Sonic hedgehog myocardial gene therapy: tissue repair through transient reconstitution of embryonic signaling

Wnt1 is a proangiogenic molecule, enhances human endothelial progenitor function, and increases blood flow to ischemic limbs in a HGF-dependent manner

Human endothelial progenitor cells (hEPCs) participate in neovascularization of ischemic tissues. Function and number of hEPCs decline in patients with cardiovascular disease, and therapeutic strategies to enhance hEPC function remain an important field of investigation. The Wnt signaling system, comprising 19 lipophilic proteins, regulates vascular patterning in the developing embryo. However, the effects of Wnts on hEPCs and the adult vasculature remain unclear. We demonstrate here that Wnt1 is expressed in a subset of endothelial cells lining the murine embryonic dorsal aorta and is reactivated in malignant angiosarcoma, suggesting a strong association of Wnt1 with angiogenesis. We investigate the effects of Wnt1 in enhancing hEPC function and blood flow to ischemic tissues and show that Wnt1 enhances the proliferative and angiogenic functions of hEPCs in a hepatocyte growth factor (HGF)-dependent manner. Injection of Wnt1-expressing hEPCs increases blood flow and capillary density in murine ischemic hindlimbs. Furthermore, injection of Wnt1 protein alone similarly increases blood flow and capillary density in ischemic hindlimbs, and this effect is associated with increased HGF expression in ischemic muscle. These findings demonstrate that Wnt1, a marker of neural crest cells and hitherto unknown angiogenic function, is a novel angiogenic protein that is expressed in developing endothelial cells, exerts salutary effects on postnatal hEPCs, and can be therapeutically deployed to increase blood flow and angiogenesis in ischemic tissues.

Left-ventricular remodeling after myocardial infarction is associated with a cardiomyocyte-specific hypothyroid condition

Similarities in cardiac gene expression in hypothyroidism and left ventricular (LV) pathological remodeling after myocardial infarction (MI) suggest a role for impaired cardiac thyroid hormone (TH) signaling in the development of heart failure. Increased ventricular activity of the TH-degrading enzyme type 3 deiodinase (D3) is recognized as a potential cause. In the present study, we investigated the cardiac expression and activity of D3 over an 8-wk period after MI in C57Bl/6J mice. Pathological remodeling of the noninfarcted part of the LV was evident from cardiomyocyte hypertrophy, interstitial fibrosis, and impairment of contractility. These changes were maximal and stable from the first week onward, as was the degree of LV dilation. A strong induction of D3 activity was found, which was similarly stable for the period examined. Plasma T(4) levels were transiently decreased at 1 wk after MI, but T(3) levels remained normal. The high D3 activity was associated with increased D3 mRNA expression at 1 but not at 4 and 8 wk after MI. Immunohistochemistry localized D3 protein to cardiomyocytes. In vivo measurement of TH-dependent transcription activity in cardiomyocytes using a luciferase reporter assay indicated a 48% decrease in post-MI mice relative to sham-operated animals, and this was associated with a 50% decrease in LV tissue T(3) concentration. In conclusion, pathological ventricular remodeling after MI in the mouse leads to high and stable induction of D3 activity in cardiomyocytes and a local hypothyroid condition.

Pleiotropic beneficial effects of sonic hedgehog gene therapy in an experimental model of peripheral limb ischemia

We have previously shown that the signaling pathway of the embryonic morphogen Sonic hedgehog (Shh) is recapitulated in the postnatal skeletal muscle in response to ischemia. We have also demonstrated that Shh is an indirect angiogenic agent upregulating various families of angiogenic growth factors and that Shh gene therapy improves angiogenesis and heart function in experimental models of myocardial ischemia. Based on these findings, we hypothesized that Shh gene therapy is beneficial in an experimental model of peripheral ischemia. We found that intramuscular (i.m.) treatment with a plasmid encoding the Shh human gene (phShh) increased blood flow, capillary density, and arteriole density in mice in which peripheral circulation of the hindlimb was disrupted by removal of the common femoral artery. Shh gene therapy also enhanced vasculogenesis, by increasing the number of circulating bone marrow (BM)-derived endothelial precursors and improving the contribution of these cells to the process of neovascularization. Finally, phShh treatment induced upregulation of prototypical angiogenic, arteriogenic, and vasculogenic factors, such as vascular endothelial growth factor (VEGF), angiopoietin 1 (Ang-1), and stromal cell-derived factor-1 (SDF-1α). These data suggest that Shh gene therapy merits further investigation for its ability to trigger the expression of potent trophic factors and stimulate pleiotropic aspects of neovascularization in the setting of ischemia.

miR-499 regulates mitochondrial dynamics by targeting calcineurin and dynamin-related protein-1

Myocardial infarction is a leading cause of mortality worldwide. Here we report that modulation of microRNA-499 (miR-499) levels affects apoptosis and the severity of myocardial infarction and cardiac dysfunction induced by ischemia-reperfusion. We found that both the α- and β-isoforms of the calcineurin catalytic subunit are direct targets of miR-499 and that miR-499 inhibits cardiomyocyte apoptosis through its suppression of calcineurin-mediated dephosphorylation of dynamin-related protein-1 (Drp1), thereby decreasing Drp1 accumulation in mitochondria and Drp1-mediated activation of the mitochondrial fission program. We also found that p53 transcriptionally downregulates miR-499 expression. Our data reveal a role for miR-499 in regulating the mitochondrial fission machinery and we suggest that modulation of miR-499 levels may provide a therapeutic approach for treating myocardial infarction.

Blockade of the sonic hedgehog signalling pathway inhibits choroidal neovascularization in a laser-induced rat model

Sonic hedgehog (Shh) signaling has recently been shown to be involved in the pathological angiogenesis in response to tissue hypoxia and ischemic injury. Hypoxia/ischemia is considered to play an important role in the development of choroidal neovascularization (CNV). This study was aimed to examine the effect of blockade of the Shh signaling pathway on CNV and the underlying mechanism. A total of 64 male Brown-Norway (BN) rats were used in this study. One eye of each rat underwent laser photocoagulation. The other eye served as normal control. After the laser treatment, the 64 rats were divided into four groups (n=16 in each group): Blank control group, in which no intravitreal administration was given; cyclopamine group, recombinant Shh N-terminals protein (rShh) group and phosphate-buffered saline (PBS) group, in which cyclopamine (a Shh inhibitor), rShh (a Shh activator) and PBS were intravitreally injected into the laser-treated eyes respectively every other day for a total of four intravitreal injections immediately after the laser treatment. Fourteen days after the intravitreal administration, the changes of CNV-related variables, including positive CNV lesion percentage, CNV membrane area and CNV membrane thickness, were evaluated by fluorescein angiography, indocyanine green angiography and pathological examinations. The mRNA and protein expression of PTCH1, Gli1, HIF-1(α), VEGF and DLL4 in each group on 14 days of CNV model was detected by real-time quantitative PCR and western blot analysis, and the relationship between the Shh cascade and the HIF-1(α)-VEGF-DLL4 cascade in CNV was analyzed. The results showed that the CNV membrane area and the CNV membrane thickness were decreased by 62.5% and 41.9% in the cyclopamine group and increased by 85.7% and 64.3% in the rShh group in comparison to those in the blank control group (P<0.01 for each). There was no significant difference in the CNV membrane area and thickness between the blank control group and PBS group (P=0.102 and P=0.063, respectively). Real-time quantitative PCR revealed a 5.23-, 4.14-, 2.97-, 2.78- and 2.39-fold up-regulation of the mRNA expression of PTCH1, Gli1, HIF-1(α), VEGF and DLL4 genes in the laser-treated eyes compared with the normal control eyes in the control group. In the cyclopamine group, the mRNA and protein expression of Gli1, HIF-1(α), VEGF and DLL4 was significantly down-regulated (P<0.05 for each) while the expression of PTCH1 showed no significant changes at the mRNA (P=0.293) and protein level (P=0.304). The mRNA expression and protein expression (P=0.001 and P=0.021, respectively) of PTCH1, Gli1, HIF-1(α), VEGF and DLL4 was significantly increased in the rShh group when compared with the control group. The expression level of these genes was related to the severity of the CNV. It was concluded that intravitreal administration of cyclopamine can effectively inhibit the formation of laser-induced experimental CNV by down-regulating the expression of the HIF-1(α)-VEGF-DLL4 cascade in CNV. The Shh signaling pathway as an upstream signaling pathway of HIF-1(α)-VEGF-DLL4 cascade is implicated in the development of experimental CNV.

Varying phenotypes in swine versus murine transgenic models constitutively expressing the same human Sonic hedgehog transcriptional activator, K5-HGLI2 Delta N

This study was undertaken to characterize the effects of constitutive expression of the hedgehog transcriptional activator, Gli2, in porcine skin. The keratinocyte-specific human transgene, K5-hGli2 Delta N, was used to produce transgenic porcine lines via somatic cell nuclear transfer techniques. In mice, K5-hGli2 Delta N induces epithelial downgrowths resembling basal cell carcinomas. Our porcine model also developed these basal cell carcinoma-like lesions, however gross tumor development was not appreciated. In contrast to the murine model, diffuse epidermal changes as well as susceptibility to cutaneous infections were seen in the swine model. Histologic analysis of transgenic piglets revealed generalized epidermal changes including: epidermal hyperplasia (acanthosis), elongated rete ridges, parakeratotic hyperkeratosis, epidermal neutrophilic infiltration, capillary loop dilation and hypogranulosis. By 2 weeks of age, the transgenic piglets developed erythematic and edematous lesions at high contact epidermal areas and extensor surfaces of distal limb joints. Despite antibiotic treatment, these lesions progressed to a deep bacterial pyoderma and pigs died or were euthanized within weeks of birth. Non-transgenic littermates were phenotypically normal by gross and histological analysis. In summary, constitutive expression of the human hGli2 Delta N in keratinocytes, results in cutaneous changes that have not been reported in the K5-hGli2 Delta N murine model. These findings indicate a need for a multiple species animal model approach in order to better understand the role of Gli2 in mammalian skin.

Non-cell-autonomous signaling by Shh in tumors: challenges and opportunities for therapeutic targets

IMPORTANCE OF THE FIELD

The Hedgehog (Hh) pathway is required during many developmental events; in adults the Hedgehog pathway is involved in the maintenance of several stem cell niches. It is therefore not surprising that aberrantly regulated Hh pathway activity can cause birth defects in the developing organism, as well as neoplastic disease later in life.

AREAS COVERED IN THIS REVIEW

As a consequence of the involvement in pathogenesis, the Hh pathway components are subject to an intense scrutiny as potential targets for therapeutic agents. We aim to provide an overview of the biology of the Hh proteins and the cellular response, in conjunction with potential therapeutic interventions.

WHAT THE READER WILL GAIN

Specifically, we focus on the recently discovered non-cell-autonomous Shh signaling used by tumors and the implications of this for the design of treatment strategies. This should provide the reader with up-to-date knowledge on the role of the Hh pathway in tumor progression and the options to treat these malignancies.

TAKE HOME MESSAGE

An important concept that we advocate in this review is the need to recognize the need to target both the stromal and the tumor compartment in malignancies that rely on paracrine Shh signaling.

Microparticles carrying Sonic hedgehog favor neovascularization through the activation of nitric oxide pathway in mice

Background

Microparticles (MPs) are vesicles released from plasma membrane upon cell activation and during apoptosis. Human T lymphocytes undergoing activation and apoptosis generate MPs bearing morphogen Shh (MPs^Shh+) that are able to regulate in vitro angiogenesis.

Methodology/Principal Findings

Here, we investigated the ability of MPs^Shh+ to modulate neovascularization in a model of mouse hind limb ischemia. Mice were treated in vivo for 21 days with vehicle, MPs^Shh+, MPs^Shh+ plus cyclopamine or cyclopamine alone, an inhibitor of Shh signalling. Laser doppler analysis revealed that the recovery of the blood flow was 1.4 fold higher in MPs^Shh+-treated mice than in controls, and this was associated with an activation of Shh pathway in muscles and an increase in NO production in both aorta and muscles. MPs^Shh+-mediated effects on flow recovery and NO production were completely prevented when Shh signalling was inhibited by cyclopamine. In aorta, MPs^Shh+ increased activation of eNOS/Akt pathway, and VEGF expression, being inhibited by cyclopamine. By contrast, in muscles, MPs^Shh+ enhanced eNOS expression and phosphorylation and decreased caveolin-1 expression, but cyclopamine prevented only the effects of MPs^Shh+ on eNOS pathway. Quantitative RT-PCR revealed that MPs^Shh+ treatment increased FGF5, FGF2, VEGF A and C mRNA levels and decreased those of α5-integrin, FLT-4, HGF, IGF-1, KDR, MCP-1, MT1-MMP, MMP-2, TGFβ1, TGFβ2, TSP-1 and VCAM-1, in ischemic muscles.

Conclusions/Significance

These findings suggest that MPs^Shh+ may contribute to reparative neovascularization after ischemic injury by regulating NO pathway and genes involved in angiogenesis.

Frequent deregulations in the hedgehog signaling network and cross-talks with the epidermal growth factor receptor pathway involved in cancer progression and targeted therapies

The hedgehog (Hh)/glioma-associated oncogene (GLI) signaling network is among the most important and fascinating signal transduction systems that provide critical functions in the regulation of many developmental and physiological processes. The coordinated spatiotemporal interplay of the Hh ligands and other growth factors is necessary for the stringent control of the behavior of diverse types of tissue-resident stem/progenitor cells and their progenies. The activation of the Hh cascade might promote the tissue regeneration and repair after severe injury in numerous organs, insulin production in pancreatic beta-cells, and neovascularization. Consequently, the stimulation of the Hh pathway constitutes a potential therapeutic strategy to treat diverse human disorders, including severe tissue injuries; diabetes mellitus; and brain, skin, and cardiovascular disorders. In counterbalance, a deregulation of the Hh signaling network might lead to major tissular disorders and the development of a wide variety of aggressive and metastatic cancers. The target gene products induced through the persistent Hh activation can contribute to the self-renewal, survival, migration, and metastasis of cancer stem/progenitor cells and their progenies. Moreover, the pivotal role mediated through the Hh/GLI cascade during cancer progression also implicates the cooperation with other oncogenic products, such as mutated K-RAS and complex cross-talk with different growth factor pathways, including tyrosine kinase receptors, such as epidermal growth factor receptor (EGFR), Wnt/beta-catenin, and transforming growth factor-beta (TGF-beta)/TGF-beta receptors. Therefore, the molecular targeting of distinct deregulated gene products, including Hh and EGFR signaling components and other signaling elements that are frequently deregulated in highly tumorigenic cancer-initiating cells and their progenies, might constitute a potential therapeutic strategy to eradicate the total cancer cell mass. Of clinical interest is that these multitargeted approaches offer great promise as adjuvant treatments for improving the current antihormonal therapies, radiotherapies, and/or chemotherapies against locally advanced and metastatic cancers, thereby preventing disease relapse and the death of patients with cancer.

Inhibition of endogenous hedgehog signaling protects against acute liver injury after ischemia reperfusion

PURPOSE

Although Hedgehog (Hh) signaling is required for endodermal commitment and hepatogenesis, the possibility that it regulates liver injury after ischemia reperfusion (I/R) has not been considered. Therefore, we determined the expression pattern of Hh signaling and its role in liver injury following I/R using Hh antagonist cyclopamine (CYA).

METHODS

Sprague-Dawley rats were randomly divided into three groups. Sham group underwent a sham operation with no liver I/R. Vehicle or CYA preconditioned I/R groups underwent liver ischemia for 90 min followed by reperfusion for 1 h. Liver tissue and blood were analyzed for gene expression, histological and biochemical evaluation.

RESULTS

Hedgehog ligands were upregulated after reperfusion injury. Serum levels of aspartate transaminase and alanine transaminase, inflammatory cytokines, neutrophil infiltration, and tissue damage were significantly less in CYA-pretreated rats compared with vehicle-pretreated rats. CYA also decreased the phosphorylated form of JNK and ERK.

CONCLUSIONS

This study provides evidence that endogenous Hh signaling is an early mediator of liver injury and inflammation after I/R. CYA abrogates normothermic I/R injury in rats by inhibiting the MAPK pathway and decreasing the acute inflammatory response. This novel strategy of preconditioning livers with Hh antagonist may have effective therapeutic potential in preventing acute liver injury.

Neuroprotective mechanisms of brain-derived neurotrophic factor against 3-nitropropionic acid toxicity: therapeutic implications for Huntington's disease

3-Nitropropionic acid (3-NP) is an irreversible inhibitor of mitochondrial succinate dehydrogenase that has been used to explore the molecular mechanisms of cell death associated with mitochondrial dysfunction and neurodegeneration for Huntington's disease (HD). Brain-derived neurotrophic factor (BDNF) is a neurotrophin that may regulate neuronal survival and differentiation. Experimental evidence derived from both clinical as well as basic research suggests a close association between BDNF deficiency and HD pathogenesis. In this review, we focus on recent progress in the molecular mechanisms responsible for the BDNF-mediated neuroprotective effects against mitochondrial dysfunction induced by 3-NP. Delineation of BDNF-mediated neuroprotective actions against 3-NP toxicity may add in the development of therapeutic intervention for HD where mitochondrial dysfunction is known to play a crucial role in pathogenesis of this devastating disease.

Hypoxia induces a hedgehog response mediated by HIF-1alpha

Recently, it has become clear that the developmental hedgehog pathway is activated in ischaemic adult tissue where it aids in salvaging damaged tissue. The exact driving force for the initial hedgehog response is unclear and as most physiological and cellular processes are disturbed in ischaemic tissue, hedgehog-activating signals are hard to dissect. Here, we demonstrate that hypoxia per se is able to induce a rapid systemic hedgehog response in adult mice, as evident from expression of the pathway ligand, Sonic hedgehog, as well as the pathway activity marker Patched1 in various organs. Using in vitro models of hypoxia, we showed that the hedgehog response was transient and preceded by the accumulation of HIF-1alpha, which we hypothesized to communicate between hypoxia and hedgehog expression. Indeed, pharmacological inhibition, knockdown or genetic ablation of HIF-1alpha abolished hedgehog pathway activation. In conclusion, we have established that hypoxia is translated into a hedgehog response through HIF-1alpha and this mechanism is likely to be responsible for the hedgehog response observed in various ischaemia models.

Inhibition of melanoma angiogenesis by telomere homolog oligonucleotides

Telomere homolog oligonucleotides (T-oligos) activate an innate telomere-based program that leads to multiple anticancer effects. T-oligos act at telomeres to initiate signaling through the Werner protein and ATM kinase. We wanted to determine if T-oligos have antiangiogenic effects. We found that T-oligo-treated human melanoma (MM-AN) cells had decreased expression of vascular endothelial growth factor (VEGF), VEGF receptor 2, angiopoeitin-1 and -2 and decreased VEGF secretion. T-oligos activated the transcription factor E2F1 and inhibited the activity of the angiogenic transcription factor, HIF-1α. T-oligos inhibited EC tubulogenesis and total tumor microvascular density matrix invasion by MM-AN cells and ECs in vitro. In melanoma SCID xenografts, two systemic T-oligo injections decreased by 60% (P < .004) total tumor microvascular density and the functional vessels density by 80% (P < .002). These findings suggest that restriction of tumor angiogenesis is among the host's innate telomere-based anticancer responses and provide further evidence that T-oligos may offer a powerful new approach for melanoma treatment.

Gene therapy for ischemic heart disease

Current pharmacologic therapy for ischemic heart disease suffers multiple limitations such as compliance issues and side effects of medications. Revascularization procedures often end with need for repeat procedures. Patients remain symptomatic despite maximal medical therapy. Gene therapy offers an attractive alternative to current pharmacologic therapies and may be beneficial in refractory disease. Gene therapy with isoforms of growth factors such as VEGF, FGF and HGF induces angiogenesis, decreases apoptosis and leads to protection in the ischemic heart. Stem cell therapy augmented with gene therapy used for myogenesis has proven to be beneficial in numerous animal models of myocardial ischemia. Gene therapy coding for antioxidants, eNOS, HSP, mitogen-activated protein kinase and numerous other anti apoptotic proteins have demonstrated significant cardioprotection in animal models. Clinical trials have demonstrated safety in humans apart from symptomatic and objective improvements in cardiac function. Current research efforts are aimed at refining various gene transfection techniques and regulation of gene expression in vivo in the heart and circulation to improve clinical outcomes in patients that suffer from ischemic heart disease. In this review article we will attempt to summarize the current state of both preclinical and clinical studies of gene therapy to combat myocardial ischemic disease. This article is part of a Special Section entitled "Special Section: Cardiovascular Gene Therapy".

Update on gene therapy for myocardial ischaemia and left ventricular systolic dysfunction or heart failure

Despite considerable advances in pharmacological, surgical and technology-based cardiovascular therapy, left ventricular dysfunction and heart failure are increasingly prevalent health problems. Recent studies suggest that angiogenic gene therapy can restore perfusion in ischaemic myocardial tissue, and that the transfer of nonangiogenic genes may correct defects in calcium handling that contribute to abnormal contractile function in patients with heart failure; however, large clinical trials of gene therapy for treatment of left ventricular dysfunction and heart failure have yet to be completed, and only a small number of genes have been evaluated in patients. Researchers continue to investigate new genes, combinations of genes and approaches that combine gene and cell therapy, and to develop novel expression vectors and delivery systems; collectively, these refinements promise to improve both patient response and safety.

Cardiomyocyte-specific inactivation of thyroid hormone in pathologic ventricular hypertrophy: an adaptative response or part of the problem?

Recent studies in various rodent models of pathologic ventricular hypertrophy report the re-expression of deiodinase type 3 (D3) in cardiomyocytes. D3 inactivates thyroid hormone (T3) and is mainly expressed in tissues during development. The stimulation of D3 activity in ventricular hypertrophy and subsequent heart failure is associated with severe impairment of cardiac T3 signaling. Hypoxia-induced signaling appears to drive D3 expression in the hypertrophic cardiomyocyte, but other signaling cascades implicated in hypertrophy are also capable of stimulating transcription of the DIO3 gene. Many cardiac genes are transcriptionally regulated by T3 and impairment of T3 signaling will not only reduce energy turnover, but also lead to changes in gene expression that contribute to contractile dysfunction in pathologic remodeling. Whether stimulation of D3 activity and the ensuing local T3-deficiency is an adaptive response of the stressed heart or part of the pathologic signaling network leading to heart failure, remains to be established.

Sonic hedgehog is a critical mediator of erythropoietin-induced cardiac protection in mice

Erythropoietin reportedly has beneficial effects on the heart after myocardial infarction, but the underlying mechanisms of these effects are unknown. We here demonstrate that sonic hedgehog is a critical mediator of erythropoietin-induced cardioprotection in mice. Treatment of mice with erythropoietin inhibited left ventricular remodeling and improved cardiac function after myocardial infarction, independent of erythropoiesis and the mobilization of bone marrow-derived cells. Erythropoietin prevented cardiomyocyte apoptosis and increased the number of capillaries and mature vessels in infarcted hearts by upregulating the expression of angiogenic cytokines such as VEGF and angiopoietin-1 in cardiomyocytes. Erythropoietin also increased the expression of sonic hedgehog in cardiomyocytes, and inhibition of sonic hedgehog signaling suppressed the erythropoietin-induced increase in angiogenic cytokine expression. Furthermore, the beneficial effects of erythropoietin on infarcted hearts were abolished by cardiomyocyte-specific deletion of sonic hedgehog. These results suggest that erythropoietin protects the heart after myocardial infarction by inducing angiogenesis through sonic hedgehog signaling.

Sonic hedgehog induces angiogenesis via Rho kinase-dependent signaling in endothelial cells

The morphogen Sonic hedgehog (Shh) promotes neovascularization in adults by inducing pro-angiogenic cytokine expression in fibroblasts; however, the direct effects of Shh on endothelial cell (EC) function during angiogenesis are unknown. Our findings indicate that Shh promotes capillary morphogenesis (tube length on Matrigel increased to 271+/-50% of the length in untreated cells, p=0.00003), induces EC migration (modified Boyden chamber assay, 191+/-35% of migration in untreated cells, p=0.00009), and increases EC expression of matrix metalloproteinase 9 (MMP-9) and osteopontin (OPN) mRNA (real-time RT-PCR), which are essential for Shh-induced angiogenesis both in vitro and in vivo. Shh activity in ECs is mediated by Rho, rather than through the "classic" Shh signaling pathway, which involves the Gli transcription factors. The Rho dependence of Shh-induced EC angiogenic activity was documented both in vitro, with dominant-negative RhoA and Rho kinase (ROCK) constructs, and in vivo, with the ROCK inhibitor Y27632 in the mouse corneal angiogenesis model. Finally, experiments performed in MMP-9- and OPN-knockout mice confirmed the roles of the ROCK downstream targets MMP-9 and OPN in Shh-induced angiogenesis. Collectively, our results identify a "nonclassical" pathway by which Shh directly modulates EC phenotype and angiogenic activity.

Nuclear factor kappaB-activated monocytes contribute to pancreatic cancer progression through the production of Shh

Recently, it was reported that Hh signaling is activated in tumor stromal cells but not in tumor cells themselves and that stromal cells may play a role in the proliferation of cancer cells. This suggests the possibility that stromal cells have an important role in the proliferation of tumor cells that may be mediated through Hh signaling. In this report, we present for the first time that inflammation-stimulated monocytes produce Shh through activation of the NF-kappaB signaling pathway, and that the Shh produced promotes the proliferation of pancreatic cancer cells in a paracrine manner through Hh signaling.

The Hedgehog morphogen in myocardial ischemia-reperfusion injury

The developmental Hedgehog (Hh) protein family is known to be pivotal in many embryonic patterning events and the number of processes in which Hh plays an essential role is expanding persistently. Recently, it has become clear that the Hh pathway is not only active in the developing embryo but also in the adult organism. For example, Hh has been suggested to salvage ischemia-induced tissue damage although endogenous Hh might be deleterious during the early phase of myocardial ischemia-reperfusion. The current review provides an overview of the history of Hh biology and discusses some novel insights on Hh cell biology. Hh function in pathophysiology as well as recent findings concerning Hh signaling in ischemia models, especially in light of cardiovascular disease, is discussed in more detail and future perspectives are proposed.

Continuous Delivery of Stromal Cell-Derived Factor-1 from Alginate Scaffolds Accelerates Wound Healing

Proper wound diagnosis and management is an increasingly important clinical challenge and is a large and growing unmet need. Pressure ulcers, hard-to-heal wounds, and problematic surgical incisions are emerging at increasing frequencies. At present, the wound-healing industry is experiencing a paradigm shift towards innovative treatments that exploit nanotechnology, biomaterials, and biologics. Our study utilized an alginate hydrogel patch to deliver stromal cell-derived factor-1 (SDF-1), a naturally occurring chemokine that is rapidly overexpressed in response to tissue injury, to assess the potential effects SDF-1 therapy on wound closure rates and scar formation. Alginate patches were loaded with either purified recombinant human SDF-1 protein or plasmid expressing SDF-1 and the kinetics of SDF-1 release were measured both in vitro and in vivo in mice. Our studies demonstrate that although SDF-1 plasmid- and protein-loaded patches were able to release therapeutic product over hours to days, SDF-1 protein was released faster (in vivo Kd 0.55 days) than SDF-1 plasmid (in vivo Kd 3.67 days). We hypothesized that chronic SDF-1 delivery would be more effective in accelerating the rate of dermal wound closure in Yorkshire pigs with acute surgical wounds, a model that closely mimics human wound healing. Wounds treated with SDF-1 protein ( n = 10) and plasmid ( n = 6) loaded patches healed faster than sham ( n = 4) or control ( n = 4). At day 9, SDF-1-treated wounds significantly accelerated wound closure (55.0 ± 14.3% healed) compared to nontreated controls (8.2 ± 6.0%, p < 0.05). Furthermore, 38% of SDF-1-treated wounds were fully healed at day 9 (vs. none in controls) with very little evidence of scarring. These data suggest that patch-mediated SDF-1 delivery may ultimately provide a novel therapy for accelerating healing and reducing scarring in clinical wounds.

Hedgehog signaling induces arterial endothelial cell formation by repressing venous cell fate

In vertebrate embryos, the dorsal aorta and the posterior cardinal vein form in the trunk to comprise the original circulatory loop. Previous studies implicate Hedgehog (Hh) signaling in the development of the dorsal aorta. However, the mechanism controlling specification of artery versus vein remains unclear. Here, we investigated the cell-autonomous mechanism of Hh signaling in angioblasts (endothelial progenitor cells) during arterial-venous specification utilizing zebrafish mutations in Smoothened (Smo), a G protein-coupled receptor essential for Hh signaling. smo mutants exhibit an absence of the dorsal aorta accompanied by a reciprocal expansion of the posterior cardinal vein. The increased number of venous cells is equivalent to the loss of arterial cells in embryos with loss of Smo function. Activation of Hh signaling expands the arterial cell population at the expense of venous cell fate. Time-lapse imaging reveals two sequential waves of migrating progenitor cells that contribute to the dorsal aorta and the posterior cardinal vein, respectively. Angioblasts deficient in Hh signaling fail to contribute to the arterial wave; instead, they all migrate medially as a single population to form the venous wave. Cell transplantation analyses demonstrate that Smo plays a cell-autonomous role in specifying angioblasts to become arterial cells, and Hh signaling-depleted angioblasts differentiate into venous cells instead. Collectively, these studies suggest that arterial endothelial cells are specified and formed via repressing venous cell fate at the lateral plate mesoderm by Hh signaling during vasculogenesis.

Hedgehog promotes neovascularization in pancreatic cancers by regulating Ang-1 and IGF-1 expression in bone-marrow derived pro-angiogenic cells

Background

The hedgehog (Hh) pathway has been implicated in the pathogenesis of cancer including pancreatic ductal adenocarcinoma (PDAC). Recent studies have suggested that the oncogenic function of Hh in PDAC involves signaling in the stromal cells rather than cell autonomous effects on the tumor cells. However, the origin and nature of the stromal cell type(s) that are responsive to Hh signaling remained unknown. Since Hh signaling plays a crucial role during embryonic and postnatal vasculogenesis, we speculated that Hh ligand may act on tumor vasculature specifically focusing on bone marrow (BM)-derived cells.

Methodology/Principal Findings

Cyclopamine was utilized to inhibit the Hh pathway in human PDAC cell lines and their xenografts. BM transplants, co-culture systems of tumor cells and BM-derived pro-angiogenic cells (BMPCs) were employed to assess the role of tumor-derived Hh in regulating the BM compartment and the contribution of BM-derived cells to angiogenesis in PDAC. Cyclopamine administration attenuated Hh signaling in the stroma rather than in the cancer cells as reflected by decreased expression of full length Gli2 protein and Gli1 mRNA specifically in the compartment. Cyclopamine inhibited the growth of PDAC xenografts in association with regression of the tumor vasculature and reduced homing of BM-derived cells to the tumor. Host-derived Ang-1 and IGF-1 mRNA levels were downregulated by cyclopamine in the tumor xenografts. In vitro co-culture and matrigel plug assays demonstrated that PDAC cell-derived Shh induced Ang-1 and IGF-1 production in BMPCs, resulting in their enhanced migration and capillary morphogenesis activity.

Conclusions/Significance

We identified the BMPCs as alternative stromal targets of Hh-ligand in PDAC suggesting that the tumor vasculature is an attractive therapeutic target of Hh blockade. Our data is consistent with the emerging concept that BM-derived cells make important contributions to epithelial tumorigenesis.

Sonic Hedgehog gene delivery to the rodent heart promotes angiogenesis via iNOS/netrin-1/PKC pathway

Background

We hypothesized that genetic modification of mesenchymal stem cells (MSCs) with Sonic Hedgehog (Shh) transgene, a morphogen during embryonic development and embryonic and adult stem cell growth, improved their survival and angiogenic potential in the ischemic heart via iNOS/netrin/PKC pathway.

Methods/Principal Findings

MSCs from young Fisher-344 rat bone marrow were purified and transfected with pCMV Shh plasmid (^ShhMSCs). Immunofluorescence, RT-PCR and Western blotting showed higher expression of Shh in ^ShhMSCs which also led to increased expression of angiogenic and pro-survival growth factors in ^ShhMSCs. Significantly improved migration and tube formation was seen in ^ShhMSCs as compared to empty vector transfected MSCs (^EmpMSCs). Significant upregulation of netrin-1 and iNOS was observed in ^ShhMSCs in PI3K independent but PKC dependent manner. For in vivo studies, acute myocardial infarction model was developed in Fisher-344 rats. The animals were grouped to receive 70 µl basal DMEM without cells (group-1) or containing 1×10^6EmpMSCs (group-2) and ^ShhMSCs (group-3). Group-4 received recombinant netrin-1 protein injection into the infarcted heart. FISH and sry-quantification revealed improved survival of ^ShhMSCs post engraftment. Histological studies combined with fluorescent microspheres showed increased density of functionally competent blood vessels in group-3 and group-4. Echocardiography showed significantly preserved heart function indices post engraftment with ^ShhMSCs in group-3 animals.

Conclusions/Significance

Reprogramming of stem cells with Shh maximizes their survival and angiogenic potential in the heart via iNOS/netrin-1/PKC signaling.

Outgrowth endothelial cells: sources, characteristics and potential applications in tissue engineering and regenerative medicine

Endothelial progenitor cells from peripheral blood or cord blood are attracting increasing interest as a potential cell source for cellular therapies aiming to enhance the neovascularization of tissue engineered constructs or ischemic tissues. The present review focus on a specific population contained in endothelial progenitor cell cultures designated as outgrowth endothelial cells (OEC) or endothelial colony forming cells from peripheral blood or cord blood. Special attention will be paid to what is currently known in terms of the origin and the cell biological or functional characteristics of OEC. Furthermore, we will discuss current concepts, how OEC might be integrated in complex tissue engineered constructs based on biomaterial or co-cultures, with special emphasis on their potential application in bone tissue engineering and related vascularization strategies.

Distinct roles for cell-autonomous Notch signaling in cardiomyocytes of the embryonic and adult heart

RATIONALE

The Notch signaling pathway is important for cell-cell communication that controls tissue formation and homeostasis during embryonic and adult life, but the precise cell targets of Notch signaling in the mammalian heart remain poorly defined.

OBJECTIVE

To investigate the functional role of Notch signaling in the cardiomyocyte compartment of the embryonic and adult heart.

METHODS AND RESULTS

Here, we report that either conditional overexpression of Notch1 intracellular domain (NICD1) or selective silencing of Notch signaling in the embryonic cardiomyocyte compartment results in developmental defects and perinatal lethality. In contrast, augmentation of endogenous Notch reactivation after myocardial infarction in the adult, either by inducing cardiomyocyte-specific Notch1 transgene expression or by intramyocardial delivery of a Notch1 pseudoligand, increases survival rate, improves cardiac functional performance, and minimizes fibrosis, promoting antiapoptotic and angiogenic mechanisms.

CONCLUSIONS

These results reveal a strict requirement for cell-autonomous modulation of Notch signaling during heart morphogenesis, and illustrate how the same signaling pathway that promotes congenital heart defects when perturbed in the embryo can be therapeutically redeployed for the treatment of adult myocardial damage.

Loss of glypican-3 function causes growth factor-dependent defects in cardiac and coronary vascular development

Glypican-3 (Gpc3) is a heparan sulfate proteoglycan (HSPG) expressed widely during vertebrate development. Loss-of-function mutations cause Simpson-Golabi-Behmel syndrome (SGBS), a rare and complex congenital overgrowth syndrome with a number of associated developmental abnormalities including congenital heart disease. We found that Gpc3-deficient mice display a high incidence of congenital cardiac malformations like ventricular septal defects, common atrioventricular canal and double outlet right ventricle. In addition we observed coronary artery fistulas, which have not been previously reported in SGBS. Coronary artery fistulas are noteworthy because little is known about the molecular basis of this abnormality. Formation of the coronary vascular plexus in Gpc3-deficient embryos was delayed compared to wild-type, and consistent with GPC3 functioning as a co-receptor for fibroblast growth factor-9 (FGF9), we found a reduction in Sonic Hedgehog (Shh) mRNA expression and signaling in embryonic mutant hearts. Interestingly, we found an asymmetric reduction in SHH signaling in cardiac myocytes, as compared with perivascular cells, resulting in excessive coronary artery formation in the Gpc3-deficient animals. We hypothesize that the excessive development of coronary arteries over veins enables the formation of coronary artery fistulas. This work has broad significance to understanding the genetic basis of coronary development and potentially to molecular mechanisms relevant to revascularization following ischemic injury to the heart.

Gene therapy with the angiogenic cytokine secretoneurin induces therapeutic angiogenesis by a nitric oxide-dependent mechanism

RATIONALE

The neuropeptide secretoneurin induces angiogenesis and postnatal vasculogenesis and is upregulated by hypoxia in skeletal muscle cells.

OBJECTIVE

We sought to investigate the effects of secretoneurin on therapeutic angiogenesis.

METHODS AND RESULTS

We generated a secretoneurin gene therapy vector. In the mouse hindlimb ischemia model secretoneurin gene therapy by intramuscular plasmid injection significantly increased secretoneurin content of injected muscles, improved functional parameters, reduced tissue necrosis, and restored blood perfusion. Increased muscular density of capillaries and arterioles/arteries demonstrates the capability of secretoneurin gene therapy to induce therapeutic angiogenesis and arteriogenesis. Furthermore, recruitment of endothelial progenitor cells was enhanced by secretoneurin gene therapy consistent with induction of postnatal vasculogenesis. Additionally, secretoneurin was able to activate nitric oxide synthase in endothelial cells and inhibition of nitric oxide inhibited secretoneurin-induced effects on chemotaxis and capillary tube formation in vitro. In vivo, secretoneurin induced nitric oxide production and inhibition of nitric oxide attenuated secretoneurin-induced effects on blood perfusion, angiogenesis, arteriogenesis, and vasculogenesis. Secretoneurin also induced upregulation of basic fibroblast growth factor and platelet-derived growth factor-B in endothelial cells.

CONCLUSIONS

In summary, our data indicate that gene therapy with secretoneurin induces therapeutic angiogenesis, arteriogenesis, and vasculogenesis in the hindlimb ischemia model by a nitric oxide-dependent mechanism.

The Hedgehog transcription factor Gli3 modulates angiogenesis

RATIONALE

The Gli transcription factors are mediators of Hedgehog (Hh) signaling and have been shown to play critical roles during embryogenesis. Previously, we have demonstrated that the Hh pathway is reactivated by ischemia in adult mammals, and that this pathway can be stimulated for therapeutic benefit; however, the specific roles of the Gli transcription factors during ischemia-induced Hh signaling have not been elucidated.

OBJECTIVE

To investigate the role of Gli3 in ischemic tissue repair.

METHODS AND RESULTS

Gli3-haploinsufficient (Gli3(+/-)) mice and their wild-type littermates were physiologically similar in the absence of ischemia; however, histological assessments of capillary density and echocardiographic measurements of left ventricular ejection fractions were reduced in Gli3(+/-) mice compared to wild-type mice after surgically induced myocardial infarction, and fibrosis was increased. Gli3-deficient mice also displayed reduced capillary density after induction of hindlimb ischemia and an impaired angiogenic response to vascular endothelial growth factor in the corneal angiogenesis model. In endothelial cells, adenovirus-mediated overexpression of Gli3 promoted migration (modified Boyden chamber), small interfering RNA-mediated downregulation of Gli3 delayed tube formation (Matrigel), and Western analyses identified increases in Akt phosphorylation, extracellular signal-regulated kinase (ERK)1/2 activation, and c-Fos expression; however, promoter-reporter assays indicated that Gli3 overexpression does not modulate Gli-dependent transcription. Furthermore, the induction of endothelial cell migration by Gli3 was dependent on Akt and ERK1/2 activation.

CONCLUSIONS

Collectively, these observations indicate that Gli3 contributes to vessel growth under both ischemic and nonischemic conditions and provide the first evidence that Gli3 regulates angiogenesis and endothelial cell activity in adult mammals.

Sonic hedgehog regulates angiogenesis and myogenesis during post-natal skeletal muscle regeneration

Sonic hedgehog (Shh) is a morphogen-regulating crucial epithelial-mesenchymal interactions during embryonic development, but its signalling pathway is considered generally silent in post-natal life. In this study, we demonstrate that Shh is de novo expressed after injury and during regeneration of the adult skeletal muscle. Shh expression is followed by significant up-regulation of its receptor and target gene Ptc1 in injured and regenerating muscles. The reactivation of the Shh signalling pathway has an important regulatory role on injury-induced angiogenesis, as inhibition of Shh function results in impaired up-regulation of prototypical angiogenic agents, such as vascular endothelial growth factor (VEGF) and stromal-derived factor (SDF)-1alpha, decreased muscle blood flow and reduced capillary density after injury. In addition, Shh reactivation plays a regulatory role on myogenesis, as its inhibition impairs the activation of the myogenic regulatory factors Myf-5 and MyoD, decreases the up-regulation of insulin-like growth factor (IGF)-1 and reduces the number of myogenic satellite cells at injured site. Finally, Shh inhibition results in muscle fibrosis, increased inflammatory reaction and compromised motor functional recovery after injury. These data demonstrate that the Shh pathway is functionally important for adult skeletal muscle regeneration and displays pleiotropic angiogenic and myogenic potentials in post-natal life. These findings might constitute the foundation for new therapeutic approaches for muscular diseases in humans.

Sonic hedgehog improves delayed wound healing via enhancing cutaneous nitric oxide function in diabetes

Sonic hedgehog (SHH) plays an important role in postnatal tissue repair. The present study tested the hypothesis that impaired SHH pathway results in delayed wound healing by suppressing cutaneous nitric oxide (NO) function in type 1 diabetes. Adult male C57/B6 mice and streptozotocin (STZ)-induced type 1 diabetic mice were used. Although cutaneous SHH and Patched-1 (Ptc-1 encoded by PTCH, PTCH 1) proteins were increased significantly on day 4 after wounding compared with day 0 in normal mice, both were decreased significantly in STZ-induced diabetic mice. Topical application of SHH restored wound healing delay in STZ-induced diabetic mice, with a concomitant augmentation of both cutaneous constitutive nitric oxide synthase (NOS) activity and nitrite level. The effects of SHH on wound healing and cutaneous NO function were markedly inhibited by SHH receptor inhibitor cyclopamine. After 24-h treatment in vitro, SHH (5-20 microg/ml) significantly increased cutaneous endothelial NOS protein expression, NOS activity and NO level in normal mice and STZ-induced diabetic mice in a concentration-dependent manner, an effect that was blunted by cyclopamine and NOS inhibitor N(omega)-nitro-L-arginine methyl ester. The phosphatidylinositol 3-kinase inhibitor LY-294002 significantly blunted the increase of NOS activity and NO level induced by SHH treatment in human umbilican vein endothelial cells. These results demonstrate that the SHH pathway is activated in a normal wound, and its reduction results in impaired NO function and wound healing in diabetes. Strategies aimed at augmenting the endogenous SHH pathway may provide an effective means in ameliorating delayed diabetic wound healing.

Microparticles harbouring Sonic Hedgehog: role in angiogenesis regulation

Sonic Hedgehog (Shh) is a morphogen involved in embryonic development of nervous system. Also, it has been shown that recombinant Shh can modulate angiogenesis under ischemic conditions. However, angiogenic effects of endogenous Shh have not been completely elucidated. Using small membrane-derived vesicles expressing Shh (MPs(Shh+)), we have shown that, although MPs(Shh+) decrease endothelial cell proliferation and migration, they are able to favour angiogenesis through the increase of both endothelial cell adhesion and expression of pro-angiogenenic factors. Activation of proteins implicated in cell adhesion, such as Rho A, as well as upregulation of pro-angiogenic factors were sensitive to inhibition of Shh pathway. Although whole composition of MPs(Shh+) needs to be characterized to understand potential effects of MPs(Shh+), these results highlight a new role of MPs(Shh+) in vascular pathophysiology and may have significant implication for therapy in pathologies associated with altered angiogenesis in order to re-address angiogenic switch.

Sonic hedgehog is a potent chemoattractant for human monocytes: diabetes mellitus inhibits Sonic hedgehog-induced monocyte chemotaxis

The aim of the present study was to evaluate the expression of hedgehog (Hh) signaling molecules and the chemotactic activity of Sonic hedgehog (Shh) in monocytes from control (CTR) and diabetic patients with or without coronary artery disease (CAD). Previously several studies demonstrated that exogenous administration of Shh can induce angiogenesis and accelerate repair of ischemic myocardium and skeletal muscles. Blood samples were collected from (1) CTR (n = 25); (2) patients with stable CAD without diabetes mellitus (CAD−DM, n = 10); and (3) with stable CAD with DM (CAD+DM, n = 15). Monocytes were isolated by Percoll gradient and subjected to PCR and chemotaxis analysis. Hh signaling molecules were expressed in human monocytes, and Shh-induced monocyte chemotaxis. Shh-stimulated migration of monocytes from CTR measured 172.5 ± 90% and a maximal stimulation was observed at Shh concentration of 1 μg/ml. However, Shh failed to induce migration of monocytes from CAD+DM (94.3 ± 27%, P < 0.001 vs. CTR). The impaired response to Shh was associated with strong transcriptional upregulation of the receptor Ptc, while expression of downstream molecules was not altered. Moreover, Ptc is strongly expressed in macrophages of human aortic atherosclerotic plaque. Thus, Shh is a potent chemoattractant for monocytes and it activates classical signaling pathways related to migration. The Shh signaling was negatively affected by DM which might be involved in the pathogenesis of DM-related complications.

Hedgehog signalling: emerging evidence for non-canonical pathways

Hedgehog (HH) signalling is involved in the development of numerous embryonic tissues. In humans,germline mutations in hedgehog pathway components cause congenital malformations and somatic mutations are associated with cancers. The basic framework of the HH pathway was elucidated in the fruitfly, Drosophila melanogaster, and this pathway is largely conserved in vertebrates, although some important differences have been noted. The current paradigm of the "canonical" pathway views HH signalling as a series of repressive interactions which culminates in GLI-mediated transcriptional regulation of a variety of cellular processes. Definitions of "non-canonical" signalling stem from examples where the response to HH morphogen deviates from this paradigm and, according to current reports, three general scenarios of noncanonical HH signalling can be defined: (1) Signalling that involves HH pathway components but which is independent of GLI-mediated transcription; (2) Direct interaction of HH signalling components with components of other molecular pathways; and (3) "Non-contiguous" or "atypical" interaction of core HH pathway components with one another. Currently, the evidence supporting non-canonical HH signalling is not conclusive. However, Sonic hedgehog (SHH) has been shown to regulate cell migration and axon guidance in several contexts, and some of these processes are independent of downstream components of the HH pathway, and presumably the transcriptional response to morphogen. Furthermore, biochemical studies have shown that the HH receptor, PTCH1, can directly interact both with Cyclin B1 and caspases, to inhibit cell proliferation and to promote apoptosis, respectively, and that these functions are inhibited in the presence of morphogen. Genetic analysis of orthologues of the HH pathway in nematode worms further supports the notion that PTCH1-related molecules can function independently of other components of the canonical HH pathway, and the phenotypes of mice with point mutations in the Ptch1 gene offer clues as to the processes that non-canonical HH signalling might regulate. While none of these evidences are conclusive,collectively they point to the existence of added complexity in the HH pathway in the form of non-canonical pathways. A major difficulty in studying this problem is that canonical and non-canonical pathways are likely to act in parallel, and so in many situations it will not be possible to implicate non-canonical responses in certain cellular processes simply by excluding a role for the canonical pathway-directed analyses of non-canonical HH signalling are therefore necessary. The aim of this review is to present the cumulative evidence supporting non-canonical HH signalling, with the hope of promoting further enquiry into this area.

Sonic hedgehog mediates BDNF-induced neuroprotection against mitochondrial inhibitor 3-nitropropionic acid

Sonic hedgehog (SHH), a morphogen critical for embryogenesis, has also been shown to be neuroprotective. We have recently reported that pretreatment of rat cortical neurons for 8 h with brain-derived neurotrophic factor (BDNF; 100 ng/ml) affords protection against neurotoxicity of 3-nitropropionic acid (3-NP; 2.5 mM for 24 h), a mitochondrial complex II inhibitor. However, whether SHH is involved in BDNF-mediated neuroprotection remains unknown. Herein we tested whether BDNF induces SHH expression and if so, whether BDNF induction of SHH contributes to the observed neuroprotective effects. We found BDNF (100 ng/ml) increased SHH expression at both mRNA and protein levels. BDNF protection against 3-NP was abolished by cyclopamine (CPM; 5 microM), the SHH pathway inhibitor. Preconditioning of cortical neurons with N-terminal fragment of SHH (SHH-N; 0.1-1 ng/ml) was sufficient to confer resistance. These results indicate that BDNF induces SHH expression, which contributes to neuroprotection against 3-NP toxicity in rat cortical neurons.

The relative potency and safety of endothelial progenitor cells and unselected mononuclear cells for recovery from myocardial infarction and ischemia

Endothelial progenitor cells (EPCs) are a subset of the total mononuclear cell population (tMNCs) that possess an enhanced potential for differentiation within the endothelial-cell lineage. Typically, EPCs are selected from tMNCs via the expression of both hematopoietic stem-cell markers and endothelial-cell markers, such as CD34, or by culturing tMNCs in media selective for endothelial cells. Both EPCs and tMNCs participate in vascular growth and regeneration, and their potential use for treatment of myocardial injury or disease has been evaluated in early-phase clinical studies. Direct comparisons between EPCs and tMNCs are rare, but the available evidence appears to favor EPCs, particularly CD34+ cells, and the potency of EPCs may be increased as much as 30-fold through genetic modification. However, these observations must be interpreted with caution because clinical investigations of EPC therapy are ongoing. We anticipate that with continued development, EPC therapy will become a safe and effective treatment option for patients with acute myocardial infarction or chronic ischemic disease.

Vascular endothelial growth factors in cardiovascular medicine

The discovery of vascular endothelial growth factors (VEGFs) and their receptors has considerably improved the understanding of the development and function of endothelial cells. Each member of the VEGF family appears to have a specific function: VEGF-A induces angiogenesis (i.e. growth of new blood vessels from preexisting ones), placental growth factor mediates both angiogenesis and arteriogenesis (i.e. the formation of collateral arteries from preexisting arterioles), VEGF-C and VEGF-D act mainly as lymphangiogenic factors. The study of the biology of these endothelial growth factors has allowed a major progress in the comprehension of the genesis of the vascular system and its abnormalities observed in various pathologic conditions (atherosclerosis and coronary artery disease). The role of VEGF in the atherogenic process is still unclear, but actual evidence suggests both detrimental (development of a neoangiogenetic process within the atherosclerotic plaque) and beneficial (promotion of collateral vessel formation) effects. VEGF and other angiogenic growth factors (fibroblast growth factor), although initially promising in experimental studies and in initial phase I/II clinical trials in patients with ischemic heart disease or peripheral arterial occlusive disease, have subsequently failed to show significant therapeutic improvements in controlled clinical studies. Challenges still remain about the type or the combination of angiogenic factors to be administered, the form (protein vs. gene), the route, and the duration of administration.

Shared circuitry: developmental signaling cascades regulate both embryonic and adult coronary vasculature

Ischemic heart disease is the most common cause of heart failure and is among the leading causes of mortality worldwide. Therapies used for the treatment of this disease aim to restore blood flow to severely narrowed or occluded coronary arteries by either catheter-based or surgical means. Although these strategies prove efficacious for many patients, a substantial number of individuals fail to improve following these procedures. Recently, a noninvasive strategy has been proposed, focusing on the use of endogenous growth factors that trigger the growth of new coronary arteries. Using the developing heart as a model, several groups have identified some of the key pathways that not only govern the development of the coronary vascular system but also promote the growth of the adult coronary vasculature. Here, we review the major morphological events and signaling cascades that mediate the formation of the coronary vasculature in the embryo. We further describe the mechanism by which many of these same pathways also regulate the adult coronary vasculature and their potential use in the treatment of ischemic heart disease.

Microparticles harboring Sonic Hedgehog promote angiogenesis through the upregulation of adhesion proteins and proangiogenic factors

Microparticles (MPs) are small fragments generated from the plasma membrane after cell stimulation or apoptosis. We have recently shown that MPs harboring the morphogen Sonic Hedgehog (MPs(Shh+)) correct endothelial injury by release of nitric oxide from endothelial cells [Agouni, Mostefai, Porro, Carusio, Favre, Richard, Henrion, Martínez and Andriantsitohaina (2007) FASEB J., 21, 2735-2741]. Here, we show that MPs(Shh+) induce the formation of capillary-like structures in an in vitro model using human endothelial cells, although they inhibited cell migration. Besides, MPs(Shh+) regulate cell proliferation. Both cell adhesion and expression of proteins involved in this process such as Rho A and phosphorylation of focal-activated kinase were increased by MPs(Shh+), via a Rho-associated coiled-coil-containing protein kinase inhibitor-sensitive pathway. We demonstrate that MPs(Shh+) increase messenger RNA and protein levels of proangiogenic factors as measured by quantitative reverse transcription-polymerase chain reaction and western blot. In spite of vascular endothelial growth factor expression, conditioned media from endothelial cells treated avec MPs(Shh+) reduces angiogenesis. Interestingly, the effects induced by MPs(Shh+) on the formation of capillary-like structures, expression of adhesion molecules and proangiogenic factors were reversed after silencing of the Shh receptor, using small interfering RNA or when Sonic Hedgehog (Shh) signaling was pharmacologically inhibited with cyclopamine. Taken together, we show that Shh carried by MPs(Shh+) regulate angiogenesis probably through both a direct and an indirect mechanisms, and we propose that MPs harboring Shh may contribute to the generation of a vascular network in pathologies associated with tumor growth.

Paradoxical dysregulation of the neural stem cell pathway sonic hedgehog-Gli1 in autoimmune encephalomyelitis and multiple sclerosis

OBJECTIVE

Neurovascular niches have been proposed as critical components of the neural stem cell (NSC) response to acute central nervous system injury; however, it is unclear whether these potential reparative niches remain functional during chronic injury. Here, we asked how central nervous system inflammatory injury regulates the intrinsic properties of NSCs and their niches.

METHODS

We investigated the sonic hedgehog (Shh)-Gli1 pathway, an important signaling pathway for NSCs, in experimental autoimmune encephalomyelitis (EAE) and multiple sclerosis (MS), and its regulation by inflammatory cytokines.

RESULTS

We show that Shh is markedly upregulated by reactive and perivascular astroglia in areas of injury in MS lesions and during EAE. Astroglia outside the subventricular zone niche can support NSC differentiation toward neurons and oligodendrocytes, and Shh is a critical mediator of this effect. Shh induces differential upregulation of the transcription factor Gli1, which mediates Shh-induced NSC differentiation. However, despite the increase in Shh and the fact that Gli1 was initially increased during early inflammation of EAE and active lesions of MS, Gli1 was significantly decreased in spinal cord oligodendrocyte precursor cells after onset of EAE, and in chronic active and inactive lesions from MS brain. The Th1 cytokine interferon-gamma was unique in inducing Shh expression in astroglia and NSCs, while paradoxically suppressing Gli1 expression in NSCs and inhibiting Shh-mediated NSC differentiation.

INTERPRETATION

Our data suggest that endogenous repair potential during chronic injury appears to be limited by inflammation-induced alterations in intrinsic NSC molecular pathways such as Gli1.

Possible novel targets for therapeutic angiogenesis

An increasing number of studies about the molecular basis of angiogenesis are rapidly disclosing novel signal pathways involved in the blood vessel formation process. This review will focus on bone morphogenic proteins, Hedgehog, Notch, ephrins, neuropilins, neurotrophins and netrins. These recently discovered angiogenesis mediators are involved in vascular development during embryogenesis and, interestingly, they are shared between the nervous and vascular systems. They represent new potential targets in the vasculature and suggest novel therapeutic opportunities.

Hedgehog signaling to distinct cell types differentially regulates coronary artery and vein development

Vascular development begins with formation of a primary capillary plexus that is later remodeled to give rise to the definitive vasculature. Although the mechanism by which arterial and venous fates are acquired is well understood, little is known about when during vascular development arterial and venous vessels emerge and how their growth is regulated. Previously, we have demonstrated that a hedgehog (HH)/vascular endothelial growth factor (VEGF) and angiopoeitin 2 (ANG2) signaling pathway is essential for the development of the coronary vasculature. Here, we use conditional gene targeting to identify the cell types that receive HH signaling and mediate coronary vascular development. We show that HH signaling to the cardiomyoblast is required for the development of coronary veins, while HH signaling to the perivascular cell (PVC) is necessary for coronary arterial growth. Moreover, the cardiomyoblast and PVC appear to be the exclusive cell types that receive HH signals, as ablation of HH signaling in both cell types leads to an arrest in coronary development. Finally, we present evidence suggesting that coronary arteries and veins may be derived from distinct lineages.

Direct injection of kit ligand-2 lentivirus improves cardiac repair and rescues mice post-myocardial infarction

Myocardial infarction (MI) and subsequent adverse remodeling cause heart failure. Previously we demonstrated a role for Kit ligand (KL) in improving cardiac function post-MI. KL has two major isoforms; KL-1 is secreted whereas KL-2 is predominantly membrane bound. We demonstrate here first that KL-2-deficient mice have worse survival and an increased heart/bodyweight ratio post-MI compared to mice with reduced c-Kit receptor expression. Next we synthesized recombinant lentiviral vectors (LVs) that engineered functional expression of murine KL-1 and KL-2. For in vivo analyses, we directly injected these LVs into the left ventricle of membrane-bound KL-deficient Sl/Sl(d) or wild-type (WT) mice undergoing MI. Control LV/enGFP injection led to measurable reporter gene expression in hearts. Injection of LV/KL-2 attenuated adverse left ventricular remodeling and dramatically improved survival post-MI in both Sl/Sl(d) and WT mice (from 12 to 71% and 35 to 73%, respectively, versus controls). With regard toward beginning to understand the possible salutary mechanisms involved in this effect, differential staining patterns of Sca-1 and Ly49 on peripheral blood (PB) cells from therapeutically treated animals was found. Our data show that LV/KL-2 gene therapy is a promising treatment for MI.

Hedgehog signaling is critical for maintenance of the adult coronary vasculature in mice

Hedgehog (HH) signaling has emerged as a critical pathway involved in the pathogenesis of a variety of tumors. As a result, HH antagonists are currently being evaluated as potential anticancer therapeutics. Conversely, activation of HH signaling in the adult heart may be beneficial, as HH agonists have been shown to increase coronary vessel density and improve coronary function after myocardial infarction. To investigate a potential homeostatic role for HH signaling in the adult heart, we ablated endogenous HH signaling in murine myocardial and perivascular smooth muscle cells. HH signaling was required for proangiogenic gene expression and maintenance of the adult coronary vasculature in mice. In the absence of HH signaling, loss of coronary blood vessels led to tissue hypoxia, cardiomyocyte cell death, heart failure, and subsequent lethality. We further showed that HH signaling specifically controlled the survival of small coronary arteries and capillaries. Together, these data demonstrate that HH signaling is essential for cardiac function at the level of the coronary vasculature and caution against the use of HH antagonists in patients with prior or ongoing heart disease.

Permanent coronary artery occlusion: cardiovascular MR imaging is platform for percutaneous transendocardial delivery and assessment of gene therapy in canine model

PURPOSE

To provide evidence that vascular endothelial growth factor (VEGF) genes delivered transendocardially with magnetic resonance (MR) imaging guidance may neovascularize or improve vascular recruitment in occlusive infarction.

MATERIALS AND METHODS

All experimental procedures received approval from the institutional committee on animal research. Dogs with permanent coronary artery occlusion were imaged twice (3 days after occlusion for assessment of acute infarction; a mean of 50 days after occlusion +/- 3 [standard error of the mean] for assessment of chronic infarction). A mixture of plasmid VEGF and plasmid LacZ (n = 6, treated animals) or plasmid LacZ and sprodiamide (n = 6, placebo control animals) was delivered to four sites. MR fluoroscopy was used to target and monitor delivery of genes. The effectiveness of this delivery approach was determined by using MR imaging methods to assess perfusion, left ventricular (LV) function, myocardial viability, and infarct resorption. Histologic evaluation of neovascularization was then performed.

RESULTS

MR fluoroscopic guidance of injectates was successful in both groups. Treated animals with chronic, but not those with acute, infarction showed the following differences compared with control animals: (a) steeper mean maximum upslope perfusion (200 sec(-1) +/- 32 vs 117 sec(-1) +/- 15, P = .02), (b) higher peak signal intensity (1667 arbitrary units +/- 100 vs 1132 arbitrary units +/- 80, P = .002), (c) increased ejection fraction (from 27.9% +/- 1.2 to 35.3% +/- 1.6, P = .001), (d) smaller infarction size (as a percentage of LV mass) at MR imaging (8.5% +/- 0.9 vs 11.3% +/- 0.9, P = .048) and triphenyltetrazolium chloride staining (9.4% +/- 1.5 vs 12.7% +/- 0.4, P = .05), and (e) higher vascular density (as number of vessels per square millimeter) at the border (430 +/- 117 vs 286 +/- 19, P = .0001) and core (307 +/- 112 vs 108 +/- 17, P = .0001).

CONCLUSION

The validity of plasmid VEGF gene delivered with MR fluoroscopic guidance into occlusive infarction was confirmed by neovascularization associated with improved perfusion, LV function, and infarct resorption.

Endothelial progenitor cells in neovascularization of infarcted myocardium

Historically, revascularization of ischemic tissue was believed to occur through the migration and proliferation of endothelial cells in nearby tissues; however, evidence accumulated in recent years indicates that a subpopulation of adult, peripheral-blood cells, collectively referred to as endothelial progenitor cells (EPCs), can differentiate into mature endothelial cells. After ischemic insult, EPCs are believed to home to sites of neovascularization, where they contribute to vascular regeneration by forming a structural component of capillaries and by secreting angiogenic factors; new evidence indicates that EPCs can also differentiate into cardiomyocytes and smooth-muscle cells. These insights into the molecular and cellular processes of tissue formation suggest that cardiac function may be preserved after myocardial infarction by transplanting EPCs into ischemic heart tissue, thereby enhancing vascular and myocardial recovery. This therapeutic strategy has been effective in animal models of ischemic disorders, and results from randomized clinical trials suggest that cell-based strategies may be safe and feasible for treatment of myocardial infarction in humans and have provided early evidence of efficacy. However, the scarcity of EPCs in the peripheral blood and evidence that several disease states reduce EPC number and/or function have prompted the development of several strategies to overcome these limitations, such as the administration of genetically modified EPCs that overexpress angiogenic growth factors. To optimize therapeutic outcomes, researchers must continue to refine methods of EPC purification, expansion, and administration, and to develop techniques that overcome the intrinsic scarcity and phenotypic deficiencies of EPCs.

Biological approaches to ischemic tissue repair: gene- and cell-based strategies

Gene therapy is a potential therapeutic strategy for treatment of ischemic vascular diseases; however, the clinical application of gene therapy has met some anticipated challenges. Recent randomized, controlled trials suggest that patients with cardiovascular disease may also benefit from cell-based therapies, and the optimal treatment regimen may combine both approaches to take advantage of potential synergy between the underlying therapeutic mechanisms. This review discusses recent research into both gene and cell therapy and considers the potential application of a combined treatment approach for cardiovascular and cerebrovascular ischemic diseases.

Hedgehog signalling in vascular development

The Hedgehog family of proteins are powerful morphogens mediating embryonic development as well as adult morphogenesis and carcinogenesis. For example, excess hedgehog activity has been implicated in basal cell carcinoma, medulloblastoma and rhabdomyosarcoma. More recently, hedgehog signalling has been implicated in angiogenesis. While hedgehog signalling in adult angiogenesis may constitute a simple recapitulation of that in embryonic development, it should be appreciated that Hedgehog signalling occurs in embryonic angiogenesis in different developmental contexts. This article reviews the role of Hedgehog signalling in both embryonic and postnatal vascular development. The temporal importance of a window of hedgehog dependent angiogenesis during development is emphasised and illustrated using a whole mouse embryo culture system.