Defined culture medium for stem cell differentiation: applicability of serum-free conditions in the mouse embryonic stem cell test

Cell Reprogramming and Differentiation Utilizing Messenger RNA for Regenerative Medicine

The COVID-19 pandemic generated interest in the medicinal applications of messenger RNA (mRNA). It is expected that mRNA will be applied, not only to vaccines, but also to regenerative medicine. The purity of mRNA is important for its medicinal applications. However, the current mRNA synthesis techniques exhibit problems, including the contamination of undesired 5'-uncapped mRNA and double-stranded RNA. Recently, our group developed a completely capped mRNA synthesis technology that contributes to the progress of mRNA research. The introduction of chemically modified nucleosides, such as N1-methylpseudouridine and 5-methylcytidine, has been reported by Karikó and Weissman, opening a path for the practical application of mRNA for vaccines and regenerative medicine. Yamanaka reported the production of induced pluripotent stem cells (iPSCs) by introducing four types of genes using a retrovirus vector. iPSCs are widely used for research on regenerative medicine and the preparation of disease models to screen new drug candidates. Among the Yamanaka factors, Klf4 and c-Myc are oncogenes, and there is a risk of tumor development if these are integrated into genomic DNA. Therefore, regenerative medicine using mRNA, which poses no risk of genome insertion, has attracted attention. In this review, the author summarizes techniques for synthesizing mRNA and its application in regenerative medicine.

Comparative assessment of toxic responses in 3D embryoid body differentiation model and mouse early embryos treated with 5-hydroxytryptophan

Pluripotent stem cells recapitulate in vitro the early developmental stages and are considered promising cell models for predictive developmental toxicity studies. To investigate the consistency between adverse drug effects on early development and the early stages of embryonic stem cell differentiation in three-dimensional (3D) in vitro culture, the toxic responses to 5-hydroxytryptophan (5-HTP; 0.5-2 mM) were evaluated in early mouse embryos and the embryoid body (EB) differentiation model. 3D architectures, developmental and differentiation dynamics and the cell death rates were analyzed in early mouse embryos (E2.5-E5.5) and EBs at 1 and 6 days of differentiation using a combination of confocal immunofluorescence microscopy with high content imaging analysis and quantitative gene expression analysis. Comparative analysis of toxic responses in early embryos and EBs revealed a similar dose- and stage-dependent decrease in the 5-HTP toxic effects during development and differentiation. The integral toxic responses in the early embryos and EBs were significantly dependent on their 3D architecture and cellular composition. Treatment with 5-HTP (1 mM and above) induced developmental arrest, growth inhibition, and increased cell death in the early embryos without the trophoblasts (E2.5) and those with impaired trophoblasts and in early EBs, whereas later embryos and EBs were more resistant due to the protection of the extraembryonic tissues. This study demonstrates that the EB differentiation model is a relevant 3D-model of early mammalian development and can be useful for the predictive evaluation of toxic and teratogenic effects in embryos at the preimplantation and early post-implantation developmental stages.

Look-alikes may not act alike: Gene expression regulation and cell-type-specific responses of three valproic acid analogues in the neural embryonic stem cell test (ESTn)

In vitro assays to assess developmental neurotoxicity of chemicals are highly desirable. The murine neural embryonic stem cell test (ESTn) can mimic parts of early differentiation of embryonic brain and may therefore be useful for this purpose. The aim of this study was to investigate whether this test is able to rank the toxic potencies of three valproic acid analogues and to study their mode of action by investigating their individual effects on four cell types: stem cells, neurons, astrocytes and neural crest cells. Using immunocytochemical read-outs and qPCR for cell type-specific genes, the effects of valproic acid (VPA), 2-ethylhexanoic acid (EHA) and 2-ethyl-4-methylpentanoic (EMPA) were assessed. VPA and EHA but not EMPA downregulated cell type-specific differentiation makers and upregulated stem cell related markers (Fut4, Cdh1) at different time points during differentiation. Expression of Gfap, a marker for astrocytes, was dramatically downregulated by VPA and EHA, but not by EMPA. This finding was verified using immunostainings. Based on the number and extent of genes regulated by the three compounds, relative potencies were determined as VPA > EHA > EMPA, which is consistent with in vivo developmental toxicity potency ranking of these compounds. Thus, ESTn using a combination of morphology, gene and protein expression readouts, may provide a medium-throughput system for monitoring the effects of compounds on differentiation of cell types in early brain development.

Combining mouse embryonic stem cells and zebrafish embryos to evaluate developmental toxicity of chemical exposure

The assays in this study utilize mouse embryonic stem cells (mESCs) and zebrafish embryos to evaluate the potential developmental toxicity of industrial and pharmaceutical chemicals. A set of eleven chemicals of known mammalian in vivo teratogenicity were tested in the assays and correlations to mammalian data. Using mESCs, proliferation, differentiation, and cytotoxicity of the chemicals were measured. In zebrafish embryos, lethality and the lowest effect level concentrations for morphological malformations were determined. Clustering of the assays based on frequency of affected assays resulted in a ranking of the test compounds that correlated to in vivo rodent data (R = 0.88, P < 0.001). We conclude that the combination of ESC- and zebrafish-based assays provides a valuable platform for the prioritization of pharmaceutical and industrial chemicals for further testing of developmental toxicity in rodents.

Ascorbic acid-mediated enhanced cardiomyocyte differentiation of mouse ES-cells involves interplay of DNA methylation and multiple-signals

Embryonic stem cells (ES-cells) provide a good model system to study lineage-specific differentiation. Though, the differentiation of ES-cells to cardiomyocytes is documented, a clear understanding of the molecular mechanism of differentiation and improved functional-differentiation efficiency are yet to be achieved. In this regard, ascorbic acid (Aa) is shown to be one of the effective cardiac inducers in ES-cells. But, its mechanism is poorly understood. We therefore, investigated the mechanism of Aa-mediated cardiomyocyte differentiation of ES-cells. Here, we describe the potential involvement of epigenetic (DNA methylation) as well as integrin- and Erk- signaling systems during cardiomyocyte differentiation. Transgenic GS-2 ES-cells and wild-type D3 ES-cells were differentiated to cardiomyocytes, in the presence or absence of Aa and with or without inhibitors of Erk-, collagen- and integrin- pathways. At specific time points, differentiated states of ES-cells were scored by gene expression analyses and the proportion of functional cTnI⁺ cardiomyocytes. DNA methylation changes of Isl-1, BMP-2, GATA-4 and α-MHC in cardiogenic cells, following stimulation with Aa, were analyzed by using methylation specific PCR (MSP). We observed that Aa, when applied in initial phase of ES-cell differentiation, consistently enhanced cardiac differentiation (99%) over that observed during spontaneous differentiation (70%). This was associated with enhanced expressions of cardiogenesis-associated genes. A two-fold increase in cTnI⁺ cells was observed, with appropriate myofibril arrangement. The observed effect of Aa was due to enhanced collagen and integrin signaling, coupled with a high p-ERK1/2 expression, downstream. Besides, the involvement of DNA methylation in regulating the expression of cardiac genes i.e., Isl-1 and α-MHC was also observed. Overall, this study, for the first time, demonstrates that Aa-mediated cardiac enhancement is brought about, mechanistically, through the interplay of epigenetic changes in DNA methylation of cardiac genes (Isl-1 and α-MHC) and integrin signaling system.

Undifferentiated murine embryonic stem cells used to model the effects of the blue-green algal toxin cylindrospermopsin on preimplantation embryonic cell proliferation

Undifferentiated mouse embryonic stem cell (mES) proliferation in vitro resembles aspects of in vivo pre-implantation embryonic development. mES were used to assess the embryo-toxicity of cylindrospermopsin (CYN), a water contaminant with an Australian Drinking Water Guideline (ADWG) of 1 μg/L. mES exposed to 0-1 μg/mL CYN for 24-168 h were subjected to an optimised crystal violet viability assay. mES exposed to retinoic acid ± 1 μg/L CYN differentiated into neural-like cells confirmed by morphological examination and RT-PCR for Oct4, Brachyury and Nestin. The CYN No Observed Effect Concentration (OEC) was 0.5 μg/mL, the Lowest OEC was 1 μg/mL (p < 0.001, n = 3), and the IC50 was 0.86 μg/mL after 24 h. The ADWG 1 μg/L CYN did not affect differentiation or proliferation after 72 h, but decreased proliferation after 168 h (p < 0.05). We conclude that higher algal bloom-associated CYN concentrations have the potential to impair in vivo pre-implantation development, and the mES crystal violet assay has broad application to screening environmental toxins.

Curcumin affords protection against valproic acid induced teratogenicity by curtailing oxidative stress and inhibiting CYP2C9 activity

The toxic metabolite (E)-2,4-diene-VPA is involved in generation of oxidative stress subsequently contributing in induction of malformations and anomalies and that curcumin affords dose dependent amelioration of the anomalies exerted by VPA.

Efficient reprogramming of naïve-like induced pluripotent stem cells from porcine adipose-derived stem cells with a feeder-independent and serum-free system

Induced pluripotent stem cells (iPSCs) are somatic cells reprogrammed by ectopic expression of transcription factors or small molecule treatment, which resemble embryonic stem cells (ESCs). They hold great promise for improving the generation of genetically modified large animals. However, few porcine iPSCs (piPSCs) lines obtained currently can support development of cloned embryos. Here, we generated iPSCs from porcine adipose-derived stem cells (pADSCs), using drug-inducible expression of defined human factors (Oct4, Sox2, c-Myc and Klf4). Reprogramming of iPSCs from pADSCs was more efficient than from fibroblasts, regardless of using feeder-independent or feeder-dependent manners. By addition of Lif-2i medium containing mouse Lif, CHIR99021 and PD0325901 (Lif-2i), naïve-like piPSCs were obtained under feeder-independent and serum-free conditions. These successfully reprogrammed piPSCs were characterized by short cell cycle intervals, alkaline phosphatase (AP) staining, expression of Oct4, Sox2, Nanog, SSEA3 and SSEA4, and normal karyotypes. The resemblance of piPSCs to naïve ESCs was confirmed by their packed dome morphology, growth after single-cell dissociation, Lif-dependency, up-regulation of Stella and Eras, low expression levels of TRA-1-60, TRA-1-81 and MHC I and activation of both X chromosomes. Full reprogramming of naïve-like piPSCs was evaluated by the significant up-regulation of Lin28, Esrrb, Utf1 and Dppa5, differentiating into cell types of all three germ layers in vitro and in vivo. Furthermore, nuclear transfer embryos from naïve-like piPSCs could develop to blastocysts with improved quality. Thus, we provided an efficient protocol for generating naïve-like piPSCs from pADSCs in a feeder-independent and serum-free system with controlled regulation of exogenous genes, which may facilitate optimization of culture media and the production of transgenic pigs.

Engraftment of mouse embryonic stem cells differentiated by default leads to neuroprotection, behaviour revival and astrogliosis in parkinsonian rats

We report here protection against rotenone-induced behavioural dysfunction, striatal dopamine depletion and nigral neuronal loss, following intra-striatal transplantation of neurons differentiated from murine embryonic stem cells (mES). mES maintained in serum free medium exhibited increase in neuronal, and decrease in stem cell markers by 7th and 10th days as revealed by RT-PCR and immunoblot analyses. Tyrosine hydroxylase, NURR1, PITX3, LMX1b and c-RET mRNA showed a significant higher expression in differentiated cells than in mES. Dopamine level was increased by 3-fold on 10th day as compared to 7 days differentiated cells. Severity of rotenone-induced striatal dopamine loss was attenuated, and amphetamine-induced unilateral rotations were significantly reduced in animals transplanted with 7 days differentiated cells, but not in animals that received undifferentiated ES transplant. However, the ratio of contralateral to ipsilateral swings in elevated body swing test was significantly reduced in both the transplanted groups, as compared to control. Striatal grafts exhibited the presence of tyrosine hydroxylase positive cells, and the percentage of dopaminergic neurons in the substantia nigra was also found to be higher in the ipsilateral side of 7 days and mES grafted animals. Increased expression of CD11b and IBA-1, suggested a significant contribution of these microglia-derived factors in controlling the limited survival of the grafted cells. Astrocytosis in the grafted striatum, and significant increase in the levels of glial cell line derived neurotrophic factor may have contributed to the recovery observed in the hemiparkinsonian rats following transplantation.

Zebularine regulates early stages of mESC differentiation: effect on cardiac commitment

Lineage commitment during embryonic stem cell (ESC) differentiation is controlled not only by a gamut of transcription factors but also by epigenetic events, mainly histone deacetylation and promoter DNA methylation. The DNA demethylation agent 5'-aza-2'-deoxycytidine (AzadC) has been widely described as an effective promoter of cardiomyogenic differentiation in various stem cell types. However, its toxicity and instability complicate its use. Therefore, the purpose of this study was to examine the effects of zebularine (1-(β-D-ribofuranosyl)-1,2-dihydropyrimidin-2-1), a stable and non-toxic DNA cytosine methylation inhibitor, on mouse ESC (mESC) differentiation. Herein, we report that treating embryoid bodies, generated from mESCs, with 30 μM zebularine for 7 days led to greater cell differentiation and induced the expression of several cardiac-specific markers that were detected using reverse transcription-polymerase chain reaction (RT-PCR), real-time PCR, immunostaining and flow cytometry. Zebularine enhanced the expression of cardiac markers and the appearance of beating cells that responded to cardiac drugs, including ion channel blockers (diltiazem) and β-adrenergic stimulators (isoproterenol). Gene promoter methylation status was assessed using methylation-specific PCR (MSP) and validated by bisulfite sequencing analysis. Global gene expression profiling using microarrays showed that zebularine-differentiated cells are distinct from control ESCs. Pathway analysis revealed an enhancement of cellular processes such as embryonic development, cardiovascular system development and function. In addition, the whole-cell proteins exhibited different profiles as analyzed by two-dimensional differential-in-gel-electrophoresis. Our results indicate that zebularine regulates mesodermal differentiation of mESCs, controls promoter methylation of crucial cardiac genes and may help to improve cardiomyogenic differentiation.

Rational development of a serum-free medium and fed-batch process for a GS-CHO cell line expressing recombinant antibody

A serum-free medium (CHO-SFM) together with a fed-batch process was developed for the cultivation of a recombinant GS-CHO cell line producing TNFR-Fc. According to the metabolic characteristics of GS-CHO cell, a basal medium was prepared by supplementing DMEM:F12:RPMI1640 (2:1:1) with amino acids, insulin, transferrin, Pluronic F68 and some other ingredients. Statistical optimization approaches based on Plackett-Burman and central composite designs were then adopted to identify additional positive determinants and determine their optimal concentrations, which resulted in the final CHO-SFM medium formulations. The maximum antibody titer reached was 90.95 mg/l in the developed CHO-SFM, which was a 18 % and 10 fold higher than that observed in the commercial EX-CELL™ 302 medium (76.95 mg/l) and basal medium (8.28 mg/l), respectively. Subsequently, a reliable, reproducible and robust fed-batch strategy was designed according to the offline measurement of glucose, giving a final antibody yield of 378 mg/l, which was a threefold improvement over that in conventional batch culture (122 mg/l) using CHO-SFM. In conclusion, the use of design of experiment (DoE) method facilitated the development of CHO-SFM medium and fed-batch process for the production of recombinant antibody using GS-CHO cells.

Assaying embryotoxicity in the test tube: current limitations of the embryonic stem cell test (EST) challenging its applicability domain

Testing for embryotoxicity in vitro is an attractive alternative to animal experimentation. The embryonic stem cell test (EST) is such a method, and it has been formally validated by the European Centre for the Validation of Alternative Methods. A number of recent studies have underscored the potential of this method. However, the EST performed well below the 78% accuracy expected from the validation study using a new set of chemicals and pharmaceutical compounds, and also of toxicity criteria, tested to enlarge the database of the validated EST as part of the Work Package III of the ReProTect Project funded within the 6th Framework Programme of the European Union. To assess the performance and applicability domain of the EST we present a detailed review of the substances and their effects in the EST being nitrofen, ochratoxin A, D-penicillamine, methylazoxymethanol, lovastatin, papaverine, warfarin, β-aminopropionitrile, dinoseb, furosemide, doxylamine, pravastatin, and metoclopramide. By delineation of the molecular mechanisms of the substances we identify six categories of reasons for misclassifications. Some of these limitations might also affect other in vitro methods assessing embryotoxicity. Substances that fall into these categories need to be included in future validation sets and in validation guidelines for embryotoxicity testing. Most importantly, we suggest conceivable improvements and additions to the EST which will resolve most of the limitations.

Neural differentiation of mouse embryonic stem cells as a tool to assess developmental neurotoxicity in vitro

Mouse embryonic stem cells (mESCs) represent an attractive cellular system for in vitro studies in developmental biology as well as toxicology because of their potential to differentiate into all fetal cell lineages. The present study aims to establish an in vitro system for developmental neurotoxicity testing employing mESCs. We developed a robust and reproducible protocol for fast and efficient differentiation of the mESC line D3 into neural cells, optimized with regard to chemical testing. Morphological examination and immunocytochemical staining confirmed the presence of different neural cell types, including neural progenitors, neurons, astrocytes, oligodendrocytes, and radial glial cells. Neurons derived from D3 cells expressed the synaptic proteins PSD95 and synaptophysin, and the neurotransmitters serotonin and γ-aminobutyric acid. Calcium ion imaging revealed the presence of functionally active glutamate and dopamine receptors. In addition, flow cytometry analysis of the neuron-specific marker protein MAP2 on day 12 after induction of differentiation demonstrated a concentration dependent effect of the neurodevelopmental toxicants methylmercury chloride, chlorpyrifos, and lead acetate on neuronal differentiation. The current study shows that D3 mESCs differentiate efficiently into neural cells involving a neurosphere-like state and that this system is suitable to detect adverse effects of neurodevelopmental toxicants. Therefore, we propose that the protocol for differentiation of mESCs into neural cells described here could constitute one component of an in vitro testing strategy for developmental neurotoxicity.