Functional characterization of cardiomyocytes derived from murine induced pluripotent stem cells in vitro

Electrophysiological Properties of Tetraploid Cardiomyocytes Derived from Murine Pluripotent Stem Cells Generated by Fusion of Adult Somatic Cells with Embryonic Stem Cells

Most cardiomyocytes (CMs) in the adult mammalian heart are either binucleated or contain a single polyploid nucleus. Recent studies have shown that polyploidy in CMs plays an important role as an adaptive response to physiological demands and environmental stress and correlates with poor cardiac regenerative ability after injury. However, knowledge about the functional properties of polyploid CMs is limited. In this study, we generated tetraploid pluripotent stem cells (PSCs) by fusion of murine embryonic stem cells (ESCs) and somatic cells isolated from bone marrow or spleen and performed a comparative analysis of the electrophysiological properties of tetraploid fusion-derived PSCs and diploid ESC-derived CMs. Fusion-derived PSCs exhibited characteristics of genuine ESCs and contained a near-tetraploid genome. Ploidy features and marker expression were also retained during the differentiation of fusion-derived cells. Fusion-derived PSCs gave rise to CMs, which were similar to their diploid ESC counterparts in terms of their expression of typical cardiospecific markers, sarcomeric organization, action potential parameters, response to pharmacologic stimulation with various drugs, and expression of functional ion channels. These results suggest that the state of ploidy does not significantly affect the structural and electrophysiological properties of murine PSC-derived CMs. These results extend our knowledge of the functional properties of polyploid CMs and contribute to a better understanding of their biological role in the adult heart.

Bioactive Lipid O-cyclic phytosphingosine-1-phosphate Promotes Differentiation of Human Embryonic Stem Cells into Cardiomyocytes via ALK3/BMPR Signaling

Adult human cardiomyocytes have an extremely limited proliferative capacity, which poses a great barrier to regenerative medicine and research. Human embryonic stem cells (hESCs) have been proposed as an alternative source to generate large numbers of clinical grade cardiomyocytes (CMs) that can have potential therapeutic applications to treat cardiac diseases. Previous studies have shown that bioactive lipids are involved in diverse cellular responses including cardiogenesis. In this study, we explored the novel function of the chemically synthesized bioactive lipid O-cyclic phytosphingosine-1-phosphate (cP1P) as an inducer of cardiac differentiation. Here, we identified cP1P as a novel factor that significantly enhances the differentiation potential of hESCs into cardiomyocytes. Treatment with cP1P augments the beating colony number and contracting area of CMs. Furthermore, we elucidated the molecular mechanism of cP1P regulating SMAD1/5/8 signaling via the ALK3/BMP receptor cascade during cardiac differentiation. Our result provides a new insight for cP1P usage to improve the quality of CM differentiation for regenerative therapies.

Therapeutic effects of CXCR4+ subpopulation of transgene-free induced cardiosphere-derived cells on experimental myocardial infarction

OBJECTIVES

Myocardial infarction (MI) is the most predominant type of cardiovascular diseases with high mortality and morbidity. Stem cell therapy, especially cardiac progenitor cell therapy, has been proposed as a promising approach for cardiac regeneration and MI treatment. Previously, we have successfully generated cardiac progenitor-like cells, induced cardiosphere (iCS), via somatic reprogramming. However, the genome integration characteristic of virus-based reprogramming approach hampered their therapeutic applications due to the risk of tumour formation. In the current study, we aim to establish a safer iCS generation strategy with transgene-free approaches.

MATERIALS AND METHODS

Four transgene-free approaches for somatic reprogramming, including episome, minicircle, self-replicative RNA, and sendai virus, were compared, from the perspective of cardiac progenitor marker expression, iCS formation, and cardiac differentiation. The therapeutic effects were assessed in the mouse model of MI, from the perspective of survival rate, cardiac function, and structural alterations.

RESULTS

The self-replicative RNA approach produced more iCS, which had cardiomyocyte differentiation ability and therapeutic effects on the mouse model of MI with comparable levels with endogenous cardiospheres and iCS generated with retrovirus. In addition, the CXCR4 (C-X-C chemokine receptor 4) positive subpopulation of iCS derived cells (iCSDC) delivered by intravenous injection was found to have similar therapeutic effects with intramyocardial injection on the mouse model of MI, representing a safer delivery approach.

CONCLUSION

Thus, the optimized strategy for iCS generation is safer and has more therapeutic potentials.

A realistic appraisal of the use of embryonic stem cell-based therapies for cardiac repair

Despite the well-documented capacity of embryonic stem cells (ESCs) to differentiate into cardiomyocytes, transplantation of ESCs or ESC-derived cells is plagued by several formidable problems, including graft rejection, arrhythmias, and potential risk of teratomas. Life-long immunosuppression is a disease in itself. Transplantation of human ESC-derived cells in primates causes life-threatening arrhythmias, and the doses used to show efficacy are not clinically relevant. In contemporary clinical research, the margin of tolerance for such catastrophic effects as malignancies is zero, and although the probability of tumours can be reduced by ESC differentiation, it is unlikely to be completely eliminated, particularly when billions of cells are injected. Although ESCs and ESC-derived cells were touted as capable of long-term regeneration, these cells disappear rapidly after transplantation and there is no evidence of long-term engraftment, let alone regeneration. There is, however, mounting evidence that they act via paracrine mechanisms-just like adult cells. To date, no controlled clinical trial of ESC-derived cells in cardiovascular disease has been conducted or even initiated. In contrast, adult cells have been used in thousands of patients with heart disease, with no significant adverse effects and with results that were sufficiently encouraging to warrant Phase II and III trials. Furthermore, induced pluripotent stem cells offer pluripotency similar to ESCs without the need for lifelong immunosuppression. After two decades, the promise that ESC-derived cells would regenerate dead myocardium has not been fulfilled. The most reasonable interpretation of current data is that ESC-based therapies are not likely to have clinical application for heart disease.

TRPV1 channels regulate the automaticity of embryonic stem cell-derived cardiomyocytes through stimulating the Na+ /Ca2+ exchanger current

Calcium controls the excitation-contraction coupling in cardiomyocytes. Embryonic stem cell-derived cardiomyocytes (ESC-CMs) are an important cardiomyocyte source for regenerative medicine and drug screening. Transient receptor potential vanilloid 1 (TRPV1) channels are nonselective cation channels that permeate sodium and calcium. This study aimed to investigate whether TRPV1 channels regulate the electrophysiological characteristics of ESC-CMs. If yes, what is the mechanism behind? By immunostaining and subcellular fractionation, followed by western blotting, TRPV1 was found to locate intracellularly. The staining pattern of TRPV1 was found to largely overlap with that of the sarco/endoplasmic reticulum Ca²⁺ -ATPase, the sarcoplasmic reticulum (SR) marker. By electrophysiology and calcium imaging, pharmacological blocker of TRPV1 and the molecular tool TRPV1β (which could functionally knockdown TRPV1) were found to decrease the rate and diastolic depolarization slope of spontaneous action potentials, and the amplitude and frequency of global calcium transients. By calcium imaging, in the absence of external calcium, TRPV1-specific opener increased intracellular calcium; this increase was abolished by preincubation with caffeine, which could deplete SR calcium store. The results suggest that TRPV1 controls calcium release from the SR. By electrophysiology, TRPV1 blockade and functional knockdown of TRPV1 decreased the Na⁺ /Ca2⁺ exchanger (NCX) currents from both the forward and reverse modes, suggesting that sodium and calcium through TRPV1 stimulate the NCX activity. Our novel findings suggest that TRPV1 activity is important for regulating the spontaneous activity of ESC-CMs and reveal a novel interplay between TRPV1 and NCX in regulating the physiological functions of ESC-CMs.

Stem cell therapy: a potential for the perils of pancreatitis

Acute and chronic pancreatitis carry a significant disease burden and there is no definite treatment that exists for either. They are associated with local and systemic inflammation and lead to numerous complications. Stem cell therapy has been explored for other disease processes and is a topic of research that has gained momentum with regards to implications for acute and chronic pancreatitis. They not only carry the potential to aid in regeneration but also prevent pancreatic injury as well as injury of other organs and hence the resultant complications. Stem cells appear to have immunomodulatory properties and clinical potential as evidenced by numerous studies in animal models. This review article discusses the types of stem cells commonly used and the properties that show promise in the field of pancreatitis.

Negative chronotropic and inotropic effects of lubiprostone on iPS cell-derived cardiomyocytes via activation of CFTR

Background

Lubiprostone (LBP) is a novel chloride channel opener that has been reported to activate chloride channel protein 2 (ClC-2) and cystic fibrosis transmembrane conductance regulator (CFTR). LBP facilitates fluid secretion by activating CFTR in the intestine and is used as a drug for treating chronic constipation. While ClC-2 and CFTR expression has been confirmed in cardiomyocytes (CMs), the effect of LBP on CMs has not yet been investigated. Thus, the present study aimed to investigate the effect of LBP on CMs using mouse-induced pluripotent stem (iPS) cell-derived CMs (iPS-CMs).

Methods

We induced mouse iPS cells into CMs through embryoid body (EB) formation. We compared the differentiated cells to CMs isolated from adult and fetal mice using gene expression, spontaneous beating rate, and contraction ratio analyses.

Results

Gene expression analysis revealed that, in the iPS-CMs, the mRNA expression of the undifferentiated cell markers Rex1 and Nanog decreased, whereas the expression of the unique cardiomyocyte markers cardiac troponin I (cTnI) and cardiac troponin T (cTNT), increased. Immunostaining showed that the localization of cTnI and connexin-43 in the iPS-CMs was similar to that in the primary fetal CMs (FCMs) and adult CMs (ACMs). LBP decreased the spontaneous beating rate of the iPS-CMs and FCMs, and decreased the contraction ratio of the iPS-CMs and ACMs. The reduction in the beating rate and contraction ratio caused by LBP was inhibited by glycine hydrazide (GlyH), which is a CFTR inhibitor.

Conclusion

These results suggest that LBP stimulates CFTR in CMs and that LBP has negative chronotropic and inotropic effects on CMs. LBP may be useful for treating cardiac diseases such as heart failure, ischemia, and arrhythmia.

Advances in Pluripotent Stem Cells: History, Mechanisms, Technologies, and Applications

Over the past 20 years, and particularly in the last decade, significant developmental milestones have driven basic, translational, and clinical advances in the field of stem cell and regenerative medicine. In this article, we provide a systemic overview of the major recent discoveries in this exciting and rapidly developing field. We begin by discussing experimental advances in the generation and differentiation of pluripotent stem cells (PSCs), next moving to the maintenance of stem cells in different culture types, and finishing with a discussion of three-dimensional (3D) cell technology and future stem cell applications. Specifically, we highlight the following crucial domains: 1) sources of pluripotent cells; 2) next-generation in vivo direct reprogramming technology; 3) cell types derived from PSCs and the influence of genetic memory; 4) induction of pluripotency with genomic modifications; 5) construction of vectors with reprogramming factor combinations; 6) enhancing pluripotency with small molecules and genetic signaling pathways; 7) induction of cell reprogramming by RNA signaling; 8) induction and enhancement of pluripotency with chemicals; 9) maintenance of pluripotency and genomic stability in induced pluripotent stem cells (iPSCs); 10) feeder-free and xenon-free culture environments; 11) biomaterial applications in stem cell biology; 12) three-dimensional (3D) cell technology; 13) 3D bioprinting; 14) downstream stem cell applications; and 15) current ethical issues in stem cell and regenerative medicine. This review, encompassing the fundamental concepts of regenerative medicine, is intended to provide a comprehensive portrait of important progress in stem cell research and development. Innovative technologies and real-world applications are emphasized for readers interested in the exciting, promising, and challenging field of stem cells and those seeking guidance in planning future research direction.

2-Cl-C.OXT-A stimulates contraction through the suppression of phosphodiesterase activity in human induced pluripotent stem cell-derived cardiac organoids

Background

2-Cl-C.OXT-A (COA-Cl) is a novel synthesized adenosine analog that activates Sphingosine-1-phosphate 1 receptor (S1P1R) and combines with the adenosine A1 receptor (A1R) in G proteins and was shown to enhance angiogenesis and improve the brain function in rat stroke models. However, the role of COA-Cl in hearts remains unclear. COA-Cl, which has a similar structure to xanthine derivatives, has the potential to suppress phosphodiesterase (PDE), which is an important factor involved in the beating of heart muscle.

Methods and results

Cardiac organoids with fibroblasts, human induced pluripotent stem cell-derived cardiac myocytes (hiPSC-CMs), and hiPSC-derived endothelial cells (hiPSC-ECs) were cultured until they started beating. The beating and contraction of organoids were observed before and after the application of COA-Cl. COA-Cl significantly increased the beating rate and fractional area change in organoids. To elucidate the mechanism underlying these effects of COA-Cl on cardiac myocytes, pure hiPSC-CM spheroids were evaluated in the presence/absence of Suramin (antagonist of A1R). The effects of COA-Cl, SEW2871 (direct stimulator of S1P1R), two positive inotropes (Isoproterenol [ISO] and Forskolin [FSK]), and negative inotrope (Propranolol [PRP]) on spheroids were assessed based on the beating rates and cAMP levels. COA-Cl stimulated the beating rates about 1.5-fold compared with ISO and FSK, while PRP suppressed the beating rate. However, no marked changes were observed with SEW2871. COA-Cl, ISO, and FSK increased the cAMP level. In contrast, the level of cAMP did not change with PRP or SEW2871 treatment. The results were the same in the presence of Suramin as absence. Furthermore, an enzyme analysis showed that COA-Cl suppressed the PDE activity by half.

Conclusions

COA-Cl, which has neovascularization effects, suppressed PDE and increased the contraction of cardiac organoids, independent of S1P1R and A1R. These findings suggest that COA-Cl may be useful as an inotropic agent for promoting angiogenesis in the future.

Defining human cardiac transcription factor hierarchies using integrated single-cell heterogeneity analysis

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have become a powerful tool for human disease modeling and therapeutic testing. However, their use remains limited by their immaturity and heterogeneity. To characterize the source of this heterogeneity, we applied complementary single-cell RNA-seq and bulk RNA-seq technologies over time during hiPSC cardiac differentiation and in the adult heart. Using integrated transcriptomic and splicing analysis, more than half a dozen distinct single-cell populations were observed, several of which were coincident at a single time-point, day 30 of differentiation. To dissect the role of distinct cardiac transcriptional regulators associated with each cell population, we systematically tested the effect of a gain or loss of three transcription factors (NR2F2, TBX5, and HEY2), using CRISPR genome editing and ChIP-seq, in conjunction with patch clamp, calcium imaging, and CyTOF analysis. These targets, data, and integrative genomics analysis methods provide a powerful platform for understanding in vitro cellular heterogeneity.

Human induced pluripotent stem cell derived cardiomyocytes are a powerful model for cardiogenesis and disease in vitro. Here the authors comprehensively map cardiac differentiation using multiple modalities, including single-cell RNA seq and CyTOF, in cells with a gain  or loss of function in key cardiac transcription factors.

Generation of Progesterone-Responsive Endometrial Stromal Fibroblasts from Human Induced Pluripotent Stem Cells: Role of the WNT/CTNNB1 Pathway

Defective endometrial stromal fibroblasts (EMSFs) contribute to uterine factor infertility, endometriosis, and endometrial cancer. Induced pluripotent stem cells (iPSCs) derived from skin or bone marrow biopsies provide a patient-specific source that can be differentiated to various cells types. Replacement of abnormal EMSFs is a potential novel therapeutic approach for endometrial disease; however, the methodology or mechanism for differentiating iPSCs to EMSFs is unknown. The uterus differentiates from the intermediate mesoderm (IM) to form coelomic epithelium (CE) followed by the Müllerian duct (MD). Here, we successfully directed the differentiation of human iPSCs (hiPSCs) through IM, CE, and MD to EMSFs under molecularly defined embryoid body culture conditions using specific hormonal treatments. Activation of CTNNB1 was essential for expression of progesterone receptor that mediated the final differentiation step of EMSFs before implantation. These hiPSC-derived tissues illustrate the potential for iPSC-based endometrial regeneration for future cell-based treatments.

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We developed a molecularly defined system for differentiating hiPSCs to EMSFs

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hiPSC-derived EMSFs undergo decidualization in response to hormonal stimulation

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D14 embryoid bodies recapitulate the molecular signature of primary EMSFs

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The WNT/CTNNB1 pathway is required for induction of EMSF from hiPSCs

Cardiac Stem Cells in the Postnatal Heart: Lessons from Development

Heart development in mammals is followed by a postnatal decline in cell proliferation and cell renewal from stem cell populations. A better understanding of the developmental changes in cardiac microenvironments occurring during heart maturation will be informative regarding the loss of adult regenerative potential. We reevaluate the adult heart's mitotic potential and the reported adult cardiac stem cell populations, as these are two topics of ongoing debate. The heart's early capacity for cell proliferation driven by progenitors and reciprocal signalling is demonstrated throughout development. The mature heart architecture and environment may be more restrictive on niches that can host progenitor cells. The engraftment issues observed in cardiac stem cell therapy trials using exogenous stem cells may indicate a lack of supporting stem cell niches, while tissue injury adds to a hostile microenvironment for transplanted cells. Engraftment may be improved by preconditioning the cultured stem cells and modulating the microenvironment to host these cells. These prospective areas of further research would benefit from a better understanding of cardiac progenitor interactions with their microenvironment throughout development and may lead to enhanced cardiac niche support for stem cell therapy engraftment.

Direct Reprogramming of Adult Human Somatic Stem Cells Into Functional Neurons Using Sox2, Ascl1, and Neurog2

Reprogramming of somatic cells into induced pluripotent stem cells (iPS) or directly into cells from a different lineage, including neurons, has revolutionized research in regenerative medicine in recent years. Mesenchymal stem cells are good candidates for lineage reprogramming and autologous transplantation, since they can be easily isolated from accessible sources in adult humans, such as bone marrow and dental tissues. Here, we demonstrate that expression of the transcription factors (TFs) SRY (sex determining region Y)-box 2 (Sox2), Mammalian achaete-scute homolog 1 (Ascl1), or Neurogenin 2 (Neurog2) is sufficient for reprogramming human umbilical cord mesenchymal stem cells (hUCMSC) into induced neurons (iNs). Furthermore, the combination of Sox2/Ascl1 or Sox2/Neurog2 is sufficient to reprogram up to 50% of transfected hUCMSCs into iNs showing electrical properties of mature neurons and establishing synaptic contacts with co-culture primary neurons. Finally, we show evidence supporting the notion that different combinations of TFs (Sox2/Ascl1 and Sox2/Neurog2) may induce multiple and overlapping neuronal phenotypes in lineage-reprogrammed iNs, suggesting that neuronal fate is determined by a combination of signals involving the TFs used for reprogramming but also the internal state of the converted cell. Altogether, the data presented here contribute to the advancement of techniques aiming at obtaining specific neuronal phenotypes from lineage-converted human somatic cells to treat neurological disorders.

Investigation of human iPSC-derived cardiac myocyte functional maturation by single cell traction force microscopy

Recent advances have made it possible to readily derive cardiac myocytes from human induced pluripotent stem cells (hiPSC-CMs). HiPSC-CMs represent a valuable new experimental model for studying human cardiac muscle physiology and disease. Many laboratories have devoted substantial effort to examining the functional properties of isolated hiPSC-CMs, but to date, force production has not been adequately characterized. Here, we utilized traction force microscopy (TFM) with micro-patterning cell printing to investigate the maximum force production of isolated single hiPSC-CMs under varied culture and assay conditions. We examined the role of length of differentiation in culture and the effects of varied extracellular calcium concentration in the culture media on the maturation of hiPSC-CMs. Results show that hiPSC-CMs developing in culture for two weeks produced significantly less force than cells cultured from one to three months, with hiPSC-CMs cultured for three months resembling the cell morphology and function of neonatal rat ventricular myocytes in terms of size, dimensions, and force production. Furthermore, hiPSC-CMs cultured long term in conditions of physiologic calcium concentrations were larger and produced more force than hiPSC-CMs cultured in standard media with sub-physiological calcium. We also examined relationships between cell morphology, substrate stiffness and force production. Results showed a significant relationship between cell area and force. Implementing directed modifications of substrate stiffness, by varying stiffness from embryonic-like to adult myocardium-like, hiPSC-CMs produced maximal forces on substrates with a lower modulus and significantly less force when assayed on increasingly stiff adult myocardium-like substrates. Calculated strain energy measurements paralleled these findings. Collectively, these findings further establish single cell TFM as a valuable approach to illuminate the quantitative physiological maturation of force in hiPSC-CMs.

Stem cells and heart disease - Brake or accelerator?

After two decades of intensive research and attempts of clinical translation, stem cell based therapies for cardiac diseases are not getting closer to clinical success. This review tries to unravel the obstacles and focuses on underlying mechanisms as the target for regenerative therapies. At present, the principal outcome in clinical therapy does not reflect experimental evidence. It seems that the scientific obstacle is a lack of integration of knowledge from tissue repair and disease mechanisms. Recent insights from clinical trials delineate mechanisms of stem cell dysfunction and gene defects in repair mechanisms as cause of atherosclerosis and heart disease. These findings require a redirection of current practice of stem cell therapy and a reset using more detailed analysis of stem cell function interfering with disease mechanisms. To accelerate scientific development the authors suggest intensifying unified computational data analysis and shared data knowledge by using open-access data platforms.

From iPSC towards cardiac tissue-a road under construction

The possibility to generate induced pluripotent stem cells (iPSC) opens the way to generate virtually all cell types of our human body. In combination with modern gene editing techniques like CRISPR/CAS, a new set of powerful tools becomes available for life science. Scientific fields like genotype and cell type-specific pharmacology, disease modeling, stem cell biology, and developmental biology have been dramatically fostered and their faces have been changed. However, as golden as the age of iPSC-derived cells and their manipulation has started, the shine begins to tarnish. Researchers face more and more practical problems intrinsic to the system. These problems are related to the specific culturing conditions which are not yet sufficient to mimic the natural environment of native stem cells differentiating towards adult cells. However, researchers work hard to uncover these factors. Here, we review a common standard approach to generate iPSCs and transduce these to iPSC cardiomyocytes. Further, we review recent achievements and discuss their current limitations and future perspectives. We are on track, but the road is still under construction.

Expandable Cardiovascular Progenitor Cells Reprogrammed from Fibroblasts

Stem cell-based approaches to cardiac regeneration are increasingly viable strategies for treating heart failure. Generating abundant and functional autologous cells for transplantation in such a setting, however, remains a significant challenge. Here, we isolated a cell population with extensive proliferation capacity and restricted cardiovascular differentiation potentials during cardiac transdifferentiation of mouse fibroblasts. These induced expandable cardiovascular progenitor cells (ieCPCs) proliferated extensively for more than 18 passages in chemically defined conditions, with 10(5) starting fibroblasts robustly producing 10(16) ieCPCs. ieCPCs expressed cardiac signature genes and readily differentiated into functional cardiomyocytes (CMs), endothelial cells (ECs), and smooth muscle cells (SMCs) in vitro, even after long-term expansion. When transplanted into mouse hearts following myocardial infarction, ieCPCs spontaneously differentiated into CMs, ECs, and SMCs and improved cardiac function for up to 12 weeks after transplantation. Thus, ieCPCs are a powerful system to study cardiovascular specification and provide strategies for regenerative medicine in the heart.

Nicotine plus a high-fat diet triggers cardiomyocyte apoptosis

Cigarette smoking is an important risk factor for diabetes, cardiovascular disease and non-alcoholic fatty liver disease. The health risk associated with smoking can be aggravated by obesity. Smoking might also trigger cardiomyocyte (CM) apoptosis. Given that CM apoptosis has been implicated as a potential mechanism in the development of cardiomyopathy and heart failure, we characterize the key signaling pathways in nicotine plus high-fat diet (HFD)-induced CM apoptosis. Adult C57BL6 male mice were fed a normal diet (ND) or HFD and received twice-daily intraperitoneal (IP) injections of nicotine (0.75 mg/kg body weight [BW]) or saline for 16 weeks. An additional group of nicotine-treated mice on HFD received twice-daily IP injections of mecamylamine (1 mg/kg BW), a non-selective nicotinic acetylcholine receptor antagonist, for 16 weeks. Nicotine when combined with HFD led to a massive increase in CM apoptosis that was fully prevented by mecamylamine treatment. Induction of CM apoptosis was associated with increased oxidative stress and activation of caspase-2-mediated intrinsic pathway signaling coupled with inactivation of AMP-activated protein kinase (AMPK). Furthermore, nicotine treatment significantly (P < 0.05) attenuated the HFD-induced decrease in fibroblast growth factor 21 (FGF21) and silent information regulator 1 (SIRT1). We conclude that nicotine, when combined with HFD, triggers CM apoptosis through the generation of oxidative stress and inactivation of AMPK together with the activation of caspase-2-mediated intrinsic apoptotic signaling independently of FGF21 and SIRT1.

Murine transgenic iPS cell line for monitoring and selection of cardiomyocytes

We report here a transgenic murine induced pluripotent stem cell (iPSC) line expressing puromycin N-acetyltransferase (PAC) and enhanced green fluorescent protein (EGFP) under the control of α-myosin heavy chain promoter. This transgenic cell line reproducibly differentiates into EGFP-expressing cardiomyocytes (CMs) which can be generated at high purity with puromycin treatment and exhibit molecular and functional properties of immature heart muscle cells. This genetically modified iPSC line can be used for assessment of the utility of CMs for myocardial repair, pharmacological and toxicological applications and development of improved cardiac differentiation protocols.

Generation of Induced Cardiospheres via Reprogramming of Skin Fibroblasts for Myocardial Regeneration

Recent pre-clinical and clinical studies have suggested that endogenous cardiospheres (eCS) are potentially safe and effective for cardiac regeneration following myocardial infarction (MI). Nevertheless the preparation of autologous eCS requires invasive myocardial biopsy with limited yield. We describe a novel approach to generate induced cardiospheres (iCS) from adult skin fibroblasts via somatic reprogramming. After infection with Sox2, Klf4, and Oct4, iCS were generated from mouse adult skin fibroblasts treated with Gsk3β inhibitor-(2'Z,3'E)- 6-Bromoindirubin-3'-oxime and Oncostatin M. They resembled eCS, but contained a higher percentage of cells expressing Mesp1, Isl1, and Nkx2.5. They were differentiated into functional cardiomyocytes in vitro with similar electrophysiological properties, calcium transient and contractile function to eCS and mouse embryonic stem cell-derived cardiomyocytes. Transplantation of iCS (1 × 10⁶ cells) into mouse myocardium following MI had similar effects to transplantation of eCS but significantly better than saline or fibroblast in improving left ventricular ejection fraction, increasing anterior/septal ventricular wall thickness and capillary density in the infarcted region 4 weeks after transplantation. No tumor formation was observed. iCS generated from adult skin fibroblasts by somatic reprogramming and a cocktail of Gsk3β inhibitor-6-Bromoindirubin-3'-oxime and Oncostatin M may represent a novel source for cell therapy in MI. Stem Cells 2016;34:2693-2706.

Genome Editing of the CYP1A1 Locus in iPSCs as a Platform to Map AHR Expression throughout Human Development

The aryl hydrocarbon receptor (AHR) is a ligand activated transcription factor that increases the expression of detoxifying enzymes upon ligand stimulation. Recent studies now suggest that novel endogenous roles of the AHR exist throughout development. In an effort to create an optimized model system for the study of AHR signaling in several cellular lineages, we have employed a CRISPR/CAS9 genome editing strategy in induced pluripotent stem cells (iPSCs) to incorporate a reporter cassette at the transcription start site of one of its canonical targets, cytochrome P450 1A1 (CYP1A1). This cell line faithfully reports on CYP1A1 expression, with luciferase levels as its functional readout, when treated with an endogenous AHR ligand (FICZ) at escalating doses. iPSC-derived fibroblast-like cells respond to acute exposure to environmental and endogenous AHR ligands, and iPSC-derived hepatocytes increase CYP1A1 in a similar manner to primary hepatocytes. This cell line is an important innovation that can be used to map AHR activity in discrete cellular subsets throughout developmental ontogeny. As further endogenous ligands are proposed, this line can be used to screen for safety and efficacy and can report on the ability of small molecules to regulate critical cellular processes by modulating the activity of the AHR.

Generation of electrophysiologically functional cardiomyocytes from mouse induced pluripotent stem cells

Induced pluripotent stem (iPS) cells can efficiently differentiate into the three germ layers similar to those formed by differentiated embryonic stem (ES) cells. This provides a new source of cells in which to establish preclinical allogeneic transplantation models. Our iPS cells were generated from mouse embryonic fibroblasts (MEFs) transfected with the Yamanaka factors, the four transcription factors (Oct4, Sox2, Klf4 and c-Myc), without antibiotic selection or MEF feeders. After the formation of embryoid bodies (EBs), iPS cells spontaneously differentiated into Flk1-positive cardiac progenitors and cardiomyocytes expressing cardiac-specific markers such as alpha sarcomeric actinin (α-actinin), cardiac alpha myosin heavy chain (α-MHC), cardiac troponin T (cTnT), and connexin 43 (CX43), as well as cardiac transcription factors Nk2 homebox 5 (Nkx2.5) and gata binding protein 4 (gata4). The electrophysiological activity of iPS cell-derived cardiomyocytes (iPS-CMs) was detected in beating cell clusters with optical mapping and RH237 a voltage-sensitive dye, and in single contracting cells with patch-clamp technology. Incompletely differentiated iPS cells formed teratomas when transplanted into a severe combined immunodeficiency (SCID) mouse model of myocardial infarction. Our results show that somatic cells can be reprogrammed into pluripotent stem cells, which in turn spontaneously differentiate into electrophysiologically functional mature cardiomyocytes expressing cardiac-specific makers, and that these cells can potentially be used to repair myocardial infarction (MI) in the future.

Cardiotrophin-1 promotes cardiomyocyte differentiation from mouse induced pluripotent stem cells via JAK2/STAT3/Pim-1 signaling pathway

BACKGROUND

The induced pluripotent stem cell (iPSC) has shown great potential in cellular therapy of myocardial infarction (MI), while its application is hampered by the low efficiency of cardiomyocyte differentiation. The present study was designed to investigate the effects of cardiotrophin-1 (CT-1) on cardiomyocyte differentiation from mouse induced pluripotent stem cells (miPSCs) and the underlying mechanisms involved.

METHODS

The optimal treatment condition for cardiomyocyte differentiation from miPSCs was established with ideal concentration (10 ng/mL) and duration (from day 3 to day 14) of CT-1 administration. Up-regulated expression of cardiac specific genes that accounted for embryonic cardiogenesis was observed by quantitative RT-PCR. Elevated amount of α-myosin heavy chain (α-MHC) and cardiac troponin I (cTn I) positive cells were detected by immunofluorescence staining and flow cytometry analysis in CT-1 group.

RESULTS

Transmission electron microscopic analysis revealed that cells treated with CT-1 showed better organized sacromeric structure and more mitochondria, which are morphological characteristic of matured cardiomyocytes. Western blot demonstrated that CT-1 promotes cardiomyocyte differentiation from miPSCs partly via JAK2/STAT3/Pim-1 pathway as compared with control group.

CONCLUSIONS

These findings suggested that CT-1 could enhance the cardiomyocyte differentiation as well as the maturation of mouse induced pluripotent stem cell derived cardiomyocytes by regulating JAK2/STAT3/Pim-1signaling pathway.

Dynamic Support Culture of Murine Skeletal Muscle-Derived Stem Cells Improves Their Cardiogenic Potential In Vitro

Ischemic heart disease is the main cause of death in western countries and its burden is increasing worldwide. It typically involves irreversible degeneration and loss of myocardial tissue leading to poor prognosis and fatal outcome. Autologous cells with the potential to regenerate damaged heart tissue would be an ideal source for cell therapeutic approaches. Here, we compared different methods of conditional culture for increasing the yield and cardiogenic potential of murine skeletal muscle-derived stem cells. A subpopulation of nonadherent cells was isolated from skeletal muscle by preplating and applying cell culture conditions differing in support of cluster formation. In contrast to static culture conditions, dynamic culture with or without previous hanging drop preculture led to significantly increased cluster diameters and the expression of cardiac specific markers on the protein and mRNA level. Whole-cell patch-clamp studies revealed similarities to pacemaker action potentials and responsiveness to cardiac specific pharmacological stimuli. This data indicates that skeletal muscle-derived stem cells are capable of adopting enhanced cardiac muscle cell-like properties by applying specific culture conditions. Choosing this route for the establishment of a sustainable, autologous source of cells for cardiac therapies holds the potential of being clinically more acceptable than transgenic manipulation of cells.

Combining hypoxia and bioreactor hydrodynamics boosts induced pluripotent stem cell differentiation towards cardiomyocytes

Cardiomyocytes (CMs) derived from induced pluripotent stem cells (iPSCs) hold great promise for patient-specific disease modeling, drug screening and cell therapy. However, existing protocols for CM differentiation of iPSCs besides being highly dependent on the application of expensive growth factors show low reproducibility and scalability. The aim of this work was to develop a robust and scalable strategy for mass production of iPSC-derived CMs by designing a bioreactor protocol that ensures a hypoxic and mechanical environment. Murine iPSCs were cultivated as aggregates in either stirred tank or WAVE bioreactors. The effect of dissolved oxygen and mechanical forces, promoted by different hydrodynamic environments, on CM differentiation was evaluated. Combining a hypoxia culture (4 % O2 tension) with an intermittent agitation profile in stirred tank bioreactors resulted in an improvement of about 1000-fold in CM yields when compared to normoxic (20 % O2 tension) and continuously agitated cultures. Additionally, we showed for the first time that wave-induced agitation enables the differentiation of iPSCs towards CMs at faster kinetics and with higher yields (60 CMs/input iPSC). In an 11-day differentiation protocol, clinically relevant numbers of CMs (2.3 × 10(9) CMs/1 L) were produced, and CMs exhibited typical cardiac sarcomeric structures, calcium transients, electrophysiological profiles and drug responsiveness. This work describes significant advances towards scalable cardiomyocyte differentiation of murine iPSC, paving the way for the implementation of this strategy for mass production of their human counterparts and their use for cardiac repair and cardiovascular research.

Gene Expression Profiling of H9c2 Myoblast Differentiation towards a Cardiac-Like Phenotype

H9c2 myoblasts are a cell model used as an alternative for cardiomyocytes. H9c2 cells have the ability to differentiate towards a cardiac phenotype when the media serum is reduced in the presence of all-trans-retinoic acid (RA), creating multinucleated cells with low proliferative capacity. In the present study, we performed for the first time a transcriptional analysis of the H9c2 cell line in two differentiation states, i.e. embryonic cells and differentiated cardiac-like cells. The results show that RA-induced H9c2 differentiation increased the expression of genes encoding for cardiac sarcomeric proteins such as troponin T, or calcium transporters and associated machinery, including SERCA2, ryanodine receptor and phospholamban as well as genes associated with mitochondrial energy production including respiratory chain complexes subunits, mitochondrial creatine kinase, carnitine palmitoyltransferase I and uncoupling proteins. Undifferentiated myoblasts showed increased gene expression of pro-survival proteins such as Bcl-2 as well as cell cycle-regulating proteins. The results indicate that the differentiation of H9c2 cells lead to an increase of transcripts and protein levels involved in calcium handling, glycolytic and mitochondrial metabolism, confirming that H9c2 cell differentiation induced by RA towards a more cardiac-like phenotype involves remodeled mitochondrial function. PI3K, PDK1 and p-CREB also appear to be involved on H9c2 differentiation. Furthermore, complex analysis of differently expressed transcripts revealed significant up-regulation of gene expression related to cardiac muscle contraction, dilated cardiomyopathy and other pathways specific for the cardiac tissue. Metabolic and gene expression remodeling impacts cell responses to different stimuli and determine how these cells are used for biochemical assays.

Sensing Cardiac Electrical Activity With a Cardiac Myocyte--Targeted Optogenetic Voltage Indicator

RATIONALE

Monitoring and controlling cardiac myocyte activity with optogenetic tools offer exciting possibilities for fundamental and translational cardiovascular research. Genetically encoded voltage indicators may be particularly attractive for minimal invasive and repeated assessments of cardiac excitation from the cellular to the whole heart level.

OBJECTIVE

To test the hypothesis that cardiac myocyte-targeted voltage-sensitive fluorescence protein 2.3 (VSFP2.3) can be exploited as optogenetic tool for the monitoring of electric activity in isolated cardiac myocytes and the whole heart as well as function and maturity in induced pluripotent stem cell-derived cardiac myocytes.

METHODS AND RESULTS

We first generated mice with cardiac myocyte-restricted expression of VSFP2.3 and demonstrated distinct localization of VSFP2.3 at the t-tubulus/junctional sarcoplasmic reticulum microdomain without any signs for associated pathologies (assessed by echocardiography, RNA-sequencing, and patch clamping). Optically recorded VSFP2.3 signals correlated well with membrane voltage measured simultaneously by patch clamping. The use of VSFP2.3 for human action potential recordings was confirmed by simulation of immature and mature action potentials in murine VSFP2.3 cardiac myocytes. Optical cardiograms could be monitored in whole hearts ex vivo and minimally invasively in vivo via fiber optics at physiological heart rate (10 Hz) and under pacing-induced arrhythmia. Finally, we reprogrammed tail-tip fibroblasts from transgenic mice and used the VSFP2.3 sensor for benchmarking functional and structural maturation in induced pluripotent stem cell-derived cardiac myocytes.

CONCLUSIONS

We introduce a novel transgenic voltage-sensor model as a new method in cardiovascular research and provide proof of concept for its use in optogenetic sensing of physiological and pathological excitation in mature and immature cardiac myocytes in vitro and in vivo.

Susceptibility of murine induced pluripotent stem cell-derived cardiomyocytes to hypoxia and nutrient deprivation

Introduction

Induced pluripotent stem cell-derived cardiomyocytes (iPS-CMs) may be suitable for myocardial repair. While their functional and structural properties have been extensively investigated, their response to ischemia-like conditions has not yet been clearly defined.

Methods

iPS-CMs were differentiated and enriched from murine induced pluripotent stem cells expressing enhanced green fluorescent protein (eGFP) and puromycin resistance genes under the control of an α-myosin heavy chain (α-MHC) promoter. iPS-CMs maturity and function were characterized by microscopy, real-time PCR, calcium transient recordings, electrophysiology, and mitochondrial function assays, and compared to those from neonatal murine cardiomyocytes. iPS-CMs as well as neonatal murine cardiomyocytes were exposed for 3 hours to hypoxia (1% O₂) and glucose/serum deprivation, and viability, apoptosis markers, reactive oxygen species, mitochondrial membrane potential and intracellular stress signaling cascades were investigated. Then, the iPS-CMs response to mesenchymal stromal cell-conditioned medium was determined.

Results

iPS-CMs displayed key morphological and functional properties that were comparable to those of neonatal cardiomyocytes, but several parameters indicated an earlier iPS-CMs maturation stage. During hypoxia and glucose/serum deprivation, iPS-CMs exhibited a significantly higher proportion of poly-caspase-active, 7-aminoactinomycin D-positive and TUNEL-positive cells than neonatal cardiomyocytes. The average mitochondrial membrane potential was reduced in “ischemic” iPS-CMs but remained unchanged in neonatal cardiomyocytes; reactive oxygen species production was only increased in “ischemic” iPS-CMs, and oxidoreductase activity in iPS-CMs dropped more rapidly than in neonatal cardiomyocytes. In iPS-CMs, hypoxia and glucose/serum deprivation led to upregulation of Hsp70 transcripts and decreased STAT3 phosphorylation and total PKCε protein expression. Treatment with mesenchymal stromal cell-conditioned medium preserved oxidoreductase activity and restored pSTAT3 and PKCε levels.

Conclusion

iPS-CMs appear to be particularly sensitive to hypoxia and nutrient deprivation. Counteracting the ischemic susceptibility of iPS-CMs with mesenchymal stromal cell-conditioned medium may help enhance their survival and efficacy in cell-based approaches for myocardial repair.

How to mend a broken heart: adult and induced pluripotent stem cell therapy for heart repair and regeneration

The recently developed ability to differentiate primary adult stem cells and induced pluripotent stem cells (iPSCs) into cardiomyocytes is providing unprecedented opportunities to produce an unlimited supply of cardiomyocytes for use in patients with heart disease. Here, we examine the evidence for the preclinical use of such cells for successful heart regeneration. We also describe advances in the identification of new cardiac molecular and cellular targets to induce proliferation of cardiomyocytes for heart regeneration. Such new advances are paving the way for a new innovative drug development process for the treatment of heart disease.

Fetal heart extract facilitates the differentiation of human umbilical cord blood-derived mesenchymal stem cells into heart muscle precursor cells

Human umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs) are a promising stem cell source with the potential to modulate the immune system as well as the capacity to differentiate into osteoblasts, chondrocytes, and adipocytes. In previous publications, UCB-MSCs have been successfully differentiated into cardiomyocytes. This study aimed to improve the efficacy of differentiation of UCB-MSCs into cardiomyocytes by combining 5-azacytidine (Aza) with mouse fetal heart extract (HE) in the induction medium. UCB-MSCs were isolated from umbilical cord blood according to a published protocol. Murine fetal hearts were used to produce fetal HE using a rapid freeze-thaw procedure. MSCs at the 3rd to 5th passage were differentiated into cardiomyocytes in two kinds of induction medium: complete culture medium plus Aza (Aza group) and complete culture medium plus Aza and fetal HE (Aza + HE group). The results showed that the cells in both kinds of induction medium exhibited the phenotype of cardiomyocytes. At the transcriptional level, the cells expressed a number of cardiac muscle-specific genes such as Nkx2.5, Gata 4, Mef2c, HCN2, hBNP, α-Ca, cTnT, Desmin, and β-MHC on day 27 in the Aza group and on day 18 in the Aza + HE group. At the translational level, sarcomic α-actin was expressed on day 27 in the Aza group and day 18 in the Aza + HE group. Although they expressed specific genes and proteins of cardiac muscle cells, the induced cells in both groups did not contract and beat spontaneously. These properties are similar to properties of heart muscle precursor cells in vivo. These results demonstrated that the fetal HE facilitates the differentiation process of human UCB-MSCs into heart muscle precursor cells.

N-glycans: phenotypic homology and structural differences between myocardial cells and induced pluripotent stem cell-derived cardiomyocytes

Cell surface glycans vary widely, depending on cell properties. We hypothesized that glycan expression on induced pluripotent stem cells (iPSCs) might change during cardiomyogenic differentiation toward the myocardial phenotype. N-glycans were isolated from iPSCs, iPSC-derived cardiomyocytes (iPSC-CM), and original C57BL/6 mouse myocardium (Heart). Their structures were analyzed by a mapping technique based on HPLC elution times and MALDI-TOF/MS spectra. Sixty-eight different N-glycans were isolated; the structures of 60 of these N-glycans were identified. The quantity of high-mannose type (immature) N-glycans on the iPSCs decreased with cardiomyogenic differentiation, but did not reach the low levels observed in the heart. We observed a similar reduction in neutral N-glycans and an increase in fucosylated or sialyl N-glycans. Some structural differences were detected between iPSC-CM and Heart. No N-glycolyl neuraminic acid (NeuGc) structures were detected in iPSC-CM, whereas the heart contained numerous NeuGc structures, corresponding to the expression of cytidine monophosphate-N-acetylneuraminic acid hydroxylase. Furthermore, several glycans containing Galα1-6 Gal, rarely identified in the other cells, were detected in the iPSC-CM. The expression of N-glycan on murine iPSCs changed toward the myocardial phenotype during cardiomyogenic differentiation, leaving the structural differences of NeuGc content or Galα1-6 Gal structures. Further studies will be warranted to reveal the meaning of the difference of N-glycans between the iPSC-CM and the myocardium.

Bioluminescent imaging of genetically selected induced pluripotent stem cell-derived cardiomyocytes after transplantation into infarcted heart of syngeneic recipients

Cell loss after transplantation is a major limitation for cell replacement approaches in regenerative medicine. To assess the survival kinetics of induced pluripotent stem cell (iPSC)-derived cardiomyocytes (CM) we generated transgenic murine iPSC lines which, in addition to CM-specific expression of puromycin N-acetyl-transferase and enhanced green fluorescent protein (EGFP), also constitutively express firefly luciferase (FLuc) for bioluminescence (BL) in vivo imaging. While undifferentiated iPSC lines generated by random integration of the transgene into the genome retained stable FLuc activity over many passages, the BL signal intensity was strongly decreased in purified iPS-CM compared to undifferentiated iPSC. Targeted integration of FLuc-expression cassette into the ROSA26 genomic locus using zinc finger nuclease (ZFN) technology strongly reduced transgene silencing in iPS-CM, leading to a several-fold higher BL compared to iPS-CM expressing FLuc from random genomic loci. To investigate the survival kinetics of iPS-CM in vivo, purified CM obtained from iPSC lines expressing FLuc from a random or the ROSA26 locus were transplanted into cryoinfarcted hearts of syngeneic mice. Engraftment of viable cells was monitored by BL imaging over 4 weeks. Transplanted iPS-CM were poorly retained in the myocardium independently of the cell line used. However, up to 8% of cells survived for 28 days at the site of injection, which was confirmed by immunohistological detection of EGFP-positive iPS-CM in the host tissue. Transplantation of iPS-CM did not affect the scar formation or capillary density in the periinfarct region of host myocardium. This report is the first to determine the survival kinetics of drug-selected iPS-CM in the infarcted heart using BL imaging and demonstrates that transgene silencing in the course of iPSC differentiation can be greatly reduced by employing genome editing technology. FLuc-expressing iPS-CM generated in this study will enable further studies to reduce their loss, increase long-term survival and functional integration upon transplantation.

Production of functional coagulation factor VIII from iPSCs using a lentiviral vector

The use of induced pluripotent stem cells (iPSCs) as an autologous cell source has shed new light on cell replacement therapy with respect to the treatment of numerous hereditary disorders. We focused on the use of iPSCs for cell-based therapy of haemophilia. We generated iPSCs from mesenchymal stem cells that had been isolated from C57BL/6 mice. The mouse iPSCs were generated through the induction of four transcription factor genes Oct3/4, Klf-4, Sox-2 and c-Myc. The derived iPSCs released functional coagulation factor VIII (FVIII) following transduction with a simian immunodeficiency virus vector. The subcutaneous transplantation of iPSCs expressing FVIII into nude mice resulted in teratoma formation, and significantly increased plasma levels of FVIII. The plasma concentration of FVIII was at levels appropriate for human therapy at 2-4 weeks post transplantation. Our data suggest that iPSCs could be an attractive and prospective autologous cell source for the production of coagulation factor, and that engineered iPSCs expressing coagulation factor might provide a cell-based therapeutic strategy appropriate for haemophilia.

Myocardial regeneration of the failing heart

Human heart failure (HF) is one of the leading causes of morbidity and mortality worldwide. Currently, heart transplantation and implantation of mechanical devices represent the only available treatments for advanced HF. Two alternative strategies have emerged to treat patients with HF. One approach relies on transplantation of exogenous stem cells (SCs) of non-cardiac or cardiac origin to induce cardiac regeneration and improve ventricular function. Another complementary strategy relies on stimulation of the endogenous regenerative capacity of uninjured cardiac progenitor cells to rebuild cardiac muscle and restore ventricular function. Various SC types and delivery strategies have been examined in the experimental and clinical settings; however, neither the ideal cell type nor the cell delivery method for cardiac cell therapy has yet emerged. Although the use of bone marrow (BM)-derived cells, most frequently exploited in clinical trials, appears to be safe, the results are controversial. Two recent randomized trials have failed to document any beneficial effects of intracardiac delivery of autologous BM mononuclear cells on cardiac function of patients with HF. The remarkable discovery that various populations of cardiac progenitor cells (CPCs) are present in the adult human heart and that it possesses limited regeneration capacity has opened a new era in cardiac repair. Importantly, unlike BM-derived SCs, autologous CPCs from myocardial biopsies cultured and subsequently delivered by coronary injection to patients have given positive results. Although these data are promising, a better understanding of how to control proliferation and differentiation of CPCs, to enhance their recruitment and survival, is required before CPCs become clinically applicable therapeutics.

Reprogramming approaches in cardiovascular regeneration

OPINION STATEMENT

Reconstitution of cardiac muscle as well as blood vessels to provide sufficient oxygenation and nutrients to the myocardium is an important component of any therapeutic approach for cardiac repair after injury. Recent reports of reprogramming somatic cells directly to cells of another lineage raised the possibility of using cell reprogramming for cardiac regenerative therapy. Here, we provide an overview of the current reprogramming strategies to generate cardiomyocytes (CMs), endothelial cells (ECs) and smooth muscle cells (SMCs), and the implications of these methods for cardiac regeneration. We also discuss the challenges and limitations that need to be addressed for the development of future therapies.

Detailed analysis of the genetic and epigenetic signatures of iPSC-derived mesodiencephalic dopaminergic neurons

Induced pluripotent stem cells (iPSCs) hold great promise for in vitro generation of disease-relevant cell types, such as mesodiencephalic dopaminergic (mdDA) neurons involved in Parkinson’s disease. Although iPSC-derived midbrain DA neurons have been generated, detailed genetic and epigenetic characterizations of such neurons are lacking. The goal of this study was to examine the authenticity of iPSC-derived DA neurons obtained by established protocols. We FACS purified mdDA (Pitx3^Gfp/+) neurons derived from mouse iPSCs and primary mdDA (Pitx3^Gfp/+) neurons to analyze and compare their genetic and epigenetic features. Although iPSC-derived DA neurons largely adopted characteristics of their in vivo counterparts, relevant deviations in global gene expression and DNA methylation were found. Hypermethylated genes, mainly involved in neurodevelopment and basic neuronal functions, consequently showed reduced expression levels. Such abnormalities should be addressed because they might affect unambiguous long-term functionality and hamper the potential of iPSC-derived DA neurons for in vitro disease modeling or cell-based therapy.

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Purification of iPSC-derived mdDA neurons and primary embryonic mdDA neurons

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Comparative gene-expression profiling and DNA methylation mapping of mdDA neurons

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High similarity but also differences between primary and iPSC-derived mdDA neurons

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Differences mainly in genes involved in neuron differentiation and development

Modulation of L-type calcium current by intracellular magnesium in differentiating cardiomyocytes derived from induced pluripotent stem cells

Intracellular Mg(2+), which is implicated in arrhythmogenesis and transient cardiac ischemia, inhibits L-type Ca(2+) calcium channel current (ICaL) of adult cardiomyocytes (CMs). We take the advantage of an in vitro model of CMs based on induced pluripotent stem cells to investigate the effects of intracellular Mg(2+) on the phosphorylation or dephosphorylation processes of L-type Ca(2+) channels (LTCCs) at early and late stages of cardiac cell differentiation. Using the whole-cell patch-clamp technique, we demonstrate that increasing intracellular Mg(2+) concentration [Mg(2+)]i from 0.2 to 5 mM markedly reduced the peak of ICaL density, showing less effect on both the activation and inactivation properties in the late differentiation stage (LDS) of CMs more so than in the early differentiation stage (EDS). Increasing the [Mg(2+)]i from 0.2 to 2 mM in the presence of cAMP-dependent protein kinase A significantly decreased ICaL in LDS (70%) and in EDS (36%) CMs. In addition, the effect of forskolin was greatly attenuated in the presence of 2 mM [Mg(2+)]i in LDS but not in EDS CMs. The effect of forskolin was enhanced in the presence of ATP-γ-S in LDS CMs compared with EDS CMs. The exposure of both EDS and LDS CMs to 2 mM [Mg(2+)]i considerably reduced the effects of isobutylmethylxanthine (IBMX) and okadaic acid on ICaL. Our results provide evidence for differential regulation of LTCCs activities by cytosolic Mg(2+) concentration in developing cardiac cells and confirm that Mg(2+) acts under conditions that favor opening of the LTCCs caused by channel phosphorylation.

Small molecules enable cardiac reprogramming of mouse fibroblasts with a single factor, Oct4

It was recently shown that mouse fibroblasts could be reprogrammed into cells of a cardiac fate by forced expression of multiple transcription factors and microRNAs. For ultimate application of such a reprogramming strategy for cell-based therapy or in vivo cardiac regeneration, reducing or eliminating the genetic manipulations by small molecules would be highly desirable. Here, we report the identification of a defined small-molecule cocktail that enables the highly efficient conversion of mouse fibroblasts into cardiac cells with only one transcription factor, Oct4, without any evidence of entrance into the pluripotent state. Small-molecule-induced cardiomyocytes spontaneously contract and exhibit a ventricular phenotype. Furthermore, these induced cardiomyocytes pass through a cardiac progenitor stage. This study lays the foundation for future pharmacological reprogramming approaches and provides a small-molecule condition for investigation of the mechanisms underlying the cardiac reprogramming process.

Differentiation of reprogrammed mouse cardiac fibroblasts into functional cardiomyocytes

Fibroblasts can be reprogrammed by ectopic expression of reprogramming factors to yield induced pluripotent stem (iPS) cells that are capable of transdifferentiating into diverse types of somatic cell lines. In this study, we examined if functional cardiomyocytes (CMs) can be produced from mouse cardiac fibroblasts (CFs), using iPS cell factor-based reprogramming. CFs were isolated from Oct4-GFP-C57 mice and infected with a retrovirus expressing the Yamanaka reprogramming factors, Oct4, Sox2, Klf4, and c-Myc to reprogram the CFs into a CF-iPS cell line. Primary mouse embryonic fibroblast cells (MEFs) were used as a control. We found that the dedifferentiated CF-iPS cells showed similar biological characteristics (morphology, pluripotent factor expression, and methylation level) as embryonic stem cells (ESs) and MEF-iPS cells. We used the classical embryoid bodies (EBs)-based method and a transwell CM co-culture system to simulate the myocardial paracrine microenvironment for performing CF-iPS cell cardiogenic differentiation. Under this simulated myocardial microenvironment, CF-iPS cells formed spontaneously beating EBs. The transdifferentiated self-beating cells expressed cardiac-specific transcription and structural factors and also displayed typical myocardial morphology and electrophysiological characteristics. CFs can be dedifferentiated into iPS cells and further transdifferentiated into CMs. CFs hold great promise for CM regeneration as an autologous cell source for functional CM in situ without the need for exogenous cell transplantation in ischemic heart disease.

Current status of induced pluripotent stem cells in cardiac tissue regeneration and engineering

Myocardial infarction (MI) is associated with damage to the myocardium which results in a great loss of functional cardiomyocytes. As one of the most terminally differentiated organs, the endogenous regenerative potentials of adult hearts are extremely limited and insufficient to compensate for the myocardial loss occurring after MI. Consequentially, exogenous regenerative strategies, especially cell replacement therapy, have emerged and attracted increasing more attention in the field of cardiac tissue regeneration. A renewable source of seeding cells is therefore one of the most important subject in the field. Induced pluripotent stem cells (iPSCs), embryonic stem cell (ESC)-like cells that are derived from somatic cells by reprogramming, represent a promising candidate due to their high potentials for self-renewal, proliferation, differentiation and more importantly, they provide an invaluable method of deriving patient-specific pluripotent stem cells. Therefore, iPSC-based cardiac tissue regeneration and engineering has been extensively investigated in recent years. This review will discuss the achievements and current status in this field, including development of iPSC derivation, in vitro strategies for cardiac generation from iPSCs, cardiac application of iPSCs, challenges confronted at present as well as perspective in the future.

Using human induced pluripotent stem cells to treat retinal disease

The eye is an ideal target for exploiting the potential of human induced pluripotent stem cell (hiPSC) technology in order to understand disease pathways and explore novel therapeutic strategies for inherited retinal disease. The aim of this article is to map the pathway from state-of-the art laboratory-based discoveries to realising the translational potential of this emerging technique. We describe the relevance and routes to establishing hiPSCs in selected models of human retinal disease. Additionally, we define pathways for applying hiPSC technology in treating currently incurable, progressive and blinding retinal disease.

Distinct iPS Cells Show Different Cardiac Differentiation Efficiency

Patient-specific induced pluripotent stem (iPS) cells can be generated by introducing transcription factors that are highly expressed in embryonic stem (ES) cells into somatic cells. This opens up new possibilities for cell transplantation-based regenerative medicine by overcoming the ethical issues and immunological problems associated with ES cells. Despite the development of various methods for the generation of iPS cells that have resulted in increased efficiency, safety, and general versatility, it remains unknown which types of iPS cells are suitable for clinical use. Therefore, the aims of the present study were to assess (1) the differentiation potential, time course, and efficiency of different types of iPS cell lines to differentiate into cardiomyocytes in vitro and (2) the properties of the iPS cell-derived cardiomyocytes. We found that high-quality iPS cells exhibited better cardiomyocyte differentiation in terms of the time course and efficiency of differentiation than low-quality iPS cells, which hardly ever differentiated into cardiomyocytes. Because of the different properties of the various iPS cell lines such as cardiac differentiation efficiency and potential safety hazards, newly established iPS cell lines must be characterized prior to their use in cardiac regenerative medicine.

The protein coexpression problem in biotechnology and biomedicine: virus 2A and 2A-like sequences provide a solution

Synthetic biology enables us to create genes virtually at will. Ensuring that multiple genes are efficiently coexpressed within the same cell in order to assemble multimeric complexes, transfer biochemical pathways and transfer traits is more problematic. Viruses such as picornaviruses accomplish exactly this task: they generate multiple different proteins from a single open reading frame. The study of how foot-and-mouth disease virus controls its protein biogenesis led to the discovery of a short oligopeptide sequence, ‘2A’, that is able to mediate a cotranslational cleavage between proteins. 2A and ‘2A-like’ sequences (from other viruses and cellular sequences) can be used to concatenate multiple gene sequences into a single gene, ensuring their coexpression within the same cell. These sequences are now being used in the treatment of cancer, in the production of pluripotent stem cells, and to create transgenic plants and animals among a host of other biotechnological and biomedical applications.

Electronic "expression" of the inward rectifier in cardiocytes derived from human-induced pluripotent stem cells

BACKGROUND

Human-induced pluripotent stem cell (h-iPSC)-derived cardiac myocytes are a unique model in which human myocyte function and dysfunction are studied, especially those from patients with genetic disorders. They are also considered a major advance for drug safety testing. However, these cells have considerable unexplored potential limitations when applied to quantitative action potential (AP) analysis. One major factor is spontaneous activity and resulting variability and potentially anomalous behavior of AP parameters.

OBJECTIVE

To demonstrate the effect of using an in silico interface on electronically expressed I(K1), a major component lacking in h-iPSC-derived cardiac myocytes.

METHODS

An in silico interface was developed to express synthetic I(K1) in cells under whole-cell voltage clamp.

RESULTS

Electronic I(K1) expression established a physiological resting potential, eliminated spontaneous activity, reduced spontaneous early and delayed afterdepolarizations, and decreased AP variability. The initiated APs had the classic rapid upstroke and spike and dome morphology consistent with data obtained with freshly isolated human myocytes as well as the readily recognizable repolarization attributes of ventricular and atrial cells. The application of 1 µM of BayK-8644 resulted in anomalous AP shortening in h-iPSC-derived cardiac myocytes. When I(K1) was electronically expressed, BayK-8644 prolonged the AP, which is consistent with the existing results on native cardiac myocytes.

CONCLUSIONS

The electronic expression of I(K1) is a simple and robust method to significantly improve the physiological behavior of the AP and electrical profile of h-iPSC-derived cardiac myocytes. Increased stability enables the use of this preparation for a controlled quantitative analysis of AP parameters, for example, drug responsiveness, genetic disorders, and dynamic behavior restitution profiles.

Electrophysiological integration and action potential properties of transplanted cardiomyocytes derived from induced pluripotent stem cells

AIMS

Induced pluripotent stem cell-derived cardiomyocytes (iPSCM) are regarded as promising cell type for cardiac cell replacement therapy. We investigated long-term electrophysiological integration and maturation of transplanted iPSCM, which are essential for therapeutic benefit.

METHODS AND RESULTS

Murine iPSCM expressing enhanced green fluorescent protein and a puromycin resistance under control of the α-myosin heavy chain promoter were purified by antibiotic selection and injected into adult mouse hearts. After 6-12 days, 3-6 weeks, or 6-8 months, viable slices of recipient hearts were prepared. Slices were focally stimulated by a unipolar electrode placed in host tissue, and intracellular action potentials (APs) were recorded with glass microelectrodes in transplanted cells and neighbouring host tissue within the slices. Persistence and electrical integration of transplanted iPSCM into recipient hearts could be demonstrated at all time points. Quality of coupling improved, as indicated by a maximal stimulation frequency without conduction blocks of 5.77 ± 0.54 Hz at 6-12 days, 8.98 ± 0.38 Hz at 3-6 weeks and 10.82 ± 1.07 Hz at 6-8 months after transplantation. AP properties of iPSCM became more mature from 6-12 days to 6-8 months after transplantation, but still differed significantly from those of host APs.

CONCLUSION

Transplanted iPSCM can persist in the long term and integrate electrically into host tissue, supporting their potential for cell replacement therapy. Quality of electrical integration improves between 6-12 days and 6-8 months after transplantation, and there are signs of an electrophysiological maturation. However, even after 6-8 months, AP properties of transplanted iPSCM differ from those of recipient cardiomyocytes.

Induced pluripotent stem cell technology and direct conversion: new possibilities to study and treat Parkinson's disease

Recent developments in in vitro disease modeling and regenerative medicine have placed induced pluripotent stem cells (iPSCs) in the center of attention as a unique source to study Parkinson's disease. After only 5 years of intensive research, human iPSCs can be generated without viral integration and under xeno-free conditions. This, combined with increasingly sophisticated methods to differentiate iPSCs into functional dopaminergic (DA) neurons, led us to recapitulate the most important findings concerning the use of iPSC technology as a prospective tool to treat symptoms of Parkinson's disease as well as to obtain insight in disease related cell pathogenesis. Moreover, we touch upon some of the latest discoveries in which patient-derived autologous DA neurons come into even more direct reach thanks to a method that allows transdifferentiation of fibroblasts into DA neurons.

Induced pluripotent stem cell-derived cardiac progenitors differentiate to cardiomyocytes and form biosynthetic tissues

The mammalian heart has little capacity to regenerate, and following injury the myocardium is replaced by non-contractile scar tissue. Consequently, increased wall stress and workload on the remaining myocardium leads to chamber dilation, dysfunction, and heart failure. Cell-based therapy with an autologous, epigenetically reprogrammed, and cardiac-committed progenitor cell source could potentially reverse this process by replacing the damaged myocardium with functional tissue. However, it is unclear whether cardiac progenitor cell-derived cardiomyocytes are capable of attaining levels of structural and functional maturity comparable to that of terminally-fated cardiomyocytes. Here, we first describe the derivation of mouse induced pluripotent stem (iPS) cells, which once differentiated allow for the enrichment of Nkx2-5(+) cardiac progenitors, and the cardiomyocyte-specific expression of the red fluorescent protein. We show that the cardiac progenitors are multipotent and capable of differentiating into endothelial cells, smooth muscle cells and cardiomyocytes. Moreover, cardiac progenitor selection corresponds to cKit(+) cell enrichment, while cardiomyocyte cell-lineage commitment is concomitant with dual expression of either cKit/Flk1 or cKit/Sca-1. We proceed to show that the cardiac progenitor-derived cardiomyocytes are capable of forming electrically and mechanically coupled large-scale 2D cell cultures with mature electrophysiological properties. Finally, we examine the cell progenitors' ability to form electromechanically coherent macroscopic tissues, using a physiologically relevant 3D culture model and demonstrate that following long-term culture the cardiomyocytes align, and form robust electromechanical connections throughout the volume of the biosynthetic tissue construct. We conclude that the iPS cell-derived cardiac progenitors are a robust cell source for tissue engineering applications and a 3D culture platform for pharmacological screening and drug development studies.

Reprogramming of mouse renal tubular epithelial cells to induced pluripotent stem cells

Kidney disease has reached epidemic proportions and is associated with high mortality and morbidity rates. Stem cell-based therapy may effectively treat kidney damage by cell transplantation. The breakthrough discovery using a combination of four transcription factors to reprogram genetically somatic cells into induced pluripotent stem (iPS) cells was a milestone in stem cell therapy. The lentivirus was packaged containing OCT4, SOX2, c-MYC and KLF4 transcription factors and then transfected mouse renal tubular epithelial cells (RTECs). The colonies were picked up at 21 days and were tested by cytochemistry, immunofluorescence assay and quantitative real-time polymerase chain reaction. Viral transgene expression levels were also assessed by quantitative analysis. Additionally, embryoid bodies from iPS cells were formed, and immunofluorescence and teratoma assays were performed. Karyotype analysis of mouse RTEC-derived iPS cells was also performed. The iPS cells were indistinguishable from mouse embryonic stem cells with respect to colony morphology, the expression of pluripotency-associated transcription factors and surface markers, embryoid body-mediated differentiation potential and teratoma assays. Quantitative polymerase chain reaction demonstrated that the lentiviral transgenes were largely silenced. The mouse RTEC-derived iPS cells exhibited a normal karyotype of 40,XY. iPS cells can be produced using mouse RTECs, which would be helpful in investigations to ameliorate the symptoms of kidney disease and to slow the progression of kidney disease by in vitro and in vivo animal studies.