Decreased Hypoxia-Induced Neovascularization in Angiopoietin-2 Heterozygous Knockout Mouse through Reduced MMP Activity

Abstract

Background/Aims: Proliferative diabetic retinopathy is characterized by the formation of retinal neovascularization. Angiopoietin-2 (Ang-2) and matrix metalloproteinase (MMP) play a critical role in angiogenesis. However, the precise location and function of Ang-2 during formation of retinal neovascularizations driven by hypoxia in relation to MMP activity have not been elucidated. In this study, we investigated the response of Ang-2 heterozygous knockout retinas (Ang2^+/- mouse) to hypoxia and its link to MMP activity in an oxygen-induced retinopathy (OIR) model. Methods: Pre-retinal neovascularizations were quantitated in vertical sections. Intra-retinal angiogenesis was assessed by whole mount immunofluorescence staining of retinas. MMP activity was examined in retinal protein lysate and whole mount retinal in situ zymography. Results: Ang2^+/- retinas subjected to the OIR model showed 33 % reduced neovascularization and 271 % increased avascular zones at postnatal day 17. In the OIR model, Ang-2 was modestly expressed in pre-retinal neovascularizations and venules, but strongly in arterioles and capillary sprouts. MMPs were activated in close association to where Ang-2 is expressed. MMP activity was substantially decreased in Ang2^+/- retinas. Conclusions: Our present data suggest the spatially concomitant expression of Ang2 and MMPs, and that Ang2 modulates hypoxia-induced neovascularization by regulating MMP activity.