Protein disulfide isomerase A1 as a novel redox sensor in VEGFR2 signaling and angiogenesis.

VEGFR2 signaling in endothelial cells (ECs) is regulated by reactive oxygen species (ROS) derived from NADPH oxidases (NOXs) and mitochondria, which plays an important role in postnatal angiogenesis. However, it remains unclear how highly diffusible ROS signal enhances VEGFR2 signaling and reparative angiogenesis. Protein disulfide isomerase A1 (PDIA1) functions as an oxidoreductase depending on the redox environment. We hypothesized that PDIA1 functions as a redox sensor to enhance angiogenesis. Here we showed that PDIA1 co-immunoprecipitated with VEGFR2 or colocalized with either VEGFR2 or an early endosome marker Rab5 at the perinuclear region upon stimulation of human ECs with VEGF. PDIA1 silencing significantly reduced VEGF-induced EC migration, proliferation and spheroid sprouting via inhibiting VEGFR2 signaling. Mechanistically, VEGF stimulation rapidly increased Cys-OH formation of PDIA1 via the NOX4-mitochondrial ROS axis. Overexpression of "redox-dead" mutant PDIA1 with replacement of the active four Cys residues with Ser significantly inhibited VEGF-induced PDIA1-CysOH formation and angiogenic responses via reducing VEGFR2 phosphorylation. Pdia1+/- mice showed impaired angiogenesis in developmental retina and Matrigel plug models as well as ex vivo aortic ring sprouting model. Study using hindlimb ischemia model revealed that PDIA1 expression was markedly increased in angiogenic ECs of ischemic muscles, and that ischemia-induced limb perfusion recovery and neovascularization were impaired in EC-specific Pdia1 conditional knockout mice. These results suggest that PDIA1 can sense VEGF-induced H2O2 signal via CysOH formation to promote VEGFR2 signaling and angiogenesis in ECs, thereby enhancing postnatal angiogenesis. The oxidized PDIA1 is a potential therapeutic target for treatment of ischemic vascular diseases.

Notch1 and Notch4 core binding domain peptibodies exhibit distinct ligand-binding and anti-angiogenic properties.

The Notch signaling pathway is an important therapeutic target for the treatment of inflammatory diseases and cancer. We previously created ligand-specific inhibitors of Notch signaling comprised of Fc fusions to specific EGF-like repeats of the Notch1 extracellular domain, called Notch decoys, which bound ligands, blocked Notch signaling, and showed anti-tumor activity with low toxicity. However, the study of their function depended on virally mediated expression, which precluded dosage control and limited clinical applicability. We have refined the decoy design to create peptibody-based Notch inhibitors comprising the core binding domains, EGF-like repeats 10-14, of either Notch1 or Notch4. These Notch peptibodies showed high secretion properties and production yields that were improved by nearly 100-fold compared to previous Notch decoys. Using surface plasmon resonance spectroscopy coupled with co-immunoprecipitation assays, we observed that Notch1 and Notch4 peptibodies demonstrate strong but distinct binding properties to Notch ligands DLL4 and JAG1. Both Notch1 and Notch4 peptibodies interfere with Notch signaling in endothelial cells and reduce expression of canonical Notch targets after treatment. While prior DLL4 inhibitors cause hyper-sprouting, the Notch1 peptibody reduced angiogenesis in a 3-dimensional in vitro sprouting assay. Administration of Notch1 peptibodies to neonate mice resulted in reduced radial outgrowth of retinal vasculature, confirming anti-angiogenic properties. We conclude that purified Notch peptibodies comprising EGF-like repeats 10-14 bind to both DLL4 and JAG1 ligands and exhibit anti-angiogenic properties. Based on their secretion profile, unique Notch inhibitory activities, and anti-angiogenic properties, Notch peptibodies present new opportunities for therapeutic Notch inhibition.

Exercise improves angiogenic function of circulating exosomes in type 2 diabetes: Role of exosomal SOD3.

Exosomes, key mediators of cell-cell communication, derived from type 2 diabetes mellitus (T2DM) exhibit detrimental effects. Exercise improves endothelial function in part via the secretion of exosomes into circulation. Extracellular superoxide dismutase (SOD3) is a major secretory copper (Cu) antioxidant enzyme that catalyzes the dismutation of O2•- to H2 O2 whose activity requires the Cu transporter ATP7A. However, the role of SOD3 in exercise-induced angiogenic effects of circulating plasma exosomes on endothelial cells (ECs) in T2DM remains unknown. Here, we show that both SOD3 and ATP7A proteins were present in plasma exosomes in mice, which was significantly increased after two weeks of volunteer wheel exercise. A single bout of exercise in humans also showed a significant increase in SOD3 and ATP7A protein expression in plasma exosomes. Plasma exosomes from T2DM mice significantly reduced angiogenic responses in human ECs or mouse skin wound healing models, which was associated with a decrease in ATP7A, but not SOD3 expression in exosomes. Exercise training in T2DM mice restored the angiogenic effects of T2DM exosomes in ECs by increasing ATP7A in exosomes, which was not observed in exercised T2DM/SOD3-/- mice. Furthermore, exosomes overexpressing SOD3 significantly enhanced angiogenesis in ECs by increasing local H2 O2  levels in a heparin-binding domain-dependent manner as well as restored defective wound healing and angiogenesis in T2DM or SOD3-/- mice. In conclusion, exercise improves the angiogenic potential of circulating exosomes in T2DM in a SOD3-dependent manner. Exosomal SOD3 may provide an exercise mimetic therapy that supports neovascularization and wound repair in cardiometabolic disease.

Endothelial Notch signaling directly regulates the small GTPase RND1 to facilitate Notch suppression of endothelial migration.

To control sprouting angiogenesis, endothelial Notch signaling suppresses tip cell formation, migration, and proliferation while promoting barrier formation. Each of these responses may be regulated by distinct Notch-regulated effectors. Notch activity is highly dynamic in sprouting endothelial cells, while constitutive Notch signaling drives homeostatic endothelial polarization, indicating the need for both rapid and constitutive Notch targets. In contrast to previous screens that focus on genes regulated by constitutively active Notch, we characterized the dynamic response to Notch. We examined transcriptional changes from 1.5 to 6 h after Notch signal activation via ligand-specific or EGTA induction in cultured primary human endothelial cells and neonatal mouse brain. In each combination of endothelial type and Notch manipulation, transcriptomic analysis identified distinct but overlapping sets of rapidly regulated genes and revealed many novel Notch target genes. Among the novel Notch-regulated signaling pathways identified were effectors in GPCR signaling, notably, the constitutively active GTPase RND1. In endothelial cells, RND1 was shown to be a novel direct Notch transcriptional target and required for Notch control of sprouting angiogenesis, endothelial migration, and Ras activity. We conclude that RND1 is directly regulated by endothelial Notch signaling in a rapid fashion in order to suppress endothelial migration.

Unique functions for Notch4 in murine embryonic lymphangiogenesis.

In mice, embryonic dermal lymphatic development is well understood and used to study gene functions in lymphangiogenesis. Notch signaling is an evolutionarily conserved pathway that modulates cell fate decisions, which has been shown to both inhibit and promote dermal lymphangiogenesis. Here, we demonstrate distinct roles for Notch4 signaling versus canonical Notch signaling in embryonic dermal lymphangiogenesis. Actively growing embryonic dermal lymphatics expressed NOTCH1, NOTCH4, and DLL4 which correlated with Notch activity. In lymphatic endothelial cells (LECs), DLL4 activation of Notch induced a subset of Notch effectors and lymphatic genes, which were distinctly regulated by Notch1 and Notch4 activation. Treatment of LECs with VEGF-A or VEGF-C upregulated Dll4 transcripts and differentially and temporally regulated the expression of Notch1 and Hes/Hey genes. Mice nullizygous for Notch4 had an increase in the closure of the lymphangiogenic fronts which correlated with reduced vessel caliber in the maturing lymphatic plexus at E14.5 and reduced branching at E16.5. Activation of Notch4 suppressed LEC migration in a wounding assay significantly more than Notch1, suggesting a dominant role for Notch4 in regulating LEC migration. Unlike Notch4 nulls, inhibition of canonical Notch signaling by expressing a dominant negative form of MAML1 (DNMAML) in Prox1+ LECs led to increased lymphatic density consistent with an increase in LEC proliferation, described for the loss of LEC Notch1. Moreover, loss of Notch4 did not affect LEC canonical Notch signaling. Thus, we propose that Notch4 signaling and canonical Notch signaling have distinct functions in the coordination of embryonic dermal lymphangiogenesis.

The P-type ATPase transporter ATP7A promotes angiogenesis by limiting autophagic degradation of VEGFR2.

VEGFR2 (KDR/Flk1) signaling in endothelial cells (ECs) plays a central role in angiogenesis. The P-type ATPase transporter ATP7A regulates copper homeostasis, and its role in VEGFR2 signaling and angiogenesis is entirely unknown. Here, we describe the unexpected crosstalk between the Copper transporter ATP7A, autophagy, and VEGFR2 degradation. The functional significance of this Copper transporter was demonstrated by the finding that inducible EC-specific ATP7A deficient mice or ATP7A-dysfunctional ATP7Amut mice showed impaired post-ischemic neovascularization. In ECs, loss of ATP7A inhibited VEGF-induced VEGFR2 signaling and angiogenic responses, in part by promoting ligand-induced VEGFR2 protein degradation. Mechanistically, VEGF stimulated ATP7A translocation from the trans-Golgi network to the plasma membrane where it bound to VEGFR2, which prevented autophagy-mediated lysosomal VEGFR2 degradation by inhibiting autophagic cargo/adapter p62/SQSTM1 binding to ubiquitinated VEGFR2. Enhanced autophagy flux due to ATP7A dysfunction in vivo was confirmed by autophagy reporter CAG-ATP7Amut -RFP-EGFP-LC3 transgenic mice. In summary, our study uncovers a novel function of ATP7A to limit autophagy-mediated degradation of VEGFR2, thereby promoting VEGFR2 signaling and angiogenesis, which restores perfusion recovery and neovascularization. Thus, endothelial ATP7A is identified as a potential therapeutic target for treatment of ischemic cardiovascular diseases.

Human induced pluripotent stem cell-derived atrial cardiomyocytes carrying an SCN5A mutation identify nitric oxide signaling as a mediator of atrial fibrillation.

Mutations in SCN5A, encoding the cardiac sodium channel, are linked with familial atrial fibrillation (AF) but the underlying pathophysiologic mechanisms and implications for therapy remain unclear. To characterize the pathogenesis of AF-linked SCN5A mutations, we generated patient-specific induced pluripotent stem cell-derived atrial cardiomyocytes (iPSC-aCMs) from two kindreds carrying SCN5A mutations (E428K and N470K) and isogenic controls using CRISPR-Cas9 gene editing. We showed that mutant AF iPSC-aCMs exhibited spontaneous arrhythmogenic activity with beat-to-beat irregularity, prolonged action potential duration, and triggered-like beats. Single-cell recording revealed enhanced late sodium currents (INa,L) in AF iPSC-aCMs that were absent in a heterologous expression model. Gene expression profiling of AF iPSC-aCMs showed differential expression of the nitric oxide (NO)-mediated signaling pathway underlying enhanced INa,L. We showed that patient-specific AF iPSC-aCMs exhibited striking in vitro electrophysiological phenotype of AF-linked SCN5A mutations, and transcriptomic analyses supported that the NO signaling pathway modulated the INa,L and triggered AF.

Electrophysiologic and molecular mechanisms of a frameshift NPPA mutation linked with familial atrial fibrillation.

A frameshift (fs) mutation in the natriuretic peptide precursor A (NPPA) gene, encoding a mutant atrial natriuretic peptide (Mut-ANP), has been linked with familial atrial fibrillation (AF) but the underlying mechanisms by which the mutation causes AF remain unclear. We engineered 2 transgenic (TG) mouse lines expressing the wild-type (WT)-NPPA gene (H-WT-NPPA) and the human fs-Mut-NPPA gene (H-fsMut-NPPA) to test the hypothesis that mice overexpressing the human NPPA mutation are more susceptible to AF and elucidate the underlying electrophysiologic and molecular mechanisms. Transthoracic echocardiography and surface electrocardiography (ECG) were performed in H-fsMut-NPPA, H-WT-NPPA, and Non-TG mice. Invasive electrophysiology, immunohistochemistry, Western blotting and patch clamping of membrane potentials were performed. To examine the role of the Mut-ANP in ion channel remodeling, we measured plasma cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP) levels and protein kinase A (PKA) activity in the 3 groups of mice. In H-fsMut-NPPA mice mean arterial pressure (MAP) was reduced when compared to H-WT-NPPA and Non-TG mice. Furthermore, injection of synthetic fs-Mut-ANP lowered the MAP in H-WT-NPPA and Non-TG mice while synthetic WT-ANP had no effect on MAP in the 3 groups of mice. ECG characterization revealed significantly prolonged QRS duration in H-fsMut-NPPA mice when compared to the other two groups. Trans-Esophageal (TE) atrial pacing of H-fsMut-NPPA mice showed increased AF burden and AF episodes when compared with H-WT-NPPA or Non-TG mice. The cardiac Na+ (NaV1.5) and Ca2+ (CaV1.2/CaV1.3) channel expression and currents (INa, ICaL) and action potential durations (APD90/APD50/APD20) were significantly reduced in H-fsMut-NPPA mice while the rectifier K+ channel current (IKs) was markedly increased when compared to the other 2 groups of mice. In addition, plasma cGMP levels were only increased in H-fsMut-NPPA mice with a corresponding reduction in plasma cAMP levels and PKA activity. In summary, we showed that mice overexpressing an AF-linked NPPA mutation are more prone to develop AF and this risk is mediated in part by remodeling of the cardiac Na+, Ca2+ and K+ channels creating an electrophysiologic substrate for reentrant AF.

Modification of Cardiac Progenitor Cell-Derived Exosomes by miR-322 Provides Protection against Myocardial Infarction through Nox2-Dependent Angiogenesis.

Myocardial infarction (MI) is the primary cause of cardiovascular mortality, and therapeutic strategies to prevent or mitigate the consequences of MI are a high priority. Cardiac progenitor cells (CPCs) have been used to treat cardiac injury post-MI, and despite poor engraftment, they have been shown to inhibit apoptosis and to promote angiogenesis through poorly understood paracrine effects. We previously reported that the direct injection of exosomes derived from CPCs (CPCexo) into mouse hearts provides protection against apoptosis in a model of acute ischemia/reperfusion injury. Moreover, we and others have reported that reactive oxygen species (ROS) derived from NADPH oxidase (NOX) can enhance angiogenesis in endothelial cells (ECs). Here we examined whether bioengineered CPCexo transfected with a pro-angiogenic miR-322 (CPCexo-322) can improve therapeutic efficacy in a mouse model of MI as compared to CPCexo. Systemic administration of CPCexo-322 in mice after ischemic injury provided greater protection post-MI than control CPCexo, in part, through enhanced angiogenesis in the border zones of infarcted hearts. Mechanistically, the treatment of cultured human ECs with CPCexo-322 resulted in a greater angiogenic response, as determined by increased EC migration and capillary tube formation via increased Nox2-derived ROS. Our study reveals that the engineering of CPCexo via microRNA (miR) programing can enhance angiogenesis, and this may be an effective therapeutic strategy for the treatment of ischemic cardiovascular diseases.

COMP-Angiopoietin-1 accelerates muscle regeneration through N-cadherin activation.

Angiopoietin-1 modulates vascular stability via Tie2 on endothelial cells. In our previous study, we also showed it acts as an inhibitor of cardiomyocyte death. However, it remains poorly understood how Ang1 regulates myogenesis during muscle regeneration. Here we found that COMP-Ang1 (cAng1) enhances muscle regeneration through N-cadherin activation. Muscle fiber regeneration after limb muscle damage by ischemic injury was enhanced with cAng1 treatment. Mechanistically cAng1 directly bound to N-cadherin on the myoblast surface in a Ca2+ dependent manner. The interaction enhanced N-cadherin activation via N-cadherin/p120-catenin complex formation, which in turn activated p38MAPK (but not AKT or ERK) and myogenin expression (but not myoD) as well as increasing myogenin+ cells in/ex vivo. After transplantation of GFP-expressing myoblasts (GFP-MB), we showed an increased generation of GFP+ myotubes with adenovirus cAng1 (Adv-cAng1) injection. Adv-cAng1, however, could not stimulate myotube formation in N-cadherin-depleted GFP-MB. Taken together, this study uncovers the mechanism of how cAng1 promotes myoblast differentiation and muscle regeneration through the N-cadherin/p120-catenin/p38MAPK/myogenin axis.

Redox Regulation of Mitochondrial Fission Protein Drp1 by Protein Disulfide Isomerase Limits Endothelial Senescence.

Mitochondrial dynamics are tightly controlled by fusion and fission, and their dysregulation and excess reactive oxygen species (ROS) contribute to endothelial cell (EC) dysfunction. How redox signals regulate coupling between mitochondrial dynamics and endothelial (dys)function remains unknown. Here, we identify protein disulfide isomerase A1 (PDIA1) as a thiol reductase for the mitochondrial fission protein Drp1. A biotin-labeled Cys-OH trapping probe and rescue experiments reveal that PDIA1 depletion in ECs induces sulfenylation of Drp1 at Cys644, promoting mitochondrial fragmentation and ROS elevation without inducing ER stress, which drives EC senescence. Mechanistically, PDIA1 associates with Drp1 to reduce its redox status and activity. Defective wound healing and angiogenesis in diabetic or PDIA1+/- mice are restored by EC-targeted PDIA1 or the Cys oxidation-defective mutant Drp1. Thus, this study uncovers a molecular link between PDIA1 and Drp1 oxidoreduction, which maintains normal mitochondrial dynamics and limits endothelial senescence with potential translational implications for vascular diseases associated with diabetes or aging.

Atorvastatin prevents endothelial dysfunction in high glucose condition through Skp2-mediated degradation of FOXO1 and ICAM-1.

OBJECTIVE: The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor atorvastatin has been reported to exert vasculo-protective action in diabetes. We investigated the vasculo-protective mechanism of atorvastatin by evaluating its effect on two major pathogenic molecules, FOXO1 and ICAM1, mediated by S-phase kinase-associated protein 2 (Skp2) in diabetic endothelial dysfunction. APPROACH AND RESULTS: [1] FOXO1: Hyperglycemic condition increased FOXO1 protein level in endothelial cells, which was reversed by atorvastatin. This atorvastatin effect was obliterated by treatment of protease inhibitor, suggesting that atorvastatin induces degradation of FOXO1. Immunoprecipitation showed that atorvastatin facilitated the binding of Skp2 to FOXO1, leading to ubiquitination and degradation of FOXO1. [2] ICAM-1: Increased ICAM1 in high glucose condition was reduced by atorvastatin. But this effect of atorvastatin was obliterated when Skp2 was inhibited, suggesting that atorvastatin enhances binding of Skp2 to ICAM1 leading to degradation. Actually, ubiquitination and degradation of ICAM-1 were reduced when Skp2 was inhibited. In vitro monocyte adhesion assay revealed that atorvastatin reduced monocyte adhesion on endothelial cells in high glucose condition, which was reversed by Skp2 knock-down. CONCLUSION: Atorvastatin strengthens Skp2 binding to FOXO1 or ICAM1, leading to ubiquitination and degradation. Skp2-dependent ubiquitination of major pathogenic molecules is the key mechanism for statin's protective effect on endothelial function in diabetes.

ARQ 092, an orally-available, selective AKT inhibitor, attenuates neutrophil-platelet interactions in sickle cell disease.

Previous studies identified the Ser/Thr protein kinase, AKT, as a therapeutic target in thrombo-inflammatory diseases. Here we report that specific inhibition of AKT with ARQ 092, an orally-available AKT inhibitor currently in phase Ib clinical trials as an anti-cancer drug, attenuates the adhesive function of neutrophils and platelets from sickle cell disease patients in vitro and cell-cell interactions in a mouse model of sickle cell disease. Studies using neutrophils and platelets isolated from sickle cell disease patients revealed that treatment with 50-500 nM ARQ 092 significantly blocks αMß2 integrin function in neutrophils and reduces P-selectin exposure and glycoprotein Ib/IX/V-mediated agglutination in platelets. Treatment of isolated platelets and neutrophils with ARQ 092 inhibited heterotypic cell-cell aggregation under shear conditions. Intravital microscopic studies demonstrated that short-term oral administration of ARQ 092 or hydroxyurea, a major therapy for sickle cell disease, diminishes heterotypic cell-cell interactions in venules of sickle cell disease mice challenged with tumor necrosis factor-α. Co-administration of hydroxyurea and ARQ 092 further reduced the adhesive function of neutrophils in venules and neutrophil transmigration into alveoli, inhibited expression of E-selectin and intercellular adhesion molecule-1 in cremaster vessels, and improved survival in these mice. Ex vivo studies in sickle cell disease mice suggested that co-administration of hydroxyurea and ARQ 092 efficiently blocks neutrophil and platelet activation and that the beneficial effect of hydroxyurea results from nitric oxide production. Our results provide important evidence that ARQ 092 could be a novel drug for the prevention and treatment of acute vaso-occlusive complications in patients with sickle cell disease.

Endothelial Antioxidant-1: a Key Mediator of Copper-dependent Wound Healing in vivo.

Copper (Cu), an essential nutrient, promotes wound healing, however, target of Cu action and underlying mechanisms remain elusive. Cu chaperone Antioxidant-1 (Atox1) in the cytosol supplies Cu to the secretory enzymes such as lysyl oxidase (LOX), while Atox1 in the nucleus functions as a Cu-dependent transcription factor. Using mouse cutaneous wound healing model, here we show that Cu content (by X-ray Fluorescence Microscopy) and nuclear Atox1 are increased after wounding, and that wound healing with and without Cu treatment is impaired in Atox1-/- mice. Endothelial cell (EC)-specific Atox1-/- mice and gene transfer of nuclear-target Atox1 in Atox1-/- mice reveal that Atox1 in ECs as well as transcription factor function of Atox1 are required for wound healing. Mechanistically, Atox1-/- mice show reduced Atox1 target proteins such as p47phox NADPH oxidase and cyclin D1 as well as extracellular matrix Cu enzyme LOX activity in wound tissues. This in turn results in reducing O2- production in ECs, NFkB activity, cell proliferation and collagen formation, thereby inhibiting angiogenesis, macrophage recruitment and extracellular matrix maturation. Our findings suggest that Cu-dependent transcription factor/Cu chaperone Atox1 in ECs plays an important role to sense Cu to accelerate wound angiogenesis and healing.

Copper Transport Protein Antioxidant-1 Promotes Inflammatory Neovascularization via Chaperone and Transcription Factor Function.

Copper (Cu), an essential micronutrient, plays a fundamental role in inflammation and angiogenesis; however, its precise mechanism remains undefined. Here we uncover a novel role of Cu transport protein Antioxidant-1 (Atox1), which is originally appreciated as a Cu chaperone and recently discovered as a Cu-dependent transcription factor, in inflammatory neovascularization. Atox1 expression is upregulated in patients and mice with critical limb ischemia. Atox1-deficient mice show impaired limb perfusion recovery with reduced arteriogenesis, angiogenesis, and recruitment of inflammatory cells. In vivo intravital microscopy, bone marrow reconstitution, and Atox1 gene transfer in Atox1(-/-) mice show that Atox1 in endothelial cells (ECs) is essential for neovascularization and recruitment of inflammatory cells which release VEGF and TNFα. Mechanistically, Atox1-depleted ECs demonstrate that Cu chaperone function of Atox1 mediated through Cu transporter ATP7A is required for VEGF-induced angiogenesis via activation of Cu enzyme lysyl oxidase. Moreover, Atox1 functions as a Cu-dependent transcription factor for NADPH oxidase organizer p47phox, thereby increasing ROS-NFκB-VCAM-1/ICAM-1 expression and monocyte adhesion in ECs inflamed with TNFα in an ATP7A-independent manner. These findings demonstrate a novel linkage between Atox1 and NADPH oxidase involved in inflammatory neovascularization and suggest Atox1 as a potential therapeutic target for treatment of ischemic disease.

Direct conversion of adult skin fibroblasts to endothelial cells by defined factors.

BACKGROUND: Cell-based therapies to augment endothelial cells (ECs) hold great therapeutic promise. Here, we report a novel approach to generate functional ECs directly from adult fibroblasts. METHODS AND RESULTS: Eleven candidate genes that are key regulators of endothelial development were selected. Green fluorescent protein (GFP)-negative skin fibroblasts were prepared from Tie2-GFP mice and infected with lentiviruses allowing simultaneous overexpression of all 11 factors. Tie2-GFP(+) cells (0.9%), representing Tie2 gene activation, were detected by flow cytometry. Serial stepwise screening revealed 5 key factors (Foxo1, Er71, Klf2, Tal1, and Lmo2) that were required for efficient reprogramming of skin fibroblasts into Tie2-GFP(+) cells (4%). This reprogramming strategy did not involve pluripotency induction because neither Oct4 nor Nanog was expressed after 5 key factor transduction. Tie2-GFP(+) cells were isolated using fluorescence-activated cell sorting and designated as induced ECs (iECs). iECs exhibited endothelium-like cobblestone morphology and expressed EC molecular markers. iECs possessed endothelial functions such as Bandeiraea simplicifolia-1 lectin binding, acetylated low-density lipoprotein uptake, capillary formation on Matrigel, and nitric oxide production. The epigenetic profile of iECs was similar to that of authentic ECs because the promoters of VE-cadherin and Tie2 genes were demethylated. mRNA profiling showed clustering of iECs with authentic ECs and highly enriched endothelial genes in iECs. In a murine model of hind-limb ischemia, iEC implantation increased capillary density and enhanced limb perfusion, demonstrating the in vivo viability and functionality of iECs. CONCLUSIONS: We demonstrated the first direct conversion of adult fibroblasts to functional ECs. These results suggest a novel therapeutic modality for cell therapy in ischemic vascular disease.

Snail as a potential target molecule in cardiac fibrosis: paracrine action of endothelial cells on fibroblasts through snail and CTGF axis.

Ischemia/reperfusion (I/R) injury to myocardium induces death of cardiomyocytes and destroys the vasculature, leading to cardiac fibrosis that is mainly mediated by the transdifferentiation of fibroblasts to myofibroblasts and the collagen deposition. Snail involvement in fibrosis is well known; however, the contribution of Snail to cardiac fibrosis during I/R injury and its underlying mechanisms have not been defined. We showed that I/R injury to mouse hearts significantly increases the expression of Snail. An in vitro hypoxia/reoxygenation (Hy/Reoxy) experiment showed that the cell source of Snail induction is endothelial cells rather than cardiac fibroblasts (cFibroblasts) or cardiomyoblasts. When Snail was overexpressed in endothelial cells, they underwent endothelial-to-mesenchymal transition (EndMT) but showed very poor capacity for collagen synthesis. Instead, reoxygenation- or Snail overexpression-mediated EndMT-like cells noticeably stimulated transdifferentiation of fibroblasts to myofibroblasts via secretion of connective tissue growth factor (CTGF). The injection of a peroxisome proliferator-activated receptor-γ (PPAR-γ) agonist, a selective Snail inhibitor, remarkably suppressed collagen deposition and cardiac fibrosis in mouse I/R injury, and significantly improved cardiac function and reduced Snail and CTGF expression in vivo. Our findings suggested a new mechanism of cell-to-cell communication between EndMT-like cells and fibroblasts for fibrosis induction and implicated Snail as a potential target molecule in cardiac fibrosis after I/R injury.

FOXO1 impairs whereas statin protects endothelial function in diabetes through reciprocal regulation of Kruppel-like factor 2.

AIMS: Krüppel-like factor 2 (KLF2) is implicated as a key molecule maintaining endothelial function. This study was designed to evaluate the reciprocal regulation of KLF2 by the forkhead transcription factor FOXO1, and the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor atorvastatin, in hyperglycaemic conditions. METHODS AND RESULTS: Exposure of human umbilical vein endothelial cells to 30 mM glucose activated FOXO1 and suppressed KLF2. These effects were reversed by FOXO1 small interfering RNA. Adenoviral transfection of constitutively active FOXO1 suppressed KLF2 expression. Interestingly, atorvastatin inhibited FOXO1 by increasing phosphorylation and also by inhibiting nuclear localization and replenished KLF2 in high-glucose conditions. This effect of atorvastatin was attenuated by mevalonate. Chromatin immunoprecipitation analysis demonstrated that glucose increased whereas atorvastatin decreased FOXO1 binding to the promoter region of the KLF2 gene. In the vessels of Otsuka Long-Evans Tokushima Fatty rats, animal models of type 2 diabetes, FOXO1 was activated and KLF2 was suppressed, and this was reversed by atorvastatin treatment. The arteries from Otsuka Long-Evans Tokushima Fatty rats showed impairment of endothelium-dependent vasodilatation, and both atorvastatin and KLF2 gene therapies restored it. CONCLUSIONS: Suppression of KLF2 by FOXO1 may be a plausible mechanism of diabetic endothelial dysfunction. High-glucose-induced, FOXO1-mediated KLF2 suppression was reversed by atorvastatin, suggesting that intensive statin treatment could be a therapeutic option in diabetic vascular dysfunction.

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.

Secondary sphere formation enhances the functionality of cardiac progenitor cells.

Loss of cardiomyocytes impairs cardiac function after myocardial infarction (MI). Recent studies suggest that cardiac stem/progenitor cells could repair the damaged heart. However, cardiac progenitor cells are difficult to maintain in terms of purity and multipotency when propagated in two-dimensional culture systems. Here, we investigated a new strategy that enhances potency and enriches progenitor cells. We applied the repeated sphere formation strategy (cardiac explant → primary cardiosphere (CS) formation → sphere-derived cells (SDCs) in adherent culture condition → secondary CS formation by three-dimensional culture). Cells in secondary CS showed higher differentiation potentials than SDCs. When transplanted into the infarcted myocardium, secondary CSs engrafted robustly, improved left ventricular (LV) dysfunction, and reduced infarct sizes more than SDCs did. In addition to the cardiovascular differentiation of transplanted secondary CSs, robust vascular endothelial growth factor (VEGF) synthesis and secretion enhanced neovascularization in the infarcted myocardium. Microarray pathway analysis and blocking experiments using E-selectin knock-out hearts, specific chemicals, and small interfering RNAs (siRNAs) for each pathway revealed that E-selectin was indispensable to sphere initiation and ERK/Sp1/VEGF autoparacrine loop was responsible for sphere maturation. These results provide a simple strategy for enhancing cellular potency for cardiac repair. Furthermore, this strategy may be implemented to other types of stem/progenitor cell-based therapy.