Regulation of cardiotrophin-1 expression in mouse embryonic stem cells by HIF-1alpha and intracellular reactive oxygen species

β3-Adrenoceptor Agonism to Mimic the Biological Effects of Intrauterine Hypoxia: Taking Great Strides Toward a Pharmacological Artificial Placenta

At different stages of life, from embryonic to postnatal, varying oxygen concentrations modulate cellular gene expression by enhancing or repressing hypoxia-inducible transcription factors. During embryonic/fetal life, these genes encode proteins involved in adapting to a low-oxygen environment, including the induction of specific enzymes related to glycolytic metabolism, erythropoiesis, angiogenesis, and vasculogenesis. However, oxygen concentrations fluctuate during intrauterine life, enabling the induction of tissue-specific differentiation processes. Fetal well-being is thus closely linked to the physiological benefits of a dynamically hypoxic environment. Premature birth entails the precocious exposure of the immature fetus to a more oxygen-rich environment compared to the womb. As a result, preterm newborns face a condition of relative hyperoxia, which alters the postnatal development of organs and contributes to prematurity-related diseases. However, until recently, the molecular mechanism by which high oxygen tension alters normal fetal differentiation remained unclear. In this review, we discuss the research trajectory followed by our research group, which suggests that early exposure to a relatively hyperoxic environment may impair preterm neonates due to reduced expression of the β3-adrenoceptor. Additionally, we explore how these impairments could be prevented through the pharmacological stimulation of the remaining β3-adrenoceptors. Recent preclinical studies demonstrate that pharmacological stimulation of the β3-adrenoceptor can decouple exposure to hyperoxia from its harmful effects, offering a glimpse of the possibility to recreating the conditions typical of intrauterine life, even after premature birth.

NADPH Oxidase 4: Crucial for Endothelial Function under Hypoxia-Complementing Prostacyclin

Aim: The primary endothelial NADPH oxidase isoform 4 (NOX4) is notably induced during hypoxia, with emerging evidence suggesting its vasoprotective role through H2O2 production. Therefore, we aimed to elucidate NOX4's significance in endothelial function under hypoxia. Methods: Human vessels, in addition to murine vessels from Nox4-/- mice, were explored. On a functional level, Mulvany myograph experiments were performed. To obtain mechanistical insights, human endothelial cells were cultured under hypoxia with inhibitors of hypoxia-inducible factors. Additionally, endothelial cells were cultured under combined hypoxia and laminar shear stress conditions. Results: In human occluded vessels, NOX4 expression strongly correlated with prostaglandin I2 synthase (PTGIS). Hypoxia significantly elevated NOX4 and PTGIS expression and activity in human endothelial cells. Inhibition of prolyl hydroxylase domain (PHD) enzymes, which stabilize hypoxia-inducible factors (HIFs), increased NOX4 and PTGIS expression even under normoxic conditions. NOX4 mRNA expression was reduced by HIF1a inhibition, while PTGIS mRNA expression was only affected by the inhibition of HIF2a under hypoxia. Endothelial function assessments revealed hypoxia-induced endothelial dysfunction in mesenteric arteries from wild-type mice. Mesenteric arteries from Nox4-/- mice exhibited an altered endothelial function under hypoxia, most prominent in the presence of cyclooxygenase inhibitor diclofenac to exclude the impact of prostacyclin. Restored protective laminar shear stress, as it might occur after thrombolysis, angioplasty, or stenting, attenuated the hypoxic response in endothelial cells, reducing HIF1a expression and its target NOX4 while enhancing eNOS expression. Conclusions: Hypoxia strongly induces NOX4 and PTGIS, with a close correlation between both factors in occluded, hypoxic human vessels. This relationship ensured endothelium-dependent vasodilation under hypoxic conditions. Protective laminar blood flow restores eNOS expression and mitigates the hypoxic response on NOX4 and PTGIS.

Adipocyte-Derived Exosomal NOX4-Mediated Oxidative Damage Induces Premature Placental Senescence in Obese Pregnancy

Background

A recent study has reported that maternal obesity is linked to placental oxidative damage and premature senescence. NADPH oxidase 4 (NOX4) is massively expressed in adipose tissue, and its induced reactive oxygen species have been found to contribute to cellular senescence. While, whether, in obese pregnancy, adipose tissue-derived NOX4 is the considerable cause of placental senescence remained elusive.

Methods

This study collected term placentas from obese and normal pregnancies and obese pregnant mouse model was constructed by a high fat diet to explore placental senescence. Furthermore, adipocyte-derived exosomes were isolated from primary adipocyte medium of obese and normal pregnancies to examine their effect on placenta functions in vivo and vitro.

Results

The placenta from the obese group showed a significant increase in placental oxidative damage and senescence. Exosomes from obese adipocytes contained copies of NOX4, and when cocultured with HTR8/SVneo cells, they induced severe oxidative damage, cellular senescence, and suppressed proliferation and invasion functions when compared with the control group. In vivo, adipocyte-derived NOX4-containing exosomes could induce placental oxidative damage and senescence, ultimately leading to adverse pregnancy outcomes.

Conclusion

In obesity, adipose tissue can secrete exosomes containing NOX4 which can be delivered to trophoblast resulting in severe DNA oxidative damage and premature placental senescence, ultimately leading to adverse pregnancy outcomes.

The regulation of cardiac intermediary metabolism by NADPH oxidases

NADPH oxidases (NOXs), enzymes whose primary function is to generate reactive oxygen species, are important regulators of the heart's physiological function and response to pathological insults. The role of NOX-driven redox signalling in pathophysiological myocardial remodelling, including processes such as interstitial fibrosis, contractile dysfunction, cellular hypertrophy, and cell survival, is well recognized. While the NOX2 isoform promotes many detrimental effects, the NOX4 isoform has attracted considerable attention as a driver of adaptive stress responses both during pathology and under physiological states such as exercise. Recent studies have begun to define some of the NOX4-modulated mechanisms that may underlie these adaptive responses. In particular, novel functions of NOX4 in driving cellular metabolic changes have emerged. Alterations in cellular metabolism are a recognized hallmark of the heart's response to physiological and pathological stresses. In this review, we highlight the emerging roles of NOX enzymes as important modulators of cellular intermediary metabolism in the heart, linking stress responses not only to myocardial energetics but also other functions. The novel interplay of NOX-modulated redox signalling pathways and intermediary metabolism in the heart is unravelling a new aspect of the fascinating biology of these enzymes which will inform a better understanding of how they drive adaptive responses. We also discuss the implications of these new findings for therapeutic approaches that target metabolism in cardiac disease.

Stem Cell Differentiation into Cardiomyocytes: Current Methods and Emerging Approaches

Cardiovascular diseases (CVDs) are globally known to be important causes of mortality and disabilities. Common treatment strategies for CVDs, such as pharmacological therapeutics impose serious challenges due to the failure of treatments for myocardial necrosis. By contrast, stem cells (SCs) based therapies are seen to be promising approaches to CVDs treatment. In such approaches, cardiomyocytes are differentiated from SCs. To fulfill SCs complete potential, the method should be appointed to generate cardiomyocytes with more mature structure and well-functioning operations. For heart repairing applications, a greatly scalable and medical-grade cardiomyocyte generation must be used. Nonetheless, there are some challenges such as immune rejection, arrhythmogenesis, tumorigenesis, and graft cell death potential. Herein, we discuss the types of potential SCs, and commonly used methods including embryoid bodies related techniques, co-culture, mechanical stimulation, and electrical stimulation and their applications, advantages and limitations in this field. An estimated 17.9 million people died from CVDs in 2019, representing 32 % of all global deaths. Of these deaths, 85 % were due to heart attack and stroke.

Nox4 Promotes RANKL-Induced Autophagy and Osteoclastogenesis via Activating ROS/PERK/eIF-2α/ATF4 Pathway

Receptor activator of nuclear factor-κB ligand (RANKL) has been found to induce osteoclastogenesis and bone resorption. However, the underlying molecular mechanisms remain unclear. Via conducting a series of biochemical experiments with in vitro cell lines, this study investigated the role and mechanism of NADPH oxidase 4 (Nox4) in RANKL-induced autophagy and osteoclastogenesis. In the current study, we found that RANKL dramatically induced autophagy and osteoclastogenesis, inhibition of autophagy with chloroquine (CQ) markedly attenuates RANKL-induced osteoclastogenesis. Interestingly, we found that the protein level of Nox4 was remarkably upregulated by RANKL treatment. Inhibition of Nox4 by 5-O-methyl quercetin or knockdown of Nox4 with specific shRNA markedly attenuated RANKL-induced autophagy and osteoclastogenesis. Furthermore, we found that Nox4 stimulated the production of nonmitochondrial reactive oxygen species (ROS), activating the critical unfolded protein response (UPR)-related signaling pathway PERK/eIF-2α/ATF4, leading to RANKL-induced autophagy and osteoclastogenesis. Blocking the activation of PERK/eIF-2α/ATF4 signaling pathway either by Nox4 shRNA, ROS scavenger (NAC) or PERK inhibitor (GSK2606414) significantly inhibited autophagy during RANKL-induced osteoclastogenesis. Collectively, this study reveals that Nox4 promotes RANKL-induced autophagy and osteoclastogenesis via activating ROS/PERK/eIF-2α/ATF4 pathway, suggesting that the pathway may be a novel potential therapeutic target for osteoclastogenesis-related disease.

Cell differentiation in the cardiac embryonic stem cell test (ESTc) is influenced by the oxygen tension in its underlying embryonic stem cell culture

Oxygen (O₂) levels in the mammalian embryo range between 2.4% and 8%. The cardiac embryonic stem cell test (ESTc) is a model for developmental toxicity predictions, which is usually performed under atmospheric O₂ levels of 20%. We investigated the chemical sensitivity of the ESTc carried out under 20% O₂, using embryonic stem cells (ESC) cultured under either 20% O₂ or 5% O₂. ESC viability was more sensitive to valproic acid (VPA) but less sensitive to flusilazole (FLU) when cultured under 5% versus 20% O₂. For beating cardiomyocyte differentiation, lower ID₅₀ values were found for FLU and VPA when the ESCs had been cultured under 5% versus 20% O₂. At differentiation day 4, gene expression values were primarily driven by the level of O₂ during ESC culture instead of exposure to FLU. In addition, using ESCs cultured under 5% O₂ tension, VPA enhanced Nes (ectoderm) expression. Bmp4 (mesoderm) was enhanced by VPA when using ESCs cultured under 20% O₂. At differentiation day 10, using ESCs cultured under 5% instead of 20% O₂, Nkx2.5 and Myh6 (cardiomyocytes) were less affected after exposure to FLU or VPA. These results show that O₂ tension in ESC culture influences chemical sensitivity in the ESTc. This enhances awareness of the standard culture conditions, which may impact the application of the ESTc in quantitative hazard assessment of chemicals.

Role of novel biomarkers in diabetic cardiomyopathy

Diabetic cardiomyopathy (DCM) is commonly defined as cardiomyopathy in patients with diabetes mellitus in the absence of coronary artery disease and hypertension. As DCM is now recognized as a cause of substantial morbidity and mortality among patients with diabetes mellitus and clinical diagnosis is still inappropriate, various expert groups struggled to identify a suitable biomarker that will help in the recognition and management of DCM, with little success so far. Hence, we thought it important to address the role of biomarkers that have shown potential in either human or animal studies and which could eventually result in mitigating the poor outcomes of DCM. Among the array of biomarkers we thoroughly analyzed, long noncoding ribonucleic acids, soluble form of suppression of tumorigenicity 2 and galectin-3 seem to be most beneficial for DCM detection, as their plasma/serum levels accurately correlate with the early stages of DCM. The combination of relatively inexpensive and accurate speckle tracking echocardiography with some of the highlighted biomarkers may be a promising screening method for newly diagnosed diabetes mellitus type 2 patients. The purpose of the screening test would be to direct affected patients to more specific confirmation tests. This perspective is in concordance with current guidelines that accentuate the importance of an interdisciplinary team-based approach.

HIF-1α regulates osteoclast activation and mediates osteogenesis during mandibular bone repair via CT-1

OBJECTIVES

Hypoxia is one of the characteristics of microenvironmental changes after orthognathic surgery for fractures. HIF-1α is a main regulator of the hypoxic response and plays a crucial role in bone formation, remodelling, and homeostasis. Osteoclasts participate in bone absorption and affect osteogenesis, and osteoclasts differentiate in a path from the oxygen-rich bone marrow to oxygen-deficient bone lesions. Thus, we aimed to study the key functions of HIF-1α in osteoclasts during mandibular healing after osteotomy.

MATERIALS AND METHODS

The function of HIF-1α in osteoclasts during fracture healing in osteoclast-specific HIF-1α-conditional-knockout mice was investigated in mandibular osteotomy. Primary osteoclasts were used to explore the expression of HIF-1α and cardiotrophin-1 (CT-1) at both the mRNA and protein levels. The ability of BMSCs co-cultured with conditioned media from osteoclast-specific HIF-1α-knockout primary osteoclasts was detected using osteoclast-mediated osteogenesis experiments.

RESULTS

Hypoxia-inducible factor-1α increased osteoclastogenesis and bone resorption, and a delay in bone healing was found in osteoclast-specific HIF-1α-conditional-knockout mice compared with normal mice. HIF-1α-knockout primary osteoclasts inhibited bone resorption and CT-1 expression, and HIF-1α enhanced the osteoclast-mediated stimulation of BMSC differentiation by secreting CT-1.

CONCLUSIONS

Hypoxia-inducible factor-1α can play a key role in the physiology and pathogenesis of bone resorption by promoting osteoclastogenesis during fracture and influencing osteogenesis through CT-1 during bone healing.

Hypoxia induces an endometrial cancer stem-like cell phenotype via HIF-dependent demethylation of SOX2 mRNA

Endometrial cancer stem cells (ECSCs) are stem-like cells endowed with self-renewal and differentiation abilities, and these cells are essential for cancer progression in endometrial cancer (EC). As hallmarks of the tumour microenvironment (TME), hypoxia and hypoxia-inducing factors (HIFs) give rise to the dysregulation of tumour stemness genes, such as SOX2. Against this backdrop, we investigated the regulatory mechanisms regulated by HIFs and SOX2 in ECSCs during EC development. Here, ECSCs isolated from EC cell lines and tissues were found to express stemness genes (CD133 and aldehyde dehydrogenase, ALDH1) following the induction of their ECSC expansion. Notably, m⁶A methylation of RNA and HIF-1α/2α-dependent AlkB homologue 5 (ALKBH5) participate in the regulation of HIFs and SOX2 in EC, as confirmed by the observations that mRNA levels of m⁶A demethylases and ALKBH5 significantly increase under hypoxic conditions in ECSCs. Moreover, hypoxia and high ALKBH5 levels restore the stem-like state of differentiated ECSCs and increase the ECSC-like phenotype, whereas the knockdown of HIFs or ALKBH5 significantly reduces their tumour initiation capacity. In addition, our findings validate the role of ALKBH5 in promoting SOX2 transcription via mRNA demethylation, thereby maintaining the stem-like state and tumorigenicity potential of ECSCs. In conclusion, these observations demonstrate a critical role for m⁶A methylation-mediated regulation of the HIF-ALKBH5-SOX2 axis during ECSC expansion in hypoxic TMEs.

Oxygen tension influences embryonic stem cell maintenance and has lineage specific effects on neural and cardiac differentiation

The importance of oxygen tension in in vitro cultures and its effect on embryonic stem cell (ESC) differentiation has been widely acknowledged. Research has mainly focussed on ESC maintenance or on one line of differentiation and only few studies have examined the potential relation between oxygen tension during ESC maintenance and differentiation. In this study we investigated the influence of atmospheric (20%) versus physiologic (5%) oxygen tension in ESC cultures and their differentiation within the cardiac and neural embryonic stem cell tests (ESTc, ESTn). Oxygen tension was set at 5% or 20% and cells were kept in these conditions from starting up cell culture until use for differentiation. Under these oxygen tensions, ESC culture showed no differences in proliferation and gene and protein expression levels. Differentiation was either performed in the same or in the alternative oxygen tension compared to ESC culture creating four different experimental conditions. Cardiac differentiation in 5% instead of 20% oxygen resulted in reduced development of spontaneously beating cardiomyocytes and lower expression of cardiac markers Nkx2.5, Myh6 and MF20 (myosin), regardless whether ESC had been cultured in 5% or 20% oxygen tension. As compared to the control (20% oxygen during stem cell maintenance and differentiation), neural differentiation in 5% oxygen with ESC cultured in 20% oxygen led to more cardiac and neural crest cell differentiation. The opposite experimental condition of neural differentiation in 20% oxygen with ESC cultured in 5% oxygen resulted in more glial differentiation. ESC that were maintained and differentiated in 5% oxygen showed an increase in neural crest and oligodendrocytes as compared to 20% oxygen during stem cell maintenance and differentiation. This study showed major effects on ESC differentiation in ESTc and ESTn of oxygen tension, which is an important variable to consider when designing and developing a stem cell-based in vitro system.

Cardiotrophin-1 Deficiency Abrogates Atherosclerosis Progression

Cardiotrophin-1 (CT-1) is associated with cardiovascular (CV) diseases. We investigated the effect of CT-1 deficiency in the development and progression of atherosclerosis in double knockout Apoe-/-ct-1-/- mice. Apoe-/- C57Bl/6 or Apoe-/-ct-1-/- C57Bl/6 mice were fed a normal chow diet (NCD) or a high-cholesterol diet (HCD). After sacrifice, serum triglycerides, total cholesterol, low-density lipoprotein cholesterol (LDL-C), free fatty acids and systemic paracrine factors were measured. Intraplaque lipid and collagen content were quantified in the aortic sections. Immune cell populations in spleen, lymph nodes and aorta were analysis by flow cytometry. Apoe-/-ct-1-/- mice in accelerated atherosclerosis exhibited a reduction of total cholesterol, LDL-C, atherosclerotic plaques size in the aortic root and in the abdominal aorta and improved plaque stability in comparison to Apoe-/- mice. CT-1 deficiency in Apoe-/- mice on (HCD) promoted atheroprotective immune cell responses, as demonstrated by a rise in plasma anti-inflammatory immune cell populations (regulatory T cells, Tregs; regulatory B cells, Bregs and B1a cells) and atheroprotective IgM antibodies. CT-1 deficiency in advanced atherosclerosis mediated regulation of paracrine factors, such as interleukin (IL)-3, IL-6, IL-9, IL-15, IL-27, CXCL5, MCP-3, MIP-1α and MIP-1β. In a model of advanced atherosclerosis, CT-1 deficiency induced anti-inflammatory and atheroprotective effects which resulted in abrogation of atheroprogression.

Combination of Ligusticum Chuanxiong and Radix Paeonia Promotes Angiogenesis in Ischemic Myocardium through Notch Signalling and Mobilization of Stem Cells

Objective

To study the cardioprotective mechanism by which the combination of Chuanxiong (CX) and Chishao (CS) promotes angiogenesis.

Methods

Myocardial infarction (MI) mouse models were induced by ligation of the left anterior descending coronary artery. The effects on cardiac function were evaluated in the perindopril tert-butylamine group (PB group) (3 mg/kg/d), CX group (55 mg/kg/d), CS group (55 mg/kg/d), and CX and CS combination (CX-CS) group (27.5 mg/kg/d CX plus 27.5 mg/kg/d CS). RO4929097, an inhibitor of Notch γ secretase, was used (10 mg/kg/d) to explore the role of Notch signalling in the CX-CS-induced promotion of angiogenesis in the myocardial infarcted border zone (IBZ). The left ventricular ejection fraction (LVEF) and percentage of MI area were evaluated with animal ultrasound and Masson staining. The average optical densities (AODs) of CD31 and vWF in the myocardial IBZ were detected by immunofluorescence. Angiogenesis-related proteins including hypoxia-inducible factor 1-alpha (HIF-1α), fibroblast growth factor receptor 1 (FGFR-1), Notch1 and Notch intracellular domain (NICD), and stem cell mobilization-related proteins including stromal cell-derived factor 1 (SDF-1), C-X-C chemokine receptor type 4 (CXCR-4), and cardiotrophin1 were detected by western blot analysis.

Results

Compared with the model group, the CX-CS and PB groups both showed markedly improved LVEF and decreased percentage of MI area after 21 days of treatment. Although the CX group and CS group showed increased LVEF and decreased MI areas compared with the model group, the difference was not significant. The AOD of CD31 in the IBZ in both the model and the CX-CS-I group was markedly reduced compared with that in the sham group. CX-CS significantly increased the CD31 AOD in the IBZ and decreased the AODs of CD31 and vWF in the infarct zone compared with those in the model group. The expression of HIF-1α in both the model group and the CX-CS group was higher than that in the sham group. Compared with the model group, the expression of FGFR-1, SDF-1, cardiotrophin1, Notch1, and NICD was increased in the CX-CS group. Notch1 and NICD expression in the CX-CS-I group was reduced compared with that in the CX-CS group.

Conclusions

The combination of CX and CS protected cardiomyocytes in the IBZ better than CX or CS alone. The mechanism by which CX-CS protects ischemic myocardium may be related to the proangiogenesis effect of CX-CS exerted through Notch signalling and the mobilization of stem cells to the IBZ.

Inhibition of cardiotrophin‑1 overexpression is involved in the anti‑fibrotic effect of Astrogaloside IV

Astragaloside IV (AsIV), one of the major active ingredients in Astragalus membranaceus, has demonstrated remarkable antifibrotic effects via its antioxidative activity. Cardiac fibrosis is an important pathological mechanism during cardiac remodelling associated with heart failure. In the present study, the mechanism underlying the antifibrotic effect of AsIV upon isoprenaline (ISO) stimulation was investigated. AsIV significantly improved cardiac fibrosis in vivo and dose‑dependently inhibited ISO‑induced CF proliferation in vitro. The ISO‑triggered elevation in reactive oxygen species (ROS) levels was remarkably inhibited by AsIV, as well as ROS scavenger N‑acetylcysteine (NAC), and not affected by cardiotrophin‑1 (CT‑1) knockdown. In addition, AsIV effectively reversed ISO‑induced upregulation of CT‑1 expression, which was blunted by pretreatment with NAC. Cardiac fibroblast (CF) proliferation and collagen Ι overexpression induced by ISO stimulation were effectively abrogated by AsIV, NAC, and CT‑1 small interfering RNA transfection. Taken together, these results demonstrated that AsIV was able to effectively inhibit ISO‑induced CF proliferation and collagen production through negative regulation of ROS‑mediated CT‑1 upregulation.

Cobalt chloride induces RhoA/ROCK activation and remodeling effect in H9c2 cardiomyoblasts: Involvement of PI3K/Akt and MAPK pathways

Chronic heart failure is a serious complication of myocardial infarction, one of the major causes of death worldwide that often leads to adverse cardiac hypertrophy and poor prognosis. Hypoxia-induced cardiac tissue remodeling is considered an important underlying etiology. This study aimed to delineate the signaling profiles of RhoA/ROCK, PI3K/Akt, and MAPK and their involvement in regulation of remodeling events in cultured H9c2 cardiomyoblast cells. In addition to its growth-suppressive effect, the hypoxia-mimetic chemical, cobalt chloride (CoCl₂) significantly induced RhoA kinase activation as revealed by increased MBS phosphorylation and ROCK1/2 expression in H9c2 cells. CoCl₂ treatment up-regulated type I collagen and MMP-9, but did not affect MMP-2, implicating its role in tissue remodeling. Kinetic signal profiling study showed that CoCl₂ also elicited Smad2 hyperphosphorylation and its nuclear translocation in the absence of TGF-β1. In addition, CoCl₂ activated Akt-, ERK1/2-, JNK-, and p38 MAPK-mediated signaling pathways. Kinase inhibition experiments demonstrated that hydroxyfasudil, a RhoA kinase inhibitor, significantly blocked the CoCl₂- and lysophosphatidic acid-evoked Smad2 phosphorylation and overexpression of type I collagen and MMP-9, and that PI3K and ERK interplayed with RhoA and its downstream Smad2 signaling cascade. In conclusion, this study demonstrated that RhoA/ROCK, PI3K/Akt, and MAPK pathways are mechanistically involved in the CoCl₂-stimulated tissue remodeling in H9c2 cardiomyoblast cells. Targeting signaling mediators might be used to mitigate hypoxia-related Smad2 phosphorylation and cardiac remodeling events in ischemic cardiomyopathy.

Melatonin promotes cardiomyogenesis of embryonic stem cells via inhibition of HIF-1α stabilization

Melatonin, a molecule involved in the regulation of circadian rhythms, has protective effects against myocardial injuries. However, its capability to regulate the maturation of cardiac progenitor cells is unclear. Recently, several studies have shown that melatonin inhibits the stabilization of hypoxia-inducible factors (HIFs), important signaling molecules with cardioprotective effects. In this study, by employing differentiating mouse embryonic stem cells, we report that melatonin significantly upregulated the expression of cardiac cell-specific markers (myosin heavy chains six and seven) as well as the percentage of myosin heavy chain-positive cells. Importantly, melatonin decreased HIF-1α stabilization and transcriptional activity and, in contrast, induced HIF-2α stabilization. Interestingly, the deletion of HIF-1α completely inhibited the pro-cardiomyogenic effect of melatonin as well as the melatonin-mediated HIF-2α stabilization. Moreover, melatonin increased Sirt-1 levels in a HIF-1α-dependent manner. Taken together, we provide new evidence of a time-specific inhibition of HIF-1α stabilization as an essential feature of melatonin-induced cardiomyogenesis and unexpected different roles of HIF-1α stabilization during various stages of cardiac development. These results uncover new mechanisms underlying the maturation of cardiac progenitor cells and can help in the development of novel strategies for using melatonin in cardiac regeneration therapy.

Genomic analyses identify agents regulating somatotroph and lactotroph functions

Isolated hormone deficiency might be caused by loss of a specific type of endocrine cells, and regenerating these missing cells may provide a new option for future treatment. It is known that POU1F1 lineage cells can differentiate into thyrotroph, somatotroph, and lactotroph. However, there is no effective way of controlling pituitary stem/progenitor cells to differentiate into a specific type of endocrine cell. We thereby analyzed multiple genomic publications related to POU1F1 and pituitary development in this study to identify genes and agents regulating POU1F1 lineage cell differentiation. ANOVA analyses were performed to obtain differentially expressed genes. Ingenuity pathway analyses were performed to obtain signaling pathways, interaction networks, and upstream regulators. Venn diagram was used to determine the overlapping information between studies. Summary statistics was performed to rank genes according to their frequency of occurrence in these studies. The results from upstream analyses indicated that 326 agents may regulate pituitary cell differentiation. These agents can be categorized into 12 groups, including hormones and related pathways, PKA-cAMP pathways, p53/DNA damaging/cell cycle pathways, immune/inflammation regulators, growth factor and downstream pathways, retinoic/RAR pathways, ROS pathways, histone modifications, CCAAT/enhancer binding protein family, neuron development/degeneration pathways, calcium related and fat acid, and glucose pathways. Additional experiments demonstrated that H₂O₂ and catalase differentially regulate growth hormone and prolactin expression in somatolactotroph cells, confirming potential roles of ROS pathway on regulating somatotroph and lactotroph functions.

HIF-1alpha Deficiency Attenuates the Cardiomyogenesis of Mouse Embryonic Stem Cells

Cardiac cell formation, cardiomyogenesis, is critically dependent on oxygen availability. It is known that hypoxia, a reduced oxygen level, modulates the in vitro differentiation of pluripotent cells into cardiomyocytes via hypoxia inducible factor-1alpha (HIF-1α)-dependent mechanisms. However, the direct impact of HIF-1α deficiency on the formation and maturation of cardiac-like cells derived from mouse embryonic stem cells (mESC) in vitro remains to be elucidated. In the present study, we demonstrated that HIF-1α deficiency significantly altered the quality and quantity of mESC-derived cardiomyocytes. It was accompanied with lower mRNA and protein levels of cardiac cell specific markers (myosin heavy chains 6 and 7) and with a decreasing percentage of myosin heavy chain α and β, and cardiac troponin T-positive cells. As to structural aspects of the differentiated cardiomyocytes, the localization of contractile proteins (cardiac troponin T, myosin heavy chain α and β) and the organization of myofibrils were also different. Simultaneously, HIF-1α deficiency was associated with a lower percentage of beating embryoid bodies. Interestingly, an observed alteration in the in vitro differentiation scheme of HIF-1α deficient cells was accompanied with significantly lower expression of the endodermal marker (hepatic nuclear factor 4 alpha). These findings thus suggest that HIF-1α deficiency attenuates spontaneous cardiomyogenesis through the negative regulation of endoderm development in mESC differentiating in vitro.

Cardiotrophin-1 promotes cardiomyocyte differentiation from mouse induced pluripotent stem cells via JAK2/STAT3/Pim-1 signaling pathway

BACKGROUND

The induced pluripotent stem cell (iPSC) has shown great potential in cellular therapy of myocardial infarction (MI), while its application is hampered by the low efficiency of cardiomyocyte differentiation. The present study was designed to investigate the effects of cardiotrophin-1 (CT-1) on cardiomyocyte differentiation from mouse induced pluripotent stem cells (miPSCs) and the underlying mechanisms involved.

METHODS

The optimal treatment condition for cardiomyocyte differentiation from miPSCs was established with ideal concentration (10 ng/mL) and duration (from day 3 to day 14) of CT-1 administration. Up-regulated expression of cardiac specific genes that accounted for embryonic cardiogenesis was observed by quantitative RT-PCR. Elevated amount of α-myosin heavy chain (α-MHC) and cardiac troponin I (cTn I) positive cells were detected by immunofluorescence staining and flow cytometry analysis in CT-1 group.

RESULTS

Transmission electron microscopic analysis revealed that cells treated with CT-1 showed better organized sacromeric structure and more mitochondria, which are morphological characteristic of matured cardiomyocytes. Western blot demonstrated that CT-1 promotes cardiomyocyte differentiation from miPSCs partly via JAK2/STAT3/Pim-1 pathway as compared with control group.

CONCLUSIONS

These findings suggested that CT-1 could enhance the cardiomyocyte differentiation as well as the maturation of mouse induced pluripotent stem cell derived cardiomyocytes by regulating JAK2/STAT3/Pim-1signaling pathway.

Photodynamic activation as a molecular switch to promote osteoblast cell differentiation via AP-1 activation

In photodynamic therapy (PDT), cells are impregnated with a photosensitizing agent that is activated by light irradiation, thereby photochemically generating reactive oxygen species (ROS). The amounts of ROS produced depends on the PDT dose and the nature of the photosensitizer. Although high levels of ROS are cytotoxic, at physiological levels they play a key role as second messengers in cellular signaling pathways, pluripotency, and differentiation of stem cells. To investigate further the use of photochemically triggered manipulation of such pathways, we exposed mouse osteoblast precursor cells and rat primary mesenchymal stromal cells to low-dose PDT. Our results demonstrate that low-dose PDT can promote osteoblast differentiation via the activation of activator protein-1 (AP-1). Although PDT has been used primarily as an anti-cancer therapy, the use of light as a photochemical "molecular switch" to promote differentiation should expand the utility of this method in basic research and clinical applications.

Nuclear Nox4 Role in Stemness Power of Human Amniotic Fluid Stem Cells

Human amniotic fluid stem cells (AFSC) are an attractive source for cell therapy due to their multilineage differentiation potential and accessibility advantages. However the clinical application of human stem cells largely depends on their capacity to expand in vitro, since there is an extensive donor-to-donor heterogeneity. Reactive oxygen species (ROS) and cellular oxidative stress are involved in many physiological and pathophysiological processes of stem cells, including pluripotency, proliferation, differentiation, and stress resistance. The mode of action of ROS is also dependent on the localization of their target molecules. Thus, the modifications induced by ROS can be separated depending on the cellular compartments they affect. NAD(P)H oxidase family, particularly Nox4, has been known to produce ROS in the nucleus. In the present study we show that Nox4 nuclear expression (nNox4) depends on the donor and it correlates with the expression of transcription factors involved in stemness regulation, such as Oct4, SSEA-4, and Sox2. Moreover nNox4 is linked with the nuclear localization of redox sensitive transcription factors, as Nrf2 and NF-κB, and with the differentiation potential. Taken together, these results suggest that nNox4 regulation may have important effects in stem cell capability through modulation of transcription factors and DNA damage.

Connecting Mitochondria, Metabolism, and Stem Cell Fate

As sites of cellular respiration and energy production, mitochondria play a central role in cell metabolism. Cell differentiation is associated with an increase in mitochondrial content and activity and with a metabolic shift toward increased oxidative phosphorylation activity. The opposite occurs during reprogramming of somatic cells into induced pluripotent stem cells. Studies have provided evidence of mitochondrial and metabolic changes during the differentiation of both embryonic and somatic (or adult) stem cells (SSCs), such as hematopoietic stem cells, mesenchymal stem cells, and tissue-specific progenitor cells. We thus propose to consider those mitochondrial and metabolic changes as hallmarks of differentiation processes. We review how mitochondrial biogenesis, dynamics, and function are directly involved in embryonic and SSC differentiation and how metabolic and sensing pathways connect mitochondria and metabolism with cell fate and pluripotency. Understanding the basis of the crosstalk between mitochondria and cell fate is of critical importance, given the promising application of stem cells in regenerative medicine. In addition to the development of novel strategies to improve the in vitro lineage-directed differentiation of stem cells, understanding the molecular basis of this interplay could lead to the identification of novel targets to improve the treatment of degenerative diseases.

Stimulation of cardiomyogenesis from mouse embryonic stem cells by nuclear translocation of cardiotrophin-1

BACKGROUND

Cardiotrophin-1 (CT-1) controls cardiomyogenesis of mouse embryonic stem (ES) cells.

OBJECTIVES

To investigate the signaling pathway underlying the action of CT-1 on cardiac cell differentiation.

METHODS

Protein expression was analyzed by western blot technique and cardiac areas by immunohistochemistry. Calcium, reactive oxygen species (ROS) and nitric oxide (NO) were assessed by microfluorometry using fluo-4, H2DCF, and DAF-2DA, respectively. Gene inactivation of CT-1 was achieved by siRNA technology.

RESULTS

CT-1 as well as its receptor gp 130 were transiently upregulated during differentiation of ES cells. Exogenous CT-1 enhanced cardiomyogenesis, increased the cardiac transcription factors MEF2c, Nkx-2.5, TEAD3 and GATA4, the cardiac proteins α-actinin, MLC2a, MYH7, MLC1a, MLC2v and HCN4 as well as vascular endothelial growth factor (VEGF), platelet-derived growth factor-BB (PDGF-BB), fibroblast growth factor-2 (FGF-2) and atrial natriuretic peptide (ANP). CT-1 downregulation by small interfering RNA (siRNA) inhibited cardiomyogenesis and decreased VEGF, PDGF-BB, FGF-2 and ANP expression. CT-1 raised intracellular calcium which was abolished by the intracellular calcium chelator BAPTA, AM and thapsigargin. Moreover, CT-1 treatment increased ROS, followed by NO generation and NOS3 activation. During ES cell differentiation CT-1 was translocated to the cell nucleus. Exogenous CT-1 induced nuclear translocation of endogenous CT-1, which was inhibited by BAPTA, the NOS inhibitor L-N(G)-Nitroarginine methyl ester (l-NAME), the radical scavenger N-(2-mercaptopropionyl)-glycine (NMPG) as well as the janus kinase 2 (JAK2) inhibitor AG490 and the PI3 kinase (PI3K) inhibitor LY294002.

CONCLUSIONS

Nuclear translocation of CT-1 regulates cardiomyogenesis of ES cells and involves calcium, NO, ROS as well as CT-1 regulated signaling pathways.

The human Nox4: gene, structure, physiological function and pathological significance

Increased generation of reactive oxygen species (ROS) has been implicated in the pathogenesis of a variety of diseases such as cardiovascular diseases and cancer. NADPH oxidase (Nox), a multicomponent enzyme, has been identified as one of the key sources of ROS. Nox4, one of the seven members of Nox family (Nox1, Nox2, Nox3, Nox4, Nox5, Duox1 and Duox2), has been extensively investigated in recent years. Its unique structures result in the constitutive generation of hydrogen peroxide (H2O2) as the main product. As a key oxygen sensor, Nox4-derived H2O2 plays diverse roles in cell proliferation, migration and death. Increased expression of Nox4 in cancer has been observed, which participates in metastasis, angiogenesis and apoptosis. Expression of Nox4 in endothelial cells actively mediated endothelial activation, dysfunction and injury, which contributes to the development of atherosclerosis, hypertension, cardiac hypertrophy and among others. This article explores the experimental studies related to the gene, structure, physiological function and pathological significance of Nox4. As Nox4 might serve as a potential target for the therapy of cardiovascular diseases and cancer, the Nox4 inhibitor is also discussed in this article.

HIF2α induces cardiomyogenesis via Wnt/β-catenin signaling in mouse embryonic stem cells

Background

Embryonic stem cells (ESCs) are pluripotent stem cells and can differentiate into cardiomyocytes when cultured in appropriate conditions. The function of hypoxia-inducible factors (HIFs) has been identified in directing the formation of cardiac lineages. The purpose of this study was to investigate the ability of HIF2α to induce differentiation of ESCs into cardiomyocytes and to explore the potential underlying molecular mechanisms.

Methods

Cardiac differentiation from mouse ESCs was analyzed using the “hanging drop” method, and success was determined by assaying the numbers of beating embryoid bodies and the expression level of cardiac markers. The expression of HIF2α was then manipulated during cardiac differentiation with piggyBac transposon and the lentivirus system. The underlying mechanism was finally examined via administering selective inhibitors of the Wnt/β-catenin signaling pathway.

Results

Overexpressing HIF2α can significantly drive mouse ESCs to form cardiomyocytes. Contrarily, knockdown of HIF2α inhibits the emergence of cardiac cells. In addition, the cardiomyogenesis-promoting effect of HIF2α occurred by increasing the protein level of β-catenin, an effector that contributes to cardiac differentiation at an early stage of ESC differentiation.

Conclusion

HIF2α has a cardiomyogenesis-promoting effect in ESCs via enhancing the activation of the Wnt/β-catenin signaling pathway. Our results may be beneficial for generating and applying cardiomyocytes from ESCs safely and effectively in the future.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0447-7) contains supplementary material, which is available to authorized users.

Expression patterns of sarcomeric α-actin, α-actinin and UCP2 in the myocardium of Kunming mice after exposure to c-terminal polypeptide of cardiotrophin-1

Cardiotrophin-1 (CT-1) activates a distinct form of cardiac muscle cell hypertrophy in which the sarcomeric units are assembled in series. The aim of the study was to determine the expression pattern of sarcomeric contractile protein α-actin, specialized cytoskeletal protein α-actinin and mitochondrial uncoupling protein-2 (UCP2) in myocardial remodeling induced by chronic exposure to CT-1. Kunming mice were intraperitoneally injected with carboxy-terminal polypeptide (CP) of CT-1 (CT-1-CP, 500 μg·kg(-1)· day(-1)) for 1, 2, 3 and 4 week (s), respectively (4 groups obtained according to the injection time, n=10 each, with 5 males and 5 females in each group). Those injected with physiological saline for 4 weeks served as controls (n=10, with 5 males and 5 females). The heart tissues of mice were harvested at 1, 2, 3 or 4 week (s). Immunohistochemistry (IHC) and Western blotting (WB) were used to detect the distribution and expression of sarcomeric α-actin, α-actinin and mitochondrial UCP2 in myocardial tissues. IHC showed that α-actin was mainly distributed around the nuclei of cardiomyocytes, α-actinin concentrated around the striae and UCP2 scattered rather evenly in the plasma. The expression of α-actin was slightly greater than that of α-actinin and UCP2 in the control group (IHC: χ(2)=6.125; WB: F=0.249, P>0.05) and it gradually decreased after exposure to CT-1-CP. There was no significant difference in the expression of α-actin between the control group and the CT-1-CP-treated groups (χ (2)=7.386, P>0.05). But Western blotting revealed significant difference in the expression of α-actin between the control group and the 4-week CT-1-CP-treated group (F=2.912; q=4.203, P<0.05). Moreover, it was found that the expression of α-actinin increased stepwise with the exposure time in CT-1-CP-treated groups and differed significantly between CT-1-CP-treated groups and the control group (ICH: χ (2)=21.977; WB: F=50.388; P<0.01). The expression of UCP2 was initially increased (WB: control group vs. 1- or 2-week group, q values: 5.603 and 9.995, respectively, P<0.01) and then decreased (WB: control group vs. 3-week group, q=4.742, P<0.01; control group vs. 4-week group, q=0.558, P>0.05). It was suggested that long-term exposure to CT-1-CP could lead to the alteration in the expression of sarcomeric α-actin, α-actinin and mitochondrial UCP2. The different expressions of sarcomeric structure proteins and mitochondrial UCP2 may be involved in myocardial remodeling.

Blocking autocrine VEGF signaling by sunitinib, an anti-cancer drug, promotes embryonic stem cell self-renewal and somatic cell reprogramming

Maintaining the self-renewal of embryonic stem cells (ESCs) could be achieved by activating the extrinsic signaling, i.e., the use of leukemia inhibitory factor (LIF), or blocking the intrinsic differentiation pathways, i.e., the use of GSK3 and MEK inhibitors (2i). Here we found that even in medium supplemented with LIF, mESCs still tend to differentiate toward meso-endoderm lineages after long-term culture and the culture spontaneously secretes vascular endothelial growth factors (VEGFs). Blocking VEGF signaling with sunitinib, an anti-cancer drug and a receptor tyrosine kinase (RTK) inhibitor mainly targeting VEGF receptors (VEGFRs), is capable of maintaining the mESCs in the undifferentiated state without the need for feeder cells or LIF. Sunitinib facilitates the derivation of mESCs from blastocysts, and the mESCs maintained in sunitinib-containing medium remain pluripotent and are able to contribute to chimeric mice. Sunitinib also promotes iPSC generation from MEFs with only Oct4. Knocking down VEGFR2 or blocking it with neutralizing antibody mimicks the effect of sunitinib, indicating that blocking VEGF/VEGFR signaling is indeed beneficial to the self-renewal of mESCs. We also found that hypoxia-inducible factor alpha (HIF1α) and endoplasmic reticulum (ER) stress are involved in the production of VEGF in mESCs. Blocking both pathways inhibits the expression of VEGF and prevents spontaneous differentiation of mESCs. Interestingly, LIF may also exert its effect by downregulating HIF1α and ER stress pathways and subsequent VEGF expression. These results indicate the existence of an intrinsic differentiation pathway in mESCs by activating the autocrine VEGF signaling. Blocking VEGF signaling with sunitinib or other small molecules help to maintain the mESCs in the ground state of pluripotency.

Roles of reactive oxygen species in the fate of stem cells

SIGNIFICANCE

Stem cells are characterized by the properties of self-renewal and the ability to differentiate into multiple cell types, and thus maintain tissue homeostasis. Reactive oxygen species (ROS) are a natural byproduct of aerobic metabolism and have roles in cell signaling. Regulation of ROS has a vital role in maintaining "stemness" and differentiation of the stem cells, as well as in progression of stem-cell-associated diseases.

RECENT ADVANCES

As of late, much research has been done on the adverse effects of ROS in stem cells. However, recently it has become apparent that in some cases redox status of the stem cell does have a role in maintaining its identity as such. Both pluripotent and multipotent stem cell types have been reported to possess enzymatic and nonenzymatic mechanisms for detoxification of ROS and to correct oxidative damage to the genome as well as the proteome.

CRITICAL ISSUES

Although context dependent and somewhat varied among different stem cell types, the correlation seems to exist between antioxidant defense level and stem cell fate change (i.e., proliferation, differentiation, and death). Changes in stem cell redox regulation may affect the pathogenesis of various human diseases.

FUTURE DIRECTIONS

Dissecting the defined roles of ROS in distinct stem cell types will greatly enhance their basic and translational applications. Here, we discuss the various roles of ROS in adult, embryonic, and induced pluripotent stem cells.

Reactive oxygen species in normal and tumor stem cells

Reactive oxygen species (ROS) play an important role in determining the fate of normal stem cells. Low levels of ROS are required for stem cells to maintain quiescence and self-renewal. Increases in ROS production cause stem cell proliferation/differentiation, senescence, and apoptosis in a dose-dependent manner, leading to their exhaustion. Therefore, the production of ROS in stem cells is tightly regulated to ensure that they have the ability to maintain tissue homeostasis and repair damaged tissues for the life span of an organism. In this chapter, we discuss how the production of ROS in normal stem cells is regulated by various intrinsic and extrinsic factors and how the fate of these cells is altered by the dysregulation of ROS production under various pathological conditions. In addition, the implications of the aberrant production of ROS by tumor stem cells for tumor progression and treatment are also discussed.

An ENU mutagenesis-derived mouse model with a dominant Jak1 mutation resembling phenotypes of systemic autoimmune disease

Within the Munich, Germany, N-ethyl-N-nitrosourea mouse mutagenesis program, we isolated a dominant Jak1 mouse model resembling phenotypic characteristics related to autoimmune disease. Chromosomal sequencing revealed a new Jak1 (p.Ser645Pro) point mutation at the conserved serine of the pseudokinase domain, corresponding to a somatic human mutation (p.Ser646Phe) inducing a constitutive activation of the Janus kinase (JAK)/STAT pathway. Morphologically, all Jak1(S645P+/-) mice showed a progressive structural deterioration of ears starting at the age of 4 months, with mononuclear cell infiltration into the dermis. Female mutant mice, in particular, developed severe skin lesions in the neck from 7 months of age. The IHC analysis of these lesions showed an activation of Stat3 downstream to Jak1(S645P) and elevated tissue levels of IL-6. Histopathological analysis of liver revealed a nodular regenerative hyperplasia. In the spleen, the number of Russell bodies was doubled, correlating with significant increased levels of all immunoglobulin isotypes and anti-DNA antibodies in serum. Older mutant mice developed thrombocytopenia and altered microcytic red blood cell counts. Jak1(S645P+/-) mice showed phenotypes related to impaired bone metabolism as increased carboxy-terminal collagen cross-link-1 levels and alkaline phosphatase activities in plasma, hypophosphatemia, and strongly decreased bone morphometric values. Taken together, Jak1(S645P+/-) mice showed an increased activation of the IL-6-JAK-STAT pathway leading to a systemic lupus erythematosus-like phenotype and offering a new valuable tool to study the role of the JAK/STAT pathway in disease development.

Update on the pathophysiological activities of the cardiac molecule cardiotrophin-1 in obesity

Cardiotrophin-1 (CT-1) is a heart-targeting cytokine that has been reported to exert a variety of activities also in other organs such as the liver, adipose tissue, and atherosclerotic arteries. CT-1 has been shown to induce these effects via binding to a transmembrane receptor, comprising the leukaemia inhibitory factor receptor (LIFR β ) subunit and the glycoprotein 130 (gp130, a common signal transducer). Both local and systemic concentrations of CT-1 have been shown to potentially play a critical role in obesity. For instance, CT-1 plasma concentrations have been shown to be increased in metabolic syndrome (a cluster disease including obesity) probably due to adipose tissue overexpression. Interestingly, treatment with exogenous CT-1 has been shown to improve lipid and glucose metabolism in animal models of obesity. These benefits might suggest a potential therapeutic role for CT-1. However, beyond its beneficial properties, CT-1 has been also shown to induce some adverse effects, such as cardiac hypertrophy and adipose tissue inflammation. Although scientific evidence is still needed, CT-1 might be considered as a potential example of damage/danger-associated molecular pattern (DAMP) in obesity-related cardiovascular diseases. In this narrative review, we aimed at discussing and updating evidence from basic research on the pathophysiological and potential therapeutic roles of CT-1 in obesity.

Cardiotrophin-1 induces sarcoplasmic reticulum Ca(2+) leak and arrhythmogenesis in adult rat ventricular myocytes

AIMS

Plasma levels of cardiotrophin-1 (CT-1) are elevated in several cardiovascular diseases and are correlated with the severity of the pathology. However, the mechanisms by which this inflammatory cytokine participates in the pathology of the heart are not completely understood. It is well established that alterations in intracellular calcium ([Ca(2+)](i)) handling are involved in cardiac dysfunction during heart failure, but it is unknown whether CT-1 modulates [Ca(2+)](i) handling in adult cardiomyocytes. Here we have analyzed for the first time the effects of CT-1 on [Ca(2+)](i) homeostasis in adult rat cardiomyocytes.

METHODS AND RESULTS

L-type calcium current (I(CaL)) was recorded using patch-clamp techniques, and [Ca(2+)](i) transients and Ca(2+) sparks were viewed by confocal microscopy. Treatment of cardiomyocytes with 1 nM CT-1 for 20-60 min induced a significant increase in I(CaL) density, [Ca(2+)](i) transients, and cell shortening compared with control cells. Our study reveals that CT-1 increases I(CaL) by a protein kinase A-dependent mechanism, and Ca(2+) sparks by a Ca(2+)/calmodulin kinase II-dependent and protein kinase A-independent mechanism. Cardiomyocytes treated with CT-1 exhibited a higher occurrence of arrhythmogenic behaviour, manifested as spontaneous Ca(2+) waves and aftercontractions.

CONCLUSION

Our findings provide evidence that cardiomyocytes treated with CT-1 present high spontaneous Ca(2+) release during diastole, a mechanism linked to arrhythmogenicity in the pathologic heart.

Hypoxic priming of mESCs accelerates vascular-lineage differentiation through HIF1-mediated inverse regulation of Oct4 and VEGF

Hypoxic microenvironment plays an important role in determining stem cell fates. However, it is controversial to which direction between self-renewal and differentiation the hypoxia drives the stem cells. Here, we investigated whether a short exposure to hypoxia (termed 'hypoxic-priming') efficiently directed and promoted mouse embryonic stem cells (mESCs) to differentiate into vascular-lineage. During spontaneous differentiation of embryoid bodies (EBs), hypoxic region was observed inside EB spheroids even under normoxic conditions. Indeed, hypoxia-primed EBs more efficiently differentiated into cells of vascular-lineage, than normoxic EBs did. We found that hypoxia suppressed Oct4 expression via direct binding of HIF-1 to reverse hypoxia-responsive elements (rHREs) in the Oct4 promoter. Furthermore, vascular endothelial growth factor (VEGF) was highly upregulated in hypoxia-primed EBs, which differentiated towards endothelial cells in the absence of exogenous VEGF. Interestingly, this differentiation was abolished by the HIF-1 or VEGF blocking. In vivo transplantation of hypoxia-primed EBs into mice ischemic limb elicited enhanced vessel differentiation. Collectively, our findings identify that hypoxia enhanced ESC differentiation by HIF-1-mediated inverse regulation of Oct4 and VEGF, which is a novel pathway to promote vascular-lineage differentiation.

Controlling embryonic stem cell growth and differentiation by automation: enhanced and more reliable differentiation for drug discovery

Despite significant use in basic research, embryonic stem cells have just begun to be used in the drug discovery process. Barriers to the adoption of embryonic stem cells in drug discovery include the difficulty in growing cells and inconsistent differentiation to the desired cellular phenotype. Embryonic stem cell cultures require consistent and frequent handling to maintain the cells in a pluripotent state. In addition, the preferred hanging drop method of embryoid body (EB) differentiation is not amenable to high-throughput methods, and suspension cultures of EBs show a high degree of variability. Murine embryonic stem cells passaged on an automated platform maintained ≥ 90% viability and pluripotency. We also developed a method of EB formation using 384-well microplates that form a single EB per well, with excellent uniformity across EBs. This format facilitated high-throughput differentiation and enabled screens to optimize directed differentiation into a desired cell type. Using this approach, we identified conditions that enhanced cardiomyocyte differentiation sevenfold. This optimized differentiation method showed excellent consistency for such a complex biological process. This automated approach to embryonic stem cell handling and differentiation can provide the high and consistent yields of differentiated cell types required for basic research, compound screens, and toxicity studies.

Cobalt chloride pretreatment promotes cardiac differentiation of human embryonic stem cells under atmospheric oxygen level

Our previous study demonstrated the direct involvement of the HIF-1α subunit in the promotion of cardiac differentiation of murine embryonic stem cells (ESCs). We report the use of cobalt chloride to induce HIF-1α stabilization in human ESCs to promote cardiac differentiation. Treatment of undifferentiated hES2 human ESCs with 50 μM cobalt chloride markedly increased protein levels of the HIF-1α subunit, and was associated with increased expression of early cardiac specific transcription factors and cardiotrophic factors including NK2.5, vascular endothelial growth factor, and cardiotrophin-1. When pretreated cells were subjected to cardiac differentiation, a notable increase in the occurrence of beating embryoid bodies and sarcomeric actinin-positive cells was observed, along with increased expression of the cardiac-specific markers, MHC-A, MHC-B, and MLC2V. Electrophysiological study revealed increased atrial- and nodal-like cells in the cobalt chloride-pretreated group. Confocal calcium imaging analysis indicated that the maximum upstroke and decay velocities were significantly increased in both noncaffeine and caffeine-induced calcium transient in cardiomyocytes derived from the cobalt chloride-pretreated cells, suggesting these cells were functionally more mature. In conclusion, our study demonstrated that cobalt chloride pretreatment of hES2 human ESCs promotes cardiac differentiation and the maturation of calcium homeostasis of cardiomyocytes derived from ESCs.

HIF-1-mediated up-regulation of cardiotrophin-1 is involved in the survival response of cardiomyocytes to hypoxia

AIMS

Cardiotrophin-1 (CT-1) is a cytokine of the interleukin-6 superfamily which is up-regulated in cardiac diseases, in part via hypoxia-dependent mechanisms. However, no evidence for a direct regulation of CT-1 gene (CTF1) promoter by hypoxia inducible factor-1 (HIF-1) has been provided.

METHODS AND RESULTS

Hypoxia increased CT-1 mRNA levels in the murine adult cardiomyocyte cell line HL-1 in a time-dependent manner. Interestingly, in a murine model (C57BL/6), we show that systemic hypoxia also significantly up-regulated CT-1 in myocardial tissue. The effect of hypoxia on CT-1 expression was mediated through a transcriptional mechanism, since hypoxia increased luciferase activity of constructs containing CTF1 promoter sequences. The increase in CT-1 levels was significantly reduced by drugs that prevent calcium mobilization, such as lercanidipine, or that inhibit the activation of the PI3K/Akt pathway (wortmannin) or mammalian target of rapamycin (rapamycin). The CT-1 elevation was similarly induced by HIF-1α over-expression in co-transfection experiments and prevented by HIF-1α silencing. The direct interaction of HIF-1α with the CTF1 promoter was confirmed through site-directed mutagenesis of hypoxia response elements, electrophoreric mobility shift, and ChIP assays. Hypoxia induced HL-1 apoptosis (measured as annexin-V binding or caspase 3/7 activity) which was increased when CT-1 was silenced in knocked-down cells by lentiviral vectors.

CONCLUSION

Hypoxia increased CT-1 levels in cardiac cells (in vitro and in vivo) through a direct regulation of CTF1 promoter by HIF-1α. This CT-1 activation by hypoxia may protect cells from apoptosis, thus supporting a protective role for CT-1 as a survival factor for cardiomyocytes.

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.

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.

Cardiotrophin-1 in cardiovascular regulation

Cardiotrophin (CT)-1 was discovered by coupling expression cloning with an embryonic stem cell-based model of cardiogenesis. Comparison of similarity in amino acid sequence and conformational structure indicates that CT-1 is a member of the interleukin (IL)-6 type cytokine family that shares the transmembrane signaling protein, glycoprotein (gp) 130 as a receptor. These cytokines mediate overlapping pleiotropic actions on a variety of cell types including cardiac myocytes, hepatocytes, megakaryocytes, osteoclasts, and neuronal cells. CT-lmediates its hypertrophic and cytoprotective properties through the Janus kinase/signal transducers and activators of transcription (JAK/STAT), mitogen-activated protein (MAP) kinase, phosphatidylinositol (PI) 3 kinase, and nuclear factor kappa B (NFkappaB) pathways. CT-1 gene and protein are distributed not only in the heart, but also in the pulmonary, renal, gastrointestinal, cerebral, and muscular tissues. CT-1 could also be synthesized and secreted from vascular endothelial cells and adipocytes. CT-1 has hypertrophic actions on the cardiac myocytes, skeletal muscle cells, and smooth muscle cells as well as cytoprotective actions on the cardiac myocytes, neuronal cells, and hepatocytes. CT-1 is circulating in the body, and its plasma concentration is increased in various cardiovascular and renal diseases such as hypertension, congestive heart failure, myocardial infarction, valvular heart disease, metabolic syndrome, and chronic kidney disease. Treatment with CT-1 is beneficial in experimental animal models of cardiovascular diseases. CT-1 specifically protects the cardiac myocytes from ischemic damage when CT-1 is given not only prior to the ischemia, but also given at the time of reoxygenation. Current evidence suggests that CT-1 plays an important role in the regulation of the cardiovascular system.

mTORC1 signaling under hypoxic conditions is controlled by ATM-dependent phosphorylation of HIF-1α

The mTOR complex-1 (mTORC1) coordinates cell growth and metabolism, acting as a restriction point under stress conditions such as low oxygen tension (hypoxia). Hypoxia suppresses mTORC1 signaling. However, the signals by which hypoxia suppresses mTORC1 are only partially understood, and a direct link between hypoxia-driven physiological stress and the regulation of mTORC1 signaling is unknown. Here we show that hypoxia results in ataxia telangiectasia mutated (ATM)-dependent phosphorylation of hypoxia-inducible factor 1-alpha (HIF-1α) on serine(696) and mediates downregulation of mTORC1 signaling. Deregulation of these pathways in pediatric solid tumor xenografts suggests a link between mTORC1 dysregulation and solid tumor development and points to an important role for hypoxic regulation of mTORC1 activity in tumor development.

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.

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.

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.

Cobalt chloride decreases EC-SOD expression through intracellular ROS generation and p38-MAPK pathways in COS7 cells

It is known that cells suffer a chronic hypoxic condition during the development of proximal tubulointerstitial disease. However, it is accepted that extracellular-superoxide dismutase (EC-SOD) protects the cells from oxidative stress. The purpose of this study was to elucidate the regulation of EC-SOD expression in cells under hypoxia. The results show that the expressions of EC-SOD mRNA and protein in cobalt chloride (CoCl(2))-treated COS7 cells decreased in a dose- and time-dependent manner, whereas the expressions of other SOD isoforms (Cu/Zn-SOD and Mn-SOD) were not changed. The down-regulation of EC-SOD mRNA was suppressed by pre-treatment with the antioxidant trolox and the p38 mitogen-activated protein kinase (p38-MAPK) inhibitor SB203580. It is concluded that the expression of EC-SOD is decreased through ROS and p38-MAPK signalling cascades and that the down-regulation of EC-SOD leads to a decrease in the resistance to oxidative stress of COS7 cells under hypoxia induced by CoCl(2).