Claudin5 Mediates Lrp5-regulated Retinal Blood Vessel Growth

Abstract

Purpose: : Defective retinal vasculature is the primary cause of proliferative retinopathy. Mutations in Wnt signaling, a pathway fundamentally important throughout embryonic development and in disease, cause defective development of retinal vasculature. However the molecular mechanisms by which the Wnt pathway governs normal vascular growth and vascular integrity are not fully delineated. Mice lacking the Wnt co-receptor low-density lipoprotein receptor-related protein 5 (Lrp5) have delayed retinal blood vessel growth and increased vascular leakage. In this study, we investigated the molecular mechanisms of loss of Lrp5 in causing defective retinal blood vessel growth.

Methods: : Retinas isolated from Lrp5 KO and wild type (WT) mice were examined by western blot and immnohistochemistry. Gene expression was quantified with qRT-PCR in whole retina and on laser-captured retinal vessels. Spheroid assays were performed with human retinal microvascular endothelial cells. Proliferative retinopathy was induced by exposing neonatal mice to 75% oxygen from postnatal day 7 to 12.

Results: : Loss of Lrp5 in retinas results in increased vascular leakage and significant down-regulation of claudin5, a tight junction protein essential for the integrity of blood retinal barrier. Blocking claudin5 significantly suppresses Wnt-pathway driven endothelial cell sprouting in vitro in a spheroid assay. Importantly, inhibition of claudin5 significantly suppresses retinal vessel formation in vivo both during development and in oxygen-induced retinopathy.

Conclusions: : These results demonstrate a previously unknown link between Lrp5 and claudin5 and suggest a novel role of tight-junction protein claudin5 as a critical mediator linking vascular permeability and angiogenesis. These findings may translate into new treatment approaches for proliferative retinopathies and other disorders associated with pathologic angiogenesis and vessel leakage.

Keywords: retinal neovascularization • development • cell adhesions/cell junctions