Phosphoglycerate kinase (PGK) 1 succinylation modulates epileptic seizures and the blood-brain barrier

Epilepsy is the most common chronic disorder in the nervous system, mainly characterized by recurrent, periodic, unpredictable seizures. Post-translational modifications (PTMs) are important protein functional regulators that regulate various physiological and pathological processes. It is significant for cell activity, stability, protein folding, and localization. Phosphoglycerate kinase (PGK) 1 has traditionally been studied as an important adenosine triphosphate (ATP)-generating enzyme of the glycolytic pathway. PGK1 catalyzes the reversible transfer of a phosphoryl group from 1, 3-bisphosphoglycerate (1, 3-BPG) to ADP, producing 3-phosphoglycerate (3-PG) and ATP. In addition to cell metabolism regulation, PGK1 is involved in multiple biological activities, including angiogenesis, autophagy, and DNA repair. However, the exact role of PGK1 succinylation in epilepsy has not been thoroughly investigated. The expression of PGK1 succinylation was analyzed by Immunoprecipitation. Western blots were used to assess the expression of PGK1, angiostatin, and vascular endothelial growth factor (VEGF) in a rat model of lithium-pilocarpine-induced acute epilepsy. Behavioral experiments were performed in a rat model of lithium-pilocarpine-induced acute epilepsy. ELISA method was used to measure the level of S100β in serum brain biomarkers' integrity of the blood-brain barrier. The expression of the succinylation of PGK1 was decreased in a rat model of lithium-pilocarpine-induced acute epilepsy compared with the normal rats in the hippocampus. Interestingly, the lysine 15 (K15), and the arginine (R) variants of lentivirus increased the susceptibility in a rat model of lithium-pilocarpine-induced acute epilepsy, and the K15 the glutamate (E) variants, had the opposite effect. In addition, the succinylation of PGK1 at K15 affected the expression of PGK1 succinylation but not the expression of PGK1total protein. Furthermore, the study found that the succinylation of PGK1 at K15 may affect the level of angiostatin and VEGF in the hippocampus, which also affects the level of S100β in serum. In conclusion, the mutation of the K15 site of PGK1 may alter the expression of the succinylation of PGK1 and then affect the integrity of the blood-brain barrier through the angiostatin / VEGF pathway altering the activity of epilepsy, which may be one of the new mechanisms of treatment strategies.

Exercise training ameliorates cognitive dysfunction in amyloid beta-injected rat model: possible mechanisms of Angiostatin/VEGF signaling

Vascular endothelial growth factor (VEGF) regulates angio/neurogenesis and also tightly links to the pathogenesis of Alzheimer's disease (AD). Although exercise has a beneficial effect on neurovascular function and cognitive function, the direct effect of exercise on VEGF-related signaling and cognitive deficit in AD is incompletely understood. Therefore, the purpose of this study was to investigate the protective effect of exercise on angiostatin/VEGF cascade and cognitive function in AD model rats. Wistar male rats were randomly divided into five groups: control (CON), injection of DMSO (Sham-CON), CON-exercise (sham-EX), intrahippocampal injection of Aβ (Aβ), and Aβ-exercise (Aβ-EX). Rats in EX groups underwent treadmill exercise for 4 weeks, then the cognitive function was measured by the Morris Water Maze (MWM) test. mRNA levels of hypoxia-induced factor-1α (HIF-1α), vascular endothelial growth factor (VEGF), vascular endothelial growth factor receptor 2 (VEGFR2), and angiostatin were determined in hippocampus by RT-PCR. We found that spatial learning and memory were impaired in Aβ-injected rats, but exercise training improved it. Moreover, exercise training increased the reduced mRNA expression level of VEGF signaling, including HIF1α, VEGF, and VEGFR2 in the hippocampus from Aβ-injected rats. Also, the mRNA expression level of angiostatin was elevated in the hippocampus from Aβ-injected rats, and exercise training abrogated its expression. Our findings suggest that exercise training improves cognitive function in Aβ-injected rats, possibly through enhancing VEGF signaling and reducing angiostatin.

The Role of Fibrinolytic Regulators in Vascular Dysfunction of Systemic Sclerosis

Systemic sclerosis (SSc) is a connective tissue disease of autoimmune origin characterized by vascular dysfunction and extensive fibrosis of the skin and visceral organs. Vascular dysfunction is caused by endothelial cell (EC) apoptosis, defective angiogenesis, defective vasculogenesis, endothelial-to-mesenchymal transition (EndoMT), and coagulation abnormalities, and exacerbates the disease. Fibrinolytic regulators, such as plasminogen (Plg), plasmin, α2-antiplasmin (α2AP), tissue-type plasminogen activator (tPA), urokinase-type plasminogen activator (uPA) and its receptor (uPAR), plasminogen activator inhibitor 1 (PAI-1), and angiostatin, are considered to play an important role in the maintenance of endothelial homeostasis, and are associated with the endothelial dysfunction of SSc. This review considers the roles of fibrinolytic factors in vascular dysfunction of SSc.

Aerobic training and l-arginine supplementation promotes rat heart and hindleg muscles arteriogenesis after myocardial infarction

Arteriogenesis is a main defense mechanism to prevent heart and local tissues dysfunction in occlusive artery disease. TGF-β and angiostatin have a pivotal role in arteriogenesis. We tested the hypothesis that aerobic training and l-arginine supplementation promotes cardiac and skeletal muscles arteriogenesis after myocardial infarction (MI) parallel to upregulation of TGF-β and downregulation of angiostatin. For this purpose, 4 weeks after LAD occlusion, 50 male Wistar rats were randomly distributed into five groups: (1) sham surgery without MI (sham, n = 10), (2) control-MI (Con-MI, n = 10), (3) l-arginine-MI (La-MI, n = 10), (4) exercise training-MI (Ex-MI, n = 10), and (5) exercise and l-arginine-MI (Ex + La-MI). Exercise training groups running on a treadmill for 10 weeks with moderate intensity. Rats in the l-arginine-treated groups drank water containing 4 % l-arginine. Arteriolar density with different diameters (11-25, 26-50, 51-75, and 76-150 μm), TGF-β, and angiostatin gene expression were measured in cardiac (area at risk) and skeletal (soleus and gastrocnemius) muscles. Smaller arterioles decreased in cardiac after MI. Aerobic training and l-arginine increased the number of cardiac arterioles with 11-25 and 26-50 μm diameters parallel to TGF-β overexpression. In gastrocnemius muscle, the number of arterioles/mm(2) was only increased in the 11 to 25 μm in response to training with and without l-arginine parallel to angiostatin downregulation. Soleus arteriolar density with different size was not different between experimental groups. Results showed that 10 weeks aerobic exercise training and l-arginine supplementation promotes arteriogenesis of heart and gastrocnemius muscles parallel to overexpression of TGF-β and downregulation of angiostatin in MI rats.

PLASMINOGEN AND ANGIOSTATIN LEVELS IN FEMALE BENIGN BREAST LESIONS

It is known that benign breast tissue exhibit relatively low angiogenic capacity. Activation of angiogenesis in mammary pre-malignant lesions could be associated with disease progression and high risk of transformation into the breast cancer. However, insight into the underlying molecular mechanisms involved in angiogenesis regulation in non-cancerous breast pathologies is still poorly defined. The purpose of the present study was to determine levels of plasminogen and its proteolytic fragments (angiostatins) in mammary dysplasia (mastopathy and breast cyst) and benign neoplasms (fibroadenomas). Plasminogen and angiostatins were analyzed using immunoblotting and quantified by densitometric scanning. The significant increase in plasminogen levels was found in fibrocystic, cysts, and non-proliferatious fibroadenoma masses (4.7-, 3.7-, and 3.5-fold, respectively) compared to healthy breast tissues (control). In the same benign lesions, 6.7-, 4-, and 3.7-fold increase in plasminogen 50 kDa fragment (angiostatin) levels as compared with control were also observed. Activation of matrix metalloproteinase-9, which was detected using gelatine zymography, could be responsible for plasminogen cleavage and abundance of angiostatin infibrocystic and cyst masses. In contrast, dramatic decrease of both plasminogen and angiostatin levels (3.8- and 5.3-folds, respectively) was shown in tissues of proliferatious form of fibroadenoma in comparison with that of the dormant type of this neoplasm. Based on the obtained results, we concluded that angiostatin, a potent vessel growth inhibitor and anti-inflammatory molecule, can play a crucial role in pathophysiology of non-cancerous breast diseases. Further studies are needed to evaluate potential diagnostic and clinical implications of these proteins for prediction and therapy of benign breast pathologies.

[Role of angiostatins in diabetic complications]

Angiogenesis is a process through which new blood vessels form from pre-existing vessels. Angiogenesis is regulated by a number of factors of peptide nature. Disbalance of angiogenic system appears to be the major causative factor contributing vascular abnormalities in diabetes mellitus, resulting in various complications. Angiostatins, which are kringle-containing fragments of plasminogen/plasmin, are known to be powerful physiological inhibitors of neovascularization. In the present review, current literature data on peculiarities of production of angiostatins and their functioning at diabetes mellitus are summarized and analyzed for the first time. Also, role of angiostatins in the pathogenesis of typical diabetic complications, including retinopathies, nephropathies and cardiovascular diseases, is discussed. Data presented in this review may be useful for elaboration of novel effective approaches for diagnostics and therapy of vascular abnormalities in diabetes mellitus.

[Effect of yifei qinghua granule on VEGF, bFGF, angiostatin, and endostatin in Lewis lung cancer mice: an experimental study]

OBJECTIVE

To observe the effect of Yifei Qinghua Granule (YQG) on vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), angiostatin, and endostatin in tumor tissue of Lewis Lung cancer mice, and to explore its anti-tumor mechanisms.

METHODS

Totally 70 C57BL/6 mice were randomly divided into the model group, the low, medium, and high dose YQG groups, the gefitinib group, the gefitinib plus medium dose YQG group, and the cyclophosphamide (CTX) group, 10 in each group. The models were established by subcutaneously injecting Lewis lung cancer cells from the right axilla of C57BL/6 mice. Mice in the model group were given with 0.4 mL pure water by gastrogavage, once daily. Mice in the low and medium dose YHG groups were given with YHG at the daily dose of 5 and 10 g/kg by gastrogavage, once daily. Those in the high dose YHG group were given with YHG at 10 g/kg by gastrogavage, twice daily. Those in the gefitinib group were given with gefitinib 100 mg/ kg by gastrogavage, once daily. Those in the gefitinib plus medium dose YHG group were given with gefitinib at 100 mg/kg by gastrogavage in the morning and YHG at 10 g/kg by gastrogavage in the afternoon. All medication was started from the 2nd day of inoculation, lasting 14 successive days. Those in the CTX group were given CTX at 60 mg/kg by peritoneal injection on the 3rd and the 7th day of the experiment. Mice were sacrificed at the fifteenth day of the experiment. Tumors were taken out. Expressions of VEGF, bFGF, angiostatin, and endostatin in the tumor tissue were detected using immunohistochemical assay.

RESULTS

Compared with the model group, the expression of VEGF significantly decreased, expressions of angiostatin and endostatin significantly increased in each group (P < 0.01). The expression of bFGF significantly decreased in the gefitinib group (P < 0.05). There was no statistical difference in VEGF among all groups (P > 0.05). The angiostatin expression was significantly higher in the CTX group than in the low dose YQG group (P < 0.01). The expression of endostatin was significantly higher in the high dose YQG group and the gefitinib plus medium dose YQG group than in the low and the medium dose YQG groups (P < 0.01). The expression of endostatin was significantly higher in the gefitinib plus medium dose YQG group than in the gefitinib group (P < 0.05).

CONCLUSION

The action mechanism of YQG in treating lung cancer might be achieved through reducing the expression of angiogenesis promoting factor VEGF and increasing expressions of angiogenesis inhibitors angiostatin and endostatin.

Radio-sensitivities and angiogenic signaling pathways of irradiated normal endothelial cells derived from diverse human organs

The purpose of the present investigation was to study the effects of ionizing radiation on endothelial cells derived from diverse normal tissues. We first compared the effects of radiation on clonogenic survival and tube formation of endothelial cells, and then investigated the molecular signaling pathways involved in endothelial cell survival and angiogenesis. Among the different endothelial cells studied, human hepatic sinusoidal endothelial cells (HHSECs) were the most radio-resistant and human dermal microvascular endothelial cells were the most radio-sensitive. The radio-resistance of HHSECs was related to adenosine monophosphate-activated protein kinase and p38 mitogen-activated protein kinase-mediated expression of MMP-2 and VEGFR-2, whereas the increased radio-sensitivity of HDMECs was related to extracellular signal-regulated kinase-mediated generation of angiostatin. These observations demonstrate that there are distinct differences in the radiation responses of normal endothelial cells obtained from diverse organs, which may provide important clues for protection of normal tissue from radiation exposure.

[Fibrinolysis components and angiogenesis regulation by example of burn-induced corneal neovascularization in rabbits]

Increased plasminogen level in tear fluid was found within 28 days and increased plasmin activity in 1-3 and 21 days after alkali burn of cornea, this is the time of cornel ulcers development. Increased plasminogen level and plasmin activity in cornea, conjunctiva and intraocular fluid was found in three days after trauma. Subconjunctival injections of angiostatin K1-4,5 (a product of plasminogen metabolism) during 3 weeks resulted in significant suppression of corneal neovascularization within 14 days and of active branching of the vessels in the following. The use of angiostatin reduced depth and area of corneal ulcers. Obtained data shows the promising potential of development of medications based on angiostatin K1-4,5 for suppression of corneal neovascularization and for treatment of diseases associated with corneal ulceration.

Mitochondrial division/mitophagy inhibitor (Mdivi) ameliorates pressure overload induced heart failure

BACKGROUND

We have previously reported the role of anti-angiogenic factors in inducing the transition from compensatory cardiac hypertrophy to heart failure and the significance of MMP-9 and TIMP-3 in promoting this process during pressure overload hemodynamic stress. Several studies reported the evidence of cardiac autophagy, involving removal of cellular organelles like mitochondria (mitophagy), peroxisomes etc., in the pathogenesis of heart failure. However, little is known regarding the therapeutic role of mitochondrial division inhibitor (Mdivi) in the pressure overload induced heart failure. We hypothesize that treatment with mitochondrial division inhibitor (Mdivi) inhibits abnormal mitophagy in a pressure overload heart and thus ameliorates heart failure condition.

MATERIALS AND METHODS

To verify this, ascending aortic banding was done in wild type mice to create pressure overload induced heart failure and then treated with Mdivi and compared with vehicle treated controls.

RESULTS

Expression of MMP-2, vascular endothelial growth factor, CD31, was increased, while expression of anti angiogenic factors like endostatin and angiostatin along with MMP-9, TIMP-3 was reduced in Mdivi treated AB 8 weeks mice compared to vehicle treated controls. Expression of mitophagy markers like LC3 and p62 was decreased in Mdivi treated mice compared to controls. Cardiac functional status assessed by echocardiography showed improvement and there is also a decrease in the deposition of fibrosis in Mdivi treated mice compared to controls.

CONCLUSION

Above results suggest that Mdivi inhibits the abnormal cardiac mitophagy response during sustained pressure overload stress and propose the novel therapeutic role of Mdivi in ameliorating heart failure.

Angiostatins decrease in the kidney of newborn piglets after hypoxia-reoxygenation

Little is known about the expression of kidney angiostatin in the hypoxia and reoxygenation of neonates. In this study, we compared the effect of 21% and 100% reoxygenation on kidney levels of angiostatin and its related factors in newborn piglets subjected to hypoxia-reoxygenation. Newborn piglets were subjected to 2h hypoxia followed by 1h of reoxygenation with either 21% or 100% oxygen and observed for 4days. There were 3 isoforms (38, 43 and 50kDa) of angiostatins identified in the kidney tissue of newborn piglets with the 38kDa being the major isoform (~60%). The 38kDa, but not 43 and 50kDa, angiostatin isoform correlated significantly with the levels of total angiostatin and plasminogen (r=0.95 and r=0.58, respectively). On day 4 of recovery in 100% hypoxic-reoxygenated group, there were decreases in kidney tissue levels of plasminogen, total angiostatin, angiostatin (38 and 43kDa, but not 50kDa), whereas no significant changes were found in the 21% hypoxic-reoxygenated group when compared to the sham-operated piglets with no hypoxia-reoxygenation. Both 21% and 100% hypoxic-reoxygenated groups did not show significant changes in kidney tissue levels of 50kDa angiostatin, MMP-2, MMP-9 and HIF-1alpha. In comparison to 21% oxygen, neonatal resuscitation with 100% oxygen decreased the kidney tissue levels of plasminogen and angiostatin that may play a role in neonatal kidney injury and altered renal development in adulthood.

Anti-angiogenic effect of high-dose resveratrol in a swine model of metabolic syndrome

BACKGROUND

Resveratrol has been reported to induce angiogenesis in ischemic tissue. We hypothesized that high-dose resveratrol would improve native angiogenesis in a swine model of metabolic syndrome and chronic myocardial ischemia.

METHODS

Yorkshire swine were fed a normal diet (Control, n = 7), hypercholesterolemic diet (HCD, n = 7), or hypercholesterolemic diet with supplemental resveratrol (100 mg/kg/day orally, HCD-R; n = 7) beginning 1 month prior to surgery. Chronic ischemia was created by placing an ameroid constrictor on the left circumflex coronary artery. After 7 weeks, swine underwent functional MRI, coronary angiography, and serum and heart tissue harvest for analysis.

RESULTS

HCD-R animals had lower body mass index (P < .001), total cholesterol (P < .001), low-density lipoprotein (LDL; P < .001), blood glucose levels (P < .001), and systolic blood pressure (P = .03) than HCD animals. There was no difference in regional myocardial function at 7 weeks (P = .25). Coronary angiograms revealed no difference in Rentrop collateral scores (P = .68). Staining for platelet endothelial cell adhesion molecule-1 demonstrated higher capillary density in the Control group (versus HCD and HCD-R; P = .02). Immunoblotting demonstrated decreased expression of the pro-angiogenic protein vascular endothelial (VE)-cadherin (P = .002) and an increase in anti-angiogenic proteins angiostatin (P = .001) and thrombospondin (P = .02) in the HCD and HCD-R groups. Matrix metalloprotease 2 (MMP 2; P = .47) and MMP 9 (P = .12) were not different among groups.

CONCLUSION

Supplemental resveratrol positively modified cardiovascular risk factors including body mass index, cholesterol, glucose tolerance, and systolic blood pressure. However, it did not increase native collateral formation in the ischemic myocardium. This may be a result of increased angiostatin and thrombospondin leading to decreased expression of VE-cadherin and other pro-angiogenic factors.

[Observation of the changes in ventral prostatic microcirculation in castrated rats]

OBJECTIVE

Castrated rats exhibit significant shrinkage of the ventral prostate and apoptosis of prostatic cells, which can be attributed to the reduced blood supply to the prostate. But what causes the blood decrease in the prostate remains unknown. This study aims to explore the molecular mechanism of the changes in the microcirculation of the ventral prostate of rats following castration.

METHODS

We randomized 24 male adult rats into 6 groups of equal number, and collected their ventral prostates at 0, 1/2, 1, 2, 3 and 7 d, respectively, after castration. Then we observed the changes of the microvessels under the transmission electron microscope, detected the apoptosis of endothelial cells by TUNEL, and determined the expressions of VEGF, endostatin, angiostatin and angiopoietin-2 by Western blot.

RESULTS

The castrated rats showed dramatic changes in the microvessels of the ventral prostate, obvious apoptosis of the endothelial cells, down-regulated expression of VEGF, and up-regulated expressions of endostatin and angiostatin, while angiopoietin-2 remained unchanged.

CONCLUSION

The decreased level of VEGF and increased levels of endostatin and angiostatin might underlie the mechanism of the changes in the microcirculation of the ventral prostate of rats following castration.

[The cloning expression, purification and activity of human angiostatin K (1-3) gene]

OBJECTIVE

To clone the sequence of human Angiostatin cDNA and obtain the protein of recombinant angiostatin for further development.

METHODS

Fresh human liver tissue was used for the extraction of total RNA and amplified the Angiostatin cDNA through RT-PCR method . After the recombinant plasmid pET30a-Angiostatin was constructed and confirmed, it was transduced into Rosetta (DE3). Then the transformation was used for fermentation and induced expression. The protein was identified by Western Blot and purified by Ni-NTA affinity chromatography.

RESULTS

The sequence of human Angiostatin cDNA was identical with genebank. Angiostatin (K1-3) was expressed and purified. The target protein made up 30% of the total bacterial protein. The purity is above 90%.

CONCLUSION

Angiostatin K (1-3) can be reached using fusion vector pET30a. The product have the biological activity.

Expression of angiogenesis inhibitors in human bladder cancer may explain rapid metastatic progression after radical cystectomy

Angiogenesis is essential for tumor growth and progression. It has been demonstrated that the expression of angiogenesis stimulators (e.g. basic fibroblast growth factor and vascular endothelial growth factor) correlates to tumor progression in various human tumor types. Furthermore, endogenous angiogenesis inhibitors (e.g. angiostatin and endostatin) have been isolated from human tumor models and have been successfully used to treat tumors in mice and humans. In the present study, the expression of angiostatin, endostatin and thrombospondin-1 in four different human bladder cancer cell lines with different tumorigenic potential (MGH-U4, RT-4, RT-112 and UMUC-3) were investigated. A subset of bladder carcinoma patients demonstrates rapid metastatic progression after removal of the primary tumor, although no evidence of metastasis is diagnosed before the surgical procedure. A potential mechanism to explain this phenomenon is suggested. Angiostatin, endostatin and thrombospondin-1 was detected in the conditioned media of four human bladder cancer cell lines using Western blotting. Angiostatin was purified and amino acid sequenced via mass spectrometry. The biological activity of angiostatin was determined by proliferation assays using endothelial cells, smooth muscle cells and fibroblasts. Tumor characteristics of the four human bladder carcinoma models were investigated in vitro and in vivo. All the bladder carcinoma cell lines employed in this study produced two biologically active variants of the angiostatin molecule (38 and 49 kDa). Endostatin and thrombospondin-1 were only produced by the low malignancy MGH-U4 and RT-4 bladder carcinoma models. This study identified the expression of different antiangiogenic molecules in human bladder carcinoma. The expression of antiangiogenic molecules seems to be a characteristic of low malignancy bladder carcinomas. The sudden lack of expression of antiangiogenic molecules as a consequence of surgical removal of highly malignant bladder carcinomas may explain the rapid metastatic progression of a subset of bladder carcinomas.

Angiostatin overexpression is associated with an improvement in chronic kidney injury by an anti-inflammatory mechanism

Angiostatin, a proteolytic fragment of plasminogen, is a potent anti-angiogenic factor recently shown also to have an inhibitory effect on leukocyte recruitment and macrophage migration. Because both angiogenesis and inflammation play key roles in the progression of chronic kidney disease, we evaluated the effect of angiostatin treatment in the rat remnant kidney model. Rats were pretreated for 4 wk with recombinant adeno-associated viruses expressing either angiostatin or green fluorescence protein. Chronic renal disease was then induced by a subtotal nephrectomy, and rats were killed 8 wk later for analysis. Angiostatin treatment was associated with significantly less proteinuria but no alterations in serum creatinine, creatinine clearance, and blood urea nitrogen levels. Treatment with angiostatin reduced renal peritubular capillary number and decreased urinary nitric oxide levels. Despite reducing capillary density, angiostatin diminished interstitial fibrosis in association with reduced macrophage and T-cell infiltration and renal monocyte chemoattractant protein-1 mRNA levels. In conclusion, angiostatin overexpression was associated with attenuated renal disease progression in a model of chronic kidney injury, likely because of its anti-inflammatory actions. However, its anti-angiogenic actions suggest countering effects that could partially offset its benefit in chronic kidney diseases.

No evidence for vasculogenesis regulation by angiostatin during mouse embryonic stem cell differentiation

During embryogenesis, the formation of blood vessels proceeds by both vasculogenesis and angiogenesis. Both processes appear to be finely regulated. To date, factors and genes involved in the negative regulation of embryonic vasculogenesis remain largely unknown. Angiostatin is a proteolytic fragment of plasminogen that acts as an inhibitor of angiogenesis. In this study, we analyzed the potential role of angiostatin during early stages of embryonic stem (ES) cell endothelial in vitro differentiation, as a model of vasculogenesis. We found an early expression of the known angiostatin binding sites (angiomotin, alphav integrin and c-met oncogene) during ES cell differentiation. Nevertheless, we did not detect any significant effect of angiostatin on mesoderm induction and on differentiation commitment into cells of the endothelial lineage. In both control and angiostatin-treated conditions, the temporal and extent of formation of the Flk1 positive and Flk-1/CD31 (PECAM-1) positive cell populations were not significantly different. Quantitative RT-PCR experiments of endothelial gene expression (Flk-1, PECAM-1 and tie-2) confirm a lack of interference with early steps of endothelial differentiation in embryoid bodies. No evidence for an angiostatin effect on endothelial cord-like formation could be detected at later differentiation stages. On the other hand, angiostatin inhibits vascular endothelial growth factor-induced endothelial sprouting from embryoid bodies cultured in three dimensional type I collagen gels. Taken together, these findings support a selective inhibitory effect on the sprouting angiogenesis response for angiostatin during embryonic vascular development.

Effects of D-4F on vasodilation, oxidative stress, angiostatin, myocardial inflammation, and angiogenic potential in tight-skin mice

Systemic sclerosis (scleroderma, SSc) is an autoimmune, connective tissue disorder that is characterized by impaired vascular function, increased oxidative stress, inflammation of internal organs, and impaired angiogenesis. Tight skin mice (Tsk−/+) have a defect in fibrillin-1, resulting in replication of many of the myocardial and vascular features seen in humans with SSc. D-4F is an apolipoprotein A-I (apoA-I) mimetic that improves vascular function in diverse diseases such as hypercholesterolemia, influenza, and sickle cell disease. Tsk−/+ mice were treated with either phosphate-buffered saline (PBS) or D-4F (1 mg·kg−1·day−1 for 6–8 wk). Acetylcholine and flow-induced vasodilation were examined in facialis arteries. Proinflammatory HDL (p-HDL) in murine and human plasma samples was determined by the cell-free assay. Angiostatin levels in murine and human plasma samples were determined by Western blot analysis. Hearts were examined for changes in angiostatin and autoantibodies against oxidized phosphotidylcholine (ox-PC). Angiogenic potential in thin sections of murine hearts was assessed by an in vitro vascular endothelial growth factor (VEGF)-induced endothelial cell (EC) tube formation assay. D-4F improved endothelium-, endothelial nitric oxide synthase-dependent, and flow-mediated vasodilation in Tsk−/+ mice. Tsk−/+ mice had higher plasma p-HDL and angiostatin levels than C57BL/6 mice, as did SSc patients compared with healthy control subjects. Tsk−/+ mice also had higher triglycerides than C57BL/6 mice. D-4F reduced p-HDL, angiostatin, and triglycerides in the plasma of Tsk−/+ mice. Tsk−/+ hearts contained notably higher levels of angiostatin and autoantibodies against ox-PC than those of control hearts. D-4F ablated angiostatin in Tsk−/+ hearts and reduced autoantibodies against ox-PC by >50% when compared with hearts from untreated Tsk−/+ mice. Angiogenic potential in Tsk−/+ hearts was increased only when the Tsk−/+ mice were treated with D-4F (1 mg·kg−1·day−1, 6–8 wk), and cultured sections of hearts from the D-4F-treated Tsk−/+ micewere incubated with D-4F (10 μg/ml, 5–7 days). Failure to treat the thin sections of hearts and Tsk−/+ mice with D-4F resulted in loss of VEGF-induced EC tube formation. D-4F improves vascular function, decreases myocardial inflammation, and restores angiogenic potential in the hearts of Tsk−/+ mice. As SSc patients have increased plasma p-HDL and angiostatin levels similar to the Tsk−/+ mice, D-4F may be effective at treating vascular complications in patients with SSc.

Angiostatin-like activity of a monoclonal antibody to the catalytic subunit of F1F0 ATP synthase

The antiangiogenic protein angiostatin inhibits ATP synthase on the endothelial cell surface, blocking cellular proliferation. To examine the specificity of this interaction, we generated monoclonal antibodies (mAb) directed against ATP synthase. mAb directed against the beta-catalytic subunit of ATP synthase (MAb3D5AB1) inhibits the activity of the F(1) domain of ATP synthase and recognizes the catalytic beta-subunit of ATP synthase. We located the antibody recognition site of MAb3D5AB1 in domains containing the active site of the beta-subunit. MAb3D5AB1 also binds to purified Escherichia coli F(1) with an affinity 25-fold higher than the affinity of angiostatin for this protein. MAb3D5AB1 inhibits the hydrolytic activity of F(1) ATP synthase at lower concentrations than angiostatin. Like angiostatin, MAb3D5AB1 inhibits ATP generation by ATP synthase on the endothelial cell surface in acidic conditions, the typical tumor microenvironment where cell surface ATP synthase exhibits greater activity. MAb3D5AB1 disrupts tube formation and decreases intracellular pH in endothelial cells exposed to low extracellular pH. Neither angiostatin nor MAb3D5AB1 showed an antiangiogenic effect in the corneal neovascularization assay; however, both were effective in the low-pH environment of the chicken chorioallantoic membrane assay. Thus, MAb3D5AB1 shows angiostatin-like properties superior to angiostatin and may be exploited in cancer chemotherapy.

Rapamycin-regulated control of antiangiogenic tumor therapy following rAAV-mediated gene transfer

Regulated gene expression may be required for the clinical development of certain gene therapies. Several approaches have been developed that allow pharmacologic control of transgene expression, including the dimerizer-regulated transcriptional system in which rapamycin or its analogs function as transcriptional inducers. These compounds can also act as direct antitumor agents via inhibition of mammalian target of rapamycin (mTOR). We describe the development of an optimized recombinant adeno-associated virus (AAV) expression cassette that allows dimerizer-regulated gene expression from a single vector in vitro and in vivo. After demonstrating multiple cycles of rapamycin-dependent transgene induction following a single administration of an AAV vector in vivo, application of this regulated AAV gene expression system to the pharmacologic control of antiangiogenic therapy was evaluated in preclinical tumor models. Dimerizer-regulated vectors were constructed encoding a soluble inhibitor of the vascular endothelial growth factor (VEGF) pathway. In two subcutaneous models of glioblastoma, regulated expression of the VEGF inhibitor via recombinant AAV-mediated gene transfer, in combination with rapamycin, was shown to decrease tumor growth rate significantly. The dual properties of rapamycin--as a transcriptional inducer and mTOR inhibitor--are exploited in combination with an AAV-encoded antiangiogenic agent to provide a novel approach for the treatment of malignant diseases.

Hierarchical mechanochemical switches in angiostatin

We wish to propose a novel mechanism by which the triggering of a biochemical signal can be controlled by the hierarchical coupling between a protein redox equilibrium and an external mechanical force. We have characterized this mechanochemical mechanism in angiostatin, and we have evidence that it can switch the access to partially unfolded structures of this protein. We have identified a metastable intermediate that is specifically accessible under thioredoxin-rich reducing conditions, like those met by angiostatin on the surface of a tumor cell. The structure of the same intermediate accounts for the unexplained antiangiogenic activity of angiostatin. These findings demonstrate a new link between redox biology and mechanically regulated processes.

Plasminogen and angiostatin interact with heat shock proteins

Previous studies from this laboratory have demonstrated that plasminogen and angiostatin bind to endothelial cell (EC) surface-associated actin via their kringles in a specific manner. Heat shock proteins (hsps) like hsp 27 are constitutively expressed by vascular ECs and regulate actin polymerization, cell growth, and migration. Since many hsps have also been found to be highly abundant on cell surfaces and there is evidence that bacterial surface hsps may interact with human plasminogen, the purpose of this study was to determine whether human plasminogen and angiostatin would interact with human hsps. ELISAs were developed in our laboratory to assess these interactions. It was observed that plasminogen bound to hsps 27, 60, and 70. In all cases, binding was inhibited (85-90%) by excess (50 mM) lysine indicating kringle involvement. Angiostatin predominantly bound to hsp 27 and to hsp 70 in a concentration- and kringle-dependent manner. As observed previously for actin, there was concentration-dependent inhibition of angiostatin's interaction with hsp 27 by plasminogen. In addition, 30-fold molar excess actin inhibited (up to 50%), the interaction of plasminogen with all hsps. However, 30-fold molar excess actin could only inhibit the interaction of angiostatin with hsp 27 by 15-20%. Collectively, these data indicate that (i) while plasminogen interacts specifically with hsp 27, 60, and 70, angiostatin interacts predominantly with hsp 27 and to some extent with hsp 70; (ii) plasminogen only partially displaces angiostatin's binding to hsp 27 and (iii) actin only partially displaces plasminogen/angiostatin binding to hsps. It is conceivable therefore that surface-associated hsps could mediate the binding of these ligands to cells like ECs.

Altered angiogenic balance in ulcerative colitis: a key to impaired healing?

Angiogenesis is an essential component of ulcer healing since it assures delivery of oxygen and nutrients to the healing site. Previous studies demonstrated increased serum and tissue levels of vascular endothelial growth factor (VEGF, the most potent angiogenic growth factor) in patients with active ulcerative colitis (UC) and animal models of UC. However, there is no explanation why the healing of UC-related mucosal injury is impaired despite increased expression of VEGF. Expression of angiogenesis inhibitors, angiostatin and/or endostatin, in UC has not been determined before. We examined expression of VEGF, angiostatin, and endostatin in two models of experimental UC. The results revealed that in addition to increased VEGF, both endostatin and angiostatin levels were markedly (2-3-folds) increased in colonic mucosa at early stage of experimental UC. This is the first demonstration that colitis triggers increase in angiostatin and endostatin levels. The results may explain why mucosal lesions heal slowly despite increased VEGF levels, and may provide a novel and mechanistic insight into UC.

X-ray crystallographic structure of the angiogenesis inhibitor, angiostatin, bound to a peptide from the group A streptococcal surface protein PAM

The crystal structure of the human Pg-derived angiogenesis inhibitor, angiostatin, complexed to VEK-30, a peptide from the group A streptococcal surface protein, PAM, was determined and refined to 2.3 A resolution. This is the first structure of angiostatin bound to a ligand and provides a model of the interaction between Pg and streptococcal-derived pathogenic proteins. VEK-30 contains a "through-space isostere" for C-terminal lysine, wherein Arg and Glu side chains, separated by one helical turn, bind within the bipolar angiostatin kringle 2 (K2) domain lysine-binding site. VEK-30 also makes several contacts with K2 residues that exist outside of the canonical LBS and are not conserved among the other Pg kringles, thus providing a molecular basis for the selectivity of VEK-30 for K2. The structure also shows that Pg kringle domains undergo significant structural rearrangement relative to one another and reveals dimerization between two molecules of angiostatin and VEK-30 related by crystallographic symmetry. This dimerization, which exists only in the crystal structure, is consistent with the parallel coiled-coil full-length PAM dimer expected from sequence similarities and homology modeling.

Diverse signaling pathways through the SDF-1/CXCR4 chemokine axis in prostate cancer cell lines leads to altered patterns of cytokine secretion and angiogenesis

The establishment of metastatic bone lesions in prostate cancer (CaP) is a process partially dependent on angiogenesis. Previously we demonstrated that the stromal-derived factor-1 (SDF-1 or CXCL12)/CXCR4 chemokine axis is critical for CaP cell metastasis. In this investigation, cell lines were established in which CXCR4 expression was knocked down using siRNA technology. When CaP cells were co-transplanted with human vascular endothelial cells into SCID mice, significantly fewer human blood vessels were observed paralleling the reductions in CXCR4 levels. Likewise, the invasive behaviors of the CaP cells were inhibited in vitro. From these functional observations we explored angiogenic and signaling mechanisms generated following SDF-1 binding to CXCR4. Differential activation of the MEK/ERK and PI3K/AKT pathways that result in differential secretion IL-6, IL-8, TIMP-2 and VEGF were seen contingent on the cell type examined; VEGF and TIMP-2 expression in PC3 cells are dependent on AKT activation and ERK activation in LNCaP and LNCaP C4-2B cells leads to IL-6 or IL-8 secretion. At the same time, expression of angiostatin levels were inversely related to CXCR4 levels, and inhibited by SDF-1 stimulation. These data link the SDF-1/CXCR4 pathway to changes in angiogenic cytokines by different signaling mechanisms and, suggest that the delicate equilibrium between proangiogenic and antiangiogenic factors may be achieved by different signal transduction pathways to regulate the angiogenic phenotype of prostate cancers. Taken together, our results provide new information regarding expression of functional CXCR4 receptor-an essential role and potential mechanism of angiogenesis upon SDF-1 stimulation.

Differential binding of plasminogen, plasmin, and angiostatin4.5 to cell surface beta-actin: implications for cancer-mediated angiogenesis

Angiostatin4.5 (AS4.5) is the product of plasmin autoproteolysis and consists of kringles 1 to 4 and approximately 85% of kringle 5. In culture, cancer cell surface globular beta-actin mediates plasmin autoproteolysis to AS4.5. We now show that plasminogen binds to prostate cancer cells and that the binding colocalizes with surface beta-actin, but AS4.5 does not bind to the cell surface. Plasminogen and plasmin bind to immobilized beta-actin similarly, with a Kd of approximately 140 nmol/L. The binding is inhibited by epsilon-aminocaproic acid (epsilonACA), indicating the requirement for a lysine-kringle domain interaction. Using a series of peptides derived from beta-actin in competitive binding studies, we show that the domain necessary for plasminogen binding is within amino acids 55 to 69 (GDEAQSKRGILTLKY). Substitution of Lys61 or Lys68 with arginine results in the loss of the ability of the peptide to block plasminogen binding, indicating that Lys61 and Lys68 are essential for plasminogen binding. Other actin peptides, including peptides with lysine, did not inhibit the plasminogen-actin interaction. AS4.5 did not bind actin at concentrations up to 40 micromol/L. Plasminogen, plasmin, and AS4.5 all contain kringles 1 to 4; however, kringle 5 is truncated in AS4.5. Isolated kringle 5 binds to actin, suggesting intact kringle 5 is necessary for plasminogen and plasmin to bind to cell surface beta-actin, and the truncated kringle 5 in AS4.5 results in its release from beta-actin. These data may explain the mechanism by which AS4.5 is formed locally on cancer cell surfaces and yet acts on distant sites.

Angiogenesis-associated protein annexin II in breast cancer: selective expression in invasive breast cancer and contribution to tumor invasion and progression

Many advanced human tumors including breast cancer overproduce plasmin that is known to promote angiogenesis and metastasis. The mechanism of this effect is poorly understood. Here we report that annexin II, an endothelial co-receptor for tPA (tissue-type plasminogen activator) and plasminogen, was undetectable in normal and hyperplastic ductal epithelial cells and ductal complexes. By contrast, it was consistently expressed in invasive breast cancer and ductal carcinoma in situ (DCIS) indicating its involvement in breast cancer. Using the well established invasive/metastatic MDA-MB231 cell line and the noninvasive/nonmetastatic MCF-7 human breast cancer cell line, we investigated the mechanism by which annexin II regulates breast cancer progression and metastasis. Western and Northern blot analyses demonstrate selective expression of annexin II in MDA-MB231 cells but not in poorly invasive MCF-7 cells suggesting its participation in invasive breast cancer. Since annexin II is a receptor for plasminogen, we tested whether MDA-MB231 cells are capable of producing plasmin in vitro. MDA-MB231 cell membranes induced plasmin generation in a time-dependent manner while those from MCF-7 cells failed to convert plasminogen to plasmin. The generated plasmin is capable of degrading ECM consequently facilitating cell invasion and migration, biological functions required for angiogenesis and metastasis. Plasmin generation and its dependent invasion and migration can be blocked by a monoclonal antibody to annexin II or angiostatin, potent inhibitors of angiogenesis, breast cancer, and metastasis. Our findings indicate that annexin II-dependent localized plasmin generation by human breast cancer cells could contribute to angiogenesis and metastasis. These results suggest that annexin II may be an attractive target for new anti-angiogenic and anti-breast cancer therapies.

Anti-angiogenesis mediated by angiostatin K1-3, K1-4 and K1-4.5. Involvement of p53, FasL, AKT and mRNA deregulation

The molecular mechanism mediated by multiple forms of angiostatin via acting on proliferating vascular endothelium remains elusive. To address whether three forms of angiostatin, K1-3, K1-4 or K1-4.5, utilized similar or distinct pathways to mediate anti-angiogenesis, we adopted an adenoviral expression system to express secretable angiostatin molecules for CM collection. The anti-angiogenic activity of K1-3, K1-4 or K1-4.5 was confirmed by using proliferation, migration, tube formation and apoptotic assays of human endothelial cells. These angiostatin molecules at comparable expression level inhibited various in vitro angiogenesis assays with some variations. Furthermore, K1-3, K1-4 or K1-4.5 increased the expression of p53 protein and its downstream effectors, enhanced FasL-mediated signaling pathways, and decreased activation of AKT. At least three different receptors, Fas, integrin alpha(v)beta3 and ATP synthase, were involved in the anti-angiogenic action of angiostatin molecules. Besides, the expression of 189 genes at mRNA level was significantly altered by K1-3, K1-4 or K1-4.5. More than 70% of these genes participate in growth, inflammation, apoptosis, migration and extracellular matrix. Taken together, K1-3, K1-4 and K1-4.5, regardless of the number of kringles in the angiostatin molecules, mediated anti-angiogenesis via mostly similar pathways. We are the first to demonstrate the involvement of DAPK1 in the mediation of anti-angiogenesis by angiostatin.

Angiostatin and plasminogen share binding to endothelial cell surface actin

Previous studies from this laboratory have demonstrated that plasminogen binds to endothelial cell surface-associated actin via its kringles in a dose-dependent and specific manner. The purpose of this study was to determine whether angiostatin, a proteolytic fragment of plasminogen, shares binding properties with plasminogen. Our results indicated that like plasminogen, angiostatin bound to actin in a time-, concentration-, and kringle-dependent manner. Furthermore, this binding was significantly inhibited by excess plasminogen, suggesting that both proteins shared binding motifs on the actin molecule. Fluorescence studies demonstrated that angiostatin bound to intact endothelial cells through its kringles, and this binding was also inhibited by plasminogen but not by unrelated proteins. Ligand blot analyses on endothelial cell lysates indicated that angiostatin interacted with a 42 kDa protein, which was identified as actin. Furthermore, an anti-actin antibody inhibited binding of angiostatin to endothelial cells by approximately 25%. These results suggest that angiostatin and plasminogen share binding to endothelial cell surface actin and, therefore, that angiostatin has the potential to inhibit plasmin-dependent processes such as cell migration-movement.

Growth inhibitory effect of triple anti-tumor gene transfer using Semliki Forest virus vector in glioblastoma cells

The gene delivery of multiple tumor suppressors can provide an efficient tumor therapy in the case of malignant human glioblastomas containing multiple genetic alteration and inactivation. As such, the current study presents a new delivery system that can simultaneously express three anti-tumor genes using a Semliki Forest virus (SFV) vector in the expectation of combined or synergistic effects of angiogenesis inhibition by angiostatin and apoptosis induction by p53, PTEN and the rSFV particle itself. Recombinant SFV (rSFV) containing three anti-tumor genes (rSFV-Agt/p53/PTEN) were found to efficiently transduce and express each anti-tumor gene in glioblastoma cells. In addition, rSFV-Agt/p53/PTEN also resulted in a more effective induction of apoptosis in vitro and inhibition of tumor growth in nude mice when compared with other rSFVs containing only one or two anti-tumor genes. Accordingly, the current results demonstrate that a triple anti-tumor gene transfer using an rSFV vector would be a powerful strategy for regional cancer gene therapy.

Angiostatin overexpression in Morris hepatoma results in decreased tumor growth but increased perfusion and vascularization

Growth of malignant tumors is dependent on sufficient blood supply. Thus, inhibition of tumor angiogenesis is emerging as a promising target in the treatment of malignancies. Human angiostatin (hANG) is one of the most potent inhibitors of endothelial cell proliferation, angiogenesis, and tumor growth in vivo. However, its mechanisms operating in vivo are not well understood.

METHODS

To obtain more information about functional changes in the angiogenic process, we established Morris hepatoma (MH3924A) cell lines expressing hANG (hANG-MH3924A). The effects of hANG expression on proliferation and apoptosis of human umbilical vein endothelial cells (HUVECs) were measured in coculture experiments in vitro. To evaluate changes in tumor perfusion and blood volume, H2 15O and 68Ga-DOTA-albumin (DOTA is 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid) were used for PET studies in vivo. Additionally, immunohistologic quantification of vascularization, apoptosis, and proliferation as well as gene array analyses were performed.

RESULTS

Our in vitro experiments demonstrate reduced proliferation and increased apoptosis in HUVECs when being cocultured with hANG-MH3924A. In support, tumor growth of hANG-MH3924A is diminished by 95% in vivo. However, tumor perfusion and blood volume are increased in hANG-MH3924A corresponding to an increased microvessel density. Furthermore, hANG-transfected tumors show changes in expression of genes related to apoptosis, stress, signal transduction, and metabolism.

CONCLUSION

hANG expression leads to inhibition of tumor growth, increased apoptosis, and changes in the expression of multiple genes involved in stress reactions, signal transduction, and apoptosis, which indicates a multifactorial reaction of tumors. An enhanced microvessel density is seen as part of these reactions and is associated with increased perfusion as measured by PET.

Therapeutic potential of angiostatin in diabetic nephropathy

Angiostatin is a proteolytic fragment of plasminogen and a potent angiogenic inhibitor. Previous studies have shown that angiostatin inhibits retinal neovascularization and reduces retinal vascular permeability in diabetic retinopathy. Here, it is reported for the first time that angiostatin is also implicated in diabetic nephropathy (DN). Angiostatin levels are dramatically decreased in the kidney of streptozotocin-induced diabetic rats. Consistently, diabetic kidneys also showed decreased expression and proteolytic activities of matrix metalloproteinase-2, an enzyme that releases angiostatin from plasminogen. Adenovirus-mediated delivery of angiostatin significantly alleviated albuminuria and attenuated the glomerular hypertrophy in diabetic rats. Moreover, angiostatin treatment downregulated the expression of vascular endothelial growth factor and TGF-beta1, two major pathogenic factors of DN, in diabetic kidneys. In cultured human mesangial cells, angiostatin blocked the overexpression of vascular endothelial growth factor and TGF-beta1 that were induced by high glucose while increasing the levels of pigment epithelium-derived factor, an endogenous inhibitor of DN. Moreover, angiostatin effectively inhibited the high-glucose-and TGF-beta1-induced overproduction of proinflammatory factors and extracellular matrix proteins via blockade of the Smad signaling pathway. These findings suggest that the decrease of angiostatin levels in diabetic kidney may contribute to the pathologic changes such as inflammation and fibrosis in DN. Therefore, angiostatin has therapeutic potential in DN as a result of its anti-inflammatory and antifibrosis activities.

Corneal angiogenic privilege: angiogenic and antiangiogenic factors in corneal avascularity, vasculogenesis, and wound healing (an American Ophthalmological Society thesis)

PURPOSE

To determine the molecular basis of corneal avascularity during wound healing and determine the role of angiogenic and antiangiogenic factors in corneal vasculogenesis.

METHODS

The expression of proangiogenic factors (vascular endothelial growth factor [VEGF]; basic fibroblast growth factor [bFGF]; matrix metalloproteinase-2 [MMP-2]; and membrane-type 1-MMP [MT1-MMP]) and antiangiogenic factors (pigment epithelium-derived factor [PEDF]; angiostatin; restin; and endostatin) was analyzed in avascular corneas and in models of corneal neovascularization (bFGF pellet implantation, intrastromal injection of MT1-MMP cDNA, and surgically induced partial limbal deficiency).

RESULTS

Immunohistochemistry demonstrated the presence of antiangiogenic factors (PEDF, angiostatin, restin, and endostatin) and proangiogenic molecules (VEGF, bFGF, MMP-2, and MT1-MMP) in the cornea after wounding. Proangiogenic MMPs were upregulated in stromal fibroblasts in the vicinity of invading vessels following bFGF pellet implantation. Corneal neovascularization (NV) was also induced by intrastromal injection of MT1-MMP naked cDNA in conjunction with de-epithelialization. Partial limbal deficiency (HLD-) resulted in corneal NV in MMP-7 and MMP-3 knockout mice but not in wild type controls.

CONCLUSIONS

Corneal angiogenic privilege is an active process involving the production of antiangiogenic factors to counterbalance the proangiogenic factors (which are upregulated after wound healing even in the absence of new vessels). Our finding that the potent antiangiogenic factors, angiostatin and endostatin, are colocalized with several MMPs during wound healing suggests that MMPs may be involved in the elaboration of these antiangiogenic molecules by proteolytic processing of substrates within the cornea.

Angiostatin's molecular mechanism: aspects of specificity and regulation elucidated

Tumor growth requires the development of new vessels that sprout from pre-existing normal vessels in a process known as "angiogenesis" [Folkman (1971) N Engl J Med 285:1182-1186]. These new vessels arise from local capillaries, arteries, and veins in response to the release of soluble growth factors from the tumor mass, enabling these tumors to grow beyond the diffusion-limited size of approximately 2 mm diameter. Angiostatin, a naturally occurring inhibitor of angiogenesis, was discovered based on its ability to block tumor growth in vivo by inhibiting the formation of new tumor blood vessels [O'Reilly et al. (1994a) Cold Spring Harb Symp Quant Biol 59:471-482]. Angiostatin is a proteolytically derived internal fragment of plasminogen and may contain various members of the five plasminogen "kringle" domains, depending on the exact sites of proteolysis. Different forms of angiostatin have measurably different activities, suggesting that much remains to be elucidated about angiostatin biology. A number of groups have sought to identify the native cell surface binding site(s) for angiostatin, resulting in at least five different binding sites proposed for angiostatin on the surface of endothelial cells (EC). This review will consider the data supporting all of the various reported angiostatin binding sites and will focus particular attention on the angiostatin binding protein identified by our group: F(1)F(O) ATP synthase. There have been several developments in the quest to elucidate the mechanism of action of angiostatin and the regulation of its receptor. The purpose of this review is to describe the highlights of research on the mechanism of action of angiostatin, its' interaction with ATP synthase on the EC surface, modulators of its activity, and issues that should be explored in future research related to angiostatin and other anti-angiogenic agents.

Angiomotin Regulates Endothelial Cell-Cell Junctions and Cell Motility

We have previously identified angiomotin by its ability to bind to and mediate the anti-angiogenic properties of angiostatin. In vivo and in vitro data indicate an essential role of angiomotin in endothelial cell motility. Here we show that angiostatin binds angiomotin on the cell surface and provide evidence for a transmembrane model for the topology of both p80 and p130 angiomotin isoforms. Immunofluorescence analysis shows that angiomotin co-localized with ZO-1 in cell-cell contacts in endothelial cells in vitro and in angiogenic blood vessels of the postnatal mouse retina in vivo. Transfection of p80 as well as p130 angiomotin in Chinese hamster ovary cells resulted in junctional localization of both isoforms. Furthermore, p130 angiomotin could recruit ZO-1 to actin stress fibers. The p130 but not p80 isoform could be coprecipitated with MAGI-1b, a component of endothelial tight junctions. Paracellular permeability, as measured by diffusion of fluorescein isothiocyanate-dextran, was reduced by p80 and p130 angiomotin expression with 70 and 88%, respectively, compared with control. Angiostatin did not have any effect on cell permeability but inhibited the migration of angiomotin-expressing cells in the Boyden chamber assay. We conclude that angiomotin, in addition to controlling cell motility, may play a role in the assembly of endothelial cell-cell junctions.

[Expression and biological activity of human angiogenesis inhibitor angiostatin in insect cells]

BACKGROUND & OBJECTIVE

Angiogenesis is the essential process for tumor growth and metastasis. Angiostatin, a potent endogenous inhibitor of angiogenesis, could selectively inhibit proliferation of vascular endothelial cells. This study was to construct recombinant angiostatin-baculovirus, and explore the expression and biological activity of recombinant angiostatin in insect cells.

METHODS

The angiostatin baculovirus transfer vector pBlueBacHis2B was co-transfected with virus DNA into insect Sf9 cells to construct recombinant baculovirus. The recombinant virus was screened by plaque assay, and confirmed and amplified by polymerase chain reaction (PCR) to produce large scale, high-titer virus stock. The expression of the recombinant protein at different time points was detected by SDS-PAGE and Western blot. The recombinant protein was purified by ProBond purification system. Inhibitory effect of recombinant angiostatin on human umbilical vein endothelial cells (HUVECs) was examined by MTT assay. Its anti-angiogenesis effect was confirmed by in vivo chorioallantoic membrane (CAM) test.

RESULTS

Recombinant angiostatin baculovirus with a high virus titer (2 x 10(8) pfu/ml) was constructed successfully. Recombinant angiostatin (53 ku) was effectively expressed in Sf9 cells, and its pure degree was about 90% of insect cellular total soluble proteins. The recombinant angiostatin obviously inhibited proliferation of endothelial cells with the 50% inhibitory concentration (IC(50)) of 2.3 microg/ml, and remarkably inhibited the growth of vessels in CAM.

CONCLUSIONS

The baculovirus expression system could be used to construct high-titer recombinant angiostatin-virus stock, and highly express the recombinant angiostatin in insect cells. In vitro and in vivo experiments confirmed that angiostatin could inhibit proliferation of vascular endothelial cells.

Angiogenesis in fatal acute Kawasaki disease coronary artery and myocardium

Angiogenesis has been shown to be dysregulated in coronary artery (CA) aneurysms in the chronic phase of Kawasaki disease (KD). Neovascularization may occur in inflammatory-related vascular diseases because many angiogenesis mediators are secreted by inflammatory cells. We hypothesized that inflammation of the acute KD CA aneurysm could lead to dysregulation of angiogenesis mediators and subsequent neovascularization. To investigate this hypothesis, acute fatal KD cardiac tissues were immunostained for angiogenic inducers and inhibitors. Microvessel density was determined and the degree of inflammation assessed. Marked inflammation and angiogenesis were found in acute KD CA aneurysms and myocardium, with the highest microvessel density seen in patients who died 2-3 weeks after onset of the disease. Expression of proangiogenic proteins was higher than expression of inhibitors in KD CA aneurysms and myocardium. Angiogenesis mediators were localized to inflammatory cells in the myointima, adventitia, and myocardium. We conclude that significant neovascularization occurs in acute KD CA aneurysms and myocardium much sooner after onset of the disease than has been previously reported, that multiple angiogenesis factors are involved, and that dysregulation of angiogenesis likely contributes to KD vasculopathy.

Angiostatin is negatively associated with coronary collateral growth in patients with coronary artery disease

Angiostatin, an inhibitor of tumor angiogenesis, is produced by the actions of matrix metalloproteinases (MMP) on plasminogen. Recently, we reported that angiostatin levels are increased in a model of inadequate coronary collateral growth and angiogenesis in response to ischemia, despite high levels of vascular endothelial growth factor (VEGF). We hypothesized that angiostatin levels are negatively associated with collateral formation in patients. Coronary angiograms from 37 patients undergoing coronary bypass surgery were evaluated for the absence of angiographically visible collaterals (Rentrop scores of 0) or the presence of Rentrop classification grade 3 (well developed) collaterals. Pericardial fluid was obtained from each patient during the bypass procedure, and the sample was analyzed for angiostatin, plasminogen, and VEGF (Western analysis) and for combined activities of MMP-2 and MMP-9 (zymographic analysis). In patients with no collaterals, angiostatin level was greater compared with that in patients with well-developed collaterals (3.1 +/- 0.2 vs. 2.3 +/- 0.1 optical density units, P < 0.05). Neither MMP activities nor VEGF levels were different between the two groups of patients. The higher levels of angiostatin in patients with no visible collaterals were reflective of a higher concentration of plasmin/plasminogen (6.2 +/- 0.7 vs. 4.2 +/- 0.5 optical density units, P < 0.05) compared with those in patients with well-developed collateral vessels. Our results support the concept that the growth inhibitor angiostatin may have a negative impact on coronary collateral growth in patients. Perhaps therapies attempting to provoke coronary collateral growth should incorporate approaches to limit or neutralize the effects of growth inhibitors.

Quantitative analysis of vascular endothelial growth factor, microvascular density and their clinicopathologic features in human hepatocellular carcinoma

BACKGROUND

Angiogenesis is known to be essential to the survival, growth, invasion, and metastasis of tumor cells. Vascular endothelial growth factor (VEGF) are an important angiogenic factor regulating tumor angiogenesis, but its significance and tumor pathologic features are unclear in hepatocellular carcinoma (HCC). In the present study, we analyzed expression of tissue VEGF, alteration of microvascular density (MVD) in microvessel angiogenesis, development and metastasis of HCC, and level of serum VEGF in differential diagnosis of benign and malignant liver diseases.

METHODS

Tumor specimens were prospectively collected from HCC patients undergoing resection. Total RNAs were extracted and the expression levels were detected from different parts of HCC tissues. The cellular distributions of VEGF and MVD of liver tumors and their paracancerous and distal cancerous tissues were investigated by streptavidin peroxidase (S-P) immunohistochemistry, respectively. The VEGF levels of circulating blood and hepatoma tissues were measured by enzyme-linked immunosorbent assay.

RESULTS

The incidence of VEGF expression was 63.9% in HCCs (23/36 cases), 78.3% in non-encapsulated HCCs (18/23), and 90.9% in HCCs with extrahepatic metastasis (10/11), respectively. The VEGF expression was tightly correlated with MVD (P<0.01). The MVD in HCC with metastasis, low differentiation or non-encapsulation was significantly higher than that in HCC with intact capsule, high differentiation, or no metastasis. No significant difference was found between VEGF, MVD, tumor size, and hepatitis virus infection. The level of total RNA in HCC tissues was significantly lower but the VEGF level significantly higher than those in paracancerous or distal cancerous ones (P<0.01). The abnormal expression levels of VEGF in sera of HCC patients were directly correlated with the metastasis and recurrence of tumors.

CONCLUSION

The high expression of VEGF and abnormality of tissue MVD are useful predictors for vascular invasion and metastasis of liver tumors.

Bacillolysin MA, a Novel Bacterial Metalloproteinase That Produces Angiostatin-like Fragments from Plasminogen and Activates Protease Zymogens in the Coagulation and Fibrinolysis Systems

We isolated a novel protease that converts plasminogen to angiostatin-like fragments (BL-angiostatins) from a culture of Bacillus megaterium A9542 through a single-step chromatography on CM-cellulose. The protease, designated bacillolysin MA (BL-MA), belongs to a family of neutral metalloproteinases based on the nucleotide sequence of its gene. At an enzyme:substrate ratio of 1:540, BL-MA cleaved human plasminogen mainly at Ser441-Val442 to form BL-angiostatin and miniplasminogen with a K(m) of 3.0 +/- 0.8 microM and a k(cat) of 0.70 +/- 0.09 s(-1). The resulting BL-angiostatins inhibited the proliferation, migration, and tube formation of vascular endothelial cells at concentrations of 1-10 microg/ml. Although BL-MA failed to activate plasminogen, it increased urokinase-catalyzed activation of plasminogen caused by production of miniplasminogen, which is highly susceptible to activation. In addition, BL-MA was active in converting prourokinase, prothrombin, coagulation factor X, and protein C to their active forms. BL-MA enhanced both the clotting of human plasma and clot dissolution in the presence of prourokinase. Thus, BL-MA affects blood coagulation and fibrinolysis systems and can be used to produce angiostatin-like plasminogen fragments and active serine proteases of human plasma.

Combined immunotherapy and antiangiogenic therapy of cancer with microencapsulated cells

An alternative form of gene therapy involves immunoisolation of a nonautologous cell line engineered to secrete a therapeutic product. Encapsulation of these cells in a biocompatible polymer serves to protect these allogeneic cells from host-versus-graft rejection while recombinant products and nutrients are able to pass by diffusion. This strategy was applied to the treatment of cancer with some success by delivering either interleukin 2 or angiostatin. However, as cancer is a complex, multifactorial disease, a multipronged approach is now being developed to attack tumorigenesis via multiple pathways in order to improve treatment efficacy. A combination of immunotherapy with angiostatic therapy was investigated by treating B16-F0/neu melanoma-bearing mice with intraperitoneally implanted, microencapsulated mouse myoblasts (C2C12) genetically modified to deliver angiostatin and an interleukin 2 fusion protein (sFvIL-2). The combination treatment resulted in improved survival, delayed tumor growth, and increased histological indices of antitumor activity (apoptosis and necrosis). In addition to improved efficacy, the combination treatment also ameliorated some of the undesirable side effects from the individual treatments that have led to the previous failure of the single treatments, for example, inflammatory response to IL-2 or vascular mimicry due to angiostatin. In conclusion, the combination of immuno- and antiangiogenic therapies delivered by immunoisolated cells was superior to individual treatments for antitumorigenesis activity, not only because of their known mechanisms of action but also because of unexpected protection against the adverse side effects of the single treatments. Thus, the concept of a "cocktail" strategy, with microencapsulation delivering multiple antitumor recombinant molecules to improve efficacy, is validated.

A multiprong approach to cancer gene therapy by coencapsulated cells

Immune-isolation of nonautologous cells with microencapsulation protects these cells from graft rejection, thus allowing the same recombinant therapeutic cell line to be implanted in different recipients. This approach was successful in treating HER2/neu-expressing tumors in mice by delivering an interleukin-2 fusion protein (sFvIL-2), or angiostatin. However, treatment with interleukin-2 led to profuse inflammation, while angiostatin delivery did not result in long-term tumor suppression, in part due to endothelial cell-independent neovascularization (vascular mimicry). We hypothesize that coencapsulating the two producer cells in the same microcapsules may enhance the efficacy and ameliorate the above side effects. Hence, B16-F0/neu tumor-bearing mice were implanted with sFvIL-2- and angiostatin-secreting cells coencapsulated in the same alginate-poly-L-lysine-alginate microcapsules. However, this protocol only produced an incremental but not synergistic improvement, as measured with greater tumor suppression and improved survival. Compared to the single sFvIL-2 treatment, the coencapsulation protocol showed improved efficacy associated with: mobilization of sFvIL-2 from the spleen; a higher level of cytokine delivery systemically and to the tumors; increased tumor and tumor-associated endothelial cell apoptosis; and a reduced host inflammatory response. However, compared to the single angiostatin treatment, the efficacy was reduced, primarily due to a "bystander" effect in which the angiostatin-secreting cells suffered similar transgene silencing as the coencapsulated cytokine-secreting cells. Nevertheless, the level of "vascular mimicry" of the single angiostatin treatment was significantly reduced. Hence, while there was no synergy in efficacy, an incremental improvement and some reduction in undesirable side effects of inflammation and vascular mimicry were achieved over the single treatments.

Recombinant adeno-associated virus vector expressing angiostatin inhibits preretinal neovascularization in adult rats

Clinically, preretinal neovascularization (PNV) induced by vessel occlusion is one of the leading causes to induce blindness. The present study was designed to determine if a recombinant adeno-associated viral vector expressing mouse angiostatin (rAAV-angiostatin) can inhibit experimental PNV in an adult Sprague-Dawley rat model. rAAV-angiostatin and rAAV-lacZ were delivered by intravitreal injections to the right and left eyes of rats. Transgenetic expression of angiostatin in the retina was determined by reverse-transcriptase polymerase chain reaction (RT-PCR). PNV was established by rose-bengal-assisted laser-induced retinal vein occlusion 21 days after the viral injections. The total number and sizes of the neovascular tufts were analyzed 14 days after venous occlusion using retinal flat mount by fluorescein-isothiocyanate-dextran angiography. Electroretinograms (ERGs) were recorded to study any possibility of retinal toxicity of rAAV-angiostatin 3 months after the injections. Angiostatin gene expression in the retina was detectable by RT-PCR, and ERG analysis showed no reduction of b-waves in the rAAV-angiostatin-injected eyes. The number and size of neovascular tufts were significantly lower in rAAV-angiostatin-injected eyes (p = 0.001) than controls. These findings indicated that rAAV-angiostatin successfully suppressed experimental PNV, and no retinal toxicity of the rAAV-angiostatin injection was observed according to ERG recordings.

Proteomic approach to identify acute phase response-related proteins with low molecular weight in loach skin following injury

Proteome analysis by two-dimensional gel electrophoresis (2-DE) together with mass spectrometry was applied to screen acute phase response (APR)-related proteins with low molecular weight in loach skin following injury. Furthermore, Western blotting and function tests were applied to confirm the results obtained from the proteomic study. Fifteen APR-related proteins with sixteen spots (PLA with two spots) on a 2-DE map were identified in this study. Furthermore, six were known acute phase proteins including galactose-binding lectin (GBL), lysozyme, C3, CD59, double PLA and 50s ribosomal protein; while ATP kinase, zinc finger protein 183, alpha-neurotoxin homology, angiostatin, serine/threonine kinase, metalloproteinase inhibitor, regulator of G-protein 4, cryptdin-9 and disintegrin trigranin were found by our lab to be APR-related proteins. In addition, our results suggest that proteomes with low molecular weight can be characterized by 2-DE with a Tris-tricine system followed by mass spectrometry.

Interacting Partners for Kringle Domains Of Plasminogen: Common Binding With K1 and K5 Domains

We have identified MAZR and Rgl2 as specific interacting partners for kringle domains in angiostatin (K1-4) and K5 using yeast two hybrid screening. Both K1 and K1-4 have strong interaction with MAZR and Rgl2 whereas K5 only binds with Rgl2. No interaction of K2, K3, and K4 with either of these binding proteins was detected. We suggest that a common binding motif may exist near LBS-4 that is required for binding with Rgl2 but not with MAZR.

Myocardial angiogenesis

Coronary angiogenesis and collateral growth are chronic adaptations to myocardial ischemia, which are aimed at restoring coronary blood flow and salvaging myocardium in an ischemic region. Although we have assumed that myriad numbers of growth factors are involving in this adaptation, details in the underlying mechanisms, i.e., number of angiogenic factors, angiostatic factors, their receptors/signaling cascades, interactions/crosstalk among the signaling pathways and receptors, and the time course of expression/function of a particular factor or pathway during the successful adaptation are still unclear; they are, probably, harmonized like a symphony. Although there is as of yet no consensus about the mechanisms and causal factors for these cononary adaptations to ischemia, recent evidence strongly suggests that a balance between growth factors and growth inhibitors is critical. In this review we introduce vascular endothelial growth factor, angiopoietins, and angiostatin, as factors playing pivotal roles in coronary angiogenesis and collateral growth.

N-acetyl-cysteine promotes angiostatin production and vascular collapse in an orthotopic model of breast cancer

The antioxidant N-acetyl-cysteine (NAC) has been shown to be chemopreventive in clinical studies, and in recent studies, has shown promise in preventing tumor progression. Although the effects of NAC on tumorigenesis have been associated with decreased angiogenesis, the mechanism of the anti-angiogenic activity has not been determined. In the following study, we describe a novel mechanism whereby NAC therapy blocks MDA-MB-435 breast carcinoma cell proliferation and metastasis in an in vivo tumorigenic model. Athymic nude mice bearing MDA-MB-435 xenografts were treated with systemic NAC daily for 8 weeks. NAC treatment resulted in endothelial cell apoptosis and reduction of microvascular density within the core of the tumor leading to significant tumor cell apoptosis/necrosis. Angiostatin accumulated in tumors from NAC-treated but not control animals. Additional studies using a vascular endothelial growth factor-dependent chicken chorioallantoic membrane angiogenic assay recapitulated NAC-induced endothelial apoptosis and coordinate production of angiostatin, a potent endothelial apoptotic factor. In vitro studies showed angiostatin was formed in endothelial cultures in a vascular endothelial growth factor- and NAC-dependent manner, a process that requires endothelial cell surface plasminogen activation. These results suggest that systemic NAC therapy promotes anti-angiogenesis through angiostatin production, resulting in endothelial apoptosis and vascular collapse in the tumor.

Expression of angiostatin cDNA in human hepatocellular carcinoma cell line SMMC-7721 and its effect on implanted carcinoma in nude mice

AIM: To transfect murine angiostatin cDNA into human hepatocellular carcinoma cell line SMMC-7721 and to investigate its effects on implanted carcinoma in nude mice.

METHODS: A eukaryotic expression vector of pcDNA3.1-mAST containing murine angiostatin was constructed. Then pcDNA3.1-mAST plasmid was transfected into cell line SMMC-7721 by Lipofectamine. The resistant clone was screened by G418 filtration and identified by RT-PCR and Western blotting. Nude mice were divided into three groups of 10 each. Mice in blank control group were only injected with SMMC-7721 cells. Mice in vector control group were injected with SMMC-7721 cells transfected with pcDNA3.1 (+) vector, whereas mice in angiostatin group were injected with SMMC-7721 cells transfected with pcDNA3.1-mAST plasmid. Volume, mass and microvessel density (MVD) of the tumors in different groups were measured and compared.

RESULTS: Murine angiostatin cDNA was successfully cloned into the eukaryotic expression vector pcDNA3.1 (+). pcDNA3.1-mAST was successfully transfected into SMMC-7721 cell line and showed stable expression in this cell line. No significant difference was observed in the growth speed of SMMC-7721 cells between groups transfected with and without angiostatin cDNA. Tumor volume, mass and MVD in the angiostatin group were significantly lower than those in the blank control group and vector control group (P < 0.01). The inhibitory rate of tumor reached 78.6%. Mass and MVD of the tumors only accounted for 34.6% and 48.9% respectively of those in the blank control group.

CONCLUSION: Angiostatin cDNA could be stably expressed in human hepatocellular carcinoma cell line SMMC-7721 without obvious inhibitory effects on the growth of SMMC-7721 cells. When implanted into nude mice, SMMC-7721 cells transfected with angiostatin cDNA show a decreased tumorigenic capability. It suggests that angiostatin can inhibit tumor growth through its inhibition on angiogenesis in tumors.