Notch signaling in ocular vasculature development and diseases

MicroRNA-29-mediated cross-talk between metabolic organs in the pathogenesis of diabetes mellitus and its complications: A narrative review

Diabetes mellitus (DM) is a heterogeneous group of disorders characterized by hyperglycemia. Microribonucleic acids (microRNAs) are noncoding RNA molecules synthesized in the nucleus, modified, and exported to the extracellular environment to bind to their complementary target sequences. It regulates protein synthesis in the targeted cells by inhibiting translation or triggering the degradation of the target messenger. MicroRNA-29 is one of noncoding RNA that can be secreted by adipose tissue, hepatocytes, islet cells, and brain cells. The expression level of the microRNA-29 family in several metabolic organs is regulated by body weight, blood concentrations of inflammatory mediators, serum glucose levels, and smoking habits. Several experimental studies have demonstrated the effect of microRNA-29 on the expression of target genes involved in glucose metabolism, insulin synthesis and secretion, islet cell survival, and proliferation. These findings shed new light on the role of microRNA-29 in the pathogenesis of diabetes and its complications, which plays a vital role in developing appropriate therapies. Different molecular pathways have been proposed to explain how microRNA-29 promotes the development of diabetes and its complications. However, to the best of our knowledge, no published review article has summarized the molecular mechanism of microRNA-29-mediated initiation of DM and its complications. Therefore, this narrative review aims to summarize the role of microRNA-29-mediated cross-talk between metabolic organs in the pathogenesis of diabetes and its complications.

Comparison of Glutathione Nanoparticles, CoEnzyme Q10, and Fish Oil for Prevention of Oxygen-Induced Retinopathy in Neonatal Rats

Notch ligands and receptors are important for cell specification and angiogenesis, but their role in oxygen-induced retinopathy (OIR) is not well studied. Delta-like ligand (DLL)-4/Notch inhibits angiogenesis, while Jagged-1/Notch promotes angiogenesis. We tested the hypothesis that early supplementation with antioxidants and/or fish oil curtails severe OIR by inducing DLL-4/Notch and reducing Jagged-1/Notch. Newborn rats were exposed to brief intermittent hypoxia (IH) during hyperoxia, during which they received daily oral supplements of (1) fish oil, (2) coenzyme Q10 (CoQ10) in olive oil (OO), (3) glutathione nanoparticles (nGSH), (4) fish oil + CoQ10, or (5) OO (controls) from birth (P0) to P14. At P14, the pups were placed in room air (RA) until P21, with no further treatment. Oxidative stress, apoptosis, ocular histopathology, and Notch signaling were assessed. Neonatal IH resulted in severe retinal damage consistent with retinopathy of prematurity (ROP). Retinal damage was associated with induced oxidative stress and Jagged-1/Notch signaling, as well as reduced DLL-4/Notch signaling. All treatments reversed these outcomes, but nGSH produced the most beneficial outcomes. Severe OIR promoted the induction of Jagged-1/Notch and curtailed DLL-4/Notch, which was an effect that could be reversed with nGSH supplementation. These findings may indicate a potential alternate pathway for ROP treatment and/or prevention.

Decoding functional cell-cell communication events by multi-view graph learning on spatial transcriptomics

Cell-cell communication events (CEs) are mediated by multiple ligand-receptor (LR) pairs. Usually only a particular subset of CEs directly works for a specific downstream response in a particular microenvironment. We name them as functional communication events (FCEs) of the target responses. Decoding FCE-target gene relations is: important for understanding the mechanisms of many biological processes, but has been intractable due to the mixing of multiple factors and the lack of direct observations. We developed a method HoloNet for decoding FCEs using spatial transcriptomic data by integrating LR pairs, cell-type spatial distribution and downstream gene expression into a deep learning model. We modeled CEs as a multi-view network, developed an attention-based graph learning method to train the model for generating target gene expression with the CE networks, and decoded the FCEs for specific downstream genes by interpreting trained models. We applied HoloNet on three Visium datasets of breast cancer and liver cancer. The results detangled the multiple factors of FCEs by revealing how LR signals and cell types affect specific biological processes, and specified FCE-induced effects in each single cell. We conducted simulation experiments and showed that HoloNet is more reliable on LR prioritization in comparison with existing methods. HoloNet is a powerful tool to illustrate cell-cell communication landscapes and reveal vital FCEs that shape cellular phenotypes. HoloNet is available as a Python package at https://github.com/lhc17/HoloNet.

Pathophysiology of Retinopathy of Prematurity

Retinopathy of prematurity (ROP) is a complex disease involving development of the neural retina, ocular circulations, and other organ systems of the premature infant. The external stresses of the ex utero environment also influence the pathophysiology of ROP through interactions among retinal neural, vascular, and glial cells. There is variability among individual infants and presentations of the disease throughout the world, making ROP challenging to study. The methods used include representative animal models, cell culture, and clinical studies. This article describes the impact of maternal-fetal interactions; stresses that the preterm infant experiences; and biologic pathways of interest, including growth factor effects and cell-cell interactions, on the complex pathophysiology of ROP phenotypes in developed and emerging countries.

Microglial Galectin3 enhances endothelial metabolism and promotes pathological angiogenesis via Notch inhibition by competitively binding to Jag1

Microglia were considered as immune cells in inflammation until their angiogenic role was widely understood. Although the pro-inflammatory role of microglia in retinal angiogenesis has been explored, little is known about its role in pro-angiogenesis and the microglia-endothelia interaction. Here, we report that galectin-3 (Gal3) released by activated microglia functions as a communicator between microglia and endothelia and competitively binds to Jag1, thus inhibiting the Notch signaling pathway and enhancing endothelial angiogenic metabolism to promote angiogenesis. These results suggest that Gal3 may be a novel and effective target in the treatment of retinal angiogenesis.

Gliquidone improves retinal injury to relieve diabetic retinopathy via regulation of SIRT1/Notch1 pathway

Background

Diabetic retinopathy (DR) is a common and potentially devastating microvascular complication of diabetes mellitus (DM). The main features of DR are inflammation and oxidative damage. Gliquidone (GLI) is confirmed to be a hypoglycemic drug by oral administration. The current study is aimed to investigate the role and mechanism of GLI on the pathogenesis of DR.

Methods

High glucose (HG)-induced human retinal endothelial cells (HRECs) were used to explore the anti-inflammatory and anti-oxidant effects of GLI on DR in vitro. Streptozotocin (STZ)-induced DM rats were used to investigate the effects of GLI on retinal structures, inflammation, and oxidative stress. The levels of SIRT1/Notch1 pathway-related proteins were determined by western blotting.

Results

GLI treatment promoted the viability and inhibited the apoptosis of HG-induced HRECs. Meanwhile, the levels of interleukin (IL)-6, IL-1β, tumour necrosis factor alpha and reactive oxygen species were suppressed, while both catalase and superoxide dismutase were elevated after GLI treatment in HG-induced HRECs. Furthermore, we found that Silencing information regulator 2 related enzyme 1 (SIRT1) silencing reversed the inhibiting effects of GLI on the levels of protein Notch1 and effector genes Hes1 and Hey2. Similar anti-inflammatory and anti-oxidant effects of GLI in STZ-induced DM rats were observed. Additionally, GLI administration also repressed vascular hyperpermeability in vivo.

Conclusion

GLI may be an effective agent to improve DR through repression of inflammation and oxidative stress via SIRT1/Notch1 pathway.

Case Report: Alagille Syndrome Presenting with Angioid Streaks

SIGNIFICANCE

Alagille syndrome is rare genetic disease, which affects liver and heart function. Cases are frequently diagnosed late, and a complete ocular examination aids in the diagnosis. Although ophthalmic manifestations are usually benign, occasionally, sight-threatening complications occur.

PURPOSE

The case presented herein highlights a rare condition, which usually can be diagnosed by the ophthalmological findings. However, in this particular case report, the complication of angioid streaks and choroidal neovascularization is reported for the first time in Alagille syndrome.

CASE REPORT

Α 32-year-old woman diagnosed with Alagille syndrome presented with diminution of vision in the left eye. The cause was choroidal neovascularization related to angioid streaks. She was treated with intravitreal injections of ranibizumab but developed an extensive macular scar. A few years later, she developed the same complication in the right eye and was treated similarly.

CONCLUSIONS

Alagille syndrome has many ophthalmic manifestations, most of them benign with minimal threat to vision. Herein for the first time, we present a case of Alagille syndrome with angioid streak-related choroidal neovascularization, which resulted in severe vision loss.

Up-regulation of MiR-145-5p promotes the growth and migration in LPS-treated HUVECs through inducing macrophage polarization to M2

MiR-145-5p is high-expressed in human vascular endothelial cells (HUVECs) and alternatively activated macrophages (M2). However, whether miR-145-5p can reduce HUVEC damage by regulating macrophage immunophenotype is less reported. THP-1 was stimulated by Phorbolate-12-myristate-13-acetate, LPS and IFN-γ, and IL-4 to differentiate into macrophages (M0, M1 and M2). The expressions of macrophage markers were detected by Western blotting, and the expressions of miR-145-5p and kruppel-like factor-14 (KLF14) were detected by qRT-PCR. Dual-luciferase reporter assay was used to analyze the targeted relationship of miR-145-5p and KLF14. HUVEC injury was induced by LPS and then co-cultured with M1 transfected by miR-145-5p mimic. The effect of miR-145-3p on proliferation and metastasis of LPS-induced HUVECs was detected by MTT, clone formation, scratch assay and Transwell. We found that the expression of miR-145-5p was higher in M2 than that in M1. MiR-145-5p expression was down-regulated during M2-to-M1, but up-regulated during M1-to-M2. The expressions of IL-1β and iNOS were down-regulated, while the protein expressions of CCL17 and Arg-1 were up-regulated by miR-145-5p mimic in M0. The viability, proliferation, migration and invasion of HUVECs were promoted, however, LDH activity of the HUVECs was inhibited by mimics. In addition, KLF14 was predicted as the target gene for miR-145-5p in HUVECs. Collectively, our results demonstrate that miR-145-5p inhibited cell proliferation of LPS-treated HUVECs possibly through regulating macrophage polarization to M2.

Bioinformatics analysis of key genes and miRNAs associated with Stanford type A aortic dissection

Background

Aortic dissection is one of the most detrimental cardiovascular diseases with a high risk of mortality and morbidity. This study aimed to examine the key genes and microRNAs associated with Stanford type A aortic dissection (AAD).

Methods

The expression data of AAD and healthy samples were downloaded from two microarray datasets in the Gene Expression Omnibus (GEO) database to identify highly preserved modules by weighted gene co-expression network analysis (WGCNA). Differentially expressed genes (DEGs) and differentially expressed miRNAs (DEmiRNAs) were selected and functionally annotated. The predicted interactions between the DEGs and DEmiRNAs were further illustrated.

Results

In two highly preserved modules, 459 DEGs were identified. These DEGs were functionally enriched in the HIF1, Notch, and PI3K/Akt pathways. Furthermore, 6 DEmiRNAs that were enriched in the regulation of vasculature development and HIF1 pathway, were predicted to target 23 DEGs.

Conclusions

Our study presented several promising modulators, both DEGs and DEmiRNAs, as well as possible pathological pathways for AAD, which narrows the scope for further fundamental research.

VEGF Production Is Regulated by the AKT/ERK1/2 Signaling Pathway and Controls the Proliferation of Toxoplasma gondii in ARPE-19 Cells

The retina is the primary site of Toxoplasma gondii infection in the eye, and choroidal neovascularization in ocular toxoplasmosis is one of the most important causes of visual impairment. Vascular endothelial growth factor (VEGF) is one of the key regulators of blood vessel development, however, little is known about the mechanisms of T. gondii-induced VEGF production in ocular toxoplasmosis. Here, we investigate the effect of T. gondii on VEGF production regulation in human retinal pigment epithelium ARPE-19 cells and attempted to unveil the underlying mechanism of this event by focusing on the interaction between parasite and the selected host intracellular signaling pathways. T. gondii infection increased the expression of VEGF mRNA and protein in ARPE-19 cells in parasite burden- and infection time-dependent manner. The proportional increase of VEGF upstream regulators, HIF-1α and HO-1, was also observed. T. gondii induced the activation of host p-AKT, p-ERK1/2, and p-p38 MAPK in ARPE-19 cells in a parasite-burden dependent manner. However, VEGF expression decreased after the pre-treatment with PI3K inhibitors (LY294002 and GDC-0941), ERK1/2 inhibitor (PD098059), and p38 MAPK inhibitor (SB203580), but not JNK inhibitor (SP600125), in a dose-dependent manner. The anti-VEGF agent bevacizumab or VEGF siRNA transfection prominently inhibited the activation of p-AKT and p-ERK1/2, but not p-p38 MAPK and JNK1/2 in T. gondii-infected ARPE-19 cells. Bevacizumab treatment or VEGF siRNA transfection significantly inhibited the proliferation of T. gondii tachyzoites in the host cell, dose-dependently, but not invasion of parasites. VEGF-receptor 2 (VEGF-R2) antagonist, SU5416, attenuated VEGF production and tachyzoite proliferation in T. gondii-infected ARPE-19 cells in a dose-dependent manner. Collectively, T. gondii prominently induces VEGF production in ARPE-19 cells, and VEGF and AKT/ERK1/2 signaling pathways mutually regulate each other in T. gondii-infected ARPE-19 cells, but not p38 MAPK and JNK1/2 signaling pathways. VEGF and VEGF-R2 control the parasite proliferation in T. gondii-infected ARPE-19 cells. From this study, we revealed the putative mechanisms for VEGF induction as well as the existence of positive feedback between VEGF and PI3K/MAPK signaling pathways in T. gondii-infected retinal pigment epithelium.

Integrin α5β1 promotes BMCs mobilization and differentiation to exacerbate choroidal neovascularization

Choroidal neovascularization (CNV) is an acknowledged pathogenic mechanism of various ocular diseases, and in situ cells and mobilized bone marrow-derived cells (BMCs) are thought to participate in this process. We aimed to evaluate the roles of integrin α5 in BMCs and vascular endothelial cells (VECs) in the CNV process mediated by SDF-1/CXCR4 signaling. Adult wild-type mice were engrafted with whole BMCs obtained from GFP transgenic mice and then laser injured to induce CNV. BMCs and RF/6A cells were cultured to discover the mechanism of CNV in vitro. BMCs were mobilized to CNV areas, which expressed elevated SDF-1 and CXCR4. When SDF-1 was intravitreally injected, the number of BMCs was profoundly increased. In the SDF-1-treated group, the levels of integrin α5 expressed on BMCs and VECs were significantly higher than those on the cells in the control group. SDF-1 significantly increased the expression and positive ratio of integrin α5, which was involved in the recruitment and differentiation of BMCs into BMC-derived VECs, and these effects were suppressed by the CXCR4 inhibitor AMD3100. The PI3K/AKT pathway rather than the ERK pathway mediated SDF-1/CXCR4 induction of integrin α5. Integrin α5 suppression efficiently prevented the production of TGF-β and bFGF but not VEGF. Inhibiting the SDF-1/CXCR4-PI3K/AKT-integrin α5 axis reduced CNV severity. Integrin α5 participates in BMC recruitment and differentiation in SDF-1/CXCR4-induced CNV and inhibition of this pathway may be a new approach to inhibit CNV.

Role of Smad4 from ocular surface ectoderm in retinal vasculature development

AIM

To investigate how signals from lens regulate retinal vascular development and neovascularization.

METHODS

Le-Cre transgenic mouse line was employed to inactivate Smad4 in the surface ectoderm selectively. Standard histological and whole-mount retina staining were employed to reveal morphological changes of retinal vasculature in Smad4 defective eye. cDNA microarray and subsequent analyses were conducted to investigate the molecular mechanism underlying the vascular phenotype. Quantitative polymerase chain reaction (qPCR) was carried out to verify the microarrays results.

RESULTS

We found that inactivation of Smad4 specifically on surface ectoderm leads to a variety of retinal vasculature anomalies. Microarray analyses and qPCR revealed that Sema3c, Sema3e, Nrp1, Tie1, Sox7, Sox17, and Sox18 are significantly affected in the knockout retinas at different developmental stages, suggesting that ocular surface ectoderm-derived Smad4 can signal to the retina and regulates various angiogenic signaling in the retina.

CONCLUSION

Our data suggest that the cross-talk between ocular surface ectoderm and retina is important for retinal vasculature development, and Smad4 regulates various signaling associated with sprouting angiogenesis, vascular remodeling and maturation in the retina of mice.

miR-29a/b cluster suppresses high glucose-induced endothelial-mesenchymal transition in human retinal microvascular endothelial cells by targeting Notch2

Several studies have previously reported that endothelial cells contributed to pathological fibrosis in proliferative diabetic retinopathy (PDR) through endothelial-mesenchymal transition (EndMT); however, the precise mechanism of this interaction has not been completely elucidated. The present study investigated the expression of microRNA (miR)-29a/b cluster in human retinal microvascular endothelial cells (HRMECs) and examined its functional role in high glucose (HG)-induced EndMT. HRMECs were exposed to glucose at concentrations of 5, 15, 30 and 50 mM for 7 days and reverse transcription-quantitative polymerase chain reaction, western blotting and immunofluorescence were conducted to determine the expression of genes associated with miR-29a/b and EndMT. A luciferase reporter gene assay was also performed to confirm the association between miR-29a/b and neurogenic locus notch homolog protein 2 (Notch2). The expression levels of miR-29a/b, and endothelial markers vascular endothelial cadherin and cluster of differentiation 31 were decreased, whereas the expression levels of Notch2 and mesenchymal markers, including α-smooth muscle actin, fibroblast-specific protein 1 (also named S100 calcium binding protein A4, S100A4), fibronectin and SNAI1 were increased in HRMECs under HG (30 nM) conditions. In addition, Notch2 was identified as a target of miR-29a and miR-29b. Overexpression of miR-29a/b downregulated the expression of Notch2 and subsequently suppressed HG-induced EndMT. Taken together, the results of the present study revealed that the miR-29/Notch2 signaling pathway may participate in the regulation of HG-induced EndMT, and may serve as a potential molecular target during fibrosis in PDR.

The Carcinogenic Role of the Notch Signaling Pathway in the Development of Hepatocellular Carcinoma

The Notch signaling pathway, known to be a highly conserved signaling pathway in embryonic development and adult tissue homeostasis, participates in cell fate decisions that include cellular differentiation, cell survival and cell death. However, other studies have shown that aberrant in Notch signaling is pro-tumorigenic, particularly in hepatocellular carcinoma (HCC). HCC is one of the most common malignant tumors in the world and has a high mortality rate. Growing evidence supports that Notch signaling plays a critical role in the development of HCC by regulating the tumor microenvironment, tumorigenesis, progression, angiogenesis, invasion and metastasis. Accordingly, overexpression of Notch is closely associated with poor prognosis in HCC. In this review, we focus on the pro-tumorigenic role of Notch signaling in HCC, summarize the current knowledge of Notch signaling and its role in HCC development, and outline the therapeutic potential of targeting Notch signaling in HCC.

NOTCH1 signaling induces pathological vascular permeability in diabetic retinopathy

Diabetic macular edema is a major complication of diabetes resulting in loss of central vision. Although heightened vessel leakiness has been linked to glial and neuronal-derived factors, relatively little is known on the mechanisms by which mature endothelial cells exit from a quiescent state and compromise barrier function. Here we report that endothelial NOTCH1 signaling in mature diabetic retinas contributes to increased vascular permeability. By providing both human and mouse data, we show that NOTCH1 ligands JAGGED1 and DELTA LIKE-4 are up-regulated secondary to hyperglycemia and activate both canonical and rapid noncanonical NOTCH1 pathways that ultimately disrupt endothelial adherens junctions in diabetic retinas by causing dissociation of vascular endothelial-cadherin from β-catenin. We further demonstrate that neutralization of NOTCH1 ligands prevents diabetes-induced retinal edema. Collectively, these results identify a fundamental process in diabetes-mediated vascular permeability and provide translational rational for targeting the NOTCH pathway (primarily JAGGED1) in conditions characterized by compromised vascular barrier function.

The Role of Dll4/Notch Signaling in Normal and Pathological Ocular Angiogenesis: Dll4 Controls Blood Vessel Sprouting and Vessel Remodeling in Normal and Pathological Conditions

Background

Retina is the highest oxygen-demanding and vascularized tissue in the body. Retinal development and function require proper vascularization and blood vessel function and integrity. Dll4 is most prominently expressed in the endothelium of angiogenic blood vessels and in quiescent arteries and capillaries in all tissues and organs of the mammalian species, and it is the key regulator of blood vessel sprouting.

Results

Dll4 is a transmembrane protein that acts as a ligand for Notch receptors 1 and 4. Genetic deletion of Dll4 causes severe abnormalities in embryonic and postnatal vascular development. Deletion of even a single Dll4 allele results in almost complete embryonic lethality due to severe vascular abnormalities, the phenomenon called haploinsufficiency indicating the critical role of Dll4/Notch in vascular development. Dll4/Notch pathway interplays at multiple levels with other signaling pathways including VEGF, Wnt/Fzd, and genes controlling vascular toning. Multiple studies of the effects of Dll4 inhibition were performed in the developing retina to elucidate the key functions of Dll4 in normal and pathological angiogenesis. Several genetic approaches and therapeutic molecules were tested to evaluate the biological and therapeutic effects of acute and prolonged Dll4 inhibition in the eye and oncology.

Conclusions

All current studies demonstrated that Dll4 controls blood vessel sprouting, growth, and remodeling in normal and pathological conditions as well as arterial-venous differentiation. Genetic and therapeutic Dll4 modulation studies show that Dll4 inhibition can promote blood vessel sprouting and might be useful to stimulate vessel growth in the ischemic retina and Dll4 is the key modulator of the postangiogenic vascular remodeling that ultimately defines vascular patterning.

Resveratrol reverses the adverse effects of bevacizumab on cultured ARPE-19 cells

Age-related macular degeneration (AMD) and proliferative diabetic retinopathy (PDR) are one of the major causes of blindness caused by neo-vascular changes in the retina. Intravitreal anti-VEGF injections are widely used in the treatment of wet-AMD and PDR. A significant percentage of treated patients have complications of repeated injections. Resveratrol (RES) is a polyphenol phytoalexin with anti-oxidative, anti-inflammatory and anti-proliferative properties. Hence, we hypothesized that if RES is used in combination with bevacizumab (BEV, anti-VEGF), it could reverse the adverse effects that precipitate fibrotic changes, drusen formation, tractional retinal detachment and so on. Human retinal pigment epithelial cells were treated with various combinations of BEV and RES. There was partial reduction in secreted VEGF levels compared to untreated controls. Epithelial-mesenchymal transition was lower in BEV + RES treated cultures compared to BEV treated cultures. The proliferation status was similar in BEV + RES as well as BEV treated cultures both groups. Phagocytosis was enhanced in the presence of BEV + RES compared to BEV. Furthermore, we observed that notch signaling was involved in reversing the adverse effects of BEV. This study paves way for a combinatorial strategy to treat as well as prevent adverse effects of therapy in patients with wet AMD and PDR.

Myeloid-Specific Blockade of Notch Signaling Attenuates Choroidal Neovascularization through Compromised Macrophage Infiltration and Polarization in Mice

Macrophages have been recognized as an important inflammatory component in choroidal neovascularization (CNV). However, it is unclear how these cells are activated and polarized, how they affect angiogenesis and what the underlining mechanisms are during CNV. Notch signaling has been implicated in macrophage activation. Previously we have shown that inducible disruption of RBP-J, the critical transcription factor of Notch signaling, in adult mice results in enhanced CNV, but it is unclear what is the role of macrophage-specific Notch signaling in the development of CNV. In the current study, by using the myeloid specific RBP-J knockout mouse model combined with the laser-induced CNV model, we show that disruption of Notch signaling in macrophages displayed attenuated CNV growth, reduced macrophage infiltration and activation, and alleviated angiogenic response after laser induction. The inhibition of CNV occurred with reduced expression of VEGF and TNF-α in infiltrating inflammatory macrophages in myeloid specific RBP-J knockout mice. These changes might result in direct inhibition of EC lumen formation, as shown in an in vitro study. Therefore, clinical intervention of Notch signaling in CNV needs to pinpoint myeloid lineage to avoid the counteractive effects of global inhibition.

Implication of AMP-activated protein kinase in transient receptor potential vanilloid type 1-mediated activation of endothelial nitric oxide synthase

We investigated whether AMP-activated protein kinase (AMPK), a multifunctional regulator of energy homeostasis, is involved in transient receptor potential vanilloid type 1 (TRPV1)-mediated activation of endothelial nitric oxide synthase (eNOS) in endothelial cells (ECs) and mice. In ECs, treatment with evodiamine, the activator of TRPV1, increased the phosphorylation of AMPK, acetyl-CoA carboxylase (ACC) and eNOS, as revealed by Western blot analysis. Inhibition of AMPK activation by compound C or dominant-negative AMPK mutant abrogated the evodiamine-induced increase in phosphorylation of AMPK and eNOS and NO bioavailability, as well as tube formation in ECs. Immunoprecipitation and two-hybrid analysis demonstrated that AMPK mediated the evodiamine-induced increase in the formation of a TRPVl-eNOS complex. Additionally, TRPV1 activation by evodiamine increased the phosphorylation of AMPK and eNOS in aortas of wild-type mice but did not activate eNOS in aortas of TRPV1-deficient mice. In mice, inhibition of AMPK activation by compound C markedly decreased evodiamine-evoked angiogenesis in matrigel plugs and in a hind-limb ischemia model. Moreover, evodiamine-induced phosphorylation of AMPK and eNOS in aortas of apolipoprotein E-deficient (ApoE^−/−) mice was abrogated in TRPVl-deficient ApoE^−/− mice. In conclusion, TRPV1 activation may trigger AMPK-dependent signaling, which leads to enhanced activation of AMPK and eNOS and retarded development of atherosclerosis.

Bone marrow-derived cells in ocular neovascularization: contribution and mechanisms

Ocular neovascularization often leads to severe vision loss. The role of bone marrow-derived cells (BMCs) in the development of ocular neovascularization, and its significance, is increasingly being recognized. In this review, we discuss their contribution and the potential mechanisms that mediate the effect of BMCs on the progression of ocular neovascularization. The sequence of events by which BMCs participate in ocular neovascularization can be roughly divided into four phases, i.e., mobilization, migration, adhesion and differentiation. This process is delicately regulated and liable to be affected by multiple factors. Cytokines such as vascular endothelial growth factor, granulocyte colony-stimulating factor and erythropoietin are involved in the mobilization of BMCs. Studies have also demonstrated a key role of cytokines such as stromal cell-derived factor-1, tumor necrosis factor-α, as well as vascular endothelial growth factor, in regulating the migration of BMCs. The adhesion of BMCs is mainly regulated by vascular cell adhesion molecule-1, intercellular adhesion molecule-1 and vascular endothelial cadherin. However, the mechanisms regulating the differentiation of BMCs are largely unknown at present. In addition, BMCs secrete cytokines that interact with the microenvironment of ocular neovascularization; their contribution to ocular neovascularization, especially choroidal neovascularization, can be aggravated by several risk factors. An extensive regulatory network is thought to modulate the role of BMCs in the development of ocular neovascularization. A comprehensive understanding of the involved mechanisms will help in the development of novel therapeutic strategies related to BMCs. In this review, we have limited the discussion to the recent progress in this field, especially the research conducted at our laboratory.

miR-342-5p Is a Notch Downstream Molecule and Regulates Multiple Angiogenic Pathways Including Notch, Vascular Endothelial Growth Factor and Transforming Growth Factor β Signaling

Background

Endothelial cells (ECs) form blood vessels through angiogenesis that is regulated by coordination of vascular endothelial growth factor (VEGF), Notch, transforming growth factor β, and other signals, but the detailed molecular mechanisms remain unclear.

Methods and Results

Small RNA sequencing initially identified miR‐342‐5p as a novel downstream molecule of Notch signaling in ECs. Reporter assay, quantitative reverse transcription polymerase chain reaction and Western blot analysis indicated that miR‐342‐5p targeted endoglin and modulated transforming growth factor β signaling by repressing SMAD1/5 phosphorylation in ECs. Transfection of miR‐342‐5p inhibited EC proliferation and lumen formation and reduced angiogenesis in vitro and in vivo, as assayed by using a fibrin beads–based sprouting assay, mouse aortic ring culture, and intravitreal injection of miR‐342‐5p agomir in P3 pups. Moreover, miR‐342‐5p promoted the migration of ECs, accompanied by reduced endothelial markers and increased mesenchymal markers, indicative of increased endothelial–mesenchymal transition. Transfection of endoglin at least partially reversed endothelial–mesenchymal transition induced by miR‐342‐5p. The expression of miR‐342‐5p was upregulated by transforming growth factor β, and inhibition of miR‐342‐5p attenuated the inhibitory effects of transforming growth factor β on lumen formation and sprouting by ECs. In addition, VEGF repressed miR‐342‐5p expression, and transfection of miR‐342‐5p repressed VEGFR2 and VEGFR3 expression and VEGF‐triggered Akt phosphorylation in ECs. miR‐342‐5p repressed angiogenesis in a laser‐induced choroidal neovascularization model in mice, highlighting its clinical potential.

Conclusions

miR‐342‐5p acts as a multifunctional angiogenic repressor mediating the effects and interaction among angiogenic pathways.

The development of blood-retinal barrier during the interaction of astrocytes with vascular wall cells

Astrocytes are intimately involved in the formation and development of retinal vessels. Astrocyte dysfunction is a major cause of blood-retinal barrier injury and other retinal vascular diseases. In this study, the development of the retinal vascular system and the formation of the blood-retinal barrier in mice were investigated using immunofluorescence staining, gelatin-ink perfusion, and transmission electron microscopy. The results showed that the retinal vascular system of mice develops from the optic disc after birth, and radiates out gradually to cover the entire retina, taking the papilla optica as the center. First, the superficial vasculature is formed on the inner retinal layer; then, the vasculature extends into the inner and outer edges of the retinal inner nuclear layer, forming the deep vasculature that is parallel to the superficial vasculature. The blood-retinal barrier is mainly composed of endothelium, basal lamina and the end-feet of astrocytes, which become mature during mouse development. Initially, the naive endothelial cells were immature with few organelles and many microvilli. The basal lamina was uniform in thickness, and the glial end-feet surrounded the outer basal lamina incompletely. In the end, the blood-retinal barrier matures with smooth endothelia connected through tight junctions, relatively thin and even basal lamina, and relatively thin glial cell end-feet. These findings indicate that the development of the vasculature in the retina follows the rules of "center to periphery" and "superficial layer to deep layers". Its development and maturation are spatially and temporally consistent with the functional performance of retinal neurons and photosensitivity. The blood-retinal barrier gradually becomes mature via the process of interactions between astrocytes and blood vessel cells.

Notch signaling regulates col1α1 and col1α2 expression in airway fibroblasts

Subepithelial fibrosis is one of the common pathological features of asthmatic airway remodeling. During subepithelial fibrosis, type I collagen becomes the most abundant extracellular protein component. Studies have shown that Notch signaling participates in the progression of fibrosis; however, whether Notch signaling is involved in regulating type I collagen expression in airway fibroblasts remains unclear. The aim of the present study was to examine whether Notch signaling can regulate type I collagen expression in airway fibroblasts and to explore the underlying molecular mechanisms. Here, the expression of Notch signaling components was examined in mouse L929 cells and human MRC-5 cells. After upregulating or downregulating Notch signaling in these cell lines, col1α1 and col1α2 expression was examined. Using gene reporter assays, site-directed mutagenesis, and ChIP assays, the role of Hes1 binding sites in both the mouse and human COL1A1 and COL1A2 promoters was investigated. This study revealed that Notch signaling-related molecules (including Notch1, Hes1, and others) are expressed in L929 and MRC-5 cells and that Notch signaling regulates the expression of col1α1 and col1α2 in both cell lines. Additionally, over-expression of the Notch intracellular domain resulted in activation of the COL1A1 and COL1A2 promoters, and site-directed mutagenesis reporter assays revealed that Hes1 proteins might augment both mouse and human COL1A1 and COL1A2 promoter activity. Furthermore, ChIP assays confirmed that Hes1 binds to the COL1A1 and COL1A2 promoters in both L929 and MRC-5 cells. Therefore, it is reasonable to assume that Notch signaling can directly upregulate COL1A1 and COL1A2 promoter activity through a Hes1-dependent mechanism, which could serve as a possible target for pharmacotherapy of airway subepithelial fibrosis.

Radiosurgery inhibition of the Notch signaling pathway in a rat model of arteriovenous malformations

Object

Notch signaling has been suggested to promote the development and maintenance of arteriovenous malformations (AVMs), but whether radiosurgery inhibits Notch signaling pathways in AVMs is unknown. The aim of this study was to examine molecular changes of Notch signaling pathways following radiosurgery and to explore mechanisms of radiosurgical obliteration of “nidus” vessels in a rat model of AVMs.

Methods

One hundred eleven rats received common carotid artery–to–external jugular vein anastomosis to form an arteriovenous fistula (AVF) model. Six weeks postoperatively, dilated small vessels and capillaries formed a nidus. The rats with AVFs received 25-Gy radiosurgery. The expression of Notch1 and Notch4 receptors and their ligands, Delta-like1 and Delta-like4, Jagged1, Notch downstream gene target HES1, and an apoptotic marker caspase-3 in nidus vessels in the AVF rats was examined immunohistochemically and was quantified using LAS-AF software at 7 time points over a period of 42 days postradiosurgery. The interaction events between Notch1 receptor and Jagged1, as well as Notch4 receptor and Jagged1, were quantified in nidus vessels in the AVF rats using proximity ligation assay at different time points over 42 days postradiosurgery.

Results

The expression of Notch1 and Notch4 receptors, Delta-like1, Delta-like4, Jagged1, and HES1 was observed in nidus vessels in the AVF rats pre- and postradiosurgery. Radiosurgery enhanced apoptotic activity (p < 0.05) and inhibited the expression of Notch1 and Notch4 receptors and Jagged1 in the endothelial cells of nidus vessels in the AVF rats at 1, 2, 3, 7, 21, 28, and 42 days postradiosurgery (p < 0.05). Radiosurgery suppressed the interaction events between Notch1 receptor and Jagged1 (p < 0.001) as well as Notch4 receptor and Jagged1 (p < 0.001) in the endothelial cells of nidus vessels in the AVF rats over a period of 42 days postradiosurgery. Radiosurgery induced thrombotic occlusion of nidus vessels in the AVF rats. There was a positive correlation between the percentage of fully obliterated nidus vessels and time after radiosurgery (r = 0.9324, p < 0.001).

Conclusions

Radiosurgery inhibits endothelial Notch1 and Notch4 signaling pathways in nidus vessels while inducing thrombotic occlusion of nidus vessels in a rat model of AVMs. The underlying mechanisms of radiosurgery-induced AVM shrinkage could be a combination of suppressing Notch receptor signaling in blood vessel endothelial cells, leading to a reduction in nidus vessel size and thrombotic occlusion of nidus vessels.

Inhibition of tumor angiogenesis and tumor growth by the DSL domain of human Delta-like 1 targeted to vascular endothelial cells

The growth of solid tumors depends on neovascularization. Several therapies targeting tumor angiogenesis have been developed. However, poor response in some tumors and emerging resistance necessitate further investigations of new drug targets. Notch signal pathway plays a pivotal role in vascular development and tumor angiogenesis. Either blockade or forced activation of this pathway can inhibit angiogenesis. As blocking Notch pathway results in the formation of vascular neoplasm, activation of Notch pathway to prevent tumor angiogenesis might be an alternative choice. However, an in vivo deliverable reagent with highly efficient Notch-activating capacity has not been developed. Here, we generated a polypeptide, hD1R, which consists of the Delta-Serrate-Lag-2 fragment of the human Notch ligand Delta-like 1 and an arginine-glycine-aspartate (RGD) motif targeting endothelial cells (ECs). We showed that hD1R could bind to ECs specifically through its RGD motif and effectively triggered Notch signaling in ECs. We demonstrated both in vitro and in vivo that hD1R inhibited angiogenic sprouting and EC proliferation. In tumor-bearing mice, the injection of hD1R effectively repressed tumor growth, most likely through increasing tumor hypoxia and tissue necrosis. The amount and width of vessels reduced remarkably in tumors of mice treated with hD1R. Moreover, vessels in tumors of mice treated with hD1R recruited more NG2(+) perivascular cells and were better perfused. Combined application of hD1R and chemotherapy with cisplatin and teniposide revealed that these two treatments had additive antitumor effects. Our study provided a new strategy for antiangiogenic tumor therapy.

Notch1 and 4 signaling responds to an increasing vascular wall shear stress in a rat model of arteriovenous malformations

Notch signaling is suggested to promote the development and maintenance of cerebral arteriovenous malformations (AVMs), and an increasing wall shear stress (WSS) contributes to AVM rupture. Little is known about whether WSS impacts Notch signaling, which is important for understanding the angiogenesis of AVMs. WSS was measured in arteriovenous fistulas (AVF) surgically created in 96 rats at different time points over a period of 84 days. The expression of Notch receptors 1 and 4 and their ligands, Delta1 and 4, Jagged1, and Notch downstream gene target Hes1 was quantified in “nidus” vessels. The interaction events between Notch receptors and their ligands were quantified using proximity ligation assay. There was a positive correlation between WSS and time (r = 0.97; P < 0.001). The expression of Notch receptors and their ligands was upregulated following AVF formation. There was a positive correlation between time and the number of interactions between Notch receptors and their ligands aftre AVF formation (r = 0.62, P < 0.05) and a positive correlation between WSS and the number of interactions between Notch receptors and their ligands (r = 0.87, P < 0.005). In conclusion, an increasing WSS may contribute to the angiogenesis of AVMs by activation of Notch signaling.

Novel targets against retinal angiogenesis in diabetic retinopathy

Proliferative diabetic retinopathy (PDR), characterized by pathologic retinal angiogenesis, is a major cause of blindness in the USA and globally. Treatments targeting vascular endothelial growth factor (VEGF) have emerged as a beneficial part of the therapeutic armamentarium for this condition, highlighting the utility of identifying and targeting specific pathogenic molecules. There continues to be active research into the molecular players regulating retinal angiogenesis, including pro-angiogenic factors, anti-angiogenic factors, and integrins and matrix proteinases. New insights have been especially prominent regarding molecules which regulate specialized endothelial cells called tip cells, which play a lead role in endothelial sprouting. Together, these research efforts are uncovering new, important molecular regulators of retinal angiogenesis, which provide fertile areas for therapeutic exploration. This review discusses potential molecular targets, with an emphasis towards newer targets.