Update on Endogenous Inhibitors of Angiogenesis

Isthmin: A multifunctional secretion protein

Isthmin is a polypeptide secreted by adipocytes that was first detected in Xenopus gastrula embryos. Recent studies have focused on the biological functions of isthmin in growth and development, angiogenesis, and metabolism. Distinct spatiotemporal expression of isthmin-1 (ISM-1) was observed during growth and development. ISM-1 plays an important role in the occurrence and development of cancer by regulating cell proliferation, migration, angiogenesis, and immune microenvironments. Moreover, ISM-1, as a newly identified insulin-like adipokine, increases adipocyte glucose uptake and inhibits hepatic lipid synthesis. However, the biological function of ISM-1 remains largely unknown. In this review, we highlight the structure and physiological functions of isthmin and explore its application potential, contributing to a better understanding of its function and providing prevention and treatment strategies for various diseases.

Recent Advances in Anti-Metastatic Approaches of Herbal Medicines in 5 Major Cancers: From Traditional Medicine to Modern Drug Discovery

Metastasis is the main cause of cancer-related death. Despite its high fatality, a comprehensive study that covers anti-metastasis of herbal medicines has not yet been conducted. The aim of this study is to investigate and assess the anti-metastatic efficacies of herbal medicines in the five major cancers, including lung, colorectal, gastric, liver, and breast cancers. We collected articles published within five years using PubMed, Google Scholar, and Web of Science with "cancer metastasis" and "herbal medicine" as keywords. Correspondingly, 16 lung cancer, 23 colorectal cancer, 10 gastric cancer, 10 liver cancer, and 18 breast cancer studies were systematically reviewed. The herbal medicines attenuated metastatic potential targeting various mechanisms such as epithelial mesenchymal transition (EMT), reactive oxygen species (ROS), and angiogenesis. Specifically, the drugs regulated metastasis related factors such as matrix metalloproteinase (MMP), serine-threonine protein kinase/extracellular regulated protein kinase (AKT/ERK), angiogenic factors, and chemokines. Overall, the present study is the first review, comprehensively investigating the anti-metastasis effect of herbal medicines on five major cancers, providing the experimental models, doses and durations, and mechanisms. Herbal medicines could be a potent candidate for anti-metastatic drugs.

High preoperative plasma vasohibin-1 concentration predicts better prognosis in patients with non-small cell lung carcinoma

BACKGROUND AND AIM

Vasohibin-1 (VASH1) is an angiogenesis inhibitor synthesized and secreted by endothelial cells, whose expression is induced by angiogenic stimuli such as vascular endothelial growth factor. We have previously demonstrated that VASH1 is immunohistochemically evident in endothelial cells in the tumor microenvironment of patients with non-small cell lung cancer (NSCLC) and is positively correlated with that of vascular endothelial growth factor in cancer cells. Here, we determined the preoperative plasma concentration of VASH1 in patients with NSCLC and evaluated the association between the preoperative VASH1 levels and certain outcomes.

METHODS

We analyzed presurgical plasma VASH1 concentrations in a total of 79 lung cancer patients (51 males and 28 females; 34-83 y of age; 46 adenocarcinomas, 27 squamous cell carcinomas, and 6 other types) who underwent lung resection. The impact of preoperative VASH1 level was analyzed using clinical characteristics and prognosis.

RESULTS

Plasma VASH1 concentration ranged from 34.1 to 1190.4 fmol/mL. We divided the patients into 3 groups according to plasma VASH1 level for this assessment: low VASH1 group (n = 26), medium VASH1 group (n = 27), and high VASH1 group (n = 26). The death and recurrence rates of the high, medium, and low VASH1 groups were 5.5, 16.2, and 12.7 per 100 person-years, respectively. Multivariate adjusted hazard ratio of death and recurrence of the high VASH1 group was lower than that of the low VASH1 group (hazard ratio 0.42; 95% CI 0.17-0.99).

CONCLUSION

The present analysis suggests that high preoperative plasma VASH1 concentration is associated with better prognosis in patients with NSCLC. We propose preoperative VASH1 level as a biomarker for the prognosis of patients with non-small cell lung carcinoma.

The expression of vasohibin-1 and its prognostic significance in bladder cancer

Angiogenesis is important in the development of solid tumors. Vasohibin-1 (VASH-1) is an endothelium-derived protein that acts as an inhibitor of angiogenesis in many different types of cancer. However, the expression of VASH-1 and its clinical value in bladder cancer remain unknown. The current study analyzed the expression of VASH-1, as well as the expression of the angiogenesis-related factors vascular endothelial growth factor-A, hypoxia inducible factor-1α and cluster of differentiation 34 in bladder cancer tissues from 50 patients using immunohistochemistry. The associations between the expression of these factors and the clinicopathological characteristics of the patients were assessed. The current study demonstrated that VASH-1 is primarily expressed in the cytoplasm of bladder cancer cells and in a fraction of vascular endothelial cells. Furthermore, the expression of VASH-1 was positively associated with the tumor stage (P<0.01), pathological grade (P<0.01) and distant metastasis (P<0.05) but not with patient age or sex (P>0.05). Spearman rank correlation tests indicated that levels of those four factors were positively correlated with each other. Kaplan-Meier analysis indicated that high expression of these four factors was significantly associated with lower 5-year overall survival and progression-free survival rates. Collectively, the results of the current study suggest that VASH-1 is clinically significant in bladder cancer and its high expression may predict the progression and prognosis of patients with bladder cancer. The present study also implies that VASH-1 may be a novel target for vascular targeting therapy.

Proteolytic inactivation of anti-angiogenic vasohibin-1 by cancer cells

Vasohibin-1 (VASH1) is an angiogenesis inhibitor synthesized by endothelial cells (ECs) under conditions associated with physiological and pathological angiogenesis including cancers. VASH1, which is a 44-kDa protein, is processed after its translation and secretion, and a 29 kDa product cleaved both N-terminal and C-terminal end loses its anti-angiogenic activity. Here, we tested whether cancer cells modulate the processing of VASH1. When mouse EC line MS1 stably overexpressing the human VASH1 gene (MS1-hVASH1) and various cancer cell lines were co-cultured, there was an increased processing of hVASH1 protein in the culture media. This augmented processing was abrogated by a general cysteine protease inhibitor, E-64, and also by a specific calpain inhibitor, MDL28170. Recombinant hVASH1 protein was degraded by µ-calpain in vitro, which degradation was blocked by calpeptin. Conditioned media from co-cultures had little effect on the migration of human umbilical vein endothelial cells, but exhibited an inhibitory effect on their migration when collected in the presence of MDL28170; and this inhibitory effect was blocked by neutralizing anti-hVASH1 mAb. These results indicate that cancer cells proteolytically inactivate VASH1 protein secreted by ECs in the tumour microenvironment.

The expression of miR-125b regulates angiogenesis during the recovery of heat-denatured HUVECs

BACKGROUND

In previous studies we found that miR-125b was down-regulated in denatured dermis of deep partial thickness burn patients. Moreover, miR-125b inhibited tumor-angiogenesis associated with the decrease of ERBB2 and VEGF expression in ovarian cancer cells and breast cancer cells, etc. In this study, we investigated the expression patterns and roles of miR-125b during the recovery of denatured dermis and heat-denatured human umbilical vein endothelial cells (HUVECs).

METHODS

Deep partial thickness burns in Sprague-Dawley rats and the heat-denatured cells (52°C, 35 s) were used for analysis. Western blot analysis and real-time PCR were applied to evaluate the expression of miR-125b and ERBB2 and VEGF. The ability of angiogenesis in heat-denatured HUVECs was analyzed by scratch wound healing and tube formation assay after pri-miR-125b or anti-miR-125b transfection.

RESULTS

miR-125b expression was time-dependent during the recovery of heat-denatured dermis and HUVECs. Moreover, miR-125b regulated ERBB2 mRNA and Protein Expression and regulated angiogenesis association with regulating the expression of VEGF in heat-denatured HUVECs.

CONCLUSIONS

Taken together our results show that the expression of miR-125b is time-dependent and miR-125b plays a regulatory role of angiogenesis during wound healing after burns.

Baicalin attenuates laser-induced choroidal neovascularization

PURPOSE

To determine whether intravitreally-injected baicalin inhibits the growth of choroidal neovascularization (CNV) experimentally induced via laser photocoagulation through analysis of angiogenic factors.

MATERIALS AND METHODS

Six CNVs were induced in the left eyes of 8-week-old male Brown Norway rats. Immediately after the induction of CNV, 4 μl of baicalin solution (0.1, 1 or 5 nmol) and 4 μl of a solution containing 100 μg of bevacizumab were slowly injected into the vitreous cavity under direct observation with an operating microscope. At 14 days after CNV induction, fluorescein angiography (FA) was performed, and choroidal flat mounts were produced for quantitative assessment of CNV. The levels of the anti-angiogenic proteins vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF) and matrix metalloproteinase-2 (MMP-2) were determined via Western blot analysis.

RESULTS

FA of bevacizumab- and baicalin-treated rats showed significantly reduced CNV and leakage from the CNV lesions compared to control rats at day 14. Choroidal flat mounts revealed that baicalin inhibited the growth of CNV lesions in a dose-dependent manner. Western blot analysis demonstrated that baicalin significantly attenuated the up-regulation of VEGF, PDGF and MMP-2.

CONCLUSION

Baicalin suppressed laser-induced CNV formation in rats. These results suggest that baicalin should be considered as a candidate drug for treating exudative age-related macular degeneration.

Histamine synergistically promotes bFGF-induced angiogenesis by enhancing VEGF production via H1 receptor

Histamine, a major mediator present in mast cells that is released into the extracellular milieu upon degranulation, is well known to possess a wide range of biological activities in several classic physiological and pathological processes. However, whether and how it participates in angiogenesis remains obscure. In the present study, we observed its direct and synergistic action with basic fibroblast growth factor (bFGF), an important inducer of angiogenesis, on in vitro angiogenesis models of endothelial cells. Data showed that histamine (0.1, 1, 10 µM) itself was absent of direct effects on the processes of angiogenesis, including the proliferation, migration, and tube formation of endothelial cells. Nevertheless, it could concentration-dependently enhance bFGF-induced angiogenesis as well as production of vascular endothelial growth factor (VEGF) from endothelial cells. The synergistic effect of histamine on VEGF production could be reversed by pretreatments with diphenhydramine (H1-receptor antagonist), SB203580 (selective p38 mitogen-activated protein kinase (MAPK) inhibitor) and L-NAME (nitric oxide synthase (NOS) inhibitor), but not with cimetidine (H2-receptor antagonist) and indomethacin (cyclooxygenase (COX) inhibitor). Moreover, histamine could augment bFGF-incuced phosphorylation and degradation of IκBα, a key factor accounting for the activation and translocation of nuclear factor κB (NF-κB) in endothelial cells. These findings indicated that histamine was able to synergistically augment bFGF-induced angiogenesis, and this action was linked to VEGF production through H1-receptor and the activation of endothelial nitric oxide synthase (eNOS), p38 MAPK, and IκBα in endothelial cells.

Vasohibin-1 expression is regulated by transforming growth factor-β/bone morphogenic protein signaling pathway between tumor-associated macrophages and pancreatic cancer cells

Vasohibin-1 has been detected in endothelial cells as an intrinsic angiogenesis inhibitor. Both tumor-associated macrophages (TAMs) and transforming growth factor-β (TGF-β)/bone morphogenic protein (BMP) signaling have been reported to promote angiogenesis in cancer. However, whether vasohibin-1 expression is regulated by TGF-β/BMP signaling between TAMs and cancer cells remains unclear. The expression of TGF-β1, TGF-β2, BMP-4, and BMP-7 in TAMs and the expression of vasohibin-1, vascular endothelial growth factor-A (VEGF-A), and VEGF-C in two pancreatic cancer cell lines (a nonmetastatic cell line Panc-1 and a distant metastatic cell line HPAF-II) were measured by real-time reverse transcription-polymerase chain reaction (RT-PCR). The TGF-β receptor 1 and BMP receptor 1 were inhibited by the inhibitor SB-431542 and LDN193189, respectively. Thereafter, vasohibin-1, VEGF-A, and VEGF-C expression was detected by real-time RT-PCR. We found that the expression of TGF-β1, TGF-β2, BMP-4, and BMP-7 was upregulated in TAMs cocultured with pancreatic cancer cells. Vasohibin-1, VEGF-A, and VEGF-C mRNA expression in pancreatic cancer cells was upregulated by TAMs. Vasohibin-1 expression in pancreatic cancer cells cocultured with TAMs was upregulated significantly when TGF-β receptors or BMP receptors were inhibited, but VEGF-C expression was downregulated. Therefore, Vasohibin-1 expression is regulated by the TGF-β/BMP signaling between TAMs and pancreatic cancer cells. These results might shed a new light on the antiangiogenesis therapy in the pancreatic cancer.

Targeted microbubbles in the experimental and clinical setting

BACKGROUND

Microbubbles have improved ultrasonography imaging techniques over the past 2 decades. Their safety, versatility, and easiness of use have rendered them equal or even superior in some instances to other imaging modalities such as computed tomography and magnetic resonance imaging. Herein, we conducted a literature review to present their types, general behavior in tissues, and current and potential use in clinical practice.

METHODS

A literature search was conducted for all preclinical and clinical studies involving microbubbles and ultrasonography.

RESULTS

Different types of microbubbles are available. These generally improve the enhancement of tissues during ultrasonography imaging. They also can be attached to ligands for the target of several conditions such as inflammation, angiogenesis, thrombosis, apoptosis, and might have the potential of carrying toxic drugs to diseased sites, thereby limiting the systemic adverse effects.

CONCLUSIONS

The use of microbubbles is evolving rapidly and can have a significant impact on the management of various conditions. The potential for their use as targeting agents and gene and drug delivery vehicles looks promising.

The vasohibin family: a novel family for angiogenesis regulation

Angiogenesis, a formation of neovessels, is regulated by the local balance between angiogenesis stimulators and inhibitors. A number of such endogenous regulators of angiogenesis have been found in the body. Recently, vasohibin-1 (VASH1) was isolated as a negative feedback regulator of angiogenesis produced by endothelial cells (ECs) and subsequently vasohibin-2 (VASH2) as a homologue of VASH1. It was then explored that VASH1 is expressed in ECs to terminate angiogenesis, whereas VASH2 is expressed in cells other than ECs to promote angiogenesis in the mouse model of angiogenesis. This review will focus on the vasohibin family members, which are novel regulators of angiogenesis.

A microarray analysis of angiogenesis modulation effect of Xuefu Zhuyu Decoction on endothelial cells

OBJECTIVE

To study the angiogenesis modulation mechanism of Xuefu Zhuyu Decoction () on the endothelial cell line ECV304.

METHODS

ECV304 cells were treated with 2.5% Xuefu Zhuyu Decoction-containing serum (XFZYD-CS) for 24 h, 48 h or 72 h. Thiazolyl blue tetrazolium bromide (MTT), fluorescence activating cell sorter (FACS), migration, adhesion and in vitro tube formation assays were conducted to confirm an angiogenesis effect of XFZYD at 3 time points. An analysis of angiogenesis regulator profiles was performed at 3 times with real-time polymerase chain reaction (RT-PCR) superarray.

RESULTS

At 48 h, XFZYD-CS induced ECV304 significantly improved cell viability, number in S phase, migration, adhesion and tube formation. At 24 h and 72 h, only cell migration was elevated. Microarray results showed that the expression of 27 angiogenesis-related genes was changed.

CONCLUSION

XFZYD-CS treatment induced angiogenesis on ECV304 cells with significant cellcular changes occurring at 48 h and genetic changes as early as 24 h.

Isthmin is a novel secreted angiogenesis inhibitor that inhibits tumour growth in mice

Anti-angiogenesis represents a promising therapeutic strategy for the treatment of various malignancies. Isthmin (ISM) is a gene highly expressed in the isthmus of the midbrain–hindbrain organizer in Xenopus with no known functions. It encodes a secreted 60 kD protein containing a thrombospondin type 1 repeat domain in the central region and an adhesion-associated domain in MUC4 and other proteins (AMOP) domain at the C-terminal. In this work, we demonstrate that ISM is a novel angiogenesis inhibitor. Recombinant mouse ISM inhibited endothelial cell (EC) capillary network formation on Matrigel through its C-terminal AMOP domain. It also suppressed vascular endothelial growth factor (VEGF)-basic fibroblast growth factor (bFGF) induced in vivo angiogenesis in mouse. It mitigated VEGF-stimulated EC proliferation without affecting EC migration. Furthermore, ISM induced EC apoptosis in the presence of VEGF through a caspase-dependent pathway. ISM binds to αvβ5 integrin on EC surface and supports EC adhesion. Overexpression of ISM significantly suppressed mouse B16 melanoma tumour growth through inhibition of tumour angiogenesis without affecting tumour cell proliferation. Knockdown of isthmin in zebrafish embryos using morpholino antisense oligonucleotides led to disorganized intersegmen-tal vessels in the trunk. Our results demonstrate that ISM is a novel endogenous angiogenesis inhibitor with functions likely in physiological as well as pathological angiogenesis.

The vasohibin family: Novel regulators of angiogenesis

Angiogenesis is thought to be regulated by the local balance between angiogenesis stimulators and angiogenesis inhibitors. A number of endogenous regulators of angiogenesis have been found in the body. We recently isolated vasohibin-1 (VASH1) as a negative feedback regulator of angiogenesis produced by endothelial cells, and VASH2 as a homologue of VASH1 thereafter. We found that VASH1 was expressed in endothelial cells to terminate angiogenesis, whereas VASH2 promoted angiogenesis, in the mouse model of angiogenesis. This mini-review will focus on the vasohibin family in relation to the regulation of angiogenesis.

Mutual Balance between Vasohibin-1 and Soluble VEGFR-1 in Endothelial Cells

Vasohibin-1 (VASH1) is a VEGF-inducible gene of endothelial cells (ECs) that acts as a negative feedback regulator of angiogenesis. To further characterize the function of VASH1, we transfected human VASH1 gene into the mouse EC line MS1, established stable VASH1 expressing clones, and determined gene alteration by cDNA microarray analysis. Among the various angiogenesis-related genes, vascular endothelial growth factor type 1 receptor (VEGFR-1) and its alternative spliced form, soluble VEGFR1 (sVEGFR-1), were found to be the most significantly down-regulated genes. Transient overexpression of VASH1 in human umbilical vein endothelial cells confirmed the down-regulation of VEGFR-1 and sVEGFR-1. sVEGFR-1 is a decoy receptor for VEGF and inhibits angiogenesis. Interestingly, when sVEGFR-1 was overexpressed in ECs, it inhibited the expression of VASH1 in turn. These results suggest that VASH1 and sVEGFR-1, two angiogenesis inhibitors, mutually balance their expressions in ECs.

Isolation of a small vasohibin-binding protein (SVBP) and its role in vasohibin secretion

Upon stimulation with angiogenic factors, vascular endothelial cells (ECs) secrete a negative-feedback regulator of angiogenesis, vasohibin-1 (VASH1). Because VASH1 lacks a classical signal sequence, it is not clear how ECs secrete VASH1. We isolated a small vasohibin-binding protein (SVBP) composed of 66 amino acids. The level of Svbp mRNA was relatively high in the bone marrow, spleen and testes of mice. In cultured ECs, Vash1 mRNA was induced by VEGF, and Svbp mRNA was expressed constitutively. The interaction between VASH1 and SVBP was confirmed using the BIAcore system and immunoprecipitation analysis. Immunocytochemical analysis revealed that SVBP colocalized with VASH1 in ECs. In polarized epithelial cells, SVBP accumulated on the apical side, whereas VASH1 was present throughout the cells and partially colocalized with SVBP. Transfection of SVBP enhanced VASH1 secretion, whereas knockdown of endogenous SVBP markedly reduced VASH1 secretion. SVBP increased the solubility of VASH1 protein in detergent solution and inhibited the ubiquitylation of VASH1 protein. Moreover, co-transfection of SVBP significantly augmented the inhibitory effect of VASH1 on EC migration. These results indicate that SVBP acts as a secretory chaperone for VASH1 and contributes to the anti-angiogenic activity of VASH1.

Vasohibin-1 as a potential predictor of aggressive behavior of ductal carcinoma in situ of the breast

Vasohibin-1 is a recently identified negative feedback regulator of angiogenesis induced by VEGF-A and bFGF. In this study, we first evaluated mRNA expression of vasohibin-1 and CD31 in 39 Japanese female breast carcinoma specimens including 22 invasive ductal carcinoma (IDC) and 17 ductal carcinoma in situ (DCIS) using a real-time quantitative RT-PCR (QRT-PCR) with LightCycler system. In addition, we also immunolocalized vasohibin-1 and CD31 and compared their immunoreactivity to nuclear grades and histological grades of 100 carcinoma cases (50 IDC and 50 DCIS). There were no statistically significant differences of CD31 mRNA expression and the number of CD31 positive vessels between DCIS and IDC (P = 0.250 and P = 0.191, respectively), whereas there was a statistically significant difference in vasohibin-1 mRNA expression and the number of vasohibin-1 positive vessels in DCIS and IDC (P = 0.022 and P < or = 0.001, respectively). There was a significant positive correlation between vasohibin-1 mRNA level and Ki-67 labeling index in DCIS (r(2) = 0.293, P < or = 0.001). In addition, vasohibin-1 mRNA expression was correlated with high nuclear and histological grades in DCIS cases and a significant positive correlation was detected between the number of vasohibin-1 positive vessels and Ki-67 labeling index or nuclear grade or Van Nuys classification of carcinoma cells (P < or = 0.001, respectively). These results all indicate the possible correlation between aggressive biological features in DCIS including increased tumor cell proliferation and the status of neovascularization determined by vasohibin-1 immunoreactivity.

The Vasohibin Family

Angiogenesis is regulated by the local balance between angiogenesis stimulators and inhibitors. A number of endogenous angiogenesis inhibitors have been found in the body. The origin of these inhibitors is mostly extrinsic to the vasculature. Recently, however, vascular endothelial cells themselves have been found to produce angiogenesis inhibitors including vasohibin-1. These intrinsic inhibitors are thought to regulate angiogenesis by an auto-regulatory or negative-feedback mechanism. This review will focus on vasohibin-1 produced by vascular endothelial cells and on its homologue, vasohibin-2.

Endogenous angiogenesis inhibitor vasohibin1 exhibits broad-spectrum antilymphangiogenic activity and suppresses lymph node metastasis

During cancer progression, the angiogenesis that occurs is involved in tumor growth and hematogenous-distant metastasis, whereas lymphangiogenesis is involved in regional lymph node metastasis. Angiogenesis is counterregulated by various endogenous inhibitors; however, little is known about endogenous inhibitors of lymphangiogenesis. We recently isolated vasohibin1 as an angiogenesis inhibitor intrinsic to the endothelium and further demonstrated its anticancer activity through angiogenesis inhibition. Here, we examined the effect of vasohibin1 on lymphangiogenesis. Vasohibin1 exhibited broad-spectrum antilymphangiogenic activity in the mouse cornea induced by factors including VEGF-A, VEGF-C, FGF2, and PDGF-BB. We then inoculated highly lymph node-metastatic cancer cells into mice and examined the effect of vasohibin1 on lymph node metastasis. Tail-vein injection of adenovirus containing the human vasohibin1 gene inhibited tumor lymphangiogenesis and regional lymph node metastasis. Moreover, local injection of recombinant vasohibin1 inhibited lymph node metastasis. These results suggest vasohibin1 to be the first known intrinsic factor having broad-spectrum antilymphangiogenic activity and indicate that it suppresses lymph node metastasis.

Vasohibin-1 expression in endothelium of tumor blood vessels regulates angiogenesis

In this study, we characterized the significance of the vascular endothelial growth factor-inducible angiogenesis inhibitor vasohibin-1 to tumors. In pathological sections of non-small cell lung carcinoma, vasohibin-1 was present in the endothelial cells of blood vessels of the tumor stroma, but not in the lymphatics. In cancer cells, the presence of vasohibin-1 was associated with hypoxia-inducible factor 1alpha/vascular endothelial growth factor and fibroblast growth factor-2 expression. We then examined the function of vasohibin-1 in the mouse by subcutaneously inoculating with Lewis lung carcinoma cells. Resultant tumors in vasohibin-1(-/-) mice contained more immature blood vessels and fewer apoptotic tumor cells than tumors in wild-type mice. In wild-type mice that had been inoculated with Lewis lung carcinoma cells, tail vein injection of adenovirus containing the human vasohibin-1 gene inhibited tumor growth and tumor angiogenesis. Moreover, the remaining tumor vessels in adenoviral human vasohibin-1 gene-treated mice were small, round, and mature, surrounded by mural cells. The addition of adenoviral human vasohibin-1 gene to cisplatin treatment improved cisplatin's antitumor activity in mice. These results suggest that endogenous vasohibin-1 is not only involved in tumor angiogenesis, but when sufficient exogenous vasohibin-1 is supplied, it blocks sprouting angiogenesis by tumors, matures the remaining vessels, and enhances the antitumor effect of conventional chemotherapy.

Distinctive localization and opposed roles of vasohibin-1 and vasohibin-2 in the regulation of angiogenesis

We recently isolated a novel angiogenesis inhibitor, vasohibin-1, and its homologue, vasohibin-2. In this study we characterize the role of these 2 molecules in the regulation of angiogenesis. In a mouse model of subcutaneous angiogenesis, the expression of endogenous vasohibin-1 was low in proliferating ECs at the sprouting front but high in nonproliferating endothelial cells (ECs) in the termination zone. In contrast, endogenous vasohibin-2 was preferentially expressed in mononuclear cells mobilized from bone marrow that infiltrated the sprouting front. When applied exogenously, vasohibin-1 inhibited angiogenesis at the sprouting front where endogenous vasohibin-1 was scarce but did not influence vascularity in the termination zone where endogenous vasohibin-1 was enriched. Exogenous vasohibin-2 prevented the termination of angiogenesis in the termination zone and increased vascularity in this region. Angiogenesis was persistent in the termination zone in the vasohibin-1 knockout mice, whereas angiogenesis was deficient at the sprouting front in the vasohibin-2 knockout mice. Supplementation of deficient proteins normalized the abnormal patterns of angiogenesis in the vasohibin knockout mice. These results indicate that vasohibin-1 is expressed in ECs in the termination zone to halt angiogenesis, whereas vasohibin-2 is expressed in infiltrating mononuclear cells in the sprouting front to promote angiogenesis.

Microenvironment changes (in pH) affect VEGF alternative splicing

Vascular endothelial growth factor-A (VEGF-A) has several isoforms, which differ in their capacity to bind extracellular matrix proteins and also in their affinity for VEGF receptors. Although the relative contribution of the VEGF isoforms has been studied in tumor angiogenesis, little is known about the mechanisms that regulate the alternative splicing process. Here, we tested microenvironment cues that might regulate VEGF alternative splicing. To test this, we used endometrial cancer cells that produce all VEGF isoforms as a model, and exposed them to varying pH levels, hormones, glucose and CoCl₂ (to mimic hypoxia). Low pH had the most consistent effects in inducing variations in VEGF splicing pattern (VEGF121 increased significantly, p < 0.001, when compared to VEGF145, 165 or 189). This was accompanied by activation of the p38 stress pathway and SR proteins (splicing factors) expression and phosphorylation. SF2/ASF, SRp20 and SRp40 down-regulation by siRNA impaired the effects of pH stimulation, blocking the shift in VEGF isoforms production. Taken together, we show for the first time that acidosis (low pH) regulates VEGF-A alternative splicing, may be through p38 activation and suggest the possible SR proteins involved in this process.

Angiogenesis in diabetic nephropathy

Angiogenesis, the formation of new blood vessels from pre-existing vasculature, plays a key role in both physiologic and pathologic events, including wound healing, cancer, and diabetes. Neovascularization has been implicated in the genesis of diverse diabetic complications such as retinopathy, impaired wound healing, neuropathy, and, most recently, diabetic nephropathy. Diabetic nephropathy is one of the major microvascular-associated complications in diabetes and is the leading cause of end-stage renal disease worldwide. In this review we describe the major factors involved in the pathologic glomerular microvascular alterations in response to hyperglycemia and the possible use of anti-angiogenic therapies for the treatment of diabetic nephropathy.

The Vasohibin Family

Biological phenomena are under the precise control by the genome. For the regulation of angiogenesis, proangiogenic genes such as VEGFs and angiopoietins are highly conserved, act specifically on endothelial cells, and play a fundamental role. In this sense, nature should prepare specific antiangiogenic genes as well. However, this counterpart of genomic regulation of angiogenesis remains to be established. We recently isolated a novel endothelium-derived angiogenesis inhibitor and named it vasohibin. Vasohibin is dominantly expressed in endothelial cells, induced by the stimulation with VEGF or FGF-2, and selectively affects on endothelial cells and inhibits angiogenesis. Although the mechanism of how vasohibin inhibits angiogenesis remains to be elucidated, our discovery of vasohibin as an endothelium-derived VEGF-inducible angiogenesis inhibitor should shed light on the genomic basis of the negative regulation of angiogenesis.