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

A sonic hedgehog signaling domain in the arterial adventitia supports resident Sca1+ smooth muscle progenitor cells

We characterize a sonic hedgehog (Shh) signaling domain restricted to the adventitial layer of artery wall that supports resident Sca1-positive vascular progenitor cells (AdvSca1). Using patched-1 (Ptc1(lacZ)) and patched-2 (Ptc2(lacZ)) reporter mice, adventitial Shh signaling activity was first detected at embryonic day (E) 15.5, reached the highest levels between postnatal day 1 (P1) and P10, was diminished in adult vessels, and colocalized with a circumferential ring of Shh protein deposited between the media and adventitia. In Shh(-/-) mice, AdvSca1 cells normally found at the aortic root were either absent or greatly diminished in number. Using a Wnt1-cre lineage marker that identifies cells of neural crest origin, we found that neither the adventitia nor AdvSca1 cells were labeled in arteries composed of neural crest-derived smooth muscle cells (SMCs). Although AdvSca1 cells do not express SMC marker proteins in vivo, they do express transcription factors thought to be required for SMC differentiation, including serum response factor (SRF) and myocardin family members, and readily differentiate to SMC-like cells in vitro. However, AdvSca1 cells also express potent repressors of SRF-dependent transcription, including Klf4, Msx1, and FoxO4, which may be critical for maintenance of the SMC progenitor phenotype of AdvSca1 cells in vivo. We conclude that a restricted domain of Shh signaling is localized to the arterial adventitia and may play important roles in maintenance of resident vascular SMC progenitor cells in the artery wall.

Cell-free embryonic stem cell extract-mediated derivation of multipotent stem cells from NIH3T3 fibroblasts for functional and anatomical ischemic tissue repair

The oocyte-independent source for the generation of pluripotent stem cells is among the ultimate goals in regenerative medicine. We report that on exposure to mouse embryonic stem cell (mESC) extracts, reversibly permeabilized NIH3T3 cells undergo dedifferentiation followed by stimulus-induced redifferentiation into multiple lineage cell types. Genome-wide expression profiling revealed significant differences between NIH3T3 control and ESC extract-treated NIH3T3 cells including the reactivation of ESC-specific transcripts. Epigenetically, ESC extracts induced CpG demethylation of Oct4 promoter, hyperacetylation of histones 3 and 4, and decreased lysine 9 (K-9) dimethylation of histone 3. In mouse models of surgically induced hindlimb ischemia or acute myocardial infarction transplantation of reprogrammed NIH3T3 cells significantly improved postinjury physiological functions and showed anatomic evidence of engraftment and transdifferentiation into skeletal muscle, endothelial cell, and cardiomyocytes. These data provide evidence for the generation of functional multipotent stem-like cells from terminally differentiated somatic cells without the introduction of retroviral mediated transgenes or ESC fusion.

Antioxidant gene therapy for cardiovascular disease: current status and future perspectives

Excessive production of reactive oxygen species has been implicated to play an important role in a number of cardiovascular pathologies, including hypertension, atherosclerosis, myocardial infarction, ischemia/reperfusion injury, and restenosis after angioplasty or venous bypass grafting. The formation of reactive oxygen species is balanced out by antioxidant defenses, and augmenting this defense by antioxidant therapies could therefore provide a potential means to treat conditions in which the formation of reactive oxygen species exceeds the capability of natural protective mechanisms. In this review, we summarize the studies in which antioxidant gene therapy has been used successfully to treat cardiovascular diseases. We also discuss the current limitations of antioxidant gene therapy and envision future therapeutic targets and methodological approaches for an improved outcome.

Endogenous hedgehog expression contributes to myocardial ischemia-reperfusion-induced injury

The developmentally important hedgehog (Hh) pathway is activated in ischemic tissue, and exogenously administered Sonic hedgehog (Shh) supports tissue repair after cardiac ischemia. Hence, it is currently assumed that the endogenous increase in Shh during ischemia serves a beneficial role in limiting cardiac tissue damage. To prove or refute this hypothesis, we treated mice with the smoothened (Smo) inhibitor cyclopamine to block the Hh pathway during myocardial ischemia and reperfusion. The experimental induction of myocardial ischemia resulted in activation of the Hh pathway and hallmark features of myocardial damage, such as left ventricular dilatation and reduced cardiac output. Unexpectedly, cyclopamine treatment ameliorated left ventricular dilatation and cardiac output. As the beneficial effect of exogenous Shh was suggested to depend on reduced apoptosis, increased vascularization, and reduced fibrosis, we subsequently assessed the effect of cyclopamine on these processes. Vascularization was similar in cyclopamine-treated and control-treated animals, but increased apoptosis and reduced fibrosis were observed in the cyclopamine-treated animals. Thus, Hh seems to exert a dualistic action in cardiac ischemia in which high exogenous levels are able to foster tissue repair and endogenous Hh seems to be deleterious.

Accumulation of hedgehog-responsive progenitors parallels alcoholic liver disease severity in mice and humans

BACKGROUND & AIMS

Improving outcomes in alcoholic liver disease (ALD) necessitates better understanding of how habitual ethanol (EtOH) consumption alters normal regenerative mechanisms within the liver. Hedgehog (Hh) pathway activation promotes expansion of progenitor populations in other tissues. We evaluated the hypothesis that chronic EtOH exposure activates Hh signaling in liver.

METHODS

Hh signaling, liver progenitors, transforming growth factor (TGF)-beta induction, and liver damage were compared in mice fed chow, high-fat diets (HF), or HF + EtOH for 4 weeks. Susceptibility to TGF-beta-mediated apoptosis was compared in Hh-responsive liver cells (eg, immature cholangiocytes and oval cells) and mature hepatocytes (which are unresponsive to Hh). Hepatic accumulation of Hh-responsive cells were compared in controls and ALD patients and correlated with a discriminant function (DF) that predicts subacute mortality.

RESULTS

Hh signaling and numbers of Hh-responsive cells were increased in HF mice and greatest in HF+EtOH mice. In both, progenitor and stromal cell populations harbored Hh-responsive cells. More ductular-type progenitors and fibrosis markers were noted in HF+EtOH mice than in HF mice. The former also expressed more TGF-beta-1. TGF-beta-1 treatment selectively promoted the viability of Hh-responsive immature liver cells and caused mature hepatocytes that survived to produce Hh ligands. Hh-responsive cells were increased in ALD patients. Lobular accumulation of Hh-responsive immature ductular cells was greater in those with a DF >32 than those with a DF <32.

CONCLUSIONS

Hh signaling is increased in ALD and may influence ALD outcomes by promoting hepatic accumulation of immature ductular cells.

Activation of Notch-mediated protective signaling in the myocardium

The Notch network regulates multiple cellular processes, including cell fate determination, development, differentiation, proliferation, apoptosis, and regeneration. These processes are regulated via Notch-mediated activity that involves hepatocyte growth factor (HGF)/c-Met receptor and phosphatidylinositol 3-kinase/Akt signaling cascades. The impact of HGF on Notch signaling was assessed following myocardial infarction as well as in cultured cardiomyocytes. Notch1 is activated in border zone cardiomyocytes coincident with nuclear c-Met following infarction. Intramyocardial injection of HGF enhances Notch1 and Akt activation in adult mouse myocardium. Corroborating evidence in cultured cardiomyocytes shows treatment with HGF or insulin increases levels of Notch effector Hes1 in immunoblots, whereas overexpression of activated Notch intracellular domain prompts a 3-fold increase in phosphorylated Akt. Infarcted hearts injected with adenoviral vector expressing Notch intracellular domain treatment exhibit improved hemodynamic function in comparison with control mice after 4 weeks, implicating Notch signaling in a cardioprotective role following cardiac injury. These results indicate Notch activation in cardiomyocytes is mediated through c-Met and Akt survival signaling pathways, and Notch1 signaling in turn enhances Akt activity. This mutually supportive crosstalk suggests a positive survival feedback mechanism between Notch and Akt signaling in adult myocardium following injury.

Endothelial progenitor cells in regenerative medicine and cancer: a decade of research

Endothelial progenitor cells (EPCs) are a heterogeneous subpopulation of bone marrow mononuclear cells that have an enhanced potential for differentiation within the endothelial cell lineage. In response to ischemic injury, EPCs are mobilized from the bone marrow to the peripheral circulation and home to the sites of new vessel growth, where they become incorporated into the growing vasculature. Thus, EPCs can be therapeutically useful for treating ischemic injury or for delivering anti-cancer agents to tumors.

Sonic hedgehog is an autocrine viability factor for myofibroblastic hepatic stellate cells

BACKGROUND/AIMS

Factors released during liver injury, such as platelet derived growth factor-BB (PDGF), promote accumulation of myofibroblastic hepatic stellate cells (MFB) that drive the pathogenesis of cirrhosis. The hedgehog (Hh) pathway regulates remodeling of other injured tissues. This study evaluates the hypothesis that autocrine production of Sonic hedgehog (Shh) promotes MFB growth.

METHODS

Primary rat hepatic stellate cells (HSC) were treated without or with PDGF, a pharmacologic inhibitor of PDGF-regulated kinases, adenovirus expressing activated or dominant negative AKT, or Hh signaling inhibitors. Shh production, expression of Hh inhibitors and target genes, and HSC growth were assessed.

RESULTS

HSC expressed Shh, Hh pathway components, and the Hh inhibitor, Hip. During culture Hip expression fell, Shh production increased, and Hh target gene expression was induced. Neutralizing Shh antibodies promoted apoptosis. Adding PDGF increased Shh expression and MFB growth. Both processes followed activation of AKT and were abrogated by AKT inhibitors. Adenoviral delivery of activated AKT up-regulated Shh expression, demonstrating a direct role for AKT in regulating Shh expression. Shh-neutralizing antibodies and other Hh pathway inhibitors blocked the mitogenic effects of PDGF.

CONCLUSIONS

These results identify Shh as an autocrine growth factor for MFB and suggest a role for Hh signaling in the pathogenesis of cirrhosis.

Purification and bioassay of hedgehog ligands for the study of cell death and survival

The Hedgehog (Hh) family of secreted ligands-composed of Sonic Hedgehog (Shh), Indian Hedgehog (Ihh), and Desert Hedgehog (Dhh)-possesses many roles during embryonic development, adult homeostasis, and cancer. The specific functions of the Hh proteins are intertwined with their requirement as survival factors in Hh-responsive cells. However, studies designed to dissect the anti-apoptotic role of Hhs have been hindered by the lack of simple approaches to purify large quantities of recombinant ligands in the average laboratory setting because of the natural modifications of these proteins with palmitic acid and cholesterol. In this chapter, we provide a comprehensive protocol for the expression of Shh, Ihh, and Dhh in Escherichia coli as fusion proteins with calmodulin-binding peptide to allow easy and rapid purification. The ligands are engineered with a new N-terminus containing two isoleucine residues to provide an essential hydrophobic interphase for achieving high biologic activity. The protocol includes a detailed description of a method for determination of the specific activity of the generated proteins by use of a cell culture-based luciferase approach.

Fibroblast growth factors and Hedgehogs: at the heart of the epicardial signaling center

Over the past several years, increasing attention has been focused on understanding signaling pathways that control key events during midgestational heart development. During this period of development, the heart tube transforms into a functioning organ that must maintain its own blood supply and grow and respond to the physiologic needs of the organism. A critical event that occurs during midgestational heart development is the formation of the epicardium, which functions as a source of cells and as a signaling center that regulates myocardial growth and coronary vascular development. This review will describe our understanding of the role and the mechanism by which the epicardium governs these developmental events, primarily as a result of studies in the mouse. We focus on two key growth factor pathways: fibroblast growth factor and Hedgehog signaling.

Hepatic accumulation of Hedgehog-reactive progenitors increases with severity of fatty liver damage in mice

Progenitors regenerate fatty livers but the mechanisms involved are uncertain. The Hedgehog pathway regulates mesendodermal progenitors and modulates mesenchymal-epithelial interactions during tissue remodeling. To determine if Hedgehog signaling increases in liver progenitors during fatty liver injury, we compared expression of Hedgehog ligands and target genes across a spectrum of injury. Leptin-deficient ob/ob mice with fatty livers and their healthy lean littermates were studied before and after exposure to the hepatotoxin, ethionine. At baseline, ob/ob mice had greater liver damage than controls. Ethionine induced liver injury in both ob/ob and lean mice, with greater injury occurring in ob/ob mice. After ethionine, the ob/ob mice developed liver atrophy and fibrosis. Liver injury increased hepatic accumulation of progenitors, including ductular cells that produced and responded to Hedgehog ligands. A dose-response relationship was demonstrated between liver injury and expansion of Hedgehog-responsive progenitors. In severely damaged, atrophic livers, nuclei in mature-appearing hepatocytes accumulated the Hedgehog-regulated mesenchymal transcription factor, Gli2 and lost expression of the liver epithelial transcription factor, hepatocyte nuclear factor 6 (HNF-6). Hepatic levels of collagen mRNA and pericellular collagen fibrils increased concomitantly. Hence, fatty liver injury increases Hedgehog activity in liver progenitors, and this might promote epithelial-mesenchymal transitions that result in liver fibrosis.

Adenoviral vector-mediated transfer of the Indian hedgehog gene modulates lymphomyelopoiesis in vivo

Indian hedgehog (Ihh) plays an essential role in angiogenesis, hematogenesis, and epiphysis formation during embryogenesis. In the present study, we injected an adenoviral vector (Adv) carrying the mock-control (Adv-control) or Ihh (Adv-Ihh) gene into severe combined immunodeficiency (SCID) or BALB/c mice to evaluate the effects of lhh on the regulation of postnatal hematopoiesis in vivo. After the i.v. injection of Adv-Ihh, the expression of vector-derived Ihh mRNA was detected in the liver. Four weeks after administration of Adv-Ihh to SCID mice, we observed an increase in the number of c-Kit+ cells and clonogenic cells per 10(5) mononuclear cells in the bone marrow compared with Adv-control-administered mice. Moreover, after administration of Adv-Ihh to BALB/c mice, the number of splenic B220+IgM(low)CD23(int)CD21(int) B lymphocytes and CD4+ T lymphocytes was strongly increased. Furthermore, the number of thymic double-negative (DN)2, DN3, CD8+ immature single-positive, and CD4+/CD8- cells was significantly elevated relative to the number in mice that received the control Adv vector. Our results suggest that enhanced signaling by Ihh can modulate the proliferation and differentiation of splenic B lymphocytes and thymic T lymphocytes during bone marrow hematopoiesis in vivo. Thus, modulation of the hedgehog signaling pathway may provide a therapeutic strategy to stimulate lymphomyelopoiesis in vivo.

STAT3-dependent mouse embryonic stem cell differentiation into cardiomyocytes: analysis of molecular signaling and therapeutic efficacy of cardiomyocyte precommitted mES transplantation in a mouse model of myocardial infarction

Pluripotent embryonic stem (ES) cell therapy may be an attractive source for postinfarction myocardial repair and regeneration. However, the specific stimuli and signal pathways that may control ES cell-mediated cardiomyogenesis remains to be completely defined. The aim of the present study was to investigate (1) the effect and underlying signal transduction pathways of leukemia inhibitory factor (LIF) and bone-morphogenic protein-2 (BMP-2)-induced mouse ES cell (mES-D3 line) differentiation into cardiomyocytes (CMC) and (2) the efficacy of CMC precommitted mES cells for functional and anatomical cardiac repair in surgically-induced mouse acute myocardial infarction (AMI) model. Various doses of LIF and BMP-2 and their inhibitors or blocking antibodies were tested for mES differentiation to CMC in vitro. CMC differentiation was assessed by mRNA and protein expression of CMC-specific markers, Connexin-43, CTI, CTT, Mef2c, Tbx5, Nkx2.5, GATA-4, and alphaMHC. LIF and BMP-2 synergistically induced the expression of CMC markers as early as 2 to 4 days in culture. Signaling studies identified STAT3 and MAP kinase (ERK1/2) as specific signaling components of LIF+BMP-2-mediated CMC differentiation. Inhibition of either STAT3 or MAPK activation by specific inhibitors drastically suppressed LIF+BMP-2-mediated CMC differentiation. Moreover, in mouse AMI, transplantation of lentivirus-GFP-transduced, LIF+BMP-2 precommitted mES cells, improved post-MI left ventricular functions, and enhanced capillary density. Transplanted cells engrafted in myocardium and differentiated into CMC and endothelial cells. Our data suggest that LIF and BMP-2 may synergistically enhance CMC differentiation of transplanted stem cells. Thus augmentation of LIF/BMP-2 downstream signaling components or cell type specific precommitment may facilitate the effects of ES cell-based therapies for post-MI myocardial repair and regeneration.

The sonic hedgehog signaling network in development and neoplasia

The sonic hedgehog (SHH) pathway was first defined genetically in fruit flies. Subsequently, the SHH network has been shown to be critical for normal mammalian development, by mediating interactions between stromal and epithelial cells. Recent evidence suggests that, deregulation of SHH signaling is important in the pathogenesis of cancer. Further, some observations suggest that a SHH paracrine mechanism mediating tumor-mesenchymal interactions may contribute to the metastatic capacity of cancer. Preclinical studies demonstrate that tumor cells in which SHH is deregulated are dependent on signaling through this pathway for the maintenance of proliferation and viability. SHH antagonists have been identified and show promise in inhibiting tumor growth in preclinical studies. The utility of these agents in the management of cancer patients awaits the outcome of ongoing and future clinical trials.

Sonic hedgehog induces transcription-independent cytoskeletal rearrangement and migration regulated by arachidonate metabolites

Sonic hedgehog (Shh) is a morphogen pivotal for development and tissue maintenance. Biological effects of Shh are mediated through a pathway that involves binding to patched1 (Ptch1), thereby releasing Smoothened (Smo) from inhibition resulting in the activation of Gli transcription factors, which mediate the induction of Shh target genes. Here, we describe a novel signal transduction pathway for Shh, which is transcription/translation-independent, SuFu insensitive, and consequently independent of Gli-mediated induction of transcription. Through this alternative pathway Shh, transduced via Smo, induced altered cell morphology together with lamellipodia formation. Migration assays demonstrate that this cytoskeletal rearrangement mediates the migratory response to Shh. This Shh-induced, Smo mediated migration utilizes and requires the metabolism of arachidonic acid through the 5-lipoxygenase pathway. These data provide a link between a seemingly novel Gli-independent Hh signaling pathway and the leukotriene metabolism, and might explain the developmental abnormalities observed in both patients with defective leukotriene metabolism as well as in rodent models of defective Rho family GTPase signaling.

Enhanced voluntary alcohol consumption after estrogen supplementation negates estrogen-mediated vascular repair in ovariectomized mice

Preclinical and observational studies in ovariectomized (OVX) animals and pre- and postmenopausal women, respectively, have suggested the cardioprotective effects of estrogen replacement therapy. However, randomized clinical trials have not confirmed estrogen-mediated cardioprotection. Although uncertainties about the duration and optimal type of estrogen replacement regimen might explain the disparity, other factors that may mask the protective effects of 17beta-estradiol (E2) on cardiovascular outcome need scrutiny. Increased ethanol consumption may be one such factor. We examined the effect of E2 supplementation on ethanol consumption in OVX mice and the effect of ethanol consumption on E2-mediated vascular repair, in vivo. OVX mice implanted with E2 pellets consumed significantly more ethanol, compared with those receiving placebo pellets. E2-induced increase in ethanol consumption was not affected by the absence of either estrogen receptor-alpha or -beta. Reendothelialization after carotid artery denudation was repressed, and neovascularization in ischemic hind limbs was blunted in mice consuming ethanol, despite E2 supplementation. In vitro, ethanol dose-dependently attenuated E2-induced endothelial cell (EC) proliferation and tube formation activity and enhanced EC apoptosis, suggesting that ethanol blocks E2-induced EC survival and function. Taken together our data suggest that increased ethanol consumption after E2 supplementation blunts the beneficial effects of E2 on EC function and that novel approaches to estrogen replacement for cardioprotection may benefit from the control of alcohol consumption.

Small-molecule modulators of Hh and Wnt signaling pathways

Hedgehog (Hh) and Wnt signaling pathways play key roles in growth and patterning during embryonic development and in the postembryonic regulation of stem cell number in the epithelia. Numerous studies link aberrant modulation of these pathways to specific human diseases. This article focuses on general aspects of Hh and Wnt signal transduction and biologic molecules involved in the respective signaling cascades. Specifically, the authors summarize small-molecule modulators of both pathways that show promise as therapeutic modalities.

Current Status of Cardiovascular Gene Therapy

Gene transfer for the therapeutic modulation of cardiovascular diseases is an expanding area of gene therapy. During the last decade several approaches have been designed for the treatment of hyperlipidemias, post-angioplasty restenosis, hypertension, and heart failure, and for protection of vascular by-pass grafts and promotion of therapeutic angiogenesis. Adenoviruses (Ads) and adeno-associated viruses (AAVs) are currently the most efficient vectors for delivering therapeutic genes into the cardiovascular system. Gene transfer using local gene delivery techniques have been shown to be superior to less-targeted intra-arterial or intra-venous applications. To date, no gene therapy drugs have been approved for clinical use in cardiovascular applications. In preclinical studies of therapeutic angiogenesis, various growth factors such as vascular endothelial growth factors (VEGFs) and fibroblast growth factors (FGFs), have shown positive results. Gene therapy also appears to have potential clinical applications in improving the patency of vascular grafts and in treating heart failure. Post-angioplasty restenosis, hypertension, and hyperlipidemias (excluding homozygotic familial hypercholesterolemia) can usually be managed satisfactorily by conventional approaches, and are therefore less favored areas for gene therapy. The development of technologies that can ensure long-term, targeted, and regulated gene transfer, and a careful selection of target patient populations, will be very important for the progress of cardiovascular gene therapy in clinical applications.

Inhibition of Sonic Hedgehog Signaling Reduces Chronic Rejection and Prolongs Allograft Survival in a Rat Orthotopic Small Bowel Transplantation Model

BACKGROUND

Although acute graft rejection can be successfully controlled by immunosuppressive agents, chronic rejection (CR), which is characterized by arteriosclerosis in the donor organ vessels, is a major hurdle to long-term allograft survival. Sonic hedgehog (Shh), a morphogen critical in embryogenesis, also promotes peripheral immunity, which prompted us to investigate if inhibition of Shh signaling could reduce CR and thereby enhance allograft survival.

METHODS

In a rat orthotopic small bowel transplantation model, FK506 prevented acute rejection; however, recipients eventually lost their grafts by CR. Anti-Shh antibody or isotype control were administered to animals at day 30 postoperatively. Graft survival, tissue fibrosis, vascular occlusion, and expression of vascular endothelial growth factor (VEGF) were investigated.

RESULTS

Immunostaining revealed that Shh and the Hedgehog receptor Patched 1 (Ptc1) are strongly expressed in CR grafts and that Ptc1 expression partially overlapped with that of ED-1, a macrophage marker. In contrast, only minimal expression of Shh and Ptc1 was detected in syngeneic grafts. Grafts survival was significantly prolonged after anti-Shh antibody treatment compared with the immunoglobulin G control (116 vs. 77.5 days). Collagen deposition and vascular occlusion in the mesentery were markedly reduced in recipients of the anti-Shh antibody. Specific transcripts and protein expression for VEGF, which was present mainly in the blood vessels, were reduced.

CONCLUSION

In a rat small bowel transplantation model, anti-Shh antibody treatment reduced CR and prolonged graft survival. These beneficial effects of Shh treatment may occur partly by reducing VEGF expression in the blood vessels of the allografts.

Enhancing repair of the mammalian heart

The injured mammalian heart is particularly susceptible to tissue deterioration, scarring, and loss of contractile function in response to trauma or sustained disease. We tested the ability of a locally acting insulin-like growth factor-1 isoform (mIGF-1) to recover heart functionality, expressing the transgene in the mouse myocardium to exclude endocrine effects on other tissues. supplemental mIGF-1 expression did not perturb normal cardiac growth and physiology. Restoration of cardiac function in post-infarct mIGF-1 transgenic mice was facilitated by modulation of the inflammatory response and increased antiapoptotic signaling. mIGF-1 ventricular tissue exhibited increased proliferative activity several weeks after injury. The canonical signaling pathway involving Akt, mTOR, and p70S6 kinase was not induced in mIGF-1 hearts, which instead activated alternate PDK1 and SGK1 signaling intermediates. The robust response achieved with the mIGF-1 isoform provides a mechanistic basis for clinically feasible therapeutic strategies for improving the outcome of heart disease.

Sonic hedgehog carried by microparticles corrects endothelial injury through nitric oxide release

Microparticles (MPs) are small fragments generated from the plasma membrane after cell stimulation. Among the candidate proteins harbored by MPs, we recently showed that sonic hedgehog (Shh) is present in MPs generated from activated/apoptotic human T lymphocytes [Martínez et al., Blood (2006) vol. 108, 3012-3020]. We show here that Shh carried by MPs induces nitric oxide (NO) release from endothelial cells, triggers changes in the expression and phosphorylation of enzymes related to the NO pathway, and decreases production of reactive oxygen species. When PI3-kinase and ERK signaling were specifically inhibited, the effects of MPs were reversed. In vivo injection of MPs in mice was also able to improve endothelial function by increasing NO release, and it reversed endothelial dysfunction after ischemia/reperfusion. Silencing the effects of Shh with cyclopamine, a specific inhibitor of Shh, or siRNA, an inhibitor of the Shh receptor Patched, strongly reduced production of NO elicited by MPs. Taken together, we propose that the biological message carried by MPs harboring Shh may represent a new therapeutic approach against endothelial dysfunction during acute severe endothelial injury.

Nrf2 Gene Transfer Induces Antioxidant Enzymes and Suppresses Smooth Muscle Cell Growth In Vitro and Reduces Oxidative Stress in Rabbit Aorta In Vivo

Background— Reactive oxygen species (ROS) play a major role in vascular inflammation and pathophysiology of many vascular diseases such as atherosclerosis and injury-induced neointima formation after balloon angioplasty. Nuclear factor E2–related factor-2 (Nrf2) is a transcription factor orchestrating antioxidant and cytoprotective responses on oxidative and electrophilic stress, and it has been shown to have antiinflammatory effects in vascular cells in vitro. We therefore postulated that Nrf2 gene transfer would have salutary effects on vascular inflammation after angioplasty.

Methods and Results— Transduction of vascular smooth muscle cells (VSMCs) with Nrf2-expressing adenovirus increased the expression of several antioxidant enzymes including heme oxygenase-1 (HO-1) compared with β-galactosidase (AdLacZ)-transduced controls. Moreover, Nrf2 gene transfer also inhibited vascular smooth muscle cell (VSMC) proliferation, and the effect was partially reversed by the HO inhibitor Sn(IV) protoporphyrin. In vivo, adenoviral gene transfer effectively reduced oxidative stress determined by antibody staining against oxidized epitopes of LDL, as well as inhibited vascular inflammation assessed by the macrophage cell count and monocyte chemoattractant protein-1 (MCP-1) staining. However, the antiproliferative effects of Nrf2 in vivo were counterbalanced with diminished apoptosis in neointimal VSMCs, resulting in no change in neointimal hyperplasia.

Conclusions— Nrf2 gene transfer or Nrf2-inducing drugs may have therapeutic applications in vascular diseases in which inflammation and oxidative stress play a role. However, the contrasting growth inhibitory and antiapoptotic effects of Nrf2 need to be considered in pathological conditions in which SMC proliferation plays a critical role.

Rebuilding the coronary vasculature: hedgehog as a new candidate for pharmacologic revascularization

Myocardial infarction and ischemic heart disease are among the most common causes of morbidity and mortality in the industrial world. Surgical and percutaneous intravascular approaches are commonly used to treat these diseases. Regrettably, a significant number of patients are either ineligible or demonstrate suboptimal responses to these therapies. In an attempt to provide such patients improved therapeutic options, much effort has been spent developing noninvasive approaches to restore coronary vascular perfusion. One such strategy, termed therapeutic revascularization or angiogenesis, involves administration of proangiogenic factors, which improve coronary perfusion by promoting growth of the coronary vasculature. Thus far, two potential proangiogenic factors have been intensively examined, fibroblast growth factor and vascular endothelial growth factor. Unfortunately, despite their apparent efficacy in animal models, neither factor has performed adequately in the clinic to date. Within the past year a new factor, hedgehog, has been shown to effectively promote the growth of the coronary vasculature and thus has been proposed as a novel candidate for therapeutic revascularization. In this review, we discuss the discovery of the hedgehog pathway as an essential regulator of the development of the coronary vasculature, as an inducer of adult coronary vascular growth, and as a therapeutic in the treatment of ischemic heart disease.

Alternative Splicing of Ryanodine Receptors Modulates Cardiomyocyte Ca 2+ Signaling and Susceptibility to Apoptosis

Ca 2+ release via type 2 ryanodine receptors (RyR2) regulates cardiac function. Molecular cloning of human RyR2 identified 2 alternatively spliced variants, comprising 30- and 24-bp sequence insertions; yet their role in shaping cardiomyocyte Ca 2+ signaling and cell phenotype is unknown. We profiled the developmental regulation and the tissue and species specificity of these variants and showed that their recombinant expression in HL-1 cardiomyocytes profoundly modulated nuclear and cytoplasmic Ca 2+ release. All splice variants localized to the sarcoplasmic reticulum, perinuclear Golgi apparatus, and to finger-like invaginations of the nuclear envelope (nucleoplasmic reticulum). Strikingly, the 24-bp splice insertion that was present at low levels in embryonic and adult hearts was essential for targeting RyR2 to an intranuclear Golgi apparatus and promoted the intracellular segregation of this variant. The amplitude variability of nuclear and cytoplasmic Ca 2+ fluxes were reduced in nonstimulated cardiomyocytes expressing both 30- and 24-bp splice variants and were associated with lower basal levels of apoptosis. Expression of RyR2 containing the 24-bp insertion also suppressed intracellular Ca 2+ fluxes following prolonged caffeine exposure (1 mmol/L, 16 hours) that protected cells from apoptosis. The antiapoptotic effects of this variant were linked to increased levels of Bcl-2 phosphorylation. In contrast, RyR2 containing the 30-bp insertion, which was abundant in human embryonic heart but was decreased during cardiac development, did not protect cardiomyocytes from caffeine-evoked apoptosis. Thus, we provide the first evidence that RyR2 splice variants exquisitely modulate intracellular Ca 2+ signaling and are key determinants of cardiomyocyte apoptotic susceptibility.

Tumor necrosis factor-alpha receptor p75 is required in ischemia-induced neovascularization

BACKGROUND

Aging is a risk factor for coronary and peripheral artery disease. Tumor necrosis factor-alpha (TNF-alpha), a proinflammatory cytokine, is expressed in ischemic tissue and is known to modulate angiogenesis. Little is known about the role of TNF-alpha receptors (TNFR1/p55 and TNFR2/p75) in angiogenic signaling.

METHODS AND RESULTS

We studied neovascularization in the hindlimb ischemia model in young and old TNFR2/p75 knockout (p75KO) and wild-type age-matched controls. Between days 7 to 10 after hindlimb surgery, 100% of old p75KOs experienced autoamputation of the operated limbs, whereas none of the age-matched wild-type mice exhibited hindlimb necrosis. Poor blood flow recovery in p75KO mice was associated with increased endothelial cell apoptosis, decreased capillary density, and significant reductions in the expression of vascular endothelial growth factor and basic fibroblast growth factor-2 mRNA transcripts in ischemic tissue and in circulating endothelial progenitor cells. The number of circulating bone marrow-derived endothelial progenitor cells was significantly reduced in p75KO mice. Transplantation of wild-type bone marrow mononuclear cells into irradiated old p75KO mice 1 month before hindlimb surgery prevented limb loss.

CONCLUSIONS

Our present study suggests that ischemia-induced endothelial progenitor cell-mediated neovascularization is dependent, at least in part, on p75 TNF receptor expressed in bone marrow-derived cells. Specifically, endothelial cell/endothelial progenitor cell survival, vascular endothelial growth factor expression, endothelial progenitor cell mobilization from bone marrow, endothelial progenitor cell differentiation, and ultimately ischemia-induced collateral vessel development are dependent on signaling through TNFR2/p75. Furthermore, because TNFR2/p75 becomes an age-related limiting factor in postischemic recovery, it may be a potential gene target for therapeutic interventions in adult vascular diseases.

Regulation of cavernous nerve injury-induced apoptosis by sonic hedgehog

Thirty to eighty-seven percent of patients treated by radical prostatectomy experience erectile dysfunction (ED). The reduced efficacy of treatments in this population makes novel therapeutic approaches to treat ED essential. We propose that abundant apoptosis observed in penile smooth muscle when the cavernous nerve (CN) is cut (mimicking the neural injury which can result from prostatectomy) is a major contributing factor to ED development. We hypothesize that decreased Sonic hedgehog (SHH) signaling is a cause of ED in neurological models of impotence by increasing apoptosis in penile smooth muscle. We examined this hypothesis in a bilateral CN injury model of ED. We found that the active form of SHH protein was significantly decreased 1.2-fold following CN injury, that SHH inhibition causes a 12-fold increase in smooth muscle apoptosis in the penis, and that SHH treatment at the time of CN injury was able to decrease CN injury-induced apoptosis (1-3-fold) in a dose-dependent manner. These results show that SHH stabilizes the alterations of the corpora cavernosal smooth muscle following nerve injury.

Making or breaking the heart: from lineage determination to morphogenesis

The cues governing cardiac cell-fate decisions, cardiac differentiation, and three-dimensional morphogenesis are rapidly being elucidated. Several themes are emerging that are relevant for childhood and adult heart disease and the growing field of stem cell biology. This review will consider our current understanding of cardiac cell-fate determination and cardiogenesis--largely derived from developmental studies in model organisms and human genetic approaches--and examine future implications for diagnosis, prevention, and treatment of heart disease in the young and old.

Hedgehog Morphogen in Cardiovascular Disease

In this review, we focus on the basic biology of the important developmental Hedgehog (Hh) protein family, its general function in development, pathway mechanisms, and gene discovery and nomenclature. Hh function in cardiovascular development and recent findings concerning Hh signaling in ischemia models are discussed in more detail, and future perspectives are proposed. In light of the recent discovery of Hh transport by insect lipophorin, we also hypothesize a role for low-density lipoprotein (LDL) in mammalian Hh transport, creating a surprising role for LDL in cardiovascular disease.

Nuclear factor-kappaB contributes to hedgehog signaling pathway activation through sonic hedgehog induction in pancreatic cancer

The hedgehog (Hh) signaling pathway, which functions as an organizer in embryonic development, is implicated in the development of various tumors. In pancreatic cancer, pathway activation is reported to result from aberrant expression of the ligand, sonic Hh (Shh). However, the details of the mechanisms regulating Shh expression are not yet known. We hypothesized that nuclear factor-kappaB (NF-kappaB), a hallmark transcription factor in inflammatory responses, contributes to the overexpression of Shh in pancreatic cancer. In the present study, we found a close positive correlation between NF-kappaB p65 and Shh expression in surgically resected pancreas specimens, including specimens of chronic pancreatitis and pancreatic adenocarcinoma. We showed that blockade of NF-kappaB suppressed constitutive expression of Shh mRNA in pancreatic cancer cells. Further activation of NF-kappaB by inflammatory stimuli, including interleukin-1beta, tumor necrosis factor-alpha, and lipopolysaccharide, induced overexpression of Shh, resulting in activation of the Hh pathway. Overexpression of Shh induced by these stimuli was also suppressed by blockade of NF-kappaB. NF-kappaB-induced Shh expression actually activated the Hh pathway in a ligand-dependent manner and enhanced cell proliferation in pancreatic cancer cells. In addition, inhibition of the Hh pathway as well as NF-kappaB suppressed the enhanced cell proliferation. Our data suggest that NF-kappaB activation is one of the mechanisms underlying Shh overexpression in pancreatic cancer and that proliferation of pancreatic cancer cells is accelerated by NF-kappaB activation in part through Shh overexpression.

Molecular pathways regulating pro-migratory effects of Hedgehog signaling

The Hedgehog proteins play a crucial role in metazoan embryo development. Constitutive activation of the pathway is associated with multiple types of cancer. Recent experimental data suggest involvement of Hedgehog signaling in vascular remodeling, germ cell migration, and axon guidance. The molecular mechanisms underlying these effects remain elusive. Here we show that yolk sac-derived endothelial cells and embryonic fibroblasts can directly respond to the Hedgehog signal by increased migration in an in vitro scratch (wound) assay. We also identify Hedgehog transcriptional target genes in these cells, many of which participate in cell migration, axon guidance, and angiogenesis processes. Inhibition of one such molecular pathway, neuropilin-flavomonooxygenase, blocks Hedgehog-induced cell migration. These findings suggest that Hedgehog signaling directly affects embryonic endothelial and fibroblast cell migration via molecules and pathways known to regulate cell migration in response to a variety of environmental cues.

Local Controlled Intramyocardial Delivery of Platelet-Derived Growth Factor Improves Postinfarction Ventricular Function Without Pulmonary Toxicity

Background— Local delivery methods can target therapies to specific tissues and potentially avoid toxicity to other organs. Platelet-derived growth factor can protect the myocardium, but it also plays an important role in promoting pulmonary hypertension. It is not known whether local myocardial delivery of platelet-derived growth factor during myocardial infarction (MI) can lead to sustained cardiac benefit without causing pulmonary hypertension.

Methods and Results— We performed a randomized and blinded experiment of 127 rats that survived experimental MI or sham surgery. We delivered platelet-derived growth factor (PDGF)-BB with self-assembling peptide nanofibers (NFs) to provide controlled release within the myocardium. There were 6 groups with n≥20 in each group: sham, sham+NF, sham+NF/PDGF, MI, MI+NF, and MI+NF/PDGF. Serial echocardiography from 1 day to 3 months showed significant improvement of ventricular fractional shortening, end-systolic dimension, and end-diastolic dimension with local PDGF delivery ( P <0.05 for MI+NF/PDGF versus MI or MI+NF). Catheterization at 4 months revealed improved ventricular function in the controlled delivery group (left ventricular end-diastolic pressure, cardiac index, +dP/dt, −dP/dt, and time constant of exponential decay all P <0.05 for MI+NF/P versus MI or MI+NF). Infarcted myocardial volume was reduced by NF/PDGF therapy (34.0±13.3% in MI, 28.9±12.9% in MI+NF, and 12.0±5.8% in MI+NF/PDGF; P <0.001). There was no evidence of pulmonary toxicity from the therapy, with no differences in right ventricular end-systolic pressure, right ventricular dP/dt, bromodeoxyuridine staining, or pulmonary artery medial wall thickness.

Conclusions— Intramyocardial delivery of PDGF by self-assembling peptide NFs leads to long-term improvement in cardiac performance after experimental infarction without apparent pulmonary toxicity. Local myocardial protection may allow prevention of heart failure without systemic toxicity.

Fibroblast growth factor signals regulate a wave of Hedgehog activation that is essential for coronary vascular development

Myocardial infarction and ischemic heart disease are the leading cause of death in the industrial world. Therapies employed for treating these diseases are aimed at promoting increased blood flow to cardiac tissue. Pharmacological induction of new coronary growth has recently been explored, however, clinical trials with known proangiogenic factors have been disappointing. To identify novel therapeutic targets, we have explored signaling pathways that govern embryonic coronary development. Using a combination of genetically engineered mice and an organ culture system, we identified novel roles for fibroblast growth factor (FGF) and Hedgehog (HH) signaling in coronary vascular development. We show that FGF signals promote coronary growth indirectly by signaling to the cardiomyoblast through redundant function of Fgfr1 and Fgfr2. Myocardial FGF signaling triggers a wave of HH activation that is essential for vascular endothelial growth factor (Vegf)-A, Vegf-B, Vegf-C, and angiopoietin-2 (Ang2) expression. We demonstrate that HH is necessary for coronary vascular development and activation of HH signaling is sufficient to promote coronary growth and to rescue coronary defects due to loss of FGF signaling. These studies implicate HH signaling as an essential regulator of coronary vascular development and as a potential therapeutic target for coronary neovascularization. Consistent with this, activation of HH signaling in the adult heart leads to an increase in coronary vessel density.

Sonic hedgehog protein promotes bone marrow-derived endothelial progenitor cell proliferation, migration and VEGF production via PI 3-kinase/Akt signaling pathways

AIM

To investigate the effects of Sonic hedgehog (shh) protein on bone marrow- derived endothelial progenitor cells (BM-EPC) proliferation, migration and vascular endothelial growth factor (VEGF) production, and the potential signaling pathways involved in these effects.

METHODS

Bone marrow-derived Flk-1(+) cells were enriched using the MACS system from adult Kunming mice and then BM-EPC was cultured in gelatin-coated culture dishes. The effects of shh N-terminal peptide on BM-EPC proliferation were evaluated using the MTT colorimetric assay. Cell migration was assayed using a modified Boyden chamber technique. The production of VEGF was determined by ELISA and immunofluorescence analysis. The potential involvement of PKC and PI3K signaling pathways was explored using selective inhibitor or Western blot.

RESULTS

The proliferation, migration and VEGF production in BM-EPC could be promoted by endogenous shh N-terminal peptide at concentrations of 0.1 microg/mL to 10 microg/mL, and could be inhibited by anti-shh antibodies. Shh-mediated proliferation and migration in BM-EPC could be partly attenuated by anti-VEGF. Phospho-PI3-kinase expression in newly separated BM-EPC was low, and it increased significantly when exogenous shh N-terminal peptide was added, but could be attenuated by anti-human/mouse shh N-terminal peptide antibody. Moreover, the inhibitor of the PI3-kinase, but not the inhibitor of the PKC, significantly inhibited the shh-mediated proliferation, migration and VEGF production.

CONCLUSION

Shh protein can stimulate bone marrow-derived BM-EPC proliferation, migration and VEGF production, which may promote neovascularization to ischemic tissues. This results also suggests that the PI3-kinase/Akt signaling pathways are involved in the angiogenic effects of shh.

Topical sonic hedgehog gene therapy accelerates wound healing in diabetes by enhancing endothelial progenitor cell-mediated microvascular remodeling

BACKGROUND

Sonic hedgehog (Shh) is a prototypical morphogen known to regulate epithelial-mesenchymal interaction during embryonic development. Recent observations indicate that exogenous administration of Shh can induce angiogenesis and may accelerate repair of ischemic myocardium and skeletal muscle. Because angiogenesis plays a pivotal role in wound repair, we hypothesized that activation of the hedgehog pathway may promote a favorable effect on microvascular remodeling during cutaneous wound healing and thereby accelerate wound closure. Because diabetes is associated with impaired wound healing, we tested this hypothesis in a diabetic model of cutaneous wound repair.

METHODS AND RESULTS

In Ptc1-LacZ mice, cutaneous injury resulted in LacZ expression, indicating that expression of the Shh receptor Patched was induced and therefore that the Shh signaling pathway was intact postnatally and upregulated in the process of wound repair. In diabetic mice, topical gene therapy with the use of naked DNA encoding for Shh resulted in significant local gene expression and acceleration of wound recovery. The acceleration in wound healing was notable for increased wound vascularity. In bone marrow transplantation models, the enhanced vascularity of the wound was shown to be mediated, at least in part, by enhanced recruitment of bone marrow-derived endothelial progenitor cells. In vitro, Shh promoted production of angiogenic cytokines from fibroblasts as well as proliferation of dermal fibroblasts. Furthermore, Shh directly promoted endothelial progenitor cell proliferation, migration, adhesion, and tube formation.

CONCLUSIONS

These findings suggest that a simple strategy of topically applied Shh gene therapy may have significant therapeutic potential for enhanced wound healing in patients with impaired microcirculation such as occurs in diabetes.