Ординатура / Офтальмология / Английские материалы / Ocular Therapeutics Eye on New Discoveries_Yorio, Clark, Wax_2007

NI vessel growth in retina ↓ VEGF

Resolution of ROP

↑ VEGF

Proliferative retinopathy Retinal detachment

VEGF

IGF-1

slow vessel destruction including loss of pericytes, increased vascular permeability and capillary occlusion. These changes lead to vascular dysfunction and loss, resulting in retinal ischemia. This in turn leads to an increased expression of hypoxia-induced angiogenic growth factors, including VEGF, to trigger retinal neovascularization. These new vessels grow on the surface of retina or into the vitreous. Formation of fibrous membrane by this pathological neovascularization, combined with traction caused by vitreous attachment, can lead to tractional retinal detachment. Elevated levels of VEGF also induce increased permeability in these vessels, increasing the risk of vitreous hemorrhage.

Several independent biochemical pathways have been suggested to link hyperglycemia with microvascular dysfunction. These include (1) polyol accumulation: the pathway converting excess intracellular glucose into sugar alcohols via activity of the enzyme aldose reductase; (2) formation of advanced glycation end products

(AGEs) initiated by the glycolytic intermediate glyceraldehyde-3-phosphate; (3) activation of protein kinase C by the overflow of glycolytic intermediates into synthesis of diacyl-glycerol, which is a known potent stimulus for PKC; and (4) oxidative stress from increased formation of reactive oxygen species (Fong et al., 2004). These processes are thought to modulate the disease process through their effects on cellular metabolism, as well as production and signaling of growth factors such as VEGF, GH, IGF-1, transforming factor β (TGF-β) and pigment epithelium-derived growth factor (PEDF).

Increased expression of VEGF has been demonstrated in the vitreous of patients with diabetic retinopathy (Adamis et al., 1994; Aiello et al., 1994; Malecaze et al., 1994). In animal studies, oxygen-induced ischemic retinopathy is used to mimic certain aspects of proliferative retinopathy since diabetic animals do not develop pathological vascular proliferation. It is thought that diabetic animals do not have

a long enough lifespan to accumulate the vascular changes needed for pathological proliferation to occur. In the mouse model of hyproxic retinopathy, a soluble VEGFneutralizing VEGF receptor chimera was shown to suppress retinal neovascularization (Aiello et al., 1995). Inhibition of PKC-β was also shown to prevent the neovascular and permeability effects of VEGF in animals (Aiello et al., 1997).

GH and IGF-1 have been suspected to play a role in diabetic retinopathy since the observation that hypophysectomy led to regression of proliferative retinopathy (Wright et al., 1969). Diabetic dwarf patients with low IGF-1 also have reduced incidence of proliferative retinopathy. Other evidence include observations of diabetic retinopathy progression in states of elevated IGF-1 during puberty, pregnancy, and upon rapid improvement of metabolic control (Chantelau, 1998; Chew et al., 1995). The finding that inhibiting GH or IGF-1 suppresses retinal neovascularization (Smith et al., 1997, 1999) further raised the interest of using growth hormone-inhibitory and antiproliferative somatostin analogs to treat severe proliferative diabetic retinopathy.

TGF-β is produced by pericytes in the retina. Levels of TGF-β are usually high in normal eyes and may inhibit endothelial proliferation (Sharp, 1995). Active proliferative diabetic retinopathy patients have lower vitreal levels of TGF-β, which may promote angiogenesis (Spranger et al., 1999). PEDF is expressed by retinal pigment epithelium and is also a potent inhibitor of angiogenesis (Dawson et al., 1999). System injection of PEDF reduces retinal neovascularization in the mouse model of ischemicinduced retinopathy (Stellmach et al., 2001).

C. Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is the primary cause of blindness in the elderly in developed countries. There are two major forms of AMD: the exudative (wet) type and the non-exudative (dry)

type. The exudative type of AMD is characterized by pathological outgrowth of new vessels from the choroid, extending through Bruch’s membrane and into the subretinal area. Increased vessel leakiness, in association with choroidal neovascularization (CNV), can lead to accumulation of fluid or blood in the posterior part of the retina, resulting in detachment of the RPE and retina.

Several growth factors, including VEGF, bFGF and TGF-β have been identified in human choroidal neovascularization at increased levels (Frank et al., 1996; Kliffen et al., 1997). Among these VEGF plays a central role in the development of choroidal neovascularization. In animal studies with laser-induced CNV, increased expression of VEGF is found in RPE cells and inflammatory cells at the site of CNV (Ishibashi et al., 1997). Inhibition of VEGF with soluble receptor or neutralizing antibodies reduces CNV (Honda et al., 2000; Krzystolik et al., 2002). Subretinal injection of viral vectors expressing VEGF results in lesions characteristic of clinical CNV, with development of new vessels breaching Bruch’s membrane and the RPE (Baffi et al., 2000; Spilsbury et al., 2000). However, overexpression of VEGF in RPE in a transgenic animal model only induces choroidal neovascularization in the choroidal space, without invasion into the Bruch’s membrane (Schwesinger et al., 2001). The difference in these results may be explained by damage to the Bruch’s membrane and inflammation associated with subretinal injection, suggesting that the development of invasive CNV may require both elevated VEGF levels and defects in Bruch’s membrane. In the clinic, the defects in Bruch’s membrane are visible in many ocular conditions with CNV, accompanied by varying degrees of inflammation (Schlingemann, 2004).

Increased oxidative stress has been proposed as an important mechanism in the pathogenesis of AMD (Beatty et al., 2000). Oxidative stress is pro-inflammatory and might cause invasion of macrophages

resulting in the local destruction of Bruch’s membrane. The presence of macrophages has been demonstrated in the outer side of Bruch’s membrane in eyes with drusen, possibly attracted by RPE secreted monocyte chemoattractant proteins (Grossniklaus et al., 2002). Increased oxidative stress is also likely to lead to overexpression of many growth factors, including VEGF, by RPE.

Hypoxia has also been suggested to play a role in the development of CNV. Hypoxiainduced VEGF is secreted by RPE basally (toward choriocapillaris) and VEGF receptors are expressed on the choroidal endothelium facing the RPE, suggesting that VEGF is a survival factor for choriocapillaris in a hypoxia-driven feedback mechanism (Grossniklaus et al., 2002). With age, especially in AMD, Bruch’s membrane undergoes important changes, such as membrane thickening and decreased permeability due to the accumulation of lipids (Moore et al., 1995; Ramrattan et al., 1994). These changes may result in less efficient diffusion of VEGF across Bruch’s membrane. It is therefore possible that RPE-secreted VEGF is unable to reach the choriocapillaris to support it, leading to vascular atrophy, resulting in hypoxia in the outer retina. In response to the hypoxia, RPE would increase the expression of VEGF, which would then accumulate due to the thickened and less permeable Bruch’s membrane. In the presence of a rupture in Bruch’s membrane, invasive CNV may be initiated by these high levels of VEGF. This hypothetical scenario is supported by animal experiments with overexpression of VEGF (Baffi et al., 2000; Spilsbury et al., 2000).

In addition to the upregulation of angiogenic factors such as VEGF, hypoxia also suppresses a potent anti-angiogenic factor, pigment-epithelial derived factor (PEDF). Therefore hypoxia leads to an inversion of the VEGF/PEDF ratio which may promote angiogenesis (Gao et al., 2001). It has been shown that PEDF levels are decreased in the vitreous of patients with AMD and in the rat model of CNV (Holekamp et al., 2002; Renno et al., 2002). The efficacy of PEDF in

inhibiting neovascularization has been suggested in numerous models of AMD.

VI. CURRENT THERAPY

FOR PATHOLOGICAL

ANGIOGENESIS

dynamic therapy in AMD.

The aim of laser photocoagulation is to induce the regression of new vessels, by obliterating ischemic areas, decreasing the increased permeability of vessels and inducing choroiretinal adhesion (Petrovic and Bhisitkul, 1999). The end result in most cases is regression of new vessels, as well as reduction in exudates and edema. Nevertheless, despite photocoagulation, retinopathy progresses in a significant proportion of patients. Moreover, laser treatment for subfoveal CNV due to AMD is suboptimal, due to the inevitable destruction of the foveal retina. The introduction of photodynamic therapy (PDT) offered the first selective treatment for CNV, allowing for closure of choroidal neovessels in membranes with relative sparing of the overlying retina. However, the visual results still leave room for improvement. Overall, preventive interventions to treat ocular angiogenesis are much more desirable.

Since neovessel formation is a key phenomenon in ocular diseases with pathological angiogenesis, preventive measures are aimed at inhibiting the growth of new vessels and/or correcting the decreased permeability of these neovessels. Among the several growth factors that can influence

ocular vascular proliferation, VEGF exerts great influence. The strong supportive evidence from animal studies defined VEGF as a therapeutic target for treatment of ocular diseases in which neovascularization leads to blindness.

Several anti-VEGF therapies are currently in use or in late stage clinical trials. Avastin (bevacizumab), a recombinant humanized monoclonal antibody against VEGF, was the first anti-angiogenesis drug approved by the FDA in 2004. It was approved for patients with metastatic carcinoma of the colon or rectum. Months later, Macugen (pegaptanib), a 28-base oligonucleotide (aptamer) that binds VEGF (2002), was approved for the treatment of the wet or neovascular form of age-related macular degeneration, marking the advent of anti-VEGF therapy for ocular disease. More recently, Lucentis (ranibizumab), a humanized monoclonal antibody fragment against VEGF related to Avastin, was also approved for the treatment of the wet form of age-related macular degeneration. Both Macugen and Lucentis are currently being investigated in the treatment of diabetic macular edema. Avastin is widely used off label for treatment of AMD.

VII. FUTURE THERAPY

BOX 21.1

The use of anti-VEGF therapy is the first medical treatment for AMD, and is likely to be useful for proliferative retinopathy based on our understanding of the mechanism of the disease. However, prevention of vessel loss will be even more important in the treatment of retinopathy. There are currently many active areas of research that suggest manipulation of currently approved pharmacological interventions

or even dietary interventions may help prevent the ischemia that results in the destructive aspects of neovascularization in diabetic retinopathy and retinopathy of prematurity. Neuroprotective agents may play the same role in AMD by preventing degeneration of the neural retina. Anti-inflammatory agents may also be important in future preventive treatment of ocular angiogenesis. This is currently an active area of research.

VIII. REFERENCES AND

RECOMMENDED READING

(2002). Preclinical and phase 1A clinical evaluation of an anti-VEGF pegylated aptamer (EYE001) for the treatment of exudative age-related macular degeneration. Retina 22, 143–152.

Adamis, A.P., Miller, J.W., Bernal, M.T., D’Amico, D.J., Folkman, J., Yeo, T.K., Yeo, K.T. (1994). Increased vascular endothelial growth factor levels in the vitreous of eyes with proliferative diabetic retinopathy.

Am. J. Ophthalmol. 118, 445–450.

Aiello, L.P., Avery, R.L., Arrigg, P.G., Keyt, B.A., Jampel, H.D., Shah, S.T., Pasquale, L.R., Thieme, H., Iwamoto, M.A., Park, J.E. et al. (1994). Vascular endothelial growth factor in ocular fluid of patients with diabetic retinopathy and other retinal disorders.

N. Engl. J. Med. 331, 1480–1487.

Aiello, L.P., Bursell, S.E., Clermont, A., Duh, E., Ishii, H., Takagi, C., Mori, F., Ciulla, T.A., Ways, K., Jirousek, M., Smith, L.E., King, G.L. (1997). Vascular endothelial growth factor-induced retinal permeability is mediated by protein kinase C in vivo and suppressed by an orally effective beta-isoform-selective inhibitor. Diabetes 46, 1473–1480.

Aiello, L.P., Pierce, E.A., Foley, E.D., Takagi, H., Chen, H., Riddle, L., Ferrara, N., King, G.L., Smith, L.E. (1995). Suppression of retinal neovascularization in vivo by inhibition of vascular endothelial growth factor (VEGF) using soluble VEGF-receptor chimeric proteins. Proc. Natl Acad. Sci. USA 92, 10457–10461.

Alon, T., Hemo, I., Itin, A., Pe’er, J., Stone, J., Keshet, E. (1995). Vascular endothelial growth factor acts as a survival factor for newly formed retinal vessels and has implications for retinopathy of prematurity. Nat. Med. 1, 1024–1028.

Antoniades, H.N., Scher, C.D., Stiles, C.D. (1979). Purification of human platelet-derived growth factor. Proc. Natl Acad. Sci. USA 76, 1809–1813.

Ash, J.D., Overbeek, P.A. (2000). Lens-specific VEGF-A expression induces angioblast migration and proliferation and stimulates angiogenic remodeling.

Dev. Biol. 223, 383–398.

Ashton, N. (1966). Oxygen and the growth and development of retinal vessels. In vivo and in vitro studies. The XX Francis I. Proctor Lecture. Am. J. Ophthalmol. 62, 412–435.

Baffi, J., Byrnes, G., Chan, C.C., Csaky, K.G. (2000). Choroidal neovascularization in the rat induced by adenovirus mediated expression of vascular endothelial growth factor. Invest. Ophthalmol. Vis. Sci.

41, 3582–3589.

Beatty, S., Koh, H., Phil, M., Henson, D., Boulton, M. (2000). The role of oxidative stress in the pathogenesis of age-related macular degeneration. Surv. Ophthalmol. 45, 115–134.

Beck, H., Acker, T., Wiessner, C., Allegrini, P.R., Plate, K.H. (2000). Expression of angiopoietin-1, angiopoietin-2, and tie receptors after middle cerebral artery occlusion in the rat. Am. J. Pathol. 157, 1473–1483.

Bergsten, E., Uutela, M., Li, X., Pietras, K., Ostman, A., Heldin, C.H., Alitalo, K., Eriksson, U. (2001). PDGF- D is a specific, protease-activated ligand for the PDGF beta-receptor. Nat. Cell. Biol. 3, 512–516.

Betsholtz, C., Karlsson, L., Lindahl, P. (2001). Developmental roles of platelet-derived growth factors.

Bioessays 23, 494–507.

Campbell, K. (1951). Intensive oxygen therapy as a possible cause of retrolental fibroplasia; a clinical approach. Med. J. Aust. 2, 48–50.

Campochiaro, P.A., Hackett, S.F. (2003). Ocular neovascularization: a valuable model system. Oncogene 22, 6537–6548.

Carmeliet, P., Moons, L., Luttun, A., Vincenti, V., Compernolle, V., De Mol, M., Wu, Y., Bono, F., Devy, L., Beck, H., Scholz, D., Acker, T., DiPalma, T., Dewerchin, M., Noel, A., Stalmans, I., Barra, A., Blacher, S., Vandendriessche, T., Ponten, A., Eriksson, U., Plate, K.H., Foidart, J.M., Schaper, W., Charnock-Jones, D.S., Hicklin, D.J., Herbert, J.M., Collen, D., Persico, M.G. (2001). Synergism between vascular endothelial growth factor and placental growth factor contributes to angiogenesis and plasma extravasation in pathological conditions. Nat. Med. 7, 575–583.

Chan-Ling, T., Gock, B., Stone, J. (1995). The effect of oxygen on vasoformative cell division. Evidence that “physiological hypoxia” is the stimulus for normal retinal vasculogenesis. Invest. Ophthalmol. Vis. Sci. 36, 1201–1214.

Chantelau, E. (1998). Evidence that upregulation of serum IGF-1 concentration can trigger acceleration of diabetic retinopathy. Br. J. Ophthalmol. 82, 725–730.

Chew, E.Y., Mills, J.L., Metzger, B.E., Remaley, N.A., Jovanovic-Peterson, L., Knopp, R.H., Conley, M., Rand, L., Simpson, J.L., Holmes, L.B. et al. (1995). Metabolic control and progression of retinopathy.

The Diabetes in Early Pregnancy Study. National Institute of Child Health and Human Development Diabetes in Early Pregnancy Study. Diabetes Care 18, 631–637.

Claesson-Welsh, L. (1994). Platelet-derived growth factor receptor signals. J. Biol. Chem. 269, 32023–32026.

Claxton, S., Fruttiger, M. (2003). Role of arteries in oxygen induced vaso-obliteration. Exp. Eye Res. 77, 305–311.

Cogan, D.G., Toussaint, D., Kuwabara, T. (1961). Retinal vascular patterns. IV. Diabetic retinopathy.

Arch. Ophthalmol. 66, 366–378.

Davis, S., Aldrich, T.H., Jones, P.F., Acheson, A., Compton, D.L., Jain, V., Ryan, T.E., Bruno, J., Radziejewski, C., Maisonpierre, P.C., Yancopoulos, G.D. (1996). Isolation of angiopoietin-1, a ligand for the TIE2 receptor, by secretion-trap expression cloning. Cell 87, 1161–1169.

Dawson, D.W., Volpert, O.V., Gillis, P., Crawford, S.E., Xu, H., Benedict, W., Bouck, N.P. (1999). Pigment epithelium-derived factor: a potent inhibitor of angiogenesis. Science 285, 245–248.

Dorrell, M.I., Aguilar, E., Friedlander, M. (2002). Retinal vascular development is mediated by endothelial filopodia, a preexisting astrocytic template and specific R-cadherin adhesion. Invest. Ophthalmol. Vis. Sci. 43, 3500–3510.

Dorrell, M.I., Otani, A., Aguilar, E., Moreno, S.K., Friedlander, M. (2004). Adult bone marrow-derived stem cells use R-cadherin to target sites of neovascularization in the developing retina. Blood 103, 3420–3427.

Dumont, D.J., Gradwohl, G., Fong, G.H., Puri, M.C., Gertsenstein, M., Auerbach, A., Breitman, M.L. (1994). Dominant-negative and targeted null mutations in the endothelial receptor tyrosine kinase, tek, reveal a critical role in vasculogenesis of the embryo. Genes Dev. 8, 1897–1909.

Enge, M., Bjarnegard, M., Gerhardt, H., Gustafsson, E., Kalen, M., Asker, N., Hammes, H.P., Shani, M., Fassler, R., Betsholtz, C. (2002). Endotheliumspecific platelet-derived growth factor-B ablation mimics diabetic retinopathy. Embo. J. 21, 4307–4316.

Epstein, A.C., Gleadle, J.M., McNeill, L.A., Hewitson, K.S., O’Rourke, J., Mole, D.R., Mukherji, M., Metzen, E., Wilson, M.I., Dhanda, A., Tian, Y.M., Masson, N., Hamilton, D.L., Jaakkola, P., Barstead, R., Hodgkin, J., Maxwell, P.H., Pugh, C.W., Schofield, C.J., Ratcliffe, P.J. (2001). C. elegans EGL-9 and mammalian homologs define a family of dioxygenases that regulate HIF by prolyl hydroxylation. Cell 107, 43–54.

Flynn, J.T. (1983). Acute proliferative retrolental fibroplasia: multivariate risk analysis. Trans. Am. Ophthalmol. Soc. 81, 549–591.

Fong, D.S., Aiello, L.P., Ferris, F.L. III, Klein, R. (2004). Diabetic retinopathy. Diabetes Care 27, 2540–2553.

Frank, R.N., Amin, R.H., Eliott, D., Puklin, J.E., Abrams, G.W. (1996). Basic fibroblast growth factor and vascular endothelial growth factor are present in epiretinal and choroidal neovascular membranes.

Am. J. Ophthalmol. 122, 393–403.

Freyberger, H., Brocker, M., Yakut, H., Hammer, J., Effert, R., Schifferdecker, E., Schatz, H., Derwahl, M. (2000). Increased levels of platelet-derived growth factor in vitreous fluid of patients with proliferative diabetic retinopathy. Exp. Clin. Endocrinol. Diabetes

108, 106–109.

Fruttiger, M. (2002). Development of the mouse retinal vasculature: angiogenesis versus vasculogenesis.

Invest. Ophthalmol. Vis. Sci. 43, 522–527.

Fruttiger, M., Calver, A.R., Kruger, W.H., Mudhar, H.S., Michalovich, D., Takakura, N., Nishikawa, S., Richardson, W.D. (1996). PDGF mediates a neuronastrocyte interaction in the developing retina. Neuron 17, 1117–1131.

Gao, G., Li, Y., Zhang, D., Gee, S., Crosson, C., Ma, J. (2001). Unbalanced expression of VEGF and PEDF in ischemia-induced retinal neovascularization.

FEBS Lett. 489, 270–276.

Gariano, R.F., Gardner, T.W. (2005). Retinal angiogenesis in development and disease. Nature 438, 960–966.

Gariano, R.F., Sage, E.H., Kaplan, H.J., Hendrickson,A.E. (1996). Development of astrocytes and their relation to blood vessels in fetal monkey retina. Invest. Ophthalmol. Vis. Sci. 37, 2367–2375.

Gerhardt, H., Golding, M., Fruttiger, M., Ruhrberg, C., Lundkvist,A.,Abramsson,A., Jeltsch, M., Mitchell, C., Alitalo, K., Shima, D., Betsholtz, C. (2003). VEGF guides angiogenic sprouting utilizing endothelial tip cell filopodia. J. Cell. Biol. 161, 1163–1177.

Gogat, K., Le Gat, L., Van Den Berghe, L., Marchant, D., Kobetz,A., Gadin, S., Gasser, B., Quere, I.,Abitbol, M., Menasche, M. (2004). VEGF and KDR gene expression during human embryonic and fetal eye development. Invest. Ophthalmol. Vis. Sci. 45, 7–14.

Grant, M.B., May, W.S., Caballero, S., Brown, G.A., Guthrie, S.M., Mames, R.N., Byrne, B.J., Vaught, T., Spoerri, P.E., Peck, A.B., Scott, E.W. (2002). Adult hematopoietic stem cells provide functional hemangioblast activity during retinal neovascularization. Nat. Med. 8, 607–612.

Grossniklaus, H.E., Ling, J.X., Wallace, T.M., Dithmar, S., Lawson, D.H., Cohen, C., Elner, V.M., Elner, S.G., Sternberg, P. Jr. (2002). Macrophage and retinal pigment epithelium expression of angiogenic cytokines in choroidal neovascularization. Mol. Vis. 8, 119–126.

Hackett, S.F., Ozaki, H., Strauss, R.W., Wahlin, K., Suri, C., Maisonpierre, P., Yancopoulos, G., Campochiaro, P.A. (2000). Angiopoietin 2 expression in the retina: upregulation during physiologic and pathologic neovascularization. J. Cell. Physiol. 184, 275–284.

Hackett, S.F., Wiegand, S., Yancopoulos, G., Campochiaro, P.A. (2002). Angiopoietin-2 plays

an important role in retinal angiogenesis. J. Cell. Physiol. 192, 182–187.

Hammes, H.P., Lin, J., Renner, O., Shani, M., Lundqvist, A., Betsholtz, C., Brownlee, M., Deutsch, U. (2002). Pericytes and the pathogenesis of diabetic retinopathy. Diabetes 51, 3107–3112.

Hammes, H.P., Lin, J., Wagner, P., Feng, Y., Vom Hagen, F., Krzizok, T., Renner, O., Breier, G., Brownlee, M., Deutsch, U. (2004). Angiopoietin-2 causes pericyte dropout in the normal retina: evidence for involvement in diabetic retinopathy. Diabetes 53, 1104–1110.

Heldin, C.H., Wasteson, A., Westermark, B. (1985). Platelet-derived growth factor. Mol. Cell. Endocrinol. 39, 169–187.

Heldin, C.H., Westermark, B. (1990). Platelet-derived growth factor: mechanism of action and possible in vivo function. Cell. Regul. 1, 555–566.

Hellstrom,A.,Carlsson,B.,Niklasson,A.,Segnestam,K., Boguszewski, M., de Lacerda, L., Savage, M., Svensson, E., Smith, L., Weinberger, D., Albertsson Wikland, K., Laron, Z. (2002). IGF-I is critical for normal vascularization of the human retina. J. Clin. Endocrinol. Metab. 87, 3413–3416.

Hellstrom, A., Engstrom, E., Hard, A.L., AlbertssonWikland, K., Carlsson, B., Niklasson, A., Lofqvist, C., Svensson, E., Holm, S., Ewald, U., Holmstrom, G., Smith, L.E. (2003). Postnatal serum insulin-like growth factor I deficiency is associated with retinopathy of prematurity and other complications of premature birth. Pediatrics 112, 1016–1020.

Hellstrom, A., Perruzzi, C., Ju, M., Engstrom, E., Hard, A.L., Liu, J.L., Albertsson-Wikland, K., Carlsson, B., Niklasson, A., Sjodell, L., LeRoith, D., Senger, D.R., Smith, L.E. (2001). Low IGF-I suppresses VEGF-survival signaling in retinal endothelial cells: direct correlation with clinical retinopathy of prematurity. Proc. Natl Acad. Sci. USA 98, 5804–5808.

Hellstrom, M., Kalen, M., Lindahl, P., Abramsson, A., Betsholtz, C. (1999). Role of PDGF-B and PDGFRbeta in recruitment of vascular smooth muscle cells and pericytes during embryonic blood vessel formation in the mouse. Development 126, 3047–3055.

Henkind, P., Hansen, R.I., Szalay, J. (1979). Ocular circulation, in: Physiology of the Human Eye and Visual System (R.E. Records, ed.), pp. 98–155. Harper & Row, New York.

Hoch, R.V., Soriano, P. (2003). Roles of PDGF in animal development. Development 130, 4769–4784.

Holekamp, N.M., Bouck, N., Volpert, O. (2002). Pigment epithelium-derived factor is deficient in the vitreous of patients with choroidal neovascularization due to age-related macular degeneration.

Am. J. Ophthalmol. 134, 220–227.

Honda, M., Sakamoto, T., Ishibashi, T., Inomata, H., Ueno, H. (2000). Experimental subretinal neovascularization is inhibited by adenovirus-mediated

soluble VEGF/flt-1 receptor gene transfection: a role of VEGF and possible treatment for SRN in age-related macular degeneration. Gene Ther. 7, 978–985.

Ishibashi, T., Hata, Y., Yoshikawa, H., Nakagawa, K., Sueishi, K., Inomata, H. (1997). Expression of vascular endothelial growth factor in experimental choroidal neovascularization. Graefe’s Arch. Clin. Exp. Ophthalmol. 235, 159–167.

Ishida, S., Yamashiro, K., Usui, T., Kaji, Y., Ogura, Y., Hida, T., Honda, Y., Oguchi, Y., Adamis, A.P. (2003). Leukocytes mediate retinal vascular remodeling during development and vaso-obliteration in disease. Nat. Med. 9, 781–788.

Jaakkola, P., Mole, D.R., Tian, Y.M., Wilson, M.I., Gielbert, J., Gaskell, S.J., Kriegsheim, A., Hebestreit, H.F., Mukherji, M., Schofield, C.J., Maxwell, P.H., Pugh, C.W., Ratcliffe, P.J. (2001). Targeting of HIF-alpha to the von Hippel-Lindau ubiquitylation complex by O2-regulated prolyl hydroxylation. Science 292, 468–472.

Janzer, R.C., Raff, M.C. (1987). Astrocytes induce blood–brain barrier properties in endothelial cells. Nature 325, 253–257.

Jo, N., Mailhos, C., Ju, M., Cheung, E., Bradley, J., Nishijima, K., Robinson, G.S., Adamis, A.P., Shima, D.T. (2006). Inhibition of platelet-derived growth factor B signaling enhances the efficacy of anti-vascular endothelial growth factor therapy in multiple models of ocular neovascularization. Am. J. Pathol. 168, 2036–2053.

Kim, I., Kim, H.G., Moon, S.O., Chae, S.W., So, J.N., Koh, K.N., Ahn, B.C., Koh, G.Y. (2000). Angiopoietin- 1 induces endothelial cell sprouting through the activation of focal adhesion kinase and plasmin secretion. Circ. Res. 86, 952–959.

Klein, R., Klein, B. (1995). Vision Disorders in Diabetes. Diabetes in America, ed. 2.

Kliffen, M., Sharma, H.S., Mooy, C.M., Kerkvliet, S., de Jong, P.T. (1997). Increased expression of angiogenic growth factors in age-related maculopathy.

Br. J. Ophthalmol. 81, 154–162.

Klinghoffer, R.A., Mueting-Nelsen, P.F., Faerman, A., Shani, M., Soriano, P. (2001). The two PDGF receptors maintain conserved signaling in vivo despite divergent embryological functions. Mol. Cell 7, 343–354.

Koblizek, T.I., Weiss, C., Yancopoulos, G.D., Deutsch, U., Risau, W. (1998). Angiopoietin-1 induces sprouting angiogenesis in vitro. Curr. Biol. 8, 529–532.

Krzystolik, M.G., Afshari, M.A., Adamis, A.P., Gaudreault, J., Gragoudas, E.S., Michaud, N.A., Li, W., Connolly, E., O’Neill, C.A., Miller, J.W. (2002). Prevention of experimental choroidal neovascularization with intravitreal anti-vascular endothelial growth factor antibody fragment. Arch. Ophthalmol. 120, 338–346.

LaRochelle, W.J., Jeffers, M., McDonald, W.F., Chillakuru, R.A., Giese, N.A., Lokker, N.A.,

Sullivan, C., Boldog, F.L., Yang, M., Vernet, C., Burgess, C.E., Fernandes, E., Deegler, L.L., Rittman, B., Shimkets, J., Shimkets, R.A., Rothberg, J.M., Lichenstein, H.S. (2001). PDGF-D, a new protease-activated growth factor. Nat. Cell. Biol. 3, 517–521.

Li, X., Ponten, A., Aase, K., Karlsson, L., Abramsson, A., Uutela,M.,Backstrom,G.,Hellstrom,M.,Bostrom,H., Li, H., Soriano, P., Betsholtz, C., Heldin, C.H., Alitalo, K., Ostman, A., Eriksson, U. (2000). PDGF-C is a new protease-activated ligand for the PDGF alpha-receptor. Nat. Cell. Biol. 2, 302–309.

Lindahl, P., Johansson, B.R., Leveen, P., Betsholtz, C. (1997). Pericyte loss and microaneurysm formation in PDGF-B-deficient mice. Science 277, 242–245.

Lindblom, P., Gerhardt, H., Liebner, S., Abramsson, A., Enge, M., Hellstrom, M., Backstrom, G., Fredriksson, S., Landegren, U., Nystrom, H.C., Bergstrom, G., Dejana, E., Ostman, A., Lindahl, P., Betsholtz, C. (2003). Endothelial PDGF-B retention is required for proper investment of pericytes in the microvessel wall. Genes Dev. 17, 1835–1840.

Lobov, I.B., Rao, S., Carroll, T.J., Vallance, J.E., Ito, M., Ondr, J.K., Kurup, S., Glass, D.A., Patel, M.S., Shu, W., Morrisey, E.E., McMahon, A.P., Karsenty, G., Lang, R.A. (2005). WNT7b mediates macrophageinduced programmed cell death in patterning of the vasculature. Nature 437, 417–421.

Lofqvist, C., Engstrom, E., Sigurdsson, J., Hard, A.L., Niklasson, A., Ewald, U., Holmstrom, G., Smith, L.E., Hellstrom, A. (2006). Postnatal head growth deficit among premature infants parallels retinopathy of prematurity and insulin-like growth factor-1 deficit. Pediatrics 117, 1930–1938.

Luttun, A., Tjwa, M., Moons, L., Wu, Y., AngelilloScherrer, A., Liao, F., Nagy, J.A., Hooper, A., Priller, J., De Klerck, B., Compernolle, V., Daci, E., Bohlen, P., Dewerchin, M., Herbert, J.M., Fava, R., Matthys, P., Carmeliet, G., Collen, D., Dvorak, H.F., Hicklin, D. J., Carmeliet, P. (2002). Revascularization of ischemic tissues by PlGF treatment, and inhibition of tumor angiogenesis, arthritis and atherosclerosis by anti-Flt1. Nat. Med. 8, 831–840.

Maglione, D., Guerriero, V., Viglietto, G., Delli-Bovi, P., Persico, M.G. (1991). Isolation of a human placenta cDNA coding for a protein related to the vascular permeability factor. Proc. Natl Acad. Sci. USA 88, 9267–9271.

Maisonpierre, P.C., Suri, C., Jones, P.F., Bartunkova, S., Wiegand, S.J., Radziejewski, C., Compton, D., McClain, J., Aldrich, T.H., Papadopoulos, N., Daly, T.J., Davis, S., Sato, T. N., Yancopoulos, G.D. (1997). Angiopoietin-2, a natural antagonist for Tie2 that disrupts in vivo angiogenesis. Science 277, 55–60.

Malecaze,F.,Clamens,S.,Simorre-Pinatel,V.,Mathis,A., Chollet, P., Favard, C., Bayard, F., Plouet, J. (1994). Detection of vascular endothelial growth factor messenger RNA and vascular endothelial growth

factor-like activity in proliferative diabetic retinopathy. Arch. Ophthalmol. 112, 1476–1482.

Michaelson, I.C. (1948). The mode of development of the vascular system of the retina, with some observations on its significance for certain retinal diseases. Trans. Ophthalomol. Soc. UK 68, 137–181.

Miller, H., Miller, B., Ryan, S.J. (1986). The role of retinal pigment epithelium in the involution of subretinal neovascularization. Invest. Ophthalmol. Vis. Sci.

27, 1644–1652.

Miller, J.W., Adamis, A.P., Shima, D.T., D’Amore, P.A., Moulton, R.S., O’Reilly, M.S., Folkman, J., Dvorak, H.F., Brown, L.F., Berse, B. et al. (1994). Vascular endothelial growth factor/vascular permeability factor is temporally and spatially correlated with ocular angiogenesis in a primate model. Am. J. Pathol. 145, 574–584.

Mitchell, C.A., Risau, W., Drexler, H.C. (1998). Regression of vessels in the tunica vasculosa lentis is initiated by coordinated endothelial apoptosis: a role for vascular endothelial growth factor as a survival factor for endothelium. Dev. Dyn. 213, 322–333.

Moore, D.J., Hussain, A.A., Marshall, J. (1995). Agerelated variation in the hydraulic conductivity of Bruch’s membrane. Invest. Ophthalmol. Vis. Sci. 36, 1290–1297.

Mori, K., Gehlbach, P., Ando, A., Dyer, G., Lipinsky, E., Chaudhry, A.G., Hackett, S.F., Campochiaro, P.A. (2002). Retina-specific expression of PDGF-B versus PDGF-A: vascular versus nonvascular proliferative retinopathy. Invest. Ophthalmol. Vis. Sci. 43, 2001–2006.

Nambu, H., Nambu, R., Oshima, Y., Hackett, S.F., Okoye, G., Wiegand, S., Yancopoulos, G., Zack, D.J., Campochiaro, P.A. (2004). Angiopoietin 1 inhibits ocular neovascularization and breakdown of the blood–retinal barrier. Gene Ther. 11, 865–873.

Niehrs, C. (2004). Norrin and frizzled; a new vein for the eye. Dev. Cell 6, 453–454.

Ohh, M., Park, C.W., Ivan, M., Hoffman, M.A., Kim, T.Y., Huang, L.E., Pavletich, N., Chau, V., Kaelin, W.G. (2000). Ubiquitination of hypoxiainducible factor requires direct binding to the betadomain of the von Hippel–Lindau protein. Nat. Cell. Biol. 2, 423–427.

Ohlmann, A., Scholz, M., Goldwich, A., Chauhan, B.K., Hudl, K., Ohlmann, A.V., Zrenner, E., Berger, W., Cvekl, A., Seeliger, M.W., Tamm, E.R. (2005). Ectopic norrin induces growth of ocular capillaries and restores normal retinal angiogenesis in Norrie disease mutant mice. J. Neurosci. 25, 1701–1710.

Oshima, Y., Deering, T., Oshima, S., Nambu, H., Reddy, P.S., Kaleko, M., Connelly, S., Hackett, S.F., Campochiaro, P.A. (2004). Angiopoietin-2 enhances retinal vessel sensitivity to vascular endothelial growth factor. J. Cell. Physiol. 199, 412–417.

Oshima, Y., Oshima, S., Nambu, H., Kachi, S., Takahashi, K., Umeda, N., Shen, J., Dong, A.,

Apte, R.S., Duh, E., Hackett, S.F., Okoye, G., Ishibashi, K., Handa, J., Melia, M., Wiegand, S., Yancopoulos, G., Zack, D.J., Campochiaro, P.A. (2005). Different effects of angiopoietin-2 in different vascular beds: new vessels are most sensitive. FASEB J. 19, 963–965.

Otani, A., Dorrell, M.I., Kinder, K., Moreno, S.K., Nusinowitz, S., Banin, E., Heckenlively, J., Friedlander, M. (2004). Rescue of retinal degeneration by intravitreally injected adult bone marrowderived lineage-negative hematopoietic stem cells.

J. Clin. Invest. 114, 765–774.

Otani, A., Kinder, K., Ewalt, K., Otero, F.J., Schimmel, P., Friedlander, M. (2002). Bone marrow-derived stem cells target retinal astrocytes and can promote or inhibit retinal angiogenesis. Nat. Med. 8, 1004–1010.

Ozaki, H., Hayashi, H., Vinores, S.A., Moromizato, Y., Campochiaro, P.A., Oshima, K. (1997). Intravitreal sustained release of VEGF causes retinal neovascularization in rabbits and breakdown of the blood– retinal barrier in rabbits and primates. Exp. Eye Res. 64, 505–517.

Ozaki, H., Seo, M.S., Ozaki, K., Yamada, H., Yamada, E., Okamoto, N., Hofmann, F., Wood, J.M., Campochiaro, P.A. (2000). Blockade of vascular endothelial cell growth factor receptor signaling is sufficient to completely prevent retinal neovascularization. Am. J. Pathol. 156, 697–707.

Petrovic, V., Bhisitkul, R.B. (1999). Lasers and diabetic retinopathy: the art of gentle destruction. Diabetes Technol. Ther. 1, 177–187.

Pichiule, P., LaManna, J.C. (2002). Angiopoietin-2 and rat brain capillary remodeling during adaptation and deadaptation to prolonged mild hypoxia.

J. Appl. Physiol. 93, 1131–1139.

Pierce, E.A., Avery, R.L., Foley, E.D., Aiello, L.P., Smith, L.E. (1995). Vascular endothelial growth factor/vascular permeability factor expression in a mouse model of retinal neovascularization. Proc. Natl Acad. Sci. USA 92, 905–909.

Pierce, E.A., Foley, E.D., Smith, L.E. (1996). Regulation of vascular endothelial growth factor by oxygen in a model of retinopathy of prematurity. Arch. Ophthalmol. 114, 1219–1228.

Ramrattan, R.S., van der Schaft, T.L., Mooy, C.M., de Bruijn, W.C., Mulder, P.G., de Jong, P.T. (1994). Morphometric analysis of Bruch’s membrane, the choriocapillaris, and the choroid in aging. Invest. Ophthalmol. Vis. Sci. 35, 2857–2864.

Ray, S., Gao, C., Wyatt, K., Fariss, R.N., Bundek, A., Zelenka, P., Wistow, G. (2005). Platelet-derived growth factor D, tissue-specific expression in the eye, and a key role in control of lens epithelial cell proliferation. J. Biol. Chem. 280, 8494–8502.

Rehm, H.L., Zhang, D.S., Brown, M.C., Burgess, B.,

sensorineural deafness in a mouse model of Norrie disease. J. Neurosci. 22, 4286–4292.

Renno, R.Z.,Youssri,A.I., Michaud, N., Gragoudas, E.S., Miller, J.W. (2002). Expression of pigment epitheliumderived factor in experimental choroidal neovascularization. Invest. Ophthalmol. Vis. Sci. 43, 1574–1580.

Robinson, G.S., Pierce, E.A., Rook, S.L., Foley, E., Webb, R., Smith, L.E. (1996). Oligodeoxynucleotides inhibit retinal neovascularization in a murine model of proliferative retinopathy. Proc. Natl Acad. Sci. USA 93, 4851–4856.

Robitaille, J., MacDonald, M.L., Kaykas, A., Sheldahl, L.C., Zeisler, J., Dube, M.P., Zhang, L.H.,

Hayden, M.R., Goldberg, Y.P., Samuels, M.E. (2002). Mutant frizzled-4 disrupts retinal angiogenesis in familial exudative vitreoretinopathy. Nat. Genet. 32, 326–330.

Rousseau, B., Larrieu-Lahargue, F., Bikfalvi, A., Javerzat, S. (2003). Involvement of fibroblast growth factors in choroidal angiogenesis and retinal vascularization. Exp. Eye Res. 77, 147–156.

Saint-Geniez, M., D’Amore, P.A. (2004). Development and pathology of the hyaloid, choroidal and retinal vasculature. Int. J. Dev. Biol. 48, 1045–1058.

Saishin,Y., Silva, R.L., Saishin,Y., Callahan, K., Schoch, C., Ahlheim, M., Lai, H., Kane, F., Brazzell, R.K., Bodmer, D., Campochiaro, P.A. (2003). Periocular injection of microspheres containing PKC412 inhibits choroidal neovascularization in a porcine model.

Invest. Ophthalmol. Vis. Sci. 44, 4989–4993. Sato,T.N.,Tozawa,Y.,Deutsch,U.,Wolburg-Buchholz,K.,

Fujiwara, Y., Gendron-Maguire, M., Gridley, T., Wolburg, H., Risau, W., Qin, Y. (1995). Distinct roles of the receptor tyrosine kinases Tie-1 and Tie-2 in blood vessel formation. Nature 376, 70–74.

Schlingemann, R.O. (2004). Role of growth factors and the wound healing response in age-related macular degeneration. Graefes. Arch. Clin. Exp. Ophthalmol.

242, 91–101.

Schwesinger, C., Yee, C., Rohan, R.M., Joussen, A.M., Fernandez, A., Meyer, T.N., Poulaki, V., Ma, J.J., Redmond, T.M., Liu, S., Adamis, A.P., D’Amato, R.J. (2001). Intrachoroidal neovascularization in transgenic mice overexpressing vascular endothelial growth factor in the retinal pigment epithelium.

Am. J. Pathol. 158, 1161–1172.

Sengupta, N., Caballero, S., Mames, R.N., Butler, J.M., Scott, E.W., Grant, M.B. (2003). The role of adult bone marrow-derived stem cells in choroidal neovascularization. Invest. Ophthalmol. Vis. Sci. 44, 4908–4913.

Seo, M.S., Kwak, N., Ozaki, H., Yamada, H., Okamoto, N., Yamada, E., Fabbro, D., Hofmann, F., Wood, J.M., Campochiaro, P.A. (1999). Dramatic inhibition of retinal and choroidal neovascularization by oral administration of a kinase inhibitor. Am. J. Pathol. 154, 1743–1753.

Sharp, P.S. (1995). The role of growth factors in the development of diabetic retinopathy. Metabolism 44, 72–75.

Shih, S.C., Ju, M., Liu, N., Smith, L.E. (2003). Selective stimulation of VEGFR-1 prevents oxygen-induced retinal vascular degeneration in retinopathy of prematurity. J. Clin. Invest. 112, 50–57.

Shui, Y.B., Wang, X., Hu, J.S., Wang, S.P., Garcia, C.M., Potts, J.D., Sharma, Y., Beebe, D.C. (2003). Vascular endothelial growth factor expression and signaling in the lens. Invest. Ophthalmol. Vis. Sci. 44, 3911–3919.

Smith, L.E. (2005). IGF-1 and retinopathy of prematurity in the preterm infant. Biol. Neonate 88, 237–244.

Smith, L.E., Kopchick, J.J., Chen, W., Knapp, J., Kinose, F., Daley, D., Foley, E., Smith, R.G., Schaeffer, J.M. (1997). Essential role of growth hormone in ischemia-induced retinal neovascularization. Science 276, 1706–1709.

Smith, L.E., Shen, W., Perruzzi, C., Soker, S., Kinose, F., Xu, X., Robinson, G., Driver, S., Bischoff, J., Zhang, B., Schaeffer, J.M., Senger, D.R. (1999). Regulation of vascular endothelial growth factordependent retinal neovascularization by insulin-like growth factor-1 receptor. Nat. Med. 5, 1390–1395.

Smith, L.E., Wesolowski, E., McLellan, A., Kostyk, S.K., D’Amato, R., Sullivan, R., D’Amore, P.A. (1994). Oxygen-induced retinopathy in the mouse. Invest. Ophthalmol. Vis. Sci. 35, 101–111.

Soriano, P. (1994). Abnormal kidney development and hematological disorders in PDGF beta-receptor mutant mice. Genes Dev. 8, 1888–1896.

Spilsbury, K., Garrett, K.L., Shen, W.Y., Constable, I.J., Rakoczy, P.E. (2000). Overexpression of vascular endothelial growth factor (VEGF) in the retinal pigment epithelium leads to the development of choroidal neovascularization. Am. J. Pathol. 157, 135–144.

Spranger, J., Meyer-Schwickerath, R., Klein, M., Schatz, H., Pfeiffer, A. (1999). Deficient activation and different expression of transforming growth factor-beta isoforms in active proliferative diabetic retinopathy and neovascular eye disease. Exp. Clin. Endocrinol. Diabetes 107, 21–28.

Stalmans, I., Ng, Y.S., Rohan, R., Fruttiger, M., Bouche, A., Yuce, A., Fujisawa, H., Hermans, B., Shani, M., Jansen, S., Hicklin, D., Anderson, D.J., Gardiner,T.,Hammes,H.P.,Moons,L.,Dewerchin,M., Collen, D., Carmeliet, P., D’Amore, P.A. (2002). Arteriolar and venular patterning in retinas of mice selectively expressing VEGF isoforms. J. Clin. Invest. 109, 327–336.

Stellmach, V., Crawford, S.E., Zhou, W., Bouck, N. (2001). Prevention of ischemia-induced retinopathy by the natural ocular antiangiogenic agent pigment epithelium-derived factor. Proc. Natl Acad. Sci. USA 98, 2593–2597.

Stone, J., Itin, A., Alon, T., Pe’er, J., Gnessin, H., Chan-Ling, T., Keshet, E. (1995). Development of retinal vasculature is mediated by hypoxia-induced

vascular endothelial growth factor (VEGF) expression by neuroglia. J. Neurosci. 15, 4738–4747.

Suri, C., Jones, P.F., Patan, S., Bartunkova, S., Maisonpierre, P.C., Davis, S., Sato, T.N., Yancopoulos, G.D. (1996). Requisite role of angiopoietin-1, a ligand for the TIE2 receptor, during embryonic angiogenesis. Cell 87, 1171–1180.

Tallquist, M.D., Klinghoffer, R.A., Heuchel, R., Mueting-Nelsen, P.F., Corrin, P.D., Heldin, C.H., Johnson, R.J., Soriano, P. (2000). Retention of PDGFR-beta function in mice in the absence of phosphatidylinositol 3’-kinase and phospholipase Cgamma signaling pathways. Genes Dev. 14, 3179–3190.

Terry, T.L. (1944). Retrolental fibroplasia in the premature infant: V. Further studies on fibroplastic overgrowth of the persistent tunica vasculosa lentis.

transgenically overexpressing angiopoietin-1. Science 286, 2511–2514.

Tobe, T., Ortega, S., Luna, J.D., Ozaki, H., Okamoto, N., Derevjanik, N.L., Vinores, S.A., Basilico, C., Campochiaro, P.A. (1998). Targeted disruption of the FGF2 gene does not prevent choroidal neovascularization in a murine model. Am. J. Pathol. 153, 1641–1646.

Tolentino, M.J., Miller, J.W., Gragoudas, E.S., Jakobiec,F.A.,Flynn,E.,Chatzistefanou,K.,Ferrara,N., Adamis, A.P. (1996). Intravitreous injections of vascular endothelial growth factor produce retinal ischemia and microangiopathy in an adult primate.

Ophthalmology 103, 1820–1828.

Torczynski, E. (1982). Choroid and Suprachoroid. Ocular Anatomy, Embryology and Teratology. Harper & Row, Philadelphia.

Uemura, A., Ogawa, M., Hirashima, M., Fujiwara, T., Koyama, S., Takagi, H., Honda, Y., Wiegand, S.J., Yancopoulos, G.D., Nishikawa, S. (2002). Recombinant angiopoietin-1 restores higher-order architecture of growing blood vessels in mice in the absence of mural cells. J. Clin. Invest. 110, 1619–1628.

Vinores, S.A., Youssri, A.I., Luna, J.D., Chen, Y.S., Bhargave, S., Vinores, M.A., Schoenfeld, C.L., Peng, B., Chan, C.C., LaRochelle, W., Green, W.R., Campochiaro, P.A. (1997). Upregulation of vascular endothelial growth factor in ischemic and non-ischemic human and experimental retinal disease. Histol. Histopathol. 12, 99–109.

Wang, G.L., Jiang, B.H., Rue, E.A., Semenza, G.L. (1995). Hypoxia-inducible factor 1 is a basic-helix- loop-helix-PAS heterodimer regulated by cellular O2 tension. Proc. Natl Acad. Sci. USA 92, 5510–5514.

Watanabe, T., Raff, M.C. (1988). Retinal astrocytes are immigrants from the optic nerve. Nature 332, 834–837.

West, H., Richardson, W.D., Fruttiger, M. (2005). Stabilization of the retinal vascular network by reciprocal feedback between blood vessels and astrocytes. Development 132, 1855–1862.

Wilkinson-Berka, J.L., Babic, S., De Gooyer, T., Stitt, A.W., Jaworski, K., Ong, L.G., Kelly, D.J., Gilbert, R.E. (2004). Inhibition of platelet-derived growth factor promotes pericyte loss and angiogenesis in ischemic retinopathy. Am. J. Pathol. 164, 1263–1273.

Wise, G.N. (1961). Factors influencing retinal new vessel formation. Am. J. Ophthalmol. 52, 637–650.

Wright, A.D., Kohner, E.M., Oakley, N.W., Hartog, M., Joplin, G.F., Fraser, T.R. (1969). Serum growth hormone levels and the response of diabetic retinopathy to pituitary ablation. Br. Med. J. 2, 346–348.

Xu, Q., Wang, Y., Dabdoub, A., Smallwood, P.M., Williams, J., Woods, C., Kelley, M.W., Jiang, L., Tasman, W., Zhang, K., Nathans, J. (2004). Vascular development in the retina and inner ear: control by Norrin and frizzled-4, a high-affinity ligandreceptor pair. Cell 116, 883–895.

Yi, X., Mai, L.C., Uyama, M., Yew, D.T. (1998). Timecourse expression of vascular endothelial growth factor as related to the development of the retinochoroidal vasculature in rats. Exp. Brain Res. 118, 155–160.

Young, T.L., Anthony, D.C., Pierce, E., Foley, E., Smith, L.E. (1997). Histopathology and vascular endothelial growth factor in untreated and diode laser-treated retinopathy of prematurity. J. Aapos. 1, 105–110.

Zhang, H.R. (1994). Scanning electron-microscopic study of corrosion casts on retinal and choroidal angioarchitecture in man and animals. Prog. Ret. Eye Res. 13, 243–270.

Zhao, S., Overbeek, P.A. (2001). Regulation of choroid development by the retinal pigment epithelium. Mol. Vis. 7, 277–282.

Zhu, W.H., Guo, X., Villaschi, S., Francesco Nicosia, R. (2000). Regulation of vascular growth and regression by matrix metalloproteinases in the rat aorta model of angiogenesis. Lab. Invest. 80, 545–555.