g., CRISPR-Cas systems), has abetted the development of cell engineering approaches. Lessons learned from the development of RNA-interference (RNA-i) therapies can spur the translation of genome editing, such as those enabling the translation of human pluripotent stem cell engineering. In this review, we discuss the opportunities and the challenges of repurposing bacterial nucleases for genome editing, while appreciating their roles, primarily at the epigenomic granularity. First, we discuss the evolution of high-precision, genome editing technologies, highlighting CRISPR-Cas9. They exist in the form of programmable nucleases, engineered with sequence-specific localizing domains, and with the ability to revolutionize human stem cell technologies through precision targeting with greater on-target activities. Next, we highlight the major challenges that need to be met prior to bench-to-bedside translation, often learning from the path-to-clinic of complementary technologies, such as RNA-i. Finally, we suggest potential bioinformatics developments and CRISPR delivery vehicles that can be deployed to circumvent some of the challenges confronting genome editing technologies en route to the clinic.

Cellular Reprogramming Using Protein and Cell-Penetrating Peptides

Recently, stem cells have been suggested as invaluable tools for cell therapy because of their self-renewal and multilineage differentiation potential. Thus, scientists have developed a variety of methods to generate pluripotent stem cells, from nuclear transfer technology to direct reprogramming using defined factors, or induced pluripotent stem cells (iPSCs). Considering the ethical issues and efficiency, iPSCs are thought to be one of the most promising stem cells for cell therapy. Induced pluripotent stem cells can be generated by transduction with a virus, plasmid, RNA, or protein. Herein, we provide an overview of the current technology for iPSC generation and describe protein-based transduction technology in detail.

Identification of the early and late responder genes during the generation of induced pluripotent stem cells from mouse fibroblasts

BACKGROUND

The generation of induced pluripotent stem cell (iPSC), a substitute for embryonic stem cell (ESC), requires the proper orchestration of a transcription program at the chromatin level. Our recent approach for the induction of pluripotent stem cells from fibroblasts using protein extracts from mouse ESCs could overcome the potential tumorigenicity risks associated with random retroviral integration. Here, we examine the epigenetic modifications and the transcriptome of two types of iPSC and of partially reprogrammed iPSCs (iPSCp) generated independently from adult cardiac and skin fibroblasts to assess any perturbations of the transcription program during reprogramming.

RESULTS

The comparative dissection of the transcription profiles and histone modification patterns at lysines 4 and 27 of histone H3 of the iPSC, iPSCp, ESC, and somatic cells revealed that the iPSC was almost completely comparable to the ESC, regardless of their origins, whereas the genes of the iPSCp were dysregulated to a larger extent. Regardless of the origins of the somatic cells, the fibroblasts induced using the ESC protein extracts appear to be completely reprogrammed into pluripotent cells, although they show unshared marginal differences in their gene expression programs, which may not affect the maintenance of stemness. A comparative investigation of the iPSCp generated by unwanted reprogramming showed that the two groups of genes on the pathway from somatic cells to iPSC might function as sequential reprogramming-competent early and late responders to the induction stimulus. Moreover, some of the divergent genes expressed only in the iPSCp were associated with many tumor-related pathways.

CONCLUSIONS

Faithful transcriptional reprogramming should follow epigenetic alterations to generate induced pluripotent stem cells from somatic cells. This genome-wide comparison enabled us to define the early and late responder genes during the cell reprogramming process to iPSC. Our results indicate that the cellular responsiveness to external stimuli should be pre-determined and sequentially orchestrated through the tight modulation of the chromatin environment during cell reprogramming to prevent unexpected reprogramming.

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.

Gene and Cell Therapy for β-Thalassemia and Sickle Cell Disease with Induced Pluripotent Stem Cells (iPSCs): The Next Frontier

In recent years, breakthroughs in human pluripotent stem cell (hPSC) research, namely cellular reprogramming and the emergence of sophisticated genetic engineering technologies, have opened new frontiers for cell and gene therapy. The prospect of using hPSCs, either autologous or histocompatible, as targets of genetic modification and their differentiated progeny as cell products for transplantation, presents a new paradigm of regenerative medicine of potential tremendous value for the treatment of blood disorders, including beta-thalassemia (BT) and sickle cell disease (SCD). Despite advances at a remarkable pace and great promise, many roadblocks remain before clinical translation can be realistically considered. Here we discuss the theoretical advantages of cell therapies utilizing hPSC derivatives, recent proof-of-principle studies and the main challenges towards realizing the potential of hPSC therapies in the clinic.

Targeted release of transcription factors for cell reprogramming by a natural micro-syringe

Ectopic expression of defined transcription factors (TFs) for cell fate handling has proven high potential interest in reprogramming differentiated cells, in particular for regenerative medicine, ontogenesis study and cell based modelling. Pluripotency or transdifferentiation induction as TF mediated differentiation is commonly produced by transfer of genetic information with safety concerns. The direct delivery of proteins could represent a safer alternative but still needs significant advances to be efficient. We have successfully developed the direct delivery of proteins by an attenuated bacterium with a type 3 secretion system that does not require challenging and laborious steps for production and purification of recombinant molecules. Here we show that this natural micro-syringe is able to inject TFs to primary human fibroblasts and cord blood CD34⁺ hematopoietic stem cells. The signal sequence for vectorization of the TF Oct4 has no effect on DNA binding to its nucleic target. As soon as one hour after injection, vectorized TFs are detectable in the nucleus. The injection process is not associated with toxicity and the bacteria can be completely removed from cell cultures. A three days targeted release of Oct4 or Sox2 embryonic TFs results in the induction of the core pluripotency genes expression in fibroblasts and CD34⁺ hematopoietic stem cells. This micro-syringe vectorization represents a new strategy for TF delivery and has potential applications for cell fate reprogramming.

Therapeutic Transdifferentiation: A Novel Approach for Ischemic Syndromes

The technological development of induced pluripotent stem cells (iPSCs) has overcome many of the limitations of adult and embryonic stem cells. We have found that activation of innate immunity signaling is necessary for this process, as it facilitates epigenetic plasticity in cells by a process called transflammation. More recently, we have discovered that transflammation also facilitates the transdifferentiation of cells directly from one somatic cell type to another. This insight may lead to a promising therapeutic pathway that avoids reverting cells all the way back to pluripotency before achieving a cell type of interest. While there is much therapeutic promise to transflammation and transdifferentiation, there is also evidence that transdifferentiation plays a role in some pathological conditions, including atherosclerosis. Ultimately, better understanding of transflammation will facilitate the development of regenerative therapies.

Protein-Induced Pluripotent Stem Cells Ameliorate Cognitive Dysfunction and Reduce Aβ Deposition in a Mouse Model of Alzheimer's Disease

Transplantation of stem cells into the brain attenuates functional deficits in the central nervous system via cell replacement, the release of specific neurotransmitters, and the production of neurotrophic factors. To identify patient‐specific and safe stem cells for treating Alzheimer's disease (AD), we generated induced pluripotent stem cells (iPSCs) derived from mouse skin fibroblasts by treating protein extracts of embryonic stem cells. These reprogrammed cells were pluripotent but nontumorigenic. Here, we report that protein‐iPSCs differentiated into glial cells and decreased plaque depositions in the 5XFAD transgenic AD mouse model. We also found that transplanted protein‐iPSCs mitigated the cognitive dysfunction observed in these mice. Proteomic analysis revealed that oligodendrocyte‐related genes were upregulated in brains injected with protein‐iPSCs, providing new insights into the potential function of protein‐iPSCs. Taken together, our data indicate that protein‐iPSCs might be a promising therapeutic approach for AD. Stem Cells Translational Medicine2017;6:293–305

10th anniversary of iPS cells: the challenges that lie ahead

In 2006, induced pluripotent stem (iPS) cells were generated by Yamanaka and Takahashi for the first time from a mouse fibroblast culture by introducing four factors. In the 10 years since then, this breakthrough discovery has been making waves in the fields of biology and medical science. For example, various technologies for generating iPS cells have been developed, and we have cultivated a better understanding of the mechanisms involved in reprogramming. In addition, many researchers have explored the applications of iPS cells, such as drug discovery, the study of disease mechanisms and regenerative medicine, and the development of advanced technologies for the differentiation and qualification of the cells. Furthermore, the concept of iPS cell generation has inspired a number of studies that do not use iPS cells. We herein review and discuss the past, present and future of iPS cells and their related issues.

Stem Cells in Skeletal Tissue Engineering: Technologies and Models

This review surveys the use of pluripotent and multipotent stem cells in skeletal tissue engineering. Specific emphasis is focused on evaluating the function and activities of these cells in the context of development in vivo, and how technologies and methods of stem cell-based tissue engineering for stem cells must draw inspiration from developmental biology. Information on the embryonic origin and in vivo differentiation of skeletal tissues is first reviewed, to shed light on the persistence and activities of adult stem cells that remain in skeletal tissues after embryogenesis. Next, the development and differentiation of pluripotent stem cells is discussed, and some of their advantages and disadvantages in the context of tissue engineering are presented. The final section highlights current use of multipotent adult mesenchymal stem cells, reviewing their origin, differentiation capacity, and potential applications to tissue engineering.