Stimulation of ES-cell-derived cardiomyogenesis and neonatal cardiac cell proliferation by reactive oxygen species and NADPH oxidase

The permeability transition pore controls cardiac mitochondrial maturation and myocyte differentiation

Although mature myocytes rely on mitochondria as the primary source of energy, the role of mitochondria in the developing heart is not well known. Here, we find that closure of the mitochondrial permeability transition pore (mPTP) drives maturation of mitochondrial structure and function and myocyte differentiation. Cardiomyocytes at embryonic day (E) 9.5, when compared to E13.5, displayed fragmented mitochondria with few cristae, a less-polarized mitochondrial membrane potential, higher reactive oxygen species (ROS) levels, and an open mPTP. Pharmacologic and genetic closing of the mPTP yielded maturation of mitochondrial structure and function, lowered ROS, and increased myocyte differentiation (measured by counting Z bands). Furthermore, myocyte differentiation was inhibited and enhanced with oxidant and antioxidant treatment, respectively, suggesting that redox-signaling pathways lie downstream of mitochondria to regulate cardiac myocyte differentiation.

Mitochondria determine the differentiation potential of cardiac mesoangioblasts

An understanding of cardiac progenitor cell biology would facilitate their therapeutic potential for cardiomyocyte restoration and functional heart repair. Our previous studies identified cardiac mesoangioblasts as precommitted progenitor cells from the postnatal heart, which can be expanded in vitro and efficiently differentiated in vitro and in vivo to contribute new myocardium after injury.Based on their proliferation potential in culture, we show here that two populations of mesoangioblasts can be isolated from explant cultures of mouse and human heart.Although both populations express similar surface markers, together with a panel of instructive cardiac transcription factors, they differ significantly in their cellular content of mitochondria. Slow dividing (SD) cells, containing many mitochondria, can be efficiently differentiated with 5-azacytidine (5-aza) to generate cardiomyocytes expressing mature structural markers. In contrast, fast dividing (FD) mesoangioblasts, which contain decreased quantities of mitochondria, do not respond to 5-aza treatment.Notably, increasing mitochondrial numbers using pharmacological nitric oxide (NO) donors reverses the differentiation block in FD mesoangioblasts and leads to a progressive maturation to cardiomyocytes; conversely decreasing mitochondrial content, using respiratory chain inhibitors and chloramphenicol, perturbs cardiomyocyte differentiation in SD populations. Furthermore, isolated cardiac mesoangioblasts from aged mouse and human hearts are found to be almost exclusively mitochondria low FD populations, which are permissive for cardiomyocyte differentiation only after NO treatment. Taken together,this study illustrates a key role for mitochondria in cardiac mesoangioblast differentiation and raises the interesting possibility that treatments, which increase cellular mitochondrial content, may have utility for cardiac stem cell therapy.

Redox modification of cell signaling in the cardiovascular system

Oxidative stress is presumed to be involved in the pathogenesis of many diseases, including cardiovascular disease. However, oxidants are also generated in healthy cells, and increasing evidence suggests that they can act as signaling molecules. The intracellular reduction-oxidation (redox) status is tightly regulated by oxidant and antioxidant systems. Imbalance between them causes oxidative or reductive stress which triggers cellular damage or aberrant signaling, leading to dysregulation. In this review, we will briefly summarize the aspects of ROS generation and neutralization mechanisms in the cardiovascular system. ROS can regulate cell signaling through oxidation and reduction of specific amino acids within proteins. Structural changes during post-translational modification allow modification of protein activity which can result in altered cellular function. We will focus on the molecular basis of redox protein modification and how this regulatory mechanism affects signal transduction in the cardiovascular system. Finally, we will discuss some techniques applied to monitoring redox status and identifying redox-sensitive proteins in the heart. This article is part of a Special Section entitled "Post-translational Modification."

NADPH oxidase and eNOS control cardiomyogenesis in mouse embryonic stem cells on ascorbic acid treatment

Ascorbic acid (AA) increases cardiomyogenesis of embryonic stem (ES) cells. Herein we show that treatment of mouse ES cells with AA enhanced cardiac differentiation accompanied by an upregulation of the NADPH oxidase isoforms NOX2 and NOX4, phosphorylation of endothelial nitric oxide synthase (eNOS), and cyclic GMP (cGMP) formation, indicating that reactive oxygen species (ROS) as well as nitric oxide (NO) may be involved in cardiomyogenesis. In whole mount embryoid bodies as well as isolated Flk-1-positive (Flk-1(+)) cardiovascular progenitor cells ROS elevation by AA was observed in early stages of differentiation (Days 4-7), and absent at Day 10. In contrast NO generation following incubation with AA was absent at Day 4 and increased at Days 7 and 10. AA-mediated cardiomyogenesis was blunted by the NADPH oxidase inhibitors diphenylen iodonium (DPI) and apocynin, the free radical scavengers N-(2-mercaptopropionyl)-glycine (NMPG) and ebselen, and the NOS inhibitor L-NAME. Downregulation of NOX4 by short hairpin RNA (shRNA) resulted in significant inhibition of cardiomyogenesis and abolished the stimulation of MHC-ß and MLC2v gene expression observed on AA treatment. Our data demonstrate that AA stimulates cardiomyocyte differentiation from ES cells by signaling pathways that involve ROS generated at early stages and NO at late stages of cardiomyogenesis.

Maternal Oct1/2 is required for Nodal and Vg1/Univin expression during dorsal-ventral axis specification in the sea urchin embryo

The TGFβ family member Nodal is expressed early in the presumptive ventral ectoderm of the early sea urchin embryo and its activity is crucial for dorsal-ventral (D/V) axis specification. Analysis of the nodal promoter identified a number of critical binding sites for transcription factors of different families including Sox, Oct, TCF and bZIP, but in most cases the specific factors that regulate nodal expression are not known. In this study, we report that the maternal factor Oct1/2 functions as a positive regulator of nodal and that its activity is essential for the initiation of nodal expression. Inhibition of Oct1/2 mRNA translation produced embryos with severe axial defects similar to those observed following inhibition of Nodal function. We show that perturbing Oct1/2 function specifically disrupted specification of the ventral and dorsal ectodermal regions and that these effects were caused by the failure of nodal to be expressed early in development. Furthermore, we identified the key gene vg1/univin, which is also necessary for nodal expression, as an additional factor that was completely dependent on Oct1/2 for its zygotic expression. These data demonstrate that the maternal Oct1/2 protein plays an early and essential role in D/V axis specification by initiating the expression of nodal and vg1/univin, two genes that act at the top of the D/V ectoderm gene regulatory network.

Bioenergetics, mitochondria, and cardiac myocyte differentiation

Cardiac metabolism is finely tuned, and disruption of myocardial bioenergetics can be clinically devastating. Many cardiomyopathies that present early in life are due to disruption of the maturation of these metabolic pathways. However, this bioenergetic maturation begins well before birth, when the embryonic heart is first beginning to beat, and continues into the mature animal. Thus, the changes in energy production seen after birth are actually part of a continuum that coincides with the structural and functional changes that occur as the cardiac myocyte differentiates and the heart undergoes morphogenesis. Therefore, although bioenergetics and mitochondrial biology have not been studied in great detail in the developing heart, bioenergetic maturation should be considered an important component of normal myocyte differentiation.Although events occurring after birth will be discussed, this review will focus on the changes in bioenergetics and mitochondrial biology that coincide with myocyte differentiation and cardiac morphogenesis. The relationship of these changes to the etiology and presentation of cardiomyopathies will be used as a starting point for this discussion. Then, after reviewing cardiac development and mitochondrial biology, the published data on bioenergetics and mitochondrial structure and function in the developing heart will be presented. Finally, the case will be made that mitochondria may be critical regulators of cardiac myocyte differentiation and cardiac development.

Stimulation of cardiomyogenesis of embryonic stem cells by nitric oxide downstream of AMP-activated protein kinase and mTOR signaling pathways

Nitric oxide (NO) is a key regulator of cardiomyogenesis of embryonic stem (ES) cells. However, signaling pathways involving the energy sensor AMP-activated protein kinase (AMPK) and/or mammalian target of rapamycin (mTOR) resulting in NO generation and stimulation of cardiomyogenesis are currently not known. Herein, the role of AMPK- versus mTOR-regulated signaling pathways and the impact of NO for cardiomyogenesis of mouse ES cells were investigated. Activation of AMPK by 5-amino-4-imidazolecarboxamide riboside (AICAr) or metformin as well as inactivation of AMPK by compound C (Comp C), siRNA ablation of AMPKα2, or exogenous ATP stimulated cardiomyogenesis of ES cells. Inhibition of AMPK by Comp C resulted in phosphorylation of mTOR and generation of NO. NO generation was likewise achieved when AMPK was either activated by AICAr or mTOR was inhibited by rapamycin, suggesting that NO generation occurred by two mutually active parallel signaling pathways, one being AMPK dependent and mTOR independent (AICAr pathway) and the other being AMPK independent and mTOR dependent (Comp C pathway). Consequently, cardiomyogenesis as well as NO generation was completely abrogated when ES cells were cultivated in the presence of rapamycin and Comp C, which inhibit both signaling pathways. The impact of NO for cardiomyogenesis of ES cells was corroborated in experiments showing that the effects of Comp C on cardiomyogenesis of ES cells were abolished by the NO synthase inhibitors NG-monomethyl-l-arginine and N (G)-nitro-l-arginine methyl ester. In summary, our data demonstrate that NO generation downstream of AMPK and mTOR is activated by distinct, interacting signaling pathways that initiate cardiomyogenesis of ES cells.

Redox signaling in cardiac myocytes

The heart has complex mechanisms that facilitate the maintenance of an oxygen supply-demand balance necessary for its contractile function in response to physiological fluctuations in workload as well as in response to chronic stresses such as hypoxia, ischemia, and overload. Redox-sensitive signaling pathways are centrally involved in many of these homeostatic and stress-response mechanisms. Here, we review the main redox-regulated pathways that are involved in cardiac myocyte excitation-contraction coupling, differentiation, hypertrophy, and stress responses. We discuss specific sources of endogenously generated reactive oxygen species (e.g., mitochondria and NADPH oxidases of the Nox family), the particular pathways and processes that they affect, the role of modulators such as thioredoxin, and the specific molecular mechanisms that are involved-where this knowledge is available. A better understanding of this complex regulatory system may allow the development of more specific therapeutic strategies for heart diseases.

Mitochondrial H2O2 generated from electron transport chain complex I stimulates muscle differentiation

Mitochondrial reactive oxygen species (mROS) have been considered detrimental to cells. However, their physiological roles as signaling mediators have not been thoroughly explored. Here, we investigated whether mROS generated from mitochondrial electron transport chain (mETC) complex I stimulated muscle differentiation. Our results showed that the quantity of mROS was increased and that manganese superoxide dismutase (MnSOD) was induced via NF-κB activation during muscle differentiation. Mitochondria-targeted antioxidants (MitoQ and MitoTEMPOL) and mitochondria-targeted catalase decreased mROS quantity and suppressed muscle differentiation without affecting the amount of ATP. Mitochondrial alterations, including the induction of mitochondrial transcription factor A and an increase in the number and size of mitochondria, and functional activations were observed during muscle differentiation. In particular, increased expression levels of mETC complex I subunits and a higher activity of complex I than other complexes were observed. Rotenone, an inhibitor of mETC complex I, decreased the mitochondrial NADH/NAD(+) ratio and mROS levels during muscle differentiation. The inhibition of complex I using small interfering RNAs and rotenone reduced mROS levels, suppressed muscle differentiation, and depleted ATP levels with a concomitant increase in glycolysis. From these results, we conclude that complex I-derived O(2)·(-), produced through reverse electron transport due to enhanced metabolism and a high activity of complex I, was dismutated into H(2)O(2) by MnSOD induced via NF-κB activation and that the dismutated mH(2)O(2) stimulated muscle differentiation as a signaling messenger.

NADPH oxidase-derived reactive oxygen species mediate decidualization of human endometrial stromal cells in response to cyclic AMP signaling

Differentiation of human endometrial stromal cells into specialized decidual cells is critical for embryo implantation and survival of the conceptus. Initiation of this differentiation process is strictly dependent on elevated cAMP levels, but the signal intermediates that control the expression of decidual marker genes, such as prolactin (PRL) and IGFBP1, remain poorly characterized. Here we show that cAMP-dependent decidualization can be attenuated or enhanced upon treatment of primary cultures with a nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor (diphenylen iodonium) or activator (apocynin), respectively. Time-course analysis demonstrated that cAMP enhances endogenous reactive oxygen species production, apparent after 12 h of stimulation, which coincides with a dramatic increase in decidual PRL and IGFBP1 expression. Knockdown of the Rho GTPase RAC1, which disables activation of the NADPH oxidase homologs NADPH oxidase (NOX)-1, NOX-2, and NOX-3, had no effect on PRL or IGFBP1 expression. In contrast, silencing of NOX-4, or its cofactor p22(PHOX), inhibited the expression of both decidual markers. Finally, we show that the NOX-4/p22(PHOX) complex regulates the DNA-binding activity of CCAAT/enhancer binding protein-β, a key regulator of human endometrial stromal cell differentiation. Thus, NOX-4 activation and reactive oxygen species signaling play an integral role in initiating the endometrial decidual response in preparation of pregnancy.

Regulation of myocardial growth and death by NADPH oxidase

The NADPH oxidases (Nox) are transmembrane proteins dedicated to producing reactive oxygen species (ROS), including superoxide and hydrogen peroxide, by transferring electrons from NAD(P)H to molecular oxygen. Nox2 and Nox4 are expressed in the heart and play an important role in mediating oxidative stress at baseline and under stress. Nox2 is primarily localized on the plasma membrane, whereas Nox4 is found primarily on intracellular membranes, on mitochondria, the endoplasmic reticulum or the nucleus. Although Nox2 plays an important role in mediating angiotensin II-induced cardiac hypertrophy, Nox4 mediates cardiac hypertrophy and heart failure in response to pressure overload. Expression of Nox4 is upregulated by hypertrophic stimuli, and Nox4 in mitochondria plays an essential role in mediating oxidative stress during pressure overload-induced cardiac hypertrophy. Upregulation of Nox4 induces oxidation of mitochondrial proteins, including aconitase, thereby causing mitochondrial dysfunction and myocardial cell death. On the other hand, Noxs also appear to mediate physiological functions, such as erythropoiesis and angiogenesis. In this review, we discuss the role of Noxs in mediating oxidative stress and both pathological and physiological functions of Noxs in the heart.

Redox stimulation of cardiomyogenesis versus inhibition of vasculogenesis upon treatment of mouse embryonic stem cells with thalidomide

Thalidomide [α-(N-phthalimido)-glutarimide] exerts antiangiogenic properties and causes cardiac malformations in embryos. Herein the effects of thalidomide on cardiovascular differentiation were investigated in mouse embryonic stem (ES) cell-derived embryoid bodies. Thalidomide inhibited the formation of capillary-like blood vessels and decreased tumor-induced angiogenesis in confrontation cultures of embryoid bodies and multicellular prostate tumor spheroids, but stimulated cardiomyogenesis of ES cells. The number of CD31- and CD144-positive endothelial cells was not impaired, suggesting that thalidomide acted on vascular tube formation and cell migration rather than endothelial differentiation. Thalidomide increased reactive oxygen species generation, which was abolished by the NADPH oxidase inhibitor VAS2870 and the complex I respiratory chain inhibitor rotenone. Conversely, thalidomide decreased nitric oxide (NO) generation and endothelial NO synthase activity. VAS2870 abrogated thalidomide stimulation of cardiomyogenesis, whereas inhibition of vasculogenesis persisted. In NOX-1 and NOX-4 shRNA gene-inactivated ES cells, cardiomyogenesis was severely impaired and thalidomide failed to stimulate cardiac cell commitment. The NO donor S-nitrosopenicillamine reversed the antiangiogenic effect of thalidomide and increased capillary structure formation, whereas scavenging NO by 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and inhibition of endothelial NO synthase by N(G)-nitro-l-arginine methyl ester decreased cardiovascular differentiation. Our data demonstrate that thalidomide causes an imbalance of reactive oxygen species/NO generation, thus stimulating cardiomyogenesis and impairing vascular sprout formation.

Mitochondrial reactive oxygen species mediate cardiomyocyte formation from embryonic stem cells in high glucose

Accumulating evidence points to reactive oxygen species (ROS) as important signaling molecules for cardiomyocyte differentiation in embryonic stem (ES) cells. Given that ES cells are normally maintained and differentiated in medium containing supraphysiological levels of glucose (25 mM), a condition which is known to result in enhanced cellular ROS formation, we questioned whether this high glucose concentration was necessary for cardiomyocyte lineage potential. We show here that ES cells cultured in physiological glucose (5 mM), maintained their general stemness qualities but displayed an altered mitochondrial metabolism, which resulted in decreased ROS production. Furthermore, ES and induced pluripotent stem (iPS) cells differentiated in lower glucose concentrations failed to generate cardiomyocyte structures; an effect mimicked with antioxidant treatments using catalase, N-acetyl cysteine and mitoubiquinone, under high glucose conditions in ES cells. Molecular analysis revealed that ES cells differentiated in 5 mM glucose had reduced expression of the pro-cardiac NOX4 gene and diminished phosphorylation of p38 mitogen-activated protein kinase (MAPK), together with specific changes in the cardiac transcriptional network. These outcomes could be reversed by supplementation of low glucose cultures with ascorbic acid, paradoxically acting as a pro-oxidant. Furthermore, forced expression of an upstream p38 MAPK kinase (MKK6) could bypass the requirement for ROS during differentiation to cardiomyocytes under low glucose conditions, illustrating a key role for p38 in the cardiac differentiation program. Together these data demonstrate that endogenous ROS control is important for cardiomyocyte formation from ES cells, and furthermore that supraphysiological glucose, by supplying ROS, is absolutely required.

PKC-δ signalling pathway is involved in H9c2 cells differentiation

H9c2 are rat heart embryonic myoblasts, with skeletal muscle properties, which terminally differentiate by fusing and forming multinucleated myotubes. Here we investigated the possible involvement of Protein Kinases C (PKCs) in H9c2 cell differentiation and explored the interplay of these enzymes both with reactive oxygen species (ROS), upstream physiological mediators of cell differentiation, and with nitric oxide (NO), downstream target of PKC activation, known for being involved in apoptosis induction in differentiated myoblasts. Cells were induced to differentiate (6 days) under low serum culture conditions and assayed for the expression of cell cycle (cyclin A) and differentiation markers (morphology and myogenin). Both ROS and in vivo production of NO were found increased after 6 days of differentiation, when the activation of PKC-δ isoform was 14-fold increased compared with the undifferentiated control cells. The parallel analysis of apoptotic features demonstrated a small increase in Annexin-V+ cells and a concomitant increase in PARP cleavage and Bax expression. Interestingly, a reduced percentage of differentiated cells was obtained both in the presence of Rottlerin, a highly selective PKC-δ pharmacologic inhibitor, and, moreover, with the use of PKC-δ siRNA technology, further supporting the involvement of PKC-δ in switching on the events related to skeletal muscle myoblast differentiation.

Static electromagnetic fields induce vasculogenesis and chondro-osteogenesis of mouse embryonic stem cells by reactive oxygen species-mediated up-regulation of vascular endothelial growth factor

Electromagnetic fields (EMFs) are used to treat bone diseases. Herein, the effects of static EMFs on chondroosteogenesis and vasculogenesis of embryonic stem (ES) cells and bone mineralization of mouse fetuses were investigated. Treatment of differentiating ES cells with static EMFs (0.4-2 mT) stimulated vasculogenesis and chondro-osteogenesis and increased reactive oxygen species (ROS), which was abolished by the free radical scavengers trolox, 1,10-phenanthroline (phen), and the NAD(P)H oxidase inhibitor diphenylen iodonium (DPI). In contrast, EMFs of 10 mT field strength exerted inhibitory effects on vasculogenesis and chondro-osteogenesis despite robust ROS generation. EMFs of 1 mT and 10 mT increased and decreased vascular endothelial growth factor (VEGF) expression, respectively, which was abolished by DPI and radical scavengers. EMFs activated extracellular-regulated kinase 1/2 (ERK1/2), p38, and c-jun N-terminal kinase (JNK), which was sensitive to DPI treatment. The increase in VEGF by EMFs was inhibited by the ERK1/2 inhibitor U0126 but not by SB203580 and SP600125, which are p38 and JNK inhibitors, respectively, suggesting VEGF regulation by ERK1/2. Chondroosteogenesis and vasculogenesis of ES cells was blunted by trolox, DPI, and the VEGF receptor-2 (flk-1) antagonist SU5614. In mouse fetuses 1 mT EMFs increased and 10 mT EMFs decreased bone mineralization, which was abolished in the presence of trolox. Hence, EMFs induced chondro-osteogenesis and vasculogenesis in ES cells and bone mineralization of mouse fetuses by a ROS-dependent up-regulation of VEGF expression.

Reactive oxygen species: A radical role in development?

Reactive oxygen species (ROS), mostly derived from mitochondrial activity, can damage various macromolecules and consequently cause cell death. This ROS activity has been characterized in vitro, and correlative evidence suggests a role in various pathological conditions. In addition to this passive ROS activity, ROS also participate in cell signaling processes, though the relevance of this function in vivo is poorly understood. Throughout development, elevated cell activity is probably accompanied by highly active metabolism and, consequently, the production of large amounts of ROS. To allow proper development, cells must protect themselves from these potentially damaging ROS. However, to what degree ROS could participate as signaling molecules controlling fundamental and developmentally relevant cellular processes such as proliferation, differentiation, and death is an open question. Here we discuss why available data do not yet provide conclusive evidence on the role of ROS in development, and we review recent methods to detect ROS in vivo and genetic strategies that can be exploited specifically to resolve these uncertainties.

p22phox-dependent NADPH oxidase activity is required for megakaryocytic differentiation

Transient reactive oxygen species (ROS) production is currently proving to be an important mechanism in the regulation of intracellular signalling, but reports showing the involvement of ROS in important biological processes, such as cell differentiation, are scarce. In this study, we show for the first time that ROS production is required for megakaryocytic differentiation in K562 and HEL cell lines and also in human CD34(+) cells. ROS production is transiently activated during megakaryocytic differentiation, and such production is abolished by the addition of different antioxidants (such as N-acetyl cysteine, trolox, quercetin) or the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor diphenylene iodonium. The inhibition of ROS formation hinders differentiation. RNA interference experiments have shown that a p22(phox)-dependent NADPH oxidase activity is responsible for ROS production. In addition, the activation of ERK, AKT and JAK2 is required for differentiation, but the activation of phosphatidylinositol 3-kinase and c-Jun N-terminal kinase seems to be less important. When ROS production is prevented, the activation of these signalling pathways is partly inhibited. Taken together, these results show that NADPH oxidase ROS production is essential for complete activation of the main signalling pathways involved in megakaryocytopoiesis to occur. We suggest that this might also be important for in vivo megakaryocytopoiesis.

Metabolic oxidation regulates embryonic stem cell differentiation

Metabolites offer an important unexplored complement to understanding the pluripotency of stem cells. Using mass spectrometry-based metabolomics, we show that embryonic stem cells are characterized by abundant metabolites with highly unsaturated structures whose levels decrease upon differentiation. By monitoring the reduced and oxidized glutathione ratio as well as ascorbic acid levels, we demonstrate that the stem cell redox status is regulated during differentiation. Based on the oxidative biochemistry of the unsaturated metabolites, we experimentally manipulated specific pathways in embryonic stem cells while monitoring the effects on differentiation. Inhibition of the eicosanoid signaling pathway promoted pluripotency and maintained levels of unsaturated fatty acids. In contrast, downstream oxidized metabolites (e.g., neuroprotectin D1) and substrates of pro-oxidative reactions (e.g., acyl-carnitines), promoted neuronal and cardiac differentiation. We postulate that the highly unsaturated metabolome sustained by stem cells makes them particularly attuned to differentiate in response to in vivo oxidative processes such as inflammation.

Reactive oxygen species enhance differentiation of human embryonic stem cells into mesendodermal lineage

Recently, reactive oxygen species (ROS) have been studied as a regulator of differentiation into specific cell types in embryonic stem cells (ESCs). However, ROS role in human ESCs (hESCs) is unknown because mouse ESCs have been used mainly for most studies. Herein we suggest that ROS generation may play a critical role in differentiation of hESCs; ROS enhances differentiation of hESCs into bi-potent mesendodermal cell lineage via ROS-involved signaling pathways. In ROS-inducing conditions, expression of pluripotency markers (Oct4, Tra 1-60, Nanog, and Sox2) of hESCs was decreased, while expression of mesodermal and endodermal markers was increased. Moreover, these differentiation events of hESCs in ROS-inducing conditions were decreased by free radical scavenger treatment. hESC-derived embryoid bodies (EBs) also showed similar differentiation patterns by ROS induction. In ROS-related signaling pathway, some of the MAPKs family members in hESCs were also affected by ROS induction. p38 MAPK and AKT (protein kinases B, PKB) were inactivated significantly by buthionine sulfoximine (BSO) treatment. JNK and ERK phosphorylation levels were increased at early time of BSO treatment but not at late time point. Moreover, MAPKs family-specific inhibitors could prevent the mesendodermal differentiation of hESCs by ROS induction. Our results demonstrate that stemness and differentiation of hESCs can be regulated by environmental factors such as ROS.

Differential responses to oxidative stress and calcium influx on expression of the transforming growth factor-beta family in myoblasts and myotubes

Changes in gene expression of TGF-beta family members and their receptors in response to treatment with H(2)O(2) and a calcium ionophore, A23187, were examined in C2C12 myoblasts and myotubes. The expression of Myf5, an initial regulator of myogenesis, was increased by A23187, and H(2)O(2) inhibited the up-regulation of Myf5. Treatment with H(2)O(2) decreased the expression of MHC IIb, a protein component of the myofibrils, irrespective of the presence of A23187, suggesting an inhibitory role of oxidative stress for myogenesis. Expression of ligands and receptors for the TGF-beta family was modulated in response to H(2)O(2) and A23187. Treatment with H(2)O(2) decreased expression of TGF-beta3, BMP-4, ALK4, ALK5, and ActRIIB, and increased expression of inhibin alpha and inhibin betaA in either the myoblast stage or the myotube stage, or both. A23187 potentiated down-regulation of BMP-4 and ALK4 expression, and up-regulation of TGF-beta1, TGF-beta2, inhibin alpha, inhibin betaA, ALK2, and ALK3 expression. These results indicate that oxidative stress and Ca(2+) influx affect expression of the TGF-beta family in C2C12 myoblasts and myotubes.

Endogenous reactive oxygen species are essential for proliferation of neural stem/progenitor cells

It is widely thought that accumulation of reactive oxygen species (ROS) causes injury to cells. In this study, we investigated the effect of endogenous ROS on the proliferation of neural stem/progenitor cells derived from the hippocampus of embryonic mice. The cells were treated with free radical-scavenging agents [3-methyl-1-phenyl-2-pyrazolin-5-one (edaravone) or 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (tempol)], an NADPH oxidase inhibitor (apocynin), catalase, a nitric oxide synthase inhibitor [N(omega)-nitro-L-arginine methyl ester hydrochloride (L-NAME)] or a peroxynitrite generator (SIN-1) during the culture period. Edaravone and tempol had the ability to decrease endogenous ROS in the cells exposed for periods from 1 to 24h, with attenuation of the proliferation activity of the cells during culture. Apocynin and L-NAME were also effective in attenuating cell proliferation but not cellular damage. Conversely, SIN-1 was capable of promoting the proliferation activity. However, catalase had no effect on the proliferation activity of the cells during culture. Furthermore, tempol significantly decreased the level of NFkappaB p65, phospho-cyclic AMP response element-binding protein, and beta-catenin within the nucleus of the cells. These data suggest that endogenous ROS and nitric oxide are essential for the proliferation of embryonic neural stem/progenitor cells.

Bacterial-modulated host immunity and stem cell activation for gut homeostasis

Although it is widely accepted that dynamic cross-talk between gut epithelia and microorganisms must occur to achieve gut homeostasis, the critical mechanisms by which gut-microbe interactions are regulated remain uncertain. In this issue of Genes & Development, Buchon and colleagues (pp. 2333-2344) revealed that the reaction of the gut to microorganisms is not restricted to activating immune systems, but extends to integrated responses essential for gut tissue homeostasis, including self-renewal and the differentiation of stem cells. Further investigation of the connection between immune response and stem cell regulation at the molecular level in the microbe-laden mucosal epithelia will accelerate our understanding of the regulatory mechanisms of gut homeostasis and of the pathogenesis of diseases such as chronic inflammatory diseases and colorectal cancers.

Novel role of NADPH oxidase in angiogenesis and stem/progenitor cell function

Neovascularization is involved in normal development and wound repair as well as ischemic heart disease and peripheral artery disease. Both angiogenesis and vasculogenesis [de novo new vessel formation through mobilization of stem/progenitor cells from bone marrow (BM) and their homing to the ischemic sites] contribute to the formation of new blood vessels after tissue ischemia. Angiogenesis is dependent on cell proliferation, migration, and capillary tube formation in endothelial cells (ECs). Stem/progenitor cells have been used for cell-based therapy to promote revascularization after peripheral or myocardial ischemia. Excess amounts of reactive oxygen species (ROS) are involved in senescence and apoptosis of ECs and stem/progenitor cells, causing defective neovascularization. ROS at low levels function as signaling molecules to mediate cell proliferation, migration, differentiation, and gene expression. NADPH oxidase is one of the major sources of ROS in ECs and stem/progenitor cells, and is activated by various growth factors, cytokines, hypoxia, and ischemia. ROS derived from NADPH oxidase play an important role in redox signaling linked to angiogenesis ECs, as well as stem/progenitor cell mobilization, homing, and differentiation, thereby promoting neovascularization. Understanding these mechanisms may provide insight into NADPH oxidase and its mediators as potential therapeutic targets for ischemic heart and limb disease.

Redox regulation and its emerging roles in stem cells and stem-like cancer cells

The existence of cancer stem cells has impelled the pursuit to understanding and characterizing this subset of cells, which are thought to be responsible for tumor recurrence and to contribute to therapy resistance. Recent studies suggest that cancer stem cells seem to possess properties similar to those of normal stem cells, revealing a possible therapeutic strategy/target. For this to be feasible, it is imperative to understand the relation between cancer cells, cancer stem cells, and normal stem cells. Cancer cells have been found to be in a state of redox imbalance, an alteration in the homeostasis between oxidants and antioxidants, resulting in increased oxidants within the cell. Studies have shown redox balance plays an important role in the maintenance of stem cell self-renewal and in differentiation. Very little is known about the redox status in cancer stem cells. In this review, we focus on the sites of oxidant generation and the regulation of redox status in cancer cells and stem cells. In addition, evidence that supports the involvement of redox homeostasis for stem cell self-renewal, differentiation, and survival are reviewed. Given the significance of redox in stem cells, we also discuss the possibility of exploiting the redox status in cancer stem cells as a novel therapeutic strategy.

Inhibition of ref-1 stimulates the production of reactive oxygen species and induces differentiation in adult cardiac stem cells

Redox effector protein-1 (Ref-1) plays an essential role in DNA repair and redox regulation of several transcription factors. In the present study, we examined the role of Ref-1 in maintaining the redox status and survivability of adult cardiac stem cells challenged with a subtoxic level of H2O2 under inhibition of Ref-1 by RNA interference. Treatment of cardiac stem cells with a low concentration of H2O2 induced Ref-1-mediated survival signaling through phosphorylation of Akt. However, Ref-1 inhibition followed by H2O2 treatment extensively induced the level of intracellular reactive oxygen species (ROS) through activation of the components of NADPH oxidase, like p22( phox ), p47( phox ), and Nox4. Cardiac differentiation markers (Nkx2.5, MEF2C, and GATA4), and cell death by apoptosis were significantly elevated in Ref-1 siRNA followed by H2O2-treated stem cells. Further, inhibition of Ref-1 increased the level of p53 but decreased the phosphorylation of Akt, a molecule involved in survival signaling. Treatment with ROS scavenger N-acetyl-L-cysteine attenuated Ref-1 siRNA-mediated activation of NADPH oxidase and cardiac differentiation. Taken together, these results indicate that Ref-1 plays an important role in maintaining the redox status of cardiac stem cells and protects them from oxidative injury-mediated cell death and differentiation.

Generation of human embryonic stem cell-derived mesoderm and cardiac cells using size-specified aggregates in an oxygen-controlled bioreactor

The ability to generate human pluripotent stem cell-derived cell types at sufficiently high numbers and in a reproducible manner is fundamental for clinical and biopharmaceutical applications. Current experimental methods for the differentiation of pluripotent cells such as human embryonic stem cells (hESC) rely on the generation of heterogeneous aggregates of cells, also called "embryoid bodies" (EBs), in small scale static culture. These protocols are typically (1) not scalable, (2) result in a wide range of EB sizes and (3) expose cells to fluctuations in physicochemical parameters. With the goal of establishing a robust bioprocess we first screened different scalable suspension systems for their ability to support the growth and differentiation of hESCs. Next homogeneity of initial cell aggregates was improved by employing a micro-printing strategy to generate large numbers of size-specified hESC aggregates. Finally, these technologies were integrated into a fully controlled bioreactor system and the impact of oxygen concentration was investigated. Our results demonstrate the beneficial effects of stirred bioreactor culture, aggregate size-control and hypoxia (4% oxygen tension) on both cell growth and cell differentiation towards cardiomyocytes. QRT-PCR data for markers such as Brachyury, LIM domain homeobox gene Isl-1, Troponin T and Myosin Light Chain 2v, as well as immunohistochemistry and functional analysis by response to chronotropic agents, documented the impact of these parameters on cardiac differentiation. This study provides an important foundation towards the robust generation of clinically relevant numbers of hESC derived cells.

The mouse as a model system to study cardiac regeneration

Cardiomyocytes exhibit robust proliferative activity during development. After birth, cardiomyocyte proliferation is markedly reduced. Consequently, regenerative growth in the postnatal heart via cardiomyocyte proliferation (including, by inference, via proliferation of stem cell-derived cardiomyocytes) is limited and often insufficient to effect repair following injury. Here we review methodologies which employ the mouse as a model system to study cardiac regeneration, and in particular cardiomyocyte replenishment, in health and disease.

Role of nox2-based NADPH oxidase in bone marrow and progenitor cell function involved in neovascularization induced by hindlimb ischemia

Bone marrow (BM) is the major reservoir for endothelial progenitor cells (EPCs). Postnatal neovascularization depends on not only angiogenesis but also vasculogenesis, which is mediated through mobilization of EPCs from BM and their recruitment to the ischemic sites. Reactive oxygen species (ROS) derived from Nox2-based NADPH oxidase play an important role in postnatal neovascularization; however, their role in BM and EPC function is unknown. Here we show that hindlimb ischemia of mice significantly increases Nox2 expression and ROS production in BM-mononuclear cells (BMCs), which is associated with an increase in circulating EPC-like cells. Mice lacking Nox2 show reduction of ischemia-induced flow recovery, ROS levels in BMCs, as well as EPC mobilization from BM. Transplantation of wild-type (WT)-BM into Nox2-deficient mice rescues the defective neovascularization, whereas WT mice transplanted with Nox2-deficient BM show reduced flow recovery and capillary density compared to WT-BM transplanted control. Intravenous infusion of WT- and Nox2-deficient BMCs into WT mice reveals that neovascularization and homing capacity are impaired in Nox2-deficient BMCs in vivo. In vitro, Nox2-deficient c-kit+Lin- BM stem/progenitor cells show impaired chemotaxis and invasion as well as polarization of actins in response to stromal derived factor (SDF), which is associated with blunted SDF-1-mediated phosphorylation of Akt. In conclusion, Nox2-derived ROS in BM play a critical role in mobilization, homing, and angiogenic capacity of EPCs and BM stem/progenitor cells, thereby promoting revascularization of ischemic tissue. Thus, NADPH oxidase in BM and EPCs is potential therapeutic targets for promoting neovascularization in ischemic cardiovascular diseases.

Intracellular redox status and oxidative stress: implications for cell proliferation, apoptosis, and carcinogenesis

Oxidative stress can be defined as the imbalance between cellular oxidant species production and antioxidant capability. Reactive oxygen species (ROS) are involved in a variety of different cellular processes ranging from apoptosis and necrosis to cell proliferation and carcinogenesis. In fact, molecular events, such as induction of cell proliferation, decreased apoptosis, and oxidative DNA damage have been proposed to be critically involved in carcinogenesis. Carcinogenicity and aging are characterized by a set of complex endpoints, which appear as a series of molecular reactions. ROS can modify many intracellular signaling pathways including protein phosphatases, protein kinases, and transcription factors, suggesting that the majority of the effects of ROS are through their actions on signaling pathways rather than via non-specific damage of macromolecules; however, exact mechanisms by which redox status induces cells to proliferate or to die, and how oxidative stress can lead to processes evoking tumor formation are still under investigation.

Derive and conquer: sourcing and differentiating stem cells for therapeutic applications

Although great progress has been made in the isolation and culture of stem cells, the future of stem-cell-based therapies and their productive use in drug discovery and regenerative medicine depends on two key factors: finding reliable sources of multipotent and pluripotent cells and the ability to control their differentiation to generate desired derivatives. It is essential for clinical applications to establish reliable sources of pathogen-free human embryonic stem cells (ESCs) and develop suitable differentiation techniques. Here, we address some of the problems associated with the sourcing of human ESCs and discuss the current status of stem-cell differentiation technology.

Reactive oxygen species and upregulation of NADPH oxidases in mechanotransduction of embryonic stem cells

Deciphering the differentiation pathway of embryonic stem (ES) cells is a challenging task not only for basic research, but also for clinicians who intend to use ES cells for cell transplantation approaches. We have shown that reactive oxygen species (ROS) play a primordial role in the differentiation of mouse ES cells toward the cardiovascular cell lineage. During differentiation, ES cells robustly generate ROS, which interfere with signaling pathways that direct cardiac and vascular commitment. Differentiating ES cells expression of Nox-1, Nox-2, and Nox-4 has been demonstrated. We have shown that mechanical strain application to embyoid bodies grown from ES cells initiates the cardiovascular differentiation program. Under these conditions, a burst of ROS generation occurs which is followed by induction of Nox-1 and Nox-4 and a feed-forward upregulation of ROS production.

Peroxisome proliferator-activated receptor alpha agonists enhance cardiomyogenesis of mouse ES cells by utilization of a reactive oxygen species-dependent mechanism

Peroxisome proliferator-activated receptors (PPARalpha, -beta and -gamma) are nuclear receptors involved in transcriptional regulation of lipid and energy metabolism. Since the energy demand increases when cardiac progenitor cells are developing rhythmic contractile activity, PPAR activation may play a critical role during cardiomyogenesis of embryonic stem (ES) cells. It is shown that ES cells express PPARalpha, -beta, and -gamma mRNA during differentiation of ES cells towards cardiac cells. Treatment with PPARalpha agonists (WY14643, GW7647, and ciprofibrate) significantly increased cardiomyogenesis and expression of the cardiac genes MLC2a, ANP, MHC-beta, MLC2v, and cardiac alpha-actin. Furthermore, WY14643 increased PPARalpha gene expression and the expression of the cardiogenic transcription factors GATA-4, Nkx2.5, DTEF-1, and MEF 2C. In contrast, the PPARalpha antagonist MK886 decreased cardiomyogenesis, whereas the PPARbeta agonist L-165,041 as well as the PPARgamma agonist GW1929 were without effects. Treatment with PPARalpha, but not PPARbeta, and PPARgamma agonists and MK886, resulted in generation of reactive oxygen species (ROS), which was inhibited in the presence of the NADPH oxidase inhibitors diphenylen iodonium (DPI) and apocynin and the free radical scavengers vitamin E and N-(2-mercapto-propionyl)-glycine (NMPG), whereas the mitochondrial complex I inhibitor rotenone was without effects. The effect of PPARalpha agonists on cardiomyogenesis of ES cells was abolished upon preincubation with free radical scavengers and NADPH oxidase inhibitors, indicating involvement of ROS in PPARalpha, mediated cardiac differentiation. In summary, our data indicate that stimulation of PPARalpha but not PPARbeta and -gamma enhances cardiomyogenesis in ES cells using a pathway that involves ROS and NADPH oxidase activity.

Hypoxia-Dependent Regulation of Nonphagocytic NADPH Oxidase Subunit NOX4 in the Pulmonary Vasculature

Nonphagocytic NADPH oxidases have recently been suggested to play a major role in the regulation of physiological and pathophysiological processes, in particular, hypertrophy, remodeling, and angiogenesis in the systemic circulation. Moreover, NADPH oxidases have been suggested to serve as oxygen sensors in the lung. Chronic hypoxia induces vascular remodeling with medial hypertrophy leading to the development of pulmonary hypertension. We screened lung tissue for the expression of NADPH oxidase subunits. NOX1, NOXA1, NOXO1, p22phox, p47phox, p40phox, p67phox, NOX2, and NOX4 were present in mouse lung tissue. Comparing mice maintained for 21 days under hypoxic (10% O(2)) or normoxic (21% O(2)) conditions, an upregulation exclusively of NOX4 mRNA was observed under hypoxia in homogenized lung tissue, concomitant with increased levels in microdissected pulmonary arterial vessels. In situ hybridization and immunohistological staining for NOX4 in mouse lungs revealed a localization of NOX4 mRNA and protein predominantly in the media of small pulmonary arteries, with increased labeling intensities after chronic exposure to hypoxia. In isolated pulmonary arterial smooth muscle cells (PASMCs), NOX4 was localized primarily to the perinuclear space and its expression levels were increased after exposure to hypoxia. Treatment of PASMCs with siRNA directed against NOX4 decreased NOX4 mRNA levels and reduced PASMC proliferation as well as generation of reactive oxygen species. In lungs from patients with idiopathic pulmonary arterial hypertension (IPAH), expression levels of NOX4, which was localized in the vessel media, were 2.5-fold upregulated. These results support an important role for NOX4 in the vascular remodeling associated with development of pulmonary hypertension.