Angiogenesis inhibitor endostatin is a distinct component of elastic fibers in vessel walls

Deciphering the focal role of endostatin in Alzheimer's disease

Alzheimer's disease (AD) is a paramount chronic neurodegenerative condition that has been affecting elderly people since the 1900s. It causes memory loss, disorientation, and poor mental function. AD is considered to be one of the most serious problems that dementia sufferers face. Despite extensive investigation, the pathological origin of Alzheimer's disease remains a mystery. The amyloid cascade theory and the vascular hypothesis, which stresses the buildup of Aβ plaques, have dominated research into dementia and aging throughout history. However, research into this task failed to yield the long-awaited therapeutic miracle lead for Alzheimer's disease. Perhaps a hypothetical fragility in the context of Alzheimer's disease was regarded as a state distinct from aging in general, as suggested by the angiogenesis hypothesis, which suggests that old age is one state associated with upregulation of angiogenic growth factors, resulting in decreased microcirculation throughout the body. There has also been evidence that by controlling or inhibiting the components involved in the sequence of events that cause angiogenesis, there is a visible progression in AD patients. In Alzheimer's disease, one such antiangiogenic drug is being used.

Tumor-associated lymphocytes and macrophages are related to stromal elastosis and vascular invasion in breast cancer

The tumor microenvironment plays a critical role in breast cancer progression. Here, we investigated tumor-infiltrating lymphocytes (TILs) and associations with macrophage numbers, tumor stromal elastosis, vascular invasion, and tumor detection mode. We performed a population-based retrospective study using data from The Norwegian Breast Cancer Screening Program in Vestfold County (2004-2009), including 200 screen-detected and 82 interval cancers. The number of TILs (CD45+, CD3+, CD4+, CD8+, and FOXP3+) and tumor-associated macrophages (CD163+) was counted using immunohistochemistry on tissue microarray slides. Lymphatic and blood vessel invasion (LVI and BVI) were recorded using D2-40 and CD31 staining, and the amount of elastosis (high/low) was determined on regular HE-stained slides. High numbers of all TIL subsets were associated with LVI (p ≤ 0.04 for all), and high counts of several TIL subgroups (CD8+, CD45+, and FOXP3+) were associated with BVI (p ≤ 0.04 for all). Increased levels of all TIL subsets, except CD4+, were associated with estrogen receptor-negative tumors (p < 0.001) and high tumor cell proliferation by Ki67 (p < 0.001). Furthermore, high levels of all TIL subsets were associated with high macrophage counts (p < 0.001) and low-grade stromal elastosis (p ≤ 0.02). High counts of CD3+, CD8+, and FOXP3+ TILs were associated with interval detected tumors (p ≤ 0.04 for all). Finally, in the luminal A subgroup, high levels of CD3+ and FOXP3+ TILs were associated with shorter recurrence-free survival, and high counts of FOXP3+ were linked to reduced breast cancer-specific survival. In conclusion, higher levels of different TIL subsets were associated with stromal features such as high macrophage counts (CD163+), presence of vascular invasion, absence of stromal elastosis, as well as increased tumor cell proliferation and interval detection mode. Our findings support a link between immune cells and vascular invasion in more aggressive breast cancer. Notably, presence of TIL subsets showed prognostic value within the luminal A category.

Circulating Vascular Basement Membrane Fragments are Associated with the Diameter of the Abdominal Aorta and Their Expression Pattern is Altered in AAA Tissue

OBJECTIVE

Abdominal aortic aneurysm (AAA) is characterised by enhanced proteolytic activity, and extracellular matrix (ECM) remodelling in the vascular wall. Type IV and XVIII collagen/endostatin are structural proteins in vascular basement membrane (VBM), a specialised ECM structure. Here the association between plasma levels of these collagens with the aortic diameter and expansion rate is studied, and their expression in aortic tissue characterised.

METHODS

This was a retrospective population based cohort study. Type IV and XVIII collagen/endostatin were analysed in plasma by ELISA assay in 615 men, divided into three groups based on the aortic diameter: 1) normal aorta ≤ 25 mm, 2) sub-aneurysmal aorta (SAA) 26-29 mm, and 3) AAA ≥ 30 mm. Follow up data were available for 159 men. The association between collagen levels and aortic diameter at baseline, and with the expansion rate at follow up were analysed in ordinal logistic regression and linear regression models, controlling for common confounding factors. Tissue expression of the collagens was analysed in normal aorta (n = 6) and AAA (n = 6) by immunofluorescence.

RESULTS

Plasma levels of type XVIII collagen/endostatin (136 ng/mL [SD 29] in individuals with a normal aorta diameter, 154 ng/ml [SD 45] in SAA, and 162 ng/ml [SD 46] in AAA; p = .001) and type IV collagen (105 ng/mL [SD 42] normal aorta, 124 ng/ml [SD 46] SAA, and 127 ng/ml [SD 47] AAA; p = .037) were associated with a larger aortic diameter. A significant association was found between the baseline levels of type XVIII/endostatin and the aortic expansion rate (p = .035), but in the multivariable model, only the initial aortic diameter remained significantly associated with expansion (p = .005). Altered expression patterns of both collagens were observed in AAA tissue.

CONCLUSION

Plasma levels of circulating type IV and XVIII collagen/endostatin increase with AAA diameter. The expression pattern of VBM proteins is altered in the aneurysm wall.

Distinct functions of the dual leucine zipper kinase depending on its subcellular localization

The dual leucine zipper kinase DLK induces β-cell apoptosis by inhibiting the transcriptional activity conferred by the β-cell protective transcription factor cAMP response element binding protein CREB. This action might contribute to β-cell loss and ultimately diabetes. Within its kinase domain DLK shares high homology with the mixed lineage kinase (MLK) 3, which is activated by tumor necrosis factor (TNF) α and interleukin (IL)-1β, known prediabetic signals. In the present study, the regulation of DLK in β-cells by these cytokines was investigated. Both, TNFα and IL-1β induced the nuclear translocation of DLK. Mutations within a putative nuclear localization signal (NLS) prevented basal and cytokine-induced nuclear localization of DLK and binding to the importin receptor importin α, thereby demonstrating a functional NLS within DLK. DLK NLS mutants were catalytically active as they phosphorylated their down-stream kinase c-Jun N-terminal kinase to the same extent as DLK wild-type but did neither inhibit CREB-dependent gene transcription nor transcription conferred by the promoter of the anti-apoptotic protein BCL-xL. In addition, the β-cell apoptosis-inducing effect of DLK was severely diminished by mutation of its NLS. In a murine model of prediabetes, enhanced nuclear DLK was found. These data demonstrate that DLK exerts distinct functions, depending on its subcellular localization and thus provide a novel level of regulating DLK action. Furthermore, the prevention of the nuclear localization of DLK as induced by prediabetic signals with consecutive suppression of β-cell apoptosis might constitute a novel target in the therapy of diabetes mellitus.

Breast cancer stromal elastosis is associated with mammography screening detection, low Ki67 expression and favourable prognosis in a population-based study

Background

Mammography screen-detected breast cancers have a better prognosis than predicted from established prognostic markers. A search for additional features that are characteristic for these tumours and their prognosis is needed to reduce overtreatment, a recognized challenge in breast cancer patient management today. Here, we have investigated the occurrence and importance of tumour elastosis.

Methods

We performed a population based retrospective study of breast cancers detected in the Norwegian Breast Cancer Screening Programme in Vestfold County during 2004–2009. In total, 197 invasive screen-detected cancers and 75 interval cancers in patients aged 50–69 years were compared with regard to standard clinico-pathological parameters and tumour shape, as well as ER, PR, HER2 and Ki67 expression. In particular, the presence of elastotic material in tumours was graded on a 4-tiered scale (score 0–3).

Results

Screen-detected cancers had a significantly higher content of stromal elastosis than interval cancers (p < 0.001). High content of elastosis (score 3) correlated strongly with stellate tumour shape, low histological grade, and ER+/HER2- status. Further, high elastosis score was significantly associated with lower Ki67 expression. In survival analyses, cases with high elastosis demonstrated increased recurrence free (p = 0.03) and disease-specific survival (p = 0.11) compared to cases with low elastosis.

Conclusion

There is a strong correlation between the presence of tumour elastosis, stellate tumour shape and mammography detection of breast cancers. To our knowledge, this is the first time elastosis has been studied in relation to breast cancer detection method. Presence of elastosis is associated with low tumour cell proliferation (Ki67) and a good prognosis.

Virtual Slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/13000_2014_230

Study on the role of environmental parameters and HIF-1A gene polymorphism in coronary collateral formation among patients with ischemic heart disease

OBJECTIVES

To evaluate the association between collateral formation and some environmental factors along with a polymorphism in HIF-1A gene in selected Iranian patients with CAD.

DESIGN AND METHODS

Patients with ≥ 70% narrowing in at least one coronary vessel according to coronary angiography were enrolled. The patients' demographic, clinical and biochemical data were collected. The presence of C1772T polymorphisms within HIF-1A was analyzed using the polymerase chain reaction-based restriction fragment length polymorphism (PCR-RFLP).

RESULTS

There is no significant difference between the patients with and without collaterals according to the frequency of T allele or HIF-1A variants. The higher severity of coronary vessel obstruction was positive predictor of collateral formation (OR=1.026, 95%, CI: 1.02-0.04, p<0.001), whereas aging and cigarette smoking were negative predictors (OR=0.95, 95% CI: 0.91-0.99, p<0.05; OR=0.30, 95% CI: 0.11-0.79, p <0.05; respectively).

CONCLUSIONS

The findings indicate not any significant association between collateral formation and polymorphic variants of HIF-1A and P582S substitution does not appear to influence the collateral formation in patients with myocardial ischemia.

Integrin α2-deficient mice provide insights into specific functions of collagen receptors in the kidney

Background

Integrins are important cellular receptors for collagens. Within the glomerulus, podocytes regulate the integrity of the glomerular basement membrane (GBM) by sensing the presence of collagen and regulating collagen IV synthesis. The present study evaluates the role of integrin α2 (ITGA2) in cell-matrix interaction.

Methods and Results

ITGA2-deficient mice had normal renal function but moderate proteinuria and enhanced glomerular and tubulointerstitial matrix deposition. Electron microscopy demonstrated irregular podocyte-matrix interaction, causing pathological protrusions towards the urinary (podocyte) side of the GBM. These characteristic subepithelial bulges mimic the renal phenotype of mice, which are deficient in another collagen receptor, discoidin domain receptor (DDR)1. Using immunogold staining, ITGA2 expression was found to localize to the basolateral site of the podocyte foot processes. ITGA2-deficient mice overexpressed transforming growth factor (TGF)β and connective tissue growth factor (CTGF) compared with wild-type mice. Using in situ hybridization, tubular cells were found to be the primary site of TGFβ synthesis and podocytes the source of CTGF in ITGA2-deficient mice.

Conclusion

These findings support our hypothesis that both these collagen receptors (ITGA2 and DDR1) play a similar role within the kidney. Further, cell-matrix interaction via collagen receptors seems to be crucial for maintenance of normal GBM architecture and function. Targeting collagen receptors such as ITGA2 might be a new form of treatment for progressive fibrotic diseases.

Loss of collagen-receptor DDR1 delays renal fibrosis in hereditary type IV collagen disease

Alport syndrome is a hereditary type IV collagen disease leading to progressive renal fibrosis, hearing loss and ocular changes. End stage renal failure usually develops during adolescence. COL4A3-/- mice serve as an animal model for progressive renal scarring in Alport syndrome. The present study evaluates the role of Discoidin Domain Receptor 1 (DDR1) in cell-matrix interaction involved in pathogenesis of Alport syndrome including renal inflammation and fibrosis. DDR1/COL4A3 Double-knockouts were compared to COL4A3-/- mice with 50% or 100% expression of DDR1, wildtype controls and to DDR1-/- COL4A3+/+ controls for over 6years. Double-knockouts lived 47% longer, mice with 50% DDR1 lived 29% longer and showed improved renal function (reduction in proteinuria and blood urea nitrogen) compared to animals with 100% DDR1 expression. Loss of DDR1 reduced proinflammatory, profibrotic cells via signaling of TGFbeta, CTGF, NFkappaB and IL-6 and decreased deposition of extracellular matrix. Immunogold-staining and in-situ hybridisation identified podocytes as major players in DDR1-mediated fibrosis and inflammation within the kidney. In summary, glomerular epithelial cells (podocytes) express DDR1. Loss of DDR1-expression in the kidney delayed renal fibrosis and inflammation in hereditary type IV collagen disease. This supports our hypothesis that podocyte-matrix interaction via collagen receptors plays an important part in progression of renal fibrosis in Alport disease. The blockade of collagen-receptor DDR1 might serve as an important new therapeutic concept in progressive fibrotic and inflammatory diseases in the future.

The changes in various hydroxyproline fractions in aortic tissue of rabbits are closely related to the progression of atherosclerosis

Background

The most important function of collagen and elastin is to induce several mechanical parameters which are known to play a dominant role in governing mechanical properties of the blood vessels. The aortic tissue of rabbit is one of the important sources of collagen and elastin. The effects of high fat diet (HFD) on the hydroxyproline (Hyp) fractions in serum and aortic tissues of rabbits and collagen content in the aortic tissues of rabbits have not been documented before. The present study was undertaken to investigate the changes in Hyp fractions in serum and aortic tissues of rabbits and collagen content in the aortic tissues of rabbits during the progression of atherosclerosis. The atherosclerotic model used in this study was the New Zealand white rabbit (male; 12 weeks old). Twenty five rabbits were individually caged, and divided into control group (NOR; n = 10) and HFD group (CHO; n = 15). The control group was fed (100 g/day) of normal (NOR) diet for a period of 15 weeks. The HFD group was fed normal diet supplemented with 1.0% cholesterol plus 1.0% olive oil (100 g/day) for the same period of time.

Results

We found that the TC, LDLC, and TG (mg/dl) were significantly (p < 0.001) increased in HFD rabbits compared with control rabbits with percentage normalized changes of 1198%, 1591%, and 710%, respectively. The peptide-bound Hyp in the serum was significantly (P < 0.05) increased in HFD rabbits compared with control rabbits with percentage normalized change of 517% while it significantly (P < 0.01) decreased in aortic tissues of HFD rabbits compared with control rabbits with percentage normalized change of 65%. The protein-bound Hyp in the serum was significantly (P < 0.01) increased in HFD rabbits compared with control rabbits with percentage normalized change of 100%; the protein-bound Hyp in the aortic tissues of control rabbits was 235.30 ± 55.14 (Mean ± SD) while it was not detectable (ND) in HFD rabbits. Total serum Hyp showed no significant (P < 0.05) change in HFD rabbits compared with control rabbits while it was significantly (P < 0.05) decreased in aortic tissues of HFD rabbits compared with control rabbits with percentage normalized change of 73%. The total collagen was significantly (p < 0.01) decreased in aortic tissues of HFD rabbits compared with control rabbits with percentage normalized change of 73% which was supported by histological study.

Conclusions

These results suggest that percentage decrease in various Hyp fractions in aortic tissue of HFD rabbits are closely related to percentage decrease of collagen content in aortic tissues of HFD rabbits. These results also suggest that it may be possible to use the changes in various Hyp fractions in aortic tissues of rabbits as an important risk factor during the progression of atherosclerosis.

Cloning, expression and in vitro evaluation of recombinant canine Tum5, an angiostatic domain of mammalian type IV collagen

The process of new blood vessel formation within and around neoplastic tissue, termed angiogenesis, is a significant factor in the development, progression and metastasis of malignant tumours in all species. A major cause of death in cancer patients is the development of treatment-resistant metastatic disease, which may be avoided by therapies that target the genetically stable population of vascular endothelial cells within tumours. Tumstatin is a small protein formed by the cleavage of the alpha-3 subunit of the non-collagenous domain of mammalian type IV collagen. Recombinant human Tumstatin has been shown to have potent angiostatic properties in vitro and in vivo. Tumstatin is a potent initiator of apoptosis and inhibits the proliferation and migration of vascular endothelial cells in cell culture. Recently, a fragment of Tumstatin, termed Tum5, has been shown to have biologic activity similar to the parent compound. The systemic administration of angiostatic proteins like Tum5 may result in the remission of established tumours, while preventing or delaying the onset of clinically detectable metastasis. Recombinant canine Tum5 (cTum5) was cloned and its protein expression induced in a prokaryotic vector. The resulting cTum5 protein caused dose-dependent inhibition of vascular endothelial cells in vitro, which appears to be mediated through apoptosis.

Endostatin expression in neurons during the early stage of cerebral ischemia is associated with neuronal apoptotic cell death in adult hypertensive rat model of stroke

Endostatin (ES) has been recognized as a potent anti-angiogenic factor. We here investigated the expression of ES in ischemic brain and the consequence of cells expressing ES after stroke in adult stroke-prone renovascular hypertensive rats. A single dose of Ca-074ME, a membrane-permeable cathepsin B (CB) specific inhibitor, or vehicle was given by intraperitoneal injection immediately after distal middle cerebral artery occlusion (dMCAO), ES expression was evaluated using fluorescent immunohistochemistry staining, and CB enzyme activity was tested by measuring the free 7-amino-4-methylcoumarin (AMC) released by CB from its' specific substrate, the Z-Arg-Arg-7-amido-4-methylcoumarin. ES immunoreactivity (IR) was significantly up-regulated as early as 6 h and returned to baseline level at 3 days in peri-infarct area following dMCAO. Double-staining experiment revealed that the majority of ischemia-induced ES positive cells were neurons. Furthermore, ES was co-labeled with CB and Cleaved Caspase-3(Asp175) whereas treatment with Ca-074ME reduced up-regulation of ES expression and attenuated apoptosis in peri-infarct neurons. Collectively, our data suggest that peri-infarct neurons express ES during the early stage of cerebral ischemia and treatment with Ca-074ME attenuates ES expression and apoptosis in peri-infarct neurons.

The first draft of the endostatin interaction network

Endostatin is a C-terminal proteolytic fragment of collagen XVIII that is localized in vascular basement membrane zones in various organs. It binds to heparin/heparan sulfate and to a number of proteins, but its molecular mechanisms of action are not fully elucidated. We have used surface plasmon resonance (SPR) arrays to identify new partners of endostatin, and to give further insights on its molecular mechanism of action. New partners of endostatin include glycosaminoglycans (chondroitin and dermatan sulfate), matricellular proteins (thrombospondin-1 and SPARC), collagens (I, IV, and VI), the amyloid peptide Abeta-(1-42), and transglutaminase-2. The biological functions of the endostatin network involve a number of extracellular proteins containing epidermal growth factor and epidermal growth factor-like domains, and able to bind calcium. Depending on the trigger event, and on the availability of its members in a given tissue at a given time, the endostatin network might be involved either in the control of angiogenesis, and tumor growth, or in neurogenesis and neurodegenerative diseases.

A synaptic nidogen: developmental regulation and role of nidogen-2 at the neuromuscular junction

Background

The skeletal neuromuscular junction is a useful model for elucidating mechanisms that regulate synaptogenesis. Developmentally important intercellular interactions at the neuromuscular junction are mediated by the synaptic portion of a basal lamina that completely ensheaths each muscle fiber. Basal laminas in general are composed of four main types of glycosylated proteins: laminins, collagens IV, heparan sulfate proteoglycans and nidogens (entactins). The portion of the muscle fiber basal lamina that passes between the motor nerve terminal and postsynaptic membrane has been shown to bear distinct isoforms of the first three of these. For laminins and collagens IV, the proteins are deposited by the muscle; a synaptic proteoglycan, z-agrin, is deposited by the nerve. In each case, the synaptic isoform plays key roles in organizing the neuromuscular junction. Here, we analyze the fourth family, composed of nidogen-1 and -2.

Results

In adult muscle, nidogen-1 is present throughout muscle fiber basal lamina, while nidogen-2 is concentrated at synapses. Nidogen-2 is initially present throughout muscle basal lamina, but is lost from extrasynaptic regions during the first three postnatal weeks. Neuromuscular junctions in mutant mice lacking nidogen-2 appear normal at birth, but become topologically abnormal as they mature. Synaptic laminins, collagens IV and heparan sulfate proteoglycans persist in the absence of nidogen-2, suggesting the phenotype is not secondary to a general defect in the integrity of synaptic basal lamina. Further genetic studies suggest that synaptic localization of each of the four families of synaptic basal lamina components is independent of the other three.

Conclusion

All four core components of the basal lamina have synaptically enriched isoforms. Together, they form a highly specialized synaptic cleft material. Individually, they play distinct roles in the formation, maturation and maintenance of the neuromuscular junction.

Coexpression of osteogenic and adipogenic differentiation markers in selected subpopulations of primary human mesenchymal progenitor cells

Knowledge of the basic mechanisms controlling osteogenesis and adipogenesis might provide new insights into the prevention of osteoporosis and age-related osteopenia. With the help of magnetic cell sorting and fluorescence activated cell sorting (FACS), osteoblastic subpopulations of mesenchymal progenitor cells were characterized. Alkaline phosphatase (AP) negative cells expressed low levels of osteoblastic and adipocytic markers. AP positive cells expressed adipocytic markers more strongly than the AP negative cell populations, thus suggesting that committed osteoblasts exhibit a greater adipogenic potential. AP negative cells differentiated to the mature osteoblastic phenotype, as demonstrated by increased AP-activity and osteocalcin secretion under standard osteogenic culture conditions. Surprisingly, this was accompanied by increased expression of adipocytic gene markers such as peroxisome proliferator-activated receptor-gamma2, lipoprotein lipase and fatty acid binding protein. The induction of adipogenic markers was suppressed by transforming growth factor-beta1 (TGF-beta1) and promoted by bone morphogenetic protein 2 (BMP-2). Osteogenic culture conditions including BMP-2 induced both the formation of mineralized nodules and cytoplasmic lipid vacuoles. Upon immunogold electron microscopic analysis, osteoblastic and adipogenic marker proteins were detectable in the same cell. Our results suggest that osteogenic and adipogenic differentiation in human mesenchymal progenitor cells might not be exclusively reciprocal, but rather, a parallel event until late during osteoblast development.

Nidogens-Extracellular matrix linker molecules

Nidogens/entactins are a family of highly conserved, sulfated glycoproteins. Biochemical studies have implicated them as having a major structural role in the basement membrane. However despite being ubiquitous components of this specialized extracellular matrix and having a wide spectrum of binding partners, genetic analysis has shown that they are not required for the overall architecture of the basement membrane. Rather in development they play an important role in its stabilization especially in tissues undergoing rapid growth or turnover. Nidogen breakdown has been implicated as a key event in the basement membrane degradation occurring in mammary gland involution. A number of studies, most compellingly those in C. elegans, demonstrated that nidogens may have other nonstructural roles and be involved in axonal pathfinding and synaptic transmission.

Inflammatory angiogenesis in atherogenesis--a double-edged sword

The adventitia and the outer layers of media of an atherosclerosis-prone arterial wall are vascularized by vasa vasorum. Upon growth of an atherosclerotic lesion in the intima, neovascular sprouts originating from the adventitial vasa vasorum enter the lesion, the local proangiogenic micromilieu in the lesion being created by intramural hypoxia, by increased intramural oxidant stress, and by inflammatory cell infiltration (macrophages, T cells and mast cells). The angiogenic factors present in the lesions include various growth factors, chemokines, cytokines, proteinases, and several other factors possessing direct or indirect angiogenic activities, while the current list of antiangiogenic factors is smaller. An imbalance between endogenous inducers and inhibitors of angiogenesis, with a predominance of the former ones, is essential for the development of neovessels during the progression of the lesion. By providing oxygen and nutrients to the cells of atherosclerotic lesions, neovascularization initially tends to prevent cellular death and so contributes to plaque growth and stabilization. However, the inflammatory cells may induce rupture of the fragile neovessels, and so cause intraplaque hemorrhage and ensuing plaque destabilization. Pharmacological inhibition of angiogenesis in atherosclerotic plaques with ensuing inhibition of lesion progression has been achieved in animal models, but clinical studies aiming at regulation of angiogenesis in the atherosclerotic arterial wall can be designed only after we have reached a firm conclusion about the role of angiogenesis at various stages of lesion development--good or bad.

Loss of fibulin-2 expression is associated with breast cancer progression

Fibulin-2, an extracellular matrix protein expressed by normal epithelia, was found to be down-regulated in several breast cancer cell lines. Fibulin-2 protein expression was also decreased in breast cancer tissue samples as evaluated by immunohistochemistry. Reintroduction of Fibulin-2 into breast cancer cell lines that do not express Fibulin-2 reduced cancer cell motility and invasion in vitro but had no effect on cell growth and adhesion properties. Together with evidence that Fibulin-2 contributes to wound healing and inhibits smooth muscle cell migration, our findings suggest that loss of Fibulin-2 expression may facilitate migration and invasion in breast cancer.

Plaque neovascularization and antiangiogenic therapy for atherosclerosis

The concept that neovascularization of the vessel wall may play a fundamental role in the pathophysiology of atherosclerosis was proposed more than a century ago. In recent years, supportive experimental evidence for this hypothesis (such as the finding that neointimal microvessels may increase delivery of cellular and soluble lesion components to the vessel wall) has been underscored by clinical studies associating plaque angiogenesis with more rapidly progressive high-grade disease. Attention has also focused on a possible role for microvessel-derived intraplaque hemorrhage in the development of acute lesion instability. The interest of clinicians in this phenomenon has been spurred by the potential to target vessel wall neovascularization with angiogenesis inhibitors, a therapeutic approach that has been associated with impressive reductions in plaque progression in animal models of vascular disease. The rationale for pursuing an "antiangiogenic" strategy in the treatment of patients with vascular disease, and a framework for further preclinical evaluation of such therapy, is presented here.

Vitreous fluid biomarkers

Interactions between cells and the network of secreted proteins are associated with the ocular disease. In most cases, clinical appearcance is sufficiently diagnostic. However, in cases of nonspecific or atypical clinical presentation, diagnostic sampling of vitreous fluid can aid diagnosis and treatment for ocular disease. Progresses in the basic sciences, particularly molecular biology, and advances in surgical instrumentation have greatly enhanced the diagnostic armamentarium. These developments also have led to a better understanding of the pathophysiological processes involved in ocular diseases and have prompted evolution of new therapeutic modalities. In this chapter, we review techniques for vitreous fluid sampling and biomarker quantitation thereof. The molecular biology of bioactive vitreous fluid factors is also discussed with respect to their clinical involvement in the development of ocular disease.

Angiogenesis in atherosclerosis: gathering evidence beyond speculation

PURPOSE OF REVIEW

The present review summarizes evidence for several functions of neovascularization in plaque growth that sustain perfusion beyond limits of diffusion from the artery lumen and outer adventitial vasa vasorum, deposit proatherogenic plasma molecules, recruit immune cells and progenitors, and promote intraplaque hemorrhage. Recent approvals of antiangiogenesis drugs for clinical use in cancer and macular degeneration improve the feasibility of testing whether such agents inhibit plaque angiogenesis and incidental atherosclerosis.

RECENT FINDINGS

Improvements in large and small animal models of atherosclerosis and knowledge of the molecular regulation of angiogenesis in development and disease have advanced understanding of plaque angiogenesis. Genetic modifications of angiogenesis molecules in mouse strains susceptible to atherosclerosis provide experimental means to identify native molecules that regulate plaque angiogenesis. Studies of plaque angiogenesis are aided by micro-computed tomography techniques that image vasa vasorum anatomy in relation to the atheroma.

SUMMARY

Greater knowledge of plaque angiogenesis regulation is needed to design treatments that target the most critical regulatory pathways. Evolutions in angiogenesis inhibitor treatments for cancer and other diseases call for a need to understand the distinct cardiovascular profiles of different agents to rationally combine agents for optimal selectivity and efficacy in the intended vascular bed.

A new mechanism for prolactin processing into 16K PRL by secreted cathepsin D

Cathepsins are lysosomal enzymes that were shown to release the antiangiogenic fragments 16K prolactin (PRL), endostatin, and angiostatin by processing precursors at acidic pH in vitro. However, the physiological relevance of these findings is questionable because the neutral pH of physiological fluids is not compatible with the acidic conditions required for the proteolytic activity of these enzymes. Here we show that cathepsin D secreted from various tissues is able to process PRL into 16K PRL outside the cell. To specifically target extracellular proteolysis, we used tissues from PRL receptor-deficient mice, which are unable to internalize PRL. As assessed by the use of specific inhibitors of proton extruders, we show that the proteolytic activity of cathepsin D requires local acid secretion driven by Na(+)/H(+) exchangers and H(+)/ATPase. Although it is usually assumed that cathepsin-mediated generation of antiangiogenic peptides occurs in the moderately acidic pericellular milieu found in malignant tumors, we propose a new mechanism explaining the extracellular activity of this acidic protease under physiological pH. Our data support the concept that secreted lysosomal enzymes could be involved in the maintenance of angiogenesis dormancy via the generation of active antiangiogenic peptides in nonpathological contexts.

Serum endostatin and bFGF as predictive factors in advanced breast cancer patients treated with letrozole

INTRODUCTION

To investigate the value of baseline serum levels of VEGF, bFGF, endostatin and their ratio as predictive factors of response to endocrine therapy in patients with metastatic breast cancer (MBC) and positive ER treated with letrozole after tamoxifen failure.

MATERIALS AND METHOD

The serum levels of endostatin, VEGF and bFGF were determined in postmenopausal patients with progressing MBC from serum samples obtained before initiation of letrozole. The relation between serum angiogenic factor levels and TTP was investigated.

RESULTS

Seventy-six patients (45.2%) presented a high endostatin level (> 24.6 ng/ml), 40% low bFGF levels (0 pg/ml) and 50.4% low VEGF (=/< 187 ng/ml). With a median follow-up of 22 months, the median TTP was 12.3 months. Median TTP was worse in patients with high endostatin concentration as well as in the low bFGF group, but was not affected when VEGF was considered. When the two factors were combined, the median TTP of patients with endostatin > 24.6 ng/ml and bFGF equal 0 pg/ml was 9.5 months versus 19.5 months in patients with endostatin =/< 24.6 ng/ml and bFGF > 0 pg/ml.

CONCLUSIONS

The baseline levels of bFGF and endostatin are predictive factors of efficacy in patients with MBC treated with letrozole and can select groups with different TTP.

Enhanced antiangiogenic therapy with antibody-collagen XVIII NC1 domain fusion proteins engineered to exploit matrix remodeling events

Antiangiogenic therapy is nowadays one of the most active fields in cancer research. The first strategies, aimed at inhibiting tumor vascularization, included upregulation of endogenous inhibitors and blocking of the signals delivered by angiogenic factors. But interaction between endothelial cells and their surrounding extracellular matrix also plays a critical role in the modulation of the angiogenic process. This study introduces a new concept to enhance the efficacy of antibody-based antiangiogenic cancer therapy strategies, taking advantage of a key molecular event occurring in the tumor context: the proteolysis of collagen XVIII, which releases the endogenous angiogenesis inhibitor endostatin. By fusing the collagen XVIII NC1 domain to an antiangiogenic single-chain antibody, a multispecific agent was generated, which was efficiently processed by tumor-associated proteinases to produce monomeric endostatin and fully functional trimeric antibody fragments. It was demonstrated that the combined production in the tumor area of complementary antiangiogenic agents from a single molecular entity secreted by gene-modified cells resulted in enhanced antitumor effects. These results indicate that tailoring recombinant antibodies with extracellular matrix-derived scaffolds is an effective approach to convert tumor progression associated processes into molecular clues for improving antibody-based therapies.

Endostatin/Collagen XVIII Accumulates in Patients with Traumatic Brain Injury

In patients with traumatic brain injury (TBI), hypoperfusion contributes to ongoing and expanding areas of neuronal damage long after the initial trauma has ceased. In order to evaluate whether the antiangiogenic protein endostatin may play a role in this process, we analyzed its spatial distribution in brains of 18 patients with TBI. We observed an increase of endostatin/collagen XVIII(+) macrophages/microglial cells but not astrocytes up to day 14 and a consequent decrease to day 16 post-TBI. In addition, paracellular endostatin/collagen XVIII deposits were detected. In vitro experiments revealed that microglial endostatin release is induced predominantly by hypoxia and, to a lesser extent, by reactive oxygen intermediates. Common NO synthase inhibitor pharmacotherapy with aminoguanidine and L-NAME completely abolished endostatin release from microglial cells, raising hopes of altering endostatin release in vivo.

Moderate antiangiogenic activity by local, transgenic expression of endostatin in Rip1Tag2 transgenic mice

Many previous reports have demonstrated that systemic administration of endostatin (ES), a proteolytic cleavage product of collagen type XVIII and an endogenous angiogenesis inhibitor, represses tumor angiogenesis in different preclinical tumor models with varying efficacy. For example, systemic delivery of recombinant ES to rat insulin promoter 1 (Rip1)T-antigen 2 (Tag2)-transgenic mice, a mouse model of pancreatic beta-cell carcinogenesis, has repressed tumor angiogenesis efficiently and with it, tumor growth. Here, we report that the transgenic expression of ES in Rip1ES-transgenic mice only interferes moderately with tumor growth in Rip1Tag2;Rip1ES double-transgenic mice. Tumor incidence is not reduced by the local expression of ES, and tumor outgrowth and progression to tumor malignancy are only retarded slightly. A significant effect of local ES expression on tumor angiogenesis is only apparent during the early stages of tumor development, where less angiogenic hyperplastic lesions are observed. Although efficiently produced and secreted by transgenic beta cells, locally expressed ES appears to be sequestered in the microenvironment, and its systemic levels are not increased. The results indicate that the antiangiogenic functions of ES critically depend on the mode of delivery and the site of expression: although its systemic application represses tumor angiogenesis and tumor growth efficiently, locally expressed ES appears to be less effective, and hence, additional mechanisms of solubilization or activation of latent ES seem to be required. These results have important implications about the modes of delivery used in antiangiogenic, therapeutic strategies, which are based on the antiangiogenic activities of ES.

Tissue Endostatin Correlates Inversely with Capillary Network in Rat Heart and Skeletal Muscles

The role of angiostatic factors, including endostatin, in regulating physiological angiogenesis is poorly understood. We used normal adult rats under physiological resting conditions to examine the relationship between tissue endostatin, VEGF, and capillary density (CD) in the heart (high metabolic activity) versus the skeletal muscle (relatively low metabolic activity). The heart (left ventricle, LV) and skeletal muscle (anterior tibialis, AT) were dissected from 12-week-old male Sprague-Dawley rats. Transverse cryosections of LV and AT were stained with FITC-conjugated GS-I-lectin. CD was determined by analysis of randomly acquired digital images of the cryosections using Optimas software. Tissue protein levels of endostatin and VEGF were determined by ELISA assays. Tissue endostatin levels were lower in the LV and higher in the AT (135 +/- 39 vs. 663 +/- 114 pg/mg) and VEGF levels were higher in the LV and lower in the AT (41 +/- 3 vs. 27 +/- 4 pg/mg), respectively (n = 7, P < 0.01). CD in LV and AT were 3632 +/- 428 and 437 +/- 44/mm2, respectively (P < 0.01). We demonstrated that an 8.3-fold greater capillary density is related to a 4.9-fold lower level of tissue endostatin and a 1.5-fold higher level of tissue VEGF in the heart (LV) versus the skeletal muscle (AT) of normal rats under physiological resting conditions. Also, exercise training increased capillary density, decreased tissue endostatin and increased tissue VEGF in the skeletal muscle (AT). These findings suggest that tissue endostatin content correlates inversely with capillary network in the muscle tissues with different metabolic activity, and that tissue endostatin may play a very important role in the metabolic control of angiogenesis under physiological conditions.

Endostatin influences endothelial morphology via the activated ERK1/2-kinase endothelial morphology and signal transduction

Endostatin, the proteolytic fragment of collagen XVIII, is known to be a potent inhibitor of angiogenesis. However, to date, only limited knowledge exists with regard to the effects of endostatin on vessel morphology and the underlying signaling pathway. The aim of the present work was therefore to determine the impact of endostatin and its collagen XV analogue restin on vessel development during wound healing and embryonic angio- and vasculogenesis. Time lapse experiments and electron microscopy demonstrate similar morphological changes evoked by endostatin and the ERK1/2-kinase inhibitor PD98059. Furthermore, we show that ERK1/2 phosphorylation, a crucial signaling event in vascular morphogenesis, is regulated by endostatin via the protein phosphatase 2A PP2A. These findings provide new insight into a key signaling pathway of vascular remodeling evoked by a matrix-derived factor.

Differential Expression of Collagen Types XVIII/Endostatin and XV in Normal, Keratoconus, and Scarred Human Corneas

PURPOSE

This study was designed to clarify the expression of 2 closely related collagen (Col) types XVIII and XV, and the proteolytically derived endostatin fragment of ColXVIII in normal, keratoconus, and scarred human corneas.

METHODS

Immunohistochemistry, in situ hybridization, immunoelectron microscopy, and Western immunoblotting were used for human corneal samples obtained from penetrating keratoplasty.

RESULTS

In the normal cornea, ColXVIII was immunolocalized to the corneal and conjunctival epithelial basement membrane (EBM), Descemet s membrane, and the limbal and conjunctival capillaries. Immunoreaction for endostatin was otherwise similar, but it also was present in corneal epithelial cells. Western immunoblotting showed that normal cornea contains several endostatin fragments ranging from 20 to 100 kDa. ColXV was present in the EBM of the limbus and conjunctiva, but not in EBM of the clear cornea. In situ hybridization revealed that corneal basal epithelial cells were responsible for the synthesis of ColXVIII mRNA. Keratoconus cases were characterized by an irregular EBM immunoreactivity for ColXVIII and endostatin and patchy immunoreactivity beneath EBM. In scarred corneas, highly increased immunoreactivity for ColXVIII, endostatin, and ColXV was present within stroma.

CONCLUSIONS

The results indicate that ColXVIII and ColXV are differentially expressed in normal human corneas. Constant expression of ColXVIII by corneal EBM suggests that it is an important structural molecule. Aberrant expression of ColXVIII, endostatin, and ColXV in keratoconus and scarred corneas emphasizes the active role these molecules in the wound healing process.

Endostatin, the proteolytic fragment of collagen XVIII, induces vasorelaxation

Collagen XVIII is an important component of the extracellular matrix and is expressed in basement membranes. Its degradation results in the generation of endostatin claimed to possess antiangiogenic activity. To date, only limited knowledge exists with regard to the cellular signaling of this molecule. We show in single-cell measurements using the Ca2+ indicator fura-2 acetoxy methylester (fura-2 AM) and the nitric oxide (NO) indicator 4,5-diaminofluorescein diacetate that application of endostatin (ES) (5 pmol/L, 100 ng/mL) induced Ca2+ spikes and an increase of NO production in human and murine endothelial cells. The NO response was independent of an increase in cytosolic Ca2+ and blocked by the endothelial NO synthase (eNOS) inhibitor NG-nitro-L-arginine methyl ester and by incubation with pertussis toxin known to inhibit G(i/o) proteins. The physiological relevance of this novel signaling pathway of ES was assessed with isometric force measurements in large and small arteries of mouse. Physiological concentrations of ES were found to decrease vascular tone in an endothelium-dependent manner. This occurred via an Arg-Gly-Asp (RGD) peptide-independent pathway through activation of G(i/o) proteins, phosphatidylinositol 3-kinase, Akt, and eNOS. We conclude that the proteolytic matrix fragment ES is a prominent vasorelaxing agent. Because ES is constantly released into the blood, it is a novel regulator of blood pressure and, therefore, represents an interesting pharmacological target.

Hypoxia-induced increase of endostatin in murine aorta and lung

In the lung, hypoxia induces pulmonary hypertension caused by vasoconstriction and vascular remodeling. Additionally, hypoxia is an inducer of angiogenesis, which is assumed to counteract pulmonary hypertension. We asked whether the anti-angiogenic factor endostatin--a cleavage product of collagen XVIII--participates in the vascular alterations induced by hypoxia. By employing Western blotting of tissue extracts of murine brain, liver and heart an endostatin fragment of 22 kDa was detectable, whereas in lung and aorta additional bands of 24 and 26 kDa were found. The amount of these larger fragments was increased in tissues obtained from mice housed for 4 days or 3 weeks at hypobaric hypoxia. By immunohistochemistry endostatin was detected in association with elastic fibers and in close neighborhood to smooth muscle cells of intrapulmonary vessels and the aorta. In the lung, the activity of matrix metalloproteinases (MMP) known to generate endostatin by cleavage of collagen XVIII was increased (MMP-2) and decreased (proMMP-9), respectively, by hypoxia. Elevated amounts of endostatin within the aortic wall of mice exposed to hypobaric hypoxia may stabilize the vascular wall by inhibition of microvascular sprouting. The surprising finding of increased endostatin in the lung presumably contributes to the development of pulmonary hypertension by reduction of angiogenesis.

Generation of biologically active endostatin fragments from human collagen XVIII by distinct matrix metalloproteases

Endostatin, a potent inhibitor of endothelial cell proliferation, migration, angiogenesis and tumor growth, is proteolytically cleaved from the C-terminal noncollagenous NC1 domain of type XVIII collagen. We investigated the endostatin formation from human collagen XVIII by several MMPs in vitro. The generation of endostatin fragments differing in molecular size (24-30 kDa) and in N-terminal sequences was identified in the cases of MMP-3, -7, -9, -13 and -20. The cleavage sites were located in the protease-sensitive hinge region between the trimerization and endostatin domains of NC1. MMP-1, -2, -8 and -12 did not show any significant activity against the C-terminus of collagen XVIII. The anti-proliferative effect of the 20-kDa endostatin, three longer endostatin-containing fragments generated in vitro by distinct MMPs and the entire NC1 domain, on bFGF-stimulated human umbilical vein endothelial cells was established. The anti-migratory potential of some of these fragments was also studied. In addition, production of endostatin fragments between 24-30 kDa by human hepatoblastoma cells was shown to be due to MMP action on type XVIII collagen. Our results indicate that certain, especially cancer-related, MMP family members can generate biologically active endostatin-containing polypeptides from collagen XVIII and thus, by releasing endostatin fragments, may participate in the inhibition of endothelial cell proliferation, migration and angiogenesis.

Endostatin signaling and regulation of endothelial cell-matrix interactions

The growth and survival of a malignant tumor are dependent on the formation and maintenance of its own microvasculature, a process termed angiogenesis. Inhibition of this phenomenon is an emerging strategy in cancer therapy. The extracellular matrix surrounding the vascular endothelial cells contains cryptic protein domains, which are exposed by changes in the proteolytic homeostasis of the tumor microenvironment. These fragments transmit local signals, which regulate vascular endothelial cell proliferation and migration. Endostatin, the proteolytic fragment of collagen type XVIII, is a potent inhibitor of tumor angiogenesis in various mouse models and is currently in clinical trials for therapeutic use in human cancer. Multiple cell surface receptors have been described for endostatin, but the signals transmitted by these receptors resulting in the inhibition of angiogenesis have so far been poorly characterized. Studies on the effects of endostatin on cultured endothelial cells suggest that the antimigratory and antiproliferative properties of this molecule are the major mechanisms underlying its antiangiogenic potential. These effects may be a consequence of endostatin modulation of endothelial cell-matrix interactions and pericellular proteolysis.

Endostatin binds biglycan and LDL and interferes with LDL retention to the subendothelial matrix during atherosclerosis

Retention of lipoproteins to proteoglycans in the subendothelial matrix (SEM) is an early event in atherosclerosis. We recently reported that collagen XVIII and its proteolytically released fragment endostatin (ES) are differentially depleted in blood vessels affected by atherosclerosis. Loss of collagen XVIII/ES in atherosclerosis-prone mice enhanced plaque neovascularization and increased the vascular permeability to lipids by distinct mechanisms. Impaired endothelial barrier function increased the influx of lipoproteins across the endothelium; however, we hypothesized that enhanced retention might be a second mechanism leading to the increased lipid content in atheromas lacking collagen XVIII. We now demonstrate a novel property of ES that binds both the matrix proteoglycan biglycan and LDL and interferes with LDL retention to biglycan and to SEM. A peptide encompassing the alpha coil in the ES crystal structure mediates the major blocking effect of ES on LDL retention. ES inhibits the macrophage uptake of biglycan-associated LDL indirectly by interfering with LDL retention to biglycan, but it has no direct effect on the macrophage uptake of native or modified lipoproteins. Thus, loss of ES in advanced atheromas enhances lipoprotein retention in SEM. Our data reveal a third protective role of this vascular basement membrane component during atherosclerosis.

Fibulin-1 acts as a cofactor for the matrix metalloprotease ADAMTS-1

ADAMTS-1 is a metalloprotease that has been implicated in the inhibition of angiogenesis and is a mediator of proteolytic cleavage of the hyaluronan binding proteoglycans, aggrecan and versican. In an attempt to further understand the biological function of ADAMTS-1, a yeast two-hybrid screen was performed using the carboxyl-terminal region of ADAMTS-1 as bait. As a result, the extracellular matrix protein fibulin-1 was identified as a potential interacting molecule. Through a series of analyses that included ligand affinity chromatography, co-immunoprecipitation, pulldown assays, and enzyme-linked immunosorbent assay, the ability of these two proteins to interact was substantiated. Additional studies showed that ADAMTS-1 and fibulin-1 colocalized in vivo. Furthermore, fibulin-1 was found to enhance the capacity of ADAMTS-1 to cleave aggrecan, a proteoglycan known to bind to fibulin-1. We confirmed that fibulin-1 was not a proteolytic substrate for ADAMTS-1. Together, these findings indicate that fibulin-1 is a new regulator of ADAMTS-1-mediated proteoglycan proteolysis and thus may play an important role in proteoglycan turnover in tissues where there is overlapping expression.

Laminin γ3 Chain Binds to Nidogen and Is Located in Murine Basement Membranes

Recently a novel laminin gamma3 chain was identified in mouse and human and shown to have the same modular structure as the laminin gamma1 chain. We expressed two fragments of the gamma3 chain in mammalian cells recombinantly. The first, domain VI/V, consisting of laminin N-terminal (domain VI) and four laminin-type epidermal growth factor-like (domain V) and laminin N-terminal modules, was shown to be essential for self-assembly of laminins. The other was domain III3-5, which consists of three laminin-type epidermal growth factor-like modules and is predicted to bind to nidogens. The gamma3 VI/V fragment was a poor inhibitor for laminin-1 polymerization as was the beta2 VI/V fragment. The gamma3 III3-5 fragment bound to nidogen-1 and nidogen-2 with lower affinity than the gamma1 III3-5 fragment. These data suggested that laminins containing the gamma3 chain may assemble networks independent of other laminins. Polyclonal antibodies raised against gamma3 VI/V and gamma3 III3-5 showed no cross-reaction with homologous fragments from the gamma1 and gamma2 chains of laminin and allowed the establishment of gamma chain-specific radioimmunoassays and light and electron microscopic immunostaining of tissues. This demonstrated a 20-100-fold lower content of the gamma3 chain compared with the gamma1 chain in various tissue extracts of adult mice. The expression of gamma3 chain was highly tissue-specific. In contrast to earlier assumptions, the antibodies against the gamma3 chain showed light microscopic staining exclusively in basement membrane zones of adult and embryonic tissues, such as the brain, kidney, skin, muscle, and testis. Ultrastructural immunogold staining localized the gamma3 chain to basement membranes of these tissues.

Classification analysis of the transcriptosome of nonlesional cultured dermal fibroblasts from systemic sclerosis patients with early disease

OBJECTIVE

To compare the transcriptosome of early-passage nonlesional dermal fibroblasts from systemic sclerosis (SSc) patients with diffuse disease and matched normal controls in order to gain further understanding of the gene activation patterns that occur in early disease.

METHODS

Total RNA was isolated from early-passage fibroblasts obtained from nonlesional skin biopsy specimens from 21 patients with diffuse SSc (disease duration <5 years in all but 1) and 18 healthy controls who were matched to the cases by age (+/-5 years), sex, and race. Array experiments were performed on a 16,659-oligonucleotide microarray utilizing a reference experimental design. Supervised methods were used to select differentially expressed genes. Quantitative polymerase chain reaction (PCR) was used to independently validate the array results.

RESULTS

Of the 8,324 genes that passed filtering criteria, classification analysis revealed that <5% were differentially expressed between SSc and normal fibroblasts. Individually, differentially expressed genes included COL7A1, COL18A1 (endostatin), DAF, COMP, and VEGFB. Using the panel of genes discovered through classification analysis, a set of model predictors that achieved reasonably high predictive accuracy was developed. Analysis of 1,297 gene ontology (GO) classes revealed 35 classes that were significantly dysregulated in SSc fibroblasts. These GO classes included anchoring collagen (30934), extracellular matrix structural constituent (5201), and complement activation (6958, 6956). Validation by quantitative PCR demonstrated that 7 of 7 genes selected were concordant with the array results.

CONCLUSION

Fibroblasts cultured from nonlesional skin of patients with SSc already have detectable abnormalities in a variety of genes and cellular processes, including those involved in extracellular matrix formation, fibrillogenesis, complement activation, and angiogenesis.

Increased endostatin/collagen XVIII expression correlates with elevated VEGF level and poor prognosis in hepatocellular carcinoma

Liver is the primary source for collagen XVIII, the precursor of angiogenesis inhibitor, endostatin. However, the role of endostatin/collagen XVIII expression during liver carcinogenesis remains elusive. Therefore, we studied its expression in five hepatoma cell lines and 105 hepatocellular carcinoma specimens. The poorly differentiated hepatoma cell lines exhibited increased endostatin/collagen XVIII levels compared with the well-differentiated ones. In hepatoma tissues, endostatin/collagen XVIII expression was detected in various types of liver cells and was significantly stronger in adjacent nontumor tissues than that in tumors (P<0.001). Endostatin/collagen XVIII expression in nontumor tissues correlated with tumor stages (P=0.014) and expression of vascular endothelial growth factor (P=0.007), but not the stages of hepatic fibrosis (P>0.05). Kaplan-Meier analysis showed that patients with higher endostatin/collagen XVIII expression had significantly shorter overall survival (P=0.011) and disease-free survival (P=0.0034). Moreover, endostatin/collagen XVIII level was an independent prognostic factor for tumor recurrence (P=0.034) by multivariate analysis. In conclusion, increased endostatin/collagen XVIII expression correlated with hepatoma progression and predicted poor prognosis for patients with hepatocellular carcinoma.

Endostatin expression in pancreatic tissue is modulated by elastase

Pancreatic tumours are scirrhous, avascular tumours, suggesting that they may produce angiogenesis inhibitors that suppress the growth of the vasculature to the tumour and metastases. We have sought evidence for the angiogenesis inhibitor, endostatin, in normal and cancerous pancreatic tissue. Using Western blotting, we found mature 20 kDa endostatin in cancer tissue but not in normal tissue. Several endostatin-related peptides of higher mol wt were present in both tissues. Extracts from normal tissue were able to degrade exogenous endostatin, whereas extracts from cancer were without effect. Although the exocrine pancreas secretes inactive proenzymes of trypsin, chymotrypsin and elastase, their possible role in this degradation was examined. The trypsin/chymotrypsin inhibitor, Glycine max, did not prevent the degradation of endostatin by normal pancreatic extracts but elastatinal, a specific inhibitor of elastase, reduced the rate of degradation. Extracts of pancreatic tumours did not express any detectable elastase activity, but an elastase (Km 1.1 mM) was expressed by extracts of normal pancreas. We conclude that endostatin is present and stable in pancreatic cancer tissues, which may explain their avascular nature, but that normal pancreatic tissue expresses enzymes, including elastase, which rapidly degrade endostatin. The stability of endostatin may have implications for its therapeutic use.

The minimal active domain of endostatin is a heparin-binding motif that mediates inhibition of tumor vascularization

Endostatin constitutes the COOH-terminal 20,000 Da proteolytic fragment of collagen XVIII and has been shown to possess antiangiogenic and antitumorigenic properties. In the present study, we have investigated the role of the heparin-binding sites in the in vivo mechanism of action of endostatin. The majority of the heparin binding is mediated by arginines 155/158/184/270 in endostatin, but there is also a minor site constituted by arginines 193/194. Using endostatin mutants lacking either of these two sites, we show that inhibition of fibroblast growth factor-2-induced angiogenesis in the chicken chorioallantoic membrane requires both heparin-binding sites. In contrast, inhibition of vascular endothelial growth factor-A-induced chorioallantoic membrane angiogenesis by endostatin was only dependent on the minor heparin-binding site (R193/194). These arginines were also required for endostatin to inhibit fibroblast growth factor-2- and vascular endothelial growth factor-A-induced chemotaxis of primary endothelial cells. Moreover, we show that a synthetic peptide corresponding to amino acids 180-199 of human endostatin (which covers the minor heparin-binding site) inhibits endothelial cell chemotaxis and reduces tumor vascularization in vivo. Substitution of arginine residues 193/194 for alanine attenuates the antiangiogenic effects of the peptide. These data show an essential role for heparin binding in the antiangiogenic action of endostatin.

Endostatin uncouples NO and Ca2+ response to bradykinin through enhanced O2*- production in the intact coronary endothelium

The present study tested the hypothesis that endostatin stimulates superoxide (O2*-) production through a ceramide-mediating signaling pathway and thereby results in an uncoupling of bradykinin (BK)-induced increases in intracellular Ca2+ concentration ([Ca2+]i) from nitric oxide (NO) production in coronary endothelial cells. With the use of high-speed, wavelength-switching, fluorescence-imaging techniques, the [Ca2+]i and NO levels were simultaneously monitored in the intact endothelium of freshly isolated bovine coronary arteries. Under control conditions, BK was found to increase NO production and [Ca2+]i in parallel. When the arteries were pretreated with 100 nM human recombinant endostatin for 1 h, this BK-induced NO production was reduced by 89%, whereas [Ca2+]i was unchanged. With the conversion rate of L-[3H]arginine to L-[3H]citrulline measured, endostatin had no effect on endothelial NO synthase (NOS) activity, but it stimulated ceramide by activation of sphingomyelinase (SMase), whereby O2*-. production was enhanced in endothelial cells. O2*-. scavenging by tiron and inhibition of NAD(P)H oxidase by apocynin markedly reversed the effect of endostatin on the NO response to BK. These results indicate that endostatin increases intracellular ceramide levels, which enhances O2*-. production through activation of NAD(P)H oxidase. This ceramide-O2*-. signaling pathway may contribute importantly to endostatin-induced endothelial dysfunction.

Increased angiogenic response in aortic explants of collagen XVIII/endostatin-null mice

Endostatin, a proteolytic fragment of basement membrane-associated collagen XVIII, has been shown to be a potent angiogenesis inhibitor both in vivo and in vitro when given at high concentrations. The precise molecular mechanisms by which it functions and whether or not it plays a role in physiological regulation of angiogenesis are not clear. In mice with targeted null alleles of Col18a1, there appears to be no major abnormality in vascular patterns or capillary density in most organs. Furthermore, the growth of experimental tumors is not increased. However, a detailed analysis of induced angiogenesis in these mice has not been performed. Therefore, we compared the angiogenic responses induced by in vitro culture of aortic explants from collagen XVIII/endostatin-null mice (ko) to wild-type (wt) littermates. We found a twofold increase in microvessel outgrowth in explants from ko mice, relative to wt explants. This increased angiogenesis was reduced to the wt level by the addition of low levels (0.1 microg/ml) of recombinant mouse or human endostatin during the culture period. To address cellular/molecular mechanisms underlying this difference in angiogenic response between ko and wt mice, we isolated endothelial cells from both strains and compared their biological behavior. Proliferation assays showed no difference between the two types of endothelial cells. In contrast, adhesion assays showed a striking difference in their ability to adhere to fibronectin suggesting that collagen XVIII/endostatin may regulate interactions between endothelial cells and underlying basement membrane-associated components, including fibronectin, such that in the absence of collagen XVIII/endostatin, endothelial cells are more adhesive to fibronectin. In the aortic explant assay, characterized by dynamic processes of microvessel elongation and regression, this may result in stabilization of newly formed vessels, reduced regression, and a net increase in microvessel outgrowth in explants from ko mice compared to the wt littermates.

Loss of collagen XVIII enhances neovascularization and vascular permeability in atherosclerosis

BACKGROUND

Plaque neovascularization is thought to promote atherosclerosis; however, the mechanisms of its regulation are not understood. Collagen XVIII and its proteolytically released endostatin fragment are abundant proteoglycans in vascular basement membranes and the walls of major blood vessels. We hypothesized that collagen XVIII in the aortic wall inhibits the proliferation and intimal extension of vasa vasorum.

METHODS AND RESULTS

To test our hypothesis, we bred collagen XVIII-knockout (Col18a1(-/-)) mice into the atherosclerosis-prone apolipoprotein E-deficient (ApoE(-/-)) strain. After 6 months on a cholesterol diet, aortas from ApoE(-/-);Col18a1(-/-) and ApoE(-/-);Col18a1(+/-) heterozygote mice showed increased atheroma coverage and enhanced lipid accumulation compared with wild-type littermates. We observed more extensive vasa vasorum and intimal neovascularization in knockout but not heterozygote aortas. Endothelial cells sprouting from Col18a1(-/-) aortas were increased compared with heterozygote and wild-type aortas. In contrast, vascular permeability of large and small blood vessels was enhanced with even heterozygous loss of collagen XVIII but was not suppressed by increasing serum endostatin to wild-type levels.

CONCLUSIONS

Our results identify a previously unrecognized function for collagen XVIII that maintains vascular permeability. Loss of this basement membrane proteoglycan enhances angiogenesis and vascular permeability during atherosclerosis by distinct gene-dose-dependent mechanisms.