The Role of Laminins in the Retinal Vascular Basement Membrane

Abstract

The vascular basement membrane (vBM) of the central nervous system (CNS) is a highly specialized structure that is composed of various extracellular matrix (ECM) proteins and has many functions, including providing a point of adhesion for the cells of the vasculature, serving as a physical barrier, and providing an interface for communication with endothelial cells. One family of ECM molecules, laminins, are responsible for many of these specialized functions. There are 16 known isoforms of laminin, each consisting of a single α, β, and γ-chain. The distribution of these isoforms in the CNS vBM, however, remains unknown. Here, we used the retina to examine the distribution of laminin chains in the CNS vBM throughout development, as well as the roles of β2-containing laminins in vBM organization and γ3-containing laminins in arterial morphogenesis. The results presented in Chapter 2 demonstrate that there are dramatic changes in the temporal and spatial patterning of many of the laminin chains in the retinal vasculature throughout development, particularly the α2, α5, and γ3-chains. We deleted a key component of the CNS vBM, the laminin β2-chain, to gain a deeper understanding of how laminins affect vBM structure. Deletion of the β2-chain leads to decreased expression of several partner chains, including α2, α5, and γ3. Interestingly, the deletion of laminin β2 also leads to increased deposition of two other ECM molecules, agrin and perlecan, in the BMs of retinal veins and arteries, respectively. We also provide strong evidence that astrocytes contribute laminin 221 to the retinal vBM and that this laminin may directly regulate AQP4 expression in vascular associated astrocytic endfeet. The results presented in Chapter 3 demonstrate that laminins are involved in regulating arterial morphogenesis. Specifically, we found that γ3-containing laminins signal through dystroglycan to induce Dll4-Notch signaling, leading to decreased vascular branching and increased smooth muscle coverage: hallmarks of the arterial phenotype. Taken together, the work presented here further elucidates the structural and functional roles for laminins in the CNS vBM.