Differential Protein Expression of LRP and Receptor-associated Ligands in Neovascular Rat Retinas and Patients with Neovascular Eye Disease

Abstract

Abstract: : Purpose: The α2-macroglobulin receptor LRP is a high molecular-weight receptor of the LDL receptor gene family. Its ability to bind and internalize both proteinases and proteinase-inhibitor complexes suggests that it has a major role in modulating extracellular proteinase activity. We investigated the presence of LRP and receptor-associated ligands in an ischemia-induced retinal neovascularization rat model and in patients with neovascular eye diseases. Methods: To induce retinal neovascularization, immediately after birth, litters of Wistar rats were placed in variable oxygen concentration for 14 days, after which rats were moved to room air for an additional 4 days before being sacrificed. Eyes were processed histopathologically and removed retinal tissues were stored at -20 °C. Human vitreous samples of patients with proliferative diabetic retinopathy (PDR), neovascular glaucoma and other vitreoretinal diseases were extracted. LRP was visualized in retinas by immunohistochemical staining. Western blot was performed with protein extracts of retinal tissue and human vitreous, and levels of LRP and receptor-associated ligands were analyzed by densitometry. Metalloproteinases (MMPs) activity was determined by zymography. Results: LRP showed increased staining in neovascular rat retinas. By western blot, LRP was present at high levels, revealing a significant increase under neovascular conditions. Immunoreactive band of α2-Macroglobulin (α2-M) was detected both in extracts of neovascular rat retinas and in human vitreous samples from neovascular glaucoma and PDR. These results correlated with the activity level of MMP-2 and MMP-9. Conclusions: LRP is overexpressed in neovascular retinas and patients with neovascular eye disease; this appears to correlate with the augmented levels of LRP-associated ligands such as α2-M and MMPs. This suggests LRP may play a role in modulating retinal neovascularization by regulating proteolytic activity.

Keywords: retinal neovascularization • retina • retinal degenerations: cell biology