Abstract
Abstract: :
Purpose: Macular degenerations are characterized by alterations in the structure of Bruch’s membrane (BrM) leading to changes in adhesion and metabolism. The exact composition and role of its constituent proteins and their receptors in aging and degenerative processes has not been well defined. The aim of this study is to characterize major ECM molecules, including laminins and collagens, and their receptors in BrM. Furthermore, the role of laminins in BM is investigated in knockout (KO) mouse models lacking laminin chains. Methods: Immunohistochemistry was performed on fresh frozen mouse, rat, bovine and human donor retina sections of different ages; freshly isolated RPE and RPE cell lines were used for western blot analysis and RT–PCR. The ultra structure of the RPE–BM complex in netrin 4, laminin γ3, laminin ß2, and laminin γ3/ß2 KO mice was investigated by electron microscopy. Results: The laminin chains α3, α5, ß1, ß2, γ1, γ2, γ3 are expressed in BrM in rat, bovine and human retinae, whereas the laminin chains α1, α2, α4, ß3 are not expressed, suggesting the presence of laminins 6 (α3ß1γ1), 7 (α3ß2γ 1), 10 (α5ß1γ1), 11 (α5ß2γ1), 13 (α3ß2γ3), and 15 (α5ß2γ3). Additional extracellular matrix components of BrM include nidogen, perlecan and netrin 4. Known laminin binding transmembrane molecules, including integrins and collagen XVII, are expressed near the RPE basement membrane, and may, thereby, serve as laminin receptors in the RPE. Protein transfer blots demonstrated, that homogenates of isolated bovine and rat RPE contain laminin chain and receptor protein. Similarly, RT–PCR of RNA from rat (RPE–J) and human (ARPE–19) RPE cell cultures revealed the presence of RNA for laminins. The RPE/BrM/choroid complex in KO mice lacking netrin 4, laminin ß2, or laminin γ3 does not show major ultra structural changes at the EM level. Conclusions: Laminins and their receptors are expressed in RPE basement membrane. The coordinate expression of extracellular matrix components including laminins and their receptors may play a critical role in stabilizing adhesion and metabolism in the RPE/Bruch’s membrane complex. Age or disease related changes in these expression patterns might contribute to the understanding of the early pathogenesis of macular degeneration or dystrophy.
Keywords: extracellular matrix • Bruch's membrane • retinal pigment epithelium