Low-density lipoprotein receptor-related protein-1 (LRP-1) expression in a rat model of oxygen-induced retinal neovascularization

The low-density lipoprotein receptor-related protein-1 (LRP-1) is a high-molecular weight receptor of the LDL receptor gene family. Its ability to bind and internalize both proteinases and proteinase-inhibitor complexes from the extracellular space suggests that it has a major role in modulating uncontrolled retinal cell proliferation. In order to test this assumption, we investigated the expression of LRP-1 and receptor-associated ligands in a rat model of oxygen-induced retinal neovascularization. Wistar albino rats were placed into incubators at birth and exposed to an atmosphere alternating between 50% and 10% of oxygen every 24 h. After 14 days, the animals were allowed to recover in room air and sacrificed at postnatal day 20 (P20). The protein expression of LRP-1 and alpha(2)-macroglobulin (alpha M-2) in the retina from unexposed and hyperoxiaexposed rats was investigated by Western blot. The localization of LRP-1 after neovascularization was assessed by immunohistochemical staining. The activity of metalloproteinases (MMPs) was determined by zymography. Histological analysis was done to quantitate the neovascular response in these animals. Western blot analysis showed that LRP-1 was expressed, along with alpha M-2, in the retina of rats with oxygen-induced neovascularization at P20. By immunohistochemical analysis, positive staining for LRP-1 appeared in cells extending from the inner limiting membrane (ILM) to the outer limiting membrane (OLM). The cells of the retina that expressed LRP-1 were identified by immunofluorescence as Muller cells. Zymographic analysis demonstrated increased activity of MMP-2 and MNIP-9 under neovascular conditions. This is the first demonstration of the involvement of LRP-1 in retinal neovascularization. In retinas of rats with oxygen-induced neovascularization, the expression of LRP-1 and alpha M-2 was increased along with an enhanced activity of MMPs, suggesting that LRP-1 expression may play a role in modulating retinal neovascularization by regulating proteolytic activity. (c) 2006 Elsevier Ltd. All rights reserved.