Role of Angiomotin, an Angiostatin-Binding Membrane Associated Protein, in Choroidal Neovascularization

Abstract

Purpose:: Angiostatin, a fragment of plasminogen, has shown efficacy in inhibiting angiogenesis and tumor growth in pre-clinical models including during choroidal neovascularization (CNV). The clinical use of the angiostatin is, however, restricted by the low half-life in circulation and high production costs. We have previously shown that angiomotin mediates angiostatin inhibition of endothelial migration and tube formation in vitro. In addition, targeting angiomotin using DNA vaccination inhibits angiogenesis and tumor growth in vivo. Here we have studied the potential role of angiomotin in CNV in mice.

Methods:: Immunohistochemistry using anti-angiomotin was performed on human surgical CNV specimens. The effect of either overexpression or inhibition of angiomotin was studied in the laser induced CNV model. Overexpression of angiomotin was achieved by driving angiomotin expression of angiomotin with TIE endothelial-specific promoter in transgenic mice. Activity of endogenous angiomotin was targeted by either intra-ocular injections of angiomotin siRNA or by systemic treatment with therapeutic angiomotin-specific antibodies. Area of vascularization of CNV lesions was quantified by PECAM immunofluorescence stainings of choroidal flat-mounts.

Results:: Immunopositive staining for angiomotin was detected in vessels of surgical CNV specimens. CNV lesion size was increased in angiomotin transgenic mice (+112%, p< 0.001). Targeting angiomotin by either anti-angimotin (-55%) or angiomotin siRNA (-53%) significantly inhibited CNV formation (p < 0.001).

Conclusions:: Overexpression of Angiomotin in endothelial cells increases vascularization of CNV lesions. In contrast, targeting angiomotin either by siRNA knock down or by using angiomotin-specific antibodies efficiently inhibits CNV. These findings provide a rationale for using angiomotin siRNA or antibodies for treatment of neovascular age-related macular degeneration.

Keywords: age-related macular degeneration • choroid: neovascularization • pathology: experimental