Thinking outside the liver: Induced pluripotent stem cells for hepatic applications

The discovery of induced pluripotent stem cells (iPSCs) unraveled a mystery in stem cell research, after identification of four re-programming factors for generating pluripotent stem cells without the need of embryos. This breakthrough in generating iPSCs from somatic cells has overcome the ethical issues and immune rejection involved in the use of human embryonic stem cells. Hence, iPSCs form a great potential source for developing disease models, drug toxicity screening and cell-based therapies. These cells have the potential to differentiate into desired cell types, including hepatocytes, under in vitro as well as under in vivo conditions given the proper microenvironment. iPSC-derived hepatocytes could be useful as an unlimited source, which can be utilized in disease modeling, drug toxicity testing and producing autologous cell therapies that would avoid immune rejection and enable correction of gene defects prior to cell transplantation. In this review, we discuss the induction methods, role of reprogramming factors, and characterization of iPSCs, along with hepatocyte differentiation from iPSCs and potential applications. Further, we discuss the location and detection of liver stem cells and their role in liver regeneration. Although tumor formation and genetic mutations are a cause of concern, iPSCs still form a promising source for clinical applications.     

Small molecules and extrinsic factors promoting differentiation of stem cells into insulin-producing cells

In the modern world, type-2 diabetes mellitus has become a leading public healthcare problem, due to major risks of morbidity and mortality. Prevalence has increased significantly in recent decades. Treatment involves oral hypoglycemic agents or insulin replacement therapy. Development is ongoing for cell-based diabetes therapies using stem cells with the potential to differentiate into insulin-producing cells (IPCs): embryonic stem cells (ESCs), mesenchymal stem cells (MSCs), induced pluripotent stem cells (iPSCs), and stem cells from adult pancreas, liver, central nervous system, bone marrow and adipose tissue. Successful induction of iPSCs, however, depends on the quantity and quality of available stem cells and the development of adapted protocols determining the environment of extrinsic factors and involvement of small molecules. Validating such new cell therapies must be founded on this experimental rationale.     

Cartilage tissue engineering using differentiated and purified induced pluripotent stem cells

The development of regenerative therapies for cartilage injury has been greatly aided by recent advances in stem cell biology. Induced pluripotent stem cells (iPSCs) have the potential to provide an abundant cell source for tissue engineering, as well as generating patient-matched in vitro models to study genetic and environmental factors in cartilage repair and osteoarthritis. However, both cell therapy and modeling approaches require a purified and uniformly differentiated cell population to predictably recapitulate the physiological characteristics of cartilage. Here, iPSCs derived from adult mouse fibroblasts were chondrogenically differentiated and purified by type II collagen (Col2)-driven green fluorescent protein (GFP) expression. Col2 and aggrecan gene expression levels were significantly up-regulated in GFP+ cells compared with GFP− cells and decreased with monolayer expansion. An in vitro cartilage defect model was used to demonstrate integrative repair by GFP+ cells seeded in agarose, supporting their potential use in cartilage therapies. In chondrogenic pellet culture, cells synthesized cartilage-specific matrix as indicated by high levels of glycosaminoglycans and type II collagen and low levels of type I and type X collagen. The feasibility of cell expansion after initial differentiation was illustrated by homogenous matrix deposition in pellets from twice-passaged GFP+ cells. Finally, atomic force microscopy analysis showed increased microscale elastic moduli associated with collagen alignment at the periphery of pellets, mimicking zonal variation in native cartilage. This study demonstrates the potential use of iPSCs for cartilage defect repair and for creating tissue models of cartilage that can be matched to specific genetic backgrounds.     

Generation of pancreatic insulin-producing cells from rhesus monkey induced pluripotent stem cells

Aims/hypothesis  

The generation of induced pluripotent stem cells (iPSCs) provides a promising possibility for type 1 diabetes therapy. However, the generation of insulin-producing cells from iPSCs and evaluation of their efficacy and safety should be achieved in large animals before clinically applying iPSC-derived cells in humans. Here we try to generate insulin-producing cells from rhesus monkey (RM) iPSCs.     

iPSC technology‐based regenerative therapy for diabetes

The directed differentiation of human pluripotent stem cells, such as embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs), into pancreatic endocrine lineages has been vigorously examined by reproducing the in vivo developmental processes of the pancreas. Recent advances in this research field have enabled the generation from hESCs/iPSCs of functionally mature β‐like cells in vitro that show glucose‐responsive insulin secretion ability. The therapeutic potentials of hESC/iPSC‐derived pancreatic cells have been evaluated using diabetic animal models, and transplantation methods including immunoprotective devices that prevent immune responses from hosts to the implanted pancreatic cells have been investigated towards the development of regenerative therapies against diabetes. These efforts led to the start of a clinical trial that involves the implantation of hESC‐derived pancreatic progenitors into type 1 diabetes patients. In addition, patient‐derived iPSCs have been generated from diabetes‐related disorders towards the creation of novel in vitro disease models and drug discovery, although few reports so far have analyzed the disease mechanisms. Considering recent advances in differentiation methods that generate pancreatic endocrine lineages, we will see the development of novel cell therapies and therapeutic drugs against diabetes based on iPSC technology‐based research in the next decade.     

Xeno-Free Materials for Stabilizing Basic Fibroblast Growth Factor and Enhancing Cell Proliferation in Human Pluripotent Stem Cell Cultures

Induced pluripotent stem cells (iPSCs) are widely considered important for developing novel regenerative therapies. A major challenge to the growth and proliferation of iPSCs is the maintenance of their undifferentiated status in xeno- and feeder-free conditions. Basic fibroblast growth factor (bFGF) is known to contribute to the expansion of stem cells; however, bFGF is notoriously heat-labile and easily denatured. Here, we investigate the effects of a series of synthetic sulfated/sulfonated polymers and saccharides on the growth of iPSCs. We observed that these materials effectively prevented the reduction of bFGF levels in iPSC culture media during storage at 37 °C. Some of the tested materials also suppressed heat-induced decline in medium performance and maintained cell proliferation. Our results suggest that these sulfated materials can be used to improve the expansion culture of undifferentiated iPSCs and show the potential of cost effective, chemically defined materials for improvement of medium performance while culturing iPSCs.     

RNA-Based Tools for Nuclear Reprogramming and Lineage-Conversion: Towards Clinical Applications

The therapeutic potential of induced pluripotent stem cells (iPSCs) is well established. Safety concerns remain, however, and these have driven considerable efforts aimed at avoiding host genome alteration during the reprogramming process. At present, the tools used to generate human iPSCs include (1) DNA-based integrative and non-integrative methods and (2) DNA-free reprogramming technologies, including RNA-based approaches. Because of their combined efficiency and safety characteristics, RNA-based methods have emerged as the most promising tool for future iPSC-based regenerative medicine applications. Here, I will discuss novel recent advances in reprogramming technology, especially those utilizing the Sendai virus (SeV) and synthetic modified mRNA. In the future, these technologies may find utility in iPSC reprogramming for cellular lineage-conversion, and its subsequent use in cell-based therapies.     

Generation of Induced Pluripotent Stem Cells from Amniotic Fluid Cells of a Fetus with Hb Bart’s Disease

Induced pluripotent stem cells (iPSCs) derived from diseased patients behave as a powerful tool for biomedical research and may provide a source for replacement therapies. In this study, we generated iPSCs from amniotic fluid cells of a fetus with Hb Bart’s (γ4) disease (– –/– –). The established iPSCs showed pluripotency similar to that of human embryonic stem cells. They were able to differentiate into various somatic cell types and maintained normal karyotypes after long periods of culture in vitro. The patient-specific iPSCs offer a valuable model for advancing α-thalassemia (α-thal) research and early treatment of the affected fetuses.     

体外定向诱导人工诱导多功能干细胞向心肌细胞分化

长期以来人们一直在研究心肌再生的可能性。人工诱导多功能干细胞由于其在跨越了胚胎干细胞所面临的医学伦理学问题的同时具有多分化潜能而成为人们研究的热点。在体外定向诱导人工诱导多功能干细胞向心肌细胞分化的试验中,研究者对细胞进行向心肌细胞分化的诱导,检测其分化效率;对分化的心肌细胞进行基因、蛋白水平的验证,并对细胞电生理特性进行比较分析,发现其与正常心肌细胞在各个方面均相似。这些研究为寻找心肌损伤后心肌细胞再生提供了理论基础,并为人们研究心肌细胞在疾病病因学、明确药物效能以及最终的患者特异性治疗方面有广泛的应用价值,为转化医学提供了前景。     

Efficient generation of transgene-free induced pluripotent stem cells from normal and neoplastic bone marrow and cord blood mononuclear cells

Reprogramming blood cells to induced pluripotent stem cells (iPSCs) provides a novel tool for modeling blood diseases in vitro. However, the well-known limitations of current reprogramming technologies include low efficiency, slow kinetics, and transgene integration and residual expression. In the present study, we have demonstrated that iPSCs free of transgene and vector sequences could be generated from human BM and CB mononuclear cells using non-integrating episomal vectors. The reprogramming described here is up to 100 times more efficient, occurs 1-3 weeks faster compared with the reprogramming of fibroblasts, and does not require isolation of progenitors or multiple rounds of transfection. Blood-derived iPSC lines lacked rearrangements of IGH and TCR, indicating that their origin is non-B- or non-T-lymphoid cells. When cocultured on OP9, blood-derived iPSCs could be differentiated back to the blood cells, albeit with lower efficiency compared to fibroblast-derived iPSCs. We also generated transgene-free iPSCs from the BM of a patient with chronic myeloid leukemia (CML). CML iPSCs showed a unique complex chromosomal translocation identified in marrow sample while displaying typical embryonic stem cell phenotype and pluripotent differentiation potential. This approach provides an opportunity to explore banked normal and diseased CB and BM samples without the limitations associated with virus-based methods.     

Is aging a barrier to reprogramming? Lessons from induced pluripotent stem cells

The discovery of induced pluripotent stem cells (iPSCs) has the potential to revolutionize the field of regenerative medicine. In the past few years, iPSCs have been the subject of intensive research towards their application in disease modeling and drug screening. In the future, these cells may be applied in cell therapy to replace or regenerate tissues by autologous transplantation. However, two major hurdles need to be resolved in order to reach the later goal: the low reprogramming efficiency and the safety risks, such as the integration of foreign DNA into the genome of the cells and the tumor formation potential arising from transplantation of residual undifferentiated cells. Recently, aging emerged as one of the barriers that accounts, at least in part, for the low reprogramming efficiency of bona fide iPSCs. Here, we review the molecular pathways linking aging and reprogramming along with the unanswered questions in the field. We discuss whether reprogramming rejuvenates the molecular and cellular features associated with age, and present the recent advances with iPSC-based models, contributing to our understanding of physiological and premature aging.     

Erythroid differentiation of human induced pluripotent stem cells is independent of donor cell type of origin

Epigenetic memory in induced pluripotent stem cells, which is related to the somatic cell type of origin of the stem cells, might lead to variations in the differentiation capacities of the pluripotent stem cells. In this context, induced pluripotent stem cells from human CD34⁺ hematopoietic stem cells might be more suitable for hematopoietic differentiation than the commonly used fibroblast-derived induced pluripotent stem cells. To investigate the influence of an epigenetic memory on the ex vivo expansion of induced pluripotent stem cells into erythroid cells, we compared induced pluripotent stem cells from human neural stem cells and human cord blood-derived CD34⁺ hematopoietic stem cells and evaluated their potential for differentiation into hematopoietic progenitor and mature red blood cells. Although genome-wide DNA methylation profiling at all promoter regions demonstrates that the epigenetic memory of induced pluripotent stem cells is influenced by the somatic cell type of origin of the stem cells, we found a similar hematopoietic induction potential and erythroid differentiation pattern of induced pluripotent stem cells of different somatic cell origin. All human induced pluripotent stem cell lines showed terminal maturation into normoblasts and enucleated reticulocytes, producing predominantly fetal hemoglobin. Differences were only observed in the growth rate of erythroid cells, which was slightly higher in the induced pluripotent stem cells derived from CD34⁺ hematopoietic stem cells. More detailed methylation analysis of the hematopoietic and erythroid promoters identified similar CpG methylation levels in the induced pluripotent stem cell lines derived from CD34⁺ cells and those derived from neural stem cells, which confirms their comparable erythroid differentiation potential.     

诱导性多能干细胞与心血管疾病

诱导性多能干细胞（induced pluripotent stem cells,iPSCs）可通过对多种终末分化的体细胞进行外源性重编程而获得。iPSCs作为自体来源的细胞,在组织修复领域有着巨大的应用前景。然而,iPS诱导技术尚存在诸如制备率低、成瘤风险增加和整合基因残留等一系列问题。现结合国内外最新研究成果,在介绍有关解决iPSCs自身缺陷上所取得的研究进展的同时,重点对iPSCs的心肌定向诱导分化、iPS细胞源性心肌细胞的细胞特性以及其在心血管疾病再生医学临床治疗的最新研究进展做一综述。     

Modeling Viral Infectious Diseases and Development of Antiviral Therapies Using Human Induced Pluripotent Stem Cell-Derived Systems

The recent biotechnology breakthrough of cell reprogramming and generation of induced pluripotent stem cells (iPSCs), which has revolutionized the approaches to study the mechanisms of human diseases and to test new drugs, can be exploited to generate patient-specific models for the investigation of host–pathogen interactions and to develop new antimicrobial and antiviral therapies. Applications of iPSC technology to the study of viral infections in humans have included in vitro modeling of viral infections of neural, liver, and cardiac cells; modeling of human genetic susceptibility to severe viral infectious diseases, such as encephalitis and severe influenza; genetic engineering and genome editing of patient-specific iPSC-derived cells to confer antiviral resistance.