Effect of bone morphogenetic protein-4 (BMP-4) on cardiomyocyte differentiation from mouse embryonic stem cell

Cardiac Differentiation of Adipose Tissue-Derived Stem Cells Is Driven by BMP4 and bFGF but Counteracted by 5-Azacytidine and Valproic Acid

Objective

Bone morphogenetic protein 4 (BMP4) and basic fibroblast growth factor (bFGF) play important roles in embryonic heart development. Also, two epigenetic modifying molecules, 5'-azacytidine (5'-Aza) and valproic acid (VPA) induce cardiomyogenesis in the infarcted heart. In this study, we first evaluated the role of BMP4 and bFGF in cardiac trans-differentiation and then the effectiveness of 5´-Aza and VPA in reprogramming and cardiac differentiation of human adipose tissue-derived stem cells (ADSCs).

Materials and Methods

In this experimental study, human ADSCs were isolated by collagenase I digestion. For cardiac differentiation, third to fifth-passaged ADSCs were treated with BMP4 alone or a combination of BMP4 and bFGF with or without 5'-Aza and VPA pre-treatment. After 21 days, the expression of cardiac-specific markers was evaluated by reverse transcription polymerase chain reaction (RT-PCR), quantitative real-time PCR, immunocytochemistry, flow cytometry and western blot analyses.

Results

BMP4 and more prominently a combination of BMP4 and bFGF induced cardiac differentiation of human ADSCs. Epigenetic modification of the ADSCs by 5'-Aza and VPA significantly upregulated the expression of OCT4A, SOX2, NANOG, Brachyury/T and GATA4 but downregulated GSC and NES mRNAs. Furthermore, pre-treatment with 5'-Aza and VPA upregulated the expression of TBX5, ANF, CX43 and CXCR4 mRNAs in three-week differentiated ADSCs but downregulated the expression of some cardiac-specific genes and decreased the population of cardiac troponin I-expressing cells.

Conclusion

Our findings demonstrated the inductive role of BMP4 and especially BMP4 and bFGF combination in cardiac trans-differentiation of human ADSCs. Treatment with 5'-Aza and VPA reprogrammed ADSCs toward a more pluripotent state and increased tendency of the ADSCs for mesodermal differentiation. Although pre-treatment with 5'-Aza and VPA counteracted the cardiogenic effects of BMP4 and bFGF, it may be in favor of migration, engraftment and survival of the ADSCs after transplantation.

Cardiac Remodeling: Endothelial Cells Have More to Say Than Just NO

The heart is a highly structured organ consisting of different cell types, including myocytes, endothelial cells, fibroblasts, stem cells, and inflammatory cells. This pluricellularity provides the opportunity of intercellular communication within the organ, with subsequent optimization of its function. Intercellular cross-talk is indispensable during cardiac development, but also plays a substantial modulatory role in the normal and failing heart of adults. More specifically, factors secreted by cardiac microvascular endothelial cells modulate cardiac performance and either positively or negatively affect cardiac remodeling. The role of endothelium-derived small molecules and peptides—for instance NO or endothelin-1—has been extensively studied and is relatively well defined. However, endothelial cells also secrete numerous larger proteins. Information on the role of these proteins in the heart is scattered throughout the literature. In this review, we will link specific proteins that modulate cardiac contractility or cardiac remodeling to their expression by cardiac microvascular endothelial cells. The following proteins will be discussed: IL-6, periostin, tenascin-C, thrombospondin, follistatin-like 1, frizzled-related protein 3, IGF-1, CTGF, dickkopf-3, BMP-2 and−4, apelin, IL-1β, placental growth factor, LIF, WISP-1, midkine, and adrenomedullin. In the future, it is likely that some of these proteins can serve as markers of cardiac remodeling and that the concept of endothelial function and dysfunction might have to be redefined as we learn more about other factors secreted by ECs besides NO.

The acceleration of cardiomyogenesis in embryonic stem cells in vitro by serum depletion does not increase the number of developed cardiomyocytes

The differentiation of pluripotent embryonic stem (ES) cells into various lineages in vitro represents an important tool for studying the mechanisms underlying mammalian embryogenesis. It is a key technique in studies evaluating the molecular mechanisms of cardiomyogenesis and heart development and also in embryotoxicology. Herein, modest modifications of the basic protocol for ES cell differentiation into cardiomyocytes were evaluated in order to increase the yield and differentiation status of developed cardiomyocytes. Primarily, the data show that ES cell cultivation in the form of non-adherent embryoid bodies (EBs) for 5 days compared to 8 days significantly improved cardiomyogenic differentiation. This is illustrated by the appearance of beating foci in the adherent EBs layer at earlier phases of differentiation from day 10 up to day 16 and by the significantly higher expression of genes characteristic of cardiomyogenic differentiation (sarcomeric alpha actinin, myosin heavy chain alpha and beta, myosin light chain 2 and 7, and transcriptional factor Nkx2.5) in EBs cultivated under non-adherent conditions for 5 days. The ratio of cardiomyocytes per other cells was also potentiated in EBs cultivated in non-adherent conditions for only 5 days followed by cultivation in adherent serum-free culture conditions. Nevertheless, the alteration in the percentage of beating foci among these two tested cultivation conditions vanished at later phases and also did not affect the total number of cardiomyocytes determined as myosin heavy chain positive cells at the end of the differentiation process on day 20. Thus, although these modifications of the conditions of ES cells differentiation may intensify cardiomyocyte differentiation, the final count of cardiomyocytes might not change. Thus, serum depletion was identified as a key factor that intensified cardiomyogenesis. Further, the treatment of EBs with N-acetylcysteine, a reactive oxygen species scavenger, did not affect the observed increase in cardiomyogenesis under serum depleted conditions. Interestingly, a mild induction of the ventricular-like phenotype of cardiomyocytes was observed in 5-day-old EBs compared to 8-day-old EBs. Overall, these findings bring crucial information on the mechanisms of ES cells differentiation into cardiomyocytes and on the establishment of efficient protocols for the cardiomyogenic differentiation of ES cells. Further, the importance of determining the absolute number of formed cardiomyocyte-like cells per seeded pluripotent cells in contrast to the simple quantification of the ratios of cells is highlighted.

Cardiomyogenesis of embryonic stem cells upon purinergic receptor activation by ADP and ATP

Purinergic signaling may be involved in embryonic development of the heart. In the present study, the effects of purinergic receptor stimulation on cardiomyogenesis of mouse embryonic stem (ES) cells were investigated. ADP or ATP increased the number of cardiac clusters and cardiac cells, as well as beating frequency. Cardiac-specific genes showed enhanced expression of α-MHC, MLC2v, α-actinin, connexin 45 (Cx45), and HCN4, on both gene and protein levels upon ADP/ATP treatment, indicating increased cardiomyogenesis and pacemaker cell differentiation. Real-time RT-PCR analysis of purinergic receptor expression demonstrated presence of P2X1, P2X4, P2X6, P2X7, P2Y1, P2Y2, P2Y4, and P2Y6 on differentiating ES cells. ATP and ADP as well as the P2X agonists β,γ-methylenadenosine 5'-triphosphate (β,γ-MetATP) and 8-bromoadenosine 5'-triphosphate (8-Br-ATP) but not UTP or UDP transiently increased the intracellular calcium concentration ([Ca(2+)](i)) as evaluated by the calcium indicator Fluo-4, whereas no changes in membrane potential were observed. [Ca(2+)](i) transients induced by ADP/ATP were abolished by the phospholipase C-β (PLC-β) inhibitor U-73122, suggesting involvement of metabotropic P2Y receptors. Furthermore, partial inhibition of [Ca(2+)](i) transients was achieved in presence of MRS2179, a selective P2Y1 receptor antagonist, whereas PPADS, a non-selective P2 receptor inhibitor, completely abolished the [Ca(2+)](i) response. Consequently, cardiomyocyte differentiation was decreased upon long term co-incubation of cells with ADP and P2 receptor antagonists. In summary, activation of purinoceptors and the subsequent [Ca(2+)](i) transients enhance the differentiation of ES cells toward cardiomyocytes. Purinergic receptor stimulation may be a promising strategy to drive the fate of pluripotent ES cells into a particular population of cardiomyocytes.

Effects of C-Reactive Protein on the Cardiac Differentiation of Mouse Embryonic Stem Cells

A major challenge in stem cell therapy for cardiac repair is how to obtain normally functioning stem cell-derived cardiomyocytes. We aim to address the effects of C-reactive protein (CRP) on the cardiac differentiation of embryonic stem (ES) cells. Immunostaining, Western blotting and electrophysiology were employed. A hundred fifty milligran/liters CRP significantly reduced the percentage of cardiomyocytes differentiated from mouse ES cells, while it may also promote sarcomere development compared to 30 mg/L CRP treatment. Further examination of the action potential (AP) in individual ES cell-derived cardiomyocytes showed that there exist three types of cardiomyocytes: artial-like (A-like), ventricular-like (V-like), and pacemaker-like (P-like). A hundred fifty milligran/liters CRP treatment decreased the P-like cardiomyocytes, whereas it increased the A-like. Such inhibitory effect and alteration were not significant at 30 mg/L CRP treatment. Moreover, 150 mg/L CRP significantly increased the APD90 (90% of duration of AP) and decreased the spontaneous firing rate of AP in P-like cells, while had little effect on other electrophysiological characteristics, including APA (AP amplitude) and MDP (maximum diastolic potential). This study revealed the effect of CRP on the cardiac differentiation of ES cells. It provides an in vitro pathological model and may be of importance to the future work of ES cell-based therapy in clinical applications and in vivo pathological studies.

Glypican4 promotes cardiac specification and differentiation by attenuating canonical Wnt and Bmp signaling

Glypicans are heparan sulphate proteoglycans (HSPGs) attached to the cell membrane by a glycosylphosphatidylinositol (GPI) anchor, and interact with various extracellular growth factors and receptors. The Drosophila division abnormal delayed (dally) was the first glypican loss-of-function mutant described that displays disrupted cell divisions in the eye and morphological defects in the wing. In human, as in most vertebrates, six glypican-encoding genes have been identified (GPC1-6), and mutations in several glypican genes cause multiple malformations including congenital heart defects. To understand better the role of glypicans during heart development, we studied the zebrafish knypek mutant, which is deficient for Gpc4. Our results demonstrate that knypek/gpc4 mutant embryos display severe cardiac defects, most apparent by a strong reduction in cardiomyocyte numbers. Cell-tracing experiments, using photoconvertable fluorescent proteins and genetic labeling, demonstrate that Gpc4 'Knypek' is required for specification of cardiac progenitor cells and their differentiation into cardiomyocytes. Mechanistically, we show that Bmp signaling is enhanced in the anterior lateral plate mesoderm of knypek/gpc4 mutants and that genetic inhibition of Bmp signaling rescues the cardiomyocyte differentiation defect observed in knypek/gpc4 embryos. In addition, canonical Wnt signaling is upregulated in knypek/gpc4 embryos, and inhibiting canonical Wnt signaling in knypek/gpc4 embryos by overexpression of the Wnt inhibitor Dkk1 restores normal cardiomyocyte numbers. Therefore, we conclude that Gpc4 is required to attenuate both canonical Wnt and Bmp signaling in the anterior lateral plate mesoderm to allow cardiac progenitor cells to specify and differentiate into cardiomyocytes. This provides a possible explanation for how congenital heart defects arise in glypican-deficient patients.

Both BMP4 and serum have significant roles in differentiation of embryonic stem cells to primitive and definitive endoderm

Differentiation of embryonic stem (ES) cells is a heterogeneous process which is influenced by different parameters, including growth and differentiation factors. The aim of the present study was to investigate the effect of bone morphogenetic protein-4 (BMP4) signaling on differentiation of mouse ES cells to endodermal lineages. For this purpose, differentiation of the ES cells was induced by embryoid body (EB) formation through hanging drop method. During the suspension stage, EBs were treated with BMP4 in a medium containing either fetal bovine serum (FBS) or knockout serum replacement (KoSR). After plating, EBs showed differentiation to a heterogeneous population of specialized cell types. Two weeks after plating, all the experimental groups expressed three germ layer markers and some primitive and definitive endoderm-specific genes. Quantitative real-time PCR analysis showed higher expression levels of Sox17, Pdx1, Cdx2 and Villin mRNAs in the KoSR plus BMP4 condition and higher Gata4 and Afp expression levels in the FBS plus BMP4 condition. Formation of visceral endoderm and derivatives of definitive endoderm was detected in the BMP4 treated EBs. In conclusion, we demonstrated that both BMP4 signaling and serum composition have significant roles in differentiation of mouse ES cells towards endodermal lineages.

Bone morphogenetic proteins: indications and uses

The BMPs are a group of growth factors that have varied roles in the development and maintenance of many organ systems. Several of the BMPs have osteogenic potential, and exert their effects via complex and highly regulated pathways. At present, only rhBMP-2 and rhBMP-7 are available for clinical use, but only rhBMP-2 is readily available, and from a practical standpoint is considered the only commercially available BMP. Only a few studies exist on BMP use in foot and ankle surgery, but these have shown promising results with low complication rates. BMP is an adjuvant to bone healing,and does not substitute for structural bone needs. In addition, rhBMP-2 outside spinal fusions is considered to be US Food and Drug Administration off-label, and should be used only in patients who are at high risk for bone healing problems.

The expression of NPPA splice variants during mouse cardiac development

Natriuretic peptide precursor-A (NPPA) is an early and specific marker for functional myocardium of the embryonic heart. NPPA gene encodes for a precursor of atrial natriuretic peptide (ANP). So far, three alternatively spliced variants have been reported for NPPA in human. In mouse, no alternatively spliced transcript of NPPA has been reported. In the current study, we investigated the expression of NPPA gene during cardiac differentiation of mouse adipose-tissue-derived stem cells (ADSCs) and embryonic stem (ES) cells. As revealed by reverse-transcription polymerase chain reaction analysis, 2-week-differentiated cells expressed some cardiac-specific makers, including ANP. Three additional intron-retained splice variants of NPPA were also detected during cardiac differentiation of the ADSCs and ES cells. In addition, we detected three intron-retained splice variants of NPPA in 8.5-day mouse embryonic heart. In the mature cardiomyocytes of 1-week-old mice, only the correctly spliced isoform of NPPA gene was expressed. Freshly isolated stromal vascular fraction also expressed one intron-retained isoform of NPPA gene. In conclusion, our findings have provided evidence for the expression of intron-retained splices of NPPA mRNA during the early stages of mouse cardiogenesis as well as in the mouse adipose tissue.

Atrial and ventricular specification of ADSCs is stimulated by different doses of BMP4

To investigate the effect of BMP4 on cardiomyocyte differentiation of adipose tissue-derived stem cells (ADSCs), mouse ADSCs were treated with different concentrations of BMP4 in media containing fetal bovine serum (FBS) or Knockout™ Serum Replacement (KoSR). 3 weeks after cardiac induction, differentiated ADSCs expressed some cardiac-specific genes and proteins. BMP4 treatment upregulated the expression of cardiac transcription factors. In both FBS and KoSR-supplemented media, lower concentrations of BMP4 had a positive effect on the expression of MLC2A gene, while MLC2V was more expressed with higher concentrations of BMP4. BMP4 treatment in KoSR supplemented medium was more efficient for cardiac induction. Supplementation of culture media with insulin-transferrin-selenium improved the expression of MLC2A gene. The results of this study indicated that BMP4 is important for cardiac differentiation of the ADSCs. However, BMP4 was not enough for structural and functional maturation of the ADSC-derived cardiomyocytes.

Regulation of PTEN/Akt pathway enhances cardiomyogenesis and attenuates adverse left ventricular remodeling following thymosin β4 Overexpressing embryonic stem cell transplantation in the infarcted heart

Thymosin β4 (Tβ4), a small G-actin sequestering peptide, mediates cell proliferation, migration, and angiogenesis. Whether embryonic stem (ES) cells, overexpressing Tβ4, readily differentiate into cardiac myocytes in vitro and in vivo and enhance cardioprotection following transplantation post myocardial infarction (MI) remains unknown. Accordingly, we established stable mouse ES cell lines, RFP-ESCs and Tβ4-ESCs, expressing RFP and an RFP-Tβ4 fusion protein, respectively. In vitro, the number of spontaneously beating embryoid bodies (EBs) was significantly increased in Tβ4-ESCs at day 9, 12 and 15, compared with RFP-ESCs. Enhanced expression of cardiac transcriptional factors GATA-4, Mef2c and Txb6 in Tβ4-EBs, as confirmed with real time-PCR analysis, was accompanied by the increased number of EB areas stained positive for sarcomeric α-actin in Tβ4-EBs, compared with the RFP control, suggesting a significant increase in functional cardiac myocytes. Furthermore, we transplanted Tβ4-ESCs into the infarcted mouse heart and performed morphological and functional analysis 2 weeks after MI. There was a significant increase in newly formed cardiac myocytes associated with the Notch pathway, a decrease in apoptotic nuclei mediated by an increase in Akt and a decrease in levels of PTEN. Cardiac fibrosis was significantly reduced, and left ventricular function was significantly augmented in the Tβ4-ESC transplanted group, compared with controls. It is concluded that genetically modified Tβ4-ESCs, potentiates their ability to turn into cardiac myocytes in vitro as well as in vivo. Moreover, we also demonstrate that there was a significant decrease in both cardiac apoptosis and fibrosis, thus improving cardiac function in the infarcted heart.

Angiotensin II promotes cardiac differentiation of embryonic stem cells via angiotensin type 1 receptor

As embryonic stem cells (ESCs) represent an attractive candidate cell source for obtaining cardiomyocytes to be used in cell replacement therapy, it is thus of considerable importance to understand the mechanism by which cardiac differentiation is regulated. In previous studies, we have shown that angiotensin type 1 receptor (AT1R) expressed in cardiomyocytes derived from mouse embryonic stem cells. However, little is known about the role of AT1R in cardiac differentiation, which plays a key role in cardiac physiology and pharmacology. In the present study, we demonstrated that AT1R agonist significantly enhanced cardiac differentiation as determined by increased percentage of beating embryoid bodies and a higher expression level of cardiac markers. On the contrary, AT1R agonist stimulated differentiation was reversed in the presence of AT1R antagonist. In addition, by administering selective inhibitors we found that the effect of AT1R was driven via extracellular-signal regulated kinase, c-Jun NH2-terminal kinase and p38 mitogen-activated protein kinase pathways. These findings suggest that AT1R signaling plays a key role in cardiac differentiation of ESCs.

Stem cell and tissue engineering research in the Islamic republic of Iran

During the last few years, the Islamic republic of Iran has consistently grown in nearly all scientific fields and achieved considerable success in producing science and developing technology. The Iranian government and scientific community have jointly started programs to support the creation of new scientific opportunities and technology platforms for research in the domain of stem cell and tissue engineering. In addition, clinical translation of basic researches in the fields of stem cell and regenerative medicine has been amongst the top priorities. Interestingly, the public sector, media, and authorities are also actively monitoring these attainments. In spite of this nationwide interest, however, there is currently a dearth of analytical information on these accomplishments. To address this issue, here we introduce the key decisions made by the country's policy makers and also review some of the Iranian researchers' publications in this field.

Impact of stirred suspension bioreactor culture on the differentiation of murine embryonic stem cells into cardiomyocytes

Background

Embryonic stem cells (ESCs) can proliferate endlessly and are able to differentiate into all cell lineages that make up the adult organism. Under particular in vitro culture conditions, ESCs can be expanded and induced to differentiate into cardiomyocytes in stirred suspension bioreactors (SSBs). However, in using these systems we must be cognizant of the mechanical forces acting upon the cells. The effect of mechanical forces and shear stress on ESC pluripotency and differentiation has yet to be clarified. The purpose of this study was to investigate the impact of the suspension culture environment on ESC pluripotency during cardiomyocyte differentiation.

Results

Murine D3-MHC-neo^r ESCs formed embyroid bodies (EBs) and differentiated into cardiomyocytes over 25 days in static culture and suspension bioreactors. G418 (Geneticin) was used in both systems from day 10 to enrich for cardiomyocytes by eliminating non-resistant, undifferentiated cells. Treatment of EBs with 1 mM ascorbic acid and 0.5% dimethyl sulfoxide from day 3 markedly increased the number of beating EBs, which displayed spontaneous and cadenced contractile beating on day 11 in the bioreactor. Our results showed that the bioreactor differentiated cells displayed the characteristics of fully functional cardiomyocytes. Remarkably, however, our results demonstrated that the bioreactor differentiated ESCs retained their ability to express pluripotency markers, to form ESC-like colonies, and to generate teratomas upon transplantation, whereas the cells differentiated in adherent culture lost these characteristics.

Conclusions

This study demonstrates that although cardiomyocyte differentiation can be achieved in stirred suspension bioreactors, the addition of medium enhancers is not adequate to force complete differentiation as fluid shear forces appear to maintain a subpopulation of cells in a transient pluripotent state. The development of successful ESC differentiation protocols within suspension bioreactors demands a more complete understanding of the impacts of shear forces on the regulation of pluripotency and differentiation in pluripotent stem cells.

Electron microscopic study of mouse embryonic stem cell-derived cardiomyocytes

Differentiation of embryonic stem cell (ESC)-derived embryoid bodies (EBs) is a heterogeneous process. ESCs can differentiate in vitro into different cell types including beating cardiomyocytes. The main aim of the present study was to develop an improved preparation method for scanning electron microscopic study of ESC-derived cardiac bundles and to investigate the fine structural characteristics of mouse ESCs-derived cardiomyocytes using electron microscopy. The mouse ESCs differentiation was induced by EBs' development through hanging drop, suspension and plating stages. Cardiomyocytes appeared in the EBs' outgrowth as beating clusters that grew in size and formed thick branching bundles gradually. Cardiac bundles showed cross striation even when they were observed under an inverted microscope. They showed a positive immunostaining for cardiac troponin I and α-actinin. Transmission and scanning electron microscopy (TEM & SEM) were used to study the structural characteristics of ESC-derived cardiomyocytes. Three weeks after plating, differentiated EBs showed a superficial layer of compact fibrous ECM that made detailed observation of cardiac bundles impossible. We tried several preparation methods to remove unwanted cells and fibers, and finally we revealed the branching bundles of cardiomyocytes. In TEM study, most cardiomyocytes showed parallel arrays of myofibrils with a mature sarcomeric organization marked by H-bands, M-lines and numerous T-tubules. Cardiomyocytes were connected to each other by intercalated discs composed of numerous gap junctions and fascia adherences.

Beta-adrenergic signals regulate cardiac differentiation of mouse embryonic stem cells via mitogen-activated protein kinase pathways

As embryonic stem cell-derived cardiomyocytes (ESC-CMs) have the potential to be used in cell replacement therapy, an understanding of the signaling mechanisms that regulate their terminal differentiation is imperative. In previous studies, we discovered the presence of adrenergic and muscarinic receptors in mouse embryonic stem cells (ESCs). However, little is known about the role of these receptors in cardiac differentiation and development, which is critically important in cardiac physiology and pharmacology. Here, we demonstrated that a β-adrenergic receptor (β-AR) agonist significantly enhanced cardiac differentiation as indicated by a higher percentage of beating embryoid bodies and a higher expression level of cardiac markers. Application of β1-AR and β2-AR antagonists partly abolished the effect of the β-AR agonist. In addition, by administering selective inhibitors we found that the effect of β-AR was driven via p38 mitogen-activated protein kinase and extracellular-signal regulated kinase pathway. These findings suggest that ESCs are also a target for β-adrenergic regulation and β-adrenergic signaling plays a role in ESC cardiac differentiation.

Exogenous expression of human apoA-I enhances cardiac differentiation of pluripotent stem cells

The cardioprotective effects of high-density lipoprotein cholesterol (HDL-C) and apolipoprotein A1 (apoA-I) are well documented, but their effects in the direction of the cardiac differentiation of embryonic stem cells are unknown. We evaluated the effects of exogenous apoA-I expression on cardiac differentiation of ESCs and maturation of ESC-derived cardiomyocytes. We stably over-expressed full-length human apoA-I cDNA with lentivirus (LV)-mediated gene transfer in undifferentiated mouse ESCs and human induced pluripotent stem cells. Upon cardiac differentiation, we observed a significantly higher percentage of beating embryoid bodies, an increased number of cardiomyocytes as determined by flow cytometry, and expression of cardiac markers including α-myosin heavy chain, β-myosin heavy chain and myosin light chain 2 ventricular transcripts in LV-apoA-I transduced ESCs compared with control (LV-GFP). In the presence of noggin, a BMP4 antagonist, activation of BMP4-SMAD signaling cascade in apoA-I transduced ESCs completely abolished the apoA-I stimulated cardiac differentiation. Furthermore, co-application of recombinant apoA-I and BMP4 synergistically increased the percentage of beating EBs derived from untransduced D3 ESCs. These together suggests that that pro-cardiogenic apoA-I is mediated via the BMP4-SMAD signaling pathway. Functionally, cardiomyocytes derived from the apoA-I-transduced cells exhibited improved calcium handling properties in both non-caffeine and caffeine-induced calcium transient, suggesting that apoA-I plays a role in enhancing cardiac maturation. This increased cardiac differentiation and maturation has also been observed in human iPSCs, providing further evidence of the beneficial effects of apoA-I in promoting cardiac differentiation. In Conclusion, we present novel experimental evidence that apoA-I enhances cardiac differentiation of ESCs and iPSCs and promotes maturation of the calcium handling property of ESC-derived cardiomyocytes via the BMP4/SMAD signaling pathway.

Transforming growth factor-beta superfamily in mouse embryonic stem cell self-renewal

Embryonic stem (ES) cells are pluripotent cells that maintain the capability of undifferentiated self-renewal in culture. As mouse ES cells have the capacity to give rise to all the tissues of the body, they are an excellent developmental biology model system and a model for regenerative therapies. The extracellular cues and the intracellular signaling cascades that regulate ES cell self-renewal and cell-fate choices are complex and actively studied. Many developmental signaling pathways regulate the ES cell phenotype, and their intracellular programs interact to modulate the gene networks controlling ES cell pluripotency. This review focuses on the current understanding and outstanding questions of the roles of the transforming growth factor-beta-related signaling pathways in regulating pluripotency and differentiation of mouse ES cells. The complex dichotomic roles of bone morphogenetic protein signaling in maintaining the undifferentiated state and also inducing specific cell fates will be reviewed. The emerging roles of Nodal signaling in ES cell self-renewal will also be discussed.

Cardiac cell generation from encapsulated embryonic stem cells in static and scalable culture systems

Heart diseases are major causes of morbidity and mortality linked to extensive loss of cardiac cells. Embryonic stem cells (ESCs) give rise to cardiomyocyte-like cells, which may be used in heart cell replacement therapies. Most cardiogenic differentiation protocols involve the culture of ESCs as embryoid bodies (EBs). Stirred-suspension bioreactor cultures of ESC aggregates may be employed for scaling up the production of cardiomyocyte progeny but the wide range of EB sizes and the unknown effects of the hydrodynamic environment on differentiating EBs are some of the major challenges in tightly controlling the differentiation outcome. Here, we explored the cardiogenic potential of mouse ESCs (mESCs) and human ESCs (hESCs) encapsulated in poly-L-lysine (pLL)-coated alginate capsules. Liquefaction of the capsule core led to the formation of single ESC aggregates within each bead and their average size depended on the concentration of seeded ESCs. Encapsulated mESCs were directed along cardiomyogenic lineages in dishes under serum-free conditions with the addition of bone morphogenetic protein 4 (BMP4). Human ESCs in pLL-layered liquid core (LC) alginate beads were also differentiated towards heart cells in serum-containing media. Besides the robust cell proliferation, higher fractions of cells expressing cardiac markers were detected in ESCs encapsulated in LC than in solid beads. Furthermore, we demonstrated for the first time that ESCs encapsulated in pLL-layered LC alginate beads can be coaxed towards heart cells in stirred-suspension bioreactors. Encapsulated ESCs yielded higher fractions of Nkx2.5- and GATA4-positive cells in the bioreactor compared to dish cultures. Differentiated cells formed beating foci that responded to chronotropic agents in an organotypic manner. Our findings warrant further development and implementation of microencapsulation technologies in conjunction with bioreactor cultivation to enable the production of stem cell-derived cardiac cells appropriate for clinical therapies and applications.

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.

Spontaneously beating cardiomyocytes derived from white mature adipocytes

AIMS

Adipose stromal cells and dissociated brown adipose tissue have been shown to generate cardiomyocyte-like cells. However, it is not clear whether white mature adipocytes have the same potential, even though a close relationship has been found between adipocytes and vascular endothelial cells, another cardiovascular cell type. The objective of this study was to examine if white adipocytes would be able to supply cardiomyocytes.

METHODS AND RESULTS

We prepared a highly purified population of lipid-filled adipocytes from mice, 6-7 weeks of age. When allowed to lose lipids, the adipocytes assumed a fibroblast-like morphology, so-called dedifferentiated fat (DFAT) cells. Subsequently, 10-15% of the DFAT cells spontaneously differentiated into cardiomyocyte-like cells, in which the cardiomyocyte phenotype was identified by morphological observations, expression of cardiomyocyte-specific markers, and immunocytochemical staining. In addition, electrophysiological studies revealed pacemaker activity in these cells, and functional studies showed that a beta-adrenergic agonist stimulated the beating rate, whereas a beta-antagonist reduced it. In vitro treatment of newly isolated adipocytes or DFAT cells with inhibitors of bone morphogenetic proteins (BMP) and Wnt signalling promoted the development of the cardiomyocyte phenotype as determined by the number or beating colonies of cardiomyocyte-like cells and expression of troponin I, a cardiomyocyte-specific marker. Inhibition of BMP was most effective in promoting the cardiomyocyte phenotype in adipocytes, whereas Wnt-inhibition was most effective in DFAT cells.

CONCLUSION

White mature adipocytes can differentiate into cardiomyocyte-like cells, suggesting a link between adipocyte and cardiomyocyte differentiation.

Recombinant bone morphogenetic protein-2 (rhBMP-2) in high-risk ankle and hindfoot fusions

BACKGROUND

The purpose of this study was to evaluate the effect of rhBMP-2 on bone healing in patients who undergo high-risk ankle & hindfoot fusions.

MATERIALS & METHODS

Patients who underwent high-risk, elective ankle and hindfoot fusions treated with rhBMP-2 augmentation were reviewed for clinical outcomes and complications. A total of 112 fusion sites (69 patients) were reviewed for analysis. The mean age of the patients was 52 years (range, 21 to 84 years). There were 37 males (53%) and 32 females (47%). Forty-four patients (64%) were smokers and 13 patients (19%) were diabetic. A history of high-energy trauma was present in 47 (68%) patients and avascular necrosis of the talus was present in 22 patients (32%). Forty-five patients (65%) had multiple risk-factors. The exclusion criteria were peripheral vascular disease, infection, and patients who were not available for the usual follow-up protocol. Internal and/or external fixation was utilized for ankle and hindfoot fusions. Bone graft was used only for patients who had defects or malalignment. Postoperatively, nonweightbearing radiographs were taken every 2 to 4 weeks (3 views per site). When plain radiographic union was evident, a confirmatory CT scan was obtained.

RESULTS

Overall, 108 fusion sites went on to union (96% union rate) at a mean time of 11 weeks (as assessed by a CT scan) [ankle joint at 10 weeks; subtalar joint at 12.3 weeks; talonavicular joint at 12.7 weeks and calcaneocuboid joint at 10.9 weeks]. Different union times between ankle, subtalar, talonavicular, and calcaneocuboid joint were not significant (p = 0.2571, Kruskal-Wallis Test Nonparametric ANOVA). All sites: [No graft] vs. [Autograft] vs. [Allograft]: p = 0.2421 (Kruskal-Wallis Test Nonparametric ANOVA), were not statistically significant. Complications included nonunion in 5 of 112 joints in 3 patients (4% joint nonunion rate; 4% patient nonunion rate) [subtalar joint, n = 2; talonavicular joint, n = 1; and calcaneocuboid joint, n = 1]. Two patients had wound complications and one other patient had a deep infection; all were successfully treated with local wound care, negative-pressure dressings and antibiotics.

CONCLUSION

We believe rhBMP-2 is an effective adjunct for bone healing in patients who undergo high-risk ankle and hindfoot fusions. Low complication rates were observed in this study.

Effects of TGF-beta1 and hydrostatic pressure on meniscus cell-seeded scaffolds

The combinatorial effects of TGF-beta1 and hydrostatic pressure (HP) were investigated on meniscus cell-seeded PLLA constructs using a two-phase sequential study. The objective was to identify potentially synergistic effects of these stimuli toward enhancing the biomechanical and compositional characteristics of the engineered constructs. In Phase I, the effects of TGF-beta1 were examined on the ability of meniscus cells to produce ECM. In Phase II, meniscus cell-seeded PLLA constructs were cultured for 4 wks with a combination of TGF-beta1 and HP (10 MPa, 0 Hz or 10 MPa, 0.1 Hz). TGF-beta1 was found to increase collagen and GAG deposition in the scaffolds 15-fold and 8-fold, respectively, in Phase I. In Phase II, the combination of TGF-beta1 and 10 MPa, 0 Hz HP resulted in 4-fold higher collagen deposition (additive increase), 3-fold higher GAG deposition and enhanced compressive properties (additive and synergistic increases), when compared to the unpressurized no growth factor culture control. Though significant correlations were observed between the compressive properties (moduli and viscosity), and the GAG and collagen content of the constructs, the correlations were stronger with collagen. This study provides robust evidence that growth factors and HP can be used successfully in combination to enhance the functional properties of in vitro engineered knee meniscus constructs.

Embryonic stem cell transplantation: promise and progress in the treatment of heart disease

Cardiovascular diseases remain the leading cause of death worldwide, and the burden is equally shared between men and women around the globe. Cardiomyocytes that die in response to disease processes or aging are replaced by scar tissue instead of new muscle cells. Although recent reports suggest an intrinsic capacity for the mammalian myocardium to regenerate via endogenous stem/progenitor cells, the magnitude of such a response appears to be minimal and has yet to be realized fully in cardiovascular patients. Despite the advances in pharmacotherapy and new biomedical technologies, the prognosis for patients diagnosed with end-stage heart failure appears to be grave. While heart transplantation is a viable option, this life-saving intervention suffers from an acute shortage of cardiac organ donors. In view of these existing issues, donor cell transplantation is emerging as a promising strategy to regenerate diseased myocardium. Studies from multiple laboratories have shown that transplantation of donor cells (e.g. fetal cardiomyocytes, skeletal myoblasts, smooth muscle cells, and adult stem cells) can improve the function of diseased hearts over a short period of time (1-4 weeks). While long-term follow-up studies are warranted, it is generally perceived that the beneficial effects of transplanted cells are mainly due to increased angiogenesis or favorable scar remodeling in the engrafted myocardium. Although skeletal myoblasts and bone marrow stem cells hold the highest potential for implementation of autologous therapies, initial results from phase I trials are not promising. In contrast, transplantation of fetal cardiomyocytes has been shown to confer protection against the induction of ventricular tachycardia in experimental myocardial injury models. Furthermore, results from multiple laboratories suggest that fetal cardiomyocytes can couple functionally with host myocytes, stimulate formation of new blood vessels, and improve myocardial function. While it is neither practical nor ethical to test the potential of fetal cardiomyocytes in clinical trials, embryonic stem (ES) cells serve as a novel source for generation of unlimited quantities of cardiomyocytes for myocardial repair. The initial success in the application of ES cells to partially repair and improve myocardial function in experimental models of heart disease has been quite promising. However, multiple hurdles need to be crossed before the potential benefits of ES cells can be translated to the clinic. In this review, we summarize the current knowledge of cardiomyocyte derivation and enrichment from ES-cell cultures and provide a brief survey of factors increasing cardiomyogenic induction in both mouse and human ES cultures. Subsequently, we summarize the current state of research using mouse and human ES cells for the treatment of heart disease in various experimental models. Furthermore, we discuss the challenges that need to be overcome prior to the successful clinical utilization of ES-derived cardiomyocytes for the treatment of end-stage heart disease. While we are optimistic that the researchers in this field will sail across the hurdles, we also suggest that a more cautious approach to the validation of ES cardiomyocytes in experimental models would certainly prevent future disappointments, as seen with skeletal myoblast studies.

Effect of bone morphogenetic protein-4 on cardiac differentiation from mouse embryonic stem cells in serum-free and low-serum media

In spite of previous reports, the precise role of bone morphogenetic proteins (BMPs) on cardiomyocyte differentiation, especially in the absence or presence of minimum amount of serum in culture medium is still unclear. So, the aim of the present study was to investigate the effect of BMP-4 on mouse embryonic stem cells (ESCs)-derived cardiomyocyte differentiation in serum-free and low-serum media. The mouse ESCs differentiation to cardiomyocytes was induced by embryoid bodies' (EBs') development through hanging drop, suspension and plating stages. Different models of differentiation were designed according to addition of fetal bovine serum (FBS) or knockout serum replacement (KoSR) to the medium of three stages. 10 ng/ml BMP-4 was added throughout the suspension period. Up to 30 days after plating, contraction and beating frequency were monitored and evaluated daily. The growth characteristics of cardiomyocytes were assessed by cardioactive drugs, immunocytochemistry, transmission electron microscopy (TEM) and reverse transcription-polymerase chain reaction (RT-PCR). In the complete absence of serum, neither control nor BMP-4 treated groups resulted in cardiac differentiation. Addition of FBS to hanging drop stage resulted in the appearance of beating cardiac clusters in some BMP-4 treated EBs. In the best designed differentiation model in which only hanging drop and the first 24 h of plating stage was carried out at the presence of FBS, the BMP-4 treatment resulted in cardiac differentiation in EBs characterized by positive immunostaining for the applied antibodies, chronotropic response to the cardioactive drugs and cardiac-specific genes expression at different developmental stages. These cardiomyocytes showed immature myofibrils and numerous intercellular junctions. In conclusion, BMP-4 is unable to induce cardiomyocyte differentiation from mouse ESCs in serum-free models, and at least small amount of FBS in hanging drop stage is necessary. Furthermore, serum factors are not strictly necessary after the initial activation, but they do favor a better differentiation of cardiomyocytes.