Negative regulators of angiogenesis: important targets for treatment of exudative AMD

Abstract

Angiogenesis contributes to the pathogenesis of many diseases including exudative age-related macular degeneration (AMD). It is normally kept in check by a tightly balanced production of pro- and anti-angiogenic factors. The up-regulation of the pro-angiogenic factor, vascular endothelial growth factor (VEGF), is intimately linked to the pathogenesis of exudative AMD, and its antagonism has been effectively targeted for treatment. However, very little is known about potential changes in expression of anti-angiogenic factors and the role they play in choroidal vascular homeostasis and neovascularization associated with AMD. Here, we will discuss the important role of thrombospondins and pigment epithelium-derived factor, two major endogenous inhibitors of angiogenesis, in retinal and choroidal vascular homeostasis and their potential alterations during AMD and choroidal neovascularization (CNV). We will review the cell autonomous function of these proteins in retinal and choroidal vascular cells. We will also discuss the potential targeting of these molecules and use of their mimetic peptides for therapeutic development for exudative AMD.

Keywords: PEDF; angiogenesis; endothelial cells; pericytes; retinal pigment epithelial cells; thrombospondins.

Figure 1

Factors associated with pathogenesis of AMD and CNV. A) Dysregulated production of angioregulatory factors will affect various aspects of angiogenesis contributing to vascular dysfunction and proliferation. B) The organization of RPE-choroid complex under normal conditions (top panel), and its disorganization in AMD and development of choroidal neovascularization (lower panel).

Figure 2

Domain organization of TSP1 and function of TSP1-derived peptides from these domains.

Figure 3

Domain organization of PEDF and function of PEDF derived peptides from these domains.

Figure 4

PEDF deficiency minimally affects choroidal neovascularization. A) Serpinf1 +/+ and Serpinf1 −/− mice (6-weeks of age; female) were subjected to laser-induced photocoagulation. The area of neovascularization was assessed as previously described [183]. B) The quantitative assessment of data. Please note no significant difference in areas of neovascularization in Serpinf1 −/− mice compared with Serpinf1 +/+ mice (P> 0.05; n=20 eyes). Bar=50 μm.

Figure 5

PEDF deficiency does not exacerbate loss of retinal ganglion cells in response to nerve crush. Serpinf1 +/+ and Serpinf1 −/− mice (8 weeks of age; male and female) were subjected to nerve crush procedure (Crush) or procedure without crush (control) as described previously [184, 185]. Animals were sacrificed two-weeks later and retinal flat mounts were evaluated for number of BRN3A (brain-specific homeobox/POU domain protein 3A) positive cells per 100 μm² [186]. A) Representative images of retinal flatmounts stained with BRN3A antibody. B) The mean number of BRN3A positive cells per 100 μm². Please note the dramatic decrease in cell number following nerve crush in Serpinf1 +/+ and Serpinf1 −/− mice. The differences between Serpinf1 +/+ and Serpinf1 −/− mice were not significant (P> 0.05; n=8). C) The mean percentage of cells remaining, relative to control. There was no significant difference in percentage of cells remaining in Serpinf1 +/+ compared with Serpinf1 −/− mice (P> 0.05; n=8).