Expression of Extracellular Matrix Molecules Including Laminins and Their Receptors in Bruch’s Membrane

Abstract

Abstract: : Purpose: Alterations in Bruch’s membrane are thought to be critical in the development of macular degenerations including age-related macular degeneration. However the exact composition of Bruch’s membrane is not well understood. The aim of this study is to determine the composition of extracellular matrix (ECM) molecules, including the major ECM components, the laminins, and their binding partners in Bruch’s membrane as well as their expression during development and aging. Methods: Immunohistochemistry, immunoprecipitation and western blot analyse were performed on mouse and rat retinal/RPE tissue of different ages (postnatal day 5 to 38 months). Polyclonal and monoclonal antibodies against single laminin chains (alpha2, alpha3, alpha4, alpha5, beta1, beta2, beta3, gamma1, gamma2, gamma3), whole laminin molecules (laminin5), integrins (alpha3, alpha6, beta1, beta4), and nidogen were used. Expression patterns of wild type animals were compared to those in knockout mice lacking specific laminin chains. Results: Bruch’s membrane was immunoreactive for the laminin chains alpha1, alpha2, alpha5, beta1, beta2, gamma1, gamma3. Surprisingly, the component laminin chains of laminin 5 (alpha3, beta3, gamma2) were not detected in Bruch’s membrane or RPE. Additionally, nidogen colocalized with several laminin chains in Bruch’s membrane as expected. Several of the laminin binding integrins, are expressed both in the RPE and Bruch’s membrane. The expression of the laminin chains and the integrins were seen as early as P5 in rat retina. Conclusions: The coordinate expression of laminins and integrins may play a role in stabilizing the adhesion of Bruch’s membrane and the RPE. Changes in these expression patterns might contribute to the understanding of the early pathogenesis of macular degeneration and RPE detachment.

Keywords: extracellular matrix • Bruch's membrane • retinal pigment epithelium