In vitro differentiation of rat embryonic stem cells into functional cardiomyocytes. Cell Res. 2011;21:1316-1331. [PMID: 21423272 DOI: 10.1038/cr.2011.48]

MLL3/MLL4 methyltransferase activities control early embryonic development and embryonic stem cell differentiation in a lineage-selective manner

H3K4me1 methyltransferases MLL3 (KMT2C) and MLL4 (KMT2D) are critical for enhancer activation, cell differentiation and development. However, roles of MLL3/4 enzymatic activities and MLL3/4-mediated enhancer H3K4me1 in these processes remain unclear. Here we report that constitutive elimination of both MLL3 and MLL4 enzymatic activities prevents initiation of gastrulation and leads to early embryonic lethality in mice. However, selective elimination of MLL3/4 enzymatic activities in embryonic, but not extraembryonic, lineages leaves gastrulation largely intact. Consistent with this, embryonic stem cells (ESCs) lacking MLL3/4 enzymatic activities can differentiate toward the three embryonic germ layers but show aberrant differentiation to extraembryonic endoderm (ExEn) and trophectoderm. The failure in ExEn differentiation can be attributed to markedly reduced enhancer-binding of the lineage-determining transcription factor GATA6. Furthermore, we show that MLL3/4-catalyzed H3K4me1 is largely dispensable for enhancer activation during ESC differentiation. Together, our findings suggest a lineage-selective, but enhancer activation-independent, role of MLL3/4 methyltransferase activities in early embryonic development and ESC differentiation.

Genome-scale screening in a rat haploid system identifies Thop1 as a modulator of pluripotency exit

OBJECTIVES

The rats are crucial animal models for the basic medical researches. Rat embryonic stem cells (ESCs), which are widely studied, can self-renew and exhibit pluripotency in long-term culture, but the mechanism underlying how they exit pluripotency remains obscure. To investigate the key modulators on pluripotency exiting in rat ESCs, we perform genome-wide screening using a unique rat haploid system.

MATERIALS AND METHODS

Rat haploid ESCs (haESCs) enable advances in the discovery of unknown functional genes owing to their homozygous and pluripotent characteristics. REX1 is a sensitive marker for the naïve pluripotency that is often utilized to monitor pluripotency exit, thus rat haESCs carrying a Rex1-GFP reporter are used for genetic screening. Genome-wide mutations are introduced into the genomes of rat Rex1-GFP haESCs via piggyBac transposon, and differentiation-retarded mutants are obtained after random differentiation selection. The exact mutations are elucidated by high-throughput sequencing and bioinformatic analysis. The role of candidate mutation is validated in rat ESCs by knockout and overexpression experiments, and the phosphorylation of ERK1/2 (p-ERK1/2) is determined by western blotting.

RESULTS

High-throughput sequencing analysis reveals numerous insertions related to various pathways affecting random differentiation. Thereafter, deletion of Thop1 (one candidate gene in the screened list) arrests the differentiation of rat ESCs by inhibiting the p-ERK1/2, whereas overexpression of Thop1 promotes rat ESCs to exit from pluripotency.

CONCLUSIONS

Our findings provide an ideal tool to study functional genomics in rats: a homozygous haploid system carrying a pluripotency reporter that facilitates robust discovery of the mechanisms involved in the self-renewal or pluripotency of rat ESCs.

Rho Kinases in Embryonic Development and Stem Cell Research

The Rho-associated coiled-coil containing kinases (ROCKs or Rho kinases) belong to the AGC (PKA/PKG/PKC) family of serine/threonine kinases and are major downstream effectors of small GTPase RhoA, a key regulator of actin-cytoskeleton reorganization. The ROCK family contains two members, ROCK1 and ROCK2, which share 65% overall identity and 92% identity in kinase domain. ROCK1 and ROCK2 were assumed to be functionally redundant, based largely on their major common activators, their high degree kinase domain homology, and study results from overexpression with kinase constructs or chemical inhibitors. ROCK signaling research has expanded to all areas of biology and medicine since its discovery in 1996. The rapid advance is befitting ROCK’s versatile functions in modulating various cell behavior, such as contraction, adhesion, migration, proliferation, polarity, cytokinesis, and differentiation. The rapid advance is noticeably driven by an extensive linking with clinical medicine, including cardiovascular abnormalities, aberrant immune responsive, and cancer development and metastasis. The rapid advance during the past decade is further powered by novel biotechnologies including CRISPR-Cas and single cell omics. Current consensus, derived mainly from gene targeting and RNA interference approaches, is that the two ROCK isoforms have overlapping and distinct cellular, physiological and pathophysiology roles. In this review, we present an overview of the milestone discoveries in ROCK research. We then focus on the current understanding of ROCK signaling in embryonic development, current research status using knockout and knockin mouse models, and stem cell research.

Myosin light chain 2 marks differentiating ventricular cardiomyocytes derived from human embryonic stem cells

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) have great value for studies of human cardiac development, drug discovery, disease modeling, and cell therapy. However, the mixed cardiomyocyte subtypes (ventricular-, atrial-, and nodal-like myocytes) and the maturation heterogeneity of hPSC-CMs restrain their application in vitro and in vivo. Myosin light chain 2 (MYL2, encoding the ventricular/cardiac muscle isoform MLC2v protein) is regarded as a ventricular-specific marker of cardiac myocardium; however, its restricted localization to ventricles during human heart development has been questioned. Consequently, it is currently unclear whether MYL2 definitively marks ventricular hESC-CMs. Here, by using a MYL2-Venus hESC reporter line, we characterized a time-dependent increase of the MYL2-Venus positive (MLC2v-Venus⁺) hESC-CMs during differentiation. We also compared the molecular, cellular, and functional properties between the MLC2v-Venus⁺ and MYL2-Venus negative (MLC2v-Venus^-) hESC-CMs. At early differentiation stages of hESC-CMs, we reported that both MLC2v-Venus^- and MLC2v-Venus⁺ CMs displayed ventricular-like traits but the ventricular-like cells from MLC2v-Venus⁺ hESC-CMs displayed more developed action potential (AP) properties than that from MLC2v-Venus^- hESC-CMs. Meanwhile, about a half MLC2v-Venus^- hESC-CM population displayed atrial-like AP properties, and a half showed ventricular-like AP properties, whereas only ~ 20% of the MLC2v-Venus^- hESC-CMs expressed the atrial marker nuclear receptor subfamily 2 group F member 2 (NR2F2, also named as COUPTFII). At late time points, almost all MLC2v-Venus⁺ hESC-CMs exhibited ventricular-like AP properties. Further analysis demonstrates that the MLC2v-Venus⁺ hESC-CMs had enhanced Ca²⁺ transients upon increase of the MLC2v level during cultivation. Concomitantly, the MLC2v-Venus⁺ hESC-CMs showed more defined sarcomeric structures and better mitochondrial function than those in the MLC2v-Venus^- hESC-CMs. Moreover, the MLC2v-Venus⁺ hESC-CMs were more sensitive to hypoxic stimulus than the MLC2v-Venus^- hESC-CMs. These results provide new insights into the development of human ventricular myocytes and reveal a direct correlation between the expression profile of MLC2v and ventricular hESC-CM development. Our findings that MLC2v is predominantly a ventricular marker in developmentally immature hESC-CMs have implications for human development, drug screening, and disease modeling, and this marker should prove useful in overcoming issues associated with hESC-CM heterogeneity.

Cooperative Binding of ETS2 and NFAT Links Erk1/2 and Calcineurin Signaling in the Pathogenesis of Cardiac Hypertrophy

Supplemental Digital Content is available in the text.

Cardiac hypertrophy is an independent risk factor for heart failure, a leading cause of morbidity and mortality globally. The calcineurin/NFAT (nuclear factor of activated T cells) pathway and the MAPK (mitogen-activated protein kinase)/Erk (extracellular signal-regulated kinase) pathway contribute to the pathogenesis of cardiac hypertrophy as an interdependent network of signaling cascades. How these pathways interact remains unclear and few direct targets responsible for the prohypertrophic role of NFAT have been described.

Disruption of histamine/H1R signaling pathway represses cardiac differentiation and maturation of human induced pluripotent stem cells

Background

The efficiency and quality of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are crucial for regenerative medicine, disease modeling, drug screening, and the study of the development events during cardiac specification. However, their applications have been hampered by the differentiation efficiency, poor maturation, and high interline variability. Recent studies have reported that histamine plays important roles in hematopoietic stem cell proliferation and neutrophil maturation. However, its roles in cardiovascular tissue regeneration have not been thoroughly investigated. In the current study, we identified a novel physiological function of the histamine/histamine 1 receptor (H₁R) signal in regulating the differentiation of hiPSC-CMs and heart development.

Methods

Transgenic zebrafish model (cmlc2: mCherry) was treated with histamine and histamine receptor (HR) antagonists. Histological morphology and ultrastructure of zebrafish heart were measured. Histamine-deficient pregnant mice (HDC^−/−) were treated with H₁R antagonist (pyrilamine) by intragastric administration from E8.5 to E18.5. Cardiac histological morphology and ultrastructure were analyzed in neonatal mice, and cardiac function in adult mice was measured. In vitro, histamine and HR antagonists were administrated in the culture medium during hiPSC-CM differentiation at different stages. The efficiency and maturation of cardiac differentiation were evaluated. Finally, histamine-treated hiPSC-CMs were transplanted into ischemic myocardium to detect the possible therapeutic effect.

Results

Administration of H₁R antagonist during heart development induced cardiac dysplasia in zebrafish. Furthermore, using histidine decarboxylase (HDC) knockout mice, we examined abnormal swelling of myocardial mitochondria and autophagy formation under the condition of endogenous histamine deficiency. Histamine significantly promoted myocardial differentiation from human induced pluripotent stem cells (hiPSCs) with better structure and function via a H₁R-dependent signal. The activation of histamine/H₁R signaling pathway augmented hiPSC-derived cardiomyocyte (hiPSC-CM) differentiation through the ERK1/2-STAT3 signaling pathway. In addition, histamine-pre-treated hiPSC-CMs were transplanted into the ischemic hearts of myocardial injured mice and exhibited better survival and myocardial protection.

Conclusions

Thus, these findings indicated that histamine/H₁R and its downstream signals were not only involved in cardiac differentiation but also provided a better survival environment for stem cell transplanted into ischemic myocardium.

A novel approach to differentiate rat embryonic stem cells in vitro reveals a role for RNF12 in activation of X chromosome inactivation

X chromosome inactivation (XCI) is a mammalian specific, developmentally regulated process relying on several mechanisms including antisense transcription, non-coding RNA-mediated silencing, and recruitment of chromatin remodeling complexes. In vitro modeling of XCI, through differentiation of embryonic stem cells (ESCs), provides a powerful tool to study the dynamics of XCI, overcoming the need for embryos, and facilitating genetic modification of key regulatory players. However, to date, robust initiation of XCI in vitro has been mostly limited to mouse pluripotent stem cells. Here, we adapted existing protocols to establish a novel monolayer differentiation protocol for rat ESCs to study XCI. We show that differentiating rat ESCs properly downregulate pluripotency factor genes, and present female specific Xist RNA accumulation and silencing of X-linked genes. We also demonstrate that RNF12 seems to be an important player in regulation of initiation of XCI in rat, acting as an Xist activator. Our work provides the basis to investigate the mechanisms directing the XCI process in a model organism different from the mouse.

Laminin promotes differentiation of rat embryonic stem cells into cardiomyocytes by activating the integrin/FAK/PI3K p85 pathway

The generation of germline competent rat embryonic stem cells (rESCs) allows the study of their lineage commitment. Here, we developed a highly efficient system for rESC-derived cardiomyocytes, and even the formation of three-dimensional (3D)-like cell clusters with cTNT and α-Actinin. We have validated that laminin can interact with membrane integrin to promote the phosphorylation of both phosphatidylinositol 3-kinase (PI3K) p85 and the focal adhesion kinase (FAK). In parallel, GATA4 was up-regulated. Upon inhibiting the integrin, laminin loses the effect on cardiomyocyte differentiation, accompanied with a down-regulation of phosphorylation level of PI3K p85 and FAK. Meanwhile, the expression of Gata4 was inhibited as well. Taken together, laminin is a crucial component in the differentiation of rESCs into cardiomyocytes through increasing their proliferation via interacting with integrin pathway. These results provide new insights into the pathways mediated by extracellular laminin involved in the fate of rESC-derived cardiomyocytes.

Small-molecule-based generation of functional cardiomyocytes from human umbilical cord-derived induced pluripotent stem cells

The purpose of this study was to investigate the cardiac-differentiation potential of induced pluripotent stem cells (iPSCs) generated from human umbilical cord-derived mesenchymal cells. Spontaneous beating colonies were observed at day 7 after the sequential addition of CHIR99021 and IWP-4. The combined use of CHIR99021 and IWP-4 downregulated the expression of pluripotency markers while upregulating cardiac transcription factors and cardiomyocyte-specific markers. The derived cardiomyocytes demonstrated typical sarcomeric structures and action-potential features; most importantly, the derived cells exhibited responsiveness to β-adrenergic and muscarinic stimulations. The analyses of molecular, structural, and functional properties revealed that the derived cardiomyocytes were similar to cardiomyocytes derived from BJ foreskin fibroblast cells. In summary, our results demonstrate that functional cardiomyocytes can be generated from human umbilical cord-derived cells. The methodology described here has potential as a means for the production of functional cardiomyocytes from discarded human umbilical cord tissue.

Efficient generation of functional cardiomyocytes from human umbilical cord-derived virus-free induced pluripotent stem cells

We have previously demonstrated that human umbilical cord-derived mesenchymal stem cells (UC-MSCs) can differentiate into cardiomyocyte-like cells. However, no contracting cells were observed during differentiation. In this study, we generated induced pluripotent stem cells (iPSCs) from UC-MSCs using mRNA reprogramming and focused on the differentiation of reprogrammed iPSCs into functional cardiomyocytes. For cardiac differentiation, the spontaneously contracting cell clusters were present on day 8 of differentiation. Immunostaining studies and cardiac-specific gene expression confirmed the cardiomyocyte phenotype of the differentiated cells. Electrophysiology studies indicated that iPSCs derived from UC-MSCs had a capacity for differentiation into nodal-, atrial-, and ventricular-like phenotypes based on action potential characteristics, and the derived cardiomyocytes exhibited responsiveness to β-adrenergic and muscarinic stimulations. Moreover, the derived cardiomyocytes displayed spontaneous intracellular Ca²⁺ transients. These results demonstrate that functional cardiomyocytes can be generated from reprogrammed UC-MSCs, and the methodology described here will serve as a useful protocol to obtain functional cardiomyocytes from human mesenchymal stem cells.

IP3R-mediated Ca2+ signals govern hematopoietic and cardiac divergence of Flk1+ cells via the calcineurin-NFATc3-Etv2 pathway

Ca2+ signals participate in various cellular processes with spatial and temporal dynamics, among which, inositol 1,4,5-trisphosphate receptors (IP3Rs)-mediated Ca2+ signals are essential for early development. However, the underlying mechanisms of IP3R-regulated cell fate decision remain largely unknown. Here we report that IP3Rs are required for the hematopoietic and cardiac fate divergence of mouse embryonic stem cells (mESCs). Deletion of IP3Rs (IP3R-tKO) reduced Flk1+/PDGFRα- hematopoietic mesoderm, c-Kit+/CD41+ hematopoietic progenitor cell population, and the colony-forming unit activity, but increased cardiac progenitor markers as well as cardiomyocytes. Concomitantly, the expression of a key regulator of hematopoiesis, Etv2, was reduced in IP3R-tKO cells, which could be rescued by the activation of Ca2+ signals and calcineurin or overexpression of constitutively active form of NFATc3. Furthermore, IP3R-tKO impaired specific targeting of Etv2 by NFATc3 via its evolutionarily conserved cis-element in differentiating ESCs. Importantly, the activation of Ca2+-calcineurin-NFAT pathway reversed the phenotype of IP3R-tKO cells. These findings reveal an unrecognized governing role of IP3Rs in hematopoietic and cardiac fate commitment via IP3Rs-Ca2+-calcineurin-NFATc3-Etv2 pathway.

Generation of functional cardiomyocytes from rat embryonic and induced pluripotent stem cells using feeder-free expansion and differentiation in suspension culture

The possibility to generate cardiomyocytes from pluripotent stem cells in vitro has enormous significance for basic research, disease modeling, drug development and heart repair. The concept of heart muscle reconstruction has been studied and optimized in the rat model using rat primary cardiovascular cells or xenogeneic pluripotent stem cell derived-cardiomyocytes for years. However, the lack of rat pluripotent stem cells (rPSCs) and their cardiovascular derivatives prevented the establishment of an authentic clinically relevant syngeneic or allogeneic rat heart regeneration model. In this study, we comparatively explored the potential of recently available rat embryonic stem cells (rESCs) and induced pluripotent stem cells (riPSCs) as a source for cardiomyocytes (CMs). We developed feeder cell-free culture conditions facilitating the expansion of undifferentiated rPSCs and initiated cardiac differentiation by embryoid body (EB)-formation in agarose microwell arrays, which substituted the robust but labor-intensive hanging drop (HD) method. Ascorbic acid was identified as an efficient enhancer of cardiac differentiation in both rPSC types by significantly increasing the number of beating EBs (3.6 ± 1.6-fold for rESCs and 17.6 ± 3.2-fold for riPSCs). These optimizations resulted in a differentiation efficiency of up to 20% cTnT^pos rPSC-derived CMs. CMs showed spontaneous contractions, expressed cardiac markers and had typical morphological features. Electrophysiology of riPSC-CMs revealed different cardiac subtypes and physiological responses to cardio-active drugs. In conclusion, we describe rPSCs as a robust source of CMs, which is a prerequisite for detailed preclinical studies of myocardial reconstruction in a physiologically and immunologically relevant small animal model.

Biophysical subsets of embryonic stem cells display distinct phenotypic and morphological signatures

The highly proliferative and pluripotent characteristics of embryonic stem cells engender great promise for tissue engineering and regenerative medicine, but the rapid identification and isolation of target cell phenotypes remains challenging. Therefore, the objectives of this study were to characterize cell mechanics as a function of differentiation and to employ differences in cell stiffness to select population subsets with distinct mechanical, morphological, and biological properties. Biomechanical analysis with atomic force microscopy revealed that embryonic stem cells stiffened within one day of differentiation induced by leukemia inhibitory factor removal, with a lagging but pronounced change from spherical to spindle-shaped cell morphology. A microfluidic device was then employed to sort a differentially labeled mixture of pluripotent and differentiating cells based on stiffness, resulting in pluripotent cell enrichment in the soft device outlet. Furthermore, sorting an unlabeled population of partially differentiated cells produced a subset of “soft” cells that was enriched for the pluripotent phenotype, as assessed by post-sort characterization of cell mechanics, morphology, and gene expression. The results of this study indicate that intrinsic cell mechanical properties might serve as a basis for efficient, high-throughput, and label-free isolation of pluripotent stem cells, which will facilitate a greater biological understanding of pluripotency and advance the potential of pluripotent stem cell differentiated progeny as cell sources for tissue engineering and regenerative medicine.

Transplantation of rat embryonic stem cell-derived retinal progenitor cells preserves the retinal structure and function in rat retinal degeneration

INTRODUCTION

Degenerative retinal diseases like age-related macular degeneration (AMD) are the leading cause of blindness. Cell transplantation showed promising therapeutic effect for such diseases, and embryonic stem cell (ESC) is one of the sources of such donor cells. Here, we aimed to generate retinal progenitor cells (RPCs) from rat ESCs (rESCs) and to test their therapeutic effects in rat model.

METHODS

The rESCs (DA8-16) were cultured in N2B27 medium with 2i, and differentiated to two types of RPCs following the SFEBq method with modifications. For rESC-RPC1, the cells were switched to adherent culture at D10, while for rESC-RPC2, the suspension culture was maintained to D14. Both RPCs were harvested at D16. Primary RPCs were obtained from P1 SD rats, and some of them were labeled with EGFP by infection with lentivirus. To generate Rax::EGFP knock-in rESC lines, TALENs were engineered to facilitate homologous recombination in rESCs, which were cotransfected with the targeting vector and TALEN vectors. The differentiated cells were analyzed with live image, immunofluorescence staining, flow cytometric analysis, gene expression microarray, etc. RCS rats were used to mimic the degeneration of retina and test the therapeutic effects of subretinally transplanted donor cells. The structure and function of retina were examined.

RESULTS

We established two protocols through which two types of rESC-derived RPCs were obtained and both contained committed retina lineage cells and some neural progenitor cells (NPCs). These rESC-derived RPCs survived in the host retinas of RCS rats and protected the retinal structure and function in early stage following the transplantation. However, the glia enriched rESC-RPC1 obtained through early and longer adherent culture only increased the b-wave amplitude at 4 weeks, while the longer suspension culture gave rise to evidently neuronal differentiation in rESC-RPC2 which significantly improved the visual function of RCS rats.

CONCLUSIONS

We have successfully differentiated rESCs to glia enriched RPCs and retinal neuron enriched RPCs in vitro. The retinal neuron enriched rESC-RPC2 protected the structure and function of retina in rats with genetic retinal degeneration and could be a candidate cell source for treating some degenerative retinal diseases in human trials.

Rat embryonic stem cells create new era in development of genetically manipulated rat models

Embryonic stem (ES) cells are isolated from the inner cell mass of a blastocyst, and are used for the generation of gene-modified animals. In mice, the transplantation of gene-modified ES cells into recipient blastocysts leads to the creation of gene-targeted mice such as knock-in and knock-out mice; these gene-targeted mice contribute greatly to scientific development. Although the rat is considered a useful laboratory animal alongside the mouse, fewer gene-modified rats have been produced due to the lack of robust establishment methods for rat ES cells. A new method for establishing rat ES cells using signaling inhibitors was reported in 2008. By considering the characteristics of rat ES cells, recent research has made progress in improving conditions for the stable culture of rat ES cells in order to generate gene-modified rats efficiently. In this review, we summarize several advanced methods to maintain rat ES cells and generate gene-targeted rats.

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.

Comparative study of directional differentiation of human and mouse embryonic stem cells into cardiomyocytes

This comparative study investigates the method, efficiency, and anti-hypoxic ability of cardiomyocytes, directionally induced from human (h) and mouse (m) embryonic stem cells (ESCs). hESCs were induced into cardiomyocytes by suspension culture, without inducers, or adherent culture using the inducers activin A and BMP4. mESCs were induced into cardiomyocytes by hanging-drop method, without inducers or induced with vitamin C. All four methods successfully induced ESCs to differentiate into cardiomyocytes. There was a significant difference between groups with and without inducers. A significant difference was found between mESC and hESC groups with inducers. The average beating frequency of cardiomyocytes differentiated from hESC was lower than cardiomyocytes differentiated from mESC, while the average beating frequency of cardiomyocytes differentiated from the same cell line, despite different culture methods, did not differ. Beating cardiomyocytes of each group were positive for cTnT staining. Spontaneous action potentials of beating cardiomyocytes were detected by patch-clamp experiments in each group. Different apoptotic ratios were detected in beating cardiomyocytes in each group and the difference between cardiomyocytes induced from mESCs and hESCs was statistically significant. The differentiation efficiencies in the groups without inducers were significantly higher than those without inducers. The induction of mESCs was more simple and efficient compared with hESCs. Without the presence of other protective factors, the anti-hypoxic ability of cardiomyocytes induced from hESCs was stronger and the beating times were longer in vitro compared with mESCs.

An optimized and simplified system of mouse embryonic stem cell cardiac differentiation for the assessment of differentiation modifiers

Generating cardiomyocytes from embryonic stem cells is an important technique for understanding cardiovascular development, the origins of cardiovascular diseases and also for providing potential reagents for cardiac repair. Numerous methods have been published but often are technically challenging, complex, and are not easily adapted to assessment of specific gene contributions to cardiac myocyte differentiation. Here we report the development of an optimized protocol to induce the differentiation of mouse embryonic stem cells to cardiac myocytes that is simplified and easily adapted for genetic studies. Specifically, we made four critical findings that distinguish our protocol: 1) mouse embryonic stem cells cultured in media containing CHIR99021 and PD0325901 to maintain pluripotency will efficiently form embryoid bodies containing precardiac mesoderm when cultured in these factors at a reduced dosage, 2) low serum conditions promote cardiomyocyte differentiation and can be used in place of commercially prepared StemPro nutrient supplement, 3) the Wnt inhibitor Dkk-1 is dispensable for efficient cardiac differentiation and 4) tracking differentiation efficiency may be done with surface expression of PDGFRα alone. In addition, cardiac mesodermal precursors generated by this system can undergo lentiviral infection to manipulate the expression of specific target molecules to assess effects on cardiac myocyte differentiation and maturation. Using this approach, we assessed the effects of CHF1/Hey2 on cardiac myocyte differentiation, using both gain and loss of function. Overexpression of CHF1/Hey2 at the cardiac mesoderm stage had no apparent effect on cardiac differentiation, while knockdown of CHF1/Hey2 resulted in increased expression of atrial natriuretic factor and connexin 43, suggesting an alteration in the phenotype of the cardiomyocytes. In summary we have generated a detailed and simplified protocol for generating cardiomyocytes from mES cells that is optimized for investigating factors that affect cardiac differentiation.

Kisspeptin-10 modulates the proliferation and differentiation of the rhesus monkey derived stem cell line: R366.4

The rhesus monkey embryonic stem cell line R366.4 has been identified to differentiate into a number of cell types. However, it has not been well characterized for its response to drugs affecting reproductive endocrinology. Kisspeptins (KPs) are ligands for the GPR-54, which is known to modulate reproductive function. The current study was designed to determine the effect of the KP-10 peptide on R366.4 cells and to investigate the role of KP-GPR54 in the cell proliferation process. Four different doses (0.1, 1, 10, and 100 nM) of KP-10 and control were selected to evaluate cell growth parameters and cellular morphological changes over a 72 hr period. The cells were treated with kisspeptin-10 during the early rosette stage. Proliferation rates, analyzed by flow cytometry and cell count methods, were found to be decreased after treatment. Moreover, the number of rosettes was found to decrease following KP-10 treatments. Morphological changes consisting of neuronal projections were also witnessed. This suggested that KP-10 had an antiproliferative effect on R366.4 cells leading to a differentiation state and morphological changes consistent with neuronal stem cell development. The R366.4 stem cell line differentiates based on kisspeptin signaling and may be used to investigate reproductive cell endocrinology in vitro.

Highly efficient induction and long-term maintenance of multipotent cardiovascular progenitors from human pluripotent stem cells under defined conditions

Cardiovascular progenitor cells (CVPCs) derived from human pluripotent stem cells (hPSCs), including human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs), hold great promise for the study of cardiovascular development and cell-based therapy of heart diseases, but their applications are challenged by the difficulties in their efficient generation and stable maintenance. This study aims to develop chemically defined systems for robust generation and stable propagation of hPSC-derived CVPCs by modulating the key early developmental pathways involved in human cardiovascular specification and CVPC self-renewal. Herein we report that a combination of bone morphogenetic protein 4 (BMP4), glycogen synthase kinase 3 (GSK3) inhibitor CHIR99021 and ascorbic acid is sufficient to rapidly convert monolayer-cultured hPSCs, including hESCs and hiPSCs, into homogeneous CVPCs in a chemically defined medium under feeder- and serum-free culture conditions. These CVPCs stably self-renewed under feeder- and serum-free conditions and expanded over 10(7)-fold when the differentiation-inducing signals from BMP, GSK3 and Activin/Nodal pathways were simultaneously eliminated. Furthermore, these CVPCs exhibited expected genome-wide molecular features of CVPCs, retained potentials to generate major cardiovascular lineages including cardiomyocytes, smooth muscle cells and endothelial cells in vitro, and were non-tumorigenic in vivo. Altogether, the established systems reported here permit efficient generation and stable maintenance of hPSC-derived CVPCs, which represent a powerful tool to study early embryonic cardiovascular development and provide a potentially safe source of cells for myocardial regenerative medicine.

Differentiation of rat iPS cells and ES cells into granulosa cell-like cells in vitro

Premature ovarian failure (POF) is an ovarian defect characterized by the premature depletion of ovarian follicles before 40 years of age, representing one major cause of female infertility. Stem cells provide the possibility of a potential treatment for POF. In this study, rat embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) were co-cultured with granulosa cells (GCs) to differentiate to GC-like cells. The level of estradiol (E2) analyzed by radioimmunoassay showed that the E2 concentration of the culture supernatant of co-cultured rat iPSCs and ESCs increased in a time-dependent manner, compared with the GCs group that has an opposite trend. The expression of follicle-stimulating hormone receptor (FSHR) was confirmed by immunostaining. These results indicated that rat iPSCs and ESCs were effectively induced to GC-like cells through indirect cell-to-cell contact. Real-time polymerase chain reaction was performed to analyze the expression level of marker genes in POF, including BMP15, FMR1, FSHR, INHA, AMH, NOBOX, FOXO3, EIF2B, FIGLA, and GDF9. The BMP15, FSHR, INHA, AMH, NOBOX, and GDF9 genes were significantly up-regulated in iPSCs and ESCs co-cultured with GCs in comparison with cells that were not co-cultured. Thus, here we demonstrated an available method to differentiate rat iPSCs and ESCs into GC-like cells in vitro for the possible cell therapy of POF.

Efficient generation of rat induced pluripotent stem cells using a non-viral inducible vector

Current methods of generating rat induced pluripotent stem cells are based on viral transduction of pluripotency inducing genes (Oct4, Sox2, c-myc and Klf4) into somatic cells. These activate endogenous pluripotency genes and reprogram the identity of the cell to an undifferentiated state. Epigenetic silencing of exogenous genes has to occur to allow normal iPS cell differentiation. To gain more control over the expression of exogenous reprogramming factors, we used a novel doxycycline-inducible plasmid vector encoding Oct4, Sox2, c-Myc and Klf4. To ensure efficient and controlled generation of iPS cells by plasmid transfection we equipped the reprogramming vector with a bacteriophage φC31 attB site and used a φC31 integrase expression vector to enhance vector integration. A series of doxycycline-independent rat iPS cell lines were established. These were characterized by immunocytochemical detection of Oct4, SSEA1 and SSEA4, alkaline phosphatase staining, methylation analysis of the endogenous Oct4 promoter and RT-PCR analysis of endogenous rat pluripotency genes. We also determined the number of vector integrations and the extent to which reprogramming factor gene expression was controlled. Protocols were developed to generate embryoid bodies and rat iPS cells demonstrated as pluripotent by generating derivatives of all three embryonic germ layers in vitro, and teratoma formation in vivo. All data suggest that our rat iPS cells, generated by plasmid based reprogramming, are similar to rat ES cells. Methods of DNA transfection, protein transduction and feeder-free monolayer culture of rat iPS cells were established to enable future applications.

Ascorbic acid enhances the cardiac differentiation of induced pluripotent stem cells through promoting the proliferation of cardiac progenitor cells

Generation of induced pluripotent stem cells (iPSCs) has opened new avenues for the investigation of heart diseases, drug screening and potential autologous cardiac regeneration. However, their application is hampered by inefficient cardiac differentiation, high interline variability, and poor maturation of iPSC-derived cardiomyocytes (iPS-CMs). To identify efficient inducers for cardiac differentiation and maturation of iPSCs and elucidate the mechanisms, we systematically screened sixteen cardiomyocyte inducers on various murine (m) iPSCs and found that only ascorbic acid (AA) consistently and robustly enhanced the cardiac differentiation of eleven lines including eight without spontaneous cardiogenic potential. We then optimized the treatment conditions and demonstrated that differentiation day 2-6, a period for the specification of cardiac progenitor cells (CPCs), was a critical time for AA to take effect. This was further confirmed by the fact that AA increased the expression of cardiovascular but not mesodermal markers. Noteworthily, AA treatment led to approximately 7.3-fold (miPSCs) and 30.2-fold (human iPSCs) augment in the yield of iPS-CMs. Such effect was attributed to a specific increase in the proliferation of CPCs via the MEK-ERK1/2 pathway by through promoting collagen synthesis. In addition, AA-induced cardiomyocytes showed better sarcomeric organization and enhanced responses of action potentials and calcium transients to β-adrenergic and muscarinic stimulations. These findings demonstrate that AA is a suitable cardiomyocyte inducer for iPSCs to improve cardiac differentiation and maturation simply, universally, and efficiently. These findings also highlight the importance of stimulating CPC proliferation by manipulating extracellular microenvironment in guiding cardiac differentiation of the pluripotent stem cells.

Musashi1 expression cells derived from mouse embryonic stem cells can be enriched in side population isolated by fluorescence activated cell sorter

Background

Purifying stem cells is an inevitable process for further investigation and cell-therapy. Sorting side population (SP) cells is generally regarded as an effective method to enrich for progenitor cells. This study was to explore whether sorting SP could enrich for the Musashi1 (Msi1) positive cells from Msi1 high expression cells (Msi1^high cells) derived from mouse embryonic stem cells (ESCs) in vitro.

Results

In this study, Msi1^high cell population derived from ESCs were stained by Hoechst 33342, and then the SP and non-SP (NSP) fractions were analyzed and sorted by fluorescence activated cell sorter. Subsequently, the expressions of Msi1 and other markers for neural and intestinal stem cells in SP and NSP were respectively detected. SP and NSP cells were hypodermically engrafted into the backs of NOD/SCID mice to form grafts. The developments of neural and intestinal epithelial cells in these grafts were investigated. SP fraction was identified and isolated from Msi1^high cell population. The expression of Msi1 in SP fraction was significantly higher than that in NSP fraction and unsorted Msi1^high cells (P< 0.05). Furthermore, the markers for neural cells and intestinal epithelial cells were more highly expressed in the grafts from SP fraction than those from NSP fraction (P< 0.05).

Conclusions

SP fraction, isolated from Msi1^high cells, contains almost all the Msi1-positive cells and has the potential to differentiate into neural and intestinal epithelial cells in vivo. Sorting SP fraction could be a convenient and practical method to enrich for Msi1-positive cells from the differentiated cell population derived from ESCs.