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

Proteolytically Derived Endogenous Angioinhibitors Originating from the Extracellular Matrix

Angiogenesis, a neovascularization process induced from the existing parent blood vessels, is a prerequisite for many physiological and pathological conditions. Under physiological conditions it is regulated by a balance between endogenous angioinhibitors and angioactivators, and an imbalance between them would lead to pathological conditions such as cancer, age-related macular degeneration (AMD), diabetic retinopathy, cardiovascular diseases, etc. Several proteolytically generated endogenous molecules have been identified which exhibit angioinhibition and/or antitumor activities. These angioinhibitors interact with endothelial and tumor cells by binding to distinct integrins and initiate many of their intracellular signaling mechanisms regulating the cell survival and or apoptotic pathways. The present review will focus on the extracellular matrix derived angioinhibitors, and their mechanisms of actions that point to the clinical significance and therapeutic implications.

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.

Persistent vascular normalization as an alternative goal of anti-angiogenic cancer therapy

Angiogenesis is recognized as one of the principal hallmarks of cancers. Cancers contain newly formed immature vessels devoid of firm coverage by pericytes. Several drugs targeting vascular endothelial growth factor signals are now in clinical use for anti-angiogenic cancer treatment. Those drugs transiently normalize tumor vessels and ultimately provoke vascular regression. This regression causes tumor hypoxia, which could trigger certain cancer cells to become more invasive and metastatic. Normalized vessels do not induce tumor hypoxia, and may protect from cancer cell intravasation and enhance anticancer treatment with chemotherapeutic agents, radiation, or immune therapy. Thus, persistent vascular normalization could be an alternative goal of anti-angiogenic cancer treatment.

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.

Angiogenesis and chronic kidney disease

The number of patients requiring renal replacement therapy due to end-stage renal disease (ESRD) is increasing worldwide. The prevalence of chronic kidney disease (CKD), and the importance of CKD as a risk factor in development of ESRD and in complicating cardiovascular disease (CVD) have been confirmed. In recent years, the involvement of angiogenesis-related factors in the progression of CKD has been studied, and the potential therapeutic effects on CKD of modulating these factors have been identified. Vascular endothelial growth factor (VEGF)-A, a potent pro-angiogenic factor, is involved in the development of the kidney, in maintenance of the glomerular capillary structure and filtration barrier, and in the renal repair process after injury. VEGF-A is also involved in the development of early diabetic nephropathy, demonstrated by the therapeutic effects of anti-VEGF-A antibody. Angiopoietin (Ang)-1 induces the maturation of newly formed blood vessels, and the therapeutic effects of Ang-1 in diabetic nephropathy have been described. In experimental models of diabetic nephropathy, the therapeutic effects of angiogenesis inhibitors, including angiostatin, endostatin and tumstatin peptides, the isocoumarin NM-3, and vasohibin-1, have been reported.

Further analysis of the involvement of angiogenesis-related factors in the development of CKD is required. Determining the disease stage at which therapy is most effective and developing an effective drug delivery system targeting the kidney will be essential for pro-or anti-angiogenic strategies for patients with CKD.

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, a negative feedback regulator of angiogenesis, ameliorates renal alterations in a mouse model of diabetic nephropathy

OBJECTIVE

The involvement of proangiogenic factors such as vascular endothelial growth factor as well as the therapeutic efficacy of angiogenesis inhibitors in early diabetic nephropathy has been reported. Vasohibin-1 (VASH-1) is a unique endogenous angiogenesis inhibitor that is induced in endothelial cells by proangiogenic factors. We investigated the therapeutic efficacy of VASH-1 in an early diabetic nephropathy model.

RESEARCH DESIGN AND METHODS

Streptozotocin- induced type 1 diabetic mice received intravenous injections of adenoviral vectors encoding VASH-1 (AdhVASH-1) or beta-gal (AdLacZ) every other week and were killed after 28 days.

RESULTS

Treatment with AdhVASH-1 resulted in sustained increase in the protein levels of VASH-1 in the liver and sera, in the absence of any inflammatory alterations. AdhVASH-1 treatment significantly suppressed renal hypertrophy, glomerular hypertrophy, glomerular hyperfiltration, albuminuria, increase of the CD31(+) glomerular endothelial area, F4/80(+) monocyte/macrophage infiltration, the accumulation of type IV collagen, and mesangial matrix compared with AdLacZ-treated diabetic mice. Increase in the renal levels of transforming growth factor-beta1, monocyte chemoattractant protein-1, and receptor for advanced glycation end products in diabetic animals was significantly suppressed by AdhVASH-1 (real-time PCR and immunoblot). VASH-1 significantly suppressed the increase of transforming growth factor-beta, monocyte chemoattractant protein-1, and receptor for advanced glycation end products, induced by high ambient glucose in cultured mouse mesangial cells. Increased phosphorylation of VEGFR2 was suppressed in AdVASH-1-treated diabetic animals and in cultured glomerular endothelial cells. Endogenous mouse VASH-1 was localized to the mesangial and endothelial area in glomeruli of diabetic mice.

CONCLUSIONS

These results suggest the potential therapeutic efficacy of VASH-1 in treating early diabetic nephropathy potentially mediated via glomerular endothelial and mesangial cells.

Vasohibin inhibits angiogenic sprouting in vitro and supports vascular maturation processes in vivo

BACKGROUND

The murine homologue of human vasohibin (mVASH1), a putative antiangiogenic protein, was investigated for its effects on in vitro and in vivo angiogenesis.

METHODS

Cell growth and migration were analyzed in murine fibroblasts, smooth muscle cells and endothelial cells. Angiogenic sprouting was studied in human umbilical vein endothelial cells (HUVECs) in the spheroid sprouting assay. In vivo effects on blood vessel formation were investigated in the chorioallantoic membrane (CAM) assay and in the C57BL/6 melanoma xenograft model.

RESULTS

Purified murine and human VASH1 protein induced apoptosis of murine fibroblasts in vitro, but not of vascular aortic smooth muscle cells (AoSMC) or endothelial cells. Adenoviral overexpression of murine and human VASH1 inhibited capillary sprouting of HUVECs in the spheroid assay. Administration of recombinant murine and human VASH1 inhibited growth of large vessels in the CAM assay and promoted the formation of a dense, fine vascular network. Murine VASH1-overexpressing B16F10 melanomas displayed a reduction in large vessels and vascular area. Moreover, tumors showed more microvessels that stained positive for the mural cell markers alpha-smooth muscle cell actin (ASMA) and proteoglycan (NG2).

CONCLUSION

Our data imply that murine VASH1 causes angiogenic remodelling by inhibiting angiogenic sprouting and large vessel growth, thereby supporting the formation of a vascular bed consisting predominantly of mature microvessels.

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.

Suppression of Sproutys has a therapeutic effect for a mouse model of ischemia by enhancing angiogenesis

Sprouty proteins (Sproutys) inhibit receptor tyrosine kinase signaling and control various aspects of branching morphogenesis. In this study, we examined the physiological function of Sproutys in angiogenesis, using gene targeting and short-hairpin RNA (shRNA) knockdown strategies. Sprouty2 and Sprouty4 double knockout (KO) (DKO) mice were embryonic-lethal around E12.5 due to cardiovascular defects. The number of peripheral blood vessels, but not that of lymphatic vessels, was increased in Sprouty4 KO mice compared with wild-type (WT) mice. Sprouty4 KO mice were more resistant to hind limb ischemia and soft tissue ischemia than WT mice were, because Sprouty4 deficiency causes accelerated neovascularization. Moreover, suppression of Sprouty2 and Sprouty4 expression in vivo by shRNA targeting accelerated angiogenesis and has a therapeutic effect in a mouse model of hind limb ischemia. These data suggest that Sproutys are physiologically important negative regulators of angiogenesis in vivo and novel therapeutic targets for treating peripheral ischemic diseases.