Oligodeoxynucleotides inhibit retinal neovascularization in a murine model of proliferative retinopathy

The 67-kd laminin receptor is preferentially expressed by proliferating retinal vessels in a murine model of ischemic retinopathy

Endothelial cell association with vascular basement membranes is complex and plays a critical role in regulation of cell adhesion and proliferation. The interaction between the membrane-associated 67-kd receptor (67LR) and the basement membrane protein laminin has been studied in several cell systems where it was shown to be crucial for adhesion and attachment during angiogenesis. As angiogenesis in the pathological setting of proliferative retinopathy is a major cause of blindness in the Western world we examined the expression of 67LR in a murine model of hyperoxia-induced retinopathy that exhibits retinal neovascularization. Mice exposed to hyperoxia for 5 days starting at postnatal day 7 (P7) and returned to room air (at P12) showed closure of the central retinal vasculature. In response to the ensuing retinal ischemia, there was consistent preretinal neovascularization starting around P17, which persisted until P21, after which the new vessels regressed. Immunohistochemistry was performed on these retinas using an antibody specific for 67LR. At P12, immunoreactivity for 67LR was absent in the retina, but by P17 it was observed in preretinal proliferating vessels and also within the adjacent intraretinal vasculature. Intraretinal 67LR immunoreactivity diminished beyond P17 until by P21 immunoreactivity was almost completely absent, although it persisted in the preretinal vasculature. Control P17 mice (not exposed to hyperoxia) failed to demonstrate any 67LR immunoreactivity in their retinas. Parallel in situ hybridization studies demonstrated 67LR gene expression in the retinal ganglion cells of control and hyperoxia-exposed mice. In addition, the neovascular intra- and preretinal vessels of hyperoxia-treated P17 and P21 mice labeled strongly for 67LR mRNA. This study has characterized 67LR immunolocalization and gene expression in a murine model of ischemic retinopathy. Results suggest that, although the 67LR gene is expressed at high levels in the retinal ganglion cells, the mature receptor protein is preferentially localized to the proliferating retinal vasculature and is almost completely absent from quiescent vessels. The differential expression of 67LR between proliferating and quiescent retinal vessels suggests that this laminin receptor is an important and novel target for future chemotherapeutic intervention during proliferative vasculopathies.

Angiogenesis promoted by vascular endothelial growth factor: regulation through alpha1beta1 and alpha2beta1 integrins

Vascular endothelial growth factor (VEGF), also known as vascular permeability factor, is a cytokine of central importance for the angiogenesis associated with cancers and other pathologies. Because angiogenesis often involves endothelial cell (EC) migration and proliferation within a collagen-rich extracellular matrix, we investigated the possibility that VEGF promotes neovascularization through regulation of collagen receptor expression. VEGF induced a 5- to 7-fold increase in dermal microvascular EC surface protein expression of two collagen receptors-the alpha1beta1 and alpha2beta1 integrins-through induction of mRNAs encoding the alpha1 and alpha2 subunits. In contrast, VEGF did not induce increased expression of the alpha3beta1 integrin, which also has been implicated in collagen binding. Integrin alpha1-blocking and alpha2-blocking antibodies (Ab) each partially inhibited attachment of microvascular EC to collagen I, and alpha1-blocking Ab also inhibited attachment to collagen IV and laminin-1. Induction of alpha1beta1 and alpha2beta1 expression by VEGF promoted cell spreading on collagen I gels which was abolished by a combination of alpha1-blocking and alpha2-blocking Abs. In vivo, a combination of alpha1-blocking and alpha2-blocking Abs markedly inhibited VEGF-driven angiogenesis; average cross-sectional area of individual new blood vessels was reduced 90% and average total new vascular area was reduced 82% without detectable effects on the pre-existing vasculature. These data indicate that induction of alpha1beta1 and alpha2beta1 expression by EC is an important mechanism by which VEGF promotes angiogenesis and that alpha1beta1 and alpha2beta1 antagonists may prove effective in inhibiting VEGF-driven angiogenesis in cancers and other important pathologies.

Vascular endothelial growth factor and severity of nonproliferative diabetic retinopathy mediate retinal hemodynamics in vivo: a potential role for vascular endothelial growth factor in the progression of nonproliferative diabetic retinopathy

PURPOSE

To determine the effect of vascular endothelial growth factor and retinopathy level on retinal hemodynamics in nondiabetic and diabetic rats and to evaluate retinal hemodynamics in nondiabetic and diabetic patients.

METHODS

Forty-eight diabetic and 22 nondiabetic patients had their diabetic retinopathy levels determined from fundus photographs according to Early Treatment Diabetic Retinopathy Study (ETDRS). Fluorescein angiograms were recorded from the left eye by video fluorescein angiography. Retinal blood flow was calculated from the digitized angiograms. Human recombinant vascular endothelial growth factor or vehicle alone was injected intravitreally into 13 nondiabetic and 11 diabetic rats.

RESULTS

Retinal blood flow decreased 33% in patients with ETDRS retinopathy level 10 compared with control patients (P = .001) and increased sequentially in more advanced stages of retinopathy, with a strong correlation between retinal blood flow and retinopathy level (r2 = 0.434, P = .001). In the diabetic rats, retinal blood flow was decreased 35.6% (P = .01). Vascular endothelial growth factor maximally increased retinal blood flow by 36.1% in nondiabetic rats after 25 minutes (P = .001) and by 73.7% in diabetic rats after only 5 minutes (P = .01) and caused a greater response in diabetic than in nondiabetic rats.

CONCLUSIONS

Retinal blood flow increases with advancing nonproliferative diabetic retinopathy in humans, and diabetes accentuates the vascular endothelial growth factor-induced increase in retinal blood flow and venous dilation in rats. Vascular endothelial growth factor may contribute to the changes in retinal hemodynamics and morphology observed in early diabetic retinopathy.

Vascular endothelial growth factor and ocular neovascularization

Okamoto et al have developed an extremely useful and interesting model of retinal and subretinal neovascularization. Using molecular techniques, they have developed a transgenic model driven by overexpression of VEGF, a growth factor demonstrated to play an important role in neovascularization in many ocular diseases. They have been able to demonstrate that VEGF overexpression is sufficient to cause intraretinal and subretinal neovascularization. The mouse model is relatively cheap and reliable, does not require any exogenous agent, and has many characteristics of clinical intraocular neovascularization. The new vessels develop in the outer retina and subretinal space and have a characteristic histological appearance. They leak fluorescein on angiography, demonstrating their similarity to human disease and allowing identification and grading of neovascularization in vivo. The model can be used to investigate molecular mechanisms of VEGF-dependent neovascularization, with applications beyond ocular eye disease. The model can also be used to study anti-angiogenic agents that have the potential to treat common blinding diseases such as age-related macular degeneration. Okamoto et al have made a substantial contribution to the angiogenesis field with this work, and one looks forward to future investigations.

Transgenic mice with increased expression of vascular endothelial growth factor in the retina: a new model of intraretinal and subretinal neovascularization

Vascular endothelial growth factor (VEGF) has been implicated in retinal neovascularization (NV), but it has been difficult to produce retinal NV with exogenous VEGF. We investigated the effect of increased VEGF expression in the retina using tissue-specific, gain-of-function transgenic mice in which the bovine rhodopsin promoter is coupled to the gene for human VEGF. Three founder mice were obtained and used to generate transgenic lines. One of the lines shows increased expression of VEGF in the retina by reverse transcription coupled to polymerase chain reaction and Northern blots, and the VEGF is localized to photoreceptors by immunohistochemistry. These mice demonstrate new vessels originating from the deep capillary bed of the retina that extend beneath the photoreceptor layer into the subretinal space where they form clumps of blood vessels surrounded by proliferated retinal pigmented epithelial cells. The appearance is similar to subretinal NV seen in some patients, except that the blood vessels originate from the retinal vasculature rather than the choroidal vasculature. One of the other two lines of mice did not show increased expression of VEGF and did not have NV; the other line showed retinal degeneration. This study demonstrates that over-expression of VEGF in the retina is sufficient to cause intraretinal and subretinal NV and provides a valuable new animal model.

Retinal development: communication helps you see the light

Recent studies suggest that interactions between neurons, glial cells and endothelial cells are critical in determining the structure of the retina and the optic nerve. Dysregulation of these interactions can lead to disruption of retinal architecture and impairment of vision.

Antisense oligonucleotides inhibit vascular endothelial growth factor/vascular permeability factor expression in normal human epidermal keratinocytes

In psoriatic lesions, epidermal keratinocytes overexpress vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) and transforming growth factor alpha (TGF-alpha). TGF-alpha has been shown to induce VEGF/VPF in normal human epidermal keratinocytes in vitro. By using a 19-mer antisense phosphorothioate oligodeoxynucleotide (PS-ODN) complementary to bases 6-24 relative to the translational start site of the VEGF/VPF mRNA, the control sense and mismatched PS-ODNs, we examined modulation of VEGF/VPF induction by TGF-alpha in vitro. Normal human epidermal keratinocytes were treated with PS-ODNs and Lipofectin for 8 h prior to the addition of TGF-alpha. Inhibition was assayed at the level of secreted protein by capture ELISA and mRNA expression was assayed by Northern blot analysis. The anti-sense PS-ODN was capable of inhibiting VEGF/VPF RNA and protein to near-basal levels. This inhibition was concentration dependent. No effect was observed with the sense or mismatch control PS-ODNs. These studies suggest that antisense oligonucleotide technology may be a potential therapy for the inhibition of angiogenesis associated with certain skin disorders such as psoriasis.