Endothelial survival factors and spatial completion, but not pericyte coverage of retinal capillaries determine vessel plasticity

Comparison of the Behavior of Perivascular Cells (Pericytes and CD34+ Stromal Cell/Telocytes) in Sprouting and Intussusceptive Angiogenesis

Perivascular cells in the pericytic microvasculature, pericytes and CD34+ stromal cells/telocytes (CD34+SCs/TCs), have an important role in angiogenesis. We compare the behavior of these cells depending on whether the growth of endothelial cells (ECs) from the pre-existing microvasculature is toward the interstitium with vascular bud and neovessel formation (sprouting angiogenesis) or toward the vascular lumen with intravascular pillar development and vessel division (intussusceptive angiogenesis). Detachment from the vascular wall, mobilization, proliferation, recruitment, and differentiation of pericytes and CD34+SCs/TCs, as well as associated changes in vessel permeability and functionality, and modifications of the extracellular matrix are more intense, longer lasting over time, and with a greater energy cost in sprouting angiogenesis than in intussusceptive angiogenesis, in which some of the aforementioned events do not occur or are compensated for by others (e.g., sparse EC and pericyte proliferation by cell elongation and thinning). The governing mechanisms involve cell-cell contacts (e.g., peg-and-socket junctions between pericytes and ECs), multiple autocrine and paracrine signaling molecules and pathways (e.g., vascular endothelial growth factor, platelet-derived growth factor, angiopoietins, transforming growth factor B, ephrins, semaphorins, and metalloproteinases), and other factors (e.g., hypoxia, vascular patency, and blood flow). Pericytes participate in vessel development, stabilization, maturation and regression in sprouting angiogenesis, and in interstitial tissue structure formation of the pillar core in intussusceptive angiogenesis. In sprouting angiogenesis, proliferating perivascular CD34+SCs/TCs are an important source of stromal cells during repair through granulation tissue formation and of cancer-associated fibroblasts (CAFs) in tumors. Conversely, CD34+SCs/TCs have less participation as precursor cells in intussusceptive angiogenesis. The dysfunction of these mechanisms is involved in several diseases, including neoplasms, with therapeutic implications.

Biochemical mechanism underlying the pathogenesis of diabetic retinopathy and other diabetic complications in humans: the methanol-formaldehyde-formic acid hypothesis

Hyperglycemia in diabetic patients is associated with abnormally-elevated cellular glucose levels. It is hypothesized that increased cellular glucose will lead to increased formation of endogenous methanol and/or formaldehyde, both of which are then metabolically converted to formic acid. These one-carbon metabolites are known to be present naturally in humans, and their levels are increased under diabetic conditions. Mechanistically, while formaldehyde is a cross-linking agent capable of causing extensive cytotoxicity, formic acid is an inhibitor of mitochondrial cytochrome oxidase, capable of inducing histotoxic hypoxia, ATP deficiency and cytotoxicity. Chronic increase in the production and accumulation of these toxic one-carbon metabolites in diabetic patients can drive the pathogenesis of ocular as well as other diabetic complications. This hypothesis is supported by a large body of experimental and clinical observations scattered in the literature. For instance, methanol is known to have organ- and species-selective toxicities, including the characteristic ocular lesions commonly seen in humans and non-human primates, but not in rodents. Similarly, some of the diabetic complications (such as ocular lesions) also have a characteristic species-selective pattern, closely resembling methanol intoxication. Moreover, while alcohol consumption or combined use of folic acid plus vitamin B is beneficial for mitigating acute methanol toxicity in humans, their use also improves the outcomes of diabetic complications. In addition, there is also a large body of evidence from biochemical and cellular studies. Together, there is considerable experimental support for the proposed hypothesis that increased metabolic formation of toxic one-carbon metabolites in diabetic patients contributes importantly to the development of various clinical complications.

A Synopsis of Signaling Crosstalk of Pericytes and Endothelial Cells in Salivary Gland

The salivary gland (SG) microvasculature constitutes a dynamic cellular organization instrumental to preserving tissue stability and homeostasis. The interplay between pericytes (PCs) and endothelial cells (ECs) culminates as a key ingredient that coordinates the development, maturation, and integrity of vessel building blocks. PCs, as a variety of mesenchymal stem cells, enthrall in the field of regenerative medicine, supporting the notion of regeneration and repair. PC-EC interconnections are pivotal in the kinetic and intricate process of angiogenesis during both embryological and post-natal development. The disruption of this complex interlinkage corresponds to SG pathogenesis, including inflammation, autoimmune disorders (Sjögren’s syndrome), and tumorigenesis. Here, we provided a global portrayal of major signaling pathways between PCs and ECs that cooperate to enhance vascular steadiness through the synergistic interchange. Additionally, we delineated how the crosstalk among molecular networks affiliate to contribute to a malignant context. Additionally, within SG microarchitecture, telocytes and myoepithelial cells assemble a labyrinthine companionship, which together with PCs appear to synchronize the regenerative potential of parenchymal constituents. By underscoring the intricacy of signaling cascades within cellular latticework, this review sketched a perceptive basis for target-selective drugs to safeguard SG function.

Pericyte-Specific Ninjurin1 Deletion Attenuates Vessel Maturation and Blood Flow Recovery in Hind Limb Ischemia

Supplemental Digital Content is available in the text.

Objective—

Angiogenesis, entire step from endothelial cells (ECs) sprouts to vascular maturation, is a critical response to ischemia. To form functional mature vessels, interactions between ECs and pericytes are essential. Ninj1 (ninjurin1) is an adhesion molecule that contributes to the pathogenesis of neuroinflammation. We recently demonstrated that Ninj1 is expressed in pericytes during angiogenesis. However, the role of Ninj1 in angiogenesis under pathophysiological ischemic conditions has not yet been elucidated.

Approach and Results—

Ninj1 was detected in microvessels, and its expression was enhanced in ischemic tissues after mouse hindlimb ischemia. Knockdown of Ninj1 was performed by injection of biodegradable microspheres releasing Ninj1-small interfering RNA into muscle tissues. Alternatively, pericyte-specific Ninj1 knockout was induced by tamoxifen treatment of NG2-CreERT/Ninj1-flox mice. Ninj1 knockdown/knockout reduced the formation of blood-circulating functional vessels among total CD31⁺ microvessels within ischemic tissues and subsequently attenuated color Doppler–assessed blood flow recovery. Ninj1 overexpression enhanced expression of Anpt (angiopoietin) 1, whereas Ninj1 knockdown enhanced the endogenous Anpt1 antagonist, Anpt2 expression in pericytes and inhibited the association of pericytes with ECs and subsequent formation of capillary-like structure, that is, EC tube surrounded with pericytes in 3-dimensional gel culture.

Conclusions—

Our data demonstrate that Ninj1 is involved in the formation of functional matured vessels through the association between pericytes and ECs, resulting in blood flow recovery from ischemia. These findings further the current our understanding of vascular maturation and may support the development of therapeutics for ischemic diseases.

Interplay between CCN1 and Wnt5a in endothelial cells and pericytes determines the angiogenic outcome in a model of ischemic retinopathy

CYR61-CTGF-NOV (CCN)1 is a dynamically expressed extracellular matrix (ECM) protein with critical functions in cardiovascular development and tissue repair. Angiogenic endothelial cells (ECs) are a major cellular source of CCN1 which, once secreted, associates with the ECM and the cell surface and tightly controls the bidirectional flow of information between cells and the surrounding matrix. Endothelium-specific CCN1 deletion in mice using a cre/lox strategy induces EC hyperplasia and causes blood vessels to coalesce into large flat hyperplastic sinuses with no distinctive hierarchical organization. This is consistent with the role of CCN1 as a negative feedback regulator of vascular endothelial growth factor (VEGF) receptor activation. In the mouse model of oxygen-induced retinopathy (OIR), pericytes become the predominant CCN1 producing cells. Pericyte-specific deletion of CCN1 significantly decreases pathological retinal neovascularization following OIR. CCN1 induces the expression of the non-canonical Wnt5a in pericyte but not in EC cultures. In turn, exogenous Wnt5a inhibits CCN1 gene expression, induces EC proliferation and increases hypersprouting. Concordantly, treatment of mice with TNP470, a non-canonical Wnt5a inhibitor, reestablishes endothelial expression of CCN1 and significantly decreases pathological neovascular growth in OIR. Our data highlight the significance of CCN1-EC and CCN1-pericyte communication signals in driving physiological and pathological angiogenesis.

Involvement of plasmalogens in post-natal retinal vascular development

Objective

Proper development of retinal blood vessels is essential to ensure sufficient oxygen and nutrient supplies to the retina. It was shown that polyunsaturated fatty acids (PUFAs) could modulate factors involved in tissue vascularization. A congenital deficiency in ether-phospholipids, also termed “plasmalogens”, was shown to lead to abnormal ocular vascularization. Because plasmalogens are considered to be reservoirs of PUFAs, we wished to improve our understanding of the mechanisms by which plasmalogens regulate retinal vascular development and whether the release of PUFAs by calcium-independent phospholipase A2 (iPLA2) could be involved.

Methods and Results

By characterizing the cellular and molecular steps of retinal vascular development in a mouse model of plasmalogen deficiency, we demonstrated that plasmalogens modulate angiogenic processes during the early phases of retinal vascularization. They influence glial activity and primary astrocyte template formation, endothelial cell proliferation and retinal vessel outgrowth, and impact the expression of the genes involved in angiogenesis in the retina. These early defects led to a disorganized and dysfunctional retinal vascular network at adult age. By comparing these data to those obtained on a mouse model of retinal iPLA2 inhibition, we suggest that these processes may be mediated by PUFAs released from plasmalogens and further signalling through the angiopoietin/tie pathways.

Conclusions

These data suggest that plasmalogens play a crucial role in retinal vascularization processes.

Advances in our understanding of diabetic retinopathy

Diabetic retinopathy remains the most common complication of diabetes mellitus and is a leading cause of visual loss in industrialized nations. The clinicopathology of the diabetic retina has been extensively studied, although the precise pathogenesis and cellular and molecular defects that lead to retinal vascular, neural and glial cell dysfunction remain somewhat elusive. This lack of understanding has seriously limited the therapeutic options available for the ophthalmologist and there is a need to identify the definitive pathways that initiate retinal cell damage and drive progression to overt retinopathy. The present review begins by outlining the natural history of diabetic retinopathy, the clinical features and risk factors. Reviewing the histopathological data from clinical specimens and animal models, the recent paradigm that neuroretinal dysfunction may play an important role in the early development of the disease is discussed. The review then focuses on the molecular pathogenesis of diabetic retinopathy with perspective provided on new advances that have furthered our understanding of the key mechanisms underlying early changes in the diabetic retina. Studies have also emerged in the past year suggesting that defective repair of injured retinal vessels by endothelial progenitor cells may contribute to the pathogenesis of diabetic retinopathy. We assess these findings and discuss how they could eventually lead to new therapeutic options for diabetic retinopathy.

Pericytes from infantile hemangioma display proangiogenic properties and dysregulated angiopoietin-1

OBJECTIVE

Infantile hemangioma (IH) is a rapidly growing vascular tumor affecting newborns. It is composed of immature endothelial cells and pericytes that proliferate into a disorganized mass of blood vessels. We isolated pericytes from IH (Hem-pericytes) to test our hypothesis that Hem-pericytes are unable to stabilize blood vessels.

METHODS AND RESULTS

We injected pericytes in vivo, in combination with endothelial cells, and found that Hem-pericytes formed more microvessels compared with control retinal pericytes. We, thereby, analyzed proangiogenic properties of the Hem-pericytes. They grew fast in vitro, and were unable to stabilize endothelial cell growth and migration, and expressed high levels of vascular endothelial growth factor-A compared with retinal pericytes. Hem-pericytes from proliferating phase IH showed lower contractility in vitro, compared with Hem-pericytes from the involuting phase and retinal pericytes. Consistent with a diminished ability to stabilize endothelium, angiopoietin 1 was reduced in Hem-pericytes compared with retinal pericytes. Normal retinal pericytes in which angiopoietin 1 was silenced produced conditioned medium that stimulated endothelial cell proliferation and migration.

CONCLUSIONS

We report the first successful isolation of patient-derived pericytes from IH tissue. Hem-pericytes exhibited proangiogenic properties and low levels of angiopoietin 1, consistent with a diminished ability to stabilize blood vessels in IH.

Human pericyte-endothelial cell interactions in co-culture models mimicking the diabetic retinal microvascular environment

Pericytes regulate vascular tone, perfusion pressure and endothelial cell (EC) proliferation in capillaries. Thiamine and benfotiamine counteract high glucose-induced damage in vascular cells. We standardized two human retinal pericyte (HRP)/EC co-culture models to mimic the diabetic retinal microvascular environment. We aimed at evaluating the interactions between co-cultured HRP and EC in terms of proliferation/apoptosis and the possible protective role of thiamine and benfotiamine against high glucose-induced damage. EC and HRP were co-cultured in physiological glucose and stable or intermittent high glucose, with or without thiamine/benfotiamine. No-contact model: EC were plated on a porous membrane suspended into the medium and HRP on the bottom of the same well. Cell-to-cell contact model: EC and HRP were plated on the opposite sides of the same membrane. Proliferation (cell counts and DNA synthesis), apoptosis and tubule formation in Matrigel were assessed. In the no-contact model, stable high glucose reduced proliferation of co-cultured EC/HRP and EC alone and increased co-cultured EC/HRP apoptosis. In the contact model, both stable and intermittent high glucose reduced co-cultured EC/HRP proliferation and increased apoptosis. Stable high glucose had no effects on HRP in separate cultures. Both EC and HRP proliferated better when co-cultured. Thiamine and benfotiamine reversed high glucose-induced damage in all cases. HRP are sensitive to soluble factors released by EC when cultured in high glucose conditions, as suggested by conditioned media assays. In the Matrigel models, addition of thiamine and benfotiamine re-established the high glucose-damaged interactions between EC/HRP and stabilized microtubules.

Phase I dose-escalation study and biomarker analysis of E7080 in patients with advanced solid tumors

PURPOSE

E7080, an oral multitargeted receptor tyrosine kinase inhibitor, has antiangiogenic and antitumor activity. This Phase I study investigated maximum tolerated dose (MTD), dose-limiting toxicity (DLT), pharmacokinetics (PK), pharmacodynamics (PD), and efficacy in patients with advanced solid tumors.

EXPERIMENTAL DESIGN

In this sequential, dose-escalation, open-label study E7080 was administered orally twice daily in a 2-week-on/1-week-off cycle. Plasma angiogenic proteins, circulating endothelial cells (CEC) and circulating progenitor cells (CEP) were measured for biomarker analysis.

RESULTS

Twenty-seven patients (median age 53 years, performance status 0/1) were enrolled. E7080 was escalated from 0.5 to 1, 2, 4, 6, 9, 13, 16, and 20 mg bid by conventional 3-patient cohorts. During cycle 1, no grade 3/4 toxicity was observed up to 13 mg bid. DLTs included grade 3 AST/ALT increase in 1 patient at 16 mg bid and grade 3 platelet count decrease in 2 patients at 20 mg bid. The MTD of 13 mg bid was determined. After repeated doses, C(max) and area under the plasma concentration-time curve increased in a dose-dependent manner. After 14 days' treatment, c-kit(+) CEPs and CECs significantly decreased in cycle 1, but c-kit(-) CEPs and CECs did not. Change from baseline in c-kit(+) CEC ratio in cycle 1 and baseline SDF1α, c-kit(+) CEPs and c-kit(+) CEP ratio significantly correlated with the E7080 therapeutic effect.

CONCLUSION

E7080 has manageable toxicity up to 13 mg bid when administered in a 2-week-on/1-week-off cycle and shows preliminary activity for durable disease control. Biomarker analysis suggested antiangiogenic activity correlated with antitumor activity in patients with a wide range of solid tumors.

Altered vascular expression of EphrinB2 and EphB4 in a model of oxygen-induced retinopathy

EphrinB2 ligands and EphB4 receptors are expressed on endothelial cells (EC) of arteries and veins, respectively, and are essential for vascular development. To understand how these molecules regulate retinal neovascularization (NV), we evaluated their expression in a model of oxygen-induced retinopathy (OIR). EphrinB2 and EphB4 were expressed on arterial and venous trunks, respectively, and on a subset of deep capillary vessels. EphB4 expression was reduced following hyperoxia, while ephrinB2 expression remained unaltered. In addition, a subset of EphB4-positive veins regressed in a caspase-3-dependent manner during hyperoxia. Arteriovenous malformations were also observed with loss of arterial-venous boundaries. Finally, both ephrinB2 and EphB4 were expressed on a subset of neovascular tufts following hyperoxia. These data confirm the contribution of ECs from both venous and arterial origins to the development of retinal NV.

Vasoregression linked to neuronal damage in the rat with defect of polycystin-2

Background

Neuronal damage is correlated with vascular dysfunction in the diseased retina, but the underlying mechanisms remain controversial because of the lack of suitable models in which vasoregression related to neuronal damage initiates in the mature retinal vasculature. The aim of this study was to assess the temporal link between neuronal damage and vascular patency in a transgenic rat (TGR) with overexpression of a mutant cilia gene polycystin-2.

Methods

Vasoregression, neuroglial changes and expression of neurotrophic factors were assessed in TGR and control rats in a time course. Determination of neuronal changes was performed by quantitative morphometry of paraffin-embedded vertical sections. Vascular cell composition and patency were assessed by quantitative retinal morphometry of digest preparations. Glial activation was assessed by western blot and immunofluorescence. Expression of neurotrophic factors was detected by quantitative PCR.

Findings

At one month, number and thickness of the outer nuclear cell layers (ONL) in TGR rats were reduced by 31% (p<0.001) and 17% (p<0.05), respectively, compared to age-matched control rats. Furthermore, the reduction progressed from 1 to 7 months in TGR rats. Apoptosis was selectively detected in the photoreceptor in the ONL, starting after one month. Nevertheless, TGR and control rats showed normal responses in electroretinogram at one month. From the second month onwards, TGR retinas had significantly increased acellular capillaries (p<0.001), and a reduction of endothelial cells (p<0.01) and pericytes (p<0.01). Upregulation of GFAP was first detected in TGR retinas after 1 month in glial cells, in parallel with an increase of FGF2 (fourfold) and CNTF (60 %), followed by upregulation of NGF (40 %) at 3 months.

Interpretation

Our data suggest that TGR is an appropriate animal model for vasoregression related to neuronal damage. Similarities to experimental diabetic retinopathy render this model suitable to understand general mechanisms of maturity-onset vasoregression.

Inhibition of Rho-dependent kinases ROCK I/II activates VEGF-driven retinal neovascularization and sprouting angiogenesis

Vascular endothelial growth factor (VEGF) is an endothelial-specific growth factor that activates the small GTPase RhoA. While the role of RhoA for VEGF-driven endothelial migration and angiogenesis has been studied in detail, the function of its target proteins, the Rho-dependent kinases ROCK I and II, are controversially discussed. Using the mouse model of oxygen-induced proliferative retinopathy, ROCK I/II inhibition by H-1152 resulted in increased angiogenesis. This enhanced angiogenesis, however, was completely blocked by the VEGF-receptor antagonist PTK787/ZK222584. Loss-of-function experiments in endothelial cells revealed that inhibition of ROCK I/II using the pharmacological inhibitor H-1152 and ROCK I/II-specific small-interfering RNAs resulted in a rise of VEGF-driven sprouting angiogenesis. These functional data were biochemically substantiated by showing an enhanced VEGF-receptor kinase insert domain receptor phosphorylation and extracellular signal-regulated kinase 1/2 activation after inhibition of ROCK I/II. Thus our data identify that the inhibition of Rho-dependent kinases ROCK I/II activates angiogenesis both, in vitro and in vivo.

Heterogeneity of angiogenesis and blood vessel maturation in cartilage tumors

Cartilage tumors have a special angiogenic phenotype, with blood vessels arranged predominantly in pericartilage fibrous septa and relatively low microvessel density (MVD), except in dedifferentiated chondrosarcomas. To further elucidate angiogenesis in cartilage tumors, we used double-labeling immunohistochemistry to determine microvessel pericyte coverage index (MPI) and proliferating capillary index (PCI), referring to blood vessel maturation and angiogenic activity in enchondromas, conventional chondrosarcomas, and dedifferentiated chondrosarcomas. Altogether, we found high MPIs (>70%) especially in dedifferentiated chondrosarcomas but without a correlation to the grade of malignancy. PCI was significantly higher in conventional chondrosarcomas grades II and III than in enchondromas, chondrosarcomas grade I, and dedifferentiated chondrosarcomas. Thus, PCI positively correlated with the previously reported differential expression of vascular endothelial growth factor (VEGF)-A in cartilage tumors. Altogether, cartilage tumors exhibit a heterogeneous but predominantly mature angiogenic phenotype with differential proliferative activity.

Anti-angiogenic properties of a sulindac analogue

BACKGROUND AND PURPOSE

Angiopoietins (Ang) are crucial for new blood vessel formation and exert their effects by acting on the Tie2 receptor. We have recently described a sulindac analogue 2-((1E,Z)-1-benzylidene-5-bromo-2-methyl-1H-inden-3-yl)acetic acid; termed C-18 from now onwards) that inhibits Tie2 receptor activity in kinase assays in vitro. Here, we have assessed the ability of C-18 to inhibit angiogenesis-related properties of endothelial cells and tested its selectivity for the Tie2 receptor.

EXPERIMENTAL APPROACH

For in vitro experiments human umbilical vein endothelial cells (HUVEC) were used. Proliferation was measured using the MTT assay; migration assays were performed in a modified Boyden chamber and tube-like structure formation was determined on matrigel. The effects of C-18 in vivo were evaluated in the chicken chorioallantoic membrane (CAM).

KEY RESULTS

Pre-treatment of HUVEC with C-18 blocked Ang-1-stimulated migration, but also abolished vascular endothelial cell growth factor (VEGF)- and fibroblast growth factor 2-induced responses. Incubation with C-18 inhibited serum-induced proliferation in a concentration-dependent manner; C-18 was, however, without effect on Ang-1-induced survival. In addition, we observed that C-18 did not inhibit ligand-induced receptor phosphorylation of Tie2 or VEGFR2. On the other hand, C-18 blocked activation of members of the mitogen-activated protein kinase family and of the Ser/Thr kinase Akt induced by both VEGF and Ang-1. Furthermore, incubation of CAMs with C-18 led to a dose-dependent inhibition of vascular length.

CONCLUSIONS AND IMPLICATIONS

C-18 did not act as a Tie2 inhibitor, as originally thought, but rather inhibited growth factor-stimulated signalling pathways that regulate endothelial cell migration and potently reduces neovascularization in vivo.

Pericytes: gatekeepers in tumour cell metastasis?

Tumour cells use two major routes to spread during metastasis, e.g. lymph vessels and blood vessels within or surrounding the primary tumour. The growth rate of the primary tumour often correlates with the quantity of new blood vessels that form within the tumour. However, qualitative abnormalities of the tumour vasculature profoundly affect the perfusion of the primary tumour and the escape of tumour cells into the circulation. In this paper, we review recent evidence for a novel role of the supporting mural cells in limiting blood-borne metastasis.

Incipient diabetic retinopathy--insights from an experimental model

Vascular complications of chronic hyperglycemia including diabetic retinopathy are an increasing therapeutic and socioeconomic challenge. The epidemiology of diabetic eye disease has been well described, and there is as yet no clear indication for a reduction of incidence of blindness. Due to the complex multifactorial nature of the damage to diabetic vessels, it had been difficult to identify key targets for treatment and prevention. Novel techniques to study molecules and mechanisms involved in retinal vessel development and vascular cell interactions improved the understanding of retinal cell biology and pathobiology. A unifying concept has been proposed which links hyperglycemia-induced mitochondrial overproduction of reactive oxygen species with long-known biochemical alterations such as the formation of advanced glycation end products or the activation of the protein kinase C pathway. Specific inhibitors were identified that inhibited multiple biochemical abnormalities downstream of oxidative stress induced by high glucose.

Angiopoietin: a TIE(d) balance in tumor angiogenesis

Angiopoietins (ANG-1 and ANG-2) and their TIE-2 receptor tyrosine kinase have wide-ranging effects on tumor malignancy that includes angiogenesis, inflammation, and vascular extravasation. These multifaceted pathways present a valuable opportunity in developing novel inhibition strategies for cancer treatment. However, the regulatory role of ANG-1 and ANG-2 in tumor angiogenesis remains controversial. There is a complex interplay between complementary yet conflicting roles of both the ANGs in shaping the outcome of angiogenesis. Embryonic vascular development suggests that ANG-1 is crucial in engaging interaction between endothelial and perivascular cells. However, recruitment of perivascular cells by ANG-1 has recently been implicated in its antiangiogenic effect on tumor growth. It is becoming clear that TIE-2 signaling may function in a paracrine and autocrine manner directly on tumor cells because the receptor has been increasingly found in tumor cells. In addition, alpha(5)beta(1) and alpha(v)beta(5) integrins were recently recognized as functional receptors for ANG-1 and ANG-2. Therefore, both the ligands may have wide-ranging functions in cellular activities that affect overall tumor development. Collectively, these TIE-2-dependent and TIE-2-independent activities may account for the conflicting findings of ANG-1 and ANG-2 in tumor angiogenesis. These uncertainties have impeded development of a clear strategy to target this important angiogenic pathway. A better understanding of the molecular basis of ANG-1 and ANG-2 activity in the pathophysiologic regulation of angiogenesis may set the stage for novel therapy targeting this pathway.

Triamcinolone suppresses retinal vascular pathology via a potent interruption of proinflammatory signal-regulated activation of VEGF during a relative hypoxia

We examined the effect of triamcinolone acetonide (TA), a corticosteroid, on the relationship between vascular pathophysiology and vascular endothelial growth factor (VEGF) activation in the retina of a rat model of oxygen-induced retinopathy (OIR). OIR was induced by exposure of hyperoxia (80% oxygen) to Sprague-Dawley (SD) rats from P2 to P14 and then returned to normoxic conditions. TA was intravitreal-injected once into the right eye of OIR rats at P15. Effects of TA on vascular pathophysiology or changes of various genes in response to hypoxia and/or proinflammation under hypoxic retina were assessed by the Evans-blue method, fluorescein isothiocyanate-dextran (FITC-D) infusion, immunoblotting, and ELIZA. TA not only reduced retinal neovascularization and vascular leakage in the OIR-rat retina, but also blocked the induction of hypoxia-response proinflammatory genes before it negatively controlled VEGF activation. These findings suggest a potential that TA suppresses retinal neovascular pathophysiology via proinflammation-mediated activation of VEGF during hypoxia.