Protective role of CXCR7 activation in neonatal hyperoxia-induced systemic vascular remodeling and cardiovascular dysfunction in juvenile rats.

Neonatal hyperoxia induces long-term systemic vascular stiffness and cardiovascular remodeling, but the mechanisms are unclear. Chemokine receptor 7 (CXCR7) represents a key regulator of vascular homeostasis and repair by modulating TGF-ß1 signaling. This study investigated whether pharmacological CXCR7 agonism prevents neonatal hyperoxia-induced systemic vascular stiffness and cardiac dysfunction in juvenile rats. Newborn Sprague Dawley rat pups assigned to room air or hyperoxia (85% oxygen), received CXCR7 agonist, TC14012 or placebo for 3 weeks. These rat pups were maintained in room air until 6 weeks when aortic pulse wave velocity doppler, cardiac echocardiography, aortic and left ventricular (LV) fibrosis were assessed. Neonatal hyperoxia induced systemic vascular stiffness and cardiac dysfunction in 6-week-old rats. This was associated with decreased aortic and LV CXCR7 expression. Early treatment with TC14012, partially protected against neonatal hyperoxia-induced systemic vascular stiffness and improved LV dysfunction and fibrosis in juvenile rats by decreasing TGF-ß1 expression. In vitro, hyperoxia-exposed human umbilical arterial endothelial cells and coronary artery endothelial cells had increased TGF-ß1 levels. However, treatment with TC14012 significantly reduced the TGF-ß1 levels. These results suggest that dysregulation of endothelial CXCR7 signaling may contribute to neonatal hyperoxia-induced systemic vascular stiffness and cardiac dysfunction.

c-Myc Drives inflammation of the maternal-fetal interface, and neonatal lung remodeling induced by intra-amniotic inflammation.

Background: Intra-amniotic inflammation (IAI) is associated with increased risk of preterm birth and bronchopulmonary dysplasia (BPD), but the mechanisms by which IAI leads to preterm birth and BPD are poorly understood, and there are no effective therapies for preterm birth and BPD. The transcription factor c-Myc regulates various biological processes like cell growth, apoptosis, and inflammation. We hypothesized that c-Myc modulates inflammation at the maternal-fetal interface, and neonatal lung remodeling. The objectives of our study were 1) to determine the kinetics of c-Myc in the placenta, fetal membranes and neonatal lungs exposed to IAI, and 2) to determine the role of c-Myc in modulating inflammation at the maternal-fetal interface, and neonatal lung remodeling induced by IAI. Methods: Pregnant Sprague-Dawley rats were randomized into three groups: 1) Intra-amniotic saline injections only (control), 2) Intra-amniotic lipopolysaccharide (LPS) injections only, and 3) Intra-amniotic LPS injections with c-Myc inhibitor 10058-F4. c-Myc expression, markers of inflammation, angiogenesis, immunohistochemistry, and transcriptomic analyses were performed on placenta and fetal membranes, and neonatal lungs to determine kinetics of c-Myc expression in response to IAI, and effects of prenatal systemic c-Myc inhibition on lung remodeling at postnatal day 14. Results: c-Myc was upregulated in the placenta, fetal membranes, and neonatal lungs exposed to IAI. IAI caused neutrophil infiltration and neutrophil extracellular trap (NET) formation in the placenta and fetal membranes, and neonatal lung remodeling with pulmonary hypertension consistent with a BPD phenotype. Prenatal inhibition of c-Myc with 10058-F4 in IAI decreased neutrophil infiltration and NET formation, and improved neonatal lung remodeling induced by LPS, with improved alveolarization, increased angiogenesis, and decreased pulmonary vascular remodeling. Discussion: In a rat model of IAI, c-Myc regulates neutrophil recruitment and NET formation in the placenta and fetal membranes. c-Myc also participates in neonatal lung remodeling induced by IAI. Further studies are needed to investigate c-Myc as a potential therapeutic target for IAI and IAI-associated BPD.

Endothelial c-Myc knockout enhances diet-induced liver inflammation and fibrosis.

Endothelial cells play an essential role in inflammation through synthesis and secretion of chemoattractant cytokines and expression of adhesion molecules required for inflammatory cell attachment and infiltration. The mechanisms by which endothelial cells control the pro-inflammatory response depend on the type of inflammatory stimuli, endothelial cell origin, and tissue involved. In the present study, we investigated the role of the transcription factor c-Myc in inflammation using a conditional knockout mouse model in which Myc is specifically deleted in the endothelium. At a systemic level, circulating monocytes, the chemokine CCL7, and the extracellular-matrix protein osteopontin were significantly increased in endothelial c-Myc knockout (EC-Myc KO) mice, whereas the cytokine TNFSF11 was downregulated. Using an experimental model of steatohepatitis, we investigated the involvement of endothelial c-Myc in diet-induced inflammation. EC-Myc KO animals displayed enhanced pro-inflammatory response, characterized by increased expression of pro-inflammatory cytokines and leukocyte infiltration, and worsened liver fibrosis. Transcriptome analysis identified enhanced expression of genes associated with inflammation, fibrosis, and hepatocellular carcinoma in EC-Myc KO mice relative to control (CT) animals after short-exposure to high-fat diet. Analysis of a single-cell RNA-sequencing dataset of human cirrhotic livers indicated downregulation of MYC in endothelial cells relative to healthy controls. In summary, our results suggest a protective role of endothelial c-Myc in diet-induced liver inflammation and fibrosis. Targeting c-Myc and its downstream pathways in the endothelium may constitute a potential strategy for the treatment of inflammatory disease.

Hypoxic Stress Decreases c-Myc Protein Stability in Cardiac Progenitor Cells Inducing Quiescence and Compromising Their Proliferative and Vasculogenic Potential.

Cardiac progenitor cells (CPCs) have been shown to promote cardiac regeneration and improve heart function. However, evidence suggests that their regenerative capacity may be limited in conditions of severe hypoxia. Elucidating the mechanisms involved in CPC protection against hypoxic stress is essential to maximize their cardioprotective and therapeutic potential. We investigated the effects of hypoxic stress on CPCs and found significant reduction in proliferation and impairment of vasculogenesis, which were associated with induction of quiescence, as indicated by accumulation of cells in the G0-phase of the cell cycle and growth recovery when cells were returned to normoxia. Induction of quiescence was associated with a decrease in the expression of c-Myc through mechanisms involving protein degradation and upregulation of p21. Inhibition of c-Myc mimicked the effects of severe hypoxia on CPC proliferation, also triggering quiescence. Surprisingly, these effects did not involve changes in p21 expression, indicating that other hypoxia-activated factors may induce p21 in CPCs. Our results suggest that hypoxic stress compromises CPC function by inducing quiescence in part through downregulation of c-Myc. In addition, we found that c-Myc is required to preserve CPC growth, suggesting that modulation of pathways downstream of it may re-activate CPC regenerative potential under ischemic conditions.

Stromal derived factor-1 mediates the lung regenerative effects of mesenchymal stem cells in a rodent model of bronchopulmonary dysplasia.

BACKGROUND: Mesenchymal stem cells (MSCs) attenuate lung injury in experimental models of bronchopulmonary dysplasia (BPD). Stromal derived factor-1 (SDF-1), a chemokine secreted by MSCs, modulates angiogenesis and stem cell recruitment. Here we tested the hypothesis that SDF-1 mediates MSC protective effects in experimental BPD by modulating angiogenesis. METHODS: SDF-1 was knocked down in MSCs using lentiviral vectors carrying anti-SDF-1 short hairpin RNA (MSC-SDF KD). Non-silencing short hairpin RNA was used as control (MSC-NS control). Newborn rats exposed to normoxia or hyperoxia (FiO2 = 0.85) for 3 weeks, were randomly assigned to receive a single intra-tracheal injection (IT) of MSC-NS control or MSC-SDF KD (1 × 106 cells/50 µl) or placebo on postnatal day 7. The degree of alveolarization, lung angiogenesis, inflammation, and pulmonary hypertension (PH) were assessed at postnatal day 21. RESULTS: Administration of IT MSC-NS control improved lung alveolarization, angiogenesis and inflammation, and attenuated PH in newborn rats with hyperoxia-induced lung injury (HILI). In contrast, knockdown of SDF-1 in MSCs significantly reduced their beneficial effects on alveolarization, angiogenesis, inflammation and PH. CONCLUSIONS: The therapeutic benefits of MSCs in neonatal HILI are in part mediated by SDF-1, through anti-inflammatory and angiogenesis promoting mechanisms. Therapies directly targeting this chemokine may provide a novel strategy for the treatment of BPD.

Physiological and hypoxic oxygen concentration differentially regulates human c-Kit+ cardiac stem cell proliferation and migration.

Cardiac stem cells (CSCs) are being evaluated for their efficacy in the treatment of heart failure. However, numerous factors impair the exogenously delivered cells' regenerative capabilities. Hypoxia is one stress that contributes to inadequate tissue repair. Here, we tested the hypothesis that hypoxia impairs cell proliferation, survival, and migration of human CSCs relative to physiological and room air oxygen concentrations. Human endomyocardial biopsy-derived CSCs were isolated, selected for c-Kit expression, and expanded in vitro at room air (21% O2). To assess the effect on proliferation, survival, and migration, CSCs were transferred to physiological (5%) or hypoxic (0.5%) O2 concentrations. Physiological O2 levels increased proliferation (P < 0.05) but did not affect survival of CSCs. Although similar growth rates were observed in room air and hypoxia, a significant reduction of ß-galactosidase activity (-4,203 fluorescent units, P < 0.05), p16 protein expression (0.58-fold, P < 0.001), and mitochondrial content (0.18-fold, P < 0.001) in hypoxia suggests that transition from high (21%) to low (0.5%) O2 reduces senescence and promotes quiescence. Furthermore, physiological O2 levels increased migration (P < 0.05) compared with room air and hypoxia, and treatment with mesenchymal stem cell-conditioned media rescued CSC migration under hypoxia to levels comparable to physiological O2 migration (2-fold, P < 0.05 relative to CSC media control). Our finding that physiological O2 concentration is optimal for in vitro parameters of CSC biology suggests that standard room air may diminish cell regenerative potential. This study provides novel insights into the modulatory effects of O2 concentration on CSC biology and has important implications for refining stem cell therapies.

Endothelial Mesenchymal Transition: Comparative Analysis of Different Induction Methods.

BACKGROUND: Endothelial-Mesenchymal-Transition (EndMT) plays an essential role in cardiovascular development, and recently became an attractive therapeutic target based on evidence supporting its involvement in fibrosis and cancer. Important questions that remain to be answered are related to the molecular mechanisms that control EndMT in different organs and distinct pathological conditions. The lack of a detailed protocol for induction of EndMT and the assumption that TGF-ß isoforms play similar roles on different types of endothelial cells, limit progress in the field. The aim of this study was to compare the induction of EndMT by TGF-ß isoforms in endothelial cells of different sources, and define a detailed protocol for EndMT assessment in vitro. RESULTS: We compared the dose-dependent effect of TGF-ß isoforms, under normoxia and hypoxia, on the induction of EndMT in human coronary and pulmonary artery endothelial cells. Our results suggest that endothelial cells undergo spontaneous EndMT with time in culture under the conditions tested. The extent of EndMT induction by TGF-ß was dependent on the dose and endothelial cell type. Furthermore, the potential of TGF-ß to induce EndMT was reduced under hypoxia relative to normoxia. CONCLUSIONS: Our work suggests that the response of endothelial cells to TGF-ß is intrinsic to the dose, cell type and environment. Optimization of induction conditions may be essential, as pathways triggering EndMT may vary during development and pathological conditions. Therefore, caution is needed regarding indiscriminate use of TGF-ß to induce EndMT for mechanistic studies.

Bone marrow-derived c-kit+ cells attenuate neonatal hyperoxia-induced lung injury.

Recent studies suggest that bone marrow (BM)-derived stem cells have therapeutic efficacy in neonatal hyperoxia-induced lung injury (HILI). c-kit, a tyrosine kinase receptor that regulates angiogenesis, is expressed on several populations of BM-derived cells. Preterm infants exposed to hyperoxia have decreased lung angiogenesis. Here we tested the hypothesis that administration of BM-derived c-kit(+) cells would improve angiogenesis in neonatal rats with HILI. To determine whether intratracheal (IT) administration of BM-derived c-kit(+) cells attenuates neonatal HILI, rat pups exposed to either normobaric normoxia (21% O2) or hyperoxia (90% O2) from postnatal day (P) 2 to P15 were randomly assigned to receive either IT BM-derived green fluorescent protein (GFP)(+) c-kit(-) cells (PL) or BM-derived GFP(+) c-kit(+) cells on P8. The effect of cell therapy on lung angiogenesis, alveolarization, pulmonary hypertension, vascular remodeling, cell proliferation, and apoptosis was determined at P15. Cell engraftment was determined by GFP immunostaining. Compared to PL, the IT administration of BM-derived c-kit(+) cells to neonatal rodents with HILI improved alveolarization as evidenced by increased lung septation and decreased mean linear intercept. This was accompanied by an increase in lung vascular density, a decrease in lung apoptosis, and an increase in the secretion of proangiogenic factors. There was no difference in pulmonary vascular remodeling or the degree of pulmonary hypertension. Confocal microscopy demonstrated that 1% of total lung cells were GFP(+) cells. IT administration of BM-derived c-kit(+) cells improves lung alveolarization and angiogenesis in neonatal HILI, and this may be secondary to an improvement in the lung angiogenic milieu.

Agonists of growth hormone-releasing hormone stimulate self-renewal of cardiac stem cells and promote their survival.

The beneficial effects of agonists of growth hormone-releasing hormone receptor (GHRH-R) in heart failure models are associated with an increase in the number of ckit(+) cardiac stem cells (CSCs). The goal of the present study was to determine the presence of GHRH-R in CSCs, the effect of GHRH-R agonists on their proliferation and survival, and the mechanisms involved. We investigated the expression of GHRH-R in CSCs of different species and the effect of GHRH-R agonists on their cell proliferation and survival. GHRH-R is expressed in ckit(+) CSCs isolated from mouse, rat, and pig. Treatment of porcine CSCs with the GHRH-R agonist JI-38 significantly increased the rate of cell division. Similar results were observed with other GHRH-R agonists, MR-356 and MR-409. JI-38 exerted a protective effect on survival of porcine CSCs under conditions of oxidative stress induced by exposure to hydrogen peroxide. Treatment with JI-38 before exposure to peroxide significantly reduced cell death. A similar effect was observed with MR-356. Addition of GHRH-R agonists to porcine CSCs induced activation of ERK and AKT pathways as determined by increased expression of phospho-ERK and phospho-AKT. Inhibitors of ERK and AKT pathways completely reversed the effect of GHRH-R agonists on CSC proliferation. Our findings extend the observations of the expression of GHRH-R by CSCs and demonstrate that GHRH-R agonists have a direct effect on proliferation and survival of CSCs. These results support the therapeutic use of GHRH-R agonists for stimulating endogenous mechanisms for myocardial repair or for preconditioning of stem cells before transplantation.

MicroRNA-20a constrains p300-driven myocardial angiogenic transcription by direct targeting of p300.

OBJECTIVE: To characterize downstream effectors of p300 acetyltransferase in the myocardium. BACKGROUND: Acetyltransferase p300 is a central driver of the hypertrophic response to increased workload, but its biological targets and downstream effectors are incompletely known. METHODS AND RESULTS: Mice expressing a myocyte-restricted transgene encoding acetyltransferase p300, previously shown to develop spontaneous hypertrophy, were observed to undergo robust compensatory blood vessel growth together with increased angiogenic gene expression. Chromatin immunoprecipitation demonstrated binding of p300 to the enhancers of the angiogenic regulators Angpt1 and Egln3. Interestingly, p300 overexpression in vivo was also associated with relative upregulation of several members of the anti-angiogenic miR-17∼92 cluster in vivo. Confirming this finding, both miR-17-3p and miR-20a were upregulated in neonatal rat ventricular myocytes following adenoviral transduction of p300. Relative expression of most members of the 17∼92 cluster was similar in all 4 cardiac chambers and in other organs, however, significant downregulation of miR-17-3p and miR-20a occurred between 1 and 8 months of age in both wt and tg mice. The decline in expression of these microRNAs was associated with increased expression of VEGFA, a validated miR-20a target. In addition, miR-20a was demonstrated to directly repress p300 expression through a consensus binding site in the p300 3'UTR. In vivo transduction of p300 resulted in repression both of p300 and of p300-induced angiogenic transcripts. CONCLUSION: p300 drives an angiogenic transcription program during hypertrophy that is fine-tuned in part through direct repression of p300 by miR-20a.

Stem cell factor improves lung recovery in rats following neonatal hyperoxia-induced lung injury.

BACKGROUND: Stem cell factor (SCF) and its receptor, c-kit, are modulators of angiogenesis. Neonatal hyperoxia-induced lung injury (HILI) is characterized by disordered angiogenesis. The objective of this study was to determine whether exogenous SCF improves recovery from neonatal HILI by improving angiogenesis. METHODS: Newborn rats assigned to normoxia (RA: 20.9% O2) or hyperoxia (90% O2) from postnatal day (P) 2 to 15, received daily injections of SCF 100 µg/kg or placebo (PL) from P15 to P21. Lung morphometry was performed at P28. Capillary tube formation in SCF-treated hyperoxia-exposed pulmonary microvascular endothelial cells (HPMECs) was determined by Matrigel assay. RESULTS: As compared with RA, hyperoxic-PL pups had decrease in alveolarization and in lung vascular density, and this was associated with increased right ventricular systolic pressure (RVSP), right ventricular hypertrophy, and vascular remodeling. In contrast, SCF-treated hyperoxic pups had increased angiogenesis, improved alveolarization, and attenuation of pulmonary hypertension as evidenced by decreased RVSP, right ventricular hypertrophy, and vascular remodeling. Moreover, in an in vitro model, SCF increased capillary tube formation in hyperoxia-exposed HPMECs. CONCLUSION: Exogenous SCF restores alveolar and vascular structure in neonatal rats with HILI by promoting neoangiogenesis. These findings suggest a new strategy to treat lung diseases characterized by dysangiogenesis.

c-Myc is essential to prevent endothelial pro-inflammatory senescent phenotype.

The proto-oncogene c-Myc is vital for vascular development and promotes tumor angiogenesis, but the mechanisms by which it controls blood vessel growth remain unclear. In the present work we investigated the effects of c-Myc knockdown in endothelial cell functions essential for angiogenesis to define its role in the vasculature. We provide the first evidence that reduction in c-Myc expression in endothelial cells leads to a pro-inflammatory senescent phenotype, features typically observed during vascular aging and pathologies associated with endothelial dysfunction. c-Myc knockdown in human umbilical vein endothelial cells using lentivirus expressing specific anti-c-Myc shRNA reduced proliferation and tube formation. These functional defects were associated with morphological changes, increase in senescence-associated-ß-galactosidase activity, upregulation of cell cycle inhibitors and accumulation of c-Myc-deficient cells in G1-phase, indicating that c-Myc knockdown in endothelial cells induces senescence. Gene expression analysis of c-Myc-deficient endothelial cells showed that senescent phenotype was accompanied by significant upregulation of growth factors, adhesion molecules, extracellular-matrix components and remodeling proteins, and a cluster of pro-inflammatory mediators, which include Angptl4, Cxcl12, Mdk, Tgfb2 and Tnfsf15. At the peak of expression of these cytokines, transcription factors known to be involved in growth control (E2f1, Id1 and Myb) were downregulated, while those involved in inflammatory responses (RelB, Stat1, Stat2 and Stat4) were upregulated. Our results demonstrate a novel role for c-Myc in the prevention of vascular pro-inflammatory phenotype, supporting an important physiological function as a central regulator of inflammation and endothelial dysfunction.

C-kit(+) cells isolated from developing kidneys are a novel population of stem cells with regenerative potential.

The presence of tissue specific precursor cells is an emerging concept in organ formation and tissue homeostasis. Several progenitors are described in the kidneys. However, their identity as a true stem cell remains elusive. Here, we identify a neonatal kidney-derived c-kit(+) cell population that fulfills all of the criteria as a stem cell. These cells were found in the thick ascending limb of Henle's loop and exhibited clonogenicity, self-renewal, and multipotentiality with differentiation capacity into mesoderm and ectoderm progeny. Additionally, c-kit(+) cells formed spheres in nonadherent conditions when plated at clonal density and expressed markers of stem cells, progenitors, and differentiated cells. Ex vivo expanded c-kit(+) cells integrated into several compartments of the kidney, including tubules, vessels, and glomeruli, and contributed to functional and morphological improvement of the kidney following acute ischemia-reperfusion injury in rats. Together, these findings document a novel neonatal rat kidney c-kit(+) stem cell population that can be isolated, expanded, cloned, differentiated, and used for kidney repair following acute kidney injury. These cells have important biological and therapeutic implications.

S-nitrosoglutathione reductase (GSNOR) enhances vasculogenesis by mesenchymal stem cells.

Although nitric oxide (NO) signaling promotes differentiation and maturation of endothelial progenitor cells, its role in the differentiation of mesenchymal stem cells (MSCs) into endothelial cells remains controversial. We tested the role of NO signaling in MSCs derived from WT mice and mice homozygous for a deletion of S-nitrosoglutathione reductase (GSNOR(-/-)), a denitrosylase that regulates S-nitrosylation. GSNOR(-/-) MSCs exhibited markedly diminished capacity for vasculogenesis in an in vitro Matrigel tube-forming assay and in vivo relative to WT MSCs. This decrease was associated with down-regulation of the PDGF receptorα (PDGFRα) in GSNOR(-/-) MSCs, a receptor essential for VEGF-A action in MSCs. Pharmacologic inhibition of NO synthase with L-N(G)-nitroarginine methyl ester (L-NAME) and stimulation of growth hormone-releasing hormone receptor (GHRHR) with GHRH agonists augmented VEGF-A production and normalized tube formation in GSNOR(-/-) MSCs, whereas NO donors or PDGFR antagonist reduced tube formation ∼50% by murine and human MSCs. The antagonist also blocked the rescue of tube formation in GSNOR(-/-) MSCs by L-NAME or the GHRH agonists JI-38, MR-409, and MR-356. Therefore, GSNOR(-/-) MSCs have a deficient capacity for endothelial differentiation due to downregulation of PDGFRα related to NO/GSNOR imbalance. These findings unravel important aspects of modulation of MSCs by VEGF-A activation of the PDGFR and illustrate a paradoxical inhibitory role of S-nitrosylation signaling in MSC vasculogenesis. Accordingly, disease states characterized by NO deficiency may trigger MSC-mediated vasculogenesis. These findings have important implications for therapeutic application of GHRH agonists to ischemic disorders.

Activation of growth hormone releasing hormone (GHRH) receptor stimulates cardiac reverse remodeling after myocardial infarction (MI).

Both cardiac myocytes and cardiac stem cells (CSCs) express the receptor of growth hormone releasing hormone (GHRH), activation of which improves injury responses after myocardial infarction (MI). Here we show that a GHRH-agonist (GHRH-A; JI-38) reverses ventricular remodeling and enhances functional recovery in the setting of chronic MI. This response is mediated entirely by activation of GHRH receptor (GHRHR), as demonstrated by the use of a highly selective GHRH antagonist (MIA-602). One month after MI, animals were randomly assigned to receive: placebo, GHRH-A (JI-38), rat recombinant GH, MIA-602, or a combination of GHRH-A and MIA-602, for a 4-wk period. We assessed cardiac performance and hemodynamics by using echocardiography and micromanometry derived pressure-volume loops. Morphometric measurements were carried out to determine MI size and capillary density, and the expression of GHRHR was assessed by immunofluorescence and quantitative RT-PCR. GHRH-A markedly improved cardiac function as shown by echocardiographic and hemodynamic parameters. MI size was substantially reduced, whereas myocyte and nonmyocyte mitosis was markedly increased by GHRH-A. These effects occurred without increases in circulating levels of growth hormone and insulin-like growth factor I and were, at least partially, nullified by GHRH antagonism, confirming a receptor-mediated mechanism. GHRH-A stimulated CSCs proliferation ex vivo, in a manner offset by MIA-602. Collectively, our findings reveal the importance of the GHRH signaling pathway within the heart. Therapy with GHRH-A although initiated 1 mo after MI substantially improved cardiac performance and reduced infarct size, suggesting a regenerative process. Therefore, activation of GHRHR provides a unique therapeutic approach to reverse remodeling after MI.

Heterogeneity in SDF-1 expression defines the vasculogenic potential of adult cardiac progenitor cells.

RATIONALE: The adult myocardium has been reported to harbor several classes of multipotent progenitor cells (CPCs) with tri-lineage differentiation potential. It is not clear whether c-kit+CPCs represent a uniform precursor population or a more complex mixture of cell types. OBJECTIVE: To characterize and understand vasculogenic heterogeneity within c-kit+presumptive cardiac progenitor cell populations. METHODS AND RESULTS: c-kit+, sca-1+ CPCs obtained from adult mouse left ventricle expressed stem cell-associated genes, including Oct-4 and Myc, and were self-renewing, pluripotent and clonogenic. Detailed single cell clonal analysis of 17 clones revealed that most (14/17) exhibited trilineage differentiation potential. However, striking morphological differences were observed among clones that were heritable and stable in long-term culture. 3 major groups were identified: round (7/17), flat or spindle-shaped (5/17) and stellate (5/17). Stellate morphology was predictive of vasculogenic differentiation in Matrigel. Genome-wide expression studies and bioinformatic analysis revealed clonally stable, heritable differences in stromal cell-derived factor-1 (SDF-1) expression that correlated strongly with stellate morphology and vasculogenic capacity. Endogenous SDF-1 production contributed directly to vasculogenic differentiation: both shRNA-mediated knockdown of SDF-1 and AMD3100, an antagonist of the SDF-1 receptor CXC chemokine Receptor-4 (CXCR4), reduced tube-forming capacity, while exogenous SDF-1 induced tube formation by 2 non-vasculogenic clones. CPCs producing SDF-1 were able to vascularize Matrigel dermal implants in vivo, while CPCs with low SDF-1 production were not. CONCLUSIONS: Clonogenic c-kit+, sca-1+ CPCs are heterogeneous in morphology, gene expression patterns and differentiation potential. Clone-specific levels of SDF-1 expression both predict and promote development of a vasculogenic phenotype via a previously unreported autocrine mechanism.

A Myc-Slug (Snail2)/Twist regulatory circuit directs vascular development.

Myc-deficient mice fail to develop normal vascular networks and Myc-deficient embryonic stem cells fail to provoke a tumor angiogenic response when injected into immune compromised mice. However, the molecular underpinnings of these defects are poorly understood. To assess whether Myc indeed contributes to embryonic vasculogenesis we evaluated Myc function in Xenopus laevis embryogenesis. Here, we report that Xc-Myc is required for the normal assembly of endothelial cells into patent vessels during both angiogenesis and lymphangiogenesis. Accordingly, the specific knockdown of Xc-Myc provokes massive embryonic edema and hemorrhage. Conversely, Xc-Myc overexpression triggers the formation of ectopic vascular beds in embryos. Myc is required for normal expression of Slug/Snail2 and Twist, and either XSlug/Snail2 or XTwist could compensate for defects manifest by Xc-Myc knockdown. Importantly, knockdown of Xc-Myc, XSlug/Snail2 or XTwist within the lateral plate mesoderm, but not the neural crest, provoked embryonic edema and hemorrhage. Collectively, these findings support a model in which Myc, Twist and Slug/Snail2 function in a regulatory circuit within lateral plate mesoderm that directs normal vessel formation in both the vascular and lymphatic systems.

Jun kinase delays caspase-9 activation by interaction with the apoptosome.

Activation of c-Jun N-terminal kinase 1/2 (JNK) can delay oxidant-induced cell death, but the mechanism is unknown. We found that oxidant stress of cardiac myocytes activated both JNK and mitochondria-dependent apoptosis and that expression of JNK inhibitory mutants accelerated multiple steps in this pathway, including the cleavage and activation of caspases-3 and -9 and DNA internucleosomal cleavage, without affecting the rate of cytochrome c release; JNK inhibition also increased caspase-3 and -9 cleavage in a cell-free system. On activation by GSNO or H(2)O(2), JNK formed a stable association with oligomeric Apaf-1 in a approximately 1.4-2.0 mDa pre-apoptosome complex. Formation of this complex could be triggered by addition of cytochrome c and ATP to the cell-free cytosol. JNK inhibition abrogated JNK-Apaf-1 association and accelerated the association of procaspase-9 and Apaf-1 in both intact cells and cell-free extracts. We conclude that oxidant-activated JNK associates with Apaf-1 and cytochrome c in a catalytically inactive complex. We propose that this interaction delays formation of the active apoptosome, promoting cell survival during short bursts of oxidative stress.