Skeletal and cardiac myogenesis accompany adipogenesis in P19 embryonal stem cells

Corexit-EC9527A Disrupts Retinol Signaling and Neuronal Differentiation in P19 Embryonal Pluripotent Cells

Corexit-EC9500A and Corexit-EC9527A are two chemical dispersants that have been used to remediate the impact of the 2010 Deepwater Horizon oil spill. Both dispersants are composed primarily of organic solvents and surfactants and act by emulsifying the crude oil to facilitate biodegradation. The potential adverse effect of the Corexit chemicals on mammalian embryonic development remains largely unknown. Retinol (vitamin A) signaling, mediated by all-trans retinoic acid (RA), is essential for neural tube formation and the development of many organs in the embryo. The physiological levels of RA in cells and tissues are maintained by the retinol signaling pathway (RSP), which controls the biosynthesis of RA from dietary retinol and the catabolism of RA to polar metabolites for removal. RA is a potent activating ligand for the RAR/RXR nuclear receptors. Through RA and the receptors, the RSP modulates the expression of many developmental genes; interference with the RSP is potentially teratogenic. In this study the mouse P19 embryonal pluripotent cell, which contains a functional RSP, was used to evaluate the effects of the Corexit dispersants on retinol signaling and associated neuronal differentiation. The results showed that Corexit-EC9500A was more cytotoxic than Corexit-EC9527A to P19 cells. At non-cytotoxic doses, Corexit-EC9527A inhibited retinol-induced expression of the Hoxa1 gene, which encodes a transcription factor for the regulation of body patterning in the embryo. Such inhibition was seen in the retinol- and retinal- induced, but not RA-induced, Hoxa1 up-regulation, indicating that the Corexit chemicals primarily inhibit RA biosynthesis from retinal. In addition, Corexit-EC9527A suppressed retinol-induced P19 cell differentiation into neuronal cells, indicating potential neurotoxic effect of the chemicals under the tested conditions. The surfactant ingredient, dioctyl sodium sulfosuccinate (DOSS), may be a major contributor to the observed effect of Corexit-EC9527A in the cell.

Transplantated mesenchymal stem cells derived from embryonic stem cells promote muscle regeneration and accelerate functional recovery of injured skeletal muscle

We previously established that mesenchymal stem cells originating from mouse embryonic stem (ES) cells (E-MSCs) showed markedly higher potential for differentiation into skeletal muscles in vitro than common mesenchymal stem cells (MSCs). Further, the E-MSCs exhibited a low risk for teratoma formation. Here we evaluate the potential of E-MSCs for differentiation into skeletal muscles in vivo and reveal the regeneration and functional recovery of injured muscle by transplantation. E-MSCs were transplanted into the tibialis anterior (TA) muscle 24 h following direct clamping. After transplantation, the myogenic differentiation of E-MSCs, TA muscle regeneration, and re-innervation were morphologically analyzed. In addition, footprints and gaits of each leg under spontaneous walking were measured by CatWalk XT, and motor functions of injured TA muscles were precisely analyzed. Results indicate that >60% of transplanted E-MSCs differentiated into skeletal muscles. The cross-sectional area of the injured TA muscles of E-MSC–transplanted animals increased earlier than that of control animals. E-MSCs also promotes re-innervation of the peripheral nerves of injured muscles. Concerning function of the TA muscles, we reveal that transplantation of E-MSCs promotes the recovery of muscles. This is the first report to demonstrate by analysis of spontaneous walking that transplanted cells can accelerate the functional recovery of injured muscles. Taken together, the results show that E-MSCs have a high potential for differentiation into skeletal muscles in vivo as well as in vitro. The transplantation of E-MSCs facilitated the functional recovery of injured muscles. Therefore, E-MSCs are an efficient cell source in transplantation.

Sympathetic neurons modulate the beat rate of pluripotent cell-derived cardiomyocytes in vitro

Although stem cell-derived cardiomyocytes have great potential for the therapy of heart failure, it is unclear whether their function after grafting can be controlled by the host sympathetic nervous system, a component of the autonomic nervous system (ANS). Here we demonstrate the formation of functional connections between rat sympathetic superior cervical ganglion (SCG) neurons and pluripotent (P19.CL6) cell-derived cardiomyocytes (P19CMs) in compartmentalized co-culture, achieved using photolithographic microfabrication techniques. Formation of synapses between sympathetic neurons and P19CMs was confirmed by immunostaining with antibodies against β-3 tubulin, synapsin I and cardiac troponin-I. Changes in the beat rate of P19CMs were triggered after electrical stimulation of the co-cultured SCG neurons, and were affected by the pulse frequency of the electrical stimulation. Such changes in the beat rate were prevented when propranolol, a β-adrenoreceptor antagonist, was added to the culture medium. These results suggest that the beat rate of differentiated cardiomyocytes can be modulated by electrical stimulation of connected sympathetic neurons.

Differential effects of retinoids and inhibitors of ERK and p38 signaling on adipogenic and myogenic differentiation of P19 stem cells

All-trans-retinoic acid (atRA) is an essential signaling molecule in embryonic development. It regulates cell differentiation by activating nuclear retinoic acid receptors (RAR) and retinoid-X receptors (RXR), which both control gene expression. In addition, atRA could act in the cytoplasm by modulating the activity of mitogen-activated protein kinases (MAPK) ERK and p38, which also have a role in cell differentiation. AtRA can induce the differentiation of P19 embryonic carcinoma stem cells into adipocytes, cardiomyocytes, and skeletal muscle cells, concurrently, in the same culture. We postulated that combinations of atRA, atRA analogs exhibiting selectivity for RAR or RXR, and inhibitors of ERK and p38 signaling (ERKi and p38i) could be used to favor one mesodermal fate over the others in the P19 model. In a first series of experiments, we replaced atRA by an agonist of RXR (LG100268) or RAR (TTNPB) to preferentially stimulate one group of receptors over the other. LG100268 was as adipogenic and myogenic as atRA, whereas TTNPB strongly induced adipogenesis, but not myogenesis. ERKi enhanced the myogenic action of atRA, and p38i increased both adipogenesis and myogenesis. In a second series of experiments, we combined atRA with an RAR or RXR antagonist (RARatg or RXRatg) to preferentially deactivate each receptor group in turn. The combinations atRA+RXRatg and atRA+RARatg, including or not ERKi, had similar mesodermal actions as atRA. In contrast, there was no myogenesis with atRA+RXRatg+p38i treatment, and there were no myogenesis and no adipogenesis with the atRA+RARatg+p38i combination. Overall, the results indicate that p38 has a role in mesodermal differentiation that depends on the retinoid context. Indeed, p38 in conjunction with RXR is important in myogenesis, and p38 and RAR in adipogenesis. Under the conditions tested, it was possible to stimulate adipogenesis with a block on myogenesis, whereas increased myogenesis was accompanied by adipogenesis.

The retinol signaling pathway in mouse pluripotent P19 cells

atRA (all-trans-retinoic acid), the active metabolite of retinol (vitamin A), is essential for embryogenesis and maintenance of cellular phenotype in adults. Chemicals that interfere with the metabolism of retinol to atRA, therefore, are a human health concern. During development of a screen for disruptors of this signaling pathway, we investigated whether the mouse pluripotent P19 cell metabolizes retinol to atRA and thus can be used in a cell-based screen for disruptors of the pathway. We found that retinol induced the identical pattern of homeobox gene expression as atRA and its precursor, retinal. Retinol was 160-fold less potent than atRA as an inducer, however. In spite of its lower potency, increased Hoxa1 gene expression was detected 30 min after retinol exposure and increased 40-fold by 2 h. Rdh10 and Aldh1a2/Raldh2, which together convert retinol to atRA in the embryo, were the predominant alcohol and aldehyde dehydrogenases expressed in P19 cells. The cell expressed high mRNA levels of retinol binding proteins, Rbp1 and Rbp4, and the 13,14-dihydroretinol saturase, Retsat. It also expressed all Rar and Rxr isotypes, Crabp1&2, the three Cyp26 genes, and both β-carotene-cleaving genes, Bcmo1 and Bco2. The basal expression levels and retinol responsiveness of 25 pathway-related genes were quantitated by RT-qPCR. A test of the Aldh1a2 inhibitor, citral, showed that the disruption of the pathway was easily detected and quantitated showing that the P19 cell provides an in vitro model system for identifying and exploring the mechanism of action of chemicals that interfere with this critical cellular pathway.

CD133 positive embryonal rhabdomyosarcoma stem-like cell population is enriched in rhabdospheres

Cancer stem cells (CSCs) have been identified in a number of solid tumors, but not yet in rhabdomyosarcoma (RMS), the most frequently occurring soft tissue tumor in childhood. Hence, the aim of this study was to identify and characterize a CSC population in RMS using a functional approach. We found that embryonal rhabdomyosarcoma (eRMS) cell lines can form rhabdomyosarcoma spheres (short rhabdospheres) in stem cell medium containing defined growth factors over several passages. Using an orthotopic xenograft model, we demonstrate that a 100 fold less sphere cells result in faster tumor growth compared to the adherent population suggesting that CSCs were enriched in the sphere population. Furthermore, stem cell genes such as oct4, nanog, c-myc, pax3 and sox2 are significantly upregulated in rhabdospheres which can be differentiated into multiple lineages such as adipocytes, myocytes and neuronal cells. Surprisingly, gene expression profiles indicate that rhabdospheres show more similarities with neuronal than with hematopoietic or mesenchymal stem cells. Analysis of these profiles identified the known CSC marker CD133 as one of the genes upregulated in rhabdospheres, both on RNA and protein levels. CD133(+) sorted cells were subsequently shown to be more tumorigenic and more resistant to commonly used chemotherapeutics. Using a tissue microarray (TMA) of eRMS patients, we found that high expression of CD133 correlates with poor overall survival. Hence, CD133 could be a prognostic marker for eRMS. These experiments indicate that a CD133(+) CSC population can be enriched from eRMS which might help to develop novel targeted therapies against this pediatric tumor.

TGF-beta superfamily regulates a switch that mediates differentiation either into adipocytes or myocytes in left atrium derived pluripotent cells (LA-PCS)

Many stem cell studies have focused on the subject of cell fate and the signal molecules that modulate the regulatory switches for a given differentiation pathway. Genome-wide screens for cell fate determination signals require a cell source that differentiates purely into a single cell type. From adult rat left atrium, we established LA-PCs that differentiates into cardiac/skeletal myocytes or adipocytes with almost 100% purity. In this study, we compared gene expression profiles of undifferentiated LA-PCs with those of differentiated cells [adipocytes (Adi) or cardiac/skeletal myocytes (Myo)] to identify the signals that set the regulatory switch for adipocyte or myocyte differentiation. Microarray analysis verified the feasibility of genome-wide screening by this method. Using a pathway analysis screen, we found that members of the TGF-beta superfamily signal transduction pathways modulate the adipocyte/myocyte differentiation switch. Further analysis determined that recombinant TGF-beta inhibits adipogenesis and induces myogenesis simultaneously in a dose-dependent manner. Moreover, noggin induces differentiation into fully developed beating cardiac myocytes in vitro. These results provided new insight into the molecules that modulate the differentiation switch and validated a screening method for their identification.

Chemical induction of cardiac differentiation in p19 embryonal carcinoma stem cells

P19 cells, a pluripotent cell line derived from a teratocarcinoma induced in C3H/HeHa mice, have been widely used as a model system to study cardiac differentiation. We have used these cells to evaluate the extent to which exposure to DMSO and/or cardiogenol C for 4 days in suspension culture enhanced their differentiation into cardiomyocytes. Cardiac differentiation was assessed by observing beating clusters and further confirmed using immunocytochemical, biochemical, and pharmacological approaches. The presence of functional gap junctions in differentiated P19 cells was identified through calcium wave analyses. Proliferation rate and cell death were analyzed by BrdU incorporation and activated caspase-3 immunodetection, respectively. Beating clusters of differentiated P19 cells were only found in cultures treated with DMSO. In addition, groups treated with DMSO up-regulated cardiac troponin-T expression. However, when DMSO was used together with cardiogenol C the up-regulation was less than that with DMSO alone, approximately 1.5 times. Moreover, P19 cells cultured in DMSO or DMSO plus 0.25 microM cardiogenol C had lower proliferation rates and higher numbers of activated caspase-3-positive cells. In summary, using several methodological approaches we have demonstrated that DMSO can induce cardiac differentiation of P19 cells but that cardiogenol C does not.