Inhibition of ocular neovascularization by hedgehog blockade

A cis-regulatory module underlies retinal ganglion cell genesis and axonogenesis

Atoh7 is transiently expressed in retinal progenitor cells (RPCs) and is required for retinal ganglion cell (RGC) differentiation. In humans, a deletion in a distal non-coding regulatory region upstream of ATOH7 is associated with optic nerve atrophy and blindness. Here, we functionally interrogate the significance of the Atoh7 regulatory landscape to retinogenesis in mice. Deletion of the Atoh7 enhancer structure leads to RGC deficiency, optic nerve hypoplasia, and retinal blood vascular abnormalities, phenocopying inactivation of Atoh7. Further, loss of the Atoh7 remote enhancer impacts ipsilaterally projecting RGCs and disrupts proper axonal projections to the visual thalamus. Deletion of the Atoh7 remote enhancer is also associated with the dysregulation of axonogenesis genes, including the derepression of the axon repulsive cue Robo3. Our data provide insights into how Atoh7 enhancer elements function to promote RGC development and optic nerve formation and highlight a key role of Atoh7 in the transcriptional control of axon guidance molecules.

Sonic Hedgehog Intron Variant Associated With an Unusual Pediatric Cortical Cataract

Purpose

To identify the genetic basis of an unusual pediatric cortical cataract demonstrating autosomal dominant inheritance in a large European–Australian pedigree.

Methods

DNA from four affected individuals were exome sequenced utilizing a NimbleGen SeqCap EZ Exome V3 kit and HiSeq 2500. DNA from 12 affected and four unaffected individuals were genotyped using Human OmniExpress-24 BeadChips. Multipoint linkage and haplotyping were performed (Superlink-Online SNP). DNA from one affected individual and his unaffected father were whole-genome sequenced on a HiSeq X Ten system. Rare small insertions/deletions and single-nucleotide variants (SNVs) were identified in the disease-linked region (Golden Helix SVS). Combined Annotation Dependent Depletion (CADD) analysis predicted variant deleteriousness. Putative enhancer function and variant effects were determined using the Dual-Glo Luciferase Assay system.

Results

Linkage mapping identified a 6.23-centimorgan support interval at chromosome 7q36. A co-segregating haplotype refined the critical region to 6.03 Mbp containing 21 protein-coding genes. Whole-genome sequencing uncovered 114 noncoding variants from which CADD predicted one was highly deleterious, a novel substitution within intron-1 of the sonic hedgehog signaling molecule (SHH) gene. ENCODE data suggested this site was a putative enhancer, subsequently confirmed by luciferase reporter assays with variant-associated gene overexpression.

Conclusions

In a large pedigree, we have identified a SHH intron variant that co-segregates with an unusual pediatric cortical cataract phenotype. SHH is important for lens formation, and mutations in its receptor (PTCH1) cause syndromic cataract. Our data implicate increased function of an enhancer important for SHH expression primarily within developing eye tissues.

In-depth transcriptomic analysis of human retina reveals molecular mechanisms underlying diabetic retinopathy

Diabetic Retinopathy (DR) is among the major global causes for vision loss. With the rise in diabetes prevalence, an increase in DR incidence is expected. Current understanding of both the molecular etiology and pathways involved in the initiation and progression of DR is limited. Via RNA-Sequencing, we analyzed mRNA and miRNA expression profiles of 80 human post-mortem retinal samples from 43 patients diagnosed with various stages of DR. We found differentially expressed transcripts to be predominantly associated with late stage DR and pathways such as hippo and gap junction signaling. A multivariate regression model identified transcripts with progressive changes throughout disease stages, which in turn displayed significant overlap with sphingolipid and cGMP-PKG signaling. Combined analysis of miRNA and mRNA expression further uncovered disease-relevant miRNA/mRNA associations as potential mechanisms of post-transcriptional regulation. Finally, integrating human retinal single cell RNA-Sequencing data revealed a continuous loss of retinal ganglion cells, and Müller cell mediated changes in histidine and β-alanine signaling. While previously considered primarily a vascular disease, attention in DR has shifted to additional mechanisms and cell-types. Our findings offer an unprecedented and unbiased insight into molecular pathways and cell-specific changes in the development of DR, and provide potential avenues for future therapeutic intervention.

Stress Signal Regulation by Na/K-ATPase As a New Approach to Promote Physiological Revascularization in a Mouse Model of Ischemic Retinopathy

Purpose

The identification of target pathways to block excessive angiogenesis while simultaneously restoring physiological vasculature is an unmet goal in the therapeutic management of ischemic retinopathies. pNaKtide, a cell-permeable peptide that we have designed by mapping the site of α1 Na/K-ATPase (NKA)/Src binding, blocks the formation of α1 NKA/Src/reactive oxygen species (ROS) amplification loops and restores physiological ROS signaling in a number of oxidative disease models. The aim of this study was to evaluate the importance of the NKA/Src/ROS amplification loop and the effect of pNaKtide in experimental ischemic retinopathy.

Methods

Human retinal microvascular endothelial cells (HRMECs) and retinal pigment epithelium (ARPE-19) cells were used to evaluate the effect of pNaKtide on viability, proliferation, and angiogenesis. Retinal toxicity and distribution were assessed in those cells and in the mouse. Subsequently, the role and molecular mechanism of NKA/Src in ROS stress signaling were evaluated biochemically in the retinas of mice exposed to the well-established protocol of oxygen-induced retinopathy (OIR). Finally, pNaKtide efficacy was assessed in this model.

Results

The results suggest a key role of α1 NKA in the regulation of ROS stress and the Nrf2 pathway in mouse OIR retinas. Inhibition of α1 NKA/Src by pNaKtide reduced pathologic ROS signaling and restored normal expression of hypoxia-inducible factor 1-α/vascular endothelial growth factor (VEGF). Unlike anti-VEGF agents, pNaKtide did promote retinal revascularization while inhibiting neovascularization and inflammation.

Conclusions

Targeting α1 NKA represents a novel strategy to develop therapeutics that not only inhibit neovascularization but also promote physiological revascularization in ischemic eye diseases.

MLN4924 inhibits hedgehog signaling pathway and activates autophagy to alleviate mouse laser-induced choroidal neovascularization lesion

Neovascular age-related macular degeneration (nAMD), featured as choroidal neovascularization (CNV), can cause blindness in the elderly population. MLN4924, a highly selective small-molecule inhibitor of NEDD8 (neuronal precursor cell-expressed developmentally down-regulated protein 8)-activating enzyme (NAE), inhibits the proliferation, angiogenesis and inflammation of multiple cancers via up-regulating hedgehog pathway-regulated autophagy. MLN4924 intraperitoneal injection mitigated the leakage, area and volume of mouse laser-induced CNV lesion. Additionally, compared to CNV 7 d group, MLN4924 treated mouse retina-retinal pigment epithelium (RPE)-choroid complex showed decreased expression of hedgehog pathway-associated molecules patched 1 (PTCH1), smoothened (SMO), GLI family zinc finger 1 (GLI1) and GLI family zinc finger 2 (GLI2) with increased expression of autophagy-associated molecules sequestosome 1 (p62) and LC microtubule-associated protein 1 light chain 3 (LC3). Meanwhile, human choroidal endothelial cells (HCECs) exposed to hypoxia condition also showed decreased expression of hedgehog pathway-associated molecules and increased expression of autophagy-associated molecules. Compared to hypoxia + MLN4924 group, SMO agonist SAG up-regulated hedgehog pathway and down-regulated autophagy, whereas autophagy inhibitor PIK-III inhibited autophagy with no effect on hedgehog pathway, indicating that MLN4924 facilitated autophagy of HCECs via hindering hedgehog pathway under hypoxia condition. Finally, MLN4924 inhibited proliferation, migration and tube formation of HCECs via boosting hedgehog pathway-regulated autophagy. In summary, MLN4924 relieved the formation of mouse laser-induced CNV lesion might via up-regulating hedgehog pathway-regulated autophagy. The results provide a potential interfering strategy for nAMD targeting the autophagy of choroidal endothelial cells.

Functions of Endothelial Cilia in the Regulation of Vascular Barriers

The vascular barrier between blood and tissues is a highly selective structure that is essential to maintain tissue homeostasis. Defects in the vascular barrier lead to a variety of cardiovascular diseases. The maintenance of vascular barriers is largely dependent on endothelial cells, but the precise mechanisms remain elusive. Recent studies reveal that primary cilia, microtubule-based structures that protrude from the surface of endothelial cells, play a critical role in the regulation of vascular barriers. Herein, we discuss recent advances on ciliary functions in the vascular barrier and suggest that ciliary signaling pathways might be targeted to modulate the vascular barrier.

Role of Hedgehog Signaling in Vasculature Development, Differentiation, and Maintenance

The role of Hedgehog (Hh) signaling in vascular biology has first been highlighted in embryos by Pepicelli et al. in 1998 and Rowitch et al. in 1999. Since then, the proangiogenic role of the Hh ligands has been confirmed in adults, especially under pathologic conditions. More recently, the Hh signaling has been proposed to improve vascular integrity especially at the blood–brain barrier (BBB). However, molecular and cellular mechanisms underlying the role of the Hh signaling in vascular biology remain poorly understood and conflicting results have been reported. As a matter of fact, in several settings, it is currently not clear whether Hh ligands promote vessel integrity and quiescence or destabilize vessels to promote angiogenesis. The present review relates the current knowledge regarding the role of the Hh signaling in vasculature development, maturation and maintenance, discusses the underlying proposed mechanisms and highlights controversial data which may serve as a guideline for future research. Most importantly, fully understanding such mechanisms is critical for the development of safe and efficient therapies to target the Hh signaling in both cancer and cardiovascular/cerebrovascular diseases.

GLI3 repressor but not GLI3 activator is essential for mouse eye patterning and morphogenesis

Since 1967, it is known that the loss of GLI3 causes very severe defects in murine eye development. GLI3 is able to act as a transcriptional activator (GLI3-A) or as a transcriptional repressor (GLI3-R). Soon after the discovery of these GLI3 isoforms, the question arose which of the different isoforms is involved in eye formation - GLI3-A, GLI3-R or even both. For several years, this question remained elusive. By analysing the eye morphogenesis of Gli3^XtJ/XtJ mouse embryos that lack GLI3-A and GLI3-R and of Gli3^Δ699/Δ699 mouse embryos in which only GLI3-A is missing, we revealed that GLI3-A is dispensable in vertebrate eye formation. Remarkably, our study shows that GLI3-R is sufficient for the creation of morphologically normal eyes although the molecular setup deviates substantially from normality. In depth-investigations elucidated that GLI3-R controls numerous key players in eye development and governs lens and retina development at least partially via regulating WNT/β-CATENIN signalling.

Dl-3-N-butylphthalide promotes angiogenesis and upregulates sonic hedgehog expression after cerebral ischemia in rats

INTRODUCTION

Dl-3-N-butylphthalide (NBP), a small molecule drug used clinically in the acute phase of ischemic stroke, has been shown to improve functional recovery and promote angiogenesis and collateral vessel circulation after experimental cerebral ischemia. However, the underlying molecular mechanism is unknown.

AIMS

To explore the potential molecular mechanism of angiogenesis induced by NBP after cerebral ischemia.

RESULTS

NBP treatment attenuated body weight loss, reduced brain infarct volume, and improved neurobehavioral outcomes during focal ischemia compared to the control rats (P < 0.05). NBP increased the number of CD31⁺ microvessels, the number of CD31⁺ /BrdU⁺ proliferating endothelial cells, and the functional vascular density (P < 0.05). Further study demonstrated that NBP also promoted the expression of vascular endothelial growth factor and angiopoietin-1 (P < 0.05), which was accompanied by upregulated sonic hedgehog expression in astrocytes in vivo and in vitro.

CONCLUSION

NBP treatment promoted the expression of vascular endothelial growth factor and angiopoietin-1, induced angiogenesis, and improved neurobehavioral recovery. These effects were associated with increased sonic hedgehog expression after NBP treatment. Our results broadened the clinical application of NBP to include the later phase of ischemia.

Sonic hedgehog signaling regulates hypoxia/reoxygenation-induced H9C2 myocardial cell apoptosis

The sonic hedgehog (Shh) signaling pathway has been reported to protect cells against hypoxia/reoxygenation (H/R) injury; however, the role of Shh and relevant molecular mechanisms remain unclear. In the present study, the rat cardiomyoblast cell line H9C2 was subjected to hypoxia and serum-starvation for 4 h. Cells were subsequently reoxygenated using 95% O₂ and 5% CO₂. Reverse transcription-quantitative polymerase chain reaction was performed to quantify the expression of Shh mRNA, while cell apoptosis was assessed using flow cytometry. Caspase-3 activity and p53 expression were measured by western blotting and an MTT assay was subsequently used to assess cell viability. In addition, reactive oxygen species levels were measured using dichlorofluorescein and H/R-induced changes in the activation of superoxide dismutase, catalase, phosphorylated-endothelial nitric oxide synthase, phosphorylated-protein kinase B (Akt) and mammalian target of rapamycin activation were assessed using western blotting. H/R treatment decreased the cell viability of H9C2 cells, but activated endogenous Shh signaling. The activation of Shh signaling protected H9C2 myocardial cells from H/R-induced apoptosis and restored cell viability. In the present study, Shh signaling was demonstrated to serve a protective role against H/R by activating the phosphoinositol 3-kinase (PI3K)/Akt pathway and promoting the expression of anti-oxidant enzymes to ameliorate oxidative stress. In summary, Shh signaling attenuated H/R-induced apoptosis through via the PI3K/Akt pathway.

Expression and significance of the Hedgehog signal transduction pathway in oxygen-induced retinal neovascularization in mice

Aim

The aim of the study was to investigate the signal transduction mechanism of Hedgehog–vascular endothelial growth factor in oxygen-induced retinopathy (OIR) and the effects of cyclopamine on OIR.

Methods

An OIR model was established in C57BL/6J mice exposed to hyperoxia. Two hundred mice were randomly divided into a control group, an OIR group, an OIR-control group (treated with isometric phosphate-buffered saline by intravitreal injection), and a cyclopamine group (treated with cyclopamine by intravitreal injection), with 50 mice in each group. The retinal vascular morphology was observed using adenosine diphosphatase and number counting using hematoxylin and eosin-stained image. Quantitative real-time quantitative polymerase chain reaction was used to detect mRNA expression. Protein location and expression were evaluated using immunohistochemistry and Western blot.

Results

The OIR group and OIR-control group demonstrated large-area pathological neovascularization and nonperfused area when compared with the control group (both P<0.05). The area of nonperfusion and neovascularization in the cyclopamine group was significantly reduced compared with the OIR and OIR-control groups (both P<0.05). Compared with the control group, the OIR and OIR-control groups had more vascular endothelial cells breaking through the inner limiting membrane. The number of new blood vessel endothelial cell nuclei in the cyclopamine group was significantly reduced (both P<0.05) when compared with the OIR and OIR-control groups. The mRNA and protein expressions of Smoothened, Gli1, and vascular endothelial growth factor in the signal pathway of the OIR and OIR-control groups were significantly higher than those of the control group; however, in the cyclopamine group, these factors were reduced when compared with the OIR and OIR-control groups (all P<0.05).

Conclusion

Our data suggest that abnormal expression of the Hedgehog signaling pathway may be closely associated with the formation of OIR. Inhibiting the Smoothened receptor using cyclopamine could control retinal neovascularization, providing new ideas and measures for the prevention of oxygen-induced retinal neovascularization.

Downregulation of MicroRNA 29a/b exacerbated diabetic retinopathy by impairing the function of Müller cells via Forkhead box protein O4

BACKGROUND

Diabetic retinopathy is a neurological disease, which can lead to blindness in severe cases. The pathogenesis underlying diabetic retinopathy is unclear. The aim of this study was to explore the role of dysregulated microRNA 29a/b in the onset and progression of diabetic retinopathy.

METHODS

Diabetes mellitus was induced in rats using 60 mg/kg of streptozotocin. Glucose (5.5 and 25 mM) was used to stimulate rat retinal Müller cells. Real-time polymerase chain reaction and Western blot analyses were used to determine gene expression. A luciferase reporter assay was conducted to validate the relationship of microRNA 29a/b with glioma-associated oncogene homolog 1 and Forkhead box protein O4.

RESULTS

The expression of microRNA 29a/b and glutamine synthetase decreased in both diabetes mellitus rats and rat retinal Müller cells stimulated with high glucose, whereas the expression of sonic hedgehog, glioma-associated oncogene homolog 1, glial fibrillary acidic protein, and vascular endothelial growth factor, as well as the content of glutamate, increased. Dysregulated microRNA 29a/b was directly regulated by the sonic hedgehog-glioma-associated oncogene homolog 1 signalling pathway, and microRNA 29a and microRNA 29b targeted Forkhead box protein O4 and regulated its expression.

CONCLUSION

Downregulation of microRNA 29a/b, mediated by the sonic hedgehog-glioma-associated oncogene homolog 1 signalling pathway, exacerbated diabetic retinopathy by upregulating Forkhead box protein O4.

Intravitreal itraconazole inhibits laser-induced choroidal neovascularization in rats

Choroidal neovascularization (CNV) is a major cause of severe visual loss in patients with age-related macular degeneration (AMD). Recently, itraconazole has shown potent and dose-dependent inhibition of tumor-associated angiogenesis. We evaluated the anti-angiogenic effect of itraconazole in a rat model of laser-induced CNV. After laser photocoagulation in each eye to cause CNV, right eyes were administered intravitreal injections of itraconazole; left eyes received balanced salt solution (BSS) as controls. On day 14 after laser induction, fluorescein angiography (FA) was used to assess abnormal vascular leakage. Flattened retinal pigment epithelium (RPE)-choroid tissue complex was stained with Alexa Fluor 594-conjugated isolectin B4 to measure the CNV area and volume. Vascular endothelial growth factor receptor 2 (VEGFR2) mRNA and protein expression was determined 1, 4, 7, and 14 days after intravitreal injection by quantitative RT-PCR or Western blot. VEGF levels were analyzed by enzyme-linked immunosorbent assay (ELISA). Intravitreal itraconazole significantly reduced leakage from CNV as assessed by FA and CNV area and volume on flat mounts compared with intravitreal BSS (p = 0.002 for CNV leakage, p<0.001 for CNV area and volume). Quantitative RT-PCR showed significantly lower expression of VEGFR2 mRNA in the RPE-choroid complexes of itraconazole-injected eyes than those of BSS-injected eyes on days 7 and 14 (p = 0.003 and p = 0.006). Western blots indicated that VEGFR2 was downregulated after itraconazole treatment. ELISA showed a significant difference in VEGF level between itraconazole-injected and BSS-injected eyes on days 7 and 14 (p = 0.04 and p = 0.001). Our study demonstrated that intravitreal itraconazole significantly inhibited the development of laser-induced CNV in rats. Itraconazole had anti-angiogenic activity along with the reduction of VEGFR2 and VEGF levels. Itraconazole may prove beneficial for treating CNV as an alternative or adjunct to other therapies.

The inner blood-retinal barrier: Cellular basis and development

The blood-retinal barrier (BRB) regulates transport across retinal capillaries maintaining proper neural homeostasis and protecting the neural tissue from potential blood borne toxicity. Loss of the BRB contributes to the pathophysiology of a number of blinding retinal diseases including diabetic retinopathy. In this review, we address the basis of the BRB, including the molecular mechanisms that regulate flux across the retinal vascular bed. The routes of transcellular and paracellular flux are described as well as alterations in these pathways in response to permeabilizing agents in diabetes. Finally, we provide information on exciting new studies that help to elucidate the process of BRB development or barriergenesis and how understanding this process may lead to new opportunities for barrier restoration in diabetic retinopathy.

Hedgehog Signaling Components Are Expressed in Choroidal Neovascularization in Laser-induced Retinal Lesion

Choroidal neovascularization is one of the major pathological changes in age-related macular degeneration, which causes devastating blindness in the elderly population. The molecular mechanism of choroidal neovascularization has been under extensive investigation, but is still an open question. We focused on sonic hedgehog signaling, which is implicated in angiogenesis in various organs. Laser-induced injuries to the mouse retina were made to cause choroidal neovascularization. We examined gene expression of sonic hedgehog, its receptors (patched1, smoothened, cell adhesion molecule down-regulated by oncogenes (Cdon) and biregional Cdon-binding protein (Boc)) and downstream transcription factors (Gli1-3) using real-time RT-PCR. At seven days after injury, mRNAs for Patched1 and Gli1 were upregulated in response to injury, but displayed no upregulation in control retinas. Immunohistochemistry revealed that Patched1 and Gli1 proteins were localized to CD31-positive endothelial cells that cluster between the wounded retina and the pigment epithelium layer. Treatment with the hedgehog signaling inhibitor cyclopamine did not significantly decrease the size of the neovascularization areas, but the hedgehog agonist purmorphamine made the areas significantly larger than those in untreated retina. These results suggest that the hedgehog-signaling cascade may be a therapeutic target for age-related macular degeneration.

Quantitative Proteomics Analysis of Vitreous Humor from Diabetic Retinopathy Patients

Initial triggers for diabetic retinopathy (DR) are hyperglycemia-induced oxidative stress and advanced glycation end-products. The most pathological structural changes occur in retinal microvasculature, but the overall development of DR is multifactorial, with a complex interplay of microvascular, neurodegenerative, genetic/epigenetic, immunological, and secondary inflammation-related factors. Although several individual factors and pathways have been associated with retinopathy, a systems level understanding of the disease is lacking. To address this, we performed mass spectrometry based label-free quantitative proteomics analysis of 138 vitreous humor samples from patients with nonproliferative DR or the more severe proliferative form of the disease. Additionally, we analyzed samples from anti-VEGF (vascular endothelial growth factor) (bevacizumab)-treated patients from both groups. In our study, we identified 2482 and quantified the abundancy of 1351 vitreous proteins. Of these, the abundancy of 230 proteins was significantly higher in proliferative retinopathy compared with nonproliferative retinopathy. This specific subset of proteins was linked to inflammation, complement, and coagulation cascade proteins, protease inhibitors, apolipoproteins, immunoglobulins, and cellular adhesion molecules, reflecting the multifactorial nature of the disease. The identification of the key molecules of the disease is critical for the development of new therapeutic molecules and for the new use of existing drugs.

Hedgehog and Resident Vascular Stem Cell Fate

The Hedgehog pathway is a pivotal morphogenic driver during embryonic development and a key regulator of adult stem cell self-renewal. The discovery of resident multipotent vascular stem cells and adventitial progenitors within the vessel wall has transformed our understanding of the origin of medial and neointimal vascular smooth muscle cells (SMCs) during vessel repair in response to injury, lesion formation, and overall disease progression. This review highlights the importance of components of the Hh and Notch signalling pathways within the medial and adventitial regions of adult vessels, their recapitulation following vascular injury and disease progression, and their putative role in the maintenance and differentiation of resident vascular stem cells to vascular lineages from discrete niches within the vessel wall.

Gene networks: dissecting pathways in retinal development and disease

During retinal neurogenesis, diverse cellular subtypes originate from multipotent neural progenitors in a spatiotemporal order leading to a highly specialized laminar structure combined with a distinct mosaic architecture. This is driven by the combinatorial action of transcription factors and signaling molecules which specify cell fate and differentiation. The emerging approach of gene network analysis has allowed a better understanding of the functional relationships between genes expressed in the developing retina. For instance, these gene networks have identified transcriptional hubs that have revealed potential targets and pathways for the development of therapeutic options for retinal diseases. Much of the current knowledge has been informed by targeted gene deletion experiments and gain-of-functional analysis. In this review we will provide an update on retinal development gene networks and address the wider implications for future disease therapeutics.

Shh signaling from the nucleus pulposus is required for the postnatal growth and differentiation of the mouse intervertebral disc

Intervertebral discs (IVD) are essential components of the vertebral column. They maintain separation, and provide shock absorbing buffers, between adjacent vertebrae, while also allowing movements between them. Each IVD consists of a central semi-liquid nucleus pulposus (NP) surrounded by a multi-layered fibrocartilagenous annulus fibrosus (AF). Although the IVDs grow and differentiate after birth along with the vertebral column, little is known about the mechanism of this. Understanding the signals that control normal IVD growth and differentiation would also provide potential therapies for degenerative disc disease, which is the major cause of lower back pain and affects a large proportion of the population. In this work, we show that during postnatal growth of the mouse, Sonic hedgehog (Shh) signaling from the NP cells controls many aspects of growth and differentiation of both the NP cells themselves and of the surrounding AF, and that it acts, at least partly, by regulating other signaling pathways in the NP and AF. Recent studies have shown that the NP cells arise from the embryonic notochord, which acts as a major signaling center in the embryo. This work shows that this notochord-derived tissue continues to carry out a major signaling function in the postnatal body and that the IVDs are signaling centers, in addition to their already known functions in the mechanics of vertebral column function.

Investigational Notch and Hedgehog inhibitors--therapies for cardiovascular disease

INTRODUCTION

During the past decade, a variety of Notch and Hedgehog pathway inhibitors have been developed for the treatment of several cancers. An emerging paradigm suggests that these same gene regulatory networks are often recapitulated in the context of cardiovascular disease and may now offer an attractive target for therapeutic intervention.

AREAS COVERED

This article briefly reviews the profile of Notch and Hedgehog inhibitors that have reached the preclinic and clinic for cancer treatment and discusses the clinical issues surrounding targeted use of these inhibitors in the treatment of vascular disorders.

EXPERT OPINION

Preclinical and clinical data using pan-Notch inhibitors (γ-secretase inhibitors) and selective antibodies to preferentially target notch receptors and ligands have proven successful but concerns remain over normal organ homeostasis and significant pathology in multiple organs. By contrast, the Hedgehog-based drug pipeline is rich with more than a dozen Smoothened (SMO) inhibitors at various stages of development. Overall, refined strategies will be necessary to harness these pathways safely as a powerful tool to disrupt angiogenesis and vascular proliferative phenomena without causing prohibitive side effects already seen with cancer models and patients.

Efficacy of intravitreal captopril on oxygen-induced retinopathy in mice

AIM

To study the inhibitory effect of intravitreal captopril on oxygen-induced retinopathy (OIR) in mice.

METHODS

Eighty postnatal day (P)7 C57BL/6J mice were randomly divided into treated group and control group with forty mice in each group. The mice were exposed to 75% ± 2% oxygen for 5 days (P7-P11) and then returned to room air for 5 days (P12-P17) to induce retinal neovascularization (RNV). Beginning on P12, the mice in treated group received daily intravitreal injections of captopril (3.0mL/kg), while those in control group received daily intravitreal injections of phosphate-buffered saline (PBS) (3.0mL/kg) through P17. After anesthetized at P17, one eye was chosen randomly as experimental eye and were enucleated. RNV was examined by Adenosine diphosphate-ase (ADPase) stained retina flat-mounts and was quantitated histologically by counting the neovascular endothelial cell nuclei anterior to inner limiting membrane (ILM). The expressions of matrix metalloproteinase-2 (MMP-2) and vascular endothelial growth factor (VEGF) were measured by immunohistochemical method.

RESULTS

Comparing with control group, more regular distributions, better branch and reduced density of RNV were observed in eyes of treated group. The number of neovascular cell nuclei was less in treated group than that in control group (t=6.135, P<0.01). Stain of MMP-2 and VEGF was weaker in treated group than that in control group.

CONCLUSION

The results indicate that captopril can significantly inhibit RNV in OIR mice.

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.

Genome-wide analysis of copy number variants in age-related macular degeneration

Age-related macular degeneration (AMD) is a complex genetic disease, with many loci demonstrating appreciable attributable disease risk. Despite significant progress toward understanding the genetic and environmental etiology of AMD, identification of additional risk factors is necessary to fully appreciate and treat AMD pathology. In this study, we investigated copy number variants (CNVs) as potential AMD risk variants in a cohort of 400 AMD patients and 500 AMD-free controls ascertained at the University of Iowa. We used three publicly available copy number programs to analyze signal intensity data from Affymetrix GeneChip SNP Microarrays. CNVs were ranked based on prevalence in the disease cohort and absence from the control group; high interest CNVs were subsequently confirmed by qPCR. While we did not observe a single-locus "risk CNV" that could account for a major fraction of AMD, we identified several rare and overlapping CNVs containing or flanking compelling candidate genes such as NPHP1 and EFEMP1. These and other candidate genes highlighted by this study deserve further scrutiny as sources of genetic risk for AMD.

Activation of the sonic hedgehog signaling controls human pulmonary arterial smooth muscle cell proliferation in response to hypoxia

The hedgehog signal pathway plays a crucial role in the angiogenesis and vascular remodeling. However, the function of this pathway in the pulmonary vascular smooth cell proliferation in response to hypoxia remains unknown. In this study, we have demonstrated that the main components of the hedgehog pathway, including sonic hedgehog (SHH), patched1 (PTCH1), smoothened (SMO), GLI and hypoxia-inducible factor 1 (HIF1) are expressed in the human pulmonary arterial smooth muscle cells (HPASMCs). Interestingly, hypoxia significantly enhanced the expression of SHH and HIF1, facilitated the translocation of GLI1 into the nuclei, and promoted the proliferation of HPASMCs. Furthermore, direct activation of the SHH pathway through incubation with the purified recombinant human SHH or with purmorphamine and SAG, two Smo agonists, also enhanced the proliferation of HPASMCs. Importantly, the treatment with anti-SHH and anti-HIF1 antibodies or cyclopamine, a specific SMO inhibitor, markedly inhibited the nuclear translocation of GLI1 and cell proliferation in the HPASMCs induced by hypoxia and activation of the SHH pathway. Moreover, the treatment with cyclopamine increased apoptosis in the hypoxic HPASMCs. These data strongly demonstrate for the first time that the SHH signaling plays a crucial role in the regulation of HPASMC growth in response to hypoxia.

Regulation of the expression balance of angiopoietin-1 and angiopoietin-2 by Shh and FGF-2

Sonic hedgehog (Shh) is a typical morphogen to regulate epithelial-mesenchymal interactions during embryonic development. Shh is also an indirect angiogenic agent upregulating other angiogenic factors, including angiopoietin-1 (Ang-1). Recent studies revealed that angiogenesis induced by Shh is characterized by distinct large-diameter vessels with less branching. Ang-1 promotes blood vessel maturation, and angiopoietin-2 (Ang-2) counteracts Ang-1 activity and regulates vascular branching. Thus, we hypothesized that Shh-induced angiogenesis is affected by expression of Ang-1 and Ang-2, and we investigated the regulatory system of angiopoietins by Shh in vitro. Shh enhanced Ang-1 expression but did not enhance vascular endothelial growth factor in fibroblasts. The upregulation of Ang-1 expression by Shh was significantly decreased by fibroblast growth factor-2 (FGF-2), a potent angiogenic factor. Furthermore, FGF-2 increased the expression of Ang-2 in endothelial cells. These findings suggest that Shh and FGF-2 regulate the expression balance of vascular morphogens Ang-1 and Ang-2 and are involved in angiogenesis.

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.

Indian hedgehog signaling from endothelial cells is required for sclera and retinal pigment epithelium development in the mouse eye

The development of extraocular orbital structures, in particular the choroid and sclera, is regulated by a complex series of interactions between neuroectoderm, neural crest and mesoderm derivatives, although in many instances the signals that mediate these interactions are not known. In this study we have investigated the function of Indian hedgehog (Ihh) in the developing mammalian eye. We show that Ihh is expressed in a population of non-pigmented cells located in the developing choroid adjacent to the RPE. The analysis of Hh mutant mice demonstrates that the RPE and developing scleral mesenchyme are direct targets of Ihh signaling and that Ihh is required for the normal pigmentation pattern of the RPE and the condensation of mesenchymal cells to form the sclera. Our findings also indicate that Ihh signals indirectly to promote proliferation and photoreceptor specification in the neural retina. This study identifies Ihh as a novel choroid-derived signal that regulates RPE, sclera and neural retina development.

Proliferative and cell fate effects of Hedgehog signaling in the vertebrate retina

The retina is an excellent system for delving into the question of how cell fate, number and organization are regulated in the central nervous system. Multipotential progenitor cells in the immature retina proliferate, exit the cell cycle and generate neurons and one glial cell type in a prescribed temporal sequence. While some aspects of progenitor behavior are controlled cell intrinsically, extrinsic signals present in the retina environment have been shown to impact on proliferation, differentiation and cell fate of progenitors. Intercellular signaling proteins of the Hedgehog (Hh) family regulate several aspects of visual system development in vertebrates--ranging from early eye field patterning to retinal and optic nerve development. This review highlights the role of Hh signaling on retinal progenitor proliferation and diversification.

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.